JP7577459B2 - Method for estimating the useful life of components - Google Patents

Description

The present invention relates to a method for estimating the useful life of a component.

A method is known in which a product is exposed to a high-temperature and high-humidity environment to evaluate the degree of deterioration of the components.
For example, Patent Document 1 discloses a method for evaluating the degree of deterioration of an adhesive by comparing the adhesive strength of an epoxy resin-based adhesive that crosslinks through urethane bonds in an accelerated test for up to 20 days in an environment of 80°C and 85% RH with the peak intensity ratio measured by infrared spectroscopy.

JP 2011-191274 A

As described above, methods for evaluating the degree of deterioration of components are known, but few methods are known that can specifically estimate the useful life of components.
An object of the present invention is to provide a method for estimating the useful life of a component, which is capable of estimating the useful life of a component.

The present invention has the following aspects.
[1] A method for estimating the useful life of a component, comprising the following steps (A) to (F):
Step (A): A step of measuring the degree of deterioration of an actual aged product of the component, and creating a graph (a) in which the degree of deterioration (vertical axis) is plotted against the number of years elapsed (horizontal axis).
Step (B): A step of subjecting the component before actual use to an accelerated deterioration test, measuring the degree of deterioration of the component after the accelerated deterioration test, and creating a graph (b) in which the degree of deterioration (vertical axis) is plotted against the number of test days (horizontal axis) to obtain a deterioration curve.
Step (C): A step of obtaining a graph (c) by superimposing the graph (a) and the graph (b) so that the plot of the graph (a) approximates the deterioration curve.
Step (D): A step of calculating an acceleration factor (α) of the accelerated deterioration test based on the graph (c) from an arbitrary number of years elapsed and the number of test days corresponding to the degree of deterioration at that number of years elapsed, using the following formula (1).
Acceleration factor (α) = any number of years passed / number of test days ... (1)
Step (E): A step of conducting a functional evaluation test on the component after the accelerated deterioration test, and determining the number of test days (β) of the accelerated deterioration test required for the component to lose its function.
Step (F): A step of calculating the service life (γ) of the member using the following formula (2).
Service life (γ) = acceleration factor (α) × number of test days (β) ... (2)
[2] The method for estimating the useful life of a component according to [1] above, wherein the accelerated deterioration test accelerates factors similar to the actual environment of the component, and the factors are one or more selected from the group consisting of ultraviolet light, humidity, temperature, oxygen, acid, alkali, and organic solvents.
[3] The method for estimating a service life of a component according to [2] above, wherein the component has a glass transition point, and the accelerated degradation test is carried out in an environment at or above the glass transition point of the component.
[4] The method for estimating the useful life of a member according to [2] or [3], wherein the accelerated deterioration test is carried out in an environment with a humidity of more than 95% RH and not more than 100% RH.
[5] The method for estimating the useful life of a member according to any one of [2] to [4], wherein the accelerated degradation test is carried out in an environment of more than 100° C.
[6] The method for estimating a useful life of a member according to any one of [2] to [5] above, wherein the accelerated deterioration test is carried out in an aerobic environment.
[7] The method for estimating useful life of a component according to any one of [1] to [6], wherein the number of test days (β) is 5 days or more.
[8] The method for estimating a useful life of a member according to any one of [1] to [7], wherein the member has a glass transition point, and an average temperature of an actual environment of the member is equal to or lower than the glass transition point of the member.
[9] The method for estimating the useful life of a member according to any one of [1] to [8], wherein the functional evaluation test is one or more selected from the group consisting of a combined cycle test, a salt spray test, thickness measurement before and after the accelerated aging test, weight measurement before and after the accelerated aging test, transmittance measurement, and an electrochemical test.
[10] The method for estimating the useful life of a member according to any one of [1] to [9] above, wherein the degree of deterioration is determined by a chemical analysis method.
[11] The method for estimating the useful life of a member according to any one of [1] to [9] above, wherein the degree of deterioration is determined by a mechanical analysis method.
[12] The method for estimating the useful life of a member according to any one of [1] to [9] above, wherein the degree of deterioration is determined by a physical analysis method.
[13] The method for estimating the useful life of a component according to any one of [1] to [12], wherein the component is a coating material.
[14] The method for estimating the useful life of a component according to [13], wherein the coating material is a baked coating film.
[15] The method for estimating the useful life of a member according to [14], wherein the accelerated deterioration test is carried out in an environment below a maximum temperature reached during a baking treatment of the baked coating film.
[16] The method for estimating the useful life of a component according to any one of [13] to [15], wherein the coating material is formed on a surface of a metal, the coating material has rust prevention properties, and the rust area rate after the functional evaluation test is an index of functional loss of the component.
[17] The method for estimating the useful life of a component according to any one of [13] to [15], wherein the coating material is formed on a surface of a metal, the coating material has rust-preventive properties, and the average metal thickness loss of a cross section in a rusted area after the functional evaluation test is used as an index of functional loss of the component.
[18] The method for estimating a useful life of a component according to [16] or [17], wherein the metal is black carbon steel.
[19] The method for estimating a useful life of a member according to any one of [1] to [18], wherein the member contains a thermosetting resin.
[20] The method for estimating a useful life of a member according to any one of [1] to [19] above, wherein the member has a thickness of 5 to 100 μm.
[21] The method for estimating the useful life of a member according to any one of [1] to [20], wherein the useful life (γ) is at least twice the elapsed age of the actual used product.
[22] The method for estimating the useful life of a member according to any one of [1] to [21], wherein the useful life (γ) is 60 years or more.
[23] The method for estimating a useful life of a component according to any one of [1] to [22] above, wherein the deterioration curve is nonlinear.
[24] The method for estimating a useful life of a component according to any one of [1] to [23], wherein the number of test days (β) is in a nonlinear region on the deterioration curve.

The present invention provides a method for estimating the useful life of a component that can estimate the useful life of a component.

FIG. 1A is a schematic diagram of an example of graph (a) in which the degree of deterioration (vertical axis) is plotted against the number of years (horizontal axis) of an actual aged component, and FIG. 1B is a schematic diagram of an example of graph (b) in which the degree of deterioration (vertical axis) is plotted against the number of test days (horizontal axis) of a component after an accelerated deterioration test. FIG. 2 is a schematic diagram showing an example of a graph (c) obtained by superimposing the graph (a) shown in FIG. 1(a) and the graph (b) shown in FIG. 1(b).

The present invention will be described in detail below.
The following embodiments are merely examples for explaining the present invention, and are not intended to limit the present invention to these embodiments. The present invention can be implemented in various forms without departing from the spirit of the present invention.
In the present invention, "actual exposure" refers to exposure in an environment in which a member is used as a product, and "actually exposed aged product" refers to a part that has been used in an actual exposure environment. When estimating a long-term service life in the present invention, the actual exposure period is preferably 3 years or more, more preferably 10 years or more, and even more preferably 20 years or more.

The present invention is a method for estimating the useful life of a component.
The target members include, for example, coating materials. Coating materials are formed on the surfaces of metals such as columns and beams of steel-framed houses. Coating materials include, for example, coating films, film coats, sheet laminates, and the like. Among these, coating films include coating films made of paints used for painting building materials, and in particular, coating films formed on the surfaces of metals such as columns and beams of steel-framed houses are preferred, and examples of coating films with long service lives include baked coating films. The present invention is suitable for specifically estimating the service life of members that are expected to have such long service lives.
When the coating material is formed on the surface of a metal, the metal is preferably carbon steel, more preferably black carbon steel.

The components contained in the member are not particularly limited, and examples thereof include thermosetting resins that are excellent in solvent resistance, heat resistance, and high hardness. Examples of thermosetting resins include epoxy resins, phenolic resins, melamine resins, unsaturated polyester resins, polyimides, crosslinked products of thermoplastic resins, and crosslinked products of elastomers. Among these, epoxy resins are preferred from the viewpoint of excellent durability such as water resistance and chemical resistance, and strength.
The thickness of the member is not particularly limited, but considering the influence of the accelerated deterioration test described below when it is performed in an environment at or above the glass transition point of the member, the thinner the better. Specifically, the thickness is preferably 5 to 100 μm, more preferably 5 to 60 μm, and even more preferably 10 to 40 μm.

The method for estimating the useful life of a component of the present invention includes the following steps (A) to (F).
Step (A): A step of measuring the degree of deterioration of an actual aged product of the component, and creating a graph (a) in which the degree of deterioration (vertical axis) is plotted against the number of years elapsed (horizontal axis).
Step (B): A step of subjecting the component before actual use to an accelerated deterioration test, measuring the degree of deterioration of the component after the accelerated deterioration test, and creating a graph (b) in which the degree of deterioration (vertical axis) is plotted against the number of test days (horizontal axis) to obtain a deterioration curve.
Step (C): A step of obtaining a graph (c) by superimposing the graph (a) and the graph (b) so that the plot of the graph (a) approximates the deterioration curve.
Step (D): A step of calculating an acceleration factor (α) of the accelerated deterioration test based on the graph (c) from an arbitrary number of years elapsed and the number of test days corresponding to the degree of deterioration at that number of years elapsed, using the following formula (1).
Acceleration factor (α) = any number of years passed / number of test days ... (1)
Step (E): A step of conducting a functional evaluation test on the component after the accelerated deterioration test, and determining the number of test days (β) of the accelerated deterioration test required for the component to lose its function.
Step (F): A step of calculating the service life (γ) of the member using the following formula (2).
Service life (γ) = acceleration factor (α) × number of test days (β) ... (2)

<Step (A)>
Step (A) is a step of measuring the degree of deterioration of an actual aged product of the member, and creating a graph (a) in which the degree of deterioration (vertical axis) is plotted against the number of years elapsed (horizontal axis).
When the target component is a coating material formed on the surface of metal such as columns and beams of a steel frame house, the coating material is sampled from a house that has been built for, for example, three years or more, and the degree of deterioration is measured. The number of times and timing of sampling of the coating material are not particularly limited, but it is preferable to sample the coating material a total of three or more times every few years after construction. It is sufficient to periodically sample the coating material until about 30 years have passed since construction, but the number of years for sampling may be extended as necessary. For example, it is preferable to sample the coating material a total of about six times every five years until 30 years have passed since construction.

The actual exposure environment of the member is not particularly limited, but examples thereof include an environment exposed to ultraviolet light, an environment exposed to moisture, an environment affected by temperature, an environment exposed to oxygen, and an environment exposed to acid, alkali, or organic solvent.
An environment in which ultraviolet rays are irradiated is, for example, an environment in which sunlight is irradiated onto a member.
An environment exposed to moisture refers to an environment where the components are affected by moisture if the absolute humidity is not 0%, and this also applies when the components are installed inside the walls of a house, i.e., in the structural environment. The average humidity of the actual environment of the components is often 20-90% RH in the structural environment of a house. The "average humidity" here refers to the average humidity of the environment to which the components are actually exposed over a one-year period.
An environment that is affected by temperature is assumed to be subject to thermal degradation depending on the temperature of the environment in which the component is installed, for example, inside the wall of a house. If the component has a glass transition point, the average temperature of the actual exposure environment of the component is preferably equal to or lower than the glass transition point of the component. The "average temperature" here refers to the average temperature of the environment to which the component is actually exposed over a one-year period, and in the case of the structural environment of a house, it is generally 10 to 30°C.
An environment exposed to oxygen means an environment in which oxygen is present in the location where the component is installed, and the oxygen concentration in the framework of a house is generally about 21%.
The environment in which the member is exposed to an acid, an alkali, or an organic solvent refers to an environment in which the member is in contact with an acid, an alkali, or an organic solvent. For example, an example of an environment in which the member is in contact with an alkali is a state in which the member is in contact with concrete.

The degree of deterioration of an actual aged product can be determined by chemical analysis, mechanical analysis, and physical analysis.
Examples of chemical analysis techniques include infrared spectroscopy (IR) and gel permeation chromatography (GPC).
When IR is used, the intensity of a peak having an absorption maximum in a specific region is measured, and the degree of deterioration of the actual aged product is measured from the ratio of the intensity of the peak having an absorption maximum in another specific region. For example, when the actual aged product is a coating material, IR measurement is performed on the sampled coating material, and the peak intensity of the functional group of interest, the peak intensity ratio of the functional group of interest and the reference functional group, or the ratio of the peak intensities of multiple functional groups of interest from the obtained infrared absorption spectrum (IR spectrum) are used as indicators of the degree of deterioration. For example, when tracking the hydrolysis of an ester group, the peak intensity derived from C=O of a carboxy group having a maximum absorption in the 1720±20 cm ^-1 region, the peak intensity derived from an acid having a maximum absorption in the 1655±20 cm ^-1 region, and the ratio of the peak intensities including them are obtained. When tracking the hydrolysis of a urethane group, in addition to the above peaks, the peak intensity derived from N-H having a maximum absorption in the 1540±20 cm ^-1 region and the ratio of the peak intensities including them are obtained. In addition, a functional group that is thought to hardly deteriorate over time in the case of moist heat deterioration, such as a peak at 1510±20 cm ^-1 of a benzene ring or a peak derived from an inorganic substance (e.g., 570±20 cm ^-1 ), can be used as a reference peak, and the ratio of the peak intensity that changes due to the deterioration can be used as a peak intensity ratio. Furthermore, by taking the ratio of these peak intensity ratios, the ratio between the functional groups that change can be used as an index of the degree of deterioration.
When GPC is used, the mass average molecular weight of an actual aged product is measured and used as an index of the degree of deterioration.

Examples of mechanical analysis methods include pencil hardness measurement, cross-cut testing, thickness measurement, weight measurement, and the like.
In the measurement of pencil hardness, the pencil hardness of an actual aged product is measured by a method in accordance with JIS K 5600-5-4:1999, and the result is used as an index of the degree of deterioration.
The cross-cut test is carried out in accordance with JIS K 5600-5-6:1999. In other words, 25 cross-cut patterns, each measuring 1 mm x 1 mm, are formed on the surface of an actual aged product, adhesive tape is applied to the surface, and the number of cross-cut patterns remaining after the adhesive tape is peeled off is counted and used as an index of the degree of deterioration.
In the thickness measurement, the thickness of an actual aged product is measured according to a method in accordance with JIS K 5600-5-7:2014, and this is used as an index of the degree of deterioration.
In weight measurement, the weight of an actual aged product is measured and used as an index of the degree of deterioration.

Examples of physical analysis methods include electrochemical testing and measurement of the permeation rate of degradation factors.
Examples of electrochemical tests include electrochemical impedance (EIS) method and ion permeation resistance measurement method (RST method, for example, the method described in JP 2016-217822 A).
In the EIS method, the resistance value of an actual aged product is measured and used as an index of the degree of deterioration.
In the RST method, the ion permeation resistance value of an actual aged product is measured and used as an index of the degree of deterioration.
In the measurement of the deterioration factor transmission rate, the oxygen transmission rate of an aged product in actual exposure is measured by a method conforming to JIS K 7126: 2006, and this is used as an index of the degree of deterioration. Alternatively, the water vapor transmission rate of an aged product in actual exposure is measured by a method conforming to JIS K 7129: 2019, and this is used as an index of the degree of deterioration.

Among the above, from the viewpoint of being able to verify the chemical deterioration mechanism, it is preferable to determine the degree of deterioration of an actual exposed aged product by chemical analysis methods. In particular, when a component contains a thermosetting resin, it is preferable to determine the degree of deterioration of an actual exposed aged product of this component by IR.

In the step (A), for example, a graph (a) is obtained in which the degree of deterioration according to the number of years elapsed (vertical axis) is plotted against the number of years elapsed of an actual aged product (horizontal axis), as shown in FIG. 1(a) as a schematic diagram.
In FIG. 1(a), the black dots plot the deterioration index (e.g., IR peak intensity ratio) of actual aged products recovered from actual homes on the vertical axis, and the number of years since construction on the horizontal axis.

<Step (B)>
Step (B) is a step of conducting an accelerated degradation test on the component before actual exposure, measuring the degree of degradation of the component after the accelerated degradation test, and creating a graph (b) in which the degree of degradation (vertical axis) is plotted against the number of test days (horizontal axis) to obtain a degradation curve.
In step (B), a member (test piece) having the same composition as the member before the actual test is prepared, and the accelerated deterioration test is performed on the test piece. For example, if the member before the actual test is a coating material (i) formed on the surface of metal such as a pillar or beam of a steel frame house, a coating material (ii) having the same composition as the coating material (i) formed on the surface of the same type of metal as the pillar or beam is used as the test piece for the accelerated deterioration test.

In accelerated deterioration tests, it is preferable to accelerate one or more factors selected from the group consisting of factors similar to the actual environment of the material, specifically ultraviolet light, humidity, temperature, oxygen, acid, alkali, and organic solvents. For example, ultraviolet light, humidity, and temperature can be deterioration factors for materials used outdoors. Furthermore, humidity and temperature can be deterioration factors for materials used in spaces that are shielded from sunlight, such as pillars and beams in a house, which are located between the exterior wall and the interior material. When used in a normal atmospheric environment, oxygen can be a deterioration factor. Furthermore, when used in contact with materials that show acidity, such as wood, acids can be a deterioration factor, and when used in contact with materials that show alkalinity, such as concrete, alkalis can be a deterioration factor. Furthermore, materials that have double bonds or benzene rings are prone to ultraviolet light deterioration, and materials that have ester groups, urethane groups, and amide groups are prone to hydrolysis, so the deterioration factors to be accelerated are selected based on the environment and materials used.

An example of specific accelerated deterioration test conditions is shown below.
When humidity is accelerated in the accelerated deterioration test, the accelerated deterioration test is preferably performed in an environment with a humidity of more than 70% RH and not more than 100% RH from the viewpoint of increasing the acceleration factor (α), and more preferably in an environment with a humidity of more than 95% RH and not more than 100% RH. When the actual environment is an aerobic environment, it is more preferable that the accelerated deterioration test is also performed in an aerobic environment.
When accelerating the temperature in the accelerated deterioration test, it is preferable to increase the temperature in order to increase the acceleration factor (α). Specifically, it is preferable to carry out the test in an environment above 100°C, and more preferably in an environment above 100°C and in an oxygen-containing environment. At this time, the humidity is not particularly limited, but it is preferable to carry out the test in an environment above 95% RH and below 100% RH. In addition, the upper limit of the temperature is preferably lower than the maximum temperature during molding of the member or the curing reaction temperature. When the member is a baked coating film, it is preferable to carry out the accelerated deterioration test in an environment below the maximum temperature reached during the baking treatment of the baked coating film, and more preferably in an environment below 150°C. In the case where the deterioration factor is present to a certain extent in the member compared to the deterioration reaction of the member due to the large diffusion of the deterioration factor in the usage environment and the thin thickness of the member, it is often acceptable to set the accelerated temperature to the glass transition point or higher, even if the actual environment is below the glass transition point of the member. From this viewpoint, the thickness of the member to which the present invention can be preferably applied is 5 to 100 μm, more preferably 5 to 60 μm, and further preferably 10 to 40 μm.
When accelerating temperature and humidity in the accelerated deterioration test, it is preferable to use a highly accelerated life test such as PCT (Pressure Cooker Test) or HAST (Highly Accelerated Temperature and Humidity Stress Test), which can perform accelerated tests in a humid and hot environment of over 100° C. When performing accelerated deterioration tests in a humid and hot environment of over 100° C. and in an aerobic environment, Air-HAST, which can perform HAST in an oxygen environment, is suitable.
When the accelerated deterioration test is carried out by HAST or Air-HAST, the temperature is preferably higher than 100° C. and not higher than 150° C., more preferably 105 to 140° C., and even more preferably 110 to 135° C., and the humidity range is preferably 70 to 100% RH, and more preferably 96 to 100% RH. An example of particularly preferred temperature and humidity conditions is a temperature of 130° C. and a humidity of 100% RH.

In order to estimate the service life of a material that is less susceptible to deterioration, the accelerated deterioration test is preferably carried out for 5 days or more, more preferably 10 days or more, even more preferably 20 days or more, and particularly preferably 30 days or more.
The accelerated degradation test may be carried out continuously or intermittently. When the accelerated degradation test is carried out intermittently, it is preferable to carry out the accelerated degradation test for a total of 5 days or more.
Although there is no particular upper limit on the number of test days, for example, when the accelerated temperature is 130°C, the number of days required to confirm functional loss is within 100 days for most components, and for most of those components, it is within 60 days. In addition, when the accelerated temperature is changed, the number of accelerated days can be set by analogy using the 10°C double rule, which states that a difference of 10°C roughly doubles the reaction rate.

In step (B), the degree of deterioration of the component (test piece) after the accelerated deterioration test is measured. The degree of deterioration of the test piece is determined in the same manner as the method for measuring the degree of deterioration of an actual aged product, for example, by the chemical analysis method, mechanical analysis method, or physical analysis method described above.

In step (B), a graph (b) is obtained in which the degree of deterioration (vertical axis) according to the number of test days in the accelerated deterioration test is plotted against the number of test days (horizontal axis), as shown, for example, in FIG. 1(b), and a deterioration curve of the plot is obtained.
In FIG. 1( b ), the plot of open triangles indicates the degradation index of the components subjected to the accelerated degradation test (for example, the IR peak intensity ratio, which is the same index as in FIG. 1( a )) on the y-axis and the number of days of the accelerated degradation test on the x-axis.

<Step (C)>
Step (C) is a step of obtaining a graph (c) by superimposing the graph (a) and the graph (b) so that the plot of the graph (a) approximates the deterioration curve.
Specifically, the scale of the horizontal axis of graph (a) and graph (b) is adjusted so that the plot of graph (a) approximates the deterioration curve, and graph (a) and graph (b) are superimposed.

By approximating the plot of graph (a) to the deterioration curve of graph (b), for example, graph (c) as shown in Fig. 2 can be obtained. Graph (c) shown in Fig. 2 is a graph obtained by superimposing graph (b) on graph (a) by setting the horizontal axis scale of graph (b) shown in Fig. 1(b) to the same scale as that of graph (a) shown in Fig. 1(a).
The approximation can be adjusted according to the safety factor to be set. When a high safety factor is set for approximating the deterioration curve of graph (b) through the center of the plot group of graph (a), an appropriate adjustment is made such that the deterioration curve of graph (b) is approximated through the plot of the plot group of graph (a) that has the greatest degree of deterioration compared to the number of years that have passed, and the scale of the horizontal axis is set to obtain the superimposed graph (c).

<Step (D)>
Step (D) is a step of calculating an acceleration factor (α) of the accelerated deterioration test based on the graph (c) using an arbitrary number of years elapsed and the number of test days corresponding to the degree of deterioration at that number of years elapsed, using the following formula (1).
Acceleration factor (α) = any number of years passed / number of test days ... (1)

For example, in the case of graph (c) shown in Figure 2, the number of test days corresponding to the degree of deterioration after 20 years is 8 days, so the acceleration factor (α) for the accelerated deterioration test is calculated as 20 [years] / 8 [days] = 2.5 [years/day].

<Step (E)>
Step (E) is a step of conducting a function evaluation test on the component after the accelerated deterioration test, and determining the number of test days (β) of the accelerated deterioration test required for the component to lose its function.
Examples of the functional evaluation tests include a composite cycle test, a salt spray test, thickness measurement before and after an accelerated deterioration test, weight measurement before and after an accelerated deterioration test, transmittance measurement, electrochemical test, etc. These test methods and measurement methods may be performed alone or in combination.

The combined cycle test and salt spray test are used to evaluate the functionality of components after accelerated deterioration tests. In particular, when the components are coating materials formed on the surfaces of metals such as pillars and beams of steel-framed houses, the rust prevention properties of the components (here, the coating materials) are evaluated. In other words, the combined cycle test or salt spray test, which are accelerated corrosion tests for the metal that is the base material of the coating materials, are performed on the painted metal to evaluate the barrier properties of the coating materials against metal deterioration factors, i.e., rust prevention properties.
When a combined cycle test or a salt spray test is performed as a functional evaluation test, it is preferable to use the rust area ratio after the combined cycle test or the salt spray test as an index of the functional loss of the component. Specifically, when the component is a coating material formed on the surface of a metal, the ratio of the area of the rust generated after the functional evaluation test to the area of the coating material before the functional evaluation test (rust area ratio) is obtained, and this is used as an index of the loss of the rust prevention function of the component. Then, for example, when the function of the component is considered to be lost when the rust area ratio becomes 50%, the number of test days of the accelerated deterioration test required for the rust area ratio to become 50% is set as the test days (β). For example, as shown in Figures 1(b) and 2, if a functional evaluation test is performed on a component after the accelerated deterioration test for 60 days, and the rust area ratio after the functional evaluation test is 50%, the test days (β) is 60 days.
The rust area ratio at which the functionality of the component is deemed to have been lost may be appropriately determined depending on the type of component and the intended use.

In addition, the average metal thickness loss (also called the average metal thickness loss rate) of the cross section in the rusted region after the combined cycle test or salt spray test may be used as an index of the functional loss of the component. Specifically, when the component is a coating material formed on the surface of a metal, the ratio (amount of metal thickness loss) of the metal thickness in the region of rust (rusted region) generated after the functional evaluation test to the metal thickness before the functional evaluation test is calculated, and the average metal thickness loss is used as an index of the functional loss of the component. The average metal thickness loss may be calculated over the entire rusted region based on the weight change of the metal before and after the accelerated deterioration test after removing the coating material and the metal corrosion product, or the average metal thickness may be calculated for a part of the rusted region, for example, the weight change in the range where the most rust is generated, or for a region of a certain length (for example, 10 mm) in the cross-sectional image. Then, for example, when the function of the component is considered to be lost when the average metal thickness loss reaches 10%, the number of days of the accelerated deterioration test required for the average metal thickness loss to reach 10% is set as the number of test days (β).
The average metal thickness reduction amount at which the function of the component is deemed to be lost may be appropriately determined depending on the type of component and the intended use.

The combined cycle test is performed in accordance with JASO M 609. Specifically, one cycle is composed of a salt spray process in which a 5% by mass aqueous sodium chloride solution is sprayed on the member after the accelerated deterioration test at 35° C. for 2 hours, a high-temperature drying process in which the member after the salt spray process is dried at 60° C. and a humidity of 20 to 30% RH for 4 hours, and a wetting process in which the member after the high-temperature drying process is wetting at a temperature of 50° C. and a humidity of 95% RH for 2 hours. The combined cycle test is preferably performed for 60 to 360 cycles, more preferably 120 to 180 cycles.
The salt spray test is performed in accordance with JIS Z 2371: 2015. Specifically, a 5% by mass aqueous sodium chloride solution is sprayed onto the member (test piece) after the accelerated deterioration test at 35° C. for preferably 500 hours or more, more preferably 1000 hours or more.

When evaluating the function of a component by measuring the thickness before and after the accelerated deterioration test, the ratio of the thickness of the component after the accelerated deterioration test to the thickness of the component before the accelerated deterioration test (the rate of change in thickness) is used as an index of the loss of function of the component. For example, if the function of the component is considered to be lost when the rate of change in thickness reaches 30%, the number of test days of the accelerated deterioration test required for the rate of change in thickness to reach 30% is set as the number of test days (β). In this case, when calculating the service life of a coating material such as a coating film as the component of interest, the rate of change in thickness is the rate of change in thickness of the coating material before and after the accelerated deterioration test of the coating material.
The rate of change in thickness at which the function of the component is deemed to be lost may be appropriately determined depending on the type of component and the purpose of use.

When evaluating the function of a component by measuring the weight before and after the accelerated deterioration test, the ratio of the weight of the component after the accelerated deterioration test to the weight of the component before the accelerated deterioration test (weight change rate) is used as an index of the loss of function of the component. For example, if the function of the component is considered to be lost when the weight change rate reaches 30%, the number of test days of the accelerated deterioration test required for the weight change rate to reach 30% is set as the test number (β). In this case, when calculating the service life of a coating material such as a coating film as the component of interest, the weight change rate is the weight change rate of the coating material before and after the accelerated deterioration test of the coating material.
The rate of weight change at which the function of a component is deemed to have been lost may be appropriately determined depending on the type of component and the intended use.

When the function of a member is evaluated by measuring the transmittance, the method for measuring the transmittance may be the method for measuring the degradation factor permeation rate exemplified above in the explanation of step (A).
The oxygen or water vapor transmission rate of the component before and after the accelerated aging test is measured, and the oxygen or water vapor transmission rate of the component after the accelerated aging test is used as an index of the loss of function of the component. For example, if the function of the component is considered to be lost when the oxygen transmission rate at 23°C, 50% RH, and 1 atm becomes 30 mg/ ^cm2 /year, the number of test days of the accelerated aging test required for the oxygen transmission rate to reach 30 mg/ ^cm2 /year is taken as the number of test days (β). Alternatively, if the function of the component is considered to be lost when the water vapor transmission rate at 25°C and 95% RH becomes 1 g/ ^cm2 /year, the number of test days of the accelerated aging test required for the water vapor transmission rate to reach 1 g/ ^cm2 /year is taken as the number of test days (β).
The oxygen or water vapor transmission rate at which the function of the component is deemed to have been lost may be appropriately determined depending on the type of component and the intended use.

When the function of the member is evaluated by electrochemical testing, examples of the electrochemical test include the EIS method and the RST method exemplified above in the explanation of step (A).
When evaluating the function of a component by the EIS method, the resistance of the component is measured before and after the accelerated aging test, and the resistance of the component after the accelerated aging test is used as an index of the loss of function of the component. For example, if the function of the component is considered to be lost when the resistance at 1 kHz reaches 10 ⁵ Ω·cm ² , the number of test days of the accelerated aging test required for the resistance to reach 10 ⁵ Ω·cm ² is defined as the test period (β).
When evaluating the function of a component by the RST method, the ion permeation resistance of the component is measured before and after the accelerated degradation test, and the ion permeation resistance of the component after the accelerated degradation test is used as an index of the loss of function of the component. For example, if the function of the component is considered to be lost when the ion permeation resistance reaches 1 MΩ, the number of test days of the accelerated degradation test required for the ion permeation resistance to reach 1 MΩ is set as the test number (β).
The resistance value or ion permeation resistance value at which the function of the component is deemed to have been lost may be appropriately determined depending on the type of component and the purpose of use.

Among the above, from the viewpoint of high accuracy in functional evaluation of components, the composite cycle test, thickness measurement before and after accelerated deterioration test, and RST method are preferred as functional evaluation tests, and the composite cycle test is more preferred when the component is a coating material formed on the surface of a metal.

The number of test days (β) is preferably 5 days or more, more preferably 10 days or more, even more preferably 20 days or more, and particularly preferably 30 days or more.
When the accelerated deterioration test is carried out intermittently, the total number of test days (β) is preferably 5 days or more.

<Step (F)>
Step (F) is a step of calculating the service life (γ) of the member using the following formula (2).
Service life (γ) = acceleration factor (α) × number of test days (β) ... (2)

For example, in the case of graph (c) shown in Figure 2, the acceleration rate (α) of the accelerated deterioration test is 2.5 [years/day] as described above. In addition, if a functional evaluation test is conducted on a component after 60 days of accelerated deterioration testing, and the rust area rate after the functional evaluation test is 50%, and the component is deemed to have lost its function, the number of test days (β) is 60 days, so the useful life (γ) of the component is calculated to be 2.5 [years/day] x 60 [days] = 150 [years].

Through the above-mentioned steps (A) to (F), the service life (γ) of the component can be estimated.

The above-described method for estimating the useful life of a component of the present invention can estimate the useful life (γ) of a component by a simple operation of performing an accelerated deterioration test on a component (test piece) having the same composition as the component before actual exposure, performing a functional evaluation test on the component after the accelerated deterioration test, and measuring the degree of deterioration of the component after the accelerated deterioration test. Even if the very early induction period is excluded, the deterioration behavior after the deterioration curve often shows a nonlinear behavior. The present invention can be preferably applied to a component whose deterioration curve shows a nonlinear behavior. In addition, the present invention can be preferably applied even if the number of test days (β) is in a nonlinear region on the deterioration curve. In addition, if the measurement of the degree of deterioration of a component after actual exposure is performed for about 30 years, data that can show a trend can be collected in many cases, so that the useful life (γ) of the component can be estimated in a relatively short period of time compared to the length of the estimated useful life.
The method for estimating the useful life of a component of the present invention is suitable when the useful life (γ) of the component is at least twice the elapsed years of an actually aged product, and is particularly suitable when the useful life (γ) of the component is at least 60 years. For example, for a component that has been elapsed for 20 years but can be expected to have a useful life of 100 or 200 years, estimation can be made in a relatively short period of time, such as several tens of days.
According to the present invention, since it is possible to estimate the useful life, it becomes possible, for example, to formulate a maintenance program for the entire product and to set component specifications that are suited to the entire product.

Claims (22)

A method for estimating a useful life of a component in a space shielded from sunlight , comprising the steps of:
Step (A): measuring the degree of deterioration of an actual aged product in the space of the component, and creating a graph (a) in which the degree of deterioration (vertical axis) is plotted against the number of years elapsed (horizontal axis);
Step (B): performing an accelerated deterioration test on the component before actual use, measuring the degree of deterioration of the component after the accelerated deterioration test, and creating a graph (b) in which the degree of deterioration (vertical axis) is plotted against the number of test days (horizontal axis) to obtain a deterioration curve;
Step (C): obtaining a graph (c) by superimposing the graph (a) and the graph (b) so that the plot of the graph (a) approximates the deterioration curve;
Step (D): A step of calculating an acceleration factor (α) of the accelerated deterioration test based on the graph (c) from an arbitrary number of years passed and the number of test days corresponding to the degree of deterioration at that number of years passed, using the following formula (1);
Acceleration factor (α) = any number of years passed / number of test days ... (1)
Step (E): A step of performing a function evaluation test on the component after the accelerated deterioration test, and determining the number of test days (β) of the accelerated deterioration test required for the component to lose its function;
Step (F): A step of calculating the service life (γ) of the member using the following formula (2);
Service life (γ) = acceleration factor (α) × number of test days (β) ... (2)
Including,
The member is a coating film having a metal base,
The accelerated deterioration test is carried out in an environment having a humidity of more than 70% RH and not more than 100% RH, and a temperature of more than 100°C. The method for estimating the useful life of a component according to claim 1, wherein the component has a glass transition point and the accelerated deterioration test is carried out in an environment at or above the glass transition point of the component. The method for estimating a useful life of a component according to claim 1 or 2 , wherein the accelerated deterioration test is carried out in an oxygen-containing environment. The method for estimating useful life of a component according to any one of claims 1 to 3 , wherein the number of test days (β) is 5 days or more. The method for estimating a useful life of a member according to any one of claims 1 to 4 , wherein the member has a glass transition point, and an average temperature of an actual environment of the member is equal to or lower than the glass transition point of the member. The method for estimating a useful life of a member according to any one of claims 1 to 5, wherein the functional evaluation test is one or more selected from the group consisting of a combined cycle test, a salt spray test, thickness measurement before and after the accelerated aging test, weight measurement before and after the accelerated aging test, transmittance measurement, and an electrochemical test. The method for estimating useful life of a component according to any one of claims 1 to 6 , wherein the degree of deterioration is determined by a chemical analysis method. The method for estimating useful life of a component according to any one of claims 1 to 6 , wherein the degree of deterioration is determined by a mechanical analysis method. The method for estimating useful life of a component according to any one of claims 1 to 6 , wherein the degree of deterioration is determined by a physical analysis method. The method for estimating the useful life of a member according to any one of claims 1 to 9 , wherein the coating film is a baked coating film. The method for estimating a useful life of a member according to claim 10 , wherein the accelerated deterioration test is carried out in an environment below a maximum temperature reached during a baking treatment of the baked coating film. The method for estimating the useful life of a component according to any one of claims 1 to 11 , wherein the coating film has rust-preventive properties, and a rust area rate after the functional evaluation test is used as an index of functional loss of the component. The method for estimating the useful life of a component according to any one of claims 1 to 11 , wherein the coating film has rust prevention properties, and an average metal thickness reduction amount of a cross section in a rusted region after the functional evaluation test is used as an index of functional loss of the component. The method for estimating the useful life of a component according to any one of claims 1 to 13 , wherein the metal is black carbon steel. The method for estimating a useful life of a member according to any one of claims 1 to 14 , wherein the coating film contains a thermosetting resin. The method for estimating useful life of a component according to any one of claims 1 to 15 , wherein the useful life (γ) is 60 years or more. The method for estimating a useful life of a component according to any one of claims 1 to 16 , wherein the component has a thickness of 5 to 100 µm. The method for estimating the useful life of a component according to any one of claims 1 to 17 , wherein the useful life (γ) is at least twice the elapsed age of the actual used product. The method for estimating the useful life of a component according to any one of claims 1 to 18 , wherein the deterioration curve is non-linear. The method for estimating the useful life of a component according to any one of claims 1 to 19 , wherein the number of test days (β) is in a nonlinear region on the deterioration curve. A method for estimating a useful life of a component, comprising the steps of:
Step (A): measuring the degree of deterioration of the actual aged product of the component, and creating a graph (a) in which the degree of deterioration (vertical axis) is plotted against the number of years elapsed (horizontal axis);
Step (B): performing an accelerated deterioration test on the component before actual use, measuring the degree of deterioration of the component after the accelerated deterioration test, and creating a graph (b) in which the degree of deterioration (vertical axis) is plotted against the number of test days (horizontal axis) to obtain a deterioration curve;
Step (C): obtaining a graph (c) by superimposing the graph (a) and the graph (b) so that the plot of the graph (a) approximates the deterioration curve;
Step (D): A step of calculating an acceleration factor (α) of the accelerated deterioration test based on the graph (c) from an arbitrary number of years passed and the number of test days corresponding to the degree of deterioration at that number of years passed, using the following formula (1);
Acceleration factor (α) = any number of years passed / number of test days ... (1)
Step (E): performing a functional evaluation test on the component after the accelerated deterioration test, and determining the number of test days (β) of the accelerated deterioration test required for the component to lose its function;
Step (F): A step of calculating the service life (γ) of the member using the following formula (2);
Service life (γ) = acceleration factor (α) × number of test days (β) ... (2)
Including,
The component is a coating material,
The coating material is formed on the surface of black carbon steel, the coating material has rust-preventive properties, and the rust area rate after the functional evaluation test is an indicator of functional loss of the component. A method for estimating a useful life of a component, comprising the steps of:
Step (A): measuring the degree of deterioration of the actual aged product of the component, and creating a graph (a) in which the degree of deterioration (vertical axis) is plotted against the number of years elapsed (horizontal axis);
Step (B): performing an accelerated deterioration test on the component before actual use, measuring the degree of deterioration of the component after the accelerated deterioration test, and creating a graph (b) in which the degree of deterioration (vertical axis) is plotted against the number of test days (horizontal axis) to obtain a deterioration curve;
Step (C): obtaining a graph (c) by superimposing the graph (a) and the graph (b) so that the plot of the graph (a) approximates the deterioration curve;
Step (D): A step of calculating an acceleration factor (α) of the accelerated deterioration test based on the graph (c) from an arbitrary number of years passed and the number of test days corresponding to the degree of deterioration at that number of years passed, using the following formula (1);
Acceleration factor (α) = any number of years passed / number of test days ... (1)
Step (E): performing a functional evaluation test on the component after the accelerated deterioration test, and determining the number of test days (β) of the accelerated deterioration test required for the component to lose its function;
Step (F): A step of calculating the service life (γ) of the member using the following formula (2);
Service life (γ) = acceleration factor (α) × number of test days (β) ... (2)
Including,
The component is a coating material,
The coating material is formed on the surface of black carbon steel, the coating material has rust-preventive properties, and the average metal loss in the cross section in the rusted area after the functional evaluation test is used as an indicator of functional loss of the component.

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