Advancing in Packaging Inks Without PTFE

Micronized polytetrafluoroethylene (PTFE) powder provides desired properties for coating and ink applications, including excellent mechanical properties, chemical resistance and low coefficient of friction. With the publication of the Stockholm Convention in 2019, the use of raw materials containing more than 25 ppb of perfluorooctanoic acid (PFOA) began to be restricted. This global restriction on PFOA and its salts, which are persistent organic pollutants (POPs), has also affected traditional PTFE use. The need for PFOA-compliant PTFE or PTFE-free alternatives has become significantly important. In this article, we present new technology that can be used as an alternative to PTFE. These PTFE-free formulations will enable the achievement of performance and properties similar to formulations containing PTFE. In addition, new additives provide significantly improved mechanical resistance and considerably lower coefficient of friction, making them excellent functional alternatives to PTFE-based additives. The advantages of halogen-free additives include good compatibility in inks and coatings, as well as easier dispersion and processing due to lower density compared to PTFE.

1. Introduction

PTFE is a fluoropolymer that provides many desired properties used widely in various industries, including exceptional chemical resistance, low coefficient of friction, good resistance to heat and low temperature and improved surface durability. These properties make the additive beneficial in the coating industry, particularly for tinplate, coil and graphic arts applications. Specifically, PTFE particles are used to create surface texture, also known as the "layer/ball bearing" effect, contributing to these desired properties. [caption id="attachment_136206" align="aligncenter"] Figure 1. Illustration and SEM image of the layer/ball bearing effect[/caption] Recent regulations concerning PFOA have affected PTFE use due to production processes where irradiation is widely used to obtain PTFE. The irradiation process used to create the small particles required in the ink industry has also been proven to produce PFOA. For this reason, traditional PTFE must be replaced by low PFOA PVDF or PVDF-free resins, using low PFOA PTFE or PTFE-free alternatives. Within the framework of these new regulations, ink formulators and manufacturers must be prepared so that their formulations are compatible with their own ink technology. EU legislation requires that no manufacturer place on the market any product containing more than 25 parts per billion (ppb) of PFOA or have processing containing more than 25 ppb of PFOA. Wax additives (surface modifiers) play an important role in reducing or eliminating technical difficulties during the phase of replacing traditional PTFE with low PFOA PTFE or PTFE-free alternatives in customer products. PTFE-free surface modifiers have been developed using new alternative raw materials that function similarly to PTFE. The purpose of this article is to present wax additives that can be substituted in formulations currently using PTFE-based waxes.

2. Materials and Printing Substrates

Leneta 3NT-31 gloss-coated book printing ink drawdown cards from Leneta Company (USA) were used without processing. Blue pigment concentrations were purchased from Helio Beit GmbH (Germany) and used without modification. Wetting agents, defoamers and surfactants were supplied by Biesterfelf GmbH (Germany). Water-based styrene acrylic resin dispersion was obtained from Lubrizol (China). Water-based styrene acrylic resin is known as the "vehicle" in ink and is the polymer that forms a soft, flexible, film form in the final printed ink film after drying. The vehicle serves as a binder in transporting the pigment and its adhesion to the printed surface. Wax Additive and Incorporation Four different waxes were examined in the study. Wax was added to the ink formulations by dropping the calculated wax weight while stirring continuously at room temperature for 10 minutes. The wax amount was 2% by weight of the total formulation. Table 1 shows the characteristics and physical properties of the waxes used. The reference sample is a PTFE-based wax additive and was used for comparison. Samples 1, 2 and 3 are PTFE-free waxes. The control is an ink formulation without wax. [caption id="attachment_136192" align="aligncenter"] Table 1: Physical properties of waxes[/caption] Printing Preparation For these studies, printed ink films were applied with hand printing inks on the back of Leneta 3NT-31 using a Weller Flexi-Proofer. The Flexi-Proofer consists of a rubber roller in contact with an engraved anilox metal cylinder. A few drops of ink are dropped between the two cylinders and a simple draw-down process is performed by rolling the ink-coated anilox roller over the film to print on paper. Dry film thickness is 5µm. Water-based samples were dried at room temperature for at least 24 hours.

3. Experimental Procedures

To observe the effects of these waxes, abrasion resistance, gloss and the coefficient of friction of the ink with PTFE-free wax were analyzed. Standard test methods used by the industry were used to evaluate the printing properties of the ink systems for testing. All tests were performed at room temperature and 50% relative humidity. Gloss Analysis Gloss is a function of surface smoothness, ink formulations and ink film smoothness. A Micro-Tri-Gloss gloss meter (BYK, Germany) was used to test gloss in printing. Gloss measurement was performed at 60° and 85° light reflection angles. Data collection was performed at 3 different positions across the area of the printed ink film and average values were reported as final values in gloss units. Coefficient of Friction Coefficient of friction (CF) measurement is a ratio that defines the surface roughness of a material. Param MXD-02 was used for coefficient of friction measurement. This test device was designed in accordance with ISO Standard ISO-8205-109. Measurements for all tests were made following ISO Standards. As a result, the static coefficient of friction and kinetic coefficient of friction specified in the standard are presented. Abrasion Resistance A Sutherland 200 abrasion tester with a 1.82 Kg test block was used to determine the abrasion resistance of the printed samples. The printed sample was abraded on white paper with forward and backward movements at controlled speed with 30 cycles, corresponding to a total of 60 repetitions. Unprinted white paper was used to clearly show ink transfer. Upon completion, samples were visually examined to check ink transfer.

4. Results and Discussion

Gloss is an important parameter in printing inks because gloss affects print quality and generally provides better color depth. Figure 1 presents gloss results measured with a gloss meter at 60° and 85° angles. The results show that gloss values are comparable for all ink formulations and waxes at 60°. The ink formulation prepared with wax sample 3 shows slightly higher gloss retention at 60° and 85° compared to the wax-free ink formulation (control formulation) and other samples. This is characterized as the surface smoothness of the ink film. These findings also demonstrate that PTFE-free wax alternatives are very effective in improving gloss retention of printed ink. [caption id="attachment_136195" align="aligncenter"] Figure 2: Gloss Data Analysis Results[/caption] Coefficient of Friction Paper and film packaging coefficient of friction is an important parameter in the processing of printing inks. Controlling the coefficient of friction provides processors with optimized performance properties as well as the ability to avoid molding, transport and storage problems. The CF results of the PTFE-free wax-containing ink formulation against the PTFE-based wax-containing ink formulation and control formulation are shown in Figure 2, and static CF and kinetic CF values are compared. The data clearly show reductions in both static and kinetic coefficients of friction of the wax-containing formulation as well as good film slip. Additionally, the PTFE-free wax-containing formulation showed comparable results to the PTFE wax-containing formulation. [caption id="attachment_136197" align="aligncenter"] Figure 3: Coefficient of friction data analysis results in water-based acrylic inks[/caption] Abrasion Resistance Measurements Following a series of abrasion tests, white paper samples were visually evaluated based on the amount of ink transferred to unprinted white paper. The visual rating scale is 1 to 10; 1 represents high degree of ink transfer (1=very poor) and 10 represents no ink transfer (10=perfect). According to the results determined in the abrasion visual examination shown in Figure 3, the wax-containing formulation showed better abrasion resistance compared to the wax-free control formulation. [caption id="attachment_136199" align="aligncenter"] Figure 4: Abrasion Resistance Analysis Results. 10= Perfect, 1= Very Poor[/caption] Figure 4 shows the results of the abrasion test images. According to the images, the wax-free ink formulation showed the least adequate ink resistance to the abrasion process, being the formulation that transferred the most ink to white paper. The wax-containing ink formulations showed high abrasion resistance, causing slight ink transfer. The increased abrasion resistance with the new PTFE-free wax additives is likely an effect of improved mechanical properties. Furthermore, in Figures 3 and 4, it can be seen that PTFE-free additives improve abrasion resistance in ink formulations as effectively as commercially available PTFE-containing waxes. [caption id="attachment_136201" align="aligncenter"] Figure 5: Images of Abrasion Test Results[/caption]

Conclusion

PTFE-free waxes provide many benefits when used in place of PTFE-containing waxes. When these waxes are incorporated into an ink formulation, they not only improve gloss retention but also reduce coefficient of friction and abrasion resistance. The results demonstrate the potential of these PTFE-free additives to be used as alternatives to PTFE-based products.

Author: Gehan Eltanany Technical Marketing Manager Lubrizol GmbH

Author: Dave Seline Global Business Development Manager Lubrizol

Compiler: Çise Karamehmetoğlu Sales Manager Fuchs Kimya

Compiler: Fırat Pınar Sales Manager Fuchs Kimya