Method for spreading fiber bundles, spread fiber sheet, and method for manufacturing a fiber-reinforced sheet

A method for spreading fiber bundles, comprising the steps of feeding a fiber bundle formed of a plurality of fibers in a fiber length direction and moving the fibers in a width direction while bending the fibers by letting a fluid pass through the fiber bundle in a movable region set so that the fibers can move in the width direction, thereby spreading the fiber bundle,

• wherein in the movable region, a set of regions Si (i=1, . . . , n) each including a pair of a fiber-spreading region Ai (i=1, . . . , n) and an expansion region Bi (i=1, . . . , n) are arranged in a feeding direction of the fiber bundle in a number of n (n≧2), the fiber-spreading region Ai moving the fibers in the width direction while bending the fibers by letting a fluid pass through the fiber bundle, thereby spreading the fiber bundle to a spread width Wi,
• wherein the expansion region Bi, which is set on the upstream side in the feeding direction corresponding to the fiber-spreading region Ai and in which the width of the fiber bundle expands toward the end with movement of the fibers in the width direction in the fiber-spreading region Ai, has a length Li in the feeding direction;
• wherein in the region sets Sj j=2, . . . , n), a spread width Wj−1 of the fiber-spreading region Aj−1, a spread width Wj of the fiber-spreading region Aj, and a length Lj of the fiber bundle in the feeding direction in the expansion region Bj are set to satisfy:
• 0<(Wj−Wj−1)/2Lj≦tan 30°, and
• wherein the fiber bundle is spread by being fed so as to sequentially pass through the region set Si.