US20060148989A1

US20060148989A1 - Power transmission belts having enhanced properties

Info

Publication number: US20060148989A1
Application number: US11/026,769
Authority: US
Inventors: George Burrowes; Mike Gregg
Original assignee: Goodyear Tire and Rubber Co
Current assignee: Goodyear Tire and Rubber Co
Priority date: 2004-12-31
Filing date: 2004-12-31
Publication date: 2006-07-06
Also published as: CN1837276A; BRPI0505652B1; US7655729B2; CN1837276B; US20060148990A1; BRPI0505652B8; BRPI0505652A

Abstract

The present invention is directed to the incorporation of of functionalized polyethylenes, in amount of about 4% to 50% by weight based upon the weight of the elastomer, into ethylene alpha olefin elastomers, such as EPDM elastomer compositions, which are crosslinked by peroxides, which results in improved properties, such as hardness and modulus of elongation, and can result in improved higher abrasion resistance, wear resistance, coefficient of friction, tensile strength, and high temperature properties, which are beneficial to power transmission products, such as power transmission belts.

Description

BACKGROUND OF THE INVENTION

The present invention is directed to improved ethylene-alpha-olefin elastomers, especially EPDM-based elastomers, for use in manufacturing power transmission belts. More specifically, the invention is directed to such elastomers which incorporate certain types of functionalized polyethylenes will result in belts having enhanced physical properties.
Power transmission belts are known. See for example, U.S. Pat. No. 6,561,937 (Wegele); U.S. Pat. No. 6,695,734 (Hedberg et al); U.S. Pat. No. 5,610,217 (Yamell et al) and U.S. Pat. No. 6,251,977 (George et al). Proposals have already been made on numerous occasions to use EPDM (ethylene propylene diene terpolymer) elastomers cured by organic peroxides in the manufacture of power transmission belts, because of the qualities and advantages of such elastomers such as cost, operating temperature range, and ability to withstand oxygen and ozone, such EPDM-based elastomers having additives which improve their dynamic properties such as resistance to fatigue and to wear, their breaking strength, and their modulus of elasticity, and also their adhesion to traction cords, which additives are generally constituted by metallic salts of α,β-unsaturated organic acids (in particular zinc methacrylate) plus reinforcing fillers such as carbon black and possibly fibers, e.g. aramid fibers. For example, the Yarnell '217 patent teaches the use of α,β-unsaturated organic acids in peroxide cured EPDM elastomers. The George et al '977 patent teaches the inclusion, in peroxide cured elastomers, of an elastomer grafted with maleic anhydride which reacts with the α,β-unsaturated organic acid metallic salt included in the composition to reinforce the curing of the EPDM-based elastomer and to improve its dynamic characteristics, such as in particular its modulus of elasticity, its breaking strength, and its hardness. The elastomer grafted with maleic anhydride can be a polybutadiene, polyisoprene, polypropylene, or an ethyl vinyl acetate (EVA) copolymer, and the elastomer is used as a power transmission belt.
Oxidized polyethylenes are known and are taught by U.S. Pat. Nos. 2,683,141 and 3,060,163 to Erchak. They are used to form stable, translucent emulsions for use in floor waxes, in coatings for asbestos shingles, paper and textiles, and in inks for application to various surfaces. They have been incorporated into EPDM compositions, such as those described in U.S. Pat. No. 4,990,568 to Benefield et al. In Benefield the EPDM is admixed with an oxidized or carboxylated polyolefin, in at an amount of 2 to 20% of the elastomer, to improve the problem of adherence of coatings applied to the surfaces of articles formed from the thermoplastic elastomers.

SUMMARY OF THE INVENTION

The present invention is the result of the discovery that the incorporation of functionalized polyethylenes into ethylene alpha olefin elastomers, such as EPDM elastomer compositions, which are cured by peroxides, will result in improved properties, such as hardness and modulus of elongation, and can result in improved higher abrasion resistance, wear resistance, coefficient of friction, tensile strength, and high temperature properties. Enhancement of these properties is beneficial to power transmission products, such as power transmission belts. Further, the formulation results in a reduction in the viscosity of the uncured compound, and results in easier processing conditions.
The incorporation of the functionalized polyethylene is at an amount of about 4% to 50% by weight based upon the weight of the elastomer. When the composition is cured by the peroxide that is included in the mixture, the functionalized polyethylene is also crosslinked into the composition, and the result is an improved belting composition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a differential scanning calorimeter graph of the exotherms of uncured versus cured compounds of a composition containing functionalized polyethylene;
FIG. 2 is a differential scanning calorimeter graph, similar to FIG. 1, of the exotherms of uncured versus cured compounds of a composition containing another functionalized polyethylene;

DETAILED DESCRIPTION OF THE INVENTION

The structures of power transmission belts are well know and illustrated in patents such as U.S. Pat. Nos. 6,251,977, 6,561,937, and 5,610,217, the disclosures of which are incorporated herein by reference. The belt is designed to rotate any rotary member, and can be of the “poly-V” type. As such it would have an inside surface and a certain number of circumferential ribs of trapezoidal cross-section, where the ribs are mutually parallel and extend over the entire length of the belt and are designed to be engaged in grooves of complementary shape in the pulleys on which the belt is mounted.
The belt has at least one sheet of traction cords which are embedded in the ethylene-alpha-olefin elastomer of the belt, between its top surface and the ribs, with the cords being spiral-wound inside the belt and with the number of turns thereof being a function of the mechanical characteristics desired of the belt.
The ethylene-alpha-olefin elastomers useful in the present invention include but are not limited to copolymers composed of ethylene and propylene units (EPM), ethylene and butene units, ethylene and pentene units, or ethylene and octene units (EOM), and terpolymers composed of ethylene and propylene units and an unsaturated component (EPDM), as well as mixtures thereof. As the unsaturated component of EPDM, any appropriate non-conjugated diene may be used, including for example, 1,4-hexadiene, dicyclopentadiene or ethylidenenorbornene (ENB). The ethylene-alpha-olefin elastomer preferred in the present invention contains from about 35% by weight to about 80% by weight of the ethylene unit, from about 65% by weight to about 25% by weight of the propylene or octene unit, and 0-10% by weight of the unsaturated component. In a more preferred embodiment, the ethylene-alpha-olefin elastomer contains from about 55% to about 78% by weight of the ethylene unit, and in a most preferred embodiment, the ethylene-alpha-olefin elastomer contains from about 65% to about 75% of the ethylene unit. At these more preferred ethylene unit content levels, endless belts incorporating as their main belt body portions the ethylene-alpha-olefin elastomic compositions of this preferred embodiment of the present invention exhibit improved pilling resistance. The most preferred ethylene-alpha-olefin elastomer is EPDM.
To form the elastomer composition of the present invention the ethylene-alpha-olefin elastomer may optionally be blended with less than 50% by weight, more preferably up to about 25%, and most preferably from about 5% to about 10% based on the total elastomeric content of the composition of a second elastomeric material including but not limited to silicone rubber, polychloroprene, epichlorohydrin, hydrogenated nitrile butadiene rubber, natural rubber, ethylene-vinyl-acetate copolymer, ethylene methacrylate copolymers and terpolymers, styrene butadiene rubber, nitrile rubber, chlorinated polyethylene, chlorosulfonated polyethylene, alkylated chlorosulfonated polyethylene, transpolyoctenamer, polyacrylic rubbers, butadiene rubber, and mixtures thereof, to fine-tune certain mechanical properties such as high temperature performance and tack.
The elastomer may incorporate metal salts of α,β-unsaturated organic acids. The metal salts of α.,β-unsaturated organic acids that can be useful in the present invention are metal salts of acids such as for example, acrylic, methacrylic, maleic, fumaric, ethacrylic, vinyl-acrylic, itaconic, methyl itaconic, aconitic, methyl aconitic, crotonic, alpha-methylcrotonic, cinnamic, and 2,4-dihydroxy cinnamic acids. These salts may be of zinc, cadmium, calcium, magnesium, sodium or aluminum, and are preferably those of zinc. The preferred metal salts of α.,β-unsaturated organic acids are zinc diacrylate and zinc dimethacrylate. The most preferred metal salt of unsaturated organic acid is zinc dimethacrylate. Amounts of the metal salt useful in the present invention may range from about 1 to about 30 phr, and are preferably from about 5 to about 20 phr. In the most preferred embodiment, the metal salt is zinc dimethacrylate used in an amount of about 5 phr when used in conjunction with EPDM mixed with up to about 10% of silicone rubber, and from about 10 to about 20 phr and more preferably about 15 phr when used in conjunction with the other ethylene-alpha-olefin elastomers useful in the present invention.
The functionalized polyethylenes that can be employed in the present invention include oxidized polyethylenes and copolymers of polyethylene, such as ethylene maleic anhydride and ethylene-vinyl acetate copolymers, which will crosslink with the elastomer to increase the hardness and modulus of the elastomer, which in turn, leads to improved belt properties, especially for power transmission belts. The preferred functionalized polyethylenes include oxidized polyethylene, ethylene-vinyl acetate copolymer, and ethylene maleic anhydride copolymer. Functionalized polyethylenes are available from Honeywell International Inc. under the brand name A-C polyethylene, including A-C 307a and 395A, which are oxidized polyethylenes, A-C 400A, which is an ethylene-vinyl acetate copolymer, and A-C 575A, which is an ethylene-maleic anhydride copolymer.
Oxidized polyethylene wax materials suitable for use in the practice of this invention are described in U.S. Pat. Nos. 2,683,141 and 3,060,163, which are incorporated herein by reference. According to the latter patent, normally solid, hard, waxy polymers of ethylene having an average molecular weight between about 1,000 and 3,000 are subjected, in the liquid phase, to the action of an oxygen-containing gas to cause reaction of between 2-17 pounds of oxygen per 100 pounds of wax, i.e. to provide an oxidized polyethylene wax containing at least 1 percent and preferably 1-8 percent by weight of oxygen, and acid numbers of not more than about 50, and preferably between 10 and 45.
The oxidized polyethylene is characterized by having a minimum number average molecular weight above 1000 and preferably at least about 1200, as determined by high temperature vapor pressure osmometry, containing between 1-5 percent by weight of total oxygen, and having an acid number of from 10 to about 35. The described oxidized polyethylene is obtained by oxidation of polyethylene in molten or finely divided solid form, with free oxygen containing gas, usually air, generally at elevated temperature, until the desired oxygen content is obtained. Starting materials for making the oxidized polyethylene suitable for use in the practice of this invention include low molecular weight, low density or linear low density polyethylene waxes having densities in the range of about 0.91 to about 0.96 as, for example, prepared by the process described in U.S. Pat. No. 2,683,141, as well as high density, linear polyethylene as, for example, prepared in the presence of such well know catalysts as the “Phillips” or “Ziegler” type catalysts, having densities in the range of about 0.93-0.97 or above. The low molecular weight, low density polyethylene starting material can be oxidized by contacting in the molten state with a stream of air until the desired oxygen content has been obtained. The high density, linear polyethylene starting material is usually oxidized by contact, preferably in the finely divided solid state, with free oxygen-containing gas, usually air, at temperatures ranging from 100° C. up to, but not including, the crystalline melting point of the polyethylene, until the desired oxygen content has been obtained.
The ethylene-alpha-olefin elastomeric compositions useful in the endless belts of the present invention further comprise from about 25 to about 250 phr and preferably from about 25 to about 100 phr of a reinforcing filler such as carbon black, calcium carbonate, talc, clay or hydrated silica, or mixtures of the foregoing. The incorporation of from 1 to 30 phr of a metal salt of an unsaturated organic acid and from about 25 to about 250 phr and preferably about 25 to about 100 phr of reinforcing filler in the peroxide-cured ethylene-alpha-olefin elastomeric composition preserves the heat stability of conventional peroxide-cured elastomers, while providing the tear strength and dynamic properties usually associated with sulfur cured elastomers.
The free-radical producing curatives useful in the present invention are those suitable for curing ethylene-alpha-olefin elastomers and include for example, organic peroxides and ionizing radiation. The preferred curative is an organic peroxide, including but not limited to dicumyl peroxide, bis-(t-butyl peroxy-diisopropyl benzene, t-butyl perbenzoate, di-t-butyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, alpha.-alpha.-bis(t-butylperoxy) diisopropylbenzene. The preferred organic peroxide curative is alpha.-alpha.-bis(t-butylperoxy) diisopropylbenzene. Cure-effective amounts of organic peroxide for purposes of the present invention are typically from about 2 to about 10 phr. Preferred levels of organic peroxide are from about 4 to about 6 phr. Sulfur may optionally be added to the organic peroxide curative as part of a mixed cure system in an amount of from about 0.01 to about 1.0 phr, to improve the cured elastomer's Young's modulus without negatively affecting its tear resistance.
Other conventional ethylene-alpha-olefin elastomer additives, process and extender oils, antioxidants, waxes, pigments, plasticizers, softeners and the like may be added according to common rubber processing practice without departing from the present invention. For example, in a preferred embodiment of the present invention, the elastomeric composition also contains from about 0.5 to about 1.5 phr of an antiozonant or antioxidant and from about 5 to about 15 phr of a paraffinic petroleum oil plasticizer/softener.
The ethylene-alpha-olefin elastomeric compositions useful in the present invention may be prepared by any conventional procedure such as for example, by mixing and milling the ingredients in an internal mixer or mill, such as a two stage Banbury mixer. It should be noted that in blending some of the functionalized polyethylenes, attaining temperatures above the melting point of the polyethylene grade may be necessary to achieve processing of the mixed materials, and thus a uniform blend. But, this is not believed to be necessary for all materials.
Typically, a belt made out of an EPDM elastomer of the invention has the following composition prior to curing:

- EPDM: 100 parts by weight;
- functionalized polyethylene: 5 to 100 parts by weight (preferable: 20 to 80);
- carbon black: 10 to 100 parts by weight (preferable: 50 to 60);
- electrically conductive carbon black: 1 to 10 parts by weight (preferable: 5 to 6);
- antioxidant: 0.5 to 8 parts by weight (preferable: 1.5 to 3);
- organic peroxide: 0.5 to 15 parts by weight (preferable: 2 to 10);
- curing coagent: 0.5 to 10 parts by weight (1 to 8);
- metal salts of {acute over (α)},β-unsaturated organic acids (optional): 2 to 25 parts by weight;
- plasticizer: 1 to 20 parts by weight (preferable: 1 to 10).

The composition of the elastomer of the invention may also be blended with:

- hydrogenated nitrile butadiene rubber (HNBR) constituting 2 to 20 parts by weight approximately to improve resistance to oils and to solvents, or nitrile butadiene rubber (NBR) in the same quantities and for the same purpose;
- polybutadiene (BR) constituting 2 to 20 parts by weight approximately to improve dynamic properties and resistance to abrasion;
- chloro-sulfonated polyethylene with alkyl groups (ACSM) constituting 2 to 40 parts by weight approximately to increase resistance to oils and resistance to tearing; and
- natural rubber comprising 2 to 20 parts by weight approximately to improve raw adhesion, so that the composition of the invention then has 98 to 80 parts by weight of EPDM.

In addition, it may also have polyamide, aramid, polyester, rayon, cotton, or glass fibers constituting 3 to 30 parts by weight approximately to improve the transverse strength of the belt manufactured with the elastomer composition.

EXAMPLE

In order to demonstrate the present invention, belt compositions were made and tested. The following composition was mixed and compounded in a two stage Banbury mixer in a manner typical for rubber compounding:

- EPDM: 100 parts by weight;
- functionalized polyethylene: 10% by weight;
- carbon black: 50 parts by weight;
- electrically conductive carbon black: 3 to 4 parts by weight;
- antioxidant: 1.5 to 3 parts by weight; and
- dicumyl peroxide: 16.67 parts by weight

The compositions were shaped into test specimens or sheets, cured at about 340° F., for about 30 minutes, and evaluated using a RPA 2000 rubber process analyzer. The results are set forth in Tables I and II.

	TABLE I


		RPA 2000 Rubber
		Process Analyzer
	Mettler	“Cure” Data

Ex-	Functionalized		Drop			MaxS′ −
ample	Polyethylene	sg	Point	Min S′	Max S′	Min S′
No.	Employed	(g/cc)	(° F.)	(dNm)	(dNm)	(dNm)

1	None			3.266	34.96	31.70
2	A-C 307A	0.98	284	2.32	31.76	29.44
	Oxidized
	Polyethylene
3	A-C 395A	1.00	279	2.33	25.31	22.98
	Oxidized
	Polyethlene
4	A-C 575A	0.92	223	2.239	27.11	24.87
	Ethylene-
	Maleic
	Anhydride
	Copolymer

Note:
A-C polyethylenes & copolymers are available from Honeywell International, Inc.

TABLE II


		A-C 575A	A-C	307A
TEST	CONTROL	Example	Example

Tensile Strength	1460.3	1392.8	1667.8
(MPa)
Elongation (%)	141	175	156
Modulus (MPa)
10%	64.9	116.5	203.9
25%	138.7	215.5	343.2
50%	246.2	322.3	492.7
100%	712.9	609.3	903.8
141%	1460.3
156%			1667.8
175%		1392.8
Hardness (Shore A)	66	73	80

As can be seen from the data above and the DSC (differential scanning calorimeter) scans shown in FIGS. 1 and 2, the functionalized polyethylene is crosslinked with the EPDM and the resulting composition provides improved properties for the belting material. The DSC scans of uncured A-C 307A compound, FIG. 1, and A-C 575A compound, FIG. 2, show melt point peaks for the functionalized polyethylenes at 127.97° C. and 93.59° C. respectively, along with the DiCup cure exotherm at 185-186° C. The same melt point peaks are absent from the DSC scans of cured samples of these compounds and show that the functionalized polyethylenes are crosslinked into the compounds on cure.
The foregoing embodiments of the present invention have been presented for the purposes of illustration and description. These descriptions and embodiments are not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above disclosure. The embodiments were chosen and described in order to best explain the principle of the invention and its practical applications to thereby enable others skilled in the art to best utilize the invention in its various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the invention be defined by the following claims.

Claims

1. An organic peroxide curable elastomer composition comprising:

(a) ethylene-alpha-olefin elastomer,

(b) an organic peroxide curing agent, and

(c) 4 to 50% by weight, based upon the weight of the ethylene-alpha-olefin elastomer, of a functionalized polyethylene.

2. The elastomer composition of claim 1 wherein ethylene-alpha-olefin elastomer is ethylene-propylene-diene terpolymer.

3. The elastomer composition of claim 1 wherein the functionalized polyethylene is crosslinkable with the ethylene-alpha-olefin elastomer.

4. The elastomer composition of claim 1 wherein the functionalized polyethylene is an oxidized polyethylene.

5. The elastomer composition of claim 1 wherein the functionalized polyethylene is a copolymer of polyethylene and maleic anhydride.

6. The elastomer composition of claim 1 wherein wherein the functionalized polyethylene is present in an amount of 5 to 100 parts by weight.

7. The elastomer composition of claim 1 wherein wherein the functionalized polyethylene is present in an amount of 20 to 80 parts by weight.

8. The elastomer composition of claim 1 wherein the cured compound is in the form of a power transmission belt.

9. The elastomer composition of claim 1 wherein the cured compound is in the form of a power transmission belt selected from the group consisting of synchronous belts, v-belts, and multi-V-ribbed belts.

10. The elastomer composition of claim 1 wherein the composition further includes a filler.

11. The elastomer composition of claim 1 wherein the composition further includes a reinforcing fiber.

12. The elastomer composition of claim 1 wherein the composition further includes a salt of an α,β-unsaturated organic acid.

13. The elastomer composition of claim 12 wherein the salt of an α,β-unsaturated organic acid is zinc diacrylate.

14. The elastomer composition of claim 1 wherein the elastomer is a blend of elastomers.

15. The elastomer composition of claim 1 wherein the uncured composition comprises the following:

(a) 100 parts by weight of ethylene-alpha-olefin elastomer,

(b) 5 to 100 parts by weight of a functionalized polyethylene which is crosslinkable with the elastomer, and

(c) 0.5 to 10 parts by weight of an organic peroxide curing agent.