Process for manufacturing composite articles

Abstract

The present invention relates to the use of thermoplastic polymer compositions for impregnating reinforcing materials in the form of fabric or industrial fabrics for the manufacture of composite materials. The field of the invention is that of composite materials as well as molding/consolidation processes and obtained parts. The invention more particularly relates to a method of manufacturing a composite article by injection molding comprising at least the steps of introducing at least one reinforcement fabric into a preheated mold, partial closure of the mold, a temperature rise step of the mold, optionally a step of maintaining the temperature of the mold before injection of a thermoplastic polymer composition, a step of injecting a thermoplastic polymer composition into the mold, a step of mold closure to the final part thickness allowing the flow of the resin through the reinforcing fabric, a cooling step and a recovery step of the obtained composite article.

Claims

1. A process for manufacturing a composite article by injection molding a polymer composition comprising at least one semi-crystalline thermoplastic polymer and/or at least one amorphous thermoplastic polymer, comprising the following steps: (a) Introducing at least one reinforcement material into a preheated mold having a temperature T.sub.1 that is in the range of from 50° C. to a temperature T.sub.1.sup.max, wherein T.sub.1.sup.max is defined as follows:
T.sub.1.sup.max=T.sub.g.sup.max+40° C.,  (i) if the polymer composition has no melting transition, or if the polymer composition has at least one melting transition and the highest melting temperature T.sub.m.sup.max of the polymer composition is lower than T.sub.g.sup.max+40° C., wherein T.sub.g.sup.max denotes the highest glass transition temperature of the polymer composition, or
T.sub.1.sup.max=T.sub.m.sup.max,  (ii) if the polymer composition has at least one melting transition and the highest melting temperature T.sub.m.sup.max of the polymer composition is equal or greater than T.sub.g.sup.max+40° C.; and (b) after the introducing, partially closing the mold including the at least one reinforcement material, such that the mold exhibits an open gap with a volume of from 70% to 200% of the polymer volume to be injected; and (c) after the partial closing, raising the temperature of the mold to a temperature T.sub.2 that is in the range of from T.sub.2.sup.min to T.sub.2.sup.max, wherein T.sub.2.sup.min and T.sub.2.sup.max are defined as follows:
T.sub.2.sup.min=T.sub.g.sup.max+50° C., T.sub.2.sup.max=T.sub.g.sup.max+300° C.,  (i) if the polymer composition has no melting transition, or
T.sub.2.sup.min=T.sub.g.sup.max+50° C., T.sub.2.sup.max=T.sub.g.sup.max+150° C.,  (ii) if the polymer composition has at least one melting transition and the highest melting temperature T.sub.m.sup.max of the polymer composition is lower than T.sub.g.sup.max+40° C., or
T.sub.g.sup.min=T.sub.m.sup.max+10° C., T.sub.2.sup.max=T.sub.m.sup.max+100° C.,  (iii) if the polymer composition has at least one melting transition and the highest melting temperature T.sub.m.sup.max of the polymer composition is equal or greater than T.sub.g.sup.max+40° C.; and (d) optionally maintaining the raised temperature of the mold for a period of time; and (e) after the raising the temperature and the optional maintaining, injecting a polymer composition having a melt viscosity of from 5 to 200 Pa.Math.s, determined according to ISO 11403-2 at the temperature of step (c) and a shear rate of 100 s−1, into the mold, filling the free cavity obtained by partial closure of the mold; and (f) after the injecting, closing the mold to the final thickness of the part, maintaining the temperature of step (c), employing a compression rate of from 0.001 to 0.5 mm/s and permitting the mold pressure to rise to a range of from 0.2 to 17.5 MPa; and (g) after the mold pressure rises, cooling the mold to a temperature T.sub.3 that is in the range of from T.sub.3.sup.min to T.sub.3.sup.max, wherein T.sub.3.sup.min and T.sub.3.sup.max are defined as follows:
T.sub.3.sup.min=T.sub.g.sup.min−100° C., T.sub.3.sup.max=T.sub.g.sup.min+50° C.,  (i) if the polymer composition has no crystallization transition, and wherein T.sub.g.sup.min denotes the lowest glass transition temperature of the polymer composition, or
T.sub.3.sup.min=T.sub.c.sup.min−120° C., T.sub.3.sup.max=T.sub.c.sup.min+25° C.,  (ii) if the polymer composition has at least one crystallization transition, and wherein T.sub.c.sup.min denotes the lowest crystallization temperature of the polymer composition; and (h) after the cooling, opening the mold, ejecting and recovering the produced composite article.

2. The process of claim 1, wherein the preheated mold has a temperature in the range of from 75° C. to T.sub.1.sup.max.

3. The process of claim 1, wherein the reinforcement material is heated before introduction into the mold.

4. The process of claim 1, wherein temperature raising step (c) is carried out in a period of from 1 minute to 30 minutes.

5. The process of claim 1, wherein injection step (e) is carried out in a period of from 10 seconds to 2 minutes.

6. The process of claim 1, wherein the composite article comprises from 20% to 65% by volume, of reinforcing material, based on the total volume of the composite article.

7. The process of claim 1, wherein the variation of viscosity of the polymer composition amounts to less than ±20%.

8. The process of claim 1, wherein the semi-crystalline polymer comprises a fully aliphatic polyamide or a partially aromatic polyamide or mixtures thereof.

9. The process of claim 1, wherein the semi-crystalline polymer comprises a polyphenylene sulphide or a mixture of two or more polyphenylene sulfides.

10. The process of claim 1, wherein the polymer composition comprises at least one polyamide and at least one polyphenylene sulphide.

11. The process of claim 1, wherein the amorphous thermoplastic polymer is at least one from the group consisting of: polyacrylate, polystyrene, polycarbonate, polyurethane, polydimethylphenylene ether, polyarylether sulfone, polyetherimide, and polyamideimide.

12. The process of claim 1, wherein the polymer composition comprises a mixture comprising at least one semi-crystalline and at least one amorphous polymer.

13. The process of claim 1, wherein the polymer composition comprises a mixture comprising at least one polymer having a glass transition temperature of from 5° C. to 80° C., and at least one polymer having a glass transition temperature of from 81° C. to 250° C.

14. The process of claim 1, wherein the polymer composition comprises a mixture comprising at least one polymer having a melt viscosity of from 1 to 50 Pas and at least one polymer having a melt viscosity of from 75 to 350 Pa.Math.s.

15. The process of claim 1, wherein the polymer composition exhibits a melt viscosity η of from 10 to 125 Pa.Math.s.

16. The process of claim 1, further comprising: placing the composite article as recovered in step (h) into a second mold and subsequently at least partially overmolding, via injection molding, the surface of the composite article with a second polymer composition wherein, during the overmolding, the temperature difference between the injected second polymer composition and the composite article is lower than 175° C.

17. The process of claim 1, wherein in step (f) the mold pressure is permitted to rise to a range of from 0.5 to 10 MPa.

18. The process of claim 16, wherein the temperature difference between the injected second polymer composition and the composite article is lower than 150° C.

19. The process of claim 16, wherein the temperature difference between the injected second polymer composition and the composite article is lower than 125° C.

Description

DESCRIPTION OF THE FIGURES

(1) FIG. 1: Typical process unit. C: injection press, including plastification and injection unit; B: high temperature mold; A: mold closure unit; D: heating/cooling system.

(2) FIG. 2: Typical process cycle. P: Pressure; T: Temperature; P.sub.max: maximum pressure; T.sub.0: introduction temperature (steps (a), (b) of claim 1); A: heating step (c) of claim 1; T.sub.1: maximum temperature; B: temperature maintenance step (d) of claim 1; C: injection step (e) of claim 1; D: compression step (f) of claim 1; E: cooling step (g) of claim 1.

(3) FIG. 3: Scetch of high temperature mold along process cycle. A: injection of polymer composition; B: mold closure (compression); (a): introduction of preform; (b): closure to initial thickness; (c): injection; (d): closure to final thickness and venting; (e): mold opening.

EXAMPLES

A) Polymers

(4) A-1: Aliphatic polyamide (PA 6): Evolite® XS1480 (Solvay)

(5) A-2: Aliphatic polyamide (PA 66): Evolite® XA1481 (Solvay)

(6) A-3: Aliphatic polyamide (PA 66): Technyl® 22FE1 (Solvay)

(7) A-4: Polyphenylene sulfide (PPS): Ryton® QA200N (Solvay)

(8) A-5: Polyphenylene sulfide blend (PPS): Ryton® QA321N (Solvay)

(9) A-6: Polyphenylene sulfide blend (PPS): Ryton® QA200N/Ryton® QA321N (50/50; w/w) (Solvay)

(10) A-7: Compound based on aliphatic polyamide (PA 6): Technyl® C246 SIV30 (Solvay)

(11) A-8: Compound based on Polyphenylene sulfide (PPS): Ryton® R-4-240 (Solvay)

(12) Melt viscosities (η) of polymer compositions (ISO 11403-2, at 100 s.sup.−1):

(13) A-1: 15 Pa.Math.s at T=300° C.; 30 Pa.Math.s at T=285° C.

(14) A-2: 50 Pa.Math.s at T=275° C.

(15) A-3: 75 Pa.Math.s at T=275° C.

(16) A-4: 290-300 Pa.Math.s at T=300° C.; 75-80 Pa.Math.s at T=350° C.

(17) A-5: 25-30 Pa.Math.s at T=300° C.; 15-18 Pa.Math.s at T=350° C.

(18) A-6: 50 Pa.Math.s at T=325° C.

(19) A-7: 2,000-2,500 Pa.Math.s at T=270° C.

(20) A-8: 2,250-2,500 Pa.Math.s at T=300° C.

B) Reinforcement Materials

(21) B-1: Plain-weave glass fabric (600 g/m.sup.2): G-Weave 600P AC 80 (Chromarat)

(22) B-2: Twill-weave glass fabric 2×2 (650 g/m.sup.2): G-Weave 650T/PA (Chromarat)

(23) B-3: Twill-weave carbon fiber fabric (650 g/m.sup.2); C-Weave 650T 12K HS (Chromarat)

C) Procedure

(24) Device used for tests according to the invention: injection press, high temperature mold, heating/cooling system.

(25) 1) Injection molding press: electric press, closing force: 125 tons (Select H470-125T from Billion (France)). Plasticizing unit: 40 mm diameter, having an L/D of 23.5 and capable of operating at up to 400° C. Adapted valve and hot runner with controlled shaft/valve. Control of cycle by automation. A specially developed software was used.

(26) 2) High-temperature mold (400° C.), developed by G. Pernoud (France). Molding cavity of 190×270 mm, with an adjustable depth of from 2.5 mm to 5 mm. Avoidance of leaks is assured by a 0.02 mm controlled functional clearance between the fixed and the mobile block independently of the temperature. Heating is conducted by electric cartridges (40 kW) capable of operating at a temperature of up to 400° C. Cooling is conducted by circulation of an air/water mixture. Instrumentation: thermocouples (16), and pressure sensors (6).

(27) 3) Heating/cooling with regulation from Pinette Emidecau Industries (France). Heating by electric cartridges (36). Regulation of 8 zones (4 in mobile block of mold/4 in fixed block of mold) Heating rate: 50° C./min. Cooling by circulation of air/water mixture in the mold. Cooling rate: 100 to 150° C./min. Supervision/control by automation and retrieval of parameters from the different temperature and pressure sensors.

(28) Communication between the press automation and the heating/cooling system automation.

(29) Mold closure is displacement controlled at 0.01 mm. Plates of sizes 190×270×2.5 mm or 190×270×e (with e of from 2 to 5 mm) were made. Injection flow sequence is programmed as to a defined profile, typically 2-10-6-4 cm.sup.3/s. All parts are completely boxed for good insulation and thermal regulation. Temperature ramps are employed in step (c) of the process of 25 to 50° C./minute. For cooling, a temperature ramp of 50 to 150° C./minute is employed in step (g) of the process.

Procedure A

(30) Reinforcement material is placed in the preheated (125° C.) mold which is then partially closed and heated to a temperature of about 300° C. in a few minutes (step (c)). Mold cavity temperature is maintained at 280° C. for 1.5 minutes (step (d)). The polymer composition is injected at 290° C. (step (e)) and a pressure of <0.1 MPa employing a rate of from 2 to 10 cm.sup.3/second to fill the free cavity. Injection is stopped, and the mold is gradually closed (step (f)) employing a pressure rate of from 0.005 to 0.030 MPa.Math.s.sup.−1 until the desired final part thickness has been reached. Cooling is started. Mold temperature is permitted to drop to about 125° C. The mold is opened and the composite article ejected.

Procedure B

(31) In a variant of Procedures A and C, and to reduce cycle time, the temperature maintenance step (step (d)) is omitted, and gradual closure of the mold (step (f)) conducted already during (step (e)), i.e. the injection of the polymer composition.

Procedure C

(32) Reinforcement material is placed in the preheated (150° C.) mold which is then partially closed and heated to a temperature of about 290° C. in a few minutes (step (c)). Mold cavity temperature is maintained at 270° C. for 1.5 minutes (step (d)). The polymer composition is injected at 280° C. (step (e)) and a pressure of <0.1 MPa with a rate of from 2 to 10 cm.sup.3/second to fill the free cavity. Injection is stopped, and the mold is gradually closed (step (f)) employing a pressure rate of from 0.0025 to 0.035 MPa.Math.s.sup.−1 until the desired final part thickness has been reached. Cooling is started. Mold temperature is permitted to drop to about 150° C. The mold is opened and the composite article ejected.

Procedure D

(33) Reinforcement material is placed in the preheated (150° C.) mold which is then partially closed and heated to a temperature of about 350° C. in a few minutes (step (c)). Mold cavity temperature is maintained at 325° C. for 1.5 minutes (step (d)). The polymer composition is injected at 335° C. (step (e)) and a pressure of <0.1 MPa with a rate of from 2 to 10 cm.sup.3/second to fill the free cavity. Injection is stopped, and the mold is gradually closed (step (f)) employing a pressure rate of from 0.003 to 0.05 MPa.Math.s.sup.−1 until the desired final part thickness has been reached. Cooling is started. Mold temperature is permitted to drop to about 150° C. The mold is opened and the composite article ejected.

Procedure E (Comparative Procedure)

(34) The procedure of Procedure A was employed with the exception that mold temperature was set to 200° C. (i.e. below the melting temperature of the molding composition, as disclosed in US 2013/0001817 A1).

Example 1

(35) Polymer: A-1; Reinforcement: B-2 (5 plies)

Example 2

(36) Polymer: A-1; Reinforcement: B-2 (6 plies)

Example 3

(37) Polymer: A-2; Reinforcement: B-2 (6 plies)

Example 4

(38) Polymer: A-6; Reinforcement: B-2 (5 plies)

Comparative Example (Employing Procedure E)

(39) Polymer: A-1; Reinforcement: B-2 (6 plies); fiber content: 50% by volume

(40) TABLE-US-00001 TABLE 1 Results (Procedures A (Ex. 1 & 2) and C (Ex. 3) Ex. 1 Ex. 2 Ex. 3 Ex. 4 Comp. Ex. Density (g/cm.sup.3) 1.6 1.87 1.85 Fiber content 43 50 50 50 (% by volume) (target) Tensile Strength 390 495 425 0 (MPa) Flexural Strength 280 480 310 (MPa) Tensile Modulus 21.5 22 23 (GPa) Microstructure good (no very very no visible good good impregnation porosity)

(41) TABLE-US-00002 TABLE 2 Results (Procedure B) Ex. 1 Ex. 2 Ex. 3 Ex. 4 Density (g/cm.sup.3) 1.6 1.87 1.85 Fiber content 43 50 50 (% by volume) Tensile Strength 395 490 430 (MPa) Tensile Modulus 22 21.5 23.5 (GPa) Flexural Strength 275 482 315 (MPa)

Example 5: Overmolding (Procedure F)

(42) Composite articles as made by any of Procedures A-D are used as is for overmolding, or such articles that have previously been overmolded with polymer coat of a thickness of from 0.2 to 2.5 millimeters) according to this Procedure F.

(43) Overmolded composite articles as per the present invention were made by injection molding the overmolding resin composition (Polymer A-7) in a thickness of about 1 to 1.5 mm onto composite articles (thickness 1.75 mm: 4 plies) by the procedure as described below:

(44) 190×270×1.75 mm composite plates made by Procedure A from Polymer A-1 were placed into a mold cavity as inserts and were over injection molded with Polymer A-7 using an injection molding machine (Select H470-125T Dixit3 (from Billion, France)) having a maximum locking force of 1,250 kN. A high temperature mold (from G. Pernoud, France) was used, capable to operate at temperatures exceeding 400° C. The mold was electrically heated to a temperature of from 100° C. to 180° C. Before the over injection molding step, the composite articles had been preheated to 100° C. for 15 minutes or came from step (h) of the process of the present invention at a temperature falling below T.sub.c.sup.min or T.sub.g.sup.min. The injection molding machine was set at a melt injection temperature of 270° C. Pressure of the mold was set to less than 10.0 MPa for about 1 minute, followed by 20.0 MPa for about 1 to 3 additional minutes and subsequently cooled to below 125° C.

(45) Bond strength. Overmolded composite articles made by Procedure F were cut into 1.25 cm wide by 6.5 cm long test specimens using a diamond blade and water cooling. A four point method by supporting the beam on the tensile side (outer span) of the specimens was used to characterize adhesion/bond strength of the overmolded resin composition to the composite structure.

(46) The tests were conducted at 2.0 mm/min using a universal test machine (Instron).

(47) Beam specimens (12.5 mm×65 mm) were machined from overmolded composite plates. The overmolded layers of the beams were notched prior to testing by using a low speed diamond saw to cut through approximately 95% of the depth of the overmolded layer. A fresh razor blade was used to sharpen the prenotch by sliding it across the prenotch. The notched side of the specimens was placed on the outer span supports and the laminate was loaded. The resulting load-displacement curves exhibit a peak, then drop sharply, and finally exhibit a plateau which corresponds to the adhesion level.

(48) Table 3 lists results obtained from overmolding specimens.

(49) TABLE-US-00003 TABLE 3 Results of overmolding tests O 1 O 2 O 3 O 4 Mold temperature 80 120 140 160 T (° C.) Matrix resin PA6 PA6 PA6 PA6 Overmolding resin PA6 PA6 PA6 PA6 (260° C.) Bond Strength (N)  70

(50) As shown in Table 3, the adhesion between an overmold of thermoplastic polymer composition and a composite article is a function of the temperature difference between melt temperature and composite insert temperature.