Method of preparing a 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 process for preparing a glossing and opacifying coating composition comprising: mixing, with glossing and opacifying coating composition components, 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, at a titanium dioxide:SMGCC weight ratio from 75:25 to 98:2, to obtain a glossing and opacifying coating composition having a pigment volume concentration (PVC) of from 5% 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 process according to claim 1, wherein the SMGCC is provided in the form of an aqueous suspension or dispersion.

3. The process according to claim 1, wherein the glossing and opacifying coating composition components comprises at least one resin.

4. The process according to claim 3, wherein the resin is a latex and/or acrylate-based binder.

5. The process according to claim 4, wherein the acrylate-based binder is in the form of an aqueous emulsion.

6. The process according to claim 1, wherein the glossing and opacifying coating composition has a PVC of from 10 to 30 vol.-%.

7. The process according to claim 1, wherein the glossing and opacifying coating composition has a PVC of from 15 to 25 vol.-%.

8. The process according to claim 1, wherein the glossing and opacifying coating composition has a PVC of from 17 to 21 vol.-%.

9. The process according to claim 1, wherein the SMGCC has a volume median diameter d.sub.50 of 0.08 to 0.3 m.

10. The process according to claim 1, wherein the SMGCC has a volume median diameter d.sub.50 of 0.1 to 0.2 m.

11. The process according to claim 1, wherein the SMGCC has a d.sub.98/d.sub.50 of greater than 3.

12. The process according to claim 1, wherein the SMGCC has a d.sub.98 of less than or equal to 0.4 m.

13. The process according to claim 1, wherein the titanium dioxide:SMGCC weight ratio is from 75:25 to 90:10.

14. The process according to claim 1, wherein the titanium dioxide:SMGCC weight ratio is from 80:20 to 85:15.

15. The process according to claim 1, wherein the glossing and opacifying coating composition components are selected from the group consisting of one or more of a resin, a binder, a pigment, a defoamer, a levelling agent, a flatting agent, a preservative, an optical brightener, a light stabilizer, a reheological additive, a thickener, a dispersant, a solvent, a filler, an anti-settling agent, a surfactant, a metal, and a UV absorber.

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 grain 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).

(15) $\frac{\begin{array}{c}\mathrm{Total}\mathrm{sum}\mathrm{by}\mathrm{volume}\mathrm{of}\mathrm{all}\mathrm{pigments}+\\ \mathrm{extenders}\mathrm{in}\mathrm{paint}100\%\end{array}}{\mathrm{Total}\mathrm{sum}\mathrm{by}\mathrm{volume}\mathrm{of}\mathrm{all}\mathrm{solid}\mathrm{ingredients}\mathrm{in}\mathrm{paint}}$

(16) Critical Pigment Volume Concentration (CPVC, %)

(17) 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).

(18) Materials:

(19) SMGCC

(20) 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.

(21) TABLE-US-00001 vol.-% < vol.-% < vol.-% < d.sub.98 d.sub.50 SMGCC Solids (wt-%) SSA (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

(22) Titanium Dioxide

(23) 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

(24) 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.

(25) 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 6.4 6.5 6.5 6.5 wt-% solids content (g) Ammonia, 24 wt-% (g) 4 4 4 4 Paraffin-based mineral oil mixture 7 7 7 7 containing 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-% 550 557 557 557 active 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

(26) 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.