WO2003035994A1

WO2003035994A1 - Panel composed of a structural sheet of fiber reinforced resin and a decorative slab of stone or ceramic material

Info

Publication number: WO2003035994A1
Application number: PCT/EP2002/006444
Authority: WO
Inventors: Marcello Toncelli
Original assignee: TECHNOGRANITI Srl
Current assignee: TECHNOGRANITI Srl
Priority date: 2001-06-18
Filing date: 2002-06-12
Publication date: 2003-05-01
Anticipated expiration: 2003-12-18
Also published as: ITTV20010081A0; ITTV20010081A1

Abstract

Thin composite panel (10) consisting of a fiber reinforced resin sheet (14) - formed with non-twisted single-filament fibres, preferably interwoven in the form of matting, which are embedded in a hardenable resin - and of a slab (12) of stone or ceramic material. The fiber reinforced resin sheet performs a structural function while the slab of stone or ceramic material has a mainly decorative function.

Description

PANEL COMPOSED OF A STRUCTURAL SHEET OF FIBER REINFORCED RESIN AND A DECORATIVE SLAB OF STONE OR CERAMIC MATERIAL

The present invention relates to a thin composite panel formed by a slab of stone material combined with a reinforcing element.

As is well-known, natural stone is regarded as being the most highly valued cladding material. Slabs of natural stone with large thicknesses - usually 20-30 mm or more - are used, in order to compensate for the fragility of stone which is due to its low mechanical strength and its inherent fissures.

Nowadays, moreover, as a result of the latest technology which has gradually been introduced in the building industry and the furnishing components sector, there is a growing demand for cladding panels which have thicknesses much smaller than those conventionally used for natural stone slabs, so that there is an increasing interest in finding technological solutions suitable for manufacturing thin and strong decorative panels using stone materials.

While it is understood that the definitions used below are not limiting in nature, it should be clarified that the term "thin" applied to a panel, the ornamental function of which is provided by the stone material, is intended to indicate a panel thickness which is substantially less than that which, for a given application, would need to be adopted if a full-thickness stone slab were used. For example, it seems reasonable to define as "thin" a composite panel containing stone material, also with an overall thickness of 9.6 millimetres, if this panel is able to replace, with an adequate if not superior mechanical performance, a slab of natural stone with a thickness of 20 millimetres. In the same manner it is possible to define as thin a composite panel with a thickness of 7.6 millimetres when it is compared to a slab of natural stone having a thickness of 15 millimetres.

Technical literature is full of suggestions for solving the problem of reinforcing thin slabs of stone material, although the suggestions in most cases have not found a practical industrial application.

Among the various solutions adopted, as a first example it is possible to mention the product marketed as Mastercarpet, which is described and claimed in European patent application No. 95201590.7 filed on 15/6/1995 and issued as EP 0 698 483 in the name of the same Applicant. This patent application relates to a method for manufacturing thin reinforced slabs of stone material, on the rear face of which a matting of glass fibre (or other suitable fibre such as, for example, carbon or Kevlar fibres) impregnated with epoxy resin is applied as a reinforcement.

The said reinforcement applied to the rear face increases considerably the maximum breaking load on this face so that if loads are applied on the opposite face of the reinforced slab (namely on the visible face), the slab flexes, generating a concavity which is directed towards the visible surface which is therefore compressed, while the rear surface - where the matting is applied - is tensioned. Since the fibre matting reinforcement impregnated with resins has a considerable capacity to withstand tensile stresses, the slab of stone material thus reinforced manages to withstand extremely well the loads applied to the visible face.

Although this product is innovative and represents a step forward as compared to prior products, it has the intrinsic limitations of those panels, which have a structure responding in a very non-uniform manner to the flexural stress exerted in either direction on the panel.

In fact, when the panel is subject to loads acting in the opposite direction, the visible face is subject to tensile stresses which may cause breakage of the material owing to the intrinsic f agility of the stone.

Moreover, the glass fibre matting may be prone to peeling since, along the sides and in particular the corners of the product, for the most varied reasons, the thin reinforcement may become detached and this phenomenon may spread causing the gradual separation of the glass fibre matting from the surface of the slab, thus adversely affecting the functionality of the product.

During handling of the product on the preparation or installation site, as well as when the opposite face is subjected to process steps such as sizing and polishing, the product undergoes the most varied stresses and as a result of its different capacity of the reinforced slab to withstand the stresses in the two directions described above, breakages and/or cracks may occur, preventing its utilization.

A second example of a product known for some time consists of a aluminium cellular (or "honeycomb") panel which is closed on the two opposite surfaces by thin layers (or "skins" in technical jargon) of glass fibre. A thin layer of stone material is applied to one of the two surfaces of the cellular panel, onto the outwer face of the skin. The structure of this cellular panel is very rigid, as is the structure of the composite product formed by the honeycomb panel and the layer of stone material.

This product as well sufers from the serious defect of peeling which causes separation of the layer or skin from the face opposite to the one on which the layer of stone material is applied.

Another particular aspect which reduces the range of uses of the composite honeycomb/stone material panel is the honeycomb structure as such, which does not provide any support for the fasteners required for vertically fixing the panel to the support structures. Moreover, along the periphery of the panels, the cavities corresponding to the open cells remain exposed, thus requiring a finishing operation for some utilizations of the product.

The object of the present invention is to provide a panel which does not have the drawbacks mentioned above, which is thin and therefore light but, at the same time, withstands adequately (i.e. without breakages which prevent practical use thereof) the stresses in both directions to which it is subject during the various processing steps and during the handling deriving from its use, which is also not affected by peeling and which has along the whole of its perimeter a full-thickness uninterrupted rib.

This object is achieved by means of a composite panel of the above mentioned type, namely a thin panel comprising a slab of stone material combined with a reinforcing element, characterized in that said reinforcing element consists of an unbreakable structural sheet of reinforced resin which is formed by bundles of non-twisted single-filament fibres embedded in a hardenable resin, said structural sheet of fiber reinforced resin being formed separately so as to combined, once hardened, with the slab of natural stone and/or agglomerate material and/or sheet of ceramic material.

It should be noted that, in so doing, unlike the first example of the above cited prior art, it is no longer the slab of stone material which is reinforced in one direction only by a thin sheet consisting of a glass-fibre matting impregnated with resin, but instead a fiber reinforced resin structural element is manufactured and hardened separately, i.e. a sheet which per se has a high intrinsic capacity to withstand the most widely varying stresses in both directions, a lining element of stone or ceramic material with a mainly decorative function being subsequently applied onto the said structural element.

It is understood that the wording "fiber reinforced resin sheets" is understood as meaning sheets manufactured using inorganic fibres of a varying nature such as glass fibre, carbon fibre, Kevlar fibre, basalt fibre, aramide fibre or other types of fibres, the common features of said fibres being that they are non-twisted, single-filament and interwoven in the form of matting and that they are to be used in one or more mats of varying weight arranged one on top of the other. The wording "impregnated with resin" is understood as indicating that the sheets are manufactured by impregnating the fibres with structural resins such as polyester resin, epoxy resin, acrylic resin, pol urethane resin or other resins. In the continuation of this description, for the sake of clarity reference is made preferably to glass fibres, polyester resin and a slab of natural stone material, without this having a limiting intention or effect.

In the first example of the above cited prior art, the stone material element of the panel has a considerable thickness compared to the thin fibreglass layer which acts as a reinforcement when the load is applied on the side where the stone material is situated. On the contrary, according to the present invention, the slab of stone material is not required to contribute to the mechanical strength thereof since the fiber reinforced resin sheet always has a thickness and a rigidity sufficient for ensuring as such that the thin composite panel has the necessary rigidity and robustness.

It is worth noting that the fiber reinforced resin sheet has a high capacity to withstand any type of stress to which it is subjected and, in particular, owing to its rigidity, resists equally well both stresses which flex it in one direction and stresses which flex it in the opposite direction.

Therefore, if the fiber reinforced resin sheet is combined with a slab of stone material, the thin composite panel thus obtained has excellent stress-resistant characteristics. In particular these characteristics are exhibited also in the case where the forces are applied such as to bend the thin composite panel with the convexity directed on the side where the stone material is situated, namely in the case where said stone material is subject to a tensile stress, as will be explained more clearly below.

It should be noted, moreover, that the thickness and the rigidity of the fiber reinforced resin sheet which is combined with the slab of stone material are such as to prevent the possibility of peeling since both the combined elements are rigid and remain constantly parallel with each other along the joining line of the said slab and of the said sheet.

These and other features of the present invention will emerge more clearly from the following description of an embodiment thereof provided by way of a non-limiting illustration with reference to the following drawings in which:

- Figure 1 shows a cross-section of a composite panel according to the present invention;

- Figure 2 shows a partially sectioned plan view of the composite panel according to Figure 1;

- Figure 3 shows a partial cross-section through the structural fiber reinforced resin sheet of the panel according to Figure 1;

- Figures 4 and 5 show a sectional view of thin composite panels with different thickness ratios, compared to Figure 1, of the slab of stone material and the structural fiber reinforced resin sheet.

In Figure 1, reference numeral 10 denotes overall a composite panel comprising a slab of stone material 12 combined with a sheet of fiber reinforced resin 14.

The slab of stone material 12 consists of natural stone material such as, for example, granite, marble and travertine, alabaster, slate, porphyry and the like.

Provided that, in the thin composite panel, it has a mainly decorative function, instead of being natural stone material, the slab may be an agglomerate of stone material or of ceramic material, such as those described in Italian patent Nos. 1,056,388, 1,117,346 and European patent No. 0,378,275 in the name of the same applicant (to which reference should be made for further details) and distributed under the trade names Bretonstone and Lapitech.

The fiber reinforced resin sheet 14, as can be noted more clearly from Figures 2 and 3, consists of a matrix 15 made in a hardenable structural resin embedding bundles of single- filament fibres 16 which are non-twisted and interwoven in the form of matting 18. In the embodiment shown in Figures 2 and 3 there are four mats which are arranged one on top of the other. In a fiber reinforced resin sheet 14, the quantity in weight terms of the single- filament fibres 16 must be equivalent at least to 50%. '

The resin preferably used for the manufacture of the structural sheets is polyester resin which is suitable for the purpose and low-cost. It is also possible to use other structural resins, such as those above mentioned, with appropriate characteristics.

The fiber reinforced resin sheet is combined with the slab of stone material when the catalysis reaction of the resin has taken place, so that the structural sheet of fibreglass has hardened and achieved its dimensional stability.

In the manufacture of fiber reinforced resin sheets, preferably non-twisted single- filament fibres impregnated with polyester resin are preferably used since the linear heat expansion coefficient of these sheets after hardening, - when the preferred fibre/resin volumetric ratio of about 65/35 is observed - is much the same as that of the slab of stone material, namely about 8-12 x 10^"6.

In this way, since the expansion coefficients of the two combined materials are similar, upon variation in the temperature, there are no relative movements of a significant value which affect the integrity of the joint between the two materials.

The reinforcing fibres used in the resin sheets may also be of another type, such as, for example, carbon fibres, aramide (Kevlar) fibres, basalt fibres or the like, provided that the structural sheet of fiber reinforced resins manufactured with these types of fibres other than glass fibres assume values of linear heat expansion coefficient which are similar to those of the conventional sheets glass fiber sheets which have been described above.

The thin composite panel according to the present invention is formed by two elements, namely a structural part consisting of single-filament fibre, in particular glass fibre impregnated with polyester resin, and a lining part consisting of stone material, each of the two elements having its own characteristics as regards both deformability and resistance to compressive/tensile stresses, which in turn depend on the nature of the material, the elastic modulus and other non-intrinsic parameters such as, for example, the thickness.

After their manufacturing process and until the final installation, this panel is mainly subject to flexural stresses which produce a tensile stress in the streched part of the cross- section and a compressive stress in the compressed part of the same. For as long as these stresses remain below the respective maximum affordable loads - namely a loaid below the ultimate tensile strength in the streched part of the cross-section, the composite panel withstands the flexural stresses to which it is subject.

In consideration of the low tensile strength of stone material, one would imagine seem that a composite panel - in which the slab of stone layer is positioned in the stretched part of the cross-section - were only able to withstand a flexural stress providing a tensile stress of a value lower than its ultimate tensile strength, thereby resulting in a serious limitation in use.

The composite panels according to the present invention were instead found not to suffer from such a limitation, to the extent that the maximum stress corresponds to the maximum tensile strength of the fiber reinforced resin sheet.

In other words, it was experimentally proved that the composite panels according to the present invention are able to withstand flexural stresses which stretch the part of the cross- section made with stone material beyond its ultimate tensile strength without affecting the integrity and functionality of the composite panel.

Without reporting specific theoretical explanations and interpretations of the results achieved with the present invention, the following remarks seem to be of relevance.

The effect of a very high stress, beyond the corresponding ultimate tensile strength, in the part made with stone material of the composite panel is the generation of microscopic fissures in the stone material such that the same is relieved of the stress exerted on it by the fiber reinforced resin sheet which is easily able to withstand a a big tensile load.

The said microscopic "additional" fissures do not affect the quality and the solidity of the thin composite panel to a greater degree than the larger or smaller fissures which naturally do already exist in the stone material before it is applied onto the fiber reinforced resin sheet. The more rigid and resistant the fiber reinforced resin sheet is, the more effectively it will prevent any microscopic fissure generated in the stone material from becoming a manufacturing defect of the thin composite panel which therefore will be able to withstand the loads exerted on it.

In the very moment the stone material, it does no longer form a resistant section which means that the neutral axis of the cross-section of the thin composite panel is displaced towards the centre of the structural sheet of fiber reinforced resin. It is in this manner always ensured that the panel does not come to rupture since the high tensile strength of the fiber reinforced resin sheet offsets the intrinsic fragility of the slab of stone material, thereby neutralising the effects - in terms of the strength of the panel as a whole - of the newly generated microscopic fissures and of the fissures which may already naturally be present.

In daily practice a composite panel has for example to withstand stresses which arise during the manufacturing process and the subsequent transportation and installation steps, including the situations where it is the slab of stone material to be subjected to tensile stresses.

In order to perform such a function, the fiber reinforced resin sheet must therefore have an intrinsic rigidity and strength which is at least sufficient to withstand the stresses resulting from the panel own weight.

Therefore, the thickness of the fiber reinforced resin sheet must vary depending on the overall thickness and weight of the composite panel. With regard to its physical and mechanical properties, it was possible to establish that the preferred thickness of the fiber reinforced resin sheet should correspond to 45% of the overall thickness of the composite panel, apart from the thickness (in the region of 0.6 mm) of the thin layer joining together the two sheets which form said panel. Taking a composite panel with an overall thickness of 7.6 mm as an example for the above given definition of the term "thin panel", on the basis of the preferred ratio between the overall thickness of the composite panel and the thickness of the structural fiber reinforced resin sheet, the latter will have a thickness of 2.80 mm [i. e. (7.6 - 0.6) x 0.40], while the slab of stone material will have a thickness of 4.20 mm.

A thin composite panel, on the other hand, with a thickness of 10.6 mm should be composed of me joining layer (0.6 mm thickness), a slab of stone material with a thickness of 6 mm and a fiber reinforced resin sheet with a thickness of 4 mm.

A fiber reinforced resin sheet formed by bundles of non-twisted single-filament glass fibres interwoven in the form of a matting and polyester resin is approximately composed, in terms of volume parts, of 53% fibre and 47% resin; since the specific density of the resin is about 1.12 and the density of the fibres is about 2.35, the resulting weight ratio glass/resin is about 70/30.

It should be noted that, in order to manufacture one square metre of fiber reinforced resin sheet with a thickness of 4 mm, about 5 kg glass fibres and about 2.10 kg polyester resin are required. In practice, instead of a single matting with a weight of about 5 kg, preferably, but not necessarily, 5 mats - each with an unit weight of 1 kg/m² - or any other suitable combination of number and unit weight of mats will be used.

Where fiber reinforced resin sheets of a bigger or a smaller thickness are to be manufactured, a larger or a smaller overall weight of glass fiber mats and polyester resin will be used.

One of the possible methods for manufacturing a thin composite panel as above described consists of the following steps:

1. Manufacturing the fiber reinforced resin sheet;

2. Sawing a block of stone material using known machines and techniques, so as to obtain therefrom a plurality of slabs, each of them being of a suitable thickness for manufacturing two thin composite panels;

3. Applying, onto each of the two opposite faces of the slab of stone material (as obtained in step 2), one layer or mat of non-twisted single-filament glass fibres, impregnated with resin, said layer or mat being intended to form the adhesive element for joining a fiber reinforced resin sheet (as obtained in step 1) to one of the two faces of the stone slab (as obtained in step 2);

4. Applying a fiber reinforced resin sheet onto each of the two surfaces of each one of the above mentioned slabs of stone material (as obtained in step 2), thus obtaining a semi- finished product where the adhesive layers or mats obtained in step 3 are located between the fiber reinforced resin sheets and the stone material (step 2);

5. Sawing the semi-finished product obtained in step 4 along the mid plane of its cross-sectio so as to realize two thin composite panels therefrom as final products.

In order to manufacture in step 1 the fiber reinforced resin sheet, one or more mats are deposited in a flat form which are made with glass fibre having the characteristics indicated hitherto and an unit weight suitable for the manufacture of composite sheets with the desired final thickness. A quantity of about 430 g of polyester resin for about each 1000 g of glass fiber is poured and spread over the mats and, by means of a suitably rolling action, the resin is made to impregnate the mats uniformly, thus obtaining a green sheet of fiber reinforced resin sheet.

Said green sheet is hardened, in accordance with known techniques, by means of either a cold-catalysis or hot-catalysis process of the impregnating resin.

In order to achieve an optimum bond between the fiber reinforced resin sheet and the slab of stone material (as obtained in step 3), one green mat or layer of glass fibre, with a weight for example of 500 g/m², impregnated with epoxy resin, is applied onto the faces of the slab of stone material (as obtained in step 2) so that any unevenness present in the surfaces of the slab of stone material and the fiber reinforced resin sheet is mutually offset.

Once hardened, the said mat or layer of glass fiber for joining together the fiber reinforced resin sheet and the slab of stone material, will have an average thickness of about 0.6 mm. The surface of the stone slab must be cleaned and dried before the matting is applied onto it, said matting being subsequently impregnated on the said slab by means of a rolling operation. In the described step, epoxy resins shall be used which, during hardening, undergo a negligible retraction.

In order to perform step 5, namely the subdivision of the slabs (obtained from sawing a stone block and treated as described in step 4) into two panels, it is possible to use conventional frames suitably equipped with special slab-carrying carriages. A suitable apparatus is described in the Italian Utility model application No. TV2000U000030 filed on 21.7.2000 in the name of the Dario Toncelli.

The manufacture of a thin composite panel according to the present invention may also be obtained in other ways. For example, the panel may be obtained by combining the fiber reinforced resin sheet with a slab of stone material already sawn to the desired thickness or reduced to the desired thickness by means of a mechanical sizing and/or smoothing step. Also in the case of a panel manufactured with slabs of ceramic agglomerate (for example of the Lapitech type already mentioned), the said slabs will have the desired thickness and will each be combined with a single fiber reinforced resin sheet in order to obtain the panel.

Taking into account in each case the characteristics and defects of the actual stone material, it may be useful to modify the ratio between the thickness of the fiber reinforced resin sheet and that of the slab of stone material. For example a fiber reinforced resin sheet might be of 4 mm thickness and a slab of stone material of 3 mm with a resulting fibreglass/overall panel thickness ratio of 4:7, not considering the thickness of the joining layer (see Figure 1). As shown in Figure 5, the fiber reinforced resin sheet might have in specific applications the same thickness as the slab of stone material with a resulting fibreglass/overall panel thickness ratio of 1 :2, relative to the overall thickness of the panel, not considering the thickness of the joining layer. Figure 4 shows on the other hand an examplary panel in which the thickness of the fibreglass layer is less than the thickness of the slab of stone material.

In any case, from the preceding examples it shall be realized that the joining line between the fiber reinforced resin sheet and the slab of stone material is rather close to the neutral axis of the cross-section of the composite panel and consequently is only subjected to a low stress.

Thanks to the invention, a series of architectural components will be available for the building and the furnishing industries which hitherto were technically not feasible with the use of stone material, despite its aesthetic value, in consideration of the heaviness and fragility, as well as to the difficulties in the industrial processing, transporting, storin and handling.

It is important to note that the described process for manufacturing the thin composite panels also per se involves the repair and consolidation of slabs of stone material which are defective and up to now considered as difficult or impossible to utilize despite the intrinsic value and cost of the same.

From an economic point of view it is interesting to note how a thin composite panel according to the invention can have a price on the installation site that, in several applications, can compete with that of a conventional slab of stone material and this is even more true in case of a high value stone material.

Comparing the weights per unit area, it can be noted that a thin composite panel with a thickness of 7.6 mm has a weight of about 16.5 kg/m², while a stone slab with a thickness of 2 cm weighs about 54 kg/m².

It is obvious that any type of modification which is conceptually similar falls within the scope of protection of the present invention.

Claims

1. Composite panel (10) comprising a slab (12) of stone material combined with a reinforcing element (14), characterized in that said reinforcing element (14) consists of an unbreakable structural sheet of reinforced resin which is formed by bundles of non-twisted single-filament fibres (16) embedded in a hardenable resin, said structural sheet of fiber reinforced resin being formed separately so as to combined, once hardened, with the slab (12) of natural stone and/or agglomerate material and/or sheet of ceramic material.

2. Composite panel (10) according to Claim 1, characterized in that said non- twisted single-filament fibres (16) are interwoven in the form of matting (18).

3. Composite panel (10) according to Claim 1, characterized in that said single- filament fibres (16) consist of material of the inorganic or organic type.

4. Composite panel (10) according to Claim 3, characterized in that said single- filament fibres (16) are chosen from among glass fibres, basalt fibres, ceramic fibres, carbon fibres, aramide fibres, Kevlar fibres and the like.

5. Composite panel (10) according to Claim 1, characterized in that said hardenable resin is chosen from among polyester resins, epoxy resins, acrylic resins, polyurethane resins and the like.

6. Composite panel (10) according to any one of the preceding claims, characterized in that said slab of natural stone material (12) is a slab made with material chosen from among granite, marble, travertine, alabaster, slate, porphyry, botticino and similar materials. ,

7. Composite panel (10) according to Claim 1, characterized in that said slab of stone material (12) is a slab made with a material consisting of a quartz agglomerate and/or other stone materials bonded together by an organic or inorganic binder.

8. Composite panel (10) according to Claim 1, characterized in that said slab (12) is made with ceramic materials.

9. Composite panel (10) according to Claim 1, characterized in that said slab of stone material (12) has a thickness of between 3 and 15 mm and said structural sheet of fiber reinforced resin has a thickness of between 2 and 10 mm.

10. Composite panel (10) according to Claim 1, characterized in that a thin layer of fibres impregnated with a hardenable resin which is arranged between the fiber reinforced resin sheet (14) and the slab (12) of stone material.

11. Composite panel (10) according to any of the preceding claims, characterized in that the ratio between the thickness of the fiber reinforced resin sheet (14) and the overall thickness of the composite panel (10) is equal to or greater than 2:5.

12. Composite panel (10) according to any of the preceding claims, characterized in that the fiber reinforced resin sheet (14) has a content, in terms of weight, of single- filament fibres of at least 50%.

13. Composite panel (10) according to any of the preceding claims, characterized in that fiber reinforced resin sheet (14) is made with a volume ratio fibres to resin in the range of 53:47 to 47:53

14. Method for manufacturing a composite panel according to Claim 1, characterized in that, in order to combine the fiber reinforced resin sheet (14) and the slab of natural stone material or agglomerate or ceramic material (12), one layer or mat of fibres impregnated with a hardenable resin is arranged between them.

15. Method for the manufacture a the composite panel according to Claim 14, characterized in that said hardenable resin is epoxy resin.