Packaging Offset Featured Technology (2)
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Web-sheet feeder
In recent years, a new web-sheet feeder has been developed. The web is continuously cut into single sheets, and the cutting length can be adjusted steplessly according to the needs of the printing paper. The cutting precision can generally reach ± (0.2-0.5) mm, and the width is the width of the web. The cut sheet of paper is fed directly to the sheetfed offset press at a certain step, or the web-single sheet feeder is installed behind the original sheet-fed feeder, and the web- The sheet feeding table is lengthened and directly connected to the original sheet feeder paper feeding table. The two paper feeding methods can be replaced.
The main advantages of using a web-single feeder are: first, it can store a large amount of paper, reduce the number of paper changes and downtime, and improve the utilization of the machine; secondly, the web is cheaper than a single sheet and can be reduced. 5% to 25% of the paper cost, if coated cardboard or film, the coil can be used to obtain higher economic benefits; once again, completely solve the double or multiple paper feeding failure; finally, the operator does not need to stack paper , reduce labor intensity.
The main problem with the web-single feeder is that, first of all, the web is not as pre-selected as a single sheet of paper, so the requirements for the web are high, requiring no or very few splices. The paper roll standard can not be wrinkled, the paper itself can not have quality defects (such as small holes, breaks, tears, etc.); secondly, the dry moisture of the web paper can not be dried by drying like a sheet of paper, so The dry moisture of the directly used web should have certain requirements, and the effect of environmental dryness on the paper quality should be paid attention to during the storage of the paper roll. Finally, for the flatness of the paper, the best for the large paper roll, the more The worse the paper core, the thicker the paper, the greater the difference, so thick paper, paper near the core of the paper may affect the use, and a flat paper device is required.
Connection quality inspection
At present, customers have higher and higher requirements for printing quality. It is difficult to meet the needs of offline manual inspection, and offline inspection is labor-intensive and time-consuming. Therefore, various online quality inspection devices are constantly emerging. For example, in 1993, KBA launched Quality Check, and now introduces the new system Qualitronic II. It is mounted on the front of the take-up reel and can detect printed sheets or embossed sheets. If the detected sheet differs from the standard proof, the error message on the sheet will be displayed on the console display. In addition, the Hawkeye connection detection system on the Roland 700 allows all prints to be inspected online, and the results are stored on the hard drive for reference and future reference. The basic principle is: use the camera to scan the print line by line, and compare the test result with the standard value (the signed sample detection value) stored in the image processor in advance. Once the problem is found, the system will make a sound and can The warning signal is displayed, and the fault location and type are displayed on the display at the same time. The inserting mechanism on the delivery device inserts a mark at the problematic printed sheet.
Wire quality inspection devices are generally expensive, and are often used in applications where quality requirements are extremely stringent. Careful input-output ratio analysis should be performed at the time of purchase.
Large format offset press
Large-scale packaging prints (such as various milk boxes, beverage boxes, home appliance boxes, and vegetable crates) are becoming more and more stringent. In the past, it was not only labor-intensive, time-consuming, and quality to meet the requirements. At this time, the large-format offset printing machine appeared at the right time. At present, the format of the sheetfed offset printing machine can reach 1510mm×2050mm, which is very obvious in the field of packaging. These large format offset presses can not only print a variety of advertisements, posters and corrugated cardboard, but also directly print corrugated cardboard, which improves efficiency and quality. Not only the sheetfed offset press is expanding the printing format, but the web offset press is also increasing the printing area. The commercial web press LITHOMAN IV has a maximum width of 1980mm and a cutting size of 552~630mm. Manroland prefers to increase its width to 2500mm and the cutting size to 1260mm.
Large format offset presses are generally more expensive. When used, it must have large-format plate making equipment, paper cutters and paper turnover equipment matched with the format. For publication printing, it is also necessary to equip the corresponding folding machine. Therefore, before preparing for purchase, careful market research and input-output ratio analysis should be done on the printing.
Packaging web offset press
In China, there are fewer web offset presses in packaging printing, but in foreign countries, not only have applications but also are very extensive. The biggest difference between the web offset press for packaging and the web offset press for publishing is that the folding machine is rarely used, and the post-printing process is often used, or it is cut into single sheets, or re-rolled and then taken offline. machining.
Since the web offset press for packaging does not have a folding machine, the thickness of the printed material is not limited by the folding machine, and the paper can be quantified up to 250g/m2 or higher. The printing thickness can reach 650g/m2, which is more suitable for packaging printing, which makes the web offset printing machine play a greater role in the packaging printing field.
In the following, I will only introduce the configuration of the printing size variable web offset press and the common web offset press.
1. Print size variable web offset press
An important feature of packaging printing is that the printing size often changes, and the printing size of the traditional web offset printing machine is often fixed, leaving an impression that is not suitable for packaging printing. The development of modern technology can completely solve this problem. At present, the printing size variable web offset press mainly has the following three categories.
(1) Adopt plug-in method
Similar to the insert of the form printing machine, according to the size of the printed matter, the printing unit parts with different drum diameters are required, and when printing different sizes of printed materials, different printing unit components are replaced.
The problems with this solution are: first, many plug-ins, high cost, inconvenient replacement and storage; second, the general printing size can only be changed in stages, especially when using traditional gear transmission, it is more difficult to achieve Level change.
(2) sleeve technology replacement roller
When the printing size is changed, the printing cylinder sleeves of different sizes are replaced, and the water supply and the ink supply system are unchanged, and the watering roller and the inking roller are swung in an angle to adapt to the change of the diameter of the roller.
This solution is obviously more convenient and cost-effective than replacing the plug-in method. The stepless transmission technology can realize stepless change. The gear printing size can only be changed in stages, and the diameter of the drum can only be changed within a certain range.
With a seamless plate cylinder and a seamless blanket cylinder, continuous printing like a gravure press can be achieved.
(3) Adjust the tape
Only half of the blanket cylinder is loaded with a blanket, and the print length can only be less than the length of the blanket. In the absence of a blanket, the web control is quickly returned by the web control unit to prepare for the next print. Each cycle consists of two steps: advancement and retraction (return). The web control device is typically controlled by a computer to automatically calculate the change in length and speed of each retracted tape as a function of print size.
Obviously, the method of adjusting the paper tape is the most convenient method for the variable offset size of the web offset printing machine, and can realize the stepless change of the printing size, but the control system is complicated, and the accuracy of the tape control mechanism and the control system determines the phase. The accuracy of the connection between two adjacent prints. This method of adjusting the tape utilizes the principle of variable size printing and can also be used on a unit type web press.
Regardless of the variable-size web offset press, it is not only expensive, but it also adds a lot of trouble. Therefore, when the print specifications are relatively fixed, the traditional fixed-size web offset press is used. If the web offset press with common specifications can be selected, it is good to negotiate with the manufacturer to order a reel of special specifications. Paper offset press.
2. Configuration of common packaging web offset press
In order to give full play to the high-efficiency advantage of the web offset press, the necessary connection devices should be configured after the press. The main ones are as follows. The specific configuration should be determined according to the requirements of the printed matter and the specific conditions of the enterprise.
(1) Rewinding: Rewinding after printing is completed. Make corrugated cardboard or take off-line processing as needed. The advantage is that it is adaptable, flexible, and cheap. The disadvantage is that it needs to be processed offline after rewinding. Suitable for products with frequent changes, many varieties, and small batch sizes.
(2) Cross-cutting and receiving: cut into single sheets and collect them. Corrugated cardboard can be made, if it needs to be processed, it can be taken offline. The utility model has the advantages of strong adaptability, flexibility, convenient product replacement, simple cross-cutting device structure and low price; the disadvantage is that after cross-cutting, it is still necessary to perform offline processing such as offline die cutting. Suitable for products with frequent changes, many varieties, and small batch sizes.
(3) Die cutting, indentation, cross cutting, stacking, packing (packing).
(4) Die cutting, indentation, stripping, cross cutting, stacking, packing (packing).
(5) Die cutting, indentation, cross cutting, gluing, paste box.
(6) Die cutting, indentation, window opening, glue coating, transparent film, cross cutting, boxing.
The biggest advantages of the latter four methods are high efficiency, stable product quality, small footprint, and suitable for products with relatively fixed conditions. The connected die-cutting and indenting equipment can be either flat or round. The flat die cutting and creasing machine is suitable for medium and low speed machines, with many varieties and a small number of printing. The price is cheap, the molding plate is replaced, and the operation and maintenance are convenient. The circular die-cutting and creasing machine is more suitable for high-speed machines, small varieties and large-volume printing, but it is expensive. The structure and manufacturing precision of the die-cutting drum determine the service life and die-cutting precision, and the maintenance is not convenient.