Gaining a competitive advantage in industrial textile printing with integrated pre-treatment.
An Article by Oliver Lüdtke, Kornit Digital, Director of Marketing Kornit Digital Europe.
Inkjet printing is a very clearly defined process, in which the volume of each individual drop of ink is precisely defined, using primarily piezo printheads. In addition, firing is precisely timed and sophisticated hardware and software technologies operating in the background ensure colour accuracy. However, this precision is stifled the minute the droplet hits a textile substrate. The uneven surface absorbs the ink and leads to a high increase in tonal value, such that the applied ink can sometimes be barely visible after drying. The way to counter these effects is by pre-treating the textile material. This ensures that the drop of ink remains on the surface and retains its shape, preventing tonal value increase. In addition, the additives contained in the pre-treatment improve bonding of the pigments with the textile material.
Pre-treatment is clearly necessary, and manufacturers have developed a number of different approaches. All Kornit Digital systems, from Breeze through to Vulcan, provide integrated pre-treatment, making it an inextricable component of the printing process. Our direct printing systems contain a nozzle system at the rear of the machine, spraying the pre-treatment onto the textile. Only the nozzles required to cover the printed image are activated. On the return journey to the print zone, any excess liquid is automatically removed with a rubber squeegee and any potentially risen fibres are smoothed out. The pre-treatment is not dried prior to printing; instead, the ink is applied to the wet pre-treatment layer – a “wet-in-wet” process.
Ink tanks inside the Allegro print carriage (detail), far right: the pre-treatment.
This type of pre-treatment provides a number of benefits:
• Using a machine to apply the pre-treatment ensures even distribution, preventing irregularities and striping during printing.
• Adapting the pre-treated area to the specific image results in less pre-treatment being used overall.
• Kornit pre-treatments do not require any thickening agents that may leave stains on the textile.
• This also prevents blocked nozzles.
• The ideal amount per cm2 can be calculated individually for each textile and stored in a media database for later use in case of repeat orders.
It is important to note, that the textile contains a relatively large amount of liquid due to the wet-in-wet process. This means that a sufficiently large hot-air drier needs to be available for final drying.
Kornit Avalanche HD6 row of nozzles in operation
Integrated pre-treatment also offers benefits in terms of production workflow, as an entire step in the process is removed. With an external treatment, an interface with the printing process is created that requires attention. Which textiles should I pre-treat, and how many? How many buffers should I plan for? What happens, if I pre-treat too many or too few textiles? In addition, pre-treated textiles must be processed within a certain time frame. All this simply goes away, when textiles are pre-treated in real time inside the machine.
Internal pre-treatment also brings clear cost benefits. The pre-treatment concentrate is currently available from Kornit dealers at 32 euros for 5 litres, resulting in 20 litres of finished pre-treatment solution. The amount required varies wildly, depending on the textile’s absorbency and image size. Assuming an average application amount of 30 to 50ml, the pre-treatment cost per textile adds up to just a few euro cents.
The pre-treated T-shirt is scraped after spraying
By contrast, the costs for external pre-treatment include the purchase price of the pre-treatment device, drying, the pre-treatment solution and operator costs. Supposing that a single operator costs around 15 euros an hour and is capable of treating and drying one piece of textile per minute, the personnel costs alone are significantly higher than the Kornit pre-treatment.
The concept of internal pre-treatment is in line with Kornit’s overall philosophy: whilst the systems may not be the cheapest in terms of purchase price, the level of automation and relatively low costs for ink, pre-treatment and other consumables do tend to make it the more cost-effective choice for the production from 30 to 50 textiles per day.
Our web printing system Allegro also offers integrated pre-treatment. However, with this machine we are going one step further by printing the pre-treatment onto the textile via the printhead, like an eighth colour. This provides precise control of the application amount, down to the last pixel. The relatively low amount of liquid and the integrated drier ensure that the printed and dried textile web is available within seven minutes.