30 августа, 2015 
Malyar by Kevin O’Hara LRSC and Morrison Barbour BSc
(i) Automotive OEM
Traditionally acrylic/melamine and alkyd/melamine systems have been used for high quality original finishes on automobiles. Two component acrylic urethane used in some OEM applications offer:
• low cure temperature
• excellent durability
• high solids/low VOC
• high gloss
• chemical resistance, especially to acid rain
• chip resistance
• flexibility
The higher percentage of plastic components in automobiles, combined with their temperture sensitivity, has also resulted in an increase in usage of two pack acrylic polyurethanes, offering similar, if not improved, performance characteristics to traditional coatings.
A typical clear, high build overlacquer for low bake curing is given below. It is suitable for use in a COB system over a basecoat. A typical basecoat formulation for COB application is given in the TSA chapter.
HIGH BUILD CLEAR TOPCOAT FOR AUTOMOBILES
|
Parti |
pbw |
|
Hydroxyl functional acrylic resin ^ |
48.00 |
|
Baysilon OL17 (20%) |
0.46 |
|
Baysilon A (5%) |
0.18 |
|
Dibutyl tin dilaurate (5%) |
0.05 |
|
Tinuvin 900 |
0.67 |
|
Tinuvin 292 |
0.33 |
|
Butyl acetate |
12.56 |
|
Methoxy propyl acetate |
4.19 |
|
Ethyl acetate |
1.40 |
|
Part II |
|
|
Desmodur N3390 |
13.63 |
|
Butyl acetate |
12.83 |
|
Methoxy propyl acetate |
4.27 |
|
Ethyl acetate |
1.43 |
|
Total |
100.00 |
|
NOTE:(a) e. g. Synocure 865SD, 70% solution in ethyl 3-ethoxy propionate (EEP), 3.1% hydroxyl |
Specification (Mixed)
Viscosity (BS, B4,25°C) 23 secs
Vehicle solids 46.70%
Mix parts I & II and spray apply to basecoat.
|
TABLE 5-3: PHYSICAL PROPERTIES OF CLEAR TOPCOAT OF FORMULATION 5-1
|
The overlacquer must be able to adhere well to the basecoat, which contains wax, and set rapidly to avoid disruption of the basecoat. Top coats require UV stabilisers for extra protection. Methoxyl propyl acetate is a slow evaporating solvent to help levelling during cure. Desmodur N3390 is an HMDI based isocyanurate adduct, soft and aliphatic for improved flexibility and weather resistance. Baysilon OL17 is a flow agent. Baysilon A improves the surface slip.
The types of resin used in this market include:
Synocure 865SD Synocure 859SA Setalux C1152XX51/SS60 Desmophen A365
Опубликовано в рубрике 