The method of CD printing you choose is governed by some key factors. These are as follows:
- How many CDs do you need printed?
- What is the intended use of the end product?
- Is the budget tight for the project?
- What sort of artwork is intended for the discs? Photographic images or block colours?
Once these factors have been considered, you can make a decision about which CD printing process is most appropriate for your particular project.
Let's take a look at each of the processes in turn and their pros and cons.
Digital CD Printing
This CD printing method utilises a printer that employs the same process as an inkjet printer that many home users will be familiar with. In fact, many home printers can be equipped with a CD printing tray for use with pre-manufactured CDRs with a printable surface. A company printing CDs professionally will most likely be using an inkjet printer that is specifically for the printing of CDs. These printers have an auto-loading mechanism enabling the unattended printing of up to 200 CDs. The printer automatically loads unprinted discs and unloads the finished discs onto separate spindles.
Digital CD printing using one of these printers is slow but there are no fixed set up costs involved. This is fine if the order quantity of discs is less than 100, or 200 if there is no fixed, imminent deadline for the order.
This method of printing is capable of producing highly professional looking CDs as an inkjet printer can print at very high resolutions. The printed surface does need protection though and a layer of clear lacquer needs to be applied to the discs to prevent moisture coming into contact with the ink through handling or exposure to damp environments. This necessity adds significantly to the overall project time. Printable discs are available which have a specially formulated surface that becomes water resistant after printing but they are more expensive than regular printable discs and so a decision has to be made depending upon the urgency of the project; extra expense for water resistant discs or extra time for the application of a layer of clear lacquer?
CD Screen Printing
CD Screen printing is ideal for artwork designs that involve solid areas of colour. Screen printing is carried out using a machine with a rotating bed that has 5 separate stations where a different colour of ink can be applied. The CDs can have a base colour applied first over the whole disc area which means that a screen printed CD design can consist of a total of 6 different colours maximum.
The ink used in the CD screen printing process is UV sensitive and as each colour is applied at a station, the disc moves under a UV lamp as it rotates round to the next station. The UV lamp cures the ink and this only requires a moment of exposure.
As the process name suggests the screen printing is applied through the use of very fine mesh screens. There is a separate screen for each colour in the artwork design. To create a screen, a film is produced which has the areas where ink is not to be applied to the disc, blacked out. The new screen is initially coated with a thermal emulsion. The film and the screen are aligned on top of each other using guide marks and are put into an exposure unit. When the screen is exposed to a hot, bright light, the area of thermal emulsion not protected by the dark area on the film is cured. The screen is then washed with a water spray and the areas of uncured emulsion wash away to reveal the mesh.
The screen is then fixed at its station. Once all the screens have been prepared in this way, the printing can begin. The CDs are loaded onto the machine by an automated robotic arm system. They are placed into a platen which holds the disc firmly in position. At each station, ink is added on top of the mesh screen and a rubber squeegee blade passes over the top pressing the mesh down onto the disc surface and forcing the ink through the fine mesh holes and onto the surface of the disc. The ink application stroke takes about a second and each station applies ink to a disc simultaneously as soon as the first 5 discs have been fed into the system. This speed means that a screen printing machine can print more than 3500 discs in an hour so large orders can be completed quickly.
There are, however, significant fixed set up costs due to the requirement for screens and films. These can be reduced by limiting the artwork to fewer colours, with a single colour print onto a silver disc being the most cost effective print. The fixed costs do mean that this CD printing process is only really viable for orders of over 100 discs.
The CD screen printing process is capable of producing a truly amazing CD print at a very high resolution due to the use of extremely fine mesh screens. It is not ideal, though, for printing photographic images due to the presence of subtle colour gradients in these images. What makes the screen printing process truly unique is the availability of fluorescent and metallic inks which can really add a WOW factor to your CD print.
Lithographic (Offset) CD Printing
This printing process is very different from the screen printing process and the two printing machines are set up very differently. The lithographic process takes advantage of the fact that the printing ink and water do not mix much like oil and water.
The artwork image is applied to a lithographic CD printing plate using a laser. The printing plate surface is rough in texture and is pre-coated with a thermally reactive emulsion.
The printing plates are treated using chemicals to enable removal of the exposed area of the thermal emulsion from the printing plate. Once the printing plate has been prepared, the area containing the artwork image is made ink receptive and water repellent. The areas on the CD printing plate that are not to be printed are made to attract water but not the ink. The printing plates are then assembled onto a rotating cylinder on the lithographic printer.
As the printing plate goes through each rotation, it passes over a set of rollers which apply water to the plate, the water is attracted to the rough surface, where ink is not to be applied to the disc.
Next the printing plate passes over the rollers as ink is added. The ink is attracted to the smooth areas of the printing plate. A cylinder wrapped in a rubber blanket then rolls over the plate and picks up the ink. The CD artwork image is then transferred from the rubber blanket cylinder onto the CD which is securely held in a metal platen. Once again, this process is very fast which many parts of the process happening simultaneously and many discs being printed in conjunction.
The ink used is UV sensitive as for screen printing so when the discs are exposed to a UV light they cure immediately.
Lithographic printing is perfect for printing photographic images as it can deal with areas of subtle colour gradient very well. It's not so good, however, for large areas of solid colour as there can be an ink coverage discrepancy which can lead to a “patchy” print on the CD.
As with CD screen printing, lithographic printing has a fixed setup cost regardless, in this case, of how many colours are involved in the print. It only becomes economically viable for print runs of 100 discs or more and the more discs are printed, the lower the unit cost goes.
CD Printing Artwork Points to Check
It is very important to present your supplier with as high a resolution image, as possible. The better quality the image, the better quality the end product will be. Make sure you check that all images, especially photographic images, are in their original format. It is not sufficient to transfer a low resolution 100dpi image into a file template created at 300 dpi. The original image will not print well and you will be disappointed with the result.
Check that dark photographic images print well by running test prints before you commit to the production run. If the image is to be screen printed then providing the supplier with a pantone reference code for each of the colours in the artwork will ensure that the print will appear exactly as you anticipate. If you already have a printed disc and you are looking for a re-run, ask your supplier about colour matching. Most suppliers will provide this service and it will give you peace of mind that the end product will remain consistent with previous projects.
Summary
To summarise the above information depending upon the intended end use for your CDs:
- If you only need a short run of less than 100 discs, digital printing will be the most cost effective CD printing method. There is certainly no compromise with print quality but there are no fixed set up costs.
- If your image to be printed is based on a photograph then Lithographic printing is the way to go.
- If your image consists of 1 or more solid colour areas, then screen printing is the CD printing method to choose for a pin sharp result. Fluorescent and metallic artwork also requires screen printing.
