US3358434A

US3358434A - Low elongation synthetic rope

Info

Publication number: US3358434A
Application number: US472574A
Authority: US
Inventors: Frank C Mccann
Original assignee: TUBBS CORDAGE Co
Current assignee: TUBBS CORDAGE Co
Priority date: 1965-07-16
Filing date: 1965-07-16
Publication date: 1967-12-19
Anticipated expiration: 1984-12-19

Description

Dec. 19, 1967 C ANN 3,358,434

LOW ELONGATION SYNTHETIC ROPE Filed July is. 1965- INVENTOR. FRANK C. McCA /v \crw'nsmd iioumsnmi A TTORNEYS United States Patent 3,358,434 LGW ELGNGATION SYNTHETIC RSPE Frank C. McCann, Grange, Calif., assignor to Tuhbs Cordage Company, San Francisco, Calif. Filed July 16, 1965, Ser. No. 472,574 9 Claims. (Cl. 57-444) ABSTRACT OF THE DISCLOSURE A synthetic polyolefin rope formed from twisted polyolefin yarn and a central core of pre-stretched polyester fiber. The presence of the polyester fiber in minor amounts, i.e., up to about 25% by weight, provides the rope with low elongation properties similar to that obtained with rope formed entirely of polyester fiber.

This invention relates to synthetic rope. More specifically, it pertains to rope made from a novel combination of filaments of at least two types of thermoplastic synthetic resin, one type being a polyolefin and the other type being a polyester, with the resultant product being characterized by its low elongation properties.

A number of thermoplastic synthetic fibers, possessing a wide variety of properties, have been developed. Certain polyolefin filaments, such as polypropylene, have the advantage and properties of high resistance to chemical and biological degradation, heat resistance, and dielectric strength. Their use is sometimes limited by their relatively high elongation.

On the ohter hand, suitably prepared polyester filaments, such as Mylar (trademark of Du Pont for polyester of diethylene glycol and terephthalic acid), have been found to possess high strength and very low elongation as well as the other advantages of synthetic fibers. Unfortunately, these filaments are quite costly and therefore not always suited for use in ropes where a large cross-sectional dimension is necessary. Such a rope might have a tensile strength greatly in excess of that required. The excess of structural properties would in effect be wasted in the attempt to provide a given cross-sectional dimension.

The present invention provides an all synthetic rope that can be economically manufactured to have the desired larger cross-sectional dimensions. This is achieved through the predominate use of the relatively inexpensive polyolefin fibers, such as polypropylene. While using these polyolefin fibers the product of the invention eliminates the undesired elongation of polyolefins through combination with a relatively minor amount of pre-stretched polyester threads in the strands of the rope as will be discussed more fully hereinafter.

The rope of this invention has low dielectric properties together with the chemical resistance of synthetics. The rope is economically feasible for use where cost is a limiting factor and Where the cross-sectional dimensions of the rope are critical, such as in the cases where the rope is to be hand grasped, i.e. certain aspects of sailing and in other special cases such as in rope operated extension ladders. These uses require low elongation which is not found in polyolefins previously available but which requirement is satisfied by the present ropes.

Aside from the cross-sectional dimensions or bulk, another advantage over pure polyester rope of the same 3,358,434 Patented Dec. 1%, 1967 strength (which would have a small cross section) is found in an added safety feature. When the polyester content elongation is exceeded causing the polyester filaments to break, the large polyolefin content of the rope is still available as a backstop. While the polyolefin fibers may elongate under the forces at work, these forces may not be sufiicient to cause a break of the polyolefins entirely and thus will avoid a complete severance of the rope long enough to take corrective action.

In the accompanying drawings:

FIG. 1 is an elevation of a three strand rope constr-ucted in accordance with the present invention;

FIG. 2 is a cross-section of the rope of FIG. 1 showing the relationship of the polyolefin and polyester components thereof; and

FIG. 3 is a cross-section taken through an alternate embodiment of the present invention in which the rope is in braided form instead of the twisted form of FIGS. 1 and 2.

In general, the present rope may be constructed with one or more strands twisted together in conventional fashion. Each strand is formed with a plurality of twisted polyolefin yarns. Each strand also contains a central core of pre-stretched polyester thread in an amount sufiicient to significantly decrease the elongation of the polyolefin yarns.

Alternatively, and as shown in FIG. 3, the invention may be utilized in the fabrication of braided type rope in which one or more braided outer coverings of a polyolefin surrounds a core of parallel filaments. At least some of the filaments are pre-stretched polyester thread.

The term pre-stretched polyester thread as used in this specification and claims includes those polymers formed by the condensation reaction of an alkylene glycol with a phthalic acid. The reaction between two such materials, e.g. ethylene glycol and terephthalic acid is illustrated by the following equation.

When this condensation reaction is catalytically accelerated, the resulting chain reaction produces a polyester of diethylene glycol and terephthalic acid. The polyester is generally obtained in a continuous transparent, highly flexible film form. A number of commercially available polyester films which generally possess the properties desired herein and are commercially available under such trademarks as the following: Dacron, Kodel, Vycron and Fortrel. The material known as Mylar is especially useful for present purposes. All of these materials are polyesters of the above general type with minor variations developed by the proprietor of the trademark.

The polyester film as supplied by the manufacturer must be processed or pre-stretched into a thread form prior to use in the manufacture of the instant ropes. In general, the polyester film is run between two capstans under tension. At the same time, heat is applied to the film. The combination of heat and tension reduces the film to a thread configuration and substantially removes the elongation of the material. At this point the threads 3 are ready for incorporation in the present ropes. Polyester thread of this type is well-known in the art and commercially available.

Polyolefin as used in this application is meant to include conventional filaments which are characterized by their relatively low elastic recovery, low tensile strength and low density. Such filaments or yarns generally have molecular weights less than about 100,000 and are extruded from such resin polymers as polyethylene and polypropylene. Polypropylene yarns are preferred for present purposes.

As noted above, the rope of this invention is made with differing amounts of the two types of synthetic resins. The polyolefin is the predominate component of the rope with the polyester forming a central core along the longitudinal axis of the rope. In general, the results desired are best achieved where the polyester core comprises about 10-25% by weight of the two synthetics utilized in the rope, with the polyolefin, therefore, running from about 7590% of the rope depending upon the polyester content. A particularly advantageous rope has been made with polypropylene and Mylar polyester wherein the Mylar constitutes about 15% by weight of the rope.

The strands for the rope may be made by conventional methods and machines. In the preferred embodiment, a plurality of polyester threads are utilized rather than one large single thread, and these threads are twisted and inserted as a central core for helically wound outer polyolefin yarns. In the preferred embodiment three strands are twisted in the usual fashion to form a rope with each strand having the polyester core as noted. While the polyester could be intermixed with the polyolefin, a significant advantage in the manufacture of the rope is obtained through the use of the central core concept.

Referring to the drawings showing the preferred three strand rope, FIG. 1 shows

strands

1, 2 and 3 helically interwoven in conventional (regular twist) configuration. The end of strand No. 1 is shown with its yarns 4, 5 and 6 separated so that the central polyester core 7 is exposed.

In the cross-sectional view of FIG. 2 the relationship of the parts can be more clearly seen. The three

strands

1, 2 and 3 are similar and only strand 3 is illustrated in detail. Strand 3 is composed of polyolefins such as polypropylene yarns 4, 5 and 6 which are helically wound about a central core 7, which constitutes the polyester threads. Polyester thread 7 is a plurality of individual polyester threads which take on a helical twist during manufacture of the rope.

In the alternate embodiment shown in FIG. 3, a braided rope is illustrated. The rope contains an outer covering 8 made from a polyolefin, such as polypropylene, and in which the filaments are intertwined in conventional braid configuration. The outer covering may be made in a plu rality of layers if desired. The central core 9 is formed with a plurality of relatively straight parallel longitudinal filaments. The bulk of the filaments may be made of any suitable material and will generally be a polyolefin similar to that used in forming the outer covering 8. The central core also contains a plurality of pre-stretched polyester threads 10 to provide the low elongation properties of the rope.

The rope illustrated in FIG. 3 will generally exhibit less elongation than the twisted rope illustrated in FIGS. 1 and 2. The central core filaments of the braid are actually shorter in a given length of rope as compared with the length of polyester thread found in the same length of twisted rope. In the twisted rope the center filaments are longer since they define a helix along the rope, whereas the center filaments of the braid are relatively straight and parallel. As a result, when the elongation forces are applied to the rope of this invention, a certain amount of untvvisting of the filaments in the twisted rope must occur before the central polyester thread becomes loaded. The elongation which occurs during this untwisting move- Ineut is avoided in the braid rope since the polyester 4 thread is immediately stressed when elongation forces are applied.

The rope obtained from the above constructions can be made to have the equivalent strength of naturally occurring fiber rope together with desirable bulk at a reasonably low cost. At the same time, the new rope of this invention eliminates the elongation properties of the previously known low cost synthetics and retains the usual properties of synthetic such as chemical resistance and resistance to biological degradation as well as the desirable dielectric properties.

While a good deal of variation in proportions is possible depending upon the requirements for the rope end product the following figures will demonstrate the advantageous properties of the present invention. Thus, a diameter, 3 strand polypropylene (regular twist) rope is made up containing 15% by weight pre-stretched Mylar polyester. The polyester was inserted as a twisted central core for each of the strands of the polypropylene. This rope had an elongation of 1.8% under a 200 lb. load. The same size rope made entirely from polypropylene has an elongation of 5% under the same load making it unacceptable for many uses.

' Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it is understood that certain changes and modifications may be practiced within the spirit of the invention as limited only by the scope of the appended claims. 7

What is claimed is:

1. An improved synthetic polyolefin rope characterized.

by low elongation properties comprising: at least one strand formed from a plurality of twisted polyolefin yarns and a central core for said strand of pre-stretched polyester thread in an amount sufiicient to significantly decrease the elongation of said polyolefin yarns.

2. A synthetic rope in accordance with claim 1 wherein said central core comprises a plurality of twisted polyester threads, and said polyolefin is selected from the group consisting of polypropylene and polyethylene.

3. A synthetic rope in accordance with claim 2 wherein said polyolefin is polypropylene.

4. A synthetic rope in accordance with claim 1 wherein said strand contains about 10-25% by weight of polyester thread.

5. A synthetic, two-component, fibrous rope comprising: three helically wound strands, each strand composed of a central core constituting about 15% by weight of the strand of twisted prestretched Mylar polyester threads, and an outer covering for each of said strands of a plurality of twisted and helically wound polypropylene yarns.

6. An improved low elongation rope formed from at least two different synthetic resin comprising: a plurality of helically wound strands, each of said strands composed of an outer covering formed from a plurality of twisted and helically wound yarns of polyolefin selected from the group consisting of polypropylene and polyethylene, and

a central core for each of said strands, constituting about.

1025% by Weight thereof, of polyester threads formed from polyester film that has been drawn into thread form under heat and tension.

7. An improved synthetic polyolefin rope characterized by low elongation properties comprising: an outer cover formed from a plurality of polyolefin yarns and a central core for said outer cover, including a suflicient amount of pre-stretched polyester thread to significantly decrease the elongation of the polyolefin yarns.

8. A synthetic rope in accordance with claim 7 wherein said polyolefin is selected from the group consisting of polypropylene and polyethylene.

9. A synthetic braided rope of low elongation comprising: a plurality of parallel elongate polyolefin yarns, a plurality of pro-stretched polyester threads mixed with said polyolefin yarns and parallel thereto, and a braided 5 6 covering for said polyolefin yarns and polyester threads FOREIGN PATENTS formed from polyolefin y 585,066 10/1959 Canada.

811,501 4/1959 Great Britain.

References Cited 996,874 6/1965 Great Britain.

UNITED STATES PATENTS 5 891,618 9/1959 Great Britain. 2 v gigg; 28 73 FRANK I. COHEN, Primary Examiner. 3,205,649 9/ 1965 Nishet et al. 5-7-140 DONALD E. WATKINS, Assistant Examiner.

3,315,455 4/1967 Stoller 57144

Claims

1. AN IMPROVED SYNTHETIC POLYOLEFIN ROPE CHARACTERIZED BY LOW ELONGATION PROPERTIES COMPRISING: AT LEAST ONE STRAND FORMED FROM A PLURALITY OF TWISTED POLYOLEFIN YARNS AND A CENTRAL CORE FOR SAID STRAND OF PRE-STRETCHED POLYESTER THREAD IN AN AMOUNT SUFFICIENT TO SIGNIFICANTLY DECREASE THE ELONGATION OF SAID POLYOLEFIN YARNS.