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peel adhesion test iconPeel and Adhesion Testing

Adhesive strength is measured for many purposes. Some bonds are designed not to break in use (e.g. construction materials), some are designed to allow separation in normal use (e.g. a foil lid), and others are designed to be resealed a number of times (e.g. resealable bag tape). Some things peel without a separate adhesive layer, such as an induction-welded foil, or grip seal bags, and some adhesive joins for security come apart but must not reseal. Adhesive bonding can be measured by tensile testing, shear testing or compression testing, but where there is flexibility in a joined layer, a peel test is appropriate.

A universal tester can be used for any peel test. It will capture high frequency data points, and produce a characteristic curve that will show the strength and evenness of the adhesion. The advantage of using a Mecmesin universal tester is that it can also be used for adhesive shear and compression tests, or coatings pull-off tests.

Predictable opening

Packaging is mainly for the protection or preservation of contents—from physical damage or contamination—and may experience wide variations in temperature from manufacturer to end user. Increasingly, it is designed to open easily by peeling rather than tearing, and without mechanical aid. However, when peelable seals are bonded too strongly, elements can break off, the packaging can delaminate, fail unpredictably or not open fully, or the ability to peel at all can be lost. In the case of resealable packaging, performance must be tested for repeat use. Pressure sensitive tapes and labels are tested in similar ways, for their use in diverse applications.

Reliable adhesion

For fixing one thing to another, adhesive strength (or resistance) is usually what matters most. Some things must not peel apart, such as copper tracks on circuit boards. For others, such as labels, tapes, coatings, inks, laminated cards, or transdermal drug-delivery patches, consistent retention or removal by peeling can both be equally important. In many cases, peelable elements also carry important information that must not be destroyed or lost. Adhesives themselves are frequently tested in lap shear joints, where compressive and tensile tests may both be required, and coatings must be subjected to pull-off strength methods.

Brand image

Aside from the direct cost of wastage from failure, seal and adhesive performance, and coatings durability, are part of a company’s brand, and reflect on perceived product quality and reliability. Peel and adhesion testing is therefore a vital element in quality assurance, as well as in the design of new packaging and closure methods. As packaging design changes in response to environmental concerns, containers need to be stronger whilst using less in materials. And with an ageing population, many consumables, including medical items, need to be accessible to the less strong and dexterous. Peel strength really matters.

Types of peel test

90 degree peel test floating roller peel test 90 degree constant angle PSA tape peel test wheel fixture 180 degree peel adhesion test T-peel test for peel strength in flexible bonds
Floating roller or (without rollers)
moving table
Floating roller (115 degrees) Peel wheel 180 degree peel T-peel

 

Standard test methods tend to prescribe the speed and angle of separation in order to be repeatable. A tester can ensure the consistent speed, but fixtures are required to maintain the correct angle. Any angle can be used, providing it is applied accurately for each test. If a package with a peelable lid is known to be typically opened by hand at 45 degrees, that may be a better internal standard for comparison.

Where one bonded layer is significantly more flexible (e.g. semi-rigid packaging) than the other, a 90 degree test may be most appropriate. Here the holding of the two parts is important, and Mecmesin regularly designs and manufactures custom vacuum-operated holders for preformed plastic retorts and trays. A laminated ID card, by contrast, has a slightly flexible substrate, so a horizontal floating roller fixture can be used. As the peeled layer is pulled vertically up and off, the card is free to move horizontally, maintaining a 90 degree angle of separation. If the substrate is quite rigid (e.g. copper tracks on a printed circuit board), it can simply be secured down, but must still travel proportionately across as the peeled layer is pulled up, to maintain the angle. This is done with an assisted, or moving table fixture.

Pressure sensitive adhesive (PSA) tape can be peel tested from a standard metal surface at 90 degrees, or at 180 degrees (i.e. pulled back on itself). For 90 degrees, a friction-free wheel fixture may be used, or at 115 degrees (ASTM D3167 and equivalents) using a specified floating roller. Both fixtures ensure a constant angle of separation. (The latter largely replaces the climbing drum method.) For 180 degree tests, the tape can be applied to a vertical metal plate which is pulled up, away from the secured end of the tape. For tapes with a backing strip, a 180 degree peel can be achieved by pulling the sample against a supporting plate. Where the adhesive is intended for clinical use (e.g. a pharmaceutical transdermal patch), a special substrate is required to mimic skin.

Two bonded layers that are equally flexible, such as a sterile medical syringe package, or a laminated belt, when pulled apart will form a T shape. The angle of separation is 180 degrees, but this is called a T-test. The horizontal part of the sample may require finger support so that the angle remains constant through the test. In all 180 degree tests there needs to be sufficient column height in the universal tester for adequate sample length and peel distance.

A similar test to peel for pressure sensitive adhesive tapes is the loop tack method. Here the adhesive side of a loop of the tape is lowered onto a substrate without being rolled or pressed, and then lifted off, to measure the tensile strength of the adhesion or 'tack'.

peel adhesion loop tack test

Mecmesin has a range of universal testers, grips and fixtures suitable for all standard peel tests, and designs and supplies custom fixtures where standard grips are unsuitable.

Related test types

See examples of our capabilities

Peel adhesion test standards

  • Afera 5001 : self adhesive tapes - measurement of peel adhesion from stainless steel or from its own backing (and other Afera standards)
  • ASTM D413 : rubber property - adhesion to flexible substrate
  • ASTM D429 : rubber property - adhesion to rigid substrates
  • ASTM D903 : peel or stripping strength of adhesive bonds
  • ASTM D1876 : peel resistance of adhesives (T-peel test)
  • ASTM D2918 : durability assessment of adhesive joints stressed in peel
  • ASTM F 2256 : strength properties of tissue adhesives in T-peel by tension loading
  • ASTM D3167 : floating roller peel resistance of adhesives
  • ASTM D3330 : peel adhesion of pressure-sensitive tape
  • ASTM D6496 : determining average bonding peel strength between the top and bottom layers of needle-punched geosynthetic clay liners
  • ASTM F88 : seal strength of flexible barrier materials
  • BS EN 868-5 : packaging materials and systems for medical devices which are to be sterilized. Heat and self-sealable pouches and reels of paper and plastic film construction. Requirements and test methods
  • BS EN 1464 : adhesives. Determination of peel resistance of high-strength adhesive bonds. Floating roller method
  • BS EN 1719 : adhesives for paper and board, packaging and disposable sanitary products. Tack measurement for pressure-sensitive adhesives. Determination of loop tack
  • BS EN 1895 : adhesives for paper and board, packaging and disposable sanitary products. 180°. ‘T’ peel test for a flexible-to-flexible assembly
  • BS EN 12242 : touch and close fasteners. Determination of peel strength
  • DIN 53289 : testing of adhesives for metals and adhesively bonded metal joints; floating roller peel test
  • FINAT FTM1, FTM2, FTM3 : peel adhesion of pressure sensitive adhesive tapes and labels
  • FINAT FTM9 : loop tack measurement
  • ISO 4578 : adhesives - Determination of peel resistance of high-strength adhesive bonds - Floating-roller method
  • ISO 6133 : rubber and plastics - Analysis of multi-peak traces obtained in determinations of tear strength and adhesion strength
  • ISO 8510 : adhesives - Peel test for a flexible-bonded-to-rigid test specimen assembly - Part 1: 90 degree peel and Part 2: 180 degree peel
  • ISO 10373 : identification cards - test methods - part 1 general characteristic tests
  • ISO 11339 : T-peel test for flexible-to-flexible bonded assemblies
  • ISO 14676 : adhesives - Evaluation of the effectiveness of surface treatment techniques for aluminum - Wet-peel test by floating-roller method
  • ISO 11607-1 : packaging for terminally sterilized medical devices - Part 1: Requirements for materials, sterile barrier systems and packaging systems
  • PSTC 16 : Loop tack adhesion

More peel / adhesion standards

See Mecmesin’s range of peel adhesion testers