TOKYO (Reuters) -Shares of Japan's struggling Nissan Motor ( NSANF ) tumbled more than 6% on Tuesday, extending declines into a second day after it expanded an issuance of convertible bonds announced just this week.

In a filing, the automaker cited robust demand for the six-year bonds during book building as the reason for increasing the offering to 200 billion yen ($1.4 billion) from 150 billion yen.

Stock investors, however, were less than enthusiastic, given that the bonds can be converted to new shares and are potentially dilutive. The stock finished down 6.4% at 315.5 yen in Tokyo trade, adding to a 4.9% drop on Monday when Nissan ( NSANF ) announced the issue.

Nissan ( NSANF ) also announced on Monday plans to sell $4 billion worth of U.S. dollar- and euro-denominated senior unsecured bonds. That comes after Reuters recently reported the automaker has asked some suppliers to allow it to delay payments to free up short-term funds, illustrating its scramble to boost cash. 

Hit by deteriorating sales and an ageing vehicle lineup, Nissan ( NSANF ) reported a $4.5 billion net loss for the financial year that ended in March.

It has declined to disclose a forecast for the current financial year, when it will have about 700 billion yen in debt come due. Its debt ratings have been cut to "junk" by all three major credit-rating firms.

Nissan ( NSANF ) said proceeds from the convertible bonds will be used to invest in new products and technologies, such as electrification and software-defined vehicles. Proceeds from the senior unsecured bonds will be used to refinance outstanding debt, according to a term sheet. 

Coupons on the senior unsecured debt will be in the mid-7% area for the five-year tranche, high-7% area for the seven-year tranche and low-8% area for the 10-year tranche, the term sheet showed.

The coupon on a five-year dollar bond worth $800 million in March 2021 was originally 2% but is now trading at a little over 6%, LSEG data showed. The coupon on a seven-year bond issued at the same time worth $600 million was 2.75% but is now at more than 6.5%.

The cost of insuring Nissan's ( NSANF ) 5-year debt against default is now at its highest in at least a decade and a half, according to LSEG data.

It is also far more expensive to buy insurance on Nissan ( NSANF ) debt than that of any other major Japanese corporation, LSEG data also shows.