Standard process
The hundred grid knife method, also known as the grid test method, is a standardized method widely used to evaluate the adhesion properties of coatings, inks, and other materials on substrates. This method uses a specific specification of a tool to cut a grid-like scratch on the surface of the coating and evaluates the adhesion level based on the peeling of the coating in the scratched area. This process is designed to provide a clear and repeatable set of procedures for ink adhesion testing in printing, packaging, automotive, electronics, and industrial coatings.
Test Principle:
The core principle of the Baige knife method is to simulate the adhesion failure behavior of the coating when it is subjected to external force. Using a hundred grid knife with multiple parallel blades, grid lines are cut perpendicular to each other on the surface of the ink coating, cutting through the coating to the substrate. Subsequently, pressure-sensitive tape is used to paste on the grid area and quickly peel off, and the adhesion level is evaluated according to the standard grading table by observing the peeling area ratio of the ink in the grid. The effectiveness of this method is based on the evaluation of the interfacial bond strength between the coating and the substrate.
Instrument and material preparation
Before testing, ensure that the following instruments and materials meet the requirements of relevant standards (e.g., ASTM D3359, ISO 2409). All tools should be clean and in good condition.
Key instruments and materials include:
Baige knife: The tooth spacing is usually 1 mm or 2 mm, depending on the coating thickness and test standard.
Pressure-sensitive tape: width not less than 20 mm, adhesion in accordance with standard specifications (e.g. 3M™ 600 tape or equivalent).
Soft-bristled brushes or balloon blowers: Used to remove debris from cutting.
Magnifying glass or light microscope: For observing peeling details, the recommended magnification is 2x to 10x.
Illumination Light Source: Ensure that the grid area is evenly lit for easy evaluation.
Standard rating graph: used to compare and determine the adhesion level.
Sample preparation
The test should be performed in a standard laboratory environment with a recommended temperature of 23±2°C and a relative humidity of 50±5%. The specimen should be a flat, clean ink coating adhered to the surface of a substrate (such as metal, plastic, glass, etc.), and the coating should be completely cured. Before testing, the specimen should be placed in the above environment for at least 24 hours to achieve equilibrium. The test area should be free of defects, bubbles, or contamination.
Procedure:
The following steps are based on the common standard process, and the specific parameters should follow the standard document adopted.
Cut the grid: Place the hundred grid knife perpendicular to the surface of the specimen, apply even, sufficient pressure, and cut at a smooth speed. Start by cutting a set of parallel lines in one direction, with line spacing determined by the knife tooth spacing. Then rotate it 90 degrees and cut another set of parallel lines to form a grid pattern. The cut should penetrate the ink layer to the substrate, which can be confirmed by hearing or sight.
Clean up debris: Use a soft-bristled brush or blow balloon to gently remove ink debris from cutting diagonally along the grid to avoid affecting the tape adhesion effect.
Apply the tape: Take a piece of pressure-sensitive tape, the length should completely cover the grid area and leave a surplus. Align the tape center to the grid area to ensure bubble-free adhesion to the coating surface. Apply even pressure with your fingers or eraser to ensure that the tape is in full contact with the coating.
Tear off the tape: Quickly and smoothly peel off the tape at an angle of nearly 180 degrees within 60±30 seconds of application. The peeling process should be continuous and avoid pauses.
Outcome evaluation: Immediately observe the grid area with the naked eye or magnifying glass in uniform light. The peeling is compared with the standard rating map to determine the adhesion level.
Result evaluation and grading
Adhesion grades are usually classified from 0 to 5, with 0 representing the best adhesion (no spalling) and 5 representing the worst adhesion (spalling area greater than 65%). For specific grading criteria, please refer to the table below:
| grade | Description |
| 0 | The cut edges are completely smooth and there is no peeling in the grid |
| 1 | There are small pieces of peeling at the intersection of the cut, and the peeling area is ≤5% |
| 2 | Peeling off at the cutting edges or intersections, > 5% to ≤15% of the area |
| 3 | The cutting edges are partially or completely stripped and part of the mesh is peeled off, with an area > 15% to ≤35% |
| 4 | The cut edges are stripped off, and some or all of the mesh is peeled off, with an area > 35% to ≤65% |
| 5 | The degree of peeling exceeds level 4, and the area > 65% |
The report should document the test conditions, tool specifications, tape type, rating grade, and any anomalies. If the results of different mesh regions are significantly different, the reasons should be noted and analyzed.
Notes:
The test results may be affected by a variety of factors, and attention should be paid to during operation:
Tool Sharpness: Blunt knives can lead to incomplete cuts, affecting the evaluation of peeling behavior.
Cutting Pressure and Speed: Uneven pressure or too fast speed can lead to inconsistent cutting depths.
Tape application and peeling: The application time, pressure, and tear angle should be strictly consistent to ensure comparable results.
Coating status: coating thickness, curing degree, substrate roughness, etc. will affect the adhesion performance.
Ambient temperature and humidity: Deviations from standard conditions can alter the physical properties of the coating or tape.
It is recommended to regularly calibrate the tooth spacing and sharpness of the hundred grid knives and verify the effectiveness of the testing process using standard reference samples.
Summary
As a classic and efficient adhesion testing method, the strict implementation of the standard process is essential for obtaining reliable, comparable data. Through standardized operation and meticulous evaluation, this method can provide strong support for the optimization of ink formulation, the improvement of substrate treatment process and product quality control. In practical applications, it is recommended to adapt the test parameters in combination with specific industry standards and product requirements.
References
ASTM D3359-17, Standard Test Methods for Rating Adhesion by Tape Test
ISO 2409:2013, Paints and varnishes — Cross-cut test
GB/T 9286-1998, Colored paints and varnishes - Grid test of paint film