Method for testing stability of automobile coating color in short time and application thereof

Abstract

The invention discloses a method for testing the stability of the color of an automobile coating in a short time, which comprises the following steps: providing a substrate containing a composite coating to be tested, and recording the substrate as a substrate 1; wherein the composite coating to be detected sequentially comprises electrophoretic paint, floating coat, colored paint and varnish which are combined with a substrate; irradiating the substrate 1 by adopting a metal halogen lamp, testing and recording the absolute value of the chromatic aberration of the composite coating to be tested before and after irradiation, calculating the relative values of the chromatic aberration before and after irradiation, and respectively recording the relative values as L1, a1 and b1; if L1, a1 and b1 are all in a required range, the stability of the color of the automobile coating film is qualified in a short time; if at least one of L1, a1 and b1 is not in the required range, the stability of the automobile coating color in a short period is unqualified. The method can be used for directly and accurately detecting the color change of the vehicle body coating in a short period, and the problem that the normal traffic is influenced due to obvious color difference between the vehicle body and the exterior trimming part coating on site is prevented.

Description

Technical Field

[0001] This invention relates to the technical field of coating testing. More specifically, it relates to a method for testing the short-term stability of automotive coating colors and its application. Background Technology

[0002] With rapid economic growth, family cars have become mass-market consumer goods, entering countless households. Currently, my country ranks first in the world in both automobile production and sales. With the rapid development of the automotive industry and the upgrading of consumption, car body colors are becoming increasingly diversified, and traditional black, white, and gray are far from meeting the growing consumer demand. Especially with the promotion and popularization of new energy vehicles, car body colors are increasingly emphasizing fashion and personalization. To meet the growing demand for personalized and highly saturated car body colors, various high-chroma pigments and effect pigments (such as colored aluminum, glass powder, and color-changing pearlescent powder) have been widely used in automotive coatings.

[0003] Since automobiles consist of exterior parts such as the body, bumpers, door handles, rearview mirrors, and fuel tank cap, the color of the body and these exterior parts must be identical on-site. Color difference in automotive body paint is a very complex and difficult-to-control problem encountered at every painting site. Compared to applications of paint in other fields, the requirements for color difference control in automotive paint are much stricter.

[0004] With the increasing popularity of high-chroma pigments and effect pigments, the color stability of automotive coatings has become a greater challenge. Since automotive coatings require baking at temperatures above 140°C to cure, the added pigments not only need strong weather resistance but also excellent high-temperature baking stability. After painting and assembly, cars are parked in outdoor parking lots for a certain period before being shipped for sale. If the pigments have poor stability, they are prone to noticeable discoloration under sunlight in a short period, causing a serious color difference between the car body and exterior parts, making delivery impossible.

[0005] In addition, since the car body is generally composed of a composite coating consisting of an intermediate coat, a color coat, and a clear coat, apart from the electrophoretic primer, the clear coat may also be affected by grease, smoke, and volatile substances produced by auxiliary materials in the environment. These substances may react with nitrogen oxides and sulfur oxides to produce colored metallic complexes, which decompose rapidly under sunlight, causing the car body color to change significantly in a short period of time (with white being the most obvious), making it unable to match the exterior parts.

[0006] Currently, there is no method to test the color difference stability of automotive coatings in the short term. The industry primarily assesses coating stability by testing its anti-aging properties through accelerated aging or long-term natural exposure. However, these methods typically involve testing periods exceeding 2000 hours, and natural aging tests generally last 1-2 years, making it impossible to accurately detect the true extent of color difference changes in automotive coatings in the short term.

[0007] In view of this, it is necessary to develop a test method for the color stability of automotive coatings to detect color changes of body paint in a short period of time and prevent significant color differences between the paint on the body and exterior parts on site. Summary of the Invention

[0008] Based on the above facts, the purpose of this invention is to provide a method for testing the short-term stability of automotive coating colors and its application. This method allows for direct and accurate detection of short-term color changes in vehicle body coatings, preventing significant color differences between the coatings on the vehicle body and exterior trim, which could affect normal product delivery.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for testing the short-term stability of automotive coating color includes the following steps:

[0011] A substrate containing the composite coating to be tested is provided, denoted as substrate 1; wherein the composite coating to be tested comprises, in sequence, an electrophoretic paint, a mid-coat, a color paint, and a clear coat bonded to the substrate;

[0012] The substrate 1 was irradiated with a metal halide lamp. The absolute values ​​of the color difference of the composite coating before and after irradiation were tested and recorded. The relative values ​​of the color difference before and after irradiation were calculated and recorded as △L1, △a1 and △b1, respectively.

[0013] If △L1, △a1, and △b1 are all within the required range, it indicates that the stability of the car coating color in the short term is qualified.

[0014] If at least one of △L1, △a1, and △b1 is outside the required range, it indicates that the stability of the car coating color is unqualified in the short term.

[0015] Furthermore, if at least one of △L1, △a1, and △b1 is not within the required range, the test method further includes a step of determining the factors affecting the stability of the coating color in the short term, which specifically includes:

[0016] A substrate containing a coating formed by the paint as described above is provided, denoted as substrate 2, and a substrate containing a coating formed by the varnish as described above is provided, denoted as substrate 3;

[0017] Substrate 2 and substrate 3 were irradiated with metal halide lamps, and the absolute values ​​of the color difference of the coatings on substrate 2 and substrate 3 before and after irradiation were measured and recorded. The relative values ​​of the color difference before and after irradiation were calculated and denoted as ΔL. 色 , △a 色 and △b 色 , △L 清 , △a 清 and △b 清 ;

[0018] If △L 色 , △a 色 , △b 色 , △L 清 , △a 清 and △b 清 If at least one of them is not within the required range, then the following judgment is made:

[0019] If only △L 色 , △a 色 and △b 色 If at least one of the components is not within the required range, it indicates that the paint in the automotive coating is a factor affecting the color stability of the coating in the short term.

[0020] If only △L 清 , △a 清 and △b 清 If at least one of the components is not within the required range, it indicates that the clear coat in the automotive coating is a factor affecting the color stability of the coating in the short term.

[0021] If △L 色 , △a 色 and △b 色 At least one of them and △L 清 , △a 清 and △b 清 If at least one of the components is not within the required range, it indicates that both the color paint and the clear coat in the automotive coating are factors affecting the color stability of the coating in the short term.

[0022] Furthermore, in the test method, if L 清 , △a 清 and △b 清 and △L 色 , △a 色 and △b 色 If all requirements are met, the test method further includes the following steps:

[0023] A substrate containing the intermediate coat and the color paint in sequence is provided, denoted as substrate 4; a substrate containing the intermediate coat and the clear coat in sequence is provided, denoted as substrate 5; and a substrate containing the color paint and the clear coat is provided, denoted as substrate 6.

[0024] Substrates 4, 5, and 6 were irradiated with metal halide lamps, and the absolute values ​​of the color difference of the coatings on substrates 4, 5, and 6 before and after irradiation were measured and recorded. The relative values ​​of the color difference before and after irradiation were calculated and denoted as ΔL. 中色 , △a 中色 and △b 中色 , △L 中清 , △a 中清 and △b 中清 , △L 色清 , △a 色清 and △b 色清 ;

[0025] Factors affecting the color stability of the coating film can be determined based on the relative value of the color difference.

[0026] Furthermore, the factors affecting the color stability of the coating film determined based on the relative value of color difference include:

[0027] If △L 中色 , △a 中色 and △b 中色 If at least one of the components is not within the required range, it indicates that the paint is a factor affecting the color stability of the automotive coating.

[0028] If only △L 中清 , △a 中清 , △b 中清 , △L 色清 , △a 色清 , △b 色清 If at least one of the components is not within the required range, it indicates that the clear coat is a factor affecting the color stability of the automotive coating.

[0029] Furthermore, the required range refers to the relative value of the 45° role difference, all of which satisfy:

[0030] If the paint in the composite coating to be tested is not white, then the following conditions must be met:

[0031] |△L|≤0.5, |△a|≤0.5 and |△b|≤0.5; or

[0032] If the paint in the composite coating to be tested is white, then the following conditions must be met:

[0033] |△L|≤0.3, |△a|≤0.3 and |△b|≤0.3.

[0034] Furthermore, the irradiation time of the metal halide lamp is 5-7 days.

[0035] Furthermore, the substrate is a steel plate or an aluminum plate.

[0036] Furthermore, the coating process of the composite coating is one of 3C2B, 3C1B, IPP or CCT.

[0037] On another front, the present invention provides the application of the test method described above in detecting the short-term stability of automotive coatings.

[0038] Furthermore, the automotive coating is applied using 3C2B, 3C1B, IPP, or CCT coating processes.

[0039] The beneficial effects of this invention are as follows:

[0040] The testing method provided by this invention can directly, accurately, and quickly detect the color stability of automotive coatings by detecting color difference changes in composite coatings, thus preventing color mismatch issues from occurring on the entire vehicle. The testing method uses a metal halide lamp to irradiate the paint film; the spectrum of the metal halide lamp is close to that of natural light, making the conditions more stable and the test results more accurate. This testing method is applicable to coating systems with different coating processes such as 3C2B, 3C1B, IPP, or CCT. The testing conditions are simple and readily available, and more closely resemble actual usage scenarios. It can quickly and effectively confirm the short-term color stability of automotive coatings, allowing for targeted improvements and responses, and avoiding serious color differences on-site. Detailed Implementation

[0041] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0042] After a car is painted and assembled, it is parked in an outdoor parking lot before being sold. During this period, the coating on the car body may undergo significant color changes under sunlight due to factors such as poor pigment stability, resulting in a serious color difference between the car body and exterior parts, making the car unusable for delivery. Currently, there is no method for testing the short-term color difference stability of automotive coatings. One specific embodiment of this invention provides a method for testing the short-term stability of automotive coating color, which includes the following steps:

[0043] 1) Provide a substrate containing the composite coating to be tested, denoted as substrate 1; wherein the composite coating to be tested comprises, in sequence, an electrophoretic paint, a mid-coat, a color paint and a clear coat bonded to the substrate.

[0044] In this step, the substrate can be a steel plate or an aluminum plate that is compatible with the composite coating to be tested.

[0045] In this step, to better reflect the actual situation, the selection, application method, and dosage ratio of the electrophoretic paint, intermediate coat, color paint, and clear coat in the composite coating to be tested are all the same as the actual automotive coating conditions. In the preparation of each coating in the other steps described below, the selection, application method, and dosage ratio of the coatings are also the same as the actual automotive coating conditions, and will not be repeated here.

[0046] For example, the coating method for forming a composite coating on the substrate can be one of 3C2B, 3C1B, IPP, or CCT. That is, this test method is suitable for testing the color stability of automotive paint films obtained by coating automobiles using one of the coating methods of 3C2B, 3C1B, IPP, or CCT.

[0047] Furthermore, in this embodiment, "stable performance in the short term" includes the period from when the vehicle is painted and assembled, and then parked (e.g., in an outdoor parking lot) until it is delivered from the factory. An exemplary duration could include 3-7 days, etc.

[0048] 2) Irradiate substrate 1 with a metal halide lamp, test and record the absolute value of the color difference of the composite coating before and after irradiation, calculate the relative value of the color difference before and after irradiation, and record them as △L1, △a1 and △b1 respectively.

[0049] If △L1, △a1, and △b1 are all within the required range, it indicates that the stability of the car coating color in the short term is qualified.

[0050] If at least one of △L1, △a1, and △b1 is outside the required range, it indicates that the stability of the car coating color is unqualified in the short term.

[0051] Irradiating the paint film with a metal halide lamp provides more stable conditions and more accurate test results, as the spectrum of the metal halide lamp is close to that of natural light. The preferred irradiation time is 5-7 days, more preferably 7 days. This more accurately simulates the effect of sunlight exposure (especially unobstructed outdoor exposure) on the coating color when a car is parked in an outdoor parking lot. More preferably, the irradiation time is 7 days.

[0052] In this embodiment, a multi-angle colorimeter can be used to measure the absolute value of the 45° color difference before and after irradiation at the same position of the coating under test. The parameters tested include L value, a value, and b value. The difference in the absolute value of the color difference before and after irradiation is the color difference change. For example, △L is the difference between the L value of the coating after irradiation and the L value of the coating before exposure; △a is the difference between the a value of the coating after irradiation and the a value of the coating before irradiation; and △b is the difference between the b value of the coating after irradiation and the b value of the coating before irradiation.

[0053] In this embodiment, the scope of compliance refers to:

[0054] If the paint in the composite coating to be tested is not white, then the following conditions must be met:

[0055] |△L|≤0.5, |△a|≤0.5 and |△b|≤0.5; or

[0056] If the paint in the composite coating to be tested is white, then the following conditions must be met:

[0057] |△L|≤0.3, |△a|≤0.3 and |△b|≤0.3.

[0058] In this step, if the paint in the composite coating being tested is not white, then △L1, △a1, and △b1 within the required ranges are |△L1|≤0.5, |△a1|≤0.5, and |△b1|≤0.5, respectively; if the paint in the composite coating being tested is white, then |△L1|≤0.3, |△a1|≤0.3, and |△b1|≤0.3. Subsequent steps are similar and will not be elaborated here.

[0059] By setting the difference value to meet the required range as described above, the test results become more accurate.

[0060] In some examples, if at least one of △L1, △a1, and △b1 is not within the required range, the test method further includes a step of determining factors affecting the short-term stability of the coating color, which specifically includes:

[0061] 3) Provide a substrate containing a coating formed by the paint as described above, denoted as substrate 2, and a substrate containing a coating formed by the varnish as described above, denoted as substrate 3;

[0062] Substrate 2 and substrate 3 were irradiated with metal halide lamps, and the absolute values ​​of the color difference of the coatings on substrate 2 and substrate 3 before and after irradiation were measured and recorded. The relative values ​​of the color difference before and after irradiation were calculated and denoted as ΔL. 色 , △a 色 and △b 色， △L 清 , △a 清 and △b 清 ;

[0063] If △L 色 , △a 色 , △b 色 , △L 清 , △a 清 and △b 清 If at least one of them is not within the required range, then the following judgment is made:

[0064] If only △L 色 , △a 色 and △b 色If at least one of the components is not within the required range, it indicates that the paint in the automotive coating is a factor affecting the color stability of the coating in the short term.

[0065] If only △L 清 , △a 清 and △b 清 If at least one of the components is not within the required range, it indicates that the clear coat in the automotive coating is a factor affecting the color stability of the coating in the short term.

[0066] If △L 色 , △a 色 and △b 色 At least one of them and △L 清 , △a 清 and △b 清 If at least one of the components is not within the required range, it indicates that both the color paint and the clear coat in the automotive coating are factors affecting the color stability of the coating in the short term.

[0067] This study found that, under normal circumstances, electrophoretic paint and intermediate coat are not directly exposed to sunlight and do not affect the short-term color change of automotive body coatings. Therefore, the factors causing poor color stability of automotive body coatings are mainly related to the color paint and clear coat layers. Specifically: color paint usually contains a variety of different color pigments, and the stability of different color pigments varies, thus affecting short-term color changes; clear coat, being the outermost layer of the paint film, comes into contact with volatiles from the baking of the underlying coating and volatile substances in the environment. Under the influence of sunlight, these volatiles may change, causing significant short-term color changes in the paint film. Therefore, clear coat also affects short-term color stability.

[0068] Based on this, by further testing the relative color difference between the paint and clear coats formed separately in the composite coating under test before and after light exposure, we can more accurately determine the factors affecting the stability of the automotive coating color in the short term.

[0069] In some examples, in the test method, if L 清 , △a 清 and △b 清 and △L 色 , △a 色 and △b 色 If all requirements are met, the test method further includes the following steps:

[0070] 4) A substrate containing the intermediate coat and the color paint in sequence is provided, referred to as substrate 4; a substrate containing the intermediate coat and the clear coat in sequence is provided, referred to as substrate 5; and a substrate containing the color paint and the clear coat in sequence is provided, referred to as substrate 6.

[0071] Substrates 4, 5, and 6 were irradiated with metal halide lamps, and the absolute values ​​of the color difference of the coatings on substrates 4, 5, and 6 before and after irradiation were measured and recorded. The relative values ​​of the color difference before and after irradiation were calculated and denoted as ΔL. 中色 , △a 中色 and △b 中色 , △L 中清 , △a 中清 and △b 中清 , △L 色清 , △a 色清 and △b 色清 ;

[0072] Factors affecting the color stability of the coating film can be determined based on the relative value of the color difference.

[0073] Specifically, the factors affecting the color stability of the coating film determined based on the relative value of color difference include:

[0074] If △L 中色 , △a 中色 and △b 中色 If at least one of the components is not within the required range, it indicates that the paint is a factor affecting the color stability of the automotive coating.

[0075] If only △L 中清 , △a 中清 , △b 中清 , △L 色清 , △a 色清 , △b 色清 If at least one of the components is not within the required range, it indicates that the clear coat is a factor affecting the color stability of the automotive coating.

[0076] It is understandable that in this scheme, if △L 中色 , △a 中色 and △b 中色 At least one of them, and △L 中清 , △a 中清 , △b 中清 If at least one of the components is outside the required range, it indicates that both the color paint and the clear coat are factors affecting the color stability of the automotive coating.

[0077] Normally, if the color paint is substandard and affects the paint film color under light, a single layer of color paint can produce a noticeable color difference. Clear coat, being a transparent coating, generally does not show significant color changes when applied as a single layer. If neither a single layer of color paint nor a single layer of clear coat shows a significant color change, further verification of the color changes after applying the intermediate coat + clear coat and the color paint + clear coat composite is necessary. If a significant color difference exists, it indicates poor compatibility with the clear coat, confirming its influence. This step accurately and quickly eliminates the possibility that the color paint and / or clear coat are the factors affecting the paint film and causing poor color stability of the vehicle body coating.

[0078] Compared to step 3), which provides a substrate containing only paint and varnish to assess color difference before and after irradiation, the elimination method in step 4) is more accurate and further confirms the accuracy of the judgment in step 3). Additionally, this step can further verify whether the interactions between the coatings affect the short-term stability of the automotive coating color.

[0079] Furthermore, it should be noted that step 4) above can also be performed without any restrictions. That is, regardless of whether "L" is satisfied... 清 , △a 清 and △b 清 and △L 色 , △a 色 and △b 色 If all conditions are within the required range, proceed to step 4) to further verify whether the interaction between the coatings affects the short-term stability of the automotive coating color.

[0080] In some examples, the method further includes the step of adjusting the formulation of the composite coating to be tested after determining the factors affecting the stability of the coating color in the short term.

[0081] Specifically: If the clear coat is a factor affecting the stability of the coating color in the short term, determine which of the following values ​​(ΔL, Δa, and Δb) is outside the required range for the clear coat, and then adjust the original absolute value of the color difference of the parameter outside the required range. For example, if the test shows that ΔL = 0.5 for the clear coat, then lower the original L value of the composite coating by 0.5 units to ensure color matching between the vehicle body and exterior trim.

[0082] If the paint color is a factor affecting the stability of the coating color in the short term, determine which of the following values ​​(ΔL, Δa, and Δb) is outside the required range for the paint color, and then adjust the original absolute value of the color difference for that parameter. For example, if the test shows that Δb = -0.5 for the paint color, then increase the original b value of the composite coating by 0.5 units to ensure color matching between the vehicle body and exterior trim.

[0083] To address the need for color matching across different parts of a vehicle, the detection method provided in this invention directly and accurately detects the color stability of the automotive paint to be used by detecting color difference changes in composite coatings. Further testing of the color difference stability of each individual coating layer and the interactions between coatings accurately identifies the coating causing discoloration, enabling rapid and effective improvements and responses to prevent severe color differences between the paint used on-site and different parts of the vehicle body.

[0084] According to another specific embodiment of the present invention, the test method described above is provided for the application of detecting the short-term stability of automotive coatings.

[0085] In some examples, the automotive coating is applied using 3C2B, 3C1B, IPP, or CCT coating processes.

[0086] The technical solution of the present invention will be described below with reference to some specific embodiments:

[0087] Materials and equipment involved in the following embodiments:

[0088] 1. Matching steel or aluminum plates;

[0089] 2. Matching electrophoretic paint, intermediate coat, color paint and clear coat;

[0090] 3. Spray gun;

[0091] 4. Drying oven;

[0092] 5. Multi-angle colorimeter.

[0093] Example 1

[0094] The color stability of the AR-2300 white base coat (BACH) composite coating, consisting of the water-based paint AR-2300 white intermediate coat (BACH) and the matching AR-200 white intermediate coat (BACH) and MAC O-1700 clear coat (BACH), was determined by testing.

[0095] Customer feedback indicated that after one week of outdoor use, a significant color difference was observed between the car body and the bumper. Continuous testing showed that the b-value at a 45° angle decreased by approximately 0.6 before stabilizing. The laboratory verified this feedback using the method described in this invention.

[0096] The method for testing the short-term stability of automotive coating color specifically includes the following steps:

[0097] a) Under standard conditions, the matching AR-200 white intermediate coat (BACH), AR-2300 color white coat (BACH) and MAC O-1700 clear coat (BACH) were sequentially sprayed onto the matching electrophoresis plate and dried to obtain the composite coating plate to be tested.

[0098] b) Take a piece of the composite coating plate to be tested, record the initial absolute value of the color difference, and irradiate it with a metal halide lamp for 7 days;

[0099] c) Record the absolute value of the color difference after 7 days of irradiation of the composite coating, and calculate whether the color difference change before and after meets the standard (white requires |△L|, |△a|, |△b| ≤ 0.3). The results are shown in Table 1. Table 1 shows that after 7 days of irradiation, the AR-2300 set of white (BACH) composite coating meets the standard for △L and △a, but the △b value exceeds the standard range, consistent with customer feedback. This indicates a mismatch with the color difference of the exterior parts, and the short-term color stability of the composite coating is unacceptable. Therefore, the following steps are continued to test the coating that caused the discoloration:

[0100] d) The aforementioned paint and varnish were individually sprayed onto the tinplate and dried. The color difference of each single-layer paint and varnish layer was then verified under a metal halide lamp for 7 days to meet the standard requirements. The results are shown in Table 1. Table 1 shows that there was no significant change in color difference between the single-layer paint and varnish. At this point, the following steps were continued to test the coating that caused the discoloration:

[0101] e) Spray intermediate coat + color paint, intermediate coat + clear coat, and color paint + clear coat onto the electrophoresis plates and dry them. Verify whether the color difference change of the coatings meets the standard requirements after 7 days of irradiation with a metal halide lamp. The results are shown in Table 1. As can be seen from Table 1, the color difference of intermediate coat + color paint meets the standard, while the color difference Δb of intermediate coat + clear coat and color paint + clear coat both exceed the standard range.

[0102] f) Through the verification of steps d) and e), it was confirmed that the MAC O-1700 varnish (BACH) caused the composite coating Δb value to exceed the standard range.

[0103] Since the clear coat cannot be changed, in order to ensure the color matching between the body and the exterior parts, the b-value of the AR-2300 BACH composite coating was increased by 0.6 from the original standard value at the factory. After the b-value decreased and stabilized on site, it approached the standard value. On-site feedback indicated that color difference control was carried out according to this solution. After the color stabilized, the color matching between the body and the exterior parts met the factory requirements.

[0104] Table 1

[0105]

[0106] Example 2

[0107] The color stability of the AR-2000 Everest White composite coating was determined by testing the water-based paint AR-2000 Everest White drying topcoat and its matching AQU-6008 water-based white intermediate coat and Kansai clear varnish.

[0108] The method for testing the short-term stability of automotive coating color specifically includes the following steps:

[0109] a) Under standard conditions, AQU-6008 water-based white intermediate coat, AR-2000 Everest white baking topcoat and Kansai varnish were sequentially sprayed onto the matching electrophoresis plate and dried to obtain the composite coating plate to be tested.

[0110] b) Take a piece of the composite coating plate to be tested, record the initial absolute value of the color difference, and irradiate it with a metal halide lamp for 7 days;

[0111] c) Record the absolute value of the color difference of the composite coating after 7 days of exposure, and calculate whether the color difference change before and after meets the standard (white requires |△L|, |△a|, |△b| ≤ 0.3). The results are shown in Table 2. Table 2 shows that after 7 days of natural exposure, the AR-2000 Everest White baked topcoat composite coating has △L and △a within the standard range, but △b exceeds the standard range, posing a risk of color mismatch with the exterior parts. The short-term color stability of the composite coating is unqualified. Therefore, the following steps are continued to test the coating that caused the discoloration:

[0112] d) Spray the colored paint and clear varnish separately on the electrophoresis plate and dry them. Verify whether the color difference change of the single coating layer meets the standard requirements after 7 days of irradiation with a metal halide lamp. The results are shown in Table 2. It can be seen that the color difference of the single layer of colored paint △b exceeds the standard range, while the color difference of the single layer of clear varnish meets the standard range. It is confirmed that the colored paint causes the composite coating △a to exceed the standard range.

[0113] Table 2

[0114]

[0115] The formulation of the water-based paint AR-2000 Everest White baking topcoat was improved by replacing and adjusting the colorant. The improved composite coating was tested using the methods described above, and the results are shown in Table 2. It can be seen that the color difference variation of the composite coating meets the standard range. Field use feedback indicates good color matching between the vehicle body and exterior trim.

[0116] Example 3

[0117] The color stability of the composite coating consisting of water-based paint Base Coat IPP G2 Maple Orange, its matching intermediate coat IPP G2 Light Grey, and Clearcoat PU 2K HD was tested to determine its color stability. The method for testing the short-term stability of the automotive coating color specifically includes the following steps:

[0118] a) Under standard conditions, the matching IPP G2 LIGHT GREY, BASECOAT IPP G2 Maple Orange and CLEARCOAT PU 2K HD varnishes were sequentially sprayed onto the matching electrophoresis plate and dried to obtain the composite coating plate to be tested.

[0119] b) Take a composite coating plate to be tested, record the initial absolute value of color difference, and irradiate it with a metal halide lamp for 7 days;

[0120] c) Record the absolute value of the color difference after 7 days of irradiation of the composite coating, and calculate whether the color difference change before and after meets the standard requirements (|△L|, |△a|, |△b| are all ≤0.5). The results are shown in Table 3. As can be seen from Table 3, after 7 days of irradiation, the △L, △a, and △b of the BASE COAT IPP G2 Maple Orange composite coating all exceed the standard range, and △b is seriously out of standard. There is a serious risk of color mismatch with the exterior parts, and the color stability of the composite coating is unqualified in the short term. At this time, continue to test the coating that caused the discoloration in the following steps:

[0121] d) The aforementioned colored paint and varnish were sprayed separately onto the tinplate and dried. The color difference change of each single coating was verified after 7 days of irradiation with a metal halide lamp to see if it met the standard requirements. The results are shown in Table 3. As can be seen from Table 3, the color difference of the single-layer colored paint (ΔL, Δa, Δb) exceeded the standard range, while the color difference of the single-layer varnish met the standard range. It was confirmed that the colored paint caused the composite coating's ΔL, Δa, and Δb to exceed the standard range.

[0122] Table 3

[0123]

[0124] Due to the color characteristics of the water-permeable paint BASE COAT IPP G2 Maple Orange, the pigment in the formula cannot be replaced or adjusted, and the formula cannot be improved. Therefore, it is determined that the formula cannot meet the conditions for mass production, and this color will not be mass-produced.

[0125] Example 4

[0126] The color stability of the composite coating consisting of water-based paint (AR2300 Ice Crystal Blue) (BAIC) and its matching water-based intermediate coat paint - light gray (AR 200) (BAIC) and MAC O-1700 clear coat (BAIC) was tested to determine the color stability of the water-based paint (AR2300 Ice Crystal Blue) (BAIC) composite coating.

[0127] The method for testing the short-term stability of automotive coating color specifically includes the following steps:

[0128] a) Under standard conditions, spray the matching water-based intermediate coating paint - light gray (AR 200) (BAIC), water-based color paint (AR2300 ice crystal blue) (BAIC) and MAC O-1700 varnish (BAIC) sequentially onto the matching electrophoresis plate and dry them to obtain the composite coating to be tested.

[0129] b) Take a composite coated plate, record the initial chromaticity value, and irradiate it with a metal halide lamp for 7 days;

[0130] c) Record the absolute values ​​of the color difference of the composite coating after 7 days of exposure, and calculate whether the color difference changes before and after exposure meet the standard requirements (|△L|, |△a|, |△b| are all ≤0.5). The results are shown in Table 4. It can be seen that after 7 days of natural exposure, the L, a, and b values ​​of the water-based paint (AR2300 Ice Crystal Blue) (BAIC) composite coating did not change significantly, and the color stability was good.

[0131] Feedback from on-site use indicated that the colors of the vehicle body and exterior trim matched well.

[0132] Table 4

[0133]

[0134] Example 5

[0135] The color stability of the composite coating consisting of solvent-based color paint SP M-95 cool white baking topcoat (BAIC) and its matching Jinlitai white intermediate coat and O-440CLEAR clear coat was determined by testing.

[0136] The method for testing the short-term stability of automotive coating color specifically includes the following steps:

[0137] a) Under standard conditions, the matching Jinlitai white intermediate coating, SP M-95 cold white baking topcoat (BAIC) and O-440 CLEAR clear varnish were sequentially sprayed onto the matching electrophoresis plate and dried to obtain the composite coating to be tested;

[0138] b) Take a composite coated plate, record the initial chromaticity value, and irradiate it with a metal halide lamp for 7 days;

[0139] c) Record the absolute values ​​of color difference of the composite coating after 7 days of exposure, and calculate whether the color difference changes before and after the exposure meet the standard requirements (|△L|, |△a|, |△b| are all ≤0.3). The results are shown in Table 5. It can be seen that after 7 days of natural exposure, the L, a, and b values ​​of the SP M-95 cool white baking topcoat (BAIC) composite coating did not change significantly, and the color stability was good.

[0140] Feedback from on-site use indicated that the colors of the vehicle body and exterior trim matched well.

[0141] Table 5

[0142]

[0143] Verification Example 1

[0144] The color stability of the AR-2300 white base coat (BACH) composite coating, consisting of the water-based paint AR-2300 white intermediate coat (BACH) and the matching AR-200 white intermediate coat (BACH) and MAC O-1700 clear coat (BACH), was determined by testing.

[0145] The method for testing the short-term stability of automotive coating color specifically includes the following steps:

[0146] a) Under standard conditions, spray the matching water-based AR-200 white intermediate coat (BACH), water-based color paint AR-2300 white base coat (BACH), and MAC O-1700 clear varnish (BACH) sequentially onto the matching electrophoresis plate and dry them to obtain the composite coating plate to be tested.

[0147] b) Take a composite coated board, record the initial color value, and place it outdoors to be exposed to natural sunlight;

[0148] c) Record the color difference data of the composite coating after natural exposure for different days to verify the effect of exposure time on the stability of color difference changes. The results are shown in Table 6. It can be seen that after 7 days of natural exposure, the L value, a value and b value of the water-based paint AR-2300 white (BACH) no longer changed significantly, and the color tended to stabilize in the short term, indicating that the verification conditions and verification methods provided in this invention are reasonable and effective.

[0149] Table 6

[0150]

[0151] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method of testing the stability of the color of an automobile coating film over a short period, characterized by, The test method comprises the following steps: providing a substrate containing a composite coating to be tested, denoted as substrate 1; wherein the composite coating to be tested comprises, in sequence, an electrophoretic paint, a base coat, a color paint and a clear paint combined with the substrate; irradiating the substrate 1 with a metal halide lamp, testing and recording the absolute values of color difference of the composite coating to be tested before and after irradiation, and calculating the relative values of color difference before and after irradiation, denoted as △L1, △a1 and △b1, respectively; if all of △L1, △a1 and △b1 are within the required range, it indicates that the short-term stability of the automobile coating film color is qualified; if at least one of △L1, △a1 and △b1 is not within the required range, it indicates that the short-term stability of the automobile coating film color is unqualified.

2. The test method of claim 1, wherein, if at least one of △L1, △a1 and △b1 is not within the required range, the test method further comprises a step of further judging the factors affecting the short-term stability of the coating film color, which specifically comprises: respectively providing a substrate containing a coating formed by the color paint as described above, denoted as substrate 2, and a substrate containing a coating formed by the clear paint as described above, denoted as substrate 3; The metal halogen lamp is used to irradiate the substrate 2 and the substrate 3 respectively, the absolute values of the color difference of the coating on the substrate 2 and the substrate 3 before and after irradiation are respectively tested and recorded, the relative values of the color difference before and after irradiation are calculated, and are respectively recorded as ΔL 色 , Δa 色 and Δb 色， ΔL 清 , Δa 清 and Δb 清 ; If at least one of △L 色 , △a 色 , △b 色 , △L 清 , △a 清 and △b 清 is not within the required range, the following determination is made: If at least one of △L 色 , △a 色 and △b 色 is not within the required range, it is indicated that the color paint in the automobile coating film is a factor affecting the color stability of the coating film in the short term; If at least one of △L 清 , △a 清 , and △b 清 is not within the required range, it is indicated that the clear paint in the automobile coating film is a factor affecting the color stability of the coating film in the short term; If △L 色 , △a 色 and △b 色 At least one of them and △L 清 , △a 清 and △b 清 If at least one of the components is not within the required range, it indicates that both the color paint and the clear coat in the automotive coating are factors affecting the color stability of the coating in the short term.

3. The test method of claim 2, wherein, In the aforementioned test method, if L 清 , △a 清 and △b 清 and △L 色 , △a 色 and △b 色 If all requirements are met, the test method further includes the following steps: providing a substrate containing a coating formed by the base coat and the color paint in sequence, denoted as substrate 4, a substrate containing a coating formed by the base coat and the clear paint in sequence, denoted as substrate 5, and a substrate containing a coating formed by the color paint and the clear paint in sequence, denoted as substrate 6; The metal halogen lamp is used to irradiate the substrate 4, the substrate 5 and the substrate 6 respectively, the absolute values of the color difference of the coating on the substrate 4, the substrate 5 and the substrate 6 before and after irradiation are tested and recorded respectively, the relative values of the color difference before and after irradiation are calculated, and are recorded as ΔL 中色 , Δa 中色 and Δb 中色 respectively, ΔL 中清 , Δa 中清 and Δb 中清 respectively, ΔL 色清 , Δa 色清 and Δb 色清 respectively. judging the factors affecting the stability of the coating film color according to the relative values of color difference.

4. The test method of claim 3, wherein, the judging the factors affecting the stability of the coating film color according to the relative values of color difference comprises: If at least one of ΔL 中色 , Δa 中色 and Δb 中色 is not within the required range, it is indicated that the color paint is a factor affecting the color stability of the coating film of the automobile. If only △L 中清 , △a 中清 , △b 中清 , △L 色清 , △a 色清 , △b 色清 If at least one of the components is not within the required range, it indicates that the clear coat is a factor affecting the color stability of the automotive coating.

5. The test method according to any one of claims 1 to 4, characterized in that, the required range refers to the relative values of color difference at 45° of the coating, which all satisfy: if the color paint in the composite coating to be tested is not white paint, it satisfies: |△L|≤0.5, |△a|≤0.5 and |△b|≤0.5; or if the color paint in the composite coating to be tested is white paint, it satisfies: |△L|≤0.3, |△a|≤0.3 and |△b|≤0.

3.

6. The test method according to any one of claims 1 to 4, characterized in that, the irradiation time of the metal halide lamp is 5-7 days.

7. The test method according to any one of claims 1 to 4, characterized in that, the substrate is a steel plate or an aluminum plate.

8. The test method of claim 1, wherein, the coating process of the composite coating is one of 3C2B, 3C1B, IPP or CCT.

9. The use of the test method according to any one of claims 1-8 in detecting the short-term stability of an automobile coating film.

10. Use according to claim 9, characterized in that, the automobile coating film is coated by using the coating process of 3C2B, 3C1B, IPP or CCT.

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