Cord comprising multifilament para-aramid yarn comprising non-round filaments

Abstract

A cord including multifilament para-aramid yarn comprising filaments, wherein the filaments have a non-round cross section having a smaller and a larger dimension, where the cross-sectional aspect ratio between the larger and the smaller dimension is 1.5-10 and the smaller dimension of the cross section has a maximum of 50 m and wherein the para-aramid has at least 90% para bonds between the aromatic moieties. The cords have excellent fatigue properties.

Claims

1. Cord comprising a multifilament para-aramid yarn comprising filaments, wherein the filaments have a non-round cross section having a smaller dimension and a larger dimension, where a cross-sectional aspect ratio between the larger dimension and the smaller dimension is in a range from 1.5 to 10 and the smaller dimension of the cross section has a maximum thickness of 50 m, wherein the para-aramid has at least 90% para bonds between the aromatic moieties, and wherein the cord comprises a resorcinol-formaldehyde-latex adhesive.

2. Cord of claim 1, wherein the cross-sectional aspect ratio between the larger dimension and the smaller dimension is in the range from 2 to 8.

3. Cord of claim 1, wherein the larger dimension has a maximum length of 100 m.

4. Cord of claim 1, wherein the para-aramid yarn is para-phenylene terephthalamide yarn.

5. Cord of claim 1, having a linear density of at least 25 dtex.

6. A tire, belt, hose, flowline, rope or umbilical incorporating the cord of claim 1.

7. Process to manufacture a cord comprising multifilament para-aramid yarn comprising filaments, wherein the filaments have a non-round cross section having a smaller dimension and a larger dimension, where a cross-sectional aspect ratio between the larger dimension and the smaller dimension is in a range from 1.5 to 10 and the smaller dimension of the cross section has a maximum thickness of 50 m, wherein the para-aramid has at least 90% para bonds between the aromatic moieties, and wherein the cord comprises a resorcinol-formaldehyde-latex adhesive, comprising the steps of: i) dissolving the para-aramid in sulfuric acid to obtain a dope; ii) extruding the dope through a spinneret having multiple non-round nozzles to obtain a multifilament yarn, where the nozzles have a rectangular cross section; iii) coagulating the multifilament yarn in an aqueous solution, iv) combining at least two of the obtained multifilament yarns.

8. Cord of claim 1, wherein the cross-sectional aspect ratio between the larger dimension and the smaller dimension is in the range from 2.5 to 6.

Description

EXAMPLES

(1) 1. Preparation of Cords

(2) Yarns of non-round shape were spun from PPTA dissolved in 99.8% H.sub.2SO.sub.4. For samples 1-3, the yarns were spun with a spinneret with rectangular holes with dimensions of 25020 micron (504 openings). For samples 4-5, the same polymer solution was used but a spinneret with rectangular holes of 25035 micron (252 openings). Resulting non-round filament yarn had filament dimensions with a width between 25-50 m and a thickness between 8-16 m for samples 1-3 and filament dimensions with a width of 9-18 m and a thickness of 25-55 m for samples 4-5. The different PPTA multifilament yarns according to the invention, having a non-round cross-section (oval, similar to a rice grain) and a cross sectional aspect ratio (CSAR) of ca. 3 (samples 1-3) and between 2.5 and 3.5 (samples 4-5, see indication below) were prepared having different moduli:

(3) First Set of Experiments:

(4) Sample 1: low nominal modulus (60 GPa), 1680 dtex

(5) Sample 2: medium nominal modulus (80 GPa), 1680 dtex

(6) Sample 3: high nominal modulus (105 GPa) variant, 1680 dtex

(7) As comparison two control multifilament yarns were prepared comprising filaments having a round cross section and having different nominal moduli:

(8) Control 1: Twaron 1000 (70 GPa), 1680 dtex

(9) Control 2: Twaron 2100 (60 GPa), 1680 dtex

(10) Second Set of Experiments:

(11) Sample 4: low nominal modulus (55 GPa), 1680 dtex, CSAR: 3.5

(12) Sample 5: low nominal modulus (50 GPa) variant, 1680 dtex, CSAR: 2.5

(13) As comparison two control multifilament yarns were prepared comprising filaments having a round cross section and having different nominal moduli:

(14) Control 3: Twaron 1000 (70 GPa), 1680 dtex

(15) Control 4: Twaron 2100 (60 GPa), 1680 dtex

(16) Cords were prepared by twisting using a Saurer Allma CC2 direct cabler. Each cord was prepared from two PPTA yarns, each having a nominal linear density of 1680 dtex.

(17) The yarns were comprised of round filaments (control 1-4) or non-round filaments (according to the invention, sample 1-5).

(18) The cords were constructed as: 1680 dtex; x1Z330 x2S330 turns per meter Double bath dipping took place on an electrically heated Litzler single end Computreater with the following dipping sequence: pre-dip dip trough/drying/curing/RFL dip trough/curing.

(19) Pre-dip drying conditions: 120 seconds at 150 C.

(20) Pre-dip curing conditions: 90 seconds at 240 C.

(21) RFL curing conditions: 90 seconds at 235 C.

(22) Tension in each of the dip through steps: 2.5N

(23) Tensions in all three ovens: 8.5N

(24) Composition of the Pre-Dip:

(25) TABLE-US-00002 Chemicals: Wet Solids (De-mineralized) water 978.2 g Piperazine (water free) 0.5 g 0.5 g Aerosol OT75% 1.3 g 1.0 GE-100 epoxide 20.0 g 20.0 g Total 1000.0 g 21.5 g

(26) Aerosol OT 75: Dioctyl sodium sulfosuccinate in 6% ethanol and 19% water (from Cytec Industries B.V.)

(27) GE100 epoxide: Mixture of di- and trifunctional epoxided on the basis of glycidyl glycerin ether (from Raschig)

(28) Composition of the RFL Dip:

(29) TABLE-US-00003 Wet Solids A. (De-mineralized) water 365.7 g Ammonium hydroxide (25%) 10.3 g 2.6 g Penacolite R50 (50%) pre-condensed RF resin 55.6 g 27.8 g B. VP-latex Pliocord 106 (40%) 407.0 g 162.8 g C. Formaldehyde (37%) 18.5 g 6.8 g (De-mineralized) water 142.9 g Total 1000.0 g 200.0 g

(30) For the Twaron D2200 dipped cord used as tensile layer in the AFF test an RFL dip with the same relative composition but a 25% solids content was used.

(31) Penacolite R50 (from Indspec Chemical Corporation)

(32) Pliocord VP106 (from OMNOVA Solutions)

(33) Directly after dipping of each of the cords, the dipped material was sealed in an air tight laminated aluminum bag to prevent deterioration of the RFL layer due to environmental exposure (ozone, moist etc.).

(34) 2. Determination of Properties of Yarns and Cords

(35) The mechanical properties of the yarns and cords (undipped, dipped and after fatigue testing) were determined according to standard ASTM D7269-10 Standard Test Methods for Tensile Testing of Aramid Yarns 1. For dipped cords, for the determination of the breaking tenacity (BT) the linear density of the cords was corrected for the solids pick up due to the treatment with the adhesive.

(36) Solids pick up is determined by means of the linear density method. From the linear weight of the dipped cord A (after conditioning for at least 16 hours at 20 C. and 65% R.H.) is subtracted the linear weight of the same cord B that has experienced the same dipping sequence but without the pre-dip and RFL dip (air-dipped), also after conditioning for at least 16 hours at 20 C. and 65% R.H. The percentage solids pick up is calculated as: (AB)/B*100%.

(37) The breaking toughness is defined as the surface area below the tensile curve, as defined in ASTM D885.

(38) The linear density of yarns and cords was determined according to ASTM D1907.

(39) The dimensions of the filaments are measured by embedding the yarn in resin and preparing sections by cutting perpendicular to the yarn extension direction. By optical microscopy the dimensions of the filament cross section are determined.

(40) Twist Efficiency

(41) The twist efficiency is determined based on the breaking tenacities (BT) of the original yarn from which the twisted yarn or cord is made:

(42) Twist efficiency (%, tenacity based) TE-T=Breaking Tenacity of the twisted yarn or cord/original breaking tenacity of the original yarn.

(43) The twist efficiency indicates how much of the original yarn tenacity is retained in the cord construction.

(44) Twist-dip efficiency (%, tenacity based) TDE-T=Breaking Tenacity of the dipped twisted yarn or cord/original breaking tenacity of the original yarn.

(45) The twist-dip efficiency indicates how much of the original yarn tenacity is retained in the dipped twisted cord construction.

(46) The Goodrich block fatigue is determined for dipped para-aramid cords in accordance with ASTM D6588. The cords are embedded in a rubber compound Master compound 02-8-1638 available from QEW Engineered Rubber, Hoogezand, The Netherlands. Prior to use of the Master compound, curatives must be added and mixed. These curatives are 0.9 phr N-cyclohexyl-2-benzothiazylsulfenamide (CBS-powder) and 4 phr insoluble sulfur added to 179 phr Master compound. Mixing took place on a 2-roll mill.

(47) Vulcanization conditions used are 18 minutes at 150 C. in an electrical heated press at a pressure of 18 tons. The mold is not pre-heated. Condition for block fatigue test:

(48) TABLE-US-00004 Number of cords per block 1 Compression [C], (%) 18% Elongation [E], (%) 2% Running Times 1.5, 6 and 24 hours Frequency: 40 Hz (2400 rpm) Number of cycles: 216k-cycles, 864k-cycles and 3.46M-cycles

(49) Per running time, the percentage retained strength was calculated based on the following equation: percentage retained strength=breaking strength of the dipped cord subjected to block or disc fatigue testing/breaking strength of the original dipped cord*100%.

(50) The flexural fatigue of the cords was determined with the Akzo Nobel Flex Fatigue test. A rubber strip approximately 25 mm wide is flexed around a spindle at a given load. The rubber strip comprises two cord layers, the upper tensile layer containing a material of very high modulus (Twaron D2200 was used) and the lower cord layer which is situated closer to the spindle contains the cords to be tested. The cords are embedded in the rubber compound Master compound 02-8-1638 available from QEW Engineered Rubber, Hoogezand, The Netherlands. Prior to use of the Master compound, curatives must be added and mixed with the Master compound. As curatives were used 0.9 phr N-cyclohexyl-2-benzothiazylsulfenamide (CBS-powder) and 4 phr insoluble sulfur added to 179 phr Master compound. Mixing took place on a 2-roll mill. A schematic presentation of the rubber strip and the test set-up is given in FIG. 4. The Twaron D2200 tensile layer carries almost the full tensile load because of its comparatively high stiffness. The test cords of the bottom layer experience bending, deformation due to axial compression, and pressure from the upper cord layer.

(51) Rubber strip building (in layers on top of each other): 1 mm Master compound 02-8-1638/8 dipped test cords (as described above) with a spacing of 2 mm center to center/1 mm Master compound 02-8-1638/tensile layer of double bath dipped cords Twaron D2200, 1610 dtex x1Z200, x25200/2 mm Master compound 02-8-1638. The 1 mm Master compound side is facing the pulley. Vulcanization conditions used are 18 minutes at 150 C. in an electrical heated press at a pressure of 18 tons. The mold is not pre-heated.

(52) The production of the tensile layer cord was done on Lezzeni ring twist equipment. Dipping of the cord from the tensile layer (Twaron D2200 cords) is identical to that of the sample and control cords with the only exception that RFL was used with a concentration of 25%.

(53) Tensile layer end-count: is 28 cords per inch.

(54) Bending and deformation in the presence of the lateral pressure causes degradation of the cord. After the strip has been flexed, the cords are carefully removed from the strip (e.g. with a splitter device from e.g. FortunaWerke GmbH type UAF 470) and the retained strength of the cords is determined using capstan clamps. The retained strength values were measured both in Newtons and as a percentage of the original dipped cord breaking strength. The percentage is the ratio of the retained strength to the strength of the original dipped cord.

(55) Flex Fatigue Test Conditions Used:

(56) Stroke: 45 mm

(57) Pulley load: 340N

(58) Pulley diameter: 25 mm

(59) Strap width: 25 mm

(60) Strap length: approximately 44 cm

(61) Running time: 2 hours (36 kcycles)

(62) Bend of the strap over the pulley: 1725

(63) PRS (percentage retained strength) is calculated based on original dipped cord breaking strength.

Experiment 1: Properties of the Yarns and Cords of the Invention of Samples 1-3

(64) The properties of the multifilament yarns of samples 1-3 and controls 1-2 are shown in table 1.

(65) TABLE-US-00005 TABLE 1 Sample 1 Sample 2 Sample 3 Control 1 Control 2 Property 60 GPa 80 GPa 105 GPa 70 GPa 60 GPa Linear density (dtex) 1711 1698 1680 1727 1708 Breaking strength (N) 327 336 322 359 369 Elongation at break (%) 3.89 3.26 2.56 3.53 4.17 BS loss compared to 9 6 10 Control 1 (%) BS loss compared to 11 9 13 Control 2 (%) Breaking tenacity (mN/tex) 1911 1979 1919 2076 2159 Breaking toughness (J/g) 34.9 30.9 24.1 34.9 42.6 Chord Modulus (GPa) 57.5 77.6 103.1 73.1 61.3 Cross sectional shape Rice grain Rice grain Rice grain Round Round (BS: breaking strength)

(66) As can be seen from the data of table 1 the multifilament yarn of the invention comprising non-round filaments lack some breaking strength in comparison to the control yarns which comprise conventional round filaments, for all 3 examples of experiment 1. Also, the samples according to the invention cover a wide modulus range.

(67) Subsequently, cords were prepared from the above described yarns. Each cord (1680 dtex x2, Z330/S330) was made from two multifilament yarns, each yarn having a twist (one positive and one negative) of ca. 330 turns per meter and the cord having a twist factor of ca. 165.

(68) The properties of the undipped cords are shown in table 2.

(69) TABLE-US-00006 TABLE 2 Sample 1 Sample 2 Sample 3 Control 1 Control 2 Property 60 GPa 80 GPa 105 GPa 70 GPa 60 GPa Linear density (dtex) 3703 3659 3622 3723 3674 Breaking strength (N) 501 512 504 561 576 BS loss compared to 13 9 10 Control 1 (%) BS loss compared to 13 11 13 Control 2 (%) Elongation at break (%) 5.66 5.03 4.49 5.43 6.07 Breaking tenacity (mN/tex) 1353 1399 1393 1507 1569 Breaking toughness (J/g) 31 28.4 24.9 33.6 38.9 Chord Modulus (GPa) 28.5 33.7 39.6 32.1 28.6 Twist efficiency (%) 71 71 73 73 73

(70) The undipped cords according to the invention have a lower breaking strength compared to the control cords. This loss of strength is even more pronounced in the cords, compared to the difference in breaking strength of the control yarns. Therefore, the cords according to the invention usually have an equal to lower twist-efficiency than cords comprising multifilament yarns having round filaments. Surprisingly, this is different in the multifilament yarns made of co-poly-para-phenylene/3,4-oxydiphenylene terephthalamide having non-round filaments as described in U.S. Pat. No. 5,378,538.

(71) Such cords have a better twist efficiency (utilization in tenacity) compared to yarns of the same polymer but having round filaments, even at different twist levels.

(72) The sample and control cords were dipped according to the above described process and the cord properties were determined (table 3).

(73) TABLE-US-00007 TABLE 3 Property Sample 1 Sample 2 Sample 3 Control 1 Control 2 Linear density (dtex) 3743 3734 3774 3803 3753 Breaking strength (N) 513 513 492 595 608 BS loss compared to 14 14 17 Control 1 (%) BS loss compared to 16 16 19 Control 2 (%) Elongation at break (%) 4.84 4.21 3.86 4.9 5.39 Breaking tenacity (mN/tex) 1450 1460 1395 1669 1722 Breaking toughness (J/g) 31.7 27.7 23.7 36.5 41.6 Chord Modulus (GPa) 34.6 40.8 42.7 38.3 35.9 Twist-dip efficiency (%) 78 76 76 83 83

(74) The dipped cords according to the invention (samples 1-3) have a substantially lower breaking strength (BS) compared to the control cords. In comparison with the yarns and the cords, the BS loss of the dipped sample cords in comparison to the controls are more pronounced due to lower twist-dip efficiencies. The twist-dip efficiency of the dipped cords according to the invention is lower than of the control cords, this is even more pronounced for the dipped cords than the untreated cords (see Table 2). Surprisingly, dipped cords comprising multifilament yarns made of co-poly-para-phenylene/3,4-oxydiphenylene terephthalamide and having non-round filaments as described in U.S. Pat. No. 5,378,538 have a higher twist-dip efficiency than cords comprising multifilament yarn having round filaments and made from the same polymer.

(75) The dipped cords were used in the Goodrich Block Fatigue test and in the Akzo Nobel Flex Fatigue test to determine their fatigue behavior.

(76) Surprisingly, the Goodrich Block Fatigue test shows a clear difference between the sample cords and the control cords. The sample cords (according to the present invention) have a higher absolute retained strength already after 1.5 hours of block fatigue testing than the control cords comprising round filaments even though the original dipped cord strengths of the samples were at least 14% lower than those of the controls. This unexpected effect is depicted in FIG. 1a.

(77) FIG. 1b shows the Goodrich Block Fatigue results of the tested cords for different test running times, i.e. stress exposure times (1.5, 6 or 24 hours). The effect can be observed at all time points, especially after 24 hours of testing. This indicates that the yarns and cords according to the invention can delay the process of block fatigue effectively.

(78) FIG. 2 shows the relative retained strength (GBF-PRS) of the sample and control cords. All cords according to the invention have a higher relative retained strength, thus a lower fatigue, than the control cords. This applies for cords of the invention irrespective of their modulus, however, the effect is more pronounced for cords with a lower modulus.

(79) Also the Akzo Nobel Flex Fatigue (AFF) of the cords according to the invention is better than of the control cords. As can be seen in FIGS. 3a and 3b, the (percentage) retained strength of the sample cords is much higher than the (percentage) retained strength of the control cords.

Experiment 2: Properties of the Yarns and Cords of the Invention of Samples 4-5

(80) The properties of the multifilament yarns of samples 4-5 and controls 3-4 are shown in table 4.

(81) TABLE-US-00008 TABLE 4 Sample 4 Sample 5 Control 3 Control 4 Property 55 GPa 50 GPa 70 GPa 60 GPa Linear density (dtex) 1729 1723 1719 1715 Breaking strength (N) 308 307 361 366 Elongation at break (%) 3.91 4.25 3.56 4.10 BS loss compared to 15 15 Control 3 (%) BS loss compared to 16 16 Control 4 (%) Breaking tenacity 1783 1784 2100 2133 (mN/tex) Breaking toughness (J/g) 33.0 36.0 35.8 41.6 Chord Modulus (GPa) 53.5 48.5 73.4 61.7 Cross sectional shape Rice grain Rice grain Round Round (BS: breaking strength)

(82) As can be seen from the data of table 4, similarly to samples 1-3, the non-round yarns according to the invention have lower breaking strength compared to the control yarns comprising round filaments.

(83) Subsequently, cords were prepared from the above described yarns. Each cord (1680 dtex x2, Z330/S330) was made from two multifilament yarns, each yarn having a twist (one positive and one negative) of ca. 330 turns per meter and the cord having a twist factor of ca. 165. The undipped cord properties are shown in table 5.

(84) TABLE-US-00009 TABLE 5 Sample 4 Sample 5 Control 3 Control 4 Property 55 GPa 50 GPa 70 GPa 60 GPa Linear density (dtex) 3713 3687 3678 3651 Breaking strength (N) 439 415 559 582 Elongation at break 5.65 5.59 5.36 6.05 (%) BS loss compared to 21 26 Control 3 (%) BS loss compared to 25 29 Control 4 (%) Breaking tenacity 1182 1125 1520 1594 (mN/tex) Breaking toughness 26.7 26.3 33.8 40.0 (J/g) Chord Modulus (GPa) 26.7 24.9 32.8 29.3 Twist efficiency (%) 66 63 72 75

(85) Again, the undipped cords according to the invention have lower breaking strength compared to the control cords. The twist efficiency of the sample cords is again lower than of the control cords, which is different in the multifilament yarns made of co-poly-para-phenylene/3,4-oxydiphenylene terephthalamide having non-round filaments as described in U.S. Pat. No. 5,378,538

(86) The sample and control cords were dipped according to the above described process and the cord properties were determined (table 6).

(87) TABLE-US-00010 TABLE 6 Sample 4 Sample 5 Control 3 Control 4 Property 55 GPa 50 GPa 70 GPa 60 GPa Linear density (dtex) 3573 3550 3545 3530 Breaking strength (N) 472 454 593 592 Elongation at break (%) 4.90 4.94 4.87 5.54 BS loss compared to 20 23 Control 3 (%) BS loss compared to 20 23 Control 4 (%) Breaking tenacity 1321 1278 1673 1678 (mN/tex) Breaking toughness (J/g) 31.3 29.0 38.8 42.2 Chord Modulus (GPa) 34.0 30.6 41.2 34.6 Twist-dip efficiency (%) 74.2 71.6 79.5 78.6

(88) Surprisingly, dipped cords comprising multifilament yarns made of co-poly-para-phenylene/3,4-oxydiphenylene terephthalamide and having non-round filaments as described in U.S. Pat. No. 5,378,538 have a higher twist-dip efficiency than cords comprising multifilament yarn having round filaments and made from the same polymer.

(89) The dipped cords were used in the Goodrich Block Fatigue test (FIG. 4) and the Akzo Nobel Flex Fatigue test (FIG. 5) to determine their fatigue behavior.

(90) Again, the sample cords show an improved fatigue behavior compared to cords comprising para-aramid multifilament yarns comprising filaments with a round cross section. As can be seen from FIGS. 4 and 5, even though the sample cords 4 and 5 start at a lower absolute strength, during the block fatigue test, they loose relatively little strength compared to the control cords. Thus, the sample cords show better block fatigue behavior. Also the flex fatigue behavior is better than that of control cords comprising round filaments (FIG. 6).

(91) In conclusion, even though the yarns and the untreated and dipped cords according to the invention initially have a lower breaking strength, the cords show an improved block and flexural fatigue behavior under stress compared to conventional cords having the same cord and yarn linear density but comprising filaments having a round cross section. Surprisingly, after compression and bending stress the absolute value of the remaining breaking strength of the cords of the invention is higher than that of conventional cords comprising filaments with a round cross section. Therefore, the cords of the invention are especially suited for applications where compression and/or bending stresses occur.

(92) FIG. 1 shows the results of the Goodrich Block fatigue test as absolute retained strength for shorter testing times (FIG. 1a) and longer testing times (FIG. 1b) for samples 1-3 and controls 1-2.

(93) FIG. 2 shows the results of the Goodrich Block fatigue test as relative retained strength compared to the cord strength before stress exposure for samples 1-3 and controls 1-2.

(94) FIG. 3 shows the results of the AFF test as absolute retained strength of cords (FIG. 3a) and relative retained strength (FIG. 3b) the for samples 1-3 and controls 1-2.

(95) FIG. 4 shows the results of the Goodrich Block fatigue test as absolute retained strength for shorter testing times (FIG. 4a) and longer testing times (FIG. 4b) for samples 4-5 and controls 3-4.

(96) FIG. 5 shows the results of the Goodrich Block fatigue test as relative retained strength compared to the cord strength before stress exposure for samples 4-5 and controls 3-4.

(97) FIG. 6 shows the results of the AFF test as absolute retained strength of cords (FIG. 6a) and relative retained strength (FIG. 6b) the for samples 4-5 and controls 3-4.

(98) FIG. 7 shows a schematic overview of the test set-up of the AFF test (FIG. 7a) and the rubber strip that is used in the AFF test (FIG. 7b). a=25 mm diameter pulley, b=AFF strap, c=layer of test cords, n=8, d=layer of tensile cords (Twaron D2200).

(99) FIG. 8 shows a cross section of the multifilament para-aramid yarn of the invention (lower panel) and of conventional multifilament yarn (upper panel).