1. Technical Field
The present invention relates to a roller used for transporting, or the like a medium such as a paper, a separation device including the roller, an image reading apparatus such as a scanner, and a recording apparatus.
2. Related Art
In order to secure a transport performance for various media, a surface of a roller is in contact with a surface of the medium and transports the medium, it is desirable that this kind of rollers is elastically slightly crushed a surface thereof which is brought into contact therewith and the contact area between the surface of the medium and the surface of the roller increases. In the related art, the crush is realized using a foamed rubber material as a material for the roller.
In addition to the foamed rubber material, an elastomer is used to realize the crush (JP-A-2008-241739 or the like).
However, in order to secure the transport performance of the roller by the foamed rubber material, a high-quality material is required, resulting in a problem of high cost. In addition, cracks are likely to be generated from the foamed portion as a starting point over time, and when repeated deformation is added, it is difficult for the shape thereof to be returned to the original shape thereof, resulting in a problem that the durability of the roller is lowered.
In a roller using an elastomer other than the foamed rubber material, although there is no problem that cracks are likely to be generated from a foamed portion such as a foamed rubber material as a starting point, since the elastomer generally has a rubber hardness higher than that of a foamed rubber material, in order to secure the transport performance of the roller due to the crush, it is difficult to select a proper material and degrees of freedom of selection is lowered. As a result, there is a problem of high cost.
In addition, there are the following problems from the manufacturing aspect of the roller.
Generally, the roller is manufactured by pouring a raw material into a mold and filling the mold with the raw material, as in insert molding or the like. In the insert molding or the like, although it is necessary to secure fluidity when pouring and filling the mold with the raw material thereof, even in a structure in which the roller penetrates from one side surface to the other side surface in the axial direction thereof, it is difficult to secure the fluidity and the time required for completion of filling is likely to be long. Therefore, heat history at the time of curing the raw material is likely to be changed according to locations, and there is a problem that a shape accuracy of an outer peripheral surface of the roller as the final molded product is likely to be reduced.