Polyester Straps Useful in Binding Applications, Methods of Manufacture, Systems and Uses Thereof

Abstract

The present invention relates to polyester straps, methods of their manufacture, systems and uses thereof, particularly as may be used in binding applications of discrete articles into bundles. The polyester straps comprise voids extending into the interior of the strap from one or more of the surfaces there

Claims

1. A plastic strap formed of an at least partially crystalline thermoplastic material which is ultrasonically welded, the plastic strap having a length, a width and a thickness, two substantially parallel major faces having a width and a length separated by the thickness, at least one of the major faces having a plurality of voids extending into the thickness from the major face, each of the voids having straight boundary lines at their periphery wherein they intersect a major face of the plastic strap, each of the voids present in the interior of the plastic strap and having a depth, a void surface area and a void volume measurable from the major face of the plastic strap, wherein per unit length of the plastic strap the cumulative void surface area is from 20% to 90%, and the cumulative void volume is from 5% to 65 in the region of the plastic strap which is subsequently ultrasonically welded and at least partially melted forming a bond therebetween.

2. The plastic strap of claim 1, wherein the plastic strap comprises a substantial portion of a polyalkylene terephthalate.

3. The plastic strap of claim 2, wherein the polyalkylene terephthalate is polyethylene terephthalate.

4. The plastic strap of claim 1 which has a width not in excess of 5 mm.

5. The plastic strap claim 1 wherein the voids are present in an array.

6. The plastic strap of claim 1 wherein the voids have boundary lines of parallelogram shape having four apices and which voids have a pyramidal cross-section.

7. The plastic strap of claim 1 wherein peripheral boundary of most of the voids present on a major face of a plastic strap are entirely within the width of the plastic strap, but which include incomplete voids having peripheral boundaries which intersect the and edge of the plastic strap.

8. The plastic strap of claim 1, wherein the cumulative void volume is from 25% to 30% in the region of the plastic strap which is subsequently ultrasonically welded and at least partially melted forming a bond therebetween.

9. The plastic strap of claim 8, which has a width not in excess of 5 mm.

10. A process for tensile bundling of loads which comprises the steps of, utilizing a plastic strap according to claim 1, forming a loop about the load with the plastic strap, and, ultrasonically welding parts of the looped plastic strap.

11. The process of claim 10 where the plastic strap has a width no in excess of 5 mm.

12. A bundled load comprising an ultrasonically welded formed loop of a plastic strap according to claim 1.

Description

EXAMPLES

Example 1 (E1)

[0051] A plastic strap was formed substantially from a polyethylene terephthalate, having a composition of 99.9% wt. PET, exhibiting an intrinsic viscosity of 0.78. The plastic strap was formed by extrusion, having a width in the range of between 4.5 to 5.1 mm, having a thickness in the range of between 0.30 mm to 0.45 mm by passing a melt of the PET through an extruder die, shaped with a rectangular orifice having dimensions 25 mm1.56 mm and is simultaneously drawn and quenched by a factor of 2 to 2.2which essentially reduced the cross-sectional dimension of the strap from the orifice's dimensions to about 11.5 mm0.8 mm. The plastic strap was reheated and stretched again by a factor of 2.5 to 3.2 along its length. The resultant strap had a mass of 1.55 to 1.75 grams per meter of length, a tensile strength of >40 kgF, and a degree (extent) of embossment of from 15% to 30%. Thereafter the strap was embossed with the to provide a pattern of voids as depicted in FIG. 5.

[0052] Two of the foregoing embossed straps were layered in register, and at an overlap region were welded using an ultrasonic welding apparatus, SONIXS (ex. EAM-Mosca Corp.) at the following protocol: Weld time between 80-120 ms (preferably 100 ms), Cool time between 100-500 ms (preferably 100 ms) and strap tension between 260N and 350 N (Preferably 310N). The resultant ultrasonically welded and now joined straps were evaluated for weld strength and weld efficiency. It was determined that the weld strength was approximately 33 kgF, and the weld efficiency (weld strength/tensile strength) was approximately 71%.

Comparative Example 1 (C1)

[0053] A plastic strap formed substantially from a polypropylene polymer having a composition of 99% wt. polypropylene (PP), and a Melt Flow Index of 1.2. The plastic strap was formed by extrusion, having a width in the range of between 4.40 mm-5.10 mm, having a thickness in the range of between 0.40 mm to 0.55 mm by passing a melt of the PP through an extruder die, and quenching the extruded plastic strap. The resultant strap had a mass of 1.45 to 1.60 grams per meter of length, a tensile strength of 54 kgF, and a degree (extent) of embossment of from 15% to 35%. The resultant pattern was as depicted in FIG. 4.

[0054] Two of the foregoing polypropylene straps were layered in register, and at an overlap region were welded using an ultrasonic welding apparatus, SONIXS (ex. EAM-Mosca Corp.) at the following protocol: Weld time between 80-120 ms, cool time between 100-500 ms, and strap tension between 325N and 580 N. The resultant ultrasonically welded and now joined straps were evaluated for weld strength and weld efficiency. It was determined that the world strength was approximately 35 kgF, and the weld efficiency (weld strength/tensile strength) was approximately 65%.

Comparative Example 2 (C2)

[0055] A plastic strap formed substantially from a polypropylene polymer having a composition of 99% wt. polypropylene (PP), and a Melt Flow Index of 1.2. The plastic strap was formed by extrusion, having a width having a nominal width of 5 mm, a nominal thickness of 0.5 mm (actual dimensions are given in the following Table C2) by passing a melt of the PP through an extruder die, and quenching the extruded plastic strap. The resultant strap had a mass of 1.45 to 1.60 grams per meter of length, a tensile strength of 54 kgF, and a degree (extent) of embossment of from 15% to 35%. The resultant pattern was as depicted in FIG. 4.

[0056] Sample lengths of two of the foregoing polypropylene straps were layered in register, and at an overlap region were welded using an ultrasonic welding apparatus, SONIXS (ex. EAM-Mosca Corp.) at the following protocol: Weld time between 80-120 ms, cool time between 100-500 ms, and strap tension between 325N and 580 N. The resultant ultrasonically welded and now joined straps were evaluated for weld strength and weld efficiency; the results are reported on the following Table C2. It was determined that the weld strength was approximately 35 kgF, and the weld efficiency (weld strength/tensile strength) was approximately 65%.

TABLE-US-00001 TABLE C2 (5 mm Polypropylene Strapping) Thick- Tensile Weld Width ness Weight Void Strength Strength Weld (mm) (mm) (g/m) Volume % (KgF) (KgF) Eff. 4.64 0.45 1.54 55.88 38.57 0.69 4.66 0.45 1.6 55.75 35.83 0.64 4.65 0.45 1.57 18.66% 55.815 37.2 66.65% 4.92 0.5 1.56 0.3031 50.65 30.02 0.59 4.88 0.5 1.6 0.2794 44.7 29.82 0.67 4.90 0.50 1.58 29.17% 47.675 29.92 62.99%

[0057] As can be appreciated from the reported results of the foregoing table, each of the four samples of embossed PP strapping, two of which had an emboss/void percentage of 18.66%, and two of which had an emboss/void percentage of 29.17% were tested for weld strength. Notably the former two samples exhibited a 66.65% weld strength, the latter two sample exhibited a 62.99% weld strength which were considered to be very similar. Notably the differences in the emboss/void percentage appeared to have little effect on the weld efficiencies of the PP strap.

Example 2 (E2)

[0058] A plastic strap was formed substantially from a polyethylene terephthalate, having a composition of 99.9% wt. PET, exhibiting an intrinsic viscosity of 0.78. The plastic strap was formed by extrusion, having a nominal width of 9 mm, having a thickness in the range of between 0.50 mm to 0.65 mm by passing a melt of the PET through an extruder die, shaped with a rectangular orifice having dimensions 64 mm by 4 mm and is simultaneously drawn and quenched by a factor of about 4.25which essentially reduced the cross-sectional dimension of the strap from the orifice's dimensions to about 8.7 mm0.62 mm. The plastic strap was reheated and stretched again by a factor of 1.1 to 1.2 along its length. The resultant strap had a mass of 6.15 to 6.35 grams per meter of length, a tensile strength of >90 kgF. Samples of the resultant strap were subjected to two different degrees of embossment, approx. 15% and approximately 25% (actual extent of embossment is reported on the following table) utilizing an embossing roller 30 as depicted in the drawing figures. The patterned embossment was as in FIG. 4.

[0059] For purposes of testing ultrasonic weld strength, two of the foregoing embossed straps were layered in register, and at an overlap region were welded using an ultrasonic welding apparatus, SONIXS (ex. EAM-Mosca Corp.) at the following protocol: Weld time between 80-120 ms (preferably 100 ms), Cool time between 100-500 ms (preferably 100 ms) and strap tension between 260N and 350 N (preferably 310N). The resultant ultrasonically welded and now joined straps were evaluated for weld strength and weld efficiency.

[0060] The results from three samples of each of the two embossed straps are reported in the following Table E2.

TABLE-US-00002 TABLE E2 (9 mm PET Strapping) Thick- Tensile Weld Width ness Weight Void Strength Strength Weld (mm) (mm) (g/m) Volume % (KgF) (KgF) Eff. 8.78 0.61 6.28 0.1582 181.27 99.81 0.55 8.8 0.62 6.34 0.1285 185.83 124.22 0.67 8.77 0.62 6.28 0.1626 187.04 149.32 0.80 8.78 0.62 6.30 14.98% 184.7133 124.45 67.25% 8.98 0.65 6.18 0.2469 96.9 89.57 0.92 9.04 0.67 6.18 0.2453 90.99 90.92 1.00 8.96 0.65 6.18 0.2469 92.34 86.41 0.94 8.99 0.66 6.18 24.64% 93.41 88.96667 95.31%

[0061] Notably the PET strap exhibited very satisfactory weld efficiencies, particularly with higher percentages of embossment/void %. It was surprisingly observed that for the same nominal width and thickness of the PET strap, there was a 41.7% increase in weld efficiency notwithstanding the 64.4% increase in the embossment/void %.

[0062] This result was considered to be surprising in view of the fact that the deeper embossments did not detract from the weld strengths as might have otherwise been expected, as the deeper embossments would have reduced the cross-sectional thickness of the strap in the region of the embossments. While not wishing to be bound by the following, it is believed that the semi-crystalline nature of the polymer used in forming the strap played a role in the weld efficiencies realized.

Comparative Example 3 (C3)

[0063] A plastic strap formed substantially from a polypropylene polymer having a composition of 99% wt. polypropylene (PP), and a Melt Flow Index of 1.2. The plastic strap was formed by extrusion, having a width having a nominal width of 9 mm, a nominal thickness of 0.5 mm (actual dimensions are given in the following Table C3) by passing a melt of the PP through an extruder die, and quenching the extruded plastic strap. The resultant strap had a mass of 2.85 grams to 2.95 grams per meter of length, a tensile strength of >70 kgF, and a degree (extent) of embossment of from 25% to 45%.

[0064] Sample lengths of two of the foregoing polypropylene straps were layered in register, and at an overlap region were welded using an ultrasonic welding apparatus, SONIXS (ex. EAM-Mosca Corp.) at the following protocol: Weld time between 80-120 ms, cool time between 100-500 ms, and strap tension between 325N and 580 N. The resultant ultrasonically welded and now joined straps were evaluated for weld strength and weld efficiency; the results are reported on the following Table C3.

TABLE-US-00003 TABLE C3 (9 mm Polypropylene Strapping) Thick- Tensile Weld Width ness Weight Void Strength Strength Weld (mm) (mm) (g/m) Volume % (KgF) (KgF) Eff. 8.26 0.5 2.92 0.247 101.16 70.52 0.70 8.29 0.53 8.26 0.51 2.92 0.2623 92.68 81.97 0.88 8.31 0.54 8.23 0.5 2.91 0.2501 97.68 74.29 0.76 8.33 0.53 8.28 0.52 2.92 25.31% 97.17 75.59 78.07% 8.43 0.68 2.91 45.55% 71.79 59 0.82 8.47 0.71 8.42 0.69 2.92 45.75% 73.7 62.15 0.84 8.48 0.71 8.41 0.69 2.91 45.87% 73.19 67.93 0.93 8.47 0.71 8.45 0.70 2.91 45.72% 72.89 63.03 86.44%

[0065] It is again observed that the nominal 9 mm PP straps, that the differences in the emboss/void percentage appeared to have little effect on the weld efficiencies of the PP strap.

Example 4 (E4)

[0066] A plastic strap was formed substantially from a polyethylene terephthalate, having a composition of 99.9% wt. PET, exhibiting an intrinsic viscosity of 0.78. The plastic strap was formed by extrusion, having a width in the range of between 4.5 to 5.1 mm, having a thickness in the range of between 0.30 mm to 0.45 mm by passing a melt of the PET through an extruder die, shaped with a rectangular orifice having dimensions 25 mm1.56 mm and is simultaneously drawn and quenched by a factor of 2 to 2.2which essentially reduced the cross-sectional dimension of the strap from the orifice's dimensions to about 11.5 mm0.8 mm. The plastic strap was reheated and stretched again by a factor of 2.5 to 3.2 along its length. The resultant strap had a mass of 1.55 to 1.75 grams per meter of length, a tensile strength of >40 kgF, and a degree (extent) of embossment of from 15% to 30%. Thereafter the strap was embossed with a patterned roller to provide a pattern of voids as depicted on FIG. 5.

[0067] Samples of the of the foregoing embossed straps were layered in register, and at an overlap region were welded using an ultrasonic welding apparatus, SONIXS (ex. EAM-Mosca Corp.) at the following protocol: Weld time between 80-120 ms (preferably 100 ms), Cool time between 100-500 ms (preferably 100 ms) and strap tension between 260N and 350 N (Preferably 310N). The resultant ultrasonically welded and now joined straps were evaluated for weld strength and weld efficiency. The results of this test are indicated in the following table:

TABLE-US-00004 TABLE E4 (5 mm PET Strapping) Thick- Tensile Weld Width ness Weight Void Strength Strength Weld (mm) (mm) (g/m) Volume % (KgF) (KgF) Eff. 4.93 0.36 2.07 0.14206 58.23 31.15 0.53 4.88 0.36 2.04 0.145823 57.61 40.33 0.70 4.91 0.37 2.06 0.166211 60.4 42.81 0.71 4.90 0.36 2.06 15.14% 58.75 38.10 64.79% 4.85 0.46 1.88 0.388738 31 28 0.90 4.89 0.45 1.87 0.384198 30 24 0.80 4.89 0.415 1.85 0.339404 40 33 0.83 4.88 0.44 1.87 37.08% 33.67 28.33 84.27%

[0068] As is visible from the above results, the greater void % of 37.08% of the latter three samples did not detract from the weld efficiency, but was rather improved as compared to the former three samples having a void % of 15.14%. All of the straps exhibited satisfactory tensile strength.

[0069] Consistent with the above testing protocols, in particular the use of an ultrasonic welder for providing the weld joining together of the respective straps (which of course, may be representative of the two ends of a continuous loop of a particular strap, used in bundling an array or plurality of discrete articles and keeping them bundled, due to the tension within the continuous loop formed as consequence of the ultrasonic welding step of these two ends) is believed due to the enhancement in the narrowed strap of E1, viz., the embossed PET strap having a preferred embossment pattern on at least one of the major faces of the PET strap, the mechanical properties of the embossed PET strap the PET being partially crystalline in nature, and the combination of the ultrasonic welding step used, now make possible the use of narrower PET straps than those previously thought in bundling applications of discrete articles. This is in part also made possible by the use of ultrasonic welding in forming a continuous loop of the embossed PET strap, and the nature of energy transfer of ultrasonic welding, which induces frequency/oscillation in the region of the weld joint formed from overlapping straps, which contrasts with thermal and/or frictional welding which, on the relatively small mass of PET strap within the weld joint would induce molecular crystallization in the regions immediately adjacent to the weld joint, possibly within the region of the weld joint itself. Such would induce strap embrittlement along the weld, and cause the thermal and/or frictional welded joint to fail, particularly under the tensile condition to which the continuous loop of PET strap would be subjected in a conventional bundling operation. Surprisingly the present inventors have overcome such a shortcoming, and provide an unexpected but technically satisfactory solution wherein a narrow, embossed PET strap may be used. Such is unexpected from the prior art, which suggests only wider PET straps in such applications, and in particular wherein the continuous loop of PET strap formed from such wider PET straps were also welded utilizing a thermal and/or frictional welding step.

[0070] Again, the examples and embodiments disclosed herein and in the drawing figures (and photographs) are by way of illustration and not by way of limitation. Further embodiments of plastic strap, and processes for their production and use are also feasible in full within the present inventive scope.