The present invention relates to an inert filler composition, particularly useful in providing coatings, paints, adhesives, plasters and resins.

Quartz or silicon dioxide (Si0 ₂ ) is the most present mineral on earth's surface; its high purity, hardness and its inert characteristics make it one of the most used materials in various industrial fields.

It is in fact known to use quartz in the building sector, where it is used in the production of coatings, paints, adhesives, plasters and resins for floors. In particular, quartz-based fillers are used to fill superficial imperfections or give structure to coatings, paints, adhesives, plasters and resins during application to both internal and external surfaces, with the possibility to modify the characteristics of the application surfaces also depending on the particle size of the fillers used.

Furthermore, quartz is characterized by high hardness, equal to 7 on the Mohs scale, high resistance to chemical agents and a high grade of whiteness, characteristics which make it an indispensable component widely used in fillers.

The use of quartz as reinforcing filler when it is introduced in rubbers or in tire mixtures is also known.

In contrast with the characteristics mentioned above, which make quartz an indispensable component in the field of fillers, it is known however that the free crystalline silica that is present in quartz and in minerals that comprise it is harmful to health, especially the fine breathable fractions. In fact, workers who inhale dust containing silica in percentages higher than 1% are at risk of silicosis, a pneumoconiosis caused by the inhalation of dust containing silica (Si0 ₂ ) in the crystalline state, that leads to dose-dependent progressive pulmonary fibrosis. In particular, high-risk processes are work in mines, stone cutting, abrasive production, foundry work, production of glass or ceramics, work in the refractory industry, and people assigned to surface cleaning or to the fading of jeans by sandblasting are also exposed. The danger depends not only on the percentage of crystalline silica present in the inhaled air but also on the holding time in the environment.

It is therefore necessary to develop alternative filling compositions, which have characteristics that are similar or superior to known products based on quartz but without having their drawbacks, and in particular which allow to limit the release of crystalline silica and therefore to limit the exposure of workers of the sector to free crystalline silica.

The aim of the present invention is therefore to provide a filler composition that is capable of meeting the need described above and has high technical characteristics in terms of hardness, grade of whiteness and chemical resistance to acids and bases.

Within this aim, an object of the present invention is to provide a composition that allows to reduce the emissions of free crystalline silica into the environment.

Moreover, an object of the present invention is to provide a filler composition that allows to replace the quartz-based fillers generally used in the production of coatings, paints, adhesives, plasters and resins as well as in rubber and in tires.

Another object of the present invention is to provide a method that allows to provide the inert filler composition in a simple and economical manner.

This aim and these and other objects that will become better apparent hereinafter are achieved by an inert filler composition comprising a frit, wherein said frit has an oxide composition comprising 1 to 80% by weight of silica (Si0 ₂ ), 0.1 to 30% by weight of alumina (A1 ₂ 0 ₃ ), and 10 to 40% by weight of calcium oxide (CaO), on the total weight of the frit, and wherein said frit is free of free crystalline silica.

The aim and objects of the present invention are achieved also by a method for preparing an inert filler composition according to the invention, comprising the steps of:

i) providing a mixture comprising 0.1 to 81% by weight of quartz, 0.1 to 31% by weight of alumina (A1 ₂ 0 ₃ ), and 9 to 72% by weight of calcium carbonate (CaC0 ₃ ) on the total weight of the mixture;

ii) melting the mixture provided in i) at a temperature comprised between 500°C and 1550°C;

iii) cooling the molten material obtained in step ii), obtaining a solid mass, wherein said cooling step is achieved by direct cooling by dropping the molten material into water or by lamination of the molten material.

Finally, the aim and objects of the present invention are achieved by a product selected from the group consisting of coatings, paints, adhesives, plasters and resins, preferably selected from paints and resins, wherein said product comprises the inert filler composition according to the invention.

Further characteristics and advantages of the invention will become better apparent from the following detailed description and from the accompanying drawings, wherein:

Figure 1 shows the X-ray diffraction spectrum (XRD) of a filler composition according to the present invention;

Figure 2 shows the XRD spectrum of a commercial filler composition;

Figure 3 shows the XRD spectrum of free crystalline silica.

In a first aspect, the present invention relates to an inert filler composition (a filler) comprising a frit, wherein said frit has an oxide composition comprising 1 to 80% by weight of silica (Si0 ₂ ), 0.1 to 30% by weight of alumina (A1 ₂ 0 ₃ ), and 10 to 40% by weight of calcium oxide (CaO), each on the total weight of the frit, and wherein said frit is free of free crystalline silica.

In one embodiment of the invention, the inert filler composition comprises a frit which has an oxide composition essentially constituted by 1 to 80% by weight of Si0 ₂ , 0.1 to 30% by weight of A1 ₂ 0 ₃ , and 10 to 40% by weight of CaO, on the total weight of the frit, and wherein said frit is free of free crystalline silica.

In one embodiment, the oxide composition of the frit further comprises one or more of:

- 0.05 to 20% by weight of potassium oxide (K ₂ 0) on the total weight of the frit,

- 0.05 to 20% by weight of sodium oxide (Na ₂ 0) on the total weight of the frit.

In another embodiment, the oxide composition of the frit further comprises:

- up to 20% by weight of magnesium oxide (MgO),

- up to 20% by weight of potassium oxide (K ₂ 0),

- up to 20% by weight of sodium oxide (Na ₂ 0),

- up to 0.3% by weight of ferric oxide (Fe ₂ 0 ₃ ),

- up to 0.3% by weight of titanium dioxide (Ti0 ₂ ),

on the total weight of the frit.

In another embodiment of the filler composition according to the invention, the oxide composition of the frit further comprises one or more compounds selected from the group consisting of: barium oxide (BaO), zinc oxide (ZnO), strontium oxide (SrO), boron trioxide (B ₂ 0 ₃ ), cerium oxide (Ce0 ₂ ), bismuth oxide (Bi ₂ 0 ₃ ), cadmium oxide (CdO), chromium(III) oxide (Cr ₂ 0 ₃ ), copper oxide (CuO), fluorine (F), lithium oxide (Li ₂ 0), manganese oxide (MnO), molybdenum oxide (Mo0 ₃ ), nitrogen dioxide (N0 ₂ ), phosphorus pentoxide (P ₂ 0 ₅ ), and tin oxide (SnO).

Preferably, in the filler composition according to any of the embodiments described above, silica (Si0 ₂ ) is in a quantity comprised between 65 and 70% by weight on the total weight of the frit.

Preferably, in the filler composition according to any of the above embodiments, calcium oxide (CaO) is in a quantity comprised between 28 and 30% by weight on the total weight of the frit.

Preferably, in the filler composition according to any of the above embodiments, alumina (A1 ₂ 0 ₃ ) is in a quantity comprised between 2 and 5% by weight on the total weight of the frit.

The content of P ₂ 0 ₅ in the frit can vary between 0 and 10% by weight on the total weight of the frit. Zr0 ₂ is virtually absent (<0.5% by weight on the total weight of the frit).

As regards the impurities of the raw materials, such as Fe ₂ 0 ₃ and Ti0 ₂ , a maximum content of 0.05% by weight on the total weight of the frit is required in order to obtain absolute white (approx. L>92 in the CIELAB color space); above 0.5% by weight on the total weight of the frit, one obtains a frit that is noticeably colored and is adapted only for manufacturing of plates in dark color.

The use in the frit of raw materials that generate S0 ₃ is not provided.

Again as regards the raw materials, the use of quartz entails the presence of granules of different hue and the presence of impurities that lead to the defect known as“black spot”; the use of the frit instead entails great homogeneity and an absence of black spots.

In another embodiment, the frit of the filler composition according to any of the above embodiments is in the form of granules with a diameter comprised between:

a) 0.1 and 100 pm, or

b) 100 and 200 pm, or

c) 200 and 4000 pm.

Obviously, in addition to the above components, the inert filler composition of the present invention can further comprise also other additives conventionally used in the production of fillers, such as for example carbonates, such as calcium carbonate, and silicates, such as for example feldspars. Preferably, the inert filler composition according to the invention can be obtained by means of the method of the second aspect of the present invention.

In a second aspect, the present invention relates to a method for preparing an inert filler composition according to any of the above embodiments, said method comprising the steps of:

i) providing a mixture comprising 0.1 to 81% by weight of quartz, 0.1 to 31% by weight of alumina (A1 ₂ 0 ₃ ), and 9 to 72% by weight of calcium carbonate (CaC0 ₃ ) on the weight of the mixture;

ii) melting the mixture provided in i) at a temperature comprised between 500°C and 1550°C;

iii) cooling the molten material obtained in step ii), obtaining a solid mass, wherein said cooling step is achieved by direct cooling by dropping the molten material into water or by lamination of the molten material.

In one embodiment of the method described above, the mixture of step i) further comprises one or more of:

- up to 35% by weight of sodium carbonate,

- up to 30% by weight of potassium carbonate.

In one embodiment of the method described above, said mixture of step i) further comprises one or more of:

- up to 21% by weight of magnesite,

- up to 20% by weight of dolomite,

- up to 35% by weight of sodium carbonate,

- up to 30% by weight of potassium carbonate,

- up to 80% by weight of sodium feldspar, and

- up to 80% by weight of potassium feldspar,

on the total weight of the mixture.

Feldspars are a group of minerals that constitute about 60% of the earth’s crust and are divided in four groups: sodium feldspars, potassium feldspars, calcium feldspars and barium feldspars.

Within the scope of the present invention, “sodium feldspar” is understood as a mineral that comprises 63-77% by weight of Si0 ₂ , 18-22% by weight of A1 ₂ 0 ₃ and 9-11% by weight of Na ₂ 0 on the total weight of the mineral, in addition to traces of Ti0 ₂ , Fe ₂ 0 ₃ , K ₂ 0, CaO and MgO.

Within the scope of the present invention,“potassium feldspar” is understood as a mineral that comprises 77-93% by weight of Si0 ₂ , 6-8% by weight of A1 ₂ 0 ₃ and 5-7% by weight of K ₂ 0 on the total weight of the mineral, in addition to traces of Ti0 ₂ , Fe ₂ 0 ₃ , Na ₂ 0, CaO and MgO.

Within the scope of the present invention,“quartz” is understood as a mineral constituted by Si0 ₂ for more than 99% by weight on the total weight of the mineral, with traces of A1 ₂ 0 ₃ , Ti0 ₂ , Fe ₂ 0 ₃ , Na ₂ 0, CaO, MgO and K ₂ 0.

Within the scope of the present invention,“alumina” is understood as a compound constituted by aluminum oxide (A1 ₂ 0 ₃ ) for more than 99% by weight on the total weight of the compound, with traces of Fe ₂ 0 ₃ , Na ₂ 0, CaO, MgO and Si0 ₂

In another embodiment, the mixture of step i) further comprises one or more compounds selected from the group consisting of barium carbonate (BaC0 ₃ ), strontium carbonate (SrC0 ₃ ), zinc oxide (ZnO), zirconium silicate (ZiSi0 ₂ ), boric acid (H ₃ B0 ₃ ), borax (Na ₂ [B ₄ 0 ₅ (0H) ₄ ] -8H ₂ 0), cerium oxide (Ce0 ₂ ), bismuth oxide (Bi ₂ 0 ₃ ), copper oxide (CuO), fluorine, lithium feldspars, calcium feldspars, barium feldspars, nepheline, lithium carbonate (Li ₂ C0 ₃ ), calcium phosphate (Ca ₃ (P0 ) ₂ ) and tin oxide (SnO).

In one embodiment, in the method according to the invention the frit is in the form of incoherent material, i.e., in granules of various shapes, non- porous and/or non-hollow and/or non-fibrous granules.

In one embodiment, the alumina used as raw material is in the form of granules with a diameter comprised between 0.01 and 0.3 mm. In a conventional melting process for forming frit, these granules would generate inclusions inside the cooled glass because of the limited holding time of the molten material in the furnace and of the melting point. It is known that the melting point of glass furnaces is usually much lower than the melting point of alumina. The use in the mixture of raw materials of one or more metallic carbonates selected from LiC0 ₃ , CaC0 ₃ , MgC0 ₃ and dolomite in the specified percentages allows, differently from the background art, the total reaction of the alumina with other raw materials and/or components derived from the raw materials. The components are obtained by melting or chemical reaction of one or more raw materials during the melting process. The result of these chemical-physical processes is the formation of new amorphous phases containing Al. The use of the above cited carbonates also facilitates convective motions in the melting furnace, facilitating the alumina reaction process; this process has been described earlier only in the case of furnaces with a much longer holding time of the raw materials inside the furnace (longer than 1 h).

In the method according to the invention, during the melting process, preferably, all the alumina has reacted with other raw materials and/or components derived from the raw materials as a consequence of melting or chemical reaction of one or more raw materials.

In the method according to the invention, preferably the glass contains crystalline or amorphous inclusions obtained starting from raw materials that have undergone a thermal sintering or melting process before the melting process.

In one embodiment of the method according to the invention, the cooling step is achieved by direct cooling by dropping the molten material in water.

In another embodiment of the method according to the invention, the cooling step is achieved by lamination of the molten material, preferably by means of rollers cooled internally with water.

The cooled solid mass is then preferably subjected to a milling step, for example by means of roller units and/or toothed or smooth granulators, and subsequently sorted by particle size with, for example, rotational sieves, nutation sieves or an air selector.

Different particle sizes can thus be selected, according to the intended use, and can be divided into three major families generally known as:

MICRONIZED POWDERS: fillers with particle dimensions up to 100 pm;

MICRO-GRITS: fillers with particle dimensions comprised between 100 and 200 pm;

GRAIN: fillers with particle dimensions comprised between 200 and

4000 pm.

In one embodiment of the method according to the present invention, step ii) is performed at a temperature between 1350°C and 1550°C.

In the method according to the present invention, refinement and/or annealing processes are absent.

In one embodiment, the process for producing the frit entails:

1) preparing a mixture of materials;

2) melting in a methane/air-fired or methane/oxy gen-fired continuous furnace at the temperature of 1350-1550°C. Refinement processes are not provided (the glass is not kept in the furnace for a prolonged period of time);

3) the molten mixture is poured into a water bath, in which a fast cooling and the forming of glass occur. As an alternative, the molten mixture is poured between two water-cooled cylinders made of steel, leading to a quick cooling and the forming of a thin sheet of glass.

The process can contain the further steps of:

4) breaking up the sheet, generating small flakes;

5) milling a fraction of the glass by dry milling with an alumina ball mill; 6) screening the milled glass or separating the milled glass with an air selector in order to obtain a fraction with a diameter of less than 45 microns;

7) milling a portion of the glass in a roll crusher (cylinder-type crusher) in order to obtain a coarser fraction with a diameter between 100 and 4000 microns.

In one embodiment, the glass is obtained by using a mixture of raw materials subjected, completely or partially, to a preliminary thermal treatment that has led to a variable degree of sintering and/or melting. The diameter of the granules of such thermally treated raw materials is comprised between 2 and 20 mm.

In one embodiment, the holding time of the mixture of materials in the melting furnace is shorter than 1 h, leading to the forming of a glass within which there are amorphous or crystalline inclusions derived from the incomplete reaction and/or melting of one or more components of the raw materials. These inclusions allow to reduce the holding time of the molten material inside the furnace to times shorter than or equal to 1 h, with consequent increase in hourly productivity of the furnace and/or reduction of the production costs of the glass. Furthermore, the presence of inclusions gives the glass decorative effects such as, by way of non-exhaustive examples, the increase of the opacity of the glass containing inclusions and the diffusion of the incident light on the inclusions. The inclusions can be colorless or colored. The diameter of the inclusions depends on the diameter of the granules of thermally treated raw materials, on the composition of the mixture of raw materials introduced in the furnace, on the holding time and on the temperature of the furnace.

In a third aspect, the present invention relates to a product selected from the group consisting of coatings, paints, adhesives, plasters and resins, preferably selected from paints and resins, wherein said product comprises the inert filler composition according to the invention.

The invention will now be described with reference to the following non-limiting examples:

Example 1 : Preparation of the inert filler composition dkg

a) The following are added in a rotating blade mixer:

- 597 g of silicon dioxide,

- 3 g of alumina,

- 400 g of calcium oxide;

b) mixing occurs for 10 minutes at 1200 rpm;

c) the mixture obtained in a) is discharged into a“chamotte” clay pot, which is resistant up to 1600 °C;

d) the mixture is heated to a temperature of 1480-1550 °C for 30-45 minutes;

e) the molten mixture obtained in d) is cooled by pouring it into a container full of water at ambient temperature.

The formulations studied allow to obtain a frit which, after the processes described above, has technical characteristics similar to quartz, but is free of free crystalline silica, as demonstrated by analysis with D2Phaser model x-ray diffractometer (Bruker) performed on a sample of filler composition according to the invention. As can be seen, in the XRD spectrum of the filler composition of the invention (Figure 1) there is no peak which indicates the presence of free crystalline silica, but only the typical curve of a glass, while in the XRD spectrum of a filler composition of the commercial type (Figure 2) the presence of free crystalline silica can instead be noticed.

Example 2 - Preparation and comparison between water-based paint with quartz filler and water-based paint with inert filler (300 a)

Two water-based paints are prepared, the first (invention) comprising 25% by weight of inert filler according to the invention, and the second (comparison) comprising 25% by weight of quartz.

For preparing 300-gram samples of water-based paint, the following method is followed:

a) the following are added in a 1L cylindrical container provided with mechanical stirrer:

Table 1

75g of inert filler contain:

A1 ₂ 0 ₃ 3.75 ± 1.5 g

K ₂ 0 5.25 ± 1.5 g

MgO 6 ± 1.5 g

Si0 ₂ 41.25 ± 7.5 g

CaO 18.75 ± 7.5 g

Fe ₂ 0 ₃ up to 0.0375g Ti0 ₂ up to 0.0375g

CuO up to 0.015g

Cr0 ₃ up to 0.015g;

b) the reagents are mixed by means of a column-type mixer with a dissolver made of plastic at a speed of 1000-1200 rpm for 30 minutes;

c) the mixture thus obtained is left to rest for at least one hour;

d) the samples are applied in parallel on a white sheet of paper or cardboard and left to dry for at least 12 hours;

e) for each water, -based paint, colorimetry data are acquired by means of a spectrophotometer (X-Rite eXact™ CieLab).

Table 2

From the colorimetric data of the samples obtained by means of a spectrophotometer, shown in Table 2, it is possible to notice that the two formulations have a similar grade of whiteness.

Example 3 - Preparation and comparison between a resin agglomerate with quartz filler a resin agglomerate with cristobalite-based filler and a resin agglomerate with inert filler ( 100 a)

Three resin agglomerates are prepared, the first comprising 85% by weight of inert filler of the invention, the second comprising 85% by weight of cristobalite and the third comprising 85% by weight of quartz. For preparing 100-gram samples of resin agglomerate, the following method is followed:

a) the following are added in a 1L cylindrical container provided with mechanical stirrer:

Table 3

b) the three different fillers are mixed with titanium oxide by means of a column-type mixer with dissolver made of plastic at a speed of 1000- 1500 rpm for 5 minutes;

c) 13g of resin comprising 2g of Ti0 ₂ are added to each formulation and mixing is performed at a speed of 300-500 rpm for 5 minutes;

d) the compounds thus obtained are poured into plastic molds and left to harden for 2 hours at 80 °C.

Table 4 compares the parameters of the three resin agglomerates obtained with the method described above.

Table 4

The colorimetric values relate to a value detected with a spectrophotometer (X-Rite eXact™ CieLab).

The surface hardness determined according to the UNI EN 101 : 1992 standard with the Mohs scale is the ability to withstand scratching and incision. The materials are classified 1 to 10 depending on the increasing hardness of the minerals that are used for scoring them.

As can be seen from Table 4, the inert filler composition of the invention allows to provide products with high technical characteristics in terms of hardness and grade of whiteness.

In practice it has been found that the inert filler composition of the present invention improves the background art, since it provides a material comprising a frit with technical characteristics comparable to quartz, including grade of whiteness and hardness, but free of free crystalline silica, by means of a process with reduced harmful emissions for workers in the sector and for the environment.

The characteristics of the inert filler composition according to the invention allow its use in numerous applications, such as for example water- based paint and resins.

The disclosures in Italian Patent Application no. 102018000008603, from which this application claims priority, are incorporated herein by reference.