Every Batch COA Passes, So Why Won't the Customer Approve? (Spec Pass ≠ Customer Pass)
Standards and Customer Windows
Grade specifications are the minimum common language of the industry; major customers' raw-material technical agreements are typically stricter. During development, strive to obtain the customer's raw rubber technical agreement rather than benchmarking solely against national standards.
Even when both batches are "qualified," the magnitude of batch-to-batch variation can still determine process stability on the customer's production line—this is why a run of consecutive multi-batch COAs is more convincing than a single COA.
A Sound Validation Perspective
The approval chain is: spec compliance → batch-to-batch consistency → stable compound processing → equivalent vulcanizate performance → full product qualification → supplier-system approval. A failure at any stage invalidates all preceding "passes."
The smallest unit of failure is "factory × grade × formulation × product." A single failure should not be extrapolated to mean the entire grade is unqualified; conversely, a single favorable COA cannot represent the entire factory.