Sign Africa Journal November / December 2018 | Page 37

Tired of working for a boss? FEATURE now in ‘tower’ mode, i.e. the row of nozzles is vertically upwards. The nozzles shoot sideways onto the sides of each punnet as it moves horizontally past. The ink pressure at the top of the print head is always going to be less than the ink pressure at the bottom of the print head. For this to work, we need a print head with a wide ‘pressure window’. A combination of the non-wet coating on the inkjet print head, and the shape of the tiny nozzle cone, allows the ink meniscus to survive a significant change in ink pressure along the length of the print head. Ink Throw Distance: pulp cartons usually have a textured surface and are not highly accurate in their overall dimensions. There may be individual paper fibres sticking up. They also tend to have steps or lips in their design in order to add strength. All of this means that the inkjet print head cannot get close to the carton or there is likely to be a crash. From our experience at IIJ, we are normally asking the inkjet print head to ‘throw’ the ink drops between 3 and 5mm to the carton surface. To an extent, this conflicts with the customer’s desire for the highest possible print quality. High quality print needs small ink drops, but small ink drops won’t fly far before they lose momentum and blow away. The best compromise seems to be around 14pL drop size. Quality is still rated as ‘good’ but we can print well onto cartons with curved or stepped surfaces. Environment Dust: Pulp carton is dusty. Dust gets onto the inkjet print head nozzle faces and interferes with jetting. This causes missing nozzles in the print and production has to pause while the print heads are cleaned. The most important thing to consider is how to prevent dust reaching the inkjet print heads in the first place. Airflow is very important, so an air-knife may be used to remove dust from the carton well before it approaches the inkjet, and the area around the inkjet might be kept at a positive air pressure. It’s also important that when cleaning of the print heads is eventually required, the process is very quick and minimises down-time. Heat and humidity: if we are printing the cartons soon after manufacture then we have hot, wet cartons passing close to the inkjet heads. The heat could potentially cause drying of the ink in the nozzles, while the humidity could cause condensation i.e. water droppings forming on the cooler inkjet print heads. As with dust issues, the solution involves airflow. Gently blow away the warm, wet air and the problems are resolved. Drying Drying of the printed ink should not be forgotten. Our experience is that on dry cartons a near infra-red (NIR) lamp is an effective solution for drying the ink. However, if the decoration is to be done in-line directly after carton manufacture then the situation is different. In that case, the pulp is still wet – perhaps around 7% water by weight depending on the manufacturing process. Since the ink is water-based, this doesn’t seem to impact print quality – but it does make drying difficult since in effect the dryer is drying the carton as well as the ink. In this case, we have found that hot air can work very well (although it takes up a lot of space). Demand for pulp carton is about to explode, and the use of inkjet for decoration may well be the ‘next big thing’ for our industry. From under R13,000 Printing on T-Shirts, Mugs, Tiles, Clocks, Keyrings, Coasters and hundreds of other products Print white ink on all kinds of things! We also sell Raw Materials & Consumables for all these systems & V inyl Cutting iles s • T ore! g u M m uch irts • T-Sh gs and m in Keyr tion a m i Subl inting Pr ELECTRONICS Ink throw distance testing. Industrial Inkjet Ltd Pieter Le Grange [email protected] [phone] www.industrialij.com www.SignAfrica.com | NOV/DEC 2018 ISSUE 98 Head Office (JHB) - T: [phone] | Fax: [phone] | [email protected] SMS SIGN and your email to 40840 or email us for a free catalogue (sms charged at R2.50) Branches in Johannesburg, Cape Town and Bloemfontein | www.jgelectronics.com We have been providing profitable business opportunities for more than 28 years 37