Process for preparation of polyamide materials with improved long-term usability

Abstract

The invention relates to a method for producing polyamide materials with improved long-term usability. The invention relates to a method for the long-term stabilization of polyamides and to the use of specific additive compositions for the long-term stabilization of polyamides.

Description

[0001] This application is a divisional application of an application filed on October 16, 2017, with application number 201780077370.7 and invention name “Method for preparing polyamide material with improved long-term usability”. Technical Field

[0002] The present invention relates to a method for the long-term stabilization of polyamides and to the use of specific additive compositions for the long-term stabilization of polyamides. Background Art

[0003] In the presence of atmospheric oxygen, at temperatures above 70°C or by high-energy radiation to the polyamide surface, thermal or photooxidative reactions occur. The surface turns yellow and becomes increasingly dull and cracked. These surface changes lead to embrittlement of the material and thus to impairment of the mechanical properties of the molded parts. By adding appropriate stabilizers, oxidative damage to polyamide can be delayed, so that the time until embrittlement of the polyamide parts can be delayed.

[0004] A distinction is usually made between stabilizers for different temperature ranges. Typical classes of stabilizers for polyamides are copper stabilizers and stabilizers based on sterically hindered phenols. Sterically hindered phenols are mainly used in combination with auxiliary antioxidants, especially with phosphites. These blends of sterically hindered phenols and phosphites are hereinafter referred to as phenolic stabilizers or phenolic antioxidants. Copper stabilizers typically include at least one copper compound and at least one other halogen-containing component known as a synergist. The combination of a copper compound and a halogen-containing synergist is hereinafter referred to as a copper stabilizer.

[0005] To date, copper stabilizers have been mainly used in practice only when applications require high continuous operating temperatures in the range above 150° C. In addition to the problems of discoloration and lower tracking resistance that typically occur when using typical copper stabilizers (combinations of copper salts and halogen salts), the main reason for this is that, according to current views, copper-based heat stabilizers are inferior to phenolic antioxidants in the temperature range below 150° C. with regard to stabilization against loss of mechanical properties.

[0006] Therefore, phenolic antioxidants are mainly used for requirements in the temperature range below 150° C. In applications requiring polyamide materials to be stable over a very wide temperature range, copper stabilizers (for high temperature stabilization) have hitherto been combined with phenolic antioxidants in practice. This leads to high stabilization costs, making polyamide materials stabilized in this way economically less attractive.

[0007] This becomes clear from the most important reference books on plastic additives, which teach experts and users that copper stabilizers are very effective above 150° C., while phenolic antioxidants are more effective at temperatures below 150° C. compared to copper stabilizers. Examples are:

[0008] "Plastics Additives Handbook", Hans Zweifel, Ralph D. Maier and Michael Schiller (6th edition, 2009), pages 80-84.

[0009] "Resistance and Stability of Polymers", Gottfried Ehrenstein and Sonja Pongratz, Carl Hanser Verlag 01.10.2013, Chapter 3.7.8, pages 308-313.

[0010] "Iodine Chemistry and Application", Tatsuo Kaiki, (1st edition), Kapitel 31, S.551f.

[0011] • Speech by JR Pauquet and AG Ortli (Ciba) at the World Congress POLYAMIDE 2000, Zurich, Switzerland, 14-16 March 2000.

[0012] The online platform "Specialchem" also reveals this principle: http: / / polymeradditives.specialchem.com / selection-guide / light-stabilizers-and-antioxidants-for-polyamides / heatstabilizers-for-aliphatic-polyamides /

[0013] The publication "Polyamide composition stabilized with copper salt and aliphatic halogenated phosphate" DE 198476216 discloses a polyamide composition, characterized in that it contains at least one copper salt and at least one halogen-containing aliphatic phosphate as stabilizers, whereby an increase in the continuous service temperature in the temperature range above 150° C., improved anti-tracking properties and reduced discoloration can be achieved immediately after injection molding and after conditioning.

[0014] DE 198 47 626 A1 discloses polyamide compositions stabilized with copper salts and aromatic halogen compounds. The teaching focuses on the stabilization of polyamides while increasing the continuous use temperature. Heat aging tests at temperatures of 150° C. and 165° C. show that the data from the tests at 150° C. do not differ in terms of measurement accuracy from the comparative data of the tested conventional stabilizers with salt-like halogen compounds. A significant improvement in the stabilization effect is achieved only at higher temperatures, stabilization at elevated continuous use temperatures (above 165° C.) according to the purpose of the teaching.

[0015] Patent specification EP 1 121 388 B1 “Polyamide compositions stabilized with copper complexes and organic halogen compounds” discloses polyamide compositions which contain at least one copper complex and at least one organic halogen compound for stabilization, whereby improved thermal stability at temperatures above 150° C., improved tracking resistance and low discoloration are achieved immediately after injection molding and after conditioning. Summary of the invention

[0016] Due to the continuously growing field of application of plastic-based materials, for example in the automotive industry, there is a search for more stabilized compositions, especially for continuous use temperatures in the range below 150° C., especially for polyamides. Typical continuous use temperatures are temperatures with a maximum temperature in the vicinity of 120° C., which are often required, for example, in the electrical and automotive industries. In this temperature range, phenol / phosphite blends are typically used as stabilizers, but even with increased use amounts, these do not allow stabilization beyond a maximum time range.

[0017] The present invention therefore has the object of proposing a method by means of which the desired stabilization can be achieved at relatively low to moderate continuous use temperatures, i.e. in particular ensuring that the polyamide composition exhibits improved long-term stabilization against heat over a wide range (also at elevated temperatures above 150° C. and up to 180° C.), while being particularly effectively stabilized at temperatures below 150° C. to significantly extend the feasible service life, preferably in terms of the following two aspects:

[0018] a) Maintain tensile strength and impact strength (prevent embrittlement);

[0019] b) The elongation at break is very well preserved, while at the same time, the tensile strength and impact strength are well preserved.

[0020] This task is solved by the technical solution of the present invention. The preferred configuration is described in the following specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The half-life of the elongation at break of various Examples and Comparative Examples under heat storage at 120°C is shown. DETAILED DESCRIPTION

[0022] Surprisingly, the present invention enables the desired stabilization of polyamides by using known components, which have hitherto been used exclusively for high-temperature stabilization in the prior art. However, significantly improved stabilization can be achieved at continuous use temperatures below 150° C., for example 120° C., especially compared to compounds previously used to stabilize polyamides at lower continuous use temperatures. The stabilizers used according to the invention are well dispersible in polyamides, so that they are easy to process. The stabilizers according to the invention can be introduced into the polyamides and distributed therein by conventional methods. In addition, the stabilizer component can be easily compounded for use, for example by compounding with a matrix of conventional materials such as waxes or polymers. The present invention thus enables the following advantages to be achieved:

[0023] 1. The stabilization of unreinforced and reinforced polyamides against prolonged exposure to temperatures below 150° C. is improved. Deterioration and thus reduction in performance is delayed as long as possible, in particular the mechanical properties of tensile strength and impact strength are maintained as long as possible.

[0024] 2. The elongation at break generally decreases particularly rapidly and significantly with heat aging. Therefore, an advantage that is particularly important for the practical application of polyamide materials is the possibility based on the invention of significantly extending the maintenance of the elongation at break during long-term storage under temperature stress (at temperatures below 150° C.) compared to phenolic antioxidants. The high elongation at break of the polymer matrix (also in the reinforced polyamide) leads to a significant improvement in the application properties of the entire material and an increase in the energy absorption capacity.

[0025] 3. The amount of stabilizer used can be adapted to the desired stabilization time (product life), since the stabilizers used according to the invention prolong the stabilization performance when the amount used increases, an effect which is not particularly evident in the case of phenolic stabilizers. Even in the case of a significant increase in the amount used, these stabilizers do not show any extension of the stabilization effect very quickly. On the contrary, at high doses (e.g. in the range of more than 1%), there may even be a deterioration in the stabilization effect. Figure 1 The half-life of the elongation at break (measured at 120° C.) of polyamide 6.6 with different stabilizers is shown. Sample R01 is an unstabilized polyamide, samples R02 and R09 are polyamides stabilized with phenolic stabilizers (the same polyamide 6.6 is used in all samples), whereby the amount of phenolic antioxidant used in sample R09 is twice that of R02. However, this has hardly any effect on the half-life of the elongation at break. Sample R07 is a stabilized sample according to the invention (the amount of stabilizer is equivalent to that in sample R02). Here, the dramatic and surprising increase in the half-life (i.e. the time taken until the elongation at break drops to half of the original value) achieved compared to the phenolic stabilizer is already evident. For sample R014, the amount used is again twice (compared to R07) - this shows a very clear further extension of the half-life. This effect can also be clearly seen in samples R06 and R13 stabilized according to the invention (twice the amount of additive compared to R06). This huge stabilization effect of the method of the present invention can also be used to use a small amount of stabilizer to ensure the level of continuous use time that can be achieved with phenolic stabilizers. This leads to cost advantages, label-free advantages and the possibility of low halogen content, so that it is easy to use in difficult electrical and electronic applications.

[0026] 4. Due to the improved stabilization, thinner components can be made, since the material thickness previously considered necessary (due to desired redundancy or corresponding safety factors) can be reduced (since the polyamide stabilized according to the invention can withstand loads for a longer time even with a smaller material thickness).

[0027] 5. According to the present invention, the following advantages can also be achieved:

[0028] Long-term delay of degradation and the accompanying decrease in performance properties, in particular prolonged maintenance of mechanical properties such as tensile strength, elongation at break and impact strength;

[0029] Effective stabilization (and prevention of embrittlement) of polyamides over a very wide temperature range, even at temperature peaks of up to 200° C. (e.g. for materials which have to withstand relatively low continuous use temperatures, whereby temperature peaks occur during the life cycle), without any impairment of the material qualities which have to be expected (due to the known effectiveness of the combination of copper component and synergist used according to the invention at high temperatures). Phenolic stabilizers alone are not suitable for such applications, since they cannot prevent a rapid degradation of the essential properties at high temperatures (>150° C.). For such application requirements under different temperature loads, it is no longer necessary, due to the stabilization method according to the invention, to use different stabilizer systems for different temperature ranges (e.g. a combination of both phenolic stabilizers and copper stabilizers);

[0030] The color is neutral or only slightly discolored after adjustment;

[0031] No or at least only acceptable influence on tracking resistance, which is very important for use in the electrical and electronics industry.

[0032] Thus, surprisingly, improved stabilization can be achieved by using the following method: stabilizing polyamide with copper compounds, appropriately in combination with synergistically acting halogen-containing aliphatic phosphates. Polyamide compositions provided with this stabilizer combination exhibit better stabilization at temperatures below 150°C, preferably below 145°C, such as below 140°C, below 130°C, such as below 125°C, and in particular below 120°C, compared to conventional copper stabilizers and / or organic stabilizers (phenolic antioxidants alone and in combination with phosphites). In particular, the tensile strength and impact strength of these polyamide compositions at temperatures below 150°C are maintained at high levels for a longer period of time.

[0033] Furthermore, it has surprisingly been found that the combination of copper with a complex of a halogenated aliphatic phosphoric acid ester, in particular, enables the elongation at break after heat aging to be maintained at a high level for a much longer time than previously known stabilizer systems for polyamides, and also compared to combinations of copper salts or other copper compounds (not copper complexes) with halogenated phosphoric acid esters or with other halogen compounds including halogen salts. This effect occurs in particular at temperatures below 150° C. At higher temperatures, for example at 180° C., there are no differences with regard to the maintenance of the elongation at break compared to stabilization with conventional copper stabilizers.

[0034] In summary, therefore, the stabilizer combination used according to the invention can achieve long-term stabilization in a very wide temperature range with a single stabilizing component (the combination used according to the invention). The following description and examples show that, in addition to the surprising stabilization discussed above at temperatures below 150°C in the case of the combination used according to the invention, stabilization at a temperature range significantly above 150°C, for example from above 180°C to about 200°C, is also feasible. In the state of the art, it is considered that a combination of different stabilizers is necessary for such stabilization in such a wide temperature range. Typically, for stabilization at low temperatures, the use of the described phenolic compounds is considered to be basic, but at temperatures above 150°C, they no longer have any practical effect. Therefore, in the state of the art, for example, if stabilization is desired in a temperature range of 120°C to 180°C, it is necessary to use, for example, a combination of a phenolic antioxidant with other copper stabilizers for a temperature range above 150°C. In accordance with the findings of the present invention, such a combination will no longer be necessary, because the specific stabilizer combination of the present invention can safely cover the entire temperature range.

[0035] Thus, in addition to the methods and uses shown for long-term stabilization at temperatures below 150°C, the present invention also provides a system that enables polyamides to be safely stabilized over a wide temperature range, including temperatures below 150°C and temperatures above 150°C. The temperature range above 150°C extends in particular to above 160°C, including above 180°C, and generally up to 200°C. Thus, as described herein, the present invention makes it possible to replace the combination of several different stabilization systems that are considered necessary in the state of the art by a single system. Therefore, the stabilized polyamide composition of this aspect of the invention preferably comprises only the temperature stabilization system described herein as a stabilizer. This simplifies the compounding process at the same time and enables cost savings, since in particular the phenolic system can be omitted. For this purpose, as shown in particular by the following experimental data, an entire improved system will be available, so that a significant extension of the stabilization period can also be achieved.

[0036] If stabilization is desired over an even wider temperature range, i.e., in particular at temperatures above 200° C., known high-temperature stabilizers for polyamides can be used. In particular, polyols having more than 2 hydroxyl groups can be used for this purpose. Known examples of such compounds are polyols having 2 to 12 hydroxyl groups and a molecular weight of 64 to 2000 g / mol. Particularly suitable examples are pentaerythritol, dipentaerythritol and tripentaerythritol, in particular dipentaerythritol. Such compounds can be introduced into the polyamide in a conventional manner. Particularly suitable is the introduction via a premix, preferably via a masterbatch, whereby the mixture or masterbatch also comprises other stabilizing components according to the invention. The amount of such higher temperature stabilizers can be selected by an expert based on known information or determined by simple tests of the desired polyamide composition.

[0037] In the case of the polyamide compositions stabilized according to the invention based on copper complexes and halogenated aliphatic phosphates, very good color and high tracking resistance are simultaneously achieved. This also allows the use in areas requiring high tracking resistance in the form of CTI values ​​(Comparative Tracking Index) of 600 V (for unreinforced polyamides).

[0038] Surprisingly in connection with the present invention, by combining a copper component with a specific synergist, as defined in the technical solution of the present invention, an unexpected improvement in the stabilization of polyamides can be achieved, which outperforms two typical phenolic stabilizers and cannot be achieved using other combinations of known copper stabilizers and halogen-containing synergists. This is particularly shown in the following examples, where conventional copper systems (copper salts and halogen salts, or copper complexes and halogen-containing organic compounds (not aliphatic phosphates)) cannot achieve the effect achieved by the combination according to the present invention.

[0039] The copper stabilizer used according to the present invention consists of a mixture of two basic components, namely a copper compound and a specific halogen-containing compound (also referred to herein as a synergist). The copper compound used according to the present invention can be any copper salt (CuI, CuBr, copper acetate, CuCN, copper stearate...) or any other copper compound such as CuO, Cu2O, copper carbonate or any copper complex. The synergist used according to the present invention is a halogen-containing aliphatic phosphate.

[0040] Typical usage amounts of these two components are given as follows: Cu:halogen ratio of 1:1 to 1:50 (molar ratio), preferably 1:4 to 1:20, more preferably 1:6 to 1:15.

[0041] The amount of copper and halogen in the polyamide is selected according to the desired use of the polyamide and the desired stabilization. There is no limit on the amount of copper used, as long as it does not negatively affect the mechanical properties of the polyamide. The amount of copper used is generally in the range of 1 to 1000 ppm of Cu, preferably 3 to 200 ppm of Cu, and more preferably 5 to 150 ppm of Cu. Specific examples are 33 ppm, 66 ppm and 100 ppm. The amount of synergist used (in each case based on ppm of halogen) is obtained from the above ratio. The amount of synergist added is not subject to any particular restrictions. However, an addition greater than 1% generally does not improve the stabilizer effect. Typical amounts are in the range of 10 to 10,000 ppm. The preferred amount is in the range of 30 to 2000 ppm, more preferably 50 to 1500 ppm.

[0042] According to the invention, all conventional polyamides can be stabilized. Polyamides are polymers with recurring amide groups -CO-NH- in the main chain. They are formed from:

[0043] (a) aminocarboxylic acids or their functional derivatives such as lactams; or

[0044] (b) Diamines and dianhydrides or their functional derivatives.

[0045] By varying the monomer building blocks, a wide variety of polyamides is available. The most important representatives are polyamide 6 from ε-caprolactam, polyamide 6.6 from hexamethylenediamine and adipic acid, polyamide 6.10 and 6.12, polyamide 11, polyamide 12, PACM-12 and polyamide 6-3-T, PA 4.6 and semiaromatic polyamides (polyphthalamide PPA).

[0046] However, according to the invention, also all other polyamides can be stabilized, for example copolyamides with other segments, for example with polyesters, or copolymers of polyamides. Blends of different polyamides and blends of polyamides with other polymers can also be stabilized. Polyamide 6 and polyamide 6.6 are particularly preferred.

[0047] The stabilizer blends according to the invention can be used in all previously mentioned polyamides and blends, both in unfilled and unreinforced polyamides and in filled and reinforced polyamides. As fillers / reinforcement materials, glass fibers, carbon fibers, glass spheres, diatomaceous earth, fine-grained minerals, talc, kaolin, phyllosilicates, CaF2, CaCO3 and aluminum oxides can be used.

[0048] The copper complex used according to the present invention is a complex of copper with ligands such as triphenylphosphine, mercaptobenzimidazole, glycine, oxalate and pyridine. Chelate ligands such as ethylenediaminetetraacetates, acetylacetonates, ethylenediamines, diethylenetriamines, triethylenetetramines, phosphine chelate ligands or bipyridines can also be used. Examples of preferred phosphine chelate ligands are 1,2-bis(dimethylphosphino)-ethane, bis(2-diphenylphosphinoethyl)-phenylphosphine, 1,6-(bis(diphenylphosphino))-hexane, 1,5-bis(diphenylphosphino)-pentane, bis(diphenylphosphino)methane, 1,2-bis(diphenylphosphino)ethane, 1,3-bis(diphenylphosphino)propane, 1,4-bis(diphenylphosphino)butane and 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl.

[0049] These ligands can be used to form complexes individually or in combination. The required synthesis is known to experts or is recorded in the professional literature about complex chemistry. Usually, in addition to the above-mentioned ligands, these complexes can also contain typical inorganic ligands such as water, chloride, cyano ligands, etc.

[0050] Copper complexes with the complex ligands triphenylphosphines, mercaptobenzimidazoles, acetylacetonates and oxalates are preferred. Triphenylphosphines and mercaptobenzimidazoles are particularly preferred.

[0051] The preferred copper complexes used according to the invention are usually formed by the reaction of copper (I) ions with phosphine or mercaptobenzimidazole compounds. For example, these complexes can be obtained by reacting triphenylphosphine with copper (I) halides suspended in chloroform (G. Kosta, E. Reisenhofer and L. Stafani, J. Inorg. Nukl. Chem. 27 (1965) 2581). However, copper (II) compounds can also be reacted reductively with triphenylphosphine to obtain copper (I) adduct compounds (FU Jardine, L. Rule, AG Vohrei, J. Chem. Soc. (A) 238-241 (1970)).

[0052] However, the complexes used according to the invention can also be produced by any other suitable method. Suitable copper compounds for the preparation of these complexes are copper (I) or copper (II) salts of halogenated hydrogen acids, hydrocyanic acid, or copper salts of aliphatic carboxylic acids. Examples of suitable copper salts are copper (I) chloride, copper (I) bromide, copper (I) iodide, copper (I) cyanide, copper (II) chloride, copper (II) acetate or copper (II) stearate.

[0053] Copper(I) iodide and copper(I) cyanide are particularly preferred.

[0054] In principle, all alkyl or aryl phosphines are suitable. Examples of phosphines that can be used according to the invention are triphenylphosphine (TPP), substituted triphenylphosphines, trialkylphosphines and diarylphosphines. An example of a suitable trialkylphosphine is tri-(n-butyl)phosphine. In general, triphenylphosphine complexes are more stable than trialkylphosphine complexes. Triphenylphosphine is also economically preferred because it is commercially available.

[0055] Examples of suitable complexes can be represented by the following formula:

[0056] [Cu(PPh3) 3X ], [Cu2X2(PPh3)3], [Cu(PPh3)X]4 and [Cu(PPh3)2X], wherein X is selected from Cl, Br, I, CN, SCN or 2-MBI.

[0057] However, the complexes that can be used according to the invention may also contain additional complex ligands. Examples are bipyridine (e.g., CuX(PPh3)(bipy), wherein X is Cl, Br or I), bichinoline (e.g., CuX(PPh3)(biquin), wherein X is Cl, Br or I) and 1,10-phenanthroline, o-phenylenebis(dimethylarsine), 1,2-bis(diphenylphosphino)ethane and terpyridine.

[0058] These complexes are usually non-conductive and diamagnetic. They are usually colorless and accumulate as water-soluble crystals that melt without decomposing. The complexes are easily soluble in polar organic solvents such as DMF, chloroform and hot ethanol.

[0059] The copper salt used according to the invention may be any copper salt.

[0060] Salts of monovalent or divalent copper with inorganic or organic acids are preferred.

[0061] Examples of suitable copper salts are copper (I) salts, such as CuI, CuBr, CuCI or CuCN; copper (II) salts, such as CuCI2, CuBr2, CuI2, copper acetate, copper sulfate, copper stearate, copper propionate, copper butyrate, copper lactate, copper benzoate or copper nitrate; and ammonium complexes of the above salts.

[0062] Compounds such as copper acetylacetonate or copper EDTA may also be used. Mixtures of different copper salts may also be used. Copper powder may also be used as desired.

[0063] Preferred are copper (I) halides and copper salts of organic acids. Copper (I) iodide and copper acetate are particularly preferred.

[0064] The above copper components may be used alone or as a mixture of two or more components.

[0065] The synergist used according to the invention is a halogen-containing aliphatic phosphoric acid ester.

[0066] According to the present invention, at least one halogen-containing aliphatic phosphate is used, preferably in the form of tris (halogenated hydrocarbon) -phosphate or phosphonate. Tris (bromoalkyl) phosphates (brominated aliphatic phosphates) are preferred. In particular, in these compounds, no hydrogen atom is connected to the alkyl C atom at the α position relative to the C atom connected to the halogen. This means that dehydrohalogenation reaction will not occur. Exemplary compounds are tris (3-bromo-2,2-bis (bromomethyl) propyl) phosphate, tris (dibromo neopentyl) phosphate, tris (trichloro neopentyl) phosphate, tris (chlorodibromo neopentyl) phosphate and tris (bromodichloro neopentyl) phosphate. Preferred are tris (dibromo neopentyl) phosphate and tris (tribromo neopentyl) phosphate.

[0067] Mixtures of several halogen-containing aliphatic phosphates can also be used. In addition, mixtures of halogen-containing aliphatic phosphates and aromatic halogenated compounds such as brominated polystyrenes or poly (pentabromobenzyl) acrylates can also be used. Tris (halogenated aromatic) phosphates or phosphonates can also be used as aromatic halogenated compounds, for example, tris (2,4-dibromophenyl) phosphate, tris (2,4-dichlorophenyl) phosphate and tris (2,4,6-tribromophenyl) phosphate. However, it is preferred to use only halogenated aliphatic phosphates as synergists.

[0068] Preferred combinations (hereinafter referred to as stabilizer blends) are combinations of copper salts, especially CuI, and phosphates described herein, especially brominated phosphates, and combinations of copper complexes, especially complexes with TPP ligands, and phosphates described herein, especially brominated phosphates.

[0069] The polyamide and stabilizer blend are melted together and mixed, or the polyamide is melted first and then the stabilizer blend is mixed in, the latter being preferred. In a preferred design, the stabilizer blend is added to the molten polyamide in the form of a premix (concentrate or masterbatch).

[0070] Suitable mixing equipment is familiar to the expert and includes mixing mills, discontinuously operated internal mixers and kneaders, continuously operated extruders and kneaders and static mixers. It is preferred to use continuously operated extruders, both single-screw extruders and twin-screw extruders, which enable good mixing. Usually, the polyamide is first melted in the extruder and then the stabilizer blend is metered (by weight or volume) through a suitable opening. These processes and the necessary equipment are known to the expert.

[0071] However, it is also possible to add the stabilizing component during the production of the polyamide, ie to the monomer mixture. This allows very good mixing without additional mixing, which reduces production costs and time.

[0072] If a preconcentrate of the stabilizer blend is used, this can be produced in a discontinuously operated mixer, such as a Buss Kneader, which enables a very good, uniform distribution. Usually, however, a continuous mixer is used, such as a twin-screw extruder or a ZSK extruder. The same polyamide is usually used as matrix material and then mixed with the preconcentrate. However, different polyamides or polymers can also be selected. Optionally, further additives can be added during the production of the masterbatch.

[0073] Alternatively, the preconcentrate can be produced in another preferred embodiment by mixing the stabilizer blend with other additives and / or additives such as lubricants, release agents, nucleating agents, etc., followed by coagulation or granulation, compression or tableting. The relevant processes and the necessary equipment are known to the expert.

[0074] However, the additives and / or further components can also be used separately in the process according to the invention, for example by separate dosing during the production of the stabilized polyamide according to the invention.

[0075] Another positive effect of the invention relates to the aspects of occupational safety, environmental protection and suitability for electrical and electronic applications (regardless of the content of halogen-containing compounds). Typical copper stabilizers and halogen-containing materials are subject to specific regulations in accordance with CLP Regulation No. 1272 / 2008 with regard to labeling, transportation, storage and handling.

[0076] The key problem of using halogenated materials is corrosion, especially electrical corrosion. In this regard, halogens, especially bromine and chlorine, and iodine, are considered to be harmful to electronic components due to the interaction of halide anions with intermetallic phases. Therefore, the requirement for reducing halogen content is now common in the electrical and electronic industry. According to the international standards IEC 61249-2-21 and EN 61249-2-21 and IPC 4101 of PCB materials (printed circuit boards), it is considered that the material containing less than 1500ppm of Cl and Br when the maximum amount of Br and Cl is 900ppm is halogen-free. Due to its excellent effectiveness, the stabilizer combination used according to the present invention can be used in low doses, so that it can be close to the corresponding limit value. It is also possible to keep the concentration of copper and halogen low during the production of the stabilizer combination, for example, by producing the above-mentioned pre-concentrate. In this way, under the advantages described above, low-concentration additives (related to the stabilizer combination of the present invention) become easy to obtain. Overall, this also simplifies the handling of the stabilizer components used according to the invention for the user, since no labeling is required according to GHS / CLP Regulation (EC) No. 1272 / 2008. This leads to reduced storage and transport costs, among other things.

[0077] Such materials also present less risk in terms of environmental hazards and occupational safety.

[0078] The following examples illustrate the invention.

[0079] Example :

[0080] In all examples, the polyamides were compounded with the stabilizers mentioned in a conventional manner and the mechanical and other properties to be tested were evaluated on test plaques. The aging conditions in each case are indicated.

[0081] Polyamide 6.6 (Ultramid A27 E) from BASF was used.

[0082] Compounding was carried out using a twin-screw extruder from Leistritz ZSE27MAXX-48D.

[0083] Additives were metered by weight during compounding.

[0084] After drying, standard test bars "Demag Ergotech 60 / 370-120 size" for determining the mechanical properties (ISO 527) and impact strength (ISO 179 / 1eU) were produced from the compounds on a Demag Ergotech 60 / 370-120 size injection molding machine.

[0085] The test bars were stored in a convection oven at the temperatures given in the examples (120° C., 140° C., 150° C. and 180° C.).

[0086] The elastic modulus [MPa], tensile strength [MPa] (elongation [%]) and breaking stress [MPa] (elongation [%]) were measured in a tensile test according to ISO 527 using a Zwick Z010 static materials testing machine.

[0087] The impact strength was measured in a Charpy impact bending test according to ISO 179 / 1eU using a pendulum impact tester HIT PSW 5.5J.

[0088] Chemical compounds and abbreviations used:

[0089] TPP: triphenylphosphine; P(C6H5)3

[0090] PDBS: polydibromostyrene; [CH2-CH(C6H3Br2)-] n

[0091] Phosphate 1: tris-(tribromoneopentyl)-phosphate; C 15 9H 24 O4P

[0092] Phenol / phosphite blend B1171: 1.1 mixture of tris-(2,4-di-tert-butylphenyl)phosphite and N,N'-hexane-1,6-diylbis(3-(3,5-di-tert-butyl-4-hydroxyphenylpropionamide))

[0093] Table 1: Stabilization of polyamide 6.6 itself; heat aging at 120 °C

[0094] Comparative tests using phenolic antioxidants and other copper stabilizers (combinations according to the invention and comparative variants); tensile strength, elongation at break and impact strength were measured for the corresponding test pieces.

[0095] In the case of the copper stabilizer, a Cu concentration of 33 ppm and a halogen concentration of 400 ppm were used.

[0096] Measure until the impact strength drops to 10 kJ / m 2 In addition, the time until the tensile strength drops to 90% of the initial strength value and the time until the elongation at break reaches half of the initial value are measured (half-value measurement).

[0097]

[0098] Table 2: Stabilization of polyamide 6.6 itself; heat aging at 120 °C

[0099] Comparative tests using phenolic antioxidants and copper stabilizers (combinations of the invention and comparative variants);

[0100] The tensile strength and elongation at break were measured for the corresponding test pieces.

[0101] In the case of the copper stabilizer, a Cu concentration of 66 ppm and a halogen concentration of 800 ppm were used.

[0102] The time until the tensile strength dropped to 70% of the initial strength value and the time until the elongation at break reached half of the initial value (half-value measurement) were measured.

[0103]

[0104]

[0105] Table 3: Stabilization of polyamide 6.6 itself; heat aging at 180 °C

[0106] Comparative tests using copper stabilizers (combinations according to the invention and comparative variants);

[0107] The tensile strength, elongation at break and impact strength were measured for the corresponding test pieces.

[0108] In the case of copper stabilizer, a Cu concentration of 100 ppm and a halogen concentration of 1200 ppm were used.

[0109] The time until the impact strength, tensile strength and elongation at break reach half of the respective initial value was determined (half-value measurement).

[0110]

[0111] Table 4: Color and tracking resistance of polyamide 6.6

[0112] Comparative tests using phenolic antioxidants and other copper stabilizers (combinations of the invention and comparative variants);

[0113] Add 100ppm Cu / 1000ppm halogen for copper stabilizer.

[0114] Test plates of 3×5 cm and 3 mm thick were produced from the above pellets on an injection molding machine and the CTI value was measured in accordance with the IEC-60112 standard. The test plates were visually evaluated for discoloration.

[0115]

[0116] * Typical formulations for stabilizer blends adjusted in such a way that the addition amount is in the range of 0.5 to 3% stabilizer (based on the polyamide content).

[0117] Tables 1 to 4 summarize various tests and comparative tests. These impressively demonstrate the advantages of the invention. Table 1 shows, for example, that the stabilizer components used according to the invention can maintain the mechanical property characteristics of the stabilized polyamide in a very good range for a much longer time compared to standard phenolic stabilizers and also compared to known copper systems. Although the stabilizer systems cuprous iodide / potassium iodide and copper complexes and aromatic halogen compounds show a stabilizing effect comparable to that of phenolic stabilizers, high levels of polyamide stabilized according to the invention cannot be achieved.

[0118] Table 2 summarizes the corresponding experiments, but with increasing amounts of stabilizer. This shows that an increase in the amount of phenolic stabilizer leads only to a slight improvement compared to lower contents. An equilibrium is reached here, so that even further increases in the input amounts do not lead to any further improvements. On the contrary, the stabilizer combination of the invention shows a clear extension of the stabilizing effect.

[0119] Table 3 summarizes the heat aging tests at high temperatures. This shows that the combination according to the invention and the conventional copper system (here cuprous iodide / potassium iodide) show approximately the same stabilization effect, which again can be taken as evidence that the improved stabilization effect at low temperatures is surprising for the combination according to the invention, since these stabilizers do not differ significantly in their stabilization effect at typical higher temperatures.

[0120] Table 4 lists tests and comparative tests which show the suitability of individual stabilizers for the stabilization of polyamides for use in electrical / electronic components. The CTI value is particularly relevant in this context, since in many areas stabilized polyamides are only used if the CTI value is 600 V or at least not very far below 600 V. It is shown here that the stabilizer combination of the invention, in particular the stabilizer combination of the invention which does not contain salt-based components, meets this requirement. In contrast, typical salt-based copper stabilizers are not suitable for these uses.

[0121] These tests and comparative tests have shown once again that the polyamides stabilized according to the invention have excellent performance characteristics. With the stabilizer components used according to the invention, the properties can be specifically controlled over a wide range of substrate properties. On the other hand, the mechanical stability of the polyamide to be stabilized can be adjusted over a wide range, which is much higher than the effect achieved by conventional phenolic stabilizers in the low to medium temperature range, even when used in small amounts. At the same time, stabilized polyamides can also be obtained which have a high tracking resistance (high CTI values) and show no or only a low tendency to discoloration after adjustment. This once again confirms the outstanding performance characteristics of the stabilizer combination used according to the invention.

[0122] In order to demonstrate the surprising effect of the stabilizers used according to the invention, in particular compared to known phenolic stabilizers, the half-life of the elongation at break of compositions using PA 6.6 was evaluated for different combinations.

[0123] Table 5: Half-life [h] of the elongation at break of polyamide 6.6 as a function of stabilization.

[0124] Comparative test using phenolic antioxidant and copper stabilizer (combination of the present invention);

[0125] The elongation at break was measured for the corresponding test pieces.

[0126] The time until the elongation at break reaches half of the initial value is measured (half-value measurement).

[0127]

[0128] The data in the table above show that, compared with a typical phenol / phosphite system (B1171), in the case of the variants of the invention, in particular at 120° C. and 140° C., a better (longer) retention of the elongation at break is achieved in polyamide 6.6. At the same time, it becomes clear that the use of the invention also provides protection against temperature peaks above 150° C., i.e., temperature ranges in which phenol / phosphite-based stabilizers have only a very slight effect. This applies in particular to temperatures in the range above 170° C., at which the effectiveness of these stabilizers is no longer shown. Due to the high effectiveness of the stabilizers according to the invention, very good long-term use properties of the respective materials can be achieved over a wide temperature range, even at low concentrations of copper and halogen in the polyamide. Due to the low concentrations required for this, bright colors, good electrical properties, low stabilization costs and a significantly reduced tendency to electrical corrosion can be achieved, among other things.

Claims

1. A method for stabilizing polyamide at a temperature below 150° C., characterized in that The polyamide is mixed with a copper compound and a halogen-containing aliphatic phosphate ester.

2. Use of a composition comprising a copper compound and a halogen-containing aliphatic phosphate for stabilizing polyamide at temperatures below 150°C.

3. The method according to claim 1 or the use according to claim 2, characterized in that The stabilization of the polyamide takes place at temperatures below 145°C, in particular below 130°C.

4. The method according to claim 1 or 3 or the use according to claim 2 or 3, characterized in that The copper compound is a copper (I) salt, a copper (II) salt, or a copper complex.

5. The method or use according to claim 4, characterized in that The copper (I) salt is selected from CuI, CuBr, CuCl, CuCN, Cu2O, or a mixture thereof.

6. The method or use according to claim 4, characterized in that The copper (II) salt is selected from copper acetate, copper stearate, copper sulfate, copper propionate, copper butyrate, copper lactate, copper benzoate, copper nitrate, CuO, CuCl2, or a mixture thereof.

7. The method or use according to claim 4, characterized in that The copper complex is selected from copper acetylacetonate, copper oxalate, copper EDTA, [Cu(PPh3)3X], [Cu2X2(PPH3)3], [Cu(PPh3)X], [Cu(PPh3)2X], [CuX(PPh3)(bipy)], [CuX(PPh3)(biquin)], wherein X=Cl, Br, I, CN, SCN, or 2-mercaptobenzimidazole.

8. The method or use according to any one of claims 1 to 7, characterized in that The halogen-containing aliphatic phosphate is tri(halogenated hydrocarbon)phosphate or phosphonate.

9. The method or use according to claim 8, characterized in that The tris(halogenated hydrocarbon)phosphate is selected from tris(3-bromo-2,2-bis(bromomethyl)propyl)phosphate, tris(dibromoneopentyl)phosphate, tris(trichloroneopentyl)phosphate, tris(bromodichloroneopentyl)phosphate, tris(chlorodibromoneopentyl)phosphate, tris(tribromoneopentyl)phosphate, or a mixture thereof.

10. The method or use according to any one of claims 1 to 9, further comprising at least one halogenated aromatic compound and / or at least one polyol having more than 2 hydroxyl groups, preferably a polyol having 2 to 12 hydroxyl groups and a molecular weight of 64 to 2000 g / mol, particularly preferably pentaerythritol, dipentaerythritol and tripentaerythritol, in particular dipentaerythritol.

11. The method or use according to claim 10, characterized in that The halogenated aromatic compound is selected from brominated polystyrenes, poly(pentabromobenzyl)acrylates, tris(2,4-dibromophenyl)phosphate, tris(2,4-dichlorophenyl)phosphate, tris(2,4,6-tribromophenyl)phosphate, or a mixture thereof.

12. The method or use according to any one of claims 1 to 11, characterized in that The polyamide is selected from reinforced or unreinforced PA 6, PA 6.6, PA 4.6, PA 11, PA 12, or a mixture thereof.

13. A method for stabilizing polyamide in a temperature range below 150°C and above 150°C, characterized in that The polyamide is mixed with a copper compound and a halogen-containing aliphatic phosphate ester.

14. Use of a composition comprising a copper compound and a halogen-containing aliphatic phosphoric ester for stabilizing polyamide in a temperature range below 150°C and above 150°C.

15. The method according to claim 13 or the use according to claim 14, wherein the copper compound, the halogen-containing aliphatic phosphate and / or the polyamide are as described in any one of claims 3 to 12.

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