Performance of polyester and modified polyester coil coatings exposed in different environments with high UV radiation

Coil coating is a continuous strip coating technology, which enjoyed rapid growth. It provides a cost-effective method of applying a coating to a metal substrate with a low solvent emission, and nowadays paints of different nature are applied this way on a range of metal substrates, for a large variety of products and uses.

Coil coatings can be more or less degraded by high UV radiation. However, differences in distribution of light intensity as a function of wavelength between exposure environments, can lead to significant differences in the degradation results, depending on coating nature. In this work, the behaviour of polyester and silicone polyester coatings exposed in three different high UV environments (natural atmosphere and two accelerated UV tests), was studied. Coatings of two different colours (blue and brown) were considered for each paint system. Colour change, gloss and chalking measurements and, visual inspections of coating defects were carried out. In order to explain their corresponding performance, chemical changes on coil coated exposed surfaces were studied by to Fourier transform infrared spectroscopy equipped with a photoacustic detector (PAS/FTIR).     

Effect of nano-sized calcium carbonate on cure kinetics and properties of polyester/epoxy blend powder coatings

Today's strict environmental laws pose significant challenges for coating's formulators to look for eco-friendly products. Powder coatings, particularly polyester/epoxy blends have demonstrated their ability as alternatives to traditional solvent-borne coatings. Recently, the use of nanoparticles such as nano-CaCO₃ (nCaCO₃) has been suggested as a beneficial strategy towards powder coating application with improved properties. Here, we study the effect of nCaCO₃ on morphology, cure behavior, adhesion and hardness of polyester/epoxy systems. The nanoparticles shape, size and dispersion state were investigated through X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) methods. Furthermore, isothermal cure characterization of the neat and filled systems was performed using a torque rheometer. The most important finding based on the rheological studies was the catalytic effect of nCaCO₃ on cure reaction of polyester/epoxy, leading to the shorter curing time. Moreover, the kinetic analyses of rheograms revealed a marked decrease in the activation energy of the cure process upon raising nCaCO₃ content. Interestingly, pull-off adhesion and hardness tests showed that the hardness and adhesion strength were dramatically increased by the addition of nCaCO₃ into the polyester/epoxy system compared to pure blend resin. Therefore, considering the strong competition in powder coating market, the use of nCaCO₃ as a commercial and inexpensive nanofiller is necessary not only to reduce the dwell time which has benefits in terms of the energy consumption and economics, but also to improve the performance of final polyester/epoxy coating.     

The influence of Ce-based coatings as pretreatments on corrosion stability of top powder polyester coating on AA6060

Cerium-based conversion coatings (CeCCs) are one of the most prospective alternatives to the widely used chromate conversion coatings (CCCs) due to their anticorrosion efficiency, environmentally friendly nature and low cost. In this work, the CeCCs on AA6060 were prepared by immersion into aqueous cerium salt solutions at room temperature, and subsequently post-treated in heated phosphate solution. The effect of counter ion (nitrate and chloride) on the coating properties was studied testing CeCCs as sole or conversion layers for the top polyester coating. Since the 60 μm thick polyester coating was applied, an artificial defect of 0.8 mm hole was introduced to faster assess the differences between pretreatments. The system with CCC pretreatment was used as reference. Corrosion properties were investigated in 0.5 M NaCl solution by electrochemical impedance spectroscopy while the adhesion strength was measured by NMPR (N-methyl-2-pyrrolidone) and pull-off tests. As shown, the post-treated chloride-based CeCC offered better protection than crack-free thin nitrate-based CeCC, when used as sole coatings. On the other hand, it was brought to evidence that in combination with top powder polyester coating, the CeCC deposited from nitrate solution exhibited better protection compared to protective system pretreated with chloride-based one. Excellent polyester coating adhesion was found independently on aluminium surface pretreatment.     

Synthesis and characterization of transparent and high impact resistance polyurethane coatings based on polyester polyols and isocyanate trimers

A series of polyester polyols were synthesized by polycondensation reaction using adipic acid (AA), 1,4-cyclohexanedicarboxylic acid (1,4-CHDA), and 1,6-hexanediol (HDO), 1,4-cyclohexanedimethanol (1,4-CHDM) and trimethylol propane (TMP), in which the molar ratio of the reactants AA/1,4-CHDA was varied. These series of polyols were reacted with isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HDI), alone or in combination, to form polyurethane (PU) coatings.     

Synthesis and characterization of acrylic-grafted polyester coatings for automotive pre-coated metal

An automotive pre-coated metal (PCM) system has been investigated to remove the wet coating process, such as pre-treatment, dip coating and spray coating for environmental regulations. However, automotive pre-coated metal sheets must have high flexibility and stiffness to overcome the harsh conditions such as encountered in cutting, press and the stamping process. For these reasons, a series of acrylic-grafted polyester coatings (i.e., AGP-0, AGP-10, AGP-20, AGP-30) were designed to satisfy both the surface hardness and the formability for an automotive PCM. The characteristics of the resins were measured by GPC, FT-IR and ¹H NMR. The viscoelastic behavior and flexibility was evaluated using DMA and UTM. The physical properties such as pendulum hardness, pencil hardness and adhesion were measured to define the effect of incorporating acrylates. A cylindrical deep drawing tester was used to evaluate the formability of coatings.     

Synthesis and characterization of flexible polyester coatings for automotive pre-coated metal

An automotive pre-coated metal system has investigated to remove the wet coating process, such as pre-treatment, dip coating and spray coating for environmental regulations. However, automotive pre-coated metal sheets must have high flexibility and formability to overcome the harsh conditions such as cutting, press and stamping process. For these reasons, flexible polyester coatings were designed to control flexibility using polycarbonatediol. The characteristics, curing behavior and viscoelastic property of the resins were measured by FT-IR, GPC, rheometer, DSC, RPT and DMA. The flexibility was evaluated using a texture analyzer. A nano-scratch tester, equipped optical microscope can measure the scratch resistance of coatings and the scratched surface morphology.With increasing polycarbonatediol content, the final frequency and the storage modulus increased and the T_g of the coatings decreased. This is related to the high mobility of the chain segment in polycarbonatediol. In terms of the flexibility and scratch resistance, CP-3 had high elongation value and good scratch resistance resulting from optimized stamping, pressing and cutting process in automotive pre-coated metal system. Therefore, polycarbonatediol is a powerful factor affecting the flexibility and scratch resistance of polyester coatings.     

Morphology and thermo-mechanical properties of new hybrid coatings based on polyester/melamine resin and pyrogenic silica

Polyester/melamine (PM)-based formulations used in coil-coating applications were modified with pyrogenic silicas of different types. The influence of the chemical modification of the silica surface on various properties was investigated. The viscosity of filled PM formulations was measured. Transmission electron microscopy and dynamic mechanical measurements were used to characterize nanocomposite films. Roughness and gloss measurements were done on nanocomposite coatings. The results show that the viscosity and morphology observed are directly linked to the balance and nature of the interactions developed between the silica surface and the organic medium. Both hydrophilic and hydrophobic silica lead to too high viscosity of the filled formulation, to different silica dispersion and, as a consequence, to low gloss coatings. However with an adequate organo-modification of the silica, formulations compatible with the process and having a high gloss can be obtained. Additionally, the surface modification of silica has no obvious influence on the dynamic mechanical properties.     

Influence of cycloaliphatic compounds on the properties of polyurethane coatings

A series of polyester polyol resin was synthesized by using 1,4-cyclohexanedimethanol (1,4-CHDM) and three different diacids: 1,3-cyclohexanedicarboxylic acid (1,3-CHDA), isophthalic acid (IPA) and adipic acid (AA). The solubility and viscosity of the polyester polyols were determined by using methyl ethyl ketone (MEK). All the polyester polyols were crosslinked with hexamethylene diisocyanate (HDI) isocyanurate to form polyurethane coating films. These films were evaluated for their mechanical and chemical resistance properties. Studies on the film characteristics revealed that the polyurethane films based on cycloaliphatic diacid generally showed comparatively better performance properties than the polyurethane film based on aromatic and linear aliphatic diacids in general.     

Synthesis and characterization of elastomeric polyester coatings for automotive pre-coated metal

An automotive pre-coated metal system (PCM) has been investigated to replace wet coating process, such as pre-treatment, dip coating and spray coating, to address environmental regulations. However, automotive pre-coated metal sheets must have high flexibility and stiffness to overcome harsh conditions such as cutting, press and stamping processes. For these reasons, elastomeric polyester coatings were designed to improve scratch resistance and to impart reflow characteristic for an automotive PCM. The characteristics, curing behavior and viscoelastic property of the resins were measured by ¹H NMR, GPC, RPT and DMA. The flexibility was evaluated using a texture analyzer. A nano scratch tester, equipped with an optical microscope was used to measure the scratch resistance of coatings and the scratched surface morphology. An Amtec laboratory car wash test and a sharp knife were used to evaluate the reflow property of the coatings. Change of the damaged surface morphology was measured using a mini-SEM.     

聚氨酯型不饱和聚酯涂料的研究

通过对反应过程中和涂膜酸值和粘度测定以及涂膜性能测定和红外光谱分析研究了聚氨酯型不饱和聚酯树脂的反应温度、反应时间、醇酸比、TDI用量、饱和酸与不饱和酸配比、交联剂聚苯乙烯用量等对涂料性能的影响。研究表明:反应温度170℃,反应时间3 h,乙二醇、邻苯二甲酸酐与顺丁烯二酸酐物质的量比为1.4:3:7,—NCO与—OH物质的量比为1:1,每15 g树脂中加入交联剂苯乙烯5 g,固化体系0.3 g,填料10 g,可制得物理力学性能较好的聚氨酯型不饱和聚酯涂料,涂膜硬度为5 H,附着力1级,柔韧性0.5 mm,抗冲击性50 cm。     

An essential work of fracture study of the toughness of thermoset polyester coatings

The fracture toughness of a range of thermoset polyester paints with different cross-link densities has been studied, using the essential work of fracture (EWF) method. The glass transition temperature, T_g, of each of the materials was measured using differential scanning calorimetry, and found to lie between 8 and 46 °C. EWF tests were performed on the paint films at a range of temperatures around the measured glass transition temperature of each material. The essential work of fracture, w_e, at T_g was found to decrease with increasing cross-link density from around 20 kJ/m² at a cross-link density of 0.4 × 10⁻³ mol/cm³ to around 5 kJ/m² for cross-link densities of approximately 1 × 10⁻³ mol/cm³ or higher. A maximum in the essential work of fracture was observed at around T_g when w_e was plotted versus temperature, which could be attributed to the effect of an α-relaxation at a molecular level. The polyesters were found to be visco-elastic, and the applicability of the EWF test to the study of these visco-elastic thermoset materials is discussed.     

以废聚酯制备聚氨酯涂料

以2,4–甲苯二异氰酸酯与三羟甲基丙烷制备了含有─NCO的A组分,将废聚酯通过醇解、酯化、缩聚等步骤制得不饱和聚酯,再与N,N–二甲基苯胺混合均匀作为含有─OH的B组分,将A、B两组分混合制得聚氨酯涂料。讨论了A、B组分的合成工艺,获得了最佳合成条件:制备A组分时,m(TDI)∶m(TMP)=3.86~3.89,θ=(85±5)°C,t=1~1.5h;制备B组分时,θ(醇解)=190~210°C,t(醇解)=3~3.5h;θ(酯化)=130~150°C,t(酯化)=100min;θ(缩聚)=200°C。当mA∶mB=1.05∶1时,所得涂膜表面坚硬光滑,附着力0级,硬度6H,耐水性测试240h无变化,盐雾试验48h无变化。     

Effects of highly absorbing pigments on near infrared cured polyester/melamine coil coatings

In order to expand available colour range for an industrial coil coating line a range of 25 μm polyester melamine coatings were applied to galvanised steel substrate and rapidly cured using near infrared (NIR) radiative curing. The purpose was to improve understanding of this relatively new curing technology and identify any problems associated with differing absorption of a range of coloured coatings. It has been suggested that in order to increase efficiency of NIR cure, NIR absorbers should be added to the coating formulation. UV/Vis/NIR spectroscopy was used to deduce the parts that coating and substrate absorption play in topcoat cure and lab scale trials were run on coatings throughout the colour range with their heating profiles and surface finish being recorded and assessed. The results showed that in this particular application having a coating that absorbs too strongly in the NIR region can actually result in solvent boil defects due to cross linking and film formation occurring prior to solvent removal.     

Side-chain polyesters and polyester hydrochlorides based on terephthalic acid

Side-chain polyesters and polyester hydrochlorides were synthesized from α-(bis(2-hydroxyethyl)amino)-ω-(4′-methoxy biphenyl-4-oxy) alkanes with different spacer lengths (Cn-diol, n=6, 8, 10) and terephthaloyl chloride. Since N-substituted diethanolamine acts as a stronger acid acceptor than triethylamine or pyridine, polyester hydrochlorides are formed during polyesterification instead of polyesters. Polyesters can be prepared from a chloroform solution of polyester hydrochlorides by extraction of HCl. During the polyesterification, linear polymers as well as cyclic oligomers are formed. All polymers were analyzed by ¹H NMR, size exclusion chromatography (SEC), differential scanning calorimetry (DSC), X-ray spectroscopy (XND) and polarizing optical microscopy (POM). Polyesters and polyester hydrochlorides differ greatly in solubility and thermal properties. Although no liquid crystalline phase transitions were detected for either kind of polymer, an ordered structure was observed in XRD experiments for both polymers and was ascribed to a crystal smectic E phase.     

Alkaline hydrolysis: A facile method to manufacture superhydrophobic polyester fabric by fluorocarbon coating

For the fabrication of the “lotus-type” fibers a combination of two major requirements, low surface energy and the magnified of the degree of roughness, should be utilized. In this research, the possible surface roughening effect of alkaline hydrolysis of the polyester fibers was applied to manipulate surface topography while fluorocarbon polymer layer generates low surface energy. The results were compared with the method which created variety of surface roughness by changing the size of the nano-silica particles using the 3 M water/oil repellency test, sliding (tilt) angle, microscopy (SEM), decay of hydrophobicity, self-cleaning, tensile properties, abrasion fastness, and air permeability.The results indicated the usefulness of the conventional polyester weight reduction process to control surface roughness for engineering superhydrophobic fabric with sliding angle as low as 7°. Due to the applied conditions this process presents new facile procedure for industrial scale manufacturing of ultrahydrophobic polyester fabric.     

Enzymatic hydrolysis of canola oil with hydrodynamic cavitation

A hydrodynamic cavitation system based on a venturi was used to test the effectiveness of cavitation for enhancing the enzymatic hydrolysis of canola oil using lipase from Candida rugosa. Cavitation led to the production of fine oil-in-water and water-in-oil emulsions with the enzyme in the water phase. Using venturi inlet pressures of up to 8 bar, the yield of fatty acids was only about 60% of the maximum possible. In contrast, a simple stirred batch reactor produced over 90% of the maximum possible yield with reaction rates equal to, or better than, those obtained in a cavitating system. It was concluded that cavitation inhibited the reaction in some way and is not effective for intensification of hydrolysis.     

聚己二酸己二醇酯型聚氨酯水乳液的合成及性能研究

以己二酸、己二醇为原料合成聚己二酸己二醇酯二醇,并制备成聚氨酯水乳液。研究了乳液成膜物的耐水解性和物理性能。结果表明：聚己二酸己二醇酯为基础的聚氨酯乳液,其成膜物拉伸强度高、硬度大、耐水解性能优良,可用作皮革涂饰剂。     

有机硅改性聚酯的合成及其粉末涂料的性能

利用有机硅中间体合成了有机硅改性聚酯树脂。通过IR、GPC、SEM等分析了改性聚酯的结构与形态 ,用电子探针分析了改性聚酯的表面组成 ,考察了有机硅含量对改性树脂玻璃化温度、熔融黏度、对水的接触角及表面张力的影响。研究发现 ,改性聚酯中的含硅聚酯在表面富集 ,大大降低了聚酯树脂的表面张力 ,提高了其粉末涂料的涂膜耐候性。相对于纯聚酯树脂 ,有机硅质量分数为 1 %可使树脂的表面张力从 49.5降到 2 8.4mN/m ;经 2 1 6h中波紫外线照射后 ,涂膜的光泽保留率从 81 %上升到 91 .3 %。含有机硅质量分数超过 5 %后 ,涂膜的抗冲性能下降。     

Seed oil based polyester polyols for coatings

The hydroformylation of seed oil based fatty acid methyl esters leads to aldehyde intermediates that can be hydrogenated to give novel seed oil based monomers. In this study, the seed oil based monomers were polymerized with low molecular weight diols to produce novel aliphatic polyester polyols with very low viscosities. The seed oil polyester polyols provide environmentally friendly (green) coating formulations with low volatile organic compound emissions which lead to coatings with superior physical properties, such as exceptional hydrolytic resistance and flexibility. From these polyester polyols, waterborne polyurethane dispersions were also developed with excellent stability resulting in coatings with superior physical properties (i.e., good toughness and abrasion resistance), and exceptional hydrolytic and acid resistance.