US3642971A - Heat stabilization of polyamide fibers bristles and foils - Google Patents

Abstract

A PROCESS FOR THE HEAT STABILIZATION OF POLYAMIDE FIBERS, BRISTLES AND FOILS WITH COPPER COMPOUND, AREOMATIC AMINES, AND ALKALI, HALIDES. THE COPPER COMPOUND AND AMINES ARE INCORPORAED IN THE STARTING MATERIALS PRIOR TO THE POLYMERIZATION. THE ALKALI HALIDES AND ANY OTHER COMPONENTS OF THE STABILIZER ARE ADDED ONLY UPON THE FORMATION OF FIBERS, BRISTLES OR FOILS, PRIOR TO STRETCHING.

Description

United States Patent US. Cl. 264-136 6 Claims ABSTRACT OF THE DISCLOSURE A process for the heat stabilization of polyamide fibers, bristles and foils with copper compounds, aromatic amines, and alkali halides. The copper compounds and amines are incorporated in the starting materials prior to the polymerization. The alkali halides and any other components of the stabilizer are added only upon the formation of fibers, bristles or foils, prior to stretching.

This application is a continuation-in-part of copending application Ser. No. 666,931, filed Sept. 11, 1967, now abandoned.

The invention relates to the improvement of the heat stability characteristics of polyamides.

Linear polyamides produced, e.g., by polycondensation of epsilon-aminocarboxylic acids, caprolactam (nylon-6), or of hexamethylene diamine and adipic acid (nylon-66), have unsatisfactory resistance to atmospheric oxygen at elevated temperatures.

Attempts have been made to increase heat stability by adding compounds such as lactams or diamine-dicarboxylic acid salts to the polymers or to the starting products. Copper salts of inorganic or organic acids, combined with inorganic or organic halogen compounds, particularly idoine compounds, have been found to be effective. Other additives which may be employed include for example phosphorus compounds, thioglycolic acid, chromium compounds, and certain aromatic amines, such as di-beta-naphthyl-p-phenylenediamine, N-phenylbeta naphthylamine, or N acyl p aminophenol, and especially mercaptobenzimidazole.

Difiiculties are encountered in the practical application of all of these combinations. Extraction of the lower molecular weight constituents from the finished polymer is generally required. Addition of iodine and copper compounds to the starting products which form the polyamides disadvantageously results in the major portion of the added compounds, especially the iodine compounds, being removed during the extraction.

A mixture of, e.g., a copper compound with alkali iodides in the required concentration can be dusted on the extracted chip prior to spinning. While good heat stability thus is attained, the distribution of the stabilizers in the polyamides is not uniform. This leads to a considerable decrease in their strength characteristics, particularly when fibers, bristles and foils are produced. The reason for this drawback is that the stabilize components cannot be applied uniformly even when dusted. This is especially true in the presence of inorganic halogen compounds. Moreover, insoluble precipitates form in the melt, upon addition of the stabilizers to the polyamide forming starting products. Upon spinning, using either method of stabilizer addition, the stabilizer components precipitate at the outer edge of the spinning nozzles. Thus frequent changing of the spinning nozzles is required. Finally, a further disdvantage of dusting poly- 3,642,971 Patented Feb. 15, 1972 amide formers with organic compounds in that very high thermal stability of these organic compounds is required. Therefore, a number of effective organic compounds, cannot be used due to their thermal instability.

It is the obect of the invention to devise a method of stabilizing polyamide fibers, bristles and foils with the compound named, while doing away with the drawbacks mentioned. This is accomplished by adding a first group of stabilizer components directly to the starting materials from which the polyamides are produced. These first components are copper compounds and organic nitrogen compounds, such as organic amines. The second component group, consisting of alkali halides and any other material known for the purpose, is incorporated only upon shaping of the polyamides into fibers, bristles or foils, but prior to their stretching. These second components are applied to the surfaces of the polyamides in the form of solutions or suspensions.

In one embodiment, the second components are added to the spinning preparations of the fibers or the like. This permits the stabilizers to penetrate into the interior of the freshly spun fiber since the spinning preparation is applied to the dry and absorptive amorphous filament. This can be accomplished, e.g., by leading the filament through two rollers. It also is feasible to add the second component with other additives, such as light stabilizers, optical bleaches, and the like. This latter procedure has the added advantage that no special operational step is required and hence saves expenses.

The process according to the invention, as compared with processes wherein application occurs after stretching, also effects a wash-resistant fixing of the second component on the fiber because the stretching operation following spinning leads to a compaction and orientation of the fiber structure whereby, due to the occurring crystallization, the initially porous structure is closed and the accessibility of solubilizing agent to the inner regions of the fibers is substantially decreased after stretching.

A desirable effect of the separate addition of copper compounds such as potassium iodide to the starting materials and, is that the precipitation of copper-I-iodide, which occurs upon simultaneous addition is prevented. Precipitation of the copper compounds precipitation destroys the particularly effective stabilizing capacity of the copper salt and potassium iodide.

When the ingredients of the second components of the stabilizer combination are of mutually poor compatibility, i.e., when the different compounds together yield insoluble precipitates or when the storage life of the solution or emulsion is insufiicient, the two incompatible ingredients can be applied using two different sets of rollers.

In a further embodiment, the second components of the stabilizer combination are applied as an aqueous solution or in an organic solvent, to the spinning fiber on the first roller set. If desired, additional second component may be applied by means of a second roller set. This enables an application in several layers, and incompatible ingredients which, however, are soluble in water or organic solvents, can be applied.

Conversely, it is possible to apply the stabilizer component solely on the surface of the fiber by using the first roller set for the spinning preparation alone with the second roller set applying the stabilizer. In this manner, the stabilizer acts only on the surface of the fiber where damage caused by oxidation is the greatest. If undesirable side effects of the stabilizer occur, due to catalytic chain disintegration, these side effects will be limited to the fiber surface.

The invention now will be more fully explained by the following examples. However, it should be understood that these are given merely for the purpose of illustrating the invention and not for the purpose of limiting same.

Further, it is intended to cover all modifications and variations which do not constitute a departure from the spirit and scope of the invention as hereinafter claimed.

Percentages named in the examples are by weight, where applicable. Temperatures are in degrees centigrade.

The stabilizing effect of the combinations in the examples was determined by subjecting the stretched fibers to the action of hot air at 160 for 48 hours in a circulating air oven. The stabilizing effect was determined by ascertaining the percent decrease in specific viscosity of a 1% polyamide solution of 96% sulfuric acid. Aging tests, showing the percent decrease in tensile strength of the fibers, being proportional to the lowering of the viscosity, were not carried out.

The examples are equally valid for fibers, foils and bristles manufactured as described.

EXAMPLE 1 0.03% copper-II-acetate. H and 0.13% mercaptobenzimidazole were added to epsilonaminocaprolactam in a polymerization vessel. Chips manufactured by the polymerization were freed from oligomers by extraction with water, melted in a melt extruder at 270 and spun through a 34-hole nozzle to fibers of a total titer of 585 denier.

As a second stabilizer component, 80 g./l. aqueous KI solution were applied to the spinning preparation by conducting it through two rollers. The amount of potassium iodide corresponded to an iodine content of 0.1, calculated on the weight of the fibers. The yarn thus obtained was then stretched in proportions of 1:3.505 over a heated stretcher.

The decrease in specific viscosity, measured as described above, was

Polyamide chips, produced from episilonaminocaprolactam having a solution viscosity of 1.94 (0.5% solution in m-cresol) were powdered with a mixture of 0.03% copper-I-chloride and 0.13% mercaptobenzimidazole, calculated on the weight of the chips. The mixture had been ground to a fine dust. Spinning and stretching were carried out as in Example 1, but without addition of KI to the spinning preparation. The specific viscosity drop was 6%.

We claim as our invention:

1. In a process for heat stabilizing a polyamide fiber, bristle or foil, produced by polymerizing, starting materials selected from the group consisting of epsilonamino carboxylic acid and caprolactam, and hexamethylene diamine and adipic acid to produce a polyamide then spinning and stretching same, said heat stabilizing being accomplished by adding to said polyamide a compound selected from the group consisting of heat stabilizing copper salts, organic aromatic amines and mixtures thereof, and a heat stabilizing alkali halide, the improvement which comprises incorporating said compound with the starting materials prior to their polymerization and applying said alkali halide to the surface of said produced polyamide upon the spinning of same into a fiber, bristle or foil and prior to the stretching.

2. A process as defined in claim 1 wherein said alkali halide is potassium iodide and the amount of said potassium iodide applied to the surface of the produced polyamide corresponds to an iodine content of 0.010.5% calculated on the weight of the fiber, bristle or foil.

3. A process as defined in claim 2 wherein said potassium iodide is applied in the form of an aqueous solution or suspension.

4. A process as defined in claim 1 wherein said compound is a mixture of a copper salt and mercaptobenzimidazole and said alkali halide is potassium iodide, said copper salt being present in an amount of substantially 0.010.1% by weight calculated on the materials to be polymerized, said mercaptobenzimidazole being present in an amount of substantially 0.01-0.13 weight percent and said potassium iodide is present in an amount which corresponds to an iodine content of 001-05 weight percent calculated on the weight of the fiber, bristle or foil.

5. The process as defined in claim 1 wherein said copper salt is copper-III-acetate.

6. The process as defined in claim 1 wherein said copper salt is copper-I-chloride.

References Cited UNITED STATES PATENTS 2,630,421 3/1953 Stamafott 260-458 2,705,227 3/1955 Stamafott 260-45.7 2,945,010 7/1960 Caldwell et al 260- 3,275,594 9/1966 Bond 264-211 3,282,892 11/1966 Griehl 260-4575 3,308,091 3/1967 Zapp 260-785 C 3,318,827 5/1967 Whittker 260-18 3,459,702 8/1969 Tazewell 260-785 C JAY H. WOO, Primary Examiner US. Cl. X.R.

117-7, 138.8 N; 260-457 R, 45.75 C, 45.9 R, 45.8 N, 78; 264-210 F, 211