JP2006133167A - Method for evaluating heat resistance of rubber composition and method for producing heat resisting rubber composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for evaluating heat resistance of a rubber composition after vulcanization. <P>SOLUTION: The heat resistance evaluation method for rubber composition comprises, chemically analyzing and determining, in a vulcanized rubber obtained by sulfur-vulcanizing a rubber composition mainly composed of a diene-based rubber, the amount of sulfur which binds to rubber molecules present in the vulcanized rubber by combustion/infrared detection method, determining a value Gg representing the amount of sulfur cross-linkage bound between two rubber molecules from a modulus (Gf) at 100% elongation in tensile test of the vulcanized rubber, mixing amounts of carbon black and/or silica in the rubber composition (volume fraction ψ) and DBP absorption amounts of the carbon black and/or silica mixed, and predicting thermal deterioration resistance of the vulcanized rubber by the value of Gg/bound sulfur amount. A heat resisting rubber composition is produced by selecting rubber components, compositions of carbon black and/or silica and sulfur, and a vulcanization condition. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for evaluating the heat aging resistance of a rubber composition in which carbon black and / or silica and sulfur are blended with a rubber component mainly composed of a diene rubber, and the heat resistance using such an evaluation method. The present invention relates to a method for producing a rubber composition for a tread that is suitable for extending the life of a rubber composition, particularly a pneumatic radial tire.

  Conventionally, when a rubber composition such as a rubber composition for a tire tread is sulfur vulcanized, the vulcanization time is first determined by measuring the vulcanization rate of the rubber composition at an arbitrary vulcanization temperature with a rheometer. It was general. The thermal degradation characteristics of the vulcanized belt coat rubber were estimated by putting the vulcanized rubber in an oven and accelerated aging to determine the elongation of the rubber material and the rate of change in modulus. Based on the results, the rubber composition was estimated. We were seeking vulcanization conditions for the product. However, this method cannot accurately grasp the heat aging characteristics of the vulcanized rubber product due to heat aging under different heat aging promotion conditions from the actual vehicle, and it is also possible to increase the temperature of the rubber product. It is common to vulcanize the rubber composition under the conditions, and in order to prevent uneven vulcanization of the internal rubber in the vulcanized rubber because the heat aging characteristics of the vulcanized rubber are not accurately grasped. In general, the vulcanization time is longer than the actually required vulcanization time. However, when a rubber product such as a tire is manufactured by such a method, there is a problem that the heat aging characteristic of the vulcanized rubber becomes insufficient, for example, the life of the tire is shortened.

  In order to solve the above problem, we have determined the ratio between the crosslinking density estimated from the value of 100% modulus (M100) of the tensile test and the amount of sulfur bond determined by solid state NMR method in the belt coating rubber of the natural rubber compounding system. "Sulfur bonds are used for intermolecular crosslinking", and this "efficiency" is a measure for predicting the heat resistance of vulcanized rubber. ) Has been proposed (see Patent Document 1). Since then, the application development of this technology has been studied. However, the solid-state NMR method is not suitable for measuring the amount of sulfur bonds such as high vinyl BR and SBR, and there is a limit to applying this method to the compound in the tire tread portion. I noticed that there was a point.

Application for Japanese Patent Application No. 2003-122065 (filed on April 25, 2003)

  In order to solve the above problems, the present inventors have developed a method capable of evaluating the heat resistance after vulcanization for a wide range of rubber compositions such as high vinyl BR and SBR, and chemical analysis ( It is possible to predict the heat aging resistance by obtaining the bound sulfur amount by acetone extraction and subsequent combustion / infrared detection method) and using this value instead of the value from the NMR method of Patent Document 1 described above. I found.

  Accordingly, the present invention provides a method for evaluating the heat resistance after vulcanization of a rubber composition by measuring the amount of bound sulfur after vulcanization of the rubber composition, and thereby has excellent heat resistance and is long. It is an object of the present invention to provide a method for producing a rubber composition having a long life, for example, a rubber composition suitable for a tire tread.

  According to the present invention, a rubber composition containing 100 parts by weight of a rubber component mainly composed of a diene rubber, 5 to 120 parts by weight of carbon black and / or silica, and 1 to 10 parts by weight of sulfur is sulfur vulcanized. The amount of sulfur bonded to the rubber molecules present in the vulcanized rubber (the amount of bound sulfur) is obtained by chemical analysis by combustion / infrared detection and the vulcanized rubber is pulled. Modulus (Gf) at 100% elongation in the test (measured in accordance with JIS K6251), blending amount of carbon black and / or silica (volume fraction φ) in the rubber composition, and blended carbon black and / or silica DBP (dibutyl phthalate) oil absorption (measured according to JIS K6217-4) of formula (I) and (II):

To obtain a value Gg representative of the amount of crosslinked sulfur bonded between two rubber molecules, and to predict the heat deterioration resistance of the vulcanized rubber according to the value of Gg / bonded sulfur amount Is provided.

  According to the present invention, the heat-resistant rubber composition is selected by selecting a rubber component, carbon black and / or silica, and sulfur composition and vulcanization conditions so that the Gg / bonded sulfur ratio is 120 or more. A method of manufacturing an article is provided.

  According to the present invention, the amount of sulfur bound to the rubber molecules of sulfur in the vulcanized rubber is determined by a combination with a chemical analysis method (acetone extraction followed by combustion / infrared detection method). Compared with the above-mentioned values, the amount of bound sulfur can be obtained widely regardless of the type of diene rubber, so that the heat resistance of a wide range of vulcanized rubber can be more correctly evaluated than the above-mentioned method.

  In the process of studying rubber for tire tread, for example, which has high durability against heat aging, the present inventors do not crosslink between rubber molecules, and sulfur compounded to rubber molecules does not crosslink between rubber molecules. It has been found that the greater the amount of structure bonded, the lower the durability of the vulcanized rubber against thermal aging.

  Further, the present inventors have further studied the efficiency of the sulfur compounded in the rubber composition used for cross-linking between molecules during the process of studying rubber for tire tread having high durability against heat aging. It was found that it was necessary to select vulcanization conditions suitable for the rubber composition in order to produce a vulcanized rubber having high durability against heat aging, depending on the temperature and time conditions.

  By vulcanizing (crosslinking) the rubber with sulfur, sulfur (S or Sx) is bonded in a crosslinked manner between the rubber molecules to obtain a vulcanized rubber. However, in fact, there are many sulfurs that do not contribute to crosslinking in the vulcanized rubber. For example, sulfur binds to one rubber molecule to form a branch, or binds to the same rubber molecule to form a loop. These bonded sulfurs cause a cross-linking reaction when heat is applied while the rubber product is in use, causing the rubber product to harden and become brittle or brittle, thereby reducing the product life.

  The present inventors have found that the efficiency with which sulfur is used for crosslinking is greatly affected by the vulcanization conditions of the rubber composition. However, it is difficult to accurately determine the durability of vulcanized rubber against heat aging by conventional technology, and there is no vulcanization condition that satisfies the heat aging durability of all rubber blends made for belt coats at the same time. Therefore, a simple and accurate analysis method for obtaining optimum vulcanization conditions for each rubber compound was desired.

  According to the present invention, a vulcanized rubber sample is subjected to acetone extraction based on JIS K 6229 and then subjected to quantitative analysis of sulfur content in the extraction residue based on JIS Z 2616. For the quantitative analysis, an infrared absorption method is used. This is a kind of dry decomposition method in which sulfur in a sample is quantified with sulfur oxide by heating the sample to a high temperature in an oxygen stream. Specifically, sulfur in the vulcanized rubber is separated from other components as sulfur dioxide, sent to an infrared absorption cell, and the amount of sulfur is measured by measuring the infrared absorption amount of sulfur dioxide using a non-dispersive infrared analyzer. calculate. In principle, this method can be applied to samples having a sulfur content of 0.001% or more. Although the operation is simple and the influence of interfering elements is small, sulfur trioxide is not quantified, so correction with a standard sample is generally required. The measuring instrument is commercially available, for example, as EMIA-V series from HORIBA, Ltd., and is also described in, for example, JP-A-11-64319.

  According to the present invention, among the added sulfur, the amount of sulfur (C-Sx-C) crosslinked in a crosslinked state between two rubber molecules and bonded to one rubber molecule in a branch or loop form Only the total amount of sulfur (C-Sx-) that does not contribute to crosslinking is obtained. This is referred to as a sulfur bond amount in the present invention. Among these sulfurs, the latter (ie, sulfur that is not bonded in a crosslinked state between two rubber molecules) is cured more than necessary due to crosslinking between the rubber molecules, causing heat aging. Become.

  On the other hand, the value of Gg based on the 100% modulus in the tensile test of vulcanized rubber mainly correlates with the value of crosslinking density, that is, the amount of sulfur crosslinked between two rubber molecules in the number of bonded sulfur. References A. Ahagon, Rubber Chem. Technol., 59, 187 (1986)

  According to the present invention, the heat aging property (heat resistance) of the rubber composition includes a diene rubber as a main component, for example, 40% by weight or more, more preferably 60% by weight or more of the total rubber amount, and the rubber component. Preferably 5 to 120 parts by weight, more preferably 40 to 80 parts by weight, and preferably 1 to 10 parts by weight, more preferably 2 to 7 parts by weight of general-purpose carbon black and / or silica per 100 parts by weight. The rubber composition can be evaluated.

  If the proportion of the diene rubber in the rubber composition to be evaluated for heat resistance is too small, sulfur vulcanization hardly occurs, which is not preferable. Further, if the amount of carbon black and / or silica is too large, the proportion of rubber is small, and it is not preferable because deterioration of the rubber is hardly visible. On the other hand, if the ratio of sulfur is too small, the experimental error increases, which is not preferable. Conversely, if the ratio is too large, vulcanization unevenness of the internal rubber increases, which is not preferable.

  The rubber component of the rubber composition in the present invention is mainly a diene rubber such as natural rubber (NR), polyisoprene rubber (IR), various polybutadiene rubbers (BR), various styrene butadiene copolymer rubbers (SBR) and the like. Components, for example, 40% by weight or more, preferably 60% by weight or more of the total amount of rubber components, and particularly when SBR is contained in diene rubbers by 40% by weight or more, particularly 60% by weight or more, the Tg increases. This is preferable because the wet friction performance is improved.

  According to the present invention, the heat resistance after vulcanization of the rubber composition can be obtained by the ratio of Gg (crosslinked sulfur amount) / bound sulfur amount obtained by the formula (I). Excellent heat resistance is exhibited when the ratio of Gg / bonded sulfur amount is 120 or more, and further excellent heat resistance is exhibited at 140 to 170. Therefore, in the production of the heat resistant rubber composition according to the present invention, the composition (type and amount, etc.) of the constituent components and the vulcanization conditions (temperature, time, etc.) can be set to the Gg / bonded sulfur amount by repeating normal experiments. The desired heat resistant rubber composition can be obtained by selecting the ratio to be 120 or more.

  In the present invention, the total amount of carbon bonded to sulfur (bond S) is determined by measuring the amount of sulfur bonds by chemical analysis (acetone extraction followed by combustion / infrared detection method). On the other hand, by correcting the 100% modulus (M100) value of the tensile test with the goose gold formula (excluding the volume effect of the filler), the standard Gg of the crosslinking density of the rubber part is obtained by the formulas (I) and (II). It is done. The value of Gg / bonded sulfur amount is a ratio at which the sulfur bond contributes to intermolecular crosslinking, and by selecting the composition of the blending components and vulcanization conditions so that this value is 120 or more, preferably 140 to 170, the desired value is obtained. A rubber composition having excellent heat aging resistance can be obtained.

  In addition to the essential components described above, the rubber composition according to the present invention includes other reinforcing agents (fillers) such as clay and talc, vulcanization or crosslinking accelerators, various oils, anti-aging agents, plasticizers, and other tires. Various additives that are generally blended for general rubber can be blended, and these additives are kneaded and vulcanized into a composition by a general method to vulcanize or crosslink. Can be used. The blending amounts of these additives may be conventional conventional blending amounts as long as the object of the present invention is not adversely affected.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, it cannot be overemphasized that the scope of the present invention is not limited to these Examples.

Examples 1-6 and Comparative Examples 1-6
Sample preparation In the formulation shown in Table I, ingredients other than the vulcanizing agent (vulcanization accelerator and sulfur) were kneaded for 5 minutes with a 250 ml Banbury mixer, and when 165 ± 5 ° C was reached, the master batch was released. Obtained. A vulcanization accelerator and sulfur were kneaded with this master batch with an open roll to obtain a rubber composition.

  Next, the obtained rubber composition was press vulcanized in a 15 × 15 × 0.2 cm mold under the conditions of temperature and vulcanization time shown in Table I to prepare a vulcanized rubber sheet. The physical properties of vulcanized rubber were measured by the method. The results are shown in Table I.

Method for Measuring 100% Modulus (M100) A rubber composition sample was press vulcanized and formed into a sheet having a thickness of 2 mm. A No. 3 dumbbell-shaped test piece was punched from this sheet, and 100% modulus was measured in accordance with JIS K 6251.

Heat aging resistance test No. 3 dumbbell-shaped test piece was punched out from a sample vulcanized rubber with a 2mm sheet, left in an oven at 80 ° C for 96 hours, and then subjected to a tensile test according to JIS K 6251 to give 100% modulus. The increase rate when compared with the value before heat aging in the (M100) value was defined as the heat aging resistance index. It shows that it is inferior to heat aging resistance, so that this figure is large.

Bond sulfur content measurement Rubber pieces after acetone extraction of vulcanized rubber samples according to JIS K 6229 are measured with a HORIBA carbon / sulfur analyzer (EMIA), and combustion / infrared detection according to JIS Z 2616 The amount of bound sulfur contained in the vulcanized rubber was determined from the amount of sulfur dioxide detected by the method.

Table I Footnote RSS # 3: Natural rubber Nipol BR1220: BR made by Nippon Zeon
Nipol 1502: emulsion polymerization SBR manufactured by Nippon Zeon
Nipol 1712: Nippon Zeon's emulsion polymerization SBR (37.5% oil exhibition)
NS116: Solution polymerization SBR (high vinyl) manufactured by Nippon Zeon
Toughden 4350: Solution polymerization SBR manufactured by Akzo (high styrene, high vinyl, 50% oil)
Toughden 1524: Akzo solution polymerization SBR (low styrene, low vinyl, 20% oil)

SAF: Tokai Carbon Carbon Black Seast 9M (DBP oil absorption: 113 ml / 100 g)
N234: Showa Cabot carbon black show black (DBP oil absorption: 125 ml / 100 g)
HAF: Carbon black seast KHP made by Tokai Carbon (DBP oil absorption: 102 ml / 100 g)
N339: Showa Cabot carbon black show black (DBP oil absorption: 120 ml / 100 g)
FEF: Tokai Carbon Carbon Black Seast F (DBP oil absorption: 121ml / 100g)
Silica: Nippon Silica nip seal AQ (DBP oil absorption: 175 ml / 100 g)

StA: Nippon Oil & Fats Beads Stearate Zno: Toho Zinc Ginseng R
6C: Anti-aging agent Santoflex 6PPD made by FLEXSYS
WAX: Sannouchi Aroma Oil from Ouchi Shinsei Chemical: Process X-140 from Japan Energy
Si75: coupling agent, Nippon Unicar A-1589

Sulfur: Fine powdered sulfur with oil from Jinhua seal oil (5% oil content)
Accelerator 1: Santocure CBS made by FLEXSYS
Accelerator 2: Vulcanization accelerator Santocure TBBS made by FLEXSYS
Accelerator 3: Vulcanization accelerator PERKACIT DPG made by FLEXSYS

  According to the present invention, the amount of sulfur bonded to rubber molecules in the vulcanized rubber can be determined by chemical analysis, so that the heat resistance (heat aging resistance) after vulcanization of a wide range of rubber compositions can be correctly evaluated. For example, it is useful for producing a heat resistant rubber composition for a tread of a pneumatic tire.

Claims (3)

Vulcanization obtained by sulfur vulcanization of a rubber composition containing 100 parts by weight of a rubber component mainly composed of a diene rubber, 5 to 120 parts by weight of carbon black and / or silica, and 1 to 10 parts by weight of sulfur. In rubber, the amount of sulfur bonded to rubber molecules present in the vulcanized rubber (bonded sulfur amount) is obtained by chemical analysis by combustion / infrared detection method and vulcanized rubber tensile test (according to JIS K6251) The modulus (Gf) at 100% elongation, the blending amount of carbon black and / or silica in the rubber composition (volume fraction φ), and the DBP (dibutyl phthalate) of the blended carbon black and / or silica. ) Formula (I) and (II) using the oil absorption (measured according to JIS K6217-4):

To obtain a value Gg representative of the amount of crosslinked sulfur bonded between two rubber molecules, and to predict the heat deterioration resistance of the vulcanized rubber according to the value of Gg / bonded sulfur amount .   The method for evaluating the heat resistance of a rubber composition according to claim 1, wherein 40 parts by weight or more of styrene-butadiene copolymer rubber (SBR) is contained in 100 parts by weight of the diene rubber.   The heat-resistant rubber, wherein the rubber component, carbon black and / or silica, and the composition of sulfur and vulcanization conditions are selected so that the ratio of Gg / bonded sulfur amount in claim 1 or 2 is 120 or more. A method for producing the composition.