Polyamide material with improved long-term performance

Abstract

The present invention relates to a method for the long-term stabilization of polyamides and to the use of a specific additive composition for the long-term stabilization of polyamides.

Description

Technical Field

[0001] The present invention relates to polyamide materials having improved long-term use performance, a method for long-term stabilization of polyamides, and the use of specific additive compositions for long-term stabilization of polyamides. Background Art

[0002] In the presence of atmospheric oxygen, at temperatures above 70 °C or by high-energy radiation, thermal or photo-oxidation reactions occur on the surface of polyamides. In this case, the surface turns yellow, becomes increasingly dull and cracked. This leads to embrittlement of the material and thus to impairment of the mechanical properties of the molded parts. By adding suitable stabilizers, the oxidative damage of the polyamides can be retarded, and thus the time until the polyamide parts become brittle can be delayed.

[0003] Here, there is generally a distinction between stabilizers for different temperature ranges. The traditional stabilizer classes for polyamides are copper-based stabilizers, secondary aromatic amines, and sterically hindered phenol-based stabilizers. In this case, sterically hindered phenols are mostly used in combination with co-antioxidants, in particular phosphites or phosphonates. The blend of sterically hindered phenols with phosphites or phosphonates is hereinafter referred to as phenolic stabilizers or phenolic antioxidants. Copper-based stabilizers generally comprise at least one copper compound and at least one other halogen-containing component called a synergist. The combination of the copper compound with the halogen-containing synergist is hereinafter referred to as a copper stabilizer.

[0004] For automotive applications in the engine compartment, the housings for controllers, plug connectors, and sensors are usually made of polyamide materials because polyamides can particularly well withstand the boundary conditions required there. Here, the high ambient temperatures to which the components are exposed play an important role. In this case, the increasing miniaturization and the increasingly dense packaging of the components have led to a gradual increase in temperature requirements.

[0005] In recent years, manufacturers have increasingly faced corrosion problems, especially electrocorrosion, which has led to corresponding malfunctions. Analysis of the corroded contacts has shown that iodides and bromides, which are identified as components of copper-based stabilizers in the polyamide materials used, are mainly involved in the corrosion process.

[0006] In order to reliably prevent failures, there is an increasing demand for copper-free and halogen-free polyamide materials. In the sensitive automotive electronics sector, the demand for materials with particularly low copper and halogen content is already largely recognized. However, at the same time, polyamide materials should have stability in many applications, where the tensile strength under a thermal load of 150 °C drops to 50% only after a duration of at least 2,000 hours or, depending on the application, even after at least 3,000 hours. These combined requirements (copper-free and moreover maintaining mechanical property values over a long period at high temperatures) cannot be achieved with the common stabilization schemes for aliphatic polyamides (without using copper stabilizers), or can only be achieved with great difficulty. Therefore, manufacturers currently have to resort to expensive special thermoplastics, such as polyphenylene sulfide and partially aromatic polyamides, and thus there is a search for new solutions for essentially aliphatic polyamide materials for electrical applications, which have improved working properties at high temperatures and do not require the addition of copper compounds and halogen compounds for stabilization.

[0007] In the prior art, there are already systems for stabilizing polymers against thermo-oxidative damage and the resulting molecular degradation, which largely dispense with copper-containing and halogen-containing components. The addition of polyols (polyhydric alcohols) to polyamides or alternatively the addition of iron compounds is considered a solution for making polyamides suitable for temperatures in the range >200 °C and in the range 180 °C to 200 °C. However, at temperatures below the above (below 200 °C, especially below 180 °C), the action of the polyols or iron compounds is only less pronounced. For these stabilizers, it is assumed that they do not act in polyamides like classical antioxidants, but rather they form a protective layer at elevated temperatures in the presence of oxygen, which protective layer is oxygen-impermeable or only slightly permeable as a barrier ("patina") and thus prevents further oxidation of the underlying polyamide range.

[0008] Since the formation of such a barrier layer is necessary for the effectiveness of the polyol or iron compound, a sealing step (annealing step) at elevated temperatures is absolutely necessary, even if the actual temperature requirements are lower than the above temperatures. This concept has been referred to as "Shielding" or barrier technology in a series of publications as a solution to very high temperature requirements, especially in engines and transmissions (see: "Superior resistance to thermo-oxidative and Chemical degradation in Polyamides and polyphthalamides", Technical Library Society of Plastic Engineers, January 2011, S. Mok et al.; Dr. Kremers, SKZ conference on April 19, 2016; Dr. Gauge, AMI Performance Polyamides 2017; " maximiert", Kunststoffe 3 / 2010, pp. 66 - 70; Brochure of BASF Endure). This means that there must be a longer residence time at elevated temperatures, typically at temperatures of 200 °C and above. However, due to the corresponding storage at elevated temperatures, the requirement to carry out the "sealing step" severely limits the application possibilities and is the main obstacle to using this technology at temperatures below this elevated temperature range. In addition, this practice is also not possible for unreinforced polyamides because unreinforced polyamides are severely damaged during the sealing step at such high temperatures.

[0009] The technology described here, which is based on the formation of a barrier layer at extremely high temperatures, is currently used for reinforced polyamide materials that are permanently exposed to extremely high temperatures (>200 °C) during use. For example, this is the case with turbochargers, which ensure extremely high pressures and temperatures in the engine compartment, especially in the charge air section. In a turbocharged diesel engine, there are temperatures of up to 240 °C between the turbocharger and the charge air cooler. In this context, polyamide components made of polyamide compositions containing additives that "form a barrier" are used. They are, for example, charge air cooler end caps, resonators, and charge air pipes.

[0010] The prior art to date has described partially aromatic polyamide compositions containing glass fibers and polyols, which have significantly improved long-term stability at extremely high temperatures. WO2010 / 014785A1 discloses glass fiber-reinforced partially aromatic polyamides for the high-temperature range, which additionally contain polyols and secondary aromatic amines or sterically hindered amines (or combinations of these two classes of substances). To date, no solution has been proposed for non-reinforced polyamide compositions in the low-temperature range.

[0011] Another possibility for stabilizing polyamides in the temperature range above 180 °C is described in EP2641932A1 and EP2828322. By adding iron salts, such as iron oxalate, either alone or in combination with another heat stabilizer such as a copper salt-based additive, the retention time in the high-temperature range can be significantly extended. In these methods, a high-temperature treatment to produce a surface barrier layer is considered essential. To reduce the carbonization effect that occurs in this case, EP 1 780 241 A1 proposes the use of nanoscale fillers.

[0012] EP3115407A1 relates to a heat-stabilized polyamide-based composition based on iron oxalate and dipentaerythritol in combination with each other for the temperature range above 180 °C.

[0013] EP3059283 discloses various polyamide compositions having improved heat resistance for electrical applications, which contain substances having a polyol structure and having at least an epoxy group or a carbodiimide group. Thereby, a coupling reaction with the polyamide can be achieved, which is important for the technology disclosed in EP 3059283. The tendency of the polyol to migrate into the polyamide is minimized by reactive coupling with the polyamide matrix. However, the preparation of such polyols having additional reactive epoxy groups or carbodiimide groups is complex and costly and has therefore not been implemented in practice. A polyol component that is chemically directly coupled to the polyamide matrix is also disclosed in EP 2 829 576 A1.

[0014] EP2881439 describes a glass fiber-reinforced polyamide composition having improved heat resistance at high temperatures, which composition contains a polyol and a copolymer of an olefin and at least one methacrylate or acrylate defined by MFI. In the examples mentioned, the polyamide material is aged at 200 °C. Similar compositions are also disclosed in EP 2 878 630 A1. However, it is considered here that the polyamide composition must contain partially aromatic polyamides or polyamide 4 / 6. However, this document does not show stabilization by iron compounds or reinforcing materials such as glass fibers in the sense of the present invention described below.

[0015] EP 3093312A1 discloses a polyamide composition having improved heat resistance at high temperatures above 180 °C, which contains a citrate, dipentaerythritol and at least one filler or reinforcing material in addition to the polyamide.

[0016] CN 108070253 A discloses a polyamide composition. Here, it is adapted to the stability at high temperatures of 200 °C or higher. Therefore, the described composition must contain nanoparticles having a specific particle size. In addition, a halogen-containing and / or copper-containing stabilizer is used. It is not shown in this document that, as described in the following specification of the present invention, iron compounds and / or reinforcing materials exhibit a stabilizing effect, especially in a composition without a copper-containing and / or halogen-containing stabilizer. JP 2019116607 A describes a composition having good surface gloss. What is important here is the use of halogen-containing components, especially alkaline earth metal halides.

[0017] Another type of polyamide composition, where the stability at elevated temperatures represents a particular challenge, is impact-modified polyamide. In this case, due to the presence of a polyamide component and a rubber-elastic polymer component, the particular challenge lies in achieving temperature stability despite the chemically very different main polymer components. This problem is particularly pronounced under a temperature load above 140 °C.

[0018] Object of the invention

[0019] Due to the continuously increasing fields of application of plastic-based materials, such as in the automotive field, there is a search for better stabilizing components, especially for a continuous use temperature of 100 °C to 170 °C, such as especially 150 °C, and particularly also for polyamides, especially those with aliphatic units. In this context, a traditional practical requirement for non-reinforced polyamides is that when the polyamide material is thermally aged at 150 °C, the half-life of its tensile strength is at least 2000 hours, or even at least 3000 hours depending on the application. In combination with this, other requirements to be met are having no or only a minor impact on electrical properties such as tracking resistance and no increase in the tendency to corrosion. These points are very important for use in the electronics and electrical industries. The expansion in the field of electric vehicles additionally increases the demand for materials that meet the special requirements of this field. For example, although the requirements for thermal stability further remain high or even become more stringent, the use of ionic stabilizer systems must be largely abandoned. The stability of polyamides, especially the product properties related to electrical applications, must be ensured over a long period of time, while also requiring thermal stability in a higher temperature range (such as a large amount of heat released during rapid battery discharge, etc.). These requirements that cannot be achieved with traditional systems (and sometimes are contrary to them) must be reliably met for the expansion of electric vehicles. To improve the stability of substantially aliphatic reinforced polyamides under load at a temperature in the range of 100 to 170 °C (typical value 150 °C), a practical requirement is that when the reinforced polyamide material is thermally aged at 150 °C, the tensile strength drops by at most 10% even after 1000 hours. In combination with this, other requirements to be met are having no or only a slight impact on electrical properties such as tracking resistance, and no increase in the tendency to corrosion. These points are very important for applications in the electronics and electrical industries. In addition, at the same time, the reinforced polyamide material is required to have good processability and fluidity.

[0020] On the other hand, there is a need for systems for stabilizing impact-modified polyamides, especially at high temperatures above 140 °C.

[0021] Therefore, the object of the present invention is to provide a method that can achieve the required stability at the above-mentioned continuous use temperature, that is, especially enabling polyamide compositions to have improved long-term stability for heating in a wide range (even at high temperatures above 150 °C and up to 170 °C and in special cases even above 170 °C), and at the same time, at temperatures below 150 °C, effectively stabilizing in terms of significantly extending the possible service life, preferably in at least one option of a) to c), especially a) and b), and c), optionally c) and b):

[0022] a) being suitable for electrical applications simultaneously (low ionic component content);

[0023] b) and with regard to the suitability for reinforced and unreinforced polyamides;

[0024] c) Also for impact-modified polyamides.

[0025] Here, it is also important that the object is achieved in such a way that it can also be applied without problems on an industrial scale. This includes, for example, suppressing as much as possible the formation of unwanted soiling layers when using polyols or other additives known in the field of polyamides. The formation of such soiling layers can occur on the one hand on the manufactured polyamide molded parts, which, in addition to impairing the aesthetics, also leads to a reduction in the stabilizing effect (since these substances can no longer perform their functions), and on the other hand, the formation of soiling layers can also occur on the equipment used in production, which can lead to production interruptions (for example, by shortening the production cycle, because production has to be stopped to clean the equipment). With the technical solution of the object described here, such problems should not occur or should only occur within reasonable limits. Summary of the Invention

[0026] The object is achieved by the subject matter of claims 1 and 2 and by the subject matter of the independent claims. Preferred embodiments are given in the dependent claims and in the following description.

[0027] The following description particularly includes a detailed description of substantially aliphatic unreinforced and reinforced polyamide materials. Those skilled in the art will understand that these descriptions can also be used in a similar manner for the claimed and disclosed uses and the described methods and are effective for them. Similarly, those skilled in the art will understand that these descriptions are equally applicable to partially aromatic polyamides and impact-modified polyamides. Detailed Description of the Invention

[0028] Surprisingly, the present invention can achieve the required stability of polyamides by using components that are already known but have hitherto been known in other contexts or for other methods in the prior art. However, in the case of simultaneous suitability for electrical applications, significantly improved stability can be achieved at a sustained use temperature of 100 °C to 170 °C, particularly 150 °C. Here, the stabilizers used according to the invention can be well dispersed in the polyamide, making it easy to handle. The stabilizers according to the invention can be introduced into the polyamide by conventional methods and distributed there; furthermore, the stabilizer components can be simply used in a compounded manner, for example, prepared by compounding with a matrix of common materials such as waxes or polymers. Therefore, the present invention can also achieve the following advantages:

[0029] 1. Improve the stability of unreinforced and reinforced polyamides against long-term continuous loads at the temperatures mentioned. Delay the elimination and reduction of the relevant functional properties for as long as possible, particularly maintain the mechanical properties for as long as possible.

[0030] 2. This can be achieved with essentially aliphatic polyamides or with partially aromatic polyamides. At the same time, the principles described here can also be applied to polyamides impact-modified by adding suitable components (rubber-elastic components as blend components or grafted polyamides).

[0031] 3. The stabilized polyamides are particularly useful for electrical applications where high demands are placed on the absence of ionic components such as copper salts, halogen-containing alkali metal salts, etc.

[0032] 4. The amount of stabilizer or the type of stabilizer mixture can be matched to the desired stabilization time (service life of the product) and to the specific requirements taking into account the presence or absence of ionic components. Due to the very good stability obtained with the basic components according to the invention, it is possible, for example, to use a small amount of copper stabilizer to achieve a further improvement in stability without significantly affecting the electrical properties (tracking resistance) due to the very small addition of these components. This can be achieved in particular when using copper complexes.

[0033] 5. Due to the improved stability, the components can, if necessary, be formed thinner because the material thickness hitherto considered necessary (due to the required redundancy or corresponding safety factor) can be reduced (since the polyamides stabilized according to the invention can themselves withstand a longer time at a smaller material thickness).

[0034] Surprisingly, improved stability can be achieved when using polyol compounds or iron compounds without having to use the activation by heat treatment described in the prior art as necessary to produce a barrier layer. This is particularly advantageous since very thin components can thus also be manufactured where it is not possible to produce a barrier layer (carbonization of the surface) since otherwise the mechanical properties would be unacceptably impaired.

[0035] Important for the present invention is on the one hand the use of a polyol component, preferably a polyol having 2 or more 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 (and mixtures thereof), in particular dipentaerythritol. In another preferred embodiment, the polyol is a dendritic polymer having terminal OH groups. The molecular weight of such a dendritic polymer is preferably 1000 to 2000 g / mol. In this case, the number of hydroxyl groups is preferably 6 to 60 hydroxyl groups. An example is a hydroxyl-functional dendritic polyester formed by the polymerization of a polyol core with 2,2-dimethylolpropionic acid and having good thermal stability. In another embodiment, sugar alcohols and cycloalcohols can also be used as polyol compounds, where mannitol, erythritol and inositol are preferred.

[0036] A second alternative according to the invention is to use iron compounds, preferably iron(II) compounds, in particular iron oxalate.

[0037] According to the invention, these components are used together with the reinforcing materials described herein, or in the case of using polyol compounds, together with copper-free and halogen-free antioxidants, or together with the reinforcing materials described herein and additionally with copper-free and halogen-free antioxidants.

[0038] The amount of the polyol component is generally 0.1 to 7% by weight (all data, including those below, for example for iron compounds, are based on the entire compound), preferably 0.5 to 5% by weight, particularly preferably 1 to 4% by weight, especially 1 to 3% by weight.

[0039] The amount of the iron compound is generally 0.1 to 1% by weight, especially 0.2 to 0.6% by weight

[0040] According to the invention, it is preferred to use the polyol component.

[0041] The copper-free and halogen-free antioxidant is preferably a secondary aromatic amine or a sterically hindered phenol, which is usually used in combination with a phosphite (this combination is also referred to as a phenolic antioxidant hereinafter, or this combination is included as an antioxidant when naming the sterically hindered phenol). A combination of copper-free and halogen-free antioxidants is also possible. However, it is preferred to use a secondary aromatic amine or a sterically hindered phenol alone (usually in combination with a co-antioxidant such as a phosphite), without using other copper-free and halogen-free stabilizers.

[0042] The secondary aromatic amines used in the present invention can be either monomeric or polymeric secondary aromatic amines. Preferably, the molecular weight of these components is 260 g / mol or higher, more preferably 350 g / mol or higher. A secondary aromatic amine is a compound in which the amine-nitrogen atom is linked to two organic substituents, at least one, preferably both substituents being aromatic. Suitable examples are 4,4'-bis(α,α-dimethylbenzyl)diphenylamine (commercially available, for example, under the name Naugard 445), p-(p-toluenesulfonamido)diphenylamine (commercially available, for example, under the name Naugard SA), the reaction product of diphenylamine and acetone (commercially available, for example, under the name Aminox), N,N'-di-(2-naphthyl)-p-phenylenediamine, 4,4'-bis(α-methyldiphenylmethyl)diphenylamine and other compounds known to those skilled in the art, such as those disclosed in EP 0 509 282 B1.

[0043] However, amine stabilizers having both aromatic substituents and aliphatic substituents are equally suitable, i.e. for example alkyl-aryl-substituted amines or alkyl-aryl-substituted phenylenediamines. Examples are phenylenediamines such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, or N-phenyl-N'-isopropyl-p-phenylenediamine. Within the scope of the present invention, systems based on 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ), preferably polymeric TMQ, can also be used. Condensation products of diphenylamine, such as alkylated diphenylamine or arylated diphenylamine, with ketones and / or aldehydes are also possible. Here, the condensation products are preferred, which can also be oligomers or polymers, for example condensation products obtained from diphenylamine and acetone or obtained from diphenylamine and acetone and formaldehyde.

[0044] In this case, surprisingly, these amines show better results than, for example, known HALS stabilizers.

[0045] The amount of secondary aromatic amine is generally from 0.05 to 3% by weight (all data are based on the amount of polyamide), preferably from 0.1 to 2% by weight, particularly preferably from 0.25 to 1.5% by weight, especially from 0.5 to 1.25% by weight.

[0046] Suitable sterically hindered phenols are compounds in which there are steric filling substituents such as tert-butyl adjacent to the phenolic hydroxyl group. A particularly suitable example of such a stabilizer is 2,6-di-tert-butyl-methylphenol. However, of course, other such stabilizers can also be used, including also dimeric structures, i.e. two phenolic groups connected by a suitable organic unit, such as 2,2'-methylenebis(6-tert-butyl-4-methylphenol) etc., as well as bifunctional phenols, thiobisphenols such as 4,4'-thio-bis-6(tert-butyl-m-cresol), polyfunctional phenols, polyphenols, for example reaction products of butylated p-cresol with dicyclobutadiene.

[0047] The amount of the phenolic component is generally from 0.01 to 3% by weight (all data are based on the amount of polyamide), preferably from 0.1 to 2% by weight, particularly preferably from 0.25 to 1.5% by weight, especially from 0.5 to 1.25% by weight.

[0048] The fillers and reinforcing materials used according to the invention can be present in the form of fibers or particles (or any transitional form). Suitable are organic and inorganic fillers and reinforcing materials. Preferred examples are glass fibers, carbon fibers, glass spheres, ground glass, diatomaceous earth, wollastonite, talc, kaolin, layered silicates, CaF2, CaCO3 and alumina. Nanoscale materials can also be used, especially those in which the one-dimensional D50 value is less than 900 nm.

[0049] Suitable as nanoscale fillers are substances that can be added at any stage of production and are finely dispersible in the nanoscale here. The alternative nanoscale fillers according to the invention can be surface-treated. However, untreated fillers or mixtures of untreated and treated fillers can also be used. The nanoscale fillers preferably have a particle size of less than 500 nm in at least one dimension. The fillers are preferably minerals that already have a layered structure, such as layered silicates and double hydroxides.

[0050] The nanoscale fillers used according to the invention are preferably selected from oxides and oxide hydrates of metals or metalloids. In particular, the nanoscale fillers are selected from oxides and oxide hydrates of the following elements: boron, aluminum, calcium, gallium, indium, silicon, germanium, tin, titanium, zirconium, zinc, yttrium or iron.

[0051] In a specific embodiment of the invention, the nanoscale filler is silica or silica hydrate. In one embodiment, the nanoscale filler is present as a uniformly dispersed layered material in the polyamide molding compound. Before entering the matrix, their layer thickness is 0.7 to 1.2 nm, and the spacing between the mineral layers is at most 5 nm.

[0052] The minerals that already have a layered structure and are preferred according to the invention are natural and synthetic layered silicates and double hydroxides, such as hydrotalcite. According to the invention, nanoscale fillers based on silicone, silica or silsesquioxane are also suitable.

[0053] The layered silicates in the sense of the present invention are understood to mean 1:1 and 2:1 layered silicates. In these systems, the layers of SiO4 tetrahedra are regularly connected to the layers of M(O,OH)6 octahedra. Here, M represents a metal ion, such as Al, Mg, Fe. In the case of 1:1 layered silicates, one tetrahedral layer and one octahedral layer are connected to each other respectively. Examples of this are kaolin minerals and serpentine minerals.

[0054] In the case of 2:1 layered silicates, in each case, two tetrahedral layers and one octahedral layer are combined. If not all octahedral sites are occupied by cations required to compensate for the negative charges of the SiO4 tetrahedra and hydroxide ions, charged layers occur. This negative charge is balanced by introducing monovalent cations such as potassium, sodium or lithium or divalent cations such as calcium into the space between the layers. Examples of 2:1 layered silicates are talc, vermiculite, illite and smectite, where smectite also includes montmorillonite, which can be easily swollen by water due to their layer charge. In addition, cations can be easily obtained through the exchange process.

[0055] The nano-fillers are preferably selected from natural and synthetic layered silicates, in particular from the group consisting of bentonite, smectite, montmorillonite, saponite, beidellite, nontronite, hectorite, talc, vermiculite, illite, pyrosite, kaolin minerals and serpentine minerals, double hydroxides, or such fillers based on silicone, silica or silsesquioxane, with montmorillonite being particularly preferred.

[0056] The fillers and reinforcing materials can also be surface-treated. Surface modification based on aminoalkylsilanes or aminoalkylsiloxanes or aminoalkyltrialkoxysilanes is particularly preferred.

[0057] Particularly preferably, fibrous reinforcing materials, in particular glass fibers (particularly preferably made of E-glass) and carbon fibers, are used on the one hand, and glass spheres are used as non-fibrous reinforcing materials on the other hand. In the context of the present invention, the use of glass fibers and glass spheres is due to their good availability and favorable price basis and especially due to their particularly good effect. Glass spheres and glass fibers can also be used in combination. Here, the glass fibers are particularly used in the form of short glass fibers for the preparation of polyamide materials for injection molding and / or extrusion. If the method according to the invention is to be used for the preparation of high-modulus composite materials, glass fibers are preferably used as continuous fibers and / or long glass fibers. In the case of such composite materials, the preparation of the pre-concentrates with reinforcing materials (long glass fibers or continuous glass fibers) described below is of course not feasible. However, when preparing such composite materials, other pre-concentrates can also be used, also with other reinforcing materials, such as short glass fibers, glass spheres or other particulate reinforcing materials. In addition, multiple fiber materials can also be used in combination. When using glass spheres, hollow or filled glass spheres can be used. In particular, solid glass spheres made of borosilicate glass or silicate glass with a diameter of 5 to 250 μm, so-called "microspheres", are used.

[0058] It is known from the prior art (which has also been confirmed within the scope of the present invention) that during aging at a temperature of 90 to 170 °C when using polyol compounds, the polyol compounds can migrate significantly to the surface. Such aging experiments are measurements of the properties of the test materials at the service temperature that occurs during the use of the corresponding polyamide molded parts. This migration results in the formation of a severe soiling layer on the surface of the polyamide molded body, fiber, monofilament or foil. This surface soiling layer has a negative impact on electrical properties such as the CTI value. In addition, they are very unsightly in terms of visual appearance and interfere with the adhesion properties within the scope of gluing, painting or other surface treatments. Due to this problem, it is usually not possible to use polyol compounds at these service temperatures (in the test series: aging temperature).

[0059] Accordingly, another object of the present invention is to overcome the said problems and to provide compositions and polyamide moldings prepared therefrom, which particularly contain polyol compounds and, however, show a significantly reduced tendency to form a surface staining layer when subjected to thermal aging at <170 °C.

[0060] Surprisingly, this problem can be solved by adding, in addition to the polyol compound, a high concentration of glass beads and / or fibrous reinforcing materials, preferably carbon fibers and / or glass fibers, particularly preferably glass fibers, to the polyamide (which results in a fiber-reinforced polyamide composition); or by first adding the polyol compound together with glass beads or with fibrous reinforcing materials, preferably carbon fibers and / or glass fibers, particularly preferably glass fibers, to a carrier, preferably a polymeric carrier. As a special embodiment, glass beads and glass fibers can also be added to the pre-concentrate simultaneously. In the first step, the pre-concentrate is prepared in a manner known to those skilled in the art together with a carrier, preferably a polymeric carrier. Here, for example, the polyol compound, a copper-free antioxidant and glass fibers are introduced into the melt and evenly distributed in the polymeric carrier. Then, this additive is incorporated into the polyamide to be modified in the melt. This can also be carried out when preparing high-modulus composites with long glass fibers or continuous fibers as described above. In the case of other polyamides to be modified, the content of glass fibers (or carbon fibers or glass beads) can be kept very low in this way, and it is no longer necessary to additionally meter in glass fibers or glass beads during the kneading of the polyamide (to avoid blooming of the polyol compound). This variant results in polyamide compositions with such a low proportion of fibers or glass beads that they can be regarded as non-reinforced polyamide compositions. Here, the addition of fibers or beads to the pre-concentrate (polyol masterbatch) serves only to prevent the polyol compound from migrating to the surface of the molding under the use conditions involving elevated temperatures.

[0061] According to the present invention, the polyamide and the stabilizer component are melted together and mixed, or kneaded by a suitable method (especially when using glass fibers or glass beads). Alternatively, the polyamide is first melted and then the stabilizer component is incorporated, for example, in the form of a blend. In a preferred embodiment, the stabilizer component is added to the molten polyamide in the form of a premix (concentrate or masterbatch).

[0062] If a pre-concentrate of the stabilizer component is used, the pre-concentrate can be prepared in a discontinuous mixer that enables very good uniform distribution, such as in a Buss kneader. However, continuous mixers are usually used, such as, preferably, twin-screw extruders or ZSK extruders. Here, the same polyamide can be used as the matrix material, which is then mixed with the pre-concentrate. However, other polyamides or other polymers or non-polymeric materials can also be selected. Optionally, other additives can be added during the preparation of the masterbatch.

[0063] In another preferred embodiment in combination with one of the embodiments mentioned above or below, the additive according to the invention further comprises at least one additional ingredient selected from the following: antioxidants, nucleating agents, stabilizers, lubricants, release agents, slip agents, fillers, colorants, flame retardants and fire retardants, plasticizers, impact modifiers, antistatic agents, processing aids, and other polymers or mixtures thereof commonly compounded with polyamides. The additive particularly preferably further comprises a nucleating agent and / or a lubricant. Thereby, the modified additive and the additives further required for the desired final application can be introduced into the polyamide in one processing step. This simplifies polyamide processing because the incorporation process and the mixing stage can be additionally omitted.

[0064] In a preferred embodiment in combination with one of the embodiments mentioned above or below, the pre-concentrate is provided in the form of a mixture of one or more additives and a carrier. Preferably, the carrier is a polymer carrier which can be easily incorporated into the polyamide to be modified and can be easily dispersed or dissolved therein. In addition, the polymer carrier is preferably thermally stable at the typical processing temperatures of polyamides, contains or forms as few volatile components as possible and does not change color during processing.

[0065] Preferably, the polymer carrier is selected from polymers or copolymers of the following monomers: ethylene, propylene or other olefins, methacrylic acid, vinyl acetate, acrylic acid, acrylates, or methacrylates. Particularly preferably, the polymer carrier is an ethylene-vinyl acetate copolymer (EVA) or an olefin-acrylate copolymer or an olefin-methacrylate copolymer, in particular an ethylene-methyl acrylate copolymer (EMA), an ethylene-ethyl acrylate copolymer (EEA) or an ethylene-butyl acrylate copolymer (EBA). Particularly preferably, ethylene-methyl acrylate copolymer (EMA) or ethylene-vinyl acetate copolymer (EVA) is used as the carrier. It has surprisingly been shown that the migration tendency of the polyol component can be significantly reduced by using the copolymers described herein as the carrier of the pre-concentrate. When using the copolymers described herein as the carrier component of the polyol-containing pre-concentrate, this effect is particularly pronounced and is therefore preferred within the scope of the present invention.

[0066] In one embodiment, the carrier is a polyamide, and all common polyamides are possible, preferably PA6 or PA6.6.

[0067] As a further embodiment, it is also possible to use a polymer carrier material having reactive groups, for example a copolymer of an olefin with maleic anhydride or glycidyl methacrylate. Examples are ethylene-ethyl acrylate-glycidyl methacrylate terpolymer (E-EA-GMA), ethylene-butyl acrylate-glycidyl methacrylate terpolymer (E-BA-GMA), ethylene-vinyl acetate copolymer functionalized with maleic anhydride (E-VA-MA), styrene-ethylene-butene-styrene copolymer functionalized with maleic anhydride (SEBS-MA).

[0068] Surprisingly, it has been shown that when using such polymers, in particular copolymers of olefins with vinyl acetate or acrylate or methacrylate, the formation of a soiling layer on the manufactured polyamide workpiece is reduced, which is advantageous since on the one hand a possibly disturbing soiling layer on the workpiece is suppressed and on the other hand no residues occur in the mold during the production of the polyamide workpiece, so that production can be carried out for a long time without cleaning.

[0069] In another embodiment, it is also possible to use non-polymeric carriers. Examples are lubricants such as primary and secondary fatty acid amide waxes, such as ethylene-bis-stearamide (EBS), erucamide and stearamide, metal soaps such as metal stearates, paraffin waxes, polyolefin waxes, Fischer-Tropsch waxes, fatty acid esters of pentaerythritol, polar synthetic waxes (such as oxidized polyolefin waxes or grafted polyolefin waxes) or other waxes, and also other substances known as additives for polyamides. Preferred are EBS, erucamide, long-chain esters of pentaerythritol and oxidized polyolefin waxes.

[0070] In a preferred embodiment, the carrier, preferably a polymer carrier, ideally has a melting point below the melting point of the polyamide to be processed. On the one hand, this enables the additive to be gently and energy-efficiently introduced into the carrier during the preparation of the pre-concentrate, and moreover this simplifies the introduction into the polyamide.

[0071] However, it is also possible to add stabilizing components during the preparation of the polyamide, i.e. the monomer mixture. Thereby very good thorough mixing can be achieved without an additional mixing process, which reduces production costs and time.

[0072] However, the additives and / or additional materials mentioned can also be used alone in the process according to the invention, for example by being metered in individually during the preparation of the polyamide stabilized according to the invention.

[0073] According to the invention, all common polyamides can be stabilized and used within the scope of the invention. Polyamides are polymers having repeating carbonamide groups -CO-NH- in the main chain. They are formed from the following substances:

[0074] (a) an aminocarboxylic acid or a functional derivative thereof, such as a lactam; or

[0075] (b) a diamine and a dicarboxylic acid or a functional derivative thereof.

[0076] A variety of polyamides can be obtained by varying the monomer structural units. The most important representatives are aliphatic polyamides, such as polyamide 6 from ε-caprolactam, polyamide 6.6 from hexamethylenediamine and adipic acid, polyamide 6.10 and 6.12, polyamide 10.10, polyamide 12.12, polyamide 11, polyamide 12, PACM-12, and polyamide 6-3-T, PA4.6, and partially aromatic polyamides (polyphthalamide PPA), such as PA6T, PA6T / 6I, or PA6T / 6.6. Impact-modified polyamides can also be used within the scope of the present invention, which includes grafted polyamides and mixtures of polyamides with modifying components such as rubber elastic polymers.

[0077] The impact-modified polyamides to be used within the scope of the present invention are especially polyamides compounded with impact modifiers, elastomers, and / or rubbers. Examples of such components are EPM or EPDM rubbers, elastomeric copolymers derived from ethylene and acrylic monomers, ABS elastomers, ASA elastomers, NR elastomers, SES elastomers, SEBS elastomers, or SIS elastomers, butadiene-based elastomers, isoprene-based elastomers, silicone rubbers, and mixtures thereof. These elastomeric impact modifiers are present in mixing ratios with polyamides known to those skilled in the art.

[0078] However, according to the present invention, all other polyamides can also be stabilized, such as other copolyamides or copolymers of polyamides with other segments, such as with polyesters. Blends of different polyamides and blends of polyamides with other polymers can also be stabilized. Herein, polyamide 6, polyamide 6.6, and copolyamides derived from amide 6 and polyamide 6.6 are particularly preferred.

[0079] Accordingly, the present invention provides a system that can reliably stabilize polyamides over a wide temperature range, which includes temperatures below 150 °C and also includes temperatures of 150 °C or higher. In particular, the temperature range of 150 °C or higher extends up to 160 °C or higher, including 170 °C. Thus, the present invention can achieve stabilization in the desired temperature range (100 °C to 170 °C), whereby copper compounds can be dispensed with, and halogen compounds can also be dispensed with, while the high-temperature treatment for generating a barrier layer described in the prior art can be dispensed with. Thus, the stabilized polyamide composition in this aspect of the present invention preferably contains only the copper-free and halogen-free system described herein for stabilizing temperature as a stabilizer. However, within the scope of the present invention, in application fields where this is permitted, the use of these components is not excluded. Thus, in particular as demonstrated by the following experimental data, an overall improved system is provided, whereby a significantly extended stabilization period can also be achieved.

[0080] In another embodiment, the polyol can also be combined with a copper stabilizer, preferably based on a copper complex (particularly preferably based on a copper complex combined with a non-ionic halogen-containing synergist). This additionally allows for improved long-term stability even at temperatures above 160 °C. In this case, an upstream sealing process for forming a protective layer is also not required. Furthermore, this combination allows for formulating a material with a low copper and halogen content, such that the electrical properties of the corresponding material are only slightly adversely affected or not at all. This is particularly applicable when using copper complexes and organic halogen compounds, as they have a minimal (adverse) impact on the electrical properties.

[0081] Furthermore, the polyamide composition based on the main components described herein stabilized with the present invention simultaneously achieves a very high tracking resistance. Furthermore, this high tracking resistance is not adversely affected after thermal aging. This also allows for use in fields where a high tracking resistance with a CTI value (Comparative Tracking Index) of 600 V (for non-reinforced polyamide) is required. This is demonstrated by the experiment for evaluating the blooming of the polyol component described below.

[0082] Surprisingly, in relation to the present invention, by combining the polyol component with specific synergists (i.e., reinforcing materials or halogen-free and copper-free antioxidants), as defined in claims 1 to 9, an unexpectedly improved stabilization of polyamides can be achieved, which exceeds conventional copper stabilizers and cannot be achieved with other combinations. This is particularly also confirmed in the following examples, where the conventional systems as well as the iron-based stabilizers described in the prior art cannot achieve the effects with the combinations according to the present invention.

[0083] The copper stabilizers that can be optionally used according to the present invention can be freely selected. Typical examples include mixtures of two main components, namely copper compounds and specific halogen-containing compounds (also referred to herein as synergists). The copper compounds used can be any copper salts (CuI, CuBr, copper acetate, CuCN, copper stearate,...) or any other copper compounds, such as CuO, Cu2O, copper carbonate or any complex of copper. The synergist used according to the present invention is a halogen-containing component, such as halogenated polymers, alkali metal or alkaline earth metal salts (such as KI, KBr, etc.), or organic compounds having halogen substituents, such as halogen-containing aromatic or aliphatic phosphates.

[0084] These two components are generally used in amounts to give a Cu:halogen ratio of 1:1 to 1:50 (molar ratio), preferably 1:4 to 1:20, more preferably 1:6 to 1:15.

[0085] The amounts of copper and halogen in the polyamide are selected according to the desired use of the polyamide and the desired additional stability. The amount of copper used herein is not limited as long as the mechanical properties of the polyamide are not adversely affected. However, with regard to the stabilized polyamides provided in the foregoing part within the scope of the present invention that have good performance in electrical applications, this additional copper stabilizer is used only in small amounts in an optional manner to achieve particularly good stability. For conventional stabilization, the amount of copper used is 1 to 1000 ppm Cu, preferably 3 to 200 ppm Cu, more preferably 5 to 150 ppm Cu. Within the scope of the present invention, the amount of copper used is generally in a lower range, i.e., preferably 200 ppm or less, especially 150 ppm or less, more preferably 100 ppm, 75 ppm or 50 ppm or less. Accordingly, the amount of the synergist (based on ppm halogen respectively) is derived from the ratio disclosed above. The addition amount of the synergist is not particularly limited. However, an addition amount exceeding 1% generally does not result in an improvement in the stabilizer effect. The amount used is generally 10 to 10,000 ppm. The preferred amount is 30 to 2000 ppm, more preferably 50 to 1500 ppm.

[0086] Optional copper complexes used according to the present invention are complexes of copper with ligands such as triphenylphosphine-based, mercaptobenzimidazole-based, glycine, oxalate, and pyridine. Chelating ligands such as ethylenediaminetetraacetate, acetylacetonate, ethylenediamine-based, diethylenetriamine-based, triethylenetetramine-based, phosphine chelating ligands, or bipyridine-based can also be used. Examples of preferred phosphine chelating 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'-binaphthalene.

[0087] These ligands can be used alone or in combination to form complexes. The syntheses required for this are known to those skilled in the art or described in the specialized literature of coordination chemistry. Generally, in addition to the above ligands, these complexes can also contain conventional inorganic ligands such as water, chloride ions, cyano ligands, etc.

[0088] Copper complexes with complexing ligands such as triphenylphosphine-based, mercaptobenzimidazole-based, acetylacetonate, and oxalate are preferred. Triphenylphosphine-based and mercaptobenzimidazole-based are particularly preferred.

[0089] Preferred copper complexes used according to the present invention are generally formed by the reaction of copper(I) ions with phosphine compounds or mercaptobenzimidazole compounds. For example, these complexes can be obtained by the reaction of triphenylphosphine with copper(I) halide suspended in chloroform (G. Kosta, E. Reisenhofer, and L. Stafani, J. Inorg. Nukl. Chem. 27 (1965) 2581). However, copper(II) compounds can also be reductively transformed with triphenylphosphine to obtain copper(I) addition compounds in this way (F. U. Jardine, L. Rule, A. G. Vohrei, J. Chem. Soc. (A) 238 - 241 (1970)).

[0090] However, the complexes used in an optional manner according to the present invention can also be prepared by any other suitable method. Suitable copper compounds for preparing these complexes are copper(I) salts or copper(II) salts of hydrohalic 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.

[0091] In principle, all alkylphosphines or arylphosphines are suitable. Examples of phosphines that can be used according to the present invention are triphenylphosphine (TPP), substituted triphenylphosphines, trialkylphosphines and diarylphosphines. An example of a suitable trialkylphosphine is tri-(n-butyl)phosphine. Generally, triphenylphosphine complexes are more stable than trialkylphosphine complexes. In addition, from an economic point of view, triphenylphosphine is also preferred due to its commercial availability.

[0092] Examples of suitable complexes can be presented by the following formula:

[0093] [Cu(PPh3)3X], [Cu2X2(PPh3)3], [Cu(PPh3)X]4 and [Cu(PPh3)2X], where X is selected from Cl, Br, I, CN, SCN or 2-MBI.

[0094] However, the complexes that can be used alternatively according to the present invention may also contain other complex ligands in addition. Examples are bipyridine (e.g., CuX(PPh3)(bipy), where X is Cl, Br or I), biquinoline (e.g., CuX(PPh3)(biquin), where X is Cl, Br or I) and 1,10-phenanthroline, o-phenylenebis(dimethylarsine), 1,2-bis(diphenylphosphino)ethane and terpyridine.

[0095] The copper salts that can be used alternatively according to the present invention can be any arbitrary copper salts.

[0096] Preferably salts of monovalent or divalent copper with inorganic or organic acids.

[0097] Examples of suitable copper salts are copper(I) salts such as CuI, CuBr, CuCl or CuCN, copper(II) salts such as CuCl2, 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.

[0098] In addition, compounds such as copper acetylacetonate or copper EDTA can also be used. Mixtures of different copper salts can also be used. Optionally, copper powder can also be used.

[0099] The synergists used alternatively for the copper component according to the present invention are not limited by the above; in addition to alkali metal halides, especially KI and KBr, halogenated polymers are preferred, organic compounds having a halogen as a substituent, such as halogen-containing aromatic compounds, such as brominated polystyrene or poly(pentabromobenzyl) acrylate, and halogen-containing aromatic and aliphatic phosphates or phosphonates, such as tri(haloaromatic) phosphates or phosphonates, for example tris(2,4-dibromophenyl) phosphate, tris(2,4-dichlorophenyl) phosphate and tris(2,4,6-tribromophenyl) phosphate.

[0100] Examples of halogen-containing aliphatic phosphates are tri(haloalkyl) phosphates or phosphonates. Tri(bromoalkyl) phosphates (brominated aliphatic phosphates) are preferred. In particular, in these compounds, no hydrogen atom is bonded to the alkyl-C atom in the α-position of the C-atom bonded to the halogen. Thus, no dehydrohalogenation reaction occurs. Example compounds are tris(3-bromo-2,2-bis(bromomethyl)propyl) phosphate, tris(dibromoneopentyl) phosphate, tris(trichloroneopentyl) phosphate, tris(chlorodibromoneopentyl) phosphate, and tris(bromodichloroneopentyl) phosphate. Tris(dibromoneopentyl) phosphate and tris(tribromoneopentyl) phosphate are preferred.

[0101] Particularly preferred herein is brominated polystyrene which is halogenated, especially bromine-substituted on the aromatic ring.

[0102] However, as described above, the present invention achieves the required stability by using the main components defined in the claims and above, and thus the present invention is particularly also capable of operating without copper-containing and without halogen-containing components. In an embodiment, the polyamide composition stabilized by the present invention thus does not contain a copper-containing component / compound; or does not contain a halogen-containing compound, especially a halide of an alkali metal and / or alkaline earth metal element; or does not contain a copper-containing component / compound and does not contain a halogen-containing compound, especially a halide of an alkali metal and / or alkaline earth metal element.

[0103] The corrosion problem, especially electrocorrosion, is crucial in the use of polyamides. In this case, halogens, especially bromine and chlorine, and also iodine, are considered harmful to electronic components due to the interaction of halide anions with the intermetallic phase. Therefore, there is now a widespread demand in the electrical and electronic industries for reducing the halogen content. The present invention uses a halogen-free stabilizer, so there are no problems here. Even when a halogen-containing stabilizer is used within the scope of the present invention (as an additional stabilizer to produce, for example, specific performance characteristics), the amount used is small, so that there is no concern about electrocorrosion problems in these embodiments either, because due to good efficacy, a small dosage can be given, thereby complying with the corresponding limits.

[0104] The following examples illustrate the present invention.

[0105] In all examples, the polyamide was compounded in a conventional manner with the mentioned stabilizers, either directly or as a pre-concentrate in a carrier, and the mechanical and other properties to be tested were evaluated on specimens. The aging conditions are given separately.

[0106] Polyamide 6.6 (Ultramid A27 E) from BASF was used.

[0107] The kneading is carried out using a Leistritz twin-screw extruder ZSE27MAXX-48D.

[0108] The additives are added by weight measurement during kneading.

[0109] After drying, standard test bars for determining mechanical properties (ISO527) and impact resistance (ISO179 / 1eU), namely "Demag Ergotech 60 / 370-120concept", are manufactured from the kneaded material on an injection molding machine.

[0110] In a hot air circulation oven, the test samples are stored at the temperatures mentioned in the examples.

[0111] The measurements of elastic modulus [MPa], tensile strength [MPa] (elongation [%]), and breaking stress [MPa] (elongation [%]) are carried out in a tensile test according to ISO527 using a static material testing machine Zwick Z010.

[0112] The measurement of impact resistance is carried out according to ISO179 / 1eU in a Charpy impact bending test using a pendulum impact machine HIT PSW5.5J.

[0113] Compounds and abbreviations used:

[0114] Irganox 1098: N,N'-hexane-1,6-diylbis(3-(3,5-ditert-butyl-4-hydroxyphenylpropanamide))

[0115] Irgaphos 168: tris-(2,4-ditert-butylphenyl) phosphite

[0116] Naugard 445: 4,4'-bis(α,α-dimethylbenzyl) diphenylamine

[0117] Chimassorb 944: poly[[6-[(1,1,3,3-tetramethylbutyl)amino]-1,3,5-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-piperidyl)imino]-1,6-hexanediyl[(2,2,6,6-tetramethyl-4-piperidyl)imino]])

[0118] Iron oxalate is used in polyamide 6 in the form of a 5% iron(II) oxalate dihydrate masterbatch.

[0119] H324: Brüggolen H324, a stabilizer based on copper iodide and potassium iodide.

[0120] H3386: Brüggolen H3386, a stabilizer based on a copper complex with an organic halogen-containing synergist.

[0121] Copolymer A: Ethylene-methyl acrylate copolymer

[0122] Copolymer B: Ethylene-butyl acrylate copolymer

[0123] Copolymer C: Ethylene-vinyl acetate copolymer

[0124] Copolymer D: Ethylene-acrylic acid copolymer

[0125] Filler A: Calcined silica

[0126] Filler B: Montmorillonite

[0127] Filler C: Boehmite

[0128] Filler D: Glass beads with a particle size in the range of 35 μm

[0129] Example 1

[0130] The additives mentioned in Table 1 were kneaded with PA6.6 and the half-life of the tensile strength was determined.

[0131] Table 1: Stability of polyamide 6.6, un-reinforced, thermal aging at 150 °C

[0132]

[0133] The comparative examples of this table show that in the prior art to date, sufficient (i.e., a tensile strength half-life of at least 2000 hours) stability of un-reinforced polyamides can only be achieved with copper-based stabilizers (H324 and H3386). The efficiency of using phenolic or amine-based (secondary aromatic amine) stabilizers alone or in combination is not sufficient for this, even at very high concentrations, and this can even be counterproductive. The requirements of being copper-free and halogen-free simultaneously cannot be met with the known comparative variants to date. The combination of polyols according to the invention with phenolic or secondary aromatic amine-based antioxidants has led to success, with the combination with secondary aromatic amines alone showing the best results. In contrast, polyols alone show only a very slight effect even at high concentrations at 150 °C. In this temperature range, the combination of polyols and HALS stabilizers is also not suitable to a sufficient extent.

[0134] Example 2

[0135] The additives mentioned in Table 2a were kneaded with PA6.6, and the formation of a fouling layer was evaluated. For this purpose, the polyamide granules were stored in a hot air circulation oven at 150 °C for 68 hours, and then the formation of the fouling layer was visually evaluated. In the case of the examples according to the invention using pre-concentrates VK1 to VK13, the pre-concentrates with the compositions given here in the relevant copolymers A, B, C, or D were first prepared and then kneaded with the polyamide.

[0136] Pre - concentrate:

[0137]

[0138] The pre - concentrate is prepared on a twin - screw extruder Leistritz ZSE 27 MAXX 48D at 100 °C to 180 °C (in the corresponding temperature profile) with a production rate of 10 kg / h.

[0139] Table 2a: Formation of a fouling layer in polyamide 6.6 after aging at 150 °C in the case of using various stabilizers according to the invention and in the case of comparative examples

[0140]

[0141]

[0142] As shown by the results of the comparative variants in Table 2a, polyols tend to migrate and bloom during thermal storage. This effect was not observed when using secondary aromatic amines alone or stabilizers based on copper complexes alone. Although the combination of polyols and secondary aromatic amines according to the invention leads to a significantly enhanced migration tendency and to the formation of a significantly thicker fouling layer on the finished part (the index in Table 2a increases from rating 3 to rating 7), the stabilizing effect is very good. The same situation was similarly observed when polyols were combined with copper - based stabilizers. The examples according to the invention obtained by directly adding dipentaerythritol and Naugard 445 show an increased fouling layer formation (rating 7), but are excellent in terms of thermal stability. Since this fouling layer formation is a serious problem in many application areas, the present invention also aims to solve this problem. Therefore, another decisive additional object of the present invention is to significantly reduce this enhanced migration tendency, because otherwise the practical usability will be severely limited. It has been found that by using a suitable polymer pre - concentrate, the migration tendency of the additives according to the invention in non - reinforced polyamides during thermal storage can be significantly reduced. As shown by the results of using the filler - free pre - concentrate in Table 2a, in this case, the choice of the polymer carrier is very important for the successful reduction of the migration tendency. For example, the reduction of the migration tendency was not achieved with ethylene - acrylic acid copolymer, and the migration tendency was slightly reduced with ethylene - butyl acrylate copolymer. In contrast, in the case of using ethylene - methyl acrylate copolymer and in the case of using ethylene - vinyl acetate copolymer as the carrier material of the pre - concentrate, the migration tendency was significantly reduced.

[0143] Therefore, it is particularly effective and thus particularly preferred within the scope of the present invention to use a copolymer composed of an olefin and methyl acrylate or to use a copolymer composed of an olefin and vinyl acetate. Another important measure for reducing the formation of the contamination layer is to use fillers and reinforcing materials, and it is preferred to incorporate them into the pre-concentrate. Glass spheres or fibers are preferably used, and glass fibers or carbon fibers are particularly preferred. The experimental results of the variants with pre-concentrates VK6, VK7, VK8, VK9, VK10, VK11, and VK13 clearly demonstrate this. If a pre-concentrate without fillers is not used, it has been shown that when added to the polyamide to be modified during compounding, a high concentration of glass fibers (or other fibers or glass spheres or fillers), usually 20 - 40%, must be used to achieve a significantly reduced formation of the contamination layer. This concentration should be higher than 10% to obtain sufficient effect. However, surprisingly, directly incorporating glass fibers (or glass beads or carbon fibers, etc.) into the pre-concentrate is significantly more effective in reducing the formation of the contamination layer. Thus, even at low glass fiber contents of <5% and even <2% based on the finished compound respectively, the migration tendency and thus the formation of the contamination layer could be well suppressed. Similarly, this also applies when using glass spheres. Due to the small to very small content of fillers and reinforcing materials, the finished compound itself can be classified as not reinforced in principle. Another effective measure for minimizing the formation of the contamination layer is the combination of glass fibers and carbon fibers or glass fibers and glass spheres in the pre-concentrate. In this way, the formation of the contamination layer can be further minimized, and at the same time, the required fiber content can also be reduced (e.g., <0.5% carbon fiber and <1.0% glass fiber). Due to the low fiber content, the flow properties can be formed such that injection molding is very good and can have excellent flow properties. This shows that within the scope of the present invention, a module is provided, which makes it possible to purposefully control different requirements. Here, as shown by the listed results, the selection of the polymer carrier material, the selection of the filler / reinforcing material, and the concentration of the components in the pre-concentrate are important influencing factors for the results to be obtained. By appropriately selecting and combining the polymer carrier material and the filler in the pre-concentrate, the formation of the contamination layer during thermal storage can even be completely prevented. Therefore, not only can the additional migration tendency caused by the combination of polyols and other antioxidants be suppressed, but the migration tendency can be largely prevented, thus obtaining significantly better results (in terms of the absence of the contamination layer) than when using polyols alone. In addition, it is also shown (as the results in Table 2b also prove) that these numerous measures for reducing migration within the scope of the present invention have no negative impact on the application properties of the finished parts such as mechanical properties and thermal stability.

[0144] At the same time, it has been confirmed by experiments that when fibers (or spheres) are added to the pre-concentrate, using fibrous reinforcing materials (such as glass fibers) or glass spheres, either at a high concentration or at a low concentration in the blend, unexpectedly reduces the migration tendency of additives, especially the polyol component, to an extent that cannot be achieved to the same degree with other particulate reinforcing materials. In addition, by reducing or completely preventing the migration of the polyol component, the amount of the polyol component can also be reduced (because none or at least only a very small proportion is lost due to migration), without having an adverse effect on stability. This in turn leads to a further reduction in migration to the surface (because there is less polyol component in the blend). In this way, excellent performance characteristics can be achieved.

[0145] Table 2b: Stability of unreinforced polyamide 6.6, especially with additives in the form of pre-concentrates according to the invention; thermal aging at 150 °C

[0146]

[0147] The thermal aging results presented here at 150 °C show that when using polymer pre-concentrates (especially with the additional use of fillers), similar thermal stability is achieved as when directly using individual stabilizing components during compounding. This means that, as described above, by using fillers in the pre-concentrate, the formation of a soiling layer during thermal aging can be significantly inhibited without any loss in stabilizing efficiency.

[0148] The flowability of the variant is determined by means of an HKR (high-pressure capillary viscometer). The results show that compared to the variant without added filler, the apparent viscosity related to the injection molding process (at a shear rate of 1000 s -1 -1) and thus the flowability of the polyamide material itself is maintained at the same level and does not deteriorate by adding fibers or other fillers (VK9 contains 30% glass fibers) to the pre-mixture. Therefore, the usability of pre-concentrates with reinforcing materials such as glass fibers or carbon fibers is very good for processing the resulting polyamide materials in injection molding and extrusion.

[0149] Example 3

[0150] The additives mentioned in Table 3 are compounded with PA6.6 and the time until the tensile strength drops to 90% of the initial value is determined.

[0151] Table 3: Stability of unreinforced and reinforced polyamide 6.6; thermal aging at 120 °C Experiments with dipentaerythritol and iron oxalate (comparative variant of the combination according to the invention);

[0152]

[0153] At relatively low temperatures such as here 120 °C, polyols, just like iron oxalate alone in polyamide, only show a very small effect on the service life of the material. This also applies if glass fibers are used alone or fillers are used alone. Surprisingly, a distinct synergistic effect and a significantly improved long-term stability are also achieved by means of a suitable combination of polyols or iron compounds with glass fibers at temperatures from 100 to 170 °C, and this surprisingly without an upstream "sealing step". It is also shown in this regard that the flow properties can be improved by using a polyol component, even when glass fibers or glass spheres are used in the pre-concentrate (to prevent migration in the finished workpiece), so that no disadvantages are observed in processing / molding by using fibers or spheres in the pre-concentrate (which results in a certain proportion of fibers or spheres in the compound).

[0154] Example 4

[0155] The additives mentioned in Table 4 were compounded with PA6.6 and the time until the tensile strength had dropped to 90% of the initial value after thermal aging was determined.

[0156] Table 4: Stability of non-reinforced and reinforced polyamide 6.6; experiments with dipentaerythritol for thermal aging at 170 °C (inventive combinations and comparative variants);

[0157]

[0158] When the storage temperature is increased from 120 °C as in Example 3 to 170 °C as in Example 4, it is shown that when dipentaerythritol is used alone in the non-reinforced polyamide, the service life of the polyamide material is longer compared to the lower temperature of 120 °C. This property is fundamentally different from the action of known antioxidants, in the case of which the Arrhenius equation applies according to the textbooks, so that the logarithm of the retention time decreases linearly with the reciprocal of the temperature (1 / T). This principle is used in accelerated aging tests to predict the service life at low temperatures from data at high temperatures. However, Tables 3 and 4 show that the lower the aging temperature, the worse the effect of the polyol. A distinctly improved effect with regard to the long-term stability of the material is only achieved at very high temperatures (according to the general academic view on the formation of a "protective layer"). Therefore, the principle of accelerated aging tests cannot be applied to materials with polyols.

[0159] Surprisingly, however, if, instead of using higher aging temperatures (for forming the protective layer), a method is used in which glass fibers and / or fillers are mixed with the polyol in the melt simultaneously during the preparation of the compound (see Table 4), the required long-term stability of the polyamide material is achieved even at higher temperatures of 100 to 170° C. This is all the more surprising because, although glass fibers or other fillers alone have a positive effect on the long-term stability of the material, this is relatively insignificant and, in most cases, is insufficient to meet the high demands placed on metal replacements in practice, particularly in the automotive sector.

[0160] Example 5

[0161] The additives mentioned in Table 5 were mixed with PA6.6 and the tensile strength was measured after storage at 150° C. for 2000 hours (relative to the initial value after the mix preparation).

[0162] Table 5: Stability of reinforced polyamide 6.6: heat aging at 150°C

[0163]

[0164] Table 5 shows that a significant improvement in thermal stability can also be achieved when using fillers in particulate form (i.e., not fibrous form), as the polyol component and the reinforcing component again demonstrate an unexpected synergistic effect. However, this synergistic effect is significantly more pronounced when using glass fibers and becomes even more pronounced over longer storage times. Of particular importance here is the fact that, according to the present invention, the tensile strength values remain high over extended periods, whereas these values are significantly reduced when using fillers or glass fibers alone, particularly over very long heat aging times (which are more representative of actual requirements during use).

[0165] Example 6

[0166] The additives mentioned in Table 6 were mixed with PA6.6, and the time for the tensile strength to drop to 90% of the initial value was measured.

[0167] Table 6: Stability of reinforced polyamide 6.6 (35% glass fiber content); heat aging at 200°C

[0168] Comparative experiments using dipentaerythritol and various antioxidants

[0169]

[0170] Conventional stabilizers for polyamides (with the exception of copper stabilizers) show no effect at elevated temperatures above 170°C, in particular above 190°C. Even with copper-based antioxidants, the effect at temperatures of 200°C and above is only very slight. In polyamide compositions in which polyols are also used, it is clear that the polyols are crucial for this effect at these very high temperatures. The addition of other stabilizers does not lead to an increase in the stabilization time.

[0171] Therefore, the significance of additional stabilizers based on phenols, amines, or copper-based antioxidants for long-term stability at a temperature of 200°C is negligible. This is in contrast to the stabilization achieved according to the invention at lower temperatures (see Table 1), where the combination with other stabilizers of this type showed a surprising and significant effect on the long-term stability of unreinforced polyamide materials in the temperature range of 100 to 170°C. These experiments therefore show that the stability achievable according to the invention runs counter to the expectations of those skilled in the art. Consequently, those skilled in the art would not have foreseen that the long-term stabilization achieved within the temperature range according to the invention could actually be achieved.

[0172] Example 7

[0173] The additives mentioned in Table 7 were mixed with PA6.6 and the time for the tensile strength to drop to 90% of the initial value was measured.

[0174] Table 7: Stability of polyamide 6.6 reinforced with glass fibers; thermal aging experiments at 150° C. with dipentaerythritol, glass fibers and additives (combinations according to the invention and comparative variants);

[0175]

[0176] The results in Table 7 show that, contrary to the prior art assumption that high-temperature sealing of polyol-based stabilizer systems is necessary to achieve significant improvements in stability, the polyol / GF system exhibits significantly improved stability at a storage temperature of 150° C. without high-temperature sealing at, for example, 200° C. The polyol / GF / secondary aromatic amine combination according to the present invention also exhibits excellent stability at 150° C.

[0177] It is thus clear that only the specific combination according to the invention exhibits the ability to stabilize polyamides over a long period of time in the temperature range of 100 to 170° C., while dispensing with copper-based stabilizers and ionic stabilizer components such as copper salts and halogen salts.

[0178] Table 8: CTI values

[0179] On an injection molding machine, test plaques measuring 3×5 cm and 3 mm thick are manufactured from the compositions described in Table 8, and the CTI values, which are particularly relevant for electrical applications, are measured according to standard IEC-60112.

[0180]

[0181] The results in Table 8 show that, in addition to the improved thermal properties, the impact on the electrical properties, in particular on the tracking resistance, remains very low. Furthermore, this enables such stabilizers to be used in the E&E field, where, in addition to increased heating shape stability, a high CTI value is also required. Similarly, in many cases, the crucial anti-corrosion effects of the various stabilizers should not be adversely affected by the compositions of the present invention.

Claims

1. A method for stabilizing a polyamide at a temperature of 100 °C to 170 °C, characterized in that, A polyamide is mixed with a polyol compound and a halogen - free and copper - free antioxidant, wherein the polyol compound or the polyol compound together with the halogen - free and copper - free antioxidant or the polyol compound together with the halogen - free and copper - free antioxidant and another antioxidant are used in the form of a pre - concentrate in a polymer carrier, and the carrier material for the pre - concentrate is a polymer selected from ethylene - vinyl acetate copolymer (EVA) or ethylene - methyl acrylate copolymer or ethylene - butyl acrylate copolymer.

2. A method for stabilizing a polyamide at a temperature of 100°C to 170°C, characterized in that, A polyamide is mixed with a polyol compound or an iron compound and a reinforcing material, wherein the polyol compound or the polyol compound together with the halogen - free and copper - free antioxidant or the polyol compound together with the halogen - free and copper - free antioxidant and another antioxidant are used in the form of a pre - concentrate in a polymer carrier, and the carrier material for the pre - concentrate is a polymer selected from ethylene - vinyl acetate copolymer (EVA) or ethylene - methyl acrylate copolymer or ethylene - butyl acrylate copolymer.

3. Use of a polyol compound and a halogen - free and copper - free antioxidant for stabilizing a polyamide at a temperature of 100 °C to 170 °C, wherein the polyol compound or the polyol compound together with the halogen - free and copper - free antioxidant or the polyol compound together with the halogen - free and copper - free antioxidant and another antioxidant are used in the form of a pre - concentrate in a polymer carrier, and the carrier material for the pre - concentrate is a polymer selected from ethylene - vinyl acetate copolymer (EVA) or ethylene - methyl acrylate copolymer or ethylene - butyl acrylate copolymer.

4. Use of a polyol compound or an iron compound and a reinforcing material for stabilizing a polyamide at a temperature of 100 °C to 170 °C, wherein the polyol compound or the polyol compound together with the halogen - free and copper - free antioxidant or the polyol compound together with the halogen - free and copper - free antioxidant and another antioxidant are used in the form of a pre - concentrate in a polymer carrier, and the carrier material for the pre - concentrate is a polymer selected from ethylene - vinyl acetate copolymer (EVA) or ethylene - methyl acrylate copolymer or ethylene - butyl acrylate copolymer.

5. The method according to claim 1 or 2 or the use according to claim 3 or 4, characterized in that, The polyol compound is a polyol having 2 or more hydroxyl groups.

6. The method according to claim 1 or the use according to claim 3, wherein a reinforcing material is additionally incorporated.

7. The method according to claim 2 or the use according to claim 4, wherein a halogen - free and copper - free antioxidant is additionally used.

8. The method or use according to claim 7, wherein the halogen - free and copper - free antioxidant is selected from secondary aromatic amines or alkyl - aryl substituted amines or hindered phenols, the latter usually being combined with a secondary antioxidant.

9. The method according to claim 2 or the use according to claim 4, wherein the reinforcing material is selected from glass fibers or carbon fibers or glass beads or other fillers, including nano - scale fillers.

10. The method according to claim 1 or 2 or the use according to claim 3 or 4, wherein a copper compound and / or a halogen - containing synergist is additionally used.

11. The method or use according to claim 10, wherein the copper compound is a copper(I) salt, a copper(II) salt or a copper complex.

12. The method or use according to claim 10, wherein the halogen-containing synergist is a halogen-containing polymer.

13. The method according to claim 1 or 2 or the use according to claim 3 or 4, characterized in that, The polyamide is an aliphatic or partially aromatic polyamide, optionally each impact-resistant modified.

14. The method according to claim 1 or 2 or the use according to claim 3 or 4, wherein the pre-concentrate additionally comprises glass beads or fibrous reinforcing materials or other fillers.

15. A polyamide material obtainable by the method according to any one of the preceding claims or by using the use according to any one of the preceding claims.

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