JP6540337B2 - Method to evaluate the crack performance of polymeric materials - Google Patents

Description

The present invention relates to a method of evaluating the crack performance of polymeric materials.

Cracks in rubber materials such as tires are considered to grow due to residual strain, starting from the fact that the C 結合 C bond of the diene polymer is broken due to environmental factors such as ozone, heat and oxygen. Therefore, in order to evaluate the crack performance of the rubber material, it is important to measure the residual strain (strain amount) of the rubber material.

As a method of evaluating the crack performance of a rubber material, a method of evaluating the crack performance by calculating the strain amount from the opening amount of the cut provided on the bottom of the tread groove of the tire (see Patent Documents 1 to 3), the finite element method There is known a method of analyzing the amount of distortion by the method (see Patent Document 4).

JP, 2013-1774467, A Unexamined-Japanese-Patent No. 2013-112121 JP 2012-131352 A JP, 2006-001361, A

In a tire, since cracks occur not only in the bottom of the tread groove but also in the wall, it is necessary to also consider the amount of strain of the tread groove wall in order to accurately evaluate the crack performance.

According to the methods described in Patent Documents 1 to 3, although the strain amount of the bottom of the tread groove can be detected, the strain amount of the wall of the tread groove can not be detected. Further, not only the amount of strain due to the structure but also the orientation of the rubber molecules generated at the time of vulcanization is considered to affect the crack performance, but the methods described in Patent Documents 1 to 3 can not detect this effect. .

On the other hand, according to the method described in Patent Document 4, not only the strain amount of the bottom of the tread groove but also the strain amount of the wall of the tread groove can be detected. However, the method described in Patent Document 4 is a method of obtaining the amount of strain by simulation, and does not obtain an actual amount of strain of the tire. Further, even the method described in Patent Document 4 can not detect the influence of the orientation of rubber molecules generated at the time of vulcanization.

As described above, the methods described in Patent Documents 1 to 4 do not sufficiently detect the factor that affects the crack performance of the polymer material, and there is room for improvement in terms of the accuracy of the evaluation.

An object of the present invention is to solve the above-mentioned problems and to provide a method capable of evaluating the crack performance of a polymer material with high accuracy.

The present invention irradiates a polymer material with high brightness X-rays, calculates the degree of orientation of the polymer from the amount of X-ray absorption measured while changing the energy of the X-ray, and based on the degree of orientation of the obtained polymer , And a method of evaluating the crack performance of a polymeric material.

It is preferable to use, as the polymer material, a rubber material containing one or more types of diene-based rubber, or a composite material in which the above-mentioned rubber material and one or more types of resin are composited.
In addition, the high brightness X-ray preferably has a photon number of 10 ⁷ (photons / s) or more and a brightness of 10 ¹⁰ (photons / s / mrad ² / mm ² /0.1% bw) or more.
Furthermore, it is preferable that the energy range scanned using high-intensity X-rays is 4000 eV or less.

In the present invention, the X-ray absorption spectrum of the K-shell absorption edge of the carbon nucleus obtained by scanning high-intensity X-rays in the energy range of 260 to 400 eV is used with the sample angle or the X-ray polarization angle at constant intervals. The X-ray absorption spectrum of each angle obtained after measurement is normalized based on the following (Equation 1), and then waveform separation is performed, and the peak area or peak intensity belonging to the π ^* transition around 285 eV Is calculated, and the obtained peak area or peak intensity is normalized based on the following (formula 2), and then plotted on XY coordinates to perform elliptic fitting to calculate ellipticity, and the obtained ellipticity From the above, it is preferable to calculate the degree of orientation of the polymer based on the following (formula 3).

According to the present invention, since the crack performance of the polymer material is evaluated from the degree of orientation of the polymer calculated based on the amount of X-ray absorption, a factor affecting the crack performance of the polymer material is sufficiently detected Thus, the crack performance can be evaluated with high accuracy.

It is a figure explaining the relationship between the polarization of a high-intensity X ray, and the angle of a sample. It is a graph which shows the X-ray absorption spectrum of carbon K shell absorption edge vicinity measured in the state of FIG. It is a figure which shows the axial direction of the bottom in a tread groove of a tire, and a wall. It is a graph which shows the state which plotted the peak area or peak intensity of each normalized angle on XY plane, and performed elliptical fitting. It is a figure which shows the relationship of an average orientation degree, the orientation degree of the circumferential direction, the orientation degree of an axial direction, and an orientation angle | corner. It is a graph which shows the result of having performed elliptical fitting by the sample 1. FIG. It is a graph which shows the result of having performed elliptical fitting by the sample 2. FIG.

In the present invention, high-intensity X-rays are irradiated to a polymer material, the amount of X-ray absorption is measured while changing the energy of X-rays, and the degree of orientation of the polymer calculated based on this amount of X-ray absorption It is a method to evaluate the crack performance of molecular materials.

As described above, since cracks in polymer materials such as rubber grow due to residual strain, it is important to measure residual strain in the evaluation of crack performance. The residual strain is caused by the orientation of the polymer. The lower the degree of orientation of the polymer, the lower the residual strain, and the higher the degree of orientation of the polymer, the larger the residual strain. Therefore, as in the present invention, by calculating the degree of orientation of the polymer and evaluating the crack performance based thereon, it is possible to make a highly accurate evaluation.

In the present invention, the degree of orientation of the polymer is calculated from the amount of X-ray absorption measured while irradiating X-rays with high brightness to the polymer material and changing the energy of the X-rays. In this method, the degree of orientation of the polymer at an arbitrary location can be calculated by changing the location irradiated with high-intensity X-rays, so crack performance of not only the bottom of the tread groove but also the wall can be easily achieved. It can be evaluated.

In the present invention, to measure the amount of X-ray absorption, an X-ray absorption spectrum in the vicinity of the absorption edge of a specific element of interest is measured using high-intensity X-rays (NEXAFS (X-ray absorption fine structure near absorption edge) : Near Edge X-ray Absorption Fine Structure) can be adopted, and since soft X-rays have absorption of light elements, the chemical state of the soft material can be analyzed in detail.

The NEXAFS method requires a continuous X-ray generator for the light source to scan with X-ray energy, and measures the high S / N ratio and the S / B ratio X-ray absorption spectrum 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, so NEXAFS measurement Best for Here, bw indicates the band width of the X-ray emitted from the synchrotron.

The brightness (photons / s / mrad ² / mm ² /0.1% bw) of the high brightness X-ray is preferably 10 ¹⁰ or more, more preferably 10 ¹² or more, and the upper limit is not particularly limited. Further, the photon number (photons / s) of the high brightness X-ray is preferably 10 ⁷ or more, more preferably 10 ⁹ or more, and the upper limit is not particularly limited. Furthermore, the energy range scanned with the high-brightness X-ray is preferably 4000 eV or less, more preferably 1500 eV or less, and still more preferably 1000 eV or less, and the lower limit is not particularly limited.

As a measurement method of NEXAFS, three methods of a transmission method, a fluorescence method and an electron yield method are representatively used, and for example, the method described in JP-A-2012-141278 can be applied. Although the embodiment of the present invention is performed using an electron yield method, the present invention is not limited to this, and various detection methods may be used, or may be combined and measured simultaneously.

The degree of orientation of the polymer in the polymer material can be calculated by analyzing the X-ray absorption spectrum of the polymer material using the above-described electron yield method.

As a method of calculating the degree of orientation of the polymer, for example, the X-ray absorption spectrum of the K-shell absorption edge of the carbon nucleus obtained by scanning high-intensity X-rays in the energy range of 260 to 400 eV The angle of polarization of the line is measured at constant intervals, and the X-ray absorption spectrum of each angle obtained is normalized based on (Equation 1) below, and waveform separation is performed to obtain a π ^* transition around 285 eV. After calculating the peak area or peak intensity belonging to and normalizing the obtained peak area or peak intensity based on the following (Equation 2), the ellipticity is plotted by plotting on XY coordinates and ellipticity And calculating the degree of orientation of the polymer based on the following (Equation 3) from the obtained ellipticity.

Since the peak of the π ^* transition around 285 eV corresponds to a C = C bond, the degree of orientation of a polymer having a C = C bond such as a rubber molecule can be obtained by the above method.

Here, in the above method, the energy of the high luminance X-ray is preferably in the range of 260 to 350 eV. In the above method, before performing the operation of the above (Equation 1), the background is evaluated by evaluating from the slope in front of the absorption end.

In the above method, the total area of the X-ray absorption spectrum in the above (formula 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.

FIG. 1 is a view for explaining the relationship between the polarization of a high brightness X-ray and the angle of a sample, and FIG. 2 is a graph showing an X-ray absorption spectrum near the carbon K-shell absorption edge measured in the state of FIG. It is. As shown in FIG. 1, when irradiating a sample in which a polymer is oriented in a certain direction with high brightness X-rays, the direction of polarization of high brightness X-rays and the direction of C = C in the main chain of the polymer In the state in which C = C in the main chain can be detected in the state in which (1) in FIG. 1 is aligned, the sample is rotated and in the state in which the respective directions are not aligned (state in the right in FIG. C = C in the chain can not be detected sufficiently. Therefore, as shown in FIG. 2, in the X-ray absorption spectrum measured after the rotation of the sample, the peak intensity of π ^* of C = C is smaller than that before the rotation. Using this relationship, the degree of orientation of the polymer can be determined from the peak intensity of the X-ray absorption spectrum.

In addition, if it is a sharp peak by the bond in the principal chain of polymer | macromolecule, you may use peaks other than the peak of (pi) ^* of C = C. Although it is possible in principle to use a C ^* C σ ^* peak, this peak is not suitable for the present invention because it is broad as shown in FIG.

High-brightness X-rays are generally horizontally polarized as shown in FIG. 2, but the polarization direction (polarization angle) can be changed by using a polarization variable undulator.

Hereafter, the procedure in the case of evaluating the crack performance of the tread groove of a tire using the said method is demonstrated.

FIG. 3 is a view showing an axial direction of a bottom and a wall in a tread groove of a tire. First, the reference direction is determined, and the axial direction and the change direction of the high-intensity X-ray are set to 0 °. Then, in the energy range of 260 to 400 eV (preferably 260 to 350 eV), high-intensity X-rays are scanned in the necessary range of the K-shell absorption edge of the carbon nucleus to obtain an X-ray absorption spectrum. This operation is performed a plurality of times while changing the angle of the sample or the angle of polarization of the X-ray.
In the following description, the case where the sample angle is measured at 0 °, 30 °, 60 °, and 90 ° (i = 4) is described as an example, but the angle to be measured and the number of times of measurement are limited thereto. It is possible to change as appropriate.

Because subtle changes such as the distance of the sample from the light source affect the size of the X-ray absorption spectrum, it is difficult to measure the absolute value of the NEXAFS method, and the NEXAFS measurement result of the K-shell absorption edge of carbon atom It can not simply compare. Therefore, using the above (formula 1), normalization is performed so that the peak area of the K-shell absorption edge of the carbon atom is 1. Specifically, first, the normalization constant α is calculated based on (Equation 1) for the X-ray absorption spectrum before normalization, and then corrected to a spectrum obtained by multiplying the X-ray absorption spectrum before normalization by α ( By normalizing), it is possible to directly compare peaks between samples. This operation is performed on the X-ray absorption spectrum of each angle (0 °, 30 °, 60 °, 90 °).

Next, the X-ray absorption spectrum after normalization is waveform separated, and the peak area or peak intensity of C ^* C π ^* is calculated. This operation is performed on the X-ray absorption spectrum of each angle, and then the peak area or peak intensity s (n _i ) of each angle is normalized using the above (Equation 2). In this example, (Equation 2) is as follows. Based on this equation, the peak area or peak intensity S (n _i ) of each angle after normalization is calculated.

Next, the peak area or peak intensity S (n _i ) after normalization of each angle is plotted on the XY plane to perform elliptic fitting. Thereby, as shown in FIG. 4, the orientation angle (average orientation angle) is obtained. Then, the degree of orientation (average degree of orientation) is calculated using the above (formula 3). As the value of the degree of orientation is smaller, the polymer is not oriented and the residual strain is small, that is, the crack performance is excellent.

From the average degree of orientation and the orientation angle, as shown in FIG. 5, the degree of orientation in the circumferential direction can be calculated. For example, in the case of a polymer material used for the tread of a tire, it is considered that rubber molecules are stretched during extrusion as one of the causes of circumferential orientation, and one of the causes of the axial direction. It is conceivable that the rubber molecules are oriented along the shape of the mold during press working. Therefore, by separately calculating the degree of orientation in the circumferential direction and the degree of orientation in the axial direction, it is possible to analyze in detail the cause of the orientation.

The above-mentioned polymer material applicable to the present invention is not particularly limited, and conventionally known materials may be mentioned. For example, a rubber material containing one or more kinds of diene-based rubber, the rubber material and one or more kinds of resins Composite composite materials 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), Polymers having double bonds such as halogenated butyl rubber (X-IIR) and styrene isoprene butadiene rubber (SIBR) can be mentioned.

The resin is not particularly limited, and examples thereof include those widely used in the rubber industry, such as petroleum resins such as C5 aliphatic petroleum resins and cyclopentadiene petroleum resins. The degradation analysis method of the present invention can be suitably applied to these materials.

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

<Preparation of Samples 1 and 2>
According to the contents of the composition described below, materials other than sulfur and vulcanization accelerator are filled in 1.7L Banbury made by Kobe Steel Co., Ltd. so that the filling rate is 58%, and reach 140 ° C at 80 rpm. The mixture was kneaded until the mixture was obtained.
Sulfur and a vulcanization accelerator were added to the obtained kneaded product to obtain an unvulcanized rubber composition.
The obtained unvulcanized rubber composition was vulcanized at 160 ° C. for 20 minutes to produce a vulcanized rubber composition, which was evaluated in Comparative Example 1 described later.
Further, the obtained unvulcanized rubber composition is molded into a tread shape, laminated with other tire members, molded into a tire, and vulcanized at 160 ° C. for 20 minutes to manufacture a test tire, which will be described later. Example 1 and Comparative Example 2 were evaluated.
(Blended)
Natural rubber (NR): TSR 20 (30 parts by mass)
Styrene butadiene rubber (SBR): Nippon Zeon Co., Ltd. Nipol 1502 (70 mass parts)
Carbon black: Show black N 351 (N ₂ SA: 71 m ² / g) (30 parts by mass) manufactured by Cabot Japan Ltd.
Silica: Ultrasil VN3 (60 parts by mass) manufactured by Degussa
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa (3 parts by mass)
Oil: Process X-140 (10 parts by mass) manufactured by Japan Energy Co., Ltd.
Anti-aging agent: Noclac 6C (N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine) (4 parts by mass) manufactured by Ouchi Emerging Chemical Industry Co., Ltd.
Wax: Ozo Ace 0355 (2.5 parts by mass) manufactured by Nippon Seiwa Co., Ltd.
Zinc oxide: Ginkgo R (3 parts by mass) manufactured by Toho Zinc Co., Ltd.
Stearic acid: A lees from Nippon Yushi Co., Ltd. (2 parts by mass)
Powdered sulfur: 5% oil-treated powdered sulfur (soluble sulfur containing 5% by mass of oil) manufactured by Tsurumi Chemical Industry Co., Ltd. (1.2 parts by mass)
Vulcanization accelerator: Noxceler CZ (N-cyclohexyl-2-benzothiazylsulfenamide) manufactured by Ouchi Emerging Chemical Industry Co., Ltd. (1 part by mass)

Example 1
The X-ray absorption spectrum of each sample was measured using the NEXAFS method under the following conditions, and the degree of orientation of the bottom of the tread groove of each sample was calculated using (Equation 1) to (Equation 3) above.
At the time of measurement, the test piece cuts out the bottom of the tread groove of the test tire (unused product) manufactured by the above method to about 1 mm × 2 mm × 0.5 mm based on the axial direction defined in FIG. A product from which blooms have been removed using a Soxhlet extraction method according to K6229 or the like.
The results of elliptic fitting for each sample are shown in FIGS. As shown in FIG. 6, the fitting result of the sample 1 almost overlapped with the perfect circle.
(Equipment used, measurement conditions)
NEXAFS: NEXAFS measuring device attached to BL12 beam line at Saga Prefectural Kyushu Synchrotron Light Research Center Brightness: 5 × 10 ¹² (photons / s / mrad ² / mm ² /0.1% bw)
Photon number: 2 × 10 ⁹ (photons / s)
Measured photon energy range: 275 eV to 320 eV
Measured sample angle: 0 °, 30 °, 60 °, 90 °

Comparative Example 1
(Ozone degradation test)
The slab (vulcanized rubber composition) of the vulcanized rubber composition prepared by the above method is subjected to the ozone degradation test of JIS-K 6259, and then using the “appendix 1 (definition) crack evaluation method” of JIS-K 6259 The crack performance was evaluated.

Comparative Example 2
(Vehicle survey)
The crack performance was evaluated using the test method of JIS-K6259 "Annex 1 (Described) Crack Evaluation Method" according to JIS-K 6259 after the test tire was mounted on an actual vehicle after being manufactured by the above method.

Vehicle surveys are based on actual usage, so we will use this as a standard.
In the actual vehicle survey, the result that the sample 1 is more excellent in the crack performance than the sample 2 was obtained.
In the ozone deterioration test, a result contrary to the actual vehicle investigation in which the sample 2 had better crack performance than the sample 1 was obtained.
On the other hand, in Example 1, the sample 1 had a lower degree of orientation than the sample 2 and obtained the same result as the actual vehicle investigation that the crack performance is excellent.

From the above results, it has become clear that the crack performance can be evaluated with high accuracy by the method of the present invention.

In addition, although the case where the distortion amount of the bottom of the tread groove of a tire was measured was demonstrated in the present Example, the distortion amount of the wall of a tread groove is also measured by changing the irradiation location of high-intensity X ray. It is possible. Although the degree of orientation in the circumferential direction can be analyzed only by the amount of strain at the bottom of the tread groove, the degree of orientation in the circumferential direction can be analyzed in more detail by additionally measuring the amount of strain in the tread groove wall. it can.

Moreover, although the case where the crack performance of the tread groove of a tire was evaluated was demonstrated in the present Example, this invention is not limited to this, It is also possible to apply to other tire members, such as a sidewall, It is also possible to apply to products other than a tire as long as it uses a polymer material.

Claims (5)

The polymer material is irradiated with high-intensity X-rays, and the degree of orientation of the polymer is calculated from the amount of X-ray absorption measured while changing the energy of the X-rays,
A method of evaluating the crack performance of a polymer material based on the degree of orientation of the obtained polymer. The crack performance of the polymer material according to claim 1, wherein the polymer material is a rubber material containing one or more kinds of diene-based rubber, or a composite material in which the rubber material and one or more resins are compounded. how to. The high-intensity X-ray according to claim 1 or 2, wherein the number of photons is 10 ⁷ (photons / s) or more and the luminance is 10 ¹⁰ (photons / s / mrad ² / mm ² /0.1% bw) or more. How to assess the crack performance of molecular materials. The method for evaluating the crack performance of a polymer material according to any one of claims 1 to 3, wherein an energy range of scanning with high brightness X-rays is 4000 eV or less. The X-ray absorption spectrum of the K-shell absorption edge of the carbon nucleus obtained by scanning high-intensity X-rays in the energy range of 260 to 400 eV is measured by changing the sample angle or the X-ray polarization angle at constant intervals. ,
After normalizing the obtained X-ray absorption spectrum of each angle based on the following (formula 1), waveform separation is performed to calculate the peak area or peak intensity belonging to the π ^* transition around 285 eV,
After normalizing the obtained peak area or peak intensity based on the following (formula 2), the ellipticity is calculated by plotting on XY coordinates and performing elliptic fitting,
The method to evaluate the crack performance of the polymeric material in any one of Claims 1-4 which calculates the degree of orientation of a polymer | macromolecule based on the following (Formula 3) from the obtained ellipticity.

Images