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Invisible but functional
UV-protecting coatings
Sirris Smart Coating Application Lab
27/10/2016 1© sirris | www.sirris.be ...
Weathering of materials
27/10/2016 2© sirris | www.sirris.be | info@sirris.be |
Solar radiation (UV)
Moisture (dew, humidi...
What is UV radiation/light?
27/10/2016 3© sirris | www.sirris.be | info@sirris.be |
Damage by UV radiation
27/10/2016 4© sirris | www.sirris.be | info@sirris.be |
Loss of mechanical properties and
gloss, di...
 Absorption of UV-radiation by polymer or impurity
 Polystyrenes, aromatic polyesters, aromatic polyurethanes, …
absorb ...
Stabilisation against UV light
27/10/2016 6
 By mixing in the material/plastic
 By coating
 Liquid light stabilizers in...
Stabilizers: UV absorbers
27/10/2016 7
 Organic UV absorber molecules:
 2-(2-hydroxyphenyl)-benzotriazoles (BTZ)
 hydro...
Stabilizers: UV absorbers
27/10/2016 8
 Why are UV absorbers photostable?
 ESIPT mechanism: rapid and efficient dissipat...
Stabilizers: UV screeners
27/10/2016 9© sirris | www.sirris.be | info@sirris.be |
 Inorganic oxide particles TiO2, ZnO, C...
Stabilizers: UV screeners
27/10/2016 10
 Inorganic oxide particles TiO2, ZnO, CeO2
 Mechanism:
 Bandgap absorption
 Sc...
Stabilizers: Radical scavengers
27/10/2016 11
 Interrupt the chain reaction of polymer degradation
 2 different classes:...
UV-protecting coatings
27/10/2016 12
 Combination of UV
stabilizers in clearcoat:
 1,5-2% UV absorber:
color retention
...
UV-protecting coatings
27/10/2016 13
 Combination of UV
stabilizers in clearcoat:
 1,5-2% UV absorber:
color retention
...
Applications
27/10/2016 14© sirris | www.sirris.be | info@sirris.be |
Evaluation methods
27/10/2016 15
 Assess the stability of coatings towards weatherability:
 Outdoor exposure
 Florida (...
Testing of coating durability of a printed PVC canvas
27/10/2016 16
Challenge: acquire insights in the durability
of coate...
27/10/2016© sirris | www.sirris.be | info@sirris.be |
+32 498 91 93 14
heidi.vandenrul@sirris.be
Heidi Van den Rul, progra...
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Invisible but functional - uv-protecting coatings

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Smart coating roadshow - 30 September 2016
Invisible but functional - uv-protecting coatings

Publié dans : Technologie
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Invisible but functional - uv-protecting coatings

  1. 1. Invisible but functional UV-protecting coatings Sirris Smart Coating Application Lab 27/10/2016 1© sirris | www.sirris.be | info@sirris.be |
  2. 2. Weathering of materials 27/10/2016 2© sirris | www.sirris.be | info@sirris.be | Solar radiation (UV) Moisture (dew, humidity, rain) Heat Pollutants (ozone, acid rain) Salt water Global plot of UV levels in July—dark brown being the highest (NASA/Goddard Space Flight Center, Scientific Visualization Studio)
  3. 3. What is UV radiation/light? 27/10/2016 3© sirris | www.sirris.be | info@sirris.be |
  4. 4. Damage by UV radiation 27/10/2016 4© sirris | www.sirris.be | info@sirris.be | Loss of mechanical properties and gloss, discoloration of plastics Discoloration of dyes roughening, colour changing, cracking of wood Obelisk of Thutmosis I
  5. 5.  Absorption of UV-radiation by polymer or impurity  Polystyrenes, aromatic polyesters, aromatic polyurethanes, … absorb UV light  Acrylates, aliphatic polyesters,… cannot absorb light, but technical polymers contain impurities that can absorb uv-light  chromophore = functional group that absorbs the energy  Molecule becomes excited (in a higher energy state)  UV-photons have enough energy to break chemical bonds of organic compounds, resulting in the formation of free radicals Effect of UV radiation on polymers 27/10/2016 5© sirris | www.sirris.be | info@sirris.be | Photooxidative degradation
  6. 6. Stabilisation against UV light 27/10/2016 6  By mixing in the material/plastic  By coating  Liquid light stabilizers in solvent- and waterborne coatings  Solid light stabilizers with melting point close to extrusion temperature for powder coatings © sirris | www.sirris.be | info@sirris.be | UV absorbers / screeners (compete for the) absorption of UV- light and avoid radical formation Quenchers Destroy the excited state of chromophores, accept the energy of the chromophore and release it as harmless heat or radiation Radical scavengers Destruction of already formed radicals Peroxide decomposers Destruction of peroxide radicals
  7. 7. Stabilizers: UV absorbers 27/10/2016 7  Organic UV absorber molecules:  2-(2-hydroxyphenyl)-benzotriazoles (BTZ)  hydroxyphenyl-s-triazines (HPT)  2-hydroxy-benzophenones (BP)  oxalanilides  Requirements for good uv protection:  Absorb at the wavelength where the polymer has a maximum sensitivity  Triazoles and triazines give the broadest protection  Don’t absorb > 400 nm – undesired colour  Filter efficiency ~ Lambert Beer law 𝐸 = 𝜀. 𝑐. 𝑑  Concentration, film thickness, extinction coefficient  Absorb better and faster than substrate  dissipate absorbed energy quickly  repeatedly run this cycle © sirris | www.sirris.be | info@sirris.be |
  8. 8. Stabilizers: UV absorbers 27/10/2016 8  Why are UV absorbers photostable?  ESIPT mechanism: rapid and efficient dissipation of absorbed energy © sirris | www.sirris.be | info@sirris.be |
  9. 9. Stabilizers: UV screeners 27/10/2016 9© sirris | www.sirris.be | info@sirris.be |  Inorganic oxide particles TiO2, ZnO, CeO2  Mechanism:  Bandgap absorption  Scattering of light
  10. 10. Stabilizers: UV screeners 27/10/2016 10  Inorganic oxide particles TiO2, ZnO, CeO2  Mechanism:  Bandgap absorption  Scattering of light  Transparency of coating (micron – nanoparticles)  Distribution of stabilizer must be optimized  Good compatibility with other components of formulation  Avoid agglomeration of oxide particles  Suppress photocatalytic activity © sirris | www.sirris.be | info@sirris.be |
  11. 11. Stabilizers: Radical scavengers 27/10/2016 11  Interrupt the chain reaction of polymer degradation  2 different classes:  Cyclic: hindered amine light stabilizers (HALS) © sirris | www.sirris.be | info@sirris.be |  Non-cyclic: phenolic antioxidants 2,2,6,6- tetramethyl -piperidine
  12. 12. UV-protecting coatings 27/10/2016 12  Combination of UV stabilizers in clearcoat:  1,5-2% UV absorber: color retention  1% HALS radical scavenger: gloss retention, prevention from cracking, improve life time of UV absorber © sirris | www.sirris.be | info@sirris.be | Reproduced from “light stabilizers”, Thomas Bolle, from “Additives for coatings”, J. Bieleman
  13. 13. UV-protecting coatings 27/10/2016 13  Combination of UV stabilizers in clearcoat:  1,5-2% UV absorber: color retention  1% HALS radical scavenger: gloss retention, prevention from cracking, improve life time of UV absorber © sirris | www.sirris.be | info@sirris.be | Reproduced from “light stabilizers”, Thomas Bolle, from “Additives for coatings”, J. Bieleman ΔE after 54 months exposure in Florida of clearcoats with different UV- absorbers over a basecoat with different pigmentations
  14. 14. Applications 27/10/2016 14© sirris | www.sirris.be | info@sirris.be |
  15. 15. Evaluation methods 27/10/2016 15  Assess the stability of coatings towards weatherability:  Outdoor exposure  Florida (tropical climate) worldwide standard  Arizona (dry desert climate)  Australia (high UV doses)  Jacksonville Florida (tropical + air pollution)  Artificially accelerated weathering  To drastically reduce evaluation times  Xenon  QUV  Empirical correlation to outdoor exposure: 1 hr Q.U.V. ~ 17 hrs natural radiation 1000 hrs = 1.5 m QUV ~ 2 yrs natural radiation 8:1 – 25:1 © sirris | www.sirris.be | info@sirris.be |
  16. 16. Testing of coating durability of a printed PVC canvas 27/10/2016 16 Challenge: acquire insights in the durability of coated PVC canvas  Fading of color?  Cracking of canvas due to longterm outdoor exposure?  Testing of two kinds of coating © sirris | www.sirris.be | info@sirris.be | Contribution Sirris  QUV weathering tests (ISO 4892-3)  1000 hrs  Evaluation of the coating compared to uncoated canvas • Visual evaluation • Colorimetry (L,a,b-determination) • Gloss measurements • Bending tests (cracking of canvas?) Results  QUV on uncoated canvas shows degradation of the color and gloss  Coated canvas shows low degradation  No cracking on both coated and uncoated canvas
  17. 17. 27/10/2016© sirris | www.sirris.be | info@sirris.be | +32 498 91 93 14 heidi.vandenrul@sirris.be Heidi Van den Rul, program manager coatings

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