In recent years, the image quality of digital printing has been increasing, almost equivalent to that of offset printing. In the printing industry, digital printing systems capable of meeting the needs of small lot, short delivery, and variable printing have been increasingly introduced.
While offset printing is designed to print a large volume of the same page, digital printing is capable of repeating a set of printing processes for each copy; one copy of a book can be completed if the printed sheets of paper are bound as a postprocessing step. Konica Minolta established an inline system that enables integrated automatic processing from receipt of data to binding, by coordinating printing and binding processes in a digital printing system.
Conventional systems are capable of binding including saddle binding, stitch binding, and punching. However, there has been a growing demand for a binding system that achieves a superb finish equivalent to that of magazines and books available at bookstores.
The conventional saddle-stitch binding function built into MFPs etc., is referred to as the leaf gathering method. Specifically, the center of sheets of paper is stapled before the paper is folded in half. For this reason, in thick booklets (with a large number of pages), the spine becomes round, and booklets open too easily.
For this reason, the saddle stitching method which is used in commercial binding is employed to achieve a superb, functional finish with a sharp fold.
In the general saddle stitching process, the paper folding process is performed separately, requiring a long production line ranging from a few meters to dozens of meters. Konica Minolta developed a new method to reduce the size of this process to such an extent that it could be built into a digital printing system. Specifically, the folding process is directly connected with the saddle stitching process: a crease is created in the center of a paper sheet, and the sheet is allowed to glide onto a saddle without changing its form.
Konica Minolta achieved case binding (glue binding) of up to 300 sheets and 30 mm in thickness in a digital printing system.
Digital printing is characterized by variable printing, i.e. the content is changed for each copy as in the case of address printing. Variable binding is an advanced feature that is designed to change the page layout and thickness of the booklet for each copy. Binding can be continuously performed by measuring the thickness of each booklet (resolution: 0.1 mm) and pasting the cover. The system can be expanded to arrange paper sheets (both text and cover) in two or more settings, or to arrange paper sheets of different sizes. Once the settings are completed, A4 binding can be performed after B5 binding, for example.
In the general case binding process, glue is applied to the spine area of a stack of text paper sheets before the stack is wrapped with a cover; in the final process, the stack is cut on three sides (except for the spine) for finishing. Konica Minolta’s high-precision paper alignment technology eliminated the need for cutting on three sides, achieving superb binding that requires cutting of the cover only and therefore significantly reduces waste paper. In the case of an A4 booklet of 100 sheets (thickness: 8 mm), the amount of waste paper is 1/60 of that of the conventional process.
Konica Minolta’s digital printing systems meet the new needs of POD and office printing by (i) increasing the quality of printed matter derived from small lot variable printing to a level close to commercial binding and (ii) offering full-fledged binding solutions for personal teaching materials at cram schools and prep schools, corporate financial statements, and manuals, among others.
In binding, paper alignment is a critical factor. If paper is not aligned properly, a superior finish cannot be ensured. In case binding, if the surface on which glue is applied is not aligned, some of the pages may not be glued, resulting in missing pages.
Konica Minolta applied its high-precision paper handling technology, which has been refined in many years of copier development operations etc., to binding technology that is among the highest in the industry.
Horizontal alignment (in the length direction of booklets)
As the number of pages increases, the center of the paper stack sags, causing the stack of paper to be curved, resulting in stitch misalignment. The horizontal alignment plates open and close every time a sheet of paper is fed, to align the paper stack. Cushioning materials are added on the upper part of the horizontal alignment plates to make the plates tilt inwards. Because horizontal alignment plates are made from elastic PET sheets, force is evenly applied to the paper stack from both sides. The center of the paper stack can be fixed even if the curve changes in varying degrees.
Vertical alignment (in the width direction of booklets)
In a mechanism to align the paper stack in the vertical direction, a paper pressure arm is used to allow sheets of paper to stack closely to each other. The top and bottom of the paper stack are aligned by clamping sheets of paper with the vertical alignment plate and the base plate.
Thickness alignment (pressing)
If the paper stack is directly compressed and stitched while air is still trapped between sheets of paper, the stack may be significantly misaligned. For this reason, the paper stack is clamped many times in the stacking process to remove trapped air.
Konica Minolta achieved case binding with superb finish and perfectly aligned edges, through an alignment operation coordinated in all the directions (vertical, horizontal, and thickness). Konica Minolta’s case binding solution ensures that each sheet of paper is properly glued on its edge, to produce robust booklets.