By Gaurav Chandra Srivastav
Stain Resistance or Graffiti Resistance
Failure of the paint to resist absorption of dirt and stains
Reasons:
- Not sufficient surface slip
- Soft Top Coating
- Use of incorrect wetting & dispersing agent in formulation
- Not sealing the capillaries of paint film
Solutions:
- Identifying the correct wetting & dispersing agent
- Identify the correct dosage of surface sealing additives
- Ensure dirt pickup resistant additives in formulation
- Ensure antiblocking agents in formulation
- Ensure heat resistance of cured binder film (It should not get soft & tacky at high temperatures)
Stone Chipping
Mechanical damage to the paint surface and film build due to flying stones (e.g. chippings, stones and debris).
Reasons:
Film flexibility is not as per specification
Incorrect calculation of age of film
Stones of various weight, shape and size are flung onto the paintwork at varying levels of energy (velocity and size). Depending on the impact force, the top-coats and also the primer/surfacer coats can be damaged down to the substrate (metal, plastic or electrocoat). Moisture may then penetrate the paint film and further flaking can occur.
Solutions:
Check & ensure the use of flexibilizer as per specification in formulation
Selection of binder & calculation of aging of film
There is no total protection against stone chips. Areas most greatly at risk can be given treatment of additional anti-chip and underbody protection coatings for extra protection to avoid corrosion of the substrate. (E.g. appropriate primer and/or the use of a soft face additive in the top-coats or clear lacquer to increase to increase the flexibility).
Telegraphing or Picture Framing
Telegraphing is a defect that involves the reproduction of surface features on an undercoat or substrate by the coating applied over it due to fingerprints, wipe marks, detergent residues.
Picture Framing is an effect of non-uniform color that can appear when a wall is painted with a roller, but is brushed at the corners, architraves and cornices. The brushed areas generally appear darker, resembling the “frame” of a “picture”.
Reasons:
The main cause of this defect is flow due to surface tension: flow away from residues such as finger oils and sanding dirt or flow away from sharp edges of sand scratches.
Aluminum flakes in automotive metallic coatings line up along fingerprints or wipe marks, leaving silvery streaks noticeable from a considerable distance.
Solutions:
- Decrease the surface tension of top coat or base coat
- Ensure proper cleaning of surface before coating
- Apply wet on wet coating & design product accordingly
- Prevent the defects of primer while designing formulation
Uneven Gloss or Poor Sheen Uniformity
Uneven gloss is a patchy appearance on the surface giving uneven sheen levels.
Reasons:
- Incorrect thinning solvent
- Uneven absorption by the substrate
- Moisture contamination
- Incorrect missing of paint (2K systems)
Solutions:
- Check datasheet & ensure for correct thinner
- Apply sealer coat or patch the porous substrate
- Ensure air supply to pump id dry & moisture free
- Ensure moisture is not in surface between or after application
- Check mixing ratio in 2K systems (consult datasheet)
- Ensure surface additive in formulation & dosage