Dyeing articles composed of melamine and aramid fibers

The present invention relates to fabrics and yarns made from melamine fibers and processes for imparting color characteristics to them.

Melamine fibers are useful in applications requiring resistance to heat and flame. Examples of such applications include upholstery, drapery material, fire fighting apparel, etc. Such applications might be considered so utilitarian because of their role in preserving life and property that appearance is a minor secondary consideration. This is not true, however, and style plays an important part of fabric selection. Therefore, it is important that the fabrics made with melamine be dyeable to desired shades. Because the chemistry of the melamine fiber is different than the more commonplace man-made synthetic fibers, the dyestuffs known to dye these more common fibers do not necessarily dye melamine fibers.

Melamine fibers are often blended with other fibers such that most melamine fabrics are actually blends of melamine and other types of fiber. In particular melamine fibers are blended with aramid fibers, for example, p-aramids, m-aramids. The same concerns of dyeability apply to fabrics made from blends of melamine fibers and aramid fibers as apply to all melamine fabrics. Methods for dyeing these fabrics are desirable.

In addition, novel color effects are sought in the industry. Dyeing methods that cause unique or attractive appearances in the fabric subjected to the method are considered beneficial. One popular color effect is called "chambray". Chambray fabrics are exemplified by worn denim jeans. Usually, this effect is accomplished by process steps, e.g., stone washing, after the dyeing process. In addition, the denim effect is usually achievable with dyes that do not exhibit good washfastness to cellulosic materials combined with the use of undyed warp yarns in the starting fabric. Upon washing, certain dyes exhibit poor fastness to washing resulting in a lighter appearance and more noticeable uncolored warp yarns.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method for dyeing blended melamine-aramid fiber fabrics.

This and related objects and advantages are achieved with a process for dyeing heat and flame resistant articles that are made from melamine fibers and aramid fibers. The process involves exposing a fabric that is made from melamine fibers and aramid fibers to a dyebath containing basic dye, sodium nitrate, and at least one carrier. The fabric is dyed at a temperature exceeding about 100°C such that the aramid fiber is dyed, the melamine fiber is substantially undyed and the fabric exhibits a chambray appearance. The melamine fiber is preferably a melamine-formaldehyde fiber comprising the condensation product of melamine and formaldehyde in a molar ratio of two moles of formaldehyde to one mole melamine; one or more hydroxyoxaalkylmelamines; and, optionally, other additives in small amounts and makes up between about 20% and about 50% by weight of the fabric. In the process, the carrier is preferably selected from the group consisting of: acetophenone; methyl benzoate; benzaldehyde; benzyl alcohol; benzyl alcohol/acetophenone mixtures; cyclohexanone; N-cyclohexyl-2-pyrrolidone; N-octyl pyrrolidone; N,N-diethyl (meta-toluamide; N,N-dimethylformamide; mixtures of N-butyl and N-isopropyl phthalimide; aryl ethers; benzamides and dimethylamides; aryl ether; aryl ether; and aromatic ketone, and the dyeing is preferably at a temperature of at least 120°C.

A heat and flame resistant chambray fabric comprises from about 20% to nearly 100% melamine fiber that is substantially undyed and dyed aramid fiber such that the fabric exhibits a chambray appearance. The fabric may be woven, non-woven or knitted.

Related objects and advantages of the present invention will be apparent to those of ordinary skill in the art after reading the following detailed description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

To promote an understanding of the principles of the present invention, descriptions of specific embodiments of the invention follow and specific language is used to describe the same. It will be understood that no limitation of the scope of the invention is intended by the use of this specific language and that alterations, modifications, equivalents and further applications of the principles of the invention discussed are contemplated as would normally occur to one ordinarily skilled in the art to which the invention pertains.

The following detailed description of the present invention refers to dyeing articles in the form of fabrics, yarns, etc. It is believed that there is no limitation of the particular form the article may take, i.e., it may be in fabric, yarn, web, thread, fiber, sliver, tow, etc., form.

The invention relates to standard methods for imparting color to fiber in all of these constructions, e.g., dyeing, printing, etc. Preferably, the process is a dyeing process. The dyeing process may be in an aqueous or non-aqueous bath. Currently, an aqueous bath is preferred.

The melamine fiber is blended with aramid fiber to make a mixed component yarn. The terms "fabric" and "yarn" and "fiber" should be considered interchangeable and given their broadest interpretation consistent with the art for the purposes of the present invention.

For the purposes of describing the dyeing effects achieved with the present invention, the terms "dyed" (and related words) and "stained" (and related words) are used to describe different responses to a particular dyestuff. These terms are used in accordance with the general meaning given to them by those who are ordinarily skilled in this art.

The present invention concerns dyed heat and flame resistant fabrics. In general, such fabrics as used in this context are those having a limiting oxygen index of greater than about 28 as measured by ASTM D-2863-77, more preferably at least 30.

DYED FABRICS (AND YARNS) FROM BLENDS OF MELAMINE FIBER AND ARAMID FIBER (ARAMID DYED)

One aspect of the present invention is a process for dyeing an article constructed from heat and flame resistant melamine fiber and aramid fiber wherein the aramid fiber is dyed but the melamine fiber is not substantially dyed. The article to be dyed is placed for about 30 to about 120 minutes in a dyebath containing a basic dye or blend of dyes, sodium nitrate and a carrier. The dyebath is heated to at least about 100°C to about 190°C (or more). This aspect of the present invention and fabrics made thereby are illustrated in Examples 1A - 1C.

The fabric (or yarn) is composed of melamine with other fibers selected from m-aramid fibers and p-aramid fibers.

The fabric may be in any form: woven, nonwoven, knitted, etc. The blend level may be from about 20% to nearly 100% melamine fiber by weight. Preferably, the amount of melamine fiber in the blend will be no more than about 60% by weight. Other fiber types could also be present.

The melamine fiber may be any melamine fiber, but is preferably a melamine- formaldehyde fiber that is essentially the condensation product of melamine and formaldehyde in a molar ratio of two moles of formaldehyde to one mole of melamine and containing hydroxyoxaalkylmelamines and, possibly, other additives in small amounts. One suitable melamine fiber is Basofil® fiber available from BASF Corporation, Mt. Olive, NJ.

The dye in the dye bath is one or more basic dyes. Sodium nitrate (or equivalent) and a carrier are also present. Suitable carriers include acetophenone; methyl benzoate; benzaldehyde; benzyl alcohol; benzyl alcohol/acetophenone mixtures; cyclohexanone; N-cyclohexyl-2-pyrrolidone; N-octyl pyrrolidone; N,N-diethyl (meta-toluamide); N,N-dimethylformamide; mixtures of N-butyl and N-isopropyl phthalimide; aryl ethers; and benzamides and dimethylamides. Examples of these include Polydyol NN; C-Prodye NM; Cadra NEX; Dymex; and Cindye NMX. Swelling agents such as N-methyl-2-pyrrolidone; N,N-dimethylacetamide; dimethylsulfoxide; and N,N-dimethylformamides may also be used.

Other materials may also be present in the dyebath according to conventional dyeing practice. These materials include, for example, leveling agents, anti-foaming agents, dispersing agents, lubricating agents and chelating agents and combinations of these.

The temperature of the dyebath is in the range of about 100°C to about 190°C (or more), and preferably at least about 120°C The precise temperature will depend on the dyestuff used and should be readily determinable by those of ordinary skill in the art.

The fabric will stay in the dyebath for a period of time that will also depend on the dyestuff and will be readily determinable by those of ordinary skill in the art. Typical times range from about 30 to about 120 minutes.

After the dyeing step is complete and the fabric or yarn is dyed to the desired shade, typical, optional, subsequent steps may be used. For example, after scouring may be used if desired for a particular result.

Surprisingly, it was discovered that the dyed fabric exhibits a unique chambray appearance without any subsequent process steps (e.g., stone-washing) that are often used to enhance a chambray effect. Surprisingly, the aramid fiber is dyed but the melamine fiber is not (it could be stained) and the fabric exhibits a chambray appearance without further process steps.

Another related aspect of the present invention is a melamine/aramid fiber blend fabric. This fabric may be made according to the above process, and will exhibit a chambray appearance due to the dyeing of the aramid fiber but not the melamine fiber to any significant degree.

EXAMPLE 1

Aramid/Melamine Fiber Blend Fabrics (Aramid Dyed) (Chambray Appearance)

Example 1A: Dyeing with Basic Dye

A 30s singles cotton count ring spun yarn sample of 50% by weight of Basofil® melamine fiber and 50% Nomex® 462 m-aramid fiber is circular knit into tubes, scoured, dyed and afterscoured as outlined below.

Scouring

The knit tube is scoured in a bath at a weight ratio of 15:1 (bath:fabric). The bath contains:

• demineralized water;
• 0.50 grams per liter Kieralon NB-OL; and
• 0.50 grams per liter soda ash

The bath is heated to 75ºC and held at 75ºC for 20 minutes. Samples are rinsed thoroughly in warm and cold water.

The scoured sample is placed into the dye vessel at a 15:1 (bath:fabric) ratio. The bath contains demineralized water at 60°C. Thirty (30) grams per liter Cindye® C-45 is added to the bath. The bath is heated at 1.5°C per minute to 75°C and held for 15 minutes at 75°C. 2.0% Uniperol® W is added and the sample is held at 75°C for 10 minutes. 2.0% Basacryl® Blue X-3GL (C.I. Basic Blue 41) (available from BASF Corporation, Charlotte, NC) is added and the sample is held at 75°C for 10 minutes. 15 grams per liter Sodium Nitrate is added to the bath and the pH is adjusted to 2.5 with citric acid. The bath is heated at 1.5°C per minute to 135°C and run at 135°C for 60 minutes. The bath is emptied at 70°C and the sample is rinsed with hot and cold water.

Afterscouring

The dyed knit tube is afterscoured at a 15:1 (bath:fabric) ratio in a bath containing:

• demineralized water; and
• 1.0 gram per liter Tanapon® X-70.

The bath pH is adjusted to 4.5 with acetic acid. The bath is heated to 75°C and run at 75°C for 20 minutes. The bath is cooled and samples are rinsed thoroughly with warm and cold water. The sample is then centrifugally extracted and tumble dried.

Example 1B: Dyeing with Basic Dye

Another sample is scoured, dyed and afterscoured by the procedures outlined in

Example 1A, except the dye is 2.0% Basacryl® Yellow X-2GL (C.I. Basic Yellow 65) (available from BASF Corporation, Charlotte, NC).

Example 1C: Dyeing with Basic Dye

Another sample is scoured, dyed and afterscoured by the procedures outlined in Example 1A, except the dye is 2.0% Basacryl® Red GL (C.I. Basic Red 29) (available from BASF Corporation. Charlotte, NC).In Examples 1A - 1C, the aramid fiber is dyed while the melamine fiber is not substantially colored. The fabrics have a pleasing chambray appearance.