PROCEDURE FOR CONTROLLING THE CHEMICAL REACTION IN MULTI-LAYER CERAMIC DECORATIONS

Abstract

Procedure for controlling the chemical reaction in multi-layer ceramic decorations, according to interfacial and surface properties, in which the ceramic coating formulation is broken down into two separate compounds: on the one hand, a bottom layer formed by a glaze with part of the necessary oxides to obtain the ceramic effect, applied in the conventional manner over the ceramic substrate, and on the other hand, a top layer formed by an ink with the other necessary part of the oxides, applied by injection over the previous layer. The ceramic product is finished off with a firing process. This procedure has the advantage of regulating the penetration of the oxides of the top layer throughout the profile of the bottom layer, thus achieving an adequate concentration of oxides in the zone nearest to the surface, which permits optimization of the chemical reaction and thus, of the ceramic effect obtained.

Claims

1- Procedure for controlling the chemical reaction in multi-layer ceramic decorations of the type used to obtain a decorated ceramic product (7), using, separately, a glaze (2) with part of the necessary oxides and an ink (4) for decoration by injection with the other necessary part of the oxides, characterised in that the control of the chemical reaction between both layers is carried out by regulating the glaze PSD, which is characterised by values of D90 <30 μm, in order to reduce pore size and, proportionally, the speed and depth of penetration of the ink by capillary suction.

2- Procedure for controlling the chemical reaction in multi-layer ceramic decorations, according to claim 1, wherein, furthermore, the regulation of ink penetration is carried out by including in the formulation, different types of organic additives of the so-called film-forming additives, which reduce the number of pores present in the glaze, thus slowing down or blocking ink penetration.

3- Procedure for controlling the chemical reaction in multi-layer ceramic decorations, according to claim 2, wherein the film-forming additives to be used can be selected from among different types of polymers: polyoxyethylene derivatives, vinylic polymers such polyvinylpyrrolidone (PVP), acrylic polymers, cellulose polymers such as ethyl cellulose (EC), hydroxypropyl cellulose (HPC), hydroxypropyl methylcellulose (HPMC), hydroxy methyl ethyl cellulose (HMEC) or cellulose acetophthalate (CA), polyoxyl derivatives, phthalate esters, triethyl citrate and triethylamine, diethyl citrate and propylene glycol.

4- Procedure for controlling the chemical reaction in multi-layer ceramic decorations, according to claim 1, wherein the ink (4) is formulated by selecting only some of the necessary oxides to obtain the ceramic effect, using, depending on the type of ink (4) chosen, glaze formulations that provide the rest of the oxides required for the chemical reaction, as well as those that will form the vitreous substrate.

5- Procedure for controlling the chemical reaction in multi-layer ceramic decorations, according to claim 1, wherein the ink (4) is formed mainly by iron oxides or salts, with a concentration by weight of between 30 and 60% of the total weight of the ink.

6- Procedure for controlling the chemical reaction in multi-layer ceramic decorations, according to claim 1, wherein the ink (4) is formed mainly by modified iron phosphates, with a concentration by weight of between 30 and 60% of the total weight of the ink.

Description

DESCRIPTION OF THE FIGURES.

[0027] To gain a better understanding of the object of the present invention, the following explanatory figures are included.

[0028] FIG. 1 shows a block diagram of the application procedure.

[0029] FIG. 2 shows a graph of the evolution of metallic gloss according to the weight of ink applied and the PSD of the glazes

[0030] FIG. 3 shows a graph of the evolution of colouring according to the weight of ink applied and the PSD of the glazes

[0031] FIG. 4 shows a cross section of glazes with different glaze PSD under SEM (scanning electron microscope) at 15,000 times magnification.

PREFERRED EMBODIMENT OF THE INVENTION

[0032] The procedure for controlling the chemical reaction when two overlying layers are used to decorate a ceramic product, that is the object of the present invention, basically comprises, as can be seen in FIG. 1 of the attached drawing, the separate use of a glaze (2) with part of the necessary oxides to obtain the desired ceramic effect and an ink (4) for decorating by injection, with the other necessary part of the oxides. Both layers must react chemically with each other, in a controlled way, by regulating the penetration of ink by capillary suction, by acting on the number and size of the glaze pores, and thus achieving the desired ceramic effect. This ceramic effect consists of obtaining visual effects or special textures: metallic gloss, matt texture, surfaces protected by devitrification of crystalline species, etc.

[0033] This separate use is carried out by means of a first phase of application (3) of the glaze (2) on a ceramic base (3), followed by a second phase of decorating by injection (5) of a special ink (4) over the layer previously deposited on the ceramic base (1), completed by a third phase of firing (6).

[0034] The phase of application (3) of the glaze (2) on a ceramic base (1) is carried out by means of a process chosen from amongst the group formed by: bell, airbrush, rotary, disc or waterfall.

[0035] The phase of injection (5) of the ink (4) is preferably carried out using a standard inkjet head such as those commonly used for decorating ceramic products. This process involves the penetration of the ink (4) in the glaze (2).

[0036] The firing phase (6) is carried out by means of a normal ceramic cycle, from traditional double firing at 900° C. to high-temperature porcelain stoneware firing at 1300° C. This firing involves the diffusion of the ink oxides inside the melted glaze which permits the chemical reaction between both, giving rise to the desired ceramic effect.

[0037] The ink (4) is formulated by selecting only some of the oxides needed to obtain the ceramic effect, since the technique of inkjet printing only allows a very light weight to be applied. Depending on the type of ink (4) chosen, glaze formulations are used that provide the rest of the oxides that are necessary for the chemical reaction, as well as those that form the vitreous substrate.

[0038] In its formulation the glaze allows the penetration of ink by capillary suction to be regulated by means of two mechanisms: [0039] a) Preferably, by regulating the PSD of the glaze in order to modify the mean pore size and, in this way, adjust the speed and depth of ink penetration. By reducing the PSD of the glaze, the mean pore size decreases and the speed and depth of ink penetration is reduced proportionally. Thus, in glazes with a PSD characterised by having D90<30 μm, reductions of between 50 and 75% in the required weight of ink to be applied per surface unit can be obtained, due to lower ink penetration. [0040] b) Furthermore, the formulation includes different types of organic additives, the so-called film-forming additives, to slow down or block ink penetration by reducing the number of open pores, which decreases the speed of absorption by the glaze. The film-forming additives to be used can be selected from among different types of polymers: polyoxyethylene derivatives, vinylic polymers such polyvinylpyrrolidone (PVP), acrylic polymers, cellulose polymers such as ethyl cellulose (EC), hydroxypropyl cellulose (HPC), hydroxypropyl methylcellulose (HPMC), hydroxy methyl ethyl cellulose (HMEC) or cellulose acetophthalate (CA), polyoxyl derivatives, phthalate esters, triethyl citrate and Triacetylamine, diethyl citrate and propylene glycol.

[0041] Thus, thanks to these two mechanisms for controlling the penetration of ink by capillary suction, the addition of reagents is optimized, reducing the weight of ink that has to be applied.

[0042] In a specific embodiment of the invention, the ink (4) is mainly formed by iron oxides or salts, with a concentration by weight of between 30 and 60% of the total weight of the ink. In this embodiment the glaze employed as the substrate has a PSD characterised by a value of D90<30 μm. As a result of this specific embodiment a ceramic tile is obtained with a metallic effect decoration that can be measured by colorimetric and gloss measurement techniques.

[0043] In another specific embodiment of the invention, the ink (4) is mainly formed by modified iron phosphates, with a concentration by weight of between 30 and 60% of the total weight of the ink. In this embodiment the glaze employed as the substrate has a PSD characterised by having a value of 20 μm<D90<30 μm. Resulting from this specific embodiment a ceramic tile is obtained with a metallic effect decoration that can be measured by colorimetric and gloss measurement techniques.

[0044] A technical expert will easily comprehend that the characteristics of different embodiments can be combined with the characteristics of other possible embodiments, provided that the combination is technically possible.

EXAMPLES

Example 1

Effect of Glaze PSD on the Penetration of Ink and on the Profile of the Compositions of the Glaze Layer. Its Influence on Obtaining Metallic Effects

[0045] Maintaining the standard formulation of the substrate glaze and just modifying milling conditions, several samples with a decreasing PSD have been prepared in order to study the influence that this variable has on the permeability or penetrability of the ink in the glaze and consequently on the surface characteristics related to the aesthetic appearance to be evaluated.

[0046] The results reveal an evolution in metallic gloss .sup.0M for each glaze PSD as the weight of the ink applied is increased (deriving from the design resolution used). As can be seen in Table 1 and its corresponding FIG. 2, for this case an optimal point, where the metallic gloss is maximized, is located in the zone close to D90=28.9 μm and Ink weight=21.6 g/m.sup.2.

TABLE-US-00001 TABLE 1 Metallic gloss values, in GU, in terms of glaze PSD and ink weight applied Resolution [dpi] (Weight [g/m.sup.2]) 400 600 800 1200 θ.sub.M (8.33) (16.6) (21.6) (35) Glaze A (38.6) 3.6 12.3 36.1 50.6 D90 (μm) B (32.6) 3.6 11.1 42.4 59.4 C (28.9) 4.7 29.3 68.5 41.8 D (18.9) 21.2 51.3 20.7 −1.6 E (13.3) 30.0 8.6 −1.8 −7.1

[0047] Furthermore, in view of the colour variations that exist depending on glaze PSD and the layer of ink applied, the chromatic coordinates of the different applications have been determined, resulting in the data indicated in Table 2.

TABLE-US-00002 TABLE 2 Chromatic coordinates of decorated glazes depending on glaze PSD and ink resolution applied. Resolution [dpi] CIELAB Coordinates 400 600 800 1200 Glaze (D90 [μm]) A L* 54.3 48.0 52.2 63.4 (38.6) a* 12.9 5.0 −0.7 −1.2 b* 22.6 2.9 −1.5 1.8 C* 26.0 5.7 1.6 2.1 B L* 53.2 45.8 52.4 65.7 (32.6) a* 14.1 5.7 −0.6 −1.1 b* 23.5 3.1 −0.8 4.2 C* 27.4 6.5 1.0 4.3 C L* 49.9 52.3 63.9 65.4 (28.9) a* 13.5 1.1 −2.5 −1.5 b* 19.0 −1.0 −0.5 3.4 C* 23.3 1.5 2.6 3.7 D L* 54.0 59.5 52.5 46.2 (18.9) a* 9.0 −0.7 −0.7 −0.3 b* 8.1 −0.6 −1.0 −1.4 C* 12.1 1.0 1.2 1.5 E L* 55.0 46.8 45.1 43.6 (13.3) a* 4.7 1.9 −0.3 −0.1 b* 4.1 −0.4 −1.8 −1.8 C* 6.3 1.9 1.8 1.8

[0048] FigureError! Reference source not found. shows the L*values, compared to the C* values of the previous table, for the A, D and E test series (for the sake of simplicity tests series B and C are not shown since their results are very similar to test A). The notation employed for the points shown is S(r/100), where S is the series (glaze used) and r/100 is the resolution employed in ink application divided by 100. Thus, for example, A(4) is the point corresponding to glaze A, with a PSD of D90=38.6 μm, with an ink decoration applied at a resolution of 400 dpi.

[0049] As can be seen in Error! Reference source not found.—the test series for glaze A (D90=38.6 μm), with a COARSER PSD, begins with point A(4) whose C* value is quite high, it does not have a metallic appearance and is located in a non-metallic colour zone that we have called Z1. As the resolution for ink application is increased, points A(6), A(8) and A(12), chromaticity C* decreases and luminosity L* increases, entering a metallic gloss zone that we have called Z2.

[0050] For a MEDIUM PSD distribution, such as that of D (D90=18.9 μm), the series begins at point D(4), with a non-metallic colour, reaching the Z2 metallic zone, points D(6) and D(8), more quickly than in the previous case and subsequently reaching a point, D(12), where the values of L* and C* are minimal, affording a blackish appearance due to ink saturation. We have called this saturation zone the Z3 zone.

[0051] Lastly, test series E, with a FINE PSD (D90=13.3 μm) begins at point E(4) on the boundary of the metallic zone where we have metallic gloss but excessive colouring. As ink resolution is increased, the series evolves very rapidly towards points E(6), E(8) and E(12) that are already in the Z3 saturation zone. That is, when the PSD is too fine there is not an optimal point for the development of a metallic effect.

[0052] Error! Reference source not found.—also shows that with a greater PSD in glazes with a low ink weight, a reddish non-metallic tone with a low gloss index is obtained, but as more ink is added, aesthetic properties improve, reaching the metallic gloss effect zone. However, with finer distributions the metallic effect zone is reached with a smaller proportion of ink than is the case with coarser distributions although, consequently, the passage from a reddish appearance to a saturated (graphite-type) appearance occurs sooner with this type of distribution. For this reason, for this example, medium sizes are considered to be optimal because the aesthetic appearance of fine glaze distributions is more sensitive to an increase in ink weight and with just small variations there is a more marked change.

[0053] This phenomenon depends on the particle size of the ink, the number and distribution of sizes of glaze pores (deriving from the glaze PSD and the physical properties of the liquid medium (surface tension and viscosity). The influence of the glaze PSD lies in the fact that as it gets finer, the glaze mean size/ink mean size ratio is reduced, reducing ink penetration. To verify this, scanning electron microscopy tests have been performed (fError!

[0054] Reference source not found.) of the profile of test specimens corresponding to the series: A (COARSE glaze PSD), D (MEDIUM) and E (FINE), all of which are decorated with ink at an intermediate resolution of 600 dpi.

[0055] As can be observed in the image on the left of Error! Reference source not found.—, when the PSD is FINE, the ink cannot penetrate the glaze layer sufficiently during thermal treatment for an adequate chemical diffusion of the atoms contributed by the ink to take place inside the glass and a balanced distribution of the oxides that form part of the reaction is not achieved, so that said reaction does not occur and the effect is not obtained. This would correspond to point E(6) of Error! Reference source not found.

[0056] In the centre of Error! Reference source not found. the case of a MEDIUM PSD can be seen. The ink penetrates the glaze layer, the oxides are suitably diffused inside the glass and the chemical reaction occurs and there is surface recrystallization which gives rise to the observed metallic effect, corresponding to point D(6) of Error! Reference source not found.

[0057] Finally, on the right of FIG. 4 we have the case of COARSE PSD. There is an excessive penetration of the ink in the glaze so that when the corresponding thermal treatment is carried out, the chemical diffusion generated causes an excessive dispersion of the oxides so that the concentration required for the chemical reaction to take place is not reached, resulting in a coloured surface but without a metallic gloss, corresponding to point A(6) of Error! Reference source not found.

[0058] All of the information referring to examples or embodiments, including the tables, form part of the description of the invention. A technical expert will easily comprehend that the characteristics of different embodiments can be combined with the characteristics of other possible embodiments provided that the combination is technically possible, such as, for example, combining the optimal point obtained in example 1, which maximizes metallic gloss, in the zone close to D90=28.9 μm and ink weight=21.6 g/m.sup.2, by adding to the glaze a cellulose derivative such as ethyl cellulose (EC) in the non-limitative proportion of 0.5% by weight of the total of the glaze formula (excluding load water), which would give rise to a glaze surface of a more plastic nature, reducing ink penetration even further.