Method for manufacturing coloured glass-ceramic slab articles from a base mix, glass frit for manufacturing the base mix and coloured glass-ceramic slab article so obtained

Abstract

Method for manufacturing coloured glass-ceramic slab articles from a base mix, including the steps of (a) preparing a mix comprising a colouring pigment, at least one binder and a preponderant amount of a glass frit having a specific composition, (b) distributing the mix in a forming support, (c) compacting the mix, (d) drying the mix, (e) sintering the compacted and dried mix by firing to obtain a slab article, and (f) cooling the articles under conditions such as to preventeven partialdevitrification and/or crystallization of the glass frit. Also relating to a glass frit for manufacturing base mixes and a coloured glass-ceramic slab article obtained from the base mix.

Claims

1. A method for manufacturing coloured glass-ceramic slab articles from a base mix, comprising the following steps: (a) preparing a mix comprising a preponderant amount, greater than 45% by weight, of a glass frit, at least one binder and a colouring agent or pigment; (b) distributing the mix in a support or in a forming mould; (c) compacting the mix contained in the support or in the mould; (d) drying the compacted mix; (e) sintering the compacted and dried mix by firing and obtaining the glass-ceramic slab article; and (f) cooling the article obtained from the firing under conditions which avoid a devitrification and/or crystallization, even only partial, of the glass frit; characterized in that the glass frit comprises: a weight amount of silica (SiO.sub.2) comprised between 55% and 62% relative to an overall weight of the frit; a weight amount of alumina (Al.sub.2O.sub.3) comprised between 16% and 22% relative to the overall weight of the frit; a weight amount of sodium oxide (Na.sub.2O) comprised between 0.3%, and 3% relative to the overall weight of the frit; a weight amount of potassium oxide (K.sub.2O) comprised between 2% and 6% relative to the overall weight of the frit; a weight amount of calcium oxide (CaO) comprised between 12% and 18% relative to the overall weight of the frit; and a weight amount of magnesium oxide (MgO) comprised between 0.4% and 3% relative to the overall weight of the frit.

2. The method according to claim 1, characterized in that the cooling step is performed so that the period for cooling from the maximum firing temperature to room temperature is not more than 4 hours.

3. The method according to claim 1, characterized in that said colouring agent or pigment is added to said mix before said step 0) for distributing the mix in the temporary support.

4. The method according to claim 3, characterized in that the weight amount of pigment added to the mix is comprised between 1% and 3%.

5. The method according to claim 1, characterized in that the slab article has a predefined colour corresponding to the used pigment, at the end of the manufacturing process.

6. The method according to claim 5, characterized in that said pigment is black so that the colour of the slab article is black.

7. The method according to claim 1, characterized in that the glass frit is resistant to devitrification and/or crystallization, even only partial, both after heating during the firing step of the mix and after subsequent cooling of the article.

8. The method according to claim 1, characterized in that the glass frit determines a hardness of the glass-ceramic slab article greater than or equal to 5 Mohs.

9. The method according to claim 1, characterized in that said binder is an organic binder and/or an inorganic binder.

10. The method according to claim 9, characterized in that said inorganic binder is a water dispersion of colloidal silica.

11. The method according to claim 9, characterized in that said organic binder is chosen from the group comprising polyvinyl alcohol, water-soluble cellulose and a polysaccharide.

12. The method according to claim 1, characterized in that the compaction of the mix is performed by vacuum vibro-compression.

13. The method according to claim 1, characterized in that the sintering step is performed in a furnace at a temperature of about 1200 C.

14. The method according to claim 1, characterized in that the mix, in addition to the glass frit, comprises a weight amount of between 25-40% of feldspar and/or clay minerals.

15. A glass frit for manufacturing a base mix intended for the manufacture of glass-ceramic slab articles, comprising: a weight amount of silica (SiO.sub.2) comprised between 55% and 62% relative to an overall weight of the frit; a weight amount of alumina (Al.sub.2O.sub.3) comprised between 16% and 22% relative to the overall weight of the frit; a weight amount of sodium oxide (Na.sub.2O) comprised between 0.3% and 3% relative to the overall weight of the frit; a weight amount of potassium oxide (K.sub.2O) comprised between 2% and 6% relative to the overall weight of the frit; a weight amount of calcium oxide (CaO) comprised between 12% and 18% relative to the overall weight of the frit; and a weight amount of magnesium oxide (MgO) comprised between 0.4% and 3% relative to the overall weight of the frit; wherein the glass frit is at least partially resistant to one or more of devitrification and crystallization.

16. A slab article made of a coloured glass-ceramic obtained by a manufacturing method according to claim 1.

17. The slab article according to claim 16 characterized by having a transparent effect on visible surfaces of the article.

18. The method according to claim 14, characterized in that the feldspar and/or clay minerals comprise kaolin.

19. The slab article according to claim 17 characterized by having a black colour.

20. The glass frit of claim 15, wherein said resistance of the glass frit to one or more of devitrification and crystallization is imparted on the glass frit based on its composition and the weight amount of the alumina (Al.sub.2O.sub.3) thereof.

21. The glass frit of claim 15, wherein said resistance of the glass frit to one or more of devitrification and crystallization is maintained during/after prior heating of the glass frit to a firing temperature and subsequent cooling thereof to room temperature.

Description

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(1) The advantages and characteristic features of the present invention will emerge more clearly from the detailed description below of an example of embodiment provided by way of a non-limiting example.

(2) The present invention relates to a method for manufacturing coloured glass-ceramic slab articles from a base mix and a coloured glass-ceramic slab article obtained by means of the manufacturing method using a base mix.

(3) The base mix contains a vitreous material, preferably a glass frit, having the aforementioned composition as well as one or more colouring agents or pigments for obtaining the desired colouring. Moreover, the material of the finished articles may be defined as being glass-ceramic in accordance with the definition provided above.

(4) In a manner known per se, the method comprises: a) a step of preparing the mix comprising a preponderant amount, greater than 45% by weight, of glass frit, at least one colouring agent or pigment and at least one binder and b) a step of distributing the mix in a mould or forming support.

(5) As mentioned above, in this context the expression preponderant amount indicates an amount of glass frit greater than 45% relative to the overall weight of the mix.

(6) Conveniently, as already mentioned above, the mix may contain an amount of about 25-40% by weight of feldspar and/or clay minerals, in particular kaolin and/or similar materials, in addition to the glass frit.

(7) Distribution of the mix is performed by means of machines known in the field, comprising for example a hopper and an extractor belt. Moreover, the deposition of the mix inside the mould or the support may be performed in several stages.

(8) Optionally, after deposition of the mix in the support, a mesh of metallic or ceramic material may be embedded in the mix in order to reinforce the structure thereof after the hardening obtained by means of firing of the mix.

(9) Advantageously, the binder which forms the mix may be an organic binder and/or an inorganic binder. By way of example, the inorganic binder is an aqueous dispersion of colloidal silica, while the organic binder is chosen from the group comprising polyvinyl alcohol, water-soluble cellulose or a polysaccharide.

(10) The glass frit with the aforementioned composition is resistant toeven only partialdevitrification and/or crystallization both during the heating which occurs during the firing step and during the cooling which occurs in the following step.

(11) In particular, the composition of the frit and the weight amount of alumina described above prevent the glass frit from even only partial devitrification or crystallization during cooling from the maximum firing temperature to room temperature.

(12) However, so that the devitrification is entirely negligible and insignificant, cooling from the maximum temperature to room temperature must preferably not exceed 4 hours.

(13) The colouring agent or pigment may be added to the base mix in a predefined weight amount. The pigment addition step is performed before step b) described above so that the pigment is mixed with the mix. Suitably, the weight amount of pigment added to the mix is between 1% and 3%.

(14) The transparent nature of the slab articles made with the method according to the present invention makes the colouring agent or pigment added to the mix visible.

(15) In particular, the colouring of the pigment is particularly deep and intense, even if the pigment is incorporated within the body of the slab article. Preferably, the pigment added to the mix has a black colour.

(16) In fact, it has been noted that this colour gives the slab article a high-quality aesthetic effect at the end of the manufacturing process. However, differently coloured pigments may also be used, without thereby departing from the scope of protection of the present invention.

(17) The method for manufacturing slab articles comprises a step c) for compacting, preferably by means of vacuum vibro-compression, the mix contained in the support, a mix drying step d), a step e) of sintering the compacted and dried mix by means of firing to obtain the slab element, and a step f) of cooling the article under conditions such as to prevent even only partial devitrification and/or crystallization of the glass frit.

(18) The compaction step may be performed by means of a press provided with a ram under vacuum conditions for application of a pressure on the mix contained in the support, together with a vibrating movement of predetermined frequency and for a predetermined time period.

(19) The drying step is performed in order to eliminate the water from the mix and may also help activate the binder.

(20) Conveniently, the step e) of performing sintering by means of firing may be performed in a roller furnace at about 1200 C.

(21) Advantageously, before the firing step, a step of depositing and drying a layer of refractory material (known as slip) on the bottom surface of the slab, in order to prevent adhesion of the slab to the furnace rollers, may be performed.

(22) During sintering, the dried article is fired to a temperature close to 1200 C., preferably between 1160 C. and 1200 C., in particular between 1170 C. and 1200 C.

(23) Advantageously, the method described above may be performed by means of plants which are widely known in the sector for the manufacture of slab articles made of ceramic material, without the need to make modifications or changes and by setting suitable operating conditions for the time and temperature.

(24) At the end of the production process, the slab article may undergo further finish-machining operations which are not described in detail since known to the person skilled in the art.

(25) From the above description it is now clear how with the manufacturing method, the glass frit and the coloured slab article it is possible to achieve advantageously the predefined objects.

(26) In particular, it is clear how the glass frit used for producing the mix intended for the manufacture of coloured glass-ceramic slab articles is able to provide a transparent effect on the visible surfaces of the article so that it is possible to view from outside the pigment added to the base mix also at a deep level. In fact, owing to the weight amount of alumina, and consequently of the other elements used, it is possible to obtain a transparent effect with a predefined colour, preferably black using black pigments, of the finished article.

(27) The characteristic features of the various solutions shown here may be combined with each other according to specific needs and wishes, as may be easily imagined by the person skilled in the art.