JP2015152533A - Method of inspecting chemical state of sulfur - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an evaluation method for acquiring accurate information of a chemical state of sulfur in various polymer materials such as a polymer material in which sulfur exists nonuniformly.SOLUTION: In the method of inspecting the chemical state of sulfur, X rays of a beam size of vertical 500 μm × horizontal 500 μm or less are radiated to a sulfur-containing polymer material in which sulfur exists nonuniformly, and the X-ray absorbed amount is measured while the energy of the X rays is changed.

Description

The present invention relates to a method for examining the chemical state of sulfur in various polymer materials such as a polymer material in which sulfur is unevenly present.

In order to evaluate changes in chemical state due to deterioration of polymer materials containing sulfur, such as sulfur-crosslinked diene rubbers, physical property tests such as Swell (swelling test) and infrared spectroscopy (FT-IR) are generally used. The method is used.

The Swell test is a method for obtaining a network chain density by swelling a sulfur-crosslinked polymer material with toluene and the like, and since the entire change is observed, only the sulfur-crosslinked portion cannot be evaluated. In the FT-IR method, functional groups such as C═O and OH can be detected, but the sensitivity of the S—S bond is low.

Further, in Patent Document 1, as a degradation analysis method for measuring the amount of X-ray absorption irradiated to a polymer material and analyzing the degradation state of the polymer, a polymer is obtained from the total peak area at the K-shell absorption edge of oxygen atoms. There has been proposed a method for obtaining the amount of oxygen or ozone combined with a material. However, even with this method, it is difficult to evaluate only the sulfur cross-linked portion.

JP 2012-141278 A

An object of the present invention is to solve the above-mentioned problems and to provide an evaluation method capable of obtaining highly accurate information on the chemical state of sulfur in various polymer materials such as a polymer material in which sulfur is present nonuniformly. To do.

The present invention is a method for investigating a chemical state of sulfur by irradiating a sulfur-containing polymer material with X-rays having a beam size of 500 μm × horizontal 500 μm or less and measuring X-ray absorption while changing the energy of the X-rays. About.

The sulfur-containing polymer material is preferably one in which sulfur is present non-uniformly.
The X-ray absorption near the sulfur K-shell absorption edge and / or the sulfur L-shell absorption edge is measured by setting the energy range scanned using the X-ray to 2300 to 4000 eV and / or 100 to 280 eV. It is preferable.

The X-ray preferably has a photon number of 10 ⁷ photons / s or higher and a luminance of 10 ¹⁰ photons / s / mrad ² / mm ² /0.1% bw or higher.

According to the present invention, a sulfur-containing polymer material is irradiated with X-rays having a beam size of 500 μm vertical × 500 μm horizontal, and the X-ray absorption is measured while changing the energy of the X-rays. Since this is a method of examining, it is possible to obtain highly accurate information about the chemical state of sulfur in the material.

Schematic showing the state of irradiating X-rays to the entire sample in which sulfur is uniformly present Schematic showing a state in which X-rays are irradiated to the entire sample in which sulfur is unevenly present Schematic showing a state in which X-rays with a large beam size are irradiated to the entire sample in which sulfur is uniformly present Schematic showing a state in which X-rays with a small beam size are irradiated to a predetermined portion of a sample in which sulfur is unevenly present X-ray absorption spectra at various sulfur concentrations (before normalization) X-ray absorption spectra at various sulfur concentrations (after normalization) X-ray absorption spectra with different beam sizes (after normalization) XAFS spectra of sulfur-crosslinked rubber near the sulfur K-shell absorption edge obtained by X-ray irradiation with various beam sizes

The present invention irradiates various sulfur-containing polymer materials such as sulfur-containing polymer materials in which sulfur is present non-uniformly with X-rays having a beam size of 500 μm vertical × 500 μm horizontal or less and changing the energy of the X-rays. This is a method for examining the chemical state of sulfur by measuring the amount of absorption.

XAFS (X-ray Absorption Fine Structure) method at the sulfur K absorption edge, etc., as a method for examining the chemical state of sulfur-containing polymer composite materials such as rubber materials using sulfur-containing compounds such as sulfur vulcanizing agents In general, the following transmission method, fluorescence method, electron yield method and the like are widely used as the XAFS method.

(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. Examples of the detector include a Lytle detector and a semiconductor detector. In the case of the transmission method, when X-ray absorption measurement of an element having a small content in a sample is performed, the background is increased due to the X-ray absorption of an element having a small content and a large content, so that the S / B ratio is poor. It becomes a spectrum. On the other hand, in the fluorescence method (especially when an energy dispersive detector or the like is used), it is possible to measure only the fluorescent X-rays from the target element, so that the influence of the element having a large content is small. Therefore, it is effective when measuring an X-ray absorption spectrum of an element having a small content. In addition, since fluorescent X-rays have strong penetrating power (low interaction with substances), it is possible to detect fluorescent X-rays generated inside the sample. Therefore, this method is the most suitable method for obtaining bulk information after the transmission method.

(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 addition, there is a feature that the surface is sensitive (information about several nm on the sample surface). 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.

As described above, the transmission method is a basic measurement method of XAFS, and is a method of detecting the incident light intensity and the X-ray intensity transmitted through the sample and measuring the X-ray absorption amount. In other words, it is difficult to measure unless the target compound has a certain concentration (eg, several wt% or more). The electron yield method is a surface-sensitive method, and information on the surface of a sample of about several tens of nanometers can be obtained. On the other hand, the fluorescence method has the characteristics that information from a part deeper than the surface can be obtained compared to the electron yield method, and the measurement can be performed even when the concentration of the target compound is low.

The XAFS method is a method to measure the X-ray absorption at the target atom by irradiating X-rays, and the X-ray energy that can be absorbed depends on the difference in chemical state (bonding). It is a simple method. However, sulfur bridges in rubber are monosulfide bonds, disulfide bonds, and polysulfide bonds, and have different sulfur bond lengths and close peak energy detected in the spectrum. Moreover, zinc sulfide is also produced | generated by the mixing | blending of a zinc oxide. Thus, since the chemical state of sulfur in the rubber is complicated, it becomes a broad spectrum when compared with the XAFS spectrum of a compound in which no other component such as sulfur or zinc sulfide exists. Therefore, it is generally difficult to measure with high accuracy in materials containing other components.

In the XAFS measurement, an average amount of absorption at a portion (beam size) irradiated with all X-rays is obtained. Therefore, for example, in the case of a sample in which sulfur is uniformly present as shown in the left diagram of FIG. 1, the intensity of light transmitted through the sample is uniform (that is, the amount of X-ray absorption is uniform), so that correct information can be obtained. Is possible. However, since it is difficult to sufficiently diffuse sulfur in a polymer composite material such as rubber, sulfur usually exists in a non-uniform state. Accordingly, generally, as shown in the left diagram of FIG. 2, the intensity of light transmitted through the sample is nonuniform (that is, the amount of X-ray absorption is also nonuniform) depending on the irradiation location, and the spectrum becomes broad. When the XAFS spectrum becomes broad, it is difficult to separate peaks corresponding to each chemical state, and it is difficult to obtain highly accurate information.

Therefore, the present invention is an evaluation method in which a uniform chemical state of sulfur can be measured and an accurate spectrum can be obtained by reducing the X-ray location (beam size) irradiated on the sample. Specifically, as shown in FIG. 3, when the beam size is large, the amount of X-ray absorption varies depending on the irradiation location due to the non-uniform presence of sulfur, and it is difficult to obtain an accurate spectrum. . On the other hand, as shown in FIG. 4, when the beam size is reduced, the X-ray absorption amount becomes the same even if the irradiation place is different, so that an accurate spectrum can be obtained.

More specifically, first, in the case of the transmission method, when the incident X-ray intensity is I _{0 and the} transmitted X-ray intensity is I, the following equation (1) is established. According to this, μt = μ _M ρt is It will be established.

Then, the concentration of sulfur in the state where sulfur exists uniformly as shown in the right figure of FIG. 1 is 1, and the concentration of light and dark places where sulfur concentration is unevenly present as shown in the right figure of FIG. each concentration of 2, if the concentration of 3, for example, it is preferable to satisfy the mu (linear absorption coefficient) and the sample thickness t (cm) obtained by multiplying the _{μt (= μ M ρt) <} 3 relationships, more preferably Myuti < 2, more preferably 0.5 <μt <2, particularly preferably 1 <μt <2. Thereby, an accurate measurement becomes possible. If the amount of sulfur contained in normal rubber is μt <2, the locations of concentration 1 and concentration 2 satisfy μt <2, while the concentration 3 portion does not contain sulfur and is present as a lump. Since μt> 2 at this point, accurate measurement becomes difficult. Therefore, the amount of elements (here, the amount of sulfur) to be measured may be determined so that μt = μ _M ρt <2.

なお、蛍光法は、前記式（１）とは少し式が異なるが、通常、式（１）から適切な量を見積もることができる。 The above formula (1) is established on the assumption that the element to be measured is sufficiently uniform. However, in the case of a rubber sample or the like, it is difficult to sufficiently disperse sulfur, and as shown in FIG. It is thought that it is uneven. Therefore, when the beam size is large, the following formula (2) is obtained, and the beam size in FIG. 8 described later has a shape in which the peak near 2470 eV is crushed like a spectrum of vertical 1 mm × horizontal 2 mm, which is highly accurate. The result is not obtained.

The fluorescence method is slightly different from the equation (1), but usually an appropriate amount can be estimated from the equation (1).

Specifically, first, when each location of concentration 1, concentration 2, and concentration 3 is measured, an X-ray absorption amount (before normalization) as shown in FIG. 5 is obtained, and then in Japanese Patent Laid-Open No. 2012-141278. By normalizing by the described method, spectra having almost the same shape can be obtained at locations of concentration 1 and concentration 2 as shown in FIG. In this way, even for a sample with a non-uniform sulfur concentration, the entire sample is irradiated with a large beam size at a concentration 1 by reducing the beam size as shown in FIG. The amount of X-ray absorption is about the same as that of the case, and accurate measurement is possible.

On the other hand, the concentration 3 is caused by the fact that the sulfur concentration is too high and the linearity of the X-ray absorption amount and the detectable signal is lost, and the phenomenon that the signal is not correctly detected occurs. In particular, the peak around 2470 eV (SS bond) The peak) is too strongly absorbed and is not detected correctly, and the peak becomes smaller when the spectrum is normalized as shown in FIG. This means that the S—S bond ratio is detected to be small, resulting in an inaccurate spectrum.

As described above, when a sample having a non-uniform sulfur concentration is irradiated with different beam sizes as shown in FIGS. 3 and 4, the case of FIG. 4 having a smaller beam size is larger as shown in FIG. Compared to the third case, an accurate X-ray absorption spectrum can be obtained. Therefore, according to the method of the present invention in which the beam size is adjusted to be small, it is possible to obtain a highly accurate XAFS spectrum even for a polymer material in which sulfur is present non-uniformly.

The sulfur-containing polymer material used in the method of the present invention is not particularly limited as long as it is a polymer material containing sulfur. For example, a conventionally known sulfur-containing rubber composition can be used, for example, a sulfur vulcanizing agent. And rubber compositions containing a sulfur-containing compound, a rubber component, and other compounding materials. In addition, in the sulfur-containing polymer material, the existence state of sulfur is not limited, and the present invention can also be suitably applied to materials that exist non-uniformly.

Examples of the sulfur-containing compound include sulfur vulcanizing agents such as powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

As rubber components, natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), halogenated Examples thereof include diene rubbers such as butyl rubber (X-IIR) and styrene isoprene butadiene rubber (SIBR). The rubber component may contain one or more modifying groups such as hydroxyl groups and amino groups.

Furthermore, as the rubber component, a composite material in which the rubber component and one or more kinds of resins are combined can also be used. 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.

Sulfur-containing polymer materials include carbon black, silica and other fillers, silane coupling agents, zinc oxide, stearic acid, anti-aging agents, waxes, oils, vulcanizing agents other than sulfur, vulcanization accelerators, etc. You may mix | blend a well-known compound of the rubber | gum field | area suitably. Such a rubber material (rubber composition) is manufactured using a known kneading method or the like. Examples of such rubber materials include tire rubber materials (tire rubber compositions).

The present invention irradiates various sulfur-containing polymer materials such as sulfur-containing polymer materials with non-uniform sulfur by irradiating X-rays with a beam size of 500 μm vertical x 500 μm horizontal or less and changing the energy of the X-rays to absorb X-rays. The X-ray absorption amount can be measured, for example, by performing XAFS (X-ray Absorption Fine Structure) measurement.

In XAFS, generally, the region where the peak from the absorption edge (energy at which absorption rises) to about 50 eV appears is the XANES (X-ray Absorption Near Edge Structure) region, and a gentle vibration component with higher energy appears. The area to be called is called an EXAFS (Extended X-ray Absorption Fine Structure) area.

In the XANES region, when the sample is irradiated with X-rays near the absorption edge of the target atom, electrons in the core level transition to an excited state, so what kind of atom the target atom is bonded to ( Chemical state). On the other hand, in the EXAFS region, inner-shell electrons leave the nucleus and are ejected as photoelectrons. At that time, since photoelectrons are represented as waves, if there are other atoms nearby, the waves interfere and return. Therefore, information such as the number of atoms around the central atom, atomic species, and interatomic distance can be obtained. In general, in the XANES region, by separating the peaks corresponding to each bond, it is possible to know which bond and how much in the measured substance. The present invention is effective for both the XANES region and the EXAFS region.

Since the XAFS method scans with X-ray energy, 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 luminance of at least 10 ¹⁰ (photons / s / mrad ² / mm ² /0.1% bw) or more and is a continuous X-ray source. Ideal for. Note that bw represents the band width of X-rays emitted from the synchrotron.

The X-ray luminance (photons / s / mrad ² / mm ² /0.1% bw) is preferably 10 ¹⁰ or more, more preferably 10 ¹¹ or more. Although an upper limit is not specifically limited, It is preferable to use the X-ray intensity below the extent that there is no radiation damage.

Further, the number of photons (photons / s) of the X-ray is preferably 10 ⁷ or more, more preferably 10 ⁹ or more. Although an upper limit is 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 (1) 2300 to 4000 eV and (2) 100 to 280 eV. By scanning the above ranges, the X-ray absorption amount of sulfur near the sulfur K shell absorption edge and the sulfur L shell absorption edge can be measured, respectively, and information on the chemical state of sulfur in the material can be obtained. In the case of (1), it is more preferably 2350-3500 eV, and in the case of (2), more preferably 150-260 eV.

The present invention irradiates X-rays with a beam size of 500 μm vertical × 500 μm horizontal, but there are mainly the following two methods for adjusting the beam size to be vertical 500 μm × horizontal 500 μm or less. is there.
(1) A method of condensing the X-ray beam at the measurement position with a condensing mirror, etc. (2) A method of reducing the beam size by cutting excess light with a slit

In general, the X-ray beam at the measurement position is often collected by a condensing mirror or the like. However, in some cases, the beam size is large. Therefore, in the present invention, it is desirable to reduce the beam size by a slit. The beam size is preferably vertical 200 μm × horizontal 200 μm or less, more preferably vertical 50 μm × horizontal 50 μm or less. Thereby, it is possible to measure the chemical state of the uniform cross-linked portion and improve the accuracy. This method is effective for all transmission methods, fluorescence methods, and electron yield methods.

As described above, by adopting the method of the present invention, it is possible to accurately obtain information on the chemical state of the sulfur compound in the material even in a polymer composite material in which sulfur is present non-uniformly.

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

<Examples and Comparative Examples>
(Rubber material)
In accordance with the following blending contents, materials other than sulfur and vulcanization accelerator were charged into a 1.7 L Banbury mixer manufactured by Kobe Steel Co., Ltd. so that the filling rate was 58%, and until reaching 140 ° C. at 80 rpm. Kneaded (Step 1). Sulfur and a vulcanization accelerator were added to the kneaded material obtained in step 1 in the following composition, and vulcanized at 160 ° C. for 20 minutes to obtain a rubber material (step 2).

(Combination)
Natural rubber 50 parts by mass, butadiene rubber 50 parts by mass, carbon black 60 parts by mass, oil 5 parts by mass, anti-aging agent 2 parts by mass, wax 2.5 parts by mass, zinc oxide 3 parts by mass, stearic acid 2 parts by mass, powder 1.2 parts by mass of sulfur and 1 part by mass of vulcanization accelerator.
The materials used are as follows.
Natural rubber: TSR20
Butadiene rubber: BR150B manufactured by Ube Industries, Ltd.
Carbon Black: Show Black N351 manufactured by Cabot Japan
Oil: Process X-140 manufactured by Japan Energy Co., Ltd.
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.

With respect to the produced rubber material, XAFS measurement in the vicinity of the sulfur K-shell absorption edge was performed by irradiating X-rays having various beam sizes described below, and respective XAFS spectra were obtained.
(1) Vertical 15μm x Horizontal 15μm
(2) Vertical 100 μm x Horizontal 100 μm
(3) Vertical 1mm x Horizontal 2mm

<XAFS measurement>
For each sample, an X-ray absorption spectrum was obtained using XAFS.
(Device used)
XAFS: SPring-8 BL27SU B-branch XAFS measurement system (measurement conditions)
Luminance: 1 × 10 ¹⁶ photons / s / mrad ² / mm ² /0.1% bw
Number of photons: 5 × 10 ¹⁰ photons / s
Spectrometer: Crystal spectrometer Detector: SDD (silicon drift detector)
Measurement method: Fluorescence method Energy range: 2360-3500 eV

As shown in FIG. 8, peaks indicating the chemical state of sulfur were observed at 2471 eV, 2478 eV, and 2480 eV, but it became clear that the peak was smaller and broader as the beam size was larger. . This is because the area to be measured is large and includes a non-uniform portion of cross-linking. From the above, it has been found that the beam size can be reduced so that it can be measured with high accuracy, and the effectiveness of the evaluation method of the present invention has been proved.

Claims (4)

A method for examining the chemical state of sulfur by irradiating a sulfur-containing polymer material with X-rays having a beam size of 500 μm vertical × 500 μm horizontal and measuring the X-ray absorption while changing the energy of the X-rays. The method for investigating the chemical state of sulfur according to claim 1, wherein the sulfur-containing polymer material contains sulfur nonuniformly. Claims for measuring the X-ray absorption of sulfur near the sulfur K-shell absorption edge and / or sulfur L-shell absorption edge by setting the energy range scanned using X-rays to 2300 to 4000 eV and / or 100 to 280 eV. Item 3. A method for examining the chemical state of sulfur according to item 1 or 2. The X-ray has a photon number of 10 ⁷ photons / s or more and a luminance of 10 ¹⁰ photons / s / mrad ² / mm ² /0.1% bw or more. How to check the status.

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