JPH10251452A - Rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber compsn. which can be further improved in mechanical properties without detriment to the resistances to heat and abrasion inherent in a hydrogenated NBR. SOLUTION: This compsn. contains fine nylon particles dispersed in a hydrogenated NBR elastomer matrix and also contains a functional ethylenic copolymer. The ethylenic copolymer may be one having units derived from ethylene and units derived from maleic anhydride. The compsn. may further contain at least either zinc oxide or magnesium oxide, which is capable of crosslinking the ethylenic copolymer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition, and more particularly to a rubber composition suitable for belt applications having excellent heat resistance, abrasion resistance and flex fatigue resistance.

[0002]

2. Description of the Related Art Hydrogenated NBR is a rubber having improved heat resistance and low-temperature characteristics while maintaining oil resistance and wear resistance of NBR. However, unless the water addition rate is 100%, a double bond will remain in the molecule,
The heat resistance remains at a level of about 120 to 130 ° C. in a normal grade.

Silicon rubber and acrylic rubber are known as rubbers having higher heat resistance than hydrogenated NBR. However, these rubbers have insufficient mechanical strength, abrasion resistance, oil resistance and the like. It is not used for automotive belt applications such as V-ribbed belts.

In recent years, automobile belts have been increasingly required to have high heat resistance, wear resistance to high-speed rotation, and chipping resistance.
BR (hereinafter, also referred to as HNBR) has been required. For this purpose, composite systems such as those reinforced by adding short fibers such as glass, nylon, and aramid to HNBR, and HNBR reinforced with zinc methacrylate have been adopted.

As the short fiber reinforced HNBR, for example, the following has been proposed. HNB obtained by kneading low-density polyethylene (LDPE) with nylon to extrude the nylon into fibrous form in the LPDE and kneading the obtained LPDE and HNBR
R / nylon / low density polyethylene polymer.
For example, SHP polymer of Ube Industries, Ltd. is known. In this polymer, during kneading, LDPE and H
High dispersion is achieved by the structural affinity of NBR.

Further, in Japanese Patent Application Laid-Open No. 2-145631, when HNBR and nylon are melt-kneaded in one step,
It has been shown that the addition of an acid anhydride such as maleic anhydride improves the compatibility.

However, the external addition of the nylon short fibers does not make it possible to reduce the size of the short fibers to be charged. If the amount of the nylon short fibers is increased, the heat generation under dynamic conditions such as foreign substance mixing cannot be suppressed. Further, in the case of the HNBR / nylon / LPDE system, the melting point of LPDE directly becomes the limit of the heat resistance of the rubber, so that high-temperature running properties are inferior.

[0008] The zinc methacrylate salt reinforced HNBR developed for the same purpose realizes the fine dispersion of the zinc polymethacrylate salt in the HNBR on the order of nanometers, and achieves a further increase in strength and wear resistance of the HNBR. doing. But,
The high cost of the polyzinc methacrylate and the zinc methacrylate reinforced HNBR thus obtained
Has disadvantages such as high running heat generation property and inferior compression permanence since only peroxide crosslinking is possible.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks, and has as its object the purpose of HNB.
The object of the present invention is to provide a rubber composition capable of further improving mechanical properties while maintaining the original heat resistance and wear resistance.

It is yet another object of the present invention to provide a rubber composition for belts that is also capable of sulfur crosslinking.

[0011]

Means for Solving the Problems The rubber composition of the present invention comprises:
Fine particles made of nylon are dispersed in a hydrogenated NBR elastomer matrix and contain a functional group-containing ethylene-based copolymer, thereby achieving the above object.

In a preferred embodiment of the present invention, the functional group-containing ethylene copolymer is a copolymer containing ethylene and maleic anhydride as components.

In a preferred embodiment of the present invention, the composition further contains a metal oxide capable of cross-linking the functional group-containing ethylene copolymer.

[0014] In a preferred embodiment of the present invention, the metal oxide is at least one selected from the group consisting of zinc oxide and magnesium oxide.

The operation of the present invention is as follows.

The rubber composition of the present invention comprises fine particles of nylon dispersed in a hydrogenated NBR elastomer matrix, and contains a functional group-containing ethylene copolymer so that the finely divided nylon is contained in HNBR. It can be filled to reinforce it, and the functional group-containing ethylene copolymer acts as a compatibilizer between the HNBR elastomer and the nylon fine particles. In this case, the size of the dispersed nylon fine particles is about 0.1 μm. Therefore, it is possible to further improve the mechanical properties while maintaining the heat resistance and wear resistance due to the use of HNBR. In particular, when reactive processing (dynamic crosslinking method) using a metal oxide is used, an alloy in which the morphology is microscopically controlled can be obtained. Further, since the obtained rubber composition can be crosslinked with sulfur, a more suitable composition can be supplied to the belt.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Nylon used in the present invention is:
A thermoplastic resin having an amide bond -CO-NH- in the main chain, for example, nylon 4,6,8,11,12, nylon 66,610,612 and the like, and further nylon 6 / 66,6 / 12, 6/66/610, 6/66
And N-substituted nylons such as N-hydroxymethyl and N-methoxymethyl.

The functional group-containing ethylene copolymer used in the present invention is a copolymer of ethylene and a monomer having a functional group and having a reactive unsaturated group capable of reacting with ethylene. The functional group may be any group capable of reacting with the metal oxide, and examples thereof include maleic anhydride (acid anhydride group), a carboxyl group, and an epoxy group. Preferred are maleic anhydride (anhydride group) and carboxyl group.

Specific examples of the monomer having a functional group include dicarboxylic acids such as maleic acid and fumaric acid, and dicarboxylic anhydrides. Further, acrylic acid or a derivative thereof shown below can also be used.

Acrylic acid, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, acrylamide, glycidyl acrylate, 2-hydroxypropyl acrylate, 2-cyanoethyl acrylate, acrylonitrile, methyl acrylate, Ethyl acrylate,
N-butyl acrylate, isobutyl acrylate and the like. These may be used as a mixture of two or more of them within the scope of the present invention.

For example, a polymer obtained by copolymerizing ethylene, an alkyl acrylate and a monomer having a crosslinkable group can be used.

A preferred functional group-containing ethylene copolymer is a copolymer containing ethylene and maleic anhydride as constituents.

Commercially available functional group-containing ethylene copolymers include the following.

(1) Resin-form (at room temperature) functional group-containing ethylene copolymer Lexpearl ET, RB series, Adtex ER
(Manufactured by Nippon Polyolefin Co., Ltd.) JP-A-60-240749, JP-A-1-1-1
What is described in 56309 can also be used for this invention.

(2) Rubber-form (at room temperature) functional group-containing ethylene copolymer Terpolymer of ethylene / methyl acrylate / crosslinkable carboxyl group monomer, VAMAC G (Showa Denko
-DuPont) Such a functional group-containing ethylene copolymer is HNBR.
It functions as a compatibilizer between the elastomer and the nylon fine particles.

In the present invention, it is preferable to further contain a metal oxide capable of crosslinking the functional group-containing ethylene copolymer. As the metal oxide, a monovalent or divalent metal oxide can be used. For example, zinc oxide, magnesium oxide, potassium oxide, barium oxide, cadmium oxide, calcium oxide, chromium oxide, zirconium oxide,
Examples include tin oxide, copper oxide, iron oxide, lead oxide, cobalt oxide, manganese oxide, and mixtures thereof. Especially,
Zinc oxide or magnesium oxide is preferred.

In the rubber composition of the present invention, if necessary,
In addition, a filler, a coloring agent, a vulcanizing agent, a vulcanization accelerator, a vulcanization aid, an antioxidant, and the like can be added.

Examples of the filler include silica, mica, talc, clay, calcium carbonate, carbon black, titanium oxide, alumina, aluminum hydroxide and the like. SRF-LM can be used as the carbon black.

As the vulcanizing agent, known sulfur and organic peroxides can be used.

Examples of the organic peroxide include known ones such as dicumyl peroxide, t-butyl peroxide, lauroyl peroxide and benzoyl peroxide.

Examples of the antioxidants include amines, amine-aldehyde reactants, amine-ketone reactants, phenols and the like. Particularly, a quinoline-based polymer (a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline) is preferable.

As the vulcanization aid, fatty acids are preferably used, for example, stearic acid, palmitic acid, oleic acid, myristic acid and the like, and preferably stearic acid and palmitic acid.

In the rubber composition of the present invention, the above HNB
The mixing ratio of R, nylon, and the functional group-containing ethylene copolymer is usually 20 to 80: 4 to 64: 4 by weight ratio.
~ 64. Preferably, 40-65: 35-60:
35 to 60. When the rubber composition contains a metal oxide, the content ratio is preferably 0.1 to 20 parts by weight based on 100 parts by weight of the total of HNBR, nylon and the functional group-containing ethylene copolymer.

Typically, HNBR is 30-70% by weight
(Preferably 40-65% by weight), nylon is 1-70%
Wt% (preferably 15 to 60 wt%), and the functional group-containing ethylene-based copolymer is 1 to 70 wt% (preferably 15 to 60 wt%).
60% by weight) and 0.5 to 20% by weight (preferably 1 to 10% by weight) of the metal oxide.

In the rubber composition of the present invention, HNBR
Fine particles made of nylon are dispersed in an elastomer matrix. Here, the shape of the fine particles is not particularly limited, but may be spherical, elliptical, fibrous, or any shape other than those, and the average size is usually 0.05 to 0.5 μm, and particularly preferably 0.1 to 0.5 μm. 05
０．２0.2 μm is preferred.

Next, a method for producing the rubber composition of the present invention will be described.

The rubber composition of the present invention can be produced, for example, according to the following method.

(1) HNBR / nylon / maleic acid-containing ethylene acrylate resin system in which metal oxide (for example, zinc oxide) is added Maleic acid-containing ethylene acrylate resin includes:
It can be obtained by copolymerizing maleic anhydride with a random block copolymer of ethylene and acrylate.
As a commercially available product, for example, Lexpearl ET manufactured by Nippon Polyolefin Co., Ltd. can be used. It acts as a compatibilizer for HNBR and nylon. Further, it has a compatibilizing effect due to the reaction between maleic anhydride and the acid amide group of nylon and a compatibilizing effect due to the structural affinity between the ethylene component and HNBR.

The maleic acid-containing ethylene acrylate resin is mixed with HNBR and nylon by a kneader (for example,
Using a twin screw extruder or an internal mixer), the mixture is kneaded in one step, and then zinc oxide is added for crosslinking the maleic acid-containing ethylene acrylate resin. The addition of zinc oxide retains the tendency for thermoplasticity, but then acts as a good co-vulcanization accelerator when vulcanizing the matrix HNBR.

After cooling, the mixture is kneaded with a general molding machine (roll, internal mixer, etc.) at a melting point (from 80 ° C.) of the maleic acid-containing ethylene acrylate resin to less than the melting point of nylon, and a crosslinking agent for HNBR, an auxiliary agent, filler Etc. are blended. By performing this secondary crosslinking (press crosslinking) with peroxide or sulfur, an HNBR-based composition can be obtained.

(2) HNBR / nylon / maleic acid-containing ethylene acrylate resin composition to which metal oxide (eg, magnesium oxide) is added Nylon and maleic acid-containing ethylene acrylate resin (random block copolymer) Is kneaded at a temperature equal to or higher than the melting point of nylon to obtain an alloy having an island in which the nylon is dispersed, a sea-island structure in which the maleic acid-containing ethylene acrylate resin is the sea, or a bicontinuous structure.

The obtained alloy is cooled and solidified (pelletized).
After that, it is kneaded with HNBR in an internal mixer. At this time, the temperature in the mixer was adjusted to the melting point of the maleic acid-containing ethylene acrylate resin (80 to 100 ° C).
The above is not more than the melting point of nylon (in the case of nylon 6, the melting point is around 220 ° C.). For example, 80-1
80 ° C. is preferred. Thereby, the shape of the finely dispersed nylon fine particles can be maintained in HNBR, and the dispersed nylon fine particles can be prevented from aggregating and becoming huge.

At the time of kneading, stearic acid and magnesium oxide (MgO) are added. During kneading, stearic acid / magnesium oxide specifically reacts with a ramaleic acid-containing ethylene acrylate resin dam block copolymer to rapidly increase its viscosity. By utilizing this reactivity, for example, HNB in which maleic acid-containing ethylene acrylate resin is in the sea
In R / nylon / ramaleic acid-containing ethylene acrylate resin dam block copolymer-based alloys, the reaction by magnesium oxide causes a phase structure inversion, and this incomplete phase inversion causes an IPN structure. An HNBR-based composition in which the polymer structure is fixed by the effect is obtained. At this time, the above-mentioned rubber vulcanizing agent, compounding agent and the like may be added.

Thereafter, the HNBR can be cross-linked by adding a usual peroxide or sulfur. If the crosslinking temperature is set so as not to exceed the melting point of nylon (for example, 14
0-200 ° C.), and the morphology in which the nylon before cross-linking is finely dispersed in HNBR is maintained. However, the crosslinking temperature may or may not exceed the melting point of nylon.
If the crosslinking temperature under pressure exceeds the melting point of nylon, adhesion of nylon fine particles may start, but HNBR
This is because the morphology is expected to be fixed without growing macroscopically than the competitive reaction with cross-linking.

(3) Metal oxides (for example, HNBR / nylon / crosslinkable group-containing ethylene / acrylic rubber)
System to which magnesium oxide is added In place of the maleic acid-containing ethylene acrylate resin used in the compositions (1) and (2), a crosslinkable group-containing ethylene acrylic rubber (for example, Showa Denko, DuPont) Vamac) can be used for the same purpose.

That is, HNBR was added to an alloy obtained by kneading nylon and ethylene / acryl rubber, and H
NBR and a crosslinkable group-containing ethylene acrylic rubber were kneaded. The compatibility between the HNBR and the ethylene / acrylic rubber is quite good, and co-crosslinking is possible (Japanese Patent Laid-Open No. 6-93).
145).

Next, at the time of kneading with HNBR, stearic acid and magnesium oxide were added. With this addition, i
Compatibility could be promoted by n-situ reaction introduction. By setting the temperature at this time to about 100 ° C. or higher and lower than the melting point of nylon, adhesion of nylon can be prevented. At this time, rubber additives and compounding agents may be added.

The HNBR composition was crosslinked by a usual method. The crosslinking temperature may or may not exceed the melting point of nylon. It is believed that the adhesion of the nylon begins when the melting point of the pressurized nylon is exceeded, but the morphology can be expected to be fixed without growing macroscopically due to the competitive reaction with the crosslinking of the HNBR rubber. The dispersion level of the alloy obtained as above is around 0.1 μm, and the dispersion level of the composition reinforced with the polyzinc methacrylate salt is 20 μm.
It is an area that fills the gap between nm and 10 μm or more of the nylon short fiber reinforcement system.

In the above methods (1), (2) and (3),
The following can be used as the crosslinking agent for HNBR rubber.

(A) TMTD + sulfur (B) Vulcanization accelerator (CBS) + peroxide + sulfur (C) isocyanurate compound + peroxide
Among these crosslinking agents, a particularly preferable one is a system using the peroxides of (B) and (C). However, peroxides are originally inferior in crack growth resistance and are considered to be inferior. Sulfur vulcanization is preferred because of high heat generation under static conditions.

[0051]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments.

Examples 1 to 4 A system in which zinc oxide was added to a HNBR / nylon / maleic acid-containing ethylene-acrylate resin composition at the time of melt-kneading (above the melting point of nylon), in the number of parts shown in Table 1, HNBR, nylon 6. A maleic acid-containing ethylene acrylate resin (Lexpearl ET manufactured by Nippon Polyolefin Co., Ltd.) was blended and extruded in one step at a temperature equal to or higher than the melting point of nylon 6. At this time, stearic acid and zinc oxide were added simultaneously in the number of parts shown in Table 1.

After cooling, the mixture was kneaded using a molding machine (roll) at a temperature (100 to 120 ° C.) higher than the melting point of maleic acid-containing ethylene acrylate resin and lower than the melting point of nylon. , Stearic acid, HNB
As a crosslinking agent for R, sulfur, carbon black (SFR carbon black), vulcanization accelerator (CBS: N-cyclohexyl-2-benzothiazyl sulfanamide), peroxide (PO: dicumyl peroxide), antioxidant ( D
Q: 2,2,4-trimethyl-1,2-dihydroquinoline polymer) and kneaded to obtain a rubber composition.

Comparative Examples 1 and 2 A rubber composition was obtained in the same manner as in Example 1 except that the maleic acid-containing ethylene acrylate resin was not blended and the blending was as shown in Table 1.

Examples 5 to 8 A system in which magnesium oxide was added to a HNBR / nylon / maleic acid-containing ethylene acrylate resin composition. Nylon 6 and maleic acid-containing ethylene acrylate resin (Nippon Polyolefin Co., Ltd.) (stock)
Melt-kneaded at a temperature (230 ° C.) higher than the melting point of nylon to obtain an alloy in which the nylon is an island and the maleic acid-containing ethylene acrylate resin is a sea-island structure or a bicontinuous phase.

Next, HNBR was added to the obtained alloy in the number shown in Table 2 and kneaded. The temperature at the time of kneading was a temperature equal to or higher than the melting point of the maleic acid-containing ethylene acrylate resin and lower than the melting point of nylon. Next, to this mixture:
Stearic acid and magnesium oxide were added as crosslinking agents for the maleic acid-containing ethylene acrylate resin in the number shown in Table 2.

Next, stearic acid,
As a crosslinking agent for HNBR, sulfur, carbon black, a vulcanization accelerator (CBS: N-cyclohexyl-2-benzothiazyl sulfanamide), a peroxide (PO: dicumyl peroxide), an antioxidant (DQ: 2,2) , 4-Poly (trimethyl-1,2-dihydroquinoline)) and kneaded to obtain a rubber composition.

Comparative Examples 3 to 6 Rubber compositions were obtained in the same manner as in Example 5 except that the maleic acid-containing ethylene / acrylate resin was not used and the compounds were mixed as shown in Table 2.

Examples 9 to 12 HNBR / Nylon / Crosslinkable Group-Containing Ethylene Acrylic Rubber-Based Composition Added Magnesium Oxide HNBR and Crosslinkable Group-Containing Ethylene Acrylic Rubber (manufactured by Showa Denko, DuPont) Vamac).

Next, the HNBR composition was crosslinked by a usual method. The crosslinking temperature is the melting point of nylon, in terms of the number of parts shown in Table 3, stearic acid, sulfur as a crosslinking agent for HNBR, carbon black, vulcanization accelerator (CBS: N-cyclohexyl-2-benzothiazyl sulfanamide), peroxide (PO: dicumyl peroxide) and an antioxidant (DQ: polymer of 2,2,4-trimethyl-1,2-dihydroquinoline) were mixed and kneaded to obtain a rubber composition.

Comparative Examples 7 to 9 Rubber compositions were obtained in the same manner as in Example 9 except that the ethylene / acryl rubber was not used and the compounds shown in Table 3 were used.

The mechanical properties, oil resistance and heat aging resistance of the rubber compositions obtained in Examples 1 to 12 and Comparative Examples 1 to 9 were evaluated. The evaluation method is described below.

(1) Mechanical Properties The rubber compositions obtained in the above Examples and Comparative Examples were
A sheet (2 mm thick) was prepared by press vulcanization at 40 ° C for 40 minutes. A No. 3 dumbbell according to JIS K 6301 was punched out from the vulcanized sheet, and this dumbbell was subjected to a tensile tester (Autograph AGS-500 manufactured by Shimadzu Corporation).
B) at a room temperature (25 ° C.) at a tensile speed of 500 mm / min and a 100% modulus (M100: kg / cm
² ), maximum tensile strength (Tb: kg / cm ² ), and elongation at break (Eb:%) were determined. The hardness of the vulcanized sheet was represented by Shore A hardness.

(2) Oil resistance According to JIS K 6301, width 2 cm × length 5 cm
A vulcanized sheet having a thickness of 2 mm was immersed in JIS No. 3 oil at 100 ° C for 72 hours, and the volume change rate (%) before and after immersion of the sheet was measured. For the volume measurement before and after the test, a specific gravity measuring device manufactured by Toyo Seiki Co., Ltd. was used.

(3) Heat Aging Resistance The vulcanized sheet obtained in (1) above was aged in a rotary thermostat at 140 ° C. for 4 days, and the degree of change in mechanical properties was determined. Evaluation of mechanical properties was as described in (1) above.

The results are shown in Tables 1 to 3.

[0067]

[Table 1]

[0068]

[Table 2]

[0069]

[Table 3]

[0070]

According to the present invention, it is possible to disperse fine nylon particles of a minute size which cannot be achieved by external addition of short fibers. Also, by changing the material composition ratio and kneading conditions, the particle size or shape of the dispersed nylon fine particles can be changed, and a rubber composition in an optimal state according to the application can be provided. As a result, the heat resistance, abrasion resistance, and mechanical properties of HNBR can be improved by adding nylon fine particles, and the internal heat generated due to the composite can be minimized. The rubber composition of the present invention having such characteristics can be suitably used for an automobile timing belt, a V-ribbed belt, and the like.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08L 77:00) (C08F 210/02 222: 06)

Claims (4)

[Claims] 1. A rubber composition comprising a hydrogenated NBR elastomer matrix in which fine particles made of nylon are dispersed and contain an ethylene copolymer having a functional group. 2. The rubber composition according to claim 1, wherein the functional group-containing ethylene copolymer is a copolymer containing ethylene and maleic anhydride as constituents. 3. The rubber composition according to claim 1, further comprising a metal oxide capable of crosslinking the functional group-containing ethylene copolymer. 4. The rubber composition according to claim 3, wherein the metal oxide is at least one selected from the group consisting of zinc oxide and magnesium oxide.