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Hyperbranched Aliphatic Polyesters as Thermoset Resins for Thermally Cured Coil-Coatings
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
SSAB Tunnplåt AB.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.ORCID iD: 0000-0003-3201-5138
(English)Manuscript (Other academic)
Abstract [en]

Two hydroxy-functional hyperbranched aliphatic polyesters based on 2,2-dimethylol propionic acid (bis-MPA) and a partially aromatic conventional polyester have been studied as thermoset resins for solvent-borne thermally cured polyester cross-linked with melamine coatings for pre-coated sheet metal, i.e. coil-coatings. The hyperbranched polyesters differ with respect to ratio of the end-groups being either hydroxyls or alkyl esters. The rheological properties of formulations with different polyester resin composition and reactive diluent, i.e. rape seed methyl ester (RME), content have been evaluated with viscosity measurements. Films cured either under industrial cure conditions to obtain a peak metal temperature (PMT) of 232-241°C or at a lower temperature, i.e. 130°C, on untreated or organic primer coated hot dipped galvanized (HDG) steel substrates have been prepared. The film properties have been evaluated with differential scanning calorimetry (DSC), and conventional film characterization techniques i.e. adhesion, impact, Erichsen cupping, pencil hardness, micro hardness, scratch and chemical resistance tests. Formulations possessing high drying ability with maintained suitable film application viscosity were obtained using a hyperbranched polyester resin and a reactive diluent. It is proposed that a solvent-free polyester/melamine formulation with sufficient film properties to withstand the rough forming procedures associated with coil-coatings can be obtained by further modification of the resin and greater amounts of reactive diluent.

Keyword [en]
Hyperbranched polyester resin, fatty acids, reactive diluents, coatings, thermal curing, film properties
National Category
Polymer Chemistry
URN: urn:nbn:se:kth:diva-4853OAI: diva2:87
QC 20100817Available from: 2008-09-04 Created: 2008-09-04 Last updated: 2010-08-17Bibliographically approved
In thesis
1. Thermally cured coil-coatings utilizing novel resins and fatty acid methyl esters as reactive diluents
Open this publication in new window or tab >>Thermally cured coil-coatings utilizing novel resins and fatty acid methyl esters as reactive diluents
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Solvent-borne thermally cured coil-coating resins contain large amounts of volatile organic solvents in order to obtain suitable flow for film application. This work describes how the expensive and environmental hazardous volatile organic solvent content of a solvent-borne thermally cured polyester/melamine coil-coating system can be reduced by introduction of fatty acid methyl esters (FAMEs) as reactive diluents and modification of the polyester binder resin. The evaluated reactive diluents, two rape seed methyl esters (RMEs), two linseed oil methyl esters (LMEs), and a tall oil methyl ester (TOME) have been evaluated both in a fully formulated clear-coat system and via model studies.

Viscosity measurements of wet paint mixtures showed that formulations with hyperbranched polyester binder hold lower viscosity than conventional polyester binder resins and that FAME works as a diluent. Fully formulated clear-coats were cured under simulated industrial coil-coating cure conditions and in a convection oven at lower temperatures respectively. FAME increases the mobility of the system enhancing the film formation process. Free-standing clear-coat films were analyzed with Raman, carbon-14 dating, extraction, dynamic mechanical analysis, and visual observation. Incorporation of FAME could not be confirmed by Raman analysis. However, carbon-14 dating indicated the presence of FAME that could not be extracted from the films. The mechanical properties of the films were also affected by the addition of FAMEs, oven temperature, choice of co-solvent, and flash-off period. Conventional film characterization tests on substrate supported coatings indicated that binder resin structure and cure conditions affect the final film properties.

Model studies were performed to clarify how FAME can chemically react through transesterification with the hydroxyl-groups of the polyester. The transesterification reaction between different FAMEs and primary alcohols with and without tertiary hydrogen was monitored with 1H-NMR and real time IR. Evaporation and side reactions, e.g. alkene reactions, are competing factors to the transesterification reaction. The study showed that fatty acid structure, reaction time, and temperature affect the transesterification conversion, degree of side reactions, and choice of catalyst.

A pigmented fully formulated polyester/melamine formulation with a reactive diluent was cured at full scale in an industrial coil-coating production facility. Evaluation of the final film properties showed that the coating fulfills the specification of conventional polyester/melamine coil-coating systems.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. 59 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2008:56
Coatings, Coil-coatings, Thermal cure, Reactive diluents, Fatty acids, Transesterification, Hyperbranched polyester resins, Film properties
National Category
Polymer Chemistry
urn:nbn:se:kth:diva-4857 (URN)978-91-7415-097-1 (ISBN)
Public defence
2008-09-19, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
QC 20100817Available from: 2008-09-05 Created: 2008-09-04 Last updated: 2010-08-17Bibliographically approved

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Johansson, KatarinaJohansson, Mats K. G.
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