Automotive Refinishing

31 августа, 2015

Malyar

The two pack acrylic polyurethane was introduced to the automotive refinish markets in the 1970’s as an alternative to the existing synthetic cellulose and thermoplastic acrylic systems. Although their development in this market was rather slow, by the late 1980’s the polyurethane coating dominated the refinish market of Western Europe.

The advantages offered by the acrylic include:

• air dry/low bake

• fast dry/low dust pick up

• early fuel resistance

• exceptional durability

• high build

• performance in metallics

The acrylic two pack coating produces coatings with similar aesthetics and performance characteristics to the original OEM coating, albeit cured at room temperature or under low bake conditions. This has become increasingly important in the automotive refinish market with the extensive use of plastic components. A typical air drying refinish clearcoat formulation is as follows:

FORMULATION 5-2:

HIGH BUILD VEHICLE REFINISH CLEARCOAT

Parti
Hydroxyl functional acrylic resin(b*	63.09
Wacker silicone oil LO50 (10% in xylene)	0.77
Tinuvin 1130	1.15
Tinuvin 292	0.38
Methoxy propyl acetate	1.54
Solvesso 100	1.92
Xylene	1.92
Butyl acetate	6.15
Part II
Desmodur N3390	23.08
Total	100.00

(b) 70% in butyl acetate, 4.1% hydroxyl

Viscosity (seconds, Ford cup 4 Solids content (by weight)

Подпись: 25 secs 60% 396 gms/litre >8 voc

Pot life (hours)

TABLE 5-4:

PHYSICAL PERFORMANCE OF HIGH BUILD VR REFINISH (10 DAYS AIR DRY) OF

FORMULATION 5-2

Physical Performance (10 Days Air Dry)
Dust dry (minutes)	8-15
Tack free (hours)	2-4.5
Pendulum hardness (seconds) (10 days air dry)	210
Petrol resistance 30 minutes (10 days air dry)	unaffected

Mix Parts I & II and thin to spray viscosity in a 60:25:15 blend of butyl acetate/xylene/Solvesso 100. Solvesso 100 and methoxy propyl acetate help to adjust levelling. Again, the use of UV absorbers is essential. The silicone oil improves wetting over the waxy base basecoat. Use of catalyst is optional, but its presence can reduce pot life.

A starting formulation for a white gloss vehicle refinishing paint might be :

FORMULATION 5-3: HIGH BUILD WHITE GLOSS PAINT

Part A
Rutile titanium dioxide	26.61
Hydroxy acrylic (70 %nvc)	46.50
Butyl acetate	3.65
Methoxy propyl acetate	1.23
Ethyl acetate	0.41
Part В
Aliphatic polyisocyanate	15.78
Butyl acetate	4.03
Methoxy propyl acetate	1.34
Ethyl acetate	0.45
Total	100.00

Pigment: binder ratio Vehicle solids Total solids

Подпись: Mix parts A and B. Thin to spray viscosity with 9:3:1 butyl acetate : methoxy propyl acetate: ethyl acetate.

A suitable acrylic is Synocure 865SD, 70 %nvc in EEP with an OH content of 1.09%. In combination with a suitable isocyanate, such as Desmodur N3390, lacquers with a non volatile content greater than 45% at spray viscosity are possible.

The types of resins used include:

Macrynal SM510 Macrynal SM515 Synocure 85IS Synocure 858SA Setalux C1151SS51 Setalux C1154SS51 Desmophen A165 Desmophen A365

For high solid/VOC compliant coatings Synocure E94166 and Macrynal VSM1565 are recommended.