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.     

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 a novel hydroxyl-terminated polydimethylsiloxane for application in the silicone-modified acrylic-grafted polyester resins

Monoallyl-end-capped polypropylene glycol (MPG) was successfully synthesized by the reaction of polypropylene glycol and allyl chloride. Also, hydrogen-terminated polydimethylsiloxane (H-PDMS) was prepared by the reaction of dichlorodimethylsilane and chlorodimethylsilane (CDMS). Then, MPG and H-PDMS were reacted to produce hydroxyl-terminated polydimethylsiloxane (OH-PDMS) as silicone which is used to prepare automotive pre-painted or coil-coated metals (PCM). This pre-coated metal PCM system was investigated to remove the wet-coating process, such as pre-treatment and spray coating for environmental regulations. However, automotive pre-coated metal must have high flexibility and stiffness to overcome the harsh conditions such as those encountered in the cutting, pressing, and stamping process. For these reasons, a series of silicone-modified acrylic-grafted polyester (SAGP) resins (e.g. SAGP-0–SAGP-10) were designed to satisfy both the hardness and the flexibility for an automotive PCM. The OH-PDMS (silicone) was characterized by Fourier transform-infrared (FT-IR), ¹H-NMR, and ¹³C-NMR spectroscopic techniques. The results showed that the targeted product was successfully carried out. The structural elucidation of the synthesized SAGP was carried out by FT-IR spectroscopic technique. Thermal properties of the resins were studied using thermogravimetric analysis and differential scanning calorimetry. The flexibility of the resins was measured by tensile test. The contact angle measurement can be measured by the water repellence of the coating surface, which is a standard method to evaluate cleanable characteristics. The surface free energy was calculated by the contact angle measurement.     

电镀锡板表面抗划伤性的研究Ⅱ.软熔工艺对电镀锡板表面抗划伤性的影响

移植QHQ型涂膜铅笔划痕硬度仪用来测试电镀锡板的抗划伤性。用此方法研究了软熔处理以及不同软熔方式对电镀锡板抗划伤性的影响，实验结果表明：软熔处理对薄镀锡板可以提高镀锡板表面抗划伤性，在电阻软熔基础上增加感应软熔后，在一定条件下可进一步提高电镀锡板的抗划伤性，并从理论上进行了初步探讨。通过对电镀锡板表面形貌结果表明，表面抗划伤性与镀层晶粒大小和致密性有关。     

Formulation and performance evaluation of hydroxyl terminated hyperbranched polyesters based poly (ester–urethane–urea) coatings on mild steel

A low molecular weight, anticorrosive hyperbranched poly (ester–urethane–urea) [HB-P(EUU)] coatings were formulated using 2nd generation hydroxyl terminated hyperbranched polyesters (OH–HBPEs), isophorone di-isocyanate (IPDI) as a cross linking agent and dibutyltin dilaurate (DBTDL) as a catalyst with certain additives. First, NCO terminated prepolymers (HBPEUs) were formulated by reacting OH–HBPEs with IPDI at NCO:OH ratio of 1.1:1 for 4 h at 70–80 °C, then HBPEUs were mixed with DBTDL and various additives and finally coated on pretreated cold rolled mild steel (MS) substrates by dip coating method. Before applying on MS substrates, viscosity and volume solid of coatings were measured. The molecular structure of HBPEUs was characterized by ATR-FTIR and ¹H NMR analysis. Surface morphology of coated panels was characterized by atomic force microscopy (AFM) and found that coating components were homogeneously distributed and surface was smooth and crack free. Performance of coated substrates was evaluated by various tests such as cross hatch and pull off adhesion, abrasion resistance, scratch resistance, impact resistance, flexibility, and pencil hardness. UV stability of coated substrates was evaluated by UV-whether-o-meter and corrosion resistance property was evaluated by salt spray, humidity, polarization and electrochemical impedance (EIS) test. Results were also compared with polyurethane coating based on linear polyester. HB-P(EUU) coatings showed excellent enhancement in mechanical, durability as well as corrosion resistance properties than their linear counterpart.     

Formulation and performance evaluation of hydroxyl terminated hyperbranched polyesters based poly (ester–urethane–urea) coatings on mild steel

A low molecular weight, anticorrosive hyperbranched poly (ester–urethane–urea) [HB-P(EUU)] coatings were formulated using 2nd generation hydroxyl terminated hyperbranched polyesters (OH–HBPEs), isophorone di-isocyanate (IPDI) as a cross linking agent and dibutyltin dilaurate (DBTDL) as a catalyst with certain additives. First, NCO terminated prepolymers (HBPEUs) were formulated by reacting OH–HBPEs with IPDI at NCO:OH ratio of 1.1:1 for 4 h at 70–80 °C, then HBPEUs were mixed with DBTDL and various additives and finally coated on pretreated cold rolled mild steel (MS) substrates by dip coating method. Before applying on MS substrates, viscosity and volume solid of coatings were measured. The molecular structure of HBPEUs was characterized by ATR-FTIR and ¹H NMR analysis. Surface morphology of coated panels was characterized by atomic force microscopy (AFM) and found that coating components were homogeneously distributed and surface was smooth and crack free. Performance of coated substrates was evaluated by various tests such as cross hatch and pull off adhesion, abrasion resistance, scratch resistance, impact resistance, flexibility, and pencil hardness. UV stability of coated substrates was evaluated by UV-whether-o-meter and corrosion resistance property was evaluated by salt spray, humidity, polarization and electrochemical impedance (EIS) test. Results were also compared with polyurethane coating based on linear polyester. HB-P(EUU) coatings showed excellent enhancement in mechanical, durability as well as corrosion resistance properties than their linear counterpart.     

A macroscopically nondestructive method for characterizing surface mechanical properties of polymeric coatings under accelerated weathering

The surface of coatings and plastics is the first target in any degradation process initiated by ultraviolet (UV) radiation or mechanical stress (via scratch and abrasion). Surface damage can lead to changes in optical, morphological, and mechanical properties and can result in pathways for ingress of moisture and corrosive agents. Current test methods for monitoring performance of protective coatings focus on chemical properties and optical properties, such as color and gloss measurements, or invasive tests such as abrasion and cross-cut adhesion. In this study, a macroscopically nondestructive performance protocol using nanoindentation metrology via a well-controlled scratch test was applied to evaluate the scratch resistance and monitor the surface mechanical property changes in a protective coating under accelerated weathering. Polyurethane (PU) coatings with different polyol compositions were chosen for this study. Coating specimens were exposed to high-intensity UV radiation at 55°C and 75% RH conditions. Exposed specimens were removed at specified UV exposure times for surface modulus/hardness and scratch resistance characterization via nanoindentation and scratch test. The effect of polyol type and UV radiation dose on the scratch damage (scratch morphology) was investigated and correlated with the surface hardness and modulus of the materials.     

Structure/property relationships in flexible alkoxysilane automotive coatings

Flexible automotive coatings are susceptible to scratch and mar damage, especially during finishing and assembly operations. One-component (1K) flexible clearcoats exhibit very good scratch and mar resistance, but unfortunately suffer from poor durability and environmental etch resistance. Two-component clearcoats offer improvements in both etch and durability, but at the expense of scratch and mar. In this paper, the concept and properties of 1K flexibilized silane clearcoats for use on automotive plastics will be introduced and their structure/property relationships examined as they apply to scratch and mar. The role of coating crosslink density, toughness, glass transition temperature (T_g), and surface profile on the scratch damage of coated plastic substrates will be described. In addition, a new scratch methodology, termed Scratcho, is utilized to determine relative scratch performance and is compared to conventional scratch resistance testing. Results to date indicate that hardness, as affected by the glass transition temperature, and crosslink density, as it contributes to higher essential work values, both affect resultant scratch propensity of the flexible coatings. The relative ranking of different coating systems employing alternate crosslinkers (e.g., isocyanate and melamine) is also presented and compared to the newly developed silane crosslinked coatings. Presented at the 28th International Waterborne, High-Soids, and Powder Coatings Symposium, Feb. 21–23, 2001, in New Orleans. LA. 377 Fairall St., Ajax, Ont., L1S 1R7, Canada. 401 Southfield Rd., P.O. Box 6231, Dearborn, MI 48121-6231.     

Evaluation of durability of nano-silica containing clear coats for automotive applications

In automotive application, multilayer coating systems are typically used to guarantee protection from corrosion phenomena and aesthetic properties. A coating system's appearance and its durability is becoming increasingly important for automotive original equipment manufacturers. Clear coats are required to maintain long term aesthetic appearance, color and gloss stability to weathering and mechanical damage. One key property is scratch and mar resistance. The use of nano-fillers is a promising strategy to increase the abrasion resistance without affecting the optical clarity of high gloss coatings.     

Characterization of polyurethane foam as heat seal coating in medical pouch packaging application

In this study the use of polyurethane foam (PUF) as a heat seal coating for potential application in medical pouch packaging were investigated. We prepared PUF coatings at various foam densities and cell densities through mechanical foaming at various stirring speeds; then used a LUMisizer to examine their stabilities. After applying PUF coatings of various foam densities onto a medical packaging material (Tyvek?) at various thicknesses, then employed impulse heat sealing with linear low density polyethylene (LLDPE) films to fabricate medical pouches. In addition to investigating the morphology, tack properties, adhesion, scratch resistance, flexibility, and durability of the PUF coats, the peel strength and air permeability of the medical pouches were also measured. Increasing the foam density of the PUF coatings increased their stability; the PUF coats prepared at a higher foam density exhibited greater tackiness (<1 g/cm²), adhesion (5B), scratch resistance (HB), flexibility (passes), and durability (ΔYI ≤ 5). The peel strength measured in the T-peel configuration increased upon increasing the foam density and decreasing the coating thickness of the PUF coat/LLDPE pouches. The air permeability of the pouches increased upon increasing the foam density and cell density of the PUF coat/LLDPE pouches. Morphological studies using scanning electron microscopy were consistent with the experimental results.     

Rheology and roll coating dynamics of metallic basecoats for automotive pre-coated metal sheet

Rheological behavior and coating dynamics of solvent-based metallic basecoats using 3-roll coaters were investigated for the application process based on pre-coated metal (PCM) sheet technology that can promisingly diminish the environmental pollutants in automotive OEM line. Rheological properties of the metallic basecoats related to optical appearance and color variations were measured by altering the content of aluminum (Al) flake and temperature of the coating solution. The results showed that the basecoats exhibited a very weak shear-thinning behavior regardless of Al flake contents in this study. However, their elastic behaviors were intensified with increasing the Al flake content. From the 3-roll coating experiments with forward and reverse coating modes, the operability windows in the coating process, demarcating the uniform coating flow from defects, were established. In particular, it was possible to elucidate the relationship between the capillary number and speed ratio conditions for the desired coating thickness in roll coating systems accompanied with reverse coating mode between the pick-up and metering rolls. It was verified from the cross-sectional images of coating layers that most of Al flakes inside the basecoat layer were oriented parallel to the coating surface under the continuous roll coating flows.     

家电板用黑色导电背漆的研制

讨论了家电板用黑色导电背漆的研制,着重讨论了导电材料的选用、树脂、颜填料及助剂对涂膜导电性能的影响。     

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

Polyester-based nanocomposites coatings were synthesized by the in situ polymerization with high speed homogenizer process at the various contents of organic modified montmorillonite (OMMT) to disperse into the polyester matrix. The dispersion state of organoclay was examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The absence of reflection pattern of organoclay and TEM study revealed that organoclay was partially intercalated and exfoliated into the polymer matrix. Mechanical property of polyester-based nanocomposites coatings (PE/OMMT) improved the tensile strength and good formability at the deep drawing test. The viscoelastic behavior of PE/OMMT nanocomposites coatings was observed by dynamic mechanical analysis (DMA). When the content of organoclay was increased, the stiffness of the PE/OMMT nanocomposites coatings increased considerably and T_g of each cured coatings shifted to a lower temperature. Anti-corrosion property was examined by the salt spray test. CNC-3 had little rust after 600 h and it implies that nano-sized layered silicate of organoclay effectively increases the length of the diffusion pathways water molecules. And nano-sized layered silicate of organoclay might be decreased the permeability and could make higher corrosion resistance of PE/OMMT nanocomposites coatings. From those results, CNC-3 had good formability in the deep drawing and also had good anti-corrosion property. So, CNC-3 would be an appropriate coating for automotive pre-coated metal.     

Influence of a hard transition layer on the microstructure and properties of diamond-like carbon/hydroxyapatite composite coating prepared by magnetron sputtering

The nanostructured diamond-like carbon/hydroxyapatite composite coating (DLC/HA) was deposited using magnetron sputtering technique with a densely packed columnar cross-sectional structure and a uniform granular surface morphology. After heat treatment, the amorphous structure of the coating was transformed into a crystal structure. Nanohardness and scratch tests results demonstrated the DLC transition layer significantly enhanced the nanohardness of Ti6Al4V substrates from 4.8 GPa to 10.4 GPa, and increased critical load from 16.6 N (pure HA layer) to 26.5 N (DLC layer) without obvious brittle fracture, flaking and delamination. Electrochemical and immersion tests results demonstrated that DLC/HA composite coatings with a dense gradient transition interlayer had better corrosion resistance and could prevent harmful metal ions being released into the SBF solution more effectively than single HA coatings. Furthermore, active Ca²⁺ ions can be rapidly released from the coating surface during initial immersion in the SBF solution, and facilitated the formation of bone-like apatite.     

Visco-elastic visco-plastic analysis of scratch resistance of organic coatings

The sensitivity of automotive coatings to scratching, particularly coatings for plastics has been a growing concern among automakers. Scratching may result from such predelivery events as polishing minor defects embedded in the paint, or postdelivery events such as car wash bristles, dirt embedded under a cloth utilized in polishing the car, tree branches, and the like. Warranty cannot separate out which event is the more prevalent (e.g., predelivery or postdelivery to the customer) form of damage on plastics. Data available on coatings for metal, however, does suggest that isocyanate-based crosslinked systems perform more poorly than their melamine-based crosslinked counterparts when exposed to in plant (predelivery) handling. Coatings on plastics, while lower in modulus than coatings on steel, are still subject to scratch events, albeit they have a greater tendency to “self-heal” once scratching events have occurred. This work attempts to correlate the scratch resistance behavior of three different one-component hydroxyl-functional acrylic or polyester-acrylic-melamine-crosslinked systems. Relationships between the tensile and indentation properties of the coatings were found to be related to the initial warranty data of the coating systems. Most importantly, it was apparent that the critical depth to fracture of the flexible coatings may be the relevant indicator of field performance for coatings on plastics. For metals, the relevant indicator to field performance is often only critical load to fracture, negating the influence of indentation depth. This variance is important to consider since coatings on plastic are often softer and more resilient to surface abrasions than their counterparts on metal.     

Nylon 11/silica nanocomposite coatings applied by the HVOF process. II. Mechanical and barrier properties

Nylon 11 coatings filled with nominal 0–15 vol % of nanosized silica or carbon black were produced using the high velocity oxy‐fuel combustion spray process. The scratch and sliding wear resistance, mechanical, and barrier properties of nanocomposite coatings were measured. The effect of powder initial size, filler content, filler chemistry, coating microstructure, and morphology were evaluated. Improvements of up to 35% in scratch and 67% in wear resistance were obtained for coatings with nominal 15 vol % contents of hydrophobic silica or carbon black, respectively, relative to unfilled coatings. This increase appeared to be primarily attributable to filler addition and increased matrix crystallinity. Particle surface chemistry, distribution, and dispersion also contributed to the differences in coating scratch and wear performance. Reinforcement of the polymer matrix resulted in increases of up to 205% in the glass storage modulus of nanocomposite coatings. This increase was shown to be a function of both the surface chemistry and amount of reinforcement. The storage modulus of nanocomposite coatings at temperatures above the glass transition temperature was higher than that of unfilled coatings by up to 195%, depending primarily on the particle size of the starting polymer powder. Results also showed that the water vapor transmission rate through nanoreinforced coatings decreased by up to 50% compared with pure polymer coatings. The aqueous permeability of coatings produced from smaller particle size polymers (D‐30) was lower than the permeability of coatings produced from larger particles because of the lower porosities and higher densities achieved in D‐30 coatings. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2272–2289, 2000     

Manufacture and characterization of free-standing epoxy-polyester films

The present investigation analyzes the deformation behaviour under static and dynamic loading conditions of electrostatically sprayed epoxy-polyester powder coatings by local and uniaxial tests, trying to account for the separate contribution of the raw polymeric material alone and of the adhesion to the underlying metal substrate. First, thermo-rheological properties of the basic material (i.e., the thermosetting powder paints) were characterized by differential scanning calorimetry (DSC) and rheometry. Secondly, free-standing films were manufactured by electrostatic spraying of the thermosetting powders onto stainless steel substrates pre-coated with an intermediate layer of silicon-based heat curable release coating. The resulting free standing-films were macroscopically characterized by combined dynamic-mechanical analyses (DMA) and tensile tests. Finally, local mechanical characterization of the coating performance was carried out by micro-scale depth sensing scratch and indentation on coatings ‘free-standing’ and ‘rigidly adhering’ onto metal substrate.     

On the electrochemical and structural behavior of biologically degraded automotive coatings; Part 1: Effect of natural and simulated bird droppings

Environmental factors can potentially deteriorate automotive coatings. These include UV radiation, humidity, hot–cold shocks as well as aggressive chemical compounds. In addition, natural occurring materials such as bird droppings and tree gums are also enable to affect the coatings. The present work aims to study the degradation of an automotive coating system exposed to natural and simulated bird droppings. To this end, structural analysis of samples was studied using FT-IR spectroscopy, optical and atomic force microscopes. Also, the mechanical and electrochemical behaviors of coatings were investigated by DMTA and electrochemical impedance spectroscopy (EIS). It was found that the biological materials significantly affect the mechanical and chemical properties of the coatings, resulting in a decrease in corrosion resistance. A two-time constant semicircle was observed for degraded coatings after a short time as a result of electrolyte diffusion into the coating/metal interface. The behavior of the coatings was then discussed based on the formation of surface defects.     

Flash IR pre-curing of the decorative layer in metal-flake powder coatings

Metal-flake powder coatings are a special class of metallic paint finishes composed of two superimposed layers: a pigmented decorative base coat and an overlaying transparent protective top coat. In the present investigation, a novel curing procedure for such bilayer coatings is proposed. Flash IR pre-curing of the base coat promotes the formation of a surface diffusion barrier and limits movement of the decorative pigments and metal flakes around their initial positions. Oven baking after deposition of the top coat then completes curing of the bilayer coating. The influence of the IR intensity and irradiation time on the final properties of bilayer coatings was investigated. The visual appearance, surface morphology and scratch resistance were evaluated. Experimental findings revealed that the hybrid IR/oven baking curing procedure is a viable method for obtaining bilayer powder coatings with outstanding properties in a shorter processing time and with considerable energy savings.     

Synthesis of UV-curable polysiloxanes containing methacryloxy/fluorinated side groups and the performances of their cured composite coatings

Three novel UV-curable polysiloxanes consisting of polysiloxane backbone with methacryloxy/fluorinated side groups were synthesized, and their structures were characterized by FT-IR, ¹H NMR and ¹³C NMR. A series of UV-cured composite coatings based on the synthesized polysiloxanes and an epoxy methacrylate were obtained through photopolymerization. Their gel content, flexibility, hardness, gloss, contact angle, thermal behavior as well as water absorption ratio were investigated. Results found that the siloxane component could enhance the flexibility and gloss of coatings, while the presence of fluorinated groups could improve the hardness. The combination of silicon and fluorine in the same polymer could increase thermal stability and water resistance of the coatings and decrease their surface energy simultaneously. The observation of the fractured-surface morphology showed that the polysiloxanes could be well dispersed in the epoxy methacrylate to some extent. A suitable addition of such polysiloxane in photocurable coating matrixes may provide excellent properties for the cured coatings and widen their applications.