US3260697A - Polyamide compositions containing a phenol, a phosphate, a manganese salt, and an acid anhydride as stabilisers - Google Patents

Description

of manufacture, as,

United States Patent corporate Filed Nov. 21, 1962, Ser. No.

No Drawing. Claims priority, application Great Britain, Nov.

Claims. (Cl. 260-4555) This invention relates to synthetic polyamide compositions, to processes for their production and to shaped articles, including textile fibres, made from such compositions.

Polyamides, such as polyhexamethylene adipamide and polycaprolactam, are widely used for many purposes because of their remarkable mechanical strength. Their main field of application is the production of synthetic fibres, but they also find increasing use in other branches for example, in the production of tools and machine parts. The excellent properties of these polyamides are, however, considerably impaired by their tendency to become yellow under various conditions in the presence of oxygen. The yellowing occurs, for example, when polyarnides are subjected to elevated temperatures, when they are repeatedly washed with hot water, and when they are exposed to light and then kept for some time in the dark.

, This sensitiveness of polyamides is especially inconvenent for the textile industry, where it is desired to obtain fibres and (fabrics of a pure white or of coloured shades unimpaired by any yellowish tinge. It is, therefore, very disturbing that discolouration occurs during some stages of manufacture, e.g. when the molten polyamide is discharged from an autoclave, in melt-spinning, and above all, in the dry heat-setting of spun filaments and of knitted or woven fabrics. The troublesome yellowing which appears during these processes may be partially removed by a bleaching treatment, eg with sodium chlorite, but such treatment requires an additional working step and may also be harmful to the fibre or fabric. It is, however, known that bleaching with sodium chlorite, while removing the colour present for the time being, considerably increases the tendency of the fibre to future discolouration.

Substances such as phenols and amines, which are antioxidants, have been proposed as stabilizers as it is generally assumed that oxidation is a primary cause of the discolouration of poly am-ides. Other substances described as stabilizers include manganese salts and phosphorus compounds, and it has also been proposed to use combinations of two or more stabilizing substances. Thus, United States Patent No. 2,887,462 describes the use of salts of manganese with certain reducing acids, and United States Patent No. 2,984,647 mentions manganese phosphates. British Patent No. 689,629 proposes manganese or copper salts of salicylic or anth-ranilic acid, and French Patent No. 1,099,407 suggests a combination of manganese and copper salts. All these combinations are described as being efiective against damage by light. As stabilizing agents for polyamides against heat, British Patent No. 652,947 proposes copper salts of mono-carboxylic acids together with diketones, United States Patent No. 2,705,227 describes a combination of copper, inorganic near Lucerne, Switzer- Suisse, Emmena Swiss body 3,260,697 Patented July 12, 1966 ice halogen salts, and phosphorus compounds, and German Auslegeschrift No. 1,111,376 mentions a mixture of cerium (III) and/ or titanium (Ill) salts and hypophosphoric acids. This German specification also points out that the addition of aliphatic oarboxylic acids does not stabilize p-olyarnides against the effects of light or heat. None of the above-mentioned combinations of stabilizers have, however, yet led to any final and completely satisfactory solution of the problem of yellowing caused by heat and light.

The present invention provides synthetic polyamide compositions, especially suitable for making textile fibres, which are substantially free from colour and possess a substantial stability against discolouration caused by heat and light. The expression free from colour is used herein to mean absence of any undesired colouration of the polyamide, but doesnot exclude colour intentionally produced by the addition of dyes or pigments.

The synthetic polyamide compositions of the invention comprise a composite stabilizing agent consisting essentially of (l) a thermally stable phenol, (2) a salt or ester of an inorganic phosphorus oxy-acid, (3) a manganese salt, and (4) an organic carboxylic acid anhydride. It will, of course, be understood that all the components of the stabilizing agent must be such that they will not themselves give rise to any colour when incorporated in the poly-amide, either because they are coloured per se or because they give rise to coloured substances on irradiation or heating to the temperatures used during manufacture or processing of polyamides. Thus, phthalic anhydride, which is unstable to light, cannot be used as component (4). The components of the stabilizing agent must comply with the stated limitations. Thus, for example, simple phenols cannot be used as they are oxidized too quickly, but thermally stabilized phenols containing, e.g. one or more tertiary butyl groups such as 2,5-di-tert-butyl hydroquinone, 2,2 methyl-bis-(4-methyl-G-tert-butylQphenol), 2,2-methylene-bis-(4-ethyl-6-tert butyl-phenol), or 4,4ibutylidene bis(6-tert butyl-m-cresol) have been found to be very suitable. As the second component, sodium hypophoshite and triphenyl phosphate, which are both relaible, are preferred. For the manganese salt, manganous lactate, manganous oxalate and manganous hypophosphite are very suitable. As the acid anhydride component, benzoic acid anhydride and hexa-hydro-phthalic acid anhydride are very satisfactory. A further advantage of the invention is that these acid anhydrides, in addition to acting as stabilizers, act also as chain terminators for the polycondensation process for making the polyamides. They can, therefore, replace the acetic acid which is usually employed for this purpose. The conventional type of chain terminating mono-oarboxylic acid cannot (as shown in the Example 11 below) be used to replace component (4) in the stabilizing agent of the invention.

The relative quantities of the various components of the stabilizing agent used for optimum results will differ with the specific nature of the components. However, combinations giving especially good protection contain between 0.02 and 0.2% of 2,5-di-tert butyl-hydro-quinone, 2,2 methylene-bis-(4 methyl-6-tert-butyl-phenol), 2,2- methylene-bis-(4-ethyl-6-tertbutylphenol) or 4,4'4butylidene bis-(6-tert-butyl-m-cresol), between 0.05 and 0.5% of sodium hypophosp'hite or triphenyl phosphate, between 20 and parts of manganese per million parts of polyamide in the form of m-ang-aneous lactate, manganous oxalate, or man-ganous hylpophosph-ite, and between 0.2 and acteristic of this that afforded by any of the components taken alone. As shown in Example II, combinations containing only three of the not give the same satisfactory results.

The stabilizers have the further advantage that they work well in the presence of titanium dioxide, which is usually incorporated in polyamides as a delustering pigment and which is known to increase considerably their sensitivity to light. Dyeing and addition of optical brightening agents do not impair the effects of the stabilizer combination of this turbed by its presence in the polyamide.

The excellent protection afforded by the new four-component stabilizer against heat is especially important in the textile industry, because polyamides are necessarily heated at several stages in the manufacture of textile fibres. Although poly-condensation is carried out in a nitrogen atmosphere, traces of oxygen are still present, and, in any case, oxidation is possible when the molten mass is discharged from an autoclave or extruded from a spinneret. Unprotected polyamide chips and fi'bres have, therefore, a distinct ivory colour, while compositions containing the four-component stabilizing agent of the present delustered. Further discolouration polyamides usually occurs in the dry heat-setting process, and this operation causes considerable yellowing of unprotected fibres and makes an additional bleaching treatment necessary. It is, of great value that polyamide fibres and fabrics produced in accordance with the present invention do not need bleaching, that they possess and keep a bright, pure white, and that when dyed, they preserve a clear and distinct colour shade foils, tools, and many other goods.

The four components of the stabilizing agent are incorporated in the polyamides during tion process of manufacture of the polyamides, and the stabilizers.

The reasons for the discolouration of polyamides have not yet been finally ascertained, but the surprisingly good protection afforded by the use of radicals formed from traces of impurities under the influence of heat or light. These radicals are oxidized in the presence of air to peroxides which, in turn, trigger the formation of polyamide peroxides. The decomposition of the polyamide peroxides then leads to unsaturated compounds which react with free amine end groups with the formation of heterocyclic substances, e.g. pyrroles. The pyrroles finally react by condensation with keto-enol groups in the polyamide, thus producing the actual yellow-coloured materials.

Such a view of the reaction mechanism is substantiated by various observations. When a polyamide is heated for some time in an oxygen-containing atmosphere it shows an increasing oxygen absorption, a fairly constant peroxide concentration, a decrease of the number of amine end groups and a corresponding increase of the pyrrole concentration, as can be seen from the following table:

HEATING OF POLYHEXAMETHYLENE ADIPAMIDE 150 C. IN AIR Oxygent Peroxide Ooncentra- Pyrrole eon- Time (Hours) absorption concentration of amine tents Specific (g./kg.) tion end groups absorption (mg/kg.) (mMol/kg.) at 530 my 1 1 Determined in a 0.4%

polyamide solution in 90% formic acid dyed with 1% dimethyl-amino-benzaldehyde.

ployed as a component of the stabilizer, is added as chain terminator.

The polyhexamethylene adipamide compositions are prepared as follows: A 50% aqueous solution of hexamethylene diamine adipate is evaporated until a concentration of 75 to is achieved and is then heated in stabilizers, of any optical brightening agents can take place at various stages during manufacture. In Examples I to III the phenolic compound, the phosphorus compound, and the manganese salt are mixed with the 50% solution of hexamethylene diamine adipate. The titanium dioxide, in the form of a 20% aqueous dispersion, and, if desired,

In Examples V and the 50% hexamet after the Water has been evaporated.

The polycaprolactam composition is made by warming caprolactam to C., mixing it with 1% of water and heating it in an autoclave for 2 hours at 250 C. Then dioxide or optical brightening agents can take place at In Example IV the manganese salt are added to the caprolactam together with the 1% of water, and the carboxylic acid anhydride,

dissolved in a little ethanol, is added when the pressure has been released.

From the polyamide compositions obtained, fibres are melt-spun in the usual manner, and compared with containing no stabilizer ferent combinations of only three of the four stabilizers used in the present invention. The relative viscosity is determined at 25 C. on an 11% solution of the polyamide composition in 90% formic acid. The heating test is carried out with a Thermotest Rhodiaceta developed by Rhodiaceta S.A., Paris, and made by Societe pour la Difiusion dAppareils de Mesure et de Controle, S.A., Tassin-la-Demi-Lune, Rhone, France. In this test small hanks of yarn are brought into contact during 60 seconds with heated metal plates having a temperature between 210 and 240 C., after which the colour of the yarn is judged visually.

When carrying out the irradiation test, fibres not containing an optical brightening agent are used, because these agents are decomposed by light and may become yellow themselves. The fibres are exposed to sunlight of an intensity equal to rating 7 of the blue standard, according to test 95810 of the Swiss Standards Institution (SNV), and subsequently kept in the dark for three months, after which the colours of the light-exposed and the unexposed fibres are compared.

All percentages of quantities of materials mentioned in the following examples are by weight of the total weight of the polyamide composition.

Example I A polyamide composition is made from kg. of hexamethylene diamine adipate containing 47.3 g. (=l.l%) of titanium dioxide and, as stabilizers, 2.15 g. 0.05%) of 2,5-di-tert-butyl-hydroquinone, 4.3 g. 0.1%) of sodium hypophosphite, 0.645 g. (=0.015%) of manganous lactate, equal to 30 parts of manganese per million parts of polyamide, and 23.65 g. (=0.55%) of benzoic acid anhydride. The polyamide chips obtained are pure white.

Polyamide chips made for comparison in the same manner containing 1.1% of titanium dioxide and 0.17% of acetic acid as chain terminator, but no stabilizing agents, have a distinct ivory colour.

Example II Fibres are melt-spun from a polyamide composition made from 5 kg. of hexamethylene diamine adipate containing 47.3' g. (=1.1%) of titanium dioxide, 4.3 g. (=0.1%) of an optical brightening agent Uvitex MP made by Ciba A.G., Basel, Switzerland, a stilbene derivative, and, as stabilizers, 2.15 g. 0.05%) of 2,5-di-tertbutyl-hydroquinone, 4.3 g. (=0.1%) of sodium hypophosphite, 0.645 g. (=0.015%) of manganous lactate, equal to 30 parts of manganese per million parts of polyamide, and 23.65 g. (=0.55%) of benzoic acid anhydride. The relative viscosity of the fibres is 31.5, their tensile strength 5.9 g./denier, and their elongation at break 27.6%. No difference could be detected in the colour of the fibres before and after heating to 225 C.; in both cases the fibres are pure White.

Fibres made in the same manner, but without the addition of an optical brightening agent, are subjected to the irradiation test. Bothv the light-exposed and the unexposed fibres show the same whiteness.

Fibres made for comparison in the same manner containing titanium dioxide and 0.17 of acetic acid as chain terminator, but no stabilizing agents, have a relative viscosity of 32.2, a tensile strength of 5 g./denier, and an elongation at break of 27.1%. While the colour of the fibres is originally ivory-white, it becomes strongly yellow when the fibres are heated to 225 C. or when they are subjected to the irradiation test.

Fibres are made for comparison in the same manner containing 1.1% of titanium dioxide and only three stabilizers, i.e.:

(a) 0.1% of sodium hypophosphite, 0.015% of manganous lactate, equal to 30 parts of manganese per million parts of polyamide, and 0.55% of benzoic acid anhydride, or

(b) 0.05% of 2,5-di-tert-butyl-hydroquinone, 0.015% of manganous lactate, equal to 30 parts of manganese per million parts of polyamide, and 0.55 of benzoic acid anhydride, or

(c) 0.05% of 2,5-di-tert-butyl-hydroquinone, 0.1% of sodium hypophosphite, and 0.55 of benzoic acid anhydride, or

(d) 0.05% of 2,5-di-tert=butyl-hydroquinone, 0.1% of sodium hypophosphite, and 0.015% of manganous lactate, equal to 30 parts of manganese per million parts of polyamide (adding 0.17% of acetic acid as chain terminator) While the colour of all four kinds of fibres is originally ivory white, it becomes more or less distinctly yellow when the fibres are heated to 220 C. or when they are subjected to the irradiation test.

Example Ill Fibres are melt-spun from a polyamide composition made from 5 kg. of hexamethylene diamine adipate containing 1.1% of titanium dioxide, 0.1% of Uvitex MP, and, as stabilizers, 0.05% of 2,5-di-tert-butyl-hydroquinone, 0.25% of triphenyl phosphate, 0.01% of manganous oxalate, equal to 38 parts of manganese per million parts of polyamide, and 0.55 of hexahydrophthalic acid anhydride. The relative viscosity of the fibres is 34.5, their tensile strength 6.2 g./denier, and their elongation at break 24.1%. The colour of the fibres both before and after heating to 225 C. is a pure white.

Example 1V Fibres are melt-spun from a polyamide composition made from 5 kg. of cap -rolactam containing as stabilizers 0.05% of 2,5-di-tert-butyl-hydroquinone, 0.1% of sodium hypophosphite, 0.01% of manganous oxalate, equal to 38 parts of manganese per million parts of polyamide, and 0.225% of benzoic acid anhydride. The relative. viscosity of the fibres is 28.5, their tensile strength 5.0 g./ denier, 'and their elongation at break 15.3%. The colour of the fibres both before and after heating to 210 C. or when subjected to the irradiation test is a pure white.

Fibres made for comparison in the same manner containing 0.17 of acetic acid as chain terminator and no stabilizing agents are originally white, but become strongly yellow when heated to 210 C.

Example V Fibres are melt-spun from a polyamide composition made from 1000 kg. of hexamethylene diamine adipate containing 1.9% of titanium dioxide and, as stabilizers, 0.05% of 2,2-methylene bis-(4-methyl-6-tert-butyl-phenol), 0.3% of triphenyl phosphate, 0.01% of manganous oxalate, equal to 38 parts of manganese per million pants of polyamide, and 0.4% of benzoic acid anhydride. The relative viscosity of the fibres is 36.6, their tensile strength 5.8 g./denier, and their elongation at break 31.1%. The colour of the fibres both before and after heating to 225 C. is a pure white. When the fibres are subjected to the irradiation test, both the light-exposed and the unexposed fibres show .the same whiteness.

Example VI Fibres are melt-spun from a polyamide composition made from 1000 kg. of hexamethylene diamine adipate containing 1.9% of titanium dioxide and, as stabilizers, 0.05% of 4,4 bu tylidene bis-(6-tert-butyl-m-cresol), 0.3% of triphenyl phosphate, 0.01% of manganous oxalate, equal to 38 pants of manganese per million pants of polyamide, and 0.4% of benzoic acid anhydride. The relative viscosity of the fibres is 34.5, their tensile strength 7.2 g./denier, and their elongation at break 16.6%. The colour of the fibres both before and after heating to 225 C. or when subjected to the irradiation test is a pure white.

I claim:

1. Synthetic polyamide compositions which are substantially free from colour and of good stability against discoloration by heart and light, in which have been inpolycontden's-ation (1) between 0.02 and 0.2% of a thermally stable phenol containing at least one tertiary-butyl group selected from the class consisting of 2,S-di-tert-butyl-hydroquinone, 2,2-methylene-bis-(4-methyl-6-tert-butyl-phenol), 2,2 methylenebis-(4-ethyl-6- tert-butyl-phenol), and 4,4'-butylidene bis- (6-tert-butyl-m-cresol), (2) between 0.05 and 0.5% of a compound selected from the class which consists of salts and esters of inorganic phosphorus oxy-acids, (3) between 20 and 80 parts of manganese per million parts of said polyamide composition in the form of a compound selected from the class consisting of manganous lactate, manganous oxalate and manganous hypophosphite, and 1% of a mononuclear cyclic organic acid anhydride selected from the group which consists of the anhydrides of benzoic acid and hexahydrophthalic acid, the proportions being based on the total weight of the composition.

2. Synthetic polyamide textile fibres which are substantially firee from colour and of good stability against discoloration by heat and light, in which have been incorporated during polycondensation 1) between 0.02 and 0.2% of a thermally stable phenol containing at lea-st one tentiary-bu'tyl group selected from the class consisting of 2,S-di-tert-butyl-hydroquinone, 2,2-methylene-bis-(4-methyl-6-tert-bu.tyl-phenol), 2,2 methylenebis-(4ethyl-6- tert-butyl-phenol), and 4,4-butylidene bis- (6-tert-butyl-m-cresol), (2) between 0.05 and 0.5% of a compound selected from the class which consists of salts and estens of inorganic phosphorus oxy-acids, 3) between 20 and pants of manganese per million parts of consists and hexahydrophthalic on the total weight of References Cited by the Examiner UNITED STATES PATENTS 2,510,777 6/1950 Gray 260*78 2,705,227 3/1955 Stamatofi 260-4575 2,849,446 8/1956 Sullivan 45.95 2,966,476 12/1960 Kralove et al. 26045.95 3,117,948 1/1964 Notarbatolo et al. 260-45.75

FOREIGN PATENTS 495,790 11/1938 Great Britain. 955,259 6/ 1949' France. 1,052,679 3/1959 Germany. 1,220,968 11/1960 France.

OTHER REFERENCES Perry, N. L., Stabilizers, 1963 Modern Plastics Encyclopedia, Vol. 40, No. 1A, September 1962, pp. 502 505, p. 502 relied upon.

LEON J. BERCOVITZ, Primary Examiner. G. W. RAUCHF USS, Assistant Examiner.

Claims (1)

1. SYNTHETIC POLYAMIDE COMPOSITIONS WHICH ARE SUBSTANTIALLY FREE FROM COLOUR AND OF GOOD STABILITY AGAINST DISCOLORATION BY HEAT AND LIGHT, IN WHICH HAVE BEEN INCORPORATED DURING POLYCONDENSATION (1) BETWEEN 0.02 AND 0.2% OF A THERMALLY STABLE PHENOL CONTAINING AT LEAST ONE TERTIARY-BUTYL GROUP SELECTED FROM THE CLASS CONSISTING OF 2,5-DI-TERT-BUTYL-HYDROQUINONE, 2,2''-METHYLENE-BIS-(4-METHYL-6-TERT-BUTYL-PHENOL), 2,2''-METHYLENEBIS-(4-ETHYL-6-TERT-BUTYL-PHENOL), AND 4,4''-BUTYLIDENE BIS(6-TERT-BUTYL-M-CRESOL), (2) BETWEEN 0.05 AND 0.5% OF A COMPOUND SELECTED FROM THE CLASS WHICH CONSISTS OF SALTS AND ESTERS OF INORGANIC PHOSPHORUS OXY-ACIDS, (3) BETWEEN 20 AND 80 PARTS OF MANGANESE PER MILLION PARTS OF SAID POLYAMIDE COMPOSITION IN THE FORM OF A COMPOUND SELECTED FROM THE CLASS CONSISTING OF MANGANOUS LACTATE, MANGANOUS OXALATE AND MANGANOUS HYPOPHOSPHITE, AND (4) BETWEEN 0.2 AND 1% OF A MONONUCLEAR CYCLIC ORGANIC ACID ANHYDRIDE SELECTED FROM THE GROUP WHICH CONSISTS OF THE ANHYDRIDES OF BENZOIC ACID AND HEXAHYDROPHTHALIC ACID, THE PROPORTIONS BEING BASED ON THE TOTAL WEIGHT OF THE COMPOSITION.