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Paper Choices

Printips: March 2004

Paper Clips: How to Select the Right Paper for the Job
As printers, we love paper. Paper adds a design element, influences the impression and contributes to the overall appeal of a printed piece. Paper is also a critical variable in how well a job runs on press, in a high-speed copier or digital printer, or through the laser printer on your desktop.
For most printing jobs, there is a paper whose characteristics are best for the application. For example, if the printed piece is a trifold brochure, a sheet with good folding characteristics will be best. If the piece has significant ink coverage, then a paper with superior ink holdout will perform best.
Here at Printlocal.com, it is our job to guide you through the many possibilities to match the paper to your printing project. This will be easier if you understand how the characteristics of paper affect the appropriateness for a specific printed piece.
Finish
The finish or surface of the paper has a significant effect on the final appearance of a printed piece. During manufacturing, paper fibers align themselves in an arrangement of peaks and valleys on the surface of the paper. The height of the peaks and depth of the valleys affects how the ink film lays on the surface. Ink film is approximately one micron thick; on a paper with little difference between the peaks and valleys, the ink density will be even, making the image appear sharp.
During the papermaking process, the paper surface can be altered by a process called calendaring. The paper is pressed between two rollers called calendars that smooth the surface. The greater the amount of calendaring, the smoother the surface.
Paper surface can also be altered by sizing or coating. Sizing is a solution added to paper to make it less absorbent. Sizing (rosin, glue, gelatin, starch or modified cellulose) added to paper pulp is called internal sizing, while external or surface sizing treats the surface of the paper after it has dried. Sizing improves ink holdout.
Coating the surface of paper makes it smoother, imparts a sheen or gloss and improves ink holdout. Kaolin clay is used as both filler and coating to impart gloss to paper. The gloss of the paper also affects the gloss of the ink - the glossier the paper, the glossier the ink. Depending on how much light the coating reflects, it will be termed gloss (high reflectivity) or matte (low reflectivity).
Writing, text and cover papers may be given a finish either during the papermaking process or after it is completed. Popular finishes include smooth, vellum, cockle, felt, laid, and linen.

Brightness, Whiteness and Color
The brightness of a sheet of paper measures the percentage of a wavelength of blue light it reflects. Most papers reflect 60-90% of light; the closer to 100, the brighter the paper. The brightness of a paper affects readability, the perception of ink color and the contrast between light and dark hues.

Brightness is not related to either color or whiteness. Although there are many papers called white, all have a definite hue. Most have a blue white tint though there is a wide shade variety. Like brightness, the hue of the white affects the perception of ink color and contrast. Off-white sheets produce less glare.
Paper color is determined during the papermaking process by adding pigment to the pulp. The perception of ink color can be altered depending on the color of the paper.
Grain
The fibers in paper lie in a single direction. As paper pulp moves forward on the papermaking machine's wire screen, the fibers tend to align themselves in the direction of movement. When the grain runs the length of the paper, it is said to be long; when the grain is across the width of the paper, it is said to be short.

Grain direction directly affects paper strength and flexibility and therefore is important when a printed piece will be folded or made into a booklet. Folding long grain stresses paper fibers; folding short grain actually breaks them. When a fold must be made on the short grain, it is customary to score the sheet first to evenly break the fibers.

Grade
There are five basic categories of paper, called grades: bond, offset or uncoated book, coated book, text, and cover. Papers in different grades vary in content, appearance, end use and original purpose. For example, the name bond was originally given to paper that was used to print bond and stock certificates. Today it is used to refer to paper used for letterheads, duplicating and photocopying. Similarly, book paper was originally used to print books and cover paper was used for book covers.

Within each grade there are other distinctions depending on the brightness, opacity and fiber content of the paper. Uncoated writing, bond, offset, duplicating and photocopying papers can also be referred to as fine papers.

Basis Weight, Caliper and Bulk
The basis weight of paper is the weight in pounds of a ream (500 sheets) of paper cut to the basic size of its category. The basic size for bond paper is 17"x22"; for text, offset and coated papers 25"x38"; and 20"x26" for cover paper. A ream of bond in its basic size weighs 20 pounds; the equivalent weight for offset paper is 50 pounds and for cover is 27 pounds. Pounds is often indicated by using the # sign, as in 20# bond. Basis weight is also called substance.

Each paper grade has a range of basis weights: 16#-24# for bond; 50#-70# for offset; 50#-100# for coated book; 60#-100# for text; and 60#-100# for cover.

The thickness of paper is called the caliper; it is measured in thousands of an inch and referred to as point size. (This is different than the point size in typography, which measures the height of characters in a font.) One-thousandth of an inch equals one point, so ten-point paper has a thickness of 0.01 inch. The caliper of paper is not related to basis weight - a smaller-sized, thick sheet may have the same basis weight as a thinner paper in a larger basic size.

Paper bulk defines thickness relative to basis weight. A paper may be bulkier than another grade while still having the same basis weight.

What it all means
From this description, we hope you can see that selecting paper means more than choosing a color and grade. Our knowledgeable customer service staff <here insert the name of your CSRs and salesmen> will guide you toward the grade that is best for your project. Call us at <insert your telephone number> for more information.

Vocabulary
Beat to a pulp: the first step in making paper out of cotton. The cotton fibers and water are beaten to a pulp in a Hollander beater.
Calendar: the use of two rolls (calendars) to squeeze paper and smooth the surface. A sheet may be run between a series of calendars that squeeze the sheet in several directions to smooth the surface in all directions.
Coating: substances applied to a finished sheet of paper to protect it or make it shiny.
Converting: a step in papermaking in which the sheet coming off the end of the paper machine is changed into a useable paper product.
De-Inking: the process of extracting the ink and coatings from printed papers so that the fibers can be used again as a secondary fiber source.
Effluent: the liquid discharge or waste products of the papermaking process. Often includes a small amount of suspend solids and dissolved chemicals. Because most modern paper mills now contain wastewater treatment plans, effluent now can be discharged into rivers.
Fourdrinier Paper Machine: a papermaking machine invented by a Frenchman, Nicolas Louis Robert in 1798, developed in England by Brian Donkin for Henry and Sealy Fourdrinier, but not placed into operation until 1804. The Fourdrinier Paper Machine was the first papermaking machine to make continuous paper. Prior to this machine, paper was made in single separate sheets.
Secondary paper: any recycled fibers, waste papers, or other sources of pulp and fiber that come from a previously created product or process.
Virgin fiber: wood fiber that has never been recycled.
Waste paper: recycled paper that cannot be used as the surface of a sheet. Often used as the inside layer of a three-layer sheet.

Q&A
Q. How does a tree become paper?
A. Two types of trees are used to make paper: hardwood trees such as cottonwood and softwood trees such as Douglas fir and Ponderosa pine. Softwood trees provide long fibers that add strength to paper; hardwood trees provide shorter fibers that improve the ability of the paper to take a finish.

Paper mills often own forests from which trees are harvested. After cutting, trees are transported to the mill and converted to wood chips. The chips are sorted by size, then sent to a digester where they are cooked at high pressure to dissolve lignin, a substance in wood that holds the cellulose fibers together.

Because lignin is brown in color, the pulp that emerges from the digester is brown. It can be used for paper products such as cardboard, but for other purposes, the pulp must be bleached using a combination of chemicals and heat.

After bleaching, the pulp is moved to a papermaking machine called a Fourdrinier. The pulp or stock is sprayed onto a continuous screen called a wire that moves in an endless belt. Water is drained and sucked out of the porous wire; the pulp, which is about 3% solids when placed on the wire, is about 7% solids at the end of the wire.

From the wire, the stock is picked off the screen by a felt moving at the same speed. The stock goes through a series of rollers to squeeze out more water. At the end of this process, called the press section, the stock is 40-50% solids.

Next, the stock moves to the dryer that is composed of a series of rollers that are heated from the inside by dry steam and from the outside by hot air. After drying is complete, the stock is about 95% solids.

To improve the ability of the paper to take ink, a special coating called sizing is applied to the paper, then it is once again dried before being collected on a large roll at the end of the paper machine. From start to finish the paper travels approximately a quarter of a mile.

Tricks & Tips
Embossing is a way to add impact and appeal to business stationery, presentation folders, invitations, annual reports, personal stationery or other printed products. Embossing raises the surface of selected areas of paper to create a dimensional effect. Many things can be embossed - type, a border, a logo or other image, for example. If the embossed area has not been printed, it is said to be blind embossed.

Embossing requires that paper be subjected to heat and pressure between two dies - one right-reading and one reversed. The force and heat causes the paper to assume the form of the dies. Embossing can be as high as 1/8 inch, and the area around the embossing can become smooth and shiny, known an ironing.

Paper to be embossed must be carefully selected so it will assume the shape of the die without breaking or tearing. In general, the best paper for embossing is soft and uncoated with a high cotton content. Papers that are hard or have coating at more at risk for cracking and breaking during the embossing process. The critical factor is not bulk or thickness but tensile strength.

Ask your printer to see samples of embossed materials - you will quickly see how important the paper selection is.

Idea Corner
A watermark is a translucent image that is added to the fibers of paper during the papermaking process. Fine writing papers such as those used for business stationery are characterized by watermarks. Hold a sheet of Crane's or Strathmore paper up to the light and you will see the watermark clearly. When watermarked paper is used to print letterheads and envelopes, it conveys a subtle sense of prestige.

A watermark can also provide a security feature. Since genuine watermarked paper cannot be duplicated, documents printed on it are protected by the watermark. For example, when United States currency was redesigned in 1995, a watermark of Benjamin Franklin was added to the $100 bill.

A genuine watermark is made while paper is still wet and moving through the wire portion of the Fourdrinier papermaking machine. The pulp or stock passes under a cylinder called a dandy roll on which the watermark design is located. The watermark design displaces the fibers, which alters the thickness and opacity of the paper in those areas. It is the variation in opacity that is seen as the watermark.

There are three positions for a watermark: localized meaning that the mark falls in the same position on every sheet (within a tolerance of one-half inch); centralized meaning the mark appears in the same vertical line on the sheet, though its top-to-bottom location may vary; and random meaning the watermark falls anywhere on the sheet. In this instance, the watermark may appear more than once on a single sheet.

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