US 3645085 A
A hairy lustrous yarn of isotactic polypropylene which has a rectangular cross section and a luster index above 2.
Description (OCR text may contain errors)
United States Patent Rassart Feb. 29, 1972  HAIRY LUSTROUS YARN  Inventor: Nestor Sylvain Rassart, Drummondville,
Quebec, Canada  Assignee: Chemcell Limited, Montreal, Quebec,
Canada  Filed: Nov. 13, 1969  Appl.No.: 871,648
Related US. Application Data  Continuation of Ser. No. 709,458, Feb. 29, 1968,
3,242,035 3/1966 White ..28/1X 3,361,859 l/l968 Cenzato.. ...264/210UX 3,366,722 H1968 Tessier ..264/168 Primary Examine -Stanley N. Gilreath Assistant Examiner-Werner H. Schroeder Attorney-Leonard Horn and Steven Murphy  ABSTRACT A hairy lustrous yarn of isotactic polypropylene which has a rectangular cross section and a luster index above 2.
The method of making same which comprises:
a. melt extruding a melt-eirtrudable isotactic polypropylene blend in the form of a ribbon.
b. immediately gas quenching the ribbon to a temperature above the glass transition temperature of isotactic polypropylene.
c. attenuating the quenched ribbon at a temperature above said glass transition temperature.
d. gas fibrillating the attenuated ribbon.
1 Claims, 5 Drawing Figures Patented Feb. 29, 1972 v GR 2 QM... NA/WA g INVENTOR Nestor Sylvuin RASSART Y [j PATENT AGEN T J HAIRY LUSTROUS YARN This is a continuation of application Ser. No. 709,458, filed Feb. 29, 1968, now abandoned.
This invention relates to a remarkably bright hairy polypropylene yarn, and to the process of making the same, especially to a continuous process.
Generally, polypropylene is extruded as filaments. The filaments are then stretched and heat relaxed in an oven to produce a crimp yarn which has elastic properties, but no special brightness.
There has now been found a new bright yarn which may easily be produced. The yarn is generally manufactured by melt extruding polypropylene into a ribbon, immediately quenching the latter to a temperature still above the glass transition temperature of isotactic polypropylene and successively attenuating at a temperature above the glass transition temperature of isotactic polypropylene and gas fibrillating said ribbon.
In a particular embodiment, before extrusion, the polypropylene is melted and, once in the molten stage, a viscosity gradient is allowed to develop by heating preferentially one side of the molten material. The molten material is then extruded as a ribbon in a direction substantially perpendicular to the direction of the gradient, the ribbon is immediately gas quenched. It may then be stretched and gas fibrillated.
Still in another embodiment, one side of the ribbon producing die may be insulated so as to produce a viscosity gradient on the ribbon at extrusion. As the ribbon leaves the extruder, it is immediately air quenched to a temperature above the glass transition temperature of the isotactic polypropylene and successively attenuated at a temperature above the glass transition temperature of polypropylene, gas fibrillated and heat relaxed.
The polypropylene, which may be used in accordance with the invention, is melt-extrudable isotactic polypropylene, commonly used for the production of polypropylene yarn and the like. The isotactic polypropylene, in powder form, is generally blended with conventional stabilizers. Pigments, dye additives and other ingredients may also be added, if desired. However, these materials should be used in limited quantities so as not to have an adverse effect on the properties of the rib-- bon and the yarn resulting thereof.
Before melt extrusion, the polypropylene and the other materials should be well mixed to ensure the production of a ribbon of uniform characteristics. Mixing may be carried out in any conventional way. Melt extrusion is then generally carried'out at a temperature between 230 C. and 260 C.
Any apparatus generally used for the melt extrusion of polypropylene and which is provided with a ribbon-producing die may be used. The extruders as described in French Pat. No. 1,405,360 dated May 27, 1964, or Canadian application Ser. No. 008,l53 filed Dec. I9, 1967 or U.S. Pat. application 691,569 filed Dec. 15, 1967, Franklin James, may advantageously be used providing that the spinnerette is replaced by a flat or circular film-producing die. If a flat film producing die is used, the ribbon has ends or selvedges on the sides. With a circular film-producing die, a fibrillated hose is obtained. The hose is more uniform and may be drawn or stretched as a two-layer flat sheet. Drawing of hoses is easier in comparison to single sheets which possess hems. After extrusion, it is important to cool the ribbon immediately but to a temperature still above the glass transition temperature of the isotactic polypropylene. This operation seems to establish a viscosity gradient within the ribbon. In a preferred embodiment, air is blasted on the ribbon as it emerges from the lips of the die. Though air is used, any inert gas, which will not react with the ribbon, may be used.
The ribbon, which has low tensile strength at this stage, is heated and drawn or stretched, while hot, with-conventional stretching apparatus. The hot-melt drawing or attenuating operation is carried out at temperatures between 60 C.-l 10 C., and preferably l l C. The drawing ratio is generally from 2 to and preferably near its maximum.
After drawing, the ribbon is usually gas fibrillated by passing it through an air jet. The yarn thus obtained may then be collected by any known means. If desired, any other gas which will not affect the chemical properties of 'the ribbon may be used.
As already mentioned, if a viscosity gradient is set in the ribbon prior to extrusion, the ribbon formed may not only be air quenched and successively attenuated and gas fibrillated but also heat relaxed to produce a hairy lustrous crinkled yarn.
Having now generally described the invention, the following drawings will serve to illustrate particular embodiments of the invention in which:
FIG. 1 is a schematic view of a setup for producing bright yarn according to the invention.
FIG. 2 is an enlarged cross section of the lowest portion of the die of FIG. 1, taken along line 2-2.
FIG. 3 is the top view of the cooling device of FIG. 2.
FIG. 4 is a cross-sectional view of a gas jet.
FIG. 5 is a cross-sectional view of a yarn produced in accordance with the invention.
The setup of FIG. 1 comprises a melt-extruder which is partly shown at 10, having at its end a nut 12 for retaining the die shown in FIG. 2 as 50. Adjacent to the die a cooling device 14. As soon as the ribbon 16 emerges from the die it is quenched by gas arriving from inlets l8 and 19 (shown on FIG. 2) of the gas-quenching device, but the temperature is not permitted to drop below the glass transition temperature of isotactic polypropylene. After cooling, the ribbon 16 moves around a first guide roll 20 and between nip rollers 22. Thus ribbon is pulled out at constant speed, which is regulated according to the size of the yarn desired.
The ribbon 16 passes around a second guide roll 24, into inlet 26 of a heating tube 28, and through the heating tube 28. As it leaves the outlet 30 of the heating tube 28, the ribbon I6 is passed between a second pair of nip rolls 32. Both sets of nip rolls 22 and 32 are driven, the nip rolls 32 being driven at a faster speed than the nip rolls 22, so as to cause the ribbon to be attenuated during its passage through the heat tube 28. The heat stretching tube 28 may be one as described in principle in Canadian Pat. No. 699,470 or copending U.S. application Ser. No. 488,832 filed July 26, 1965, now U.S. Pat. No. 3,277,228. Other conventional stretching devices may be used, if desired. After being attenuated, the ribbon passes around guide roll 34 and through gas jet 38, where it is fibrillated and becomes a hairy yarn of remarkable brightness. The yarn is made up of filaments having rectangular cross section. The width of the filaments corresponds to the thickness of the stretched film and their length depends upon the efficiency of the fibrillation process used and is a function of such variables as pressure, residence time, geometry of the channel.
The yarn is then pulled around a pair of nip rolls 40 and wound up by 'a conventional takeup device 42 which has a speed controller 44.
The extruder head and the cooling device are better shown on FIG. 2. The end of the extruder comprises (shown on FIG. 2) a die 50 and a gasket 52 which are secured to the extruder head by means of nut 12. The die 50 has an elongated slot 54 through which the film or ribbon l6 emerges. The width of the slot is generally 0.04 inch or less. The gasket 52, which prevents cooling of the die, has an orifice which is larger than slot 54; As soon as the ribbon 16 emerges from the die, it is quenched above the glass transition temperature by the cooling device 14 which has gas inlets l8 and 19.
In another embodiment of gasket element 52 covers only half of the spinnerette to produce a temperature gradient.
In a particular embodiment, the cooling device 14 comprises a cylinder 56 having mounted thereon top portions 58 and 60 and sides 62 and 64. The lowest portion of the cylinder 56 which is bevelled, forms with the side 62 and the top 58 a chamber 66 having a slot or gas outlet 68. Similarly the side 64 and top'60 forms a chamber 70 with gas outlet 72. Gas inlets l8 and 19are connected through cylinder 56 and feeds in the cooling gas in chambers 66 and 70, which then escapes 1m nni nInL' through 68 and 72. An amount of air in the order of about 1 s.c.f.m. per square inch of slit has generally been found satisfactory to effectuate proper quenching in accordance with the invention. The top portion 58 and 60 are better shown in FIG. 3 mounted on cylinder 56 with the gas inlets 18 and 19.
The gas jet may be any jet conventionally used. FIG. 4 shows a jet which may be used in accordance with the invention, where the ribbon 16 goes through inlet 72, moves along passage 74 and leaves the air jet through outlet 76 as a highly bright yam. In accordance with the invention the air could be fed perpendicular to the ribbon as at 78, or could also be fed at an angle in the direction of the ribbon as shown by the dotted line at 80 or therebetween.
The final yarn is made of filaments having a rectangular cross section and having a luster index greater than 2 and generally greater than 4. Yarn of a total denier of 1,200-1,900, with a tenacity between 1.2-2.5 g./d. and an elongation of between 8-15 percent is generally obtained. In the case of crinkled yarn, 10-12 crinkles per inch are generally found.
If a viscosity gradient has been set in polypropylene before extrusion, that is before leaving the die, the yarn may then be heat relaxed. This relaxation is generally conducted in a hotair oven maintained between 100 C. and 150 C., and preferably 125 C. The yarn may be moved in the oven by means of a set of driven rollers rotatably mounted in the interior of the oven and on which the yarn is allowed to move for a few seconds. During the relaxation operation, the yarn shrinks and produces a crinkled effect. There are numerous ways of setting viscosity gradient. For example some means have been described in patent application Ser. No. 008,153, invented by Frank James.
Numerous variations of the basic process may be obtained as illustrated in the following examples.
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Isotactic stabilized flakes having an intrinsic viscosity of 2.8 were melt extracted in a Killoran, Barnett, Guay extruder, at a temperature of 240 C., at a rate of l lb.lhr., through a slot 1.25 inches 0.030 inch on a die 0.020 inch thick. A gasket having a slot larger than the die orifices prevented cooling of the die by an air flow that was blown through two thin slits on each side of the ribbon when it leaves the extrusion orifice. Being colled so rapidly, the ribbon had no time to relax and had a width of 1.1 inches. It was pulled at a speed of 50 f.p.m. and immediately drawn at a ratio of 3 to 1 into a tube stretcher maintained at a temperature of 105 C. The drawn film was then passed through an entangling air jet at a speed of 200 f.p.m. A contraction of about percent was due to entanglement during this last operation. A hairy lustrous yarn of isotactic polypropylene which comprises filaments of rectangular cross section was obtained. A cross-sectional view of the yarn is shown in FIG. 5 under a magnitude of 200 times the original. The yarn had a total denier of 1,600, a tenacity of 1.5 g./d., and percent elongation.
The luster index of the yarn obtained was compared against wool and nylon.
The yarn obtained from Example 1 was wound on a 2-by-2- inch aluminum plate in several layers until the background streaks or excessive hairiness. Using a Lumetron" type 402E Calorimeter adapted with a galvenometer, the pad which exhibited the highest visual luster was inserted in the same holder with the yarns running parallel with the incident light beam. The photocell was set at an angle of 45 and the instrument was balanced until the reflectance measure was near 90 percent of the reading dial, which was recorded as the specular reflectance of the sample.
The photocell was then set at an angle of 90 and the reflectance was measured as the direct-angle reflectance. The ratio of the specular reflectance at 45 reading over the directangle reflectance reading 90 was obtained and is defined as the luster index. The luster index was also defined for the other two samples and are indicated in Table 1 TABLE 1 LUSTER INDEX Specular Direct Angle Luster Reflectance Reflectance Index Wool 78.9% 48.4% 1.63
Nylon 90.0% 51.2% 1.76
Fibrillated PP 45.7% 10.8% 4.23
EXAMPLE 2 EXAMPLE 3 A hairy and bright yarn was obtained in processing polypropylene stabilized flakes of a lower molecular weight (intrinsic viscosity 2.1) in the same extrusion machine as described in Example 1. Extrusion temperature was lowered to 220 C. and the material was processed as in Example 1. The same type of material was obtained having a total denier of 1,200.
EXAMPLE 4 The same polymer as used in Example 3 was'processed according to conditions described in Example 2, but drawn at a ratio of 2.7 to l. A self-crimped yarn was obtained in these conditions similar to the one of Example 2.
Having thus disclosed the invention, what is claimed is:
1. A hairy, lustrous, self-crimping yarn of isotactic polypropylene which comprises filaments having rectangular cross sections, a luster index of 4, a tenacity between about 1.2 to 2.5 grams per denier, an elongation of between 8 to 15 percent, at least 10 to 12 crinkles per inch and a total denier of from 1,200 to 1,900.