science

Pressure-sensitive adhesive

Pressure-sensitive adhesive is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Pressure-sensitive adhesive rather than just read about it. In short: Pressure-sensitive adhesive (PSA, self-adhesive, self-stick adhesive) is a type of nonreactive adhesive which forms a bond when pressure is applied to a surface not requiring any solvents, water, or heat. It is used in pressure-sensitive tapes, labels, glue dots, stickers, sticky note pads, automobile trim, and a wide variety of other products.

Key takeaways

Pressure-sensitive adhesive belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Pressure-sensitive adhesive to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Pressure-sensitive adhesive from memory before moving on to harder problems.

Reference excerpt

Pressure-sensitive adhesive (PSA, self-adhesive, self-stick adhesive) is a type of nonreactive adhesive which forms a bond when pressure is applied to a surface not requiring any solvents, water, or heat. It is used in pressure-sensitive tapes, labels, glue dots, stickers, sticky note pads, automobile trim, and a wide variety of other products. As the name "pressure-sensitive" indicates, the degree of bond is influenced by the amount of pressure which is used to apply the adhesive to the surface. Surface factors such as smoothness, surface energy, cleanliness, etc. also affect the resulting bond. PSAs are usually designed to form a bond and hold properly at room temperatures. PSAs typically reduce or lose their tack at low temperatures and reduce their shear holding ability at high temperatures, though there are special adhesives made to function at high or low temperatures.

Structural and pressure-sensitive adhesives Adhesives may be broadly divided in two classes: structural and pressure-sensitive. To form a permanent bond, structural adhesives harden via processes such as evaporation of solvent (for example, white glue), reaction with UV radiation (as in dental adhesives), chemical reaction (such as two part epoxy), or cooling (as in hot melt). In contrast, pressure-sensitive adhesives (PSAs) form a bond simply by the application of light pressure to marry the adhesive with the adherend. Pressure-sensitive adhesives are designed with a balance between flow and resistance to flow. The bond forms because the adhesive is soft enough to flow, or wet, the adherend. The bond has strength because the adhesive is hard enough to resist flow when stress is applied to the bond. Once the adhesive and the adherend are in proximity, there are also molecular interactions such as van der Waals forces involved in the bond, which contribute significantly to the ultimate bond strength. PSAs exhibit viscoelastic (viscous and elastic) properties, both of which are used for proper bonding. In contrast with structural adhesives, whose strength is evaluated as lap shear strength, pressure-sensitive adhesives are characterized by their shear and peel resistance as well as their initial tack. These properties are dependent, among other things, on the formulation, coating thickness, rub-down and temperature. "Permanent" pressure-sensitive adhesives are initially pressure-sensitive and removable (for example to recover mislabeled goods) but after hours or days change their properties, by becoming less or not viscous, or by increasing the bond strength, so that the bond becomes permanent.

Effects of shape The adhesive bonding of a tape or label can be affected by its shape. Tapes with pointed corners start to detach at those corners; adhesive strength can be improved by rounding the corners.

Applications

Examples of permanent applications include safety labels for power equipment, foil tape for HVAC duct work, automotive interior trim assembly, and sound/vibration damping films. Some high performance permanent PSAs exhibit high adhesion values and can support kilograms of weight per square centimeter of contact area, even at elevated temperature. These build adhesion to a permanent bond after several hours or days.

Removal Removable adhesives create a temporary bond and can often be taken off after months or years without leaving residue. They’re used in protective films, masking tapes, sticky notes and bookmarks, price labels, promotional materials, and skin-contact products like dressings, EKG electrodes, athletic tape, and transdermal patches. Some are made to stick and unstick repeatedly; they have low adhesion and can't support much weight. Sometimes clean removal of pressure sensitive tape can be difficult without damaging the substrate that it is adhered to. Pulling it off slowly and at a low peel angle helps reduce damage. Adhesive residue can be softened with heat or certain organic solvents. Extreme cold (like dry ice or freeze spray) can turn viscoelastic materials glassy and is useful for removing many PSAs.

Manufacture Pressure-sensitive adhesives are manufactured with either a liquid carrier or in 100% solid form. Articles such as tapes and labels are made from liquid PSAs by coating the adhesive on a support and evaporating the organic solvent or water carrier, usually in a hot air dryer. The dry adhesive may be further heated to initiate a cross-linking reaction and increase molecular weight. 100% solid PSAs may be low viscosity polymers that are coated and then reacted with radiation to increase molecular weight and form the adhesive (radiation cured PSA); or they may be high-viscosity materials that are heated to reduce viscosity enough to allow coating, and then cooled to their final form (hot melt PSA, HMPSA).

Composition

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Pressure-sensitive adhesive

Start with the simplest possible case. Write down what Pressure-sensitive adhesive claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Pressure-sensitive adhesive before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Pressure-sensitive adhesive ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Pressure-sensitive adhesive

In research: Pressure-sensitive adhesive appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Pressure-sensitive adhesive in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Pressure-sensitive adhesive is common in secondary-school and first-year university syllabi. It links to neighbouring topics Adhesives, Stationery, so understanding it makes those chapters shorter.
In everyday life: Look for Pressure-sensitive adhesive outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Pressure-sensitive adhesive in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Pressure-sensitive adhesive means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Pressure-sensitive adhesive out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Pressure-sensitive adhesive in simple terms?

Why does Pressure-sensitive adhesive matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Pressure-sensitive adhesive?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Pressure-sensitive adhesive.