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Saturday, June 25, 2016

Fluff/ Debris and Hickeys- Clarification

  (Written by N.R. Jayaraman)

Questions and Clarifications

With reference to my clarifications published vide Part-1 to Part-IV on the subject ‘Printing defects on the Canadian Currencies and Coupons’ which were in response to the original articles of Mr Hitesh Doshi  (Ref:-Doshi.H. / Email: Hitesh Doshi, he has raised few more important queries and sought elucidation on the subject further. They are reproduced below in the form of ‘Question and Clarifications’ for the benefit of readers:


Sr No 1:- 
Quote:- With respect to fluff and debris there is often a term that I have seen used called a hickey? Many textbooks have provided an explanation of how hickeys happen. You do not seem to have used that term and I was wondering the reason for that. - :Unquote


Let there be no confusion on Fluff and Debris on one side and Hickies on the other. Both are different terms meant to express two different types of problems and vary in behavior. While Fluff/ debris cause void spots in the print, the hickies may or may not cause white spots. Either there will be a hazy, non sharp, uneven white ring around the hickey spot or there may be a dab like appearance in the midst of the print. This is the reason why the term hickies have not been used along with the term Fluff/ debris in my article as they were basically two different problems. Quite often people may get confused with the prints which have hickey problem, and appear with void rings as though they are fluff.


Sr. No -2
Quote:- Also I have another article that is coming up (I will share that with you as soon as it is published) which discusses the differences when the debris is stuck to the plate or the blanket. I am wondering if you believe it makes any difference    :Unquote


The following narration will clear the doubt on the behavior of Fluff/ debris and that of Hickeys when they stick to the plate or the blanket surface.

a) The problem of Fluff or debris occurring on the Dry Offset printing process is not related to the Ink but related only to the paper surface and the blanket. The problem of Fluff/Debris will also not occur either in the Letterpress or in the Intaglio process of printing as the paper on which the print is made is in direct contact with the plate and not through the blanket.

b) The extraneous particle called Fluff/ debris emanating from the surface of the paper stick to the surface of the Offset printing blanket during printing process. Once the particle is stuck on the blanket, from then on they resist the transfer of the image from the plate over their surface (over the particle), resulting in the print to appear with voids or no image spots in those areas where they are stuck. This is because they are shiny and non absorbent material and may have been converted to such nature during bleaching and calendaring process in the paper mill which polishes their surface, and when they embed on to the surface of the paper as dried particles, their surface remains polished and therefore reject the inked image. The fact is that the  ink slips away from the surface of the particles stuck on the blanket. 

c) The Fluff/ debris is directly related to blanket vis-a- vis Paper surface. Till the particle stuck to the blanket is removed, the void will continue to appear on subsequent sheets that follow the first sheet affected with fluff. The appearance of voids on the print will also be uniform in size and shape on all prints alike the embedded foreign particle sitting on the blanket surface. 

d) Only in Letterpress and Intaglio printing the paper has direct contact with the plate. In letterpress printing process only the coated stocks and inferior quality paper made from low quality wood and other mechanical pulp transfer the fluff/ debris from their surface on to the plate/blocks which in turn pass on them to the inking rollers in contact with them. Thus the ink gets contaminated with the accumulation of the paper dust and debris and when they continue to ink the plate it results in the reproduction of unsharp, hazy image on paper but will not show any voids on print.

e) Now take the case of Hickies. When extraneous particle stick to the surface of the plate, they interfere in the plate receiving proper inking  over the image for further transfer to the paper. Be sure 95% of the particles may have been from the ink rollers which may have received the hardened particle like dried ink or other dried particles from the ink duct. During the inking process some of those particles travelling in the inking rollers get released from their surface and stick to the surface of the plate. Do not expect the extraneous particle over the Plate to behave like the extraneous particle on the blanket. Either the plate will hold it for some time or instantly transfer it back to the inking rollers or transfer it on to the blanket or on to the paper directly depending upon the process deployed for printing. The resultant image on the print will be a blotch on the printed image with a hazy void ring around them which will also be not uniform in size and shape and vary from print to print. 

f) Some times the extraneous particle thus stuck on the surface of the plate will remain there firmly. During the inking process, while the image areas receive normal inking, the spot where the extraneous particle is stuck on the plate will also receive the ink but particle being slightly raised from image level, the outer portions of the particle will not receive the ink properly. This is the reason why when the image gets transferred on to the surface of the paper, the print will appear with a blotch of ink surrounded by a ring of void in those areas where the foreign particle is stuck on the plate. Such a particles are called Hickies. In this process few sheets printed without removing the Hickey will show the blotch mark but the important point to be noted here is that the appearance of the blotch surrounded by a ring of void may not be uniform since in the continuous inking process, some quantity of the ink may also intrude into the sides of the foreign particle on the plate and reduce the effect of void.  The effect will thus be fluctuating. 

g) Sometimes the top layer of the ink in the duct gets dried and form a thin layer of dried film. If the operator failed to remove them they too would get mixed with the ink in the ink duct and transfer them on to the inking rollers. During inking process, such hardened particles which had traveled along with ink stick to the surface of the plate. Such hardened or contaminated ink particles cause the problem of hickies in Letterpress printing process or even in the wet Offset printing process. Both result in the reproduction of the same effect – a blotch surrounded by void rings on print in the areas where the dried ink film particles were stuck on the plate. However such occurrences are very low in Offset compared to the Letterpress printing.

h) The blotch of ink being wet, the blanket in wet Offset printing process picks it up and either hold it for a while or transfer it on to the paper surface. However in this process only few sheets will be affected before the operator notices them to stop the machine and remove the hickey.

i) If it is letterpress printing process, the ink blotch on the plate will transfer it on to the paper and the next one or few sheet will show unsharp image on the same spot, but the subsequent sheets will begin to take normal print.

j) Till the particle stuck to the plate/ blanket surface is removed, the subsequent sheets that follow the first sheet affected with the hickies problem will show some kind of a patch image on the print whose appearance will also be not uniform in size and shape on all prints. 

k) Sometimes the high viscose ink may pull out the paper coating or paper fibers when the plate transfer the image on to the paper surface. The pulling out of the fiber will show irregular shaped voids in print as the internal bond of the paper comes out unable to withstand the tack of the ink. At first sight the void appearance on  print will appear as though it was Fluff problem. Actually it is not and may have been the cause of high viscose ink. This is also a kind of an hickey only. 

l) The problem of Hickies occurs both in wet Offset and Letter Press printing process and rarely in Dry Offset and Intaglio printing. But again they do not result in printing of halo or void images. They will result in a dab like appearance encircled by a pattern like ring of irregular shaped void.

m) In Intaglio printing the problem of Hickies normally do not surface and  are very rare because after the plate receive the ink the surface is automatically wiped out to remove the excess ink by a unit fitted with Teflon blades. Therefore any blotch of ink stuck to the plate will be removed before printing. Beyond this, even if some ink spill falls from the duct on to the blanket of the impression cylinder, the back side of the paper will only be affected which can also be called unusual hickey. Therefore any extraneous particles like dried ink film or other hardened material sticking to the surface of the plate or the impression blanket cylinder in the Intaglio process will not cause voids/ ink blotch problem on the print. Only broken image problem or spreading of ink on the print showing unsharp image occurs in Intaglio. 

n) The problem of Hickies is directly related to the ink. Since the plate is in direct contact with the paper, during the process of printing the dust and other extraneous particles over the surface of the paper may also get adhered to the surface of the plate. The plate is in direct contact with the inking rollers to receive the ink. The inking rollers are in direct contact with the Ink duct. Now the paper dust once transferred on to the paper will also move to the inking roller and from the inking rollers they travel to the ink duct too and affect the ink in the fountain. The more and more dust thus getting transferred from the paper to the plate to the inking roller and to the ink in the ink duct like a chain will contaminate the ink in the ink fountain. Such of those dust when mix  with the ink converts some quantity of the ink into hardened lump like formation here and there. This happens when the machine is stopped for some time for any purpose. When such hardened particles travels back through the inking rollers and adhere on to the plate surface, they too cause problem like hickey.

o) In short the Hickey is the result of the following:
  • Poorly ground ink
  • High tacky ink
  • Top layer of the Ink partially dried in duct and continue to transfer ink with a thin film of dried ink
  • Paper dust getting mixed up in the ink duct to convert it to high tack ink
  • Too much dust in the atmospheric condition
p) One may ask, when the fluff or debris adhered to the blanket surface  resist the transfer of the inked image from the plate to cause void in print, how come the dried ink particle stuck on the plate can accept ink.

q) As I mentioned earlier the reason for the Fluff/ Debris stuck on the surface of the blanket refusing to accept ink  because they may have become non absorbent during bleaching and calendaring process which polishes its surface in paper manufacturing. The surface of the particle turns into glazed surface and therefore the ink slips away from sticking on them.

r) However any other dust or other particles like dried ink film if get stuck to the plate, they will receive the ink from the inking rollers as the particles mostly belong to that of ink and fibers from paper which are not only non absorbent in nature abut are also in semi wet condition.

s) In short the fluff and debris stuck to the blanket surface in Dry Offset printing process will result in halo or void to appear in print. Their appearance, shape and size will be uniform in all sheets; however the print on the paper with hickey spot will show imperfect image with or without halo whose size, shape and appearance will also be not uniform.

t) This is the huge difference between the behavior of Fluff/debris and Hickey stuck on the surface of the blanket and plate.


Sr. No -3 
Quote:- Also I have read that in addition to the static related material such debris can also be contributed from particles of dried ink etc. This type of material cannot be removed by the static removal device that you mentioned but I have read that there are other ways that the presses automatically clean to remove hickey causing material without stopping the presses -: Unquote


a) The Hickeys resultant problem on account of ink cannot be removed by the anti static rods like the one fitted on Offset machines to eliminate the static from the surface of the paper after which only the print gets transferred on to the paper surface. Static electricity occurs only on dry surfaces which are not wet. The Hickies are semi wet material partly stuck on the plate or blanket and therefore the anti static rods have no role to play to remove them from there.

b) The anti static rod cum dedusting unit is an ancillary equipment fitted on the machine that works in sync with the machine to remove the floating extraneous material from the surface of the paper and not those partially embedded particles from the surface of the paper or from the surface of the plate or blanket cylinder. 

c) There are few equipment and units available to remove the fluff/ debris  from the paper surface and the hickeys from the plate or blanket surface, both equipments, both of them attachable to the machine for online cleaning .

The normal process of removing Fluff/ Debris and Hickies are:

(i) In order to remove the fluff/ debris, one has to  stop the machine, clean the blanket surface manually with some cleaning solvents and restart the machine. Similarly to clean the Hickeys the same procedure is adapted. 

(ii) However to remove fluff/ debris or Hickies on machines fitted with online cleaning attachments, the machine is not stopped but the impression and feeder unit is disengaged. The washer/ cleaner unit is immediately engaged to clean the surface of the blanket or hickeys remover that wipes away the hickeys while the machine is still running and then the impression unit is re engaged again to continue the printing. These processes depend on the type of unit attached.


Sr; No -4 :- 
Quote:- With respect to the broken image I have a question. Lets say the plate is damaged from the beginning. How many imprints would you expect from one damaged offset plate before the plate would be routinely replaced? In other words how many sheets can a plate be expected to print before it is replaced. The reason this is important is because the question arises whether an individual plate is damaged or whether the master has been damaged. The reason why this question arises is because the number of sheets that have been affected are in the order of more than a million sheets. - Unquote   


I am totally surprised how the Canadian Currencies with such glaring mistakes are issued in millions without getting them weeded out during inspection process? Is it the policy of the Central bank that Currencies and security Coupons with such mistakes are acceptable as long as the security feature are not affected ? Always certain parameters are defined for the acceptance of defects on the printed Currencies and accordingly the tolerance limits are set with +/- variations for inspection and acceptance, but not to this extent as seen in the samples analyzed by you. However if such instances occur by mistake of the inspectors that is a different story.

In India and many other countries I have seen such defective notes are not issued from the press and even by mistake if such have been issued they are tracked in banks and removed without further issuing them. Are the Canadian notes with such major defects issued in big lots? I still doubt.

a) Generally well processed plates can print not less than 10 million sheets plus in which each sheet will have the same image in multiple ups in the order of 20 to even 40 notes per sheet depending upon the size of the Currency and the size of the sheet used for printing them. That means more than one million pieces of notes per normal shift working in a day is easily achievable per machine. We have experienced even more.

In light of the above simple arithmetic no printer will continue the printing with damaged image (minimum one damaged note per sheet) unless it is emergency to produce few million currencies for issue urgently. Simultaneously damage free image plates will be made ready and replaced as quickly as possible. Especially the Currency printers will not continue the printing with plate that has damaged image once the defect is noticed. Printing the image with broken design will not be acceptable by banks and therefore replacement of them in the bundles after processing will only add up the cost on account of loss of paper, loss of ink, consumables, labor involved in printing and sorting.

b) If the master is damaged it will be immediately got rectified before further plates are processed. No plates are prepared for printing from the defective master.

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