Introduction Overview
In the modern packaging and printing industry, the scratch resistance of ink coatings is directly related to the protection of product appearance and the durability of information transmission. As a tool for simulating mechanical wear behavior, the linear wear resistance tester can effectively evaluate the resistance of coatings in transportation, handling and daily use environments. This technical article focuses on the specific application of this equipment in packaging printing ink coating detection, and systematically expounds its test principles, operation points and data interpretation methods in combination with relevant standards and experimental methods.
Test Principle:
The linear wear resistance tester uses a friction head equipped with a specific load to reciprocate the coating surface in a straight trajectory. The friction head can be made of different materials (such as emery, felt, or rubber) and geometry to simulate actual contact scenes. During testing, the equipment quantifies scratch resistance by recording the number of friction cycles required before the coating is destroyed or the number of friction cycles at a specific depth. The normal pressure per unit area can be converted from the load to the contact area, expressed as:
σ = F / A
where σ is the contact pressure (unit: Pa), F is the applied normal force (unit: N), and A is the effective area of contact between the friction head and the coating (unit: m²).
Key points for test preparation
1. Sample preparation: Evenly apply the printing ink coating to the standard substrate (such as white cardboard, plastic film, or metal foil) to ensure consistent coating thickness and set drying conditions according to the ink technical parameters.
2. Environmental adjustment: The specimen is placed in an environment with a temperature of 23±2°C and a relative humidity of 50±5% for no less than 4 hours to eliminate the influence of environmental differences on the mechanical properties of the coating.
3. Friction head selection: Choose the friction head material according to the actual application scenario, the common combinations are as follows:
| Friction head material | Simulate the scene |
| emery sandpaper | Scratches with hard objects during transportation |
| Felt cloth | Finger or flexible packaging contact |
| Rubber tip | Eraser wipe or rub |
Test procedure
Secure the prepared sample on the test surface, ensuring no folds or displacement. Set the length of the friction head stroke (usually 25 to 100 mm), the reciprocating speed (approx. 60 cycles/min) and the total number of cycles. A predetermined load is applied, generally ranging from 5 to 20 Newtons. After starting the device, the coating surface changes are inspected with a magnifying glass or visually at certain intervals (e.g. every 100 times). Record the number of times you first see a noticeable scratch, such as substrate exposure or coating peeling. Each set of samples was repeated at least 3 times, with the median as the result.
The result is determined
Scratch resistance is expressed as the number of failures, which is the number of cycles when the coating is destroyed. At the same time, it can be combined with the width or depth of the scratch to assist in determining it. For example, measuring scratch width using a digital microscope, the relationship between width change and the number of frictions can reflect the gradual destruction of the coating. When collating the data, care should be taken to distinguish between complete coating failure and minor scratches, as the former is usually more in line with the tolerance standards of real-world usage scenarios.
Standard reference
This method refers to a number of common testing guidelines at home and abroad, including:
- Operating Specification for Linear Abrasion Tester (General Document for Mechanical Part)
- Friction Resistance Standards for Printed Coatings (Packaging Materials)
- Scratch resistance test methods for coatings (surface treatment technical literature)
Influencing factors
The main factors affecting the test results include: friction head hardness, load setpoint, stroke speed and ambient humidity. Increased loads or excessive friction head hardness can shorten the number of failures, while high humidity may soften some water-based ink coatings and reduce wear resistance. In addition, the roughness and surface energy of the substrate can also indirectly interfere with test repeatability. It is recommended that the above parameters be clearly listed in the report to facilitate cross-laboratory control.
Use Cases:
Taking a water-based gravure ink as an example, under the conditions of 25 mm stroke, 10 Newton load and emery sandpaper friction head, the number of coating failures is 450 times. The same batch of solvent-based inks was 680 times under the same conditions, indicating that the solvent-based system had better scratch resistance. This data provides a quantitative basis for packaging suppliers to adjust ink formulations. In addition, by changing the friction head material, it is possible to evaluate the applicable scenarios of film packaging and paper packaging separately.
Notes:
The friction head should be cleaned before and after the test to avoid residual particulate matter affecting the subsequent results. The friction head needs to be replaced after wearing to a certain extent, usually every 5000 cycles or obvious shape deformation as a replacement cycle. Uniform force is required when the sample is fixed to prevent local displacement of the thin substrate during testing. The original graph or photo should be kept for review when the data is recorded.
Epilogue
Linear abrasion testing machines provide a controlled and repeatable means of inspection for the packaging and printing industry, helping to optimize the scratch resistance of ink coatings from a material science perspective. Combined with appropriate standardized operation and data analysis methods, the device can serve multiple aspects from laboratory R&D to on-site quality control. In the future, with the development of friction head diversity and automated measurement technology, its application fields are expected to expand further. The quoted article is indicated:
1. "General Guide to Friction Resistance Test of Printing Coatings", a compilation of industry technical data
2. "Linear Abrasion Tester Operation Manual", common equipment parameters in the machinery industry
3. "Analysis of Surface Coating Wear Mechanism", Journal of Materials Engineering