JP6075246B2 - Rubber seal material life evaluation method - Google Patents

Description

  The present invention relates to a rubber seal material life evaluation method, and more particularly to a rubber seal material life evaluation method using pulsed NMR (nuclear magnetic resonance).

  In evaluating the life of a rubber seal material used in an environment where thermal degradation is mainly used, a temperature acceleration test in which a constant compression displacement is applied under a multi-temperature environment is generally performed. As an evaluation index, a compression set that is closely related to a change in seal performance with time is often used. When compression set is used as an evaluation index, the time for compression set to reach the limit value at each acceleration temperature is estimated, and the time to reach the limit value at the operating environment temperature by linear extrapolation of the Arrhenius plot is used as the lifetime. presume. However, when the dimension measurement error increases, such as when the target member is small or the member is deformed due to long-term temperature acceleration, the applicability as an evaluation index of compression set is reduced.

  Further, in many cases, the initial compression rate is unknown for an O-ring or a rubber sheet that is mounted on a device in advance. In this case, since the compression set which is the amount of strain with respect to the dimension compressed in the initial stage is not obtained, the applicability as an evaluation index of the compression set similarly decreases.

  Although mechanical properties such as hardness and elongation may be used as an evaluation index for the life of the rubber seal material, it is often not an appropriate evaluation index from the viewpoint of measurement accuracy and correlation with a decrease in seal performance. Similarly, the crosslink density indicating the state of the rubber structure can be used as an evaluation index, but since the rubber material is a composite material such as oil, ash, and carbon, the sealing performance can be improved only by grasping the rubber structure. Deterioration may not be grasped.

As a technique for measuring and evaluating the crosslinked state of rubber, the spin-spin relaxation time T ₂ of the rubber is measured by pulse NMR, and the average relaxation time MT ₂ is calculated based on the obtained spin-spin relaxation time T _2. Method of calculating and evaluating the degree of crosslinking of rubber (Patent Document 1: Japanese Patent Application Laid-Open No. 2002-71595), average relaxation time MT ₂ measured by pulse method NMR, and durability obtained from a running test result of a rubber belt A method for estimating the durable life of a rubber belt from the relationship with the life (Patent Document 2: Japanese Patent Laid-Open No. 2001-249091) has been proposed.

  When observing the rubber cross-linking structure, mainly the cross-linking points between rubber molecules and the (hard) part constrained by a reinforcing material such as carbon using a pulse NMR apparatus, the observation result is not necessarily the rubber cross-linking structure. It does not accurately reflect the overall condition.

In Patent Document 3 (Japanese Patent Laid-Open No. 2011-38945), a T ₂ relaxation curve obtained by pulsed NMR measurement using the Carr-Purcell-Meiboom-Gill (CPMG) method as a sequence is separated into two components having different relaxation times. A method for analyzing the physical properties of rubber by multiple regression analysis of each relaxation time and component ratio is described.

Patent Document 4 (Japanese Patent Application Laid-Open No. 2012-173093) discloses a rubber material inspection method using a pulsed NMR apparatus, which uses a Carr-Purcell-Meiboom-Gill (CPMG) method to determine the spin-spin relaxation time T ₂ of rubber. measured, resulting the T ₂ relaxation curve (free induction decay curve), and short T ₂ ^S component of the relaxation time is divided into a long T ₂ ^L component of the relaxation time, the relaxation time of the T ₂ ^L component A method for inspecting a rubber material for predicting the breaking elongation Eb is described.

JP 2002-71595 A JP 2001-249091 A JP 2011-38945 A JP 2012-173093 A

The above Patent Documents 1 to 4 do not describe applicability as an index for evaluating the life of the rubber seal material in place of compression set. That is, the deterioration evaluating the rubber compositions according to the T ₂ relaxation time measured by pulse method NMR by Patent Document 1 to 4, which was proposed a method utilizing a physical property value correlated with specific measurement items such crosslinking density and hardness Yes, it does not describe how to use it as an index to capture the decrease in sealing performance. The crosslink density and hardness often correlate with a decrease in sealability, but there are also cases where the sealability decreases even though there is no change in the crosslink density over time. It may not be possible to grasp.

Further, in the degradation evaluation using the conventional pulse method NMR, a high mobility component and a short mobility component when the T ₂ relaxation curve measured using the pulse method NMR is approximated to two components in waveform separation. Are used together. In this case, the applicability of the material divided into three or more components having different motility is lowered. In addition, even when the two components can be approximated, if the relaxation time varies greatly depending on the mobility, the applicability of the method of measuring the T ₂ relaxation time for any component is reduced, and the reliability of the value is accordingly reduced. Decreases.

  An object of the present invention is to provide a method for evaluating the life of a rubber sealing material, which can evaluate the life of the rubber sealing material with high accuracy by pulsed NMR.

In the rubber seal material life evaluation method of the present invention, the spin-spin relaxation time T ₂ of the rubber seal material is measured by pulse NMR, and the obtained T ₂ relaxation curve (free induction decay curve) is converted to T ₂ ^{S having} a short relaxation time. The component is divided into a component and a T ₂ ^L component having a long relaxation time, and the life of the rubber seal material is evaluated based on the T ₂ ^S.

In the present invention, when thermal degradation is considered to be dominant, a constant compression displacement is applied to a test piece of an unused rubber material having the same composition as the rubber seal material to be measured, and the test piece is placed under an accelerated temperature condition. measured the T ₂ relaxation time of each specimen Request T ₂ ^S is a relaxation time of less molecular mobility component. Further, the compression set was measured for a plurality of test strips to determine the calibration relationship compression set and T ₂ ^S. Based on the calibration relationship, a limit value (lower limit value) of T ₂ ^S to be evaluated corresponding to a predetermined upper limit value of compression set is determined. Then, the time for T ₂ ^S measured for the measurement target rubber seal material to reach the limit value is obtained, and the time to reach the limit value at the use environment temperature (for example, normal temperature) is further estimated as the lifetime by linear extrapolation of the Arrhenius plot. preferable.

In the present invention, devices having a seal portion can be evaluated as a specimen. In this case, the specimen mounted with the sealing material is placed under an accelerated temperature condition, and then the compression set and T ₂ ^{S of} the rubber sealing material mounted on the specimen are measured to estimate the lifetime by the same method. It is possible.

At that time, when the initial compression ratio is unknown, the sealing performance is determined by performing an airtight test of each specimen after acceleration, and the T ₂ relaxation time of the rubber seal material attached to each specimen is measured. seeking T ₂ ^S, defined limit T ₂ ^S to maintain the sealing performance (the lower limit), the measured T ₂ ^S estimates the time to reach this limit, further use by linear extrapolation of the Arrhenius plot It is preferable to estimate the time to reach the limit value at the environmental temperature as the lifetime of the sealing material of the equipment.

After obtaining T ₂ ^S as described above, calibration relation with compression set and determination of limit value based on it, determination of limit value capable of maintaining seal performance, estimation of time to reach limit value, Arrhenius plot In performing life estimation based on linear extrapolation, the value of T ₂ ^S itself can be used instead of the value of T ₂ ^S between each accelerated product and unaccelerated product. In this case, the limit value of the difference between T ₂ ^S between the accelerated product and the non-accelerated product is not the lower limit value but the upper limit value.

In the present invention, the T ₂ relaxation time is measured using a pulsed NMR apparatus instead of the compression set measured after promoting the deterioration of the rubber seal material, and the durability is evaluated based on the time-dependent change data. It is. The present invention is a method developed to have a function as an alternative to compression set having a high correlation with sealability, and can accurately estimate the life based on the change in sealability with time, and can also be used for initial compression. Since the rate is unknown, it is possible to evaluate the life of the sealing material even when the compression set cannot be measured.

In the present invention, only a component having a short mobility of T ₂ relaxation time can be targeted, and the life of the rubber seal material can be accurately evaluated by selecting an optimum pulse application method according to the material. . Note that measurement by pulsed NMR is not limited by the shape of the sample, and can be measured regardless of the shape of the sample and the state of breakage.

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In the method for evaluating the lifetime of the rubber seal material of the present invention, T ₂ ^{S of the} rubber seal material is determined by pulse method NMR. Rubber materials for the rubber seal material include acrylonitrile butadiene rubber (NBR), hydrogenated acrylonitrile butadiene rubber (HNBR), fluorine rubber (FKM), urethane rubber (U), silicone rubber (VMQ, FVMQ), ethylene propylene diene rubber (EPDM). ), Ethylene propylene rubber (EPM), chloroprene rubber (CR), acrylic rubber (ACM), butyl rubber (IIR), styrene butadiene rubber (SBR), and the like. The rubber seal material may be annular (annular, elliptical, triangular, quadrilateral, pentagonal or more polygonal) or any other shape such as an acyclic sheet.

As a result of experiments by the present inventor, it was confirmed that T ₂ ^S has a good correlation with compression set of various rubber seal materials. Compression set is an effective index for evaluating the life of rubber seals. Estimate the time for compression set to reach the upper limit at each acceleration temperature, and reach the upper limit at the ambient temperature by linear extrapolation of the Arrhenius plot. The time can be accurately estimated as the lifetime.

  However, when the size measurement error increases, such as when the size of the rubber seal material is small or when the member is deformed due to long-term temperature acceleration, the applicability as an evaluation index of compression set decreases.

  Further, in many cases, the initial compression rate is unknown for an O-ring or a rubber sheet that is mounted on a device in advance. In this case as well, there is a problem that applicability as an evaluation index of compression set similarly decreases.

In the present invention, since T ₂ ^S having a good correlation with compression set is used as an evaluation index, even when the size of the rubber seal material is small, or when deformation of the member due to long-term temperature acceleration occurs, The life of the rubber seal material can be accurately evaluated. Even if the initial compression rate is unknown, the life of the rubber seal material can be evaluated.

In the present invention, the measurement of the spin-spin relaxation time T ₂ by pulsed NMR is preferably performed by the solid echo method.

In order to obtain T ₂ ^S from the T ₂ relaxation curve obtained by the pulse method NMR, the relaxation curve is curve-fitted into the following formula (1),
^{_{F (t) = A 2S exp}} (-t / T 2 S) m + A 2L exp (-t / T 2 L) m ... (1)
T ₂ ^S is obtained. In the formula (1), A _2S is the intensity at t = 0 of the component having a short relaxation time, A _2L is the intensity at t = 0 of the component having a long relaxation time, and t is the observation time. In addition, m varies depending on the object, but is often 1 in the case of rubber.

In order to evaluate the life of a rubber seal material used in an environment where thermal degradation is dominant, a predetermined compression ratio is determined for a plurality of unused rubber test pieces having the same rubber composition as the rubber seal material to be evaluated. A compressive displacement is given, and this is left still for a predetermined time (multiple steps) at acceleration temperature (3 steps or more, for example, 60, 80, 100 ° C.). Then, the the T ₂ relaxation time were measured for each sample at every predetermined elapsed time, obtaining the T ₂ ^S. In addition, compression set is measured for a plurality of specimens with different elapsed times. Based on this result, a calibration relationship between the compression set and T ₂ ^S (for example, the graph shown in FIG. 2A) is obtained. Further, based on this calibration relationship, a limit value of T ₂ ^S corresponding to a predetermined upper limit value of compression set is obtained.

When evaluating equipment having a sealing material as a specimen, place the specimen under accelerated temperature conditions, and then measure T ₂ relaxation time of the rubber sealing material attached to the specimen to obtain T ₂ ^S. A calibration relationship (for example, the graph shown in FIG. 2A) between compression set and T ₂ ^S measured for a plurality of test pieces having different elapsed times is obtained, and compression permanent determined in advance based on the calibration relationship. A limit value of T ₂ ^S corresponding to the upper limit value of the strain is obtained.

At that time, when the initial compression ratio is unknown, the sealing performance is determined by performing an airtight test of each specimen after temperature acceleration, and T ₂ relaxation time is measured for each specimen to obtain T ₂ ^S. The limit value (lower limit value) of T ₂ ^S that can maintain the sealing performance is determined.

After obtaining T ₂ ^S , when determining the calibration relationship with compression set, the limit value based on it, and the limit value that can maintain the sealing performance, the value of T ₂ ^S itself is not used. It is also possible to use the difference in T ₂ ^S between accelerated and unaccelerated products. In this case, the limit value of the difference between T ₂ ^S between the accelerated product and the non-accelerated product is not the lower limit value but the upper limit value.

T ₂ relaxation time is measured by pulse method NMR for the rubber seal material to be evaluated, and T ₂ ^S is obtained. The difference obtained T ₂ ^S or T ₂ ^S of each accelerating articles (accelerated temperature conditions in at specimens) and non-accelerated articles (not placed accelerated temperature conditions specimen) seek time to reach the limit value Further, the time to reach the limit value at the operating environment temperature is estimated as the life of the rubber seal material of the equipment by linear extrapolation of the Arrhenius plot, and the life of the rubber seal material is evaluated.

[Example 1]
A flat test piece of 39 mm × 19 mm × 6.5 mm thickness cut out from an unused ring packing having an outer diameter of 199.5 mm using high nitrile NBR as a base polymer was subjected to T ₂ ^S and T ₂ ^L using pulsed NMR. (JMN-MU25, Solid Echo method, 90 ° pulse 2.0 μsec, repetition time 4 sec, integration number 8 times). Moreover, about this flat plate test piece, swelling amount (toluene, 37 degreeC) and acetone soluble part (Soxhlet extraction, 8 hours) were measured.

[Example 2]
A constant compression displacement was applied to the same flat plate test piece as in Example 1 using a spacer with a compression ratio of 10%, and this was applied to an air thermostat set at an acceleration temperature (60, 80, 100 ° C.). It left still until test time (about 1000-12800 hours) passed.

  The compression set was measured for the test piece after the accelerated temperature treatment, and the same measurement as in Example 1 was performed.

[Results and Discussion]
FIG. 1 shows a change with time of the compression set of a test piece subjected to accelerated temperature treatment. It can be seen that the compression set increases with time at any acceleration temperature of 60, 80, and 100 ° C.

For the test pieces, it approximates the 2 components the T ₂ relaxation curve measured at 20 ° C. using the pulsed NMR technique in waveform separation.

FIG. 2A shows the relationship between T ₂ ^S and compression set, and FIG. 2B shows the relationship between T ₂ ^L and compression set. As shown in FIGS. 2 (a) and 2 (b), there is a good correlation that T ₂ ^S and T ₂ ^L become smaller as the compression set increases.

3A and 3B show the relationship between acetone-soluble matter and T ₂ ^S and T ₂ ^L. As shown in FIGS. 3A and 3B, there is a correlation in which T ₂ ^S and T ₂ ^L become smaller as the acetone-soluble content decreases.

4 (a) and 4 (b), toluene swelling measured for the test pieces subjected to accelerated temperature treatment under the same conditions as T ₂ ^S and T ₂ ^L in 20 ° C. measurement of the test piece subjected to accelerated temperature treatment in Example 2 in FIGS. The relationship of quantity is shown. There is no correlation between T ₂ ^S and T ₂ ^L measured at 20 ° C. and the toluene swelling amount.

There is no correlation between T ₂ ^S and T ₂ ^L and the amount of swelling, whereas the reason why there is a certain correlation between T ₂ ^S and T ₂ ^L and acetone-soluble components is that the amount of swelling depends on the crosslinking density. Since it is related, in this test piece, since the time-dependent change of the crosslinking density was small, it is thought that there was no correlation between T ₂ ^S , T ₂ ^L and the swelling amount. On the other hand, since the change in acetone-soluble content is related to the change in the residual amount of plasticizer, in this test piece, the mobility of molecular chains, that is, T ₂ ^S and T ₂ ^L are mainly caused by volatilization of the plasticizer. Presumed to have been reduced.

FIG. 5 shows the measurement temperature of pulse method NMR and the component ratio of T ₂ ^S and T ₂ ^L as a result of measuring a sample in an unaccelerated test piece in Example 1 that was not subjected to acetone extraction and swelling with toluene. The relationship is shown. It can be confirmed that the component ratio of T ₂ ^S decreases with increasing temperature and almost disappears at 70 ° C.

FIG. 5 also shows the component ratio of T ₂ ^S and T ₂ ^L measured at 20 ° C. after the acetone-soluble component was extracted and swollen with toluene. As shown in FIG. 5, T ₂ ^S almost disappears after toluene swelling.

From the above, it can be estimated that T ₂ ^S captures the relaxation time of the portion where molecular mobility is low in the molecular chain and near the crosslinking point, and T ₂ ^L captures the relaxation time of the portion where influence of entanglement is small. In the test pieces of Examples 1 and 2, T ₂ ^{S at} 20 ° C. is considered to mainly capture the mobility of the molecular chain in the vicinity of the entanglement point.

[Examples 3 and 4]
The O-ring of the pressure regulator equipped with a diaphragm with an O-ring made of high nitrile NBR rubber as the base polymer instead of the flat plate test piece cut out from the ring packing was mounted on the pressure regulator. Measurements similar to those of Examples 1 and 2 were performed, and the results are shown in FIGS. FIGS. 6 to 8 (a) show the relationship between T ₂ ^S and compression set, acetone solubles and swelling, and FIGS. 6 to 8 (b) show T ₂ ^L , compression set and acetone acceptable. The relationship between a soluble content and the amount of swelling is shown.

As shown in FIGS. 6 to 8, T ₂ ^S shows a good correlation with compression set, acetone-soluble component, and swelling amount. With respect to this test piece, both the crosslink density and the residual amount of plasticizer changed with time, and it is assumed that a certain correlation was observed in both. On the other hand, in the case of this sample, the correlation between T ₂ ^L , compression set, acetone-soluble content, and swelling amount is low.

From these results, the time-dependent change in T ₂ ^S of the rubber seal material placed in an environment where thermal deterioration is dominant shows a good correlation with compression set regardless of the shape, composition, and deterioration mechanism of the material, It was confirmed that the life evaluation index is highly reliable. In addition, in the sealing material targeted in this test, a correlation between T ₂ ^S measured at 20 ° C. and compression set was confirmed.

[Example 5]
A plurality of unused flat rubber test pieces identical to those used in Example 1 were subjected to constant compression displacement with a compression rate of 10% using spacers as in Example 2, and this was applied to acceleration temperatures of 60 ° C. and 80 ° C. Or in an air thermostat set to 100 ° C. Then, the T ₂ relaxation time was measured for each test piece in the same manner as in Example 2 every 1000 hours, 1500 hours, 3000 hours, 5000 hours, 7000 hours (only at 100 ° C.), or 12800 hours (60, 80 ° C.), and T ₂ ^S And the compression set was measured. Based on this result, the relationship between the processing time for each acceleration temperature and T ₂ ^S is shown in FIG. Further, a calibration relationship between compression set and T ₂ ^S was obtained. This calibration relationship is as shown in FIG.

Based on this calibration relationship, T ₂ ^S corresponding to a predetermined upper limit value of compression set (80% in this example) was obtained and found to be 81 μsec. Therefore, this 81 μsec is set as the limit value of T ₂ ^S.

When the elapsed time until the test piece held at each acceleration temperature reaches the T ₂ ^S limit value (81 μsec) is read from FIG. 9,
2820hr at 100 ° C
8329 hr at 80 ° C
28431hr at 60 ° C
Met. This processing temperature and elapsed time were Arrhenius plotted to obtain the Arrhenius diagram shown in FIG. The vertical axis in FIG. 10 is the natural logarithm value 1n (1 / h) which is the reciprocal of the elapsed time h. The horizontal axis is 1000 / K, which is 1000 times the reciprocal of the processing temperature (absolute temperature) K.

  In FIG. 10, the elapsed time until reaching the limit value with the use environment temperature of 20 ° C. (the reciprocal of the absolute temperature is 1000 / K is 1000 / (273 + 20) = 3.41) is obtained for the obtained straight line. As a result, it was 537663 hr (about 61 years) as follows.

That is, the vertical axis value corresponding to the horizontal axis value of 3.41 in FIG. 10 is −13.195.
e ^-13.195 = 1 / h
From h = 1 / e ^-13.195
= 1 / 1.8599 × 10 ⁻⁶
= 537663 hr
Therefore, it was evaluated that the lifetime of this O-ring when held at 20 ° C. was about 61 years.

Claims (7)

Spin rubber seal member in pulse method NMR - measuring the spin relaxation time T _2,
The obtained T ₂ relaxation curve (free induction decay curve) is divided into a T ₂ ^S component having a short relaxation time and a T ₂ ^L component having a long relaxation time,
A method for evaluating the life of a rubber seal material, wherein the life of the rubber seal material is evaluated based on the T ₂ ^S. In claim 1,
A step of applying a constant compression displacement to an unused test piece having the same composition as the rubber seal material to be evaluated and placing it under accelerated temperature conditions, and then measuring the compression set of a plurality of test pieces,
Measuring T ₂ ^S of each test piece to obtain a calibration relationship between T ₂ ^S and compression set;
Obtaining a limit value of T ₂ ^S to be evaluated corresponding to a predetermined upper limit value of compression set based on the calibration relationship;
A method for evaluating the life of a rubber seal material, comprising: T ₂ ^S measured for the rubber seal material to be evaluated and a step of evaluating the life of the rubber seal material to be evaluated based on the limit value. In claim 2, when determining the calibration relationship compression set and the T ₂ ^S, the test piece placed on accelerated temperature conditions (hereinafter, referred to as acceleration products.) And placed not test piece to the acceleration temperature conditions A method for evaluating the life of a rubber seal material, wherein a calibration relationship between a difference in T ₂ ^S (hereinafter referred to as an unaccelerated product) and compression set is obtained. In claim 1, an apparatus equipped with a rubber seal material is placed under an accelerated temperature condition as a specimen, and then a sealing performance is determined by performing an airtight test of each specimen, and the rubber seal material attached to the specimen is measured. A method for evaluating the life of a rubber sealing material, characterized in that T ₂ ^S is obtained by measuring T ₂ relaxation time, and obtaining a limit value of T ₂ ^S that can maintain sealing performance. In Claim 4, it is called the test piece (hereinafter referred to as an accelerated product) of the specimen under the accelerated temperature condition and the test piece (hereinafter referred to as an unaccelerated product) of the specimen that was not under the accelerated temperature condition. ) And determined the T ₂ ^S for the in determining the limit value of T ₂ ^S that the sealing performance can be maintained, for differences in T ₂ ^S of each accelerating product and the non-accelerated products sealing performance can be maintained, the limit value A method for evaluating the life of a rubber sealing material, characterized in that: 6. The rubber sealing material according to claim 2, wherein the time required for the measured T ₂ ^S to reach the limit value is determined, and the limit value is reached at the operating environment temperature by linear extrapolation of the Arrhenius plot. A method for evaluating the life of a rubber sealing material, characterized in that the time is estimated as the life of a rubber sealing material for equipment. 6. The T ₂ ^S of the test piece according to claim 3 or 5 (hereinafter referred to as “accelerated product”) and the test piece that was not subjected to the accelerated temperature condition (hereinafter referred to as “unaccelerated product”). Establish the limit value of the difference, estimate the time when the difference between T ₂ ^S of each accelerated product and the unaccelerated product reaches this limit value, and further calculate the time to reach the limit value at the operating environment temperature by linear extrapolation of the Arrhenius plot A method for evaluating the life of a rubber seal material, wherein the life of a seal portion of equipment is estimated.

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