Synthetic Filaments Coated With A Lubricating Finish

Abstract

A lubricating finish composition for filaments, yarns and cords used as reinforcement in rubber articles is composed of a polyorganosiloxane oil and a microcrystalline or polyalkylene wax dispersed in a dialkyl phthalate oil having 8 to 14 carbon atoms in each of the alkyl groups. A desirable combination of good adhesion and fatigue resistance is provided in reinforced rubber tires.

Description

BACKGROUND OF THE INVENTION

This invention relates to yarns and cords composed of synthetic filaments having a lubricating finish composition on their surfaces. More particularly, it concerns filaments coated with a finish which are particularly useful for industrial yarns and cords used as reinforcement in rubber tires.

Vehicle tires are subjected to stresses and flexes which cause gradual physical breakdown in filaments of reinforcing cords, a phenomenum called "fatigue." As pointed out in Patterson U.S. Pat. No. 3,475,204, resistance to fatigue can be improved by applying a lubricating finish to the filaments, but it is quite difficult to find a satisfactory finish which does not cause a serious lowering of cord-to-elastomer adhesion. Finish compositions containing a wide variety of oils and added materials have been tried in attempts to obtain adequate adhesion with improved resistance to fatigue.

Several processing characteristics are desirable for a satisfactory lubricating finish composition. It should be one which is readily prepared and is stable on standing, without phase-separation in layers. It should be easily applied to form a uniform coating on filaments, so a reasonably low viscosity without use of volatile components is desirable to avoid having to dry the applied coating. It should not form appreciable deposits on hot rolls used in after-treatments, since a rapid rate of deposit formation would cause unacceptable process interruptions. It should not fume objectionably on hot rolls used in after-treatments. It should not have a deleterious effect on the normal physical properties of cords prepared for use in tires and other reinforced articles.

SUMMARY OF THE INVENTION

The present invention includes synthetic filaments, yarns and cords having the surfaces of the filaments coated with a lubricating finish composition which has satisfactory processing characteristics and provides a desirable combination of rubber-adhesion and fatigue resistance properties when the cords are used as reinforcement in tires.

In accordance with the invention, the synthetic filaments are coated with a lubricating finish composition containing linear polyorganosiloxane oil and microcrystalline wax or polyalkylene wax dispersed in dialkyl phthalate oil carrier having from 8 to 14 carbon atoms in each of the alkyl groups of the phthalate ester or esters. The proportions of the specified ingredients are from 0.1 to 25 weight percent of the polyorganosiloxane oil, from 0.1 to 10 weight percent of the wax, and at least 65 weight percent of the dialkyl phthalate oil carrier.

The finish composition may optionally contain an organic antioxidant at a concentration of about 0.1 to 3 percent by weight. Suitable antioxidants are those of the sterically hindered phenolic type, such as 2,2'-thiobis(4-methyl-6-t-butylphenol); 2,2'-methylene-bis(4-methyl-6-tertiary-butylphenol); 4,4'-thiobis(2-t-butyl-5-methylphenol); and 4,4'-butylidene-bis(6-t-butyl-m-cresol).

Suitable oil carriers are the synthetic, non-volatile, di- esters of orthophthalic acid and fatty alcohols containing from about 8 through 14 carbon atoms in their alkyl chain. A particularly preferred oil because of its ease of use as a medium for forming the dispersion of the wax consists essentially of diundecyl phthalate.

Suitable polyorganosiloxane oils are of the linear type polymer wherein the organo-substituents are selected from the group consisting of lower alkyl and aryl substituents, particularly wherein they are methyl or phenyl.

Suitable polyalkylene waxes and microcrystalline waxes for this invention are those described in Columns 1 and 2 of U.S. Pat. No. 3,155,537. Among the polyalkylene waxes, the polyethylene waxes are preferred. These polyethylene waxes may be either oxidized or non-oxidized and preferably have a melting point (ASTM E-28-51T) between 80.degree.C. and 200.degree.C., a penetration number (100 gms./5 sec./77.degree.F.) between 1 and 10 an acid number between 9 and 50, and a saponification number between 9 and 100.

The microcrystalline waxes may be either oxidized or non-oxidized and preferably have a melting point (ASTM D-127-49) between 80.degree.C. and 150.degree.C., a penetration number (100 gms./5 sec./77.degree.F.) between 1 and 10, an acid number between 10 and 50, and a saponification number between 30 and 100.

DESCRIPTION OF THE INVENTION

The finish composition may be applied to filaments, yarns or cords at any convenient stage of processing by known techniques, such as by wiping contact with a rotating roll dipping into the finish. It is preferably applied to yarns as an overlay finish following a drawing operation which increases molecular orientation and tenacity. The finish normally may be applied at a concentration of from about 0.1 to 5 percent, preferably 0.5 to 1.5 percent, based on the weight of the filaments.

Any of the known synthetic filaments may be used in this invention. The invention is of particular value when used on filaments in yarns and cords of high tenacity for use in reinforcement of elastomeric structures, i.e. tires. Preferred filaments include those of polyamides and of polyesters. Particularly suitable polyamides include the nylons such as 6-nylon and 66-nylon, and also the aromatic polyamides such as poly(meta-phenylene isophthalamide) and poly(p-phenylene-terephthalamide). The invention is particularly useful for polyester filaments of poly(ethylene terephthalate) which are to be subjected to very high temperatures during the usual cord hot-stretching employed in the manufacture of tires. In such preparations, temperatures as high as 470.degree.F. (243 .degree.C.) are employed.

The finish composition is conveniently prepared by dissolving the solid wax in the heated ester, stirring in the remaining ingredients and allowing the mixture to cool with stirring. Optionally, the polysiloxane may be stirred in after cooling. The solid wax precipitates as a fine dispersion from the solution as it cools. The particle size, and hence the stability and viscosity of the resulting dispersion, depend on the relative solubility-temperature relationship between the wax, the ester and the rate of cooling. Diundecyl phthalate is particularly preferred in this respect because of the ready manner in which the wax dissolves in the hot ester and forms a stable dispersion upon cooling. Where a phenolic antioxidant is employed, it is preferred that the heating not be continued after the addition of the antioxidant.

For a finish of the composition of Item F-O of Example I, the effect of cooling time on finish viscosity is demonstrated by the composition having a Brookfield viscosity in centipoise at 28.degree.C. of 181 when cooled from 110.degree. to 30.degree.C. in 15 minutes; the viscosity is 50 for cooling in 133 minutes and 45 upon cooling 151 minutes. The preferred heating temperature is in the range of 105.degree.-110.degree.C. The composition is actually a three-phase dispersion system in that the polysiloxane oil is insoluble in both the wax and the ester.

The most preferred ester is diundecyl phthalate, the di-ester of orthophthalic acid and undecanol, wherein the alcohol is about 65 percent linear and 35 percent branched chain alcohols which are 99.5 percent undecanol.

A preferred wax is an emulsifiable polyethylene wax of the "oxidized type" containing both ester linkages as represented by saponification value and free carboxyl groups represented by an acid value. Such polymers may be obtained either by oxidation processes or by copolymerization with the appropriate small amounts of modifiers. Such materials are solids which generally soften in the region of 100.degree.-110.degree.C. Preferred ranges are an acid number of 12-18, a viscosity in centipoise at 125.degree.C. of 900-1500 and a molecular weight in the region of 3,000.

A typically preferred polysiloxane is polydimethyl-siloxane having a viscosity at 77.degree.F. ( 25 .degree.C.) of 100 centistokes, a specific gravity of 0.968 and a refractive index of 1.4030 with a surface tension of 20.9 dynes per centimeter, all at 77.degree.F. ( 25 .degree.C.).

EXAMPLE I

This example demonstrates improved flex fatigue performance in combination with high levels of adhesion which results from the combination of the wax and polysiloxane lubricants of the invention.

The test finishes are applied to finish-free poly(ethylene terephthalate) high tenacity, industrial yarn (Type 68 Dacron, E. I. du Pont Company, Inc.) of 1,000 denier and 192 filaments on a coning machine using a conventional rotating finish applicator roll which is partially immersed in a reversoir of the finish composition. The finish content on yarn (FOY) is controlled by manipulating the rpm of the applicator roll. Three ends of the treated yarn for each item are twisted and plied into a 1,000/1/3 ply cord construction using 8 turns/inch Z twist (3.15/cm.) in the singles and 8 turns/inch (3.15/cm.) S twist in the plying.

Cords are prepared in this way from the finish compositions as shown in Table I.

TABLE I ______________________________________ % Ingredients.sup.a Item % FOY DUP Wax Si AO ______________________________________ F-O 1.1 97 2 0.5 0.5 F-1 1.1 97.5 2 0 0.5 F-2 0.9 99 0 0.5 0.5 F-3 0.6 99.5 0 0 0.5 ______________________________________ .sup.a DUP = diundecyl phthalate wax = emulsifiable polyethylene wax as described above Si = polydimethylsiloxane, 100 cs AO = 2,2'-thiobis(4-methyl-6-t-butylphenol) % by weight of the total composition

The cords are dipped and hot-stretched using a two-step adhesive system with an epoxide/isocyanate subcoat and an RFL overlay of the type generally described in U.S. Pat. No. 3,307,966. For the subcoat the cord is treated at 470.degree.F. (243 .degree.C.) under an elongation of 8 percent and relaxed 4 percent at a temperature of 425.degree.F. (218 .degree.C.) for the RFL application. Physical properties of the dipped and stretched cords are shown in Table II.

TABLE II ______________________________________ Break % Adhes. Break Strength, Elong., Tenacity, Item Pickup lbs. (kg.) % gpd F-0 3.4 50.5 ( 23.0) 15.3 7.1 F-1 3.4 50.6 ( 23.0) 16.2 7.1 F-2 3.3 49.0 ( 22.3) 15.5 7.1 F-3 4.1 49.1 ( 22.3) 15.3 7.0 ______________________________________

Relative flex fatigues of the cords in a typical test rubber stock of 50 percent natural and 50 percent styrene/butadiene rubber are tested using the disc fatigue method as described in U.S. Pat. No. 3,475,204, Col. 4, lines 17-35. Adhesion properties are compared at 140.degree.C. using a two-ply strip adhesion test of the type described in U.S. Pat. No. 3,307,966, Col. 3, lines 43-58. Results are shown in Table III.

TABLE III ______________________________________ Two-Ply Adhesion, Fatigue, % Strength Item lbs./in. (kg./cm.) Loss ______________________________________ F-0 59 (10.6 ) 32 F-1 63 (11.3 ) 59 F-2 60 (10.7 ) 75 F-3 58 (10.4 ) 77 ______________________________________

It is seen that Item F-0 containing both the wax and the poly(dimethylsiloxane) provides equivalent adhesion with a synergistic improvement in flex fatigue properties as shown by the lowest strength loss in the disc fatigue test.

EXAMPLE II

This example compares the processability and dispersion stability of a finish of the invention with similar finishes employing a different ester not of the invention.

A finish composition the same as for Item F-0 in Example I is compared with ones of similar composition except instead of the diundecyl phthalate it is replaced by the same amount of isocetyl stearate (also called hexadecyl stearate) as Item A and by polyoxyethylene of 300 average molecular weight fully esterified with lauric acid as Item B.

Upon standing 54 hours upon cooling Item A shows a solid phase phase layer separated at the bottom of the container; Item B shows a layer of solid phase separation at the top of the liquid. Item F-0 remains as a uniformly, turbid oil with no appearance of phase separation in layers.

When applied to filaments of poly(ethylene terephthlate) following drawing and prior to contact with hot rolls, only Item F-0 processes acceptably, with Items A and B resulting in an unacceptably rapid rate of deposit formation on the rolls.

Claims

We claim:

1. A synthetic filament coated with a lubricating finish composition consisting essentially of a linear polydimethylsiloxane oil and microcrystalline or polyalkylene wax dispersed in dialkyl phthalate oil carrier having from 8 to 14 carbon atoms in each of said alkyl groups, the proportions of the specified ingredients being from 0.1 to 25 weight percent of the polydimethylsiloxane oil, from 0.1 to 10 weight percent of the wax and at least 65 weight percent of the dialkyl phthalate oil carrier.

2. The coated filament defined in claim 1 wherein the finish composition contains from 0.1 to 3 weight percent of an organic antioxidant.

3. The coated filament defined in claim 1 wherein the dialkyl phthalate oil carrier consists essentially of diundecyl phthalate.

4. The coated filament defined in claim 1 wherein the wax is a polyethylene wax having a melting point between 80.degree.C. and 200.degree.C., a penetration number between 1 and 10, and a saponification number between 9 and 100.

5. The coated filament defined in claim 1 wherein the wax is a microcrystalline wax having a melting point between 80.degree.C. and 150.degree.C., a penetration number between 1 and 10, an acid number between 10 and 50, and a saponification number between 30 and 100.

6. The coated filament defined in claim 1 wherein the polydimethylsiloxane oil is a polydimethylsiloxane having at 25.degree.C. a viscosity of 100 centistokes, a specific gravity of 0.968, a refractive index of 1.4030, and a surface tension of 20.9 dynes per centimeter.

7. The coated filament defined in claim 1 wherein there is from 0.1 to 5 weight percent of the finish composition, based on the weight of the filament.

8. The coated filament defined in claim 1 wherein the synthetic filament consists essentially of polyethylene terephthalate.

9. An industrial yarn composed of the coated filaments defined in claim 1.

10. A high-tenacity tire-cord composed of the coated filaments defined in claim 1.