A detection method for the water resistance and whiteness performance of stone-like coatings

Abstract

The present invention discloses a method for testing the water whitening resistance of real stone paint under conditions of large temperature difference, windy and low humidity, including: (1) paint preparation; (2) substrate treatment; (3) panel preparation; (4) curing: placing the cement pressure plate in a forced air drying oven with the temperature controlled at 3-7°C and the humidity controlled at 30%RH±5%RH for curing; (5) soaking: placing the pressure plate vertically or obliquely in a water tank at 23±2°C so that part of the area is immersed in water and part of the area is not; (6) drying: placing the soaked cement pressure plate in a forced air drying oven with the temperature controlled at 3-7°C and the humidity controlled at 30%RH±5%RH for drying; (7) dehumidification; (8) determination. The present invention discovers the synergistic effect of the three major factors of large temperature difference, low humidity and windy on the water whitening of real stone paint. This test method cures and dries under conditions of low temperature, low humidity and forced air, and can further detect the water whitening resistance of real stone paint after being affected by the weather later.

Description

Technical Field

[0001] The present invention relates to the field of architectural coatings, and particularly to a method for detecting the water whitening resistance of stone-like paint. Background Art

[0002] Stone-like paint is a synthetic resin emulsion sand wall architectural paint that forms a decorative coating with a stone texture on the surface of a building, using synthetic resin emulsion as the main binder and sand grains, stone particles and stone powder as aggregates. Stone-like paint not only has a decorative effect similar to marble and granite, but also has good acid and alkali resistance, pollution resistance, strong adhesion, and light fading. It can effectively prevent the erosion of the building cement base by the harsh external environment, extend the life of the building; the construction is simple, easy to dry and time-saving. Due to its strong decorative properties, wide application range and economic benefits, it has been widely used.

[0003] However, in some cases at present, the stone-like paint coating is prone to turn white when exposed to water after drying, especially in the initial drying stage (12h). When it rains, after being washed by rainwater for a long time, the coating will become soft, turn white and show color mottling, which is called the "water whitening" phenomenon in the industry.

[0004] Regarding the color mottling and whitening phenomena that occur during the construction of stone-like paint, the following reasons are mainly considered at present: One is that the thickness of the stone-like paint coating is relatively thick and the water volatilization is slow. Especially when the environmental temperature is low (<10°C) and the relative humidity is high (>80%), the water cannot volatilize completely. After applying the topcoat, it becomes hazy and white, with uneven colors; the second is that the paint film itself is relatively hydrophilic, and water penetrates through the coating and enters the interior of the paint film, resulting in a difference in refractive index, causing whitening and color fading. In severe cases, it will cause swelling and peeling. This kind of water whitening generally basically recovers after the water dries; the third is the difference in construction techniques, which leads to uneven local thickness or the surface state of the paint film, resulting in uneven covering and gloss, and thus uneven colors. For the difference in color depth, people may also often call the locally lighter areas white. The first and the third are mainly related to construction, while the second is related to product quality problems, that is, the product has poor water whitening resistance.

[0005] At present, this special case of water whitening of stone-like paint is generally included in the determination scope of water resistance (water resistance and water whitening resistance are different). For architectural emulsion enterprises and architectural coating enterprises, without a strict and reliable test method to accurately evaluate the water whitening resistance of their own coatings, it will greatly affect the further upgrading of products.

[0006] "JG / T - 24 Synthetic Resin Emulsion Sand - textured Architectural Coatings" and "GB / T 1733 - 1993 Method for Determining Water Resistance of Paint Films" disclose the test methods for the water resistance of paint films. The water resistance test methods of these two documents are as follows: After curing in the standard environment for 14 days, seal the edges and backs, then soak in deionized water at 23 ± 2°C for 96 hours, and then place it in the standard environment for 3 hours, and observe the surface state. This method mainly aims at the tolerance of the paint film to water after a specified drying time when the paint film is formulated. For high - quality stone - like paints, it is easy to pass the test when the test cycle is long enough and the drying conditions are ideal enough. However, the paint film does not have any performance in the initial stage after construction, so it is also the stage most vulnerable to environmental influences. Therefore, this method cannot measure the defects caused by the influence of water on stone - like paints when the early construction conditions are not ideal. That is to say, this method cannot detect the water - whitening resistance of stone - like paints.

[0007] CN201611268026 discloses a test method for the water - whitening resistance of stone - like paint at low temperature and high humidity, CN201310364859 discloses a test method for the water resistance of paint at low temperature in the initial stage, CN201510003338 discloses a device and method for determining the early outdoor rain - shower performance of paint, CN201120028763 discloses a device for testing the initial water resistance of sand - textured coatings, and CN201520004600 discloses a device for determining the early outdoor rain - shower performance of paint. The above patents on the early construction performance test methods of stone - like paints mainly focus on how the stone - like paint tolerates water under certain conditions after early construction, that is, only for the situation where the paint itself is not completely dried and formed into a film in the early stage or the water resistance of the paint itself is relatively poor. They all advocate that under the conditions of curing in a high - humidity and low - temperature environment and being impacted by rain, phenomena such as blistering, peeling, and color change that may occur when the paint film absorbs water when encountering water.

[0008] Moreover, the test methods for simulating rainwater in the above patent documents only consider the impact of water. The main purpose of simulating rainwater is to simulate the physical damage caused by its impact. However, it ignores the situations of snowmelt, frost melt, dew condensation, or water leakage, etc., which are only infiltrating, without impact water droplets or water flows. In these situations, the effects or microscopic effects of water on the interior of the paint film have nothing to do with whether the water flow has impact force, and still can cause the water - whitening phenomenon. In addition, during the actual test process, the water flow size, water flow speed, water flow drop, water flow temperature, and flow rate at each water outlet of the flushing device are affected by factors such as water pressure and are not easy to control. Even if it can be achieved, it is not easy to make the test conditions repeat consistently for different batches of tests. As a detection means, it is not conducive to control.

[0009] Furthermore, the entire process of these test methods and device testing is not highly standardized and is cumbersome. The final judgment can only be made by human qualitative judgment and cannot be accurately evaluated. Therefore, there is a high possibility of misjudgment in the entire parallel comparison test process. Summary of the invention

[0010] After long-term practice and observation, the present invention has found that under completely different circumstances from the above, water whitening can also occur in real stone paint. This water whitening is normal when the paint film is initially dry, and it does not bulge, fall off or turn white when immersed in water after drying. In addition, there is no obvious abnormality after the water is naturally dried at room temperature after immersion in water. However, under dry conditions with large temperature difference, low humidity and wind (different from the "high humidity is easy to cause water whitening of real stone paint" believed in the prior art), obvious whitening will occur after being rained, and once it occurs, it is almost impossible to fully recover under natural conditions. That is to say, when the existing test method is used for testing, the real stone paint may have excellent performance and is considered not to be prone to water whitening, but water whitening still occurs after the final application, which shows that the existing test method for the water whitening resistance of real stone paint has certain defects.

[0011] Existing test methods are inaccurate when used in areas with large temperature differences (e.g., large temperature differences between day and night) and windy conditions (there is also wind during high-altitude operations), especially in seasonal weather with low air humidity. In such areas and seasons, even if the existing test methods show that the real stone paint has good performance and will not appear water-white, if it rains on the second or third day after construction, there is still a high probability that water-whitening will occur after a sunny day.

[0012] In order to overcome the defect that there is no systematic and targeted test method for water-whitening resistance in the prior art to measure the water-whitening resistance of different real stone paints, the present invention has developed a method for testing the water-whitening resistance of real stone paint under conditions of large temperature difference (temperature difference is 13-22°C), windy and low humidity (generally refers to humidity below 40% RH) based on long-term practice and observation.

[0013] The technical solution of the present invention is as follows:

[0014] A method for testing the water whitening resistance of real stone paint under conditions of large temperature difference, wind and low humidity, comprising the following steps:

[0015] (1) Paint preparation: Stir the real stone paint evenly;

[0016] (2) Substrate treatment: Apply colorless transparent primer on the asbestos-free fiber cement pressure board and let it dry for more than 2 hours;

[0017] (3) board making: applying a batch of real stone paint on the asbestos-free fiber cement pressure board treated in step (2);

[0018] (4) Curing: Place the asbestos-free fiber cement pressure plate processed in step (3) into a blast drying oven with the temperature controlled at 3 - 7°C and the humidity controlled at 30% RH ± 5% RH for curing;

[0019] (5) Soaking: Place the cured asbestos-free fiber cement pressure plate vertically or obliquely into a water tank at 23 ± 2°C, allowing some areas to be immersed in water and some areas not to be immersed;

[0020] (6) Drying: Place the soaked asbestos-free fiber cement pressure plate into a blast drying oven with the temperature controlled at 3 - 7°C and the humidity controlled at 30% RH ± 5% RH for drying;

[0021] (7) Dehumidifying: Take out the dried asbestos-free fiber cement pressure plate and blow dry the condensed water on the surface with a fan until the surface is dry;

[0022] (8) Judgment: Visually observe the degree of water whiteness, or measure ΔL with a color difference meter to judge the degree of water whiteness. ΔL represents the difference in lightness values between the immersed area and the non-immersed area.

[0023] As described above, since the present invention discovers the synergistic effect of the three major factors of large temperature difference, low humidity, and wind on the water whiteness of real stone paint, a test scheme of the present invention is designed for this situation. Different from the existing test methods which advocate curing and drying in an environment of low temperature and high humidity, the test method of the present invention cures and dries under the conditions of low temperature, low humidity, and blowing, which can further detect the water whiteness resistance performance of real stone paint after being affected by the weather in the later stage, rather than only focusing on the water whiteness resistance performance or water resistance of the paint film in the initial stage (the detection of the water whiteness resistance performance of the paint film in the initial stage is insufficient. For example, in areas with large temperature differences and strong winds, the paint film has no abnormality after drying, does not turn white when exposed to water, does not blister or peel off, and there is no obvious color difference after the water naturally evaporates at normal temperature. However, it will still turn significantly white after being re-rained and dried in an environment of low temperature, low humidity, and wind, which results in an incomplete and inaccurate detection of the water resistance performance of real stone paint).

[0024] The temperature change during the entire testing process of the present invention has experienced three temperature stages: low temperature → normal temperature (which can also be a higher ambient temperature) → low temperature. Through a large number of experiments, it has been found that the water-white test phenomenon is most obvious under such periodic temperature changes. That is to say, "a large temperature difference", rather than just low temperature, has an impact on water whiteness. For example, in the actual environment, the situation where the temperature difference is most likely to occur is day and night. In actual construction, it is basically during the day, and it may enter the night just after construction. If the temperature difference between day and night in a certain area is large, then in fact, the paint film on the wall has just experienced an environment with a large temperature difference (even in some cases, the actual temperature is not low, but only the temperature difference is large). In addition, there is also likely to be night wind (the wall surface at high altitude will definitely have wind). If a low-humidity situation occurs (different from the high-humidity situation considered in the prior art that will cause water whiteness), then some real stone paints may be more likely to exhibit the water-white phenomenon.

[0025] In addition, different from the existing detection methods which are all set to simulate rainwater, according to the situation where water whiteness is caused under the conditions of a large temperature difference, low humidity and blowing, the present invention adopts an infiltrating soaking method instead of an impact water flow method, which can simulate situations such as snow melting, frost melting, dew condensation or water leakage that only have infiltration and no impact. In these situations, the action or microscopic action of water on the inside of the paint film has nothing to do with whether the water flow has impact force. Moreover, by adopting the infiltrating soaking method, the present invention can avoid the defect that it is difficult to control the water flow size, water flow speed and drop, water flow temperature and flow rate at each water outlet of the flushing device due to factors such as water pressure, making it easier to control the repeatability of tests for different batches.

[0026] Furthermore, in the existing detection methods, the real stone paint is coated on the cement board by spraying. During the spraying process of the real stone paint, due to the different sizes of the colored sand particles, the gun-out speed is directly different, which directly leads to the uneven distribution of the colored sand particle components in the longitudinal direction of the entire coating and inconsistent surface effects. In addition, during the spraying process, there are also differences in the speed of water loss, unstable material discharge and air pressure, and the influence of different gun-running speeds and distances. Even people with very high construction skills cannot ensure that the conditions are the same every time when changing the gun, and can only make the thickness in the same area relatively uniform (as mentioned above, whether the thickness is uniform also has an impact on the water-white phenomenon. If there are thickness differences, it may cause changes in gloss and covering power at different angles, resulting in color differences). As a detection method related to appearance (color), the control of conditions is crucial. Both the uniform thickness and the uniform distribution of the colored sand components in the horizontal and longitudinal directions need to be strictly controlled, so as to minimize the appearance differences caused by construction. The detection method of the present invention uses a scraping method instead of spraying, which can maximize the avoidance of color differences and surface state problems that may occur during the coating process, making the repeatability of tests for different batches better and the appearance detection results more accurate.

[0027] As a further improvement of the above technical solution, the paint mixing operation in step (1) is as follows: Shake and mix the colored sand evenly, then mix the pre-prepared slurry without emulsion with the emulsion evenly, and finally manually stir the colored sand, the mixed slurry and the emulsion evenly (for example, manually stir with a paint mixing knife (specification: large 4 inches)). This method can avoid excessive bubbles generated by mechanical stirring, can be prepared and used immediately without leaving overnight, and can evenly mix the paint to the greatest extent, with less consumption for one-time preparation and no excessive waste.

[0028] As a further improvement of the above technical solution, the non-asbestos fiber cement pressure plate used in step (2) has a specification of 150*70*6 mm. Before using the test plate, apply a coat of colorless transparent primer and dry it for 1 - 2 h for standby.

[0029] As a further improvement of the above technical solution, the test plate in step (3) is obtained by filling the paint in a stainless steel mold frame with a thickness of 2 mm and a rectangular hole in the middle. The application method in step (3) is scraping, which can avoid the inconsistent surface effect of color difference caused by spraying, make the components of the paint film evenly distributed in the horizontal and vertical directions, and the application conditions are easy to control. For example, the test plate in step (3) is obtained by filling the paint in a mold frame with a thickness of 2 mm. The mold frame is made of stainless steel with sufficient rigidity to prevent deformation and bending during long-term use. There is a rectangular hole in the middle, the size of the rectangular hole is 140*65 mm, and the outer frame size is 200*125 mm. The whole mold frame and the middle rectangular hole are processed by laser cutting or wire cutting, with no burrs at the corners and the plate surface smooth and flat, so that the scraping is smooth without great resistance.

[0030] As a further improvement of the above technical solution, a tool is used for scraping in step (3), and the tool is one of a paint mixing knife, an ink stirring knife, a rubber collecting knife, and a solder paste stirring knife. A tool is used for scraping in step (3). For example, the size is 5 inches (blade length 125 mm, blade width 19 mm, thickness 1 mm, total length 255 mm). The blade surface needs to be smooth and straight, with sufficient rigidity and not easy to bend, to ensure the scraping effect, make the surface of the paint film flat without pits, and the thickness uniform.

[0031] As a further improvement of the above technical solution, the curing time in step (4) is 18 - 24 h. During the curing period, it is necessary to ensure that the surfaces of all test plates can be blown by the built-in air blower. To ensure good drying and strength of the test plates and no bulging or peeling during the soaking period, the curing time can be appropriately extended.

[0032] As a further improvement of the above technical solution, in step (5), the soaking is carried out under the conditions of a temperature of 23±2°C and a humidity of 50%±5%RH. The soaking time is 4 - 6h, and the soaking height is 1 / 3 - 1 / 2 of the height of the test panel. At the same time, the test medium needs to be left standing overnight under the conditions of a temperature of 23±2°C and a humidity of 50%±5%RH to ensure consistency with the soaking environment in step (5). The test medium is a liquid, which can be one of tap water, pure water, and acid rain solution, preferably pure water, and the test results are the most obvious under this condition.

[0033] As a further improvement of the above technical solution, the drying time in step (6) is 4h - 6h until the surface of the soaked area of the test panel is dry without water marks. The top layer of the forced-air drying oven is equipped with a blowing device, and it is necessary to ensure that the surfaces of all the soaked areas of the test panels can be blown by the built-in air blower until the surface of the soaked area is dry to a good degree without water marks and does not feel soft when pinched with fingers.

[0034] As a further improvement of the above technical solution, after the test panel in step (7) is taken out of the low-temperature box, it needs to be blown by an electric fan in a standard environment for 1 - 2h to dry the dew formed on the surface of the paint film due to the moisture in the air until the surface of the test panel is completely dry and the temperature of the test panel drops to room temperature, and there is no obvious cold feeling when touched with fingers.

[0035] As a further improvement of the above technical solution, a large temperature difference means a temperature difference of 13 - 22°C.

[0036] As a further improvement of the above technical solution, low humidity means less than 40%RH.

[0037] As a further improvement of the above technical solution, during the determination process in step (8), when the visual results are significantly different, the determination and ranking can be directly carried out by visual inspection. If the visual results are not significantly different, a color difference meter can be used to measure the difference ΔL in lightness value between the soaked area (measurement area) and the unsoaked area (standard area) according to specific steps to assist in determining the degree of low-temperature water whiteness. For example, the color difference meter is the X-Rite CI6X series, the color space is selected as Lab, the test light source is D65 / 10, the test mode is comparison, and the SPEX test method is selected. The test steps are as follows: Use the color difference meter to select three points for testing in the area (standard area) 1 cm inward from the edge of the unsoaked area of the paint film, and the result is the average value of the three points as the initial value L1. Then, select three points for testing in the area 1 cm inward from the edge of the unsoaked area of the paint film (measurement area), and the result is the average value L2 of the three points. The final result is expressed as ΔL = L2 - L1. After verification by multiple test formulations, water whiteness mainly affects the change of the L value, so the L value can be used to characterize the degree of water whiteness.

[0038] According to the newly discovered causes of water whiteness in the present invention, the present invention provides a test method for the water whiteness resistance of real stone paint under conditions of large day-night temperature difference, windy, and low humidity. In addition to reducing the appearance errors caused by paint formulation and application, the present invention uses a simple and controllable method to simulate six conditions, namely, three environmental factors (temperature difference, blowing wind, low humidity) and three process factors (curing, soaking in water, drying), from the influencing principle of water whiteness. At the same time, the harshness of the test conditions is controllable, and differential results can be obtained. Therefore, it has better screening performance, can well screen out real stone paints with excellent or poor water whiteness resistance, and can visually judge and grade them, thus facilitating product development and product screening for building enterprise consumers. In addition, the entire test process has a high degree of standardization, less error introduced during the test process, simple operation, easy implementation, and the entire test cycle is only 2.5 days, with short time and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Shows the test results of the water whiteness resistance of the real stone paint in Example 1 of the present invention.

[0040] Figure 2 Shows the test results of the water whiteness resistance of the real stone paint in Example 2 of the present invention.

[0041] Figure 3 Shows the test results of the water whiteness resistance of the real stone paint in Example 3 of the present invention.

[0042] Figure 4 Shows the test results of the water whiteness resistance of the real stone paint in Example 4 of the present invention.

[0043] Figure 5 Shows the test results of the water whiteness resistance of the real stone paint in Example 5 of the present invention.

[0044] Figure 6 Shows the test results of the water whiteness resistance of the real stone paint in Example 6 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0046] In addition, it should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. Unless otherwise specified, the technical means not described in the embodiments can be implemented in a manner well known to those skilled in the art. For those skilled in the art, without departing from the essence and scope of the present invention, various modifications, substitutions, and improvements made to the material composition, dosage, time, temperature, etc. in these embodiments also fall within the scope defined by the appended claims of this application. It should be specifically noted that the specific parameters defined in the present invention should have an allowable error range.

[0047] The real stone paint building emulsion is an ordinary commercially available product that can meet the building coating standards. The present invention selected 12 different formulations for testing. All the real stone paints were prepared in one go in sufficient quantity, and the total amount of paint prepared was 300 g, which was used for inter-group result comparison in Examples 1-5. Example 6 was for intra-group result comparison test, and its test formulation was Formulation 1.

[0048] Example 1 (Low-temperature and low-humidity forced-air curing - soaking in water - drying in standard environment)

[0049] The test method for the water whitening resistance of the real stone paint under this condition includes the following steps:

[0050] (1) Paint preparation: First, calculate the dosage according to the total required paint amount of 300 g and the composition and ratio of the colored sand in Formulation 1 respectively. Then, sequentially weigh various sand materials with a total amount of N into a 250 ml sample can A, shake it with a shaker for 5 min to disperse evenly. Then, calculate the dosage according to the total amount of 2*(300 - N) and the ratio of the slurry (excluding the emulsion) to the emulsion in Formulation 1, and then weigh and pour it into sample can B. Stir it evenly with a high-speed disperser at a speed of 400 - 800 r / min (it is necessary to prepare an excess amount) to obtain a mixed slurry (containing the emulsion). Finally, weigh a mixed slurry with an amount of (300 - N) from sample can B and pour it into sample can A, and manually scrape the edge and stir with a paint mixing knife until the sand materials at the bottom and on the wall of the can are completely wetted and there is no caking, and the stirring is smooth without resistance. Prepare the paint samples required for Formulations 2-12 according to the same steps;

[0051] (2) Substrate treatment: Take 12 non-asbestos fiber cement pressure plates with a specification of 150*70*6 mm, brush a colorless and transparent primer on their upper surfaces with a brush, and dry for more than 2 h for standby;

[0052] (3) Plate making: Place a steel formwork with an inner frame size of 140*65 mm, an outer frame size of 200*125 mm, and a thickness of 2 mm on an asbestos-free fiber cement pressure plate, align the corners, and then use a 5-inch paint mixing knife to scrape the paint samples of Formulas 1-12 along the long side direction of the formwork onto 12 asbestos-free fiber cement pressure plates in sequence. Scrape one test plate for each paint sample. After each scraping, the formwork and the paint mixing knife need to be cleaned and dried;

[0053] (4) Curing: Place the scraped test plates parallelly into the top layer of a low-temperature and low-humidity forced-air drying oven for curing. Control the temperature at 5°C and the relative humidity at 30%RH ± 5%RH. The curing time is 24 h. After curing, use your finger to press to ensure that the paint film is hard enough and does not become soft. In addition, fill a bucket with enough tap water and place it in a constant temperature and humidity chamber (23 ± 2°C, 50% ± 5%RH) overnight;

[0054] (5) Soaking: Take out the cured test plates from the low-temperature box, and then place them upright or obliquely into a water tank with a square-hole partition board (to fix the test plates to prevent them from tipping over). Pour tap water into it until the water depth reaches 1 / 2 of the test plate height, and soak for 5 h;

[0055] (6) Drying: Take out the test plates from the water tank, place them face up parallelly into a constant temperature and humidity chamber (23 ± 2°C, 50% ± 5%RH) for natural drying. The drying time is 18 h. After drying, use your finger to press to ensure that the paint film is hard enough and does not become soft;

[0056] (7) Dehumidification: Test plates dried at room temperature do not require the dehumidification step;

[0057] (8) Judgment: Observe the degree of whitening of the test plates with the eyes, rank the results, or use a color difference meter to measure the difference ΔL in lightness value between the soaked area and the unsoaked area to assist in judging the low-temperature water whitening degree.

[0058] The test results of the water whitening resistance performance of the real stone paints of Formulas 1-12 under this condition are as shown in Table 1 below and Figure 1 as follows.

[0059] Table 1: Test results obtained in Example 1

[0060]

[0061] Note: "√" indicates that it is hard enough to be pinched with a finger after curing and has sufficient strength; "Y" indicates that there is no blistering, peeling, or obvious color difference after soaking.

[0062] Example 2 (Low-temperature and low-humidity forced-air curing - soaking - low-temperature and low-humidity forced-air drying)

[0063] The test method for the water whitening resistance performance of real stone paint under this condition includes the following steps:

[0064] (1) Paint preparation: To ensure consistent paint sample conditions, 12 paint samples (Formulas 1 - 12) prepared in Example 1 were used for testing.

[0065] (2) Substrate treatment: Take 12 asbestos-free fiber cement pressure plates with dimensions of 150*70*6 mm. Brush a colorless transparent primer on their upper surfaces with a brush and let it dry for more than 2 h for standby.

[0066] (3) Panel preparation: Place a steel formwork with an inner frame size of 140*65 mm, an outer frame size of 200*125 mm, and a thickness of 2 mm on the asbestos-free fiber cement pressure plate, align the corners, and then use a 5-inch paint mixing knife to scrape the paint samples of Formulas 1 - 12 along the long side direction of the formwork onto the 12 asbestos-free fiber cement pressure plates in sequence. Scrape one test panel for each paint sample. After each scraping, the formwork and the paint mixing knife need to be cleaned and dried.

[0067] (4) Curing: Place the scraped test panels parallel into the top layer of a low-temperature and low-humidity forced-air drying oven for curing. Control the temperature at 5°C and the relative humidity at 30%RH ± 5%RH. The curing time is 24 h. After curing, use finger tapping to ensure that the paint film is hard enough and does not become soft. In addition, fill a bucket with enough tap water and place it in a constant temperature and humidity chamber (23 ± 2°C, 50% ± 5%RH) overnight.

[0068] (5) Soaking: Take out the cured test panels from the low-temperature box, then place them upright or obliquely into a water tank with a square-hole partition board (to fix the test panels to prevent them from tipping over), and pour tap water into it until the water depth reaches 1 / 2 of the test panel height. The soaking duration is 5 h.

[0069] (6) Drying: Take out the test panels from the water tank, place them face up and parallel into the top layer of a low-temperature and low-humidity forced-air drying oven for drying. Control the temperature at 5°C and the relative humidity at 30% ± 5%RH. The drying time is 18 h. After drying, use finger tapping to ensure that the paint film is hard enough and does not become soft.

[0070] (7) Dehumidification: Take out the dried test panels from the low-temperature box and place them flat in a constant temperature and humidity chamber (23 ± 2°C, 50% ± 5%RH). Blow the surface of the test panels with a fan for 2 h until the surface is dry and there is no obvious cold feeling when touched with fingers, so as to remove the dew formed by the moisture in the air on the surface of the test panels.

[0071] (8) Judgment: Observe the whitening degree of the test panels with eyes, rank the results, or measure the difference ΔL in lightness value between the soaked area and the unsoaked area using a color difference meter to assist in judging the low-temperature water whitening degree.

[0072] The water whitening resistance test results of the real stone paints of Formulas 1 - 12 under this condition are shown in Table 2 below and Figure 2 as follows.

[0073] Table 2: Test Results Obtained in Example 2

[0074]

[0075] Example 3 (Curing in Standard Environment - Soaking in Water - Drying with Low Temperature and Low Humidity and Blowing Air)

[0076] The test method for the water whitening resistance of the stone-like paint under this condition includes the following steps:

[0077] (1) Paint preparation: To make the paint sample conditions consistent, 12 paint samples (Formulas 1 - 12) prepared in Example 1 were used for the test;

[0078] (2) Substrate treatment: Take 12 asbestos-free fiber cement pressure plates with a specification of 150*70*6 mm, and brush a colorless transparent primer on their upper surfaces with a brush, and let it dry for more than 2 h for standby;

[0079] (3) Panel making: Place a steel formwork with an inner frame size of 140*65 mm, an outer frame size of 200*125 mm, and a thickness of 2 mm on the asbestos-free fiber cement pressure plate, align the corners, and then use a 5-inch paint mixing knife to scrape the paint samples of Formulas 1 - 12 on the 12 asbestos-free fiber cement pressure plates in sequence along the long side direction of the formwork. Scrape 1 test panel for each paint sample, and after each scraping, the formwork and the paint mixing knife need to be cleaned and dried;

[0080] (4) Curing: Place the scraped test panels parallel in a thermostatic and humidistatic chamber (23 ± 2°C, 50% ± 5% RH) for natural curing in sequence. The curing time is 24 h. After the curing is completed, use your finger to press to ensure that the paint film is hard enough and does not become soft. In addition, fill a bucket with enough tap water and place it in the thermostatic and humidistatic chamber (23 ± 2°C, 50% ± 5% RH) overnight;

[0081] (5) Soaking in water: Take out the cured test panels from the low-temperature box, and then place them vertically or obliquely in a water tank with a square-hole partition board (to fix the test panels to prevent them from tipping over), and pour tap water into it until the water depth reaches 1 / 2 of the test panel height, and soak for 5 h;

[0082] (6) Drying: Take out the test panels from the water tank, place them face up parallel on the top layer of a low-temperature and low-humidity air-blowing drying oven for drying. The temperature is controlled at 5°C, and the relative humidity is controlled at 30% ± 5% RH. The drying time is 18 h. After the drying is completed, use your finger to press to ensure that the paint film is hard enough and does not become soft;

[0083] (7) Dehumidification: Take out the dried test panels from the low-temperature box and place them flat in a thermostatic and humidistatic chamber (23 ± 2°C, 50% ± 5% RH), and blow air at the surface of the test panels with a fan for 2 h until the surface is dry and there is no obvious cold feeling when touched with fingers, so as to remove the dew formed by the moisture in the air on the surface of the test panels;

[0084] (8) Judgment: Observe the whiteness degree of the test panel with the eyes, rank the results by grading, or use a color difference meter to measure the difference ΔL in lightness value between the immersed area and the non-immersed area to assist in judging the low-temperature water whiteness degree.

[0085] The water resistance and whiteness performance test results of the stone-like paints of Formulas 1-12 under this condition are shown in Table 3 below and Figure 3 as follows.

[0086] Table 3: Test results obtained in Example 3

[0087]

[0088] Example 4 (low-temperature and low-humidity forced-air curing - soaking in water - drying in a standard environment, soaking in water again - low-temperature and low-humidity forced-air drying)

[0089] The test method for the water resistance and whiteness performance of the stone-like paint under this condition includes the following steps:

[0090] (1) Paint preparation: To make the paint sample conditions consistent, 12 paint samples (Formulas 1-12) prepared in Example 1 were used for the test;

[0091] (2) Substrate treatment: Take 12 non-asbestos fiber cement pressure plates with a specification of 150*70*6 mm, brush a colorless and transparent primer on their upper surfaces with a brush, and dry for more than 2 h for standby;

[0092] (3) Panel preparation: Place a steel formwork with an inner frame size of 140*65 mm, an outer frame size of 200*125 mm, and a thickness of 2 mm on the non-asbestos fiber cement pressure plate, align the corners, and then use a 5-inch paint mixing knife to scrape the paint samples of Formulas 1-12 on the 12 non-asbestos fiber cement pressure plates along the long side direction of the formwork in turn. Scrape 1 test panel for each paint sample, and clean the formwork and the paint mixing knife and dry them after each scraping;

[0093] (4) Curing: Place the scraped test panels parallel in turn on the top layer of a low-temperature and low-humidity forced-air drying oven for curing. Control the temperature at 5°C and the relative humidity at 30% RH ± 5% RH. The curing time is 24 h. After the curing is completed, use your finger to ensure that the paint film is hard enough and does not become soft. In addition, fill a bucket with enough tap water and place it in a constant temperature and humidity chamber (23 ± 2°C, 50% ± 5% RH) overnight;

[0094] (5) First soaking in water: Take out the cured test panels from the low-temperature box, and then place them vertically or obliquely in a water tank with a square-hole partition board (to fix the test panels to prevent them from tipping over), pour tap water into it until the water depth reaches 1 / 2 of the height of the test panels, and soak for 5 h;

[0095] (6) First drying: Take out the test panel from the water tank, place it face up and parallel in a constant temperature and humidity chamber (23 ± 2°C, 50% ± 5% RH) for natural drying. The drying time is 18 hours. After drying, ensure that the paint film is hard enough by finger tapping and does not become soft.

[0096] (7) First dehumidification: For test panels dried at room temperature, the dehumidification step is not required.

[0097] (8) First determination: Observe the whitening degree of the test panel with the eyes, rank the results, or measure the difference in lightness value ΔL between the immersed area and the non-immersed area using a color difference meter to assist in determining the low-temperature water whitening degree.

[0098] (9) Second soaking: Place the dried test panel upright or obliquely again in a water tank with a square-hole partition (to fix the test panel to prevent it from tipping over), and pour tap water into it until the water depth reaches 1 / 2 of the test panel height. Soak for 5 hours.

[0099] (10) Second drying: Take out the test panel from the water tank, place it face up and parallel on the top layer of a low-temperature and low-humidity forced-air drying oven for drying. The temperature is controlled at 5°C and the relative humidity is controlled at 30% ± 5% RH. The drying time is 18 hours. After drying, ensure that the paint film is hard enough by finger tapping and does not become soft.

[0100] (11) Second dehumidification: Take out the dried test panel from the low-temperature oven and place it flat in a constant temperature and humidity chamber (23 ± 2°C, 50% ± 5% RH). Blow air towards the surface of the test panel with a fan for 2 hours until the surface is dry and there is no obvious cold feeling when touched with fingers, to remove the dew formed by the moisture in the air on the surface of the test panel.

[0101] (12) Second determination: Observe the whitening degree of the test panel with the eyes, rank the results, or measure the difference in lightness value ΔL between the immersed area and the non-immersed area using a color difference meter to assist in determining the low-temperature water whitening degree.

[0102] The water whitening resistance test results of the real stone paint of Formulas 1 - 12 under this condition are as shown in Table 4 below and Figure 4 as follows.

[0103] Table 4: Test results obtained in Example 4

[0104]

[0105]

[0106] Example 5 (comparing the differences between "low-temperature high-humidity forced-air curing - soaking - low-temperature high-humidity forced-air drying" and "low-temperature low-humidity forced-air curing - soaking - low-temperature low-humidity forced-air drying")

[0107] The test method for the water whitening resistance of real stone paint under this condition includes the following steps:

[0108] (1) Paint preparation: To ensure consistent paint sample conditions, 4 paint samples (Formulas 1 - 4) prepared in Example 1 were used for testing.

[0109] (2) Substrate treatment: Take 8 asbestos - free fiber cement pressure plates with dimensions of 150*70*6 mm. Brush a colorless transparent primer on their upper surfaces with a brush and let it dry for over 2 h for standby.

[0110] (3) Plate making: Place a steel formwork with an inner frame size of 140*65 mm, an outer frame size of 200*125 mm, and a thickness of 2 mm on the asbestos - free fiber cement pressure plate, align the corners, and then use a 5 - inch paint mixing knife to scrape the paint samples of Formulas 1 - 4 along the long side direction of the formwork on the 8 asbestos - free fiber cement pressure plates in sequence. Scrape 2 test plates for each paint sample. After each scraping, clean the formwork and the paint mixing knife and dry them.

[0111] (4) Curing: Take one of the 2 test plates scraped with each formula and place them separately in the top layer of a low - temperature and low - humidity forced - air drying oven and a low - temperature and high - humidity forced - air drying oven for curing. Control the temperature at 5°C, and the relative humidity at 30%RH ± 5%RH (low humidity) and 70%RH ± 5%RH (high humidity) respectively. The curing time is 24 h. After curing, ensure that the paint film is hard enough by finger pressing and does not feel soft. In addition, fill a bucket with enough tap water and place it in a constant - temperature and constant - humidity chamber (23 ± 2°C, 50% ± 5%RH) overnight.

[0112] (5) Soaking: Take out the cured test plates from the low - temperature oven, then place them upright or obliquely in a water tank with a square - hole partition board (to fix the test plates to prevent them from toppling), pour tap water into it until the water depth reaches 1 / 2 of the test plate height, and soak for 5 h.

[0113] (6) Drying: Take out the test plates from the water tank, place them face - up and parallel in the top layer of the corresponding low - temperature and low - humidity forced - air drying oven and low - temperature and high - humidity forced - air drying oven for drying. Control the temperature at 5°C, and the relative humidity at 30%RH ± 5%RH (low humidity) and 70%RH ± 5%RH (high humidity) respectively. The drying time is 18 h. After drying, ensure that the paint film is hard enough by finger pressing and does not feel soft.

[0114] (7) Dehumidification: Take out the dried test plates from the low - temperature oven and place them flat in a constant - temperature and constant - humidity chamber (23 ± 2°C, 50% ± 5%RH). Blow air on the surface of the test plates with a fan for 2 h until the surface is dry and there is no obvious cold feeling when touched with fingers to remove the dew formed by the moisture in the air on the surface of the test plates.

[0115] (8) Judgment: Observe the degree of whitening of the test plates with the eyes, rank the results, or measure the change value of L with a color difference meter to assist in judging the degree of low - temperature water whiteness.

[0116] The water whitening resistance test results of the stone-like paints of Formulas 1-4 under these two conditions are shown in Table 5 below and Figure 5 as follows.

[0117] Table 5: Test results obtained in Example 5

[0118]

[0119]

[0120] Example 6 (comparing the differences in different water moistening conditions, including the type and temperature of water)

[0121] The test method for the water whitening resistance of the stone-like paint under this condition includes the following steps:

[0122] (1) Paint preparation: To make the paint sample conditions consistent, the paint sample of Formula 1 was used for the test according to the paint preparation method of Example 1;

[0123] (2) Substrate treatment: Take 8 asbestos-free fiber cement pressure plates with specifications of 150*70*6 mm, brush a colorless and transparent primer on their upper surfaces with a brush, and dry for more than 2 h for standby;

[0124] (3) Panel making: Place a steel formwork with an inner frame size of 140*65 mm, an outer frame size of 200*125 mm, and a thickness of 2 mm on the asbestos-free fiber cement pressure plate, align the corners, and then use a 5-inch paint mixing knife to scrape the paint sample of Formula 1 on the 8 asbestos-free fiber cement pressure plates along the long side direction of the formwork in sequence. Two test panels form a group, with a total of 4 groups, which are respectively marked as groups a, b, c, and d. After each scraping is completed, the formwork and the paint mixing knife need to be cleaned and dried;

[0125] (4) Curing: Place the scraped test panels parallelly in the top layer of a low-temperature and low-humidity blast drying oven for curing. The temperature is controlled at 5°C, the relative humidity is controlled at 30% RH ± 5% RH, and the curing time is 24 h. After the curing is completed, use your finger to ensure that the paint film is hard enough and does not become soft. In addition, fill a bucket with sufficient acidic tap water (PH = 5.32), pure water, and conventional tap water A, and place them in a constant temperature and humidity chamber (23 ± 2°C, 50% ± 5% RH) overnight. Place conventional tap water B in a low-temperature and low-humidity blast drying oven with a temperature controlled at 5°C and a relative humidity controlled at 30% RH ± 5% RH overnight;

[0126] (5) Water immersion: Take out the well-cured test panels of groups a, c, and d from the low-temperature box, and then place them vertically or obliquely in a water tank with a square-hole partition board (to fix the test panels to prevent them from tipping over). Inject water under different conditions into it. For group a test panels, inject acidic tap water (pH = 5.32) at 23 ± 2 °C, for group c test panels, inject pure water at 23 ± 2 °C, and for group d test panels, inject conventional tap water A at 23 ± 2 °C until the water depth reaches 1 / 2 of the test panel height. Group b test panels are directly immersed in conventional tap water B at 5 °C in the low-temperature box, and similarly control the immersion height to 1 / 2 and the immersion duration to 5 h;

[0127] (6) Drying: Take out the test panels of groups a, b, c, and d from the water tank, place them face up in parallel on the top layer of a low-temperature and low-humidity forced-air drying oven for drying. Control the temperature at 5 °C and the relative humidity at 30% ± 5% RH. The drying time is 18 h. After drying, it is necessary to ensure that the paint film is hard enough by finger tapping and does not become soft;

[0128] (7) Dehumidification: Take out the dried test panels from the low-temperature box and place them flat in a constant-temperature and constant-humidity chamber (23 ± 2 °C, 50% ± 5% RH). Blow air at the surface of the test panels with a fan for 2 h until the surface is dry and there is no obvious cold feeling when touched with fingers, so as to remove the condensation formed by the moisture in the air on the surface of the test panels;

[0129] (8) Judgment: Observe the degree of whitening of the test panels with the eyes, rank the results, or use a color difference meter to measure the difference ΔL in lightness value between the immersed area and the non-immersed area to assist in judging the degree of low-temperature water whitening.

[0130] The test results of the water whitening resistance of the real stone paint of Formula 1 under different water-wetting conditions are as shown in Table 6 below and Figure 6 shown below.

[0131] Table 6: Test results obtained in Example 6

[0132]

[0133] From the test results of the water whitening resistance of different paint samples obtained in Examples 1-5, it can be seen that in a low-temperature environment of 5 °C, whether it is high humidity or low humidity, the paint film can obtain sufficient strength after 24 h, and there is no blistering, peeling, or obvious color difference change after soaking in water for 5 h. However, it will still be affected by the subsequent drying conditions and turn white to varying degrees, indicating that after construction, not only the initial drying degree and the ability to resist the impact of water need to be considered, but also the quality of the paint film drying and the impact of the subsequent drying conditions on the paint film after the micro-action of water on the paint film, that is, the ability of water whitening resistance.

[0134] By comparing the test results of the water whitening resistance of different paint samples obtained in Examples 1-2, it can be seen that for the test panels cured in a low-temperature and low-humidity air-blowing environment, there is no abnormality after soaking and drying at room temperature. However, if they are dried continuously in a low-temperature and low-humidity air-blowing environment after soaking, severe whitening will occur. That is to say, if some real stone paints are tested using the existing test methods, their water whitening resistance performance will be shown to be good. However, in fact, once exposed to a low-temperature, low-humidity, and windy environment, severe water whitening will still occur. This shows that the existing water whitening resistance test method is defective and inaccurate and comprehensive.

[0135] In addition, it can be seen from Example 3 that after the test panels cured at room temperature are soaked in water and then dried in a low-temperature and low-humidity air-blowing environment, there is almost no water whitening phenomenon. Only a few formulations have extremely slight water whitening due to formulation differences, indicating that the drying quality of the previous paint film and the environmental conditions during the drying process after being affected by water will largely affect the degree of water whitening.

[0136] From the test results of the water whitening resistance of different paint samples obtained in Example 4, it can be seen that for the test panels of the paint samples cured in a low-temperature and low-humidity air-blowing environment, there is no abnormality after soaking and drying at room temperature. However, if they are soaked again and then dried in a low-temperature and low-humidity air-blowing environment after soaking, obvious water whitening will still occur. This shows that the weather can continuously affect the paint film, indicating that not only the drying degree of the previous paint film and the resistance to water impact need to be investigated, but also the microscopic action of water and the impact of the later drying conditions on the paint film need to be considered. It can also be found again that the water whitening resistance performance is related to the drying quality of the previous paint film and the drying conditions after being microscopically affected by water. Further, it shows that the existing water whitening resistance test method is defective and inaccurate and comprehensive.

[0137] From the test results of the water whitening resistance of different paint samples obtained in Examples 5 and 6, it can be seen that by comparing the L, a, and b values measured by a color difference meter, the a and b values of two test panels of the same paint sample are close, and the difference in lightness value ΔL and color difference ΔE between the immersed area and the non-immersed area of the same test panel are very close, indicating that water whitening mainly affects the change in lightness L. In addition, the visual result (such as the attached figure in Example 5) cannot be well judged, but we can well judge through the size of ΔL. Therefore, the difference in lightness value ΔL between the immersed area and the non-immersed area can be used to well characterize the degree of low-temperature water whitening.

[0138] Moreover, from the test results of the water whitening resistance of different paint samples obtained in Example 5, it can be seen that the ΔL of the test panels tested in a low humidity environment is larger than that of the test panels tested in a high humidity environment, indicating that curing and drying are more likely to cause low temperature water whitening in a low temperature and low humidity air blowing environment than in a low temperature and high humidity air blowing environment, which shows that low humidity is closer to the essence of water whitening. In the prior art, it is generally believed that water whitening occurs in the paint film in a high humidity environment, but the present invention finds that there is no necessary connection between water whitening and a high humidity environment, and a low humidity environment can also cause water whitening, and even the water whitening caused by a low humidity environment is more serious than that caused by a high humidity environment. Currently, the existing test methods mainly focus on whether the paint film is abnormal after preliminary curing and whether the paint film is abnormal after being affected by water in the middle stage, but ignore whether water whitening occurs after drying in the later stage or continuing to be affected by rainwater and then drying. The method of the present invention makes up for the defects of the existing test methods and makes the detection of the water whitening resistance of the real stone paint more comprehensive and accurate.

[0139] It can be seen from Example 6 that different infiltration conditions have different degrees of influence on the final water whitening, and the severity of water whitening (from severe to mild) is in the order of: Group c (pure water at 25°C) > Group a (tap water at 25°C, PH = 5.32) > Group d (conventional tap water A at 25°C) > Group b (conventional tap water B at 5°C). This shows that at 25°C, in terms of the type of water, pure water has the most obvious effect on this type of water whitening, followed by acidic water, and conventional tap water is the weakest. In addition, by comparing the data of Group b and Group d, it can be found that for the infiltration temperature, the effect of tap water at 25°C is significantly greater than that of low temperature water (5°C). The test panels in Group b were tested in an environment of 5°C throughout the whole process, while the test panels in Groups a, c, and d were all affected by water at 25°C in an environment of 25°C. Especially for the test panels in Group d, the water quality is also conventional tap water, but due to the temperature of 25°C during the test, the water whitening of the test panels under this condition is significantly more serious than that of the test panels tested under low temperature conditions throughout the whole process, indicating that the temperature difference existing during the drying and infiltration processes is also a factor that has a very great influence on this water whitening.

Claims

1. A method for testing the water whitening resistance of real stone paint under conditions of large temperature difference, windy and low humidity, comprising the following steps: (1) Paint preparation: Stir the real stone paint evenly. (2) Substrate treatment: Brush a colorless and transparent primer on an asbestos-free fiber cement pressure plate and dry it for standby. (3) Panel preparation: Scrap the real stone paint on the asbestos-free fiber cement pressure plate treated in step (2). (4) Curing: Place the asbestos-free fiber cement pressure plate treated in step (3) in a forced air drying oven with the temperature controlled at 3 - 7°C and the humidity controlled at 30% RH ± 5% RH for curing. (5) Soaking: Place the cured asbestos-free fiber cement pressure plate vertically or obliquely into a water tank at 23 ± 2°C, so that part of the area is immersed in water and part of the area is not. (6) Drying: Place the soaked asbestos-free fiber cement pressure plate in a forced air drying oven with the temperature controlled at 3 - 7°C and the humidity controlled at 30% RH ± 5% RH for drying. (7) Dehumidification: Take out the dried asbestos-free fiber cement pressure plate and blow dry the condensed water formed on the surface with a fan until the surface is dry. (8) Judgment: Visually observe the degree of water whitening, or measure ΔL with a color difference meter to judge the degree of water whitening. ΔL represents the difference in lightness values between the immersed area and the non-immersed area. A large temperature difference means a temperature difference of 13 - 22°C, and low humidity means a humidity below 40% RH. In step (5), the soaking is carried out under the condition of a humidity of 50% ± 5% RH, the soaking time is 4 - 6 h, and the soaking height is 1 / 3 - 1 / 2 of the height of the test panel. The water in the water tank in step (5) is one of tap water, pure water, and acid rain solution, and is left standing overnight at a temperature of 23 ± 2°C and a humidity of 50% ± 5% RH.

2. The method according to claim 1, characterized in that: In step (1), the paint preparation operation is as follows: Vigorously mix the colored sand evenly, then mix the pre-prepared slurry without emulsion with the emulsion evenly, and finally manually stir the colored sand, the mixed slurry, and the emulsion evenly.

3. The method according to claim 1, characterized in that, The asbestos-free fiber cement pressure plate used in step (2) has a specification of 150 * 70 * 6 mm.

4. The method according to claim 1, characterized in that, The test panel in step (3) is obtained by filling the paint in a stainless steel mold frame with a thickness of 2 mm and a rectangular hole in the middle.

5. The method according to claim 1, characterized in that: In step (3), a tool is used for scraping, and the tool is one of a paint mixing knife, an ink stirring knife, a rubber collecting knife, and a solder paste stirring knife.

6. The method according to claim 1, characterized in that: In step (4), the curing time is 18 - 24 h.

7. The method according to claim 1, characterized in that: In step (6), the drying time is 4 h - 6 h until the surface of the soaked area of the test panel is dry without water marks.

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