For investigation of influence by the feed throat shape to pellet behavior and feeding rate of pellets under the hopper, quartz glass blocks with three kinds of feed throat shape, which include straight shaped wall surface A, taper shaped wall surface B, and single side taper shaped wall C, were installed into the under part of the hopper, then visualization analysis was performed. Three materials, PP (hot cut alone and recycled material 70wt% admixture), and GPPS (cold cut) were compared.
 By the visualized observation under the continuous plastication process, the pellet-feeding rate is large in the order of B, A, C, however, significant difference was not observed regarding the pellet filling status into the screw flight channel. On the other hand, under the reciprocating plastication process, it has been confirmed that the influence by difference of the feed throat shape can be observed only in almost the first half of the charging process, in addition, no clear differences in pellet-filling rate can be observed between A and B, and C. It is the smallest in the injection process, moreover significant differences by the shape difference were observed in the case of recycled material admixture.
 By using a pellet-feeding rate measuring device from the under part of the hopper, it has been indicated the pellet-feeding rate at recycled material admixture of PP decreases regardless of the shapes, and shows the lowest value especially in C, furthermore, B is proper for recycled material since the metering time shows shortest value with smaller variance.
 As for GPPS, it has been confirmed that the metering time variance is small regardless of the shapes, and metering time itself is the shortest in A. Regardless of the materials, although the shape C has small backflow with stable pellet-feeding, the feeding rate becomes lower at high screw rotation rate.
 The difference of the pellet-feeding rate from the under part of the hopper has an effect on theplastication capacity (metering time) in all of three types of resin. It has been indicated that the difference in three kinds of feed throat shape easily affects reciprocating plastication capacity directly in the case of using a material which has low pellet-feeding rate such as recycled material, or in the case of using a material which has high melting rate such as amorphous resin.

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