JP2010013262A - Rubber composition for conveyor belt, method for manufacturing the same, and conveyor belt - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a conveyor belt for reducing power consumption by focusing on a crosslinking form after vulcanizing, a method for manufacturing the conveyor belt, and the conveyor belt. <P>SOLUTION: The conveyor belt 1 is composed of an upper-face cover rubber layer 2 which is to be a conveying surface 5, a reinforcement layer 3, and a lower-face cover rubber layer 4. At least an outer layer 16 composing a back surface of the lower-face cover rubber layer 4 is the rubber composition for the conveyor belt containing diene rubber, carbon black, and sulfur system vulcanizing agent. The content of the diene rubber is 55-80 mass%. The content of the carbon black is 10-40 pts.mass based on 100 pts.mass of the diene rubber. Polysulfide network chain density after vulcanization is more than 45%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

Conveyor belts are often used for transporting materials, etc., but they are required to be larger and stronger due to increased transport volume and improved transport efficiency. Has also appeared.
For this reason, the equipment cost and the power consumption are increasing, and a belt conveyor system with low cost and low power consumption is demanded. In particular, the cost of the belt conveyor is reduced by improving the rubber characteristics constituting the belt. Low power consumption is being studied.

For example, in Patent Document 1, “loss of physical property of rubber on the inner surface of a belt that is in contact with the pulley of the conveyor belt in a conveyor belt that is used in a conveyance system for an article that is wound between a driving pulley and an idle pulley and travels. A conveyor belt characterized in that the factor (tan δ) and the dynamic elastic modulus (E ′) are 0.04 ≦ tan δ ≦ 0.12 and E ′ ≧ 20 kgf / cm ² , respectively. A conveyor belt used in a system for conveying articles that are wound around an idler pulley, and the inner surface rubber of the conveyor belt is a polymer comprising 40 to 100 parts by weight of natural rubber and 60 to 0 parts by weight of BR rubber. The conveyor belt characterized by blending 20 to 55 parts by weight of carbon black ”.

Further, according to the present applicant, “a rubber composition for a conveyor belt containing 30 to 65 parts by mass of carbon black having colloidal characteristics shown below with respect to 100 parts by mass of a rubber component.
1) Nitrogen adsorption specific surface area (N ₂ SA) is 80 (m ² / g) or less 2) Iodine adsorption amount (IA) is 70 (mg / g) or less 3) Dibutyl phthalate (DBP) oil absorption is 100 (cm ³⁾ / 100 g) or more ”or“ a rubber composition for conveyor belts having a frequency coefficient of 10 Hz, a dynamic strain of 2%, and a loss coefficient tan δ at 20 ° C. of more than 0.120 and not more than 0.200 ”(Patent Documents). 2).

Further, the present applicant has made the following notice: “A rubber component comprising natural rubber (NR) and polybutadiene rubber (BR), carbon black, silica, a silane coupling agent, and diethylene glycol.
The ratio of natural rubber to polybutadiene rubber (NR / BR) in the rubber component is 80/20 to 25/75,
The carbon black content is 15 to 35 parts by mass with respect to 100 parts by mass of the rubber component,
The silica content is 5 to 25 parts by mass with respect to 100 parts by mass of the rubber component,
The content of the silane coupling agent is 0.5 to 3 parts by mass with respect to 100 parts by mass of the rubber component,
The rubber composition for conveyor belts whose content of the said diethylene glycol is 0.5-4.5 mass parts with respect to 100 mass parts of said rubber components. Is proposed (see Patent Document 3).

JP-A-11-139523 Japanese Patent Laid-Open No. 2004-18752 JP 2008-38133 A

  However, the conveyor belts described in Patent Documents 1 to 3 are basically intended to reduce the power consumption by reducing the tan δ value, but no study has been made on the crosslinked form after vulcanization. There wasn't.

  Then, this invention makes it a subject to provide the rubber composition for conveyor belts, the manufacturing method of a conveyor belt, and a conveyor belt which can aim at low power consumption paying attention to the crosslinked form after vulcanization.

As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that the polysulfide network chain density is focused, and by setting this to a predetermined value, power consumption can be sufficiently reduced. Completed the invention.
That is, the present invention provides the following (1) to (4).

(1) A rubber composition for a conveyor belt containing a diene rubber, carbon black and a sulfur vulcanizing agent,
The diene rubber content is 55 to 80% by mass,
The carbon black content is 10 to 40 parts by mass with respect to 100 parts by mass of the diene rubber,
A rubber composition for a conveyor belt having a polysulfide network chain density after vulcanization of more than 45%.

  (2) The rubber composition for a conveyor belt according to (1), wherein the content of the sulfur vulcanizing agent is 2.5 to 4 parts by mass with respect to 100 parts by mass of the diene rubber.

(3) A conveyor belt manufacturing method for manufacturing a conveyor belt by vulcanizing a rubber composition for a conveyor belt,
A conveyor belt having a low-temperature vulcanization step of vulcanizing the rubber composition for conveyor belts according to (1) or (2) at a temperature of 100 ° C. or more and less than 140 ° C. so that the polysulfide network chain density exceeds 45%. Manufacturing method.

(4) A conveyor belt obtained by the production method according to (3) above,
It consists of a top cover rubber layer, a reinforcing layer and a bottom cover rubber layer,
A conveyor belt, wherein at least the back surface of the lower cover rubber layer is formed of the rubber composition for conveyor belts according to (1) or (2).

  As described below, according to the present invention, a rubber composition for a conveyor belt, a method for manufacturing a conveyor belt, and a conveyor belt capable of reducing power consumption by focusing on a crosslinked form after vulcanization are provided. It is useful because it can.

The present invention is described in detail below.
The rubber composition for conveyor belts of the present invention is a rubber composition for conveyor belts containing a diene rubber, carbon black and a sulfur vulcanizing agent,
The diene rubber content is 55 to 80% by mass,
The carbon black content is 10 to 40 parts by mass with respect to 100 parts by mass of the diene rubber,
A rubber composition for a conveyor belt having a polysulfide network chain density of more than 45% after vulcanization.
Next, each component of the rubber composition for conveyor belts of this invention is explained in full detail.

<Diene rubber>
Specific examples of the diene rubber contained in the rubber composition for conveyor belts of the present invention include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), 1,2-butadiene rubber, Examples include styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), ethylene-propylene-diene rubber (EPDM), and these may be used alone. Two or more kinds may be used in combination.

In the present invention, among these diene rubbers, it is preferable to use natural rubber (NR) and polybutadiene rubber (BR) in combination.
Moreover, it is preferable that the amount ratio (NR / BR) of natural rubber and polybutadiene rubber is 90 / 10-25 / 75, more preferably 80 / 20-50 / 50, and 75 / 25-60. More preferably, it is / 40.
When the content ratio of NR and BR is in the above range, the resulting rubber composition for conveyor belts of the present invention has good rupture strength and abrasion resistance after vulcanization, and maintains basic physical properties as a conveyor belt. can do. This is considered to be because the compatibility between NR and BR is improved, and the reinforcement is further improved.

  In the present invention, BR has a weight average molecular weight of preferably 500,000 or more, and more preferably 550,000 or more. When the weight average molecular weight is within this range, the resulting rubber composition for conveyor belts of the present invention has improved rupture strength and tear strength after vulcanization, and better wear resistance.

Further, in the present invention, BR is preferably a terminal-modified polybutadiene rubber.
The terminal-modified polybutadiene rubber is not particularly limited as long as the terminal is a modified BR. Moreover, as a terminal modification | denaturation method of BR, the method of modify | modifying the terminal (active terminal) of BR using a modifier | denaturant can be used, for example.
Specific examples of such modifiers include tin halides such as tin tetrachloride and tin tetrabromide; halogenated organotin compounds such as tributyltin chloride; silicon compounds such as silicon tetrachloride and chlorotriethylsilane. An isocyanate group-containing compound such as phenyl isocyanate; an amide compound such as N-methylpyrrolidone (NMP); a lactam compound; a urea compound; an isocyanuric acid derivative;

  By using such a terminal-modified polybutadiene rubber, the loss coefficient tan δ described later after vulcanization of the rubber composition for a conveyor belt of the present invention is in a favorable range, so that the power consumption is more sufficiently reduced. be able to. This is presumably because the modified end portion contributes to crosslinking, and thus the crosslinking density after vulcanization is increased.

A commercially available product can be used as the terminal-modified polybutadiene having a weight average molecular weight of 500,000 or more.
Specific examples include Nipol BR1250H (weight average molecular weight: 570,000, NMP modified) manufactured by Nippon Zeon.

In the present invention, the content of such a diene rubber is 55 to 80% by mass and preferably 60 to 70% by mass with respect to the total mass of the rubber composition for conveyor belts of the present invention. .
When the content of the diene rubber is less than 55% by mass, the entropy elasticity effect associated with the crosslinked form cannot be exhibited due to the influence of carbon black described later, and thus power consumption cannot be reduced. Further, when the content of the diene rubber is more than 80% by mass, the resulting rubber composition for conveyor belts of the present invention has reduced rupture strength and abrasion resistance after vulcanization, and the basic physical properties as a conveyor belt are reduced. It cannot be maintained.

<Carbon black>
The carbon black is not particularly limited, but preferably contains GPF (General Purpose Furnace), and may contain other carbon blacks shown below.

  Specifically, other carbon blacks include, for example, HAF (High Absorption Furnace), SAF (Super Abrasion Furnace), ISAF (Intermediate Super Abrasion Furnace), FEF (Fast Extrusion Furnace). FT (Fine Thermal), MT (Medium Thermal), and the like.

A commercial item can be used as such carbon black.
Specifically, Asahi # 55 (manufactured by Asahi Carbon Co., Ltd.), Seast V (manufactured by Tokai Carbon Co., Ltd.), Dia Black G (manufactured by Mitsubishi Chemical Co., Ltd.), etc. Manufactured), show black N339 (manufactured by Showa Cabot), and the like.
In addition, ISAF is Show Black N220 (manufactured by Showa Cabot), SAF is Seast 9 (manufactured by Tokai Carbon Co., Ltd.), FEF is HTC # 100 (manufactured by Nippon Kayaku Carbon), and SRF is Asahi # 50 (Asahi) Examples of the FT include Asahi # 15 (Asahi Carbon Co.) and HTC # 20 (Shin Nikka Carbon Co., Ltd.).

In this invention, content of such carbon black is 10-40 mass parts with respect to 100 mass parts of said diene rubber, It is preferable that it is 20-35 mass parts, 25-33 mass parts It is more preferable that
If the carbon black content is in the above range, the resulting rubber composition for conveyor belts of the present invention will have good rupture strength and wear resistance after vulcanization, so the basic physical properties of the conveyor belt will be maintained. In addition, since the loss coefficient tan δ described later is in a favorable range, the power consumption can be sufficiently reduced. This is considered to be because the intermolecular interaction between the carbon black and the rubber component is large and the reinforcing property is improved.

  In the present invention, by using at least GPF as such carbon black, the power consumption of the conveyor belt of the present invention formed from the resulting rubber composition is further improved.

<Sulfur vulcanizing agent>
The sulfur-based vulcanizing agent is not particularly limited as long as it causes a chemical bond (crosslinking) via sulfur between the rubber of the diene rubber and the rubber.
Specific examples of the sulfur-based vulcanizing agent include powdered sulfur, precipitated sulfur, highly dispersible sulfur, surface-treated sulfur, insoluble sulfur, dimorpholine disulfide, alkylphenol disulfide, and the like. 1 type may be used independently and 2 or more types may be used together.

In this invention, it is preferable that it is 2.5-4 mass parts with respect to 100 mass parts of said diene rubbers, and, as for content of the said sulfur type vulcanizing agent, it is 2.7-3.7 mass parts. Is more preferable, and it is still more preferable that it is 3.0-3.5 mass parts.
If the content of the sulfur-based vulcanizing agent is in the above-mentioned range, the loss coefficient tanδ described later after vulcanization of the rubber composition for a conveyor belt of the present invention to be in a favorable range will be reduced. We can plan enough.

The rubber composition for conveyor belts of the present invention includes 1,3-bis (citraconimidomethyl) benzene and / or hexamethylene-1,6-bis (thiosulfate) disodium salt in addition to the components described above. It is one of the preferable embodiments to contain a hydrate.
Here, 1,3-bis (citraconimidomethyl) benzene is a compound represented by the following formula (1), and hexamethylene-1,6-bis (thiosulfate) disodium salt dihydrate is: It is a compound represented by Formula (2).

By containing these compounds, the power consumption of the resulting rubber composition for conveyor belts of the present invention can be more sufficiently reduced.
This is because the loss coefficient tan δ of the resulting rubber composition for conveyor belts of the present invention is small, but these compounds are reagents that prevent reversion (reversion) of the rubber composition (reversion inhibitor). This is an unexpected effect.

In the present invention, the content of these compounds is preferably 0.1 to 2 parts by mass, more preferably 0.2 to 1 part by mass with respect to 100 parts by mass of the diene rubber. .
This content is the total content when both 1,3-bis (citraconimidomethyl) benzene and hexamethylene-1,6-bis (thiosulfate) disodium salt dihydrate are contained. Say.

Moreover, in this invention, a commercial item can be used as these compounds.
Specifically, as 1,3-bis (citraconimidomethyl) benzene, PERKALINK 900 manufactured by FLEXSYS can be used, and hexamethylene-1,6-bis (thiosulfate) disodium salt dihydrate. For example, DURALINK HTS manufactured by FLEXSYS can be used.

  The rubber composition for conveyor belts of the present invention contains a crosslinking agent such as a vulcanizing agent other than the above sulfur-based vulcanizing agent, a vulcanization aid, and a vulcanization accelerator and a vulcanization retarder in addition to the above-described components. In addition, various compounding agents may be contained as long as the object of the present invention is not impaired.

Examples of the vulcanizing agent other than the sulfur-based vulcanizing agent include vulcanizing agents such as organic peroxides, metal oxides, phenol resins, and quinone dioximes.
Specific examples of the organic peroxide vulcanizing agent include benzoyl peroxide, t-butyl hydroperoxide, 2,4-dichlorobenzoyl peroxide, 2,5-dimethyl-2,5-di- (T-Butylperoxy) hexane, 2,5-dimethylhexane-2,5-di (peroxylbenzoate) and the like.
Other examples include magnesium oxide, risurge, p-quinonedioxime, p-dibenzoylquinonedioxime, poly-p-dinitrosobenzene, methylenedianiline, and the like.

Examples of the vulcanization accelerator include aldehyde / ammonia, guanidine, thiourea, thiazole, sulfenamide, thiuram, and dithiocarbamate vulcanization accelerators.
Specific examples of the aldehyde / ammonia vulcanization accelerator include hexamethylenetetramine (H).
Specific examples of the guanidine vulcanization accelerator include diphenyl guanidine.
Specific examples of the thiourea vulcanization accelerator include ethylene thiourea and the like.
Specific examples of the thiazole-based vulcanization accelerator include dibenzothiazyl disulfide (DM), 2-mercaptobenzothiazole, and a Zn salt thereof.
Specific examples of sulfenamide vulcanization accelerators include N-cyclohexyl-2-benzothiazolylsulfenamide (CZ), Nt-butyl-2-benzothiazolylsulfenamide (NS ) And the like.
Specific examples of the thiuram vulcanization accelerator include tetramethylthiuram disulfide (TMTD), dipentamethylene thiuram tetrasulfide, and the like.
Specific examples of the dithiocarbamate vulcanization accelerator include Na-dimethyldithiocarbamate, Zn-dimethyldithiocarbamate, Te-diethyldithiocarbamate, Cu-dimethyldithiocarbamate, Fe-dimethyldithiocarbamate, and pipecoline. Examples include pipecolyl dithiocarbamate.

  As the vulcanization aid, general rubber aids can be used together, and examples thereof include zinc white, stearic acid, oleic acid, and Zn salts thereof.

  The total content of the vulcanizing agent, the vulcanization accelerator and the vulcanization aid is preferably 0.1 to 15 parts by mass with respect to 100 parts by mass of the diene rubber. 0.5 to 10 parts by mass is more preferable. When the content range is within this range, the resulting rupture strength of the rubber composition for conveyor belts of the present invention after vulcanization becomes better, and the loss coefficient tan δ described later also becomes better.

Specific examples of the vulcanization retarder include organic acids such as phthalic anhydride, benzoic acid, salicylic acid, and acetylsalicylic acid; N-nitrosodiphenylamine, N-nitrosophenyl-β-naphthylamine, N-nitroso- Nitroso compounds such as polymers of trimethyl-dihydroquinoline; halides such as trichloromelanin; 2-mercaptobenzimidazole; santoguard PVI: and the like.
When the vulcanization retarder is contained, the content is preferably 0.1 to 0.3 parts by mass, and 0.1 to 0.2 parts by mass with respect to 100 parts by mass of the diene rubber. Is more preferable. When the range of the content is within this range, the scorch stability when the conveyor belt is extruded from the obtained rubber composition for a conveyor belt of the present invention is improved, and the productivity is improved.

Specific examples of the compounding agent include, for example, fillers other than the above-described carbon black, anti-aging agents, antioxidants, pigments (dyes), plasticizers, thixotropic agents, ultraviolet absorbers, flame retardants, and solvents. , Surfactants (including leveling agents), dispersants, dehydrating agents, rust inhibitors, adhesion-imparting agents, antistatic agents, processing aids, and the like.
As these compounding agents, those generally used for rubber compositions can be used. Their blending amounts are not particularly limited and can be arbitrarily selected.

The rubber composition for conveyor belts of the present invention is a rubber composition for conveyor belts having a vulcanized polysulfide network chain density of more than 45%.
Here, “polysulfide network chain density” refers to a monosulfide bond (crosslinking form in which rubber is bonded with one molecule of sulfur) and a disulfide bond (crosslinked form in which rubber is bonded with two molecules of sulfur) among sulfur bridges. Refers to the ratio of polysulfide bonds (crosslinked form bonded with 3 or more sulfur molecules) excluding. Specifically, it is measured by the toluene swelling method shown below.
“After vulcanization” means after vulcanization at a temperature of 100 ° C. or more and less than 140 ° C. for 45 minutes or more.

(Toluene swelling method)
In the toluene swelling method, a rubber composition for a conveyor belt after vulcanization (test piece: 7 mm × 7 mm × 1 mm) is treated with a reagent that selectively breaks sulfide bonds (see Table 1 below), and untreated This is a method for obtaining the polysulfide network chain density by applying the Flory-Rehner equation from the toluene swelling degree of the sample and each treated sample. In the present invention, this method is carried out in accordance with the method described on pages 407 to 409 of “Rubber test method (edited by Japan Rubber Association, Maruzen Co., Ltd., issued on January 30, 2006)”.
Here, in Table 1 below, “THF / toluene (1: 1)” indicates a mixed solution of 90 mL of tetrahydrofuran (THF) and 90 mL of toluene, and “THF / toluene (1: 1) + 2-fluorophenylthiol”. “+ Hydridine” indicates a mixed solution of 90 mL of THF, 90 mL of toluene, 3.31 mL (0.4 mol) of 2-propanethiol, and 3.35 mL (0.4 mol) of piperidine, “THF / toluene (1: 1) + lithium”. “Aluminum hydride” indicates a mixed solution of 200 mL of THF, 200 mL of toluene, and 10 g of lithium aluminum hydride.
The treatment with each reagent is performed by immersing the test piece and stirring at room temperature for 8 hours.
Then, it is immersed in toluene for 16 hours to determine the degree of toluene swelling.

νｔ：トータル網目鎖密度（１００％）
νｍ／νｔ×１００：モノスルフィド網目鎖密度
νｄ（＝（νｍ＋ｄ）−νｍ）／νｔ×１００：ジスルフィド網目鎖密度
νｐ（＝νｔ−（νｍ＋ｄ））／νｔ×１００：ポリスルフィド網目鎖密度

νt: Total network chain density (100%)
νm / νt × 100: monosulfide network chain density νd (= (νm + d) −νm) / νt × 100: disulfide network chain density νp (= νt− (νm + d)) / νt × 100: polysulfide network chain density

  On the other hand, the value of “above 45%” of the polysulfide network chain density is a value calculated from the experimental results in a range where tan δ is good (see FIG. 2).

  The rubber composition for conveyor belts of the present invention contains the above-mentioned diene rubber, carbon black and sulfur vulcanizing agent and, if desired, specific amounts of various compounding agents, and the polysulfide network chain density after vulcanization exceeds 45%. Thus, the loss coefficient tan δ measured by extending 10% at a measurement temperature of 20 ° C. and applying vibration with an amplitude of ± 2% at a frequency of 10 Hz is 0.04 to 0.17.

(Loss factor tan δ)
The loss coefficient tan δ is expressed by the ratio of the storage elastic modulus E ′ and the loss elastic modulus E ″ representing the dynamic properties of the rubber composition, tan δ = E ″ / E ′, and the smaller the value, the more the deformation of the rubber composition. This means that the amount of energy dissipated as heat during the period (energy loss amount) is small, and can be used as a measure of energy loss.
On the other hand, if the tan δ value is small, it is considered that power consumption can be reduced. However, if the tan δ value is too small, the breaking strength (T _B ) and breaking elongation (E _B ) are also reduced. Not stable.
In the present invention, the above-mentioned diene rubber, carbon black and sulfur vulcanizing agent and, if desired, various amounts of compounding agents are contained, and the polysulfide network chain density after vulcanization exceeds 45%, thereby reducing power consumption. And a tan δ value range (0.04 to 0.17) in which basic properties such as breaking strength and breaking elongation can be achieved at the same time.

  The rubber composition for conveyor belts of the present invention is produced by adding the above-described diene rubber, carbon black and sulfur vulcanizing agent and various compounding agents contained as desired, kneading with a Banbury mixer or the like, and then kneading roll machine Etc. can be carried out by kneading a vulcanizing agent, a vulcanization aid, and a vulcanization accelerator.

The method for producing a conveyor belt according to the present invention includes a low-temperature vulcanization process in which the rubber composition for a conveyor belt according to the present invention described above is vulcanized at a temperature of 100 ° C. or higher and lower than 140 ° C. so that the polysulfide network chain density exceeds 45%. Have
Here, the vulcanization in the low-temperature vulcanization step is not particularly limited as long as it vulcanizes the rubber composition for a conveyor belt of the present invention described above at a temperature of 100 ° C. or more and less than 140 ° C., for 45 to 300 minutes, It is preferable to carry out at a temperature of 120 to 135 ° C.

In the present invention, by carrying out such low temperature vulcanization, the rubber composition for conveyor belts of the present invention can have a polysulfide network chain density of more than 45%. Can be sufficiently reduced.
This is because, as described above, the loss coefficient tan δ is in a favorable range when the rubber composition for conveyor belts of the present invention has a polysulfide network chain density of more than 45%.

  Steps other than the low-temperature vulcanization step are not particularly limited. Specifically, for example, first, the raw materials are kneaded using a roll, a kneader, a Banbury mixer, etc., and then each cover rubber layer is used using a calendar or the like. For example, a method in which the obtained layers are laminated in a predetermined order so as to sandwich the reinforcing layer and pressed at a temperature of 100 ° C. or higher and lower than 140 ° C. for 60 minutes is preferably exemplified.

The conveyor belt of the present invention is a conveyor belt obtained by the above-described method for manufacturing a conveyor belt of the present invention, and is a conveyor belt comprising an upper cover rubber layer, a reinforcing layer and a lower cover rubber layer, and the lower cover rubber. At least the back surface of the layer is a conveyor belt formed by the rubber composition for a conveyor belt of the present invention described above.
Hereinafter, the conveyor belt according to the present invention will be described with reference to FIG. 1. The structure of the conveyor belt according to the present invention may employ the above-described rubber composition for a conveyor belt according to the present invention on the back surface of the bottom cover rubber layer. The present invention is not particularly limited to this.

FIG. 1 is a cross-sectional view schematically showing an example of a preferred embodiment of the conveyor belt of the present invention. In FIG. 1, 1 is a conveyor belt, 2 is an upper cover rubber layer, 3 is a reinforcing layer, 4 is a lower cover rubber layer, 5 is a transporting surface for transported goods, 11 and 16 are outer layers, and 12 and 15 are inner layers.
As shown in FIG. 1, the conveyor belt 1 has a reinforcing layer 3 as a central layer, and an upper surface cover rubber layer 2 and a lower surface cover rubber layer 4 are provided on both sides thereof, and the upper surface cover rubber layer 2 includes an outer layer 11 and an inner layer. The bottom cover rubber layer 4 is composed of two layers of an outer layer 16 and an inner layer 15. Here, the outer layer and the inner layer (the outer layer 11 and the inner layer 12, the outer layer 16 and the inner layer 15) of the upper surface cover rubber layer 2 and the lower surface cover rubber layer 4 may be formed using different rubber compositions.

In FIG. 1, the upper cover rubber layer 2 is composed of two layers, an outer layer 11 and an inner layer 12, but in the conveyor belt of the present invention, the number of layers constituting the upper cover rubber layer 2 is limited to two. It may be 1 or 3 or more. In the case of 3 or more, these layers may be formed using different rubber compositions. The same applies to the bottom cover rubber layer 4.
Since the outer layer 11 constituting the transported material carrying surface 5 of the upper cover rubber layer 2 is preferably formed of a rubber composition having excellent heat resistance, wear resistance, oil resistance, etc., the upper cover rubber layer 2 is 2 It is preferable that it is composed of layers.
The outer layer 16 constituting the back surface of the lower cover rubber layer 4 is formed of the above-described rubber composition for conveyor belts of the present invention, and the inner layer 15 of the lower cover rubber layer 4 is manufactured in terms of manufacturing cost and adhesiveness to the reinforcing layer 3. Therefore, the cover rubber layer 4 is preferably composed of two layers.

The core of the reinforcing layer 3 is not particularly limited, and those used for ordinary conveyor belts can be appropriately selected and used. Specific examples thereof include those made of cotton cloth and chemical fibers or synthetic fibers and rubber paste. Coated, infiltrated, folded RFL treated, special woven nylon canvas, steel cord, etc. These may be used alone or in combination of two or more May be.
Moreover, the shape of the reinforcement layer 3 is not specifically limited, As shown in FIG. 1, a sheet form may be sufficient and a wire-shaped reinforcement line may be embedded in parallel.

  The rubber composition forming the inner layer 12 of the upper surface cover rubber layer 2 and the inner layer 15 of the lower surface cover rubber 4 is not particularly limited, and a rubber composition used for a normal conveyor belt can be appropriately selected and used. Or two or more of them may be used in combination.

  The rubber composition for forming the outer layer 11 of the upper cover rubber layer 2 is not particularly limited, and a rubber composition used for a normal conveyor belt is made of basic characteristics required for the outer layer (for example, heat resistance, wear resistance, The oil resistance can be appropriately selected according to the oil resistance.

  In the conveyor belt of the present invention, at least the back surface of the lower surface cover rubber layer is formed by the rubber composition for conveyor belts of the present invention, so that the basic physical properties such as hardness, breaking strength, breaking elongation, tear strength are maintained, The power consumption can be sufficiently reduced.

In the conveyor belt of this invention, it is preferable that the thickness of a lower surface cover rubber layer is 5-20 mm, and it is more preferable that it is 6-15 mm. Here, the thickness of the lower surface cover rubber layer refers to the total thickness of these layers when the lower surface cover rubber layer is composed of an inner layer and an outer layer.
When the thickness of the lower surface cover rubber layer is within this range, even when a high-temperature transported material is used for transport, it is possible to prevent belt warping (capping) caused by rubber deterioration or the like.

Examples The rubber composition for conveyor belts of the present invention will be described in more detail below, but the present invention is not limited to these.
(Examples 1-5, Comparative Examples 1-3)
Each rubber composition for conveyor belts was prepared with the composition components (parts by mass) shown in Table 2 below with respect to 100 parts by mass of the rubber components.

The following components were used as the composition components such as the rubber components shown in Table 2 above.
・ Natural rubber (NR): RSS # 3
-Butadiene rubber (BR): Nipol BR1220 (weight average molecular weight: 460,000, terminal unmodified, manufactured by Nippon Zeon)
Styrene-butadiene rubber (SBR): Nipol SBR1502 (manufactured by Nippon Zeon)
Carbon black 2: GPF (Dia Black G, manufactured by Mitsubishi Chemical Corporation)
・ Carbon black 1: HAF (Show Black N339, manufactured by Showa Cabot)
・ Zinc oxide: 3 types of zinc oxide (manufactured by Shodo Chemical Industry Co., Ltd.)
・ Stearic acid: Beads stearic acid (manufactured by NOF Corporation)
Anti-aging agent: NOCRACK 6C (manufactured by Ouchi Shinsei Chemical Co., Ltd.)
・ Wax 1: Paraffin wax (Sunnock, Ouchi Shinsei Chemical Co., Ltd.)
・ Aroma oil: Machine oil 22 (made by Showa Shell Sekiyu KK)
・ Vulcanizing agent: Sulfur (oil-treated sulfur, manufactured by Hosoi Chemical Co., Ltd.)
・ Vulcanization accelerator: N-tert-butyl-2-benzothiazolylsulfenamide (Noxeller NS, manufactured by Ouchi Shinsei Chemical Co., Ltd.)

  Each rubber composition obtained was vulcanized under the conditions of temperature and time shown in Table 3 below, and the vulcanized polysulfide network chain density and various physical properties were measured and evaluated by the following methods. The results are shown in Table 3 below.

(1) Polysulfide network chain density (νp)
For each rubber composition after vulcanization, the Polysulfide network chain density was determined by applying the Flory-Rehner equation from the degree of swelling of toluene treated with the reagents listed in Table 1 above.

(2) Loss coefficient tan δ
A loss factor tan δ was measured using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho using a test piece cut into a strip shape (length 20 mm × width 5 mm × thickness 2 mm) from each vulcanized rubber composition prepared. The measurement was performed by extending 10% at a measurement temperature of 20 ° C. and applying vibration with an amplitude of ± 2% at a frequency of 10 Hz.

(3) Breaking strength and elongation at break Each obtained rubber composition was vulcanized at 148 ° C. for 30 minutes to prepare a vulcanized rubber composition.
Using test pieces punched out from each of the prepared vulcanized rubber compositions into a No. 3 dumbbell shape, a tensile test was conducted at a tensile speed of 500 mm / min according to JIS K6251-2004, and breaking strength (T _B ) [MPa] The elongation at break (E _B ) [%] was measured at room temperature.
If the breaking strength is 14 MPa or more, it can be evaluated as having a high breaking strength.
If the elongation at break is 400% or more, it can be evaluated as having a high breaking elongation.

From the results shown in Table 3, the vulcanized polysulfide network can be obtained by using the rubber compositions 1 and 2 containing a specific amount of diene rubber, carbon black and sulfur vulcanizing agent and, if desired, wax. It was found that the rubber compositions of Comparative Examples 1 and 2 having a chain density of 45% or less had high tan δ and could not sufficiently reduce power consumption.
In contrast, diene rubber, carbon black and sulfur vulcanizing agent, and rubber compositions 1 and 2 containing a specific amount of wax, if desired, were prepared, and the polysulfide network chain density after vulcanization exceeded 45%. It turned out that the rubber composition of Examples 1-5 used as this can fully aim at reduction of power consumption.
On the other hand, it was found that when the rubber composition 3 containing a specific amount or more of carbon black was used, tan δ was extremely high and the power consumption could not be reduced.

FIG. 1 is a cross-sectional view schematically showing an example of a preferred embodiment of the conveyor belt of the present invention. FIG. 2 is a scatter diagram showing the relationship between the polysulfide network chain density of the rubber compositions 1 to 3 and tan δ.

Explanation of symbols

1: Conveyor belt 2: Upper cover rubber layer 3: Reinforcement layer 4: Lower cover rubber layer 5: Transported material transport surface 11, 16: Outer layer 12, 15: Inner layer

Claims (4)

A rubber composition for a conveyor belt containing a diene rubber, carbon black and a sulfur vulcanizing agent,
The diene rubber content is 55 to 80% by mass,
The carbon black content is 10 to 40 parts by mass with respect to 100 parts by mass of the diene rubber.
A rubber composition for a conveyor belt having a polysulfide network chain density after vulcanization of more than 45%.   The rubber composition for a conveyor belt according to claim 1, wherein a content of the sulfur vulcanizing agent is 2.5 to 4 parts by mass with respect to 100 parts by mass of the diene rubber. A method for producing a conveyor belt, comprising vulcanizing a rubber composition for a conveyor belt to produce a conveyor belt,
A method for producing a conveyor belt comprising a low-temperature vulcanization step of vulcanizing the rubber composition for a conveyor belt according to claim 1 or 2 at a temperature of 100 ° C or higher and lower than 140 ° C so that the polysulfide network chain density exceeds 45%. . A conveyor belt obtained by the manufacturing method according to claim 3,
It consists of a top cover rubber layer, a reinforcing layer and a bottom cover rubber layer,
The conveyor belt in which the at least back surface of the said lower surface cover rubber layer is formed with the rubber composition for conveyor belts of Claim 1 or 2.

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