Automotive Coatings Formulation: Chemistry, Physics und Practices

3.7.3.2 Polyesters
Theoretically, the polyesters used for primer surfacers (see Chapter 3.5.3.1) are also suitable for 
basecoats. Optimum compatibility with cellulose acetobutyrate is achieved by basecoats com-
posed of polyesters that have rather low molecular weights, are not highly branched, and contain 
some less-polar building blocks. Table 3.7.1 shows the composition and physical characteristics of 
polyester that is typically suitable for basecoats 
[126]
.
Such polyesters also make ideal resins for preparing pigment dispersions.
Figure 3.7.6: Comparison of evaporation of solvents from 
cellulose acetobutyrate and other resins
Table 3.7.1: Composition and characteristics of a polyester for basecoats
n = m/M
Components
M
m (example)
wt-‰
1.829
ethylene glycol
62
113.4
94.3
1.371
neopentyl glycol
104
142.6
118.6
1.372
HPN
206
279.8
232.7
0.686
trimethylol propane
134
91.9
76.5
1.826
isophthalic acid
166
303.5
252.5
1.354
HHPA
154
208.5
173.4
1.371
adipic acid
146
200.2
166.5
sum
1339.9
1114.4
7.646
water
18
137.6
114.4
yield (AN = 5.0)
1202.3
1000.0
average molecular weight [g/mol] 1482 
acid number [mg KOH/g] 
5.0
degree of branching [mol/kg] 
0.57 
OH-number [mg KOH/g] 
102.5
Basecoats

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146
3.7.3.3 Amino resins
The first amino resins to be used were rather high-molecular urea resins that supported solvent 
evaporation (drying rate) and resistance to redissolving. However, specific melamine resins later 
came to be preferred, due to their superior weathering resistance and better intercoat adhesion.