SCP without password prompt using different username

I have 2 servers. Server1 and Server2. On Server1 i have the user ID user1. On Server2 I have the user id user2.

I need to be able to write a script that runs on Server1, which will scp some files down using user2@Server2. Is there any way to do this without prompting for a password? I can put the password in a config file or something if necessary.

I am not able to create user2@Server1 user by the way.