Rationale
A folding meter is a specialized testing device used to evaluate a material's resistance to breakage under repeated folding conditions. Its working principle is based on simulating the reciprocating bending stresses experienced by paper or cardboard during real-world use. The instrument usually involves clamping the specimen and repeatedly folding it at an angle between two fixed positions under specified tension until the specimen breaks. The number of folds at this time is recorded, which is the flexural resistance value of the material. This test process quantifies the flexibility of the material and the internal fiber bonding strength, and the mathematical relationship can be expressed as:
N = f(F, α, r)
where N represents the bending resistance (number of times), F is the applied tension, α is the folding angle, and r is the folding radius. This functional relationship shows that the flexural resistance is the result of the combined interaction of material properties and test parameters. Domestic and foreign standards, such as GB/T 457 and ISO 5626, clearly stipulate test conditions to ensure comparability and repeatability of results.
Mechanical properties requirements of wrapping paper
As a key material for the protection and transportation of goods, wrapping paper requires a series of specific mechanical properties to cope with the complex stresses of circulation. These properties include, but are not limited to, tensile strength, tear resistance, breaking resistance, and bending resistance. Flexural resistance is directly related to the durability of the packaged product during multiple opening, closing, extrusion or deformation. For example, the folding resistance of paper used to make shopping bags, envelopes, packaging boxes, and labels that need to be bent frequently directly affects the integrity and service life of the packaging. If the folding resistance is insufficient, it is very easy to crack or break at the crease, resulting in the failure of the packaging and the loss of the basic function of protecting the contents.
The effect of bending resistance detection
In the production and procurement of packaging paper, bending resistance testing is an indispensable part of the quality control system. With the precise measurement of the folding gauge, producers can:
First, evaluate the rationality of raw material ratio and process parameters. For example, the type of slurry, the degree of beating, the amount of additives, and the calendering process will significantly affect the fiber bonding and flexibility of the paper, which will eventually be reflected in the flexural resistance index.
Second, realize the standardized grading and control of product performance. Based on the test results, the paper can be divided into different grades to meet the needs of diverse end applications.
Third, predict the performance of terminal use. Through laboratory accelerated folding testing, the behavior of packaging paper under long-term or repeated use scenarios can be evaluated in a short period of time, providing data support for product design and improvement. This process closely links lab testing to the actual user experience.
Instrument operation points
To ensure the accuracy of test results and global comparability, strict testing standards must be followed. These standards detail key parameters such as specimen size, pre-treatment environment, instrument calibration, test speed, and tension. When operating the folding meter, the following points should be noted: the specimen should be free of creases or defects; When clamping, it is necessary to ensure that the tension is uniform and meets the standard; The temperature and humidity of the test environment should be strictly controlled, as the moisture content of the paper has a significant impact on its flexibility and strength. Standardized operation provides the basis for reliable data that allows products from different batches and origins to be compared on the same benchmark.
| Examples of core test standards | Standard focus points |
| GB/T 457 (China) | Determination of folding resistance of paper and cardboard |
| ISO 5626 (International) | Determination of paper bending resistance |
| TAPPI T423 (USA) | Paper and cardboard are resistant to folding |
| Specimen pretreatment conditions | Temperature 23°C±1°C, relative humidity 50%±2% |
| Expression of common test results | Number of double folds (MIT method) |
Industry Applications
The data generated by the bending test – usually the number of double folds required to cause the specimen to break – needs to be interpreted in the context of the specific application scenario. Higher values indicate the paper's ability to resist repeated bending. For different quantitative quantities of wrappers, the expected bending resistance range is also different. For example, the absolute value of folding resistance of high-gram containerboard paper and low-gram trademark paper can vary greatly, but both must meet the minimum requirements for their respective application areas. In the fields of food packaging, electronic product packaging, high-end gift boxes, and logistics and transportation bags, buyers include bending resistance as a key technical indicator in contract specifications to ensure that the packaging materials used can withstand the expected physical tests, reduce the breakage rate during circulation, and improve brand image and customer satisfaction.
Conclusion
In summary, the foldability meter plays a key role in the inspection of packaging paper. It transforms the fatigue properties of materials against repeated bending into quantifiable indicators through standardized mechanical testing, providing a scientific and crucial basis for the research and development, production, quality control, and final application of packaging paper. Continued attention and strict implementation of bending resistance testing will help promote the development of the packaging industry towards higher quality, more sustainable and more in line with user needs.
References
1. National Paper Industry Standardization Technical Committee. Determination of folding resistance of paper and cardboard: GB/T 457-2008[S]. Beijing: China Standard Press, 2008.
2. International Organization for Standardization. Paper — Determination of folding endurance: ISO 5626:1993[S]. Geneva: ISO, 1993.
3. TAPPI Press. TAPPI Test Methods 2023[M]. Atlanta: TAPPI Press, 2023.
4. Wang Juhua, et al. Fiber characteristics and microscopic spectrum of Chinese papermaking raw materials[M]. Beijing:China Light Industry Press, 2019.