Liquid fluorescent whitening agent

The invention belongs to the technical field of fluorescent whitening agents and preparation methods thereof, and in particular relates to a liquid fluorescent whitening agent. The invention mainly aims to solve the problems of unobvious whitening effect, poor stability and the like of an existing fluorescent whitening agent. The liquid fluorescent whitening agent provided by the invention is prepared through a method comprising the following steps: (1) weighing raw materials; (2) preparing a mixture of three-shrinkage intermediates I and II; (3) adding 4,4'-diamido diphenyl ethene-2,'-disulfonic acid into a NaOH solution to obtain a 4,4'-diamido diphenyl ethene-2,2'-sodium disulfonate aqueous solution; (4) reacting an emulsifying agent with cyanuric chloride and 4,4'-diamido diphenylethene-2,2'-sodium disulfonate to obtain a product III; (5) adding aniline into the product III to react so as to obtain a product IV; (6) adding the mixture of the products I and II into the product IV to react so as to obtain a composition of V, VI and VII; and (7) obtaining the liquid fluorescent whitening agent.