The Advantages and Disadvantages of Connection Devices for Sheetfed Offset Presses

First, web - single sheet feeder

Roll paper - The single-sheet feed machine cuts the web into individual sheets and feeds them directly to the paper feeder of a sheet-fed offset press. As web-single-sheet feeders can reduce costs and improve efficiency, they have become more and more important after 2005.

Web--Single-sheet feeder continuously cuts online web into single sheets. The cut sheet is fed directly to the front sheet of the original single-sheet paper feeder according to a certain step and position. So that the paper feeding mechanism can feed the paper into the impression cylinder, which can replace the original single-sheet paper feeder. The cutting length of the web can be adjusted steplessly according to the needs of the printing paper. The characteristics of the main wiring device and the selection cutting accuracy can generally reach ± ​​(0.2-0.5) mm, and the width is the width of the web.

There are some differences in the structure of different web-sheet feeders, but the basic principle is the same. They are generally composed of a paper roll holder, a floating roller unit, a feed roller, a cutting unit, an intruder unit, a nested printing logistics and Paper roller and other components. The function of the floating roller unit is to reduce or eliminate the change in the tension when the web is unfolded, so that the paper strip enters the feed roller more smoothly and is ready to be cut. The performance of the roller unit determines the precision of cutting the paper. Integral units and nested printing logistics, the cut sheet paper according to a single sheet offset press on the paper step requirements, the cut paper stack.

With the web-single-sheet feeder, you can cancel the original single-sheet feeder and directly connect the web-sheet feeder to the printing unit. The original sheet-fed paper-feeding machine can also be fixed, and the web-single-fed paper-feeding machine is installed behind the original single-sheet paper-fed paper-feeding machine, and the web-single-fed paper-feeding machine is transported. The table is lengthened and directly connected to the original sheet feeder paper feeder paper table. The former covers a small area and is cheap, but its flexibility is poor. The latter covers a large area and is expensive. Sheets and webs can be used. It is very flexible.

Advantage

First, large amounts of paper can be stored to reduce paper change and downtime and increase machine availability. Second, webs are cheaper than single sheets and can reduce paper costs by 5% to 25% if coated paperboard or film is used. , With coils can also obtain higher economic benefits; Third, the cutting length of paper can be adjusted steplessly, easy to use, will not produce a sheet of paper before the print head, ground feet and cause paper waste; Fourth, Can make it waste the thin paper and thin plastic that can not be used by the sheet-fed offset press to print; Fifth, completely solve the double-sheet or multi-sheet feed failure; Sixth, the operator does not need to pile paper, reducing the labor intensity.

Disadvantage

First, webs cannot be selected beforehand. Therefore, the requirements for the quality of webs are relatively high. It is required that the webs have no or few joints, the standard of the paper roll (without ellipticity, taper, etc.), and the paper roll cannot have wrinkles. Paper itself cannot have quality defects (such as holes, tears, tears, etc.). Second, web humidity is not as dry as a sheet of paper. It should have certain requirements for the dryness of directly used webs, and should pay attention to the dry humidity and the quality of the paper during the roll storage process. influences. Third, the flatness of the paper is best when it is large. The worse the core is, the thicker the paper becomes. Thicker paper, paper near the paper core may affect use, and it may be necessary to add a flat paper device. Therefore, too thick paper or cardboard, corrugated board should not be used.

Second, film, plastic sheet printing and corona treatment

Sheet-fed offset presses can also be coated on-line, such as the Roland 700, which can coat the printed material before color printing begins.
The first unit of the printing press prints viscose on the substrate and the second cylinder has a film wrapped around the blanket. After the printing material has passed, the corresponding part is covered with a film. This process is done at normal temperatures, completely avoiding the effects of temperature on the film and printed material.

Sheet-fed offset presses can now also be printed on plastic sheets, but the adhesion of the ink on the surface of the plastic sheet is poor. For this reason, online corona treatment can be provided. Such as KBA Rapida74, Rapida105 and other models can be installed in front of the first printing unit corona unit, the special material (such as plastic sheet) surface high-pressure discharge treatment, improve the adhesion of ink on the surface of the material, thereby improving the printing Quality and speed. In order to solve the problem of overprinting and other issues caused by temperature changes in the plastic printing process, KBA can also provide dedicated scratch-resistant paper guides, plastic sheeting static removal devices, and impression cylinder cooling devices.

Third, online cold stamping

Now many sheetfed offset presses can provide on-line cold-stamping devices. The first unit before foiling presses the special adhesive on the paper according to the pattern needed for the cold-foiled aluminum foil. The second unit equipped with the foil-discharging mechanism will use aluminum foil. Bonding (hot stamping) At the place where the adhesive is printed, the remaining aluminum foil is taken away by the winding mechanism above the third unit. When cold stamping is not required, the first and second units can be printed as normal as other units.

Advantage

(1) Printing and hot stamping are completed at one time, and precise overprinting can be achieved. Because the special adhesive can be used like ink, very fine pattern and text stamping can be achieved.

(2) Cold stamping without heating, will not cause paper deformation, will not affect the printing on and after the aluminum foil.

(3) can be printed on the aluminum foil, so that the aluminum foil to form any graphics and special color effects, such as printing silver and magenta on the silver foil to get gold.

(4) Since the aluminum foil can be given different colors by reprinting, the printer does not need to purchase aluminum foils of various colors, and only silver foil is required, which can reduce inventory and warehouses.

(5) The operator does not need to master the hot stamping technology, as long as the offset printing technology can be applied.

(6) When the hot stamping is not performed, the original unit can perform normal printing.

(7) Cold stamping system can be installed on old machines.

(8) Packaging printing often requires an online cold stamping device that can be installed anywhere on the machine as needed.

Disadvantage

(1) When printing on aluminum foil, the drying time of the ink is affected. If necessary, a drying device or a coating and drying device should be added.

(2) In the current hot stamping structure, the utilization rate of aluminum foil is low, especially single-scroll type. The use of multi-scroll type can improve the utilization of aluminum foil and reduce the cost of use.