Cutting down the 40,000 lb plus rolls ready for finishing (rolls or sheets)
Paper Making Kit
Plus, a Question
Paper Machines are the length of football fields!!!
Key Properties of Paper
Wood Fibers Used in Paper Manufacturing
The fibers used in paper manufacturing play a key part in what happens to it later
Weaker, yet smoother
Stronger, yet rough
Fibers Used in Paper Manufacturing
Paper can be made from MANY sources, but wood fibers are used more often
Other paper fibers sources can include:
Cotton and other plants (i.e. hemp)
Even old jeans!
Basis Weight of Paper ---- Huh?
Basis Weight is paper weight in pounds of a ream (500 sheets) in it ’s basic size
Web Printers purchase paper by weight (pounds) in rolls. Sheet fed printers typically order by number of sheets needed for the job.
The basic size for Book papers is 25 ” x 38”. The measurement of basis weight for book paper would be calculated by taking 500 sheets each measuring 25” x 38” and placing it on a scale. If the weight of the 500 sheets was 50lb., we would call that paper 50 lb. Book. If the weight was 60 lb. it would be 60 lb. book.
Basis Weight Types – Basic Sizes
Cover (20 ” x 26”)
Heavy weight papers used for book covers, advertising, direct mail, etc.
Index (22 ½ ” x 28 ½” and 25 ½“ x 30 ½ “)
Usually available in smooth and vellum finishes. Used in file folders, index cards, etc.
Tag (24 ” x 36”)
Smoother surface than index, making it ideal for high-speed folding, embossing, etc.
Bond (17 ” x 22”)
Commonly used for letters and business forms. Example: paper in your books is 20# Bond
Basis Weight Types – Basic Sizes
Board (22 ½ ” x 28 ½”)
One of the board grades, with a softer surface than index or tag. Used for POP, signage, book covers (soft), advertising etc.
(25 ” x 38”)
Much easier outside the U.S.… They use only one Basis Weight. g/m2
Let ’s look at some
Basis Weight as compared to Caliper
Basis weight is the weight in lbs of a ream of paper in its ’ basic size
Caliper is the thickness of the paper
Uniform caliper or sheet thickness is important for several reasons:
Packaging is based on Caliper
E.g. 500 printed sheets to a box. Caliper too high, the 500 printed pieces will overflow the box. If caliper is too low, the reverse will be true.
Book covers are made prior to the printed pages. If the paper caliper is too thick, the covers will not fit (tight). If caliper is too low, the covers will be too loose.
Grain and Grain Direction
During manufacturing, most paper fibers line up in a parallel manner to that of the paper machine.
Grain affects printing and should be considered:
Paper folds smoother with the grain direction and roughens or cracks when folding cross grain
Paper is stiffer in the grain direction
Formation is the physical distribution and orientation of fibers and other solid constituents in the structure of a sheet of paper which affects the appearance and other physical properties.
Formation is also referred to as “look through” because the formation can sometimes be observed by looking through the sheet.
Formation can have a big impact on print quality for:
Ink Mottle - A “wild” formed sheet will result in the ink absorbing into the structure unevenly which then causes the ink to day with a mottled appearance.
Ink Show-Through (Printed Opacity) - If a sheet is “wild” with areas of fiber surrounded by areas of no or little fiber, ink will bleed at differing rates resulting in a strong “blotchy” ink show-through.
Surface is a key to good press runnability!
Uncoated papers need to “seal” the sheet to reduce press contamination (fiber, debris, etc.).
Sizing used for uncoated paper consists of a starch applied to the paper during the paper making process.
Various types of starches are used:
Good surface sizing is critical to achieve good press performance!
Starch is applied by a simple “coating device” located between the two drying sections of the paper machine. There are several types used by paper makers to applied starch. A typical size press would look like this:
Paper Size Press Rolls Starch Solution
There are five main optical properties that influence the visual perspective of a printed sheet:
Opacity relates to the show-through of the printed image from the opposite side of the sheet, or the sheet under it.
Brightness affects the contrast, brilliance, snap or sparkle of the printed sheet. It is the percent of reflectance at a standard single wavelength.
Don ’t confuse “whiteness” with “brightness”.
Whiteness is the amount of Red , Blue and Green reflectance and that will be discussed shortly
To achieve higher brightness, paper mills use optical (Fluorescent) brighteners and dyes
Can cause problems, however, if paper printed is mixed with paper made with and without optical brighteners as a color difference will be seen when UV light is applied.
Many manufacturers have loaded up on optical brighteners recently as it makes the paper appear nicer and brighter to the naked eye. This can affect printing however – especially on facial tones
73-78.9 79-82.9 83-84.9 85-87.9 88+ AF&PA Brightness Comparison 81.9 and below 82-86.9 87-90.9 91 + NO.1 NO.2 NO.3 NO.4 GE BRIGHTNESS METER Premium Old New
Whiteness is the ratio of Red, Green and Blue reflectance.
An attribute of a diffusing surface which denotes its similarity in color to preferred or standard white.
A psychological attribute of a color stimulus. A “white” color stimulus is perceived as void or any hue or grayness.
White can be in many different hues.
Known as “cold” if on the blue side.
Known as “warm” if on the red side.
Gloss is the relative amount of incident light reflected from a surface.
Paper Gloss - Degree to which a paper surface appears “shiny”.
Printed Gloss - Degree to which a printed ink appears “shiny”.
Paper Gloss is attained by the paper maker through calendering and pigments.
The higher the calendaring, the higher the gloss.
Calendering Paper Calendar Rolls Pressure and heat combine to make the sheet shinier and glossier. However, the more you calendar, the thinner the sheet becomes.
Coated Paper Finish Examples Finish Calendering Paper Gloss Surface Suggested Matte None Not apparent Rough/toothy, non-glare Texture, Text Dull Minimal Very Low Smooth, non-glare Illustrations, Black & White Satin/Velvet Light Low - Moderate Smooth and soft to the touch Text, texture, fabrics Silk Light Moderate Smooth and silky to the touch Fine art, skin tones, detail, readability Gloss High High Smooth, shiny, slick Hard, shiny surfaces, no scuff
Gloss Finished Surface
Calendared using smooth and polished steel rolls
Highest printed ink gloss
Highest plain paper gloss of coated finishes -- reflective
Highest ink hold-out, lowest dot gain
Best for showing fine detail
Matte Finished Surface
Lowest paper gloss
Lowest printed ink gloss
Greatest amount of contrast
between paper and ink
Replicates look and feel of uncoated
End Uses: Text, charts, anywhere to minimize eyestrain, writeable
Silk / Dull Finished Surface
pattern from imparted by calendar rollers
Excellent ink holdout for sharp halftone reproduction
Richer halftones and solids than mattes
Velvet Finished Surface
Coating formula and on line calendaring technique produce a smooth, low gloss paper
Looks like a dull -- prints like a gloss
Higher paper gloss than a dull
Similar coat weight to gloss
Smoother, harder surface than a dull
More uniform printing surface than a matte
Distinctive, silky feel
A.K.A. Satin, Suede
Global Coated Papers: Worlds of Difference North American Asian European
Uncoated versus Coated Papers
Un-Coated Print Dot Coated Print Dot
Measures texture and topography
Necessary for continuous, non-mottled ink film
Higher ink gloss
More pure ink color/broader tonal range
More accurate reproduction
Greater detail for critical color
Strength of paper is more dependent on the nature of its fiber than its thickness.
High bursting strength is achieved by closely intermingling long pulp fibers during the forming of the sheet on the paper machine.
Fibers are long and tear in the cross machine direction is always higher than tear in the machine direction.
This is because the greatest number of fibers lie across the path of the cross machine.
Tear strength is important when producing a sheet with perforations. The “perf” should not fall apart of be difficult to separate.
Paper which are subjected to considerable tension in use, such as web papers, should have a high tensile strength as well as high tear strength.
Fold - Good fold endurance is important so that cracking at the fold does not occur.
Heavy weight papers need to be scored to reduce cracking.
Stretch is the amount of distortion paper undergoes under tensile strain. Stretch is generally much greater in the cross direction than in the machine direction.
Excessive stretch with web or sheetfed papers will result in poor registration or fanning problems.
The Moisture content is the percent of moisture found in the finished paper.
Can range from a low of 4.0% to a high of 7.0%.
Heat-set web paper with low moisture (< 5.0%) will dry out in the heatset oven causing cracking at the fold.
1 ton of paper at 5% moisture level will contain 100 lbs. of water!
Remember earlier when we talked about the paper machine? Paper is 95 to 98% water as it enters the paper machine! Moisture in paper plays a part from the beginning all the way through the printing process.
Paper likes to come to equilibrium with its environment.
Paper brought into a humid pressroom absorbs moisture at the edges while the rest of the pile or roll (towards the center) will remain unchanged.
As this process occurs, the edges containing more moisture will increase in size resulting in wavy edges.
Paper brought into a dry pressroom will give up moisture, at the edges first, shrinking the paper resulting in tight edges.
This will result in wrinkles, fanning and bad registration.
Specialty Grades of Paper Fancy finishes Synthetic Papers Magnetic Papers Pressure Sensitive (i.e. “sticky back”) Carbonless Etc