Zinc oxide, rubber compositions for rubber-steel cord composites, and pneumatic tires

Abstract

To provide: zinc oxide which can be used for rubber composition applications as a raw material for a vulcanized rubber with improved peel strength for a metal member such as a steel cord; a rubber composition for a rubber-steel cord composite containing the zinc oxide; and a pneumatic tire having a vulcanized rubber of the rubber composition.SOLUTION: There is provided zinc oxide containing aluminum and iron. The zinc oxide preferably has an iron content of 15 ppm or more and 100 ppm or less and an aluminum content of 40 ppm or more and 100 ppm or less, the ratio of the iron content to the aluminum content is preferably 0.2 to 2.3 times and the iron content preferably is 15 ppm or more and 80 ppm or less. The zinc oxide is preferably used for pneumatic tire applications since the zinc oxide is suitable for a rubber composition for a rubber-steel cord composite and the peel strength of a vulcanized rubber of the rubber composition is improved.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to zinc oxide, a rubber composition for a rubber - steel cord composite, and a pneumatic tire.

Background Art

[0002] Pneumatic tires are composed of vulcanized rubber and metal members such as steel cords, and many performances such as safety and low fuel consumption are required. In particular, in the belt part, which is a component of a pneumatic tire, it is required to improve the adhesion between the steel cord and the vulcanized rubber (hereinafter also referred to as "topping rubber") that covers the steel cord, that is, to improve the peeling force of the topping rubber. In order to improve the peeling force of the topping rubber, there is a technique of adding various compounding agents to the rubber composition that is the raw material of the topping rubber.

[0003] In Patent Document 1 below, as zinc oxide used as a raw material of a rubber composition, an aqueous solution containing a zinc salt is neutralized to synthesize a precipitate such as a hydroxide, which is then filtered and dried, and then heated to synthesize zinc oxide powder (also referred to as the "American method", "wet method", etc.). Zinc oxide synthesized by this method is described.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In Patent Document 1 above, it is characterized by manufacturing zinc oxide by the wet method, and the properties of zinc oxide are not particularly described.

[0006] The inventors focused on the metal composition of zinc oxide blended into the rubber composition used as a raw material in order to improve the peeling strength of topping rubber. As a result, they found that when zinc oxide with a specific metal composition is blended into the rubber composition, the vulcanized rubber exhibits a significantly improved peeling strength against metal components such as steel cords.

[0007] The present invention has been made in view of the above circumstances, and its purpose is to provide zinc oxide that can be used in rubber compositions that serve as raw materials for vulcanized rubber with improved peeling strength from metal members such as steel cords, a rubber composition for rubber-steel cord composites containing the zinc oxide, and a pneumatic tire equipped with vulcanized rubber of the rubber composition. [Means for solving the problem]

[0008] The above problem can be solved by the following configuration. That is, the present invention relates to zinc oxide (1) containing aluminum and iron.

[0009] In the above zinc oxide (1), zinc oxide (2) is preferred, wherein the iron content is 15 ppm or more and 100 ppm or less, and the aluminum content is 40 ppm or more and 100 ppm or less.

[0010] In the zinc oxide (1) or (2) described above, zinc oxide (3) is preferred in which the ratio of the iron content to the aluminum content is 0.2 to 2.3 times.

[0011] Of the above zinc oxides (1) to (3), zinc oxide (4) is preferred, in which the iron content is 15 ppm or more and 80 ppm or less.

[0012] The present invention also relates to a rubber composition containing any of the zinc oxides (1) to (4) described above, or a rubber composition for a rubber-steel cord composite containing any of the zinc oxides (1) to (4) described above.

[0013] Furthermore, the present invention relates to a pneumatic tire comprising the vulcanized rubber of the rubber composition, or a pneumatic tire comprising the vulcanized rubber of the rubber-steel cord composite. [Effects of the Invention]

[0014] To the best of the inventors' knowledge, there are no existing technologies that have thoroughly investigated the metal composition contained in zinc oxide. Under these circumstances, the inventors conducted diligent research and found that when zinc oxide with a specific metal composition, specifically zinc oxide containing aluminum and iron, is blended into a rubber composition, the vulcanized rubber exhibits improved peeling strength against metal components such as steel cords. In particular, it was found that when zinc oxide in which the iron content is 15 ppm to 100 ppm and the aluminum content is 40 ppm to 100 ppm, and furthermore, when zinc oxide in which the ratio of iron content to aluminum content is 0.2 to 2.3 times is blended into a rubber composition, the vulcanized rubber exhibits even greater peeling strength against metal components such as steel cords.

[0015] Furthermore, since pneumatic tires are used for long periods of time, the peeling force of vulcanized rubber (topping rubber) against metal components such as steel cords is required not only for the initial peeling force (hereinafter also referred to as "initial peeling force") but also for the peeling force after a long period of time has elapsed since manufacturing (the peeling force after a degradation test equivalent to the initial peeling force is also referred to as "moist heat peeling force"). In the present invention, it is preferable to incorporate zinc oxide having an iron content of 15 ppm to 80 ppm into the rubber composition, as this improves not only the initial peeling force but also the moist heat peeling force.

[0016] The vulcanized rubber of the rubber composition containing zinc oxide according to the present invention exhibits excellent peeling strength against metal components such as steel cords. For this reason, the zinc oxide according to the present invention is suitably used in rubber compositions for pneumatic tires, and particularly in rubber compositions for rubber-steel cord composites. [Modes for carrying out the invention]

[0017] The zinc oxide according to the present invention is preferably in powder form (zinc oxide powder), and preferably has a specific surface area of ​​2 to 10 [m²]. 2 [g] is more preferably 2-6 [m 2 The specific surface area of ​​the zinc oxide powder according to the present invention can be measured, for example, by the BET method (JIS R1626).

[0018] As mentioned above, the American method (wet process) is known as a method for producing zinc oxide, but there is also the French method. The French method involves heating metallic zinc to vaporize it and then oxidizing it to produce zinc oxide powder. Various materials can be selected as the raw material for metallic zinc, including distilled zinc, electrolytic zinc, and recycled zinc. Recycled zinc can be made from zinc dross, sanka ash, or electric furnace dust. The zinc oxide according to the present invention is preferably zinc oxide powder obtained by heating zinc dross to vaporize it using the French method and then oxidizing it.

[0019] The zinc oxide according to the present invention contains aluminum and iron. In particular, in the present invention, when (i) zinc oxide having an iron content of 15 ppm to 100 ppm and an aluminum content of 40 ppm to 100 ppm, or (ii) zinc oxide having an iron content ratio of 0.2 to 2.3 times that of aluminum is blended into a rubber composition, the resulting vulcanized rubber exhibits superior peeling strength against metal members such as steel cords, which is preferable. The reason why the vulcanized rubber of the zinc oxide described in (i) and (ii), especially the zinc oxide described in (ii), exhibits superior peeling strength against metal members such as steel cords is not clear, but it is presumed that the presence of trace amounts of aluminum and iron in the vulcanized rubber complicates the adhesive film (adhesive interface) with the metal member, thereby producing a so-called anchoring effect and improving the peeling strength.

[0020] Furthermore, in the present invention, zinc oxide, particularly (iii) zinc oxide with an iron content of 15 ppm or more and 80 ppm or less, is preferred when blended in a rubber composition because the vulcanized rubber exhibits excellent initial peel strength and wet heat peel strength against metal members such as steel cords. The reason why the vulcanized rubber of the rubber composition containing the zinc oxide of (iii) exhibits significantly excellent wet heat peel strength against metal members such as steel cords is not clear. However, when the iron content in zinc oxide is designed to be 15 ppm or more and 80 ppm or less, while achieving an anchor effect of the vulcanized rubber on the metal member, the influence of iron oxidation deterioration is suppressed, and it is presumed that the wet heat peel strength of the vulcanized rubber against the metal member can be maintained and improved.

[0021] When blending zinc oxide according to the present invention in a rubber composition, particularly in a rubber composition for a rubber-steel cord composite, the blending amount is preferably 1 to 15 parts by mass, more preferably 3 to 10 parts by mass, when the total amount of the rubber component is 100 parts by mass.

[0022] Zinc oxide according to the present invention can be suitably used in rubber composition applications, particularly in rubber composition applications for rubber-steel cord composites. Hereinafter, materials (other than zinc oxide) constituting the rubber composition according to the present invention, particularly the rubber composition for a rubber-steel cord composite, will be described.

[0023] The rubber composition according to the present invention, particularly the rubber composition for a rubber-steel cord composite, contains a rubber component. As the rubber component, for example, a diene rubber is preferred. The diene rubber is not particularly limited, and examples include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer, styrene-isoprene-butadiene copolymer rubber, and the like. These can be used alone or in combination of two or more.

[0024] The rubber composition according to the present invention, particularly the rubber composition for a rubber-steel cord composite, may contain carbon black and / or silica as a filler, a vulcanizing agent, a vulcanization accelerator, an antioxidant, stearic acid, a softening agent such as wax or oil, a processing aid, and the like.

[0025] As the reinforcing filler, it is preferable to use carbon black and / or silica. That is, the reinforcing filler may be carbon black alone, silica alone, or a combination of carbon black and silica. Preferably, it is carbon black alone or a combination of carbon black and silica. The content of the reinforcing filler is not particularly limited. For example, when the total amount of the rubber component is 100 parts by mass, it is preferably 10 to 140 parts by mass, more preferably 20 to 100 parts by mass, and even more preferably 30 to 80 parts by mass.

[0026] As the carbon black, for example, in addition to carbon black used in the normal rubber industry such as SAF, ISAF, HAF, FEF, GPF, etc., conductive carbon black such as acetylene black and ketjen black can be used. As the silica, wet silica, dry silica, sol-gel silica, surface-treated silica, etc. usually used for rubber reinforcement are used. Among them, wet silica is preferable.

[0027] When silica is included as a filler, it is also preferable to include a silane coupling agent. The silane coupling agent is not particularly limited as long as it contains sulfur in its molecule, and various silane coupling agents that are compounded together with silica in the rubber composition can be used. Examples include sulfidosilanes such as bis(3-triethoxysilylpropyl)tetrasulfide (e.g., Degussa's "Si69"), bis(3-triethoxysilylpropyl) disulfide (e.g., Degussa's "Si75"), bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triecethoxysilylbutyl) disulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, and bis(2-trimethoxysilylethyl) disulfide; mercaptosilanes such as γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, mercaptopropylmethyldimethoxysilane, mercaptopropyldimethylmethoxysilane, and mercaptoethyltriethoxysilane; and protected mercaptosilanes such as 3-octanoylthio-1-propyltriethoxysilane and 3-propionylthiopropyltrimethoxysilane.

[0028] Preferably, sulfur can be used as the vulcanizing agent. Any ordinary sulfur for rubber can be used, such as powdered sulfur, precipitated sulfur, insoluble sulfur, or highly dispersible sulfur. In the rubber composition according to the present invention, particularly the rubber composition for rubber-steel cord composites, the content of the vulcanizing agent is preferably 3 to 10 parts by mass when the total amount of rubber components is 100 parts by mass.

[0029] As a vulcanization accelerator, vulcanization accelerators commonly used for rubber vulcanization, such as sulfenamide-based vulcanization accelerators, thiram-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiourea-based vulcanization accelerators, guanidine-based vulcanization accelerators, and dithiocarbamate-based vulcanization accelerators, may be used individually or in appropriate mixtures.

[0030] As an anti-aging agent, you may use, individually or in appropriate combinations, any anti-aging agent commonly used for rubber, such as aromatic amine-based anti-aging agents, amine-ketone-based anti-aging agents, monophenol-based anti-aging agents, bisphenol-based anti-aging agents, polyphenol-based anti-aging agents, dithiocarbamate-based anti-aging agents, or thiourea-based anti-aging agents.

[0031] The rubber composition according to the present invention, in particular the rubber composition for rubber-steel cord composites, is obtained by kneading zinc oxide, rubber components, fillers, vulcanizing agents, and vulcanization accelerators, in addition to antioxidants, stearic acid, softeners such as waxes and oils, and processing aids, using a kneader commonly used in the rubber industry, such as a Banbury mixer, kneader, and rolls.

[0032] Furthermore, the method of blending each of the above components is not particularly limited. It may be a method in which the components other than vulcanizing agents such as vulcanizing agents and vulcanization accelerators are kneaded in advance to form a masterbatch, and the remaining components are added and kneaded further; a method in which each component is added and kneaded in any order; or a method in which all components are added and kneaded simultaneously.

[0033] The vulcanized rubber of the zinc oxide-containing rubber composition according to the present invention exhibits excellent peeling strength against metal components such as steel cords. Therefore, the rubber composition or rubber composition for rubber-steel cord composites according to the present invention is suitably usable for belt components constituting pneumatic tires. [Examples]

[0034] The present invention will be described in more detail below by illustrating some embodiments.

[0035] (Preparation of zinc oxide 1-4) Zinc dross was heated to 950°C, and air was blown into the resulting zinc vapor to induce oxidative combustion and produce zinc oxide. The produced zinc oxide was cooled and collected to recover zinc oxide powder. For zinc oxide 1, a commercially available product ("Zinc Oxide 3 Types" manufactured by Mitsui Mining & Smelting Co., Ltd.) was used. Dielectric coupled plasma emission spectrometry (ICP-OES) was performed using a PerkinElmer "Optima 8300" to measure the iron (Fe) and aluminum (Al) content in zinc oxides 1-4. The results are shown in Table 1. In Table 1, "ND" means below the detection limit.

[0036] [Table 1]

[0037] (Preparation of rubber compositions for rubber-steel cord composites) To 100 parts by mass of rubber components, the rubber compositions of Examples 4-6 and Comparative Example 2 were blended according to the formulations in Table 2, and the mixture was kneaded using a standard Banbury mixer to prepare the rubber compositions. The individual compounding agents listed in Table 2 are shown below.

[0038] • Natural rubber (NR): RSS#3 • Carbon Black: Product name "Seast 300", manufactured by Tokai Carbon Co., Ltd. • Stearic acid: Product name "Beads Stearic Acid", manufactured by NOF Corporation. • Anti-aging agent: Product name "Santoflex 6PPD", manufactured by Flexis. • Cobalt stearate: Product name "Cobalt stearate", manufactured by Japan Energy Co., Ltd. • Melamine derivative (hexamethoxymethylmelamine): Product name "Sailets 963L", manufactured by Mitsui Cytec Co., Ltd. • Resorcinol-based compounds (resorcinol-alkylphenol-formaldehyde resin): Product name "Sumikanol 620", manufactured by Sumitomo Chemical Co., Ltd. • Sulfur: Product name "Mukuron OT-20", manufactured by Shikoku Chemicals Co., Ltd. • Vulcanization accelerator: Product name "Noxellar DZ-G", manufactured by Ouchi Shinko Chemical Co., Ltd.

[0039] The initial peel strength and moist heat peel strength were evaluated using the rubber compositions of Examples 4-6 and Comparative Example 2 obtained above. Specifically, 12 steel cords for belts (3×0.20+6×0.35 mm structure, copper / zinc = 64 / 36 (mass ratio), brass plating with an adhesion amount of 5 g / kg) were arranged in parallel at a density of 25 mm. Both sides of these cords were covered with 1 mm thick rubber sheets made of each of the above rubber compositions, and these two sheets were laminated so that the cords were parallel to each other to prepare an unvulcanized sample for peel adhesion testing. The initial peel strength and moist heat peel strength were evaluated using the obtained unvulcanized sample under the following conditions.

[0040] (Initial peeling force) Unvulcanized samples of the rubber compositions obtained in Examples 4-6 and Comparative Example 2 were prepared and vulcanized at 150°C for 30 minutes. A peel-and-adhesion test was then performed using a Shimadzu Autograph DCS500, and the maximum strength at the time of peeling was measured as the initial peel force. The peel force of Comparative Example 2 is expressed as an index with the peel force set to 100, and a higher value indicates better initial peel force and superior adhesion. The results are shown in Table 2.

[0041] (Moist heat peeling force) Unvulcanized samples of the rubber compositions obtained in Examples 4-6 and Comparative Example 2 were prepared and vulcanized at 150°C for 30 minutes. The vulcanized test pieces were left in saturated steam at 105°C for 96 hours, and then a peel test was performed between the two layers of steel cords using a Shimadzu Autograph "DCS500". The maximum strength until fracture was measured as the wet heat peel strength. The wet heat peel strength of Comparative Example 2 is expressed as an index with the wet heat peel strength set to 100, and a higher value indicates better wet heat peel strength and better wet heat adhesion. The results are shown in Table 2.

[0042] [Table 2]

[0043] The results in Table 2 show that the vulcanized rubber of the rubber-steel cord composite rubber compositions according to Examples 4 to 6 all exhibit excellent initial peel strength. In particular, the vulcanized rubber of the rubber-steel cord composite rubber compositions according to Examples 4 and 5 contains zinc oxide with an iron content of 15 ppm to 80 ppm, which improves not only the initial peel strength but also the moist heat peel strength.

Claims

1. It contains zinc oxide containing aluminum and iron, The iron content in the zinc oxide is 15 ppm or more and 80 ppm or less. Rubber composition for rubber-steel cord composites.

2. The rubber composition for rubber-steel cord composite according to Claim 1, wherein the aluminum content in the zinc oxide is 40 ppm or more and 100 ppm or less.

3. The rubber composition for rubber-steel cord composite according to Claim 1, wherein the ratio of the iron content to the aluminum content in the zinc oxide is 0.2 to 2.3 times.

4. A pneumatic tire comprising vulcanized rubber of the rubber composition for rubber-steel cord composite according to any one of Claims 1 to 3.

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