Enamel composition for glass-ceramic

Abstract

Enamel composition, in particular intended for covering a glass pane of a fireplace insert, comprising at least one glass frit, at least one pigment in a content varying from 40 to 65% of the total weight of the enamel, preferably from 45 to 60%, and optionally at least one vehicle or medium, characterized in that the glass frit comprises the following constituents, within the limits defined below, limits included, expressed as percentages by weight of the total weight of the frit: TABLE-US-00001 SiO.sub.2 45-65%  Al.sub.2O.sub.3 0-13% B.sub.2O.sub.3 23-55%  Na.sub.2O 0-10% K.sub.2O 0-10% Li.sub.2O  0-10%.

Claims

1. An enamel composition, comprising: a glass frit; a pigment in a content varying from 40 to 65% of the total weight of the enamel composition; and optionally a vehicle or medium, wherein the glass fit comprises, expressed as percentages by weight of the total weight of the glass frit: TABLE-US-00008 SiO.sub.2 45-65%;  Al.sub.2O.sub.3 0-13%; B.sub.2O.sub.3 greater than 30%;  Na.sub.2O 0-10%; K.sub.2O  .sup.   0-10%; and Li.sub.2O 0-10%.

2. The enamel composition of claim 1, wherein the glass frit comprises a SiO.sub.2 content of from 47 to 57%.

3. The enamel composition of claim 1, wherein the glass frit comprises an Al.sub.2O.sub.3 content of from 2 to 8%.

4. The enamel composition of claim 1, wherein the glass frit comprises a B.sub.2O.sub.3 content of from greater than 31% to 50%.

5. The enamel composition of claim 1, wherein the glass fit comprises an Na.sub.2O content of from 2.5 to 6%.

6. The enamel composition of claim 1, wherein the glass frit comprises a K.sub.2O content of from 0.5 to 3%.

7. The enamel composition of claim 1, wherein the glass frit comprises a Li.sub.2O content of from 2 to 6%.

8. The enamel composition of claim 1, wherein the enamel composition does not contain at least one selected from the group consisting of ZrO.sub.2, BaO, MgO, CaO and SrO.

9. The enamel composition of claim 1, wherein the glass fit consists of: TABLE-US-00009 SiO.sub.2 45-65%;  Al.sub.2O.sub.3 0-13%; B.sub.2O.sub.3 greater than 31%;  Na.sub.2O 0-10%; K.sub.2O  .sup.   0-10%; and Li.sub.2O 0-10%.

10. The enamel composition of claim 1, wherein the glass frit consists of: TABLE-US-00010 SiO.sub.2 47-57%;  Al.sub.2O.sub.3 3-6%; B.sub.2O.sub.3 greater than 32%;  Na.sub.2O 2-5%; K.sub.2O  .sup.   1-2%; and Li.sub.2O 3-5%.

11. The enamel composition of claim 1, wherein the glass frit and the pigment comprise particles having a particle size that varies from 1 to 6 microns.

12. The enamel composition of claim 1, wherein relative contents of the glass frit and the pigment are 50% each.

13. The enamel composition of claim 1, wherein the pigment is an opaque black pigment.

14. A screen-printing process, the process comprising applying the enamel composition of claim 1 to a glass substrate and firing, to obtain a thickness of less than or equal to 10 microns after the firing.

15. A glass-ceramic plate covered with the enamel composition of claim 1.

16. The glass-ceramic plate of claim 15, wherein: the glass-ceramic plate is a fireplace insert; and a face of the glass-ceramic plate bearing the enamel composition is suitable to be placed on the fire side.

17. The enamel composition of claim 1, which is suitable for covering a glass pane of a fireplace insert.

18. The enamel composition of claim 1, comprising 45 to 60% of the pigment, based on the total weight of the enamel composition.

19. The enamel composition of claim 1, wherein the glass frit comprises an Al.sub.2O.sub.3 content of 3 to 6%.

20. The enamel composition of claim 1, wherein the glass frit consists of: TABLE-US-00011 SiO.sub.2 45-65%;  Al.sub.2O.sub.3 2-8%; B.sub.2O.sub.3 greater than 33%;  Na.sub.2O 2.5-6%;.sup.  K.sub.2O  0.5-3%; and Li.sub.2O 2-6%.

Description

EXAMPLES

(1) TABLE-US-00005 TABLE 1 The numerical values assigned to the oxides and to the pigments correspond to percentages by weight. Enamel: 50% opaque black Sample No. pigment C1 C2 1 2 3 SiO.sub.2 63 64 56.46 55.38 48.72 Al.sub.2O.sub.3 6.60 6.50 5.92 3.08 12.72 Na.sub.2O 3.30 5.50 2.95 5.62 5.80 K.sub.2O 1.80 1.00 1.62 8.54 1.47 B.sub.2O.sub.3 20.50 16.00 23.75 27.37 28.25 Li.sub.2O 4.80 5.00 4.30 0.00 3.03 Fe.sub.2O.sub.3 — — 5.00 — — BaO — 2.00 — — — Total for the 100.00 100.00 100.00 100.00 100.00 frit Appearance of matt matt — shiny shiny the enamel Crazing yes yes no no no Abrasion mediocre yes average yes yes resistance Opacity: ΔE* 0.32 0.27 0.57 0.18 0.22 Colorimetry/ 25.85 26.95 26.72 16.21 20.65 enamel face: L* (0.60, 0.19) (0.29, 0.30 (0.54, 0.09) (0.72, 0.57) (0.54, 0.27) (a*, b*)

(2) TABLE-US-00006 TABLE 2 The numerical values assigned to the oxides and to the pigments correspond to percentages by weight. Enamel: 50% opaque Sample No. black pigment C1 C2 4 5 6 7 SiO.sub.2 63 64 55.47 53.90 39.75 47.55 Al.sub.2O.sub.3 6.60 6.50 5.81 3.33 12.55 4.98 Na.sub.2O 3.30 5.50 2.91 3.03 5.72 2.49 K.sub.2O 1.80 1.00 1.58 1.54 1.45 1.36 B.sub.2O.sub.3 20.50 16.00 30.00 34.10 37.52 40.00 Li.sub.2O 4.80 5.00 4.23 4.08 3.00 3.62 Fe.sub.2O.sub.3 — — — — — — BaO — 2.00 — — — — Total for the frit 100.00 100.00 100.00 100.00 100.00 100.00 Appearance of the matt matt — shiny shiny shiny enamel Crazing yes yes no yes, no no slight Abrasion mediocre yes yes yes yes yes resistance Opacity: ΔE* 0.32 0.27 0.74 0.20 0.08 0.36 Colorimetry/enamel 25.85 26.95 20.33 13.49 15.78 17.55 face: L* (a*, b*) (0.60, 0.19) (0.29, 0.30 (0.75, 0.28) (0.73, 0.75) (0.87, 0.54) (0.89, 0.52)

(3) Tables 1 and 2 give results of comparative tests between enamel compositions according to the invention deposited by screen printing on a glass-ceramic plate, corresponding respectively to samples 1 to 7, and enamel compositions deposited on glass-ceramic in the same way, and that are obtained from a glass frit of the prior art, corresponding respectively to samples C1 and C2 (the results obtained for samples C1 and C2 from the frit of the prior art have been listed in both tables).

(4) The various samples, the numbers of which correspond to the compositions listed in tables 1 and 2, were prepared as follows:

(5) The frit, comprising the oxides listed in tables 1 or 2, is conventionally obtained by melting a mixture of suitable (natural or synthetic) raw materials at high temperature (above 1000° C.), then the frit is milled using a ball mill in order to obtain a particle size of 8 to 12 microns. The pigments are incorporated in order to obtain a frit/pigment weight ratio=1. The pigments used in all cases are the Co—Cr—Fe—Ni spinel and Cr—Cu spinel commercial pigments (they both gave identical results listed in table 1). The assembly is then micromilled in order to obtain grains having a particle size that varies from 5 to 6 microns.

(6) A pasting of the powder obtain is then carried out in the Ferro MX54 medium (the amount of medium varies from 40 to 60% of the total weight of the mixture). Then, on a transparent glass-ceramic plate, a thickness of 10 to 15 microns of the paste obtained during the pasting is deposited by screen printing. The assembly is fired at a temperature of 800° C. for a duration of half an hour to one hour. The thickness of the enamel layer obtained after firing on the glass substrate varies between 4 and 6 microns (only in the case of sample C2 was a thickness of 8 microns obtained after firing).

(7) Tribological and colorimetric tests were carried out. For the tribological tests, the abrasion resistance (see tables 1 and 2) corresponds to the behavior of the enamel after 10 back-and-forth passes carried out using a moistened highly abrasive pad (Spontex® red pad).

(8) The results obtained are listed in tables 1 and 2. The values assigned to the oxides are expressed as percentages by weight relative to the total composition of the frit.

(9) In all cases, all the enamels according to the invention tested, incorporating frits having a high content of boron oxide, displayed a shiny appearance that is very satisfactory for the desired application. Conversely, the enamels prepared according to the same protocol from the frit of the prior art are matt.

(10) In almost all cases, no crazing was observed on the enamels according to the invention that were tested, prepared from frits having high contents of boron oxide (only sample 7 displayed crazing). Conversely, the enamels prepared according to the same protocol from a frit of the prior art displayed crazing.

(11) The results of the abrasion tests are also satisfactory for all of the samples of enamels according to the invention that were evaluated. They displayed good mechanical strength on the glass-ceramic plate.

(12) Regarding the results of the colorimetric tests, the value of L* that makes it possible to determine if an enamel of satisfactory porosity is obtained was measured on the enamel side (the values of the other colorimetric coordinates a* and b* are added afterwards between parentheses, by way of indication). Here too, and just like the values obtained for AE* for measuring the opacity, results are obtained that confirm the conformity between the properties of the enamel according to the invention and the desired use.

(13) Tests were also carried out starting from the frit used to prepare sample 7, in order to evaluate what relative proportions of frit with respect to the pigment make it possible to obtain an enamel with optical and mechanical properties compatible with the desired use. The enamel is obtained from the frit of example 7 by following the protocol explained in detail above in the experimental section, and by using the Co—Cr—Fe—Ni spinel black pigment sold by Ferro.sup.TM under the reference 240137. Table 3 shows the results obtained.

(14) TABLE-US-00007 TABLE 3 The percentages correspond to percentages by weight. 7 8 9 (50% frit of (30% frit of (61% frit of sample 7 and sample 7 and sample 7 and 50% pigment) 70% pigment) 39% pigment) Appearance shiny matt shiny of the enamel Abrasion yes poor yes resistance Opacity: ΔE*  0.36  0.30  1.39 Colorimetry/ 17.55 23.36 10.80 enamel face: (0.89, 0.52) (0.55, 0.16) (0.84, 1.18) L* (a*, b*)

(15) It is observed that a high pigment content, typically of the order of 70% by weight relative to the frit (sample 8), degrades the abrasion resistance of the enamel (10 back-and-forth passes made using a moistened highly abrasive pad identical to that described above). A low pigment content, typically less than 40% by weight relative to the frit (sample 9), results in an enamel that is insufficiently opaque since the value obtained for AE* is much higher than 0.5.