Thermoplastic Molding Compositions Which Are Mixtures of Amorphous and Semi-Crystalline Polyamides, a Method of Preparation Thereof and Products Made Therefrom

The invention relates to thermoplastic molding compositions of an amorphous copolyamide which contain dimerized fatty acid as one building block, a semicrystalline polyamide and, optionally, a compatibility agent; the semicrystalline polyamide preferably forming the continuous phase and the amorphous copolyamide preferably forming the dispersed phase.

In EP 70 001 B2, a thermoplastic molding resin of semicrystalline polyamide and amorphous copolyamide is disclosed. In U.S. Pat. No. 4,410,661, thermoplastic polyamide blends of semicrystalline polyamide and amorphous copolyamides from isophthalic acid, terephthalic acid, hexamethylene diamine, and bis-(p-aminocyclohexyl)methane, as well as impact resistance modifiers of the olefinic or core-shell polymer type are described. The disadvantage of both molding resins is that objects made from them are very sensitive to hot--and in particular boiling--water; preforms from a molding resin with a semicrystalline polyamide fraction of 40% by weight or less, completely lose their form stability, and those with a semicrystalline polyamide fraction of greater than 40% by weight suffer a substantial reduction in their stiffness.

In U.S. Pat. No. 3,200,428, there are described glass fiber-reinforced polyamide blends based on partially semi-crystalline polyamides with a fraction of amorphous transparent polyamides constituting a maximum of 20% by weight. These polyamide blends also do not meet the requirements in the temperature range above 100.degree. C. and in a humid atmosphere.

In EP 325,030 A2, a polyamide mixture is taught having an especially low second-order transition temperature and improved gas barrier-properties; the mixture consists of a specific copolyamide and an aliphatic homopolyamide. Here, too, the mechanical properties under action of heat and moisture are insufficient.

In DE-OS 3 817 279 Al, thermoplastic molding compounds of an amorphous part-aromatic copolyamide, a semicrystalline polyamide, and up to 60% by weight of a rubber-elastic polymer are set forth. These molding compounds have the disadvantage of poor mechanical properties under the combined action of heat and water.

It was therefore the object of the present invention to develop thermoplastic polyamide compositions which can easily be shaped into parts of good stability to solvents and good stress corrosion resistance, as well as high rigidity at temperatures of at least 100.degree. C.; also, in the conditioned state, their rigidity should not diminish substantially.

Accordingly, the invention is based on the surprising finding that specific amorphous copolyamides with dimerized fatty acids as one building block, in combination with semicrystalline polyamides, impart the desired properties to the molding compositions. The stability of the compositions on processing copolyamide can be improved by the addition of a compatibility agent. All parts and percentages set forth in the specification and claims are by weight unless otherwise stated.

The thermoplastic molding compositions according to the invention comprise

a) 25-75 parts of a semicrystalline polyamide;

b) 75-25 parts of an amorphous copolyamide of

(i) 25-45 molar parts of at least one aromatic dicarboxylic acid,

(ii) 25-5 molar parts of dimerized fatty acid with 36 to 45 carbon atoms, and

(iii) 50 molar parts of at least one cycloaliphatic diamine, the sum of said acids and said amine being present in equimolar portions; and

c) 0-30 parts of a compatibility agent,

a), b), and c) totaling 100 parts.

Optionally, additives which are customary in the art may also be included.

In another aspect of the invention, the molding compositions comprise

a) 25-75 parts by weight of a semicrystalline polyamide;

b) 75-25 parts by weight of an amorphous copolyamide of

(i) 25-45 molar parts of at least one aromatic dicarboxylic acid,

(ii) 25-5 molar parts of dimerized fatty acid,

(iii) 30-50 molar parts of at least one cycloaliphatic diamine,

(iv) 0-20 molar parts of non-aromatic dicarboxylic acids,

(v) 0-20 molar parts of additional diamine,

(vi) 0-30 molar parts of lactams or .omega.-aminocarboxylic acids, the acids (i), (ii), and (iv), and the amine components (iii) and (v) being present in amounts such that the number of acid groups equals the number of amine groups, and the sum of portions of (iv), (v), and (vi) are 0-30 parts;

c) 0-30 parts of a compatibilty agent, the portions a), b) and c) totaling 100 parts.

Optionally, customary additives according to the prior art may also be included.

A preferred composition contains amorphous copolyamides of 5 to 12 molar parts of dimerized fatty acid and 38-45 molar parts of at least one aromatic dicarboxylic acid. The compatibility agent c) is present in a preferable amount of between 1 and 30 parts; especially preferred is less than 10 parts. The customary additives according to the prior art include special processing aids and stabilizers. Preferred are impact modifiers, flame retardants, fillers, and/or reinforcing fibers.

As the semicrystalline component a), a homopolyamide of .omega.-amino-carboxylic acid or lactam having 6 to 9 carbon atoms is useful. It can also be made from aliphatic diamines with 4 to 12 carbon atoms and linear dicarboxylic acids of 6 to 12 carbon atoms; wherein the ratio of--CH.sub.2 --to CONH should remain below 9. Preferred are PA 6, PA 6.6, PA 4.6, PA 6.9, PA 6.10, and PA 6.12. Suitable also are semicrystalline copolyamides with a melting point (endothermic maximum in the DSC-curve), of at least 170.degree. C. Copolyamides based on the monomers of PA 4.6, PA 6.6, PA 6.8, PA 6.9, PA 6.10, PA 6.12, PA 9.6, PA 12.6, and PA 6 are also particularly desirable. Especially preferred as the semicrystalline component are those polyamides copolyamides which have good resistance to solvents, good stress corrosion resistance, good processability in injection molding, and a melting point of at least 170.degree. C.

Preferred component b) according to the invention comprises copolyamides of

(i) at least one mononucleic and/or multinucleic aromatic dicarboxylic acid,

(ii) dimerized fatty acids having 36 to 45 carbon atoms, the dimer portion of which is preferably at least 90%; in particular at least 97%; and

(iii) at least one cycloaliphatic diamine having at least one ring containing 6 carbon atoms;

(iv) optional non-aromatic dicarboxylic acids;

(v) optional aliphatic diamines; and

(vi) optional lactams and .omega.-aminocarboxylic acids.

Preferred aromatic acids are isophthalic acid, terephthalic acid, naphthalene dicarboxylic acid, 5-tert-butyl-isophthalic acid, ##STR1## and mixtures thereof.

Preferred cyoloaliphatic diamines are at least one of 1-amino-3-aminomethyl-3', 5,5'-trimethylcyclohexane, 1,3- and 1,4-diaminocyclohexane, 1,3- and 1,4-diaminomethylcyclohexane, and Formula I: ##STR2## wherein R stands for an alkyl radical with 1 to 10 carbon atoms, preferably methyl, ethyl, or isopropyl; R' is hydrogen or alkyl having 1 to 6 carbon atoms, preferably methyl or ethyl; and x is 0 to 4. The polyamides and the copolyamides preferably have a molecular weight of at least 5,000, more preferably 10,000 to 100,000. Diamines of Formulas II to IV are preferred. ##STR3##

The optional nonaromatic dicarboxylic acids are preferably aliphatic or cycloaliphatic dicarboxylic acids with 6 to 20 carbon atoms, those with 6 to 12 carbon atoms such as adipic acid, sebacic acid, azelaic acid, dodecanedicarboxylic acid or cyclohexane dicarboxylic acid being especially preferred.

The preferred optional additional diamines are aliphatic diamines with 2 to 20 carbon atoms, those with 2 to 12 carbon atoms such as ethylene diamine, hexamethylene diamine, as well as their alkyl-substituted derivatives, and neopentane diamine being especially preferred.

The preferred optional lactams and .omega.-aminocarboxylic acids are caprolactam and lactam 12, as well as .omega.-aminohexanoic, .omega.-aminoundecanoic and .omega.-aminododecanoic acid. Also salt pairs of aliphatic diamines with 2 to 20 carbon atoms and aliphatic dicarboxylic acids with 6 to 20 carbon atoms, preferably 6.12-, 6.10-, 6.9- and 6.6- salts, can also be used.

The production of the semicrystalline homo- and co-polyamides used as semicrystalline component a), as well as that of the amorphous copolyamides used as component b), is known.

The percentages of the molding composition components a) and b), as well as the manufacturing conditions therefor, are preferably selected so that the semicrystalline polyamide a) forms the continuous phase and the amorphous copolyamide b) is the dispersed phase. The amorphous copolyamide can be maintained as the dispersed phase even in high concentrations by suitable selection of a compatibility agent and of the compounding conditions; hence the individual second-order transition temperatures of components a) and b) and the melting point of component a) remain largely unaffected.

The action of the preferred compatibility agents is based on their reactivity with the end groups of the two polyamide components a) and b). Examples of such reactive products are meltable oligomeric and/or polymeric compounds which possess groups reactive with the terminal groups of the polyamides, i.e. acid anhydride carboxylic acid, diacrylic acid, epoxies, amino, and/or carboxylic acid groups neutralized with metal salt. Other examples of reactive products are functionalized oligomeric polyolefins or copolyolefins with low second-order transition points, or styrene-maleic acid anhydride oligomers with 4 to 10 acid anhydride groups, as well as core-shell polymers which possess reactive groups, preferably carboxylic acid, diacrylic acid, maleic acid anhydride, and/or epoxy groups.

Styrene-maleic acid anhydride oligomers (e.g. SMA resins of the firm Arco (USA), Types 1000, 2000, or 3000) or polyolefins and copolyolefins of low molecular weight, functionalized with maleic acid anhydride, have only a compatibility promoting action. Their advantage is that they can be employed in quantities of less than 10%.

Impact resistance improvement of the molding compositions according to the invention can be achieved by addition of modifiers customary for polyamides. Block copolymers, e.g. those with a polystyrene hard block and a functionalized elastomer block, or grafted copolyolefins with a grafting degree of 0.2 to 2.0 molar % maleic acid anhydride and low second-order transition temperatures can provide an increase in impact resistance and, in addition, a remarkable compatibility improvement.

The advantageous combination of compatibility promotion and impact resistance increase is often also possible with core shell polymers which have a slightly crosslinked core with a second-order transition temperature less than -30.degree. C. and a crosslinked polar shell. Examples are acrylic acid esters and methacrylic acid esters, preferably alkyl acrylate or methyl methacrylate. Preferred are core-shell polymers with a shell carrying reactive groups, in particular carboxylic acid, diacrylic acid, acid anhydride or epoxy, diacrylic acid maleic acid anhydride groups being especially preferred.

The production of the molding compositions according to the invention occurs by joint melting of the semicrystalline and amorphous polyamides, advantageously with simultaneous addition of the compatibility agent and under intensive action of shearing forces. The latter ensures good homogenization and distribution of the phases. The compatibility agent stabilizes the phase structure for the subsequent thermoplastic processing steps; namely, the discharge of the melt as a strand, cooling, and either comminution or shaping of parts from the melt. The addition of the compatibility agent may also occur in a separate extrusion step. The mixing process is carried out continuously in one or several process steps. Preferably twin-screw extruders, e.g. the so-called ZSK types of the firm Werner & Pfleiderer, Stuttgart, Germany, or the so-called Buss Cokneter of the firm Buss, Pratteln, Switzerland, are used.

It is characteristic of the molding compositions according to the invention that the semicrystalline and the amorphous polyamides do not alloy or do so only partially. While the amorphous polyamide solidifies like glass, the semicrystalline polyamide forms, as it solidifies, its own characteristic crystalline and amorphous polymer fraction. The crystalline fraction can be influenced, e.g. by nucleation agents, so that it develops in fine crystalline form.

The molding compositions according to the invention can be modified in many ways. Thus, they can be mineral-filled, reinforced, and/or flame-retarded e.g. by the inclusion of magnesium hydroxide. Advantageously, processing aids and stabilizers are added to the molding compounds; these, among other things, retard decomposition by oxygen, heat, and radiation.

The compositions of this invention are in general of excellent color and are stable to discoloration. They can be pigmented or dyed, mainly by reextrusion, in all colors. Pigments and dyes, known in the art of coloration of polyamides, can be used. Preforms according to the invention can be produced by the usual shaping processes, e.g. injection molding, extruding, coextruding, and blow-molding.

Molding compounds according to the invention, without component c) (the compatibility agent), can be produced with an amorphous copolyamide proportion b) of up to about 40 parts per 100 parts of molding composition without delamination occurring. Such molding compounds have moduli of elasticity which are at least as high as those of the pure components (according to the volume--fraction mixing rule).

Molding compounds according to the invention, which contain the compatibility agent in such small amounts that it cannot act as impact resistance modifier, still show improvements in notch impact toughness. Even molding compounds according to the invention without compatibility agents show, in the conditioned state, better notch impact toughness than the pure amorphous copolyamide.

A important advantage of the molding compounds according to the invention is their very good resistance to solvents and, thereby, stress-corrosion cracking. But their very special advantage is their high rigidity, which is not--or not substantially--impaired in humid atmosphere and elevated temperatures. Thus the shear modulus curve, which is a measure of the change of stiffness on elevating temperature, of the molding compositions according to the invention is far preferable to that of "comparable" molding compounds of semicrystalline polyamide and amorphous copolyamide without dimerized fatty acid as a building block.

The examples described below are illustrative and are not to be regarded as limiting.

The components of the thermoplastic molding compositions are premixed in a tumbling mixer. If needed, lubricants, crystallization accelerators, and/or heat stabilizers are added in amounts of 0.1 to 3 parts. Thereafter the mixture is fed into the intake zone of a twin-screw extruder, Model ZSK 30 (Werner & Pfleiderer) and extruded. The products are drawn off as a strand and granulated. From the granulates, the test specimens used are produced on an injection molding machine, Model Arburg Allrounder 320-210-750.

Table 1 shows the composition of the thermoplastic molding compositions of Examples 1 to 13, Examples 11 to 13 being comparison examples.

The amorphous copolyamides are produced in conventional polyamide reactors according to the prior art. The composition of the amorphous copolyamides used in the examples is given in Table 2. Copolyamide No. 4, used in Comparison Example 11, is an amorphous copolyamide of the firm of EMS-Chemie based on hexamethylene diamine, isophthalic acid, and terephthalic acid sold under the commercial name "Grivory G 21".

Copolyamide No. 5, used in the comparison examples 12 and 13, is an amorphus copolyamide of the firm EMS-Chemie based on isophthalic acid, terephthalic acid, hexamethylene diamine, and 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane (and thus contains no dimerized fatty acid), which is sold under the commercial name "Grivory XE 3038".

Dimeric Acid 1:

A mixture of dimerized fatty acids having 36 carbon atoms containing

It is sold under the commercial name "Pripol 1009" by the firm Unichema.

Dimeric Acid 2:

A mixture of dimerized fatty acids having 36 carbon atoms containing

It is sold by the firm Henkel-Emery under the commercial name "Empol 1014".

Polyamide 6 : medium-viscous injection molding type, .eta. rel ca. 1.75

Polyamide 6.6 : medium-viscous injection molding type, .eta. rel ca. 1.8

Compatibility Agent 1:

An ethylene-propylene copolymer grafted with 0.6 mol % maleic acid anhydride having a polypropylene content of 20 mol %.

Compatibility Agent 2:

A core-shell polymer with a methyl methacrylate shell grafted with maleic acid anhydride and a core of butyl acrylate.

In Table 3 the characteristic properties of the molding composition components are compiled. In Table 4, the characteristic properties of the thermoplastic molding compositions according to the invention, as well as those of the comparison examples, are summarized. In Table 5, the mechanical properties of the components and of the thermoplastic molding compositions according to the invention, as well as those of the comparison examples, are set forth.

The characteristic properties include the second-order transition temperature Tg (measured at the beginning of the glass transition stage as Tg onset), the relative solution viscosity .eta. rel, the melt viscosity, and the melt temperature T.sub.s. The second-order transition and melt temperatures are determined by DSC (Differential Scanning Calorimetry) in the dry state. The DSC measurements are performed at a heating rate of 20.degree. C./min on a Du Pont Thermal Analyzer Model 1091B. The relative solution viscosity is determined according to DIN 53727 as 0.5% solution in m-cresol and the melt viscosity according to DIN 53735 at 270.degree. C. and 122.6 N.

The following mechanical properties are determined: Impact toughness a.sub.n and notch impact toughness a.sub.k according to Charpy (dry and conditioned) and DIN 53453 at 23.degree. C.; modulus of elongation (dry and conditioned) according to DIN 53457 at 23.degree. C.; shear modulus G (dry and conditioned) according to DIN 53445 at 23.degree. and 100.degree. C. (torsion apparatus: Nyrenne, heating rate: 1.degree. C./min, measurement frequency: 1 Hz); and stress corrosion resistance in ethanol according to DIN 53449 at 23.degree. C. For the conditioning, the materials are stored at 70.degree. C. and 62% relative humidity for 7 days.

As the values for the melt and the glass transition temperatures (which are changed only slightly, if at all) show (see Table 4), the thermoplastic molding compositions according to the invention are multiphasal. The molding compositions of the comparison examples, on the contrary, show only a single changed Tg. This proves that, in the comparison examples, the molding composition components do not form separate phases.

The scanning electron microscope photographs of FIGS. 1A, 1B, and 1C show that, by the better phase adhesion due to the compatibility agent, fine phase morphologies, and therefore good and stable mechanical properties, for the molding compositions according to the invention are achieved. Thus, the torsion modulus curves of the molding compositions according to the invention at about 100.degree. C., especially in the conditioned state, are substantially higher than the curves of the pure semicrystalline components and of the molding compositions from the comparison examples.

Molding compositions according to the invention made of semicrystalline polyamide and a high proportion of amorphous copolyamide (>40 parts per 100 parts of total compound) without any compatibility agent, on the other hand, lead to irregular strands on extrusion and to delamination in injection molded articles made therefrom.

For the scanning electron microscope photographs (REM) the samples were prepared as follows and then measured in an REM apparatus of Zeiss, Model DSM 950. After immersion in liquid nitrogen, the specimens were instantly broken. The amorphous copolyamide was eluted by treating the fracture surface with 1,3-dimethyl-2-imidazolidone (DMI). For selective extraction of the olefinic compatibility agent, toluene is used.

FIG. 1A shows the untreated fracture of a specimen from Example 1. FIG. 1B shows the fracture thereof treated with DMI whereby both the compatibility agent and the amorphous copolyamide have been eluted. In FIG. 1C only the compatibility agent was eluted with toluene at the fracture surface.

FIG. 2A shows the unmodified fracture of a specimen from Example 2. FIG. 2B shows the fracture treated with DMI in which both the amorphous copolyamide and the agent have been eluted, and FIG. 2C shows the fracture treated with toluene in which only the compatibility agent has been eluted.

FIG. 3A shows the DMI-treated fracture of a specimen from Example 9 in which the amorphous copolyamide has been eluted. FIG. 3B shows the DMI-treated fracture of a specimen from Example 10 in which the amorphous copolyamide has also been eluted.

A comparison of FIGS. 1B and 1C with FIG. 3A and of FIGS. 2B and 2C with FIG. 3B shows that the amorphous copolyamide can be eluted separately in molding compositions with and without the compatibility agent. This demonstrates that amorphous copolyamide and semicrystalline polyamide form separate phases. The compatibility agent eluted separately in FIGS. 1C and 2C leaves clearly smaller and more uniform "holes" as compared with the eluted semicrystalline polyamides. In FIGS. 1B and 2B, it can be seen that, besides the semicrystalline polyamide, the compatibility agent was also dissolved since, in addition to the large holes, the typical small holes of the compatibility agent are visible. The holes of the compatibility agent are also recognizable in the canals of the eluted amorphous copolyamide. This shows that, unlike pure impact resistance modifiers, the compatibility agent is concentrated at the phase boundary faces and creates interactions between the otherwise incompatible polyamides.

From the molding compounds of the Comparison Examples 11 to 13, on the contrary, it is not possible to eluate a polyamide component separately. This shows that these molding compounds are monophasal and the individual components are not present as separate phases.

While only a limited number of specific embodiments of the present invention have been expressly disclosed, it is, nonetheless, to be broadly construed, and not to be limited except by the character of the claims appended hereto.