JP2013117415A - Coating degradation detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable earlier detection of degradation of coating such as heavy-duty coating, etc.SOLUTION: A coating degradation detection method includes a step S101 of setting temperature (heating temperature) when an endothermic peak appears through a well-known differential scanning thermal analysis, as an initial value. Describing in more detail, the differential scanning thermal analysis is used to measure a temperature change of heat flow at an initial coating time of a measuring object. The heat flow is equivalent to a difference in temperature between a measuring object material and a reference material in the differential scanning thermal analysis. In the measured temperature change of heat flow, the endothermic peak appears. During this time, the endothermic peak is detected in a range of temperature lower than a glass-transition temperature of coating film (material constituting the coating film), and the temperature when the endothermic peak appears is set as the initial value.

Description

  The present invention relates to a coating film deterioration detection method for detecting deterioration of a coating film such as a heavy anticorrosion coating film.

  In recent years, in order to solve global environmental problems, strict environmental performance has been demanded for paints used for extending the life of structures and the like and for aesthetics. Against this background, heavy-duty anticorrosive paints that have been multilayered and formed thicker have been used for steel towers and bridge installations. These heavy anticorrosion paints, regardless of whether they are solvent-based, weak solvent-based, or water-based, have good adhesion to iron bases and are excellent in corrosion resistance and rust prevention.

  In such a heavy anticorrosion coating, it is sufficient that it can be used permanently, but in reality, there is a lifetime of each coating film. The life of the coating film is determined by the deterioration of the coating film. However, there was no way to know in advance when the coating film would deteriorate. A method for objectively and quantitatively evaluating and judging whether or not an appropriate repainting time has been reached has not been established.

  For this reason, in reality, deterioration of the heavy anticorrosive coating film is determined by visually detecting cracks, peeling, swelling, whitening, and the like. Also, “JIS.K5600-5-6: 1999. General test methods for paints—Part 5: Mechanical properties of coating film—Section 6: Adhesion (cross-cut method)” and “JISK5600-5-7 adhesion” The deterioration of the heavy anticorrosive coating film is determined by measuring the mechanical properties such as adhesion force by the method defined in “Performance (pull-off method)” (see Non-Patent Document 1).

JIS standard JIS K 5600-5-7, 1999.

  However, the deterioration determination of the heavy anticorrosion coating film described above is a method of detecting deterioration after the deterioration has already occurred, and the deterioration is determined for the first time in a state where the deterioration has greatly progressed. In this way, in a state where the deterioration has greatly progressed, it leads to an increase in the cost of repair and repair, and damage is accumulated on the base and the structure itself, making it difficult to completely regenerate, and replacing the steel material newly It had fundamental problems such as becoming.

  The present invention has been made to solve the above-described problems, and an object thereof is to detect deterioration of a coating film such as a heavy anticorrosion coating film at an earlier stage.

  The coating film deterioration detection method according to the present invention is a temperature at which an endothermic peak appears in a temperature range lower than the glass transition temperature of the coating film in the initial temperature change of the coating film to be measured by differential scanning calorimetry. The glass transition of the coating film in the first step with the initial value and the temperature change of the heat flow rate of the coating film to be measured by differential scanning calorimetry after performing differential scanning calorimetry to obtain the initial value A second step in which a temperature at which an endothermic peak appears in a temperature range lower than the temperature is set as a determination value; and a third step in which a deterioration state of the coating film is determined by comparing the initial value with the determination value.

  In the coating film deterioration detection method, in the third step, a state in which the change amount of the determination value with respect to the initial value exceeds the set reference value may be determined as coating film deterioration.

  As described above, according to the present invention, it is possible to obtain an excellent effect that the deterioration of a coating film such as a heavy anticorrosion coating film can be detected at an earlier stage.

FIG. 1 is a flowchart for explaining a coating film deterioration detection method according to an embodiment of the present invention. FIG. 2 is a characteristic diagram showing endothermic peaks that appear in the results of differential scanning calorimetry. FIG. 3 is an explanatory diagram for explaining a mechanism of enthalpy relaxation. FIG. 4 is a characteristic diagram illustrating a state in which the appearance temperature of the endothermic peak appearing in the differential scanning calorimetry analysis changes corresponding to the deterioration.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart for explaining a coating film deterioration detection method according to an embodiment of the present invention. In this coating film deterioration detection method, first, in step S101, a temperature at which an endothermic peak appears (heating temperature) is set as an initial value by well-known differential scanning calorimetry. More specifically, the temperature change of the heat flow at the initial stage of the coating film to be measured is measured by differential scanning calorimetry. The heat flow rate corresponds to the temperature difference between the measurement target substance and the reference substance in the differential scanning calorimetry. An endothermic peak appears in the temperature change of the measured heat flow rate. Among these, an endothermic peak is detected in a temperature range lower than the glass transition temperature of the coating film (material constituting the coating film), and the temperature at which this endothermic peak appears is taken as the initial value.

  Next, in step S102, the temperature change of the heat flow rate of the coating film to be measured is measured by the same differential scanning calorimetry analysis after the differential scanning calorimetry analysis for obtaining the initial value, and the measured heat flow rate is measured. The temperature at which an endothermic peak appears in the temperature range lower than the glass transition temperature of the coating film is defined as the judgment value.

  In the differential scanning calorimetry described above, for example, a part of the target coating film is peeled off, a 10 mg test piece is cut out from the part of the peeled coating film, and the cut out test piece is set as a target for the differential scanning calorimetry analysis. That's fine. In differential scanning calorimetry, a commercially available differential scanning calorimeter is used, and the temperature is raised from 0 ° C. to 100 ° C. at 2 ° C./min. From the glass state of the coating film (test piece) to be measured to the rubber state. It is only necessary to measure changes in the heat generation amount and endothermic amount from the test piece in a wide temperature range and detect the endothermic peak appearance position from the measurement result. As the differential scanning calorimeter, for example, DSC2910 model manufactured by TA Instruments can be used.

  As described above, when the determination value is detected at the stage of determining deterioration, the deterioration state of the coating film is determined by comparing the detected determination value with the initial value in step S103. The appearance temperature of the endothermic peak described above becomes a high temperature with the deterioration of the coating film. For this reason, it is possible to determine (determine) the deterioration of the coating film (resin) by increasing the temperature at which the endothermic peak appears. For example, the relationship between the progress of coating deterioration and the change in the temperature at which the endothermic peak appears is obtained in advance through experiments, etc., and the range of change relative to the initial value of the temperature at which the endothermic peak appears in a state that is judged to be degraded is specified. Just keep it. If the determination value changes beyond the specified change range with respect to the initial value, it can be determined that the deterioration has occurred.

  Next, an endothermic peak appearing in a temperature range lower than the glass transition temperature in the differential scanning calorimetry will be described in more detail. As an example, the endothermic peak detected by differential scanning calorimetry in a heavy-duty anticorrosive coating in which the undercoat and the intermediate coat are composed of a water-based epoxy resin and the topcoat is composed of a water-based urethane resin will be described. The undercoat film thickness is 50 μm, the intermediate coat film thickness is 50 μm, and the overcoat film thickness is 50 μm. A part of this heavy anticorrosion coating film is peeled off, and about 10 mg of a test piece is cut out from the part of the peeled coating film. Make sure that the cut out test specimen contains all of the top coat, intermediate coat, and undercoat.

  This test piece is attached to a differential scanning calorimeter and differential scanning calorimetry is performed. The measurement conditions are such that the heating temperature range is 0 ° C. to 100 ° C., and the rate of temperature rise is 2 ° C./min. Further, nitrogen is introduced into the heating atmosphere at 30 ml / min. By this measurement, as shown in FIG. 2, an endothermic peak exhibiting enthalpy relaxation appears in the vicinity of a certain temperature in a temperature range lower than the glass transition temperature of the coating film serving as a sample.

  As a result of the inventors' diligent research and examination, it has been found for the first time that the change in the temperature at which the endothermic peak appears correlates with the deterioration of the coating film to be measured. In terms of thermodynamics, the deterioration of the coating film is spontaneously applied when it is kept for a long time at a temperature in a glass state of about room temperature (20 to 25 ° C.), or when exposed to a harsh environment. The inventors have found that the heat capacity of the film itself is reduced and that the free volume (specific volume) is also reduced.

  What has been described above corresponds to the fact that structural relaxation of the glass state occurs and the molecular structure of the glass state changes. If the coating film in which this structural relaxation occurs is heated, in order to make up for the heat capacity that has been reduced by relaxation during the glass transition from the glass state to the rubber state at the glass state or glass transition temperature (Tg), Requires more heat energy than a non-degraded coating. This extra thermal energy appears as an endothermic peak in differential scanning calorimetry. Therefore, the state in which the endothermic peak appears corresponds to the degree of structural relaxation described above, and the increase in the temperature at which the endothermic peak appears is the degree of deterioration of the coating film due to exposure to a long time or environment. It becomes a standard.

  As shown in FIG. 3, the structural relaxation described above includes the first coupling portion 301 and the sixth coupling portion 302 existing at both ends of the six bonds of —O—C—C—C—O— in the epoxy resin. Is a relaxation phenomenon that occurs as a result of free rotation about the rotation axis. This rotation does not affect any other coupling part other than the coupling part. Therefore, even in the glass state, this relaxation occurs due to the thermal energy of the temperature. A large relaxation phenomenon that changes from a glass state to a rubber state is well known as a glass transition. The structural relaxation due to glass transition occurs in the region where the heat flow near 50 ° C. is reduced in FIG.

  Here, when the elapsed time of the coating film increases, the polymer constituting the coating film gradually reaches a thermodynamically stable equilibrium state, so that the molecular chains of the polymers approach each other, and as a result, Free volume will decrease. When the free volume decreases, the aforementioned rotational movement around the molecular chain axis becomes difficult to occur. For this reason, the temperature causing structural relaxation, that is, enthalpy relaxation, is shifted to a higher temperature side in search of higher thermal energy. In other words, the temperature at which the enthalpy relaxation occurs due to an increase in the age of the coating film increases to the high temperature side.

  For example, when the temperature showing the peak of enthalpy relaxation of the initial coating film (hereinafter referred to as enthalpy relaxation temperature) is 25 ° C., it shifts to 30 ° C., 35 ° C., 40 ° C. and the higher temperature side as the elapsed time increases. To do. Eventually, the enthalpy relaxation temperature that rises over time tends to approach a certain temperature.

  Such a phenomenon of shifting the enthalpy relaxation temperature to the high temperature side represents a change in the environment surrounding the molecular chain. As the number of years increases, molecular chains aggregate and try to approach a thermodynamic stable equilibrium state. Thus, the state of the molecular chains in the initial stage of the coating film (resin) having elasticity or viscosity before aggregation is a pseudo-equilibrium state, and tends to approach the most stable equilibrium state over time.

  Along with this aggregation, the elasticity and viscosity of the coating film, which is a polymer, disappears and exhibits embrittlement. Various deterioration symptoms appear due to this embrittlement. One of deterioration phenomena due to embrittlement is cracking. Due to embrittlement, ductility is lost and cracks occur. Also, the internal stress becomes larger than the initial state. When the internal stress increases, an extra load is applied to the coating film, resulting in a decrease in adhesion with the substrate. Decrease in adhesion causes peeling. As described above, when cracking or peeling occurs, the steel material on which the coating film is formed is easily affected by external moisture, steam, temperature, and suspended particles, and rust and corrosion easily occur. become.

  As explained above, there is a correlation between the enthalpy relaxation temperature (endothermic peak) and the state of deterioration of the coating film, so it is possible to detect deterioration in advance by capturing changes in the enthalpy relaxation temperature (a phenomenon that shifts to the high temperature side). Can be estimated. For example, when the asymptotic temperature is 50 ° C., it is possible to take specific measures such as repainting when the enthalpy relaxation temperature approaches 50 ° C. On the other hand, when the temperature difference up to the asymptotic temperature is sufficiently large as in the case where the enthalpy relaxation temperature is 30 ° C., it can be determined that there is no need for repainting. In addition, if the relationship between the progress of coating deterioration and the increase in enthalpy relaxation temperature is known in advance through experiments, it is possible to predict when and when the measured enthalpy relaxation temperature will be 50 ° C. is there.

  This will be described in more detail below using examples.

[Example 1]
In the following, a heavy anticorrosive coating film in which the undercoat and the intermediate coat are composed of a water-based epoxy resin and the topcoat is composed of a water-based urethane resin is targeted. The undercoat film thickness is 50 μm, the intermediate coat film thickness is 50 μm, and the overcoat film thickness is 50 μm. A heat cycle is applied to this heavy anticorrosive coating film under an artificial accelerated deterioration environment. For example, using a constant temperature and humidity chamber, a heat cycle (1 cycle 12 hours) from -30 ° C. to 70 ° C. is repeated up to 100 cycles at a relative humidity of 90%.

  As described above, a part of the heavy anticorrosion coating film artificially deteriorated is peeled off, and 10 mg of a test piece is cut out from the part of the peeled coating film. Make sure that the cut out test specimen contains all of the top coat, intermediate coat, and undercoat. In addition, the 1st test piece cut out from the heavy-duty anticorrosion coating film of the initial state which is not artificially degrading, the 2nd test piece cut out from the heavy-duty anticorrosion coating film made into 25 cycles, and the heavy-duty corrosion prevention made into 50 cycles A third test piece cut out from the coating film, a fourth test piece cut out from the heavy anticorrosion coating film having 75 cycles, and a fifth test piece cut out from the heavy anticorrosion coating film having 100 cycles were prepared.

  In the measurement, these test pieces are mounted on a differential scanning calorimeter to perform differential scanning calorimetry. The measurement conditions are such that the heating temperature range is 0 ° C. to 100 ° C., and the rate of temperature rise is 2 ° C./min. Further, nitrogen is introduced into the heating atmosphere at 30 ml / min. The number of measurements is one. Thus, the temperature change of the heat flow rate is measured by differential scanning calorimetry, and the temperature at which the endothermic peak appears in a temperature range lower than the glass transition temperature of the heavy anticorrosive coating film is obtained.

  As a result of the measurement of each test piece, as shown in FIG. 4, the endothermic peak that is the enthalpy relaxation temperature is shifted to the high temperature side as time passes. The enthalpy relaxation peak temperature is about 25 ° C. for the first test piece with heat cycle 0, about 32 ° C. for the second test piece with 25 heat cycles, about 42 ° C. with the third test piece with 30 heat cycles, and heat cycle 70 It was about 48 degreeC in the 4th test piece of time, and was about 49 degreeC in the 5th test piece of 100 heat cycles.

  This shift of the appearance temperature of the endothermic peak to the high temperature side represents a change in the environment surrounding the coating film (molecular chain), and the molecular chains aggregate over time, resulting in a thermodynamically stable equilibrium state. Try to get closer to.

  Here, Table 1 shows actual measurement data showing the relationship between the deterioration state of the coating film and the temperature at which the endothermic peak appears. Table 1 shows the number of heat cycles, the adhesive force, and the temperature at which the endothermic peak appears for coatings that are undercoat / intermediate epoxy coatings and topcoating urethane coatings.

  As shown in Table 1, when the number of heat cycles is zero, the adhesive force is sufficient at 4.3 MPa, and at this time, the temperature at which the endothermic peak appears is 25 ° C. Next, at a heat cycle number of 25, the adhesive force decreased to 2,1 MPa, and the endothermic peak temperature shifted to 32 ° C. and the high temperature side. When the number of heat cycles is further increased, the number of times is 50, 70, and 100, and the endothermic peak temperatures are shifted to 42 ° C, 48 ° C, and 49 ° C to the higher temperature side. In this case, the adhesive force, which is an index representing the deterioration of the coating film, is 1.5 MPa, 0.8 MPa, and 0.7 MPa, and further decreases.

  From the results of Table 1 above, it can be found that the temperature at which the endothermic peak appears is close to 50 ° C. It can be seen that the state one step before approaching this temperature, that is, the state where the appearance temperature of the endothermic peak is around 40 ° C. is 50 heat cycles. It is possible to know that the molecular chain aggregates as the internal structure of the coating film one step before this, the elasticity and viscosity possessed up to this point disappear, and the embrittlement proceeds.

  As described above, the appearance temperature of the endothermic peak rises, for example, by capturing the approach to 40 ° C. one step before the asymptotic temperature 50 ° C., the state of coating film deterioration can be estimated in advance, At this time, a specific restoration operation such as repainting can be performed. In addition, by periodically measuring, for example, once a year, it is possible to extrapolate the time and time when the endothermic peak appearance temperature rises beyond the reference value.

  As described above, according to the present invention, a coating film made of heavy anticorrosion paint that has been treated for the purpose of anticorrosion and rust prevention of outdoor iron and galvanized steel pipe facilities such as steel towers and bridge installation facilities has been conventionally used. It is possible to detect the deterioration of the coating film at an early stage by detecting a change in the coating film molecular structure peculiar to the deterioration of the coating film for the coating film whose deterioration is difficult to judge and judge.

  In the case of heavy anticorrosion coatings, repairs and repairs are costly when the deterioration is large, and it may become difficult to completely regenerate by accumulating damage to the substrate and the structure itself. It was a situation to change the steel material. On the other hand, according to the present invention, as described above, it is possible to know the deterioration of the coating film at an early stage, and it is possible to prevent wasteful costs and the like, and to perform effective maintenance management adapted to the deterioration state of the equipment. Become.

  The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious.

Claims (2)

A first step in which the temperature at which an endothermic peak appears in a temperature range lower than the glass transition temperature of the coating film in the initial temperature change of the coating film to be measured by differential scanning calorimetry is an initial value;
In the temperature change of the heat flow rate of the coating film to be measured by differential scanning calorimetry after performing differential scanning calorimetry to obtain the initial value, an endothermic peak in a temperature range lower than the glass transition temperature of the coating film A second step in which the temperature at which the
A coating film deterioration detection method comprising: a third step of determining a deterioration state of the coating film by comparing the initial value and the determination value. In the coating-film degradation detection method of Claim 1,
In the third step, the coating film deterioration detection method is characterized in that a state in which a change amount of the determination value with respect to the initial value exceeds a set reference value is determined as deterioration of the coating film.

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