Method for detecting adhesive force between coatings of color-coated product

Abstract

The invention discloses a method for detecting adhesive force between coatings of a color-coated product, which comprises the following steps of: 1) bending and flattening the front surface and the back surface of a color-coated sheet to be detected, so that the wave shape of the color-coated sheet is smaller than 1mm; 2) boiling with water; the flattened color-coated sheet is added into boiling water to be boiled; (3) taking out the boiled color-coated sheet, and air-drying or sucking the surface of the color-coated sheet; a lineation line with the length not smaller than 50 mm is arranged on the surface of the color-coated plate, and the lineation line needs to scratch a coating to a base plate; and 4) testing the hardness of the pencil from the lineation position along the direction vertical to the lineation. According to the method disclosed by the invention, the interlayer adhesive force of the color-coated product can be efficiently detected, and the stripping risk between coatings possibly existing in user side processing and later use can be effectively found; and the related test method is simple, convenient to operate and suitable for popularization and application.

Description

Technical Field

[0001] The invention belongs to the technical field of performance detection of coated steel plates, and in particular relates to a method for detecting the adhesion between coating layers of a color-coated product. Background Art

[0002] As a new type of environmentally friendly, energy-saving and easy-to-process material, color-coated plates have been widely used in the fields of construction, home appliances, decoration and decoration. With the continuous improvement of the use and quality requirements of color-coated products, light steel buildings, house structures, high-rise curtain walls, etc. have begun to use color-coated products directly on a large scale. This type of product has the advantages of being able to be formed in one go, already with a color coating, and not requiring chemical anti-corrosion treatment, spraying and other processes, and can effectively solve the VOC waste gas emissions caused by coating, and the emission of wastewater and waste residue containing heavy metals. Among them, the market usage of metal paint color-coated products has been increasing in recent years due to their unique and beautiful appearance.

[0003] The coating structure of conventional color-coated products usually includes a primer and a topcoat which are respectively disposed on the front and back of the metal substrate in sequence. In recent years, as users have increased their requirements for the film thickness of special coatings, some color-coated products no longer use the conventional coating structure of primer + topcoat, but need to use a special coating structure. For example, for coating products with a front surface greater than 45 microns, three coatings (one layer of primer + two layers of topcoat) are required, specifically including: a primer and a topcoat disposed on the back of the metal base plate, and a primer, a first layer of topcoat, and a second layer of topcoat disposed on the front of the metal substrate. For another example, for a 12-micron epoxy coating on the back, the epoxy primer needs to be applied twice, specifically including: a first layer of primer and a second layer of primer disposed on the back of the metal substrate, and a primer and a topcoat involved on the front of the metal substrate.

[0004] At present, the testing method for the bending performance of color-coated products usually adopts the "bending test", "reverse impact test", "scratch test" and "cupping test" in "GB / T13448-2019 Test Methods for Color Coated Steel Plates and Strips"; the adhesion performance between the coating and the metal substrate when the steel plate is deformed during processing can be tested. When adjacent coatings use the same type of coating, the adhesion between them is different from the traditional primer + topcoat model due to the characteristics of the coating; using traditional products with qualified adhesion performance, interlayer coating peeling and other problems will still occur during subsequent processing at the user's site. Further exploring new and efficient detection methods that more comprehensively and accurately evaluate the adhesion between coatings can effectively prevent interlayer coating peeling and other problems during user processing, which is of great significance for promotion and application. Summary of the invention

[0005] The main purpose of the present invention is to provide a method for efficiently detecting the interlayer adhesion of color-coated products in response to the problems and shortcomings of the prior art, which can effectively detect the risk of peeling between coatings during user-side processing and later use; and the test method involved is simple, easy to operate, and suitable for promotion and application.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for detecting the adhesion between coating layers of a color-coated product comprises the following steps:

[0008] 1) Bend and flatten the front and back of the color-coated plate to be tested so that the wave shape of the steel plate is less than 1mm;

[0009] 2) Boiling: Add the flattened color-coated sheet into boiling water and boil it;

[0010] 3) Take out the boiled color-coated board and air-dry or absorb the surface; set a line of not less than 50mm on the surface of the color-coated board (using a marking pen or other methods), and the marking line must cut through the coating to the substrate;

[0011] 4) Perform a pencil hardness test from the scribe line in a direction perpendicular to the scribe line.

[0012] Furthermore, the color-coated plate to be tested is placed in an environment with a temperature of 21 to 25° C. and a relative humidity of 45 to 55% for more than 24 hours before use.

[0013] In the above scheme, the control requirements of the boiling time with the coating thickness d are: d≤25μm 55~65min; 25μm <d≤30μm 85~95min;30μm<d≤35μm 100~110min;35μm<d≤40μm 115~125min。

[0014] Furthermore, all the color-coated plate samples were immersed in boiling water, and the water temperature was maintained during the boiling period and the liquid level did not drop significantly.

[0015] Furthermore, the size of the color-coated plate sample is 100-120 mm×230-250 mm, and the sample should be flat, with no oil stains, damage, or burrs on the surface.

[0016] Furthermore, the dashed line is a straight line.

[0017] In the above scheme, the marking step includes: using a pencil sharpener to sharpen the pencil until a 3-5 mm cylindrical lead is exposed (the lead should not be loose or cut), holding the pencil perpendicular to the surface of 400# sandpaper, and grinding on the sandpaper until a flat end surface and a sharp edge are obtained (the edge should not be broken or notched).

[0018] In the above scheme, the pencil hardness test steps include: 1) placing the sample horizontally on the operating table, holding the sharpened pencil so that it forms an angle of 30-50° with the coating, and applying sufficient and uniform pressure in a direction perpendicular to the marking line from the marking position, and the force is preferably enough to break the edge of the pencil or plow through the coating; 2) the pencil advances for a stroke of 5-8 mm; the pencil should be rotated 180° after being used once or re-sharpened for use; 3) starting from the hardest pencil (usually starting from 3H), the separation of the topcoat and the next layer of coating exceeding 0.5 mm is defined as plowing, and if the coating can be plowed once in 3 times, a softer pencil is used, until a pencil that cannot plow through the coating layer for 3 consecutive times is found, and the hardness of this pencil is the pencil hardness of the interlayer adhesion to be tested.

[0019] Furthermore, the pencil labels are: 5H, 4H, 3H, 2H, H, F, HB, B, 2B; among which 5H is the hardest, 2B is the softest, and the hardness decreases from 5H to 2B.

[0020] Furthermore, a pencil is placed at the drawn line, with the pencil projection line forming a 90-degree angle with the drawn line, to test the pencil hardness.

[0021] Furthermore, the pencil is a special pencil for 505 coating test.

[0022] In the above scheme, the pencil hardness test result is less than or equal to grade B and is judged as unqualified.

[0023] Furthermore, if the coating topcoat is a fluorocarbon coating, the pencil hardness test result is less than or equal to level 2B and is judged to be unqualified.

[0024] Furthermore, if the steel plate thickness is greater than 0.8 mm or the yield strength is greater than 350 MPa, and the pencil hardness test result is less than or equal to HB, it is judged as unqualified.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1) The present invention firstly boils and marks the color-coated plate in sequence, and then performs a pencil hardness test perpendicular to the marked part. The above detection method can effectively find products that may have the risk of peeling between coatings during user-side processing and later use, and effectively ensure the accuracy of the test results;

[0027] 2) The detection method involved in the present invention is relatively simple and can be used with conventional detection equipment and materials, and is suitable for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 In Application Example 1 of the present invention, (a) the sample morphology of the color-coated steel coil after the coating interlayer adhesion test and (b) the construction effect diagram;

[0029] Figure 2 Application effect diagram of the qualified color-coated steel coil described in Comparative Example 1. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below in conjunction with the embodiments to facilitate a clearer understanding of the present invention, but they do not limit the present invention.

[0031] In the following examples, the equipment and materials used include: Zhonghua 505 special pencils for coating testing, with pencil numbers of 5H, 4H, 3H, 2H, H, F, HB, B, and 2B, among which 5H is the hardest and 2B is the softest, with the hardness decreasing from 5H to 2B; No. 400 sandpaper; pencil sharpener; marking pen using a special pen for marking salt spray specimens; ruler.

[0032] Example 1

[0033] The method for detecting the adhesion between coating layers of a color-coated product of the present invention comprises the following steps:

[0034] (1) Two samples 1# and 2# of the edge of polyester 0.5mm TDC51D+AM with a yield strength of 280MPa with a total film thickness of about 22 microns were bent and flattened on the front and back sides respectively. The size of the obtained samples was 100mm×240mm. The samples were flat, with no oil stains, no damage, and no burrs on the edges. Then they were placed in an environment with a temperature of 23℃±2℃ and a relative humidity of 50±5% for at least 24 hours;

[0035] (2) Boiling: Add an appropriate amount of water to a suitable container, heat to boiling, and then immerse the entire sample obtained in step 1); heat for 1 hour, during which the water temperature is maintained and the liquid level does not drop significantly; take out the sample and immediately dry it with cold air or use absorbent paper to dry the surface of the color-coated plate;

[0036] (3) Use a pencil sharpener to sharpen the pencil until a 3-5 mm cylindrical lead is exposed (the lead should not be loose or cut), hold the pencil perpendicular to the 400# sandpaper surface, and grind it on the sandpaper until the end surface is flat and the edge is sharp (the edge should not be broken or notched); use a marking pen to draw a 60 mm straight line along the ruler, and the coating needs to be scratched to the substrate (do not use too much force to avoid scratching the substrate);

[0037] (4) Place a special Chinese pencil sharpened on sandpaper at the scribe line at a 90-degree angle to the scribe line to test the pencil hardness. The specific steps include: 1) Place the sample horizontally on the operating table, hold the sharpened pencil at a 45-degree angle to the coating, and apply sufficient and uniform pressure downward and forward from the scribe line. The force should be enough to break the edge of the pencil or plow through the coating. 2) The pencil advances for about 5-8 mm. The pencil should be rotated 180° or re-sharpened after use. 3) Start with the hardest pencil (usually starting from 3H). Plowing is defined as the separation of the topcoat and the next layer of coating exceeding 0.5 mm. If the coating can be plowed through once in 3 times, a softer pencil is used until a pencil that cannot plow through the coating layer for 3 consecutive times is found. The hardness of this pencil is the pencil hardness of the interlayer adhesion to be tested.

[0038] If the pencil adhesion test result is less than or equal to Grade B, it is judged as unqualified.

[0039] Application Example 1

[0040] The above method is used to detect the interlayer adhesion of the coating as F, which is produced by the color coating unit of Wuhan Iron and Steel Cold Rolling Plant with a thickness of 0.7mm, TDC51D+AM, and a yield strength of 280MPa, and the color-coated steel coils are used in a large storage and logistics plant in Xuchang, Henan Province (January 2024). The 840-watt type pressed tiles are used on site, and the color-coated plates are in good condition for processing and use.

[0041] Application Example 2

[0042] The above method is used to detect the interlayer adhesion of the coating as H for TS350GD+AM with a yield strength of 390MPa and a white-gray polyester color-coated steel coil with a thickness of 0.7mm produced by the color-coating unit of the cold rolling mill.

[0043] This batch of color-coated steel coils was used in a food supply plant in Shandong (March 2024). Flat composite panels were used on site, and the color-coated panels were in good condition.

[0044] Comparative Example 1

[0045] For the 0.8mm thick TS350GD+AM sea blue fluorocarbon color coated steel coils produced by the color coating unit of Wuhan Iron and Steel Cold Rolling Plant, only the existing methods in the national standards GB / T 12754 and GB / T 13448 were used to test the surface hardness of the coating. The surface hardness H of the coating was qualified, and other conventional properties such as coating adhesion were also qualified. However, this batch of color coated steel coils was used in a large factory in Baoding, Hebei, and the coating was scratched when it was used for 750-watt type tile pressing on site.

[0046] In view of the above application problems, samples of this batch of products were retrieved and further tested according to the test method described in Example 1. The results showed that the interlayer adhesion grade of this batch of products was 2B, which was judged to be unqualified, which matched the actual application effect.

[0047] Comparative Example 2

[0048] For the 0.7mm thick, grade TDC51D+AM, yield strength 318MPa tornado white polyester color coated steel coil produced by the color coating unit of Wuhan Iron and Steel Cold Rolling Plant, only the traditional method of national standard GB / T 12754 and GB / T 13448 was used to test the surface hardness of the coating. The surface hardness H of the coating was qualified, and other conventional properties such as coating adhesion were also qualified. However, when this batch of color coated steel coils was used on the roof of Terminal T3 of Xinjiang Urumqi International Airport, 680-watt pressed tiles were used on site, and the coating was scratched at the bend of the positive corner.

[0049] In view of the above application problems, samples of this batch of products were retrieved and further tested according to the test method described in Example 1. The results showed that the interlayer adhesion grade of this batch of products was 2B, which was judged to be unqualified, which matched the actual application effect.

[0050] Comparative Example 3

[0051] For the 0.5mm thick, TDC51D+AM grade, 325MPa yield strength tornado white polyester color-coated steel coils produced by the color-coating unit of Wuhan Iron and Steel Cold Rolling Plant, only the traditional methods of national standards GB / T 12754 and GB / T 13448 were used to test the surface hardness. The coating surface hardness H was qualified, and other conventional properties such as coating adhesion were also qualified; however, when this batch of color-coated steel coils were used for the wall panels of the new terminal building of Hohhot International Airport in Inner Mongolia, 840-tile pressed tiles were used on site, and the coating was scratched at the corners and bends.

[0052] Further testing was carried out using a method similar to the present invention, and the test method was roughly the same as that of Example 1, except that the boiling time was 0.5 hours, and the final hardness grade was F, which was qualified. However, when this batch of color-coated steel coils was used for the wall panels of the new terminal building of Hohhot International Airport in Inner Mongolia, 840-tile type pressed tiles were used on site, and the coating was scratched at the corners and bends.

[0053] In view of the above application problems, samples of this batch of products were retrieved and the test method described in Example 1 was further adopted. The results showed that the interlayer adhesion grade of this batch of products was 2B, which was judged to be unqualified, which matched the actual application effect.

[0054] The above embodiments are only examples for clear explanation, and are not intended to limit the implementation methods. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here, so the obvious changes or modifications derived are still within the protection scope of the invention.

Claims

1. A method for detecting the adhesion between coating layers of a color-coated product, characterized in that: The steps include: 1) Bend and flatten the front and back of the color-coated sheet to be tested so that the wave shape of the color-coated sheet is less than 1mm; 2) Boiling: Add the flattened color-coated sheet into boiling water and boil it; 3) Take out the boiled color-coated board and air-dry or absorb the surface; set a line of not less than 50mm on the surface of the color-coated board, and the line must cut through the coating to the substrate; 4) Perform a pencil hardness test from the scribe line in a direction perpendicular to the scribe line.

2. The method according to claim 1, characterized in that In step 1), the wave shape of the color-coated sheet is controlled to be less than 1 mm.

3. The method according to claim 1, characterized in that The control requirements of the boiling time with the coating thickness d are: d≤25μm 55~65min; 25μm <d≤30μm 85~95min;30μm<d≤35μm 100~110min;35μm<d≤40μm 115~125min。 4. The method according to claim 1, characterized in that: The size of the color-coated plate is 100-120 mm×230-250 mm.

5. The method according to claim 1, characterized in that: The dashed line is a straight line.

6. The method according to claim 1, characterized in that The pencil hardness test steps include: 1) placing the sample horizontally on the operating table, holding a sharpened pencil so that it forms an angle of 30 to 50 degrees with the coating, and applying sufficient and uniform pressure from the marking position in a direction perpendicular to the marking line to break the pencil edge or plow through the coating; 2) the pencil advances for a stroke of 5 to 8 mm; 3) starting from the hardest pencil, plowing is defined as the separation of the topcoat and the next layer of coating exceeding 0.5 mm. If the coating can be plowed through once out of three times, a softer pencil is used, until a pencil that cannot plow through the coating layer for three consecutive times is found, and the hardness of this pencil is the pencil hardness of the interlayer adhesion to be tested.

7. The method according to claim 1, characterized in that The pencil labels are: 5H, 4H, 3H, 2H, H, F, HB, B, 2B; among them, 5H is the hardest, 2B is the softest, and the hardness decreases from 5H to 2B.

8. The method according to claim 1, characterized in that The pencil hardness test result is less than or equal to grade B and is judged to be unqualified.

9. The method according to claim 1, characterized in that: If the coating topcoat is a fluorocarbon coating, the pencil hardness test result is less than or equal to 2B and is judged as unqualified.

10. The method according to claim 1, characterized in that If the steel plate thickness is greater than 0.8 mm or the yield strength is greater than 350 MPa, and the pencil hardness test result is less than or equal to HB, it is judged as unqualified.

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