High-Strength Hybrid Epoxy Ester Polymer

High-Performance Hybrid Epoxy Ester Polymer Industrial paints and coatings widely use resins as binders. Epoxy esters are resins obtained through the reaction of fatty acids and epoxy resin (Figure 1). Epoxy esters produced in this manner have air-drying properties and thus provide economic advantages as they require no hardener. They are preferred more than alkyd resins because they deliver products with superior color retention, better adhesion, flexibility and excellent chemical resistance compared to alkyd resins. They are widely used in many applications: as primer binder in automotive primer coating manufacture, in final-coat marine paint production, as primer binder in household appliance painting, as clear varnish filler in floor coating materials, and in metal furniture painting, among others. Urethane resins are widely used in wood and industrial paints due to their gloss, resistance to external conditions, rapid cure, and hard and filled film properties. Although they are frequently used in wood applications, their yellowing resistance is low. Faced with certain limitations in resin sector applications and the need to meet market demands as an alternative, the requirement emerged to develop a hybrid resin type that could replace imported products with low cost and high-performance properties, high added value, and competitive market positioning. Following research, it was decided to develop a hybrid product with higher yellowing resistance than urethane paints, faster drying than epoxy esters, harder film formation than any comparable product, high corrosion resistance, and superior adhesion properties. Given that the developed products have no equivalents other than those from Serkim Reçine and the originality of the work, it was aimed to contribute both to Turkey's economy and to scientific literature.

Experimental Work Conducted

Epoxy ester resins forming the base of the hybrid resin were synthesized using six different vegetable fatty acids and epoxy resin containing different fatty acid components. Modification of the epoxy ester resin with aromatic NCO and aliphatic NCO at ratios of <5% and <10% was performed and performance tests in paint were examined. The FTIR spectra of epoxy ester resulting from the reaction of epoxy resin with fatty acid are shown in the figure. Changes in the peaks seen at 1726 cm⁻¹ and 828 cm⁻¹ wavelengths resulted from the opening of the oxirane ring during the reaction between fatty acid and epoxy resin. C-H bonds resulting from the opening of the oxirane ring are observed at 2925 cm⁻¹ wavelength (Figure 2). In the FTIR spectrum of epoxy ester and aromatic NCO modification (Figure 3), the peak observed at 2236 cm⁻¹ characteristically shows N=C=O stretching vibrations of the isocyanate group in the aromatic NCO structure. Additionally, the peak observed at 1523 cm⁻¹ wavelength originates from C=N stretching vibration of the imine group and C-H stretching vibration seen at 2924 cm⁻¹ wavelength. Spectra were compared to observe structural changes that could occur following urethanized epoxy ester production.

Results

Hybrid resins converted to paint were applied as 60-micron paint films on glass and metal surfaces and results were recorded over 10 days. Overall, all films showed similar and good adhesion. No significant difference was observed in gloss results when different fatty acids were used. Since the aromatic NCO modified resin showed a higher yellowing tendency compared to the aliphatic NCO modified resin, the aliphatic NCO modified resin exhibited better gloss values.

For <5% aromatic NCO modified hybrid resin:

• On glass panels, the resin produced with low rosin acid-content fatty acid generally delivered the best performance with the highest overall performance, • In hardness values of the produced paints at day 10, the hybrid resin produced with low rosin acid-content fatty acid achieved the highest performance with 106 König hardness value.

For <10% aliphatic NCO modified hybrid resin:

• In hardness values of the produced paints at day 10, the hybrid resin produced with low rosin acid-content fatty acid achieved the highest performance with 108 König hardness value, followed by the hybrid resin produced with high ricinoleic acid-content fatty acid with 103 König hardness value. • Improvements were observed in hardness values of modified products compared to epoxy ester, and hybrid resins produced with aliphatic NCO delivered the best performance. • Following alkali resistance testing (20 days / 3% NaOH), hybrid resin films showed generally good resistance. • In salt resistance testing, when all epoxy ester and hybrid resins were tested in a salt-spray corrosion chamber, no film deterioration was observed after 20 days, indicating very good salt resistance. Following acid resistance testing (20 days / 3% H₂SO₄), epoxy ester films were found to deteriorate, but following the modification process, low rosin acid-content fatty acid hybrid resins showed good acid resistance (Figure 4). In drying test results, when the drying performance of hybrid modified resins made with six different fatty acids was evaluated, base epoxy ester resins showed machine drying times of 124-175 minutes; notable improvements in drying performance were observed with modifications. Low rosin acid-content fatty acid with <5% aromatic NCO modified hybrid resins demonstrated very good drying performance with 20-minute drying time, while fatty acids rich in oleic and linolenic acid components with <10% aliphatic NCO modified resins achieved the best drying performance at 19 minutes. Across all hybrid resin project subjects, distinct improvements in drying performance compared to epoxy ester were observed.

Discussion

This study demonstrated that hybrid resins produced through modification of epoxy ester resins with isocyanates achieved improvements in drying, gloss, hardness, adhesion, alkali, acid and salt resistance, and thermal properties, and that hybrid resins with desired characteristics can be produced. Evaluating all test results overall, the hybrid resin with low rosin acid-content fatty acid and <10% aliphatic NCO demonstrated the superior performance. Going forward, by varying the fatty acids, isocyanates, and epoxy resins used, it will be possible to produce hybrid resins with different desired characteristics in different combinations. Dr. Çiğdem Yüceel - Project and R&D Manager Serkim Reçine / Serkim Resin Şenol Demir - R&D and Production Manager Serkim Reçine / Serkim Resin Zeynel Turna - R&D and Production Manager Serkim Reçine / Serkim Resin