COMPOSITION REINFORCED CONTAINING SHORT FIBERS

BACKGROUND OF THE INVENTION

This invention is in the field of fibers, elastomeric compositions and articles; more particularly, the invention relates to low modulus short fibers, elastomeric compositions comprising the elastomer and the short fibers, and articles comprising the composition.

U.S. Patent No. 4,389,361 contains a definition for the term elastomer as a substance that can be stretched at room temperature to at least twice its original length and. after having been stretched and the stress removed, returns with force to approximately its original length in a short time. (Glossary of terms as prepared by ASTM Committee D-ll on Rubber and Rubber-like materials, published by the American Society for Testing Materials).

Elastomers are also referred to in Billmeyer. Textbook of Polymer Science, second edition, John Wiley and Sons, Inc. (1971). at pages 242-243 and 533-550 hereby incorporated by reference. Elastomers are considered as a class of high polymers which are amorphous when unstretched and must be above the glass transition temperature to be elastic. Typically, elastomeric polymers have networks of crosslinks. Crosslinks can be obtained by a vulcanization process. Crosslinking transforms an elastomer from a weak thermoplastic mass into a strong elastic, tough rubber material.

An indication of the mechanical properties of elastomers is the measurement of elongation under load, commonly characterized by the stress-strain behavior of the rubber. As the load is increased and the elongation is measured a curve results which is considered the stress-strain curve of the rubber. The elongation of the rubber sample is measured with increased load. Correspondingly a stress-strain curve develops as the load is removed. Differences between the stress-strain curve during loading and unloading represent energy losses due to internal heat generation and are commonly called a hyteresis loss. As successive cycles take place, the changes to resistance to stretching, tensile strength, energy absorption, and permanent set become smaller.

A common type of testing is to subject elastomeric materials to cyclical mechanical stresses. Most materials fail at a stress considerably lower than that required to cause rupture in a single stress cycle. This phenomena is called fatigue. Various modes of fatigue testing in common use include alternating tensile and compressive stress and cyclic flexural stress. Results are reported as plots of cyclic stress amplitude versus number of cycles to' fail. Fatigue testing is reviewed in Billmeyer at page 128.

Elastomeric compositions can include a variety of additives to improve processing, crosslinking. physical properties and age resistance. Such additives include the use of oil. vulcanization agents such as sulphur, acceleration aids to enhance vulcanization, activators to attain the full effect of the organic accelerators. Elastomeric compositions have been filled with a variety of materials including oils and other fillers. Additionally, fillers are used as reinforcement agents to improve physical properties. A widely used form of filler in common rubbers is carbon

black. Reference is made to the Vanderbilt Rubber Handbook for typical elastomeric compositions.

Attempts have been made to stiffen elastomeric compositions by incorporating short fibers. While the fiber stiffened the composition, it was deleterious to properties such as the ability to withstand cyclic strain (fatigue).

Patents disclosing fiber reinforced polymer composites include U.S. Patent Nos. 4.389,361. 4.728,698, 4.711,285, 4.393,154. 4.014.969 and 3.969,568. The patents of interest relating to fiber loaded rubber compositions generally disclose that fibrous reinforcements are used to stiffen, and strengthen elastomeric compositions.

U.S. Patent No. 4,389,361 discloses a process for molding fiber loaded rubber compounds. This patent is directed to an elastomeric compound that has chopped fibers dispersed throughout the compound. The orientation of the chopped fibers within the rubber matrix increases the modulus and strength of the compound. The orientation is achieved by milling the fiber loaded compound to break up the fibers and thereafter mold and then vulcanize the resulting product. The filaments are initially approximately 1.6 inches in length and have a diameter of 11 microns. The resulting composition has fibers of small length of approximately 0.125 inches. The fibers are used as a reinforcing additive to improve physical properties such as tensile strength and to stiffen the composition by reducing elongation and increasing the "low strength modulus". U.S. Patent No. 4,711,285 discloses a bead filler composition which contains short fiber of an organic polymer. It can be from 15 to 70 parts the short fiber based on the rubber. Short fibers are used to increase the elastic modulus of the rubber.

U.S. Patent 4,393,154 discloses a process for blending 5 to 50% by weight of a chopped fiber from

about 0.4 to 1.3 cm in length with 95 to 50% by weight of a particulate unvulcanized rubber. It is a goal of this patent to improve uniform mixing of fibers and rubber.

U.S. Patent No. 3,969,568 discloses aramid flock reinforcement of rubber using a particular adhesive. The composition is disclosed to contain rubber and adhesive compositions and a fibrous reinforcement. The composition has improved physical properties such as compression modulus and lower elongation, and a stiffer rubber.

Elastomeric compositions are known to be useful to make a variety of articles including tires, rubber hose, power tranmission belts (V-belts), flat conveyor belts, and mechanical rubber goods such as engine mounts and vibration suppressors. Typical compositions for such articles are disclosed in Babbit, The Vanderbilt Rubber Handbook. R.T. Vanderbilt Company, Inc. Chapter 11. pp. 644-810 (1988).

SUMMARY OF THE INVENTION

The present invention includes a polyamide fiber from 0.1 to 1.0 inches long having a birefringence value of from 0.02 to 0.04. The fiber preferably has a fiber modulus of less than 1x10 11 dyne/cm2 and more

11 2 preferably less than 0.6x10 dyne/cm . The polyamide is preferably selected from polycaprolactam and poly(hexamethylene adipamide).

The present invention also includes a composition comprising an elastomer and from l to 25 per hundred parts by weight of elastomer (rubber)

(phr), preferably from 2 to 10 phr, and more preferably

4 to 6 phr by weight based on the elastomer of the fiber up to 1 inches long, preferably from .1 to 1 inches long, more preferably from .125 to 1 inches long, and most preferably from .25 to 0.5 inches long.

Preferably, the fiber in general has a fiber modulus of less than 1x10 11 dyne/cm2 as measured by

ASTM-D 2256-80. The fiber is preferably a polyamide fiber having a birefringence value of less than 0.1 preferably from 0.01 to 0.05 and more preferably from 0.02 to 0.04. The birefringence value is a measure of molecular orientation effected by drawing or stretching. The birefringence is measured according to ASTM 858-82.

The composition of the present invention has a sufficient amount of a polyamide fiber having a birefringence value of from 0.02 to 0.04 to result in the composition having a greater fatigue life, as measured according to modified ASTM-D 3479-76 when compared to a composition without the fiber.

In an alternate embodiment of the present invention the composition comprises from 1 to 25 phr of a fiber from 0.1 to 1 inches long having sufficient molecular orignetation to result in a composition having equal or a greater fatigue life, measured according to modified ASTM-D-479-7, when compared to a composition without the fiber. The orientation should be low enough to have equal or better fatigue resistance as the composition without the short fiber, but high enough to improve the stiffness (modulus) of the elastomeric composition.

A preferred composition comprises an elastomer, and 1 to 25 phr of a polyamide fiber from 0.1 to 1 inches long having a birefringence value of less than 0.1 preferably 0.02 to 0.04.

The composition can additionally contain other additives conventionally used in elastomeric composition including but not limited to processing aids, crosslinking agents including curing agents, accelerators and other types of curing promoters, and age resistors. The composition can comprise other types of fillers such as particulate fillers including carbon black as well as extenders such as oil.

The present invention also includes articles made of the above recited composition. Such articles include tires, hose power transmission belts, conveyor belts and various mechanical goods. By mechanical goods it is meant all other applications including motor mounts, gaskets, seals, vibration suppressors, and the like.

Compositions useful to make the articles or components of the articles comprise an elastomer; from 25 to 175 parts per hundred parts of rubber (phr) of a filler; and up to 25 phr of a fiber up to 1.0 inches long having a sufficient molecular orientation to result in the article having a greater fatigue, according to ASTM-D 3479-76 when compared to the article comprising the article without fiber. For the purpose of the present invention this fiber is considered a separate component from a "filler".

Useful compsoitions for articles of the present invention include compositions known in the art such as disclosed in the Vanderbilt Rubber Handbook, supra, further including up to 25. preferably from 1 to 25. and more preferably 2 to 10 phr of the fiber.

Specific compositions and related articles include tire rubber compositions and tires comprising at least one component made of the composition; hose rubber compositions and hose; power transmission belts made of the compositions and belts, coveyer belt compositions and belts made of the compositions

BRIEF DESCRIPTION OF THE DRAWING

Figure 1 is a graph of the heat generation rate, 4

10 Erg/cc/sec versus temperature.

Figure 2 is a cross-sectional drawing of a portion of a tire section.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a composition comprising an elastomer and from 1 to 25 phr of fiber from 0.1 to 1.0 inches in length. The fiber modulus is

11 2 preferably less than 1x10 dynes/cm preferably

11 2 less than 0.6x10 dynes/cm and more preferably from 0.1 to .6x10 11 dynes/cm2. The composition has equal or better fatigue resistance and is stiffer than the elastomeric composition without the fiber.

The improvement can be obtained by controlling the degree of molecular orientation attained during drawing or stretching of the fiber. This property is measured as the birefringence of the fiber.

The composition is preferably a homogeneous distribution of fibers in the elastomeric composition matrix. Preferably, the fibers are randomly oriented. However, the fibers can be oriented. Such orientation can occur or be induced during processing the elastomeric composition. The composition can be made by methods such as coagulation of the elastomer in the presence of the fiber and other components of the composition. The composition can be solution blended. Preferably, the composition is made by melt blending. The elastomeric composition comprising the elastomer and fibers can be cured or crosslinked in accordance with methods known in the art.

Typical conditions for valcanizing natural rubber and/or synthetic rubber compositions including styrenebutadiene rubber compositions are to heat the composition during molding to temperatures of from 250°F to 400°F under pressure of greater than 150 psi preferably greater than 200 psi and typically from 200 to 400 psi. The time to valcanize will vary depending on the size article being treated.

Elastomers useful in the composition of the present invention include elastomers as characterized above in the Background of the Invention. Elastomers include those disclosed in Billmeyer. Textbook of Polymer Science; Babbit, the Vanderbilt Rubber Handbook, published by the R.T. Vanderbilt Company,

Inc, Connecticut. 1978, and the various U.S. Patents listed above including U.S. Patent No. 4,389,361.

Useful elastomers include but are not limited to natural rubber, synthetic polyisoprene, copolymers of styrene and butadiene, copolymers of butadiene and acrylonitrile, copolymers of butadiene and alkyl acrylates. butyl rubber, bromo b .tyl rubber, chlorobutyl rubber, neoprene (chloroprene, 2-chloro-l, 3-butadiene). olefinic rubbers such as ethylene propylene rubber (EPR) and ethylene propylene diene monomer (EPDM) rubbers, nitrile elastomers, polyacrylic elastomers, polysulfide polymers, silicone elastomers, thermoplastic elastomers, thermoplastic copolyesters, ethylene acrylic elastomers, vinyl acetate ethylene copolymers. epichlorohydrin, chlorinated polyethylene, and chemically crosslinked polyethylene, chlorosulfonated polyethylene, fluorocarbon rubber, fluorosilicone rubber, and mixtures thereof.

The fiber can be an fibrous material including monofilament yarn, or multi-filament yarn. Fibers useful in the composition of the present invention are short fibers up to 1 inch long, preferably 0.1 to 1 inch, more preferably 0.125 to 1 inch and most preferably 0.25 to 0.5 inches long. There is from 1 to 25 phr preferably 2 to 10 phr, and more preferably 4 to 6 phr of the fiber in the composition of the present invention. The short fiber filaments are preferably homogeneously distributed in the elastomer. When multi-filament yarn is used, preferably the individual yarn filaments are dispersed.

The fiber filaments useful in the composition of the present invention typically have a diameter of from 0.0001 to 0.01 inches, preferably 0.0004 to 0.002 inches. typical multi-filament yarns contain from 50 to 1500 filaments, preferably 100 to 1000 filaments. The denier per filament is preferably from 1 to 25

preferably 2 to 10, where denier is grams per 9000 meters.

Polyamide fibers useful in the composition of the present invention are preferably drawn or oriented in order to have a birefringence value of less than

0.1, preferably from 0.01 to 0.1, more preferably 0.01 to 0.05 and most preferably 0.02 to 0.04.

Birefringence is an optical term meaning double refraction. It is used in the examination of fibers to measure the degree of molecular orientation effected by stretching or drawing. For the purpose of the present invention birefringence values were measured in accordance with ASTM E 858-82.

The fiber can be selected from the group including acetate based fibers such as cellulose acetate including rayon, acrylic fibers, polyvinyl chloride fibers, fluorocarbon fibers including fibers made from polytetrafluoroethylene, polychlorotrifluoroethylene and a copolymer of fluoropolymers with ethylene and optionally other monomers, nylon including nylon 6 (polycaprolactam) and nylon 6,6 (polyhexamethylane adipamide), thermoplastic polyesters including polyethylene terephthalate, polypropylene, polyurethane, polyvinyl alcohol, polyvinylidene chloride, polyaramids and the like. Preferred polymer are polyamides and polyesters, with polycaprolactam being most preferred.

The polyamide useful as the short fiber of the present invention, has a molecular weight sufficient to form fiber. Preferably, the molecular weight is from 10,000 to 40.000 preferably 20.000 to 35.000 number average molecular weight as measured by membrane osmometry. As noted, preferred polyamides include polycaprolactam and poly(hexamethylene adipamide). Generally, polyamides are polyamides capable of forming fiber selected from the long chain synthetic polymers which have regularly occurring amide groups. Useful

polyamides can be prepared by polymerization of difunctional monomers or equivalently, their cyclized lactam; or by the reaction of a conjugate pair of monomers for example diamide and dicarboxylic acid, or a linear aminoaliphatic acid such as omega-amino undecanoic acid.

Suitable poylactams can be produced by polymerization of lactam molecules of the formula

R - C = O

N 1 /- H

where R is an alkylene group having 3 to 12, preferably 5 to 12 carbon ions.

The polyamide fiber useful in the present invention is preferably spun and drawn in one process to an amount of drawing sufficient to be within a range of elongation to result in the birefringence values of less than 0.04. preferably from 0.01 to 0.04 and most preferably from 0.02 to 0.04. The fiber is considered to be only partially oriented yarn (POY) . Typically, fibers are spun and quenched. Optionally this can be followed by a separate drawing step. In the present process there is a restriction on the total amount that the fiber is drawn. Undrawn fiber can also be used. The yarn can have a denier per filament of from 1 to 50. The yarn preferably has a denier per filament of from 1 to 10, more preferably from 2 to 8. The fiber is from 0.1 to 1.0 inches long, preferably from 0.1 to 0.250 inches long. The birefringence is less than 0.1 preferably from 0.02 to 0.04. The totaL amount the fiber is drawn, whether by stack drawn or in combination with a separate drawn step is such that the

11 2 fiber modulus is less than 1x10 dyne/cm 11 2 preferably less than 0.6x10 dyne/cm .

The fiber can be cut by any suitable means to chop or cut fiber known in the art. A preferred method is to feed the yarn between two rolls. One roll has a plurality of knives parallel to the axis of the roll and perpendicular to the direction of the fiber. The other roll is a backing roll, preferably made of rubber. The knives press against and cut through the fiber as it presses to the nip of the rolls. The necessary pressure to accomplish the cutting is attained by the knives pressing against the fiber which presses against the backing roll.

Preferably the fiber is coated with an adhesive and/or the host matrix elastomeric composition contains an adhesive promoting material which enhances adhesion between the fiber and the host elastomeric composition.

Adhesive compositions known in the art to adhere fiber and fabrics to elastomeric compositions can be used. A preferred composition is based on resorcinol formaldehyde latex. This is preferred when using nylon fiber. When using fiber such as polyester a diisocyanate-epoxy composition is preferred. The diisocyanate-epoxy composition can be used to coat polyester fiber followed by a coating with the resorcinol formaldehyde latex composition. The diisocyanate-opoxy composition is first applied to the fiber and can adhere to resorcinol formaldehyde latex which is used as a second coating. The resorcinol formaldehyde latex can then adhere to the elastomeric composition. The resorcinol formaldehyde latex can be used alone with fibers such as nylon and rayon while the use of the diisocyanate-opoxy system is used with polyaramide and polyesters.

The composition of the present invention results in an elastomeric compound that has equal or greater fatigue life as measured by a cyclic strain test such as the modified ASTM-D-3479-76 test compared to the composition without the fiber.

The modified ASTM-D-3479-76 test. Method B. was used to measure the fatigue resistance of oriented fiber in resin matrix composites. A sample was prepared from a composition formed into a sheet on a laboratory mill roll. The composition is vulcanized (crosslinked) . The sample was 0.6 cm high, and 1 cm wide. The length of the sample was in the milling direction or longitudinal direction of the sheet off of the mill. The sample is long enough so that there is a length of 2 cm between clamps. Fatigue condition used are: strain amplitude; 8.5%; pretension force, 8kg; frequency lOHz. and 130°C. Results are reported in cycles to break.

The short fibers improve the stiffness of the composition. Stiffness is indicated by yarn modulus. Modulus and other tensile properties of the yarn were measured in accordance with ASTM-D-2256-80. There is improved resistance to interface failure between the fiber and rubber due to the use of the adhesive system as well as the properties of the fibers. It is believed that by using the yarn of the present invention, the properties of the fibers are closer to that of the matrix composition that otherwise.

The composition of the present invention has lower heat generation upon cyclic tensile straining. The amount of heat generation during cyclic straining is measured as the hysteresis loss. The hysteresis loss is the area in a loop on a stress v. strain curve. A sample is stressed to a given strain. The stress is removed. A loop is formed between the stress v. strain curve upon straining the sample and the stress v. strain curve upon the stress being released. The area of this loop is lost energy which is characterized as hysteresis energy resulting in heat generation. The heat generation of the sample of the present invention was measured using an Allied High Strain Dynamic Viscoelestometer made by RJS Corporation

of Akron, Ohio. A sample made in the same manner as that used in the modified ASTM-D-3479-76 fatigue test is clamped with a sample 2 cm long between clamps. The sample is cyclically stained ± 2% at a rate of 10 cycles per minute. The temperature is raised from room temperature to 160°C at 2°C/min. The stress strain curve is read on an oscilloscope and the heat generation in erg/cc/sec (corrected for modulus) is measured. Preferably, the composition of the present invention has lower heat generation than a composition which is equivalent except that it does not contain the fiber used in the composition of the present invention.

The fiber of the present invention can be uniformly or randomly aligned in the elastomeric matrix. The fiber can be oriented within the composition by processing such as calandering.

The present invention results in a composition which has improved flexibility, low heat generation and improved resistance to fatigue as well as improved elongation to break. This is attributed to the fiber having the claimed modulus and/or birefringence values, resulting in lower modulus and longer breaking elongation. The fiber has improved flexibility. There is less stress concentration at the fiber-rubber, interface during cyclic straining. The composition is useful in a variety of rubber products which undergo continual cyclic stress including compositions used in in tires and in hose.

The present invention includes articles made of the above recited composition. Such articles include tires, hose poser transmission belts, conveyor belts and various mechanical goods which includes other applications such as motor mounts, gaskets, seals, vibration suppressors, and the like.

Compositions useful to make the articles or components of the articles comprise an elastomer; from 25 to 175 phr of a filler; and up to 25 phr of a fiber

up to 1.0 inches long having a sufficient molecular orientation to result in the composition or article having a greater fatigue, according to ASTM-D 3479-76 when compared to the article without the fiber or where the fiber has a birefringence value of less than 0.1. and in the case of polyamide fiber has a birefringence value of from 0.02 to 0.04. For the purpose of the present invention, this fiber is considered a separate component than "filler".

Preferred fillers include carbon black, silicon dioxide, and zinc oxide. Useful carbon blacks include those reviewed at pages 407-428 of The Vanderbilt Rubber Handbook, supra. Useful silicon dioxide includes clays and fumed silica. Useful clays are listed at pages 429-432 of The Vanderbilt Rubber Handbook, supra.

The compositions of the present invention can include other materials commonly used in rubber compositions. Such materials include vulcanizing agents, curing accelerators, accelerator activators and retarders, antioxidants. antiozonants, processing aids, extenders (oil) plasticizers, softners and tackifiers.

Vulcanizing agents include sulfur, sulfur bearing accelerators, and organic peroxides. Accelerators include thiazole, sulfonamide, morpholine based accelerators, and ultra accelerators such a metal dithiocarbamates, thiurams and xanthates. Activators can include zinc oxides in amounts up to 10 phr (larger amounts can be used and the zinc oxide is a filler). Other activators include alkaline compounds such as litharge, magnesia, amines, certain precipitated calcium carbonates, and the like. Cure retarders include materials such as phthalic anhydride, salicylic acid and sodium acetate. Antioxidant compounds includes amines, phenols and phosphites. Antiozanants include paraphenylenediamine derivatives, and various waxy materials. These materials are generally known in

the art and reviewed in The Vanderbilt Rubber Handbook. supra.

Useful compositions for articles of the present invention include compositions known in the art such as disclosed in The Vanderbilt Rubber Handbook, supra. further including up to 25, preferably from 1 to 25, and more preferably 2 to 10 phr of the fiber.

A composition useful in tires comprises at least one elastomer selected from the group consisting of styrene butadiene rubber, polybutadiene, rubber, natural rubber, synthetic polyisoprene. EPR, EPDM; from 25 to 100 phr of at least one filler selected from the group consisting of carbon black, and silicon dioxide; at least one curing agent; and from 1 to 25 phr of a fiber up to 1.0 inches long having sufficient molecular orientation to result in the article having a greater fatigue life, according to ASTM-D 3479-76 when compared to the composition without fiber. The fiber preferably is a polyamide fiber having a birefringence value of 0.02 to 0.04. The composition can be used in at least one component of the tire.

Figure 2 is a partial cross-sectional view of a typical passenger tire 10. Such tires and their various components are known in the art. For the purposes of the present invention a tire is a toroidal shaped article the elements of which can be made of different rubber based compositions, or fiber rubber composites with long fiber embedded or coated with a rubber composition. The tire can be divided into a tread portion 12. a sidewall portion 14 and a bead portion 16. The tire 10 has a carcass 18 which is long fiber embedded in a rubber coat composition. There are typical two fibrous layers in the carcass in a passenger tire. The carcass has an outside surface 20 and an inside surface 22. In tubeless tires there is a inner liner 24 molded adjacent to the inside surface 22. A belt 26 is located adjacent to the carcass 18 in

the tread portion 12 and extends circumferentially around the tire. The belt is made of long relatively stiff fiber embedded in a belt coat compound. There can be at least one belt layer and there are typically two belt layers in a passenger tire.

The tread portion 12 has a crown 28 and a shoulder 30. The belt 26 extends generally from shoulder to shoulder of the tire. In each shoulder 30 the belt has a circumferential belt edge 32. There can be a belt overlay 34 on the side of the belt opposite to the carcass 18. This is a layer of long fibers embedded in a rubber composition. The overlay composite is not as stiff as the belt in order to make transition from the belt to the undertread.

Adjacent to the overlay on the side opposite the carcass 18 is an undertread 36 and adjacent to the undertread is the tread 38. The undertread 36 and the tread 38 extend circumferentially around the tire in the tread portion 12.

There can be a belt edge cushion 40 located at each belt edge 32 and extending circumferentially around the tire. This helps to cushion the stiff and sometimes sharp belt edge to prevent the tire from separating at that location.

The carcass 18 extends from the tread portion 12 to the sidewall portion 14 and turns up around the bead 42 in the bead portion 16. The portion of the carcass 18 which turns up is called the turn-up 44. There can be a rubber compound above the bead 42. This is called the bead filler 46. At the outside surface of the turn-up 44 there can be a fabric embedded in a rubber coat or matrix composition. This helps to protect and maintain the turn-up. This element is called the chaffer 48.

On the outside of the carcass 18 between the shoulder and the bead 16 is a sidewall 50.

The fiber of the present invention can be including the rubber compositions useful in various tire components including the tread, overlay, belt edge, bead filler, chaffer, sidewall and belt coat.

Useful compositions to make hose rubber comprise at least one elastomer selected from the group consisting of natural rubber. EPR, EPDM, styrene butadiene rubber, nitrile rubber, and synthetic polyisoprene; from 25 to 175 phr of at least one filler selected from carbon black, zinc oxide, and silicon dioxide; at least one curing agent; and from 1 to 25 phr of a fiber up to 1.0 inches long having sufficient molecular orientation to result in the composition having a greater fatigue life, according to ASTM-D 3479-76 when compared to the hose composition without fiber. The fiber is preferably polyamide having a birefringence value of from 0.02 to 0.04.

Useful compositions to make power transmission belt comprising at least one elastomer selected from the group consisting of choroprene rubber, styrene butadiene rubber, natural rubber, and synthetic polyisoprene; from 25 to 100 phr of at least one filler selected from carbon black, silicon dioxide, and zinc oxide; at least one curing agent; and a composition comprising an elastomer and from 1 to 25 phr of a fiber up to 1.0 inches long having sufficient molecular orientation to result in the having a greater fatigue life, according to ASTM-D 3479-76 when compared to the composition without fiber. The fiber is preferably polyamide having a biref ingence value of from 0.02 to 0.04.

Useful compositions to make conveyor belts comprise at least one elastomer selected from the group consisting of natural rubber, synthetic polyisoprene. polybutadiene. epichlorohydrin. chloroprene. EPR. EPDM. nitrile rubber, and butyl rubber; from 25 to 100 phr of at least one filler selected from the group consisting

of carbon black, silicon dioxide, and zinc oxide; at least one curing agent; and from 1 to 25 phr of a fiber up to 1.0 inches long having sufficient molecular orientation to result in the composition having a greater fatigue life, according to ASTM-D 3479-76 when compared to the belt the composition without fiber. Preferably the composition comprises a polyamide fiber having a birefringence value of from 0.02 to 0.04.

Several examples are set forth below to illustrate the nature of the invention and the manner of carrying it out. However, the invention should not be considered as being limited to the details thereof. All parts are by weight unless otherwise indicated.

Examples A useful method to make fiber of the present invention is to extrude polycaprolactam having a nominal formic acid viscosity (FAV) of about 90 through a conventional spinning pot having a round pack filter and a spinnerette. The spinnerette had 204 capillaries. The capillary dimensions were 0.040 inches length x 0.040 inches diameter. The extrusion temperature was 265°C ± 3°C and the take-up speed was about 2800 meters per minute. The fiber was quenched with air using a radial inflow quench as the filaments travel down through a quench stack (tube). The stretching or drawing of the fiber occurred while it was moving through the stock. The amount of draw was controlled by the ratio of polymer throughput to the take up speed of the fiber. A through put of 48 pounds per hour produced a 6 denier per filament (dpf) product. A throughput of 60 pounds per hour produced an 8 dpf product. Lubricating oils were applied using a finished applicator roll, and the yarn taken up on a speed controlled winder.

Examples 1-7

Following are examples of polycaprolactam fibers useful in the present invention. The fibers of

Examples 1-6 were made from polycaprolactam having a nominal FAV of about 90. Examples 1 and 3 were made using the above described process. Example 2 was made using a modified spinnerette to produce a fiber with about 3 dpf. The fiber of Example 7 was made of fiber grade poly(ethylene terephthalate) having a nominal intrinsic viscosity of about 0.90.

Examples 1-3 were nylon 6 fibers only drawn as they moved through the stack. Examples 4 and 5 were nylon 6 fiber which were initially undrawn at low stack drawn (estimated take-up speed of 300-500 meters per minute). This had a birefringence value of about 0.015. This yarn was then drawn in a separate step using pairs of godet rolls with speeds selected such that the draw ratio was about 2:1. Draw ratio is the final unit length divided by the original unit length. Example 6 is nylon 6 fiber drawn to about 90% of its maximum draw ratio in a separate step after leaving the stock. The draw ratio was between 4:1 and 5:1. This is typical of high strength nylon 6 used for tire cords. Example 7 is poly(ethylene terephthalate) (PET) fiber only drawn as it moved through the stock to give equivalent elongation and tensile strength to the Examples 1-3.

Stress strain properties were measured according to ASTM-2256-80. Free shrink was measured according to

ASTM-885-85. Birefringence was measured according to

ASTM-858-82. In Table 1 the following abbreviations were used: BIREFRIN - birefringence; DPF - denier per filament; UTS - ultimate tensile strength; and Free Sh

- free shrinkage. The results are summarized in Table

1 below:

The fibers of Examples 1-7 were coated with a resorcinol formal dehyde latex (RFL) adhesive system in a single end treating unit. Example 7 was precoated with a diisocyanate epoxy composition. The resulting fibers were then cut to 1/4 inch length. The cut fibers were melt blended in a rubber composition using a laboratory internal mixer. The composition contained 100 phr natural rubber (parts per hundred of rubber). 70 phr of filler (carbon black and silica); a resorcinol bonding agent, a cobalt salt additive; 5 phr pine tar and a sulfur and sulfonamide curing system. Each example contained 6 phr of fiber. The melt blended composition was cured at 290°F for 90 minutes into sheets useful for testing for fatigue resistance

according to the modified ASTM D3479-76 test reviewed above. Tear testing was conducted according to ASTM D3182. Results are summarized in Table 2 below. Comparative 1 (Corap 1) was the rubber composition without any short fiber.

Tear (psi)

482 365 333 333 348

287

Compositions were made based on the same rubber composition as in Examples 8-14 above using the same process. Example 15 contained the same nylon 6 as used in Example 1. Example 16 contained the fully drawn nylon 6 as used in Example 6. Comparative 2 was the rubber composition without short fiber. Comparatives 3-5 were compositions containing fibers having a fiber modulus of greater than 1x10 dyne per square cm according to ASTM D2258-80. Comparative 3 contained Santoweb® cellulose fiber mode by Monsanto. Comparative 4 was PET fiber having and intrinsic viscosity of about 0.9 spun and drawn to a draw ratio of between 4:1 and 5:1. Comparative 5 was Kevlar® polyaramide, grade 29 fiber sold by DuPont. All of the fiber was about 1/4 inch in length.

The compositions were tested for fiber modulus according to ASTM-D 2256-89; fatigue resistance according to modified ASTM-D 3479-76, and Examples 15 and 16 and Comp 2 for heat generation according to the process recited above. The fiber modulus and fatigue resistance are reported in Table 3 below. The heat generation results are shown in Figure 1 for Ex. 16 (N6), Comp. 2 (rubber composition without fiber), and Comp. 4 (PET). The testing conditions included testing in at a strain amplitude of 2%, at 10 cycles per second, in the longitudinal fiber direction. Results are corrected for modulus, and reported.

*rubber tested without fiber

A review of Table 2 and 3 show that where the fiber modulus was lower than 1x10 11 dynes/cm2 the fatigue resistance was equal to or better than the comparative rubber without fiber. When nylon 6 fiber has a biref ingence value below 0.05 the fatigue resistance was much better than the control.

Examples 17-29

The following compositions useful in the indicated articles, disclosed in The Vanderbilt Rubber

Handbook, supra, (VRH) can additionally contain 5, 10, or 15 phr of polyamide fiber from 0.1 to 0.5 inches long and having a birefringence value of from 0.02 to

0.04. Amounts are in parts by weight. ^'

Trademarks, standard names, grades, and common names of materials are defined in VRH. Following is a brief summary of the designations used:

NR natural rubber

IR synthetic polyisoprene

SBR styrene butadiene rubber

BR polybutadiene rubber

SMR Standard Malaysian Rubber

CR neoprene (chloroprene)

EPR ethylene propylene rubber

EPDM ethylene propylene diene monomer rubber

CBTS DURAX;

N-cyclohexyl-2-benzothiazolesulfenamide

OBTS AMAX; N-oxydiethylenebenzothiazole-2- sulfenamide

MBTS ALTAX; benzothiazyl disulfide MBSS MORFAX; 4-morpholinyl-2-benzothiazole disulfide

TMTD METHYL TUADS; Tetramethylthiuram disulfide

VANAX NS N-tert-butyl-2-benzothiazolesuIfenamide ETHYL Tetraethylthiuram disulfide TUADS VANAX NP Activated thiadiazine VANAX A 4,4'-dithiomorpholine MBT CAPTAX; mercaptobenzothiazole TMTM UNADS; Tetramethylthiuram monsulfide TDEDC ETHYL TELLURAC; tellurium diethyldithiocarbamate

ETHYL Cadmium diethyldithiocarbamate

CADMATE

ZDMC Zinc dimethyuldithiocarbamate (Methyl

Zimate)

TMQ AGERITE RESIN D; Polymerized l,2-dihydro-2.2.4-trimethylquinoline

ADPA AGERITE SUPERFLEX;

Diphenylamine-acetone reaction products, liquid

ODPA AGERITE STALITE S; Do-OCtyl diphenylamine

AGERITE SUPERLITE; Mixture of polybutylated bisphenol A

ANTOZITE 67 N-(l,3-dimethylbutyl)-N'-phenyl-p-phenyl enedia ine REOGEN A mixture of an oil soluble sulfonic acid of high molecular weight with a paraffin oil

SUNOLITE Anti sun, checking wax made by the

Witco Chemical Co.

Carbon black designations and nomenclature are consistent with ASTM designations according to Recommended Practice D2516 and/or industry standards as presented in VRH.

EXAMPLE 17. 18

Passenger Tire Treads Composition (VRH.p 650).

EXAMPLES 19 . 20

Passenger Tire Black Sidewalls Compositions (VRH. p. 651.

EXAMPLE 21

Tire Bead Insulatio Compositionn (VRH. p. 657)

Oil Resistant. Jacketed. V-Belt Composition (VRH. p. 700).

EXAMPLES 25. 26

Conveyor Belt Compounds (VRH, P. 704) useful for belt covers.

Ex. 25 Ex. 26

EXAMPLES 27. 28

Conveyor Belt Compositions useful as friction and skim coat. (VRH. P. 705)

EXAMPLE 29

Rubber-Reclaim Steam House Tube and Cover Compositions (VRH. p. 719)

E . 29