Patent Application
20240425671
The present invention relates to a compounding agent for rubber, a rubber composition containing the compounding agent for rubber, and a tire.
In recent years, rubber compositions used for rubber products such as tires are required to have improved fracture properties in order to improve durability.
In order to solve such a problem, JP2005-507966A describes a rubber composition containing, for example, a long chain crosslinking agent represented by H(SCH2CH2OCH2CH2S)nH as a rubber composition having excellent abrasion resistance. JP2019-19310A describes a rubber composition containing, for example, a sulfur-containing oligomer having repeating units represented by —(CH2)2O(CH2)2—Sx— as a rubber composition having excellent chipping resistance (elongation at break). However, there is room for improvement in breaking strength.
In view of the above, an object of the invention is to provide a compounding agent for rubber which can improve breaking strength.
The rubber compositions described in JP2005-507966A and JP2019-19310A do not contain an inverse vulcanizate. JP2017-517603A describes an inverse vulcanizate, but does not describe compounding the inverse vulcanizate as a vulcanizing agent in a rubber composition.
The invention includes embodiments to be described below.
According to the embodiments of the invention, the breaking strength of the rubber composition can be improved.
Hereinafter, matters related to embodiments of the invention will be described in detail.
A compounding agent for rubber according to an embodiment includes an inverse vulcanizate containing, as a raw material, a terpene-based compound having a topological polar surface area of 50 Å2 or less. That is, the compounding agent for rubber includes an inverse vulcanizate synthesized from the terpene-based compound as a raw material. In the present specification, the term “inverse vulcanizate” refers to a substance having a structure in which chain sulfur is crosslinked with a small amount of an organic substance, and is different from a substance in which polymer chains of an organic substance are crosslinked with a small amount of sulfur, which is obtained by normal vulcanization.
The inverse vulcanizate is obtained by reacting an organic compound having two or more carbon-carbon double bonds with sulfur. For example, as shown in the following reaction formula, cyclic sulfur is changed into linear chain sulfur by heating. Then, the linear chain sulfur and the organic compound having two or more carbon-carbon double bonds are mixed and reacted to obtain the inverse vulcanizate. This reaction includes a nucleophilic addition reaction of a sulfur radical to a double bond. A temperature condition for mixing the linear chain sulfur and the organic compound is preferably 100° C. or higher, more preferably 120° C. or higher, and still more preferably 140° C. or higher. A catalyst such as a base or a metal salt may be used as necessary.
In the inverse vulcanizate, sulfur chains are split during vulcanization of the rubber composition, and a crosslinked structure containing carbon chains is bonded to polymer chains of a rubber component to form a crosslinked structure. By forming the crosslinked structure containing carbon chains as the crosslinked structure, a crosslinked chain is longer than that of a crosslinked structure composed of only sulfur, which is obtained by normal vulcanization. As a result, it is considered that flexibility and breaking strength of the rubber are improved. In addition, when the rubber composition is stored as an unvulcanized rubber composition, since the inverse vulcanizate is a polymer, it is considered that the inverse vulcanizate has lower migration properties and is less likely to bleed out as compared with sulfur.
In the embodiment, among the inverse vulcanizates, an inverse vulcanizate containing, as a raw material, a terpene-based compound having a topological polar surface area of 50 Å2 or less is used. That is, the inverse vulcanizate is preferably obtained by reacting sulfur with an organic compound containing a terpene-based compound having a topological polar surface area of 50 Å2 or less. It is considered that an inverse vulcanizate having a terpene chemical structure is excellent in dispersibility in the rubber composition because the inverse vulcanizate has good compatibility with a rubber component and a raw material having a low topological polar surface area of 50 Å2 or less and low polarity is used. Therefore, it is considered that crosslinking is made uniform, stress concentration during strain deformation can be prevented, and breaking strength can be further improved. The topological polar surface area is more preferably 30 Å2 or less, still more preferably 25 Å2 or less, and may be 0 Å2.
The topological polar surface area (tPSA) refers to an area of a polar part in a surface of a molecule, and is defined as a total surface sum of all polar atoms (mainly oxygen, nitrogen, and hydrogen bonded thereto). The topological polar surface area is a polarity surface area approximately calculated from only a bonding pattern (topology) of atoms in a molecule without considering a three-dimensional structure of the molecule, and is calculated by a method described in Ertl P. et al., J. Med. Chem, 43 (2000), 3714-3717. Specifically, the topological polar surface area can be calculated by commercially available molecular structural editor software, and in the present specification, a value calculated by ChemBioDraw Ultra (registered trademark) (version 13.0) provided by Revvity Signals Software is used.
The terpene-based compound is a natural compound having isoprene as a constituent unit, and is used as a concept including not only terpene that is a hydrocarbon having isoprene as a constituent unit, but also terpenoid that is a derivative having a functional group such as a carbonyl group or a hydroxy group. The terpene-based compound preferably has two or more carbon-carbon double bonds in the molecule.
Examples of the terpene-based compound having a topological polar surface area of 50 Å2 or less include acyclic monoterpene such as myrcene, citral, nerol, geraniol, geranyl nitrile, citral dimethyl acetal, geranylacetone, and linalool, cyclic monoterpene such as limonene, terpinene, terpinolene, perylaldehyde, phellandrene, dehydroxy linalool oxide, and carvone, sesquiterpene such as farnesene, farnesol, nerolidol, bisabolol, nootkatone, germacrone, caryophyllene, and cadinene, diterpene such as isophytol and geranyl-linalool, triterpene such as squalene and lanosterol, and other terpenes such as solanesol, ionone, and methyl ionone. These terpene-based compounds may be used alone or in combination of two or more kinds thereof.
The terpene-based compound is preferably a compound in which the number of heteroatoms contained in one molecule is 0 or 1. Accordingly, the terpene-based compound has low polarity, and the dispersibility of the inverse vulcanizate in the rubber composition can be improved. Examples of the heteroatom include an oxygen atom, a nitrogen atom, a sulfur atom, a silicon atom, and a phosphorus atom, and preferably an oxygen atom. The oxygen atom may be contained in the molecule of the terpene-based compound as, for example, a hydroxy group or a carbonyl group.
In one embodiment, the terpene-based compound preferably contains at least one (X) selected from the group consisting of limonene, farnesene, farnesol, myrcene, and squalene. More preferably, the terpene-based compound contains at least one (Y) selected from the group consisting of farnesene, farnesol, and myrcene.
The organic compound used as a raw material of the inverse vulcanizate may be only the terpene-based compound, or may use another organic compound having two or more carbon-carbon double bonds together with the terpene-based compound. The other organic compound may have the above heteroatoms, but is preferably a compound having no heteroatom, that is, a hydrocarbon. A boiling point of the other organic compound is not particularly limited, and is preferably 80° C. or higher, more preferably 100° C. or higher, and still more preferably 120° C. or higher. A molecular weight of the other organic compound is not particularly limited, and is preferably 100 to 3000, more preferably 100 to 500, and still more preferably 100 to 300.
Specific examples of the organic compound which may be used in combination with such a terpene-based compound include dicyclopentadiene (DCPD), diisopropenylbenzene (DIB), divinyl benzene (DVB), ethylene glycol dimethacrylate (EGDMA), 1,5,9-cyclododecatriene (CDDT), 5-vinyl-2-norbornene (VNB), 1,2,4-trivinylhexane (TVCH), tetraallyloxyethane, and 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane.
The organic compound used as the raw material of the inverse vulcanizate may be only one having two or more carbon-carbon double bonds, and may be used in combination with an organic compound having one carbon-carbon double bond as long as the effect is not impaired.
In the organic compound used as the raw material of the inverse vulcanizate, a ratio of the terpene-based compound (preferably the (X) and more preferably the (Y)) is preferably 40 mass % to 100 mass %, more preferably 50 mass % to 100 mass %, still more preferably 70 mass % to 100 mass %, and yet still more preferably 90 mass % to 100 mass %, with respect to 100 mass % of the organic compound. A ratio of a component derived from the terpene-based compound (preferably a component derived from the (X), more preferably a component derived from the (Y)) is preferably 40 mass % to 100 mass %, more preferably 50 mass % to 100 mass %, still more preferably 70 mass % to 100 mass %, and yet still more preferably 90 mass % to 100 mass %, with respect to 100 mass % of a component derived from the organic compound in the inverse vulcanizate.
In one embodiment, a sum of an amount of a carbon element and an amount of a sulfur element contained in the inverse vulcanizate (a total content ratio of the carbon element and the sulfur element) is preferably 89 mass % or more. The electronegativity of carbon is 2.55, and the electronegativity of sulfur is 2.58. The electronegativities of both are very close. It is considered that when the carbon element and the sulfur element having very close electronegativities occupy a large amount, the inverse vulcanizate has less polar separation and is more likely to be dispersed in the rubber component having low polarity. Therefore, the breaking strength is further improved. The sum of the amount of the carbon element and the amount of the sulfur element contained in the inverse vulcanizate is more preferably 90 mass % or more, and still more preferably 91 mass % or more. An upper limit of the sum is not particularly limited, and may be, for example, 99 mass % or less, or 98 mass % or less.
In the present specification, contents of the carbon element and the sulfur element are values measured by a combustion method using an organic elemental analyzer, and a detailed measurement method is as described in the column of Examples.
The content ratio of the carbon element in the inverse vulcanizate is not particularly limited, and is preferably 10 mass % to 60 mass %, more preferably 15 mass % to 50 mass %, and still more preferably 20 mass % to 45 mass %. The content ratio of the sulfur element in the inverse vulcanizate is not particularly limited, and is preferably 30 mass % to 89 mass %, more preferably 40 mass % to 84 mass %, and still more preferably 45 mass % to 79 mass %.
A mass ratio (sulfur element/carbon element) of the content ratio of the sulfur element to the carbon element in the inverse vulcanizate is not particularly limited, and is preferably 1.0 to 10, more preferably 1.0 to 5.0, and still more preferably 1.1 to 4.0.
The inverse vulcanizate is preferably in a solid state at a normal temperature of 23° C. When the inverse vulcanizate is in a solid state, it is easy to handle the inverse vulcanizate in the case of preparing the rubber composition. Here, the term “solid state” refers to a state in which the inverse vulcanizate does not have fluidity at a normal temperature of 23° C.
A glass transition point of the inverse vulcanizate is not particularly limited, and is preferably −50° C. to 60° C., more preferably −20° C. to 50° C., still more preferably −10° C. to 45° C., and yet still more preferably 0° C. to 45° C. When the inverse vulcanizate having a glass transition point of 60° C. or lower is used, the inverse vulcanizate is melted when mixed with the rubber composition, and is easily uniformly dispersed in the rubber composition. In this regard, a melting point of sulfur used in normal vulcanization is 112.8° C., which is higher than a temperature at the time of mixing with the rubber composition. Here, the term “glass transition point” is a value measured at a temperature rise rate of 20° C./min (measurement temperature range: −100° C. to 150° C.) by a differential scanning calorimetry (DSC) method in accordance with JIS K7121:2012.
The compounding agent for rubber according to the embodiment may consist of the inverse vulcanizate, or may contain an additive generally compounded in the rubber composition together with the inverse vulcanizate. In one embodiment, the compounding agent for rubber may contain the inverse vulcanizate in an amount of 30 mass % or more, 50 mass % or more, 70 mass % or more, or 100 mass %. The compounding agent for rubber is used as a crosslinking agent (vulcanizing agent) because the inverse vulcanizate forms a crosslinked structure as described above. Therefore, in one embodiment, the compounding agent for rubber is a rubber crosslinking agent (vulcanizing agent).
The rubber composition according to the embodiment contains the compounding agent for rubber. The rubber composition preferably contains a diene rubber as a rubber component together with the compounding agent for rubber.
The diene rubber refers to a rubber having a repeating unit corresponding to a diene monomer having a conjugated double bond, and has a double bond in a polymer main chain. Specific examples of the diene rubber include a natural rubber (NR), an isoprene rubber (IR), a butadiene rubber (BR), a styrene-butadiene rubber (SBR), a nitrile rubber (NBR), a chloroprene rubber (CR), a butyl rubber (IIR), a styrene-isoprene copolymer rubber, a butadiene-isoprene copolymer rubber, and a styrene-isoprene-butadiene copolymer rubber. These diene rubbers may be used alone or in combination of two or more kinds thereof. Among these, the diene rubber is preferably at least one selected from the group consisting of NR, IR, BR, and SBR. Those obtained by modifying a chain-end or a main chain as necessary (for example, a chain-end-modified SBR) or those obtained by modification to impart desired characteristics (for example, a modified NR) are also included in the concept of the diene rubber.
A content of the compounding agent for rubber in the rubber composition, as a content of the inverse vulcanizate, is preferably 0.1 parts by mass to 20 parts by mass, more preferably 0.5 parts by mass to 15 parts by mass, still more preferably 1 part by mass to 10 parts by mass, and yet still more preferably 2 parts by mass to 8 parts by mass, with respect to 100 parts by mass of the diene rubber. In addition, a content of the inverse vulcanizate is, in terms of sulfur, preferably 0.05 parts by mass to 16 parts by mass, more preferably 0.3 parts by mass to 12 parts by mass, still more preferably 0.5 parts by mass to 8 parts by mass, and yet still more preferably 1 part by mass to 5 parts by mass, with respect to 100 parts by mass of the diene rubber.
A reinforcing filler may be compounded in the rubber composition. As the reinforcing filler, carbon black and/or silica is preferably used. That is, the reinforcing filler may be carbon black alone, silica alone, or a combination of carbon black and silica. The reinforcing filler is preferably carbon black alone or a combination of carbon black and silica. A content of the reinforcing filler is not particularly limited, and may be, for example, 10 parts by mass to 140 parts by mass, 20 parts by mass to 100 parts by mass, or 20 parts by mass to 80 parts by mass, with respect to 100 parts by mass of the diene rubber.
The carbon black is not particularly limited, and various known products can be used. When the carbon black is compounded, the content thereof may be, for example, 5 parts by mass to 100 parts by mass, or 20 parts by mass to 80 parts by mass, with respect to 100 parts by mass of the diene rubber.
The silica is also not particularly limited, and wet silica such as wet-precipitated silica or wet-gelled silica is preferably used. When the silica is compounded, the content thereof may be, for example, 5 parts by mass to 40 parts by mass, or 5 parts by mass to 30 parts by mass, with respect to 100 parts by mass of the diene rubber.
In addition to the components described above, various additives generally used in the rubber composition, such as a silane coupling agent, zinc oxide, stearic acid, an antioxidant, a wax, an oil, and a vulcanization accelerator, can be compounded in the rubber composition according to the embodiment.
In the rubber composition, sulfur may be compounded in addition to the inverse vulcanizate as the vulcanizing agent (crosslinking agent), or may not be compounded. When the inverse vulcanizate and the sulfur are used in combination, a content of the vulcanizing agent (a total amount of the inverse vulcanizate and the sulfur) is not particularly limited, and is preferably 0.1 parts by mass to 20 parts by mass, and more preferably 0.5 parts by mass to 10 parts by mass, with respect to 100 parts by mass of the diene rubber.
Examples of the vulcanization accelerator include various vulcanization accelerators such as sulfenamide-based, thiuram-based, thiazole-based, and guanidine-based vulcanization accelerators, which may be used alone or in combination of two or more kinds thereof. A content of the vulcanization accelerator is not particularly limited, and is preferably 0.1 parts by mass to 7 parts by mass, and more preferably 0.5 parts by mass to 5 parts by mass, with respect to 100 parts by mass of the diene rubber.
The rubber composition according to the embodiment can be produced by kneading according to a common method by using a mixer such as a Banbury mixer, a kneader, or a roll that is normally used. That is, for example, in a first mixing stage, additives excluding the vulcanizing agent (including the inverse vulcanizate) and the vulcanization accelerator are added to and mixed with the diene rubber. Next, in a final mixing stage, the vulcanizing agent (including the inverse vulcanizate) and the vulcanization accelerator are added to and mixed with the obtained mixture, and thus a rubber composition can be prepared.
The rubber composition thus obtained can be used for various rubber products such as a tire, a rubber vibration insulator, and a conveyor belt. When the rubber composition is used in a tire, the rubber composition can be used as a tread rubber or a side wall rubber of a pneumatic tire of various applications and various sizes, such as a passenger car tire and a large tire of a truck or a bus (heavy duty tire).
The rubber composition is molded into a predetermined shape by a common method, for example, by extrusion, and becomes a vulcanized rubber by heating and vulcanizing. When the rubber composition is used for a tire, the rubber composition is molded into a predetermined shape by extrusion or the like, and is combined with other parts to produce a green tire. Thereafter, a tire can be manufactured by vulcanization molding the green tire at, for example, 130° C. to 190° C.
Hereinafter, Examples of the invention will be illustrated, but the invention is not limited to these Examples.
A topological polar surface area (tPSA) of an organic compound used as a raw material in the following Synthesis Examples A to His as follows.
For inverse vulcanizates A to H synthesized in Synthesis Examples A to H, contents of a carbon element and a sulfur element were measured by a combustion method using an organic elemental analyzer. For the measurement, an organic elemental analyzer “vario MACRO cube” (manufactured by Elementar Japan) was used. The measurement conditions were as follows: gas: helium, oxygen; standard substance: sulfanilamide; combustion tube temperature: 1150° C.; and reduction tube temperature: 850° C.
To a glass container, 2.5 g of sulfur was added and stirred at 165° C. for 15 minutes. After it was confirmed that the sulfur was dissolved, 0.5 g of dicyclopentadiene and 2.0 g of (+)-limonene were added, and the mixture was further stirred at 165° C. for 30 minutes. After it was confirmed that a color of the solution was changed, the solution was poured into a silicon mold. Thereafter, the solution was heated in an oven at 140° C. for 16 hours to obtain an inverse vulcanizate A. The obtained inverse vulcanizate A was subjected to elementary analysis. As a result, a carbon content was 31 mass %, a sulfur content was 66 mass %, and a sum thereof was 96 mass %. A glass transition point of the inverse vulcanizate A was 29° C.
To a glass container, 4.0 g of sulfur was added and stirred at 165° C. for 15 minutes. After it was confirmed that the sulfur was dissolved, 0.5 g of dicyclopentadiene and 0.5 g of (+)-limonene were added, and the mixture was further stirred at 165° C. for 30 minutes. After it was confirmed that a color of the solution was changed, the solution was poured into a silicon mold. Thereafter, the solution was heated in an oven at 140° C. for 16 hours to obtain an inverse vulcanizate B. The obtained inverse vulcanizate B was subjected to elementary analysis. As a result, a carbon content was 22 mass %, a sulfur content was 76 mass %, and a sum thereof was 97 mass %. A glass transition point of the inverse vulcanizate B was 17° C.
To a glass container, 4.0 g of sulfur was added and stirred at 175° C. for 15 minutes. After it was confirmed that the sulfur was dissolved, 2.5 g of trans-β-farnesene was added, and the mixture was further stirred at 175° C. for 60 minutes. After it was confirmed that a color of the solution was changed, the solution was poured into a silicon mold. Thereafter, the solution was heated in an oven at 140° C. for 16 hours to obtain an inverse vulcanizate C. The obtained inverse vulcanizate C was subjected to elementary analysis. As a result, a carbon content was 42 mass %, a sulfur content was 50 mass %, and a sum thereof was 92 mass %. A glass transition point of the inverse vulcanizate C was 16° C.
To a glass container, 4.0 g of sulfur was added and stirred at 175° C. for 15 minutes. After it was confirmed that the sulfur was dissolved, 2.5 g of farnesol was added, and the mixture was further stirred at 175° C. for 60 minutes. After it was confirmed that a color of the solution was changed, the solution was poured into a silicon mold. Thereafter, the solution was heated in an oven at 140° C. for 16 hours to obtain an inverse vulcanizate D. The obtained inverse vulcanizate D was subjected to elementary analysis. As a result, a carbon content was 38 mass %, a sulfur content was 53 mass %, and a sum thereof was 91 mass %. A glass transition point of the inverse vulcanizate D was 21° C.
To a glass container, 2.5 g of sulfur was added and stirred at 175° C. for 15 minutes. After it was confirmed that the sulfur was dissolved, 2.5 g of myrcene was added, and the mixture was further stirred at 175° C. for 60 minutes. After it was confirmed that a color of the solution was changed, the solution was poured into a silicon mold. Thereafter, the solution was heated in an oven at 140° C. for 16 hours to obtain an inverse vulcanizate E. The obtained inverse vulcanizate E was subjected to elementary analysis. As a result, a carbon content was 39 mass %, a sulfur content was 54 mass %, and a sum thereof was 92 mass %. A glass transition point of the inverse vulcanizate E was 0° C.
To a glass container, 3.0 g of sulfur was added and stirred at 165° C. for 15 minutes. After it was confirmed that the sulfur was dissolved, 2.0 g of squalene was added, and the mixture was further stirred at 165° C. for 45 minutes. After it was confirmed that a color of the solution was changed, the solution was poured into a silicon mold. Thereafter, the solution was heated in an oven at 140° C. for 16 hours to obtain an inverse vulcanizate F. The obtained inverse vulcanizate F was subjected to elementary analysis. As a result, a carbon content was 31 mass %, a sulfur content was 64 mass %, and a sum thereof was 95 mass %. A glass transition point of the inverse vulcanizate F was 35° C.
To a glass container, 4.0 g of sulfur was added and stirred at 165° C. for 15 minutes. After it was confirmed that the sulfur was dissolved, 1.5 g of ethylene glycol dimethacrylate and 1.0 g of dicyclopentadiene were added, and the mixture was further stirred at 165° C. for 30 minutes. After it was confirmed that a color of the solution was changed, the solution was poured into a silicon mold. Thereafter, the solution was heated in an oven at 140° C. for 16 hours to obtain an inverse vulcanizate G. The obtained inverse vulcanizate G was subjected to elementary analysis. As a result, a carbon content was 32 mass %, a sulfur content was 56 mass %, and a sum thereof was 88 mass %.
To a glass container, 4.0 g of sulfur was added and stirred at 120° C. for 15 minutes. After it was confirmed that the sulfur was dissolved, 2.5 g of divinyl benzene (isomer mixture) was added, and the mixture was further stirred at 120° C. for 30 minutes. After it was confirmed that a color of the solution was changed, the solution was poured into a silicon mold. Thereafter, the solution was heated in an oven at 120° C. for 48 hours to obtain an inverse vulcanizate H. The obtained inverse vulcanizate H was subjected to elementary analysis. As a result, a carbon content was 12 mass %, a sulfur content was 86 mass %, and a sum thereof was 98 mass %.
First, compounding ingredients excluding a vulcanizing agent (including an inverse vulcanizate) and a vulcanization accelerator were added to a diene rubber in a first mixing stage in accordance with the formulations (part by mass) illustrated in Table 1 below by using an internal mixer and kneading was performed (discharge temperature=160° C.). Next, the vulcanizing agent and the vulcanization accelerator were added to the obtained kneaded material in a final mixing stage and kneading was performed (discharge temperature=90° C.) to produce a rubber composition. Details of each component in Table 1 are as follows.
Each of the obtained rubber compositions was vulcanized at 160° C. under pressure using a metal plate as a mold to prepare a vulcanized rubber sample. At this time, for a vulcanization time, 90% vulcanization time (t90) measured in advance in accordance with JISK6300-2:2001 was applied to each rubber composition.
The obtained vulcanized rubber sample was subjected to a tensile test in accordance with the following method to evaluate fracture properties.
The results are as shown in Table 1. In Examples 1 to 7 in which the inverse vulcanizates A to F synthesized by using a terpene-based compound having a small topological polar surface area as a raw material were compounded as vulcanizing agents, both the tensile strength at break and the elongation at break were large and the breaking strength was excellent as compared with Comparative Example 1 in which the sulfur was used as a vulcanizing agent. In Example 8, the breaking strength was excellent as compared with Comparative Example 4.
In contrast, in Comparative Example 2 in which the inverse vulcanizate G synthesized by using an organic compound having a large topological polar surface area as a raw material was compounded, the elongation at break was excellent, but the tensile strength at break was greatly reduced and the breaking strength was poor as compared with Comparative Example 1. In addition, in Comparative Example 3 in which the inverse vulcanizate H obtained by using an organic compound other than a terpene-based compound having a small topological polar surface area as a raw material was compounded, the tensile strength at break was excellent, but the elongation at break was poor.
In various numerical ranges described in the specification, upper limit values and lower limit values thereof can be freely combined, and all combinations thereof are described in the present specification as preferable numerical ranges. In addition, the description of the numerical range of “X to Y” means X or more and Y or less.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-097957 | Jun 2023 | JP | national |
