GB1575339A

GB1575339A - Polyamide moulding compositions

Info

Publication number: GB1575339A
Application number: GB4940577A
Authority: GB
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1976-12-01
Filing date: 1977-11-28
Publication date: 1980-09-17
Also published as: FR2372866B1; JPS5952670B2; IT1090592B; JPS5371157A; NL7713093A; DE2654346C2; CH631195A5; DE2654346A1; FR2372866A1

Abstract

The moulding composition based on a polyamide contains up to 25% by weight of a copolymer of ethylene, acrylic acid or methacrylic acid, all or some of which is optionally in the form of a salt, and at least one ester, amide or nitrile of acrylic acid or methacrylic acid, and up to 25% by weight of polyethylene and/or ethylene-vinyl acetate copolymer. The moulding composition is suitable, with or without addition of auxiliaries, for the production of mouldings having surprisingly high notched impact strength at low temperatures.

Description

(54) POLYAMIDE MOULDING COMPOSITIONS (71) We, BAYER AKTIENGESELLSCHAFT, a body corporate organised under the laws of Germany, of 509 Leverkusen, Germany; do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: Polyamides based on r-caprolactam and adipic acid/hexamethylene diamine show outstanding properties of toughness combined with elasticity. However, optimum toughness is only obtained by a conditioning treatment, i.e. after the absorption of water.

The polyamides do not take up the necessary water in a matter of seconds or minutes. On the contrary, conditioning is a time-consuming process which lasts several days, especially since the water must not be concentrated in surface layers, but instead should be uniformly distributed throughout the entire moulding.

Accordingly, repeated efforts have been made, for example by admixture with suitable substances, to provide the polyamides having the toughness in the dry state which they otherwise only acquire by conditioning in water.

The toughness of polyamides may be improved, for example, by the addition of polyethylene. However, standard commercial-grade polyethylene is not compatible with the polyamides. Test specimens produced from such blends undergo considerable flaking when subjected to bending tests.

It is also known that copolymers of ethylene and (meth)acrylic acid or a derivative thereof, for example an ester or an amide, may be used as compatibility promoters for the otherwise incompatible mixture of polyamide and polyethylene. Blends of this type are described, for example, in German Auslegeschrift No. 1,544,706 = British patent 1072635 and in German Offenlegungsschrift No. 1,694,805 = British patent 1157569. However, these mixtures contain a high percentage of polyethylene (from 40 to 90 % by weight), whereby the E-modulus is considerably reduced. An object of the investigations which lead to the present invention was to improve toughness without appreciably affecting the level of the other properties. For example, the high stiffness and, hence the E-modulus of polyamide moulding compositions were to remain substantially intact.

It was surprisingly found that the moulding compositions show considerably higher toughness but remaining intact required polyamide properties when copolymers of at least three components are used as compatibility promoters for polyamide/polyethylene mixtures instead of hitherto used binary copolymers, for example of ethylene and (meth)acrylic acid, in which the carboxyl groups may be completely or partly present in salt form, or of ethylene and a (meth)acrylic acid amid, ester or nitrile.

Accordingly, the present invention relates to high-impact thermoplastic moulding compositions consisting of: (1) from 65 to 99.4% by weight, preferably from 65 to 96% by weight of a polyamide: (2) from 0.1 to 25% by weight, preferably from 1 to 20% by weight, of a copolymer consisting of a) 99.8 to 40 mol % ethylene b) 0.1 to 30 mol% (meth)acrylic acid, which may be partly or completely present in salt form and c) 0.1 to 30 mol % of at least one ester, amide or nitrile of (meth)acrylic acid, the sum of a) to c) amounting to 100 mol %, and (3) from 0.5 to 25% by weight, preferably from 3 to 15% by weight, of polyethylene and/or ethylene-vinyl acetate copolymer, the vinyl acetate content of the copolymer amounting to from 0.1 to 30 mol %; the sum of components (1) to (3) amounting to 100% by weight.

The at least ternary copolymers may consist, for example, of: ethylene, (meth)acrylic acid, C4-C18 preferably C3-C8 esters of (meth) acrylic acid; ethylene (meth)acrylic acid, amide of (meth)acrylic acid; or ethylene, (meth)acrylic acid, nitrile of meth ) acrylic acid.

Particularly preferred moulding compositions are those in which copolymer component (2) has the following composition: (a) 98 to 86 mole % of ethylene; (b) 1 to 6 mole % of (meth)acrylic acid which may be completely or partly present in salt form; and (c) 1 to 8 mole % of at least one ester, amide or nitrile of (meth)acrylic acid, preferably n-butyl acrylate or tertbutyl acetate the sum of components (a) to (c) amounting to 100 mole %. Suitable salts of (meth)acrylic acid are Na-, K-, Ca-, Mg-, Zn-, NH4- and amine salts, preferably Zn-salts.

In order not to reduce the stiffness of the moulding compositions excessively, the total quantity of polyethylene, ethylene-vinyl acetate copolymer (and) ternary copolymer should preferably not exceed 35 % by weight, based on the moulding composition.

In the dry state, the moulding compositions according to the present invention have an at least 30 % higher notched impact strength than moulding compositions containing comparable quantities of a binary copolymer.

The advantages afforded by using the at least ternary copolymers in accordance with the present invention are particularly noticeable at low temperatures. At -20 , the notched impact strengths are generally as much as 50 % higher than in cases where comparable binary copolymers are used.

Suitable polyamides for the moulding compositions according to the present invention are polyamide-6, polyamide-6,6, polyamide-11, polyamide-12, mixtures and block polymers of these components and copolymers of the starting substances of the polyamides, such as the corresponding lactams, adipic acid and hexamethylene diamine. It is also possible to use polyamides of which the acid component consists completely or partly of terephthalic acid and/or isophthalic acid. Polyamide-6 and polyamide-6,6 are preferably used.

The relative viscosity of the polyamide component is from 2 to 6 (as measured on a solution of 1 g of polyamide in 99 g of m-cresol at 250C). The melt index (MI) of polyethylene and of the copolymers generally amounts to from 0.1 to 30 (190í2, DIN 53 735).

The polyamide moulding compositions according to the present invention may contain the conventional reinforcing agents, fillers, pigments and auxiliaries. Such additives include: glass fibres, asbestos fibres, glass beads, talcum, wollastonite, microvite, chalk, quartz, mould release agents and lubricants, Ti02, ZnS, carbon black, and cadmium sulphide.

The additives are preferably added during the compounding of the moulding compositions either in pure form or in the form of concentrates. However, the additives may also be completely or partly present in one or more of the starting components.

Intensive-kneading twin-screw extruders are advantageously used for compounding.

However, it is also possible to use single-screw extruders and other machines of the type commonly used for processing thermoplastics, for example kneaders.

The moulding compositions produced in accordance with the present invention are suitable for the injection moulding and extrusion of high-impact mouldings.

Examples 1 to 6 In a twin-screw extruder having a screw length of 25 times the diameter, polyamide-6 (relative viscosity 2-89, as measured on a solution of 1 g of polyamide in 99 g of m-cresol at 25"C) was mixed with the quantities of copolymer and polyethylene indicated in Table 1 at temperatures of from 270 to 280"C. Test specimens were produced from the moulding composition and were used immediately after injection for determining notched impact strength in accordance with DIN 53 453 and the flexural stress at a given deflection in accordance with DIN 53 452.Immediately after injection-moulding, the polyamide component used for the production of the moulding compositions had a flexural stress at a given deflection of 120 MPa at 20"C and a notched impact strength of 2.9 KJ/m2 at 200C and 2.2 KJ/m2 at -20 C. TABLE 1 Examples Copolymers of ethylene %, by weight.Polyethylene %, by weight, Notched Flexural and of the copolymer in having MI** of poly- impact stress at a the ethylene strength given deflection composition (KI/m2) at 20 C (MPa) 20 C -20 C 1 - - 4.9 10 3.2 2.4 98 Comparison tes 2 3.4 mole % of tert.-butyl acrylate (MI**=5.8) 4 4.9 6 4.2 2.9 101 Comparison test 3 1.65 mole % of tert.-butyl acrylate and 1.7 mole % of acrylic acid (MI**=5.9) 4 4.9 6 11.8 4.8 99 4 3.4 mole % of acrylic acid (MI**=6) 4 4.9 6 3.8 2.8 103 Comparison test 5 1.65 mole % of n-butylacrylate and 1.7 mole % of acrylic acid (MI**=6.5) 4 4.9 6 10.2 4.6 97 6 1.2 mole % of acrylamide and 2.2 mole % of acrylic acid (MI**=5.6) 4 4.9 6 9.8 4.6 96 **MI = melt index (190/2) in g/10 mins.

Examples 7 to 9 In a twin-screw extruder, moulding compositions were produced as in the preceding Examples from polyamide-6 (relative viscosity 3.94, as measured on a solution of 1g of polyamide in 99 g of m-cresol at 25"C) and the copolymers indicated in Table 2 and a copolymer of ethylene and 2 mole % of vinyl acetate. Notched impact strength and flexural stress at a given deflection were determined on corresponding test specimens in accordance with DIN 53 453 and DIN 53 452, respectively. Immediately after injection moulding, the polyamide component used for the production of the moulding compositions had a flexural stress at a given deflection of 126 MPa at 200C and a notched impact strength of 3.4 KJ/m2 at 20"C and 2.4 KJ/m2 at -200C.

Copolymers of Notched impact Flexural stress at ethylen and strength (KJ/m2) a given deflection TABLE 2 2 mole %of (MPa) at 20 C vinyl acetate 20 C -20 C Examples Copolymers of ethylene % by weighte, MI = 1.6 and of copolymer (%, by weight) 7 - - 10 5.3 2.5 103 Comparison tes 8 9.7 mole % of acrylic acid (MI = 6.2) 4 6 8.5 4.1 100 Comparison test 9 3.2 mole % of dodecyl acrylate and 6.3 mole % of acrylic acid (MI = 5.1) 4 6 15.3 6.1 98 Examples 10 to 12 In a twin-screw extruder, moulding compositions were produced at temperatures of from 280 to 2900C from polyamide-6,6 (relative viscosity 2.98, as measured on a solution of 1 g of polyamide in 99 g of m-cresol at 250C) and the quantities indicated in Table 3 of copolymer and polyethylene orF ethylene/vinyl acetate copolymer.Notched impact strength and flexural stress at a given deflection were determined in the same way as in the preceding Examples. Immediately after injection moulding, the polyamide component in the moulding compositions had a flexural stress at a given deflection of 124 MPa at 200C and a notched impact strength of 2.5 KJ/m2 at 200C and 1.9 KJ/m2 at -20 C.

TABLE 3 Examples Copolymers of ethylene %, by weight. Polyethylene %, by weight, Notched impactFlexural stress and of the copolymer of poly- strength (KJ/cm2)at a given ethylene deflection 20 C -20 C (MPa) at 20 C 10 - - MI = 4.9 10 3.5 2.3 102 Comparison tes 11 1.65 mole % of n-butyl acrylate (MI = 6.5) 1.7 mole % of acrylic MI - 4.9 6 9.8 4.8 97 acid (MI = 6.5) 4 12 1.65 mole % of n-butyl acrylate and 1.7 mole % of acrylic MI = 1.6* 6 12.4 6.1 101 acid (MI = 65) 4 * copolymer of ethylene and 2 mole % of vinyl acetate.

Examples 13 to 17 In a twin-screw extruder, a copolyamide of 90 mole % of E-caprolactam, 5 mole % of isophthalic acid and 5 mole % of hexamethylene diamine (relative viscosity 2.86, as measured on a solution of 1 g of polyamide in 99 g of m-cresol at 25"C) was mixed at from 250 to 2600C with the quantities indicated in Table 4 of a copolymer and a polyethylene or an ethylene-vinyl acetate copolymer. The notched impact strength and flexural stress at a given deflection of the moulding compositions were determined in the same way as in Examples 1 to 6.Immediately after injection moulding, the polyamide component used for the production of the moulding compositions had a flexural stress at a given deflection of 108 MPa at 20"C and a notched impact strength of 3.1 KJ/m2 at 20"C and 2.3 KJ/m2 at -200C.

TABLE 4 Examples Copolymers of ethylene %, by weight. Polyethylene %, by weight, of Notched Flexural stress and of copolymer polyethylene copolymer impact at a given and 2 mole % strength deflection of vinyl (KJ/m2 (MPa) at 20 C acetate 20 C -20 C 13 - Comparison tes MI = 1.6 10 3.7 2.5 93 14 3.4 mole % of acrylic acid (MI = 6) 4 MI = 1.6 6 4.8 3.5 85 Comparison test 15 3.4 mole % of tert.-butyl acrylate (MI = 5.8) 4 MI = 1.6 6 5.2 3.3 92 Comparison test 16 1.65 mole % of n-butylacrylate and 1.7 mole % of acrylic acid (MI= 6.5) 4 MI = 1.6 6 10.9 5.7 87 17 1.65 mole % of n-butyl acrylate and 1.7 mole % of acrylic acid (MI = 6.5) 4 MI = 4.9* 6 9.4 4.1 95 18 3.4 mole % of acrylic acid (MI = 6), Comparison approximately 30% of 4 MI = 4.9* 6 5.9 3.8 94 test the carboxyl groups present in Na-salt

Claims

WHAT WE CLAIM IS:

1. Moulding compositions consisting essentially of: (1) from 65 to 99.4 % by weight of a polyamide; 2 from 0.1 to 25 % by weight of a copolymer consisting of (a) from 99.8 to 40 mole % of ethylene; from 0.1 to 30 mole % of (meth acrylic acid which may be partly or completely present in salt form; and (c) from 0.1 to 30 mole % of at least one ester, amide or nitrile of (meth)acrylic acid; the sum of components (a) to (c) being 100 mole %, and (3) from 0.5 to 25 % by weight of polyethylene and/or ethylene-vinyl acetate copolymer, the vinyl acetate content of the copolymer being from 0.1 to 30 mole %, the sum of components (1) to (3) being 100 % by weight.

2. Compositions as claimed in claim 1 consisting of: (1) from 65 to 96 % by weight of a polyamide; (2) from 1 to 20 % by weight of a copolymer of ethylene, (meth)acrylic acid, which may be completely or partly present in salt form, and at least one ester, amide or nitrile of (meth)acrylic acid; and (3) from 3 to 15 % by weight of polyethylene and/or ethylene-vinyl acetate copolymer, the vinyl acetate content of the copolymer being from 0.1 to 30 mole %; the sum of components (1) to (3) being 100 % by weight.

3. Compositions as claimed in claim 1 in which component (2) essentially consists of: (a) from 98 to 86 mole % of methylene; (b) from 1 to 6 mole % of (meth acrylic acid; which may be partly or completely present in salt form; and (c) from 1 to 8 mole % of at least one ester, amide or nitrile of (meth)acrylic acid; the sum of components (a) to (c) being 100 mole %.

4. Compositions as claimed in claim 1 in which component (2 c) is the amide, nitrile or C4-C22 ester of (meth)acrylic acid.

5. Compositions as claimed in claim 4 in which component (2 c) is the C4-Cto ester of (meth)acrylic acid.

6. Compositions as claimed in claim 5 in which component (2 c) is the n-butyl or tert.-butyl acrylate.

7. A composition as claimed in claim 1, substantially as herein described.

8. A composition as claimed in claim 1 substantially as herein described with reference to any one of the Examples.