How to Troubleshoot Common Coating and Ink Problems

By Jeff Nixon of Glass Coatings and Concepts; Douglas Canfield of Casso-Solar Technologies; Dino Fenzi of Fenzi S.p.A.; and Kris Vockler of ICD High Performance Coatings.
May 2, 2013
FABRICATION

Editor’s note: This article is the second part of a two-part series on inks and coatings. Part one addresses proper drying and curing techniques.

Possible defects and solutions for ceramic inks

Problem

 

Potential Causes

 

Potential Solutions

Delamination of film (peeling or flaking off during processing, handling or mechanical conveyance) 
  • Poor green strength of medium
  • Substrate contaminated with oil, grease or other substances
  • Surface moisture on substrate
  • Incomplete drying prior to firing
 
  • Increase green strength through medium selection
  • Check part washing system for contamination
  • Check environment for drips, leaks or airborne aerosols
  • Ensure complete drying of part before coating and heattreating processes
Pinholes (defects smaller than 1 millimeter in diameter through which background light can be seen) 
  • Old or settled enamel
  • ƒContamination of substrate (fabricating debris, silicone, oil grease, dust, etc.)
  • ƒSurface moisture on substrate
  • ƒIncomplete drying prior to firing
  • ƒScreen mesh plugged
  • ƒToo fast drying
 
  • Thoroughly remix enamel or replace with newer enamel
  • ƒCheck part washing system for contamination
  • ƒCheck environment for drips, leaks or airborne aerosols
  • ƒEnsure complete drying of part before coating and heattreating processes
  • ƒClean or replace screen
  • ƒDecrease drying rate
Blisters (bubble-like or puffy defects, sometimes rupturing the paint surface) 
  • Too fast drying
  • ƒFilm too heavy
  • ƒHeavy contamination on substrate
  • ƒToo much convection
 
  • Decrease drying rate
  • ƒApply thinner coat
  • ƒCheck substrate for contamination and determine source
  • ƒUse less convection and, if necessary, increase infrared drying
Linear streaks perpendicular to direction of part travel 
  • Chatter
  • ƒRoll deformation
 
  • If spacing between streaks is tight and irregular, check for chatter of squeegee or part, decrease squeegee angle
  • ƒIf spacing between lines equals circumference of roll, check for flat spots or other deformation on the roll
  • ƒCarefully align conveyor speeds, application equipment
Fisheyes, craters ƒ
 
  • Silicone contamination
  • ƒIncompatible contaminates in the paint, application equipment, or glass substrate:
  • Oil-based enamels: Water, polar solvents
  • Water-based enamels: Oil, grease, non-polar solvents
 
  • Ensure good housekeeping in coating preparation and application area.
  • ƒThoroughly clean application equipment when changing over between incompatible paints or enamels
  • ƒCheck environment for drips, leaks or airborne aerosols
Cracking
 
  • Too fast drying
  • ƒFilm too heavy
  • ƒToo much convection
 
  • Decrease drying rate
  • ƒApply thinner coat
  • ƒUse less convection and, if necessary, increase IR
Poor adhesion after heat treatment 
  • Under-fired part
  • ƒContamination of substrate
  • ƒEnamel too ‘hard’ for process or application
 
  • Increase firing temperature and/or time
  • ƒEnsure clean glass before coating
  • ƒSelect ‘softer’ enamel suitable to the process and application

Potential defects and solutions for silicone coatings

Problem

 

Potential Causes

 

Potential Solutions

Delamination of film (peeling or poor adhesion) 
  • Substrate contaminated with oil, grease or other substances
  • ƒSurface moisture on substrate
  • ƒProduct thickness is incorrect
 
  • Check part washing system for contamination
  • ƒCheck environment for drips, leaks or airborne aerosols
  • ƒEnsure complete drying of part
Pinholes 
  • Contamination of substrate
  • ƒScreen mesh plugged
 
  • Check part washing system for contamination
  • ƒClean or replace screen
Blisters (bubble-like or puffy defects, sometimes rupturing the paint surface) 
  • Too fast drying
  • ƒFilm too heavy
 
  • Decrease drying rate
  • ƒApply thinner coat
Mud cracking in coating ƒ 
  • Too much air movement
  • ƒDrying too fast
 
  • Reduce convection, air supply or exhaust
  • ƒUse more infrared with minimal air movement

Possible defects and solutions for organic inks, two-part inks and thermosetting inks

Problem

 

Potential Causes

 

Potential Solutions

Delamination of film (peeling or poor adhesion) 
  • Substrate contaminated with oil, grease or other substances
  • ƒSurface moisture on substrate
 
  • Check part washing system for contamination
  • ƒCheck environment for drips, leaks or airborne aerosols
  • ƒEnsure complete drying of part
  • ƒCorrect wet coating thickness
Pinholes 
  • Contamination of ink or substrate
  • ƒScreen mesh plugged
  • ƒSolvent boiling from ink
 
  • Check part washing system for contamination
  • ƒClean or replace screen
  • ƒCheck for particles in coating
Blisters (bubble-like or puffy defects, sometimes rupturing the paint surface) 
  • Too fast drying
  • ƒFilm too heavy
  • ƒSurface is skinning oven
 
  • Decrease drying rate
  • ƒApply thinner coat
  • ƒCheck substrate for contamination and determine source
  • ƒUse more convection and, if necessary, reduce the IR
Fisheyes, craters ƒ Contamination 
  • Thoroughly clean application equipment
  • ƒEnsure good housekeeping in coating preparation and application area.
Cracking 
  • Too fast drying
  • ƒFilm too heavy
  • ƒToo much convection
 
  • Decrease drying rate
  • ƒApply thinner coat
  • ƒCheck substrate for contamination and determine source
  • ƒUse less convection and, if necessary, increase IR
Poor adhesion ƒ 
  • Cure temperature not reached
  • ƒContamination of substrate
  • ƒCure is not through thickness of coating
 
  • Increase drying temperature and/or time
  • ƒEnsure clean glass before coating
  • ƒUse more infrared and less convection
Delamination of film (peeling or poor adhesion) 
  • Substrate contaminated with oil, grease, or other substances
  • ƒSurface moisture on substrate
 
  • Check part washing system for contamination
  • ƒCheck environment for drips, leaks or airborne aerosols
  • ƒEnsure complete drying of part
  • ƒCorrect wet coating thickness

The author is general manager of Glass Coatings and Concepts, a manufacturer of ceramic inks and coatings.