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'

Thursday, February 28, 2013

Computer to Plates :New concept in Plate Making



-CTP and CTiP -
Computer to Plates 
New concept in Plate Making
(Written by N.R. Jayaraman )

In the traditional method of printing, the blocks or the plates required for printing the image with or without the texts used to be prepared through a laborious process called -Block making or Plate making - using several chemicals and photographic films. The metal plates used to be coated with certain light sensitive emulsions, photographically prepared negatives or positives kept in tight contact with the coated plates and then after exposure to special light sources the plates used to be processed with several chemicals to make the images appear on the plate which will then be put on the printing machines and printed.
With the stricter laws emerging globally on pollution and environmental controls, the need to recycle the waste chemicals, setting up of waste water treatment plants / treatment of hazardous chemicals and processed solution etc became mandatory. It lead the technologists to find alternate technologies to replace the traditionally carried work pattern involving several chemical and laborious manual processes in printing some of which were time consuming too.
Basically the reasons that prompted the Printing industry to divert their traditional approach to the development of newer technology emerged due to:
1. Need to speed up the process
2. Need to drastically reduce the consumption of chemicals
3. Need to reduce the processing cost 

 
CTP:
The emergence of CTP system based on direct thermal exposure system has caused the industry to rework out the proofing processes for taking faster decisions as it has become possible to get the proofing done on ink-jet printers for color, content, position and imposition to finalize the printing.
Towards the chemical free, film free system of processing /producing the plates the CTP has been developed. Called Computer to plate (CTP), the system controlled by a computer produce directly usable printing plate for all the printing processes specially for Dry Offset, Wet Offset and Intaglio printing machines. Once the layout and the texts and images are finalized they will be laid out into printable form (layout) in the computer and directly transferred on to a pre sensitized plate which form the images on its surface without use of any further chemicals . It is done by digital printing plate imaging process and performed under daylight conditions. The thermal exposure ensures highest production quality.
The main impact of the technology is the removal of the use of the negative or positive film to image the plate, and instead the image is directly sent to the plate. The removal of the one step increased the speed, reduced the errors, and elevated the quality of the image.
Although the CTP is a new technology, it has become popular due to its cost-effectiveness. While the production of photographic film to produce a plate or block cost a great deal of time and money the direct CTP system has cut out the middleman and mid processes in order to save on both. Direct to plate printing is also environmentally friendly and has a higher productivity rate with increased sharpness of the images formed, consistency in the images on all the plates produced, higher accuracy rate in registration and details of the images. The CTP technique also avoids potential losses in quality which can occur during film processing including formation of scratches on the surface of the film which will reduce sharpness to some extent and effect variations in the exposure especially when photographic images are processed. This system is very useful specially to Security Printing Organization which produce huge volume of work and to the News Paper and Magazine publishing houses.
CTiP:
This system is also very effective tool for Intaglio Printing process and the system is called CTiP i.e Computer to Intaglio Printing. The quality of the Intaglio printing very much depends on the quality of plates produced as the images are engraved.
Unlike the traditional plate making system for Offset plates, the Intaglio process of plate making involves several steps such as production of engraved single up dies, production of individual plastic moulds which will then be assembled to the prepared layout and by galvanic deposition of nickel on the plastic moulds, nickel alto (mid plate) is prepared from which the final printable plates are produced again by electrolysis process. The CTiP replaces the entire steps and produce direct engraved plate as per pre decided layout in perfect registration. The advantages of CTiP are:
1. Production of plates will be faster
2. Error free registered images
3. Direct production of engraved images with required depths wherever necessary in the images without involving manual engraving.
4. Direct production of full sized plate with continuous compensation for sheet distortions. Due to high degree of pressure the sheets tend to get distorted in trapezoidal form which can also be vertical or horizontal. Therefore while laying out the moulds for preparation of Nickel mid plate, the layout is made in such a manner that the first row of the images in the gripper side will be gradually expanded in each row in smallest microns to compensate the expansions so that at the end of printing there will be no white margins or mis-register at the Leading edges. The CTiP automatically takes care of such allowances once no of ups in the overall image area is fed into it. This factor is very important when repetitions of the same plates are made after long intervals as the information can be stored in computer discs. 

Friday, February 22, 2013

Know everything about Paper -5

Know everything about Paper -5
(Written by : N.R. Jayaraman) 


The Paper is tested for different qualities as explained below:


PHYSICAL PROPERTIES:
1) The Thickness
2) The weight
3) Water absorption of paper 
Oil absorbency of paper

OPTICAL PROPERTIES:
1) The brightness of paper
2) The opacity of paper
3) Smoothness or Gloss

PRINTING PROPERTIES :
 1) Printability of paper- Oil absorbency
2) The print quality of paper

STRENGTH PROPERTIES : 
1) The tearing resistance
2) The Elongation
3) Bursting strength
4) Compressibility
5) Folding endurance 
 
The Paper is tested in different ways some of which are briefly explained below:

  1. The Thickness of the paper is measured by a micrometer or thickness gauge. The paper thickness will be measured in several places and average worked out. It is expressed in microns. 
  2. The GSM is nothing but grams per square inch. One meter square paper is weighed and the GSM calculated. It is expressed in GSM. 
  3. Bursting strength is measured and indicated in kPa which is Kilopaskal which is again a metric unit. The Paper sample will be placed in a equipment and forced air will be applied. The amount of air needed to burst the paper will be the bursting strength. 
  4. Opacity is the degree of light that travel through the paper. Opacity is determined by a ratio of reflectance measurements which is the measure (percent) of the amount of light passing through a sheet of paper. Several instruments and equipments are available in the market to test the opacity. The general principle is that the paper with a black object kept at the back is illuminated from the top side at a particular angle and the reflected light measured. Similarly the same paper with a white background is measured without altering any of the setting. The difference between the two is compared to work out the opacity of the paper.
  5. The Brightness of the paper is measured with a special equipment which has the scale from 0 to 100. The brightness of the paper will influence the print quality. Paper brightness is defined by the percentage of light that it reflects. Paper with a higher brightness allows colors to stand out, while lower-brightness paper is easier for reading or extended viewing.
  6. Tearing resistance indicates the ability of the paper to withstand tearing force. When a paper gets torn at the edges, how fast it can be torn in either directions will determine the tear resistance. One of the most commonly used instrument to measure the tear test is the Elmendorf Tear Tester which measures the force perpendicular to the plane of the paper required to tear multiple plies through a specified distance after the tear has been started. All the tests are carried out in specified conditions with specified size of samples. Four ply test samples are clamped to the  clamper provided on the machine and with the integral knife handle fitted on the same machine the initial cut is performed. Since the machine is pre programmed, the extent to which the initial cut is to be made etc will be uniform. Then the pendulum will be released to perform the tearing. Then the readings of both the force required for initial cut and the tear with pendulum apparatus will be computed and result obtained. 
  7.  The Tensile strength is measured by a Tensile tester by applying constant rate of elongation to the test strip of specified width and length. The tensile strength of paper is measured by applying a tensile force parallel to the plane of the paper. The tensile strength of paper being defined as the breaking force per standard width, will depend on basic weight of the paper. Tensile strength is usually quoted in kN/m. 
  8. The Water absorbency called Cobb test of the paper is measured by an equipment. The blank paper of a particular size will be first weighed. Then the same paper will be clamped on a special equipment and water poured over it and kept for specified time. Then the excess water will be removed, paper blotted with blotting paper and then weighed to determine the water absorbency of paper. 
  9. The Folding endurance is tested by an equipment  on which a specified length and width of paper will be clamped and folded many times in both ways. The number of double folds that are required to make a test piece break under standardized conditions will indicate this factor through a formula.

     CONCLUDED

    Thursday, February 21, 2013

    Know everything about Paper -4

    Know everything about Paper -4
    (Written by : N.R. Jayaraman)  



    6. Tear resistance:

    While the Tensile strength is meant to determine the point at which the paper will crack or burst, the Tear resistance is another important property for paper that is taken into account while manufacturing bond papers, cover papers and wrapping papers. Tearing resistance indicates the ability of the paper to withstand tearing force when it is subjected to. When a paper gets torn at the edges, how fast it can be torn in either directions will determine the tear resistance. The test will demonstrate whether the paper will get easily torn or strong enough to withstand the wear and tear during various usages. If the paper gets easily torn (once the edge starts tearing) then it can be considered to be a weak paper. Therefore the paper is subjected to tear resistance test in both ways i.e Machine direction and Cross direction and average worked out to determine this factor. The fiber in the paper determines the strength and therefore fibers floating in the machine direction will be more stronger, at the same time more suitable to use on jobs where creasing or scoring operations in addition to folding operations are involved. However for wrappers, covers and other such usages like packaging papers, the paper needs to be stronger in both ways. in order to ensure that the paper remains stronger in both ways, the pulp travel path wire is shaken in regular intervals to ensure that the fiber float direction is made both vertical and horizontal.

    7. Smoothness:

    The paper must have fairly a smooth and even surface to take on the print or writing on it. The smoothness is derived both by a process called sizing and super calendering. The term sizing though related with Paper making process can not be delinked with paper as the coating used in sizing influences the smoothness along with porosity of the paper . Good sized paper will have higher strength. Similarly in order to smoothen the surface of the paper the finished paper is fed in between two highly polished rollers. Therefore smoothness is an important factor in the paper.Smoothness of the paper will often determine whether or not it can be successfully printed. Smoothness also gives eye appeal as a rough paper is unattractive.

    8. Stiffness 

    Stiffness is the measure of force required to bend a paper at a specified angle and is an important property for box boards and to some extent for printing papers also. A flimsy paper without certain amount of stiffness can cause feeding and delivery problems in larger sheet run presses. At the same time on printing machines too stiff a paper may not cause feeding problem, they can cause problems in copier machines where it must traverse over, under, and around feed rollers.

    9. Dimensional Stability:

    Most physical properties of paper undergo changes as a result of atmospheric variations due to the presence of moisture in the air. Water has the effect of plasticizing the cellulose fiber and weakening of the inter fiber bonding. The electrical resistance ie static electricity (artificial sticking of paper) vary with moisture content. The amount of water plays an important role in calendaring, printing and converting process. Moisture control is also significant to the economic aspect of paper making. Poor moisture control can adversely affect many paper properties. Ability of paper to retain their exact size, which is called dimensionally stable paper is an important factor while printing multi color jobs. The paper should retain the dimensions even when affected by changes in moisture content or humidity in the press room atmosphere, during the printing .
    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.

    10. Folding endurance:

    Fold endurance i.e ability to withstand multiple folds without getting tear will show the durability of paper when repeatedly folded under constant load. Therefore the paper used for printing special documents such as bank notes and currencies need to have sufficient folding endurance. This character is important to those documents which are quite frequently handled such as Currencies and Bank notes, Maps, Archival documents, Wrapping papers etc so that they do not deteriorate faster due to repeated bending, folding, and creasing etc. In short we may say that the Folding endurance is important for carton, box boards, ammonia print paper, and cover paper etc. It is important factor for printing grades where the paper is subjected to multiple folds like in books, maps, or pamphlets. Folding endurance is a requirement in Bond, Ledger, Currency, Map, Blue Print and Record Papers.
    ......To be continued 

    Tuesday, February 19, 2013

    Know everything about Paper -3

    Know everything about Paper -3
    (Written by : N.R. Jayaraman) 


    Some of the important  properties of paper are :

    1. GSM:

    Basic weight of Paper expressed in terms of Grams per Square Meter is shortly called as GSM. The GSM indicates how dense the paper is and help the printer decide suitable paper for suitable job. The higher the GSM, the thicker the paper. The GSM help in working out the cost of a ream of paper in a given thickness, and comparison of cost of the same weight of paper per ream in different size. A ream of paper means 500 sheets in any given size. When one say 80 GSM paper the basic paper weight per square meter will be 80 grams, but if the same weight of paper when supplied in two different sizes, the total weight of the paper per ream may differ. Newsprint normally weights 45 GSM and copying paper 80 GSM. If the weight is 200 GSM or more the paper is called board.
    The GSM is determined by weighing a known size of paper after conditioning the sample for 24 hours in ideal press room condition having 23°C temp with 50% RH .


    To find out the GSM of the paper the following formula can be used:

    1000 x 1000000
    ------------------------------------------------------------------------------
    Weight of paper in Kg x length x width of paper in mm x 500


    To find out the weight in Kg of the paper the following formula can be used:

    GSM x length x width of paper in mm x 500
    ------------------------------------------------------------
    1000 x 1000000

    2. Bulk : 
     

    Bulk means thickness of paper. In strict sense it does not reflect GSM, but indirectly related to it. The thickness of the paper usually expressed in terms of thousandths of an inch, is the bulk of the paper. The thickness is influenced by the fiber which in turn influence the flexibility of paper which may sometimes cause printed quality related problem. Bulk affects the flexibility of paper and desktop printers can have difficulty with papers that are too thick.

    3. Porosity

    Porosity is the measurement of the paper surface that determine how much air can penetrate through its base. The extent of Air permissibility will influence the absorption qualities of ink on paper, the ink binding properties and strength of the paper. The Porosity will depend on the fiber formation during Paper manufacturing process. Therefore in order to further increase the porosity of the paper, the paper is coated, super calendared or surface sized with some fillers to artificially fill up the fiber gaps to reduce the level of porosity.
    If the surface of the paper is more pores it can cause show through of ink besides increasing the consumption of the ink. Porosity is an indication of absorbency or the ability of the paper to accept and allow drying of the ink on its surface. At the same time Paper with less Porosity will cause ink print smudging and ink drying problem thus causing set off. Therefore paper with sufficient porosity level will be required for printing. to print on Paper deployed for different processes of printing. Porosity is an important factor when used on high speed Web Presses as the paper may not rapidly absorb the ink to commensurate with the speed of the press. At the same time a highly pores paper will tend to curl and may not properly get stacked in the delivery pile.

    4. Sizing :


    In order to smoothen the surface of the paper for better printability and to fill up the gaps in the fibers to strengthen them that forms the paper surface, the paper is coated with special material called sizing material. They include PVA sizing, Alum, China Clay and other such material. This is done during Paper making process and also done to prevent the paper from absorbing too much moisture.

    5. Opacity

    Opacity is the measure of how much light pass through a sheet. A perfectly opaque paper is the one that is absolutely impervious to the passage of all visible light. It is the ratio of diffused reflectance and the reflectance of single sheet backed by a black body. Opacity is important in Printing Papers, Book Papers, etc. The degree to which light is not allowed to travel through a substance is called the opacity of the paper. If the opacity of the paper is more it will cause show through of the print i.e showing the front side printed matter onto the back side of the sheet of paper. Papers that contain more fibers- thickness- , degree of bleaching of the fibers, and the kind of coating etc have the ability to hold the light thus preventing the print to show on to the backside. One should understand that the thickness of paper alone is sufficient to increase the opacity , sometimes even the thinner paper will have more opacity than the thicker paper because of the fiber and filler contents.

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

    Monday, February 18, 2013

    Know everything about Paper -2

    Know everything about Paper -2
    (Written by : N.R. Jayaraman)  


    The Qualities and use of of some of the  varieties of paper  are:


    a) Writing Paper is generally made of wood or Esparto pulp and are fully sized so that the printed image or written matter does not bleed through on the other side.
    b) Kraft Paper is high strength paper made from wood pulp. They are generally meant for wrapping and packing and are used for making grocery bags, envelopes etc.
    c) Packing Paper  is   paper or paperboard used for wrapping or packing good.
    d) Paper for Security Printing : Generally all the security papers are made from cotton or linen rags to give high strength. These papers have both hidden and visible security features like security thread, water mark, invisible color fibers visible under special lights and other such features.
    e) Bond Paper: Originally these papers were meant for printing bonds (agreements) and other certificates. They are very strong and durable and has high finish some of which carry watermark too. They are also used for letterheads and printing many other print material. The thin bond paper is known as Manifold paper and are used for making manifold carbon copies.
    f) Air Mail Paper: Air mail Paper is lightweight with high opacity and good quality to withstand writing and printing . These are used for letters, flyers and other printed matter to be transported by airlines.
    g) Parchment Paper : Strictly speaking the parchment paper is made from the skins of goats or other animals. Vegetable or imitation parchment is also made to resemble animal skin finish. The acid gelatinizes the surface fibers and the dried surface is grease-proof, has a high wet strength and is very resistant to disintegration by water and many solutions. The artificial parchment paper is used for packing mainly bakery products as they have non stick surface.
    h) Granite Paper : The Paper with mottled effect used for greeting cards and other specialty printing.
    i) Linen Paper : The Paper manufactured giving linen finish to the surface used for Greeting cards, invitations etc.
    j) Acid free Paper : A type of paper, which does not contain any acidic substance that may affect acid sensitive material. Paper mostly used for printing those which require to maintain the whiteness and stay durable for many years without deteriorating early as the archival documents are exposed to heat and cold in several manner. The natural acid content of the wooden pulp is neutralized to give durability to the paper.
    k) Laser Printing Paper : The Paper meant for use on Laser printers are specifically formulated for strength, surface, and moisture properties to meet the operational requirements of those machines. The special Laser printing Paper prevents incorrect feeding, jamming in rollers, and damage to the copying equipment. may occur if incorrect paper is used. Dust and lint produced by recycled papers can build up in the printing unit and cause stacking or jamming in the rollers while the machine is running.
    l) Tissue Paper: Tissue Paper is also low quality either glazed, unglazed, or creped, and are used for a variety of purposes. Examples of different types of tissue papers include sanitary grades such as toilet, facial, napkin, towels, wipes, and special sanitary papers. Desirable characteristics in these types of tissue papers are softness, strength, and durability apart from appearance.
    m) Art paper : High quality printing Paper specially made for printing high quality photographs and illustrations especially by Letter press printing. The Paper has coating on both sides with some material like China Clay, Kaolinite, Calcium Carbonate etc. Chromo paper is one such Paper under this category. 
    n) Antique Paper : Printing paper having good bulk and opacity with rough or matte surface for printing invitations, Greeting cards etc.
    o) Azure laid Paper : A laid paper usually bluish green in color having a good writing surface. 
    p) News Print Paper : Light weight wood pulp paper of cheap quality used for printing News Papers and Magazines. It has high tensile strength to give high folding resistance quality .
    ............To be continued