Morningstar Inc said DoubleLine Capital's flagship Total Return Bond Fund is "not ratable" for a second straight year, citing a lack of information about the firm's investment process, succession planning and risk controls.

The Chicago-based investment research firm said on Friday DoubleLine had ignored or refused requests for information over the past three years, and that it could not issue a rating based on DoubleLine's public filings and statements.

"DoubleLine made a decision in February 2012 to no longer communicate with Morningstar.com's fund writers, following publication that month of a new report on DoubleLine Total Return," Loren Fleckenstein, an analyst at the fund, said in an interview on Friday.

"Since their own process for rating a fund's forward prospects requires they communicate with the investment team, I can see how they would have little choice but to continue the current non-rated classification of our fund under their forward-looking ratings system."

DoubleLine's complaints have centered mainly on Morningstar's view that Total Return, while producing outstanding results, has also taken relatively large risks.

Morningstar said in a report on Thursday that "after this fund's mid-2010 launch ... we had concerns about Jeffrey Gundlach's extensive use of so-called esoteric mortgage-backed securities, which included inverse floaters, interest-only bonds, and inverse interest-only bonds."

Morningstar senior analyst Sarah Bush, author of the report, said the securities used by fund manager Gundlach "can throw off lots of income but can also be highly volatile and suffer from bouts of illiquidity, ran at close to 25 percent in late 2010."

The fund's stake in esoterics has fallen considerably as the portfolio has grown and has run at about 4 percent-5 percent of assets since late 2012, Bush said. Given its current size, it is unlikely they will play such a significant role going forward, she added.

The DoubleLine Total Return fund retains Morningstar's highest, five-star rating, based on risk-adjusted performance rather than the forward-looking assessment given by Morningstar once a year.

Morningstar said it could not rate the Total Return Bond Fund on "process" and "parent," two of the five components used to determine its overall fund ratings, given DoubleLine's decision not to discuss the fund. The other components are "performance," "people" and "price."

Morningstar rated DoubleLine's "people" component "positive" after not rating it last year, and changed its "parent" component to "not rated" based on "insufficient information about succession planning, risk control and firm culture," Bush said in a phone interview.

Gundlach, who was named Morningstar's fixed-income manager for 2006 and widely known as the new "Bond King," started DoubleLine in December 2009 after he was fired as chief investment officer of TCW Group Inc in a dispute that led to a legal battle.

His Total Return Bond Fund has surged to $46.7 billion in assets after opening in April 2010 and beat 94 percent of peers in the past three years.