Combined Use of CAB Esters and Thermoset Acrylic Polymers in Solvent-Based Paint Formulations

1. Cellulose Esters General Information:

1.1 Cellulose Acetate (CA): The cellulose ester type with the lowest solubility in common paint solvents and compatibility with other paint polymers, and therefore its use in paint formulations is highly limited. 1.2 Cellulose Acetate Propionate (CAP): A cellulose ester type with improved solvent solubility and compatibility, commonly used particularly in applications requiring odorless dry film. 1.3 Cellulose Acetate Butyrate (CAB): The cellulose ester type with optimized solvent solubility and compatibility with other common paint polymers, featuring the most general-purpose application. Eastman cellulose acetate butyrate coding system is as follows. The important physical properties of commonly used CAB types from a paint formulation technique perspective are given in Table 1.

*: Viscosity, according to ASTM D817 (Formula A) and D1343 **: Glass Transition Temperature, °C

2) Advantages That CAB Use Brings to Formulation

CAB addition at 1–50% solid binder ratio to paint formulation according to the target application provides the following advantages: •Viscosity control / thinning ratio control, •Physical drying speed, •Flow / sag control, •Inter-coat adhesion, •Due to OH functionality, participation in cross-linking formation within thermoset binder systems resulting in higher physical and chemical resistance, •High solvent resistance, •High exterior durability, •Effect pigment orientation, •High solvent resistance, •Earlier and higher stackability, •Better gloss development, •UV stability, •Low plasticizer migration. There is no simple and definitive rule regarding the appropriate CAB type and quantity to be used in formulation; the following criteria should be considered: •The solvent system used in paint formulations, •The polymer types used in paint formulations, •The properties expected to be improved.

3) Solubility

CAB esters are polymers compatible with many common paint solvents and soluble in economical solvents, and are soluble in the following solvents: • Esters, • Ketones, • Glycol ethers, • Glycol ether esters, • Aromatic hydrocarbon solvents and alcohol blends. Additionally, they are tolerant to thinning with aromatic hydrocarbon solvents and alcohols.

4) Compatibility

The term "compatibility" is generally understood to mean that the film resulting from the cellulose ester/polymer combination is not transparent, clear or cloudy. Sometimes different laboratories may bring different compatibility interpretations to this combination. The reason for this difference is generally due to differences in the solvent system used and/or differences in drying/curing conditions or dry film thickness. Each laboratory should conduct its own compatibility tests and evaluation for specific applications.

5) An Example of a Compatibility Study

a) CAB Esters were prepared as a solution containing 15% solids in n-butyl acetate at 99% purity and above, b) Thermoset acrylic polymers to be tested for compatibility were thinned with an additional 10% n-butyl acetate, c) Mixtures were prepared from solutions (a) and (b) at the weight ratios specified in Tables 2 and 3, and; • Homogeneity and transparency of the mixture in wet phase • The mixture was applied to glass surface as a 90 micron wet film, left at room temperature for 10 minutes, then oven-dried at 80°C/30 min., and the clarity and appearance quality of the resulting dry film were evaluated.

Results

For Krolac 263 SS 60 in Tables 2A and 2B, For Krolac 295 SS 51 in Tables 3A and 3B.

Table 2A – Wet mixture

Table 2B – Dry film

Table 3A – Wet mixture

Table 3B – Dry film

6) Conclusion

The incorporation of the correct type and proportion of CAB into OH functional thermoset acrylic resin formulations cured with amino resins or isocyanate prepolymers is a valuable modification technique that imparts unique and specific properties to paint formulators. Sometimes different laboratories may bring different interpretations to the compatibility behavior of CAB esters with acrylic polymers. The reason for this difference is generally due to differences in the solvent system used and/or differences in drying/curing conditions or dry film thickness. Each laboratory should conduct its own compatibility tests and evaluation for specific applications. We hope this work serves as a simple and practical model for our colleagues working in the paint industry. Muhammet Demirkıran Sales Manager Paints, Inks and Adhesives Group Kempro Kimyasal Maddeler ve Dış Tic. A.Ş.    

7) References 1. Eastman Kodak Publication E-309 B, September 2002 2. Eastman Kodak Publication E-325-H, 10/14 3. Surface Coatings, Science & Technology, by Swaraj Paul 4. Resins for Surface Coatings by H. Coyard, P. Deligny, N. Truck 5. Organic Coatings: Science and Technology; by Zeno W. Wicks, 2007