You are in:
Stay in contact with drying technology
Unlike other heating methods, contact drying systems work by drying inks from the substrate surface to the top side of the ink. This means the technology actually works in reverse to heated air and infra red (IR) ovens, which dry from the ink's top side down to the material surface.
To achieve this effect, contact dryers utilise heated vacuum plates with a transport belt to carry the material being dried. Some dryers also use an integrated heated air blower to help eliminate solvent fumes and accelerate the drying process. Temperatures and heating rates are tightly controlled by the electronics of the contact drying system and today's contact dryers are able to heat different sections of the drying plate independently. This brings heat control in line with the exacting standards required by innovative high-tech ink formulations.
Time is of the essence
The primary benefit of adopting contact drying technology is the speed at which it can dry inks. Whether one is using solvent or water-based inks, contact dryers can be used to dry in a fraction of the time required for heated air ovens, eliminating the production bottlenecks that are typical of thicker ink applications using heated air dryers. In certain electronics applications, for example, solvent-rich inks that can take up to two hours to dry in conventional ovens can be thoroughly dried in a contact drying system in about 30 seconds. In electronics applications, where quality is gauged by measuring the resistance of the screen printed circuit, the end product created by the contact dryers and heated air dryers is the same. The only difference is in the amount of time taken to achieve this high quality standard.
Contrary to popular belief, contact dryers can improve quality because they so greatly accelerate the drying process. For example, faster drying can preclude solvents from penetrating base materials, eliminating any potential effects that the solvent may have on the base material. Any application using solvent-sensitive substrates, such as certain plastics, can benefit from the faster drying times of contact dryers. Applications using ink sensitive substrates range from new RFID products to membrane switches, ultra-light airplane cabin panels or textile transfers.
Beauty is skin deep
Contact dryers also have the potential to improve quality in those applications where so-called skin effects on thick ink layers are sometimes troublesome. The skin effect is created when the top-down drying mechanism of conventional drying systems leaves a skin of dried ink on the surface that traps moisture below. When this occurs a thin film is created on the ink surface that traps solvent or water below the skin. In roll-to-roll graphics applications this is sometimes so pronounced that layers of product tend to stick to each other. This same stickiness due to extra trapped moisture also exists in sheet-fed applications, even though it may not be as apparent. Contact dryers, because they heat from the bottom-up, avoid the skin effect altogether.
The other quality-compromising dynamic intrinsic to a conventional heated oven design is its inability to control the application of heat. Many inks now used in RFID, electronics and other high-tech applications have strict requirements for the rate at which they are dried. Today's contact drying systems have built-in temperature records and graphical displays of temperature data that enable operators to fine tune process control as never before. It is often possible to make adjustments to temperatures and store job parameters with just a few keystrokes, making it easy to duplicate an identical quality standard, with timed and controlled heating, from one job run to the next.
Controlling energy costs
With energy costs skyrocketing worldwide there is also a growing benefit from the relative energy efficiency of contact dryers, which typically use a fifth, or less, of the energy used by conventional drying systems. In a heated air oven, various sensors read the temperature of the entire oven, which functions as a single heating unit. Air in conventional ovens also tends to dissipate heat, in contrast to contact drying systems that rely on a special metal plate that works as a heat accumulator. This means that after a preliminary pre-heating time, the heating plate retains and stores heat, making the application of heat more uniform. This heated plate can be controlled in sections, with separate sensors and separate heating elements for each section, making the contact dryer a far more efficient heat scheme than conventional ovens, which are heated as a single unit in on/off heat cycles. These factors can combine to make conventional ovens an energy guzzling option, in comparison with contact drying systems.
Another benefit of contact drying technology is that contact dryers have a smaller footprint than conventional drying ovens. They can be built horizontally or vertically, as production line efficiencies and floor space require and they can be used in-line or off-line. Most new screen printing lines are modular in design, which also means that contact dryers can be readily incorporated into the production line.
As these features and benefits highlight, there are compelling reasons to consider adding contact drying technology to an operation. For the cost of a contact dryer it is possible to add new product lines that depend on the carefully controlled curing of high tech inks. Moreover, the improvements in production throughput and the cut in energy costs can combine for a rapid return-on-investment, in the order of a few months for most high volume screen printing operations.
