Optically Bonded Display Technology—OCA & LOCA , What is the LOCA process?

Optically Bonded Display Technology—OCA & LOCA

                                                                                                                                       ---- What is the LOCA process?

In full lamination, there are two main approaches: one is called LOCA lamination (liquid optically clear adhesive), and the other is OCA lamination(optically clear adhesive film).

This article focuses on the LOCA liquid adhesive lamination process.

LOCA stands for Liquid Optical Clear Adhesive. It is a special adhesive used for bonding transparent optical components and can be understood as a specially formulated glue.

LOCA adhesive comes in single-component and dual-component types. For dual-component adhesive, thorough mixing is required before dispensing.

LOCA is colorless and transparent, with a light transmittance of over 98%, excellent bonding strength, and the ability to cure at room or moderate temperatures. It also has low shrinkage upon curing and good resistance to yellowing.

Put simply, LOCA full lamination involves using liquid adhesive to bond the cover glass (CG) and the display panel together, then curing the adhesive.

There are several methods of applying LOCA, such as dispensing and coating. This article mainly discusses the dispensing method.

The dispensing process generally includes five steps: dispensing the dam adhesive, curing the dam, dispensing the main adhesive, bonding, and curing the main adhesive. Here's a brief introduction using a typical in-cell product (where the touch layer is integrated inside the LCD module ) as an example.

1. Dispensing the Dam Adhesive

The dam adhesive is dispensed around the perimeter of the CG's ink area to form a barrier, preventing the LOCA adhesive from flowing out due to gravity after being dispensed inside the area.

The dam adhesive is a high-viscosity, high-strength, single-component material with strong adhesion.

The dam is not sealed entirely; several openings are left at corners or in the middle so that LOCA can flow near the dam and allow air to escape, preventing bubbles. The exact location of the openings is determined based on the LOCA dispensing pattern.

Most products use a fishbone pattern for LOCA dispensing. In such cases, in addition to leaving gaps at the four corners, gaps also need to be left in the middle of the fishbone pattern.

Another purpose of the dam adhesive is to control the thickness of the cured LOCA. Using dispensing needles of different diameters results in different dam heights, thus controlling the final adhesive thickness.

2. Dam Curing

The dam adhesive is usually cured using UV curing, so UV-curable adhesive is typically used. After exposure to UV, the dam adhesive undergoes partial curing and is ready for the next step—dispensing the main LOCA adhesive.

At this stage, UV energy must be carefully controlled.

3. Dispensing the Main LOCA Adhesive

The dispensing parameters are critical during the LOCA application.

Typically, based on the size of the coating area on the CG and the desired adhesive thickness, one can calculate the starting point, dispensing path, and the volume of adhesive needed.

Next, the parameters are entered into the equipment's interface and fine-tuned based on test results.

Considering the ease of rework and dispensing, the LOCA adhesive is generally dispensed on the CG side.

If dispensing fails or errors occur, the CG can be cleaned with a solvent and lint-free cloth and reused.

Moreover, the shape of the CG is relatively simple, making positioning easier.

Dispensing directly on the LCD is not ideal because if errors occur, cleaning the adhesive is difficult, and the LCD substrate is thin and fragile, increasing the risk of breakage and scrapping.

4. Bonding

Bonding is the process of aligning and attaching the CG (with both dam and main adhesive applied) to the display panel. Before bonding, a CCD camera is used to align the positions to avoid misalignment.

5. Main Adhesive Curing

Finally, the LOCA adhesive is cured. If the LOCA is a thermosetting type, high-temperature curing is used with controlled temperature and time. If it’s UV-curable, then UV light is applied, with careful control of UV energy and exposure time.

At this point, the CG and display are fully bonded and can proceed to the next production step after inspection.

Comparison with OCA Lamination

The LOCA lamination process is done entirely in the open atmosphere, unlike OCA, which requires vacuum lamination equipment. Compared to OCA, LOCA equipment costs are significantly lower, but because LOCA requires a leveling process, its hourly production output is lower than that of OCA.

continuous R & D and practice, which enables us to precisely control every step in the OCA & LOCA lamination process, from accurate dispensing parameter setting to strict control of curing conditions. This ensures high - quality and stable product performance. Our advanced technology not only guarantees excellent bonding strength and high light transmittance but also effectively reduces the occurrence of defects such as bubbles and glue overflow. With Sinocrystal's mature full - lamination technology, we can provide customers with reliable and high - performance display products.