System and method for lightweight decorative slabs

Abstract

A decorative slab (1) comprising a first material portion (5) at least partially surrounding a core portion (6), wherein the first material portion (5) is made of engineered stone and comprises a first density, wherein the core portion (6) comprises a second density, and wherein said second density is lower than said first density.

Description

[0001] System and method for lightweight decorative slabs

[0002] The present invention relates to a system and method for making light weight decorative slabs, such as decorative slabs to be used for decorative cladding, like wall cladding, ceiling cladding, or floor slab, or to be used as countertops. In particular, the present invention relates to decorative slabs made of engineered stone.

[0003] Engineered stone, sometimes called composite stone, or synthetic stone, and often referred to in retail outlets as synthetic quartz, is a low-porosity or non-porous composite that has low liquid absorption. It is used commonly to make countertops, sinks, wall coverings, and other indoor building products. Although other bonded forms of minerals are available in products such as asphalt, concrete, polymer cement, the synthetic stone products are made to be polishable, stain resistant, food safe, and durable. Engineered stone often resemble cut slabs of marble are made synthetically and marketed as “quartz” or synthetic stone. An engineered stone comprises an inorganic filler like crushed stones, sands or other minerals but also recycled ceramic or glass, bonded by means of a cured resin. More in detail, with engineered stone is intended a composite material formed by an inorganic filler or a stone like material bonded together by means of a cured binder that it is cured at low temperature, wherein with low temperature is intended a temperature below 500°C. The binder is preferably a thermosetting resin. A well-known example of engineered stone and method for manufacturing thereof is represented by the so called Bretonstone® technology described, for example, in the document, WO 2007 / 138529. Said document discloses a method for manufacturing an engineered stone which comprises the step of: providing a mineral filler, for example by grinding sand or quartz; mixing the stone or stone like material with a binder, for example a resin powder, in order to obtain a mixture; depositing the mixture in a mold of a press, having shape and dimension similar to those of the final article; press the mixture applying vacuum, with the accompanying application of a vibratory motion at pre-established frequency; the semi-product obtained is then hardened by means of a heat curing process to obtain the engineered stone; the engineered stone is then subjected to finishing steps like cutting or polishing. In view of the low porosity and high content of mineral fille, decorative slabs formed by engineered stone are heavy and dense. Consequently, there is a need for a system and method to develop light weight engineered stone made decorative slabs, for example countertops, and the like.

[0004] Thereto, the present invention, according to its first independent aspect, relates to a decorative slab comprising a first material portion at least partially surrounding a core portion, wherein the first material portion is made of engineered stone and comprises a first density, wherein the core portion comprises a second density, and wherein said second density is lower than said first density. In this way, the low-density core provide many benefits. First, it reduces the total weight of the decorative slab. The first material portion has preferably a density around 2200 kilograms per cubic meter. In some embodiments, utilizing low-density cores decreases the density of the entire decorative slab can be 50%or less than the first density of a the first material portion. Thus, the structure necessary to support the weight of the decorative slab, for example a countertop, is reduced. Second, due to significantly decreased weight, the cost to ship and handle is likewise significantly reduced. Positioning and moving these decorative slab is easier compared to the heavier and denser previous products. Additionally, since the resulting product is much lighter, the application can be broadened to other technologies. Lightweight decorative slabs can be used in countertops, wall coverings, floor coverings, vanity tops, restroom stall walls and doors, bathroom vanity tops, cabinet doors, personnel doors, window frames, tub and shower surrounds, office cubical barriers, desk tops, tables, chairs, benches, and furniture building components. Another benefit is reduced cost. The cost of the mixture for forming the engineered stone is the most expensive ingredient. Replacing a significant amount of mixture with the low-density core portions, provides a comparatively less expensive product. In some embodiments there can be a reduction in raw material costs of between about 25% and 30%. Reduction of raw material can further lead to reduction of crystalline silica in the final product, thereby reducing risk of forming silicosis on whom manufactures or machines the decorative slab itself. In some embodiments, the low-density core provides high bending stiffness. The low- density core is also energy absorbent. In some embodiments, the low-density core is resistant to moisture, acids, and bases.

[0005] Preferably, the core portion can comprise voids. In this way the weight of the decorative slab can be reduced.

[0006] In a first, less preferred, embodiment said voids can comprise excavation in slab body. In this case the core portion can show a different structure than the first material portion while preferably being made of the same material. In practice said voids can define sections of the decorative slabs having a thickness being lower than the thickness in the first material portion. In this way, the structure of the voids can be designed in such a way to ensure a relatively high strength of the final decorative slab, so that impact of the lighter weight core the mechanical properties of the decorative slab can be reduced.

[0007] In a second, preferred embodiment, said core portion can comprise a foamed and / or honeycomb structure, preferably made in a dissimilar material than that of the first material portion. In this way it is possible to maintain high mechanical performances thanks to a core portion structure which can lead to a maximized flexural strength corresponding to the decreased density. In addition, the material of the core portion can be selected to improve the mechanical performances of the decorative slab and / or to improve adhesion between the first material portion and the core portion. For example, the core portion can comprise honeycomb core, for example of the kind produced and sold by ThermHex, or honeycomb pads, for example of the kind produced and sold by IntePro TITAN, and the like. Some honey-comb pads, for example, can house to up 2500 pounds between pallets. Alternatively, the core portion can comprise balloons of air, foam pellets, etc. Preferably said dissimilar material can me made of: a thermoplastic polymer, for example PE (polyethylene), PET (polyethylene terephthalate), PP (polypropylene), TPU (thermoplastic polyurethane), etc; a thermosetting polymer for example melamine resin, polyurethane, polyester etc; metal, for example aluminum or alloy thereof. The core portion can be in the form of polymeric structural panels utilizing shapes that are engineered and manufactured to have high strength to weight ratios. The most common versions are sandwich panels. They can be open honeycombs, cellular tubes, covered honeycomb, bonded minerals like perlite and vermiculite. Paper-based versions of the core portion can also be utilized. Foamed polymers shaped as sheets, pellets, spheres, rods, or other forms can also be used to lower the density of the overall part.

[0008] It is noted that in this second embodiment, the voids can be represented, for example by the honeycomb cells and or by the foam-cells. Preferably said honeycomb core, or foamed cores can comprise closed honeycomb cells or foam-cells. In this way, during manufacturing (that will be later described) the mixture forming the engineered stone material, doesn’t fill the cells of the core portions that will represent voids in the final decorative slab. In addition, in this way honeycomb core and the foamed cores can show a substantially continuous outer surface for bonding to the first material portion.

[0009] In some variants of this second embodiment, the decorative slab can comprise an covering layer, adapted to improve the bonding between the first material portion and the core portion and / or to improve the bonding of the decorative slab to an adhesive, for example a thin-set composition, during installation of the decorative slab. Preferably, said covering layer can comprise a fabric, for example a non-woven fabric. For example, said covering layer can comprise a fabric made of non-woven PET (polyethylene terephthalate).

[0010] In some embodiments, the covering layer can cover at least a surface of the core portion being exposed on an outer surface of the decorative slab. In this way, the covering layer can improve the grip with the adhesive used during installation of the decorative slab. Other materials, including those formed via injection molding, can be adhered to the covering layer.

[0011] In other embodiments, the covering layer can cover one or more of the surfaces of the core portion surrounded by the first material portion. In this way, the covering layer can improve bonding between the engineered stone material forming the first material portion, preferably the binder thereof, and the core portion. It is noted that the covering layer can cover all the outer surfaces of the core portion.

[0012] In accordance with any of the embodiments, the first material portion preferably surrounds the core portion at least in such a way that the core portion is not visible on a first main surface of the decorative slab, said first main surface being preferably the surface destined to be the visible surface during the final use of the decorative slab itself. In some embodiment, said first material portion preferably surrounds the core portion at least in such a way that the core portion is not visible on both of the opposite main surfaces of the decorative slab. Alternatively, the core portion can be exposed at the main surface being opposite to said first main surface. In this way, the presence of the core portion does not affect the aesthetic appearance of the decorative slab.

[0013] Said core portion can occupy a thickness being lower than the thickness of the decorative slab, preferably the thickness of the core portion being less than 90% of the thickness of the decorative slab, more preferably being less than 75%. Preferably the thickness of the core portion being more than 25% of the thickness of the decorative slab, more preferably being more than 50%. Said thickness of the core portion can preferably be equal to or more than 7,5 mm, more preferably equal to or more than 10 mm, for example equal to or more than 15 mm. Said thickness of the core portion can preferably be equal to or less than 27mm, more preferably equal to or less 18 mm, for example equal to or less than 22,5 mm. In this way the reduction of density can be maximized while the impact on the aesthetic and / or on the mechanical performances of the decorative slab can minimized.

[0014] The thickness of the decorative slab can be more than 10 mm, preferably around 20 mm. or 30 mm. The thickness of the decorative slab can be equal or less than 30 mm.

[0015] In accordance with any of the embodiments, the first material portion can preferably surround the core portion in such a way that the core portion is not visible on at least one, preferably a plurality of, for example on all, the external side edges of the decorative slab. In this way, the effect of the presence of the core portion on the aesthetic appearance of the decorative slab can be limited. Preferably the core portion occupies a surface on the plane of the decorative slab being equal or less than the 90%, preferably less than 80% of the surface of the decorative slab itself. In some embodiment the part of the first material portion surrounding the core portion, can have a width, measured on the plane of the decorative slab, being at least 5 mm or more, preferably 10 mm or more, for example 20mm or more.

[0016] In accordance with any of the first and second embodiment, the decorative slabs can comprise a plurality of core portions, preferably being separated by first material portions. In this case, the core portions can comprise a width measured on the plane of the decorative slab being preferably less than 1000 mm, preferably being less than 800 mm, even more preferably less than 600 mm, for example less than 500 mm. In this case, the core portions can comprise a length measured on the plane of the decorative slab being preferably less than 1000 mm, more preferably being less than 800 mm, even more preferably less than 600 mm, for example less than 500 mm. In this way, the decorative slab can be cut down to multiple sub-products in such a way that that the core portions are not exposed on the side edges of said sub-products, for example said sub-products having a predetermined dimension suitable for being used in multiple purposes. For example, a kitchen countertop, on average, has a width of 600mm, or 800 mm.

[0017] It is noted that, with slab is intended a substantial rectangular and flat form, preferably comprising a surface of minimum 1,5 square meters. In this way, the engineered stone is manufactured in a shape that is sufficiently large to be versatile and adapted to be cut according to the dimension and shape of the final destination of the engineered stone itself, like for example a kitchen or bathroom countertops. According to a preferred embodiment, the slab has a length of at least 2 m, preferably at least 2,5 m, for example 3 m or more, and a width of at least 1 m preferably 1,5 m or more, for example 2 sqm.

[0018] Preferably, the core portion is integrally made in the decorative slab, wherein with integrally made it is intended that the core portion and the first material portion are either in the same material, or that in case they are made of separate material, they are not bond each other by means of a separate adhesive or mechanical fasteners (with the exception of the intermediate material). With separate adhesive it is meant an adhesive being different from any binder used in the engineered stone. Said separate adhesive and / or fasteners can fail and / or represent weak point in the decorative slab.

[0019] In the preferred embodiment the inorganic filler comprises mineral material like any kind of stone, sands, siliceous mineral material, for example quartz, silica sand, clay, feldspar cristobalite granite, talc or calcareous mineral material, for example, calcium carbonate, marble, gypsum. The inorganic filler can also comprise ceramic, glass, metals and other inorganic material, for example recycled materials. The filler can be in the form of powder, granules, shards, grains, aggregates or any other particulate form although granules and powder forms are preferred. Preferably the filler is in powder form having an average particle dimension lower than 45 pm, preferably lower than 20 pm. The filler is preferably at least 80% by weight of the mixture, preferably more than 85% and more preferably more than 90%. According to another embodiment of the invention the filler can be in form of aggregates, grains and / or granules having a particles size distribution between 0,1 and 6,5 mm, preferably between 0,1 and 2mm, 0,1 and 0,7 mm. In the most preferred embodiment, the filler is composed by a combination of powder and grains, for example said combination can comprise at least 60 wt% of grains and / or granules and between 20 to 35 wt% of powder form wherein, for example, the granules have a particles size distribution between 0,1 and 6,5 mm and the powder have an average particle dimension lower than 45 pm, preferably lower than 20 pm. In the most preferred embodiment of the invention the inorganic filler is composed for its majority, i.e. at least 50%weight, and more preferably mainly consists, of an inorganic material that is based on silicon (Si). Silicon based material like siliceous minerals and glass show a good affinity with the binder so that the final bonding can be improved.

[0020] In some embodiments, crystalline silica, feldspar or kaolin can constitute preferred choice for the inorganic filler, or at least for a majority of the filler, as they can show a relatively white color. In some embodiments, glassy and / or amorphous inorganic fillers can be preferred for forming the majority of the inorganic filler as they can reduce the amount of free crystalline silica dust in manufacturing and / or working of the decorative element. The binder is a curable substance that is configured to be cured thereby bonding together the particles of the stone or stone like material. The binder can be in any form, i.e. liquid, solid, gel or any form that is suitable to be mixed with the filler and to be homogeneously dispersed within. In some embodiments, powder form can be preferred as reduce the possibility of contamination of the mixture from other substance, that can occur using wet form of binders. The binder can be an organic substance, for example a resin. In the most preferred example, the binder can be a thermosetting resin.

[0021] In the most preferred embodiment the binder comprises, preferably substantially consists of, polyester resin preferably unsaturated polyester resin. Less preferred alternative solutions for the binder comprise acrylic resin, epoxy resin, polyurethane, rubber, vinyl ester resin or the like. The binder is preferably less than the 20% by weight of the mixture, preferably less than the 15% and more preferably less than 10%. Polyester resins have shown a very high coupling capability with the inorganic filler.

[0022] It is noted that the binder is in a curable state when used in the manufacturing of the decorative slab, but in the end product, i.e. in the decorative slab, it is in the cured state, for example in the form of a polyester resin crosslinked with styrene monomer.

[0023] It is noted that the mixture can also comprise additives like, for example, coupling agents, catalyst, for example or reagents to activate or speed up hardening of the binder, and / or temporary bonding agent like glues or thermoplastic resins that temporarily bonds the stone or stone like material. In the most preferred example, the additives comprise at least a silane-based coupling agent to further enhance the bonding between silicon-based filler and the binder, preferably the unsaturated polyester binder. Moreover, the additive can comprise crosslinkers and / or catalysts and / or initiators to activate and / or accelerate curing of the binder. Preferably, the binder can comprise styrene monomer for crosslinking reaction with the polyester resin. The binder can comprise peroxide initiators for starting the crosslinking reaction. The accelerator can comprise or consists of cobalt. The decorative slab can comprise a decorative pattern, for example imitating veining of a natural stone. Said decorative pattern can be formed according to two main possibilities which can be implemented either alone or in combination with each other. In a first of these possibilities, said decorative pattern is formed by dispersing and / or distributing a pigment and / or a colorant in the mixture forming the engineered stone, either randomly and / or according to a predetermined pattern. In this case the decorative pattern is present at least in the first material portion. Decorative patterns according to the first possibility can be manufactured in a method as described in WO 2016 / 113652 which is herein incorporated by reference. In the second possibility said decorative pattern can be in the form of a pattern being inkjet printed on the first main surface of the decorative layer, for example in a top layer provided on top of the first main surface of the first material portion. Decorative patterns according to the first possibility can be manufactured in a method as described in WO 2019 / 070621 which is herein incorporated by reference.

[0024] In its second independent aspect, the invention relates to a method for manufacturing a decorative slab comprising the steps of: providing mixture for forming an engineered stone, said mixture comprising at least an inorganic filler and a curable binder; said mixture being provided in a mold to at least partially filling said mold; compacting said mixture; curing said binder to obtain the decorative slab; wherein: a low density core is provided in the mold before said step of compacting the mixture, wherein after curing said lightweight core becomes a core portion of the decorative slab; and / or

[0025] - the mold comprises elements adapted to form voids in a core portion of the decorative slab.

[0026] The lightweight core of the second independent aspect can be provided in the mold either before or after the mixture is provided in the mold, preferably before. In some embodiments, it is also possible that a part of the mixture is provided in the mold, than the lightweight core is inserted in the mold and then a second part of the mixture is provided in the mold. It is noted that more lightweights core can be provided in the mold. It is further noted that the lightweight core of the second independent aspect can comprise one or more of the features described in connection to the cire portion of the first independent aspect, in particular of the second preferred embodiment thereof. In particular the lightweight core can have a honeycomb structure and can be made with thermoplastic material, preferably PP.

[0027] Preferably, the elements of the mold for forming the voids in the decorative portion can be in the form ribs in the mold.

[0028] The mixture can be provided in different forms, for example in form of a pasty material or a slurry, although a dry form, for example incoherent particulate, is preferred. According to a preferred embodiment wherein the mixture is provided in form of an incoherent material, the mixture comprises a first particulate filler and a second particulate of binder mixed together, preferably in powder form. Alternatively, the incoherent particulate can be formed by granulates or pellets wherein each granule comprises the filler and the binder bonded together for forming the granule.

[0029] Before, during and / or after the step of providing the mixture into the mold, one or more colorants and / or pigments can be provided or dispersed into the mixture in such a way to form the decorative pattern, as discussed in connection to the first independent aspect.

[0030] The mold can have shape and dimension similar to those of the final product to be obtained or to those of a semi product of the process. Preferably the mold or frame has the shape and dimension similar to those of a slab or panel. In the preferred embodiment the mold is made of rubber. The mold can comprise a concave body adapted to receive the mixture and a lid adapted to close the concave body so that the mixture is completely closed into the mold. It is noted that in alternative embodiments the mixture can just be disposed onto a belt or in an open mold or frame.

[0031] Preferably the compacting step is conducted under vacuum, i.e. vacuum is generated in the mold to help extract air between the mixture particles. Preferably, vibration is applied to the mold or frame during the compacting step thereby helping to compact of the mixture particles, so that the porosity of the engineered stone is significantly reduced. According to a preferred embodiment both vacuum and vibration are applied to the mixture during the compression. In this way, it is possible to obtain a very high degree of compaction of the mixture that after curing will lead to a extremely low porosity. The vibratory energy causes the slurry to reach the corners without the need for increased pressure. The pressure can be around 8 psi with a vibrational press. Due to the vibrational energy imparted to the mold, comparatively reduced pressure is applied to the press. In some embodiments, the applied pressure does not destroy or compress the low-density core. Absent vibrational energy, this was not previously possible. Previously, sufficiently increased pressures were required to ensure the slurry was formed within the mold. Such pressures would compress and collapse the low-density core. However, utilizing vibrational energy decreases the amount of required pressure to such a level that a low- density core can be utilized without the core collapsing.

[0032] After the compacting step, the mixture in the mold is carried to a curing station. The cure of the binder can be obtained by means of radiation, heat, chemical curing or other suitable techniques. In the preferred embodiment, the curing step is conducted at a temperature below 500°C, for example below 200°C, for example at room temperature. In particular, in the preferred example the curing step can be thermally activated and continues in an exothermic reaction. The activation of the curing of the binder can occur at a temperature below 100°C. During curing the binder can adhere to the lightweight core so that the latter becomes an integral part of the decorative slab.

[0033] After curing the engineered stone forming a first material portion of the decorative slab comprises a porosity below 1% in volume, more preferably below 0,5% in volume, even more preferably below 0,2%, in volume.

[0034] After curing, the decorative slab is extracted from the mold. In some, embodiments the slab is cooled and / or conditioned before performing further steps.

[0035] After curing the method can comprise a calibration step and / or a squaring step. Calibration and squaring are mechanical machining steps that have the scope of providing to the decorative slab the final desired shape and dimension. In particular, calibration has the scope of flattening one or both the main surfaces of the decorative slab. One or more quality control can be performed during the manufacturing process.

[0036] With the intention of better showing the characteristics of the invention, in the following, as an example without any limitative character, several preferred forms of embodiments are described with reference to the accompanying drawings, wherein:

[0037] Figure 1 shows an upper perspective view of a decorative slab according to the invention.

[0038] Figure 2 shows a section along plane II of figure 1, in accordance with a first embodiment of the invention.

[0039] Figure 3 shows a section along plane II of figure 1 in accordance with a second embodiment of the invention.

[0040] Figure 4 shows a section along plane II of figure 1 in accordance with a first variant of the second embodiment.

[0041] Figure 5 shows a section along plane II of figure 1 in accordance with a second variant of the second embodiment.

[0042] Figure 6 shows some steps in a method for manufacturing the decorative slab, of the first embodiment, in accordance with the second independent aspect of the invention.

[0043] Figure 7 shows some steps in a method for manufacturing the decorative slab, of the second embodiment, in accordance with the second independent aspect of the invention.

[0044] Figure 1 shows a perspective view of a decorative slab 1 having a first main surface 2, being the upper surface of the decorative slab, and side edges 3. The decorative slab 1 has a decorative pattern 4, imitating the veining of a natural stone. In the illustrated example, the decorative pattern 4 is visible on both the first main surface and the side edges 3 of the decorative slab 1.

[0045] Figure 2 shows a section view of figure 1 illustrating a first embodiment of the decorative slab 1. The decorative slab 1 is entirely made of engineered stone and comprises a inorganic filler, for example cristobalite and / or feldspar, and a thermosetting binder, preferably polyester resin. Binder forming around 10% by weight of the engineered stone and 90% by weight being formed by the inorganic filler. The engineered stone material has a low porosity, preferably below 0,1%.

[0046] Figure 2 shows that the decorative slab 1 comprises a first material portion 5 being a perimetral portion of the slab, where the thickness T1 of the slab is substantially constant, and comprise a central core portion 6 of the slab 1 comprising voids in form of excavations 7. Said excavations being opened on the lower surface 8 of the decorative slab 1. The core portion 6 shows a variable thickness, in particular the excavations have a thickness T2 being 50% of the thickness T1 of the decorative slab 1. In the example the excavations 7 run parallel each other along the longitudinal dimension of the decorative slab 1. In this way the core portion 6 shows a density being lower than the density of the first material portion 5.

[0047] The decorative slab 1 comprises a width W1 that, in the example, of approximately 200 cm. As shown in figure 2 the first material portion 5 extends beyond edges of the core portion 6 of second width W2, for example of 5 cm (50 mm) on each side.

[0048] Figure 3 shows a second embodiment of the invention, wherein the core portion 6 comprises a honeycomb core 9 made of a dissimilar to the material of the first material portion 5. In the example, said honeycomb core 9 is made of polypropylene. In the example, the honeycomb 9 is made integrally with the first material portion 5, as it is integrated in the decorative slab during manufacturing of the engineered stone material as it will be later described. In the example, the honeycomb core 9 adheres directly (i.e. without a separate adhesive or fastener) to the engineered stone material of the first material portion 5. The first material portion 5 surrounds the honeycomb core 9 in such a way that the main surface 2 and the side edges 3 of the decorative slab 1 are made in the first material portion 5. In the example of figure 3 the honeycomb core 9 is exposed on the lower surface 8 of the decorative slab 1. The honeycomb core 9 comprises a thickness T3 being 50% of the thickness T1 of the decorative slab 1. For example, the thickness T1 of the decorative slab 1 is 20 mm, and the thickness T3 of the honeycomb 9 is 10 mm.

[0049] In the example of figure 3, the decorative slab 1 further comprises a covering layer 10 covering the exposed surface of the honeycomb core 9. The covering layer 10 is made of a fabric made of non-woven PET. The covering layer 10 can improve gripping with a thinset or an adhesive during installation of the decorative slab.

[0050] Figure 4 shows a first variant of the second embodiment of the decorative slab 1, that differs from the example of figure 3 only in that the honeycomb core 9 is completely surrounded by the first material portion 5, so that the honeycomb core 9 is not exposed on the lower surface 8 of the decorative slab 1, which, in this case, it is entirely made in the first material portion 5.

[0051] Figure 5 shows a second variant of the second embodiment of the decorative slab 1, that differs from the example of figure 4 only in that it comprises multiple core portions 6 each having a respective honeycomb core 9. In the example, the honeycomb cores 9 have a width W3 being around 50 cm and are separated by a part of the first material portion 5 having a width W4 of around 10 cm, so that the decorative slab 1 can be cut down to sub-product, along said separation part. For example, the obtained sub product can have a width of 60 cm, for example being adapted to be used as kitchen countertop, without the honeycomb core being exposed on opposite side edges of the sub product.

[0052] Figure 6 shows some steps in a method for manufacturing the decorative slab 1 of the first embodiment of figures 1 and 2. The method comprises a first step SI of providing a mixture M for forming the engineered stone in a mold 20.

[0053] The mixture being in the form of wet powders and granules of inorganic filler and binder. The inorganic filler, in the example, comprises silica sand, cristobalite, feldspar and metal-oxide pigment. The inorganic filler forms around 90% weight of the mixture M. The binder comprises unsaturated polyester resin and comprises cobalt catalyst, peroxide initiator, styrene monomer and silane-based coupling agent. The inorganic filler forming around 10% weight of the mixture M.

[0054] The mold 20 comprises a container body 21 having side and bottom walls for defining an open cavity to contain the mixture M. The mold 20 further comprises a lid 22 to close the open cavity once the mold is filled with the mixture M. In the embodiment of figure 6 the mold 20 comprises ribs 23 rising in the cavity from the bottom of the container body and adapted to realize the excavations 7 of the decorative slab of figure 2.

[0055] A coloring agent is randomly dispersed in the mixture M during filling of the mold 20 to form the decorative pattern 4.

[0056] Once the mold 20 is filled with the mixture M and closed with a lid it is carried to a compacting device 24 for the compaction of the mixture M inside the mold 20 in a compacting step S2. The compacting device 24 is adapted to apply vacuum and vibration for compacting the mixture M.

[0057] After pressing the mold 20 with the compacted mixture is carried to an oven 25 for hardening the binder in a curing step S3. In the oven 25 the mixture is heated up to 120°C to activate curing of the binder. The curing reaction continues with an exothermic reaction up to a temperature around 200°C. During curing the binder hardens and the engineered stone is formed so that the decorative slab 1 is obtained.

[0058] After curing step S3, the decorative slab 1 is cooled and extracted from the mold 20 (not necessarily in this order) and can be finished with ore mor more finishing operations S4, like for example one or more of the operations listed in the group consisting of calibration, polishing, squaring. The decorative slab 1 is finally obtained.

[0059] Figure 7 shows a second embodiment of the method for forming the decorative slab 1 of figure 3. The method of figure 7 differs from the method of figure 6 only in that the mold 20 does not comprise the ribs 23 and has a substantially flat bottom surface of the cavity. Furthermore, the method comprises a preliminary step S5 of inserting the honeycomb core 9 in the mold 20. The honeycomb core 9, in this case, preferably comprises closed honeycomb cells, so that the mixture M doesn’t fill the honeycomb cells that will represent voids in the final decorative slab. In addition, in this way honeycomb core can show a substantially continuous outer surface for bonding to the engineered stone.

[0060] In the method of figure 7, during step SI the mixture M is directed to the honeycomb core 9 inside the mold 20, during compacting step S2 the mixture is compacted against the external surfaces of the honeycomb core 9, and during curing step S3 the binder adheres to the external surfaces of the honeycomb core 9 that becomes integral part of the decorative slab 1.

[0061] The present invention is in no way limited to the hereinabove described embodiments, but such decorative slab and manufacturing method may be realized according to different variants without leaving the scope of the present invention.

[0062] Further, as is clear from the content of the description, the present invention relates to one or more of the items as listed below:

[0063] 1.- A decorative slab comprising a first material portion at least partially surrounding a core portion, wherein the first material portion is made of engineered stone and comprises a first density, wherein the core portion comprises a second density, and wherein said second density is lower than said first density.

[0064] 2.- The decorative slab according to item 1, wherein the first material portion can have a first density around 2200 kilograms per cubic meter.

[0065] 3.- The decorative slab according to item 2, wherein it can comprise a density being 50% or less than the first density of the first material portion.

[0066] 4.- The decorative slab according to any of the preceding items, wherein the core portion can comprise voids. 5.- The decorative slab according to item 4, wherein said voids can comprise excavations in the decorative slab.

[0067] 6.- The decorative slab according to item 5, wherein the core portion and the first material portion are made of the same material.

[0068] 7.- The decorative slab according to any of Items from 1 to 4, wherein said core portion comprises a foamed and / or honeycomb structure.

[0069] 8.- The decorative slab according to item 7, wherein the core portion is made of a dissimilar material than that of the first material portion.

[0070] 9.- The decorative slab according to item 8, wherein said dissimilar material can be a thermoplastic material, preferably being selected from the group consisting of a thermoplastic polymer, for example PE (polyethylene), PET (polyethylene terephthalate), PP (polypropylene), TPU (thermoplastic polyurethane).

[0071] 10.- The decorative slab according to item 8 or 9, wherein the core portion can comprise honeycomb core, for example of the kind produced and sold by ThermHex, or honeycomb pads, for example of the kind produced and sold by IntePro TITAN, and the like.

[0072] 11.- The decorative slab according to any of the preceding items, wherein the first material portion surrounds the core portion in such a way that the core portion is not visible on at least a first main surface of the decorative slab, said first main surface being preferably the surface destined to be the visible surface during the final use.

[0073] 12.- The decorative slab according to item 11, wherein the core portion is exposed at the main surface of the decorative slab being opposite to said first main surface. 13.- The decorative slab according to any of the items from 1 to 11, wherein said first material portion surrounds the core portion in such a way that the core portion is not visible on both the opposite main surfaces of the decorative slab.

[0074] 14.- The decorative slab according to any of the preceding items, wherein said core portion can occupy a thickness being lower than the thickness of the decorative slab, preferably the thickness of the core portion is:

[0075] - less than 90% of the thickness of the decorative slab, preferably less than 75%; and / or

[0076] - more than 25% of the thickness of the decorative slab, preferably more than 50%.

[0077] 15.- The decorative slab according to any of the preceding items, wherein the first material portion can surround the core portion in such a way that the core portion is not visible on at least one, preferably a plurality of, for example on all, the external side edges of the decorative slab.

[0078] 16.- The decorative slab according to item 15, wherein the core portion occupies a surface on the plane of the decorative slab being equal or less than 90%, preferably less than 80% of the surface of the decorative slab itself.

[0079] 17.- The decorative slab according to any of the preceding items, wherein the decorative slabs can comprise a plurality of core portions, preferably being separated by first material portions.

[0080] 18.- The decorative slab according to item 17, wherein the core portions can comprise a width measured on the plane of the decorative slab being preferably less than 1000 mm, more preferably being less than 800 mm, even more preferably less than 600 mm, for example less than 500 mm. 19.- The decorative slab according to any of the preceding items, wherein the slab has a length of at least 2 m, preferably at least 2,5 m, for example 3 m or more, and a width of at least 1 m preferably 1,5 m or more, for example 2 sqm.

[0081] 20.- The decorative slab according to any of the preceding items, wherein the core portion is integrally made in the decorative slab.

[0082] 21.- The decorative slab according to item 20, wherein with integrally made it is intended that the core portion and the first material portion are made of the same material in a single body.

[0083] 22.- The decorative slab according to item 20, wherein with integrally made it is intended that the core portion and the first material portion are made of separate bodies, preferably of different material, and are not bond each other by means of a separate adhesive or mechanical fastener.

[0084] 23.- The decorative slab according to any of the preceding items, wherein the engineered stone comprises an inorganic filler and a binder.

[0085] 24.- The decorative slab according to any of the preceding items, wherein the inorganic filler comprises mineral material like any kind of stone, sands, siliceous mineral material, for example quartz, silica sand, clay, feldspar cristobalite granite, talc or calcareous mineral material, for example, calcium carbonate, marble, gypsum.

[0086] 25.- The decorative slab according to item 23 or 24, wherein the inorganic filler is preferably at least 80% by weight of the engineered stone, preferably more than the 85% and more preferably more than 90%.

[0087] 26.- The decorative slab according to any of items from 23 to 25, wherein the binder is a thermosetting resin, preferably polyester resin, preferably said polyester resin being crosslinked with styrene monomer. 27.- The decorative slab according to item 26, wherein the binder is less than 20% by weight of the engineered stone, preferably less than the 15% and more preferably less than 10%.

[0088] 28.- A method for manufacturing a decorative slab, whether or not according to any of the preceding items, comprising the steps of: providing mixture for forming an engineered stone, said mixture comprising at least an inorganic filler and a curable binder; said mixture being provided in a mold to at least partially filling said mold; compacting said mixture; curing said binder to obtain the decorative slab; wherein : a low-density core is provided in the mold before said step of compacting the mixture, wherein after curing said lightweight core becomes a core portion of the decorative slab; and / or

[0089] - the mold comprises elements adapted to form voids in a core portion of the decorative slab.

[0090] 29.- The method according to item 28, wherein lightweight core can be provided in the mold either before or after the mixture is provided in the mold.

[0091] 30.- The method according to item 28, wherein a part of the mixture is provided in the mold, then the lightweight core is inserted in the mold and then a second part of the mixture is provided in the mold.

[0092] 31.- The method according to any of items from 28 to 30, wherein a plurality of lightweight cores can be provided in the mold.

[0093] 32.- The method according to any of the items from 28 to 31, wherein the lightweight core can have a honeycomb structure, preferably can be made with thermoplastic material, preferably PP.

[0094] 33.- The method according to item 28, wherein the elements of the mold for forming the voids in the core portion can be in the form ribs in the mold. 34.- The method according to any of the items from 28 to 33, wherein the mixture is provided in form of a wet particulate or wet granules.

[0095] 35.- The method according to any of items from 28 to 34, wherein the inorganic filler comprises mineral material like any kind of stone, sands, siliceous mineral material, for example quartz, silica sand, clay, feldspar cristobalite granite, talc or calcareous mineral material, for example, calcium carbonate, marble, gypsum.

[0096] 36.- The method according to any of items from 28 to 35, wherein the inorganic filler is preferably at least 80% by weight of the mixture, preferably more than the 85% and more preferably more than 90%.

[0097] 37.- The method according to any of items 28 to 36, wherein the curable binder is a thermosetting resin, preferably unsaturated polyester resin, preferably said unsaturated polyester resin and styrene copolymer.

[0098] 38.- The method according to any of items 28 to 37, wherein the binder is less than 20% by weight of the mixture, preferably less than the 15% and more preferably less than 10%.

[0099] 39.- The method according to any of items 28 to 38, wherein the mold is made of rubber and preferably comprises a container body adapted to receive the mixture and a lid adapted to close the container body so that the mixture is completely closed into the mold.

[0100] 40.- The method according to any of items 28 to 39, wherein the compacting step is conducted by applying vacuum and / or vibration.

[0101] 41.- The method according to any of the items from 28 to 40, wherein the curing step is conducted at a temperature below 500°C, for example below 200°C, for example at room temperature.

Claims

Claims1.- A decorative slab (1) comprising a first material portion (5) at least partially surrounding a core portion (6), wherein the first material portion (5) is made of engineered stone and comprises a first density, wherein the core portion (6) comprises a second density, and wherein said second density is lower than said first density.2.- The decorative slab (1) according to claim 1, wherein the core portion (6) can comprise voids.3.- The decorative slab (1) according to claim 2, wherein said voids can comprise excavations (7) in the decorative slab.4.- The decorative slab (1) according to claim 3, wherein the core portion (6) and the first material portion (5) are made of the same material.5.- The decorative slab (1) according to claim 1 or 2, wherein said core portion (6) comprises a foamed and / or honeycomb structure (9).6.- The decorative slab (1) according to claim 5, wherein the core portion (6) is made of a dissimilar material than that of the first material portion (5), preferably said dissimilar material can be a thermoplastic material, preferably being selected from the group consisting of a thermoplastic polymer, for example PE (polyethylene), PET (polyethylene terephthalate), PP (polypropylene), TPU (thermoplastic polyurethane).7.- The decorative slab (1) according to any of the preceding claims, wherein the first material portion (5) surrounds the core portion (6) in such a way that the core portion (6) is not visible on at least a first main surface (2) of the decorative slab (1), said first main surface (2) being preferably the surface destined to be the visible surface during the final use of the decorative slab (1); preferably wherein the core portion (6) is exposed at a second main surface (8) being opposite to said first main surface.8.- The decorative slab (1) according to any of the preceding claims, wherein said first material portion (5) surrounds the core portion (6) in such a way that the core portion is not visible on both the opposite main surfaces (2, 8) of the decorative slab.9.- The decorative slab (1) according to any of the preceding claims, wherein said core portion (6) can occupy a thickness (T2, T3) being lower than the thickness (Tl) of the decorative slab (1), preferably wherein the thickness (T2, T3) of the core portion (6) is:- less than 90% of the thickness (Tl) of the decorative slab (1), preferably being less than 75%; and / or- more than 25% of the thickness (Tl) of the decorative slab, preferably being more than 50%.10.- The decorative slab (1) according to any of the preceding claims, wherein the first material portion (5) surrounds the core portion (6) in such a way that the core portion (6) is not visible on at least one, preferably a plurality of, for example on all, the external side edges (3) of the decorative slab (1).11.- The decorative slab (1) according to any of the preceding claims, wherein it comprises a plurality of core portions (6).12.- The decorative slab (1) according to any of the preceding claims, wherein the core portion (6) is integrally made in the decorative slab, where with integrally made it is intended that:- the core portion (6) and the first material portion (5) are made of the same material in a single body; or .- the core portion (6) and the first material portion (5) are made of separate bodies, preferably of different material, and are not bond each other by means of a separate adhesive or mechanical fastener.13.- The decorative slab (1) according to any of the preceding claims, wherein the engineered stone comprises an inorganic filler and a binder, said binder comprising a thermosetting resin.14.- A method for manufacturing a decorative slab (1), whether or not according to any of the preceding claims, comprising the steps of: providing (SI) mixture (M) for forming an engineered stone material, said mixture comprising at least an inorganic filler and a binder; said mixture being provided in a mold (20) to at least partially filling said mold (20); compacting (S2) said mixture; curing (S3) said binder to obtain the decorative slab; wherein: a low-density core (9) is provided (S5) in the mold (20) before said step of compacting (SI) the mixture (M), wherein after curing said lightweight core becomes a core portion of the decorative slab; and / or- the mold comprises elements (23) adapted to form voids in a core portion of the decorative slab.15.- The method according to claim 14, wherein lightweight core (9) is provided in the mold either before or after the mixture is provided in the mold.16.- The method according to claim 14, wherein a part of the mixture is provided in the mold (20), then the lightweight core (9) is inserted in the mold and then a second part of the mixture is provided in the mold.17.- The method according to any of claims from 14 to 16, wherein a plurality of lightweight cores (9) can be provided in the mold.18.- The method according to any of claims from 14 to 17, wherein the lightweight core (9) can have a honeycomb structure and can be made with thermoplastic material, preferably PP.19.- The method according to claim 14, wherein the elements of the mold for forming the voids in the core portion can be in the form ribs (23) in the mold (20).20.- The method according to any of claims from 14 to 20, wherein the compacting step (S2) is conducted by applying vacuum and / or vibration.

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