Why is patent protection limited? What is the standard of the length of time? Is the patent worthless after time?

First, if the patent authorization is not given a certain time limit, it will hinder the progress of technology, so there should be a certain time limit, which is more conducive to social stability and development. Secondly, patents in China are divided into inventions, utility models and designs, in which the protection period of invention patents is 20 years from the date of filing, while that of utility model patents and design patents is 10 year from the date of filing. Third, the value of the patent has not been lost after the passage of time, and it should be analyzed according to the specific situation.