def imprint=(str)
      composite = product.imprints.first
      if composite.nil?
        composite =  ONIX::Imprint.new
        product.imprints << composite
      end
      composite.imprint_name = str
    end
def imprint=(str)
      composite = product.imprints.first
      if composite.nil?
        composite =  ONIX::Imprint.new
        product.imprints << composite
      end
      composite.imprint_name = str
    end
set a new imprint