The angle I would use is showing the value of the event for you/the company: is there one session that will allow you to have a bigger impact in your current job? Will you be able to meet people that will allow the business to grow? Try to be concrete and not too generic.
Also make sure your request is properly formatted: add the dates, a quick description of the event, maybe the speakers you're the most interested in and if you need money the budget required to travel and then add the little paragraph with the potential value.
Also, some cool readings that will give you even more info than my little paragraph: 1. How to Convince Your Boss to Send You to a Conference 2. How to Get Your Boss to Send You to a Cool Conference
Good luck and keep us posted!