Understanding the characteristics of your substrate(s) is key. Adhesive tape bonds to a wide range of substrates with varying characteristics such as texture, porosity, flexibility and surface energy. Commonly bonded substrates include high surface energy (HSE), low surface energy (LSE) and PVC plastics; HSE metals, aluminium, stainless steel, zinc, tin and lead; Glass; Wood; Cardboard; Powder-coated paint; Ceramics; Fabric; Foams; and Rubber.
To function optimally, an adhesive should have good adhesion, or physical (and sometimes chemical) bonding of one material to another because of a variety of possible molecular interactions between the substrate surface and the adhesive. It should also have good cohesion, or internal strength, as a result of a variety of molecular forces within the adhesive itself, including chemical bonds, entanglements due to high molecular weight, intermolecular interactions, and mechanical adhesion.
Although the characteristics of a tape’s adhesive can be formulated to activate upon exposure to heat or solvent, most often their needed catalyst is just pressure. Customarily, firm and even pressure during application increases bond strength. From this point, the ultimate bond strength may take between a few minutes and 72 hours to be reached. Most often, however, bonded parts can be handled immediately.
Adhesive tapes have been developed to withstand a variety of forces on the bond. From low tack, repositionable and removable to very high strength, permanent bonding, adhesive tapes and films are available in a wide range of strengths. To ensure you are using the correct adhesive strength, it is important to understand the stresses, or load, the bond will be subjected to. Consider the following:
The answers to these questions will allow a tape manufacturer to specify a product for you, along with advice on the amount of tape and coverage needed.
As a rule, tapes perform better when the primary stress is tensile or shear. Most industrial applications involve a combination of stresses.
All stress force images on this page supplied by 3M
Peel stress occurs when the pull concentrates along a thin line at the edge of the bond where at least one substrate is flexible. Once peeling has begun, the stress line stays out in front of the advancing bond separation.
Place basic stress in shear or tensile and minimise or eliminate cleavage and peel in the cases of Lap joints; Angle joints; Butt joints; Cylindrical joints; Corner joints (e.g., sheet metal, rigid members); and Stiffener joints.
Picture supplied by Nitto
Will the tape be subjected to extreme temperatures? Moisture or humidity? UV light?
Environmental conditions directly affect the performance of adhesive tape, not only during its use but when it is applied and stored. The wide range of industries and end products using adhesive tapes indicate the varying environmental conditions to which they can be exposed. This could be outdoors and subject to wind, rain and dirt or extreme temperature changes such as those which aircraft experience.
Adhesive tapes have been designed specifically to accommodate a myriad of environmental conditions, including exposure to high and low temperatures, UV light, humidity and moisture, contamination, chemicals and shock.
Thin tapes are available in wide varieties for fixing and bonding thin, lightweight and flexible materials and small rigid parts. Thin bonding tapes and films are also optimal in bonding smooth surfaces, e.g. glass, metal and plastic.
Adhesive transfer tapes have no carrier and offer the thinnest bond line. A high shear strength acrylic adhesive can be used for these.
A double-sided tape with a film or paper carrier and an acrylic or rubber adhesive can be used to obtain a thin bond line and easier handling as these are more dimensionally stable and can be chemically stable and heat-resistant. Some offer removability, such as surface protection coated adhesive films and papers, masking tape and medical tapes intended for skin contact. High-performance double-sided tapes are used as solutions in electronics and mobile devices.
Thick tapes are used for fixing or bonding thick, stiff and medium-to-heavyweight materials, including surfaces that are structured, irregular and rough. They are also used for gap-filling. Often the extent of surface mismatch and roughness determines the choice of tape thickness.
Single- and double-coated cloth, foam and very high-strength bonding tapes are used for gap filling, shock absorption, abrasion resistance, and sealing. Providing extra bond strength through the carrier, thicker bonding tapes are characterised by a long-term, high-performance bond, dimensional stability and easier handling and are used in diverse applications. Non-woven/tissue double-sided tapes are conformable, heat-resistant and hand-tearable.
Single-sided cloth varieties include duct and gaffer tapes and harnessing tape for (automotive) cabling. Double-sided cloth tapes are used for temporary applications such as carpet laying. Picture provided by Nitto
Single-sided foam tapes are often used for sealing out draughts. Double-coated foam tapes are used in mounting and holding indoors. They can accommodate expanding and contracting substrates and absorb shock and vibration.
Very high-strength bonding tapes are used in mounting, holding and joining outdoors due to their high bond strength and environmental resistance, i.e. they can withstand prolonged exposure to chemicals, varying temperatures and plasticisers.
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