Files with gradients, meshes, or color blends can be difficult for some printers to print smoothly (without discrete bands of color) or at all. Follow these general guidelines to improve the printed results:
Use a blend that changes at least 50% between two or more process-color components.
Use shorter blends. The optimum length depends on the colors in your blend, but try to keep blends shorter than 7.5 inches.
Use lighter colors, or make dark blends short. Banding is most likely to occur between very dark colors and white.
Use an appropriate line screen that retains 256 levels of gray.
If you create a gradient between two or more spot colors, assign different screen angles to the spot colors when you create color separations. If you’re not sure what the angles should be, consult your print shop.
Print to an output device that supports PostScript® Language Level 3 whenever possible.
If you have to print to an output device that supports Postscript Language Level 2, or when printing meshes that include transparency, you can choose to rasterize gradients and meshes during printing. As a result, Illustrator converts gradients and meshes from vector objects to JPEG images.