Composite pigments

Abstract

Composite pigments are provided which comprise a mineral pigment (such as kaolin clay, titanium dioxide, talc, mica or a mixture of two or more of these mineral pigments) and calcium carbonate precipitated in-situ on the surfaces of the particles of the mineral pigment.

Claims

1. A high brightness composite pigment which comprises a mineral pigment and in-situ precipitated calcium carbonate and which is produced by a plurality of carbonation cycles precipitating a calcium carbonate coating on surfaces of particles of the mineral pigment, wherein the composite pigment has a reduced amount of particles of less than 0.2 micron compared to the starting mineral pigment and an equivalent amount of particles of less than 2 microns compared to the starting mineral pigment, wherein the composite pigment comprises a uniform coating of precipitated calcium carbonate on the surfaces of the mineral pigment particles, in contrast to non-uniform unevenly distributed discrete calcium carbonate particles or aggregates of calcium carbonate particles on the surfaces of the mineral pigment particles; and wherein the content of particles less than 2 microns is at least 84.1% and not more than 93.7%.

2. A composite pigment as defined by claim 1 wherein the mineral pigment is kaolin clay, titanium dioxide, talc, mica or a mixture of two or more of these mineral pigments.

3. A composite pigment as defined by claim 2 wherein the mineral pigment is kaolin clay.

4. A composite pigment as defined by claim 3 wherein the kaolin clay is hydrous kaolin clay.

5. A composite pigment as defined by claim 3 wherein the kaolin clay is delaminated kaolin clay.

6. A composite pigment as defined by claim 3 wherein the kaolin clay is calcined kaolin clay.

7. A composite pigment as defined by claim 3 wherein the kaolin clay is a mixture of hydrous kaolin clay and calcined kaolin clay.

8. A composite pigment as defined by claim 1 wherein the amount of calcium carbonate precipitated on the surfaces of the mineral pigment is from about 5.0 to about 90.0 weight percent based on the weight of the dry composite pigment.

9. A composite pigment as defined by claim 1 wherein the amount of calcium carbonate precipitated on the surfaces of the mineral pigment is from about 10.0 to about 60.0 weight percent based on the weight of the dry composite pigment.

10. A composite pigment as defined by claim 1 wherein the amount of calcium carbonate precipitated on the surfaces of the mineral pigment is from about 20.0 to about 40.0 weight percent based on the weight of the dry composite pigment.

11. A composite pigment as defined by claim 1 wherein the composite pigment additionally comprises titanium dioxide, talc, mica or a mixture of these materials.

12. A composite pigment as defined by claim 1 wherein the difference between the percentage of particles less than 2 microns and the percentage of particles less than 0.2 microns is at least 67.2 and not more than 83.2.

13. A high brightness composite pigment which comprises a mineral pigment and precipitated calcium carbonate particles deposited as a coating on surfaces of particles of the mineral pigment, (a) wherein the composite pigment comprises a uniform coating of precipitated calcium carbonate on the surfaces of the mineral pigment particles, in contrast to non-uniform unevenly distributed discrete calcium carbonate particles or aggregates of calcium carbonate particles on the surfaces of the mineral pigment particles; and (b) wherein the difference between the percentage of particles less than 2 microns and the percentage of particles less than 0.2 microns is at least 67.2 and not more than 83.2.

14. A composite pigment as defined by claim 13 wherein the mineral pigment is kaolin clay, titanium dioxide, talc, mica or a mixture of two or more of these mineral pigments.

15. A composite pigment as defined by claim 14 wherein the mineral pigment is kaolin clay.

16. A composite pigment as defined by claim 15 wherein the kaolin clay is hydrous kaolin clay.

17. A composite pigment as defined by claim 15 wherein the kaolin clay is delaminated kaolin clay.

18. A composite pigment as defined by claim 15 wherein the kaolin clay is calcined kaolin clay.

19. A composite pigment as defined by claim 15 wherein the kaolin clay is a mixture of hydrous kaolin clay and calcined kaolin clay.

20. A composite pigment as defined by claim 13 wherein the amount of calcium carbonate precipitated on the surfaces of the mineral pigment is from about 5.0 to about 90.0 weight percent based on the weight of the dry composite pigment.

21. A composite pigment as defined by claim 13 wherein the amount of calcium carbonate precipitated on the surfaces of the mineral pigment is from about 10.0 to about 60.0 weight percent based on the weight of the dry composite pigment.

22. A composite pigment as defined by claim 13 wherein the amount of calcium carbonate precipitated on the surfaces of the mineral pigment is from about 20.0 to about 40.0 weight percent based on the weight of the dry composite pigment.

23. A composite pigment as defined by claim 13 wherein the composite pigment additionally comprises titanium dioxide, talc, mica or a mixture of these materials.

24. A composite pigment as defined by claim 13 wherein the content of particles less than 2 microns is at least 84.1% and not more than 93.7%.

25. A high brightness composite pigment which comprises a mineral pigment and in-situ precipitated calcium carbonate and which is produced by a plurality of carbonation cycles precipitating a calcium carbonate coating on surfaces of particles of the mineral pigment, wherein the composite pigment has a reduced amount of particles of less than 0.2 micron compared to the starting mineral pigment and an equivalent amount of particles of 1-2 microns compared to the starting mineral pigment, wherein the composite pigment comprises a uniform coating of precipitated calcium carbonate on the surfaces of the mineral pigment particles, in contrast to non-uniform unevenly distributed discrete calcium carbonate particles or aggregates of calcium carbonate particles on the surfaces of the mineral pigment particles; and wherein the content of particles less than 2 microns is at least 84.1% and not more than 93.7%.

26. A high brightness composite pigment as defined by claim 25, wherein the difference between the percentage of particles in the composite pigment that are less than 2 microns and the percentage of particles in the composite pigment that are less than 0.2 microns is at least 67.2 and not more than 83.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a scanning electron micrograph of a composite pigment with 20% calcium carbonate synthesized using 5 carbonation cycles, with 3.7% Ca(OH).sub.2 (slaked lime) added per carbonation cycle. FIG. 1 shows the presence of discrete calcium carbonate particles on the surface of the kaolin clay particles.

(2) FIG. 2 is a scanning electron micrograph of a composite pigment of this invention with 20% calcium carbonate synthesized using 9 carbonation cycles, with 2.1% Ca(OH).sub.2 (slaked lime) added per carbonation cycle. FIG. 2 shows the presence of a uniform calcium carbonate coating and the absence of discrete calcium carbonate particles on the surface of the kaolin clay particles.

(3) FIG. 3 is a scanning electron micrograph of a composite pigment with 30% calcium carbonate synthesized using 8 carbonation cycles, with 4.0% Ca(OH).sub.2 (slaked lime) added per carbonation cycle. FIG. 3 shows the presence of discrete calcium carbonate particles on the surface of the kaolin clay particles.

DETAILED DESCRIPTION OF THE INVENTION

(4) In accordance with the present invention, a high brightness, high gloss, high opacifying, high bulking composite pigment is provided which is comprised of a mineral pigment (preferably kaolin clay) and in-situ precipitated calcium carbonate.

(5) The kaolin clay of the composite pigment of this invention can be in several forms, examples of which include hydrous kaolin clay, delaminated kaolin clay, calcined kaolin clay and mixtures of two or more of these clays.

(6) Other mineral pigments can be used alone or in combination with the kaolin clay in this invention. Examples of such other mineral pigments include titanium dioxide, talc, mica and a mixture of two or more of these mineral pigments.

(7) In this application, the term in-situ precipitation will be understood to mean the precipitation of calcium carbonate in the presence of kaolin clay particles. It is believed the precipitation reaction forms a thin layer of calcium carbonate coating on the kaolin clay particles, and that such coating may bind the ultra fine kaolin clay particles together to form larger aggregates.

(8) In the precipitation reaction, a pre-determined amount of slaked lime (i.e., calcium hydroxide, such as can be made by adding water to quicklime) is added to kaolin clay to form a mixture. Carbon dioxide gas is then passed through the mixture until the pH of the mixture is about neutral (i.e., about 7.0).

(9) In this application, the addition of slaked lime (calcium hydroxide) to a kaolin clay slurry and subsequent passing of carbon dioxide gas through the kaolin clay/slaked lime mixture is referred to as a carbonation cycle. This invention uses a plurality (2 to 30) of carbonation cycles to obtain the desired composite pigment.

(10) The number of carbonation cycles depends on the amount of calcium carbonate desired in the resulting composite pigment. For example, a composite pigment with 5% calcium carbonate can be synthesized using 2 to 3 carbonation cycles, whereas a composite pigment with 30% calcium carbonate typically takes 10 to 15 carbonation cycles to synthesize. In general, the amount of slaked lime added to the kaolin clay slurry is about 2.0 to about 3.0% per carbonation cycle based on the weight of the dry kaolin clay.

(11) The present invention provides a method for making such composite pigments through precise control of the in-situ precipitation reaction process. The appropriate amount of calcium carbonate addition for each carbonation cycle is narrow and critical. An amount below the critical level makes the process inefficient, whereas an amount above the critical level results in composite pigments with undesirable particle size distribution and discrete PCC particles. The flow rate of CO.sub.2 gas and mixing of the slurry are also critical. The mixing can be improved by adding a baffle to the reaction vessel.

(12) The amount of calcium carbonate which is precipitated on the surfaces of the kaolin clay particles can vary depending on the desired final composite pigment. The amount of calcium carbonate generally is from about 5.0 to about 90.0 weight percent based on the weight of the dry composite pigment. A preferred amount of calcium carbonate is from about 10.0 to about 60.0 weight percent, more preferably from about 20.0 to about 40.0 weight percent, based on the weight of the dry composite pigment.

(13) The present invention is further illustrated by the following examples which are illustrative of certain embodiments designed to teach those of ordinary skill in the art how to practice this invention and to represent the best mode contemplated for carrying out this invention.

(14) For the following Examples, the following terms shall be defined as follows:

(15) Kaowhite S is a trademark for a delaminated kaolin clay product from Thiele Kaolin Company of Sandersville, Ga.; also referred to in this application as KWS.

(16) Printmax is a trademark for a fine particle size delaminated kaolin clay product from Thiele Kaolin Company.

(17) CLC refers to a cylindrical laboratory coater from Sensor & Simulation Products.

(18) LWC refers to a light weight coating study.

(19) RSV refers to relative sediment volume.

(20) KM refers to Kubelka-Munk.

(21) Slaked lime is a commonly known term for calcium hydroxide.

(22) Quicklime is a commonly known term for calcium oxide.

(23) PSD refers to particle size distribution.

(24) CC refers to calcium carbonate.

(25) Carbonation Cycle refers to the addition of slaked lime and subsequent passing of carbon dioxide through the mineral pigment/slaked lime mixture.

EXAMPLE 1

(26) A total of 3,000 g PCC grade pebble quicklime from Graymont (PA) was slaked in warm tap water with a lime to water ratio of 1:5.5. The lime slaking was performed in a 5 gallon high density polyethylene (HDPE) container equipped with a mixer by slowing adding the quicklime into the warm water in a controlled temperature range of 30 to 90 C., preferably 50 to 70 C., to yield slaked lime (Ca(OH).sub.2) with sufficient reactivity and fine particle size. The slaked lime slurry was degritted through a 325 mesh screen, which yielded a slurry at 17.8% solids.

(27) Laboratory scale (3,000 g) composite pigments were synthesized in a specifically designed 7 gallon stainless steel reactor with a porous ceramic disk-shaped gas diffuser in the bottom. A slurry of Kaowhite S delaminated kaolin was prepared from spray dried product at 15% solids.

(28) Two composite pigments with 20% calcium carbonate were synthesized using 5 and 9 carbonation cycles, and a composite pigment with 30% calcium carbonate was synthesized using 8 cycles. A predetermined amount of Ca(OH).sub.2 slurry was added to a KWS slurry, followed by delivering CO.sub.2 gas to the slurry until the pH drops to 7. This process was repeated until the desirable amount of calcium carbonate was precipitated.

(29) The experimental conditions and Sedigraph PSD, brightness, surface area of the resulting composite pigments along with KWS are reported in Table 1. The Scanning Electron Microscopy (SEM) images of these three composite pigments are shown in FIGS. 1-3.

(30) TABLE-US-00001 TABLE 1 KWS w/ KWS w/ KWS w/ 20% CC 20% CC 20% CC Composite Composite Composite Sample KWS Pigment 1 Pigment 2 Pigment 3 KWS Slurry at 16 16 14 15% Solids kg Ca(OH).sub.2 Slurry at 2,500 2,500 3,750 17.8% Solids g No. of Carbonation 5 9 8 Cycles Ca(OH).sub.2 Slurry Added 500 278 469 Per Cycle g Ca(OH).sub.2 Added Per Cycle 3.7 2.1 4.0 Based on KWS % CO.sub.2 Flow Rate 2.0 2.0 2.0 L/min. L/min. kg Ca(OH).sub.2 22.5 40.4 24.0 Sedigraph PSD % <5 m 97.8 97.9 98.6 98.2 % <2 m 84.4 89.2 84.1 89.4 % <1 m 68.0 73.1 60.6 68.3 % <0.5 m 46.8 47.4 37.4 39.6 % <0.2 m 23.0 22.0 16.8 14.4 GE Brightness 87.4 88.9 89.3 89.2 BET Surface Area m.sup.2/g 15.64 19.75 16.86 19.48 SEM micrographs FIG. 1 FIG. 2 FIG. 3

(31) The composite pigments synthesized with the above conditions yielded an unexpected particle size distribution, i.e., the content of ultrafine particles (<0.2 micron) was significantly reduced, whereas the content of fine particles (1-2 microns) was maintained or slightly increased compared to KWS, thus making the overall particle size distribution narrower.

(32) The SEM images showed that the composite pigments shown in FIGS. 1 and 3, which were synthesized with 3.7 and 4.0% Ca(OH).sub.2 addition per carbonation cycle (based on KWS), yielded discrete calcium carbonate particles on the kaolin clay surfaces. The composite pigment shown in FIG. 2, which was synthesized with 2.1% Ca(OH).sub.2 addition per carbonation cycle, yielded a uniform calcium carbonate coating on the kaolin clay surfaces. The surface area data also showed that when a uniform calcium carbonate coating was formed, the resulting composite pigment has a lower surface area compared to that when discrete calcium carbonate particles were formed. A pigment with a lower surface area has a lower binder demand, which is a desired property for a pigment.

(33) A CLC LWC offset coating study was performed for the composite pigments along with KWS as control. Coat weight, sheet gloss, GE and diffuse brightness and opacity are reported in Table 2. The data showed that the composite pigments shown in FIG. 2 with a uniform calcium carbonate coating (this invention) had significantly higher coated sheet brightness and opacity compared to the KWS control and the composite pigments shown in FIGS. 1 and 3 with discrete calcium carbonate particles formed.

(34) TABLE-US-00002 TABLE 2 KWS w/ KWS w/ KWS w/ 20% CC 20% CC 30% CC Composite Composite Composite Sample KWS Pigment 1 Pigment 2 Pigment 3 Coat Weight lb/3300 ft.sup.2 5.5 5.5 5.5 5.5 Gloss % 56 55 53 55 GE Brightness % 65.5 67.5 68.7 68.4 Diffuse Brightness % 65.9 67.4 68.7 67.9 Opacity % 84.6 84.7 85.6 84.7

(35) It was demonstrated that the amount of Ca(OH).sub.2 added per carbonation cycle is critical. When this amount is above a critical value, discrete calcium carbonate particles are formed on the kaolin clay surfaces. Only when this amount is below a critical value, a uniform calcium carbonate coating on the kaolin surface is formed. Composite pigments with a uniform calcium carbonate coating have been shown to provide desirable coating performance.

EXAMPLE 2

(36) A total of 3,000 g PCC grade quicklime from Cameuse Lime & Stone (Pittsburgh, Pa.) was slaked in warm tap water with a lime to water ratio of 1:5.5. The lime slaking was performed in a 5 gallon HDPE container equipped with a mixer by slowing adding the quicklime into the warm water in a controlled temperature range of 30 to 90 C., preferably 50 to 70 C., to yield a slaked lime (Ca(OH).sub.2) with sufficient reactivity and fine particle size. The slaked lime slurry was degritted through a 325 mesh screen, which yielded a slurry at 17.8% solids.

(37) A spray dryer feed slurry of KWS was diluted to 15% solids. In this study the effect of CO.sub.2 gas flow rate was evaluated.

(38) Two composite pigments with 30% calcium carbonate were synthesized using 15 carbonation cycles, with 2.1% Ca(OH).sub.2 addition per carbonation cycle and two CO.sub.2 gas flow rates (35 and 63 L/min.KgCa(OH).sub.2). The experimental conditions and brightness, Sedigraph PSD, surface area and rheology of the resulting composite pigments along with KWS are reported in Table 3. These composite pigments also have desirable PSD as those shown in Example 1.

(39) The data showed that Composite Pigment 5, which was synthesized with a higher CO.sub.2 gas flow rate, had a lower content of ultrafine particles compared to Composite Pigment 4, which was synthesized with a lower CO.sub.2 gas flow rate. Thus, the data showed that a higher CO.sub.2 flow rate (63 L/min.KgCa(OH).sub.2) is preferred over a lower CO.sub.2 flow rate (35 L/min.KgCa(OH).sub.2). Nevertheless, the PSD of composite pigments from the present invention is unique that only the content of the ultrafine particle was reduced while contents of fine particles with 1-2 micron sizes were maintained or even slightly increased, resulting in optimal PSD. As a result, these composite pigments are expected to have improved light scattering properties and coated sheet properties compared to composite pigments of the prior art.

(40) TABLE-US-00003 TABLE 3 KWS w/ KWS w/ 30% CC 30% CC Composite Composite KWS Pigment 4 Pigment 5 KWS Slurry at 15% Solids kg 14 14 Ca(OH).sub.2 Slurry at 17.8% Solids g 3,750 3,750 No. of Carbonation Cycles 15 15 Ca(OH).sub.2 Slurry Added Per Cycle g 250 250 Ca(OH).sub.2 Added Per Cycle 2.1 2.1 Based on KWS % CO.sub.2 Flow Rate 1.56 2.8 L/min. L/min. kg Ca(OH).sub.2 35 63 Sedigraph PSD % <5 m 98.0 98.1 98.1 % <2 m 84.9 90.4 90.0 % <1 m 70.8 70.7 71.7 % <0.5 m 53.3 39.3 37.8 % <0.2 m 23.1 10.9 6.8 GE Brightness 88.1 90.4 90.4 BET Surface Area m.sup.2/g 17.27 16.86 14.52 Solids % 67.1 65.0 66.7 SPMA Dispersant lb/ton 4.3 2.8 pH 6.5 8.5 8.6 Brookfield (#2@20 rpm) cP 160 1780 848 Hercules rpm@18 Dynes 575 561 128

(41) A CLC LWC rotogravure coating study was performed for the composite pigments along with KWS as control. Coat weight, sheet gloss, GE and diffuse brightness, opacity and rotogravure printability are reported in Table 4.

(42) Rotogravure printability was measured using the Heliotest total number of missing dots method. The Heliotest is an attachment for the IGT print tester and consists of an engraved disc with half-tone and printed line pattern, doctor blade system and a special ink. The print (110 mm in length and 7 mm in width) was made on the test paper, which is held against the printing wheel of an IGT print tester at constant force. The printability is measured in terms of length of print until 20 missing dots occur. The longer the distance from the beginning of printing to the 20.sup.th missing dot, the better the printability.

(43) TABLE-US-00004 TABLE 4 KWS w/30% CC KWS w/30% CC Composite Composite KWS Pigment 4 Pigment 5 Coat Weight lb/3300 ft.sup.2 5.0 5.0 5.0 Gloss % 47 44 43 GE Brightness % 67.4 69.8 71.1 Diffuse Brightness % 68.0 69.6 71.0 Opacity % 85.9 86.4 87.1 Printability 51 45 52 Length of print to 20.sup.th missing dots mm

(44) Note that both composite pigments yielded significantly improved coating performance compared to KWS. However, as expected from the PSD of the composite pigments, Composite Pigment 5 had improved coating performance compared to Composite Pigment 4. Coated sheet brightness and opacity were significantly improved compared to KWS and Composite Pigment 4, while the printability was maintained. This unique feature is advantageous as historically calcium carbonate pigments have been rarely used in rotogravure coating application due to poor rotogravure printability.

EXAMPLE 3

(45) The same quicklime as used in Example 2 was slaked and degritted through a 325 mesh screen. A spray dryer feed slurry of Printmax kaolin was diluted to 15% solids. Four composite pigments with 30% calcium carbonate were synthesized using 11, 13, 15 and 18 carbonation cycles, corresponding to 2.9, 2.4, 2.1% and 1.8% Ca(OH).sub.2 addition per carbonation cycle, respectively. The experimental conditions and Sedigraph PSD and brightness of the resulting composite pigments along with the Printmax kaolin feed are reported in Table 5.

(46) TABLE-US-00005 TABLE 5 Printmax w/ Printmax w/ Printmax w/ Printmax w/ 30% CC 30% CC 30% CC 30% CC Composite Composite Composite Composite Sample Printmax Pigment 6 Pigment 7 Pigment 8 Pigment 9 No. of Carbonation Cycles 11 13 15 18 Ca(OH).sub.2 Added Per Cycle 2.9 2.4 2.1 1.8 Based on Printmax % CO.sub.2 Flow Rate 65 65 65 65 L/min. kgCa(OH).sub.2 Sedigraph PSD % <5 m 99.0 99.2 99.8 98.8 98.7 % <2 m 92.8 92.9 93.9 93.7 94.6 % <1 m 76.2 68.3 71.4 70.2 74.1 % <0.5 m 47.2 36.4 38.5 36.8 38.9 % <0.2 m 20.5 13.5 14.9 13.1 15.5 GE Brightness 87.8 89.3 89.2 89.3 89.4

(47) A CLC LWC offset coating study was performed for the composite pigments along with Printmax kaolin as the control. Coat weight, sheet gloss, GE and diffuse brightness and opacity are reported in Table 6. The data are in excellent agreement with Example 1, namely a lower amount of Ca(OH).sub.2 addition per carbonation cycle, 1.8 to 2.4% based on weight of Printmax kaolin, yielded improved pigment properties and coating performance.

(48) TABLE-US-00006 TABLE 6 Printmax Printmax Printmax Printmax w/30% CC w/30% CC w/30% CC w/30% CC Composite Composite Composite Composite Sample Printmax Pigment 6 Pigment 7 Pigment 8 Pigment 9 Coat Weight 5.5 5.5 5.5 5.5 5.5 lb/3300 ft.sup.2 Gloss % 57 54 54 55 56 GE 67.9 69.8 70.0 70.4 70.7 Brightness % Diffuse 67.7 69.0 69.2 69.4 69.8 Brightness % Opacity % 85.4 85.6 85.7 85.8 86.0

EXAMPLE 4

(49) Pilot plant scale (70 lb.) composite pigments were synthesized in a specifically designed 55 gallon reactor with two AFD270 EPDM membrane disc diffusers in the bottom. Cameuse quicklime was slaked in a 50 gallon drum and degritted through a 325 mesh screen. Liquid CO.sub.2 from Air Gas South was used as the CO.sub.2 source. A spray dryer feed slurry of KWS was diluted to 15% solids. Three composite pigments with 30% calcium carbonate were synthesized using 5, 10 and 15 carbonation cycles, corresponding to 6.3, 3.2 and 2.1% Ca(OH).sub.2 addition per carbonation cycle, respectively. For comparison, a composite pigment was synthesized in the lab reactor using the same feed materials with 15 carbonation cycles. The experimental conditions, Sedigraph PSD and brightness of the resulting composite pigments along with KWS are reported in Table 7.

(50) A CLC LWC offset coating study was performed for the composite pigments along with KWS as the control. Coat weight, sheet gloss, GE and diffuse brightness and opacity are reported in Table 8. The data showed that the pilot plant scale reactor produced an optimum performance composite pigment with 30% calcium carbonate using 10 carbonation cycles (Composite Pigment 11), compare to lab scale composite pigments with 30% calcium carbonate using 15 carbonation cycles (Composite Pigment 5, Composite Pigment 8, Composite Pigment 13).

(51) TABLE-US-00007 TABLE 7 Pilot Plant Scale Lab scale KWS w/ KWS w/ KWS w/ KWS w/ 30% CC 30% CC 30% CC 30% CC Composite Composite Composite Composite Pigment Pigment Pigment Pigment Sample KWS 10 11 12 13 PCC (%) 30 30 30 30 No. of 5 10 15 15 Carbonation Cycles Ca(OH).sub.2 Added 6.3 3.2 2.1 2.1 Per Cycle Based on KWS % CO.sub.2 flow rate 75 75 75 75 (L/min. kgCa(OH).sub.2) Sedigraph PSD % <5 m 98.2 98.9 98.8 N/A 98.5 % <2 m 84.3 91.5 91.1 89.5 % <1 m 69.0 77.9 75.9 69.1 % <0.5 m 50.2 49.3 37.9 35.9 % <0.2 m 23.2 17.6 9.7 10.7 GE Brightness 88.1 90.0 90.1 89.2 89.9

(52) TABLE-US-00008 TABLE 8 Pilot Plant Scale Lab scale KWS w/ KWS w/ KWS w/ KWS w/ 30% CC 30% CC 30% CC 30% CC Composite Composite Composite Composite Pigment Pigment Pigment Pigment Sample KWS 10 11 12 13 Coat Weight 5.5 5.5 5.5 5.5 5.5 lb/3300 ft.sup.2 Gloss % 58 61 58 49 58 GE Brightness 68.8 72.0 72.8 71.7 72.9 % Diffuse 68.9 71.3 71.5 70.6 71.4 Brightness % Opacity % 85.0 86.4 86.7 85.9 86.6

(53) This invention has been described in detail with particular reference to certain embodiments, but variations and modifications can be made without departing from the spirit and scope of the invention as defined in the following claims.