a comprehensive guide to adhesive tape properties and selection Table of Contents Pressure Sensitive Tape Basics 3 T.A.P.E.S. - The 5 Factors of Adhesion 6 The Big 3: Components, Formats, and Adhesives 15 Choosing the Right Adhesive 20 Matching Tape and Application: Questions to Ask 25 Categories & Functions of Adhesive Tapes 27 Tape Glossary 32 Pressure Sensitive Tape Basics Page 3 What is a Pressure Sensitive Tape? The Pressure Sensitive Tape Council (PSTC) denes Pressure Sensitive Tape as a continuous exible strip of cloth, paper, metal or plastic coated on one or both sides with a permanently tacky adhesive at room temperature which will adhere to a variety of surfaces with light pressure (nger pressure) with no phase change (liquid to solid) and usually on a roll. The key point that dierentiates a pressure sensitive tape from other types of adhesives is that no activation by water, solvent, or heat is necessary to exert a strong adhesive force towards diverse materials such as paper, glass, wood, plastic, or metal. PRESSURE SENSITIVE ADHESIVES POLYMER VISCOELASTICITY polymeric materials in an elastomeric a large molecule consisting of many refers to the state of having the state of matter that have signicant (poly) atoms linked in a repeating, characteristics of both a liquid and a time and temperature dependencies chainlike fashion (macromolecule). solid. (viscoelasticity). They are inherently tacky and have peel and load bearing properties. THE ELEMENTS OF A PRESSURE SENSITIVE ADHESIVE Adhesion Cohesion Pressure sensitive adhesives function as a result of three separate properties: substrate substrate Adhesion, Cohesion, and Tack. bonding strength of inner strength of These three properties balance one adhesive to substrate the adhesive Tack another, meaning that it is impossible to have a tape with 100% of each. immediate grip of adhesive to substrate Page 4 The Science of Adhesion Adhesion science is a multidisciplinary science pulling elements from Physics, Chemistry, and Mechanics. The Physics of adhesion science involve SURFACE ENERGY, also called POLARITY, and the WET-OUT of adhesives to the surface to which they are applied. The Mechanics of adhesion science involve Surface Roughness and Rheological Theory, or the ow of matter under an applied stress. The Chemistry of adhesion science involves the understanding and properties of several important polymers, including Polyester, Polypropylene, Polyethylene, Polyurethane, and more. It also involves several copolymers and compounds, including Natural Rubber, Styrene Butadiene, Butyl Rubber, Silicones, and Acrylics. SURFACE TENSION AND WETTABILITY Adhesive > Substrate Adh. Adhesive = Substrate Adh. Adhesive < Substrate Adh. Page 5 T.A.P.E.S. The 5 Factors of Adhesion Page 6 TAPES - The 5 Factors of Adhesion Pressure The amount of force used to adhere the tape Adhesive Environment Any material that will usefully hold two or All conditions of the substrate and the more objects together solely by intimate surrounding environmental impacts on the surface contact adhesive bond Time Substrate The amount of time the adhesive is allowed The surface with which the adhesive will be to dwell on the surface before eective forces in direct contact are applied Page 7 TIME All In The Timing Full bond strength between the adhe- sive and substrate can take up to 72 hours. 15-150% The strength of the bond builds gradu- Increase in bond strength during ally over time and varies based on the rst few days of application tape you are using RUBBER ADHESIVE bonds grow quickly, but ACRYLIC ADHESION may take up to 72 hours to reach full strength. A very general rule is 50% total adhesion in 20 minutes, 80% within 24 hours, and 100% within 72 hours. Page 8 ADHESIVE FACTORS: Type of Adhesive, Coating Weight, Hardness of Adhesive SOFT Adhesives HARD Adhesives Low Cohesion (Inner Strength) High Cohesion (Inner Strength) Flows easily on irregular surfaces Lower tack (less ow on rough surfaces) Limited temperature resistance Higher temperature resistance Adhesive tears easily under parallel stress Higher nal bond, better resistance to parallel stress Lower nal Bond Lower initial adhesion requires higher pressure or temperature PSAs behave like liquids and solids at the THE ELEMENTS OF A PRESSURE SENSITIVE ADHESIVE same time - they are viscoelastic Adhesion Cohesion High Coat Weight = Better ow on uneven surfaces Low Coat Weight = Good ow on smooth surfaces substrate substrate bonding strength of inner strength of adhesive to substrate the adhesive LIQUID ADHESIVES Tack Liquid adhesives allow for fast wetting to create molecular contact. They can set in one of three immediate grip of adhesive to substrate ways: evaporation of a solvent, curing/cooling, or chemical cross-linking Page 9 ADHESIVE - ADHESION The most important element in determining ADHESION IS: the proper Adhesive for your application is the Adhesion of the Adhesive - or how well • Attraction between adhesive and substrate it will stick to the exact surface to which you will be applying the tape. • Most important parameter in every application Every tape has a dierent adhesion • Usually increases during the rst few days depending on the substrate, and it is most important to keep this in mind when • Must not be confused with tack choosing at tape! ADHESIVE - COHESION When considering the delicate balance for the eectiveness of a PSA, a major element is an adhesive’s cohesive factors. Cohesion refers to the inner strength of the adhesive, and directly helps create and inuence surface energy, both for the adhesive itself, and how it interacts with the substrate to which it’s being applied. Some key points to keep in mind about cohesion: • Relevant for forces parallel to the bonding area • High cohesion goes together with substrate • Higher temperature resistance • Lower tack • Higher holding power substrate Page 10 ADHESIVE - TACK Tack is the property of a pressure sensitive adhesive that allows it to adhere to a surface under very slight pressure. It is determined by the ability of the adhesives to quickly wet the surface it contacts. When measuring tack, the bond formation is recorded after less than one second at low pressure, and debonded in less than 0.01 seconds. These are adhesion tests, and are generally measured in one of two ways: Rolling ball tack is measured when a stainless steel ball is released onto a strip of tape at a 30° angle. The distance the ball travels is measured, generally in inches or centimeters. Loop tack is where a piece of tape is looped, adhesive side out, and quickly dipped onto a substrate and removed. This is generally measured in oz/in. Page 11 PRESSURE FACTORS: Application Weight Pressure Sensitive Adhesives got their Wet-Out: The condition of being completely name because they will not form a covered, and lled, with a resin - devoid of air full bond unless pressure is applied to bubbles or other occlusions preventing the fully wet-out the adhesive on the adhesive to fully bond with the substrate. substrate. The more pressure that is applied during application of the tape, the better the bond. Ideal adhesion will RULE OF THUMB have 100% wet-out, but many Most pressure sensitive adhesives take around 15lbs of pressure sensitive adhesives pressure to achieve a strong bond. You can achieve this achieve high bond strength by applying heavy pressure with your thumb along the with as little as 70% wet-out. length or by using a J-Roller or other pressure system. Page 12 ENVIRONMENT FACTORS: Air, Light, Humidity, Temperature and their Interactions The environment is a major factor when it comes to adhesion. All adhesive and backing combinations respond dierently to the same environmental conditions. Too high of a temperature and the adhesive can break down - too low and it becomes brittle. Humid climates or exposure to UV light can cause adhesive failure. Chemical or solvent exposure can completely destroy a bond with some adhesives. It’s important to know all the environmental factors when deciding on the ideal tape. Some of these include: Interior or Exterior Application Service Temperature Exposure to moisture or UV ≥50° F Ideal temperature for applying Chemical, solvent, or outgassing reactions many pressure sensitive tapes It is important to remember that most tapes insulate against heat and may take many hours to reach room temperature. If a tape gets too warm, it may become soft, and the adhesive could begin If the environmental temperature is dicult to regulate, to run. Conversely, if an adhesive is too cold, it can you can generally follow these guidelines when trying become brittle and glass-like, shattering under to select the ideal adhesive: pressure or losing tack and adhesion. 20°F to 150°F -> Rubber Adhesive 0°F to 400°F -> Acrylic Adhesive -20°F to 500°F -> Silicone Adhesive * Note: Many rubber-based adhesives (found in many masking and other tapes) are formulated for higher tempertures, and blended acrylics oer a wide range of temperature resistance. Page 13 SUBSTRATE FACTORS: Surface Energy, Surface Conditions High Surface Energy (POLAR) Other terms that refer to surface energy are Steel surface tension and polarity Aluminum Copper SURFACE TENSION AND WETTABILITY Zinc Polycarbonate Adhesive > Substrate Adh. ABS (Acrylonitrile-Butadiene-Styrene) PVC (Polyvinyl chloride) Adhesive = Substrate Adh. Low Surface Energy (NON-POLAR) Rubber Polyethylene (PE) Adhesive < Substrate Adh. Polypropylene (PP) Powder Coatings Silicone POLAR substrates are easy to bond while Teon NON-POLAR substrates present a challenge Another factor of the substrate to consider is the contour of the surface. An ideal surface will be at, but sometimes you may nd yourself battling the stresses associated with bonding along corners, convex curves, or concave angles. These stresses can cause tape to delaminate from the surface, so it is very important to take them into consideration when choosing the appropriate adhesive. Further, the presence of surface contaminants can interrupt the bond between the adhesive and the substrate.