US3715422A

US3715422A - Process for producing crinkled plastic ribbon

Info

Publication number: US3715422A
Application number: US00048752A
Authority: US
Inventors: S Chopra; H Turmel
Original assignee: CHEM Ltd
Current assignee: CHEM Ltd
Priority date: 1969-04-10
Filing date: 1970-05-18
Publication date: 1973-02-06
Anticipated expiration: 1990-02-06

Abstract

The present invention relates to a process for making a flatextruded yarn or ribbon of melt-extrudable thermoplastic material having a characteristic surface configuration, and to a method and apparatus for producing such yarn or ribbon.

Description

Unlted States Patent 1191 1111 3,715,422 Chopra et al. 1 51 Feb. 6, 1973 154] PROCESS FOR PRODUCING [56] References Cited LRINKLED PLASTlC R'BBON UNITED STATES PATENTS [75] [Inventors-Z Sohmd" f E Hawkesbu' 2,816,349 12/1957 Pamm 6121].. ,.264/177 F ry, Quebec, llllalre Marcel Turmel, 2 748 4 [1958 Fmlayson et al. ..264/177 F Quebec both f 3 219 739 11/1965 Breen et al. ..264/177 F Canada 3:266:093 8/1966 Corbett ..18/14 3 Assigneez Chemical Limited, Montreal 3,354,250 1 H1967 v Killoran et al.". ..264/176 F Quebec 3333? 5/1333 331132523111? "56 43142 1 [22] Filed: May 18, 1970- 314913405 1/1970 Palmer el al. ..264/176 F 3,562,369 2 1971 cm 1'21 61 1. ..264/210 R [211 P 48,752 3,283,378 11/1966 crar rlpton ..264/210 R 3,002,804 1961 Kilian ......264/l78 F Related '5' Apphcam Dam 3,259,938 7/1966 Martin ..18/8 Division of S61. NO. 815,044, April 10, 1969, and 6 3,366,722 1 1968 Tessier ..264/168 continuation-in-part of Ser. No. 558,120, June 16, 19 66, abandoned. Primary Examiner-Jay H. W00 1 Attorney-Leonard Horn and Steven Murphy [52] US. Cl. ..264/l68, 264/171, 264/176 F,

, 264/177 F, 264/178 F, 264/210 F 57 ABSTRACT 51 1m. 01. ..D0ld 5/22 [53] Field of Search 161/179, 181, 173 67, The present mvention relates to a process for making 161/177; 264/167, 171-, 168, 178 F, 176 F, Y I 21oF, 177F a flat-extruded yarn or ribbon of melt-extrudable thermoplastic material having a characteristic surface configuration, and to a method and apparatus for producing such yarn or ribbon.

11 Claims, 15 Drawing Figures PATENTEDFEB 6 I975 3.715.422 SHEET 1 or 4 INVENTORS SOHINDER NATH CHOPRA HILAIRE MARCEL TURMEL ATTORNEY PATENTEDFEB 61875 3.715.422 SHEET 20F 4 SOHINDER NATH CHOPRA HILAIRE MARCEL TURMEL ATTORNEY llwewrons' mgmgn 6 am 3.715.422

saw so; 4

N is 5 l 5/ 69? I V i r 744 K "67 INVENTO/PS SOHINDER NATH CHOPRA HILAIRE MARCEL TURMEL BY WW ATTORNEY mmmran 6 mm 3.715.422 sum u or 4 SOHINDERINATH CHOPRA I HILAIRE MARCEL TURMEL ATTORNEY IIWENTORS l PROCESS FOR PRODUCING CRINKLED PLASTIC RIBBON This application is a divisional application of Ser. No.

815,044, filed Apr. 10, 1969, which is a continuationin-part application of Ser. No. 558,120, filed June 16,

1966, now abandoned. Flat-extruded yarn of melt-ex inch. Above this width, more usually fromabout oneeighth inch width upwards, the word ribbon is more apt to describe the material. It is contemplated within the scope of the present invention to provide material of a width within a preferred range of about 0.0l inch to about one-quarter inch and with this dimension in mind, the material will be referred to herein as flat-extruded yarn orribbon.

Conventional thermoplastic flat-extruded yarn or ribbon is generally produced by extruding a wide sheet and slitting such sheet into narrow widths. It may also be produced by extruding the material through a relatively-narrow flat orifice. The continuous filamentary material thus produced according to the known art is smooth and slippery. The material has little aesthetic or artistic appeal and suffers from the functional disadvantage that it is difficult to knot, and that crossing filaments in a fabric containing the material tend to slip on the smooth surface. To avoid the latter disadvantage, flat yarn for use in fabrics is sometimes crimped transversely by being passed through meshed gears or by being passed through a stuffer box. Crimping of this kind weakens the lengthwise stiffness or resiliency of the yarn and does not add to its aesthetic appearance. I In accordance with one aspect of the present invention, there is provided a flat-extruded yarn or ribbonof thermoplastic material having two opposed faces, substantially straight and parallel side edges and an interior crimped region between the edges in the form of a series of blister-like depressions and protrusions on both faces.

The yarn or ribbon, in accordance with the process of theinvention, preferably has an overall width between the stated edges within the range of about 0.01 inch to about one-quarter inch, and a thickness between the faces within the range of about 0.0005 inch to about 0.005 inch. The length of the depressions and protrusions may lie within the range of'about onesixteenth inchto about one-eighth inch. The depressions and protrusions may be about 0.005 to 0.015 inch deep. The melt-extrudable thermoplastic material is preferably selected from the group consisting of polyethylene, polypropylene, and polyacetal, and the preferred material is polypropylene.

The yarn or ribbon in accordance with the invention combines artistic and aesthetic appeal with novel func? tional characteristics and advantages. Since the surface deformations do not extend the whole way across the width of the yarn or ribbon, and since the blisters add additional rigidity in the lengthwise direction to the used, for example, for tying parcels and for similar purposes.

Yarn, in accordance with the invention in about the middle or towards the smaller part of the stated width range, finds application in fabrics, especially carpet backing, for example, the type of carpet backing described and claimed in our copending application, U.S. Ser. No. 498,389, filed Oct. 20, 1965, and now US. Pat. No. 3,443,541.

In accordance with a second aspect of the present invention, there is provideda process for manufacturing a flat-extruded yarn orribbon ofmelt-extrudable thermoplastic material having two opposed faces, substantially straight and parallel side edges and an interior crimped region between the edges in the form of a series of blister-like depressions and protrusions on both faces, comprising the steps of:

yarn, the latter, exhibits an appreciable rigidity or ing a width towards the maximum of the stated range,

finds application as decorative material which may be melt extruding a flat yarn or ribbon having substantially a viscosity gradient set therein, from a melt extruder having ajet in the form of a slot and generating a substantial viscosity gradient,-

quenching the extruded yarn or ribbon to ambient temperature, and

stretching the cooled yarn or ribbon. Generally the stretching is done by driving it under tension in contact against a convexedly curved surface heated at a temperature at or above the softening point and below the melting point of the said thermoplastic material, the yarn or ribbon being taken up after stretching'at a faster speed than it is fed to the stretching surface.

Preferably, the temperature of the said curved surface is maintained within the range of about C. to about C.

Having thus generally described the invention, it is hereafter illustrated by preferred embodiments of the yarn or ribbon, and of apparatus for its manufacture, il-

lustrating the method of manufacture, which are described with reference to the accompanying drawings, in which:

FIG. l is a greatly enlarged perspective view of a crinkled yarn or ribbon in accordance with the invention;

FIG. 2 is a schematic representation of apparatus for the manufacture of the yarn or ribbon of FIG. 1, illustrating the method of manufacture;

FIG. 3 is a bottom plan view of a jet for the extruder forming part of FIG. 2;

FIG. 3a is a section along the line 3a-3a of FIG. 3;

FIG. 4 is a vertical cross-section througha heating tube forming part of the apparatus;

FIG. 5 is a front elevation of the tube of FIG. 4;

FIG. 6 is a transverse cross-section along the line 6- 6 of FIG. 4;

FIG. 7 is a transverse cross-section along the line 7- 7 of FIG. 4;

FIG. 8 is a fragmentary perspective view on a large scale of the tube of FIG. 4 partly assembled and showing its form of construction;

FIG. 9 is a transverse cross-section on a still larger scale along the line 99 of FIG. 8;

FIG. 10 is a greatly enlarged cross-section along the line 10-10 of FIG. 5;

FIG. 11 is a greatly enlarged cross-section along the line 11-11 ofFIG.5;

FIG. 12 is a side elevation on an enlarged scale of an automatic cooling and piling up mechanism;

FIG. 13 is a horizontal cross-section partly in elevation along the line l3 13 of FIG. 12; and

FIG. 14 is a diagrammatic view showing particularly the electrical circuit for supplying current to the heating unit.

With reference to FIG. 1, there is shown a yarn or ribbon l of polypropylene having, for example, the width of 0.110 inch and a thickness of, for example, 0.002 inch. The yarn exhibits a series, in alternating sequence, of blister-like protrusions 2 and depressions 3 when viewed from the top face 4 as shown in FIG. 1. The number of blisters per inch may vary between about 3 and about 10, the typical ribbon shown having, for example, 6 blisters per inch. The blisters vary in length from about one-sixteenth inch to one-eighth inch.

As shown, the yarn retains substantially straight and parallel side edges 5, and the protrusions and depressions are restricted to substantially a central region. Occasionally, a blister will extend into one or other side edge deforming that edge, and it is within the scope of the invention that such occasional departures from the norm occur.

Over a greater part of the length at least, the straight edges 5 are continuous, and there is usually a flat edge portion 6 of each surface on either side of a blister-like protrusion or depression.

The transverse shoulders lying between a depression and the adjacent protrusions add rigidity to the yarn or ribbon.

THE APPARATUS als having different intrinsic viscosity indices at a given temperature, or preferably flows of an homogeneous molten thermoplastic material, said flows having been subjected to different heat treatment prior to extrusion at the spinneret orifice.

An example of extruder suitable for this purpose has been the subject of U.S. Pat. No. 3,354,250 dated Nov. 21, 1967 owned by the same assignee, which was copending with our parent application Ser. No.

- 558,120. The said US. Pat. No. 3,354,250 is incorporated herein by reference.

As particularly seen from FIG. 10 and columns 6 and following of the said referenced patent, by the feeding screw S the polymeric material reaches an aluminum block N having elongated passages 280. By controlling the heat generated by the band heater 285, one is able to make colder the material passing through the passages 280 located near the central axis of the block N, than the material passing through the passages 280 located near the periphery of the block N or closer to the band heater 285. The molten material so treated is able to attain a substantial viscosity gradient, and may then move through the remaining portion of the extrusion apparatus up to the spinneret orifice as a substantial laminar flow (i.e., under such condition that the flow is not homogeneized).

Other means may also be used to set a viscosity gradient, such as heating more intensively the innermost portion of the molten material. If necessary, cooling could be used instead of heating. Variation of the concentration of the materials, or dilution, is also contemplated.

By substantial viscosity gradient it is meant that at the spinneret, the flat yarn or the ribbon obtained has a viscosity gradient which is such that after quenching and stretching, the flat yarn or ribbon will crimp. For example, it has been found that with polypropylene, if an apparatus as shown in FIG. 10 of US. Pat. No. 3,354,250 is used, the temperature of the heating block should be maintained at a temperature between 250300C and preferably 275-300C when the debit rate at the spinneret orifice is about 1 to 3% lbs. The spinneret being also maintained at about that temperature or about 5-10C higher.

The extruder should terminate in a spinneret having a single jet orifice in the form of a slot. A preferred jet is illustrated in FIGS. 3 and 3a. The plate 11 of the jet may typically have dimensions 0.465 inch thick by L996 total diameter. Typical dimensions of the slot 12 are 0.625 inch in length by 0.0 l 2 inch in thickness. The bottom of the jet has a central dishing bounded by a conical surface 13. Tapped holes 14 are provided for adjusting the orientation ofthe jet.

As the flat yarn or ribbon leaves the extruder, it is immediately quenched in running water at ambient temperature in the quencher 20. As shown in FIG. 2, this consists of a generally U-shaped tube having a flared inlet 21 and a flared outlet 22 for the yarn and having a separate water inlet 23 and a separate water outlet 24 in the side wall of the tube, the water inlet and outlet being arranged to provide a continuous level of running water within the U-shaped tube. As shown, the quencher tube has a vertical limb at the input where the yarn enters, the outlet limb being at an angle to the vertical.

The ribbon leaves the outlet of the quenching device with its flat side rubbing against the lips of the outlet. This helps to drain back into the quencher any water particles that may be riding on the ribbon. As shown in H0. 2, the inlet to the quencher is arranged immediately below the extruder jet. In the preferred case, the distance between the extruder jet and the inlet of the quencher is only two inches. This causes rapid cooling of the extruded ribbon or yarn. The bend of the U of the quencher should be of sufficient radius to avoid undue strain on the ribbon as it is being drawn around the convex inner surface and while it is being cooled. The radius of the U, for example, may be of the order of about four inches.

After passing out of the quencher, the yarn is passed over a first guide roll 201, and through a first pair of nip rolls 203 to a second guide roll 200 at the inlet of the heating tube R to be described. As it leaves the outlet of the stretching tube R, the yarn is passed through a second pair of nip rolls 204 to a constant tension winder 40 of conventional type.

Both the pairs of nip rolls 203 and 204 are driven, the nip rolls 204 being driven at a faster speed than the nip rolls 203 so as to cause the yarn to stretch during its passage through the heat stretching tube R The heat stretching tube R may be of the kind described in Canadian Patent 699,470. However, it is preferred to use a similar stretching tube of improved construction described in our copending application as follows:

U. S. Ser. No. 488,832, filed July 26, I965 now US. Pat. No. 3,277,228.

The improved stretching tube is shown in detail in FIGS. 4 to 14 inclusive and incorporates a device for blowing air through the tube in the event of fracture of the yarn or ribbon which would otherwise cause the tube to overheat. The blowing device is also an aid to threading the yarn or ribbon through the tube.

The tube or element R is made up of an elongated bowed trough or channel member S, formed from a single sheet of electrically conductive metal of the shape shown in FIGS. 4 to 9. The trough S has a convexly curved floor 35 which preferably increases regularly in width from the receiving end to the exit end and which 7 is bounded at each side by an upstanding integral flange or wall 37, which is of the same height throughout the length of the channel member S.

Against the outside of the trough so formed there is placed a glass fabric base laminate insulating strip 39 which lies on the top of walls 37 and bridges the trough. The trough withthe strip 39 in place is tightly wound with glass fiber tape 41 so as to form a four-sided tube ofwhich the floor 35 and walls 37 constitute three sides and the strip 39 the other side.

The inlet end of the tube is provided with a copper terminal member 43 having an opening 43a receiving the end of the tube and a connecting opening 43b. A threading nozzle in the form of a J-shaped tube 45 extends through a diagonal opening 45a in the terminal member 43 and enters the bottom of the trough S at an angle as shown. The outlet end of the trough S is also provided with a copper terminal 47 having an opening sleeve 71 also has a part projecting outside the block 53. The outer end of the sleeve 71 is internally threaded as at 71a to receive the threaded end of a nipple 72 carrying at its outer end a bayonet cap 74 held to it by a screw 74a. A thermocouple bulb 73 is positioned in the sleeve 71 with an extension passing back through the cap 74. A coil spring 75 is mounted on the extension of the bulb 73 and acts between a shoulder 73a on the bulb and the cap 74 to urge the inner end of the bulb 73 against the wall of the trough S. The extension of the bulb 73 leads to an instrument 163 (FIG. 14) where a reading may be taken of the temperature sensed by the bulb 73.

47a receiving the end of the trough S and a connecting opening 47b. The connection between the metal part of the tube R and the

terminals

43 and 47 can be by welding, brazing, or any other suitable method. This also applies to the connection between the tube and the plate 43.

The trough S is encased with insulation as follows. Elongated coated juxtaposed fiberglass blocks 51 and 53 are each provided with

grooves

55 and 57 respectively which form between them a channel receiving the tube including the trough S, and its covering. The outer face of the block 51 is clad with an aluminum facing sheet 65 and the block 53 is provided with an aluminum facing sheet 67. The

blocks

51 and 53 are clamped togetherby non-magnetic screws 61 which extend through them and their

cladding

65 and 67 periodically along the length of the heating element R.

A thermocouple device V is connected to and extends through openings in the facing sheet 65 and the block 53. This thermocouple has a base 69 which is held by screws 70 to the sheeting 65 and its underlying block 53. A sleeve 71 has a part whichextends through openings in the base 69, sheet 65 and block 53 to a point adjacent the outer surface of the trough S. The

AUTOMATIC COOLING DEVICE The automatic cooling device K is best shown in FIGS. 12 and 13. This device includes a body which is mounted on a beam 81 which extends along the length of the machine and also carries the similar stop motions for the other tubes R. The body 80 is of the cross-sectional shape shown in FIG. 13 and has a widened head 84 projecting to one side and a widened foot 85 extending to the other side and separated therefrom by a neck 86. The head 84 is provided with a bore 87 extending through it from back to front and an inlet passage 88 leading from a nipple 89 connected to an air inlet pipe 890. An outlet passage 91 extends from the bore 87 to a tee 93 connected to an air pipe 94 leading to the cooling air connection 45. A piston 95 is operably mounted in the bore 87. The piston has an intermediate narrow part 97. The front of the piston is pivotally connected by a pin 98 through a slot in a link 99 which in turn is pivotally connected to a block 100 mounting a drop wire 101. The block 100 is pivotally mounted on a bolt 103 extending through the opening in the part 85. A stop bracket 104 is mounted on the back 86.

In operation, the drop wire 101 is in the upper position shown in dotted lines and is held in that position by the yarn under tension running from the nip rolls 60 to the entrance of element R. In this position, the front thick part of the piston 95 blocks the outlet opening 91 and thus cuts off its supply of air from the inlet opening 88. When the yarn breaks, the wire 101 is no longer supported and falls from the position shown in full lines in FIG. 12. The fall is slow at first because the wire 101 is nearly vertical. The slot 99a has been provided in the link 99 which acts an an elongated pivot hole thus allowing the wire 101 to fall freely through the first half of its travel, which develops sufficient momentum to start the movement of the piston 94. The movement is completed during the second half of the travel. The fall of the wire 101 pulls the piston 94 forward and clears the exit passage 91 thus allowing the air to pass through. it from the passage 88. The air is immediately blown through the J connection 45 and into the tube R. This air serves to prevent the tube R from overheating when the yarn breaks. I

The apparatus is also provided with means for piecing up the yarn if it breaks. This includes a compressed air pipe provided with a manual valve 111. The valve 111 is connected by a pipe 112 to the tee 93 of the stretching unit. Through the tee 93 the pipe 112 is connected with the pipe 106 and thus with the J-connection 45. Byopening the valve 111 compressed air is applied immediately to the .Lconnection 45 and through the trough S. The end to be fed is introduced into the end of the trough S carrying the stream of air, thus created, and is blown by it through the trough S from inlet to outlet. Once the new end of yarn is passed through the tube and onto the takeup rollers 29 and 30, the drop wire 101 is reset by the operator into its normal upper position shown in full lines in FIG. 14 and the heating-stretching operation is continued as previously described until there is another break.

Electric current is supplied through a transformer 151 by a wire 153 through the terminal member 43 and connected by a wire 155 through the terminal member 147 (FIG. 14). The transformer is of suitable voltage and suitable amperage for heating the trough S to the desired temperature or a multiplicity of troughs in series or series parallel. The temperature may be controlled manually by means of a variable voltage device 157. A thermocouple type of temperature-indicating instrument 163 may be connected to the thermocouple V by wire 165 so as to indicate the temperature of the trough S. The instrument 163 may be connected into the electrical system so as automatically to regulate the temperature, if desired.

If desired, a number of heating elements R may be provided on a single frame to stretch yarn or ribbon from a corresponding number of extruders. They may be connected in series on a single transformer.

The trough S is made preferably from stainless steel sheet in the annealed state, or chromel sheet, or nichrome, bent into trough shape. According to a preferred construction, it is polished to a mirror" finish on the inside or yarn guiding face then vapor blasted to a so-called satin" finish. This finish preferably consists of irregularities approximately microns deep on the average, spaced in the range of to microns from peak to valley in all directions. After vapor blasting, the surface is provided with chromium plate, for example, about 0.002 inch thick. The irregularities may range from about 3 microns to about 8 microns in depth and may be spaced within the range of about 10 to 50 microns (from center to center). Where the surface of the trough S has been treated to reduce friction, as described, the curvature ofthe trough S is not critical.

Such a surface may be prepared by first polishing the metal surface to a mirror-like finish. Then blasting with a fine abrasive powder carried in a stream of air and water vapor at high velocity. This provides the surface with a multitude of microscopic indentations. The thus prepared surface is then chromium-plated. The resulting chromium-plated surface reduces the frictional resistance of thesurface to the yarn substantially to a minimum and prevents wear. For a surface of this nature, the curvature is not critical, whereas, without such a friction-free surface, it is desirable'that the curvature of the surface be such that it is relatively less curved at the inlet end to reduce the friction and it is more curved towards the outlet end, so as to provide a certain amount of friction. Thus, at the inlet end, the yarn or ribbon is not subjected to any substantial friction, and thus is not stretched before it is sufficiently softened, while towards the outlet end it is softened and is then subjected to friction and stretched. With the chromium-plated surface as described, the resistance offered to the yarn or ribbon is at a minimum and consequently, the curvature being much less critical, the stretching trough may be curved to suit a particular assembly or machine to provide a convenient location at the inlet and outlet for ease of operation.

The length of element R may be adapted to suit the machine, with the length about as long as practical without exceeding the maximum reach of the average operator. Shorter lengths can be used, but the speed of stretching would have to be reduced accordingly. If the length of the tube is increased, maintaining the same radius, the machine would have to be higher. If the radius is decreased maintaining the same length, the tube would project further out the back and occupy more floor space.

The radius of the trough S may vary from inlet to outlet with the maximum radius at the inlet and the minimum radius at the outlet. The surface may take a single curve or a series of curves of varying radii. The greater the curvature, the greater the tension on the yarn. The ideal curvature maintains contact of the surface with the yarn but is insufficient to cause drag or high friction. Preferably, the radius of the curvature of the trough S should remain within about 24 inches and about 40 inches and may vary in curvature along the length with the short radius preferably at the outlet end. A practical length is between about 4 feet and 8 feet, it being understood that when the tube is shorter, the stretching speed would be reduced.

A preferred overall length is about 6 feet from terminal to terminal, bent into an arc comprising 128)? of a circle. This shape of tube provides suitable pressure ofthe yarn against the running surface and the length is sufficient for ordinary rates of stretching. A typical trough-shaped heating element having a length of 72 inches through the first 68 W ofits curvature and then a radius of curvature of about 30 inches for the last 60 of its curvature with a transition between these two radii of curvature in between.

Theoretically, the thickness of the metal wall of the trough can vary considerably. The thicker the wall, the more amperage is required in theory, the tube could be as thin as about l/64 inch, but it would not be self-supporting. It is preferred that the metal wall of the trough be in the neighborhood of one-sixteenth inch, when constructed as shown.

A preferred metal for the manufacture of the trough S is an alloy of nickel and chrome, available on the market under the trade marks CHROMEL and NlCHROME. These metals are ideal since they have high electrical resistance, sufficient heat conductivity and are free from oxidation when operated at high temperatures. Most of the chrome-nickel stainless steel alloys, although of lower electrical resistance, are also suitable and are readily available for tube forming. The amperage used for heating must be adjusted in accordance with the resistivity of the metal used and the thickness of the wall.

The amperage used for heating may be varied to suit the composition of yarn or ribbon and dimensions being stretched. The temperature of the trough must be adjusted to heat the yarn or ribbon to its softening point. The exact temperature will vary with different types of yarn. For polypropylene, for example, the temperature is preferably within the range from about Extrusion temperature 115C. to about 155C. measured at the surface of the ple, cylindrical, D-shaped, etc. The surface of the conformation described, however, has decided advantages, and it is therefore greatly preferred.

It may be desirable to pass the yarn or ribbon through several tubes in series with a pully between them to the necessary longer residence time at higher speeds and higher stretch ratios. The tubes are normally connected in series electrically but can be connected in parallel or in any series-parallel combination. In all cases, they should preferably be calibrated so that their respective electrical resistances are identical.

The tape with which the trough S is wrapped may be plain woven glass fabric completely dry with no adhesive and coated with shellac, phenol resin, or other suitable adhesive.

The ratio of input speed to output speed may vary widely for different types of yarn or ribbon, but a preferred stretch range is between three and six times the extruded length.

The winder 40 and the drive rolls 60,61 are preferably adjustable in speed to accommodate different stretch ratios ranging from 3:1 to 12:1 and for different speeds, the element R being adjustable to different temperatures, making the apparatus suitable for a wide range of different polymers.

The tension in yarn as it leaves the final heating zone is determined by the force required for stretching at the optimum stretching temperature. The tension in the yarn as it enters the heating element equals the stretching tension minus the force required to overcome the friction caused by the yarn sliding on the surface. The curvature and length and temperature of the tube is designed so that the tension on the yarn does not increase to the stretching tension until the yarn has been heated to optimum stretching temperature. The optimum temperature varies in relation to the dimensions of the vyarn or ribbon, stretch ratio, speed and the viscosity of the parent polymer, but generally it is in the range ofabout 100C. to about 135 EXAMPLE A polypropylene ribbon was melt extruded using following extrusion conditions were used:

270C. 1% lbs. per hour 55 feet per minute Extrusion output Extrusion speed Cooling water temperature Distance of water level from jet face 2 inches Jet orifice 0.012 inefx' as inch X 14 inch deep Temperature of stretching surface 120C. Stretch ratio 4-511 Ribbon size 1100 denier, 0.002 inch thick X 0.1 10inch wide parent thickness of the ribbon was therefore 0.021 inch.

We claim: l. A process for manufacturing a flat-extruded yarn or ribbon of melt-extrudable thermoplastic material having two opposed faces, substantially straight and parallel side edges, the overall width between said edges being within the range of about 0.01 inch to about one-quarter inch and an interior crimped region between the edges in the form ofa series of blister-like depressions and protrusions'on both faces, the length of said depressions and protrusions lying within the range of about one-sixteenth inch to about one-eighth inch and the depth of said depressions and protrusions lying within the range of about 0.005 inch to 0.015 inch, comprising the steps of:

melt extruding a flat yarn or ribbon having a substantial viscosity gradient set therein from a melt extruder having a jet in the form of a slot and generating a substantial viscosity gradient,

quenching the extruded yarn or ribbon with water to ambient temperature, and heat stretching the cooled yarn or ribbon at a temperature at or above the softening point and below the melting point of the said thermoplastic material.

2. A method as claimed in claim 1 wherein said stretching is obtained by driving said cooled yarn or ribbon under tension in contact against a convexedly curved surface heated at a temperature at or above the softening point and below the melting point of the said thermoplastic material, the yarn or ribbon being taken up after stretching at a faster speed than it is fed to the stretching surface.

3. A method as claimed in claim 2 wherein the temperature of the said curved surface is maintained within the range of about C. to about 160C.

4. A method as claimed in claim 3 wherein the said thermoplastic material is polypropylene.

5. A method as claimed in claim 4 wherein the temperature of the said curved surface is maintained at about C.

6. A method as claimed in claim 7 wherein the extruded yarn or ribbon is quenched in a liquid at ambient temperature.

7. A method as claimed in claim 6 wherein the extruded yarn or ribbon is quenched by being continuously passed through a tube through which water at ambient temperature is continuously passed.

8. A method as claimed in claim 1 wherein the yarn or ribbon is stretched between about three and about 1 six times its extruded length.

9. A method as claimed in claim 5 wherein the, extruded yarn or ribbon is quenched by being continuously passed through a tube through which water at ambient temperature is continuously passed, and the yarn is stretched about 4% times its original extruded length.

10. A method as claimed in claim 2 wherein the said curved surface is one side of a heated tube whereby the yarn is heated on'all sides.

11. A method as claimed in claim 2 wherein the said curved surface is one side of a heated tube whereby the yarn is heated on all sides, and wherein the length of the tube is between about 4' and about 8 feet, the radius being sufficient to maintain contact of the yarn or ribbon against the convex surface without causing drag or high friction.

Claims

1. A process for manufacturing a flat-extruded yarn or ribbon of melt-extrudable thermoplastic material having two opposed faces, substantially straight and parallel side edges, the overall width between said edges being within the range of about 0.01 inch to about one-quarter inch and an interior crimped region between the edges in the form of a series of blister-like depressions and protrusions on both faces, the length of said depressions and protrusions lying within the range of about one-sixteenth inch to about one-eighth inch and the depth of said depressions and protrusions lying within the range of about 0.005 inch to 0.015 inch, comprising the steps of: melt extruding a flat yarn or ribbon having a substantial viscosity gradient set therein from a melt extruder having a jet in the form of a slot and generating a substantial viscosity gradient, quenching the extruded yarn or ribbon with water to ambient temperature, and heat stretching the cooled yarn or ribbon at a temperature at or above the softening point and below the melting point of the said thermoplastic material.

3. A method as claimed in claim 2 wherein the temperature of the said curved surface is maintained within the range of about 100*C. to about 160*C.

5. A method as claimed in claim 4 wherein the temperature of the said curved surface is maintained at about 120*C.

8. A method as claimed in claim 1 wherein the yarn or ribbon is stretched between about three and about six times its extruded length.

9. A method as claimed in claim 5 wherein the extruded yarn or ribbon is quenched by being continuously passed through a tube through which water at ambient temperature is continuously passed, and the yarn is stretched about 4 1/2 times its original extruded length.

10. A method as claimed in claim 2 wherein the said curved surface is one side of a heated tube whereby the yarn is heated on all sides.