WO2025061508A2

WO2025061508A2 - Synthetic stone and methods of forming synthetic stone

Info

Publication number: WO2025061508A2
Application number: PCT/EP2024/075122
Authority: WO
Inventors: Francesco Ferrari
Original assignee: SIBELCO ITALIA SpA; Sibelco Italia SpA; Sibelco Nederland NV
Current assignee: SIBELCO ITALIA SpA; Sibelco Italia SpA; Sibelco Nederland NV
Priority date: 2023-09-21
Filing date: 2024-09-09
Publication date: 2025-03-27
Anticipated expiration: 2026-03-21
Also published as: WO2025061508A3

Abstract

The present invention relates to synthetic stone. The present invention also relates to a method of forming synthetic stone.

Description

Title: SYNTHETIC STONE AND METHODS OF FORMING SYNTHETIC STONE

FIELD OF THE INVENTION

The present invention relates to synthetic stone. The present invention also relates to methods of forming synthetic stone.

BACKGROUND OF THE INVENTION

Cristobalite is a mineral obtained by calcination of pure silica sand at a temperature of approximately 1550°C; for example, at a temperature of from 1300°C to 1700°C.

At room temperature, silica sand is mainly composed of a mineralogical phase called a-quartz. When the a-quartz is heated to approximately 1550°C, the crystalline lattice of the a-quartz undergoes a phase change. Upon heating, a-quartz initially undergoes a phase change to form P-quartz. Upon further heating, P-quartz then forms tridymite and then, at higher temperatures (typically from 1300°C to 1700°C, at atmospheric pressure), cristobalite is formed.

Cristobalite is chemically stable and mechanically strong. Commercial forms of cristobalite also have a high whiteness. Owing to its ease of manufacture, cristobalite is used in many applications. For example, cristobalite is used in engineering stone (e.g. work surfaces) and in paint.

In the engineering stone market (sometimes referred to as EGS), one of the biggest markets for cristobalite is in the production of kitchen countertops (for example in the form of synthetic stone). The countertops are composed of a mineral filler and resin. The countertops typically comprise the mineral filler at a high percentage (up to 92 weight %), whilst one or more resins (optionally: 2K epoxy resins, for example Fugante™ Epoxy 2k; or, polyester resins, for example POLARIS polyester resin (produced by Ashland™)) are present in lower percentages. Cristobalite, quartz, or, cristobalite and quartz, are often incorporated in the countertops as the mineral filler. Typically, a countertop (composed of a mineral filler and resin) will require cutting prior to installation. A countertop is typically cut in a dry way with simple abrasion tools. This method of cutting the countertop generates dust that is composed of a mixture of the resin and mineral filler. The mineral dust may contain cristobalite, quartz, or, cristobalite and quartz. Cristobalite and quartz dust can lead to work related cell silicosis through inhalation.

Cristobalite and quartz have been investigated for carcinogenic properties when the minerals are dispersed in the air and therefore inhaled. The most dangerous particles are particles with a diameter below 10 pm and particles freshly generated from a high energy cutting process.

Often, synthetic stone for the EGS market is formed to be white or off white. Sometimes there is a desire to include black and/or grey and/or other coloured material in a synthetic stone. For example, it is sometimes desirable to include black and/or grey and/or other coloured veins in an otherwise white or off white synthetic stone.

There is a need for beneficial synthetic stone. In particular, there is a need for a synthetic stone containing no cristobalite, quartz, or, cristobalite and quartz; or, a synthetic stone where cristobalite, quartz, or, cristobalite and quartz is reduced to below 1 % by weight.

SUMMARY OF THE INVENTION

The present invention relates to synthetic stone with no or little cristobalite, quartz, or, cristobalite and quartz.

The present invention relates to the finding that waste glass (such as cullet), that is crystalline silica free or substantially crystalline silica free (i.e. includes less than 1 weight % silica), can be used in the production of synthetic stone. Such synthetic stone has chemical and mechanical properties similar to synthetic stone formed with quartz and/or cristobalite, whilst being free from crystalline silica or substantially crystalline silica free (i.e. include less than 1 weight % crystalline silica). The inclusion of waste glass (such as cullet) in synthetic stone also permits the formation of synthetic stone with a range of colours, making them suitable for synthetic stone production.

The present inventor discovered that use of waste glass in synthetic stone provides at least the following benefits:

Reduces the total carbon footprint of the synthetic stone (compared to using fresh, non-recycled materials).

Reduces the total content of crystalline silica.

Maintains high transparency in the synthetic stone, i.e. retains aesthetic effects.

The waste glass used in the present invention may come from one or more of the following waste glass streams: i. Container glass and/or tableware ii. Float glass iii. Pharmaceutical (pharma) glass iv. Photovoltaic (PV) glass v. Insulation glass (for example glass wool) vi. Fiber glass for reinforcement vii. LCD glass

The waste glass included in synthetic stone according to the present invention:

Can be white or near white, and, transparent or semi-transparent.

Can have a good chemical resistance.

Can have a suitable porosity of less than or equal to 6% open porosity.

The present invention is as set out in the following clauses:

1. A synthetic stone comprising: waste glass, and a binder. 2. The synthetic stone of clause 1 , wherein the waste glass is cullet.

3. The synthetic stone of clause 1 or 2, wherein the waste glass comprises, or consists of: i. container glass having the following chemical composition:

and/or; ii. float glass having the following chemical composition:

and/or; iii. pharmaceutical (pharma) glass having the following chemical composition:

and/or, iv. photovoltaic (PV) glass having the following chemical composition:

and/or, v. insulation glass (for example glass wool) having the following chemical composition:

and/or, vi. low alkali fiber glass having the following chemical composition:

and/or, vii. boron silicate fiber glass having the following chemical composition:

and/or, viii. LCD glass having the following chemical composition:

where Ul refers to unavoidable impurities.

4. The synthetic stone of any one of clauses 1 to 3, wherein the synthetic stone comprises: from 1 to 90 weight %, or from 1 to 70 weight %, or from 1 to 40 weight %, or from 1 to 30 weight%, waste glass; or, from 2 to 90 weight %, or from 2 to 70 weight %, or from 2 to 40 weight %, or from 2 to 30 weight%, waste glass; or, from 5 to 90 weight %, or from 5 to 70 weight %, or from 5 to 40 weight %, or from 5 to 30 weight%, waste glass.

5. The synthetic stone of any one of clauses 1 to 4, wherein the waste glass is in the form of granules; optionally, wherein the granules: have a particle size in a range of from 1.0 to 0.063 mm (grain particles), or have a particle size of lower than 63 micrometres (micronized powder); and/or, have a particle size DOO less than 50 micrometres, or less than 40 micrometres, or from 10 to 40 micrometres.

6. The synthetic stone of any one of clauses 1 to 5, wherein the binder comprises, or consists of, a resin; optionally, wherein the synthetic stone comprises from 6 to 20 weight % resin; optionally, wherein the resin is an epoxy resin, a polyester resin or a polyurethane resin; optionally, wherein the resin is a 2K epoxy resin.

7. The synthetic stone of any one of clauses 1 to 6, wherein the synthetic stone further comprises a pigment, a silane, a catalyst, an accelerator, or a mixture of any two, three or four of these components

8. The synthetic stone of any one of clauses 1 to 7, wherein the synthetic stone comprises: less than 1 weight % crystalline SiO2, or less than 0.5 weight % crystalline SiO2, or less than 0.1 weight % crystalline SiO2, or is free of crystalline SiCte; and/or, cristobalite, quartz, or cristobalite and quartz, at less than 1 weight %, or less than 0.5 weight %, or less than 0.1 weight %, or less than 0.01 weight %; and/or, trace amounts (less than 1 weight %, or less than 0.5 weight %, or less than 0.01 weight %) of wollastonite, diopside, calcium magnesium silicate, mica and/or titan ite. 9. The synthetic stone according to any one of clauses 1 to 8, wherein the waste glass: a. is white or near white; b. is transparent or semi-transparent; c. is chemically resistant; and/or, d. has an open porosity of less than or equal to 6%.

10. A paint composition; or, an ink composition; or, a filtration medium; or, a ceramic composition; or, a dental composition; or, a biomedical composition; or, an implant material; or, a fuel cell; or a nuclear waste immobilization composition; comprising the synthetic stone of any one of clauses 1 to 9.

11. A method of forming a synthetic stone, optionally as in any one of clauses 1 to 9, comprising the following steps: providing waste glass, mixing the waste glass with a binder, and, permitting the mixture to harden to form a synthetic stone.

12. The method of clause 11 , wherein the method further comprises: during the mixing step, adding a pigment to obtain a synthetic stone of a desired colour; and/or, during the mixing step, adding one or more components selected from the list consisting of a pigment, a silane, a catalyst, an accelerator, or a mixture of any two, three or four of these components.

13. The method of clause 11 or clause 12, wherein: the waste glass is according to any one of clauses 2, 3 or 9; and/or, the binder is according to clause 6.

14. Use of waste glass in combination with a binder in the production of a synthetic stone; optionally, wherein the synthetic stone is according to any one of clauses 1 to

DETAILED DESCRIPTION OF THE INVENTION

Some embodiments of this disclosure, illustrating all its features, will now be discussed in detail. The words "comprising," "having," "containing," and "including," and other forms thereof, are intended to be equivalent in meaning and be open ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items.

It must also be noted that as used herein and in the appended claims, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Although any products and methods similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present disclosure, the preferred products and methods are now described.

Embodiments of the present disclosure will be described more fully hereinafter. Embodiments of the claims may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. The examples set forth herein are non-limiting examples and are merely examples among other possible examples.

Some of the terms used to describe the present invention are set out below:

"Crystalline silica free” refers to a composition of matter which contains less than 1 weight % crystalline silica. The standard method of measuring crystalline silica content in a composition of matter is X-Ray Diffraction (“XRD”). Depending on the measuring equipment used, XRD can be accurate to approximately 1 weight % of a crystal phase. Therefore, a “crystalline silica free” composition includes less than 1 weight % crystalline silica. Some XRD measurement apparatus can be accurate to 0.1 weight % so it is possible to measure that a composition is free of crystalline silica with this level of accuracy. “CIELAB colour space” refers to colour space defined by the International Commission on Illumination. It expresses colour as three numerical values: L (lightness); a (green-red colour components); and, b (blue-yellow components).

“Cullet” refers to broken and/or ground waste glass. Cullet can be separated into different waste streams, depending on particle size and/or contamination. Cullet can be contaminated with organic material, metals and/or ceramic pieces.

“Fiber glass” refers to glass fibers that are used in the manufacture of a fiber-reinforced plastic. The glass fibers may be randomly arranged, flattened into a sheet or woven into glass cloth. The plastic matrix may be a thermoset polymer matrix (e.g. epoxy, polyester resin or vinyl ester resin) or a thermoplastic.

“Glass” is an amorphous, non-crystalline, solid material. Glasses are typically brittle and often optically transparent. A glass is defined as an inorganic product of fusion which has been cooled through its glass transition to the solid state without crystallising. The main component of most glasses, in general use, is silica (SiOz). Common glass is generally produced in a two step method, and then shaped to make it suitable for a variety of applications. The first step is batch mixing. The mixture of ingredients to make up the glass (typically at least, silica, sodium carbonate, calcium carbonate and recycled glass (in the form of cullet), together with small quantities of various other trace ingredients) are mixed, to ensure an even mix of ingredients, and fed into the furnace. In the second step, the mixture is heated to around 1 ,500 °C, where the ingredients melt, various chemical reactions take place and CO2 and SO2 are evolved. These chemical reactions form molten glass (or, “glass solution”) which can be moulded and cooled.

“White" refers to a colour expressed using CIELAB colour space coordinates. White has the parameters: 100 (L), 0 (a), 0 (b).

“Near white” refers to a colour expressed using CIELAB colour space coordinates. Near white has the CIELAB colour space coordinates from 90 to below 100 (L), from -0,5 to +0,5 (a), from 0 to 4 (b). “LOI” refers to loss on ignition. This measurement is conducted by strongly heating a sample of the mineral at a specified temperature and allowing any volatile substances to escape. This will continue until the mass of the mineral stops changing. The value of LOI represents the mass of moisture and volatile material present in a sample.

“Weight %” refers to the percentage weight in grams of a component of a composition in every 100 grams of a composition. For example, if a mineral composition contains quartz at 25 weight %, then there is 25 g of quartz for every 100 g of the mineral composition.

“Unavoidable impurities” refers to components present in a composition which do not affect the properties of the composition. Unavoidable impurities are present in a composition at: less than 30 weight %; or, less than 25 weight %; or, less than 20 weight %; or, less than 15 weight %; or, less than 10 weight %; or, less than 5 weight %; or, less than 4 weight %; or, less than 3 weight %; or, less than 2 weight %; or, less than 1 weight %; or less than 0.5 weight %; or less than 0.1 weight %. In some tables in this specification, “Ul” is used to refer to unavoidable impurities.

Synthetic Stone

The waste glass (such as cullet) according to the different aspects of the invention provide good properties for replacing quartz in the manufacture of synthetic stone. Waste glasses (such as cullet) have wide colorimetric properties and, when mixed with resin, they do not present an important colour deviation from the colour of mixtures of the same resin with high-quality quartz granules (of the same or a similar colour).

The waste glasses (such as cullet) is/are crystalline silica free, avoiding the toxicological risks caused by inhalation of respirable crystalline silica during their handling or afterwards, during the machining of the synthetic stone formed therewith, when compared with other feldspars, quartz or cristobalite granules. These properties, together with the high availability of waste glass (such as cullet), result in the feasibility of replacing quartz granules with the waste glass (such as cullet) of the invention, overcoming the drawbacks encountered until now and without having to modify importantly the current formulations and/or manufacturing processes, and without deteriorating the performance and the visual appearance of these products.

The use of waste glass in synthetic stone provides at least the following benefits: Reduces the total carbon footprint of the synthetic stone (compared to using fresh, non-recycled materials).

Reduces the total content of crystalline silica.

The waste glass included in synthetic stone according to the present invention: Can be white or near white, and, transparent or semi-transparent. Has a good chemical resistance.

Has a suitable porosity of less than or equal to 6% open porosity.

In the present application, the waste glass (such as cullet) may be in the form of "granules". The term “granules” refers to individual units (particles). Thus, the term encompasses units ranging from infinitesimal powder particulates with sizes on the micrometre scale up to comparatively large pellets of material with sizes on the millimetre scale. This term encompasses particulate products of a variety of shapes and sizes, including grain particles, fines, powders, or combinations of these.

The particle size, also called particle diameter, of the granules can be measured by known screening separation using sieves of different mesh size. The term "particle size" as used herein, means the range in which the diameter of the individual particles in the waste glass (such as cullet) falls. It can be measured by particle retention or passage on calibrated sieves that have measured mesh size openings, where a particle will either pass through (and therefore be smaller than) or be retained by (and therefore larger than) a certain sieve whose size openings are measured and known. Particle sizes are defined to be within a certain size range determined by a particle’s ability to pass through one sieve with larger mesh openings or “holes” and not pass through a second sieve with smaller mesh openings. For waste glass (such as cullet) with a particle size < 800 micrometres, the particle size distribution of a granule sample can be measured by laser diffraction with commercially available equipment (e.g. Malvern Panalytical Mastersizer 3000 provided with a Hydro cell). For the measurement, the granule sample might be dispersed in demineralized water assisted by an ultrasound probe. The laser diffractometer provides particle distribution curves (volume of particles vs. particle size) and the D10, D50 and D90 statistical values of the particle population of the sample (particle size values where 10%, 50% or 90% of the sample particle population lies below this value, respectively).

The composition of the granules can be obtained by X-ray fluorescence (XRF), a technique well-established in the mineral technological field. The composition of the granules indicated herein corresponds preferably to the average (calculated from at least 3 repetitions of the measurement) of the composition of samples containing a mass of granules (e.g. 1 gram of granules).

The different types of waste glass for use in the synthetic stones of the present inventions include, but are not limited to: i. Container glass and/or tableware (from recycling container glass). ii. Float glass (from window and flat glass recycling). iii. Pharmaceutical (pharma) glass (borosilicate glass obtained from recycling pharmaceutical glass). iv. Photovoltaic (PV) glass (from recycling photovoltaic glass). v. Insulation glass (for example glass wool) (from recycling glass insulation wool). vi. Fiber glass for reinforcement (from recycling composite materials or other sources of waste fiber glass). vii. LCD glass (from recycling LCD screens).

Synthetic stone of the present invention may comprise (where Ul = unavoidable impurities): i. container glass having the following chemical composition:

and/or; ii. float glass having the following chemical composition:

and/or, iv. photovoltaic (PV) glass having the following chemical composition:

and/or, vi. low alkali fiber glass having the following chemical composition:

and/or, viii. LCD glass having the following chemical composition:

The desired particle size ranges (granulometry) of the waste glass (such as cullet) can be obtained by grinding and sieving, by methods known in the art, such as grinding with ball mills or opposed grinding rollers or jaw crushers. The grinding may comprise micronizing the mineral(s) to obtain refined waste glass (such as cullet) granules with average particle size D90 less than 50 micrometres, optionally less than 40 micrometres, optionally DOO from 10 to 40 micrometres.

In some aspects, the invention is directed to the use of waste glass (such as cullet) granules for the manufacture of synthetic stone. This use reduces (potentially to zero) the crystalline silica emissions during manufacturing or mechanizing the synthetic stone, compared to synthetic stone comprising quartz and/or cristobalite. Whilst it is desirable to reduce the crystalline silica component of the claimed synthetic stones to zero, in some aspects the crystalline silica content is higher, such as less than 5 weight %, or less than 10 weight %, or less than 25 weight %, or less than 50 weight %.

Another aspect of the invention relates to a synthetic stone comprising inorganic fillers and a hardened binder, wherein the inorganic fillers comprise the refined waste glass (such as cullet) of the invention.

The amount of waste glass (such as cullet) granules in the synthetic stone preferably ranges from 2 to 70 weight%, or from 2 to 50 weight %, or from 2 to 30 weight %, in relation to the total weight of the synthetic stone. In some aspects, the amount of waste glass (such as cullet) tailings granules in the synthetic stone is at least 2 weight %, or at least 4 weight %, or at least 10 weight %, and/or at most 90 weight %, or at most 70 weight %, or at most 50 weight %, or at most 30 weight %, in relation to the total weight of the synthetic stone.

The synthetic stone can also comprise inorganic fillers different from the waste glass (such as cullet) granules of the invention, preferably selected from stone, stone-like or ceramic materials. Other inorganic fillers in the synthetic stone may include synthetic inorganic granules such as recycled silicate glass granules, silicate frit granules, ceramic granules, or mixtures thereof. Optionally, the inorganic fillers (i.e. the sum of the weights of the waste glass (such as cullet) and of the other inorganic fillers) account for at least 70 weight %, or at least 80 weight %, or at least 85 weight %, and at most 95 weight %, of the total weight of the synthetic stone.

Synthetic stone with a low crystalline silica content is preferred. Therefore, it is preferred that all, or at least 90 weight %, or at least 95 weight % or at least 99 weight %, of the inorganic fillers have a low crystalline silica content, preferably a crystalline silica (quartz, cristobalite or other crystalline polymorphs) content of from 0 to 15 weight %, or from 0 to 10 weight %, or from 0 to 7 weight %, relative to the weight of said inorganic fillers. Preferably, at least 95 weight %, more preferably at least 99 weight %, of the other inorganic fillers in the synthetic stone have a crystalline silica content of from 0 to 10 weight %, relative to the weight of said inorganic fillers.

In some aspects, the synthetic stone does not comprise greater than 5 weight %, or greater than 1 weight %, relative to the weight of the synthetic stone material, of inorganic fillers with a crystalline silica content of greater than 15 weight %, or greater than 10 weight %, relative to the weight of said inorganic fillers. It is preferred that the synthetic stone comprises from 0 to 5 weight % relative to the weight of the synthetic stone, of inorganic fillers with a content of crystalline silica of from 15 to 100 weight % relative to the weight of the inorganic fillers.

In some aspects, the synthetic stone does not comprise inorganic granules with a content of crystalline silica greater than 15 weight %, or greater than 10 weight %. In these aspects, in addition to the waste glass (such as cullet) granules according to the claims, the synthetic stone further comprises synthetic inorganic granules selected from recycled silicate glass granules, silicate frit granules, ceramic granules, or mixtures thereof. In some aspects, the synthetic stone comprises waste glass (such as cullet) granules according to the invention, and silicate glass granules (recycled, frit) with less than 1 weight % crystalline silica, preferably wherein the sum of the weights of waste glass (such as cullet) and silicate glass granules accounts for more than 50 weight %, or more than 70 weight %, or more than 90 weight %, of the weight of the synthetic stone.

In some aspects, the crystalline silica content of the synthetic stone material is less than or equal to 15 weight %, or less than or equal to 10 weight %, or less than or equal to 5 weight %, relative to the weight of the synthetic stone. The crystalline silica content of the synthetic stone material may be from 0 to 15 weight %, or from 0 to 10 weight %, or from 0 to 5 weight %, relative to the weight of the synthetic stone.

In some aspects, the waste glass (such as cullet) granules comprised in the synthetic stone have a particle size D90 less than 50 micrometres, or less than 40 micrometres, or a D90 from 10 to 40 micrometres. Optionally, the synthetic stone of the invention might incorporate the waste glass (such as cullet) granules exclusively with a particle size less than 0.1 mm. In some cases, the amount of waste glass (such as cullet) granules in the synthetic stone with a particle size less than 0.063 mm is from 10 weight % to 40 weight %, in relation to the total weight of the synthetic stone.

The weight of inorganic filler (sum of the weights of the waste glass (such as cullet) granules and/or of any other inorganic granules) in the artificial stone article is optionally from 70 to 95 weight %, optionally from 85 to 95 weight % in relation to the weight of the synthetic stone.

The hardenable binder is optionally a hardenable organic resin, more preferably an organic thermosetting resin, suitably liquid and which may be selected from the group made up of unsaturated polyester resins, methacrylate based resins, vinyl resins and epoxy resins. These hardenable organic resins are preferably reactive and can be hardened in a curing (or cross-linking) reaction.

According to some aspects, the synthetic stone has been obtained by vacuum vibrocompaction and has an apparent density in the range of from 2000 to 2600 kg/m³, or from 2100 to 2500 kg/m³. Apparent density of the synthetic stone can be measured according to EN 14617-1:2013, or any other method known in the art.

The synthetic stone may be in the form of a block, slab, tile, sheet, board or plate. The synthetic stone might be used for construction or decoration, for manufacturing counters, kitchen countertops, sinks, shower trays, walls or floor coverings, stairs or similar.

The invention is also concerned with a method of forming a synthetic stone of the invention, comprising: a) mixing a hardenable binder and an inorganic filler comprising waste glass (such as cullet), b) vacuum vibrocompacting the unhardened mixture obtained in a) in a mould, and c) hardening the compacted mixture obtained in b). For the manufacture of the synthetic stone, a hardenable binder, such as a liquid organic resin, is mixed with the waste glass (such as cullet) granules, and with any optional inorganic fillers different from the waste glass (such as cullet) granules forming an (unhardened) synthetic stone mixture. The amount of waste glass (such as cullet) granules is optionally from 1 to 90 weight %, or from 1 to 70 weight %, or from 1 to 50 weight %, or from 1 to 30 weight %, of the weight of the synthetic stone mixture. The amount of waste glass (such as cullet) granules in the synthetic stone mixture is at least 2 weight %, or at least 4 weight %, or at least 10 weight %, and/or at most 90 weight %, or at most 70 weight %, or at most 50 weight %, or at most 30 weight %, in relation to the weight of the synthetic stone. The sum of the weights of the waste glass (such as cullet) granules and/or the optional inorganic fillers (different than the waste glass (such as cullet) granules) is optionally at least 70 weight %, or at least 80 weight %, or at least 85 weight %, of the weight of the synthetic stone mixture. Optionally, the amount of hardenable binder in the synthetic stone mixture ranges from 5 to 30 weight %, or from 5 to 15 weight %.

The mixing can be achieved, for example, by stirring with the use of conventional mixers, in a manner known in the art. The hardenable binder might be an organic resin, which once hardened, serves to achieve cohesion and adherence between the inorganic fillers in the synthetic stone mixture. The organic resins are preferably thermosetting, liquid and can be selected, for example, from the group made up of unsaturated polyester resins, methacrylate-based resins, vinyl resins and epoxy resins. These resins are preferably reactive and harden in a curing or cross-linking reaction.

Additionally, additives can be included in this mixing step, selected from pigments, curing catalysts, curing accelerators, UV stabilizers, or mixtures thereof. The optional inorganic fillers (different from the waste glass (such as cullet)) might be selected from stone, stone-like or ceramic materials, recycled silicate glass granules, silicate frit granules, ceramic granules, or mixtures thereof. These fillers may be incorporated to the synthetic stone mixture with different particle sizes and can be obtained from the crushing and/or grinding of natural or artificial materials. These inorganic fillers can be sourced, for example, from specialized companies, which commercialize them already dry and classified according to their particle size.

The other inorganic fillers (different from the waste glass (such as cullet) granules) can be in the form of granules, preferably with a particle size in a range of from 2.0 to 0.063 mm (grain particles) or with a particle size lower than 63 micrometres (micronized powder). In the case of grain particles of inorganic fillers, the particle size might range from 1 .2 to 0.1 mm, or from 0.7 to 0.3 mm, or from 0.4 to 0.1 mm, or from 0.3 to 0.063 mm. The inorganic fillers (different from the waste glass (such as cullet) granules) are preferably selected from recycled silicate glass granules, silicate frit granules, ceramic granules, or mixtures thereof. The inorganic fillers (different from the waste glass (such as cullet)) may have a composition of oxides different to the composition of waste glass (such as cullet) granules of the invention.

The unhardened synthetic stone mixture may comprise other additives, such as colorants or pigments, accelerators or catalysers for the curing or hardening of the resin (e.g. free radical initiators), promoters for the adhesion between the filler and the resin (e.g. silanes). These types of additives and the proportion used thereof are known in the state of the art. Optionally, these additives may be present in the synthetic stone mixture in an amount of from 0.01 to 5.0 wt.%, based on the weight of the mixture.

The unhardened synthetic stone mixture may be transported to a distributor in a distribution device. Distribution devices suitable are known, such as those used for the distribution of the (unhardened) synthetic stone mixtures in the manufacture of quartz containing synthetic stone. This (unhardened) synthetic stone mixture is optionally movable along the length of a temporary mould. The mould, in its simplest form, might be embodied by a paper or plastic sheet. Alternatively, the mould might be a more complex elastomeric tray. The distribution device may include a feeding hopper that receives the mixture in the top opening thereof and a conveyor belt positioned below the bottom outlet opening of the hopper, which collects or extracts the mixture from the hopper and deposits it onto or into a mould (depending on whether the mould is configured as a sheet or a tray). Other distribution devices and moulds are possible within the general concept of the present disclosure. The unhardened synthetic stone mixture having been distributed in the mould can be covered with a protective sheet on its top surface and subjected to vacuum vibrocompaction. For this, in an example, the mixture is transported inside a compaction area of a press, wherein it is inserted in a sealable chamber. Then, the chamber is sealed, and vacuum is created with appropriate gas evacuation pumps. Once the desired vacuum level has been reached (e.g. from 5 to 40 mbar), the ram of the press exerts a compaction pressure simultaneously with the application of vertical vibration of the piston (e.g. oscillating at from 2.000 to 4.000 Hz). During the vacuum vibrocompaction, the air entrapped in the synthetic stone mixture is substantially evacuated.

The compacted mixture then goes to a hardening or curing stage. In this stage, depending on the type of resin, as well as the use or not of any suitable catalysts or accelerants, the mixture is suitably subjected to the effect of temperature in a curing oven, suitably heated at a temperature between from 80 to 120°C, with residence times in the oven generally varying from 20 to 60 minutes. After curing, the hardened compacted mixture is cooled to a temperature equal to or less than 40°C.

After hardening, the hardened synthetic stone obtained, which can be shaped as blocks, slabs, boards or plates, can be cut and/or calibrated to the desired final dimensions, and may be finished (polished or honed) on one or both of its larger surfaces, depending on the intended application.

The present disclosure includes all the possible combinations of embodiments and aspects disclosed herein.

Experimental

Definitions and testing methods:

XRF: Oxide analysis of the granules might be conducted by X-Ray Fluorescence in a commercial XRF spectrometer. For example, a disc of about 1 g of a sample is mixed with lithium tetraborate and calcined in air, at atmospheric pressure and at a temperature 1 ,050°C for 25 minutes prior to analysis in the spectrometer. The results are reported as relative weight percentage of oxides (SiO2, AI2O3, etc. as included in the tables) in the fired chemical composition, i.e. without any “loss on ignition” components (such as volatiles, or organic matter which evaporate or decompose during calcination). The spectrometer is previously calibrated with multipoint calibration curves of known concentration of standards. The international standard ISO 12677:2011 may be followed forXRF analysis.

XRD: Identification and quantification of crystalline phases in the granules can be done by powder X-Ray Diffraction (XRD) using MoKal radiation (0.7093A) with a commercially available device (e.g. Bruker D8 Advance) at from 2°C to 35°C for 4 hours. Once the X-ray diffraction data is obtained, it is analyzed using the Rietveld method for quantification. The content of crystalline silica phases is calculated as a weight percentage of the sample analysed. Most commercially available XRD devices are accurate to approximately 1 weight % of a crystal phase, although some XRD devices can be more accurate.

Granulometry: The particle size, also called particle diameter, of the granules can be measured by known screening separation using sieves of different mesh sizes. For waste glass (such as cullet) granules with a particle size less than 200 micrometres, the particle size distribution can be measured by laser diffraction with a commercial equipment (e.g. Malvern Panalytical Mastersizer 3000 provided with a Hydro cell). For the measurement the granule sample can be dispersed in demineralized water assisted by an ultrasound probe. The laser diffractometer provides particle distribution curves (volume of particles vs. particle size) and the D10, D50 and D90 statistical values of the particle population (particle size values where 10%, 50% or 90% of the sample particle population lies below this value, respectively).

Colorimetry: Colorimetry and transparency of the granules in a polymerized matrix can be measured from disks prepared by mixing 50 g of the granules with 50 g of a commercial unsaturated polyester resin catalyzed with 0.75 g of organic MEKP peroxide and 0.12 g of cobalt octoate (6% cobalt). After homogenization, the mixture is poured to an aluminium mould up to a thickness of 5 mm. The mixture is then hardened at 70°C for 20 minutes and allowed to reach room temperature afterwards for from 30 to 40 minutes. The aluminium mould is then removed before the colorimetry and transparency of the obtained disk is measured. The colorimetry may be measured in a commercially available spectrophotometer (e.g. Konica Minolta CM-3600d) and expressed in values of L* a* b* coordinates (CIELAB color space), where L* is lightness from black (0) to white (100), a* from green (-) to red (+) and b* from blue (-) to yellow (+).

Examples according to the invention

To form synthetic stone comprising waste glass, waste glass according to any one or more of: i. Container glass and/or tableware (from recycling container glass); ii. Float glass (from window and flat glass recycling); iii. Pharmaceutical (pharma) glass (borosilicate glass obtained from recycling pharmaceutical glass); iv. Photovoltaic (PV) glass (from recycling photovoltaic glass); v. Insulation glass (for example glass wool) (from recycling glass insulation wool); vi. Fiber glass for reinforcement (from recycling composite materials or other sources of waste fiber glass); and/or vii. LCD glass (from recycling LCD screens); is provided. 12 g of each respective waste glass is placed into separate beakers and 8 g of epoxy resin (Fugante™ Epoxy 2k) added to each beaker. The mixtures are mixed in a Speed Mixer by HausChild for 60 seconds at 3000 rpm. The mixtures are then each poured into separate alumina cups for hardening. To harden the samples, they are left for 24 hours at a temperature of 35°C and at atmospheric pressure. The colorimetric properties can be measured once the samples have hardened.

In these non-limiting examples, the resin combined with the waste glass (such as cullet) is Fugante™ Epoxy 2k, which is an epoxy resin. Alternatively, the resin can be other epoxy resins, or a polyester resin, or a polyurethane resin. Non-limiting examples of polyester resins include AROPOL™ LP 67400 (produced by INEOS™), orthophthalic (produced by Ashland™), dicyclopentadiene (produced by Ashland™), isophthalic (produced by Ashland™) and POLARIS (produced by Ashland™). Nonlimiting examples of polyurethane resins include CRETAN NR (produced by Cores™) or PUCORE NG (produced by Cores™). When forming a synthetic stone (for use in or as, for example, a kitchen countertop, facades, bathrooms or furniture) with mineral filler and resin, typically the amount of mineral filler is from 80 to 92 weight % and the amount of resin (optionally of the types listed previously) is from 8 to 20 weight %.

The samples were formed as described above (with the different options for the waste glass, i., ii., iii., iv., v., vi., through to vii.) and then colorimetry measurements were taken. Due to the high transparency of the glass, the colorimetrical coordinates were measured using an opacity chart as background, also known as Leneta™ paper (as typically used in the paint industry). This paper is split into two sides with two different standardised colours, black and white. First the samples were measured using the white background on the Leneta™ paper, then measured on the black background on the Leneta™ paper. The colorimetrical coordinates were measured by a Konica Minolta CM-3600d and expressed in values of L* a* b* coordinates (CIELAB color space). Pictures of the discs were taken putting the samples between the white and black side.

The colorimetrical results obtained from the example synthetic stone samples are set out in Table 1:

Table 1: Colorimetrical results

Conclusion

The present inventors have demonstrated that waste glass (such as cullet) can be combined with a binder to form a synthetic stone. A synthetic stone formed with these components has similar physical characteristics to a synthetic stone formed from quartz and/or cristobalite combined with a binder, without the drawback that machining the synthetic stone can lead to the formation of potentially hazardous dust. Additionally, the inclusion of waste glass (such as cullet) provides manufacturers of synthetic stone with more options for the colours of the synthetic stone, opening up the possibility of including unique colours into synthetic stone.

Reduces the total content of crystalline silica.

A waste glass included in synthetic stone according to the present invention: Can be white or near white, and, transparent or semi-transparent. Can have a good chemical resistance.

Can have a suitable porosity of less than or equal to 6% open porosity.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1 . A synthetic stone comprising: waste glass, and a binder.

2. The synthetic stone of claim 1 , wherein the waste glass is cullet.

3. The synthetic stone of claim 1 or 2, wherein the waste glass comprises, or consists of: i. container glass having the following chemical composition:

and/or; ii. float glass having the following chemical composition:

and/or, iv. photovoltaic (PV) glass having the following chemical composition:

and/or, vi. low alkali fiber glass having the following chemical composition:

and/or, viii. LCD glass having the following chemical composition:

where Ul refers to unavoidable impurities.

4. The synthetic stone of any one of claims 1 to 3, wherein the synthetic stone comprises: from 1 to 90 weight %, or from 1 to 70 weight %, or from 1 to 40 weight %, or from 1 to 30 weight%, waste glass; or, from 2 to 90 weight %, or from 2 to 70 weight %, or from 2 to 40 weight %, or from 2 to 30 weight%, waste glass; or, from 5 to 90 weight %, or from 5 to 70 weight %, or from 5 to 40 weight %, or from 5 to 30 weight%, waste glass.

5. The synthetic stone of any one of claims 1 to 4, wherein the waste glass is in the form of granules; optionally, wherein the granules: have a particle size in a range of from 1.0 to 0.063 mm (grain particles), or have a particle size of lower than 63 micrometres (micronized powder); and/or, have a particle size D90 less than 50 micrometres, or less than 40 micrometres, or from 10 to 40 micrometres.

6. The synthetic stone of any one of claims 1 to 5, wherein the binder comprises, or consists of, a resin; optionally, wherein the synthetic stone comprises from 6 to 20 weight % resin; optionally, wherein the resin is an epoxy resin, a polyester resin or a polyurethane resin; optionally, wherein the resin is a 2K epoxy resin.

7. The synthetic stone of any one of claims 1 to 6, wherein the synthetic stone further comprises a pigment, a silane, a catalyst, an accelerator, or a mixture of any two, three or four of these components

8. The synthetic stone of any one of claims 1 to 7, wherein the synthetic stone comprises: less than 1 weight % crystalline SiOs, or less than 0.5 weight % crystalline SiO2, or less than 0.1 weight % crystalline SiO2, or is free of crystalline SiO2j and/or, cristobalite, quartz, or cristobalite and quartz, at less than 1 weight %, or less than 0.5 weight %, or less than 0.1 weight %, or less than 0.01 weight %; and/or, trace amounts (less than 1 weight %, or less than 0.5 weight %, or less than 0.01 weight %) of wollastonite, diopside, calcium magnesium silicate, mica and/or titanite.

9. The synthetic stone according to any one of claims 1 to 8, wherein the waste glass: a. is white or near white; b. is transparent or semi-transparent; c. is chemically resistant; and/or, d. has an open porosity of less than or equal to 6%.

10. A paint composition; or, an ink composition; or, a filtration medium; or, a ceramic composition; or, a dental composition; or, a biomedical composition; or, an implant material; or, a fuel cell; or a nuclear waste immobilization composition; comprising the synthetic stone of any one of claims 1 to 9.

11. A method of forming a synthetic stone, optionally as in any one of claims 1 to 9, comprising the following steps: providing waste glass, mixing the waste glass with a binder, and, permitting the mixture to harden to form a synthetic stone.

12. The method of claim 11 , wherein the method further comprises: during the mixing step, adding a pigment to obtain a synthetic stone of a desired colour; and/or, during the mixing step, adding one or more components selected from the list consisting of a pigment, a silane, a catalyst, an accelerator, or a mixture of any two, three or four of these components.

13. The method of claim 11 or claim 12, wherein: the waste glass is according to any one of claims 2, 3 or 9; and/or, the binder is according to claim 6.

14. Use of waste glass in combination with a binder in the production of a synthetic stone; optionally, wherein the synthetic stone is according to any one of claims 1 to 9.