REINFORCING COMPOSITE FILAMENT, PREPREG, 3-D PRINTING TAPE AND MACHINES FOR THEIR PRODUCTION

Abstract

The invention relates to the field of composite materials and can be used for the manufacture of parts and structures made of composite materials, such as brackets, fittings, basic parts, wearable products, mesh and honeycomb structures for use in aviation, rocket and space technology, medicine, automotive industry, etc. The reinforcing composite filament which contains a roving of reinforcing fibers impregnated with a thermosetting binder and has a cross section in the shape of a circle 0.1-0.7 mm in diameter or an ellipse with ellipticity from 1 to 2 and the largest diameter of 0.1-0.7 mm; and the impregnated roving is subjected to heat or other treatment right up to a complete curing of the thermosetting binder. With the help of the claimed composite filament, a prepreg can be made by adding a thermoplastic binder. And also the tape can be produced by connecting the claimed filament or prepreg with the use of cross-links made of thermoplastic material. The filament is produced in the machine containing a bobbin holder, which is fitted with at least one bobbin with a roving of reinforcing fibers or reinforcing and functional fibers, an impregnator that impregnates the roving with a thermosetting binder, two heat treatment chambers for a complete curing of the thermosetting binder (the temperature is 70-130 C. in the first chamber, and 160-400 C. in the second chamber), a finished filament receiver fitted with at least one receiving bobbin driven by a drive that ensures the pulling of the roving through all the elements of the machine. To manufacture a prepreg, the machine is fitted with an applicator to apply a thermoplastic coating on a completely cured roving impregnated with a thermosetting binder. The invention makes it possible to reduce the complexity of the manufacture of parts with a thermoplastic matrix, which leads to a significant reduction in the cost of manufacturing parts with a thermoplastic matrix (many times lower); to reduce the time of manufacture of a product due to the lack of need for long-term polymerization of a binder; to increase the shelf life of starting materials (prepreg) and to improve the efficiency of manufacture of products from composite materials. The invention is especially useful for implementation in additive processes of the manufacture of parts from composite materials, such as 3D-printing.

Claims

1. A reinforcing composite filament which contains a roving of reinforcing fibers impregnated with a thermosetting binder and has a cross section in the shape of a circle 0.1-0.7 mm in diameter or an ellipse with ellipticity from 1 to 2 and the largest diameter of 0.1-0.7 mm; and the impregnated roving is subjected to heat or other treatment right up to a complete curing of the thermosetting binder.

2. The filament according to claim 1 wherein the roving additionally contains functional fibers made in the form of optical and/or conductive fibers.

3. The filament according to claim 1 wherein the reinforcing fibers are made in the form of carbon and/or glass and/or aramid and/or basalt and/or boron and/or metal fibers.

4. The filament according to claim 1 wherein the thermosetting binder is produced in the form of polyester, phenol-formaldehyde, urethane, epoxy, silicone, polyimide or bismaleimide resins.

5. A prepreg containing a reinforcing composite filament coated with a thermoplastic binder, and in this case the reinforcing composite filament has a cross section in the form of a circle 0.1-0.7 mm in diameter or an ellipse with an ellipticity of 1 to 2 and the largest diameter of 0.1-0.7 mm; and this filament is made of a roving of reinforcing fibers impregnated with a thermosetting binder; and this impregnated roving is subjected to heat or other treatment right up to a complete curing of the thermosetting binder, and the thermoplastic binder is applied to the cured thermosetting binder.

6. The prepreg according to claim 5 wherein the roving additionally contains functional fibers made in the form of optical and/or conductive fibers.

7. The prepreg according to claim 5 wherein the reinforcing fibers are made in the form of carbon and/or glass and/or aramid and/or basalt and/or boron and/or metal fibers.

8. The prepreg according to claim 5 wherein the thermosetting binder is produced in the form of polyester, phenol-formaldehyde, urethane, epoxy, silicone, polyimide or bismaleimide resins.

9. The prepreg according to claim 5 wherein the thermoplastic binder can be polyethylene, polyamide, polycarbonate, polyamide, polyetheretherketone, polyacetal, polyphenylene sulfide, polysulfone, polyetherimide, polypropylene, polyformaldehyde, polyamide, polystyrene, polyethylene terephthalate or their copolymers.

10. The tape containing reinforcing composite filaments produced according to claim 1 wherein the filaments or prepregs are interconnected by bridges made of thermoplastic material.

11. A composite reinforcement filament spinning machine containing a bobbin holder, which is fitted with at least one bobbin with a roving of reinforcing fibers or reinforcing and functional fibers, an impregnator that impregnates the roving with a thermosetting binder, two heat treatment chambers for a complete curing of the thermosetting binder (the temperature is 70-130 C. in the first chamber, and 160-400 C. in the second chamber), a finished filament receiver fitted with at least one receiving bobbin driven by a drive that ensures the pulling of the roving through all the elements of the machine.

12. A prepreg forming machine containing a bobbin holder, which is fitted with at least one bobbin with a roving of reinforcing fibers or reinforcing and functional fibers, an impregnator that impregnates the roving with a thermosetting binder, two heat treatment chambers for a complete curing of the thermosetting binder (the temperature is 70-130 C. in the first chamber, and 160-400 C. in the second chamber), an applicator for applying a thermoplastic coating on the fully cured roving impregnated with a thermosetting binder, and a finished prepreg receiver fitted with at least one receiving bobbin driven by a drive that ensures the pulling of the roving through all the elements of the machine.

13. A tape forming machine containing a bobbin holder, which is fitted with at least one bobbin with a roving of reinforcing fibers or reinforcing and functional fibers, an impregnator that impregnates the roving with a thermosetting binder, two heat treatment chambers for a complete curing of the thermosetting binder (the temperature is 70-130 C. in the first chamber, and 160-400 C. in the second chamber), an applicator for applying a thermoplastic coating on the fully cured roving impregnated with a thermosetting binder, a forming unit for forming a tape from cured rovings and binding them with thermoplastic bridges, and a finished tape receiver fitted with at least one receiving bobbin driven by a drive that ensures the pulling of the roving through all the elements of the machine.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0020] FIG. 1The cross section of reinforcing composite filament:

[0021] FIG. 2The micrograph of reinforcing composite filament

[0022] FIG. 3The cross section of the prepreg containing the reinforcing composite filament

[0023] FIG. 4The cross section of the prepreg tape

[0024] FIG. 5The schematic of machine for the manufacture of filament and/or prepreg

[0025] FIG. 6The cross section of the composite material produced from the prepreg

[0026] The following positions on the figures are indicated by numbers:

1matrix material of composite roving; 2reinforcing fiber; 3functional fiber (optical, conductive); 4composite filament; 5prepreg coating; 6composite filament; 7thermoplastic polymer; 8roving of reinforcing fibers; 9bobbin holder; 10impregnator; 11impregnating roller; 12impregnating roller drive; 13bath with binder; 14scraper; 15heat treatment chamber No. 1; 16reversal unit; 17heat treatment chamber No. 2; 18thermoplastic coating applicator; 19receiving drum; 20handler guide; 21finished prepreg receiver; 22finished prepreg receiver drive; 23composite filament; 24thermoplastic matrix.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The reinforcing composite filament (FIG. 1) is a fiber roving which is impregnated with matrix material 1 and cured. The roving can contain reinforcing fibers 2, such as carbon, glass, aramid, basalt, boron, metal fibers, or other and functional fibers 3, such as optical and conductive fibers, such as copper. The bundle may include a different number of fibers, for example, 2, 100, 1000, 3000, 6000 and so on. Matrix material 1 used for impregnation is a thermosetting binder based on phenol-formaldehyde, polyester, epoxy and urea, silicone, polyimide, bismaleimide and other binding materials, or a mixture of a thermosetting binder with a thermoplastic binder. Thermosets possess good processing properties, in particular, low viscosity and good adhesion to any currently used types of reinforcing fibers that allow for a good impregnation of the reinforcing fiber bundle with the matrix in the absence of pores and voids and, therefore, a joint action of the fiber and the matrix. For the production of a reinforcing composite filament, the roving is impregnated with a binder so that the volume fraction of the binder is 20-40%. For example, the volume fractions of fibers and matrix material can have a ratio of 60%:40%, 70%:30%, 80%:20%, or otherwise. The roving is then subjected to heat or other kind of treatment until the matrix material is completely cured. The temperature regime and the duration of curing depend on a particular type and grade of the matrix material. The cross section of the filament has the form of a circle 0.1-0.7 mm in diameter of or an ellipse with an ellipticity of 1 to 2 and a largest diameter of 0.1-0.7 mm. These filament sizes are associated with the following. When the filament size is less than 0.1 mm, the filament has a relatively low tensile strength, which complicates significantly its production by pulling through the units of the equipment for its production, which leads to an increase in the number of breakages, i.e. rejects and an increase in the cost of manufacturing the fiber, which negates its advantages. When the filament size is more than 0.7 mm and the shape of the cross section differs significantly from the circle, the filament in a fully cured state has a significant flexural rigidity which prevents its placing on curved surfaces to form parts of complex shape and, consequently, the achievement of the technical result is impossible. A micrograph of the finished composite filament is shown in FIG. 2.

[0028] The coated filamentprepreg (FIG. 2)is above-described composite filament 4 (FIG. 1), which is covered after curing by thermoplastic material 5, such as acrylonitrile butadiene styrene (ABS), polylactide (PLA), polyamide (PA), polyetherimide (PEI), polyacetal, polyetheretherketone (PEEK), polycarbonate (PC), polysulfone (PS), polyphenylene sulphide (PPS), polyethylene terephthalate (PET), or other thermoplastic. Coating 5 serves to ensure a minimum volume fraction of the thermoplastic in the manufacturing process of the part and can be 20-60% of the total prepreg volume, for example, 20% or 30%.

[0029] The tape made from a filament or a prepreg (FIG. 3) is a tape consisting of rows of composite filaments or rovings 6, connected to each other by thermoplastic 7, such as acrylonitrile butadiene styrene (ABS), polylactide (PLA), polyamide (PA), polyetherimide (PEI), polyacetal, polyetheretherketone (PEEK), polycarbonate (PC), polysulfone (PS), polyphenylene sulphide (PPS), polyethylene terephthalate (PET), or other thermoplastic. The volume fraction of thermoplastic 7 can be 20-60% of the total prepreg volume, for example, 20% or 30%.

[0030] The manufacture of a filament or a prepreg is performed by using the machine, the schematic of which is shown in FIG. 4. The machine consists of the following major components: bobbin holder 9, impregnation unit 10, one or more heat treatment chambers (15, 17), handler 20, finished prepreg receiving unit 21 with one or several receiving bobbins and drive 22.

[0031] One or more bobbins with initial roving 8 are installed in the bobbin holder. To ensure the roving tensioning when releasing from the bobbins, the bobbin holder may be equipped with tensioners using an axial spring braking, electromagnetic brakes or electric motors. The number of bobbins with the initial roving depends on the number of simultaneously impregnated rovings in the case of the manufacture of a prepreg roving or on the width of the tape in the case of the manufacture of a prepreg tape.

[0032] After leaving the bobbin holder, roving 8 enters impregnator 10. The Impregnator may be of a different design. In particular, it can be a system consisting of impregnating roller 11 driven by motor 12; the lower edge of the roller is immersed in binder bath 13. The binder bath is removable and has a temperature controlled and regulated heating unit. Scraper 14 is provided for removing excess binder from impregnating roller 14. The amount of binder on the roller is controlled by the clearance between the scraper and the roller. Dry roving 8 passing along the upper surface of impregnating roller 11 is soaked with a binder. The design of the impregnating device may differ from the described machine, depending on the kind of thermosetting binder is used for impregnation.

[0033] After impregnation, the roving enters the heat treatment chambers (15, 17). The chambers can be divided into zones with different temperatures to provide full curing of a thermosetting binder. The vertical arrangement of the chambers is preferred to ensure uniform distribution of the binder inside the roving. Heating can be carried out by heaters located inside the chamber or by supplying heated air to the chamber. The moving speed of the roving within the chambers and, accordingly, the residence time in them, as well as the temperature in the chambers depend on the types of a fiber and a thermosetting binder. In particular, as regards the Toray T300 3K carbon fiber and an epoxy binder, the complete curing will require the 90 C. temperature in first chamber 15, 160-200 C. in second chamber 17, the total residence time of 5-10 minute for the roving in the chambers. In the case when several vertical chambers are used, the roving reversal is provided by means of reversal unit 16. Depending on the composition of a thermosetting binder, the temperature is 70-130 C. in the first chamber, and 160-400 C. in the second chamber.

[0034] The thermosetting binder passes three stages during the manufacturing process of reinforcing composite filament: [0035] Stage Athe initial polymerization products are mixed and ready to react when heated. The reaction is also going without heating, but very slowly. The mixture can be dissolved in solvents that slow down the interaction of initial products. It is in this state that binders are stored. At this stage, the roving is impregnated with a binder. [0036] Stage Bthe solvents have been removed from the initial mixture, the products have entered into a polymerization reaction, but it is only in the initial stage. At this stage, the components of a binder are able to dissolve, melt, and be formed. Without a solvent, they are dry products, do not stick together and can be stored and transported for a long time under appropriate conditions. It is at this stage that the production of previously known prepregs is completed. The prepregs of this stage are traditionally used as a component in the production of composite parts. To complete the polymerization of binders, they must be heated to a certain temperature called the gelation temperature. [0037] Stage Cthe polymerization reactions are completed, and the binder is no longer able to melt and dissolve in solvents; at normal temperatures it is a solid monolithic glassy substance that is incapable to change its shape. At this stage, the resin is contained in the composition of the finished reinforcing composite filament.

[0038] If the machine is intended for the production of a coated prepreg roving, the machine should be equipped with thermoplastic coating applicator 18. The embodiment is a heated and thermostable chamber containing a thermoplastic polymer melt within a maintained range of temperatures from 50 to 400 C. The lower output part of the cylinder is fitted with a sizing spinneret which determines the amount of thermoplastics applied to the surface of the fiber. The supply of thermoplastics to the chamber is carried out by means of rollers if the thermoplastics is in the form of a filament, or a screw if the thermoplastics is in the form of powder or granules.

[0039] If the machine is intended for the production of a prepreg tape, thermoplastic coating applicator 18 should also form a tape from rovings, for example, by using a rectangular spinneret.

[0040] The finished prepreg is cooled down, passes around receiving drum 19 and enters finished prepreg receiving unit 21, where the prepreg is wound on the receiving bobbin. The number of receiving bobbins corresponds to the number of simultaneously manufactured rovings/tapes. The receiving bobbins are fixed to the shaft driven by traction motor 22 at a controlled speed. Laying the prepreg in a working volume of bobbins is carried out with the help of handler guide 20 operating synchronously with the drive shaft.

[0041] When manufacturing the part (FIG. 4), the prepreg is heated to a temperature higher than the processing temperature of thermoplastic matrix 24 and the glass transition temperature of the thermosetting matrix of composite rovings 23 and laid out on the mandrel forming the part. After laying out, the thermoplastic melt solidifies in the course of cooling, and the composite rovings being cooled become again rigid and form a layer of reinforced material with high mechanical characteristics. It is essential that the matrix material of the composite fiber is not melted but only softened, and the reinforcing bundle fibers located inside the bundle retain their location, which makes the arrangement of fibers more regular, improving the physical and mechanical characteristics of the material.

[0042] The described reinforcing composite filament and prepregs can be used to manufacture composite parts with a thermoplastic matrix. If in the production of a composite material with a thermoplastic matrix the traditional bundles are replaced with the described reinforcing composite filament, which is pre-impregnated with a thermosetting binder and completely cured, then, because the filament has a large diameter, this filament is easily and completely wetted with thermoplastic and allows for obtaining a composite part with a thermoplastic matrix without the use of significant pressures and complicated technological equipment. The invention is especially useful for implementation in additive processes of the manufacture of parts from composite materials, such as 3D-printing. The part is formed in such process by microextruders in which the plastic is under low pressure and unable to impregnate a reinforcing fiber roving. Replacing the traditional roving with a reinforcing composite filament, in which the roving is impregnated with a binder and completely cured, allows for the manufacture of parts containing a minimum number of pores and voids and providing high physical and mechanical characteristics.

[0043] Due to the use of the filament based on a cured binder, the complexity of the manufacture of parts with a thermoplastic matrix is reduced, which leads to a significant reduction in the cost (many times over) of the manufacture of parts with a thermoplastic matrix, because of the fact that various presses are not required and energy costs are reduced, etc. At the same time, the manufactured parts have all the advantages of parts containing a thermoplastic matrixtheir curing is not required, they are highly resistant to impact, and the raw materials have unlimited viability under normal conditions.