POLYAMIDE RESIN COMPOSITIONS

Abstract: Polyamide resin compositions containing 82-93 % by weight of a non-crystalline polyamide, 5-12 % by weight of an ethylene-propylene terpolymer, and 2.5-6 % by weight of a thermoplastic, semicrystalline polyamide resin are found to have high impact resistance and high energy absorption characteristics.

Description: TITLE POLYAMIDE RESIN COMPOSITIONS BACKGROUND OF THE INVENTION This invention relates to polyamide resin compositions having high impact resistance, high energy absorption characteristics, excellent moldability and coating properties, and low specific gravity. The compositions are useful in the production of the molded products requiring such characteristics. There are known impact-resistant polyamide resin compositions which are based on semi- or non-polyamides and compounded with at least 20% by weight of an ethylene-propylene terpolymer (called hereafter EPDM) for improving the impact resistance (see, e.g., Japanese Patent Kokoku 55-44108). Such compositions have been proposed for use in molded products requiring impact resistance, such as automotive bumpers, a fenders for automobiles, motorcycles, snowmobiles, traveling suitcases, trunks, helmets, or the like. Those polyamide resin compositions which are based on semi- or non-polyamides and compounded with EPDM, because of their high impact resistance, are suitable for the production of the molded products requiring impact resistance. If the products are molded thinner to reduce the weight, however, their elongation at break becomes low thus leading to a breakage of the molded products by small external force. Therefore, polyamide resin compositions have been demanded which have high elongation at break and nevertheless have high rigidity, thus exhibiting excellent energy absorption when an external force is applied. SUMMARY OF THE INVENTION The present invention provides a polyamide resin composition with high impact resistance and high energy absorption characteristics which consists of a polymer blend comprising 82 to 93% by weight of a non- crystalline resin, 2 to 12% by weight of EPDM, and 2.5 to 6% by weight of a thermoplastic, semicrystalline polyamide resin. The invention also provides a polyamide resin molded product wherein such polyamide resin composition is used in the production of the molded parts requiring the energy absorption characteristics. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph showing a change in breaking energy relative to a change in the content of EPDM and 66 nylon in the polyamide resin composition. Fig.2 is a plan view of a helmet molded from the polyamide resin composition of the present invention. Fig.3 is a sectional view taken substantially along the lines I-I of Fig.2. DETAILED DESCRIPTION OF THE INVENTION The present invention is based on the discovery that reducing to 7.5-18% by weight the contents of EPDM and thermoplastic, semicrystalline polyamide resin incorporated for improving the impact resistance in a conventional impact-resistant polyamide resin composition based on the non-αystalline polyamide and compounded with at least 20% by weight of EPDM and thermoplastic, semicrystalline polyamide resin can produce a polyamide resin composition having high elongation at break, high rigidity and excellent energy absorption characteristics, while retaining the impact resistance of the conventional impact-resistant polyamide resin representative of notched Izod impact strength. Based on such discovery, there was obtained a polyamide molded product with high impact resistance, high elongation at break, high rigidity, and excellent energy absorption characteristics, even if its weight is reduced by molding thinner. A non-crystalline polyamide resin, a principal component of the present polyamide resin composition, is a group of particular polyamides wherein almost no crystallization of polymer occurs or the rate of crystallization is very small, which is also called a transparent nylon. Further, the non-crystalline resin as defined herein is characterized by transparency due to non-crystalline property, provides a transparent molded article under a conventional condition of melt molding in which no loss of clarity occurs by after-crystallization upon heat treatment and water absorption treatment and does not have a definite melting point and also a measurable heat of fusion. The heat of fusion is conveniently measured by a differential scanning calorimeter (DSC). Suitable calorimeter is 990 thermal analysis apparatus manufactured by E. I. du Pont de Nemours and Company. In the present invention, those having less than 1 cal/g of heat of fusion as measured by this apparatus are defined as a non-ciystalline polyamide resin. Processes of producing such non-crystalline polyamide resins can include those by the use of particular monomers or by copolymerization and in combination therewith. For the production of non-crystalline polyamide resins it is necessary to use a structure segment to inhibit a crystallization, i.e., a monomer component containing a side chain to provide a polymer chain with its irregularity and a ring structure such as cyclohexane and phenol rings. Examples of dicarboxylic acids, aminocarboxylic acids or intramolecular amides thereof and diamines which are used for the production of such non-crystalline polyamide resins can include dicarboxylic acids such as adipic acid, sberic acid, azelaic acid, sebacic acid, dodecanoic diacid, terephthalic acid, isophthahc acid and cyclohexane- 1,4-dicarboxylic acid; caprolactam, lauric lacta or ring open products thereof, i.e., c.,ω- amino carboxylic acid; and diamines such as 1,6-hexamethylenediamine, trimemyl-l,6-hexamethylenediamine, 1,3-or 1,4- bis(_iminomethyl)cyclohexane, bis(p-aminocyclohexyl)methane(or 4,4'- ώamino-dicyclohe- ylenemethane), 4,4'-m ' amino-3,3 '-dimethyl- dicyclohexylenemethane, 4,4'-diamino-dicyclohexylenepropane, l-amino-3- __π____to-meώyl-3,5,5-trimethylcyclohexane(or isophorone diamine), 2,2,4- trimethylhexamethylenediamine and 2,4,4-trimethylhexamethylenediamine. Specific examples of the non-crystalline polyamide resins are recited below. a) Polyamides prepared from hex_unethylenediamine and a mixture of 55-100% by weight of isophthahc acid and 45-0% by weight of terephthalic acid based on the total weight of the acids, b) Polyamides prepared from a mixture of 70-100% by weight of 2,2,4-and 2,4,4-trimemylhexamethylenediamine and 30-0% by weight of hexamethylenediamine(based on the total weight of the diamines) and a mixture of 0-100% by weight of terephthalic acid and 100-0% by weight of isophthahc acid(based on the total weight of the acids), c) Polyamides prepared from i) an alicyclic diamine of 8-20 carbon atoms containing at least one cyclohexyl component, ii) 50-100% by weight of isophthahc acid 50-0% by weight of terephthalic acid, 10-50% by weight(based on the total weight of the polyamides) of a lactam of 4-12 carbons, ω-amino acid or an ahphatic dicarboxylic acid of 4-12 carbons and an aliphatic diamine of 2-12 carbons, and d) Polyamides prepared from i) 40-98 mol % of isophthalic acid based on the total acid being present, ϋ) 2-60 mol % of terephthalic acid based on the total acid being present, iii) 50-98 mol % of hexamemylenediamine based on the total amine being present and iv) 2--50 mol % of at least one aliphatic diamine having 6-20 carbons and containing at least one cyclohexane ring based on the total amine being present. The non-crystalline polyamide may be used alone or in combination with a plurality of any species to prepare a polyamide composition. EPDM, the second component constituting the polyamide resin composition of the present invention refers to a terpolymer prepared by subjecting to stereospecifϊc polymerization α-olefins of 3-6 carbons containing ethylene and propylene in the presence of dienes as a third component. The terpolymers include various types depending on a ratio of α-olefins to the third component and the kind of the third component. A rubber-like elastomer is preferred comprising 30-70% of ethylene, 60-25% of α-olefins of 3-6 carbons containing propylene and 10-5% of dienes. The dienes constituting the third component of EPDM include divinylbenzene, 1,4-cyclohexadiene, cyclooctadiene, dicyclopentadiene, ethylidene norbomene, 1,4-hexadiene, butadiene, isoprene or the like, but limiting thereto. Any dienes can be used which are copolymerized with ethylene and propylene or α-olefins other than propylene to produce a rubber-like elastomer. Examples of EPDM include copolymers of eftylene/propylene/divinyl benzene, ethylene/propylene/1,4- cyclohexadiene, ethylene/propylene/cyclooctadiene, ethylene/propylene/dicyclopentadiene, ethylene/propylene/ethylidene norbomene, ethylene/propylene/l,4-hexadiene, ethyIene/propylene/1,3- butadiene and ethylene/propylene/isoprene. EPDM may be grafted with minor amount of fumaric acid, maleic acid, monoalkylesters of these acids wherein the alkyl group contains 1-3 carbon atoms or maleic anhydride, examples of which can include copolymers of ethylene/propylene/l,4-hexadiene grafted with maleic anhydride, ethylene/propylene/l,4-hexadiene grafted with fumaric anhydride, ethylene/propylene/l,4-hexadiene/norbornadiene grafted with maleic anyhydride, ethylene/propylene/l,4-hexadiene/norbornadiene grafted with maleic monoethyl ester, ethylene/propylene/1,4- hexadiene/norbornadiene grafted with fumaric acid, ethylene /propylene/5- ethylidene-2-norbornene grafted with fumaric acid, ethylene/propylene/dicyclopentadiene grafted with monoethyl maleate, ethylene/propylene/5-propenyl-2-norbomene grafted with maleic anhydride, ethylene/propylene/l,4-hexadiene/5-ethylidene-2-norbornene grafted with fumaric acid or the like. Those EPDM may be used alone to corporate in the non- crystalline polyamide resins. More than two different EPDM may be used in admixture therewith. Further, those EPDM can be used in admixture with minor amount of other polymers or copolymers such as butadiene/acrylonitrile copolymer, styrene/maleic anhydride copolymer, ethylene/propylene copolymer, ethylene/maleic anhydride copolymer, polyethylene, butyl aαrylate/monoethyl fumarate copolymer, ethylene/methyl methacrylate copolymer, ethylene/isobutyl acrylate/methacrylic acid copolymer and metallic salts thereof. The thermoplastic semicrystalline polyamide resin which is the third component constituting the polyamide resin composition of the present invention is characterized by definite melting point having a measurable heat of fusion. The resins having a heat of fusion exceeding 1 cal/g as measured on differential scanning calorimeter are defined as thermoplastic semicrystalline polyamide resins in the present invention. The semicrystalline 66 nylon polyamide having a molecular weight of about 17000 has a heat of fusion of about 10 cal/g. Semicrystalline polyamide resins are known. They can be prepared from the condensation in equimolar amounts of an ahphatic saturated dicarboxyhc acid of 4-12 carbons having a molecular weight exceeding 10000 and an ahphatic diamine of 2-12 carbons. In this case, the diamine may be used if desired, in the amount to provide in the polyamide an amine terminal group in excess of a carboxyl terminal group. To the contrary, the dicarboxyhc acid may be used in the amount to provide an acid terminal group in excess. The polyamides can also be prepared from the derivatives of the dicarboxyhc acid and diamine such as esters, acid chlorides and amine salts thereof. Representative ahphatic dicarboxyhc acids which are used for the production of polyamides include adipic acid, pimeric acid, azelaic acid, sberic acid, sebacic acid and dodecanedionic acid. Representative ahphatic diamines include hexamethylenediamine and octamethylenediamine. The polyamides can be prepared from the autocondensation of lactam. Examples of polyamides include polyhexamethylene adipamide(66 nylon), polyhexamethylene azeramide(69 nylon), polyhexamethylene sebacamide(610 nylon), polyhexamethylene dodecanoamide(612 nylon), polybis(p- aminocyclohe-_yl)me_hanedodecanoamide or polyamides prepared fromthe ring opening polymerization of lactam such as polycaprolactam(6 nylon) and polylauryl lactam. There can be also used the polyamides prepared from the polymerization of at least one amine and acid used for the production of said polymers, for example polymers from adipic or sebacic acid and hexamethylenediamine. The blends of polyamides such as a blend of 66 nylon and 6 nylon or the copolymers such as a copolymer of nylon 66/nylon 6 are also included. The polyamide resin compositions of the present invention may contain if necessary stabilizers, pigments, fillers and other additives usually used in such resin composition, in addition to the non-crystalline polyamide EPDM and the thermoplastic semicrystalline polyamide resins. The polyamide resin compositions of the present invention can be prepared by mixing the non-crystalline polyamide resin EPDM and the thermoplastic semicrystalhne polyamide resins in the prescribed proportion, if necessary with the additives and milling it in a double-screw extruder. The milling is performed at a temperature above the melting point of the non- crystalline polyamide resin used, usually in the range of 200°C-300°C. The polyamide resin compositions as prepared by milling are molded immediately as they are or formed into chips and molded into a desired molded product using suitable injection or extrusion molding machine. The polyamide resin compositions may be molded optionally by compression molding means. The invention will be further illustrated by the following examples. EXAMPLES Example 1 i . Non-Crvstalline Polyamide Resin The non-crystalline polyamide resin used in this example has a composition of 6I/6T/PACM I/PACM T= 66.8/26.6/3.2/1.4% by weight. 61 stands for a unit of hexamethyleneώamine(HMD) and isophthahc acid(I). 6T stands for a unit of HMD and terephthalic acid(T). PACM I stands for a unit of bis(p-_umnocyclohexyl)methane(PACM) and I. PACM T stands for a unit of PACM and T. The above polyamide resin was prepared in the following manner. To 9958 lbs. of water were added 2185 lbs. of water-containing HMD having a concentration of 80% HMD and 115 lbs. of PACM containing about 59- 60% of cis, trans isomers. This mixture was heated to 60°C and 1215 lbs. of I and 778 lbs. of T were added. The pH of this salt solution was adjusted to 8.6± 0.1 with HMD. After the pH adjustment, 4.68 lbs. of sodium phenyl sulfonate were added. 6000 lbs. of the salt solution(containing 1800 lbs. of the salt) were charged in a preevaporator and the solution was concentrated to about 80% of the volume at a pressure of 20 psig. and a temperature of 120-140°C. The concentrated solution was placed into an autoclave to which were added 7.2 lbs. of glacial acetic acid and polyethylene oxide. The salt solution was heated and the pressure was elevated to 250 psig. Excessive water was flow out gradually while maintaining that pressure. When the batch temperature reached about 280°C, the pressure was dropped gradually to normal pressures within 90 minutes and the content of the autoclave was maintained at normal pressures for about 45 minutes. The polymer was extruded from the autoclave under a nitrogen pressure, cooled was cut into a pellet. The inherent viscosity was 0.73. This polymer was coated with 0.09% by weight of aluminum distearate lubricant. ii. EPDM EPDM used in this example is a mixture comprising (a) 10% of a graft copolymer with Mooney viscosity of 50-60 at 121°C by ASTM D 1646 ML-2 wherein fumaric acid is grafted onto a copolymer of ethylene/propylene/hexadiene/norbornadiene in a weight ratio of 66-70/35- 29/4.1/0.4 to provide a 1.8% fumaric acid grafting and (b) 90% of the copolymer which is not grafted with fumaric acid. iii) Thermoplastic Semicrystalline Polyamide Resin The thermoplastic semicrystalline polyamide resin used in this example is 66-nylon. iv) Preparation and Physical Properties of Polyamide Resin Composition The composition comprising 91% by weight of non-crystalline polyamide resin, 6% by weight of EPDM and 3% by weight of 66 nylon was dried, injection-molded to prepare a test piece and measured for tensile strength, elongation, flexural modulus, Uexural strength, Izod value, specific gravity, shrinkage factor and heat deformation temperature. The testing methods are recited below. (1) Tensile Strength ASTMD638 (2) Elongation ASTMD 638 (3) Flexural Modulus ASTMD 790 (4) Flexural Strength ASTM D 790 (5) Izod Value ASTM D 256 (6) Specific Gravity ASTMD 792 The results of these measurements are shown in Table 1. The energy absorption characteristics were tested over a high- velocity impact testing machine. The test ρiece(100mm X 100mm X 3-2mm) was attached to the testing machine and an impact core(tip shape: 5/8 inch hemispherical) was allowed to collide with the test piece at a speed of 7.66 m/sec to determine a displacement and stress using a load cell. The amount of energy at break was calculated from the determined values. The result is shown in Table 2. Example 2 The same non-crystalline polyamide resin, EPDM and 66 nylon as used in Example 1 were used in different proportions from those in Example 1. That is, a composition comprising 85% by weight of non-crystalline polyamide resin, 10% by weight of EPDM and 5% by weight of 66 nylon was used to prepare a test piece in a similar manner as in Example 1. The test piece was measured for the physical properties. The result is shown in Table 1. The energy absorption characteristics were tested in a similar manner as in Example 1 with the results as shown in Table 2. Comparative Example 1 The same non-crystalline polyamide resin, EPDM and 66 nylon as used in Example 1 were used in different proportions from those in Example 1. That is, a composition comprising 95% by weight of non-crystalline polyamide resin, 3% by weight of EPDM and 2% by weight of 66 nylon was used to prepare a test piece in a similar manner as in Example 1. The test piece was measured for the physical properties. The result is shown in Table 1. The energy absorption characteristics were tested in a similar manner as in Example 1 with the results as shown in Table 2. Comparative Example 2 The same non-crystalline polyamide resin, EPDM and 66 nylon as used in Example 1 were used in different proportions from those in Example 1. That is, a composition comprising 81% by weight of non-crystalline polyamide resin, 13% by weight of EPDM and 6% by weight of 66 nylon was used to prepare a test piece in a similar manner as in Example 1. The test piece was measured for the physical properties. The result is shown in Table 1. The energy absorption characteristics were tested in a similar manner as in Example 1 with the results as shown in Table 2. Comparative Example 3 A composition comprising 80% by weight of nylon 66 and 20% by weight of EPDM was used to prepare a test piece in a similar way as in Example 1. The test piece was measured for the physical properties. The result in shown in Table 1. The energy absorption characteristics were tested in a similar manner as in Example 1 with the results as shown in Table 2. Comparative Example 4 100% of non-crystalline polyamide resin was used to prepare a test piece in a similar way as in Example 1. The result is shown in Table 1. TABLE 1 Example No. Comparative Example No. 1 2 1 2 3 4 Composition (wt.%. Non-crystalline nylon 91 85 95 81 0 100 " 66 Nylon 3 5 2 6 80 0 EPDM 6 10 13 20 0 Physical Properties Tensile Strength - 810 770 870 633 527 984 (kg/cm 2 ) Elongation 176 172 177 120 60 215 Hexural Strength 1110 1010 1240 (kg/cm 2 ) Flexural Modulus 26900 22900 27400 20400 17200 28120 (kg/cm 2 ) Notched Impact Strength (cm.kg/cm) • 102.8 103.3 17.1 103.4 92.5 Specific Gravity 1.15 1.13 1.17 1.11 1.08 1.19 TABLE 2 Example No. Comparative Example No. 1 2 1 2 3 Composition (wt.%. Non-crystalline nylon 91 85 95 81 0 66 Nylon 80 EPDM 10 13 20 Measured Valued . Amount of Energy at 136 125 25 84 81 break (23°C) The energy absorption characteristics as measured for the compositions of Examples 1 and 2 as well as those of Comparative Examples 1, 2 and 3 were taken as a change in breaking energy on a change in the contents of EPDM and 66 nylon in the polyamide resin composition and plotted on a seniilogarithmic graph as shown in Fig. 1. From Fig. 1, it is found that the contents of EPDM and 66 nylon in the polyamide resin composition range from 7% to 18%, if preferred range of breaking energy(J) is assumed as 100 or more, which greatly exceeds the level satisfying JISC species which are most severe criterion in a helmet performance test defined in Japan Industry Standard. The following referential example illustrates the production of a helmet molded from the polyamide resin composition of the present invention. REFERENTIAL EXAMPLE Figs. 2 and 3 show an example of helmet molded according to the present invention. Referring to the drawings, numeral 1 designates a cap shell body having at the bottom an opening 2 for insertion of a head and at the front a sight window 3, at the circumferences of which are provided a welting la, lb of heavy-walled. The cap shell body 1 is integrally molded from the afore-described non-crystalline polyamide resin composition. Further, the shell cap body 1 is lined on the inside with a liner 4 molded from a formed polystyrene, as indicated with a chain line in Fig. 2. The inside of a liner 4 is provided with a soft cushion such as polyurethane (not shown). The shell cap body is molded by an injection molding. In this case, a melted non-crystalline polyamide resin composition is casted into a mold through a gate as shown in Fig.2 with an arrow G. The streams of the melted resin within the mold are as shown in Fig. 3 with a solid line arrow and a broken line arrow. There are the stream indicated in the solid line arrow which flows from the back to the front along a wide region of large cross-section area such as the welting and the stream indicated in the broken line arrow which flows from the back to the front along a narrow region of small cross-section area such as the shell body. Such two streams have a difference in the flow rate. The stream indicated with the solid line arrow is faster than that with the broken line arrow. Therefore, a gas pocket is apt to occur at the front head indicated at A in the shell cap body structure as shown in Figs.2 and 3. It may be responsible for defective molding. The provision of a convex lc can result in increased rate of the melted resin flowing from the back to the front along the shell body in the direction of the broken line as shown in Figs.2 and 3, while keeping the front in a filled condition before the resin in the solid line arrow reach the front, thus preventing an occurrence of a gas pocket. As is evident from the results shown in Table 2, the non- crystalline polyamide resin compositions of the present invention possess excellent energy absorption characteristics per unit weight, so that the weight of the molded product can be reduced to about 2/3 by reducing its wall thickness while keeping the energy absorption performance of the product. With regard to the mechanical properties, the polyamide resin compositions of the present invention possess an impact resistance equal to a prior impact resistant 66 nylon and still have a higher rigidity, so that about 15% reduction in wall thickness of the molded product can result in equal rigidity to prior products, thus meeting the weight-saving of the molded products such as a helmet.

Claims: CLAIMS: 1. A polyamide resin composition, with high impact resistance and high energy absorption characteristics, consisting essentially of a blend of 82 to 93% by weight of a non-crystalline polyamide, 5 to 12% by weight of an ethylene-propylene terpolymer, and 2.5 to 6% by weight of a thermoplastic, semicrystalline polyamide resin. 2. A polyamide resin molded product wherein the polyamide resin composition of Qaim 1 is used for the production of the molded product requiring high energy absorption characteristics. 3. A polyamide resin molded product of Claim 2 wherein the molded product requiring high energy absorption characteristics is helmet.

Inventors: HIRONO SACHIHIRO, HOMMA JOJI, KIMURA YOSHINOBU, KOBAYASHI FUJIO, SUNAKO AKIHIKO, YOSHIKAWA TADAO, HIRONO, SACHIHIRO, HOMMA, JOJI, KIMURA, YOSHINOBU, KOBAYASHI, FUJIO, SUNAKO, AKIHIKO, YOSHIKAWA, TADAO
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1992
Main classification: C08L77
IPC codes: C08J5, C08L77