JP2024089030A - Method for producing rubber composition containing reclaimed rubber - Google Patents

Abstract

To provide a method for producing a recycled rubber-containing rubber composition excellent in conservation after production of a rubber composition, and having suppressed physical deterioration of a vulcanizate even after long storage.SOLUTION: A method for producing a recycled rubber-containing rubber composition, comprises: a first step of producing recycled rubber by heat treatment while applying a shear force to the vulcanized rubber; and a second step of producing a rubber composition by blending the recycled rubber and a desulfurizer in addition to the rubber component and a blending agent. The desulfurizer is preferably a desulfurizer having an alkylamide group or a desulfurizer having an alkylsulfonamide group. Further, the desulfurizer is more preferably a desulfurizer that is an amide compound of an alkylamine having 12 or more carbon atoms, or a desulfurizer that is a sulfonamide compound of an alkylamine having 12 or more carbon atoms.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a rubber composition containing recycled rubber.

In recent years, with growing environmental awareness, there has been a strong demand for recycling vulcanized rubber waste generated from used tires and other rubber products.

The following Patent Document 1 describes a method for obtaining a re-vulcanizable desulfurized product in which the desulfurizing agent is an amine compound, the rubber contains an EPDM polymer, the sulfur-crosslinked rubber is heated to a temperature of 250 to 350°C during desulfurization, and the desulfurization of the sulfur-crosslinked rubber is carried out at a pressure of 5 to 10 MPa.

Japanese Patent No. 4633988

After extensive research, the inventors have found that when the desulfurized product obtained by the above-mentioned conventional technology is blended into a rubber composition, the vulcanization time and scorch time are significantly shortened, and therefore there is room for further improvement in terms of the processability of the rubber composition. In addition, rubber compositions containing the desulfurized product obtained by the above-mentioned conventional technology have poor storage stability after the rubber composition is produced, and there is concern that the physical properties of the resulting vulcanized rubber may deteriorate during long-term storage.

The present invention has been made in consideration of the above-mentioned circumstances, and its purpose is to provide a method for producing a rubber composition containing recycled rubber, which has excellent storage stability after the rubber composition is produced and in which deterioration of the physical properties of the vulcanized rubber is suppressed even after long-term storage.

The above problem can be solved by the following configuration. That is, the present invention relates to a method for producing a rubber composition containing recycled rubber (1), which comprises a first step of producing recycled rubber by applying a shear force to vulcanized rubber and heating it, and a second step of producing a rubber composition by compounding the recycled rubber and a devulcanizing agent in addition to the rubber components and compounding ingredients, and heating and mixing the resulting mixture.

In the above-mentioned method (1) for producing a rubber composition containing recycled rubber, it is preferable that the method (2) for producing a rubber composition containing recycled rubber is a devulcanizing agent having an alkylamide group.

In the above-mentioned method (1) or (2) for producing a rubber composition containing recycled rubber, it is preferable to use the method (3) for producing a rubber composition containing recycled rubber, in which the devulcanizing agent is an amide compound of an alkylamine having 12 or more carbon atoms.

In the above-mentioned method (1) for producing a rubber composition containing recycled rubber, it is preferable that the devulcanizing agent is a devulcanizing agent having an alkylsulfonamide group.

In the above-mentioned method (1) or (4) for producing a rubber composition containing recycled rubber, it is preferable to use the method (5) for producing a rubber composition containing recycled rubber, in which the devulcanizing agent is a sulfonamide compound of an alkylamine having 12 or more carbon atoms.

When an amine compound is used as a devulcanizing agent as in the conventional technology, the amino group of the amine compound is highly basic, so that rubber compositions containing devulcanized rubber obtained by mixing a devulcanizing agent made of an amine compound with vulcanized rubber tend to have significantly shorter vulcanization times and scorch times. In addition, rubber compositions containing the above-mentioned devulcanized rubber have poor storage stability after production, and there is a concern that the physical properties of the resulting vulcanized rubber may deteriorate during long-term storage.

Here, in the conventional method for producing a rubber composition containing recycled rubber, a devulcanizing agent is added to the vulcanized rubber in a process of applying a shear force while heating the vulcanized rubber to produce the reclaimed rubber, but the inventors' investigations have revealed that the rubber composition containing the recycled rubber has poor storage stability, and that the physical properties of the vulcanized rubber produced after long-term storage of the rubber composition tend to deteriorate. Based on this tendency, further investigations have revealed that, when producing a rubber composition containing recycled rubber, a devulcanizing agent is not added in the first process of producing the reclaimed rubber by applying a shear force while heating the vulcanized rubber, but the recycled rubber and the devulcanizing agent are added and mixed in the second process of producing a rubber composition by mixing the rubber components and compounding agents, and this has led to the discovery that the produced rubber composition containing recycled rubber has excellent storage stability, and the deterioration of the physical properties of the vulcanized rubber is suppressed even after long-term storage. In other words, in the method for producing a rubber composition containing recycled rubber according to the present invention, the devulcanizing agent is mixed together with the recycled rubber not in the first step of producing the recycled rubber, but in the second step of producing the rubber composition by mixing the rubber components and compounding ingredients. This makes the produced rubber composition containing recycled rubber excellent in storage stability, and prevents deterioration of the physical properties of the vulcanized rubber even after long-term storage.

In particular, in the present invention, when a desulfurizing agent having an alkylamide group is used as the desulfurizing agent, more preferably when an amide compound of an alkylamine having 12 or more carbon atoms is used as the desulfurizing agent, the rubber composition has excellent storage stability after production, and the deterioration of the physical properties of the vulcanized rubber is particularly suppressed even after long-term storage. The reason for such excellent effects can be presumed as follows.

The alkylamide group of the desulfurizing agent has a lower density of lone electron pairs on the nitrogen atom. Therefore, the alkylamide group has a lower basicity than the amino group. Therefore, even if the reclaimed rubber, rubber components, and compounding agents are heated and mixed with the desulfurizing agent having an alkylamide group in the second step, sufficient vulcanization time and scorch time can be ensured. As a result, in the second step, the reclaimed rubber and the desulfurizing agent can be selectively reacted while the rubber components and compounding agents can be kept stable, resulting in excellent storage stability after the production of the rubber composition containing reclaimed rubber, and particularly suppressing deterioration of the physical properties of the vulcanized rubber even after long-term storage.

In particular, in the present invention, when a desulfurizing agent having an alkylsulfonamide group is used as the desulfurizing agent, more preferably when a sulfonamide compound of an alkylamine having 12 or more carbon atoms is used as the desulfurizing agent, the rubber composition has excellent storage stability after production, and the deterioration of the physical properties of the vulcanized rubber is particularly suppressed even after long-term storage. The reason for such excellent effects can be presumed as follows.

The alkylsulfonamide group of the desulfurizing agent has a lower density of lone electron pairs on the nitrogen atom. Therefore, the alkylsulfonamide group has a lower basicity than the amino group. Therefore, even if the reclaimed rubber, rubber components, and compounding agents are heated and mixed with the desulfurizing agent having an alkylsulfonamide group in the second step, sufficient vulcanization time and scorch time can be ensured. As a result, the reclaimed rubber and the desulfurizing agent can be selectively reacted in the second step while the rubber components and compounding agents can be kept stable, resulting in excellent storage stability after the production of the rubber composition containing reclaimed rubber, and particularly suppressing deterioration of the physical properties of the vulcanized rubber even after long-term storage.

The method for producing a rubber composition containing recycled rubber according to the present invention includes a first step of producing recycled rubber by applying a shear force to vulcanized rubber while heating it, and a second step of producing a rubber composition by blending recycled rubber and a devulcanizing agent in addition to the rubber components and compounding ingredients, and heating and mixing them.

(First step)
In the first step, the vulcanized rubber is subjected to a heat treatment while applying a shear force to produce reclaimed rubber. Examples of methods for applying a shear force to the vulcanized rubber include a method of applying a shear force to the vulcanized rubber and a devulcanizing agent by heating and mixing the vulcanized rubber and the devulcanizing agent using a roll machine, a Banbury mixer, an extruder, a gear pump, an intermeshing mixer, a kneader, or a co-kneader that are commonly used by those skilled in the art. In the present invention, when applying a shear force to the vulcanized rubber and the devulcanizing agent, a roll machine, a Banbury mixer, an extruder, a gear pump, an intermeshing mixer, a kneader, and a co-kneader may be used alone, or any of the devices may be used in combination. When a roll machine is used, for example, a method of passing the vulcanized rubber through a roll machine known to those skilled in the art may be used. When a Banbury mixer is used, for example, a method of feeding the vulcanized rubber into a Banbury mixer and stirring the vulcanized rubber may be used. The shear pressure when applying the shear force may be the shear pressure applied to the kneaded object when using a roll machine or a Banbury mixer, and may be, for example, about 0.1 to 10 MPa.

The heating temperature in the first step is preferably controlled to 5 to 80°C, and more preferably to 15 to 40°C.

(Second step)
In the second step, in addition to the rubber component and compounding agents, reclaimed rubber and a devulcanizing agent are compounded and mixed under heating to produce a rubber composition. The compounding method of each component is not particularly limited, and may be any of the following: (i) a method in which the reclaimed rubber and the devulcanizing agent are premixed to form a master batch, then the rubber component and compounding agents other than the vulcanization-based components such as sulfur and vulcanization accelerator are further mixed to form a master batch, and finally, the vulcanization-based components such as sulfur and vulcanization accelerator are mixed; (ii) a method in which compounding agents other than the vulcanization-based components such as sulfur and vulcanization accelerator are premixed to form a master batch, and the remaining components are added and further mixed; (iii) a method in which each component is added in any order and mixed; and (iv) a method in which all components are added at the same time and mixed.

Below, we will explain each component (material) used in the manufacturing method of the reclaimed rubber-containing rubber composition according to the present invention.

As the vulcanized rubber used as the raw material for the reclaimed rubber according to the present invention, it is preferable to use a vulcanized rubber of a diene rubber. The diene rubber is not particularly limited, and examples thereof include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer, and styrene-isoprene-butadiene copolymer rubber. These may be used alone or in combination of two or more. As the diene rubber, natural rubber, butadiene rubber, and styrene butadiene rubber, or a blend of two or more of these, are preferable.

The sulfur used as the raw material for vulcanized rubber can be any ordinary rubber sulfur, such as powdered sulfur, precipitated sulfur, insoluble sulfur, or highly dispersible sulfur.

As raw materials for vulcanized rubber, a rubber composition can be used that has been vulcanized by appropriately blending, as necessary, rubber components and sulfur together with compounding agents normally used in the rubber industry, such as vulcanization accelerators, carbon black, silica, silane coupling agents, zinc oxide, stearic acid, vulcanization retarders, organic peroxides, antioxidants, softeners such as wax and oil, and processing aids.

Carbon black that is known to those skilled in the art can be used, such as SAF, ISAF, HAF, FEF, and GPF. When the total amount of rubber components in the vulcanized rubber that is the raw material for devulcanized rubber is taken as 100 parts by mass, the carbon black content is preferably 30 to 100 parts by mass, and more preferably 30 to 60 parts by mass.

As the vulcanization accelerator, sulfenamide-based vulcanization accelerators, thiuram-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiourea-based vulcanization accelerators, guanidine-based vulcanization accelerators, dithiocarbamate-based vulcanization accelerators, and other vulcanization accelerators commonly used for rubber vulcanization may be used alone or in appropriate mixtures.

As the antiaging agent, antiaging agents commonly used for rubber, such as aromatic amine antiaging agents, amine-ketone antiaging agents, monophenol antiaging agents, bisphenol antiaging agents, polyphenol antiaging agents, dithiocarbamate antiaging agents, and thiourea antiaging agents, may be used alone or in appropriate mixtures.

As the desulfurizing agent used in the present invention, it is preferable to use a compound having an alkylamide group, more preferably an amidated compound of a long-chain alkylamine compound, and particularly preferably an amide compound of an alkylamine having 12 or more carbon atoms. Particularly suitable desulfurizing agents include, for example, a compound obtained by amidating hexadecylamine (16 carbon atoms), a compound obtained by amidating dodecylamine (12 carbon atoms), or a compound obtained by amidating stearylamine (18 carbon atoms).

In addition, as the desulfurizing agent used in the present invention, it is also preferable to use a compound having an alkylsulfonamide group, more preferably a compound obtained by sulfonamidating a long-chain alkylamine compound, and particularly preferably a compound obtained by sulfonamidating an alkylamine compound having 12 or more carbon atoms. Particularly suitable desulfurizing agents include, for example, a compound obtained by sulfonamidating hexadecylamine (carbon number 16), a compound obtained by sulfonamidating dodecylamine (carbon number 12), or a compound obtained by sulfonamidating stearylamine (carbon number 18).

From the viewpoint of improving the physical properties of the vulcanized rubber of the rubber composition containing recycled rubber, the blending ratio of the devulcanizing agent to the recycled rubber is preferably 0.5 to 30 parts by mass, and more preferably 1 to 20 parts by mass, when the total amount of recycled rubber is 100 parts by mass.

In addition, from the viewpoint of improving the physical properties of the vulcanized rubber of the rubber composition containing recycled rubber, the amount of recycled rubber is preferably 1 to 30 parts by mass, and more preferably 5 to 20 parts by mass, when the total amount of the rubber component (uncrosslinked rubber) in the rubber composition is taken as 100 parts by mass.

The rubber components and compounding agents used in the second step together with the reclaimed rubber and devulcanizing agent, specifically various diene rubbers, sulfur, vulcanization accelerators, carbon black, silica, silane coupling agents, zinc oxide, stearic acid, vulcanization retarders, organic peroxides, antioxidants, softeners such as wax and oil, and processing aids, can be the same as those described above.

The reclaimed rubber-containing rubber composition has excellent storage stability after the rubber composition is produced, and the deterioration of the physical properties of the vulcanized rubber is suppressed even after long-term storage. Therefore, the method is particularly suitable for use as a method for producing a reclaimed rubber-containing rubber composition for use in pneumatic tires that have a large amount of rubber.

The following describes the invention in more detail by way of examples.

(Preparation of vulcanized rubber as raw material for devulcanized rubber)
For 100 parts by mass of the rubber component, a lab mixer manufactured by Daihan Corporation was used according to the compounding recipe in Table 1. In the first mixing stage, the compounding ingredients other than sulfur and the vulcanization accelerator were added to the rubber component and kneaded, and then in the second mixing stage, sulfur and the vulcanization accelerator were added to the obtained kneaded product and kneaded to prepare a rubber composition.

Details of each component in Table 1 are as follows.
・Natural rubber: STR20
・Carbon black: "Seast 3" manufactured by Tokai Carbon Co., Ltd.
・Zinc oxide: "Zinc oxide type 1" manufactured by Mitsui Mining & Smelting Co., Ltd.
・Anti-aging agent: "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
・Stearic acid: Kao Corporation's "Lunac S-20"
Sulfur: "Powdered sulfur for rubber 150 mesh" manufactured by Hosoi Chemical Industry Co., Ltd.
- Vulcanization accelerator: "Noccela NS" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

The rubber composition was vulcanized at 150°C for 25 minutes to produce a sheet-shaped vulcanized rubber, which was then crushed using a roll (6-inch roll manufactured by Kansai Roll Co., Ltd.) to produce reclaimed rubber 1 (first step). Reclaimed rubber 1 was stored at 25°C for two months, after which the reclaimed rubber was named reclaimed rubber 2.

(Preparation of Reclaimed Rubber-Containing Rubber Composition)
Each component was blended with respect to 100 parts by mass of the rubber component according to the blending recipe in Table 2, and kneaded using a lab mixer manufactured by Daihan Co., Ltd. to produce reclaimed rubber-containing rubber compositions according to Examples 1 to 4 and Comparative Examples 1 and 2 (second step). However, the second step was carried out in two stages: a first mixing stage in which the compounding ingredients other than sulfur and vulcanization accelerator and the devulcanizing agent were mixed with the rubber component, and a second mixing stage in which the mixture obtained after the first mixing stage was cooled to room temperature, sulfur and vulcanization accelerator were added, and the mixture was kneaded so as not to exceed 100°C to produce a reclaimed rubber-containing rubber composition.

Details of each component in Table 2 are as follows.
・Natural rubber: STR20
・Carbon black: "Seast 3" manufactured by Tokai Carbon Co., Ltd.
・Zinc oxide: "Zinc oxide type 1" manufactured by Mitsui Mining & Smelting Co., Ltd.
・Anti-aging agent: "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
・Stearic acid: Kao Corporation's "Lunac S-20"
Sulfur: "Powdered sulfur for rubber 150 mesh" manufactured by Hosoi Chemical Industry Co., Ltd.
- Vulcanization accelerator: "Noccela NS" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Desulfurizing agent 1: "Acetylated stearylamine" (desulfurizing agent having an alkylamide group, carbon number 20)

The desulfurizing agent 1 was produced by the following method.
(Desulfurization agent 1)
10.8 g of stearylamine and 6 g of pyridine manufactured by Tokyo Chemical Industry Co., Ltd. were dissolved in 500 ml of ethyl acetate manufactured by Nacalai Tesque. 5 g of acetic anhydride manufactured by Tokyo Chemical Industry Co., Ltd. was added dropwise to this solution while stirring at room temperature, and then the solution was heated to 80°C and stirred for 4 hours. After stirring, the precipitate was filtered off and the filtrate was washed three times with 100 ml of 10% aqueous citric acid solution (citric acid manufactured by Nacalai Tesque), and then an appropriate amount of anhydrous magnesium sulfate manufactured by Nacalai Tesque was added to dehydrate it. After filtering off the anhydrous magnesium sulfate, the solution was concentrated under reduced pressure to obtain a slurry. This was filtered, and the solid was washed with hexane (manufactured by Nacalai Tesque) and then vacuum dried to obtain a desulfurizing agent 2 described in the following formula (1).

The obtained rubber composition containing reclaimed rubber was vulcanized at 150° C. for 25 minutes to prepare test pieces of a predetermined shape, and the following tests were carried out using the obtained test pieces.
Breaking strength: Breaking strength was measured by a tensile test (JIS No. 3 dumbbell) in accordance with JIS K6251, and expressed as an index with the value of Comparative Example 1 set at 100. The larger the value, the better the breaking strength of the vulcanized rubber.
Breaking elongation: Breaking elongation was measured by a tensile test (JIS No. 3 dumbbell) in accordance with JIS K6251, and expressed as an index with the value of Comparative Example 1 set at 100. The larger the value, the better the breaking elongation of the vulcanized rubber.

The results in Table 2 show that the vulcanized rubber of the recycled rubber-containing rubber composition produced by the method for producing a recycled rubber-containing rubber composition according to Examples 1 to 4 has excellent breaking strength and breaking elongation. In particular, the method for producing a recycled rubber-containing rubber composition according to Examples 2 and 4 can produce vulcanized rubber with excellent breaking strength and breaking elongation, even when using recycled rubber that has been produced for a long time.

Claims (5)

A method for producing a rubber composition containing reclaimed rubber, comprising the steps of:
A first step of producing reclaimed rubber by subjecting vulcanized rubber to a heat treatment while applying a shear force;
a second step of compounding the reclaimed rubber and a devulcanizing agent in addition to the rubber component and compounding ingredients, and heating and mixing the compounded rubber to produce a rubber composition. The method for producing a rubber composition containing reclaimed rubber according to claim 1, wherein the devulcanizing agent is a devulcanizing agent having an alkylamide group. The method for producing a rubber composition containing reclaimed rubber according to claim 2, wherein the desulfurizing agent is an amide compound of an alkylamine having 12 or more carbon atoms. The method for producing a rubber composition containing reclaimed rubber according to claim 1, wherein the devulcanizing agent is a devulcanizing agent having an alkylsulfonamide group. The method for producing a rubber composition containing reclaimed rubber according to claim 4, wherein the desulfurizing agent is a sulfonamide compound of an alkylamine having 12 or more carbon atoms.