What are the standards for scratch resistance testing?

With technological advancements and rising consumer demand for product quality, scratch resistance has become an essential and important indicator for many products, particularly in electronics, automotive interiors, household goods, and industrial materials. Scratch resistance testing not only verifies material durability but also enhances brand image.

Overview of Scratch Resistance Testing

Scratch resistance testing assesses a material's ability to withstand scratches from everyday use by subjecting it to scratch testing. This testing typically utilizes specific tools and standardized testing methods. Scratch resistance directly impacts a product's lifespan and appearance. For example, the scratch resistance of a mobile phone screen impacts the user experience, while the scratch resistance of automotive paint affects the vehicle's appearance and value retention.

Common Scratch Resistance Testing Standards

Scratch resistance testing standards are primarily categorized as international and industry standards. The following are several important standards:

ASTM D3363: This standard, developed by the American Society for Testing and Materials (ASTM), is used to determine the surface hardness of coatings, plastics, and other materials. The test uses a pencil hardness scale for scratch testing, which is divided into different hardness levels. ISO 7784: Developed by the International Organization for Standardization (ISO), this standard is used to measure the resistance of surfaces to abrasion and is applicable to scratch resistance tests for paints and coatings. It primarily uses a friction tester to assess the durability of the material.

DIN 52347: A German industrial standard, it focuses on the scratch resistance of plastics and coatings. This test uses abrasion equipment that effectively simulates the scratching conditions experienced in everyday use.

GB/T 17657: This standard is a Chinese national standard primarily used for testing the physical properties of building and decorative materials, including scratch resistance. Adherence to this standard helps improve the market competitiveness of materials.

ASTM E-112: This internationally recognized scratch test standard primarily evaluates the scratch resistance of vehicle body surfaces. It uses a scraper-like test tool to scratch the surface and record the scratch depth and area to assess the durability of the surface.

ISO 22466: This standard, developed by the International Automobile Federation (FIA), is primarily used for scratch resistance testing of racing car bodies. This standard uses a test tool similar to a steel brush to brush against the surface of a vehicle body to evaluate its scratch resistance.

ASTM D422: This scratch test standard for sheet metal surfaces primarily evaluates the scratch resistance of metal surfaces. This standard uses a test tool similar to a steel brush to brush against the metal surface to record the scratch depth and area, thereby evaluating the durability of the metal surface.

These standards are crucial for product performance in the market. Strict adherence to these specifications helps companies ensure product quality and enhance consumer trust.

How a Multi-Finger Scratch Tester Works

A multi-finger scratch tester is a precision instrument used to quantitatively evaluate the mechanical properties of a material's surface, such as coating adhesion, scratch resistance, and abrasion resistance. Its core operating principle can be summarized as "simulating scratches, achieving precise measurements."

Unlike traditional single-shot scratch instruments, the most notable feature of a multi-finger scratch tester is its use of multiple independent scratch probes (i.e., "multi-fingers"). These probes can be equipped with diamond styluses of various shapes and materials. Under computer control, they can perform scratch tests simultaneously or sequentially at different locations on the sample surface during a single test.

The operating process consists of three main steps:

Load Application: The instrument first applies a normal force (i.e., load) perpendicular to the sample surface to each stylus through a precise drive system. This load can be constant or continuously increasing linearly, simulating damage of varying degrees, from minor scratches to severe cuts.

Scratch Test: While applying the preset load, the sample stage moves at a constant speed relative to the stylus, causing the stylus to create one or more scratches on the material surface. During this process, highly sensitive sensors monitor and record changes in the friction force and acoustic emission signal experienced by each stylus in real time.

Detection and Analysis: During the scratch test, when the load increases to a critical value, the coating will begin to exhibit failure symptoms such as cracking and flaking. These microscopic failures will immediately cause sudden changes in the friction force and acoustic emission signal. After the test, the scratch morphology is observed using an optical microscope or scanning electron microscope. By matching the observed failure location with the recorded signal mutation point, the critical load at which the coating fails can be precisely determined. A higher critical load indicates stronger coating adhesion or better scratch resistance.

Multi Finger Scratch Mar Tester

Applications of Multi-Finger Scratch Testers

The revolutionary nature of the multi-finger scratch tester lies in its high-throughput and efficient parallel testing capabilities. It is equipped with multiple independent scratch probes (or "fingers") that can accommodate styluses of varying shapes, sizes, and materials. During a single experimental run, these "fingers" simultaneously apply a series of precisely programmed normal loads to a single sample surface for scratch testing. This cleverly expands traditional "point" measurement to "surface" measurement covering diverse load conditions, addressing the bottlenecks of discrete data and low efficiency associated with single-test runs.

In its application landscape, the multi-finger scratch tester plays multiple key roles:

Accurately quantifying the bond strength between coatings and substrates

This is its most classic application. The instrument scratches the coating surface by applying a continuous or stepped load. High-sensitivity sensors simultaneously monitor changes in acoustic emission and friction force. Combined with subsequent microscopic observation, the instrument accurately determines the critical load between the appearance of the first crack (LC) and complete delamination (CF) of the coating from the substrate. This data serves as the gold standard for evaluating coating adhesion quality and optimizing deposition processes.

Objective Assessment of Material Scratch Resistance

Scratch resistance is a critical quality indicator for plastics, polymers, paints, and decorative coatings. The multi-finger scratch tester can simulate various degrees of damage, from light friction to hard scratches. By measuring scratch width and depth, or analyzing plastic deformation and material accumulation around the scratch using an optical microscope, it provides objective, quantifiable data supporting the material's scratch resistance rating.

Efficient Screening of Material Tribological Properties

Rapid assessment of material friction coefficient and wear resistance is essential in the development of lubricants, new composite materials, or surface treatment technologies. Using multiple fingers to simultaneously test samples with different formulations or processes allows for the acquisition of a wealth of comparative data in a short period of time, significantly accelerating the R&D process and providing a powerful boost for material screening and formulation optimization.

Compatibility and Durability Testing of Biomedical Materials

In the medical implant sector, the bond strength between coatings (such as hydroxyapatite) and the metal substrate is crucial and directly impacts the long-term stability of the implant. Furthermore, for dental restorative materials, surface scratch resistance impacts both aesthetics and plaque adhesion. Multi-finger scratch testers provide a reliable means of verifying the performance of these products, which are crucial to human health.

Operating such a precision instrument is a blend of science and human-machine art. From ensuring the flatness and fixation of the sample, carefully selecting and installing the scratching stylus, to meticulously setting the test parameters (load range, scratch speed, and scratch length), every step is crucial to the accuracy of the results. After the test, microscopic analysis of the scratch morphology and the rational interpretation of the critical load data are crucial for unlocking the underlying physical meaning of the data.

With its efficient, precise, and reliable testing capabilities, the multi-finger scratch tester has become an indispensable tool in materials science, manufacturing quality control, and cutting-edge R&D. Like a discerning referee, it impartially assesses the surface properties of various materials on a microscopic playing field, providing a solid data foundation for driving technological advancement and improving product quality.