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Substrates : Exploiting valuable surfaces
Keep swatches of every substrate you can print and show them to clients
Cucumbers and deep frozen inorganic materials are probably the most unusual substrates I have printed on in my career. Don’t ask about the cucumbers and I am sworn to secrecy regarding the inorganic materials.
Have you noticed how many new substrates are appearing to suit the needs of digital printers: or more correctly inks used in digital printers. The action of ink entering and ejecting from piezo ink jet heads is one key to digital printing and inks have to be engineered to negotiate this series of steps. This ink adaptation can compromise their long-term performance and will certainly reduce the chemistries that can be used. Changing from one discrete chemistry to another on the same machine is not practical.
Screen printing is an ink friendly process that allows an almost infinite number of mediums and ink systems to be printed onto an even wider range of substrates. This gives the designer and engineer great flexibility.
The governing factors in the selection of a substrate are:
- Is the substrate suitable for the application?
- Will the ink wet the substrate and form an adhesive bond?
- Is there anything leaching out of the substrate that will reduce that adhesive bond?
c What is the useful life of a printed substrate?
A simple fact often overlooked is understanding the effective substrate. For example, with anodised aluminium the print surface is aluminium oxide: not aluminium. Mineral filled plastics may well have an inert mineral coating. PVC with a white UV flood coat will be a cured UV ink (a thermoset material), totally different to PVC. Then there are polymers that would not be expected to accept ink such as polypropylene that has a naturally low surface energy. Only when it is pre-treated by corona discharge, flaming, plasma or liquid primer is the surface energy high enough for ink wetting.
Boundary layer
All these techniques alter the boundary layer of the material: the surface layer of molecules. These molecules are altered to let the ink bond to the surface. Sometimes ink solvents dissolve the boundary layer, other times reactive resins create a key. Whichever method is used, the chemistry can be complex. The simple rules are the surface needs to be clean, free of contaminating particles and wettable by the ink.
When you buy substrates from reputable suppliers you can be sure they have been designed for printing and the supplier should be able to recommend a suitable ink system. However, always run a test as it is not just a matter of adhesion. There could be discolouration caused by UV curing radiation, shrinkage due to curing temperatures, or even embrittlement.
Every substrate supplier tells customers to store substrate correctly. Ideal storage conditions for paper and board are 20°C and 50 per cent relative humidity (Rh). This is when paper is most stable. Paper and board should come in a moisture-proof wrapper and be left in the print shop to temperature stabilise before removing the wrapper and printing immediately. If the material requires further processing cover it in a plastic film or, if it came with a reusable moisture barrier covering, use it.
The paper and board industries have taken a tremendous hit with the unprecedented rise in energy costs. These have impacted plastics production so substrate suppliers are facing difficult times with demand for lower selling prices while carrying increased costs. Something must give and it is higher end user costs. When you look at the stunning warehouses of substrate suppliers and see the vast range of materials in stock it makes you wonder how they manage the market’s twists and turns, probably by being efficient big players.
Innovative finishes
This stock includes all types of material (paper and plastic) with a range of innovative finishes. Using these novel finishes and printing them with special effects ink gives a range of opportunities for screen printers to offer premium products. It is easy to assume that clients know all the substrates available to them.
Keep swatches of every substrate you can print and show them to clients. Don’t just stick with plastics and paper products consider: denim, silk, stainless steel, glass, ceramic, wood or even pressed leaves. You may think I have been smoking hallucinogenic pressed leaves but expanding a client’s imagination will grow your profits. Screen printers are special and can do special things.
Then there are coated and uncoated polyester films (available from companies such as MacDermid Autotype) often developed for membrane switches or in-mould decoration.
These are sophisticated combinations of polyester film and coatings. Hard coatings, textures, matte finishes, anti-reflective and one remarkable coating that is antimicrobial. Here the base polyester has a hard coating that contains a material called Microban. When microbes, such as bacteria, mould and mildew come in contact with the product surface, Microban protection penetrates the cell wall of the microbe and disrupts key cell functions so that the microbe cannot function, grow or reproduce. This coated polyester is easily screen or digitally printed and is used in hundreds of applications where cleanliness is crucial. Keyboards are a favourite place for germs to congregate but the microbe killers in these coatings deal with most, if not all, of them. These coatings are increasingly used in hospitals where hospital caught infections are an ever-growing problem.
There are more mundane applications of floor graphics where a hard coated laminate is used that is easy to print, apply and remove; yet can withstand abuse from frantic children, careering trolleys and teetering stiletto heels.
Photoluminescent materials are available as pigments in ink and as substrate. They can be as self-adhesive vinyl, rigid PVC or paper. These materials are not radioactive, non-toxic, lead and phosphorous free and present no danger to health or the environment. The most common are zinc-based and long-life versions contain magnesium strontium silicate. Time till complete decay for zinc-based is about 10-hours, while long-life versions are nearer 80-hours. Working life is likely to be 10-hours and 24-hours respectively. Health and Safety legislation specifies these materials must be used in certain signage applications such as where you need to read signs and see escape routes without light.
Backlit substrates (traditionally using neon or fluorescent tubing) are moving to light emitting diodes (LEDs). These use less power and produce equivalent light levels. As well as 85 per cent less running costs, life expectancy is up to 10-years. These attractive light sources are ideal for backlighting lettering.
An alternative is an electroluminescent material supplied by Light Tape UK. Managing director, Mike Hardcastle, has been deluged with enquiries from sign makers and PoS companies.
LightTape is said to be the longest, brightest electroluminescent lighting in the world. It can be supplied in different colours and widths, in lengths up to 100m. It can be used in flashing or steady state modes for indoor or outdoor applications.
Eye-catching designs
We are being constantly presented with new and innovative substrates, each one an opportunity for inventive screen printers to create eye-catching designs or products. Combine special effect ink with an unusual substrate and you have a premium product. Use your imagination, let the mind float free, back to the pressed leaves again! Become the JK Rowling of the screen printing industry and create your own Philosophers Stone.
