High-tenacity nylon fabrics have been difficult to dye uniformly using conventional dyeing procedures. Due to the unusually high orientation of the fiber crystallites, high denier per filament, subsequent texturizing (in some cases), and other factors, dye penetration with any degree of uniformity in these high-tenacity nylon fabrics has only been achieved through very long batch operations. Typical batch operations, such as a jig or pad roll, often produce a striated appearance with poor shade uniformity from roll-to-roll. The heavier denier, high-tenacity fabrics are also subject to moire effects or poor selvage shading.
The process of this invention, which may be conducted on a continuous dyeing range, employs a dye assistant system to effectively and uniformly dye industrial high-tenacity nylon fabrics such as Cordura.RTM., nylon antiballistic fabrics, and others as further identified below. The continuous process uses an aqueous-based, homogeneous system and produces uniform, non-striated, high-tenacity dyed nylon with exceptional fiber bundle penetration. THe process is more economical than conventional batch dyeing operations and uses commercially available range equipment. The process is continuous and the dyed fabric is of a more uniform quality, including a non-striated appearance with well-penetrated yarn bundles, from end to end and piece to piece as compared with fabrics dyed using the conventional batch procedure.
As used in this disclosure, the term high-tenacity nylon refers to fibers of a high tensile strength nylon yarn spun from poly(hexamethyleneadipamide), or 6,6 nylon, which has a draw ratio of at least 4.0, and preferably in the range of 4.6 to 5.1. Such fibers are disclosed in U.S. Pat. No. 3,433,008 to Gage, and are currently commercially available from various sources including Cordura.RTM. from DuPont, Wilmington, Del. These fibers are used to make fabrics which are in turn formed into long-wearing, abrasion-resistant articles of clothing, suitcase and handbag material, antiballistic clothing and protective devices and similar articles.
The currently preferred Cordura.RTM. product contains approximately twice as many amino end-groups as conventional nylon. The presence of these end-groups favors undesirable ring dyeing of the fabric, and makes uniform dyeing and complete penetration of the yarn bundle difficult in a continuous process. Ballistic nylons and other high-tenacity nylon products may not contain an unusually high content of amine end-groups as does Cordura.RTM., but they are also easily dyed by the process of this invention.
It is believed that the essential difference between generic 6,6 nylon and the high-tenacity nylons of concern to the present invention lies in the higher degree of structural order of these stronger nylons. The higher degree of structural order allows a wider latitude in processing operations and conditions, beyond limits that would normally be tolerated by conventional nylon fabrics. As an example, high-tenacity nylon with its higher degree of order is amenable to drastic steaming at elevated temperatures with little loss of strength.