JP7293720B2 - Steel cord adhesive rubber composition and conveyor belt - Google Patents

Description

TECHNICAL FIELD The present invention relates to a rubber composition for adhering steel cords and a conveyor belt.

Conventionally, various rubber compositions have been proposed for the purpose of improving adhesiveness to steel cords.
For example, Patent Document 1 describes a rubber composition obtained by blending 100 parts by mass of a diene rubber containing natural rubber, 40 to 80 parts by mass of carbon black, cobalt neodecanoate borate, a phenolic resin and a curing agent. The carbon black has a DBP oil absorption of 50×10 ⁻⁵ to 80×10 ⁻⁵ m ³ /kg, an iodine adsorption of 100 to 150 g/kg, and a dynamic strain of 2% at 20° C. The storage modulus (E') is 8 MPa or more, the tangent loss (tan δ) at 60°C is 0.20 or less, and the number of cycles until failure is 45,000 or more in a constant strain fatigue test at 60% strain and 400 rpm. A rubber composition has been proposed.

In addition, Patent Document 2 describes a method for bonding galvanized steel cord and rubber using a rubber composition that has excellent moisture-resistant adhesion and initial adhesiveness to galvanized steel cord, and a method for producing rubber using the bonding method. For the purpose of providing steel cord conveyor belts that are
For 100 parts by weight of sulfur vulcanizable rubber,
3 to 15 parts by weight of rosin or a rosin derivative,
0.2 to 1.0 parts by weight of the organic cobalt salt as the amount of cobalt,
A method of adhering galvanized steel cord to rubber is disclosed, wherein a rubber composition containing 3 to 50 parts by weight of an organochlorine compound is adhered to galvanized steel cord.

JP 2018-131522 A Japanese Patent No. 4449941

On the other hand, when a conveyor belt containing steel cords is used in a cold region, the rubber composition used for the coating rubber layer (cushion rubber) for coating the steel cords in the conveyor belt has adhesion to the steel cords. In addition, cold resistance is required.

Under such circumstances, the present inventors prepared a rubber composition and evaluated it with reference to Patent Document 1 etc., and found that such a composition is inferior in cold resistance, and has durability and water-resistant adhesion. It became clear that it is difficult to achieve both sexes (Comparative Examples 2 to 4).
Accordingly, an object of the present invention is to provide a rubber composition for adhering steel cords, which is excellent in cold resistance, durability and water-resistant adhesiveness. Incidentally, in the present invention, water-resistant adhesiveness includes moisture-resistant adhesiveness.
Another object of the present invention is to provide a conveyor belt that is excellent in cold resistance, durability, and water-resistant adhesiveness.

The inventors of the present invention have made intensive studies to solve the above problems, and found that a desired effect can be obtained when a rubber composition contains a rubber component containing at least polybutadiene rubber and cobalt neodecanoate borate. The discovery led to the present invention.
The present invention is based on the above knowledge and the like, and specifically solves the above problems with the following configuration.

[1] A rubber composition for adhering steel cords, containing a rubber component containing at least polybutadiene rubber and cobalt neodecanoate borate.
[2] The rubber composition for bonding steel cords according to [1], wherein the rubber component further contains natural rubber and/or styrene-butadiene copolymer rubber.
[3] The rubber composition for adhering steel cords according to [1] or [2], wherein the content of the polybutadiene rubber is 15 to 60 parts by mass with respect to 100 parts by mass of the rubber component.
[4] further contains carbon black,
The rubber composition for adhering steel cords according to any one of [1] to [3], wherein the carbon black content is 35 to 75 parts by mass with respect to 100 parts by mass of the rubber component.
[5] The steel according to any one of [1] to [4], wherein the content of the cobalt neodecanoate borate is 1.2 to 3.5 parts by mass with respect to 100 parts by mass of the rubber component. A rubber composition for cord bonding.
[6] further contains a vulcanization accelerator,
The rubber composition for adhering steel cords according to any one of [1] to [5], wherein the vulcanization accelerator is a thiazole vulcanization accelerator.
[7] The rubber composition for adhering steel cords according to [6], wherein the content of the vulcanization accelerator is 0.3 to 1.2 parts by mass with respect to 100 parts by mass of the rubber component.
[8] further containing sulfur,
The rubber composition for bonding steel cords according to any one of [1] to [7], wherein the sulfur content is 2.1 to 5.0 parts by mass with respect to 100 parts by mass of the rubber component.
[9] The rubber composition for adhering steel cords according to any one of [1] to [8], further comprising at least one selected from the group consisting of rosin, rosin derivatives, phenolic resins and chlorinated paraffins.
[10] Further containing zinc oxide,
The rubber composition for adhering steel cords according to any one of [1] to [9], wherein the zinc oxide content is 5.0 parts by mass or more with respect to 100 parts by mass of the rubber component.
[11] further contains an oil,
The rubber composition for adhering steel cords according to any one of [1] to [10], wherein the content of the oil is 2.0 parts by mass or more with respect to 100 parts by mass of the rubber component.
[12] The rubber composition for adhering steel cords according to any one of [1] to [11], which is used for adhering galvanized steel cords.
[13] A conveyor belt formed using the steel cord bonding rubber composition according to any one of [1] to [12].

The rubber composition for adhering steel cords of the present invention is excellent in cold resistance, durability and water-resistant adhesion.
In addition, the conveyor belt of the present invention is excellent in cold resistance, durability and water-resistant adhesiveness.

FIG. 1 is a cross-sectional perspective view schematically showing an example of the conveyor belt of the present invention.

The present invention will be described in detail below.
In this specification, a numerical range represented by "to" means a range including the numerical values before and after "to" as lower and upper limits.
In this specification, unless otherwise specified, each component can be used singly or in combination of two or more substances corresponding to the component. When the component contains two or more substances, the content of the component means the total content of the two or more substances.
In the present specification, each component is not particularly limited in its production method unless otherwise specified. For example, a conventionally known method can be used.
In this specification, when at least one of cold resistance, durability and water-resistant adhesion is superior, the effect of the present invention is sometimes said to be superior.

[Rubber composition for adhering steel cord]
The rubber composition for adhering steel cords of the present invention (composition of the present invention) is a rubber composition for adhering steel cords containing a rubber component containing at least polybutadiene rubber and cobalt neodecanoate borate.

Since the composition of the present invention has such a constitution, it is believed that the desired effect can be obtained. Although the reason is not clear, it is presumed to be approximately as follows.
By containing polybutadiene rubber as a rubber component, the composition of the present invention can have a brittleness temperature within a suitable range and is excellent in cold resistance.
In addition, the present inventors have found that when cobalt naphthenate is used as an organic cobalt salt, the retention of the elongation at break (EB) of the rubber in the over-vulcanized state is low and the durability of the conveyor belt is reduced. Found a problem.
Here, overvulcanization means that the rubber is further vulcanized after the normal vulcanization time (after the initial vulcanization) required in manufacturing the product. As the above-mentioned further vulcanization, specifically, for example, when the vulcanization time is longer than usual when vulcanizing unvulcanized rubber; Further vulcanization of vulcanized rubber; and further vulcanization of vulcanized rubber to make it endless.
With respect to the above problem, the present inventors have found that when cobalt neodecanoate borate is used as the organic cobalt salt, the durability of the conveyor belt can be improved while maintaining or improving the waterproof adhesion.
When the amount of cobalt contained in cobalt neodecanoate borate and cobalt naphthenate is equal, the organic acid content of cobalt neodecanoate borate is less than that of cobalt naphthenate, so the elongation at break after overvulcanization is The inventors speculate that the decrease in (EB) can be reduced.
Thus, the composition of the present invention can achieve both excellent levels of durability and water-resistant adhesion by containing cobalt borate neodecanoate.
As described above, the composition of the present invention is excellent in cold resistance, durability, and water-resistant adhesiveness.
Each component contained in the composition of the present invention will be described in detail below.

<Rubber component>
The composition of the present invention contains a rubber component containing at least polybutadiene rubber.

<Polybutadiene rubber>
The polybutadiene rubber (butadiene rubber, also referred to as "BR") contained in the composition of the present invention is not particularly limited as long as it is a homopolymer of butadiene. Incidentally, the polybutadiene rubber may be modified.

(Weight average molecular weight of polybutadiene rubber)
The weight-average molecular weight of the polybutadiene rubber is preferably 400,000 to 1,000,000, more preferably 450,000 to 800,000, from the viewpoint that the effect of the present invention is superior and the pullout force (the force required to pull out the steel cord from the rubber) increases. is more preferred.
In the present invention, the weight-average molecular weight of polybutadiene rubber is a standard polystyrene conversion value based on a measurement value by gel permeation chromatography (GPC) using cyclohexane as a solvent.

(Glass transition temperature of polybutadiene rubber)
The glass transition temperature of the polybutadiene rubber is preferably −50° C. or lower, more preferably −150 to −80° C., from the viewpoint that the effects of the present invention are excellent (especially cold resistance).
In the present invention, the glass transition temperature is based on JIS K7121: 2012, and the curve obtained when the change in heat flow rate is measured at a temperature increase of 20 ° C./min using a differential thermal analysis instrument. It can be the read value.

The content of the polybutadiene rubber is excellent due to the effects of the present invention (especially cold resistance), and the rubber after the initial vulcanization is further crosslinked by overvulcanization so that the rubber does not become too hard, and the brittleness temperature is set in an appropriate range. From the viewpoint of being able to 45 parts by weight is particularly preferred.

(Rubber other than BR)
The rubber component may contain other rubbers in addition to BR.
Examples of rubbers other than BR include natural rubber, isoprene rubber (IR), aromatic vinyl-conjugated diene copolymer rubber (eg, styrene-butadiene copolymer rubber), acrylonitrile-butadiene rubber (NBR), butyl rubber (IIR). , halogenated butyl rubber, and chloroprene rubber (CR).

The rubber component preferably further contains natural rubber and/or styrene-butadiene copolymer rubber, and more preferably contains natural rubber and styrene-butadiene copolymer rubber, from the viewpoint of achieving superior effects of the present invention.

- Natural rubber The natural rubber (NR) is not particularly limited. For example, a conventionally well-known thing is mentioned.

• Styrene-butadiene copolymer rubber The styrene-butadiene copolymer rubber is not particularly limited as long as it is a copolymer of styrene and butadiene.

(Bound styrene content of styrene-butadiene copolymer rubber)
The amount of bound styrene in the styrene-butadiene copolymer rubber is excellent due to the effect of the present invention (especially cold resistance), and the glass transition temperature of the styrene-butadiene copolymer rubber described later is low. It is preferably 5 to 40% by mass, more preferably 10 to 30% by mass, based on the total amount of the coalesced rubber.

(Vinyl content of styrene-butadiene copolymer rubber)
The vinyl content (1,2-vinyl bond content) of the styrene-butadiene copolymer rubber due to butadiene is superior to the effect of the present invention (especially cold resistance), and the glass transition temperature of the styrene-butadiene copolymer rubber described later is low. From the viewpoint that the total amount of butadiene repeating units contained in the styrene-butadiene copolymer rubber is 5 to 30% by mass, and more preferably 5 to 20% by mass.
In the present invention, the bound styrene content and the vinyl content of the styrene-butadiene copolymer rubber can be measured by ¹ H-NMR.

(Glass transition temperature of styrene-butadiene copolymer rubber)
The glass transition temperature of the styrene-butadiene copolymer rubber is preferably −50° C. or lower from the viewpoint that the effect of the present invention (particularly cold resistance) is superior.
The lower limit of the glass transition temperature of the styrene-butadiene copolymer rubber can be, for example, −100° C. or higher.

(Weight average molecular weight of styrene-butadiene copolymer rubber)
The weight average molecular weight of the styrene-butadiene copolymer rubber is not particularly limited. For example, it can be 200,000 to 3,000,000.
In the present invention, the weight-average molecular weight of the styrene-butadiene copolymer rubber is a standard polystyrene conversion value based on a measurement by gel permeation chromatography (GPC) using tetrahydrofuran as a solvent.

When the rubber component further contains, in addition to BR, the natural rubber and the styrene-butadiene copolymer rubber (three-component combination), the content of the natural rubber is superior to the effect of the present invention, and the brittleness temperature is within an appropriate range, it is preferably 20 to 42.5 parts by mass, more preferably 25 to 40 parts by mass, relative to 100 parts by mass of the rubber component.
In addition, in the case of using the three components together, the content of the styrene-butadiene copolymer rubber is superior to the effects of the present invention, and the brittleness temperature can be set within an appropriate range. 20 to 42.5 parts by mass is preferable, and 25 to 40 parts by mass is more preferable.

<Cobalt neodecanoate borate>
The cobalt neodecanoate borate contained in the composition of the present invention is a compound represented by the following formula (1).
The composition of the present invention exhibits excellent adhesion to steel cords by containing cobalt neodecanoate borate.

(Content of cobalt neodecanoate borate)
The content of cobalt neodecanoate borate is excellent due to the effect of the present invention, and the adhesion to steel cords is excellent, and the rubber after initial vulcanization is further crosslinked by overvulcanization, preventing the rubber from becoming too hard. From the viewpoint, it is preferably 1.2 to 3.5 parts by mass, more preferably more than 1.5 parts by mass and not more than 2.5 parts by mass with respect to 100 parts by mass of the rubber component.

(Carbon black)
The composition of the invention may further contain carbon black.
The carbon black is not particularly limited.
Among them, the above carbon black is preferably HAF grade carbon black or ISAF grade carbon black, and more preferably HAF grade carbon black, from the viewpoint that the effect of the present invention is superior.

(Nitrogen adsorption specific surface area of carbon black)
The nitrogen adsorption specific surface area (N ₂ SA) of the carbon black is preferably 60 to 120 m ² /g, more preferably 65 to 95 m ² /g, from the standpoint of superior effects of the present invention.
The nitrogen adsorption specific surface area of carbon black can be measured by measuring the amount of nitrogen adsorbed on the carbon black surface according to JIS K 6217-2:2017 "Part 2: Determination of specific surface area - nitrogen adsorption method - single point method".

(Carbon black content)
The content of the carbon black is preferably 35 to 75 parts by mass, more preferably 40 to 70 parts by mass, with respect to 100 parts by mass of the rubber component, from the viewpoint of achieving superior effects of the present invention.

(Vulcanization accelerator)
The compositions of the present invention may further contain vulcanization accelerators.
The vulcanization accelerator is not particularly limited. Examples thereof include thiazole-based, guanidine-based, thiuram-based, and sulfenamide-based vulcanization accelerators.
Among them, the vulcanization accelerator is preferably a thiazole-based vulcanization accelerator from the viewpoint that it is superior to the effect of the present invention and does not easily promote further cross-linking of rubber after vulcanization, and dibenzothiazyl Disulfides are more preferred.

(Content of vulcanization accelerator)
The content of the vulcanization accelerator is preferably 0.3 to 1.2 parts by mass, preferably 0.3 parts by mass, with respect to 100 parts by mass of the rubber component, from the viewpoint that the effect of the present invention is superior. More preferably less than 1.0 parts by mass, more preferably 0.4 to 0.9 parts by mass.

(sulfur)
The compositions of the invention may further contain sulfur. The sulfur is not particularly limited.

(sulfur content)
The content of sulfur is preferably 2.1 to 5.0 parts by mass with respect to 100 parts by mass of the rubber component from the viewpoint that the effects of the present invention (especially water-resistant adhesion) are excellent. 5 to 4.0 parts by mass is more preferable.

(Mass ratio of cobalt neodecanoate borate/sulfur)
When the composition of the present invention further contains sulfur, the mass ratio of the content of cobalt neodecanoate borate to the content of sulfur (cobalt neodecanoate borate/sulfur) is superior due to the effects of the present invention. From the viewpoint of excellent adhesion to the cord, 0.24 (1.2/5) to 1.7 (3.5/2.1) is preferable, and more than 0.50 and 1.0 or less is more preferable. 0.55 to 0.80 is more preferred.

(rosin, etc.)
The composition of the present invention further contains at least one selected from the group consisting of rosin, rosin derivatives, phenolic resins and chlorinated paraffins, from the viewpoint of being superior to the effects of the present invention and having excellent adhesion to steel cords. It is preferable to use rosin or a rosin derivative, a phenol resin, and chlorinated paraffin in combination.
In the present specification, rosin, rosin derivatives, phenolic resins and chlorinated paraffins may be collectively referred to as "rosin and the like" hereinafter.
The above rosin and the like can function as adhesion promoters.

・Rosin, rosin derivatives Rosin is a kind of natural resin, which is also called rosin.
Rosin derivatives include, for example, gum rosin, wood rosin, tall oil rosin extracted from pine wood with a solvent, polymers of these rosins, disproportionated rosin, maleated rosin, aldehyde-modified rosin, hydrogenated rosin and processing thereof. products, etc.
Rosin and rosin derivatives that are generally used as tackifiers can be used.
A commercially available product can be used as the rosin or rosin derivative. Specific examples include gum rosin or wood rosin manufactured by Arakawa Chemical Industries, Ltd., tall oil rosin manufactured by Harima Chemicals Group, and hydrogenated rosin manufactured by Hercules.

The content of the rosin is preferably 3 to 10 parts by mass with respect to 100 parts by mass of the rubber component from the standpoint of superior effects of the present invention and excellent adhesion to steel cords. The content of the rosin derivative is also the same as the above content of rosin.

- Phenolic resin As the phenolic resin, those that can generally be blended into rubber compositions can be used. The phenolic resin may include resins obtained by reaction of phenols and aldehydes and modified products thereof. Examples of phenols include phenol, cresol, xylenol, resorcinol, and the like. Examples of aldehydes include formaldehyde, acetaldehyde, furfural, and the like.
The composition of the present invention preferably does not contain a phenolic resin curing agent.

The content of the phenol resin is preferably 2 to 8 parts by mass with respect to 100 parts by mass of the rubber component from the standpoint of superior effects of the present invention and excellent adhesion to steel cords.

- Chlorinated paraffin The chlorinated paraffin is not particularly limited as long as it is a paraffin containing chlorine. Examples thereof include chain saturated hydrocarbon compounds having an average of 26 carbon atoms, in which all or part of the hydrogen atoms in the compounds are substituted with chlorine atoms.
The amount of chlorine contained in the chlorinated paraffin is preferably, for example, 40 to 80% by mass with respect to the total amount of chlorinated paraffin.

The content of the chlorinated paraffin is preferably 3 to 8 parts by mass with respect to 100 parts by mass of the rubber component from the viewpoint of superior effects of the present invention and excellent adhesion to steel cords.

(Total content when used together)
When rosin or a rosin derivative, a phenolic resin, and a chlorinated paraffin are used in combination, the total content of these is 100 mass of the rubber component from the viewpoint that the effect of the present invention is superior and the adhesiveness to the steel cord is excellent. It is preferably 8 to 22 parts by mass per part.
When a rosin or a rosin derivative, a phenolic resin, and a chlorinated paraffin are used in combination, the content of the phenolic resin relative to the total content of these is superior due to the effects of the present invention, from the viewpoint of excellent adhesion to steel cords. , preferably 10 to 40% by mass.

(zinc oxide)
The compositions of the invention may further contain zinc oxide. The zinc oxide is not particularly limited.

(content of zinc oxide)
The zinc oxide content is preferably 5.0 parts by mass or more with respect to 100 parts by mass of the rubber component, from the viewpoint of achieving superior effects of the present invention.
The upper limit of the zinc oxide content can be 20 parts by mass or less with respect to 100 parts by mass of the rubber component.

(oil)
The compositions of the invention may further contain oils. The above oil is not particularly limited. Examples include paraffin oil (excluding chlorinated paraffin) and aroma oil.

(oil content)
The content of the oil is preferably 2.0 parts by mass or more with respect to 100 parts by mass of the rubber component, from the viewpoint of achieving superior effects of the present invention.
The upper limit of the content of the oil can be 10 parts by mass or less with respect to 100 parts by mass of the rubber component.

The composition of the present invention can contain additives such as stearic acid and anti-aging agents in addition to the above-mentioned essential components, if necessary, as long as the objects of the present invention are not impaired.

The composition of the present invention can be produced by mixing the above-mentioned essential components and optionally the carbon black and the like using a roll mill, a Banbury mixer, or the like.

The compositions of the invention can be used, for example, to bond steel cords, in particular, for example galvanized steel cords.
Composites comprising vulcanized rubber and steel cords can be obtained by using the compositions of the present invention together with steel cords (eg galvanized steel cords) and vulcanizing them, for example. The vulcanized rubber and the steel cord can be bonded together in the composite.

Examples of the steel cords include surface-untreated steel cords and surface-untreated steel cords plated with zinc.
The above steel cord is preferably galvanized from the viewpoint of being excellent in the effect of the present invention and having excellent rust resistance.
For example, the wire diameter or cord diameter of the steel cord can be appropriately selected.

The temperature at which the composition of the present invention is vulcanized can be, for example, about 140 to 160.degree.

The brittleness temperature of the vulcanizate obtained by vulcanizing the composition of the present invention is preferably −50° C. or less, and −58° C., from the viewpoint of being superior to the effects of the present invention (especially cold resistance). The following are more preferred.
In the present invention, the composition of the present invention is vulcanized under pressure for 20 minutes under conditions of 153 ° C. and a surface pressure of 2.0 MPa to obtain a vulcanized rubber (sheet-like with a thickness of 2 mm), and the vulcanized rubber The embrittlement temperature was measured according to JIS K 6261-2:2017 "Vulcanized rubber and thermoplastic rubber-Determination of low-temperature properties-Part 2: Low-temperature impact embrittlement test".

The composition of the present invention can be suitably used, for example, in the production of conveyor belts. When the composition of the present invention is used to manufacture a conveyor belt, the composition of the present invention preferably forms a coating rubber layer (cushion rubber) for coating steel cords, for example, as a member constituting the conveyor belt.

[Conveyor belt]
Next, the conveyor belt of the present invention will be explained below.
The conveyor belt of the present invention is a conveyor belt formed using the rubber composition for adhering steel cords of the present invention.

A preferred embodiment of the conveyor belt of the present invention includes steel cords. From the viewpoint that the above-mentioned steel cord is superior in the effect of the present invention, it is preferable to use a non-surface-treated steel cord plated with zinc.

The rubber composition for adhering steel cords used in the conveyor belt of the present invention is not particularly limited as long as it is the rubber composition for adhering steel cords of the present invention.
The composition of the present invention preferably forms a coat rubber layer (cushion rubber) for coating steel cords from the viewpoint of being superior in the effects of the present invention.
One of preferred aspects of the conveyor belt of the present invention is that it further has a cover rubber layer. The rubber composition that can form the cover rubber layer is not particularly limited.

Conveyor belts of the present invention will be described below with reference to the accompanying drawings. The conveyor belt of the invention is not restricted to the accompanying drawings.
FIG. 1 is a cross-sectional perspective view schematically showing an example of the conveyor belt of the present invention.
In FIG. 1, a conveyor belt 1 has cover rubber layers 6 on both surfaces, and steel cords 2 and a coat rubber layer 4 between the cover rubber layers 6 . The coated rubber layer 4 coats the steel cord 2. - 特許庁The coat rubber layer 4 is preferably made of the steel cord bonding rubber composition of the present invention.

EXAMPLES The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these.

<Production of composition>
Each component shown in Table 1 below was used in the composition (parts by mass) shown in the same table.
First, among the components shown in Table 1 below, components other than sulfur and a vulcanization accelerator were mixed in a Banbury mixer, then sulfur and a vulcanization accelerator were added to the resulting mixture, and these were rolled using a roll. were mixed together to produce each composition.

<<Evaluation>>
The following evaluations were performed using each composition produced as described above. The results are shown in Table 1.
<Cold resistance>
Cold resistance was evaluated by brittleness temperature.
- Evaluation method Each of the above compositions was pressurized and vulcanized using a press molding machine under conditions of 153°C and a surface pressure of 2.0 MPa for 20 minutes to obtain a vulcanized rubber (sheet-like with a thickness of 2 mm).
JIS K 6261-2: 2017 "Vulcanized rubber and thermoplastic rubber-Determination of low-temperature properties-Part 2: Low-temperature impact embrittlement test" A test piece was prepared from each vulcanized rubber, Impact bending was applied to each of the above test pieces under specified conditions. When the test pieces were subjected to impact bending, the temperature at which 50% of the total number of the test pieces broke was measured, and the temperature measured as described above was defined as the "embrittlement temperature".

Evaluation Criteria In the present invention, cold resistance was evaluated to be excellent when the brittleness temperature was -50°C or lower.
When the embrittlement temperature exceeded −50° C., the cold resistance was evaluated as poor.
Cold resistance was evaluated to be better when the brittleness temperature was lower than -50°C.

<Durability>
Durability was evaluated by elongation at break (EB) retention.
- Evaluation method Each of the above compositions was vulcanized under the conditions of 153°C and a surface pressure of 2.0 MPa for 20 minutes using a press molding machine to obtain an initial vulcanized rubber.
Separately, each of the above compositions (each unvulcanized rubber composition produced as described above) was placed under conditions of 153° C. for 90 minutes to obtain a time-vulcanized rubber.
A JIS No. 3 dumbbell-shaped initial test piece (thickness: 2 mm) was punched out from each initial vulcanized rubber obtained as described above. From each aged vulcanized rubber, a aged test piece was obtained in the same manner.
According to JIS K6251:2017, the initial test piece and the aging test piece obtained as described above were subjected to a tensile test under the conditions of room temperature and a tensile speed of 500 mm/min, and the elongation at break (EB) was measured.
The retention rate of the elongation at break was calculated by applying the elongation at break values of the obtained initial test piece and the aged test piece to the following formula.
Elongation at break (EB) retention rate (%) = (elongation at break of test piece over time)/(elongation at break of initial test piece) x 100

Evaluation Criteria In the present invention, when the retention rate of elongation at break was 45% or more, the durability was evaluated as being excellent.
When the retention rate was less than 45%, the durability was evaluated as inferior.
The durability was evaluated to be superior when the retention rate was greater than 45%.

<Water resistant adhesion>
Water-resistant adhesion was evaluated with rubber.
・Evaluation method Each composition produced as described above was applied to a thickness of 15 mm on a galvanized steel cord with a diameter of 4.1 mm that had been stored in a desiccator and subjected to dust-proof and moisture-proof treatment. A composite with a steel cord (the steel cord is embedded in the composition) is formed, and the composite is vulcanized under pressure for 20 minutes at 153° C. and a surface pressure of 2.0 MPa using a press molding machine. A test piece (rubber/galvanized steel cord composite) was prepared. In the test piece, the boundary between the rubber and the steel cord where the steel cord protruded from the rubber surface was sealed with beeswax, and left in a constant temperature and humidity chamber at a temperature of 50° C. and a relative humidity of 95% for 1 week. After that, a pull-out test was performed by pulling out the steel cord from each specimen under room temperature conditions. The pull-out test was performed in accordance with DIN22131.
After the pull-out test, the state of the pulled-out steel cord was checked, and the ratio of the rubber-covered area remaining on the surface of the steel cord after the pull-out to the surface area of the initial steel cord (rubber coverage, %) was calculated. The rubber coverage calculated as described above is shown in Table 1 as rubber-covered.

Evaluation Criteria In the present invention, when the rubber attachment (rubber coverage) was 65% or more, it was evaluated as having excellent water-resistant adhesiveness.
When the rubber attachment was less than 65%, it was evaluated as having poor water-resistant adhesiveness.
It was evaluated that the water-resistant adhesiveness was more excellent when the rubber attachment was greater than 65%.

Details of each component shown in Table 1 are as follows.
- NR: Natural rubber. TSR20
SBR: Styrene-butadiene copolymer rubber. NIPOL 1502 (manufactured by Zeon Corporation). Glass transition temperature -54°C. Weight average molecular weight 490,000, bound styrene content 24% by mass, vinyl content 16% by mass

BR: Polybutadiene rubber. Nipol BR 1220, manufactured by Zeon Corporation (ZEON CORPORATION). Weight average molecular weight 500,000, glass transition temperature -105°C

・HAF grade carbon black: Shiyo Black N330T manufactured by Cabot Japan Co., Ltd. (nitrogen adsorption specific surface area 74 m ² /g)

- Phenolic resin: Sumilite Resin PR-175, Sumitomo Durez Co., Ltd. - Gum rosin: Chugoku Rosin WW, manufactured by Arai Chemical Industry Co., Ltd.
- Chlorinated paraffin (70% chlorine content): Chlorinated paraffin (70% by mass chlorine content). Trade name Empara 70S, manufactured by Ajinomoto Fine Techno Co., Ltd.

- (comparative) cobalt naphthenate (10% cobalt content): cobalt naphthenate. Cobalt content 10% by mass. Cobalt naphthenate 10%, manufactured by DIC CORPORATION

Cobalt neodecanoate borate: Cobalt neodecanoate borate represented by the following formula (1). DICNATE NBC-II manufactured by DIC CORPORATION (cobalt content 22.2% by mass)

・ Zinc oxide: 3 types of zinc oxide manufactured by Seido Chemical Industry Co., Ltd. ・ Stearic acid: YR stearate (manufactured by NOF Corporation)
・ Paraffin oil: machine oil 22 (manufactured by Showa Shell Sekiyu K.K.)

Vulcanization accelerator DM: thiazole-based vulcanization accelerator. Dibenzothiazyl disulfide. Product name Sunceller DM-PO, (Sanshin Chemical Industry Co., Ltd.)
・Sulfur: Fine powdered sulfur with Kinkain oil (manufactured by Tsurumi Kagaku Kogyo Co., Ltd.)

As is clear from the results shown in Table 1, Comparative Example 1, which did not contain cobalt borate neodecanoate and instead contained cobalt naphthenate, had low durability.
Comparative Example 2, which contained no polybutadiene rubber and all rubber components were natural rubber, was inferior in water-resistant adhesiveness.
Comparative Example 3, which does not contain polybutadiene rubber, is made entirely of natural rubber, and contains more cobalt neodecanoate borate than Comparative Example 2, was inferior in cold resistance and durability.
Comparative Example 4, which does not contain polybutadiene rubber and cobalt neodecanoate borate, contains natural rubber and SBR instead of polybutadiene rubber, and contains cobalt naphthenate instead of cobalt neodecanoate borate , is inferior in durability. rice field.

In contrast, the composition of the present invention was excellent in cold resistance, durability, and water-resistant adhesiveness.

1 Conveyor Belt 2 Steel Cord 4 Coat Rubber Layer 6 Cover Rubber Layer

Claims (12)

It contains a rubber component containing at least polybutadiene rubber and cobalt neodecanoate borate, and the content of the cobalt neodecanoate borate is 1.2 to 3.5 parts by mass with respect to 100 parts by mass of the rubber component. A rubber composition for adhering steel cords. The rubber composition for adhering steel cords according to claim 1, wherein said rubber component further contains natural rubber and/or styrene-butadiene copolymer rubber. 3. The rubber composition for adhering steel cords according to claim 1, wherein the content of said polybutadiene rubber is 15 to 60 parts by mass with respect to 100 parts by mass of said rubber component. Furthermore, it contains carbon black,
The rubber composition for adhering steel cords according to any one of claims 1 to 3, wherein the carbon black content is 35 to 75 parts by mass with respect to 100 parts by mass of the rubber component. Furthermore, it contains a vulcanization accelerator,
The rubber composition for adhering steel cords according to any one of claims 1 to 4 , wherein the vulcanization accelerator is a thiazole-based vulcanization accelerator. 6. The rubber composition for adhering steel cords according to claim 5 , wherein the content of said vulcanization accelerator is 0.3 to 1.2 parts by mass with respect to 100 parts by mass of said rubber component. Furthermore, it contains sulfur,
The rubber composition for adhering steel cords according to any one of claims 1 to 6 , wherein the sulfur content is 2.1 to 5.0 parts by mass with respect to 100 parts by mass of the rubber component. The rubber composition for adhering steel cords according to any one of claims 1 to 7 , further comprising at least one selected from the group consisting of rosin, rosin derivatives, phenolic resins and chlorinated paraffins. Furthermore, it contains zinc oxide,
The rubber composition for adhering steel cords according to any one of claims 1 to 8 , wherein the zinc oxide content is 5.0 parts by mass or more with respect to 100 parts by mass of the rubber component. In addition, it contains oil,
The rubber composition for adhering steel cords according to any one of claims 1 to 9 , wherein the content of said oil is 2.0 parts by mass or more with respect to 100 parts by mass of said rubber component. The rubber composition for adhering steel cords according to any one of claims 1 to 10 , which is used for adhering galvanized steel cords. A conveyor belt formed using the steel cord bonding rubber composition according to any one of claims 1 to 11 .

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