Surface of natural rubber was modified by radiation-induced grafting of hydrophilic monomer, 2-hydroxyethyl methacrylate (HEMA), to improve the properties of surface hardness, dry friction, wiping performance, and wear duration. The ratio of grafted-HEMA to the rubber near the surface layer of HEMA-grafted rubber was analyzed by FT-IR and expressed as composition ratio. The composition ratio was controlled from 0.29 to 0.93 by changing HEMA concentration and dose in graft polymerization. When this composition ratio was higher than 0.8, the surface hardness was higher than 70 and the coefficient of dry friction lower than 0.65. Those values became better than those of commercially available chlorinated-rubber in terms of wear and friction against glass. The surface hardness in wet state became very close to natural rubber since grafted-HEMA was softened by contacting with water. As a result, the grafted-HEMA rubber realized 95% and higher wiping performance of water on glass. Additionally, the wear resistance was eight times higher than chlorinated rubber.
Hydrophilic monomer, 2-hydroxyethyl methacrylate (HEMA), and hydrophobic monomer, 3-(methacryloyloxy)propyltris(trimethylsiloxy)silane (MPTS) were grafted on vulcanized rubber surface with simultaneous electron beam irradiation. Degree of graft polymerization was evaluated by composition ratio of imparted graft chain against trunk rubber. The composition ratio could be controlled by the monomer concentration and the irradiation dose. Grafted rubbers were evaluated by surface roughness and contact angle. Graft polymerization of HEMA decreased the contact angle from 93 to $ 70 without considerable change of the surface roughness. In the case of MPTS, the contact angle increased approximately to
108. The relationship between the contact angle of water on the modified surface and the friction at the moment of semidry was investigated as an application of the resulting rubber to wiper blade. The increase of the contact angle owing to the grafting of hydrophobic MPTS led to the decrease of Dl (deference between semi-dry state and dry friction). Instead, the decrease of the contact angle by grafting of hydrophilic HEMA resulted in the increase of Dl.
Hydrogenated amorphous carbon (a-C:H) films were deposited on rubber surface by plasma-enhanced chemical vapor deposition (CVD), using a non-equilibrium atmospheric pressure plasma torch. The effects of oxygen, in the deposition atmosphere, on the chemical and mechanical characteristics of a-C:H films were investigated. It was clarified that the amount of carbon atoms combined with oxygen atoms in the a-C:H films increased with the increase of the oxygen content in the deposition atmosphere. On the other hand, surface hardness decreased as the oxygen content increased. As a result, a very low frictional property of a-C:H films was achieved by CVD, using the non-equilibrium atmospheric pressure plasma torch with eliminating oxygen from the deposition atmosphere.
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