JP2006317414A - Vulcanized rubber and method for evaluating crosslinking structure of same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for evaluating the crosslinking structure of vulcanized rubber and capable of improving both the amount of information and analysis accuracy on the rubber physical properties of vulcanized rubber, molecular structures, composition analysis, etc. by NMR measurement using solid samples and provide vulcanized rubber. <P>SOLUTION: A narrow piece made of vulcanized rubber is used as a measurement sample. A solid high-resolution NMR device is used to perform NMR measurement with the measurement sample in a state of magic-angle spinning under solution NMR conditions. The chemical shifts and type (primary, secondary, tertiary, and quaternary) of carbon in the vulcanized rubber are identified in the method for evaluating the crosslinking structure of vulcanized rubber. The rubber physical properties of the vulcanized rubber are evaluated on the basis of a strength ratio of acquired crosslinking signals. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for evaluating a crosslinked structure of vulcanized rubber, and more specifically, by performing NMR measurement using a solid sample of vulcanized rubber, analysis information such as rubber physical properties, molecular structure, and composition analysis of vulcanized rubber. The present invention relates to a method for evaluating a crosslinked structure of a vulcanized rubber that provides high accuracy and a vulcanized rubber obtained from the evaluation result.

  In order to analyze physicochemical properties such as molecular structure and composition analysis of polymer compounds, instrumental analysis equipment such as nuclear magnetic resonance (NMR) has recently been used to provide a lot of analysis information. In the rubber industry, it is used for evaluation of the crosslinking density of vulcanized rubber and prediction of thermal deterioration (for example, Patent Documents 1 and 2).

  In the measurement by NMR, a sample to be measured is adjusted in order to obtain a clear NMR spectrum. Analyzes using various measurement samples such as liquids, solids, gases, gels, etc. are performed on the measurement target by NMR, but generally solid NMR such as vulcanized rubber is much more for measurement than solution NMR. For example, there is a drawback that the amount of information obtained is small due to reasons such as lower resolution than solution NMR and fewer pulse programs used.

In the measurement of molecular structure such as microstructure of rubber material by NMR, uncrosslinked raw rubber can be analyzed using a sample dissolved and dissolved in organic solvent such as chloroform. When analyzing vulcanized rubber by NMR, the measurement using a solid high resolution NMR apparatus is tried (for example, nonpatent literature 1).
JP 2002-71595 A JP 2004-325189 A Maki Mori, J. L. Koenig "Analysis of rubber cross-linked products by high resolution NMR" Journal of the Japan Rubber Association Vol. 71 No. 2 (1998) P26-35

However, the above-mentioned high-resolution solid-state NMR can be measured only by ¹³ C-NMR method because vulcanized rubber is not dissolved in an NMR solvent such as chloroform, and can be measured by solution NMR. ¹ H-NMR method, DEPT method, APT In fact, it is considered impossible to measure by the 2D method or the like, and the actual cross-linked structure is not analyzed in the solid sample of vulcanized rubber.

  The present invention has been made in view of the above points. By NMR measurement using a solid sample, which has been difficult to analyze the crosslinking structure of vulcanized rubber, the rubber physical properties, molecular structure of vulcanized rubber, An object of the present invention is to provide a method for evaluating the crosslinked structure of a vulcanized rubber for improving the amount of information such as composition analysis and analysis accuracy, and a vulcanized rubber having a specific crosslinked structure measured by this evaluation method. .

  The present inventor is able to perform NMR measurement under solution NMR conditions in a vulcanized rubber having a specific range of elastic modulus with weak dipole interaction and high molecular mobility in the vulcanized rubber. As a result, the present invention has been completed.

  That is, the method for evaluating the crosslinked structure of a vulcanized rubber according to the present invention uses a strip made of vulcanized rubber as a measurement sample, and performs NMR measurement under solution NMR conditions in a magic angle rotation state using a solid high-resolution NMR apparatus. The chemical shift and type (first to fourth grades) of carbon in the vulcanized rubber are identified.

  The method for evaluating the crosslinked structure of a vulcanized rubber according to the present invention further evaluates the rubber physical properties of the vulcanized rubber from the intensity ratio of the crosslinked signals obtained by the above measurement.

  In the method for evaluating a crosslinked structure of vulcanized rubber according to the present invention, the elastic modulus at 100% elongation in the tensile test of the vulcanized rubber is 0.5 to 4 MPa.

As the solution NMR conditions, any ^{one of 1} H-NMR method, DEPT method, APT method, and 2D method can be applied.

  Moreover, it is preferable that the strip length of the measurement sample used for the crosslinked-structure evaluation method of vulcanized rubber of this invention is 0.001-0.5 mm.

The method for evaluating the crosslinked structure of a vulcanized rubber according to the present invention is a solution NMR condition such as ¹ H-NMR method, DEPT method, APT method, 2D method, etc. while a vulcanized rubber having a specific range of elastic modulus is a solid sample The NMR measurement is performed at As a result, the chemical shift and type (first to fourth grades) of carbon in the vulcanized rubber, which could not be obtained by solid state NMR using a conventional solid sample, were identified from the direction of the signal, and the rubber physical properties of the vulcanized rubber, Many pieces of analysis information such as molecular structure and composition analysis can be obtained with high accuracy.

  In the present invention, the vulcanized rubber capable of NMR measurement has an elastic modulus at 100% elongation in a tensile test of 0.5 to 4 MPa, and even if it is a vulcanized rubber, the elastic modulus exceeds 4 MPa. Intramolecular mobility becomes low and measurement under solution conditions becomes difficult, and if it is less than 0.5 MPa, the intensity of the cross-linking signal becomes low and accurate measurement cannot be performed. The elastic modulus is a measured value of tensile stress measured according to JIS K6252 (using No. 3 dumbbell).

  In addition, since the length of the strip of the measurement sample is 0.001 to 0.5 mm, the NMR measurement using the solid sample of vulcanized rubber is made accurate, and the measurement is performed without the need for sample pretreatment and complicated adjustment. It can be easily implemented.

  The vulcanized rubber of the present invention has a crosslinking signal strength ratio obtained by the crosslinked structure evaluation method of vulcanized rubber of 0.1 to 10, and has rubber properties suitable for various applications. The design of vulcanized rubber can be facilitated.

  According to the crosslinked structure evaluation method for vulcanized rubber of the present invention, it is possible to accurately evaluate the crosslinked structure of the vulcanized rubber in a solid state, that is, rubber properties after vulcanization, molecular structure such as microstructure, By measuring physicochemical properties such as composition analysis under solution conditions using an NMR device, it can be obtained in a shorter time with much higher accuracy than conventional solid conditions. It has the excellent effect of being able to obtain a lot of new analytical information that was not available, and provides many guidelines for high performance research of various rubber materials, and has industrial effectiveness. .

  In addition, the use of a solid sample simplifies the preparation of the sample, and can be performed in a short time without costing the NMR measurement.

  Hereinafter, embodiments of the present invention will be described in detail.

  In the method for evaluating a crosslinked structure of a vulcanized rubber according to the present invention, examples of the rubber material to be used include a solid rubber supplied in a normal solid state and a low molecular weight liquid rubber that is liquid at room temperature.

  As solid rubber, natural rubber (NR), various styrene butadiene rubber (SBR) by solution or emulsion polymerization, various butadiene rubber (BR), isoprene rubber (IR), nitrile rubber (NBR), chloroprene rubber (CR), etc. Diene synthetic rubber, butyl rubber (IIR), chlorobutyl rubber (CIIR), olefin synthetic rubber such as ethylene propylene rubber (EPM, EPDM), polysulfide rubber (T), silicone rubber (Q), urethane rubber (U), fluorine Various synthetic rubbers such as rubber (FKM), acrylic rubber (ACM), chlorosulfonated polyethylene (CSM) and the like, and those obtained by blending one kind or two or more kinds at an arbitrary ratio are mentioned.

  In addition, liquid rubber is liquid at room temperature, but when it is cross-linked, it becomes high molecular weight and hardens to become solid rubber, and examples thereof include liquid natural rubber and liquid synthetic rubber. Examples of liquid synthetic rubber include liquid IR, liquid Various types of liquid synthetic rubbers such as SBR, liquid BR, and liquid NBR, including one or two or more of them blended at an arbitrary ratio, may be blended with the above solid rubber.

  Vulcanized rubber using the above-mentioned solid rubber, liquid rubber, or a blend thereof is crosslinked with a crosslinking agent such as a sulfur-based crosslinking agent or organic peroxide, and the sulfur-based rubber is used for ordinary rubber crosslinking. Organic peroxides such as rubber powder sulfur and oil-treated sulfur include dicumyl peroxide, 2,4-dichlorobenzoyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5 di (Tert-peroxy) -hexane and the like. Moreover, what was bridge | crosslinked using crosslinking agents, such as metal oxides, such as organic polyvalent amine, modified phenol resin, and magnesium oxide, is also used.

  In addition to the above rubber components and crosslinking agents, reinforcing agents such as carbon black and silica, vulcanization accelerators, vulcanization accelerators, zinc white, stearic acid, oils, resins, anti-aging agents, etc. These various compounding agents may be included.

  As the vulcanized rubber as the measurement sample of the present invention, a vulcanized rubber compounded and vulcanized for research in a laboratory, a sample taken from a rubber product, or the like is used. Here, the vulcanized rubber preferably has an elastic modulus at 100% elongation in a tensile test of 0.5 to 4 MPa, preferably 1 to 3 MPa. When the elastic modulus exceeds 4 MPa, such as a large amount of sulfur vulcanized rubber such as ebonite or a large amount of rubber compounded with carbon black, even in the case of vulcanized rubber, the mobility in the rubber molecule is low, making it difficult to measure under solution conditions. If the pressure is less than 0.5 MPa, the strength of the cross-linking signal is lowered and accurate measurement cannot be performed.

  Said vulcanized rubber is adjusted to the solid sample for NMR measurement which consists of a thin piece with the following adjustment methods.

[Preparation method of solid sample]
(1) Unvulcanized rubber composition obtained by adding a cross-linking agent such as sulfur and a compounding agent such as zinc white and vulcanization accelerator to raw rubber and mixing by a conventional method using a press vulcanizer or the like Vulcanized to produce vulcanized rubber.
(2) The vulcanized rubber is pulverized or cut into fine pieces having a particle size or a fine piece length of 0.001 to 0.5 mm by a freezing pulverizer, a scissors or a knife.
(3) The above-mentioned fine piece is extracted with acetone, and by-products such as metal salts derived from additives such as zinc white, vulcanization accelerator and fatty acid are filtered and removed.
(4) Acetone is removed using a vacuum dryer or the like and dried to obtain a solid sample.
If the solid sample strip is less than 0.001 mm, it will be easily scattered and difficult to handle, and if it exceeds 0.5 mm, it will be difficult to averagely store it in the solid NMR MAS probe and the measurement accuracy will decrease. It is not preferable.

  In the case of using a freeze pulverizer, a general-purpose freeze pulverizer can be used. For example, JFC-300 type manufactured by Nippon Analytical Industries, Ltd. can be used. Solution nitrogen is suitable as the freezing medium, and 10 to 500 mg of vulcanized rubber is charged into a pulverized capsule container, and pulverized until the particle diameter falls within the above range in a frozen state.

  The solid sample composed of the vulcanized rubber strip obtained as described above is subjected to NMR measurement under the solution NMR conditions using a solid high-resolution NMR apparatus as follows.

[Measurement under solution NMR conditions]
(1) A solid NMR MAS probe is set in the NMR apparatus, and a solid sample is charged in the probe.
(2) The sample is in a magic angle rotation state.
(3) A pulse program for solution such as DEPT is read into the NMR apparatus.
(4) Various settings of the NMR apparatus such as optimization of 90 ° pulse are performed.
(5) An NMR measurement is performed on a solid sample, and an NMR spectrum is obtained and analyzed.

  New analysis of the vulcanized rubber's cross-linking morphology, cis bond, trans bond, and other microstructures, polymer molecular weight, etc., which were not obtained by conventional solid condition NMR measurement, by NMR measurement under the above-mentioned solid sample solution conditions Information can be obtained directly from the vulcanized rubber in the solid state.

  By obtaining new knowledge about vulcanized rubber in this way, the physical properties of vulcanized rubber can be improved by controlling the cross-linked structure by adjusting the compounding system and cross-linking system, and the optimal rubber composition for various applications. Formulation and cross-linking systems can be developed.

  The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

  This example shows an example in which a crosslinked structure of natural rubber by sulfur crosslinking was measured using an NMR apparatus, and a solid sample of vulcanized rubber was prepared as follows.

  Using 100 parts by weight of natural rubber (RSS # 1), 2 parts by weight of powdered sulfur for rubber (a kind specified in JIS K6222) and 1 part by weight of a crosslinking accelerator CBS (specified in JIS K6202) are used for a test roll. After mixing, the obtained rubber composition was press vulcanized at 150 ° C. for 30 minutes to produce a vulcanized rubber sheet having a thickness of 1 mm. The initial elastic modulus of this vulcanized rubber is 1.1 MPa.

  After cutting the vulcanized rubber sheet into a cube having a length of about 0.1 mm on one side using a scissors, 1 g of the vulcanized rubber sheet is immersed in 150 ml of acetone for 8 hours to extract a by-product such as a metal salt, Vacuum-dried to obtain a solid sample for NMR measurement.

Nuclear magnetic resonance (NMR) apparatus: manufactured by BRUKER, DPX400 type, charged with 300 mg of solid sample into 7 mm MAS probe for solid NMR, known ¹³ C-NMR method (solid condition), DEPT135 method (solution condition), and NMR measurement was performed by APT method (solution conditions). The NMR spectrum is shown in FIGS.

FIG. 1 is a spectrum obtained by a solid condition ¹³ C-NMR method (solid high-resolution NMR) using a conventional solid sample, and FIG. 4 is an enlarged view of a main part of FIG. 2 is a spectrum obtained by a solution condition DEPT135 method (solution high resolution NMR) using a solid sample, FIG. 5 is an enlarged view of the main part thereof, and FIG. 3 is a spectrum obtained by a solution condition APT method (solution high resolution NMR) using a solid sample. 6 is an enlarged view of the main part.

Reference numerals 1 to 5 attached to each signal in each spectrum indicate signals of each carbon element in the isoprene unit of the natural rubber (see the following chemical formula), and carbon and hydrocarbons 6 to 18 (C, CH) indicated by arrows in the spectrum. , CH ₂ , CH ₃ ) are signals that appear upon vulcanization.

1 and 4, the spectra obtained by the ¹³ C-NMR method using the conventional solid sample are all upward signals, whereas the spectra obtained by the DEPT135 method using the solid sample according to the present invention are those shown in FIGS. As shown in FIG. 5, the signals of CH (3) and CH ₃ (5) appear upward, the signal of CH ₂ (1,4) appears downward, and the signal of C (2) does not appear.

  From the enlarged view of FIG. 5, the signals (7), (9), (15) to (18) appear upward, the signals (11) to (14) appear downward, and (6), (8) , (10) no longer appears. That is, (7) and (9) are tertiary carbons, (15)-(18) are primary carbons, (11)-(14) are secondary carbons, (6), (8), (10) are It turns out that it is a quaternary carbon.

As shown in FIGS. 3 and 6, in the spectrum by the APT method using the solid sample according to the present invention, the signals of CH ₂ (1, 4) and C (2) are upward, and CH (3) and CH ₃ (5) signal appears downward.

  From the enlarged view of FIG. 6, the signals (7), (9), (15) to (18) appear downward, and the signals (6), (8), (11) to (14) appear upward. . That is, (15) to (18) are primary carbon, (7) and (9) are tertiary carbon, (11) to (14) are secondary carbon, (6), (8), (10) are It turns out that it is a quaternary carbon.

  As described above, in the NMR measurement by the DEPT135 method or the APT method under the solution conditions using the solid sample, the number of hydrogen atoms bonded to the carbon atom is known, that is, the first grade, 2 constituting the vulcanized rubber crosslink. It is possible to identify the carbon atoms of grades 3, 3, and 4 from the intensity of the spectrum.

  Furthermore, the rubber physical properties of the vulcanized rubber can be evaluated from the intensity ratio of the crosslinking signal obtained from the spectrum. For example, in the vulcanized rubber having the same crosslinking density, the signal intensities of (6) and (8) in FIG. As the ratio (6) / (8) increases, a vulcanized rubber having a higher tensile strength can be obtained. This equation for the signal intensity ratio is derived from the fact that FIGS. 5 and 6 show that (6) and (8) have the same quaternary carbon structure.

  In this way, information on the signal structure that appears due to cross-linking of various synthetic rubbers including natural rubber can be easily obtained, and evaluation of the cross-linking form, which has been difficult with conventional solid samples, can be easily performed in a short time. It can be performed at high cost and with high accuracy, and greatly contributes to the analysis of the crosslinked structure of the vulcanized rubber.

  And the vulcanized rubber whose intensity ratio of the crosslinking signal measured by the said crosslinked-structure evaluation method of vulcanized rubber is 0.1-10 can express a rubber characteristic suitable for various uses.

  Vulcanized rubber with a low strength ratio of the cross-linking signal can be designed to have a large elongation although its strength, elastic modulus, hardness, etc. are low. The ratio and the like can be designed to be high, and the vulcanized rubber characteristics can be controlled to obtain an optimum vulcanized rubber.

  The method for evaluating the crosslinked structure of vulcanized rubber according to the present invention enables NMR measurement using a solid sample of a vulcanized rubber, which could only be measured under conventional solid NMR conditions, under solution NMR conditions. Can be obtained with high accuracy and a simple evaluation method, and is widely used for research and development of rubber materials. And by improving the physical properties of the vulcanized rubber, it is possible to provide rubber materials and compounding designs that are optimal for various applications.

It is a spectrum figure by < ¹³ > C-NMR method. It is a spectrum figure by DEPT135 method. It is a spectrum figure by APT method. It is a principal part enlarged view of FIG. FIG. 3 is an enlarged view of a main part of FIG. 2. It is a principal part enlarged view of FIG.

Explanation of symbols

1, 4 ... CH ₂ signal 2 ... C signal 3 ... CH signal 5 ... CH ₃ signal 6, 8, 10 ... C signal appearing by vulcanization 7, 9 ... By vulcanization Appearing CH signal 11-14 ... CH ₂ signal appearing by vulcanization 15-18 ... CH ₃ signal appearing by vulcanization

Claims (6)

Using a strip made of vulcanized rubber as a measurement sample, using a solid high-resolution NMR device, NMR measurement is performed under solution NMR conditions in a magic angle rotation state, and the chemical shift and type of carbon in the vulcanized rubber (1 A method for evaluating a crosslinked structure of a vulcanized rubber, characterized by identifying a grade to a grade 4). The method for evaluating a crosslinked structure of a vulcanized rubber according to claim 1, further comprising evaluating the rubber physical properties of the vulcanized rubber from the intensity ratio of the obtained crosslinking signals. The method for evaluating a crosslinked structure of a vulcanized rubber according to claim 1 or 2, wherein an elastic modulus at 100% elongation in a tensile test of the vulcanized rubber is 0.5 to 4 MPa. The method for evaluating a crosslinked structure of a vulcanized rubber according to claim 1 or 2, wherein the solution NMR conditions are any ^{one of 1} H-NMR method, DEPT method, APT method, and 2D method. The method for evaluating a crosslinked structure of a vulcanized rubber according to claim 1 or 2, wherein a strip length of the measurement sample of the vulcanized rubber is 0.001 to 0.5 mm. A vulcanized rubber, wherein the strength ratio of the crosslinking signal obtained by the method for evaluating a crosslinked structure of a vulcanized rubber according to any one of claims 1 to 5 is 0.1 to 10.

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