JP7528601B2 - Dialkyl peroxide compound, rubber composition, crosslinked rubber, and method for producing the same - Google Patents

Description

The present invention relates to a dialkyl peroxide compound, a rubber composition, and a crosslinked rubber and a method for producing the same.

Organic peroxides are widely used as cross-linking agents for rubber, thermoplastic elastomers, and resins, and cross-linking with organic peroxides can improve the mechanical properties and heat resistance of cross-linked rubber compared to sulfur vulcanization. This is thought to be because the carbon-carbon bonds formed by cross-linking with organic peroxides are more chemically stable than the carbon-sulfur bonds formed by sulfur cross-linking.

As organic peroxides, peroxyketals such as 1,1-bis(t-butylperoxy)cyclohexane and dialkyl peroxides such as dicumyl peroxide are used. However, peroxyketals decompose at relatively low temperatures, causing a crosslinking reaction, and there is a possibility that partial crosslinking called scorch may occur during the rubber mixing process or storage. When such scorch is a concern, dialkyl peroxides, which decompose at high temperatures, are selected.

However, when organic peroxides are used as crosslinking agents, the decomposition products of the organic peroxides remain in the crosslinked rubber and often cause odor. For example, when dicumyl peroxide is used as a crosslinking agent, acetophenone is generated as part of the decomposition products of dicumyl peroxide, and since acetophenone remains in the crosslinked rubber, it is necessary to improve the odor (Patent Document 1).

On the other hand, it is already known that the odor of crosslinked rubber can be improved depending on the type of organic peroxide, and it has been disclosed that the odor of crosslinked rubber can be reduced by using di-t-hexyl peroxide, etc. (Patent Document 2).

JP 2006-63280 A JP 2000-273244 A

As quality requirements have become more stringent in recent years, there is a demand for further odor improvement. In particular, there is a strong demand for odor improvement in products such as automobile interior parts that are used in high-temperature, enclosed spaces, and protective masks that are used close to the face.

The organic peroxides disclosed in Patent Document 2, such as di-t-hexyl peroxide, are highly volatile, and there is a problem in that the content (purity retention) of the compound changes during the production and storage of the rubber composition containing the compound.

Furthermore, the mechanical properties of the crosslinked rubber crosslinked with organic peroxides such as di-t-hexyl peroxide disclosed in the above Patent Document 2 are insufficient, and there is a demand for improved crosslinking performance.

In view of the above circumstances, the present invention aims to provide an organic peroxide (dialkyl peroxide compound) that can reduce the odor of crosslinked rubber and has excellent storage stability and crosslinking performance.

Furthermore, the present invention aims to provide a rubber composition containing the above organic peroxide (dialkyl peroxide compound), as well as a crosslinked rubber and a method for producing the same.

で表されるジアルキルペルオキシド化合物に関する。 That is, the present invention relates to a compound represented by the general formula (1):

The present invention relates to a dialkyl peroxide compound represented by the formula:

The present invention also relates to a rubber composition containing the dialkyl peroxide compound and rubber.

The present invention also relates to a crosslinked rubber formed from the rubber composition.

The present invention also relates to a method for producing a crosslinked rubber, which includes a step of heating the rubber composition at 120 to 250°C.

Although the details of the mechanism of action of the dialkyl peroxide compound of the present invention are unclear, it is presumed as follows. However, the present invention is not interpreted as being limited to this mechanism of action.

Each organic peroxide produces different decomposition products, and the dialkyl peroxide compound of the present invention produces decomposition products with low odors when crosslinking a rubber composition, making it possible to reduce the odor of crosslinked rubber. In addition, the dialkyl peroxide compound of the present invention has low volatility compared to organic peroxides such as di-t-hexyl peroxide disclosed in Patent Document 2, and therefore has excellent storage stability, making it useful as a crosslinking agent for rubber.

In addition, organic peroxides such as di-t-hexyl peroxide disclosed in Patent Document 2 generate t-hexyloxy radicals by thermal decomposition, and then rapidly undergo β-cleavage to generate alkyl radicals such as propyl radicals. These alkyl radicals such as propyl radicals do not have a very high hydrogen abstraction ability, and therefore do not have sufficient crosslinking performance. On the other hand, the dialkyl peroxide compound of the present invention generates two phenylpropyloxy radicals along with the t-hexyloxy radical. Since the β-cleavage reaction of this phenylpropyloxy radical is not very fast, the phenylpropyloxy radical reacts with the methyl radical generated by the β-cleavage reaction, but since these radicals have a high hydrogen abstraction ability, they have the effect of providing excellent crosslinking performance.

<Dialkyl peroxide compound>
The dialkyl peroxide compound of the present invention can be represented by the following general formula (1).

In the general formula (1), the substitution position of the dialkyl peroxide is not particularly limited, but in terms of obtaining a crosslinked rubber with excellent mechanical properties, the m-form, p-form, or a mixture of m-form and p-form is preferable, and in terms of availability of the raw material, the m-form is even more preferable.

で表されるヒドロペルオキシド化合物と、一般式（３）：

で表されるアルコール化合物を反応させる工程（以下、工程(Ａ)とも称す）を含む製造方法が挙げられる。 <Method for producing dialkyl peroxide compound>
The method for producing the dialkyl peroxide compound represented by the general formula (1) is not limited in any way. For example, the method for producing the dialkyl peroxide compound represented by the general formula (2):

and a hydroperoxide compound represented by general formula (3):

(hereinafter also referred to as step (A))

In step (A), the hydroperoxide compound represented by the general formula (2) and the alcohol compound represented by the general formula (3) may be commercially available products.

In the step (A), it is preferable to react 2.0 moles or more, and preferably 7.5 moles or less, of the hydroperoxide compound represented by the general formula (2) with 1.0 mole of the alcohol compound represented by the general formula (3) in order to increase the yield of the target product.

The reaction temperature in step (A) is preferably 20°C or higher, more preferably 30°C or higher, from the viewpoint of increasing the yield of the target product, and is preferably 50°C or lower, more preferably 45°C or lower, from the viewpoint of safety.

The reaction time for step (A) cannot be determined in general because it varies depending on the raw materials and reaction temperature, but from the viewpoint of increasing the yield of the target product, it is usually preferable for the reaction time to be 0.5 hours or more, more preferably 1 hour or more, and preferably 3 hours or less.

In the step (A), it is preferable to use an organic solvent. The organic solvent is not particularly limited, but is preferably an organic solvent that is inactive in the reaction system. Examples of the organic solvent include non-polar compounds such as pentane, hexane, and toluene; and polar compounds such as acetone and acetonitrile. The organic solvent may be used alone or in combination of two or more kinds.

In step (A), the amount of the organic solvent used is not particularly limited, but is usually about 3 to 300 parts by mass per 100 parts by mass of the alcohol compound.

In the previous step (A), it is preferable to use an acid catalyst. The acid catalyst is not particularly limited, but examples thereof include acetic acid, sulfuric acid, and perchloric acid. The acid catalyst may be used alone or in combination of two or more kinds.

In step (A), the amount of the acid catalyst used is not particularly limited, but it is usually preferable to use 0.02 moles or more per mole of the raw alcohol compound, and preferably 5 moles or less.

The target substance obtained can be identified using liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), infrared spectroscopy (IR), mass spectrometry (MS), etc.

<Rubber Composition>
The rubber composition of the present invention contains the dialkyl peroxide compound and a rubber. The rubber may be any known rubber that requires crosslinking by an organic peroxide, and may be used alone or in combination of two or more kinds. Examples of the rubber include ethylene-propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM), acrylonitrile-butadiene copolymer (NBR), hydrogenated acrylonitrile-butadiene copolymer (H-NBR), and ethylene-α-olefin copolymer.

<Ethylene-propylene rubber and/or ethylene-propylene-diene rubber>
The propylene content in the ethylene-propylene rubber and/or the ethylene-propylene-diene rubber is preferably 20% by mass or more, more preferably 30% by mass or more. The ethylene-propylene rubber and/or the ethylene-propylene-diene rubber preferably has a Mooney viscosity (ML1+4 100°C) of 30 or more. The ethylene-propylene rubber and/or the ethylene-propylene-diene rubber are not particularly limited in terms of the Mooney viscosity and the upper limit of the propylene content, but generally available rubbers have a Mooney viscosity (ML1+4 100°C) of about 150 or less and a propylene content of about 50% by mass or less. The ethylene-propylene rubber and/or the ethylene-propylene-diene rubber may be used alone or in combination of two or more kinds. The polymerization method of the ethylene-propylene rubber and/or the ethylene-propylene-diene rubber may be a known method.

In the ethylene-propylene-diene rubber, the diene monomers of the structural units are not particularly limited, and examples thereof include cyclic dienes such as 5-ethylidene-2-norbornene, 5-propylidene-5-norbornene, dicyclopentadiene, 5-vinyl-2-norbornene, 5-methylene-2-norbornene, 5-isopropylidene-2-norbornene, and norbornadiene; and linear non-conjugated dienes such as 1,4-hexadiene, 4-methyl-1,4-hexadiene, 5-methyl-1,4-hexadiene, 5-methyl-1,5-heptadiene, 6-methyl-1,5-heptadiene, and 6-methyl-1,7-octadiene.

Commercially available ethylene-propylene rubber and/or ethylene-propylene-diene rubber include oil-extended grades that contain plasticizers, and non-oil-extended grades that do not contain plasticizers, and the appropriate grade can be selected depending on the physical properties required of the rubber. Examples of commercially available non-oil-extended grade ethylene-propylene rubber and/or ethylene-propylene-diene rubber include trade names: "Mitsui EPT3045", "Mitsui EPTX-4010M", "Mitsui EPT4021", "Mitsui EPT4045", "Mitsui EPT4045M", and "Mitsui EPT8030M" (all EPDMs manufactured by Mitsui Chemicals), trade names: "JSREP33", "JSRT7241", "JSREP21", "JSREP51", "JSREP22", and "JSREP123" (all EPDMs manufactured by JSR Corporation), trade name: "Mitsui EPT0045" (all EPMs manufactured by Mitsui Chemicals), and trade name: "JSREP11" (all EPMs manufactured by JSR).

<Acrylonitrile-butadiene copolymer>
The nitrile content in the acrylonitrile-butadiene copolymer is preferably 20% by mass or more, more preferably 30% by mass or more. The acrylonitrile-butadiene copolymer preferably has a Mooney viscosity (ML1+4 100°C) of 30 or more. The copolymer is not particularly limited in terms of the upper limit of the Mooney viscosity and the nitrile content, but generally available copolymers have a Mooney viscosity (ML1+4 100°C) of about 90 or less and a nitrile content of about 50% by mass or less. The acrylonitrile-butadiene copolymer may be used alone or in combination of two or more kinds. A known method may be applied as a polymerization method for the acrylonitrile-butadiene copolymer.

Commercially available products of the acrylonitrile-butadiene copolymer include, for example, product names: "N238H", "N232S", and "N230SV" (all NBR manufactured by JSR).

<Hydrogenated acrylonitrile-butadiene copolymer>
The nitrile content in the hydrogenated acrylonitrile-butadiene copolymer is preferably 20% by mass or more, more preferably 30% by mass or more. The hydrogenated acrylonitrile-butadiene copolymer preferably has a Mooney viscosity (ML1+4 100°C) of 30 or more. The copolymer is not particularly limited in terms of the upper limit of the Mooney viscosity and the nitrile content, but generally available copolymers have a Mooney viscosity (ML1+4 100°C) of about 90 or less and a nitrile content of about 50% by mass or less. The hydrogenated acrylonitrile-butadiene copolymer may be used alone or in combination of two or more kinds. The polymerization method for the hydrogenated acrylonitrile-butadiene copolymer may be a known method.

Commercially available hydrogenated acrylonitrile-butadiene copolymers include, for example, products with the trade names "Zetpol 1010," "Zetpol 2001L," and "Zetpol 2020" (all H-NBR manufactured by Zeon Corporation).

<Ethylene/α-olefin copolymer>
The polymerization method of the ethylene-α-olefin copolymer can be a known method, for example, obtained by copolymerizing ethylene with an α-olefin having 3 to 20 carbon atoms. As the α-olefin, one type of α-olefin having 3 to 20 carbon atoms can usually be used alone or two or more types can be used in combination. Examples of the α-olefin having 3 to 20 carbon atoms include linear or branched α-olefins such as propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 3,3-dimethyl-1-butene, 4-methyl-1-pentene, 1-octene, 1-decene, and 1-dodecene. Among these, α-olefins having 10 or less carbon atoms are preferred, and α-olefins having 3 to 8 carbon atoms are particularly preferred. In view of ease of availability, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, and 1-octene are preferred. The ethylene/α-olefin copolymer may be a random copolymer or a block copolymer, but a random copolymer is preferred from the viewpoint of flexibility.

Furthermore, the ethylene-α-olefin copolymer may be a copolymer containing ethylene, an α-olefin having 3 to 20 carbon atoms, and a non-conjugated polyene. The α-olefin is the same as described above, and examples of the non-conjugated polyene include 5-ethylidene-2-norbornene (ENB), 5-vinyl-2-norbornene (VNB), and dicyclopentadiene (DCPD). These non-conjugated polyenes can be used alone or in combination of two or more.

The ethylene-α-olefin copolymer may be used in combination with, for example, aromatic vinyl compounds such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, methoxystyrene, vinylbenzoic acid, methyl vinylbenzoate, vinylbenzyl acetate, hydroxystyrene, p-chlorostyrene, divinylbenzene, 3-phenylpropylene, 4-phenylpropylene, and α-methylstyrene; or cyclic olefins having 3 to 20 carbon atoms such as cyclopentene, cycloheptene, norbornene, and 5-methyl-2-norbornene.

Commercially available products of the ethylene-α-olefin copolymer include, for example, TAFMER (registered trademark) manufactured by Mitsui Chemicals, Inc., ENGAGE (registered trademark) manufactured by Dow, EXACT (registered trademark) manufactured by ExxonMobil Corporation, and KERNEL (registered trademark) manufactured by Japan Polyethylene Corporation.

From the viewpoint of crosslinking torque, the dialkyl peroxide compound is preferably 0.3 parts by mass or more, and more preferably 1.0 part by mass or more, per 100 parts by mass of the rubber, and from the viewpoint of rubber elongation, it is preferably 10 parts by mass or less, and more preferably 6 parts by mass or less.

The rubber composition may also contain carbon black from the standpoint of wear resistance.

The carbon black may be commercially available, and may be furnace black, which is generally used as a reinforcing agent. From the viewpoint of kneadability and moldability when highly filling bituminous fine powder, the carbon black preferably has a nitrogen adsorption specific surface area of 20 to 60 m ² /g and a DBP oil absorption of 40 to 130 ml/100 g, such as FEF carbon black or SRF carbon black.

Commercially available carbon black products include trade names "Seat SO" and "Seat S" (both manufactured by Tokai Carbon), "Asahi #55", "Asahi #51", and "Asahi #50" (all manufactured by Asahi Carbon).

When the rubber composition contains the carbon black, the carbon black is preferably at least 5 parts by mass, and more preferably at least 20 parts by mass, per 100 parts by mass of the rubber from the viewpoint of abrasion resistance, and is preferably at most 150 parts by mass, and more preferably at most 120 parts by mass, from the viewpoint of rubber elongation.

The rubber composition may also contain other organic peroxides other than the dialkyl peroxide compounds, and two or more types may be used in combination. The rubber composition may also contain other components, such as additives commonly used in elastomer processing, such as crosslinking aids, fillers, antioxidants, anti-aging agents, UV absorbers, and flame retardants, plasticizers such as process oil, and lubricants such as stearic acid, in any ratio. The other components may be used alone or in combination of two or more types.

When the rubber composition contains the other components, the amount of the other components in the rubber composition is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, per 100 parts by mass of the rubber.

<Method of producing rubber composition>
The rubber composition can be obtained by mixing the above-mentioned components. The kneading method can be a known method generally used in the processing of elastomers, and for example, a kneading machine such as an open roll, a Banbury mixer, a kneader, an extruder, or a transfer mixer can be used, and a kneader is preferable.

<Crosslinked rubber>
The crosslinked rubber of the present invention is formed from the rubber composition. Specifically, it is obtained by heating (crosslinking) the rubber composition. The heating (crosslinking) method can be carried out by a known method, and may be appropriately determined depending on the type of organic peroxide used, the type of rubber to be crosslinked, the required physical properties, etc., and for example, a press, an extruder, etc. can be used. The heating temperature is preferably 120°C to 250°C, more preferably 130°C to 200°C. The heating time is preferably 3 minutes to 60 minutes, more preferably 3 minutes to 60 minutes.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

<Production Example 1>
<Synthesis of Dialkyl Peroxide Compound>
In a 500 mL round-bottom flask, t-hexyl hydroperoxide (85.0% purity, 171.02 g, 6.15 mol) was dissolved in hexane (3.0 g) and stirred, and glacial acetic acid (30.50 g, 0.51 mol) and dihydroxy-1,3-diisopropylbenzene (38.86 g, 6.15 mol) were added and stirred. The solution was heated to 30° C., and perchloric acid (70.0% purity, 2.34 g, 0.08 mol) was added dropwise. After the completion of the dropwise addition, the solution was stirred for 1.5 hours, and the resulting solution was washed with a 3% NaOH aqueous solution and then washed with water. The solution was then dehydrated using sodium sulfate and magnesium sulfate to obtain a mixture containing the dialkyl peroxide compound represented by the above general formula (1). The mixture was then isolated using silica gel chromatography to obtain the dialkyl peroxide compound represented by the above general formula (1) (67.87 g, purity 99.9%, yield 86%).

The structure of the dialkyl peroxide compound represented by the general formula (1) was identified by ¹ H-NMR measurement and ¹³ C-NMR measurement using an AVANCEN NMR spectrometer (manufactured by BRUCKER) and by TOFMS (manufactured by JEOL Co., Ltd.) The purity was calculated by the simple area method using LC (LC-2000Plus series manufactured by JASCO Corporation).

¹ H-NMR (CDCl ₃ , internal standard TMS); δ (ppm):
0.88(6H,t, _-OC ( _{CH3 ) 2CH2CH2CH3 )} , 1.18(12H _, s _{, -OC} ( CH3 ₎ 2CH2CH2CH3 ₎ ), 1.26-1.39 (4H, m, -OC(CH ₃ ) ₂ CH ₂ CH ₂ CH ₃ ), 1.46-1.60 (16H, m, -C( CH ₃ ) ₂ -O-O-C(CH ₃ ) ₂ CH ₂ CH ₂ CH ₃ ), 7.34 (3H, m, aroma.H), 7.59 (1H, s, aroma.H)
Molecular weight: 394

Example 1
<Production of Rubber Composition>
A roller (manufactured by Toyo Seiki Seisakusho) was heated to 50°C, and EPDM (product name "EP21", manufactured by Mitsui Chemicals, Inc.) was kneaded. While kneading, 100 g of the above EPDM was mixed with 100 g of carbon black (product name "Seat G-SO", manufactured by Tokai Carbon Co., Ltd.) and 1.97 g (5 mmol) of the dialkyl peroxide compound represented by general formula (1) obtained above, to obtain a rubber composition (rubber sheet, 10 cm x 20 cm).

<Evaluation of storage stability>
The above rubber composition was stored in an incubator at 50°C for one month, and the purity of the organic peroxide in the rubber composition was measured by GC. In the GC measurement, the organic peroxide in the rubber composition was extracted with cyclohexane, and the extract was filtered to obtain a sample, which was then loaded into a GC and heated from 50°C to 200°C for analysis. From the measurement results, the purity retention rate (%) of the organic peroxide was calculated using the following formula. The results are shown in Table 1.

<Odor Evaluation>
The rubber composition was heated at 160°C for 20 minutes to obtain a crosslinked rubber. The odor was evaluated by holding a crosslinked rubber test piece (2cm x 4cm) horizontally at a position 1cm in front of the nose and sniffing the odor. The evaluation was carried out by 10 men and women aged 24 to 55 years old, who were given a rating on a 5-point scale according to the following criteria, and then averaging the ratings. The results are shown in Table 1.
Evaluation points: 5 points: no odor, 4 points: slight odor, 3 points: odor is noticeable but not irritating, 2 points: slight irritating odor, 1 point: irritating odor.
Evaluation symbols: average score of 4.0 points or more: ⊚, average score of 3.0 points or more but less than 4.0 points: ◯, average score of 2.0 points or more but less than 3.0 points: △, average score of 1.0 points or more but less than 2.0 points: ×.

<Evaluation of crosslinking performance>
The above rubber composition was subjected to a crosslinking test at 160°C using a curastometer manufactured by JSR Trading Co., Ltd. The physical properties of the obtained crosslinked rubber are generally expressed as MH (maximum torque value), t10 (time at which the value reaches 10% of the maximum torque value), and t90 (time at which the value reaches 90% of the maximum torque value). MH indicates the degree of crosslinking, and is preferably 1.4 N·m or more. In addition, since t10 is an indicator of scorching during kneading and t90 is an indicator of the crosslinking speed, it is preferable that t10 is 2.0 minutes or more and t90/t10 is 7.0 to 7.9. The results are shown in Table 1.

Example 2
A rubber composition was obtained in the same manner as in Example 1, except that the amount of the dialkyl peroxide compound represented by the general formula (1) in Example 1 was changed to 3.95 g (10 mmol), and then the above-mentioned evaluations were carried out.

<Comparative Example 1>
A rubber composition was obtained in the same manner as in Example 1, except that the dialkyl peroxide compound represented by the general formula (1) in Example 1 was changed to 1.69 g (5 mmol) of di-(2-t-butylperoxyisopropyl)benzene (compound A), and then the above-mentioned evaluation was performed.

<Comparative Example 2>
A rubber composition was obtained in the same manner as in Example 1, except that the dialkyl peroxide compound represented by the general formula (1) in Example 1 was changed to 2.70 g (10 mmol) of dicumyl peroxide (compound B), and then the above-mentioned evaluations were carried out.

<Comparative Example 3>
A rubber composition was obtained in the same manner as in Example 1, except that the dialkyl peroxide compound represented by the general formula (1) in Example 1 was changed to 2.02 g (10 mmol) of di-t-hexyl peroxide (compound C), and then the above-mentioned evaluations were carried out.

It is clear that the dialkyl peroxide compound represented by the general formula (1) exhibits a lower odor compared to the compounds A and B, and furthermore, is superior in storage stability and crosslinking performance compared to the compound C.

Claims (4)

General formula (1):

A dialkyl peroxide compound represented by the formula: A rubber composition comprising the dialkyl peroxide compound according to claim 1 and rubber. A crosslinked rubber formed from the rubber composition according to claim 2. A method for producing a crosslinked rubber, comprising the step of heating the rubber composition according to claim 2 at 120 to 250°C.