Cao Xiaodong: About artificial accelerated aging test and natural exposure test

Cao Xiaodong is
director of the environmental laboratory of the National Paint Quality Supervision and Inspection Center and a senior engineer at the researcher level. As the first drafter, he led the drafting of a number of national standards and chaired or participated in the completion of a number of industry standards.
Coatings and Protection: Weather resistance is one of the properties of coatings, and which coating varieties value this performance more?
Cao Xiaodong: coating film coating on the surface of the object, play a protective and decorative role, coating film resistance to sunlight, air, water (acid rain), microorganisms and other environmental damage and maintain the original performance of the ability, known as coating weather resistance . Because the coating film in the process of use over time, will inevitably be affected by the interaction of internal factors and external environmental factors and some irreversible damage phenomena such as color loss, loss of light, powdering, cracking, rusting, peeling, spots, staining and so on. Therefore, as for the quality of the coating, in addition to its appearance, physics, chemistry, mechanical properties, it is more important to examine its service life, that is, the durability of the coating film itself. It is obviously very important and necessary to carry out the weather resistance test and the comprehensive evaluation after the test, which can objectively examine the performance of various comprehensive technologies of the coating film, but also evaluate its real use value.
the actual use of outdoor coating film theory needs to examine weather resistance, such as: automotive coatings, exterior building coatings, traffic bridge coatings, engineering machinery coatings, coil coatings and so on.
Coatings and Protection: What are the main properties of weather resistance? What are the evaluation methods?
Cao Xiaodong: weather resistance main inspection items are: color change, loss of light, powdering, foaming, rust, cracking, peeling, spots, gold, stain, mold and so on. Assessment can be carried out in accordance with the requirements of the relevant product standards, or in accordance with GB/T1766-2008 "color paint and varnish coating anti-aging rating method" provisions. The rating of the model is divided into two kinds of individual rating and comprehensive evaluation, and the comprehensive evaluation is divided into decorative paint and protective paint two methods, according to the degree of damage of the model can be evaluated: excellent, good, medium, can, poor, poor 6 levels.
test evaluation methods are more, including national standards, international standards, U.S. standards, etc., currently commonly used are:
(1) national standards: "color paint and varnish coating aging rating method" (GB/T 1766-2008); Regulations on the Degree of Uniform Variation of Measures and Size and Appearance ;(2) U.S. Standard: "Test Methods for Assessing the Degree of Rust on Painted Steel Surfaces" (ASTM D 610-2008); (ASTM D 714-2002 (2009);
above rating method is used in environmental tests and after the test needs to evaluate the surface performance of the coating. In addition, as mentioned earlier, before and after the environmental test of the coating's performance test, such as impact, hardness, adhesion, and so on, and then compare the data before and after, to examine the coating's tolerance to a specific environment, according to the need for test reference standards.
And Protection: From a technical and economic point of view, why do we need artificially accelerated aging tests? What is the demand situation?
Xiaodong: Natural exposure test has certain limitations, natural exposure test environmental factors are natural, they are generally not controlled by human. If the purpose of environmental testing is to find the exact environmental factors affecting the performance of the product, if you want to achieve this by manipulating the test conditions, such as artificially increasing the ambient temperature and humidity, it is basically not possible to achieve. Compared with the artificial simulation environment test, the natural climate exposure test can reflect the degree of damage to the product in a certain area and period of time, but it will be affected by many uncertainties in the test conditions.
generally speaking, the effects of natural climate exposure always vary with the differences in the natural environment (region, country, weather, season) of the exposed site. In addition, the natural climate exposure tests for coating products have a longer cycle (in multiplied years). For economic, competitive and shortening the natural aging test cycle, many product standards have chosen artificial climate aging tests to test the weather resistance of products.
and Protection: What is the correlation between accelerated aging test results and natural exposure?
: Acceleration and correlation is a pair of contradictions, acceleration is good, then the correlation is poor. No laboratory exposure test can fully simulate exposure under actual outdoor conditions.
Although there is interest in the correlation between accelerated aging tests and natural sun exposure tests, it is hoped that the following simple correspondence will be obtained: X-hour (or megajoule) accelerated aging tests - Y-month (or year) natural sun exposure tests to obtain an acceleration factor. But this is unrealistic and often ineffective.
Acceleration factor is very limited and has no universal significance, for the following reasons:
(1) the acceleration factor obtained based on the equal irradiation of artificial light sources and sunlight, without taking into account the influence of other factors such as temperature and humidity on the material, nor the performance changes of the material;
(2) Acceleration factors depend on the material, different materials or different formulations of the same material to obtain the acceleration factors will be very different;
(3) acceleration factors are related to the performance of the study,
(4) affect the natural sun exposure and accelerate the rate of aging variable factors will also greatly affect the calculated acceleration factors.
Coatings and Protection: Are there standards for aging test methods and testing methods? What other defects are there?
: Paint film aging test methods are the most used natural exposure test and artificial climate aging test.
common criteria for natural exposure testing are as follows:
GB/T 9276-1996 coating natural climate exposure test method;
ISO 2810:2004 color paint and varnish coating natural aging exposure and evaluation.
common criteria for artificial aging tests are as follows:
GB/T 1865-2009 color paint and varnish artificial climate aging and artificial radiation exposure
(filtered xenon arc radiation);
GB/T 14522-2008 Plastics, coatings, rubber materials artificial climate aging test method fluorescent UV lamps for mechanical industrial products
;
ISO 4892-3:2006 "Plastic Laboratory Light Exposure Method - Part III: Fluorescent UV Lights";
ISO 16474.2:2013 Color paint and varnish Artificial climate aging and artificial radiation exposure filtered xenon arc radiation;
ISO 16474-3:2013 color paint and varnish Laboratory light source exposure method Part 3: fluorescent UV lamps;
ASTM G154-2006 Operation of
UV fluorescence equipment for exposure of non-metallic materials;
ASTM G 152.153 Open and closed carbon arc lamp aging test method for non-metallic materials;
SAE J1960 automotive external material xenon lamp exposure test;
SAE J1885 automotive internal material xenon lamp exposure test;
DIN 75220 solar simulation equipment automotive component aging (metal halogen lamp).
and Protection: As technological innovation accelerates and the research and development process accelerates, will accelerated aging tests replace naturally exposed aging tests in the future? What are the current advances in technology?
: Natural exposure test is a better environmental test than artificial simulation environment test. Natural exposure test is carried out under the selected natural environment conditions, environmental factors are objective and true, as long as the selected test conditions and the expected use of the product environmental conditions are the same or similar, the test results have a high degree of credibility. The artificial simulation environment experiment is only a simulation of the natural environment, and often a simulation of individual or several environmental factors. Natural exposure test is the basis of artificial simulation environment test. Most of the environmental factor simulations in artificial simulation environmental experiments are carried out on the basis of the study of natural exposure tests.
without in-depth analysis of the factors affecting the test conditions in natural exposure tests, there would be no modern artificial simulated environmental experiments (at least for most manual simulated environmental experiments). For example, in artificial light aging test, the sun is the object of artificial light simulation, if people do not have a comprehensive understanding and understanding of the solar spectrum and light strength in the process of natural exposure, there will be no artificial light on today's light aging machine as a test light source and artificial light generated by the light energy to implement effective control.
natural exposure test is also an important method to evaluate the advantages and disadvantages of artificial simulation environment test. The performance changes produced by the product in the artificial simulation environment test are consistent with or similar to the performance changes produced in the natural exposure test, which indicates the high credibility of the results of the artificial simulation environment test. Because of the authenticity of natural exposure test, many product standards clearly stipulate that when the results of artificial simulation environmental test and natural exposure test results are quite different, the results of natural exposure test should prevail.
Although modern artificial simulation environment testing technology has reached a very high level, but limited by modern science and technology can achieve the high and expensive test costs, artificial simulation environment test can not be used to replace natural exposure test.