Many algorithms for searching the main paths according to a subfield technology have been suggested using patent citation networks. However, the process by which the specific field is divided into subfields is problematic, in the sense that citation information among individual patents in different subfields is lost. If convergence technologies are common among different subfields, this problem can result in an inappropriate main path being found. To resolve this problem, we propose a new algorithm capable of extracting the main paths for each subfield of a technology by using the International Patent Classification (IPC) codes of patents. The proposed algorithm is applied to the waste management field to allow core technologies in the subfields of waste disposal, waste treatment, and the reuse of waste materials to be found. Finally, a sensitivity analysis is performed by considering the standard of the component ratio along a specific path to demonstrate the robustness of the proposed algorithm in the waste management field.