The property of a material that causes it to take up a liquid
with which it is in contact. Several measures of absorbency are: (a)
the time required for the material to take up a specified volume of
liquid; (b) the rate of rise of liquid along a vertical strip dipping
into the liquid; (c) the area of a specimen wetted in a specified time;
(d) the quantity of a liquid taken up by a completely saturated
specimen. The method of measurement depends on the specific use of
paper.
Absorbent Papers
Soft, loosely felted papers that readily absorb water
solutions or liquid chemicals. They are not sized with water-repellent
agents, but may be treated with materials that enhance their wet
strength. They include blotting, filter, matrix and toweling papers,
and base paper for the manufacture of vegetable parchment, artificial
leather, vulcanized fiber and many other processed papers.
Acidity/Alkalinity
In paper, the condition that results in an acid or alkaline
solution when the paper is treated or extracted with water. In testing
paper acidity/alkalinity, the specimen is extracted with water at a
definite temperature, and the extract is tested to determine its pH
value or is titrated to determine the total amount of acid or alkali
present.
Alpha Cellulose
The portion of a celulosic material that can be filtered out
of a mixture of the fibrous material and 8% sodium hydroxide solution,
after the fibers have been previously swollen with 17.5% sodium
hydroxide solution. This determination is applicable primarily to pulps
and to papers made from cotton or chemical wood fibers. For papers
containing lignin, coatings, fillers, etc., certain corrections must be
made.
Alpha Pulp
Chemically treated wood pulp having greater than 90 percent
alpha cellulose, i.e. cellulose that is resistant to 17.5 percent
sodium hydroxide solution at 25 degrees Celsius.
Apparent Density
The apparent weight per unit volume. It is often calculated
by dividing the basis weight by the thickness, though it must be
recognized that the numerical value thus obtained depends on the
definition of the ream. Consistent numerical values can be obtained by
using in every case the basis weight in metric units (gsm) and the
thickness in millimeters.
Aqueous Coating
A water-based coating applied after paper production, either
on-machine or off-machine. An aqueous coating usually gives a gloss,
dull or matte finish and helps prevent the ink from rubbing off.
Archival Paper
Paper that is alkaline and will not deteriorate over time.
Archival papers must meet national standards for permanence: they must
be acid-free and alkaline with a pH of 7.5 to 8.5; include 2% calcium
carbonate as an alkaline reserve; and not contain any groundwood or
unbleached wood fiber.
Ash
The inorganic residue after igniting a specimen of wood, pulp or paper so as to remove combustible and volatile compounds.
Basic Size
The customary sheet size used to establish the basis weight
of a ream (500 sheets) of a given grade of paper. Basic size vary by
grade: Book is 25” x 38” while Cover is 20” x 26”.
Basis Weight
The weight in pounds, of a ream (500 sheets) of a paper cut
to a given standard (basic size). Each paper grade such as cover, bond
or book has its own basic sheet size, which determines its basis
weight.
Beater
A machine consisting of a tank or “tub” usually with a
partition or “midfeather” and containing a heavy roll revolving against
a bedplate. Both roll and bedplate may contain horizontal metal bars
set on edge. The beater may be “furnished” by either (1) pumping stock
slurry from a pulper or (2) adding pulp or wastepaper slowly with
sufficient water so that the mass may circulate and pass between the
roll and bedplate. The primary function of the beater is to initiate
the development of the fiber by cutting, bruising, fibrillating and
hydrating the fibers. Fillers, dyestuffs and sizing materials may be
added to the beater and thus incorporated with the paper stock.
Binder
A material used to cause substances to bond or adhere. In the
paper industry, binders are used widely to cause fibers to bond,
coatings to adhere or as laminates.
Bleach
An oxidizing or reducing agent used to remove color from pulp so that it has a higher brightness.
Bleaching
The process of chemically treating pulp fibers to reduce or
remove coloring matter so that the pulp is improved in terms of
whiteness or brightness.
Blotting Paper
An unsized paper used wherever absorption is the required
characteristic or where soft spongy paper is needed, even though the
absorption is of secondary importance. It is often made from rag,
cotton linters, chemical or mechanical wood pulp, or mixtures of these.
The paper is porous, bulky, of low finish and tends to possess little
strength. The normal basis weight ranges from 60-140 pounds
(19”x24”/500). Some grades are made with a smooth machine finish, which
makes them suitable for printing with coarse-screen halftones.
Brightness
The reflectivity of pulp, paper or paperboard for specified
blue light measured under standardized conditions on a particular
instrument designed and calibrated for this purpose. If a paper lacks
brightness, it will absorb too much light, and little light will
reflect back through the ink.
Broke
Paper that has been discarded anywhere in the process of
manufacture. “Wet broke” is paper taken off the wet press of a paper
machine; “dry broke” is made when paper is spoiled in going over the
dryers or through the calender, trimmed off in the rewinding of rolls,
trimmed from sheets being prepared for shipping or discarded for
manufacturing defects. It is usually returned to a repulping unit for
reprocessing.
Bursting Strength
A measure of the ability of a sheet to resist rupture when
pressure is applied to one of its sides by a specified instrument,
under specific conditions. It is largely determined by the tensile
strength and extensibility of the paper or paperboard. Testing for
bursting strength is very common although its value, except for
limited, specific purposes is questionable.
C1S
Paper that is coated on one side only; C2S – coated on both sides.
Calcium Carbonate
A chemical compound (CaCo3), occurring in nature usually from
sea deposition, or obtained commercially by chemical precipitation.
Calcite and aragonite are the two principal crystalline types with
calcite being the thermodynamically stable form. Chalk is a naturally
occurring form used only to a limited extent in papermaking because of
impurities present. The precipitated carbonate is preferred due to its
obvious higher purity and smaller particle size than the natural
product. This carbonate may be produced by precipitation of milk of
lime with carbon dioxide gas or sodium carbonate, or precipitation from
calcium chloride-sodium carbonate reactors. Calcium carbonate is used
both as a filler and as a coating pigment.
Calender
A set or “stack” of horizontal cast-iron rolls with chilled,
hardened surfaces, resting one on the other in a vertical bank at the
end of the paper machine. The paper is passed between all or part of
these rolls to increase the smoothness and gloss of its surface.
Calendering
The process of finishing a sheet of dried paper by pressing it between highly polished metal cylinders of a calender stack.
Caliper
The thickness of a single sheet of paper measured by a micrometer and expressed in thousandths of an inch.
Cellulose
The main solid constituent of woody plants, occurring widely
elsewhere in the vegetable kingdom. Chemically, it is a linear
polysaccharide of high molecular weight. Wood cellulose is the material
remaining after a large portion of the lignin and certain carbohydrates
have been removed by pulping and bleaching.
Cellulose Fiber
Main component of the walls of all plant cells; cellulose
gives plants their structural support and makes plant material fibrous.
Chlorination
In pulping, the treatment of wet pulp, with a compound
containing available chlorine, as a step in removing unwanted
non-cellulosic matter and bleaching the pulp.
Clay
A natural, earthy, fine-grained, substance used as both a
filler and a coating ingredient to improve smoothness, brightness and
opacity.
Close Formation
The formation of a sheet that is uniform and free from a wild or porous appearance when viewed by transmitted light.
Cobb Test
A method for measuring the water absorptiveness of sized
paper and paperboard, by determining the weight of water absorbed
through one surface under a definite pressure.
Color Fastness
The property of a paper, dye or dyed paper to retain its
color in normal storage or use or to resist changes in color when
exposed to light, heat or other deleterious influences.
Color Specification
The quantitative description of color. The color
specification consists of a dominant wavelength, purity and luminous
reflectivity under standardized conditions.
Commercial Match
The duplication of a paper in a mill run which does not
exactly match the sample but which is close enough to be considered
acceptable.
Contaminants
A general papermaking term applicable to extraneous and
usually harmful matter in pulp or non-fibrous raw materials. The term
is more specifically applied to such things as adhesives, wet-strength
resins, inks, dirt, coatings, asphalt, plastics, rubber, etc. found in
recyclable waste papers.
Couch Roll
A paper machine roll primarily involved in dewatering and
picking off, or couching, of the newly formed paper web from the wire
on which it was formed and partially dewatered and in the transfer of
the web to the wet press felt for further dewatering. On a fourdrinier
machine, either a suction couch roll or a pressure couch is used. The
suction couch roll consists of a heavy metal shell drilled with many
small holes through which a suction box inside this shell can apply a
high vacuum for rapid removal of water from the sheet as it is carried
by the wire over this roll immediately prior to its transfer from the
wire to a felt for passage through the wet presses. The pressure couch
consists of a pair of rolls forming a pressure nip through which the
wire and partially dewatered sheet pass for further water removal by
pressure immediately prior to transfer of the sheet from the wire to
the wet press felt. The two rolls involved are termed top couch roll
and bottom couch roll.
Cross Direction
The direction of the paper at right angles to the Machine direction.
Curl
The curvature developed when one side of a paper specimen is wetted. It was formerly used as a measure of the degree of sizing.
Dandy Roll
Used on the wet end of the paper machine to smooth the
formation, reduce bubbles and to impress a pattern if desired; the
raised areas on the wire covered dandy can give a watermark or laid
pattern.
Delignification
The process of removing lignin from wood or other cellulosic
material by means of chemicals, leaving a residue of cellulose,
hemicelluloses and other carbohydrate materials.
Dimensional Stability
The property of a sheet of paper that relates to the
constancy of its dimensions, especially as they are affected by changes
in moisture content, with compressive or tensile stresses, or with time
under stable ambient conditions.
Dirt
Any foreign matter embodied in a sheet of paper, paperboard
or pulp which has a marked contrasting color to the rest of the
material when viewed by reflected or transmitted light. In paper, it is
generally determined by reference to a standard dirt chart.
Driers
A series of steam-heated metal cylinders, 30-60 inches in
diameter, varying in number up to 130 or more, and arranged in two or
more tiers. The cylinders are gear driven, and the wet paper passes
over and under successive cylinders. The temperature of the cylinders,
their number and their speed determine the drying capacity of the
paper machine.
Dry End
The mill term for the drying section of the paper machine, consisting mainly of the driers, calenders, reels and slitters.
Technical Papers
