GB1567966A - Reinforcing elements - Google Patents

Description

(54) REINFORCING ELEMENTS (71) We, MONSANTO COMPANY, a corporation organised under the laws of the State of Delaware, United States of America, of 800 North Lindbergh Boulevard, St. Louis, Missouri 63166, United States of America do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularlv described in and by the following statement:- This invention relates to reinforcing elements comprising a bundle of aromatic oxadiazole/N-alkylhydrazide filaments impregnated with a heat cured adhesive composition of a kind useful for adhering organic tire cords to rubber.

The term "aromatic oxadiazoleiN- alkylhydrazide" as used herein means a fiber-forming copolymer consisting essentially of recurring structural units:

in a mole ratio of 20:80 to 95:5, respectively, where Ar and Ar' are each a divalent carbocyclic aromatic radical and R is a C, to C4 alkyl radical.

There is a need in the tire industry to develop a reasonably priced tire cord having adequate fatigue resistance and a high modulus and tenacity. Fatigue resistance can be attained in an organic cord by means of twist, that is, a plurality of filament bundles are each twisted in one direction and then plied together with sufficient twist in the opposite direction to provide a balanced cord. In general, as the amount of twist in a cord is increased, the elongation of the cord is increased, the fatigue resistance of the cord is improved and, unfortunately, the tenacity of modulus of the cord which are needed for tire strength and stiffness are reduced. Nevertheless, in the construction of conventional organic cords twist is used at the expense of cord tenacity and modulus in order to achieve cords having adequate fatigue resistance for tire use.

The present invention provides a novel reinforcing element that is substantially without twist yet is particularly useful for the reinforcement of rubber articles such as tires where fatigue resistance, strength and stiffness are important.

The reinforcing element of the invention is one that comprises a bundle of filaments of an organic polymer, the polymer comprising recurring units of the formula

and of the formula

in a mole ratio of 20:80 to 95:5, respectively, where Ar and Ar' are each a divalent carbocylic aromatic radical and R is a C1 to C4 alkyl radical, impregnated with a heatcured resinous adhesive composition comprising a blend of an elastomer and a resorcinol formaldehyde resin or a modification thereof, wherein the bundle contains less than 0.167 turns per inch of twist.

The invention also comprises a flexible rubber article reinforced with elements according to the invention.

The term "bundle of filaments" or "filament bundle" as used herein means a plurality of closely spaced or contiguous, parallel filaments containing less than 0.167 turns per inch (6.57 turns per meter) of twist, i.e., from Q--0.167 turns per inch of twist. The reinforcing elements of the invention are characterized in having high tenacities and moduli and exceptional fatigue resistance properties. Since the elements contain little or no twist, the tenacities and moduli of the elements, based on the fiber content thereof, are at least equal to that of the filaments from which the elements are prepared, thereby enhancing the strength and stiffness of rubber articles reinforced with the elements.

The preparation of aromatic oxadiazole/N-alkylhydrazide filaments from relatively inexpensive monomers is described in U.S. Patent 3,886,251 and British Patents 1,407,439 and 1,417,568. The aromatic oxadiazole/N-alkylhydrazide copolymers comprise the above defined recurring structural units (a) and (b), wherein Ar and Ar' are each a divalent carbocyclic aromatic radical such as

and R is an alkyl radical having 1 to 4 carbon atoms such as -CH3 or -CH2CH.

Preferably Ar and Ar' are

R is methyl and the mole ratio of (a) units to (b) units is between 40:60 and 60:40.

In preparing the elements of the present invention, a bundle of oxadiazoleiN- alkylhydrazide filaments of desired total denier, preferably 1000 to 4000, e.g. 1500 denier, is impregnated with the heat curable adhesive composition, that is, a cord-torubber bonding agent of the type conventionally applied to nylon and polyester cords to enhance the adhesion-torubber characteristics thereof. Such bonding agents are sometimes herein referred to as "dips".

Dips particularly useful in practising the present invention are the "RFL" dips comprising a dispersion of a rubber latex in an aqueous solution of a resorcinol formaldehyde resin. The term "resorcinol formaldehyde resin" as used herein includes modifications thereof, such as the resin described in U.S. Patent 3,660,202 derived from resorcinol, formaldehyde and p chlorophenol. The rubber latex is preferably a copolymer of a vinyl pyridine and a conjugated diolefin having 4 to 6 carbon atoms such as butadiene - styrene - vinyl pyridine terpolymer.

The dip may be applied to the filament bundles using conventional dipping or coating apparatus. Accordingly, dip may be applied to the bundles, for example, by introducing the bundles to a bath embodying the dip either by immersing the bundles in the dip or by use of rolls which transfer dip from the bath to the bundles.

After applying the dip the bundles are preferably passed through a suitably sized die or orifice which preferably has a curved entrance. The orifice which has a slightly larger diameter than the bundles operates to remove excess dip and to work the dip into the bundles and to meter the dip onto the bundles. Then, without allowing the bundles to contact any guides which would force the dip out of the bundles, the bundles are heated sufficiently to remove the water of the dip and to congeal the dip in place within the bundles. If desired, the dipping and/or drying operations may be repeated.

After the last drying operation, the bundles are passed through a heated environment for a sufficient period of time to cure the dip, The curing operation can be accomplished by passing the yarn through a curing oven. Thereafter, the resulting elements are collected and subsequently used in the building of rubber composites such as tires.

According to one embodiment of the invention the resulting elements are wrapped with a low denier nylon 66 yarn using a high angle of wrap and redipped to enhance the transverse strength of the elements.

The amount of dip applied to the bundles may vary over a wide range, for example 13 to 40% by weight solids, based on the weight of the bundles, and depends on factors such as the diameter of the above-mentioned orifice and the solids content of the dip.

Preferably, the elements contain between 20 and 36% by weight of heat cured adhesive composition.

When elements are prepared by the above method the filament bundles are not only impregnated with adhesive composition but the individual filaments of the bundles are also separated by the adhesive composition.

The following examples are given to further illustrate the invention. In the examples percentages and parts refer to parts by weight unless otherwise specified.

Example 1 This example illustrates the preparation of typical dips useful in making the reinforcing elements of the invention.

Dip A containing 199 //n solids was prepared by first mixing 210 cc of H2O, 0.63 cc of a 50 /n aqueous solution of NaOH, 9.23 grams of resorcinol and 13 cc of formaldehyde and allowing the resulting mixture to react for 5 hours at room temperature. Then a mixture consisting of 210 cc of a latex (40.8% solids) containing styrene - butadiene - vinyl pyridine terpolymer (a latex supplied by General Tire and Rubber Company under the trademark Gentac Latex), 50 cc of water and 7 cc of NH40H was prepared. While stirring the latter mixture, the first mixture was added thereto and stirred thoroughly.

Dip B containing 26.8% solids was prepared in the same manner as Dip A except that only 130 cc of water was used instead of 260 cc of water.

Dip C containing 23.6% solids was prepared by mixing 166.75 cc of water, 0.65 cc of NaOH (50%), 8.3 grams of resorcinol and 7.38 cc of formaldehyde and stirring the resulting mixture for 5 minutes. This mixture was added to 122 cc of Gentac Latex (40.8% solids) and the resulting mixture was stirred for 5 minutes and then allowed to stand for 4 hours. This mixture was then added to 102.55 cc of a solution of a composition derived from resorcinol, formaldehyde and p-chlorophenol comprising 35.8% by weight 2,6 - bis(2',4' dihydroxyphenylmethyl) - 4 - chlorophenol in 5N aqueous ammonia, hereinafter referred to as "Solution A". The preparation of Solution A is described in U.S. Patent 3,660,202. The resulting mixture was stirred for 5 minutes.

Dip D containing 28.1% solids was prepared by adding 62.5 cc of water to 62.5 cc of Gentac Latex (40.8% solids) and stirring for 5 minutes after which time the resulting mixture was added to 125 cc of Solution A and the resulting mixture was stirred for 10 minutes.

Dip E containing 33.8% solids was prepared in the same manner as Dip A except that only 130 cc of water was used instead of 260 cc and only 105 cc of Gentac latex was used instead of 210 cc.

Dip F containing 32.2% solids was prepared in the same manner as Dip C except that 183 cc of Gentac latex was used instead of 122 cc.

Dip G containing 35.2% solids was prepared in the same manner as Dip C except that 732 cc of Gentac latex was used instead of 122 cc.

Dip H containing 36.2% solids was prepared in the same manner as Dip C except that 976 cc of Gentac latex was used instead of 122 cc.

Dip I containing 36.2An solids was prepared in the same manner as Dip C except that 366 cc of Gentac latex was used instead of 122 cc.

Variations in the foregoing dip formulations may be obtained by reducing the amount of water used in the preparation thereof or by adding additional latex thereto. Dips should be stored in suitably sealed containers and refrigerated until needed. When needed, the dips should be allowed to warm to room temperature while sealed.

Example 2 This example illustrates the preparation of a bundle of para-phenylene oxadiazole/N-methylhydrazide filaments used in preparing elements of the present invention.

Into a 30-gallon (113.5 liter) heated glasslined reactor fitted with a motor-driven helical stirrer were pumped 4.228 Kg of fuming sulphuric acid (22 /n SO3), to which 581.5 g (3.5 moles) of terephthalic acid, 679.9 g (3.5 moles) of dimethyl terephthalate, and 925 g (7.109 moles) of hydrazine sulfate were added. The reaction mixture was stirred at 60"C to effect solution, then the temperature was raised and maintained at 1250C for 18 hours. This extremely viscous solution (8.1% polymer solids was allowed to cool to 800C and was diluted to 5% solids by stirring with 8581 g of fuming sulfuric acid (about 5% S03). The resulting polymer solution had a solution viscosity of 38,720 poise at 250C as measured by a Brookfield viscometer (#6 spindle). This polymer solution was spun to filaments by extruding it through a 6 mil (152.4 microns), 25-hole spinneret into a coagulation bath consisting of 8% aqueous sulfuric acid maintained at 230C. The spinneret was heated to 140"C and kept 1/2 inch (12.7 mm) above the coagulation liquid. After passage under a guide in the bath, the fiber was passed over a water wash roll, a neutralizing roll rotating in an aqueous 4 gn solution of sodium carbonate, through a 90"C water bath, over another wash roll, a steam-heated drying roll and finally hot stretched over a hot-shoe maintained at 3650C and wound onto a bobbin at a speed of 1279 ft./min. (389.8 m./min.). The resulting 25 filament yarn had the following tensile properties: Tenacity 16.9 gpd (grams per denier) Elongation 6.9% Modulus 265 gpd Example 3 This example illustrates a typical procedure that may be used in preparing reinforcing elements of the invention.

Filaments prepared as described in Example 2 were combined to provide a 1535 denier filament bundle having a tenacity (T) of 12.54 gpd (grams per denier), an elongation-to-break (E) of 6.53, /n, a maximum modulus (M) of 250 gpd and a toughness (To) of 0.40 gpd, which was processed according to the following procedure. The bundle was passed from a supply bobbin around a first set of godet rolls (4 wraps), down and underneath a nonrotating pulley immersed in a pan embodying Dip B, up vertically through an orifice, continuing vertically up through the focal line of an infrared line heater which removes the water from the dip, over a rotating pulley, under a tensioning pulley of the hanging weight type, over a second rotating pulley, horizontally through a 52 inch (132 cm) hot slot without contacting the hot slot surface, over another pulley, around a second set of godet rolls (4 wraps) and finally onto a conventional winder where the bundle containing the heat cured dip was collected.

The first set of godet rolls were driven to provide a bundle speed of about 7.7 ft. (2.35 m.)/min. which gives the bundle a dwell time of 33-34 seconds in the hot slot. The temperature in the hot slot was 2450C. The tension on the supply bobbin was maintained at the minimum tension required to prevent the bundle from slipping around the first set of godet rolls. The tensioning pulley and hanging weights weighed 45 grams which controlled the tension on the bundle between the two sets of godet rolls. The winder provided tension which prevented the bundle from slipping around the second set of godet rolls. The orifice was molded from epoxy resin and has a 0.25 inch (6.35 mm) diameter opening which exponentially tapers to a 0.0276 inch (0.7 mm) diameter opening. The orifice is 3/8 inch (9.6 mm) in length with 1/8 inch (3.2 mm) of its length being of 0.25 diameter, 1/8 inch of its length being of 0.0276 inch (0.070 cm) or 0.0240 (0.061 cm) diameter, 1/8 inch of its length being exponentially tapered.

The bundle was dipped at room temperature. However, the dip pan was placed in an ice bath to prevent film from forming on top of the dip.

The T/E/M/To properties of the resulting processed bundle were 13.47 gpd/7.92/-224 gpd/0.49 gpd. This element is identified hereinafter as 3A.

Example 4 This example illustrates the preparation of additional elements of the invention. In each instance a filament bundle was prepared according to the procedure described in Example 2 and processed according to the procedure described in Example 3. The dip used and other process conditions as well as the properties of the unprocessed bundles (U) and processed bundles (P) are given in the following table.

TABLE I Orifice Curing Element Denier %E Tgpd Mgpd Togpd DIP %Solids Size (in) Temp C.

U 1550 5.19 11.28 264 0.30 - - - 4A P 1550 7.53 13.02 207 0.47 B 26.8 0.0276 265 U 1551 6.61 11.80 23 0.39 - - - 4B P 1551 7.75 12.56 207 0.47 E 33.8 0.0276 245 4C P 1551 7.41 12.29 - 0.44 E 33.8 0.0276 265 4D P 1551 6.89 12.33 216 0.41 F 33.8 0.0276 265 U 1543 5.93 14.81 283 0.45 4E* P 1543 7.87 16.54 257 0.62 G 35.2 0.0240/0.0276 265 4F* P 1543 7.66 16.70 289 0.59 H 36.2 0.0240/0.0276 265 U 1542 6.34 15.21 274 0.48 4G P 1542 7.89 15.36 226 0.59 I 36.2 0.0276 265 U=unprocessed bundle P=processed bundle *=bundle dipped twice using a 0.0240 inch diameter orifice after the first dipping and a 0.0276 inch diameter orifice after the second dipping.

Example 5 This example illustrates the preparation and compression fatigue testing of representative elements of the present invention. The preparation of suitable samples for the testing of the fatigue resistance of the elements requires several steps. The final sample for testing is a 3x 1/2x 1/2 inch epoxy resin, rubber, element composite having three layers, a lx l/2x 1/2 inch rubber layer sandwiched between two 1 x l/2x 1/2 inch epoxy resin layers. The elements are positioned in the center of the rubber layer with the long axis of the fiber extending along the length of the rubber layer.

Sample Preparation The following technique was used to prepare all test samples. First, an element was vulcanized in 1x1/2x1/2 inch (2.54x1.27x1.27 cm) rubber blocks with 1 1/2-2 inches (3.81-5.08 cm) of the element extending from each end of the rubber block. This step was carried out using a mold which allows vulcanization of 20 samples at one time. Premolded rubber spacing half blocks were placed in the mold to create open areas which were used later for epoxy resin. Uncured rubber was placed in the inch sample area. The element sample was strung through the mold and tied off at each end. Additional uncured rubber and spacing half blocks were placed on top of the element and the mold was then closed. The cold mold was placed in a hot press (202--204"C) at 907 Kg pressure and after 8 minutes the pressure was increased to 9070 kg. The temperature reached 166"C after about 20 minutes and was controlled at this temperature. After 35 minutes, the heat was turned off and the mold was cooled under pressure. The samples were removed from the mold and the element was cut half way between each rubber block. Each element end was cemented to an aluminum pin (7/16x 1/8 inch) (l.lx0.3 cm) and then wrapped around the pin at least two turns and held in this position by means of a rubber ring. The samples were then placed back into position in the mold and the mold was heated at 45 50"C for 20 minutes. Epoxy resin (Shell Epon 815/curing agent U) was poured into the open cavities between the rubber blocks. The cure of the epoxy resin was continued 40 minutes at 45-500C and then at 7080 C for 60 additional minutes. The mold was permitted to cool to room temperature. The mold was then disassembled and the testing samples removed. Five testing samples were made for each of the elements identified in Examples 3 and 4.

Fatigue Testing The fatigue resistance of the elements was tested by means of a machine specially designed for this purpose. The machine has two vertically mounted, rotatable steel disks each of which is several inches thick and approximately one foot (30.48 cm) in diameter. The disks are positioned vis-a-vis one inch (2.54 cm) apart inside of a thermal housing of heavy gauge. Both disks rotate at the same speed (rpm) and each rotates about an axis which meets the other on an angle in the horizontal plane between the disks. In testing, a sample is placed between the disks with one epoxy resin end of the sample being securely clamped to the peripheral of one disk and the other epoxy resin end to the peripheral of the other disk.

One disk has means for canting it with respect to the other disk so as to provide a specific compression strain and tension strain during testing. During testing the disks rotate together. Thus, in one revolution of the disks (i.e. one cycle) the sample is first under a compression load then a tension load or visa versa. The machine has 24 stations, that is 24 samples can be tested at one time. The samples are removed and broken in an Instron using manual clamps with 1 inch (2.54 cm)x2 inch (5.08 cm) serrated faces. ("Instron" is a registered Trade Mark.) The rubber force is taken away from the maximum breaking strength before calculating the tenacity and other properties of the elements.

Using the above-described fatigue testing machine, test samples containing the elements described in Examples 3 and 4 were prepared as described above and tested. In testing the samples, the disks were canted with respect to one another so as to provide a compression strain of 7.5% and a tension strain of 2.5%. The number of cycles given in the table for each set of samples represents a value above which a large number of samples in that set failed. The results of the testing are given in Table II.

TABLE II Samples Avg. Retained /n Tenacity Number of Element Cycles Tested Failed Tenacity(gpd) Retained Samples Avg.

3A 100,000 5 0 2.93 22 5 4A 2,000,000 5 0 1.96 15 5 4B 100,000 5 1 2.31 18 4 4C 100,000 5 0 2.78 23 5 4D 100,000 5 1 2.02 16 4 4E 2,000,000 5 0 2.68 16 5 4F 2,000,000 5 0 2.49 15 5 4G 4,000,000 5 0 2.23 14.5 5 The results given in Table II show the exceptional fatigue resistance of the elements of the present invention which is attained without the use of twist.

Example 6 In this example elements made from commercially obtained poly(p phenylene terephthalamide) filaments were prepared and tested using the procedures described in Example 3-5.

Table III gives the dip used and other processing conditions as well as the properties of the unprocessed (U) and processed (P) bundles.

TABLE III T To Orifice Curing Element Denier %E (gpd) M(gpd) (gpd) Dip %Solids Size(in.) Temp"C.

U 1536 3.53 17.44 566 - - - - - CA 1536 3.85 19.13 - .33 E 33.8 0.0276 265 CB 1536 3.45 18.97 209 .29 C 23.6 0.0276 245 CC 1536 3.47 20.49 741 .31 C 23.6 0.0276 265 1517 3.24 16.99 593 .27 cd* 1517 3.20 17.94 527 .27 H 36.2 265 0.0276 *bundle dipped twice using a 0.0240 inch diameter orifice after the first dipping and a 0.0276 diameter orifice after the second dipping.

Test samples were prepared from each of the above elements CA-CD and tested as described in Example 5. The results of these tests are given in Table IV. As in Table II, the number of cycles given for each set of samples represents a value above which a large number of samples in that set failed.

TABLE IV Samples Average Retained % Tenacity # of Samples Element Cycles Tested Failed Tenacity (gpd) Retained Averaged CA 10,000 5 4 19.13 4 1 CB 10,000 5 4 18.97 3 1 CC 10,000 5 4 20.49 2 1 CD 50,000 5 3 17.94 10 2 The results in Table IV show that elements made from poly(p - phenylene terephthalamide) bundles have poor fatigue resistance when compared to elements of the present invention.

Example 7 This example demonstrates the fatigue resistance of the elements of the present invention.

Elements of the present invention were incorporated in the belts of two JR78-15 radial tires. The elements prior to being used in constructing the tires were trapped with a low denier nylon yarn at a high angle of wrap and redipped. The belts of the tires contained 14 elements per inch and the body of the tire contained conventional polyester cords. In laboratory wheel testing the tires were inflated to 24 psig (1.687 Kg/cm2 gauge) and then rotated at 30 mph (48.3 Kph) under a load of 1580 lb (716.7 Kg), three Firestone cleats on the wheel, giving 900 crown impacts per mile (1.6093 Km). The tires failed at between 4800 (7725 Km) and 5500 (8851 Km) miles due to separation of the outer body ply under the tread and not due to an apparent belt related failure. The results of this test indicate that the elements of the invention have adequate fatigue resistance for radial tire applications and certainly for biasbelted tire applications where 3,000 miles (4828 Km) without failure is deemed adequate.

Claims (9)

WHAT WE CLAIM IS:

1. A reinforcing element that comprises a bundle of filaments of an organic polymer, the polymer comprising recurring units of the formula

and of the formula

in a mole ratio of 20:80 to 95:5, respectively, where Ar and Ar' are each a divalent carbocyclic aromatic radical and R is a C1 to C4 alkyl radical, impregnated with a heatcured resinous adhesive composition comprising a blend of an elastomer and a resorcinol formaldehyde resin or a modification thereof, wherein the bundle contains less than 0.167 turns per inch of twist.

2. An element according to Claim 1, in which the elastomer is a copolymer of polyvinylpyridine, butadiene and styrene and the resin is a resorcinol-formaldehyde resin or a composition comprising 2,6 bis(2',4' - dihydroxyphenylmethyl)- 4chlorophenol.

3. An element according to either Claim 1 or Claim 2, in which the copolymer comprises recurring units of the formula

wherein Ar and Ar' are each selected from

R is -CH3 and the mole ratio of units (A) to (B) is between 60:40 and 40:60.

4. An element according to Claim 3, in which Ar and Ar' are

5. An element according to any of the preceding claims, in which the bundle has zero twist.

6. An element according to any of the preceding claims, in which the denier of the bundle is between 1000 and 4000.

7. A reinforcing element according to Claim 1, substantially as described in any of Examples 3 to 5 and 7.

8. A flexible rubber article reinforced with elements according to Claim 1.

9. An article according to Claim 8, that is a tire.