Chapter 4 Plate Making Section 4 Gravure Plate Making
The gravure printing plate is distinguished from the production method, and can be divided into two categories, one is engraved intaglio, and the other is photogravure, engraved intaglio has manual or mechanical engraved intaglio, electronic engraved intaglio.
The hand-carved gravure is carved on the copper plate with various carving knives, you can directly engrave the concave lines, or you can first apply a layer of resist film on the copper plate and scratch the resist film to expose the surface of the copper plate. Perform chemical corrosion. Mechanical engraving gravure is to engrave directly with mechanical engraving machine such as color pattern engraving machine, floating engraving machine, parallel line engraving machine and zoom engraving machine, or to etch the resist layer on the copper surface and then etch it to make intaglio.
Hand-made or mechanically engraved intaglio lines are delicate and delicate, and are mainly used for printing banknotes and bonds with anti-counterfeiting value.
Electronic engraving gravure, using an electronic engraving machine, according to the photoelectric principle, controls the engraving knife to engrave a net hole on the surface of the drum, and its area and depth change simultaneously. (See Figure 4-50b)
Photogravure, also known as photocopying, is made by continuous negative adjustment film and gravure screen, after printing, carbon paper transfer, corrosion and other processes. The plate area from bright to dark has the same cell area but different shades. The thickness of the ink layer is used to reproduce the light and dark levels of the original. (See Figure 4-20a).
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Figure 4-20 Gravure
1. Production of plate cylinder
The intaglio printing plate is not pre-made and installed on the plate table or plate cylinder, but directly on the plate cylinder, and then the plate cylinder is installed on the printing machine for printing.
The printing plate cylinder has an open hollow cylinder and a closed solid cylinder. The length and circumference of the cylinder are designed and processed according to the size of the gravure printing machine.
(1) Processing of the drum
According to the diameter of the cylinder, the intaglio cylinder can be directly processed with seamless steel pipe, or can be rolled with a steel plate for welding, and then processed.
The processing of the drum is divided into rough processing, semi-finishing and finishing. Rough machining makes the wall thickness of the drum meet the specified requirements, ensuring that when the drum rotates, the weight of each part is equal and the centrifugal force generated is also the same. Semi-finishing is to keep the shaft and the drum concentric. Finishing is the outer circle of the finishing roller, reaching the specified size.
The processing accuracy of the cylinder is directly related to the service life of the cylinder, the electroplating of the cylinder, and the quality of electro-engraving and printing. The processed drum requires uniform wall thickness, the difference between the center of the axis and the outer circle center of the drum can not exceed 2μm, the surface finish of the drum should reach Δ5, and the outside grinder should reach Δ7 or more after processing, and the diameter accuracy error is ± 0.01μm.
(2) Plating of the drum
The drum must be pre-plated before copper plating. First remove the oil stain on the surface of the drum by manual or electrolytic method, then pickle the drum, and use chemical agents to corrode the rust product oxide film on the surface of the drum. Finally, a layer of bottom nickel is plated on the surface of the iron drum, and then copper plating is performed. The copper plating layer is the plate-making layer of the gravure cylinder, and etching or plate making is performed on this layer.
The gravure cylinder adopts acid copper plating, the copper plating solution is composed of copper sulfate, sulfuric acid, additives, etc. The temperature of the plating solution is 20 ~ 35 ℃.
The quality standard of the copper layer is: the thickness of the electroplated copper layer is 100-120 μm. The surface is bright and detailed, with burrs, road marks, and pits.
(3) Turning and grinding of rollers
The copper-plated roller needs to be ground on the copper layer, so that the surface finish of the roller reaches 8-10.
Second, the gravure plate making process
The production of gravure is to expose the image of the continuous negative film to the sensitized and gridded carbon paper, and then pass the plate to the surface of the drum, develop and etch it to make the gravure plate, the plate making process is:
Carbon paper sensitization → printing → overprinting → development → filling → corrosion → chrome plating
(1) Carbon paper sensitization
Carbon paper is a photosensitive material for printing. It consists of a gelatin emulsion coated with mixed pigments on the paper base and surface. Generally, the carbon paper that is shipped from the factory has no sensitivity to the gelatin emulsion layer. Before printing, the carbon paper needs to be immersed in a 4% potassium dichromate solution for 3 minutes, taken out to dry, and the adhesive layer has photosensitivity.
(2) Printing
Exposure is carried out in two steps, first exposure of the network cable and then exposure of the negative film.
For gravure printing, use a doctor blade to remove the ink in the blank part. If the area of ​​the inked part is large, the blade will not only scrape off the ink in the blank part, but also scrape off part of the graphic part of the ink, as shown in Figure 4-21 · A As shown. Therefore, it is necessary to use a screen to expose the network line on the carbon paper to divide the graphics into grids, as shown in Figure 4-21 · B. Support the squeegee with a grid on the surface of the printing plate and text to prevent the squeegee from invading the printed part of the ink.
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Figure 4-21 The role of network cable in gravure printing
The screen used for gravure printing is shown in Figure 4-22. The ratio of the width of the transparent line and the opaque line is 1: 3 to 1: 3.5. The mesh shapes are square, brick, diamond and irregular. A square screen is usually used.
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Figure 4-22 Screen for intaglio
After the carbon paper is exposed to the network line through the screen, the negative film can be exposed to form an image latent image on the surface of the carbon paper adhesive layer.
(3) Version
The carbon paper that has been exposed to the wire and the image is attached to the surface of the polished copper plate cylinder.
At present, most of the used edition machine adopts the dry method for edition. The method of printing is shown in Figure 4-23. While adding a small amount of water between the surface of the plate cylinder and the carbon paper gelatin layer, the carbon paper is adhered to the surface of the copper roller by the pressure of the pressure roller.
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Figure 4-23 Sketch map
(4) Development
The development is divided into pre-development and formal development.
The pre-development is to immerse a part of the plate cylinder in warm water, and to separate the glue layer of the carbon paper from the paper base while rotating.
Formal development means that when the paper base is removed from the glue layer, the developer is heated to 40 ° C and maintained at a constant temperature to dissolve all the unhardened glue layer. After developing, use a fan to dry the film.
(5) Fill in the version
On the surface of the printing plate cylinder, the parts without pictures and text and the two sides of the cylinder are coated with asphalt paint to prevent corrosion of parts that should not be corroded.
(6) Corrosion
The ferric chloride etching solution is used to penetrate the hardened glue film to dissolve the copper layer on the copper surface to form a net hole. This process is called corrosion and is commonly known as rotten version.
The corrosion process is carried out in three steps. First, the gelatin layer expands and absorbs ferric chloride, and then the etching solution penetrates through the film layer to reach the copper surface. The third step is to corrode the copper surface. The etching solution reacts with lead.
Cu + 2FeCl3 = CuCl2 + 2FeCl2
In production, the plate cylinder is corroded successively with different concentrations of ferric chloride solution. Figure 4-24 shows the process of corroding the printing plate with high concentration and then low concentration etching solution. Corrosion liquids of different concentrations will be permeated and etched on the plates with different thicknesses of adhesive layers to form different depths of holes, and the printed products will reproduce a rich layer.
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Figure 4-24 The role of various concentrations of corrosive liquid
(7) Chrome plating
The gravure is made by etching on the copper layer, the hardness of copper is generally about 90 ~ 180HV. When printing, the doctor blade can easily scratch the printing plate. Due to the high hardness of metal chromium, about 800-1000HV, the wear resistance is very good, so when the gravure roll graphics are completed, then a layer of chromium is plated on the copper surface to improve the durability of the gravure.
For gravure, the process of making plates is complicated, and the quality is not easy to control. The range of use is gradually narrowing due to the application of electronic engraving gravure.
3. The plate-making process of electronic engraving gravure
Electronic engraving gravure is a plate-making method that appeared in the 1960s. It features no carbon paper for printing and no chemical corrosion. Taking the image-processed free film as the original, the engraving machine of the electronic circuit is used to directly engrave the mesh holes on the surface of the copper plate cylinder to make a printing plate.
Electronic engraved gravure has a delicate picture, rich layers and easy quality control. It is widely used in gravure printing.
(1) The basic principle of the work of electronic engraving machine
The electronic engraving machine is composed of the original drum (or scanning drum), plate cylinder, scanning head, engraving head, transmission system, electronic control system, etc.
The working principle of the electronic engraving machine is: the scanning head scans the original, and the light signals of different strengths reflected from the original are converted into electrical signals by the photoelectric converter, and then through the amplifier and data processing, the optical The strength is converted into the size of the current, and the engraving head is controlled to engrave on the copper drum.
When the electronic engraving machine works, the original cylinder and the engraving cylinder run synchronously. At the same time, the engraving system moves along the axial direction of the cylinder, and a sharp diamond knife is used to engrave the holes on the engraving cylinder according to the signal, as shown in Figure 4-25. The engraving system is controlled by the scanning system through a computer. The hole network formed on the copper drum is generated by an additional signal in the computer. This signal can make the cutter continuously vibrate regularly. The size and depth of the network hole are derived from the density of the original It was decided that the quantitative relationship between the density of the scanned original and the depth of the carved holes can be adjusted on the computer.
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Figure 4-25 Working principle of electronic engraving machine
The functions of the electronic engraving machine are more and more, such as: can change the magnification of the square person in the circle, seamlessly engrave in the circumferential direction, automatically select the level, adjust the angle of the net hole, etc.
(2) Production of electronically engraved intaglio
The production process of electronic engraving gravure is:
Scanning negatives → installing plate cylinder → testing → engraving → chrome plating
1. Scan film
In the past, scanning negative films used continuous-adjusted opalescent films, which were expensive to manufacture and the quality of the negative films was difficult to control. In the 1980s, the electronic engraving machine added an electronic conversion component to perform offset gravure conversion according to the designed procedure, that is, to engrave the gravure with a screen negative for offset printing. Therefore, most of the color separation and screen negative plates are now used.
2. Install plate cylinder
Install the printing plate on the electronic engraving machine with a crane, and remove the oil, dust and oxide on the plate before engraving. Paste the scanned film in plain clothes on the original roller.
3. test
According to the requirements of the original (scanning film) and the hue of the ink, the trial engraving value is set in combination with the printed product. For example, the paper for decorative printing is relatively rough and has strong ink absorption. The engraving depth must be 45μm-50μm to meet the printing requirements. Current and voltage on the amplifier.
4. Sculpture
The scanning head scans the original, the engraving head and the scanning head operate synchronously, and the surface of the printing plate cylinder is engraved into net holes with different depths.
The new electronic engraving machine has three shapes of dot angles, which can be arbitrarily selected during operation to avoid the occurrence of turtle text due to inaccurate overprinting. The three kinds of outlet angles are shown in Figure 4-26.
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Figure 4ï¼26 Schematic diagram of gravure angle
When engraving text, the fine strokes cannot be lost, you must use fine net line engraving. If you use 100 lines / cm, the engraving of the text can achieve a very ideal effect.
At present, the electronic engraving gravure mostly adopts a separate electronic engraving system to make plates, that is, the scanner and the electronic engraving machine are separated, and are respectively connected to the input and output interfaces of the image workstation. The scanner can scan the positive and negative images, and Yin can scan the opal film and also convert the glue to the concave. The workstation has a variety of image processing functions, which can perform overall and partial color correction, cut, combine and zoom, and color gradient on the image. Combine yellow, magenta, and cyan images with line images into one. The network line of the electronic engraving machine ranges from 31.5 to 200 lines / cm.
The gravure printing plate is distinguished from the production method, and can be divided into two categories, one is engraved intaglio, and the other is photogravure, engraved intaglio has manual or mechanical engraved intaglio, electronic engraved intaglio.
The hand-carved gravure is carved on the copper plate with various carving knives, you can directly engrave the concave lines, or you can first apply a layer of resist film on the copper plate and scratch the resist film to expose the surface of the copper plate. Perform chemical corrosion. Mechanical engraving gravure is to engrave directly with mechanical engraving machine such as color pattern engraving machine, floating engraving machine, parallel line engraving machine and zoom engraving machine, or to etch the resist layer on the copper surface and then etch it to make intaglio.
Hand-made or mechanically engraved intaglio lines are delicate and delicate, and are mainly used for printing banknotes and bonds with anti-counterfeiting value.
Electronic engraving gravure, using an electronic engraving machine, according to the photoelectric principle, controls the engraving knife to engrave a net hole on the surface of the drum, and its area and depth change simultaneously. (See Figure 4-50b)
Photogravure, also known as photocopying, is made by continuous negative adjustment film and gravure screen, after printing, carbon paper transfer, corrosion and other processes. The plate area from bright to dark has the same cell area but different shades. The thickness of the ink layer is used to reproduce the light and dark levels of the original. (See Figure 4-20a).
Figure 4-20 Gravure
1. Production of plate cylinder
The intaglio printing plate is not pre-made and installed on the plate table or plate cylinder, but directly on the plate cylinder, and then the plate cylinder is installed on the printing machine for printing.
The printing plate cylinder has an open hollow cylinder and a closed solid cylinder. The length and circumference of the cylinder are designed and processed according to the size of the gravure printing machine.
(1) Processing of the drum
According to the diameter of the cylinder, the intaglio cylinder can be directly processed with seamless steel pipe, or can be rolled with a steel plate for welding, and then processed.
The processing of the drum is divided into rough processing, semi-finishing and finishing. Rough machining makes the wall thickness of the drum meet the specified requirements, ensuring that when the drum rotates, the weight of each part is equal and the centrifugal force generated is also the same. Semi-finishing is to keep the shaft and the drum concentric. Finishing is the outer circle of the finishing roller, reaching the specified size.
The processing accuracy of the cylinder is directly related to the service life of the cylinder, the electroplating of the cylinder, and the quality of electro-engraving and printing. The processed drum requires uniform wall thickness, the difference between the center of the axis and the outer circle center of the drum can not exceed 2μm, the surface finish of the drum should reach Δ5, and the outside grinder should reach Δ7 or more after processing, and the diameter accuracy error is ± 0.01μm.
(2) Plating of the drum
The drum must be pre-plated before copper plating. First remove the oil stain on the surface of the drum by manual or electrolytic method, then pickle the drum, and use chemical agents to corrode the rust product oxide film on the surface of the drum. Finally, a layer of bottom nickel is plated on the surface of the iron drum, and then copper plating is performed. The copper plating layer is the plate-making layer of the gravure cylinder, and etching or plate making is performed on this layer.
The gravure cylinder adopts acid copper plating, the copper plating solution is composed of copper sulfate, sulfuric acid, additives, etc. The temperature of the plating solution is 20 ~ 35 ℃.
The quality standard of the copper layer is: the thickness of the electroplated copper layer is 100-120 μm. The surface is bright and detailed, with burrs, road marks, and pits.
(3) Turning and grinding of rollers
The copper-plated roller needs to be ground on the copper layer, so that the surface finish of the roller reaches 8-10.
Second, the gravure plate making process
The production of gravure is to expose the image of the continuous negative film to the sensitized and gridded carbon paper, and then pass the plate to the surface of the drum, develop and etch it to make the gravure plate, the plate making process is:
Carbon paper sensitization → printing → overprinting → development → filling → corrosion → chrome plating
(1) Carbon paper sensitization
Carbon paper is a photosensitive material for printing. It consists of a gelatin emulsion coated with mixed pigments on the paper base and surface. Generally, the carbon paper that is shipped from the factory has no sensitivity to the gelatin emulsion layer. Before printing, the carbon paper needs to be immersed in a 4% potassium dichromate solution for 3 minutes, taken out to dry, and the adhesive layer has photosensitivity.
(2) Printing
Exposure is carried out in two steps, first exposure of the network cable and then exposure of the negative film.
For gravure printing, use a doctor blade to remove the ink in the blank part. If the area of ​​the inked part is large, the blade will not only scrape off the ink in the blank part, but also scrape off part of the graphic part of the ink, as shown in Figure 4-21 · A As shown. Therefore, it is necessary to use a screen to expose the network line on the carbon paper to divide the graphics into grids, as shown in Figure 4-21 · B. Support the squeegee with a grid on the surface of the printing plate and text to prevent the squeegee from invading the printed part of the ink.
Figure 4-21 The role of network cable in gravure printing
The screen used for gravure printing is shown in Figure 4-22. The ratio of the width of the transparent line and the opaque line is 1: 3 to 1: 3.5. The mesh shapes are square, brick, diamond and irregular. A square screen is usually used.
Figure 4-22 Screen for intaglio
After the carbon paper is exposed to the network line through the screen, the negative film can be exposed to form an image latent image on the surface of the carbon paper adhesive layer.
(3) Version
The carbon paper that has been exposed to the wire and the image is attached to the surface of the polished copper plate cylinder.
At present, most of the used edition machine adopts the dry method for edition. The method of printing is shown in Figure 4-23. While adding a small amount of water between the surface of the plate cylinder and the carbon paper gelatin layer, the carbon paper is adhered to the surface of the copper roller by the pressure of the pressure roller.
Figure 4-23 Sketch map
(4) Development
The development is divided into pre-development and formal development.
The pre-development is to immerse a part of the plate cylinder in warm water, and to separate the glue layer of the carbon paper from the paper base while rotating.
Formal development means that when the paper base is removed from the glue layer, the developer is heated to 40 ° C and maintained at a constant temperature to dissolve all the unhardened glue layer. After developing, use a fan to dry the film.
(5) Fill in the version
On the surface of the printing plate cylinder, the parts without pictures and text and the two sides of the cylinder are coated with asphalt paint to prevent corrosion of parts that should not be corroded.
(6) Corrosion
The ferric chloride etching solution is used to penetrate the hardened glue film to dissolve the copper layer on the copper surface to form a net hole. This process is called corrosion and is commonly known as rotten version.
The corrosion process is carried out in three steps. First, the gelatin layer expands and absorbs ferric chloride, and then the etching solution penetrates through the film layer to reach the copper surface. The third step is to corrode the copper surface. The etching solution reacts with lead.
Cu + 2FeCl3 = CuCl2 + 2FeCl2
In production, the plate cylinder is corroded successively with different concentrations of ferric chloride solution. Figure 4-24 shows the process of corroding the printing plate with high concentration and then low concentration etching solution. Corrosion liquids of different concentrations will be permeated and etched on the plates with different thicknesses of adhesive layers to form different depths of holes, and the printed products will reproduce a rich layer.
Figure 4-24 The role of various concentrations of corrosive liquid
(7) Chrome plating
The gravure is made by etching on the copper layer, the hardness of copper is generally about 90 ~ 180HV. When printing, the doctor blade can easily scratch the printing plate. Due to the high hardness of metal chromium, about 800-1000HV, the wear resistance is very good, so when the gravure roll graphics are completed, then a layer of chromium is plated on the copper surface to improve the durability of the gravure.
For gravure, the process of making plates is complicated, and the quality is not easy to control. The range of use is gradually narrowing due to the application of electronic engraving gravure.
3. The plate-making process of electronic engraving gravure
Electronic engraving gravure is a plate-making method that appeared in the 1960s. It features no carbon paper for printing and no chemical corrosion. Taking the image-processed free film as the original, the engraving machine of the electronic circuit is used to directly engrave the mesh holes on the surface of the copper plate cylinder to make a printing plate.
Electronic engraved gravure has a delicate picture, rich layers and easy quality control. It is widely used in gravure printing.
(1) The basic principle of the work of electronic engraving machine
The electronic engraving machine is composed of the original drum (or scanning drum), plate cylinder, scanning head, engraving head, transmission system, electronic control system, etc.
The working principle of the electronic engraving machine is: the scanning head scans the original, and the light signals of different strengths reflected from the original are converted into electrical signals by the photoelectric converter, and then through the amplifier and data processing, the optical The strength is converted into the size of the current, and the engraving head is controlled to engrave on the copper drum.
When the electronic engraving machine works, the original cylinder and the engraving cylinder run synchronously. At the same time, the engraving system moves along the axial direction of the cylinder, and a sharp diamond knife is used to engrave the holes on the engraving cylinder according to the signal, as shown in Figure 4-25. The engraving system is controlled by the scanning system through a computer. The hole network formed on the copper drum is generated by an additional signal in the computer. This signal can make the cutter continuously vibrate regularly. The size and depth of the network hole are derived from the density of the original It was decided that the quantitative relationship between the density of the scanned original and the depth of the carved holes can be adjusted on the computer.
Figure 4-25 Working principle of electronic engraving machine
The functions of the electronic engraving machine are more and more, such as: can change the magnification of the square person in the circle, seamlessly engrave in the circumferential direction, automatically select the level, adjust the angle of the net hole, etc.
(2) Production of electronically engraved intaglio
The production process of electronic engraving gravure is:
Scanning negatives → installing plate cylinder → testing → engraving → chrome plating
1. Scan film
In the past, scanning negative films used continuous-adjusted opalescent films, which were expensive to manufacture and the quality of the negative films was difficult to control. In the 1980s, the electronic engraving machine added an electronic conversion component to perform offset gravure conversion according to the designed procedure, that is, to engrave the gravure with a screen negative for offset printing. Therefore, most of the color separation and screen negative plates are now used.
2. Install plate cylinder
Install the printing plate on the electronic engraving machine with a crane, and remove the oil, dust and oxide on the plate before engraving. Paste the scanned film in plain clothes on the original roller.
3. test
According to the requirements of the original (scanning film) and the hue of the ink, the trial engraving value is set in combination with the printed product. For example, the paper for decorative printing is relatively rough and has strong ink absorption. The engraving depth must be 45μm-50μm to meet the printing requirements. Current and voltage on the amplifier.
4. Sculpture
The scanning head scans the original, the engraving head and the scanning head operate synchronously, and the surface of the printing plate cylinder is engraved into net holes with different depths.
The new electronic engraving machine has three shapes of dot angles, which can be arbitrarily selected during operation to avoid the occurrence of turtle text due to inaccurate overprinting. The three kinds of outlet angles are shown in Figure 4-26.
Figure 4ï¼26 Schematic diagram of gravure angle
When engraving text, the fine strokes cannot be lost, you must use fine net line engraving. If you use 100 lines / cm, the engraving of the text can achieve a very ideal effect.
At present, the electronic engraving gravure mostly adopts a separate electronic engraving system to make plates, that is, the scanner and the electronic engraving machine are separated, and are respectively connected to the input and output interfaces of the image workstation. The scanner can scan the positive and negative images, and Yin can scan the opal film and also convert the glue to the concave. The workstation has a variety of image processing functions, which can perform overall and partial color correction, cut, combine and zoom, and color gradient on the image. Combine yellow, magenta, and cyan images with line images into one. The network line of the electronic engraving machine ranges from 31.5 to 200 lines / cm.
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