METHOD FOR THE CONTINUOUS PRODUCTION OF A COMPOSITE MATERIAL PROFILE SECTION FROM THERMOPLASTIC POLYMER HAVING HIGH FLUIDITY

Abstract

The invention relates to a method for continuous production of a composite material profile by injection-pultrusion from at least one reinforcing fabric and at least one thermoplastic polymer having high fluidity, said method being characterized in that: i) said fabric is continuously pulled with a pulling speed of at least 0.4 m.Math.min.sup.1 in the course of said process; ii) the impregnation stage is performed by injection of a polymeric composition having high fluidity through the fabric; iii) the profile is then shaped with a specific thermal profile.

The invention also relates to a profile obtained according to the method of the invention and a composite article comprising such a profile the curvature whereof may be modified in its curvature by bending and/or its profile by rotational molding.

Claims

1. A method for continuous production of a composite material profile by injection-pultrusion from at least one reinforcing fabric and at least one thermoplastic polymer, said method comprising: a) supplying a thermoplastic polymeric composition of viscosity less than or equal to 50 Pa.Math.s and based on one or more thermoplastic polymers in the molten state and, b) supplying a reinforcing fabric at a temperature less than 400 C., and greater than or equal to the temperature of said polymeric composition in the molten state, c) impregnating said fabric with said polymeric composition; d) shaping said fabric impregnated with said polymeric composition to form a shaped composite material with a profile, wherein i) said fabric is continuously pulled with a pulling speed of at least 0.4 m.Math.min.sup.1 in the course of said process; ii) the impregnation stage c) is performed by injection of said polymeric composition in the molten state through the fabric; iii) the profile is shaped in stage d) with a thermal profile such that: its surface temperature is less than the crystallization temperature of said polymeric composition if semi-crystalline and less than 125 C. above the glass transition temperature (Tg) of said polymeric composition if amorphous, and its core temperature is greater than the crystallization temperature of said polymeric composition if semi-crystalline and higher than 50 C. above the glass transition temperature (Tg) of said polymeric composition if amorphous.

2. The method as claimed in claim 1, further comprising a cooling stage following the shaping stage d), in which said profile is cooled throughout its thickness at a temperature ranging from 150 C. to 50 C.

3. The method as claimed in claim 1, in which said fabric is continuously pulled with a pulling speed ranging from 0.4 to 12 m.Math.min.sup.1 by means of a pulling apparatus positioned downstream of the channel devoted to the shaping stage.

4. The method as claimed in claim 1, in which said polymeric composition utilized at c) has in the molten state a viscosity ranging from 1 to 30 Pa.Math.s.

5. The method as claimed in claim 1, in which said polymeric composition is formed of at least one semi-crystalline or amorphous polyamide or of a mixture thereof.

6. The method as claimed in claim 5, in which said polyamide is semi-crystalline and has a weight average molecular weight Mw lying between 6,000 and 25,000 g/mol.

7. The method as claimed in claim 1, in which the impregnation stage c) and shaping stage d) proceed in a common channel comprising successively a hot entry zone, a hot impregnation zone having an injection chamber, a thermal control zone, and a shaping zone, optionally, said channel being provided with a vent, devoted to the elimination of gaseous residues or air.

8. The method as claimed in claim 1, in which the impregnation stage c) and shaping stage d) proceed in two distinct and consecutive channels, the first channel comprising successively a hot entry zone and a hot impregnation zone having an injection chamber, the second channel comprising a shaping zone, optionally, said first channel being provided with a vent, devoted to the elimination of gaseous residues or air.

9. The method as claimed in claim 1, in which the impregnation stage c) and shaping stage d) proceed in two distinct and consecutive channels, the first channel comprising successively a hot entry zone and a hot impregnation zone having an injection chamber, said first channel being provided with a vent, devoted to the elimination of gaseous residues or air, the second channel comprising a calendering machine or a train of several calendering machines at controlled temperature.

10. The method as claimed in claim 1, further comprising a temperature stabilization stage c) following the impregnation stage c) and before the shaping stage d), in which said fabric impregnated with the polymeric composition in the molten state is brought to a temperature less than 380 C. and greater by at least 10 C. than the melting point of said polymeric composition if comparable to a semi-crystalline material and greater by at least 100 C. than the glass transition temperature of said polymeric composition if comparable to an amorphous material.

11. The method as claimed in claim 1, further utilizing at least one lubricating agent, in stage c) and/or d).

12. The method as claimed in claim 11, which said lubricating agent is selected from polymer production auxiliary agents selected from: polyvinylidene fluoride, polytetrafluoroethylene, plasticizers, mineral fillers, and mixtures thereof.

13. The method as claimed in claim 1, in which the profile obtained on emergence from the shaping stage d) has, throughout its thickness, a temperature less than the crystallization temperature of the thermoplastic polymeric composition if semi-crystalline, and less than 60 C. beyond the glass transition temperature of the thermoplastic polymeric composition if amorphous.

14. The method as claimed in claim 1, in which said shaped profile has a volume of reinforcing fabric ranging from 35 to 75% relative to the total volume of the profile.

15. (canceled)

16. A composite article comprising at least one profile obtained by the method as claimed in claim 1.

Description

EXAMPLE 1: EFFECT OF THE TEMPERATURE GRADIENT REQUIRED ACCORDING TO THE INVENTION

[0225] A method for continuous production of a profile by pultrusion is performed by means of the device described above utilizing the polyamide A, namely the PA66 available from SOLVAY. This polyamide has a melting point of 260 C., a crystallization temperature of 220 C., and a melt viscosity less than 20 Pa.Math.s at a temperature of 285 C. with a shear rate of 10 s.sup.1.

[0226] In the hot entry zone, the tape is brought to the desired temperature for performing the impregnation stage, namely 300 C.

[0227] It is maintained at that temperature until total impregnation of the fabric.

[0228] In the impregnation zone, the polyamide A is injected at a temperature of 290 C.

[0229] In a first test, referred to as the control, the impregnated fabric then enters a thermal control zone on emergence from which its surface temperature is reduced to a temperature greater than the crystallization temperature of the polyamide utilized (220 C.) and its core temperature remains at a higher temperature close to the melting point of this polyamide (260 C.). In the shaping zone, the surface temperature is greater than the crystallization temperature of the polyamide, and the core temperature is higher (close to the melting point).

[0230] In a second test, according to the invention, the impregnated fabric then enters a thermal control zone on emergence from which its surface temperature is adjusted to a temperature less than the crystallization temperature of the polyamide utilized, and its core temperature is adjusted to about 250 C. i.e. lower than the melting point of this polyamide but above the crystallization point. In the shaping zone, the surface temperature is less than the crystallization temperature of the polyamide, and the core temperature remains higher (close to the melting point).

[0231] The profiles obtained have a volume ratio of fibers of 50% calculated initially and confirmed by mass loss after high temperature calcination.

[0232] The swell ratio of the profile is determined by means of the following relationship:

Swell ratio(in %)=(difference between the thickness of the final profile and the thickness of the channel)/(thickness of the channel)*100

TABLE-US-00001 Surface temperature of the profile during the shaping Swell Polyamide concerned stage ratio (in %) Polyamide A having a 250 C. 20 crystallization temperature of less than 220 C. 0 to 2.5 220 C.

[0233] It is found that the profiles obtained according to the method according to the invention, that is to say those which are shaped with a temperature profile such that their surface temperature is less than the crystallization temperature of the polyamide utilized, have a low or even negligible swell ratio, lying between 0 and 5%.

[0234] Conversely, when the shaping stage is performed on an impregnated fabric having a surface temperature greater than the crystallization temperature of the polyamide utilized (and therefore higher in the core), a swelling phenomenon is observed due to the relaxation of the folds coated with polyamide after passage through the channel.

[0235] This swelling leads to an increment in the thickness of the profile, and may moreover generate substantial inter-fold porosity (cavities).

EXAMPLE 2: EFFECT OF THE VISCOSITY OF THE POLYAMIDE

[0236] A method for continuous production of a profile by pultrusion is performed by means of the device described above utilizing either polyamide B or the polyamide C, both belonging to the Technyl PA66 range marketed by SOLVAY.

[0237] These two polyamides have the same melting point, namely 260 C., a relatively similar crystallization temperature (around 220 C.), and a different viscosity in the molten state, according or not according to the present invention.

[0238] The polyamide B, not formulated, referred to as control, has a melt viscosity from 60 to 70 Pa.Math.s, and the polyamide C, according to the invention, has a melt viscosity from 15 to 20 Pa.Math.s.

[0239] For these two polyamides, the viscosity was measured at a temperature of 275 C. and at 10 s.sup.1.

[0240] In the hot entry zone, the tape is brought to the desired temperature for performing the impregnation stage, namely 290 C.

[0241] It is maintained at this temperature until total impregnation of the fabric.

[0242] In the impregnation zone, the polyamide B or the polyamide C is injected at a temperature of 290 C.

[0243] The impregnated fabric then enters a thermal control zone on emergence from which its surface temperature is adjusted to a temperature less than 220 C. and its core temperature is adjusted to an intermediate temperature between the crystallization and the melting temperature of the polyamide utilized, typically 250 C.

[0244] The profiles obtained have a volume ratio of fibers of 50%, calculated initially and confirmed by mass loss after high temperature calcination.

[0245] The void ratio (in %) is measured by weighing (Standard ASTM D2734-94), and possibly by scanning electron microscopy (SEM). The impregnation ratio is then calculated according to the following relationship: impregnation ratio (in %)=100void ratio (in %).

TABLE-US-00002 Melt viscosity of the polyamide (at 275 C. and Impregnation Polyamide concerned at 10 s.sup.1) (in Pa .Math. s) ratio (in %) Polyamide B (control) 60 to 70 60 to 90 Polyamide C (according to the 15 to 20 95 to 99 invention)

[0246] Thus, for a pulling speed of 0.7 m/min and a volume ratio of fibers of 50%, the impregnation ratio is much higher with a polyamide according to the invention, compared to a polyamide having a viscosity greater than 50 Pa.Math.s.

EXAMPLE 3: EFFECT OF THE ADDITION OF A LUBRICATING ADDITIVE

[0247] A method for continuous production of a profile by pultrusion is performed by means of the device described above utilizing either the polyamide C of example 2, or the polyamide D.

[0248] The polyamide D comprises 98% by weight of polyamide C, and 2% by weight of Graphite (Timcal SFG6) of average grain size 6 microns.

[0249] It has the same melting and crystallization temperatures as polyamide C. It has a melt viscosity from 20 to 25 Pa.Math.s at a temperature of 275 C. and at 10 s.sup.1.

[0250] In the hot entry zone, the tape is brought to the desired temperature for performing the impregnation stage, namely 290 C. It is maintained at this temperature until total impregnation of the fabric.

[0251] In the impregnation zone, the polyamide C or polyamide D is injected at a temperature of 290 C.

[0252] The impregnated fabric then enters a thermal control zone on emergence from which its surface temperature is adjusted to a temperature less than the crystallization temperature of the polyamide utilized, and its core temperature is adjusted to a higher temperature, close to the melting point of the polyamide, typically towards 250 C.

[0253] The pulling force is appreciably decreased: typically, it changes from a level of 7 to 10 kN to less than 3 kN.

[0254] The profiles obtained have a volume ratio of fibers of 50% calculated initially and confirmed by measurement of mass loss after calcination.

[0255] This example highlights the fact that the utilization of the polyamide with a lubricating agent makes it possible to advantageously improve the stability of the profile production method.

[0256] Indeed, when the polyamide utilized is the polyamide D, it is possible to produce more than 200 m of profile continuously in a stable manner with a constant pulling force, less than 5 kN. The profile obtained has a beautiful appearance, with controlled geometry.