EPDM, HNBR and Butyl rubber compositions containing carbon black products

Abstract

A rubber composition prepared by the process comprising mixing 100 parts by weight of a rubber selected from EPDM, HNBR, and butyl rubber, and 10 to 300 parts by weight of a carbon black product having an attached organic group. The organic group has the formula --Ar--S.sub.n --Ar'-- in which Ar and Ar' are arylene groups or --Ar--S.sub.n --Ar" in which Ar is an arylene group, Ar" is an aryl group and n is 1 to 8.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the use of carbon black products in EPDM, HNBR, and butyl rubber compositions to provide increased modulus and increased bound rubber as well as other valuable properties.

2. Discussion of Related Art

EPDM, HNBR, and butyl rubber are well known rubber compositons used in a wide variety of industrial and consumer products. See McGraw-Hill Encyclopedia of Science & Technology, pp. 761-763 (McGraw-Hill, 1982). EPDM is a copolymer of ethylene-propylene-diene monomers. HNBR is a partially hydrogenated copolymer made from the copolymerization of acrylonitrile and butadiene. Butyl rubber is a copolymer of isobutylene and isoprene.

EPDM, HNBR, and butyl rubber compositions are used in a wide variety of products. These products include, for example, automotive parts, gaskets, cable and wire coatings, mechanical rubber products, cover strips for the sidewalls of tires, innertubes for tires, safety bumpers, fabric coatings, electrical wire insulation, hoses, mechanical rubber goods, and sealants for ponds or reservoirs.

One characteristic of EPDM, HNBR, and butyl rubber is their low levels of unsaturation. The low level of unsaturation in EPDM, HNBR, and butyl rubber limits the effectiveness of reinforcing agents in rubber compositions made from these rubbers. This is particularly true when compared with the use of reinforcing agents in diene rubbers which have high degrees of unsaturation. Butyl rubber, for example, is generally a polybutylene with 0.5-4.5% of a diolefin, normally 3% isoprene. The small amount of diolefin in butyl rubber provides unsaturation for reinforcement and crosslinking.

Carbon blacks have been utilized as pigments, fillers, and/or reinforcing agents in the compounding and preparation of rubber compositions. The properties of the carbon black are important factors in determining various performance properties of the rubber composition containing the carbon black. See, for example, U.S. Pat. No. 5,236,992, which is incorporated herein by reference.

It would be desirable to develop a carbon black product which would impart desirable properties to EPDM, HNBR, and butyl rubber compositions containing the carbon black product.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides new rubber compositions prepared by the process comprising mixing 100 parts by weight of a rubber selected from EPDM, HNBR, and butyl rubber, and 10 to 300 parts by weight of a carbon black product having an attached organic group of the formula --Ar--(S).sub.n --Ar'-- in which Ar and Ar' are arylene groups and n is 1 to 8, preferably 2 to 4.

In another embodiment, the invention provides a rubber composition prepared by the process comprising mixing 100 parts by weight of a rubber selected from EPDM, HNBR, butyl rubber, and 10 to 300 parts by weight of a carbon black product having an attached organic group of the formula --Ar--(S).sub.n --Ar" in which Ar is an arylene group, Ar" is an aryl group and n is 1 to 8, preferably 2 to 4.

The rubber compositions of the invention show increased modulus and increased bound rubber compared to that of the corresponding carbon blacks without the attached organic groups. Other features of the present invention will become apparent from the following detailed description of the invention and the claims.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a rubber composition prepared by the process comprising mixing 100 parts by weight of a rubber selected from EPDM, HNBR, and butyl rubber, and 10 to 300 parts by weight of a carbon black product having an attached organic group. The organic groups have the general formula --Ar--(S).sub.n --Ar'-- in which Ar and Ar' are arylene groups or the general formula --Ar--(S).sub.n --Ar" in which Ar is an arylene group and Ar" is an aryl group. In each of the general formulas the integer n varies from 1 to 8, preferably 2 to 4.

The carbon black product is prepared by reacting a carbon black with a diazonium salt corresponding to the organic group in a liquid reaction medium to attach at least one organic group to the surface of the carbon black. According to the invention, a diazonium salt is an organic compound having one or more diazonium groups. The diazonium salt can be conveniently prepared using means known in the art from a primary amine corresponding to the organic group, for example, H.sub.2 N-Ar-(S).sub.n -Ar'-NH.sub.2 or H.sub.2 N-Ar-(S).sub.n -Ar". Preferred reaction media include water, any medium containing water, and any medium containing alcohol. These carbon black products and various methods for their preparation are described in a U.S. patent application entitled "Reaction of Carbon Black with Diazonium Salts, Resultant Carbon Black Products and Their Uses," filed Dec. 15, 1994 and incorporated herein by reference. Preparation of such carbon black products are also shown in the Examples below.

These carbon black products having organic groups of the formula --Ar--(S).sub.n --Ar'-- or --Ar--(S).sub.n --Ar" are particularly useful in EPDM, HNBR, and butyl rubber compositions. In these organic groups Ar and Ar' are independently arylene groups, Ar" is an aryl and n is 1 to 8. Preferred arylene groups include phenylene groups, particularly p-phenylene groups. Preferred aryl groups include phenyl and naphthyl. The number of sulfurs present defined by n preferably ranges from 2 to 4. A particularly preferred organic group is bis-para-(C.sub.6 H.sub.4)--S.sub.2 --(C.sub.6 H.sub.4)--.

The above carbon black products may be mixed with EPDM, HNBR, or butyl rubbers by normal means known in the art, for example by milling. The rubber compositions containing the carbon black products can be cured using conventional sulfur-based or peroxide systems. Other conventionally used additives may be added to the rubber compositions of this invention.

Generally, amounts of the carbon black product ranging from about 10 to about 300 parts by weight can be used for each 100 parts by weight of the rubber in order to impart a significant degree of reinforcement. It is, however, preferred to use amounts varying from about 50 to about 200 parts by weight of carbon black product per 100 parts by weight of the rubber and especially preferred is the utilization of from about 70 to about 150 parts of carbon black product per 100 parts of the rubber.

The presence of the carbon black products discussed above improves the physical characteristics of the rubber compositions of the invention as compared with the corresponding untreated carbon blacks. Incorporating the carbon black products into the rubber compositions increases the modulus and bound rubber properties of the rubber compositions.

The following examples are intended to illustrate, not limit, this invention.

ASTM test procedures were used to evaluate the rubber compositions of the invention shown in the Examples below. Iodine number was measured using ASTM D-1510. DBPA was measured using ASTM D-2414. Tensile elongation and modulus were measured using ASTM D-412. Shore A hardness was measured using ASTM D-2240-86. Viscosity was measured using a MPT viscometer at 100.degree. C. and 100s.sup.-1 with L/D=16/1 in the capillary.

Tan .delta. was measured with a Rheometrics Dynamic Spectrometer Model RDS-2 at a constant frequency of 10 Hz, at room temperature, and in the shear mode of strain. Strain sweeps were run from 0.08% to 10% DSA. Measurements were taken at five points per decade and the maximum Tan .delta. was reported.

Bound rubber was determined as follows: A 0.5 g sample of an uncured rubber composition containing a rubber and a known amount of a carbon black was placed in a wire cage and submerged in a solvent. After standing for one day, the sample was placed in fresh solvent, and allowed to stand for three additional days at room temperature. The sample was then removed, dried in an oven, and weighed. The weight of the carbon black was subtracted from weight of the sample before and after the solvent treatment to give a value for the amount of rubber in each sample. The weight of the sample after the solvent treatment, adjusted for the weight of the carbon black and other insoluble ingredients in the composition, represents the amount of insoluble rubber remaining. Bound rubber was expressed as the percentage of the weight of insoluble rubber in the sample after standing in the solvent versus the amount of rubber in the original sample.

EXAMPLE 1

Preparation of a carbon black product

This example describes the preparation of a carbon black product for use in the present invention. Concentrated HCl (2.62 g) was diluted with 30 g and added to a stirring mixture of 1.5 g p-aminophenyl disulfide in 100 g of water. The resulting solution was cooled in an ice bath and a cold solution of 0.95 g NaNO.sub.2 in 40 g of water was added with stirring. 4-Diazophenyl disulfide is formed. The solution was added to a suspension of 150 g of pelleted carbon black (iodine number of 19 mg/g and a DBPA of 95 ml/100g) in 1200 mL of water at about 14.degree. C. with stirring. Bubbles were released. After stirring for 2 1/4 hours, the product was filtered, washed with 800 mL of ethanol, washed with 2L of water, and dried at 125.degree. C. This process produced a carbon black product having dithiodi(4,1-phenylene) groups attached to the carbon black.

EXAMPLE 2

Reference carbon black

A reference carbon black was prepared by washing 158 g of the unreacted carbon black of Example 1 with 800 mL of ethanol, about 2 L of water, and subsequently drying in an oven at 125.degree. C.

EXAMPLE 3

Preparation of a carbon black product

This example describes the preparation of a carbon black product for use in the present invention. Concentrated HCl (5.70 g) was diluted with 30 g of water and added to a stirring mixture of 3.50 g p-aminophenyl disulfide in 100 g of water. The resulting solution was cooled in an ice bath and a cold solution of 2.11 g NAN02 in 50 g of water was added with stirring. 4-Diazophenyl disulfide is formed. The solution was added to a suspension of 250g of pelleted carbon black (iodine number of 36 mg/g and a DBPA of 122 ml/100g) in 1500 mL of water at about 14.degree. C. with stirring. Bubbles were released. After stirring for 2 hours, the product was filtered, washed with 1.1 L of ethanol, washed with 3 L of water, and dried at 125.degree. C. A sample of the carbon black product that was extracted overnight with tetrahydrofuran (THF) and dried contained 1.32% sulfur, compared to 0.99% for the unreacted carbon black. Therefore, the product contained 0.05 mmol/g of dithiodi(4,1-phenylene) groups.

EXAMPLE 4

Reference carbon black

A reference carbon black was prepared by washing 250 g of the unreacted carbon black of Example 3 with 1.1 L of ethanol, about 3 L of water, and subsequently drying in an oven at 125.degree. C.

EXAMPLE 5

Use of a carbon black product in EPDM

This example illustrates the use of the carbon black product of Example 1, the washed carbon black reference of Example 2 and the unwashed carbon black reference from Example 1 in EPDM. VISTALON 5600 EPDM (81.4 g) (VISTALON is a registered trademark of Exxon Chemical Americas, Houston, Tex.) was milled in a Brabender mixer for one minute at an initial temperature of 45.degree. C. at 77 rpm. A paraffinic oil ASTM D-2226, type 104B, (122.1 g) was added and mixed for one minute. The carbon black (122.1 g) was added and mixed for 2 1/2 minutes. Zinc oxide (4.07 g) and 0.81 g of stearic acid were added and mixed for two minutes. Tetramethyl thiuram disulfide (2.2 g), 2.2 g of zinc dibutyldithiocarbamate, 2.2 g of zinc dimethyldithiocarbamate, 0.41 g of sulfur and 1.38 g of 4,4'dithiodimorpholine were added and mixed for an additional two minutes. Bound rubber was determined using toluene as the solvent at room temperature. The table below shows that the carbon black product of Example 1 is useful in EPDM and increases modulus and bound rubber.

__________________________________________________________________________ Modulus Modulus Bound Tensile Elongation 100% 300% Hardness Viscosity RubberSample MPa % MPa MPa Sh A Pa-s %__________________________________________________________________________Ex. 1 10.9 553 1.62 5.96 47 2120 8.8Ref. 12.4 731 1.26 3.75 46 2130 5.8Ex. 2Ref. 11.9 679 1.38 4.16 46 2080 7.1Unwashed__________________________________________________________________________

EXAMPLE 6

Use of a carbon black product in EPDM

This example illustrates the use of the carbon black product of Example 3, the washed carbon black reference of Example 4 and the unwashed carbon black reference from Example 3 in EPDM. VISTALON 5600 EPDM (81.4 g) was milled in a Brabender mixer for one minute at an initial temperature of 60.degree. C. at 50 rpm. A paraffinic oil ASTM D-2226, type 104B, (122.1 g) was added and mixed for one minute. The carbon black (122.1 g) was added and mixed for 2 1/2 minutes. Zinc oxide (4.07 g) and 0.81 g of stearic acid were added and mixed for two minutes. Tetramethyl thiuram disulfide (2.2 g), 2.2 g of zinc dibutyldithiocarbamate, 2.2 g of zinc dimethyldithiocarbamate, 0.41 g of sulfur and 1.38 g of 4,4'dithiodimorpholine were added and mixed for an additional two minutes. Bound rubber was determined using toluene as solvent at room temperature. The table below shows that the carbon black product of Example 3 is useful in EPDM and increases modulus and bound rubber.

__________________________________________________________________________ Modulus Modulus Bound Tensile Elongation 100% 300% Hardness Viscosity RubberSample MPa % MPa MPa Sh A Pa-s %__________________________________________________________________________Ex. 3 10.0 364 2.93 8.61 63 2260 44.8Ref. 10.6 467 2.63 7.14 62 2230 39.6Ex. 4Ref. 9.8 441 2.63 7.13 62 2150 39.8Unwashed__________________________________________________________________________

EXAMPLE 7

Use of a carbon black product in butyl rubber

This example illustrates the use of the carbon black product of Example 3, the washed carbon black reference of Example 4 and the unwashed carbon black reference from Example 3 in butyl rubber. Butyl rubber 301 (181.1g) was milled in a Brabender mixer at 40 rpm for 30 seconds at an initial temperature of 30.degree. C. A paraffinic oil ASTM D-2226, type 104B, (21.7 g) and the carbon black (135.9 g) were added and mixed for two minutes. ZnO (9.1 g) and sulfur (2.7 g) were added and milling was continued for 3 1/2 minutes. Tetramethyl thiuram disulfide (3.6 g) and mercaptobenzothiazole (1.8 g) were added and mixed for an additional 1 1/2 minutes. Bound rubber was determined using cyclohexane as solvent at room temperature. The table below shows that the carbon black product of Example 3 is useful in butyl rubber, increases modulus and bound rubber, and decreases hysteresis as shown by higher .rebound and lower Tan .delta..

__________________________________________________________________________ Modulus Modulus Bound Tensile Elongation 100% 300% Hardness Rebound Tan Viscosity RubberSample MPa % MPa MPa Sh A % .delta. Pa-s %__________________________________________________________________________Ex. 3 11.7 470 3.49 9.43 74 13.2 0.29 5020 7.54Ref. 10.6 528 2.97 7.58 70 12.2 0.35 4880 3.54Ex. 4Ref. 10.2 520 2.94 7.51 71 12.1 0.37 4850 4.42Unwashed__________________________________________________________________________

EXAMPLE 8

Preparation of a carbon black product

This example illustrates the preparation of a carbon black product useful in the rubber compositions of the present invention. A carbon black with an iodine number of 120 mg/g and a DBPA of 125 ml/100 g was used. A cold solution of 2.65 g concentrated HCl and 30 g water was added to a mixture of 2.85 g 4-aminophenyl phenyl disulfide in 50 g water that was stirring in an ice bath. A cold solution of 1.04 g NaNO.sub.2 in 30 g of water was added over a period of 10 minutes. 4-Diazophenyl phenyl disulfide chloride was formed. The diazonium suspension was added to a suspension of 122 g carbon black in about 800 g water that was stirring at 15.degree. C. Bubbles were released. After stirring for about two hours, the carbon black product was filtered off, washed with isopropanol, washed with water, and dried in an oven at about 125.degree. C. A sample of the carbon black product that had been subjected to Soxhlet extraction overnight with THF and dried had a sulfur content of 1.32%, compared to 1.08% for the untreated carbon black. Therefore, the carbon black product had 0.038 mmol/g of attached phenyldithiophenylene groups. This carbon black product may be incorporated into a rubber composition of the invention in accordance the examples above.

EXAMPLE 9

Use of a carbon black product in HNBR

Following generally the procedures of Examples 5-7, a carbon black product such as shown in Examples 1-4 and 8 may be incorporated into HNBR to form a rubber composition of the invention.

Claims

1. A rubber composition prepared by the process comprising mixing rubber selected from the group consisting of a copolymer of ethylene-propylene-diene monomers (EPDM), a partially hydrogenated copolymer of acrylonitrile and butadiene (HNBR), and a butyl rubber, and 10 to 300 parts by weight of a carbon black product per 100 parts by weight of the rubber, wherein the carbon black product has an attached organic group of the formula --Ar--(S).sub.n --Ar'-- in which Ar and Ar' are arylene groups and n is 1 to 8.

2. A rubber composition of claim 1 wherein n is 2 to 4.

3. A rubber composition of claim 1 wherein the process further comprises curing the mixture of the rubber and the carbon black product.

4. A rubber composition of claim 1 wherein Ar and Ar' are p-phenylene and n is 2 to 4.

5. A rubber composition of claim 4 wherein n is 2.

6. A rubber composition of claim 1 wherein the rubber is a copolymer of ethylene-propylene-diene monomers (EPDM).

7. A rubber composition prepared by the process comprising mixing rubber selected from the group consisting of a copolymer of ethylene-propylene-diene monomers (EPDM), a partially hydrogenated copolymer of acrylonitrile and butadiene (HNBR), and a butyl rubber, and 10 to 300 parts by weight of a carbon black product per 100 parts by weight of the rubber, wherein the carbon black product has an attached organic group of the formula --Ar--(S).sub.n --Ar"-- in which Ar is an arylene group, Ar" is an aryl group and n is 1 to 8.

8. A rubber composition of claim 7 wherein n is 2 to 4.

9. A rubber composition of claim 7 wherein the process further comprises curing the mixture of the rubber and the carbon black product.

10. A rubber composition of claim 7 wherein Ar is phenylene, Ar' is phenyl and n is 2 to 4.

11. A rubber composition of claim 10 wherein n is 2.

12. A rubber composition of claim 7 wherein the rubber is a copolymer of ethylene-propylene-diene monomers (EPDM).