Influence of different environmental test conditions on coating adhesion

Abstract: Adhesion test is a common method to assess the adhesion between the coating and the substrate.

Keywords: adhesion; coating; environmental test

0 Preface

With the continuous development of coating technology, there are more and more solutions that rely on coating as a protective layer.

1 Test part

1.

The sample used for the test this time is selected the exterior paint products of a relatively popular model of an independent brand at present, using PP+EPDM+FILLERS as the base material, spraying primer + color paint + varnish with the same surface treatment process, total thickness Control within the range of 60~120μm

1.

On the one hand, this test referred to the corporate standard of a certain independent brand exterior paint, but also made some modifications and added test items

The adhesion test uses 430P equipment from ERICHSEN, the scratch spacing is 2mm, and the number of scratches is 11*11 (Figure 1), and then paste 3M898 tape for tearing off, and inspect the adhesion results by checking the paint peeling area in the cross-cut area [1 ]

Before the environmental condition test, the first adhesion test was carried out on a certain area of ​​the sample plate and the results were checked

1.

The simulated paint has been in a state of high temperature and high humidity for a long time

The coated sample shall be stored for 336h under the environmental conditions of (50±2)℃ and (93±5)%RH

1.

The simulated paint has been soaked in water for a long time

The coated sample was immersed in deionized water at 40°C and kept for 720h
.

1.
2.
3 Condensate water[2]

The simulated paint has been in a state of high humidity and surface condensation for a long time
.

Coated samples are stored for 336h in an environment of (40±3)℃ and 100%RH
.
Condensation will form on the surface of the samples .

1.
2.
4 Xenon light illumination[3]

The simulated paint has been exposed to outdoor sunlight and frequent rain for a long time
.

Coating samples are carried out in accordance with the following conditions: the filter is a daylight filter, irradiance: 0.
50W/(m2·nm)@340nm, black mark temperature: (65±2)°C, relative humidity: (65±5) )%RH, water spray cycle: 102min without water spray, 18min with water spray, total test time: 1000h
.

1.
2.
5 UV aging[4]

The simulated paint has been in a state of alternating intense ultraviolet light and dark condensation for a long time
.

The coating samples were carried out according to the following conditions: UVB-313, irradiance 1.
05W/m2 (310nm), illumination stage: 60℃, 4h, condensation stage: 50℃, 4h, total test time: 1000h
.

1.
2.
6 Water shock

Simulate high-pressure car wash conditions in high-temperature environments

The coated sample is stored in a 90℃ environment for 4 hours, and immediately subjected to water impact after being taken out.
Impact conditions: pressure (12±0.
3) MPa, nozzle: 2506, water temperature at room temperature, spray distance 100mm, spray angle 90°, spray time 30s; The above is one cycle, and a total of 2 cycles are performed
.

2 Test results and analysis

2.
1 Adhesion test before environmental test

In this test, the first adhesion test was performed on all the samples.
The test results are shown in Table 1
.
It can be concluded from the test that the adhesion performance of the sample plate used in this round of test before the environmental condition test is good, and each coating does not fall off, which meets the comparison requirements of the subsequent environmental test.
At the same time, the grid area is in the subsequent test process.
As a scratched area that simulates actual use, an environmental condition test is carried out together and a follow-up comparison is carried out
.

2.
2 Adhesion test after environmental test

After the environmental condition test, stick the tape again to the initial grid area and tear it off to check the adhesion
.
Check the adhesion of the adhesive tape and tear off the other intact areas.
The test results are shown in Table 1
.
The following is an analysis of the results:

1) The adhesion results are not deteriorated after the treatment of constant heat and humidity and xenon light conditions, and the effect on the paint is relatively small, which can meet the design requirements
.

2) Adhesion performance after treatment with water resistance, condensed water, UV aging, and water impact environmental conditions all have different degrees of deterioration, which has a relatively large impact on the paint
.
Among them, the adhesion result of UV aging is the worst, indicating that ultraviolet radiation has a great influence on the adhesion of the coating
.

3) In the adhesion test after condensate and water impact conditions, the initial adhesion results in the cross-cut area are worse than those in other areas, indicating that the damaged coating is more likely to be affected by environmental conditions and cause performance degradation
.
Be sure to pay attention to paint protection during normal use to avoid scratches
.

4) Comparing the treatment of constant damp heat and condensed water conditions, when the temperature and humidity are close, and the time is the same, the adhesion result of the initial cross-cut area of ​​condensed water is worse than that of constant damp heat, indicating that once condensation is formed on the scratched area of ​​the paint , It will have a greater impact on the adhesion of the coating
.
In actual use, try to avoid immersing the scratched paint in water
.

5) Comparison of water-resistant environmental conditions and the standard requirements of a certain car company have been modified, the test time has been greatly extended, the severity of the test has been increased, and the impact on the adhesion performance is also more obvious
.

6) Comparison of xenon lamp illumination and UV aging condition treatment, using the conditions of light radiation + high temperature + high humidity (water spray or condensation), the adhesion result after UV aging is significantly worse than xenon lamp illumination, indicating the ultraviolet band in the radiation spectrum It has a great influence on paint performance
.

3 Conclusion

The quality of coating adhesion is an important factor that affects the ability of the coating to protect the substrate, and it is also an important factor that affects the appearance of decoration.
However, various environmental aging conditions have an important impact on the adhesion performance of the coating
.
In this paper, six different environmental aging conditions are set through experiments, and at the same time with different severity levels, to simulate normal use and simulated scratch conditions, to investigate the degradation of the coating adhesion performance, and for the follow-up in terms of test items, severity, etc.
The choice provides a basis
.
At the same time, it is also recommended that there are scratch marks on the surface of the product in the process of daily life, and the repair should be carried out as soon as possible.
Do not let the scratched area soak in water and avoid strong ultraviolet radiation, which can appropriately improve the adhesion of the coating and extend the service life of the product
.