For coating and ink applications, polytetrafluoroethylene (PTFE) in the form of micronized powders have been used for many years to impart a number of advantageous characteristics, including exceptional chemical resistance, low coefficient of friction, good resistance to heat and low temperature, and enhanced surface durability.
These properties make PTFE especially useful in the coatings industry for applications like can, coil and graphic arts. Specifically, the PTFE particles are used to create a surface texture that promotes these desired properties, which is often termed the “overlay/ball bearing” effect.
In 2019, the Stockholm Convention began restricting the use of raw materials containing >25 ppb perfluorooctanoic acid (PFOA), which has impacted the use of PTFE due to common production processes that use irradiation to make PTFE. The irradiation process that creates small particle sizes required for the inks industry has also been demonstrated to create PFOA. Within this new regulatory environment, ink formulators and manufacturers need to be prepared to adapt their inks technologies to be compliant
The good news is that PTFE-free surface modifiers have been developed using new and alternative raw materials that are functionally similar to PTFE. Wax additives (surface modifiers) play an important role in replacing traditional PTFE with low-PFOA containing PTFE or PTFE-free alternatives to meet the technical challenges of reducing or removing PFOA from customer products in multiple ways.
Following are highlights of testing done on PTFE-alternative wax additives.
Test Materials and Printing
Leneta 3NT-31 gloss finish coated book printing ink drawdown sheets from Leneta Company (USA) were used as received. Blue pigment concentrates were purchased from Helio Beit GmbH (Germany) and were used as received, without further modification. Wetting agents, defoamers and surfactants received from Biesterfeld GmbH (Germany). Water-based dispersion of styrene acrylic resin was obtained from Lubrizol (China).
The Wax Additives
Four different waxes were evaluated. Table 1 shows the identity and physical properties of the waxes used. The reference sample contains a PTFE-based wax additive and was used as a benchmark. Sample 1, sample 2 and sample 3 are PTFE-free waxes. The control is an ink formulation without wax. The printed ink films for these studies were made by hand printing inks on Leneta 3NT-31 backside. Water-based samples were dried for at least for 24 hours at room temperature.
Rub resistance, gloss and coefficient of friction of the ink with the PTFE-free waxes were analyzed. The tests followed standard methods used by the industry for evaluating print properties of ink systems.
A summary of the results for gloss measured by a gloss meter at 60°and 85° is presented in figure 1. The results show that the gloss values at 60° for all ink formulation plus waxes are comparable. Ink formulation prepared with wax sample 3 shows slightly higher gloss retention at 60° and 85° compared to the ink formulation without waxes (control formulation) and other samples. These findings also indicate that the PTFE-free wax alternatives are very effective in improving the gloss retention of the printed ink.
The Coefficient of Friction (COF)
The COF results of ink formulation containing PTFE-free waxes against ink formulation containing PTFE-based wax and control formulation are shown in figure 2 and the static COF and kinetic COF were compared. The data clearly shows the reduction in both static and kinetic COF for the formulation containing waxes, indicating good film slip. Additionally, formulation containing PTFE-free waxes showed comparable results to formulation with wax PTFE.
A Sutherland 2000 rub tester was used for determining the rub resistance of printed samples. After a series of rub tests, samples of white papers were then visually evaluated with respect to transferred ink amount on the white unprinted paper. The visual rating scale is 1 to 10, with 1 being a high degree of ink transfer (1=very poor) and 10 being no ink transfer (10=excellent). The results determined from the visual inspection of the rubs and shown in figure 3 indicate that the formulation containing waxes demonstrated similar high rub resistance compared to the control formulation containing no wax.
Rub-off test results demonstrated ink transfer onto the white uncoated paper was only extremely strong with ink formulation without waxes, indicating insufficient ink resistance to the rub-off process. Ink formulations that included waxes showed slight ink transfer, indicating high rub resistance. PTFE- free additives improved the rub resistance of the ink formulations as effectively as commercially available waxes containing PTFE.
The PTFE-free waxes offer a number of benefits when used as a replacement for waxes containing PTFE. When incorporated into an ink formulation, these waxes improve gloss retention while also reducing the coefficient of friction and rub resistance. The results demonstrated that these PTFE-free additives have the potential to be used as alternatives to PTFE-based products.
Contact a Lubrizol expert to learn more about our line of PTFE-Alternative wax additives.