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Shown below are the definitions for: R
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radiation curing Inks have been developed to eliminate solvents (VOCs) when printing by web offset, by having the ability built into the ink to become a hardened image; 100% of the ink composition becomes hardened into the dried ink film. Generally the hardening reaction is triggered by either exposure to Ultra Violet radiation (UV) or to an Electron Beam (EB). The same types of materials and principles have been applied to what is called 100% solids coating.
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rag content paper See "cotton fiber paper".
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ragged Can be "ragged left" or "ragged right"; line and type that has been "justified" to the right or left only, with the opposite side being left uneven or "ragged".
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rattle The crisp, crackling sound produced by shaking or crumpling a sheet of paper to indicate its rigidity or stiffness.
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ream weight The amount that one ream of a particular paper weighs.
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ream Sheet count of paper (500 sheets for most fine papers); see "basis weight".
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recessed printing See "gravure printing" and ..engraving".
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recycle To reuse, or to use over and over; see "de-inking".
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reducers Materials that are added to inks to reduce either ink tack or viscosity.
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reel A roll of paper.
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refiner mechanical pulp (RMP) See "groundwood"; mechanical pulp obtained by first chipping the wood, then separating the cellulose fibers by mechanical rotary refiners.
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refining See cellulose fibers and furnish, the process of preparing cellulose fibers for the making of paper, by mechanical action, whereby the individual fibers are separated from each other, flattened, and roughened (see "fibrillation") to various degrees, to obtain the desired final paper properties. The flattening action was earlier referred to as "beating" the fibers, and was accomplished in equipment called "beaters", in a batch process. Today, most refining is continuous, by means of rotating, close clearance steel bars (plates); disk refiners are the more modern equipment, used today.
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reflectance The percent of incident light reflected from an image area, where zero percent reflectance is black and 100 percent is white; see image density.
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refractive Ability to bend light from a straight course. Materials differ in refractivity, which is measured as "refractive index". The refractive index of materials used in the furnish to make paper, will to a great extent determine the differences in opacity of various types of paper, at equivalent basis weights.
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register marks Fine lines crossing at right angles and placed on original copy before color separation. Used for positioning images, registering colors, accurate cutting, etc.
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register 1) Paper: a type of bond paper for multi-ply form use; i.e. register bond. 2) Printing: when a design or form is printed in parts or steps, as in multiple colors, it is essential that all parts or inks down match exactly. When they do, they are "in register" or in registration; otherwise, they are "out of register"; see "hairline" and "commercial" register.
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relative humidity RH; percent of moisture in the air, relative to the amount of moisture it can hold without precipitation, at any given temperature measured with a psychrometer; humidity or absolute humidity is a measure of the grains of moisture per unit volume of air.
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relief printing See "letterpress" and "flexographic" printing.
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reprography Copying and duplicating.
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retention aids Materials added to the furnish of a paper machine, to help in keeping the fine particles of the furnish, with and in the formed wet mat of paper on the wire; this is to reduce losses and to retain the fines for the properties they can impart to the finished sheet of paper.
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reverse embossing A printing defect in which the stresses created in the separation of the paper from the blanket stretches the paper and actually raises the printed surface in the image areas (and generally creates a depression on the back), sufficient to distort the sheet of paper and even prevent its laying flat.
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reverse sequence In a multi-ply business form that is to be run once through the printing press or offset duplicator, the sequence (order) of the plies will normally be reversed by running once through the press. After printing, the desired sequence is the usable (crash or straight sequence-see "crash sequence"). Before printing the sequence is called "reverse" and is a "mirror" of the final desired sequence.
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rewinder A machine which takes rolls from the reel of the paper machine, the coater, or other winder, and slits and/or rewinds into smaller rolls.
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RH See "relative humidity".
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ridge A ring around the circumference of a roll or an area in a skid of paper in the machine direction that is harder or higher than an adjacent area; also called hard spot.
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RMP See "refiner mechanical pulp".
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roll crown The surface curvature shape or diameter profile of wide width rolls under high pressure (pli) to compensate for deflection and obtain a level nip or pressure across the full width.
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roll curl Also called wrap curl; see simple curl.
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roll stand Frame and mechanism for supporting a roll of paper as it unwinds and feeds into a coater, printing press, or other converting operation.
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rope Also called "corrugation"; bands of relatively uniform width which occur in the machine direction, around the roll of paper, with uniform diagonal marks present in the band. These bands result from wide areas in the cross direction, of caliper differences, resulting in a roll attempting to wind to two different diameters; if tightness of wind is great enough or the caliper differences are accentuated as in large roll diameters, the rope or corrugation can become "set" and be evidenced in the subsequent pile of sheet paper.
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rosette pattern When preparing color separations for printing, the screen angles are rotated for each process color ink. A symmetrical (but non-objectionable) "rosette" dot pattern can result, which the eye can merge into smooth color gradations. However, incorrect screening angles or the shifting of the paper during printing can result in objectionable patterns; see "moiré' patterns".
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rosin A natural resin obtained from pine trees, and when suitably modified, is used as an internal sizing agent to impart waterproofness to paper; used in acid sizing of paper, see "alum".
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rotary press A printing press that carries curved plates on a cylinder (or the plate is the surface of the cylinder), as opposed to an older style flatbed press, using flat plates and type. All elements of the press are cylindrical in shape.
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rotogravure See "gravure printing"; web gravure printing using rotary equipment.
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runnability Paper properties that effect the ability of the paper to run on coating, converting, or printing equipment.
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