Method for evaluating degree of degradation caused by thermal decomposition reaction of thermoplastic polyester resin

Abstract

To provide a method for evaluating the degree of degradation caused by the thermal decomposition reaction of polyester resin simply and accurately.SOLUTION: The method for evaluating the degree of degradation caused by the thermal decomposition reaction of thermoplastic polyester resin comprises a step of analyzing a thermoplastic polyester resin molded product using nuclear magnetic resonance spectroscopy to quantify terminal vinyl groups.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating the degree of degradation due to thermal decomposition of a thermoplastic polyester resin. [Background technology]

[0002] Polybutylene terephthalate (PBT) resin, a thermoplastic polyester resin, offers an excellent balance of mechanical and electrical properties and can withstand high temperatures. This makes it widely used in automotive components, such as connectors, as they become smaller and lighter. However, PBT resin is known to undergo material degradation due to thermal decomposition and thermooxidative decomposition in harsh operating environments, such as high temperatures. In particular, during injection molding, the resin is subjected to temperatures high enough to melt, which can significantly accelerate material degradation due to thermal decomposition. Therefore, it is important to evaluate the degree of degradation due to thermal decomposition of thermoplastic polyester resins and develop effective countermeasures against this degradation.

[0003] In response to this, Patent Document 1 discloses a method for predicting the deterioration behavior of a polyester resin due to humidity and temperature from the increase in the concentration of terminal carboxyl groups in the polyester resin. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-169810 Summary of the Invention [Problem to be solved by the invention]

[0005] However, since the increase in the concentration of terminal carboxyl groups in a polyester resin evaluated in Patent Document 1 corresponds to the total amount produced by multiple decomposition reactions such as thermal decomposition, thermal oxidative decomposition, and hydrolysis, it is not possible to evaluate only the degradation due to the thermal decomposition reaction. Therefore, the prediction method in Patent Document 1 was insufficient in accuracy for evaluating the degree of degradation due to the thermal decomposition reaction of a polyester resin.

[0006] Other known methods for evaluating the degree of degradation of polyester resins include evaluation methods based on the amount of change in mechanical properties such as molecular weight, intrinsic viscosity, or tensile elongation characteristics. However, these methods are time-consuming and complicated, and do not reveal the mechanisms of the main decomposition reactions, so they have not been able to lead to efficient countermeasures against degradation.

[0007] The present invention has been made in view of the problems inherent in the prior art, and an object of the present invention is to provide an evaluation method capable of easily and accurately evaluating the degree of degradation due to the thermal decomposition reaction of a polyester resin. [Means for solving the problem]

[0008] An evaluation method according to an embodiment of the present invention is a method for evaluating the degree of degradation due to a thermal decomposition reaction of a thermoplastic polyester resin, and includes a step of analyzing a molded article of the thermoplastic polyester resin using nuclear magnetic resonance spectroscopy to quantify the amount of terminal vinyl groups. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an evaluation method that can simply and accurately evaluate the degree of degradation due to the thermal decomposition reaction of a polyester resin. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is an example of a proton nuclear magnetic resonance ( 1 H-NMR) spectrum of a sample of a PBT resin molded article obtained by the evaluation method according to the present embodiment. [Figure 2]1 is an example of a calibration curve showing the relationship between the reciprocal of the amount of terminal vinyl groups (VI) of a standard sample of a PBT resin molded article and the reciprocal of the cylinder temperature (1000 / T), obtained by the evaluation method according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] The evaluation method according to this embodiment will be described in detail below with reference to the drawings. Note that the dimensional ratios in the drawings are exaggerated for the sake of explanation and may differ from the actual ratios.

[0012] (thermoplastic polyester resin) The evaluation method according to this embodiment is a method for evaluating the degree of degradation due to a thermal decomposition reaction of a thermoplastic polyester resin, and includes a step of analyzing a molded article of the thermoplastic polyester resin using nuclear magnetic resonance (NMR) spectroscopy to quantify the amount of vinyl end groups (VEGs).

[0013] In the present embodiment, the deterioration of thermoplastic polyester resins refers to changes in the molecular structure of the polyester. It is known that deterioration of polyester resins progresses due to thermal decomposition reactions in harsh usage environments such as high temperatures. In particular, during injection molding, the polyester resin is subjected to a high-temperature environment that melts the polyester resin, so deterioration due to thermal decomposition reactions tends to progress significantly faster.

[0014] In this embodiment, the thermoplastic polyester resin to be evaluated for the degree of degradation due to a thermal decomposition reaction is a molded article (resin molded article) made of polyester resin. The resin molded article refers to a solid product obtained by subjecting a polyester raw material solid to a molding process such as injection molding. The polyester raw material solid refers to a raw material solid made of polyester that has been stored in an environment where degradation such as hydrolysis and thermal decomposition does not occur in the polyester after production. For example, polyester pellets and polyester powder are used as the polyester raw material solid.

[0015] The evaluation method according to this embodiment is a method for evaluating the degree of degradation due to thermal decomposition of a thermoplastic polyester resin. It is known that when polyester resins are exposed to high temperatures up to their thermal decomposition temperature, the thermal decomposition of the polymer main chain generates terminal carboxyl groups (-COOH) and terminal vinyl groups (-CH=CH2). Therefore, the degree of degradation due to thermal decomposition of a thermoplastic polyester resin can be evaluated by quantifying the terminal vinyl groups (VEG). For example, it is known that the rate of thermal decomposition of PBT resin increases significantly at temperatures above 280°C, and that at temperatures above 300°C, decomposition by other mechanisms or side reactions occur, resulting in accelerated weight loss. Therefore, to prevent thermal decomposition during injection molding, PBT resins are generally molded at temperatures below 280°C. According to the evaluation method according to this embodiment, the progress of the thermal decomposition reaction under these molding conditions can be efficiently confirmed by quantifying the terminal vinyl groups (VEG).

[0016] In this embodiment, the thermoplastic polyester resin to be evaluated for the degree of degradation due to a thermal decomposition reaction is not particularly limited as long as it generates a terminal vinyl group (VEG) as the thermal decomposition reaction progresses, and examples thereof include aromatic polyesters and aliphatic polyesters.

[0017] Examples of aromatic polyesters that can be used include polyester resins primarily composed of one or more resins selected from the group consisting of polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), polypropylene terephthalate (PPT), polyhexamethylene terephthalate (PHT), poly-1,4-cyclohexylene dimethylene terephthalate (PCT), polyethylene naphthalate (PEN), polytrimethylene naphthalate (PTN), polybutylene naphthalate (PBN), polypropylene naphthalate (PPN), polyhexamethylene naphthalate (PHN), and poly-1,4-cyclohexylene dimethylene naphthalate (PCN). Here, "major component" refers to the substance with the highest mass content in the polyester resin. For example, the polyester resin used in this embodiment may be a resin primarily composed of polybutylene terephthalate (PBT).

[0018] Examples of aliphatic polyesters that can be used include polyester resins containing, as a main component, one or more resins selected from the group consisting of polyethylene adipate, polybutylene adipate, polytetramethylene adipate, polyethylene succinate, polybutylene succinate, polylactic acid, polycaprolactone, polybutylene succinate, polycaprolactone butylene succinate, and polybutylene succinate adipate.

[0019] The thermoplastic polyester resin may also contain various additives in appropriate amounts as needed, such as antioxidants, flame retardants, inorganic fillers, flame retardant assistants, processing aids, crosslinking agents, metal deactivators, antioxidants, fillers, reinforcing agents, UV absorbers, stabilizers, plasticizers, pigments, dyes, colorants, antistatic agents, and foaming agents.

[0020] (Quantitative determination of terminal vinyl groups) In this embodiment, the amount of vinyl end groups (VEG) in a resin molded product is quantified using nuclear magnetic resonance (NMR) spectroscopy, and the degree of degradation due to the thermal decomposition reaction of the thermoplastic polyester resin is evaluated. As described above, an increase in the amount of VEG in a resin molded product indicates the progress of the thermal decomposition reaction, so the degree of degradation due to the thermal decomposition reaction can be evaluated by quantifying the amount of VEG.

[0021] Nuclear magnetic resonance spectroscopy allows qualitative and quantitative analysis of multiple types of terminal functional groups, including terminal vinyl groups, in a single measurement using a small amount of sample, without using any reagents such as labeling reagents, etc. Therefore, the evaluation method according to this embodiment can provide an evaluation method that can simply and accurately evaluate the degree of degradation due to the thermal decomposition reaction of a polyester resin.

[0022] Nuclear magnetic resonance spectroscopy includes, for example, proton nuclear magnetic resonance ( 1 H-NMR spectroscopy is used, and known methods, for example, are used as qualitative and quantitative analysis methods for VEG. 1 In the case of PBT resin, the chemical shift of VEG (-CH=CH2) in H-NMR spectroscopy appears as four peaks (quadruplet) at δ 5.1 to 5.2 ppm. VEG can be quantified based on the signal derived from the CH2 protons of this VEG. In particular, the VEG signal in PBT resin has the advantage that there are no overlapping signals and it is easy to confirm and quantify, since there are no alkene hydrogens in the repeating structure of PBT resin. Therefore, PBT resin is preferred as the thermoplastic polyester resin for evaluating the degree of degradation due to thermal decomposition reaction using the evaluation method according to this embodiment.

[0023] (Prediction of cylinder temperature during molding of resin molded products) In this embodiment, when the cylinder temperature during molding of a resin molded product (sample to be evaluated) is unknown, the cylinder temperature during molding of the sample to be evaluated can be predicted from the relationship between the amount of terminal vinyl groups (VEG) in the resin molded product (standard sample) and the cylinder temperature of the injection molding machine.

[0024] First, a resin molded product (standard sample) is prepared that is made of the same material and has the same shape as the resin molded product (evaluation target sample) and is molded using the same injection molding machine. By setting the manufacturing conditions for the resin molded product (standard sample) in this manner, a calibration curve can be created that matches the melting characteristics during molding and the cooling and solidification history of the molten resin to the resin molded product (evaluation target sample). Then, multiple resin molded products (standard samples) are manufactured by performing injection molding at different cylinder temperatures. In other words, the evaluation method according to this embodiment may include a step of manufacturing multiple standard samples, which are molded products of thermoplastic polyester resin, by performing injection molding at different cylinder temperatures.

[0025] For each of the multiple resin molded products (standard samples) prepared as described above, the same method as described above was used. 1 The amount of VEG is quantified by H-NMR spectroscopy. That is, the evaluation method according to this embodiment may include a step of quantifying the amount of terminal vinyl groups by analyzing a plurality of standard samples using nuclear magnetic resonance spectroscopy.

[0026] Next, a calibration curve is created from VI (Vinyl Index), which is the reciprocal of the VEG amount, and the reciprocal of the cylinder temperature T (unit: Kelvin, K). Specifically, a calibration curve (quadratic approximation curve) is created from data plotting VI values ​​against the reciprocal of the cylinder temperature T. This calibration curve confirms that VI decreases, i.e., the VEG amount increases, as the cylinder temperature increases. The increase in the VEG amount with an increase in cylinder temperature indicates that a thermal decomposition reaction is progressing during injection molding. In this way, the evaluation method according to this embodiment may include a step of creating a calibration curve showing the relationship between the terminal vinyl group amount and cylinder temperature for multiple standard samples.

[0027] On the other hand, for the resin molded product (evaluation target sample), 1The amount of VEG is quantified by H-NMR spectroscopy. That is, the evaluation method according to this embodiment may include a step of analyzing an evaluation sample, which is a molded article of a thermoplastic polyester resin, using nuclear magnetic resonance spectroscopy to quantify the amount of terminal vinyl groups. Note that by quantifying the amount of VEG in the resin molded article (evaluation sample), the degree of degradation due to thermal decomposition reaction during injection molding can be evaluated.

[0028] Then, the VI is calculated from the VEG amount of the resin molded article (evaluation target sample). Using the calibration curve created as described above, the cylinder temperature during molding of the evaluation target sample can be predicted from the VI value of the resin molded article (evaluation target sample). That is, the evaluation method according to this embodiment may include a step of predicting the cylinder temperature during molding of the evaluation target sample from the amount of terminal vinyl groups of the evaluation target sample using the calibration curve.

[0029] As described above, the evaluation method according to the present embodiment is a method for evaluating the degree of degradation due to the thermal decomposition reaction of a thermoplastic polyester resin, and includes a step of analyzing a molded article of the thermoplastic polyester resin using nuclear magnetic resonance spectroscopy to quantify the amount of terminal vinyl groups. This allows the evaluation of the degradation due to the thermal decomposition of the thermoplastic polyester resin without measuring the terminal carboxyl group concentration or molecular weight as in the conventional method. Therefore, the evaluation method according to the present embodiment can provide an evaluation method that can easily and accurately evaluate the degree of degradation due to the thermal decomposition reaction of a polyester resin.

[0030] (Example) The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0031] In the examples, PBT resin pellets (unreinforced, natural) shown in Table 1 were used. The molding temperature recommended by the PBT resin manufacturer was 260±10°C.

[0032] [Table 1]

[0033] The MFRs shown in Table 1 were measured in accordance with Method A (manual cutting) of the Japanese Industrial Standard JIS K7210 (2014). Specifically, measurements were performed using a melt index tester D4002 manufactured by Yasuda Seiki Seisakusho Co., Ltd., under the following conditions: measurement temperature 250°C, load 325 g, MFR conversion time 10 minutes, sample preparatory conditions: 130°C x 3 hours, filling time 1 minute or less, and preheating time 5 minutes.

[0034] The melting points shown in Table 1 were measured in accordance with JIS K7121 (2012). Specifically, a differential scanning calorimeter Q100 manufactured by TA Instruments Co., Ltd. was used. The test specimen mass was 3.061 mg, the test specimen was not conditioned, the temperature calibration material was indium, the nitrogen gas flow rate was 50 ml / min, the heating rate was 10°C / min, and the measurement temperature range was -20 to 260°C.

[0035] (Production of resin molded products (standard samples)) For each of Samples A1 to A6, the PBT resin pellets were used to prepare dumbbell-shaped test pieces (Type IV, 1.6 mm thick) in accordance with ASTM D638. Specifically, a hybrid injection molding machine PNX60 manufactured by Nissei Plastic Industrial Co., Ltd. was used, and the cylinder temperatures were set to 250°C, 260°C, 270°C, 280°C, 290°C, and 300°C, respectively, the mold temperature to 60°C, and the injection speed to 100 mm / s.

[0036] (Analysis of resin molded products (standard samples)) Regarding the resin molded products (standard samples) of sample No. A1 to A6, 1 H-NMR was measured. 1 For the H-NMR measurements, a Fourier transform nuclear magnetic resonance spectrometer JNM-ECX500 manufactured by JEOL RESONANCE Co., Ltd. was used. Tetramethylsilane was used as the reference material, and the central magnetic field was 11.74 T and the observation nucleus was 1. 1 H, resonance frequency 500MHz, measurement temperature 25℃, 1H-NMR was measured. A 1:1 volumetric mixture of CDCl3 and 1,1,1,3,3,3-hexafluoro-2-propanol-d2 was used as the deuterated solvent. The analytical concentration of samples A1 to A6 in the deuterated solvent was adjusted so that the PBT resin was 5 wt. / vol.% relative to the mixed solvent.

[0037] Figure 1 shows the results of specimen No. A6 (cylinder temperature 300°C, 573K). 1 The H-NMR spectrum is shown. 1 As an analytical signal of the H-NMR spectrum, a signal (not shown) of protons (4H) on the aromatic ring was observed near the chemical shift δ of 8.1 ppm. Meanwhile, a signal (symbol 1 in Figure 1) of CH2 protons (2H, four peaks (quadruplet)) of the terminal vinyl group (-CH=CH2) was observed near the chemical shift δ of 5.1 to 5.2 ppm. Based on the ratio of the area of ​​the signal of CH2 protons to the area of ​​the signal of protons on the aromatic ring, with the protons on the aromatic ring as the reference (1000), the amount of VEG in sample No. A6 was determined to be 6.03 × 10 -3 Similarly, the amounts of VEG in Samples A1 to A5 were quantified, and VI (the reciprocal of the VEG amount) was calculated.

[0038] Table 2 shows the cylinder temperature, the reciprocal of the cylinder temperature T (unit: Kelvin, K) (1000 / T), VEG amount, and VI for samples A1 to A6. It was confirmed that VI decreased, that is, VEG amount increased, as the cylinder temperature increased. The increase in VEG amount with increasing cylinder temperature indicates that the thermal decomposition reaction during injection molding was progressing.

[0039] [Table 2]

[0040] (Creating a calibration curve) Then, as shown in Figure 2, a calibration curve was created from VI and the reciprocal of the cylinder temperature T (1000 / T). As a result, the following equation (1) was obtained as an approximation of the calibration curve. In equation (1), x represents 1000 / T (unit: 1 / K) and y represents VI. y=-9789.3x 2 +39567x-39080 (1)

[0041] (Analysis of resin molded products (samples to be evaluated)) On the other hand, for the resin molded products (evaluation samples) of samples B1 and B2, whose cylinder temperatures during molding are unknown, 1 The VEG amount was quantified by H-NMR, and the VI was calculated from the VEG amount. The cylinder temperature during molding was then predicted from the VI value using the calibration curve in Figure 2. Table 3 shows the VEG amount, VI, the reciprocal of the cylinder temperature T (1000 / T), and the predicted cylinder temperature for Samples B1 and B2.

[0042] [Table 3]

[0043] The VI value for sample No. B1 was 612. By substituting this VI value for y in equation (1) and performing calculations, the following equation (2) was obtained. -9789.3x 2 +39567x-39692=0 (2)

[0044] Calculating equation (2) based on the quadratic equation formula yielded x = 1.85. Since x is the reciprocal of the cylinder temperature T (1000 / T), the predicted cylinder temperature was determined to be 541 K. In this way, the predicted cylinder temperature of sample No. B1 was predicted to be 268°C.

[0045] The VI value for sample No. B2 was 686. By substituting this VI value for y in equation (1) and performing calculations, the following equation (3) was obtained. -9789.3x 2 +39567x-39766=0 (3)

[0046] Calculating equation (3) based on the quadratic equation formula yielded x = 1.87. Since x is the reciprocal of the cylinder temperature T (1000 / T), the predicted cylinder temperature was determined to be 534 K. In this way, the predicted cylinder temperature of sample No. B2 was predicted to be 261°C.

[0047] As described above, the evaluation method of this embodiment is a method for evaluating the degree of degradation due to a thermal decomposition reaction of a thermoplastic polyester resin, and includes a step of analyzing a molded article of the thermoplastic polyester resin using nuclear magnetic resonance spectroscopy to quantify the amount of terminal vinyl groups. Therefore, the evaluation method of this embodiment can provide an evaluation method that can simply and accurately evaluate the degree of degradation due to a thermal decomposition reaction of a polyester resin.

[0048] Although the present embodiment has been described above, the present embodiment is not limited to this, and various modifications are possible within the scope of the gist of the present embodiment.

Claims

1. A method for evaluating the degree of deterioration due to a thermal decomposition reaction of a thermoplastic polyester resin, comprising: An evaluation method comprising a step of analyzing a molded article of the thermoplastic polyester resin using nuclear magnetic resonance spectroscopy to quantify the amount of terminal vinyl groups.

2. A step of producing a plurality of standard samples, which are molded articles of the thermoplastic polyester resin, by performing injection molding while changing a cylinder temperature; a step of analyzing the plurality of standard samples using the nuclear magnetic resonance spectroscopy to quantify the terminal vinyl groups; preparing a calibration curve showing the relationship between the amount of terminal vinyl groups in the plurality of standard samples and the cylinder temperature; a step of analyzing an evaluation sample, which is a molded article of the thermoplastic polyester resin, using the nuclear magnetic resonance spectroscopy to quantify the terminal vinyl groups; a step of predicting a cylinder temperature during molding of the evaluation sample from the amount of terminal vinyl groups of the evaluation sample using the calibration curve; The evaluation method according to claim 1 , comprising:

3. The evaluation method according to claim 1 or 2, wherein the thermoplastic polyester resin is a polybutylene terephthalate resin.

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