Patent invalidity is when a prior art surfaced similar to the invention being applied for patent. Patent invalidity does not automatically happen if there are patents similar to the invention; however it is difficult to obtain a patent if there are identical patents to their invention.
Patent search could help prevent patent invalidity of an invention. Patent invalidity could be avoided by doing a thorough patent search in the database records of prior patents and publications of Patent Search Office. It is the patent counsel’s job to compare a collection of prior patents, printed publications, journals or other technical articles with the invention. But before doing so, he or she must examine each of these "references" in order to ensure that they are valid. Finally, the patent opinion discloses the likelihood that a patent will be granted on the proposed invention. This is where the patent counsel proceeds to apply for a patent.
In order to determine patent invalidity of an invention, examiners all over the world need to carefully look at each case. Patent applications often fail first time around. And this happens 80% of the time. The expense of taking out applications to the various patent offices around the world, the patent agent, of arguing a case to the examiner, paying for the very many translations, renewals etc are vast and endless. Patent can only be approved provided that no prior art comes to light. If there is such then patent invalidity applies to the case.
In some cases also where it is believed that patent infringement is committed, it is common knowledge that the first thing a solicitor will do when protecting his client who is violating a patent is to automatically try and cite patent invalidity. The lawyer sees this as looking after the “commercial interests” of his client. After all, without a patent due to patent invalidity there is no case.
Determining patent invalidity is a responsibility of the patent office. It is they who have rigorously made sure that each application has to be totally inventive and not "obvious". If the patent office has made an error in declaring patent invalidity then it all depends on them.
Still if patent is granted after careful examination, it does not mean that patent invalidity is no longer possible. The system we have today is that an invention can become "re-examined" by an "independent" (a judge) who can suddenly make a full patent invalid. So you can have a full patent for a number of years, sell you invention successfully around the world and suddenly it could be taken from you because of patent invalidity of the invention.