What is LOCA Bonding Technology?

Liquid optical clear adhesive (LOCA) is a durable bonding method that utilizes a liquid adhesive. In this article, we focus on LOCA bonding technology.

More details:

According to different forms and coating, optical transparent adhesives can be divided into three types: Optical Clear Adhesive (OCA), Liquid Optical Clear Adhesive (LOCA), and Optical Clear Film (OCF). Hence, their bonding processes are different.

Here we introduce the Liquid Optically Clear Adhesive.

LOCA Bonding Technology


Figure 2. LOCA Bonding
Figure 1. LOCA Bonding


It is colorless and transparent and can be solidified by visible light, UV, medium and high temperature, moisture, etc.

Key parameters of OCR adhesive properties include viscosity, refractive index, hardness, elongation at break, cure shrinkage, dielectric constant, acidity, and ultraviolet (UV) curing.

OCR adhesive strength is high, but the shrinkage rate is very low, and the hardness is low, which is not prone to shrinkage, faulting, discoloration, and other bad phenomena.

The refractive index of qualified OCR is about 1.5. The refractive index value of 1.53 to 1.54 is basically the same as the refractive index of the cover material, which brings high visibility. The use of OCR makes the overall refractive index of the display part basically the same, reducing the loss of light and interference caused by dispersion and scattering, and reducing the color distortion of the display image.

The hardness index of OCR generally refers to the value after full curing, this value is not the higher the better or the lower the better, to achieve a balance and can improve the overall strength of the product after curing is the most critical.
OCR curing (hardening) shrinkage requirements, the smaller the better, the smaller the shrinkage is less likely to occur shrinkage, faults, discoloration, and other bad influences.

The curing speed of OCR is fast, the pre-curing time is less than 20s, which saves manufacturing time.

The dielectric constant of OCR is usually 1.5 to 3, so the capacitive touch screen using OCR is more sensitive.

The pH value of OCR is 6.5~7.2, which is neutral and non-corrosive to ITO and materials.


For example, the bonding of the cover plate to the display modules with thick BL, LOCA makes it easier to solve the problem of filling in gaps with height differences. OCR bonds each functional layer and each module by coating, and then performs thermal curing or light curing. Based on the leveling properties of the liquid, its ability to compensate for step differences is stronger than that of OCA membrane materials.

Besides, filling the gaps between the touch screen, cover, and display with OCR can improve the contrast of the entire display module. Compared with the traditional method of using air gaps, the optical resin can suppress light scattering caused by external lighting and backlight. The optically transparent resin molded by the rapid reaction to UV irradiation has a refractive index and light transmittance similar to glass, is resistant to yellowing, is soft and can withstand the expansion and contraction of a variety of different substrates, and can solve problems caused by high and low-temperature changes during lamination.

Bonding processes

OCR has three types of adhesive application processes: pattern-filling, Dam+Fill, and coating.

LOCA Application Processes
LOCA Application Processes


The pattern-filling process has two schemes: natural curing and electrostatic curing.
In natural curing, it first performs edge curing, and then whole curing.
Electrostatic curing achieves curing through the electrostatic action of positive and negative electrodes.
The pattern-filling process is simple and can correspond to a wide range of product models, but the coating is not uniform enough and there are air bubbles concern.


In Dam+Fill, there are anti-overflow barriers.

First, OCR is pretreated by ESC electrostatic or ASC adsorption in the vacuum chamber, and then in turn for self-treatment, defoaming, and lamination. ESC electrostatic pretreatment can be coated with glue evenly, so the light transmittance is strong, ASC adsorption pretreatment in the process of adsorption will leave air, and light transmittance is lower.

Dam+Fill process is more complex and applicable to cell phone products, but there are also uneven coating and bubble residue problems.


In the coating process, OCR is sprayed onto the glass from small holes in the pipeline, and is first pretreated with side curing or full curing, and then flattened with rollers.

The coating process is particularly complex, with minimal use of OCR, easier flow control when spraying OCR, uniform coating, and no air bubbles.

LOCA bonding processes
LOCA Bonding Processes
What is LOCA bonding technology
LOCA Bonding Line

Advantages and Disadvantages of LOCA Bonding




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