WO2010143017A1

WO2010143017A1 - Multi-ply synthetic monofilament reinforcing cords

Info

Publication number: WO2010143017A1
Application number: PCT/IB2009/052479
Authority: WO
Inventors: M.Zafer Efes; Berrin Yilmaz; Luiz Gustavo Da Costa Pino
Original assignee: Kordsa Global Endustriyel Iplik Ve Kord Bezi Sanayi Ve Ticaret A.S
Priority date: 2009-06-10
Filing date: 2009-06-10
Publication date: 2010-12-16

Abstract

A multi-ply synthetic monofilament cord for tire reinforcement is made of nylon 66 monofilament fibers with 3 to 7 monofilaments in the same body. The cord characteristics are such that the monofilaments are twisted around each other by 50 - 200 tpm twist levels. Each monofilament has minimum 0.23 mm up to maximum 0.50 mm diameter, or minimum 475 dtex upto 2200 dtex. Such multi-ply synthetic monofilament cords have potential application as carcass reinforcement for tires, breaker reinforcement for tires, belt protective layer for radial truck and bus tires, belt reinforcement for tires and carcass for aircraft tires. The monofilaments are synthetic organic materials like nylon 66 or PET (polyethylene terephtalate).

Description

MULTI-PLY SYNTHETIC MONOFILAMENT REINFORCING CORDS

FIELD OF THE INVENTION

Present invention relates to tire reinforcing cords made of synthetic monofilament fibers.

BACKGROUND OF THE INVENTION;

A conventional tire cord is usually made of multifilament synthetic fibers like polyhexamethyleneadipamide (Nylon 66), polyethylene terephtalate (PET), viscose rayon and other materials for carcass, belt, breaker, overlay reinforcement in tires.

U.S. Pat. No. 5,743,975 teaches monofilament tire cord fabric utilized preferentially in radial medium truck tire as a top belt layer by replacing the steel belt. If there is a puncture on the tire and if it is deep enough to expose the steel reinforcement cords of the belt package to water and air, such exposure can cause the belt package to corrode. The corrosive material in the belt package has been replaced with a non-corrosive material like high dtex obround shaped monofilament nylon 66 . The monofilaments investigated for this purpose have min. 2200 dtex, tenacity 3.5 g/denier and max. 10000 dtex nylon 66 as a single monofilament. The single ply obround nylon monofilaments mentioned in this document are subject to cuts from sharp objects if the puncture is deep enough and such cuts will eventually grow and lead to monofilament breakages.

U.S. Pat. No. 6,634,398 teaches a chip resistant pneumatic tire especially off the road tires (OTR) and heavy duty off the road tires in which a reinforced rubber sheet with round shaped organic filaments or cords are disposed over the steel belts or breaker. The claimed organic filaments or cords have at least 2000 denier monafilaments. The dipping of the monofilaments were epoxy subcoated then RFL topcoat.

SUMMARY OF THE INVENTION

In accordance with the present invention a multi-ply synthetic monofilament cord with 3 to 7 plies were developed with improved properties compared to both synthetic single monofilaments or synthetic multifilament cords for tire reinforcement.

The multi-ply synthetic monofilament cord of the present invention has better adhesion properties compared to synthetic single monofilaments due to increased surface area for adhesion to rubber and also the cord of the present invention provide better cut resistancy over single synthetic monofilaments in case of a puncture of a sharp object cutting the surface of such cords. The surface cut of a single synthetic monofilament will eventually grow and end up with brakage while the cut on the surface of a multi-ply synthetic monofilament shall have cut resistance with the presence of other plies under such conditions.

The cord of the present invention also has better dynamic properties compared to the commonly used multifilament synthetic cords for tire reinforcement. The cord of the present invention has little heat generation, better fatigue resistance, better dynamic adhesion, improved bending stiffness and compression resistance compared to synthetic multifilament cords.

DEFINITIONS

"Twist level" indicates number of twist per meter (tpm)

"Multi-ply synthetic monofilament" refers to cords made by twisting at least 3 synthetic monofilaments in the same body.

"Thickness" is the diameter of single monofilament or multi-ply monofilament cord

"Tenacity" is the breaking strength per unit linear density of the single monofilament or multi-ply monofilament cord.

"Shrinkage" is the thermal retraction percentage of single monofilament or multi-ply monofilament cord at 177⁰C, 0.045 g/dtex tension and for 2 minutes.

"Dip A " is the adhesive system consisting of a Resorcinol-Formaldehyde-Latex (RFL) solution in which the cord is dipped in RFL solution twice.

"Dip B" is the adhesive system consisting of a Resorcinol (R) solution and a Resorcinol- Formaldehyde-Latex (RFL) solution in which the cord is dipped first in R solution then RFL solution.

DETAILED DESCRIPTION OF THE INVENTION

The multi-ply synthetic monofilament reinforcing cord of this invention comprise 3-7 ply and round cross sectional nylon 66 (polyhexamethyleneadipamide) monofilament fibers which are twisted together. The multi-ply synthetic monofilament cord comprises an RFL based adhesive.

The present invention relates to tire reinforcement cords made of 3-7 ply round shaped synthetic monofilaments which are twisted together. This type of structure has advantage over surface cut propagation and cord breakage in case of a puncture of a sharp object cutting the surface of such cords having multiple monofilaments, therefore the cord of this invention is used as belt protective layer in radial truck and bus tires. The monofilaments are synthetic organic materials like polyhexamethyleneadipamide (nylon66) and polyethylene tereplitalate (PET). Monofilaments used for the multi-ply monofilament cord of this invention are polyhexamethyleneadipamide (nylonόό), having round shaped cross-section, having diameters between 0.23 to 0.50 mm, the dtex range is 475 to 2200 dtcx. Monofilaments have a tenacity of min 60 cN/tex, whereas in general the tenacities are around 63-67 cN/tex. The elongation at break values are between 26-29%, the thermal shrinkage of monofilaments are around 2.5%. Monofilaments are twisted together with 3 to 7 plies at a twist level of 50 to 200 tpm, either in Z or S direction to make a multi-ply synthetic monofilament cord. Monofilaments are not twisted individually.

Multi-ply synthetic monofilament cords of this invention are dipped with an water based adhesive solution of Resorcinol -formaldehyde - latex (RPL) to produce a dipped cord having an adhesive property to the rubber compound of the tire. Cords of this invention are double dipped with RFL to increase the dip pick up of the cords. Coating the surface of the cord with an adhesive layer is becoming critical for a single monofilament due to lesser amount of surface area for adhesion compared to a multi-ply monofilament cord.

In an alternative embodiment, in addition to double RFL dipping, first dip was replaced by resorcinol (R) solution to activate the surface of the monofilament surface as a subcoat and as second dip RFL solution was used.

During dipping of the multi-ply synthetic monofilament cords of this invention with the adhesive solution the following parameters were used; drying temperatures of 140-160° C for 80-100 sees, curing temperatures of 220-240° C fo 40-120 sees. The tension is varied between 0.3-3.0 g/dtex during curing stage.

TESTING METHODS

Tensile and shrinkage test measurements are made after conditioning of dipped cords at 24+- 2⁰C, 24 hours at 55+-5%RH. Tensile testing is made by Instron instrument where the speed is 300 mm/min, gap distance is 254 mm and at room temperature.

Thermal shrinkage is measured by the Testrite instrument at 177⁰C, 2min, 0.045 g/dtex pretension.

The adhesion property of the cords is measured by pull out adhesion, where cords are pressed at 140°C for 20 mins, the cord embedded length is 6 mm.

The fatigue performance of the dipped cords are measured at room temperature and 70°C with different number of cycles like 130,000 , 150,000 , 170,000. Firestone Shoeshine testing instrument is used for this purpose. Three fatigue sample is prepared for each cord sample, one of them is tested for the properties before fatigue. The remaining two is fatigue tested, then soaked into toluene, dried then tested to analyse after fatigue performance. EXAMPLE;

Two examples of 3 ply nylon 66 monofilament greige and dipped cords made of 0.23 and 0.30 mm thickness monofilaments are given in Table 1. Nylon 66 multifilament cords of 1400*1 and 1400*2 construction are given as comparison. Multi-ply synthetic monofilaments have twist level of 50 tpm in Z direction. The breaking strengths of cords are retained after dipping, i.e. almost 100% conversion is obtained. The elongation at break values are sligthly decreased depending on the dipping conditions. The shrinkage values is possible to adjust with dipping conditions same as breaking elongations. There is a slight increase on the diameter of dipped cord compared to greige cord. Due to higher elongation at break values of the cords of this invention compared to synthetic multifilament cords the multi-ply synthetic monofilament cords of this invention is used as breaker in tires for the higher impact resistance and the breaking energy value

TABLE 1

Properties of 3 ply nylon 66 monofilament greige and dipped cords and comparable nylon 66 multifilament cords

Some examples of the fatigue behaviour of multi-ply nylon 66 monofilaments are given in Table 2, where the examples are not limited with those. RFL dipped multi-ply nylon 66 monofilament cords are fatigue tested at 7O⁰C for 130,000 cycles. Nylon 66 multifilament cords of 1400*1 and 1400*2 construction are given as comparison. Both multifilament and multi-ply monofilament cords loose adhesion after they ungergo certain fatigue conditions. However, the adhesion loss in the multi-ply monofilament cord of this invention is less than that of multifilament cord. Furthermore in terms of the breaking strentgh, the loss in multiply monofilaments is less than that of multifilament case. The cycle is increased upto 170,000 cycle at 7O⁰C and the multi-ply monofilaments still result in higher tensile and adhesion values compared Io multifilament cords. Since synthetic multifilaments being composed of at least 100 fine filaments, the friction between the filaments causes heat generation. Generated heat causes degradation of adhesion property and breaking strentgh in synthetic multifilament cords, especially aircraft tires reinforced with synthetic multifilament cords generate heat therefore the multi-ply synthetic monofilament cords of this invention is used as carcass for aircraft tires. 3-7 ply synthetic monofilaments do not have so much factional surfaces, so less heat is generated upon fatigue testing. Therefore the multi-ply synthetic monofilament cords of this invention have superior fatigue performance, lower heat generation compared to synthetic multifilament cords and is used as carcass in tires. Also the cord of the present invention is used as carcass material in tires due to its higher compression resistance compared to synthetic multifilament cord which is important mainly in tire crown area.

TABLE 2

Fatigue test results at 7O⁰C, 130,000 cycle of 3 ply nylon 66 monofilament cords and comparable dtex nylon 66 multifilament cords.

TABLE 3

Heat aged adhesion of 3 ply nylon 66 monofilament cords

Cords were heat aged at 121 C⁰ for 2, 6, 15, 24 hours. Dip B has better heat aged adhesion results.

In another experiment, the bending stiffness of different cords were measured. It was observed that the bending stiffness of the multi-ply nylon 66 monofilament cord of this invention was greater than the bending stiffness of equivalent dtex nylon 66 multifilament cord and smaller than the bending stiffness of equivalent dtex single nylon 66 monofilament. Another advantage of the present invention is that the multi-ply synthetic monofilament cord has 3 7 plies of monofilaments, therefore it is easier to adjust the bending stiffness of the reinforcement material. Belt reinforcement materials of tires requires to have higher bending stiffness for generating handling force, providing improved traction and tread wear performance. The multi-ply synthetic monofilament reinforcing cord of this invention has higher bending stiffness and higher compression resistance compared to synthetic multifilament cords and is used as belt in tires.

Claims

What is claimed is

1. A multi-ply synthetic monofilament reinforcing cord comprising nylon 66 (polyhexamethyleneadipamide) monofilament fibers, wherein said cord comprising 3-7 plies of monofilament fibers, wherein said monofilament fibers having round cross sectional shape and twisted together, wherein such monofilament cord comprising an RFL based adhesive

2. Cord in claim 1, wherein the synthetic monofilament fibers having the thickness between 0.23 mm to 0.50 mm or having the dtex between 475 to 2200.

3. Cord in any of the preceding claims wherein the synthetic monofilament fibers twisted together at twist levels between 50 to 200 tpm Z or S directions.

4. Cord in claim 3, wherein the monofilament fibers are PET (polyethylene terephtalate)

5. Cord in claims 3 or 4 , which is used as carcass in tires.

6. Cord in claims 3 or 4, which is used as breaker in tires.

7. Cord in claims 3 or 4, which is used as belt protective layer in radial truck and bus tires.

8. Cord in claims 3 or 4, which is used as belt for tires.

9. Cord in claims 3 or 4, which is used as carcass for aircraft tires.