Method for manufacturing a composite thermoplastic part by vacuum injection-compression-molding, device for the implementation thereof and resulting part

Abstract

A method for manufacturing a composite part including a fibrous reinforcement and a thermoplastic polymer matrix, which includes the steps of i) depositing the fibrous reinforcement in a two-part mold having a seal compressible by evacuating said mold having no vent, ii) filling the evacuated mold by injecting, in the molten state, a two-component reactive system made of a reactive thermoplastic prepolymer, the injection being carried out using a device having two distinct compartments for each one of the two reactive components mixed in a static mixer, followed by a compression and compaction of the content of the mold, and iii) removing the part from the mold, without any finishing treatment. Further, a device for implementing said method, to the resulting part and to the use of said method in an “in-mold” assembly method.

1 . A manufacturing device for implementing a process for manufacturing a structural or semi-structural composite part which may be in complex form, comprising a fibrous reinforcement and a thermoplastic polymer matrix, wherein the process comprises the following steps:
 i) depositing said fibrous reinforcement, which may be in the form of a preform, in a mold comprising two parts, one part being fixed and one mobile, with leaktight closure of said mold by means of a seal compressible by placing said mold under vacuum by means of a vacuum device, the partial pressure in the mold ranging from 1 to 10 mbar, said mold having no vent,   ii) filling said closed mold thus under vacuum by injecting, in the molten state, onto said reinforcement in the dry state a pre-metered amount, just necessary to obtain the final part, of a two-component reactive system, which is the precursor of said thermoplastic polymer, based on a reactive thermoplastic prepolymer, it being possible for the mold to be maintained under isothermal conditions at a temperature below the injection temperature and with said injection being carried out using an injection device comprising two distinct compartments for each of the two reactive components in the molten state, said reactive components being mixed before injection in the chamber of a static mixer head with a residence time in said chamber of less than 2 minutes, at a temperature which ranges from 180° C. to 400° C., with impregnation of said fibrous reinforcement and simultaneous reaction following the impregnation of said two-component reactive system under a pressure of less than 1 mbar, the creep of the resin through the reinforcement being accompanied by a compacting pressure at the end of injection ensuring complete filling of said mold, with no vent,   iii) removing said part from the mold without any finishing treatment, wherein the manufacturing device comprises:
 a) at least one melt injection device allowing the injection, in a temperature range of from 180 to 400° C., of a two-component reactive system which comprises two separate feed compartments, each equipped with a heating and temperature-regulating system, said temperature being in said ranges mentioned above, and with a feed pump, each feeding the chamber of a head of a static mixer, also having a heating and regulating system, said mixer head feeding, at at least one injection point, a molding device b) as defined below; 
 b) a vacuum compression-molding device comprising a mold composed of two parts, one fixed and the other mobile, separated by a compressible seal, thus forming a leaktight molding cavity, said device being equipped with a system for heating and regulating under isothermal conditions at a temperature below the injection temperature and with a system for placing under a vacuum, said noncompacted (or noncompressed) leaktight cavity allowing creep of the injected material, and the compacting (or compression) generated on closing the mold under vacuum ensuring both complete filling of said cavity and also transverse creep of the material with respect to the reinforcement, all this in said cavity at a pressure below 1 mbar, said mold having a leaktight closure under vacuum and comprising no vent and being fed directly by said injection device a) through a feed at the level of the outlet of the head of said static mixer. 
   
     
     
         2 . The device as claimed in  claim 1 , wherein the device comprises at least one second injection device for a single-component system, in order to allow overmolding with a thermoplastic in the molten state loaded with short or long fibers having an aspect ratio of less than 1000, this second injection device being directly connected to the same molding device b), it being possible for said thermoplastic to be fed into said injection device in the form of granules loaded with said fibers, optionally by means of a feed hopper, it being possible for said second injection device to be a single-component injection machine or an extruder. 
     
     
         3 . A structural or semi-structural composite part obtained by means of a process for manufacturing a structural or semi-structural composite part which may be in complex form, comprising a fibrous reinforcement and a thermoplastic polymer matrix, wherein the process comprises the following steps:
 i) depositing said fibrous reinforcement, which may be in the form of a preform, in a mold comprising two parts, one part being fixed and one mobile, with leaktight closure of said mold by means of a seal compressible by placing said mold under vacuum by means of a vacuum device, the partial pressure in the mold ranging from 1 to 10 mbar, said mold having no vent,   ii) filling said closed mold thus under vacuum by injecting, in the molten state, onto said reinforcement in the dry state a pre-metered amount, just necessary to obtain the final part, of a two-component reactive system, which is the precursor of said thermoplastic polymer, based on a reactive thermoplastic prepolymer, it being possible for the mold to be maintained under isothermal conditions at a temperature below the injection temperature and with said injection being carried out using an injection device comprising two distinct compartments for each of the two reactive components in the molten state, said reactive components being mixed before injection in the chamber of a static mixer head with a residence time in said chamber of less than 2 minutes, at a temperature which ranges from 180° C. to 400° C., with impregnation of said fibrous reinforcement and simultaneous reaction following the impregnation of said two-component reactive system under a pressure of less than 1 mbar, the creep of the resin through the reinforcement being accompanied by a compacting pressure at the end of injection ensuring complete filling of said mold, with no vent,   iii) removing said part from the mold without any finishing treatment,
 the composite part comprising no residual molding sprue and being able to be used after removal from the mold without any finishing treatment. 
   
     
     
         4 . The part as claimed in  claim 3 , wherein the part is a part for application in the following fields: the motor vehicle industry, road transport as parts for trucks, the railroad industry, the maritime industry, aeronautics, wind power, photovoltaics, the solar (thermal) industry, the space industry, the construction industry, civil engineering, urban furniture and equipment, signage, sports and leisure. 
     
     
         5 . The part as claimed in  claim 3 , wherein the part it is a motor vehicle part chosen from or for a body in white, an apron, tailgate, floor, side wall, roof, spring bar, front, back, side crash box, door structure and fenders. 
     
     
         6 . The part as claimed in  claim 3 , wherein said polymer of said thermoplastic matrix is semi-crystalline, having a glass transition temperature Tg above 90° C., and a melting temperature Tm below 320° C., and wherein the part is a motor vehicle part capable of being subjected to cataphoresis. 
     
     
         7 . The part as claimed in  claim 3 , wherein the part is an integral part of a complex part obtained by “in-mold” assembly in the same molding device b) or a different device of several constituents parts, among which there are plastic and/or metallic parts, and being the result of a two-component reactive system based on reactive thermoplastic prepolymers. 
     
     
         8 . The part as claimed in  claim 3 , wherein said part has thermoplastic polymer matrix resulting from a two-component reactive composition comprising, as first reactive component A1): at least one reactive thermoplastic prepolymer, bearing two identical functions not reactive with one another, and, as second reactive component A2) according to a first option for A2): at least one nonpolymeric chain extender bearing two identical functions not reactive with one another, reactive with those of said reactive prepolymer A1), or as second option for A2), at least one second reactive prepolymer, bearing two identical functions not reactive with one another, and reactive with those of said first reactive prepolymer A1), by polyaddition or by polycondensation. 
     
     
         9 . The part as claimed in  claim 3 , wherein said thermoplastic matrix is a polyamide and that said two-component reactive system, from which said thermoplastic matrix is derived, comprises at least one reactive polyamide prepolymer, bearing two identical functions not reactive with one another and at least one nonpolymeric chain extender bearing two identical functions not reactive with one another which can react with those of said reactive polyamide. 
     
     
         10 . The part as claimed in  claim 8 , wherein the part comprises a thermoplastic polymer loaded with short or long fibers having an LID aspect ratio of less than 1000, overmolded onto said part based on said two-component reactive system. 
     
     
         11 . A method of manufacturing of “net-shape” structural or semi-structural composite parts, with no need, for the use thereof, for additional machining or finishing after removal from the mold, wherein the method comprises the use of the device as claimed in  claim 1 . 
     
     
         12 . The method of  claim 11 , wherein the method comprises manufacturing of a complex and multicomponent composite part by “in-mold” assembly.