Method and apparatus for drying coated sheet material

Apparatus for drying a sheet material which is coated on a surface thereof with at least one layer of a mottle-prone coating composition containing a liquid medium that is capable of being evaporated from said coating composition by contact with a gaseous drying medium, said apparatus comprising:

• means for advancing said coated sheet material along a predetermined path through a drying zone,
• means adjacent to said path for uniformly supplying a gaseous drying medium to said coated surface so as to bring about evaporation of said liquid medium with resulting formation of spent gaseous drying medium which flows away from said path for discharge from said drying zone, and
• shield means for reducing the tendency for mottle formation in said coating, said shield means being comprised of a foraminous material which is permeable to said gaseous drying medium and being interposed between said path and said supply means in close proximity to said coated surface, so as to promote flow of said spent gaseous drying medium adjacent to the surface of said shield means which is remote from said coated surface and form between said coated surface and said shield means a quiescent region which is rich in the vapor of said liquid medium and in which flow of said spent gaseous drying medium is suppressed and uniform heat transfer conditions are promoted, whereby formation of mottle in said coating is reduced.

Apparatus for drying a sheet material which is coated on a surface thereof with at least one layer of a mottle-prone coating composition containing a liquid medium that is capable of being evaporated from said coating composition by contact with a gaseous drying medium, said apparatus comprising:

• means for advancing said coated sheet material along a predetermined path through a drying zone,
• means for supplying said gaseous drying medium to said drying zone,
• a plenum which is located within said drying zone adjacent to said path and is connected to said supply means, said plenum serving to uniformly direct said gaseous drying medium onto the coated surface of said sheet material so as to bring about the evaporation of said liquid medium with resulting formation of spent gaseous drying medium which flows away from said path for discharge from said drying zone, and
• a foraminous shield which is interposed between said plenum and said path, said shield being permeable to said gaseous drying medium and having one surface thereof in opposing spaced relationship with said plenum and the opposite surface thereof in opposing spaced relationship with said path, said shield being in close proximity to said path, so as to form a quiescent region between said shield and said coated surface which is rich in the vapor of said liquid medium and in which flow of said spent gaseous drying medium is suppressed and uniform heat transfer conditions are promoted, and being spaced from said plenum to form a region therebetween in which flow of said spent gaseous drying medium can occur without disturbing said coated surface, whereby formation of mottle in said coating is reduced.

Apparatus for drying a web which is coated on a surface thereof with at least one layer of a mottle-prone coating composition containing a liquid medium that is capable of being evaporated from said coating composition by contact with a gaseous drying medium, said apparatus comprising:

• means for advancing said coated web along a predetermined path through a drying zone,
• means for supplying said gaseous drying medium to said drying zone,
• a plenum which is located within said drying zone adjacent to said path and is connected to said supply means, said plenum serving to uniformly direct said gaseous drying medium onto the coated surface of said web so as to bring about the evaporation of said liquid medium with resulting formation of spent gaseous drying medium which flows transversely to said path for discharge from said drying zone, and
• a foraminous shield which is substantially commensurate in width with said coated surface interposed between said plenum and said path, said shield being permeable to said gaseous drying medium and having one surface thereof in opposing spaced relationship with said plenum and the opposite surface thereof in opposing spaced relationship with said path, said shield being in close proximity to said path, so as to form a quiescent region between said shield and said coated surface which is rich in the vapor of said liquid medium, and in which transverse flow of said spent gaseous drying medium is suppressed and uniform heat transfer conditions are promoted, and being spaced from said plenum to form a region therebetween in which transverse flow of said spent gaseous drying medium can occur without disturbing said coated surface, whereby formation of mottle in said coating is reduced.