physics

Liquid optically clear adhesive

Liquid optically clear adhesive is a physics 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 Liquid optically clear adhesive rather than just read about it. In short: Liquid optically-clear adhesive (LOCA) is liquid-based bonding technology used in touch panels and display devices to bind the cover lens, plastic, or other optical materials to the main sensor unit or each other. These adhesives improve optical characteristics and durability.

Key takeaways

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

Reference excerpt

Liquid optically-clear adhesive (LOCA) is liquid-based bonding technology used in touch panels and display devices to bind the cover lens, plastic, or other optical materials to the main sensor unit or each other. These adhesives improve optical characteristics and durability. LOCA glue is often hardened using ultraviolet light. Primary advantages of LOCA compared to other adhesives are its:

Re-workability Adhesion to non-even surfaces Superior optical properties Durability LOCA follows traditional die-cut film adhesives, also known as optically clear adhesives (OCA tape). LOCA also allows for thinner designs and new technologies, such as the use of silicone, that improve the properties of the final product.

Overview Optical bonding, including LOCA and non-liquid OCA tape, are used in a wide range of electronic equipment, especially those with touch panels. The adhesive bonds the touch panel to the main liquid crystal display, and also bonds any protective cover, such as the lens, to the touch panel. After application, the adhesive is cured onto the device through ultraviolet light (UV), heat, moisture, or a combination, depending on the manufacturer and specifications. Major applications include capacitive touch panels, 3D televisions (3D TV), and glass retarders. Optical bonding improves optical performance of displays. It eliminates the air gap between the cover glass and LCD, and usually includes an anti-reflective (A/R) coating (as well as anti-smudge and anti-glare treatments on the cover glass). Optical bonding improves the contrast ratio by reducing the amount of reflected light, thus improving viewability. This is especially important in outdoor applications, where direct sunlight can decrease viewability. Fresnel reflections from the glass as well as the adhesive can degrade LCD viewability. Reflection is caused by an impedance mismatch between air and the glass. The reflection makes the white brighter, but dilutes black and other colors, which decreases contrast. LOCA suppliers aim to match the refractive index of glass and clear plastic PMMA (refractive index approximately 1.5) used in displays to minimize loss. LOCA suppliers such as Momentive Materials and Henkel report an increased contrast of 400% in sunlight through the use of LOCA with anti-reflective glass, vastly improving the viewing experience. Besides the optical advantages, bonding a sheet of glass to the LCD also improves display durability. It can resist scratches, condensation, and has an improved operating temperature range. As touchpad devices become ubiquitous in consumer markets, this increased ruggedness becomes even more important. Also, reducing light loss due to reflection extends battery life, as the device can use less backlight.

LOCA advantages LOCA has many advantages compared to traditional non-liquid film type adhesives (OCA tape). Specifically, it:

Is suitable for application on uneven surfaces Can be repaired and adjusted once cured Can be used in large panels Is completely size-independent, while OCA tape must be pre die-cut Has high adhesion Ideal for filling gaps because it is a liquid Does not suffer condensation and fogging Resists extreme temperatures Requires less surface preparation Is contaminant-free, resulting in improved bubble resistance in laminations exposed to high temperature and humidity Can be applied by automated process Accommodates thinner and lighter display designs Facilitates faster development of new products and designs

Applications LOCA is generally used in displays and touch panel applications. Application is expected to increase as mobile devices, televisions, tablets, monitors and laptops migrate to touch interfaces. Although there are many varied applications, Henkel divides the applications into three categories:

Touch panel sensor assembly To bond touch panel sensors that require two layers of ITO (indium-tin-oxide) coated glass. This type of bonding will eventually be replaced by direct bonding. Cover lens bonding To fill the air gap in touch panel sensors that use a cover lens (such as clear plastic PMMA) and the glass touch panel sensor. Direct bonding To achieve the highest amount of contrast, such as in an outdoor viewing application, it is necessary to "directly bond" the cover lens to the LCD module.

Use of silicone technology While traditional adhesive chemistry relies on acrylic-based liquid, new technologies include silicone. Silicone provides new methods for curing the adhesive. The following table illustrates the difference between acrylic and silicone in single and double curing processes.

The curing process and inherent low modulus of silicone LOCA also helps reduce the amount of haze around the edges of large LCD screens. Silicone technology reduces shrinkage on substrates to less than 1% on larger displays, where acrylic technologies tend to be around 3–5%, depending on display size.

Equipment Dispensing equipment usually includes bubble free dispensers by means of a bottle or cartridge. Curing equipment usually includes UV curing lamps or spot cure systems. Major suppliers of LOCA generally offer both dispensing and curing equipment.

Notes

Worked examples

Example 1 — a first encounter with Liquid optically clear adhesive

Start with the simplest possible case. Write down what Liquid optically clear adhesive claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, 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 Liquid optically clear 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 Liquid optically clear 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 Liquid optically clear adhesive

In research: Liquid optically clear adhesive appears in physics 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 Liquid optically clear 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: Liquid optically clear adhesive is common in secondary-school and first-year university syllabi. It links to neighbouring topics Adhesives, so understanding it makes those chapters shorter.
In everyday life: Look for Liquid optically clear 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Liquid optically clear adhesive” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Liquid optically clear adhesive in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Liquid optically clear 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 Liquid optically clear adhesive out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Liquid optically clear adhesive in simple terms?

Why does Liquid optically clear adhesive matter?

Because it connects several physics 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 Liquid optically clear 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 Liquid optically clear adhesive.