Create a function in your model:
@api.multi
def send_email_notification(self):
self.ensure_one()
template_obj = self.env.ref('module_name.email_template_id')
template_obj.send_mail(self.ids[0], force_send=True)
call the function by the following XML code:
<button name="action_email_notification" string="Send Email Notification" type="object" class="oe_highlight" />

