What is the folding endurance test?

The folding endurance test, also known as the "M.I.T. Folding Endurance Test," is a commonly used test to assess the durability and resistance of paper and paperboard materials to repeated folding. It measures the number of double folds a sample can withstand before it breaks or shows signs of damage.

Here's how the folding endurance test is typically conducted:

1. Sample Preparation: Cut the paper or paperboard sample into standardized rectangular strips of specific dimensions, typically 15 mm by 100 mm.

2. Conditioning: Condition the samples in a controlled environment, usually at a specified temperature and humidity, to ensure consistent moisture content and minimize the influence of environmental factors.

3. Folding Procedure: Place the sample strip in a folding endurance tester, such as a M.I.T. Folding Endurance Tester. The tester consists of two clamps that hold the sample at both ends. The clamps move in opposite directions, causing the sample to fold and unfold repeatedly.

4. Folding Cycles: The sample is subjected to a specified number of double folds (one fold in one direction and then another fold in the opposite direction) at a constant rate. The number of folding cycles can vary depending on the testing requirements or industry standards. Commonly used values range from 8,000 to 20,000 double folds.

5. Inspection: After the specified number of folding cycles, carefully examine the sample for any visible signs of damage, such as cracks, tears, or delamination. The test is considered complete when the sample breaks or shows significant damage.

6. Recording Results: Record the number of folding cycles completed by the sample before failure or damage. This value represents the folding endurance or folding endurance index of the material.

The folding endurance test provides an indication of the durability and flexibility of paper and paperboard materials. It is widely used in the paper industry, printing industry, packaging industry, and other related fields to evaluate the suitability of materials for applications involving repeated folding, such as books, brochures, or packaging that requires folding and unfolding.