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THE CAR is in a treasure trove of printing applications. The speedometer dials, the indicator arms, the air conditioning controls, the windscreen, most of the front facia and the side windows all feature printing of some kind. Open the bonnet and printed electronic circuits are a major feature with dozens of printed sensors sending signals to help the suspension, for example, sense mistimed braking on a corner. Printing is present in almost every modern environment and it allows our technological world to operate.
The vast majority of these printing operations are analogue. Digital is starting to have an effect on applications other than graphics, but whenever a print application is more than just for aesthetic purposes the chosen ink is likely to have physical and chemical characteristics that don't lend themselves to digital printing. This may change over time, of course, as nanotechnology and other ink formulation techniques create more digital friendly chemistries.
So what are the main analogue printing processes that are used in direct product decoration? Screen printing, pad printing and hot foil blocking. Laser etching/engraving and mechanical engraving both complement the analogue processes. Sublimation decoration using digitally printed transfers on a polyester varnish or substrate also serve a useful purpose.
Parallel universe
When screen printing onto products, the key is to keep the stencil parallel to the surface being printed right the way through the print cycle, maintaining an even contact with the stencil using the squeegee. For simple profiles this is relatively easy: flat, cylindrical, oval, conical, all pose no real challenges as long as you have the right equipment. Equipment can help position the object relative to the stencil and manipulate the object, stencil and squeegee to allow parallel contact between them.
This can be a slow process if the machine is hand fed and offloaded, reaching up to 1,200 prints per hour. If the volumes are sufficient however, investing in the right equipment can speed things up. It is possible to screen print a multi-colour image at 8,000 prints per hour on bottles, DVDs, containers and objects that can be handled automatically. These will generally use UV inks or ceramic if printed onto glass. The advantage of screen printing is that with relatively simple equipment it is possible to print a huge range of products.
When printing onto objects with a flat surface, the limitation is stencil size and whether it is possible to dry/cure the ink after printing. An example application is provided by a company using sheets of titanium, two metres by three metres, that had to be printed with an exotic ink and then subjected to massive pressures and temperatures to form a honeycomb of titanium that was immensely strong. Screen printing on a hand bench with a controlled pressure squeegee was the ideal solution. This utilised a simple printing technique to create high tech solution.
The only limitation for screen printing in product decoration is the printer's ingenuity and understanding of what is possible.
Working with contours
Pad printing takes over where screen printing leaves off but even with this versatile process, understanding its capabilities is important to its success. Yes it will print on many different shapes and contours, but it will not defy the laws of physics. Although pad printing will print larger items, it is at its best printing areas up to 350 by 120mm.
Another point to remember is that the process does not lend itself to thick films of ink. Typically the dried film thickness is five micron compared to screen printing, which can go up to 300 micron but normally averages 10 to 15 micron thick.
As with screen printing, pad printing can be automated to a greater or lesser degree. With hand loading and offloading, print rates of up to 1,100 per hour are possible, but this gives the operator very little time to check the print and handle the component. On this basis outputs can vary from 250 per hour to 800 per hour. Alternatively, if the volumes are sufficient, full automation is an option. This often relies on purpose-built machines with turning devices, pumped ink, pre- and post-treatment incorporated into the system. Whatever the level of equipment complexity, ensuring that ink conditions are stable and the ambient conditions are constant is crucial to effective pad printing.
Hot stuff
The Cinderella of product marking processes is hot foil printing. This can produce effects that are impossible by other means. The process begins with a carrier film that can hold single or multicolour pigments or metallic finishes, including plain or holographic images. Printing equipment transfers what is on the carrier film to the substrate by applying heat and pressure using a platen or roller, in single prints or continuous application. The Henry vacuum from Numatic, for example, gains his personality from a heat applied transfer.
Like the other two processes hot foil printing is everywhere. Credit cards carry a holographic security logo as do all bank notes. Often what appears to be a real wood grain finish is actually a hot foil print. Heat applied transfers work in a similar way. In both cases the image is printed onto a carrier film, either by screen printing or gravure printing, and then applied to the substrate using pressure and heat.
Finally, laser etching or ablation is capable of creating a permanent mark on a variety of surfaces with attractive results. The process can also cut intricate patterns in leather, plastic, metal and wood. Even in its most basic form, a laser system can be a significant investment but one worth making if market demand is sufficient.
As with all the techniques discussed, selecting the right technique for the product and the market in hand can be the key to unleashing the hidden potential of printing.
How many of your customers have asked about the carbon footprint of your printing service?
