Backaround of the Invention Dyes are intensely colored substances used for the coloration of various substrates, including paper, leather, fur, hair, foods, drugs, cosmetics, plastics, and textile materials. They are retained in these substrates by physical adsorption, salt or metal-complex formation, solution, mechanical retention, or by the formation of covalent bonds. The methods used for the application of dyes to the substrates differ widely, depending upon the substrate and class of dye. It is by application methods, rather than by chemical constitutions, that dyes are differentiated from pigments. During the application process, dyes lose their crystal structures by dissolution or vaporization. The crystal structures may in some cases be regained during a later stage of the dyeing process. Pigments, on the other hand, retain their crystal or particulate form throughout the entire application procedure. They are usually applied in vehicles, such as paint or lacquer films, although in some cases the substrate itself may act as the vehicle, as in the mass coloration of polymeric materials.

The principal usage or application classes of dyes accounting for 85% of

production in the United States are as follows: acid dyes, basic dyes, direct dyes, disperse dyes, fluorescent brighteners, reactive dyes, sulfur dyes, and vat dyes.

Dyeing describes the imprintation of a new and often permanent color, especially by impregnating with a dye, and is generally used in connection with textiles, paper, and leather. Printing may be considered as a special dyeing process by which the dye is applied in locally defined areas in the form of a thickened solution and then fixed.

Generally, dyes are dissolved or dispersed in a liquid medium before being applied to a substrate where they are fixed by chemical or physical means, or both. Owing to its suitability, its availability, and its economy, water usually is the medium used in dye application; however, nonaqueous solvents have been studied extensively in recent years.

Textile substrates can be classified in three groups: cellulosic, protein, and synthetic polymer fibers. Economical and uniform distribution of a small amount of dye throughout the substrate and fixation of the dye are the keys to dyeing, i.e., with regard to fastness to washing, dry cleaning and to other deteriorating influences such as light. It is the enhancement of the fixation of the dye to a substrate to which the present invention is directed.

The production of dyeings of acceptable quality requires the use of many auxiliary products and chemicals. These include chemicals that improve fastness properties such as bleaching agents, wetting and penetrating agents, leveling and retarding agents, and lubricating agents. Other agents are used to speed the dyeing process or for dispersion, oxidation, reduction, or removal of dyes from poorly dyed textiles.

Dyes of similar or identical chromophoric class are used for widely differing applications and, therefore, are classified according to their usage rather than their chemical constitution. Dyes with identical or similar solubilizing groups generally display similar dyeing behavior even though their main structure may vary substantially. Another important consideration in the use of a given dye for a specific application and fastness properties of commercial dyes is found in the pattern cards issued by their manufacturers. The following classification of colorants for dyeing is used: acid, basic, direct, disperse, insoluble azo, sulfur, vat, fiber-reactive, miscellaneous dyes, and pigments.

The most common types of fibers to be dyed with acid dyes are polyamide, wool, silk, modified acrylic, and polypropylene fibers, segmented polyester-polyurethane, as well as blends of the aforementioned fibers with other fibers such as cotton, rayon, polyester, acrylic, etc. Approximately 80-85% of all acid dyes sold to the U.S. textile industry are used for dyeing nylon, 10-15% for wool, and the balance for those fibers mentioned above. Acid dyes are organic sulfonic acids; the commercially available forms are usually their sodium salts, which exhibit good water solubility.

The two major polyamide types commercially available today are nylon 6, and nylon 6,6. Both fiber types are typically very receptive to acid dyes under certain conditions. A direct relationship exists between the chemical structure of an acid dye and its dyeing and fastness properties. The dyeing process is influenced by a number of parameters, such as: dyestuff selection, type and quantity of auxiliaries, pH, temperature and time.

Polypropylene is one of the most important commercial thermoplastics and

its consumption is increasing more rapidly than the total for all thermoplastics.

Polypropylene may be extruded into sheet form for thermoforming and stamping, and also into pipes, profiles and fibers. Unmodified polypropylene fibers are hydrophobic and resistant to dyeing. Polymer composition may be modified to make the fibers more receptive to dyes. For example, addition of basic copolymers to produce an acid-dyeable fiber allows polypropylene to be dyed in combination with other fibers.

However, some of these basic copolymers create problems due to their incompatibility with polypropylene. These additives can have an effect on the extrusion efficiency and on the physical and mechanical properties of the resultant fibers.

In view of the limitations noted for dyeable fibers, efforts have recently been made by major fiber-producing companies to develop acid-dyeable polypropylene fibers. Acid-dyeable fibers have the following advantages: the cheapest dyes can be used; a wide range of colors is available; bright shades are possible; a broad palette of lightfast dyes is readily available; the possibility of joint dyeing with wool and nylon exists; and acid-dyeable polypropylene fibers would also be dyeable with disperse dyes in some cases.

Affinity and diffusion are fundamental aspects of the dyeing process. The former describes the force by which the dye is attracted to the fiber, and the latter describes the speed with which it travels within the fiber from areas of higher concentration to areas of lower concentration.

In the application of dyes, there have developed over the years three chief principles of dyeing textiles. In one case, the dye liquor is moved as the material

is held stationary. In another case, the textile material is moved without mechanical movement of the liquor. Examples of the foregoing include jig dyeing and continuous dyeing which involves the padding of the fabric. A combination of the two is exemplified by a Klauder-Weldon skein-dye machine in which the dye liquor is pumped as the skeins are mechanically turned. Another example is a jet or spray dyeing machine in which both the goods and the liquor are constantly moving.

A substantially non-mechanical dyeing process is typically referred to as exhaustion. This process involves the preparation of a dye bath containing an aqueous solution, usually water, and the dye. The textile to be dyed is then inserted into the dye bath. The temperature of the dye bath is then raised to a predetermined optimal level, with the pH of the bath being similarly maintained, and the textile material is then soaked in the bath. During this soaking process, the dye contained in the bath is absorbed into the fibers of the textile material in accordance with the principles of affinity and diffusion as described above. Once all of the dye has been absorbed, the bath is referred to as being exhausted, with only the aqueous solution being left.

The selection of proper dyeing equipment depends on the nature and volume of the material to be dyed. Raw stock and yarns are dyed by exhaust methods, whereas fabrics are dyed both by exhaust or continuous methods. The choice of method for fabrics depends largely on the volume to be dyed.

Continuous dyeing is usually employed where the volume of fabric for a particular shade is about 10,000 yards or more.

In the dyeing of fabrics, the beck is one of the oldest dyeing machines

known. It consists of a tub containing the dye liquor, and an elliptical winch or reel which is located horizontally above the dye bath. Ten or more pieces of fabric are dyed simultaneously. Each piece is drawn over the winch, and its two ends are sewn together to form an endless rope. The ropes are kept in the dyeing machine side by side, separated from each other by rods to prevent them from tangling. During the dyeing process the reel rotates, pulling the ropes out of the dye bath and dropping them back into the dye bath at the opposite side. In this way almost all the fabric is kept inside the dye bath.

Becks are used for dyeing knits and other light-weight fabrics that can be easily folded into a rope form without causing damage. Fabrics made of filament yarns that tend to break should not be dyed in a beck since the broken filaments will dye deeper. Very light fabrics should also be avoided as they may tend to float on the dye bath and tangle.

Jet dyeing machines are similar to becks in that the fabric is circulated through the dye bath in the rope form. However, in a jet the transportation of the fabric occurs by circulating the dye liquor through a venturi jet, instead of the mechanical pull of the reel in a beck. The fabric is pulled out of the main dyeing chamber by means of a high speed flow of dye liquor that passes through the venturi opening.

Modern jet dyeing machines are generally categorized as "round kier" or "cigar kier" configurations. Most fabrics can be dyed satisfactorily in convention round kier dyeing machines such as the Gaston 824 jet dyeing machine. These types of machines operate at low liquor ratio and yield very good results on most fabrics. However, certain fabrics have more of a tendency to develop crush or

pile marks due to their constructions.

Padders are used to impregnate fabrics with liquors containing dyes, dyeing assistants or other chemicals. Padding is usually followed continuously by other treatments, from drying to a series of successive treatments. The simplest padder consists of two parts: the trough containing the dye liquor, and two squeezing rollers arranged above the dye liquor. In the padding process, the fabric in its open width form, enters the trough through tension rails, passes through the dye liquor, and is then squeezed between two heavy rubber rollers with the proper hardness, under pressure. Excess dye liquor runs back into the trough.

Impregnation is typically followed by drying during which dye migration becomes a major concern. Evaporating water tends to carry with it dye particles from wet spots to dry spots on the fabric, and from the inside or back to the face of the fabric, and may lead to uneven andlor shading problems. To prevent migration, drying is done gradually, and/or a chemical migration inhibiting agent may be used to treat the dyed substrate.

Once the dyed substrate is sufficiently dried, the dye must then be fixed to the substrate so to preclude its bleeding from the substrate. One method of achieving this is through the use of a fixation oven. These ovens are used when fixation of the dyes is performed with dry heat. Both hot flue or heated cans are used for this purpose. Since temperatures as high as 21 50C are often required, the cans are heated with hot oil or gas. Contact heating, as with heated cans, has the advantage that less time is required for the fixation process as compared to the use of dry air.

Another method of fixing dyes to a substrate is by treating the substrate with a dye fixative which similarly improves the wetfastness or dry cleaning fastness of a dyed textile by precluding the dye from bleeding or migrating out of the textile material after it comes in contact with water or dry cleaning solvents.

For example, it is desirable that an article of dyed clothing retain its color while it is being washed using various laundry detergents, whether in a washing machine or by hand. Similarly, when rain water and the like comes in contact with a dyed article of clothing, the retention of the dye within the fibers of the material, rather than its migration onto other substrates is highly desirable.

The reason that a dye fixative may be necessary is dependent on the type of acid dye being employed. For example, those acid dyes that offer excellent dyeing characteristics such as good leveling, migration, and coverage of barre, have only marginal wetfastness properties. Conversely, those acid dyes that provide high wetfastness do not level very well. Obviously, the employment of the first type of acid dyes requires the use of a fixing additive to improve the relatively poor wetfastness properties of those dyes. However, it is oftentimes also desirable to further enhance the wetfastness properties of dyes already adequate in their wetfastness ability.

A number of fixing agents or dye fixatives currently being used in the industry contain formaldehyde and phenols. The environmental disadvantages associated with their use are well known. However, another serious disadvantage associated with their use in combination with dyed materials is their tendency to discolor the dyed material due to a chemical reaction between the phenols and the dye. Consequently, this results in a substantial financial loss of

product and resources.

Therefore, there is a need to provide a process and composition for enhancing the absorption of dyes in synthetic textile materials which is more environmentally friendly than currently used fixatives containing phenols and formaldehyde, while at the same time significantly decreasing the occurrence of discoloration of dyed synthetic substrates.

SUMMARY OF THE INVENTION Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term "about".

The present invention provides a process and composition for enhancing the dyeability of synthetic polymers such as polyolefins which are extruded and ultimately employed to produce products such as carpets and knit and woven apparel fabric made from polypropylene, polyamide-containing substrates, segmented polyester-polyurethane substrates, and combinations thereof, by contacting the polymer with a nitrogen-containing solid, thermally stable compound prior to extrusion of the polymer into fiber form. It has been found that the addition of a nitrogen-containing solid, thermally stable compound to polypropylene polymer prior to extrusion into fiber form enhances fiber dyeability, particularly acid dyeability.

The nitrogen-containing solid, thermally stable compound is preferably selected from the group consisting of fatty amide diethyleneamino bis-stearamide, distearic acid imidazoline, amino ethyl ethanolamine distearamide, and tetraethylene pentamine distearamide. Such nitrogen-containing compounds, with the exception of the latter, are commercially available under the tradenames Sonostat LS-101 (fatty amide

diethyleneamino bis-stearamide) having a melting point of about 108-1 1 0°C, Emery 6669 (distearic acid imidazoline) having a melting point of about 75-76"C, and Emery 6657 (amino ethyl ethanolamine distearamide) having a melting point of about 72"C.

The tetraethylene pentamine distearamide has a melting point of about 75"C and is identified herein as SF-7845. The afore-mentioned products are available from Henkel Corporation, Emery Group, Cincinnati, Ohio.

The amount of nitrogen-containing solid, thermally stable compound that should be present is an amount sufficient to enhance the dyeability of synthetic polymers such as polypropylene, preferably from about 1% by weight to about 20% by weight, based on the weight of polypropylene, and more preferably from about 5% by weight to about 15% by weight, based on the weight of polypropylene.

Various methods can be employed to add the dye-receptive, nitrogen- containing compound to the polypropylene. For example, the dye-receptive compound can be incorporated into the polypropylene polymer using standard techniques commonly used for the incorporation of antioxidants, ultraviolet light absorbers, internal lubricants, and the like. Techniques therefore involve the addition of the dye-receptive material to polypropylene in powder or flake form followed by thorough mixing, melting and subsequent extrusion followed by pelletizing the concentrate. The concentrate is subsequently "let down" by dilution with "barefoot" or virgin pellets to the desired level. The mixture of concentrate (which might also contain antioxidants, etc.) and virgin pellets are then fed to an extruder which melts and thoroughly homogenizes the mixture of pellets prior to extrusion into fiber form. Alternate methods of incorporating the additive can be used such as adding the dye receptor additive to molten polymer followed by mixing,

extrusion, and pelletizing to form a concentrate, or by tumbling a mixture of polymer pellets with the additive in the absence of heat followed by extrusion and pelletizing to form the concentrate. Still another technique is to add the dye receptive compound to powder or flake material and extrude the mixture directly into fiber form or make pellets at the desired concentration. Any of these known standard methods in standard practice is acceptable. As with other polymer additives, it is essential that the dye receptor molecule be uniformly dispersed in the extruded fiber to obtain optimum dyeability results.

DETAILED DESCRIPTION OF THE INVENTION The manufacture of products made from polypropylene is typically from polypropylene extruded into sheet form, pipes, profiles or fibers. The wide variety of polypropylene fibers ranges from the thick, continuous filaments for carpeting and rope to the fine staple and melt-blown fibers for nonwovens. Polypropylene fibers are inexpensive and have desirable properties. Their density is 20% lower than that of the next lightest commercial fiber. In addition to the obvious cost considerations, low density reduces the weight of the final product, such as insulation. Stiffness is intermediate between polyester and nylon. In most applications the modulus is sufficient to compete with nylon on a cost-performance basis. Polypropylene is hydrophobic and does not absorb water. Fiber finishing costs are reduced because less energy is required to evaporate water from the fabric. The low moisture absorption is also an advantage in insulating fabrics maintaining low thermal conductivity. Polypropylene is resistant to waterborne stains, although oil-based stains are sometimes difficult to remove. Abrasion resistance is superior to that of other commercial textile fibers, with the exception of nylon. Polypropylene can be

washed or treated with boiling water.

The carpeting market is the largest market for polypropylene fiber today; over 90% of the tufted carpets in the United States have a polypropylene primary backing.

Nylon dominates the household carpet market for face yarn, where tufted carpets are common. Polypropylene as a face yarn has been limited by its reputation as a cheaper, less desirable product but yarns with improved resilience are becoming available. Earlier polypropylene carpets did not have the feel and luster required in household carpets; few colors were available. In Europe, especially in Italy, polypropylene as a carpet fiber is more common. Over one-quarter of all carpet fiber produced in Italy is polypropylene. These fibers are typically used in combination with wool or other fibers in tufted carpets. Use of polypropylene in commercial or institutional carpets has increased dramatically in the 1 980s. The bulked continuous filament (BCF) yams are well suited for the loop-pile styles common in this market.

The low cost of polypropylene fibers has aided in the penetration into this market.

Superior stain resistance and low moisture absorption reduce maintenance costs, which is important in commercial carpet selection. In 1995 approximately 600 million pounds of BCF was used as carpet face yarns and an equal amount as carpet backing. The use of polypropylene fibers in upholstery has expanded rapidly in the past few years, and accounts for more than 25% of all upholstery fibers consumed in 1983. The heavy BCF yarns used in the early 1 970s because of their durability and stain resistance are combined with finer yarns that improve the appearance. In 1983, upholstery fabrics used about 30 x 103 t of polypropylene fiber in the United States.

In most cases involving polypropylene, colored yarns, carpets, or other fabrics

have resulted from the incorporation of pigments into the polymer prior to the conversion of the non-dyeable polypropylene polymer into fiber. The use of melt- dyed (by the incorporation of pigments) fibers has created inventory problems and has lessened the flexibility of the fiber producer since color of the fiber product has already been determined. The ability to produce a natural color fiber which can be subsequently dyed in a wide selection of colors greatly enhances the options of the fiber manufacturer and the fabric manufacturer. One of the obvious advantages of this invention is to provide that flexibility.

Disposable nonwoven fabrics have been the most rapidly expanding market for polypropylene fiber in the past decade. Disposable baby diapers are a recent market ($3.1 x 109/yr) with extensive use of polypropylene nonwoven fibers, primarily in the cover stock. Disposable diapers for incontinency constitute a $2 x 108/yr market. This market is expected to increase significantly as the U.S. population ages and the need for institutionalized geriatric care increases. Nonwoven fabrics are used in disposable surgical gowns, sponges, and dressings, and other medical apparel, reducing the risk of infection. These markets consume almost $300 x 106 of nonwoven fabric annually. Non-woven polypropylene fabrics are also used in underground construction; more than 167 x 106 m2 of these fabrics was used in 1984, compared with less than 8 x 106 m2 in 1975. These fabrics are primarily used to provide ground stabilization and reinforcement in construction and road paving, providing drainage in soil retention and erosion control. Polypropylene offers the advantages of low moisture absorption and resistance to biological degradation.

Nonwoven polypropylene fabrics are also used in automobiles in rear shelf panels, air-duct insulation, and seat parts.

The manufacture of apparel fabric made from polypropylene is typically accomplished pursuant to two textile manufacturing methods, knitting and weaving.

With respect to the knitting process, there are two specific methods, warp knitting and circular knitting. In general, however, knitting is a method of constructing fabric by interlocking a series of loops of one or more yarns. Warp knitting involves combining yarns which run lengthwise in the fabric. The yarns are prepared as warps on beams with one or more yarn for each needle. Examples of this type of knitting include tricot and raschel knits. Circular knitting is a more common type of knitting in which one continuous yarn runs crosswise in the fabric making all of the loops in course. The fabric is in the form of a tube.

Weaving is the process of interlacing two yarns of similar materials so that they cross each other at right angles to produce a woven fabric.

In contrast to the foregoing knitted or woven apparel fabrics, a tufted carpet is produced on a tufting machine which is essentially a multi-needle sewing machine which pushes the pile yarns through a primary backing fabric and holds them in place to form loops as the needles are withdrawn from the backing fabric.

In general, apparel fabric is knit or woven from fine dimension yarns, in contrast to carpet which is produced from large dimension yarns. It is thus desirable to provide dyes impregnated in knit and woven apparel fabric made from polyamide- containing substrates, segmented polyester-polyurethane substrates, polypropylene, or combinations thereof in order to prevent or reduce the likelihood of their bleeding and/or fading out when exposed to water, chemical laundering detergents, and sunlight in as ecologically safe a manner as possible. It has now been found that by employing a process wherein a polyamide-containing substrate, segmented

polyester-polyurethane substrate, polypropylene, or combination thereof is modified by the addition of a nitrogen-containing, dye-receptive, thermally stable compound selected from the group consisting of fatty amide diethyleneamino bis-stearamide, distearic acid imidazoline, amino ethyl ethanolamine distearamide, and tetraethylene pentamine distearamide that the dyeability of the polymers is significantly enhanced, particularly with respect to acid dyes. When the afore-mentioned nitrogen- containing, dye-receptive compound is not present, it has been found that polypropylene fibers fail to exhibit color when dyed with acid dyes.

The tendency of a dye to bleed and/or fade out of a substrate upon contact with water or detergents relates to the wash-fastness, or more generally "color- fastness" of the substrate. More particularly, color-fastness means the resistance of a material to change in any of its color characteristics, to transfer of its colorant(s) to adjacent materials, or both, as a result of exposure of the material to any environment that might be encountered during the processing, testing, storage or use of the material.

According to the invention, the dyeability of a product such as fabric made from polyamide-containing substrates, segmented polyester-polyurethane substrates, polypropylene substrates or combinations thereof is enhanced by contacting the polymers thereof prior to extrusion with the afore-mentioned nitrogen- containing, thermally stable compounds in a sufficient amount such that the product has improved dye acceptance and coloration, and color-fastness particularly with respect to exposure to water and various cleaning products such as laundry detergents and dry cleaning solvents.

The amount of nitrogen-containing, thermally stable compound used should

The amount of nitrogen-containing, thermally stable compound used should be sufficient to effectively enhance the dyeability of the polymers, particularly polypropylene. The types of polymers which may be treated with the dye-receptive compounds of the invention will vary, but may include those employed to produce carpets and articles of apparel made of a polyamide substrate, segmented polyester-polyurethane substrate, polypropylene and combinations thereof. For example, polyamide substrates such as nylon 6 or 6.6, or segmented polyester- polyurethane substrates such as Lycra which may be used for making swimsuits or aerobics apparel and other forms of apparel, can be treated with the dye-receptive composition of the present invention in order to improve their weffastness and colorfastness. Preferably, the amount of dye-receptive compound present in the polymer composition is from about 10 to 20 weight percent based on the weight of the polymer composition. Most preferably, the amount of dyeability enhancing compound is at least about 10 weight percent, based on the weight of the polymer composition when the substrate is polypropylene. When the substrate is nylon, the amount of dyeability enhancing compound is at least about 10 weight percent, based on the weight of the substrate composition.

Generally, the dye-receptive compound is applied to the polymer prior to extrusion and mixed therewith. The temperature of the melt during extrusion is preferably between about 1 900C and about 260"C, and most preferably about 230"C. to 245"C. It should be noted, however, that the temperature ranges are dependent on many variables including particularly the type of polymer being extruded, the molecular weight of the polymer, and the melt viscosity.

The dye receptor compound can also be used in conjunction with other

conventional polymer additives such as antioxidants, ultra-violet light stabilizers, flame retardants, internal lubricants, and the like. These can be dispersed together with the dye receptor additive in the polymer prior to fiber extrusion. It should be noted, however, that the substrate can be treated with the dyeability enhancing compound in any known manner without departing from the spirit of the invention, so long as contacting the polymer substrate with the disclosed dyeability enhancing compound composition is performed and the dye receptor compound is applied uniformly and rendered homogeneously within the resultant fiber.

Propylene can be produced by a variety of laboratory methods. The most common and practical system is the dehydration of n-propanol and 2-propanol with sulfuric acid and an aluminum sulfate catalyst. Phosphorus pentoxide or phosphoric acid can also be used as dehydrating agents.

High purity (99%) propylene is easily obtained in high yield by dehydrating 2- propanol over a catalyst of activated alumina at temperatures over 2400C.

Propylene is a by-product of ethylene produced by steam cracking or of gasoline produced by catalytic cracking. The molecular structure of the polymer is determined mainly by the size and structural order of the macromolecule on which its physico-mechanical properties depend. Polypropylene may be extruded into sheets for thermoforming and stamping, into pipes, profiles and fibers.

High molecular weight, low melt-flow materials provide the required melt strength. Incorporation of ionomers or fillers improves melt rheology. Single-screw extruders with high length-diameter ratios (24:1 to 30:1) provide good mixing of the melt. Back pressures of 10 to 20 Mpa (1500 to 3000 psi) improve melt uniformity.

Melt temperatures of 230"C to 2600C are commonly used for sheeting. Higher

temperatures cause degradation, discoloration, loss of properties, "plate-out," and necking. Adapter and die temperatures are kept close to the melt temperature.

Extrusion conditions for the production of pipes are similar to those for sheets.

However, the die is kept at a lower temperature than the melt to control the external tube dimensions. Sheets are cooled on a series of rolls under conditions that minimize orientation and drawdown; the rolls are kept at 90-100"C.

Melt spinning produces a broad range of polypropylene fibers, ranging from fine (0.1 tex as 1 den) staple to coarse continuous filaments. Fiber strength (tenacity) and other properties depend on processing conditions and molecular weight. Highly drawn fibers with tenacities as high as 1.2 N/tex (14 g/den) have been produced; however, most commercial fibers have tenacities of 0.44 to .79N/tex (5 to 9 g/den). High tenacity fibers have low elongation and are undesirable for many applications. Fibers with noncircular cross sections provide texture and luster, whereas circular polypropylene fibers are waxy. Most carpet and upholstery yarns are noncircular. Melt-spun fibers are produced by extrusion through a die plate containing many small holes, referred to as a spinneret. The molten filaments are stretched by an applied force, usually from a takeup wheel, as they are air cooled. The melt-drawn fibers are stretched at a temperature below the crystalline melting point, in a process referred to as cold drawing. This operation provides the orientation necessary for desirable physical properties. The oriented, cold-drawn fiber is annealed or heat set to ensure dimensional stability.

Considering the melting point of polypropylene polymers (170"C), relatively high extrusion temperatures are required for melt spinning polypropylene because of the high viscosity and viscoelasticity of the melt. Typical screw temperatures are

about 240"C, but the spinneret can be as hot as 300"C for fine fibers.

Polypropylene melts expand as they flow out of the spinneret holes, a phenomenon referred to as die swell. In most melt-spinning operations the diameter of the extruded filament just after the die plate may be two or three times that of the spinneret hole. The swelling increases as the size of the die holes is reduced; therefore this effect determines the minimum diameter of melt-spun polypropylene fibers. Spinnerets are designed to accommodate die swell and other phenomena caused by the viscoelasticity of the melt. Gradually tapered capillaries minimize the disturbance of the flow streamlines near the die exit. This minimizes the energy stored as elasticity and the consequent swell as the melt is allowed to expand freely.

Viscoelasticity, and therefore die swell, can be reduced by using a polymer with a narrow molecular weight distribution. Thermal or peroxide-induced degradation is an effective method of narrowing molecular weight distribution. The lower melt viscosity of the degraded polymer also reduces die swell. Newer controlled rheology polymers have also improved extrusion performance. The throughput and number of holes in a spinneret are lower for polypropylene than for nylon and polyester, which are less viscoelastic. The number of holes in a spinneret used for continuous filaments can vary from 10 to 150. Spinnerets used for thin filaments in staple fiber production may contain as many as 2000 holes.

Large vertical air-cooling chambers, or chimneys, are required to cool the molten filament and allow adequate time for crystallization under an applied extensional force. Chimneys can be as high as 15 m, accommodating spinning speeds of 1000 m/min. The filaments are melt drawn by tension on the takeup reel, and the crystals are partially oriented by this force. Increased extension increases

the crystalline orientation. The properties of the final fiber are determined by the structure of the melt-drawn fiber. Fibers with a paracrystalline, smectic structure are more easily subsequently drawn into high tenacity fibers than those with the stable monoclinic structure.

Cold drawing typically takes place together with melt spinning. For staple fiber, separate processes are sometimes used. In either case the fiber is stretched from 2 to 10 times its length by forces applied by a series of takeup reels. As in melt drawing, higher draw ratios can be obtained when the fiber is in the smectic rather than the monoclinic form. Nonuniform thinning of the drawn fiber, or necking, can occur if the undrawn fiber is too crystalline. Although this extensional process is referred to as cold drawing, it frequently takes place above 700C. The maximum extension obtainable by drawing and the resulting crystalline orientation and fiber strength are related to the drawing temperature, the polymer polydispersity, and the orientation of the undrawn fiber. If the cold-drawing temperature is above 70"C, the smectic crystals are gradually converted to the stable monoclinic form. Otherwise, a heat-aging or annealing process between 70 and 140"C is required to relieve the stresses induced during the drawing process and minimize shrinkage. This process increases fiber crystallinity and density.

The following non-limiting examples serve to illustrate the invention. In the following examples, all ratios are by weight and percentages are weight percentages unless otherwise indicated.

The following test method was used to evaluate the effectiveness of the dyeability enhancing compounds of this invention.

I. Colorfastness To Water: AATCC Test Method 107-1991.

Test Solution Freshly boiled distilled water or deionized water from an ion-exchange apparatus.

Procedure (1) The test specimen is immersed in the test solution at room temperature with occasional agitation to insure thorough wetting out for a period of 15 minutes.

(2) The test specimen is then removed from the test solution and is then passed through a wringer to remove excess liquor when the weight of the test specimen is more than 3 times its dry weight. Whenever possible, the wet weight should be 2.5- 3.0 times the dry weight of the test specimen.

(3) The test specimen is then placed between glass or plastic plates and inserted into the specimen unit of an AATCC perspiration tester. The perspiration tester is adjusted to produce a pressure of 4.536 kg on the test specimen.

(4) The test specimen is then heated in an oven at 380 j10 C. for approximately 18 hours.

(5) The test specimen is then removed from the unit and hung in air at room temperature to complete the drying procedure.

Evaluation Method For Color Change The test specimen was then rated on a scale from 5 to 1 for color, based on the Gray Scale for Color Change. The scale is from 5 to 1, with 5 representing negligible or no change in color, and 1 representing a significant change in color.

The dyeability enhancing compounds of this invention provided improved color shade and colorfastness to polypropylene fabric as shown in the following examples.

Example I To a polypropylene polymer was added about 10% by weight of fatty amide diethyleneamino bis-stearamide having a melting point of about 108"C-1100C commercially available from Henkel Corporation, Emery Group, Cincinnati, Ohio under the tradename Sonostat LS-101. The mixture was heated to 2000C to melt and homogenize the blend. The melt mixture was then extruded through a spinneret at a temperature of about 240"C to form the fibers which were subsequently drawn. The yarns were knitted into tubing and dyed using Acid Red 182. Colorfastness to water was examined by AATCC TM 107-1991 and found to provide a value of 4 to 5 and lighffastness of 5.

Example II A masterbatch of polypropylene polymer and distearic acid imidazoline having a melting point of about 750C commercially available from Henkel Corporation, Emery Group, Cincinnati, Ohio under the tradename Emery 6669 was prepared and let down with virgin polymer to achieve about a 10% by weight mixture of the additive in the polymer. The mixture was extruded into fibers through a spinneret at a temperature of about 2400C. After cooling, the fibers were drawn and knitted into tubing. The knitted tubing was dyed using Acid Red 182 and examined for colorfastness and lighffastness as in Example I and found to provide a value of 4 to 5, and 5 respectively.

Example III To polypropylene powder was added about 10% by weight of amino ethyl

ethanolamine distearamide having a melting point of about 72"C commercially available from Henkel Corporation, Emery Group, Cincinnati, Ohio under the tradename Emery 6657. The mixture was heated to about 200"C and thoroughly homogenized prior to extrusion through a spinneret at a temperature of about 240"C to form the fibers. After cooling, the fibers were drawn, dyed in skein form with Acid Green 25, and examined for colorfastness to water and lighffastness as in Example I and found to provide a value of 3 to 4, and 3 respectively.

Example IV A concentrate of polypropylene polymer and tetraethylene pentamine distearamide having a melting point of about 75"C and available from Henkel Corporation as SF-7845 was prepared in pellet form and let down with virgin polymer to produce a mixture containing about 10% of the dye receptor in the polymer. The mixture of pellets was heated to a temperature of about 240"C and extruded into fibers. The fibers were drawn and knitted into tubing. The knitted tubing was dyed using Acid Green 25. The dyed fibers were examined for colorfastness to water and lighffastness as in Example I and found to provide a value of 3 to 4, and 3 respectively.