The below is quoted from a much longer article 'Morals and Marriage: The Catholic Background to Sex' by T.G. Wayne. It has both the Nihil obstat and Imprimatur, so it is free of doctrinal error. This is just the passage most relevant to the question:
The morality of a human act is not only determined by a consideration of its general nature. The abstract must be made concrete. Consequently the personal motives for a particular action must also be taken into account. In this connection it may be asked: should husband and wife seriously intend to have a child whenever they have intercourse and should they try to restrict intercourse to those times when the conception of a child is possible?
The answer is negative. There are other valid reasons for intercourse besides procreation. These are the healthy expression of passion, the fostering of mutual love, the strengthening of the sacramental bond of marriage. These are worthy motives, implying the human love and devotion of marriage, including more than the mere appetite for pleasure, which is not a sufficient motive for any action. The intention of trying to have a child is not necessary as a regular motive.
All healthy married people who are capable of bearing and rearing children are under some obligation in the matter, but the command applies more directly to their married state than to each and every act of intercourse. There may be good reasons for intercourse, the bodily and spiritual welfare of them both, at times when conception is impossible or unlikely or undesirable. Of course they must reserve their impulses, for marriage does not legitimize sex indulgence in any form, but rather requires the exercise of purity as much as does a single life. On this supposition, however, the satisfaction of sex without the intention of procreating is according to the divinely-appointed nature of marriage, so long as the act is life-offering, serving to strengthen the sacramental bond and to assure the stability of family life on which the welfare of children in general depends.