Does patent expiration violate advertising law?

It's illegal. Article 12 of the Advertising Law of People's Republic of China (PRC) * * If an advertisement involves a patented product or patented method, it shall indicate the patent number and patent type. Those who have not obtained the patent right shall not lie in advertisements that they have obtained the patent right. It is forbidden to use patent applications that have not been granted patent rights and patents that have been terminated, revoked or invalid for advertising.