Why use Eastman cellulose esters for coatings and inks?

Good surface appearance

Whether the defects are in the paint, on the substrate, or caused by additives, the addition of CAB can remove the effects of paint and surface contamination (WD-40® is an example). Good wetting on compromised surfaces yields overall improvement in finished appearance.

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Good flow and leveling

Due to their rheology profile (near Newtonian at low shear) and surface tension equalization properties, cellulose esters—especially the lower-molecular-weight grades—improve the flow and leveling of a coating.

Spray coating usually produces some irregularities that must level out as the paint dries to avoid defects such as orange peel, mounding, and cratering. When the coating is too elastic, too viscous, or both, leveling forces are inadequate to overcome these defects. Using cellulose esters allows you to overcome this problem.

Levels of 1%–10% CAB (based on resin solids) are used with thermosetting acrylic resins or polyester resins for flow control.

Good sag resistance

In many coating formulations, additions of 1%–5% CAB (based on resin solids) will improve flow and leveling while maintaining good sag resistance.

Rapid film formation

CAB can be used as a film former, as a reactive polyol in curing coatings, and as an additive to other film formers.

The reactive hydroxyl groups contained in CABs may be cross-linked with urea-formaldehyde, melamine, or polyisocyanate resins. They provide the ability to formulate a variety of curing coatings and inks. Selecting higher-hydroxyl cellulose esters such as Eastman CAB 553-0.4 for use in curing systems produces films with high cross-link density and excellent chemical and physical properties.

Due to its high glass transition temperature (Tg), CAB provides excellent hardness and hardness development.

As an example, the addition of 15%–30% CAB (based on resin solids) in thermosetting acrylic enamels provides a coating that dries like a lacquer on a hard surface and can be sanded to remove orange peel, sags, or embedded dirt. Spot repairs can then be made with the original coating composition. During the final bake at converting temperature, the enamel reflows to eliminate sand marks and provides a glossy thermoset finish.

Fast dry to touch

Due to its high Tg, CAB provides rapid dry-to-touch times for reduced dirt pickup. It increases productivity and prevents surface defects with fast dry to touch. Reduction in dry time also decreases the occurrence of coating contamination, enables coatings to harden faster for early mar resistance, and speeds turnaround times.

Enhanced pigments dispersion

Due to their rheological properties, cellulose esters prevent color separation in multi-pigmented systems (commonly called pigment flooding and floating).

Cellulose esters also prevent pigment separation and provide good pigment wetting. Because of its good pigment-wetting characteristics (particularly the higher hydroxyl types), CAB is used to enhance pigment dispersion without negative effects on coating performance.

As an illustration, 10%–20% CAB (based on resin solids) is used with both thermoplastic and thermosetting acrylic resins as a pigment dispersion medium.

Outstanding metal finish

Used as viscosity control agents, cellulose esters provide excellent pigment flake orientation and give coatings a brighter finish with more flop.

CAB provides excellent redissolve resistance and prevents strike-in caused by solvents in the topcoat.

Heat and moisture stability

Due to its cellulosic polymer nature and its pendant groups, CAB has good heat and moisture stability (exterior durability). Eastman CAB films are water resistant, although they do transmit a degree of water vapor.

Other factors being equal, higher butyryl content leads to higher moisture resistance. This property may be altered by the addition of plasticizers, waxes, resins, and other additives or by a high hydroxyl level. If any degree of moisture resistance is required from a film of high-hydroxyl butyrate, it is necessary to react the hydroxyls with an isocyanate or amino resin or some other reactive intermediate.

Ultraviolet stability

One of the important characteristics of CAB in coatings is its ability to resist degradation due to exposure to ultraviolet light compared to other cellulose derivatives such as nitrocellulose. This property is very important for automotive coatings that need superior exterior durability. It is also important when producing white or pastel wood coatings that don’t yellow when exposed to sunlight.