US 3611699 A
Descripción (El texto procesado por OCR puede contener errores)
Oct. 12, 1971 wm JR" ETAL 3,611,699
FIBROUS YARN PRODUCT Filed March 8, 1968 JOHN M. WININGERJR. AUGUST K. MEYER INVENTORS ATTORNES 3,611,699 Patented Get. 12, 1971 US. Cl. 57--140 R 4 (Ilaims ABSTRACT OF THE DISCLOSURE A textile product manufactured from a cellular thermoplastic film which is slit into ribbons that are subsequently oriented to give them strength. Such ribbons when processed into woven fabrics or the like fracture into interconnected filaments having the appearance and hand of yarn but having sufficient coherency that twisting is not required.
This application is a continuation-in-part of our copending application Ser. No. 624,564 filed Mar. 20, 1967.
This invention relates to an improved fibrous product and, more particularly, this invention relates to an improved product comprised of cellular, thermoplastic ribbon yarns which need not be twisted prior to processing.
Historically, heavy, burlap-type fabrics have been manufactured from natural fiber materials such as jute, hemp, sisal, and cotton. However, natural fiber materials have been found to possess a number of disadvantages which make their use in certain circumstances, undesirable for present day purposes. For example, natural fiber materials are susceptible to attack by mold bacteria, as well as by various insects, which cause decay and rotting out of the fibers. This disadvantage, alone, causes products formed from natural fibers to lose their strength, as well as usefulness, in many applications. Synthetic fibers have found wide usage in yarns but have historically been extruded continuous filaments, cut into staple, and then formed by conventional textile techniques into thread, yarn, and the like. As with all yarns produced from staple fibers, twist must be imparted to such products to give them suflicient coherency to Withstand subsequent processing.
To circumvent the natural fiber decay problem, it has been proposed to manufacture fibrous products from thermoplastic materials as it is well known that such materials generally possess a high degree of resistance to degradation by mold, bacteria, water, and mildew. Nevertheless, difficulties have been found to exist in fibrous products manufactured with thermoplastics. For example, fibers of a synthetic, thermoplastic cut into staple retain the lack of coherency when formed into yarns as discussed above and therefore must be twisted prior to processing to insure strength and integrity. Also, the thermoplastic fibrous products of the past do not have a soft hand when formed into heavy burlap-type fabrics.
The above enumerated difficulties related to fibrous products produced from natural and synthetic fibers have been resolved in accordance with this invention by slitting a drafted cellular thermoplastic film sheet into ribbons. When subsequently processed, as for example by weaving, these ribbons are fibrillated and transformed into a web of interconnected strands having a yarn-like hand and appearance. The yarn so formed has good coherency because of the strand interconnection thus, making preprocessing twisting unnecessary. Further, a yarn-like material formed by the above-described process is useful in manufacturing non-woven fabrics as needle damage is reduced because the needle can pierce the yarn without breaking a substantial portion of the webs strands.
In general, the method for producing a textile product according to this invention includes the steps of first providing a thermoplastic material with a blowing agent, extruding the thermoplastic material into film sheet form, slitting the sheet into ribbons, orienting the ribbons, and suitably processing the ribbons into the desired product whereupon they fibrillate into a yarn-like form. During extrusion, the blowing agent causes the formation of bubbles or cavities in the extruded sheet, thereby resulting in a cellular film product whose bulk to weight ratio is not affected to any appreciable degree when compared to a non-cellular film of the same material. The cells or cavities in the sheet result in modified spots in the film or spots susceptible to little longitudinal orientation which, as will be more fully explained hereinafter, form portions of the film along which separation or fracture into fibers is not normally easily effected. Since the spots may form points in the film which are relatively weak in the longitudinal direction after orientation, during fibrillation or fracture, separation occurs longitudinally of the film except at the modified spots resulting in a lace or mesh-like web of numerous interconnected fibrils and strands having substantially no loose ends. In addition, the method of this invention permits a manufacturer to produce a film having a predetermined range of fracturability or separation values since by varying the blowing agent content of the thermoplastic material and the processing conditions, the cellular effect in the extruded film sheet can be controlled and, hence, the degree and type of resulting fibrillation can also be controlled.
Accordingly, it is an object of this invention to provide a thermoplastic fibrous product wherein its inherent coherency is suflicient to eliminate the necessity for twisting before processing into an end product.
Another object of this invention is to provide a thermoplastic fibrous product having randomly interconnected strands giving the product good coherency.
A still further object of this invention is to provide a method for manufacturing a yarn-like product which has sufficient inherent coherency to eliminate the necessity for the usual twisting.
Other objectives and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings in which:
FIG. 1 is a diagrammatic view of a typical equipment line for producing fibrous products in accordance with the principles of this invention;
FIG. 2 is an enlarged view, taken lengthwise, of a fibrous product manufactured according to the principles of this invention:
FIG. 3 is a highly magnified view of the fibrous product section illustrated in FIG. 2; and
FIG. 4 shows a plurality of ribbons as they appear before fibrillation or fracturing.
A typical equipment line for producing the cordage products, in accordance with the principles of this invention, is depicted in FIG. 1 and includes an extruder 10 having a hopper 1'2 and an extruder die 14. Guide rolls 16, 18, and 20 direct extruded film 22 through a quench bath 24 and to a slitter 26 which cuts the film to ribbons 40 of the desired width. A heat controlled oven 28 is located downstream from the extruder 10 and a first set of S-wrap rolls 30 is positioned at the inlet end 32 of the oven with a second set of S-wrap rolls 34 positioned at the outlet end 36 of the oven 28. Downstream from the S-wrap rolls 3 4 is located a conventional type winder 38 to receive the slit film.
In operation, the extruder 10 is fed with a thermoplastic material from the hopper 12, the thermoplastic material is heated to the molten state and the thermoplastic material having been blended with a blowing agent of an amount less than that required to effect an appreciable increase in bulk to weight ratio when compared to a film having no blowing agent, is extruded from the die 14 as a film sheet having very small cavities or cells therein. The cellular film sheet 22 is drawn away from the die through quench bath '24 and through slitter 26 by means of the S- wrap rolls 30 and is drafted or drawn in heated oven 23 by rotating the S-wrap rolls 34 at a higher peripheral speed than the rolls 30. This treating of the ribbons 40 slit from the film sheet, that is, drafting while heated, causes them to become substantially unilaterally, longitudinally oriented and enhances the strength characteristics thereof in the longitudinal direction and creating lines of potential or incipient cleavage in this direction. Orientation also elongates' the cells or cavities thus serving to create the aforediscussed modified portions having less longitudinal orientation and strength extending in the lengthwise direction of the ribbons. These modified portions provide points of interconnection for fibrils extending transversely of the film when it is fibrillated resulting in a product which is an integral, interconnected, web of synthetic, thermoplastic material. After orientation the cellular ribbons 40 are suitably packaged on spools or beams on the winder 38.
A highly oriented film or ribbon as described above will fibrillate or fracture along the lines of potential cleavage when subjected to a stressing force or shock. This force may be in the form of fluid forces applied in a fracturing air jet as described in US. Pat. No. 3,293,844 or mechanical forces as described in U.S. Pat. No. 2,980,982. The forces may be applied in a number of ways to achieve film fracturing or fibrillation. For example, it has been found that when such an oriented film is processed on a textile loom it is fractured or fibrillated into a yarn-like form.
A fibrillated thermoplastic film sheet in accordance with this invention forms an integral, interconnected, fine lace or mesh-like web preferably comprising a multiplicity of fibrils 42 integrally interconnected with one another and integral with and interconnecting adjacent relatively large strands 44 that are themselves integrally but discontinuously interconnected at points 46-, see FIG. 3. Substantially all of the fibrils and strands are connected at both ends to the web and thus, very few loose ends are present in the finished product. It has been found that a web produced from a film in which no blowing agent was present and fibrillated to the maximum possible, will have on the order of 5.0 loose ends per /2 inch width per one inch length while a web produced-under the same conditions from a film having a blowing agent therein will have less than 10 loose ends per /2 inch width per one inch length.
As best shown in FIG. 4, prior to processing the ribbons 40 are completely coherent on an individual basis. For this reason, they are strong enough to withstand the rigors of such processing without the twisting necessary when staple yarn is employed. After processing, however, the ribbons are fibrillated or fractured into the yarn-like material shown in FIGS. 2 and 3. If desired, the ribbons can be partially fractured before processing. This added to the additional fracturing of processing produces the desired end product. In this manner, the degree of fibrillation of fracturing can be controlled.
The products according to this invention are preferably formed from crystalline, thermoplastic, synthetic materials such as, for example, polyolefins. Among the polyolefins, we have found that polypropylene is the preferred useful material. When a general purpose polypropylene is used, it is preferable to have a melt flow value within the range of 2.5 to 70 gms./l min., as determined by ASTM Test D1238-32T.
It is preferred to utilize a film sheet having a thickness of 1.5 to 2.5 mils prior to fibrillation; however, film shee having a thickness between 1 mil and mils are useful 4 also under the principles of this invention. Also, it is preferred that the bubbles carried by the film sheet have an average diameter no greater than the thickness of the sheet.
In prior art yarn products coherency is the result of frictional contact only. The product according to our invention has many fibrils providing the lace-like network that interconnects the main strands 32, as mentioned. In the preferred embodiment, there are of the order of forty interconnecting fibrils 42 per inch of strand 44. The many strand interconnections found in the product according to this invention results in a yarn-like product which is less likely to separate or unravel than present commercial yarns.
In general, the film sheet is produced by first intimately associating a blowing agent with a crystalline thermoplastic material. The thermoplastic material is then extruded into film sheet form, the blowing agent causing the formation of bubbles or cells in the film sheet. In the formation of the cellular film sheet we prefer to utilize a chemical blowing agent that functions by providing gas upon being subjected to an elevated temperature. However, other types of blowing or sheet forming techniques may also be used.
The incorporation of the blowing agent with the crystalline thermoplastic material prior to extrusion permits the formation of bubbles in the film sheet as the thermoplastic is extruded from the die. However, a blowing agent must be selected that has a decomposition temperature within the temperature range at which the thermoplastic material is extruded and the temperature along the extruder barrel must be regulated to being the temperature of the advancing stock gradually to or above the decomposition temperature of the blowing agent. Preferably, the temperature is regulated so that the blowing agent decomposes or vaporizes in or close to the head of the extruder, the liberated gas thus being expanded in the molten thermoplastic as the latter goes through the head and exits from the die, thereby providing the cellular film sheet. Preferably, the blowing agent and the temperature-pressure profile for the extruder are selected such that the bubbles formed in the extruded film sheet are of a diameter no greater than the thickness of the film sheet itself.
Any suitable blowing agent useful with the material f the film may be used to advantage according to the principles of this invention. Satisfactory agents used with polyolefins such as polypropylene include azodicarbonamides. Other useful blowing agents include azobisisobutyronitrile; benzenesulfonylhydrazide; diazoaminobenzene; N,N-dimethyl N,N dinitrosoterephthalamide; dinitrosopentamethylene tetramine; 4,4'diphenyldisulfonylazide; 4,4'oxybis(benzene sulfonyl hydrazide); and sodium borohydride. The blowing agent will be selected primarily on criteria that includes the rate of gas release, the ease of dispersion with the thermoplastic, storage stability, toxicity, and cost.
The blowing agent is intimately mixed with the crystalline thermoplastic material either by blending or by surface coating. Preferably, in the case of a solid blowing agent having a relatively low particle size, thermoplastic material pellets are dusted with the blowing agent. On the other hand, if the particle size is so large that the blowing agent particles tend to settle to the bottom of the hopper rather than become homogeneously distributed, a carrier material is useful. By a carrier material, we mean a material within which the blowing agent particles may be suspended or dispersed and then coated onto the thermoplastic pellets. Suitable carrier materials include, for example, mineral oil and diethylene glycol. Homogeneous distribution of the blowing agent with the thermoplastic is important since this is one of the primary factors contributing to uniform cell structure distribution in the film sheet. Uniform cell structure provides better physical properties in the film sheet than when a non-uniform cell structure is present.
The amount of the blowing agent used is one factor which effects control of fibrillation or fracturability and, thus, hand and other properties of the fibrillated ribbons including bulk to weight ratio. Generally, the higher the percentage of the blowing agent that is used, the higher the number of web interconnection points and the higher the bulk to weight ratio-and vice versa, of the fractured film. Preferably, the percent blowing agent used is not greater than about .35 by weight.
It is believed that the amount of blowing agent causes an increase or decrease in the number of web interconnecting points by controlling the number of before discussed modified spots in the film. The greater the number of modified spots the greater the number of fibrils and 6 ml. The ribbons are woven into a fabric during which process fracturing or fibrillation thereof occurs.
As a control, polypropylene pellets are extruded into a film without a blowing agent or carrier into a non-cellular film under the conditions set forth above but at a draft ratio of 10:1. The ribbons thus produced have a denier of about 1500 and a density of about 0.90 gm./ml. and are fibrillated or fractured in the manner described above.
Lengths of ribbon cut from both cellular and noncellular film are tested for physical properties with the following results. In each case Sample A is cellular and Sample B is a non-cellular film.
Samples A and B were broken (Without twist) at 1, 5, 10, and inch gage lengths. The results are as follows:
web interconnection points. Conversely, the fewer the number of modified spots the fewer the number of fibrils and web interconnection points. It is apparent, therefore, that by adding more or less blowing agent, the inherent fracturability of a film, under a given set of fibrillating conditions, can be controlled.
While not wishing to be bound by any particular explanation of the manner in which the modified spots accomplish the desired result, it is believed that the following is an accurate description of such. It is apparent that around the cells or cavities there will be some resistance to longitudinal orientation. Therefore, fracturing will produce not only strands and fibrils extending parallel to the longitudinal axis of the web but also a number extending transversely to the axis as best shown in FIG. 3. Thus, a spot is modified only in that the strength of the film in the longitudinal direction is less than it would be if such a spot was not present.
After being formed by extrusion, the film sheet is slit into ribbons 40 and treated in such a manner so as t enhance its strength characteristics. Such treating is common in the thermoplastic film art and generally includes the step of hot drawing to substantially longitudinally, unilaterally orient the ribbons. It is preferred that the ri bons be drawn within the ratios of 3:1 to 15:1 at 300- 375 F.
Subsequently, the oriented, cellular ribbon or ribbons are processed into a final product such as by weaving into a fabric. The stress on the ribbon or ribbons during processing causes them to fracture into the form shown in FIGS. 2 and 3. Thus, the final product has the appearance and hand of one woven from conventional staple yarns but with the use yarn twisting step eliminated.
This invention is further described by the following examples. All percentages are expressed as percent by weight unless otherwise stated.
EXAMPLE I Polypropylene pellets having a density of 0.890 to 0.910 gm./ml. are surface coated with azodicarbonamide (Kempore 150 sold by National Polychemicals, Inc.) as a blowing agent in diethylene glycol as a carrier material to 0.2% azodicarbonamide and 0.1% diethylene glycol. The coated pellets are extruded at a temperature of 450 F. into a cellular film sheet having a thickness of about 5 mils, the film is quenched at 90100 F., slit into ribbons, drafted at a ratio of 9:1 in an oven heated to 355 to 390 F. to induce longitudinal orientation, and wound into ribbon packages. The ribbons have an average denier of about 1500 and an average density of about 0.891 gm./
It can be readily seen that, in untwisted form the modified polypropylene has higher strength at longer gage lengths. The long gage lengths are to be compared to the unsupported lengths to which yarns are subjected in weaving operations. It is believed that the reason for increased strength for Sample A (produced from cellular film) is the large number of interconnecting fibrils joining each of the large filaments or strands.
EXAMPLE II The exact procedure of Example I is followed except that the blowing agent is added to a weight percent of 0.1%. A ribbon product is obtained which when fibrillated has a yarn-like appearance and feel.
In general, the polymeric material found to be useful in the present invention is those crystalline polymers susceptible to a high degree of molecular orientation, particularly olefinic polymers including crystalline polyethylenes, polypropylenes, and polyallomers. Other polymeric materials such as polystyrene, polyesters, polyamides, and copolymers or mixtures of these materials can be used.
By following the teachings of this disclosure it is apparent that a ribbon yarn useful in textile manufacturing can be produced. This yarn is strong, economical to produce and need have no twist imparted thereto prior to processing.
The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.
1. An improved yarn-like product adapted to be processed into a textile product and comprising:
(a) a ribbon of a crystalline, synthetic, thermoplastic material, substantially molecularly oriented in the longitudinal direction and being substantially free from molecular orientation along the transverse direction, the orientation being interrupted by modified areas in the material; and
(b) said ribbon having a density which is substantially the same as the density of a ribbon of the same material which is free from internal cells, said ribbon having a high degree of coherency in its untwisted state, the ribbon being characterized in that when it it processed into a textile product it will fracture into an interconnected web having discontinuously connected, parallel strands further interconnected with a plurality of fibrils to form a yarn-like product having a high degree of coherency.
2. An improved product as set forth in claim 11 wherein the thickness of said ribbon is between 1.0 and 5.0 mils.
3. An improved product as set forth in claim 2. wherein said material is a polyolefin.
8 4. An improved product as set forth in claim 3 wherein 3,214,899 11/1965 Wininger, IL, et a1. 28-1 FIB said polyolefin is polypropylene. 3,402,548 9/ 1968 Wininger, Jr., et a1. 281 FIB References Cited JOHN PETRAKES, Primary Examiner UNITED STATES PATENTS 5 Us CL XR. 3,003,304 10/1961 Rasmussen 28-1 FIB 3,137,611 6/1964 Krolik, Jr. 2s 1 FIB 28 D1G' 1; 161 169