In recent years, we have observed an increase in the market demand for rigid front panels made of glass or plastic. QWERTY has decided to use its previous experience in laminating various surface types (elastic-elastic, elastic-rigid) to develop and implement a new technology for laminating rigid materials, known as optical bonding. 

Bonding involves combining the display (LCM) with the touch panel and a glass or plastic front.

There are several bonding methods: 

Two basic display bonding techniques are Air Gap and Optical Bonding.  

3D visualization of Air Gap and Optical Bonding display bonding techniques.

Air Gap is a standard technique for bonding displays. It involves using a double-sided adhesive tape frame placed around the display to bond it to the front. It is an inexpensive and universal technology for connecting displays, allowing for easy screen or glass front replacement without the need for specific tools. However, the air gap can impact the screen’s clarity, particularly in bright light, due to additional light refraction. Displays with air gaps are also more prone to mechanical damage and moisture-related damage. As a result, they are not the ideal solution for outdoor use or in challenging conditions.  

Optical bonding is the process of bonding a display to a touch panel/front using optically clear adhesive, either in solid or liquid form, to bond a touch panel/front to a display surface. This process includes applying glue to the display surface and then bonding the display to the touch panel/front. While this solution requires specialized equipment and is time-consuming, it offers superior optical parameters (such as reduced light reflections and improved contrast), environmental resistance (including dust and moisture condensation), and mechanical durability. 

Demonstrator showcasing optical bonding and bonding with an air gap pocket for a 5.7′ display with an anti-glare glass panel and a custom digital print on glass. 

Comparison of materials used for optical bonding. 

There are two basic types of optically pure adhesives used for optical bonding: 

  • Solid  
    • OCA (Optical Clear Adhesive) 
    • SOCA (Silicone Optical Clear Adhesive) 
    • SCA (Solid Clear Adhesive) 
  • Liquid 
    • LOCA (Liquid Optical Clear Adhesive) 

Comparison of optically clear adhesives in terms of parameters: 

OCA – Optically clear acrylic adhesive – features transparency and light transmittance of over 90%, strong bonding capability, cures at room or elevated temperature, and has minimal shrinkage. It turns yellow under the influence of UV factors. 
SOCA – Optically clear silicone adhesive – known for its transparency and light transmittance exceeding 90%, weak bond strength, and cures at room temperature. It is delicate in mechanical processing and highly resistant to yellowing. It shows excellent vibration and shock absorption properties. 
SCA – Solid Clear Adhesive – in its original form, it comes in semi-transparent sheets with minimal adhesion. It can be easily applied to the display. Due to high temperature and pressure conditions, the glue changes its viscosity and spreads on the display without air bubbles. This technology requires the use of specialist equipment. 
Whether it is necessary to cure the adhesive with UV rays depends on the recommendations of the manufacturers of the aforementioned optically clear adhesives. 
LOCA – Liquid, optically clear adhesive (also referred to as OCR – optically clear resin) – is found in liquid form with different viscosities, depending on the size of the laminated area. It is characterized by transparency and light transmittance above 98%, good bonding strength, cures at room temperature, and has greater shrinkage. The process is complicated and requires precise dosing. It is difficult to control the flow, and there is a risk of air bubbles during dispensing, leveling, and lamination. Preliminary and final UV curing is possible, but it increases production costs.  

To sum up  

QWERTY, drawing on its previous experience in laminating flexible surfaces, conducted research and refined the technology to meet the growing market demand for optically clear laminating of rigid surfaces. The R&D department’s research has contributed to a comprehensive understanding of various techniques, materials, machinery, and procedures required for optical bonding. As optical bonding experts, we are prepared to customize a solution to meet the customer’s requirements. Our services include guidance in selecting a display based on specific parameters, as well as choosing the optimal bonding method from the available options. Our activities are characterized by great flexibility; we can work with client-provided materials or procure our own from trusted suppliers. Our product offerings include finishing for acrylic and glass surfaces, such as AG (Anti-Glare), AF (Anti-Fingerprint), and AR (Anti-Reflective). Additionally, our extensive experience in digital and screen printing, coupled with access to a wide range of high-quality materials processed with plotters and CNC machines, positions QWERTY as an expert in integrating displays and sensors with touch panels/fronts. 

Kamil Kwiatek, R&D