US3412954A - Form stable coreless packages of foamed thermoplastic twine and processes of manufacture - Google Patents

Description

INVENTOR. H A HOOD m, .bfi

H. A. HOOD TWINE AND PROCESSES OF MANUFACTURE Filed 001,. 28, 1965 FORM STABLE CORELESS PACKAGES OF FOAMED THERMOPLASTIC Nov. 26, 1968 A T TORNE' V5 United States Patent O 3,412,954 FORM STABLE CORELlESS PACKAGES OF FOAMED THERMOPLASTIC TWINE AND PROCESSES OF MANUEACTURE Henry Alexander Hood, Moorestown, NJ., assignor to Wall Industries, Inc., a corporation of Delaware Filed Oct. 28, 1965, Ser. No. 505,467 9 Claims. (Cl. 242-159) ABSTRACT OF THE DISCLOSURE Foamed thermoplastic twine is either Iheated to a temperature in the range of 100 F. to 185 F. below the melting point thereof and immediately wound on a core, or wound on the core and then heated to such temperature. After cooling, the core is removed to provide a form stable coreless package of twine.

This invention relates to improved foamed thermoplastic twine and coreless packages thereof.

The well-known advantages of cords, yarns and twines formed of thermoplastics make them acceptable for many potential uses. Such yarns and twines are generally light weight, inert against rotting and deterioration due to many chemicals, do not absorb water, have little stretch and have a high tensile strength. Many potential uses of synthetic fibres and twines require a package of the twine that is coreless and form stable, such as for use in baling machines. Synthetic twines exhibit a degree of livelness or tendency to untwist and slip against themselves which frequently causes coreless packages of the twines to telescope and/ or become uneven and unfit for use in many applications.

Accordingly, typical objects of this invention are to provide:

(l) Improved foamed thermoplastic twine;

(2) Form stable coreless packages of thermoplastic twine; and

(3) An improved method for producing form stable coreless packages of thermoplastic twine.

Other objects, aspects and advantages of this invention will become apparent to one skilled in the art upon further study of this disclosure and the appended claims.

It -has been determined that if foamed synthetic monoiilaments are used, at least in part, to form twines, the resulting twine exhibits less slippage, improved knotting and lighter weight than synthetic twines previously available.

Broadly, in accordance with this invention, foamed synthetic twines are heat treated to set the twine in position as wound into a package. Preferably, the twine is heated just prior to being wound onto a core and then cooled while on the core with the core being removed at the conclusion of the cooling. However, satisfactory heat setting can be obtained by heating and cooling the wound package of twine while on a core. After cooling and the twine is set, the core is removed, leaving a form stable coreless package of twine.

In the drawings, FIGURE l is a diagrammatic representation of a process in accordance with one embodiment of the invention, FIGURE 2 is a diagrammatic representation of a process in accordance with another embodiment of the invention, and FIGURE 3 is an elevational View, partly in cross-section, of a form stable coreless package of twine produced by either the process of FIG- URE 1 or the process of FIGURE 2.

The twines applicable to this invention may comprise a single strand or a plurality of strands. The single strand twine is formed by twisting a plurality of foamed mono- CII rice

filaments together and the multi-strand twine is formed by twisting two lore more strands, each comprising a plurality of foamed monofilaments, together in the direction opposite to that of the individual strands. In the multi-strand twines, all or a portion of the strands may have the same number of turns per inch or they all may have a different twist ratio.

This invention is applicable to foamed twines formed from any synthetic material capable of being formed into monolaments and which are form settable by heating and cooling. At present, satisfactory twines are readily made from olen polymers which include yhomopolymers and copolymers formed by polymerizing olens having 2 to 8 carbon atoms per molecule such as polyethylene, polypropylene, ethylene-butene-l copolymer, poly-l-butene, poly-2-methy1 pentene, polyisobutylene, and the like. The polymers used for the twine applicable to this invention can contain stress cracking and oxidation inhibitors, vulcanizatiou inhibitors, llers, pigments, and the like. The applicable polymers can be produced by any suitable process. The polymerization process described and claimed by Hogan et al. in U.S. 2,825,721 (1958) produces polymers very acceptable for the fabrication of monolaments and twines.

Various gaseous, liquid and solid foaming agents can be utilized to produce the foamed monoilaments. In general, these agents comprise materials which are gaseous at the temperatures of the molten plastic or polymer at the extrusion die. Solid materials which decompose at these temperatures and yield gaseous products tor components which react with other ingredients present in the melt to produce gaseous products are applicable. Any inert gas which is nondeleterious to the polymer or plastic being extruded is feasible. Such gases include N2, steam, CO2, low boiling hydrocarbons (propane, bfutane, pentane), and Freon. Liquids include water, ammonia, and hydrocarbons which vaporize at the extrusion temperatures as pressure outside of the die is released. Solid materials include p,poxybis(benzenesulfonyl hydrazide) which is sold under the trade name of Celogeu by Naugatuck Chemical, a division of the United States Rubber Company; l,1-azo-bisformamide, diazoaminobenzene, dinitrosopentamethylenetetramine, 4-nitrobenzene sulfonic acid hydrazide, beta-naphthalene sulfonic acid hydrazide, diphenyl-4,4di (sulfonyl azide), and mixtures of materials such as sodium bicarbonate with a solid acid such as tartaric acid. The amount of foaming agent can be any suitable value, and is usually in the range of 0.01 to 50 weight percent of the polymer being processed, with the preferred range being from 1 to l5 weight percent.

The temperature employed for the heat treatment required in this invention will vary depending upon the filament and twine diameters and the type of polymer used to form the twine. The temperature to which the twine is heated will be below the melting point thereof and generally will be within a range of to 185 F. below the melting point of the polymer. For the higher melting point polymers, such as polypropylene, the twine temperature of treatment generally will be between and F. with the preferred value being approximately half that of the melting point of the polymer measured in F.

When heating the wound package to set the twine in place, the heating rate can vary from l0 to 30 F. per hour. Heating rates :higher than 30 F. per hour cause distortion of the package due to differential shrinkage and shortening of the outer layers due to a temperature differential from the outside to the inside of the package. The extended iheating periods required by heating rate less than 10 F. Iper hour tend to deteriorate the polymer. Generally, the twine will be maintained under a tension of: 1 to 10 pounds during winding to obtain a tight uniform packing.

The following examples will illustrate the lpresent invention in greater detail, but are not intended to be construed as limiting the invention.

Example I Polypropylene having a density of 0.91 grams/ cc. as determined by ASTM D1505-63T is blended with 0.22 weight percent of 1,1azobisf0rmamide, a blowing agent and the blend is extruded into 5 80 denier foamed monoiilaments. Forty of these monolaments are twisted together with a Z twist of 12 turns per foot to form baler twine. Such twine possesses superior knot retention characteristics as compared to baler twine made from nonfoamed monofilaments. These superior characteristics improve the use of synthetic twines in the farming industry (baling machines) and also for general industrial use.

Example II Polypropylene twine as prepared in Example I is passed through a radiant heating zone and the twine is heated to about 160 F. The heated twine is immediately wound onto a tapered core being lOl/2 inches long and tapering in diameter from 2% inches at one end to 2%. inches at the opposite end under a tension of from about l to about pounds and at a rate of 450 feet per minute until the spool of twine is about 9 inches in diameter and 917/2 inches long. The resulting spool is allowed to cool to ambient room temperature air for 5 hours and the core is then removed with ease. After storage of the coreless package at room temperature for one day, no significant telescoping of the twine occurs and the package of twine is completely satisfactory for use in baling machines, Further, after storage of the heat treated coreless package formed in this example at 130 F. for 16 hours, the package is satisfactory and had not telescoped.

Example III Polypropylene twine as prepared in Example I is passed through a radiant heating zone and the twine is heated to about 160 F. The heated twine is immediately Wound onto a tapered core being lOl/2 inches long and tapering in diameter from 21A inches at one end to 2% inches at the opposite end under a tension of from about l to about 10 pounds and at a rate of 450 feet per minute until the spool of twine is about 9 inches in diameter and 91/2 inches long. The core is removed from the spool immediately and the resulting spool is allowed to cool to ambient room temperature air for 5 hours. After storage of the coreless package at room temperature for one day, the center portion of the package has telescoped out the end about 1/2 inch and the inner windings are axially displaced relative to the outer winding. The package of twine is unsatisfactory for use in baling machines.

Example IV Polypropylene twine as prepared in Example I is wound onto a tapered core being 101,42 inches long and tapering in diameter from 21A inches at one end to 2% inches at the other end under a tension from about 1 to about 10 pounds at a rate of about 450 feet per minute until the spool of twine is 9 inches in diameter and 91/2 inches long. The core is then immediately removed and the coreless package of twine is stored at room temperature. Inspection of the package after one day shows the center portion of the package is telescoping out the end about 1/2 inch and the inner windings are axially displaced relative to the outer winding. The package is completely unsatisfactory for future use in baler equipment.

Example V Polypropylene twine as prepared in Example I is wound onto a tapered core being 101/2 inches long and tapering in diameter from 2%, inches at one end to 2% inches at the other end under a tension from about 1 to about 10 pounds at a rate of about 450 feet per minute until the spool of twine is 9 inches in diameter and 91/2 inches long. The package of twine is stored at room temperature. After 5 hours of storage the core is removed with great difficulty. Inspection of the package after one day of storage shows the center portion of the package is telescoping out the end about 1/2 inch and the inner windings are axially displaced relative to the outer winding. The package is completely unsatisfactory for future use in baler equipment.

Example VI A package of polypropylene twine as formed in Example IV with the core removed and at a temperature of about F. is heated in a convective oven for 4 hours and l5 minutes at which time the temperature of the twine reaches 160 F. After cooling, removal of the core, and storage for one day, the coreless package of twine does not exhibit any telescoping and is a form-stable package of synthetic twine satisfactory for many uses.

Example VII A package of polypropylene twine as formed in Example IV with the core therein and at a temperature of about 80 F. is heated in a convective oven for 4 hours and 15 minutes at which time the temperature of the twine reaches 160 F. The core is removed immediately after the package leaves the oven, and the package is allowed to cool. After cooling and storage for l day, the coreless package of twine exhibits telescoping and is unsatisfactory for many uses.

Example VIII A package of polypropylene twine as formed in EX- ample IV with the core therein and at a temperature of about 80 F. is heated in a convective oven for 4 hours and 15 minutes at which time the temperature of the twine reaches 160 F. After cooling and storage for one day, the coreless package of twine is misshapen and unsatisfactory for many uses.

From these examples it is seen that the problem of telescoping of coreless packages of synthetic twine is eliminated by the practice of this invention.

To one skilled in the art it will be apparent that many variations and modifications of this invention can be practiced in view of the foregoing disclosure without departing from the spirit and scope thereof. For instance, another heating means that may be used for heating the strand or wound package is frictional heating. This may be accomplished by sliding the surface of the strand over another surface so as to induce frictional heat on the strand surface or it may be by flexing or twisting of the strand so as to induce relative movement between the contacting monotilaments making up the strand thereby inducing frictional heat. Ultrasonics may also be used to induce heating within the strand or wound package. Other forms of inducing heating such as dielectric heating, if the strand is non-conductive, and inductive heating, if the strand is electrically conductive, may also be used. Also, it will be apparent that many of the variables employed in the examples will vary depending upon the synthetic material and physical properties of the twine and package.

I claim:

1. A method of providing a form stable coreless package of twine formed of a foamed thermoplastic material capable of being form set by heating and cooling, comprising heating the foamed thermoplastic twine to a temperautre in the range -of F. to 185 F. below the melting point of said thermoplastic material, substantially immediately winding the thus heated twine onto a core to form a package, cooling said heated twine While Wound on said core, and removing said core from the resulting cooled twine.

2. A method in accordance with claim 1 wherein said thermoplastic material is polypropylene.

3. A method in accordance with claim 2 wherein the temperature to which the twine is heated is in the range of 160 F. to 195 F.

4. A form stable coreless package of foarned thermoplastic twine prepared in accordance with the method of claim 1.

5. A method of providing a form stable coreless package of twine formed of a oamed thermoplastic material capable of being form set by heating and cooling, comprising Winding the foamed thermoplastic twine on a core to form -a package, heating the package to a temperature in the range of 100 F. to 185 F. below the melting point of said thermoplastic material at a rate of from 10 F. to 30 F. per hour, allowing the temperature of the thus `heated package to lower to room temperature, and removing the core from the thus cooled package.

6. A method in accordance with claim 5 wherein said twine is wound onto said core under a tension of 1 to 10 pounds.

7. A method in accordance with claim 6 wherein said thermoplastic material is polypropylene.

8. A method in accordance with claim 7 wherein the temperature to which said package is heated is in the range of 160 F. to 195 F.

9. A form stable coreless package of oamed thermoplastic twine prepared in accordance with the method of claim 5.

References Cited UNITED STATES PATENTS 2,425,060 7/ 1943 Ingersoll.

3,046,632 7/ 1962 Tsutsumi 28-62 XR 3,118,161 1/1964 Cramton.

3,256,258 6/1966 Herrman.

3,262,257 7/1966 Martin.

FOREIGN PATENTS 39-7262 5/1964 Japan.

JULIUS FROME, Primary Examiner.

PHILIP E. ANDERSON, Assistant Examiner.

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