A former worker at Ajinomoto Co. has filed a suit against the food maker over the patented production method for the artificial sweetener aspartame, his lawyers said Sunday.

Masayoshi Naruse, 61, is demanding 2 billion yen for his contribution to the product’s development.

He lodged the suit with the Tokyo District Court, claiming he did not receive a proper reward for his contribution to developing the mass production method for the sweetener. In Japan, aspartame is sold under the product name Pal Sweet.

According to the lawyers, Naruse, a former head of the process development division of Ajinomoto’s Central Research Laboratories, helped develop the method in 1982.

Ajinomoto obtained a patent for the method in Japan and the United States in 1988 and 1992, respectively.

The major food maker made profits of about 24.1 billion yen with the new technology, including royalties for licensing the patents to U.S. companies, the lawyers said.

Naruse said that Ajinomoto paid him only 10 million yen as a reward for his part in the development of the process, but that he deserves a greater share of the profits. He claimed that he was only rewarded as an employee, and has received nothing for giving the firm the right to use the patent.

He said he did not “have the courage” to file the suit while he was working for the company. He retired from the firm last year.

In May, the Osaka District Court ruled in a different case that firms should be considered to have made a 50 percent contribution to any invention or breakthrough.

Naruse says he is entitled to 50 percent, or 10 billion yen, of the profit Ajinomoto gained through licensing the patents. He is seeking a portion of this in the lawsuit.

An Ajinomoto spokesman expressed surprise at the suit, saying, “We recognized the importance of the patent and paid 10 million yen to Mr. Masayoshi Naruse in December 2000 based on an in-house rule regulating rewards for patents.”

The spokesman said the company will consider filing a countersuit against Naruse after looking at the details of his lawsuit.

Under the Patent Law, patent rights are given to the inventor, not the company, even if it was part of the employee’s job to develop something for the firm. The law stipulates that companies must pay employees for using the patent after taking into consideration the extent of its own contribution in the matter.

This concept has not been widely recognized, even among parties handling intellectual property rights, until recent years.

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