Process for producing shaped articles of a polymer composition containing a polyamide, halogen-free flame retardant and glass fibers

Abstract

The invention relates to a process for producing shaped articles comprising the steps of: compounding a polymer composition (A) containing a polyamide, a halogen-free melamine based flame retardant and at most 15 wt. % of glass fibers into pellets, compounding a polymer composition (B) containing a polyamide, more than 15 wt. % of glass fibers, and not containing halogen-free melamine based flame retardant into pellets, producing a mixture comprising the pellets of polymer composition (A) and (B), molding the mixture comprising the pellets of polymer composition (A) and (B) into shaped articles.

Claims

1. A process for producing shaped articles comprising the steps of: (a) forming polymer pellets (A) of a polymer composition (A) by compounding in a first kneader a polyamide, a halogen-free melamine based flame retardant and at most 15 wt. % of glass fibers, (b) forming polymer pellets (B) of a polymer composition (B) by compounding in a second kneader a polyamide and more than 15 wt. % of glass fibers in the absence of a halogen-free melamine based flame retardant, (c) producing a mixture of pellets comprising the polymer pellets (A) of polymer composition (A) and the polymer pellets (B) of polymer composition (B), and (d) injection molding into articles the mixture of pellets comprising the polymer pellets (A) of polymer composition (A) and the polymer pellets (B) of polymer composition (B).

2. The process according to claim 1, wherein the mixture comprises, based on total weight of the mixture of the polymer pellets (A) and the polymer pellets (B), 50-90 wt. % of the polymer pellets (A) of the polymer composition (A) and 50-10 wt. % of polymer pellets (B) of the polymer composition (B).

3. The process according to claim 1, wherein the polyamide in the polymer compositions (A) and (B) has a melting point below 260 C. as measured by DSC, according to ISO 11357-1:1997 under nitrogen atmosphere (purge 50 ml/min) using a heating and cooling rate of 20 K/min.

4. The process according to claim 1, wherein the polyamide comprises polyamide-6 (PA-6) or polyamide-66 (PA-66).

5. The process according to claim 1, wherein the polymer composition (A) contains 15-30 wt. % halogen-free melamine based flame retardant.

6. The process according to claim 1, wherein the halogen-free melamine based flame retardant of polymer composition (A) is phosphorous-free.

7. The process according to claim 1, wherein the halogen-free melamine based flame retardant is selected from the group consisting of melamine, melamine cyanurate, melam, melem and mixtures thereof.

8. The process according to claim 1, wherein the output of at least one of the first and second kneaders when producing the polymer pellets (A) and (B) of the polymer compositions (A) and (B), respectively, is more than 100 kg/hour.

9. The process according to claim 1, wherein the pellets (A) of composition (A) and the pellets (B) of composition (B) have a length dimension and either a width dimension or a diameter dimension, and wherein a ratio of the length of the pellets (A) of composition (A) to the length of the pellets (B) of composition (B) as well as a ratio of either the width of the pellets (A) of composition (A) to the width of the pellets (B) of composition (B) or a ratio of the diameter of the pellets (A) of polymer composition (A) to the diameter of the pellets (B) of polymer composition (B) is each between 0.5 and 1.5.

10. The process according to claim 1, wherein the pellets (A) of composition (A) and the pellets (B) of composition (B) have a length dimension and either a width dimension or a diameter dimension, and wherein a ratio of the length of the pellets (A) of composition (A) to the length of the pellets (B) of composition (B) as well as a ratio of either the width of the pellets (A) of composition (A) to the width of the pellets (B) of composition (B) or a ratio of the diameter of the pellets (A) of polymer composition (A) to the diameter of the pellets (B) of polymer composition (B) is each between 0.8 and 1.2.

Description

EXAMPLES

(1) Ingredients:

(2) PA6: Akulon K122 from DSM

(3) Glass fiber: 173X-11p from 3B fiberglass

(4) Flame retardant: melamine cyanurate MC50 from BASF

(5) Flame retardant: Exolit OP1311 from Clariant

(6) Mold release agent: ethylene-bis-stearamide (Acrawax C) from Lonza

(7) Experimental.

(8) All compositions were compounded on a 40 mm co-rotating twin screw extruder (Berstorff ZE40/48UTS). The polymer, flame retardants and mold release agent were added to the feed opening of the extruder, the glass fibers were dosed downstream to the extruder, where the polymer was in the molten state. The pellets were mixed in a tumble dryer. The final pellet mixtures were molded into various test samples for property testing using an Engel 75A injection moulding machine: 80801.5 mm plaques for GWIT testing. 1.5 mm UL94V specimen for the vertical burning test ISO 527-1A specimen for tensile testing.
GWIT tests were conducted in accordance with IEC60695-2-13, tensile tests were done in accordance with ISO527 and vertical burning tests were conducted in accordance to UL 94V.
Table 1 gives an overview of the experiments performed.

(9) TABLE-US-00001 TABLE 1 experiments performed CE-A CE-B (A) (B) E1 PA6 56.8 44.3 46.4 39.34 glass-fiber 25 25 10 60 MRA 0.2 0.2 0.66 MeCy 12.5 17.9 OP1311 18 18 25.7 (A) 70 (B) 30 strand integrity OK foamed OK OK tensile modulus [Mpa] 9000 x 11000 tensile strenght [Mpa] 130 x 115 eab [%] 2 x 2 GWIT @ 1.5 mm [ C.] 775 x 825 UL 94V @ 1.5 mm V0 x V0

Comparative Experiment A and B

(10) In comparative experiment A (CE-A) the polymer composition does not contain any melamine cyanurate, but different flame retardants. It shows that the flame retardant is thermally sufficiently stable to survive the processing of glass filled PA6 on a twin screw extruder. The material can be pelletized and is usable for injection-molding to transform it into shaped articles. However the GWIT levels are below 800 C. and therefor do not fulfill the requirements.

(11) Comparative experiment B (CE-B) proves that when Melamine cyanurate is added to the formulation of CE-A the material can no longer be pelletized due to massive degradation of the melamine cyanurate resulting in foaming of the extruded strand. Such material cannot be used for injection-molding.

Example I

(12) A composition (A) containing a high amount of the flame retardants, among which the melamine cyanurate and a small amount of glass fibers is produced that can be stranded into good quality pellets. Further a highly glass fiber filled composition (B) is produced, which does not contain flame retardant. Also this composition was easily be stranded into good quality pellets. See further table 1 (A) and (B).

(13) The two compositions (A) and (B) were mixed in a 30:70 ratio to obtain the final granulate mixture that was injection molded into the test samples articles. Compared to CE-A this sample has better GWIT ratings and compared to CE-B this route allows for the production of shaped articles by injection molding.