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Paper Technology
by By Herbert Wong, Jr.—NOCCC Hardware SIG Leader ocug@SingularityTechnology.com - February 22, 2001 at 13:14:35:
Paper is the most important component in the printing process, imparting distinctive characteristics to the image. The appropriate paper must be selected for every print job or you will not get the desired result, expensive ink will be wasted, and you’ll be very disappointed.Paper is responsible for retaining the structural integrity of the ink as the printer applied it. No matter how good the printer is able to apply an image matrix, bad paper can transform a photographic image into something out of the Sunday comic section.
Intro—Paper is usually made from one of two pulp manufact-uring processes. Mechanically ground pulp is used in ground-wood papers. It can contain impurities that are visible in the finished product. Chemically created pulp is used to make free sheets. It is so called because its impurities are removed and bleached out.
The manufacturing process can affect the longevity of the paper. As with anything else, cost and environmental considerations are significant factors. Strong chemical agents can reduce the manufacturing cost, but acid in paper can cause it to quickly yellow and make it brittle. For longer-lived applications, acid free or neutral pH papers are desired.
Opaque is used to describe papers that have been chemically treated and processed to increase opacity or .blocking the transmission of light through the paper. Paper that is more opaque will reduce the amount that printing on one side will show through on the other side. Papers that are thick, coated, rough, dark, and groundwood are more opaque than papers that are thin, uncoated, smooth, light, and free (respectively).
During the manufacturing process, the fibers in the pulp are aligned. Grain long sheets have the fibers parallel to the longest edge of the paper. Grain short sheets have the fibers running perpendicular to the longest edge. Folding of the paper is cleanest and easiest when done parallel to the grain.
Paper should be labeled to indicate the grain direction by listing it last. A ream of paper labeled 8-1/2”x11” is grain long, whereas as a label with 11”x8-1/2” is grain short. The grain long direction can also be indicated by underlining the parallel edge such as 8-1/2”x11” or 11”x17.”
Calendaring is a manufacturing process that runs the paper through a series of rollers. Various degrees of calendaring can be applied. The attributes of the paper are changed. Paper with less calendaring is more opaque, whiter, more bulky, less glossy, less smooth, less brittle, and has less ink holdout. Paper with more calendaring is less opaque, less white, less bulky, glossier, more smooth, more brittle, and has more ink holdout.
Orientation—Which side is the top of the paper? An unopened ream of paper placed flat on a table has a label on one of the 8-1/2” vertical sides. When that label is right side up, the first printing surface should be face up on the stack. That label should also be on the end-flap that isn’t split in two.
The top of a textured paper is the more textured of the two sides. If there is a watermark, it should be on the top surface with the lettering right side up.
Grades—There are many grades of papers available, but this discussion will be restricted to a few of the types that might be most commonly used, bond, text, uncoated book (also called offset), coated book, and cover.
Bond typically is used to present character. It can have texture, color, weight, and quality. Typing papers with significant cotton content are bond papers. Photocopy, business forms, and legal documents can also be bonds.
Bond paper is usually printed only on one side. If a watermark is present, the watermark should be viewable, correctly oriented with the lettering right side up.
Text is for applications that are more important, where quality has priority over cost. These are premium papers.
Text refers to the deeply textured look and feel of the paper. Not all text papers have textured surfaces. Smooth surfaces are also available.
Uncoated book, also called offset, is available in a large number of forms. Many applications are cost constrained so it is generally used in lighter stocks compared to text papers.
Coated book is for the best reproductions where quality and color accuracy are important. Coated book is made from a base sheet of uncoated book. One or both surfaces can have a coating. The coating is not always desirable. For greater adhesion (or other purposes), some papers are coated on only one side.
The coating keeps the ink from being absorbed by the underlying fibers. This is called holdout. Since the ink remains on the surface, it can be more vibrant and detailed. Paper that absorbs the ink will blur the resulting image, producing poor colors and dull images.
Coated book from the United States and Canada typically is two-thirds base sheet and one-third coating. Coated, from continents with less forestry products, can be one-half base sheet and one-half coating.
Coatings can also hide flaws in the base sheet. Some low-rated coated papers have groundwood content.
Coated papers are rated as cast, ultra premium, premium, #1, #2, #3, #4, and #5.
Cover is usually heavier stock. It can have a matching bond, text, or book sheet.
Brightness—Brightness is the amount (percentage) of light that white paper reflects. The maximum reflectivity would be one hundred percent. A #1 gloss reflects 85 to 88 percent; #2 gloss reflects 83 or 84 percent, and #3 from 79 to 82 percent.
Brightness must be selected based upon the application. A very bright paper might be appropriate for some photographs. An extremely reflective paper will be very hard to read under the fluorescent lights of an office. Using a less reflective paper will increase productivity and readability.
Paper for Printers (see resources below) suggests some brightness ratings and applications printed by laser printers. Business forms should use 81-to-88 brightness. Desktop published reports: 88-to-92 for mostly text, 90-to-95 for text and graphics, 90-to-95 for letterheads and envelopes, and 94-to-97 to photocopy or print offset.
Color—The color of a paper will alter the color of the ink. Photographs in particular will be greatly affected. However, the effect of color can be a benefit by setting a tone or mood.
White papers are not all the same. A wide assortment of white paper is available. Make tests prints to evaluate the results.
Make note that white refers to the paper’s color while brightness describes the reflectivity of the paper. They are not interchangeable.
Basic Size—Each grade of paper has a basic size that is used to determine its basis weights. Bond is seventeen inches by twenty-two inches. Text, offset, uncoated-book, and coated-book are twenty-five inches by thirty-eight inches. Cover is twenty inches by twenty-six inches.
Five hundred sheets of basic size paper determine the basis weight. Twenty-pound (20#) bond is a paper (bond) that comes from five hundred sheets of bond paper that are seventeen inches by twenty-two inches and weigh twenty pounds.
Consider 50# uncoated-book paper. It sounds much more robust than the 20# bond paper. However, a letter size (8-1/2” x 11”) sheet of each will weigh the same. That is due to the much larger twenty-five inches by thirty-eight inches basic size of the book paper.
Another way to think about this is to visualize how twenty pounds of pulp could be formed into five hundred sheets of paper. The resulting bond basic size would be 374 square-inches (17’x22’) while the book paper would be 950 square-inches (25”x38”).
Consider 40# book to be equivalent to 16# bond, 50# book to 20# bond, 60# book to 24# bond, and 70# book to 28# bond.
Conclusion—The paper you use for printing will greatly affect the result you achieve. The paper that is good for electrophotographic (ex. - laser, LED, photocopier) reproduction is different from inkjet paper. Paper that is good for one brand (or even model) of inkjet may not be suitable for another printer. Third party inkjet cartridges may require different paper than OEM cartridges.
The best paper for the desired results and cost can only be determined by testing a broad array of paper. It may be significantly less expensive to test many papers before printing many sheets. Besides, you’ll never know just how good your printer is until you see the best results.
Resources—Papers for Printing by Mark Beach and Ken Russon (Coast to Coast Books Inc.; ISBN 0-943381-02-9)
What the Printer Should Know About Paper by William Bureau (Graphic Arts Technical Foundation; ISBN 0-88362-119-3).
You can also find this article on the Web site at http://www.noccc.org/. The latest revision can be found at http://www.SingularityTechnology.com/articles/papertech.html.
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