Abstract
A substrate having a scratch resistance enhancing coating with improved cleanability and methods for producing such a coating are provided. The coating includes at least one high refractive index transparent hard material layer and includes aluminum nitride. The coating exhibits a contact angle for water of greater than 75.
Claims
1. A coated substrate comprising: a substrate; and a coating on the substrate, the coating being a coating, the coating comprising a transparent hard material layer having a refractive index in a range from 1.8 to 2.3 at a wavelength of 550 nm, wherein the hard material layer includes aluminum nitride and a material selected from a group consisting of nitrides, carbides, carbonitrides, and any combinations thereof, and wherein the coating has a contact angle for water of greater 75.
2. The coated substrate as claimed in claim 1, wherein the hard material layer comprises crystalline aluminum nitride with a hexagonal crystal structure exhibiting a predominantly (001) preferred orientation.
3. The coated substrate as claimed in claim 2, wherein the hexagonal crystal structure exhibiting the (001) preferred orientation has a proportion of:
x.sub.(001)=I.sub.(001)/(I.sub.(001)+I.sub.(100)) and/or
y.sub.(001)=I.sub.(001)/(I.sub.(001)+I.sub.(101)) as determined by an XRD measurement of the coating, that is greater than 0.5.
4. The coated substrate as claimed in claim 2, wherein the hexagonal crystal structure has an average crystallite size is at most 25 nm.
5. The coated substrate as claimed in claim 1, wherein the coating has a mean roughness of less than 1.3 nm and/or a RMS roughness of less than 2 nm.
6. The coated substrate as claimed in claim 1, wherein the coating has a coefficient of static friction of less than 0.3 and/or a coefficient of sliding friction of less than 0.2.
7. The coated substrate as claimed in claim 1, wherein the coating exhibits a contact angle for water of 80 and/or a contact angle for ethylene glycol of 70, and/or a contact angle for diiodomethane of 55.
8. The coated substrate as claimed in claim 1, wherein the coating exhibits polar and/or dispersive surface energy of less than 50 mN/m.
9. The coated substrate as claimed in claim 1, wherein the coating exhibits a modulus of elasticity at a test load of 10 mN from 80 to 250 GPa and/or wherein the coating has a ratio of hardness to the modulus of elasticity of at least 0.08.
10. The coated substrate as claimed in claim 1, wherein the aluminum nitride of the hard material layer is doped with one or more nitrides and/or carbides and/or carbonitrides of elements selected from the group consisting of silicon, boron, zirconium, titanium, nickel, chromium, and carbon.
11. The coated substrate as claimed in claim 10, wherein the aluminum content in the hard material layer, based on the dopant material, is greater than 50 wt %.
12. The coated substrate as claimed in claim 1, wherein the hard material layer has a proportion of oxygen in that is at most 10 at %.
13. The coated substrate as claimed in claim 1, wherein the hard material layer has a thickness from 1 to 2000 nm.
14. The coated substrate as claimed in claim 1, wherein the substrate selected from the group consisting of a glass ceramic, a LAS glass ceramic, a glass, a sapphire glass, a borosilicate glass, an aluminosilicate glass, a soda-lime glass, a synthetic quartz glass, a lithium aluminosilicate glass, an optical glass, and an optical crystal.
15. The coated substrate as claimed in claim 1, wherein the substrate is a glass ceramic having a coefficient of thermal expansion .sub.2 0-300 of less than 2*10.sup.6 K.sup.1.
16. The coated substrate as claimed in claim 1, wherein the substrate further comprises decorated areas, at least in sections thereof, and wherein the decorated areas are disposed between the substrate and the coating.
17. The coated substrate as claimed in claim 1, further comprising an adhesion promoting layer arranged between the substrate and the coating.
18. The coated substrate as claimed in claim 1, wherein the hard material layer has a degree of crystallization of at least 50%.
19. A coated substrate comprising: a substrate; and a coating on the substrate, the coating comprising a transparent hard material layer with a refractive index in a range from 1.8 to 2.3 at a wavelength of 550 nm, wherein the coating has a contact angle for water of greater 75, wherein the hard material layer comprises aluminum nitride, and wherein the coating has a mean roughness of less than 1.3 nm and/or a RMS roughness of less than 2 nm.
20. A coated substrate comprising: a substrate, the substrate comprising a glass ceramic having a coefficient of thermal expansion .sub.2 0-300 of less than 2*10.sup.6 K.sup.1; and a coating on the substrate, the coating comprising a transparent hard material layer with a refractive index in a range from 1.8 to 2.3 at a wavelength of 550 nm, wherein the hard material layer includes aluminum nitride, and wherein the coating has a contact angle for water of greater 75.
21. A coated substrate comprising: a substrate; a coating on the substrate, the coating comprising a transparent hard material layer with a refractive index in a range from 1.8 to 2.3 at a wavelength of 550 nm, wherein the hard material layer includes aluminum nitride, and wherein the coating has a contact angle for water of greater 75; and one or more decorated areas on the substrate, the one or more decorated areas being disposed between the substrate and the coating.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
(2) The invention will now be described in more detail by way of exemplary embodiments and with reference to the drawings, wherein:
(3) FIG. 1 is a schematic view of a substrate coated according to the invention;
(4) FIG. 2 is a schematic view of an embodiment of the invention comprising an additional adhesion promoting layer;
(5) FIG. 3 shows an EDX spectrum of one exemplary embodiment;
(6) FIG. 4 shows an XRD spectrum of a further exemplary embodiment;
(7) FIG. 5 shows XRD spectra of two AlN-based layers with (100) and (101) preferred orientation as comparative examples;
(8) FIG. 6 shows XRD spectra of two crystalline exemplary embodiments and one exemplary embodiment with an amorphous AlN-based layer;
(9) FIG. 7 is a graphic representation of contact angles of the AlN-based samples shown in FIG. 6;
(10) FIG. 8 is a graphic representation of the surface energy of the AlN-based samples shown in FIG. 6;
(11) FIG. 9 is a graphic representation of static and sliding friction of the AlN-based samples shown in FIG. 6;
(12) FIG. 10 schematically illustrates the experimental setup for determining the coefficient of static friction;
(13) FIGS. 11a and 11b are graphic representations of the sticking tests performed on different exemplary embodiments and on a non-coated substrate as a comparative example;
(14) FIGS. 12a to 12c are AFM images of the AlN-based samples shown in FIG. 6; and
(15) FIGS. 13a to 13c are photographs of different coated substrates with different preferred orientations after a mechanical stress test with sand.
DETAILED DESCRIPTION
(16) FIG. 1 schematically illustrates a substrate coated according to the invention. Here, the substrate 2 is coated with a hard material layer 1. Hard material layer 1 comprises crystalline AlN, and the AlN crystallites have a (001) preferred orientation. Due to the layer properties of hard material layer 1, in particular its great hardness and high modulus of elasticity, a layer thickness of the hard material layer of <100 nm, preferably even only 50 nm already suffice to obtain an easy-to-clean effect and to protect the substrate 2 against mechanical stress and from scratches. However, layers of greater thickness of up to 2000 nm are likewise conceivable.
(17) FIG. 2 schematically shows a further exemplary embodiment in which a further layer 3 is disposed between substrate 2 and hard material layer 1. The additional layer 3 may be a decorative layer or an adhesion promoting layer, for example. Layers 3 comprising several sublayers, such as a decorative layer and an adhesion promoting layer, are likewise possible. The substrate may be completely or only partially covered by layer 3. In this case, the hard material layer is disposed above the additional layer 3, that means the additional layer 3 is therefore located between substrate 2 and hard material layer 1. In embodiments in which the additional layer 3 is an adhesion promoting layer, layer 3 is preferably a doped AlN layer or a mixed layer. Depending on the composition of the adhesion promoting layer, the latter may for example have a coefficient of thermal expansion between the coefficients of thermal expansion of the substrate 2 and that of the hard material layer 1. In this way the adhesion promoting layer 3 allows to reduce stresses between substrate 2 and hard material layer 1. The adhesion promoting layer 3 preferably has a thickness in a range from 1 to 900 nm, more preferably in a range from 1 to 500 nm, most preferably in a range from 1 to 50 nm. According to one exemplary embodiment, the coated substrate has, as the adhesion promoting layer 3, an Al.sub.2O.sub.3 coating with a layer thickness of 50 nm between glass substrate 2 and hard material layer 1.
(18) FIG. 3 shows the spectrum of energy dispersive X-ray (EDX) spectroscopy or energy dispersive x-ray analysis of one exemplary embodiment of a hard material layer according to the invention. The hard material layer in this exemplary embodiment is an AlN layer alloyed or doped with silicon.
(19) FIG. 4 shows the X-ray diffraction (XRD) spectrum of an exemplary embodiment of a substrate coated according to the invention. In this exemplary embodiment, an SiO.sub.2 substrate was coated with an AlN-based hard material layer, and an XRD spectrum of the coated substrate was acquired. Spectrum 4 has three reflections that can be associated with the three orientations (100), (001), and (101) of the hexagonal crystal structure of AlN. It can clearly be seen that the hard material layer predominantly has a (001) preferred orientation. The corresponding reflection at 36 is much more pronounced than the reflections of the (100) orientation (33.5) and of the (101) orientation (38).
(20) The proportion of the crystal structure exhibiting the (001) preferred orientation can be determined from spectrum 4 as follows:
(21) TABLE-US-00001 I.sub.(001) [counts] I.sub.(100) [counts] I.sub.(101) [counts] 12,312 3,717 2,678
x.sub.(001)=I.sub.(001)/(I.sub.(001)+I.sub.(100)); and
y.sub.(001)=I.sub.(001)/(I.sub.(001)+I.sub.(101))
(22) In this exemplary embodiment, fraction x.sub.(001) is 0.76, and fraction y.sub.(001) is 0.82.
(23) FIG. 5 shows XRD spectra of hard material layers which actually have a similar composition as that of the exemplary embodiment shown in FIG. 4, but exhibit other preferred orientations of the crystal structure. Spectrum 5 can be associated with a comparative example having a (100) preferred orientation, and spectrum 6 can be associated with a comparative example having a (101) preferred orientation.
(24) The hard material layer exhibiting the (100) preferred orientation (curve 6) was deposited with a high target-substrate spacing (>15 cm) and low sputtering power of 13 W/cm.sup.2. Processing temperature was about 100 C. The hard material layer exhibiting the (101) preferred orientation (curve 5) was deposited at an even lower sputtering power of 9.5 W/cm.sup.2. The target-substrate spacing and the processing temperature were similar to the deposition conditions of the hard material layer exhibiting the (100) preferred orientation.
(25) FIG. 6 shows the X-ray diffraction (XRD) spectra of two crystalline exemplary embodiments 4 and 7 and of an amorphous sample 8. Exemplary embodiment 7 is an AlN-based hard material layer with an x.sub.(001) proportion of 0.6 and an y.sub.(001) proportion of 0.73. Thus, the proportion of the (001) orientation is less than in exemplary embodiment 4. Comparative Example 7 was deposited at a sputtering power in a range of more than 15 W/cm.sup.2 with a low target-substrate spacing ranging from 10 to 12 cm. Processing temperature was 250 C. Example 8 is an amorphous AlN hard material layer.
(26) For examples 4, 7, and 8 the contact angles for water, ethylene glycol, diiodomethane, and n-hexadecane were determined. For determining the contact angles, the samples were first cleaned and stored at room temperature for 12 hours so that the detergent completely evaporated. Then, 3.5 l of the liquids listed in Table 1 were applied to each of the sample surfaces, and the contact angle was determined in accordance with DIN 55660-2. The results are shown in FIG. 7.
(27) TABLE-US-00002 TABLE 1 Contact angles of samples 4, 7, and 8 Contact angle [] Sample Water Ethylene glycol Diiodomethane n-Hexadecane 4 88 77 65 18 7 89 75 62 18 8 90 77 63 15
(28) The hard material layers 4, 7, and 8 exhibit relatively large contact angles for the polar substances water, ethylene glycol, and diiodomethane, so that the coatings are not or only slightly wetted by the aforementioned liquids.
(29) FIG. 8 graphically illustrates surface energies OWRK polar and OWRK dispersive. The OWRK polar surface energy was calculated from the contact angle for water, the dispersive surface energy was calculated from all of the contact angles listed in Table 1.
(30) FIG. 9 shows sliding friction and static friction values of samples 4, 7, 8 and of the non-coated substrate. The substrate is a glass ceramic, that means it has a very smooth surface. The coefficient of sliding friction was determined using a metal ball with a diameter of 1 mm as a friction partner. The coefficient of static friction was determined using an inclined plane 10 and a stainless steel plate 11 with a weight 12 of 50 g. A schematic test setup for determining the coefficient of static friction is illustrated in FIG. 10. The test body will begin to slide when the downward force is equal to the maximum adhesive force. At an angle the adhesive force is overcome, the coefficient of static friction can be determined from tan .
(31) Surprisingly, sliding and static friction values for samples 4 and 7 are lower than for the non-coated glass ceramic (substrate). In particular static friction can be reduced by the coating. Sample 8 has the lowest sliding and static friction values.
(32) FIGS. 11a and 11b show the results of a so-called sticking test. The sticking test is intended to evaluate the cleanability of a respectively coated substrate with regard to contamination that is caused in practice if the coated substrate is employed as a cooktop, for example. For this purpose, the samples to be tested are first cleaned. Then, a defined amount of a mixture including several components is applied to the sample surface. The mixture contains components with a high sugar content, components with a high protein content, and components with a high fat content. The so treated samples are heated using a hot plate so that the mixture is baked so as to stick on the sample. Then, a sponge cloth impregnated with a cleaning liquid is swiped over the sample surface of the cooled sample with a load of 4.25 kg, and the decrease of contamination for this cleaning stroke is determined.
(33) FIG. 11A shows the results of such a sticking test performed on samples 7, 8, and 4, and on a non-coated substrate 13 as a comparative example. In the case of samples 7, 8, and 4, the contaminated surface area is significantly reduced already with 15 strokes, after cleaning with 50 strokes the contamination area has almost halved. In case of the non-coated glass substrate, by contrast, this area could only be reduced by less than 10% even after 50 strokes.
(34) FIG. 11B illustrates the results of the sticking test on a coating 14 according to the invention in dependence on layer thickness thereof. The corresponding values are shown in Table 2 below.
(35) TABLE-US-00003 TABLE 2 Results of sticking test shown in FIG. 11b Number of cleaning Total surface Sample Layer thickness steps contamination 14a 50 nm 0 500 15 387 50 214 14b 1500 nm 0 495 15 352 50 188 13 non-coated glass 0 541 ceramic 15 530 50 507
(36) Sample 14 has a thickness of only 50 nm here, the thickness of sample 14b is 1.5 m. Again, a non-coated glass ceramic substrate serves as a comparative sample. From FIG. 11b it becomes clear that both samples 14a and 14b exhibit good cleanability. Surprisingly, the removal of contaminations per cleaning operation as a measure of cleanability is comparable for samples 14a and 14b, although the layer thickness of sample 14b is substantially greater. For both samples, the degree of contamination can be reduced by about of the initial value by 15 strokes. Thus, sample 14a with a layer thickness of only 50 nm also exhibits very good cleanability.
(37) FIGS. 12a to 12c show AFM images of the samples 4, 7, and 8. A characterization of the surface texture and determination of the roughness of the coatings was accomplished by AFM. The samples to be tested were cleaned by blowing and discharged immediately before the measurement. Sample preparation was performed according to the ASTM E 1829 2009-01 and ASTM E 1078 2009-01 standards. The roughness values were determined in accordance with standards ASTM E 2382 2004-01, AAW_OF_0002, and ISO TR 14187 2011-08. The size of the measurement area was 2 m2 m. The roughness values obtained in this manner are listed in Table 3 below.
(38) TABLE-US-00004 TABLE 3 Roughness values Sample RMS [nm] Ra [nm] 4 1.1 0.9 7 1.9 1.5 8 0.6 0.4
(39) FIGS. 13a to 13c illustrate the influence of the preferred orientation of the crystal structure on the mechanical resistance of the respective hard material layers. FIGS. 13a to 13c are photographs of different coated substrates after a stress test with sand. In this test sand was placed on the coated substrates and was then loaded with load bodies and oscillated 100 times in a container. FIG. 13a shows the photograph after the stress test of a sample having a coating with (101) preferred orientation, FIG. 13b shows a corresponding photograph of a sample with (100) preferred orientation, and FIG. 13c shows a photograph of a sample with a (001) preferred orientation according to the invention. As can be clearly seen from FIGS. 13a to 13c, the samples exhibiting the (101) and (100) preferred orientations have a much higher number of scratches after the stress test than the sample having a (001) preferred orientation.
(40) It has thus been disclosed that the invention in particular relates to a substrate having a coating that increases scratch resistance and which exhibits improved cleanability. The coating preferably comprises at least one high refractive index transparent hard material layer and especially includes aluminum nitride, inter alia. The coating has a contact angle for water of >75. The invention also relates to a method for producing such a coating.
