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'

Friday, September 22, 2017

Guide to printing students- 3

Guide to printing students
-Few objective Questions and answers- 
Written by : N.R. Jayaraman
Pre note:-
The articles are meant to help the students gain knowledge and effectively compete in the interviews and nothing else. Please note that these are not to be published by anyone for commercial purpose without the written permission from the author since the theme and illustrative examples have been compiled exclusively by the author for the benefit of the student community. THIS WILL BE PERIODICALLY PUBLISHED.


10) What is register mark ? Briefly explain. 
  • Registration marks are guide marks placed outside the image area to help the printer to accurately register images from each subsequent plates printed over the previous printed image in order to get the true colour effect desired in multi colour jobs. 
  • In multi colour job each colour is printed separately through different plates and therefore the register marks are necessary to ensure that the images from each plate is aligned one over the other. 
  • They will also get printed along with main text and images printed on the substance, but will be outside the print area and gets trimmed off when the printed material is ultimately trimmed to correct intended size and shape. 
  •  Also the register marks are guide to position the images or texts printed in a specific position on the printed substance so that when they are trimmed to correct size, the margins meant on each is maintained. 
  • The register marks vary from single cross to cross in circles and other shapes to help the printer register the images correctly in true position. 
11) What is meant by gripper margin or gripper edge ?
The gripper margin is the blank area left on the edges of the sheets to allow the sheets to get firmly gripped by a set of grippers. This margin is reserved for grabbing the sheets for printing by a row of metal clips called grippers found fitted on an impression or transfer cylinder, or other device in an infeed system of the printing machine. The gripped sheets are carried through the press for printing. The edge of the sheet containing the gripper margin is known as the gripper edge.  

12) Why do you need gripper margin  ?
If no gripper margin is kept, there will be no space for the paper to be gripped and the sheets can not be inserted into the print unit for printing.
13) What is meant by grain and cross direction of paper and why is it important for printing ?
The direction in which the longer fibbers lie is called the grain direction, also called machine direction. The fiber formation takes place during paper manufacturing and the grain direction is indicated on the packed paper. Long grain paper refers to paper in which the fibers run in the same direction as the longest measurement of the paper (Length of paper and not width). Short grain paper refers to paper in which the fibers run in the shortest direction (width) of the paper. This factor -grain direction- assumes importance as the expansion or shrinkage of paper (dimensional stability )is directly related to this. Paper is stronger and less sensitive to changes in relative humidity in the machine direction than in the cross direction of the paper.
The paper will get easily torn when torn parallel with the grain. Where the job requires folding, the printer will adjust the paper direction accordingly and use the paper. Experts say that the laser printers require long grain paper for the best results since the heat produced in the laser printers causes some curl in the sheets resulting problem in feeding. Paper folds easier and straighter when folded parallel with the grain direction.

14) What is meant by dimensional stability? Why is it so important in press rooms?
  • Ability of paper under print, and other substrates used for processing the printing plates to retain their exact size –without getting expanded or shrunk due to atmospheric changes is called dimensional stability. The paper and other substrates used for printing should retain the dimensions even when changes in moisture content or humidity in the press room atmosphere takes place
  • Two important materials in printing -paper and process films- are directly affected by this factor.  The Paper and films being cotton and cellulose fibers or acetate or polyester bases used for printing should maintain their original dimensions  even as atmospheric changes occurs. 
  • As for the Paper,  dimensional stability may change size of the paper slightly during the printing process thus causing mis register. Therefore the paper used for the multi color printing is conditioned to the room temperature for few days before commencing printing to maintain dimensional stability. 
  • As for the films which are processed in graphic arts section for preparing the printing plates, those that have low dimensional stability may change size and cause mis register  as  the printing plates are prepared from those negatives/positives.  
  • The dimensional stability cause problems in two areas in printing. If the press room is not air conditioned, the problem on account of dimensional stability can cause severe register problems when multi colour printing is carried out. 
  • Cotton fibers which is the main constituent of the paper, swell or shrink in diameter during extreme weather conditions and variation in the moisture content in the air. Since most of the fiber in the sheet are aligned in the machine run direction, absorption and de-absorption of moisture by paper causes the change in cross direction as the paper fibers when absorb water expand primarily in width, but only slightly in length. 
  • Uneven dimensional changes cause undesirable cocking and curling.
15) Name few  materials which are used for making printing plates.
The plates for printing are prepared from metals like Zinc, Alluminium or  the combination of metals like Steel, Chromium, Copper, Nickel etc. Besides the said metals plates  printing plate is also prepared on Polymer plates.
to be continued...............4

Tuesday, September 19, 2017

Guide to printing students- 2

Guide to printing students
-Few objective Questions and answers- 
Written by : N.R. Jayaraman
Pre note:-
The articles are meant to help the students gain knowledge and effectively compete in the interviews and nothing else. Please note that these are not to be published by anyone for commercial purpose without the written permission from the author since the theme and illustrative examples have been compiled exclusively by the author for the benefit of the student community. THIS WILL BE PERIODICALLY PUBLISHED. 

5) What type of feeders are fitted on the printing machines ?
Three types of feeders are fitted on the printing machines. They are:
  • Fiction feeder in which the paper is pushed by a hard rubber roller or some such device in to the feed board. Examples: Small Offset machines like Romayar, Rota print Offset machine, Duplicating machines, Copiers, Digital printers etc. 
 
  • Suction feeders in which the sheets are sucked by few suckers which push them into the feeding station. Again there are two types of suction feeders fitted on the machine. One is called sheet feeder and the other is called continuous feeder. In sheet fed machine the suckers are near the front edge of the paper while in continuous feeder, the suckers are on the back edge of the paper.

  • Web or Reel fed machines in which cut sheets are not fed as  no feeder is fitted on the web  machines. Instead   reel of paper is loaded into the special paper travelling mechanism consisting of several rollers through which the paper travel and gets printed and delivered either in roll form or as cut sheets if cutting station is made available in the delivery end of the machine.
6) What is the basic difference between sheet fed machine and continuous sheet fed machines ?
In sheet fed machine the sheets are fed  one after the other as the suckers fitted on the pile board suck the paper from the front edges of the piled paper and then move it into the feed board. Therefore until the first sheet sucked and forwarded fully entered into the feed board, the next sheet can not be sucked and forwarded. The production of sheets per hour will be less compared to the continuous feeder pile as one sheet after the other is only forwarded for printing.
In the continuous sheet feeder machine the suckers continue to suck the back edges of the sheets piled on the pile board at some interval and forward them into the feed table without waiting for the first forwarded sheet to completely clear the pile board. Therefore  before the first sheet forwarded  reaches the front lays, a part of the next sheet will continue to travel below the top sheet to reach the front lay. This process continues and thus a part of few sheets will be running one below the other to reach the front lay.  
However the mechanism has been so designed that there will be no clash of sheets in reaching the front lay and till the top sheet above the next sheet below fully enters into the print station, the next sheet below will not reach the front lay. The movement of sheets have been timed so. The production of sheets per hour will be much higher in continuous feeder as compared to the sheet fed machine as one sheet after the other is continuously forwarded for printing.

7) How do you ensure that the sheets fed on the machine gets correctly aligned for register
The registration of the sheets are done with the help of guide mechanism in the shape of metal tabs called front and side lays fitted on the feed board. They help the travelling sheets stay in perfect right angle before being gripped by the grippers of the print station to get prints on them.
 
The front lay is set in such a manner that the  specific amount of margin of the top edge of the sheet as pre set is maintained on all the sheets that travel  and similarly the side lay is also pre set to maintain certain margin on the side edge of the sheet. Both the margins are necessary for perfect registration of the printed images and to remain allowance for trimming of the sheets to final size required 

The front lay ensures that each sheet that touches it before entering into the print station gets the print exactly in the same position on the top side. Similarly the side lay ensures that each paper that touches its side wall before entering into the print station gets the print exactly in the same position leaving specific margin on both sides. This aspect is very essential especially while printing multi colour jobs which are super imposed one upon the other.

Thus the front and side lays are positioned in such a manner that as soon as the forwarded sheet touches the front lays, immediately the side lays pulls them to to touch its side wall to ensure that the sheet travel into the print station is fully aligned at right angle for registration of  the images on paper

8) Where are the front and side lays fitted on the web fed machine ?
In the web fed machines no lays are fitted. However side guides are given to ensure that the reel of paper travel maintaining the side margin. Care is taken to prepare the layout to position the images correctly on the plate which will be fitted in a specific position on the cylinder. The correct positioning of the plate on the cylinder will ensure actual margin required on both sides. However minor adjustment of margin required is made by revolving the plate cylinder in either direction - clockwise or anti clockwise and in either directions on the sides. Some times for side margin, the web holding bar or side guides are also moved in either direction to adjust the overall margin on the reel fed into the machine. 

9) Generally one sheet is only required to enter into the feed board. How will you prevent more no of sheets enter into the feed board ?
Each machine is fitted with double and triple sheet detector fitted between the pile oard and feed board on the machines which is a special device that is adjusted to allow only one sheet in the case of single sheet feeder or two to three sheets in case of continuous feeders to enter into the feed board.  

This device attached on the forwarding roller  will detect more than the preset no of sheets entering into the feed board and stop the machine when more than pre set no of sheet gets fed at one point of time. 

The double-sheet detector can either be mechanical or electrically operated and shuts off the feeding unit and impression of the printing unit. The gap between the sheet detector and feeder roller is set either to allow a single sheet to pass trough in the case of single sheet feeder or for two sheets thickness in the case of continuous feeders. 

to be continued...............3

Sunday, September 17, 2017

Guide to printing students- 1

Guide to printing students 
-Few objective Questions and answers- 
Written by : N.R. Jayaraman
Pre note:-
Many students have been approaching me time and again in individual capacity requesting for supply of objective question and answer book available if any with me to help them attend the interviews. Since I have already given away all my books to few students many years ago, I am publishing the question and answer series in printing in order to help the those students who attend the interviews. The articles are meant to help the students gain knowledge and effectively compete in the interviews and nothing else. Please note that these are not to be published by anyone  for commercial purpose without  the written permission from the author since the theme and illustrative examples have been compiled exclusively by the author for the benefit of the student  community.  THIS WILL BE PERIODICALLY PUBLISHED.

1) What are the basic printing processes?
Earlier there were only four basic printing processes which existed. All other printing processes were later developed and offshoots of the above four process only. The four processes were :
  • Letterpress Printing
  • Offset Printing 
  • Gravure 
  • Silkscreen Printing 
2) Explain the basic principles of the above four printing processes?
  Letterpress - 
  • Printing with relief plates where the image areas are in raised position where as the non image areas are much below the image areas. 
  • Image transfer is directly on paper from the printing plate which is called forme plate or from moulded plates as it contains both composed text material and illustrative blocks, both of which are tightened together on the forme plate
  • The forme plate is used on flat bed platen machines while the moulded plate is mounted on rotary machines.
  • The ink used is neither liquid nor stout but is solid and soft.
  • These days instead of moulded plates Photo Polymer plates are used. 
  • The inking system in both platen and Rotary machine is also in direct contact with printing plates. 
  • Printing of multi tonal image by halftone process is possible.
  Conventional Offset:  
  • Printing with metal plates having both image and non image areas lying in the same plane (same surface).
  • This process works based on oil and water repellent theory. 
  • Paper is not in direct contact with printing plate, but gets the image transfer through intermediary blanket cylinder. 
  • The inking system is in direct contact with printing plates, but additionally one more dampening system is also in direct contact with the plate. 
  • First the dampening system dampens the plate followed by the inking system which inks the plate.
  • The ink used is neither liquid, nor stout and fairly solid, but not to the extent of Letterpress machine inks and is soft.
  • The image from the plate gets transferred on to a blanket cylinder which in turn transfers the image on to the paper. 
  • Printing of multi tonal image by halftone process is possible.
c) Gravure:  
  • Printing with plates having image areas in sunken portion of the cylinder.
  • Image transfer is directly on paper from the printing plate (Cylinder). 
  • The inking system is in direct contact with the plate along with a wiping system (Doctor blade) which removes the excess ink from the non image areas of the plate surface. 
  • The ink used is liquid in nature and not soft or solid.
  •  Printing of multi tonal image by halftone process is not possible, but with the use of a different other type of screen, multi tonal color printing is made possible. 
d) Silk Screen: 
  • In this process a thin mesh screen works as the plate to transfer the images.
  •  The image areas will be left open and non image areas are blocked on the mesh screen. 
  • Image transfer is directly on paper from the image carrying mesh. 
  • The ink used is loose and semi solid
  • The printed images will give slight relief feel when rubbed by hand. 
  • Printing of multi tonal image not possible. Only line work with cut colours can be printed.
3) What are the other known printing processes? Briefly explain them.
The other printing processes which have emerged based on above four printing processes are:
a) Flexographic Printing : 

  • This is based on Letterpress printing. Instead of relief metallic plates or blocks, rubber stereo with embossed image is used as printing plate.
  •  Image transfer is directly on paper from the rubber stereo plate. 
  • The inking system is also in direct contact with printing plates. 
  • The basic principle is same like Letterpress printing but instead of oily ink, liquid water or alcohol based ink is used to facilitate quick drying on the printed surface
b) Dry Offset Printing:  
  • This is combination of Wet offset and Letterpress printing processes. 
  • The plate used for printing is similar to Letterpress printing i.e the images are in relief form on the plate which receives the inking directly from inking system without intermediate dampening system.
  • The image from the plate is not directly transferred on to the paper. Instead the image from the relief plate is first transferred on to the blanket cylinder which in turn transfers it on to the paper. 

c) Intaglio printing: 
  • This is offshoot of Gravure process. The principle is same- printed image in etched portion of the cylinder-  but instead of liquid ink, very hard and stout ink is used to print the image which will give relief effect on paper which can be felt by hand by rubbing over the printed image with finger. But it has to be tested only after ink dries, lest the printed ink will come out.
  • In one plate where the images are engraved, multi colored ink can be applied by specially cut rollers to print multi color images, but they will be cut colors only and not not give the effect of colour effect by  super imposing process
  • The ink is applied on the plate through an intermediary cut roller which has specific color image areas carved out on them. 
d) Digital Printing: 
  • This is based on the Xerox process which in one sense is an offshoot of Offset process. At one point of time direct typing or drawing on a paper based plates with laminated coating on their back used to be fitted on small offset presses and printed. They were known as Rotamasta plates.
  • Like  oil and water repellent theory which was the basis of wet Offset printing, the Xerox works on the principle of opposing negative and positive ions. The positive ions charged on the photo conductor drum absorb the powdered ink instead of oily ink which is used for transferring the image in other conventional processes and transfers it on to the paper by corona charge.
4) What are the two major divisions in the printing process ?
The two major divisions of printing process are grouped as Security printing and Non Security printing. 
  • Printing the images without carrying overt and covert features which are anti copying in nature is called Non Security printing.  
  • The printing of images incorporating several kinds of overt and covert features which are anti copying in nature is called Security printing. 
  • Printing text books, magazines, news papers, leaflets, pamphlets, posters, several labels, coupons, advertisements, catalogues, stickers etc are covered broadly under Non Security printing. 
  • The Security printing covers printing of Bank Notes, Currencies, Stamps, Stamp papers, Brand protection Labels and cartons, various money Coupons, Licenses, Passports etc
to be continued...............2