Method for specifying state of polyamide resin by chemiluminescence and apparatus used therefor

Abstract

To provide a method for specifying a state in which main-chain degradation of a polyamide resin progresses most by utilization of chemiluminescence (CL).SOLUTION: A method for specifying a state in which main-chain degradation of a polyamide resin progresses most includes: a light-emission amount measuring step of arranging a polyamide resin in an oxidation-promoting gas atmosphere and measuring a temporal change in an amount of chemiluminescence emitted from the polyamide resin while increasing a temperature at a constant rate from an initial temperature K1 to a final temperature K2 with K1<K2; and a peak-detection step of detecting, on the basis of the temporal change in the amount of chemiluminescence measured in the light-emission amount measuring step, a time at which the amount of chemiluminescence becomes maximum.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a method for identifying the state of a polyamide resin by chemiluminescence and an apparatus used therefor. [Background technology]

[0002] Polyamide resins such as polyamide 6 and polyamide 6·6 are known as typical engineering plastics. Due to their excellent heat resistance, strength, and rigidity, polyamide resins are widely used in automotive parts, electrical and electronic parts, building materials, and other applications. Demand for polyamide resins is particularly high for automotive parts, and they are used as raw resins for engine covers, door mirrors, console boxes, and other components. While engineering plastics generally have excellent durability, oxidation due to aging is inevitable.

[0003] For example, Non-Patent Document 1 describes a method for evaluating the oxidative degradation of a substance using chemiluminescence (hereinafter sometimes simply referred to as "CL"). Non-Patent Document 1 explains that CL is a luminescence phenomenon in which electrons are excited to an energy level one or more steps higher by energy generated by a chemical reaction and are emitted when they deactivate from that energy level to the ground state, and shows that the degree of oxidative degradation of a polymer can be evaluated by highly sensitively detecting weak luminescence from peroxides produced by the oxidation reaction of a polymer. Generally, the greater the amount of CL luminescence, the greater the amount of peroxides in the sample. In this case, the sample is evaluated to be more deteriorated.

[0004] Methods for evaluating the oxidative degradation of materials using CL are often carried out on olefins (Non-Patent Documents 2-4), and the evaluation results for olefins are relatively stable. In particular, for olefins, the evaluation method that measures the integrated CL luminescence amount is the mainstream (Non-Patent Document 5). On the other hand, research on polyamide resins is still limited (Non-Patent Documents 6-7). [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] JIS K 7351:2018, "Highly sensitive measurement method for weak luminescence of peroxides contained in plastics" [Non-patent document 2] Satoru Sato et al., "Recent Trends in Highly Sensitive Chemiluminescence Measurement Methods: From the Detection of Microoxidation of Resins to Curing Reactions," Journal of the Adhesion Society of Japan, Vol. 55, No. 6, 2019, pp. 236-246 [Non-patent document 3] Fujio Oishi, "Application of Chemiluminescence to Polymer Degradation Research," Material Life, 1998, Vol. 10, No. 1, pp. 3-15 [Non-patent document 4] Yasunori Endo, "Establishment of a rapid and accurate evaluation method for food oxidative deterioration (1)", Kochi Prefectural Industrial Technology Center Research Report, 2018, No. 49, pp. 26-30 [Non-Patent Document 5] Tohoku Electronics Industry Co., Ltd., "Measurement of the oxidation stabilizer effect of plastic pellets by chemiluminescence", [online], [Retrieved April 23, 2024], Internet,<URL:https: / / www.aperza.com / catalog / page / 7594 / 21699 / > , <URL:https: / / uploads.strikinglycdn.com / files / 58170d69-ec6a-4be2-82c3-12d97c4f7144 / clpj2014_003.pdf?id=116080> [Non-patent document 6] B. Lanska and 2 others, "Chemiluminescence of polyamides III. Luminescence accompanied thermooxidation of lactam-based polyamides stabilized by antioxidants", Polymer Degradation and Stability, 2001, Volume 72, Issue 2, p. 249-258 [Non-Patent Document 7] Pierfrancesco Cerruti and 3 others, "Chemiluminescence from oxidation of polyamide 6,6: II. The effect of metal salts", Polymer Degradation and Stability, 2004, Volume 84, Issue 2, p. 199-206 Summary of the Invention [Problem to be solved by the invention]

[0006] The inventors' investigations revealed that accurate evaluation of the microdegradation of polyamide resins by measuring the CL luminescence intensity, as with olefins, is difficult. Two types of samples were prepared: polyamide 6 containing a phenolic antioxidant and polyamide 6 without a phenolic antioxidant. Each sample was placed in an oven for a predetermined period of time to allow oxidative degradation to proceed. Samples with different degrees of oxidative degradation were prepared by varying the time the samples were placed in the oven. The CL luminescence intensity of each sample was measured in an inert gas atmosphere for a total of 1 hour, with the temperature rising from 25°C to 200°C at a rate of 5°C / min and then isothermal from 200°C. The results are shown in Figure 1-1 (horizontal axis: time the sample was placed in the oven, vertical axis: CL luminescence intensity). Theoretically, the CL luminescence intensity should increase with increasing time in the oven due to the progress of oxidative degradation of the polyamide resin. However, as shown in Figure 1-1, the CL luminescence intensity decreased during the microdegradation period (when the sample was placed in the oven for a relatively short time), contrary to this theory. This phenomenon is thought to be due to the fact that polyamide resins have functional groups that make them more reactive with oxygen than olefins. Polyamide resins are more likely to generate peroxides than olefins during processing, such as extrusion and molding, and are presumed to contain more peroxides at the start of heating in an oven. These initial peroxides gradually decompose and decrease with heating in the oven, but as the heating time increases, new peroxides are generated. If the rate at which these new peroxides are generated exceeds the rate at which the initial peroxides are decomposed, the overall amount of peroxides increases, and the CL integrated light emission is thought to increase. Thus, even when attempting to evaluate the microdegradation of polyamide resins, which tend to accumulate peroxides during processing, appropriate evaluation is difficult because different phenomena occur than with polyolefins.

[0007] Furthermore, when we investigated the difference in CL integrated light emission intensity depending on whether or not an antioxidant was added, we found unexpected results. Polyamide resins containing antioxidants are less susceptible to oxidative degradation than polyamide resins without antioxidants, so it is expected that the CL integrated light emission intensity will decrease (for example, Figure 9 of Non-Patent Document 3 shows this expected result for olefins). However, contrary to this expectation, a phenomenon occurred in which the CL integrated light emission intensity increased for polyamide resins containing antioxidants, although the mechanism is unknown, as shown in Figure 1-1.

[0008] Therefore, the inventors evaluated the oxidative degradation of polyamide resins by changing the atmosphere from an inert gas to an oxygen gas atmosphere and measuring the change in CL emission intensity over time under isothermal conditions. Appendix F of Non-Patent Document 1 describes a method for estimating lifetime by measuring the oxidative induction time (OIT). For example, as shown in Figure F.1 of Non-Patent Document 1, the CL emission chart obtained for polyolefins clearly shows a peak rise, allowing for a clear definition of the oxidative induction time (a schematic diagram is shown in Figure 2 of the present disclosure). However, despite being subjected to the same conditions as polyolefins, polyamide resins exhibit multiple peaks, as shown in Figure 1-2, and the emission intensity continues to increase over time, resulting in a complex CL emission chart. Therefore, it is difficult to clearly define the oxidative induction time as with olefins. Thus, it is difficult to identify the oxidative degradation state of polyamide resins using CL, and direct measurement is still often performed using physical properties such as molecular weight and tensile properties.

[0009] As described above, it is difficult to identify the state of a polyamide resin using CL. The present invention was made in response to these problems in the prior art, and an object of the present invention is to provide a method for identifying the state in which main chain degradation of a polyamide resin is most advanced by utilizing CL. [Means for solving the problem]

[0010] As a result of intensive research to solve the above problems, the inventors of the present invention, when identifying the state in which the main-chain decomposition of the polyamide resin progresses most, placed the polyamide resin in an oxidation-promoting gas atmosphere and increased the temperature at a constant rate from an initial temperature K1 to a final temperature K2 (where K1 < K2), while measuring the change over time in the amount of chemiluminescence emission from the polyamide resin. According to the state identification method having a light emission amount measurement step and a peak detection step of detecting the time at which the chemiluminescence emission amount becomes maximum based on the change over time in the chemiluminescence emission amount measured in the light emission amount measurement step, it was found that the state of the polyamide resin can be evaluated with a high degree of relevance to the timing when the mechanical properties of the polyamide resin are impaired, and the present invention was completed.

[0011] The present invention is described below. [1] A method for identifying the state in which the main-chain decomposition of a polyamide resin progresses most, comprising: a light emission amount measurement step of placing a polyamide resin in an oxidation-promoting gas atmosphere and measuring the change over time in the amount of chemiluminescence emission from the polyamide resin while increasing the temperature at a constant rate from an initial temperature K1 to a final temperature K2 (where K1 < K2); and a peak detection step of detecting the time at which the chemiluminescence emission amount becomes maximum based on the change over time in the chemiluminescence emission amount measured in the light emission amount measurement step. [2] The state identification method according to [1], wherein the measurement in the light emission amount measurement step is performed by a chemiluminescence analyzer or a CCD camera. [3] The state identification method according to [1] or [2], wherein the final temperature K2 is less than the melting point of the polyamide resin. [4] An apparatus for identifying the state in which the main-chain decomposition of a polyamide resin progresses most, comprising: a polyamide resin sample chamber having oxidation-promoting gas control and heating control; <00,00074>a detection element for detecting the amount of chemiluminescence emission from the polyamide resin in the sample chamber; a light receiving unit including the detection element; a detection unit that records the change over time in the amount of chemiluminescence light detected by the detection element and detects the time when the amount of chemiluminescence light reaches its maximum. [Effects of the Invention]

[0012] According to the present invention, it is possible to evaluate the state in which main chain decomposition of a polyamide resin is most advanced, which was previously difficult. Since the present invention uses CL to evaluate the state of a polyamide resin, it is simple and convenient, eliminating the need for physical property evaluation tests such as molecular weight and tensile properties that were previously required. Furthermore, because the state of a polyamide resin can be evaluated in a short time, differences between samples (e.g., differences in degradation due to the presence or absence of additives) can be quickly checked. This facilitates material selection and material modification. Furthermore, the present invention can be applied to polyamide resins containing antioxidants, which have complex luminescence behavior and have not previously been used for CL. [Brief explanation of the drawings]

[0013] [Figure 1-1] Figure 1-1 is a graph showing the results of measuring the integrated CL luminescence intensity of polyamide 6 containing a phenolic antioxidant and polyamide 6 not containing a phenolic antioxidant under a nitrogen gas atmosphere, with the temperature rising from 25°C to 200°C at a rate of 5°C / min and then being isothermal from 200°C (total 1 hour). [Figure 1-2] FIG. 1-2 is a graph showing the results of measuring the CL emission amount of polyamide 6 under isothermal conditions at 140° C. in an oxygen gas atmosphere. [Figure 1-3] Figure 1-3 is a graph showing the results of measuring the CL emission intensity of polyamide 6·6 under an oxygen gas atmosphere at a temperature increase rate of 1.0°C / min. [Figure 2] FIG. 2 is a schematic diagram showing the change over time in the CL emission intensity of polyolefins under isothermal conditions in an oxygen gas atmosphere. [Figure 3] FIG. 3 shows the CL emission charts obtained in Examples 1 to 3. [Figure 4] FIG. 4 shows the results of the physical property measurements obtained in Examples 1 to 3. [Figure 5] Figure 5 is a graph comparing the results of the CL emission amount and physical properties obtained in Example 2. [Figure 6-1] Figure 6-1 shows the CL emission charts obtained in Examples 3 to 4. [Figure 6-2] Figure 6-2 is a graph comparing the results of the CL emission amount and the elongation at break obtained in Examples 3 to 4. [Figure 7] Figure 7 shows the CL emission charts obtained in Examples 1 to 6. [Figure 8] Figure 8 is a schematic diagram showing an example of the state specifying device of the present invention. [Figure 9] Figure 9 shows the results of the integral type equal change rate method used for the kinematic analysis.

MODE FOR CARRYING OUT THE INVENTION

[0014] The present invention is a method for specifying the state in which the main chain decomposition of a polyamide resin progresses most, placing the polyamide resin in an oxidation-promoting gas atmosphere, measuring the change over time in the CL emission amount from the polyamide resin while raising the temperature at a constant rate from an initial temperature K 1 to a final temperature K 2 (where K 1 < K 2), and a peak detection step of detecting the time when the CL emission amount becomes maximum (hereinafter sometimes simply referred to as "deterioration time" or "Td") based on the change over time in the CL emission amount measured in the emission amount measurement step, and relates to a state specifying method having the above. Specifying the state in which the main chain decomposition of the polyamide resin progresses most leads to predicting the timing when the mechanical properties of the polyamide resin are impaired by oxidative degradation. As a result of investigations by the present inventors, it was found that the deterioration time when the CL emission amount becomes maximum particularly coincides with the timing when the elongation at break significantly decreases. Since the time when the elongation at break significantly decreases is also the timing when the main chain decomposition of the polyamide resin progresses most, by specifying the timing when such oxidative degradation of the polyamide resin progresses most, the susceptibility to oxidative degradation of the polyamide resin can be easily compared between samples.

[0015] In the present invention, the light emission amount measurement step is carried out in an oxidation-promoting gas atmosphere. In the measurement in an inert gas atmosphere widely applied to olefins, since the sample is not oxidized during the measurement, the oxidation state corresponding to the peroxide contained in the sample can be evaluated. On the other hand, when measuring in an oxidation-promoting gas atmosphere as in the present invention, the oxidation of the sample proceeds during the measurement. In the present invention, this property is utilized, and by measuring in an oxidation-promoting gas atmosphere, the process in which the polyamide resin oxidizes over time can be grasped more accurately. Examples of the oxidation-promoting gas include oxygen, air, ozone, etc., and oxygen is preferably used.

[0016] In the light emission amount measurement step, a temperature-rising measurement is carried out in which the temperature is raised at a constant rate from the initial temperature K1 to the final temperature K2 (where K1 < K2). As shown in FIGS. 1-3, the temperature-rising measurement has a shorter measurement time than the isothermal measurement, and the state in which the main chain decomposition progresses most can be specified in a short time.

[0017] The initial temperature K1 is preferably 25 to 80°C, more preferably 35 to 70°C, and still more preferably 45 to 60°C. By starting the measurement from a relatively low temperature, it becomes easier to specify the state of the polyamide resin.

[0018] The final temperature K2 is preferably above the initial temperature K1 and below the melting point of the polyamide resin to be measured, preferably 100 to 300°C, more preferably 130 to 290°C, and still more preferably 160 to 280°C. When the final temperature K2 is equal to or higher than the melting point of the polyamide resin to be measured, the polyamide resin may melt during the measurement, making the measurement difficult.

[0019] The temperature-rising rate is appropriately set based on the measurement time, the initial temperature K1, the final temperature K2, etc., but is preferably 0.1 to 3.5°C / min, more preferably 0.2 to 3.0°C / min, and still more preferably 0.3 to 2.5°C / min. The shape of the CL emission chart obtained becomes sharper as the temperature-rising rate increases. Also, the measurement time can be shortened as the temperature-rising temperature increases. On the other hand, as the temperature-rising temperature decreases, the peak resolution becomes higher, so the peak position of the CL emission amount can be measured more accurately.

[0020] In this way, in the luminescence amount measurement step, the change over time in the amount of CL luminescence from the polyamide resin is measured. This measurement yields a CL luminescence chart (horizontal axis: time, vertical axis: CL luminescence amount). The measurement in the luminescence amount measurement step can be performed using a CL analyzer or a CCD camera. Specific measurement methods and devices will be described later.

[0021] The end point of the luminescence intensity measurement step is not particularly limited, but it is advisable to continue the measurement until a mountain-shaped CL emission chart is obtained. In the obtained mountain-shaped CL emission chart, the point at which the CL emission intensity is maximum is defined as the peak in the present invention. The luminescence intensity measurement step should be continued until the CL emission intensity has decreased to 5 to 70% (more preferably 10 to 60%) of the CL emission intensity measured at the peak after the deterioration time has elapsed. Alternatively, the luminescence intensity measurement step should be continued until 0.3 × Td to Td (more preferably 0.4 × Td to 0.8 × Td) has elapsed after the deterioration time (Td). By continuing the measurement for a sufficient period of time after the peak is confirmed, the peak position of the CL emission intensity can be accurately determined. This point should also be taken into consideration when setting the measurement time in the luminescence intensity measurement step.

[0022] In the next peak detection step, the degradation time is detected based on the change over time in the CL emission intensity measured in the luminescence intensity measurement step. By comparing the detected degradation times between samples, it is possible to evaluate which samples are less susceptible to oxidative degradation. The longer the time required for the main chain of a sample to decompose, the longer the degradation time. In other words, when the degradation times of multiple samples are measured under the same conditions, samples with longer degradation times can be evaluated as less susceptible to oxidative degradation. Thus, the degradation time determined in the present invention can be used as an evaluation index for oxidative degradation of polyamide resins.

[0023] It is also possible to perform reaction kinetic analysis using the ambient temperature (degradation temperature) at which the CL emission intensity is at its maximum. In the present invention, the CL emission intensity is measured while increasing the temperature at a constant rate, so the constant rate method is preferably used for kinetic analysis.

[0024] The present invention may further include a matching step of matching the degradation time with the state in which main chain decomposition of the polyamide resin progresses most. By linking the degradation time with the timing in which main chain decomposition of the polyamide resin progresses most, it becomes possible to easily compare the susceptibility of polyamide resins to oxidative degradation between samples.

[0025] In this disclosure, a polyamide resin is a polymer having an amide group as the main structural unit of the polymer main chain. Since the subject of this disclosure is CL emission derived from the main chain of the polyamide resin (i.e., derived from the amide group), the present invention can be widely applied to polyamide resins having an amide group. Examples of polyamide resins include aliphatic polyamide resins (including alicyclic polyamide resins) and semi-aromatic polyamide resins, which can be used alone or in combination of two or more. Among these, aliphatic polyamide resins are preferred as polyamide resins.

[0026] Examples of aliphatic polyamide resins include polyamide 5, polyamide 6, polyamide 6·6, polyamide 4·6, polyamide 6·10, polyamide 6·12, polyamide 6·14, polyamide 6·13, polyamide 6·15, polyamide 6·16, polyamide 9·2, polyamide 9·10, polyamide 9·12, polyamide 9·13, polyamide 9·14, polyamide 9·15, polyamide 6·16, polyamide 9·36, polyamide 10·10, polyamide 10·12, polyamide 10·13, polyamide 10·14, polyamide 11, polyamide 12, polyamide 12·10, polyamide 12·12, polyamide 12·13, and polyamide 12·14. Among these, polyamide 5, polyamide 6, polyamide 6·6, polyamide 6·10, polyamide 11, and polyamide 12 are preferred, and polyamide 6 and polyamide 6·6 are more preferred.

[0027] Examples of semi-aromatic polyamide resins include polyamide 4T (T: terephthalic acid), polyamide 4I (I: isophthalic acid), polyamide 6T, polyamide 6I, polyamide 7T, polyamide 8T, polyamide 9T, polyamide 10T, polyamide 11T, polyamide 12T, polyamide M5T (M5: methylpentadiamine), polyamide 6T / 6, polyamide 6T / 11, polyamide 6T / 12, polyamide 6T / 46, polyamide 6T / 66, polyamide 6T / 610, polyamide 6T / 612, polyamide 6T / 6I, polyamide 6T / 6I / 66, and polyamide 6T / M5T.

[0028] The polyamide resin may contain resins other than polyamide resin, but the content of resins other than polyamide resin is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 3 parts by mass or less, still more preferably 1 part by mass or less, and particularly preferably 0.1 parts by mass or less, per 100 parts by mass of polyamide resin, with the lower limit being 0 parts by mass. The lower the content of resins other than polyamide resin, the more appropriately the state of the polyamide resin can be evaluated by CL.

[0029] The polyamide resin may contain additives such as antioxidants, flame retardants, antistatic agents, release agents, lubricants, adhesion improvers, nucleating agents (including crystallization agents), compatibilizers, stabilizers, reinforcing agents (including various minerals such as glass filler, carbon fiber, and talc), elastomers for improving toughness, and amorphous resins for controlling crystallization. These may be used alone or in combination of two or more.

[0030] Hereinafter, the state identifying device according to the present invention will be described in detail with reference to the drawings showing embodiments. However, the present invention is not limited to the illustrated examples, and it is possible to carry out the present invention by making appropriate modifications within the scope that can conform to the purpose described above and below, and all of these modifications are included in the technical scope of the present invention.

[0031] FIG. 8 is a schematic diagram showing an example of a state determining device of the present invention. The present invention encompasses a device for determining the state in which main chain decomposition of a polyamide resin is most advanced. The state determining device 10 of the present invention includes a polyamide resin sample chamber 3 having an oxidation-promoting gas control 1 and a heating control 2, a detection element 5 that detects the amount of CL emission from the polyamide resin 4 in the sample chamber 3, a light-receiving unit 6 equipped with the detection element 5, and a detection unit 7 that records the change over time in the amount of CL emission detected by the detection element 5 and detects the time when the amount of CL emission is at its maximum. The state determining device 10 of the present invention can appropriately evaluate the susceptibility of polyamide resin to oxidative degradation.

[0032] The oxidation-promoting gas control 1 can adjust the inside of the polyamide sample chamber 3 to an oxidation-promoting gas atmosphere. The heating control 2 can also manage the temperature inside the polyamide sample chamber 3. The heating control 2 may further include a heating unit 9, and the inside of the polyamide sample chamber 3 is heated by the heat emitted from the heating unit 9.

[0033] A polyamide resin 4 used as a sample is contained in a polyamide sample chamber 3. The polyamide sample chamber 3 may be provided with a sample container 8 capable of sealingly containing the polyamide resin 4. In order to measure weak luminescence due to CL, the polyamide sample chamber 3 is preferably a dark room.

[0034] The CL from the heated polyamide resin 4 is captured by the light receiving unit 6 and detected as CL by the detection element 5. Data regarding the change over time in the amount of CL emission acquired by the detection element 5 is sent to the detection unit 7 and recorded by the detection unit 7. The detection unit 7 determines the deterioration time. The detection unit 7 may perform noise cancellation processing on the data regarding the change over time in the amount of CL emission. [Example]

[0035] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples, and it is possible to carry out the invention by making appropriate modifications within the scope of the above and below-described aims, and all such modifications are included in the technical scope of the present invention.

[0036] <Creating dumbbell test specimens> In Examples 1-3, polyamide 6·6 (Ascend Performance Materials, trade name "Vydyne 21Z") alone was fed into a twin-screw extruder (CONTINENT MACHINERY INDUSTRIES, "CM-MTE31"), while in Examples 4-6, the polyamide 6·6 was fed with an antioxidant (BASF Japan, trade name "Irganox 245") at a concentration of 0.3 wt%. The mixture was melt-mixed in the barrel and extruded into strands. The strands extruded from the die were cooled in water and cut into pellets using a strand cutter. The mixture was then injection-molded into 127 mm x 12.7 mm x 0.4 mm flat plates using an injection molding machine (Sodick, "LA40"), which were then punched into small dumbbell shapes conforming to ASTM D-1822-L. Dumbbell test specimens were prepared by cutting 12 mm from each end to fit onto the sample pan.

[0037] <Examples 1 to 3> 1) Measurement of CL emission from polyamide resin A dumbbell test piece made of polyamide resin to which no antioxidant was added was placed in the sample chamber (Tohoku Electronics Industries Co., Ltd., product name "Heated Sample Chamber (CLS-ST5)") of a chemiluminescence analyzer (Tohoku Electronics Industries Co., Ltd., product name "Ultra-Weak Emission Detection Spectrometer (CLA-FS5)"), and the amount of CL emission from the polyamide resin was measured while the temperature was raised at a constant temperature from an initial temperature of 50°C in an oxygen gas atmosphere (heating rate: 0.5°C / min (Example 1), 1.0°C / min (Example 2), 2.0°C / min (Example 3)). A CL emission chart was obtained. Figure 3 shows the CL emission chart obtained at each heating rate. In Example 1, the CL emission amount was measured from the start of measurement until 400 minutes later (finishing temperature: 250°C). At this time, it was confirmed that no new peak was formed after the main peak was confirmed and the CL emission amount continued to decrease. Therefore, in Example 2, the measurement of the CL emission amount was stopped when the CL emission amount had decreased by 55% from the point at which the CL emission amount was maximum, and in Example 3, when the CL emission amount had decreased by 45% from the point at which the CL emission amount was maximum.

[0038] 2) Measurement of polyamide resin properties In the CL emission chart obtained in 1), dumbbell test pieces were taken out at the following six emission points, and the amount of amino terminals, the amount of acid terminals, the weight-average molecular weight, and the tensile elongation at break were measured. The measurement methods for each physical property are shown in 2-1) to 2-4) below. The measurement results are shown in Figure 4. <Lighting point> BL: Start of measurement (blank) 1st point: The point at which the CL light output begins to rise 2nd point: The point at which the first small peak (shoulder peak) of CL emission reaches its maximum (peak top). 3rd point: The point where the CL light emission intensity changes from a small peak to the main peak (the point where the slope of the CL light emission chart changes) 4th point: The point at which the CL light output reaches its maximum 5th point: When the CL light output has decreased by 15% from the maximum.

[0039] 2-1) Amino terminal amount 10-15 mg of sample was dissolved in 0.6 mL of solvent (0.3 mL of deuterated benzene (CD6): 0.3 mL, 0.3 mL of deuterated hexafluoroisopropanol (HFIP-d)), followed by centrifugation. 8 μL of 0.2 M triethylamine (TEA) / deuterated chloroform (CDCl3) was added to the resulting supernatant, and proton nuclear magnetic resonance spectroscopy ( 1 H-NMR measurements were carried out, and the amount of amino terminal was calculated from the integral value of the obtained components. The peak of the amino terminal was detected in the vicinity of 2.4 to 2.5 ppm in the NMR spectrum.

[0040] 2-2) Acid terminal amount In the same manner as in "2-1) Amino terminal amount," proton nuclear magnetic resonance spectrum ( 1 H-NMR measurement was carried out, and the amount of acid terminals was calculated from the integral value of the obtained components. The peak of the acid terminals was used, which was detected in the vicinity of 2.1 to 2.2 ppm in the NMR spectrum.

[0041] 2-3) Weight average molecular weight 2.0 mg of sample was weighed and dissolved in 4 mL of 10 mM hexafluoroisopropanol (HFIP) / sodium trifluoroacetate solution, and then filtered through a 0.2 μm pore size membrane filter. The resulting sample solution was analyzed by gel permeation chromatography (GPC) to determine the weight-average molecular weight. Note that the molecular weight was converted to standard polymethyl methacrylate (PMMA). Equipment: Tosoh "HLC-8320GPC" Columns: Tosoh "TSKgel SuperHM-H x 2", "TSKgel SuperH2000" Flow rate: 0.2mL / min Injection volume: 10μL Temperature: 40℃ Detector: RI

[0042] 2-4) Tensile elongation at break In accordance with JIS K6251:2023, the tensile elongation at break was measured using a dumbbell test piece and an autograph (AGX-1kNVD, manufactured by Shimadzu Corporation) with a load cell of 1 kN, a grip distance of 30 mm, and a tensile speed of 10 mm / min. Note that because the dumbbell test piece was small and measurement was difficult, the tensile elongation at break was calculated based on the displacement of the grip distance rather than the displacement of the gauge length.

[0043] As shown in Figure 4, the physical properties were confirmed to be equivalent at each emission point, regardless of the heating rate.

[0044] 3) Comparison of CL emission intensity and physical properties Taking the temperature rise rate of 1.0°C / min (Example 2) as an example, the CL emission amount and physical properties were compared. The results are shown in Figure 5. The amount of amino terminals decreased from the early stage of the BL~1st point. The amount of acid terminals increased in the latter half of the 2nd point and beyond, along with the increase in CL emission. Although the mechanism is unclear, as shown in formula (I), in the early stages of oxidative degradation, the amino terminals trap the peroxide radicals generated by oxidation, causing a reaction that inhibits the radical chain reaction, which is thought to accelerate the consumption of amino terminals. On the other hand, as oxidative degradation progresses, the radical trapping function of the amino terminals is lost, causing the decomposition of the polyamide main chain and the generation of acid terminals. It is presumed that the CL emission at the BL~3rd point is mainly due to reactions at the amino terminals.

[0045] [ka]

[0046] We also examined the weight-average molecular weight and tensile elongation at break. The weight-average molecular weight gradually decreased after the first point and then increased between the fourth and fifth points. It is presumed that after the first point, the polyamide resin decomposition reaction began along with the reaction of the amino terminals, and the crosslinking reaction progressed between the fourth and fifth points. Meanwhile, the tensile elongation at break gradually decreased between the first and second points, then dropped sharply after the second point and leveled off between the fourth and fifth points. It is presumed that after the second point, the polyamide resin decomposition reaction became the main reaction, causing the tensile elongation at break to drop sharply. Furthermore, since it remained level between the fourth and fifth points, it is believed that main-chain decomposition was largely completed by the fourth point. Therefore, it is presumed that main-chain decomposition of the polyamide resin began after the second point, and the large CL emission between the third and fourth points is primarily due to main-chain decomposition of the polyamide resin.

[0047] The above results indicate that the degradation time at which the CL emission intensity reaches its maximum coincides with the timing at which the tensile elongation at break is significantly reduced (i.e., the state in which main chain degradation of the polyamide resin is most advanced). Because the influence of the amino terminal can be suppressed at the peak point, the oxidative degradation state of the polyamide resin can be evaluated with high sensitivity.

[0048] Example 4 Using a dumbbell test piece formed from a polyamide resin containing an antioxidant, the CL emission amount was measured in the same manner as in Example 1, except that the heating rate was set to 2.0°C / min, and a CL emission chart was obtained. Furthermore, using the dumbbell test piece, the tensile elongation at break was measured in the same manner as in Example 1. Figure 6-1 shows the CL emission charts obtained in Examples 3 and 4 side by side. Figure 6-2 compares the results of the CL emission amount and tensile elongation at break obtained in Examples 3 and 4. For systems containing an antioxidant, the emission points were set to the following seven points: <Lighting point> BL: Start of measurement (blank) 1st point: The point at which the CL light output begins to rise 2nd point: The start point of the small peak (shoulder peak) formed by adding antioxidants 3rd point: The point at which the small peak formed by adding the antioxidant reaches its maximum (peak top) 4th point: The point where the CL light emission intensity changes from a small peak to the main peak (the point where the slope of the CL light emission chart changes) 5th point: The point at which the CL light output reaches its maximum 6th point: When the CL light output has decreased by 15% from the maximum.

[0049] As shown in Figure 6-1, the polyamide resin containing an antioxidant (Example 4) exhibited a longer degradation time than the polyamide resin without an antioxidant (Example 3). This indicates that the time required for main chain decomposition of the polyamide resin in Example 4 was longer, and Example 4 can be evaluated as a polyamide resin less susceptible to oxidative degradation. It is also important to note that the polyamide resin containing an antioxidant (Example 4) exhibited a higher CL emission intensity than the polyamide resin without an antioxidant (Example 3). Previously, it was believed that the inclusion of an antioxidant in olefins reduced the CL emission intensity (leading to an assessment that oxidative degradation of the resin was suppressed). However, in contrast, the polyamide resin containing an antioxidant did not exhibit a decrease in CL emission intensity, which should have suppressed oxidative degradation and reduced the CL emission intensity. This is presumably the reason why the conventional method using the integrated CL emission intensity, as shown in Figure 1-1, was unable to adequately evaluate the oxidative degradation state of the polyamide resin containing an antioxidant. According to the method of the present invention, by comparing the degradation time between samples rather than the CL emission amount, it is possible to appropriately evaluate which sample is less susceptible to oxidative degradation.

[0050] Furthermore, as shown in Figure 6-1, a shoulder was observed near the third point in the polyamide resin containing an antioxidant (Example 4) (the area enclosed by the dotted line in Figure 6-1), which did not appear in the polyamide resin without an antioxidant (Example 3). The CL emission intensity increased sharply immediately after this shoulder was observed. Furthermore, as shown in Figure 6-2, while the CL emission intensity increased, the tensile elongation at break significantly decreased. These facts suggest that the main chain degradation of the polyamide resin progressed significantly after the antioxidant activity disappeared, and therefore the shoulder is presumed to be derived from the antioxidant. This fact also indicates that the conventional method of evaluating heat resistance due to differences in resin composition or additive performance by aligning the measurement time and evaluating the magnitude of the integrated CL emission intensity regardless of the peak in the CL emission chart is not necessarily appropriate. When evaluating the oxidative degradation resistance of a polyamide resin using CL, it is necessary to identify the timing of oxidative degradation of the resin (i.e., identify the state in which main chain degradation of the polyamide resin is most advanced). In the present invention, this timing is evaluated in relation to the degradation time.

[0051] <Examples 5 and 6> The CL emission intensity was measured and a CL emission chart was obtained in the same manner as in Example 4, except that the temperature rise rate was 1.0°C / min (Example 5) and 0.5°C / min (Example 6). The CL emission charts obtained in Examples 1 to 6 are shown side by side in Figure 7. As shown in Figure 7, the polyamide resins containing antioxidants (Examples 4 to 6) showed a longer degradation time than the polyamide resins without antioxidants (Examples 1 to 3). As mentioned above, this shows that the polyamide resins containing antioxidants took a longer time to undergo main chain decomposition, and it can be said that the antioxidant-containing polyamide resins of Examples 4 to 6 are resins that are more resistant to oxidative degradation.

[0052] 4) Peak-based reaction kinetics The atmospheric temperatures (deterioration temperatures) at which the CL emission amount was at its maximum in Examples 1 to 6 are summarized below. Example 1 (without antioxidant): 0.5°C / min, degradation temperature: 192.6°C Example 2 (without antioxidant): 1.0°C / min, degradation temperature: 205.8°C Example 3 (without antioxidant): 2.0°C / min, degradation temperature: 216.8°C Example 4 (with antioxidant) 2.0°C / min, degradation temperature 236.7°C Example 5 (with antioxidant) 1.0°C / min, degradation temperature 227.0°C Example 6 (with antioxidant) 0.5°C / min, degradation temperature 215.1°C The activation energy ΔE was calculated using the above series of data obtained from measurements at different heating rates. In the present invention, the analytical formula of the integral constant rate method proposed by Akabira et al. (Akabira Takeo et al., "Research Report of Chiba Institute of Technology (Science and Engineering Edition)", Vol. 16, 22 (1971)) was used to perform kinetic analysis using the following formula (Eq. 1):

number

[0053] (In Eq. 1, ΔE: activation energy (kJ / mol), β: heating rate (℃ / min), T1: degradation temperature (K), R: gas constant)

[0054] The results are shown in Figure 9. The activation energy ΔE obtained from Examples 1 to 3 A is approximately 100 (= 12059 × 8.31 / 1000) kJ / mol, and the activation energy ΔE calculated from Examples 4 to 6 B is approximately 124 (= 14899 × 8.31 / 1000) kJ / mol, and ΔE A <ΔE B In other words, it is clear that Examples 4 to 6, which contain an antioxidant, have better heat resistance. As described above, according to the present invention, it is also possible to perform kinetic analysis using the ambient temperature at which the CL emission intensity is maximized. [Explanation of symbols]

[0055] 1. Pro-oxidant gas control 2 Heating control 3 Polyamide resin sample chamber 4 Polyamide resin (sample) 5. Detector element 6 Light receiving part 7. Detection Unit 8 Sample container 9 Heating section 10. State Identification Device

Claims

1. A method for identifying a state in which main chain decomposition of a polyamide resin progresses most, comprising: a light emission measurement step of placing a polyamide resin in an oxidation-promoting gas atmosphere, and measuring the change over time in the amount of chemiluminescence light emitted from the polyamide resin while increasing the temperature from an initial temperature K1 to an end temperature K2 (where K1<K2) at a constant rate; and and a peak detection step of detecting the time at which the chemiluminescence luminescence amount reaches a maximum based on the change over time in the chemiluminescence luminescence amount measured in the luminescence amount measurement step.

2. The method for specifying a condition according to claim 1, wherein the measurement in the luminescence amount measuring step is carried out using a chemiluminescence analyzer or a CCD camera.

3. The condition specifying method according to claim 1 or 2, wherein the end temperature K2 is lower than the melting point of the polyamide resin.

4. An apparatus for identifying a state in which main chain decomposition of a polyamide resin progresses most, a polyamide resin sample chamber with pro-oxidant gas control and heating control; a detection element for detecting the amount of chemiluminescence emitted from the polyamide resin in the sample chamber; a light receiving unit including the detection element; a detection unit that records the change over time in the amount of chemiluminescence light detected by the detection element and detects the time when the amount of chemiluminescence light reaches its maximum.

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