Impact-resistant and rigid polyamide compositions

Abstract

A molding composition including a thermoplastic processable polyamide, an elastomer, and an epoxy having a plurality of epoxide groups.

Description

The present invention is directed to impact-resistant and rigid polyamide compositions, more specifically such compositions which provide a high measure of rigidity and dimensional stability.

BACKGROUND OF THE INVENTION

Polyolefins have poor compatibility with a polyamide matrix. As a result, it is difficult to obtain blends which are both processable and practical and various expedients have been adopted in an attempt to solve this problem.

British Patent 998439 (German 1,241,606) teaches achieving high impact resistance by mixing two polyolefins into the rigid polyamides. In order to overcome the incompatibility problem, the olefins have unsaturated carboxylic acids grafted thereon.

Swiss Patent 649566 seeks to solve the same problem by introducing polyolefins based upon ethylene, propylene, and 1,4-hexadiene or 2,5-norbornadiene. These materials are activated by the introduction of .alpha., .beta. unsaturated dicarboxylic acids, anhydrides, or esters. Thus, the high bending E-modulus of the polyamide is modified by the unsaturated additives. Molded shapes prepared from such compositions have good impact and notched bar impact properties and high ductility. However, they are not sufficiently rigid, nor are they dimensionally stable. In other words, they have a great tendency to creep, which makes them unsuitable for many uses.

Another approach to the same problem is the introduction of core/shell polymers or grafted copolyolefins into rigid amorphous copolyamides. Such compositions are disclosed in U.S. Pat. Nos. 4,410,661 and 4,536,541. However, mixtures of the foregoing type exhibit substantial and undesirable shrinkage at elevated temperatures, even after only a short period of time. Therefore, shapes produced from such compositions are unsuitable for any use wherein exposure to elevated temperatures is involved.

A narrower improvement is shown in German 3,436,362, wherein rigid polyamides derived from terephthalic acid, isophthalic acid and alkanediamines form the basic material. To this is added copolymers of ethylene and/or acrylates to which carboxyl groups are grafted.

European Patent 27,198 teaches the addition of a core/shell polymer as a modifier of impact resistance. Acrylic acid derivatives are grafted onto a polybutadiene or butadiene/styrene core. This improves the impact resistance, but results in a substantial loss in stiffness. The patent teaches compensating for this loss by the addition of glass fibers.

U.S. Pat. No. 4,180,494 teaches the impact-resistance modifiers of the present invention, and German 3,339,000 teaches the use of similar core/shell polymers in conjunction with polyamides. However, molded shapes of this character are usually unsatisfactory, as they are not dimensionally stable. In particular, they tend to creep and to be highly susceptible to shrinkage under heat.

British Patent 1,069,176 seeks high thermal and dimensional stability for molded shapes by the addition of cross-linking diepoxides.

British 1,376,537 and German 2,144,687 introduce epoxide resins into plastomeric materials. These are substantially dimensionally stable and rigid; however, their impact-resistance is insufficient. Moreover, the presence of a high concentration of fillers and reinforcing agents produces a high density which, in many cases, is to be avoided.

Thus, there is a substantial need for polymeric materials which are impact-resistant, rigid, and dimensionally stable. In addition, such materials should be capable of simple injection molding. Such materials are used as casings and other protective parts in machines, vehicle bodies, etc.

BRIEF DESCRIPTION OF THE INVENTION

It is, therefore, desirable to provide molding compositions which are impact-resistant, rigid, dimensionally stable, without an excessive increase in density. Such products should have minimal creepage and shrinkage.

In accordance with the present invention, the foregoing requirements are met by the use of thermoplastic, processable polyamide compositions which contain an elastomer impact resistance modifier and an epoxide having more than one epoxide group.

In particular, it has been found that the combination of the epoxy compound and the impact resistance modifier in the polyamide produces a synergistic effect. The amount of modifier can be substantially reduced without impairing the desired impact properties. As a result, an improved relationship between resistance and rigidity can be obtained. Moreover, cost savings can also be realized. The shapes made from the foregoing materials are particularly stable and have minimal shrinkage when subjected to elevated temperatures.

DETAILED DESCRIPTION OF THE INVENTION

Polyamides which have been used as molding materials are generally useful in the present invention.

For example, specific mention is made of semicrystalline and amorphous copolyamides, e.g. those made from diamines and acidic monomers. Suitable diamines include hexamethylene diamine and its derivatives, mono and dicycloaliphatic diamines and derivatives thereof (especially of the alkylated bis(4-aminocyclohexyl)methane type) etc. The acids comprise isophthalic acid and terephthalic acid which may be substituted by other aromatic or aliphatic dicarboxylic acids.

Polyamide 6; polyamide 6,6; polyamide 6,10; polyamide 11; polyamide 12; and polyamide 6,12 have all been found to be suitable. Typical ether amides are reaction products of H.sub.2 N--(R--O).sub.n R--NH.sub.2 with dicarboxylic acids. The ether ester amides have ester linkages in addition to the --NH--CO-- linkages. The foregoing materials are preferably used in amounts of at least 40% by weight of the total molding composition.

The molding compositions preferably contain at least 3% by weight of the impact resistance modifying material, based upon the total molding composition. More preferably, 5 to 30% by weight is used and 10 to 20% by weight is most desirable.

Such modifiers include copolymers of .alpha. olefins which are activated by subsequent grafting with an unsaturated copolyolefin, preferably an .alpha.-unsaturated acid, and most preferably 1.0 mol % of an unsaturated dicarboxylic acid. This results in a maximum of 2.0 mol % carboxylic groups; ethylene is not more than 90 mol %, the rest preferably comprising propylene and/or 1-butene. Also, core/shell polymers are suitable. Preferably, these comprise a copolyolefin core which contains a butadiene or acrylate, and a shell of grafted vinyl compounds, e.g. acrylates. The metallic salts of the grafted copolymers (Ionomers) are not recommended because of the decrease in the number of adhesion sites.

Epoxy compounds suitable for use in the present invention are those which have at least two epoxy groups. Preferably, these are terminal, i.e. located at the ends of the molecule. Of special desirability are those epoxies having more than one glycidyl ether group in the molecule. They increase the molecular weight by linking the polyamide molecules. Very small amounts are sufficient; often an optimum can be found at less than 1% by weight, based on the total molding composition. It is preferred to use 0.05 to 5% and most preferred to use 0.1 to 1.0%, based on the molding composition. Polymeric epoxy compounds containing at least two epoxy groups or glycidyl groups in each molecule are also useful in the present invention.

Diglycidyl ethers having the formula Y--O--X--O--Y have been found especially advantageous. Y is an epoxide carrying radical and X is a divalent radical taken from the class consisting of alkyl having 2 to 10 carbons and aralkyl having 7 to 20 carbons. Those which are derivatives of neopentyl glycol and/or bisphenol A are deserving of particular mention.

Preparation of the compositions of the present invention is substantially conventional. The ingredients are premixed in the usual types of apparatus; such as, vibrating mixers, stirring mixers, mills, or phase mixers. Processing takes place in the melted form using screw machines such as extruders or plasticorders. These devices produce the compositions as granulates, strands, etc. which are then formed in injection molding machines or extruders in the usual manner.

Of course, normal additives, such as stabilizers, pigments, lubricants, emulsifiers, release agents, colorants, flame retardants, mineral or metallic fillers, reinforcing agents, etc. can all be included as needed.

EXAMPLES

The polyamide starting material was mixed sequentially with the impact resistance modifier and the epoxy compound. The combination was homogenized on a Werner Pfleiderer ZSK 30 two-phase extruder at 220.degree. to 290.degree. C. Thereupon, extrusion took place to yield a strand which was comminuted to form a uniform granulate. The granulate was dried under nitrogen at 80.degree. to 90.degree. C. and a vacuum of 30 to 50 mbar. Test bodies were then prepared using an Arburg extruder (type 320-210-250) and the various properties of the test bodies were measured.

The results are shown in Tables I to V herein. Some of the samples contain no epoxy and constitute comparisons with the prior art. The compositions set forth in Tables I to IV contain copolyolefin modifiers derived from ethylene, propylene, 1-butene modified with maleic acid anhydride. Table V displays the results of tests using the core/shell polymer. The melt viscosities are in Pas at 270.degree. C. and 122.6N.

The impact and notch resistances were measured according to DIN 53453 dry at 23.degree. C. No break is indicated by nb. The bending E modulus and the limit bending stress were determined in accordance with DIN Norm 53452 and the shrinkage values in the longitudinal direction are in accordance with DIN tension bars 53445/3. They were measured after storage for 24 hours in a circulating air oven at 100.degree. C. and, in another test, for 1 hour at 140.degree. C. The shrinkage values were determined for DIN tension bars 53445/3 after dry storage for 24 hours after injection molding. The values are given in percentages.

In Tables I, V and VI, polyamide 6 (melting point 221.degree. C.) was used. In Table II, an amorphous polyamide which is the reaction product of hexamethylenediamine and isophthalic acid was the starting material. It had a glass transition temperature of 140.degree. C.

Table III shows the results of the use of Grilamid TR 55 (T.sub.g 155.degree. C.) which is also described in U.S. Pat. No. 4,356,300. Table IV describes the use of polyamide 12 having a melting point of 178.degree. C. All the foregoing polyamides are commercial products of EMS-Chemie AG of Domat/Ems, Switzerland.

The preferred epoxy compound of Tables I to V is neopentyl diglycidyl ether, also known as 2,2'-(2,2-dimethyl-1,3-propanediyl)-bis(oxymethylene)bisoxirane. In Table II, test (1), 1,4-butanediglycidyl ether was used. Table VI shows the use of the diglycidyl ether derived from bisphenol A. G1302, a product of EMS-Chemie AG, has a molecular weight of 385.

TABLE I__________________________________________________________________________Polyamide 6 - moulding materials with impact-resistance-modifier derivedfrom dicarboxylic acids-grafted copolyolefines__________________________________________________________________________ 5 6 7 2 4 Impact Notch Bending Impact- 3 Melt Resis- Impact E Modu- 1 Resis- Digly- Viscos- tance Resist lus0 Poly- tance cidyl ity 23.degree. C./ 23.degree. C./ 23.degree. C./Test amid- modifier ether (270.degree./ dry dry dryNo. wt. % wt. % wt. % 122.6N) kJ/m2 kJ/m2 N/mm2__________________________________________________________________________(a) PA 6 0 0 350 nb 6.0 2000A28 100pure(b) PA 6 0 0.4 `403 nb 4.1 2645E 5006 99.6(c) PA 6 15 -- 578 nb 35.4 1203E 5179 85(d) PA 6 15 0.2 1363 nb 38.1 1950E 5178 84.8(e) PA 6 15 0.4 1342 nb 44.7 1940E 5005 84.6(f) PA 6 15 0.5 1032 nb 53.3 1870E 5487 84.5(g) PA 6 12 0.5 1177 nb 32 2160E 5180 87.5(h) PA 6 10 1.0 6071 nb 39 1243E 4913 89.0(i) PA 6 10 3.0 >10000 nb 69.5 2625E 4796 87.0(k) PA 6 20 0.4 681 nb 14.3 1667E 5007 73.6 (-40.degree.) 50.4(e) 75 20 5.0 >10000 nb nb 2045E 4575(l) 77.7 19.4 2.9 2065 nb 66.6 2039E 4574 nb 30.6(E 3752) (-20.degree.) (-20.degree.)(m) 80 20 -- 136 nb 42 1517A 28NZ__________________________________________________________________________ 10 12 8 9 Elon- 11 Exten- Limit Yield gation Tensile sion 13 140 Bending Stress at Strength at Shrinkage ShrinkageTest Stress 23.degree. C./ Yield 23.degree. C./dry Break after afterNo. N/mm2 dry % N/mm2 % 24 h/100.degree. C. 1 h/140.degree. C.__________________________________________________________________________(a) 100 85 10 55 10 -0.36 -0.75A28pure(b) 109 -- -- -- -- -0.22 -0.32E 5006(c) 84 57.3 7.0 42 17.2 -0.38 -0.47E 5179(d) 83 56.3 7.8 65.3 264 -0.30 -0.36E 5178(e) 79.6 -- -- -- -- -0.28 -0.35E 5005(f) 80 -- -- -- -- -- --E 5487(g) 90 42 7.3 53.3 144 -0.16 -0.33E 5180(h) 91.3 -- -- -- -- -- --E 4913(i) 104 -- -- -- -- -- --E 4796(k) 68.6 -0.28 -0.40E 5007(e) 77.7 -- -- -- -- -- --E 4575(l) 79.6 -- -- -- -- -- --E 4574(E 3752)(m) 62 45 5 50 150 -0.47 -0.58A 28NZ__________________________________________________________________________ TABLE II__________________________________________________________________________Amorphous copolyamide (type XE 3038) derived from hexamethylenediamine/isophthalicacid with impact-resistance-modifier (impact-resistance-modifier as inTable I)__________________________________________________________________________ 5 6 7 2 4 Impact Notch Bending Impact- 3 Melt Resis- Impact E Modu- 8 1 Resis- Digly- Viscos- tance Resist lus Limit0 Poly- tance cidyl ity 23.degree. C./ 23.degree. C./ 23.degree. C./ BendingTest amid- modifier ether (270.degree./ dry dry dry StressNo. wt. % wt. % wt. % 122.6N) kJ/m2 kJ/m2 N/mm2 N/mm2__________________________________________________________________________(a) A2771 100 0 0 1755 40% nb 1.5 2960 166XE 3038 60% 60(b) 99.7 0 0.3 2643 40% nb 1.6 3120 125E 6248 60% 58(c) 86.8 13 0.2 2643 nb 47.0 2350 114E 6248(d) E4471 85 15 -- -- nb 38 1991 100.3E 6603(e) 84.8 15 0.2 2994 nb 51.3 2238 110E 5864(f) 84.7 15 0.3 3407 nb 49.2 2241 112E 5864(g) 84.6 15 0.4 4440 nb 49.9 2288 114E 5866(h) 80 20 -- 4027 nb 42.2 1880 93E 5275(i) 79.9 20 0.1 4801 nb 43.6 1920 92E 6753(k) 79.8 20 0.2 -- nb 45.6 2110 102E 6601(l) 84.7 15 0.3 4130 nb 47.1 2299 114E 5867__________________________________________________________________________ 13 14 10 12 Longi- Longi- 15 9 Elon- 11 Exten- tudinal tudinal % Yield gation Tensile sion Shrink- Shrink- Injection0 Stress at Strength at age age ShrinkageTest 23.degree. C./ Yield 23.degree. C./dry Break after after afterNo. dry % N/mm2 % 24 h/100.degree. C. 1 h/140.degree. C. 24 h__________________________________________________________________________(a) A2771 110 10.5 70 62 0.0132 -0.332 +0.218XE 3038(b) -- -- -- -- -0.33 -1.1E 6248(c) 73 8 55 25 -0.05 -0.54E 6248(d) E4471 -- -- -- -- +.17 -2.0-4.0E 6603(e) 68 9 55 46 -0.092 -3.8E 5864(f) 70 7 57 61 -0.07 -3.1 +0.315E 5864(g) 70 7 54 25 -0.03 -2.6E 5866(h) 65 7 56 65 +0.188 -5.0-8.0 -0.5-0.E 5275(i) -- -- -- -- +0.02 -3.9 +0.374E 6753(k) 67 6.5 56 8 -0.071 -2.36E 6601(l) 70 8.5 53 18 -0.04 -3.6E 5867__________________________________________________________________________ TABLE III__________________________________________________________________________Amorphous Copolyamide TR55 (impact-resistance-modifier as in Table__________________________________________________________________________I) 5 6 7 2 4 Impact Notch Bending Impact- 3 Melt Resis- Impact E Modu- 8 1 Resis- Digly- Viscos- tance Resist lus Limit0 Poly- tance cidyl ity 23.degree. C./ 23.degree. C./ 23.degree. C./ BendingTest amid- modifier ether (270.degree./ dry dry dry StressNo. wt. % wt. % wt. % 122.6N) kJ/m2 kJ/m2 N/mm2 N/mm2__________________________________________________________________________(a) 100 0 0 1200-1500 nb 5.0 2100 118TR55(b) E5428 99.7 0 0.3 2189 nb 5.26 2160 --E5716 99.7 0 0.3 1241 nb 5.09 2080 119(c) 99.6 0 0.4 1446 nb 5.03 2190 --E 5482(d) 90 10 -- 1516 nb 21.9 1730 101F3-55(e) 89.7 10 0.3 3511 nb 23.8 1860 98E 6180(f) 85 15 -- 1454 nb 30.9 1737 89F3-56(g) 84.6 15 0.4 2601 nb 34.9 1780 88E 5255(h) 80 20 -- 1755 nb 37.7 1504 77F3-57(i) 79.6 20 0.4 2815 nb 40.2 1800 95E 7287__________________________________________________________________________ 13 14 10 12 Longi- Longi- 15 9 Elon- 11 Exten- tudinal tudinal % Yield gation Tensile sion Shrink- Shrink- Injection0 Stress at Strength at age age ShrinkageTest 23.degree. C./ Yield 23.degree. C./dry Break after after afterNo. dry % N/mm2 % 24 h/100.degree. C. 1 h/140.degree. C. 24 h__________________________________________________________________________(a) 75 8 60 30 -0.07 -0.09 0.8-1.0TR55(b) E5428 -- -- -- -- -- --E5716 80 11 55 24(c) -- -- -- -- -0.16 0.4E 5482(d) 64 20 54 33 -0.30 -1.3 -0.5F3-55(e) 64 10 50 50 -0.08 -0.36 -0.36E 6180(f) 50.7 21 48 36 -0.50 -1.2 -0.53F3-56(g) 60 10 52 82 -0.23 - 0.98E 5255(h) 21 22 44 36 -0.58 -2.6 -0.69F3-57(i) 68 18 57 28 -0.073 -0.24 -0.40E 7287__________________________________________________________________________ TABLE IV__________________________________________________________________________Polyamide 12 with impact-resistance-modifier (impact-resistance-modifieras in Table I)__________________________________________________________________________ 5 6 7 2 4 Impact Notch Bending Impact- 3 Melt Resis- Impact E Modu- 1 Resis- Digly- Viscos- tance Resist lus0 Poly- tance cidyl ity 23.degree. C./ 23.degree. C./ 23.degree. C./Test amid- modifier ether (270.degree./ dry dry dryNo. wt. % wt. % wt. % 122.6N) kJ/m2 kJ/m2 N/mm2__________________________________________________________________________Gril- 100 -- -- nb 14.4 1256amid(a) L25(b) 99.75 -- 0.25 1853 nb 15.6 1420E6413(c) 99.6 -- 0.4 -- nb 23.2 1680E5254(d) 91.7 8 0.3 3698 nb 72.8 1350E6424(e) 89.7 10 0.3 3089 nb 65.3 1290E6423(f) 86.0 10 4.0 >10000 nb nb 2243E3535(g) 90 10 -- 320 nb nb 380E3536__________________________________________________________________________ 13 14 10 12 Longi- Longi- 8 9 Elon- 11 Exten- tudinal tudinal Limit Yield gation Tensile sion Shrink- Shrink-0 Bending Stress at Strength at age ageTest Stress 23.degree. C./ Yield 23.degree. C./dry Break after afterNo. N/mm2 dry % N/mm2 % 24 h/100.degree. C. 1 h/140.degree. C.__________________________________________________________________________Gril- 64 44 9 47 178 +0.25 +0.9amid(a) L25(b) 65 45 7 44 126 +0.20 +0.82E6413(c) 72 50 7 60 153 +0.13 +0.5E5254(d) 60 40 8 44 120 -0.14 +0.8E6424(e) 57 38 10 46 140 -0.24 -0.6E6423(f) 122 -- -- -- -- -- --E3535(g) 58 38 23 42 280 -0.36 +1.15E3536__________________________________________________________________________ TABLE V__________________________________________________________________________Polyamide 6 with impact-resistance-modifier derived from core-sheathpolymers__________________________________________________________________________ 5 6 7 2 4 Impact Notch Bending Impact- 3 Melt Resis- Impact E Modu- 1 Resis- Digly- Viscos- tance Resist lus0 Poly- tance cidyl ity 23.degree. C./ 23.degree. C./ 23.degree. C./Test amid- modifier ether (270.degree./ dry dry dryNo. wt. % wt. % wt. % 122.6N) kJ/m2 kJ/m2 N/mm2__________________________________________________________________________(a) 100 -- -- 350 nb 4.0 2000A28 pure(b) 91.6 8 0.4 372 nb 7.3 2570E 5253(c) 89.6 10 0.4 454 nb 14.4 2360E 5004(d) 84.6 15 0.5 -- nb 18.5 2380E 5223(e) 75 25 -- 434 nb 38 1572A28 NT(f) 74.6 25 0.4 2394 nb 60% nb 1698E 5008 40% 50(h) 72 25 3.0 5369 nb 42.8 2005E 4572(i) 70 25 5.0 -- nb nb 1974E 5473__________________________________________________________________________ 13 14 10 12 Longi- Longi- 8 9 Elon- 11 Exten- tudinal tudinal Limit Yield gation Tensile sion Shrink- Shrink-0 Bending Stress at Strength at age ageTest Stress 23.degree. C./ Yield 23.degree. C./dry Break after afterNo. N/mm2 dry % N/mm2 % 24 h/100.degree. C. 1 h/140.degree. C.__________________________________________________________________________(a) 100 83 10 55 30 -0.36 -0.75A28 pure(b) 106 73 7 54 10 -0.28 -0.48E 5253(c) 97 ` -- -- -- -- -0.40 -0.50E 5004(d) 91 63 7 51 123 -0.42 -0.34E 5223(e) 66.2 45 5 40 110 -0.65 -0.57A28 NT(f) 69.6 -- -- -- -- -0.48 -0.39E 5008(h) 78.5 -- -- -- -- -- --E 4572(i) 76.8 -- -- -- -- -- --E 5473__________________________________________________________________________ TABLE VI__________________________________________________________________________Polyamide 6 with impact-resistance-modifier (C elastomeric copolyolefinetype) and diglycidyl ether 4 5 6 2 Melt Impact Notch 7 10 12 Impact- 3 Viscos- Resis- Impact Bending 8 9 Elon- 11 Exten- 1 Resis- Digly- ity tance Resist E Modu- Limit Yield gation Tensile sion0 Poly- tance cidyl (270.degree./ 23.degree. C./ 23.degree. C./ lus Bending Stress at Strength atTest amid- modifier ether 122.6N) dry dry 23.degree. C./ Stress 23.degree. C./ Yield 23.degree. C./dry BreakNo. wt. % wt. % wt. % kJ/m2 kJ/m2 N/mm2 dry N/mm2 dry % N/mm2 %__________________________________________________________________________A28NZ 80% 20 -- 136 nb 42 1517 62 45 5 50 150E7716 84.2% 15 0.8% 814 nb 44.4 1951 78 56 6 62 150 G1302E7718 79.2% 20 0.8% 2808 nb 53.8 1760 69 48 7 51 135 G1302__________________________________________________________________________

Claims

1. A rigid molding composition consisting essentially of a thermoplastic processible polyamide, an elastomer, and an epoxy having a plurality of epoxide groups, said epoxy has the formula

Y--O--X--O--Y

wherein Y is an epoxide carrying radical and X is a divalent radical taken from the class consisting of alkyl of two to ten carbon atoms and aralkyl of seven to twenty carbon atoms, wherein said elastomer is at least one copolymer of an .alpha.-olefin grafted with an unsaturated dicarboxylic acid, said elastomer comprising 3 to 20 percent by weight of said composition.

2. The composition of claim 1 wherein said polyamide comprises at least 40% by weight of said composition.

3. The composition of claim 1 wherein said amount is 10 to 20%.

4. The composition of claim 1 wherein said epoxy is neopentyl diglycidyl ether, bisphenol A derived diglycidyl ether, or a mixture thereof.

5. The composition of claim 1 wherein said epoxy comprises 0.01 to 15% by weight of said composition.

6. The composition of claim 5 wherein said epoxy comprises 0.05 to 5.0% by weight of said composition.

7. The composition of claim 1 wherein said copolyolefin comprises a maximum of 90 mol % ethylene and is grafted with a maximum of 1 mol % of unsaturated dicarboxylic acid thereby providing a maximum of 2 mol % active carboxylic groups.

8. The composition of claim 6 wherein said epoxy comprises 0.1 to 1.0% by weight of said composition.