High‐solids mar resistant clearcoats prepared from an isophthalate‐based oligoester and a melamine resin. Study and characterization of mar resistance with scanning probe microscopy method

Abstract

:A new series of high-solids [low-VOC (volatile organic compound)content] mar resistant clearcoats (CL-series) were prepared upon crosslinking of a new-synthesized hydroxyl-terminated isophthalate-based liquid oligoester (L-311) with an hexakis(methoxymethylol)melamine (HMMM) resin, via an acid-catalyzed etherification reaction. The chemical, physical, and mechanical properties of the CL-clearcoats were compared to those of a reference clearcoat (CRO). An attempt was made to investigate the effect that the amounts of catalyst and melamine resin had on the clearcoats' physical, chemical, and mechanical properties, and moreover, to correlate these properties to the films chemical structures. The new-formulated high-solids clearcoats (CL-series) presented enhanced processability and higher NVW values (lower VOC content) than the reference clearcoat CRO, and their properties (pencil hardness, knoop hardness, adhesion, impact resistance, solvent and gasoline resistance, mar resistance, and flexibility) were better or comparable to those of the CRO. More specifically, the mar resistance of the CL-clearcoats series was investigated by applying both the crockmeter test and a novel method that employed a modified scanning probe microscope. In addition, we identified and characterized the different responses of the CRO and certain CL-clearcoats to marring stress. The experimental data regarding the mar resistance of the new-formulated clearcoats fully justified our polymer design strategy, verifying our expectations for the possibility of preparing glossy, high-solids mar-resistant clearcoats that could present enhanced processability and solvent resistance, relatively high pencil hardness, and at the same time very good elastic recovery to marring stress.

Novel high‐solids pigmented coatings prepared from a new‐synthesized isophthalate‐based oligoester, a melamine resin, and various fillers

“…This behavior could be attributed to the fact that the filler W300 has substantially higher pH (=9.9 as a 10% slurry) than A480 and A150 (pH = 3.5–5.0) do. Probably an amount of the Lewis‐acid catalyst used for the crosslinking reaction (acid‐catalyzed transetherification4, 5) of the binder (L‐311) and the crosslinker (melamine resin) was consumed when the significantly basic filler W300 was used. Therefore, a higher curing temperature was applied for the crosslinking without changing the amount of the catalyst.…”

“…For measuring the mar resistance of the PA‐ and PW‐pigmented coatings series, we applied the following three methods: (i) the crockmeter test4, 5; (ii) the analysis with a modified scanning probe microscope5, 9–17; and (iii) the Taber abrasion test. The modified scanning probe microscopy method did not work in the case of the pigmented coatings because the surfaces were too rough6 to be penetrated correctly by the diamond tip and at the same time to afford reliable and reproducible results.…”

“…As regards the crockmeter test, not surprisingly, we observed an increase in every angle degree of the gloss. The marring of the surface, according to the experimental procedure we had applied in the case of the clearcoats4, 5 or even when we replaced the BonAmi ® cleaning powder with an aluminum powder (harsher marring), resulted in the smoothing of the film's surface and subsequently to a decrease of the light scattering (higher measured gloss at a specific angle degree gloss). From all three methods, only the method of the Taber abrasion gave some reliable and repeatable results and mar resistance was recorded as the inverse wear index, F [= I −1 , cycles/cg (wear index l , weight loss (cg) per number of cycles)] (see Experimental, Characterization Methods) of the corresponding coating.…”

“…Attempts to measure the micro‐mar resistance (MMR) and microindentation hardness (MIH) of the new formulated pigmented coatings were performed by using a Digital Instruments Nanoscope III ® , scanning probe microscope, modified as previously reported 5, 9–17. The test5, 9–17 employed a modified scanning probe microscope (SPM) to mar the material and conventional scanning probe microscope to measure and characterize the results 5, 9–17…”

“…We previously studied3 the effect of the different transesterification parameters on the synthesis of high‐solids liquid hydroxyl‐terminated isophthalate‐based oligoesters and the results obtained from that investigation led us to the preparation of a new‐synthesized high‐solids hydroxyl‐terminated isophthalate‐based oligoester, L‐311, which presented enhanced processibility. In previous works, we used the L‐311 for the preparation of high‐solids mar‐resistant clearcoats4, 5 and talc (3MgO · 4SiO 2 · H 2 O)‐pigmented coatings 6…”