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.
