(Corrects third bullet and second paragraph to show the threshold has not yet been lowered)
* Extends end of offer period to April 18 from March 14
* Cites ongoing talks with Chinese regulator
* To cut minimum acceptance threshold to 75 percent
* Says does not expect to have to extend offer again
FRANKFURT, March 14 (Reuters) - German liquid crystal maker Merck KGaA extended the offer period for its planned takeover of Britain's AZ Electronic Materials for a fifth time on Friday, citing ongoing talks with Chinese antitrust regulators.
It also said it would lower the minimum acceptance threshold to 75 percent from 95 percent once the deal had been approved in China, which means that only at least three quarters of shares in AZ would need to be tendered for the deal to go through.
Merck, the world's largest maker of liquid crystals used in TVs and tablet and smartphone screens, agreed in December to buy AZ for $2.6 billion to expand its range of specialist chemicals for hi-tech gadgets.
By Friday, 64.2 percent of AZ shares had been tendered.
Merck extended the offer period until April 18 on Friday, from March 14, giving it just over a month to obtain approval of the deal from Chinese antitrust regulators and reach the new lower minimum acceptance threshold.
Az Electronic generates the bulk of its revenue in Asia. China's new-found clout in regulating global mergers is causing headaches for some companies seeking high-stakes deals that need Beijing's approval.
"Merck has continued to have constructive dialogue with MOFCOM (the Ministry of Commerce of the People's Republic of China) and Merck expects to obtain Chinese antitrust clearance by 18 April 2014," the company said in a statement, adding it did not expect to have to extend the offer period a sixth time.
Merck's chief executive Karl-Ludwig Kley said last week he was confident the planned takeover could be completed in the first half of this year.
BoA Merrill Lynch advised Merck on the deal, while Rothschild, Goldman Sachs and UBS advised AZ. (Reporting by Maria Sheahan; Editing by David Goodman and Sophie Walker)