JP7523313B2 - Rubber composition and tire - Google Patents

Description

The present invention relates to a rubber composition and a tire.

When vulcanizing a rubber composition to manufacture rubber products such as tires, if the vulcanization time is too long, reversion (reversion) due to over-vulcanization occurs, and the physical properties of the rubber product deteriorate. In particular, reversion (reversion) due to over-vulcanization is likely to occur in rubber compositions in which a vulcanization system containing sulfur is blended with isoprene-skeleton rubber such as isoprene rubber (IR) or natural rubber (NR). However, it is difficult to solve the problem of reversion by increasing the amount of sulfur or vulcanization accelerator blended into the rubber composition.

On the other hand, if scorching (scorch, premature vulcanization) occurs before vulcanization in the process of producing a rubber product from the rubber composition, it becomes difficult to produce a product having the desired physical properties, so it is necessary to sufficiently ensure the scorch stability of the rubber composition. Therefore, when considering the suppression of reversion of the rubber composition (improvement of reversion resistance), it is also necessary to pay sufficient attention to ensuring the scorch stability of the rubber composition.
In response to this, for example, Patent Document 1 below discloses a rubber composition obtained by compounding 20 to 150 parts by mass of a reinforcing filler and a compound containing a monovalent functional group having a nitrogen-containing 1,3-dipole with 100 parts by mass of a rubber component consisting of at least one of natural rubber and synthetic rubber, as a technology for achieving both reversion resistance and scorch stability of a rubber composition. However, the rubber composition disclosed in Patent Document 1 does not sufficiently achieve both reversion resistance and scorch stability, and further improvement has been required.

On the other hand, it is possible to suppress reversion to some extent by adding zinc oxide to the rubber composition, but since there is concern about zinc oxide being depleted, an increase in the amount is not preferable.
In response to this, by incorporating a eutectic compound, it is possible to suppress reversion without incorporating additional zinc oxide (see Patent Document 2 below).

JP 2007-70439 A International Publication No. 2019/089788

However, the inventors of the present invention have found that, as described in Patent Document 2, compounding a eutectic compound changes the time until crosslinking begins in the rubber composition (induction time), and if the time until crosslinking begins becomes too short, this can cause scorching before vulcanization.

Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional technology and to provide a rubber composition capable of suppressing reversion while maintaining scorch stability (preventing the occurrence of tanning).
Another object of the present invention is to provide a tire in which deterioration of physical properties caused by scorch (discoloration) and reversion is suppressed.

The gist of the present invention, which solves the above problems, is as follows:

The rubber composition of the present invention is a rubber composition including a rubber component and a eutectic compound,
The eutectic compound includes a hydrogen bond acceptor;
The hydrogen bond acceptor is characterized in that it has an ionic bond energy of 98 kcal/mol or more.
The rubber composition of the present invention can suppress reversion while maintaining scorch stability.

In a preferred embodiment of the rubber composition of the present invention, the eutectic compound is a mixture of the hydrogen bond acceptor and the hydrogen bond donor. In this case, the eutectic compound is easily synthesized.

In another preferred embodiment of the rubber composition of the present invention, the hydrogen bond acceptor is an onium salt. In this case, the eutectic compound is easy to synthesize and obtain, and is inexpensive.

Here, it is preferable that the onium salt is at least one selected from the group consisting of ammonium salts, sulfonium salts, and phosphonium salts. In this case, the eutectic compound is easier to synthesize and obtain, and is inexpensive.

It is further preferred that the onium salt is a quaternary ammonium salt. In this case, the eutectic compound is easier to synthesize and obtain, and is also less expensive.

In the rubber composition of the present invention, it is preferable that the hydrogen bond donor is at least one selected from the group consisting of urea derivatives, alkylene glycols, and carboxylic acids. In this case, the eutectic compound is easy to synthesize and obtain, and is inexpensive.

In another preferred embodiment of the rubber composition of the present invention, the content of the eutectic compound is more than 0.4 parts by mass per 100 parts by mass of the rubber component. In this case, the effect of suppressing reversion of the rubber composition is enhanced.

In another preferred embodiment of the rubber composition of the present invention, the rubber component contains an isoprene skeleton rubber, and the content of the isoprene skeleton rubber is 50 parts by mass or more per 100 parts by mass of the rubber component. In this case, reversion is less likely to occur, and the excellent physical properties of the isoprene skeleton rubber can be maximized.

The rubber composition of the present invention further contains a crosslinking agent and a crosslinking accelerator, and the content of the crosslinking accelerator is preferably more than 2.7 parts by mass per 100 parts by mass of the rubber component. In this case, it is possible to obtain a crosslinked rubber with a high crosslink density (network density) while suppressing reversion.

The rubber composition of the present invention is preferably used for tires. In tire production, problems such as scorch and reversion are likely to occur, but the rubber composition of the present invention can suppress these problems even when used in tires.

The tire of the present invention is characterized by containing the above-mentioned rubber composition. The tire of the present invention is suppressed from deteriorating in physical properties due to scorch or reversion.

According to the present invention, it is possible to provide a rubber composition capable of suppressing reversion while maintaining scorch stability.
Moreover, according to the present invention, it is possible to provide a tire in which deterioration of physical properties caused by scorch and reversion is suppressed.

The rubber composition and tire of the present invention will be described in detail below with reference to examples of the embodiments.

<Rubber Composition>
The rubber composition of the present invention includes a rubber component and a eutectic compound. The eutectic compound of the rubber composition of the present invention includes a hydrogen bond acceptor, and the hydrogen bond acceptor has an ionic bond energy of 98 kcal/mol or more.

Since the rubber composition of the present invention contains a eutectic compound containing a hydrogen bond acceptor, reversion can be suppressed.
On the other hand, during the period until the start of crosslinking of the rubber composition (induction period of the crosslinking reaction), an ionic chemical reaction proceeds (for example, in the case where a crosslinking accelerator is included, an ionic cleavage reaction of the crosslinking accelerator proceeds), and then the crosslinking reaction starts. Here, it is considered that the ionic chemical reaction is promoted by the presence of a hydrogen bond acceptor (ionic compound) contained in the eutectic compound in the rubber composition.
In contrast, in the rubber composition of the present invention, the ionic bond energy of the hydrogen bond acceptor (ionic compound) contained in the eutectic compound is 98 kcal/mol or more, that is, it is strongly ionic bonded, so the degree of ionization (degree of dissociation) between the cation and the anion in the eutectic compound is small, and the contribution to the ionic reaction in the rubber composition is small (for example, when a crosslinking accelerator is included, the contribution to stabilization of the ionic reaction product derived from the crosslinking accelerator is small, so it is considered that it is difficult to promote the ionic cleavage reaction of the crosslinking accelerator). Therefore, in the rubber composition of the present invention, the progress of the ionic chemical reaction in the period until the start of crosslinking is slow, and as a result, the rubber composition of the present invention has a long time until the start of crosslinking and is excellent in scorch stability.
Therefore, the rubber composition of the present invention can suppress reversion while maintaining scorch stability (preventing the occurrence of tanning).

(Rubber component)
The rubber composition of the present invention contains a rubber component, and the rubber component preferably contains a diene rubber. The proportion of the diene rubber in the rubber component is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 100% by mass.

The diene rubber may be natural rubber (NR), synthetic diene rubber, or may contain both. Examples of the synthetic diene rubber include isoprene rubber (IR), styrene-butadiene rubber (SBR), butadiene rubber (BR), styrene-isoprene rubber (SIR), chloroprene rubber (CR), styrene-isoprene-butadiene terpolymer rubber, isoprene-butadiene copolymer rubber, and ethylene-propylene-diene terpolymer rubber. The rubber component may be one type alone or a blend of two or more types. The rubber component may be unmodified or modified.

The rubber component preferably contains an isoprene skeleton rubber. Here, the isoprene skeleton rubber is a rubber composed of isoprene units, specifically, isoprene rubber (IR) and natural rubber (NR). The content of the isoprene skeleton rubber is preferably 50 parts by mass or more, more preferably 80 parts by mass or more, and even more preferably 90 parts by mass or more, and may be 100 parts by mass, per 100 parts by mass of the rubber component. Since isoprene skeleton rubber is prone to reversion, it is possible to make reversion less likely by using it in combination with a eutectic compound while maximizing the excellent physical properties (durability, etc.) of the isoprene skeleton rubber.

(eutectic compound)
The rubber composition of the present invention contains a eutectic compound, which has the effect of suppressing reversion of the rubber composition.
The eutectic compound includes a hydrogen bond acceptor. Here, the eutectic compound is preferably a mixture product of a hydrogen bond acceptor and a hydrogen bond donor. In this case, the eutectic compound can be easily synthesized.

The hydrogen bond acceptor is an ionic compound having an ionic bond energy of 98 kcal/mol or more. If the ionic bond energy of the hydrogen bond acceptor is less than 98 kcal/mol, the time until the start of crosslinking of the rubber composition becomes short, and the scorch stability of the rubber composition deteriorates.
From the viewpoint of ensuring a more appropriate time until the start of crosslinking, the ionic bond energy of the hydrogen bond acceptor is preferably 100 kcal/mol or more and 150 kcal/mol or less.
Here, in the present invention, the ionic bond energy of the hydrogen bond acceptor can be calculated using GaussView 5.0 (Revision 5.0, software manufactured by Gaussian, Inc., USA, product name). Specifically, structure optimization and energy calculation are performed for each chemical structure at the B3LYP/6-31G level. When the energies obtained by the above method for each hydrogen bond acceptor and the cation part and anion part, which are the components, are designated as E1, E2, and E3, respectively, the ionic bond energy E can be calculated by E=E1-E2-E3.

The eutectic compound may be in a liquid state, and when it is in a liquid state, it is also called a eutectic solvent or a deep eutectic solvent (DES), and is in a liquid state at room temperature (23° C.). The eutectic compound does not need to form a eutectic at the temperature of use, but two or more components (eutectic components) are precipitated simultaneously upon cooling to form a eutectic.
In one or more embodiments, a eutectic compound has a lower melting point than each of the compounds that are combined. As a result, a eutectic compound includes a composition formed by combining two or more compounds.
Without wishing to be bound by any particular theory, it is believed that the eutectic components react or interact in other ways to form the complex.
Thus, any reference to a eutectic compound, or eutectic combination, eutectic pair, or eutectic complex includes combinations and reaction products or complexes between the combined components that result in a lower melting point than each of the individual components. For example, in one or more embodiments, a useful eutectic compound (eutectic composition) can be defined by the following formula (1):
Cat ⁺ X ^- zY... (1)

In formula (1), Cat ⁺ is a cation, ^X- is a counter anion (e.g., a Lewis base), Y is a molecule (e.g., a hydrogen bond donor) that interacts with the counter anion, and z refers to the number of Y molecules that interact with the counter anion (e.g., a Lewis base).
Examples of Cat ⁺ include ammonium ion, phosphonium ion, and sulfonium ion.
X ⁻ includes, for example, a halide ion.
Examples of Y include urea derivatives, alkylene glycols, and carboxylic acids.
In one or more embodiments, z is a number that achieves a deep eutectic solvent, and in other embodiments, a number that achieves a complex that has a lower melting point than each of the eutectic components.

In one or more embodiments, useful eutectic compounds include combinations of acids and bases, which may include Lewis acids and bases or Bronsted acids and bases.
In one or more embodiments, useful eutectic compounds include a combination of a quaternary ammonium salt and a metal halide (referred to as a Type I eutectic compound), a combination of a quaternary ammonium salt and a metal halide hydrate (referred to as a Type II eutectic compound), a combination of a quaternary ammonium salt and a hydrogen bond donor (referred to as a Type III eutectic compound), or a combination of a metal halide hydrate and a hydrogen bond donor (referred to as a Type IV eutectic compound).

--Hydrogen bond acceptor--
The hydrogen bond acceptor is preferably an onium salt, since the eutectic compound is easy to synthesize and obtain, and is inexpensive.

Here, the onium salt is preferably at least one selected from the group consisting of ammonium salts, sulfonium salts, and phosphonium salts. In this case, the eutectic compound is easier to synthesize and obtain, and is inexpensive.

Among the onium salts, quaternary ammonium salts are particularly preferred. In this case, the eutectic compound is easier to synthesize and obtain, and is also less expensive.

In one or more embodiments, the quaternary ammonium salt is a solid at 20°C.
In these or other embodiments, the metal halide and the hydrogen bond donor are solids at 20°C.

In one or more embodiments, useful quaternary ammonium salts (which may also be referred to as "ammonium compounds") can be defined by formula (2):
(R ¹ ) (R ² ) (R ³ ) (R ⁴ )-N ⁺ -Φ ^-... (2)

In formula (2), each of R ¹ , R ² , R ³ , and R ⁴ is individually hydrogen or a monovalent organic group, or two of R ¹ , R ² , R ³ , and R ⁴ combine to form a divalent organic group, and Φ is a counter anion.
In one or more embodiments, at least one of R ¹ , R ² , R ³ , and R ⁴ , in other embodiments, at least two of R ¹ , R ² , R ³ , and R ⁴ , and in still other embodiments, at least three of R ¹ , R ² , R ³ , and R ⁴ , are not hydrogen.

In one or more embodiments, the counter anion (e.g., Φ ⁻ ) is selected from the group consisting of halide (X ⁻ ), nitrate (NO ₃ ⁻ ), tetrafluoroborate (BF ₄ ⁻ ), perchlorate (ClO ₄ ⁻ ), triflate (SO ₃ CF ₃ ⁻ ), trifluoroacetate (COOCF ₃ ⁻ ).
In one or more embodiments, Φ ^{1 -} is a halide ion (such as a chloride ion, a bromide ion, etc.), and in certain embodiments, Φ ^{1 -} is a chloride ion.

In one or more embodiments, the monovalent organic group comprises a hydrocarbyl group and the divalent organic group comprises a hydrocarbylene group.
In one or more embodiments, the monovalent and divalent organic groups contain heteroatoms (such as, but not limited to, oxygen and nitrogen, and/or halogen atoms).
Thus, monovalent organic groups include alkoxy, siloxy, ether, and ester groups, as well as carbonyl or acetyl substituents.
In one or more embodiments, the hydrocarbyl and hydrocarbylene groups contain from 1 (or an appropriate minimum number) to about 18 carbon atoms, in other embodiments from 1 to about 12 carbon atoms, and in other embodiments from 1 to about 6 carbon atoms. The hydrocarbyl and hydrocarbylene groups may be branched, cyclic, or linear. Typical types of hydrocarbyl groups include alkyl groups, cycloalkyl groups, aryl groups, alkylaryl groups, and the like. Typical types of hydrocarbylene groups include alkylene groups, cycloalkylene groups, arylene groups, alkylarylene groups, and the like.
In certain embodiments, the hydrocarbyl groups are selected from the group consisting of methyl, ethyl, butyl, propyl, octadecyl, phenyl, and benzyl groups.
In certain embodiments, the hydrocarbyl group is a methyl group and the hydrocarbylene group is an ethylene or propylene group.

Useful classes of ammonium compounds include secondary ammonium compounds, tertiary ammonium compounds, and quaternary ammonium compounds. In these or other embodiments, the ammonium compounds include, but are not limited to, ammonium halides, such as ammonium chloride.
In certain embodiments, the ammonium compound is a quaternary ammonium chloride.
In certain embodiments, R ¹ , R ² , R ³ , and R ⁴ are hydrogen and the ammonium compound is ammonium chloride.
In one or more embodiments, the ammonium compound is asymmetric.

In one or more embodiments, the ammonium compound includes a hydroxy group and can be defined by formula (3):
(R ¹ )(R ² )(R ³ )-N ⁺ -(R ⁴ -OH)Φ ^-... (3)

In formula (3), each R ¹ , R ² , and R ³ is individually hydrogen or a monovalent organic group, or two of R ¹ , R ² , and R ³ combine to form a divalent organic group, R ⁴ is a divalent organic group, and Φ ⁻ is a counter anion.
In one or more embodiments, at least one of R ¹ , R ² , and R ³ , in other embodiments at least two of R ¹ , R ² , and R ³ , and in yet other embodiments at least three of R ¹ , R ² , and R ³ are not hydrogen.

An example of an ammonium compound defined by formula (3) is trimethyl(hydroxymethyl)ammonium chloride.

In one or more embodiments, the ammonium compound includes a halogen-containing substituent and can be defined by formula (4):
Φ ^- - (R ¹ ) (R ² ) (R ³ ) -N ⁺ -R ⁴ X ... (4)

In formula (4), R ¹ , R ² , and R ³ are each hydrogen or a monovalent organic group, or when two of R ¹ , R ² , and R ³ are bonded to form a divalent organic group, R ⁴ is a divalent organic group, X is a halogen atom, and Φ ⁻ is a counter anion.
In one or more embodiments, at least one of R ¹ , R ² , and R ³ , in other embodiments at least two of R ¹ , R ² , and R ³ , and in yet other embodiments at least three of R ¹ , R ² , and R ³ are not hydrogen.
In one or more embodiments, X is chlorine.

An example of an ammonium compound defined by formula (4) is trimethyl(chloromethyl)ammonium chloride.

Specific examples of the ammonium salt include tetramethylammonium chloride, triethylmethylammonium chloride, glycidyltrimethylammonium chloride, tetramethylammonium bromide, tetraethylammonium bromide, glycidyltrimethylammonium bromide, etc., with tetramethylammonium chloride being particularly preferred.

The sulfonium salt is preferably a tertiary sulfonium salt. Specific examples of the sulfonium salt include trimethylsulfonium chloride, triethylsulfonium chloride, diethylmethylsulfonium chloride, trimethylsulfonium bromide, triethylsulfonium bromide, and diethylmethylsulfonium bromide.

The phosphonium salt is preferably a quaternary phosphonium salt. Specific examples of the phosphonium salt include tetramethylphosphonium chloride, tetramethylphosphonium bromide, and triethylmethylphosphonium bromide.

--Hydrogen bond donor--
The hydrogen bond donors (HBD compounds) include, but are not limited to, amines, amides, carboxylic acids, alcohols, and the like.
In one or more embodiments, the hydrogen bond donor comprises a hydrocarbon chain moiety, which in one embodiment comprises at least 2, in another embodiment at least 3, and in another embodiment at least 5 carbon atoms, and in one embodiment comprises less than 30, in another embodiment less than 20, and in yet another embodiment less than 10 carbon atoms.

In one or more embodiments, useful amines include compounds defined by formula (a):
R ¹ -(CH ₂ ) _x -R ² ... (a)

In formula (a), R ¹ and R ² are -NH ₂ , -NHR ³ , or -NR ³ R ⁴ , and x is an integer of at least 2.
Here, ^R3 and ^R4 include the monovalent organic groups described above, and an alkyl group is preferable.
In one or more embodiments, x is from 2 to about 10, in other embodiments from about 2 to about 8, and in yet other embodiments from about 2 to about 6.

Specific examples of useful amines include aliphatic amines, ethylenediamine, diethylenetriamine, aminoethylpiperazine, triethylenetetramine, tris(2-aminoethyl)amine, N,N'-bis(2-aminoethyl)piperazine, piperazineethylenediamine, tetraethylenepentamine, propyleneamine, aniline, substituted anilines, and combinations thereof.

In one or more embodiments, useful amides include compounds defined by formula (b):
R-CO- _NH2 ... (b)

In formula (b), R is H, _NH2 , _CH3 or _CF3 .

Specific examples of useful amides include, but are not limited to, urea, 1-methylurea, 1,1-dimethylurea, 1,3-dimethylurea, thiourea, benzamide, acetamide, and combinations thereof.

In one or more embodiments, useful carboxylic acids include mono-, di-, and tri-functional organic acids. These organic acids can include alkyl acids, aryl acids, and mixed alkyl-aryl acids.
Specific examples of monofunctional carboxylic acids include, but are not limited to, aliphatic acids, phenylpropionic acid, phenylacetic acid, benzoic acid, and combinations thereof.
Specific examples of difunctional carboxylic acids include, but are not limited to, oxalic acid, malonic acid, adipic acid, succinic acid, and combinations thereof.
Specific examples of trifunctional carboxylic acids include, but are not limited to, citric acid, tricarballylic acid, and combinations thereof.

Types of alcohols include, but are not limited to, monols, diols, and triols.
Specific examples of mono-ols include aliphatic alcohols, phenols, substituted phenols, and mixtures thereof.
Specific examples of diols include ethylene glycol, propylene glycol, resorcinol, substituted resorcinols, and mixtures thereof.
Specific examples of triols include glycerol, benzenetriol, and mixtures thereof.

The hydrogen bond donor is preferably at least one selected from the group consisting of urea derivatives, alkylene glycols, and carboxylic acids. In this case, the eutectic compound is easy to synthesize and obtain, and is inexpensive.

The urea derivative includes a compound defined by the following formula (c):
R ₂ N-CX-NR ₂ ... (c)

In formula (c), R is H or a monovalent organic group, and X is O (oxygen atom) or S (sulfur atom). As the monovalent organic group, a monovalent hydrocarbon group which may have a heteroatom is preferable.

Specific examples of urea derivatives include, but are not limited to, urea, 1-methylurea, 1,1-dimethylurea, 1,3-dimethylurea, thiourea, and combinations thereof.

As the alkylene glycol, ethylene glycol having 2 carbon atoms, propylene glycol having 3 carbon atoms, and butylene glycol having 4 carbon atoms are preferred, and ethylene glycol is particularly preferred.

Preferred carboxylic acids include phenylpropionic acid, phenylacetic acid, benzoic acid, oxalic acid, malonic acid, adipic acid, succinic acid, citric acid, and tricarballylic acid.

--Metal halides--
Types of metal halides include, but are not limited to, chlorides, bromides, iodides, and fluorides.
In one or more embodiments, these metal halides include, but are not limited to, transition metal halides.
Those skilled in the art can easily envision the corresponding metal halide hydrates.

Specific examples of useful metal halides include, but are not limited to, aluminum chloride, aluminum bromide, aluminum iodide, zinc chloride, zinc bromide, zinc iodide, tin chloride, tin bromide, tin iodide, iron chloride, iron bromide, iron iodide, and combinations thereof.
Those skilled in the art can easily envision the corresponding metal halide hydrates.
For example, aluminum chloride hexahydrate and copper chloride dihydrate represent the above halides.
In addition, metal halides in combination with quaternary ammonium salts form Type I eutectic compounds, metal halide hydrates in combination with quaternary ammonium salts form Type II eutectic compounds, and metal halide hydrates in combination with hydrogen bond donors form Type IV eutectic compounds.

--Preparation of eutectic compound--
One skilled in the art can select appropriate eutectic raw materials in appropriate molar ratios to provide a eutectic composition of the desired eutectic compound.
One of ordinary skill in the art will understand that the molar ratio of the first compound of the pair (eg, Lewis base) to the second compound of the pair (eg, Lewis acid) will vary based on the compounds selected.
The melting point of the eutectic compound lies between the melting points of the two constituent components, and the melting point of the eutectic compound is determined depending on the molar ratio.
However, the molar ratio of the first compound to the second compound can be varied to result in a suppression of the melting point of the eutectic solvent relative to the individual melting points of the first and second compounds that is nevertheless not a minimum melting point.
Thus, the practice of one or more embodiments of the present invention involves forming a eutectic solvent at a molar ratio outside the eutectic point.

In the eutectic compounds, the compounds of the eutectic pair and the molar ratio of the first compound to the second compound of the pair are selected to produce a mixture having a melting point less than 130°C in one or more embodiments, less than 110°C in other embodiments, less than 100°C in other embodiments, less than 80°C in other embodiments, less than 60°C in other embodiments, less than 40°C in other embodiments, and less than 30°C in yet other embodiments.
Additionally, the compounds of the eutectic pair, as well as the molar ratios of the compounds, are selected to produce mixtures that, in these or other embodiments, have a melting point greater than 0°C, in other embodiments greater than 10°C, in other embodiments greater than 20°C, in other embodiments greater than 30°C, and in yet other embodiments greater than 40°C.

In the eutectic compound, the molar ratios of the compounds of the eutectic pair, as well as the second compound of the first compound pair, are selected in one or more embodiments to result in a eutectic solvent that has the capacity or ability to dissolve the desired metal compound, which may be referred to as solubility or dissolving power.
As will be appreciated by those skilled in the art, this solubility can be quantified based on the mass of metal compound dissolved in a given mass of eutectic solvent when a saturated solution is prepared at a particular temperature and pressure for a particular time.
The eutectic solvent is selected to achieve a solubility of zinc oxide of greater than 100 ppm in one or more embodiments, greater than 500 ppm in other embodiments, greater than 1000 ppm in other embodiments, greater than 1200 ppm in other embodiments, greater than 1400 ppm in other embodiments, and greater than 1600 ppm in still other embodiments, at 50° C. under atmospheric pressure for 24 hours, where ppm is measured on a mass solute to mass solvent basis.

In one or more embodiments, the eutectic compound is formed by combining a first compound with a second compound in an appropriate molar ratio to provide a solvent composition (i.e., a liquid composition at a desired temperature).
The eutectic mixture can be mechanically agitated by using a variety of techniques, including, but not limited to, solid state mixing or blending techniques.
Generally speaking, the eutectic mixture to form the eutectic compound is mixed or otherwise agitated until a visually homogenous liquid is formed.
The eutectic mixture may also be formed at elevated temperatures. For example, the eutectic compound may be formed by heating the eutectic mixture to a temperature greater than 50° C. in one embodiment, greater than 70° C. in another embodiment, and greater than 90° C. in another embodiment.
Mixing can be continued while the eutectic mixture is heated. Once the desired mixture is formed, the eutectic solvent can be cooled to room temperature.
In one or more embodiments, the cooling of the eutectic mixture can be done at a controlled rate, such as a rate of less than 1° C./min.

In one or more embodiments, useful eutectic compounds may be commercially available. For example, deep eutectic solvents are available from Scionix under the trade name "Ionic Liquids."
Useful eutectic compounds are also generally known as described in U.S. Patent Publications U.S. 2004/0097755 A1 and U.S. 2011/0207633 A1, both of which are incorporated herein by reference.

In the eutectic compound, a combination of a quaternary ammonium salt and a hydrogen bond donor is preferred, and the molar ratio (quaternary ammonium salt/hydrogen bond donor) is preferably 1/100 to 10/1, more preferably 1/10 to 5/1, even more preferably 1/5 to 2/1, and particularly preferably 1/5 to 1/1. This is because a eutectic compound is efficiently generated when the molar ratio (quaternary ammonium salt/hydrogen bond donor) is in the range of 1/100 to 10/1. In particular, if the molar ratio is 1/100 or more, the melting point is lower than that of a quaternary ammonium salt, which is preferred, and if it is 10/1 or less, the melting point is lower than that of a hydrogen bond donor, which is preferred. In this case, the temperature of the eutectic mixture of the quaternary ammonium salt and the hydrogen bond donor is set so that a eutectic solvent is generated within a range of preferably 50 to 150°C, more preferably 70 to 120°C.

The amount of the eutectic compound is preferably more than 0.4 parts by mass, more preferably 0.41 parts by mass or more, per 100 parts by mass of the rubber component. When the amount of the eutectic compound is more than 0.4 parts by mass per 100 parts by mass of the rubber component, the effect of suppressing reversion becomes large.
The amount of the eutectic compound is preferably 1.2 parts by mass or less per 100 parts by mass of the rubber component. When the amount of the eutectic compound is 1.2 parts by mass or less per 100 parts by mass of the rubber component, the balance between scorch stability and reversion resistance is further improved.

(Cross-linked system)
The rubber composition of the present invention preferably further contains a crosslinking agent and a crosslinking accelerator. When the rubber composition contains a crosslinking agent and a crosslinking accelerator, the crosslinking rate is improved, the productivity of the rubber composition is improved, and a crosslinked rubber having a high crosslink density is easily obtained.

--Crosslinking agent--
The crosslinking agent has the effect of crosslinking the rubber component, and examples of the crosslinking agent include sulfur-based crosslinking agents and peroxide-based crosslinking agents.

Examples of the sulfur-based crosslinking agent include powdered sulfur, sulfur flowers, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur, and other sulfur-containing compounds such as amine disulfide, polymer polysulfide, sulfur olefin adducts, sulfur chloride, and sulfur dichloride; and insoluble polymeric sulfur. These may be used alone or in combination.

The peroxide-based crosslinking agent may be diacyl peroxides, dialkyl peroxides, hydroperoxides, peroxyketals, alkyl peresters, percarbonates, ketone peroxides, etc. More specifically, preferred examples include perbenzoic acid, benzoyl peroxide, cumene peroxide, dicumyl peroxide, 1,1-bis(1,1-dimethylethylperoxy)cyclohexane, t-butylperoxylaurate, t-butylperoxy-2-ethylhexanate, etc. These may be used alone or in combination.

The content of the crosslinking agent is preferably 0.1 to 15 parts by mass, and more preferably 1 to 10 parts by mass, per 100 parts by mass of the rubber component. By keeping the content of the crosslinking agent within the above range, excellent heat resistance can be obtained without impairing durability such as elongation fatigue properties and energy saving properties.

--Crosslinking accelerator--
The crosslinking accelerator has the effect of accelerating crosslinking by the crosslinking agent. The crosslinking accelerator is likely to generate radicals and cause reversion, but by using the crosslinking accelerator in combination with the eutectic compound, crosslinking (vulcanization) of the rubber composition that is likely to cause reversion can be most efficiently performed.

When a sulfur-based crosslinking agent (vulcanizing agent) is used as the crosslinking agent, it is preferable to use a sulfenamide-based vulcanization accelerator, a guanidine-based vulcanization accelerator, a thiazole-based vulcanization accelerator, a thiuram-based vulcanization accelerator, a dithiocarbamate-based vulcanization accelerator, or the like as the crosslinking accelerator (vulcanization accelerator). Among these, sulfenamide-based vulcanization accelerators are preferred. Specific examples of the sulfenamide-based vulcanization accelerator include N-cyclohexyl-2-benzothiazolylsulfenamide (CZ), N,N-dicyclohexyl-2-benzothiazolylsulfenamide, and N-tert-butyl-2-benzothiazolylsulfenamide (NS).

When using a peroxide-based crosslinking agent as the crosslinking agent, it is preferable to use triallyl cyanurate, trimethylolpropane trimethacrylate, N,N'-m-phenylene bismaleimide, etc. as a crosslinking accelerator.

The content of the crosslinking accelerator is preferably more than 2.7 parts by mass, more preferably 2.8 parts by mass or more, and more preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component. When the content of the crosslinking accelerator is more than 2.7 parts by mass per 100 parts by mass of the rubber component, it is possible to obtain a crosslinked rubber with a high crosslink density (mesh density) while suppressing reversion.

(Other ingredients)
The rubber composition of the present invention may further contain an elastomer component such as a thermoplastic elastomer (TPE). Examples of the thermoplastic elastomer include a styrene-based thermoplastic elastomer (TPS), an olefin-based thermoplastic elastomer (TPO), an amide-based thermoplastic elastomer (TPA), a urethane-based thermoplastic elastomer (TPU), an ester-based thermoplastic elastomer (TPC), and a dynamically crosslinked thermoplastic elastomer (TPV). Among these, a styrene-based thermoplastic elastomer (TPS) is preferred.
Examples of the styrene-based thermoplastic elastomer (TPS) include styrene/butadiene/styrene (SBS) block copolymers, styrene/isoprene/styrene (SIS) block copolymers, styrene/butadiene/isoprene/styrene (SBIS) block copolymers, styrene/butadiene (SB) block copolymers, styrene/isoprene (SI) block copolymers, styrene/butadiene/isoprene (SBI) block copolymers, styrene/ethylene/butylene/styrene (SEBS) block copolymers, styrene/ethylene/propylene/styrene (SEPS) block copolymers, styrene/ethylene/propylene/styrene (SEEPS) block copolymers, styrene/ethylene/butylene (SEB) block copolymers, styrene/ethylene/propylene (SEP) block copolymers, and styrene/ethylene/ethylene/propylene (SEEP) block copolymers.

In addition to the above-mentioned rubber components, eutectic compounds, crosslinking systems (crosslinking agents, crosslinking accelerators), and elastomer components, the rubber composition of the present invention may contain compounding agents that are commonly used in the rubber industry, such as fillers, softeners, fatty acids, antioxidants, zinc oxide (zinc oxide), etc., which may be appropriately selected and compounded within a range that does not impair the purpose of the present invention. Commercially available products can be used as these compounding agents.

Examples of the filler include carbon black, silica, etc. These fillers may be used alone or in combination of two or more.
The amount of the filler is not particularly limited, and is preferably in the range of 10 to 150 parts by mass, and more preferably 20 to 100 parts by mass, per 100 parts by mass of the rubber component.

Examples of the softening agent include aromatic oils, paraffin oils, naphthenic oils, vegetable oils other than castor oil, low PCA oils such as MES, TDAE, and SRAE, and heavy naphthenic oils.
Suitable low PCA oils include a variety of plant-derived oils that can be harvested from vegetables, nuts and seeds.
Examples of plant-derived oils include soybean oil, sunflower oil, safflower oil, corn oil, linseed oil, cottonseed oil, rapeseed oil, cashew oil, sesame oil, camellia oil, jojoba oil, macadamia nut oil, coconut oil, and palm oil.
The content of the softener, relative to 100 parts by mass of the rubber component, is preferably 1 part by mass or more, more preferably 5 parts by mass or more, even more preferably 7 parts by mass or more, and particularly preferably 10 parts by mass or more, and is preferably 35 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 25 parts by mass or less.

Examples of the fatty acid include stearic acid, palmitic acid, arachidic acid, oleic acid, linoleic acid, arachidonic acid, etc. Among these, stearic acid is preferred.
The content of the fatty acid is not particularly limited, and is preferably in the range of 0.1 to 5 parts by mass, and more preferably 1 to 4 parts by mass, per 100 parts by mass of the rubber component.

Examples of the antioxidant include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6C), 2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMDQ), 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (AW), and N,N'-diphenyl-p-phenylenediamine (DPPD).
The content of the antioxidant is not particularly limited, and is preferably in the range of 0.1 to 5 parts by mass, and more preferably 1 to 4 parts by mass, per 100 parts by mass of the rubber component.

The amount of zinc oxide (zinc white) is not particularly limited, but is preferably in the range of 1 to 10 parts by mass, and more preferably 2 to 8 parts by mass, per 100 parts by mass of the rubber component.

(others)
The rubber composition of the present invention can be produced, for example, by mixing and kneading the rubber component with the eutectic compound and various compounding agents appropriately selected as necessary using a Banbury mixer, a roll, or the like, and then heating and extruding the mixture.

The rubber composition of the present invention can be used for various rubber products including tires. In particular, the rubber composition of the present invention is preferable as a rubber composition for tires. Tires are composed of various rubber components, and each component has a different shape, thickness, etc., so it is difficult to give a uniform heat history during vulcanization, which makes it easy for problems such as premature vulcanization and reversion to occur. In contrast, the rubber composition of the present invention has excellent scorch stability and reversion resistance, so that even when applied to tires, premature vulcanization and reversion can be suppressed.

<Tires>
The tire of the present invention is characterized by including the above-mentioned rubber composition. The tire of the present invention is inhibited from deterioration of physical properties due to scorch (discoloration) and reversion.
As described above, a tire is composed of various rubber components, and since each component has a different shape, thickness, etc., it is difficult to impart a uniform thermal history during vulcanization, which makes it prone to problems such as premature vulcanization and reversion. However, when it is desired to adjust the vulcanization time to match other components, the above-mentioned rubber composition of the present invention, which has excellent scorch stability and reversion resistance, can be suitably used.

Preferred embodiments of the tire of the present invention include run-flat tires, retread tires, etc.

Run-flat tires have side reinforcing rubber on the side and are thicker than regular tires, which means that the vulcanization time is likely to be long and the tire surface is prone to reversion. In contrast, the rubber composition of the present invention described above has excellent reversion resistance and is therefore suitable for use in run-flat tires.

In addition, recycled tires are made by removing the tread rubber from used tires, replacing them with new tread rubber, and then vulcanizing the tires. However, the base tire (the tire case) obtained by removing the tread rubber is prone to reversion because it has already been through a vulcanization process. In contrast, the rubber composition of the present invention described above has excellent resistance to reversion, making it suitable for use in base tires (the tire case).

Depending on the type of tire to be applied, the tire of the present invention may be obtained by molding an unvulcanized rubber composition and then vulcanizing it, or by molding a semi-vulcanized rubber that has been subjected to a pre-vulcanization process or the like, and then further vulcanizing it. The tire of the present invention may be a pneumatic tire or a solid tire, but is preferably a pneumatic tire. Here, the gas to be filled into the pneumatic tire may be normal air or air with an adjusted oxygen partial pressure, or an inert gas such as nitrogen, argon, or helium.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

<Preparation of Rubber Composition>
According to the compounding recipe shown in Table 1, isoprene rubber (IR), antioxidant, zinc oxide, fatty acid, and eutectic compound were kneaded in a Banbury mixer operated at 70 RPM (revolutions per minute) and a maximum temperature of 145° C. (first kneading stage).
Next, according to the formulation shown in Table 1, the kneaded product obtained in the first kneading stage, zinc oxide, sulfur, and a crosslinking accelerator were kneaded in a Banbury mixer operated at 70 RPM (revolutions per minute) and at a maximum temperature of 100° C. (second kneading stage).
Thereafter, the kneaded product obtained in the second kneading stage was cooled to room temperature (23° C.) to prepare a rubber composition. The obtained rubber composition was evaluated for the time until the start of crosslinking formation and reversion by the following method.

<Time until the start of crosslinking and method for evaluating reversion>
Using each of the prepared rubber compositions, the 10% vulcanization time {tc(10)} (unit: min), maximum torque time {tc(max)} (unit: min), maximum torque value (Fmax) (unit: dN·m), minimum torque value (Fmin) (unit: dN·m), and torque value (Fx) (unit: dN·m) 8 minutes after the maximum torque time were measured using a curastometer (Toyo Seiki Co., Ltd., "Model RLR-4 Rotary Rheometer") in accordance with JIS K6300-2.
The time until the onset of crosslinking and reversion were defined as follows:
Time to start crosslinking = tc (10)
Reversion = (Fmax - Fx) / (Fmax - Fmin)
The time until the start of crosslinking formation in each example was expressed as an index, with the time until the start of crosslinking formation in Comparative Example 1 being set at 100. A larger index value indicates a longer time until the start of crosslinking formation and better scorch stability.
The reversion of each example was expressed as an index, with the reversion of Comparative Example 1 being set at 100. The smaller the index value, the smaller the reversion (reversion) and the more excellent the reversion resistance.

*1 IR: Isoprene rubber, manufactured by JSR, product name "JSR IR2200"
*2 Antioxidant: N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (antioxidant 6C), manufactured by Sumitomo Chemical Co., Ltd., trade name "Antigen 6C"
*3 Zinc oxide: Zinc oxide, manufactured by Hakusui Tech Co., Ltd., product name "Zinc oxide type 2"
*4 Fatty acid: stearic acid, NOF Corporation, trade name "Kiri Stearic Acid"
*5 Eutectic compound 1: A mixture of hydrogen bond acceptor and hydrogen bond donor prepared by the following method. Ionic bond energy of hydrogen bond acceptor = 97.9 kcal/mol
*6 Eutectic compound 2: A mixture of hydrogen bond acceptor and hydrogen bond donor prepared by the following method. Ionic bond energy of hydrogen bond acceptor = 100.8 kcal/mol
*7 Eutectic compound 3: A mixture of hydrogen bond acceptor and hydrogen bond donor prepared by the following method. Ionic bond energy of hydrogen bond acceptor = 100.8 kcal/mol
*8 Sulfur: Eastman MFG Japan, product name "CRYSTEX HS 0T20"
*9 Crosslinking accelerator: N-tert-butyl-2-benzothiazolylsulfenamide (vulcanization accelerator NS), manufactured by Ouchi Shinko Chemical Industry, product name "Noccela NS-P"

<Method for preparing eutectic compounds 1 to 3>
The hydrogen bond acceptor and the hydrogen bond donor were mixed in the molar ratio shown in Table 2, heated to confirm that they had become a homogeneous liquid, and then cooled to room temperature to prepare a eutectic compound.

From a comparison between Comparative Example 1, Comparative Example 2, and Example 1-2 in Table 1, it can be seen that by compounding a eutectic compound, reversion can be suppressed and the reversion resistance of the rubber composition can be improved.
In addition, a comparison between Comparative Example 2 and Example 1-2 shows that when the ionic bond energy of the hydrogen bond acceptor used in the eutectic compound is 98 kcal/mol or more, the time until the start of crosslinking is extended and the scorch stability of the rubber composition is improved.

The rubber composition of the present invention can be used in a variety of rubber products, including tires.

Claims (8)

A rubber composition comprising a rubber component and a eutectic compound,
The eutectic compound includes a hydrogen bond acceptor;
the eutectic compound is a mixture product of the hydrogen bond acceptor and the hydrogen bond donor;
The hydrogen bond acceptor has an ionic bond energy of 98 kcal/mol or more;
The hydrogen bond acceptor has the following formula (2):
(R ¹ ) (R ² ) (R ³ ) (R ⁴ )-N ⁺ -Φ ^-... (2)
wherein R ¹ , R ² , R ³ , and R ⁴ in formula (2) are each an alkyl group having 1 to 6 carbon atoms, and Φ 1 ^- is a halide ion . The rubber composition according to claim 1 , wherein the quaternary ammonium salt is tetramethylammonium chloride . The rubber composition according to claim 1 or 2 , wherein the hydrogen bond donor is at least one selected from the group consisting of urea derivatives, alkylene glycols, and carboxylic acids. The rubber composition according to any one of claims 1 to 3 , wherein the content of the eutectic compound is more than 0.4 parts by mass based on 100 parts by mass of the rubber component. The rubber component contains an isoprene skeleton rubber,
The rubber composition according to any one of claims 1 to 4 , wherein the amount of the isoprene skeleton rubber is 50 parts by mass or more based on 100 parts by mass of the rubber component. Further, a crosslinking agent and a crosslinking promoter are included,
The rubber composition according to any one of claims 1 to 5 , wherein the content of the crosslinking accelerator is more than 2.7 parts by mass based on 100 parts by mass of the rubber component. The rubber composition according to any one of claims 1 to 6 , which is for use in tires. A tire comprising the rubber composition according to any one of claims 1 to 7 .