The ability to predict the weathering performance of the clearcoat system over a short period of time is essential for the design and development of coating production. Thus, the primary objective of the present study is to investigate whether it is possible to predict the weathering performance of an automotive paint system through determination of surface roughness, R a, and micro-hardness before and after various weathering exposure times (0, 24, 168, 336, 504, 672 hours) and when employing two different detergent materials (house-use detergent and car wash detergent). The data were analysed using a pair-sample t-Test, with 0.05 level of significance. It was found that the total net of degradation in the clearcoat level during the first 24 hours was R a ≈ 30.3 nm (for surface roughness) and 1.358 HV (for the μ-hardness) when using the house-use detergent. In contrast, it was found to be R a ≈ 4.6 nm (for surface roughness) and 1.133 HV (for μ-hardness) when using the car wash detergent. Also, increased time of weathering (up to 672 hours) increases the R a and μ-hardness values. It can therefore be concluded that the effect of house-use detergent was more severe than that of car wash detergent on the clearcoat system.
In general, surfaces are not perfect [
Outdoor weathering conditions can severely affect the long-term aesthetic appeal of a car [
these factors plays a greater or lesser role depending on both the coating and the particular geographic location in which a layer is exposed. In these studies, the degradation effects of biological materials such as bird droppings and raw eggs have also been paid attention to recently [
The substrate used throughout the experiments was a white-coloured painted automotive, from the Toyota Company, KSA, model 2016. Around 74 samples with identical dimensions’ length of 30 × 30 × 0.85 mm were studied in this investigation. Abrasive waterjet cutting technology (from TecnoCut waterjet cutting systems) was used to excise sections of similar shape from the front of the painted automotive body surface, as shown in
In order to perform the experiment, the surface roughness and micro-hard- ness were measured in an air-conditioned room with an ambient temperature of 20˚C ± 1˚C and a relative humidity of 40% ± 5% RH. The different detergents (car wash detergent or house-use detergent) were then applied using a stylus-typ Taly-Surf® (Taylor Hobson Precision, Inc., UK) and Vickers indentation micro- hardness (Micro-hardness, Zwick Roell Indentec ZHV1-AFC, Germany).
After that, the sample was washed with either car wash detergent or house-use detergent as shown in
samples were subjected to differing weathering exposure times (0, 24, 168, 336, 504, 672 hours) along with the two different detergent materials (house-use detergent and car wash detergent). The outdoor weathering tests were carried out in Makkah, a dry place with high temperature. The temperature (˚C) and relative humidity (%RH) were monitored and recorded each time the samples were collected
Finally, after various exposure times, all samples were measured in an air- conditioned room, with an ambient temperature of 20˚C ± 1˚C and a relative humidity of 40% ± 5% RH using a contact-type surface roughness and micro- hardness test.
The effects of the two different detergents (car wash detergent and house-use detergent) on the appearance of automotive paint systems were studied in an outdoor weathering test. The initial phase investigated the degradation during the first 24 hours and the later phase investigated subsequent degradation (0, 24, 168, 336, 504, 672 hours). All the tests took place in weathering environments which imposed different kinds of degradations (e.g., temperature, humidity and so on) on a clearcoat automotive body surface during the investigation, see
These can be particularly important factors when comparing the weathering behavior of a series of different time exposures vs. the temperature. Objects painted darker colours will typically be hotter than lighter objects. This temperature difference can lead a coating’s degradation rate to be significantly color- dependent. As a guide, the temperature of a series of steel panels painted with different colours of automotive topcoats (CC/BC) is shown in
colour-independent and that the action of temperature during the serving time may have less effect. It can still however be considered as an accelerated process as regards degradation of the clearcoat systems. Therefore, paint systems that are hotter will tend to be subjected to greater mechanical stresses than those that are exposed to lower temperature extremes, again favouring light colours over dark colours.
The surface roughness profile, indentation micro-hardness and scanning electronic microscopy (SEM) were used to assess the effect of the detergents on the appearance of the automotive clearcoat systems. Details of the surface roughness procedure have been reported elsewhere [
In general, since the weather is incapable of repeating itself exactly, any outdoor exposure test is unique. The data were analysed using pair-sample t-Test, with 0.05 level of significance. For the house-use detergent, as shown in
those which were obtained after exposure (mean = 0.088 µm, ±SD = 0.008 µm) (t(−2.2) = 23, p = 0.0001. The total net of degradation in the clearcoat level during the first 24 hours was 30.3 nm when using the house-use detergent, whereas it was 4.6 nm when using the car wash detergent. This may be attributed to the chemical influences of the house-use detergent being in contrast to the car wash detergent and causing the clearcoat surface to dissolve. Another reason for the greater value of the surface roughness in the clearcoat level can be the ascribed to the size of different peak-to-valley created by the process of painting on the production line. It can be seen clearly in the micro-hardness test that the weather is variable and thus materials exposed to it are in fact being exposed to a constantly changing environment (e.g., temperature, humidity, etc.).
In this section, Vicker’s diamond under the load, P, was fixed at 300 g (2.942 N) and the application time was kept at 15 seconds. Apparently, the weathering performance of the clearcoat indirectly reflected the mechanical performance of the micro-hardness. The data were analysed using a pair-sample t-Test, with 0.05 level of significance. For the house-use detergent, the micro-hardness measurements obtained before the exposure (mean = 16.629 HV, ±SD = 0.396 HV) were significantly lower than those which were achieved after exposure (mean = 17.988 HV, ±SD = 0.313 HV) (t(−14.8) = 23, p = 0.0001. For the car wash detergent, the micro-hardness measurements obtained before the exposure (mean = 16.842 HV, ±SD = 0.588 HV) were significantly lower than those which were obtained after exposure (mean = 17.975 HV, ±SD = 0.450 HV) (t(−9.8) = 23, p = 0.0001. The total net of degradation in the clearcoat level during the first 24 hours was 1.358 HV when using the house-use detergent whereas it was 1.133 HV when using the car wash detergent.
According to the micro-hardness tests, it can be concluded that the major degradation mechanism of the clearcoat system exposed to house-use detergent and car wash detergent is chemical rather than physical. Besides, weathering gives rise to non-uniform degradation of clearcoats which themselves contain composite structures with low and high crosslink density domains. Therefore, weathering may cause the development of local stresses in the clearcoat level, enlarge the pathway passages of water and result in a reduction in the barrier properties and an increase in water uptake, i.e., losses in corrosion resistance. Study of other properties of the clearcoat surface such as micro-hardness as measured by the Vickers micro-hardness test was sufficiently sensitive to aging by weathering as presented in
with no crack or delamination occurring in the region dominated by the clearcoat level still exists. This is a natural behaviour, and is called reverse indentation size effect (RISE), in which plastic deformation is predominant. It can be concluded that the weathering test has various effects on the visco-elastic behaviour of the clearcoat system depending on the low or high exposure times.
The data were analysed using a pair-sample t-Test, with 0.05 level of significance. For the house-use detergent, the micro-hardness measurements obtained before the exposure (mean = 13.86 HV, ±SD = 0.553 HV at 10 g) until reach (mean = 21.56 HV, ±SD = 0.08 HV at 1000 g) were significantly lower than those which were obtained after exposure (mean = 15.04 HV, ±SD = 0.048 HV at 10 g) until reach (mean = 22.22 HV, ±SD = 0.193 HV at 1000 g) (t(-12.5) = 7, p = 0.0001. For the car wash detergent, the micro-hardness measurements obtained before the exposure (mean = 14.08 HV, ±SD = 0.132 HV at 10 g) until reach (mean = 21.38 HV, ±SD = 0.146 HV at 1000 g) were significantly lower than those which were obtained after exposure (mean = 15.4 HV, ±SD = 0.0632 HV at 10 g) until reach (mean = 22.1 HV, ±SD = 0.379 HV at 1000 g) (t(−2.9) = 7, p = 0.0001.
Young’s Modulus, E, (MPa) | House-use detergent | Car wash detergent | ||
---|---|---|---|---|
before exposure time (mean ± SD) | after exposure time (mean ± SD) | before exposure time (mean ± SD) | after exposure time (mean ± SD) | |
1613.9 ± 257.7 | 1728.6 ± 241.2 | 1668.7 ± 215.2 | 1724.6 ± 219.4 |
The results of the 4-week outdoor exposure are presented in
Sunlight reaching the earth’s surface contains a broad range of wavelengths from 280 to 1400 nm. The worst aspect is the ultraviolet (UV) which is in the range of <380 nm. Most polymer materials are very sensitive to this aspect of the sunlight. For instance, polyesters and alkyds have absorption peaks of around 315 and 280 - 310 nm, respectively [
In
In
measurements obtained before the exposure (mean = 16.425 HV, ±SD = 0.043 HV) were significantly lower than those which were achieved after exposure (mean = 18.650 HV, ±SD = 0.502 HV). The total net of degradation in the clearcoat level was 1.825 HV when using the house-use detergent whereas it was 2.225 HV when using the car wash detergent. So, the micro-hardness value of the clearcoat system increased dramatically during the weathering cycle.
To investigate the surface morphology of the clearcoat system during the weathering cycle, scanning electronic microscopy (SEM) was used.
In the meantime, nano-scale voids and micro-cracks designated by the solid yellow arrows to guide the eye are found in
Therefore, the SEM electronic micrographic analysis confirms the results of surface roughness, Ra, and indentation micro-hardness. The clearcoat system with house-use detergent shows the highest surface roughness and micro-hard- ness values.
This paper presents studies on the repeatability performance of the clearcoat layer of an automotive exposed to the impact of outside experimental factors depending on the exposure time along with two different detergents (house-use and car wash). The general conclusions obtained are shown below:
1) For the surface roughness, the total net of degradation in the clearcoat level during the first 24 hours was 30.3 nm when using the house-use detergent whereas it was 4.6 nm when using the car wash detergent.
2) For the micro-hardness, the total net of degradation in the clearcoat level during the first 24 hours was 1.358 HV when using the house-use detergent whereas it was 1.133 HV when using the car wash detergent.
3) The total net of degradation after 4-week outdoor exposure was 0.014 µm for Ra when using the house-use detergent whereas it was 0.007 µm when using the car wash detergent.
4) The total net of degradation after 4-week outdoor exposure was 1.825 HV for micro-hardness when using the house-use detergent whereas it was 2.225 HV when using the car wash detergent.
In conclusion, car wash detergent indicated lower values of both Ra and HV after the various times of weathering exposure, whereas house-use detergent indicated otherwise.
The authors have no conflicts of interest.
The authors received no financial support for the research and/or for the publication of this article.
Alsoufi, M.S., Ba- wazeer, T.M., Alhazmi, M.W. and Azam, S. (2017) The Effect of Detergents on the Appearance of Automotive Clearcoat Systems Studied in an Outdoor Weathering Test. Materials Sciences and Applications, 8, 521-536. https://doi.org/10.4236/msa.2017.87036