you mean in mold labeling? we also make such mold for container. the process is to insert a label to mold cavity, the label will be static charged to stick to mold surface.
to sucess the process, product design is very important, must consider the flow of plastic, flow direction can't shift the label.
Plastic material is another consideration, normally we use PP, label will be BOPP.
Some material with higher shrinkage will affect the label position, ex. HDPE.
Another similiar process is called in-mold-transfer, it's used in some lay-top case. This process will transfer ink into plastic.