Automotive repair finishes

Paint imperfections or mechanical damage can occur post-manufacture. Due to the many heat sensitive parts on the car, (for example, tyres, interior plastic trimmings), it is not possible to repaint the vehicle with the standard paint and subject the whole vehicle to the original curing process, which took place at 120°C or above. Special repair coatings have therefore been developed to eope with this situation. Two routes are possible  

The standard thermosetting acrylic can be catalysed with up to 3% of an organic acid such as p.toluene sulphonic acid or acid butyl phosphate. This is added to the paint immediately prior to repainting and reduces the curing threshold temperature from 120 to 85-90 C. Local infra red heaters are used to cure the repainted area. Alternatively, in extreme cases the whole vehicle can be repainted and put through a low bake oven. 

Typical starting formulations for automotive finishes are given below  

Hydroxy acrylic (55% wt. solids) Butylated melamine formaldehyde resin (55% wt. 36.40  

The above formulation should be thinned to spray application with around 10% by volume solvent to a viscosity of 25-30 secs Ford No. 4 Cup. 

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For several reasons, ranges of pigments have been rationalized in recent years, causing a withdrawal of a considerable number of pigments from the market. The rationale behind the removal of these pigments, when known to us, is given. Since these brands will still be used for some years, for example in automotive repair finishes, we have continued to describe their properties in the new edition. 

Illinois. A 30 percent minimum TE is required for automotive. Automotive VOC limits (lb/gal) are primer/surface, 2.8 topcoat, 2.8 repair, 4.8. The rules allow higher VOC limits for automotive topcoats if the finishing method can be demonstrated to achieve a TE of over 65 percent. In such cases, topcoats may be used with a VOC of up to 3.6. For the wood industry, a minimum TE of 65 percent is required with the... 

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