Storage Stable Thermosetting Powder Coating Compositions Comprising an Epoxy Crosslinker and a Polyester Resin Prepared From Citric Acid And/or Citric Acid Anhydride, and Powder Coatings Thereof Having at Least Good Chemical Resistance and at Least Very Good Adhesion

A thermosetting powder coating composition (abbreviated as TPCC) comprising a constituent B (abbreviated as B) in an amount of at least 25 and at most 100 pph of TPCC, wherein the B consists of a polyester resin component (abbreviated as PRC) and an epoxy crosslinker (abbreviated as EPX) that is able to react with the PRC, wherein:

• the PRC consists of one or more carboxylic acid functional polyester resins (each one of them abbreviated as CAPR), each of which has:
• an acid value (abbreviated as AV) determined titrimetrically according to the ISO 2144:2000, of at least 38 and at most 84 mg KOH/g, and a hydroxyl value (abbreviated as OHV) determined titrimetrically according to the ISO 4629-2:2016, that is lower than the AV,
• a glass transition temperature (abbreviated as Tg) of at least 40 and at most 90° C.,
• a number average molecular weight (abbreviated as Mn) determined via Size Exclusion Chromatography of at least 1400
• and at most 10000 Da, and
• wherein the CAPR is the polycondensation reaction product of:
• at least components A1 and A2, and optionally one or any combination of components A2′, A3 and A4,
• or
• at least components A1, A2′ and A3, and optionally one or any combination of components A2 and A4,
• and wherein the CAPR comprises polycondensed residues of the components A1, A2, A2′, A3 and A4 as mentioned above, and as each one of the components A1, A2, A2′, A3 and A4 is described below:
• component A1 is selected from the group consisting of diols, and mixtures thereof,
• component A2 is selected from the group consisting of citric acid, citric acid anhydride, and mixtures thereof,
• component A2′ is selected from the group consisting of C1-alkyl monoesters of citric acid, C2-alkyl monoesters of citric acid, C1-alkyl diesters of citric acid, C2-alkyl diesters of citric acid, C1-alkyl-C2-alkyl diesters of citric acid, C1-alkyl triester of citric acid, C2-alkyl triester of citric acid, C1-alkyl-C2-alkyl triesters of citric acid, and mixtures thereof,
• component A3 is selected from the group consisting of dicarboxylic acids, dicarboxylic acid anhydrides, and mixtures thereof, and
• component A4 is selected from the group consisting of tricarboxylic acids other than citric acid, tricarboxylic acid anhydrides other than citric acid anhydride, tetracarboxylic acids, tetracarboxylic acid anhydrides, trialcohols, tetralcohols, hexalcohols, and mixtures thereof,
• wherein the total amount of the polycondensed residues of A2 (abbreviated as WA2) when present in the CAPR, is at least 2.0 and at most 8.0 mol % based on CAPR, and wherein the total amount of the polycondensed residues of A2′ (abbreviated as WA2′) when present in the CAPR, is at least 2.0 and at most 8.0 mol % based on CAPR, and wherein the total amount of the polycondensed residues of A2 and A2′ (abbreviated as WA2/A2′) when both polycondensed residues of A2 and A2′ are present in the CAPR, is at least 2.0 and at most 8.0 mol % based on CAPR, and
• wherein the total amount of monomers used for the preparation of the CAPR is 100 mol %, and wherein the PRC has an acid value (abbreviated as AVPRC) determined titrimetrically according to the ISO 2144:2000, of at least 38 and at most 84 mg KOH/g, and a hydroxyl value (abbreviated as OHVPRC) determined titrimetrically according to the ISO 4629-2:2016, that is lower than the AVPRC,
• and
• the EPX consists of one or more epoxy compounds (abbreviated as CEPX) selected from the group consisting of i) epoxy resins and ii) epoxy monomers, wherein each of the epoxy resins and each of the epoxy monomers:
• is solid at 23±1° C. and atmospheric pressure,
• is able to react with the PRC,
• has more than one oxirane groups,
• and
• wherein the EPX has an epoxy equivalent weight (abbreviated as EEWEPX) determined via manual titration according to the ASTM D1652-11(2019), of at least 560 and at most 950 g/eq,
• and
• wherein the ratio R is at least 0.8 and at most 2.0, and wherein the ratio R is determined according to the following equation:
• R=(56100×WEPX)/(WPRC×AVPRC×EEWEPX)
• wherein
• each of the EEWEPX and AVPRC is as determined above,
• WEPX:
• is the amount of EPX in the constituent B (in pph of B),
• WPRC:
• is the amount of PRC in the constituent B (in pph of B),
• and
• wherein the aggregate of WEPX and WPRC is equal to 100 pph of B.