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'

Sunday, May 15, 2016

Printing defects on Canadian Currencies - Analysis


Brief summary :

Recently I had an interesting interaction with one Mr. Hitesh Doshi, who is settled in Canada and teaches in the Architectural Science Department at Ryerson University, Canada. He is interested in the design aspects of bank notes. He generally writes articles on 'Printing variations on Currencies' after analyzing the defective Currencies and security Coupons in circulation and sought my views on the subject matter. Based on the illustrations made available to me I sent him my feedback and promised to write an article explaining various aspects involved in the processes deployed for the production of Currencies and security documents, which can generate certain mistakes. Since Mr. Hitesh Doshi appears to be not a printer by profession and gives his opinion based on vast experience and knowledge, I give below my own views after analyzing the images of the defective Currencies and Coupons sent by him since the subject matter will be of interest to the printers in the security printing units and to the  students community in printing. 

Case Study: 1

The study below is based on the article reproduced under ‘Holy CTC coupon and Recurring ink patch on sequence of CT coupons’ ( Ref:- Doshi, H. (2016). Holy CTC Coupon and Recurring Ink Patch on Sequence of CT Coupons, The Collector, Vol. 26, No.1, 2016, pp. 8-10.- Email: by Hitesh Doshi - hdoshi@ryerson.ca). The illustration of the defective Security Coupons taken up for study is shown below:



  • The above illustration is a set of 5¢ coupons which has been printed both by Offset and Intaglio process. 

  • It showed a typical ink patch (shown in red colour in coupon No 0325109308)with some design elements in it on the back side of the printed paper.
  • The colour of the Ink patch (green) appeared to match with the colour of the intaglio ink used in the front side (face on which the patch is visible from the back side) of the coupon.
  • The shape of the ink patch too matched with the shape of a hole (torn area shown in Red colour) found in one of the papers printed with coupon No 0325109308. The intensity of the ink patch in each of the printed coupons varied (Coupons No 0325109308 No 0325109318, No 0325109321, No 0325109321 and No 0325109335) .
  • Information on coupons missing from the sequence of coupons shown has not been available.

These were the basic information I could gather from the published article under reference.

Now few important question that arises are:
  • How did the defects including the hole on the paper miss the final inspection both in the paper mill and printing press and not rejected before put to circulation.
  • Was the inspection carried out manually or on automated machines?
  • Which one of the processes has generated the ink patch to appear on paper? Was it from Offset, Intaglio, Set off or otherwise ?
  • Why did the ink patch appear only on every third serial no of the coupon printed and not found in all sheets ?
  • How could the ink patch appear on the back side of the coupon when the colour of the ink patch match with the colour of the Intaglio ink printed in the front side?
Analysis:

We are not discussing the first two points above as they are not responsible to cause this kind of print defect (as found on the coupons) and fall under the ambit of procedural aspects of inspection in the paper mill and printing plant.

Let us agree that a sheet torn in the middle (a hole) has been erroneously printed for any reason. Generally in the Currency and security document printing plants the major printing processes deployed for printing them are in the order of Offset printing, Intaglio printing followed by Numbering with a fleet of numbering boxes fitted on the cylinders of the numbering machines. The printed sheets are lastly examined for quality before dispatch.

Let us also assume that the defective coupons taken up for analysis has been first subjected to printing by Offset process. There are two types of Offset machines in use. One of them is Standard Offset printing machine which prints only one side of the paper in one pass. The configuration of this kind of machines printing one side in one pass are such that after one side is printed, the same paper lots have to be reversed and fed again with reverse side showing up to take the second print. When the paper is fed in the print unit, the inked plates attached to the plate cylinder transfers the print onto a blanket cylinder which in turn pass the print on to the paper surface when the paper travels through the blanket and impression cylinders. So the paper does not receive the prints directly from the inked image plates.

The second type of Offset printing machines are configured in such a manner that both sides of the paper (front and back) are printed in one pass. These are called Perfecting machines. In such machines instead of the impression cylinder pressing the paper against the blanket cylinder to receive the prints on its surface, one more blanket cylinder to simultaneously transfer the print on opposite sides of the paper and also to function as impression cylinder against each has been provided. The plate cylinder first transfer the respective side images on to the blanket cylinders attached to them which in turn transfer the image on to both sides of the paper surface in one go. Thus effectively there will be two blanket cylinders in position to transfer prints on both sides of the paper surface in one pass when the paper travel in between them,and also each cylinders acting as impression cylinder for the other. In these machines too the paper does not receive the prints directly from the ink imaged plates.

Let us see how far these two machines can generate the kind of defect during printing as seen in the coupons taken up for analysis.

Standard 
Offset Machine:

Let us now analyze how the paper torn in the middle when subjected to printing in Standard Offset printing machine can affect the print results on subsequent sheets that follow continuously one after the other behind the sheet with hole that had passed the print junction.

See the illustrations below to understand the after effects of the print after a sheet with a hole had been printed on these type of machines.




Illustration No 1:- Let us assume that the back side has been taken up for printing first. The inked image gets transferred on to the blanket from the plate cylinder which in turn transfers it to the back side of the paper as the paper pass through the blanket and the impression cylinder.

Illustration No 2:- Suppose while printing the back side, a sheet with a big hole had also been erroneously got fed into the print system. As usual the inked image gets transferred from the plate to the blanket and from blanket on to the entire surface of the paper, including the portion which had a hole (no paper pulp covering it). During the process of transfer the image gets not only transferred on to the surface of the paper but also on the surface of the impression cylinder through the torn area of the paper as the impression cylinder is in kiss touch with the blanket cylinder. Since there is no paper surface to receive the print in the torn area, the impression cylinder exposed to the blanket cylinder naturally receive the impression of the inked image. This means the patch of inked image equivalent to the size and shape of the torn area on paper gets printed on the impression cylinder which otherwise would have been printed on the paper surface.


Now the next few sheets that follow the sheet with hole which had been printed will receive the design element from the surface of the impression cylinder on to their surface (Paper). Which side of the paper will receive the illegally transferred inked image ? It will only be transferred on the other side of (non print side) the paper at that time. However the illegal image (image transferred on the impression cylinder) will not continue to get transferred beyond next five or six sheets that travel behind the torn sheet as the image on the impression cylinder surface will not have heavy deposition of ink and fade away quickly from the surface of the cylinder after transferring the feeble image on to the next four or five sheets. The subsequent sheets that are under feeding will however receive the image in the normal manner.

Illustration No 3:- Once the back side printing gets completed, the paper lot is reversed and again piled on the machine with non printed (blank side) side showing up to take the front side printing to complete the printing process on both sides. The piled lot of paper will also have in the middle of the lot, the papers printed with the illegal image (transferred from the impression cylinder during first run) as well as the sheet with the hole which may not have been removed as they were not inspected at that point of time. 

Illustration No 4:- As printing of the front side is carried out with another design element on the plate (another plate is inserted incorporated with different other image for the front side printing) few sheets with the back side feeble image already printed on their surface will also get overprinted with the front side image having different other design element. The spot thus over printed with two design elements -back and front designs- will show a patch of slightly darker conglomerated image.

Illustration No 5:-The enlarged version of the above conglomerated image is shown.


Illustration No 6:- The model images under 3(i) (ii) and (iii) above illustrate how only few of the successive sheets travelling behind the torn sheet have received the patch of illegally formed conglomerated images on their back side while the other sheet gets the print image in the normal manner.

NOTE:
  • Few important aspects need to be kept in mind while analyzing the print effect on the sheets printed by Standard Offset printing machine when a torn sheet (hole in the middle) has also been fed and printed along with good sheets.
  • When printing with one of the sheets having a hole, only few of the printed paper will be affected - either the back or the front side - whichever is printed in the second time.
  • The illegally transferred image (through the sheet with a big hole) on to the impression cylinder cause the print to appear as patch of conglomerated image equivalent to the size and shape of the holed area of the paper.
  • The conglomerated image will be formed only on the side of the paper which is fed into the machine after reversing the paper for second side printing.
  • Only four or five sheets that follow the torn sheet during the first side printing process will receive the conglomerated image on their back side however gradually losing the intensity of the print image and disappear by itself.
  • Remember that only few sheet that travel continuously behind the sheet torn and pass the print area will receive the feeble conglomerated image (four to five) and the print transfer of the illegal image will not be confined to only every third sheet that travel.
  • The Offset tints will also be not darker in shade similar to the ink used in Intaglio printing. They will always be lighter in shade due to Offset design elements.
THEREFORE IN LIGHT OF THE PROCESS EXPLAINED ABOVE, IT IS REASONABLE TO THINK THAT THE DISTINCT, DARK IMAGE PATCH ON EVERY THIRD PRINT AS SEEN IN THE INSTANT CASE UNDER ANALYSIS, CAN NOT OCCUR DURING THE PRINTING PROCESS BY STANDARD OFFSET MACHINE.

Perfecting 
Offset Machine:

Let us now analyze how the paper torn in the middle when subjected to printing in Perfecting printing machines can affect the print results on subsequent sheets that follow continuously one after the other behind the sheet with hole that had passed the print junction.

The configuration of the Perfecting Offset machines are such that they print both sides of the paper in one pass by the use of two blanket cylinders. Both the blanket cylinders are meant to not only transfer the print images on both sides of the paper surface in one pass, but also to perform the role of impression cylinder against each other. This is a major drift from the Standard Offset machine which prints only one side of the paper in one pass when the paper travel in between the Impression and Blanket cylinders where the print process takes place.

See above the illustrations to understand the effect on the prints when paper with a big hole also got fed erroneously.


Illustration No 1:- As usual the inked image gets transferred from the plate cylinders to the blanket cylinders which in turn transfer the image on to the entire surface of both sides of the paper in one pass when the paper travel through them. Thus both sides of the paper gets printed simultaneously in one pass.

Illustration No 2:- Suppose during the process of printing - which prints both sides of the paper in one pass- one sheet with a big hole had also erroneously got fed into the print system. During the process of printing while the entire paper surface will receive the inked image from the respective blankets on both sides, in the area where the paper has hole (torn) the blankets which are in kiss touch (face to face during contact) at the point of transfer of image, gets the images transferred on to them from the other side of the blanket.

Since there is no paper surface to receive the print in the torn area, both the blanket cylinders in kiss touch in that area will naturally receive the impression of the inked image on to them.
 
Illustration No 3:-The enlarged version of the above print image is shown.

Illustration No 4:- Since there is no paper surface to receive the print in the torn area it will cause a conglomeration of different other image in the particular area (where the paper is torn and between the blanket cylinders) on both sides of the blankets. The images from both front and back will thus form different other pattern of image contrary to approved one, and the conglomerated image will get transferred on to both sides of the next set of few sheets (following the torn sheet) arriving there to take the print.


Illustration No 5:- Model image shown under 2 (i, ii, iii) and 3 (i, ii, iii) above to illustrate the appearance of conglomerated image on the successive sheets that pass through the two blanket cylinders following the torn sheet.

NOTE:-
  • Few important aspects need to be kept in mind while analyzing the print effect on Perfecting Offset printing machine when a torn sheet (hole in middle) is also fed and printed along with good sheets.
  • When printing with one of the sheets having a hole, while only one side of the printed paper will be affected in the Standard Offset printing machine - either the back or the front side- whichever is printed second time, in the case of Perfecting Offset machine the effect of illegally transferred image formed through the paper hole will be visible on both sides of the paper in view of the configuration of the machine as explained earlier.
  • The illegally transferred image (through the sheet with a big hole) on to the blanket cylinders cause the print to appear as a patch of conglomerated image equivalent to the size and shape of the holed area of the paper.
  • The conglomerated image will be formed on both sides of the paper in one pass. Here too only those few successive four or five sheets that follow the torn sheet during the printing process will receive the conglomerated image on both sides however gradually losing the intensity of the print image and disappear by itself as may be seen in above illustration as shown under 2(i, ii, iii) and 3 (i, ii, iii).
  • Remember that each sheet that continuously travel behind the sheet torn and pass the print area will receive the feeble conglomerated image (four to five) and the print transfer of the illegal image will not be confined to only every third sheet that travel.
  • The Offset tints will also be not darker in shade similar to the ink used in Intaglio printing. They will always be lighter in shade due to Offset print design elements.
THEREFORE IN LIGHT OF THE PROCESS EXPLAINED ABOVE, IT IS REASONABLE TO THINK THAT THE DISTINCT, DARK IMAGE PATCH ON EVERY THIRD PRINT AS SEEN IN THE INSTANT CASE UNDER ANALYSIS, CAN NOT OCCUR DURING THE PRINTING PROCESS BY PERFECTING TYPE OF OFFSET MACHINE.

Standard 
Intaglio Machine:

Let us now analyze how the paper torn in the middle when subjected to printing in Standard Intaglio printing machines can affect the print results on subsequent papers that follow continuously one after the other behind the sheet with hole that had passed the print junction. Let us also assume that the sheet under Intaglio print has been the same paper lots printed on the Offset machine having a sheet with a hole inside.

The Standard Intaglio printing machine prints only one side of the paper in one pass. Though some of the firms claim that both sides Intaglio printing machines are also in the offing, the same has not been seen in use anywhere. Therefore we confine our analysis to the printing on a Standard Intaglio machine.

The Standard Intaglio printing machines used for printing of Currencies are equipped with two or three segments i.e the cylinder divided into to 2-3 segments to take on two or three plates at a time for faster reproduction. Therefore let us analyze the problem with three segmented cylinder machine. See illustrations shown below.


Illustration No 1:- The Standard Intaglio is configured in such a manner that the plates transfer the inked images directly on to the surface of the paper when the paper travel under it. A plain Impression cylinder covered with a special fabric called Intaglio blanket press the paper against the plate to pull out the ink on to the paper surface from the recessed plate.

The Intaglio design element may consist of one or even few more colours to transfer all of them in one pass by a technique called use of few cut rollers for inking each colour. It is a different technical issue and not discussed here as the same have no impact to the present problem of ink patch seen on the security Coupons under analysis.

Illustration No 2:- Let us assume that even during Intaglio printing process both sides Offset printed sheet with one of the sheet having a big hole had been erroneously fed into the printing system. As the holed paper reach the print area, in the usual manner the inked image gets transferred from the Intaglio plate to the entire surface of the paper including the portion which was holed (no paper pulp covering it). In the area where the paper had hole, the plate image transfers the image on to the impression cylinder blanket exposed through the paper hole .

Let us also assume that this occurs when the paper reached the third segment of the cylinder which is in contact for printing. While the image gets transferred on to the paper surface, in the area where the paper is torn, the image gets transferred on to the blanket of the third segment of the impression cylinder through the hole area. Since there is no paper surface to receive the print in the torn area, naturally the impression cylinder exposed to the plate cylinder will receive the impression of the inked image.

This means the patch of inked image equivalent to the size and shape of the torn area on paper is printed on the third segment of the impression cylinder blanket which otherwise would have been transferred on to the paper surface. In respect of other two segments the the other set of paper travelling behind the paper with hole gets printed on its entire surface normally. What will then be the overall effect of the illegally transferred image on the third segment of the impression cylinder?

Be clear to the fact that the illegally transferred inked image on the impression cylinder will transfer the image only on to the back side of the paper in the form of reverse image instead of transferring it in the front side as the front side of the paper is facing the plate cylinder to take the readable image print directly.

Illustration No 3:- Now as the printing continue, when the next set of sheets that follow the sheet with hole enter the print area only the paper that pass the third segment of the cylinder will receive on its back side the illegally inked image deposited earlier on the blanket of the impression cylinder. While the paper that travel through segments 1 and 2 will receive normal print (as no illegal image has been transferred in those segments) only the sheets that gets the print on the third segment will receive the illegally transferred image. Thus it is clear that only every third sheet that travel will receive the illegal image on its back side while the paper under other two segments remain unaffected.

Illustration No 4:- However the illegal image will not continue to get transferred beyond five or six sheets as the inked image on the blanket of the impression cylinder surface will not have heavy deposition of ink and looses its density quickly from the cylinder surface after transferring it on to four or five sheets that pass through the third segment of the cylinder.

NOTE:-
  • An important aspect need to be kept in mind while printing on Standard Intaglio machine. When printing with one of the sheets having a hole, only one side of the printed paper which is sans Intaglio print will be affected.
  • The affected paper will have the illegal image transferred on to their surface only on the back side.
  • A very important aspect in respect of a holed sheet getting print in Intaglio need to be noted. The Intaglio ink being very stout, the paper would normally get torn further while getting released from the impression blanket because of high pressure applied in that area to pull out the paper from the face of the plate cylinder. So a reasonably big holed sheet getting Intaglio print and getting delivered in the pile intact can not be expected or noticed as the machine stops further printing when this occurs.
  • The illegally transferred image (through the sheet with a big hole inside) on the blanket in the impression cylinder will cause the print to appear as patch of non readable image.
THEREFORE IN LIGHT OF THE PROCESS EXPLAINED ABOVE ESPECIALLY APPEARANCE OF THE PATCH OF IMAGE IN REVERSE FORM , IT IS REASONABLE TO THINK THAT THE DISTINCT, DARK IMAGE PATCH ON EVERY THIRD PRINT AS SEEN IN THE INSTANT CASE UNDER ANALYSIS, CAN ONLY HAPPEN DURING THE PRINTING PROCESS BY STANDARD INTAGLIO MACHINE.

Set Off Problem :  

There is yet an other angle in the Intaglio printing process. Will the Ink patch as seen in the instant case could occur on account of a technical problem called set off, a term expressed for the images printed with Intaglio ink on the paper leaving some impression on the back side of the paper falling over them in a piled lot?

In the printing plants we notice that while printing on any smooth surface paper or coated stock of paper like art paper, it may so happen that the ink from the front side of the previously printed sheet transfer some amount of ink on to the back side of the next printed sheet that fall over it in the delivery pile. Such an undesirable ink transfer is called the Set Off. This happens due to the wet printing ink which fails to dry quickly as the absorbing power of the coated stock is much lower. Therefore suitable ink to match the paper stock is selected for the specific printing process. Even otherwise some sort of low quality absorbent paper used to be inserted between each of the printed sheets to prevent the set off.

Such practice is very normal in Letterpress printing while printing coated Art papers. Similar practice is therefore carried out in Standard Intaglio printing machine where the Currencies printed are of superfine calendered surface. In high speed Intaglio machines, between each printed sheets some unprinted sheet of low quality will be inserted to prevent the good paper getting spoiled.


Generally the Intaglio ink takes minimum 48 hours to dry while inks to completely dry in twenty four hours are also available in the name of quick set type of Inks. With standard Intaglio inks, the manufacturer say that it takes minimum 48 hours to dry and therefore the printed sheets with standard Intaglio inks are interleaved with another low quality paper to prevent Intaglio print impression getting stuck on to the back side of the next printed sheet resting on it in the piled lot of paper. The configuration of standard Intaglio printing machines have arrangement to interleave low quality non polish surfaced blank sheets in between each printed sheets when they fall in the delivery pile to prevent set off on account of slow drying ink.


The set off on account of non drying of the Intaglio ink may not confine itself to only one area or show as specific patterned patches. It will generally be spread over the whole sheet as dots of ink - minor in some areas and more in others or no set off in some other area where the ink deposition is found less.


If the paper lots are wavy then the wavy areas are prone to transfer some ink dots on wavy areas above them due to weight of the paper lot. The wavy areas will have tighter contact on paper than non wavy areas. However the set off in even the wavy paper will not leave patch of image as noticed in the instant case.

NOTE:-

  • In light of above factual position of the Intaglio inks, the set off on the back side of the printed sheet generated from the top side of the previous printed sheet cannot result in perfect transfer of a patch as seen in the instant case where the ink patch as seen is almost uniform in shape and size though they are found to be only on few sheets.
  • In either case the set off will not occur only on every third sheet. Either the set off will be spread on entire surface of the sheet or no set off at all.
  • Some times when the paper is wavy, the wavy areas could exert a bit more pressure in those areas compared to other flat surfaces of the paper lot. But still the image transfer will not be uniform like the patch image shown in print above.
THEREFORE IN LIGHT OF THE PROCESS EXPLAINED ABOVE, IT IS REASONABLE TO THINK THAT THE DISTINCT, DARK IMAGE PATCH ON EVERY THIRD PRINT AS SEEN IN THE INSTANT CASE UNDER ANALYSIS, CAN NOT OCCUR DUE TO SET OFF.

Ink Spill and 
Ink Droplets :  

Sometimes the abnormal ink spilling of inks from the ducts carrying the printing ink, fitted above the plate cylinder also causes ink patches to appear on paper. In such cases also patch of ink can be seen on the printed paper.

Either the ink spill or droplets fall directly on the running paper or when the feeder miss a sheet and leave the impression or blanket cylinder exposed without paper over them. In such time when the spilled ink falls on the surface of the cylinder they transfer it on to the paper while running which cause a simple patch of any shape and size, but not any image pattern to appear over the paper.

The effect of the ink droplets fallen on the cylinder surface and getting transferred on to the paper surface is shown in the illustration above.

THEREFORE IN LIGHT OF THE PROCESS EXPLAINED ABOVE, IT IS REASONABLE TO THINK THAT THE DISTINCT, DARK IMAGE PATCH ON EVERY THIRD PRINT AS SEEN IN THE INSTANT CASE UNDER ANALYSIS, CAN NOT OCCUR DUE TO INK SPILL OR INK DROPLETS.


CONCLUSION
Considering all aspects as discussed above, it is reasonable to conclude that the distinct, dark image patch appearing on every third print as seen in this instant case under study cannot have occurred due to Ink Spill, Ink Droplets, Set off or even during any of the two Offset printing processes. It may have possibly occurred only during the intaglio printing process.

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