Adhesion promoter for solventborne primer surfacers

A process for improving adhesion of a primer surfacer, the process comprising formulating at least one organic solvent and at least one additive into a solventborne primer surfacer, wherein the at least one additive is preparable by reacting

• (a) at least one alpha,omega-hydroxy-functionalized oligoester which possesses the following structural formula (I):
• where
• the radicals R1 independently of one another are a linear or cyclic alkylene radical,
• the radicals R2 independently of one another are an alkylene or alkenylene radical, the ratio of alkylene to alkenylene radicals being such that the alpha,omega-hydroxy-functionalized oligoester of the structural formula (I) possesses a theoretical carbon-carbon double bond content of 1 to 2.5 mmol/g, and
• the index in is such that the number-average molecular weight of the alpha,omega-hydroxy-functionalized oligoester of the structural formula (I) is 1000 to 3000 g/mol,
• wherein the alpha,omega-hydroxy-functionalized oligoester possesses an OH number of 30 to 160 mg KOH/g, and a weight-average molecular weight of 2800 to 10 000 g/mol, and
• (b) at least one alkoxysilane of the structural formula (II)
• A-R—Si(R′)x(OR″)3-x
• where
• A is an OH-reactive functional group,
• R is an aliphatic radical having 2 to 12 carbon atoms, a cycloaliphatic radical having 3 to 12 carbon atoms, an aromatic radical having 6 to 12 carbon atoms, or an araliphatic radical having 7 to 18 carbon atoms,
• the radical R′ is a C1 to C12 alkyl radical,
• R″ is a methyl or ethyl radical, and
• x is 0 to 2,
• with the proviso that at least 90 mol % of all the OH groups of the alpha,omega-hydroxy-functionalized oligoester have been reacted with an OH-reactive functional group A,
• and,
• the sum of the weight percentage fractions of all additives of the invention is 0.5 to 10 wt %, based on the total amount of the solventborne primer surfacer.