- Printed materials are available for immediate use, thanks to UV LED technology
- Wipe- and scratch-proof marking
- Solvent-resistant marking with clear typeface
- Emission-free LED technology with low energy consumption
- Can print bar codes
One printing method offering both high flexibility and resistance at a low cost is printing with UV-curing fluid. Here, a special fluid is used with a print head similar to that of inkjet printers; it is applied to the component to be marked and subsequently cured using a light source.
Individual drops of fluid are formed in the print head and propelled at the component. To create the desired print image, the print head travels over the component and applies the fluid line by line. In the same step, UV radiation cures the fluid. The component is not heated up, either during printing or curing.
This print technology can be used in many areas of application. Plastic marking labels can be marked as well as pretreated metal labels.
UV printers from Phoenix Contact use solvent-free printing fluid. This fluid consists of three main parts:
- A UV initiator, which initiates the photochemical reaction to cure the fluid on the printing substrate
- A bonding material, which functions as the carrier matrix for the printing
- Color pigment for coverage
The key to the UV digital printing technology is photochemically-induced polymerization. UV radiation converts the fluid initiators into radicals. Radicals are molecules with one free electron that wants to create a bond. The radicals activate molecules in the bonding components, called monomers, and bond with them to form chains and matrices. Such chains are referred to as polymers. They surround the color pigments and thereby cure the ink. The printing process is completely free of emissions, as the fluid used is free of solvents or volatile substances.
Inks containing solvents
In addition to UV-curing fluids, inks that contain solvents can also be used. If
these are not used, there is a risk of drying out. To cure the ink, the component is heated for several minutes following the printing process. Depending on the material and ink used, it is heated to temperatures between +70°C and +200°C.
The component must cool down before it can be used. Not all materials are suitable for this process; plastics in particular can warp at these high temperatures. Generally, the solvents in these inks vaporize when exposed to the effects of these temperatures. Furthermore, it must be ensured that the dried ink will not be dissolved by other solvents. This is why UV-curing fluid is used in Phoenix Contact products.
Basically, there are two different ways of transferring inks and fluids onto components.
|Continuous inkjet||Drop-on-Demand inkjet (DOD)|
|Firing off the ink drops||If required (during the actual printing process)||Permanent|
|Inks/fluids||With a high solvent content||Containing solvent or solvent-free|
|Nozzles||An individual nozzle with continuous jet||High number of nozzles with vertically delivered drops|
|Resolution||Low (e.g. for cable marking)||High (for high-quality printouts)|
In DOD inkjets, two different print head technologies can be used:
- Bubble jet method: A vapor bubble is generated here through electrical heating, which then pushes the drops out of the nozzle thanks to the resulting pressure. Ink containing a solvent is required to generate the vapor bubble. Bubble jets are used in inexpensive printers, e.g., for private users.
- Piezo jet method: Here, the nozzle channels consist of piezo crystals, which are moved by electrical pulses in waves. The drops are then fired out in this way. Piezo jets are high-quality, durable print heads that are used in UV printing, for example. The BLUEMARK ID and BLUEMARK ID COLOR also use the piezo jet method.
UV lamps (burners) are frequently used as UV light sources. Their use is associated with high heat generation due to their construction. These burners are particularly powerful, but also have a large variance of emitted UV light. As such, a UV C burner (100–280 nm wave length) also emits light in the UV A (315–380 nm) and UV B range (280–315 nm).
LEDs are an alternative to the burner lamps. UV LEDs emit light in a very narrow range (UV A), and therefore have significantly lower variance than the burners. The UV-induced, photochemical polymerization is often in a wavelength range of 200 to 400 nanometers. The minimal heat generation is an additional advantage. This allows the creation of smaller and lighter printers, such as the BLUEMARK from Phoenix Contact.