In the most general terms, wood coatings are materials that are applied to wood to enhance the natural beauty of the wood and protect it from damage. While this may seem simple, the wide range of application conditions, end uses, and customer expectations for wood finishing require formulators to carefully select the materials they use in order to enhance the appearance and performance of their wood coatings, paints, stains, lacquers, and finishes.
Eastman Materials for Wood Coatings
Eastman produces a number of products that allow coatings formulators to create high quality wood finishes that satisfy important market drivers including higher durability surfaces, optimized unit cost, improved appearance, and increasing regulatory requirements. The product families listed below provide unique benefits to coatings formulations for wood surfaces and are commonly used to enhance the appearance and durability of finishes.
The benefits and recommended usage of these products in wood coating and finish formulations is highlighted in detail below.
Eastman CAB
Cellulose esters, specifically cellulose acetate butyrate, are natural, biobased polymers that are commonly used as coresins or additives in solvent-based coating and finish formulations. Eastman Cellulose Esters find widespread use in two component acrylic urethane coatings, radiation curable coatings, and acid-cured coatings for wood substrates and provide a number of benefits to solvent-borne wood coating systems including:
Faster hardness development
Increased resistance to yellowing caused by UV light
Improved flow and leveling characteristics
Reduced variation of film thickness
Improved wetting, penetration, and pore definition
Reduction of shrinkage in UV cure systems
Protection from mechanical damage
Selecting the appropriate cellulose acetate butyrate grades to screen for your application is typically based on three variables; butyryl content, hydroxyl content, and viscosity.
Many key properties of a wood coating system such as hardness, reactivity, and chemical resistance can be optimized by formulating with a CAB that has the correct properties for your system and application. The impact of balancing butyryl content, hydroxyl content, and viscosity are described below.
For a CAB with Greater
Choose a CAB with
Compatibility
Higher Butyryl Content
Solubility
Higher Butyryl or Hydroxyl Content
Reactivity
Higher Hydroxyl Content
Toughness
Higher Viscosity
Hardness
Lower Butyryl or Higher Hydroxyl Content
Chemical Resistance
Lower Butyryl Content
Flexibility
Higher Butyryl Content
Moisture Resistance
Lower Hydroxyl Content
Adhesion
Higher Butyryl and Hydroxyl Content
In general, Cellulose acetate butyrate polymers with a higher butyryl content have greater compatibility with other resins and are recommended for initial screening when formulating a coating for wood. Once compatibility has been established other grades of cellulose acetate butyrate can be evaluated to optimize specific physical properties of the coating formulation. Suggested cellulose acetate butryate resins for initial screening and recommended usage levels are listed in the table below.
Eastek™ are water based dispersions of sulfopolyester resins that are produced by melt phase polymerization of glycols and diacids followed by dispersion in water. On dispersion, the polyesters in Eastek™ form micellar aggregates approximately 10 - 50 nm in diameter that are electrostatically stabilized in water without the need for surfactants of amine neutralizing additives.
Comparison to Other Waterborne Polymers
Eastek™ dispersions have good compatibility with most ingredients commonly used in wood coating formulations and are often used as a binder in waterborne wood primers and intercoat systems for wood. Eastek™ polyesters provide a number of unique benefits to wood primers including:
Improved appearance of coatings on a variety of wood types
Harmonizing effect: improved penetration ensures uniform color and colored stain appearance
Low odor
Non-skinning
Fast drying time
Excellent adhesion
Outstanding gloss and clarity
Easy to formulate
Resistant to mechanical damage
Lightfastness and resistance to yellowing
Most Eastek™ polyesters will form films without the use of a coalescent, however, if desired films can be plasticized by blending with a lower Tg Eastek™ grade or a suitable co-solvent. Because there are no stabilizing amines or surfactants in Eastek™ dispersions the viscosity if independent of pH and adjustments of viscosity during the coating process are not needed. Eastek™ polyester grades that are suggested for use in wood primer formulations are listed in the table below.
Property
Eastek™ 1000
Eastek™ 1100
Eastek™ 1200
Eastek™ 1300
Eastek™ 1400
Water Dispersibility
++
+++
+
++
++
Tg (°C)
38
55
63
36
29
Film Forming Temp (°C)
< 5
5
27
12
< 5
Hydroxyl Number
5.0
5.3
< 10
< 10
5.0
Solids (wt%)
30
33
30
30
30
pH
6.0
6.2
6.6
6.0
6.0
Viscosity (cP)
60
89
99
14
15
Eastman SAIB
Eastman Sucrose Acetate Isobutyrate (SAIB) is often used as an extender in wood sealers and top coats. When added to sealers and coatings it may serve to increase nonvolatile content by 10-15% solids without any significant increase to viscosity. In nitrocellulose lacquers that also contain hard resins and plasticizers, Eastman SAIB can replace the nonoxidizing alkyd resins that are commonly used to produce a low-viscosity lacquer at a given solids level. Starting point formulations for SAIB into nitrocellulose wood lacquer are available upon request.
Eastman Solus™ 2100
Eastman Solus™ 2100 Performance Additives are a ultra low molecular weight cellulose ester that offers improved compatibility with alkyd resins when compared to standard cellulose acetate butyrate. Alkyd urethane wood coatings for furniture are typically formulated utilizing nitrocellulose, particularly where low gloss is required. Nitrocellulose, however, imparts excessive yellowing in the coating and replacing it with Solus™ 2100 reduces yellowing and improves the UV durability of the finish. The benefits of incorporating Solus™ 2100 into an alkyd urethane wood finish offers the following benefits:
Improved resistance to yellowing under UV light
Improved dry-to-touch time
Excellent flow and leveling characteristics
Higher solids content at application viscosity. Lower VOC levels.
Polyolefin Adhesion Promoter
Wood-filled polyolefin composites are rapidly gaining global popularity. The main applications for these composites is furniture, decorative profiles, and as a replacement for exterior wood. Propylene is one of the most common polyolefins used in these composites and can often cause adhesion problems during the application of paint to these wood-plastic composites. Eastman chlorinated and non-chlorinated polyolefin adhesion promoters are used in primers, paints, and finishes to improve adhesion to polypropylene, polyethylene, and other plastics and allow for wood-filled polyolefin composites to be painted like natural wood.
