Ribbon cassette with ink ribbon slack prevention mechanism

摘要

A ribbon cassette includes a ribbon supply spool, and a ribbon take up spool that takes up an ink ribbon from the ribbon supply spool by rotating in a first rotation direction. The ribbon take up spool is provided with an engaging portion including first and second walls arranged in the second rotation direction in this order. The first wall is defined along a plane including a rotation axis of the ribbon take up spool. The second wall is inclined to face outside the ribbon take up spool. The ribbon cassette further includes an engaging member. The engaging member resiliently engages with the engaging portion by dropping into a space defined between the first and second walls and thereby prevents the ribbon take up spool from rotating in a second rotation direction opposite to the first rotation direction. The engaging member, however, comes off from the engaging portion when the ribbon take up spool rotates in the first direction.