The interlayer bonding strength of paper is an important indicator to measure the bonding strength between fibers within the paper, which directly affects the printing adaptability, mechanical strength and final use performance of the paper. The Scott test, which is a classic evaluation method, provides key data for paper quality control and process optimization by measuring the energy required to separate the internal bonding layers of paper.
Test Principle:
The Scott type internal bond strength tester is based on the peel work principle. The core mechanism is to securely bond the test head to both sides of the paper sample using a specific adhesive, with the upper collet holding the sample and the lower collet peeling the test head vertically upwards at a constant rate. The force required for the interlayer separation process is continuously recorded, and by calculating the area under the force-displacement curve, the energy required to peel off the inner bonding layer of the paper, i.e., the internal bond strength, is usually expressed in joules per square meter (J/m²).
Calculate the internal binding strength (IBThe basic formula is:
IB = E / A
Among them,E represents the total energy consumed by the stripping process (unit: J),A Represents the effective bonding area of the test head to the paper (in m²). Total energy E It can be obtained by integrating force-displacement curves.
Testing process
The standard testing process includes four stages: sample preparation, bonding, curing, and testing. First, the paper samples were treated in equilibration under standard temperature and humidity conditions (e.g., 23±1°C, 50±2% RH). Subsequently, the test head is adhered to both sides of the sample using double-sided adhesive or a specific liquid adhesive and ensures sufficient curing to create a strong connection. Finally, the assembled sample is placed in the tester and the test program is started to complete the measurement.
To ensure the comparability and accuracy of the results, the following parameters need to be strictly controlled:
| The sample is balanced at temperature and humidity | 23°C, 50% RH |
| Adhesive type: | Standard pressure-sensitive adhesive or epoxy |
| Bonded area | Usually 10 cm² or 25 cm² |
| Stripping rate | Common range: 100-300 mm/min |
| Data acquisition frequency | Not less than 100 Hz |
Influencing factors
Test results are influenced by a variety of factors. The characteristics of the paper itself, such as fiber type, pulp degree, wet chemical additives (such as dry strength agents) and pressing process, are intrinsic factors that determine its intrinsic bonding strength. External factors include the temperature and humidity of the test environment, adhesive performance and uniformity, and curing time and pressure. Abnormal test curve patterns, such as large force fluctuations or early peeling, often indicate problems with delamination, uneven thickness, or poor adhesion.
The internal bonding strength value needs to be interpreted in conjunction with the specific paper category standards. For example, high-grade coated papers often require high interlayer bonding to prevent lint pulling during printing, while certain specialty papers that require flexibility may have different strength ranges. This test has practical value for evaluating the effect of slurry ratio, calendering process adjustment and new additives.
Scope of application:
The Scott test method is one of the main methods for evaluating the Z-directional bond strength of paper. Compared with other methods such as tensile energy absorption method, it more directly simulates the failure mode of interlayer separation. This method is widely used in the R&D and quality inspection process of the paper industry, and is suitable for all kinds of cultural paper, packaging cardboard, special paper and its laminated materials, but it is not suitable for materials that have obvious delamination or low strength.
Pay attention to safety regulations during operation, such as wearing protective gloves to handle adhesives, and regularly calibrate the instrument to ensure the reliability of test results. Through rigorous operation and data analysis, Scott's in-house strength testing provides a solid basis for understanding and improving paper product quality.
References
TAPPI T569 pm-00. Internal bond strength of paperboard.
ISO 15754: 2009. Paper and board — Determination of z-directional tensile strength.
Papermaking Analysis and Testing (3rd Edition), China Light Industry Press.