US3121278A

US3121278A - Production of uniformly pill-resistant polyamide fibers

Info

Publication number: US3121278A
Application number: US182084A
Authority: US
Inventors: Ira G Epstein
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1962-03-23
Filing date: 1962-03-23
Publication date: 1964-02-18
Anticipated expiration: 1981-02-18
Also published as: BE629974A

Description

assists Patented Feb, 18, 1964- This invention relates to the production of which are resistant to pilling and fuzzing in articles.

Fibers prepared from synthetic linear polyares have proved superior to natural fibers in many respects and are particularly noteworthy for their increased durability. However, when fibers of staple length are employed in many end-uses, such as in loosely-woven fabrics, certain types of carpets and the like, the finished a1 'ticle becomes unsatisfactory in appearance after short usage due to excessive pilling and fuzzing. Filling refers to the formation of little balls of fiber on the surface of the finished article due to the entanglement of loose fibers. Less; well-defined fiber entanglements are called fuzz.

Effectively pill-resistant polyarnide fibers and a process for their production have been disclosed by Matray Stine in US. Patent No. 3,050,822 and in a continuationin-part thereof bearing Serial No. 177,762, filed March 6, 1962. In those disclosures, the pill-resistant fibers have een described as having frequent spaced weal: spots their lengths. The accumulation of pills fuzz in finished articles prepared with such fibers is avoided by breakage of the anchoring fibers at the weak spots, which are characterized with respect to frequency and severity by a value no greater than 0.80 for :3 ratio of Tl/TQ where T is the average break tenacity in grams/ denier of a one-inch sample length and T is the average break tenacity of rninirnun -length samples (Zero distance be tween the tester jaws). The fibers have also been characterized as to weak spot severity by a significant reduction in loop toughness to a value of from 227, preferably 2l5, and by a reduction in molecular weight at the weak spots. They have been further characterized as to weak spot severity, abrasion resistance and. durability by a value of at least 150 for the expression IvI.W.OG0

toughness therein where M.W. is the molecular weight of the poly amide.

The most important object of my invention is to 3 a simple and economical process for producing the p resistant polyamide fibers described by Matray and Stine.

A further important objective is the provision of process variations which lead to the production of more uniform pill-resistant fibers.

These and other objectives are accomplished by continuously and uniformly applying an aqueous peroxide solution containing from 5-30% by weight of hydrogen peroxide to a pluralit of drawn polyamide filaments as they advance to a continuous mechanical crimping opera tion wherein the tow is crimped and excess peroxide solution squeezed out. Subsequently, the tow is steamed for a time sufficient to substantially complete the reaction of hydrogen peroxide with the fiber. Preferably, the hydrogen peroxide sol fore the tow enters the crimper.

Where reported herein, loop toughness and tenc' y values are determined as described by Matray and Etine.

*1 is applied by spraying just be- Example Polyhexamethylene adiparnide is prepared, melt extruded, and cold drawn in the conventional manner to form a 7900-filament tow. Filament denier of the drawn tow is 12. The tow is crimped mechanically by passing it through a stutter box crimper where it is subjected to sufficient pressure to provide an average of crimps/ inch in the filaments. it is fed to the stutter box crimper at a rate of 400 y.p.n1. As the tow enters the crimper, it is sprayed with a 15% aqueous hydrogen peroxide solution at a rate of one gallon/minute. Excess hydrogen peroxide solution is squeezed out in the crirnper and drained off for recirculation to the sprayer. The emergent tow contains, by analysis, 2.8% hydrogen peroxide based on the dry weight of the fiber. This crimped, peroxide-treated tow is placed in a rectangular container, the bottom of which consists of a coarse screen to permit passage of gases upwardly through the container. The container of treated tow is then placed in an autoclave where a vacuum equivalent to inches of mercury is applied for 5 minutes. Steam at 36 p.s.i.g. (l34.5 C.) is then passed upwardly through the mass of fiber for 50 minutes. The steam is supplied by perforated pipes located beneath the container, and the autoclave and container are provided with peripheral seals which prevent the escape or" steam around the outside of the container. By this means, the steam is caused to pass upwardly through the fiber mass in a uniform fashion to complete the reaction of peroxide with the fiber.

The steamed tow is then dried and cut to 4 /2 inch staple in the conventional marmer. By measurement, T is found to be 1.02 grid. and T is 2.25 g.p. cl., giving a T /T ratio of 0.45. The loop toughness of the treated fiber is 4 as compared to a value of 200 for the untreated fiber.

Uniformity of the fiber, as measured by point-to-point variation in the tenacity of samples taken from the autoclave basket, is significantly better than that of fibers prepared by mping and subsequently applying the peroxide by spraying it on the fibers in a centrifuge. The interfilanient variation within the tow is also improved as compared to tow treated by the centrifuge process, the coefficient of variation being 39% as compared to 49% for the centrifuge process.

When the staple is processed into yarn by the conventional woolen system and a oz./sq. yd. plain velvetweave carpet is fabricated therefrom, it is found to be equivalent in pilling and fuzzing erforrnance to a wool carpet of similar construction and has a durability 3 to 4 times that of the wool carpet.

The foregoing example illustrates the advantages of the process of this invention in the simple and economical production of fibers having improved uniformity relative to those produced in other practicable commercial proc esses. In this respect, the previously disclosed centrifuge process of Natray and Stine, although suitable and practical for large-scale, commercial production, is less desirable from the standpoint of initial investment and cost of operation.

The peroxide solution may be added to the tow in any suitable fashion prior to crimping provided that the application is reasonably uniform and an excess of solution over that required to achieve the desired level of tenacity and toughness is employed. Such an excess insures a reasonably uniform distribution of solution over the fibers. Preferably, there should be very little delay between the application of peroxide and the crimping operation since it is desirable that most of the reaction take place after crimping to provide a desirable spot-weakened product. As disclosed by Matray and Stine, the reaction tends to be preferential to the crimp nodes, and, consequently, the yarn should be crimped during most of the reaction in order to provide the most desirable product. The preferred procedure is to spray the peroxide on the tow as it enters the crimper. in this manner, the need for a separate solution-removal step is avoided.

The conncentration of the hydrogen peroxide solution applied to the fibers should be in the range of 5 to 30% in order to achieve the necessary weakening of the fibers while, at the same time, avoiding degradation beyond the point of satisfactory utility. Preferably, the concentration is in the range -20%. It will, of course, have to be adjusted in consideration of the amount of solution remaining in the fiber after the crimping step. This will depend to a considerable extent upon the pressure required to develop the desired crimp in the fiber although some control of the amount of liquid removed may usually be achieved by suitable adjustment of the crimper feed rollers.

In order to prevent premature decomposition of the peroxide, very pure material must be used in preparing the aqueous peroxide solution and the materials of construction for the equipment employed in handling the solution must be carefully selected. Contamination with metal ions, e. g., copper, iron, manganese, chromium, lead and cobalt, should be avoided as these ions are known to catalyze a decomposition of hydrogen peroxide. The hydrogen peroxide used to make up the more dilute solutions should be of good purity and should preferably contain stabilizing agents (e.g., sodium stannate and sodium pyrophosphate) which inactivate small amounts of catalytically active substances. The most suitable material for use in tanks and other containers is aluminum of high purity. Stainless steel (300 series) may be used for limited contact at room temperature if properly passivated. Parts which cannot be fabricated from aluminum or stainless steel should be made of a synthetic resin, e.g., nylon or polyoxymethylene, or should be coated with a resin such as polyvinylchloride.

The only requirement relative to the crimper employed is that it be a pressure type crimper designed for continuous operation. A conventional stutter box crimper is satisfactory. Crimpers of this type are described in U.S. Patents Nos. 2,311,174, 2,734,229, and 2,917,784. The crimper should, of course, be made from corrosionresistant mate-rial and the materials of construction should not be such as to contaminate the peroxide solution with undesirable metal ions as indicated above.

The steaming operation should be carried out in such a manner as to apply the steam as uniformly as possible to all the fibers. To accomplish this, the steam is preferably forced through the fiber mass by positive pressure as described in the example. The temperature and time in the steaming operation should be adjusted to substantially complete the reaction of the peroxide with the fiber. Preferably, the steaming period should be held to the minimum necessary to achieve that result since excessive heating may result in discoloration of the fiber. Preferably, the steam temperature should be held below 145 C. and the optimum range is 125-140 C.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. In a process including the steps of drawing nylon filaments, crimping the drawn filaments in a stutter box and cutting staple from the crimped filaments, the added steps of: spraying an aqueous solution of hydrogen peroxide on the filaments as they advance to the stufier box and heating the crimped filaments, the time-temperature 4 relationship of the heating step being such as to complete the reaction of hydrogen peroxide and nylon.

2. In a process including the steps of drawing nylon filaments, crimping the drawn filaments and cutting staple from the crimp'ed filaments, the added steps of: spraying an aqueous solution containing 5-30% by weight of hydrogen peroxide on the filaments as they advance to be crimped, gathering the crimped filaments in a closed container and steaming the filaments in said container, the time-temperature relationship of the steaming step being such as to complete the reaction of hydrogen peroxide and nylon.

3. In the production of staple, the successive steps of: treating continuously advancing nylon filaments with an aqueous solution of hydrogen peroxide; passing the treated filaments to a stuffer box wherein they are crimped under pressure; exposing the crimped filaments to a vacuum atmosphere; heating the filaments, the time-temperature relationship of the heating step being such as to complete the reaction of hydrogen peroxide and nylon; and cutting staple from the filaments.

4. In the production of yarn, the steps of: treating drawn nylon filaments with an aqueous solution of hydrogen peroxide; crimping the treated filaments in a stufier box; and heating the crimped filaments.

5. The process of claim 4 wherein, in advance of the heating step, the crimped filaments are exposed to a vacuum atmosphere.

6. In a process including the steps of drawing nylon filaments, crimping the drawn filaments in a stuffer box and cutting staple from the crimped filaments, the added steps of: spraying an aqueous solution of hydrogen peroxide on the filaments as they advance to the s-tufier box and heating the crirnped filaments, the time-temperature relationship of the heating step to the concentration of peroxide in the crimped filaments being such as to produce weak spots in the length of each filament and to reduce its loop toughness to a value of from 2-27.

7. The process of claim 6 wherein the concentrationtime-temper-ature relationship of the treating-heating steps is such as to produce weak spots in the filament, predominantly at crimp nodes, said weak spots being characterized as to frequency and severity by a value of less than 0.80 for the ratio T T o where T is the break tenacity in grams/ denier of a one-inch sample and T is the break tenacity of a Zero-length sample, said filament being further characterized by a value of at least for the expression toughness where M.W. is the molecular weight of the polyamide in the filament and by a toughness of from 2-15.

References Cited in the file of this patent FOREIGN PATENTS 1,154,495 France Apr. 10, 1958 1,024,482 Germany "Feb. 20, 1958 1,033,175 Germany July 3, 1958 1,034,133 Germany July 17, 1958

Claims

1. IN A PROCESS INCLUDING THE STEPS OF DRAWING NYLON FILAMENTS, CRIMPING THE DRAWN FILAMENTS IN A STUFFER BOX AND CUTTING STAPLE FROM THE CRIMPED FILAMENTS, THE ADDED STEPS OF: SPRAYING AN AQUEOUS SOLUTION OF HYDROGEN PEROXIDE ON THE FILAMENTS AS THEY ADVANCE TO THE STUFFER BOX AND HEATING THE CRIMPED FILAMENTS, THE TIME-TEMPERATURE RELATIONSHIP OF THE HEATING STEP BEING SUCH AS TO COMPLETE THE REACTION OF HYDROGEN PEROXIDE AND NYLON.