Paint & Coatings Industry - May 2008 - (Page 56)

The Development of New SMA Esters as Pigment Waterborne Coatings I mproving pigment dispersion is a vital aspect of performance in water-based inks and coatings. The elements of dispersing are wetting of pigment agglomerates, separation of the agglomerates into discrete primary particles and maintenance of particle separation once it is achieved. Often, dispersion formulations can possess adequate pigment wetting, but not long-term stability (maintenance of particle separation). This creates problems such as gelling, loss of color, gloss or transparency (or opacity in the case of opaque pigments). The key to attainment of good pigment wetting/processability is to utilize a polymer with chemical moieties that have an affinity for the particle surface. This enhances pigment wetting by the polymer. In addition, the polymer architecture can also be designed so that adequate steric stability is obtained; this provides good long-term dispersion stability by maintaining particle separation. Hydrophobicity Index Since esters of styrene maleic anhydride copolymers (SMA® esters) have been successfully used in both waterborne and solventborne pigment dispersions, FIGURE 1 | Structure of SMA ester. O OC CO CH y ( CH CH )x( CH ) ( CH CH 2 x O ) (CH C OR CH (1-y) n CO OH ) FIGURE 2 | SMA ester solutions. Foam height vs. time after mixing. 245 Foam Height (ml) 225 205 185 165 145 125 0 30 Time (sec) 60 300 NTX7633 NTX7634 NTX7635 NTX7636 NTX7637 NTX7638 NTX7639 NTX7643 Ester A Ester B an attempt was made to further understand why these materials work so well. These SMA esters are polymeric surface active agents and they contain both hydrophilic anhydride, acid and ester groups, as well as hydrophobic styrene and ester chain groups (R), as shown in Figure 1. To further quantify the balance between hydrophilic groups and hydrophobic groups within the molecules, a hydrophobicity index was defined as: total molecular weight of the hydrophobic groups/ total molecular weight of the SMA ester. For the two most commercially successful SMA esters that are used as pigment dispersants, SMA Ester A and SMA Ester B, the hydrophobicity index values are 74.3 and 71.1, respectively. To design improved dispersants, it was thought that perhaps the hydrophobicity index of the new esters would need to have a similar value to that of either SMA Ester A and SMA Ester B. To study this, a series of SMA alkyl esters were made from SMA resins with styrene to maleic anhydride ratios ranging from 1:1 up to 4:1, and using alkyl alcohols ranging from C3 (propyl) to C18 (stearyl). Within this group, esters were chosen that have a hydrophobicity index ranging from 66.5 – 77.1, which includes the range of SMA Esters A and B, and these are highlighted in Table 1. To test the pigment dispersing capabilities of the new esters, pigment dispersions were made with lithol rubine, phthalocyanine blue and diarylide yellow pigments, and the initial dispersion viscosities, aged dispersion viscosities, color development and ink properties were compared with dispersions and inks made with SMA Ester A and SMA Ester B. Unfortunately, all of the new esters produced dispersions that had both higher viscosities and much less color development than those made with the SMA Ester A and SMA Ester B. At this point, it was concluded that while the hydrophobicity index of the dispersant may be important, the type of alcohol and the resulting ester chain may also be important. Therefore, additional esters were made with different types of alcohols. The hydrophobicity indices of these esters are shown in Table 2 in comparison with those of SMA Ester A and SMA Ester B. Note that all of the new esters except NTX 7643 have hydrophobicity indices that fall within the range of SMA Esters A and B (71.1 - 74.3) By William R. Dougherty, Robert B. Adams and Disa Grant | Sartomer Company, Inc., Exton, PA; and Lisa Fine | Flexo Tech, Inc., Columbus, OH 56 MAY 2008 | W W W . P C I M A G . C O M http://WWW.PCIMAG.COM

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Paint & Coatings Industry - May 2008 Contents Viewpoint Industry News Calendar of Events Company News Mergers and Acquisitions Names in the News Charlotte Dining Guide Exhibits-in-Print Waterborne Alkyds Break Through the Performance Barrier New Matting Agents for Waterborne Coatings and Varnishes Silicon-Based Technology for the Coatings Industry High-Performance Microgrinding The Development of New SMA Esters as Pigment Dispersants for Waterborne Coatings and Inks The Right Choice New Coating Technology Expands Color Choices for Vinyl Building Products BioPreferred Federal Biobased Products-Preferred Procurement Program European Union's REACH Regulation Sustainability - The New Nano Improved Dirt Pickup Resistance Critical to Future Coating Innovation NanoNews Protective Coatings NDT - Energy-Saving Paint Static Electricity - The Hidden Danger in Hazardous Areas Wacker Chemie - A Profile of Success Materials Watch Products and Literature Classifieds Advertiser Index

Paint & Coatings Industry - May 2008

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