3 ideas
Bi Sheng made movable type from baked clay in the 1040s, and the scholar Shen Kuo recorded it. Woodblock printing still dominated China for centuries. A script with thousands of distinct characters made casting, storing and sorting type costly. A carved block could be kept and reprinted cheaply in small runs whenever demand appeared, while set type had to be broken up after each job.
Printing was assembled from techniques already in use rather than invented from nothing. Carved seals supplied the mirror-image relief stamp. Ink rubbings from stone inscriptions supplied the transfer of an image from a carved surface onto paper. Buddhist demand to multiply charms and sutras for religious merit supplied the reason to scale up. The earliest surviving dated printed book is the Diamond Sutra of 868 CE.
Papermaking stayed in the Chinese sphere for centuries and moved west mainly by transferring skilled people, not texts. The traditional account holds that Chinese papermakers captured at the Battle of Talas in 751 started production in Samarkand. From there the craft passed through Baghdad, Damascus and Egypt, and reached Europe by way of Islamic Spain and Italy roughly a thousand years after its origin.