US3791129A - Rope and its manufacture - Google Patents

Abstract

Rope having improved working qualities and hand without need to contain sizing or lubricants consists of a plurality of strands of fibrillated polyolefin film having a delustered surface. The film is delustered by surface abrasion prior to fibrillation and twisting into strands. Such rope exhibits low internal friction producing its good working qualities and low abrasion to objects in which it comes in contact producing its improved hand.

Description

United States Patent [191 Shuford Feb. 12, 1974 ROPE AND ITS MANUFACTURE [75] Inventor: Abner P. Shuford, Hickory, NC.

[73] Assignee: Shuford Mills, Inc., Hickory, NC.

[22] Filed: Sept. 3, 1971 [21] Appl. N0.: 177,784

OTHER PUBLICATIONS Textile Month Magazine pp. 79, November 1970.

Primary Examiner-Donald E. Watkins Attorney, Agent, or Firm-Kemon, Palmer & [52] US. Cl. 57/140 R, 57/157 R, 57/167 Estabrook [51] Int. Cl D02g 3/06 [58] Field of Search 57/167, 140 R, 157 R; 57 ABSTRACT 28/DIG' 1 Rope having improved working qualities and hand without need to contain sizing or lubricants consists of [56] References a plurality of strands of fibrillated polyolefin film hav- UNITED STATES PATENTS ing a delustered surface. The film is delustered by sur- 3,371,477 3/1968 Miribel 211/1310. 1 UX face abrasion prior to fibrillation and twisting into 3,470,591 10/1969 Goppel 28/DlG. 1 UX strands. Such rope exhibits low internal friction pro- 3,639,573 2/1972 PO11 28/DIG. l X ducing good working qualities and low abrasion to 3333929 2/1966 Rasmussen 28/DIG- I UX objects in which it comes in contact producing its im- 3,461,662 8/1969 Meyer et a1 57/167 X proved hand. 3,496,716 2/1970 Howard at a]. 57/167 X 3,423,888 1/1969 Brown 28/D1G. 1 4 Claims, 3 Drawing Figures EXTRUSION QUENCHING SLITTING DRAWING W ROPE TWISTING FIBRILLATING DELUSTERING we FORMING PATENTEUFEB 12 m4 3.791.; 129

EXTRUSION QUENCHING sunme DRAWING j ROPE' TWISTING I FIBRILLATING DELUSTERiNG FORMING ROPE AND ITS MANUFACTURE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention concerns rope which is made of a plurality of strands of fibrillated polyolefin film having a delustered surface. It also concerns the manufacture of such rope by an operation which involves extrusion of polyolefin film, orientation of the film, delustering, fibrillation, twisting of the film into a strand and then forming rope from a plurality of the strands.

2. Description of the Prior Art It is well known to form ropes from strands of extruded thermoplastic material. Such ropes may be made by twisting a narrow strip of plastic material which has been oriented in the direction of its length and then plying together a plurality of such twisted strands (see U.S. Pat. No. 2,403,317). Other ropes of synthetic fibers have been made by plying together extruded filaments of plastic materials including polyolefins (see U.S. Pat. No. 3,145,525). Also, ropes have been formed by extrusion of a plastic film, slitting film into narrow strips, fibrillating the strips, twisting the fibrillated strips to form threads and then plying together a plurality of these threads into a rope (see U.S. Pat. No. 3,371,477). The present invention is concerned with improvements in this latter type of rope, namely, a rope made of a plurality of strands of fibrillated film.

The fibrillation of films or strips of extruded thermoplastic material which have beenoriented by stretching sufficiently to permit the film to be fibrillated is well known in the art. Various techniques have been developed for producing thefibrillation of the oriented plastic film. One general method involves subjecting the oriented film in narrow strips to the impact of an air jet, e.g., see US. Pat. Nos. 3,214,899; 3,293,844 and 3,242,035). Another method is to subject the oriented film to sand blasting or similar impact of a jet of fine solid particles against the film while it is stretched out and under tension (see U.S. Pat. No. 3,371,477). A further procedure involves passing an oriented plastic film between an opposed pair of rotating wire brushes or similar rollers which have piercing means projecting from their surface (see U.S. Pat. No. 3,302,501). Additional methods include beating of an oriented film (see U.S. Pat. No. 2,853,741 folding orientedplastic film (see U.S. Pat. No. 3,003,304) and pleating transverse to the longitudinal direction of an orientedplastic film (see U.S. Pat. No. 3,165,563).

Rope which has been made of extruded thermoplastic material may exhibit a variety of undesirable qualities. For example, it may be of a stiff nature and act more like a wire cable than a conventional rope made of vegetable or animal fibers. Also, the rope may exhibit a somewhat abrasive quality so that it is detrimental to the hands of persons using the rope, to sheaves or other articles with which the rope comes in contact. It is desirable for rope to have a soft non-abrasive nature so that it is easy to tie and handle and will exhibit a minimum of wear to sheaves or other objects over which it passes or comes in contact. Thisdesirable feature is referred to in the trade as hand.

Another disadvantage which may be exhibited by rope made of strands of extruded plastic material is a tendency toward internal friction. A rope under stress may develop a tremendous amount of internal friction which then may lead to rapid reduction in tensile strength of the rope and its useful life. The expression working is used in the rope trade to describe a quality of a rope not to exhibit a substantial amount of internal friction. Thus, a rope of improved working quality will have a minimum of internal friction and correspondingly an extended useful life.

Yet another disadvantage of ropes made of extruded thermoplastic material is an artificial or synthetic appearance as compared with conventional ropes made of animal or vegetable fibers. Ropes made of syntheticplastic materials tend to have a shiny artificial appearance which is objectionable to a variety of purchasers and users of rope.

Notwithstanding the great amount of prior knowledge and development of ropes made of synthetic plastic materials as discussed above, there exists a need for improvements in this class of product, i.e., improvements in the working qualities, the hand qualities, and appearance of rope formed of strands of extruded thermoplastic material are desirable.

OBJECTS A principle object of this invention is the provision of improved ropes made of extruded thermoplastic material. Further objects include the provision of:

l. Rope made of a plurality of strands of extruded thermoplastic material, which rope exhibits improved working qualities and handwithout use of sizing or lubricants.

2. Such rope which possesses an appearance comparable to rope made of conventional naturally occurring fibers.

3. New methods of making rope from thermoplastic synthetic resins.

4. Rope which has an appearance similar to natural jute or sisal rope but which possesses substantially higher strength and is not subject to mildew, rotting or the like as occurs with natural jute or sisal rope.

Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detaileddescription, while indicating preferred embodiments of the invention, is given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. It should also be understood the foregoing abstract ofthe disclosure is for the purpose of providing a non-legal brief statement to serve as a searching-scanning tool for scientists, engineers and researchers and is not intended to limit the scope of the invention as disclosed herein nor is it intended it should be used ininterpreting or in any way limiting the scope of fair meaning of the appended claims.

SUMMARY OF THE INVENTION The foregoing objects are accomplished in accordance with the present invention by forming rope out of a plurality of strands of fibrillated polyolefin film that have a delustered surface. In the preferred embodiment, the polyolefin is polypropylene which has been orientedin the longitudinal direction of the strand by drawing the polyolefin film at a ratio of at least 3 to l and the delustered surface is obtained by abrasion of the surface of the film prior to fibrillation and as a separate step from the fibrillation.

The foregoing objects are also, in part, accomplished by a method of making rope from polyolefin material which comprise the following steps:

a extruding a film of solid polyolefin resin,

b drawing the film in the direction of its longitudinal axis at a ratio of at least 3 to l,

c delustering the surface of the film by abrading at least one surface of the film,

(I fibrillating the resulting delustered film,

e twisting the fibrillated film of step d into a strand, and

f forming a rope from a plurality of strands resulting from step e.

BRIEF DESCRIPTION OF THE DRAWING In further explanation of the invention, reference is made to the accompanying drawing in which:

FIG. 1 is a block flow diagram of the new methods of the invention.

FIG. 2 is a diagrammatic side view of drawing and delustering section of apparatus used in making rope in accordance with the invention.

FIG. 3 is a diagrammatic top view of a fibrillator in accordance with the invention.

With reference to FIG. 2, polyolefin film 2 traveling in the direction of the arrow from an extruder via a slitter and water-bath quencher (not shown) passes through a first pair of nip rolls 4 into the hot-air oven 6. The heated film 2a exits from the oven 6 and passes to the deluster 8. This comprises a frame 10 that carries circular plate 12 that may be rotated in the plane of the frame 10 so that the drums l4 and 16 carried by the plate 12 may be offset in varying amount with respect to the direct path of travel of the film 2a from the oven 6 to the guide roller 18 rotatably mounted on the frame 10. The drums have coated abrasive sheets cemented thereto as discussed in more detail hereinafter.

The bottom surface of the film 2a contacts the abrasive surface of drum 14 substantially tangentially while the drum is rotated in a direction opposite to the direction of travel of the film. Also, the top surface of the film similarly contacts drum 16 which is rotated in the same direction as drum 14.

The film after passing over the guide roller goes through the nip of the second pair of rollers 20. The rollers 20 rotate at a higher rate than rollers 4 and this differential results in the drawing of the film between the rollers 4 and rollers 20 producing the oriented film 2b.

With reference to FIG. 3, the film 2b from the nip rollers 20 as strips 22a pass in the direction of the arrow to the fibrillator 24. This comprises a drum 26 that rotates on the shaft 28 and has a multiplicity of blades 30 extending therefrom. The strips 22a are intercepted by the rotating blades 30 and the action of the blades converts the strips of film by fibrillation into webs or ribbons 22b of intertwined fibers and fibrils. These ribbons then pass to twisters (not shown) where they are twisted into strands or yarns.

DESCRIPTION OF PREFERRED EMBODIMENT A quantity of isotactic polypropylene containing about 5 percent of a light tan pigment was obtained from a commercial supplier of the resin in the form of small pellets or chips designed for use in an extruder. A film of this polypropylene extrusion composition 30 cm. wide and 0.1 mm. thick was extruded into a water bath. The cooled film was withdrawn to a slitter consisting of a plurality of revolving discs with knife edges which sliced the film into strips approximately 3 cm. in width. From this slitter the strips passed between a first pair of nip rollers to a hot-air oven maintained at a temperature of about 150 C.

The film was led from the hot-air oven to a pair of abrasion drums each of which was about 20 cm. in diameter and about 30 cm. wide. Around the outside surface of each of these drums there was fixed by suitable cement a sheet of coated abrasive paper bearing abrasive grains of a size designated by the coated abrasives industry as size 400. These drums were spaced apart from one another a distance equal to about three times their diameter and they were rotated at a speed of about revs. per minute in a direction opposite to direction that the strips were drawn past them so the strips contacted one drum tangentially on one side and the other drum tangentially on the other side. As the strips emerged from these abrasive rollers on the downstream side, they had a delustered appearance as compared with the shiny or glossy appearance possessed before contact with the abrasive rollers.

The stretched and abraded polypropylene strips were then passed to a fibrillator which consisted of a drum from which pieces of hacksaw blade about 30 cm. in length extended at intervals about 4 cm. apart, the drum being about l0 cm. in diameter and about 30 cm. wide. The drum was revolved at a speed of about 1,000 revolutions per minute and the film was passed across the drum so that the blades extending therefrom intercepted the path of travel of polypropylene film. This step resulted in the strips each being fractured into a web of interlaced thin filaments or fibrils. These narrow webs or ribbons of fibrillated polypropylene were then passed to take ups for storage.

In the next step of the operation, the fibrillated ribbons of polypropylene were fed from the take ups and passed through textile twisters in which the ribbon was twisted into a yarn having about two turns per inch of yarn. This twisted yarn was led from the twister to a winder where the yarn was wound into a finished package.

In the final step of the operation, twelve yarns each delivered from a separate package positioned in a conventional rope-braiding machine were passed through the braider and formed into a braided rope having a diameter of about 6 mm. The resulting rope had a light tan appearance that looked very much like natural jute or-sisal but possessed a tensile strength approximately three times that of a rope of comparable construction and size made of the natural jute or sisal fibers.

DISCUSSION OF DETAILS A variety of thermoplastic materials may be used to form the extruded films used in making rope in accordance with the invention. Polymers capable of possessing appreciable amount of crystallinity which will retain orientation after being cold-drawn may be used. Isotatic polyolefins are preferred including high-density polyethylene, isotatic polypropylene and comparable polyolefins. Other usable polymers for forming the films include vinylidene chloride polymers, isotatic polystyrene, polyamides, polyesters and polyacrylonitrile. Crystalline copolymers can also be used.

The thermoplastic material is formed into a film of suitable width and thickness by extrusion. A wide variety of extrusion equipment is commercially available for this purpose. The width of the extruded film prior to cold-drawing is not critical and may be as narrow as about cm. or as wide as about 100 cm. The thickness of the film can also be varied but will be controlled by the desired thickness in the strand which is to be fibrillated. Since the original extruded film will be colddrawn at a ratio of at least 3 to l, and may be as high as to 1, and since the thickness diminishes approximately proportional to the ratio of cold-drawing, extruded film will have a corresponding thickness. Advantageously, the thickness of the strands of film in the final rope will be about 0.01 to 1.0 mm. Hence, depending upon the degree of cold-drawing, the thickness of the extruded film as obtained directly from the extrusion die may be from about 0.03 to 20 mm. Most satisfactory operations according to the invention are obtained when the drawing of the film in the direction of its longitudinal axis is at a ratio of between about 6 to l and 10 to 1 and the extruded film prior to colddrawing is between about 0.05 to 10 mm.

Cold-drawing of the extruded film to form the oriented films which are fibrillated in the methods of the invention can be accomplished by a wide variety of commercial equipment. Normally two different pairs of rollers are used which are operated so that the downstream pair rotates at a speed which is greater in speed than the up-stream pair of rollers proportional to the amount of drawing to which the extruded film is to be subjected. Also, in the drawing operation, the extruded film can be advantageously heated, such as in an elongated oven, to an elevated temperature while undergoing the drawing. Steam or hot air ovens can be used at temperatures advantageously between about 70 to 150 and preferably to 90 to 120 C. Infrared radiation heaters, dielectric heaters or the like may be used in place of air or steam ovens.

Delustering of the film in accordance with the invention, is preferably conducted simultaneous with or after the drawing and orientation of the film. Delustering is performed by passing the oriented film into contact with a surface to which there is affixed abrasive grains. Such abrasive grain may be of varied size but is advantageously of a size between about 100 and 600 mesh on a standard sizing sieve. Advantageously, the contact of the film in the abrasion step is accomplished by passing the film over revolving drums (rollers) to which coated abrasive sheets have been fixed with the drums driven in a direction opposite to the direction of travel of the film between the nip of the drums. Drums at least as wide as the width of the parallel array of strips passing over them should be used and they may be of various diameters, e.g., 2 cm. to 20 cm. or larger. The drums may be offset from the travel path of the strip array in different degrees to impose various pressures upon the surfaces of the strips depending, in part, upon the size of the abrasive grain in the coated abrasive affixed to the periphery of the rollers. Pressures between 0.1 and 100 lbs. per square inch and preferably between 1 and 10 lbs. per square inch can be used.

After quenching the extruded film and before orientation and delustering, it is advantageously slit into narrow strips or ribbons. This can be accomplished by any suitable cutting means including fixed means cutting blades, rolling disc cutters, flame jets, wires or the like. Preferably, the film is slit prior to orientation and delustering into ribbons or strips that are 1 to 20 cm. wide and preferably 5 to 10 cm.

Fibrillation of the resulting strips of delustered and oriented film can be accomplished in any of the manners known in the art including those discussed previously herein. However, the preferred results are obtained in accordance with the invention by fibrillating the strips by passing them over a plurality of blades that are rotated around an axis transverse to the axis of travel of the strip. Blades about 30 cm. in length, 0.01 to 1 mm. in width may be used mounted so as to extend from a drum at intervals of about 4 cm. apart. Such blade-carrying drums may be operated at various speeds depending upon their diameter and the speed with which the plastic strips are passed over the rotating blades, e.g., between about to 2,000 revolutions perminute. per minute.

The passage of the delustered film over the rotated blades produces fibrillation of the strips causing it to be transformed into a'web composed of numerous intertwined fibers or fibrils interconnected with one another at various points. Such fibrillated webs or ribbons may be then directly conveyed to a twisting operation. However, because the speed of throughput in the twisting step may not correspond to the speed of throughput in the fibrillation step, it is advantageous to collect the fibrillated ribbons from the output of the fibrillation operation, store such collected ribbons and then use them in a subsequent twisting operation.

Twisting of the fibrillated ribbons may be accom plished on any of a variety of twisters which are used in the yarn and related textile field. Preferably, the fibrillated ribbons are twisted into yarns with a degree of twist which may be between about 0.1 to 20 turns per inch of length of twisted yarn and advantageously between about 0.5 and 5 turns per inch of yarn.

The yarn may be directly passed from the twister to a rope-forming operation with sufficient number of twisters used to correspond to the number of strands of yarn which will be required for the final rope. However, again because of differential in speed of operations between the twisting and rope-forming steps, it is desirable to collect the yarn from the twister in a package which will be of suitable size to be handled in any of a variety of rope-forming machines either the laid (twisted) rope type or the braided type. The twisting or braiding of the yarns obtained in accordance with the invention, will follow conventional rope-forming practice and the use of conventional rope-forming machinery. Commonly three-ply rope will be made if the rope is of the laid variety while 6 to IZ-strand rope or even higher number of strands may be used where the rope is of a braided variety. Any suitable size rope may be formed in accordance with the invention, the conventional sizes being from about one-eighth of an inch to 6 inches with the major volume being in the onequarter to 1 inch sizes.

The embodiments of the invention in which an exclusive property or right is claimed are defined as follows:

1. Rope consisting of a plurality of twisted strands of fibrillated polyolefin film the surfaces of which are delustered by multiple abrasions of the form that result from drawing polyolefin film in its longitudinal direction across a surface bearing abrasive grain of about 100 to 600 mesh size.

2. A method of making a rope from polyolefin material to possess improved working qualities and hand without the use of sizing or lubricants comprising:

a. extruding a film of solid polyolefin resin,

b. drawing the film in the direction of its longitudinal axis at a ratio of at least 3 to l,

c. delustering the surface of the film by abrading at least one surface of the film by passing the film into tangential contact with a drum covered with coated abrasive sheets bearing abrasive grains of about 100 to 600 mesh size, said drum being mounted for rotation on an axis transverse to the axis of passage of said film,

d. fibrillating the resulting dulustered film,

e. twisting the fibrillated film of step 11 into a strand, and

f. forming a rope from a plurality of strands resulting from step e."

3. The method of claim 2 wherein there is a plurality of said drums each of which is rotated in a direction opposite to the direction of travel of said film and one surface of said film contacts at least one of said drums and the other surface of the film contacts at least another of said drums.

4. The method of claim 2 wherein the pressure of contact between the surface of the film and the drum is between about 1 to 10 lbs. per square inch.

Claims (4)

1. Rope consisting of a plurality of twisted strands of fibrillated polyolefin film the surfaces of which are delustered by multiple abrasions of the form that result from drawing polyolefin film in its longitudinal direction across a surface bearing abrasive grain of about 100 to 600 mesh size.

2. A method of making a rope from polyolefin material to possess improved working qualities and hand without the use of sizing or lubricants comprising: a. extruding a film of solid polyolefin resin, b. drawing the film in the direction of its longitudinal axis at a ratio of at least 3 to 1, c. delustering the surface of the film by abrading at least one surface of the film by passing the film into tangential contact with a drum covered with coated abrasive sheets bearing abrasive grains of about 100 to 600 mesh size, said drum being mounted for rotation on an axis transverse to the axis of passage of said film, d. fibrillating the resulting dulustered film, e. twisting the fibrillated film of step ''''d'''' into a strand, and f. forming a rope from a plurality of strands resulting from step ''''e.''''

3. The method of claim 2 wherein there is a plurality of said drums each of which is rotated in a direction opposite to the direction of travel of said film and one surface of said film contacts at least one of said drums and the other surface of the film contacts at least another of said drums.

4. The method of claim 2 wherein the pressure of contact between the surface of the film and the drum is between about 1 to 10 lbs. per square inch.

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