JP2014115101A - Chemical state measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chemical state measuring method which achieves accurate measurement of a chemical state of a surface of a rubber material, especially a change of the chemical state, which is caused from the surface, such as deterioration (deterioration state of the rubber material).SOLUTION: In a chemical state measuring method, a surface analysis method using an X-ray is applied after a bloomed material is removed from a surface of a rubber material, so that a chemical state of the surface of the rubber material is measured.

Description

The present invention relates to a chemical state measurement method capable of accurately examining a chemical state of a rubber material surface, in particular, a change in chemical state resulting from the surface such as deterioration.

X-ray photoelectron spectroscopy (XPS method), high-intensity X-rays are used as methods for examining changes in the chemical state of rubber materials containing rubber components such as diene rubber, especially changes in the chemical state arising from the rubber material surface such as deterioration. Using X-rays such as a method of measuring an X-ray absorption spectrum near the absorption edge of a specific element of interest (NEXAFS (Near Edge X-ray Absorption Fine Structure) method) There is a known technique (see Patent Document 1).

The XPS method and the NEXAFS method are surface-sensitive measurement methods having a detection depth of the surface to several tens of nanometers. For example, in order to investigate the chemical state of a polymer, the XPS method uses a spectrum near the carbon 1s orbit, and the NEAXFS method uses a As in the spectrum near the carbon K-shell absorption edge, generally measurement focusing on carbon is performed.

However, in the conventional evaluation method, it is difficult to accurately measure the change in the chemical state on the surface of the deteriorated rubber material or the like. Therefore, it is desired to provide an evaluation method that can accurately measure the change in the surface state. Yes.

JP 2012-141278 A

An object of the present invention is to solve the above-mentioned problems and to provide a chemical state measuring method capable of accurately measuring a chemical state of a rubber material surface, in particular, a change in a chemical state (deterioration state of a rubber material) generated from the surface such as deterioration. And

The present invention relates to a chemical state measuring method for measuring a chemical state on a rubber material surface by applying a surface analysis method using X-rays after removing a bloom on the rubber material surface.

The chemical state measurement method is preferably a method of measuring a deterioration state of the rubber material by examining a change in the chemical state generated from the surface of the rubber material.
The chemical state measurement method is preferably a method of removing a bloom on the rubber material surface using a solvent, and an organic solvent can be suitably used as the solvent.

The chemical state measurement method is preferably a method of removing blooms on the rubber material surface using a solvent extraction method.

According to the present invention, after removing a bloom on the surface of the rubber material, a chemical state measurement method for measuring the chemical state on the surface of the rubber material by applying a surface analysis method using X-rays. The exact chemical state of the surface can be measured. Therefore, it is possible to accurately measure changes in the chemical state caused by the surface such as deterioration, and to evaluate the deterioration state of the rubber material.

XPS spectrum of C1s of rubber material (with or without wiping treatment). NEXAFS spectrum in the vicinity of the carbon K-shell absorption edge (Example 1 and Comparative Example).

The chemical state measurement method of the present invention is a method for measuring a chemical state on the surface of a rubber material by applying a surface analysis method using X-rays after removing a bloom on the surface of the rubber material.

As a method of examining the surface state of rubber materials including diene rubber, etc., the spectrum near the carbon 1s orbit, the spectrum near the carbon K shell absorption edge, etc. are measured using a surface sensitive technique such as XPS or NEXAFS. That is, spectrum measurement for carbon is used, but such rubber materials are generally blended with chemicals such as waxes and anti-aging agents, and these chemicals precipitate on the surface (bloom). Deterioration suppressing effect is exhibited.

Here, the wax that blooms is a hydrocarbon, which is composed of carbon, just like rubber. Therefore, using the surface sensitive method, the chemical state of the rubber on the surface of the rubber material where the chemical state has changed due to deterioration, etc. In order to investigate the above, it is necessary to remove blooms (surface precipitates made of wax, anti-aging agents, etc.) that are considered to have an adverse effect on the spectrum, that is, to remove carbon components other than rubber in advance. Is presumed to be necessary.

Until now, when examining the surface of a rubber material whose chemical state has changed due to deterioration or the like using the XPS method, the surface of the rubber material is made of a paper waste such as Kimwipe (manufactured by Nippon Paper Crecia Co., Ltd.). A pretreatment such as wiping with a solution moistened with acetone is performed.

FIG. 1 shows XPS spectra in C1s of a sample subjected to such a wiping treatment on the surface of a rubber material and a sample not subjected to the wiping treatment. Thus, the difference in spectrum depending on the presence or absence of wiping can be confirmed. As described above, in the XPS method, the C—C bond and C—H bond of wax and the C═C bond of rubber appear in the same peak. Therefore, although the intensity of the spectrum changes depending on the presence or absence of the wiping treatment, the shape does not change, so it is actually possible to measure without being able to accurately confirm whether or not bloom such as wax has been sufficiently removed. It is.

As described above, the conventional method cannot measure the accurate chemical state of the surface, but in the method of the present invention, before carrying out the surface analysis such as the XPS method or the NEXAFS method, the rubber surface is previously used using a solvent or the like. By removing the blooms, it is possible to eliminate the influence of carbon components such as waxes other than rubber, so that the accurate chemical state of the rubber material surface can be measured. Therefore, an accurate chemical state can be measured by the XPS spectrum or the NEXAFS spectrum, and the deterioration state (degree of deterioration) can also be accurately measured by comparing the spectra before and after the deterioration.

In the present invention, first, the bloom on the surface of the rubber material is removed.
The rubber material used in the present invention is not particularly limited, and a conventionally known rubber composition can be used, and examples thereof include a rubber composition containing a rubber component, a wax, an antiaging agent, and the like.

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.

The wax is not particularly limited, and examples thereof include petroleum wax and natural wax. Examples of petroleum waxes include paraffin wax and microcrystalline wax. Examples of natural waxes include plant waxes such as candelilla wax and carnauba wax, animal waxes such as beeswax and lanolin, and mineral waxes such as ozokerite.

The anti-aging agent is not particularly limited, and those used in the rubber field can be used. For example, amine-based (naphthylamine-based, diphenylamine-based, p-phenylenediamine-based, etc.), quinoline-based, hydroquinone derivatives, phenol Type (monophenol type, bisphenol type, trisphenol type, polyphenol type, etc.), thiobisphenol type, imidazole type (benzimidazole type, etc.), thiourea type, phosphorous acid type, organic thioacid type antioxidant, metal carbamate Examples include salt.

For rubber materials, conventionally known compounds in the rubber field such as fillers such as carbon black and silica, silane coupling agents, zinc oxide, stearic acid, oil, vulcanizing agents, vulcanization accelerators and crosslinking agents are appropriately used. You may mix | blend. Such a rubber material (rubber composition) can be produced using a known kneading method or the like. Examples of such rubber materials include tire rubber materials (tire rubber compositions).

The method for removing the bloom material is not particularly limited as long as it can remove the bloom material composed of wax, an antioxidant, and the like, and examples thereof include a method using a solvent. As a removal method, a method using a tool such as a spatula is conceivable. However, like the method of wiping the surface with the above-mentioned waste cloth or the like, it is considered difficult to completely remove the bloom, and the rubber itself This method is not suitable because it is possible to change the chemical state.

As a method of removing blooms using a solvent, a method of wetting (impregnation) in a solvent under a predetermined condition such as room temperature or a heating state, a solvent extraction using an extraction device such as a Soxhlet extractor, etc. Extraction method (solvent extraction method). Of these, extraction methods such as Soxhlet extraction are preferred, and Soxhlet extraction is particularly preferred from the viewpoint of efficiently removing blooms.

As the Soxhlet extraction, an extraction operation by a Soxhlet extraction method according to JISK6229 can be performed. For example, an extraction flask provided at the bottom of a Soxhlet extractor is filled with a solvent (solvent), and a predetermined amount of rubber prepared as a test piece of an appropriate size in a paper or sintered glass container provided in the middle part. This can be done by putting the material and connecting a cooling tube at the top.

The extraction time such as Soxhlet extraction is not particularly limited as long as it can remove the blooms and does not change the chemical state of the rubber, and may be appropriately set according to the components of the rubber material applied to the present invention. For example, the extraction time for Soxhlet extraction is preferably 10 to 36 hours. If it is less than 10 hours, the bloom on the surface may not be sufficiently removed, and if it exceeds 36 hours, rubber molecules that have deteriorated and become shorter may be removed.

In the removal (wetting and extraction) using a solvent, an organic solvent is suitable as a usable solvent. Examples of the organic solvent include monohydric alcohols such as methanol, ethanol, propanol and butanol; polyhydric alcohols such as ethylene glycol, propylene glycol and butylene glycol; ketones such as acetone and methyl ethyl ketone; esters such as methyl acetate and ethyl acetate. Linear and cyclic ethers such as tetrahydrofuran and diethyl ether; polyethers such as polyethylene glycol; halogenated hydrocarbons such as dichloromethane, chloroform and carbon tetrachloride; hydrocarbons such as hexane, cyclohexane and petroleum ether; Aromatic hydrocarbons such as benzene and toluene; Of these, highly polar organic solvents are preferred, and acetone and ethanol are more preferred from the viewpoint that the blooms such as wax on the surface can be sufficiently removed. These can be used alone or in combination of two or more.

In the present invention, the surface analysis method using X-rays is applied to the obtained sample (rubber material subjected to the removal treatment) after removing the bloom on the surface of the rubber material in advance. As such a surface analysis method, XPS method (X-ray photoelectron spectroscopy), NEXAFS method (X-ray absorption fine structure near absorption edge) and the like are preferable because the chemical state of the rubber material surface can be accurately measured.

Here, as the XPS method, a conventionally known method can be used. For example, the chemical state of the surface can be examined by measuring a spectrum near the carbon 1s orbit. The NEXAFS method can examine the chemical state of the surface by, for example, the method described in JP2012-141278A. Specifically, the NEXAFS method can be examined by measuring a spectrum near the carbon K-shell absorption edge. It is done.

In the present invention, by applying the XPS method to a rubber material (sample) from which surface blooms have been sufficiently removed by solvent extraction or the like, an accurate chemical state in which the influence of wax or an antioxidant is sufficiently suppressed can be obtained. It can be measured. Therefore, in the XPS spectrum of the rubber material before and after deterioration, the peak of the C═C bond of rubber appears without the appearance of the C—C bond or C—H bond peak attributed to the wax. Before and after, the exact chemical state of the rubber on the rubber material surface is examined. Furthermore, the deterioration state (degree of deterioration) can also be examined by comparing the peak intensity and area of the C = C bond before and after deterioration.

Similarly, the accurate chemical state of the surface can be measured by applying the NEXAFS method to the sample. Therefore, the exact chemical state of the rubber on the surface of the rubber material can be similarly examined before and after deterioration, and the deterioration state (degradation degree) can also be examined by comparing the peak intensity and area before and after deterioration.

Since the NEXAFS method is difficult to measure absolute values, the measurement results between samples cannot be simply compared. Therefore, for example, by measuring and analyzing the X-ray absorption spectrum of the rubber material using the electron yield method by the following method, the degree of deterioration (%), the contribution rate of oxygen deterioration and ozone deterioration (%), oxygen · The amount of ozone combined (degradation index) can be analyzed accurately.

Specifically, the energy of the high-intensity X-ray is normalized by the following (Equation 1) based on the X-ray absorption spectrum obtained by scanning the necessary range of the K-shell absorption edge of the carbon atom in the range of 260 to 400 eV. The constants α and β are calculated, and the X-ray absorption spectrum of the K-shell absorption edge of the carbon atom corrected using the normalized constants α and β is separated into waveforms, and the resulting π ^* transition near 285 eV is attributed. It is possible to obtain the degree of deterioration by the following (Equation 2) using the peak area.
(Formula 1)
[Total area of X-ray absorption spectrum of measurement range in sample before deterioration] × α = 1
[Total area of X-ray absorption spectrum in the measurement range of the sample after deterioration] × β = 1
(Formula 2)
[1-[(Peak area of π ^* after degradation) × β] / [(Peak area of π ^* before degradation) × α]] × 100 = Degree of degradation (%)

By measuring a sample from which blooms have been removed, the exact chemical state of the rubber material surface can be examined both before and after deterioration. Further, by comparing the respective spectra, the degree of deterioration (%) of the rubber material after deterioration can be calculated, and an accurate deterioration rate analysis can be performed. Specific analysis can be performed by the method described in Japanese Patent Application Laid-Open No. 2012-141278.

Further, the X-ray absorption spectrum of the K-shell absorption edge of oxygen atoms obtained by scanning the high-intensity X-ray energy in the range of 500 to 600 eV is separated into waveforms, and the peak top energy is 532 to 532.7 eV. It is also possible to calculate the contribution rate of oxygen deterioration and ozone deterioration by the following (Equation 3), assuming that the low energy side peak in the range is oxygen deterioration and the high energy side peak in the range of 532.7 to 534 eV is ozone deterioration. is there.
(Formula 3)
[Peak area of oxidation degradation] / [(Peak area of ozone degradation) + (Peak area of oxidation degradation)] × 100 = Oxygen degradation contribution rate (%)
[Ozone degradation peak area] / [(ozone degradation peak area) + (oxidation degradation peak area)] × 100 = ozone degradation contribution rate (%)

Since the exact chemical state of the rubber material surface can be examined by measuring the sample after removing the bloom from the sample after deterioration, the contribution rate (%) of oxygen deterioration and ozone deterioration in the rubber material after deterioration can be calculated. Therefore, it is possible to accurately analyze the contribution rate of each deterioration factor. Specific analysis can be performed by the method described in Japanese Patent Application Laid-Open No. 2012-141278.

Further, based on the X-ray absorption spectrum of the K-shell absorption edge of the carbon atom after deterioration, the normalization constant γ is obtained by the following (formula 4), and the oxygen atom is It is also possible to determine the amount of oxygen and ozone bound to the rubber material by correcting the total peak area at the K shell absorption edge.
(Formula 4)
[Total area of X-ray absorption spectrum of K-shell absorption edge of carbon atom] × γ = 1
(Formula 5)
[Peak area of K-shell absorption edge of oxygen atom] × γ = Amount of oxygen and ozone combined (index)

Since the exact chemical state of the rubber material surface can be examined by measuring the sample after removing the bloom from the sample after deterioration, the amount of oxygen / ozone bound to the rubber material due to deterioration can be measured accurately. It becomes possible to do. Specific analysis can be performed by the method described in Japanese Patent Application Laid-Open No. 2012-141278.

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 sample)
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). A rubber sample was obtained by adding sulfur and a vulcanization accelerator to the kneaded product obtained in step 1 in the following composition and vulcanizing at 160 ° C. for 20 minutes (step 2).

(Combination)
Natural rubber 50 parts, butadiene rubber 50 parts, carbon black 60 parts, oil 5 parts, anti-aging agent 2 parts, wax 2.5 parts, zinc oxide 3 parts, stearic acid 2 parts, powder 1.2 parts by weight of sulfur and 1 part by weight of a vulcanization accelerator (Comparative Example 3 does not contain a wax and an antioxidant)
The materials used are as follows. In addition, the deteriorated rubber sample was deteriorated under the following conditions.
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.
(Deterioration conditions)
Ozone degradation: 40 ° C, 50 pphm (24 hours)
Oxygen degradation: 80 ° C. Oxygen: Nitrogen = 5: 1 (168 hours)

After the pretreatment described in Table 1 was performed on the produced rubber sample, NEXAFS measurement in the vicinity of the carbon K-shell absorption edge was performed to obtain an X-ray absorption spectrum (NEXAFS spectrum). In Example 4 and Comparative Example 6, XPS measurement was performed to obtain an XPS spectrum. FIG. 2 shows NEXAFS spectra obtained in Example 1 and Comparative Examples 1 to 3.

(Device used)
NEXAFS: SEX Prefectural Kyushu Synchrotron Light Research Center NEXAFS measurement system attached to BL12 beam line XPS: AXIS Ultra manufactured by Kratos

[NEXAFS measurement]
Using NEXAFS, measure the degree of degradation (%), oxygen and ozone degradation contribution rate (%), and degradation index (index) by performing the following degradation rate analysis, degradation contribution rate analysis, and degradation index measurement for each sample. did. Moreover, the presence or absence of the influence of the bloom thing in the spectrum obtained by implementation of the following rubber information was evaluated. The results are shown in Table 1. The measurement conditions of NEXAFS were as follows. In the measurement, a rubber sample was processed with a microtome so as to have a thickness of 100 μm or less, and then stored in a vacuum desiccator.
(Measurement conditions for NEXAFS)
Luminance: 5 × 10 ¹² photons / s / mrad ² / mm ² /0.1% bw
Number of photons: 2 × 10 ⁹ photons / s

(Deterioration rate analysis)
High energy 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 1) 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 deterioration (%) was obtained from (Equation 2) based on the peak area attributed to the π ^* transition near 285 eV.

(Deterioration contribution analysis)
High energy X-ray energy was scanned in the range of 500 to 600 eV to obtain an X-ray absorption spectrum of the K-shell absorption edge of oxygen atoms. This spectrum is waveform-separated, and the low energy peak at the peak top of 532 to 532.7 eV is defined as oxygen degradation, and the high energy peak at 532.7 to 534 eV is defined as ozone degradation. The contribution rate of deterioration was calculated.

(Deterioration index measurement)
Based on the X-ray absorption spectrum at the K-shell absorption edge of the deteriorated carbon atom obtained by the deterioration rate analysis, the normalization constant γ was determined from (Equation 4). Using this constant, the total peak area at the K-shell absorption edge of oxygen atoms was corrected (normalized), and the amount of oxygen and ozone bound to the rubber material (degradation index) was determined from (Equation 5).

(Rubber information)
The obtained NEXAFS spectrum and XPS spectrum were evaluated according to the following criteria as to whether rubber information was obtained without being affected by other carbon contamination such as wax.
○: Accurate information on the surface of the rubber material was obtained.
X: Accurate information on the surface of the rubber material could not be obtained.

In the spectrum of Comparative Example 3 in FIG. 2, the C = C bond of the rubber was detected because it was a measurement of a sample manufactured with a formulation in which carbon contaminants did not bloom on the sample surface. On the other hand, in Comparative Example 1 where no pretreatment was performed, C═C bond was not detected, and instead, C—H bond was increased. From this result, C—H of the wax covered on the surface was obtained. Bonding was detected, and it became clear that the C = C bond of rubber was not detected. In Comparative Example 2 in which the sample surface was wiped with waste, the C = C bond increased slightly and the C—H bond decreased slightly, but the amount of C═C bond detected was smaller than that in Comparative Example 3, so that the surface As a result, it was not possible to remove the wax that had bloomed, and accurate measurement was not possible.

In contrast, in Example 1, the C═C bond and C—H bond amounts were detected to the same extent as in Comparative Example 3, so that the wax blooming on the surface could be sufficiently removed, and the chemical state of the rubber surface was changed. It became clear that it can be measured accurately. Further, the XPS measurement of Example 4 was able to be measured accurately in the same manner. Furthermore, in the deteriorated rubber samples of Comparative Examples 4 to 5 that were not subjected to pretreatment, the degree of deterioration and the like could not be calculated, whereas in the deteriorated rubber samples of Examples 2 to 3 in which the bloom was removed by pretreatment, Calculation was possible.

Claims (5)

A chemical state measuring method for measuring a chemical state on the surface of a rubber material by applying a surface analysis method using X-rays after removing a bloom on the surface of the rubber material. The chemical state measuring method according to claim 1, wherein a deterioration state of the rubber material is measured by examining a change in a chemical state generated from the surface of the rubber material. The chemical state measuring method according to claim 1 or 2, wherein a bloom is removed from the surface of the rubber material using a solvent. The chemical state measuring method according to claim 3, wherein the solvent is an organic solvent. The chemical state measuring method according to any one of claims 1 to 4, wherein a bloom material on a rubber material surface is removed using a solvent extraction method.

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