CN115901615A

Movatterモバイル変換

Info

Publication number: CN115901615A
Application number: CN202211709750.7A
Authority: CN
Inventors: 杨志平; 魏大力; 陈�光; 张荣金; 张雨昊; 赵凯利; 聂晓霖
Original assignee: Nanjing Kerun Industrial Media Co ltd; Nanjing Kerun Industrial Technology Co ltd
Current assignee: Nanjing Kerun Industrial Media Co ltd; Nanjing Kerun Industrial Technology Co ltd
Priority date: 2022-12-29
Filing date: 2022-12-29
Publication date: 2023-04-04

Abstract

The invention discloses a method for evaluating the wet adhesion of a metal organic coating, which comprises the following steps: coating an organic coating on a metal base material, scribing 3x3 square lattices with the side length of a on a sample to be tested by using a cutter, wherein the scribing depth is that a paint film penetrates to reach the surface of the metal base material; completely immersing the sample into an aqueous NaCl solution; adhering a transparent pressure-sensitive adhesive tape to the grid-dividing position of the sample to enable the adhesive tape to be tightly adhered to the coating, then smoothly tearing the adhesive tape away from the coating within 0.5-1 s, and sequentially repeating the operations along the four sides of the square grid-dividing direction; using an image pickup device with a magnifying function to carry out microscopic shooting on the square lattices in the right center of the square lattices; firstly, carrying out gray level processing on the picture, then carrying out morphological processing, converting the picture into a binary image, extracting the maximum outline on the binary image and calculating the ratio of the area of the outline to the total area of the picture; and judging the wet adhesion of the coating according to the residual paint ratio.

Description

Method for evaluating wet adhesion of metal organic coating

Technical Field

The invention relates to a method for evaluating the wet adhesion of a metal organic coating.

Background

The failure mode of the organic coating with defects in a corrosion environment is cathode stripping, the mechanism is that the metal base material is subjected to electrochemical corrosion in the corrosion environment, and the adhesion of the organic coating and the metal base material is damaged due to cathode reaction products. The conventional method for evaluating the cathodic disbonding resistance of the organic coating has long experimental period, strong artificial subjectivity and poor reproducibility. The key to affecting the cathodic disbonding resistance of a coating is the adhesion of the organic coating to the substrate in the wet state, also known as the wet adhesion of the coating. Currently, there is no method for objectively and quantitatively evaluating the wet adhesion of organic coatings.

The existing method for evaluating the wet adhesion of the organic coating mainly depends on manually removing the stripped coating by a blade after the coating is soaked in a corrosive medium for a long time, and then the size of the wet adhesion of the coating is evaluated by measuring the maximum stripped width of the coating, for example, the evaluation method for the wet adhesion of a metal heavy anti-corrosion coating disclosed by Chinese patent CN114544485 has the advantages that the experimental period of the method is longer (more than or equal to 600 h), the mode of manually removing the stripped coating by the blade has stronger artificial subjectivity, the maximum stripped width of the measured coating is easily influenced by defects of coating shrinkage holes, needle holes and the like, the difference of experimental results obtained by different operators is larger, and the reproducibility is poorer.

Disclosure of Invention

The purpose of the invention is as follows: the invention aims to provide a method for evaluating the wet adhesion of a metal organic coating, which can effectively shorten the experimental period, quickly evaluate the wet adhesion of a paint film on a metal base material and has the advantages of short experimental period and good reproducibility.

The technical scheme is as follows: the method for evaluating the wet adhesion of the metal organic coating comprises the following steps:

(1) Coating an organic coating on a metal base material to obtain a sample to be tested; the coating modes comprise electrophoresis, powder spraying, blade coating, roll coating, brush coating and dip coating;

(2) Scribing a square scribing lattice of 3x3 on a sample to be tested by using a cutter, wherein the scribing depth is that a paint film penetrates through the surface of a metal base material; the square grid consists of nine square grids with side length a;

(3) Preparing a NaCl aqueous solution with the concentration of 3-10 wt%, completely immersing the sample to be tested in the step (2) into the NaCl aqueous solution, and simultaneously mechanically stirring at more than 500 revolutions per minute; performing experiment at 30-70 ℃ for 12-48 hours;

(4) Cleaning the sample treated in the step (3) with deionized water, removing surface corrosion products, absorbing the surface moisture of the sample with absorbent paper, immediately adhering the sample to the grid of the sample with a transparent pressure-sensitive adhesive tape, pressing with fingers to ensure that the adhesive tape is tightly adhered to the coating, smoothly tearing the adhesive tape from the coating within 0.5-1 s, and sequentially repeating the operations along the four sides of the square grid, wherein each side is operated for four times;

(5) Using an image pickup device with a magnifying function to carry out microscopic shooting on the square lattices in the right center of the square lattices;

(6) Firstly, carrying out gray level processing on the picture, and then carrying out morphological processing (including but not limited to expansion, corrosion, opening operation and closing operation) to enable the boundary between the residual paint film part on the picture and the exposed metal substrate after the paint film is stripped to be clear; then converting the picture into a binary image, extracting the maximum contour on the binary image and calculating the ratio of the contour area to the total area of the picture;

(7) And (3) determining the ratio of the residual area of the paint film to the whole square lattice as a residual paint ratio A, dividing different coating wet adhesion grades according to the value of A obtained by calculation, and judging the coating wet adhesion according to the residual paint ratio.

Wherein, in the step (2), a =2mm when the paint film thickness is 0-40 μm, a =3mm when the paint film thickness is 40-80 μm, and a =4mm when the paint film thickness is more than 80 μm.

Wherein, in the step (3), the concentration of the NaCl aqueous solution is 3-10 wt%, the temperature is 30-70 ℃, and mechanical stirring of more than 500 revolutions per minute is simultaneously applied in the soaking process; the experimental time was 12 to 48 hours. There are three test protocols: the test time h was 12 hours when t =70 ℃, 24 hours when t =50 ℃ and 48 hours when t =30 ℃.

Wherein, naCl should be analytically pure or have a purity higher than that, the water used should be deionized water, and the conductivity of the deionized water is less than 10 muS/cm.

Wherein in the step (4), the width of the transparent pressure sensitive adhesive tape is larger than that of the square grid.

In the step (5), if a =2mm, the magnification of the imaging device is 25 to 50 times.

In the step (7), when the ratio of 80% to A is more than or equal to 0, the corresponding wet adhesion grade of the coating is 0 grade; when A is more than or equal to 60% and less than 80%, the corresponding wet adhesion grade of the coating is grade 1; when A is more than or equal to 40% and less than 60%, the corresponding wet adhesion grade of the coating is grade 2; when A is more than or equal to 20% and less than 40%, the corresponding wet adhesion grade of the coating is grade 3; when A is less than 20%, the corresponding wet adhesion rating of the coating is 4.

Has the beneficial effects that: compared with the prior art, the invention has the following remarkable advantages: the method is suitable for testing the wet adhesion of various coatings and various metal base material systems, and has wide applicability and simple and convenient operation; the method has short experimental period, and can quickly evaluate the wet adhesive force of the paint film, thereby greatly shortening the experimental time; the method for removing the pressure-sensitive adhesive from the test piece greatly reduces the influence of artificial subjective factors, so that the test result is more objective and real and has good reproducibility.

Drawings

FIG. 1 is a schematic illustration of a wet adhesion test specimen;

FIG. 2 is a photograph of the wet adhesion test of examples 1 to 6.

Detailed Description

Example 1

Cold-rolling the sheet: bao steel DC04

Pretreatment: is free of

Organic coating: guanxi HT800C electrophoretic paint

The invention relates to a method for evaluating the wet adhesion of a metal organic coating, which comprises the following steps:

(1) As shown in fig. 1, a square 3 × 3 grid is scribed on the sample by a cutter, and the depth of the scribing is the depth penetrating the paint film to reach the surface of the metal substrate; the thickness of a paint film is 20.5 mu m, and the square lattices consist of nine square lattices with the side length of 2 mm;

(2) Preparing a NaCl aqueous solution with the concentration of 5wt%, completely immersing the sample to be tested in the step (2) into the NaCl aqueous solution, and simultaneously applying mechanical stirring of more than 500 revolutions per minute; experiment at 70 deg.C for 12 hr;

(4) Cleaning the sample treated in the step (3) with deionized water, removing surface corrosion products, absorbing the surface moisture of the sample with absorbent paper, immediately adhering the sample to the grid of the sample with a transparent pressure-sensitive adhesive tape, pressing with fingers to ensure that the adhesive tape is tightly adhered to the coating, smoothly tearing the adhesive tape from the coating within 0.5-1 s, and sequentially repeating the operations along the four sides of the square grid, wherein each side is operated for four times; the width of the transparent pressure sensitive adhesive tape is larger than the width (6 mm) of the square grid;

(5) Using an image pickup device which is magnified by 25 times to carry out microscopic shooting on the square lattices at the right centers of the square lattices;

(6) Firstly, carrying out gray level treatment on the picture, and then carrying out morphological treatment to enable the boundary between the residual paint film part on the picture and the exposed metal base material after the paint film is stripped to be clear; then converting the picture into a binary image, extracting the maximum contour on the binary image and calculating the ratio of the contour area to the total area of the picture;

(7) The paint residue ratio A of the paint film residual area in the entire square lattice was 2.16%, as shown in FIG. 2.

Example 2

Cold-rolling the sheet: bao steel DC04

Pretreatment: KR-S210 pretreatment of Kerun film

Organic coating: guanxi HT800C electrophoretic paint

(1) As shown in fig. 1, a square 3 × 3 grid is scribed on the sample by a cutter, and the depth of scribing is that the paint film penetrates to the surface of the metal substrate; the thickness of a paint film is 20.0 mu m, and the square lattices consist of nine square lattices with the side length of 2 mm;

(7) The paint residue ratio A of the paint film residual area in the entire square lattice was 60.7%, as shown in FIG. 2.

Example 3

Hot-dip galvanized sheet: bao steel DC54D + Z

Pretreatment: KR-S210 pretreatment of Kerun film

Organic coating: guanxi HT800C electrophoretic paint

(1) As shown in fig. 1, a square 3 × 3 grid is scribed on the sample by a cutter, and the depth of scribing is that the paint film penetrates to the surface of the metal substrate; the thickness of a paint film is 19.6 mu m, and the square lattices consist of nine square lattices with the side length of 2 mm;

(7) The residual paint ratio A of the residual paint film area in the entire square lattice was 47.9%, as shown in FIG. 2.

Example 4

Cold-rolling the sheet: bao steel DC04

Pretreatment: KR-SP110 pretreatment before Kerun phosphating

Organic coating: guanxi HT800C electrophoretic paint

(1) As shown in fig. 1, a square 3 × 3 grid is scribed on the sample by a cutter, and the depth of scribing is that the paint film penetrates to the surface of the metal substrate; the thickness of a paint film is 20.1 mu m, and the square lattices consist of nine square lattices with the side length of 2 mm;

(4) Cleaning the sample treated in the step (3) with deionized water, removing surface corrosion products, absorbing the surface moisture of the sample with absorbent paper, immediately adhering the sample to the grid of the sample with a transparent pressure-sensitive adhesive tape, pressing with fingers to ensure that the adhesive tape is tightly adhered to the coating, smoothly tearing the adhesive tape from the coating within 0.5-1 s, and sequentially repeating the operations along the four sides of the square grid, wherein each side is operated for four times; the width of the transparent pressure-sensitive adhesive tape is larger than the width (6 mm) of the square grid;

(7) The paint residue ratio A of the paint film residual area in the entire square lattice was 70.2%, as shown in FIG. 2.

Example 5

Aluminum alloy plate: 6061 aluminium alloy

Pretreatment: KR-S210 pretreatment of Kerun film

Organic coating: guanxi HT800C electrophoretic paint

(1) As shown in fig. 1, a square 3 × 3 grid is scribed on the sample by a cutter, and the depth of scribing is that the paint film penetrates to the surface of the metal substrate; the thickness of a paint film is 20.9 mu m, and the square lattices consist of nine square lattices with the side length of 2 mm;

(7) The residual paint ratio A of the residual paint film area in the entire square lattice was 87.6%, as shown in FIG. 2.

Example 6

Aluminum alloy plate: bao steel DC04

Pretreatment: KR-S110 pretreatment before Kerun vitrification

Organic coating: tiger silver powder coating

(1) As shown in fig. 1, a square 3 × 3 grid is scribed on the sample by a cutter, and the depth of the scribing is the depth penetrating the paint film to reach the surface of the metal substrate; the thickness of a paint film is 60.3 mu m, and the square grid is composed of nine square grids with the side length of 3 mm;

(4) Cleaning the sample treated in the step (3) by using deionized water, removing a surface corrosion product, absorbing the water on the surface of the sample by using absorbent paper, immediately adhering the sample to the grid of the sample by using a transparent pressure-sensitive adhesive tape, pressing the sample by using fingers to ensure that the adhesive tape is tightly adhered to the coating, smoothly tearing the adhesive tape from the coating within 0.5-1 s, and sequentially repeating the operations along the four sides of the square grid, wherein each side is operated for four times; the width of the transparent pressure sensitive adhesive tape is larger than the width (9 mm) of the square grid;

(5) Using an image pickup device which is magnified by 35 times to carry out microscopic shooting on the square lattices at the right centers of the square lattices;

(7) The residual paint ratio A of the residual paint film area in the entire square lattice was 0%, as shown in FIG. 2.

Table 1 shows the wet adhesion comparison of different paint film coatings applied to different metal substrates of examples 1 to 6

As can be seen from table 1, by comparing examples 1, 2 and 4, the wet adhesion of the electrophoretic paint film subjected to film pretreatment and phosphating pretreatment is improved from 4 grade to 1 grade compared with the wet adhesion of the electrophoretic paint film not subjected to coating pretreatment, although the improvement of the wet adhesion of the electrophoretic paint film subjected to film pretreatment and the phosphating pretreatment are the same as 1 grade, the improvement of the wet adhesion of the coating subjected to film pretreatment is weaker than that of the phosphating pretreatment, and a residual paint ratio difference of about 10% still exists; the comparison of examples 2, 3 and 5 shows that the wet adhesion of the electrophoretic paint under the same pretreatment conditions is as follows: 6061 aluminum alloy plate > DC04 steel plate > DC54D + Z galvanized plate; it can be seen from the comparison of example 2 and example 6 that the wet adhesion of the powder coating under the same pretreatment conditions is much lower than that of the electrodeposition coating. The method can quickly and effectively evaluate the wet adhesion of different substrates, different coatings and matching coatings of different pretreatment.

Claims

1. A method for evaluating the wet adhesion of a metal organic coating is characterized by comprising the following steps:

(1) Coating an organic coating on a metal base material to obtain a sample to be tested;

(3) Completely immersing the sample to be tested in the step (2) into a NaCl aqueous solution;

(4) Cleaning the sample treated in the step (3) with deionized water, removing surface corrosion products, absorbing the surface moisture of the sample, adhering the sample to the grid-dividing position of the sample by using a transparent pressure-sensitive adhesive tape to enable the adhesive tape to be tightly adhered to the coating, smoothly tearing the adhesive tape from the coating within 0.5-1 s, and sequentially repeating the operations along the four sides of the square grid-dividing position;

(6) Firstly, carrying out gray processing on the picture, and then carrying out morphological processing to enable the boundary between the residual paint film part on the picture and the metal base material after the paint film is stripped to be clear; then converting the picture into a binary image, extracting the maximum contour on the binary image and calculating the ratio of the contour area to the total area of the picture;

(7) And (3) determining the ratio of the residual area of the paint film to the whole square grid as a residual paint ratio A, dividing different coating wet adhesion grades according to the calculated value of A, and judging the coating wet adhesion according to the residual paint ratio.

2. The method of evaluating the wet adhesion magnitude of a metal organic coating according to claim 1, wherein: in the step (2), a =2mm when the paint film thickness is 0 to 40 μm, a =3mm when the paint film thickness is 40 to 80 μm, and a =4mm when the paint film thickness is more than 80 μm.

3. The method for evaluating the wet adhesion magnitude of a metal-organic coating according to claim 1, wherein: in the step (3), the concentration of the NaCl aqueous solution is 3-10 wt%, the temperature is 30-70 ℃, and mechanical stirring of more than 500 revolutions per minute is simultaneously applied in the soaking process; the experimental time was 12 to 48 hours.

4. The method of evaluating the wet adhesion magnitude of a metal organic coating according to claim 1, wherein: in the step (4), the width of the transparent pressure-sensitive adhesive tape is larger than that of the square grid.

5. The method of evaluating the wet adhesion magnitude of a metal organic coating according to claim 1, wherein: in the step (5), if a =2mm, the magnification of the image pickup apparatus is 25 to 50 times.

6. The method of evaluating the wet adhesion magnitude of a metal organic coating according to claim 1, wherein: in the step (7), when the content of A is more than or equal to 80%, the corresponding wet adhesion grade of the coating is 0 grade; when A is more than or equal to 60% and less than 80%, the corresponding wet adhesion grade of the coating is grade 1; when A is more than or equal to 40% and less than 60%, the corresponding wet adhesion grade of the coating is grade 2; when A is more than or equal to 20% and less than 40%, the corresponding wet adhesion grade of the coating is grade 3; when A is less than 20%, the corresponding wet adhesion rating of the coating is 4.