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Ch.18 from the Offset Lithographic Technology Book.

Laura Roberts

on 2 February 2017

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Transcript of Paper

Physical Properties
of Paper

Paper Classifications
Book Paper
Cover Paper
Bristol Paper
Whiteness and Brightness
Pick Resistance
Dimensional Stability
Paper Origins
Pulp Production
Making Paper
History of Paper
The word paper comes from the word papyrus, a reed the ancient Egyptians used for making a writing material.
The manufacture of paper for printing involves
two processes: pulp production and paper manufacture.

Pulp production includes debarking, chipping, pulping, bleaching, beating, refining, adding nonfiberous ingredients, and cleaning the pulp.

Paper manufacture includes forming the paper, producing watermarks, removing water, drying the paper, and finishing the paper.

Paper is made with what are known as cellulose fibers - the basic structure of plants.

Wood fiber sources are divided into softwoods (coniferous) and hardwoods (desidious).
Dimensional stability is the ability of the paper to retain
its original length and width when exposed to moisture.
The term finishing refers to any action performed
on the sheet after it has been removed from the paper machine.

The word finish is also used to the degree of smoothness of a paper's surface.

Paper with an antique finish is characterized by a rough surface intended to simulate old, handmade paper. Eggshell simulates the rough surface of an egg. Vellum simulates the texture of ancient vellum. Machine finish has a smooth , low-gloss finish. Embossed finishes are created by embossing patterns like tweed, linen, and pebble.
A paper's whiteness refers to the extent to which it reflects nearly equal amount of RBG light from its surface. White light is formed from roughly equal parts of the visible spectrum. Therefore, in order for a paper to be pure white, it has to reflect nearly equal amounts of RBG light.
Book is a classification containing several categories of paper- most of which are intended for two-sided printing. Book papers carry high filler content to improve opacity because of the need to carry printing on both sides. The basic size for all book papers is 25"x38".
Cover paper is used primarily to cover and protect other printed materials. This paper is heavy, strong, easy to fold, and available in a wide variety of colors. This paper is used for business cards, booklets, catalogs, pamphlets, covers, programs, and mailing pieces.
Index bristol is a heavyweight paper used for index cards, menus, and mailing pieces.
The basic size of index bristol is 25.5"x 30.5".
Learning Objectives
When you have completed this presentation and the assigned activities related to this chapter, you will be able to do the following:
Summarize the papermaking process and list the various stages involved.

Identify paper requirements for sheetfed and webfed presses.

Give examples of various paper properties and explain how they affect a paper's printability, print quality, and runability.

List the paper classifications and indicate their identifying characteristics.

Explain basic size, substance weight, ream weight, and M weight (Mwt.)

Describe the various sizes and styles of envelopes.

Determine the number of sheets required for a printing job.

Calculate the purchase price for an order of paper.

Determine the appropriate paper for various jobs.
The material on which a job is printed, called a substrate, plays several roles in influencing the effectiveness of the finished job.

The substrate usually contributes to the visual impact of the job, often represents 35%-55% of the final cost of a printed job, and might even determine which printing process is used.

To select a substrate - whether it is paper, paperboard, or a synthetic paper - that is cost-effective and meets the aesthetic and printing requirements of a particular job, a working knowledge of paper is necessary.

Paper and paper products are so
much a part of everyday life
that people take the
material for granted.
It was not until over 2000 years later that paper making was developed in china. Ts'ai Lun, is credited with the discovery of making paper in 105 AD. This official mixed debarked mulberry branches, hemp, and rags with water. The resulting slurry was cooked, beaten, poured onto molds, and pressed into flat sheets, which were hung to dry in the sun.
This new product and the process became very popular and paper mills were established throughout China.

In 1798, Frenchman Nicolas Louis Robert invented a papermaking machine that made paper by pouring a slurry of pulp over a continuous conveyor belt made of wire screen.

In 1812, they put the world's first paper machine known
as the fourdrinier machine into operation.
Softwood trees include pine, fire, spruce, and hemlock.

Hardwood trees include oak, polar, gum, beech, maple, birch, and chestnut.

Fiber from both types of wood are used in most papers because the long and thick softwood fibers give the sheet strength,
and the shorter and thinner hardwood fibers fill in the low places between
the softwood fibers and make
the sheet smoother.
Pulping is the process of reducing wood to individual fibers, and the product of the pulping process is called pulp.

After logs have been debarked, they are reduced
to chips.

The mixture of water and dissolved paper pulp is called slurry.

Chemical pulp is prepared by pressure-cooking chips in a large enclosed container called a digester.
Treating the Pulp
After logs have been debarked, they are reduced to chips, which are cooked
in a digester to separate them into individual fibers and stored in the blow
pit before moving onto further treatment stages - washing;
bleaching; refining, and the addition of fillers, sizing, dyes, and pigments.

The pulp goes through washers, which remove spent chemicals used in the digester, and then is sent over a series of screens and centrifugal cleaners that remove small pieces of uncooked wood and grit.

In a series of carefully controlled operations, the pulp passes through four stages of bleaching to whiten the
paper fibers.

The refining stage (also known as the beating stage) pulp fibers are flattened, frayed and sometimes shortened.

Many additives are incorporated into the pulp during the refining process.

Fillers are finely ground particles of clay or chalk added to pulp to improve the paper's opacity (reduce the passage
of light).

Sizing is used to make paper less absorbent. Writing on newsprint with an ink pen demonstrates how excessive absorbency allows feathering, which hurts image quality.

An excessive absorption of dampening solution can weaken the sheet and slow the drying of ink.

Solving both problems requires two types of sizing: internal and external. Internal sizing is achieved when fibers are coated during the refining process with rosin that reduce their absorbency. External sizing usually consists of applying a starch to both sides of paper before the paper is removed from the paper machine.

Dyes and pigments are added to the pulp during refining to give the paper color.
Manufacturing Paper
The forming of paper starts at the wet end of the fourdrinier machine, where a slurry of 99% water and 1% fiber flow from the head box across a continuously forward-moving mesh wire screen called a forming wire.

The water drains from the pulp through the wire screen as it moves along, leaving a mat of fiber on the surface of the wire.

Rollers and suction boxes under the wire screen support the screen and accelerate the removal of water.

The side of the paper against the screen is called the wire side, and the top side is called the felt side.
Receiving, Handling,
and Storing Paper
Paper represents a large financial investment and should be given the proper attention.

It is important to handle the paper carefully and not to accept deliveries if the packaging is damaged.
The side of the paper against the screen is called the wire side, and the top side is called the felt side.

At this point, the pulp passes under a dandy roll to break up any bubbles that might have formed. The dandy roll also produces watermarks when it carries designs on raised metals. A watermark is a symbol or logo identifying the brand of paper.

As the web o0f paper emerges from the drier section of the papermaking machine it is forced between heavy iron calender rolls, which make the paper's caliper (thickness) more consistent.

Supercalendering is the process of sending coated paper through a series of rollers that polish the coating to form a glossy finish.
The forming of paper starts at the wet end of the fourdrinier machine, where a slurry of 99% water and 1% fiber flow from the head box across a continuously forward-moving mesh wire screen called a forming wire.

The water drains from the pulp through the wire screen as it moves along, leaving a mat of fiber on the surface of the wire.

Rollers and suction boxes under the wire screen support the screen and accelerate the removal of water.
Paper that is delivered during the winter should be allowed to warm up to the indoor temperature before they are unwrapped.

Paper rolls should be stored on their ends to avoid flattening one side of the roll.

Paper should be stored away from heat or cold.
As the paper move from the wet end of the papermaking machine toward the dry end, the fibers tend to align themselves in the direction they are traveling, and this alignment of fibers is referred to a the grain of the paper.
Fiber Length
A paper's opacity, or show-through, refers to the extent to which light passes through the sheet.

A sheet with high opacity allows the passage of very little light, and sheets with poor opacity allow printed images to show through to the reverse side.
Paper Requirements
Offset presses can print on almost any kind of paper. For quality work, they should meet certain basic criteria.

The ink has a high tack level and can exert enough pull against the paper to pull away part of the surface because offset printing uses a paste ink, instead of a liquid ink. For this reason, offset paper must have stronger fiber-to-fiber bond than is needed for other printing processes.

In offset lithography, the paper receives both ink and dampening solution. To prevent the softening and weakening of the sheet by excessive absorption of dampening solution, offset paper receives internal sizing, as well as surface sizing.

The softening and weakening of the paper surface can cause picking (the lifting of clumps of paper fibers) and a transfer of fibers or coating to the blanket.

Excessive moisture pickup of the dampening system can also cause the sheet to curl and expand across both dimensions.

Webfed-offset also requires a high tear strength
to avoid paper tearing from the tension.
Sheetfed-offset prints from a stack of paper.

Webfed-offset prints from a roll of paper.
Fiber length is important to paper's tear strength, its resistance to tearing. A sheet's tear strength is proportional to the length of its fibers. Longer fibers require more effort to tear the paper.

Fiber length also contributes to fold strength - the resistance to weakening and coming apart at the fold.
Coating paper in matte, dull, and gloss finishes improve the ink holding ability and reduces feathering out.
The ability of a paper to resist surface rupturing
during printing is its pick resistance, or surface strength. During lithographic printing, the ink film on the blanket splits. One-half stays on the blanket, and the other
transfers to the paper.

Picking occurs when the ink fails to split and the surface
of the paper ruptures. When these lifted materials, known as hickies, stick to the blanket, they accept dampening solution and repel ink.
Other Picking Problems
Linting is the result of loosely bonded fibers that break off and are carried by the offset blanket to the ink rollers.

Powdering is the lifting by ink of individual filler
particles from paper during printing.

Piling is the accumulation of paper fibers and other debris on the printing plate or blanket or both in the image and nonimage areas.

Scumming is the adhering of ink to the nonimage
areas of the plate.
Substance Weight
Paper mills produce paper in various weights. The weight of a paper is measured by it substance weight, or basis weight. The substance weight is the weight, in pounds, of a ream (500 sheets) in a specified size, known as the basic size.

The basic size is not the same for all classifications of paper. For example, the basic size for bond and other business papers is 17"x22". The basic size for cover paper is 20"x26". The basic size for offset paper is 25"x 35".
Substance Weight
Paper flatness is a measurement of how much the paper curls or becomes wavy.
A sheet's squareness describes the sheet being exactly 90º at all four corners.
Ink Drying
Ink drying can be a serious problem when paper quality is poor or in cases where paper and ink are not compatible. Offset inks are formulated to print and dry on a wide range of papers. Variations in paper quality can result in slow drying.
Utility Paper
Papers that do not belong in these first four classifications are grouped together and termed utility papers.
These papers are also known as miscellaneous papers. Newsprint, label paper, synthetic paper, and mineral sheets are included.
Paper classifications are used to identify and categorize the hundreds of different types of paper.
Business Paper
Business papers include sheets commonly found in the business world.
The basic size for all business papers is 17"x22". The most common category
of business paper is bond paper, which is used primarily for letterhead stationary, business forms, writing, typing, and photocopying.

Carbonless bond papers are used to transfer and copy written, printed, or typed images between sheets.

Unlike regular, papers, carbonless papers use a chemical transfer system to create images.
Coated back (CB) has the back side of the tops sheet in the carbonless set coated with encapsulated chemicals.

Coated front-and-back (CFB) is carbonless paper sheet between the first and last sheets with a receptor coating on top and an encapsulated coating on the back.

Coated front (CF) has the last sheet of carbonless paper with a receptor coating only on the front.
Uncoated offset paper is commonly used to print newsletters, direct-mail pieces, journals, and fliers.

Coated offset paper is commonly used for posters, magazines, brochures, fliers, and other jobs requiring four-color printing.

Text paper are used in brochures, menus, announcements, annual reports, and any other piece intended to convey a richness of texture or finish.
Newsprint is a popular utility sheet made primarily from groundwood pulp.
Environmentally Friendly Paper
Many graphic designers and print buyers specify papers that are considered environmentally friendly.
Recycled Paper
Recycled paper is produced from pulp made from recovered paper and paper products, manufacturing waste, nonpaper materials, and wood residues.
Paper Made with Alternative Chemicals
A second environmental concern involves the chemistry used in the bleaching of wood pulp to produce white paper. Therefore bleaching substitutes are used in place of chlorine gas as a bleaching agent.
International Organization
for Standardization (ISO)
Metric Sizes of Paper
Standard U.S. paper sizes have evolved over many years. Today, nearly all printing presses are manufactured outside the United States, and their sizes are expressed in metric terms.

To standardize printing-paper sizes, the ISO has developed a system, being adopted in many countries, using the metric system.
Paper-Swatch Books
Paper-swatch books are valuable sources of information because they provide samples of every color and weight of paper for a particular sheet.
ISO Basic Weight System
Paper using the U.S. customary system of measurement is presently sold by the pounds per ream. The international paper sizes relate all basic weights to the A0 sheet size. The ISO metric basic weight system for paper is expressed in grams per square meter.
Universal Basic Size
For a number of years, printers and paper manufacturers have proposed to substitute a universal basic size for the current practice of having a different basic size for each paper classification.
Envelopes are manufactured in many sizes. Most styles are available in several sizes, usually ordered by number. For example a No. 10 envelope is for business
use and measures 9.5" x 4.125".
Estimating and
Cutting Paper
Paper is an expensive material and can account for up to one-half of the
total cost of a printed job.

The printer must calculate the amount of required paper and how images will be arranged on the press sheet to avoid waste.
Estimating Spoilage Allowance
In calculating the amount of paper needed for a job, it is necessary to add in a certain percentage of pres sheets, to allow for spoilage. This percentage is called the spoilage allowance and is included to allow for the sheets needed to set up the press (makeready) and for the sheets that are printed badly during the run.
Selecting and Ordering Paper
When selecting paper for a particular printed piece, the following factors should be considered:
Paper is compatible with printing process and ink
Price is important
Paper that is heavier than necessary leads to high mailing costs
Paper surface and finish should be considered
Paper size
Colored paper
Four-color printing on neutral white, but type is printed on soft white
Paper-grain direction
Specialty Papers
Carbonless Paper
It is paper coated with microcapsules that under pressure, transfer an image to a sheet or sheets underneath it.
Pressure Sensitive
It is paper that has a form of adhesive substance which, in dry form, will remain sticky at room temperature and will bond to another surface under minimal pressure and without moistening.
Gummed Label
It is a label with an adhesive applied to one side.
Plastic Based
It is printing on materials made of plastic, i.e. plastic credit cards
Metal Based
It is printing on materials made of metal, i.e. cell phone inserts
Paper Characteristics
Offset Paper

Suitable paper properties: dimensional stability, resistance to curling, high surface strength, a surface free from foreign particles, and a high level of resistance to moisture penetration. Weight and sizes: bond, coated, text,cover, offset, index, and label.

Paper Conditioning: If paper is moved from storage to a location with a different temperature and humidity, the paper should be conditioned to the new location before use. This helps to prevent jams and miss feeds in the printer.

The color of the paper and texture effect the output of the image quality.
Digital Paper

Suitable paper properties: paper must be free of dust, correct frictional properties, resistance to curling, proper electrical characteristics, suitable smoothness, static resistance. Weight and sizes: bond, coated, text, book, offset, index, and label.

Paper Conditioning: If paper is moved from storage to a location with a different temperature and humidity, the paper should be conditioned to the new location before use. This helps to prevent jams and miss feeds in the printer.

Unsuitable papers: conductive paper, contains talk, contains stearate or plasticizers.
Specialty Paper for Digital Press
Specialty media such and carbonless, labels,tabs and transparencies, coated paper, synthetics, ID cards, labels and magnets can be run of digital presses.
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