Dyne Pen Test Procedure
Paul
Although the technique is only considered appropriate for polyethylene and polypropylene films, for years, dyne testing has been the prevalent approach to assessing the cleanliness and surface energy of a wide range of material surfaces in terms of quality. Their widespread use and affordability have made them a popular choice among manufacturers despite their lack of precision, potential damage to material surfaces, and risk to users. While the science supporting dyne measurements as outlined in the ASTM standard is reliable, their application in a manufacturing setting and on other materials does little to avert or mitigate adhesion failure.
Dyne testing is typically used to gauge the wetting tension of non-absorbent, polymer-based materials. Dyne test solutions typically come in a set with a surface tension number associated with each dyne test pen or dyne test ink.
These standards outline the procedure for determining the wetting tension of polypropylene and polyethylene film and sheeting only. These specific guidelines should be followed to achieve the most consistent and reliable results on material surfaces. It's well-known, however, that significant variation occurs between technicians even when evaluating the same materials [see, for example, R.J. Caimi, L.K. Derr, T.J. Dunn, Precision of the surface energy test, Converting Magazine, 10 (6) (1992) 62.].
This picture shows a series of dyne solutions applied to a uniform piece of material. Which would you consider to be the highest surface tension fluid that remained spread out? 40? 44? The behavior of 42 looks a lot like 48 or 50. It can be difficult to reach a confident conclusion.
As mentioned, dyne testing was specifically designed for polyethylene and polypropylene films. While employing this procedure and the specified chemicals for films made from different polymers can be feasible, the user must determine the suitability and importance of using materials other than a polyolefin.
Dyne testing is commonly used in manufacturing environments where materials are tested before adhesion processes like bonding, sealing, coating, painting, and printing.
Another common use is validating material surfaces after surface treatment processes like corona treatment, flame treatment, and plasma treatment.
Producers have observed discrepancies between the different brands of dyne pen manufacturers, making it impossible to equate one surface tension number across all brands. This inconsistency makes it challenging to understand precisely what the pens offer and whether they provide the necessary information. Additionally, some brands offer a broader range of numbers than others, implying that the required numbers for your surface might not even be accessible.
Not only is dyne ink potentially damaging to the user, but it is considered a destructive test. Once a dyne test has been conducted, the part is rendered contaminated and unsuitable for further production use. This increases the rate of product waste and does not permit 100% inspection.
As mentioned, the ASTM standard for dyne testing is based on examining non-absorbent polyolefins: polyethylene and polypropylene films. The standard makes clear that using dyne tests on any other material should be studied comprehensively prior to use in order to ensure repeatability and reliability.
Many film manufacturers include slip agents in polymer formulations. These are lubricants that bloom to the surface and reduce friction as the film passes through processing equipment. If too much is present on the surface of the film, these compounds can interfere with the surface treatment and adhesion of printing inks and adhesives. Slip agents are readily soluble in many solvents, including those found in dyne solutions. As a result, dyne pen inks simply dissolve slip agents without detecting their presence on the surface. However, slip agents are, in general, not very soluble in water.
Our experience with thousands of bonding failures across hundreds of leading manufacturers reveals a surprising truth: the material or process is rarely to blame. Instead, these issues often stem from human decisions and complex environmental factors that traditional methods like dyne testing miss due to their limitations.
In general, the ability of a substrate to anchor inks, coatings, or adhesives is directly related to its surface energy. If the substrate surface energy does not significantly exceed the surface tension of the fluid which is to cover it, wetting will be impeded and a poor bond will result. Thus, for most solvent based printing, plastics need to be treated to 36 to 40 dynes/cm; water based inks usually require 40 to 44 dynes/cm; some laminating and coating applications require surface energies of 50 dynes/cm or more. Clearly, surface energy must be assessed before printing, coating, or laminating is attempted.
To ensure replicability of this test, material preparation and test technique must be standardized. ASTM Std. D6182 documents suggested conditioning methods. Unfortunately, this standard is untenable for treated film testing; conditioning times range from 24 to 96 hours. Such rigorous controls may be of value for R & D, but for normal QC testing, much shorter conditioning times should be used. Standardization of ambient, substrate, and test solution temperature is critical, as is inspection methodology. Have one trainer instruct all testers to minimize variability. Relative humidity should not be excessive; higher RH tends to increase data variability. Finally, the elapsed time between extrusion or coating to test (or from test to printing, etc.) must be controlled.
2.4 Test at least three points across the sample; 1/4, 1/2, and 3/4 across the film section. It is good practice to test the outer edges as well. For non-film materials, test locations must be determined in-house.
2.5.3 Use a light touch to draw the pen across the test sample in two or three parallel passes. Disregard the first pass(es); to flush any contamination from the tip, and to ensure that the test fluid layer is thin enough for accurate measurement, evaluate only the last pass.
2.5.4 If the last ink swath remains wetted out on the test sample for three seconds or more, repeat steps 2.5.2 and 2.5.3 with the next higher dyne level marker. If the last ink swath beads up, tears apart, or shrinks into a thin line within one second or less, repeat steps 2.5.2 and 2.5.3 with the next lower dyne level marker. If the ink swath holds for one to three seconds before losing its integrity, the dyne level of the marker closely matches that of the sample.
Finally, a few qualifying words. Surface energy is critically important to many converting operations. Unfortunately, it is not the sole determinant of product suitability. Other factors, such as surface topography, coating rheology, and chemical incompatibility, must also be considered. This is why broad-based communications with vendors and customers is so important. But at least by systematically measuring substrate surface energy, you will have a sound starting point from which to resolve other problems which may arise.
This report is provided by Diversified Enterprises, 101 Mulberry St., Suite 2N, Claremont, NH 03743. It is intended to provide quality control information for converters and others who need to measure surface energy. We believe all information contained herein is accurate. Diversified Enterprises will not, however, under any circumstances by held responsible for any losses or damages incurred by any party using this report.
Wondering why Diversified Enterprises is the best choice to supply your dyne testing needs? This document contains important information about our products and services. Particularly those who do not currently use Diversified Enterprises as their dyne testing supplier will find helpful comparison points to help you choose the best dyne testing supplies from the best supplier in the world. Learn more...
In order to determine the surface energy of a material, engineers often utilize the dyne test, also known as the ink method. This testing method is based on the ASTM/ISO 9277 standard for measuring the surface energy. It can be performed using various specialized equipment, such as dyne pens.
In summary, markers play a crucial role in the dyne testing process, providing a quick and easy way to measure the surface energy of materials. By selecting the appropriate marker and taking steps to minimize external factors, engineers can ensure accurate and reliable results from the dyne test.
Contamination is a common issue that can affect the accuracy of dyne test results. Contaminants can prevent the dyne ink from properly wetting the surface, leading to inaccurate results. Some common sources of contamination include oils, grease, dirt, dust, and fingerprints.
The test pen works by measuring the force required to draw a liquid through a small hole in the pen tip. The higher the surface tension of the liquid, the more force is required. This force is then converted into a dyne-level reading.
Using a dyne pen is straightforward. First, unscrew the cap and remove the nib. Next, dip the nib into the liquid to be tested. Finally, screw the cap back on and press the tip of the pen onto the surface to be tested.
Dyne test results can also be used to determine the cleanliness of a surface prior to bonding or sealing. A dyne level of 10 dynes/cm or less indicates that the surface is clean and suitable for these applications.
Overall, the dyne test is an incredibly useful tool for technicians who need to evaluate material compatibility or troubleshoot adhesion-related issues. When performed correctly, this testing method can provide valuable insights that can save time and money in the long run.
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