JP6460730B2 - Vulcanized rubber composition for tire and pneumatic tire - Google Patents

Description

The present invention relates to a vulcanized rubber composition for tires and a pneumatic tire.

As rubber rubber vulcanization accelerating aids, metal oxides such as zinc oxide and carboxylic acids such as stearic acid are generally used (for example, Patent Document 1). These react with each other in the vulcanization process to form carboxylic acid metal salts. This metal salt of carboxylic acid has the effect of promoting the vulcanization reaction of rubber. However, it has been found that many conventional metal compounds remain unreacted after vulcanization.

There is also known a method in which a carboxylic acid metal salt is directly blended into a rubber blend.

JP 2013-028716 A

As a result of intensive studies by the present inventors, there are many metal oxides that remain unreacted even after vulcanization, because the reaction between the compounded metal oxide and the carboxylic acid is insufficient, and there are many metal oxides in the rubber. This is because the remaining metal oxide becomes the nucleus of the heterogeneous structure of cross-linking, and this non-uniform structure of cross-linking reduces the rubber strength (strength at break, elongation at break).
Furthermore, as a result of intensive studies, when the reaction between the metal oxide and the carboxylic acid occurs in the latter half of the vulcanization process, the diffusion of the carboxylic acid metal salt generated by the reaction does not occur sufficiently, and the carboxylic acid metal around the metal oxide. It was also found that a portion with a high salt concentration was formed, which became the nucleus of the heterogeneous structure of the cross-linking.
On the other hand, a method is known in which a carboxylic acid metal salt itself is blended with rubber. This method can prevent a large amount of undissolved metal oxide and non-uniform concentration of the carboxylic acid metal salt. It was also found that the salt cannot be bonded between members when molding as a tire because the salt has low solubility in rubber and blooms on the rubber surface.
The present invention solves the above-mentioned problems and eliminates the problem of poor adhesion at the time of molding, and the vulcanized rubber composition for tires with reduced non-uniform cross-linking structure, and a pneumatic tire using the rubber composition The purpose is to provide.

As a result of intensive studies based on the above-mentioned knowledge, the present inventor blended a metal oxide and a carboxylic acid into rubber, and left the metal oxide and the carboxylic acid unreacted during kneading, so that the metal carboxylate Suppression of salt formation, and consequently suppression of bleeding of the carboxylic acid metal salt to the rubber surface, and further reaction of 50 mol% or more of the metal oxide within 5 minutes after the start of vulcanization, It has been found that the heterogeneous structure of crosslinking can be reduced by reducing the undissolved residue and ensuring the time for diffusing the metal carboxylate produced by the reaction of the metal oxide.
That is, the present invention includes a kneading step of kneading a rubber component, a metal oxide, and a carboxylic acid to prepare an unvulcanized rubber composition;
A vulcanized rubber composition for a tire obtained by a method comprising a vulcanization step of vulcanizing an unvulcanized rubber composition prepared by the kneading step to prepare a vulcanized rubber composition,
In the kneading step, the metal oxide is substantially unreacted,
In the vulcanization step, the reaction rate of the metal oxide after 5 minutes from the start of vulcanization is 50 mol% or more,
The present invention relates to a vulcanized rubber composition for tires having a volume fraction φc of 2.5% or less at a cross-linked dense portion derived from a non-uniform cross-linking structure.

In the unvulcanized rubber composition, the compounding amount of the metal oxide with respect to 100 parts by mass of the rubber component is preferably 1.5 to 3.0 parts by mass, and the compounding amount of the carboxylic acid is preferably 5.0 to 10 parts by mass. .

The carboxylic acid is preferably a fatty acid.

When the volume fraction φc irradiates the vulcanized rubber composition with X-rays or neutron rays, q represented by the following (formula 3-1) is 10 nm ⁻¹ or less. 1 nm obtained by curve fitting with the following (formula 3-2) to (formula 3-6) to the scattering intensity curve I _(q) obtained by X-ray scattering measurement or neutron scattering measurement. it is preferable that calculated using the number N _c per unit volume of the scatterer having a correlation length .XI _c of ～100Myuemu.

The X-ray scattering measurement is preferably a small-angle X-ray scattering measurement, and the neutron scattering measurement is preferably a small-angle neutron scattering measurement.

The present invention also relates to a pneumatic tire having a vulcanized rubber composition for tires.

The tire vulcanized rubber composition is preferably a tread rubber.

According to the present invention, a rubber component, a metal oxide, and a carboxylic acid are kneaded to prepare an unvulcanized rubber composition, and the unvulcanized rubber composition prepared by the kneading step is added. A vulcanized rubber composition for a tire obtained by a production method including a vulcanization step of vulcanizing to prepare a vulcanized rubber composition, wherein the metal oxide is substantially unreacted in the kneading step, In the vulcanization step, the reaction rate of the metal oxide after 5 minutes from the start of vulcanization is 50 mol% or more, and the volume fraction φc of the cross-linked dense portion derived from the heterogeneous structure of cross-linking is 2.5. % Of the vulcanized rubber composition for tires, the non-uniform structure of cross-linking is reduced without causing the problem of poor adhesion during molding, and good rubber strength (strength at break, strength at break) Elongation) is obtained.

An example of the scattering intensity curve obtained by SANS measurement.

The tire vulcanized rubber composition of the present invention comprises a kneading step of kneading a rubber component, a metal oxide, and a carboxylic acid to prepare an unvulcanized rubber composition, and an unvulcanized prepared by the kneading step. A vulcanized rubber composition for a tire obtained by a production method comprising a vulcanization step of preparing a vulcanized rubber composition by vulcanizing a vulcanized rubber composition, wherein the metal oxide is substantially contained in the kneading step. In the above vulcanization process, the reaction rate of the metal oxide after 5 minutes from the start of vulcanization is 50 mol% or more, and the volume fraction of the cross-linked dense part derived from the heterogeneous structure of the cross-linking The rate φc is 2.5% or less.

Thus, the rubber of the carboxylic acid metal salt is obtained by kneading the metal oxide and the carboxylic acid with the rubber component instead of the carboxylic acid metal salt, and leaving the metal oxide and the carboxylic acid unreacted during the kneading. Bleeding to the surface can be suppressed, ensuring good adhesion during molding, and further, 50 mol% or more of the metal oxide is reacted within 5 minutes after the start of vulcanization, so that the metal oxide remains undissolved. By ensuring the time for diffusing the carboxylic acid metal salt produced by the reaction between the metal oxide and the carboxylic acid into the rubber composition, the cross-linked structure can be made uniform and the heterogeneous structure of the cross-linked can be reduced. Good rubber strength (strength at break, elongation at break) can be obtained.

(Vulcanized rubber composition)
The vulcanized rubber composition for tires of the present invention has a volume fraction φc of 2.5% or less at a cross-linked dense part derived from a non-uniform structure of cross-linking in the vulcanized rubber. Thereby, good rubber strength (strength at break, elongation at break) can be obtained. φc is preferably 2.0% or less, more preferably 1.7% or less, and the lower limit of φc is not particularly limited.

(Calculation method of φc)
Hereinafter, a method for calculating φc will be described. By calculating φc by the following method, the measurement error can be suppressed to be small, and φc can be calculated with high measurement accuracy. Specifically, it can measure by the method as described in the below-mentioned Example.

The calculation of φc is possible by irradiating the vulcanized rubber composition for tire with X-rays or neutron rays and performing X-ray scattering measurement or neutron scattering measurement.

By measuring small-angle X-ray scattering and small-angle neutron scattering of a vulcanized rubber composition for tires, the correlation length ξ of 0.1 nm to 100 μm, which is estimated to correspond to the distance between crosslink points of the polymer, is obtained. By calculating the correlation lengths _{ｂ b} and Ξ _c of 1 nm to 100 μm, which are assumed to be equivalent, and calculating the number N _c per unit volume of scatterers (non-uniform network structure) having this correlation length Ξ _c , φc can be calculated. Thus, by measuring X-ray scattering and neutron scattering, φc of the vulcanized rubber composition for tires can be calculated with high accuracy.

As X-ray scattering measurement, SAXS (Small-angle X-ray Scattering, small angle X-ray scattering (scattering angle: usually 10 degrees or less)) measurement that measures the scattering intensity by irradiating the vulcanized rubber composition for tire with X-ray is suitable. Can be adopted. In small-angle X-ray scattering, the structural information of a substance can be obtained by measuring X-rays that are scattered by irradiating the substance with X-rays and have a small scattering angle. Regular structures such as phase separation structures at the nanometer level can be analyzed.

In order to obtain detailed molecular structure information from the SAXS measurement, it is desirable that an X-ray scattering profile with a high S / N ratio can be measured. Therefore, the X-rays emitted from the synchrotron preferably have a luminance of at least 10 ¹⁰ (photons / s / mrad ² / mm ² /0.1% bw) or more. Note that bw represents the band width of X-rays emitted from the synchrotron. Examples of such synchrotrons include beam lines BL03XU and BL20XU of a large synchrotron radiation facility SPring-8 owned by the High Brightness Optical Science Research Center.

The luminance (photons / s / mrad ² / mm ² /0.1% bw) of the X-ray is preferably 10 ¹⁰ or more, more preferably 10 ¹² or more. Although an upper limit is not specifically limited, It is preferable to use the X-ray intensity below the extent that there is no radiation damage.

Further, the number of photons (photons / s) of the X-ray is preferably 10 ⁷ or more, more preferably 10 ⁹ or more. Although an upper limit is not specifically limited, It is preferable to use the X-ray intensity below the extent that there is no radiation damage.

Moreover, as a neutron scattering measurement, SANS (Small-Angle Neutron Scattering Small Angle Neutron Scattering (scattering angle: usually 10 degrees or less)) measurement in which a vulcanized rubber composition for tires is irradiated with a neutron beam to measure a scattering intensity is suitably employed. it can. In small-angle neutron scattering, the structural information of a substance can be obtained by measuring the neutron beam scattered by irradiating the substance with a neutron beam and having a small scattering angle, and the microphase of the vulcanized rubber composition for tires can be obtained. Analyze ordered structures at the nanometer level, such as separated structures.

In the SANS measurement, a method using a known magnetic structure or deuteration method can be used. When employing the deuteration method, for example, the vulcanized rubber composition for tires is swollen with a deuterated solvent, and the vulcanized rubber composition for tires in an equilibrium state in the deuterium solvent is irradiated with a neutron beam, Scattering intensity can be measured. Here, as the deuterated solvent for swelling the vulcanized rubber composition for tire, deuterated water, deuterated hexane, deuterated toluene, deuterated chloroform, deuterated methanol, deuterated DMSO ((D ₃ C)) ₂ S = O), deuterated tetrahydrofuran, deuterated acetonitrile, deuterated dichloromethane, deuterated benzene, deuterated N, N-dimethylformamide and the like.

Neutron rays used for neutron scattering measurement such as SANS can be obtained by using a beam line SANS-J of the JRR-3 research reactor owned by the Japan Atomic Energy Agency.

Similar to the SAXS measurement, the neutron flux intensity (neutrons / cm ² / s) of the neutron beam is preferably 10 ³ or more, more preferably 10 ⁴ in that a neutron scattering profile having a high S / N ratio can be obtained. That's it. Although an upper limit is not specifically limited, It is preferable to use the neutron flux intensity below the grade which does not have radiation damage.

In the X-ray and neutron scattering measurement, from the point that it is necessary to measure a finer molecular structure of the vulcanized rubber composition for tire, using the X-ray and neutron beam, It is preferable to measure in the region where q is 10 nm ⁻¹ or less. The q (nm ⁻¹ ) region is desirable from the viewpoint that smaller information can be obtained as the numerical value increases. Therefore, the q region is more preferably 20 nm ⁻¹ or less.

X-rays scattered in the SAXS measurement are detected by an X-ray detection device, and an image is generated by an image processing device or the like using X-ray detection data from the X-ray detection device.

Examples of the X-ray detector include a two-dimensional detector (X-ray film, nuclear dry plate, X-ray imaging tube, X-ray fluorescence intensifier tube, X-ray image intensifier, X-ray imaging plate, X-ray CCD. , Amorphous body for X-rays, etc.), a line sensor one-dimensional detector can be used. What is necessary is just to select an X-ray detection apparatus suitably according to the kind, state, etc. of the vulcanized rubber composition for tires to be analyzed.

As the image processing apparatus, an apparatus capable of generating a normal X-ray scattering image based on X-ray detection data obtained by the X-ray detection apparatus can be appropriately used.

The SANS measurement can be measured by the same principle as the SAXS measurement. The scattered neutron beam is detected by the neutron beam detection device, and the image is generated by the image processing device using the neutron beam detection data from the neutron beam detection device. Is done. Here, as described above, as the neutron beam detection device, a known two-dimensional detector, a one-dimensional detector, and an image processing device that can generate a known neutron scattering image can be used. Good.

Next, the analysis method of the scattering intensity curve obtained by X-ray scattering measurement and neutron scattering measurement of the vulcanized rubber composition for tire will be specifically described.
For the vulcanized rubber composition for tires, when carrying out the SAXS measurements and SANS measurements, for example, by analyzing scattering intensity curve obtained in the following manner, scatterers having correlation length .XI _c of 1Nm～100myuemu ( The number _Nc per unit volume of (non-uniform network structure) can be determined.

Curve fitting is performed on the scattering intensity curve I _(q) obtained by SAXS measurement and SANS measurement in FIG. 1 using the following (Formula 3-2) to (Formula 3-6), and the fitting parameter is minimized. Obtained by the square method.

Among the obtained fitting parameters, estimated that the correlation length of 0.1Nm～100myuemu xi] is equivalent to the cross point distance of the polymer, the correlation length .XI _b and .XI _c of 1nm~100μm corresponds uneven network structure size of the polymer Is done. And as described above, by using the number N _c per unit volume scatterers (heterogeneous network structure) having the correlation length .XI _c, by calculating the volume of the scatterer from the density of the heterogeneous structure, the φc It can be calculated. Therefore, X-ray scattering measurement such as SAXS or neutron scattering measurement such as SANS is performed, and _Nc is obtained by curve fitting using (Formula 3-2) to (Formula 3-6), thereby vulcanizing for tires. The φc of the rubber composition can be calculated.

(Method for producing vulcanized rubber composition)
The tire vulcanized rubber composition of the present invention comprises a kneading step of kneading a rubber component, a metal oxide, and a carboxylic acid to prepare an unvulcanized rubber composition, and an unvulcanized prepared by the kneading step. And a vulcanization step of preparing a vulcanized rubber composition by vulcanizing the vulcanized rubber composition. In the rubber composition after vulcanization, the predetermined φc is such that the metal oxide is substantially unreacted in the kneading step, and the reaction of the metal oxide after 5 minutes from the start of vulcanization in the vulcanization step. The rate can be 50 mol% or more, and it can be applied depending on the blending amount of the metal oxide or carboxylic acid, the blending ratio of the carboxylic acid or metal oxide, a predetermined vulcanization temperature, or the like.

Hereinafter, the manufacturing method of the vulcanized rubber composition for tires of this invention is demonstrated.

<Kneading process>
In the kneading step, a rubber component, a metal oxide, and a carboxylic acid are kneaded with a rubber kneader to prepare an unvulcanized rubber composition. The kneading step preferably includes the following base kneading step and finishing kneading step. In addition, as a rubber kneading apparatus, a conventionally well-known thing can be used, For example, closed type equipment, such as a Banbury mixer and a kneader, an open roll, etc. are mentioned. A similar kneader can also be used in the kneading step described below.

<< Base kneading process >>
In the base kneading step, for example, a rubber component, a metal oxide, and a carboxylic acid are kneaded with a rubber kneading apparatus.

In the base kneading step, the kneading temperature is not particularly limited, but is preferably 110 to 180 ° C., more preferably 120 to 160 ° C. from the viewpoint of suppressing deterioration of the compound and more favorably dispersing the compound in the rubber composition. It is. The kneading time is not particularly limited, but is preferably 3 to 7 minutes, more preferably 4 to 5 minutes.

Examples of the rubber component include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), epoxidized natural rubber (ENR), acrylonitrile butadiene rubber (NBR), chloroprene rubber ( CR), butyl rubber (IIR), styrene-isoprene-butadiene copolymer rubber (SIBR), and ethylene-propylene diene rubber (EPDM). These diene rubbers may be used alone or in combination of two or more. Among these, NR and IR are preferable because the predetermined φc can be more suitably obtained.

Examples of the metal oxide include zinc oxide and magnesium oxide. These metal oxides may be used alone or in combination of two or more. Among these, zinc oxide is preferable because it has good reactivity with carboxylic acid, has a strong vulcanization acceleration effect, and can more suitably obtain the predetermined φc.

As carboxylic acid, if it is a compound which has a carboxy group, it will not specifically limit, Acrylic acid, methacrylic acid, a fatty acid, etc. are mentioned. Of these, fatty acids are preferred. Examples of fatty acids include butyric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, pentadecylic acid, margaric acid, behenic acid, lignoceric acid, Saturated fatty acids such as serotic acid, montanic acid, and melicic acid; unsaturated fatty acids such as crotonic acid, myristoleic acid, palmitoleic acid, oleic acid, eicosenoic acid, erucic acid, linoleic acid, linolenic acid, arachidonic acid, vaccenic acid, etc. Is mentioned. These carboxylic acids may be used alone or in combination of two or more. The number of carbon atoms of the fatty acid is preferably 6 to 30, more preferably 8 to 25, and still more preferably 10 to 22, from the reason that the predetermined φc is more suitably obtained.
Among them, saturated fatty acids are preferable, lauric acid, myristic acid, stearic acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, pentadecylic acid, palmitic acid, margaric acid, arachidic acid, behenic acid, lignoceric acid, Serotic acid, montanic acid, and melissic acid are more preferable, lauric acid, myristic acid, and stearic acid are more preferable, and stearic acid is particularly preferable.

In the base kneading step, in addition to the above components, compounding agents conventionally used in the rubber industry, for example, reinforcing fillers such as carbon black and silica, silane coupling agents, antioxidants, ozone deterioration inhibitors such as waxes, etc. An anti-aging agent, a softening agent such as oil, and the like may be kneaded with the above components.

Even if the metal oxide and the carboxylic acid are kneaded in the base kneading step, a carboxylic acid metal salt is usually not generated. Therefore, in order to avoid the problem of poor adhesion during molding, the amount of the carboxylic acid metal salt charged and kneaded in the base kneading step is preferably 0. 1 mass part or less, More preferably, it is 0.05 mass part or less, More preferably, it is 0 mass part.
The reason why the metal oxide and the carboxylic acid do not react in the base kneading step is not clear, but is presumed as follows. The reaction does not proceed even if the metal oxide and the carboxylic acid are mixed in a state where no rubber component is present and the temperature is raised to the same temperature as the kneading temperature. Therefore, the rubber component may have some solvent effect. In the base kneading process, since the rubber component, the metal oxide and the carboxylic acid are not sufficiently mixed, the solvent effect cannot be obtained. As a result, the metal oxide and the carboxylic acid react in the base kneading process. Presumed not to be.

<< Finish kneading process >>
In the finish kneading step, for example, the kneaded material kneaded in the base kneading step, the vulcanizing agent, and the vulcanization accelerator are kneaded with a rubber kneading device to prepare an unvulcanized rubber composition.

In the final kneading step in which the vulcanizing agent and the vulcanization accelerator are kneaded, vulcanization may progress if the kneading temperature increases. In addition, the reaction between the metal oxide and the carboxylic acid may proceed. Therefore, in the final kneading step, the kneading temperature is preferably 110 ° C. or lower, more preferably 100 ° C. or lower, and further preferably 90 ° C. or lower in order to suppress the progress of vulcanization. The lower limit of the kneading temperature is not particularly limited, but is preferably 70 ° C. or higher, more preferably 80 ° C. or higher in order to more suitably disperse the vulcanizing agent and vulcanization accelerator in the rubber composition. The kneading time is not particularly limited, but is preferably 3 to 7 minutes, more preferably 4 to 5 minutes.

As the vulcanizing agent, for example, sulfur, alkylphenol / sulfur chloride condensate, and the like can be suitably used. Of these, sulfur is preferable. Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

Examples of the vulcanization accelerator include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine or aldehyde-ammonia, imidazoline, or xanthate vulcanization accelerators. Etc. These vulcanization accelerators may be used alone or in combination of two or more. Of these, sulfenamide vulcanization accelerators are preferred.

Specific examples of the sulfenamide-based vulcanization accelerator include tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N -Dicyclohexyl-2-benzothiazolylsulfenamide (DCBS), N, N-diisopropyl-2-benzothiazolesulfenamide and the like. Of these, CBS is preferable.

(Unvulcanized rubber composition)
Here, the unvulcanized rubber composition prepared by the kneading step (preferably the base kneading step and the finishing kneading step) will be described.

In the unvulcanized rubber composition, the compounding amount of the metal oxide with respect to 100 parts by mass of the rubber component is preferably 1.5 to 3.0 parts by mass, more preferably 1.5 to 2.5 parts by mass. When the compounding amount of the metal oxide is within the above range, the predetermined φc is more suitably obtained. Further, if it is less than 1.5 parts by mass, good vulcanization behavior cannot be obtained, and rubber strength (strength at break, elongation at break) may be reduced. It is necessary to throw a large amount of carboxylic acid in order to react the carboxylic acid, and the carboxylic acid does not completely dissolve in the rubber but blooms on the rubber surface, which may make adhesion during tire molding difficult.

In the unvulcanized rubber composition, the blending amount of the carboxylic acid with respect to 100 parts by mass of the rubber component is 5.0 to 10 parts by mass, more preferably 5.0 to 8.0 parts by mass. When the blending amount of the carboxylic acid is within the above range, the predetermined φc is more preferably obtained. On the other hand, if the amount is less than 5.0 parts by mass, the blended metal oxide cannot be sufficiently reacted, and a lot of undissolved metal oxide is generated, which may lead to uneven crosslinking. If the amount exceeds 10 parts by mass, the carboxylic acid may not be completely dissolved in the rubber but blooms on the rubber surface, which may make adhesion during tire molding difficult.

In the unvulcanized rubber composition, the blending ratio of the carboxylic acid and the metal oxide (the blending amount of the carboxylic acid (parts by mass) / the blending amount of the metal oxide (parts by mass)) is preferably 3.0 to 7. 0, more preferably 4.8 to 6.8. When the ratio is within the above range, the predetermined φc is more suitably obtained, and better rubber strength (strength at break, elongation at break) is obtained.

In the unvulcanized rubber composition, the compounding amount of the reinforcing filler with respect to 100 parts by mass of the rubber component is preferably 5 to 150 parts by mass, more preferably 10 to 100 parts by mass. When the compounding amount of the reinforcing filler is within the above range, better rubber strength (strength at break, elongation at break) can be obtained.

In the unvulcanized rubber composition, the compounding amount of sulfur with respect to 100 parts by mass of the rubber component is preferably 0.5 to 8 parts by mass, more preferably 0.8 to 3 parts by mass. When the amount of sulfur is within the above range, the predetermined φc is more suitably obtained.

In the unvulcanized rubber composition, the blending amount of the vulcanization accelerator with respect to 100 parts by mass of the rubber component is preferably 0.5 to 5 parts by mass, more preferably 0.8 to 3 parts by mass. When the blending amount of the vulcanization accelerator is within the above range, the predetermined φc is more preferably obtained.

<Vulcanization process>
In the vulcanization step, the vulcanized rubber composition is prepared by vulcanizing the unvulcanized rubber composition prepared in the kneading step.

The vulcanization temperature is preferably 140 ° C. for the reason that the reaction rate of the metal oxide after 5 minutes from the start of vulcanization can be preferably 50 mol% or more, and the predetermined φc can be obtained more suitably. As mentioned above, More preferably, it is 150 degreeC or more, More preferably, it is 155 degreeC or more. Although an upper limit is not specifically limited, Preferably it is 250 degrees C or less, More preferably, it is 200 degrees C or less, More preferably, it is 180 degrees C or less.
The vulcanization time is not particularly limited, but is preferably 10 to 30 minutes, more preferably 15 to 25 minutes, because the predetermined φc can be more suitably obtained.

In the present invention, the metal oxide is substantially unreacted in the kneading step. That is, during the kneading, the reaction between the metal oxide and the carboxylic acid is suppressed, and the metal oxide and the carboxylic acid do not substantially react to form a carboxylic acid metal salt. Bleed to the surface can be suppressed, and good adhesion during molding can be secured.
In the present specification, the fact that the metal oxide is substantially unreacted in the kneading step specifically means that the reaction rate of the metal oxide after completion of the kneading step is preferably 5 mol% or less, More preferably, it is 1 mol% or less, More preferably, it is 0.5 mol% or less, Especially preferably, it is 0.1 mol% or less, Most preferably, it is 0 mol% (unreacted).
In this specification, when a carboxylic acid metal salt is used, the reaction rate of the metal oxide includes, in addition to the actual reaction rate of the metal oxide used, a carboxylic acid metal salt that is added separately. Assuming that the product is a metal oxide, the reaction rate is calculated. That is, the reaction rate of the metal oxide means the content ratio (mol%) of the metal derived from the carboxylic acid metal salt in a total of 100 mol% of the metal derived from the metal oxide and the metal derived from the carboxylic acid metal salt. For example, when only a carboxylic acid metal salt is used without using any metal oxide, the reaction rate of the metal oxide is 100 mol%.

Furthermore, in this invention, in the said vulcanization | cure process, the reaction rate of the metal oxide 5 minutes after a vulcanization start is 50 mol% or more. This reduces the undissolved structure of the cross-linking by reducing the undissolved residue of the metal oxide and ensuring time for diffusing the carboxylic acid metal salt generated by the reaction of the metal oxide and the carboxylic acid into the rubber composition. And good rubber strength (strength at break, elongation at break) can be obtained.
The reaction rate of the metal oxide after 5 minutes from the start of vulcanization is preferably 60 mol% or more, more preferably 70 mol% or more, still more preferably 80 mol% or more, and particularly preferably 90 mol% or more. The upper limit of the reaction rate is not particularly limited, and may be 100 mol%.
In the present specification, the start of vulcanization, that is, the vulcanization time of 0 minutes means the moment when unvulcanized rubber is put into the vulcanizer.
In order to make the reaction rate of the metal oxide 5 minutes after the start of vulcanization within the above range, for example, the blending amount of the metal oxide or the blending amount of the carboxylic acid is set to the above amount or the blending of the carboxylic acid and the metal oxide The ratio may be set within the above range, or the vulcanization temperature may be set to the above temperature.

In the present specification, the reaction rate of the metal oxide is calculated by quantifying the metal oxide remaining in the rubber composition. The quantitative determination of the metal oxide can be performed by an X-ray absorption fine structure method (XAFS method), and specifically by the method described in the examples.

Since the X-ray absorption fine structure method (XAFS method) scans with X-ray energy, the light source requires a continuous X-ray generator, and a high S / N ratio and S / B are required to analyze a detailed chemical state. It is necessary to measure the X-ray absorption spectrum of the ratio.
Also, in order to continuously measure the X-ray scattering method (SAXS method) and the X-ray absorption fine structure method (XAFS method), it is necessary to shorten the measurement time required for one cycle. The measurement requires high-intensity X-rays emitted from a synchrotron or a linear accelerator.
Therefore, the X-rays emitted from the synchrotron or the linear accelerator have a luminance of at least 10 ¹⁰ [photons / sec / mrad ² / mm ² /0.1% bw] or more and are a continuous X-ray source. It is optimal for XAFS measurement. In addition, bw shows the band width of the X-ray radiated | emitted from a synchrotron or a linear accelerator.

The luminance [photons / sec / mrad ² / mm ² /0.1% bw] of the high-intensity X-ray is preferably 10 ¹⁰ or more, more preferably 10 ¹² or more. Although an upper limit is not specifically limited, It is preferable to use the X-ray intensity below the extent that there is no radiation damage.

The number of photons of the high-intensity X-ray is preferably 10 ⁷ [photons / sec] or more, more preferably 10 ⁹ or more. Although an upper limit is not specifically limited, It is preferable to use the X-ray intensity below the extent that there is no radiation damage.

The X-ray energy when measuring X-ray scattering (SAXS method) is limited to a range not affected by the anomalous dispersion effect by the compound to be blended, and specifically, the real part of the anomalous dispersion term in (Equation 1) When f '(E) is in the range of -2 or more and SAXS is measured with X-ray energy outside this range, an accurate scattering pattern cannot be obtained due to the anomalous dispersion effect of the blended zinc.
(Formula 1) f (Q, E) = f ₀ (Q) + f ′ (E) + iF ″ (E)
f (Q, E): atomic scattering factor f ₀ (Q): Thomson scattering factor f ′ (E): real part F ″ (E) of anomalous dispersion term i: imaginary part of anomalous dispersion term

When performing the X-ray absorption fine structure method (XAFS method), it is desirable that the energy range scanned with X-rays includes the K-shell absorption edge of the inorganic compound to be identified among the blended inorganic compounds, Specifically, the real part f ′ (E) of the anomalous dispersion term in (Equation 1) is in the range of −2 or more, and if it is outside this range, the absorption edge of the K shell of the inorganic compound can be scanned. It is impossible to identify the compound in the polymer material.

The following three methods are typically used as the XAFS measurement method. In the embodiments of the present invention, the transmission method is used. However, the present invention is not limited to this, and various detection methods may be used, or simultaneous measurement may be performed in combination.
(Transmission method)
This is a method for detecting the X-ray intensity transmitted through a sample. For measurement of transmitted light intensity, a photodiode array detector or the like is used.
(Fluorescence method)
This is a method for detecting fluorescent X-rays generated when a sample is irradiated with X-rays. In the case of the transmission method, when X-ray absorption measurement of an element having a small content in a sample is performed, the background is increased due to the X-ray absorption of an element having a small content and a large content, so that the S / B ratio is poor. It becomes a spectrum. On the other hand, in the fluorescence method (especially when an energy dispersive detector or the like is used), it is possible to measure only the fluorescent X-rays from the target element, so that the influence of the element having a large content is small. Therefore, it is effective when measuring an X-ray absorption spectrum of an element having a small content. In addition, since fluorescent X-rays have strong penetrating power (low interaction with substances), it is possible to detect fluorescent X-rays generated inside the sample. Therefore, this method is the most suitable method for obtaining bulk information after the transmission method.
(Electron yield method)
This is a method for detecting a current flowing when a sample is irradiated with X-rays. Therefore, the sample needs to be a conductive material. Since the polymer material is an insulator, until now, the X-ray absorption measurement of the polymer material has mostly used a sample with a sample placed on a substrate by vapor deposition or spin coating, but in the present invention, A high S / B ratio and S / N ratio measurement can be realized by processing (cutting) the polymer material into a microtome of 100 μm or less, preferably 10 μm or less, more preferably 1 μm or less, and even more preferably 500 nm or less.

The pneumatic tire of this invention has the said vulcanized rubber composition (vulcanized rubber) for tires. The vulcanized rubber is not particularly limited, and examples thereof include tread rubber, sidewall rubber, breaker rubber, carcass rubber, band rubber, clinch rubber, bead apex rubber, and inner liner rubber. Of these, tread rubber is preferable.

The pneumatic tire of this invention can manufacture a pneumatic tire by a normal method using the said unvulcanized rubber composition. That is, the unvulcanized rubber composition obtained by the kneading step is extruded according to the shape of the tire member, molded by a normal method on a tire molding machine, and bonded together with other tire members. Form a vulcanized tire. The unvulcanized tire can be manufactured by heating and pressing the unvulcanized tire in a vulcanizer by the vulcanization step.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.
The various chemicals used in the examples are described below.
Isoprene rubber (IR): Nippon IR 2200 manufactured by Zeon Corporation
Zinc oxide: Zinc Hua No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Stearic acid lauric acid manufactured by Wako Pure Chemical Industries, Ltd .: Lauric acid myristic acid manufactured by Wako Pure Chemical Industries, Ltd .: Wako Pure Chemical Industries, Ltd. Zinc myristate manufactured by: Zinc stearate manufactured by Wako Pure Chemical Industries, Ltd. Magnesium stearate manufactured by Wako Pure Chemical Industries, Ltd .: Magnesium oxide sulfur manufactured by Wako Pure Chemical Industries, Ltd .: Sulfur powder vulcanized by Karuizawa Sulfur Co., Ltd. Accelerator: Noxeller CZ (N-cyclohexyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

(Manufacture of vulcanized rubber composition)
(Base kneading process)
The components shown in Table 1 were kneaded in amounts shown in Table 1 with respect to 100 parts by mass of IR using a 1.7 L Banbury mixer (kneading temperature: 150 ° C., kneading time: 5 minutes).
(Finish kneading process)
A kneaded product (IR 100 parts by mass) kneaded in the base kneading step, 1.0 part by mass of sulfur, and 1.0 part by mass of a vulcanization accelerator are kneaded with a biaxial open roll to prepare an unvulcanized rubber composition. (Kneading temperature: 90 ° C., kneading time: 5 minutes).
(Vulcanization process)
In the vulcanization step, a vulcanized rubber composition was prepared by vulcanizing the unvulcanized rubber composition prepared in the finish kneading step at 160 ° C. for 20 minutes. In Comparative Example 4 only, the vulcanization temperature was 135 ° C.

The obtained unvulcanized rubber composition and vulcanized rubber composition were evaluated as follows, and the test results are shown in Table 1.

<Vulcanization speed t10>
Each unvulcanized rubber composition was subjected to a vulcanization test at a measurement temperature of 160 ° C. using a vibration type vulcanization tester (curlastometer) described in JIS K6300, and time and torque plotted. A sulfur velocity curve was obtained. When the minimum value of the torque of the vulcanization rate curve is ML, the maximum value is MH, and the difference (MH−ML) is ME, time t10 (minute) to reach ML + 0.1ME was calculated.

<Mold adhesion by surface bloom (adhesion test)>
Adhesive strength of an unvulcanized rubber composition at a temperature of 23 ° C. and a humidity of 55% under conditions of a rising speed of 30 mm / min and a measurement time of 2.5 seconds using a PICMA / tack tester manufactured by Toyo Seiki Seisakusho Co., Ltd. (N) was measured.
When the adhesive strength was less than 1.5N, it was judged that molding was impossible, and when it was 1.5N or more, molding was possible.

<Quantification of zinc oxide and zinc stearate>
For the unvulcanized rubber composition and the rubber composition 5 minutes after the start of the vulcanization process, the amount of zinc oxide and zinc stearate remaining in the rubber composition is determined using the X-ray absorption fine structure method (XAFS method). The reaction rate of the metal oxide (zinc oxide) was calculated based on the quantitative value of zinc oxide.
(XAFS device)
XAFS equipment installed in SPring-8 BL08B2 (conditions)
The energy of high-intensity X-rays was scanned in the range of 9000 eV to 10500 eV, and the K-shell absorption edge of zinc atoms and a broad vibration component spectrum were measured. This is a region called XANES (X-ray Absorption Near Edge Structure: X-ray absorption edge vicinity structure), 9600 eV to 9700 eV, and EXAFS (Extended X-ray Absorption Fine Structure: Wide structure called X-ray Absorption Structure X-ray Absorption Structure) It was separated into a range of 9700 eV to 10500 eV.
XANES uses a standard sample spectrum of a zinc compound, EXAFS uses a distance between bonds including zinc obtained by Fourier transform of the obtained vibration component, and thereby a zinc compound contained in a sample. The mass ratio of was derived.
(Detector)
A permeation method using an ionization chamber filled with nitrogen was used.

<Measurement of cross-linking uniformity>
The method used was a small angle neutron scattering method (SANS method).
(SANS equipment)
SANS: SANA equipment (40mSANS) attached to the reactor HANARI (High-flux Advanced Application Reactor) owned by Korea's KAERI (Korea Atomic Energy Research Institute)
(Measurement condition)
Neutron beam wavelength: 7.49 mm
Neutron beam flux at the sample position: 5.5 × 10 ⁷ neutrons / cm ² · sec
Distance from sample to detector: 1.14 m, 4.7 m (Note that in order to obtain further information on the small angle side, measurement was performed using a focusing lens under the condition of a distance of 40 m from the sample to the detector.)
(Detector)
ODELRA, 21000N

A plate-like sample (molded product) having a thickness of about 1 mm was attached to a sample holder in a state of equilibrium swelling with deuterated toluene, and the sample was irradiated with neutron beams at room temperature. The distance from the sample to the detector was 1.14 m, 4.7 m, and the absolute scattering intensity curve obtained from the focusing lens measurement was combined by the method of least squares. The combination of the three curves fixed the scattering intensity curve obtained from the measurement of the focusing lens measurement with the distance from the sample to the detector, and shifted the scattering intensity curve obtained from the 4.7 m and 1.14 m measurements.
Next, curve fitting is performed on the scattering intensity curve I _(q) obtained by the SANS measurement method using (Formula 3-2) to (Formula 3-6), and a fitting parameter Ξc (1 nm to 100 μm) is obtained. The correlation length (non-uniform network structure size of the polymer)) is obtained by the least square method, and the volume fraction φc is calculated from the number Nc of scatterers per unit volume having the correlation length Ξc from the obtained correlation length Ξc. Asked. About the value of the obtained volume fraction (phi) c, a target value is 2.5% or less, and it is so favorable that a value is small. In addition, it implemented in the area | region where q represented by the said (Formula 3-1) is 10 nm <^-1> or less.

<Measurement of strength at break and elongation at break>
Using a No. 3 dumbbell-shaped test piece made of a vulcanized rubber composition, a tensile test was performed at room temperature in accordance with JIS K 6251 “Vulcanized rubber and thermoplastic rubber-Determination of tensile properties”. Strength TB (MPa) and elongation at break EB (%) were measured. It shows that it is excellent in elongation at break, so that EB is large. It shows that it is excellent in the strength at the time of break, so that TB is large.
The result is shown as an index when the result of Example 1 is set to 100, and the larger the value, the better the result. A good index was determined when the index was 90 or higher.

A kneading step of kneading a rubber component, a metal oxide, and a carboxylic acid to prepare an unvulcanized rubber composition, and a vulcanized rubber by vulcanizing the unvulcanized rubber composition prepared by the kneading step. A vulcanized rubber composition for a tire obtained by a production method including a vulcanization step for preparing a composition, wherein the metal oxide is substantially unreacted in the kneading step, and in the vulcanization step, Example in which the reaction rate of the metal oxide after 5 minutes from the start of vulcanization is 50 mol% or more, and the volume fraction φc of the cross-linked dense part derived from the heterogeneous structure of the cross-linking is 2.5% or less Has reduced the non-uniform structure of cross-linking without causing the problem of poor adhesion during molding, and good rubber strength (strength at break, elongation at break) was obtained.

Claims (7)

A kneading step of kneading a rubber component containing natural rubber or isoprene rubber , a metal oxide, and a carboxylic acid to prepare an unvulcanized rubber composition;
A vulcanized rubber composition for a tire obtained by a production method comprising a vulcanizing step of vulcanizing an unvulcanized rubber composition prepared by the kneading step to prepare a vulcanized rubber composition,
In the kneading step, the metal oxide is substantially unreacted,
In the vulcanization step, the reaction rate of the metal oxide after 5 minutes from the start of vulcanization is 50 mol% or more,
A vulcanized rubber composition for tires having a volume fraction φc of 2.5% or less in a cross-linked dense part derived from a non-uniform cross-linking structure. In the unvulcanized rubber composition, the compounding amount of the metal oxide with respect to 100 parts by mass of the rubber component is 1.5 to 3.0 parts by mass, and the compounding amount of the carboxylic acid is 5.0 to 10 parts by mass. The vulcanized rubber composition for tires described. The vulcanized rubber composition for tire according to claim 1 or 2, wherein the carboxylic acid is a fatty acid. The volume fraction φc is
By irradiating the vulcanized rubber composition with X-rays or neutron rays, X-ray scattering measurement or neutron scattering measurement is performed in a region where q represented by the following (Formula 3-1) is 10 nm ⁻¹ or less, and X Correlation length _{ｃ c of 1} nm to 100 μm obtained by curve fitting with the following (formula 3-2) to (formula 3-6) to the scattering intensity curve I _(q) obtained by the line scattering measurement or neutron scattering measurement The vulcanized rubber composition for tire according to any one of claims 1 to 3, wherein the vulcanized rubber composition for tire is calculated using the number _Nc per unit volume of scatterers having

The vulcanized rubber composition for tire according to claim 4, wherein the X-ray scattering measurement is a small-angle X-ray scattering measurement, and the neutron scattering measurement is a small-angle neutron scattering measurement. A pneumatic tire having the vulcanized rubber composition for a tire according to any one of claims 1 to 5. The pneumatic tire according to claim 6, wherein the tire vulcanized rubber composition is a tread rubber.

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