PRIOR ART Conventional polyamide resins, such as nylon 66, nylon 6, nylon 612, etc., are aliphatic polyamide resins with a certain level of heat resistance and excellent mechanical characteristics. Consequently. these resin compositions are used in a wide range of applications. such as resin moldings as substitutes for metal parts and resin moldings as substitutes for parts made of heat-settings resins. However, in applications when moisture is absorbed, aliphatic polyamides exhibit characteristic property losses, especially reduced rigidity.

Semi-aromatic polyamides, whose monomer contains aromatic dicarboxylic acid and/or aromatic diamine, are known to have superior heat and moisture resistance in comparison to the above-mentioned conventional aliphatic polyamides. An example of such polyamide resins can be found in U.S. Patent 5,378,800. The high glass transition temperature of aromatic polyamides is important to provide excellent mechanical properties at high temperature and with moisture. However, due to high glass transition temperature, the crystallization in the molded article of aromatic polyamide is incomplete under molding conditions.

When cooling occurs with incomplete crystallization. the molded articles undergo dimensional deformation when they are later exposed to temperatures above its glass transition temperature. Such dimensional changes are significant for thin parts such as electric insulators. connecting devices. fasteners, etc. In order to obtain molded articles of such compositions without this problem, it is necessary to carry out molding with a high-temperature mold, or to subject the molded article to heat annealing, but these processes lengthen the molding cycle and decrease productivity.

SUMMARY OF INVENTION The present invention provides a high-impact polyamide resin composition which comprises:

(a) a semi-aromatic polyamide formed from an aromatic dicarboxylic acid and an aliphatic diamine; said aromatic dicarboxylic acid being terephthalic acid or a mixture of terephthalic acid and isophthalic acid; said aliphatic diamine being hexamethylene diamine or a mixture of hexamethylene diamine and 2-methyl pentamethylene diamine; (b) an aliphatic polyamide formed from aliphatic dicarboyxlic acids and aliphatic diamines, or an aliphatic polyamide formed from aliphatic aminocarboxylic acids; (c) an elastomeric polymer; and (d) optionally an inorganic filler.

The polyamide resin composition of this invention has good dimensional stability after molding and the molded articles retain properties well at high temperature and with moisture.

DETAILED DESCRIPTION OF THE INVENTION The following are the nylons referred to herein: Nylon 6 is polycaprolactam, or H-[HN(CH2)5 CO]"-OH; Nylon 66 is poly(hexamethylene adipamide), or H-[HN(CH2)6 NHCO(CH2)4 CO]n-OH; Nylon 612 is poly(hexamethylene dodecanoamide), or H-[HN(CH2)6 NHCO(CH2),0 CO]n-OH; Nylon 46 is poly(tetramethylene adipamide), or H-[HN(CH2)4 NHCO(CH2)4 CO]n-OH; Nylon 11 is poly(l 1-aminoundecanoamide), or H-[HN(CH2),0 CO]"-OH; Nylon 12 is polylaurolactam, or H-[HN(CH2)11 CO]n-OH.

In the present invention, the semi-aromatic polyamide (a) has an intrinsic viscosity in sulfuric acid at 250C in the range of 0.2 - 3.0. Also, the melting point is in the range of 280 - 330"C. When a mixture of terephthalic acid and isophthalic acid is used as decarboxylic acid defined in (a), the mixture preferably contains less than 40 mole percent, based on the mixture of isophthalic acid. The mixture of hexamethylene diamine and 2 -methylpentamethylene diamine preferably contains at least 40%, preferably 40 - 90 mole percent based on the mixture, of hexamethylene diamine. This semi-aromatic polyamide can be manufactured by means of polycondensation which is, for example, described in U. S. Patent 5,378,800.

The aliphatic polyamide (b) is used for adjusting the glass transition temperature of the polyamide resin composition of this invention according to the intended application of use. Examples of the polyamide (b) include nylon 66,

nylon 6, nylon 610, nylon 612, nylon 46, nylon 11, nylon 12, etc., and mixtures thereof. When these aliphatic polyamides are blended with the semi-aromatic polyamide (a) to form the polyamide resin component of the invention, it is possible to adjust the glass transition temperature of the claimed polyamide resin composition. Among the aliphatic polyamide resins, nylon 66, nylon 6, nylon 612, and nylon 46 are preferably used. Nylon 66 and nylon 6 are most preferably used.

In the present invention the semi-aromatic polyamide (a) and the aliphatic polyamide (b) can be mixed in any ratios as desired, but the ratio of (a) to (b) greater than about 1/1 and less than or equal to about 20/1 is preferably used.

When the ratio (a) to (b) is smaller than 1/1, the resin composition does not have enough high moisture and heat resistance. When the ratio (a) to (b) is greater than about 20/1, the glass transition temperature of the resin composition is high, and it causes dimensional deformation of the molded article after molding.

The elastomeric polymer (c) is added for impact toughness. Examples of elastomeric polymers include ethylene/alpha-olefin polymers, ethylene/propylene/diene polymers, ethylene/aromatic vinyl monomer/diene polymers, ethylene/acrylate/methacrylate/unsaturated epoxy polymers, etc., and a mixture thereof. Polyethylene, polypropylene, other polyolefins, olefin copolymers, and polyolefin copolymer ionomers are also appropriately used as elastomeric polymers in the present invention. Ethylene-propylene polymer, ethylene-propylene-diene monomer polymer, or ethylene-styrene-diene monomer polymer, or a mixture thereof is preferably used. Examples of diene monomers include butadiene, 1,4-hexadiene, norbornadiene. Elastomeric polymer used in the present invention may be partially modified with grafted unsaturated carboxylic acid. Maleic anhydride is preferably used for such modifications. The polyamide composition preferably contains from 5 weight percent to 30 weight percent of elastomeric polymer in the total of weight of (a), (b) and (c). When less than 5 weight percent of an elastomeric polymer (c) is used, the resin composition becomes too brittle. When more than 30 weight percent of an elastomeric polymer is used, the resin composition loses its rigidity. Most preferably from 10 to 20 weight percent of elastomeric polymer in the total of (a), (b), and (c) is used.

In the present invention, the resin compostion can optionally contain inorganic fillers. Examples of inorganic fillers include glass fiber, carbon fiber, potassium titanate, whiskers, talc, mica, etc., and a mixture thereof. Preferably, the weight percent of an inorganic filler (d) in the total weight of (a), (b), (c), and (d) is less than 65%.

The method of manufacturing the polyamide composition of the present invention may be carried out by means of any conventional well-known method.

For example, a semi-aromatic polyamide, an aliphatic polyamide, an elastomeric polymer, and optionally an inorganic filler may be dry mixed, melted, kneaded and extruded using a biaxial extruder or other melt-kneader to form pellets. Or a polyamide resin composition containing an elastomeric polymer and a polyamide resin composition containing inorganic filler may be melted, kneaded, as well as molded, on an injection molding machine to form the polyamide resin compostion of the present invention.

Additives commonly employed with synthetic resins, such as thermal stabilizers, plasticizers, antioxidants, nucleating agents, dyes, pigments, organic fillers, and mold-release agents may be blended with the polyamide resin composition of the present invention, provided that the characteristics are not lost.

EXAMPLES The present invention is explained in detail below.

Materials used in the examples were: (a) Semi-aromatic polyamide; copolyamide formed from terephthalic acid, hexamethylene diamine, and 2-methylpentamethylene di amine, in which the molar ratio of hexamethylene diamine to 2-methylpentamethylene diamine was 50 to 50; produced by E. I. du Pont de Nemours and Company.

(b) aliphatic polyamide: (bl) polyamide 66; produced by E. I. du Pont de Nemours and Company.

(b2) polyamide 612; produced by E. I. du Pont de Nemours and Company.

(b3) polyamide 46; produced by DSM.

(c) elastomeric polymer: (cl) maleic anhydride graft modified ethylene/propylene polymer; produced by Mitsui Petrochemical Industries.

(c2) maleic anhydride graft modified ethylene/propylene/diene polymer; produced by E. I. du Pont de Nemours and Company.

(c3) ethylene/propylene/diene polymer; produced by E. I. du Pont de Nemours and Company.

Following ASTM test methods were used: Tensile strength and elongation: ASTM D638-94b Flexural modulus and strength: ASTM D790-92 Notched Izod impact strength: ASTM D256-93a Example 1 A mixture of 1 1.2 keg of material (a); 5.6 kg of material (by), 3 kg of material (cl); 145 g heat stabilizer and antioxidants; and 70 g talc were dry-blended and fed into a ZSK-40 twin-screw extruder (manufactured by Werner & Pfeiderer Corp.) set at 3200C. The extruded resin was pelletized, molded, and tested. Mechanical properties were measured according to the ASTM, using 1/8-inch thick test pieces molded with mold temperature at 700C. Conditioned flexural modulus was measured using 1/8-inch thick test pieces which were conditioned in boiling aqueous solution of 50% potassium acetate for 72 hours.

Dimensions were measured before and after annealing at 1 600C for 24 hours for 1-mm thick test pieces molded with mold temperature at 400C , and the change was calculated as (length difference between before and after annealing)/(length before annealing) X 100.

Example 2 Test pieces were prepared and tested as in Example 1, except that material (bl) was replaced by the same amount of material (b2).

Example 3 Test pieces from a mixture of 10.7 kg of material (a); 5.3 kg of material (b3); 3.6 kg of material (cl); 290 g heat stabilizer and antioxidants; and 80 g talc were prepared and tested as in the Example 1.

Example 4 A mixture of 7.8 kg of material (a); 3.8 kg of material (bl); 1.36 kg of material (c2); and 0.68 kg of material (c3) were dry-blended and fed into a ZSK-30 extruder set at 3100C. The extruded resin was pelletized and molded and tested for mechanical properties as molded and as conditioned as in the Example 1.

Example 5 Test piecies from a mixture of 13.9 kg of material (a); 2.9 kg of material (b 1); 3-kg of material (cm); 145 g heat stabilizer and antioxidants; and 70 g talc were prepared and tested as in the Example 1.

Example 6 Test pieces from a mixture of 3.8 kg of material (a); 7.8 kg of material (bl); 1.36 kg of material (c2); and 0.68 kg of material (c3) were processed and tested as in the Example 4.

COMPARATIVE EXAMPLES Example 7 Test pieces from a mixture of 16.7 kg of material (a); 3 kg of material (cl), 200 g heat stabilizer and antioxidants; and 70 g talc were prepared and tested as in the Example 1.

Example 8 Test pieces from a mixture of 13.2 kg of material (a); 6.6 kg of material (bl); 80 g heat stabilizer; and 70 g talc were prepared and tested for mechanical properties and dimension as in the Example 1.

Example 9 Test pieces from a mixture of 11.6 kg of material (bl); 0.95 kg of material (c2); and 1.09 kg of material (c4) were dry-blended and fed into a ZSK-30 extruder set at 2700C and tested as in the Example 1

The test results are shown in Table 1.

Table 1 Examples (1) (2) | (3) (4) (5) (6) wt. ratio of(a)/(b) 2 2 2 2 5 0.5 aliphatic polyamide bl b2 b3 bl bl bl elastomeric polymer c 1 c 1 c I c2+c4 c l c2+c4 Tensile strength (MPa) 57.0 54.0 53.7 70.8 59.4 66.7 Elongation at break (%) 26 23 22 18 21 26 Flexural modulus (MPa) As molded 1960 1836 1898 2173 1952 1949 As conditioned 2240 2093 2095 2329 2426 1598 Notched Izod Impact (J/m) 728 101 855 780 656 721 Dimension change (%) 2.7 ~ 2.4 3.4 - 4.1 - Comparative Examples (7) (8) (9) wt.ratioof(a)/(b) infin. 2 0 aliphatic polyamide - bl bl elastomeric polymer cl - c2+c4 Tensile strength (MPa) 63.2 109 62.0 Elongation at break (%) 21 4.9 40 Flexural modulus (MPa) As molded 1904 2975 2281 As conditioned 2385 1035 Notched Izod Impact (J/m) 358 43 632 Dimension change (%) 7.0 ~ 1.4 - As has been described above, the polyamide compositions of the present invention retained properties at high temperature and with moisture while its molded articles exhibiting dimensional stability after molding and annealing.

Although particular embodiments of the present invention have been described in the foregoing description, it will be understood by those skilled in the art that the invention is capable of numerous modifications, substitutions and rearrangements without departing from the spirit or essential attributes of the invention. Reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.

In addition to the components discussed above, the compositions of this invention may contain additives commonly employed with synthetic resins, such as colorants, mold release agents, antioxidants, tougheners, nucleating agents, ultraviolet light and heat stabilizers and the like. An example of a common filler is magnesium hydroxide.