Method and apparatus for analyzing resin materials

Abstract

This invention provides a resin material analysis method and apparatus that can non-destructively evaluate the degree of hydrolysis in resin materials containing hydrolyzable polymers. [Solution] A resin material analysis method comprising: a reference measurement step of obtaining multiple reference spectra by performing near-infrared spectroscopy on multiple reference samples composed of resin materials having different degrees of hydrolysis progression for a resin material containing a hydrolyzable polymer; a target measurement step of obtaining a target spectrum by performing near-infrared spectroscopy on a target sample composed of the resin material whose degree of hydrolysis progression is unknown; and an estimation step of estimating the degree of hydrolysis progression in the target sample by comparing the target spectrum with the multiple reference spectra in a wavelength region including the contribution of near-infrared absorption by hydroxyl groups (A, B).

Description

Technical Field

[0001] The present disclosure relates to a method for analyzing resin materials and an apparatus for analyzing resin materials.

Background Art

[0002] As constituent materials for automotive components, aircraft components, electrical and electronic devices, etc., various resin materials are used. When these various devices and components are continuously used over a long period of time, deterioration due to the denaturation of the polymer that constitutes the resin material may become a problem. In particular, when the polymer is one having hydrolysis properties such as polyester or polyamide, hydrolysis may occur in an environment such as high temperature and high humidity. When hydrolysis of the polymer occurs, a decrease in molecular weight and changes in physical and chemical properties may occur.

[0003] In view of such effects of hydrolysis, methods for determining the presence or absence and degree of hydrolysis of polymers have been proposed so far. For example, Non-Patent Document 1 lists several analysis methods for the degree of deterioration due to hydrolysis of polybutylene terephthalate (PBT). Specifically, as methods for determining the progress of hydrolysis, measurement of molecular weight, measurement of the amount of terminal COOH groups by titration, measurement of the oxidation onset temperature (OOT) by a differential scanning calorimeter (DSC), etc. are listed.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Several methods are known for evaluating the degree of hydrolysis of polymers, including those listed in Non-Patent Document 1. However, all of these methods are based on molecular weight measurement, chemical analysis, and physical property measurement, and involve destructive analysis. In other words, it is necessary to separate the resin material to be analyzed for the degree of hydrolysis and subject it to analysis. Therefore, it is desirable to be able to perform non-destructive analysis of the degree of hydrolysis of resin materials constituting various devices and components. If the degree of hydrolysis can be evaluated by non-destructive analysis, it may be possible to improve convenience, for example, in determining whether a component made of a given resin material can be used continuously in that device or component, or in implementing countermeasures if hydrolysis is progressing.

[0006] In view of the above, the objective is to provide a resin material analysis method and a resin material analysis apparatus that can non-destructively evaluate the degree of hydrolysis progression in resin materials containing hydrolyzable polymers. [Means for solving the problem]

[0007] The resin material analysis method according to this disclosure includes a reference measurement step of obtaining multiple reference spectra by performing near-infrared spectroscopy measurements on multiple reference samples composed of resin materials with different degrees of hydrolysis progression for a resin material containing a hydrolyzable polymer; a target measurement step of obtaining a target spectrum by performing near-infrared spectroscopy measurements on a target sample composed of the resin material whose degree of hydrolysis progression is unknown; and an estimation step of estimating the degree of hydrolysis progression in the target sample by comparing the target spectrum with the multiple reference spectra in a wavelength region that includes the contribution of near-infrared absorption by hydroxyl groups.

[0008] The resin material analysis apparatus described herein is used to perform the resin material analysis method described above. [Effects of the Invention]

[0009] The resin material analysis method and resin material analysis apparatus described herein are capable of non-destructively evaluating the degree of hydrolysis progression in resin materials containing hydrolyzable polymers. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 shows near-infrared spectra of polybutylene terephthalate with different degrees of hydrolysis, as examples of reference spectra used in the resin material analysis method of this disclosure. [Figure 2] Figure 2 shows a score plot obtained from principal component analysis of the reference spectrum as an example of performing the estimation process using multiple regression analysis. [Figure 3] Figure 3 shows data verifying the accuracy of the estimation process, illustrating the relationship between measured and estimated elapsed time in a high-temperature, high-humidity environment for both the reference sample and the target sample. [Modes for carrying out the invention]

[0011] [Description of Embodiments in this Disclosure] First, embodiments of this disclosure will be listed and described. The resin material analysis method and resin material analysis apparatus according to this disclosure have the following configurations.

[0012] [1] The resin material analysis method according to the present disclosure includes a reference measurement step of obtaining multiple reference spectra by performing near-infrared spectroscopy on multiple reference samples composed of resin materials having different degrees of hydrolysis, for a resin material containing a hydrolyzable polymer; a target measurement step of obtaining a target spectrum by performing near-infrared spectroscopy on a target sample composed of the resin material whose degree of hydrolysis is unknown; and an estimation step of estimating the degree of hydrolysis in the target sample by comparing the target spectrum with the multiple reference spectra in a wavelength region that includes the contribution of near-infrared absorption by hydroxyl groups.

[0013] The resin material analysis method described herein utilizes near-infrared (NIR) spectroscopy to evaluate the degree of hydrolysis in a resin material. In NIR spectra, absorption peaks originating from hydroxyl groups (OH groups) are clearly observed, and the intensity of these absorption peaks sensitively reflects the amount of OH groups present. As polymer hydrolysis progresses, the concentration of OH groups increases. Therefore, by focusing on the wavelength range of the peak originating from OH groups in the NIR spectrum and comparing multiple reference spectra obtained for a reference sample with the target spectrum obtained for the target sample, the degree of hydrolysis in the target sample can be estimated in comparison with the reference sample. NIR spectra can be obtained by irradiating the sample with NIR light and detecting components including the contribution of NIR absorption by the sample, such as reflected and transmitted light. Thus, the degree of hydrolysis in the sample can be evaluated non-destructively. NIR spectrum measuring devices are small and highly portable, making them convenient for measuring resin materials that constitute various devices and components.

[0014] [2] In the embodiment described in [1] above, the polymer may have at least one of an ester bond and an amide bond. Polymers containing ester bonds, such as polyester, and polymers containing amide bonds, such as polyamide, are widely used as constituent materials for automotive components, aircraft components, electrical and electronic equipment, etc. When resin materials containing these polymers are placed in a high-temperature and high-humidity environment, hydrolysis of the ester bonds and amide bonds tends to proceed. However, by applying the resin material analysis method of this disclosure to these resin materials, the progress of hydrolysis can be sensitively detected, and the obtained information can be used for inspection and maintenance of equipment and components.

[0015] [3] In the aspect of [1] or [2] above, in the estimation step, the wavelength region may include a region of 1800 nm or more and 2000 nm or less. In the region of 1800 nm or more and 2000 nm or less, a distinct peak structure derived from the O-H stretching vibration of the OH group appears. Therefore, by performing the estimation step while paying attention to the wavelength region including this region, it is possible to sensitively and with high accuracy estimate the degree of progress of hydrolysis in the target sample.

[0016] [4] In any of the aspects from [1] to [3] above, the comparison between the plurality of reference spectra and the target spectrum in the estimation step may be performed using multiple regression analysis. Then, the changes in the NIR spectrum can be accurately and simply associated with the degree of progress of hydrolysis and reflected in the evaluation of the degree of hydrolysis in the target sample.

[0017] [5] The resin material analyzer according to the present disclosure executes any of the resin material analysis methods from [1] to [4] above. In the resin material analysis method, as described above, the NIR spectra of the reference sample and the target sample are measured, and by comparing the spectra of both, the degree of progress of hydrolysis in the target sample can be evaluated non-destructively. The resin material analyzer according to the present disclosure becomes an apparatus that can non-destructively evaluate the degree of progress of hydrolysis for a resin material containing a hydrolyzable polymer by implementing the analysis method.

[0018] [Details of Embodiments of the Present Disclosure] The resin material analysis method and the resin material analyzer according to the embodiments of the present disclosure will be described below with reference to the drawings.

[0019] <Outline of Resin Material Analysis Method and Resin Material Analyzer> In the resin material analysis method according to the embodiments of the present disclosure, for a resin material containing a hydrolyzable polymer, the degree of progress of hydrolysis is evaluated using near-infrared (NIR) spectroscopy.

[0020] In the resin material analysis method according to an embodiment of the present disclosure, a reference measurement step, a target measurement step, and an estimation step are performed in this order. The reference measurement step and the target measurement step include a step of performing NIR spectroscopic measurement using a NIR spectroscopic measurement device. In the estimation step, analysis of the NIR spectra obtained in the reference measurement step and the target step is performed.

[0021] The resin material analysis apparatus according to an embodiment of the present disclosure is configured as an apparatus that executes the above resin material analysis method. The resin material analysis apparatus can be configured to include both a spectroscopic measurement device that measures the NIR spectra in the reference measurement step and the target measurement step, and an analysis device such as a computer equipped with software that analyzes the obtained NIR spectra and performs the estimation step. Alternatively, it can be configured as an analysis device that performs the reference measurement step and the target measurement step by reading the NIR spectra obtained by an independent spectroscopic measurement device, and performs the estimation step on the read spectra.

[0022] <Analysis target> In the resin material analysis method according to an embodiment of the present disclosure, the resin material to be analyzed is not particularly limited as long as it contains a polymer having hydrolyzability. For example, the resin material may preferably contain a polymer having at least one of an ester bond and an amide bond as a hydrolyzable functional group. Specific examples of those polymers include polyester and polyamide. Hereinafter, mainly, a resin material containing polybutylene terephthalate (PBT) will be used as an example to explain each step of the resin material analysis method.

[0023] <Reference measurement step> In the reference measurement step, NIR spectroscopy is performed on multiple reference samples to obtain multiple reference spectra. The reference samples are prepared using the same type of resin material as the target sample whose degree of hydrolysis is to be evaluated. The multiple reference samples are composed of resin materials with different degrees of hydrolysis. Different degrees of hydrolysis refer to states in which the density of hydrolyzed functional groups differs from one another, and also include forms in which no hydrolysis has occurred. It is preferable that one of the multiple reference samples be composed of a sample in which hydrolysis has not occurred substantially. In the reference sample, hydrolysis can be advanced by placing the resin material in a high temperature and / or high humidity environment. To make the degree of hydrolysis different in multiple reference samples, it is sufficient to differ at least one of the temperature, humidity, and time during which hydrolysis occurs. In particular, it is preferable to prepare multiple reference samples by varying the time spent in a high temperature and high humidity environment with predetermined temperature and humidity.

[0024] Once the reference samples are prepared, NIR spectroscopy is performed on each reference sample. NIR spectroscopy can be performed using a known NIR spectrometer. For the measurement, NIR light is incident on the reference sample, and the transmitted or reflected light is detected. Then, the absorbance at each wavelength is calculated from the intensity of the incident and detected light, and this is obtained as the NIR spectrum. The conditions for NIR spectroscopy should be kept consistent among multiple reference samples. The range of measurement wavelengths in NIR spectroscopy is not particularly limited, but it is preferable to set the wavelength range to include at least the contribution of NIR absorption by hydroxyl groups (OH groups) and the range of 1800 nm to 2000 nm.

[0025] As a specific example, Figure 1 shows NIR spectra obtained by reflectance measurements for several PBT samples with different degrees of hydrolysis. In the reference measurement process, it is sufficient to prepare a group of NIR spectra as shown in Figure 1. For the samples corresponding to each spectrum shown in Figure 1, hydrolysis was induced by placing the samples under pressure cooker conditions of 120°C and 85%RH humidity for the elapsed time indicated in the figure, referring to JIS C60068. Samples with an elapsed time of 0 hours are the initial samples before being placed in a high-temperature, high-humidity environment, and essentially no hydrolysis has occurred.

[0026] In the spectral group shown in Figure 1, changes occur in the spectra with elapsed time under high temperature and high humidity conditions. In each spectrum, two distinct peaks, indicated by symbols A and B, appear in the region between 1800 nm and 2000 nm, and the spectral changes with elapsed time are particularly pronounced in the region containing these peaks A and B. Peaks A and B include the contribution of NIR from the OH group. More specifically, peaks A and B include the contribution of OH stretching vibrations of the OH group.

[0027] Detailed observation of spectral changes in the wavelength range of 1800 nm to 2000 nm with increasing elapsed time under high temperature and high humidity conditions reveals a tendency for the heights of peaks A and B, relative to the background level (the region shorter than peak A and longer than peak B), to increase with increasing elapsed time under high temperature and high humidity conditions. The increase in peak height is particularly pronounced in peak A. Furthermore, the peak widths of peaks A and B tend to widen with increasing elapsed time. In particular, the increase in peak width is significant in the region of peak A that is longer wavelengths than the peak.

[0028] The changes in peaks A and B reflect the increasing concentration of OH groups in the resin material as the elapsed time under high temperature and high humidity conditions increases. As shown in equation (1) below, when PBT undergoes hydrolysis, OH groups are generated along with carboxyl groups. In other words, the changes in Figure 1 with increasing elapsed time reflect the progress of PBT hydrolysis. From this, it can be seen that the degree of hydrolysis can be estimated from the state of the NIR spectrum, especially the state in the wavelength region between 1800 nm and 2000 nm. [ka]

[0029] <Target Measurement Process> In the target measurement process, NIR spectroscopy is performed on the target sample whose degree of hydrolysis is to be evaluated, i.e., the target sample whose degree of hydrolysis is unknown. The NIR spectroscopy should be performed in the same manner as for the reference sample. The conditions for NIR spectroscopy should be the same for the target sample and each reference sample.

[0030] <Estimated process> In the estimation step, the target spectrum obtained in the target measurement step is compared with multiple reference spectra obtained in the reference measurement step. The comparison is performed on the NIR spectrum in a wavelength region that includes at least the contribution of NIR absorption by OH groups. Preferably, the comparison is performed in a wavelength region that includes the region between 1800 nm and 2000 nm. Based on the comparison results, the degree of hydrolysis progression in the target sample is estimated.

[0031] In the comparison, the degree of hydrolysis in the target sample is correlated to the degree of hydrolysis in the reference sample based on which of the series of reference spectra shown in Figure 1 the target spectrum is closest to, and / or how close it is to one or more reference spectra, within the set wavelength range. For example, if the state of the target spectrum is sufficiently similar to a certain reference spectrum, it can be estimated that the degree of hydrolysis in the target sample is equivalent to the degree of hydrolysis in the reference sample that gives that reference spectrum. Alternatively, if the state of the target spectrum is intermediate between two reference spectra, it can be estimated that the degree of hydrolysis in the target sample is equivalent to the degree of hydrolysis in the two reference samples that give those two reference spectra, respectively. As shown in the series of spectra in Figure 1, the generation of OH groups due to the progression of hydrolysis is clearly reflected in the increase in peak height and width of peak A, particularly peak A, which appears in the region between 1800 nm and 2000 nm. Therefore, if the height and / or width of these peaks in the target spectrum are similar to those in a certain reference spectrum, it can be estimated that the progression of hydrolysis in the target sample is similar to that of the reference sample that gives that reference spectrum. Furthermore, if the height and / or width of these peaks in the target spectrum are midway between the height and / or width of the peaks in two reference spectra, it can be estimated that the progression of hydrolysis in the target sample corresponds to an intermediate stage between the progression of hydrolysis in the two reference samples that give those two reference spectra, respectively.

[0032] When comparing each reference spectrum with the target spectrum, one method for determining the similarity between the reference spectrum and the target spectrum is to directly determine the similarity of the overall shape of the spectrum in a predetermined wavelength range. Alternatively, one method is to compare representative values ​​extracted from the spectrum, such as absorbance, peak height, peak integral intensity, and peak width at a predetermined wavelength, such as the peak of a certain peak (e.g., peak A). As will be explained later, a method utilizing multiple regression analysis such as principal component analysis is also preferable. Furthermore, machine learning may be used. When using machine learning, a learning model can be created by performing machine learning using the relationship between the group of reference spectra and the degree of hydrolysis progression as training data, and then applying that learning model to the target spectrum.

[0033] When comparing a reference spectrum with a target spectrum using the methods described above, it is preferable to pre-process each NIR spectrum prior to the comparison. Examples of pre-processing include wavelength range extraction, spectrum averaging, standardization, smoothing, and background removal. Of these, smoothing can be performed using methods such as the Savitzky-Golay method.

[0034] Furthermore, when correlating the degree of hydrolysis in the target sample with the degree of hydrolysis in the reference sample based on the comparison results of the reference spectrum, the degree of hydrolysis experienced by the target sample can be directly correlated to the hydrolysis conditions experienced by the reference sample, such as "equivalent to hydrolysis at a temperature of X°C and a humidity of Y%RH for Z hours." Alternatively, the degree of hydrolysis in the reference sample can be ranked in multiple stages, and the degree of hydrolysis in the target sample can be correlated to these ranks. In addition, if the degree of hydrolysis in each reference sample, which is a known sample, is quantitatively determined in advance by molecular weight measurement or chemical analysis, in the form of the amount of OH groups generated, the degree of hydrolysis in the target sample can also be quantitatively estimated. Alternatively, focusing on the fact that the physical properties of the resin material change due to hydrolysis, the physical properties (elastic modulus, tensile strength, elongation at break, etc.) of each reference sample can be evaluated, and then the physical properties exhibited by the target sample can be estimated. The estimation of physical properties can be carried out, for example, using multiple regression analysis such as principal component regression analysis.

[0035] <Examples of applications of resin material analysis methods> As described above, by performing NIR spectroscopy measurements on multiple reference samples and the target sample, and comparing the obtained NIR spectra, the degree of hydrolysis progression in the target sample can be estimated. As reference samples, as explained in relation to Figure 1, multiple samples can be prepared by allowing hydrolysis to progress on a model test piece under controlled conditions, such as pressure cooker conditions, and varying the degree of hydrolysis. On the other hand, as the target sample, materials that actually constitute parts of devices or components, such as automotive parts, aircraft parts, and electrical and electronic equipment, can be suitably applied. Materials that have undergone actual use for a certain period of time can also be applied. In this way, by applying constituent materials from devices and components actually used as target samples and estimating the degree of hydrolysis and the resulting deterioration in those constituent materials, it is possible to determine, for example, whether measures to counteract the progression of hydrolysis, such as replacement or maintenance, should be taken for parts containing those constituent materials. Furthermore, information on the progression of hydrolysis can be used as basic information for future consideration and development of constituent materials, as well as for consideration of the usage environment of constituent materials.

[0036] NIR absorption spectroscopy is a technique that quantitatively obtains information about the chemical state of an object to be evaluated simply by the incidence and detection of light on the object. Therefore, in the resin material analysis method according to this embodiment, the degree of hydrolysis in the object to be evaluated can be evaluated non-destructively and non-invasively. This is particularly advantageous when the object to be evaluated constitutes a device or component that is actually used, as described above. Furthermore, in the resin material analysis method according to this embodiment, the degree of hydrolysis is evaluated by focusing on the contribution of NIR absorption originating from OH groups, so the degree of OH group formation due to hydrolysis can be evaluated sensitively and with high accuracy.

[0037] <Evaluation of hydrolysis using multiple regression analysis> Finally, we will specifically explain one example of a method for performing the estimation process: using multiple regression analysis. Here, we will describe a form of multiple regression analysis that uses principal component analysis (PCA).

[0038] First, each reference spectrum is subjected to appropriate preprocessing, such as averaging, standardization (normalization), and smoothing using the Savitzky-Golay method, and then principal component analysis is performed on the reference spectrum group. Then, the scores of multiple principal components are extracted. For example, the scores of the first and second principal components can be extracted. As a specific example, Figure 2 shows the score plots of the first and second principal components obtained when principal component analysis is performed on the reference spectrum group shown in Figure 1. In Figure 1, for the sake of simplicity, only one spectrum is displayed for each elapsed time, but in reality, four spectra were obtained for each elapsed time by changing the sample individual, and Figure 2 shows the results obtained using all four spectra for each elapsed time.

[0039] Next, the target spectrum is pre-processed as appropriate, similar to the reference spectrum, and the loading is calculated for each principal component (the first and second principal components in the example above). Then, the score for each principal component is calculated from the obtained loading. The score obtained from the target spectrum is then compared with the score plot (map) obtained from the reference spectrum, as shown in Figure 2, and the degree of hydrolysis in the target sample can be estimated based on the distribution and values ​​of the scores. Specifically, if the score obtained from the target spectrum is close to the score of the reference spectrum obtained under a certain hydrolysis condition, or if it is located near the region where the plot points of the reference spectrum obtained under a certain hydrolysis condition are distributed, it can be estimated that the target sample has undergone a degree of hydrolysis similar to that which would occur under that hydrolysis condition.

[0040] In the example shown in Figure 2, for the reference spectrum group, the four plotted points representing the same elapsed time under hydrolysis conditions, i.e., high temperature and high humidity, generally show a downward-sloping distribution. In other words, as the first principal component score increases, the second principal component score tends to decrease. For example, the dashed lines show the approximate straight lines for the plotted points at elapsed times of 0 and 5 hours, respectively (lines C and D). As the elapsed time increases, the region where the plotted points are distributed shifts in the direction where the first principal component score decreases, as indicated by the arrows in the figure. When the first and second principal component scores obtained from the target spectrum are plotted in the figure, the position of the plotted points can be estimated to be close to the region where the plotted points for which elapsed time obtained from the reference spectrum are distributed, depending on which elapsed time corresponds to which degree of hydrolysis progression in the target sample. For example, if the position of the plotted point obtained from the target spectrum is between lines C and D, and is close to line D, it can be estimated that the target sample has undergone hydrolysis equivalent to that which would occur if it were left at a temperature of 120°C and a humidity of 85% RH for nearly 5 hours.

[0041] Furthermore, Figure 3 shows an example of the results of the estimation process using the results of principal component analysis. Here, the degree of hydrolysis is estimated using the same reference spectrum as in Figure 1 and the score plot obtained in the same way as in Figure 2. Specifically, principal component analysis was performed on multiple reference spectra with different elapsed times in a high-temperature, high-humidity environment (120°C, 85%RH) as described above, and the first and second principal components were extracted to create score plots. Note that while the score plots in Figure 2 were created using 4 data points for each elapsed time, here 2 data points (3 points in some cases) were used for each elapsed time. Then, scores were calculated for the first and second principal components extracted by principal component analysis above for these reference spectra and multiple target spectra. Here, the multiple target spectra were measured on target samples in the same high-temperature, high-humidity environment (120°C, 85%RH) as the reference sample, where the resin material was left for a predetermined time, and these were not used to create the score plots above.

[0042] Using the scores calculated above for the reference spectrum and the target spectrum, the degree of hydrolysis progression was estimated based on its position on the score plot, converted to a value representing the elapsed time in a high-temperature, high-humidity environment (120°C, 85%RH). In Figure 3, the horizontal axis represents the actual elapsed time in a high-temperature, high-humidity environment (measured value), and the vertical axis represents the elapsed time in a high-temperature, high-humidity environment obtained as a result of the estimation (estimated value). As shown in Figure 3, estimated values ​​that reproduce the measured values ​​well were obtained not only for each reference sample but also for the target sample across the entire range of elapsed time. Furthermore, the agreement between the estimated value of the target sample and the estimated value of the reference sample was also high. From these results, it is confirmed that the resin material analysis method according to this embodiment can estimate the degree of hydrolysis progression by estimation step with high accuracy.

[0043] Although embodiments of the present disclosure have been described in detail above, the present invention is not limited in any way to the above embodiments, and various modifications are possible without departing from the spirit of the present invention.

Claims

1. Regarding resin materials containing hydrolyzable polymers, A reference measurement step involves performing near-infrared spectroscopy measurements on multiple reference samples composed of resin materials with different degrees of hydrolysis progression to obtain multiple reference spectra, A target measurement step involves performing near-infrared spectroscopy on a target sample composed of the aforementioned resin material whose degree of hydrolysis is unknown, in order to obtain a target spectrum. A resin material analysis method comprising: an estimation step of estimating the degree of hydrolysis progression in a target sample by comparing the target spectrum with a plurality of reference spectra in a wavelength region that includes the contribution of near-infrared absorption by hydroxyl groups.

2. The resin material analysis method according to claim 1, wherein the polymer has at least one of an ester bond and an amide bond.

3. The resin material analysis method according to claim 1, wherein in the estimation step, the wavelength range includes a region of 1800 nm to 2000 nm.

4. The resin material analysis method according to claim 1, wherein the comparison of a plurality of reference spectra and the target spectrum in the estimation step is performed using multiple regression analysis.

5. A resin material analyzer that performs the resin material analysis method according to any one of claims 1 to 4.

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