JPH042901B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a test method for evaluating the durability of painted metal products. When painted metal products used as exterior panels for automobiles, construction materials, home appliances, etc. are used outdoors in natural environments, their surfaces gradually deteriorate.
If the corrosion of the base metal for painting progresses, the value as a product will no longer be met. Outdoor exposure tests, sunshine weather meter tests, dual cycle weather meter tests, combined cycle tests, etc. have traditionally been used to predict the lifespan of painted metal products and evaluate the durability of paint films. It is being said. However, outdoor exposure tests require a long period of time to evaluate the durability of the product due to the high protective effect of the coating itself. In addition, in other conventional test methods, the degree of deterioration of the test piece is determined by visual observation and optical or spectroscopic methods, so it is difficult to determine the extent to which corrosion of the underlying metal has progressed. It has drawbacks that cannot be evaluated. On the other hand, if painted metal products are measured using an electrochemical measurement method, it is possible to quantitatively evaluate the degree of corrosion at the interface between the paint film and the underlying metal, which is difficult to judge from the degree of external deterioration alone. be. However, such measurements are generally very difficult because the coating has a high resistance. From this viewpoint, the present invention adds improvements that could not be made using conventional test methods in order to evaluate the durability of painted metal products. That is, according to the present invention, a painted metal test piece mounted on a holder is rotated to separate the test piece into a liquid phase part made of a corrosive solution and a gas phase part made of air, an inert gas, or a corrosive gas. The test piece and the liquid phase are brought into contact with each other sequentially and repeatedly, and during contact with the gas phase, the test piece is irradiated with ultraviolet rays to accelerate the deterioration of the test piece. Provided is a durability evaluation test method for coated metal products, which is characterized by electrochemically measuring changes in current value or polarization curves between coated metal products. According to the present invention, accelerated deterioration and electrochemical measurement of painted metal test pieces can be performed continuously in one device, and the deterioration behavior and degree of corrosion of the test piece can be continuously and It can be evaluated quantitatively. Next, an outline of the present invention will be explained with reference to the drawings. FIG. 1 shows a test device main body container used in the present invention, which is preferably made of glass or Teflon resin to prevent deterioration of the container itself, but may also be made of acrylic resin. Further, the size of the container can be designed in various ways depending on the size of the coated metal test piece to be used. A lid 2 is attached to the container 1 and can be removed when installing a test piece and taking out and putting in a test solution. 3 is a painted metal test piece holder which will be described later, and container 1
The holder itself can be rotated at any constant rotational speed while maintaining an airtight interior. 4 is a partition plate that separates the gas phase part and the liquid phase part in the container, so that the ultraviolet rays irradiated from the ultraviolet lamp described later hit only the part of the coated metal test piece in the gas phase part in the container. It also serves as a shielding board.
The liquid phase portion of the container 1 is provided with insertion ports for a reference electrode 8 made of a Luggin capillary, a counter electrode 9, a temperature regulator 10, a temperature control heater 11, and the like. Reference numeral 5 denotes an ultraviolet lamp for photodeterioration of painted metal test pieces, and the lamp is inserted into the gas phase portion of the container 1 through the insertion opening of the lid 2. In order to prevent the ultraviolet lamp from heating, it may be installed outside the container 1 and irradiate the coated metal test piece inside the test chamber with ultraviolet light through a quartz glass plate. 6 and 6' are pipes for introducing corrosive gas into the gas phase inside the container, and oxygen, air, inert gas, sulfur dioxide gas, etc. can be introduced depending on the type of corrosion accelerating factor in the gas phase. do. Further, if necessary, pipes 7 and 7' for introducing the above gas into the test solution may be provided. FIG. 2 is an explanatory cross-sectional view of a painted metal test holder, in which the test piece is shielded from the solution and gas phase except for a certain exposed surface, and this exposed surface is used as a test electrode for electrochemical measurements. To prevent the solution from entering the holder, the holder is preferably made of Teflon resin, which has strong water repellency. The rotary shaft 21 of the holder is hollow, and a lead wire 22 is inserted thereinto which uses a painted metal test piece as an electrode and connects it to an external measuring device for electrochemical measurement. The holder is installed in the container shown in FIG. 1, and part of the exposed surface of the test piece 20 is in contact with the gas phase side, and the other part is in contact with the solution. The holder is rotated by an external power transmission mechanism through a rotating shaft, which subjects the coated metal specimen to wet/dry cycles, heat cycles, ultraviolet irradiation cycles, corrosive environment cycles, etc. These cycles can be set in various ways depending on the test conditions for accelerating deterioration. FIG. 3 is an explanatory diagram of various holders, and holder A shown in FIG. a is a holder suitable for measuring one coated metal test piece. When measuring multiple test pieces in parallel, set multiple holders A in the test equipment container, or set one holder A to each holder B to C shown in Figures b and c.
It is also possible to have a structure in which one holder has a plurality of exposed parts. In the case of holder B or C, set the test piece and lead wire in each, and
It has switching contacts so that only the test piece immersed in the solution is electrically connected to the external measuring device. Next, examples of the present invention will be described. A Teflon resin holder that can be rotated at a constant speed by an external drive power source is inserted into an acrylic resin container with a width of 150 mm, depth of 100 mm, and height of 120 mm (all inner dimensions). A painted metal test piece is attached to this holder through an opening with a diameter of 30 mm so that it comes into contact with the test liquid (liquid phase) and gas phase inside the test device.
The lead wire was led from the back side of the test piece to the outside of the test equipment container through the rotating shaft of the holder. In addition, a pen-shaped ultraviolet lamp with a wavelength of 253.7 mm and a light emitting part with a diameter of 5 mm and a length of 22 mm was installed in the gas phase inside the test equipment container. 0.049M NaCl in the test equipment container
A mixed solution of 0.001 mol HCl was poured into the exposed surface of the painted metal test piece so as to cover the lower half of the exposed surface, heated with a heater, and the temperature was controlled at 50°C with a mercury regulator. In addition, in order to keep the liquid level of the test liquid constant and to shield the exposed surface of the coated metal test piece on the test liquid side from ultraviolet rays, an acrylic resin plate was attached in contact with the test liquid surface. A silver-silver chloride reference electrode with a Luggin capillary for electrochemical measurements and a gold counter electrode were inserted into the test solution and connected to a potentiometer along with leads from the painted metal specimen. In addition, air was introduced into the gas phase side inside the test device container. Under the above test conditions, the coated metal test piece shown in Table 1 was mounted on a Teflon resin holder, and while the holder was rotated at a speed of 42.4 minutes/time, the potential of the test piece was adjusted using a potentiometer to adjust the potential of the test piece to the silver-silver chloride electrode. The change in current value when held at +0.5V as a standard was recorded on a recorder. In addition, the polarization curve and analytical resistance value in a potential range of -1.0 V to +0.5 V based on a silver-silver chloride electrode were measured as appropriate.

【table】

[Table] As a result, even in a coated metal test piece with an initial polarization resistance of 10 ⁹ Ωcm ² and high insulation resistance, the polarization current of +0.5V rose sharply several hundred hours after the start of the test, and the subsequent polarization resistance decreased. It showed a low value of 10 ⁵ to 10 ⁶ Ωcm ² . Furthermore, it was found that there was agreement between the current rise time and the polarization resistance value of the initial coated metal test piece in terms of corrosion resistance, and it became clear that this can be used as a measure of the corrosion resistance of the test piece. In addition, chalking on the exposed surface and local blistering of the coating film were observed on the test piece after the polarization current was applied, indicating a highly accelerated deterioration behavior. As described above, according to the present invention, by setting the operating conditions of the test device to appropriate conditions, the deterioration acceleration rate is extremely high, and various electrochemical characteristics can be continuously tracked over time. It is possible to obtain a test method for evaluating the durability of painted metal products. The advantages of the invention are as follows. (1) By electrochemically measuring the corrosion behavior at the interface between the coating film and the underlying metal (potential or constant current polarization measurement, immersion potential measurement, polarization resistance measurement, impedance measurement, etc.), spectroscopic measurement can It is possible to directly evaluate the durability of painted metal test pieces that cannot be determined. (2) Electrochemical measurements are very easy to measure because they handle electrical signals such as voltage and current. (3) Since changes over time in electrochemical characteristic values associated with deterioration of painted metal products can be measured continuously and with high precision, the deterioration behavior of test pieces can be easily tracked. (4) By electrochemically polarizing the test piece,
Can provide a corrosion-promoting effect. (5) Wetting/drying cycles, thermal cycles, and heat cycles applied by rotating the specimen holder in various deterioration accelerating environments set within the test equipment.
By combining UV irradiation cycles, etc., it is possible to realize a form of deterioration that is close to the actual environment due to various deterioration accelerating factors of painted metal products. Furthermore, these cycles are variable and very easy to control. (6) The size of the painted metal test piece used is a few tens of millimeters square, and the equipment itself is small and inexpensive.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a test apparatus used in an example of the present invention. FIG. 2 is an explanatory cross-sectional view of the painted metal test piece holder. FIGS. 3a to 3c are explanatory diagrams of various holders. Holder A shown in figure a is for a single test piece used in the example, b
Holders B and C shown in Figures and Figures c are for simultaneous measurement of multiple test pieces. 1... Main container, 2... Lid, 3... Painted metal test piece holder, 4... Shielding plate, 5... Ultraviolet lamp, 6 and 6'... Gas inlet and outlet, 7 and 7'... Gas inlet and outlet in test solution. Outlet, 8...Reference electrode, 9...Counter electrode, 10...Temperature control sensor, 11...
Heater, 12... Monitor sensor.

Claims (1)

[Claims] 1 Rotating the painted metal test piece attached to the holder and sequentially and repeatedly bringing the test piece into contact with a liquid phase part made of a corrosive solution and a gas phase part made of air, an inert gas, or a corrosive gas, Upon contact with the gas phase part, the test piece is irradiated with ultraviolet rays to accelerate the deterioration of the test piece, while changing the current value or polarization between the test piece and the liquid phase part. A test method for evaluating the durability of painted metal products, which is characterized by electrochemically measuring a curve.