Marc I. Johnson, Texture Technologies Corp. 6 Patton Drive, Hamilton, MA Tel

Transcription

1 Abstract Novel Automated Method for Analyzing Peel Adhesion Ben Senning, Territory Manager, Texture Technologies Corp, Hamilton, MA Marc Johnson, President, Texture Technologies Corp, Hamilton, MA Most commercially available peel instruments conduct tests at fixed peel speeds. When companies wish to evaluate the speed sensitivity of their tapes operators must therefore conduct tests at many different speeds and each curve needs to be independently analyzed for the relevant metrics. Typical peel sample sleds also have chatter which impacts how well the tests are able to maintain the targeted peel speeds. A texture analyzer can conduct peel tests at multiple peels speeds through a single long stroke. When used in conjunction with an automated linear stage the system can be programmed to instantly and simultaneously change speeds multiple times through a single stroke. Synchronized carriages are able to precisely maintain target test conditions without any sled chatter. The resulting forces vs. distance (or time) curves have individual plateaus for each of the many test speeds. The software program automatically quantifies the mean force and other relevant quality of peel metrics for each of the variable number of speed conditions. This paper examines the results of 90 degree peel tests on a variety of commercially available rubber, acrylic and silicone single-coated pressure sensitive tapes that were tested using the automated variable speed testing regimen. The system has been developed to allow customers to very efficiently quantify the speed sensitivity of their tapes. Marc I. Johnson, Texture Technologies Corp. 6 Patton Drive, Hamilton, MA Tel marcj@texturetechnologies.com Mr. Marc Johnson is President of Texture Technologies Corp, the North American distributor of SMS s TA.XTPlus Texture Analyzer. Since 1993 Mr. Johnson has been designing test fixtures and protocols to solve industrial and academic client testing problems in the adhesive, pharmaceutical, cosmetic and food industries. He is a frequent lecturer on issues related to industrial texture and adhesive measurement. Marc Johnson was graduated from Hobart College with a BA in Economics and from The Wharton School, University of Pennsylvania with an MBA. Before joining Texture Technologies, Mr. Johnson was responsible for commercial real estate acquisitions on behalf of domestic and international pension funds.

2 NOVEL AUTOMATED METHOD FOR ANALYZING PEEL ADHESION Ben Senning, Territory Manager, Texture Technologies Corp, Hamilton, MA Marc Johnson, President, Texture Technologies Corp, Hamilton, MA Constant 90⁰ peel tests are typically performed with sled fixtures, which are driven by wires and pulleys that must be aligned in an exactly perpendicular manner in order for the sled stage to move horizontally at the same speed that the crossarm moves upwards. The adhesive industry uses this method because the fixtures are relatively cheap and easy to use. Sled based 90⁰ peel systems often have difficulty maintaining peel speeds because of how tapes backing influence peel behaviors and inconsistently drawn down adhesives introduce chatter. The initial slack alignment also needs to be precise or else load cells may be improperly zeroed and peel angles can deviate from the targeted 90⁰ ideal. Ironically, higher quality sleds with ultra-smooth bearings can be among the most variable because the sleds can move independently from the wire with less effort. The result of these variables is that the tape/plate interface peel is often highly erratic. This paper addresses how we used a texture analyzer and an automated linear stage to work in unison to eliminate these mechanical issues with peel testing. By synchronizing the stage with the cross arm, the peel angles and peel speeds are perfectly maintained throughout the full peel. Additionally, tapes can be mounted with a uniform initial slack force so load cells can be properly zeroed and measured peel forces are accurate. This method generates peel replicates that are influenced by fewer non-product variables and the resulting measured peel forces are much more repeatable. This method also uses a preprogrammed starting position so that mounted samples are located into an exact starting position, allowing a higher throughput of test replicates. This study explores how the peel tests can be conducted at variable speeds, rather than at a single constant speed. That allows researchers, with the same number of replicates as they would ordinarily deploy for their peel tests, to collect information about how their tapes behave under different peel conditions. Types and Sources of Tapes To demonstrate these tests we established a baseline set of experiments using various brands, types and widths of office tape. Among the samples which we used were store-bought Scotch Invisible ¾ and ½ wide tapes, Staples Invisible ¾ wide tape, Caliber Invisible ¾ and ½ wide tapes, Scotch Transparent ½ wide tape, and Caliber Transparent ½ wide tape. We used the same tapes for the multi-speed peel tests and then also evaluated Scotch and FrogTape brand Delicate and Multi-surface painter s tape (both 0.94 wide); Staples Packaging tape (cut to 1.00 wide strips); as well as two natural rubber adhesive tapes (0.94 and 0.97 wide) and a synthetic rubber tape. Sample Preparation We used 9 long strips which were prepared by folding over the last inch of tape to create a handling tab. This handling tab was clamped into an upper grip. The opposite end of each sample was placed gently on a bright annealed polished stainless steel test panel and set in place using a standard 4½ pound rubber roller. The tab was held in the air by hand so that the tape did not come into contact with the test panel until the roller rolled over the tape and bonded it against the test panel. The tests were conducting in an office that was at between 60 o and 65 o F. Three replicates of each tape were tested. The instrument layout can be seen in Pictures 1 & 2 below.

3 Pictures 1 & 2 Set Up of Peel Tests on Linear Stage Test Settings For the single speed tests we programmed the instrument and the linear stage to maintain a constant 90⁰ peel angle by synchronizing both devices to move at 5.08 mm/second for a peel distance of 180 mm. For the multi-speed tests the texture analyzer and linear stage were synchronized at six increasing speeds for 30 mm long segments each. The six peel speeds used were 5.0 mm/sec, 10.0 mm/sec, 15.0 mm/sec, 20.0 mm/sec, 25.0 mm/sec, and 30.0 mm/sec. These speeds and peel lengths can be easily altered to address specific research or QC objectives. These tests can be accomplished very efficiently. It took under 40 seconds each to conduct and analyze the single speed tests and under 20 seconds each to conduct and analyze the multi-speed tests. Test Analysis and Results For the single speed tests the mean peel strength (in both grams and lb/inch width units) was automatically calculated between 30 mm and 150 mm of the 180 mm stroke (Plot 1 below). For the multi-speed tests mean peel strength and peel quality metrics were automatically calculated from the 10 mm through 25 mm sections of each of the six 30 mm segments (Plot 2 & 3). A jagged line analysis was folded into the ordinary 90⁰ peel macro in order to analyze the quality of the peel. The jagged line analysis has the following elements: Calculates the number of positive peaks at a chosen force threshold Calculates the linear distance of the jagged line Creates a corresponding smooth line using a Savitzky-Golay filter set to 100 running points Calculates the linear distance of the smooth line Calculates Jagged/Smooth Ratio as a quality of peel metric In this study we used a threshold of 1 gram to pick up the largest number of peaks possible for each replicate. The number of peaks and the Jagged/Smooth Ratio for the single speed tests can be seen in Table 1 and in Table 3 for the multi-speed tests. Among these office tapes, the Scotch Invisible ¾ tape recorded the highest and the Scotch Invisible ½

4 recorded the lowest mean nominal force. On a mean strength basis, The Scotch Transparent ½ was the strongest of the office tapes (Table 1). From a quality of peel perspective, the two transparent tapes were the smoothest and experienced the fewest peak force events. The Caliber Invisible ¾ tape recorded the largest number of 1 gram peaks and had the largest Jagged/Smooth Ratio, suggesting that its adhesive bonds released more irregularly and more sharply than the other office tapes. Table 1. Analysis of 30mm - 120mm for Single Speed Tests Mean Mean Number of Positive 1g Peaks Jagged/Smooth Ratio % Caliber Invisible.75" Scotch Invisible.75" Staples Invisible.75" Caliber Invisible.5" Scotch Invisible.5" Caliber Transparent.5" Scotch Transparent.5" Table 1. Analysis of 30 mm -120 mm for Single Speed Tests Plot 1. Average Office Tape Single Speed Peel Tests Distance (mm) Plot 2. Typical Multi-speed Peel Test on an Office Tape

5 User 1: Smoothed Distance (mm) Plot 3. Typical Multi-speed Peel Test on Office Tape with Analysis of Peel Quality Plot 3 shows the quality of peel analysis as it was applied to an office tape. Note the smoothed line that is plotted on the second Y axis. The ratio of the length of those segments, compared the lengths of the original jagged segments, allows the degrees of jaggedness to be compared between tapes of different strengths. The quality of peel can be influenced by the quality of the adhesive layer, the cavitation which occurs during peel action, by the backing, and many other factors. In all events, knowing quality of peel metrics, in addition to mean peel strengths, will assist researchers to formulate tapes to specific applications. All of the peel strengths for all of the tapes evaluated for this study increased at each sped step in comparison to their previous speed with two exceptions. Those two were the synthetic rubber adhesive tape and one of the natural rubber adhesive tapes, both of which exhibit slightly lower forces at 30.0 mm/sec then they measured at 25.0 mm/second. These metrics can be seen listed in Table 3 and depicted in Plots 4-6 and Charts 1-3. (lb/in) Scotch Transparent.5 Caliber Transparent.5 Scotch Invisible.75 Caliber Invisible.5 Scotch Invisible.5 Caliber Invisible.75 Staples Invisible Distance (mm) -0.1 Plot 4. Representative Office Tapes at Six Speeds

6 mm/s 10 mm/s 15 mm/s 20 mm/s 25 mm/s 30 mm/s Scotch Invisible.75 in Caliber Invisible.75 in Staples Invisible.75 in Scotch Invisible.5 in Caliber Invisible.5 in Scotch Transparent.5 in Caliber Transparent.5 in Chart 1. of Office Tapes at Six Speeds (lb/in) Scotch blue Delicate.94 Six FrogTape Multisurface.94 Six FrogTape Delicate.94 Six Scotch Blue Multisurface.94 Six Distance (mm) Plot 5. Representative Painter s Tapes at Six Speeds

7 mm/s 10 mm/s 15 mm/s 20 mm/s 25 mm/s 30 mm/s Scotch Blue Multi.94 in Frog Tape Multi.94 in Scotch Blue Delicate.94 in Frog Tape Delicate.94 in Chart 2. of Painter s Tapes at Six Speeds (lb/in) Natural Rubber Six PVI Natural Rubber 001 Synthetic Rubber Six 001 Staples Packaging Six Distance (mm) Plot 6. Representative Rubber & Packaging Tapes at Six Speeds

8 mm/s 10 mm/s 15 mm/s 20 mm/s 25 mm/s 30 mm/s Synthetic Rubber.94 in Natural Rubber B.94 in Natural Rubber A.97 in Staples Packaging 1.00 in Table 2 Chart 3. of Rubber & Packaging Tapes at Six Speeds Ratio Speed 6 to Speed 1 Scotch Invisible.75 in 134% Caliber Invisible.75 in 137% Staples Invisible.75 in 158% Scotch Invisible.5 in 147% Caliber Invisible.5 in 139% Scotch Transparent.5 in 127% Caliber Transparent.5 in 137% Scotch Blue Multi.94 in 150% Scotch Blue Delicate.94 in 158% Frog Tape Multi.94 in 137% Frog Tape Delicate.94 in 158% Synthetic Rubber.94 in 113% Natural Rubber A.97 in 133% Natural Rubber B.94 in 150% Staples Packaging 1.00 in 117% The magnitude of peel force increases due to speed changes were not consistent between the tapes tested, as can be seen on Charts 1-3 and shown in Table 2. Some products, like the Staples Packaging Tape or the synthetic rubber tape were highly insensitive to different peel speeds. Their peel strengths increased 17% and 13% respectively, when the speeds were increased 600%. The Staples Invisible ¾, Scotch and FrogTape brand Delicate painter s tapes all demonstrated a 58% increase in peel strength over the same speed change. The quality of peel metrics dropped proportionally for all tapes as the peel speeds increased. In particular, at the faster speeds the visible cavitation patterns all became more uniform. Pictures 3 and 4 show close-up screen captures from high definition videos that were captured while the tapes were peeled. These particular close-up pictures were taken during the 3 rd speed (15 mm/sec) segments. Notice that the cavitation patterns were more consistent among the painter s tapes than among the natural & synthetic rubber tapes. A further investigation will be made on these tapes to explore peel quality behaviors at increasingly slow peel forces, since the videos (to be shown in the presentation) suggests that cavitation differences are more apparent at the slower speeds.

9 Picture 3 High Definition Video Screen Capture of Painter s Tapes during Speed #3 Picture 4 High Definition Video Screen Capture of Rubber Tapes during Speed #3 Conclusions Constant 90⁰ peel testing has been conducted on sled/pulley systems and synchronized mechanical peel testing instruments for many years now. This paper introduces the ability to evaluate the peel performance of tapes under an array of different speeds during a single peel stroke. The study also demonstrates that the analysis of these relatively complex stepping plots can be automated and evaluated for both peel strength and quality of peel metrics. Acknowledgments I would like to thank Mr. Ben Senning, Territory Manager for Texture Technologies Corp, for conducting all of the testing and analysis that supported this paper.

10 Table 3 Complete set of Multiple Speed Peel Test Data Mean Values (n=3) Speed 1 5 mm/s Speed 2 10 mm/s Speed 3 15 mm/s Speed 4 20 mm/s Speed 5 25 mm/s Speed 6 30 mm/s # 1g Peaks Jagged/ Smooth Ratio Scotch Invisible.75 in Caliber Invisible.75 in Staples Invisible.75 in Scotch Invisible.5 in Caliber Invisible.5 in Scotch Transparent.5 in Caliber Transparent.5 in Scotch Blue Multi.94 in Scotch Blue Delicate.94 in Frog Tape Multi.94 in Frog Tape Delicate.94 in Synthetic Rubber.94 in 1, , , , , , Natural Rubber A.97 in Natural Rubber B.94 in , , , Staples Packaging 1.00 in