EP2488348A1

EP2488348A1 - Sheet and method of making sheet for support structures and tires

Info

Publication number: EP2488348A1
Application number: EP10771603A
Authority: EP
Inventors: Alessandro Volpi
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 2009-10-13
Filing date: 2010-10-13
Publication date: 2012-08-22
Also published as: US20110086224A1; JP2013507540A; CN102858518A; BR112012008632A2; WO2011046994A1

Abstract

A planar sheet comprises a plurality of polyamide yarns (20, 30, 40) having a yarn modulus of from 3.7 to 6.8 N/dtex, an elongation to break of from 2.9 to 4.7 % and a denier of from 130 to 15,000 and a plurality of steel wires (21, 31, 41) wherein the steel wire is provided with a first crimp and a second crimp, the first crimp lying in a plane that is substantially different from the plane of the second crimp. The first and second crimp pitches and amplitudes of the steel wire are such that, when the steel wire and polyamide yarns are combined, the elongation to break of the wire is similar to that of the polyamide yarn. The wires and yarns are arranged such that they are oriented parallel to each other within the planar sheet. The sheet has utility in the construction of elastomeric components for tires and belts.

Description

TITLE

Sheet and Method of Making Sheet for

Support Structures and Tires

BACKGROUND OF THE INVENTION

1 . Field of the Invention

The present invention relates to a planar sheet useful for the reinforcement of tires and support structures.

2. Description of the Related Art

Combinations of aramid fibers and metal strands have been disclosed in United States Patent Application Publication 2004/0123930.

BRIEF SUMMARY OF THE INVENTION

This invention relates to a planar sheet that comprises

(a) a plurality of polyamide yarns having a yarn modulus of from 3.7 to 6.8

N/dtex, an elongation to break of from 2.9 to 4.7% and a denier of from 130 to 15,000,

(b) a plurality of steel wires having a major cross sectional dimension of from 0.04 to 1 .10 mm, wherein

(1 ) the steel wire is provided with a first crimp and a second crimp, the first crimp lying in a plane that is at least 20° different from the plane of the second crimp,

(2) the first and second crimp pitches and amplitudes of the steel wire are such that the elongation to break of the wire is no greater than 20% different from that of the polyamide yarn, (3) the steel wire has a composition comprising a minimum carbon content of 0.60 to1 .10 %, a manganese content ranging from 0.20 % to 0.90 %. and a silicon content ranging from 0.10 % to 0.90 %, and

(4) the steel wires and polyamide

This invention also relates to a method of forming a planar sheet, comprising the steps of:

(a) providing a plurality of polyamide yarns having a yarn modulus of from 3.7 to 6.8 N/dtex, an elongation to break of from 2.9 to 4.7 % and a denier of from 130 to 15,000,

(b) optionally twisting a plurality of polyamide yarns into a cabled yarn,

(c) providing a plurality of steel wires having a major cross sectional dimension of from 0.04 to 1 .10 mm and a composition comprising a minimum carbon content of from 0.60 to 1 .10%, a manganese content ranging from 0.20 % to 0.90 %, and a silicon content ranging from 0.10 % to 0.90 %,

(d) determining the desired pitch, amplitude and planar arrangement of crimps to be applied to the steel wire such that the crimps lie in two planes that are at least 20° different from each other and the steel wire has an elongation to break no greater than 20% different from that of the polyamide yarn,

(e) crimping the steel wire in accordance with the crimp parameters determined in step (d),

(f) optionally twisting a plurality of steels wires into a cabled wire, and

(g) combining the desired number of steel wires and / or steel cords, and the desired number of polyamide yarns and / or polyamide cords in a planar arrangement such that all the yarns, wires and cords are oriented parallel to each other.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a general view of a planar sheet of the invention. Figure 2 shows in cross section one combination of yarns and wires arranged in a sheet structure.

Figure 3 shows in cross section another combination of yarns and wires arranged in a sheet structure.

Figure 4 shows in cross section a further combination of yarns and wires arranged in a sheet structure.

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a planar sheet and by "planar" it is meant a structure having length and width dimensions that are considerably greater than the thickness dimension. In the context of this invention, the surfaces of the planar sheets may not be perfectly flat but may be of a ribbed nature. By "cord" it is meant a strand comprising at least one polyamide yarn and at least one steel wire that have been twisted together to form a hybrid cord. By "hybrid" it is meant the cord contains at least two different materials A cord can also mean a plurality of polyamide yarns that have been twisted together to form a polymaide cord or a plurality of steel wires that have been twisted together to form a steel cord.

One feature of this invention is that, when combined, the elongation at break of both the polyamide yarn and steel wire is similar. The elongation at break of the steel wire should be no more than +/- 20% different to that of the polyamide yarn. More preferably the elongation difference should be no more than +/- 10% and most preferably no more than + / - 5%. By virtue of having matching or near matching elongations at break when combined, the polyamide yarn and steel wire in the cord will break at essentially the same time when the cord is subjected to a tensile load. The steel wire is tailored to match the elongation at break of the polyamide yarn by a double crimping process described below. Crimped wire provides a wire having a higher elongation at break when compared to a similar non-crimped wire. A further aspect of this invention is that polyamide yarn may be used that has a modulus much lower than the 6.5 N/dtex specified in United States Patent Application Publication 2009/015917.

"Filament" as used herein means a relatively flexible, macroscopically homogeneous body having a high ratio of length to width across its cross- sectional area perpendicular to its length. Herein, the term "fiber" is used interchangeably with the term "filament".

A "yarn" is an assemblage of fibres or filaments to form a continuous strand. In the context of this invention, the term "yarn" also encompasses a "cabled yarn". A cabled yarn is a yarn formed by twisting together two or more yarns. In this invention the polyamide yarn is formed as part of the filament spinning process.

Polyamide Fiber and Yarn

Aramid is the preferred polyamide polymer. The term "aramid" means a polyamide wherein at least 85% of the amide (-CONH-) linkages are attached directly to two aromatic rings. Suitable aramid fibers are described in Man-Made Fibres - Science and Technology, Volume 2, Section titled Fibre-Forming Aromatic Polyamides, page 297, W. Black et al., Interscience Publishers, 1968. Aramid fibers and their production are, also, disclosed in U.S. Patents 3,767,756; 4,172,938; 3,869,429; 3,869,430; 3,819,587;

3,673,143; 3,354,127; and 3,094,51 1 .

The preferred aramid is a para-aramid. The preferred para-aramid is poly (p-phenylene terephthalamide) which is called PPD-T. By PPD-T is meant the homopolymer resulting from mole-for-mole polymerization of p- phenylene diamine and terephthaloyi chloride and, also, copolymers resulting from incorporation of small amounts of other diamines with the p-phenylene diamine and of small amounts of other diacid chlorides with the terephthaloyi chloride. As a general rule, other diamines and other diacid chlorides can be used in amounts up to as much as about 10 mole percent of the p-phenylene diamine or the terephthaloyi chloride, or perhaps slightly higher, provided only that the other diamines and diacid chlorides have no reactive groups which interfere with the polymerization reaction. PPD-T, also, means copolymers resulting from incorporation of other aromatic diamines and other aromatic diacid chlorides such as, for example, 2, 6-naphthaloyl chloride or chloro- or dichloroterephthaloyl chloride or 3, 4'-diaminodiphenylether.

Additives can be used with the aramid and it has been found that up to as much as 10 percent or more, by weight, of other polymeric material can be blended with the aramid. Copolymers can be used having as much as 10 percent or more of other diamine substituted for the diamine of the aramid or as much as 10 percent or more of other diacid chloride substituted for the diacid chloride or the aramid.

Continuous para-aramid fibers are generally spun by extrusion of a solution of the p-aramid through a capillary into a coagulating bath. In the case of poly(p-phenylene terephthalamide), the solvent for the solution is generally concentrated sulfuric acid, the extrusion is generally through an air gap into a cold, aqueous, coagulating bath. Such processes are generally disclosed in U.S. Patent No. 3,063,966; 3,767,756; 3,869,429, & 3,869,430. The filament cross section is circular or essentially circular. Para-aramid filament yarns are available commercially as Kevlar® fibers, which are available from E. I. du Pont de Nemours & Co., Wilmington, DE (DuPont) and Twaron® fibers, which are available from Teijin, Ltd.

The polyamide yarn of this invention has a yarn modulus in the range of from 3.7 to 6.8 N/dtex, more preferably in the range of from 3.7 to 6.0 N/dtex and most preferably in the range from 4.4 to 5.4 N/dtex. The yarn also has an elongation to break of from 2.9 to 4.7 %, more preferably from 3.0 to 4.0 % and a denier of from 130 to 15000. Examples of yarns having these properties is Kevlar® 29, Kevlar® 1 19 and Kevlar® 129 from DuPont.

Steel Wire

The steel composition comprises a carbon content of from 0.60 % to 1 .1

%, a manganese content ranging from 0.20 to 0.90 % and a silicon content ranging from 0.10 to 0.90 %. Other elements such as sulphur, phosphorous, chromium boron, cobalt, nickel and vanadium may each be present at a level below 0.5%.

The steel wire may have cross sections comprising one or more axes of symmetry. For example, an oval or rectangular cross section has two axes of symmetry and a triangular cross section has three axes of symmetry. In preferred embodiments, the steel wire cross section is round, or is essentially round. The major cross sectional dimension of the wire is in the range of from

0.04 mm to 1 .1 mm and more preferably from 0.07 mm to 0.60 mm. In the case of a round cross section, this dimension is the diameter. The wire is typically provided with a coating conferring affinity for rubber. Such coatings include those that can react with sulphur atoms in the rubber, such as copper, zinc and alloys of such metals, for example brass. In a preferred embodiment, zinc is used as the coating substrate when polyamide yarns form the outer surface of the hybrid cord, otherwise brass is the preferred coating material.

Crimping

The steel wire is crimped to produce a wire having a wave form.

Preferably the wire has a first and second crimp where the first crimp lies in a plane that is substantially different from the plane of the second crimp. By substantially different we mean that the crimp planes differ by an angle of at least 20°, more preferably by an angle of at least 60° and most preferably by an angle of at least 80°. The first and second crimps have a crimp pitch and crimp amplitude. Typical values for amplitude are from 0.5 to 1 .0mm and values for pitch from 2.0 to 16.0 mm. However other crimp and pitch values may also be utilized with this invention.

Depending on the elongation at break of the polyamide yarn being used, the angle of the crimp planes and the first and second crimp pitches and amplitudes are calculated to give a steel wire having an elongation at break close to that of the polyamide yarn. Preferably the elongation at break of the steel wire is no greater than 20% different from that of the polyamide yarn, more preferably the difference is no greater than 10% and most preferably the difference is no greater than 5%. Ideally the elongations at break of the polyamide yarn and steel wire are the same. Typical values for elongation at break of the steel wire are in the range of from 2.3 to 5.7 % and more preferably from 2.4 to 4.8%.

The steel wire may be crimped by passing them through toothed wheels. Such a process is described in European Patent (EP) 1036235 B1 . Crimped wires of this type are available from N. V. Bekaert S.A., Zwevegem, Belgium under the tradename High Impact Steel.

Forming the Planar Sheet

In one embodiment, this invention relates to a method of forming a planar sheet, comprising the steps of:

(b) optionally twisting a plurality of polyamide yarns into a polyamide cord.

(d) determining the desired pitch, amplitude and planar arrangement of crimps to be applied to the steel wire such that the crimps lie in two planes that are at least 20° different from each other and the steel wire has an elongation to break no greater than 20% different from that of the polyamide yarn, (e) crimping the steel wire in accordance with the crimp parameters determined in step (d),

(f) optionally twisting a plurality of steels wires into a steel cord, and

(g) combining the desired number of steel wires and / or steel cords and the desired number of polyamide yarns and / or polyamide cords in a planar arrangement such that all the yarns, wires and cords are oriented in a direction parallel to each other.

In another embodiment, this invention also relates to a method of forming a planar sheet, comprising the steps of:

(b) providing a plurality of steel wires having a major cross sectional dimension of from 0.04 to 1 .10 mm and a composition comprising a minimum carbon content of from 0.60 to 1 .10%, a manganese content ranging from 0.20 % to 0.90 %, and a silicon content ranging from 0.10 % to 0.90 %,

(c) determining the desired pitch, amplitude and planar arrangement of crimps to be applied to the steel wire such that the crimps lie in two planes that are at least 20° different from each other and the steel wire has an elongation to break no greater than 20% different from that of the polyamide yarn,

(d) crimping the steel wire in accordance with the crimp parameters determined in step (c),

(e) twisting at least one crimped steel wire with at least one polyamide yarn to form a composite hybrid steel-polyamide cord,, and

(g) combining the desired number of steel wires, polyamide yarns and composite hybrid steel-polyamide cords in a planar arrangement such that all the yarns, wires and cords are oriented parallel to each other. Wire cords are produced by twisting a plurality of the steel wires together to form a unitary multi-wire cabled wire structure. Preferably, the number of steel wires cabled together is either two or three. Similarly a plurality of polyamide yarns may also be cabled together to form a multi-yarn cabled cord structure. Preferably, the number of aramid yarns cabled together is either two or three. Individual yarns of polyamide may, of course, also be twisted with steel wire to produce a composite polyamide-steel cord. In preferred embodiments the total number of polyamide yarns in the composite cord is from one to ten and the total number of steel wires in the composite cord is from one to eight. In preferred embodiments, the twist multiplier of the yarn and wire forming the cord is at least 0.8. Twist multiplier is a term well understood in the textile arts. Methods such as twisting, plying or cabling to combine the polyamide yarn and steel wire into a cord are well known in the art and are further detailed in chapter 3.2 of Wellington Sears Handbook of Industrial Textiles.

The planar sheet comprises yarns, wires or cords all oriented in the same direction. This is normally referred to as the X or machine direction. The plane of the sheet is referred to as the XY plane. The Y direction is

orthogonal to the X direction. Such an arrangement is shown generally in Fig. 1 where the X direction is shown by 10 and the Y direction by 1 1 . There are a variety of ways in which polyamide yarns or cords and crimped steel wires or cords may be combined to form a planar sheet suitable for use with rubbers and elastomers. One such embodiment is shown in cross section in Fig. 2 where polyamide yarns, 20, alternate with steel wires, 21 . In another embodiment as in Fig. 3, a plurality of polyamide yarns are arranged to form a first sub-section, 30 and a plurality of wires arranged to form a second subsection, 31 . These subsections are then arranged adjacent to each other. Fig. 4 shows a further extension on this concept where two arrays of polyamide yarns 40 comprising a different number of yarns in each array are combined with two arrays of wires, 41 with these wire arrays also having a different number of wires in each array. As can be seen, the potential combinations of polyamide and steel both in terms of number of yarns or crimped wires and their positioning in the sheet relative to each other is quite extensive. The above description is not limited to polyamide yarn or steel wire. Polyamide cord, steel cord or composite steel-polyamide cord may also be included in the above structures. Thus a planar sheet could comprise polyamide yarns, polyamide cords, steel wire, steel cords and composite steel-polyamide cords. The length and width of the planar sheet is only limited by manufacturing constraints.

Methods of aligning yarns, wires and cords are well known in the textile, rope and wire forming industries. Such methods include the use of creels and beams to assemble the materials prior to feeding the individual strands through a collimating station and winding up the final assembly on a spool. Alternatively, sheets may be cut to length after collimation. Binders, films and adhesives may optionally be used to assist in maintaining the cohesiveness of the planar sheet. Another means of achieving this is to incorporate some light binder yarns in the Y direction either on the surface of or woven into the sheet.

In preferred embodiments, the weight percentage of polyamide in the sheet is from 10 to 50 weight percent based on the total weight of polyamide and steel.

Support Structures and Tires

The planar sheet is useful for example in passenger car tires, truck and bus tires as well as motorcycle tires. In comparison to pure steel reinforcement cord, the composite hybrid cord reduces weight in the tire and improves rolling resistance.

To incorporate the planar sheet into a tire, one or more sheets is incorporated into a matrix to form a support structure, in the form of a carcass, a bead reinforcement chafer (a composite strip for low sidewall reinforcement), or of a belt strip. The matrix can be any polymeric material that can keep multiple cords in a fixed orientation and placement with respect to each other. Typical materials are thermoset materials such as rubbers; however it is also possible to use thermoplastic materials such as thermoplastic vulcanisates and copolyetheresters. The support structure is then fitted into the structure of the tire, typically under the tread. If desired, the composite hybrid cord can be used in other support structures for use in applications that need elastomeric reinforcement.

Claims

1 . A planar sheet, comprising:

(a) a plurality of polyamide yarns having a yarn modulus of from 3.7 to 6.8 N/dtex, an elongation to break of from 2.9 to 4.7% and a denier of from 130 to 15,000,

(2) the first and second crimp pitches and amplitudes of the steel wire are such that the elongation to break of the wire is no greater than 20% different from that of the polyamide yarn,

(3) the steel wire has a composition comprising a minimum carbon content of 0.60 to1 .10 %, a manganese content ranging from 0.20 % to 0.90 %. and a silicon content ranging from 0.10 % to 0.90 %, and

(4) the steel wires and polyamide yarns are oriented parallel to each other within the planar sheet.

2. The planar sheet of claim 1 , wherein the polyamide yarn comprises poly (paraphenylene terephthalamide) filaments.

3. The planar sheet of claim 1 , wherein the polyamide yarn has a modulus of from 3.7 to 6.0 N/dtex.

4. The planar sheet of claim 1 , wherein the polyamide yarn has a modulus of from 4.4 to 5.4 N/dtex.

5. The planar sheet of claim 1 , wherein the polyamide yarn has an elongation to break of from 3.0 to 4.0%.

6. The planar sheet of claim 1 , wherein the cross section of the steel wire round or essentially round.

7. A support structure for a tire, comprising the planar sheet of claim 1 in the form of a belt, a carcass, or a bead.

8. A tire comprising the planar sheet of claim 1 .

9. A method of forming a planar sheet, comprising the steps of:

(b) optionally twisting a plurality of polyamide yarns into a cabled yarn,

(f) optionally twisting a plurality of steels wires into a cabled wire, and

10. A method of forming a planar sheet, comprising the steps of:

(e) twisting at least one crimped steel wire with at least one polyamide yarn to form a composite hybrid steel-polyamide cord. into a steel cord, and

(g) combining the desired number of steel wires or cords, polyamide yarns or cords and composite hybrid steel-polyamide cords in a planar arrangement such that all the yarns, wires and cords are oriented parallel to each other.

1 1 . The method of claim 9 or 10, wherein the polyamide yarn comprises poly (paraphenylene terephthalamide) filaments.

12. The method of claim 9 or 10, wherein the polyamide yarn has a modulus of from 3.7 to 6.0 N/dtex.

13. The method of claim 9 or 10, wherein the polyamide yarn has a modulus of from 4.4 to 5.4 N/dtex.

14. The method of claim 9 or 10, wherein the polyamide yarn has an elongation to break of from 3.0 to 4.0%.

15. The method of claim 9 or 10, wherein the cross section of the steel wire is round or essentially round.