THERMOPLASTIC COMPOSITION HAVING HIGH FLUIDITY

Abstract

The invention concerns a thermoplastic composition having high fluidity in the molten state, comprising at least: (a) one thermoplastic polymer matrix; (b) one oligomer selected from cyclic ester oligomers, ether oligomers and mixtures thereof, said oligomer having a degree of polymerization of between 2 and 25; and (c) one phenolic polymer; said compounds (b) and (c) being present in a weight ratio (c)/(b) varying from 0.25 to 6, and preferably from approximately 0.75 to 2.75.

The invention also concerns a process for producing a composite article from such a composition by impregnating a reinforcement such as a fabric or a preform, the composite article obtained according to this process, and the use of an oligomer (b) in combination with at least one phenolic polymer (c), as a plasticizing additive in a thermoplastic polymer matrix.

Claims

1. A thermoplastic composition having high fluidity in molten state, comprising at least: (a) one thermoplastic polymer matrix; (b) one oligomer selected from cyclic ester oligomers, ether oligomers and mixtures thereof, said oligomer having a degree of polymerization of between 2 and 25; and (c) one phenolic polymer; said compounds (b) and (c) being present in a weight ratio (c)/(b) varying from 0.25 to 6.

2. The composition as claimed in claim 1, wherein said matrix comprises at least one polyamide.

3. The composition as claimed in claim 1, wherein said polyamide is selected from polyamides obtained by polycondensation of at least one aliphatic dicarboxylic acid with an aliphatic or cyclic diamine, polyamides obtained by polycondensation of at least one aromatic dicarboxylic acid and an aliphatic or aromatic diamine, polyamides obtained by polycondensation of at least one amino acid or lactam with itself, or blends thereof and (co)polyamides.

4. The composition as claimed in claim 2, said polyamide comprising hydroxyaromatic units chemically bonded to the chain of the polyamide.

5. The composition as claimed in claim 2, said polyamide having a weight-average molecular weight Mw of between 10 000 and 50 000 g/mol.

6. The composition as claimed in claim 2, said polyamide being selected from PA 66, PA 6.10, PA 6.12, PA 12.12, PA 4.6, MXD 6, PA 6, PA 7, PA 9T, PA 10T, PA 11, PA 12, PA 6T/61, PA 6T/61/66, copolyamides deriving therefrom, and blends thereof.

7. The composition as claimed in claim 1, said oligomer having a melting point Mp lower than or equal to that of the thermoplastic polymer matrix and a viscosity lower than that of the thermoplastic polymer matrix in the molten state.

8. The composition as claimed in claim 7, said oligomer being selected from: cyclic polyester oligomers such as cyclized poly(butylene terephthalate) or mixtures containing same; lactide oligomers, or mixtures containing same; lactone oligomers, or mixtures containing same; alkylene carbonate oligomers selected from ethylene carbonate, propylene carbonate, butylene carbonate and mixtures thereof; and mixtures thereof.

9. The composition as claimed in claim 1, said oligomer being selected from: ethylene glycol oligomers; propylene glycol oligomers; and mixtures thereof.

10. The composition as claimed in claim 1, said phenolic polymer being a product of condensation of phenol and formaldehyde.

11. The composition as claimed in claim 1, said phenolic polymer comprising units of formula (I) below: ##STR00005## wherein R represents a hydrogen atom or a linear or branched alkyl group comprising from 1 to 20 carbon atoms optionally comprising heteroatoms, m is between 6 and 15, and n is between 5 and 22.

12. The composition as claimed in claim 1, having, in the molten state, a viscosity of less than 75 Pa.Math.s.

13. The composition as claimed in claim 1, comprising: (a) from 80% to 99.8% by weight of polyamide(s); (b) from 0.1% to 10% by weight of cyclic ester oligomer(s), of ether oligomer or of a mixture or mixtures thereof; and (c) from 0.1% to 12% by weight of phenolic polymer(s).

14. A process for producing a composite article comprising at least one step of impregnating a reinforcing fabric or a preform with a composition as claimed in claim 1 in the molten state.

15. The process as claimed in claim 14, characterized in that it is a pultrusion process, preferably by direct injection, or an RTM process by closed-molding injection.

16. A composite article obtained by means of the process as claimed in claim 14.

17-19. (canceled)

Description

EXAMPLES

Example 1

Thermoplastic Compositions

[0207] Several compositions in accordance with the invention or outside the invention, based on polyamide PA66 22FE1 sold by Solvay under the name Stabamid, are prepared.

[0208] Thermoplastic polymer: the molecular weight is obtained by measurement using gel permeation chromatography (GPC), also known as size exclusion chromatography (SEC).

[0209] In the case of the polyamides, the GPC measurements of the PA6 and PA66 are carried out in dichloromethane (solvent and eluent), after chemical modification of the PA in order to solubilize it. A UV detector is used because the chemically modified PA has a UV chromophore. The calculation of the distribution of weights and also the average weights Mn and Mw is carried out in polystyrene equivalents after calibration using commercial standards. Absolute-weight measurements are carried out by viscometric detection. Mn and Mw values may be calculated from the entire distribution or after truncation of the low weights if it is not desired to take into account the contribution of the oligomers.

[0210] The polyamide of control composition (PA66 22FE1) has a melting point of 260° C. Its melt viscosity is measured according to the protocol previously detailed by means of a Rheometrics RDA3 rheometer (rheometer comprising a cone-plate device, 25 mm in diameter) at a temperature of 280° C., and is 70 Pa.Math.s.

[0211] The various compositions prepared all comprise polyamide PA66 22FE1, and either novolac resin (Rhenosin RB sold by the company Rhein Chemie) or cyclized poly(butylene terephthalate) (CBT 100 sold by Cyclics Corporation), or both, in the weight contents indicated in the table below. These compositions are obtained by melt-blending of the various constituents by extrusion using a Prism 25D twin-screw extruder. The rods coming out of the extruder are run into a water cooling tank and subsequently granulated.

[0212] The viscosity is then measured in the same way as for the polyamide PA66 22FE1 alone (control).

[0213] The results obtained are shown in table 1 below.

TABLE-US-00001 TABLE 1 Viscosity CBT resin at 10 Hz PA66 22FE1 (% by Novolac 280° C. (% by weight) weight) (% by weight) (Pa .Math. s) Control 100 0 0 68 Composition 1 94 0 6 42 (outside the invention) Composition 2 90 0 10 35 (outside the invention) Composition 3 96 4 0 25 (outside the invention) Composition 4 80 20 0 45 (outside the invention) Composition 5 90 4 6 20 (in accordance) Composition 6 86 4 10 15 (in accordance) Composition 7 88 6 6 12 (in accordance) Composition 8 80 8 12 10 (in accordance)

[0214] These results underline that the combined use of a plasticizer and of an antiplasticizer according to the invention in an antiplasticizer/plasticizer weight ratio in accordance with the invention makes it possible to very significantly reduce the melt viscosity of thermoplastic polymers such as PA66, thus promoting the impregnation of fibrous reinforcements with these compositions in the molten state.

[0215] The stability of the melt viscosity of the compositions obtained is evaluated through the melt viscosity values measured at t=0 min, t=10 min and t=15 minutes at a temperature of 280° C. (molten state).

[0216] The results obtained are shown in table 2 below.

TABLE-US-00002 TABLE 2 Stability of the Viscosity at 280° C. Measurement at 10 Hz as a function of time (0 -> 15 min) Viscosity Viscosity at Viscosity at Viscosity at at t.sub.15 min t.sub.0 (Pa .Math. s) t.sub.5 min (Pa .Math. s) t.sub.10 min (Pa .Math. s) (Pa .Math. s) Control 55 60 62 65 Composition 1 38 40 42 43 (outside the invention) Composition 2 32 34 35 35 (outside the invention) Composition 3 29 26 25 23 (outside the invention) Composition 4 35 40 45 43 (outside the invention) Composition 5 22 21 20 20 (in accordance) Composition 6 18 16 15 15 (in accordance) Composition 7 18 17 12 12 (in accordance) Composition 8 19 15 10 10 (in accordance)

[0217] This table shows that, in addition to allowing a significant reduction in the melt viscosity of thermoplastic polymers such as PA66, the compositions according to the invention have a melt viscosity which is stable or which slightly decreases over time, thereby also promoting the impregnation of fibrous reinforcements with these compositions in the molten state. On the other hand, the melt viscosity of the compositions outside the invention instead has a tendency to increase over time.

[0218] It should be noted that the addition of these compounds to the polyamide PA66 22FE1 has no effect on its glass transition temperature Tg or on its melting point Mp, when the cumulative content of plasticizer and antiplasticizer is less than 12%.

Example 2

Preparation of a Composite

[0219] The thermoplastic composition 5 of the previous example is used in this example for the preparation of a composite.

[0220] The reinforcing fabric used is an 8-harness satin glass fiber fabric having a grammage of 500 g/m.sup.2.

[0221] The thermoplastic composition in question is used in the form of granules or powder (low-viscosity polymer).

[0222] The powders are obtained by cryogenic milling, either in dry ice, or in liquid nitrogen, and are then dried (RH=0) for 12 h at 110° C. under vacuum.

[0223] Composite parts are prepared using a Schwabenthan (Polystat 300A) hydraulic press comprising two temperature-controlled plates: heating plates (heating resistances) and cooled plates (circulation of water). A metal mold having a cavity with dimensions of 150 mm×150 mm or 200×300 mm is used.

[0224] To produce a composite containing 60% by volume of glass fibers with the fabric having a grammage of 500 g/m.sup.2, introduced between the plates is a metal frame into which is placed a preform consisting of an alternating stack comprising 6 glass fabric sheets and uniformly distributed powder between each, the two external layers being glass fabric sheets.

[0225] The temperature of the plates of the press is increased beforehand to 275° C. (in the case of PA66) before introduction of the preform. At this temperature, the pressure is applied between 1 and 25 bar and maintained at this value; degassing operations may optionally be rapidly performed. The assembly is kept at the same temperature and pressure, without degassing, for a period of time sufficient to have good impregnation (stabilization of the pressure and of the distance between plates). The mold is then transferred onto the cooled-plate device and maintained at a pressure between 1 and 5 bar for a period of less than 5 minutes.

[0226] The cycle time is greater than 20 minutes for viscosities above 250 Pa.Math.s; it is reduced to approximately 10 minutes for viscosities between 200 and 700 Pa.Math.s; finally, for low viscosities (less than 50 Pa.Math.s), the cycle time becomes less than 5 minutes and the pressure may be notably decreased (less than 5 bar).

[0227] The composite parts thus obtained have a size of 150×150 mm or 200×300 mm and a thickness of approximately 2 mm.

[0228] The plasticizer/antiplasticizer combination provides the polyamide with excellent hot-wettability on fabric. This makes it possible to obtain a good level of interfacial cohesion between the polymer and the fibers of the reinforcement.

[0229] The very low viscosity of the thermoplastic compositions according to the invention thus allows excellent consolidation (void content: 0.1%) for a fiber content by volume of 60% and a short cycle time (less than 5 minutes). Thus, an overall cycle of 30 minutes may comprise 15 minutes of heating/5 minutes of temperature hold (T>Mp) and 10 min of cooling. The void content is measured by weighing (ASTM standard D2734-94), and optionally verified by observation using scanning electron microscopy (SEM) for low contents.

[0230] The cycle time corresponds to the total duration between the bringing of the mold to temperature and the cooling under pressure.