The company is expecting U.S. packaging makers AptarGroup and Morgan Stanley Capital Partners-backed Comar to submit final offers for its Medical Specialties unit later this month, they added.

Clariant, which is working with William Blair on the divestment, initially also received interest from private equity groups such as Triton, most of which are no longer in the running, the sources said.

Clariant's medical products include drop-in desiccants for pill bottles, to help preserve drugs and extend their shelf life, closure systems for medical packaging, as well as vials that protect medicine strips.

The business has been marketed with 2019 expected earnings before interest, tax, depreciation and amortization of 24 million Swiss Francs (£19.4 million), one of the sources said, adding that the unit was expected to sell for less than 300 million.

Last year, Clariant announced it would combine activities such as additives and higher-value speciality masterbatches with parts of Saudi Arabia's Saudi Basic Industries' speciality chemicals in a new joint venture.

That left Clariant's remaining Plastics & Coatings activities including medical specialties, standard masterbatches and pigments businesses with 2017 revenues of 1.56 billion Swiss francs, and earnings before interest, tax, depreciation and amortisation of 182 million francs.

Clariant also started the sale of its pigments business earlier this year, but delayed that process as the outlook for the chemicals industry deteriorated, a source said.

Clariant, Aptar, Triton and William Blair declined to comment, while Comar was not available for comment.

(Additional reporting by John Miller; Editing by Elaine Hardcastle)

By Arno Schuetze