Verfahren zur Herstellung von modifizierten Alkydharzen

A process for the production of alkyd resins comprises the reaction of one or more compounds of a first category, viz. polycarboxylic acids and/or anhydrides thereof, with one or more compounds of a second category, viz. compounds containing one epoxy group or at least two hydroxyl groups and also a chain, as defined of at least 7 atoms in the molecule, the only compound of the second category present or at least one of the compounds of the second category being an ester of a saturated aliphatic monocarboxylic acid in which the carboxyl group is attached to a tertiary and/or a quaternary carbon atom, and with one or more compounds of a third category, viz. compounds containing at least one epoxy group or at least two hydroxyl groups and chains of not more than 6 atoms in the molecule, in which process after a stage in which the ratio of the quantity of compounds of the second category incorporated in the reaction mixture (expressed in equivalents) to the quantity of compounds of the third category incorporated in the mixture (also expressed in equivalents) is lower than the final value of this ratio, in a later stage while the reaction is continued this ratio is increased to the final value by the addition of one or more compounds of the second category (with or without simultaneous addition of compounds of the first and third categories) said final value being situated between 0.2 and 20. The number of atoms which determines the chain length is the sum of the number of any interrupting atoms (e.g. o, s, n) and of the carbon atoms. Specified polycarboxylic acids are succinic, xylyl succinic, alkyl or alkenyl succinic, adipic, sebacic, maleic, fumaric, phtha lic, isophthalic, terephthalic, tetrahydrophthalic, diglycollic, dimerised fatty acids of drying oils, Diels-Alder adducts, trimellitic, pyromellitic, citric and aconitic acids. As compounds of the second category, which may be used with the ester of the saturated aliphatic monocarboxylic acid, these are specified epoxy alkanes, epoxy alkyl ethers, epoxy alkyl esters of monocarboxylic acids, partial esters of polyhydroxy compounds with monocarboxylic acids, and polyalkylene glycols. Specified compounds of the third category are ethylene oxide, propylene oxide, 2,3-epoxybutane, di-epoxybutane, glycidol, ethylene glycol, propylene glycol, glycerol, pentaerythritol, trimethylol propane and 1,2,6-hexanetriol. Catalysts for the esterification are acids, the chlorides of magnesium, aluminium or zinc, ion-exch