David Jones will increase its investment in its credit card business by around A$8 million over the next 18 months in an effort to increase demand and support earnings when a profit subsidy from its partner, American Express, runs out in 2014.The department store group outlined plans for its cards business as part of a strategic update for the company yesterday. The firm also released its half-year profit.David Jones said it now expected earnings before interest and tax from its financial services business to be flat at $49.4 million in each of its 2012 and 2013 financial years. David Jones had been reporting consistent rises of 7.5 per cent for this division, with the rigid increase in profit due to its contract with American Express.The profit from this business will "broadly halve to a sustainable base", the company said in a presentation released yesterday.American Express took over as issuer of the David Jones card in 2008, issuing a general-purpose credit card in place of the charge card that was a cornerstone of the company's business model for decades. David Jones sold $374 million in store card receivables to American Express in August 2008.Assuming the profit split from 2014 is along the lines of a 50:50 split with American Express, it appears the latter has been handing over all of the profit of the co-brand to its department store partner.To revive the cards business, the partners plan to introduce a platinum card, to sweeten rewards on the existing store card, push harder on the sale of insurance products and promote additional marketing gimmicks, including a "card member flower show".