The published articles are meant to primarily educate the students in printing to supplement their knowledge in the field of Printing. These are not simple Glossary of printing terms, but to the extent possible every term has been explained in brief so that it can be of some use to the students who appear in some sort of examinations and interviews.
I served the Printing Industry for over 40 years
in various capacities, a major part in an Security Printing Organization. In order not to waste the printing and paper related knowledge which I gained over years, I decided to keep them in public domain for the reason stated in prepara. Most of the illustrations - over 90% - have been generated by me to explain the terms suitably.
While I am not sure to what extent the published content will help, if the content is going to be of use to some one in some manner, I will be greatly satisfied.
Your views may be sent to me (
nrj_1945@yahoo.com) for my record and correction wherever needed.

TOTAL NO OF PRINTING TERMS

POSTED TILL NOVEMBER, 2012

- Over 400 terms-

Click on this line to read from 'A'

Wednesday, June 15, 2016

Printing defects on Canadian Currencies : Part - 4



Brief summary

This is in continuation with my earlier article written in the same subject under the title Analysis on 'Printing defects on Canadian Currencies'. All those articles were based on articles written by Mr. Hitesh Doshi who teaches in the Architectural Science Department at Ryerson University, Canada 
(Ref:-Doshi.H. / Email: Hitesh Doshi -hdoshi@ryerson.ca).

The present analysis Case Study:4 is also on 'Printing defects on Canadian Currencies' and based on another article written by Mr. Hitesh Doshi titled  'Truncated issue on $20 frontier series polymer Canadian Bank Note' (Ref: Truncated issue on $20 frontier series polymer Canadian bank note Canadian Paper Money Society Journal 2015 ).

Mr. Hitesh Doshi has analyzed the possible causes of the defects seen in Image-1 and Image-2 as shown below and therefore it is necessary that the origin and actual technical problem is fully understood in all aspects. One of the most common technical problem faced by printers is occurrence of white spots called fluff or lint or debris as differently coined by the printers, that show voids or no print spots on the images in the ultimate print at the end of Offset printing process.

Four probable conditions have been mentioned in the article published. The probable conditions mentioned are:

Quote
1. Condition happened post-production
2. Condition happened during production but after printing of all ink
3. Condition happened during production but after printing of the 'Issue' text
4. Condition happened during production where portion of the 'Issue' text was never printed
Unquote


Yes, the cause of the truncated image is attributable to probable cause mentioned under Sr No 4 mentioned above. The portion of the text 'issue' has been printed as broken image. 


Analysis 

Both paper and Polymer substances are used for printing the Currencies and both have the tendency of fluffing and linting. This is unavoidable. Let us discuss the behavioral pattern of the paper used for printing the currencies and which are generally made from 100 % combed cotton having longer fibers. While some paper manufacturers add small percentage of recycled paper from the same mill to reduce the manufacturing cost, they are careful not to mix wood pulp or other mechanical pulps along with the cotton fibre pulp which will not only deteriorate the quality of print on the Currencies but also generate many working problems during printing. For reducing the manufacturing cost of paper, the suppliers quietly add the recycled paper pulp beyond the percentage permitted or add the ready bleached pulp cakes available in the market which are mixture of many other varieties of paper. With this combination when the paper is manufactured one will see endless problem of fluff and linting leading to the reproduction of prints with voids on the printed surface. No doubt, adding ready made pulp cakes help in reducing the manufacturing cost, but it also reduces the profit part of the printer due to the technical problems faced working with paper or other substances  prone to fluffing.

In addition to the short length of fibers inherited in the ready made pulp cakes, in whatever manner the readily available pulp cakes are treated in the beating process and filtered during the process of paper making, some amount of extraneous particles like fine chips of wood, crystallized gelatine, albumen flakes etc pass through the filters and mix with the final pulp that flows over the paper mesh to form the paper in the paper making process. Except the bigger particle, it is not possible to filter away the smaller sized extraneous particles. Loose material in the recycled paper or re-pulped paper may include threads, gelatine and plastic material, pollen etc and when they sit on the surface of the paper, they cause several technical problems during printing. Such floating extraneous dirt particles on the surface of the paper are the main culprit  that cause the problem of fluff and debris during printing.

Voids on the printed image 

How does the fluff and debris settle on paper and subsequently affect the print quality? During the paper making process when the pulp that forms the sheet of paper keep flowing on the mesh screen to form the paper, the extraneous dirt particles too flow along with the pulp and stay on the surface of the paper being formed and gets settled on it during drying process. During super calendaring process, they are all pressed on to the surface of the paper.Though the extraneous materials may appear to be firmly adhered with the surface of the paper, in reality it is not. While part of the floating material remain non bonded on surface of the paper due to static electricity generated during paper making process, some percentage of them partly remain fixed with the paper surface as if they have been pasted with gum. Till the static is removed from the surface, those floating elements will also not come out. Thus the paper that are prone to fluffing will have both floating and partially embedded extraneous material on them.

Once the paper making process is completed, those paper lot is packed and sent to the printers. Theoretically the static remains on the surface of the paper even after packing. Usually the static affected papers when subjected to printing refuse to release the dust and dirt particles from the surface unless some apparatus is engaged to remove the static from their surface during the printing process. 


If this problem of fluff or voids is to be eliminated during printing, the static on the paper surface need to be first taken out and extraneous particles removed. Sheet by sheet removal of static and the extraneous particles by wiping with semi dried damp cloth or some other means is not feasible as the quantity will be enormous. Therefore in order to eliminate the static on paper which cause the problem of fluff, a small unit called anti static cum dedusting unit is attached at the end of the feeder board, but before the impression unit. It is an attachment that has anti static rods and dedusting unit to suck away the loose particles. When the surface static is removed from the surface of the paper by the anti static rods, the dedusting unit sucks out the extraneous particles and other dust released from the static removed paper surface. However the partly stuck extraneous particles do not get loosened from the paper surface by the anti static unit and continue to remain there still. 
When the anti static and dedusting process failed to remove the partly adhered particles, they continue to remain adhered on the paper surface and reach the print station. When the paper pass through the blanket to receive the ink impression from its surface, the extraneous particles partly remaining on paper and not visible to the naked eye gets released under pressure between cylinders and gets stuck on to the blanket surface. Once the particle gets adhered to the blanket surface from then on the inked image from the plate refuses to transfer the image on those particles stuck with the blanket while the other portion of the images get normally transferred. When the inked image from the blanket gets transferred on to the paper surface the image will show voids on the print on those places where the extraneous particles on the blanket have not accepted the image transfer.

Printers call the voids as paper fluff which continues to print void images on the same position and in the same shape and appearance continuously on the entire set of sheets that continue to travel unless the machine is stopped and blanket cleaned to remove the dirt.

The peculiarity of those extraneous particles stuck on the blanket is that they do not accept the ink from the plate cylinder which transfers the image on to the blanket for re transfer on to the paper surface. Because the extraneous particles do not accept ink, the image is printed along with non inked areas which in technical term is called voids. Why the extraneous particles adhered on the surface of the blanket fails to accept the ink from the plate is that their surface becomes highly polished during super calendaring process and therefore the surface becomes  non absorbent due to which they repel the ink.

Similar to the paper substance which has the debris stuck to the surface during manufacturing process, the polymers too have their own family of extraneous material that gets stuck on their surface. The extraneous material partially or firmly stuck on Polymer substance when subjected to print process cause voids in the printed image as the loose particles get stuck to the surface of the blanket exactly in the same manner as it occurs during the print process on paper. Remember an important aspect on the image printed. The size, shape and appearance of the void is uniform on all the notes thus confirming the theory that the extraneous particle called fluff adhered over the blanket surface has been the possible reason for the said defect  even on the Polymer substance used for printing the currencies. This may be the cause for the defect as seen in the image shown under Image-1 above.

Note an important aspect; the void image is similar in all notes and of the same shape and size as seen in the Image-1 shown above.

Truncated image

The reasons for the second problem of broken or truncated image is explained below. 


While it is not known whether Wet Offset printing technique or Dry Offset printing  is deployed for printing the currencies in the Canadian security printing press, only general observation can be given for the causes.

The Currency note printers all over the world appears to generally use only relief imaged plates to print the Currencies and Dry Offset process which works in the simpler manner than the conventional Wet Offset machines that work on grease and water repellent theory.

Two reasons is attributable to the defect as seen in the above images under Image-2

Dry Offset print process:-

1) The image 'issue' on the relief Offset plate meant for the Dry Offset printing, may have got damaged in that particular portion by losing the relief depth if some hard object in the same shape and appearance as seen in the image may have pressed the image on the plate during impression. The extraneous object could be dried ink particles or particle from the cleaning cloth. The relief of the image on the plate may have gone down below the kiss touch point between the plate and the blanket cylinder.

2) If above have not happened, then it is possible that the blanket may have been damaged or punctured in that particular portion by  pressure of some extraneous particle to the extent where the image is truncated. Sometimes the blanket gets punctured by some hard particles.  The effect is non transfer of the image from the damaged area of the blanket causing truncated printed image.


3) Thirdly the problem of big sized fluff particle could have also been the cause that get stuck to the blanket and prevent further transfer of full image.

Wet Offset process:

Here too either the plate may have got damaged due to some scratch occurred  while handling the plate on the machine or hard particle has pressed the plate in that portion to the extent of truncated image or the blanket may have been damaged as pointed out under Dry Offset process.  

CONCLUSION 

==================== 
                                                           

In both the cases of printing by Dry Offset and Wet Offset process the result will be the reproduction of the truncated print as it appears on the Image-2 above if the plate had lost the image depth, or blanket was punctured or the extraneous particle like fluff stuck to the blanket surface preventing ink transfer from that particular portion truncated. Note an important aspect; the truncated image is similar and of the same shape and size as seen in the Image-2 shown above.

If the inspection machine failed to detect it, then defective Currency will go out for circulation as is the present case. The defect is very glaring and it surprises how it has passed for circulation.

Since various aspects involved in the issue of voids in print and truncated images have been explained in detail, the observations expressed  in the original article have not been taken up for analysis.

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