Chao-Ching Chang

Preparation of water-resistant antifog hard coatings on plastic substrate.

A novel water resistant antifog (AF) coating for plastic substrates was developed, which has a special hydrophilic/hydrophobic bilayer structure. The bottom layer, acting both as a mechanical support and a hydrophobic barrier against water penetration, is an organic-inorganic composite comprising colloidal silica embedded in a cross-linked network of dipentaethritol hexaacrylate (DPHA). Atop this layer, an AF coating is applied, which incorporates a superhydrophilic species synthesized from Tween-20 (surfactant), isophorone diisocyanate (coupling agent), and 2-hydroxyethyl methacrylate (monomer). Various methods, e.g., FTIR, SEM, AFM, contact angle, and steam test, were employed to characterize the prepared AF coatings. The results indicated that the size and the continuity of the hydrophilic domains on the top surface increased with increasing added amount of T20, however, at the expense of hardness, adhesiveness, and water resistivity. The optimal T20 content was found to be 10 wt %, at which capacity the resultant AF coating was transparent and wearable (5H, hardness) and could be soaked in water for 7 days at 25 °C without downgrading of its AF capability.

Preparation of polymer/silica composite antiglare coatings on poly(ethylene terphathalate) (PET) substrates

Abstract3-(Trimethoxysilyl) propyl methacrylate and fluoroalkylsilane modified silica particles were UV-cured with the multifunctional crosslinking agent, dipentaerythritol hexaacrylate (DPHA), to prepare antiglare (AG) coatings that exhibit high hardness. Modified silica was used to impart surface roughness whereas DPHA was used to provide hardness and adhesiveness. The formed AG coatings were characterized in terms of topological, optical, and mechanical properties. It was found that with the increase of DPHA content in the coatings, the surface roughness and haze decreased while the gloss and clarity increased. For samples containing 40 and 50 wt% DPHA, the optical properties are comparable to commercial AG products for flat panel display and touch panels. These prepared coatings also demonstrate high hardness of 5–6H and 100% adhesion on poly(ethylene terphathalate) substrates.

Preparation of hydrophobic nanosilica-filled polyacrylate hard coatings on plastic substrates

Colloidal silica nanoparticles synthesized from tetraethoxysilane via a sol–gel process were surface-modified first by 3-(trimethoxysilyl)propyl methacrylate, and then by trimethylethoxysilane (TMES). The former agent acts both as a coupling agent and as a C=C provider, whereas the latter agent is used to prevent particle aggregation and to increase hydrophobicity of the coating. The modified silica particles were UV-cured together with the monomer, 2-hydroxyethyl methacrylate (2-HEMA), and the crosslinking agent, dipentaerythritol hexaacrylate (DPHA), to form highly transparent hard coatings on plastic (PMMA and PET) substrates. Both differential scanning calorimetric and thermal gravimetric analyses of the hybrid materials indicated enhanced thermal stability with respect to the neat HEMA–DPHA copolymer. Furthermore, due to the incorporation of TMES, hydrophobicity of the hybrid coating increased considerably with increasing modified silica content. In the extreme case, an antiabrasive hard coating (7H on PMMA) with a water contact angle of 99° was obtained at the silica content of 15 wt%.