LCD Screen Manufacturing Coated With PI Liquid

LCD Screen Manufacturing Coated With PI Liquid – PI Coating – Ultrasonic Coating – Cheersonic

PI liquid is a key process in the manufacturing of LCD screens, mainly used to form alignment films and control the alignment direction of liquid crystal molecules. The following are the main steps and related points of the PI liquid process:

Substrate cleaning
Before ultrasonic coating with PI solution, the glass substrate needs to be strictly cleaned to remove organic matter, particles, and impurities on the surface. Usually, EUV cleaning, brush cleaning, high-pressure water vapor spray (HPMJ) and other methods are used, and finally, moisture is removed by inclined airflow drying (A/K drying) to ensure the cleanliness of the substrate surface.

PI liquid preparation
PI solution is a precursor solution of polyimide, mainly composed of polyamic acid (PAA) and solvent NMP (N-methylpyrrolidone). Before use, defoaming treatment is required to remove bubbles from the raw materials and avoid bubble defects during ultrasonic coating. The defoaming time is usually 8-12 hours, and impurities are removed through a filter.

Ultrasonic Coating
PI liquid is ultrasonic coated onto a glass substrate using methods such as ultrasonic coating or relief printing. Ultrasonic coating parameters include ultrasonic coating speed, wet film thickness, ultrasonic coating gap, etc., which need to be strictly controlled to ensure uniform PI film thickness. During letterpress printing, PI liquid is directly coated onto the substrate through ultrasonic nozzles.

Pre bake
The PI liquid after ultrasonic coating needs to be pre dried and heated by an infrared hot plate to evaporate the solvent (such as NMP) in the PI liquid, forming a preliminary PI film. The pre drying temperature and time should be adjusted according to the characteristics of the PI liquid to avoid excessive temperature that may cause delamination or uneven film thickness of the PI liquid.

Curing
The pre baked PI film needs to be cured by high-temperature heating to induce imidization reaction of polyamide acid (PAA) and convert it into polyimide (PI), forming a stable alignment film. The curing process is usually carried out in stages:

Low temperature stage: 160-180 ℃, remove residual solvents;
Imidation stage: 230-250 ℃, complete the imidization reaction;
High temperature curing stage: 450-470 ℃, further improving the mechanical properties and stability of PI film.
During the curing process, nitrogen gas needs to be continuously introduced to prevent yellowing of the PI film, and the oxygen content should be strictly controlled (<100ppm).

Alignment (Rubbing)
The cured PI film needs to undergo alignment treatment, using brushes or mechanical friction to make the molecular arrangement direction on the surface of the PI film consistent, providing guidance for the orientation of liquid crystal molecules. After assembly, the substrate needs to be cleaned again to remove residual impurities and brush debris.

The quality of PI liquid process directly affects the display performance of LCD screens, such as contrast, response speed, and viewing angle. During the production process, it is necessary to strictly control the parameters of each link to ensure that the thickness, uniformity, and alignment accuracy of the PI film meet the requirements.

About Cheersonic

Cheersonic is the leading developer and manufacturer of ultrasonic coating systems for applying precise, thin film coatings to protect, strengthen or smooth surfaces on parts and components for the microelectronics/electronics, alternative energy, medical and industrial markets, including specialized glass applications in construction and automotive.

Our coating solutions are environmentally-friendly, efficient and highly reliable, and enable dramatic reductions in overspray, savings in raw material, water and energy usage and provide improved process repeatability, transfer efficiency, high uniformity and reduced emissions.

Chinese Website: Cheersonic Provides Professional Coating Solutions