Paper is one of the four major inventions in ancient China. It is a sheet-like fiber product used for writing, printing, painting or packaging. It is generally composed of an aqueous suspension of pulp-treated plant fibers, which are staggered on the Internet. Pressed and dried.
1. Composition of paper
Paper is composed of plant fibers, fillers, rubber materials, color materials, etc.
(1) Plant fiber
Plant fiber is the basic component of paper. The plant fiber used as the raw material for papermaking must be easy to dissociate during pulping. The cellulose content in plant fiber is high and the content of lignin is low; the required strength, length and width; sufficient Elasticity and interweaving ability; abundant sources and low cost, suitable for mass production and other conditions.
Fibers commonly used in papermaking in China are: straw, wheat straw, reed, bamboo, wood, hemp, cotton, etc. Waste cotton, waste cloth, waste hemp, waste paper, etc. are also the main raw materials for papermaking.
In the process of making pulp, the plant fiber manager is processed to remove lignin, pectin, resin, fat and other components contained in the plant fiber, and only the active ingredients such as cellulose and hemicellulose are retained.
The nature of the paper depends on the physical and chemical properties of the selected plant fibers and the pulping method under certain conditions.
(2) Filler
The paper composed of interwoven fibers has many voids, which must be filled with fillers to increase flexibility, reduce the transparency and elasticity of the paper, make the surface uniform, and adapt to the requirements of use.
Commonly used fillers include kaolin, talc, gypsum powder, carbonic acid, and barium sulfate. Generally, talc is used for printing paper, and kaolin and barium sulfate are used for advanced printing paper.
The amount of filler is generally about 20%. Too much filler will affect the quality of the paper, reduce the tensile strength and toughness, hinder the absorption of ink, and easily fall off powder during printing.
(3) Rubber compound
The glue is added to fill the gaps on the surface of the paper, reduce the capillary effect in the paper, and improve the water resistance of the paper. After sizing, it can also improve the gloss and strength of the paper and prevent the paper surface from fluffing.
Commonly used rubber compounds include rosin, aluminum sulfate, alum, starch, water glass, caseic acid, etc.
According to the different requirements of various papers, there are various sizing methods, including sizing in paper, surface sizing, heavy sizing and light sizing. The amount of sizing varies greatly, ranging from 0.25 to 9% of the weight of the slurry. Excessive sizing will also affect the ink absorption performance of the paper.
(4) Color
Vegetable fiber has a certain color, but it is still not pure white after bleaching, but it is slightly yellowish or light green, which can not meet the requirements of white paper, so it is necessary to add colorants for color adjustment and whitening treatment.
The commonly used color materials for making white paper are royal blue and ultramarine, etc., and certain fluorescent whitening agents should be added for making high-grade paper.
When manufacturing colored paper, it is also necessary to use colorants, mostly inorganic pigments or organic dyes.
2. Types of paper
There are many types of paper, and the Ministry of Light Industry of China is divided into 17 categories (11 types of paper and 6 types of cardboard) according to the different uses of various papers
Paper 11 types are: printing paper, writing paper, drawing, drawing paper, electrical insulation paper, cigarette paper, suction paper, meter paper, photosensitive paper, transfer paper (base paper), industrial technology paper, packaging paper.
The 6 types of paperboard are: bound paperboard, box paperboard, insulating paperboard, industrial technical paperboard, construction paperboard, shoe paperboard.
3. Paper specifications
Paper specifications are generally calibrated according to type, size, and weight.
(1) Type: The type of paper is divided into flat paper and roll paper in printing paper. Web paper is used in high-speed rotary printing presses, and most flat printing papers are used for printing.
(2) Size: According to the original national standard GB147-59, the size of the base paper for printing, writing and drawing is: the width of the roll base paper is set to 1575 (ie 2 × 787), 1092, 880, 787 mm; flat base paper The size is set to 880 × 1230, 850 × 1168, 880 × 1092, 787 × 1092, 787 × 960 and 690 × 960 mm.
National standard GB786-87 stipulates that the standard of book and magazine format and its format size will be printed in 880 × l230, 900 × 280, 1000 × 1400 mm uncut single paper size to adapt to international cultural exchanges. Adopting international standards, and due to equipment, paper supply, etc., the original 787 × 1092 mm paper format can still be used during the transition period (up to 2000 AD), but it is a non-standard format to be phased out, that is, paper production The size specification will transition to the new national standard.
(3) Weight: The weight of the paper is expressed by the theorem and order weight. Usually expressed in quantitative terms.
Quantitative, also known as gram weight, is the prescribed weight per square meter of paper. The standard specification is expressed in grams, that is, grams per square meter (g / m2), such as: 60 grams per square meter, .... Below 200 g / m2 (including 200 g / m2) is called paper, and above 200 g / m2 is called cardboard.
Let the weight represent the total weight of 500 sheets. For example, 52 grams of paper with a size of 880 × 1230 mm weighs more than 28 kg.
4. Printing paper
Among the printing papers, there are also papers with different properties and characteristics, such as newsprint, letterpress printing paper, offset printing paper, offset printing coated paper, dictionary paper, map paper, sea drawings, gravure printing paper, weekly newspaper, Draw newspapers, whiteboard, written paper, etc.
(1) Newsprint
Mainly used for printing newspapers and letterpress books and periodicals. The paper is soft, has good elasticity and plasticity, and has strong ink absorption performance. The ink can be fastened on the paper surface. The paper surface is pressed by a calender. Fuzzing, the printing on both sides is relatively clear and solid, has a certain mechanical strength, can be suitable for high-speed rotary printing, and has good opacity. Because the raw materials used are mainly mechanical wood pulp, which contains essential elements and impurities, the paper should not be stored for a long time, the paper is easy to yellow and become brittle, the paper has strong absorption, poor water resistance, and the paper is easily damaged.
(2) Letterpress printing paper
It is mainly used for printing collections, classic works, general books, textbooks, magazines, etc. of letterpress printing machines. Its characteristics are similar to newsprint, and its quality is worse than newsprint. The smoothness, water resistance and whiteness of the paper are better than newsprint. The ink absorption capacity is not as good as newsprint, but the ink absorption is even.
(3) Offset printing paper
Mainly for lithographic printing of color pictorials, picture albums, posters, color trademarks and some advanced publications.
Offset paper is divided into single-sided offset paper and double-sided offset paper. Single-sided bite-off paper is often used for color posters, cigarette cases, and trademarks. Double-sided offset paper is used to print pictures, illustrations, maps, etc.
Offset paper should have low elasticity and strong water resistance to prevent paper deformation during multi-color overprinting, inaccurate overprinting, and should not be brushed, powdered, or tight in texture to prevent the adhesion of ink in multiple printing. Under the action, it will cause the phenomenon of hair pulling and de-powdering, making the blots have white spots, which affects the quality of the print; the ink absorption should not be too high, it can hinder the penetration of the connecting material in the ink, make the ink dry on the paper surface to form a film, and ensure the printing The gloss of the product; the surface is smooth to ensure that the imprint is solid, and the paper must be free of sand and other debris to prevent damage to the blanket and printing plate.
(4) Offset printing coated paper
Also known as coated paper. It is made by coating a layer of inorganic paint on the paper surface of the coating base paper and then super-calendering. The paper has a smooth surface and high whiteness. It is designed for offset printing of single-color or multi-color art pictures, illustrations, and pictorials. , Pictures, commodity trademarks, product samples, calendars, etc.
Coated paper has a high degree of smoothness, and can obtain very fine and smooth dots during printing, which can better reproduce the level and confusion of the original. The paper surface should not be de-powdered and layered. The ink absorption of the paper is generally not too fast If the ink absorption is too fast, the blot will be dull, and in serious cases, the blot will be powdered.
(5) Dictionary paper
Mainly for letterpress printing dictionaries, pocket manuals, reference books, scientific and technological materials, high-quality printed materials, etc., light weight, there are four kinds of 25 ~ 40 g / m2.
The dictionary paper is light and book-like, and requires good opacity (to prevent through-printing), uniform fiber structure, smooth paper surface, and consistent thickness. The dictionary paper is relatively soft and the edges of the paper are easily curled.
(6) Map paper and sea drawings
Map paper is suitable for offset printing of multicolor topographic maps, maps and atlases. It is divided into special numbers and number one. Special numbers are used to print topographic maps and number one is used to print maps and atlases. Sea charts are suitable for offset printing on multicolor charts.
The color of map paper and sea drawing paper is white, and the dustiness is small, especially there must be no black dust greater than 1 mm in length (to avoid confusion with map symbols), the two sides are smooth, the organization is tight and tough, the elasticity is small, the elasticity can print the precise Graphics, folding endurance is much higher than that of offset paper, and the length of sea drawings is also very high.
(7) Gravure printing paper
Mainly used in monochrome and color gravure printing pictorials, art pictures, illustrations and other paper.
Gravure paper requires that the paper is white and strong, with good smoothness and water resistance. There should be no obvious dusting during printing, and there is a phenomenon of fluffing.
The original gravure printing paper includes printing paper with high quality and not easy to be counterfeited, such as banknotes and postage stamps. Now, banknote paper and stamp paper are separately separated.
(8) Whiteboard
It is used for printing various product packaging cartons and product decoration backing paper, and can also print various educational pictures.
The fiber structure of whiteboard paper is more uniform, the surface layer has filler and rubber components, the surface is coated with a layer of paint, and it is calendered by multiple rollers, so the texture of the cardboard is compact, and the paper surface is generally whiter and smoother, with more uniform ink absorption , Less surface de-powdering and fluffing phenomenon, paper quality has better folding endurance.
(9) Synthetic paper
It is mainly used for printing advanced art works, maps and dictionaries.
Synthetic paper is made of chemical raw materials. General supplies hydrocarbons are the main raw materials, and some additives are added. It has soft texture, strong tensile strength, good water resistance, light and cold resistance, mildew resistance, and good stability. And other characteristics, and resistant to chemical corrosion. In the temperature range of -60 ~ 60 ℃, can be used as a variety of printing paper.
Synthetic paper is not only suitable for printing, but it is also an ideal packaging material because it is non-toxic, pollution-free, and breathable. It is clean and dust-free, and does not lose paper powder. It is an ideal paper for the information industry. It is now replacing ordinary paper as office paper and electronic computer paper in ultra-clean rooms.
5. Printing performance of paper
The printing performance of the paper determines whether it can be printed smoothly in the printing process, and whether high-quality prints can be obtained. Of course, the printing conditions are also closely related to the printing conditions and ink performance.
The general requirements for the quality of printing paper are as follows: the color of the paper is as white as possible, and each paper in the same batch of paper should have the same texture, the dustiness of the paper should not exceed the allowable range; the minimum light transmittance and the same gloss; it has guaranteed normal printing The mechanical strength, paper thickness, tightness, structure and other properties should be the same in the same batch, if the difference is large. It will increase the difficulty in the printing process and reduce the quality of the printed matter. The water content is between 6 and 8%. The edge of the flat paper should be at a right angle, and the slope error should not exceed ± 3 mm.
The printing performance of paper mainly includes:
(1) Smoothness
Smoothness is the most important printing performance of paper. No matter what kind of printing, the prints printed on paper with a smoother surface, the outline of writing and images are relatively clear, this is because the paper with high smoothness can Good contact with the plate surface, so that the ink layer on the printing plate can be transferred to the paper surface uniformly; the paper with low smoothness, due to the uneven surface during printing, the paper surface and the printing plate contact during imprinting It must be uneven, and the transfer of the ink layer will be affected, so that the transfer of the ink layer to the paper surface will be uneven. In lithography, the elastic blanket is used as an indirect transfer ink layer, so the smoothness requirement is not very high, but when printing advanced products, in order to ensure that the reproduction of the gradation is not lost, the smoothness should also be selected. High paper to print.
For paper with low smoothness, when printing pressure is appropriately increased during printing, it can properly compensate for the phenomenon of imprinting due to unevenness.
The gloss of the paper also depends on the smoothness of the paper surface. Paper with a very smooth surface is shiny, while paper with a rough surface is dull.
(2) Ink absorption of paper
Paper ink absorption is the degree of paper absorption of ink. The more the paper absorbs the ink, the stronger the ink absorption of the paper, and the worse the paper. The strength of the ink absorption is mainly a reflection of the penetration of the binder in the ink.
The absorbability of paper for ink mainly depends on the size of the gap between the paper fibers, that is, the tightness of the paper. When the gap between the paper fibers is small, there are few brooming fibers, which affects the fiber capillary action. The ink absorption is poor. If the gap is too large, it will not only absorb more connecting material, but also will absorb the pigment together, resulting in the phenomenon of through-printing.
The ink absorption of paper is related to the structure of the paper itself. It is also related to the viscosity of the ink, and to the printing pressure and the length of the printing time.
(3) Elasticity and plasticity of paper
During the printing process, various deformations occur in the paper. For example, during letterpress printing, because the printed part of the plate is convex, the printing plate presses the paper tightly, so that the paper is deformed and not flat.
Paper under the action of machinery, due to different pressures, will produce sensitive elastic deformation, hysteretic elastic deformation and plastic deformation. The paper will change its shape and size instantaneously under the action of external force. When the external force stops, the paper will immediately return to its original shape and size, which is called sensitive elastic deformation; the paper is affected by external force and changes within a certain time interval Own shape and size. When the external force stops, the paper gradually returns to its original shape and size, which is called hysteresis. When the external force is canceled, the paper still maintains the deformation caused by the external force, which is called plastic deformation. Sensitive elastic deformation and hysterelastic deformation are reversible deformations, and plastic deformation is irreversible deformation.
The deformation of the paper depends on the humidity, calendering and compaction of the paper itself. The fiber has elasticity, and the sensitive elasticity of the fiber is beneficial to the printing process.
(4) Surface strength of paper
The surface strength of the paper is particularly important for the wear resistance, dusting and hair loss of the surface during printing. To get a clear dot, it is necessary to use inks with higher viscosity. If the paper strength is not enough, it is easy to produce dusting 1. Hair loss and adhesion to the surface of the plate. If the viscosity of the ink is low, the ink and fountain solution are emulsified in lithographic printing, and the blank part of the printing plate will become dirty.
(5) Moisture content of paper
The weight of moisture contained in the paper as a percentage of the weight of the paper is called the moisture content of the paper.
The water content of the paper affects the printing quality. If the water content of the paper is too much, the strength of the paper will be reduced. Under the action of external force, the fiber will be pulled out, the plasticity will be enhanced, and the printing drying speed will be affected; if the paper has too little water content The paper is brittle and easily damaged, and static electricity can also be generated.
The fiber of the paper is hygroscopic. The temperature and humidity of the surrounding environment determine the water content of the paper. The water content of the paper is balanced with the environmental temperature and humidity. The humidity changes with the temperature. The relative humidity in the air changes by 10%. The water content of the paper The change is 1%. Therefore, to control the moisture content in the paper, the temperature and humidity of the workshop must be controlled. Generally, the temperature is controlled at 18 ° -24 ° C, and the relative humidity is controlled at 60-65% to maintain the balance of moisture content.
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