NCO Index & Hardener Matching: Calculation to Validation
Description of changes in performance that may result from the ratio of active hydrogen to isocyanate equivalents, hardener selection and deviation theory, reducing the empirical fixed ratio.
Create a basis for equivalent calculations
Resin end determines the amount of live hydrogen on the basis of metamine equivalent, and hardener end isocyanate equivalent on the basis of NCO content. Reactive materials are calculated and pigments, solvents and non-reactive aids are converted to the final A.B. mass in order to obtain the correct production ratio.
There may be permissible fluctuations in the parameters of different batches of raw materials, and key products should clearly use nominal or measured values in quality agreements and establish matching adjustment rules.
NCO, not as high as possible.
The appropriate adjustment of the NCO index can affect the degree of interconnectivity, early hardness and resistance to chemistry, but excess isocyanate may increase the risk of flarity, residual reaction, humidity sensitivity and bubbles; Shortfalls can lead to surface adhesiveness, water resistance and reduced mechanic performance.
The optimal range depends on the resin combination, hardener functionality and the use of the scene, which should be determined through a gradient test, and the empirical values of other systems cannot be directly replicated.
Impact of the hardener structure
The aliphatic isocyanate systems are usually used in high-resilient scenarios, and different HDI derivatives or combination structures change viscosity, official capacity, reaction speed, hardness and flex. The selection also requires attention to ionomers, solvent composition, colour and regulatory information.
There may also be reactions between hardener and pigments, catalytic components and hydroxyl radicals. All potential active hydrogen sources in the formulation list should be included in the assessment.
From calculation to experimental validation
Set low, target and high gradients by theoretical values to compare pot life, touch-dry, hard development, stretching, attachment, water resistance and chemical resistance under the same film thickness and conservation conditions. The test plate shall observe both bubbles, constrictions and inter-layeral states.
A thick membrane injection sample may differ from a thin membrane expression, so both the mechanical sample and the actual coating need to be validated.
Production and field measurements
The mass production is based on calibrated weighing equipment and controls the balance of batches, temperature and mixing in groups A and B. On-site estimates based on barrel scales or visual measurements are prohibited; When partial packagings are used, they should be quantified in an accurate manner and tools should be prevented from being contaminated.
The dichotomy of material cannot be compensated by extended conservation. Leaks, errors or mixing should be detected, separated from the corresponding area and treated according to technical options.