TECHNOLOGICAL DEPENDANCE OF FOLDING ON THE SORT AND QUALITY OF PAPER IN FINISHING PROCESSES - FOLDING 12 PAGES FOLDS

Brekalo S., Babić D.

Summary

Materials, equipment and its features differ a lot from what it used to be. Constant technological development and production of papers in wide assortments with very different characteristics is changing folding possibilities today.
This work is about folding 12 pages folds with papers that are widely used in graphic production.
In this research three schemes were used, folded and compared. They were folded on different sorts of paper, with different weights, thicknesses and coatings. The goal was to explore which fold gives best results for cracking and creasing and to determine which fold should be used for everyday work in a printing company. The results were compared and recommendations made for each fold in this research. Boundaries of folding 12 pages folds were made depending on the thickness and weights of paper.
The experimental part of folding was done on Heidelberg folding machines in Zrinski d.d., printing and publishing company from Čakovec. For that authors are very grateful to the staff and directors who helped this research.

Key words: signatures, fold, folding machine, creasing, paper cracking, imposition, 12 pages fold

1. Introduction

Finishing industry is constantly evolving and major technology developments are happening. They make work easier, bring higher efficiency and often, they bring changes that make prior knowledge useless.Demands of the market are constantly changing and the mission of the graphic environment is to accommodate them.Developments of modern machines give broader capabilities in binding processes (Babić, D., 1998.).
Decision to standardize certain factors in the workflow of a bindery was derived form already mentioned reasons and series of mistakes that were happening in production processes. Mistakes in workflows happen from situations that sometimes can not be foreseen and are a part of everyday life in a graphic company.
Capability to fold paper on folding machines depends on number of factors (Kipphan, H., 2001.). This work studies influence of sorts, weights and thicknesses of paper on determining a scheme that can be folded and the capability of making quality folds for 12 pages folds.

2. EXPERIMENTAL PART

2.1. Problem description

The goal of this research was to determine relations between paper characteristics and different kinds of 12 pages folds, while folding on folding machines. 12 pages folds can be folded in different ways depending on the buckle plate used. Not all paper that is usually used in print production can be folded in 12 pages folds.
This research was made so it can show which fold gives the best results with different sorts of paper while conserving quality, without cracking and creasing. The problem was also in determining the recommended boundaries of folding. Boundaries of folding depend on thicknesses and weights of paper and the fold that is used on the folding machine (Furler, A. 1983.).
The plan was to give fundamental starting point in production planning. Experiences of the workers working on folding machines are also implemented in this research.
In this work assumption was made that the fold made directly influences the quality of the fold.
While thriving to get quality folds one should count in lots of parameters that are important and can directly influence the final result of folding. Those are: weight, thickness and the sort of paper, humidity of the paper and the environment, temperature, type of fold and preparation of the machine for the fold (Kipphan, H., 2001.). Planning and making good folds are essential for the final product and the speed and ease of production workflows. When correct decision is made and optimal imposition scheme chosen in production planning a lot of problems will be overpassed in finishing processes and the quality is almost guarantied.

2.2. Methodology

This research involved experimental folding on folding machines, measuring parameters that influence folding and grading samples of folded signatures that were made in the experimental part.
Before folding paper was left in the bindery for 24 hours so the temperature of the paper can equalize with the temperature in the binding area. They were wrapped with plastic foil to preserve humidity. In that time measuring of temperature and relative humidity was also made to be sure that they were optimal. Ten measurements were made for each sort of paper with HygroPalm 1 and HygroClip HS28 Sword.
To measure paper thickness 10 samples were cut from each paper stock used. The paper thicknesses given here are the middle value of measurements made ( SeeTable 1.)
Folding samples were made on Heidelberg Stahlfolder KD 78 Proline in Printing and publishing company Zrinski d.d., Čakovec, Croatia. The quality of samples was judged visually while using the “Babić method” on 10 samples for each paper and fold made.
Grades derived in that way were used in making this research. All the folds made were graded with grades from 1-5, from bad to excellent. Tables with pictures and explanations were used to judge the grade of each sample. Grades in the results below are a middle value of the grades for each fold. For this research 3 folds that give 12 pages were folded (Folding Techniques, 2004.).
Papers were selected depending on there weights and sorts (Golubović, A., 1973.). For each scheme assumption was made on the possibility of folding depending on the paper used. So in this research only papers that were likely to cause problems were selected.  (See Table 2. and 3.)

Table 1. Weight, thickness, relative humidity and temperature for each paper used

Table 2. Comparison of the plan and folds made

Table 3. Explanation of the markings used in tables

3. RESAULTS

When showing the results in this research markings shown in Table 3. are used. Weight of the paper is a number after the marking of the sort, shown in g/m2.  (Example: BIB40 is a biblical paper with weight 40 g/m2). Voluminous paper has an extra mark of 1,5 or 2,0. This extra mark shows volume of the paper.

Table 4. Results derived from folded samples

In Figure 1. an explanation of the markings on the imposition sheet is given. Imposition sheet pictures describe the fold. The numbers of pages shown on the imposition defer depending if the page is on the front or the back side of the sheet. Printed sheets are usually inserted in the folding machine with back side facing up.

Figure 1. Explanation of the imposition sheet

Figure 2. Explanation of the folding scheme

Figure 2. shows the folding scheme. Folding scheme explains the directio n of the paper through the folding machine and units used to fold the paper sheet.

3.1. S1

Figure 3. S1; Description of folding: 2/3 of the sheet buckle plate 1 up, 1/3 of the folded sheet buckle plate 2 down, 1/2 knife perpendicular

This fold gives bad results in the case of wrinkling because air gets trapped in the paper in second parallel fold. Wrinkling occurs when folding perpendicular folds with the knife unit.
Advantage of this fold is in the closed head of the signature which makes it easier to load on wire stitching and sowing machines. Perforation is only possible on the spine of the sheet.
Folding boundaries can be set to 90 g/m2 for wood free paper and around 90 g/m2 for mat and glossy coated papers with no apparent creasing. With an “x” in Table 4. it’s marked which papers are usually folded in printing company Zrinski d.d.
Problem of this fold is not being able to perforate the signature in the head or legs of the sheet. The signature is closed which results in air getting trapped in the sheet. Trapped air will cause creasing.
When preparing the sheet for production one should bare in mind to make pages which are closed inside the sheet shorter for 1-2 mm. This is to prevent pages to get folded again in the second buckle plate.
With cracking expected results were gained. Wood free papers didn’t crack extremely until 120 g/m2. Glossy coated papers started to crack around 135 g/m2, and matt papers around 115 g/m2. Cracks occur because of paper thickness and its coating. Voluminous papers crack more because they are thicker and fibres are not connected like in other sorts of paper.
Problems with static electricity can occur with 2/3 of the sheet getting in first buckle plate, especially with smaller paper surface masses and coated papers.

3.2. S2

Figure 4. S2; Description of folding: 1/3 of the sheet buckle plate 1 up, 1/3 of the folded sheet buckle plate 3 up, 1/2 knife perpendicular

Folding of S2 gave similar results to S1 which was expected. There are some differences in grades derived from folds made, but they can be neglected.
Folding boundaries with creasing can be set to 80-90 g/m2 for wood free paper and around 90 g/m2 for mat and glossy coated paper. Perforation is only possible on the spine of the sheet and like S1 the head of the signature is closed which makes it easier to load on wire stitching and sowing machines.
Compared to S1, this fold has the same possibilities of folding considering cracking and creasing. Cracking boundaries are set like in the scheme S1.
But S2 fold is better, because with it higher working speeds can be achieved. Reason for this is in the first fold. 2/3 of paper must get in the first buckle plate with S1 so the distances between two consecutive sheets must be wider. Bacause of that we get lower working speeds and fewer sheets being folded.

3.3. S3

The results with this fold are good because folds aren’t closed and the air doesn’t get trapped. Both sides of the sheet are open. With this fold higher weights of paper can be folded.
This signature needs 8 mm folio in the second part of the sheet, in right margin, to be able to insert it properly on sowing and stitching machines with grippers (not vacuum).
Perforation is only possible on the spine of the sheet.
Schemes A and B have the same folded sheet but they have different folding schemes. Folding scheme for B is rotated for 1800. Unlike A and B scheme C is open in the head with its first page.
Scheme A was folded in this research because it is frequently being used in printing Company Zrinski d.d..
Cracking boundaries are similar to S1 and S2.
Compared to S1 and S2, this fold gives best results considering creasing. S3 has best results because air doesn’t get trapped in the signature while it is open in the legs and the head of the signature. The air is free to leave the sheet when making the perpendicular knife folds.
Folding boundaries with creasing can be set to 160 g/m2 for wood free paper. But when folding this heavy paper folding rollers could get damaged because of high paper thickness. The machine gets pretty noisy when folding higher grammage papers.
For mat and glossy coated papers boundary is set to 200 g/m2.

A. B. C.
Figure 4. S2; Description of folding:
A:1/3  buckle plate 2 down, 1/3 buckle plate 3 up, 1/2 knife perpendicular
B:1/3  buckle plate 1 up, 1/3 buckle plate 2 down, 1/2 knife perpendicular
C:1/3  buckle plate 1 up, 1/3 buckle plate 2 down, 1/2 knife perpendicular

4. CONCLUSION

Boundaries set in this work aren’t strict. They depend on a lot of factors like conditions in the environment, preparation of the machine, sort, thickness and weight of the paper and selected fold to be made. Because papers defers a lot in production processes even among same weights and sorts this boundaries can not be taken strictly and can only be taken as guidelines for paper folding. When using boundary measures it is better to try the fold before using it in production process.
When selecting the fold to use in the production process it is recommended to use S3 because it gives best folding results, with attention paid to folio when signature is to be wirestiched.

Table 5. Folding boundaries

5. LITERATURE

Babić, D., (1998), Uvod u grafičku tehnologiju, Grafički centar za ispitivanje i projektiranje, Zagreb.
Bendig, E. (1990.) Lehrbuch der industriellen Buchbinderei. VEB Fachbuchverlag, Leipzig
Böttcher, W. (1985.) Persch, F. Fadensiegeln Modernes Bindeverfahren für Bücher und Broschüren, VEB Fachbuchverlag, Leipzig
Brekalo, S. (2007.) Tehnološka ovisnost savijanja o vrsti i kvaliteti papira u knjigoveštvu, Zrinski d.d., Čakovec
Folding Techniques, (2004.) Heidelberger Druckmaschinen AG, Heidelberg
Furler, A. (1983.) Falzen in der Praxis, Stahl GmbH & Co, Ludwigsburg
Hinderliter, H. (1997.) Understanding Digital Imposition, GATF, Sewickley (PA)
Golubović, A., (1973.) Tehnologija izrade i svojstva papira, VGŠ, Zagreb,
Kipphan, H., (2001.) Handbook of print media, Heidelberger Druckmaschinen AG, Heidelberg
Liebau, D., Heinze, I. (1997.) Industrielle Buchbinderei. Verlag Beruf + Schule, Itzehoe