A thin sheet of cellulose in the form of fibers irregularly interlaced and couched from a suspension of fiber and water.
Even after people in China began to use paper, it took another thousand years before people were using paper all over Eurasia. In India, the history of handmade paper started in the year 1522 A.D when Emperor Babar came to India.
The most common source of paper is wood pulp from pulpwood trees, such as spruce. However, other vegetable fiber materials including cotton, hemp, linen, and rice may be used. Kaolin, starch and other products are used as auxiliary materials in the paper production process.
Paperboard is the stiff type of paper often referred to as "cardboard." Paperboard is used in food packaging (such as cereal boxes), and is used to make many other types of products such as shoe boxes, video game boxes, book covers, etc. Click here for more information about paper manufacturing.
A printing and writing paper which contains little or no mechanical woodpulp. For statistical purposes any paper which contains less than 10% mechanical pulp is categorized as woodfree. If the proportion is greater than 10% it is categorized as mechanical paper. Woodfree paper may be coated (CWF) or uncoated (UWF). Woodfree paper is sometimes known as "fine paper."
The sheet is in Long Grain if the longer dimension is parallel to grain (MD) direction.
The sheet is in short grain if the shorter dimension is parallel to grain direction.
Great confusion exists in the use of the terms Whiteness and Brightness. Brightness is the percentage reflectance of Blue Light only at a wave length of 457 mµ. Whiteness is the percentage reflectance of light at all wavelengths
Their relevance to Paper:
Brightness is the amount of reflectance of blue light at effective wave length of 457 nm.
Brightness test is designed basically to measure the effectiveness of bleaching in removing yellowness.
Spectral reflectance curves of same type of pulps are similar in shape. Hence a reading at a single wave length is sufficient indication of the shape of the curve.
The spectral reflectance curve for an unbleached pulp starts of with a relatively low reflectance in the violet end of the spectrum and raises rapidly to a fairly high value in the extreme red end of the spectrum. Hence unbleached pulp is yellow in color.
Bleaching raises the spectral reflectance curve over the whole range, but the increase is greatest in the blue violet range and less in the red range.
If one were to choose an area of the spectrum in which to take measurements which would best correlate with observable changes in Brightness during the bleaching process, the blue area would be the best. Since the spectral reflectance curves are different for papers of different tints, though they are made with same type of pulps, measurement at a single wave length is not sufficient to indicate the shape of the curve.
Hence Brightness values do not indicate the color /whiteness of the paper.
Whiteness is the amount of reflectance of white light at all wave lengths across the visible spectrum.
Whiteness is a combination of the total reflectance of white light and the uniformity of the reflectance at all the wave lengths.
A perfect white would have 100 % reflectance at all wave lengths of visible light. • Most white papers will have a total reflectance of 50-90% with variation at different wave lengths as high as 20-30%.
All though the whiteness is dependent on both total reflectance and uniformity of reflectance, the uniformity is much more important than the total reflectance.
Whiteness and Yellowness are very subjective quantities which are greatly dependent upon individual preference
All papers have yellow cast, the uniformity of reflectance becomes a measure of yellowness.
If reflectance measurements are made with a green filter and blue filter, the difference between the two readings is a measure of yellowness and the reading with green filter is a measure of total reflectance.
From the studies of whiteness ratings made visually, it is known that yellowness is about four times as importance as the total reflectance.
Hence, when four times yellowness is subtracted from the reflectance measured with green filter the result is a measure of whiteness.
Matt coated paper generally has enough coating thickness to cover the fibre base sheet, but only minimal calendering is applied. Because the surface of matt paper is rough, light is scattered and paper gloss is low. Printed ink gloss on matt papers is better than on uncoated paper, but is still low because the ink pigments do not lie evenly, thus dispersing light in more directions and because some of the resins sink onto the sheet. With silk coated paper, the papermaker uses a combination of coating formula and calendering technique to produce a smooth, low gloss paper. Silk coated paper is smooth, with a uniform printed ink gloss and a distinctive, silky feel. Dull paper is fully coated and calendered. The differences between dull and silk paper is not always clear. In general, dull paper is rougher, glossier and has better printed ink gloss than silk. Dull paper has excellent ink holdout for sharp halftone reproduction. Gloss paper is fully coated and calendered. It is extremely smooth and has excellent ink holdout.
Bulk is the volume per unit weight and is expressed as cc/gm. Bulk = Thickness in microns Basis weight gm/m2
Curl is the waviness of a sheet of paper generally seen along its edges. Curling is generally the result of physical stresses or changes in humidity/moisture content (due to exposure to high temperature) and may occur at the paper mill, in the pressroom, on press/photocopy machine or after binding. Paper tends to curl along, rather than across, the grain of the paper.
Smoothness is concerned with surface contour of paper.
Gloss is the property of a surface which causes it to reflect light specularly, e.g. like a mirror and which is responsible for its shiny or lustrous appearance.
Smoothness is measured by different instruments like Bekk, Bendtsen,Schefield, Gurley, etc. and is important in Printing Papers, Bag paper, etc.
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