TREA

Process for simultaneously dyeing and improving the flame-resistant properties of aramid fibers

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Information

  • Patent Grant
  • 4759770
  • Patent Number
    4,759,770
  • Date Filed
    Wednesday, June 4, 1986
    38 years ago
  • Date Issued
    Tuesday, July 26, 1988
    35 years ago
Information
Abstract
Simultaneous dyeing and flame-resistant property improvement of poly(m-phenyleneisophthalamide) fibers using a swelling agent to introduce a dye and a fire retardant into the fiber. The dyed fiber has properties of strength approximating the original undyed fiber, fire retardance greater than the untreated fiber and is conveniently dyed to an unlimited range of colors with high color yield and relatively good lightfastness at a reasonable cost. An aqueous dimethylsulfoxide solution is used as the swelling agent.
Description
Claims
  • 1. A process for the simultaneous dyeing and flame retarding a poly(m-phenyleneisophthalamide) fiber, comprising the steps of:
  • (1) contacting a dyeable poly(m-phenyleneisophthalamide) fiber with a solution of an organic swelling agent adapted to swell said fiber and selected from the group consisting of N-methylpyrrolidone, dimethylsulfoxide, and dimethylacetamide, and a diluent, in which the weight ratio of swelling agent to diluent is from about 70:30 to 90:10, a solvent-compatible dyestuff dissolved in said solution and a flame retardant, the solution maintained at a temperature in the range of about 65.degree. F. to about 200.degree. F.;
  • (2) heating the poly(m-phenyleneisophthalamide) fiber treated in step (1) to fix said dye and said flame retardant to said fiber;
  • (3) washing the fiber to remove any residual dye, organic swelling agent or flame retardant; and
  • (4) drying the fiber.
  • 2. The process of claim 1, in which the solution contains a mixture of dimethylsulfoxide and water.
  • 3. The process of claim 2, in which said solution contains a mixture of dimethylsulfoxide and water in a weight ratio of about 90:10.
  • 4. A process of simultaneously dyeing and flame retarding a poly(m-phenyleneisophthalamide) fiber comprising the sequential steps of:
  • (a) contacting a dyeable poly(m-phenyleneisophthalamide) fiber with a dyebath solution containing (1) an organic polar solvent swelling agent selected from the group consisting of dimethylsulfoxide, N-methylpyrrolidone and dimethylacetamide, (2) a compatible inert diluent to dilute the swelling agent and protect the fiber from degradation in which the weight ratio of swelling agent to diluent is from about 70:30 to 90:10, (3) a dye dissolved in the solution, and (4) a flame retardant to improve the flame-resistant properties of the fiber, provided that
  • the swelling agent is adapted to swell the fiber and allow the dye and the flame retardant to enter into and become fixed in the fiber, and
  • the swelling agent and inert diluent are present in proportions such that the mechanical strength of the dyed fiber is at least 80% of the strength of the untreated fiber,
  • (b) heating the fiber to fix the dye and the flame retardant in the fiber;
  • (c) washing the fiber to remove residual dye, organic swelling agent or flame retardant; and
  • (d) drying the fiber.
  • 5. The process of claim 4 in which the diluent (2) is selected from the group consisting of water, xylene, ethylene glycol, lower alkanols and 4-butyrolactone.
  • 6. The process of claim 4 in which the dye (3) is selected from the group consisting of acid dyes, mordant dyes, basic dyes, direct dyes, disperse dyes and reactive dyes.
  • 7. The process of claim 4 in which step (a) is conducted at a temperature in the range of room temperature to about 200.degree. F.
  • 8. The process of claim 4 in which the strength of the dyed fiber is at least 90% of the strength of an untreated fiber.
  • 9. The process of claim 7 in which the swelling agent (1) is dimethylsulfoxide and the diluent (2) is water.
  • 10. Fibers of poly(m-phenyleneisophthalamide) dyed and flame-retardant treated by the process of claim 4.
  • 11. A process for the continuous dyeing and simultaneous flame retarding of poly(m-phenyleneisophthalamide) fiber comprising the steps of:
  • (i) contacting solvent-swellable, dyeable poly(m-phenyleneisophthalamide) fibers with a liquid swelling agent system containing a dye and a flame retardant dissolved in an organic swelling agent selected from the group consisting of dimethylsulfoxide, N-methylpyrrolidone, and dimethylacetamide and an inert diluent in which the weight ratio of swelling agent to diluent is from about 70:30 to 90:10, and allowing the thus contacted fiber to swell and admit the dye and the flame retardant into the swollen fiber;
  • (ii) heating the fiber to fix the dye and the flame retardant in the fiber;
  • (iii) washing the fiber to leave substantially no liquid swelling agent in the fiber.
  • 12. The process of claim 11 in which the dyed fiber has at least 80% of the strength of the undyed, untreated poly(m-phenyleneisophthalamide) fiber.
  • 13. The process of claim 12 in which the dyed fiber has at least 90% of the strength of the undyed, untreated poly(m-phenyleneisophthalamide) fiber.
  • 14. The process of claim 11 in which the dyeing in step (i) is conducted at a temperature in the range of from room temperature up to about 200.degree. F.
  • 15. A process for the continuous dyeing and simultaneous flame retarding of a fabric comprising poly(m-phenyleneisophthalamide) fibers to a level shade, said process comprising the steps of:
  • (1) applying a dye solution of at least 70 parts by weight of an organic swelling agent selected from the group consisting of N-methylpyrrolidone, dimethylsulfoxide and dimethylacetamide, an inert diluent, a tinctorial amount of a dyestuff and a flame retardant, to a woven or knit fabric containing poly(m-phenyleneisophthalamide) fibers, the dye solution applied at a temperature in the range of from room temperature up to about 200.degree. F.;
  • (2) heating the fabric to fix the dye and the flame retardant in the poly(m-phenyleneisophthalamide) fibers;
  • (3) washing the heated fabric to remove any residual dye, organic swelling agent or flame retardant from the fabric; and
  • (4) drying the thus treated fabric.
  • 16. A woven or knit fabric having a Limiting Oxygen Index (ASTM D-2863-77) of greater than 27% in which the poly(m-phenyleneisophthalamide) fibers are dyed by the process of claim 15.
  • 17. A dyed, flame-resistant knit or woven fabric consisting essentially of poly(m-phenyleneisophthalamide) fibers containing within the fiber an amount of cyclic phosphonate flame retardant sufficient to impart a Limiting Oxygen Index (ASTM D-28633-77) greater than 0.27.
  • 18. The fabric of claim 17 having a Limiting Oxygen Index in the range of 28% to about 45%.
CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of earlier application Ser. No. 863,038, filed May 14, 1986 now U.S. Pat. No. 4,710,700. This invention relates to simultaneously dyeing and improving the flame-resistant properties of aramid fibers, especially poly(m-phenyleneisophthalamide) fibers, and more particularly to the continuous dyeing and improving the flame-resistant properties of aramid fibers in which the dye and fire retardant are introduced into the fiber while the fiber is in a solvent-swollen state. Aramid fibers are highly resistant to heat decomposition, have inherent flame retardant properties are frequently used in working wear for special environments where flame retardant properties are required. Fabrics made of these fibers are extremely strong and durable, and have been widely adopted for military applications where personnel have the potential to be exposed to fire and flame, such as aircraft pilots, tank crews and the like. There is a need for dyed fabrics that have flame-resistant properties even greater than the undyed fabrics or dyed fabrics. Meta-linked aromatic polyamide fibers (aramid fibers) are made from high molecular weight polymers that are highly crystalline and have either a high or no glass transition temperature. These inherent desirable properties of aramid fibers also create difficulties for fiber processing in other areas; specifically, aramids are difficult to dye. Fiber suppliers currently recommend a complicated exhaust dyeing procedure with a high carrier (acetophenone) content; the process is conducted at high temperatures over long periods of time and often results in a product having an unpleasant odor. Such dyeing conditions require substantial amounts of energy both to maintain dyeing temperature and for the treatment of waste dye baths. Polar organic solvents have also been used to swell the fiber or create voids in the fiber structure to enhance dyeability. These procedures involve solvent exhaust treatments at elevated temperatures with subsequent dyeing. Another source of dyed aramid fiber is solution dyed aramid yarn, available from the producer, prepared by solution dyeing in which a quantity of dye or pigment is mixed with the molten polymer prior to extrusion of the polymer into fine fibers; the dye or pigment becomes part of the fiber structure. Solution dyed fibers are more costly than the undyed fibers due, in part, to the additional costs of manufacture, and must be used in the color provided by the supplier, leaving the weaver with only a limited choice of colors. Solution dyed fibers offer relatively good lightfastness whereas some undyed aramid fibers, particularly Nomex, yellow following exposure to UV light. Because of this potential for yellowing, although deep, rich colorations, particularly dark blue and navy blue, are achievable they still lack acceptable lightfastness. More recently, a process has been described in U.S. Pat. No. 4,525,168 in which acid or anionic dyes are introduced into aramid fibers by coupling the dye to a dye site receptor which, in turn, is attached to the fiber. The process includes first swelling the fiber in a strong polar solvent and, while in the swollen condition, introducing a substance capable of forming a strong chemical bond with an anionic dye into the swollen fiber. This dye site receptor substance is an amine, typically hexamethylenediamine. The procedure described requires at least three steps, first pretreating the fiber in a solution of solvent/swelling agent, the diamine and a wetting agent, then drying to shrink the fiber and incorporate the diamine dye site receptor into the fiber. The thus pretreated fabric is then dyed with an anionic dye. Aramid fibers described and purported to be successfully dyed in U.S. Pat. No. 4,198,494 are sold under the trademarks Nomex and Kevlar by DuPont, and under the trademark Conex by Teijin Limited of Tokyo, Japan. It is an object of the present invention to provide a continuous process for simultaneously dyeing and improving the flame-resistant properties of a dyeable, compatible aromatic polyamide fiber that will yield acceptable colorfastness without detracting from the inherent strength of the aramid fibers. Another object of this invention is to provide a continuous process adapted to simultaneously dye and fire retard large quantities of compatible aromatic polyamide fabric on a commercial scale at less cost than prior procedures.

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Entry
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Continuation in Parts (1)
Number Date Country
Parent 863038 May 1986