Layered Curing of Thixotropic Coating Fluid in Static Pipes

After curing, the coating has insufficient hardness, a sticky surface, poor solvent resistance, or decreased adhesion, and obvious indentations can be seen when pressed with a fingernail. Incomplete curing means that the reactive groups in the coating are not fully crosslinked into a three-dimensional network structure, and residual low-molecular-weight components cause performance to fall short of standards. Incompletely cured coatings continue to post-cure during subsequent use, and their performance changes unstably over time.

1. Comprehensive factors: the thixotropic agent forms a strong network through hydrogen bonds in the static state, exceeding the recoverable threshold. 2. Substrate surface condition factors: The surface tension, cleanliness, and microscopic roughness of the substrate are the basic conditions for coating adhesion and leveling. When the substrate surface tension is lower than the coating fluid surface tension, wetting is insufficient and cratering occurs; surface contamination causes local adhesion failure; this is the primary direction for troubleshooting coating defects. 3. Curing process factors: Curing temperature and time determine the completion degree of the coating crosslinking reaction—insufficient temperature or insufficient time leads to incomplete curing (tacky, low hardness, poor solvent resistance), excessive temperature or excessive time leads to over-curing (embrittlement, yellowing, cracking); the curing window of the coating fluid system must be precisely matched.

1. Process parameter optimization and adjustment: Design the liquid supply system for dead-corner-free all-day circulation. 2. Mold/tooling improvement and maintenance: Before stopping production, replace the coating fluid in the pipes with flushing solvent. 3. Systematic troubleshooting method: Troubleshooting of coating problems follows the order of "substrate → coating fluid → coating head → curing → environment". First check the substrate surface tension (corona treatment effect) and cleanliness, then verify the coating fluid viscosity, solid content, and degassing status, then check the coating head gap and cleanliness, further verify the curing temperature and time, and finally evaluate the influence of ambient temperature, humidity, and cleanliness. 4. Preventive management: Establish standardized process parameter cards and quality control limits for each mold/product, and regularly conduct process capability index (CPK) evaluations. For recurring problems, use fishbone diagrams or 5Why analysis to trace the root cause, and solidify countermeasures as PFMEA control points. Establish a regular equipment maintenance system and implement life management for key tooling such as dies/spinnerets/calender rolls/coating heads.

The essence of incomplete curing is that the crosslinking reaction has not reached the designed conversion rate. The core of the solution is the precise matching of the three elements of "temperature + time + formulation": ensure that the curing temperature and time are within the recommended window of the coating fluid system, verify the curing agent ratio and validity period, and for UV curing, regularly test the lamp light intensity and replace it in time.