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Paper & Pulp Dictionary Glossary "D"

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 Definitions for commonly used terms, words and phrases used in the pulp and paper trade

 

 

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Damp Streaks
 Streaks caused by uneven pressing of drying during paper manufacturing.
Dampening
The process of keeping the non-image areas of lithographic plates to be ink repellent by applying aqueous Fountain solution to the plate from the Dampening system.
Dandy Roll
A hollow wire covered roll that rides on the paper machine wire and compacts the newly formed wet web to improve the formation and if required to impart watermark or laid finish the paper.


Dandy Roll with Pan

Debossing
Pressing letters or illustrations into a sheet of paper using a metal or plastic die to create a depressed (debossed) image.
Deciduous Trees
Broad leafed or hardwood trees which lose their leaves in fall such as birch, maple etc.
Decker
A drum type filter used for pulp thickening.
Deckle
The width of the wet sheet as it comes off the wire of a paper machine. Also defied as the wood frame resting on or hinged to the edges of the mould that defines the edges of the sheet in handmade papermaking or strap or board on the wet end of a paper machine that determines the width of the paper web.
Deckle Edge
The untrimmed, feathery edges of paper formed where the pulp flows against the deckle.
Deculator
A device that removes entrained and dissolved air from dilute stock furnish by applying vacuum as the stock is sprayed into an open chamber, usually at the outlet of cleaners.
Decurler
A device on a web press or sheeter used to remove paper curl.
Defibration
Separation of wood fibers by mechanical and/or chemical means.
Deflaker
Deflaker mechanically treat the fiber flakes and bundles of fibers in the stock in order that they are broken down into individual fibers in a suspension if possible. This is done for a number of reasons and in a number of positions within the system. It can be installed to reduce remaining flakes after a pulper, in the broke system to reduce flakes going back to the machine from the broke pulpers and can also be used in the final stages of a screening system in a recycled fiber line to treat the concentrated rejects and the flakes contained within it.
Degree of Polymerization (DP)
As applied to cellulose, refers to the average number of glucose unit in each cellulose molecule of a pulp sample. Usually determined by the CED viscosity test.
Deinked Pulp (DIP)
Paper pulp produced by deinking of recovered paper
Deinking
The process of removing inks, coatings, sizing, adhesives and/ or impurities from waste paper before recycling the fibers into a new sheet.
Deinking Cell
A vessel or chest used to treat recycled paper with chemical to remove ink.
Delamination
The separation of the layers of a multiplex paper/paperboard.
Delignification
The removal of lignin, the material that binds wood fibers together, during the chemical pulping process.
Deliquescent
Material that has the ability to absorb enough moisture from the surrounding atmosphere to revert it to a liquid form. Examples of deliquescent include calcium chloride and ammonium nitrate.
Densitometer
A sensitive photoelectric instrument that measures the density of photographic images or of colors. Used in quality control to accurately determine the consistency of color throughout the run.
Deresination
Reducing the resin (pitch) content of wood prior to cooking either by storage or using bleaching chemicals to reduce the resin content in pulp.
Digester
The reaction vessel in which wood chips or other plant materials are cooked with chemical to separate fiber by dissolving lignin.
Digital Printing
1. Printing by imaging systems that are fed imaging information as digital data from pre-press systems.
2. Computer –to-plate Systems, which use printing plates, or other images carriers that do not require intermediate films.
3. Computer-to-print (Plateless): Systems that produce reproductions directly on the substrate without the need for intermediate films or plates
A. Electronic printers: Electrophotographic printers, for black or single color, used for short-run variable information and on-demand book publishing.
B. Color copiers: Usually Electrophotographic printers, for spot or four color process printing, used for making one or several copies of spot or four color process subjects.
C. Electronic printing systems: Electrophotographic, magnetographic, monographic, field effect, ink jet or thermal transfers printing. For One-colour, four color process or up to six-color printing. Used for some degree of variable information, on-demand. Examples of use are direct mail, temporary product labels for trade shows, billboard posters and the like.
Dimensional Stability
The ability of paper or paperboard to maintain size. It is the resistance of paper to dimensional change with change in moisture content or relative humidity. Dimensional stability is essential for keeping forms in registration during printing and keeping sheets from jamming or wrinkling on press or in laser printers.
For more details on Dimensional Stability, please read Dimensional Stability Notes by Chuck Green
Dioxin
A group of 75 chlorinated compounds. Dioxins are formed in a complex process, where chlorine combines with other additives during bleaching..
Direct Cooking
Batch cooking in which digester contents are heated by blowing steam directly into the digester.
Direct Dye
Dye molecules that are sufficiently large and planar that they tend to remain on a fiber surface without need of a fixative. Direct dyes have moderate lightfastness but duller shades
Directionality
Dependency of a given paper property on the orientation of the fiber in paper e.g. CD or MD.
Dirt 
Dirt in paper consists of any imbedded foreign matter or specks, which contrast in color to the remainder of the sheet.
Dirt Count
The average amount of dirt specks in a specific size of paper area. Both virgin sheets and recycled sheets have "dirt," although recycled paper usually has a slightly higher dirt count than virgin paper. However, it rarely affects recycled paper's quality and use.
Dispersion
Following the deinking process of waste papers, residual ink particles are dispersed into tiny bits that are usually invisible to the eye. Bleaching the fibers helps to remove the last of the inks and improve paper brightness.
Dispersants
Substances such as phosphates or acrylates that cause finely divided particles to come apart and remain separate from each other in suspension.
Displacement Washing
An event of pulp washing in which washing liquid displaces free liquor from a pulp bed in order to improve the washing; enables washing with reduced amount of water.
Dissolving Pulp
A high purity special grade pulp made for processing in to cellulose derivatives including rayon and acetate.
Doctor Blade
Thin metal plate or scraper in contact with a roll along its entire length to keep it clean. Blades are also used for creping.
Document Paper
Document paper is paper with a high ageing resistance. It is woodfree but may also contain rags or be fully made from rags and is used for documents that have to be preserved for a longer period.
Double Coating
Coating of paper or paperboard twice on one or both sides.
Down Cycling
Every time cellulose fibers are recycled they deteriorate slightly and become contaminated, so the new product is of lower quality than the original product which went to form the waste; the progressive deterioration of fibers means that there is a limit to the number of times they can be recycled, thus the term down cycling is used as a more accurate description of recycling.
Drainage or Dewatering
Removal of water from wet web during formation of paper sheet.
Draw
Difference in speed between two adjacent section of the paper machine.
Dregs
The solids which settle down in the clarifiers in the Causticizing process.
Drum Reel
The reel drum (also called a "pope reel") is motor driven under sufficient load to ensure adequate tension on the sheet coming from the calendars.  The web wraps around the reel drum and feeds into the nip formed between the drum and the collecting reel.
 

Drum Washer
One type of pulp washers; uses pressure gradient and filtration for dewatering and displacement.
Dry Coating
Coating method in which a binder is applied to the paper surface followed by dry coating pigment.
Dry End
That part of the paper machine where the paper is dried, surface sized, calendered and reeled.
Dry Line
The dry line is the location on a Fourdrinier paper machine forming section where the appearance of the wet web of paper changes abruptly. Before the dry line the furnish has a glossy, wet appearance. After the dry line the wet web appears dull. The optical change is related to the effect of fibers poking through the air-water interface. On a well-adjusted paper machine the dry line ought to be straight. Increased refining and lower freeness of the pulp tend to move the dry line in the direction of the couch. Chemicals that promote drainage tend to move the dry line in the direction of the slice.
Dry Offset
Uses a rotary letterpress plate on an offset press. Because the image is relief, the method requires no dampening. Image is transferred to a rubber blanket, then to paper.
Dryer Felt
A continuous cotton and or synthetic belt and used in the dryer section of a paper machine to press and maintain positive contact of the web against the surface of the dryer cylinder.


Dryer Cylinders & Dryer Felt

Dryer Screen
A type of dryer felt made of synthetic material, with very high open area  to provide easy escape to vapors formed due to water evaporation. Dryer screens are used in the later part of dryer section where paper is >60% dry to avoid any screen impression.
Drying
This is the final stage of water removal from wet web of the paper formed on wire. After pressing the moisture content of the web is apprx. 40-45%. The remaining water (up to 95% dryness) is removed by evaporation . This is done by moving the web around a series of steam heated iron drums in the dry end of the paper machine.
Duplex Bag
Two-ply bags.
Duplex Board
Paperboard made with two plies or layers. Normally two layers are formed and joined together at wire part.
Duplex Paper
Paper made with two plies or layers. Normally two layers are formed and joined together at wire part.
Dust
Loose flecks of fiber, filler and/or coating on the paper that sometimes sticks to the printing blanket and prevents ink from reaching the paper surface.
Dye
A chemical compound having the ability to absorb visible light over a certain range of wavelengths so that the diffusely reflected light appears colored. Dye can be basic, acidic or direct.
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