Coated Papers and Docutech Imaging

No. 4 February 1997 Coated Papers and Docutech Imaging In many segments of the graphic arts WHO SHOULD community, coated printing papers are presumed Conventional Printing READ THIS to be the best choice for quality imaging. This is BULLETIN: due to certain characteristics that optimize the Coated papers and conventional offset Any person offset printing process. lithography seem to be made for one another. This who specifies The xerographic process changes all the is primarily due to the effective interaction of the paper to be expected benefits. In the worst case, a job may be ink on paper. Offset inks are absorbed into the imaged via the unprintable. At best, results will be very different paper. Harder and smoother surfaces control Paper Docutech than expected. absorption better. Also, offset ink is transparent, process. This issue of TechTopics will show how allowing the surface characteristics of the paper to coated papers differ in response when the shine through. A premium coated sheet will cause direct imaging process is used in place of the printed portion of the paper to appear as conventional lithography. brilliant as the paper itself. Note: Paper mills often include descriptions of the What are Coated Papers? properties of paper with their swatch books. The Strictly speaking, coated papers are those descriptions usually refer to the use of paper in ofset printing. This information is useless for containing a mixture of pigments (such as clay or determing the suitablility for Docutech. calcium carbonate) and binders (like starch and latex) that have been applied to the surface during or immediately following the papermaking process. Docutech Imaging The purpose of this coating is to help fill in the peaks and valleys of the paper to provide a smooth, The Docutech reacts differently because it flat printing surface. uses dry carbon-based toner in place of ink. This Types toner is permanently fused to the paper using All coated papers fall roughly into three pressure combined with heat. This in and of itself categories: matte, dull and gloss. The difference creates challenges. between the three is supercalendaring, the process Ppaer mills are still grappling with the unique of passing the newly coated paper through a series problems presented by this proces, just as when of rapidly rotating stainless steel rollers to polish the offset process (which adds extra moisture to the paper’s surface. the paper) caused problems when it first became Simply put, matte finish papers are coated, but popular. Some papers are simply not up to the not supercalendared; gloss finish papers are. Dull challenge of high speed digital imaging. finish papers are very lightly supercalendared. First, dry toner is not in any way absorbed Matte (and dull) finish papers have, as the name into the paper, but instead merely rests on the implies, a relatively dull surface. Gloss finish surface of the paper. As a rule, the smoother papers have a shiny surface. the surface, the better the quality, but only up to a point. Note: The term glossy is sometimes used to refer to The surface of a typical gloss coated paper is all coated papers. This should be avoided, because too slick for Docutech toner to adhere to properly. of the obvious confusion that may result. A common problem can be flaking, in which the toner actually chips off, leaving a clean white The type of finish in no way reflects the quality sheet behind! of the paper. Matte or gloss; each has its purpose. Second, toner is opaque, which means that it Quality of coated book papers is measured (in reflects its own properties, not those of the paper ascending order) as #3, #2, #1, and Premium #1. beneath. This is very important. Quality Docutech The following information focuses on the imaging from Copies Overnight is indistinguish- differences between conventional printing able from offset when uncoated paper is used. and Docutech reproduction on coated papers. Not so with coated! While coated paper enhances the gloss of the • Forget colors. Only one paper mill, Appleton, offset ink, the same gloss serves to make Docutech makes coated paper in any shade beside white toner look extremely flat by comparison to the or cream. Appleton’s are not suitable for paper surface itself. Docutech imaging. Additional Considerations • Finally, remember that neither coated nor uncoated book paper is “better”. The “better” A few more considerations related specifically paper is the one best suited to the task at hand. to Docutech imaging: • The high-speed process utilizes a silicone based The following is experpted from oil as a fusing agent. Totally invisible on The Basis of Quality in Paper by uncoated stock, this necessary chemical may Arthur B. Little. sometimes leave barely perceptible horizontal streaks on coated papers. “There is, in a word, no such thing as a general • The heat plus pressure inherent in the high basis for quality in paper and no other possible speed imaging process can actually break down basis for quality in the case of any particular paper the clay coating. This is especially a problem on than its suitability for its intended use. Good longer runs. writing paper is bad blotting. Good newsprint is • Virtually all paper manufacturers, as well as poor wrapping, etc. In no case can the properties of Xerox, maker of the Docutech, refuse to a good paper be defined until the specific use for guarantee acceptable results when using coated which the paper is intended has been stated. The papers on the Docutech. properties which confer high qualities upon a paper intended for one purpose are precisely those The Solution which condemn it for another. Stretch is a After conducting extensive experimentation, desirable property for a bag paper, it may be fatally Copies Overnight has observed that each problem objectionable in a paper for lithography. Opacity is previously described decreases as gloss is reduced. a principal element in determining the quality of For this reason, Copies Overnight recommends the Bible paper. Transparency is equally important in obvious solution: when imaging coated papers, glassine paper. Certain grades of book paper base first look to a dull or matte finish. their claim to quality mainly on the extent to which they bulk for weight.” General Considerations Here are a few more points to ponder when General Information considering specifying coated paper: • Coated paper costs more than an equivalent Call for Technical Assistance... uncoated bond or book weight paper. Our staff will gladly answer your questions • Gloss is a very bad choice for technical material about software applications, digital files since the glare can make them hard to read. preparation and transmission and our high-speed What makes a fancy brochure attractive can be document printing services. a detriment to a text filled book or manual. Details • Lower brightness. In fact, many premium #1 (630) 690-2044 This technical bulletin was coated papers have about the same brightness produced on rating (85) as uncoated economy grade copy paper! our Docutech system from a • A better measure of comparison between coated QuarkXPress and uncoated paper is caliper (thickness), not 3.32 digital file. The paper stock weight. See the chart below. is 65 lb. Eastern Opaque Cover, Approximate caliper of papers (comparative) Polar White. Index tab die cutting and lam- inating per- 50 60 70 80 formed on our Scott system. 60 70 80 90 O N R 70 80 90 Using tomorrow’s technology today. 80 90 50