Fluorocarbon Aluminum Panel Testing

Fluorocarbon aluminum panel inspection mainly conducts scientific testing and analysis on the coating thickness, coating adhesion, impact resistance, chemical corrosion resistance, weatherability and artificial accelerated aging, and color and gloss uniformity, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Coating thickness: The coating thickness gauges are used to measure the dry film thicknesses of the fluorocarbon coatings, usually including the local minimum values and average values. According to GB/T 17748-2016, for the aluminum panels used as the outdoor decorative panels, the minimum local film thicknesses should not be lower than 25μm, and the average values should not be lower than 30μm. This is the basis of ensuring that the coatings have the sufficient physical barriers and weatherability.

Coating adhesion: The bonding strengths between the coatings and aluminum substrates are evaluated through the cross-cut method or circle-cut method. Usually adopting the cross-cut spacing of 1mm or 2mm, using the dedicated adhesive tapes to pull up vertically, and evaluating the grades according to the percentages of the coating peeling areas. Grade 0 (no peeling) is the best. It is the key indicator of judging whether the coatings are easy to peel off.

Impact resistance: The falling weight impact testing machines are used for the testing. The impact heads of the specified masses are released to freely fall from the specified heights, impacting the front or back surfaces of the specimens, observing whether the cracking or peeling occurs in the coatings. This item is used to simulate the capabilities of the panels to resist the external force impacts during the transportation, installation or use.

Chemical corrosion resistance: The specimens are exposed to the chemical reagents of the specific concentrations, such as the hydrochloric acid, sodium hydroxide and detergents, observing whether the defects such as the gloss loss, discoloration, blistering and peeling occur on the coating surfaces within the specified times. This testing evaluates the chemical stability of the panels in the complex environments such as the acid rain and cleaning agents.

Weatherability and artificial accelerated aging: The xenon lamp aging test chambers or UV fluorescent aging chambers are used to simulate the long-term outdoor illumination, temperature, humidity and condensation environments. After the coatings are aged for the specified times (such as 1000 hours and 2000 hours), their color changes (ΔE), gloss retention rates and powdering grades are tested, to predict their actual service lives.

Color and gloss uniformity: The color difference meters and gloss meters are used to carry out the multi-point measurements at the different positions of the panel surfaces. The color difference ΔE values are usually required to be less than 1.5 or comply with the agreements of the two parties, and the gloss deviations should be within the agreed ranges, to ensure the visual effect consistency of the large-area installations.

Testing Scope

Substrate materials and states: The testing objects are mainly the aluminum alloy sheets, and the common designations are 1100, 3003 and 3004. The states (such as H24), thickness tolerances, flatness and the qualities of the surface pre-treatments (such as the chromating or phospho-chromating treatments) need to be confirmed. This is the bottom-layer guarantee of the coating properties.

Coating system types: The testing covers the different fluorocarbon resin systems, such as the PVDF (polyvinylidene fluoride) coatings and FEVE (fluoroethylene and vinyl ether copolymer) coatings. The resin contents need to be clarified (the PVDF resin contents are usually not lower than 70%), and the different processes such as the two-coat, three-coat or four-coat (including the primers, topcoats and clearcoats) need to be distinguished.

Finished panel properties: The testing is for the finished fluorocarbon aluminum panels that have completed the coating and forming processes, including the conventional flat panels, special-shaped panels, perforated panels and curved panels. Their overall properties need to be evaluated, not only the coating test plates, to reflect the qualities of the actual products.

Application environment classification: According to GB/T 17748, the testing scope needs to correspond to the use scenarios of the products, mainly divided into the outdoor use and indoor use. The testing items of the outdoor panels are more comprehensive and the indicators are stricter, especially focusing on the long-term durability items such as the weatherability and salt spray resistance.

Specific function requirements: For the aluminum panels with the special function requirements, the testing scope will be correspondingly extended. For example, for the use in the coastal or chemical factory areas, the salt spray corrosion testing needs to be strengthened; for the use in the fire protection areas, the combustion performance grade (such as the A2 grade) testing needs to be added.

Production process monitoring: The testing is also applied to the quality control during the production processes, such as the testing of each batch of the coatings, and the online monitoring of the pre-treatment film weights and coating wet film thicknesses, ensuring the process stability and product consistency.

Testing Methods

Standard reference method: Mainly according to the relevant requirements for the coated aluminum panels in the national standard GB/T 17748-2016 (Aluminum-plastic composite panels for building curtain walls), as well as GB/T 23443-2009 (Aluminum panels for building decoration). At the same time, with reference to the international standards such as ASTM D 6577 (industrial grade PVDF coating standard) for the specific item testing.

Instrumental analysis method: The precision instruments are used for the quantitative testing. For example, the magnetic or eddy current thickness gauges are used to measure the film thicknesses, the color difference meters are used to measure the colors, the gloss meters are used to measure the gloss, and the impact testing machines are used to test the impact resistance. The artificial accelerated aging completely relies on the controllable laboratory aging equipment.

Visual and sensory evaluation method: After the specific testing items, the visual observation needs to be combined. For example, after the adhesion cross-cut testing, the conditions of the debris picked up by the tapes are observed under the standard light conditions; after the chemical corrosion resistance testing, whether there are the visible defect changes on the surfaces is observed.

Accelerated environment simulation method: The salt spray test chambers are used to simulate the marine atmospheric environments, evaluating the corrosion resistance; the constant temperature and humidity chambers are used to test the heat and humidity resistance; the boiling water resistance testing (immersing the specimens in the boiling water) is used to quickly evaluate the coating adhesion stability. These methods can evaluate the long-term properties within the relatively short times.

Physical mechanical testing method: Including the pencil hardness testing (evaluating the coating surface hardnesses), bending testing (evaluating the coating flexibility and crack resistance) and abrasion resistance testing (such as the Taber abrasion testing), mainly evaluating the mechanical properties of the coatings.

Sampling and specimen preparation specifications: The testing methods include the strict sampling provisions. The samples should be randomly selected from the production batches, and the sizes need to meet the requirements of the various testing items. For the destructive testing, a sufficient number of parallel specimens need to be prepared, and the specimen edges need to be properly edge-sealed, to avoid the edge effects affecting the results.

Testing Standards

Domestic Standards:

1. GB/T 17748-2016, Aluminum-plastic composite panels for building curtain walls

2. GB/T 23443-2009, Aluminum panels for building decoration

International Standards:

1. ASTM D 6577, Standard guide for testing industrial protective coatings

2. ISO 9227, Corrosion tests in artificial atmospheres — Salt spray tests

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Coating thickness gauge: Divided into the magnetic thickness gauges (for the steel substrates) and eddy current thickness gauges (for the non-ferromagnetic metals such as the aluminum). The equipment needs to be regularly calibrated with the standard foils. During the measurement, the multiple representative points need to be selected on the panel surfaces, to calculate the average thicknesses and minimum local thicknesses.

Adhesion tester: Including the mechanical or electric cross-cut testers (ensuring the sharp cutting edges and precise spacings), circle-cut testers and dedicated pressure-sensitive adhesive tapes. During the testing, the tapes need to be quickly pulled at the 90° angle perpendicular to the scratches. It is the key equipment of evaluating the coating system qualities.

Artificial weathering aging test chamber: Mainly including the xenon lamp aging chambers and UV fluorescent aging chambers. The xenon lamp spectra are the closest to the full solar spectra, often used to simulate the comprehensive outdoor aging; the UV fluorescent aging mainly examines the destructive effects of the UV ultraviolet rays and condensed water, with the relatively short testing periods.

Salt spray corrosion test chamber: Used to simulate the marine or salt-containing humid atmospheric environments. The 5% sodium chloride solutions are atomized, and the continuous or cyclic spraying is carried out on the specimens at the constant temperature of 35℃. Through the observation of the coating blistering and corrosion spread degrees after the specified times (such as 1000 hours and 3000 hours), the corrosion resistance is evaluated.

Color difference meter and gloss meter: The color difference meters calculate the color difference ΔE by measuring the L*, a*, b* values between the specimens and standard plates. The gloss meters most commonly measure at the 60° incidence angle, and can also be supplemented with the measurements at the 20° (high gloss) or 85° (low gloss) angles. These two instruments are the necessary tools of controlling the product appearance consistency.

Impact testing machine and bending testing machine: The falling weight impact testing machines release the impact heads of the specified masses through the adjustable-height guide tubes. The bending testing machines (such as the three-point bending or mandrel bending testing devices) are used to evaluate the crack resistance of the coatings when the aluminum panels are bent and deformed, particularly important for the aluminum panels needing the edge folding processing.