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'

Tuesday, October 25, 2016

Unique Security feature in Digital Printing



(Written by N.R. Jayaraman)
 
For the first time in the world of Digital printing, we were amazed to hear that sometime in the year 2010 or so, a not easy to reproduce security feature, printable by Digital printing has been developed by the pioneers in the field of Graphic arts products- M/s Kodak Ltd. One of the giants in the manufacture of Photographic products like films, papers and systems all under the roof Graphic systems, M/s Kodak continues to contribute their innovations to the print industry. Their ‘NexPress’ Digital printing machine is feather in the cap of Digital printing technology which has Fifth Imaging Solutions beyond CMYB or CMYK (Cyan, Magenta, Yellow and Key colour i.e Black) printing process. Perhaps for the first time, the application of security feature in print form, not easy to counterfeit on Secure documents have been made possible in the Digital Printing using dry ink (toner).


The Kodak NexPress is the world’s best Digital color printer as per the industry news. Larger color gamut is reportedly available in this machine more than that reproducible by CMYK and this Digital printer offers to print close to 85% of PMS (Pantone matching System) colours using dry powder technology. NexPress is four color process commercial Digital printing and has the look and feel of offset printing. This machine is featured to even allow colours to be printed in different sequences and combinations, broadening the spectrum of applications that can be produced.

A brief on Pantone Color Matching System will be useful to understand the impact of the colour effect NexPress offers.  The Pantone is a standardized color reproduction system uniformly used by different printers in different locations around the world, to reproduce identical colour effect of any specific shade on any material printed. The Pantone system has 1114 colour spots all of which cannot be simulated by conventional CMYK process of printing and the colours in Pantone are described by their allocated number. Each shade in Pantone colour is a mixture of certain % of different colours to arrive at the specific shade.

The Pantone colours are in the form of chip books, each one of them showing how the same colour will look on Coated, Uncoated and Matt finish stock. The printer will be able to pick up the exact shade of ink for all kinds of stocks to be printed- coated, uncoated, matt finish or even plastic based  on which the prints are made. For example, the specific colour is very essential in the registered or patented logos and other registered or patented  printed images
as standardized by the firms. Whatever print material the firm produces, they expect the very same colour shade to appear in their logos or print images (registered shades) printed on variety of stocks such as coated, uncoated, matt finish or even plastic based. The shade has to be same on every bit printed. They may be printed in different locations too.   The printers adhering to the Pantone system without direct contact with one another can match the exact colours printed in a press by using the Pantone colour code inks. Though Pantone is not the only color standardization system available, world over it is perhaps the most widely used system which most of the standard printers understand. Therefore printing close to Pantone colours will be a big leap forward in the art of Digital Printing .

Coming back to NexPress, as per user industry, the NexPress reportedly offers excellent image quality and a shade better than Offset suitable for all applications. NexPress seamlessly prints on virtually any kind of paper—coated or uncoated, textured or smooth. NexPress offers saturated high-contrast colours and crisp detail better than the one reproduced through Offset or by photographic image reproduction process on coated and uncoated papers. 



The machine supports use of a wide range of substrate types for printing in several sizes, weights and thicknesses. The machine has five color configuration, the fifth being imaging solution that enable gold printing effects. In an exhibition held in Drupa, the M/s Kodak reportedly showcased Gold print solution accompanied by samples of Pearlescent and Neon print options through the fifth imaging unit on NexPress Digital printing machine, all with Dry toner inks and not wet inks. The expansion of Gold and Pearlescent and Neon print solutions to Digital printing with dry toner will pursue new customers and market so claim the market watchers.

It is claimed that the major advantage of NexPress is the upgradability available on all the NexPress machines including for adding new inline UV coating which gives gloss and satin finish to the prints again through the fifth imaging unit solution. NexPress is able to produce  unique invisible 2-D and QR bar codes on promotional and direct mail material to help track the forged material/products and also be able to print Dimensional Printing (2 and 3 D print). 

 

Besides above the features the other important major breakthrough in Digital Printing is the possibility to print security feature using a patented Red fluorescing dry powder for the protection of documents, packaging and promotional products and direct mail material. Kodak NexPress RFDI (Red Fluorescing Dry Ink) a patented product of Kodak, is transparent and virtually invisible to the naked eye when printed but show red fluorescing when viewed with appropriate wavelength in an ultraviolet (UV) light source as supplied by the firm as testing gadget. Red Fluorescing Dry Ink is applied inline, and is ideal wherever visible bar codes are used for workflow automation, mailing systems and even MIS (Managed Internet Service which gives high speed dedicated internet access to stay connected with customers, business partners and employees) connectivity.

The Red fluorescing dry powder ink allows clear bar codes to be printed inline  encompassed with variable data printing, allowing each printed piece to be marked with unique information. When the invisible part of the print is illuminated with an ultraviolet light source it fluoresces a red colour. The intensity of the red can be controlled by the amount of Red Fluorescing Dry Ink that is printed on the page.

Kodak NexPress Red Fluorescing Dry Ink called RFDI which reportedly provides increased security to printed documents especially for the publishing and packaging industry. The RFDI has also passed all health and safety regulations. It is claimed that the invisible ink can be used to print unobtrusive images and non-reproducible bar codes on prints of secured documents, which then can be read with specialized bar code readers thus enhancing the security feature. For printing Red Fluorescing Dry Ink the machine requires installation of the RFDI station in the Fifth Imaging Unit, attachment of which reportedly requires less than 30 minutes so say the users forum.

Two units in India - Kozhikode in Kerala and Coimbatore in Tamilnadu are reportedly equipped with NexPress machines.

Friday, October 21, 2016

Inkless and erasable ink technologies

Inkless and erasable ink technologies

(Written by N.R. Jayaraman)

Printing technology has moved far away from the conventional system of inking the plates or blocks for printing the images on paper. The conventional method of printing has extended its wings to Digital printing, Inkless printing and reusable paper technology, slowly discarding conventional mediums such as use of printing plates, ink and other material. In several diversions  part of technology is opening  up the avenue for  the use of the once printed paper several times without  subjecting them for re pulping for re use immediately after one time print. Also the diversion was towards no ink or dry ink technology. At the same time it is also equally true that the normal use of ink or paper for conventional printing cannot be eliminated and they have their own importance or need for certain fields.

In earlier era, multiple copies of circulars, notices, agenda, pronouncements and announcements, minutes of meetings etc used to be issued on prints reproduced through small branch of printing called duplicating machines (Cyclostyle) using cut stencils or  small time manually operated Xerox machines using coated selenium plates or print through typed, xeroxed, hand drawn or hand written Paper masters on table top mini offset machines called Rota print. However  though liquid ink was used on mini offset and  duplicating machines, the quantity used was  not even one tenth as used to be on normal printing machines. Powdered toner ink was used on photo copiers.  


Once print was made on the paper the same paper could not be reused unless recycled and reprocessed making fresh paper. Though these days the electronic prints i.e prints on electronic media began to be used to reduce to load of Ink and Paper which indirectly impacted the environment, still in certain areas print on paper remained necessary. 
 
A survey revealed that it was universally practiced phenomenon by majority of users in several industries that huge part of printed copies such as recorded minutes of meetings, seminars and other discussions in use in the business firms and companies were disposed off within 24 hours and not retained permanently as they were meant to be preliminary draft or notes for discussion or follow up note of briefs for next plan of action etc and once the use of contents in the copies were over, such printed papers were discarded by shredding or torn and thrown away. 
 
The process of producing multiple prints using stencils and copies from Xerox helped in the cause of environment control by reducing the load of liquid, oily printing inks even though those processes did not fully eliminate the use of inks in some form or the other- liquid or dry. Similarly they could also not reduce the consumption of paper as well. In pursuit of achieving ink less printing and reusable paper technology without subjecting them to re pulping immediately after one time print, world over research continued to find alternate technologies to replace ink and one time only usable paper. It was realized in the industry that even partial reduction of use of ink and paper will help in the direction of pollution control and cleaner environment from the print industry.  


In the direction of reducing the paper and ink, first came the thermal printing machines, simpler to operate, durable and dependable for short run copies. Special pre coated chemically treated paper- perhaps embedded with some kind of dye crystals reacting to heat was used on Thermal printer. The heat beams from the machine fused the areas where the images had to appear resulting print to appear the way it was typed or fed from memory console, which in one sense was photographic based technology.

A different other thermal  machine used chemically treated ribbon which when targeted by the light beam melted the ribbon to stick to the paper surface to print the text. Mass quantity of prints could not be however produced on account of cost.  Different kinds of chemically treated  paper were also not fully Eco friendly. The recycling of the chemically treated paper for reuse posed certain other issues. Thus in this process, only use of ink was eliminated, but not the paper. The paper once used could not be reused again.

The research kept on continued for the invention of many time reusable paper with erasable ink the effort of which enabled the emergence of both ink less printing and several times reusable paper for use on Xerox and Fax machines without need to recycle the paper immediately after one time use.

Pioneers in the field of electronic products, Toshiba took lead in the innovation of reusable paper for printing (Copying) with erasable toner (ink) from its surface so that their invention would lend big helping hand towards the cause of environmental protection from print industry. The firm reportedly developed a machine that enabled the machine to erase the printed images from the surface of the paper so that the same paper can be used multiple times for printing (copying) after erasing the contents again and again. The firm claimed that the ink or toner worked like a normal ink but when subjected to certain amount of heat it became invisible print thus allowing the user to reprint some other text on the same surface of the paper. 


 
Technically the toner that had formed the image became colorless transparent one due to reaction from heat, but in effect, the toner still stayed over the paper invisible to human eyes. Once the purpose of the print taken was over, the print could be erased for reuse of the same paper again. According to the spokesman, the paper with erasable toner is reusable up to five times which may play big role in reducing paper cost. Also, in the machine which probably is still under exhaustive testing, there is an option to scan and save the printed texts and images subjected for erasing, so that as and when needed they can still be reprinted. For the present the reusable paper, toner and the unit is reportedly developed only by Toshiba. 

Like Toshiba, the Xerox Corp too reportedly come out with a technology that enabled auto disappearance of the print from the surface of the paper. Though it is not known whether the machine has come into the market, the process in development reportedly is a machine whose intake was special paper for printing but the images printed lasted only for few hours i.e up to one full day on their surface. The firm claimed that the machine will not need toner or traditional methods of printing process. Instead a light beam with specific wavelength was used as writer and the image once formed as dark readable print can also be erased by heat instantly. However if left as it is the prints disappeared on its own in the next 24-48 hours period.  
 

Thus three types of innovation under development may in future replace the ink and paper and and pave way for the introduction of many times usable paper and erasable ink. 
========================== 
End Note: Entire illustrations shown above are all artistic impression of the author to explain the concept of the technologies in offing

Saturday, October 8, 2016

The difference between commercial and Security printing

The difference between commercial and Security printing 

(Written by :  N.R. Jayaraman)

Though one refers the printing processes as Letterpress, Offset, Gravure, Intaglio, Screen printing, Flexo printing and latest as the Digital printing, the term Security printing process is not one amongst the independent printing processes, but it is an extension operating with some of the basic process from them.

Security printing is theoretically a congregation or combination of several printing techniques interlinked to protect the print on the essential documents produced for specific need especially for the use by Governmental agencies. Such documents include Currencies, Bank Notes, cheques, Passports, Certificates, ID cards, Stamp papers, university certificates, and Licenses etc.

On another side the same concept of Security printing has also been extended to the production of Brand protection covering labels of pharmaceutical products, automobile parts, life saving drugs, and many other such important documents which have higher face value in terms of product as well the price compared to normal products. Higher value does not reflect the aspect of cost alone, but even lower priced ones require protection against counterfeits to retain the specialized brand name prestigious to some of the firms in the midst of overwhelming percentage of goods counterfeited and that the counterfeiters are not diminishing.

In light of this background a significant section of the Graphic arts industry practices the art of Security printing. Protection of print through the process of Security printing has secure operational procedures and features to prevent a print being forged or counterfeited with same appearance along with their inherent qualities, and the forged ones remaining undetectable to public eye.

However even the Security printing practices have their own limitations in curbing the menace as the counterfeiters practice the art of counterfeiting with more impunity using relatively low cost technology that includes digital computers, color copying machines, and image scanners. Thus, it has become extremely important for Security printers to remain ahead of counterfeiters and forgers by using the latest security features and aspects.

How different is the Security Printing compared to conventional art of printing? How are the prints on documents protected ?

If you need an answer first one will have to understand the basic process involved in the conventional and the Security Printing techniques before understanding deeper concept of Security Printing. 


Conventional printing process:-
In conventional printing process the first stage is to convert the multi tone originals into several printable plates or blocks to reproduce multi colour original effect on print. This is achieved by super imposing primary colours, one colour above the other by the technique called colour separate and then print. At least four basic colour separated plates/ blocks are required to print in individual color components like cyan, magenta, yellow and black colours to match the original.   
The coloured original may comprise of many shades and the shades too in different hues and tones. For example the shades may be bluish green, darkish green, pinkish, pure blue, pure yellow or pure Red while several other shades have merged with them. Let them be any shade or colour, always remember that they fall within the range of Rainbow spectrum of colours only. Thus the effect of any shade is as closely as possible archived on print by reproducing them with three to four plates using primary colour inks. This means the primary colours produce secondary and tertiary colours by different tonal values of the primary colours. Say yellow plus blue gives green. Blue plus Red gives Violet. Red plus yellow gives orange and yellow plus Red plus Blue may give black etc. The conversion process, i.e original to printable image format, is carried out to prepare a basic material for making the plates/blocks. The basic material is photographic films called halftone and continuous tone negatives or positives through a process camera or a scanner. Generally in the conventional processing technique a set of four halftone negatives/positives are prepared using colour filters and halftone screens to print yellow, cyan, magenta and black colours on paper to render the true colour image as per original copy - all processed manually. However with latest developments even direct to plate equipments supply colour separated plates/blocks replacing the manual processing photographic techniques. 
Once the colour separated halftone negatives/positives are prepared, so many plates and blocks are prepared and each plate or block is printed with four basic coloured inks such as cyan, magenta, yellow and black, known as CMYK. While registering the images on the substrate on which they are printed the dots in each plate sit in an angle of 15 to 30 degree from each which in technical term is called juxtaposition of dots and give the desired colour effect as close as possible on print. 
Unless halftone screens are used, the continuous tone shades in the photos cannot be converted into printable form. And unless the screens are positioned in a particular screen angle with a difference of 30° for each colour separated negative or positive, the juxtaposition of dots i.e. printed side by side cannot be achieved and all dots will fall one upon other to give one single colour image. Again the resultant image will be one dark image.

This is the basic structure of processing in the conventional printing process, whether it is Letterpress, Offset or Gravure.

Security printing process:- 
The basic processing is the main deviation in the case of Security printing compared to the conventional printing. Security printing technique is devoid of colour separated, halftone screened negatives or positives to reproduce the original colour print. Further the primary colour inks like Yellow, Magenta and Cyan are also not used to print juxtaposition of dots to reproduce the coloured original. No screens or colour filters are used for colour separation. In short, basically the Security printing is reproduction of the coloured original in true form incorporating lines and other patterns of varying sizes and thicknesses on the plates or blocks sans juxtaposition of dots on print.
The photographs or portraits are first converted into elements consisting of minute dots and lines of varying thicknesses, wavy patterns, Guilloche designs and several types of straight lines and with micro letters in between.

The artist converts the continuous tone photographic image or portraits into various tonal values with lines, dots and other patterns by hand engraving them on metal blocks which is used as base for further processing. The separately engraved blocks with shades are finally joined together to form the printable image as close as possible to the original. Now automatic processing equipments and machineries have also come to convert the continuous tone images of the original to the desired pattern printable as line work.

Since the colour original is not colour separated into three or four colour negatives or positives using colour filters and screens they remain difficult to colour copy or counterfeit. If the security printed print is copied, the lines will be converted into several minute pixels instead of continuous lines or wavy lines due to use of different angles in the engraved elements and therefore the forged one will not match with the original design elements. To naked eye it may appear to be near original, but even with a small magnifier the print will reveal it to be counterfeited.


How are the colour effects arrived on the reproduced prints then ? The various colour effects are not derived by super imposing the images one on top of the other using conventional shades like Yellow, Blue and Red. The relief images from Dry Offset plates or images from plane plates of Wet Offset are printed in subdued colour combinations through a process called Rainbow printing in which the colours merge in a varying, uneven manner creating a spectrum of colour effect. This again makes the copying difficult to reproduce by colour copying or scanning. 

 In Security printing different colour shades are formed wherever the design elements cross over in Rainbow printing. The colours used are also subdued and are not easily copyable to reflect true tone of the original either by a scanner or in colour copiers. Moreover Ghost images and Latent images are printed using special technique which is not possible in conventional printing process. These are some of the major specialties in Security printing.

How the images on print gets further protection from forgery or counterfeiting is by the use of several elements in combination like overt and covert features such as layers of colour elements printed one on top of other, intricate designs, special inks, the tactile feel of inks and completely different printing techniques deployed. Generally three levels provide security on the print. Level one may be by overt features, such as optical variable ink and watermarks, security threads etc identifiable by naked eye. Level two may include the covert features which may require certain gadgets or instruments like a microscope, enlargers, UV lights, Infra Red lights etc to authenticate the features. Level three may be most complex, involvement of certain chemicals such as markers or taggants mixed with printing ink which can be authenticated only by specially designed user specific Gadgets to read the material as supplied by the same manufacturers who supply the taggants or by specially trained forensic agencies and chemical labs.

The machineries and equipments used in the production of the security documents employ only the same basic machineries and equipments used in conventional printing, but the difference is that they are modified ones to transfer the images with special inks, intricate processes with special attachments. Prima facie the Security Printing too is only an extended arm of conventional Offset, Letterpress and Gravure printing techniques, but deployed in modified manner through modified machineries and equipments.

The background designs in security printing consist of intricate lines and patterns that do not copy or scan well. Since they are generally printed in lighter colours, designs in several areas disappear when scanning is attempted. The design elements such as Guilloche patterns, invisible image, Ghost images, E-Beam image etc are produced with very special inks. The micro letters printed are so small (about 1/100") that it may appear as a solid line and if photocopied or scanned the letters will becomes a solid line. The Ghost images are also invisible on print and appear only when viewed in one or two directions. Therefore if scanned or attempted to colour copy the images is resorted the designs will break into pixels instead of lines or dots as per original.

Even conventional Wet offset and Dry offset machines are used as one part of security printing to print base elements over which the other design elements are placed using Colour changing inks, Thermo inks, Solvent sensitive inks, OVI, Magnetic inks, Bio-metric inks, Fugitive inks, invisible inks, Taggants Coin reactive inks, Bleeding inks, UV Invisible Fluorescent Inks, Erasable inks, OVI, Penetrating inks, Magnetic inks, Thermo chromic inks, Infra Red inks, Fluorescent inks, Magnetic inks, Chemical reacting inks etc through user specific machines specially manufactured for use by them with special attachments.

Generally the dotted designs are avoided as they can be easily copied. Since the colour original is not colour separated into three or four colour negatives or positives using colour filters and screens for Security printing they remain difficult to colour copy or counterfeit.

Another major aspect in Security printing is the use of special substances on which the prints are taken. While in conventional printing process, various kinds of paper substances and substrates including plastic foils available in the market is used, in Security printing only specific and specially manufactured substrates and Paper bases are used which are end user specific material made to order and not available elsewhere in the market except with the manufacturer who will also be not supplying them to any other user.

The others elements that add up security on the prints are OVD patches,Holograms, Hot stamping, use of specific instrument detectable Taggants in ink, highly sensitive water marks, product specific printing concepts like PEAK and STEP etc and many other such products available with the manufacturers of security processes which are extremely difficult to copy for counterfeiting. The special effect and type of numbering is another important aspect in Security printing whose numbering boxes are not supplied by general numbering machine manufacturers. They are country specific or user specific made to order and numbering on the wheels that print them are engraved manually, not available in market.

In short the security printing processes has a fleet of specialized machineries and equipments as though they are made for each other. They include end to end usable process in which the entire sheets printed are cut to specific sizes, contain specific no of pieces per bundle, strapped, polythene wrapped, shrink packed and labelled all in one process, one machine, entire operations automatically carried without manual intervention.


Machinery and equipments used Security printing process:-
The reproduction of the above security documents are carried out by specialized machineries and equipments as below:

Dry Offset Printing: The process involve use of plates having the images to be printed in relief format. The machine prints on both sides of the completely room conditioned paper/substance in one pass in perfect register. The most difficult registration process involved in this is see through register in which a complete image is split into two parts, and each part is placed on each side of the sheet. When they pass through the printing machine the images fall exactly in same position on both sides in one pass and when the sheet is viewed against light, you can see the complete image in perfect registration.

The second most important aspect involved in this process of printing is rainbow pattern of printing- several shades side by side, one after the other in which subdued colours are used. The colours merge and show the image in series of shades.

Intaglio printing: The substance on which the image is printed takes almost few tons of pressure on them and show raised image on the surface which can be felt by the touch of finger. The images on the plate will be sunken and uses specialized hard ink which when dry gives relief.

Inspection of printed sheets before numbering: The entire sheets printed by Dry Offset and Intaglio are manually inspected to sort out the all good sheets and sheets with defects.

Numbering: Several numbering boxes are fitted on this rotary machine which numbers the sheets in the pattern set. The sheets are numbered either in continuous numbering pattern or part numbering of all good prints.

Cutting and packing: The numbered sheets are again checked to mark defective sheets and processed on automatic cutting cum packing machines in which the entire sheets printed are cut to specific sizes, contain specified no of pieces per bundle, strapped, polythene wrapped, shrink packed and labelled all in one process, one machine, entire operations automatically carried without manual intervention.

Thursday, October 6, 2016

What a printer should know about ink ?

(Written by N.R. Jayaraman)

ORIGIN OF INKS
 
Do you know the root of present day printing Ink ? When the era of displaying something in writing began, in 2500 BC some kind of writing inks were prepared in Egypt and China by mixing soot (material drawn out from black smoke) with natural gums which were made into the shape of sticks and rods and dried. Subsequently they were dipped into water and used as black colour pencil like medium.

3000 years or so when Chinese introduced some kind of printing, they used coloured earth material, colours derived from plants and vegetables and mixed them with gum to give a colour it and used them as ink to apply on the engraved  wooden blocks for printing on some substance. However invention of actual printing ink came up only after Gutenberg invented the printing process in the year 1440 or so. First he too used only soot as the base material for making black coloured ink and mixed it with oil instead of gum and used them for inking the engraved blocks for taking prints. Later on as technological developments began to appear, the printing process itself progressed, and coloured inks began to be used with oils and varnishes as medium to carry coloured pigments.

Various types of printing Inks  are in use today to suit the needs of several processes of printing carried out by different types of printing machines. The printing Inks are formulated with specific qualities to suit each process on which they are deployed such as Letterpress Printing, Offset Printing, Intaglio Printing, Gravure Printing, Silk Screen Printing, Flexographic printing and finally Digital Printing. Yet the basic structure and composition of the ink remains same except change in material and % of composition, only the carrier vehicle or medium changed.


HOW DOES THE INK DRY ? 

 
Any printing ink for that matter dry only by three means on any printed surface. The process of drying takes place by:

  • Absorption or penetration into the substance on which the printing  takes place.
  • Oxidation- when the oxygen in the atmosphere reacts with the ink over a substance the layer is oxidized by natural forces thereby taking away the wetness from it to firmly stay over the surface.
  • Evaporation process, though similar but another kind in oxidation process, allow the solvents in the ink to quickly get released from the printed ink by evaporation  to allow the particles to solidify and remain on the printed surface.It applies to inks with alcohol base.
  • Polymerization which is oxidation cum evaporation process. It applies to highly viscose oily inks.
  • With special formulations, the ink is also made to dry by curing with UV light, hot air etc without getting their hues affected.
Whatever is the means the mode of drying of ink on a substance on which they are printed,  the theory is that  slight penetration by the solvents of the ink do place on the surface, lest they will be chalked away from the surface. The penetration would be to the extent that the base of the ink has some hold on the surface on which it is printed. 

One crucial factor to be borne in mind in the process of drying is the Ph of the substance used. The Ph factor has direct relation to ink drying properties.
Based on the speed of drying required, the ink formulations are modified.
 

COMPOSITION OF THE INK 

The composition of the ink generally confines to these components :- 


1. The colorant or Pigment:- The Pigment is an important material in the formulation of ink. The Pigment is in the form of finely ground powders or granules and acts as the coloring agent. The amount of pigment used influences the color strength of the ink.

  • Two types of pigments are in use. They are Organic and Inorganic pigments. It is suffice if we know the basic difference between them as it is scientific subject.
  • The Organic Pigments are derived from chemical process and from plants or products of plants; they have smaller particle size; bright and transparent; have high degree of colour strength properties; usually safer to handle but are slightly expensive and therefore used on costly inks.
  • The Inorganic Pigments are derived from metals or minerals; are larger in particle size; more opaque in nature; often dull in shades with low colour strength properties; not fully safer to handle, but are not expensive. They get easily dispersed in carrier.
2. The Carrier Vehicle like varnishes and oils :-  Different types of varnishes are prepared to suit different kinds of inks, but they are all made by mixing the resins, solvents and additives to form a homogeneous mixture. The Vehicle or carrier of the pigment is the liquid that holds the particles of pigment and other material together and facilitate free flow of ultimate ink on the ink rollers and ink fountains. Varnishes and vehicles play  critical role in ink manufacturing as varnishes and vehicles also affect the final properties of the ink, such as printability, resistance properties and visual characteristics. While pigments provide the color, varnishes and vehicles are responsible for carrying the pigments to the substrate on which it is printed.
  • Though there are many kinds of vehicles available in the form of Oils and Varnishes, generally processed varnish is used for mixing with the pigment.
  • The type of vehicle used can affect both the shade and the value of the ink color. The color of the vehicle itself, its ability to wet the pigment articles, and even the chemical interaction between the vehicle and pigment can affect the shade or purity.
  • Sometimes in combination with certain solvents they are also added to adjust the viscosity of the ink.
3. The Modifier or Driers: - The modifiers also called driers are added to control the drying properties of the ink to suit specific process for which the ink is intended. They also play significant role in other factors such as smell, scuff resistance, and fading. 

4. Resins:- Resins are primarily binders that bind all the ingredients of ink together so that while printing on a substance it binds the ink to the substance. They also contribute to glossiness, resistance to heat, chemicals etc.
 

5. Wax:- This promotes rub resistance.

MACHINERY AND EQUIPMENT FOR  MANUFACTURING INKS:- 

 
How are the final inks made ?  Only limited machineries and equipments are available for manufacturing the printing ink. Once the Varnish is manufactured, the process of ink making begins by mixing pigment with the varnish. The pigment added with the varnish in a big drum is mixed well by mixers. 
While mixing  the pigment  does not get dispersed well with the varnish and remain in clump form. Those clumps must be broken up and the pigment dispersed evenly through the resin into the varnish to make it an effective paste.  Therefore the  Pigment cum Varnish clumps must be broken up in such a way that there is complete dispersal of pigments into the Varnish. This process is done on ink grinding machines called Roll mills.

The printing inks are generally ground through the three roll mill, a heavy duty ink grinding machine where three cylinders running in opposite directions grind the heavy clump of  pigments already mixed up along with other components and varnish  to break down the clump of agglomerates to the desired pigment particle size. With selective pressure between rollers, selective speeds and selective temperature maintained in the cylinders of the Triple roll mill,  the clumps of pigments are evenly ground to make necessary thickness of pigments (in microns) to suit the printing machine requirement.

Of course though other than Triple roll mill, there are no of other types of machineries and equipments in many sizes are available to do this process of grinding and mixing Pigments with Varnish, only the triple roll mill is used by the major ink manufacturing units.

Three roll mill is especially effective for pigment dispersion in high viscosity paste for offset and Intaglio base inks. However it will be difficult to mill  liquid ink on a three roll mill since the solvent will evaporate in the course of running.

TYPES OF PRINTING PROCESSES AND PROPERTIES OF INK USED:- 


Letterpress printing is one of the oldest printing techniques by which the copies are produced by repeated, direct impression from  inked block or composed type matter. Most of the presses earlier were flat bed type till the Rotary printing came.

Since Letterpress process involves printing  by relief imaged blocks or composed metal types, the ink properties should be such that it stick on to the surface of the metallic images and then transfer the same amount of ink on to the surface on which they are printed. Therefore the ink should neither be very hard, nor very soft.

Since the blocks or type matter directly contact the paper surface, the inks formulated are such that they dry on paper without pulling away the paper fibbers from surface as the inks are slightly more viscose (thicker) in nature than the Offset inks. Also the inks will have to quickly dry on the coated surface of the paper without causing back side impression called set off. Whether the Letterpress printing is done trough Rotary or the Flat bed machine, the basic properties of the ink used in them remain the same.

Letterpress uses moderate thick (paste) inks whose tack varies according to the speed of the machine deployed. The type of substance used in this process is both coated and non coated paper and therefore the ink required for this process is to dry by absorption (penetration), oxidation, or by polymerization through evaporation depending upon the kind of stocks being printed.  Since the highly clay coated art paper is preferred to be printed by this process, the ink used has to dry by oxidation cum polymerization.

Almost all letterpress inks are translucent which means that when one color over another is overprinted it creates a third color. It also means on large inked areas, you’ll see a little paper show-through. The technologist say that the letterpress ink generally consist of 15 to 25 % pigments rest being varnish, driers, resins etc.

Offset Printing inks are more viscous than other types of inks, and since the ink film is thinner with offset printing, the pigment content must be higher which is up to 25 % as the technologists say. Offset presses deposit ink films that are about half the thickness of films deposited in letterpress process. And since offset printing is based on the fact that oil and water do not mix, inks formulated for the process contain significant amounts of water-repellent materials. The inks may have to withstand reaction from the fountain solutions which may sometimes be used in some of the wet Offset machines and therefore the inks should not emulsify and impair the body of ink, its shade or drying properties of the ink or cause tinting on the non printing areas of the plate and printed sheets.

Unlike Letterpress process which print on the substances by relief plates, the Offset process has two divisions in printing techniques - one printing on surfaces by relief image plates and the other plane surface plates. The Dry Offset printing machines have no water fountain to wet the plate before inking as the plate have print areas in relief format. The ink from the rollers get directly charged on to the relief plates and are therefore different from the ink used on wet Offset printing machine. The ink used on the Dry Offset machine however has different qualities as against the inks used on Letterpress and wet Offset inks. The quality of ink used on Dry Offset is such that a thin layer of ink from the plate is transferred on to the blanket surface without smudging and set off.

Sheet fed offset presses primarily use partial quick drying inks, which dry rapidly without the drying apparatus. However some of the modern Offset machines are equipped with radiation curing devices, as is needed for quick-set infrared ink, ultraviolet curing ink, and electron beam curing ink and therefore the composition of the inks are entirely different than conventional Offset inks.

The Web offset inks tend to be less viscose and have less tack than sheet fed Offset machine inks.

In Intaglio printing, highly viscose ink is used and the composition is made in such a manner that the pigmentation is very heavy, and the varnish used have higher tackiness compared to other processes. The qualities of the ink used in Intaglio will be such that it tends to slightly loosen while inking the plate due to heat generated apparatus fixed in the ink fountain and the plate cylinders. At the same time, once the ink is transferred on to the substance on which it is printed, the ink has to slowly dry on the substance by slight penetration cum oxidation cum polymerization process to ensure that the relief effect of the ink required is also not lost.

In respect of Screen printing inks, the composition has higher Pigmentation (say 30 % as technologists say) rest being Binders, solvents and additives. Screen process printing requires paste inks that are thicker, but able to pass through the small holes in the screen and leave sharp prints on the substance. They must also perform well under the action of a squeeze which is used for pushing the ink into the screen holes. The binder added to screen printing ink must be compatible with the surface on which it will be printed. The solvents used should also not be overly volatile, as early evaporation would cause the remaining ink dry non the screen.

In Flexography Printing Process liquid ink used which  has to dry very fast as this process is used to print on corrugated boxes, multi-wall sacks, paper sacks, plastic bags made up of various materials such as plastic, paper and others. The printing plates are flexible and made of rubber or plastic. The  ink  used is mostly water based and the process of drying of ink is by evaporation. The solvent (vehicle) is made up of an alcohol, ethyl, propyl, or isopropyl etc. The vehicle is generally alcohol based ones as it facilitates quick drying by evaporation. Typical resins used in flexographic inks include acrylics, cellulose esters, nitrocellulose, poly amides, modified rosins, and ketone etc.

The principle components of the ink used in Gravure printing is also alcohol based and materials like esters, ketone, glycols and water are used for the solvent part and cellulose, vinyl, acrylic and polymers and organic and mineral pigments are added for coloring and other properties. The selection of solvent should be such that the pigments dissolve in the binder and eventually evaporate during drying process. The ink used on this process should have higher colour value and being liquid, it has to stay inside the pits on the cylinder and also transfer the ink on to the paper surface in true tone and strength without causing smudging on the edges.

The inks used for Ink jet printing consist of dyes mixed with a highly fluid vehicle or carrier that form very small drops by picking up an electrical charge, and can be deflected properly to fall in the right place for the formation of a printed character or image.

Inks used in Xerography or Electrostatic printing is called toner which consists of a fine, dry powder coated with the desired color imparted by a colored resin binder. No varnish or oil base is used for dispensing the pigments as it is dry printing process and ink gets fused by slight heat. The important consideration is not only the particle size, but electrical properties  as the  electrostatically  charged plate hold the image which gets transferred on to the surface of the paper.
 

REQUIREMENTS OF INKS 
 
1) Visual properties of inks are result of pigment in relation to the type of carrier or vehicle used. The properties include appearance, transparency or opacity, and gloss. The amount of pigment affects color strength of the ink, and the type of vehicle used can affect both the hue and the value of the ink color. The color of the vehicle itself, its ability to wet the pigment, and even the chemical reaction between the vehicle and pigment can affect the shade. Therefore the proper selection of vehicle and pigment is important to suit the specific process of printing for which the ink is made.

2) Since in multi colour printing, the colour overprinted on the previous colour printed below should be partially opaque but not to completely mask the color beneath it, the ink should have certain amount of transparency  to show the original colour printed below or to merge with them to form another colour wherever such colour changes are required to match the shades of the original. Generally on patch colour work the fully opaque ink is used and not when the printing is multi coloured reproduction having varying shades.

3) On the other side semi  transparent ink is also required in multi colour work. A semi transparent ink does not hide the color beneath it, but mix with them to create a third color. Therefore for the multi colour reproduction work printed by colour separation, the quality of the inks should be semi transparent. The choice of colorant and the degree to which it is dispersed through the vehicle are the most important factors in determining the transparency of an ink.

4) Another quality of the ink is glossiness. It refers to the ability of the ink to glow i.e reflect the shade as though it is shining. The extent of gloss depends upon the composition of the ink, thickness or layer of the ink film deposited on the surface of the substrate.

5) Runnability refers to trouble free running of the ink on press, i.e smooth flow of ink on rollers, transfer on to the the paper without losing the characteristic like body, temperature stability, length, tack, adhesion and drying etc. 


6) Viscosity refers to the characteristics of flow on inking rollers. Some of the inks used in different processes of printing are highly viscose and some moderate depending upon the press on which they are used. However whether they are highly viscose or moderately viscose they should flow evenly on the chain of inking rollers which carry a thin layer of ink to apply on the plate which transfer it to  the substance on which prints are made.

7) The ink has to withstand the heat generated by the friction  chain of rotating rollers. Normally the ink is manufactured taking into consideration the optimum temperature to which they will not lose their properties.  If however the ink reacts to the heat, then it will have deleterious effect on an ink’s body affecting the runnability.

8)  Length describes the tendency of the ink to form long or short threads when stretched or pulled from the ink fountain while mixing them on the running press. Length of the ink is very important factor for flow of ink. The best Inks are those which are neither excessively long nor short as excess of either one affects the runnability.

9) Tack refers to the stickiness of the ink. The ink should have sufficient tack to stick on the inking rollers but not to fly away from them and fall on blankets or plates as sprays of ink. The tackiness of the ink also play an important role in plucking away the fibbers from the paper surface. Too high a tack may pull out the fibbers from the surface of paper. In multi-color printing, the first ink printed must have greater tack than the ink that will be printed on top of it subsequently.