Dr Akshay Joshi: The print defect investigator

Priya Raju (PR): What was the reason behind selecting this topic for your study?

Akshay Joshi (AJ): The study is focused on exploring the effect of gravure process parameters on printability and print defects such as mottle, dot skips and voids. The surface imperfections in the films lead to uneven ink transfer resulting in print defects. The occurrence of print defects is usually detected either during the print run or in any of the finishing process, leads to rejection of the printed shrink films. There was an imminent need for determination of optimum process parameters to minimise such print defects and corresponding losses incurred. 

 

PR: Your thoughts about the shrink sleeve market scenario?

AJ: Polymers, especially shrink films, find extensive applications in the field of print packaging. The shrink sleeve market is majorly based on films like PVC (Poly Vinyl Chloride) and PET G (Glycol-modified Polyethylene Terephthalate), is evolving at a rate of 10-15% per annum. The shrink films are printed by gravure process for the applications such as beverages, carbonated soft drinks and cosmetics. However, printing on these films is a major challenge as the surface imperfections cannot be eliminated during their manufacturing. 

 

PR: What were the challenges faced by you during this study?

AJ: The occurrence of imperfections such as gels and black specks is random in nature. Further, the problem of print mottle is evident in both solids and halftone areas. These defects depreciate printability and degrade the selling potential of the product. 

 

PR: Where were the experiments conducted?

AJ: The majority of the experiments were conducted at the PVG College in Pune. The experiment design was established in association with my project guide Dr Swati Bandyopadhyay of the printing department at the Jadavpur University. Moreover, specialised ink tests were conducted at the BYK factory in Pune.

 

PR: Which parameters were crucial in the study?

AJ: There were five parameters namely line screen, stylus angle, ink viscosity, press speed and impression roller hardness which were critical. A total of 478 trials on two substrates namely PVC and PET G for the PhD work. All these parameters helped in minimising the print defects such as mottle, voids and dot skips. However, the significance level varied with the type of defect.

 

PR: Can you please explain the significance of the above mentioned parameters?

AJ: For example, impression roller hardness, press speed and interaction of stylus angle with viscosity were the most significant factors in minimising solid mottle. Whereas in ink viscosity, line screen and the combination of stylus angle with speed and hardness were the key interactions found to be the most significant parameters affecting halftone mottle. 

 

AJ: It comes down to optimising the results by tuning the settings that provide the closest and most consistent output. Inferences from this project can surely come in handy while making such adjustments in press settings.

 

PR: How can other printers benefit from this?

AJ: The findings of this study will help in reducing internal and external rejections and the corresponding losses incurred. It shall help them to optimise the process parameters with their given conditions and help to keep a tight control over the parameters so as to attain consistent print quality with minimised print defects. The statistical model developed shall provide a good prediction of print defects such as mottle, dot skips and voids on both PVC and PET G films. This can help in better utilisation of resources, higher business profitability and lesser environmental damage.  

 

PR: How do you plan to take this project forward?

AJ: On the academic front, I believe we have various things to cover. There are a lot of other print defects that the industry struggles with. I would like to continue my efforts in this direction and focus on other defects as well.

 

AJ: Regarding the market implementation of this project, I would like the key learning from this project to be implemented phase-wise, since implementing the entire improvements in one go will be overwhelming.