Flame retardant brightly coloured reinforced polyamide moulding compositions.

0001The invention relates to thermoplastic molding compositions containing<ul id="ul0001" list-style="none"><li>A) 10-90% by weight of a polyamide,</li><li>B) 7-60% by weight of a reinforcing filler,</li><li>C) 1-40% by weight of titanium dioxide,</li><li>D) 1 - 20% by weight of red phosphorus, and</li><li>E) 1 - 40% by weight of a rubber.</li></ul>

0002The invention further relates to the use of such molding compositions for the production of moldings and the moldings obtainable from the molding compositions.

0003From DE-AS-19 31 387 it is known that red phosphorus is an effective flame retardant for reinforced or filled polyamides. It is disadvantageous, however, that the red phosphorus colors the polyamides deep red or dark brown, which is not acceptable for some applications.

0004To avoid these disadvantages, undyed flame retardants, for example halogenated organic compounds, or nitrogen-containing compounds, for example melamine cyanurate (DE-OS 27 40 092), have been used as flame retardants.

0005However, halogenated organic compounds have a negative influence on the tracking resistance of the molded articles produced from the molding compositions, so that molded articles equipped in this way cannot be used in the field of electrical engineering. In addition, synergists such as antimony trioxide, which are largely toxicologically very questionable, are required to improve effectiveness. The same applies to the halogenated organic compounds released in the event of fire and the hydrogen chloride, which is also highly corrosive.

0006The use of melamine cyanurate as a flame retardant in reinforced polyamides prevents the wicking of the reinforcing filler (cf. EP-A-19768).

0007As an alternative to replacing the red phosphorus with other flame retardants with the disadvantages described above, it is also possible to over-dye the red phosphorus-treated polyamides with white pigments, such as titanium dioxide or zinc sulfide.

0008From DE-OS 22 26 932 it is known, however, that the reinforced polyamides pigmented with hard inorganic pigments such as titanium dioxide have significantly worse mechanical properties than the corresponding unpigmented materials due to the notch effect of the titanium dioxide on the reinforcing filler.

0009The use of the softer zinc sulfide is therefore not possible, since the chemical stability of the red phosphorus (with regard to phosphinic and phosphoric acid formation) in the polyamide is significantly impaired.

0010It was an object of the present invention to over-color the red color of the phosphor used as flame retardant in flame-retardant reinforced polyamides with white pigments without reducing the stability of the phosphor and significantly influencing the good reinforcing properties of the reinforcing fillers.

0011According to the invention, this object is achieved by the thermoplastic molding compositions defined at the outset.

0012The polyamides used as component A) are known per se. Semi-crystalline or amorphous resins with a molecular weight (weight average) of at least 5000, as described, for example, in German Offenlegungsschriften 20 71 250, 20 71 251, 21 30 523, 21 30 948, 22 41 322, 23 12 966, 25 12 606 and 33 93 210 are preferred.

0013Examples include polyamides which are derived from lactams with 7-13 ring members, such as polycaprolactam, polycapryllactam and polylaurine lactam, and polyamides which are obtained by reacting dicarboxylic acids with diamines. Alkanedicarboxylic acids having 6 to 12, in particular 6 to 10, carbon atoms and aromatic dicarboxylic acids can be used as dicarboxylic acids. Only adipic acid, azelaic acid, sebacic acid, dodecanedioic acid and terephthalic and / or isophthalic acid may be mentioned here.

0014Particularly suitable diamines are alkane diamines having 6 to 12, in particular 6 to 8, carbon atoms, and also m-xylylenediamine, di- (4-aminophenyl) methane, di- (4-aminocyclohexyl) methane, 2,2-di- (4 -aminophenyl) propane or 2,2-di- (4-aminocyclohexyl) propane. Polyamides obtainable by copolymerization of two or more of the aforementioned monomers or mixtures of two or more polyamides are also suitable.

0015Processes for the production of these polyamides, as well as the polyamides themselves, are known per se and described in the literature, so that further details are not necessary here.

0016The relative viscosity of the polyamides is generally in the range from 2.2 to 4.5, measured in 1% strength by weight solution in 96% strength sulfuric acid at 25 ° C.

0017The proportion of component A) in the molding compositions according to the invention is 10 to 90, preferably 20 to 70 and in particular 25 to 60% by weight, based on the total weight of the molding compositions.

0018In principle, all fillers which bring about an improvement in the mechanical properties of the molding compositions are suitable as reinforcing fillers B). Fibrous fillers such as glass fibers, carbon fibers or fibrous silicates such as wollastonite are preferred. Glass balls can also be used advantageously.

0019When using glass fibers, these can be equipped with a size and an adhesion promoter for better compatibility with the polyamide. In general, the glass fibers have a diameter in the range from 6 to 20 μm. The incorporation into the molding compositions can take place both in the form of short glass fibers and in the form of endless strands (rovings). In the finished injection molded part, the average length of the glass fibers is preferably in the range from 0.08 to 0.5 mm.

0020The proportion of the reinforcing fillers B) in the molding compositions according to the invention is 7 to 60, preferably 10 to 55 and in particular 15 to 50% by weight, based on the total weight of the molding compositions.

0021Titanium dioxide C) is used in amounts of 1 to 40, preferably 2 to 30 and in particular 5 to 25% by weight, based on the total weight of the molding compositions. Both rutile, anatase and brookite types can be used. The average particle size, ie the particle size above and below which the particle size of 50% by weight of the particles is (d₅₀), is preferably in the range from 0.0001 to 0.01 mm, in particular in the range from 0.0001 to 0.001 mm .

0022The titanium dioxide can generally also be incorporated into the compositions as a batch in the rubber used as component E. The concentration of the TiO₂ in this batch can be up to 80, preferably up to 60% by weight, based on the rubber.

0023For better incorporation into the molding compositions, the titanium dioxide used can be coated on the surface with known inorganic or organic compounds (adhesion promoters).

0024The red phosphorus used as flame retardant D) can be used directly, as is commercially available. However, there are also products on the market in which the red phosphorus is coated on the surface with low molecular weight liquid substances such as silicone oil, paraffin oil or esters of phthalic acid or adipic acid or polymers or oligomers. Concentrates of red phosphorus, for example in a polyamide, are also suitable as flame retardants.

0025The average particle size (d₅₀) of the phosphor particles distributed in the molding compositions is preferably in the range from 0.0001 to 0.5, in particular from 0.001 to 0.2 mm.

0026The molding compositions according to the invention contain 1 to 40, in particular 5 to 35 and particularly preferably 8 to 30,% by weight of a rubber as component E).

0027In principle, all rubbers are suitable which, when mixed with polyamides, result in an improvement in the impact resistance compared to pure polyamide.

0028In general, these are copolymers which are preferably composed of at least two of the following monomers as main components: ethylene, propylene, butadiene, isobutene, isoprene, chloroprene, vinyl acetate, styrene, acrylonitrile and acrylic and methacrylic acid esters with 1 to 18 ° C -Atoms in the alcohol component.

0029Rubbers which contain reactive components which allow adhesion with the amine or carboxyl end groups of the polyamide are preferred. Olefinically unsaturated carboxylic acids and their anhydrides may be mentioned as reactive components.

0030Rubbers E) are described, for example, in Houben-Weyl, Methods of Organic Chemistry, Vol. 14/1 (Georg-Thieme-Verlag, Stuttgart, 1961), pages 392 to 406 and in the monograph by CB Bucknall, "Toughened Plastics" (Applied Science Publishers, London, 1977).

0031Some preferred types of such elastomers are presented below.

0032The first preferred group is the so-called ethylene-propylene (EPM) or ethylene-propylene-diene (EPDM) rubbers, which preferably have a ratio of ethylene residues to propylene residues in the range from 40:60 to 90:10.

0033The Mooney viscosities (MLI + 4/100 ° C.) of such uncrosslinked EPM or EPDM rubbers (gel contents generally below 1% by weight) are preferably in the range from 25 to 100, in particular from 35 to 90 (measured on the large rotor after 4 minutes running time at 100 ° C according to DIN 53 523).

0034EPM rubbers generally have practically no more double bonds, while EPDM rubbers can have 1 to 20 double bonds / 100 carbon atoms.

0035Examples of diene monomers for EPDM rubbers are conjugated dienes such as isoprene and butadiene, non-conjugated dienes having 5 to 25 carbon atoms such as penta-1,4-diene, hexa-1,4-diene, hexa-1,5- diene, 2,5-dimethylhexa-1,5-diene and octa-1,4-diene, cyclic dienes such as cyclopentadiene, cyclohexadienes, cyclooctadienes and dicyclopentadiene as well as alkenylnorbornenes such as 5-ethylidene-2-norbornene, 5-butylidene-2-norbornene , 2-methallyl-5-norbornene, 2-isopropenyl-5-norbornene and tricyclodienes such as 3-methyl-tricyclo (5.2.1.0.2.6) -3,8-decadiene or mixtures thereof. Hexadiene-1,5,5-ethylidene-norbornene and dicyclopentadiene are preferred. The diene content of the EPDM rubbers is preferably 0.5 to 50, in particular 1 to 8,% by weight, based on the total weight of the rubber.

0036EPM or EPDM rubbers can preferably also be grafted with reactive carboxylic acids or their derivatives. Only acrylic acid, methacrylic acid and their derivatives and maleic anhydride are mentioned here.

0037Another group of preferred rubbers are copolymers of ethylene with acrylic acid and / or methacrylic acid and / or the esters of these acids. In addition, the rubbers can also contain dicarboxylic acids, such as maleic acid and fumaric acid, or derivatives of these acids, such as esters and anhydrides, and / or epoxy groups. These dicarboxylic acid derivatives or epoxy groups are preferably added by adding dicarboxylic acid or Monomers containing epoxy groups of the general formulas I or II or III or IV are incorporated into the rubber to form the monomer mixture<chemistry id="chem0001" num="0001"><img file="EP0255901A2_D0001.tif" /></chemistry> where R¹ - R⁹ represent hydrogen or alkyl groups with 1 to 6 carbon atoms and m is an integer from 0 to 20, n is an integer from 0 to 10 and p is an integer from 0 to 5.

0038R¹ - R⁷ are preferably hydrogen, and m has the value 0 or 1 and n is 1. The corresponding compounds are maleic acid, fumaric acid, maleic anhydride, alkyl glycidyl ether or vinyl glycidyl ether.

0039Preferred compounds of the formulas I, II and III are maleic acid, maleic anhydride and epoxy group-containing esters of acrylic acid and / or methacrylic acid, glycidyl acrylate and glycidyl methacrylate being particularly preferred.

0040The ethylene content of the copolymers is generally in the range from 50 to 98% by weight, the proportion of monomers containing epoxy group n and the proportion of the acrylic acid and / or methacrylic acid ester in each case in the range from 1 to 49% by weight.

0041Copolymers of are particularly preferred 50 to 98, in particular 60 to 95% by weight of ethylene, 0.5 to 40, in particular 3 to 20% by weight of glycidyl acrylate and / or glycidyl methacrylate, acrylic acid and / or maleic anhydride, 1 to 45, in particular 10 to 35% by weight of n-butyl acrylate and / or 2-ethylhexyl acrylate.

0042Further preferred esters of acrylic and / or methacrylic acid are the methyl, ethyl, propyl and i- or t-butyl esters.

0043In addition, vinyl esters and vinyl ethers can also be used as comonomers.

0044The ethylene copolymers described above can be prepared by processes known per se, preferably by random copolymerization under high pressure and elevated temperature. Appropriate methods are described in the literature.

0045The melt index of the ethylene copolymers is generally in the range from 1 to 80 g / 10 min (measured at 190 ° C. and 2.16 kg load).

0046Preferred elastomers (rubbers) C) are also graft copolymers with butadiene, butadiene / styrene, butadiene / acrylonitrile and acrylic esters, as described, for example, in DE-A-16 94 173 and DE-A-23 48 377.

0047Of these, the so-called ABS polymers are to be mentioned in particular, as are described in DE-A-20 35 390, DE-A-22 48 242 and EP-A-22 216, the latter being particularly preferred.

0048Graft polymers can also be used as rubber C) 25 to 98% by weight of an acrylate rubber with a glass transition temperature of below -20 ° C as a graft base (base polymer) and 2 to 75% by weight of a copolymerizable ethylenically unsaturated monomer, the homo- or copolymers of which have a transition temperature of more than 25 ° C., as a graft layer (graft shell) be used.

0049The graft base is acrylate or methacrylate rubbers, which may contain up to 40% by weight of other comonomers. The C₁-C8 esters of acrylic acid or methacrylic acid and their halogenated derivatives as well as aromatic acrylic acid esters and mixtures thereof are preferred. As comonomers in the graft base are acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, acrylamides, methacrylamides and vinyl-C₁-C₆-alkyl ethers.

0050The graft base can be uncrosslinked or partially or fully crosslinked. Crosslinking is achieved, for example, by copolymerization of preferably 0.02 to 5% by weight, in particular 0.05 to 2% by weight, of a crosslinking monomer with more than one double bond. Suitable crosslinking monomers are described, for example, in DE-A-27 26 256 and EP-A-50 265.

0051Preferred crosslinking monomers are triallyl cyanurate, triallyl isocyanurate, triacryloylhexahydro-s-triazine and trialkylbenzenes.

0052If the crosslinking monomers have more than 2 polymerizable double bonds, it is advantageous to limit their amount to not more than 1% by weight, based on the graft base.

0053Particularly preferred graft bases are emulsion polymers with a gel content of more than 60% by weight (determined in dimethylformamide at 25 ° C. according to M. Hoffmann, H. Krömer, R. Kuhn, Polymeranalytik, Georg-Thieme-Verlag, Stuttgart, 1977).

0054Acrylate rubbers with a diene core, as described, for example, in EP-A-50 262, are also suitable as a graft base.

0055Particularly suitable graft monomers are styrene, α-methylstyrene, acrylonitrile, methacrylonitrile and methyl methacrylate or mixtures thereof, in particular those of styrene and acrylonitrile in a weight ratio of 1: 1 to 9: 1.

0056The grafting yield, ie the quotient of the amount of the grafted-on monomer and the amount of the grafted monomer used, is generally in the range from 20 to 80%.

0057Rubbers based on acrylates which can be used according to the invention are described, for example, in DE-A-24 44 584 and DE-A-27 26 256.

0058The rubbers C preferably have a glass transition temperature of below -30 ° C, in particular of below -40 ° C.

0059It is understood that mixtures of the types of rubber listed above can also be used.

0060In addition to the essential components A) to E), the molding compositions according to the invention can contain customary additives and processing aids. Their proportion is generally up to 60, preferably up to 50,% by weight, based on the total weight of components A) to E).

0061Typical additives are, for example, stabilizers and oxidation retardants, agents against heat decomposition and decomposition by ultraviolet light, lubricants and mold release agents, colorants such as dyes and pigments (except titanium dioxide), non-reinforcing fillers and plasticizers.

0062Oxidation retarders and heat stabilizers which can be added to the thermoplastic compositions according to the invention are, for example, halides of metals of group I of the periodic system, for example sodium, potassium, lithium halides, if appropriate in combination with copper (I) halides , for example chlorides, bromides or iodides. Sterically hindered phenols, hydroquinones, substituted representatives of this group and mixtures thereof, preferably in concentrations of up to 1% by weight, based on the weight of the mixture, can be used.

0063Examples of UV stabilizers are various substituted resorcinols, salicylates, benzotriazoles and benzophenones, which are generally used in amounts of up to 2.0% by weight.

0064Lubricants and mold release agents, which are generally added in amounts of up to 1% by weight of the thermoplastic composition, are stearic acids, stearyl alcohol, alkyl stearates and amides, and esters of pentaerythritol with long-chain fatty acids.

0065The additives also include stabilizers that prevent the decomposition of the red phosphorus in the presence of moisture and atmospheric oxygen. An example of this is zinc oxide and cadmium oxide.

0066The molding compositions according to the invention can be produced by processes known per se by mixing the starting components in conventional mixing devices, such as screw extruders, Brabender mills or Banbury mills, and then extruding them. After the extrusion, the extrudate is cooled and crushed. The mixing temperatures are generally in the range from 220 to 300 ° C.

0067The titanium dioxide can be added directly to the melt or mixed with the polyamide granules in the form of powder or in a mixture with rubber.

0068The molding compositions according to the invention are distinguished by a light color with practically unchanged impact strength compared to unpigmented molding compositions.

example 1

0069Polyhexamethylene adipic acid amide with a K value of 72 (according to Fikentscher, Cellulose-Chemie <u style="single">13</u>, 1932, p. 58) were mixed in a fluid mixer with 10% by weight of titanium dioxide and 10% by weight of an ethylene-n-butyl acrylate-maleic anhydride terpolymer (composition 66: 33: 1% by weight) and then in an extruder Melted at 270 to 290 ° C. At the same time, 6% by weight of red phosphorus was introduced as a powder under an argon atmosphere. 35% by weight of glass fibers were metered in as an endless strand (roving) via an opening further downstream.

0070The homogeneous mixture was pressed out, drawn off in strands, cooled and then granulated.

0071Test specimens were injected from the granules and their impact strength was determined in accordance with DIN 53 453. The fire test was carried out based on UL 94.

0072The color assessment was carried out on the test specimens using a RAL color table.

0073To determine the soluble phosphorus, standard small rods measuring 4 × 6 × 50 mm were injected. 50 of these standard small bars were stored in distilled water at 60 ° C for 100 days. The evaporated water was replenished at regular intervals. After this time, a water sample was taken and the content of soluble phosphorus (phosphoric acid) in water was determined.

Example 2

0074The procedure was as in Example 1, except that instead of the ethylene-n-butyl acrylate-maleic anhydride rubber, an ethylene-propylene rubber grafted with 0.5% by weight of maleic anhydride (ethylene: propylene weight ratio = 3: 1) was used.

Example 3

0075The procedure was as in Example 1, except that instead of the glass fibers, fibrous wollastonite was used as reinforcing agent, which was mixed as a batch with the polyamide in granular form before extrusion.

Comparative Example 1

0076Polyhexamethylene adipinamide as in Example 1 was melted in an extruder and, as described in Example 1, 35% by weight of glass fibers and 6% by weight of red phosphorus were introduced into the melt. The further processing was carried out as in Example 1.

Comparative Example 2

0077The procedure was as in Example 1, but no rubber was added.

Comparative Example 3

0078The procedure was as in Example 1, but no titanium dioxide was added.

0079The results of the tests can be found in the table below.<tables id="tabl0001" num="0001"><img file="EP0255901A2_D0002.tif" /></tables>