AU2015252038B2 - Coating composition comprising submicron calcium carbonate-comprising particles, process to prepare same and use of submicron calcium carbonate- comprising particles in coating compositions - Google Patents

Abstract

COATING COMPOSITION COMPRISING SUBMICRON CALCIUM CARBONATE-COMPRISING PARTICLES, PROCESS TO PREPARE SAME AND USE OF SUBMICRON CALCIUM CARBONATE-COMPRISING PARTICLES IN COATING COMPOSITIONS A coating composition comprising an aqueous dispersion of submicron natural ground calcium carbonate particles contained in a liquid binder, wherein the resultant coating may constitute either a clear coat or a glossing and opacifying coating, depending upon the presence of certain additives such as a mineral pigment (e.g., TiO 2). The composition is characterised in that comprises, in the case of a clear coating, at least one ground natural calcium carbonate having a median diameter of between 0.05 and 0.15 p m, while in the case of a glossing and opacifying coating, at least one ground natural calcium carbonate having a median diameter of between 0.05 and 0.3 pm and at least one pigment having a refractive index of greater than or equal to 2.5.

Description

COATING COMPOSITION COMPRISING SUBMICRON CALCIUM CARBONATECOMPRISING PARTICLES, PROCESS TO PREPARE SAME AND USE OF SUBMICRON CALCIUM CARBONATE-COMPRISING PARTICLES IN COATING

COMPOSITIONS

Technical Field

The present invention relates to coating compositions comprising submicron natural ground calcium carbonate-comprising particles (hereafter SMGCC). The invention further relates to a process for preparing coating compositions containing SMGCC, and to the use of SMGCC in coating compositions. The coating composition(s), depending upon their composition, may be used to form either clear coatings, or else they may be formulated as glossing and opacifying coating compositions. The entire contents of provisional patent application no. 61/400,648 filed July 30, 2010 and entitled “Coating Composition Comprising Submicron Calcium Carbonate Comprising Particles, Process to Prepare Same and Use of Submicron Calcium Carbonate-Containing Particles in Coating Compositions” are specifically incorporated herein by reference.

Brief Description of the Drawings

Figures 1A and IB are photomicrographs of Omya XC-6600-34 CaCCf; and

Figure 2 is a series of particle size distribution curves containing data for a series of samples whose D98 value is < 0.3 pm. The values for D90, D5o and D20 for these samples can be determined by comparing the x and y-axis.

Summary of the Invention

The first aspect of the present invention provides a glossing and opacifying coating composition comprising an aqueous ground calcium carbonate dispersion, wherein the ground calcium carbonate is substantially dispersed and has a mean particle size D50 (Mai) of less than 1 micron; wherein the ground calcium carbonate is dispersed in at least one binder including vinyl-acrylic, styrene-acrylic, acrylic dispersions, solution acrylics, alkyds, polymers containing ester groups including polyesters, polyester-based polyureas and polyester-based polyamides, and; wherein the glossing and opacifying coating composition has a pigment volume concentration (PVC) of from 5 % up to the critical pigment volume concentration (CPVC) and at least one pigment having a refractive index of greater than or equal to 2.5.

The second aspect of the present invention provides a method of forming a glossing and opacifying composition wherein: a) at least one ground calcium carbonate having a D50 (Mai) of between 0.05 and 0.3 pm is provided, b) at least one pigment having a refractive index of greater than or equal 2.5 is provided, c) at least one binder is provided, and d) the ground calcium carbonate of step a) is mixed with the pigment of step b) and the binder of step c).

The third aspect of the present invention provides use of a glossing and opacifying composition according to the first aspect of the invention for coating substrates.

The fourth aspect of the present invention provides a coated substrate coated with a glossing and opacifying composition according to the first aspect of the invention.

Background and Detailed Description

The aqueous nanoparticle dispersion of this invention can be used to make coatings and films for porous and non-porous substrates, such as papers, non-woven materials, textiles, leather, wood, concrete, masonry, metals, house wrap and other building materials, fibreglass, polymeric articles, personal protective equipment (such as hazardous material protective apparel, including face masks, medical drapes and gowns and firemen’s turnout gear) and the like. Applications include papers and non-woven materials, fibrous materials, films, sheets, composites and other articles, inks and decorative and industrial coatings, flock and other adhesives and personal care products such as skin care, hair care and nail care products, livestock and seed applications, and the like.

Any fibrous material can be coated, impregnated or otherwise treated with the compositions according to the invention by methods well known to those skilled in the art, including carpets as well as textiles used in clothing, upholstery, tents, awnings, airbags and the like. Suitable textiles include fabrics, yams and blends, whether woven, non-woven or knitted and whether natural, synthetic or regenerated. Examples of suitable textiles include cellulose acetate, acrylics, wool, cotton, jute, linen, polyesters, polyamides, regenerated cellulose (i.e., rayon) and the like.

The compositions, depending upon their intended application, may be dispersed in a variety of binders including, but not limited to, vinyl-acrylic, styrene-acrylic, acrylic dispersions, solution acrylics, alkyds (e.g., SOYA, TOFA, sunflower, etc.), polyurethanes dispersed in either water or solvent, etc., hereinafter referred to as “binder media”.

Additionally, the compositions according to the invention can be used as adhesives or to augment or supplement adhesive types well known to those skilled in the art. Thus, in the application discussed above wherein the compositions are used as adhesives or to augment or supplement various known adhesive types, particularly desirable properties can be obtained by varying the type and amount of the aqueous nanoparticles used, along with choosing a complementary binder medium from one or more of those listed above, or by incorporating other binder media that would be well known to those of ordinary skill in this art.

As noted above, coatings containing the compositions according to the invention may optionally be formulated as substantially transparent coatings, i.e., typically referred to as ‘clear coats’, or alternately as coatings that serve a glossing and opacifying function. The clear coating composites produced when the aqueous dispersions are applied and dried, exhibit excellent gloss and clarity. Moreover, so long as the D98 particle size of the substantially dispersed nanoparticles contained in the coating composition is < 350 nm, preferably < 300 nm and the D50 is < 200 nm, preferably < 150 nm, the coatings obtained will be essentially transparent, provided of course that they are free or essentially free of additional components which would comprise their transparency properties.

For purposes of exemplifying and not limiting, the invention, one useful binder medium for forming, e.g., clear coatings according to the invention are polymers containing ester groups such as, for example, polyesters, polyester-based polyurethanes, polyester-based polyureas and polyester-based polyamides. These various binders, however, have less than desirable water-resistance properties due to the hydrolysis group contained therein.

It has been determined, furthermore, that the water resistant properties of such polyester-based polyurethanes can be remarkably enhanced, without affecting the transparency properties of these materials to any significant degree, by combining with the polymer binder a substantially dispersed nano-particle proton scavenger, such as natural ground calcium carbonate-comprising particles. The resultant coating composition, therefore, which again is described only for exemplifying (and not limiting) the invention, thus constitutes a hydrolytically stable polyurethane nanocomposite comprising a solid polyester-polyurethane polymer binder containing proton-scavenger nanoparticles in a substantially dispersed form. One particular useful example of such a formulation would constitute a colloidally stable aqueous dispersion comprising water, a polyester-polyurethane polymer binder and substantially dispersed proton scavenger nanoparticles such as SMGCC.

In the meaning of the present invention the term “substantially dispersed” means that the nanoparticles are properly dispersed in the aqueous medium in order to prevent settling or syneresis of the nanoparticles. This is usually achieved via the addition of well-known dispersants comprising homo- or copolymer chains. If necessary, the chains may be partially or completely neutralized by cations such as sodium, lithium, magnesium, calcium, potassium or ammonium.

Coatings having the composition of the exemplary formulation described above, therefore, constitute polyurethane compositions which, e.g., have improved hydrolytic stability over prior art polyurethane compositions. As used herein the term polyurethane is used generically to describe polymers including oligomers (e.g., prepolymers) which contain the urethane group, i.e., -0-C(=0)-NH- regardless of how they are made. As is well known, these polyurethanes can contain additional groups such as urea, allophanate, biuret, carbodiimide, oxazolidinyl, isocynurate, uretdione, alcohol, amine, hydrazide, siloxane, silane, ketone, olefin, etc., in addition to the urethane groups.

This invention includes, as noted herein the use of substantially dispersed nanoparticles (referring to the primary crystallites or particles of the proton scavenger and or the aggregates of the proton scavenger) of proton scavenger nanoparticles to enhance the water-resistant (hydrolytic stability) of thermoplastic polyurethanes containing polyester segments within the polyurethane polymer or prepolymer. Thermoplastic polyurethanes are made with the same components as waterborne polyester polyurethanes (polyurethane dispersions in water) immediately below but typically the thermoplastic polyurethanes have substantially less or no water-dispersibility enhancing compound(s). In one embodiment the hydrolytically stable polyurethane is a thermoplastic polyurethane. The technology for making and using thermoplastic polyurethanes are well known and described for example in US 6,777,466 B2 and J. K. Backus et al., "Polyurethanes," in: Encyclopedia of Polymer Science and Engineering. Vol. 13, H F. Mark et al., Ed, pp. 243-303 (1988), the entire disclosure of which is incorporated herein by reference.

Furthermore, the invention in one embodiment relates to polyester polyurethanes which are derived from aqueous dispersions and which, when dried and cured, produce solid polyester segment containing polyurethane products which are tough and, depending on the other ingredients present (e.g., absence of T1O2 or other pigment), can be a transparent.

Further in accordance with this invention, it has been found that the susceptibility of polyester polyurethanes to degrade through hydrolysis can be essentially completely eliminated by incorporating into the polymer a substantially dispersed nanoparticle (referring to the aggregate and/or the ultimate particles/crystallite) proton scavenger.

Certain materials are known to react with, bind to, or otherwise capture protons, i.e., hydrogen ions, when exposed thereto in solid, liquid and/or gaseous media. Calcium carbonate, is a good example as are the other alkali and earth-alkali metal carbonates, i.e., L12CO3, BeC03, MgC03, SrCC>3, BaCC>3, and RaC03. Other examples of carbonates which will scavenge protons include carbonates of Fe(H), Fe(III), Μη(Π), Zn, Ag, Hg(I), Hg(II), Cu(II), Pb(II), Bi(III).

Calcium carbonate has the formula CaC03. It is a common substance found in rock in all parts of the world, and is the main component of shells of marine organisms, snails, pearls, and eggshells. Calcium carbonate is found naturally as the following minerals and rocks: aragonite, calcite, vaterite or (p-CaC03), chalk, limestone, marble, travertine. The vast majority of calcium carbonate used in industry is extracted by mining or quarrying. Pure calcium carbonate (e.g., for food or pharmaceutical use), can be produced from a pure quarried source (usually marble). Ground calcium carbonate (GCC) is produced through mechanical grinding of naturally occurring calcium carbonate rocks: marble, limestone and chalk. GCC in pigment formulations provides good rheology and high brightness at low cost. Alternatively, crude calcium carbonate is calcinated into calcium oxide (quicklime). Water is added to give calcium hydroxide, and carbon dioxide is passed through this solution to precipitate the desired calcium carbonate, known as precipitated calcium carbonate (PCC). This process produces very pure calcium carbonate crystals. The crystals can be tailored to a variety of different shapes and sizes, depending on the specific reaction process used. The three main shapes of PCC crystals are aragonite, rhombohedral, and scalenohedral. Within each crystal type, the PCC process can control mean particle size, size distribution, and surface area. Precipitated calcium carbonate is used as a mineral pigment throughout the world for paper production. It is valued for its high brightness and light scattering characteristics in paper filling and coating applications.

Other examples of inorganic compounds which will scavenge protons include silicates of Ba, Ca, Mg, Al, Cr(III), Fe(II), Fe(III), Mn(II), Zn, Ag, Cu(II), Pb(II); sulfides of Fe(II), Mn(II), Zn, Ag, Hg(I), Hg(II), Cu(II), Pb(II), Bi(III), Sn(II); oxides and hydroxides of the above metals; and hydroxyapatite, which is a naturally occurring mineral form of calcium apatite.

Examples of organic compounds which will scavenge protons include 1,8-bis-(dimethylamino)naphthalene, l,8-bis(hexamethyltriaminophosphazenyl)naphthalene and 2,6-di-tert-butylpyridine.

Any combination of the above scavenges may be used.

In accordance with this invention, it has been found that these proton scavengers materials form will substantially reduce or even completely eliminate the susceptibility of polyester polyurethanes to degrade though hydrolysis without introducing any significant haze into the polymer, but only if they are incorporated into the polymer in a substantially dispersed nanoparticle and/or high surface area form.

In this regard, nanoparticles are typically obtained commercially in powder or dispersion form, both aqueous and organic. Although the individual/primary (crystallites for CaCO,) particles in these products may be in the nano size range, these particles usually combine into larger agglomerates in which the nanoparticles are relatively closely-packed with one another usually in three dimensions.

Therefore, when these nanoparticle powders and dispersions are used to make nanoparticle-containing polymers, the nanoparticles remain in the form of these larger agglomerates. In other words, the nanoparticles are not substantially dispersed in the polymer mass. In accordance with this invention, it has been found that proton scavenger nanoparticles will substantially reduce or even completely eliminate the susceptibility of polyester polyurethanes to degrade though hydrolysis, but only if they are incorporated into the polymer mass ultimately formed in a substantially dispersed and/or high surface area form.

An example of substantially dispersed (but loosely aggregated having a high surface area (e.g. 41 m2/g) arrangement is shown in Figs. 1A and IB. The primary nano crystallites of Omya XC-6600-34 from Omya form flocks of various shape and dimensions with a substantial portion of the surface exposed to the matrix they are in. From this perspective, the most effective form of flocculation is a trains or chains of particles. Such an arrangement into relatively large Hoc particles can introduce some haze to the nanocomposites, but will still be effective in retarding ester hydrolysis because large portion of the nanoparticles surfaces is exposed to the matrix.

In one embodiment where the ultimate particle/crystallite diameter is small, desirably the D50 is less than 1 micron, more desirably less than 500 nm, more desirably less than 100 nm, and preferably less than 50 nm. In a similar embodiment, desirably the D90 is less than 1 micron, more desirably less than 500 nm, more desirably less than 100 nm, and preferably less than 50 nm. In one embodiment, the nitrogen BET surface area is greater than 20 m /g; more desirably greater than 30 m /g; still more 2 2 desirably greater than 35 m /g and preferably about 40 or more m /g.

In one embodiment, the particle size of the proton scavenger nanoparticles when in the substantially dispersed form desired by this invention can vary widely, and essentially any particle size in the nanoparticle size range can be used. For the purposes of the present invention, nano particles and substantially dispersed nanoparticles are defined as particles which have at least one of the three dimensions of less than about 250 nm (D90) but will normally be less than about 150 nm. In other embodiments, the mean particle size will be about 100 nm or less (D90), 75 nm or less, or even 50 nm or less. In some embodiments, the particle size may even be as low as 25 nm or less, 10 nm or less, or even 5 nm or less. In general, the mean particle size, D50, of these substantially dispersed nanoparticles may be as large as 250 nm (nanometers) but will normally be less than 100 nm. Substantially dispersed nanoparticles having a mean particle size of about 75 nm or less, more typically 50 nm or less, or even 40 nm or less are interesting. In other embodiments, the mean particle size will be 30 nm or less, 25 nm or less, or even 10 nm or less. In some embodiments, the particle size may even be as low as 5 nm or less, 2 nm or less, or even 1 nm or less.

Particle size is usually characterized by particle size distribution, since all particles in a batch of particles do not have an identical particle size. Thus, in some embodiments of the invention, it is desirable that the nanoparticle batch have a D90 of less than 250 nm (i.e., 90% of volume of the particles in the batch have equivalent diameters less than 250 nm). Nanoparticle batches with D90’s of 150 nm or less, 100 nm or less, more typically 75 nm or less, or even 50 nm or less, 25 nm or less, 10 nm or less, or even 5 nm or less are especially interesting.

Of particular interest are nanoparticle batches having Dgo’s of about 100 nm or less, and especially 75 nm or less, or even 50 nm or less, since nanoparticles of this size when substantially dispersed in a polymer matrix become essentially transparent to the naked eye.

The aqueous nanoparticle/polyester-polyurethane dispersions of this invention, both in prepolymer and chain extended form, can be used to make coatings and films for porous and non-porous substrates such as papers, non-woven materials, textiles, leather, wood, concrete, masonry, metals, house wrap and other building materials, fiberglass, polymeric articles, personal protective equipment (such as hazardous material protective apparel, including face masks, medical drapes and gowns, and firemen's turnout gear), and the like. Applications include papers and non-wovens, fibrous materials, films, sheets, composites, and other articles, inks and printing binders, flock and other adhesives, and personal care products such as skin care, hair care, and nail care products, livestock and seed applications, and the like.

Any fibrous material can be coated, impregnated or otherwise treated with the compositions of this invention by methods well known to those skilled in the art, including carpets as well as textiles used in clothing, upholstery, tents, awnings, air bags, and the like. Suitable textiles include fabrics, yams, and blends, whether woven, non-woven, or knitted, and whether natural, synthetic, or regenerated. Examples of suitable textiles include cellulose acetate, acrylics, wool, cotton, jute, linen, polyesters, polyamides, regenerated cellulose (Rayon), and the like.

Compositions of this invention can also be used to produce articles made of standalone films and objects such as personal protective equipment. Examples of protective items include gloves and condoms.

In addition, the compositions of this invention can be used as adhesives or to augment or supplement adhesive types well known to those skilled in the art. For example, particular adhesive properties can be achieved by varying type and amount of isocyanates, type, amount, and molecular weight of polyols, and the amount of poly(alkylcnc oxide) side chain units.

The polyester-polyurethane nanoparticle composites produced when the aqueous dispersions of this invention are applied and dried, whether or not the polyester-polyurethane is chain extended, exhibit exceptional resistance to degradation by hydrolysis, in particular a resistance to hydrolysis comparable to that of the much more expensive polycarbonate polyurethane resins. Moreover, so long as the D90 particle size of the substantially dispersed nanoparticles used is < 75 nm, preferably < 50 nm or even < 40 nm, the polyurethanes obtained will be essentially transparent, provided of course that they are free or essentially free of other materials which would compromise their transparency properties.

Finally, the principles of the present invention can be applied to other technologies for manufacturing aqueous polyurethane dispersions. For example, this invention can be applied to the technique for manufacturing breathable polyurethane dispersions (i.e. dispersions which form layers of breathable polyurethanes) described in U.S. Patent No. 6,897,281, as well as to the technique for manufacturing core-shell polyurethane dispersions described in U.S. Published Patent Application No. 20050004306. The disclosures of the above patent and published applications are incorporated herein by reference.

Polyurethanes based on polyester macroglycols are known to be susceptible to hydrolysis. The hydrolytic stability of the improved product is attributed to the presence of a proton scavenger in highly dispersed form having significant surface area (increasing the probability that the proton scavenger will be able to scavenge protonic species before the cause hydrolytic chain scission in the polyester portion of the polyurethane). The polyurethane can be in the form of a film, coating or shaped article. The proton scavenger is preferably an inorganic carbonate salt such as calcium carbonate. If the aggregates of the proton scavenger are small relative to the wavelength of light the polyurethane composition will be substantially transparent to visible light. If the proton scavenger, e.g. calcium carbonate, is comprised of loosely aggregated primary crystallites, that are in the 5-100 nanometer weight average diameter, it will have high surface area (e.g. >40 m /g) will be effective at scavenging protons.

In order to further exemplify the clear coatings formulated according to the invention, several working examples of such clear coat formulations are provided below. In these examples, the following raw materials were used: • DOW - SG30 Acrylic Latex (binder medium) • Bayhydrol 110 - Polyurethane Dispersion (binder medium) • Deionized Water • Various Omya experimental SM-GCC slurries.

In addition, the following analytical and testing procedures were used in carrying out these examples: • Gloss was measured at 20°, 60°, and 75° angles utilizing a Micro TriGloss unit from B YK-Gardner, catalog #4446 • Sheen at 85° angle utilizing a Micro TriGloss unit from BYK-Gardner, catalog #4446 • Solids Content - total solids were measured by Moisture/Solids Analyzer Toledo HB 43 (Mettler Toledo Corporation) • pH Measurements - pH readings were taken using pH 510 Meter, a pH meter from BYK-Gardner, Catalog #PH-2643. • Gloss / Haze. The preferred evaluation of haze is visual because perceived haze and clarity are one of the most important properties of coatings and other articles. Haze can also be measured by objective instrumental means. Examples include the method described in ASTM D 1003-07 "Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics", measurement of gloss at different angles, measurement of L,a,b values, and also other methods described in ASTM Guide E 179-96(2003) "Standard Guide for Selection of Geometric Conditions for Measurement of Reflection and Transmission Properties of Materials", D1455 "Test Method for 60-deg Specular Gloss of Emulsion Floor Polish", D1746 "Test Method for Transparency of Plastic Sheeting", D4039 "Test Method for Reflection Haze of High-Gloss Surfaces", D4061 "Test Method for Retroreflectance of Horizontal Coatings" and D523 "Test Method for Specular Gloss".

Preparation of a Clear Gloss coating containing Calcium Carbonate Nanoparticle Dispersion

In each case an aqueous dispersion of substantially dispersed calcium carbonate nanoparticles was produced by from the following ingredients:

Ingredients Used in Example 1_

Ingredients Used in Example 2

Ingredients Used in Example 3

Ingredients Used in Example 4

Ingredients Used in Example 5

Ingredients Used in Example 6

Ingredients Used in Examnle 7

Ingredients Used in Example 8

Ingredients Used in Example 9

Ingredients Used in Example 10_i_i

Table 1

GLOSS MEASUREMENT

Malvern Malvern 75° 20° 60° 85° D(50) D(98) SG 30

Control 93 63.3 83.3 92.5 N/A N/A

Example 1 88.4 33 70.7 89.9 0.12 0.3

Example 2 83.7 19 60.2 91 0.12 0.4

Example 3 85.1 22.6 61.5 87.2 0.13 0.5

Example 4 83.2 17.7 57.8 90.5 0.13 0.3

Example 5 88.1 33.1 69.6 89 0.12 0.4

Example 6 83.6 16.6 56.5 91.4 0.13 0.5

Example 7 80.3 14.5 53 88.7 0.12 0.3

Example 8 88.4 36.6 71.9 89.8 0.13 0.4

Example 9 82.2 16.8 54.2 88.5 0.13 0.5

Example 10 81.5 16.2 53.9 90.2 0.13 0.6

The samples made with Dow SG-30 all acrylic latex were prepared using a Premier Mill Model #CM 100 high speed dissolver with a 2.5in blade. They were dispersed for 30 minutes at 900 rpm.

Ingredients Used in Example 11

Ingredients Used in Example 12

Ingredients TTspH in K vnmnl<> 13

Ingredients Used in Example 14

Ingredients Used in Example 15

Ingredients Used in Example 16

Ingredients Used in Example 17

Ingredients Used in Example 18

Ingredients Used in Example 19_

Ingredients Used in Exanmle 20

Table 2

Bayhydrol with 5% GCC loading

GLOSS MEASUREMENT 20° 60° 85°

Bavhvdrol 110 (Control) 67.5 90.9 95.9

Example 11 65.8 87.2 96.1

Example 12 741 88.6 97.9

Example 13 71.3 88.4 97.7

Example 14 72.5 88.5 98

Example 15 75.6 88.4 97.8

Table 3

Bayhydrol with 10% GCC loading

GLOSS MEASUREMENT 20° 60° 85°

Bavhvdrol 110 (Control) 67.5 90.9 95.9

Example 16 60 87 95

Example 17 64.2 89.9 95.5

Example 18 64.9 86.6 95.5

Example 19 64.3 87 95.8

Example 20 62.1 86.3 95.7

The samples made with Bayhydrol 110 were prepared using a Speed Mixer Model # DAC 150.1 FVZ-K. They were dispersed for 1 min at 2500 rpm.

Turning next, then, to a discussion of an alternate embodiment of the present invention wherein the aqueous nanoparticle dispersions described herein are utilized in forming glossing and opacifying coating compositions, it is noted that mineral pigments are widely used in known glossing and opacifying coating systems, not only to decrease formulation costs but further to improve certain properties of the coating formulation during its preparation or storage, or during or following its application to a substrate. In the realm of paint formulations, coating systems almost invariably implement titanium dioxide.

In the context of paint applications, titanium dioxide (T1O2) is commonly used, particularly in its rutile form, for providing significant opacity or hiding power. Titanium dioxide pigments marketed for use in paint formulation are well known to present a narrow particle size distribution along with a median particle diameter of between 0.2 and 0.6 pm, depending on the material and the mean particle size measurement method. Zinc sulphide and zinc oxide are similarly employed.

Titanium dioxide suffers however from being relatively high in cost, resulting in a continuing desire to find lower-cost T1O2 partial replacement pigments that do not translate in a reduction of optical and other coating composition properties. GB1404564 describes ultrafine natural calcium carbonate filled paints and pigments, wherein said natural calcium carbonate has a particle diameter of from 0.5 to 4 pm and is employed to partially replace titanium dioxide. In this vein, Imerys has commercialised Polcarb, said to be suitable for glossing paint formulations, which has a mean particle size of 0.9 pm. However, such natural calcium carbonate products do not allow the replacement of a part of T1O2 in glossing paint formulation having a pigment volume concentration below the critical pigment volume concentration without loss of gloss or opacity.

For the purpose of describing the glossing and opacifying coating compositions according to the present invention, the pigment volume concentration (PVC) is understood to refer to the fraction, quoted in %, of pigment volume relative to the total volume of the pigment plus the other components of the formulation, i.e., it accounts for the pigment volume relative to the total formulation volume.

The critical pigment volume concentration (CPVC) is defined as the pigment volume concentration whereupon the resin component of the coating formulation is no longer sufficient to entirely coat all of the pigment particles in a coating. It is well known that above the CPVC, formulations generally provide a matt finish. By contrast glossy paint formulations implement a PVC that is below the CPVC. US 5,171,631 discloses a coating composition for developing hiding on a suitable substrate, the coating composition having a pigment volume concentration (PVC) up to a critical pigment volume concentration (CPVC) and a pigment system comprising about 70-98% by volume of titanium dioxide and about 2-30% by volume of an aluminium trihydrate (ATH) spacer/extender pigment having a medium particle size of about 0.2 microns. Figure 1 of US 5,171,631 shows a D98/D50 ratio value of approximately 2.7, which corresponds to a relatively narrow particle size distribution. Although it is stated that, provided this ATH has a median particle size and particle size distribution generally similar to the median particle size and particle size distribution curve of T1O2, a portion of T1O2 may be replaced with an equal volume of ATH with no loss of hiding, Figure 2 of US 5,171,631 shows that the ATH-T1O2-comprising paint formulations generally fail to achieve the same opacity values as the control paint formulation comprising T1O2 alone.

Natural ground calcium carbonate as opposed to its synthetic counterpart, precipitated calcium carbonate (PCC), generally suffers from a broad particle size distribution and irregular particle shapes. Indeed, as natural ground calcium carbonate is prepared by the grinding down of mined calcite, marble, chalk or limestone-containing stones, it is difficult to ensure that these stones are ultimately fractioned to form fine particles having a very uniform particle size.

By contrast, PCC is formed by a process of building crystals around nucleation sites. Control of nucleation and particle size development, particularly in the size domain under a few micrometers, during PCC precipitation has, over the years, become a well studied science and PCC particles having small and very uniform particle sizes and shapes are now widely available. As in US 5,171,631, the advantages of employing a uniform particle size product as a titanium dioxide spacer are alluded to in the publication made at http://www.specialtvminerals.com/specialty-applications/specialtv-markets-for-minerals/paint-and-coatings/precipitated-calcium-carbonate-pcc-in-paint/: “precipitated calcium carbonate (PCC) is most commonly used in paint as an extender for titanium dioxide, or T1O2. The small and narrowly distributed PCC particles help space the individual T1O2 particles and maximize their hiding power.” In this domain, Specialty Minerals advertises Albafil PCC, a fine, 0.7 micron prismatic calcite, and a range of ultrafine or nano PCCs, namely Calofort S PCC, Calofort U PCC, Ultra-Pflex PCC and Multifex MM PCC, each having a median diameter of 0.07 micron.

In view of the above-discussed teachings found in the prior art, it was remarkable that the present inventors found that a ground natural calcium carbonate that is finer than ground natural calcium carbonate products previously offered in this domain, may be used to form an aqueous nanoparticle dispersion in one or more of the binder systems described above for use in forming a variety of (1) clear-coat coating compositions (see the discussion above), as well as serving as (2) a T1O2 replacement or complementary pigment in the formation of glossing and opacifying coating compositions, even in the case when this ground natural calcium carbonate features a relatively broad particle size distribution and/or a median diameter that is different from that of T1O2. By contrast to the results of US 5,171,631 achieved with ATH, the ground natural calcium carbonate employed in the present invention not only more fully maintains the gloss and opacity of the paint formulation when used to replace part of the formulation T1O2 at constant PVC, it may even lead to a gloss and/or opacity improvement.

One embodiment of a glossing and opacifying coating composition according to the invention is a composition having a PVC of from 5% up to the CPVC and characterised in that comprises at least one ground natural calcium carbonate having a median diameter (d50 (Mai)) of between 0.05 and 0.3 pm, (hereafter submicron ground natural calcium carbonate, SMGCC), and at least one pigment having a refractive index of greater than or equal to 2.5.

For the purpose of describing the glossing and opacifying coating compositions of the present application, CPVC was determined according to the measurement method given in the examples section below.

Moreover, for the purpose of further describing the glossing and opacifying coating compositions according to the present invention, the median diameter (d50 (Mai)) and d98 (Mai) were measured according to the measurement method provided in the examples section below.

Another object of the present invention resides in a process to prepare a glossing and opacifying coating composition having a PVC of from 5% up to the CPVC, characterised in that: a) at least one ground natural calcium carbonate (SMGCC) having a D50 (Mai) of between 0.05 and 0.3 pm is provided; b) at least one pigment having a refractive index of greater than or equal to 2.5 is provided; c) at least one resin (binder) is provided; d) the SMGCC of step a) is mixed with the pigment of step b) and the resin of step c). A third object of producing the glossing and opacifying coatings according to the present invention lies in the use of at least one ground natural calcium carbonate having a d50 (Mai) of between 0.05 and 0.3 pm, in a coating composition comprising at least one pigment having a refractive index of greater than or equal to 2.5, characterised in that for a coating composition having a constant PVC in the range of from 5% up to the CPVC, the gloss and/or opacity of the composition is equal to or greater than the gloss and/or opacity of the same composition implementing the pigment having a refractive index of greater than or equal to 2.5 in place of the ground natural calcium carbonate having a d50 of between 0.05 and 0.3 pm.

The gloss of a coating composition applied to a substrate was measured according to the measurement method provided in the examples section below.

The opacity of a coating composition applied to a substrate was measured according to the measurement method provided in the examples section below.

In order to more thoroughly describe the formulation of glossing and opacifying coating compositions according to the invention, the following examples are provided below. A first embodiment of such a glossing and opacifying coating comprises a coating composition having a PVC of from 5% up to the CPVC and characterised in that comprises at least one ground natural calcium carbonate having a median diameter (D50 (Mai)) of between 0.05 and 0.3 pm (hereafter submicron ground natural calcium carbonate, SMGCC), and at least one pigment having a refractive index of greater than or equal to 2.5. Preferably, the coating composition has a PVC of from 15 to 25%.

Preferably, the SMGCC has a median diameter (D50 (Mai)) of between 0.1 and 0.3 pm.

In another embodiment, the SMGCC has a D98/D50 (Mai) of greater than 3. As indicated above and in contrast to the prior art, this ground natural calcium carbonate may, in an optional embodiment, have a particle size distribution that is broad and dissimilar to the particle size distribution said pigment having a refractive index of greater than or equal to 2.5 employed in the composition. Indeed, even a bi- or multimodal SMGCC particle size distribution may be envisioned.

In a preferred embodiment, said SMGCC has a D98 of less than or equal to 1 pm, more preferably of less than or equal to 0.8 pm, even more preferably of less than or equal to 0.6 pm, and even more preferably of less than or equal to 0.4 pm.

Preferably, the SMGCC has a refraction index of approximately 1.5 to 1.7.

In another preferred embodiment, the pigment having a refractive index of greater than or equal to 2.5 is selected from one or more of the following: titanium dioxide and/or zinc sulphide and/or zinc oxide. In a more preferred embodiment, the pigment having a refractive index of greater than or equal to 2.5 is titanium dioxide. In such a case, it is preferred that the titanium dioxide : SMGCC weight ratio is of 70 : 30 to 98 : 2, and it is even more preferred that the titanium dioxide : SMGCC weight ratio is of 85 : 15 to 90 : 10.

In an alternate embodiment, the pigment contributing to the PVC of the composition is a mixture of at least one pigment having a refractive index of greater than or equal to 2.5, SMGCC and one or more of the following: clay, talc, magnesium carbonate, PCC, barium sulphate, mica and bentonite. In the case where magnesium carbonate is implemented in combination with SMGCC, this may be in the form of a dolomite.

This coating composition is characterised in that when all of said SMGCC is replaced by said pigment having a refractive index of greater than or equal to 2.5 while maintaining a constant PVC value in the range of from 15% up to the CPVC, the gloss of the SMGCC-comprising composition is within 10 % of the gloss of the composition wherein the SMGCC is fully replaced by said pigment having a refractive index of greater than or equal to 2.5. Preferably, the gloss of the SMGCC-comprising composition is within 5 %, and more preferably within 3%, of the gloss of the composition having only said pigment having a refractive index of greater than or equal to 2.5.

As shown in the examples below, it is not necessary that the SMGCC have a median diameter (D50 (Mai)) that is equivalent to the median diameter (D50 (Mai)) of said pigment having a refractive index of greater than or equal to 2.5, though this embodiment is not excluded from the present invention. The median diameter (D50 (Mai)) of SMGCC may differ from the median diameter (D5o (Mai)) of said pigment having a refractive index of greater than or equal to 2.5 by up to approximately 0.4 pm.

As also demonstrated by the examples below, said SMGCC may feature a broad and even non-uniform particle size distribution relative to the distribution of the pigment having a refractive index of greater than or equal to 2.5 is, though again this does not exclude the case where the particle size distributions of SMGCC and the pigment having a refractive index of greater than or equal to 2.5 is are similar in breadth.

Alternatively, the gloss of the SMGCC-comprising composition may be increased by at least 1 % relative to the gloss of the composition wherein the SMGCC is fully replaced by the pigment having a refractive index of greater than or equal to 2.5. Relative to this embodiment, the gloss of the SMGCC-comprising composition is preferably increased by at least 5 % relative to the gloss of the composition wherein the SMGCC is fully replaced by the pigment having a refractive index of greater than or equal to 2.5.

In a preferred embodiment, said SMGCC is dispersed with one or more dispersants. Conventional dispersants known to the skilled person can be used. The dispersant can be anionic, cationic or non-ionic. A preferred dispersant is polyacrylic acid.

The coating compositions according to the present invention (i.e., when used in forming the clear coatings as well as glossing and opacifying coatings) may be applied to a variety of substrates as discussed above, including but not limited to, concrete, wood, paper, metal and board.

In a preferred embodiment, the coating composition is applied to a substrate in an amount so as to form a layer having a thickness of between 100 and 400 um.

Following application to a substrate, a glossing and opacifying coating composition according to the invention preferably provides a gloss measured at 60° of greater than 70 %. Furthermore, following application to a substrate, the coating composition preferably provides an opacity (contrast ratio) of greater than 97%.

The present coating compositions may further include one or more of the following: optical brightener, resin (such as a latex or acrylate-based binder, preferably in the form of an aqueous emulsion), defoamer, thickener, solvent, glycol ethers and dispersant. Preferably, the coating composition has a Brookfield viscosity of from 200 to 500 mPa.s, as measured according to the measurement method provided in the examples below.

Process For Preparing a Glossing/Opacifving Coating Composition In Accordance With the Present Invention

The process results in the preparation of a coating composition having a PVC of from 5% up to the CPVC, characterised in that: a) at least one ground natural calcium carbonate (SMGCC) having a D50 of between 0.05 and 0.3 pm is provided; b) at least one resin (binder) is provided; c) the SMGCC of step a) is mixed with the resin of step b).

The SMGCC of step a) may be provided in the form of an aqueous suspension, an aqueous dispersion or as a dry powder. In a preferred embodiment, the SMGCC of step a) is provided in the form of an aqueous suspension or dispersion.

The resin is preferably a latex and/or acrylate-based binder, said acrylate-based binder preferably being in the form of an aqueous emulsion.

Use of SMGCC in Glossing/Opacifving Coating Compositions

Another object of the present invention lies in the use of at least one ground natural calcium carbonate having a D50 (Mai) of between 0.05 and 0.3 pm, in a glossing/opacifying coating composition, characterised in that for a coating composition having a constant PVC in the range of from 15% up to the CPVC, the gloss and/or opacity of the composition is equal to or greater than the gloss and/or opacity of the same composition implementing T1O2 in place of said ground natural calcium carbonate having a d50 of between 0.05 and 0.3 pm.

Another object of the present invention is the production of a paint comprising the glossing/opacifying coating composition of the invention.

Examples of Glossing/Opacifving Coating Compositions

Suspension or dispersion solids content (% equivalent dry weight)

The weight of the solid material in a suspension or dispersion is determined by weighing the solid material obtained by evaporating the aqueous phase of suspension and drying the obtained material to a constant weight.

Particle size distribution (mass % particles with a diameter < X) and median grain diameter (dso (Sedi), dso (Mai) and d<js (Mai)) of particulate material

Weight median grain diameter (dso (Sedi)) and grain diameter mass distribution of a particulate material are determined via the sedimentation method, i.e. an analysis of sedimentation behavior in a gravimetric field. The measurement is made with a Sedigraph™ 5100.

The method and the instrument are known to the skilled person and are commonly used to determine grain size of fillers and pigments. The measurement is carried out in an aqueous solution of 0.1 % by weight of Na4P207. The samples were dispersed using a high-speed stirrer and ultrasonic means.

Weight median grain diameter (dso (Mai)) was evaluated using a Malvern Mastersizer 2000 (Frauenhofer). The dgg (Mai) value, measured using a Malvern Mastersizer 2000 (Frauenhofer), indicates a diameter value such that 98 % by weight of the particles have a diameter of less than this value. BET specific surface area (m2/g) BET specific surface area values were determined using nitrogen and the BET method according to ISO 9277.

Gloss of a coated surface

Gloss values are measured at the listed angles according to DIN 67 530 on painted surfaces prepared with a coater gap of 150 and 300 pm on contrast cards.

Contrast Ratio (opacity) of a coated surface

Contrast ratio values are determined according to ISO 6504/3 at a spreading rate of 7.5 m2/l.

Suspension or dispersion Brookfield-viscosity (mPas)

Brookfield-viscosities are measured with a Brookfield DV-II Viscometer equipped with a LV-3 spindle at a speed of 100 rpm and room temperature (20 ± 3 °C).

Pigment Volume Concentration (PVC, %)

The pigment volume concentration is calculated as described in Section 6.2.3 of the book entitled “Fuellstoff ’ by Detlef Gysau (Hannover: Vincentz Network 2005).

Total sum by volume of all pigments + extenders in paint x 100%

Total sum by volume of all solid ingredients in paint

Critical Pigment Volume Concentration (CPVC, %)

The critical pigment volume concentration is a well known concentration widely used in the paint industry. It is generally considered to represent the point at which there is just enough resin to wet the pigment particles, and changes to the PVC near to the CPVC can result in abrupt changes to coating properties, such as porosity and gloss. The CPVC and its measurement method according to ISO 4618 are discussed in Section 6.2.4 of the book entitled “Fuellstoff’ by Detlef Gysau (Hannover: Vincentz Network 2005).

Materials:

SMGCC SMGCC dispersions used in the following examples are natural ground calcium carbonate (marble from Vermont) having the median particle size dso and particle size characteristics given in the table below.

Table 4

Titanium dioxide

The titanium dioxide employed in the examples herebelow consists of 95% by weight of pure rutile T1O2, with the remaining weight being accounted for in a surface treatment of alumina, zirconia and an organic surface treatment agent. This pigment features a d50 (Mai) of approximately 0.55 pm and is provided in the form of an aqueous paste having a 75% solids content. By scanning electron microscope imaging, the particles appear to be in the range of 0.2 to 0.25 pm. The refractive index of T1O2 is 2.7.

Example 21:

The following example illustrates a comparative paint composition and paint compositions according to the invention. The formulated paints were applied to a contrast card in the necessary amounts in order to measure both gloss and opacity.

Table 5

The results set forth in table 5 above demonstrate that replacing a part of T1O2 with the SMGCC according to the invention, and having d98/d50 values ranging from 2.4 to 5, results in coatings having essentially the same opacity (contrast ratio) as the comparison formulation having equal PVC but only T1O2. Gloss values are observed to be equivalent or improved relative to the comparison formulation having equal PVC but only T1O2.

Claims (20)

1. A glossing and opacifying coating composition comprising: an aqueous ground calcium carbonate dispersion, wherein the ground calcium carbonate is substantially dispersed and has a mean particle size D50 (Mai) of less than 1 micron; wherein the ground calcium carbonate is dispersed in at least one binder including vinyl-acrylic, styrene-acrylic, acrylic dispersions, solution acrylics, alkyds, polymers containing ester groups including polyesters, polyester-based polyureas and polyester-based polyamides, and; wherein the glossing and opacifying coating composition has a pigment volume concentration (PVC) of from 5 % up to the critical pigment volume concentration (CPVC) and at least one pigment having a refractive index of greater than or equal to 2.5.

2. The glossing and opacifying coating composition according to claim 1, wherein the ground calcium carbonate has a particle size D90 of less than 1 micron.

3. The glossing and opacifying coating composition according to claim 2, wherein the ground calcium carbonate has a particle size D90 of less than 50 nm.

4. The glossing and opacifying coating composition according to any one of claims 1 to 3, wherein the nitrogen BET surface area of the nanoparticles is greater than 20 m2/g.

5. The glossing and opacifying coating composition according to claim 4, wherein the nitrogen BET surface area of the nanoparticles is greater than about 40 m2/g.

6. The glossing and opacifying coating composition according to any one of claims 1 to 5, wherein the ground calcium carbonate is selected from the group comprising ground calcium carbonate derived from grinding of chalk, limestone, marble, and preferably is submicron ground calcium carbonate (SMGCC).

7. The glossing and opacifying composition according to any one of claims 1 to 6, wherein the ground calcium carbonate has a D98/D50 (Mai) of greater than 3.

8. The glossing and opacifying composition according to any one of claims 1 to 7, wherein the ground calcium carbonate has a D98 of less than or equal to 1 pm.

9. The glossing and opacifying composition according to claim 8, wherein the ground calcium carbonate has a D98 of less than or equal to 0.4 pm.

10. The glossing and opacifying composition according to any one of claims 1 to 9, wherein the ground calcium carbonate has a refraction index of approximately 1.5 to 1.7.

11. The glossing and opacifying composition according to any one of claims 1 to 10 wherein the pigment having a refractive index of greater than or equal 2.5 is selected from one or more of the following: titanium dioxide and/or zinc sulphide and/or zinc oxide, and preferably is titanium dioxide.

12. The glossing and opacifying composition according to claim 11 wherein the pigment having a refractive index of greater than or equal 2.5 is titanium dioxide and the titanium dioxide : ground calcium carbonate weight ratio is between 70 : 30 and 98 : 2, more preferably the titanium dioxide : ground calcium carbonate weight ratio is between 85 : 15 and 90 : 10.

13. A method of forming a glossing and opacifying composition wherein: a) at least one ground calcium carbonate having a D50 (Mai) of between 0.05 and 0.3 pm is provided, b) at least one pigment having a refractive index of greater than or equal 2.5 is provided, c) at least one binder is provided, and d) the ground calcium carbonate of step a) is mixed with the pigment of step b) and the binder of step c).

14. Use of a glossing and opacifying composition according to any one of claims 1 to 12 for coating substrates.

15. A coated substrate coated with a glossing and opacifying composition according to any one of claims 1 to 12.

16. The coated substrate according to claim 15, wherein the substrate is selected from porous and non-porous substrates including papers, non-woven materials, textiles, leather, wood, concrete, masonry, metals, house wrap and other building materials, fiberglass, polymeric articles, personal protective equipment, carpets, textiles used in clothing, upholstery, tents, awnings, air bags, fabrics, yarns, and blends, whether woven, non-woven, or knitted, and whether natural, synthetic, or regenerated.

17. The coated substrate according to claim 15 or claim 16, wherein the coated substrate includes papers and non-wovens, fibrous materials, films, sheets, composites inks, printing binders, flock and other adhesives, and personal hair products including skin care, hair care, and nail care products, livestock and feed applications.

18. The coated substrate according to any one of claims 15 to 17, wherein the coating composition is applied to the substrate in an amount so as to form a layer having a thickness of between 100 and 400 nm and/or wherein the glossing and opacifying coating composition provides a gloss measured at 60° of greater than 70 % and an opacity of greater than 97 %.

19. A method of forming a coated substrate coated with a glossing and opacifying composition, wherein a glossing and opacifying composition according to any one of claims 1 to 12 is applied to the substrate preferably by coating, impregnating or otherwise treating.

20. The method according to claim 19, wherein the coating composition is applied to the substrate in an amount so as to form a layer having a thickness of between 100 and 400 nm and/or wherein the coated substrate is further dried and optionally cured. OMYA International AG Patent Attorneys for the Applicant/Nominated Person SPRUSON &amp; FERGUSON