WO2016020687A1

WO2016020687A1 - Compositions for use in paper coating

Info

Publication number: WO2016020687A1
Application number: PCT/GB2015/052277
Authority: WO
Inventors: Graham M PRING; Janet Preston; Gavin BUTLER-LEE; Gholam GHABAIAN; Matthew CHEESEMAN
Original assignee: Imerys Minerals Limited
Priority date: 2014-08-08
Filing date: 2015-08-06
Publication date: 2016-02-11
Also published as: GB201414127D0

Abstract

Compositions comprising particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and/or particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate), coating compositions comprising said compositions and paper products coated with said coating compositions.

Description

COMPOSITIONS FOR USE IN PAPER COATING

TECHNICAL FIELD The present invention relates generally to a composition comprising ground alkali earth metal carbonate (e.g. ground calcium carbonate (GCC)) and/or precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate (PCC)). The present invention also relates to the use of said compositions in paper coating compositions, paper coating compositions comprising said compositions and paper products coated with said coating compositions. The present invention further relates to methods of making said compositions, coating compositions and paper products. The present invention also relates to methods of printing.

BACKGROUND OF THE INVENTION

Paper products are commonly coated with compositions to impart desirable properties on the paper products. These compositions generally comprise one or more binders and often also comprise one or more inorganic particulate materials. The one or more binders and one or more inorganic particulate materials may be selected to provide a surface which is suitable for the intended use of the paper product. For example, the binder(s) and/or inorganic particulate material(s) may be selected to provide a suitable surface for a particular type of printing (e.g. offset, flexographic, inkjet or laser printing), for example such that a printed paper product will have a desired print density. The binder(s) and/or inorganic particulate material(s) may also be selected to provide paper products which have desired levels of gloss, smoothness, brightness and porosity. Coated paper products may be used for numerous applications, for example to package goods such as food and beverage products, electronic products, automotive products, medical/pharmaceutical products and cosmetic products. The intended use of the coated paper products may influence the type of binder(s) and/or inorganic particulate material(s) that are selected for use in paper coating compositions.

The rise in the abundance of counterfeit goods (materials and packages) is of growing concern. This is particularly important in the packaging of luxury goods, medicines and pharmaceutical products, where issues of safety as well as loss of profit are raised. For this reason, the tracking and marking of products is of increasing interest. It is suggested that packaging for medicines and pharmaceutical products should be marked with a code, for example variable data codes such as bar codes and QR codes. These codes can be printed using standard offset, or flexographic printing, but are more commonly printed using a laser marking system or inkjet printer, which can allow a different and unique print to be easily applied to every package.

Most coated paper products that are used for packaging have a surface which is optimized for offset or flexographic printing. Thus, the surfaces of these paper products are generally not optimized for inkjet printing using water-based inks. This may result in slow drying of the ink, smudging, wicking and interbleed of the printed inks.

It is therefore desirable to provide improved or at least alternative coating compositions which allow adequate inkjet printing without significantly disrupting the offset and/or flexographic printing capabilities of coated paper products. For example, it may be desirable to provide coating compositions which can be used to coat paper products to provide an improved surface for inkjet printing (e.g. a surface which allows faster drying of the inkjet ink and/or faster water absorption and/or decreased smudging). It may also be desirable to provide coating compositions which can be used to coat paper products which have a desired level of gloss and/or brightness and/or smoothness and/or porosity. It is also desirable to provide coating compositions which have a desired coating strength, which is important for offset printing.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, there is provided a composition comprising particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate (GCC)) and/or particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate (PCC)). The composition may consist of or consist essentially of particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate (GCC)) and/or particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate (PCC)).

In certain embodiments of the first aspect of the present invention, the particulate ground alkali earth metal carbonate has a particle size distribution (psd) steepness factor ranging from about 30 to about 55, for example about 45 to about 55, and/or the particulate precipitated alkali earth metal carbonate has a psd steepness factor ranging from about 35 to about 70, for example about 55 to about 65. This particular embodiment thus forms a second aspect of the present invention. The composition of the second aspect of the present invention may be adapted to be used as an additive in a coating composition. In accordance with a third aspect of the present invention, there is provided a coating composition comprising at least one binder, particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and/or particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate). For example, the coating composition of the second aspect of the present invention may comprise a composition of the first or second aspect of the present invention.

In accordance with a fourth aspect of the present invention, there is provided a paper product having a coating which comprises at least one binder, particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and/or particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate). For example, the paper product of the fourth aspect of the present invention may be coated with a coating composition of the third aspect of the present invention. For example, the paper product of the fourth aspect of the present invention may have a coating which comprises a composition of the first or second aspect of the present invention. The coating may comprise, consist of, or consist essentially of a composition of the first or second aspect of the present invention and kaolin. The kaolin may be present in an amount of up to about 50 wt% based on the total weight of the coating.

In accordance with a fifth aspect of the present invention, there is provided a use of a composition comprising particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and/or particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate) in a paper coating composition. For example, a composition of the first or second aspect of the present invention may be used in a paper coating composition.

In accordance with a sixth aspect of the present invention, there is provided a method of making a composition comprising combining particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate) (e.g. a method of making a composition of the first or second aspects of the present invention). In accordance with a seventh aspect of the present invention, there is provided a method of making a coating composition comprising combining particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate), particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate) and at least one binder (e.g. a method of making a coating composition of the third aspect of the present invention).

In accordance with an eighth aspect of the present invention, there is provided a method of making a paper product comprising coating paper with a coating composition comprising at least one binder, particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate) (e.g. coating paper with a coating composition of the third aspect of the present invention). In accordance with a ninth aspect of the present invention, there is provided a method of printing on a paper product, wherein the paper product is coated with a composition comprising at least one binder, particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and/or particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate) (e.g. a paper product of the fourth aspect of the present invention). The method may, for example, comprise inkjet printing. The method may, for example, comprise laser printing. The method may also, for example, comprise offset and/or flexographic printing.

In certain embodiments of any aspect of the present invention, the particulate ground alkali earth metal carbonate is particulate ground calcium carbonate (GCC).

In certain embodiments of any aspect of the present invention, the particulate precipitated alkali earth metal carbonate is particulate precipitated calcium carbonate (PCC).

In certain embodiments of any aspect of the present invention, the ground alkali earth metal carbonate has a particle size distribution (psd) steepness factor ranging from about 30 to about 55. In certain embodiments of any aspect of the present invention, the ground alkali earth metal carbonate has a particle size distribution (psd) steepness factor ranging from about 45 to about 55. For example, the ground alkali earth metal carbonate may have a particle size distribution (psd) steepness factor ranging from greater than about 45 to about 55. For example, the ground alkali earth metal carbonate may have a particle size distribution (psd) steepness factor ranging from about 48 to about 52. In certain embodiments of any aspect of the present invention, the precipitated alkali earth metal carbonate has a particle size distribution (psd) steepness factor ranging from about 35 to about 70. In certain embodiments of any aspect of the present invention, the precipitated alkali earth metal carbonate has a particle size distribution (psd) steepness factor ranging from about 55 to about 65. For example, the precipitated alkali earth metal carbonate may have a particle size distribution (psd) steepness factor ranging from greater than about 55 to about 65. For example, the precipitated alkali earth metal carbonate may have a particle size distribution (psd) steepness factor ranging from about 58 to about 64. In certain embodiments of any aspect of the present invention, the precipitated alkali earth metal carbonate and ground alkali earth metal carbonate are present in the composition in a weight ratio ranging from about 100:0 to about 0: 100, for example about 90:10 to about 30:70 precipitated alkali earth metal carbonate.ground alkali earth metal carbonate. For example, the precipitated alkali earth metal carbonate and ground alkali earth metal carbonate may be present in the composition in a weight ratio ranging from about 80:20 to about 40:60 precipitated alkali earth metal carbonate:ground alkali earth metal carbonate. For example, the precipitated alkali earth metal carbonate may be present in the composition in a weight ratio ranging from about 75:25 to about 50:50 precipitated alkali earth metal carbonate:ground alkali earth metal carbonate.

In certain embodiments of any aspect of the present invention, the ground alkali earth metal carbonate has a d₅₀ ranging from about 0.7 μιη to about 1.2 pm. For example, the ground alkali earth meta! carbonate may have a d₅₀ ranging from about 0.8 ym to about 1.0 pm.

In certain embodiments of any aspect of the present invention, the precipitated alkali earth metal carbonate has a d₅₀ ranging from about 0.2 pm to about 1.2 pm. For example, the precipitated alkali earth metal carbonate may have a d₅₀ ranging from about 0.3 pm to about 0.5 pm. In certain embodiments of any aspect of the present invention, from about 84 wt% to about 95 wt% of ground alkali earth metal carbonate particles are smaller than about 2 m. For example, from about 85 wt% to about 94 wt% of ground alkali earth metal carbonate particles may be smaller than about 2 pm. For example, from about 87 wt% to about 91 wt% of ground alkali earth metal carbonate particles may be smaller than about 2 pm.

In certain embodiments of any aspect of the present invention, from about 70wt% or from about 90 wt% to about 99 wt% of precipitated alkali earth metal carbonate particles are smaller than about 2 pm. For example, from about 92 wt% to about 98 wt% of precipitated alkali earth metal carbonate particles may be smaller than about 2 pm. For example, from about 94 wt% to about 98 wt% of precipitated alkali earth metal carbonate particles may be smaller than about 2 pm. For example, from about 70 wt% to about 76 wt% of precipitated alkali earth metal carbonate particles may be smaller than about 2 pm.

In certain embodiments of any aspect of the present invention, from about 45 wt% to about 60 wt% of ground alkali earth metal carbonate particles are smaller than about 1 μιη. For example, from about 47 wt% to about 57 wt% of ground alkali earth metal carbonate particles may be smaller than about 1 pm. For example, from about 50 wt% to about 55 wt% of ground alkali earth metal carbonate particles may be smaller than about 1 pm.

In certain embodiments of any aspect of the present invention, from about 40wt% or from about 85 wt% to about 95 wt% of precipitated alkali earth metal carbonate particles are smaller than about 1 pm. For example, from about 88 wt% to about 93 wt% of precipitated alkali earth metal carbonate particles may be smaller than about 1 pm. For example, from about 89 wt% to about 92 wt% of precipitated alkali earth metal carbonate particles may be smaller than about 1 pm. For example, from about 40 wt% to about 46 wt% of precipitated alkali earth metal carbonate particles may be smaller than about 1 pm.

In certain embodiments of any aspect of the present invention, from about 14 wt% to about 25 wt% of ground alkali earth metal carbonate particles are smaller than about 0.5 pm. For example, from about 16 wt% to about 23 wt% of ground alkali earth metal carbonate particles may be smaller than about 0.5 pm. For example, from about 17 wt% to about 21 wt% of ground alkali earth metal carbonate particles may be smaller than about 0.5 μηη.

In certain embodiments of any aspect of the present invention, from about 10 wt% or from about 45 wt% to about 60 wt% of precipitated alkali earth metal carbonate particles are smaller than about 0.5 μηη. For example, from about 48 wt% to about 58 wt% of precipitated alkali earth metal carbonate particles may be smaller than about 0.5 μσι. For example, from about 50 wt% to about 56 wt% of precipitated alkali earth metal carbonate particles may be smaller than about 0.5 μητι. For example, from about 10 wt% to about 15 wt% of precipitated alkali earth metal carbonate particles may be smaller than about 0.5 μιη.

In certain embodiments of the first or second aspect of the present invention, the composition has an emtec intensity (Emtec PDA C-02) equal to or less than about 50% after 5 seconds. For example, the composition may have an emtec intensity equal to or less than about 48% after 5 seconds. For example, the composition may have an emtec intensity equal to or less than about 45% after 5 seconds.

In certain embodiments of the first or second aspect of the present invention, the composition has an emtec intensity equal to or less than about 35% after 10 seconds. For example, the composition may have an emtec intensity equal to or less than about 30% after 10 seconds. For example, the composition may have an emtec intensity equal to or less than about 25% after 10 seconds. In certain embodiments of the first or second aspect of the present invention, the composition has a smearing index value of greater than about 8.5 after 15 seconds. For example, the composition may have a smearing index value equal to or greater than about 9 after 15 seconds. In certain embodiments of the third aspect of the present invention, the total combined weight of ground alkali earth metal carbonate and/or precipitated alkali earth metal carbonate in the coating composition is equal to or less than about 50 wt% based on the total weight of inorganic particulate material in the coating composition. For example, the total combined weight of ground alkali earth metal carbonate and/or precipitated alkali earth metal carbonate in the coating composition may be equal to or less than about 40 wt% based on the total weight of inorganic particulate material in the coating composition. For example, the total combined weight of ground alkali earth metal carbonate and/or precipitated alkali earth metal carbonate in the coating composition may be equal to or less than about 20 wt% based on the total weight of inorganic particulate material in the coating composition.

In certain embodiments of the third aspect of the present invention, the coating composition further comprises another inorganic particulate material. For example, the coating composition may further comprise one or more of alkaline earth metal carbonate (for example dolomite, i.e. CaMg(C0₃)₂), metal sulphate (for example gypsum), metal silicate, metal oxide (for example iron oxide, chromia, antimony trioxide or silica), metal hydroxide, wollastonite, bauxite, talc (for example, French chalk), mica, zinc oxide (for example, zinc white or Chinese white), titanium dioxide (for example, anatase or rutile), zinc sulphide, calcium carbonate (for example precipitated calcium carbonate (PCC), ground calcium carbonate (GCC) or surface-modified calcium carbonate), barium sulphate (for example, barite, blanc fixe or process white), alumina hydrate (for example, alumina trihydrate, light alumina hydrate, lake white or transparent white) and clay (for example kaolin, hydrous kaolin, calcined kaolin, China clay or bentonite). In certain embodiments of the third aspect of the present invention, the coating composition further comprises from about 10 wt% to about 90 wt% of the other inorganic particulate material based on total solids content of the inorganic particulate material in the coating composition. For example, the coating composition may comprise from about 30 wt% to about 70 wt% of the other inorganic particulate material based on total solids content of the inorganic particulate material in the coating composition. For example, the coating composition may comprise from about 50 wt% to about 60 wt% of the other inorganic particulate material based on total solids content of the inorganic particulate material in the coating composition. In certain embodiments of the third aspect of the present invention, the coating composition may comprise from about 7 wt% to about 25 wt% of one or more binders based on addition to the total solids content of the inorganic particulate material of the coating composition. For example, the coating composition may comprise from about 9 wt% to about 15 wt% of one or more binders based on addition to the total solids content of the inorganic particulate material of the coating composition. For example, the coating composition may comprise from about 11 wt% to about 13 wt% of one or more binders based on addition to the total solids content of the inorganic particulate material of the coating composition.

In certain embodiments of the third aspect of the present invention, the coating composition has an emtec intensity equal to or less than about 50% after 5 seconds. For example, the coating composition may have an emtec intensity equal to or less than about 48% after 5 seconds. For example, the coating composition may have an emtec intensity equal to or less than about 45% after 5 seconds. In certain embodiments of the third aspect of the present invention, the coating composition has an emtec intensity equal to or less than about 35% after 10 seconds. For example, the coating composition may have an emtec intensity equal to or less than about 30% after 10 seconds. For example, the coating composition may have an emtec intensity equal to or less than about 25% after 10 seconds.

In certain embodiments of the third aspect of the present invention, the coating composition has a smearing index value of greater than about 8.5 after 15 seconds. For example, the coating composition may have a smearing index value equal to or greater than about 9 after 15 seconds.

In certain embodiments of the fourth aspect of the present invention, the paper product is board.

In certain embodiments of the fourth aspect of the present invention, the paper product has a coat weight ranging from about 5 gsm to about 20 gsm. For example, the paper product may have a coat weight ranging from about 5 gsm to about 10 gsm. For example, the paper product may have a coat weight ranging from about 5 gsm to about 8 gsm. In certain embodiments of the fourth aspect of the present invention, the paper product has an emtec intensity equal to or less than about 50% after 5 seconds. For example, the paper product may have an emtec intensity equal to or less than about 48% after 5 seconds. For example, the paper product may have an emtec intensity equal to or less than about 45% after 5 seconds. In certain embodiments of the fourth aspect of the present invention, the paper product has an emtec intensity equal to or less than about 35% after 10 seconds. For example, the paper product may have an emtec intensity equal to or less than about 30% after 10 seconds. For example, the paper product may have an emtec intensity equal to or less than about 25% after 10 seconds.

In certain embodiments of the fourth aspect of the present invention, the paper product has a smearing index value of greater than about 8.5 after 15 seconds. For example, the paper product may have a smearing index value equal to or greater than about 9 after 15 seconds.

In certain embodiments of any aspect of the present invention, the composition comprising particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and/or particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate) (e.g. a composition of the first or second aspect of the present invention) is used to increase the rate of drying of an inkjet ink on a paper product. In certain embodiments of any aspect of the present invention, the composition comprising particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and/or particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate) is used to increase the rate of water absorption of a paper product (e.g. decrease the emtec intensity). In certain embodiments of any aspect of the present invention, the composition comprising particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and/or particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate) is used to increase the smearing index value of a paper product. In certain embodiments of any aspect of the present invention, the paper product is coated with a composition comprising particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and/or particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate). The paper product may, for example, be according to any aspect or embodiment of the present invention, including any combination thereof.

Certain embodiments of any aspect of the present invention, may provide one or more of the following advantages: · satisfactory rate of drying of inkjet ink (e.g. improved rate of inkjet ink drying) - e.g. satisfactory (e.g. improved) emtec water absorption; satisfactory (e improved) smearing index (e.g. after 15 seconds);

satisfactory (e.g improved) print density and contrast when using inkjet printing; satisfactory (e.g unchanged) gloss of coated paper product;

satisfactory (e.g unchanged) roughness of coated paper product;

satisfactory (e.g unchanged) brightness of coated paper product;

satisfactory (e.g unchanged) porosity of coated paper product;

satisfactory (e.g improved) print gloss and print density when using flexographic printing;

satisfactory (e.g unchanged) print gloss and print density when using offset printing;

satisfactory (e.g. unchanged) pick strength when using offset printing.

The details, examples and preferences provided in relation to any particular one or more of the stated aspects of the present invention apply equally to all aspects of the present invention. Any combination of the embodiments, examples and preferences described herein in all possible variations thereof is encompassed by the present invention unless otherwise indicated herein, or otherwise clearly contradicted by context. BRIEF DESCRIPTION OF THE FIGURES

Figure 1 shows the TAPPI gloss at 75° of the samples described in Example 1. Figure 2 shows the PPS roughness of the samples described in Example 1.

Figure 3 shows the D65 brightness of the samples described in Example 1.

Figure 4 shows Gurley porosity of the samples described in Example 1. Figure 5 shows emtec water absorption of the samples described in Example 1.

Figure 6 shows emtec intensity after 5 seconds and 10 seconds of the samples described in Example 1. Figure 7 shows smearing index after 15 seconds of the samples described in Example 1. Figure 8 shows print density of inkjet printed samples described in Example 1.

Figure 9 shows the contrast between black QR code and the substrate of inkjet printed samples described in Example 1.

Figure 10 shows flexo print gloss of the samples described in Example 1.

Figure 1 1 shows flexo print density of the samples described in Example 1.

Figure 12 shows offset print gloss of the samples described in Example 1. Figure 13 shows offset print density of the samples described in Example 1. Figure 14 shows offset pick strength of the samples described in Example 1.

DETAILED DESCRIPTION OF THE INVENTION

Compositions

There is provided herein compositions comprising particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and/or particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate). It has surprisingly been found that the addition of these compositions to paper coating compositions results in coated paper products which have an improved rate of drying of inkjet ink (e.g. an improved emtec intensity and/or an improved smearing index). The compositions may also not significantly affect the other properties of the coated paper such as gloss, brightness, roughness and porosity. The coated paper products may also be suitable for offset and/or flexo printing. For example, the addition of a composition provided herein to a coating composition may not significantly affect the suitability of the coated product (e.g. coated paper) to be used for offset and/or flexographic printing.

Thus, the composition may be adapted to be used as an additive in a coating composition. This means that compositions of the first or third aspect of the present invention may be used as an additional component in a typical coating composition. A typical coating composition may, for example, comprise a binder and an inorganic particulate material.

The binder of the typical coating composition may, for example, be any one or more binders which are known in the art, for example any one or more of the binders described herein in relation to the coating compositions of the invention. Examples of suitable binders include starch, latex, alcohol-based binders, proteinaceous adhesives and combinations thereof. The other inorganic particulate material of the typical coating composition may, for example, be any one or more inorganic particulate materials which are known in the art, in particular any one or more inorganic particular materials that are commonly used in paper coating compositions. For example, the inorganic particulate material present in the typical coating composition may be selected from one or more of alkaline earth metal carbonate (for example dolomite, i.e. CaMg(C0₃)₂), metal sulphate (for example gypsum), metal silicate, metal oxide (for example iron oxide, chromia, antimony trioxide or silica), metal hydroxide, wollastonite, bauxite, talc (for example, French chalk), mica, zinc oxide (for example, zinc white or Chinese white), titanium dioxide (for example, anatase or rutile), zinc sulphide, calcium carbonate (for example precipitated calcium carbonate (PCC), ground calcium carbonate (GCC) or surface-modified calcium carbonate), barium sulphate (for example, barite, blanc fixe or process white), alumina hydrate (for example, alumina trihydrate, light alumina hydrate, lake white or transparent white) and clay (for example kaolin, hydrous kaolin, calcined kaolin, China clay or bentonite).

The additive (e.g. compositions of the first or third aspect of the present invention) may, for example, be present in/used in a typical coating composition in an amount less than the amount of other inorganic particulate material in the coating composition. For example, the additive (e.g. composition of the first or third aspect of the present invention) may be used in/present in a typical coating composition in an amount equal to or less than about 80 wt% of the amount of other inorganic particulate material present in the coating composition, for example equal to or less than about 60 wt%, for example equal to or less than about 50 wt%, for example equal to or less than about 40 wt%, for example equal to or less than about 30 wt%, for example equal to or less than about 20 wt% of the amount of other inorganic particulate material present in the coating composition. The composition may, for example, be an aqueous suspension/dispersion. In certain embodiments, the solids content of the aqueous suspension/dispersion ranges from about 66 wt% to about 82 wt%, for example from about 70 wt% to about 80 wt%, for example from about 74 wt% to about 79 wt%. Alternatively, the composition may, for example, be a dry mineral blend.

In certain embodiments, the composition may initially be in the form of an aqueous suspension and the aqueous suspension may then be treated to remove at least a portion or substantially all of the water to form a partially dried or essentially completely dried product. For example, at least about 10% by volume of water in the aqueous suspension may be removed from the aqueous suspension, for example, at least about 20% by volume, or at least about 30% by volume, or least about 40% by volume, or at least about 50% by volume, or at least about 60% by volume, or at least about 70% by volume or at least about 80% by volume or at least about 90% by volume, or at least about 100%) by volume of water in the aqueous suspension may be removed. Any suitable technique can be used to remove water from the aqueous suspension including, for example, by gravity or vacuum-assisted drainage, with or without pressing, or by evaporation, or by filtration, or by a combination of these techniques. The partially dried or essentially completely dried product will comprise alkali earth metal carbonate particulate material and any other optional additives that may have been added to the aqueous suspension prior to drying. The partially dried or essentially completely dried product may be stored or packaged for sale. The partially dried or essentially completely dried product may be optionally re-hydrated and incorporated in coating compositions, as described herein.

In certain embodiments, for example when the alkali earth metal carbonate (e.g. calcium carbonate) is obtained from naturally occurring sources, it may be that some mineral impurities will contaminate the ground material. For example, naturally occurring calcium carbonate occurs in association with other minerals. In general, however, the alkali earth metal carbonate (e.g. calcium carbonate) may contain less than about 5 % by weight, for example less than about 3 % by weight, for example less than about 2 % by weight of other mineral impurities based on the total dry weight of alkali earth metal carbonate (e.g. calcium carbonate) in the composition. For example, the alkali earth metal carbonate (e.g. calcium carbonate) may contain less than about 1 % by weight of other mineral impurities based on the total dry weight of alkali earth metal carbonate (e.g. calcium carbonate) in the composition. The compositions may, for example, further comprise one or more optional additives. The one or more optional additives may, for example, be selected from dispersant(s), thickener(s), biocide(s), anti-settling agent(s) and combinations thereof. The total amount of further optional additive may, for example, be less than about 10 % by weight or less than about 5 % by weight or less than about 3 % by weight or less than about 2 % by weight or less than about 1 % by weight of the composition.

The precipitated alkali earth metal carbonate and ground alkali earth metal carbonate may, for example, be present in the composition in a weight ratio ranging from about 100:0 to about 0:100, for example from about 90:10 to about 30:70 precipitated alkali earth metal carbonate:ground alkali earth metal carbonate, for example from about 90:10 to about 40:60, for example from about 90:10 to about 50:50. For example, the precipitated alkali earth metal carbonate and ground alkali earth metal carbonate may be present in the composition in a weight ratio ranging from about 85:15 to about 45:55, for example from about 80:20 to about 40:60 precipitated alkali earth metal carbonate:ground alkali earth metal carbonate, for example from about 80:20 to about 50:50 precipitated alkali earth metal carbonate:ground alkali earth metal carbonate. For example, the precipitated alkali earth metal carbonate and ground alkali earth metal carbonate may be present in the composition in a weight ratio ranging from about 75:25 to about 40:60 precipitated alkali earth metal carbonate:ground alkali earth metal carbonate, for example from about 75:25 to about 50:50, for example from about 75:25 to about 60:40, for example from about 75:25 to about 70:30.

The ground or precipitated alkali earth metal carbonate may, for example, be selected from the carbonates of beryllium, magnesium, calcium, strontium, barium and radium. The ground or precipitated alkali earth metal carbonate may each be one of these carbonates or a combination of two or more of these carbonates. For example, the ground or precipitated alkali earth metal carbonate may each be selected from one or more of magnesium or calcium carbonate. Hereinafter, the invention will tend to be discussed in terms of ground calcium carbonate and precipitated calcium carbonate. However, the invention should not be construed as limited to these materials.

Ground calcium carbonate (GCC) is typically obtained by grinding a mineral source such as chalk, marble, limestone or travertine, which may be followed by a particle size classification step, in order to obtain a product having the desired degree of fineness. The particulate solid material may be ground autogenously, i.e. by attrition between the particles of the solid material themselves, or alternatively, in the presence of a particulate grinding medium comprising particles of a different material from the calcium carbonate to be ground. Wet grinding of calcium carbonate involves the formation of an aqueous suspension of the calcium carbonate which may then be ground, optionally in the presence of a suitable dispersing agent. Reference may be made to, for example, EP-A-614948 (the contents of which are incorporated by reference in their entirety) for more information regarding the wet grinding of calcium carbonate.

Precipitated calcium carbonate (PCC) may be produced by any of the known methods available in the art. TAP PI Monograph Series No 30, "Paper Coating Pigments", pages 34-35 describes the three main commercial processes for preparing precipitated calcium carbonate which is suitable for use in preparing products for use in the paper industry, but may also be used in connection with the certain embodiments of the present invention. In all three processes, limestone is first calcined to produce quicklime, and the quicklime is then slaked in water to yield calcium hydroxide or milk of lime. In the first process, the milk of lime is directly carbonated with carbon dioxide gas. This process has the advantage that no by-product is formed, and it is relatively easy to control the properties and purity of the calcium carbonate product. In the second process, the milk of lime is contacted with soda ash to produce, by double decomposition, a precipitate of calcium carbonate and a solution of sodium hydroxide. The sodium hydroxide should be substantially completely separated from the calcium carbonate if this process is to be commercially attractive. In the third main commercial process, the milk of lime is first contacted with ammonium chloride to give a calcium chloride solution and ammonia gas. The calcium chloride solution is then contacted with soda ash to produce, by double decomposition, precipitated calcium carbonate and a solution of sodium chloride. The PCC may also be ground to obtain a product having the desired degree of fineness. For example, the PCC may be ground by the methods described above in relation to GCC.

The process for making PCC results in very pure calcium carbonate crystals and water. The crystals can be produced in a variety of different shapes and sizes, depending on the specific reaction process that is used. The three main forms of PCC crystals are aragonite, rhombohedral and scalenohedral, all of which are suitable for use in certain embodiments of the present invention, including mixtures thereof. The ground alkali earth metal carbonate (e.g. GCC) may, for example, have a particle size distribution (psd) steepness factor ranging from about 30 or from about 45 to about 55. For example, the ground alkali earth metal carbonate (e.g. GCC) may have a psd steepness factor ranging from greater than about 45 to about 55, for example the ground alkali earth metal carbonate (e.g. GCC) may have a psd steepness factor ranging from about 46 to about 54, for example from about 47 to about 53. For example, the ground alkali earth metal carbonate (e.g. GCC) may have a psd steepness factor ranging from about 48 to about 52, for example from about 49 to about 51 , for example about 50.

The precipitated alkali earth metal carbonate (e.g. PCC) may, for example, have a particle size distribution (psd) steepness factor ranging from about 55 to about 65. For example, the precipitated alkali earth metal carbonate (e.g. PCC) may have a psd steepness factor ranging from greater than about 35 to about 70, for example 55 to about 65, for example from about 56 or 57 to about 64, for example from about 56 or 57 to about 63. For example, the precipitated alkali earth metal carbonate (e.g. PCC) may have a psd steepness factor ranging from about 58 to about 64, for example from about 59 to about 63, for example about 60 to about 62, for example about 61. The composition (i.e. composition comprising ground alkali earth metal carbonate (e.g. GCC) and precipitated alkali earth metal carbonate (e.g. PCC)) may have a particle size distribution (psd) steepness factor ranging from about 30 or from about 45 to about 55 or to about 65 or to about 70. For example, the composition may have a psd steepness factor ranging from about 35 or from about 55 to about 65 or to about 70, For example, the composition may have a psd steepness factor ranging from about 46 to about 64, for example from about 47 to about 63, for example from about 48 to about 62, for example from about 49 to about 61. For example, the composition may have a psd steepness factor ranging from about 50 to about 60, for example from about 51 to about 59, for example from about 52 to about 58. For example, the composition may have a steepness factor ranging from about 53 to about 58, for example from about 54 to about 58.

The steepness factor is defined as the ratio of the d₃₀ equivalent spherical diameter (at which 30% by weight of the particles are finer) to the d₇₀ equivalent spherical diameter (at which 70% by weight of the particles are finer), multiplied by 100. Unless otherwise stated, particle size properties referred to herein are as measured in a well known manner by sedimentation of the particulate filler or material in a fully dispersed condition in an aqueous medium using a Sedigraph 5100 machine as supplied by Micromeritics Instruments Corporation, Norcross, Georgia, USA (telephone: +17706623620; web-site: www.micromeritics.com), referred to herein as a "Micromeritics Sedigraph 5100 unit". Such a machine provides measurements and a plot of the cumulative percentage by weight of particles having a size, referred to in the art as the 'equivalent spherical diameter' (e.s.d), less than given e.s.d values. The mean particle size d₅₀ is the value determined in this way of the particle e.s.d at which there are 50% by weight of the particles which have an equivalent spherical diameter less than that d₅₀ value. The d_g8i d₉₀ and the d₁₀ are the values determined in this way of the particle e.s.d. at which there are 98%, 90% and 10% respectively by weight of the particles which have an equivalent spherical diameter less than that d₉₈, d₉₀ or d₁₀ value.

The ground alkali earth metal carbonate (e.g. GCC) may, for example, have a d₅₀ ranging from about 0.7 μιη to about 1.2 pm. For example, the ground alkali earth metal carbonate (e.g. GCC) may have a d₅₀ ranging from about 0.8 pm to about 1 .1 pm, for example from about 0.8 pm to about 1 .0 pm. For example, the ground alkali earth metal carbonate (e.g. GCC) may have a d₅₀ ranging from about 0.9 pm to about 1.2 pm, for example from about 0.9 pm to about 1.1 pm, for example from about 0.9 pm to about 1.0 pm.

The precipitated alkali earth metal carbonate (e.g. PCC) may, for example, a d₅₀ ranging from about 0.2 pm to about 1 .2 pm or to about 0.6 pm. For example, the precipitated alkali earth metal carbonate (e.g. PCC) may have a d₅₀ ranging from about 0.3 pm to about 0.6 pm, for example from about 0.3 pm to about 0.5 pm

The composition (i.e. composition comprising ground alkali earth metal carbonate (e.g. GCC) and/or precipitated alkali earth metal carbonate (e.g. PCC)) may have a d₅₀ ranging from about 0.3 pm to about 1 .2 pm or to about 1.0 pm. For example, the composition may have a d₅₀ ranging from about 0.4 pm to about 0.9 pm, for example from about 0.4 pm to about 0.7 pm, for example from about 0.4 pm to about 0.6 pm. For example, the composition may have a d₅₀ ranging from about 0.5 pm to about 0.8 pm, for example from about 0.5 pm to about 0.7 pm. The ground alkali earth metal carbonate (e.g. GCC) may, for example have from about 84 wt% to about 95 wt% of particles smaller than about 2 pm. For example, the ground alkali earth metal carbonate (e.g. GCC) may have from about 85 wt% to about 94 wt%, for example from about 86 wt% to about 93 wt%, for example from about 87 wt% to about 92 wt% of particles smaller than about 2 pm. For example, the ground alkali earth metal carbonate (e.g. GCC) may have from about 87 wt% to about 91 wt% of particles smaller than about 2 pm.

The precipitated alkali earth metal carbonate (e.g. PCC) may, for example have from about 70 wt% or from about 90 wt% to about 99 wt% of particles smaller than about 2 pm. For example, the precipitated alkali earth metal carbonate (e.g. PCC) may have from about 91 wt% to about 99 wt%, for example from about 92 wt% to about 99 wt%, for example from about 91 wt% to about 98 wt%, for example from about 92 wt% to about 98 wt% of particles smaller than about 2 μιη. For example, the precipitated alkali earth metal carbonate (e.g. PCC) may have from about 93 wt% to about 98 wt%, for example from about 93 wt% to about 98 wt% of particles smaller than about 2 pm. For example, the precipitated alkali earth metal carbonate (e.g. PCC) may have from about 94 wt% to about 97 wt%, for example from about 94 wt% to about 97 wt%, for example from about 95 wt% to about 97 wt% of particles smaller than about 2 pm. The precipitated alkali earth metal carbonate (e.g. PCC) may, for example have from about 70 wt% to about 76 wt% of particles smaller than about 2 pm.

The composition (i.e. the composition comprising ground alkali earth metal carbonate (e.g. GCC) and/or precipitated alkali earth metal carbonate (e.g. PCC)) may have from about 70 wt% or from about 85 wt% to about 99 wt% of particles smaller than about 2 pm. For example, from about 86 wt% to about 97 wt%, for example from about 87 wt% to about 96 wt%, for example from about 88 wt% to about 96 wt% of particles in the composition may be smaller than about 2 pm. For example, from about 89 wt% to about 96 wt%, for example from about 89 wt% to about 95 wt%, for example from about 90 wt% to about 95 wt% of particles in the composition may be smaller than about 2 pm. For example, from about 92 wt% to about 98 wt%, for example from about 93 wt% to about 97 wt%, for example from about 93 wt% to about 96 wt% of particles in the composition may be smaller than about 2 pm. The ground alkali earth metal carbonate (e.g. GCC) may, for example, have from about 45 wt% to about 60 wt% of particles smaller than about 1 pm. For example, the ground alkali earth metal carbonate (e.g. GCC) may have from about 46 wt% to about 59 wt%, for example from about 47 wt% to about 58 wt%, for example from about 47 wt% to about 57 wt% of particles smaller than about 1 Mm. For example, the ground alkali earth metal carbonate (e.g. GCC) may have from about 48 wt% to about 56 wt%, for example from about 49 wt% to about 56 wt%, for example from about 49 wt% to about 55 wt% of particles smaller than about 1 Mm. For example, the ground alkali earth metal carbonate (e.g. GCC) may have from about 50 wt% to about 56 wt%, for example from about 50 wt% to about 55 wt%, for example from about 50 wt% to about 54 wt%, for example from about 50 wt% to about 53 wt% of particles smaller than about 1 m.

The precipitated alkali earth metal carbonate (e.g. PCC) may, for example, have from about 40 wt% or from about 85 wt% to about 95 wt% of precipitated alkali earth metal carbonate (e.g. PCC) particles smaller than about 1 pm. For example, the precipitated alkali earth metal carbonate (e.g. PCC) may have from about 86 wt% to about 94 wt%, for example from about 86 wt% to about 93 wt%, for example from about 87 wt% to about 92 wt% of particles smaller than about 1 pm. For example, from about 88 wt% to about 94 wt%, for example from about 88 wt% to about 93 wt%, for example from about 88 wt% to about 92 wt% of precipitated alkali earth metal carbonate (e.g. PCC) particles may be smaller than about 1 \im. For example, from about 89 wt% to about 94 wt%, for example from about 89 wt% to about 93 wt%, for example from about 89 wt% to about 92 wt% of precipitated alkali earth metal carbonate (e.g. PCC) particles may be smaller than about 1 im. The precipitated alkali earth metal carbonate (e.g. PCC) may, for example, have from about 40 wt% to about 46 wt% of precipitated alkali earth metal carbonate (e.g. PCC) particles smaller than about 1 pm.

The composition (i.e. the composition comprising ground alkali earth metal carbonate (e.g. GCC) and/or precipitated alkali earth metal carbonate (e.g. PCC)) may have from about 40 wt% or from about 60 wt% to about 90 wt% of particles smaller than about 1 pm. For example, from about 62 wt% to about 86 wt%, for example from about 62 wt% to about 85 wt%, for example from about 63 wt% to about 85 wt%, for example from about 64 wt% to about 85 wt%, for example from about 65 wt% to about 85 wt% of particles in the composition may be smaller than about 1 M^m- For example, the composition may have from about 67 wt% to about 85 wt%, for example from about 70 wt% to about 85 wt%, for example from about 75 wt% to about 85 wt%, for example from about 80 wt% to about 85 wt% of particles smaller than about 1 im. The ground alkali earth metal carbonate (e.g. GCC) may, for example, have from about 14 w†% to about 25 wt% of particles smaller than about 0.5 pm. For example, from about 15 wt% to about 24 wt%, for example from about 16 wt% to about 23 wt%, for example from about 17 wt% to about 22 wt% of ground alkali earth metal carbonate (e.g. GCC) particles may be smaller than about 0.5 μιτι. For example, from about 17 wt% to about 23 wt%, for example from about 17 wt% to about 22 wt%, for example from about 17 wt% to about 21 wt% of ground alkali earth metal carbonate (e.g. GCC) particles may be smaller than about 0.5 pm. The precipitated alkali earth metal carbonate (e.g. PCC) may, for example, have from about 10 wt% or from about 45 wt% to about 60 wt% of particles smaller than about 0.5 pm. For example, from about 46 wt% to about 59 wt%, for example from about 47 wt% to about 58 wt%, for example from about 48 wt% to about 57 wt% of precipitated alkali earth metal carbonate (e.g. PCC) particles may be smaller than about 0.5 μηι. For example, from about 48 wt% to about 58 wt%, for example from about 48 wt% to about 57 wt%, for example from about 48 wt% to about 56 wt%, for example from about 48 wt% to about 55 wt% of precipitated alkali earth metal carbonate (e.g. PCC) particles may be smaller than about 0.5 μηι. For example, from about 50 wt% to about 58 wt%, for example from about 50 wt% to about 57 wt%, for example from about 50 wt% to about 56 wt%, for example from about 50 wt% to about 55 wt% of precipitated alkali earth metal carbonate (e.g. PCC) particles may be smaller than about 0.5 μιη. The precipitated alkali earth metal carbonate (e.g. PCC) may, for example, have from about 10 wt% to about 15 wt% of particles smaller than about 0.5 pm. The composition (i.e. the composition comprising ground alkali earth metal carbonate (e.g. GCC) and precipitated alkali earth metal carbonate (e.g. PCC)) may have from about 10 wt% or from about 25 wt% to about 55 wt% of particles smaller than about 0.5 pm. For example, from about 26 wt% to about 54 wt%, for example from about 27 wt% to about 53 wt%, for example from about 27 wt% to about 52 wt%, for example from about 28 wt% to about 51 wt%, for example from about 29 wt% to about 51 wt% of particles in the composition may be smaller than about 0.5 pm. For example, from about 30 wt% to about 50 wt%, for example from about 30 wt% to about 48 wt%, for example from about 30 wt% to about 46 wt%, for example from about 30 wt% to about 45 wt% of particles in the composition may be smaller than about 0.5 pm. For example, from about 35 wt% to about 50 wt%, for example from about 37 wt% to about 48 wt%, for example from about 39 wt% to about 46 wt%, for example from about 40 wt% to about 46 wt% of particles in the composition may be smaller than about 0.5 Mm.

The compositions may, for example, be used in coating compositions, which may be used to form coated paper products. The rate of water absorption of a paper sample coated with a coating composition comprising a composition comprising ground alkali earth metal carbonate (e.g. GCC) and precipitated alkali earth metal carbonate (e.g. PCC) as described herein may be greater than the rate of water absorption of a paper sample coated with a corresponding coating composition that does not comprise ground alkali earth metal carbonate and precipitated alkali earth metal carbonate as described herein. The "corresponding coating composition" may, for example, be identical to the coating composition comprising the ground alkali earth metal carbonate and precipitated alkali earth metal carbonate except that it does not comprise the ground alkali earth metal carbonate and/or precipitated alkali earth metal carbonate. For example, the coating composition may comprise exactly the same binder(s) and other component(s) other than the ground alkali earth metal carbonate and precipitated alkali earth metal carbonate.

The composition may, for example have an emtec intensity that is at least about 5% less than the emtec intensity of a corresponding composition. For example, the composition may have an emtec intensity that is at least about 6%, for example at least about 7%, for example at least about 8%, for example at least about 9%, for example at least about 10%, for example at least about 1 1 %, for example at least about 12% less after 5 seconds or after 10 seconds, than the emtec intensity of a corresponding composition.

The composition may, for example, have an emtec intensity equal to or less than about 50% after 5 seconds. For example, the composition may have an emtec intensity equal to or less than about 49%, for example equal to or less than about 48%, for example equal to or less than about 47%, for example equal to or less than about 46%, for example equal to or less than about 45% after 5 seconds. For example, the composition may have an emtec intensity equal to or less than about 44%, for example equal to or less than about 43%, for example equal to or less than about 42%, for example equal to or less than about 41 %, for example equal to or less than about 40% after 5 seconds. The composition may, for example, have an emtec intensity equal to or more than about 10%, for example equal to or more than about 20%, for example equal to or more than about 30% after 5 seconds. The composition may, for example, have an emtec intensity equal to or less than about 35% after 10 seconds. For example, the composition may have an emtec intensity equal to or less than about 34%, for example equal to or less than about 33%, for example equal to or less than about 32%, for example equal to or less than about 31%, for example equal to or less than about 30% after 10 seconds. For example, the composition may have an emtec intensity equal to or less than about 29%, for example equal to or less than about 28%, for example equal to or less than about 27%, for example equal to or less than about 26%, for example equal to or less than about 25% after 10 seconds. For example, the composition may have an emtec intensity equal to or less than about 24%, for example equal to or less than about 23%, for example equal to or less than about 22%, for example equal to or less than about 21 %, for example equal to or less than about 20% after 10 seconds.

The composition may, for example, have an emtec intensity equal to or more than about 2%, for example equal to or more than about 5%, for example equal to or more than about 10% after 10 seconds.

By "emtec intensity" of the composition, it is meant the intensity of sample coated with a composition comprising a ground alkali earth metal carbonate and precipitated alkali earth metal carbonate (e.g. GCC and PCC) (e.g. a composition of the first or second aspect of the present invention) as measured using an Emtec Penetration Dynamics Analyzer PDA.C 02. The frequency of is set to either 1 MHz for board samples or 2 MHz for paper samples and the measure mode is selected to be moderately absorbant. Emtec intensity is understood in the art to vary depending on the type of paper used. The test method is described in further detail below.

The composition may, for example, have a smearing index value of greater than about 8.5 after 15 seconds. For example, the composition may have a smearing index value equal to or greater than about 9.0 after 15 seconds. For example, the composition may have a smearing index value equal to or greater than about 9.5 after 15 seconds. By "smearing index value" it is meant the smearing index value of a sample coated with a composition comprising a GCC and PCC (e.g. a composition of the first or second aspect of the present invention) and a Styrene-Butadiene latex binder and optionally additional components such as a defoamer, Carboxymethyl Cellulose, Polyvinyl Alcohol and Optical Brightening Agents. Smearing index is a comparative evaluation and is understood in the art to vary depending on the type of paper used. Smearing index is measured by printing approximately 1 cm² blocks of HP 45 Black Pigment based inkjet ink on the coated paper sample and 15 seconds after the print has been made, a finger from a skilled operator covered with a nitrile glove is contacted with the black printed block and then pulled downwards applying a constant firm pressure. Any non-dry, non-immobilized ink is dragged onto the unprinted portion of the paper. The degree of ink transfer to the paper is assessed visually and given a ranking out of 10, where 10 indicated no transfer of ink, i.e. the print has dried. The test provides a reasonable comparison between different papers when printed using the same printer and the same ink.

Coating Compositions

There is also provided herein coating compositions comprising at least one binder, a particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and/or particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate). For example, the particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate) may be a composition according to the first or second aspects of the present invention and any embodiments (including all combinations) thereof. There is further provided herein the use of particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and/or particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate) (e.g. a composition as described herein) in a coating composition, for example a paper coating composition.

The coating composition may, for example, be used to increase the rate of drying of inkjet ink on the product which is coated with the coating composition. For example, the coating compositions may be used to increase the rate of water absorption of paper samples coated with said coating compositions. For example, the coating compositions may be used to decrease the emtec intensity of paper samples coated with said coating compositions. For example, the coating compositions may be used to increase the smearing index value of paper products coated with said coating compositions.

The coating composition may, for example, be an aqueous suspension/dispersion. The solids content of the coating composition may suitably be as high as possible whilst still giving a suitably fluid composition which may be used in coating a substrate. The solids content of the coating composition may, for example, range from about 10% to about 90% by weight of the composition. For example, the solids content of the coating composition may range from about 10% to about 80%, for example from about 10% to about 70%, for example from about 10% to about 60% by weight of the composition. After application of the aqueous coating composition to the substrate, the coating composition may be allowed to dry. Thus, the coating composition may be in the form of a dry residue comprising at least one binder, particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate).

The total combined weight of ground alkali earth metal carbonate and/or precipitated alkali earth metal carbonate (e.g. GCC and PCC) in the composition may, for example, be equal to or less than about 50 wt% based on the total weight of inorganic particulate material in the coating composition. For example, the total combined weight of ground alkali earth metal carbonate and/or precipitated alkali earth metal carbonate (e.g. GCC and PCC) in the composition may be equal to or less than about 45 wt%, for example equal to or less than about 40 wt%, for example equal to or less than about 35 wt%, for example equal to or less than about 30 wt%, for example equal to or less than about 25 wt% of the total weight of inorganic particulate material in the coating composition. For example, the total combined weight of ground alkali earth metal carbonate and precipitated alkali earth metal carbonate (e.g. GCC and PCC) in the composition may be equal to or less than about 20 wt% of the total weight of inorganic particulate material in the coating composition.

The at least one binder may be selected from binders which are known in the art. Examples of suitable binders include starch, latex, alcohol-based binders, proteinaceous adhesives, cellulose-based binders and combinations thereof. The binder(s) may also be combined with one or more other binders. Starch may suitably be derived from a natural starch, e. g., natural starch obtained from a known plant source, for example, wheat, maize, potato or tapioca. Where starch is employed as a binder ingredient, the starch may be employed in an unmodified and/or modified form. An example of a suitable unmodified starch is Pearl starch. Where starch is employed as a binder ingredient in a modified form, the starch may suitably be modified by one or more chemical treatments known in the art. The starch may, for example, be oxidized to convert some of its -CH₂OH groups to -COOH groups. In some cases the starch may have a small proportion of acetyl, -COCH₃, groups. Alternatively, the starch may be chemically treated to render it cationic or amphoteric, i.e., with both cationic and anionic charges. The starch may also be converted to a starch ether, or hydroxyalkylated starch by replacing some -OH groups with, for example, -CH₂CH₂OH groups, -OCH₂CH₃ groups or -OCH₂CH₂CH₂OH groups. A further class of chemically treated starches which may be used is that known as the starch phosphates. Alternatively, the raw starch may be hydrolyzed by means of a dilute acid or an enzyme to produce a gum of the dextrin type.

Alcohol-based binders may comprise a primary alcohol having the general formula RCH₂OH, a secondary alcohol having the general formula RR'CHOH, a tertiary alcohol having the general formula RR'R"COH, or a combination thereof. R, R' and R" represent alkyl groups having from one to twenty carbon atoms. For example R, R' and R" may represent alkyl groups having from one to ten carbon atoms. The alcohol- based binder may, for example, comprise primary, secondary and/or tertiary alcohol groups, which may be attached to a polymer backbone. Alcohol-based binders may, for example, be a polymer comprising a carboniferous backbone having hydroxyl functional groups appended therefrom. For example, the alcohol-based binder may be polyvinyl alcohol. Polyvinyl alcohol may be obtained by conventional methods known in the art, such as, for example by partial or complete hydrolysis of polyvinyl acetate to remove acetate groups. Thus, a person of skill in the art will understand that polyvinyl alcohol obtained by hydrolysis of polyvinyl acetate may contain pendant acetate groups as well as pendant hydroxy groups. Thus, in embodiments, the polyvinyl alcohol is derived from partially or fully hydrolysed polyvinyl acetate. The extent of hydrolysis may be such that at least about 50 mole % of the acetate groups are hydrolysed, for example, at least about 60 mole % of the acetate groups are hydrolysed, for example, at least about 70 mole % of the acetate groups are hydrolysed, for example, at least about 80 mole % of the acetate groups are hydrolysed, for example, at least about 85 mole % of the acetate groups are hydrolysed, for example, at least about 90 mole % of the acetate groups are hydrolysed, for example, at least about 95 mole % of the acetate groups are hydrolysed or, for example, at least about 99 mole % of the acetate groups are hydrolysed. The polymer may, for example, be a copolymer of polyvinyl alcohol and other monomers, such as, for example, acetate and acrylate.

The term "latex" is used herein to mean a dispersion/suspension (e.g. aqueous dispersion/suspension) of one or more polymer(s). The polymers may, for example, be natural or synthetic. Therefore, the term "latex binder" means any composition comprising, consisting essentially of or consisting of one or more polymers, which is capable of functioning as a binder in a coating composition, for example a barrier coating composition, which may be suitable for coating a paper product. The latex binder may, for example, be natural rubber latex obtained from, for example, rubber trees. The latex binder may, for example, be a synthetic latex. The latex binder may, for example, be a styrene polymer, for example copolymers including styrene monomers. For example, the latex binder may be a copolymer comprising, consisting essentially of or consisting of alkene monomers (e.g. ethylene, propylene, butylene, butadiene) and styrene monomers. For example, the latex binder may be styrene butadiene. The latex binder may, for example, be acrylic polymer latex, polyvinyl acetate latex, styrene acrylic copolymer latex, polyurethane, polyester, polyethyleneacrylate dispersions and combinations thereof. Examples of cellulose-based binders include carboxymethyl cellulose, methyl cellulose and cellulose esters such as cellulose acetate but rate, cellulose acetate proprioonate and cellulose acetate.

Examples of proteinaceous adhesives include, for example, casein or soy protein; polyvinyl alcohol.

The coating composition may comprise from about 7 wt% to about 25 w†% of one or more binders based on addition to the total solids content of the inorganic particulate material of the coating composition. For example, the coating composition may comprise from about 8 wt% to about 20 wt%, for example from about 8 wt% to about 15 wt% of one or more binders based on addition to the total solids content of the inorganic particulate material of the coating composition. For example, the coating composition may comprise from about 9 wt% to about 25 wt%, for example from about 9 wt% to about 20 wt%, for example from about 9 wt% to about 15 wt% of one or more binders based on addition to the total solids content of the inorganic particulate material of the coating composition. For example, the coating composition may comprise from about 10 wt% to about 25 wt%, for example from about 10 wt% to about 20 wt%, for example from about 10 wt% to about 15 wt%, for example from about 11 wt% to about 13 wt% of one or more binders based on addition to the total solids content of the inorganic particulate material of the coating composition.

The coating composition may, for example, further comprise another one or more inorganic particulate material. The other inorganic particulate material may, for example, be any one or more inorganic particulate materials which are known in the art, in particular any one or more inorganic particulate materials that are commonly used in paper coating compositions. For example, the inorganic particulate material present in the typical coating composition may be selected from one or more of alkaline earth metal carbonate (for example dolomite, i.e. CaMg(C0₃)₂), metal sulphate (for example gypsum), metal silicate, metal oxide (for example iron oxide, chromia, antimony trioxide or silica), metal hydroxide, wollastonite, bauxite, talc (for example, French chalk), mica, zinc oxide (for example, zinc white or Chinese white), titanium dioxide (for example, anatase or rutile), zinc sulphide, calcium carbonate (for example precipitated calcium carbonate (PCC), ground calcium carbonate (GCC) or surface- modified calcium carbonate), barium sulphate (for example, barite, blanc fixe or process white), alumina hydrate (for example, alumina trihydrate, light alumina hydrate, lake white or transparent white) and clay (for example kaolin, hydrous kaolin, calcined kaolin, China clay or bentonite).

The amount of other inorganic particulate material in the composition (e.g, other than the ground alkali earth metal carbonate and/or (ground) precipitated alkali earth metal carbonate) may range from about 0 wt% to about 90 wt%, for example from about 5 wt% to about 90 wt%, for example from about 10 wt% to about 90 wt% based on the total solids content of the inorganic particulate material in the coating composition. For example, the amount of other inorganic particulate material in the composition may range from about 10 wt% to about 80 wt%, for example from about 15 wt% to about 75 wt%, for example from about 20w t% to about 70 wt%, for example from about 25 wt% to about 65 wt%, for example from about 30 wt% to about 60 wt%, for example from about 3 wt% to about 55 wt%, for example from about 40 wt% to about 50 wt% based on the total solids content of the inorganic particulate material in the coating composition. The amount of other inorganic particulate material in the composition may be up to about 50 wt% kaolin.

The coating compositions may, for example, comprise one or more optional additional components, if desired. Such additional components, where present, may suitably be selected from known additives for coating compositions (e.g. paper coating compositions). Some of these optional additives may provide more than one function in the coating composition. Examples of known classes of optional additives are as follows:

(a) one or more cross linkers;

(b) one or more water retention aids;

(c) one or more viscosity modifiers or thickeners;

(d) one or more lubricity or calendering aids;

(e) one or more dispersants;

(f) one or more antifoamers or defoamers;

(g) one or more optical brightening agents (OBA) or fluorescent whitening agents (FWA);

(h) one or more dyes;

(i) one or more biocides or spoilage control agents;

(j) one or more levelling or evening aids;

(k) one or more grease or oil resistance agents;

(I) one or more surfactants;

(m) one more binders;

Any of the above additives and additive types may be used alone or in admixture with each other and with other additives, if desired. The pH of the coating composition may be controlled and/or modified. For example, the pH may be controlled and/or modified, e.g. increased by using hydroxide, for example sodium hydroxide.

For all of the above additives, the percentages by weight (based on the dry weight of inorganic particulate material (100 %) present in the composition) can vary as understood by those skilled in the art. Where the additive is present in a minimum amount, the minimum amount may be about 0.01 % by weight based on the dry weight of the inorganic particulate material. The maximum amount of any one or more of the above additives may, for example, be about 5.0 % by weight based on the dry weight of the inorganic particulate material. For example, the maximum amount may be about 3.0 % or 2.0 % by weight based on the dry weight of the inorganic particulate material.

The coating composition may, for example have an emtec intensity that is at least about 5 % less than the emtec intensity of a corresponding coating composition (e.g. a coating composition that it identical to the coating composition of the invention except that it does not comprise ground alkali earth metal carbonate and precipitated alkali earth metal carbonate (e.g. GCC and PCC)). For example, the coating composition may have an emtec intensity that is at least about 6 %, for example at least about 7 %, for example at least about 8 %, for example at least about 9 %, for example at least about 10 %, for example at least about 1 1 %, for example at least about 12 % less after 5 seconds or after 10 seconds, than the emtec intensity of a corresponding coating composition.

The coating composition may, for example, have an emtec intensity equal to or less than about 50 % after 5 seconds. For example, the coating composition may have an emtec intensity equal to or less than about 49 %, for example equal to or less than about 48 %, for example equal to or less than about 47 %, for example equal to or less than about 46 %, for example equal to or less than about 45 % after 5 seconds. For example, the coating composition may have an emtec intensity equal to or less than about 44 %, for example equal to or less than about 43 %, for example equal to or less than about 42 %, for example equal to or less than about 41 %, for example equal to or less than about 40 % after 5 seconds.

The coating composition may, for example, have an emtec intensity equal to or more than about 10 %, for example equal to or more than about 20 %, for example equal to or more than about 30 % after 5 seconds.

The coating composition may, for example, have an emtec intensity equal to or less than about 35 % after 10 seconds. For example, the coating composition may have an emtec intensity equal to or less than about 34 %, for example equal to or less than about 33 %, for example equal to or less than about 32 %, for example equal to or less than about 31 %, for example equal to or less than about 30 % after 10 seconds. For example, the coating composition may have an emtec intensity equal to or less than about 29 %, for example equal to or less than about 28 %, for example equal to or less than about 27 %, for example equal to or less than about 26 %, for example equal to or less than about 25 % after 10 seconds. For example, the coating composition may have an emtec intensity equal to or less than about 24 %, for example equal to or less than about 23 %, for example equal to or less than about 22 %, for example equal to or less than about 21 %, for example equal to or less than about 20 % after 10 seconds.

The coating composition may, for example, have an emtec intensity equal to or more than about 2 %, for example equal to or more than about 5 %, for example equal to or more than about 10 % after 10 seconds.

The coating composition may, for example, have a smearing index value of greater than about 8.5 after 15 seconds. For example, the coating composition may have a smearing index value equal to or greater than about 9.0 after 15 seconds. For example, the coating composition may have a smearing index value equal to or greater than about 9.5 after 15 seconds.

Paper Products There is provided herein paper products coated with a coating composition comprising at least one binder, particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and/or particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate). The particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and/or particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate) may, for example, be a composition in accordance with the first or second aspects of the present invention, including all embodiments (in all combinations) thereof. The coating composition comprising at least one binder, particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate) may be a coating composition in accordance with the third aspect of the present invention, including all embodiments (in all combinations) thereof.

The term paper, as used in connection with the present invention, should be understood to mean all forms of paper, including board, such as, for example, white- lined board and linerboard, cardboard, paperboard, coated board, and the like. There are numerous types of paper, coated or uncoated, which may be coated using the compositions disclosed herein, including paper suitable for food packaging, perishable goods other than food, e.g., pharmaceutical products and compositions, books, magazines, newspapers and the like, and office papers. The paper may be calendered or super calendared as appropriate; for example super calendered magazine paper for rotogravure and offset printing may be made according to the present methods. Paper suitable for light weight coating (LWC), medium weight coating (MWC) or machine finished pigmentisation (MFP) may also be coated using the present compositions.

The paper may, for example, have first and second surfaces. The coating compositions described herein may, for example, be present on the first surface, the second surface or both. For example, the coating compositions may be present on the surface which faces the exterior of the paper product when it is formed into a three-dimensional product. The first and/or second surfaces may or may not have other intermediary coatings or layers between each surface and the coating composition described herein. The coating compositions may, for example, be applied directly to the paper substrate.

The paper product may, for example, have a coat weight ranging from about 5 gsm (g per m²) to about 20 gsm. For example, the paper product may have a coat weight ranging from about 5 gsm to about 15 gsm, for example from about 5 gsm to about 10 gsm. For example, the paper product may have a coat weight ranging from about 5 gsm to about 8 gsm.

The paper product may, for example have an emtec intensity that is at least about 5% less than the emtec intensity of a corresponding paper product (e.g. an identical paper coated with an identical coating composition except that it does not comprise ground alkali earth metal carbonate and precipitated alkali earth metal carbonate (e.g. GCC and PCC)). For example, the paper product may have an emtec intensity that is at least about 6%, for example at least about 7%, for example at least about 8%, for example at least about 9%, for example at least about 10%, for example at least about 1 1 %, for example at least about 12% less after 5 seconds or after 10 seconds, than the emtec intensity of a corresponding paper product.

The paper product may, for example, have an emtec intensity equal to or less than about 50% after 5 seconds. For example, the paper product may have an emtec intensity equal to or less than about 49%, for example equal to or less than about 48%, for example equal to or less than about 47%, for example equal to or less than about 46%, for example equal to or less than about 45% after 5 seconds. For example, the paper product may have an emtec intensity equal to or less than about 44%, for example equal to or less than about 43%, for example equal to or less than about 42%, for example equal to or less than about 41 %, for example equal to or less than about 40% after 5 seconds.

The paper product may, for example, have an emtec intensity equal to or more than about 10%, for example equal to or more than about 20%, for example equal to or more than about 30% after 5 seconds.

The paper product may, for example, have an emtec intensity equal to or less than about 35% after 10 seconds. For example, the paper product may have an emtec intensity equal to or less than about 34%, for example equal to or less than about 33%, for example equal to or less than about 32%, for example equal to or less than about 31 %, for example equal to or less than about 30% after 10 seconds. For example, the paper product may have an emtec intensity equal to or less than about 29%, for example equal to or less than about 28%, for example equal to or less than about 27%, for example equal to or less than about 26%, for example equal to or less than about 25% after 10 seconds. For example, the paper product may have an emtec intensity equal to or less than about 24%, for example equal to or less than about 23%, for example equal to or less than about 22%, for example equal to or less than about 21 %, for example equal to or less than about 20% after 10 seconds.

The paper product may, for example, have an emtec intensity equal to or more than about 2%, for example equal to or more than about 5%, for example equal to or more than about 10% after 10 seconds.

The paper product may, for example, have a smearing index value of greater than about 8.5 after 15 seconds. For example, the paper product may have a smearing index value equal to or greater than about 9.0 after 15 seconds. For example, the paper product may have a smearing index value equal to or greater than about 9.5 after 15 seconds. Methods of Making Compositions Comprising Ground Alkali Earth Metal Carbonate and Precipitated Alkali Earth Metal Carbonate

There is provided herein a method for making a composition comprising particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate) comprising combining particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate). The method may be for making any of the compositions disclosed herein. This includes the compositions of the first and second aspects of the present invention and all embodiments thereof, including any combination of these embodiments in all possible variations.

The compositions comprising particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and/or particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate) may, for example, be aqueous suspensions or dry mineral blends. The compositions may, for example, be prepared by any method known to those skilled in the art. For example, the particulate ground alkali earth metal carbonate and particulate precipitated alkali earth metal carbonate may be blended or mixed together.

One or both of the particulate ground alkali earth metal carbonate and particulate precipitated alkali earth metal carbonate may, for example, be provided in the form of an aqueous suspension. The aqueous suspensions may, for example, be blended together to form the final composition.

Each of the alkali earth metal carbonate components may, for example, be added to a stirred media mill with water and any additional optional additives such as dispersants, thickeners, biocides and anti-settling agents. The content may be stirred at high speed for a predetermined length of time to provide a particular particle size distribution. The resultant mineral suspension may be separated from the media using screens.

Methods of Making Coating Compositions

There is provided herein a method for making a coating composition comprising combining (e.g. mixing) at least one binder with particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and/or particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate). For example, the method may comprise combining at least one binder with a composition described herein. This includes the compositions of the first and second aspects of the present invention and all embodiments thereof, including any combination of these embodiments in all possible variations.

The method may comprise, for example, combining (e.g. mixing) the at least one binder, particulate ground alkali earth metal carbonate, particulate precipitated alkali earth metal carbonate and any other optional additives in appropriate amounts into an aqueous liquid to prepare a suspension of said components. The coating compositions may suitably be prepared by conventional mixing techniques, as will be known in the art. The particulate alkali earth metal carbonate components may, for example, be aqueous slurries. The aqueous slurry may, for example, be prepared using a suitable mixer (e.g. at high shear), following which the slurry may be blended with a solution of the binder. The resulting mixture may be screened prior to coating.

Methods of Making Paper Products There is provided herein a method of making a paper product comprising coating a paper product with a coating composition comprising at least one binder, particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate) and/or particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate). The coating composition may be as described herein. This includes the coating compositions of the third aspect of the present invention and all embodiments thereof, including any combination of these embodiments in all possible variations.

The coating process may be carried out using standard techniques which are known to the skilled person. The coating process may also involve calendering or super- calendering the coated substrate.

Methods of coating paper and other sheet materials, and apparatus for performing the methods, are widely published and well known. Such known methods and apparatus may conveniently be used for preparing coated paper. For example, there is a review of such methods published in Pulp and Paper International, May 1994, page 18 et seq. Sheets may be coated on the sheet forming machine, i.e., "on-machine," or "off- machine" on a coater or coating machine. Use of high solids compositions is desirable in the coating method because it leaves less water to evaporate subsequently. However, as is well known in the art, the solids level should not be so high that high viscosity and levelling problems are introduced. The methods of coating may be performed using an apparatus comprising (i) an application for applying the coating composition to the material to be coated and (ii) a metering device for ensuring that a correct level of coating composition is applied. When an excess of coating composition is applied to the applicator, the metering device is downstream of it. Alternatively, the correct amount of coating composition may be applied to the applicator by the metering device, e.g., as a film press. At the points of coating application and metering, the paper web support ranges from a backing roll, e.g. via one or two applicators, to nothing (i.e. just tension). The time the coating is in contact with the paper before the excess is finally removed is the dwell time - and this may be short, long or variable. The coating may added by a coating head at a coating station. According to the quality desired, paper grades are uncoated, single-coated, double-coated and even triple- coated. When providing more than one coat, the initial coat (precoat) may have a cheaper formulation and optionally coarser pigment in the coating composition. A coater that is applying coating on each side of the paper will have two or four coating heads, depending on the number of coating layers applied on each side. Most coating heads coat only one side at a time, but some roll coaters (e.g., film presses, gate rolls, and size presses) coat both sides in one pass.

Examples of known coaters which may be employed include, without limitation, air knife coaters, blade coaters, rod coaters, bar coaters, multi-head coaters, roll coaters, roll or blade coaters, cast coaters, laboratory coaters, gravure coaters, kisscoaters, liquid application systems, reverse roll coaters, curtain coaters, spray coaters and extrusion coaters.

Water may be added to the solids comprising the coating composition to give a concentration of solids which is preferably such that, when the composition is coated onto a sheet to a desired target coating weight, the composition has a rheology which is suitable to enable the composition to be coated with a pressure (i.e., a blade pressure) of between 1 and 1.5 bar. The paper may be formable or formed into a three-dimensional product, which may be suitable as food grade or pharmaceutical grade packaging. Methods of Printing

There is provided herein a method of printing a paper substrate coated with a composition comprising at least one binder, particulate ground calcium carbonate and particulate precipitated calcium carbonate (e.g. a paper product as described herein).

The method may, for example, comprise inkjet printing. The method may, for example, comprise laser printing (printing using a laser marking system). The method may, for example, comprise offset printing and/or flexographic printing. For example, the method may comprise inkjet printing and one or more of offset printing and flexographic printing. For example, the method may comprise laser printing and one or more of offset printing and flexographic printing. Offset printing is a widely used printing technique, as will be well understood by a person of ordinary skill in the art. Flexographic printing is a widely used printing technique, as will be well understood by a person of ordinary skill in the art. Rotogravure printing is a widely used printing technique, as will be well understood by a person of ordinary skill in the art.

The foregoing broadly describes certain embodiments of the present invention without limitation. Variations and modifications as will be readily apparent to those skilled in the art are intended to be within the scope of the present invention as defined in and by the appended claims.

EXAMPLES Example 1

Compositions comprising the following inorganic particulate materials were prepared.

• Calcium Carbonate A - a ground calcium carbonate slurry containing 75 wt% solids, 0.1 wt% of particles larger than 10 pm, 99 wt% of particles smaller than

2 μηι, 89 wt% of particles smaller than 1 μηι and an ISO brightness of 94.

• Calcium Carbonate B - a ground calcium carbonate slurry containing 70 wt% solids, about 0.5 wt% of particles larger than 10 pm, about 89 wt% of particles smaller than 2 μη-ι, about 52 wt% of particles smaller than 1 μιη and an ISO brightness of 82. • Calcium Carbonate C - a precipitated calcium carbonate slurry containing 72.5 wt% solids, 0.2 wt% of particles larger than 10 pm, 95 wt% of particles smaller than 2 μιη, 90 wt% of particles smaller than about 1 pm and an ISO brightness of 96.5.

• Kaolin A - a kaolin containing 64 wt% solids, 92 wt% of particles smaller than 2 pm, less than 0.1 wt% of particles larger than 10 pm, 68 wt% to 73 wt% of particles smaller than 1 pm and an ISO brightness of 88.5.

The following compositions were prepared.

> Composition A - 75 wt% Calcium Carbonate C, 25 wt% Calcium Carbonate B; Composition B - 40 wt% Calcium Carbonate C, 60 wt% Calcium Carbonate B; and

> Control Composition - 80 wt% Calcium Carbonate A, 20 wt% Kaolin A. These compositions were incorporated into coating compositions comprising 100 wt% of one or more of composition A, composition B and control composition, 14 wt% styrene-butadiene latex binder and 0.004 wt% defoamer, 0.2 wt% Carboxymethyl Cellulose, 0.1 wt% Polyvinyl Alcohol, 0.25 wt% Optical Brightening Agent and 0.1 wt% Sodium Hydroxide.

The coating compositions were used to coat uncoated linerboard paper.

Table 1.

The gloss of the unprinted samples was measured by the method described in TAPPI T480 at 75°. The results are shown in Figure 1. It was found that there was no real change in gloss when Composition A was used and only a slight decrease in gloss when Composition B was used.

The PPS (Parker Print Surf) roughness of the samples was measured using the method described in ISO 8791-4: 2007 and TAPPI T555 om-94. The results are shown in Figure 2. It was found that there was no real difference between the different coatings.

The D65 brightness (UV) of the samples was measured using the method described in ISO 11475;2004. The results are shown in Figure 3. It was found that, for the same coat weight, Composition A provided good brightness and Composition B provided only slightly decreased brightness.

The Gurley air flow porosity of the samples was measured using the method described in ISO 5636-5; 2014, TAPPI 460 om-11. The results are shown in Figure 4. It was found that, for the same coat weight, Compositions A and B did not have a great impact on air flow. The emtec water absorption (and emtec intensity) of the samples was measured by cutting samples to width of tape and long enough to cover the 35mm test area. The machine mode was set to "moderately absorbant". And each sample was run 4 to 6 times for 1 minute each. The results are shown in Figures 5 and 6. It was found that the use of both Compositions A and B increases the rate of water absorption.

The samples were printed by inkjet printing, flexo or offset printing.

The smearing index of the samples printed by inkjet printing was measured by the method described above. The samples were visually inspected and compared to reference smears. The results are shown in Figure 7. It was found that the use of both Compositions A and B result in improved drying as shown by a higher smearing index value. The inkjet print density of QR code solid area was measured using the method described in ISO 5-3 Status E. The results are shown in Figure 8. It was found that Composition A does not decrease the print density. Composition B decreases the print density only slightly. The contrast between black inkjet-printed QR code and the substrate was measured by scanning the QR code on an EpsonPerfection V500 photo and analysing the peaks of black to white on a histogram of the scan. The distance between the black peak and the white peak is the contrast where pure black is 0 and pure white is 255. The results are shown in Figure 9.

The flexo print gloss of the samples was measured using the method described in TAPPI T480 at 75°. The results are shown in Figure 10. It was found that the use of Composition A provides very good gloss properties and the use of Composition B results in only a slight decrease in gloss.

The flexo print density of the samples was measured using the method described in ISO 5-3 Status E. The results are shown in Figure 1 1. It was found that the use of Composition A provides very good print density properties and the use of Composition B results in only a slight decrease in print density. The offset print gloss of the samples was measured using the method described in TAPPI T480 at 75°. The results are shown in Figure 12. It was found that the use of Composition A provides very good gloss properties and the use of Composition B results in only a slight decrease in gloss.

The offset print density of the samples was measured using the method described in ISO 5-3 Status E. The results are shown in Figure 13. It was found that the use of Composition A provides very good print density properties and the use of Composition B results in only a slight decrease in print density.

The offset pick strength of the samples was measured using the IGT pick test. The results are shown in Figure 14. It was found that the use of Compositions A and B did not greatly decrease the pick strength. The foregoing broadly describes certain embodiments of the present invention without limitation. Variations and modifications as will be readily apparent to those skilled in the art are intended to be within the scope of the present invention as defined in and by the appended claims.

Claims

1. A composition comprising: particulate ground alkali earth metal carbonate having a particle size distribution (psd) steepness factor ranging from about 30 to about 55; and/or particulate precipitated alkali earth metal carbonate having a particle size distribution (psd) steepness factor ranging from about 35 to about 70; wherein the composition is adapted to be used as an additive in a coating composition.

2. The composition of claim 1 , wherein the particulate ground alkali earth metal carbonate is particulate ground calcium carbonate (GCC).

3. The composition of claim 1 or claim 2, wherein the particulate precipitated alkali earth metal carbonate is particulate precipitated calcium carbonate (PCC).

4. The composition of any one of claims 1 to 3, wherein the ground alkali earth metal carbonate has a particle size distribution (psd) steepness factor ranging from about 45 to about 55, for example greater than about 45 to about 55, for example from about 48 to about 52.

5. The composition of any one of claims 1 to 4, wherein the precipitated alkali earth metal carbonate has a particle size distribution (psd) steepness factor ranging from about 55 to about 70, for example from greater than about 55 to about 65, for example from about 58 to about 64.

6. The composition of any one of claims 1 to 5, wherein the ground alkali earth metal carbonate and precipitated alkali earth metal carbonate are present in the composition in a weight ratio ranging from about 100:0 to about 0: 100 precipitated alkali earth metal carbonate:ground alkali earth metal carbonate, for example from about 90: 10 to about 30:70 precipitated alkali earth metal carbonate:ground alkali earth metal carbonate, for example from about 80:20 to about 40:60 precipitated alkali earth metal carbonate:ground alkali earth metal carbonate, for example from about 75:25 to about 50:50 precipitated alkali earth metal carbonate:ground alkali earth metal carbonate.

7. The composition of any one of claims 1 to 6, wherein the ground alkali earth metal carbonate has a d₅₀ ranging from about 0.7 pm to about 1.2 μηι, for example from about about 0.8 pm to about 1.0 pm.

8. The composition of any one of claims 1 to 7, wherein the precipitated alkali earth metal carbonate has a d₅₀ ranging from about 0.2 pm to about 1.2 pm or to about 0.6 pm, for example from about 0.3 pm to about 0.5 pm.

9. The composition of any one of claims 1 to 8, wherein from about 84 wt % to about 95 wt% of ground alkali earth metal carbonate particles are smaller than about 2 pm, for example from about 85 wt % to about 94 wt% of ground alkali earth metal carbonate particles are smaller than about 2 pm, for example from about 87 wt% to about 91 wt% of ground alkali earth metal carbonate particles are smaller than about 2 pm.

10. The composition of any one of claims 1 to 9, wherein from about 70 wt% or from about 90 wt % to about 99 wt% of precipitated alkali earth metal carbonate particles are smaller than about 2 pm, for example from about 92 wt% to about 98 wt% of precipitated alkali earth metal carbonate particles are smaller than about 2 pm, for example from about 94 wt% to about 98 wt% of precipitated alkali earth metal carbonate particles are smaller than about 2 pm, for example from about 70 wt% to about 76 wt% of precipitated alkali earth metal carbonate particles are smaller than about 2 pm.

1 1. The composition of any one of claims 1 to 10, wherein from about 45 wt% to about 60 wt% of ground alkali earth metal carbonate particles are smaller than about 1 pm, for example from about 47 wt% to about 57 wt% of ground alkali earth metal carbonate particles are smaller than about 1 pm, for example from about 50 wt% to about 55 wt% of ground alkali earth metal carbonate particles are smaller than about 1 pm.

12. The composition of any one of claims 1 to 1 1 , wherein from about 40 wt% or from about 85 wt% to about 95 wt% of precipitated alkali earth metal carbonate particles are smaller than about 1 pm, for example from about 88 wt% to about 93 wt% of precipitated alkali earth metal carbonate particles are smaller than about 1 μπΊ, for example from about 89 wt% to about 92 wt% of precipitated alkali earth metal carbonate particles are smaller than about 1 μηι, for example from about 40 wt% to about 46 wt% of precipitated alkali earth metal carbonate particles are smaller than about 1 μηι.

13. The composition of any one of claims 1 to 12, wherein from about 14 wt % to about 25 wt% of ground alkali earth metal carbonate particles are smaller than about 0.5 μηι, for example from about 16 wt% to about 23 wt% of ground alkali earth metal carbonate particles are smaller than about 0.5 μηι, for example from about 17 wt% to about 21 wt% of ground alkali earth metal carbonate particles are smaller than about 0.5 μιη.

14. The composition of any one of claims 1 to 13, wherein from about 10 wt% or from about 45 wt% to about 60 wt% of precipitated alkali earth metal carbonate particles are smaller than about 0.5 μηι, for example from about 48 wt% to about 58 wt% of precipitated alkali earth metal carbonate particles are smaller than about 0.5 μηι, for example from about 50 wt% to about 56 wt% of precipitated alkali earth metal carbonate particles are smaller than about 0.5 pm, for example from about 10 wt% to about 15 wt% of precipitated alkali earth metal carbonate particles are smaller than about 0.5 μηι.

15. The composition of any one of claims 1 to 14, wherein the composition has a smearing index value of greater than about 8.5 after 15 seconds, for example a smearing index value equal to or greater than about 9 after 15 seconds.

16. A coating composition comprising at least one binder and a composition of any one of claims 1 to 15.

17. The coating composition of claim 16, wherein the total combined weight % of ground alkali earth metal carbonate and/or precipitated alkali earth metal carbonate in the coating composition is equal to or less than about 50 wt%, for example equal to or less than about 40 wt%, for example equal to or less than about 20 wt% based on the total weight of inorganic particulate material in the coating composition.

18. The coating composition of claim 16 or 17, wherein the coating composition further comprises another inorganic particulate material.

19. The coating composition of claim 18, wherein the coating composition further comprises from about 0 wt% to about 90 wt%, for example from about 20 wt% to about 70 wt%, for example from about 40 wt% to about 50 wt% of the other inorganic particulate material based on the total solids content of the inorganic particulate material of the coating composition.

20. The coating composition of any one of claims 16 to 19, wherein the binder is present in the coating composition in an amount ranging from about 7 wt% to about 25 wt%, for example from about 9 wt% to about 15 wt%, for example from about 1 1 wt% to about 13 wt% based on addition to the total solids of the inorganic particulate material of the coating composition.

21. The coating composition of any one of claims 16 to 20, wherein the coating composition has a smearing index value of greater than about 8.5 after 15 seconds, for example a smearing index value equal to or greater than about 9 after 15 seconds.

22. A paper product coated with a coating composition of any one of claims 16 to 21.

23. The paper product of claim 22, wherein the paper product is board.

24. The paper product of claim 22 or 23, wherein the paper product has a coat weight ranging from about 5 gsm to about 20 gsm, for example from about 5 gsm to about 10 gsm, for example from about 5 gsm to about 8 gsm.

25. The paper product of any one of claims 22 to 24, wherein the paper product has a smearing index value of greater than about 8.5 after 15 seconds, for example a smearing index value equal to or greater than about 9 after 15 seconds.

26. Use of a composition of any one of claims 1 to 15 in a paper coating composition.

27. The use of claim 26 to increase the rate of drying of an inkjet ink on a paper product.

28. The use of claim 26 or 27, wherein the paper product is a paper product of any one of claims 22 to 25.

29. The use of any one of claims 26 to 28 to increase the rate of water absorption of the paper product.

30. The use of any one of claims 26 to 29 to increase the smearing index value of the paper product.

31. A method of making a composition of any one of claims 1 to 15 comprising combining a particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate (GCC)) and a particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate (PCC)).

32. A method of making a coating composition of any one of claims 16 to 21 comprising combining a particulate ground alkali earth metal carbonate (e.g. ground calcium carbonate (GCC)) and/or a particulate precipitated alkali earth metal carbonate (e.g. precipitated calcium carbonate (PCC)) and a binder.

33. A method of making a paper product of any one of claims 22 to 25 comprising coating a paper product with a coating composition of any one of claims 16 to 21.

34. A method of printing on a paper product of any one of claims 22 to 25.

35. The method of claim 34, wherein the printing comprising inkjet printing or laser printing.

36. The method of claim 35, wherein the printing comprises offset printing.

37. The method of claim 35 or 36, wherein the printing comprises flexographic printing.