Partially separated fiber bundle, production method of partially separated fiber bundle, fiber-reinforced resin molding material using partially separated fiber bundle, and production method of fiber-reinforced resin molding material using partially separated fiber bundle

A partially separated fiber bundle in which separation-processed sections and not-separation-processed sections are alternately formed along a lengthwise direction of a fiber bundle comprising a plurality of single fibers, each of the separation-processed sections being separated into a plurality of bundles, the partially separated fiber bundle being characterized in that the content of the not-separation-processed sections is 3% or more and 50% or less.

A method of producing a partially separated fiber bundle wherein, while a fiber bundle comprising a plurality of single fibers travels along a lengthwise direction of the fiber bundle, a separation means provided with a plurality of projected parts is penetrated into the fiber bundle to create a separation-processed part, and entangled parts, where the single fibers are interlaced, are formed at contact parts with the projected parts in at least one separation-processed part, thereafter the separation means is removed from the fiber bundle, and after passing through an entanglement accumulation part including the entangled parts, the separation means is penetrated again into the fiber bundle, characterized in that a separation processing time t1 during being penetrated with the separation means and a time t2 from being removed with the separation means to being penetrated again into the fiber bundle satisfy Equation (1)

• 0.03≤t2/(t1+t2)≤0.5 (1).

A method of producing a partially separated fiber bundle wherein a separation means provided with a plurality of projected parts is penetrated into a fiber bundle comprising a plurality of single fibers, while the separation means is traveled along the lengthwise direction of the fiber bundle, a separation-processed part is created, and entangled parts, where the single fibers are interlaced, are formed at contact parts with the projected parts in at least one separation-processed part, thereafter the separation means is removed from the fiber bundle, and after the separation means is traveled up to a position passing through an entanglement accumulation part including the entangled parts, the separation means is penetrated again into the fiber bundle, characterized in that a separation processing time t3 during being penetrated with the separation means and a time t4 from being removed with the separation means to being penetrated again into the fiber bundle satisfy Equation (2)

• 0.03≤t4/(t3+t4)≤0.5 (2).