IL23318A - Strapping and method of making same - Google Patents

Description

Strapping and Method of making same Thomas J. Karass This invent ion relates to high tensile strength strapping.

The class ic material for this purpose has been steel strapping. It has been used for a wide variety of heavy duty purposes , for example banding, strapping and bundling boxes, cartons , bales and the like , to unitizing, to holding packages to pallets , for reinforcing tearable sheet material, as for example in grain doors for railroad cars , and for many other purposes where high tens ile s trength in the -strapping is required , Steel s trapping has certain disadvantages which have been dealt with in patents and other literature . For this reason strapping made up of juxtaposed c ords of high tens ile strength synthetic material held together adhesively in the lateral direc tion has been used with great success . This he terogeneous strapping has the disadvantage that it must be assembled in a spec ial way and that multiple e le ments have to be handled which represents an assembly problem in manufacture . Cord strapping is advantageous in that it does liot cut into packages and it can be fas tened by means of a s imply and quickly applied c lamp or seal . However, cord strapping has been relatively expens ive to manufacture and is generally bulkier than steel s trapping of comparable strength.

Theoretically, s trapping from a homogeneous plastic material would be des irable from a manufacturing point of view since plas tic s can be readi ly extruded in continuous lengths .

However, despite the availability of a wide variety of plastic materials and the ability of those skilled in the plastics art to endow them with countless different properties, plas tic material having the right c ombina tion of propertie-s for high tensile strength strapping has not been available .

The problem seems to have been that those skilled in the strapping art were not thoroughly familiar with the capabili- ties of polymeric extrudable materials, from the use of which they had been discouraged, on finding such materials, in general, had undesirable charac eristics where high tensile strength and other strapping properties are required. They apparently did not realize that the undesirable charac eristics which they had learned about could be overcome sufficiently to make flexible strapping a practical reality as a commercial article. Likewise, those skilled in the art of extrudable polymers were apparently not familiar enough with strapping problems to conceive a material, having the right combination of properties to meet the demanding requirements of high tensile strength strapping.

Existing plastic materials, extruded for other purposes, lack the properties required for strapping. These circumstances are borne out by a suggestion made recently of plastic strapping having longitudinally extending thick and thin portions in which the molecular arrangement in the respective portions is specially adjusted so that the transverse tensile strength of the strapping per unit of dross-section is greater in the thin portions than in the thick portions. This strapping, which would appear from that author's suggestions, came as a result of rejecting the concept of using plastic strapping of even thickness across its width because of the shortcomings for strapping purposes of available extruded plastic material* Having regard to the foregoing, the applicant has developed a plastic strapping material which overcomes the misconceptions of the prior art and which can be used for many of the present applications of steel or cord strapping.

This strapping is in the form of a continuous ribbon or tape preferably of substantially rectangular cross-section or at least having a thickness which does not fluctuate across the width of the tape and of which the surface is substantially even, made from a homogeneous extruded polymeric material having high tensile strength in the longitudinal direction, good tear strength in the transverse direction, and of a balanced construction so that it will not twist helically when relaxed. This combination of features may be built into the tape by extruding the polymeric material so that the ribbon as it passes through the die is substantially uniformly heated on all sides, then cooling the ribbon substantially uniformly and relatively slowly, then heating the ribbon to below its softening point and stretching it to orient the molecules uniaxially, i.e. longitudinally of the tape, then annealing it by heating it to a temperature higher than the second order transition temperature of the polymeric, but below its softening point, under relaxed conditions, to remove stress.

Preferred strapping according to the invention has the following characteristics. It has a substantially even thickness within the range from about 0.010 inch and about 0.060 inch and a width from about one-eighth of an inch to about two inches. The strapping has an elongation of not more than about 12$, preferably not more than 10$, a tensile strength of at least about sixty thou-sand pounds per square inch. It has the capacity to transmit at least about 70$ tension around a 90° corner. It has a density less than that of water. It is resistant to abrasion, to acids, to alkalies and is waterproof. It is substantially immune to the degrad ing effect of ultra-violet light on polymeric materials. It has an energy at break of at least about forty pounds per inch. It is flexible continuously without losing the tensile strength. It has high dielectric strength and high tear strength in the lateral direction. The strapping is of balanced construction, that is it will not twist in a helical direction from its normal axis.

The precise materials from which the strapping may be made and the precise conditions of manufacture will be clear to The invention will be described in more detail by reference to the accompanying drawings in which preferred embodiments are illustrated and in which: Figure 1 is a fragmentary view of strapping according to the invention.

Figure 2 is a transverse cross-section along the line 2-2 of Figure 1.

Figure 3 is a plan view showing free ends of strapping according to the invention connected together by one form of a connector.

Figure 4 is an axial cross -section along the line 3-3 of Figure 3.

Figure 5 is a perspective view showing strapping of the present invention in position about a strapped article.

Figure 6 is a plan view showing free ends of strapping according to the invention connected together by another form of connector.

Figure 7 is a side elevation of the strapping and fastener as shown in Figure 6.

Figure 8 is a plan view showing free ends of strapping according to the invention connected together by another form of connector.

Figure 9 is an axial cross -sec ion along the line 9-9 of Figure 8.

Referring more particularly to the drawings, the form of strapping of the invention shown in Figure 1 is made up of a continuous length A of homogeneous extrudable polymeric material having a substantially rectangular cross-section. The precise characteristics of the strapping are described elsewhere.

The applicant has illustrated strapping of rectangular cross-section for facility in explanation. The distinction which the applicant wishes to make is over tape which has an undulating cross-section alternating between thick and thin portions across its width. It should be understood that the present strapping does not have to be exactly rectangular but can taper somewhat in thickness say from a relatively thick portion at the middle to thinner areas at the edges or vice versa or the edges may be somewhat rounded. Registering devices can be employed as for example one or more ribs standing out from one surface of the tape adapted to register with one or more depressions at the other surface of the tape merely to facilitate rolling of the strapping into coils. But, the aim is that the strapping shall be to all intents and purposes a ribbon of substantially uniform thickness that is free of thick and thin portions across its width and in this respect similar to steel strapping and differing from cord strapping and strapping of plastic material which has a plurality of axially extending thick ribs connected by relatively thin tendons. The advantages of the present strapping are in its relative uniformity in thickness or in the fact that it does not have an uneven sur-face as in the case of card strapping or ribbed plastic strapping and can be handled in this respect like steel strapping.

Strapping of this type is employed for strapping purposes for which steel strapping or cord strapping has been previously used. A typical strapping use is in strapping a container as shown in Figures 3 to 5. The strapping A is shown surrounding the container B in transverse directions and the free ends of the strapping are shown held together by a connector or clip 0. This clip is illustrated in Canadian Patent 689,731, issued June 16, 1964, to Canadian Ribbon Tape Co. Ltd. and consists of a piece of sheet metal bent into the form of a sleeve or flat tube. The overlapping portions of the sheet metal are secured together by spot welding or a continuous line of welding. The metal forming the clip is corrugated as at 17 transversely of the overlapping portions thereof to provide rigidity for the clip and permit the use of relatively light gauge metal.

The two ends of the strapping are threaded through the clip C and the tape is drawn taut about the package B after which the clip is crimped entirely across its width so that it digs into the plastic of the strapping material in order to gain a secure purchase on the strapping. The crimps thus provide a snubbing action which restrains the ends of the tape from slipping upon one another and from slipping out of the clip. In addition to the transverse crimps, the clip is also deformed inwardly against the side edges of the strapping as shown at 20 in order to provide a more secure grip of the tape.

The holding quality of the clip may also be improved without seriously weakening the strapping by providing depressions or inwardly directed dimples 21 within the transverse crimps 18 and 19, The arrangement secures good gripping of the strapping which without such device might be difficult to connect because of the elusive properties of the plastic material preventing its being tied or otherwise connected in a normal manner.

Figures 6 and 7 illustrate another connection device useful in combination with the strapping of the invention. This device employs a buckle which is formed of a single piece of preferably round wire, the gauge of which may vary according to the size and strength of buckle desired. As seen in Figure 6, the buckle is substantially rectangular and comprises a pair of strap engaging arms on two opposite sides thereof. One of the pairs of arms comprises a first arm 110 and a second arm 111 and the other pair comprises a first arm 112 and a second arm 113. The two pairs of arms are substantially parallel to one another, as are portion of the wire and one end of said arm is connected by a straight run 114 of the wire to one end of arm 112 which latter arm constitutes an intermediate segment of the wire. Arm m is connected by a straight run 115 of the wire to one end of arm 113, run 115 being located in a common plane with run 114 and lieing beneath run 114, The other end of arm 113 terminates in a hook 116 which extends beneath and partially around arm 112. Hook 116 terminates in an upward direction. Arm 111 is connected by a straight run 118 of the wire to one end of arm 112. As shown in Figure 6, a vertical plane through run 118 would extend at an angle to a vertical plane through run 114; but, if preferred, run 118 may be located in a vertical plane which is parallel to a vertical plane through run 114, this latter arrangement being accomplished by lengthening arm 111 so that it is the same length as arm 112. As shown in Figure 7, the arms of each pair of arms are spaced apart, a distance sufficient to permit a strap 119 to be threaded therebetween and arms 111 and 113 are located in a common plane so that the buckle will rest flat upon an object such as box 120. n use, a length of strappin material is withdrawn from a supply such as a roll 121 and pulled around the box or other article to be strapped and the free end of the strap is passed upwardly through the central opening of the buckle and thence around arm 112, between arms 112 and 113 and beneath arm 113 as indicated in Figure 7. A loop 122 is then formed in the strap and pushed up through the central opening of the buckle. The loop is bent over as shown in Figure 7 and the closed end thereof moved end-wise of arm 110 and fitted over the free end of said arm. This leaves an excess amount of strap in the vicinity of the buckle but by pulling on that portion of the strap between the buckle and the roll 121, the excess is withdrawn and the strap drawn tightly about arm 110. The strap may then be cut from the roll at a point a short distance from the buckle.

The strap may be tensioned by hand or by a suitable tensioning tool. Either end of the strap may be pulled to tighten, but the portion which is looped around the package cannot expand. When portion 122 is pulled toward the left, portion 123 slides relatively freely beneath it toward the right but when portion 123 attempts to move toward the left, portion 122 is pinched beneath it and arm 111 of the buckle and will not move.

Tension on the strap produces a downward component of force on arms 110 and 112 and the downward movement of arm 110 is limited at one end by engagement of run 114 of the wire with run 115 and the downward movement of the other end of sai¾ arm is limited by engagement of the free end thereof with run 118, it being important to the strength of the buckle that arm 110 be long enough so that the free end thereof overlaps run 118. Downward movement of arm 112 is limited at one end by engagement of run 114 of the wire with run 115 and the downward movement of the other end is limited by engagement with the underlying portion of hook 116. Thus, the buckle derives its ability to withstand deformation primarily by the fact that both ends of arms 110 and 112 are supported when the strap Is under tension.

It will be apparent that when the buckle is used with a strap having two free ends, the strap may be engaged first with either the arms 110 and 111 or arms 112 and 113 and then subsequently threaded through the remaining pair. However, when used with a strap having only one free end, it is necessary to engage the free end with arms 112 and 113 because neither of these arms has a free end around which the loop 122 of the strap could be engaged.

Another way applicant connects the ends of the strapping is shown in Figures 8 and 9 ii j. .Juufci'lbu d In Canadian PalCTifAppH-ο Χίονι Jorial Nutn¾gr~ 905, 007 -f±±¾d Juuu 10 , 1004, la 'the name—of £ΡΓ1?+;Γ^Ρ Ρ -*ρτΓΚ¾¾ t-_gr The buckle comprises a flat parallelogram shaped member or blank having two long sides 210 and 211 and two short sides or ends 212 and 213 with each long side forming an acute angle with one of the short sides. Preferably the buckle is stamped from a strip of steel having a width equal to the perpendicular distance between sides 210 and 211. A rectangular opening is provided in the center of the buckle, said opening having opposed walls 214 and 215 extending parallel to the short sides of the blank and opposed walls 216 and 217 extending perpendicular to walls 214 and 215 and defining the width of the opening. This central opening is preferably just slightly wider than the strap with which the buckle is to be used. The material of the blank is removed to provide a pair of open-ended slots 218 and 219 extending parallel to the short ends of the blank. Slot 218 is between the central rectangular opening and the short side 212 of the blank and opens through the long side 210 whereas slot 219 preferably opens through long side 211 and Is located between the central opening and the short end 213. As seen in Figure 8, the lengths of slots 218 and 219 are substantially equal to the width of the central opening. Thus a buckle is provided having a pair of arms 220 and 221 at one end and a pair of arms 222 and 223 at the other, arms 220 and 222 being supported at each end and arms 221 and 223 having one end free and unsupported. The edges of the strap-engaging surfaces are rounded or beveled as shown in the drawing to avoid cutting the strap.

In Figure 9 the buckle is shown laced with a strap 224 which extends about a bale 225. In lacing the buckle, a loop 226 of the strap is shoved up through the central opening and then 227 at the other end of the strap is similarly laced through the buckle. The lacing of the strap is performed while bale 225 is under pressure in a baling press and when the press is released the bale expands thereby drawing the strap tight and under considerable tension. Because of the snubbing of the strap about the arms of the buckle there is very little if any slipping of the strap.

The tension on the strap, because of the way it is looped through the buckle, imposes forces tending to move arms 220 and 221 toward one another and to move arms 222 and 223 toward one another. The force on arras 220 and 222 is evenly distributed at the two ends of the arms since both ends are fixed but since arms 221 and 223 are each supported at only one end the entire force must of course be carried by the supported end. In order for arms 221 and 223 to be able to support as great a load as arras 220 and 222 it is necessary to provide more metal in the vicinity of the supported ends of arms 221 and 223 and it will be seen from the drawing that this is accomplished by sloping the sides 210 and 211 with respect to the ends of the buckle. The chain-dotted lines 228 and 229 indicate the size of a rectangular blank which would be required to provide the same amount of material for supporting arms 221 and 223 and 'it will be seen that a rectangular blank of this size would provide also additional support for the left hand end of arm 220 and the right hand end of arm 222. However since there is no need for arms 220 and 222 to be more strongly supported than arms 221 and 223, the buckle with the sloping sides is from a practical aspect just as strong as a buckle cut from a rectangular blank and of course uses less metal.

The applicant has described the above connecting devices since one of the problems which can arise in applying plastic strapping is the difficulty of connecting it since it does not respond to the action of normal connecting devices. The applicant has found that when using the connecting devices described in combination with the strapping an unusually secure connection is obtained.

Materials One skilled in the art will readily be able to selec from the many extrudable polymeric materials available those which are effective to provide the combination of physical characteristics defined herein by the applicant as being effective for strapping use. A preferred material is polypropylene. However, many other materials may be used as well be well understood by one skilled in the art, for example, other polyolefins, for instance polyethylene, polycarbonates, polyesters, nylons, acrylic resins, polystyrene, to mention only a few.

Such materials are long chain linear polymers which are extrudable into filaments and fibres by the melt extrusion process. The applicant does not claim per se any particular technique for the extrusion or after-treatment except that the extrusion and subsequent treatment must be such that the resulting ribbon has. high tensile strength, is balanced and has high tear strength in the lateral direction. The precautions necessary to provide these characteristics are within the skill of those in the extruding art, once they have the necessary information as to the desired characterist ics .

Generally speaking, it is preferable to maintain the extrusion temperature as low as possible to condition the material to proper extrudability, to employ as high a cooling temperature as possible so that the cooling is not abrupt, and that the orientation temperature be as high as possible without melting the polymer. The specific conditions, quantita ively speaking, will vary depending on the particular polymer employed. But having regard to the specifications set out herein for the physical characteristics of the applicant's strapping material and as to the general nature of the conditions required for producing this material, the selection of the precise quantitative conditions to produce the strapping from a given polymer can be selected by one skilled in the art.

Among the precautions which it is necessary to observe are the following. The polymer must be extruded through a nozzle having a substantially rectangular opening at a temperature effect-ive to keep it in a molten condition. The thus extruded ribbon must then be cooled sui'ficiently slowly that the material is homogeneous throughout the thickness of the strapping and so that the cooling does not result in eccentric influences which would be passed on to the final strapping material. After cooling to room temperature, the material of the strapping is reheated to the second order transition temperature and while thus heated is stretched to reorient the molecules in the longitudinal direction which is essential to give the strapping the required tensile strength.

After orientation, the material is cooled to normal temperature to provide strapping according to the invention.

Depending on the specific polymer employed, the material of one strapping may have somewhat different characteristics from strapping made from another material. For example, in the case of polypropylene, strapping of the dimensions specified may split along the longitudinal axis. However, this does not affect the tensile strength and in a sense the strapping can be compared with yarn or cord strapping wherein the tensile strength is almost entirely in the longitudinal direction and the cords are merely held in the lateral direction by adhesive means and can be readily separated. With othei* materials, the tensile strength in the It is thus seen that the plastic strapping of the invention in its preferred form has substantially the shape of steel strapping, that is it is a ribbon of substantially even thickness and balanced so that it will not normally twist when relaxed. Yet it ha£ at the same time the flexibility and the ability to be severed of cord strapping without possessing the disadvantages of either steel strapping or cord strapping which have been discussed above. The strapping exhibits the characteristics of a symmetrically extruded plastic material in the sense that there are no forces within the strapping to cause it to be unbalanced or twist and yet it exhibits the characteristics of having been axlally oriented and subsequently annealed. This results from the symmetrical heating at the extrusion die and symmetrical cooling to prevent eccentric latent stresses in the subsequently oriented and annealed ribbon which would occur if the heating or cooling were asymmetric.

In the case of plastic materials which are degradable by ultra-violet rays, the extruded plastic material may be appropriately filled with a suitable pigment which colors the material and renders the resulting extruded product substantially light stable for strapping purposes. Where necessary to control the physical properties, .plasticizers, and/or other suitable compounds such as synthetic resins, and/or other modifying agents may be added to the plastic materials. The plastic mixtures employed also have a relatively wide temperature co-efficient of softening or hardening in that the strapping is not affected by normal extremes of heat and cold encountered by strapped articles. That is to say, it does not become too brittle under cold conditions and does not soften or become elastic under warm conditions nor-mally encountered in shipping and handling of the articles to which strapping is applied.

The connecting device of Figures 6 and 7 is similar to that disclosed in Canadian Patent 638,834, issued June 16, 1964 to Canadian Gibbon Tape Co. Ltd.

HAVING HOW particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, X declare that what X claim 1B:-

Claims (10)

Claimss

1. A method of making high tensile strength strapping material, characterized in that homogeneous polymeric material is melt-extruded through a die having a substantially rectangular orifice to form a ribbon; that heat is supplied uniformly to the ribbon at all surfaces during extrusionj that the ribbon so formed is dr m away from the orifice and cooled uniformly dow to room temperature; that the ribbon is subsequently heated to below the softening point of the polymeric material and, while thus heated, is stretohed to orient the molecules ax ally to give the strapping high tensile strength and good transverse tear strength; and that the strapping is subsequently annealed to remove stress to result in the ribbon having no tendency to twist, the annealing being effected by heating the ribbon to a temperature higher than the second order transition temperature of the polymeric material, but below its softening point, under relaxed conditions and by cooling the strapping to room temperature under oontrolled conditions of temperature.

2. A method as claimed in claim 1, in which the orifice of the die haa dimensions of from about 1/Qib. of an inch to about 2 inches by .010 of an inch to about ο.οβθ of an inch.

3. · A method as claimed in claim 1 or 2, in which the polymeric material is polypropylene.

4. A method as claimed in claims 1 or 2, in which the polymeric material ·■:· nylon.

5. High tensile strength strapping material constructed f^¾s the method according to any one of claims 1 to 4.

6. High tensile strength strapping material as claimed in claim 5, in which the strapping has an elongation of not more than 10$.

7. High tensile strength strapping material as claimed in claims 5 or 6, in -which the strapping has capacity to transmit at least substantially $ tension around a 9 ° corner.

8. High tensile strength strapping material as claimed in any one of claims 5 to 7 in ^fcich the strapping has energy at break of at least forty pounds per inch and is continuously flexible without losing substan- tial tensile strength.

9. High tensile strength strapping materiel as roade by the method of any of claims 1 to 4, and substantially as herein described with reference to the accompanying drawings.

10. A method of making high tensile strength strapping material substantially as herein described.