Detailed printing paper and printing ink (2)

4. Printing paper

In printing paper, there are papers with different properties and characteristics, such as newsprint, letterpress printing paper, offset printing paper, offset printing coating paper, dictionary paper, map paper, sea drawings, gravure printing paper, weekly newspaper, Drawing newspapers, whiteboards, writing papers, etc.

(1) Newsprint

It is mainly used for printing newspapers and letterpress books. The paper is soft, has good elasticity and plasticity, and has strong ink absorption performance. The ink can be fixed on the paper faster. The paper surface is pressed by the calender and has smooth surfaces on both sides. Fleeting, both sides of the printing are relatively clear, there is a certain degree of mechanical strength, can be suitable for high-speed rotary printing, opacity is very good. Because the raw materials used are mainly mechanical pulp, containing essential elements and impurities, so the paper should not be stored for a long time, the paper tends to yellow and brittle, the paper absorbs strongly, the water resistance is poor, and the paper is easily damaged.

(2) Letterpress paper

It is mainly used for printing presses, classical works, general books, textbooks, magazines, etc. Its characteristics are similar to those of newsprint paper, and its quality is better than that of newsprint paper. The smoothness, water resistance, and whiteness of paper are better than those of newsprint. The ink absorption ability is not as good as that of newsprint, but the ink absorption is even.

(3) offset printing paper

It is mainly used for lithography color pictorials, albums, posters, color logos and some advanced publications.

Offset paper is divided into single-sided offset paper and double-sided offset paper. Single-sided seizures are often used in color posters, cigarette packs, and trademarks. Double-sided offset paper is used to print pictures, illustrations, maps, etc.

Offset paper should have low stretchability and strong water resistance to prevent paper deformation caused by multi-color overprinting. Overprinting is not allowed. It should not be napped or peeled off, and the texture should be tight so as to prevent the adhesion of the ink during multiple printing. Under the action, it will cause pulling and de-powdering phenomenon, which will cause white spots in the imprint and affect the quality of the printed product. The ink-absorption property should not be too high, it can hinder the penetration of the connecting material in the ink, and make the ink dry on the paper to form a film layer. The gloss of the product; the surface is smooth, the imprinting is guaranteed, and the paper cannot contain sand, etc. to prevent damage to the blanket and printing plate.

(4) offset printing coating paper

Also known as coated paper. It is coated with a layer of inorganic paint on the paper surface of the coating base paper, and then made by super calendering. The surface of the paper is smooth, and the whiteness is high. The monochromatic or multi-color art pictures, illustrations, and pictorials are exclusively used for offset printing. , albums, product trademarks, product samples, calendars, etc.

Coated paper has a high degree of smoothness. When printing, it can get very fine smooth and clean dots. It can reproduce the level and quality of originals. The paper should not be de-powdered and layered. The ink absorption of paper should not be too fast. If the ink is too fast, it will cause the print to be dull, and when it is serious, it will also cause imprinting.

(5) Dictionary paper

It is mainly used for the printing of dictionary printing, pocket manuals, reference books, scientific and technical materials, and high-grade prints. It has a light weight of 25-40 g/m2.

Dictionaries are light and must have good opacity (prevent printing), uniform fibrous tissue, flat paper, and uniform thickness. Dictionaries are soft and paper edges tend to curl.

(6) map paper and sea drawings

Map paper is suitable for offset multi-color topographic maps, maps, and atlases. It is divided into two special numbers and one number. Special numbers are used to print topographic maps, and number one is used to print maps and atlases. Sea drawings are suitable for offset printing of multi-color charts.

The map paper and sea drawings are white and have a small degree of dust. In particular, they cannot have black dust of more than 1 mm in length (to avoid confusion with map symbols). The two sides are smooth, the structure is tough, the flexibility is small, and they are flexible. Graphics, the degree of folding resistance is much higher than offset paper, and the length of cracks in sea drawings is also very high.

(7) Gravure printing paper

Mainly used in monochrome and color gravure printing pictorial, art pictures, illustrations and other paper.

Gravure paper requires a firm white paper with good smoothness and water resistance. It cannot have significant powder dropping during printing, and there is a phenomenon of overprinting during fluffing.

The original gravure printing paper includes printing paper money, stamps and other high-quality papers that are not easily imitated, and has now been individually separated from banknote paper and stamp paper.

(8) Whiteboard paper

It can be used for printing various kinds of goods packaging cartons and commodity mounting sheets, and it can also print various educational pictures.

The fibrous tissue of whiteboard paper is relatively uniform, the surface layer has filler and rubber composition, the surface is coated with a layer of coating material, and the surface of the paperboard is compacted by multi-roller calendering. The paper surface is generally whiter and smoother, and has more uniform ink absorption. , Surface de-powdering and lint-free phenomenon, the paper has a better degree of folding.

(9) Synthetic paper

It is mainly used for printing high-quality artwork, maps, and dictionaries.

Synthetic paper is a paper synthesized from chemical raw materials. It is generally made of hydrocarbons as the main raw material, and then added with some additives. It has a soft texture, strong tensile strength, good water resistance, light resistance, heat resistance, no mildew, and good stability. Etc. Features and resistance to chemical corrosion. In the temperature range of -60 ~ 60 °C, can be used as a variety of printing paper.

Synthetic paper is not only suitable for printing, but also because it is non-toxic, non-polluting, good ventilation, so it is also an ideal packaging material. It is clean, dust-free and does not fall off paper powder. It is an ideal paper for the information industry. It is now replacing ordinary paper to become 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 during the printing process, and whether it can obtain high-quality prints. Of course, there is a close relationship between printing conditions and printing ink properties.

The general requirements for the quality of printing papers are: the paper should be as white as possible, and each paper in the same batch of paper should have the same texture, the degree of dust of the paper must not exceed the allowable range, the minimum light transmittance and the same gloss, and the guarantee of normal printing. The mechanical strength, paper thickness, tightness, structure and other properties should be the same in the same batch, if there is a big difference. Will increase the difficulties in the printing process, reduce the quality of printed matter, water content between 6 to 8%, flat paper edge should be right angle, the slope error does not exceed ± 3 mm.

The printing properties of paper are:

(1) Smoothness

Smoothness is the most important printing performance of paper. No matter which type of printing is used, the prints printed on paper with smoother surface are more clearly printed and the contours of the handwriting and the image are relatively clear. This is because the paper with high smoothness can be imprinted. Better contact with the plate, so that the ink layer on the plate can be evenly transferred to the surface of the paper; the paper with low smoothness, due to the uneven surface during printing, the contact of the surface of the paper with the printing plate during the printing Must be uneven, the transfer of the ink layer will be affected, so that the ink layer is transferred to the paper surface is uneven. In lithography, the use of elastic blankets as indirect transfer of ink layer, so the requirement for smoothness is not very high, but in the printing of advanced products, in order to ensure the level of reproduction without loss, but also to choose the smoothness High paper to print.

Paper with a low degree of smoothness can be made to appropriately compensate for the phenomenon that the prints appear to be imaginary due to their unevenness.

The gloss of the paper also depends on the smoothness of the surface of the paper. The glossy paper on the surface is glossy, while the paper on the rough surface is dark.

(2) Ink absorption of paper

The absorbency of paper is the degree of absorption of the ink by the paper. The greater the amount of ink absorbed by the paper, the greater the ink absorption of the paper, and vice versa. The strength of ink absorption is mainly a reflection of the penetration of the binder in the ink.

Absorption of ink by paper depends mainly on the size of the gap between the fibers of the paper, that is, the degree of tightness of the paper. When the gap between the fibers of the paper is small, the deuterated fibers are also small, which affects the capillary action of the fiber. The ink absorption is poor. If the gap is too large, not only will it absorb more of the binder, but it will also absorb the pigment and create a print-through phenomenon.

The ink absorption of paper is related to the structure of the paper itself. It is also related to the viscosity of the ink, which is related to the printing pressure and the length of the stamping time.

(3) The elasticity and plasticity of paper

In the printing process, paper will be deformed. For example, when the letterpress is printed, the printing portion of the printing plate is convex and the printing plate is pressed against the paper so that the paper is deformed and not flattened.

Paper under the action of the machine, due to different pressure, will produce sensitive elastic deformation, elastic deformation and plastic deformation. Under the action of external force, paper will instantly change its shape and size. When the external force stops, the paper will immediately return to its original shape and size, which is called elastic deformation; the paper is affected by external forces and changes within a certain time interval. Your own shape and size. When the external force ceases to function, the paper gradually returns to its original shape and size, which is called the elastic deformation; when the external force is removed, the paper still retains the deformation caused by the external force, which is called plastic deformation. Sensitive elastic deformation and hysteretic elastic 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 fibers are flexible and the sensitivity of the fibers is beneficial to the printing process.

(4) Surface strength of paper

The surface strength of paper is particularly important for the abrasion resistance of the surface during printing, powder dropping, and lint removal. To obtain a clear dot, you must use a higher viscosity ink. If the paper strength is not enough, it is easy to produce powder. , hair loss phenomenon, and adhere to the surface of the plate, if the viscosity of the ink is low, in the lithography, the ink and the fountain solution emulsification, the blank part of the plate will be dirty.

(5) Water content of paper

The weight of water contained in paper accounts for the percentage of the weight of the paper, and the moisture content of the paper.

The moisture content of the paper affects the printing quality. If the paper contains too much moisture, the strength of the paper will decrease. Under the action of external force, the fibers will be pulled out, the plasticity will increase, and the drying rate of the print will be affected; if the paper has too little water content The paper is brittle and easily damaged, and it may also cause static electricity.

The fiber of the paper has hygroscopicity, the temperature and humidity of the surrounding environment determine the moisture content of the paper, the amount of water in the paper is in balance with the ambient temperature and humidity, the humidity changes with the temperature, the relative humidity in the air changes by 10%, the moisture content in the paper Change 1%, therefore, to control the moisture content in the paper, we must control the temperature and humidity of the workshop, the general temperature is controlled at 18 ° ~ 24 °C, relative humidity is controlled at 60 ~ 65%, in order to maintain the balance of water content.