JP7148020B1 - Natural rubber, rubber-steel cord composites and tires - Google Patents

Abstract

The present disclosure provides natural rubber capable of imparting good adhesion after high-humidity heat deterioration, a rubber-steel cord composite using the natural rubber, and a tire using the rubber-steel cord composite. The present disclosure relates to natural rubber having a calcium content of less than 100 ppm.

Description

The present disclosure relates to natural rubber, a rubber-steel cord composite using the natural rubber, and a tire using the rubber-steel cord composite.

Conventional rubber compositions for cord coating used in carcasses, belts, etc., are generally compounded with rubber components such as natural rubber, isoprene rubber, and styrene-butadiene rubber, reinforcing fillers such as carbon black, and the like. ing.

Adhesiveness to cords is required for such rubber compositions for covering cords, and various techniques have been proposed. ing.

The present disclosure solves the above problems and provides natural rubber capable of imparting good adhesion after high-humidity heat deterioration, a rubber-steel cord composite using the natural rubber, and a tire using the rubber-steel cord composite. intended to provide

The present disclosure relates to natural rubber having a calcium content of less than 100 ppm.

According to the present disclosure, natural rubber having a calcium content of 100 ppm or less or a natural rubber having a potassium content of less than 350 ppm can provide good adhesiveness after high-humidity heat deterioration.

[Natural rubber]
The first natural rubber of this disclosure has a calcium content of less than 100 ppm and the second natural rubber of this disclosure has a potassium content of less than 350 ppm. As a result, good adhesiveness after high-humidity heat deterioration can be imparted.

Although the reason why such effects are obtained is not necessarily clear, it is speculated as follows.
Normally, natural rubber contains a small amount of metal components, and the presence of easily oxidizable metal components is thought to cause oxidative deterioration of the rubber and reduce adhesiveness. On the other hand, the natural rubber has a high ionization tendency among the metal components and contains less calcium and potassium, which are easily oxidized.
As shown in Comparative Examples 1 to 3 below, commercially available natural rubber has a calcium content of 100 ppm or more and a potassium content of 350 ppm or more.

The calcium content of the natural rubber of the first aspect of the present disclosure may be less than 100 ppm, but is preferably 90 ppm or less, more preferably 80 ppm or less, and even more preferably 72 ppm or less. Although the lower limit is not particularly limited, it is preferably 1 ppm or more, more preferably 5 ppm or more, still more preferably 10 ppm or more, and particularly preferably 15 ppm or more. Within the above range, the effect tends to be obtained more favorably.
Calcium content can be measured by conventional methods such as ICP emission spectroscopy.

Also in the natural rubber of the first aspect of the present disclosure, it is preferable that the potassium content is low. The potassium content of the natural rubber of the first aspect of the present disclosure is preferably less than 350 ppm, more preferably 300 ppm or less, even more preferably 260 ppm or less, and particularly preferably 240 ppm or less. Although the lower limit is not particularly limited, it is preferably 30 ppm or more, more preferably 50 ppm or more, still more preferably 70 ppm or more, and particularly preferably 80 ppm or more. Within the above range, the effect tends to be obtained more favorably.
Potassium content can be measured by conventional methods such as ICP emission spectroscopy.

The potassium content of the natural rubber of the second aspect of the present disclosure may be less than 350 ppm, preferably 300 ppm or less, more preferably 260 ppm or less, and even more preferably 240 ppm or less. Although the lower limit is not particularly limited, it is preferably 30 ppm or more, more preferably 50 ppm or more, still more preferably 70 ppm or more, and particularly preferably 80 ppm or more. Within the above range, the effect tends to be obtained more favorably.

Also in the second natural rubber of the present disclosure, calcium is preferably low. The calcium content of the natural rubber of the second aspect of the present disclosure is preferably less than 100 ppm, more preferably 90 ppm or less, even more preferably 80 ppm or less, and particularly preferably 72 ppm or less. Although the lower limit is not particularly limited, it is preferably 1 ppm or more, more preferably 5 ppm or more, still more preferably 10 ppm or more, and particularly preferably 15 ppm or more. Within the above range, the effect tends to be obtained more favorably.

It should be noted that the preferred embodiments described below are applicable to both the "first natural rubber of the present disclosure" and the "second natural rubber of the present disclosure". In this specification, the description of "the natural rubber" includes both "the first natural rubber of the present disclosure" and "the second natural rubber of the present disclosure".

Further investigation by the present inventors revealed that the adhesion after high-humidity heat deterioration is also affected by the phosphorus content. And it became clear that the adhesiveness after high-humidity heat deterioration becomes further favorable by making phosphorus content more than a specific amount. It is believed that this is brought about by maintaining the higher-order structure of the polymer.

The phosphorus content of the natural rubber is preferably 300 ppm or more, more preferably 320 ppm or more, still more preferably 340 ppm or more, and particularly preferably 350 ppm or more. The upper limit is preferably 1000 ppm or less, more preferably 900 ppm or less, still more preferably 850 ppm or less, and particularly preferably 820 ppm or less. Within the above range, the effect tends to be obtained more favorably.
Phosphorus content can be measured by conventional methods such as ICP emission spectroscopy.

As a result of further investigation by the present inventors, the adhesiveness after high-humidity heat deterioration is also affected by the amount of acetone extracted and the nitrogen content measured based on JIS K 6229:2015. As a result, it became clear that the adhesiveness after high-humidity heat deterioration was further improved.

The natural rubber has an acetone extraction amount of preferably 4.5% by mass or less, more preferably 3.8% by mass or less, and even more preferably 3.0% by mass or less, as measured based on JIS K 6229:2015. Although the lower limit is not particularly limited, it is preferably 1.0% by mass or more, more preferably 1.4% by mass or more, and still more preferably 1.6% by mass or more. Within the above range, the effect tends to be obtained more favorably.

The nitrogen content of the natural rubber is preferably 0.80% by mass or less, more preferably 0.60% by mass or less, and even more preferably 0.50% by mass or less. Although the lower limit is not particularly limited, it is preferably 0.05% by mass or more, more preferably 0.15% by mass or more, and still more preferably 0.20% by mass or more. Within the above range, the effect tends to be obtained more favorably.
The nitrogen content can be measured by a conventional method such as the Kjeldahl method or a trace nitrogen meter. Nitrogen is derived from proteins and amino acids.

The natural rubber having the calcium content, potassium content, phosphorus content, acetone extractable amount, and nitrogen content within the above ranges can be obtained, for example, by subjecting natural rubber latex to a coagulation step of coagulating natural rubber latex and the natural rubber coagulated by the coagulation step. immersed in water.

(coagulation process)
In the coagulation step, the natural rubber latex is coagulated.
Natural rubber latex is collected as the sap of natural rubber trees such as the Hevea tree, and contains water, proteins, lipids, inorganic salts, etc. in addition to the rubber content, and the gel content in the rubber is based on the complex presence of various impurities. is considered a thing.
The natural rubber latex is not particularly limited, and for example, raw latex (field latex) obtained by tapping Hevea trees can be used. These may be used alone or in combination of two or more. The natural rubber latex is preferably not subjected to a high purification treatment such as saponification treatment or enzyme treatment.

The method for coagulating natural rubber latex is not particularly limited, and examples include natural coagulation in which natural rubber latex is left to stand, acid coagulation in which acid (preferably pH 3.0 or less acid) is used to coagulate, Examples include organic solvent coagulation, in which an organic solvent is used for coagulation. These may be performed singly or in combination of two or more. Furthermore, if necessary, a polymer flocculant may be used. In particular, the coagulation step is preferably a step of naturally coagulating the collected natural rubber latex or a step of acid coagulation using an acid having a pH of 3.0 or less.

The acid (preferably pH 3.0 or less) is not particularly limited, and both organic acids and inorganic acids can be used. Examples of preferred organic acids include formic acid and acetic acid, and preferred examples of inorganic acids include sulfuric acid, hydrochloric acid, and carbonic acid. These acids may be used alone or in combination of two or more.
The pH of the acid is preferably 3.0 or less, more preferably 2.0 or less, still more preferably 1.5 or less, and the lower limit is not particularly limited.

The organic solvent is not particularly limited, and examples thereof include methanol, ethanol, tetrahydrofuran, acetone and the like. These may be used alone or in combination of two or more.

The polymer flocculant is not particularly limited. Examples include molecular flocculants, nonionic polymer flocculants such as acrylamide polymers, and amphoteric polymer flocculants such as copolymers of methyl chloride quaternary salt of dimethylaminoethyl (meth)acrylate-acrylic acid salt. These may be used alone or in combination of two or more. The amount of polymer flocculant to be added can be appropriately selected.

Specific examples of the coagulation step include a method of adding an acid to natural rubber latex to adjust the pH, and further adding a polymer flocculant as necessary.

(Immersion process)
In the immersion step, the natural rubber coagulated in the coagulation step is immersed in water.

Water is not particularly limited, and examples thereof include tap water, ion-exchanged water (deionized water), distilled water, rain water, waste water, industrial water, reservoir water, river water, lake water, and sea water. These may be used alone or in combination of two or more. Among them, ion-exchanged water is preferable.

Water preferably has a hardness (calcium carbonate equivalent) of 180 mg/L or less and a total organic carbon (TOC) content of 100 mg/L or less. Water that satisfies this condition includes water (factory purified water) obtained by treating ground water and pond water in Thailand with activated carbon or the like.
Water hardness is preferably 180 mg/L or less, more preferably 120 mg/L or less, and water TOC content is preferably 100 mg/L or less, more preferably 15 mg/L or less. Since these are preferably as low as possible, the lower limit is not particularly limited.

As used herein, water is a concept that includes not only water in which solutes are not dissolved, but also aqueous solutions in which solutes are dissolved.
The solute is not particularly limited, and includes acids such as sulfuric acid; alkalis; metals such as sodium;
The content of solutes contained in water is preferably 10% by mass or less, more preferably 5% by mass or less, still more preferably 0.5% by mass or less, particularly preferably 0.1% by mass or less, and most preferably 0.5% by mass or less. 05% by mass or less, and may be 0% by mass. Within the above range, the effect tends to be obtained more favorably.

The temperature during immersion is preferably 0° C. or higher, more preferably 10° C. or higher, still more preferably 15° C. or higher, particularly preferably 25° C. or higher, preferably 40° C. or lower, more preferably 35° C. or lower, and still more preferably. is below 30°C. Within the above range, the effect tends to be obtained more favorably.

Stirring may or may not be performed during immersion (flow velocity 0 m/s).
When agitation is performed, the flow rate is 4 m/s or less because the immersion process can more gently discharge components that affect adhesion from the coagulated rubber while maintaining the properties of natural rubber. , preferably 3 m/s or less, more preferably 2 m/s or less. Within the above range, the effect tends to be obtained more favorably.

The immersion time (time for performing the immersion step) is preferably 1 day or longer, more preferably 2 days or longer, still more preferably 3 days or longer, particularly preferably 5 days or longer, most preferably 1 week or longer, and the upper limit is particularly Although not limited, it is preferably 6 months or less, more preferably 5 months or less, still more preferably 4 months or less, and particularly preferably 3 months or less. Within the above range, the effect tends to be obtained more favorably.

Examples of the immersion method include a method of immersing the natural rubber coagulated in the coagulation step in water as it is, and a method of immersing the natural rubber coagulated in the coagulation step in a stirred state in water.

The natural rubber immersed in the immersion step is further subjected to washing, dehydration, and drying (especially dehydration and drying) as necessary to obtain the natural rubber (solid rubber) of the present invention. can.

As the washing step, for example, a method of forming a natural rubber into a sheet and repeating pulverization and washing can be used.

In the dehydration step, the moisture content of the soaked natural rubber (which may be washed if necessary) is reduced by the soaking step. The dehydration method is not particularly limited as long as it can reduce the moisture content of the natural rubber, and examples thereof include a method of squeezing the natural rubber. Among them, the method of squeezing the natural rubber is preferable, and the method of squeezing the natural rubber is more preferable, because the water contained in the natural rubber can also be removed and the effect can be obtained more suitably. Examples of the method of squeezing the natural rubber include a method of passing the natural rubber through rolls and squeezing it. A creeper may be used as a device for squeezing natural rubber through rolls.

In the above production method, the immersion step is performed before the dehydration step. Therefore, before squeezing out the moisture in the coagulated rubber, components that affect adhesion are preferably and gently removed from the coagulated rubber while maintaining the properties of natural rubber. can be discharged from, and good adhesion after high-humidity heat deterioration can be imparted.

In the drying step, the natural rubber immersed in the immersion step (which may be washed and dehydrated as necessary) is dried.
The drying method is not particularly limited, and for example, a common dryer such as a trolley dryer, vacuum dryer, air dryer, and drum dryer used for drying TSR can be used.
The drying temperature and drying time are not particularly limited, and drying may be performed at 70 to 135° C. for 1 to 14 hours, for example.

[Rubber/steel cord composite]
The rubber-steel cord composite of the present invention is a rubber-steel cord composite using the above-described natural rubber, and specifically includes a cord-covering rubber composition containing the above-described natural rubber and a steel cord, More specifically, it consists of a cord coating rubber composition containing the above natural rubber and a steel cord.

Since the above natural rubber can provide good adhesiveness after high-humidity heat deterioration, the rubber-steel cord composite using the above-mentioned natural rubber can maintain the integrity of the cord and rubber even after being left in a high-humidity environment for a long period of time. Strong adhesion between

[Rubber composition for cord coating]
The rubber composition for cord coating contains the above natural rubber.

In the rubber composition for covering cords, the content of the natural rubber is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 100% by mass in 100% by mass of the rubber component. Within the above range, the effect tends to be obtained more favorably.

In the rubber composition for coating the cord, the total content of the natural rubber such as the natural rubber is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 100% by mass in 100% by mass of the rubber component. is. Within the above range, the effect tends to be obtained more favorably.

As the rubber component, other than natural rubber, epoxidized natural rubber (ENR), isoprene rubber (IR), styrene-butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), and butyl rubber are used as long as the effects are not impaired. (IIR), halogenated butyl rubber (X-IIR), styrene isoprene-butadiene rubber (SIBR), and the like may be used in combination. These may be used alone or in combination of two or more.

Carbon black is preferably blended into the cord coating rubber composition. Thereby, the strength of the rubber can be improved. Examples of carbon black include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550 and N762. These may be used alone or in combination of two or more.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 50 m ² /g or more, more preferably 65 m ² /g or more. By making it 50 m ² /g or more, the adhesiveness between the rubber composition and the tire cord tends to be improved. Further, the N ₂ SA of carbon black is preferably 150 m ² /g or less, more preferably 130 m ² /g or less. By making it 150 m ² /g or less, good low heat build-up tends to be obtained, and good adhesiveness after high-humidity heat deterioration can be obtained.
The nitrogen adsorption specific surface area of carbon black is determined according to JIS K6217-2:2001.

As carbon black, for example, products of Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Co., Ltd., Lion Corporation, Shin Nikka Carbon Co., Ltd., Columbia Carbon Co., Ltd. can be used.

The content of carbon black is preferably 5 parts by mass or more, more preferably 20 parts by mass or more, and still more preferably 40 parts by mass or more with respect to 100 parts by mass of the rubber component. When the amount is 5 parts by mass or more, the adhesiveness between the rubber composition and the tire cord tends to be improved. Also, the content of the carbon black is preferably 80 parts by mass or less, more preferably 65 parts by mass or less. By making it 80 parts by mass or less, there is a tendency that good low heat build-up is obtained and good adhesiveness after high-humidity heat deterioration is obtained.

The cord coating rubber composition preferably contains sulfur as a vulcanizing agent.
Sulfur includes powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur and the like commonly used in the rubber industry. These may be used alone or in combination of two or more.

As sulfur, for example, products of Tsurumi Chemical Industry Co., Ltd., Karuizawa Io Co., Ltd., Shikoku Kasei Kogyo Co., Ltd., Flexis Co., Ltd., Nippon Kantan Kogyo Co., Ltd., Hosoi Chemical Industry Co., Ltd., etc. can be used.

The sulfur content is preferably 2.5 parts by mass or more, more preferably 2.8 parts by mass or more, relative to 100 parts by mass of the rubber component. When the amount is 2.5 parts by mass or more, sufficient sulfur is supplied to the adhesive layer with the tire cord, and good adhesiveness tends to be obtained. Also, the content is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 6 parts by mass or less. When the amount is 10 parts by mass or less, rubber properties such as breaking stress and elongation at break tend to be sufficiently obtained.

The cord coating rubber composition preferably contains a vulcanization accelerator. Examples of vulcanization accelerators include sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamic acid-based, aldehyde-amine-based, aldehyde-ammonia-based, imidazoline-based, and xanthate-based vulcanization accelerators. be done. These may be used alone or in combination of two or more. Among them, a sulfenamide-based vulcanization accelerator is preferable because of its excellent cross-linking reactivity. Sulfenamide vulcanization accelerators include CBS (N-cyclohexyl-2-benzothiazylsulfenamide), TBBS (Nt-butyl-2-benzothiazylsulfenamide), N,N-dicyclohexyl Sulfenamide compounds such as -2-benzothiazylsulfenamide, N-oxydiethylene-2-benzothiazylsulfenamide, N,N-diisopropyl-2-benzothiazolesulfenamide, and the like.

As the vulcanization accelerator, for example, products manufactured by Kawaguchi Kagaku Co., Ltd., Ouchi Shinko Kagaku Co., Ltd., Rhein Chemie Co., etc. can be used.

The content of the vulcanization accelerator is preferably 0.5 parts by mass or more, more preferably 0.7 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 100 parts by mass of the rubber component. is 5 parts by mass or less, more preferably 2 parts by mass or less. Within the above range, the effect tends to be obtained more favorably.

The cord coating rubber composition may contain silica.
Silica is not particularly limited, and examples thereof include dry silica (anhydrous silicic acid) and wet silica (hydrous silicic acid). These may be used alone or in combination of two or more. Among them, wet-process silica is preferable because it has many silanol groups.

As silica, for example, products of Degussa, Rhodia, Tosoh Silica, Solvay Japan, Tokuyama, etc. can be used.

The N ₂ SA of silica is preferably 50 m ² /g or more, more preferably 150 m ² /g or more. Also, the N ₂ SA is preferably 300 m ² /g or less, more preferably 200 m ² /g or less.
The N ₂ SA of silica can be measured according to ASTM D3037-81.

The silica content relative to 100 parts by mass of the rubber component is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass. It is below.

When the cord coating rubber composition contains silica, it preferably contains a silane coupling agent together with silica.
The silane coupling agent is not particularly limited, and examples thereof include bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, Bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (2-triethoxysilylethyl) trisulfide, bis (4-trimethoxysilylbutyl) trisulfide, bis ( 3-triethoxysilylpropyl) disulfide, bis(2-triethoxysilylethyl) disulfide, bis(4-triethoxysilylbutyl) disulfide, bis(3-trimethoxysilylpropyl) disulfide, bis(2-trimethoxysilylethyl) ) disulfide, bis(4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3- sulfides such as triethoxysilylpropyl methacrylate monosulfide; 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane; vinyl-based such as methoxysilane; amino-based such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy-based such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. These may be used alone or in combination of two or more.

Examples of silane coupling agents that can be used include products of Degussa, Momentive, Shin-Etsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azmax Co., Ltd., Dow Corning Toray Co., Ltd., and the like.

The content of the silane coupling agent is preferably 0.1 parts by mass or more, more preferably 2 parts by mass or more, and still more preferably 3 parts by mass or more with respect to 100 parts by mass of silica. Also, the content is preferably 20 parts by mass or less, more preferably 16 parts by mass or less, and even more preferably 12 parts by mass or less.

The cord coating rubber composition may contain a plasticizer. The plasticizer is not particularly limited, but examples thereof include oils, liquid polymers (liquid diene-based polymers), and liquid resins. One type of these plasticizers may be used, or two or more types may be used in combination.

Among the plasticizers, it is preferably at least one selected from the group consisting of oils, liquid polymers, and liquid resins, more preferably oils and/or liquid polymers (liquid diene-based polymers), and further oil. preferable.

From the environmental point of view, the plasticizer preferably has a polycyclic aromatic content (PCA) of less than 3% by mass, more preferably less than 1% by mass. The polycyclic aromatic content (PCA) is measured according to the British Petroleum Institute method 346/92.

The above oils are not particularly limited, and process oils such as paraffinic process oils, aromatic process oils, and naphthenic process oils, low PCA (polycyclic aromatic) process oils such as TDAE and MES, vegetable oils and fats, and Conventionally known oils such as mixtures thereof can be used. These may be used alone or in combination of two or more. Among them, paraffinic process oils are preferred.

As oil, for example, Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., Japan Energy Co., Ltd., Orisoi Co., Ltd., H & R, Toyokuni Oil Mills Co., Ltd., Showa Shell Oil Co., Ltd., Fuji Kosan Co., Ltd. etc. products can be used.

The liquid polymer (liquid diene-based polymer) is a diene-based polymer that is liquid at room temperature (25° C.).
The liquid diene-based polymer preferably has a polystyrene-equivalent weight-average molecular weight (Mw) measured by gel permeation chromatography (GPC) of 1.0×10 ³ or more, preferably 3.0×10 ³ or more. more preferably 2.0×10 ⁵ or less, more preferably 1.5×10 ⁴ or less.
In addition, in this specification, Mw of a liquid diene polymer is a polystyrene conversion value measured by gel permeation chromatography (GPC).

Liquid diene-based polymers include liquid styrene-butadiene copolymer (liquid SBR), liquid butadiene polymer (liquid BR), liquid isoprene polymer (liquid IR), liquid styrene-isoprene copolymer (liquid SIR), and the like. be done. These may be used alone or in combination of two or more.

As the liquid diene-based polymer, for example, products of Sartomer Co., Ltd., Kuraray Co., Ltd., etc. can be used.

Examples of the liquid resin include, but are not limited to, liquid aromatic vinyl polymers, coumarone-indene resins, indene resins, terpene resins, rosin resins, and hydrogenated products thereof. These may be used alone or in combination of two or more.

Examples of the liquid resin include Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical, Nichinuri Chemical Co., ( Products of Nippon Shokubai Co., Ltd., JXTG Energy Co., Ltd., Arakawa Chemical Industry Co., Ltd., Taoka Chemical Industry Co., Ltd., etc. can be used.

The content of the plasticizer (preferably oil) is preferably 1 part by mass or more, more preferably 2 parts by mass or more with respect to 100 parts by mass of the rubber component. The content is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less. Within the above range, the effect tends to be obtained more favorably.
The plasticizer content also includes the amount of oil contained in the rubber (oil-extended rubber).

The cord coating rubber composition may contain a solid resin.
Although the resin is not particularly limited, for example, solid alkylphenol-based resin, styrene-based resin, coumarone-indene resin, terpene-based resin, rosin-based resin, acrylic-based resin, dicyclopentadiene-based resin (DCPD-based resin), etc. is mentioned. These may be used alone or in combination of two or more.

Examples of solid resins include Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical, Nichinuri Chemical Co., Ltd. ) Nippon Shokubai Co., JX Energy Co., Ltd., Arakawa Chemical Industries Co., Ltd., Taoka Chemical Co., Ltd., and other products can be used.

The content of the solid resin is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and still more preferably 5 parts by mass or more with respect to 100 parts by mass of the rubber component. Also, the content is preferably 80 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 20 parts by mass or less.

The cord coating rubber composition preferably contains organic acid cobalt.
Examples of the cobalt organic acid include cobalt stearate, cobalt boron neodecanoate, cobalt naphthenate, and cobalt neodecanoate, and cobalt stearate is preferred.

The content of the organic acid cobalt is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and still more preferably 0.08 parts by mass in terms of cobalt with respect to 100 parts by weight of the rubber component. or more, preferably 0.50 parts by mass or less, more preferably 0.20 parts by mass or less.

The cord coating rubber composition may contain zinc oxide.
As the zinc oxide, conventionally known ones can be used, for example, products of Mitsui Kinzoku Mining Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc. can be used.

The content of zinc oxide is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, still more preferably 5 parts by mass or more, and preferably 15 parts by mass with respect to 100 parts by mass of the rubber component. Below, more preferably 10 mass parts or less. Within the above range, the effect tends to be obtained more favorably.

The cord coating rubber composition may contain an antioxidant.
Examples of anti-aging agents include naphthylamine-based anti-aging agents such as phenyl-α-naphthylamine; diphenylamine-based anti-aging agents such as octylated diphenylamine and 4,4′-bis(α,α′-dimethylbenzyl)diphenylamine; -Isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, etc. p-phenylenediamine-based antioxidants; quinoline-based antioxidants such as polymers of 2,2,4-trimethyl-1,2-dihydroquinoline; 2,6-di-t-butyl-4-methylphenol, monophenolic anti-aging agents such as styrenated phenol; inhibitors and the like. These may be used alone or in combination of two or more. Among them, p-phenylenediamine anti-aging agents and quinoline anti-aging agents are preferred, and p-phenylenediamine anti-aging agents are more preferred.

As the anti-aging agent, products of Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Kagaku Kogyo Co., Ltd., Flexis, etc. can be used, for example.

The content of the anti-aging agent is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass, relative to 100 parts by mass of the rubber component. It is below the department. Within the above range, the effect tends to be obtained more favorably.

In addition to the above-mentioned components, additives generally used in the tire industry can be added to the rubber composition for coating the cord. substances), wax, calcium carbonate, mica such as sericite, aluminum hydroxide, magnesium oxide, magnesium hydroxide, clay, talc, alumina, titanium oxide, and the like. The content of each of these components is preferably 0.1 parts by mass or more and preferably 200 parts by mass or less with respect to 100 parts by mass of the rubber component.

The above rubber composition for coating a cord can be produced, for example, by kneading each of the above components using a rubber kneading device such as an open roll mixer or a Banbury mixer, followed by vulcanization.

As for kneading conditions, in the base kneading step, the kneading temperature is usually 100 to 180°C, preferably 120 to 170°C. In the finishing kneading step, the kneading temperature is usually 120°C or lower, preferably 80 to 110°C. A composition obtained by kneading a vulcanizing agent and a vulcanization accelerator is usually subjected to vulcanization treatment such as press vulcanization. The vulcanization temperature is generally 140-190°C, preferably 150-185°C.

The rubber composition for cord coating is used as a rubber composition for coating steel cords. Specifically, the breaker shown in the drawings of JP-A-2003-94918, the carcass shown in the drawings of JP-A-2009-13220, the band shown in the drawings of JP-A-6-270606, It is used for belts and the like shown in the drawings of Japanese Patent Application Laid-Open No. 2009-7408.

[Steel cord]
Steel cords constituting the rubber/steel cord composite are not particularly limited, but examples thereof include single-twisted steel cords having a 1×n configuration and layer-twisted steel cords having a k+m configuration. These may be used alone or in combination of two or more. Moreover, it may be plated with copper.
Here, the single-twisted steel cord having a 1×n configuration is a single-layer stranded steel cord obtained by twisting n filaments together. A k+m layer-twisted steel cord is a steel cord having a two-layer structure with different twisting directions and twisting pitches, with k filaments in the inner layer and m filaments in the outer layer. n is an integer of 1-27, k is an integer of 1-10, and m is an integer of 1-3. As the plating containing copper, plating with brass (brass) is suitable from the viewpoint of adhesion to the rubber composition.

A rubber-steel cord composite is obtained by coating a steel cord with the rubber composition for coating a cord. The rubber-steel cord composite can be suitably used for tire components (for example, belts, breakers, carcasses) obtained by coating the cords with rubber.

Using a peel tester, the rubber/steel cord composite was peeled from one end along the rubber/cord interface at a speed of 50 mm/min. 20 or less exposures are preferred, 6 or less exposures are more preferred, and 0 exposures are even more preferred. Within the above range, the effect tends to be obtained more favorably.

The rubber/steel cord composite has a peel resistance of preferably 100 N/25 mm or more, more preferably 100 N/25 mm or more, when peeled from one end along the rubber/cord interface at a speed of 50 mm/min using a peel tester. It is 105 N/25 mm or more, more preferably 110 N/25 mm or more, particularly preferably 120 N/25 mm or more, and the upper limit is not particularly limited. Within the above range, the effect tends to be obtained more favorably.

The rubber adhesion state and peel resistance can be achieved by using the rubber composition for coating the cord containing the natural rubber obtained by the above production method.

[tire]
The tire (pneumatic tire, solid tire, airless tire, etc.) of the present invention is a tire using the above rubber-cord composite, and can be produced, for example, by the following steps.
First, a steel cord is coated with the rubber composition for cord coating, and then molded into a member such as a belt. Next, an unvulcanized tire is prepared by laminating the molded member to another tire member. After that, a tire can be obtained by vulcanizing the unvulcanized tire.

The above tires include tires for passenger cars, tires for large passenger cars, tires for large SUVs, tires for trucks and buses, tires for motorcycles, racing tires, studless tires (winter tires), all-season tires, run-flat tires, and aircraft tires. , mining tires and the like.

EXAMPLES The present invention will be specifically described based on Examples, but the present invention is not limited to these.

Various chemicals used in the examples are described below.
Latex raw material A: Field latex obtained from a farm Latex raw material B: Field latex obtained from a farm Sulfuric acid: Sulfuric acid manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd. TOC: 0.6mg/L)
Factory purified water: Thai groundwater and pond water treated with activated carbon, etc. (hardness: 115mg/L, TOC: 9mg/L)

<Examples and Comparative Examples>
According to Table 1, natural rubber latex was coagulated by adding coagulating acid to field latex (natural rubber latex) or by natural coagulation to obtain coagulated rubber (coagulating step).

Next, in the examples, the obtained coagulated rubber was immersed in a water bath containing the water shown in Table 1 (at a temperature of 25°C and a flow rate of 0 m/s) for the storage period shown in Table 1. and stored (immersion process). In addition, Example 1 was immersed in deionized water for 1 day and then immersed in factory purified water for 2 weeks.
On the other hand, in Comparative Examples 4 and 5, the obtained coagulated rubber was stored as it was for the storage period shown in Table 1.

Next, the coagulated rubber stored over the storage period shown in Table 1 was dehydrated with a creeper (a device for squeezing using rolls), crumbed through a shredder, and dried in a dryer (70°C, 14 hours). to produce natural rubber.

(Analysis of natural rubber)
The obtained natural rubbers and the following commercial products A to C used in Comparative Examples 1 to 3 were analyzed as follows, and the results are shown in Table 1.
Commercial product A: Natural rubber made in Indonesia Commercial product B: Natural rubber made in eastern Thailand Commercial product C: Natural rubber made in southern Thailand <amount of acetone extracted>
Based on JIS K 6229:2015, the mass fraction of each natural rubber extracted with acetone was measured.
<Measurement of nitrogen content>
The nitrogen content was measured by using a trace nitrogen carbon measuring device "SUMIGRAPH NC95A (manufactured by Sumika Chemical Analysis Center, Ltd.)" to decompose and gasify each test piece, and the gas was analyzed by a gas chromatograph "GC-8A (Ltd.). Shimadzu Corporation)" was analyzed to quantify the nitrogen content.
<Measurement of calcium content, potassium content and phosphorus content>
Calcium (Ca) content, potassium (K) content and phosphorus content were determined using an ICP emission spectrometer (Optima 8300 from PerkinElmer).

Various chemicals used in the preparation of the rubber composition are collectively described below.
NR: Natural rubber produced in the above examples and comparative examples, or commercial products A to C
Carbon black: N326 (N ₂ SA: 78 m ² /g) manufactured by Mitsubishi Chemical Corporation
Cobalt stearate: cost-F manufactured by Dainippon Ink and Chemicals Co., Ltd. (cobalt content: 9.5% by mass, stearic acid content: 90.5% by mass)
Zinc oxide: Zinc White No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Antioxidant: Nocrack 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p- manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) phenylenediamine)
Oil: Process P200 (paraffinic process oil) manufactured by JOMO Co., Ltd.
Sulfur: Seimisulfur (containing 10% oil) manufactured by Nippon Kandi Kogyo Co., Ltd.
Vulcanization accelerator: Noxceler DZ (N,N-dicyclohexyl-2-benzothiazolylsulfenamide, DCBS) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.

(Preparation of rubber composition)
Using a 1.7 L Banbury mixer, 100 parts by weight of NR, 65 parts by weight of carbon black, 1.5 parts by weight of cobalt stearate, 8 parts by weight of zinc oxide, 2 parts by weight of anti-aging agent, and 2 parts by weight of oil were mixed at 150° C. for 7 hours. The mixture was kneaded for a minute to obtain a kneaded product. Next, using an open roll, the kneaded material, 5.62 parts by mass of sulfur and 1 part by mass of a vulcanization accelerator were kneaded at 100° C. for 2 minutes to obtain a sheet-like unvulcanized rubber composition.

(Evaluation of adhesion with steel cord)
An unvulcanized rubber/cord composite for forming a belt ply was produced by sandwiching the steel cord array on both sides with unvulcanized rubber sheets. By adjusting the vulcanization temperature (constant at 150° C.) and the vulcanization time for this unvulcanized rubber/cord composite, a sample for a peel test was formed. Then, each sample was subjected to a peeling test to test the adhesiveness (wet heat adhesiveness) between the rubber and the steel cord.
<Rubber cord composite>
Steel cord configuration: 2+2 x 0.23HT
Ply thickness: 1.5mm
Number of cords: 38 / 5cm
<Peeling test>
In order to evaluate wet heat adhesion, the vulcanized sample was allowed to cool naturally at room temperature and humidity, and then left in an oven at a temperature of 80° C. and a relative humidity of 95% for 300 hours for wet heat deterioration.
A peel tester was used for the peel test, and the sample was peeled from one end of the sample along the rubber/cord interface at a rate of 50 mm/min. Then, the state of adhesion of rubber to the surface of the cord on the peeled surface was observed. The peel rating was defined as follows.
Furthermore, the peel resistance (N/25 mm) when peeled under the above conditions was measured.
Table 1 shows the results. The greater the peeling score and peeling resistance, the better the adhesiveness after high-humidity heat deterioration.
5 points: The entire plating surface is completely covered with rubber 4 points: 3 to 6 plating surfaces are exposed 3 points: 7 to 20 plating surfaces are exposed 2 points: 21 plating surfaces Some parts are exposed, but 60% or more is covered with rubber as a whole 1 point: Less than 40% of the part is covered with rubber

From Table 1, it is clear that the natural rubbers of Examples can provide good adhesiveness after high-humidity heat deterioration.

The present disclosure (1) is natural rubber having a calcium content of less than 100 ppm.

(2) of the present disclosure is natural rubber having a potassium content of less than 350 ppm.

(3) of the present disclosure is the natural rubber according to (1) or (2) of the present disclosure, which has a phosphorus content of 300 ppm or more.

The present disclosure (4) is a natural rubber of any combination with any of the present disclosures (1) to (3) having an acetone extraction amount of 4.5% by mass or less as measured according to JIS K 6229:2015.

Disclosure (5) is a natural rubber in any combination with any of Disclosures (1) to (4) having a nitrogen content of 0.50% by mass or less.

The present disclosure (6) is a rubber-steel cord composite using any combination of natural rubber with any of the present disclosures (1) to (5).

The present disclosure (7) uses a peel tester and peels from one end along the rubber/cord interface at a speed of 50 mm/min, and the rubber adheres to the cord surface on the peeled surface. A rubber-steel cord composite according to (6) of the present disclosure, which is exposed below.

The present disclosure (8) uses a peel tester and peels from one end along the rubber / cord interface at a rate of 50 mm / min, and the peel resistance is 100 N / 25 mm or more. The present disclosure (6) or ( 7) The rubber/steel cord composite described above.

Disclosure (9) is a tire using a rubber-steel cord composite in any combination with any of Disclosures (6) to (8).

Claims (7)

A natural rubber having a calcium content of less than 100 ppm, a potassium content of less than 350 ppm and a phosphorus content of 300 ppm or more. 2. The natural rubber according to claim 1 , having an acetone extraction amount of 4.5% by mass or less as measured according to JIS K 6229:2015. 3. The natural rubber according to claim 1, which has a nitrogen content of 0.50% by mass or less. A rubber-steel cord composite using the natural rubber according to any one of claims 1 to 3 . When peeling along the rubber/cord interface from one end at a speed of 50 mm/min using a peel tester, the plated surface is exposed at 20 or less places in the rubber adhesion state of the cord surface on the peeled surface. Item 5. The rubber/steel cord composite according to item 4 . 6. The rubber/steel cord composite according to claim 4 or 5 , wherein the rubber/steel cord composite has a peel resistance of 100 N/25 mm or more when peeled from one end along the rubber/cord interface at a speed of 50 mm/min using a peel tester. . A tire using the rubber-steel cord composite according to any one of claims 4 to 6 .