Method for impregnating a fibrous material in an interpenetrated fluidized bed

Abstract

Manufacture of a pre-impregnated fibrous material which contains continuous fibers and a thermoplastic matrix, the material being made as a plurality of unidirectional parallel ribbons or sheets, and the method involving a step of pre-impregnating, in dry conditions, N parallel strands divided into X groups of Ni strands, by the thermoplastic matrix in powder form in a tank, ΣNi=N et X 3, one thereof from each series being immersed in the powder, each group of strands running on the same number Y of tensioning parts, and the parallel strands being separated by a spacing at least equal to the width of each strand.

Claims

1. A method for manufacturing a pre-impregnated fibrous material comprising a fibrous material made of continuous fibers and at least one thermoplastic polymer matrix, wherein said pre-impregnated fibrous material is made as a plurality of unidirectional parallel ribbons or sheets and in that said method comprises a homogeneous pre-impregnation step of said fibrous material in the form of N parallel strands by said at least one thermoplastic polymer matrix in the form of a powder in a tank, said pre-impregnation step being carried out in a dry manner in said tank, said N parallel strands being divided into X groups consisting of Ni parallel strands in the direction of travel of the strands, ΣNi=N and X≤N, X ranging from 2 to 200, each group of parallel strands running separately by means of X series consisting of Y starting pieces in the tank, with Y≥3, and of which at least one of said Y starting pieces of each series is at least partially immersed in said powder, each group of strands running on the same number Y of starting pieces, the at least one thermoplastic polymer matrix is made from: the polymers and copolymers from the family of aliphatic, cycloaliphatic or semi-aromatic polyamides (PA) (also called polyphthalamides (PPA)), polyureas, polymers and copolymers from the family of acrylics, polymers and copolymers from the poly aryl ether ketone (PAEK) family like poly(ether ether ketone) (PEEK), or poly(aryl ether ketone ketones) (PAEKK) like poly(ether ketone ketone) (PEKK) or derivatives thereof, aromatic polyether-imides (PEI), polyarylsulfides, polyolefins, polylactic acid (PLA), polyvinyl alcohol (PVA), fluorinated polymers, and mixtures thereof, said parallel strands being separated from one another in said tank with a spacing at least equal to the width of each strand, at least at said at least partially immersed starting piece, said Y starting pieces of each series in the tank being offset in the direction of travel of the strands by a distance at least greater than the thickness of each strand, the control of the amount of said at least one thermoplastic polymer matrix in said fibrous material being carried out by controlling the residence time of said N strands in the powder, the residence time in the powder being the same for each of said strands, said N strands optionally being joined together out of the powder.

2. The method according to claim 1, wherein said tank comprises a fluidized bed.

3. The method according to claim 2, wherein each Ym starting piece of each series in the fluidized bed is located at the same height from the bottom of the tank.

4. The method according to claim 2, wherein the Y starting pieces of each series in the fluidized bed are each equidistant from one another.

5. The method according to claim 2, wherein said Y starting pieces are compression rollers of convex, concave or cylindrical shape.

6. The method according to claim 2, wherein each strand of each group X penetrates into said fluidized bed and runs over at least one of said Y starting pieces of each series at least partially immersed in the powder, with an angle α2 formed between the strand and the normal of said starting piece Ym ranging from 0 to 89°.

7. The method according to claim 6, wherein after running over said at least one of said Y starting pieces of each series at least partially immersed in said powder, each strand of each group X emerges from said fluidized bed with an angle α′2 formed between the strand and the normal of said starting piece Ym ranging from 0 to 89°.

8. The method according to claim 2, wherein the residence time in the powder ranges from 0.01 s to 10 s.

9. The method according to claim 2, wherein said pre-impregnation step is carried out with spreading of each Ni parallel strands between the entry to the tank and the exit from the tank comprising said fluidized bed.

10. The method according to claim 9, wherein said spreading of each Ni parallel strands is carried out at least at one of the starting pieces Ym.

11. The method according to claim 1, wherein the starting pieces Y of each series are identical.

12. The method according to claim 2, wherein m=3 for each series, a first starting piece Y1 for each series being located above said fluidized bed after the entry to the tank and a last starting piece Y3 for each series are located above said fluidized bed before the exit from the tank, said at least partially immersed piece being located between the first starting piece Y1 and said last starting piece Y3 for each series.

13. The method according to claim 2, wherein said piece is totally immersed in said fluidized bed.

14. The method according to claim 2, wherein the fiber level in said pre-impregnated fibrous material ranges from 45 to 65% by volume.

15. The method according to claim 1, wherein a single thermoplastic polymer matrix is used and the thermoplastic polymer powder is fluidizable.

16. The method according to claim 1, wherein it further comprises at least one step of heating the thermoplastic matrix allowing said thermoplastic polymer to be melted or kept in melt condition after pre-impregnation, the at least one heating step being carried out by means of at least one heat-conducting or non-heat-conducting starting piece (E) and at least one heating system, with the exception of a heating calendar, said strand or strands being in contact with part or all of the surface of said at least one starting piece (E) and partially or totally running over the surface of said at least one starting piece (E) at the heating system.

17. The method according to claim 1, wherein it additionally comprises a step for shaping said strand or said parallel strands of said impregnated fibrous material, by calendaring using at least one heating calendar in the form of a single unidirectional ribbon or a plurality of parallel unidirectional ribbons or sheets with, in the latter case, said heating calendar comprising a plurality of calendaring grooves, in accordance with the number of said ribbons and with a pressure and/or separation between the rollers of said calendar regulated by a closed-loop control system.

18. The method according to claim 17, wherein the calendaring step is done using a plurality of heating calendars, mounted in parallel and/or in series relative to the passage direction of the fiber strands.

19. The method according to claim 17, wherein said heating calendar(s) comprise(s) an integrated induction or microwave heating system, coupled with the presence of carbon fillers in said thermoplastic polymer or mixture of thermoplastic polymers.

20. The method according to claim 17, wherein said heating calendar(s) is (are) coupled to a complementary rapid heating device, located before and/or after said (each) calendar.

21. The method according to claim 1, wherein said impregnation step(s) is (are) supplemented by a step of covering said single strand or said plurality of parallel strands after impregnation by the powder, said covering step being carried out before said calendaring step, with a molten thermoplastic polymer, which may be identical to or different from said polymer in powder form in fluidized bed.

22. The method according to claim 1, wherein said thermoplastic polymer further comprises carbon-based fillers.

23. The method according to claim 1, wherein said thermoplastic polymer further comprises liquid crystal polymers or cyclized poly(butylene terephthalate), or blends containing these as additives.

24. The method according to claim 1, wherein said at least thermoplastic polymer is selected from: polyaryl ether ketones (PAEK); polyaryl ether ketone ketone (PAEKK); polyarylsulfides; polyamides (PA); PEBAs, polyacrylates; polyolefins; and mixtures thereof.

25. The method according to claim 24, wherein said at least one thermoplastic polymer is a polymer whose glass transition temperature is such that Tg≥80° C., or a semi-crystalline polymer whose melting point Tm≥150° C.

26. The method according to claim 1, wherein said fibrous material comprises continuous fibers selected from carbon, glass, silicon carbide, basalt, and silica fibers, natural fibers especially flax or hemp, lignin, bamboo, sisal, silk, or cellulose.

Description

DESCRIPTION OF THE FIGURES

(1) FIG. 1 discloses an example of the pre-impregnation step, without being limited thereto, in a tank comprising a fluidized bed, and in which the N parallel strands (20) are separated into X=2 groups of parallel strands (21) and (22) running parallel separately on two series of starting pieces Y.sub.m (30) each consisting of three starting pieces (m=3: (31), (32) and (33)), the starting pieces (32) being totally immersed in the bed.

(2) FIG. 2 is a top and side view of the example disclosed in FIG. 1.

(3) FIG. 3 is the side view of FIG. 2 in which the angles of the groups of strands with the starting pieces are shown.

(4) FIG. 4 shows the fluidization based on the air flow rate. The air flow rate applied to the fluidized bed must be between the minimum fluidization flow rate (Umf) and the minimum bubbling flow rate (Umf).

(5) FIG. 5 shows a diagram of a heating system according to the invention with three conducting and non-conducting rollers.

EXAMPLES

Comparative Example

(6) Impregnation

(7) The impregnation was carried out as disclosed in WO 2018/115736 on a strand of Toray carbon fiber (FC) 12K T700 31E with a diameter of 7 μm and titration of the fiber at 0.8 g/m with a BACT/10T powder (0.7/1 by weight) having a D50=117 μm (D10=59 μm and D90=204 μm)

(8) Heating Step

(9) The heating system used is that disclosed in FIG. 5, but with nine stationary cylindrical rollers R′.sub.1 to R′.sub.9 with a diameter of 15 mm, each at the same level.

(10) The speed of advance of the strand is 10 m/min.

(11) The infrared used has a power of 25 kW, the height between the infrared and the axes of the rollers is 15 cm.

(12) The angles α′.sub.1 to α′.sub.9 are identical and 25°.

(13) The height h is equal to 0.

(14) The length I is 1,000 mm.

(15) The nine rollers are each separated by 43 mm.

(16) Calendering using two calendars mounted in series equipped with an IR of 1 kW each after the heating step.

Example 1

(17) Impregnation: general operating procedure

(18) The invention will be further explained with reference to the example of FIGS. 1 and 2, wherein a single tank comprising a fluidized bed is used, and the N strands are divided into X=2 groups, but it is quite obvious that this example is equally valid regardless of the number of groups X present. In the same way, three starting pieces Y.sub.m (30) per series are present, but it is quite obvious that this example is equally valid regardless of the number of starting pieces Y.sub.m (30) present.

(19) The invention therefore consists in dividing (or separating) the set N of strands present at the tank entry into two groups (1.sup.st (21) and 2.sup.nd (22) groups) (FIG. 2) of N/2 strands if N is an even number or, for example, (N+1)/2 strands (1.sup.st group) and (N−1)/2 (2.sup.nd group) respectively if N is an odd number.

(20) In top view of the set N of strands at the tank entry, the strands belong alternately to the 1.sup.st group (21) and then to the 2.sup.nd group (22).

(21) The fiber strands of the 1.sup.st group (21) plunge in the direction of the powder in the fluidized bed, after having left a first starting element denoted emb1 (31) by forming an angle α.sub.1 with the normal to this starting piece.

(22) The fiber strands of the 2.sup.nd group plunge in the direction of the powder in the fluidized bed after leaving a first starting piece denoted emb′1, forming an angle α′.sub.1 with the normal to this starting piece. The starting pieces emb1 and emb′1 are separated by a distance Demb1-emb′1 at least equal to the thickness of the strand, in particular from 5 mm to 100 mm, in particular from 10 mm to 50 mm.

(23) The fiber strands of the 1.sup.st group of fibers (21) then plunge into the fluidized bed of powder until they come into contact with a second starting piece at least partially (totally in FIGS. 1 and 2) in the fluidized bed denoted emb2. The angle formed between each fiber strand and the normal to the starting element at the point of contact is denoted α.sub.2.

(24) In the same way, the strands of the 2.sup.nd group of fibers (22) then plunge into the fluidized bed of powder until they come into contact with a second starting piece immersed at least partially (totally in FIGS. 1 and 2) in the fluidized bed denoted emb′2. The angle formed between each fiber strand and the normal to the starting piece at the point of contact is denoted α′2.

(25) In order to maintain identical paths in terms of travel time, tension of the fiber strands and friction, the starting pieces emb2 and emb′2 are separated by a distance Demb2-emb′2 equal to the distance Demb1-emb′1 and are of the same nature (material, surface, finishing, etc.).

(26) The fiber strands of the 1.sup.st group of fibers (21) emerge from the starting piece emb2 with an angle formed between each fiber strand and the normal to the starting piece denoted β.sub.2, then the strands impregnated with powder emerge from the fluidized bed of powder to come into contact with a last starting piece and denoted emb3. The angle formed between each fiber strand and the normal to the starting element at the point of contact is denoted α.sub.3.

(27) In the same way, the fiber strands of the second group of fibers (22) emerge from the starting piece emb′2 with an angle formed between each fiber strand and the normal to the starting piece denoted β′.sub.2 then the strands impregnated with powder leave the fluidized bed of powder to come into contact with a last starting piece denoted emb′3. The angle formed between each fiber strand and the normal to the starting element at the point of contact is denoted α′.sub.3.

(28) In order to maintain identical paths in terms of travel time, tension of the fiber strands and friction, the starting pieces emb3 and emb′3 are separated by a distance Demb3-emb′3 equal to the distance Demb2-emb′2 and therefore Demb1-emb′1 and are of the same nature (material, surface, finishing, etc.).

(29) In order to obtain fiber strands equivalent to one another before the ribbon or sheet is made up, in particular in terms of dimensions (width, thickness) and of the proportion of impregnated polymer as well as of the level of porosities, several parameters must be controlled, some of which are outlined below.

(30) The entry and exit angles of the fibers at the entry and exit starting rollers have a definite impact on the tension generated on the fiber strands and on the amount of powder carried by the fiber strand. It is therefore necessary for the system to be symmetrical on these points.

(31) In the system presented here, this residence time is kept for the two groups of reinforcing fiber strands by immersing in an equivalent manner the two starting systems emb1′ and emb2′; these two starting systems further having the same contact surface with the fiber strands on the two systems.

(32) The impregnation carried out according to Example 1 with a 1.sup.st group of 3 strands to produce strips 1, 3 and 5, and a 2.sup.nd group of 2 strands to produce strips 2 and 4 (identical angles α′.sub.1 and α′.sub.1 and of 17°, identical angles α.sub.3 and α′.sub.3 and of 17°, then heating step as in the comparative example) gives comparable results in homogeneity and porosity and with a resin content identical to the impregnation carried out according to the comparative example. Table I below outlines the results obtained.

(33) TABLE-US-00001 TABLE I Average BACT/10T Variability (wt %) (% by weight) Strip only 33 + or − 1.5% (comparative example Strip #1 32.6 + or − 1.7% Strip #2 33.1 + or − 1.4% Strip #3 32.7 + or − 1.6% Strip #4 32.9 + or − 1.5% Strip #5 33 + or − 1.3%