The adhesive strength of corrugated cardboard is a key indicator for evaluating its structural integrity and durability, which directly reflects the firmness of the adhesive bond between the face paper and the core paper. In the packaging, transportation, and warehousing industries, ensuring that corrugated cardboard has sufficient adhesive strength to prevent delamination, deformation, or breakage. Adhesive strength testing using a tensile testing machine is a widely recognized and standardized quantitative evaluation method that provides accurate data support for quality control and material development.
Test Principle:
The basic principle of the test is to apply a tensile force perpendicular to the cardboard plane to the corrugated cardboard specimen through a tensile testing machine until the adhesive layer separates, and the maximum force value during the separation process is recorded. This force value is combined with the specimen size to calculate the bond strength per unit area. Relevant domestic and foreign standards clearly stipulate this test method, ensuring the comparability and reliability of the test results. The main reference standards include but are not limited to: GB/T 6548, ISO 3035, TAPPI T541, etc. These standards specify in detail the preparation of specimens, test conditions, equipment requirements and calculation methods.
Sample preparation
The core equipment of the test is a tensile testing machine, which needs to be equipped with a fixture suitable for peel test, usually a flat fixture with one upper and one lower or a special adhesive strength test fixture. The equipment should meet the accuracy requirements, and the force measurement error should usually be less than ±1%. Specimen preparation is carried out strictly according to the standard: the specified size specimen (e.g. 25mm x 80mm) is cut from the sample, ensuring that the corrugated direction is parallel to the long side of the specimen. Use a special needle device or blade to carefully separate the face paper at one end of the specimen from the core paper to create a test area that can be clamped by the fixture.
Testing process
First, the two ends of the specimen separation are clamped in the upper and lower fixtures of the tensile testing machine to ensure that the clamping is firm and the force axis is aligned with the center of the specimen. Set test parameters, such as tensile speed, which are often specified in the standard as 12.5 mm/min ± 2.5 mm/min. Start the testing machine and continue to apply tension until the adhesive layer is completely separated. During the test, the device automatically records the force-displacement curve. Key operating points include: ensuring that there is no initial stress when the specimen is clamped; The test environment usually needs to be pre-treated and tested under standard temperature and humidity conditions (e.g. 23°C, 50% RH); Test at least multiple valid specimens per sample to obtain an average.
Data analysis
Bond strength is usually expressed as force per unit area, calculated as follows:
A = F / (w * n)
where A represents the bond strength in Newtons per square meter (N/m²) or kilopascal (kPa); F is the maximum peeling force recorded in the test in Newtons (N); w is the initial width of the specimen, in meters (m); n is the number of bonding threads included in the specimen (n=2 for single corrugated board; n=4 for double corrugated board, etc.). The calculation result is the arithmetic average of all valid specimens. When analyzing the data, the stability of the peeling process should be observed in combination with the force-displacement curve, and the fluctuation of the curve can reflect the uniformity of the bond.
Influencing factors
Test results are influenced by a variety of factors. Material factors include the absorbency of the base paper, fiber composition, and the type and amount of adhesive coated. The process factors involve temperature, pressure, and speed during corrugated forming. The environmental factors are mainly the temperature and humidity conditions before the test. The operating factors include specimen cutting accuracy, clamping alignment, and tensile rate control. To ensure test accuracy, the tensile testing machine needs to be calibrated regularly, specimens should be prepared and processed in strict accordance with standards, and test conditions should be clearly recorded in the report.
Summary
The determination of corrugated cardboard adhesive strength by tensile testing machine not only provides a basis for the optimization of process parameters in the production process, but also serves as the basis for evaluating the comprehensive properties of carton compressive strength and bursting strength. Stable adhesive strength helps to improve the reliability of packaged products in stacking and transportation, and reduce losses. With its objective and repeatable characteristics, this method has become the common language for upstream and downstream quality verification in the supply chain. Continuous attention to standard updates and testing technology development will further improve the level of refinement of quality control.
Citation standards
GB/T 6548 Determination of adhesive strength of corrugated cardboard
ISO 3035 Corrugated Cardboard Determination of Flat Compressive Strength
TAPPI T541 Corrugated Cardboard Adhesive Strength Test Method (Needle Picking Method)