| 摘要 |
PURPOSE:To obtain a platen capable of reducing noise by a simple constitution without use of sound-proof covers by a method in which an expanded elastic layer is provided on the periphery of the platen core and a hard and dense elastic layer is provided cylindrically on the expanded elastic layer. CONSTITUTION:An expanded elastic layer 31 is provided on the periphery of a metal platen core 30, and a hard and dense elastic layer 32 (e.g., hard rubber layer of a hardness of about 96) is provided on the layer 31. Since the expanded material used has low density and the hard rubber used has high density, there is a great difference in acoustic characteristic impedances Z1 and Z2 of both the materials, and therefore, solid sound generated by the oscillation of the hard rubber layer 32 is considerably reflected at the boundary with the expanded elastic layer 31, thus preventing the permeation of noise. Also, even on the boundary between the expanded elastic layer 31 and the core 30, solid sound is reflected due to the difference of impedances of both and transmission of solid sound from the hard rubber layer 32 to the core 30 is greatly reduced. |
