Understanding ISO 1520: A Core Standard for Coating Performance Testing

In the quality control and product development of the coating industry, the deformation resistance of coatings directly determines the durability and application value of products. As a core testing standard developed by the International Organization for Standardization (ISO), ISO 1520 provides a unified technical basis for evaluating the crack resistance and peel resistance of paint and varnish coatings through the classic “cupping test” method. From automotive body painting to furniture surface treatment, the application of this standard runs through all links of the coating industry chain, serving as an important technical support for ensuring product quality.

Essence of the Standard: Positioning and Core Value
The full name of ISO 1520 is Paints and varnishes — Cupping test. Its core positioning is to evaluate the resistance of coatings to progressive indentation deformation of the substrate by simulating the mechanical deformation that coatings may withstand in actual use. Specifically, it focuses on two key indicators: one is the crack resistance of the coating itself, and the other is the adhesion stability (peel resistance) between the coating and the metal substrate.
The value of this standard is reflected in three dimensions: for manufacturers, it serves as a quantitative basis for optimizing coating formulations and improving coating processes; for testing institutions, it provides a repeatable and comparable unified testing method; for end-users, products that meet the standard requirements mean more reliable performance, which can effectively reduce maintenance costs caused by coating failure. It is worth noting that this standard is applicable not only to single-coating systems but also to the overall or layered testing of multi-coating systems, demonstrating broad applicability.

Development and Evolution: Technical Upgrades from 1973 to 2022
The development history of ISO 1520 reflects the continuous refinement of coating testing technology. First released in 1973, the early version of the standard mainly established the basic principles and operation framework of the cupping test. With the advancement of coating technology and the expansion of application scenarios, the standard has undergone multiple revisions and upgrades. The 2006 version marked a crucial technical innovation—it not only improved the testing process but also added precision data, significantly enhancing the reliability and comparability of test results.
In the process of international promotion, ISO 1520 has been transformed into regional or national standards by many countries and regions, forming a global application system. For example, the European Union has released the EN ISO 1520 series of standards, South Korea has formulated the KS M ISO 1520-2022 version, and China has equivalently transformed it into GB/T 9753-2007 Paints and Varnishes – Cupping Test. This standard replaced the 1988 version, achieving full alignment with advanced international technical requirements. These derived standards all maintain the core technical requirements of ISO 1520, with only adaptive adjustments made based on regional industrial characteristics.

Testing Principle: Performance Verification in Simulated Deformation
The cupping test specified in ISO 1520 is essentially a mechanical performance test that simulates actual working conditions, with a concise and targeted principle: a metal test panel coated with paint is fixed on the testing equipment, and a smooth spherical punch applies pressure to the back of the test panel at a standard rate, causing the central area of the panel to gradually indent and form a “cup-shaped” deformation. During the deformation process, the coating generates stress due to stretching; when the stress exceeds its bearing limit, cracks will appear or the coating will peel off from the substrate.
Two testing modes can be adopted: one is the “pass/fail” judgment mode, where the test is conducted at a fixed indentation depth required by the product standard, and whether the coating fails is observed; the other is the quantitative testing mode, where the minimum indentation value at which the coating first cracks or peels is accurately measured by gradually increasing the indentation depth. This value directly reflects the flexibility and adhesion level of the coating. This hierarchical testing mode enables the standard to meet both the needs of batch quality screening and provide refined data for research and development.

Key Implementation Elements: Equipment, Processes, and Quality Control Points
Accurate implementation of the ISO 1520 test requires strict control of three core links: equipment, environment, and operation. Deviations in any link may lead to distorted results.
1. Core Equipment Requirements
The standard has clear regulations on the precision of testing equipment. Core equipment includes: a cupping tester (equipped with punches and test cups that meet size requirements to ensure uniform and stable force application), a coating thickness gauge (used to ensure uniform coating thickness before testing and eliminate the impact of thickness differences on results), optical magnification equipment (such as microscopes or high-power magnifiers for accurately observing microcracks), and temperature and humidity control equipment (to maintain the test environment at the standard conditions of 23±2℃ and 50±5% relative humidity). Among these, the control of the force application rate of the cupping tester is crucial; the international standard generally requires a punch movement rate of 0.2 mm/s, a parameter that directly affects the stress transmission process.
2. Standardized Operation Process
The complete testing process must comply with strict technical specifications, mainly including four steps: first, sample preparation—standard-compliant metal substrates (commonly cold-rolled steel plates or tinplates) are selected, and a uniform coating is formed using specified application methods. The coating thickness is usually controlled between 30-120 microns, and curing is completed in a standard environment; second, equipment calibration—before testing, the punch position and pressure sensor must be calibrated to ensure the equipment is in normal working condition; third, formal testing—the equipment is started, the coating status is continuously observed, and the moment when cracks first appear or peeling occurs is recorded; fourth, result evaluation—test conclusions are given by referring to the standard classification table based on indicators such as crack length and peeling area.
3. Easily Overlooked Quality Control Details
In actual testing, several details are often overlooked but directly affect the accuracy of results: substrate pretreatment must completely remove oil stains and oxide layers, otherwise, the adhesion stability of the coating will be affected; the coating thickness must be uniform—local over-thickness will cause stress concentration during testing, leading to false positive results; fluctuations in environmental temperature and humidity will change the physical properties of the coating (e.g., low temperatures make the coating brittle, resulting in lower test values); image analysis auxiliary tools should be used in result evaluation to reduce the subjective deviation of manual observation.

Industrial Value: Full-Chain Support from R&D to Application
The application value of ISO 1520 has penetrated the entire coating industry chain, serving as a technical link connecting R&D, production, and application. In the automotive manufacturing field, body coatings must withstand slight deformation during assembly and stone impacts during driving; testing based on this standard can screen coatings with excellent impact resistance, reducing post-sales paint cracking issues. In the furniture industry, the standard can evaluate the performance of wood coatings when subjected to collisions during transportation. In the architectural coating field, it can provide data support for the wind load deformation resistance of exterior wall coatings.
For enterprises, products that pass the ISO 1520 test are more likely to gain market recognition. For example, when developing water-based automotive coatings, a coating enterprise used this standard to quantitatively evaluate the impact of different resin ratios on coating flexibility. By adjusting the curing agent ratio, the cupping value of the coating was increased by 25%, and the product successfully entered the supply chain of major automotive manufacturers. Third-party testing institutions use this standard to provide fair performance verification for enterprises, serving as a “technical endorsement” for market trust.

Conclusion: Standards Lead the Upgrade of Coating Quality
As a core standard for testing the deformation resistance of coating films, the value of ISO 1520 lies not only in providing a unified testing method but also in promoting the performance upgrade and quality standardization of coating products through quantitative indicators. With industries such as new energy vehicles and high-end equipment putting forward higher requirements for coating performance, this standard is continuously optimized to adapt to new application scenarios. For coating enterprises, testing institutions, and end-users, in-depth understanding and strict implementation of ISO 1520 are not only the basis for ensuring product quality but also the key to enhancing market competitiveness.

Our product GA-6059 Cupping Tester meets this standard.

GA-6059 Cupping Tester
Scope Of Application
ISO 1520 based on international standard and national standard GB9753 cup drawing design and manufacture of QBJ type coating machine is suitable for the evaluation of paint varnish and coating of related products (single-layer coating) or supporting system under the experiment method of standard, sag experiment was carried out, and make it gradually after deformation, the cracking resistance of the coating or resistance to the performance of the separation of the metal substrate, Evaluate coating pass or not pass. The depth of the indentation can also be gradually increased to determine the minimum depth at which the coating has just begun to crack or to detach from the substrate.

Technical Indicators
1.Diameter of subsidence: 20mm
2, the maximum depth of depression: 10mm
3, compression accuracy: 0.05mm
4, digital indexing value: 0.01mm
5, the maximum compression force: 1000N
6, test specification: 70mm*70mm*0.3mm~1.25mm

Preparation of the test film
(1) The test piece is square, and its size is 70mm*70mm*0.3mm~1.25mm
(2) The material of the test piece should be polished steel plate, and meet the requirements of GB9271, and the test piece should be flat without deformation.
(3) Prepare the coating according to the standard requirements, dry it and measure its thickness. At a temperature of 23±2°C and relative humidity of 50±5%, the test was carried out after at least 16 hours of state adjustment.

Operation method
(1) single coated plate test: — automatic zero
Turn the hand wheel of the testing machine toward the downward direction (clockwise) to the end, loosen the upper part of the testing machine test piece pressing device, the metal surface of the single coating test plate down, the coating layer is inserted into the crack on the upper part of the testing machine, and the punch is aligned with the central axis of the test piece, fastening the pressing device. Press the red zero button of the instrument and the monitor will show zero. Turn the handwheel in the upward direction (counterclockwise direction) at a speed of 0.2±0.1mm/s (i.e., a turn of 2~3 seconds). When the punch hits the metal surface of the test plate, the display automatically shows zero, and the instrument lights red. Then continue to rotate the handwheel, the display reading is rising height, that is, the depth of depression, irreversible, otherwise the reading is not allowed.
(2) double-sided coated plate test, – manual zero
Turn the hand wheel of the testing machine in the downward direction (clockwise) to the end, loosen the upper test piece pressing device of the testing machine, insert the random zero adjusting steel plate into the crack of the upper part of the testing machine, and tighten the pressing device. Press the red button on the meter to make the monitor display zero. Turn the HANDwheel in the rising direction (counterclockwise direction). When the instrument lights red, that is, when the display is zero, stop turning the handwheel. Release the pressing device, then manually clear the zero (press the red button of the instrument), turn the handwheel in the upward direction at the speed of 0.2±0.1mm/s, and the indicator reading is the upward height, that is, the depth of the depression.
(3) With corrected visual acuity or 10x magnification, check the coating on the test piece for cracking or separation from the substrate.
(4) The above procedure shall be carried out on two separate test pieces. If the results are different, additional tests shall be conducted until the results of the two test pieces are consistent. If there are cracks in the substrate, the experimental results are invalid.
Determine the minimum degree of damage caused
(1) When the coating on the test piece cracks for the first time, or the coating separates from the substrate, the punch stops moving (the number on the display is the advance depth). The above tests shall be repeated on the same substrate to verify the results until they are consistent.

Machine accessories
1, 10 times a magnifying glass with light source
1. 1pcszero steel plate

Product link:

https://www.gonoava.com/product/ga-6059-cupping-tester/

Contact:

Email: arlenliu@gonoava.com
WhatsApp: 0086 18670728798(We chat)
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