AU2017221581A1

AU2017221581A1 - Rubber composition for conveyor belts, and conveyor belt

Info

Publication number: AU2017221581A1
Application number: AU2017221581A
Authority: AU
Inventors: Deqing Zou
Original assignee: Yokohama Rubber Co Ltd
Current assignee: Yokohama Rubber Co Ltd
Priority date: 2016-02-15
Filing date: 2017-02-14
Publication date: 2018-08-30
Anticipated expiration: 2037-02-14
Also published as: CN108602622A; AU2017221581B2; JPWO2017141909A1; WO2017141909A1; JP6904328B2

Abstract

The present invention provides: a rubber composition for conveyor belts, which enables the production of a conveyor belt that has a cover rubber layer having excellent wear resistance; and a conveyor belt which uses this rubber composition for conveyor belts. A rubber composition for conveyor belts according to the present invention contains a rubber component that contains 45-100% by mass of a butadiene rubber, an ultra high molecular weight polyethylene and carbon black. The content of the ultra high molecular weight polyethylene is 1.0-15.0 parts by mass relative to 100 parts by mass of the rubber component; the content of the carbon black is 25-45 parts by mass relative to 100 parts by mass of the rubber component; and the carbon black has a nitrogen adsorption specific surface area of 85-160 m

Description

RUBBER COMPOSITION FOR CONVEYOR BELT, AND CONVEYOR BELT

Technical Field [ 0001]

The present invention relates to a rubber composition for a conveyor belt and a conveyor belt.

Background Art [ 0002] A rubber belt used as a conveyor belt is a multilayer structure including: a core body (hereinafter referred to as a "reinforcing layer") made of a canvas, steel cord, and the like; an upper surface cover rubber layer and a lower surface cover rubber layer, covering the upper surface and the lower surface of the above-mentioned core body respectively. This rubber belt is bonded at both ends and processed into a loop-shaped conveyor belt to configure a belt conveyor circularly driving a conveyance path formed by a number of rollers and pulleys, thereby continuously conveying objects to be conveyed (e.g., bulk materials such as ore, gravel, and grain; and large bulk materials such as boxes, bags, and pallets) along the above-mentioned conveyance path.

[ 00 03]

The belt conveyor rotates the above-mentioned pulleys, thereby driving the conveyor belt. The electric power consumption therefor is known to become larger in general as the conveyance path length is longer and the belt conveyor has a longer machine length. This is believed to be due to the increased number of rollers supporting the conveyor belt as the machine length becomes longer, and in turn a larger motive power loss (energy loss) caused by contact of the lower surface cover rubber layer of the conveyor belt and the rollers.

[ 0004]

In relation to this, Patent Document 1 describes "a rubber composition for a conveyor belt comprising: a rubber component comprising a natural rubber (NR) and a butadiene rubber (BR), wherein a mass ratio of the natural rubber (NR) and the butadiene rubber (BR) (NR/BR) is from 90/10 to 55/45; an ultra high molecular weight polyethylene; and a carbon black; wherein a content of the ultra high molecular weight polyethylene is from 5 to 22 parts by mass per 100 parts by mass of the rubber component; a content of the carbon black is from 5 to 55 parts by mass per 100 parts by mass of the rubber component; and a content of a fatty acid amide is less than 5 parts by mass per 100 parts by mass of the rubber component" and "a conveyor belt wherein the composition is used at least in the lower surface cover belt" (Claims 1 and 4).

Citation List Patent Literature [ 0005]

Patent Document 1: JP 2012-57001 A

Summary of Invention Technical Problem [ 0 00 6]

Here, it is known that in a cover rubber layer of a conveyor belt, a failure in a micro region gradually occurs because of friction and the like repeatedly generated between the layer and objects to be conveyed. This phenomenon is called wear, and because strength against the wear (wear resistance) of the cover rubber layer directly affects the service life of the conveyor belt itself, an excellent wear resistance is required.

In addition, the present inventor examined a conveyor belt wherein the rubber composition described in Patent Document 1 was used in the cover rubber layer, and found that the wear resistance of the cover rubber layer was not sufficient.

[ 0007]

Accordingly, an object of the present invention is to provide a rubber composition for a conveyor belt, the composition enabling a conveyor belt including a cover rubber layer excellent in wear resistance to be manufactured, and a conveyor belt wherein the composition is used.

Solution to Problem [ 0008]

The present inventor, as a result of diligent studies to solve the above mentioned problems, found that a rubber composition for a conveyor belt, the composition enabling a conveyor belt including a cover rubber layer excellent in wear resistance to be manufactured, and a conveyor belt wherein the composition is used can be obtained via the rubber composition including an ultra high molecular weight polyethylene and a carbon black, the carbon black having predetermined properties, in addition to a rubber component including a butadiene rubber in a predetermined amount.

That is, the present inventor found that the above-mentioned problems can be solved by the following configuration.

[ 0 00 9] (1) A rubber composition for a conveyor belt including : a rubber component including from 45 to 100 mass% of a butadiene rubber; an ultra high molecular weight polyethylene; and a carbon black; wherein a content of the ultra high molecular weight polyethylene is from 1.0 to 15.0 parts by mass per 100 parts by mass of the rubber component; a content of the carbon black is from 25 to 45 parts by mass per 100 parts by mass of the rubber component; a nitrogen adsorption specific surface area of the carbon black is from 85 to 160 m2/g, and a dibutyl phthalate oil absorption thereof is from 105 to 140 mL/100 g. (2) The rubber composition for a conveyor belt according to (1), wherein a weight average molecular weight of the butadiene rubber is from 500000 to 1000000. (3) The rubber composition for a conveyor belt according to (1) or (2), wherein a ratio of the weight average molecular weight of the butadiene rubber to a long chain branching index (LCB value) of the butadiene rubber (weight average molecular weight/long chain branching index) is from 5.5 x 104 to 16.6 x 104. (4) The rubber composition for a conveyor belt according to any of (1) to (3), wherein a viscosity average molecular weight of the ultra high molecular weight polyethylene is from 500000 to 4000000. (5) A conveyor belt including an upper surface cover rubber layer, a reinforcing layer, and a lower surface cover rubber layer; wherein the rubber composition for a conveyor belt according to any of (1) to (4) is used at least in the upper surface cover rubber layer.

Advantageous Effects of Invention [ 0010]

According to the present invention, there can be provided a rubber composition for a conveyor belt, the composition enabling a conveyor belt including a cover rubber layer excellent in wear resistance to be manufactured, and a conveyor belt wherein the composition is used.

Brief Description of Drawings [ 0011] FIG. 1 is a cross-sectional view schematically illustrating an example of an embodiment of a conveyor belt of the present invention.

Description of Embodiments [ 0012]

The present invention will be described in detail below .

[ 0013] A feature of a rubber composition for a conveyor belt of the present invention is that in addition to a rubber component including a butadiene rubber in a predetermined amount, an ultra high molecular weight polyethylene and a carbon black, the carbon black having predetermined properties, are contained. This was discovered for the first time by designing a blend based on findings by the present inventor that in order to improve wear resistance of a cover rubber layer of a conveyor belt, in addition to results of a wear resistance test that has been performed in the related art, it is important to control a stress when a test piece is elongated by 50% (hereinafter referred to as an "M50") in a tensile test and a loss tangent (tan δ) for a vulcanized rubber composition for a conveyor belt (hereinafter, simply referred to as a "vulcanized rubber composition").

[ 0014]

Wear in the cover rubber layer of the conveyor belt is, for example, in the upper surface cover rubber layer, a failure phenomenon in a micro region of the vulcanized rubber composition caused by friction between objects to be conveyed and the cover rubber layer. The amount of wear increases as the friction force between individual objects rubbing against each other becomes larger, and the friction force varies depending on various factors, such as a load, a slip velocity, a surface roughness, and an ambient temperature. This shows that if the environment where the conveyor belt is used differs, a major factor causing wear, i.e., a factor affecting the friction force, differs. Therefore, even if a blend is designed paying attention solely to values of a wear resistance test result on a vulcanized rubber composition as in a known manner, it has been difficult to obtain a rubber composition for a conveyor belt, the composition enabling a conveyor belt including a cover rubber layer excellent in wear resistance to be manufactured, and a conveyor belt wherein the composition is used.

[ 0015]

As a result of diligent studies, however, the present inventor found that by designing a blend paying attention to an M50 and a loss tangent of a vulcanized rubber composition, in addition to a wear resistance test result on a vulcanized rubber composition, a rubber composition for a conveyor belt, the composition enabling a conveyor belt including a cover rubber layer excellent in wear resistance to be manufactured, and a conveyor belt wherein the composition is used can be obtained.

That is, finding that by applying the basic principle of solid friction to wear analysis of a conveyor belt, the principle representing a friction force F generated between individual objects as a sum of an adhesion term Fs, a hysteresis term Fe, and a digging friction term Fp (F = Fs + Fe + Fp) , a pico abrasion, an M50, and a loss tangent of a vulcanized rubber composition are controlled, and the wear resistance can be improved; the present inventor designed a blend, and accomplished the present invention .

[ 0016]

Although the components described below may be described based on representative embodiments of the present invention, the present invention is not limited to such embodiments.

Note that in the present specification a numerical range indicated using "(from)... to..." means a range including the numbers before and after "to" as the lower limit value and the upper limit value .

[ 0017]

Rubber Composition for Conveyor Belt A rubber composition for a conveyor belt according to an embodiment of the present invention (hereinafter referred to as a "rubber composition of the present invention") is a rubber composition for a conveyor belt including: a rubber component including from 45 to 100 mass% of a butadiene rubber; an ultra high molecular weight polyethylene; and a carbon black; wherein a content of the ultra high molecular weight polyethylene is from 1.0 to 15.0 parts by mass per 100 parts by mass of the rubber component; a content of the carbon black is from 25 to 45 parts by mass per 100 parts by mass of the rubber component; a nitrogen adsorption specific surface area of the carbon black is from 85 to 160 m2/g, and a dibutyl phthalate oil absorption thereof is from 105 to 140 mL/10 0 g.

Each component contained in the rubber composition of the present invention will be described in detail below.

[ 0018]

Rubber Component A rubber component contained in the rubber composition of the present invention includes from 45 to 100 mass% of a butadiene rubber (BR). In a case where the content of the butadiene rubber is less than the lower limit value, the M50 may become small, the loss tangent and the pico abrasion may become large, resulting in an inferior wear resistance.

Additionally, the content of the butadiene rubber (BR) in the above-mentioned rubber component is preferably from 55 to 100 mass%, more preferably from 75 to 95 mass%, and still more preferably from 85 to 90 mass%. In a case where the content of the butadiene rubber (BR) is not less than the lower limit value, a vulcanized product of the rubber composition of the present invention, when used in a cover rubber layer of a conveyor belt with a large load and a low speed operation, has a superior wear resistance. In a case where the content of the butadiene rubber (BR) is not greater than the upper limit value, the rubber composition has an excellent processability.

[ 0 019]

The above-mentioned rubber component may include rubbers other than a butadiene rubber (BR). Examples of the rubber other than the butadiene rubber (BR) include a natural rubber (NR), an isoprene rubber, a styrene-butadiene rubber, an ethylene-propylene-diene rubber, and the like. Among them, a natural rubber (NR) is preferable because of its excellent compatibility with a butadiene rubber (BR).

When a natural rubber (NR) is contained in the above-mentioned rubber component, a content mass ratio (NR/BR) of the content of a natural rubber (NR) to the content of butadiene rubber (BR) is preferably from 10/90 to 55/45, more preferably from 20/85 to 45/55, and still more preferably from 25/75 to 45/55. In a case where the NR/BR is within these ranges, the loss tangent of the vulcanized rubber composition becomes smaller, and a vulcanized product of the rubber composition of the present invention, when used in a cover rubber layer of a conveyor belt with a high speed operation, has a superior wear resistance.

[ 0020]

Butadiene Rubber (BR) A weight average molecular weight of a butadiene rubber (BR) in the above-mentioned rubber component is preferably from 500000 to 1000000, and more preferably from 700000 to 1000000. In a case where the weight average molecular weight is from 500000 to 1000000, the M50 in the vulcanized rubber composition tends to become larger and the loss tangent therein tends to become smaller, and a vulcanized product of the rubber composition of the present invention, when used in a cover rubber layer of a conveyor belt with a small load and/or a high speed operation, has a superior wear resistance.

Note that the weight average molecular weight is a weight average molecular weight (polystyrene basis) measured by gel permeation chromatography (GPC) with tetrahydrofuran (THF) preferably used as a solvent.

[ 0021] A Mooney viscosity of the above-mentioned butadiene rubber (BR) in an unvulcanized state is preferably from 40 to 90, and more preferably from 50 to 80. In a case where the Mooney viscosity of the butadiene rubber (BR) is within these ranges, a processability of the rubber composition is superior.

Note that the Mooney viscosity is a Mooney viscosity (ML1 + 4) at 100°C measured in accordance with JIS K6300 using a Mooney viscometer.

[ 0022] A ratio of the weight average molecular weight of the butadiene rubber to a long chain branching index (LCB value) of the above-mentioned butadiene rubber (BR) (weight average molecular weight/long chain branching index) is preferably from 5.5 x 104 to 16.6 x 104, more preferably from 5.8 x 104 to 15.3 x 104, still more preferably from 7.5 x 104 to 14.2 x 104, and particularly preferably from 8.2 x 104 to 14.2 x 104.

In a case where the ratio of the weight average molecular weight to the long chain branching index (LCB value) is from 5.5 x 104 to 16.6 x 104, the M50 in the vulcanized rubber composition tends to become larger and the loss tangent therein tends to become smaller, and a vulcanized product of the rubber composition of the present invention, when used in a cover rubber layer of a conveyor belt with a small load and/or a high speed operation, has a superior wear resistance.

Note that in the present specification, the long chain branching index (LCB value) is a value measured according to Large Amplitude Oscillatory Shear (LAOS) measurement method using an RPA2000 tester (available from Alpha Technologies). A long chain branching index with a resultant value closer to zero indicates a polymer with high linearity and a low degree of branching. Therefore, the ratio of the weight average molecular weight to the long chain branching index (LCB value) is thought to have a positive correlation with the number of molecular chain terminals per unit amount possessed by the butadiene rubber, and it is presumed that by controlling this value within the range described above, particularly the effect of further reducing the loss tangent is obtained. Note that for details about the long chain branching index (LCB value), "FT-Rheology, a Tool to Quantify Long Chain Branching (LCB) in Natural Rubber and its Effect on Mastication, Mixing Behavior and Final Properties." (Henri G. Burhin, Alpha Technologies, UK 15 Rue du Culot B-1435 Hevillers, Belgium), etc. may be referenced .

[ 0023]

Note that when the rubber composition includes two or more butadiene rubbers, the ratio of the weight average molecular weight of the butadiene rubber to the long chain branching index (LCB value) (weight average molecular weight/long chain branching index) can be calculated by the following equation.

Equation: M/L = Σ{ (Mi/Li) x aj

In the equation described above, M/L represents a ratio of a weight average molecular weight of a butadiene rubber to a long chain branching index (LCB value), and Miz Li, and a± represent, respectively, a weight average molecular weight of each butadiene rubber, LCB value thereof, and a mass fraction of each butadiene rubber to all butadiene rubbers contained in a rubber composition, and Σ represents a sum.

[ 0024]

The above-mentioned butadiene rubber (BR) can be synthesized by a known method, for example, it can be manufactured by polymerizing butadiene in an inert organic solvent, in the presence of a catalyst containing a transition metal compound. Examples of the catalyst include those of cobalt-based, vanadium-based, lithium-based, nickel-based, neodymium-based, and the like. Among them, those of cobalt-based, neodymium-based are preferred, and those of neodymium-based are more preferred. A butadiene rubber obtained by polymerizing butadiene in the presence of a neodymium-based catalyst tends to become a straight chain with a few branches in its microstructure, and the loss tangent of the vulcanized rubber composition tends to become smaller as described above.

[ 0 02 5]

Ultra High Molecular Weight Polyethylene

The rubber composition of the present invention includes an ultra high molecular weight polyethylene (U-PE), thereby enabling the M50 to be increased, while maintaining the loss tangent of the vulcanized rubber composition. This is presumed to be due to a bad compatibility of an ultra high molecular weight polyethylene with the butadiene rubber in the above-mentioned rubber component, and thus, upon being blended, while giving a small impact on the loss tangent of the rubber component itself, a U-PE is dispersed in the rubber component, thereby contributing to an improved M50.

[ 0 02 6]

The content of the above-mentioned ultra high molecular weight polyethylene (U-PE) is from 1.0 to 15.0 parts by mass per 100 parts by mass of the above-mentioned rubber component. In a case where the content of the ultra high molecular weight polyethylene (U-PE) is less than the lower limit value, the M50 of the vulcanized rubber composition is small, and the wear resistance is inferior. In contrast, in a case where the content is greater than the upper limit value, the loss tangent and the pico abrasion may become large, and as a result the wear resistance of the vulcanized rubber composition is inferior. In particular, it is more preferably from 1.0 to 12.0 parts by mass, and more preferably from 1.0 to 10.0 parts by mass; in that the vulcanized rubber composition has an excellent bending resistance .

[ 0027] A molecular weight of the above-mentioned ultra high molecular weight polyethylene (U-PE) is preferably a viscosity average molecular weight from 500000 to 4000000, and more preferably from 1000000 to 3000000. In a case where the molecular weight is within these ranges, the M50 is further improved, and a processability is hardly impaired.

Note that the viscosity average molecular weight of the ultra high molecular weight polyethylene (U-PE) is a molecular weight measured by the intrinsic viscosity method (ASTM D4020-11 X5. NOMINAL VISCOSITY AVERAGE MOLECULAR WEIGHT OF ULTRA-HIGH MOLECULAR-WEIGHT POLYETHYLENE).

[ 0028]

Additionally, an average particle size of the above-mentioned ultra high molecular weight polyethylene (U-PE) is preferably from 1 to 300 pm, and more preferably from 10 to 50 pm. In a case where the average particle size is within this range, the dispersibility in the rubber tends to become good.

The above-mentioned ultra high molecular weight polyethylene (U-PE) is available as for example, MIPELON XM220 (available from Mitsui Chemicals, Inc.), HI-ZEX MILLION 340M (available from Mitsui Chemicals, Inc.), and the like.

[ 0 02 9]

Carbon Black

The rubber composition of the present invention contains a carbon black (CB). The content of the carbon black (CB) is from 25 to 45 parts by mass and preferably from 30 to 40 parts by mass per 100 parts by mass of the above-mentioned rubber component. In a case where the content of the carbon black (CB) is less than the lower limit value, the M50 of the vulcanized rubber composition may become small and also the pico abrasion thereof may become large, and as a result the wear resistance of the vulcanized rubber composition is inferior. In contrast, in a case where the content is greater than the upper limit value, the loss tangent may become large, and as a result the wear resistance after vulcanization is inferior.

[ 0030] A nitrogen adsorption specific surface area of the above-mentioned carbon black contained in the rubber composition of the present invention is from 85 to 160 m2/g, and a dibutyl phthalate oil absorption thereof is from 105 to 140 mL/100 g. In a case where the carbon black (CB) having the above-mentioned characteristics is not contained, the M50 of the vulcanized rubber composition becomes small and the pico abrasion thereof becomes large, and as a result the wear resistance of the vulcanized rubber composition is inferior.

Examples of the carbon black having the above-mentioned characteristics include those of SAF, ISAF-HS, ISAF-LS, and HAF-HS grades; and more preferably those of HAF-HS, ISAF-HS, and ISAF-LS grades in that the M50 of the vulcanized rubber composition becomes larger and the loss tangent thereof becomes smaller, and as a result the wear resistance of the vulcanized rubber composition is superior.

Commercially available products of the carbon black are available as Show Black N110, N234, N220, and N339 (all available from Cabot Japan K.K.).

Additionally, it is more preferable that the nitrogen adsorption specific surface area of the carbon black (CB) be from 85 to 125 m2/g and the dibutyl phthalate oil absorption thereof be from 110 to 125 mL/100 g in that the M50 of the vulcanized rubber composition becomes larger and the loss tangent becomes smaller, and as a result the wear resistance of the vulcanized rubber composition is superior.

Note that the above-mentioned nitrogen adsorption specific surface area is a value measured in accordance with ASTM D4820-93 and an index indicating the smallness of the particle size of carbon black particles, and the dibutyl phthalate oil absorption is a value measured in accordance with ASTM D2414-93 and an index indicating the status of the connection of carbon black particles, the so-called size of the structure (complexity of the shape).

[ 0031]

Other Components

In addition to each component described above, the rubber composition of the present invention may contain a crosslinking agent, such as a vulcanizing agent, a vulcanization aid, and a vulcanization accelerator; and a vulcanization retarder; and furthermore may include various blending agents as long as they do not impair the object of the present invention .

[ 0032]

Examples of the vulcanizing agent include sulfur-based, organic peroxide-based, metal oxide-based, phenol resin, quinone dioxime vulcanizing agents, and the like.

Examples of the sulfur-based vulcanizing agent include a powdered sulfur, a precipitated sulfur, a highly dispersible sulfur, a surface treated sulfur, an insoluble sulfur, dimorpholine disulfide, an alkylphenol disulfide.

[ 0 0 33]

Examples of the vulcanization accelerator include aldehyde-ammonia-based, guanidine-based, thiourea-based, thiazole-based, sulfenamide-based, thiuram-based, dithiocarbamate-based vulcanization accelerators, and the like.

Examples of the sulfenamide-based vulcanization accelerator specifically include N-cyclohexyl-2-benzothiazolyl sulfenamide (CZ), N-t-butyl-2-benzothiazolyl sulfenamide (NS), and the like.

[ 0034]

As a vulcanization aid, a common aid for a rubber can be used in combination, and examples thereof include zinc oxide; stearic acid and oleic acid, and Zn salts thereof; and the like.

[ 0 0 35]

When such a vulcanizing agent, a vulcanization accelerator, and a vulcanization aid are contained, a total content thereof is preferably from 0.1 to 10 parts by mass, and more preferably from 0.5 to 5 parts by mass, per 100 parts by mass of the above-mentioned rubber component. In a case where the content is within these ranges, the advantageous effects of the present invention are superior.

[ 003 6]

Examples of the blending agent include a reinforcing agent (filler) other than the carbon black described above, an anti-aging agent, an antioxidant, a pigment (dye), a plasticizer, a thixotropy imparting agent, a UV absorbent, a flame retardant, a solvent, a surfactant (including a leveling agent), a dispersant, a dehydrating agent, an anticorrosive agent, an adhesion promoter, an antistatic agent, a processing aid, and the like.

For these blending agents, those common for a rubber composition may be used. The blending amount thereof are not particularly limited and can be selected as appropriate.

[ 0037]

Manufacturing Method

The rubber composition of the present invention can be manufactured by adding together the rubber component described above, the ultra high molecular weight polyethylene, the carbon black, and other various blending agents to be contained, kneading with a Banbury Mixer or the like, and then kneading in the vulcanizing agent, the vulcanization aid, and the vulcanization accelerator with a mixing roll machine or the like.

Additionally, the vulcanization can be performed in conditions commonly used. Specifically, it is performed, for example, by heating under conditions of a temperature as high as 148°C for 30 minutes.

[ 0038]

Conveyor Belt wherein Rubber Composition for Conveyor

Belt is Used

Configuration A conveyor belt according to an embodiment of the present invention (hereinafter referred to as a "conveyor belt of the present invention") is a conveyor belt including an upper surface cover rubber layer, a reinforcing layer, and a lower surface cover rubber layer, wherein the rubber composition of the present invention is used at least in the above-mentioned upper surface cover rubber layer.

Although the conveyor belt of the present invention will be described below using FIG. 1, the structure of the conveyor belt of the present invention is not limited thereto. For example, the rubber composition of the present invention may be used in the upper surface cover rubber layer and the lower surface cover rubber layer.

[ 003 9] FIG. 1 is a cross-sectional view schematically illustrating an example of an embodiment of a conveyor belt of the present invention. A conveyor belt 10 is a multilayer structure including a reinforcing layer 1, and an upper surface cover rubber layer 2 and a lower surface cover rubber layer 3, covering the upper and lower of the reinforcing layer.

The upper surface cover rubber layer 2 includes an outer layer 2a and an inner layer 2b in this order from a conveying surface 4. Similarly, the lower surface cover rubber layer 3 also includes an outer layer 3a and an inner layer 3b in this order from a surface (not illustrated) in contact with a driving pulley or a roller of a belt conveyor. These outer layers (2a, 3a) and inner layers (2b, 3b) may be formed respectively using the same rubber composition, or may be formed using different rubber compositions. Additionally, the outer layers (2a, 3a) and the inner layers (2b, 3b) may be multilayer structures.

[ 0040]

The conveyor belt 10 is a conveyor belt wherein the rubber composition of the present invention is used at least in the upper surface cover rubber layer 2. Therefore, at least one layer selected from the group consisting of the outer layer 2a and the inner layer 2b should only be formed using the rubber composition of the present invention. The rubber composition of the present invention is preferred as a rubber composition used for the outer layer 2a, the layer coming into a direct contact with objects to be conveyed. On the other hand, the inner layer 2b is preferably formed using any other rubber composition, because of emphasis on manufacturing cost and adhesion to the reinforcing layer 1, and for the reasons above, the upper surface cover rubber layer 2 is preferably configured with a plurality of layers.

[ 0041]

Similarly, the lower surface cover rubber layer 3 of the conveyor belt 10 is also preferably configured with a plurality of layers. In this case, the rubber composition of the present invention may be used in either of the outer layer 3a or the inner layer 3b or both, and a rubber composition other than the rubber composition of the present invention may be used in the outer layer 3a and the inner layer 3b.

[ 0042] A core body of the reinforcing layer 1 is not particularly limited, and those used for a common conveyor belt can be selected for use as appropriate. Examples thereof include: those made of a cotton cloth and a chemical fiber or a synthetic fiber, coated and permeated with a rubber paste; those treated with RFL (Resorcin Formalin Latex) and folded; a canvas, a special weave nylon canvas, and a steel cord. One of them may be used alone or two or more may be used in combination .

Additionally, the shape of the reinforcing layer 1 is not particularly limited, and it may be sheetshaped, or may be those wherein reinforcing wires are embedded in parallel.

[ 0043] A method of manufacturing the conveyor belt 10 is not particularly limited, and a method such as those commonly used can be employed. Specifically, it is performed first by kneading the rubber composition of the present invention or any other rubber composition using a roll, a kneader, a Banbury Mixer, or the like, then forming it into a sheet shape for the upper surface cover rubber layer 2 and the lower surface cover rubber layer 3 using a calendar roll or the like, next layering each resulting layer in a predetermined order so as to insert the reinforcing layer 1, and applying pressure at a temperature from 130 to 170°C for 5 to 30 minutes.

[ 0044]

The conveyor belt 10 of the present invention is excellent in wear resistance because the upper surface cover rubber layer 2, preferably the outer layer 2a thereof is formed using the rubber composition of the present invention.

Examples [ 0045]

The present invention will be described in further detail below based on examples. Materials, used amounts, proportions, treatment contents, treatment procedures, and the like shown in the examples below can be changed as appropriate as long as they do not deviate from the spirit of the present invention. Therefore, the scope of the present invention should not be restrictively interpreted by the examples shown below.

[ 004 6]

Preparations of Rubber Composition and Vulcanized Rubber Composition

Each component shown in Table 1 was blended in a blending amount (parts by mass) shown in the same table. They were uniformly kneaded using a Banbury Mixer to prepare a rubber composition of each of the examples and the comparative examples shown in Table 1. The resulting rubber composition was vulcanized at 148°C for 30 minutes to prepare a vulcanized rubber composition .

[ 0047]

Properties after Vulcanization M5 0

Using a test piece cut out into a No. 3 dumbbell shape from each vulcanized rubber composition prepared, a tensile test was performed in accordance with JIS K6251-2004 at a tensile test speed of 500 mm/min to measure an M50 (MPa) at room temperature. Obtained results are shown in Table 1 as index values on a scale where values from Comparative Example 1 is 100. The larger the value is, the better the wear resistance is when the rubber composition is used in a cover rubber layer of a conveyor belt with a small load .

Loss Tangent (tan δ)

Using a test piece cut out into a strip shape (20 mm length x 5 mm width x 2 mm thickness) from each vulcanized rubber composition prepared, loss tangent (tan δ) was measured using a viscoelastic spectrometer available from Toyo Seiki Seisaku-sho, Ltd. The measurement was performed by elongating the test piece by 10% and applying vibration with an amplitude of ± 2% at a vibration frequency of 10 Hz under a measurement temperature of 20°C. Obtained results are shown in Table 1 as index values on a scale where values from Comparative Example 1 is 100. The smaller the value is, the better the wear resistance is when the rubber composition is used in a cover rubber layer of a conveyor belt with a high speed operation.

Pico Abrasion

Pico abrasion of the vulcanized rubber composition was measured in accordance with JIS K6264 using a Pico Abrasion Tester (available from Ferry Machine Co.). Measurement conditions were: a load of 44N, a rotation speed of 60 ± 2 per minute, and a total rotation number of 80 (20 normal rotations and 20 reverse rotations were alternately repeated twice each). Obtained results are shown in Table 1 as index values on a scale where values from Comparative Example 1 is 100. The smaller the index value is, the better the wear resistance is when the rubber composition is used in a cover rubber layer of a

conveyor belt with a large load and a low speed operation .

[ 0048] [ Table 1]

[ 004 9] [ Table 2]

[ 0050]

For each composition component shown in the above-mentioned Table 1, the following were used. - NR: Natural rubber (RSS #3) - BRI: Butadiene rubber (Nipol BR 1220, a weight average molecular weight of 460000, available from ΖΕΟΝ CORPORATION, a long chain branching index of 9.5, a Mooney viscosity of 44, a butadiene rubber obtained by polymerizing butadiene in the presence of a cobalt-based catalyst) - BR2: Butadiene rubber (Ubepol BR-360L, a weight average molecular weight of 560000, available from Ube Industries, Ltd., a long chain branching index of 7.3, a Mooney viscosity of 54, a butadiene rubber obtained by polymerizing butadiene in the presence of a cobalt-based catalyst) - BR3: Butadiene rubber (Buna CB21, a weight average molecular weight of 770000, available from Lanxess, a long chain branching index of 8.5, a Mooney viscosity of 73, a butadiene rubber obtained by polymerizing butadiene in the presence of a neodymium-based catalyst) - CB1: A carbon black (Show Black N110, a nitrogen adsorption specific surface area of 144 m2/g, a dibutyl phthalate oil absorption of 115 mL/100 g, SAF grade, available from Cabot Japan K.K.) - CB2: A carbon black (Show Black N234, a nitrogen adsorption specific surface area of 123 m2/g, a dibutyl phthalate oil absorption of 123 mL/100 g, ISAF-HS grade, available from Cabot Japan K.K.) - CB3: A carbon black (Show Black N326, a nitrogen adsorption specific surface area of 81 m2/g, a dibutyl phthalate oil absorption of 75 mL/100 g, HAF-LS grade, available from Cabot Japan K.K.) - CB4: A carbon black (Show Black N220, a nitrogen adsorption specific surface area of 111 m2/g, a dibutyl phthalate oil absorption of 115 mL/100 g, ISAF-LS grade, available from Cabot Japan K.K.) - CB5: A carbon black (Show Black N339, a nitrogen adsorption specific surface area of 88 m2/g, a dibutyl phthalate oil absorption of 121 mL/100 g, HAF-HS grade, available from Cabot Japan K.K.) - U-PE: An ultra high molecular weight polyethylene (MIPELON XM220, a viscosity average molecular weight of 2200000, an average particle size of 20 pm, available from Mitsui Chemicals, Inc.) - Anti-aging agent 6C: Antigen 6C (available from Sumitomo Chemical Co., Ltd.) - Zinc oxide: Zinc Oxide III (available from Seido Chemical Industry Co., Ltd.) - Stearic acid: Stearic acid YR (available from NOF Corporation) - Paraffin wax: OZOACE-0015 (available from Nippon Seiro Co., Ltd.) - Aroma oil: A-OMIX (available from Sankyo Yuka Kogyo K.K.) - Vulcanization accelerator NS: NOCCELER NS-P (available from Ouchi Shinko Chemical Industrial Co., Ltd . ) - Sulfur: Golden Flower oil treated sulfur powder (available from Tsurumi Chemical Industry Co., Ltd.) [ 0051]

From the results shown in Table 1, it was found that the vulcanized rubber composition of Example 1 had a larger M50, a smaller loss tangent (tan δ) and a smaller pico abrasion, and was excellent in wear resistance, as compared to Comparative Example 1. Desired effects were not obtained in Comparative Example 1, and Comparative Examples 2 to 5.

By comparing Example 1, Example 2, and Example 3, it was found that Example 2 and Example 3, including BR with weight average molecular weight from 500000 to 1000000, were excellent in the M50 and the loss tangent after vulcanization, and would have a superior wear resistance when used in a cover rubber layer of a conveyor belt with a small load and/or a high speed operation. Among them, Example 3 including a butadiene rubber having a ratio of a weight average molecular weight and a long chain branching index (LCB value) (weight average molecular weight/long chain branching index) of 9.0 x 104 was found to be further excellent in the M50 and the loss tangent after vulcanization, as compared to Example 2 with the ratio of 7.6 x 104.

Additionally, by comparing Examples 6, 10, and 11, and Example 1, it was found that in the case where the nitrogen adsorption specific surface area of the carbon black (CB) is from 85 to 125 m2/g and the dibutyl phthalate oil absorption thereof is from 110 to 125 mL/100 g, the M50 of the vulcanized rubber composition becomes larger and the loss tangent becomes smaller, and as a result the wear resistance of the vulcanized rubber composition is superior.

Reference Signs List [ 0052] 10 Conveyor belt 1 Reinforcing layer 2 Upper surface cover rubber layer 3 Lower surface cover rubber layer 2a, 3a Outer layer 2b, 3b Inner layer 4 Conveying surface

Claims

Claims [ Claim 1] A rubber composition for a conveyor belt comprising : a rubber component comprising from 45 to 100 mass% of a butadiene rubber; an ultra high molecular weight polyethylene; and a carbon black; wherein a content of the ultra high molecular weight polyethylene is from 1.0 to 15.0 parts by mass per 100 parts by mass of the rubber component; a content of the carbon black is from 25 to 45 parts by mass per 100 parts by mass of the rubber component; a nitrogen adsorption specific surface area of the carbon black is from 85 to 160 m2/g, and a dibutyl phthalate oil absorption thereof is from 105 to 140 mL/10 0 g. [
Claim 2] The rubber composition for a conveyor belt according to claim 1, wherein a weight average molecular weight of the butadiene rubber is from 500000 to 1000000. [Claim
3] The rubber composition for a conveyor belt according to claim 1 or 2, wherein a ratio of the weight average molecular weight of the butadiene rubber to a long chain branching index of the butadiene rubber is from 5.5 x 104 to 16.6 x 104. [
Claim 4] The rubber composition for a conveyor belt according to any one of claims 1 to 3, wherein a viscosity average molecular weight of the ultra high molecular weight polyethylene is from 500000 to 4000000 . [
Claim 5] A conveyor belt comprising an upper surface cover rubber layer, a reinforcing layer, and a lower surface cover rubber layer; wherein the rubber composition for a conveyor belt according to any one of claims 1 to 4 is used at least in the upper surface cover rubber layer.