The history of injection moulding machines was born in the 19th century, and the boom was linked to wars

Why did God create mankind, some people say that the answer is, 'because God wants plastic'. God can create all things, but he can not make plastic, only through human beings to manufacture.
The injection moulding machine was invented at the end of the 19th century and the first machine was patented in 1872 by two brothers, John and Isaiah Hyatt. Although the machine was simple by today's standards, it soon led to the development of a nascent plastic manufacturing industry in which combs, buttons and other simple items were moulded in plastic.
In 1903, two German scientists, Arthur Eichengrun and Theodore Becker, created soluble cellulose acetate; this was significantly less flammable than previous alternatives. While the 1930s were a dark period for many, it was a decade of innovation for the plastics manufacturing industry. Many popular thermoplastics such as polyolefins, polystyrene and polyvinyl chloride (PVC) were invented during this time.
World War II reshaped human history. The Second World War promoted the aeroplane, led to huge advances in automotive technology, and enhanced the war manufacturing economy in the United States, which would later power the first phase of the post-war industrial revolution. With respect to plastics, this period also triggered a high demand for cheap, mass-produced materials. This demand after World War II led in part to material shortages. For example, the war in Asia and attacks on shipping lanes disrupted rubber production. Tanks and other war applications created a huge demand for metals. Plastics stepped in to fill the void and provide a reasonably priced alternative. As plastics grew in popularity, so did injection moulding machines. The effectiveness of this era is largely attributed to affordable, large-scale manufacturing. Plastics remained popular throughout the post-war period. As business giants recognised the huge cost advantages over rival materials, global supply chains were reassessed and plastics became entrenched in the economy and manufacturing processes of the mid-20th century.