HK1021365B - Process for ceramic products colouring - Google Patents

Description

Method for colouring ceramic articles

Technical Field

The present invention relates to compositions for coloring ceramic products and to the associated coloring process.

The compositions according to the invention consist in particular of aqueous or hydroalcoholic solutions of inorganic salts or organic derivatives of chromium in mixtures with inorganic salts or organic derivatives of metals chosen from antimony, zinc, zirconium and manganese, which make it possible to impart specific colours to the ceramics, using compositions containing a certain amount of TiO₂Said TiO ceramic matrix, said TiO₂For example, added to the ceramic body prior to molding. In addition, the solution can also be mixed with other metal cation solutions to obtain specific color.

State of the art

The use of coloured ceramics, as well as the compositions and the preparation methods for obtaining said colours, have been well known for a long time. One of the most common methods is the addition of powder pigments, in particular inorganic oxides and inorganic colouring substances, to the ceramic material before sintering (vitrified stoneware). The ceramic products produced are coloured throughout their thickness, consuming a large amount of colouring substances, which are the most expensive components.

It is considered that coloring of the inside of the ceramic article is unnecessary because the material is opaque, and for this reason, research has been conducted to develop a method of coloring only the surface of the ceramic article, which can significantly reduce the cost of the material.

A method developed for this purpose is to add pigments to the surface of ceramics (in particular bricks) which have been moulded without final pressing and sintering.

Said technique is particularly suitable for vitrified stoneware tiles, since it produces a surface layer 2-3mm thick which can also be decorated smoothly. The method can save material as it only colors a thin layer of the ceramic product; however, this method is almost infeasible because of the need for measuring and feeding devices for the amount and type of pigment used to obtain the desired product when molding the ceramic. Moreover, particularly complex products cannot be prepared in this way.

Another method is to make the surface of the ceramic material adsorb an aqueous solution of inorganic salts or metal organic derivatives (as described in Sprechsal, vol 119, No. 10, 1986 and EPA 0704411) which are converted to stable colorants at high temperatures during sintering of the ceramic, either after partial sintering (as disclosed in german patent DE 2012304) or simply after moulding and before sintering (as disclosed in swiss patent CH 575894). The aqueous solution is applied to the ceramic material, for example by dipping or spraying or a disk process or screen printing. The aqueous solution is applied to the ceramic material prior to final sintering.

This coloring method is particularly advantageous because it can provide an extremely thin colored layer. This method is widely used for flat articles (e.g. tiles for floors and walls).

Another problem with the use of aqueous coloring is the depth of penetration of the coloring substance into the ceramic material. In fact, experimental data have shown that the depth of penetration depends on various parameters, such as the viscosity and surface tension of the colouring solution, the application temperature, the amount of water sprayed on the article after application of the colouring solution, the application technique.

The latter parameter, the application technique, is of paramount importance: in fact, the amount of coloring solution applied by disc treatment or spraying can be as high as 400-600g/m²Usually up to 100-²。

The screen printing technique requires in particular that it allows to obtain only one graphic, drawing and coloured-drawing article, requiring a lower amount of colouring agent. The colorant penetrates into the ceramic material before sintering, and the ceramic material has a high amount of water or other substances after the coloring solution is applied. However, the resulting color is not as intense as that produced by other techniques.

The penetration of the colouring substance into the ceramic material is particularly important in the case of smooth vitrified stoneware tiles. The term "smooth vitrified ware" as used herein refers to vitrified ware whose surface has been ground by a diamond grinding wheel to a thickness of 0.8-1.5mm, fine ground and felt polished to a glassy surface. Obviously, the colouring of stoneware to be polished after sintering would require a depth of penetration of the colouring agent of at least 1.6 mm. Technical problem

Since the colouring of ceramic materials by disc treatment or spraying is easy to carry out, the ceramic industry is of great interest to find new substances suitable for said technology.

The technical problem to be solved is that the new substances are easily transformed into colorants which are stable at high temperatures and which are capable of giving the desired shade of colour to the article without the need to consume large amounts of colorants which are capable of penetrating deeper into the ceramic material.

Unfortunately, to date, there are few colorants on the market. In particular, the vitrified stoneware industry is perceived to lack yellow and orange shades, and therefore, there is always a need for new aesthetic solutions.

Furthermore, since yellow is the primary color, the lack of products that impart the above shades makes it impossible to obtain many other colors.

Detailed description of the invention

Applicants having years of experience in the manufacture and sale of colorants for ceramic tiles have now found that mixed aqueous or hydroalcoholic solutions of inorganic salts or organic derivatives of chromium and inorganic salts or organic derivatives of metals selected from the group consisting of antimony, zinc, zirconium and manganese, including antimony, zinc, zirconium and manganese, exhibit a yellow to orange-yellow, to orange, to light orange, to havana-orange color after sintering.

The colour formed depends on the weight ratio of antimony/chromium, zinc/chromium, zirconium/chromium, manganese/chromium in solution and, if necessary, on the TiO of the ceramic matrix (before sintering)₂Content and Al (OH)₃And (4) content.

The aqueous or hydroalcoholic solution is particularly suitable for coloured vitrified stoneware tiles, which may be smooth or not, or coloured by screen printing techniques.

It is an object of the present invention to provide a method for colouring ceramic articles made of ceramic materials, wherein the colour of the ceramic articles ranges from yellow to orange, characterised in that 0.5-10% by weight of TiO, on a dry basis, is added to the ceramic material before moulding₂Subsequently treating the moulded article with a colouring composition in the form of an aqueous or hydroalcoholic solution, wherein the colouring composition contains a mixture of inorganic salts or organic derivatives of chromium and inorganic salts or organic derivatives of a metal selected from Sb, Zn, Zr or Mn or mixtures thereof,

the composition comprisesThe concentration of the element compound is such that when 30-600g/m is applied to the ceramic surface²The composition of (3) should ensure that:

a)0.1-30g/m²chromium and 1-90g/m²Antimony, and/or

b)0.05-20g/m²Chromium and 1-60g/m²Zinc, and/or

c)0.05-20g/m²Chromium and 1-60g/m²Zirconium, and/or

d)0.05-20g/m²Chromium and 1-40g/m²The amount of manganese is such that,

the above contents are all expressed as elements.

It is an object of the present invention to provide an aqueous or hydroalcoholic solution of inorganic salts or organic derivatives of antimony and chromium, or zinc and chromium, or zirconium and chromium, or manganese and chromium, for treating molded articles made of ceramic materials which, after sintering, give the ceramic product a yellow, or orange-yellow or orange-light or orange-havana colour, said ceramic material having added to it, before molding, from 0.5% to at most 10% by weight (preferably at least 1% by weight), based on the dry basis, of TiO₂And optionally 1-8% by weight of Al (OH)₃(dry basis) or equivalent amount of Al₂O₃。

It is another object of the present invention to obtain commercially unavailable colors or shades by mixing the above inorganic salts or organic derivatives of chromium and antimony, or chromium and zinc, or chromium and zirconium, or chromium and manganese with inorganic salts or organic derivatives of other metals already known for coloring ceramic substrates, such as V, Ni, Co and Fe.

Although sulfates, hydrochlorides and nitrates are particularly inexpensive and suitable for obtaining the desired color, they generate corrosive gases during sintering; therefore, there is a need for a kiln equipped with a means for reducing combustion gases. Therefore, it is preferred to use organic derivatives that pyrolyze to water and carbon dioxide during sintering, whenever possible. Particular preference is given to salts of monocarboxylic or polycarboxylic acids having from 1 to 18 carbon atoms, optionally with from 1 to 5 substituents on the aliphatic chain, which may be hydroxyl, amino and mercapto.

Examples of non-limiting carboxylic acids are listed below: acetic acid, formic acid, propionic acid, butyric acid, lactic acid, glycolic acid, tartaric acid, citric acid, oxalic acid, maleic acid, citraconic acid, fumaric acid, gluconic acid, glycine, aminoadipic acid, aminobutyric acid, aminocaproic acid, aminocaprylic acid, 2-amino-4-hydroxybutyric acid, aminoisobutyric acid, aminolevulinic acid, thioglycolic acid.

Suitable organic derivatives according to the invention also include those having polymers and copolymers of polymeric polycarboxylic acids, such as acrylic acid or methacrylic acid, and vinyl ether copolymers of maleic anhydride and acrolein.

The amounts of inorganic salts and organic derivatives added to the ceramic material before sintering to obtain the desired colour must be such as to ensure application to the surface of the material to be coloured, they have the following colouring components:

in the case of chromium/antimony mixtures, the Sb content is from 1 to 90g/m²(preferably 3 to 48 g/m)²) The content of Cr is 0.1-30g/m²(preferably 0.8 to 15 g/m)²)

In the case of chromium/zinc mixtures, the Zn content is from 1 to 60g/m²(preferably 2 to 30 g/m)²) The content of Cr is 0.05-20g/m²(preferably 0.05-12 g/m)²)

In the case of chromium/zirconium mixtures, the Zr content is from 1 to 60g/m²(preferably 2 to 30 g/m)²) The content of Cr is 0.05-20g/m²(preferably 0.05-12 g/m)²)

In the case of chromium/manganese mixtures, the Mn content is from 1 to 40g/m²(preferably 2 to 32 g/m)²) The content of Cr is 0.05-20g/m²(preferably 0.05-12 g/m)²)

All contents are expressed in terms of elements. The higher the chromium concentration, the more gradual the color transition from orange-yellow to light orange. For example, at an antimony/chromium ratio of 6, the color is yellow with a light orange color, at a ratio of 3.3, the color is orange yellow, and at a ratio of 1.5, the color is positive orange.

A typical process for applying the coloring composition of the present invention mainly comprises the steps of: a) drying the molded article to be colored at 100 ℃ to a residual water content of up to 0.5% by weight; b) treating the article of the previous step with an aqueous solution of a coloring composition so that the coloring amount of the finally colored surface is from 30 to 600g/m²(ii) a c) Equilibrating the product of the previous step at room temperature for 8 hours, allowing it to adsorb the solution uniformly; d) sintering is then carried out according to a conventional ceramic firing schedule.

The following intermediate operating steps are optional:

-pre-treating the dried product of step a) with water between step a) and step b) to a maximum water content of 300g/m at the surface of the product²

Between step b) and step c), the product of step b) is post-treated with water to a maximum water content of 300g/m on the surface of the product²。

The aqueous colorant solutions of the present invention can be made into paste form for use on ceramic surfaces by screen printing methods by adding about 1% by weight of a thickening agent such as glucomannan.

The composition of the ceramic material used for the tests was as follows (in% by weight): A) SiO 2₂＝64.4％；Al₂O₃＝21.8％；K₂O＝3.8％；Na₂O＝0.8％；CaO＝0.6％；MgO＝0.1％；TiO₂＝0.4％；Fe₂O₃＝0.2％；ZrSiO₄＝5％；H₂O is added to 100%.

In the analysis data of ceramic body A, TiO₂0.4%. In fact, this data is simply an average analytical representation of the presence of titanium in various chemical forms, such as titanium silicate, corresponding to TiO₂The amount of (B) was 0.4%. B) SiO 2₂＝64.4％；Al₂O₃＝21.8％；K₂O＝3.8％；Na₂O＝0.8％；CaO＝0.6％；MgO＝0.1％；TiO₂＝5.4％；Fe₂O₃＝0.2％；H₂O is added to 100%.

The ceramic material B is made of 5 wt% TiO₂Instead of 5% zirconium silicate. C) SiO 2₂＝64.4％；Al₂O₃＝21.8％；K₂O＝3.8％；Na₂O＝0.8％；CaO＝0.6％；MgO＝0.1％；TiO₂＝3.4％；Fe₂O₃＝0.2％；H₂O is added to 100%.

The ceramic material C is made of 3 wt% TiO₂Instead of 5% zirconium silicate.

Examples 1 to 30

A series of coloring tests were performed according to the following method.

Molding 33cm × 33cm bricks, drying at 100 deg.C to residual water content of 0.1% (weight loss after drying at 120 deg.C for 4 hr), cooling to room temperature, and adding 50g/m²Spraying distilled water (pretreatment) and using 250g/m²The aqueous colorant solution is sprayed (treated). Once the tiles have been subjected to the treatment described, they are left at room temperature for 8 hours (levelling action) and sintered in a roller kiln according to the standard firing schedule of vitrified stoneware (maximum sintering temperature 1200 ℃).

After sintering, a tile was cut and the color penetration was determined by optical microscopy. The other brick was ground with a diamond wheel to a wear depth of 1.2mm and the thickness of the coloured layer was recorded.

The parameters used in the various tests and the results obtained are shown in table 1. Table 1(1), (2), (3), (4), (5), (6)

Of cations in solution

Content% (by weight)

(calculated by element) 1B Sb 2.81.8 orange yellow

Cr 0.852C Sb 2.81.8 orange yellow and orange yellow

Cr 0.853A Sb 2.81.8 is colorless and colorless

Cr 0.854B Sb 2.51.8 orange

Orange color of Cr 1.75C Sb 2.51.8

Cr 1.76A Sb 2.51.8 pale beige and pale beige

Cr 1.77B Sb 2.21.8 dark orange

Cr 2.558C Sb 2.21.8 dark orange

Cr 2.559A Sb 2.21.8 sand

Cr 2.5510B Sb 1.91.8 light orange

Cr 3.411C Sb 1.91.8 light orange

Cr 3.412A Sb 1.91.8 sand color

Cr 3.413B Zn 5.41.8 is pale yellow and yellowish

Cr 0.8514C Zn 5.41.8 is pale yellow

Cr 0.8515A Zn 5.41.8 light beige colorless

Cr 0.8516B Zn 4.81.8 Havana yellow

Cr 1.717C Zn 4.81.8 Havana yellow

Cr 1.718A Zn 4.81.8 Havana color light Havana color

Cr 1.719B Zr 5.41.8 was pale yellow-yellowish

Cr 0.8520C Zr 5.41.8 is pale yellow

Cr 0.8521A Zr 5.41.8 light beige colorless

Cr 0.8522B Zr 4.81.8 Havana yellow

Cr 1.723C Zr 4.81.8 Havana yellow

Cr 1.724A Zr 4.81.8 Havana color light Havana color

Cr 1.725B Mn 5.41.8 Havana yellow

Cr 0.8526C Mn 5.41.8 Havana yellow Havana

Cr 0.8527A Mn 5.41.8 light beige

Cr 0.8528B Mn 4.81.8 orange Havana color

Cr 1.729C Mn 4.81.8 orange Havana color

Cr 1.730A Mn 4.81.8 light Havana color and light Havana color

Cr 1.7(1) content% by weight of cations (i.e., metal compounds) represented by elements used in the solution of the ceramic body (3) used in example No. (2). Antimony used as antimony potassium-stabilized hydroxysuccinate (Sb/K weight ratio of 3) chromium used as chromium tris-etanoate chromium using zirconium used as zirconium bis-hydroxy-bisetanoate zirconium using manganese used as manganese bis-etanoate zinc using (4) depth of penetration of color (mm) (5) color of front surface ground flat (6) color of back surface ground flat (6)Supplementary notes

With no addition of TiO₂The ceramic material A of (1) as a comparative example was subjected to the above-mentioned tests, from which it could be concluded that the coloring was not sufficient in some cases and too light in other cases, in whatever case inconsistent with the coloring of the present invention.

Claims (10)

1. Method for colouring ceramic articles made of ceramic materials, wherein the colour of the ceramic articles ranges from yellow to orange, characterised in that 0.5-10% by weight of TiO on a dry basis is added to the ceramic materials before moulding₂Subsequently treating the moulded article with a colouring composition in the form of an aqueous or hydroalcoholic solution, wherein the colouring composition contains a mixture of inorganic salts or organic derivatives of chromium and inorganic salts or organic derivatives of a metal selected from Sb, Zn, Zr or Mn or mixtures thereof,

said groupThe concentration of the compound containing the above element compound is such that when 30 to 600g/m is applied to the surface of the ceramic²The composition of (3) should ensure that:

a)0.1-30g/m²chromium and 1-90g/m²Antimony, and/or

b)0.05-20g/m²Chromium and 1-60g/m²Zinc, and/or

c)0.05-20g/m²Chromium and 1-60g/m²Zirconium, and/or

d)0.05-20g/m²Chromium and 1-40g/m²The amount of manganese is such that,

the above contents are all expressed as elements.

2. The method of claim 1, said ceramic material containing, in addition to TiO added before molding₂In addition, it contains 1-8 wt% of Al (OH) calculated by dry basis₃Or an equivalent amount of Al₂O₃。

3. A process as claimed in claim 1 or 2, wherein the chromium, antimony, manganese, zinc or zirconium compounds used are sulfates, hydrochlorides and nitrates.

4. Composition according to claim 1 or 2, characterized in that: the compounds of chromium, antimony, zinc, zirconium and manganese are salts of monocarboxylic or polycarboxylic acids having 1 to 18 carbon atoms, optionally with 1 to 5 substituents on the aliphatic chain, which may be hydroxyl, amino and mercapto.

5. A method according to claim 1 or 2, characterized in that: comprises the following steps: a) drying the molded article to be colored at 100 ℃ to a residual water content of up to 0.5% by weight; b) treating the article of the previous step with the aqueous coloring composition solution; c) equilibrating the product of the previous step at room temperature for 8 hours; d) sintering is then carried out according to a conventional ceramic firing schedule.

6. The method according to claim 5, wherein between step a) and step b) is performedThe following intermediate steps: a.1) pretreating the dried product of step a) with water to a maximum water content of 300g/m on the surface of the product²。

7. The method according to claim 5, wherein the following intermediate steps are performed between step b) and step c): b.1) post-treating the product of step b) with water to a maximum water content of 300g/m on the surface of the product²。

8. The method according to claim 5, wherein two intermediate steps of claims 6 and 7 are performed.

9. Vitrified stoneware tile obtained according to the method of any of claims 1 to 8.

10. A vitrified stoneware tile according to claim 9, wherein the method further comprises subsequent grinding of the coloured surface to a depth of 0.8-1.5mm and final polishing of the surface.