JP2012107875A - Thermal history evaluation method for molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal history evaluation method for a molded product capable of making an accurate evaluation of a thermal load temperature or a thermal load time of the molded product influenced by thermal history as well as of facilitating a test with samples in small amounts.SOLUTION: A thermal history evaluation of a molded product comprises the steps of: conducting a quantitative analysis of a predetermined index component for a molded product that is thermally pretreated with the predetermined index component; measuring the relationship between a thermal treatment time and an amount of the index component for a plurality of thermal treatment temperatures; forming a master curve indicating the relationship between the amount of the index component and the thermal treatment time with a prescribed thermal treatment temperature used as a reference temperature; collecting a sample from the molded product influenced by thermal history to conduct the quantitative analysis of the index component to measure the amount of the index component; calculating a reference thermal load time as a thermal load time converted into the reference temperature by using the amount of index component and the master curve.

Description

  The present invention relates to a method for evaluating a heat history such as a heat load temperature and a heat load time of a molded product that has received a heat history.

  Conventionally, a connector housing for electric wire connection made of a thermoplastic resin molded product such as polybutylene terephthalate (hereinafter abbreviated as PBT) is known as a molded product. PBT has an excellent balance between mechanical and electrical properties and can withstand high temperature use. For this reason, PBT is used as a material for connectors for automobile parts that are becoming smaller and lighter.

  Molded articles used for automobile parts are used in severe environments such as high temperature environments and outdoors. In such a use environment, the molded product deteriorates itself and the mechanical strength decreases. Therefore, it is necessary to have a method for evaluating the deterioration process by grasping the usage environment of the molded product.

  For example, the following methods (1) to (3) are known as methods for evaluating the degree of deterioration of a PBT molded product.

(1) Evaluation method by mechanical strength This is a method of measuring mechanical strength such as lock strength and terminal holding force by a tensile tester.

(2) Quantitative Evaluation Method by Analysis There are measurement of average molecular weight by SEC (Size Exclusion Chromatography), measurement of terminal carboxyl group amount by titration method, and the like.

(3) Method for evaluating the thermal load temperature (for example, see Patent Document 1)
There is a technique for estimating a thermal history using a DSC (Differential Scanning Calorimeter). In this method, a sample is cut out from a molded article subjected to a thermal load, and this sample is subjected to thermal analysis using DSC. A sample subjected to a thermal load exhibits an endothermic peak different from the melting peak when the temperature is raised from room temperature. In this method, the heat load temperature is measured from the peak top temperature of the endothermic peak.

JP-A-5-10900

  The evaluation method (1) requires the entire connector as a test piece, and further requires a mating connector or terminal having a predetermined shape and size. Furthermore, unless the molded product is greatly deteriorated, there is a problem that a difference is difficult to appear between samples and accuracy is inferior.

  The evaluation method (2) is capable of accurate measurement without being restricted by the sample, but has a problem that pretreatment such as purification of the resin is necessary for the measurement. Furthermore, the evaluation by this method can only know how much the molded product has deteriorated, and cannot estimate what kind of thermal history it has received and deteriorated.

  The evaluation method (3) has a problem that the peak top temperature of the endothermic peak obtained from the DSC curve is higher than the actual heat load temperature. For example, in the case of a polyethylene resin, it becomes 3-4 degreeC, and in the case of a polypropylene resin, it becomes about 9-13 degreeC. Further, when the heat load time of the molded product becomes long, the peak top temperature shifts to the high temperature side, so that there is a problem that the accuracy is low and it is not practical.

  The present invention has been made to eliminate the above-mentioned drawbacks of the prior art, and it is possible to accurately evaluate the heat load temperature, the heat load time, and the like of the molded product that has been subjected to the heat history. In addition, there is a method for evaluating the thermal history of molded products that can be easily tested without taking a small amount of sample and requiring complicated pretreatment without being restricted by the shape and size of the sample. The purpose is to do.

In order to solve the above problems, the thermal history evaluation method of the molded product of the present invention is:
In a thermal history evaluation method for analyzing a molded product that has received a thermal history to estimate and evaluate the thermal history,
A component whose content changes according to the heat treatment time is defined as an index component, a quantitative analysis of the index component is performed on a pre-heated molded article, and a relationship between the heat treatment time at a plurality of heat treatment temperatures and the amount of the index component is measured. A master curve creating step for creating a master curve indicating a relationship between the index component amount and the treatment time with a predetermined heat treatment temperature as a reference temperature T ₀ ;
An index component measurement step for collecting a sample from a molded article that has received a thermal history and quantitatively analyzing the index component to measure the amount of the index component;
Using the index component amount and the master curve, a heat load time estimation step for obtaining a reference heat load time t ₀ as a heat load time converted to the reference temperature T ₀ ,
It is an gist evaluating the thermal history of the molded article based on the reference heat load time t _0.

In the thermal history evaluation method for the molded product,
In addition, a sample is taken from the molded product that has received a thermal history, and DSC analysis is performed using a differential scanning calorimeter, and a thermal load temperature estimation step is performed to obtain the maximum load temperature T ₁ to which the molded product was exposed during use. Prepared,
A reference heat load time t ₀ obtained by the thermal load time estimation step, using the maximum load temperature T _1, it is preferable to evaluate the thermal history of the molded article.

In the thermal history evaluation method for the molded product,
In the master curve creation step, the relationship between the transfer factor and the reciprocal of the heat treatment temperature is obtained using the Arrhenius equation, and the transfer factor a _T1 at the maximum load temperature T ₁ is determined from this relationship, and the reference temperature T ₀ is calculated from the following equation. with a heat load temperature conversion step of converting the reference heat load time t ₀ is the thermal load time to the maximum load temperature T ₁ of the heat load time real thermal load time t _1, using the actual thermal load time t ₁ It is preferable that the thermal history is evaluated.
Actual heat load time t ₁ = reference heat load time t ₀ / transfer factor a _T1

In the thermal history evaluation method for the molded product,
The thermal load temperature estimation process, which estimates the maximum load temperatures T ₁ using the endothermic peak on the low temperature side than the endothermic peak due to melting in the DSC curve, the rising temperature of the low temperature side of the endothermic peak in the differential DSC curve it is preferable to estimate the maximum load temperatures T ₁ using.

In the thermal history evaluation method for the molded product,
The molded article may be polybutylene terephthalate resin, and the indicator component may be methyl 4-methoxybutyrate that is quantified by adding pyromethylammonium hydroxide to a sample and pyrolyzing gas chromatography / mass spectrometer.

In the thermal history evaluation method for the molded product,
The relationship between the heat treatment time and the mechanical properties at the reference temperature T ₀ of the molded product is grasped in advance, the index component amount is measured, and the mechanical properties at the reference temperature T ₀ are estimated using the master curve. can do.

In the thermal history evaluation method for the molded product,
It is possible to previously form a deterioration determination unit for measuring the thermal history of the molded product integrally with the molded product body, and to form the deterioration determination unit so as to be separable from the molded product body.

  The thermal history evaluation method for a molded product according to the present invention includes a master curve creating step for creating a master curve indicating a relationship between an index component amount and a processing time with a predetermined heat treatment temperature as a reference temperature, and a molded product that has received a thermal history. A heat load time for obtaining a reference heat load time obtained by converting a heat load time into the reference temperature, using an index component measurement step of collecting a sample and quantifying the index component, and the amount of the index component and the master curve. It is possible to accurately evaluate the heat load time to which the molded product that has received the heat history is exposed by adopting a method for evaluating the heat history of the molded product based on the reference heat load time, including an estimation step. Is possible. In other words, the heat load time converted to the reference temperature can be estimated by using the master curve, so even if the environment in which the molded product is used is unknown or the temperature history of the molded product is different, the degree of deterioration can be calculated using the same standard. Can be evaluated.

  Furthermore, the thermal history evaluation method of the present invention can be easily tested without being restricted by the shape and size of the sample, collecting a small amount of sample, and requiring no complicated pretreatment.

It is a reaction formula of thermal degradation reaction of PBT. This is a reaction formula when tetramethylammonium hydroxide is added to thermally deteriorated PBT and thermally decomposed. It is a graph which shows the relationship between the amount of MMB in a bench test, and heat processing time. It is a graph of the master curve which shows the relationship between the amount of MMB and heat processing time. It is the graph which plotted the relationship between the movement amount obtained from Arrhenius formula, and the reciprocal of temperature. It is a graph which shows the DSC curve and differential DSC curve of the PBT molded article obtained by the bench test. It is a table | surface which shows the result of Examples 1-10. It is the graph which plotted the relationship between the travel distance of Examples 1-10, and the amount of MMB. It is the graph which plotted the relationship between the reference | standard heat load time of Examples 1-10, and the amount of MMB. It is a graph which shows the relationship between the heat processing time, the amount of MMB, and a mechanical characteristic when the connector terminal which consists of PBT molded products is heat-processed at 100 degreeC, and terminal retention strength is measured. It is a graph which shows the relationship between the amount of MMB and the mechanical characteristic of the graph of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present invention, after a molded article actually receives a thermal history, the extent to which the molded article has deteriorated is analyzed by taking a sample from the used molded article, and the thermal history is obtained from the analysis result. It is an accurate estimate. In this example, a thermal history evaluation method for a PBT molded product will be described. This PBT molded product is used as a connector housing for electrical connection of electrical wiring (wire harness) of an automobile.

The thermal history estimation method of the present embodiment is roughly divided into the following steps (a) to (f).
(A) Master curve preparation process This process performs a bench test about the object molded object beforehand. In the bench test, an index component whose generation amount increases in accordance with the heat treatment time is determined, processing is performed at a plurality of processing temperatures, and the relationship between the amount of the index component and the processing temperature-time is measured. A predetermined curve is set as a reference temperature, and a master curve representing the relationship between the heat treatment time and the index component amount is created.

(B) Indicator component measurement step This step involves collecting a sample from a molded article that has received the thermal history of the measurement target, performing quantitative analysis of the indicator component, and the indicator component contained in the molded article that has received the thermal history. The amount is quantified.

(C) Thermal load time estimation step Using the master curve and the index component amount of the molded product, a reference thermal load time (t ₀ ) obtained by converting the thermal load temperature into a reference temperature is obtained.

(D) Thermal load temperature estimation step A sample is taken from the molded product that has received the thermal history of the object to be measured, subjected to DSC analysis using a differential scanning calorimeter, and the maximum load temperature to which the molded product has been exposed during use ( T ₁ ) is obtained.

(E) Thermal load temperature conversion step The actual thermal load time t ₁ is obtained by converting the reference thermal load time (t ₀ ) into the thermal load time at the maximum load temperature.

(F) Thermal history evaluation process of molded product Evaluation of thermal history of molded product based on usage history of molded product, reference heat load time t ₀ , maximum load temperature (T ₁ ), actual heat load time t _1, etc. Thus, the usage status and degree of deterioration of the molded product are comprehensively determined.

Hereafter, each said process is demonstrated in detail.
(A) Master curve creation process FIG. 1 is a reaction formula of the thermal degradation reaction of PBT. As shown in FIG. 1, when PBT is oxidized due to thermal deterioration, an acid anhydride is formed. FIG. 2 is a reaction formula when tetramethylammonium hydroxide (TMAH) is added to PBT which has been thermally deteriorated and thermally decomposed. As shown in FIG. 2, when TMAH is added to the heat-degraded PBT and heated, the acid anhydride portion is hydrolyzed to produce methyl 4-methoxybutyrate (MMB). Since the portion of PBT that becomes acid anhydride increases in proportion to the thermal deterioration of PBT, measuring the amount of MMB can be used as an index indicating the degree of progress of the thermal deterioration. That is, when the molded product is PBT, MMB generated when TMAH is added to PBT and heated is used as the indicator component.

  The index component used in the present invention may be a component whose content in the molded product changes according to thermal deterioration. The indicator component may be a component whose content increases in the molded article or a component whose content decreases. The indicator component may be a component that can be quantitatively analyzed as a derivative by adding a reactive reagent or the like to the molded product to cause a chemical reaction as in the above-described example. May be used.

  The MMB is measured by pyrolysis gas chromatography / mass spectrometry on a sample obtained by adding TMAH to PBT. The amount of MMB can be quantified by measuring the sample by pyrolysis gas chromatography / mass spectrometry, detecting MMB in the reaction product during pyrolysis, and measuring the area of the detected peak. . The degree of deterioration can be evaluated from the quantitative value of MMB. As the MMB quantification method, specifically, a known method described in JP-A-2001-356116 or the like can be used.

  As a bench test, an unused PBT molded product was heat-treated (thermal aging) at 80 ° C., 100 ° C., and 120 ° C. for a predetermined time, and then a sample was taken to quantify the amount of MMB. The sample used was 0.1 mg obtained by slicing the outermost surface of the PBT molded product to a thickness of 15 μm.

  FIG. 3 is a graph showing the relationship between the amount of MMB and the heat treatment time in the bench test. As shown in FIG. 3, the relationship between the amount of MMB and the heat treatment time at each processing temperature of the PBT molded product is as shown by three time change curves. As shown in FIG. 3, the amount of MMB increases exponentially with time at any processing temperature. In addition, the amount of MMB increases greatly in a short processing time as the processing temperature increases. These results indicate that MMB is suitable as an index component of the degree of thermal oxidation degradation of PBT.

  In the graph of FIG. 3, a master curve is created using a time-temperature conversion rule based on a graph at a heat treatment temperature of 100 ° C. If the curve of the characteristic value for each temperature is translated and overlapped on the time axis, it can be made one curve. This curve is called the master curve, and the amount of translation is called the movement factor. By using the master curve, even a sample heat-treated at various temperatures can be converted into a value measured at the reference temperature of the master curve.

  In the present invention, the term “heat treatment” means that a measurer or a known person molded a material under certain conditions, but left it at a certain temperature for a certain time after molding to give a specific heat. Further, in the present invention, “thermal history” indicates that molding is performed under unknown conditions, or heat that is not specified is received under unknown or known use conditions.

In order to create a master curve specifically, the curve of heat treatment temperature 80 degreeC and 120 degreeC is shifted so that it may overlap with the graph of 100 degreeC. The curve of the heat treatment temperature of 120 ° C. translates the time axis by plus 0.14. The curve at the heat treatment temperature of 80 ° C. moves the time axis by minus 0.1 in parallel. FIG. 4 is a master curve graph showing the relationship between the amount of MMB and the heat treatment time. In this way, a master curve with a correlation coefficient of 0.893 shown in FIG. 4 was obtained. The relationship between the MMB amount (Y) of the master curve and the heat treatment time (t) shown in FIG. 4 can be expressed by the following equation (1). The thermal load time (t) converted into a heat treatment temperature of 100 ° C. can be obtained from the value obtained by measuring the amount of MMB of the sample of the molded product that has undergone the thermal history, using the relational expression of the master curve of formula (1). . The heat load time (t) converted to the reference processing temperature is referred to as a reference heat load time (t ₀ ).
Y = 3.07 × 10 ⁻⁸ × (logt) ^9.76 (1)

Next, the relationship between the transfer factor and the inverse of the heat treatment temperature is obtained using the Arrhenius equation. In the Arrhenius equation, the relationship between the transfer factor (a _T ) of each temperature, the arbitrary temperature (T), and the reference temperature (T ₀ ) can be expressed by the following equation (2).
log (a _T ) = (ΔH / 2.303R) [(1 / T) − (1 / T ₀ )] × 10 ³ (2)
In the above formula (2), ΔH is activation energy (kJ / mol), and R is a gas constant of 8.31 (J / K · mol).

In the above Arrhenius equation, when the reference temperature (T ₀ ) is 100 ° C. (373 K), the transfer factor of each temperature is obtained. When the transfer factor (a _T ) is expressed as the amount of movement at each temperature [log (a _T )], when the temperature is 80 ° C., the log (a ₈₀ ) is −0.10 and the temperature is 120 ° C. In this case, log (a ₁₂₀ ) was 0.14. FIG. 5 is a graph plotting the relationship between the amount of movement obtained from the Arrhenius equation and the inverse of temperature. As shown in the graph of FIG. 5, the relationship between the amount of movement and the reciprocal of the temperature is represented by a straight line. The straight line in the graph of FIG. 5 has an inclination of −0.83 and a correlation coefficient of 0.984, and can be expressed as a linear expression represented by the following expression (3).
log (a _T ) = − 0.83 (1 / T) × 10 ³ +2.24 (3)

When an arbitrary temperature T is substituted into the above equation (3), a transfer factor (a _T ) at an arbitrary temperature T can be obtained. Based on this transfer factor (a _T ) and the following equation (4), the reference heat load time (t ₀ ) obtained from the above equation (1) can be converted into a heat load time at an arbitrary temperature. This heat load time indicates how many hours the heat load corresponding to the molded product is received at an arbitrary temperature.
Thermal load time at an arbitrary temperature (T) = reference heat load time (t ₀ ) / transfer factor (a _T ) (4)

In the above equation (4), if the maximum load temperature T ₁ when the molded article receives a thermal history can be estimated, the heat load time at the maximum load temperature T ₁ (this is referred to as the actual heat load time t ₁ ). It can be converted to. The reference heat load time t _{0 in the} equation (4) can be obtained from the equation (1). Further, the transfer factor a _T1 of the actual heat load temperature T ₁ can be obtained from the equation (3). In other words, the actual heat load time t ₁ can be obtained by substituting the reference heat load time t ₀ and the transfer factor a _T1 into the following equation (5). Note that the actual thermal load temperatures T ₁ can be determined by DSC analysis using a differential scanning calorimeter described later (d) heat load temperature estimation process.
Actual heat load time t ₁ = reference heat load time t ₀ / transfer factor a _T1 (5)

(B) Indicator compound measuring step In this step, the amount of MMB is quantified by taking a sample from a molded article that has received a thermal history. The specific process is performed in exactly the same procedure as in the bench test. Specifically, a sample is taken from a molded product, TMAH is added to the sample, pyrolysis gas chromatography / mass spectrometry is performed, and the amount of MMB is quantified from the area of the detection peak of MMB.

(C) Thermal load time estimation step Substituting the MMB amount of the molded product obtained in the step (b) into the master curve [formula (1a) below] shown in FIG. 4 obtained in the step (a), A reference heat load time t ₀ obtained by converting the heat load temperature of the molded article into a reference temperature (T ₀ = 100 ° C.) is obtained.
Y = 3.07 × 10 ⁻⁸ × (logt ₀ ) ^9.76 (1a)

(D) Thermal load temperature estimation step A sample is taken from a PBT molded product that has received a thermal history, and a temperature rise DSC analysis is performed using a differential scanning calorimeter to obtain a DSC curve and a differential DSC curve. The sample may be about 10 mg. From the DSC curve and the differential DSC curve to determine the highest temperature at which the molded article is exposed during use as a maximum heat load temperature T _1.

  FIG. 6 is a graph showing a DSC curve and a differential DSC curve of a PBT molded article obtained in a bench test. In the bench test, an unused PBT molded product is heat-treated (annealed) for a predetermined time in a thermostatic chamber set to a predetermined temperature, then a sample for analysis is taken, and the sample is heated using a differential scanning calorimeter. Then, the temperature is raised to a temperature equal to or higher than the melting point, and the temperature rising DSC analysis is performed to obtain a DSC curve and a differential DSC curve. FIG. 6 shows the DSC for four types of samples in which the heat treatment conditions of the PBT molded product are (a) 60 ° C. for 24 hours, (b) 100 ° C. for 24 hours, (c) 140 ° C. for 4 hours, and (d) 180 ° C. for 24 hours. Analysis was performed and the obtained DSC curve and differential DSC curve were shown. The DSC analysis can be performed, for example, by collecting about 3 to 10 mg of a sample and using a commercially available DSC apparatus at a heating rate of 20 ° C./min and in a nitrogen atmosphere.

As shown in FIG. 6, an endothermic peak due to melting near 230 ° C. and an endothermic peak on the lower temperature side appear in the temperature-rising DSC curve of the PBT molded article that has received a thermal history. The endothermic peak on the low temperature side is minute and difficult to understand on the DSC curve, but a clear peak can be observed when the differential DSC curve is used. The rising temperature of the low-temperature endothermic peak of the differential DSC curve is read. This temperature is the actual load temperature of the molded article, that the maximum load temperature T _1. This maximum load temperature T ₁ means the highest temperature among the exposed temperatures in the past thermal history of the PBT.

  As shown in FIG. 6, the endothermic peak on the low temperature side of the DSC curve appears on the high temperature side as the heat treatment temperature increases. There is a correlation between the heat treatment temperature of PBT and the temperature of the low-temperature endothermic peak. The rising temperature of the differential DSC curve of the low-temperature endothermic peak of PBT is 60 ° C. when the heat treatment temperature is 60 ° C., 101 ° C. when the heat treatment temperature is 100 ° C., 139 ° C. when the heat treatment temperature is 140 ° C., and the heat treatment temperature. When the temperature was 180 ° C., it was 180 ° C. Thus, the rising temperature of the low temperature side endothermic peak of the differential DSC curve is in good agreement with the actual heat treatment temperature of the PBT molded product. As described above, in the temperature rising DSC analysis, the amount of the sample may be as small as about 10 mg, the analysis operation is easy, and the maximum load temperature of the PBT molded product can be obtained accurately and easily.

The reference heat load time t ₀ obtained in (e) heat load temperature conversion step (c) above thermal load time estimation process, using the following (Equation 5, the maximum load obtained in (d) above thermal load temperature estimation process converted into real thermal load time _{t 1} of the temperature _{T 1.}
Actual heat load time t ₁ = reference heat load time t ₀ / transfer factor a _T1 (5)
The movement factor a _T1 is a movement factor at the maximum load temperature T ₁ , and the temperature (T) of the equation (3) determined in advance using the Arrhenius equation in the (a) master curve creation step is the maximum load temperature T _1. Is obtained from the following equation (6).
log (a _T1 ) = − 0.83 (1 / T ₁ ) × 10 ³ +2.24 (6)

In this way, the sample of the PBT molded product that actually received the thermal history is analyzed, and the reference heat load time t ₀ , the maximum load temperature T ₁ , and the actual heat load time t ₁ are obtained.

(F) Thermal history evaluation process of molded product For example, when a PBT molded product is actually mounted on an automobile and receives a thermal history, the usage history of the PBT molded product such as the type of vehicle and the travel distance, the reference thermal load time t Based on data such as ₀ , maximum load temperature T ₁ , actual heat load time t _1, etc., the thermal history of the PBT molded product is evaluated to comprehensively determine the usage status, the degree of deterioration, etc. of the molded product. From the reference heat load time t ₀ , it is possible to evaluate how many hours the heat load corresponding to the PBT molded article has been subjected to the heat load time converted into the reference temperature. Also from the maximum load temperature T _1, it is possible to estimate the actual or PBT molded article is subjected to a thermal load of the maximum temperature of many times. Further, the actual heat load time t ₁ can be estimated from the reference heat load time t ₀ and the maximum load temperature T ₁ . From the actual thermal load time t _1, it is possible to PBT molded article to assess whether subjected to thermal loads of hours corresponds with the highest number of times in use.

In this evaluation method, when the reference heat load time t ₀ and the maximum load temperature T ₁ are estimated, the analysis of the indicator substance and the DSC measurement need only be performed with a very small amount of sample from the PBT molded product, and measurement is performed without pretreatment. Is possible.

Hereinafter, the example which evaluated the heat history about the molded article actually mounted in the vehicle is shown. FIG. 7 is a table showing the results of Examples 1-10. As shown in the table of FIG. 7, PBT molded products in the engine room collected from 10 types of actual vehicles whose vehicle type, registration period, mileage, etc. are known as PBT molded products subjected to heat load in the market in the first embodiment. -10 samples. Using these samples, the maximum load temperature was measured by the above-mentioned DSC analysis, and the amount of MMB was measured by adding TMAH to the above-mentioned sample and performing pyrolysis gas chromatography / mass spectrometry. From the measured values, the above method is used to calculate the heat load time when the reference temperature is 100 ° C. (reference heat load time t ₀ ), the maximum load temperature, and the load time at the maximum load temperature (actual heat load time t ₁ ). Asked. The results are shown in the table of FIG. In the table, the vehicle type A has an engine displacement of about 3000 cc, the vehicle type B has about 1500 cc, and the vehicle type C has 4000 cc or more.

  FIG. 8 is a graph in which the relationship between the travel distance and the MMB amount in Examples 1 to 10 is plotted. As shown in FIG. 8, the sample with a longer traveling distance has a larger amount of MMB and a tendency for deterioration to progress. There is a good correlation between the same vehicle type A (Examples 1 to 5). However, if the vehicle type is different, it will deviate from the straight line. For example, the fifth embodiment and the seventh embodiment differ in the amount of MMB although the traveling distance is substantially the same. Moreover, although the MMB amount of Example 6 and Example 8 is substantially the same, the travel distance is greatly different. These are due to the fact that the temperature inside the engine room differs depending on the vehicle type, and the thermal history temperature differs depending on the vehicle type.

FIG. 9 is a graph plotting the relationship between the heat load time (reference heat load time t ₀ ) at 100 ° C. and the amount of MMB. As shown in FIG. 9, a correlation with very high linearity was observed. The correlation coefficient of the straight line in FIG. 8 is 0.9678, whereas the correlation coefficient of the straight line in FIG. 9 is 0.9999. As described above, the results shown in FIGS. 8 and 9 show that the heat load time at 100 ° C. can be accurately estimated by quantifying the amount of MMB for the PBT molded product in the engine room collected from the actual vehicle. It confirms that it is possible. The method of evaluating the heat history using the reference heat load time t ₀ can accurately compare with each other even between different vehicle types, compared to the method of evaluating the heat history only with the travel distance.

Further, when looking at the maximum load temperature T1 for _each of the examples 1 to 10, the general passenger car A (Examples 1 to 5) is 83 to 86 ° C, and the small passenger car B (Examples 6 and 7) is 76 ° C. The luxury car C (Examples 8 to 10) was 90 to 113 ° C. It has been found that the actual environmental temperature of the engine room increases as the engine displacement increases. Maximum load temperatures T ₁ was estimated in this example shows that accurately reflect the environment temperature of the engine room where the connector is mounted.

Using this table, the thermal history of Examples 6 and 8 with different vehicle types will be evaluated. Among vehicle types B and C, both vehicles have the smaller amount of MMB. This indicates that the thermal oxidation deterioration is small. The maximum load temperature T ₁ is 76 ° C. in Example 6, which is 14 ° C. lower than 90 ° C. in Example 8. The actual heat load time t ₁ is 4900 hours in Example 6, which is 1100 hours longer than 3800 hours in Example 8. It can be judged that the thermal oxidation deterioration was small because the temperature at the time of traveling was as low as 76 ° C. because the small passenger car in Example 6 traveled for 1100 hours longer. In this way, by evaluating the thermal history using the maximum load temperature and actual heat load time, it is possible to obtain information such as the thermal history and usage status of molded products that could not be determined by the years of use or travel distance alone. it can.

  FIG. 10 is a graph showing the relationship between the heat treatment time, the amount of MMB, and the mechanical characteristics when a connector terminal made of a PBT molded product is heat treated at 100 ° C. and the terminal holding force is measured. The mechanical characteristics are measured from the load-stroke curve indicating the relationship between the load measured by the tensile test of the connector terminal holding force and the chuck stroke, the tensile breaking load (maximum peak value), and the elastic modulus (peak rise gradient). ) And breaking energy (peak area). As shown in FIG. 10, with respect to the heat treatment time, the mechanical properties of the molded product suddenly change from a certain time and there is an inflection point. This indicates that in the case of a molded article that has received a thermal history recovered from the market, it is difficult to quantitatively grasp the degree of deterioration only by measuring the mechanical characteristics. On the other hand, as shown in FIGS. 8 and 9, the change in the amount of MMB has a linear relationship with the heat treatment time. From the amount of MMB, it is easy to quantitatively compare the degree of deterioration.

FIG. 11 is a graph showing the relationship between the amount of MMB and the mechanical characteristics of the graph of FIG. As shown in FIG. 11, if you know the heat treatment time and the mechanical properties and the MMB amount in the reference temperature T ₀ of the molded article in advance a certain shape, and measuring the index component amount, using the master curve Since the mechanical characteristics at the reference temperature T ₀ can be estimated, it is easy to determine the life of the molded product and the degree of deterioration of the market-collected product. By determining the degree of deterioration of the molded product in this way, it is possible to determine whether the molded product can be recycled. In addition, by measuring the amount of MMB, when evaluating a molded product of a new resin composition, the amount of MMB of the resin composition can be measured without raising a mold and producing an actual molded product. Thus, it is possible to evaluate the heat-resistant oxidation performance and the like by estimating the change in mechanical characteristics.

  Further, in the evaluation method of the present invention, the thermal history can be measured with a small amount of sample, and the degree of deterioration can be determined quantitatively. Therefore, the deterioration determining part can be formed in advance on the molded product. The deterioration determination unit for measuring the thermal history of the molded product is formed integrally with the molded product body. Furthermore, it is preferable that the deterioration determination part is formed so as to be separable from the molded product body. In order to form such a shape that can be separated from the molded product body, a method of providing a notch so that it can be easily separated from the molded product body and recovered, or the deterioration judgment part as a pin-shaped protrusion that can be easily cut from the molded product body For example. These deterioration determination sections are formed where there is no interference when assembling the parts. If such a deterioration determination unit is provided in the molded product, the degree of deterioration can be evaluated by measuring the heat history without impairing the performance of the product. Thereby, the deterioration state of the whole wiring component (wire harness) can be determined, and it can be used for confirmation of a safe state and subsequent safety ensuring, or the possibility of reuse including other members can be easily performed. .

  As shown in the above embodiments, the present invention can be suitably used as a thermal history evaluation method for PBT molded products used as automotive parts. The evaluation method of the present invention is based on the case where the molded product is selected based on the heat resistance of the material used in an environment exposed to high temperatures such as the engine room of an automobile, or the thermal history of a connector mounted / used in an actual vehicle. It is particularly effective for estimation.

The present invention is not limited to the above-described embodiments, and various modifications can be made. For example, in the above embodiment, PBT is used as a molded product, but even with other resin molded products, an index component is determined in advance, a quantitative analysis method is appropriately selected, a bench test is performed, and various heat treatments are performed. the relationship between the thermal deterioration and the index component amount was measured on the molded article obtained by degradation, by creating a master curve, to determine the reference heat load time t ₀ by quantifying the index component amount from molded articles subjected to thermal degradation Can do.

Further, as long as it is a resin molded article capable of estimating thermal history by even DSC analysis a resin other than PBT, it is possible to obtain the maximum load temperatures T ₁ in the same manner. For example, in a crystalline polymer such as a polyester resin or a polyamide resin, an endothermic peak at a temperature lower than the endothermic peak of melting appears in the DSC curve, so that the maximum load temperature T ₁ can be estimated by the same procedure as in the case of PBT. . Further, the transfer factor a _T1 is determined from the maximum load temperature T ₁ or the Arrhenius equation, and the actual heat load time t ₁ can be obtained from the reference heat load time t ₀ and the transfer factor a _T1 .

t: heat load time, t ₀ : reference heat load time (heat load time converted into reference temperature), t ₁ : actual heat load time (heat load time of maximum load temperature), T: arbitrary temperature, T ₀ : Reference temperature, T ₁ : Maximum load temperature, a _T1 : Transfer factor at maximum load temperature T ₁

Claims (7)

In a thermal history evaluation method for analyzing a molded product that has received a thermal history to estimate and evaluate the thermal history,
A component whose content changes according to the heat treatment time is defined as an index component, a quantitative analysis of the index component is performed on a pre-heated molded article, and a relationship between the heat treatment time at a plurality of heat treatment temperatures and the amount of the index component is measured. A master curve creating step for creating a master curve indicating a relationship between the index component amount and the treatment time with a predetermined heat treatment temperature as a reference temperature T ₀ ;
An index component measurement step for collecting a sample from a molded article that has received a thermal history and quantitatively analyzing the index component to measure the amount of the index component;
Using the index component amount and the master curve, a heat load time estimation step for obtaining a reference heat load time t ₀ as a heat load time converted to the reference temperature T ₀ ,
Thermal history evaluation method of a molded article and evaluating the thermal history of the molded article based on the reference heat load time t _0. In addition, a sample is taken from the molded product that has received a thermal history, and DSC analysis is performed using a differential scanning calorimeter, and a thermal load temperature estimation step is performed to obtain the maximum load temperature T ₁ to which the molded product was exposed during use. Prepared,
A reference heat load time t ₀ obtained by the thermal load time estimation step, the maximum load temperatures T ₁ using a molded product of heat according to claim 1, wherein evaluating the thermal history of the molded article History evaluation method. In the master curve creation step, the relationship between the transfer factor and the reciprocal of the heat treatment temperature is obtained using the Arrhenius equation, and the transfer factor a _T1 at the maximum load temperature T ₁ is determined from this relationship, and the reference temperature T ₀ is calculated from the following equation. with a heat load temperature conversion step of converting the reference heat load time t ₀ is the thermal load time to the maximum load temperature T ₁ of the heat load time real thermal load time t _1, using the actual thermal load time t ₁ The method according to claim 2, wherein the thermal history is evaluated.
Actual heat load time t ₁ = reference heat load time t ₀ / transfer factor a _T1 The thermal load temperature estimation process, which estimates the maximum load temperatures T ₁ using the endothermic peak on the low temperature side than the endothermic peak due to melting in the DSC curve, the rising temperature of the low temperature side of the endothermic peak in the differential DSC curve The maximum load temperature T ₁ is estimated by using the method, and the thermal history evaluation method for a molded product according to claim 2 or 3.   The molded article is a polybutylene terephthalate resin, and the indicator component is methyl 4-methoxybutyrate which is quantified with a pyrolysis gas chromatography / mass spectrometer by adding tetramethylammonium hydroxide to a sample. The thermal-history evaluation method of the molded article of any one of Claims 1-4 to do. The relationship between the heat treatment time and the mechanical properties at the reference temperature T ₀ of the molded product is grasped in advance, the index component amount is measured, and the mechanical properties at the reference temperature T ₀ are estimated using the master curve. The thermal history evaluation method for a molded product according to any one of claims 1 to 5, wherein: The deterioration determination unit for measuring the thermal history in the molded product is formed integrally with the molded product main body in advance, and the deterioration determination unit is formed so as to be separable from the molded product main body. The thermal-history evaluation method of the molded article of any one of -6.