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1、Business Line Coatings Light Stabilizers for wood Light Stabilizers for wood and wood coatingsand wood coatings Ciba Specialty Chemicals January 2004 Business Line Coatings Wood: a commonly used material - naturally renewable resource - considerable importance in economy - easily available and worka
2、ble material - excellent properties, strength, low weight - very large choice in species and qualities Business Line Coatings Wood Wood applicationsapplications Construction elements (bulk wood) Flooring, Furniture, Veneers Particle and fiberboards (HDF,MDF) WPC Wood Plastic Composites Business Line
3、 Coatings Wood species Rotholz Redwood Nussbaum Walnut Teak Teak Platane Sycamore Mahagoni Mahogany Mooreiche Bog oak Kirsche Cherry Ebenholz Ebony Tanne Fir Fichte Spruce Ahorn Maple Esche Ash Edelkastanie Sweet chestnut Buche Beech Birke Birch Eiche Oak Business Line Coatings Wood coating types Fu
4、rniture, flooring and panelling (factory applied systems) - NC lacquers - Alkyd/Phenol- or UreaFormaldehyde acid catalyses systems - Polyurethanes - Polyesters (thermal curing) - UV curable Acrylate and PES systems (100% liquid, wb and powder) - Waterborne dispersions (acrylates and polyurethanes) E
5、xterior coatings (professional and DIY systems) - Oils, long oil alkyds, 2 pack polyurethanes - waterborne acrylics, polyurethanes, alkyd emulsions Business Line Coatings Substrates and coatings selection Substrates - large selection of species, colors and patterns - complex wood chemistry - most sp
6、ecies are sensitive to light exposure and degrade Photostability requirements for clear coated substrates - may differ widely depending on final application - only color stability and aesthetics needed for indoor applications - coating durability and substrate photoprotection must be guaranteed for
7、long lasting protective coatings in outdoor applications ? optimal light stabilization must be carefully selected according to performance required by end use Business Line Coatings Wood chemistry - cellulose major component of wood is cellulose High molecular weight linear polymer 1 to more than 4
8、-linked D-Glucose monomers Cellulose is arranged into ordered strands called fibrils Jute, flax, hemp, cotton 90% Conifers, broad-leafed trees 40 to 50% D-Glucose 1 4 1 -1,4-Glucan OH O O O OH O CH2OH OH OH O O O O OH O CH2OH OH OH OH CH2OHCH2OH cellulose Business Line Coatings Hemicelluloses hemice
9、lluloses are associated to cellulose branched low-molecular weight polymers composed of several kinds of sugar monomers (Polysaccharides) Pentose (Arabinose, Xylose) Hexose (Galactose, Glucose, Mannose) constitute about 25 - 30% of wood composition glue“ among cellulose fibrils and lignin structures
10、 Wood chemistry - hemicelluloses OH OH O OH O O OH O O O O OH O OH OHOOH O O OH OH CH2OH H3CO CH2OH HOH2C Pentose Hexose Business Line Coatings Wood chemistry - others Non structural organic components generically called extractives“ count for about 0.2 to 1.0% of wood composition resins (resionol a
11、cid, resinole, resene.) biocides tanning agent (tannines.) polyphenols essential oils, waxes, fatty acid esters C16-C18 terpenes (bactericides, fungicides.) cyclic diisoprenoides stilbene (diphenylethen) Inorganic components generically called ashes“ constitute about 0.2 to 1.0% of wood (up to 5% tr
12、opics) K, Ca, Mg-salts; Fe, Mn, B cations. Business Line Coatings Lignin 3D phenylpropanol polymer based on 3 structural units p-Cumarylalcohol (I) Coniferylalcohol (Guajacyl) (II) Sinapinylalcohol (Syringyl) (III) structural support and adhesive material in plants lignin constitutes about 15 - 30%
13、of wood composition Wood chemistry - lignin OH OH OMe OH OH OMe MeO OH OH (I)(II)(III) Softwood Hardwood Grass 14%80%6% 4%53%43% 30%50%20% Business Line Coatings Wood chemistry lignin structure O O O OH O OH OH O O OHOH OH O O O OH O OH O OH O O O O OH O O O O O OH O O OH MeO MeO MeO MeO MeO MeO OMe
14、 MeO MeO OMe OMe OMe MeO MeO MeO Veratrol Guaiacyl-ether Guaiacol Phenacyl“ Pathway Ketyl“ Pathway Syringyl-ether Business Line Coatings Phenacyl“ Pathway O O Lignin O-Lignin R OMe OMe -Guaiacylaceto- veratrone (-GAV) 7% OH O R Lignin O-Lignin OMe OMe -Guaiacylaceto- veratrone (-GAVH) 50% -O-4 cleav
15、age OH R O-Lignin OMe OH O R Lignin O-Lignin OMe OMe O O-Lignin R OMe tautomerization Photooxidation pathways of Lignin O O-Lignin R OMe Lignin O MeO Ketyl“ Pathway Oxidation by RO , ROO O O Lignin OMe O O Lignin Chromophores UV Light Ketone Radical Phenoxy Radical R Business Line Coatings 13 Wood a
16、nd Lignin Stabilization Strategy Excited Molecules Free Radicals Yellow Products UV light O2 Lignin Harmless Heat Harmless Colorless Products Lignin Lignin StabilizerStabilizer in in pretreatmentspretreatments UV UV AbsorbersAbsorbers oror UVA/HALS UVA/HALS Blends Blends in in top coatstop coats Bus
17、iness Line Coatings Wood Photooxidation and Photodegradation Solar radiation causes wood substrates to photodegrade - yellowing, darkening and color changes are first signs of wood surface properties alteration, even in indoor conditions - this is caused by photooxidation of lignin and other wood co
18、mponents and happens while clear coatings are keeping their full integrity Heat and humidity enhance the photoinduced deterioration - whitening and cracking of wood are further steps of degradation caused by alternate exposure to humidity and heat outdoors - wood fiber cohesion and mechanical streng
19、th are lost resulting in early failure and adhesion loss of clear top coats - coating binders themselves degrade in outdoor weathering Business Line Coatings 15 1 UV LightUV Light 400 nm VIS LightVIS Light 400400- -500nm500nm VIS LightVIS Light 500500- -700nm700nm Yellowing and Darkening is caused b
20、y photooxidation of lignin at the surface of wood Discoloration of wood indoors 1 2 Business Line Coatings Yellowing and darkening of wood indoors results from slow photooxidation processes of wood surfaces even in diffuse indoor light conditions Business Line Coatings 17 17 o oxygenxygen a air ir p
21、 pollutantsollutants UVUV- -lightlight humidity 1 cm Quarz cell 0 0.2 0.4 0.6 0.8 1 1.2 290310330350370390 Wave lengths in nm Absorbance Chim 81 Tin 99-2 CGL777 CGL 777 MPA: Highest extinction and red shifted absorbance Business Line Coatings HALS postulated radical trap mechanism N-R N-O N-OP O2 UV
22、 radiation peroxydes P POO Products (POH + P=O) Denisov cycle Business Line Coatings HALS N OCO(CH2)4 R 2 TINUVIN 292 and TINUVIN 123 - liquid difunctional HALS compounds - for enhanced exterior coating durability - to be used as such for pigmented systems - synegistic effects with UV Absorbers in c
23、lear coats TINUVIN 292 R = CH3 - general purpose HALS - basic character, pKb= 5.5 - for solvent borne PUR coatings - for water borne Acrylic systems TINUVIN 123 R = OC8H17 - NOR type HALS, low basicity, pKb= 10 - non interacting (acid cats, biocides) - no cure inhibition (driers) - for solvent borne
24、 LO Alkyd coatings - for water borne Alkyd emulsions Business Line Coatings Light Stabilizers for exterior Wood Coatings For sb Alkyd resin systems (% LS on dry resin content) Standard top coat stabilization ?2 to 4% TINUVIN 50602 to 4% TINUVIN 5060 Improved stabilizationImproved stabilization ?2% T
25、INUVIN 5060 + 1 to 2% CGL 777 MPA2% TINUVIN 5060 + 1 to 2% CGL 777 MPA Additional Primer Additional Primer or Pretreatment stabilizationor Pretreatment stabilization ? 1 to 2% 1 to 2% LIGNOSTABLIGNOSTAB 1198 1198 (on total (on total pretreatment formulationpretreatment formulation) ) Business Line C
26、oatings Light Stabilizers for exterior Wood Coatings For Acrylic dispersion systems (% LS on resin solids) Standard top coat stabilization ?3 to 5% TINUVIN 51513 to 5% TINUVIN 5151 Improved stabilization with better UV screening effect ?3 % TINUVIN 5151 + 5 to 10% CGL 3623 % TINUVIN 5151 + 5 to 10%
27、CGL 362 Additional Primer or Pretreatment stabilization ?1 to 2% 1 to 2% LIGNOSTABLIGNOSTAB 11981198(on total formulation) Business Line Coatings Recommended UVA for indoor applications 3- 10% CGL 362 (20% active UVA) 1- 2% CGL 777 MPA For improved UVA protection 1- 4% TINUVIN 11301- 3% TINUVIN 99-2
28、 Current UVA Recommendation Water borne Water borne systemssystems Acrylate dispersionsAcrylate dispersions PU PU dispersionsdispersions, WB UV, WB UV Solvent Solvent borne sytemsborne sytems 2P2P- -PUR, PUR, acid cat acid cat UF,UF, NC NC lacquerlacquer, 100% UV, 100% UV Top Top Coats Coats (% (% s
29、tabilizer stabilizer on on binder solidsbinder solids) ) Additional pretreatment stabilization for enhanced protection ?1 to 2%1 to 2% LIGNOSTABLIGNOSTAB 11981198(on total formulation) Business Line Coatings Recommended LS for exterior applications 5-10% CGL 362 + 3% TINUVIN 5151 1-2% CGL 777 MPA +
30、2 % TINUVIN 5050/5060 For improved UVA protection 3-5% TINUVIN 5151 2-4% TINUVIN 5050 for PU/PU-A systems 2-4% TINUVIN 5060 for LOAlkyd systems Current stabilizer Recommendation Water borne Water borne systemssystems Acryl and PU Acryl and PU dispersionsdispersions, , AlkydAlkyd emulsionsemulsions,
31、WB UV, WB UV Solvent Solvent borne sytemsborne sytems 2P2P- -PUR, PUPUR, PU- -AlkydsAlkyds, , LOAlkydsLOAlkyds, , PhenolicsPhenolics ApplicationApplication (% (% stabilizer stabilizer on on binder solidsbinder solids) ) Additional pretreatment stabilization for enhanced protection ?1 to 2%1 to 2% LI
32、GNOSTABLIGNOSTAB 11981198(on total formulation) Business Line Coatings LIGNOSTABLIGNOSTAB 1198 1198 applicationsapplications - indoor floor and furniture coatings (in primers and/or stains) - bulk coloration of wood veneers - exterior industrial primers - penetrating wood finishes (deck coatings, lo
33、w buid stains) - sapstain protectants for fresh sawn timber and lumber - particle boards, coatings and adhesives - wood fillers for plastic composites (WPC) New concept for wood photoprotection Business Line Coatings Enhanced photoprotection effects UV LightUV Light 400 nm VIS LightVIS Light 400400- -700 nm700 nm Substrate: WOODSubstrate: WOOD impregnated withimpregnated with Clear Coat Clear Coat stabilized withstabilized with TINUVINTINUVIN UVA and HALSUVA and HALS Lignin StabilizerLignin Stabilizer LIGNOSTABLIGNOSTAB 11981198