Qi Fubin on packaging offset printing

Nowadays, both in China and abroad, packaging offset printing has been very active. In fact, this is not new. Many exquisite packaging prints come from offset printing. With the development of economy and the improvement of living standards, the demand for packaging is increasing, and the requirements for packaging are also increasing. On the one hand, the development of the packaging market has increased demand for offset printing; on the other hand, the development of offset printing technology has also made it more suitable for packaging printing.

In addition to the general printing characteristics, packaging printing also has the characteristics of a wide range of printing, usually requiring spot color printing, anti-counterfeiting printing, hot stamping, and glazing. The packaging materials of paper products are thick, and the specifications of printed products change a lot. Many printed products require many features such as die cutting, indentation, window opening and marking.

In order to meet these demands of packaging printing, both sheet-fed offset printing presses and web offset printing presses have many innovations and breakthroughs in technology. Used on sheet-fed offset presses.

1. Corona treatment technology

In order to solve the problem of poor surface adhesion of special materials (such as plastic sheets, etc.), they can be surface treated. KBA Rapida74, Rapida105 and other models install a corona unit in front of the first printing unit to perform high-voltage discharge treatment on the surface of special materials to improve the adhesion of ink on the surface of the material, thereby improving the quality and speed of printing.

2. Laminating device

ROLAND700 can coat printed materials before the start of color printing. The first printing unit prints adhesive on the substrate, the rubber cylinder of the second printing unit is wrapped with film, and the corresponding part is covered with film when the printing material passes by. This process is completed at room temperature, completely avoiding the influence of temperature on the film and printing materials.

3. Online cold stamping system

The configuration of line cold stamping is an important feature of packaging offset presses. Inline cold stamping is Manroland's first innovative technology that was launched and patented, and won the 2006 PIA / GATF InterTech Technology Award. The connected cold stamping unit can be installed at any position of the offset press according to the needs of the cold stamping position. The original unit can print normally without hot stamping; printing and hot stamping can be completed at one time, which can achieve accurate overprinting; Make the aluminum foil form arbitrary graphics and special color effects.

Cold ironing unit

4. Corrugated cardboard printing

In order to adapt to the characteristics of thicker packaging materials, many sheet-fed offset presses have now been improved, such as the use of large paper transfer cylinders, large impression cylinders, and cylinder arrangements at seven o'clock. Many offset presses have also added the function of printing corrugated cardboard directly. Because the printing pressure required to print graphics directly on corrugated cardboard is relatively small, the printing difficulty is relatively large. In the past, only flexographic printing machines could print, or the offset printing machine first printed facial paper and then pasted on corrugated cardboard, after two processes To complete. Now the offset press has the function of printing corrugated cardboard directly, which not only reduces the process, but also greatly improves the efficiency.

5.UV offset printing

UV offset printing can not only enhance the decoration of printed matter, but also change the situation that offset printing can only print ordinary paper. Now gold and silver cardboard, aluminized paper, PET, PP, PE and other plastic sheets can be printed on offset printing machines. Greatly expanded the application space of offset printing.

UV printing usually includes UV ink printing and UV varnish glazing. It has obvious environmental advantages, and the ink layer is thick, bright and wear-resistant.

A number of surveys show that the UV offset printing market is growing at a rate of 10% today, so UV offset printing equipment is also in hot sales. Now many equipment suppliers can provide offset printing machines with UV printing function, and can be equipped with different devices according to different process requirements of users. However, the UV offset printing process has its own characteristics and needs to gradually accumulate experience. At the same time, UV offset presses have high prices and high energy consumption, and need supporting UV inks, UV varnishes, printing plates, blankets, rubber rollers, curing devices, etc., which increases printing costs virtually.

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6. Glazing

A survey shows that more than 90% of packaging prints need glazing, which fully illustrates the important position of glazing in packaging printing. In the past, off-line special glazing machines were generally used for glazing, but nowadays, glazing devices with connections are mostly used. KBA has conducted a survey of the printing industry in many countries. The proportion of orders with a wire coating system are: folding carton, about 80%; label, about 70%. Table 1 shows the respective proportions of the three main glazing methods: full glazing, partial glazing and textured glazing.

Modular coating system

Table 1 Proportion of the three main types of glazing, total glazing, partial glazing and textured glazing

The printing enterprise should choose different configurations of the glazing device of the sheet-fed offset printing machine used for packaging according to the conditions of the printed matter and the enterprise itself. The specific schemes are as follows:

(1) Add light system on the basis of 5-color machine or 6-color machine. ①Add 1 glazing unit (water-based or UV) ②Add 1 water-based glazing unit and 1 UV glazing unit ③Add 1 dispersed glazing unit and 1 water-based glazing unit ④Add 1 water-based glazing unit And a golden glazing unit ⑤ add a water-based glazing unit and a lrodin (paint with pearl glazing effect) glazing unit. The first three methods are mainly used for printing packaging materials, labels, brochures, covers, and calendars. The last two methods are mainly used for cigarette wrapping paper, perfume wrapping paper, and brochure printing. The fourth method can also be used for labels and chocolates. Wrapping paper printing.

(2) 4-color standard ink + oil pressure glazing + water-based glazing can produce matte effect, suitable for high-quality labels, packaging materials and brochure printing.

(3) Mixed standard ink + oil pressure glazing + UV glazing, its glazing effect is better than water-based glazing effect, suitable for packaging materials, labels, brochures and calendar printing.

(4) Mixed standard ink + UV highlight glaze + UV dull light. The mixed standard ink + UV highlight glazing can achieve the effect of pure UV printing, and the dull light effect far exceeds the Drip-off printing process based on thermal dispersion glazing.

(5) Opaque white + 4 color standard ink + spot color + water-based glaze + golden glaze.

After glazing, there must be a drying device. For water-based glazing, an infrared drying device is used. For UV glazing, a UV curing device is used. At present, there are three kinds of drying devices commonly used: organic group drying devices, comprehensive drying devices equipped with extended paper collecting units, and special drying units.

Just like sheet-fed offset presses, web offset presses can also perform single-sided or double-sided glazing, humidification, and silicon addition. The main function of glazing is to improve the gloss of the printed matter and protect the printed matter. It can also be coated with re-wetting glue (saliva glue). If you use glue containing special additives such as perfume, after drying, the particle capsules will be destroyed by pressure friction, and the fragrance can be Stay on the paper tape. The main function of humidification is to prevent the generation of static electricity, replenish the moisture lost by the drying of the paper tape, restore the performance of the paper, reduce the temperature, and create conditions for rewinding and cutting sheets. Adding silicon (silicon content between 2% and 10%) can protect the printed matter and prevent smudging in addition to the above functions.

7. Post-press connection processing

Post-press connection processing was originally a major advantage of web printing presses, and now sheet-fed offset printing presses have also added such functions. At present, the post-press devices that can be connected to the sheet-fed offset printing machine mainly include online cutting, numbering, embossing, punching, cutting, indentation and embossing.

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Heidelberg SM74-standard delivery with marking and pressing

(1) Online slitting

In order to solve the problem that small and medium-sized prints still need to be cut off-line after printing on large-format offset presses, companies such as Manroland and KBA have launched online cutting devices, which are generally installed on the impression cylinder of the last unit. Manroland's online slitting device has its own driving parts; KBA's online slitting device, the pressure of the cutting knife against the impression cylinder is controlled by air pressure.

(2) Numbering and embossing

In some packaging and bill printing, it is often necessary to type numbers. Previously, these jobs were completed after printing, and the numbers were printed separately. Now this work can also be processed in line, which greatly improves production efficiency.

(3) Punching, cutting, creasing, embossing

Some printed materials sometimes need to be punched, cut, indented and embossed. These special requirements can now be processed by wire processing.

8. Roll paper-sheet feeder

In recent years, a new type of web-sheet feeder has been developed. The roll paper is continuously cut into a single sheet of paper. The cutting length can be adjusted steplessly according to the needs of the printing paper. The cutting accuracy can generally reach ± ​​0.2-0.5mm, and the width is the width of the roll paper. The cut sheets of paper are fed directly to the sheet-fed offset press at a certain step. Or install the roll paper-sheet feeder behind the original sheet paper feeder, extend the roll paper-sheet feed conveyor, and directly feed the original sheet paper feeder The paper table is connected, and the two paper feeding methods can be replaced.

The main advantages of using a roll paper-sheet feeder are: First, this paper feeder can store a large amount of paper, reduce the number of paper changes and downtime, and improve the machine's utilization rate. Secondly, using roll paper is cheaper than using sheet paper, which can reduce the cost of paper by 5-25%. If it is coated cardboard or film, using coiled material can obtain higher economic benefits. Third, thoroughly solve the double or multi-sheet feeding problem. Fourth, operators no longer stack paper, reducing labor intensity.

9. Large format offset printing machine

Large-scale packaging products such as milk boxes, various beverage boxes, home appliance boxes, vegetable boxes, etc. are becoming more and more strict. In the past, printing on tissue paper by splicing was not only labor-intensive and time-consuming, but also difficult to meet the quality requirements. The large format offset press was launched in due course. At present, the size of the sheet-fed offset printing machine can already reach 1510mm x 2050mm, which shows great strength in the packaging field. These large-format offset presses can not only print various advertisements, posters and corrugated cardboard facing paper, but also directly print corrugated cardboard. It improves both efficiency and quality. Not only is the sheet-fed offset press constantly expanding the printing area. Web offset presses are also constantly expanding the printing area. Manroland commercial web offset press LITHOMAN IV has a maximum width of 1980mm and a cutting size of 552-630mm. It is also planned to increase the width of the commercial web offset press to 2500mm and the cutting size to 1260mm.

Large format offset presses are generally more expensive. To use a large-format offset press, you must have a large-format plate-making device matching its format, a large-format paper cutter, and a large-format paper turnover device in the workshop. If you make a plate printing, you also need to equip a corresponding-format folder. Before preparing to buy, careful market research and input-output ratio analysis should be done.

10. Connection quality inspection

Customers have higher and higher requirements for printing quality, and it is difficult to meet the needs by offline manual inspection. Offline machine testing is labor and time consuming. So various online quality inspection devices continue to appear. For example, KBA launched Quality Check in 1993, and now it has introduced an improved Qualitronic II. The detection system is installed in front of the take-up roller of the take-up part, and can detect printed sheets after printing, and can also detect printed sheets after glazing. If the detected printed sheet is different from the standard sample sheet, the error message on the printed sheet will be displayed on the display of the console. Manroland launched the Eagle Eye Wiring Inspection System on Roland 700. Check all printed products online, and the test results are stored on the hard disk for query and future reference. The basic principle of Hawkeye on-line detection is to use a camera to detect printed products line by line. Compare the detection result with the standard value (the value of the signed sample detection) stored in the image processor in advance. When a problematic print is detected, the system will emit a sound and visual warning signal. At the same time, the system displays the fault location and type on the display screen, and the label insertion mechanism on the delivery device immediately inserts a mark at the problematic printed sheet.

The connection quality detection device is generally more expensive, and it is mostly used in products with extremely strict quality requirements. A careful input-output ratio analysis should be done when purchasing.

11. Web offset press for packaging

Few web offset presses are used in packaging and printing in China. In foreign countries, not only has long been used, but also widely used. The biggest difference between the packaging web offset press and the publishing web offset press is that the folding machine is rarely used, and the post-press connection processing or cutting into a single sheet of paper or rewinding for offline reprocessing is widely used.

The above-mentioned new technology of offset printing machine and all connection equipments of various printing machines can be applied to web offset printing machine. And because the packaging web offset press is not equipped with a folding machine, the thickness of the printed material is not limited by the folding machine, and the weight of the printed paper can reach 250g / m2 or higher, such as the use of shaftless transmission (each Independent cylinder drive) The printing thickness can reach 650 g / m2, which is more suitable for packaging printing. Make the web offset press play a greater role in the field of packaging and printing.

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The following describes the configuration of variable-size web offset presses and commonly used web offset presses.

(1) Commonly used packaging web offset press

In order to give full play to the high-efficiency advantages of the web offset press, the required connection device should be configured after printing. There are mainly the following. The specific configuration should be determined according to the print requirements and the specific conditions of the enterprise.

 Rewind: Rewind after printing. Make corrugated cardboard face paper or perform offline processing as needed. The advantages are strong adaptability, flexibility and cheap price. The disadvantage is that after rewinding, offline post-processing is still required. It is suitable for the situation where the product changes frequently, there are many varieties and small batches.

 Cross-cutting and paper collection: cut into single sheets and collect them together. Can be used for corrugated cardboard tissue. If reprocessing is required, it can be done offline. The advantages are strong adaptability, more flexibility, and convenient product replacement. The cross-cutting device is simple in structure and cheap in price. The disadvantage is that after cross-cutting, it usually still needs offline die-cutting and other post-processing. It is suitable for the situation where the product changes frequently, there are many varieties and small batches.

 Die cutting, creasing, cross cutting, stacking, packing (packing).

 Die-cutting, creasing, scrapping, cross-cutting, stacking, packing (packing).

 Die-cutting, creasing, cross-cutting, gluing and gluing boxes.

 Die cutting, indentation, window opening, glue application, transparent film, cross-cutting, and packing.

The biggest advantages of the last four methods are high efficiency, stable product quality, and small footprint. Suitable for the situation where the product is relatively fixed. The line die cutting and creasing equipment can be flat and flat, or it can be a round die cutting and creasing machine. Flat-press die-cutting creasing machine is suitable for low-speed and medium-speed machines with many varieties and small quantities of printing. Its price is cheap, and it is convenient to replace the molding board, operation and maintenance. The round die-cutting and creasing machine is more suitable for high-speed machine, less variety and mass printing. However, the price is expensive, and the structure and manufacturing accuracy of the die-cutting drum determine the service life and the accuracy of the die-cutting, and the maintenance is not convenient.

(2) Web offset printing machine with variable printing size

An important feature of packaging printing is that the printing size changes frequently. The printing size of the traditional web offset press is often fixed. It gives the impression that the web offset press 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.

 Adopt a plug-in method: a plug-in similar to a form printing machine. According to the size of the frequently printed products, make the required printing unit parts of different cylinder diameters. When printing different sizes of prints, replace the different printing unit parts. The problem with this solution is that, first of all, there are many plug-ins, the cost is high, and replacement and storage are inconvenient. Second, the general printing size can only be changed stepwise, especially when using traditional gear transmission, it is more difficult to achieve stepless change.

 Sleeve technology to replace the cylinder: When the printing size changes, replace the printing cylinder sleeve of different sizes (usually remove the support on the operation side, remove and install the sleeve from the operation side). While the water and ink systems remain unchanged, the water and ink rollers swing at an angle in a certain direction to accommodate changes in the diameter of the cylinder. This solution is obviously more convenient and cost-effective than replacing the plug-in. The use of shaftless transmission technology (each drum is driven by a separate motor) can achieve stepless change, and the size of the gear transmission printing can only be changed in steps. And because the position of water and ink is unchanged, the diameter of the cylinder can only change within a certain range. If a seamless plate cylinder and a seamless rubber cylinder are used, continuous printing like a gravure printing machine can be achieved.

 Adjusting the paper tape: The method of adjusting the paper tape is the most convenient method for the web offset press to realize the variable printing size, and it can truly realize the stepless change of the printing size. But the control system is complicated. The accuracy of the paper tape control mechanism and control system determines the accuracy of the connection between two adjacent prints. This principle of adjusting the tape to realize variable size printing can also be applied to the unit-type web printing machine.

Regardless of the type of variable-size web offset press, not only the price is much more expensive, but the use will also increase a lot of trouble. Therefore, when the printed product specifications are relatively fixed, the traditional fixed-size web offset press is still used. It is of course good to use the common specifications of the web offset press. Web offset press.

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