Offset printing materials (top)

There are many types of substrates, and paper accounts for the largest proportion, so offset press operators should understand the characteristics of the paper and the issues to be noted in printing. In practice, all paper problems should be prevented. malfunction.

Offset printing paper is classified according to its purpose. It mainly includes the following types:

An offset printing newsprint

Offset newsprint is mainly used for lithographic offset newspapers, books and magazines, but also for offset color newspapers, color children's books and so on. Its packaging form is web. In terms of ratio of raw materials, mechanical wood pulp accounts for 70-75%, sulfite chemical wood pulp accounts for 25-30%, no filling, proper amount of added earth, and paper has a certain degree of sizing. In order to adapt to the process characteristics of the contact paper in the offset printing, the offset newsprint paper is applied with a proper amount of sizing, so that the paper has a certain water resistance, also increases the proportion of chemical wood pulp, and greatly improves the strength of the paper. Meet the needs of printing. Its main features: First, there is a higher longitudinal tension, and second, there is a good ink absorption.

When printing offset newsprint, note that:

(1) Because the paper has good ink absorption and strong water absorption, it is important to control the ink balance.
(2) Note that the web break occurs.
(3) When printing color jobs, it is necessary to pay attention to the size of the printing pressure so that the fitting meets the requirements as much as possible.

Two offset printing paper

Offset paper is generally used to print books, dictionaries, pictures, inserts, and documents that require long-term preservation. It is also used to print travel pictures, book covers, and other products. Offset paper has two types of packaging, lithographic paper and web.

Offset paper according to the ratio of raw materials, processing technology and technical indicators are divided into special number, number one, two three grades and super calendering and ordinary calendering points. No. 1 and No. 1 are used for advanced prints, and No. 2 is used for ordinary prints.

Offset paper has two types, one-sided and two-sided, depending on the processing technology and smoothness. The double-sided offset paper has seven types ranging from 70 g/m2 to 180 g/m2 in terms of basis weight, and five types of single-sided offset paper from 40 g/m2 to 80 g/m2.

Raw material ratio of offset paper: The special raw materials of No. 1 and No. 1 offset paper are bleached chemical wood pulp or bamboo pulp and bleached chemical cotton pulp. At the same time, no more than 20% bleached straw pulp and other pulps are used, and surface sizing is performed. . The bleached chemical pulp or bleached chemical bamboo pulp and cotton pulp in the No. 2 offset paper account for about 50%, and the bleached chemical pulp, reed pulp and the like with no less than 50% are used in addition. The use of filler in offset paper is 20-30%.

When printing offset paper:

(1) The offset paper has strong water absorption capacity and large expansion and contraction rate. It is necessary to pay attention to humidity adjustment so that the amount of paper wetting the wetting fluid is kept to a minimum.
(2) After the paper absorbs the acidic wetting liquid, it has an influence on the ink drying speed. Therefore, the acid value of the wetting liquid must meet the standard.
(3) The proportion of the offset paper containing the filler is slightly larger, and when the ink is too viscous, it will cause the phenomenon of de-powdering and pulling of the paper, so the ink viscosity and fluidity are properly adjusted.
(4) In the printing process, suitable desiccants should be selected according to the properties of various offset papers such as ink absorption, pH, moisture content, and different printing forms and printing processes.

Three coated paper

Coated paper is also called coated paper or coated paper. Common offset printing paper is coated with a layer of white paste on some kind of paper and then pressed. The base paper used in the coated paper is called base paper or paper blank, and the coated white paste is called paint.

Coated paper is mainly used to print high-level, fine-grained color prints, such as pictures, pictorials, calendars, samples, and advanced trademarks, and is suitable for printing networked printed matter. Most coated papers are in the form of lithographic paper, with two types of double-sided and single-faced papers. There are relatively few applications for single-sided coated papers. There are seven kinds of double-sided coated papers, from 80 g/m2 to 250 g/m2, based on the quantitative difference. . More than 250g/m2 to 300g/m2 coated paper less use.

The base paper of coated paper is generally made of 30% hardwood chemical pulp or pulp, 70% of softwood chemical pulp, or 50% of two wood pulp components. In order to increase the opacity and thickness of the paper, a certain amount of bleached wood pulp or bleached grass pulp is sometimes added. The base paper generally uses weak sizing or medium sizing, and the amount of filler is 5-15%. Sometimes, the coated paper also directly uses high-quality offset paper as the base paper.

The paint is made up of white pigments, adhesives and other auxiliary agents in a certain proportion. Commonly used white pigments include: kaolin, calcium carbonate, barium sulfate, titanium dioxide, talcum powder, and the like. Commonly used adhesives include casein, casein (soybean protein), starch, PVA, CMC, styrene-butadiene latex, and acrylic latex. Other auxiliary agents used in paints include: dispersants, plasticizers, emulsifiers, water repellents, brighteners, etc. The proportion of pigments in the paint is generally 75-90%, and the adhesive is 10-25%.

Coated paper is one of the best quality papers in offset printing, with high whiteness and smoothness, good gloss, strong water resistance, and low shrinkage. In addition, the coated paper has uniform thickness, high tightness, high opacity, good surface strength and other mechanical properties, suitable PH value, lower color shift and gray scale.

Due to the large amount of paint on the surface of the coated paper, the paper is compact, poor in elasticity and compressibility, poor in ink absorption, and high in ration.

Due to the development of the printing industry, new types of paper are emerging, and light-coated paper is one example. The so-called light-coated paper, which is between the coated paper and offset paper, the use of performance close to coated paper, the manufacturing process is similar to offset paper of the new type of paper. This kind of paper is not coated, but the amount of glue applied when the surface sizing is more. The amount of coating is only 1g/m2, so the fiber can be clearly seen on the surface. The papermaking industry will later specify a coated paper with a specific weight of 50-80g/m2 as a light coated paper with a basis weight of 80-300g/m2. It is a double coated paper with quality and cost advantages. It has been widely used in magazine journals. Printing.

When printing coated paper, note that:

(1) Since the elasticity of the coated paper is not high, the printing pressure should not be too large.
(2) The whiteness of the coated paper is high, and the ink absorption is slightly lower. Therefore, it is necessary to use light or resin type ink and paper in order to ensure the brightness of the printed matter.
(3) Coated paper is poor in ink absorption, so certain measures must be taken during the printing process to prevent the back side of the printed matter from getting dirty and drying slowly.
(4) When printing coated paper, special attention should be paid to the compatibility of the ink. Specifically speaking, the viscosity and viscosity of the ink should be adjusted so as to avoid powder failure, hair loss, and delamination.
(5) For low-quantitative copperplate paper or light-coated paper, pay attention to the adjustment of the paper feeding section because paper is thin.