Rubber composition for air floating type conveyor belt cover rubber

Abstract

To provide a rubber composition for an air floating type conveyor belt cover rubber which is excellent in flame retardancy, low friction properties, processability and aging resistance, and to provide an air floating type conveyor belt.SOLUTION: The rubber composition for an air floating type conveyor belt cover rubber contains: a rubber component containing at least a natural rubber and a styrene-butadiene rubber; carbon black; antimony trioxide; and a chlorinated paraffin. The content of the carbon black is 75 pts.mass or more based on 100 pts.mass of the rubber component. The content of the chlorinated paraffin is 15-25 pts.mass based on 100 pts.mass of the rubber component. The air floating type conveyor belt has a cover rubber layer formed using the rubber composition.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a rubber composition for an air floating conveyor belt cover rubber.

Background Art

[0002] Conventionally, when transporting coal, an air floating conveyor belt has been used as an energy-saving type conveyor belt. The air floating conveyor belt is a conveyor belt that supplies air from air supply holes provided at equal intervals in the longitudinal direction at the lower part of a circular pipe (trough) to lift the belt from the circular pipe (trough) and transport the load. In recent years, there has been a demand for measures against fires that have a great impact on safety and production in air floating conveyor belts, and the requirements for flame retardancy have been increasing.

[0003] On the other hand, rubber compositions for conveyor belts having flame retardancy and the like have been proposed. For example, Patent Document 1 aims to provide a rubber composition for a flame retardant impact resistant conveyor belt with improved impact resistance while ensuring flame retardancy, and contains 100 parts by mass of a diene rubber, 15 to 30 parts by mass of chlorinated paraffin, 1 to 12 parts by mass of antimony trioxide, and 1 to 11 parts by mass in total of a petroleum resin and / or oil, and contains 50 to 100 parts by mass of styrene-butadiene rubber in 100 parts by mass of the diene rubber. A rubber composition for a conveyor belt is described.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Generally, since the lower cover rubber of an air floating conveyor belt contacts the belt support, it is required to have low friction properties and the like. The air-floating conveyor belt has a carrier side and a return side. On the carrier side of the air-floating conveyor belt, since a load is placed on the belt, it is easy to conform to the shape of the trough due to the load of the load. However, on the return side, the load on the belt is only the self-weight of the belt, and it is difficult to conform to the shape of the return-side trough, and there is a possibility that a part of the upper cover rubber contacts the trough. When the air-floating conveyor belt is used for a long time and the rubber layer of the air-floating conveyor belt is hardened, the possibility becomes higher.

[0006] Under such circumstances, the inventor of the present invention prepared a composition with reference to Patent Document 1 and evaluated it, and it became clear that such a composition may have a large friction. Therefore, in order to improve the low friction property, when the amount of carbon black was increased, it became clear that the processability (for example, vulcanization rate) of the rubber composition may deteriorate. When a general oil is used to recover the deterioration of the processability, it was found that the aging resistance deteriorates (the rubber layer hardens during long-term use).

[0007] Therefore, an object of the present invention is to provide a rubber composition for an air-floating conveyor belt cover rubber having excellent flame retardancy, low friction property, processability, and aging resistance. Another object of the present invention is also to provide an air-floating conveyor belt.

Means for Solving the Problems

[0008] As a result of intensive studies to solve the above problems, the inventor of the present invention has found that a desired effect can be obtained by a rubber composition containing at least a rubber component containing natural rubber and styrene-butadiene rubber, a specific amount of carbon black, antimony trioxide, and a specific amount of chlorinated paraffin, and has reached the present invention. The present invention is based on the above findings and the like, and specifically solves the above problems by the following configuration.

[0009] [1] A rubber composition containing at least a rubber component including natural rubber and styrene-butadiene rubber, carbon black, antimony trioxide, and chlorinated paraffin, wherein the content of the carbon black is 75 parts by mass or more with respect to 100 parts by mass of the rubber component, and the content of the chlorinated paraffin is 15 to 25 parts by mass with respect to 100 parts by mass of the rubber component, the rubber composition for an air-floating conveyor belt cover rubber. [2] wherein the content of the natural rubber is 10 to 60% by mass in the rubber component, and the content of the styrene-butadiene rubber is 40 to 70% by mass in the rubber component, the rubber composition according to [1]. [3] wherein the content of the antimony trioxide is 1 to 10 parts by mass with respect to 100 parts by mass of the rubber component, the rubber composition according to [1] or [2]. [4] wherein the content of the carbon black is 100 parts by mass or less with respect to 100 parts by mass of the rubber component, the rubber composition according to any one of [1] to [3]. [5] wherein the carbon black contains carbon black having a nitrogen adsorption specific surface area of 70 m 2 / g or more, the rubber composition according to any one of [1] to [4]. [6] wherein the carbon black contains carbon black A having a nitrogen adsorption specific surface area of 100 to 150 m 2 / g and carbon black B having a nitrogen adsorption specific surface area of 70 to 90 m 2 / g, the rubber composition according to any one of [1] to [5]. [7] Furthermore, it contains polyethylene, the rubber composition according to any one of [1] to [6]. [8] An air-floating conveyor belt having a cover rubber layer formed using the rubber composition according to any one of [1] to [7]. [Effect of the Invention]

[0010] The rubber composition for the air floating conveyor belt cover rubber of the present invention is excellent in flame retardancy, low friction, processability, and aging resistance. Moreover, according to the rubber composition for the air floating conveyor belt cover rubber of the present invention, an air floating conveyor belt excellent in flame retardancy, low friction, processability, and aging resistance can be provided.

Brief Description of the Drawings

[0011]

Figure 1

Modes for Carrying Out the Invention

[0012] The present invention will be described in detail below. In this specification, the numerical range represented by "~" means a range including the numerical values described before and after "~". In this specification, unless otherwise specified, each component can be used alone or in combination of two or more of the substances corresponding to the component. When the component contains two or more substances, the content of the component means the total content of the two or more substances. In this specification, that at least one of flame retardancy, low friction, processability, and aging resistance is more excellent may mean that the effect of the present invention is more excellent.

[0013] [Rubber Composition for Air Floating Conveyor Belt Cover Rubber] The rubber composition for the air floating conveyor belt cover rubber of the present invention (the rubber composition of the present invention) contains a rubber component containing at least natural rubber and styrene-butadiene rubber, carbon black, antimony trioxide, and chlorinated paraffin, the content of the carbon black is 75 parts by mass or more with respect to 100 parts by mass of the rubber component, The rubber composition for an air-floating conveyor belt cover rubber is such that the content of the above-mentioned chlorinated paraffin is 15 to 25 parts by mass with respect to 100 parts by mass of the above-mentioned rubber component. Hereinafter, each component contained in the rubber composition of the present invention will be described in detail.

[0014] <<Rubber component>> In the present invention, the rubber component contains at least natural rubber and styrene-butadiene rubber.

[0015] <Natural rubber> The natural rubber (NR) contained in the rubber composition of the present invention is not particularly limited. For example, conventionally known ones can be mentioned.

[0016] <Styrene-butadiene rubber> The styrene-butadiene rubber (SBR) contained in the rubber composition of the present invention is not particularly limited. For example, conventionally known ones can be mentioned.

[0017] (Content of NR, SBR) From the viewpoint that the effects of the present invention are more excellent and the low tackiness is excellent, the content of the above-mentioned natural rubber is preferably 10 to 60% by mass in the rubber component (total amount), and more preferably 30 to 60% by mass. From the viewpoint that the effects of the present invention are more excellent and the low tackiness is excellent, the content of the above-mentioned styrene-butadiene rubber is preferably 40 to 70% by mass in the rubber component (total amount), and more preferably 40 to 45% by mass.

[0018] (Other rubbers) The rubber component can further contain rubbers other than natural rubber and styrene-butadiene rubber (other rubbers). From the viewpoint that the effects of the present invention are more excellent, other rubbers are preferably diene rubbers such as isoprene rubber (IR), butadiene rubber (BR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), and butyl rubber (IIR), and more preferably butadiene rubber (BR). ·BR The butadiene rubber that can be contained in the rubber composition of the present invention is not particularly limited. For example, conventionally known ones can be mentioned.

[0019] (Content of NR, SBR, BR) When the rubber composition of the present invention further contains butadiene rubber, the content of the above natural rubber is preferably 20 to 60% by mass, more preferably 20 to 55% by mass, from the viewpoint that the effects of the present invention are more excellent and the low tackiness is excellent, in the rubber component (total amount). In the above case, the content of the styrene-butadiene rubber is preferably 30 to 50% by mass, more preferably 35 to 45% by mass, still more preferably 40 to 45% by mass, in the rubber component (total amount), from the viewpoint that the effects of the present invention are more excellent and the low tackiness is excellent. In the above case, the content of the butadiene rubber is preferably 10 to 30% by mass, more preferably 10 to 20% by mass, in the rubber component (total amount), from the viewpoint that the effects of the present invention are more excellent and the low tackiness is excellent.

[0020] (Ratio of the content of natural rubber and styrene-butadiene rubber when further containing butadiene rubber) When the rubber composition of the present invention further contains butadiene rubber, the content of the styrene-butadiene rubber is preferably 30 to 85% by mass, more preferably 40 to 60% by mass, in the total content of natural rubber and styrene-butadiene rubber, from the viewpoint that the effects of the present invention are more excellent and the low tackiness is excellent.

[0021] (Ratio of the content of styrene-butadiene rubber and butadiene rubber when further containing butadiene rubber) When the rubber composition of the present invention further contains butadiene rubber, the content of the styrene-butadiene rubber is preferably 60 to 90% by mass, more preferably 65 to 85% by mass, in the total content of styrene-butadiene rubber and butadiene rubber, from the viewpoint that the effects of the present invention are more excellent and the low tackiness is excellent.

[0022] <Carbon black> The carbon black contained in the rubber composition of the present invention is not particularly limited. For example, conventionally known carbon blacks can be mentioned.

[0023] From the viewpoint that the effects of the present invention are more excellent and the low tackiness is excellent, the carbon black preferably contains a carbon black having a nitrogen adsorption specific surface area (N2SA) of 70 m 2 / g or more, and more preferably contains carbon black A having a nitrogen adsorption specific surface area of 100 to 150 m 2 / g and carbon black B having a nitrogen adsorption specific surface area of 70 to 90 m 2 / g. From the viewpoint that the effects of the present invention are more excellent and the low tackiness is excellent, the N2SA of carbon black A is preferably 100 to 120 m 2 / g. From the viewpoint that the effects of the present invention are more excellent and the low tackiness is excellent, the N2SA of carbon black B is preferably 75 to 85 m 2 / g. The nitrogen adsorption specific surface area of the carbon black can be measured according to JIS K6217-2:2001 "Part 2: Method for determining specific surface area - Nitrogen adsorption method - Single point method".

[0024] Examples of the carbon black include SAF (Super Abrasion Furnace), ISAF (Intermediate Super Abrasion Furnace), HAF (High Abrasion Furnace), FEF (Fast Extruding Furnace), GPF (General Purpose Furnace), SRF (Semi-Reinforcing Furnace), FT (Fine Thermal), MT (Medium Thermal), and the like.

[0025] Examples of carbon black A include ISAF grade carbon black and SAF grade carbon black. Examples of carbon black B include HAF grade carbon black and FEF grade carbon black.

[0026] <Carbon black content> In the present invention, the carbon black content is 75 parts by mass or more with respect to 100 parts by mass of the rubber component. When the carbon black content is within the above range, excellent low friction properties are obtained. When using two or more types of carbon black as the carbon black, the carbon black content means the total amount of the carbon black.

[0027] From the viewpoint that the effects of the present invention are more excellent and the low tackiness is excellent, the carbon black content is preferably 100 parts by mass or less, more preferably 80 to 95 parts by mass with respect to 100 parts by mass of the rubber component.

[0028] When the carbon black contains the above carbon black A and the above carbon black B, from the viewpoint that the effects of the present invention are more excellent and the low tackiness is excellent, the content of carbon black A is preferably 50 to 65% by mass in the total content of carbon black A and carbon black B, more preferably 55 to 65% by mass.

[0029] <<Antimony trioxide>> The antimony trioxide contained in the rubber composition of the present invention is not particularly limited. In the present invention, antimony trioxide can function as a flame retardant.

[0030] (Content of antimony trioxide) From the viewpoint that the effects of the present invention are more excellent and the low tackiness is excellent, the content of antimony trioxide is preferably 1 to 10 parts by mass, more preferably 4 to 8 parts by mass with respect to 100 parts by mass of the rubber component.

[0031] <<Chlorinated paraffin>> The chlorinated paraffin contained in the rubber composition of the present invention is not particularly limited. For example, conventionally known ones can be mentioned. In the present invention, chlorinated paraffin can function as a flame retardant and a plasticizer.

[0032] From the viewpoint of more excellent effects of the present invention and excellent low tackiness, the chlorine content of the chlorinated paraffin is preferably 60 to 80% by mass, more preferably 65 to 75% by mass, and still more preferably 68 to 72% by mass in the chlorinated paraffin.

[0033] <Content of chlorinated paraffin> In the present invention, the content of chlorinated paraffin is 15 to 25 parts by mass with respect to 100 parts by mass of the above rubber component. When the content of chlorinated paraffin is within the above range, flame retardancy, low friction property, processability and aging resistance are excellent. Also, low tackiness is excellent.

[0034] From the viewpoint of more excellent effects of the present invention and excellent low tackiness, the content of chlorinated paraffin is preferably 15 to 23 parts by mass, and more preferably 17 to 21 parts by mass.

[0035] (Polyethylene) From the viewpoint of excellent low tackiness, the rubber composition of the present invention preferably further contains polyethylene. One preferred embodiment of polyethylene is that it is a polyethylene homopolymer.

[0036] ·Weight-average molecular weight of polyethylene From the viewpoint of more excellent effects of the present invention and excellent low tackiness, the weight-average molecular weight (Mw) of polyethylene is preferably 1 million to 2.5 million, and more preferably 1.5 million to 2.3 million.

[0037] (Method for measuring the weight-average molecular weight of polyethylene) The weight-average molecular weight of polyethylene was determined as the molecular weight in terms of standard polystyrene by GPC (gel permeation chromatography). The measuring apparatus and conditions are as follows. ·Apparatus: GPC apparatus "HLC-8020" manufactured by Tosoh Corporation · Separation column: Two "GMH-HR-H" columns manufactured by Tosoh Corporation were connected in series. · Detector: "RI-8020 Differential Refractometer" manufactured by Tosoh Corporation · Eluent: Tetrahydrofuran · Eluent flow rate: 1.0 ml / min · Sample concentration: 5 mg / 10 ml · Column temperature: 40 °C

[0038] · Average particle diameter of polyethylene From the viewpoint that the effects of the present invention are more excellent and the low adhesiveness is excellent, the average particle diameter of polyethylene is preferably 1 to 300 μm, more preferably 20 to 150 μm. The average particle diameter of polyethylene may be the average particle diameter d in the weight-based particle size distribution by the Coulter counter method. 50 It may also be so. The average particle diameter of polyethylene may be a catalog value.

[0039] · Content of polyethylene From the viewpoint that the effects of the present invention are more excellent and the low adhesiveness is excellent, the content of polyethylene is preferably 3 to 10 parts by mass, more preferably 3 to 8 parts by mass with respect to 100 parts by mass of the rubber component.

[0040] From the viewpoint that the effects of the present invention are more excellent, the low adhesiveness is excellent, and the flame retardancy and low adhesiveness can be made compatible at a high level, the content of polyethylene is preferably 9 to 40% by mass, more preferably 13 to 30% by mass in the total content of the above polyethylene and the above chlorinated paraffin.

[0041] (Oil) From the viewpoint that the effects of the present invention are more excellent and the low adhesiveness is excellent, the rubber composition of the present invention preferably further contains oil (excluding chlorinated paraffin). Examples of the oil include process oil; mineral oils such as aroma oil. Examples of the above process oil include those conventionally known. The same applies to aroma oil and mineral oil. From the viewpoint that the oil has more excellent effects of the present invention and excellent low adhesiveness, it preferably contains a process oil or an aroma oil, and more preferably contains an aroma oil. As the aroma oil, for example, it refers to an oil in which the content (C A ) of aromatic hydrocarbons contained in a certain oil is 20% by mass or more in the oil. C A and C P and C N can be measured according to the ring analysis method (n-d-M method) (ASTM D3238).

[0042] · Content of oil When the rubber composition of the present invention further contains the above oil, the content of the above oil is preferably 10 to 40 parts by mass, more preferably 20 to 35 parts by mass, and still more preferably 25 to 33 parts by mass with respect to 100 parts by mass of the above rubber component. · Content of aroma oil When the rubber composition of the present invention further contains an oil and the above oil includes an aroma oil, the content of the aroma oil is preferably 90% by mass or more, more preferably 95 to 100% by mass in the total amount of the above oil.

[0043] (Additive) The rubber composition of the present invention can further contain an additive as needed. Examples of the above additive include fillers other than carbon black, vulcanizing agents such as sulfur, vulcanization accelerators, vulcanization aids such as zinc oxide and stearic acid, reversion inhibitors, silane coupling agents, anti-aging agents, antioxidants, ultraviolet absorbers, flame retardants other than chlorinated paraffin and antimony trioxide, adhesion promoters, plasticizers other than oils, etc. The type and content of each additive can be appropriately selected. From the viewpoint that the effects of the present invention are more excellent, the content of sulfur is preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the above rubber component.

[0044] The manufacturing method of the rubber composition of the present invention is not particularly limited. For example, the above-described essential components and additives (excluding vulcanizing agents, vulcanization aids, and vulcanization accelerators) that can be further used as necessary are mixed with a Banbury mixer or the like, and then a vulcanizing agent, a vulcanization aid, and a vulcanization accelerator are further added thereto and mixed.

[0045] Vulcanization of the rubber composition of the present invention can be carried out under the conditions usually employed. The vulcanization temperature can be, for example, carried out under the conditions of 140 to 150 °C. Pressure may be applied during vulcanization.

[0046] The rubber composition of the present invention is a rubber composition for the cover rubber of an air-supported conveyor belt. The rubber composition of the present invention can be applied to the upper cover rubber layer and / or the lower cover rubber layer of an air-supported conveyor belt. When the rubber composition of the present invention is applied to the upper cover rubber layer and the lower cover rubber layer of an air-supported conveyor belt, the rubber composition for the upper cover rubber layer and the rubber composition for the lower cover rubber layer may be the same or different.

[0047] [Air-supported conveyor belt] The air-supported conveyor belt of the present invention (the conveyor belt of the present invention) is an air-supported conveyor belt having a cover rubber layer formed using the rubber composition of the present invention.

[0048] The rubber composition used for the conveyor belt of the present invention is not particularly limited as long as it is the rubber composition of the present invention.

[0049] Examples of the conveyor belt of the present invention include a conveyor belt composed of an upper cover rubber layer, a reinforcing layer, and a lower cover rubber layer. It is sufficient that the upper cover rubber layer and / or the lower cover rubber layer is formed using the above rubber composition. The lower cover rubber layer can be one layer or a plurality of layers. The same applies to the upper cover rubber layer and the reinforcing layer.

[0050] [Lower cover rubber layer] From the viewpoint that the effect of the present invention is more excellent and the low adhesiveness is excellent, it is preferable that at least the back surface (the surface in contact with the roller) of the lower cover rubber layer is formed of the rubber composition of the present invention.

[0051] When the lower cover rubber layer has two or more layers, it is preferable that at least the layer corresponding to the back surface among the two or more layers is formed using the rubber composition of the present invention. All of the lower cover rubber layers (including single-layer and those having multiple layers) may be formed using the rubber composition of the present invention.

[0052] <Upper cover rubber layer> From the viewpoint that the effect of the present invention is more excellent and the low adhesiveness is excellent, it is preferable that at least the surface (the surface in contact with the conveyed object) of the upper cover rubber layer is formed of the rubber composition of the present invention.

[0053] When the upper cover rubber layer has two or more layers, it is preferable that at least the layer corresponding to the above surface among the two or more layers is formed using the rubber composition of the present invention. All of the upper cover rubber layers (including single-layer and those having multiple layers) may be formed using the rubber composition of the present invention.

[0054] <Reinforcing layer> The above reinforcing layer is not particularly limited, and those usually used for ordinary conveyor belts can be appropriately selected and used. The reinforcing layer can have, for example, a core body and an adhesive rubber (coating rubber). It is preferable that the above adhesive rubber (coating rubber) covers the core body. Examples of the material of the core body include fibers such as polyester fiber, polyamide fiber, and aramid fiber; and metals such as steel. The above fibers can be used as canvas. Canvas means a plain woven fabric. The adhesive rubber is not particularly limited. For example, conventionally known ones can be mentioned. The form of the reinforcing layer is not particularly limited. For example, it may be in the form of a sheet, or a bundle of reinforcing wires (e.g., steel cords, bundles of the above fibers) may be embedded in parallel in the reinforcing layer.

[0055] The conveyor belt of the present invention can have a reinforcing layer, for example, between the upper cover rubber layer and the lower cover rubber layer. When there are multiple layers of the reinforcing layer, a rubber composition can be disposed between the multiple reinforcing layers. The rubber composition disposed between the multiple reinforcing layers is not particularly limited. For example, conventionally known ones can be mentioned.

[0056] The thickness of the upper cover rubber layer can be, for example, 3 to 25 mm. The thickness of the lower cover rubber layer can be, for example, 3 to 20 mm. In addition, when the upper cover rubber layer is composed of two or more layers, the thickness of the upper cover rubber layer can be the sum of the thicknesses of these layers. The same applies to the thickness of the lower cover rubber layer.

[0057] Hereinafter, the conveyor belt of the present invention will be described with reference to the accompanying drawings. Note that the present invention is not limited to the accompanying drawings. FIG. 1 is a cross-sectional perspective view schematically showing an example of a preferred embodiment of the conveyor belt of the present invention. In FIG. 1, the conveyor belt 1 is composed of an upper cover rubber layer 2, a reinforcing layer 3, and a lower cover rubber layer 4, and is laminated in this order. The upper cover rubber layer 2 has an outer layer 11 and an inner layer 12. The lower cover rubber layer 4 has an inner layer 15 and an outer layer 16. When the conveyor belt 1 is applied to an air-supported belt conveyor, the outer layer 16 contacts the roller. The surface 5 of the upper cover rubber layer 2 (outer layer 11) can be the conveying surface for the conveyed object.

[0058] At least one or both of the outer layer 11 and the outer layer 16 may be formed using the rubber composition of the present invention. In the lower cover rubber layer 4, it is preferable that the outer layer 16, which is the back surface of the lower cover rubber layer 4, is formed at least by the rubber composition of the present invention. The outer layer 16 and the inner layer 15 may be formed using the rubber composition of the present invention. Further, the inner layer 15 may be an adhesive layer for adhering the reinforcing layer 3 and the outer layer 16. In the upper cover rubber layer 2, it is preferable that the outer layer 11, which is the surface of the upper cover rubber layer 2, is formed at least by the rubber composition of the present invention. The outer layer 11 and the inner layer 12 may be formed using the rubber composition of the present invention. Further, the inner layer 12 may be an adhesive layer for adhering the reinforcing layer 3 and the outer layer 11.

[0059] The conveyor belt of the present invention is not particularly limited with respect to its manufacturing method. For example, conventionally known manufacturing methods can be mentioned. Specifically, first, the rubber composition of the present invention for the lower cover rubber layer and the rubber composition of the present invention for the upper cover rubber layer are each formed into a sheet shape, and then, a sheet of the rubber composition for the upper cover rubber layer, a reinforcing layer, and a sheet of the composition of the present invention are laminated in the above order, and the obtained laminate is pressed at a temperature of 150 to 170 ° C for 10 to 60 minutes to manufacture the conveyor belt of the present invention. A sheet of another rubber composition may be disposed between the reinforcing layer and the sheet of the rubber composition of the present invention. The conveyor belt of the present invention can be used as an air-floating conveyor belt.

Examples

[0060] Examples are shown below to specifically describe the present invention. However, the present invention is not limited thereto.

[0061] <<Manufacture of Rubber Composition>> Using each component in the following Table 1 with the composition (parts by mass) shown in the same table, these were mixed with a stirrer to manufacture a rubber composition.

[0062] <<Evaluation>> Using each rubber composition manufactured as described above, the following evaluations were performed. The results are shown in Table 1. <Low Friction Property> (Evaluation Method) First, each rubber composition produced as described above was vulcanized for 30 minutes under a pressure of 3.0 MPa using a press molding machine at 150 °C to produce a vulcanized rubber with a thickness of 10 mm. The vulcanized rubber was cut into pieces with dimensions of 10 mm in length × 10 mm in width × 10 mm in thickness to produce vulcanized rubber test pieces. Next, the vulcanized rubber test piece produced as described above was placed on a disc-shaped iron plate, and a vertical load of 4.90 N was applied to the vulcanized rubber test piece to press-bond the vulcanized rubber test piece and the iron plate. Then, the iron plate was rotated at a speed of 300 mm / min, and the horizontal load applied to the rubber test piece at that time was measured. And the dynamic friction coefficient was calculated by applying the applied load and the measured horizontal load to the following formula. Dynamic friction coefficient (μk) = Horizontal load / Vertical load

[0063] (Evaluation Criteria) In the present invention, when the above dynamic friction coefficient is 0.5 μk or less, it is considered to have excellent low friction property. On the other hand, when the above dynamic friction coefficient exceeds 0.5 μk, it was evaluated that the low friction property was poor. The smaller the above dynamic friction coefficient is than 0.5 μk, the more excellent the low friction property is, and the driving resistance can be further reduced.

[0064] <Low Adhesion>[ (Evaluation Method) Using the sample in the state where the vulcanized rubber test piece and the iron plate were press-bonded after the measurement of the above horizontal load, a load cell was set on the vulcanized rubber test piece of the sample, and the vulcanized rubber test piece (sample) was lifted upward to measure the peeling strength when the vulcanized rubber test piece was peeled from the iron plate.

[0065] (Evaluation Criteria) In the present invention, when the above peeling strength is 1.0 kgf or less, it is considered to have excellent low adhesion property. The smaller the above peeling strength is than 1.0 kgf, the more excellent the low adhesion property is, and the driving resistance can be further reduced. On the other hand, when the above peeling strength exceeds 1.0 kgf, it was evaluated that the low adhesion property was poor.

[0066] <Aging Resistance>[ (Preparation of Test Specimens) First, each rubber composition manufactured as described above was vulcanized for 30 minutes under a pressure of 3.0 MPa using a press molding machine at 148°C to prepare a vulcanized sheet with a thickness of 2 mm. From this sheet, JIS No. 3 dumbbell-shaped test specimens (initial test specimens) were punched out. Next, a heat aging test was conducted on each of the above-prepared initial test specimens by placing them under the condition of 70°C for 168 hours to obtain heat-aged test specimens.

[0067] (Evaluation Method) · Aging Resistance 1 (ΔEB) For each of the above-prepared initial test specimens and each heat-aged test specimen, a tensile test was conducted in accordance with JIS K6251:2017 under the conditions of 25°C and a tensile speed of 500 mm / min to measure the elongation at break (initial EB) [%] of each initial test specimen and the elongation at break (EB after aging) [%] of each heat-aged test specimen. Each of the above-obtained initial EB and EB after aging was applied to the following formula to calculate ΔEB (%). ΔEB (%) = (EB after aging - initial EB) / initial EB × 100

[0068] · Aging Resistance 2 (ΔHS) For each of the above-prepared initial test specimens and each heat-aged test specimen, a Type A durometer hardness test was conducted in accordance with JIS K6253-3:2012 under the condition of 25°C to measure the hardness (initial HS) of each initial test specimen and the hardness (hardness after aging) of each heat-aged test specimen. Each of the above-obtained initial HS and HS after aging was applied to the following formula to calculate ΔHS. ΔHS = hardness after aging - initial HS

[0069] (Evaluation Criteria for Aging Resistance) In the present invention, when the absolute value of ΔEB is 20 or less and the absolute value of ΔHS is less than 5, it is considered to have excellent aging resistance (heat aging resistance). The smaller the absolute value of ΔEB and / or the smaller the absolute value of ΔHS, the more excellent the aging resistance (heat aging resistance). On the other hand, when the absolute value of ΔEB exceeded 20, or when the absolute value of ΔHS was 5 or more, it was evaluated that the weather resistance (heat aging resistance) was poor.

[0070] <Flammability> (Evaluation method) A fabric layer conveyor rubber belt (test piece) having each rubber composition manufactured as described above as a cover rubber layer was produced. In the above production, vulcanization was carried out by press vulcanization for 30 minutes under the condition of 150°C. Using three of each test piece manufactured as described above, a flammability test was carried out according to JIS K6324:2013, the flame duration (seconds) of each test piece was measured, and the average value (average value of three) of the flame duration of each test piece was obtained.

[0071] (Evaluation criteria) In the present invention, regarding the flame duration, in accordance with Class 3 of flammability in JIS K6324:2013, when the average value of the flame duration of each test piece obtained as described above was 60 seconds or less, it was evaluated that the flammability was excellent. The smaller the average value of the above flame duration is than 60 seconds, the more excellent the flammability is. On the other hand, when the average value of the above flame duration exceeded 60 seconds, it was evaluated that the flammability was poor.

[0072] <Processability> (Evaluation method) Each rubber composition (unvulcanized) manufactured as described above was in accordance with JIS K6300-2:2001 "Unvulcanized rubber - Physical properties - Part 2: Method for obtaining vulcanization characteristics by oscillating disk rheometer", using a rotorless vulcanization tester as a rheometer, at a temperature of 150°C, a vulcanization curve was measured with the obtained torque on the vertical axis and the vulcanization time on the horizontal axis. From the obtained vulcanization curve, the maximum value M H and the minimum value M L were obtained. (Evaluation criteria) The difference between the maximum value M H and the minimum value M L is defined as M E . M L +M ELet the time to reach a torque of ×0.95 be T95. Each T95 obtained as described above was expressed using an index with the T95 of Comparative Example 7 taken as 1.0. In the present invention, when the above index is 3.0 or less, it means that the processability (vulcanization rate) is excellent. The smaller the above index is, the better the processability. On the other hand, when the above index exceeds 3.0, it means that the processability is poor.

[0073] [Table 1]

[0074] [Table 2]

[0075] [Table 3]

[0076] The details of each component shown in Table 1 are as follows. <Rubber component> · NR: Natural rubber (RSS#3) · SBR: Styrene-butadiene rubber (Nipol 1502, manufactured by Zeon Corporation, Japan; non-oil extended) · BR: Butadiene rubber (Nipol BR1220, manufactured by Zeon Corporation, Japan)

[0077] <Carbon black> · ISAF grade carbon black: N2SA 120 m 2 / g · HAF grade carbon black: N2SA 80 m 2 / g · SRF grade carbon black: N2SA 27 m 2 / g

[0078] <Flame retardant> · Chlorinated paraffin: Empal 70S, manufactured by Dover Chemical Corporation. Chlorine content is 70% by mass in the chlorinated paraffin · Antimony trioxide: PATOX-M, manufactured by Nippon Mining & Metals Co., Ltd

[0079] · Polyethylene: High molecular weight polyethylene. Weight average molecular weight of 2 million, average particle size of 30 μm. Trade name Mipelon XM220, manufactured by Mitsui Chemicals, Inc.

[0080] <Oil> · Oil: Aroma oil (A-OMIX, manufactured by Sankyo Yuka Kogyo Co., Ltd.) (C A ) 20% by mass or more

[0081] <Vulcanizing agent · Vulcanization accelerator> · Sulfur: Fine powder sulfur (manufactured by Hosoi Chemical Industry Co., Ltd.) · Vulcanization accelerator NS: Nocceler NS-P (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) · Vulcanization accelerator TT: Sanseler TT (manufactured by Sanshin Chemical Industry Co., Ltd.)

[0082] As is clear from the results shown in Table 1, Comparative Example 1, which does not contain chlorinated paraffin and antimony trioxide, had poor aging resistance and flame retardancy. Comparative Examples 2 to 4 with a low carbon black content had poor low friction properties. Comparative Example 2 also had poor low adhesion properties. Comparative Examples 3 to 4 also had poor processability. Comparative Example 5 with a chlorinated paraffin content less than the predetermined range had poor flame retardancy. Comparative Example 6 with a chlorinated paraffin content more than the predetermined range had poor processability. Comparative Example 6 also had poor low adhesion properties. Comparative Example 7, which does not contain chlorinated paraffin and antimony trioxide, had poor aging resistance and processability.

[0083] In contrast, the rubber composition of the present invention was excellent in flame retardancy, low friction properties, processability and aging resistance. Further, the rubber composition of the present invention was also excellent in low adhesion properties.

Explanation of reference numerals

[0084] 1: Conveyor belt 2: Upper cover rubber layer 3: Reinforcing layer 4: Lower cover rubber layer 5: Surface 11, 16: Outer layer 12, 15: Inner layer

Claims

1. A rubber composition containing at least a rubber component including natural rubber and styrene-butadiene rubber, carbon black, antimony trioxide, and chlorinated paraffin, wherein the content of the carbon black is 75 parts by mass or more with respect to 100 parts by mass of the rubber component, the content of the chlorinated paraffin is 15 to 25 parts by mass with respect to 100 parts by mass of the rubber component, the content of the natural rubber is 10 to 60% by mass in the rubber component, and the content of the styrene-butadiene rubber is 40 to 70% by mass in the rubber component, a rubber composition for an air-floating conveyor belt cover rubber.

2. The rubber composition according to claim 1, wherein the content of the antimony trioxide is 1 to 10 parts by mass with respect to 100 parts by mass of the rubber component.

3. The rubber composition according to claim 1 or 2, wherein the content of the carbon black is 100 parts by mass or less with respect to 100 parts by mass of the rubber component.

4. The carbon black contains carbon black having a nitrogen adsorption specific surface area of 70 m 2 / g or more, and the rubber composition according to any one of claims 1 to 3.

5. The carbon black is carbon black A having a nitrogen adsorption specific surface area of 100 to 150 m 2 / g and carbon black B having a nitrogen adsorption specific surface area of 70 to 90 m 2 / g, and the rubber composition according to any one of claims 1 to 4.

6. Furthermore, the rubber composition according to any one of claims 1 to 5, which contains polyethylene.

7. An air-floating conveyor belt having a cover rubber layer formed using the rubber composition according to any one of claims 1 to 6.

Images