Inkjet printing: mask-rotation-only at page extremes; multipass modes

Abstract

Images are printed using marks formed in pixel arrays by a scanning print head. For transparent and glossy media, with poor absorbance, drying is enhanced by a multipass (preferably six-pass) print mode in which the total number of ink drops or spots is allocated among correspondingly multiple masks, though some may be duplicates. To further hasten drying, heat is applied--through the medium, from the opposite side as that on which ink is deposited--but the amount of heat is strictly moderated, particularly for nontransparent glossy media, to accommodate the hypersensitivity of these media to heat-induced warping. Heating for glossy media is preferably restricted to about one-third the power used for drying plain paper. Convective drying too is promoted, by operating a fan over the printed image. Certain special techniques well-suited for plain-paper printing have been found undesirable for use with plastic media; these techniques include so-called 'resolution-enhanced technology', bidirectional printing (particularly of black), and optical-density controlled printing speed. At top and bottom of each page or sheet of printing medium, where it is undesirable to operate with the pen partly off the edge of the sheet, and where also the printing medium is constrained from only one direction rather than being held taut beneath the pen, the print mask is rotated while the printing medium is held stationary--thereby entirely avoiding reliance upon accuracy of print-medium advance.