JPS5925969B2 - Paint film stepping stone test method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a stone flying test method for paint films.

When driving a car, stones on the road bounce off the car body, causing scratches on the car body paint.

For this reason, countermeasures have been taken in the past by reproducing the phenomenon of stones being hit and examining the strength of the paint film against flying stones. An example of such a test method is the coating film flying stone test method shown in FIG. 1, which is known as the Grabero test method. This test method experimentally reproduces the phenomenon of a stone hitting a paint film, and uses jaggery or crushed stones that vary in size and shape to correspond to stepping stones. When actually conducting the test, the sample stage 4 in the testing machine is used as shown in Figure 1.
The guide 6 is compressed by the compressed air introduced from the air intake port 3, which compresses the stepping stones 2 toward the test piece 1 placed at a predetermined position.
Spray through. The performance of the coating film is usually evaluated using the following A.
, B. Method A measures the size, number, and depth of the tumor, and method B measures the tumor approximately by comparing it with a standard map.This method is standardized (SAEJ400), but In such conventional paint film stepping stone testing methods, there are large variations in the size and shape of the stepping stones.

Furthermore, since a large amount of stones are sprayed, there are collisions and rebounds between the stones. For this reason, it is necessary to surround the sample stage with a protective wall 5 as shown in FIG. In addition, the resulting scratches range from large gouges to the base to scratches that are just scratches.
There are large variations in shape and size, and performance evaluation is mostly based on visual judgment, making quantitative evaluation difficult. cannot be reproduced. Therefore, it is only possible to evaluate ulcers caused by large stones. On the other hand, due to the recent improvements in paved roads and the accompanying improvements in transportation efficiency, the trend toward faster travel speeds is gradually increasing.

In a car traveling at high speed on a paved road under such conditions,
While relatively large stones such as jiyaris no longer hit the car body like a car driving on an unpaved road, on the other hand, small stones scattered on the road surface hit at high speed and cause ulcers on the paint film, but these scratches , the size and shape of the scratches are completely different from those in the case of being hit by a large stone as described above. The conventional stone flying test method for paint films has a problem in that it is impossible to evaluate cases where fine stones hit at high speeds. Under these current circumstances, the inventors of the present invention have conducted various studies to develop a coating film stepping stone test method that can evaluate coating films against such high-speed fine stones. By spraying this diamond onto a test object, it is possible to evaluate the strength of a coating film when it is hit by a fine stone at high speed, and the present invention has been achieved.

Therefore, the present invention has been made in view of the above-mentioned problem, and is made by blowing off diamond grains with compressed air and guiding the blown diamond grains through a guide so that they collide only with the undamaged skewer portion of the test piece. The purpose is to solve the above problem.

In the method of the present invention, diamond particles are used as stepping stones.
Preferably, it is within the range of .

The reason for this is that if it is smaller than 0.01f, it will be difficult for the coating film of the test piece to be coated, and if it is larger than 0.05V, almost all the dirt will reach the base, which is not practical and undesirable. The present invention will be explained below with reference to the drawings.

When performing a stone flying test on a coating film according to the method of the present invention, as shown in FIG. , air at a predetermined pressure is introduced from the compressed air intake port 3, and the tip 2a is blown onto the sample 1.

The inclination angle α of the facing sample stage can be changed to 30 degrees, 4 degrees, and 60 degrees. The evaluation is indicated by the limit pressure at which the scratches reach the base of the painted board when the air pressure is changed stepwise up to a maximum of 5k9/01ii (3 to 5 kg/CTIi is the appropriate pressure range). The speed of the diamond grains at this time can be measured by a speed detector. Next, the invention will be explained with reference to examples.

EXAMPLE Using the apparatus shown in FIG. 2, a coating film test was carried out on a sample set at an inclination angle of 30 mm using a 0.01 ton diamond as a stepping stone.

However, as the guide 6, a pipe guide with a length of 1 m and an inner diameter of 4 mm was used. The test was carried out by blowing diamond onto the sample using compressed air of 1 to 5k9/(V7f) for sample test pieces 1 to 3 of each coating thickness shown in Figure 3.The results of the performance evaluation are shown in Figure 3. The impact evaluation shows the stone chip resistance performance at the critical pressure at which the scratch reaches the substrate, that is, the air pressure at which the scratch reaches the steel plate is evaluated, and the judgment is made based on the layer that is dominant at each air pressure. .For comparison, a stone flying test of the paint film was conducted using the following method.

Reference example 1: Using the conventional device shown in Figure 1, the following conditions were met: (1) Stepping stones: No. 6 crushed stone 5007 Pressure: 2.5k9/ml (2) Stepping stones: No. 9 crushed stone (marble) 5007 Pressure: 5k
9/? A stone flying test of the paint film was conducted using the gravel test.

After making scratches, the various types of gulls were observed under a microscope, and their performance was judged based on the depth and shape of the gulls. Reference example 2:1.5
Two types of arrowheads, Nos. 7 and 57, were dropped from a height of 1 m onto the test specimen 1 tilted at 4 f.

When this test piece was observed, it was found that the same sag as in the Grobera test had occurred in the paint film, which was different from the sludge that occurs on a vehicle driven on a highway. Reference example 3: The arrowhead of reference example 2 was heated to 4f with compressed air in the same way as in the example.
The sample was sprayed horizontally onto a test piece that was tilted, but the results were the same as in Reference Example 2.

Reference example 4: Diameter 0. im, 0.2mm, 0.3mm, 0.4mm,
Five types of 0.5 mm steel balls were blown horizontally onto a test piece tilted with compressed air at a maximum of 5k9A.
? However, the scratches that appeared on the paint film of the test piece were different from the scratches that appear on the paint film of cars traveling on highways.

In the conventional test method, there was a large variation in shape and size, and the shape was different from that of the actual car paint film, whereas the paint film obtained by the method of the present invention has a large variation in shape and size. Are the scratches almost the same as those caused by cars actually driving on the highway? It was reproduced with less variation.

In addition, Fig. 3 shows coating film thicknesses of 125 to 130 μm and 80 to 8 μm.
This shows the results of testing three types of test specimens 1 to 3 of 5 μ and 105 to 110 μ by changing the pressure when spraying diamond grains. As you increase the speed, you can see that the diamond grains reach deeper layers, such as the middle coat than the top coat, the base coat than the middle coat, and the iron base coat than the base coat.

From this result, as shown in the far right column, for example, as shown in the far right column, by repeating the test 10 times, it is possible to show the stone chipping resistance performance at the maximum air pressure, where scratches do not reach the intermediate coating even with only the top coat. This makes it easier to quantify the performance compared to conventional methods, and allows the user to freely reproduce scratches that occur when driving an actual car with high precision.Also, since the number of stepping stones is small and single, it is possible to easily quantify the evaluation location and the evaluation part of the sample. At the same time, you can freely choose. This method is completely noiseless and extremely useful. With this invention, does a real car suffer on the highway like this? It seems that the reason why it turns into hot water in the same way is as follows. Actual car paint films are composed of polymer compounds and generally have viscoelastic properties. Since the scratches caused by chipping on the paint film exhibit a brittle fracture pattern similar to that of a glass fracture surface, the paint film seems to exhibit elastic behavior, and the movement of the colliding object in an extremely short period of time is considered to be elastic. It can be said that it receives energy. In other words, it can be assumed that the chipping is caused by an object hitting the object at high speed. Furthermore, since one side of the chipping scratch has a steep slope and the other side has a gentle slope, it seems that an object with an edge is hitting the paint film as if scooping it out like a spoon. By the way, the disadvantage of the test method of the present invention is that since the diamond grains are blown away with compressed air, they can be caused to collide with the test piece at high speed, that is, with the same speed or impact force as a stone hitting a car traveling on a highway. The diamond must be harder than a stone on the road and have edges, and when the diamond grains are guided by the guide, they hit the wall of the guide and are given a rotational force, causing the specimen to rotate. It is thought that upon collision, the edges of the diamond grains behave as if they are scooping up the paint film, creating the same separation as the chipping hot water that occurs on highways. It is also possible to spray two or more diamonds onto the test piece at the same time, but if the diamonds hit the same spot, the scratches will become deeper and accuracy may be lost, so don't spray too many diamonds at the same time. I don't like it.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the conventional stone-flying stone test method for paint films, FIG. 2 is an explanatory diagram of the stone-flying test method for paint films of the present invention, and FIG. 3 is a graph showing the results of stone-flying resistance performance evaluation. 1... Sample, 2... Chip material (crushed stone), 2a...
Chip material (diamond), 3--pressure air intake, 4--sample stand, 5--protective wall, 6--guide,
7...Speed detector.

Claims (1)

[Claims] 1. A flying stone test method for paint films, which is characterized by blowing away diamond particles with compressed air and guiding the blown diamond particles through a guide so that they collide only with undamaged portions of a test piece.