US3446002A - Monofilament twines - Google Patents

Description

y 7,1969 .LA. KIPPAN 3 44 MONOFILAMENT TWINES Filed March 22, 1965 INVENTOR JAMES A. KIPPAN United States Patent U.S. Cl. 57-140 7 Claims ABSTRACT OF THE DISCLOSURE A twine comprised of a bundle of substantially parallel synthetic monofilaments with a synthetic binder material in thin band form wrapped around and fused to them so as to leave exposed parts of the outer monofilaments has been found to form knots which are less susceptible to slippage while maintaining good flexibility.

This invention relates to synthetic monofilament twines.

The term twine is intended to include cords, strings and the like.

An object of the present invention is the provision of synthetic monofilament twines, and particularly twines made of polyolefins, which have superior flexing and knotting characteristics to any synthetic twines heretofore on the market.

Another object is the provision of twines having consistent characteristics throughout the length thereof, and which are rot resistant and resistant to ultraviolet radiation.

A further object is the provision of a synthetic twine having monofilaments extending substantially parallel to each other, and including means for retaining the monofilaments in their proper relationship to each other without interfering with the flexibility of the twine and without materially increasing the cost thereof.

Heretofore, twines and cords have been produced almost entirely from natural fibres. While these fibres have fulfilled their intended purpose, they are rapidly being replaced by superior synthetic fibres, for example, the rapid increase in usage of polypropylene fibres for rope construction. The natural fibres used in making twines, for example, baler twine, were generally sisal or henequen or a combination thereof. Such fibres are short and stiff and difiicult to process with consistency. In ordinary agricultural twines it is usual to find a strength variation in the twine of up to 40% throughout its length. Because of the wide strength variation in natural fibre twines, they are generally constructed larger than necessary to allow for weak spots which are inherent in their construction. Due to the shortness of natural fibres, twines constructed therefrom must be twisted with reasonable short lay to develop the strength of the fibres. Natural fibres also deteriorate rapidly from rot.

Numerous attempts have been made to construct twines and cords of oriented polyolefin monofilaments by surrounding a plurality of monofilaments with a continuous or interrupted casing of polyolefin. When the casing is constructed of polyethylene, or copolymer thereof, the coefiicient of friction of the casing is low. In a simple knot, such as tied by the mechanical knotter of a bailing machine, the casing of the twine acts as a lubricant and allows the knot to slip and roll, thus reducing knot strength. In addition, the coefficient of friction between the casing and the monofilaments is low and the monofilaments tend to slip within the casing and pull through the knot construction before assuming their proper tensile load.

The addition of inorganic fillers, to a polyethylene 3,446,002 Patented May 27, 1969 casing, in sufiicient quantity to appreciably increase the coefiicient of friction also increases the stiffness of the casing. The increased stiffness is undesirable in that an ordinary mechanical knotter can only partially close a simple knot before releasing it. When tension is applied to the main twine legs, as when a hay bale is released from the baler, the partially closed knot does not bed or close sufficiently to prevent the cut knot ends from slipping through the knot, causing failure.

When the casing is made of polypropylene or a copolymer thereof, the casing acts as a tube or partial tube and exhibits undesirable stiffness. Again, a mechanically tied knot does not fully close and the cut ends tend to pull through allowing failure.

Encased twines or cords exhibit an additional undesirable characteristic in that they resist axial twisting. When a twine or cord is pulled or payed out from the centre of a ball of twine or cord there results one axial twist for each ball circumference of twine pulled out. In the case of mechanical hay balers, the said twist, generated in the twine, tends to remain in the twine chamber of the machine and is cumulative. When sufficient axial twists accumulate in a short unsupported length of twine, the twine tends to twist upon itself forming a snarl. The resultant snarl tends to foul the tensioning devices and guides of the machine and cause twine failure.

The present invention overcomes these objections to the prior synthetic twines by a twine made up of a bundle of synthetic monofilaments extending lengthwise thereof substantially parallel to each other, and a synthetic binder in band form made of material compatible with the m-onofilament material around said monofilaments and preferably fused to and partly fitting around each of the monofilaments with which it is in contact. The binder is such that it leaves some parts of the outer filaments exposed, and forms edges extending generally circumferentially of the twine. These edges act as cleats which help to prevent any slippage at a knot formed by this twine. The monofilaments are preferably stretched or oriented in the manner well known in the industry. These monofilaments are oriented at an average draw ratio ranging from about 7 to l to about 9 to 1.

Examples of the present invention are illustrated in the accompanying drawings, in which,

FIGURE 1 is an illustration of a simple knot made with this twine,

FIGURE 2 is a perspective view, much enlarged, of a piece of twine embodying one form of the invention,

FIGURE 3 is an enlarged cross section taken on the line 33 of FIGURE 2,

FIGURE 4 is a perspective view of a piece of twine embodying an alternative form of the invention, and

FIGURE 5 is a cross section taken on the line 55 of FIGURE 4.

Referring to the drawings, FIGURE 1 illustrates a simple twine knot 10 joining two pieces of twine 11 and 12. These twines form main tension members which are brought together side by side and wound into a circular wrap 15 which is disposed substantially at right angles to the main members 11 and 12.

FIGURES 2 and 3 illustrate one of said pieces of twine, for example, twinle 11, made in accordance with the present invention. The twine is made up of a bundle of oriented synthetic monofilaments 20 extending lengthwise of the twine substantially parallel to each other. It is preferable that the monofilaments be substantially parallel with the longitudinal axis of the twine, but they may have some twist in them, and it is intended that the words substantially parallel as used herein and in the claims include this twist. A synthetic binder 22 extends around monofilaments 20 and preferably is fused to the monofilaments with which it comes into contact. For example, binder 22 comes into contact with and is fused to the outer monofilaments at 24, see FIGURE 3. As the band is applied to the outer monofilaments while it is hot enough to fuse thereto, said band also partly fits around each monofilament with which it comes into contact, as clearly shown in FIGURE 3. In this example, binder 22 is a thin band wound in a spiral around the bundle of filaments. It is to be understood that a plurality of bands may be spirally wound around the tfilaments. The spiral winding leaves gaps 26 between the windings at which some of the monofilaments are exposed. In addition to this, the binder band has side edges 28 and 29 which extend generally circumferentially of the twine and tend to act as cleats. Binder 22 cannot be shifted longitudinally of the twine because it is fused to each outer monofilament over a comparatively large contact area, and because of the portions of the binder that project inwardly between the outer filaments, as shown in FIGURE 3.

When two of these pieces of twine are tied into a knot 10, there is a certain amount of resistance to the slipping or untying of the knot by the monofilaments, when formed of some materials, which contact each other through gaps 26 of the different turns of the twine. In addition to this, the side edges 28 and 29 of the binder band which extend substantially circumferentially of the mono filarnent bundle act somewhat as cleats and prevent the turns of the twines which extend substantially at right angles to other portions of said twines from slipping along the latter. The fusing of binder 22 to the monofilaments with which it comes into contact keeps all of the monofilaments in their proper positions since the binder is fused to the outer monofilaments which form a layer and surround the inner monofilaments. A bundle of monofilaments lying side by side has great flexibility, and the spirally wound binder 22 hardly interferes with this at all since the greater percentage of the monofilaments forming the bundle are free to move relative to each other when the twin is flexed.

Monofilaments 20 of this twine are preferably made of polyolefin, such as, for example, polypropylene or linear high density polyethylene. Binder band 22 must be formed of a material that is compatible with the monofilament material so that they both react the same way to heat. It is preferable to make the binder band of the same material as the monofilaments. The binder is wound around the monofilaments while it is hot enough to fuse to each of the latter with which it comes into contact, such as at points 24 in FIGURE 3.

FIGURES 4 and illustrate an alternative form of twine. This twine is made up of a bundle of monofilaments 34 extending substantially parallel to each other, and a binder around these filaments in a plurality of annular bands 36, each of which has been applied while hot enough to fit partly around and fuse to each of the outer monofilaments with which it comes into contact. Bands 36 are axially spaced along the twine to form gaps 37 therebetween. Each band has side edges 39 and 40 which which extend substantially circumferentially of the twine and tend to act as cleats.

Monofilaments 34 and binder bands 36 can be formed of the same material as the monofilaments and binder band of FIGURES 2 and 3. In addition, the twine of FIGURES 4 and 5 functions in the same manner as the previously described twine.

The method of producing synthetic twine according to this invention comprises surrounding a continuous bundle of oriented synthetic monofilaments extending longitudinally substantially parallel to each other with a thin synthetic binder band made of material compatible with the monofilaments and which is hot enough to fuse slightly with and to ifit partly around each of the outer monofilaments with which it comes into contact, see FIGURE 5, but not sufficient materially to reduce the tensile strength of the bundle. As state above, it is preferable to use polyolefin for both the monofilaments and the binder, such as polypropylene or linear high density polyethylene. Polypropylene is preferred since it is considerably less slippery than polyethylene. The binder can be spirally wound around the mono filarnent bundle, or it may be in the form of axially spaced annular bands around said monofilaments. The binder band must be such that it lWill fuse to the outer monofilaments to a slight depth while fitting partly around said monofilaments. When polypropylene is used, the temperature should be from about 350 F. to about 625 F., whereas with polyethylene, the temperature should range from about 400 F. to about 625 F., to ensure the desired depth of fusion.

The binder band should be quite thin so as not to interfere with the flexibility of the twine. The best results obtained have been when the spiral band is from about 0.006 to about 0.200 inch wide and from about 0.004 to about 0.020 inch thick. When individual annular bands are used, these can be from about 0.006 to 0.50 inch wide and from about 0.002 to about 0.020 inch thick. The lay for a single spiral band should be from about 0.250 to about 1.900 inches, whereas for two equispaced spiral bands, the lay per spiral should be from about 0.500 to about 3.500 inches. The annular bands can be spaced apart from about 0.200 to about 2.50 inches. The depth of fusion for spiral annular bands should be from about 0.005 to about 0.003 inch. However, the gaps between the turns of the binder band help to maintain the flexibility of the twine.

As stated above, the binder provides locking edges or cleats which prevent slippage when the twine is tied into a knot. As the monofilaments form an uneven surface on the bundle in a circumferential direction, this helps to prevent slippage, particularly when polypropylene is used. The monofilaments are retained in their proper coaxial arrangement without the necessity of putting a complete casing around them. The gaps in the binder reduce the amount of material required without materially affecting the strength of the twine, and help to maintain the flexibility of said twine.

Suitable stabilizers or pigments can be added to the polyolefins which form the monofilaments and binder in order to protect them against ultraviolet degradation.

The term monofilament as used in this specification and the following claims is intended to include monofilaments of any desired cross section. The binder bands also can be of any desired cross section, although it is preferable to use bands of rectangular or oval cross section.

What I claim as my invention is:

1. A twine comprising a bundle of oriented synthetic monofilaments extending lengthwise of the. twine substantially parallel to each other and a synthetic binder in thin band form made of material compatible with the monofilament material wound around and fused to the monofilaments with which it is in contact in a manner that leaves gaps between windings of said band to expose parts of the outer monofilaments, the gaps between windings being sufficiently large to permit said exposed parts of said outer monofilaments to contact each other through said gaps upon knotting of said twine, said fused band forming edges circumferentially of the twine which edges form cleats, said edges and said exposed parts helping to prevent slippage at the knot.

2. A twine as claimed in claim 1 in which the binder is spirally wound around said bundle of monofilaments.

3. A twine as claimed in claim 2 wherein the spirally wound binder is about 0.006 to 0.200 inch wide and has a lay of about 0.250 to 1.900 inches.

4. A twine as claimed in claim 1 in which the binder is in the form of a plurality of annular bands wound around said bundle of monofilaments and axially spaced from each other to provide said gaps.

5. A twine as claimed in claim 4 wherein said annular bands are about 0.006 to 0.5 inch wide and axially spaced about 0.200 to 2.5 inches from each other.

6. A twine as claimed in claim 1 in which both the 6 monofilaments and the binder are made of polypropylene. FOREIGN PATENTS 7. A twine as claimed in claim 1 in which both the monofilaments and the binder are made of linear, high 891618 3/1962 Great Bntam' density polyethylene. ROBERT F. BURNETT, Primary Examiner.

References Cited 5 J. D. FOSTER, Assistant Examiner. UNITED STATES PATENTS 2,974,559 3/1961 Coggi r 161-176 X 3,325,990 6/1967 Laureti 57-144

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