Glass-ceramic article

Abstract

A glass-ceramic article includes at least one substrate, such as a plate, made of glass-ceramic, the substrate having a face including a microtexturing such that the arithmetic mean surface roughness Ra, measured according to standard ISO 4287, is between 0.14 and 0.40 m, and the total roughness, Rt, measured according to standard ISO 4287, is between 1.15 and 5.00 m.

Claims

1. A glass-ceramic article, comprising at least one substrate made of glass-ceramic, said substrate having a face with a micro-texturing such that an arithmetic mean surface roughness, Ra, measured according to standard ISO 4287, is between 0.14 and 0.40 m and wherein a total roughness Rt, measured according to ISO 4287, is between 1.15 and 5.00 m and wherein said substrate is a 3 to 6 mm transparent black glass-ceramic, having a light transmission TL under illuminant D65 of less than 20%, and an optical transmission of less than 30% for a wavelength of 625 nm.

2. The glass-ceramic article according to claim 1, wherein the total roughness Rt, measured according to ISO 4287, is between 1.25 and 3.00 m.

3. The glass-ceramic article according to claim 1, wherein the light transmission TL under illuminant D65 is less than 10%, and the optical transmission is less than 20% for a wavelength of 625 nm.

4. The glass-ceramic article according to claim 1, wherein the microtexturing has an asymmetry factor, Ssk, between 0.2 and 1.1 m.

5. The glass-ceramic article according to claim 4, wherein the microtexturing has an asymmetry factor, Ssk, between 0.3 and 1.0 m.

6. The glass-ceramic article according to claim 1, wherein a percentage of the surface area more than 0.8 m from the maximum height distribution is between 2 and 8%.

7. The glass-ceramic article according to claim 1, wherein an average area of hollows in said face with the micro-texturing is between 2 and 10*10.sup.3 mm.sup.2.

8. The glass-ceramic article according to claim 1, wherein a lower face of the substrate has ellipsoidal teardrops whose height is between 60 and 120 m.

9. The glass-ceramic article according to claim 8, wherein the ellipsoidal teardrops on the lower face of the substrate are spaced 250-500 m when measured edge-to-edge.

10. The glass-ceramic article according to claim 1, wherein a gloss difference between abraded and non-abraded areas in said face with the micro-texturing is less than 20% in absolute value.

11. The glass-ceramic article according to claim 1, wherein the substrate is a plate.

12. The glass-ceramic article according to claim 1, wherein the arithmetic mean surface roughness, Ra, measured according to standard ISO 4287, is between 0.15 and 0.30 m.

13. The glass-ceramic article according to claim 1, wherein the glass-ceramic article is a cooking plate.

14. A method for preparing a glass-ceramic article according to claim 1, comprising rolling mother glass between two rollers, one of which has undergone a shot-peening treatment, with particles of a material having a Vickers hardness HV1 of between 3 and 10, the mother glass thus rolled is then subjected to a ceramization process.

15. The method according to claim 14, wherein the roller which has undergone the shot-peening treatment has a roughness Ra of 0.6 to 1.2 m.

16. The method according to claim 14, wherein the roller that has undergone the shot peening treatment has a roughness Rt greater than 4 m.

17. The method according to claim 14, wherein the shot-peened roller is not subjected to a polishing treatment after the shot-peening treatment.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is an image obtained by optical interferometry of a glass-ceramic plate according to comparative example 1;

(2) FIG. 2 is an image of the same type depicting an article according to Example 1 of the invention;

(3) FIG. 3 is an image of the same type depicting an article according to Example 2 of the invention;

(4) FIG. 4 is an image of the same type depicting an article according to Example 3 of the invention.

(5) FIG. 5 is a graph that relates the gloss difference and the parameter Ssk for the three comparative examples and the three examples according to the invention.

DETAILED DESCRIPTION

(6) For the production of the glass-ceramic plates according to the invention, the surface of the upper rolling roll is modified as follows:

(7) Pneumatic shot-peening is carried out by blasting, perpendicularly to the surface of a mirror-polished roller, a shot made of steel (martensitic) comprising grains whose size is in the order of 0.5 to 1.2 mm. The blasting pressure is about 4 bars. The shot is blasted at a rate of approximately 3 kg/min. In 4 passes, we ensure the formation of a surface state said to be satiny on the surface of the roller corresponding to a roughness Ra between 0.8 and 1 m and Rt higher than 8 m.

(8) Once the shot-peening is finished, the roller is washed with alcohol.

(9) We thus obtain a particular and random texturing of the surface of the roller.

(10) The lower roller is prepared to make the spikes.

(11) The rollers prepared in this way are used to roll mother glass continuously for several tens of hours (rolling cycle) during which a ribbon of mother glass runs continuously between the two rollers. After this rolling cycle, the top roller undergoes successive polishing steps until a mirror-polished surface is obtained before it can be textured again by shot-peening as described above.

(12) The examples according to the invention are samples of rolled glass, taken at different times, during the same rolling cycle.

Example 1

(13) The sample of textured mother glass in Example 1 is taken after one hour of operation of the rolling rolls.

Example 2

(14) The sample of textured mother glass in Example 2 is taken at a time t1 corresponding to several tens of hours of operation of the rolling rolls.

Example 3

(15) The sample of textured stock glass from Example 3 is taken at a time t2 (approximately equal to twice t1) of rolling roll operation.

(16) Roughness measurements Ra and Rt are measured with a Mitutoyo Sj-400 roughness meter according to standard ISO 4287 over a 4 mm evaluation length in 15 points on 594525 mm plates. The surface characterization is completed by optical interferometry that results in the parameters Ssk, Sp and Sv established according to the standard ISO25178. All these characteristics are shown in Table 1.

(17) The three examples according to the invention have been compared to three products on the market that constitute the comparative examples: to Eurokera KB+ (comparative example 1), Kanger unpolished (comparative example 2, Kanger polished (comparative example 3).

(18) TABLE-US-00001 TABLE 1 Ra (m) Rt (m) Ssk (m) Sp (m) Sv (m) Comparative 0.1 0.2 1.0 0.2 0.41 0.21 0.65 0.12 1.09 0.09 example 1 Comparative 0.8 0.2 6.3 1.4 1.25 0.16 13.67 9.78 16.27 2.63 example 2 Comparative 0.03 0.00 0.4 0.1 0.37 0.22 0.01 0.00 0.01 0.00 example 3 Example 1 0.20 0.01 1.68 0.18 0.35 +/ 0.12 1.46 +/ 0.31 2.31 +/ 0.43 Example 2 0.17 0.03 1.41 0.22 0.69 0.12 1.10 0.32 2.26 0.11 Example 3 0.16 0.03 1.38 0.28 0.90 0.13 0.90 0.11 2.53 0.5

(19) Glass-ceramic samples are subjected to an abrasion test representative of kitchen use, as defined below.

(20) The gloss difference is measured as follows.

(21) The gloss difference is the difference between the gloss of the abraded area and the gloss of the unabraded area divided by the gloss of the unabraded area. The larger this difference is in absolute value, the greater the contrast between an abraded and unabraded area.

(22) The abraded areas are prepared with an 18 mm diameter disc obtained from a Norton silicon carbide (SiC) P240 grit abrasive paper. The disk is mounted on a Linear Abraser device marketed by Taber, and a pressure of 5 N/cm2 is applied to the SiC disk. A round trip (one cycle) is performed at a speed of 15 cycles/min on a 38.1 mm stroke. Three abraded areas are made on the samples to be characterized.

(23) The gloss is measured using a device of type Color i7 marketed by the company X-Rite.

(24) On each of the three abraded areas, three measurements are made: one in the center, two on either side of the first. The gloss value of an abraded sample is then the average gloss of the three abraded areas.

(25) On an unabraded sample, 9 measurements are also made and averaged to obtain the gloss value of the unabraded area. The gloss difference is given with a standard deviation on the mean of the gloss difference.

(26) The results are reported in Table 2.

(27) Table 2 also shows the characterization of the zones within 0.8 m of the maximum height distribution, i.e. the proportion of the surface occupied by these zones (dist 0.8), the average area of the zones and the density of the zones (see images 1 to 4)

(28) These characteristics are established through image processing performed on images obtained by optical interferometry.

(29) Areas within 0.8 m of the maximum height distribution are shown in white in FIGS. 1 to 4.

(30) TABLE-US-00002 TABLE 2 Areas within 0.8 m of the maximum height distribution Gloss Average difference (dist.sub.0.8) hollow area Density (%) (%) (*10.sup.3 mm.sup.2) (/mm.sup.2) Comparative 7.9 +/ 3.3 0.07 0.6 1.2 example 1 Eurokera KB+ Comparative 21.1 +/ 3.4 example 2 Kanger unpolished Comparative 0 example 3 Kanger polished Example 1 7.7 +/ 1.8 3.2 5.2 6.2 Example 2 11.7 +/ 4.25 3.8 4.6 8.2 Example 3 13.3 +/ 2.2 2.7 5.9 4.6

(31) It can be seen from Table 1 that the peak height and hollow depth values are significantly higher for the examples according to the invention than for the comparative example 1 (Eurokera KB+). The asymmetry factor Ssk, which is not significantly different from comparative example 1 at the beginning of the rolling cycle, decreases significantly during the rolling cycle (examples 2 and 3 according to the invention).

(32) It can be seen from Table 2 that the percentage of the surface occupied by hollows (% of surface occupied by areas located at a depth of 0.8 m with respect to the maximum of the height distribution (Sp)) obtained through an analysis of the images established by optical interferometry is much greater for the examples according to the invention than for the comparative example 1. The area as well as the density of the depressions on the surface of the glass-ceramics according to the examples of the invention are significantly larger compared to the comparative example 1. The hollows are perceptible to the naked eye as bright spots on the surface under standard observation conditions (the plates are observed with an inclination of 45 at a distance of 60 cm, with an illumination intensity of about 2,000 Lux).

(33) These characteristics are crucial to explain the decrease in defect perception. The greater density of hollows on the surface of the glass-ceramics according to the invention modifies the perception of defects present on the surface of the glass-ceramic that may occur during the plate-making method under the observation conditions described above.

(34) By way of non-limiting example, the defects whose perception is lower on the surface of the articles according to the invention compared to the surface of comparative example 1 can be bubbles whose diameter is less than 0.8 mm, isolated scratches of less than 50 mm in length, and spots of less than 1 mm in diameter.

(35) It can be seen that the gloss difference (values in Table 2) correlates with the parameter Ssk (values in Table 1) for the three comparative examples and the three examples according to the invention, as shown by the straight line plotted in FIG. 5. The R.sup.2 value is close to 1.

(36) The gloss difference (in absolute value) obtained with the glass-ceramics according to the invention is slightly higher than that of the glass-ceramic corresponding to comparative example 1 (Eurokera KB+) but remains significantly lower than that observed on the glass-ceramic corresponding to comparative example 2 (Kanger unpolished), which is considered not acceptable. The difference in gloss (in absolute value) is greater than that observed on the glass-ceramic corresponding to comparative example 3 (polished Kanger), but the manufacture of this glass-ceramic requires an additional polishing step compared to the glass-ceramics according to the examples of the invention, which is to be avoided because of the additional cost and complexity of implementing this step.

(37) The texturing profiles according to the invention make it possible to achieve a compromise that meets both the demand for masking defects that may occur during the manufacturing method of the plates and the demand for limiting the differences in gloss between the areas impacted by the abrasion and those not abraded.

(38) The texturing profiles according to the invention are particularly suitable for black or dark glass-ceramic plates, but could also be applied advantageously to opalescent, light-colored or transparent white glass-ceramic plates insofar as they can modify the surface appearance.

(39) The invention has thus made it possible to develop, in a simple and economical manner, a glass-ceramic product whose upper surface masks the glass defects that may occur during the manufacturing process and where abrasion generates only a very slight variation in gloss; while respecting the constraints, particularly thermal and mechanical, specific to the uses of said products, and maintaining durable and easy-to-clean glass-ceramic products.

(40) The articles according to the invention can in particular be used advantageously to produce a new range of cooking plates for stoves or hobs or a new range of worktops, consoles, credenzas, central islands, or fireplace inserts, etc.