Why do I have to keep installing Canon Pixma ix6850 on my iMac

I have an iMac with the latest OS. I have also got a Canon Pixma ix6850 airprint enabled printer.

However, every time I start up the computer I have to install the driver software, otherwise I get a 'can't find the printer error'.

Very frustrating and time consuming, any suggestions please?

Thanks in advance 🙂