Powder Coating Wood Substrates Paul Stiglbauer

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Powder Coating Wood SubstratesPaul Stiglbauer
Advanced Engineered Wood Composites
Center
Advisor Stephen M. Shaler, PhD
This project is funded by the USDA CSREES Wood
Utilization Research Program. Thanks to
Professor Robert Rice, University of Maine for
his advice and assistance with
measuring electrical conductivity of MDF.
Powder Coating at the University of Maine
Industrial Significance
Abstract Powder Coating is a
finishing technology in which dry paint particles
are electrostatically charged and applied to a
grounded part. The process begins with powder
particles being fluidized and charged by
friction or an electrode. The charged particles
are then propelled towards the work piece by
airflow, electric fields, or both. Theses
charged particles are electrically attracted
to the grounded work piece (Lehr 1991) (Hughes
1984). Dry wood is generally classified as a
dielectric material with a resistance between
1013 and 1015 ohms of resistance (Torgovnikov
1993). As a result, powder coating wood
products is difficult due to its lack of
conductivity. However, wood will approach the
properties of a semi-conductor as its surface
moisture increases. In addition to moisture,
temperature has a pronounced effect on the
conductivity of wood. As temperature and
moisture content increase, the conductivity of
wood increases (Skaar 1988). As a
result, powder coating wood products generally
consists of preheating a sample with enough
moisture to ensure conductivity. Preliminary
conductivity measurements on MDF have been
performed to date.
Sales North America 1 Billion Europe
1.5 Billion Rest
600 Million Growth North America 7
Percent Europe 5.8 Percent Rest
11.5 Percent

• Between 1986 and 1996 powder
• coating sales increased by over
• 300 percent.
• Currently
• 5,000 plus powder coating systems
• operating in North America
• Represents 10 percent of the total
• finishing market.

• Nordson Surecoat Spray Gun
• System Purchased 10/02
• Nordson Flexicoat Spray Booth
• Coming 07/03
• Powder Coating Lab to be
• Constructed Summer 2003

(Tullo 2000)
Powder Coating Study Objectives
Principles of Powder Coating Wood Substrates

• Composed of Pigments, Resins, and
• Additives.
• Can be either Thermosetting or
• Thermoplastic
• 95 Thermosetting

• Develop models relating temperature
• and moisture content to MDF conductivity and
• successful powder coating
• Successful powder coating will be determined
• by coating thickness on both faces of sample

Hypothetical Results
Powder

• Determine Optimal Powder Coating Window for
• conductivity and time.

• Powder is fluidized in a hopper
• Air is percolated through a membrane
• in the bottom of the hopper
• The powder behaves like a fluid and
• can be transported by a powder pump

Fluidizing
Preliminary Data (Electrical Conductivity of MDF
Surface)

• Needle-like electrode
• Applied voltage creates a local ion field
• Particle pass through via air flow and pick up
  ions
• Usually negative polarity
• Charged particles transported to preheated work
  piece
• piece by air flow and ion wind

A B C D E F
Charging

• Ions smaller and higher mobility than paint
  particles
• While in flight, ions collide repeatedly with
  neutral air molecules
• Momentum exchange takes place, resulting in an
  induced
• motion of the air itself in the same directions
  as the ions
• Accounts for main current path between gun and
  work piece
• This electrically induced movement is ion wind
  (Hughes 1984)

Within Sample Variation
Measurement Repeatability
Transfer

• Conventional Heating
• Infrared Heat
• Ultra Violet Light

Curing

• Why Powder Coat?
• Low VOC emissions
• Powder lt 1 percent by weight
• Water-based paint 15 percent
• Conventional wet paints 66
• percent
• Higher efficiency
• Powder up to 95 percent
• Wet paints less than 60 percent

Moisture Content Effect on Conductivity
Temperature Effect on Conductivity
References Lehr, W.D. 1991. Powder Coating
Systems. Mc-Graw-Hill, Inc. New York, New York.
255 pp. Tullo, A. 2000. Business. Chemical
and Engineering News. 78(41)19-28. Powder
Coating Institute. 1997. Powder coatings
technology of the future, here today.
http//www.powdercoating.org/media/casestudies/fut
ure.htm. July 02, 2002. Benson, P. 2002. The
role of thermoplastic coatings for metal
protection and corrosion protection.
Proceedings from Powder Coating 2002.
September, 24-26, 2002. Indianapolis,
Indiana. Hughes, J.F. 1984. Electrostatic
Powder Coating. John Wiley Sons. New York,
New York. 121 pp. Skaar, C. 1988. Wood-Water
Relations. Springer-Verlag. New York, New York.
283pp. Torgovnikov, G.I. 1993. Dielectric
Properties of Wood and Wood-Based Materials.
Springer-Verlag. New York, New York. 196 pp.

• Furniture
• Cabinets

Applications
Lamineer Black Powder Supplied by Morton Powder
Coatings. Image from reflected light using Leica
TCS-SP2 confocal microscope. Field of view 300 µm
x 300 µm.