On the Production of Electric Gravure Gravure Rolls

In the early 90s of last century, due to the rapid development of the domestic packaging market and the rapid renewal of international plate-making advanced equipment, plate-making equipment and technology have developed rapidly, plate-making enterprises have blossomed, and the plate material market is in short supply. In the mid to late 1990s, with the popularization and performance of computers, the quality of platemaking was greatly improved, and the platemaking cycle was continuously shortened. After nearly 20 years of rapid development, China's flexible packaging and plate making industry has also undergone an evolving process.

As the saying goes, the quality of printed matter is "three points in printing and seven points in printing." So, what is the current plate making technology in China's plastic flexible packaging industry? What is its market situation? What issues need to pay attention to in the process of printing plate making? In this issue of technical topics, the editorial department will work with you to focus on the related technologies of plate making.

Gravure printing is a kind of printing process. Its printing products have thick ink layers, bright colors, high saturation, high printing plate printing rate, stable printing quality, and high printing speed, etc., in the fields of printing, packaging and graphic publishing. Occupy an extremely important position. From the perspective of application, gravure printing is mainly used abroad for the publication of magazines, product catalogs and other fine publications, packaging and printing, and securities such as banknotes and stamps, but also for special applications such as decorative materials; India is mainly used for flexible packaging printing. With the development of domestic gravure printing technology, it has also been widely used in paper packaging, wood grain decoration, leather materials, and pharmaceutical packaging. Shanghai Shipping City Plate Making Co., Ltd. is a company that has a level in all fields. The professional plate-making companies use equipment imported from Germany or Switzerland. The quality of gravure roll produced by them is second to none in the country. The gravure roll produced has been exported to foreign countries. In recent years, gravure roll printing uses a large number of alcohol-soluble inks, water-based inks, and UV inks, which not only meets the requirements of the national green environment-friendly printing, but also adapts to various media such as films, composite materials, and paper, and thus remains in the field of packaging and printing. The ever-victorious situation has become an indispensable member of the domestic printing industry.

The production process of the gravure printing roll, from the perspective of its development process, there are a variety of process options, namely carbon paper photography, direct screening method, plastic gravure conversion electronic engraving, digital electronic engraving, laser engraving corrosion , laser direct engraving and so on. Here, I mainly talk about the most important and most widely used electronic engraving gravure printing roller production.

Judging from the production process of the gravure plate roller, there are mainly the following steps: printing plate substrate production, plate roller copper plating, manuscript (or design) image file production, plate image electronic engraving production, plate roller chrome plating . Among them, the production of the printing plate substrate and the processing of the plated copper roller are synchronous with the production of the original (or design) image file. After the processing of the plated copper roller and the original (or design) image file is completed, The electronic engraving of the plate image can be carried out, and the final printing plate is chrome plated, and the entire production process of the plate is completed.

1, printing plate matrix production

The substrate of the printing plate is generally made of seamless steel pipe, and a few of them are made of aluminum. Due to the low price and firmness of the steel tubes, steel tubes are used in most cases and weigh from 10 kg (narrow small-format printers) to several hundred kg (large-format large-format printers, monochrome gravure printers). The wall thickness of the steel pipe is from 10mm to 30mm, and the large size roller is thicker. According to the needs of the printing press, the printing plate is divided into non-shaft and shaft type. Generally, the small-sized flexible packaging printing machine uses the shaftless hollow printing plate, and the large printing machine uses the shaft printing plate. Before the production, the printing of the printing roller used in the printing machine will be provided first by the printing factory, and then the appropriate seamless steel pipe cutting, welding flange, chamfer, and grinding roller surface will be selected according to the drawing requirements. The envelope of the plate is heated on the shaft and subjected to the necessary accuracy test to meet the technical requirements of the drawing. At this point, the substrate processing of the printing plate has been completed. It should be noted here that no matter how good the original is made or how accurate the data of the electronic engraving is, if a high-precision plate matrix cannot be produced, the quality of the printed matter cannot be guaranteed. In this respect, the gravure can be said to be various. The strictest requirements in the printing plate, various precision machining equipments used in the manufacturing process strongly ensure the precision requirements of the platen roller.

2, plate roller copper plating

Regardless of whether the plate base of the printing plate is steel or aluminum (as long as it satisfies the requirements), before the copper plate is made, it is necessary to plate the pre-plated layer on the surface of the newly processed base roll. There are many methods to choose from. Such as nickel plating, cyanide copper plating. The plate copper layer is then plated. This copper layer is an electronic engraving work surface, so its quality must meet the following requirements: high purity of copper, fine product; plating surface should be smooth without dents, no stripes, etc.; coating has enough hardness And resilience. The sulphate copper plating process is an advanced, high-speed, acid, and high-temperature copper electroplating process, and its cathode current density can be varied in the range of 13-20 A/dm2. The obtained copper layer hardness is Vickers (210±10) HV. Can meet the requirements of electric engraving. Anode used in high-speed electroplating consumes more quickly. The use of spherical copper blocks for the anode can maximize the actual surface area of ​​the anode to prevent the passivation of the anode, and copper anodes can easily affect the quality of the copper layer due to poor dissolution of the pure copper anode, while the copper anode containing 0.1% of phosphorus is The presence of Cu3P (a non-stoichiometric component) dissolves uniformly and has a high dissolution rate under the same conditions. Sulfate copper plating bath general process: In this case, the anode and cathode current efficiency is close to 100%
Copper sulfate 150～300g/l

Sulfuric acid 40～110g/l

Temperature 20°C～50°C

Cathode current density 10 ~ 30A/dm2

Additive amount

It should be noted that electrolytic copper plating must meet considerable speed and quality requirements. Additives are indispensable, and their selection must be specific to the process specification. After the copper layer is plated, it needs to be manufactured through the process of grinding, combined with the grinding of the grinding machine, and polishing of the polishing machine imported from Switzerland, so that the diameter tolerance, parallelism tolerance and surface finish of the roller meet the requirements. Basically completed. The copper layer obtained by the process and other reasons may inevitably cause defects such as blisters, short scratches, and the like. The remedies are as follows: Clean the correction area, use the roller as the cathode, lead a wire from the rectifier's positive lead, and wrap the bare part with cotton, and dip the plating solution as an anode to wipe back and forth on the area to be corrected until it is completely coated with copper. Pay attention to the adjustment of the voltage so as to prevent scorching of the plating layer, resulting in that the binding force between the brush plating layer and the copper plate making layer is not strong enough and the previous work is abandoned. It can be ground with water-sanded paper or ground again.

3, manuscript (or design) image file production

First of all, to understand the customer's requirements, copy the original, or redesign on the basis of the original, and then scan the original, the scanned image should be clear, the color as close as possible to the original, the text line is clear, there is no ghost, the size does not deform, etc. , Then use professional processing software such as Photoshop, Illustrator, Freehand, Coreldraw, etc. to process images, text, gradients, etc., in accordance with customer requirements in combination with the characteristics of gravure printing. In the process, we must follow the following principles:

First, the overall adjustment of the main electricity sub-map, do not choose here to adjust the tone, where to choose to adjust the look, prone to local color cast phenomenon, can use the curve adjustment, try not to use the school. Second, can use spot color production, try to use spot color production, in order to ensure stable printing. Third, for some printing plates on small printing presses, due to their slow speed and poor transfer, the electricity subgraph and spray drawing should be slightly deepened as a whole, so as to facilitate printing by customers. Fourth, small text should be properly bold, fine lines less than 0.2mm should also be properly thickened to ensure that it can be carved out. Five, the practice of the seal should be engraved light color into the dark color, generally above 0.2mm, in order to ensure overprinting. Sixth, the image color management must be in place, otherwise the final printing plate is difficult to meet the requirements of customers.

4, printing plate image electronic engraving production

Shanghai Shipping Plate Co., Ltd. uses an advanced engraving machine imported from Germany or Switzerland after the completion of image file production, and performs RIP on the image files, and then performs operations on the electric carving workstation. The specific steps are as follows: , printing plate, trial engraving, engraving. First, according to the need to select the various colors used in the electric carving process, that is, network cable, screen angle, curve, dark tone, channel, highlight, needle angle, edge enhancement; and then according to the requirements of the customer to make imposition, imposition of the roller circumference, Engraving width, position of overprint line, position of each color pattern, number of horizontal and vertical lines, setting of engraving method (spiral, step, seamless connection); then the printing plate is ready to be engraved. Before the engraving roller, The surface of the roller is cleaned and lubricated to make it difficult to inject and scratch the surface in the engraving; then the test is engraved. According to the specified engraving process parameters, the required angle of the electric carving needle is selected, and the required dot darkening, channel, The size of the highlights can then be officially sculpted. After the engraving is completed, check the layout for any abnormalities such as scratches or injections. It is worth noting that the commonly used electric carving needles are 90°, 100°, 110°, 120°, 130°, and 140°. The electric engraving lines range from 40 lines to 200 lines, and the electric engraving angles from 30° to 60°. There are many kinds of matching process parameters, which can be used correctly. It directly affects the quality of the customer's products and must be used with care.

5, plate roller chrome

After the gravure plate roller was carved on the copper layer to form a net hole, the plate roller production was completed. However, when the ink is dropped on the non-mesh portion of the surface of the copper layer during the printing process, the copper surface is easily scratched by a doctor blade. Therefore, a hard chromium layer of about 10 μm is plated on the surface of the copper layer. At this point, a gravure plate cylinder was made. In the chrome plating process, the following steps are required: cleaning, degreasing, chrome plating, and polishing. The purpose of cleaning and degreasing is to remove grease and dirt from the layout, and polishing is to polish the burrs on the edge of the mesh during the chrome plating process. The chrome plating layer on the surface of the gravure roll has high hardness and high abrasion resistance and chemical stability. The chromium layer on the surface of the printing plate is not damaged by chrome plating. It is a necessary procedure for making a printing plate roll, and it is necessary to improve printing. The print resistance of the plate is mainly to increase the hardness of the chromium layer. If the number of impressions is to reach 800,000 revolutions, the hardness of chromium needs about 950 HV. Chromium hardness is closely related to temperature, current density, content of chromic anhydride and sulfuric acid and needs strict control.

With the continuous development and innovation of the gravure platemaking technology, the production process of the electronic engraving gravure is also constantly improving, and the areas involved are constantly expanding. It is believed that in the coming period, the electronic engraving gravure production process can still exert its uniqueness. The charm is invincible in the gravure printing industry.

Reprinted from: Global Flexible Packaging Industry