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Printing is a process technique that uses printing plates or other means to transfer graphic information on an original onto a substrate.
First, the concept and principle
Offset printing, a representative lithographic printing method, is currently the most widely used type of printing. The substrate is mainly paper, and the graphic part and the blank part of the conventional offset printing plate are on the same plane. Using the principle of ink and water repulsion (ie incompatibility), the ink and water are balanced on the printing plate to achieve the transfer of dots. The printing plate image is first printed on the rubber roller and then transferred to the paper.
Traditional offset printing, a comprehensive overall workflow: manuscripts, customer requirements → design, color separation → output film → printing → proofing → press the sample on the machine printing (during the period may need to re-make imposition, re-export and print version) → after the process (Including film, oil, polishing, hot aluminum, hit bump, cut / cut beer, folding, binding / decoration, etc.).
Note: Blanket: Printing a rubber surface is a key element in obtaining high-quality prints. All types of blankets have the same structure: the bottom layer and the surface layer. The bottom layer is composed of multiple layers of fabric fibers, each layer is independent, and there is a layer of elastic material between the two layers to control the stretchability of the blanket, which makes the blanket porous and also has a certain degree of elasticity.
The surface layer is different according to the manufacturer, may be composed of several layers of elastic materials, each layer has its own physical properties, and then these material layers with different physical properties are combined together. Afterwards, the combined blankets are wrapped on a roller, finely stretched, and finally hardened into the oven.
The difference between blankets is very large, different surface structures, profiles, hardness and compressibility make the processing process vary. The most critical element of the blanket - the surface layer should have the ability to obtain the maximum amount of ink from the plate without damaging the image, while at the same time the ability to transfer these inks as much as possible to the printing material, and at the high speed In the case of operation.
Printability: In a nutshell, printability refers to the adaptation of paper, ink, blankets, printing plates, and other factors to printing. In offset printing, the graphic ink on the plate is first embossed on the blanket cylinder and then imprinted on the paper by the blanket cylinder. In this process of ink transfer, the most prominent change is that the dots embossed on the paper are generally enlarged compared with the dots on the printing plate, and the most extensive expansion is about 50% (50%) of the dots. Why does 50% of outlets expand at most? After research and analysis by relevant experts, it was found that the number of outlets has a direct relationship with the length of outlets. Regardless of whether it is a thick or thin net, under the same printing conditions, the expanded value after printing is basically the same. However, if we use the same black-and-white manuscript to make two layouts of the same area, but the screen lines used are different in thickness (using 150 lines and 175 lines), it seems that the images on the two plates are basically the same, but on the two plates. The total number of outlets is much different. Since the total number of outlets of a thin cable exceeds the total number of outlets of a coarse cable, the total length of the outlets of the thin cable also greatly exceeds the total length of the outlets of the coarse cable. This is why thin-line screen printing is difficult to master and easy to paste.
Second, offset film
(1) Screen angle: In the four-color printing, the amplitude of the AM dots is regularly arranged, and the printed material may have the effect of affecting the beauty of the image under the overprinting of several colors, namely Moire stripes in the printing, commonly known as moire. In order to reduce the effect of moiré on the printed image, the screening angle must follow the following rules:
The angle difference between the cyan, magenta, and black plates is 30° to 60°, and the difference between the yellow plate and other plates is 15°. The main color version has a screening angle of 45°. Two commonly used screening angles are recommended: 1 Yellow Edition 90°, Magenta 75°, Cyan 15°, Black Edition 45°; 2 Yellow Edition 90°, Magenta 45°, Cyan 75° (or 15°) , Black Edition 15 ° (or 75 °). Sometimes the angle can be appropriately arranged according to the level and tone of the print to be expressed, for example, the color plate corresponding to the main hue can be highlighted with 45°.
When using a print as a manuscript, the screen angle selected for each color version should be offset from the corresponding screen angle on the original. For example, the original version is 90° in yellow, magenta is 75°, cyan is 15°, and black is 45°. Yellow 45°, magenta 30°, cyan 60°, and black 90°. When the spot color is screened, according to the actual situation, the appropriate screening angle is determined according to the above-mentioned law.
Here it is necessary to talk about the angle of screen printing commonly used in newspaper printing. Since newspapers use more “grey component substitution†(background color removal), the black version is a long tone. Therefore, the angles of the screens of the four-color newspapers are set to be 45° for black, 90° for yellow, 15° or 75° for magenta and cyan. The screen angle of the image should be 45° when printed in monochrome.
(2) Screen number: The number of common screen lines is 80lpi, 100lpi, 120lpi, 133lpi, 150lpi, 175lpi, 200lpi. In practical applications, the appropriate number of screen lines is generally selected according to the performance of the paper and the performance of the printing equipment. The printing of rough-surfaced paper, such as newsprint used in newspaper printing, is generally 80-133 lpi; offset paper is generally used. With 120-150dpi, copperplate and advanced calendered paper can choose 175lpi or 200lpi or even higher. It should be noted that do not go into the misunderstanding of the high-line cable. The high-line cable has higher technical requirements for printing plates, paper and printing machines, and operation. If they are used improperly, high-profile loss, dark-sounding convergence, and flatness may occur. Network jitter and other phenomena, in addition, if the quality of the original is poor, the use of high network cable will highlight its defects. Under normal circumstances, the resolution of the image should be 1.5 to 2 times the number of screens, and 2 times is recommended.
(3) Characteristics of the film: For the most commonly used positive-working plates, the film is positive and the film surface should be downward. (This film is called "anti-yang"). For the negative plate type, a negative image is produced with the film facing downward. The field density of the image-setter output film should be between 4.0 and 4.2, and the minimum output density should not be less than 3.5, otherwise it will affect the quality of the printing plate. Factors that affect film density are: film type, exposure intensity, development time, development temperature, etc.
Third, offset printing plate
The commonly used offset printing plates include PS plate, gravure plate, protein plate (plano plate), multi-layer metal plates and the like. The surface of each printing plate is composed of a lipophilic and hydrophobic graphic portion and a hydrophilic, oleophobic, blank portion.
PS version of the full name of pre-sensitized photosensitive resin (Pre-sensitized) version, the base plate is aluminum, thickness 0.15mm, 0.3mm, 0.5mm and other specifications. The surface of the PS plate is coated with diazo or azide compounds, with a high publishing base of about 3u. PS version is divided into positive PS version and negative PS version, positive PS version is photolytic type, blank part of the exposure decomposition, remove the coating in the developer to expose the hydrophilic layer; no part of the picture does not see light decomposition, A oleophilic layer forms. The negative PS version is a photopolymerization type. In the graphic part, light photopolymerization occurs to form a lipophilic layer; the blank part is unreacted, and the coating is removed in a developer to form a hydrophilic layer.
PS plate making process is simple, easy to grasp, and the printing quality is good.
The actual use of several other types of printing plates is relatively small and will not be described here.
Fourth, printing color sequence
Four-color printing printing color sequence, can have 24 kinds of permutations and combinations, choose the printing color sequence that accords with the ink characteristics and the law of overprinting, can make the color of the printed matter more faithful to the original, can make the picture level clear, the network spot is clear, realize correctly The gray balance. Therefore, it is necessary to arrange the printing sequence in a reasonable manner, to eliminate the unfavorable factors such as mutual overprinting, the defects of the ink itself, and the quality of the paper, so as to obtain high quality printed matter.
In the four-color printing, the bright part of the screen, the various color dots are mostly in parallel; while the intermediate dots of the middle tone are partially superimposed, and the parts are still combined; the various dots of the dark tone part are almost completely folded. Together. Therefore, the printing color sequence has little effect on the brightness adjustment. In the middle tone and shadow tone portion, it is more affected, because even the ink with good transparency has a different degree of hiding. In addition, during the wet and wet printing process, When printing the next color, the ink that is printed first will be partially removed by the blanket cylinder, so that the ink that is printed first cannot be completely presented, and the ink that is printed later can be fully rendered. Therefore, the colors that can represent the tones of the main body of the original are generally arranged in the rearmost color sequence.
Printing color sequence generally follows the following rules:
(1) The ink with poor transparency and high hiding power is in front of the color sequence;
(2) The black color is in the first color order, which is for overprinting accuracy; the yellow color is in the last color order because the adhesion of other inks on the yellow ink is very poor under the condition of warm and moist, so put the yellow The fourth color.
(3) Prints mainly in the form of characters and black solids, the printing color sequence generally uses cyan, magenta, yellow and black. However, if there is black text or a solid overprint of the yellow field, yellow should be placed on the last color;
(4) Determine the print sequence with warm and cold colors. Prints with warm colors are printed first, black, and later; magenta and yellow are printed first; cold-tone-based prints are printed first, followed by red.
(5) First printing with small ink volume and large printing with large ink volume;
(6) When there are flat nets and solid overprints in printing, the nets are generally printed first and then printed in the ground.
(7) When printing requires two colors with higher printing requirements, these two colors can be arranged to print in two adjacent color groups to improve the accuracy of registration.
(8) When the smoothness of the paper is poor, the ink with coarse pigment particles is placed on the first color; when the tightness of the paper is poor, the light color is printed first.
The printing of spot colors basically follows the above rules. It is necessary to summarize and experiment in practice to find out the color sequence that best represents the expected results.
Fifth, offset printing ink
1. Color subtracting method: The ink is based on the three primary colors of pigments, yellow, magenta, and cyan. They are non-luminous, and their characteristics are that they absorb (or subtract) one-third of the white light and reflect light of the two colors. Later on, like yellow, it absorbs (or subtracts) the violet-blue light in the white light and reflects both red and green light. After the two colors are combined, it is yellow, and the magenta absorbs the green light in the white light. Green absorbs the red light in white light. Therefore, the three primary colors of ink are called Substractive Primaries or Substractive Primary Colours.
2. Offset printing ink can be classified according to its performance:
1. Offset bright fast drying ink; 2. Non-thermosetting offset rotary ink; 3. Thermosetting offset rotary ink; 3. Press rotation ink; 4. Cardboard ink; 5. Matte ink; 6. UV drying Type ink; 7, infrared drying ink; 8, synthetic offset printing ink; 9, iron printing ink; 10, anhydrous version of the ink; 11, other kinds of special offset printing ink.
Six, talk about offset printing (waterless offset printing)
Ordinary offset printing must use dampening solution to wet the prints, and the intervention of water reduces the saturation of the ink and the color becomes not bright, which also complicates the printing process and the printing quality is difficult to control.
Waterless offset printing is also a lithographic offset printing technology. It is a lithographic printing method that uses a special silicone-coated printing plate, special ink, and a strict temperature control system on the printing press to complete the printing. The unwatermarked version is a flat intaglio with the graphic part below the surface of the printing plate. This special silica-coated printing plate has an ink-repellent silicone layer as a blank part of the printing plate, while a slight depression forms an ink-acceptable polymer (photosensitive resin) surface layer which is a graphic part.
Waterless offset printing plates are available in both positive and negative formats. Currently, the positive type waterless offset printing plate is used more often.
The positive-type waterless offset printing plate is composed of an aluminum plate base, a bottom layer, a photosensitive resin layer (3 to 3.5L1), a silicone layer (2L1), and a cover film (6u). After the exposure, the silica gel layer of the light portion (blank portion) on the printing plate undergoes a bridging reaction to undergo photocrosslinking; while the silicone layer without the light portion {image portion) is removed under the action of the developer to expose The photosensitive resin layer below. Since the photosensitive resin layer is ink-receptive, and the non-graphical portion of the silicone layer is repellent to the ink, the need for fountain solution intervention eliminates the need for selective adsorption of the ink.
Waterless offset printing has bright ink, clear dots, and better printing quality than traditional offset printing. However, the cost and technical requirements of the used printing plates and inks are relatively high, so they are limited in practical use.
FM screening technology is suitable for waterless offset printing, which can significantly improve the clarity and level of print performance. High-fidelity printing (Hi-Fi printing) can be achieved.
First, the concept and principle
Offset printing, a representative lithographic printing method, is currently the most widely used type of printing. The substrate is mainly paper, and the graphic part and the blank part of the conventional offset printing plate are on the same plane. Using the principle of ink and water repulsion (ie incompatibility), the ink and water are balanced on the printing plate to achieve the transfer of dots. The printing plate image is first printed on the rubber roller and then transferred to the paper.
Traditional offset printing, a comprehensive overall workflow: manuscripts, customer requirements → design, color separation → output film → printing → proofing → press the sample on the machine printing (during the period may need to re-make imposition, re-export and print version) → after the process (Including film, oil, polishing, hot aluminum, hit bump, cut / cut beer, folding, binding / decoration, etc.).
Note: Blanket: Printing a rubber surface is a key element in obtaining high-quality prints. All types of blankets have the same structure: the bottom layer and the surface layer. The bottom layer is composed of multiple layers of fabric fibers, each layer is independent, and there is a layer of elastic material between the two layers to control the stretchability of the blanket, which makes the blanket porous and also has a certain degree of elasticity.
The surface layer is different according to the manufacturer, may be composed of several layers of elastic materials, each layer has its own physical properties, and then these material layers with different physical properties are combined together. Afterwards, the combined blankets are wrapped on a roller, finely stretched, and finally hardened into the oven.
The difference between blankets is very large, different surface structures, profiles, hardness and compressibility make the processing process vary. The most critical element of the blanket - the surface layer should have the ability to obtain the maximum amount of ink from the plate without damaging the image, while at the same time the ability to transfer these inks as much as possible to the printing material, and at the high speed In the case of operation.
Printability: In a nutshell, printability refers to the adaptation of paper, ink, blankets, printing plates, and other factors to printing. In offset printing, the graphic ink on the plate is first embossed on the blanket cylinder and then imprinted on the paper by the blanket cylinder. In this process of ink transfer, the most prominent change is that the dots embossed on the paper are generally enlarged compared with the dots on the printing plate, and the most extensive expansion is about 50% (50%) of the dots. Why does 50% of outlets expand at most? After research and analysis by relevant experts, it was found that the number of outlets has a direct relationship with the length of outlets. Regardless of whether it is a thick or thin net, under the same printing conditions, the expanded value after printing is basically the same. However, if we use the same black-and-white manuscript to make two layouts of the same area, but the screen lines used are different in thickness (using 150 lines and 175 lines), it seems that the images on the two plates are basically the same, but on the two plates. The total number of outlets is much different. Since the total number of outlets of a thin cable exceeds the total number of outlets of a coarse cable, the total length of the outlets of the thin cable also greatly exceeds the total length of the outlets of the coarse cable. This is why thin-line screen printing is difficult to master and easy to paste.
Second, offset film
(1) Screen angle: In the four-color printing, the amplitude of the AM dots is regularly arranged, and the printed material may have the effect of affecting the beauty of the image under the overprinting of several colors, namely Moire stripes in the printing, commonly known as moire. In order to reduce the effect of moiré on the printed image, the screening angle must follow the following rules:
The angle difference between the cyan, magenta, and black plates is 30° to 60°, and the difference between the yellow plate and other plates is 15°. The main color version has a screening angle of 45°. Two commonly used screening angles are recommended: 1 Yellow Edition 90°, Magenta 75°, Cyan 15°, Black Edition 45°; 2 Yellow Edition 90°, Magenta 45°, Cyan 75° (or 15°) , Black Edition 15 ° (or 75 °). Sometimes the angle can be appropriately arranged according to the level and tone of the print to be expressed, for example, the color plate corresponding to the main hue can be highlighted with 45°.
When using a print as a manuscript, the screen angle selected for each color version should be offset from the corresponding screen angle on the original. For example, the original version is 90° in yellow, magenta is 75°, cyan is 15°, and black is 45°. Yellow 45°, magenta 30°, cyan 60°, and black 90°. When the spot color is screened, according to the actual situation, the appropriate screening angle is determined according to the above-mentioned law.
Here it is necessary to talk about the angle of screen printing commonly used in newspaper printing. Since newspapers use more “grey component substitution†(background color removal), the black version is a long tone. Therefore, the angles of the screens of the four-color newspapers are set to be 45° for black, 90° for yellow, 15° or 75° for magenta and cyan. The screen angle of the image should be 45° when printed in monochrome.
(2) Screen number: The number of common screen lines is 80lpi, 100lpi, 120lpi, 133lpi, 150lpi, 175lpi, 200lpi. In practical applications, the appropriate number of screen lines is generally selected according to the performance of the paper and the performance of the printing equipment. The printing of rough-surfaced paper, such as newsprint used in newspaper printing, is generally 80-133 lpi; offset paper is generally used. With 120-150dpi, copperplate and advanced calendered paper can choose 175lpi or 200lpi or even higher. It should be noted that do not go into the misunderstanding of the high-line cable. The high-line cable has higher technical requirements for printing plates, paper and printing machines, and operation. If they are used improperly, high-profile loss, dark-sounding convergence, and flatness may occur. Network jitter and other phenomena, in addition, if the quality of the original is poor, the use of high network cable will highlight its defects. Under normal circumstances, the resolution of the image should be 1.5 to 2 times the number of screens, and 2 times is recommended.
(3) Characteristics of the film: For the most commonly used positive-working plates, the film is positive and the film surface should be downward. (This film is called "anti-yang"). For the negative plate type, a negative image is produced with the film facing downward. The field density of the image-setter output film should be between 4.0 and 4.2, and the minimum output density should not be less than 3.5, otherwise it will affect the quality of the printing plate. Factors that affect film density are: film type, exposure intensity, development time, development temperature, etc.
Third, offset printing plate
The commonly used offset printing plates include PS plate, gravure plate, protein plate (plano plate), multi-layer metal plates and the like. The surface of each printing plate is composed of a lipophilic and hydrophobic graphic portion and a hydrophilic, oleophobic, blank portion.
PS version of the full name of pre-sensitized photosensitive resin (Pre-sensitized) version, the base plate is aluminum, thickness 0.15mm, 0.3mm, 0.5mm and other specifications. The surface of the PS plate is coated with diazo or azide compounds, with a high publishing base of about 3u. PS version is divided into positive PS version and negative PS version, positive PS version is photolytic type, blank part of the exposure decomposition, remove the coating in the developer to expose the hydrophilic layer; no part of the picture does not see light decomposition, A oleophilic layer forms. The negative PS version is a photopolymerization type. In the graphic part, light photopolymerization occurs to form a lipophilic layer; the blank part is unreacted, and the coating is removed in a developer to form a hydrophilic layer.
PS plate making process is simple, easy to grasp, and the printing quality is good.
The actual use of several other types of printing plates is relatively small and will not be described here.
Fourth, printing color sequence
Four-color printing printing color sequence, can have 24 kinds of permutations and combinations, choose the printing color sequence that accords with the ink characteristics and the law of overprinting, can make the color of the printed matter more faithful to the original, can make the picture level clear, the network spot is clear, realize correctly The gray balance. Therefore, it is necessary to arrange the printing sequence in a reasonable manner, to eliminate the unfavorable factors such as mutual overprinting, the defects of the ink itself, and the quality of the paper, so as to obtain high quality printed matter.
In the four-color printing, the bright part of the screen, the various color dots are mostly in parallel; while the intermediate dots of the middle tone are partially superimposed, and the parts are still combined; the various dots of the dark tone part are almost completely folded. Together. Therefore, the printing color sequence has little effect on the brightness adjustment. In the middle tone and shadow tone portion, it is more affected, because even the ink with good transparency has a different degree of hiding. In addition, during the wet and wet printing process, When printing the next color, the ink that is printed first will be partially removed by the blanket cylinder, so that the ink that is printed first cannot be completely presented, and the ink that is printed later can be fully rendered. Therefore, the colors that can represent the tones of the main body of the original are generally arranged in the rearmost color sequence.
Printing color sequence generally follows the following rules:
(1) The ink with poor transparency and high hiding power is in front of the color sequence;
(2) The black color is in the first color order, which is for overprinting accuracy; the yellow color is in the last color order because the adhesion of other inks on the yellow ink is very poor under the condition of warm and moist, so put the yellow The fourth color.
(3) Prints mainly in the form of characters and black solids, the printing color sequence generally uses cyan, magenta, yellow and black. However, if there is black text or a solid overprint of the yellow field, yellow should be placed on the last color;
(4) Determine the print sequence with warm and cold colors. Prints with warm colors are printed first, black, and later; magenta and yellow are printed first; cold-tone-based prints are printed first, followed by red.
(5) First printing with small ink volume and large printing with large ink volume;
(6) When there are flat nets and solid overprints in printing, the nets are generally printed first and then printed in the ground.
(7) When printing requires two colors with higher printing requirements, these two colors can be arranged to print in two adjacent color groups to improve the accuracy of registration.
(8) When the smoothness of the paper is poor, the ink with coarse pigment particles is placed on the first color; when the tightness of the paper is poor, the light color is printed first.
The printing of spot colors basically follows the above rules. It is necessary to summarize and experiment in practice to find out the color sequence that best represents the expected results.
Fifth, offset printing ink
1. Color subtracting method: The ink is based on the three primary colors of pigments, yellow, magenta, and cyan. They are non-luminous, and their characteristics are that they absorb (or subtract) one-third of the white light and reflect light of the two colors. Later on, like yellow, it absorbs (or subtracts) the violet-blue light in the white light and reflects both red and green light. After the two colors are combined, it is yellow, and the magenta absorbs the green light in the white light. Green absorbs the red light in white light. Therefore, the three primary colors of ink are called Substractive Primaries or Substractive Primary Colours.
2. Offset printing ink can be classified according to its performance:
1. Offset bright fast drying ink; 2. Non-thermosetting offset rotary ink; 3. Thermosetting offset rotary ink; 3. Press rotation ink; 4. Cardboard ink; 5. Matte ink; 6. UV drying Type ink; 7, infrared drying ink; 8, synthetic offset printing ink; 9, iron printing ink; 10, anhydrous version of the ink; 11, other kinds of special offset printing ink.
Six, talk about offset printing (waterless offset printing)
Ordinary offset printing must use dampening solution to wet the prints, and the intervention of water reduces the saturation of the ink and the color becomes not bright, which also complicates the printing process and the printing quality is difficult to control.
Waterless offset printing is also a lithographic offset printing technology. It is a lithographic printing method that uses a special silicone-coated printing plate, special ink, and a strict temperature control system on the printing press to complete the printing. The unwatermarked version is a flat intaglio with the graphic part below the surface of the printing plate. This special silica-coated printing plate has an ink-repellent silicone layer as a blank part of the printing plate, while a slight depression forms an ink-acceptable polymer (photosensitive resin) surface layer which is a graphic part.
Waterless offset printing plates are available in both positive and negative formats. Currently, the positive type waterless offset printing plate is used more often.
The positive-type waterless offset printing plate is composed of an aluminum plate base, a bottom layer, a photosensitive resin layer (3 to 3.5L1), a silicone layer (2L1), and a cover film (6u). After the exposure, the silica gel layer of the light portion (blank portion) on the printing plate undergoes a bridging reaction to undergo photocrosslinking; while the silicone layer without the light portion {image portion) is removed under the action of the developer to expose The photosensitive resin layer below. Since the photosensitive resin layer is ink-receptive, and the non-graphical portion of the silicone layer is repellent to the ink, the need for fountain solution intervention eliminates the need for selective adsorption of the ink.
Waterless offset printing has bright ink, clear dots, and better printing quality than traditional offset printing. However, the cost and technical requirements of the used printing plates and inks are relatively high, so they are limited in practical use.
FM screening technology is suitable for waterless offset printing, which can significantly improve the clarity and level of print performance. High-fidelity printing (Hi-Fi printing) can be achieved.