There are more than ten varieties of newsprint, relief paper, offset paper, coated paper, etc. used for publishing and printing, some of them are supplied in the form of web, some in the form of flat paper, some in the form of both flat paper and web. It is very important for the people in the publishing and printing industry to master the specifications and measurement methods of various printing papers.
（1） Specifications of printing paper
size
The size and shape of lithographic paper are determined by its length and width. The length and width of the printing plate are determined by the national competent department according to the opening method of the printed matter (the most commonly used geometric series is 32) and the requirements of the printing plate. The web-only specifies its width (or length), and the length (or width) of the printed sheet is cut out on the printing press. Therefore, the size of the web is essentially the same as that of the flat paper, but in different forms.
Although the length and width of the printing paper are stipulated by the competent department of the state, it is not a simple artificial stipulation, but has its scientific basis: first, it is necessary to keep the shape of all kinds of printed matter printed by the conventional opening method beautiful, so as not to make the printed books appear square or narrow strip, giving people the feeling of disharmony. Second, we should keep the similar shape of books with different opening numbers (such as 16 and 32) when using the geometric series-opening method.
From the point of view of striving for the beautiful shape of printed matter, the most appropriate ratio of the length to width ratio of paper and the finished book is the so-called "golden ratio" The ratio of length to width is 1.618:1.
In order to keep the shape of books with different opening numbers similar, it is necessary to study the paper cutting (or folding) method. Paper is generally cut in half. The length after cutting (or folding) is the width before cutting. If you want to keep the shape after cutting similar to that before cutting, you must keep the ratio of length to width before cutting. That is to say, in order to keep the shape of 32 open books similar to that of 16 open and 64 open books, the ratio of length to width of paper size must be close to 1.414:1.
Many foreign countries have adopted this aspect ratio. For example, Japan's flat paper 841 * 1189 (mm), China's international size 880 * 1230 (mm).