First, the commonly used paper printing
Paper can be divided into industrial papers, packaging papers, household papers, and cultural papers according to different uses. Among them, cultural papers include writing papers, art and drawing papers, and printing papers. In printing paper, it is divided into newsprint, letterpress printing paper, offset printing coating paper, dictionary paper, map and sea drawing, gravure printing paper, painting newspaper, weekly newspaper, whiteboard paper, writing paper, etc. according to the performance and characteristics of the paper. . In addition, some high-grade prints are also widely used in art-drawing papers.
Newsprint: Newsprint is mainly used for the printing of newspapers and some letterpress publications. It is soft and elastic, has strong ink-absorption capacity, and has certain mechanical strength. It can be adapted to various high-speed web presses. This kind of paper uses wood paddles as raw materials for manufacturing, contains more lignin and impurities, and is prone to yellowing and brittle papers, and has poor water resistance, so it is not suitable for long-term preservation.
Letterpress Printing Paper: This is a special type of paper used for letterpress printing. The properties of paper are similar to that of newsprint paper. Water resistance, color purity, paper surface smoothness is slightly better than newsprint paper, ink absorption is more uniform, but strong ink capacity is better than newsprint paper. To be bad.
Offset printing paper: Offset printing paper is a kind of paper used for offset (flat) printing, and it is divided into single-sided offset paper and offset-type offset paper. Single-sided offset paper is mainly used to print posters, packaging boxes, etc. Double-sided offset paper is mainly used for printing pictures, pictures, etc. Offset paper is compact in texture, less in stretchability, and more resistant to water, and it can effectively prevent the paper from being deformed, misplaced, napped, and powdered when it is overprinted. Can give the print better color purity.
Offset coated paper: also known as coated paper, is a kind of high-grade paper coated with a layer of inorganic coating on the surface of paper and then super-calendered. The surface of the paper is smooth and flat, with high color purity, and can be obtained when printing. Delicate and smooth network points can better reproduce the layered feeling of the manuscript, and are widely used in art pictures, albums, and commercial leaflets.
Gravure Printing Paper: Rotogravure printing paper is white and firm, with good smoothness and water resistance. It is mainly used for the printing of banknotes, stamps and other high quality and difficult to imitation prints.
Whiteboard paper: Whiteboard paper is a kind of paper with relatively uniform fibrous structure, surface layer with filler and rubber compound and coated with a layer of paint, which is produced by multi-roller calendering. The paper surface has high purity and relatively uniform color quality. The ink-absorption property has a good folding-resistance. It is mainly used for the packaging of goods, the lining of products, and the picture-charts.
Synthetic paper: Synthetic paper is made of chemical materials such as olefins and then added with some additives. It has a soft texture, strong tensile strength, high water resistance, light and heat resistance, and can resist the corrosion of chemical substances without environmental pollution. Breathable, widely used in advanced art, maps, pictures, high-grade books and other printing.
Second, the performance requirements of paper
Whether or not paper can be used for printing with high quality depends on the printability of the paper. The requirements for printing on paper are: the hue of the paper should reach the purity of the same texture as much as possible, the degree of dust of the paper must not exceed the allowable range, have the minimum light transmittance, and ensure the mechanical strength during normal printing, and the thickness of the paper. The tightness, structural characteristics, etc. should be the same in the same print batch. The edge of the paper should be right angle and the slope error cannot exceed ±3mm.
The smoothness of the paper: The smoothness of the paper directly determines the print quality of the print. The paper with high smoothness can make contact with the plate better during embossing, so that the ink layer on the plate can be evenly transferred to the surface of the paper. The paper with low smoothness will be uneven on the surface during printing. The uneven contact between the surface of the plate and the paper during imprinting causes uneven transfer of the ink layer to the surface of the paper. If the paper touches a paper with low smoothness, the pressure during printing may be appropriately increased during printing. Can properly make up for the phenomenon of imprints appearing on the surface because of its uneven surface.
Ink absorption of paper: The absorption of ink by paper depends mainly on the tightness of the fibers of the paper (the size of the gap). When the gap between the paper fibers is small, due to too little deuterated fibers, the effect of the fiber capillary is affected, resulting in the paper's ink absorption; if the gap between the paper fibers is too large, due to too much absorption of the connection material Ink pigments are also absorbed, making prints appear through the phenomenon.
The elasticity and plasticity of the paper: The paper will undergo various changes in the surrounding environment due to various processes such as printing and printing. As the external force, will instantly change their shape and size, and when the external force stops, the paper will return to the original shape and size, this deformation process is called sensitive elastic deformation; when the paper is subjected to external force In a certain period of time, it changes its shape and size. When the external force ceases to function, it slowly returns to its original shape and size. This process of deformation is called hysteretic deformation; when the external force is removed, the paper remains. In the state of deformation and shape caused by external forces, it is called plastic deformation. Sensitive elastic deformation and hysteretic elastic deformation are reversible deformations, while plastic deformation is irreversible deformation.
Paper surface strength: The surface strength of the paper determines the decisive influence of the surface on the surface of the paper during printing, such as wear resistance, resistance to powder fall, and fluff resistance. When printing, in order to get a clearer dot, some inks with higher viscosity will be used. If the surface strength of the paper is not enough, it will be easy to drop powder, hair loss, and adhere to the surface of the plate; if a lower viscosity ink is used In the lithographic printing, the ink and fountain solution emulsify, resulting in dirt in the blank area of ​​the printing plate.
The moisture content of the paper: How much water does the paper directly affect the quality of the printed matter. Excessive water content will reduce the strength of the paper. Under the action of the external force, the paper fibers will be pulled out, so that the plastic deformation will be enhanced and the print will be imprinted. The drying speed is affected; if the water content is too low, the paper will be brittle and easily damaged, resulting in static electricity. Since the moisture content of the paper has a great correlation with the surrounding environment, the humidity and temperature of the printing room should be properly arranged to maintain the balance of water content of the paper.
Third, ink
Ink is a kind of fluid substance that is uniformly dispersed in the binder by pigment particles, fillers, additives, etc., and has a certain viscosity.
1, the composition of the ink
The pigment is a color, black or white highly disperse powder material that is insoluble in water and organic solvents and plays a role of color in the ink. According to the source and chemical composition of pigment components, organic pigments and inorganic pigments can be divided into two categories: inorganic pigments are composed of non-ferrous metal oxides or some metal-insoluble metal salts, and inorganic pigments can be further divided into natural inorganic pigments (minerals). Pigments) and artificial inorganic pigments; organic pigments refer to colored organic compounds, which can also be divided into natural and synthetic categories according to their sources. Nowadays, organic inks for printing are basically synthetic organic pigments with complete colors and superior performance to inorganic pigments.
The requirements for ink pigments during printing are high, especially the color purity, dispersion, lightfastness, transparency and the like. Normally, the hue of the pigment of the color ink is required to be close to the spectral color, the saturation is as large as possible, and the pigment transparency of the three primary color inks (cyan, magenta, yellow) must be high, otherwise the quality of the printed matter will be greatly affected. Regardless of the kind of pigment, it must have good water resistance, can be quickly and uniformly combined with the binder, has good acid and alkali resistance, alcohol resistance, heat resistance and other properties.
The binder is a chemical substance that acts as a dispersing pigment, imparts proper viscosity, flowability and transferability to the ink, and fixes the pigment on the surface of the print by filming after printing, commonly known as a varnish. The binder can be made using various materials such as dried vegetable oils, mineral oils, solvents and water, and various synthetic resins. The fluidity, viscosity, neutral acid value, shade of color, water resistance, and properties of printed materials used during the use of the ink are all determined by the binder. The same pigment can use different binders to make different types of inks; the same kind. Because of the use of different pigments, the connecting material is still made of the same type of ink, because the connecting material does not have the fundamental performance to change the ink, so the quality of the ink is not only related to the pigment itself, but also depends on the connection. material.
The filler is a white transparent, translucent or opaque powdery substance that acts as a filling. Appropriate use of some pigment fillers, can reduce the amount of pigment to reduce costs, but also can adjust the ink dilute, fluidity, but also can improve the flexibility of the ink formulation design.
Additives are materials that are added to improve the ink's own performance during ink manufacturing or printing. When the ink according to the basic formula still cannot meet the requirements for use in certain characteristics, or when the requirements for printing use cannot be met due to changes in conditions, a small amount of additional material must be added to solve the problem.
2, the type of ink According to different methods, the ink can be divided into different types. Commonly used are flexographic printing inks, lithographic printing inks, gravure printing inks, screen stencil printing inks, special functional inks, and the like.
Toppan printing inks can be divided into lead-printing inks, lead-printing inks (copper inks), lead-printing plastic inks, rubber-engraving plastic inks (flexible plastic inks), letterpress inks, letterpress inks, etc. according to different characteristics. . This kind of ink basically belongs to the infiltration drying type ink, in the printing process should pay attention to the bad attachment, the powdery, the dirty and so on the appearance of the malady.
Lithographic printing inks include various offset inks, lithographic iron inks, lithographic photosensitive inks, offset thermosetting inks, and the like. Lithographic printing inks require high color strength and water resistance, and have good fluidity and drying speed.
Intaglio printing inks include various gravure inks, engraved gravure inks, gravure plastic film inks, and the like.
Silk screen printing inks include screen printing inks, screen plastic inks, oil-type inks, water-type inks, and the like.
In addition to the above-mentioned several commonly used inks, there is also an ink that can play a special effect, such as micro-particle ink, gold and silver ink, fluorescent ink, magnetic ink, security ink, conductive ink, carbon ink, monitoring ink, Temperature indication ink, color ink, edible ink, etc.
3, the characteristics of the ink
Ink is a paste adhesive with a certain degree of fluidity. Viscosity, flexion value, thixotropy, fluidity, and drying all determine the performance of the ink.
Viscosity: A property that prevents the flow of fluids. It is a measure of the ability of fluids to interact with each other and create a barrier to their relative mobility between molecules, that is, the resistance to fluid flow. The viscosity of the ink is related to the transfer of the ink in the printing process, the nature and structure of the paper, the viscosity of the ink is too large, the transfer of the ink in the printing process is not easy to uniform, and the phenomenon of pulling the paper occurs, making the printing on the printing surface; the viscosity is too small. Ink is easy to emulsify, dirty, affect the quality of printed matter. The requirements for the viscosity of the ink in the printing process depend on factors such as the printing speed of the printing press, the degree of public software on the paper structure, and changes in temperature and humidity in the surrounding environment.
Yield value: refers to the minimum movement stress required to start fluid flow. If the ink yield value is too large, the fluidity will deteriorate and it will not be easy to open. If the yield value is too small, the dots at the time of printing will easily start to halo and cause the printed matter to be unclear. The size of the yield value is related to the structure of the ink and has a direct influence on the flow of the ink. It is an important indicator for the quality of offset and gravure inks.
Thixotropy: It refers to the phenomenon that the ink is stirred by the action of stirring when the external force is stirred, and the stirring operation stops and the complex recovers to its original consistency. Due to the thixotropy of the ink, after the ink is turned by the printer on the ink roller, the fluidity is increased, the ductility is increased, and the ink is easily transferred; when the ink is transferred to the paper by printing, the external force is lost. The ink thickens from the thin and does not spill around, forming a good print. If the thixotropy of the ink is too large, the ink in the ink fountain is not easily rotated, which affects the ink transfer function of the ink roller.
Fluidity: refers to the ink under its own gravity, will flow like a liquid, by the ink viscosity, yield value and thixotropy decided, but also with the temperature is also closely linked. The fluidity of the ink is related to whether the ink can be poured from the container, transferred from the ink tank to the ink fountain of the printing press, smoothly transferred from the ink fountain, well distributed on the printing press, transferred to the printing plate, and transferred. On the substrate, it also affects the printing effect.
The length of the ink: refers to the extent to which the ink is initially drawn into a filament without breaking. The length of the ink is related to the thixotropy, yield value, and plastic viscosity of the ink. The ink with short silk ink is an ink with good printing performance in offset printing and letterpress printing. It will not cause ink flying phenomenon in the printing process. At the same time, the ink layer on the print is also uniform and thick. The length of ink is a common method when measuring ink performance.
4. Drying of ink: Drying of ink refers to the process of the ink changing from liquid or pasty to solid after the ink is attached to the printed matter on the printed matter. This process is caused by the side seams in the ink from the liquid or paste. It is completed as a solid. Because the binder used in various inks and their formulation ratios are not the same, the drying process of the ink is also not the same. After the ink is transferred from the printing plate to the surface of the printing material, part of the connecting material in the ink penetrates, the solvent in the connecting material begins to volatilize, and some of the connecting materials begin to produce a chemical reaction or a physical reaction, so that the ink on the surface of the substrate is imprinted The layer gradually increases its viscosity and hardness, eventually forming a solid film layer. In general, letterpress printing inks are mainly based on osmotic drying. Lithographic offset inks are mainly dried by oxidized conjunctiva. Gravure printing inks use volatile solutions as binders, so they are mainly based on volatile drying.