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However, a sheet of common copy paper that has a basis weight of 20 pounds (9.1 kg) does not have the same mass as the same size sheet of coarse paper (newsprint). In the former case, the standard ream is 500 sheets of 17-by-22-inch (432 by 559 mm) paper, and in the latter, 500 sheets of 24-by-36-inch (610 by 914 mm) paper.
The density can be calculated by dividing the grammage of paper (in grams per square metre or "gsm") by its caliper (usually in micrometres, occasionally in mils). [1] The "ISO 534:2011, Paper and board — Determination of thickness, density and specific volume" indicates that the paper density is expressed in grams per cubic centimeter (g/cm ...
Set-off is measured at two different time intervals, 0.35s and 3s. A freshly printed surface is pressed against a paper after 0.35s and after 3s. Then the set-off density is measured. The idea behind selecting these two timings is to know what will be the set-off when the materials are used in a high-speed press and a low-speed press.
In the US, paper density is usually measured in "pound per reams" (of 500 sheets). Typical Letter paper has a basis weight of paper of 20 or 24 pounds (9.1 or 10.9 kg) – the weight of 500 sheets (a ream) of 17-by-22-inch (431.8 by 558.8 mm) paper at 70 °F (21 °C) and at 50% humidity. [ 3 ]
Bond paper is a high-quality durable writing paper similar to bank paper but having a weight greater than 50 g/m 2. The most common weights are 60 g/m 2 (16 lb), 75 g/m 2 (20 lb) and 90 g/m 2 (24 lb). The name comes from its having originally been made for documents such as government bonds.
Similarly, two sheets of A4 can be scaled down to fit one A4 sheet without excess empty paper. This system also simplifies calculating the weight of paper. Under ISO 536 , paper's grammage is defined as a sheet's mass in grams (g) per area in square metres (unit symbol g/m 2 ; the nonstandard abbreviation "gsm" is also used). [ 5 ]
The telephone cables have a large number of conductors that are individually insulated. The paper needs to be thin (30-40 g/m 2). A normal power cable needs more insulation and therefore paper with higher paper density is used, normally 60-190 g/m 2. The paper needs to be strong, elastic, uniform and free of holes or debris.
This is then passed between hard pressure rollers (supercalendered) to further increase the density, creating a paper called glassine. The glassine is treated with starches, alginates or carboxymethyl cellulose (CMC) in a size press to fill pores or treat the paper chemically to make it fat repellent. Basis weights are usually 30–50 g/m 2. [1]