The comparison of coating adhesion test method and the influence factors are discussed

0 Introduction
is the degree to which the paint layer is firmly combined with the surface of the painted object by physical or chemical force. Coating adhesion is one of the most important indicators for evaluating a coating or coating system. The coating is applied to the surface of the object, forming a continuous coating with firm adhesion and a certain strength
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. Well-adhesive coatings have decorative, protective and other special effects that are easy to maintain and update. Therefore, the determination of coating adhesion has been widely concerned by the coating and coating industry. Coatings are also an indispensable non-metallic material for the aerospace industry. The protective effects of an aircraft's surface become critical when an aircraft is in service in a variety of harsh environments, such as alternating changes in sudden cold and heat, wet and hot climates, acid rain, and various corrosive media. In recent years, the development of new machines has put forward higher requirements for the performance of coatings, coating adhesion is the top priority. By comparing several typical adhesion test methods at home and abroad, this paper analyzes the characteristics, differences and precautions of various methods, and briefly discusses the factors affecting adhesion, and puts forward some suggestions for adhesion testing and improvement.
1 Overview and comparison of domestic adhesion test methods
At present, the domestic adhesion test method generally uses the following three methods: rowing method (GB/T 1720), zoning method (GB/T 9286) and pull method (GB/T 5210). Here's a brief introduction to its contents and considerations.
1.1 Rowing Adhesion Test method
assay overview: the adhesion test with the adhesion measuring instrument of the circle method, according to the round line scratch range of the paint film in good condition assessment of adhesion, the results are graded.
equipment and test materials: adhesion measuring instrument, needle, 4x magnifying glass, soft brush.
test steps: the preparation of a model on the horse mouth iron, paint film dry, in the constant temperature and humidity environment to determine adhesion. First check that the needle of the meter remains sharp and adjust the swing radius until the rolling line is the same as the standard radius of 5.25mm. Secure the test sample and move the lift bar back so that the tip of the needle touches the paint film. Shake the handle clockwise with 80 to 100 r/min, get a rolling line of 7.5±0.5 cm in length, remove the paint chips from scratches with a soft brush, and check the scratches and rate them with a 4x magnifying glass.
rating method: adhesion is divided into 7 grades, in order to check the intactness of each part of the paint film. The adhesion from level 1 to level 7 is reduced in turn, and level 7 is the worst. Test with 3 models, and the results are consistent with the level of at least 2 models.
: 1) Be sure to ensure that the tip of the needle sharp, otherwise the results of the judgment will be affected can not distinguish between level 1 and level 2. You can touch the tip of the needle with your finger to feel sharp before the test. After measuring multiple models, replace the needle as appropriate; 2) first try to carve a few laps, if the tip of the needle does not cross the substrate, should be added as appropriate legal code, but the force should not be too large, so as not to increase resistance and wear needle; 3) to ensure that the swing radius meets the requirements.
1.2 Profile adhesion test
assay overview: When the multi-coat is cut according to the grid shape and just penetrates the coating to reach the substrate, evaluate the resistance of the coating from the substrate, or the ability of the multi-coating system to resist separation from each other, the results are expressed in grading.
equipment and test materials: 6-edge cutting tools, transparent pressure-sensitive tape, soft brush.
test step: place the model on a hard and flat surface, make vertical cutting of 90-degree cross scratches, and the cutting tool must form a grid pattern with a specified interval on the coating at a uniform force and rate. Use a soft brush to brush back and forth several times in the verse direction of the grid, removing paint chips. Place the center point of the 75 mm transparent pressure-sensitive tape on the mesh, parallel to a set of cutting lines, flatten the part of the mesh with your fingers, press the tape hard at your fingertips to ensure good contact with the coating, and smoothly peel the tape within 5 min at an angle close to 60 degrees, at an angle of 0.5 to 1.0 s.
rating method: in a good lighting environment, visual inspection of the cutting surface coating shedding. Adhesion is divided into 6 levels, from level 0 to level 5 coating adhesion decreased in turn, level 5 is the worst. Test at least 3 different parts of the model, if the results are inconsistent, the difference is greater than 1 level unit, and then select 3 parts to retest.
Precautions: 1) According to the thickness of the substrate and coating used, the correct choice of dash interval; 2) cutting edge to maintain a sharp state, if necessary, change the cutting edge; 3) note that the tape adheres to the coating time should not be too long, peeling angle as close as possible to 60 degrees, fast and smooth peeling.
1.3 Pull-out Adhesion Test
Assay Overview: At a specified speed, apply a vertical, uniform pull on the glue surface of the sample to determine the force required for adhesion damage between the coating or between the coating and the substrate, expressed in N/cm2.
and test materials: pull test machine, fixture, test column, centering device, adhesive.
preparation of the test sample: the sample is 2 metal test column docking or combination.
test column material and surface treatment should be the same as the product. The surface of 1 test column is coated according to the specification of the test coating, with adhesive and another test column bond, the uncoated test column is uniformly coated with a thin layer of adhesive, with the help of the centering device coaxial coaxial bond, curing according to the requirements.
test step: put the sample into the upper and lower clamps of the puller, adjust to align, so that the cross-section is evenly forced. The pull-out test is carried out at an extrusion speed of 10 mm/min until it is destroyed, the load value is recorded, and the form of destruction of the section is observed.
adhesion calculation method: the load value when the sample is pulled away and destroyed divided by the cross-sectional area of the test column of the test coating, i.e. the adhesion of the coating, in N/cm2.
Forms of destruction: attachment damage is expressed as A, cohesion damage is expressed as B, the paint portion of the adhesive itself is damaged or the coating under test is pulled to represent C, and 2 or more forms of destruction, the percentage of the area of destruction should be indicated, greater than 70% is valid.
results indicate that each group of tested coating tests should be not less than 5 pairs, at least 3 pairs of arithmetic average as the test results, in the form of adhesion and destruction.
Precautions: 1) The minimum amount of adhesive should be used to produce a solid, continuous and uniform bonding surface when combining the samples;
1.4 Comparative Analysis of Domestic Test Methods
Test Environment: For non-metallic materials test environment is very important, adhesion testing should be carried out on the model under constant temperature and humidity conditions for conditioning. The standard test conditions stipulated on the national standard are: temperature (23±2) degrees C, relative humidity (50±5).
: The ringing method is suitable for the determination of a variety of single coating adhesion and is widely used. The scing method is used to measure the thickness of a coating less than 250 m, although it can also be used for multi-coating determination, but because it is not easy to determine whether the adhesion between the coating and the substrate or between the coating, so mostly used for the determination of a single coating. The pull-out method is suitable for thicker coatings (e.g. putty), single coating and multi-coating systems, but this method can be preferred when determining adhesion between coatings.
advantages and disadvantages: the drawing method and the rowing method are indirect measurement method, the result is not a simple adhesion, but also contains the deformation of the coating and damage resistance, but the operation is simple and fast, widely used. The pull method belongs to the direct measurement method, can use the number to indicate the coating adhesion, is a good way to investigate whether the coating matching is reasonable, comprehensive evaluation of the overall adhesion effect of the coating, through the adhesion inspection, you can also check the composition of the coating, especially whether the use of resin is reasonable. However, the process of pulling is complex and must wait for the adhesive to fully cure before it can be tested.
2 Overview and comparison of foreign adhesion test methods
Foreign adhesion test methods are also many, including BSS 7225 (tape binding force test), FED 141D 6301.3 (wet tape binding force after immersion) and ISO 2409 (cross scratch test) are often cited.
2. 1 BSS 7225 tape binding force test
BSS 7225 tape binding force test method is a more comprehensive coating tape binding force test method, widely used in several Boeing material specifications. The test method is divided into 3 types of 5 categories, 3 types are type I dry adhesion, type II. type immersion of water on the slurry cloth wet adhesion, III. immersion method adhesion;
type I dry adhesion: according to the category specified by the specification, select the graphic engraving sample of the cut line, if specified as class 1, there is no need to carve the sample. In accordance with the direction required by the method, the tape is pasted to the test site or the cut wire of the test, and the tape is pressed with the tape's own roller, and then the tape is rolled 2 times on the tape with the roller. Within 1 min of the tape attached to the sample, remove the tape quickly and forcely in the direction of the sample to check if the coating has come off in the subject area.
II. Wet adhesion of the water-soaked upper slurry cloth: a 4 in×4 in, clean, immersed ionized water upper slurry cloth in the test area, covered with clean polyethylene film, sealed with tape. If the above size of the upper slurry cloth cannot be used due to size or shape, use 1 or more 1 in×1 in immersion slurry cloth, the test site is 2 to 4. Keep the upper pulp cloth on the surface of the sample for a specified period of time, and the sample should always be moist during this process. Upon arrival time, move onto the slurry cloth and dry the surface of the sample with a clean upper slurry cloth. Follow the steps of dry adhesion.
III. Type immersion method adhesion: all or part of the sample immersed in deionized water, retain the specified time, after the arrival time, take out the sample, dry the sample surface with a clean upper slurry cloth. Follow the steps of dry adhesion.
Results Rating: The results are rated according to the peeling of the coating, divided into 10 levels, and the adhesion is reduced in order from level 10 (good) to level 1 (the sample coating is all off). Upon arrival time, remove the sample and dry the sample surface with a soft cloth. Within 1 min removed from the water, draw 2 parallel scratches 1 in apart with the cutting tool to penetrate the coating directly to the metal substrate.
2.2 FED 141D 6301.3 Wet tape binding force after immersion
Test procedure: Immerse the sample in distilled water to maintain 24 h, remove the sample, dry the sample surface with a soft cloth. Within 1 min removed from the water, draw 2 parallel scratches 1 in apart with the cutting tool to penetrate the coating directly to the metal substrate. Immediately attach 1 in wide protective tape, tape crosses parallel scratches, roller roll tape 8 times, quickly remove the tape and check for adhesive damage between the coating or between the coating and the substrate.
2.3 ISO 2409 cross scratch test
The ISO 2409 cross scratch test is equivalent to the GB/T 9286, not detailed here. The method is also referenced by some process specifications, sometimes after the water-resistant medium is soaked, the cross scratch test is carried out.
2.4 Comparative analysis and considerations of foreign test methods
3 methods can be used to examine the adhesion between coatings or between coatings and substrates. BSS 7225 introduces wet slurry and water-resistant adhesion tests, especially wet slurry fabrics, which are widely used. Fed141D 6301.3 is similar to the BSS 7225 Class III. Type 2 test, but it specifies that the time the sample is held in water is 24 h. The tape used in the ISO 2409 is transparent pressure-sensitive tape with a width of at least 50 mm. The BSS 7225 identifies 3M's 250-degree tape, which also meets the requirements for FED 141D 6301.3 tape. Compared with the domestic test method, a scratch test covering wet slurry or water resistance is introduced.
Notes: 1) Cutting tools to maintain a sharp state, when the cutting edge wear, should be re-polished or replaced; ) When carving with cutting tools, pay attention to a cut to the base, can not be re-cut, if necessary, replace the test site;
3 Adhesion factors
there are many factors that affect adhesion, and according to the suction thesis, the adhesion strength is due to the binding of the polar group of polymers (e.g. carpentry, hydroxyl) in the coating film to the polar group of the surface of the coating. Therefore, any factor that reduces this polar binding will result in a reduction in coating adhesion.
1) The cleanliness of the coating surface can affect the quality of adhesion. For example, when the surface of the coating has oil stains, moisture and other pollutants, will lead to a decrease in adhesion, should try to avoid the sample surface pollution, and should be carefully examined before testing, with appropriate solvents or a clean soft cloth will be cleaned of the test surface.
2) the flatness of the coating surface. When using tape adhesion, the coating surface is smooth, the tape can be well pasted on the coating surface, when peeling can truly reflect the adhesion of the coating;
3) the thickness of the coating. The adhesion test of the coating must be carried out at the specified thickness, and even if the coating of the same type of product, due to the different thickness of the coating, different levels of adhesion test results will be obtained.
4) substrate type and surface treatment is also an important factor affecting adhesion. The same paint is in