Method for manufacturing articles in the form of a slab or block with a hardening binder, and articles thus obtained

Abstract

In a method for manufacturing articles in the form of a slab or block, the articles are obtained from an initial mix comprising aggregates and a binder. Synthetic aggregates and fillers have a hardness greater than or equal to 5 Mohs, and contain silicon dioxide substantially only in amorphous form, the silicon dioxide in crystalline form being present in quantities of less than 1% by weight.

Claims

1. A method for manufacturing articles in the form of a slab or block, said articles being obtained from an initial mix comprising aggregates and a binder, characterized in that the initial mix comprises stone-like synthetic aggregates and fillers with a hardness greater than or equal to 5 Mohs, which contain silicon dioxide substantially only in amorphous form while any case of silicon dioxide in crystalline form being present in quantities of less than 1% by weight; and wherein the synthetic aggregates and fillers have the following chemical composition: 43%<SiO.sub.2<80%, 5%<CaO<30%, 0%<MgO<12%, 0%<Al.sub.2O.sub.3<25%, 0%<ZrO.sub.2<20%, 0%<Na.sub.2O <12%, and 0%<K.sub.2O <10%; the SiO.sub.2 being present substantially only in amorphous form while any case of the SiO.sub.2 in crystalline form being present in quantities of less than 1% by weight; and wherein the initial mix undergoes vacuum vibro-compression followed by a binder hardening step.

2. The method according to claim 1, characterized in that the initial mix is subjected to a rolling process in which the mix is distributed widthwise on top of a conveyor belt so that an upper surface of the mix is configured to be subjected to a pressing action by a cylinder or by a second synchronized belt situated opposite the conveyor belt.

3. The method according to claim 1, characterized in that the mix is subjected to a pressing process in which the mix is distributed widthwise on top of a support and then subjected to a pressing action by a press ram.

4. The method according to claim 1, characterized in that the mix is subjected to an extrusion process through a die having a same shape as a cross-section of the slab.

5. The method according to claim 1, characterized in that at least 70% by weight of the aggregates and fillers consists of synthetic aggregates and fillers with a hardness greater than or equal to 5 Mohs, which contain silicon dioxide substantially only in amorphous form.

6. The method according to claim 1, characterized in that said synthetic aggregates and fillers form between 70% and 100% by weight of the aggregates and fillers of the initial mix.

7. The method according to claim 1, characterized in that the chemical composition of the synthetic aggregates and fillers also comprises the following further components: 0%<B2O3<10%, 0%<ZnO<10%, 0%<BaO<10%, 0%<Li2O<5%, and 0%<P2O5<5%.

8. The method according to claim 7, characterized in that the chemical composition also comprises Fe.sub.2O.sub.3<0.1% and TiO.sub.2<0.1%.

9. The method according to claim 1, characterized in that the chemical composition also comprises Fe2O3<0.1% and TiO2<0.1%.

10. The method according to claim 1, characterized in that the binder used is of an organic nature.

11. The method according to claim 10, characterized in that the organic binder used is an unsaturated polyester resin.

12. The method according to claim 11, characterized in that an amount of the resin used is equal to less than 30% by weight.

13. The method according to claim 1, characterized in that the binder is of a cementitious nature.

14. An article in the form of a slab or block obtained from an initial mix comprising aggregates and a binder, characterized in that the initial mix comprises stone-like synthetic aggregates and fillers with a hardness greater than or equal to 5 Mohs, which contain silicon dioxide substantially only in amorphous form while any case of silicon dioxide in crystalline form being present in quantities of less than 1% by weight; and wherein the synthetic aggregates and fillers have the following chemical composition: 43%<SiO.sub.2<80%, 5%<CaO <30%, 0%<MgO <12%, 0%<Al.sub.2O.sub.3<25%, 0%<ZrO.sub.2<20%, 0%<Na.sub.2O <12%, and 0%<K.sub.2O <10%; the SiO.sub.2 being present substantially only in amorphous form while any case of the SiO.sub.2 in crystalline form being present in quantities of less than 1% by weight.

Description

(1) The object of the present invention is to solve at least partially the drawbacks of the prior art, in connection with the widespread industrial use of quartz as an aggregate and filler.

(2) A first task of the present invention is therefore to provide a method for manufacturing articles which are made without using quartz, but which have characteristics in terms of appearance and performance similar to those of products which contain quartz and which do not give rise to crystalline silicon dioxide dust during machining operations.

(3) A second task of the present invention is to provide an article made without using quartz, but which has characteristics in terms of appearance and performance similar to those of products which contain quartz and which does not give rise to crystalline silicon dioxide dust during machining operations.

(4) The object and tasks are achieved with the use of aggregates according to claim 1, with a method according to claim 10 and with an article according to claim 25.

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

(6) In particular, the idea which has occurred is to use synthetic aggregates and fillers which are very hard and semi-transparent or whitish, with an appearance similar to quartz, but which contain silicon dioxide substantially only in amorphous form in a method for manufacturing articles in slab or block form, instead of aggregates and/or fillers which are obtained from the grinding of quartz and which, during machining operations such as cutting, could cause the aforementioned problems.

(7) Essentially, the idea which has occurred is to use synthetic aggregates and fillers which are very hard and semi-transparent or whitish, with an appearance similar to quartz, but comprising silicon dioxide substantially only in amorphous form instead of quartz which during the (slab or block) machining process would produce crystalline silicon dioxide dust.

(8) The synthetic aggregate and filler containing silicon dioxide substantially only in amorphous form may be a special amorphous glass, called “frit” in technical jargon, which is very hard and semi-transparent or whitish, with an appearance similar to quartz; traces of silicon dioxide in crystalline form could be present, but in any case in amounts less than 1% by weight.

(9) A frit with these characteristics may be obtained by melting at about 1550° C. a mixture of selected natural mineral powders. The molten material output from the melting furnace is struck directly by a water jet for quick cooling, then dried, ground and separated into the desired granulometric fractions.

(10) The thinner granulometric fractions are used as fillers.

(11) In accordance with a possible embodiment of the present invention, the synthetic aggregate and filler with hardness ≥5 Mohs containing silicon dioxide substantially only in amorphous form may form at least 70% by weight of the aggregates and filler of the initial mix.

(12) Advantageously, the synthetic aggregate and filler with hardness ≥5 Mohs containing silicon dioxide substantially only in amorphous form may form between 70% and 100% by weight of the aggregates and filler of the initial mix.

(13) Advantageously, the glass frit with hardness ≥5 Mohs used may have the following chemical composition: 48%<SiO.sub.2<73%, 12%<CaO<30%, 1.5%<MgO<11%, 1.0%<Al.sub.2O.sub.3<19%, and 0%<ZrO.sub.2<20%.

(14) Or the glass frit with hardness ≥5 Mohs used may have the following chemical composition: 43%<SiO.sub.2<80%, 5%<CaO<30%, 0%<MgO<12%, 0%<Al.sub.2O.sub.3<25%, and 0%<ZrO.sub.2<20%, 0%<Na.sub.2O<12%, 0%<K.sub.2<10%.

(15) Optionally the frit may also contain the following further components: 0%<B.sub.2O.sub.3<10% %<ZnO<10% 0%<BaO<10% 0%<Li.sub.2O<5% 0%<P.sub.2O.sub.5<5%

(16) Advantageously the frit with hardness ≥5 Mohs may have a colour which has a high degree of whiteness (with L>95) or is translucent. These colours are similar to those of quartz which is used in the initial mixes of the known type.

(17) For this purpose the quantities of cromophores must be particularly low so that the aforementioned chemical composition may further comprise: Fe.sub.2O.sub.3<0.1%; and TiO.sub.2<0.1%.

(18) The hardness of the frit granules may be preferably greater than 5 Mohs and even more preferably greater than 6 Mohs.

(19) The frit used is moreover resistant to acids (except for hydrofluoric acid) and has a good resistance to strong bases. Moreover, it is characterized by a total chemical inertia and by complete water insolubility, even in hot conditions, without the need for further heat treatment. Advantageously there is no release of any metals which may be present.

(20) Moreover, the frit used has a good yield during grinding with a limited tendency to produce dust or flakes when ground.

(21) It is particularly advantageous to keep the mix paste-like. According to a possible embodiment of the present invention the binding resin consists of an amount equal to less than 30% by weight.

(22) The other steps of the method for manufacturing the article remain substantially the same as in the prior art.

(23) As regards rolling, after the mix has been prepared, it is distributed widthwise on top of a conveyor belt so that its upper surface may be subject to the pressing action of at least one cylinder. The pressing action may be provided by hydraulic or pneumatic means.

(24) In a possible variation of this process, the mix once distributed on the conveyor belt may be compacted by a second pressing belt, opposite to the first belt and synchronized with it, subject to a crushing action.

(25) Advantageously, in a manner known per se to the person skilled in the art, separating sheets of anti-adhesive material may be inserted between belt and mix and between mix and the at least one pressing cylinder (or belt).

(26) In the case where the mix is used in a pressing process, the mix is distributed widthwise on top of a support, for example a conveyor belt, and is then subjected to a pressing action by a press ram. Advantageously the press ram may have a surface area greater than that of the article to be obtained. In accordance with a possible embodiment of the present invention, the pressing force is produced by hydraulic means.

(27) Advantageously, separating sheets of anti-adhesive material may be arranged between belt and mix and between press ram and mix.

(28) As regards extrusion, the prepared mix is extruded through a die having the shape of the cross-section of the slab. The apparatus also comprises a pressing element which may be for example of the screw or hydraulic type. In accordance with a possible embodiment, once the article has been extruded, it rests for example on a conveyor belt, a film of anti-adhesive material being where necessary arranged in between.

(29) In the case instead of the BRETONSTONE® process, after the initial mix has been prepared, it is deposited inside a temporary holder, which may be a so-called tray mould (in the case of a slab) or a formwork (in the case of a block).

(30) Then the surface of the mix may be covered with a sheet of material which is similar to that forming the tray mould, or a lid in the case of a formwork for the production of blocks.

(31) The holder containing the mix is then inserted inside a bell inside which the vacuum is created and the mix is subjected via a press ram to vacuum vibro-compression.

(32) Advantageously the vacuum created may have a residual pressure of between 10 and 25 mbar.

(33) Advantageously the vacuum vibro-compression may last between 30 and 70 seconds.

(34) Once the vibro-compression operation has been completed, the atmospheric pressure is restored and the bell is opened.

(35) The slab which may be obtained by means any one of the methods described above is then transferred into a catalysis oven, in the case where resin is used as a binder, or is left to cure in the case where a cementitious binder is used.

(36) Once the article has hardened, it is extracted as required from the holder and is conveyed away for the finishing operations.

(37) The advantages which may be obtained compared to the conventional methods for manufacturing articles in the form of slabs or blocks according to the prior art are therefore evident.

(38) Firstly, it is possible to produce articles with a high-quality appearance and resistance to scratching and chemical agents which, during machining operations, such as cutting, do not result in the formation of silicon dioxide dust in crystalline form.

(39) Secondly, by preventing the formation of this component, it is possible to avoid beforehand the consequences of any incorrect behaviour of operators during the machining operations.

(40) Moreover, it is possible to obtain a slab with aesthetic, mechanical and performance characteristics very similar to those achieved with quartz, which at present are very widespread and popular on the market.

(41) The person skilled in the art, in order to satisfy specific needs, may make modifications to the embodiments described above and/or replace the elements described with equivalent elements, without thereby departing from the scope of the attached claims.