JP7457232B2 - Rubber compositions and conveyor belts - Google Patents

Description

TECHNICAL FIELD This invention relates to rubber compositions and conveyor belts.

2. Description of the Related Art Conventionally, belt conveyors have been used in steel mills, chemical factories, and the like to continuously convey materials such as raw materials. A belt conveyor is generally a device that transports objects by moving or rotating a belt (conveyor belt) using a drive device such as a roller.
In steel mills or factories such as those mentioned above, for example, belt conveyors may generate frictional heat or conveyed objects may be at high temperatures, so conveyor belts are required to have flame retardancy and heat resistance.
As a rubber composition used for forming a cover rubber layer in such a conveyor belt, for example, Patent Document 1 discloses that antimony trioxide is added to 100 parts by mass of a rubber component containing at least an ethylene/1-butene copolymer. A rubber composition containing 1 to 10 parts by weight of a brominated flame retardant and 10 to 50 parts by weight of a brominated flame retardant having a specific structure is disclosed.

Patent No. 6583518

In recent years, there has been a demand for further improvements in the performance of conveyor belts from the perspective of improving factory operating rates. Conveyor belts are required to have excellent flame retardancy), heat resistance, bending resistance, and abrasion resistance.
The present inventors referred to Patent Document 1 and found that the rubber component contained ethylene/propylene copolymer and ethylene/1-butene copolymer, and the flame retardant or flame retardant aid contained brominated flame retardant and trioxide. When a rubber composition containing antimony was evaluated, it was found that although it has excellent flame retardancy and heat resistance, there is room for improvement in at least one of flame retardancy, flex resistance, and abrasion resistance after heat aging. .

Therefore, an object of the present invention is to provide a rubber composition that can constitute a conveyor belt that has excellent flame retardancy, flame retardancy after heat aging, heat resistance, bending resistance, and abrasion resistance. Another object of the present invention is to provide a conveyor belt that is excellent in flame retardancy, flame retardancy after heat aging, heat resistance, bending resistance, and abrasion resistance.

As a result of intensive studies on the above-mentioned problems, the inventors of the present invention have found that if a rubber composition containing chlorinated polyethylene as a rubber component and a predetermined amount of antimony trioxide and a brominated flame retardant is used, flame retardancy and heat aging properties can be improved. It was discovered that a conveyor belt having excellent flame retardancy, heat resistance, bending resistance and abrasion resistance can be obtained, and the present invention was achieved.
That is, the present inventor found that the above problem could be solved by the following configuration.

[1]
A rubber component containing chlorinated polyethylene and olefin rubber,
antimony trioxide,
Contains a brominated flame retardant,
The content of the antimony trioxide is 1 to 10 parts by mass based on 100 parts by mass of the rubber component,
A rubber composition, wherein the content of the brominated flame retardant is 5 to 40 parts by mass based on 100 parts by mass of the rubber component.
[2]
The rubber composition according to [1], wherein the brominated flame retardant includes a brominated flame retardant having a melting point of 300°C or higher.
[3]
The rubber composition according to [1] or [2], wherein the brominated flame retardant is a compound represented by the below-mentioned formula (1).
In formula (1) described below, R represents an aliphatic hydrocarbon group that may contain an unsaturated bond.
[4]
The rubber composition according to any one of [1] to [3], wherein the mass ratio of the content of the chlorinated polyethylene to the content of the brominated flame retardant is 8 or less.
[5]
The rubber component consists only of the chlorinated polyethylene and the olefin rubber,
The content of the chlorinated polyethylene is 1 to 40% by mass based on the total mass of the rubber component,
The rubber composition according to any one of [1] to [4], wherein the content of the olefin rubber is 60 to 99% by mass based on the total mass of the rubber component.
[6]
The olefin rubber contains an ethylene/propylene copolymer and an ethylene/1-butene copolymer,
The rubber composition according to any one of [1] to [5], wherein the mass ratio of the content of the ethylene/1-butene copolymer to the content of the ethylene/propylene copolymer is 98 or less. .
[7]
The rubber composition according to any one of [1] to [6], which is a rubber composition for a conveyor belt.
[8]
A conveyor belt produced using the rubber composition according to any one of [1] to [7].
[9]
The conveyor belt according to [8], which has a cover rubber formed using the above rubber composition.

According to the present invention, it is possible to provide a rubber composition that can be used to form a conveyor belt that is excellent in flame retardancy, flame retardancy after heat aging, heat resistance, flex resistance, and abrasion resistance. In addition, according to the present invention, it is possible to provide a conveyor belt that is excellent in flame retardancy, flame retardancy after heat aging, heat resistance, flex resistance, and abrasion resistance.

1 is a cross-sectional view of one embodiment of a conveyor belt of the present invention. FIG. FIG. 3 is a cross-sectional view of another embodiment of the conveyor belt of the present invention.

The present invention will be explained in detail below.
In this specification, a numerical range expressed using "~" in this specification means a range that includes the numerical values written before and after "~" as lower and upper limits.
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 a component contains two or more types of substances, the content of the component means the total content of the two or more types of substances.
In this specification, unless otherwise specified, there is no particular restriction on the manufacturing method of each component. For example, conventionally known methods can be used.
In this specification, the effect of the present invention is sometimes referred to as being better if at least one of flame retardancy, flame retardance after heat aging, heat resistance, bending resistance, and abrasion resistance is better.

[Rubber composition]
The rubber composition of the present invention (hereinafter also simply referred to as "the composition") contains a rubber component containing chlorinated polyethylene and an olefin-based rubber, antimony trioxide, and a brominated flame retardant. The content of the antimony trioxide is 1 to 10 parts by mass per 100 parts by mass of the rubber component. The content of the brominated flame retardant is 5 to 40 parts by mass per 100 parts by mass of the rubber component.
According to the present composition, a conveyor belt having excellent flame retardancy, flame retardancy after heat aging, heat resistance, flex resistance and abrasion resistance can be produced. Although the details of the reason for this are not yet clear, it is presumed to be due to the following reasons.

It is presumed that by blending a predetermined amount of antimony trioxide and a brominated flame retardant into the rubber component, it was possible to achieve a high level of balance between the flame retardance and heat resistance of the conveyor belt.
The present inventor has repeatedly studied the rubber composition described in Patent Document 1, and found that there is room for improvement in the flame retardance, bending resistance, and abrasion resistance of conveyor belts after heat aging. I found it. The reason for this is presumed to be that due to the combination of antimony trioxide and a brominated flame retardant, the brominated flame retardant causes debromination, thereby accelerating the deterioration of the rubber.
To address this problem, the present inventors have discovered that by using chlorinated polyethylene as the rubber component, a conveyor belt with excellent flame retardancy, bending resistance, and abrasion resistance after heat aging can be obtained. The reason for this is presumed to be that by using chlorinated polyethylene, the structure of the chlorinated polyethylene makes it difficult to dehalogenate compared to brominated flame retardants, and does not impede the thermal stability of the olefin rubber.
The components contained in this composition and the components that can be contained will be explained below.

[Rubber component]
The rubber component in the present composition contains a chlorinated polyethylene and an olefin-based rubber.
The content of the rubber component is preferably from 30 to 60 mass %, particularly preferably from 40 to 50 mass %, based on the total mass of the composition.

The total content of chlorinated polyethylene and olefin rubber is more preferably 60 to 100% by mass, more preferably 80 to 100% by mass, based on the total mass of the rubber component, in order to achieve better effects of the present invention. Preferably, 95 to 100% by weight is particularly preferable.
Although the rubber component may contain rubbers other than chlorinated polyethylene and olefin rubber, it is preferable that the rubber component consists of only chlorinated polyethylene and olefin rubber, since the effects of the present invention are more excellent.
When the rubber component consists only of chlorinated polyethylene and the above-mentioned olefin rubber, the effect of the present invention is better, so the content of chlorinated polyethylene is 1 to 40% by mass (more preferably 1 to 40% by mass) based on the total mass of the rubber component. 1 to 20% by mass, particularly preferably 1 to 10% by mass), and the content of the olefin rubber is 60 to 99% by mass (more preferably 80 to 99% by mass, based on the total mass of the rubber component). Particularly preferably 90 to 99% by mass).

<Chlorinated polyethylene>
Chlorinated polyethylene is not particularly limited.
The chlorine content of the chlorinated polyethylene is preferably 20 to 50% by mass, particularly preferably 25 to 40% by mass, in order to obtain better effects of the present invention. Here, the chlorine content means the ratio of the content of chlorine contained in the chlorinated polyethylene to the chlorinated polyethylene.
The specific gravity of the chlorinated polyethylene is preferably 1.00 to 1.40 g/cm ³ , particularly preferably 1.15 to 1.25 g/cm ³ in view of the superiority of the present invention. The specific gravity of chlorinated polyethylene is measured according to the method for measuring specific gravity described in JIS Z 8807:2012.

The content of chlorinated polyethylene is preferably 1 to 40 mass%, more preferably 1 to 20 mass%, and particularly preferably 3 to 15 mass%, based on the total mass of the rubber component, in order to obtain a better effect of the present invention.

The mass ratio of the content of chlorinated polyethylene to the content of brominated flame retardant (content of chlorinated polyethylene/content of brominated flame retardant) is preferably 8 or less from the viewpoint of more excellent effects of the present invention. , more preferably 3 or less, further preferably 2 or less, particularly preferably 0.50 or less, and most preferably 0.35 or less. In addition, the lower limit of the above mass ratio (content of chlorinated polyethylene/content of brominated flame retardant) is preferably more than 0, and 0.10 from the viewpoint that the effects of the present invention (especially heat resistance) are more excellent. The above is more preferable, 0.15 or more is even more preferable, and more than 0.20 is particularly preferable.

The mass ratio of the content of chlorinated polyethylene to the content of antimony trioxide (content of chlorinated polyethylene/content of antimony trioxide) is 0.1 to 10. 0 is preferred, 0.3 to 6.0 is more preferred, and 0.5 to 2.0 is particularly preferred.

<Olefin rubber>
The olefin rubber is not particularly limited.
The chlorine content of the olefin rubber is preferably less than 20% by mass, particularly preferably 10% by mass or less. Here, the chlorine content means the ratio of the content of chlorine contained in the olefin rubber to the olefin rubber.
The specific gravity of the olefin rubber is preferably from 0.70 g/cm ³ to less than 1.00 g/cm 3 , particularly preferably from 0.75 to 0.99 g/cm ³ , from the standpoint of achieving better effects of the present invention ^. The specific gravity of olefin rubber can be measured in the same manner as for chlorinated polyethylene described above.

The content of the olefin-based rubber is preferably 60 to 99 mass%, more preferably 80 to 99 mass%, and particularly preferably 85 to 99 mass%, of the total mass of the rubber component, in order to obtain a better effect of the present invention.

Specific examples of olefin-based rubbers include ethylene-propylene copolymers, ethylene-1-butene copolymers, ethylene-1-octene copolymers, ethylene-propylene-diene copolymers, maleic acid modified ethylene-propylene copolymers, maleic anhydride modified ethylene-α-olefin copolymers, ethylene-glycidyl methacrylate copolymers, maleic anhydride modified ethylene-ethyl acrylate copolymers, butyl rubber, copolymers of isobutylene and aromatic vinyl or diene monomers, acrylic rubbers, and ionomers.

The olefin rubber preferably contains at least one of an ethylene/propylene copolymer and an ethylene/1-butene copolymer, from the viewpoint of achieving better effects of the present invention. Particularly preferred is a butene copolymer.

(ethylene/propylene copolymer)
The ethylene-propylene copolymer is not particularly limited as long as it is a copolymer of ethylene and propylene, and conventionally known copolymers can be used.
One of the preferred embodiments is that at least some or all of the propylene repeating units constituting the ethylene-propylene copolymer are -[CH(-CH ₃ )-CH ₂ ]-. In this case, the ethylene-propylene copolymer may have the above-mentioned branching by -CH ₃ .
One preferred embodiment of the ethylene-propylene copolymer is a copolymer in which the repeating units constituting the copolymer are only ethylene and propylene.

The weight average molecular weight of the ethylene propylene copolymer is preferably more than 100,000, more preferably 200,000 to 500,000, and particularly preferably 250,000 to 400,000, in order to achieve better effects of the present invention. .

The ethylene content of the ethylene-propylene copolymer is preferably 40 to 60% by mass, and more preferably 40% by mass or more and less than 60% by mass, because the effects of the present invention (especially heat resistance) are better. Preferably, 45 to 55% by mass is more preferable.
The ethylene content of the ethylene-propylene copolymer can be calculated based on ASTM D 3900.

The content of the ethylene-propylene copolymer is preferably 1 to 99% by mass, more preferably 35 to 85% by mass, particularly preferably 40 to 70% by mass, based on the total mass of the olefin rubber.

(ethylene/1-butene copolymer)
The ethylene/1-butene copolymer is not particularly limited as long as it is a copolymer of ethylene and 1-butene, and conventionally known copolymers can be used.
One preferred embodiment of the ethylene/1-butene copolymer is a copolymer in which the repeating units constituting the copolymer are only ethylene and 1-butene.

The Mooney viscosity of the ethylene/1-butene copolymer at 125° C. is preferably 20 or more, and 30 More preferably, the number is more than 40, and particularly preferably 40 or more. The upper limit of the Mooney viscosity is not particularly limited, but is preferably 70 or less, more preferably 55 or less.
Mooney viscosity at 125°C is the viscosity (ML1+4, 125°C) (the same applies below).

The ethylene content of the ethylene/1-butene copolymer is preferably from 60 to 90% by mass, and more preferably from 65 to 85% by mass, based on the ethylene/1-butene copolymer.
The ethylene content of the ethylene/1-butene copolymer can be calculated based on ASTM D 3900.

The content of the ethylene-1-butene copolymer is preferably 1 to 99 mass%, more preferably 15 to 65 mass%, and particularly preferably 30 to 60 mass%, based on the total mass of the olefin-based rubber.

When the olefin rubber contains an ethylene/propylene copolymer and an ethylene/1-butene copolymer, the mass ratio of the content of the ethylene/1-butene copolymer to the content of the ethylene/propylene copolymer (ethylene - Content of 1-butene copolymer/content of ethylene/propylene copolymer) is preferably 98 or less, more preferably 5 or less, and particularly preferably 2 or less, from the viewpoint of improving the effects of the present invention. In addition, the lower limit of the above mass ratio (content of ethylene/1-butene copolymer/content of ethylene/propylene copolymer) is more than 0, and 0.1, since the effect of the present invention is more excellent. It is preferably at least 0.5, particularly preferably at least 0.5.

[Antimony trioxide]
Antimony trioxide (Sb ₂ O ₃ ) contained in the present composition is not particularly limited. Antimony trioxide can function as a flame retardant aid for the brominated flame retardant described below.

The content of antimony trioxide is 1 to 10 parts by mass per 100 parts by mass of the rubber component, and from the viewpoint of obtaining a superior effect of the present invention, 2.0 to 9.0 parts by mass is preferable, 3.0 to 7.0 parts by mass is more preferable, and 5.0 to 7.0 parts by mass is particularly preferable.

[Brominated flame retardant]
The brominated flame retardant contained in the present composition is a flame retardant containing a bromine atom.
Specific examples of brominated flame retardants include compounds represented by the following formula (1), decabromodiphenyl oxide, tetradecabromo-1,4-diphenoxybenzene, octabromodiphenyl oxide, tetrabromodiphenyl oxide, and tetrabromo anhydride. Phthalic acid, tetrabromophthalate ester, 1,2-bis(2,4,6-tribromophenoxy)ethane, 2,4,6-tris(2,4,6-tribromophenoxy)-1,3,5 - triazine, 2,4-dibromophenol and its polymer, 2,6-dibromophenol and its polymer, brominated polystyrene and its polymer, ethylene bistetrabromophthalimide, hexabromocyclododecane, hexabromocyclodecane, hexabromobenzene, and pentabromobenzyl acrylate and polymers thereof. Among these, compounds represented by the following formula (1), decabromodiphenyl oxide, and ethylene bistetrabromophthalimide are preferred, and the compounds represented by the following formula (1) are particularly preferred, in view of the superior effects of the present invention.

In terms of obtaining a more excellent effect of the present invention, the brominated flame retardant preferably contains a brominated flame retardant having a melting point of 300° C. or higher, and is particularly preferably a brominated flame retardant having a melting point of 300° C. or higher.
The melting point of the brominated flame retardant is preferably 320° C. or higher, particularly preferably 340° C. or higher, in terms of achieving better effects of the present invention.
Specific examples of brominated flame retardants having a melting point of 300° C. or higher include decabromodiphenyl oxide (melting point: 305° C.), tetradecabromo-1,4-diphenoxybenzene (melting point: 380° C.), ethylenebistetrabromophthalimide (446° C.), and bis(pentabromophenyl)ethane (melting point: 350° C.) of the compounds represented by the following formula (1).
The melting point of a brominated flame retardant is the temperature at the endothermic peak due to melting measured by differential scanning calorimetry (DSC).

The brominated flame retardant is preferably a compound represented by the following formula (1), since the effects of the present invention are more excellent.

In formula (1), R represents an aliphatic hydrocarbon group that may contain an unsaturated bond.

The aliphatic hydrocarbon group may be linear, branched, cyclic, or a combination thereof. A preferred embodiment is that it is linear.
The number of carbon atoms in the aliphatic hydrocarbon group is not particularly limited. For example, it can be from 1 to 10. The number of carbon atoms is preferably 2 to 8.
The aliphatic hydrocarbon group may be saturated or unsaturated. Examples of the unsaturated bond include a vinyl group, a vinylene group, an ethynyl group, and an ethynylene group.
Examples of the hydrocarbon group include a methylene group, an ethylene group, a trimethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, and an octylene group.

Examples of the compound represented by formula (1) include bis(pentabromophenyl)ethane.
The compound represented by formula (1) is preferably bis(pentabromophenyl)ethane from the viewpoint of excellent flame retardancy.

The content of the bromine-based flame retardant is 5 to 40 parts by mass per 100 parts by mass of the rubber component, and from the viewpoint of obtaining a better effect of the present invention, 5 to 30 parts by mass is preferable, and 5 to 20 parts by mass is particularly preferable.

[Optional components]
In addition to the above components, the composition may further contain additives such as carbon black, silica, zinc oxide, stearic acid, wax, processing aids, process oil, liquid polymers, vulcanizing agents, vulcanization accelerators, crosslinking agents, antioxidants, softeners, and flame retardants other than those mentioned above, within the scope of the invention. The content of these additives can be appropriately determined within the scope of the invention.

[Method of preparing rubber composition]
The method for producing the present composition is not particularly limited, and specific examples thereof include a method in which the above-mentioned components are kneaded using a known device (e.g., a Banbury mixer, a kneader, a roll, etc.) When the present composition contains a vulcanizing agent, it is preferable to first mix the components other than the vulcanizing agent at a high temperature (preferably 100 to 160°C), cool the mixture, and then mix the vulcanizing agent.
The composition can be vulcanized or crosslinked under conventionally known vulcanization or crosslinking conditions.

[Application]
Applications of the composition are not particularly limited, but include, for example, tires (particularly pneumatic tires), hoses, and conveyor belts. Among these, the present composition is preferably a rubber composition for conveyor belts.

[Conveyor belt]
Next, the conveyor belt of the present invention will be explained.
The conveyor belt of the present invention is a conveyor belt made using the present composition. Its shape, manufacturing method, etc. are similar to known conveyor belts.

There is no particular restriction on which component of the conveyor belt of the present invention the present composition is applied to. All or part of the rubber constituting the conveyor belt of the present invention may be formed of the present composition.
Since the present composition has excellent flame retardancy, flame retardancy after heat aging, heat resistance, bending resistance, and abrasion resistance, the conveyor belt of the present invention includes a cover rubber formed using the present composition. This is mentioned as one of the preferred embodiments.

Specific configurations of the conveyor belt of the present invention include, for example, those shown below. Note that the conveyor belt of the present invention is not limited to the attached drawings.

A first embodiment of the conveyor belt of the present invention will be described using FIG. 1.
FIG. 1 is a cross-sectional view of one embodiment of a conveyor belt of the present invention. As shown in FIG. 1, the first embodiment of the conveyor belt of the present invention is a conveyor belt in which a cloth layer 1 is covered with a coat rubber (adhesive rubber) 2 to form a core layer, and the outer periphery of the core layer is covered with a cover rubber 3. It is 4. It is preferable that the cover rubber 3 is formed from the present composition.
The conveyor belt 4 in FIG. 1 has a cloth layer 1 as a core material, and the number of laminated cloth layers 1, the thickness of the cover rubber 3, the belt width, etc. can be determined as appropriate depending on the purpose of use.
Examples of the fabric layer include canvas made of woven fabric of synthetic fibers such as nylon, vinylon, and polyester.
The thicknesses T ₁ and T ₂ of the cover rubber 3 are usually about 1.5 to 20 mm.

Further, as the coat rubber 2, coat rubbers used in known conveyor belts can be used, such as natural rubber (NR), acrylonitrile butadiene rubber (NBR), styrene butadiene rubber (SBR), butadiene rubber (BR), ethylene rubber, etc. A rubber composition containing propylene rubber (EPM), ethylene propylene diene rubber (EPDM), etc. as a rubber component can be used.

Next, a second embodiment of the conveyor belt of the present invention will be described using FIG. 2.
FIG. 2 is a cross-sectional view of another embodiment of the conveyor belt of the present invention.
As shown in FIG. 2, the second embodiment of the conveyor belt of the present invention is a conveyor belt in which a steel cord 5 is covered with a cushion rubber (adhesive rubber) 6 to form a core layer, and the outer periphery of the core layer is covered with a cover rubber 7. This is belt 8. It is preferable that the cover rubber 7 is formed from the present composition.
The core material of the conveyor belt 8 is made by arranging approximately 50 to 230 steel cords 5 with a diameter of approximately 2.0 to 9.5 mm, which are made by twisting together a plurality of wires with a diameter of approximately 0.2 to 0.4 mm. Can be done. Generally, the total thickness T of the conveyor belt 8 can be about 10 to 50 mm.
Further, as the cushion rubber 6, for example, adhesive rubber that can be bonded to galvanized steel cords used in known steel conveyor belts can be used, and specifically, for example, natural rubber (NR), acrylonitrile butadiene rubber (NBR), etc. can be used. ), styrene-butadiene rubber (SBR), butadiene rubber (BR), ethylene-propylene rubber (EPM), ethylene-propylene diene rubber (EPDM), etc. can be used.

The conveyor belt of the present invention can be easily produced, for example, by interposing a cloth layer or steel cord serving as a core material between unvulcanized rubber sheets molded from the present composition, and vulcanizing the belt by heating and pressurizing it in accordance with a conventional method. can be manufactured. The vulcanization conditions are usually, for example, about 120 to 180°C, about 0.1 to 4.9 MPa, and about 10 to 90 minutes.

Since the conveyor belt of the present invention uses the composition described above, it has excellent flame retardancy, flame retardancy after heat aging, heat resistance, bending resistance, and abrasion resistance.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto.

[Manufacture of composition]
Each component in Table 1 below was used in the composition (parts by mass) shown in the same table, and these were mixed in a Banbury mixer to produce each composition.

[Evaluation test]
〔Flame retardance〕
Using each composition, samples were prepared according to JIS K6324:2013 "Flame-retardant conveyor belts - Grades and test methods" section 7.2.1 for fabric layer conveyor rubber (the dimensions of the samples were 200 mm on the long side, (Short side: 25 mm), which was used as a test sample. In each test sample (flame retardant conveyor belt), the composition forms the cover rubber and the fabric layer forms the core material.
Based on the flame retardancy evaluation (flame extinction time, unit: seconds) of JIS K6324:2013 "Flame retardant conveyor belts - Grades and test methods", the flame retardance was evaluated using the test sample according to the following criteria. . In addition, if the evaluation result is "〇", it was evaluated that the flame retardance is excellent. The results are shown in Table 1.
〇: Flame extinction time less than 10 seconds △: Flame extinction time 10 seconds or more and 30 seconds or less ×: Flame extinction time more than 30 seconds

[Flame retardancy after heat aging]
A test sample prepared in the same manner as in the above "flame retardancy" was subjected to heat aging treatment by placing it under the condition of 180° C. for 168 hours to obtain an evaluation sample after the heat aging treatment. Using the obtained test sample (after heat aging treatment), post-aging flame retardance was evaluated using the same test method and evaluation criteria as for the above-mentioned "flame retardancy". In addition, if the evaluation result is "〇", it was evaluated that the flame retardance is excellent. The results are shown in Table 1.

〔Heat-resistant〕
The heat resistance was evaluated using a test sample obtained using a rubber composition based on the elongation at break (EB, unit %) before and after heat aging treatment.
Specifically, each composition was vulcanized for 45 minutes using a press molding machine at 160° C. under a surface pressure of 3.0 MPa to produce a 2 mm thick vulcanized sheet. A JIS No. 3 dumbbell-shaped test piece was punched out from this sheet to obtain a test sample.
Using the obtained test sample (before heat aging treatment), a tensile test was conducted at room temperature at a tensile speed of 500 mm/min in accordance with JIS K6251:2017, and the elongation at break (EB, unit %) was determined. (hereinafter also referred to as "initial EB") was measured.
Further, the obtained test sample (before heat aging treatment) was subjected to heat aging treatment by placing it at 180° C. for 168 hours to obtain a test sample after heat aging treatment. Using the obtained test sample (after heat aging treatment), a tensile test was conducted under the same conditions as the test sample before heat aging treatment. (Also referred to as "post-aging EB.") was measured.
Based on the values of "initial EB" and "EB after heat aging" thus obtained, the rate of change (%) in elongation at break before and after heat aging treatment was calculated using the following formula. If the rate of change was -25% or more, it was evaluated as having excellent heat resistance. When the above change rate was -10% or more, it was evaluated that the heat resistance was better. Note that, whether the above change rate is positive or negative, the closer it is to 0%, the better the heat aging resistance is. The results are shown in the "Heat Resistance" column of Table 1.
Rate of change in elongation at break (%) before and after heat aging treatment = 100 x {(EB after heat aging) - (Initial EB)}/(Initial EB)

[Bending resistance]
A crack growth test by repeated bending was conducted according to the bending crack growth test described in JIS K6260:2017.
Specifically, test pieces described in "5.1" in JIS K6260:2017 were prepared by vulcanizing each composition for 45 minutes under a surface pressure of 3.0 MPa. A test piece with the size specified for the above bending crack growth test was prepared, and the test piece was cut with a specified cutting blade and subjected to a bending resistance test using a Demacha bending tester (temperature: 23°C). , stroke: 57 mm, speed: 300±10 rpm, total number of bends: 400,000 times). After the test, the length of the crack was measured. If the test piece did not break after the above test, it was evaluated as having excellent bending resistance. Furthermore, it was evaluated that the smaller the crack length, the better the bending resistance. In addition, a case where the test piece was broken after the above test was marked as "x".

[Abrasion resistance]
Using a press molding machine, the composition was vulcanized for 45 minutes at a press temperature of 160° C. and a surface pressure of 3.0 MPa to prepare a test sample having a diameter of 16 mm and a thickness of 6 mm.
In accordance with JIS K6264-2:2005, the test sample was subjected to an abrasion test (method A) at room temperature using a DIN abrasion tester, the amount of wear [mm ³ ] was measured, and the wear resistance was determined according to the following criteria. The gender was evaluated. In addition, if the evaluation result is "○", it was evaluated that the wear resistance is excellent. The results are shown in Table 1.
〇: Amount of wear is less than 150mm ³ ×: Amount of wear is 150mm ³ or more

Details of each component in Table 1 above are as follows.
- Ethylene-propylene copolymer: trade name "KEP-110" (manufactured by KUMHO POLYCHEM). The weight average molecular weight of the ethylene-propylene copolymer is 310,000, and the ethylene content is 52% by mass. The above ethylene/propylene copolymer (KEP-110) has a weight average molecular weight of over 100,000, so it falls under the above ethylene/propylene copolymer 1. The above-mentioned ethylene-propylene copolymer has branches due to the above-mentioned -CH ₃ because at least some or all of the propylene repeating units are -CH(-CH ₃ )-CH ₂ -.

- Ethylene/1-butene copolymer: trade name "Engage 7487" (manufactured by Dow Chemical Company). The Mooney viscosity of the ethylene/1-butene copolymer at 125° C. is 47, and its ethylene content is 74% by mass.

- Chlorinated polyethylene: trade name "Weipren6235" (manufactured by Weifang), specific gravity 1.19 g/cm ³ , chlorine content 35 ± 1% by mass

・ISAF grade carbon black: Product name “Niteron #300” (manufactured by Nippon Steel Carbon Co., Ltd.)
・Zinc oxide: Product name “3 types of zinc oxide” (manufactured by Seido Kagaku Kogyo Co., Ltd.)
・Stearic acid: Product name “Stearic acid 50S” (manufactured by Chiba Fatty Acid Co., Ltd.)
・Anti-aging agent (Nocrac MMB): Product name “Nocrac MMB” (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)

- Antimony trioxide: Product name "PATOX-M" (manufactured by Nippon Seiko Co., Ltd.), flame retardant aid - Brominated flame retardant (SAYTEX8010): Product name "SAYTEX8010" (manufactured by ALBEMARLE CORPORATION), bis (pentabromophenyl) ) ethane

・Softener: Product name "Lucant HC-3000X" (manufactured by Mitsui Chemicals), weight average molecular weight 14,000, ethylene-propylene copolymer oil ・Crosslinking agent 1 (High Cross GT): Product name "High Cross GT" (manufactured by Seiko Kagaku Co., Ltd.)
・Crosslinking agent 2 (Percadox 14-40): Trade name “Percadox 14-40” (manufactured by Kayaku Akzo)

As shown in Table 1, rubber is blended with 1 to 10 parts by mass of antimony trioxide and 5 to 40 parts by mass of a brominated flame retardant to 100 parts by mass of a rubber component containing olefin rubber and chlorinated polyethylene. It was confirmed that by using the composition, a conveyor belt having excellent flame retardancy, flame retardance after heat aging, heat resistance, bending resistance, and abrasion resistance could be obtained (Examples 1 to 7).
In addition, from the comparison of Examples 1 to 7, if the mass ratio of the content of chlorinated polyethylene to the content of brominated flame retardant is more than 0.20 and 8 or less (Example 1), the conveyor has better heat resistance. It was confirmed that a belt could be obtained.
Also, from the comparison of Examples 1 to 7, if the mass ratio of the content of chlorinated polyethylene to the content of antimony trioxide is 0.60 to 10.0 (Examples 1 to 4, 6, and 7) It was confirmed that a conveyor belt with better bending resistance could be obtained.

On the other hand, as shown in Table 1, when the rubber component does not contain chlorinated polyethylene and/or when the content of at least one of antimony oxide and bromine-based flame retardants per 100 parts by mass of the rubber component is outside the above range, it was confirmed that the conveyor belt is inferior in at least one of flame retardancy, flame retardancy after heat aging, heat resistance, flex resistance, and abrasion resistance.

1: Fabric layer 2: Coating rubber 3, 7: Cover rubber 4, 8: Conveyor belt 5: Steel cord 6: Cushion rubber

Claims (9)

a rubber component including a chlorinated polyethylene and an olefin-based rubber;
Antimony trioxide,
A brominated flame retardant is included,
The content of the antimony trioxide is 1 to 10 parts by mass based on 100 parts by mass of the rubber component,
The content of the brominated flame retardant is 5 to 40 parts by mass based on 100 parts by mass of the rubber component,
The olefin-based rubber is at least one selected from the group consisting of an ethylene-propylene copolymer (wherein the repeating units constituting the ethylene-propylene copolymer are only repeating units of ethylene and propylene), an ethylene-1-butene copolymer (wherein the repeating units constituting the ethylene-1-butene copolymer are only repeating units of ethylene and 1-butene), an ethylene-1-octene copolymer, an ethylene-glycidyl methacrylate copolymer, a maleic anhydride-modified ethylene-ethyl acrylate copolymer, butyl rubber, and a copolymer of isobutylene and a diene monomer. The rubber composition according to claim 1, wherein the brominated flame retardant includes a brominated flame retardant having a melting point of 300°C or higher. The rubber composition according to claim 1 or 2, wherein the brominated flame retardant is a compound represented by the following formula (1).

In formula (1), R represents an aliphatic hydrocarbon group which may contain an unsaturated bond. The rubber composition according to any one of claims 1 to 3, wherein the mass ratio of the content of the chlorinated polyethylene to the content of the brominated flame retardant is 8 or less. The rubber component consists only of the chlorinated polyethylene and the olefin rubber,
The content of the chlorinated polyethylene is 1 to 40% by mass based on the total mass of the rubber component,
The rubber composition according to any one of claims 1 to 4, wherein the content of the olefin rubber is 60 to 99% by mass based on the total mass of the rubber component. The olefin rubber includes the ethylene /propylene copolymer and the ethylene/ 1 -butene copolymer,
The rubber composition according to any one of claims 1 to 5, wherein the mass ratio of the content of the ethylene/1-butene copolymer to the content of the ethylene/propylene copolymer is 98 or less. . The rubber composition according to any one of claims 1 to 6, which is a rubber composition for a conveyor belt. A conveyor belt made using the rubber composition according to any one of claims 1 to 7. 9. The conveyor belt of claim 8, having a cover rubber formed using the rubber composition.