The firm put out a stock exchange announcement at 5.01pm today (13 August).
Chief executive Mike Hammond was unavailable for comment on the implications for the company.
Mulvaney said: "I can't say anything at the moment. I will be able to issue a statement on Monday".
The news was greeted with universal disbelief by senior executives at Agfa, Fuji, KPG, Screen, NCS and Openshaw.
The full statement from Litho Supplies reads:
Litho Supplies plc announces that Mr G O Mulvaney, Joint Managing Director of the Company, has resigned, with immediate effect, in order to pursue other interests. The board of Litho Supplies would like to thank Mr Mulvaney for his valued contribution to the Group and wishes him very well in his future endeavours.
The Company also announces that Mr T F C Cooper, Joint Managing Director of the Company, has served notice of his resignation as an employee and director of the Company in accordance with his service contract which requires 12 months' notice. The Company is presently in discussions with Mr Cooper regarding the timing of his departure.
This story will be updated as further details become available. Check www.printweek.com for updates.