Security printing

What is the best printing technology to use for security application?

Different types of printing techniques are suited to different applications. Sometimes you need to carry a heavier weight of ink on the substrate in order for the security feature to work properly. In other instances you need to use a technique that uses a more delicate approach, so that the detailing in the artwork adds to the security. We discuss below the pros and cons of the different styles and what is most suited to your printing job.

Offset lithographic printing

Offset litho is where a printing plate (or image) is a mirror image of the final print. The plate collects the ink from the inking roller and transfers it to the impression roller through a chain of rollers. The additional rollers, especially the impression one conforms to the surface of the substrate you are printing on and allows for finer detail printing. This is great for producing guilloche and intricate designs as you would expect on cheques and other security documents. The downside of this process is that you are unable to carry much ink and can cause problems and issues where vibrant colours and security inks such as thermochromic are difficult to print densely enough.

The image that is on the roller is either made using a light-box, chemicals and film or more recently computer to plate units, which are able to take your artwork in electronic format and produce an aluminium plate ready to wrap on to the cylinder immediately. The plates are quite durable and can last for hundreds of thousands of impressions. Once the plate is removed from the cylinder on the press it can no longer be used again. You could look at this as a security benefit – as when disposed of, it would be almost impossible for a counterfeiter to use them again.

Each colour is applied through a printing station. On a litho press with 5 printing stations it would only be capable to print five colours in one pass. Some presses provide re-insertion – this is where you can re-reel a pre printed roll and feed it back through the press again. This would allow the press to put another five colours on the substrate – however, to keep costs to reasonable measures you need to know how many stations your litho printer has, as the additional costs of running a job twice may make the cost of your project prohibitive. Usually the minimum amount of heads on a litho press is 4 and more usually you will find 6 or 8 printing stations. If you are able to reduce the colours to allow for one pass then you can save money on your printing costs. Also the clever use of split duct printing can offer you two colours from one unit (find out here).

You will also find that offset litho presses need to have some form of drying unit. This is usually in the form of UV curing units. The printer would use special lithographic inks that have an additive that accelerates the curing when exposed to ultraviolet rays. This prevents tracking which is where the ink does not dry properly and tracks up the paper (usually identifiable as a ghost image repeating up the sheet).

We recommend that you get samples from your chosen litho printer to examine the quality of their work. Try to get copies of work with some block printing or with fairly heavy coverage as someone who can print this well, without any forms of tracking, and a good ability to keep colours consistent would be a good choice for your work.

Applications

  • Government and corporation document printing
  • Brand protection and asset management
  • Cheque printing and value documents
  • Tickets and event pass production

Suitable inks

  • Any offset lithographic inks (UV curing preferred)
  • Invisible Inks
  • Biometric and taggant inks
  • Thermochromic inks (albeit not as ‘apparent’ as flexo or silk-screen processes)

Suitable substrate thickness

  • Ranging from 40gsm up to approx 200gsm (if re-inserting then 160gsm max)

Costs

  • Plates are cheap (approx £10 per plate A4)
  • Set-up costs are relatively inexpensive (if 4 colours or less)

Things to watch out for

  • Substrate needs to be supplied on roll
  • Depending upon number of colours, expect hundreds of metres of make-ready losses
  • Weight of colours – process is not good for heavy ink coverage and may look a little washed out
  • Great for intricate details such as guilloche patterns and security printing artwork
  • Suitable for split duct printing
  • Machines normally have a wide web, 20 inches wide, allowing for two-across, or more production

Flexographic printing

CHECK – Flexo printing uses a raised tablet that makes direct contact with the substrate. The printing plates are normally made of plastic or rubber and can last as long as litho plates, if not longer, depending upon the substrate you are printing on. The ink can be supplied under pressure in a chamber and this method allows for much heavier weights of ink than offset-litho methods.

This method is especially good when printing inks such as thermo-chromic or where you need to carry more ink to make the security feature more effective. The downside to flexo (even though the technology is improving year on year) is the the definition is not as fine as offset litho. You will find flexo printing on packaging and shrink sleeves due to the amount of ink you can print, you are able to print opaque colours that are vibrant and are able to sit on the surface of plastic and polypropylene. Flexo presses also use dryers and UV or LED curing lamps to dry the image before going through the next print station.

Applications

  • Plastic packaging, papers and boards
  • Brand protection labels
  • Shrink sleeve printing

Suitable inks

  • Any flexographic inks (UV curing preferred)
  • Invisible Inks
  • Biometric and taggant inks
  • Thermochromic inks

Suitable substrate thickness

  • Ranging from 90gsm up to approx 350gsm – maybe thinner, if printing on plastic film.

Costs

  • Plates are cheap (approx £25 per plate A4)
  • Set-up costs are relatively inexpensive (if 4 colours or less)

Things to watch out for

  • Substrate needs to be supplied on roll
  • Machines come in different widths, some only 10 inches wide – check beforehand
  • Many label printers have this machinery already
  • Depending upon number of colours, expect hundreds of metres of make-ready losses

Roto gravure or Intaglio printing

Intaglio printing is the same as gravure however it seems that everyone calls it rotagravure these days (well, in security print anyhow), so we will treat them as one entity.

Roto-gravure uses an etched copper cylinder protected with a thin plating of chrome, this cylinder contains the image to be printed on the substrate and, as you can expect, is very expensive to produce. The benefit of this process is that you are essentially embossing the surface and leaving a heavy ink deposit.

Gravure impression cylinders range from a few centimetres wide, through to over 5 metres wide and are able to carry significant amounts of ink to transfer to the paper or material you are passing through the press.

Probably the most common example of intaglio readily accessible is on bank notes and currency. If you have a £5, £10 or £20 note to hand you will see the words Bank of England. When you pass your fingertips over the top of the lines that make the word, you will feel that the letters are almost embossed.

This is gravure printing and, as such, is really only used in circumstances where high security is paramount.

The etched impression cylinders cost many tens of thousands of pounds to produce, however they are capable of many hundreds of thousands, if not millions of impressions which makes them suited to high volume bank-note production.

Unless you are a government looking for one of the most sophisticated methods to protect bank notes then think again about intaglio printing, however it can be copied. Read on.

You can get similar effects to intaglio by using thermography inks. This chemical process feeds the wet print through a special machine that dusts the receptive ink with a powder. The substrate is then passed into a baking unit that fuses the powder particles together, creating a raised effect like an embossing.

We’re not sure how intricate this process can be (as usually intaglio uses thin lines and swirls), but this could be one way to potentially defeat the security found in intaglio printing, or at least be good enough for non-printing specialists to realise at redemption!

Applications

  • Banknote papers and boards
  • Passports
  • Government document printing

Suitable inks

  • Any Intaglio inks (UV curing preferred)
  • Biometric and taggant inks are a possibility

Suitable substrate thickness

  • Ranging from 90gsm up to approx 200gsm depends upon hardness of substrate

Costs

  • Cylinders are very expensive (approx £4000+ per A4)
  • Set-up costs are expensive

Things to watch out for

  • Each cylinder will print one colour only and machine usually only has one print tower
  • A very few providers of this process in the world. Usually only bank-note printers.
  • Depending upon number of colours, expect hundreds of metres of make-ready losses

Silk screen printing

This method of printing uses a silk screen or stencil (imprinted with your design) which is placed over the substrate. The benefit of rotary screen printing is that it carries the most weight of ink than any of the other processes we have described so far.

This allows for thermochromic inks to be much more vibrant in colour and able to disappear or appear with the most amount of detail.

This process is also very good for colour shift inks (or optically variable inks OVI) where you can look at the print at different angles and get two completely different hues. An example of this is pearlescent paint found on cars. The amount of ink required to pull-off this type of effect requires that you carry much more ink that you can apply than offset litho or flexo.

Applications

  • Plastic packaging, papers and boards
  • Textiles, clothing, ceramics, wood, glass and plastics
  • Circuit board printing

Suitable inks

  • Silk screen approved inks (UV is optional, but preferred)
  • Invisible Inks
  • Biometric and taggant inks
  • Thermochromic inks

Suitable substrate thickness

  • Ranging from 90gsm up to much thicker calliper substrates

Costs

  • Stencils or screens are relatively inexpensive, depending upon intricacy
  • Set-up costs are relatively inexpensive – depending upon size of machine

Things to watch out for

  • Usually only print one colour at a time – depends upon type of press
  • Not good for intricate, detailed printing
  • Great for heavier weight ink application and colours

Letterpress printing

Letterpress is one of the oldest printing technologies around as has been used in the production of newspapers and other printed materials for many years. The platten consists of a typewriter effect face and used to be hand carved. To a degree this process still exists in the security printing field, however we do not have any experience working with this.

If you have more information regarding this process and it’s use for this website, we would be pleased to hear from you.