Managing workflow and environment Building better books – Part VI
In this issue, let us understand how workflow and environment can be controlled for optimum quality book production.
Workflow and environment
Workflow is the depiction of a sequence of operations carried out using one or more simple or complex mechanisms. Bookbinding workflow, begins where printing ends. The key links of the adhesive binding workflow are: folding, gathering, binding and trimming. There may be many other pre, post and intermediary steps. However, an important link that is invisible, but highly influential is: environment. Ambient temperature and relative humidity play a major role in workflow.
Smart BindingPaper is a substance that constantly interacts with the environment to balance humidity. In addition to this, while printing, moisture is either added (coldset) or removed (heatset). This leads to problems in the bookbinding workflow.
Let’s understand this more, with examples. Printed sheets in a pile are moved from an air-conditioned room to an area where the humidity is not controlled, like the open shed where the folding machines have been installed. In a pile, the edges of the paper are exposed to the ambient conditions while the central part remains unexposed. This leads to an uneven gain/loss in moisture at the edges in comparison to the inner part. The paper gains moisture, if the relative humidity is high and vice versa. Any gain or loss in moisture starts at the edges. When there is gain in moisture, the paper expands only at the edges leading to what is called as wavy edges, while a loss in moisture – leads to “cockling.”
In both cases, the paper loses its flatness and hence its machinability. It is difficult to feed such a paper in any machine for further processing. In an automatic folding machine, this leads to problems in sheet pickup, entry into the buckles/pockets, wrinkling etc. This results in wastage, increased downtime and slower production rates. Sometimes the problem is aggravated and this makes it impossible to run the paper in the machine.
Remedies for acclimitisation
Sajith PallipuramAllow sufficient time after printing, before one starts to fold. This will help the moisture content across the paper to be evenly spread. This will acclimatise the paper to the folding machine environment. The acclimatisation time can be between 8-12 hours depending upon ambient conditions. Ideally, the press and post-press environment must be maintained at the same level of humidity and temperature conditions. This will help save precious time which is needed on acclimatization.
Extreme climatic conditions
Moisture is an important component of paper. A moisture content of about 8-10 percent is necessary as it gives the flexibility to process the paper. There can be a lot of problems when paper is exposed to extreme climatic conditions. In very humid conditions, like the rainy season, the paper stock can become flimsy and difficult to process. The degree of stiffness required for optimum processing will be missing. In extreme dry weather like winter, paper can become brittle and crack especially when folded against the grain. In case of coated papers, this can lead to generation of dust.
The ideal environment for paper processing is at temperatures of 20-25°C and a relative humidity of 50-55 percent. In these conditions the paper poses the right degree of flexibility and stiffness required for processing.
Dry weather also leads to static electricity. In normal atmospheric conditions, the surrounding air would have neutralised this static charges, but in extremely dry weather, this leads to static electricity. This leads to paper in a pile sticking to each other. This means, multiple sheets enter the buckles of a folding machine, which results in frequent stopping of the machine. To solve this problem, one needs to employ ionisers or neutralizing bars. Both these technologies are helpful in taking out the static charges.
(To be continued in the next issue…)