IMPROVEMENT OF THE METHOD FOR MANUFACTURING CONGLOMERATE SLABS

Abstract

In the method for manufacturing conglomerate stone slabs using the Bretonstone technology, in the variant where the starting mixture is enclosed between two paper sheets, the improvement consists in replacing each paper sheet with a containment element consisting of a paper sheet, one surface of which has, applied thereon, a film of plastic material which is impermeable to organic vapours, impermeable to the liquids and in particular to the liquid resin constituting the binder of said mixture, resistant to the catalysis temperatures of the said resin and resistant to hot solvents and chemical vapours. Preferably, said plastic material is water-soluble, in particular polyvinyl alcohol.

Claims

1. Method for manufacturing conglomerate slabs comprising the steps of: preparing a mixture comprising granules and powders of stone material having a predetermined grain size, and an organic binder in the form of a liquid resin; pouring of said mixture on a support comprising an upper and lower temporary containment element; vibrocompression under vacuum of the mixture; and hot hardening of the compacted mixture; characterized in that the upper and/or lower temporary containment element of the mixture comprises a sheet of paper or equivalent material, at least one of its surfaces having, applied thereon, a film of plastic material which is: (i) impermeable to organic vapours; (ii) impermeable to the liquids and in particular to the liquid resin constituting the binder of said mixture; (iii) resistant to the catalysis temperatures of said resin; (iv) resistant to hot solvents and chemical vapours; and (v) soluble in water.

2. Method according to claim 1, characterized in that said polymer is a polyvinyl alcohol.

3. Method according to claim 1 or 2, characterized in that said film of plastic material has a basis weight of 10-50 g/m.sup.2 and a thickness of 10-50 m.

4. Method according to any one of claims 1-3, characterized in that said paper sheet of said containment element has a basis weight of 70-200 g/m.sup.2.

5. Method according to claim 1, characterized in that said containment element consists of a film of plastic material applied on the surface of the paper sheet opposite to the surface intended to come into contact with the mixture.

6. Method according to claim 5, characterized in that on said film of plastic material it is applied another sheet of paper.

7. Improvement according to claim 6, characterized in that said sheet of paper has a basis weight comprised between 10 and 50 g/m.sup.2.

8. Containment element for the mixture in a method and plant using the Bretonstone technology, of the type consisting of at least one sheet, i.e. upper sheet and lower sheet enclosing a layer of mixture, characterized in that each sheet consists of a paper sheet, one surface of which has, applied thereon, a film of plastic material which is: (i) impermeable to organic vapours; (ii) impermeable to the liquids and in particular to the liquid resin constituting the binder of said mixture; (iii) resistant to the catalysis temperatures of said resin; (iv) resistant to hot solvents and chemical vapours; and (v) soluble in water.

9. Mixture containment element according to claim 8, characterized in that said polymer is a polyvinyl alcohol.

10. Mixture containment element according to claim 8, characterized in that said containment element consists of a film of plastic material applied on the surface of the paper sheet opposite to the surface intended to come into contact with the mixture.

11. Containment element according to any one of claims 8-10, characterized in that said film of plastic material has a basis weight of 10-50 g/m.sup.2 and a thickness of 10-50 m and said paper sheet of said containment element has a basis weight of 70-200 g/m.sup.2.

12. Containment element according to any one of claims 8-11, characterized in that on said film of plastic material it is applied another sheet of paper.

13. Containment element according to any one of claims 8-11, characterized in that said sheet of paper has a basis weight comprised between 10 and 50 g/m.sup.2.

Description

[0028] The invention consists in using, instead of the aforementioned top and/or bottom paper sheets, a temporary containment element for the aforementioned mixture, consisting of a composite sheet, namely a sheet of paper which has, applied on at least one of its surfaces, a film of plastic material which is impermeable both to organic vapours, in particular to styrene vapours, and to resin, while maintaining this characteristic feature also at high catalysis temperatures.

[0029] More specifically, the present invention constitutes an improvement to the method of manufacturing conglomerate slabs using the Bretonstone technology, characterized in that the temporary upper and/or lower containment element for the mixture consists of a sheet of paper or equivalent material, having the known support and resistance characteristics in relation to vibrocompression mechanical stresses, at least one of its surfaces having, applied thereon, a film of plastic material which is: [0030] (i) impermeable to organic vapours; [0031] (ii) impermeable to organic liquids and in particular to the liquid resin constituting the binder of said mixture; [0032] (iii) resistant to the catalysis temperatures of said resin and [0033] (iv) resistant to hot solvents and chemical vapours, in particular to styrene vapours.

[0034] In the preferred embodiment of the present invention the plastic material forming said film is also water-soluble, in particular at room temperature. In fact, at the end of the process for formation of the rough slab, the latter is still lined on both surfaces with the aforementioned composite sheet and is transferred for the usual sizing and smoothing operations.

[0035] It is therefore evident that, during this machining phase, the film of plastic material may form fragments and machining waste which may obstruct and block up the water cooling system for the tools of the sizing and smoothing machines with obvious problems and damage.

[0036] It is therefore important that the material of the plastic film is able to decompose or dissolve in water, especially in water at room temperature.

[0037] This problem does not exist instead for the paper part of the composite sheet, since the paper is mashed up and dispersed in the water without creating any problems.

[0038] In this case also machining sludges containing pulverized agglomerate material, dissolved plastic film and cellulose are obtained, sludges being easily decanted, filter-pressed and disposed of.

[0039] A material which has these characteristics is polyvinyl alcohol (PVA).

[0040] It should be noted that, in the case of Bretonstone technology using rubber tray moulds, such a product is also sprayed as release agent for creating a lining film on the surface of the moulds made of rubber intended to come into contact with the mixture.

[0041] In this connection reference may be made to Italian patent No. 1311857.

[0042] The plastic film preferably has a basis weight of 10-50 g/m.sup.2 and a thickness of 10-50 m.

[0043] The paper instead has a basis weight which may be in the range 70-200 g/m.sup.2.

[0044] As already mentioned the film of plastic material may be applied to both the surfaces of the usual paper sheet, normally used as top and bottom sheet in the known Bretonstone technology mentioned above.

[0045] Alternatively, said film may be applied to only one of the surfaces of the paper sheet and preferably onto the outer surface, namely the surface which does not come into contact with the mixture.

[0046] In so doing, in fact, it is avoided a problem which may instead arise during the vacuum vibrocompression step, should the plastic film come into contact with the mixture. In fact, during the vacuum vibrocompression step, the combined effect of the granules of stone material present in the mixture and the simultaneous vibration causes a rubbing and therefore abrasive action on the surface immediately in contact with the mixture, i.e. the plastic film, which may be perforated or even torn, such that the desired or desirable properties of impermeability in relation to chemical agents both in the liquid state and in the vapour state are no longer guaranteed. For this reason the simple replacement of the sheet of paper with a sheet of plastic material (even if of suitable thickness) does not appear to be appropriate.

[0047] Paper, instead, because of its nature, may absorb the aforementioned frictional stresses during vacuum vibrocompression without damage or tearing.

[0048] This advantageous characteristic of paper explains and justifies its presence in the composite plastic film and paper sheet according to the present invention.

[0049] When the plastic film is realized in polyvinyl alcohol (PVA), advantageously over the film another thin sheet of paper might be applied with a basis weight of 1050 g/m.sup.2 for protecting it from the elevated environment humidity. In fact in elevated environment humidity conditions the polyvinyl film might become sticky, with the drawback of adhering the hardened slabs between each other when arranged one on another before being sized and polished.

[0050] As regards, finally, the application of the plastic film onto the layer of paper, the customary technologies, which are well known to persons skilled in the art and employed in the manufacture of engineering laminates, such as hot-bonding or spreading, may be used. In short, the advantages which can be achieved with the present invention are as follows: [0051] (a) the possibility of using a plant of the type which is simpler and less costly than the type which uses top and/or bottom paper sheets for containing the starting mixture, without the aforementioned drawbacks; [0052] (b) the possibility of maintaining use of the paper sheet in the mixture containing elements (paper is a low-cost, widely available material) by combining it with a preferably water-soluble polymer film; [0053] (c) ease of manufacture of the composite element consisting of paper sheet and plastic film applied to one of its surfaces, preferably the outer surface; [0054] (d) guarantee of resistance of the film of plastic material in relation to aggressive chemical agents such as styrene vapours and/or encrustations, with consequent elimination of the need to clean the shelves of the catalysis oven; [0055] (e) protection of the water cooling system of the rough-slab finishing machines (sizing and smoothing machines) against blockages and damage due to fragments of plastic film or machining waste, limited to the solution where the plastic film is water-soluble.

[0056] The practical implementation of the present invention may be subject to possible modifications and variations which are conceptually equivalent and within the competence of the person skilled in the art, in order to safeguard the advantageous aspects of the present invention.

[0057] For example, as regards the plastic film, it is preferably water-soluble, such as PVA, it being understood that any polymer or polymerizable material which gives rise to a water-soluble plastic film may be used. However, it is also possible to consider the use of a plastic film which is soluble in another solvent, in which case the rough-formed-slab, before the finishing steps, may be treated with a specific solvent for the plastic material forming the aforementioned film.

[0058] As regards the second component, namely the paper, it is possible and feasible to replace it with another material, such as a non-woven fabric, which performs the same function as the conventional layer of paper which is resistant to the stresses during vibrocompression, while the plastic film ensures the impermeability to chemical agents so as to safeguard the surfaces of the catalysis oven.