Coating composition comprising submicron calcium carbonate

Abstract

Coating composition providing gloss and opacity on application, having a pigment volume concentration of from 5% up to the critical pigment volume concentration and characterised in that comprises at least one ground natural calcium carbonate having a volume median diameter of between 0.05 and 0.3 m, and at least one pigment having a refractive index of greater than or equal to 2.5.

Claims

1. A glossing and opacifying coating composition comprising: (i) at least one submicron ground natural calcium carbonate (SMGCC) having a volume median particle diameter d.sub.50 of 0.05 to 0.3 m and a d.sub.98 of less than or equal to 0.6 m, and titanium dioxide, wherein the titanium dioxide: SMGCC weight ratio in the composition is from 75:25 to 98:2, and wherein the calcium carbonate is calcite, marble, chalk or limestone; and (ii) glossing and opacifying coating composition components, wherein the glossing and opacifying coating composition has a pigment volume concentration (PVC) of from 5 vol.-% up to a critical pigment volume concentration (CPVC), and wherein the glossing and opacifying coating composition, applied to a contrast card to form a layer having a thickness of 150 m or 300 m, has a gloss that is within 3% of the gloss of the same composition and thickness in which the SMGCC is fully replaced with the titanium dioxide, when gloss is measured either at a 60 or an 85 incident angle according to DIN 67530.

2. The glossing and opacifying coating composition according to claim 1, having a PVC of from 10 to 30 vol.-%.

3. The glossing and opacifying coating composition according to claim 1, having a PVC of from 15 to 25 vol.-%.

4. The glossing and opacifying coating composition according to claim 1, having a PVC of from 17 to 21 vol.-%.

5. The glossing and opacifying coating composition according to claim 1, wherein the SMGCC has a volume median diameter d.sub.50 of 0.08 to 0.3 m.

6. The glossing and opacifying coating composition according to claim 1, wherein the SMGCC has a volume median diameter d.sub.50 of 0.1 to 0.2 m.

7. The glossing and opacifying coating composition according to claim 1, wherein the SMGCC has a d.sub.98/d.sub.50 of greater than 3.

8. The glossing and opacifying coating composition according to claim 1, wherein the SMGCC has a d.sub.98 of less than or equal to 0.4 m.

9. The glossing and opacifying coating composition according to claim 1, wherein the titanium dioxide: SMGCC weight ratio is from 75:25 to 90:10.

10. The glossing and opacifying coating composition according to claim 1, wherein the titanium dioxide: SMGCC weight ratio is from 80:20 to 85:15.

11. The glossing and opacifying coating composition according to claim 1, which is paint.

12. The glossing and opacifying coating composition according to claim 1, wherein the glossing and opacifying coating composition components comprise a resin, and the resin is a latex or an acrylate-based binder.

13. The glossing and opacifying coating composition according to claim 1, further comprising one or more additives selected from the group consisting of defoamers, levelling agents, flatting agents, preservatives, optical brighteners, light stabilizers, thickeners, dispersents, solvents, water, coalescing solvents, plasticizers, anti-settling agents, dispersants, surfactants, rheology modifiers, biocides, metals, UV-absorbers, stabilizers, zinc oxide, nepheline syenite, diatomaceous earth, aluminium silicates, quartz, mica, wollastonite, colored inorganic pigments, colored organic pigments, and fillers.

14. The glossing and opacifying coating composition according to claim 1, wherein the SMGCC is dispersed with one or more dispersants.

15. The glossing and opacifying coating composition according to claim 1, having a Brookfield viscosity of from 200 to 500 mPas when measured at a rotation speed of 100 rpm at room temperature.

Description

EXAMPLES

(1) Suspension or Dispersion Solids Content (% Equivalent Dry Weight)

(2) 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.

(3) Particle Size Distribution (Volume % Particles with a Diameter <x), Volume Median Grain Diameter d.sub.50, and d.sub.98 (Diameter at which 98 Vol.-% of the Particles are Finer than d.sub.98) of Particulate Material.

(4) Volume median gain diameter d.sub.50 was evaluated using a Malvern Mastersizer 2000 (Fraunhofer). The d.sub.98 value, measured using a Malvern Mastersizer 2000 (Fraunhofer), indicates a diameter value such that 98% by volume of the particles have a diameter of less than this value.

(5) BET Specific Surface Area (m.sup.2/g)

(6) BET specific surface area values were determined using nitrogen and the BET method according to ISO 9277.

(7) Gloss of a Coated Surface

(8) 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 m on contrast cards.

(9) Contrast Ratio (Opacity) of a Coated Surface

(10) Contrast ratio values are determined according to ISO 6504/3 at a spreading rate of 7.5 m.sup.2/l.

(11) Suspension or Dispersion Brookfield-viscosity (mPas)

(12) Brookfield-viscosities are measured with a Brookfield DV-II Viscometer equipped with a LV-3 spindle at a rotation rate of 100 rpm and room temperature (203 C.).

(13) Pigment Volume Concentration (PVC, %)

(14) 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 paint100%
Total sum by volume of all solid ingredients in paint
Critical Pigment Volume Concentration (CPVC, %)

(15) The critical pigment volume concentration is a well known concentration widely used in the paint industry. CPVC in traditional coatings is considered to be the volume of pigment in relation to binder at which there is just enough binder to wet the pigment and at which the mix theoretically exhibits zero porosity (cf. e.g. Estimation of Critical Pigment Volume Concentration in Latex Paint Systems Using Gas Permeation, Manouchehr Khorassani, Saeed Pourmandian, Faramarz Afshar-Taromi, and Amir Nourhani, Iranian Polymer Journal 14 (11), 2005, 1000-1007). 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).

(16) Materials:

(17) SMGCC

(18) SMGCC dispersions used in the following examples are natural ground calcium carbonate (marble from Vermont) having the volume median particle size d.sub.50 and particle size characteristics given in the table below.

(19) TABLE-US-00001 Solids SSA vol.-% < vol.-% < vol.-% < d.sub.98 d.sub.50 SMGCC (wt-%) (m.sup.2/g) 1 m 0.5 m 0.2 m (m) (m) d.sub.98/d.sub.50 1 60 36.0 98.3 94.3 65.1 0.53 0.120 5.0 2 49 37.7 98.3 94.8 65.7 0.55 0.122 4.5 3 46 38.6 97.7 94.8 69.5 0.31 0.128 2.4
Titanium Dioxide

(20) The titanium dioxide employed in the examples herebelow consists of 95% by weight of pure rutile TiO.sub.2, with the remaining weight being accounted for in a surface treatment of alumina, zirconia and an organic surface treatment agent. This pigment features a volume median diameter d.sub.50 of approximately 0.55 m and a d.sub.98/d.sub.50 (Mal) of 1.98, and is provided in the form of an aqueous paste having a 75 wt-% solids content. By scanning electron microscope imaging, the particles appear to be in the range of 0.2 to 0.25 m. The refractive index of TiO.sub.2 is 2.7.

Example 1

(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.

(22) TABLE-US-00002 Example 1 2 3 4 Comparison (CO)/Invention (IN) CO IN IN IN Paint composition formulation Water (g) 134 120 111 108 Hydrophilic copolymer dispersant, 50 wt-% 6.4 6.5 6.5 6.5 solids content (g) Ammonia, 24 wt-% (g) 4 4 4 4 Paraffin-based mineral oil mixture containing 7 7 7 7 silicone (g) Rheotech 2000 thickener from Coatex (g) 15 15 15 15 Propylene glycol (g) 10 10 10 10 Butyl diglycol (g) 5 5 5 5 Dipropylene Glycol n-Butyl Ether (g) 10 10 10 10 Ester alcohol with Mw = 216 g/mol (g) 9 9 9 9 Acrylate binder emulsion, 48 wt-% active 550 557 557 557 content (g) TiO.sub.2 (g) 250 218 218 218 SMGCC1 (g) 39 SMGCC2 (g) 48 SMGCC3 (g) 51 Reduction of TiO.sub.2 (% weight) 0 12.8 12.8 12.8 PVC (%) 21 21 21 21 Properties on application of the paint formulation Contrast ratio at 7.5 m.sup.2/l spreading rate (%) 98.6 98.5 98.6 98.5 Gloss obtained using a coater gap of 150 m 20 51.8 50.6 50.6 55.7 60 80.3 79.7 79.7 81.7 85 93.6 95.9 96.2 96.8 Gloss obtained using a coater gap of 300 m 20 55.6 52.4 54.7 56.8 60 79.4 78.7 80.1 80.5 85 95.6 95.7 96.5 95.8

(23) The results of the above table show that replacing a part of TiO.sub.2 with the SMGCC according to the invention, and having d.sub.98/d.sub.50 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 TiO.sub.2. Gloss values are observed to be equivalent or improved relative to the comparison formulation having equal PVC but only TiO.sub.2.