A test method and evaluation system for the leveling and sagging properties of coatings.

Abstract

This invention relates to the field of coating performance testing technology, and more particularly to a testing method and evaluation system for the leveling and sagging properties of coatings. The coating is taken as a sample and tested in a rheometer: shear forces of a first low shear rate, a high shear rate, and a second low shear rate are sequentially applied to the coating, and the viscosity value of the coating over time is measured to obtain a shear rate-viscosity data curve; the recovery index RI is obtained from this curve; the viscosity value corresponding to 1 / n of the total time required from the start of the second low shear rate treatment to viscosity stabilization is obtained from the shear rate-viscosity data curve, and the viscosity value at the first low shear rate is calculated, and the ratio is used to obtain the stage recovery index RI. 1 / n The method of this invention can simultaneously measure the shear rate-viscosity data curves of multiple coatings, and can quickly and qualitatively evaluate the leveling and sagging properties of coatings at different thicknesses.

Description

Technical Field

[0001] This invention relates to the field of coating performance testing technology, and in particular to a testing method and evaluation system for coating leveling and sagging properties. Background Technology

[0002] Coatings are pseudoplastic fluids with strong rheological properties. The complex structures and varied shapes of the substrates they coat place extremely stringent demands on the coating's application performance. When a coating undergoes high-speed shearing, its viscosity rapidly decreases; however, adjusting to low-speed shearing quickly restores it to a high viscosity. This theoretically explains why, under high-speed atomization, the coating's viscosity decreases rapidly, achieving better atomization; and when the coating adheres to the substrate, it quickly returns to a high viscosity during the drying process. Key process parameters exhibited during application include spray atomization, anti-sagging properties, and leveling properties.

[0003] Leveling is primarily based on the streak model of paint brush marks. The leveling process is the gradual decrease in the amplitude of brush marks as the paint evaporates, dries, and cures. The driving force for this process is the surface tension of the paint. Generally, paints with low viscosity and large thickness have good leveling properties. Under the influence of gravity, paint "slips" off the substrate, which is commonly referred to as a "sliding" defect, or sagging. The driving force for sagging is the gravitational acceleration of the coating. Generally, paints with high viscosity and small thickness have good anti-sagging properties.

[0004] Considering both leveling and sagging phenomena, high-viscosity coatings are less prone to sagging but also less prone to leveling, while thicker coatings are easier to level but also more prone to sagging. Whether powder coatings, solvent-based coatings, or water-based coatings, their performance depends on the final coating effect. Good coating performance is characterized by excellent leveling and anti-sagging properties.

[0005] Existing methods for evaluating and testing the leveling and anti-sagging properties of coatings can only perform qualitative analysis, not quantitative analysis. These methods mainly rely on visual observation, are greatly affected by subjective factors, and are complex processes.

[0006] The most common method for evaluating and testing the leveling and sagging resistance of coatings is using a "leveling tester." This instrument provides a method for assessing the leveling performance of newly applied coatings before curing, thereby reducing or eliminating surface streaks caused by brushing or other coating processes. The leveling tester is a U-shaped applicator with a shallow gap on one side. Within this gap are five pairs of equally spaced narrow V-shaped grooves, with depths varying from 100, 200, 300, 500, to 1000 μm. The tester is 120 mm long at both ends, allowing for a 100 mm drag film to be applied in a single pass. The dragging is performed according to a standard procedure on a horizontally placed test plate or cardstock. It produces five pairs of ten streaks of varying depths. After the coating dries, the distance between each pair is observed, and the thickness of the pair with the smallest gap (i.e., when two streaks meet, a faint gap remains in the middle) is selected as the leveling performance data. The effect is as follows: Figure 2 As shown. The leveling performance is evaluated using this specially designed applicator, similar to the evaluation using the roller coating method, but with greater stability. Because various factors affect leveling and sagging, the tests for these properties should not be confused.

[0007] Besides using a leveling instrument, simulated application methods can also be used to test the leveling and anti-sagging properties of coatings. Coating application methods include: spraying (airless spraying, air spraying), roller coating, electrophoresis, trowel coating, brush coating, and curtain coating. A certain thickness of coating is applied according to the actual application method, and the surface condition of the coating is observed under specific conditions to evaluate the coating's leveling and anti-sagging effects.

[0008] As can be seen from the existing methods for evaluating coating leveling and sagging resistance described above, they have unavoidable drawbacks:

[0009] 1) The depth of the rheometer tank is only fixed and limited, which cannot test the leveling and anti-sagging properties at all thicknesses. If the thickness is not suitable, other specifications of rheometers can only be selected, but it is always limited.

[0010] 2) The leveling and anti-sagging properties of coatings are affected not only by the thickness but also by the environment, such as temperature, humidity, wind speed, and substrate.

[0011] 3) Each construction test requires more products, and the testing methods are cumbersome, inefficient, and prone to errors.

[0012] 4) Only one coating can be analyzed and compared at a time, and multiple products cannot be tested simultaneously, resulting in low efficiency; it is difficult to conduct parallel comparison tests, leading to large errors.

[0013] 5) Existing evaluation and testing methods for coating leveling and sagging resistance can only perform qualitative analysis and cannot or are very difficult to perform quantitative analysis. They mainly rely on visual observation and are greatly affected by subjective factors. Summary of the Invention

[0014] (a) Technical problems to be solved

[0015] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a test method that can simultaneously measure the shear rate-viscosity data curves of multiple coatings, and can quickly and qualitatively evaluate the leveling and sagging properties of coatings at different thicknesses.

[0016] Accordingly, the present invention also provides an evaluation system for the leveling and sagging properties of coatings, which can provide intuitive feedback on the evaluation results of coatings.

[0017] (II) Technical Solution

[0018] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0019] In a first aspect, the present invention provides a method for evaluating the leveling and sagging properties of a coating, which includes the following steps:

[0020] S1 takes the coating as a sample and tests it in a rheometer: shear forces of low shear rate, high shear rate and low shear rate are applied to the coating in sequence, and the viscosity value of the coating changes with time is measured to obtain the shear rate-viscosity data curve.

[0021] S2 obtains the stable viscosity value after the second low shear rate treatment and the viscosity value under the first low shear rate from the shear rate-viscosity data curve, and calculates the ratio to obtain the recovery index RI;

[0022] S3 obtains the viscosity value corresponding to 1 / n of the total time required from the start of the second low shear rate treatment to viscosity stabilization from the shear rate-viscosity data curve, and the viscosity value at the first low shear rate, and calculates the ratio to obtain the stage recovery index RI. 1 / n .

[0023] The setting of the first low shear rate, high shear rate, and second low shear rate shear force in this invention simulates the process of coating from storage to application and then to leveling.

[0024] R1 can be understood as the degree to which the viscosity can recover to its initial viscosity after stirring. Generally, the higher the RI, the greater the degree to which the viscosity can recover after the shear force is removed, and the better the anti-sagging property of the coating. If the leveling property of the coating is not considered, the higher the RI value, the better. An RI value below 0.6 can be considered as having no anti-sagging property.

[0025] The above RI 1 / n RI is a physical quantity that characterizes the rate of paint recovery; if RI 1 / n A higher RI value indicates that the viscosity of the coating recovers quickly after the shear force is removed, and vice versa. However, RI... 1 / nIf the RI value is too high, the paint will not have enough time to level, thus reducing its leveling properties. 1 / n If the viscosity of the paint is too low, the paint will recover too slowly and will sag.

[0026] The method of this invention can simultaneously measure multiple coatings on-site, and the curves provide a clear quantitative analysis, which in turn allows for a more accurate qualitative analysis and evaluation of the coatings' anti-sagging and leveling properties.

[0027] Optionally, the first low shear rate and the second low shear rate are 0.

[0028] Optionally, the stable viscosity value after the second low-shear rate treatment and the viscosity value at the high shear rate can be obtained from the shear rate-viscosity data curve, and the ratio can be calculated to obtain the thixotropic index TI. The above T1 thixotropic index value can be used to qualitatively identify the type of coating.

[0029] Optionally, RI and RI can be determined by varying the film thickness. 1 The optimal numerical range for / n; and the optimal numerical range for TI. Since different coating applications require different film thicknesses, the optimal numerical range for the coating can be determined by the film thickness.

[0030] Optionally, n is one of the integers between 2 and 6, preferably 2, 3, and 4, and more preferably 3.

[0031] Alternatively, when n is 3, in coatings with T1 > 200, the coating can be evaluated as having good anti-sagging and leveling properties if the following conditions are met:

[0032] When the film thickness is above 200 μm, RI 1 / 3 ≥0.85, and RI≥0.90; when the film thickness is 80~200μm, RI 1 / 3 The range is 0.70–0.85, while the range of RI is 0.60–0.90;

[0033] When the film thickness is 20–80 μm, RI1 / 3 ≤ 0.70. 0 < RI 1 / 3 <1; RI 1 / 3 <RI.

[0034] Secondly, the present invention also provides an evaluation system for the leveling and sagging properties of coatings, which includes a rheometer and a data analysis device.

[0035] The data analysis device is electrically connected to the data storage module and front-end display module of the rheometer;

[0036] The rheometer is used to measure the viscosity of the coating over time when shear forces of a first low shear rate, a high shear rate, and a second low shear rate are applied sequentially. The shear rate-viscosity data curve is obtained in the data storage module and fed back to the data analysis device.

[0037] The data analysis device obtains T1, R1, and RI from the shear rate-viscosity data curve. 1 / n The system checks whether the value meets the criteria for good anti-sagging and leveling performance, and then feeds the result back to the front-end display module.

[0038] The data analysis device of the evaluation system of the present invention stores T1, R1 and RI at different thicknesses. 1 / n The evaluation system defines the numerical range of good anti-sagging and leveling properties for n values ​​of 2, 3, 4, 5, and 6. The system can directly feed the data back to the front-end display module based on whether the values ​​meet the specified range.

[0039] (III) Beneficial Effects

[0040] The beneficial effects of this invention are: the method for testing the leveling and sagging properties of coatings in this invention, by directly obtaining the viscosity and shear rate curves through a rheometer, yields the recovery index RI and the stage recovery index RI. 1 / n The thixotropic index (TI) is used to comprehensively evaluate the leveling and anti-sagging properties of coatings. Compared with existing technologies, it can obtain the leveling and anti-sagging properties of coatings at different thicknesses and can simultaneously measure multiple coating samples. It has the characteristics of high speed and high accuracy. Attached Figure Description

[0041] Figure 1 The graphs show the shear rate versus time obtained from different samples in Example 1.

[0042] Figure 2 The image shows the effect of a leveling instrument on coatings in the background technology. Detailed Implementation

[0043] To better explain and facilitate understanding of the present invention, specific embodiments are described in detail below. To further understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below. While exemplary embodiments of the present invention are shown below, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a clearer and more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0044] This invention uses a rheometer to be more sensitive to temperature and viscosity, enabling more accurate testing of the viscosity values ​​of coatings at different shear rates, while requiring less sample.

[0045] Example 1

[0046] This embodiment provides a test method for the leveling and sagging properties of coatings, the steps of which are as follows:

[0047] S1 takes the coating as a sample and tests it in a rheometer: shear forces of low shear rate, high shear rate and low shear rate are applied to the coating in sequence, and the viscosity value of the coating changes with time is measured to obtain the shear rate-viscosity data curve.

[0048] S2 obtains the stable viscosity value after the second low shear rate treatment and the viscosity value under high shear rate from the shear rate-viscosity data curve, and calculates the ratio to obtain the thixotropic index TI;

[0049] S3 obtains the stable viscosity value after the second low shear rate treatment and the viscosity value under the first low shear rate from the shear rate-viscosity data curve, and calculates the ratio to obtain the recovery index RI;

[0050] S4 obtains the viscosity value corresponding to 1 / 3 of the total time required from the start of the second low shear rate treatment to viscosity stabilization from the shear rate-viscosity data curve, and the viscosity value at the first low shear rate, and calculates the ratio to obtain the stage recovery index RI. 1 / 3 .

[0051] Furthermore, it was determined that in coatings with T1 > 200,

[0052] When RI1 / 3 ≥ 0.85 and RI ≥ 0.90, it is applicable to film thicknesses of 200 μm and above; the coating can be characterized as pseudoplastic.

[0053] When the RI1 / 3 range is 0.70 to 0.85, and the RI range is 0.60 to 0.90, it is suitable for film thicknesses of 80 to 200 μm; the coating can be classified as a plastic-biased coating.

[0054] When RI1 / 3≤0.70, it is applicable to film thicknesses of 20~80μm, and the coating is classified as thixotropic.

[0055] When RI < 0.6, it is applicable to film thicknesses below 20 μm, and the coating can essentially have no anti-sagging properties.

[0056] The method of this embodiment was used to determine three different thickeners, named Sample 1, Sample 2, and Sample 3, respectively. The results were obtained using a rheometer. Figure 1 The shear rate-viscosity data curve shown is as follows:

[0057] In this embodiment, the setting of the first low shear rate, high shear rate, and second low shear rate shear forces simulates the process of coating from storage to application and leveling. Figure 1 T1, RI and RI obtained 1 / 3 The values ​​are shown in Table 1 below, where the thickness without sagging is obtained from experiments.

[0058] Table 1

[0059]

[0060]

[0061] From Table 1, we can obtain:

[0062] The three samples have similar initial low-shear viscosity, high-shear viscosity, and recovery viscosity values, therefore their total viscosity (TI) is similar. However, the no-flow film thickness varies significantly among the three samples, with different RI and RI values. 1 / 3 But they are quite different.

[0063] Although the RI and RI(1 / 3) of samples 1 and 2 differ by only 0.1 and 0.23 respectively, the values ​​of RI and RI(1 / 3) range from 0 to 1, so the difference between 0.1 and 0.23 is very large. Figure 1 The viscosity of sample 3 at the 1 / 3 time point has recovered to 88% of its initial value, while that of sample 1 at the 1 / 3 time point has only recovered to 57% of its initial viscosity. Therefore, RI and RI 1 / 3 The impact of sagging is absolute.

[0064] The method in this embodiment does not require spraying measurement; the sag and leveling properties can be intuitively evaluated from the graph.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for evaluating the leveling and sagging properties of a coating, characterized in that: It includes the following steps: S1 takes the coating as a sample and tests it in a rheometer: shear forces of low shear rate, high shear rate and low shear rate are applied to the coating in sequence, and the viscosity value of the coating changes with time is measured to obtain the shear rate-viscosity data curve. S2 obtains the stable viscosity value after the second low shear rate treatment and the viscosity value under the first low shear rate from the shear rate-viscosity data curve, and calculates the ratio to obtain the recovery index RI; S3 obtains the viscosity value corresponding to 1 / 3 of the total time required from the start of the second low shear rate treatment to viscosity stabilization from the shear rate-viscosity data curve, and the viscosity value at the first low shear rate, and calculates the ratio to obtain the stage recovery index RI. 1 / 3 ; The stable viscosity value after the second low shear rate treatment and the viscosity value under high shear rate are obtained from the shear rate-viscosity data curve, and the ratio is calculated to obtain the thixotropic index TI. In coatings with a TI > 200, the following conditions must be met for the coating to be considered to have good anti-sagging and leveling properties: When the film thickness is above 200 μm, RI 1 / 3 ≥0.85, and RI≥0.90; when the film thickness is 80~200μm, RI 1 / 3 The range is 0.70~0.85, and the range of RI is 0.60~0.90; When the film thickness is 20~80μm, RI 1 / 3 ≤0.70; The first low shear rate and the second low shear rate are both 0.

2. A system for evaluating the leveling and sagging properties of a coating, applied to the method for evaluating the leveling and sagging properties of the coating as described in claim 1, characterized in that: It includes a rheometer and a data analysis device; The data analysis device is electrically connected to the data storage module and front-end display module of the rheometer; The rheometer is used to measure the viscosity of the coating over time when shear forces of a first low shear rate, a high shear rate, and a second low shear rate are applied sequentially. The data curve of shear rate-viscosity is obtained in the data storage module and fed back to the data analysis device. The data analysis device obtains each TI, RI, and RI from the shear rate-viscosity data curve. 1 / 3 The system checks whether the value meets the criteria for good anti-sagging and leveling performance, and then feeds the result back to the front-end display module.

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