JP6050174B2 - Degradation analysis method - Google Patents

Description

The present invention relates to a degradation analysis method for analyzing a degradation state of a polymer material.

Generally, methods such as physical property tests such as Swell (swelling test) and infrared spectroscopy (FT-IR) are used to evaluate changes in chemical state due to deterioration of polymer materials such as sulfur-crosslinked diene rubbers. It has been.

The Swell test is a method in which a crosslinked polymer material is swollen with a low molecular weight solvent such as toluene to obtain a network chain density. By this method, the state of cutting and recombination of rubber molecules before and after deterioration is examined. However, since the entire change is observed, for example, it cannot be determined which deterioration of the polymer of the sulfur-crosslinked polymer material or the sulfur crosslinking is progressing. Moreover, in the FT-IR method, it is possible to detect functional groups such as C═O and OH generated by degradation, but since the sensitivity of SS bond is low, it is not possible to determine which degradation is the same as described above. .

Furthermore, in examining the deterioration state of the polymer material, if it is possible to know the degree of deterioration of each of the polymer and the sulfur bridge, it is considered that a more effective anti-degradation measure can be established compared to the conventional method. In the conventional method as described above, it is not possible to examine the rate of deterioration of the polymer and sulfur crosslinking.

On the other hand, non-patent documents 1 to 3 report on the measurement of the X-ray absorption spectrum of the polymer. Of course, the degradation factor is separated by the X-ray absorption spectrum, but of course the X-ray absorption spectrum and the X-ray photoelectron There is no report of degradation analysis combining spectroscopic methods.

O. Dhez, H .; Ade, S .; G. Urquhart. J. et al. Electron Spectrosc. Relat. Phenom. , 2003, 128, 85-96 Robert J. et al. Klein, Daniel A. et al. Fischer, and Joseph L. Lenhart. Langmuir. , 2008, 24, 8187-8197 Toshihiro Okajima, Surface Science. , 2002 Vol. 23, no. 6,356-366

The present invention provides a degradation analysis method that solves the above-mentioned problems and that requires a degradation rate of polymer degradation and sulfur crosslinking degradation even with a sulfur-crosslinked polymer material having low conductivity, particularly regarding the degradation state of the sulfur crosslinked polymer material. For the purpose.

The present invention relates to a sulfur crosslinked state obtained by irradiating a sulfur-crosslinked polymer material having a metal film with a thickness of 100 mm or less with X-rays having a constant energy and measuring excited and emitted photoelectrons, and The present invention relates to a degradation analysis method for obtaining a degradation rate of polymer degradation and sulfur cross-linking degradation from a polymer degradation state obtained by irradiating X-rays and measuring X-ray absorption while changing X-ray energy.

The X-ray having a constant energy is preferably 2.3 keV or more.
The metal film is preferably a metal vapor deposition film.

The polymer material is preferably a tire rubber composition. Here, the tire rubber composition preferably has a carbon black content of 50 parts by mass or less based on 100 parts by mass of the rubber component.

According to the present invention, a sulfur crosslinked polymer obtained by irradiating a sulfur crosslinked polymer material having a metal film with a thickness of 100 mm or less with X-rays having a constant energy and measuring excited and emitted photoelectrons. This is a degradation analysis method for obtaining the degradation rate of polymer degradation and sulfur crosslinking degradation from the degradation state of the polymer obtained by irradiating X-rays and measuring the X-ray absorption while changing the energy of the X-rays. Therefore, regarding the deterioration state of the sulfur-crosslinked polymer material, polymer deterioration and sulfur cross-linking can be achieved even for materials with low conductivity, such as rubber compositions for tires such as compound rubbers with a small amount of carbon black and silica compound rubbers. The deterioration rate of deterioration can be obtained. Therefore, regardless of the presence or absence of conductivity, it is possible to determine whether the deterioration of polymer degradation or sulfur cross-linking degradation is progressing for various materials, and it is possible to take deterioration resistance measures that are more effective than before. Become.

X-ray photoelectron spectrum in a carbon 1s orbit obtained by subjecting a polymer material (insulator) to measurement of XPS and HAX-PES. The schematic diagram of the sample in which the metal film was formed. The HAX-PES spectrum in the carbon 1s orbital of the sample which vapor-deposited Au with the thickness of 8 ?, and the sample which has not performed metal vapor deposition. HAX-PES spectrum in the sulfur 1s orbit of the sample which vapor-deposited Au with the thickness of 8 ?, and the sample which has not performed metal vapor deposition. X-ray photoelectron spectrum in S1s of a new blend rubber of natural rubber and butadiene rubber and a sample subjected to thermal oxygen degradation for 1 week. X-ray photoelectron spectrum at S2p of a new blend rubber of natural rubber and butadiene rubber and a sample subjected to thermal oxygen deterioration for 1 week. The graph which showed the sample electric current of the sample which vapor-deposited Au with the thickness of 8 to the tire tread compounding sample, and the sample which has not performed metal vapor deposition. X-ray absorption spectra (not specified) of polybutadiene rubbers with different thicknesses deposited with Au. NEXAFS measurement of K-shell absorption edge of carbon atoms of a new side wall compounded rubber, a sample subjected to ozone degradation for 48 hours, and a sample subjected to oxygen degradation for 1 week by Au deposition. Graph showing results (before standardization). NEXAFS measurement of K-shell absorption edge of carbon atoms of a new side wall compounded rubber, a sample subjected to ozone degradation for 48 hours, and a sample subjected to oxygen degradation for 1 week by Au deposition. Graph showing results (after normalization).

In the degradation analysis method of the present invention, a sulfur-crosslinked polymer material formed with a metal film having a thickness of 100 mm or less is irradiated with X-rays having a constant energy, and excited and emitted photoelectrons are measured to determine the sulfur-crosslinked polymer material. This is a method for determining the deterioration rate of polymer deterioration and sulfur crosslinking deterioration from the deterioration state and the deterioration state of the polymer determined by irradiating X-rays and measuring the X-ray absorption while changing the energy of X-rays. .

Known degradation factors for sulfur-crosslinked polymer materials such as vulcanized rubber (sulfur-crosslinked polymer materials) include degradation of polymer molecular chains due to ultraviolet rays, oxygen, ozone, heat, etc., and degradation of sulfur crosslinking. In order to improve the deterioration resistance, it is important to know how the polymer molecular chain and the sulfur cross-linked structure change due to factors.

With respect to this point, the degradation analysis method of the present invention first measures sulfur cross-linked by measuring excited and emitted photoelectrons by irradiating a sulfur cross-linked polymer material on which a metal film is formed with X-rays having a constant energy. For example, the sample is measured using X-ray photoelectron spectroscopy (XPS), and the sulfur bridge degradation state is determined from the peak area attributed to sulfur. Can be analyzed.

Specifically, it can be measured using an XPS method using a normal Al Kα ₁ line (1486.6 eV), a hard X-ray photoelectron spectroscopy (HAX-PES: Hard X-ray Photoluminescence Spectroscopy), and the like. However, X-ray photoelectron spectroscopy is a technique that irradiates a sample with X-rays and separates the electrons emitted by the photoelectric effect for each binding energy. Therefore, if the electrons are not supplied, the sample is charged and accurate measurement is possible. Can not. When the sample is a conductive material, electrons are supplied from the ground, and there is no problem. However, since polymer materials such as rubber are insulators, the neutralization gun is generally used to supplement the sample with electrons to prevent charging. ing.

FIG. 1 shows an X-ray photoelectron spectrum in a carbon 1s orbit obtained by subjecting a polymer material (insulator) such as rubber to XPS and HAX-PES measurements. As shown here, HAX-PES uses high X-ray energy and cannot be charged even with the use of a neutralizing gun, so the spectrum obtained is higher than the spectrum obtained by XPS measurement. It is broad. If the peak is broad, the small peak is buried and detection becomes difficult. However, when the sulfur bridge is deteriorated, oxide (SOx) is generated, and the peak of the oxide is often small. Therefore, for example, when measuring the sidewall of a tire, there is no problem if it has a good conductivity. However, when the side wall is used for measurement of a low fuel consumption formulation with a small amount of carbon black, a tread containing silica, etc. When used for measurement of materials that are difficult to ensure conductivity, it is difficult to prevent charging, and it is difficult to analyze the degradation state of sulfur crosslinking.

In contrast, in the present invention, a metal vapor deposition method or the like is applied to the sulfur cross-linked polymer material in advance to form a metal film with a predetermined thickness to increase the conductivity. A good X-ray photoelectron spectrum can be measured. Therefore, compare the spectra obtained by measuring photoelectrons excited and emitted by irradiating X-rays of a certain energy to new and deteriorated polymer materials (samples) on which a metal film is formed. Thus, a deteriorated state of sulfur crosslinking of the polymer material after deterioration is required.

Furthermore, in the present invention, new samples and samples with a metal film formed on a deteriorated polymer material are irradiated with X-rays while changing energy, and the respective spectra obtained by measuring the amount of X-ray absorption are compared. By doing so, the degradation state of the polymer material after degradation is analyzed. Specifically, an X-ray absorption spectrum near the absorption edge of a specific element is measured (NEXAFS (Near Edge X-ray Absorption Fine Structure) method). The degradation state of the polymer portion can be analyzed from the peak area of the X-ray absorption spectrum at the K-shell absorption edge of the carbon atom.

When the NEXAFS method is used, the amount of oxygen or ozone bound to the polymer material can be analyzed from the X-ray absorption spectrum near the oxygen K-shell absorption edge. It cannot be determined whether it is bonded to the cross-linked portion. Therefore, in the present invention, after ensuring conductivity with a metal film, the photoelectrons excited and emitted by irradiating X-rays with a constant energy are measured to analyze the deterioration state of the sulfur bridge, and the X-ray energy The amount of X-ray absorption was measured while changing the value, and the deterioration state of the polymer (polymer molecular chain) portion was also analyzed. Therefore, by adopting the method of the present invention, it is possible to measure the degree of deterioration of each of the polymer and the sulfur cross-link and analyze which deterioration is progressing, that is, the deterioration rate.

The polymer material (sample) provided for the present invention is one in which a metal film having a predetermined film thickness is formed on the sample surface. As a result, the conductivity of the polymer material (sample) can be increased within a range in which degradation analysis is possible, and surface charging can be prevented. Therefore, it is possible to measure HAX-PES and NEXAFS even with polymer materials with low conductivity, such as rubber compounded with a small amount of carbon black, silica compounded rubber, etc. By suppressing to the minimum, it becomes possible to perform a degradation analysis of the polymer material itself. The method for forming the metal film is not particularly limited as long as it can be formed on the sample surface, and a metal vapor deposition method or the like can be suitably used.

There are various methods such as resistance heating type, electron beam type, high frequency induction type, laser type, etc. for metal vapor deposition. A thin film is formed on the surface of a sample placed at a distant position. Any method is possible, but considering the possibility that the vapor deposition material is ionized and damages the sample, it is desirable to adopt a resistance heating type vacuum vapor deposition method in which heating is performed by passing an electric current through the vapor deposition material.

The thickness of the metal film formed on the polymer material surface is 100 mm or less, preferably 50 mm or less, more preferably 10 mm or less. When it exceeds 100%, there is a tendency to be greatly affected by the deposited metal. In particular, since the HAX-PES method can detect the surface to several tens of nanometers, when it exceeds 100 mm, most of the measurement portion becomes metal, and information on the rubber itself cannot be obtained accurately. As long as conductivity is ensured, the lower limit is not particularly limited, but is preferably 1 mm or more, more preferably 3 mm or more, and further preferably 5 mm or more.

For example, gold (Au) can be suitably used as the metal that forms the metal film. Metals other than Au can also be used, but in order to suppress the influence on the measurement, it is desirable to use a metal having no binding energy in the energy region to be measured, specifically, in the vicinity of carbon 1s and sulfur 1s.

In the present invention, a sulfur-crosslinked polymer material (hereinafter also referred to as a metal film-forming sample) having a metal film having a thickness of 100 mm or less is irradiated with X-rays having a constant energy, and excited and emitted photoelectrons are measured. From the above, the deterioration state of the sulfur bridge is obtained. As a measuring method, the aforementioned XPS (XPS method using Al Kα ₁ line, HAX-PES) or the like can be used. FIG. 2 is a schematic diagram of a sample on which a metal film is formed.

It will be specifically described with reference to FIGS. 3 to 4 that HAX-PES can be measured by forming a metal film on the sample surface.

FIG. 3 shows the HAX-PES spectrum of the polymer material in the carbon 1s orbital, and FIG. 4 shows the polymer in the sulfur 1s orbital for each of the samples deposited with Au in a thickness of 8 mm and the samples not subjected to metal deposition (Au deposition). 2 shows a HAX-PES spectrum of the material. In both FIG. 3 and FIG. 4, the sample (polymer material) not subjected to metal vapor deposition cannot prevent charging, so the peak becomes broad and the oxide peak is buried and cannot be detected. Since the sample is prevented from being charged, the peak is sharp and it is shown that the peak of the oxide can be detected. As described above, in the present invention, the sulfur-crosslinked polymer material with the metal film formed thereon is subjected to measurement such as HAX-PES, so that it is possible to detect peaks of sulfur oxides and the like, and analyze the deterioration state of sulfur crosslinking. it can.

In the present invention, as a technique for measuring the deterioration state of sulfur crosslinking by the HAX-PES method, for example, a photoelectron excited and emitted by irradiating a metal film forming sample with X-rays having a constant energy is dispersed, A method for obtaining a sulfur cross-linking deterioration degree (%) by the following (Equation 1) using the peak area attributed to the obtained sulfur oxide by waveform separation of the X-ray photoelectron spectrum measured for the photoelectron intensity corresponding to S1s ( The method 1) is mentioned.
(Formula 1)
(Peak area attributed to sulfur oxide of S1s) / (total peak area related to S1s) × 100 = sulfur cross-linking deterioration degree (%)
Thereby, the deterioration degree (%) of the sulfur bridge | crosslinking part after deterioration is obtained, and a deterioration rate can be analyzed.

In particular, by using the HAX-PES method, there is an advantage that an S1s orbit that cannot be measured by a normal XPS method can be measured. That is, in the normal XPS method, the spectrum of the S2p orbit is measured. However, since the energy of the X-ray used is low, the detection depth is from the surface to several nm, whereas in the HAX-PES method, Since the S1s trajectory can be measured and the energy of X-rays used is high, the detection depth is from the surface to several tens of nm. Therefore, according to the HAX-PES method, it is possible to analyze the deterioration of sulfur crosslinking particularly in the bulk (inside) of the sulfur crosslinked polymer material.

In Method 1, the total peak area of sulfur corresponding to S1s in (Equation 1) is obtained by integrating the spectrum within the measurement range, and the energy range can be changed depending on the measurement conditions and the like.

The energy range of the constant energy X-ray used is preferably 2.3 keV or more, more preferably 4 to 10 keV, from the viewpoint that the peak area related to sulfur S1s (sulfur 1s orbit) can be measured.

The above method 1 will be specifically described using an example of using a new NR and BR blend rubber and a sample subjected to thermal oxygen degradation for one week (both are metal film forming samples).
The measurement result of the X-ray photoelectron spectrum in S1s (1s orbit of sulfur) of these samples is shown in FIG. As shown in FIG. 5, in the deteriorated sample, the peak corresponding to the S—S bond decreases, and the peak corresponding to the sulfur oxide (SOx) increases. Therefore, the X-ray photoelectron spectrum of degraded S1s is separated into S—S bond and SOx peaks, and the peak area attributed to SOx and the total peak area related to sulfur are applied to the above (formula 1). By doing so, the sulfur crosslinking deterioration degree (%) is required.

Here, although the peak of sulfur oxide (SOx) is considered to be a plurality of peaks having different valences, in principle, as shown in FIG. It is possible to separate into peaks attributed to SOx.

In the above method 1, the sulfur crosslinking deterioration degree can be obtained in the same manner even when the peak intensity is used instead of the peak area in the above (formula 1).

Further, in the present invention, as a specific method for measuring the degradation state of sulfur crosslinking by XPS method, photoelectrons excited and emitted by irradiating a metal film forming sample with X-rays having a constant energy are dispersed, A method for obtaining the degree of sulfur cross-linking degradation (%) by the following (Equation 2) using the peak area attributed to the obtained sulfur oxide by waveform separation of the X-ray photoelectron spectrum measured for the photoelectron intensity corresponding to sulfur S2p (Method 2) is also mentioned.
(Formula 2)
(Peak area attributed to sulfur oxide of S2p) / (Total peak area related to S2p) × 100 = Deterioration degree of sulfur crosslinking (%)
Thereby, the deterioration degree (%) of the sulfur bridge | crosslinking part after deterioration is obtained, and a deterioration rate can be analyzed.

In Method 2, the total peak area related to S2p in (Expression 2) above is obtained by integrating the spectrum within the measurement range, and the energy range can be changed depending on the measurement conditions and the like.

In the above method 2, the energy range of the constant energy X-ray used is preferably 150 to 200 eV, more preferably 155 to 180 eV, in that the area of the peak related to S2p (sulfur 2p orbit) can be measured. It is.

The method 2 will be specifically described using an example of using a new blend rubber of NR and BR and a sample (both metal film forming samples) subjected to thermal oxygen deterioration for one week.
The measurement result of the X-ray photoelectron spectrum in S2p (2p orbit of sulfur) of these samples is shown in FIG. As shown in FIG. 6, in the deteriorated sample, the peak corresponding to the S—S bond decreases and the peak corresponding to the sulfur oxide (SOx) increases. Therefore, the X-ray photoelectron spectrum at S2p of the deteriorated product is waveform-separated into S—S bond and SOx peaks, and the peak area attributed to SOx and the total peak area related to S2p are applied to the above (Formula 2). By doing so, the sulfur crosslinking deterioration degree (%) is required.

Here, since the S2p orbital is spin orbital splitting, two peaks appear for one assignment, and the peak of sulfur oxide (SOx) is considered to be overlapped with a plurality of peaks having different valences. Considering in principle, as shown in FIG. 6, it is possible to largely separate the peak attributed to SS and the peak attributed to SOx.

In the above method 2, the sulfur bridge deterioration degree can be obtained in the same manner even when the peak intensity is used instead of the peak area in the above (formula 2).

In addition, in the above methods 1 and 2, oxygen-degraded products are described, but ozone-degraded products and degraded products degraded by both ozone and oxygen can be analyzed by the same method, and the degree of deterioration of sulfur crosslinking can be obtained. Is possible.

The deterioration state of the sulfur bridge in the present invention described above can be analyzed using, for example, a normal XPS apparatus such as the HAX-PES apparatus attached to the SPring-8 BL46XU beam line or AXIS Ultra manufactured by Kratos.

Furthermore, in the present invention, the degradation state of the polymer is determined by irradiating the metal film-formed sample with X-rays and measuring the X-ray absorption while changing the energy of the X-rays. As a measuring method, a NEXAFS method or the like can be used.

The NEXAFS method scans with X-ray energy, so the light source requires a continuous X-ray generator, and X-ray absorption spectra with high S / N ratio and S / B ratio are measured to analyze the detailed chemical state. There is a need to. Therefore, the X-ray emitted from the synchrotron has a brightness of at least 10 ¹⁰ (photons / s / mrad ² / mm ² /0.1% bw) and is a continuous X-ray source. Ideal for. Note that bw represents the band width of X-rays emitted from the synchrotron.

The luminance (photons / s / mrad ² / mm ² /0.1% bw) of the X-ray is preferably 10 ¹⁰ or more, more preferably 10 ¹² or more. Further, the number of photons (photons / s) of the X-ray is preferably 10 ⁷ or more, more preferably 10 ⁹ or more. Although these upper limits are not specifically limited, It is preferable to use the X-ray intensity below the extent that there is no radiation damage.

The energy range scanned using the X-ray is preferably 4000 eV or less, more preferably 1500 eV or less, and still more preferably 1000 eV or less. When it exceeds 4000 eV, there is a possibility that the deterioration state analysis in the target polymer material cannot be performed. The lower limit is not particularly limited.

The measurement can be carried out by irradiating a sample placed in an ultra-high vacuum with soft X-rays to emit photoelectrons, and in order to compensate for this, electrons flow from the ground, and the sample current is measured.

Specifically, it can be carried out by the method described below.
A sample on which a metal film having a predetermined thickness is formed is attached to a sample holder, and then placed in a vacuum chamber for performing X-ray absorption measurement. Thereafter, the continuous X-rays radiated from the synchrotron are monochromatic with a spectroscope and irradiated on the sample. At this time, secondary electrons and photoelectrons escape from the sample surface into the vacuum, but electrons are replenished from the ground to compensate for the lost electrons. Here, the current flowing from the ground is defined as the X-ray absorption intensity I, the current of the gold mesh installed in the beam line optical system is defined as the incident X-ray intensity I _0, and the X-ray absorption amount μL is obtained from the following (formula). (Electron yield method). In this method, the Lanbert-Beer equation can be applied. However, in the case of the electron yield method, it is considered that the following equation is approximately established.

The following three methods are typically used for the NEXAFS measurement method. In the embodiment of the present invention, the electron yield method was used. However, the present invention is not limited to this, and various detection methods may be used, or simultaneous measurement may be performed in combination.

(Transmission method)
This is a method for detecting the X-ray intensity transmitted through a sample. For measurement of transmitted light intensity, a photodiode array detector or the like is used.

(Fluorescence method)
This is a method for detecting fluorescent X-rays generated when a sample is irradiated with X-rays. This is effective when measuring an X-ray absorption spectrum of an element having a small content. In addition, fluorescent X-rays have a strong transmission power and can detect fluorescent X-rays generated inside the sample, which is an optimal method for obtaining bulk information.

(Electron yield method)
This is a method for detecting a current flowing when a sample is irradiated with X-rays. Therefore, the sample needs to be a conductive material. In this invention, electroconductivity is securable by forming a metal membrane | film | coat. A high S / B ratio and S / N ratio measurement is realized by processing (cutting) the polymer material into a microtome of 100 μm or less, preferably 10 μm or less, more preferably 1 μm or less, and even more preferably 500 nm or less. It is also possible. Moreover, in order to ensure conduction | electrical_connection with a board | substrate and a sample, you may use the tape which has electroconductivity and can be used in a vacuum, such as a carbon tape and a silver tape.

Another characteristic of the electron yield method is that it is surface sensitive (information on the surface of the sample about several nm). When the sample is irradiated with X-rays, electrons escape from the element, but electrons have a strong interaction with the substance, so that the mean free path in the substance is short. Furthermore, since the energy of X-rays used in the NEXAFS method is relatively low, the kinetic energy of escaped electrons is small. For this reason, electrons that can jump out of the sample surface become a part of the extreme surface layer of the sample, and this detection method is a surface-sensitive method.

Here, the fact that X-ray absorption can be measured by forming a metal film on the surface of the sample, and that the film thickness of the metal film affects the deterioration analysis of the sample will be specifically described with reference to FIGS. explain.

FIG. 7 shows sample currents of a sample obtained by vapor-depositing Au with a thickness of 8 mm on a tire tread compound sample and a sample not subjected to metal vapor deposition. The sample without metal vapor deposition has a negative value in the broken line and the X-ray absorption could not be measured, whereas the sample with Au vapor deposition had a positive sample current and X-ray absorption. It has been shown that the measurement of absorption was possible. Thus, by forming a metal film having a predetermined thickness on the sample, X-ray absorption can be measured even for a polymer material having poor conductivity.

As a metal to vapor-deposit, the metal which does not have X-ray absorption in the energy range to measure is preferable. For example, when measuring in the vicinity of the carbon K absorption edge (270 to 320 eV), gold (Au) having no absorption in this energy region can be suitably used.

FIG. 8 shows an X-ray absorption spectrum of a sample in which an Au vapor deposition film having a different film thickness is formed on polybutadiene rubber. Since a cast film is used and even a sample not subjected to metal vapor deposition can be measured, the thickness of vapor deposition is changed, and the change in the X-ray absorption spectrum is examined. It shows that the larger the change, the greater the influence of the deposited metal, and the more likely it is that accurate degradation analysis cannot be performed.

The X-ray absorption spectrum in FIG. 8 is affected by the vapor deposition film from the spectrum of the sample on which the Au vapor deposition film is not formed, and the shape of the spectrum gradually changes as the film thickness of the vapor deposition film increases. It shows that. That is, in the sample in which the Au vapor-deposited film having a thickness of 8 mm is formed, the spectrum and the shape of the sample in which the vapor-deposited film is not formed are hardly changed, whereas in the sample in which the Au vapor-deposited film having a thickness of 20 mm is formed, the shape is slightly It has been shown that there is a risk of being slightly affected by the deposited film. Although the accuracy is slightly inferior even at a thickness of 20 mm, deterioration analysis is possible.

Furthermore, by using the above-mentioned electron yield method to measure and analyze the X-ray absorption spectrum of the metal film formation sample, the degree of deterioration (%), the contribution rate of oxygen deterioration and ozone deterioration (%), and the combination of oxygen and ozone Can be analyzed. Each will be described below.

In the present invention, as a specific method for measuring the degradation state of the polymer, for example, for the metal film-formed sample, the X-ray energy is required to be K-shell absorption edge of carbon atoms in the range of 260 to 400 eV. Based on the X-ray absorption spectrum obtained by scanning the range, normalization constants α and β are calculated by the following (Equation 3), and K-shell absorption of carbon atoms corrected using the normalization constants α and β: There is a method in which the X-ray absorption spectrum at the end is waveform-separated, and the polymer degradation degree (%) is obtained by the following (Equation 4) using the peak area attributed to the π ^* transition in the vicinity of 285 eV.
(Formula 3)
[Total area of X-ray absorption spectrum in measurement range in metal film-formed sample before deterioration] × α = 1
[Total area of X-ray absorption spectrum in the measurement range in the metal film-formed sample after deterioration] × β = 1
(Formula 4)
[1-[(Peak area of π ^* after degradation) × β] / [(Peak area of π ^* before degradation) × α]] × 100 = Polymer degradation degree (%)
Thereby, the deterioration degree (%) of the polymer after deterioration is obtained, and the deterioration rate can be analyzed. Here, in the method for obtaining the degree of deterioration, it is preferable that the energy of the X-ray is in a range of 260 to 350 eV. In the method for obtaining the degree of deterioration, the background is drawn by evaluating from the slope before the absorption end before performing the operation of (Equation 3).

In the method for determining the degree of deterioration of the polymer, the total area of the X-ray absorption spectrum in (Equation 3) is obtained by integrating the spectrum within the measurement range, and the energy range can be changed depending on the measurement conditions and the like.

The method for determining the degree of deterioration of the polymer will be specifically described with reference to an example using a new sidewall compounded rubber, a sample subjected to ozone deterioration for 48 hours, and a sample subjected to oxygen deterioration for one week.
FIG. 9 shows NEXAFS measurement results of the K-shell absorption edge of the carbon atom of the Au deposited film-formed sample prepared by performing Au deposition on each of a new product, an ozone-degraded sample, and an oxygen-degraded sample. As shown in FIG. 9, in the deteriorated sample, the peak of π ^* near 285 eV is smaller than that of the new product, but it is difficult to measure the absolute value in the NEXAFS method. The reason is that subtle changes such as the distance of the sample from the light source affect the magnitude of the X-ray absorption spectrum. For the above reasons, the NEXAFS measurement result of the K-shell absorption edge of carbon atoms cannot be simply compared between samples.

Therefore, in order to compare the measured X-ray absorption spectra between samples, normalization was performed as follows (the X-ray absorption spectra of each sample were corrected so that they could be directly compared). Since the X-ray absorption amount of the carbon shell does not change before and after the deterioration, the above (Equation 3) is used to normalize the peak area of the K-shell absorption edge of the carbon atom to 1. That is, first, normalization constants α and β are calculated based on (Expression 3) for an X-ray absorption spectrum before normalization, and then corrected to a spectrum obtained by multiplying the X-ray absorption spectrum before normalization by α and β ( By normalization, the π ^* peaks between samples can be directly compared.

The spectrum of the K-shell absorption edge of the carbon atom after normalization obtained in this way is shown in FIG. The degree of deterioration is determined from the normalized spectrum using the above (Equation 4). The degree of deterioration is a reduction rate of the peak of π ^* from before deterioration to after deterioration, and indicates the deterioration rate (%) of the sample.

In the method for obtaining the degree of deterioration of the polymer, the degree of deterioration can be obtained in the same manner even when the peak intensity is used in place of the peak area in (Equation 4).

The above-described method for measuring the degradation state of the polymer can be carried out, for example, at the BL12 beam line of the Saga Kyushu Synchrotron Light Research Center.

Furthermore, in the deterioration analysis method of the present invention, for example, the contribution ratio of polymer deterioration and sulfur cross-linking deterioration can be calculated by the following (formula 5).
(Formula 5)
[Polymer degradation degree (%)] / [Sulfur crosslinking degradation degree (%)] = Contribution rate of polymer degradation and sulfur crosslinking degradation

In other words, the degree of polymer degradation (%) and the degree of sulfur crosslinking degradation (%), which indicate the degree of degradation of each polymer and sulfur crosslinking, using the method for obtaining the degree of polymer degradation or the method for obtaining the degree of sulfur crosslinking degradation as described above. By determining the ratio (ratio), it is possible to determine which deterioration is progressing more. Specifically, in the above (Equation 5), when the contribution ratio of polymer degradation and sulfur cross-linking degradation> 1, the progress of polymer degradation is larger, and the contribution ratio of polymer degradation and sulfur cross-linking degradation <1. In this case, it can be judged that the progress of sulfur cross-linking degradation is larger. Therefore, by adopting the method of the present invention, anti-deterioration measures that are more effective than conventional methods can be established.

The polymer material applicable to the present invention is not particularly limited and includes conventionally known polymer materials. For example, a rubber material containing one or more types of diene rubber, the rubber material and one or more types of resins are used. A composite material which is combined and sulfur-crosslinked can be suitably used. Examples of the diene rubber include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), Examples thereof include polymers having a double bond such as halogenated butyl rubber (X-IIR) and styrene isoprene butadiene rubber (SIBR).

The resin is not particularly limited, and examples thereof include those widely used in the rubber industry field, and examples thereof include petroleum resins such as C5 aliphatic petroleum resins and cyclopentadiene petroleum resins.

The present invention can be applied to any high-conductivity or low-conductivity polymer material without any particular limitation. For example, as the polymer material, a rubber component and a filler such as silica or carbon black can be used. It can apply suitably for the rubber composition for tires containing these. Examples of the rubber component include the diene rubber. Carbon black and silica are not particularly limited, and those commonly used in the tire field can be used.

Since the present invention is a method applicable to both high-conductivity and low-conductivity polymer materials, the amount of carbon black compounded in the tire rubber composition is not particularly limited. In particular, from the viewpoint of ensuring conductivity by a metal film, a rubber composition with a carbon black content of 50 parts by mass or less with respect to 100 parts by mass of the rubber component can be applied. Applicable.

Since the present invention can also be applied to silica-containing rubber having low conductivity, the amount of silica is not particularly limited in the above rubber composition for tires, but is preferably 5 to 90 parts by mass, more preferably 10 to 60 parts. Part by mass.

In the tire rubber composition, in addition to the above components, compounding agents generally used in the production of rubber compositions, for example, reinforcing fillers such as clay, silane coupling agents, zinc oxide, stearic acid, various Antiaging agents, oils, waxes, vulcanizing agents, vulcanization accelerators, and the like can be appropriately blended.

The rubber composition for tires is manufactured by a general method. That is, it can be produced by a method of kneading the above components with a Banbury mixer, a kneader, an open roll or the like and then vulcanizing. The rubber composition can be used for each member of a tire, and in particular, can be suitably used for a tread, a sidewall, and the like.

The present invention can also be applied to a pneumatic tire manufactured by a normal method using the above rubber composition for a tire. A pneumatic tire is a tire molding machine that extrudes a rubber composition for a tire containing the above components in accordance with the shape of each tire member such as a sidewall and a tread at an unvulcanized stage, together with other tire members. It can be manufactured by forming an unvulcanized tire by molding in the usual manner and heating and pressurizing the unvulcanized tire in a vulcanizer.

The method of the present invention can be applied to, for example, a tire rubber composition and a sample (polymer material) sampled and prepared from each member of a tire using the rubber composition, and a metal film having a predetermined film thickness is formed. Here, the thickness of the sample is not particularly limited, but is preferably 10 nm to 1 mm, and more preferably 50 nm to 100 μm.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

[Manufacture of test tires]
(Process 1)
According to the formulation shown in Tables 1-2, materials other than sulfur and a vulcanization accelerator are filled in a 1.7 L Banbury manufactured by Kobe Steel Co., Ltd. so that the filling rate is 58%, and reaches 140 ° C. at 80 rpm. Until kneaded.
(Process 2)
Sulfur and a vulcanization accelerator are added to the kneaded product obtained in Step 1, and kneaded for 3 minutes under the condition of 80 ° C. using an open roll, and each unvulcanized rubber composition for sidewall and tread is used. The thing (sidewall 1-2, tread 1-2) was obtained.
(Process 3)
The unvulcanized rubber composition of the sidewall 1 obtained in step 2 is formed into a sidewall shape, the unvulcanized rubber composition of the tread 1 is formed into a tread shape, and bonded to another tire member to form a tire, A test tire 1 was manufactured by vulcanization at 160 ° C. for 20 minutes. A test tire 2 was produced in the same manner except that the sidewall 2 was used instead of the sidewall 1 and the tread 2 was used instead of the tread 1.

The materials used for the sidewalls 1 and 2 and the treads 1 and 2 are as follows.
(material)
Natural rubber (NR): TSR20
Butadiene rubber (BR): BR150B manufactured by Ube Industries, Ltd.
Styrene butadiene rubber (SBR): Nipol 1502 manufactured by Nippon Zeon Co., Ltd.
Carbon Black N351: Show Black N351 (N ₂ SA: 71 m ² / g) manufactured by Cabot Japan
Silica: Ultrasil VN3 from Degussa
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa
Oil: Process X-140 manufactured by Japan Energy Co., Ltd.
Phenylenediamine-based anti-aging agent: NOCRACK 6C (N-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Wax: Ozoace 0355 manufactured by Nippon Seiwa Co., Ltd.
Zinc oxide: Silver candy R made by Toho Zinc Co., Ltd.
Stearic acid: Koji powder sulfur manufactured by NOF Corporation (containing 5% oil): 5% oil-treated powder sulfur manufactured by Tsurumi Chemical Co., Ltd. (soluble sulfur containing 5% by mass of oil)
Vulcanization accelerator: Noxeller CZ (N-cyclohexyl-2-benzothiazylsulfenamide) manufactured by Ouchi Shinsei Chemical Co., Ltd.

[Examples and Comparative Examples]
After sampling the test tire 1 that has been deteriorated due to market running, the sidewall 1 and the tread 1, and the deteriorated test tire 2 from the sidewall 2 and the tread 2, about 2 mm × 1 mm × 0.5 mm, respectively, According to 4, an Au vapor deposition film was formed on the sample surface by a resistance heating type vacuum vapor deposition method to prepare a test sample. After that, the sample was stored in a vacuum desiccator so that the influence of oxygen other than deterioration did not appear.

(Device used)
NEXAFS: SEX Prefectural Kyushu Synchrotron Light Research Center NEXAFS measuring device attached to BL12 beam line HAX-PES: SPring-8 HAX-PES device attached to BL46XU beam line

Using NEXAFS, the degree of polymer degradation (%) was measured by performing the following analysis for each sample before and after degradation.
The measurement conditions for NEXAFS were as follows.
Luminance: 5 × 10 ¹² photons / s / mrad ² / mm ² /0.1% bw
Number of photons: 2 × 10 ⁹ photons / s

(Polymer degradation analysis)
The X-ray energy was scanned in the range of 260 to 400 eV to obtain an X-ray absorption spectrum of the K-shell absorption edge of the carbon atom. Normalization constants α and β were calculated from (Equation 3) based on the necessary range of 260 to 350 eV in this spectrum, and the spectrum was normalized (corrected) using these constants. The normalized spectrum was separated into waveforms, and the degree of polymer degradation (%) was determined from (Equation 4) based on the peak area attributed to the π ^* transition near 285 eV.

Using HAX-PES, the degree of sulfur crosslinking deterioration (%) was measured by the following analysis for each sample after deterioration.
The measurement conditions for HAX-PES were as follows.
Measurement light source: High-intensity X-ray irradiation X-ray energy: 8 keV
Measurement output: 10 ¹³ photon / s
Measuring element and orbit: S1s
Binding energy: 2472 eV

(Sulfur crosslinking degradation analysis)
The photoelectrons excited and emitted by irradiating the above-mentioned X-rays having a constant energy were dispersed to obtain an X-ray photoelectron spectrum in which the photoelectron intensity corresponding to the sulfur S1s was measured. In the range of 2465 to 2480 eV of this spectrum, the waveform is separated into peaks corresponding to S—S bonds near 2470 eV and SOx near 2472 eV, and the peak area attributed to the obtained sulfur oxide and the range of 2465 to 2480 eV The degree of sulfur cross-linking degradation (%) was determined from (Equation 1) using the total peak area of sulfur.

(Contribution analysis of polymer degradation and sulfur crosslinking degradation)
Calculate the contribution ratio of polymer degradation and sulfur cross-linking degradation by applying the values of polymer degradation and sulfur cross-linking degradation obtained in the above polymer degradation analysis and sulfur cross-linking degradation analysis to (Equation 5). did.

Tables 3 to 4 show the results obtained by the above polymer degradation analysis, sulfur crosslinking degradation analysis, and contribution analysis.

In the sample in which the Au vapor deposition film was not formed and the sample in which the Au vapor deposition film having a thickness of 500 mm was formed, it was not possible to analyze the degree of polymer degradation, the degree of sulfur cross-linking degradation, and the contribution ratio of these samples after degradation. On the other hand, in the Example using the sample in which the Au vapor deposition film having a thickness of 8 mm was formed, any analysis was possible by using NEXAFS and HAX-PES. Therefore, the effectiveness of the evaluation method of the present invention was proved.

Claims (5)

Sulfur crosslinked polymer material with a metal film with a thickness of 100 mm or less is irradiated with X-rays of a certain energy, and the sulfur bridge degradation state and X-rays obtained by measuring excited and emitted photoelectrons are irradiated. A degradation analysis method for obtaining a degradation rate of polymer degradation and sulfur crosslinking degradation from a polymer degradation state obtained by measuring X-ray absorption while changing X-ray energy. The deterioration analysis method according to claim 1, wherein the X-ray having the constant energy is 2.3 keV or more. The deterioration analysis method according to claim 1, wherein the metal film is a metal vapor deposition film. The deterioration analysis method according to claim 1, wherein the polymer material is a tire rubber composition. The deterioration analysis method according to claim 4, wherein the tire rubber composition has a carbon black content of 50 parts by mass or less based on 100 parts by mass of the rubber component.

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