Method for measuring the rate of change in the binding amount of silane coupling agents
By detecting thiophene analogs through pyrolysis gas chromatography in unvulcanized rubber compositions, the method addresses the inability to measure silane coupling agent-polymer bond changes, facilitating the evaluation and optimization of vulcanized rubber compositions for enhanced properties.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- SUMITOMO RUBBER INDUSTRIES LTD
- Filing Date
- 2022-06-09
- Publication Date
- 2026-06-23
AI Technical Summary
Existing methods fail to measure the change in the amount of silane coupling agent-polymer bonds due to thermal degradation in silica-containing rubber compositions, which is crucial for evaluating the degradation of vulcanized rubber products.
A method involving the preparation of an unvulcanized rubber composition without vulcanizing agents or accelerators, followed by thermal decomposition to detect and quantify thiophene analogs using pyrolysis gas chromatography, allowing the measurement of silane coupling agent-polymer bond changes before and after thermal degradation.
Enables selective measurement of bond changes, enabling evaluation of vulcanized rubber composition degradation and prediction of properties like abrasion resistance, thereby optimizing manufacturing conditions for improved performance.
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Abstract
Description
[Technical Field]
[0001] This invention relates to a method for measuring the rate of change in the amount of bonding between a silane coupling agent and rubber components in a rubber composition before and after thermal degradation. [Background technology]
[0002] Conventionally, methods for evaluating the deterioration of rubber products include changes in hardness, changes in toluene swelling rate, and changes in tensile properties (for example, Patent Document 1). However, these methods all evaluate physical changes that do not involve chemical changes, or chemical changes, mainly crosslinking by sulfur. [Prior art documents] [Patent Documents]
[0003] [Patent Document 1] Japanese Patent Publication No. 2006-249403 [Overview of the project] [Problems that the invention aims to solve]
[0004] In silica-containing rubber compositions, in addition to crosslinking between rubber components (polymers) by sulfur, there are also bonds between silica, silane coupling agent, and polymer via a silane coupling agent. The silica-silane coupling agent bond is chemically stable and unlikely to change due to degradation, but the silane coupling agent-polymer bond is thought to change due to degradation. However, until now, no method has been known to measure the change in the amount of silane coupling agent-polymer bond due to thermal degradation.
[0005] The present invention aims to provide a method for selectively measuring the rate of change in the amount of bonding between a silane coupling agent and a rubber component in a rubber composition due to thermal degradation. [Means for solving the problem]
[0006] As a result of diligent research, the inventors of the present invention have found that the above problem can be solved by preparing an unvulcanized rubber composition by kneading rubber components, silica, and a silane coupling agent containing sulfur atoms without adding a vulcanizing agent or vulcanization accelerator, and by detecting and quantifying the thiophene analogs produced by thermal decomposition of the unvulcanized rubber composition before and after thermal degradation, thereby completing the present invention.
[0007] In other words, the present invention is [1] A method for measuring the rate of change in the amount of binding between a silane coupling agent and a rubber component in an unvulcanized rubber composition before and after thermal degradation, wherein the amount of binding between the silane coupling agent and the rubber component in the unvulcanized rubber composition before thermal degradation is calculated by detecting and quantifying thiophene analogs produced by thermal decomposition of the unvulcanized rubber composition before thermal degradation, which contains rubber components, silica, and a silane coupling agent, but does not contain a vulcanizing agent or a vulcanization accelerator, and the amount of binding between the silane coupling agent and the rubber component in the unvulcanized rubber composition after thermal degradation is calculated by detecting and quantifying thiophene analogs produced by thermal decomposition of the unvulcanized rubber composition after thermal degradation, obtained after thermal degradation of the unvulcanized rubber composition before thermal degradation. [2] The measurement method according to [1], wherein the quantification of the thiophene analog comprises the steps of analyzing the unvulcanized rubber composition before thermal degradation and the unvulcanized rubber composition after thermal degradation by pyrolysis gas chromatography, and calculating the peak area of the peak derived from the thiophene analog in the obtained chromatogram, respectively. [3] The measurement method according to [1] or [2], wherein thermal decomposition is carried out under conditions of 450 to 700°C and thiophene analogs are detected by a sulfur detector. [4] The measurement method according to any one of [1] to [3], wherein the thiophene analog is thiophene, 2-methylthiophene, and 3-methylthiophene. [5] A method for producing a vulcanized rubber composition, comprising the step of adding a vulcanization accelerator and a vulcanizing agent to an unvulcanized rubber composition containing a rubber component, silica, and a silane coupling agent, but not containing a vulcanizing agent and a vulcanization accelerator, and vulcanizing it, wherein the ratio of the amount of silane coupling agent to rubber component in the unvulcanized rubber composition after thermal degradation to the amount of silane coupling agent to rubber component in the unvulcanized rubber composition measured by any of the methods in [1] to [4] is 0.50 to 1.15, and the thermal degradation of the unvulcanized rubber composition is carried out by heating at 80°C for two weeks, A method for producing a tire using a vulcanized rubber composition produced by the manufacturing method described in [6] and [5], [7] An unvulcanized rubber composition containing a rubber component, silica, and a silane coupling agent, but not containing a vulcanizing agent or vulcanization accelerator, wherein the ratio of the amount of silane coupling agent to rubber component in the unvulcanized rubber composition after thermal degradation to the amount of silane coupling agent to rubber component in the unvulcanized rubber composition measured by any of the methods in [1] to [4] is 0.50 to 1.15, and the thermal degradation of the unvulcanized rubber composition is carried out by heating at 80°C for two weeks. [8] The unvulcanized rubber composition according to [7], wherein the silane coupling agent is a mercapto-silane coupling agent. [9] The unvulcanized rubber composition according to [7] or [8] further contains a carbodiimide compound. A vulcanized rubber composition obtained by vulcanizing an unvulcanized rubber composition described in any of
[10] , [7] to [9], The present invention relates to a method for evaluating the abrasion resistance of a vulcanized rubber composition obtained by adding a vulcanization accelerator and a vulcanizing agent to an unvulcanized rubber composition and vulcanizing agent, based on the rate of change in the amount of bonding between the silane coupling agent and the rubber component in the unvulcanized rubber composition before and after thermal degradation, as measured by any of the methods described in [1] to [4]. [Effects of the Invention]
[0008] According to the present invention, it is possible to selectively measure the rate of change in the amount of bonding between the silane coupling agent and the rubber component in the rubber composition due to thermal degradation, and to evaluate the degradation of the silica-containing vulcanized rubber composition at the stage of the unvulcanized rubber composition. [Brief explanation of the drawing]
[0009] [Figure 1] This is an example of a chromatogram obtained by thermal decomposition of the unvulcanized rubber composition of this disclosure. [Modes for carrying out the invention]
[0010] In the method for measuring the rate of change in the amount of binding between a silane coupling agent and a rubber component in an unvulcanized rubber composition before and after thermal degradation according to the present disclosure, the amount of binding between the silane coupling agent and the rubber component in the unvulcanized rubber composition before thermal degradation is calculated by detecting and quantifying thiophene analogs produced by thermal decomposition of the unvulcanized rubber composition before thermal degradation, which contains a rubber component, silica, and a silane coupling agent, but does not contain a vulcanizing agent or vulcanization accelerator. The amount of binding between the silane coupling agent and the rubber component in the unvulcanized rubber composition after thermal degradation is calculated by thermally degrading the unvulcanized rubber composition before thermal degradation, and then detecting and quantifying thiophene analogs produced by thermal decomposition of the obtained unvulcanized rubber composition after thermal degradation.
[0011] The quantification of the thiophene analog preferably includes the step of analyzing the unvulcanized rubber composition before thermal degradation and the unvulcanized rubber composition after thermal degradation by pyrolysis gas chromatography, and calculating the peak area of the peak derived from the thiophene analog in the obtained chromatogram.
[0012] The thermal decomposition is preferably carried out under conditions of 450 to 700°C, and thiophene analogs are preferably detected using a sulfur detector.
[0013] The thiophene analogs are preferably thiophene, 2-methylthiophene, and 3-methylthiophene.
[0014] Another embodiment of the present disclosure is a method for producing a vulcanized rubber composition, which includes a step of adding a vulcanization accelerator and a vulcanizing agent to an unvulcanized rubber composition containing a rubber component, silica, and a silane coupling agent and without containing a vulcanizing agent and a vulcanization accelerator, and then vulcanizing the composition. The ratio of the amount of the silane coupling agent bonded to the rubber component in the unvulcanized rubber composition after heat deterioration to the amount of the silane coupling agent bonded to the rubber component in the unvulcanized rubber composition measured by the above method is 0.50 to 1.15, and the heat deterioration of the unvulcanized rubber composition is carried out by heating at 80°C for 2 weeks. It is a method for producing a vulcanized rubber composition.
[0015] Another embodiment of the present disclosure is a method for producing a tire using the vulcanized rubber composition produced by the above production method.
[0016] Another aspect of the present disclosure is an unvulcanized rubber composition containing a rubber component, silica, and a silane coupling agent and without containing a vulcanizing agent and a vulcanization accelerator. The ratio of the amount of the silane coupling agent bonded to the rubber component in the unvulcanized rubber composition after heat deterioration to the amount of the silane coupling agent bonded to the rubber component in the unvulcanized rubber composition measured by the above method is 0.50 to 1.15, and the heat deterioration of the unvulcanized rubber composition is carried out by heating at 80°C for 2 weeks. It is an unvulcanized rubber composition.
[0017] Another aspect of the present disclosure is a vulcanized rubber composition obtained by vulcanizing the above unvulcanized rubber composition.
[0018] Another aspect of the present disclosure is a method for evaluating the abrasion resistance performance of a vulcanized rubber composition obtained by adding a vulcanization accelerator and a vulcanizing agent to an unvulcanized rubber composition and then vulcanizing the composition according to the change rate of the amount of the silane coupling agent bonded to the rubber component in the unvulcanized rubber composition before and after heat deterioration measured by the above method.
[0019] An embodiment of this disclosure, a method for measuring the rate of change in the amount of bonding between a silane coupling agent and a rubber component in a rubber composition before and after thermal degradation, will be described in detail below. However, the following description is illustrative for the purpose of explaining this disclosure and is not intended to limit the technical scope of the present invention to this scope only. In this specification, when a numerical range is indicated using "~", it includes the values at both ends of the range.
[0020] The rubber components relating to this disclosure can be crosslinkable rubber components commonly used in the rubber industry, such as natural rubber (NR), epoxidized natural rubber (ENR), isoprene rubber (IR), styrene-butadiene rubber (SBR), butadiene rubber (BR), ethylene propylene diene rubber (EPDM), styrene-isoprene-butadiene copolymer rubber (SIBR), styrene-isobutylene-styrene block copolymer (SIBS), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), hydrogenated nitrile rubber (HNBR), butyl rubber (IIR), ethylene propylene rubber, polynorbornene rubber, silicone rubber, polyethylene chloride rubber, fluororubber (FKM), acrylic rubber (ACM), hydrin rubber, etc. These rubber components may be used individually or in combination of two or more.
[0021] The silica relating to this disclosure is not particularly limited, and common types used in the tire industry can be used, such as silica prepared by a dry process (anhydrous silica) or silica prepared by a wet process (hydrated silica). Among these, hydrated silica prepared by a wet process is preferred because it contains a large number of silanol groups. These silicas may be used individually or in combination of two or more types.
[0022] The nitrogen adsorption specific surface area (N2SA) of silica is 90 m² from the perspective of reinforcing properties. 2 Preferably 120m / g or more. 2 More preferably 150m / g or more, 2 More preferably 170m / g or more. 2A value of 1 / g or more is particularly preferred. Furthermore, from the viewpoint of heat generation and processability, 350m 2 Preferably less than / g, 300m 2 More preferably less than / g, 250m 2 A value of less than or equal to / g is even more preferable. The N2SA of silica as used herein is the value measured by the BET method in accordance with ASTM D3037-93.
[0023] The average primary particle diameter of silica is preferably 22 nm or less, more preferably 20 nm or less, and even more preferably 18 nm or less. The lower limit of the average primary particle diameter is not particularly limited, but is preferably 1 nm or more, more preferably 3 nm or more, and even more preferably 5 nm or more. By having the average primary particle diameter of silica within the above range, the dispersibility of silica can be further improved, and the reinforcing properties, fracture properties, wear resistance, etc., can be further improved. The average primary particle diameter of silica can be determined by observing it with a transmission or scanning electron microscope, measuring 400 or more primary silica particles observed within the field of view, and averaging the results.
[0024] The silica content relative to 100 parts by mass of rubber component is not particularly limited and can be, for example, 1 to 150 parts by mass, 5 to 120 parts by mass, or 10 to 100 parts by mass, depending on the purpose of the compounding.
[0025] The silane coupling agent relating to this disclosure is not particularly limited as long as it contains a sulfur atom, and any silane coupling agent that has conventionally been used in combination with silica in the rubber industry can be used. Examples of such silane coupling agents include bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(4-trimethoxysilylbutyl)tetrasulfide, bis(3-triethoxysilylpropyl) trisulfide, bis(2-triethoxysilylethyl) trisulfide, bis(4-triethoxysilylbutyl) trisulfide, bis(3-trimethoxysilylpropyl) trisulfide, bis(2-trimethoxysilylethyl) trisulfide, bis(4-trimethoxysilylbutyl) trisulfide, bis(3-triethoxysilylpropyl) disulfide, and bis(2-triethoxysilylethyl) Silane coupling agents having a sulfide group, such as disulfide, bis(4-triethoxysilylbutyl) disulfide, bis(3-trimethoxysilylpropyl) disulfide, bis(2-trimethoxysilylethyl) disulfide, bis(4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-trimethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropylbenzothiazole tetrasulfide, and 3-trimethoxysilylpropyl methacrylate monosulfide;Examples include silane coupling agents having a mercapto group, such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and NXT-Z100, NXT-Z45, and NXT from Momentive; and silane coupling agents having a thioester group, such as 3-octanoylthio-1-propyltriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, and 3-octanoylthio-1-propyltrimethoxysilane. These silane coupling agents may be used individually or in combination of two or more. Among these, silane coupling agents having a sulfide group and silane coupling agents having a mercapto group are preferred because they have a strong bonding force with silica, resulting in a rubber composition with good abrasion resistance.
[0026] From the viewpoint of improving silica dispersibility, the content of the silane coupling agent per 100 parts by mass of rubber component is preferably 1.0 part by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 5.0 parts by mass or more. Furthermore, from the viewpoint of preventing a decrease in wear resistance, it is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less.
[0027] From the viewpoint of improving silica dispersibility, the content of the silane coupling agent per 100 parts by mass of silica is preferably 1.0 part by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 5.0 parts by mass or more. Furthermore, from the viewpoint of preventing a decrease in wear resistance, it is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less.
[0028] The rubber composition according to this disclosure preferably contains a carbodiimide compound. The bond between the silane coupling agent and the polymer consists of a carbon-sulfur bond, and its degradation (chemical cleavage) is thought to be accompanied by an oxidation reaction of sulfur (sulfone oxidation). Since such an oxidation reaction can be accelerated by the presence of water, it is thought that by incorporating a carbodiimide compound, moisture in the rubber composition can be removed and changes in the bond between the silane coupling agent and the polymer can be suppressed.
[0029] Examples of carbodiimide compounds include dicyclohexylcarbodiimide (DCC), diisopropylcarbodiimide, and ethyldimethylaminopropylcarbodiimide.
[0030] When a carbodiimide compound is included, its content per 100 parts by mass of the rubber component is preferably 1.0 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2.0 parts by mass or more. Furthermore, the content is preferably 10.0 parts by mass or less, more preferably 7.0 parts by mass or less, and even more preferably 5.0 parts by mass or less.
[0031] Sulfur is preferably used as a vulcanizing agent. Suitable sulfur varieties include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.
[0032] When sulfur is included as a vulcanizing agent, the amount of sulfur per 100 parts by mass of rubber component is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, from the viewpoint of ensuring a sufficient vulcanization reaction. Furthermore, from the viewpoint of preventing deterioration, it is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less. When oil-containing sulfur is used as the vulcanizing agent, the amount of vulcanizing agent shall be the total amount of pure sulfur contained in the oil-containing sulfur.
[0033] Examples of vulcanizing agents other than sulfur include alkylphenol-sulfur chloride condensates, 1,6-hexamethylene-dithiosulfate sodium dihydrate, and 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane. These non-sulfur vulcanizing agents can be purchased commercially from companies such as Taoka Chemical Industries, Ltd., Lanxess Corporation, and Flexis.
[0034] While not particularly limited, examples of vulcanization accelerators include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamate, aldehyde-amine or aldehyde-ammonia, imidazoline, and xanthate vulcanization accelerators.
[0035] Examples of sulfenamide-based vulcanization accelerators include (N-cyclohexyl-2-benzothiadylsulfenamide (CBS), N-(tert-butyl)-2-benzothiazolesulfenamide (TBBS), N-oxyethylene-2-benzothiazolesulfenamide, N,N'-diisopropyl-2-benzothiazolesulfenamide, and N,N-dicyclohexyl-2-benzothiazolesulfenamide. Examples of thiazole-based vulcanization accelerators include 2-mercaptobenzothiazole and dibenzothiazolyl disulfide. Examples of guanidine-based vulcanization accelerators include diphenylguanidine (DPG), diortotolylguanidine, and orthotolylbiguanidine. These vulcanization accelerators may be used individually or in combination of two or more.
[0036] The content of the vulcanization accelerator per 100 parts by mass of the rubber component is preferably 1.0 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2.0 parts by mass or more. Furthermore, the content of the vulcanization accelerator per 100 parts by mass of the rubber component is preferably 8.0 parts by mass or less, more preferably 7.0 parts by mass or less, even more preferably 6.0 parts by mass or less, and particularly preferably 5.0 parts by mass or less. By keeping the content of the vulcanization accelerator within the above range, it tends to be possible to ensure fracture strength and elongation.
[0037] In addition to the components mentioned above, the rubber composition according to this disclosure may appropriately contain compounding agents commonly used in the tire industry, such as carbon black, aluminum hydroxide, calcium carbonate, alumina, clay, talc and other reinforcing fillers other than silica, resin components, liquid polymers, oils, waxes, processing aids, antioxidants, stearic acid, zinc oxide, and the like.
[0038] <Preparation of Unvulcanized Rubber Composition> The measurement method according to this disclosure is characterized by kneading a rubber component, silica, and a silane coupling agent without adding a vulcanizing agent and a vulcanization accelerator, and subjecting the resulting unvulcanized rubber composition to thermal decomposition. The unvulcanized rubber composition may contain compounding agents other than the rubber component, silica, and silane coupling agent.
[0039] The unvulcanized rubber composition according to this disclosure can be manufactured by known methods. For example, it can be manufactured by kneading each of the above components using a rubber kneading device such as an open roll or closed kneader (Banbury mixer, kneader, etc.). The kneading conditions are not particularly limited, but usually kneading is performed at a discharge temperature of 150 to 170°C for 3 to 10 minutes. Furthermore, the obtained unvulcanized rubber composition may be subjected to remilling, which involves repeating the kneading process. From the viewpoint of improving the dispersibility of silica, remilling is preferable.
[0040] <Quantitative determination of thiophene analogs> The measurement method according to this disclosure is characterized by detecting and quantifying thiophene analogs generated by thermal decomposition of an unvulcanized rubber composition. While a bond is formed between the silane coupling agent and the polymer by the reaction of the double bond of the polymer with the sulfur functional group of the silane coupling agent, thermal decomposition of the unvulcanized rubber composition causes the diene bond to incorporate a sulfur atom, resulting in ring closure and cleavage of the carbon chain, generating a thiophene analog. By detecting and quantifying such thiophene analogs, the amount of bonding between the silane coupling agent and the polymer can be selectively measured. It is considered that thiophene analogs are not generated by thermal decomposition from silane coupling agents that react only with silica, or from silane coupling agents that do not react with either rubber components or silica.
[0041] The method for quantifying thiophene analogs is not particularly limited, but for example, it can be determined by analyzing an unvulcanized rubber composition by pyrolysis gas chromatography and calculating the peak area of the peak derived from the thiophene analog in the resulting chromatogram. The peak area of the chromatogram obtained by pyrolysis gas chromatography usually indicates the content of the component. In this disclosure, "pyrolysis gas chromatography" refers to a method in which a sample is heated by a pyrolysis apparatus, individual components contained in the gas phase components produced by this heating are separated by a separation column, and each isolated component is analyzed.
[0042] Any pyrolysis apparatus commonly used in this field can be suitably used, such as the vertical micro electric furnace pyrolyzer (product name: PY-2020iD) manufactured by Frontier Lab Co., Ltd. The temperature during pyrolysis (pyrolysis temperature) is usually in the range of 450 to 700°C, preferably in the range of 550 to 650°C. Within this temperature range, the thiophene analogs detected in this disclosure can be efficiently produced.
[0043] As for the separation column, we used the "Ultra Alloy" capillary column manufactured by Frontier Labs Co., Ltd. +Examples include "-5(MS / HT)" (5% diphenyl 95% dimethylpolysiloxane, length = 30m, inner diameter = 0.25mm, film thickness = 0.25μm).
[0044] Thiophene analogs produced by thermal decomposition are detected using a sulfur detector capable of detecting sulfur-containing components. Examples of sulfur detectors include flame photometric detectors (FPDs) and sulfur chemiluminescence detectors (SCDs). In this disclosure, the sulfur detector can achieve its purpose as long as it can quantify the thiophene analogs, and therefore, in addition to the general sulfur detectors mentioned above, mass spectrometers and the like may also be included.
[0045] The thiophene analogues to be quantified are not particularly limited as long as they are any one or more thiophene analogues. Specific examples of thiophene analogues include, for example, thiophene, 2-methylthiophene, and 3-methylthiophene. In this disclosure, from the viewpoint of quantitative accuracy, it is preferable to quantify by summing the peak areas of thiophene analogues including thiophene, 2-methylthiophene, and 3-methylthiophene, and more preferably by summing the peak areas of thiophene, 2-methylthiophene, and 3-methylthiophene. Figure 1 shows an example of a chromatogram obtained by thermal decomposition of the unvulcanized rubber composition of this disclosure.
[0046] A standard substance may be added to the unvulcanized rubber composition to prepare an analytical sample, which may then be analyzed by pyrolysis gas chromatography. The amount of binding between the silane coupling agent and the rubber component can also be quantified based on the ratio of the peak area of the peak derived from the standard sample to the peak area of the peak derived from the thiophene analog in the resulting chromatogram. The amount of binding between the silane coupling agent and the rubber component (mmol / g) can be determined, for example, by the following formula. (Amount of silane coupling agent bonded to rubber component (mmol / g)) = (Peak area of peaks originating from thiophene analogues) / (Peak area of peaks originating from standard substance) × (Constant determined from calibration curves created for the standard substance)
[0047] The standard substance is not particularly limited as long as it is a non-volatile component that can be detected by pyrolysis gas chromatography, and examples include dibenzothiophene, anthracene, phenanthrene, dodecane, and benzyl benzoate. Among these, it is preferable that the peak detected by pyrolysis gas chromatography does not overlap with that of thiophene analogs.
[0048] By the method described above, the amount of bonding between the silane coupling agent and the rubber component in the unvulcanized rubber composition before thermal degradation and the amount of bonding between the silane coupling agent and the rubber component in the unvulcanized rubber composition after thermal degradation can be calculated, and the rate of change in the amount of bonding can be determined. Thermal degradation of the unvulcanized rubber composition is carried out, for example, by heating at 80°C for two weeks.
[0049] The rate of change in the amount of bond between the silane coupling agent and the rubber component in the unvulcanized rubber composition before and after thermal degradation (CA-P bond amount change rate) can be calculated using the following formula, where A is the amount of bond between the silane coupling agent and the rubber component in the unvulcanized rubber composition before thermal degradation, and B is the amount of bond between the silane coupling agent and the rubber component in the unvulcanized rubber composition after thermal degradation. (Percentage change in CA-P binding amount (%)) = (B / A-1) × 100
[0050] The ratio (B / A) of the amount of silane coupling agent to rubber component bonded in the unvulcanized rubber composition after thermal degradation to the amount A of silane coupling agent to rubber component bonded in the unvulcanized rubber composition before thermal degradation, is preferably 0.50 to 1.15, preferably 0.52 to 1.12, more preferably 0.55 to 1.10, and particularly preferably 0.60 to 1.05. By setting B / A within the above range, it is possible to suppress the decrease in the abrasion resistance performance of the rubber composition after thermal degradation. The rate of change in the amount of silane coupling agent to rubber component bonded in the rubber composition before and after thermal degradation can be appropriately controlled by the number of remilling cycles, mixing temperature, ECU (cumulative temperature during mixing), vulcanization temperature, etc.
[0051] An unvulcanized rubber composition containing a vulcanizing agent and a vulcanizing accelerator can be obtained by adding a vulcanizing agent, a vulcanization accelerator, and other compounding agents as needed to the unvulcanized rubber composition subjected to measurement, and kneading it at, for example, 70 to 110°C for 1 to 5 minutes. A vulcanized rubber composition can be obtained by heating and pressurizing this unvulcanized rubber composition at, for example, 120 to 200°C.
[0052] An unvulcanized rubber composition containing the aforementioned vulcanizing agent and vulcanization accelerator is extruded into the shape of a predetermined tire component, and this is bonded to other components on a tire molding machine to form an unvulcanized tire. Then, the unvulcanized tire is heated and pressurized in a vulcanizing machine to obtain a tire.
[0053] The vulcanized rubber composition relating to this disclosure is not particularly limited in its use, but is preferably used as a tire component such as a tread, sidewall, inner liner, or wing. [Examples]
[0054] The present disclosure will be described below based on examples, but the present disclosure is not limited to these examples.
[0055] The various chemicals used in the examples are summarized below. SBR: Nipol NS616 (unmodified S-SBR) manufactured by Nippon Zeon Co., Ltd. Silica: ULTRASIL® VN3 manufactured by Evonik Degussa (N2SA: 175 m 2 / g, average primary particle size: 17 nm) Silane coupling agent 1: Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa Silane coupling agent 2: NXT-Z45 (a silane coupling agent having a mercapto group) manufactured by Momentive DCC: Dicyclohexylcarbodiimide Oil: Diana Process NH-70S manufactured by Idemitsu Kosan Co., Ltd. Wax: Oz Ace 0355 (manufactured by Nippon Seiro Co., Ltd.) Antioxidant: Nocrack 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Zinc oxide: Two types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Tsubaki Bead Stearic Acid manufactured by NOF Corporation Sulfur: Powder sulfur (5% oil-containing powder sulfur) manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator 1: Nocceler CZ (N-cyclohexyl-2-benzothiazolylsulfenamide (CBS)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Nocceler D (1,3-diphenylguanidine (DPG)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
[0056] <Preparation of Unvulcanized Rubber Composition and Vulcanized Rubber Composition> According to the formulation shown in Table 1, using a 1.7 L sealed Banbury mixer, chemicals other than sulfur and vulcanization accelerators were kneaded for 5 minutes until the discharge temperature reached 170°C to obtain the unvulcanized rubber compositions of Examples 1 to 5. To each of the obtained unvulcanized rubber compositions, sulfur and vulcanization accelerators were added according to the formulation shown in Table 1, kneaded for 4 minutes until the temperature reached 105°C, and press-vulcanized at 170°C for 12 minutes to prepare the vulcanized rubber compositions of Examples 1 to 5.
[0057] <Measurement of the Bonding Amount between Silane Coupling Agent and Polymer> From each obtained unvulcanized rubber composition, a 200 μg ± 5 μg test piece was cut into a cube shape to prepare analytical samples. These samples were subjected to pyrolysis gas chromatography to detect thiophene, 2-methylthiophene, and 3-methylthiophene among the pyrolysis products, and the peak area of each was determined. The total area of the peaks for thiophene, 2-methylthiophene, and 3-methylthiophene in each unvulcanized rubber composition was then calculated. Next, each unvulcanized rubber composition was subjected to thermal degradation by heating in an oven at 80°C for two weeks. The resulting thermally degraded unvulcanized rubber compositions were then subjected to pyrolysis gas chromatography, and the total area of the detected peaks for thiophene, 2-methylthiophene, and 3-methylthiophene was calculated. The total area of the peaks for thiophene, 2-methylthiophene, and 3-methylthiophene in each unvulcanized rubber composition before thermal degradation was set to 100. The total area of the peaks for thiophene, 2-methylthiophene, and 3-methylthiophene in each unvulcanized rubber composition after thermal degradation was indexed, and the amount of silane coupling agent-polymer bonding (CA-P bonding amount) in each unvulcanized rubber composition after thermal degradation was expressed as an index. The ratio (B / A) of the amount of silane coupling agent-rubber component bonding B in the unvulcanized rubber composition after thermal degradation to the amount of silane coupling agent-rubber component bonding A in the unvulcanized rubber composition before thermal degradation is also shown. The measurement conditions for pyrolysis gas chromatography are as follows.
[0058] (Measurement conditions for pyrolysis gas chromatography) Pyrolysis equipment: Frontier Lab Co., Ltd.'s vertical micro electric furnace type pyrolyzer "PY-2020iD" Pyrolysis temperature: 550℃ Gas chromatograph: Agilent Technologies, Inc. gas chromatograph "6890" (The interface heater temperature and sample inlet temperature were set to 340°C. The oven temperature was held at 40°C for 3 minutes, then increased from 40°C to 300°C at a rate of 8°C per minute, and held at 300°C for 15 minutes using a heating program. In constant pressure mode, the head pressure was set to 83kPa and the split ratio to 50:1.) Detector: Agilent Technologies, Inc.'s "Agilent 355 Chemiluminescent Sulfur Detector" (Measurement conditions: Burner temperature 800°C, hydrogen flow rate 40 mL / min, air flow rate 60 mL / min). Carrier gas: Helium Column: Frontier Lab Co., Ltd.'s capillary column "Ultra Alloy+-5 (MS / HT)" (length = 30m, inner diameter = 0.25mm, film thickness = 0.25μm)
[0059] <Abrasion resistance> For each vulcanized rubber composition, the amount of wear was measured using a Lambourne abrasion tester at room temperature, with a load of 1.0 kgf and a slip ratio of 30%. Next, each vulcanized rubber composition was subjected to thermal degradation by heating in an oven at 80°C for two weeks. The amount of wear of the resulting thermally degraded vulcanized rubber composition was then measured using a Lambourne abrasion tester under the same conditions as above. The reciprocal value of the wear amount was expressed as an exponential value, with the value of each vulcanized rubber composition before thermal degradation set to 100 (abrasion resistance performance after thermal degradation).
[0060] [Table 1]
[0061] Table 1 shows that vulcanized rubber compositions to which a vulcanization accelerator and vulcanizing agent have been added show suppressed deterioration in abrasion resistance after thermal degradation. This is because the ratio of the amount of silane coupling agent to rubber components in the unvulcanized rubber composition after thermal degradation to the amount of silane coupling agent to rubber components in the unvulcanized rubber composition before thermal degradation is within a predetermined range. It is thought that when the amount of CA-P bonds in a silica-containing rubber composition increases due to thermal degradation, stress concentration occurs at the interface between silica and rubber components when the rubber deforms, making it more susceptible to fracture.
[0062] Thus, according to the method for measuring the rate of change in the bonding amount of the silane coupling agent of the present invention, it is possible to evaluate the deterioration of the vulcanized rubber composition containing silica at the stage of the unvulcanized rubber composition, and to predict the physical properties of the rubber composition after vulcanization, such as abrasion resistance after thermal degradation. Therefore, the measurement method of the present invention can be a useful method for finding suitable manufacturing conditions that fully bring out the performance of silica.
Claims
1. A method for measuring the rate of change in the amount of bonding between a silane coupling agent and rubber components in an unvulcanized rubber composition before and after thermal degradation, The amount of binding between the silane coupling agent and the rubber component in the unvulcanized rubber composition before thermal degradation is calculated by detecting and quantifying thiophene analogs produced by thermal decomposition of the unvulcanized rubber composition before thermal degradation, which contains rubber components, silica, and a silane coupling agent, but does not contain a vulcanizing agent or vulcanization accelerator. The amount of bonding between the silane coupling agent and the rubber component in the unvulcanized rubber composition after thermal degradation is calculated by detecting and quantifying thiophene analogs produced by thermally decomposing the unvulcanized rubber composition obtained after thermal degradation of the unvulcanized rubber composition before thermal degradation.
2. The measurement method according to claim 1, wherein the quantification of the thiophene analog includes the step of analyzing the unvulcanized rubber composition before thermal degradation and the unvulcanized rubber composition after thermal degradation by pyrolysis gas chromatography, and calculating the peak area of the peak derived from the thiophene analog in the obtained chromatogram.
3. The measurement method according to claim 1 or 2, wherein thermal decomposition is carried out under conditions of 450 to 700°C, and thiophene analogs are detected by a sulfur detector.
4. The measurement method according to claim 1 or 2, wherein the thiophene analog is thiophene, 2-methylthiophene, and 3-methylthiophene.
5. A method for producing a vulcanized rubber composition, The process includes adding a vulcanization accelerator and a vulcanizing agent to an unvulcanized rubber composition containing rubber components, silica, and a silane coupling agent, but not containing a vulcanizing agent or vulcanization accelerator, and then vulcanizing it. The ratio of the amount of silane coupling agent to rubber component in the unvulcanized rubber composition after thermal degradation to the amount of silane coupling agent to rubber component in the unvulcanized rubber composition measured by the method described in claim 1 or 2 is 0.50 to 1.
15. A method for producing a vulcanized rubber composition, wherein the thermal degradation of the unvulcanized rubber composition is carried out by heating it at 80°C for two weeks.
6. A method for producing a tire using a vulcanized rubber composition produced by the manufacturing method described in claim 5.
7. A method for evaluating the abrasion resistance of a vulcanized rubber composition obtained by adding a vulcanization accelerator and a vulcanizing agent to an unvulcanized rubber composition and vulcanizing agent, based on the rate of change in the amount of bonding between a silane coupling agent and a rubber component in an unvulcanized rubber composition before and after thermal degradation, as measured by the method described in claim 1 or 2.