WO1998018999A1

WO1998018999A1 - Polyolefin-based pigment carrier system and method for coloring fiber

Info

Publication number: WO1998018999A1
Application number: PCT/US1997/019808
Authority: WO
Inventors: Bobby Garst
Original assignee: Bobby Garst
Priority date: 1996-10-30
Filing date: 1997-10-30
Publication date: 1998-05-07
Also published as: AU5098698A

Abstract

The invention is a pigment system for and method of coloring fiber which employs a polyolefin polymer base and between about 1 and about 70 weight percent pigment. The invention is also directed to a fiber colored with the pigment system and by the method. In accordance with a preferred embodiment, the polyolefin used is polyethylene which is completely free of stearates and stearic acid. The pigment is present at between about 1 and about 70 weight percent of the total pigment system and this pigment system is added at a level of between about 0.001 and about 4 percent by weight of the colored fibers.

Description

POLYOLEFIN-BASED PIGMENT CARRIER SYSTEM AND METHOD FOR COLORING FIBER

BACKGROUND OF THE INVENTION

The present invention relates to the field of coloring fibers, particularly extruded polymer fibers. The two basic options for coloring such fibers are to either disperse a color in the fiber prior to extrusion or to dye the fiber after extrusion. Nylon, in particular, is readily dyeable due to the amine groups ("dye sites") along the polymer which accept acid dyes.

Consequently, nylon fibers have traditionally been dyed with acid dyes after fiber extrusion. For example, in the carpet industry, uncolored nylon is typically extruded and draw textured. The yarn is then either dyed before tufting, or the carpet is dyed after the tufting and backing processes. On the other hand, polyolefln fibers, such as polypropylene, do not have dye sites and have traditionally been colored with pigment (sometimes referred to as a disperse dye) added before or during extrusion. This latter process is generally referred to as solution dyeing.

For various reasons, solution dyeing of nylon fibers, i.e. adding pigment to the nylon before or during extrusion, has been under development in recent years, particularly in the carpet industry. For example, solution dyed nylon fiber may offer advantages such as reduced cost, manufacturing efficiencies, and longer and more stable color life for the product.

Typically the pigments used in solution dyeing are available in a pigment system, sometimes referred to as a color concentrate. A pigment system generally includes a base polymer, sometimes called the "carrier, " loaded with between 1 and 70 weight percent of the pigment particles. Pigments in such systems are easier for the manufacturers to handle and dose. Systems also enhance the dispersion of the pigment particles in the polymer to be colored.

Most often, the base polymer used in a pigment system is selected to be the same, or at least in the same polymer family, as the polymer which will be colored by the pigment. The natural expectation is that using the same or similar base polymer for the system will thus make the system more compatible with and readily dispersed in the polymer to be colored. Thus, nylon carriers are used for pigment carriers for coloring nylon and polypropylene or polyethylene carriers are used pigment carriers for coloring polypropylene.

The base polymer for the pigment system not only needs to be compatible during extrusion of the fiber, but also during any post-extrusion processes. For example, in the production of bulk continuous filament (BCF) nylon carpet yarn, the fibers see temperatures from 65 to 200°C on the heated godets and are further processed through texturizers at temperatures well in excess of 200°C.

One disadvantage of using nylon as the base polymer for a pigment carrier is that nylon is hygroscopic, i.e. it picks up moisture if left exposed to normal air. This moisture can cause serious problems during extrusion. In particular, the presence of moisture during extrusion causes relative viscosity changes in the polymer. This results in poor runability as well as physical property changes in the yarn. The amount of moisture required to negatively impact runability is very small. For example, the maximum moisture specified by extruders of nylon chip is typically around

0.09 percent. All of this adds to the costs of processing, materials, and inventories

Consequently, nylon pigment systems require special handling such as drying operations or working under nitrogen. Although this special handling is also required when extruding nylon into fibers, it is especially problematic for making and handling pigment systems. For one thing, sophisticated manufacturers often buy pigment systems in certain basic colors and then prepare several different mixtures of those basic coiors to produce the exact color desired for the end product. Requiring all of this mixing to be conducted under nitrogen or with special drying steps is a considerable burden. Another disadvantage of using nylon is its relatively high cost compared to other polymers.

SUMMARY OF THE INVENTION Briefly stated, the invention is a pigment system for and method of coloring fiber which employs a polyolefln polymer base and between about 1 and about 70 weight percent pigment. The invention is also directed to a fiber colored with the pigment system and by the method.

In one aspect of the invention, the fiber to be colored is a polyamide fiber, such as nylon. Another aspect of the invention is to use a polyolefln for the pigment carrier which is substantially free of stearates and stearic acid. in accordance with a preferred embodiment, the polyolefln used is polyethylene which is completely free of stearates and stearic acid. The pigment is present at between about 1 and about 70 weight percent of the total pigment system and this pigment system is added at a level of between about 0.001 and about 4 percent by weight of the colored fibers. Also, the preferred polymers to be colored are nylon 6 and nylon 6,6.

One advantage of the present invention is that it provides a pigment system which is less expensive to make and to handle. In particular, the polyolefin-based pigment system does not require the special handling of a nylon-based pigment system.

Another advantage found in the preferred aspect of the invention is that polyolefin-based pigment systems which are free of stearates and stearic acid possess superb compatibility during extrusion of nylon fibers and during post-extrusion processing as well.

It should be noted that, as used herein, the term "fiber" is intended to have a relatively broad meaning including long filaments and short fibers. Unless otherwise indicated, all percentages reported herein are in terms of weight percent. The present invention, together with attendant objects and advantages, will be best understood with reference to the detailed description below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The fibers colored by the present invention can be made from various polymers including, but not limited to polyamides (nylon 6 and nylon 6,6), polyesters (PET), poly(trimethylenetheraphthalate) (PTT). Preferably, the polymers are polyamides, most preferably either nylon 6 or nylon 6,6. A suitable nylon is sold by BASF under the designation BS 700.

As noted above, the pigment system of the present invention includes a polyolefln as its base polymer. While polypropylene can be used, polyethylene is presently preferred. Suitable polyethylenes include, without limitation, linear low density polyethylene (LLDPE), substantially linear polyethylene, homogeneously branched linear polyethylene, medium density polyethylene and high density polyethylene. Currently, linear low density polyethylene is preferred because of its low cost and relative ease in handling. The most preferred linear low density polyethylene is that sold by DOW under the designation XU 81600.34. Most commercially available polyolefins include a small amount of stearates which are added by the polyolefln manufacturers as acid scavengers. Preferably, the polyolefins used in the present invention will be substantially free of any stearates or stearic acid, i.e. contains less than about 1 percent by weight. More preferably, the polyolefln contains less than about 0.1 percent, most preferably less than about 0.01 percent. It has been found that the presence of more than these trace amounts of stearates or stearic acid can cause incompatibility. For example, the stearates and stearic acid have been found to interfere with the texturing operation in making bulk continuous filament (BCF) yarn for carpet. Another property of the polyolefin base which can be specified is the average molecular weight. Preferably, the polyethylene used will have an average molecular weight between about 45,000 and about 65,000.

Another property of the polyolefin, which can be related to the molecular weight is the melt index. It is preferred to select a polyolefin with a melt index that is close to that of the polymer to be colored. For example, when coloring nylon fiber, it is preferred to have a melt index of between about 8 and 28 at 190°C. The most preferred linear low density polyethylene mentioned above has a melt index of about 18 at 190°C. The pigment used in the present invention can be one of any number of commercially available pigments. Those particularly suitable include the following designated by their Color Index (Cl) number: Pigment Yellow (PY) include PY 83 and PY 119. Pigment Red (PR) include PR 149 and PR 101. Pigment Blue (PB) include PB 15:1 and PB 15:3. Naturally, the ability to disperse within the carrier polymer and the polymer to be colored is a desirable property for the pigment. Also, the pigment should be stable in the temperature range in which the polymers are extruded. Finally, the pigment should have satisfactory lightfastness.

The level of pigment in the system can vary depending on the particular pigment or polyolefin used. It can also vary depending on the ultimate level of pigment desired for the fiber. Generally, the level of pigment will vary between about 1 and about 70 percent by weight of the system. It is preferred to have a relatively high level of pigment in the system.

Naturally, the level of pigment included in the pigment system is effected by the level of pigment system that will be added to the nylon to be colored. Preferably, the level of pigment system added to the nylon is less than about 5 percent, more preferably between about 0.001 and about 4 percent, most preferably about 3 percent.

An optional, but preferred, ingredient of the pigment system is a polyolefin/polyamide compatibilizer. This term is used to refer to compounds which enhance the miscibility of polyolefins within nylon. Suitable examples of such compatibilizers include, without limitation, maleic anhydride. Currently, maleic anhydride is most preferred. The amount of maleic anhydride is preferably between about 0.01 and about 10 percent by weight of the pigment system, more preferably between about 0.1 and about 10 percent, most preferably between about 0.1 and about 0.5 percent.

Other ingredients can be added depending on the desired properties. For example, process stablizers, such as Irgafos from Ciba Geigy, are preferably added. In addition, particularly if the carpet is for outdoor use, UV stabilizers, such as Chimasorb 944 (a hindered amine light stabilizer) from Ciba Geigy, and UV absorbers, such as Tinuvin 234 from Ciba Geigy, are also preferably added.

Various methods can be used to combine the ingredients of the pigment system. Preferably, the ingredients are dry mixed and then extruded into pellets by conventional means. The pigment system can be added to the polymer to be extruded in various ways, such as those currently used for making solution dyed fibers. Preferably, the pigment system is added to the polymer by dosing into the hopper for the extruder and mixing as is done with conventional pigment systems. Alternatively, the system can be added in molten form through a small extruder feeding into the nylon extruder.

The nylon extrusion process can be carried out on conventional equipment with conventional parameters. Most preferably, the extrusion equipment is a Neumag extruder. Most preferably, the equipment is set up with a temperature in the extrusion zone of between about 200 to 300°C. The winder is also set so as to run at between about 400 and 1500 meters/minute.

Preferably, the extruded fiber is made into BCF yarn for carpet. The BCF process is preferably carried out on conventional equipment with conventional settings. Most preferably, the BCF equipment is made by Neumag with the godets set from 300 to 3000 meters/minute with godet temperature from 50 to 220 °C, the texturizer temperature between about 100 and 300 °C, and draw ratios of from 0.5 to 6. EXAMPLES

The following examples are provided by way of illustration and explanation and as such are not to be viewed as limiting the scope of the present invention.

EXAMPLE 1

A pigment system was obtained by adding 1 part of red, yellow, black and white pigments together. One part of maleic anhydride compatabilizer was added along with 5 parts LLDPE. These ingredients were mechanically mixed and then melt extruded through a lab extruder. This color concentrate was then added to nylon pellets at 3 percent addition rate. Fifty pounds of fiber was extruded and then draw textured into BCF yarn with the equipment described above. The yarn so made was observed to have excellent color uniformity with no negative effects on the process or equipment.

EXAMPLE 2

Example 2 was performed the same as Example 1 with the exception that the color concentrate had the following composition: Two parts red, 2 parts yellow, 2 parts black, 2 parts white, 1 part compatabilizer, and 3 parts LLDPE. The color concentrate was added to nylon at the same rate and the yarn produced was likewise observed to have excellent color uniformity with no negative effects on the process or equipment.

EXAMPLE 3

Example 3 was performed the same as Example 1 with the exception that the color concentrate had the following composition: one part red, 1 part yellow, 1 part black, 1 parts white, 2 parts compatabilizer, and 14 parts LLDPE. The color concentrate was added to nylon at the same rate and the yarn produced was likewise observed to have excellent color uniformity with no negative effects on the process or equipment.

Claims

I CLAIM:

1. A pigment system for coloring polyamide fibers comprising: a polyolefin polymer base; and between about 1 and about 70 weight percent pigment.

2. The system of claim 1 wherein the polyolefin is substantially free of stearates and stearic acid.

3. The system of claim 1 wherein the polyolefin is polyethylene.

4. The system of claim 3 wherein the polyethylene is substantially free of stearates and stearic acid.

5. The system of claim 3 wherein the polyethylene is selected from the group consisting of linear low density polyethylene, substantially linear polyethylene, homogeneously branched linear polyethylene, medium density polyethylene and high density polyethylene.

6. The system of claim 3 wherein the polyethylene is linear low density polyethylene.

7. The system of claim 6 wherein the polyethylene has an average molecular weight between about 45,000 and about 65,000.

8. The system of claim 1 wherein the pigment is present in an amount between about 1 and about 70 weight percent.

9. The system of claim 1 further comprising between about 0.1 and about 10 weight percent of a polyolefin/polyamide compatibilizer.

10. The system of claim 9 wherein the compatibilizer is maleic anhydride.

11. A colored polyamide fiber comprising: > a polyamide; and between about 0.001 and about 4 weight percent pigment system dispersed in said fiber, said system comprising a polyolefin polymer base and pigment present at between about 1 and about 70 percent by weight of the pigment system.

12. The fiber of claim 11 wherein the polyamide is nylon 6 or nylon

6,6.

13. The fiber of claim 11 the polyolefin is substantially free of stearates and stearic acid.

14. The fiber of claim 11 wherein the polyolefin is polyethylene.

15. The fiber of claim 14 wherein the polyethylene is substantially free of stearates and stearic acid.

16. The fiber of claim 15 wherein the polyethylene is selected from the group consisting of linear low density polyethylene, substantially linear polyethylene, homogeneously branched linear polyethylene, medium density polyethylene and high density polyethylene.

17. The fiber of claim 14 wherein the polyethylene is linear low density polyethylene.

18. The fiber of claim 17wherein the polyethylene has an average molecular weight between about 45,000 and about 65,000.

19. The fiber of claim 11 further comprising between about 0.1 and about 10 weight percent of a polyolefin/polyamide compatibilizer.

20. The fiber of claim 19 wherein the compatibilizer is maleic anhydride.

18. The fiber of claim 11 incorporated into a bulked continuous filament yarn.

19. A method of coloring polyamide fiber comprising the steps of: combining a polyamide and a pigment system, the pigment system comprising a polyolefin and pigment, and extruding the polyamide with the pigment system into fibers.

20. The method of claim 22 wherein the polyamide is nylon 6 or nylon 6,6.

21. The method of claim 22 wherein the polyolefin is substantially free of stearates and stearic acid.

22. The method of claim 22 wherein the polyolefin is polyethylene.

23. The method of claim 25 wherein the polyethylene is substantially free of stearates and stearic acid.

24. The method of claim 25 wherein the polyethylene is selected from the group consisting of linear low density polyethylene, substantially linear polyethylene, homogeneously branched linear polyethylene, medium density polyethylene and high density polyethylene.

25. The method of claim 25 wherein the polyethylene is linear low density polyethylene.

26. The method of claim 28 wherein the polyethylene has an average molecular weight between about 45,000 and about 65,000.

27. The method of claim 22 further comprising between about .1 and about 10 weight percent of a polyolefin/polyamide compatibilizer.

28. The method of claim 30 wherein the compatibilizer is maleic anhydride.

29. The method of claim 22 wherein the extruded fiber is treated to make bulked continuous filament yarn.