Study on the test method of scratch resistance of high-gloss black paint in automotive interior

This article LiuZhou, Guo Wenbo, Hu Yujie, Fu Dan
Source: 2020 "Paint Industry" No. 11
In recent years, with the development of the visual effect trend of interior modeling, automotive interior parts such as the main and deputy dashboard, door guard panels have been widely used high-gloss black effect decoration. Spraying high-gloss black paint (also known as piano paint) is a common way for automotive interior parts to achieve high-gloss black effect, but parts coated with highlight black paint need to be improved when used in the cockpit of the car, according to experience can be divided into: (1) long-term wear resistance Risk, when the user operates and cleans in the car, the long-term frequent friction of the surface of the part, such as hand, fabric, etc. leads to the loss of scratches and gloss; Due to the black and shiny appearance properties of the highlighted black part, its surface defects are magnified, which is relatively easy for the user to detect changes in surface appearance quality

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For the interior highlight black coating, most of the domestic host plants follow the plastic parts of the scratch-resistant test method for control, specifically evaluation of high-gloss black coating scratch-resistant performance test methods are still relatively small. Therefore, the paper carried out a study on the test method of scratch resistance, hoping to obtain a method suitable for evaluating the scratch resistance of high-gloss black paint on the surface of interior parts.
1 Experimental Part
1.1 Sample Information
In this paper, 10 high-gloss black paint test models (as shown in Table 1) are selected, all of which are paint models prepared in the same process as parts of mass production models.
Table 1 Highlight Black Paint Test Model Information
1.2 Main Equipment Instruments
Portable Three-Angle Gloss Meter: BYK-4563, BYK, Germany; -rite Company; Repo Wearer: TABER5900, TABER Corporation of the United States; Electric cross-cutter: Type 430P, Erichen, Germany; TABER Grinding
Meter: AB-101, TESTERSANGYO, Japan.
1.3 test methods
all test methods are performed in accordance with the enterprise standards in Table 2.
Table 2 Domestic Automotive Factory Interior Parts Scratch Resistance Test Method
2 Results and Discussion
2.1 Domestic Automotive Factory Interiors Scratch Resistance Test Method Overview
Combined with other research results, this paper will be some domestic automotive factory interior parts scratch resistance test method can be divided into 3 categories, as shown in Table 2.
Combined with Table 2, Class 1, this article is called "pressing method", with the invasion of sharp objects to test surface hardness, to plastic parts commonly used in the Roche hardness test as a representative; The degree pen experiment, the five-finger scratch test, the cross-section test method is representative of the third category, this paper is called "wear method", using a specific friction medium (such as friction cloth, sandpaper, grinding wheel, etc.) to do a certain trajectory (such as straight lines, circles, specific curves) of the long cycle of recirivation relative movement, evaluation surface wear, evaluation indicators including color difference, gray scale changes, quality loss, gloss changes.
2.2 "Press-in" study
Loch hardness test is a method to determine hardness value by indentation plastic deformation depth, is the most commonly used hardness evaluation index of metal materials and hard plastics, is a quantitative evaluation. The 10 high-gloss black paint models were tested for Roche hardness according to GB/T3398.2-2008, with the results shown in Figure 1.
Figure 1 The coating surface of the high-gloss black coating model and the Roche hardness of the substrate surface
as visible in Figure 1, the loch hardness of the coating surface is consistent with the trend of change in the hardness of the substrate surface, and the test value is very close, indicating that the roche hardness of the high-gloss black coating coating surface basically depends on the substrate, due to the thin coating (generally 25 to 30 m), the contribution of the coating to the Lowe's hardness cannot be reflected. That is, it is not suitable to evaluate the scratch resistance of high-gloss black coating by the evaluation method of Roche hardness.
2.3 "Scratch Method" Study
Pencil hardness test is a more common method for evaluating the scratch resistance of coating film, GB/T6739-2006 by pushing the pencil with known hardness on the sample to avoid scratches Pencil hardness value to sample scratch resistance graded, Peugeot Citroen Group standard D455523-2010 as the representative of the hardness pen test using the test head diameter of 0.75mm 318 hardness rod to 0 to 2 Selected pressure in the range of 0N to perform a scratch, with the critical pressure of visible scratches as the resistance index, to Ford motor standard FLTMBO162-01-2009 as the representative of the five-finger scraping test, using a diameter of 1mm test head in 2N , 3N, 7N, 10N, 15N vertical pressure and sample to do a single relative movement, through the sample scratches, color changes, gloss change level corresponding to the force value as scratch-resistant performance indicators; The cross-scratch test method represented by the 2002 and GM standard GM14688-2007 standards uses a 1mm diameter scraper head to form mesh scratches under a specific load, and evaluates scratch resistance by testing color difference changes before and after the mesh scratch area. Based on scratch method and evaluation method, the above 4 test methods can be classified into 2 categories, namely: (1) including pencil hardness, hardness pen and five-finger scraping test method, are single linear scratching, although the test results are quantitative, but the judgment of scratch subjectivity is strong; Based on the experimental resources, this paper selects the pencil hardness test and the cross-drawing test respectively to discuss the two types of test methods.
2.3.1 Pencil Hardness Test
The results of the Pencil Hardness Test on the coating surface of the high-gloss black paint model and the pencil hardness test on the substrate surface, as shown in Figure 2.
Figure 2 Pencil hardness of high-gloss black paint models
As can be seen from Figure 2, the test results of coatings and substrates are concentrated in F-H, but there are differences in the hardness of pencils for most models and substrates, i.e. pencil hardness can reflect differences in scratch resistance of different coatings.
2.3.2 Cross-cross-blocking test
According to the Volkswagen PV3952-2002 test standard, under 10N contact force, the sample surface with a robotic arm round chisel (1mm diameter) with a 2mm interval of the cross, Table 3 gives the test results of the test area of X-L.table
table 3 highlight black paint cross-section test results
visible from table 3, measured high-gloss black paint coating surface after cross-section, before and after the test chroma L change is very small (<1%), the reason analysis is that the high-gloss black surface itself blackness value L is small, the coating surface is mainly recessed, but there will be similar plastic whitening phenomenon, so L change is not obvious. It can be seen that for the high-gloss black coating, the use of cross-scratch test method to evaluate the color difference before and after the test can not better reflect the high-gloss black coating scratch resistance performance level and differences.
2.4 "Wear method" study
relative scratch method, wear method is more suitable for simulating and evaluating the long-term wear failure caused by frequent friction in use of parts, Table 2 various methods, friction media mainly friction cloth, VELCRO belt, sandpaper grinding wheel, etc., friction cloth as friction medium Martindale friction has been documented, this paper selects the Peugeot Citroen Group standard D245011-2009 VERCRO belt friction as the representative of the straight-line round-trip friction and Nissan standard NES-M0141-2012 TABER grinding wheel round-trip friction as the representative of the test study.
2.4.1VELCRO belt friction test
The VELCRO belt friction test uses a dragon buckle belt to perform multiple round-trip linear frictions on the coating under 9N load, and to determine the scratch resistance of the high-gloss coating by the residual gloss or gloss variation rate. Figure 3 shows the results of the VELCRO belt friction test for the high-gloss black coating.
Figure 3 VELCRO strip friction test process highlight black coating surface gloss
As can be seen from Figure 3, gloss in the VELCRO belt test of high-gloss black coating surface with the increase in the number of cycles overall presents a relatively regular downward trend, more suitable for evaluating long-term wear resistance.
2.4.2 TABER grinding wheel friction
Nissan standard NES-M0141-2012 through the Taber wear test before and after the luster residue to evaluate the surface scratch resistance performance, including grinding wheel model CS-10F, load 500g, cycle times 100 times, after the test high-gloss black paint sample 60 degrees gloss results as shown in Table 4.
Table 4 highlight black paint model Taber grinding wheel friction after 60 degrees gloss
visible by table 4, the number of cycles 100 times, the paint model gloss appeared cliff-like decline, paint model residual gloss is low. Figure 4 is a sample photo after the test, it can be seen that the method grinding wheel on the paint sample surface damage is very large, the coating has been completely destroyed. That is, the method is relatively strict, it is not recommended to use this method for high-gloss black paint surface long-cycle wear performance evaluation.
Figure 4 High-gloss black paint model Taber grinding wheel friction photo
3 conclusion
This paper summarizes the domestic main plant interior parts scratch resistance-resistant performance-related testing methods, and classifies it as "press-in method", "scratch method" and "wear method" 3 categories. Based on the test results of the high-gloss black paint model, it is recommended that the "scratch method" represented by the pencil hardness test method evaluate the short-term scratch resistance of the high-gloss black coating, and the "wear method" represented by the VELCRO band friction is recommended to evaluate the long-term wear resistance of the high-gloss black coating.
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