Written by: N.R. Jayaraman
Decades back, few of the most high profile printing units in Asia engaged in the act of printing high value security documents faced a unique problem of lint /fluff problem which left several voids on the printed image during printing by Dry Offset printing process. The high degree of voids appearing as white spots of different sizes over the image on the document was unacceptable to the customer as the documents printed were sensitive in nature and had high reputation and value internationally.
The high value document paper used by the print houses were made of 100 % cotton combers (rag content) ones. The paper supplied also strictly conformed to certain vital parameters of the paper. The print houses were getting paper supplies from multiple sources of paper mills across the world besides internal paper mill. Out of several supplies, the paper supplies received from two particular mills were highly prone to fluff/ debris (void on print) problem leading to higher percentage of wastage of the printed paper inspite of the fact that the paper supplies were pre inspected before receipt and cleared acceptable for use. The print houses were losing a huge chunk of their profit though were not running in loss, but the loss on the profit was telling upon their overall performance rating.
The procedure of processing the documents in those units were as under:-
The documents were subjected to printing on very old versions and newer versions of Dry Offset printing machines available in those period of time. The problem of voids on print was faced only in Dry Offset print unit. All the Dry Offset machines were equipped with powerful dedusting unit inbuilt with anti static rods. The role of the anti static rod was to first remove the static or surface tension from the surface of the moving paper of feed board. Appearance of static or surface tension on paper is very normal in high speed machines caused by the mild rubbing by the continuously moving sheets from the feeder. Even minimum amount of rubbing cause static on paper due to the high speed of machine running. Therefore all the automatic high speed running printing machines are always inbuilt with some form of anti static devices. Once the surface tension or the static is eliminated from the surface of the paper, immediately the suction unit above the static rods under which the paper travel suck off the extraneous particles from the paper surface to allow void free print to take place.
Print by Dry Offset
Over print in Intaglio to partly hide certain areas of print
Examination of the printed documents for numbering
Weed out the defective printed sheets and sort them as all good and defective sheets
Numbering all good sheets in one pattern
Numbering the defective sheets separately by a different other pattern
- Recovering all good documents from the defective sheets numbered
- The final all good printed documents combined together and print material made ready for dispatch as per contract terms.
- Destroy the print defect sheets .
In order to keep the production cost of printing as low as possible within acceptable limits and to enhance productivity, the permissible printing defect of all sorts- manual as well as natural defects- was limited to certain percentage of the total printed sheets and workers were suitably rewarded if the end results registered the rejection level well below stipulated mark by their timely intervention to curtail the defects on the machine. The permitted rejection level in force was in sinc to standard norms as practiced by the internationally reputed print houses who were also engaged in the act of printing similar documents on mass scale, using the same kind of paper and other raw material, some of which were also from the same sources of suppliers who were supplying to then existing Print houses being refereed under existing case study.
As I said earlier, out of several supplies, strangely the paper supplies from two particular mills were only leading to more and more wastage due to several void spots appearing on the printed images which was unacceptable to the customer and therefore those printed lots with defects (voids) had to be rejected which in turn hiked the production cost of the document. In order to control the rejection accruing out of such defect, the workers were instructed that as soon as the voids were spotted by the watchful workers, they had to stop the machine, clean up for voids and then run back the machine. Since this action can not be carried out on the running machine, the machines had to be stopped, specks causing voids cleared and then machine rerun which interrupted the continuous running of the machine affecting total output producible. Internationally practiced standards were that stopping the machine once every 45 minutes to one hour gap - on an average 8 to ten stoppages in a shift of 8 hours for any kind of quality adjustment including for cleaning dust and dirt was an act of good performance by the print house. Frequent stoppages of the machine for cleaning voids reduced the running hours of the machine, controlling the constant quality of the document became more difficult, reducing the waste of paper in re-feed became more and more difficult. There was resentment in workforce as their rewards were shrinking on account of paper problem leading to higher percentage of wastage which lay beyond their control to correct.
What exactly are void spots and how do they surface? The process of image transfer on to the paper was like this. The sheets were subjected to first printing ( base colour), both sides getting printed simultaneously by Dry Offset printing process. The process of printing both sides of the paper in one pass simultaneously is called perfecting printing process. In this process of printing, the inked image from the plate gets first transferred on to the blanket cylinder on both sides which in turn transfer the images on to the paper surface. Both the blankets on front and back side in act of dual role transfer the image on to paper as well as act as impression cylinder to each other.
The voids are small to big sized white spots appearing over the printed image. The voids are the partially embedded extraneous particles on paper, which instead of getting sucked by the dedusting unit get struck to the surface of the blanket cylinder during image transfer. The embedded extraneous particle from the paper stuck on to the blanket refused to get removed by itself and continue to stay over the surface of the blanket. The properties of the said particles are that they prevent subsequent image transfer from the plate on to the surface of the blanket in those areas where they were seated thus making the area no ink acceptable zone, thus finally leaving blank spot on print to appear. Those white spots were called voids in technical term.
Actually the act of the dedusting unit with anti static rods is to suck away the loosely floating extraneous particles as released from the surface of the paper by the anti static rods. Generally the paper may contain some partially or fully embedded foreign particles which may not get released from its surface and therefore not get absorbed by the dedusting unit unless they are pulled out from the paper. As long as they remain stuck over the surface of the paper, no defective print would appear. However if they are not removed by the dedusting unit and instead get stuck on to the blanket surface due to the pulling action of the greasy ink, then the defect of void spots began to appear. While the smaller voids are permitted to pass through in consent with the customer, the bigger voids are not allowed as they are construed as broken image thus lessening the value and importance of the printed document itself. Hence the prints with large voids are not accepted.
As the problem of fluff/ debris from the paper surface causing void images began to increase affecting productivity and let loose industrial unrest, several technical committees were formed to diffuse the unrest, Discussions at several levels were held and matter debated extensively, each group airing their own technical views. Some of the technical views expressed were:
- that the voids were the result of ineffective working of the dedusting unit or less powerful anti static rods both of which failed to remove the surface tension on paper which in turn kept back the floating particles remain over the paper surface, which subsequently got stuck to the blanket surface.
- improper conditioning of the paper to press room condition
- too tacky an ink which pulled the fibbers from the paper surface
- too much pressure between blanket cylinders
- use of tacky surface blankets
- the machineries and equipments producing paper in the mills were not cleaned properly and the dust and foreign particles stuck on them fell on to the paper surface and got embedded and therefore the machineries were to be thoroughly got cleaned etc etc.
Based on the recommendation of the committees several tests, trials and other measures were taken as detailed below:
Inspite of conducting tests and trials as suggested, no meaningful result in eliminating the menace was achieved and the end result in every test and trial was almost zero in curbing the problem. Years rolled, none of the observations
of the committee members produced concrete results many of which played
less or no role at all on the vexed issue since the root cause lay
elsewhere, known only to few authorities in the paper mills that
supplied defective paper and the actual fact was kept hidden for mysterious reasons. What intrigued some of the think tankers was that while on the same conditions, the paper supplies of other mills left void, fluff free prints and when the paper supplies from the two mills which were fluff prone were used, the problem resurfaced again. As a test case, when some quantity of paper was produced in one of those two mills under the watchful eyes and presence of some members, the behaviour of those paper were found excellent on the printing machines. How could then the same machineries and equipments which were blamed to be covered with layers of dust and dirt able to produce in the presence of the members good lots of paper when the basic raw material used was the same ? This was unanswered question in the minds of isolated think tanks some of whose expression of doubts in different angles were brushed aside as irrelevant under certain pretexts and hierarchy. The unfortunate aspect of the entire exercise was that the attention of the committee members were cleverly diverted from the aspect of basic pulp making process and they concentrated only from the pulp filtering stations onward on the paper making process. Therefore for many years the problem of the paper supplies causing voids on print continued to occur on lots of paper received from the two mills without serious attempt made to track the root cause of the problem.
- Fitment of more powerful dedusting units
- Pressure between blanket cylinders adjusted
- Lesser tacky inks used
- Newer varieties of less tacky blankets tried
machineries and equipments in the paper mills frequently got cleaned in
the presence of the technical experts committees formed at various
- A set of paper was freshly manufactured in the presence of committee and tried on the machine.
Over the years it became routine affair to constitute few task forces and committees with experts drawn from paper mill, machinery manufacturers and the printing units to address the problem which as expected failed to address the problem as the root cause of the problem though known to key personnel can not be contained altogether and at the same time on surface some action plan had to be stage managed to appease the workers and to show that corrective measures are taken. To consume the huge stocks of supplies already received and kept in the warehouse of the print houses and cleared on inspection and stocked in the warehouse of paper mills, as an interim measure to artificially reduce the magnitude of the problem, lots of good quality paper received from other mills and defective paper lots received from the specific two mills were mixed and issued for printing in the print houses and the productivity kept continued. In order to maintain industrial peace, some sops were also given to the workforce at intervals to compensate the lesser pay the workers got due to higher level of rejection beyond permissible limits. The key personnel allowed the problem to die down by itself over the next few years as nobody could offer alternate solution in redressing the problem. After several years when the alternate suppliers entered into the fray, and policy changed, the problem of higher percentage of waste accruing out of the paper automatically died down considerably.
However the big question that stood unanswered in the minds of thinkers was 'what exactly caused the void on print that haunted the presses even though the papers used to be pre inspected to get nod for dispatch'? After deeply studying the problem from various angles and discussion with several experts from the same field over many years, it became known that the root cause of the problem could have been the use of higher percentage of recycled paper in the pulp beyond permissible limits. This fact could not be shared at that time in public, lest it would have created industrial unrest and wrath of key personnel. At the same time the key personnel always believed that time was the best healing factor and bad experience with bad qualities of paper as has been discussed above in their print houses will slowly fade away from the mind and hearts of the personnel in the same print houses as time passes.
It was realized that in one of the two paper mills, usually the mill itself recycled part of the trimmings from their own finished stocks and added them with good pulp at some proportion while manufacturing the paper in order to reduce the cost of manufacturing paper. This is usual practice adapted by many other paper mills too. The excess stock of trimmings which remained beyond the scope of their processing unit was sold out. In this instant case few private firms which brought the trimmings from the mills recycled them along with other paper trimmings and produced ready to use recycled pulp cakes (paper pulp) and sold them back to the same mill when the mill faced shortage of main raw material- cotton comber. The ready to use paper pulp cakes had to be procured by the paper mill to offset the shortage of main raw material due to stringent procurement policies which hit them hard and production had to be somehow kept going even if it meant partial loss on profit to the print houses due to higher percentage of rejection and to whom the supplies were sent. The said paper mill thus knowingly continued production of defect prone paper by mixing good pulp plus some percentage of recycled paper from their own mills plus certain percentage of ready made recycled paper pulp cakes brought from the private entrepreneurs.
The recycled paper cakes contained
lots of foreign particles and shorter fibers both of which did not get digested and mix well with
the pure pulp. While manufacture, the small extraneous particles which passed through even filtering process lay embedded over the surface of the paper. Those partially embedded foreign particles struck on the
surface of the paper have been the culprit in producing severe fluff/ debris problem leading to void images on the print. Nobody seriously bothered to analyze how when the same mill continued to supply good quality paper to meet the printing requirement of a specific high value document (lest the supply would have been given to some other mills), the same mill continued to maintain bad supplies for printing low value documents in the same print houses.
In the case of the second mill whose supply was terrible, it was speculated that the supply of defective paper manufactured with higher percentage of inferior quality raw material was borne out of bad business practice. Gelatin was used by this mill for coating instead of PVA coating since it was cheaper raw material. The Gelatin too has lot of extraneous particles that prevent proper bonding of fibers especially on recycled paper. It was observed that the paper mill supplied defective paper lots with Gelatin as coating material instead of PVA coating and paper manufactured with more percentage of recycled paper in their supply along with defect free lots and thus indulged in unfair trade practices possibly due to the following reasons:
However one of those two mills was blacklisted from supplies later for many reasons. The speculation and observations on both the mills which supplied bad quality paper as discussed above have no documentary proof and were heard to be so. But it was unofficially known to key personnel who were firm in their belief that the above would have only been the reasons since the supplies received from other mills who manufactured with similar processing techniques with PVA coating instead of Gelatin were able to supply very good quality paper to the same print houses.
However with passage of time, when passive authorities left, bad suppliers blacklisted and changed, the menace of bad paper supply, mainly due to mixing of recycled paper with good pulp for manufacturing the paper sharply fell down automatically. As years passed every one had also forgotten the turbulent periods of the episodes. However an important lesson learnt was that when too much recycled paper is added in the paper pulp during manufacture of quality product required for production of high value document as was needed, they will indeed cause productivity loss.
- To offer paper at lower rates in the face of stiff tenders.
- To reduce cost of manufacturing paper supply them at lower rate
- To recover recurring extra expenditures incurred on invisible cost expend while getting contract.
- To offset the extra expenditure expend on subsequent inspections
- To offset loss on profit due to several extraneous considerations which can not be spelt openly.