Matching Inkjet Paper to the Job
Checking Off the Essentials and Comparing the Papers
By Shozo "Sean" Atobe, Konica Minolta Photo Imaging USA Inc.
Even in a "paperless" office, paper remains ever present and often taken for granted, but that can’t be the case in inkjet printing. When it comes to photo quality reproduction, choosing the right paper is essential. Here’s a checklist of key points to consider:
Whiteness – The highlights in any photo-quality image can never be brighter than "paper white," so choose a paper that’s really, really white. For office documents, papers with whiteness ratings – also called brightness or reflectivity – around 85 percent look all right, but a photograph printed on this kind of paper would look pretty drab. In large-format photo-quality printing, many papers have whiteness ratings in the 90s, even the high 90s.
Drying time – The faster the paper dries, the faster you can print, and the smaller the chance of smudging as the paper exits the printer. Fast drying also cuts the risk of mottling in the image.
Compatibility with both dye and pigment inks – Ink research is leading to the rapid introduction of new and improved inks, but currently dye-type inks still have an advantage in their range of colors and price, while pigment-type inks have an advantage in image permanence.
Excellent color reproduction – Inkjet papers that allow ink to "bleed" or "blot" laterally produce images with fuzzy, irregular dots that compromise color reproduction.
Uniformity – Paper that varies from roll to roll or between sheet sizes can result in unacceptable prints that require delays and costly remakes. Adjustments shouldn’t be needed when changing rolls or sheet sizes of the same paper.
Glossiness – For media with a glossy surface, it’s necessary to use paper with a high-quality glossiness that’s free from the wavelike surface pattern visible in some glossy papers.
Inkjet Paper 101: Comparing Swelling to MicroporousPhoto-quality inkjet papers use either a "swelling" type of ink-receptive layer or a microporous type.
The swelling type of paper is simpler. The ink receptive layer includes a polymer such as gelatin, polyvinyl alcohol or polyurethane as a main ingredient. When ink drops touch the absorption layer, the polymers begin to swell and to absorb the ink. A hardening agent is added to the absorption layer to strengthen it. But a layer that is too hard will inhibit swelling and result in lower ink absorption, making it slower to dry and easier to smudge after printing than microporous papers.
Microporous inkjet paper uses an ink-absorption layer of microscopic particles of various silica or aluminum compounds, 1/10 of a millimeter or less in diameter, plus a binder such as polyvinyl alcohol. These particles are deliberately coated so they do not fit tightly together, but rather form a structure with many tiny spaces between the particles, creating a large area that absorbs ink. Where the microscopic spaces reach the surface of the paper, they form pores that allow the ink to penetrate. Because most of the water-soluble dyes used in inks have a negative charge, a positively charged compound has been added to the silica surface to change its charge to positive, helping attract the ink.
The fundamental structure of microporous inkjet paper is also the reason it dries much faster than the swelling type. First of all, its pores absorb the ink by capillary action, which is more efficient and faster than the swelling process. The fast absorption and drying of microporous paper also means ink does not overflow onto the paper surface, which would create color bleeding or spotty patterns in high-density areas.
Aug2004, Digital Output