CONTINUOUS DEVICE FOR IMPREGNATING, IN A SINGLE STEP, STRANDS OR RIBBONS OF NATURAL FIBERS, IN PARTICULAR OF LINEN

Abstract

A continuous device (1) is provided for impregnating, in a single step, strands or ribbons of natural fibers (100) with a specific aqueous polymer dispersion to consolidate the fibers at the core of the fiber bundle and to improve their mechanical strength without any need for twisting. The device includes a stretching component (10) for elongating by the strand or the ribbon of natural fibers by stretching to give them a required yarn count, an impregnating component (20) for impregnating the fibers with the aqueous dispersion, a shaper for shaping/calibrating the wrung fibers, a dryer (40) for drying the shaped/calibrated fibers, and a conditioner (50) for conditioning the dried fibers to transform them into yarn or ribbon.

Claims

1. A continuous device (1) for impregnating, in a single step, strands or ribbons of natural fibers (100), in particular of linen, with a specific aqueous polymer dispersion in order to consolidate the fibers at the core of the fiber bundle and to improve their mechanical strength without any need for twisting, comprising the following means: means (10) for elongating by the strand or the ribbon of natural fibers by stretching in order to give them the required yarn count, means (20) for impregnating the fibers with the aqueous dispersion in order to ensure the complete impregnation of the filaments with same, means (30) for shaping/calibrating the wrung fibers, means (40) for drying the shaped/calibrated fibers, and means (50) for conditioning the dried fibers to transform the dried fibers into yarn or ribbon, said aqueous polymer dispersion including at least one amorphous polymer with a Tg between approximately 50° C. and 175° C., or a semi-crystalline polymer with a melting temperature between approximately 70° C. and 220° C., said dispersion including a content by weight of said polymer between approximately 5% and 50% with dispersed particles having a number average size of less than 10,000 nm.

2. The device of claim 1, wherein the means for elongating (10) comprises a comb (14) in alternating translation movement and rotary input rolls (12) and rotary output rolls (16) arranged in front of and behind said comb, said rolls creating, by turning in the same direction, a speed differential so that the output speed of the fibers is greater than the input speed of same.

3. The device of claim 1, wherein the means for elongating (10) stretches the fibers (100) with an output ratio between approximately 1 and 25.

4. The device of claim 1, wherein the means for impregnating (20) comprises a spray system or a system of dipping in a bath of the immersion type or of a contact impregnation roll.

5. The device of claim 4, wherein the impregnation speed in the impregnation means (20) is between approximately 5 m/min and 50 m/min.

6. The device of claima degree of impregnation with polymer obtained with the means for impregnating (20) is between approximately 0.1% and more than 50% by weight of polymer for a consolidation effect, and between approximately 35% and 50% for a pre-impregnated product.

7. The device of claim 1, wherein the means (30) for shaping/calibrating the wrung fibers comprise a wringing module (32) and a shaping die (34).

8. The device of claim 7, the means (30) for shaping/calibrating the wrung fibers exert a wringing pressure of approximately 100 kg.

9. The device of claim 1, wherein the means (40) for drying are selected from infrared radiation, microwave flow, heating by induction or by furnace with extraction of the water, a pulsed-air oven or calendaring on heating rolls.

10. The device of claim 9, wherein a drying temperature is between approximately 100° C. and 250° C.

11. The device of claim 1, wherein the polymer is selected from: (co)polyamides, (co)polyesters, polyurethanes, poly(meth)acrylates, fluorinated polymers, or polyolefins.

12. The device of claim 11, wherein: said polymer is selected from a poly(meth)acrylate, including copolymers, functionalized by acid functions, or a fluorinated polymer, including copolymers, grafted with reactive functions, said aqueous dispersion is an aqueous dispersion obtained by emulsion polymerization in the presence of a surfactant, and said reactive functions can react with said natural fibers and more particularly with the linen fibers.

13. The device of claim 11, wherein said polymer is a polyurethane formed from a polyisocyanate prepolymer including an ionic group, which is dispersed in the water with chain extension in an aqueous medium.

14. The device of claim 1, wherein said polymer is dispersible (or dispersed) in the form of a powder in an aqueous medium without surfactant, and said polymer in the powder state bears ionic groups or groups that are precursors of ionic groups by neutralization in water during the preparation of said dispersion.

15. The device of claim 14, wherein said polymer is a copolyamide, bearing carboxy, sulfonic terminal groups or amine terminal groups.

16. The device of claim 15, wherein said copolyamide bears amine groups neutralized in the form of ammonium by an acid.

17. The device of claim 15, wherein said copolyamide bears carboxy groups neutralized in the form of a salt by a base.

18. The device of claim 15, wherein said copolyamide is semi-crystalline with a melting temperature less than or equal to 150° C.

19. The device of claim 15, wherein the copolyamide comprises at least one of the following monomers: 5.9, 5.10, 5.12, 5.13, 5.14, 5.16, 5.18, 5.36, 6, 6.9, 6.10, 6.12, 6.13, 6.14, 6.16, 6.18, 6.36, 9, 10.6, 10.9, 10.10, 10.12, 10.13, 10.14, 10.16, 10.18, 10.36, 11, 12, 12.6, 12.9, 12.10, 12.12, 12.13, 12.14, 12.16, 12.18, 12.36, 6.6/6, 11/10.10 and their mixtures.

20. The device of claim 15, wherein polymer is a copolyamide selected from: PA 6/6.6/12, PA 6/6.6/11/12, PA 6/12, PA 6.9/12, PA Pip.9/Pip.12/11, PA 6/IPD.6/12, PA IPD.9/12, PA6/MPMD.12/12, PA 6/6.12/12, PA 6/6.10/12, PA 6/Pip.12/12, PA 6/6.6/6.10/6.I, PA 6.10/Pip.10/Pip.12, PA 6/11/12, PA Pip.12/12, PA IPD.10/12, PA Pip.10/12, PA 6/11, PA Pip.10/11/Pip.9, PA 6/6.6/6.10, PA 6/6.10/6.12 and their mixtures.

21. The device of claim 1, wherein: said polymer is semi-crystalline with a melting temperature Tf greater than 90° C. 100° C., and the particles of said dispersion have a number average size between approximately 50 and 5000 nm.

22. The device of claim 1, wherein the content by dry weight of said polymer with respect to the dry weight of said fibers varies from 0.5% to less than 50%.

23. The device of claim 22, wherein the content by weight varies from 0.5 to 10%, and said impregnation is limited to the consolidation of said fibers to one another, in addition to a sizing.

24. The device of claim 22, wherein said content is greater than 25% and less than 50% and said impregnation, in addition to said consolidation, leads to a pre-preg of said fibers that is used or can be used separately or successively in the fabrication of composite materials.

25. The device of claim 1, wherein a viscosity of said dispersion at 25° C. varies from 10 to 1000 MPa.Math.s.

26. The device of claim 1, wherein the fibers are long fibers with L/D>2000.

27. The device of claim 1, wherein said strands or ribbons are based on linen fibers having a tex between approximately 10 and 10,000.

28-31. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] FIG. 1 is a perspective view of a device according to this invention.

[0062] FIG. 2 is a side view of FIG. 1.

[0063] FIG. 3 is a top view of FIG. 1.

DETAILED DESCRIPTION

[0064] FIGS. 1 to 3 represent a device 1 for impregnating natural fibers such as linen by means of a specific polymer, according to this invention.

[0065] This device 1 comprises, in the movement direction F of the fibers 100, means for elongating by stretching 10, impregnation means 20, shaping means 30, drying means 40 and conditioning means 50.

[0066] The means for elongating by stretching 10 comprise a pair of pinching rotary input rolls 12, a comb 14 with a system with a strip of points and a pair of pinching rotary output rolls 16. The fibers 100, for example, a ribbon of combed linen, which is thus continuous in its macroscopic form, which is 7 g/m, penetrate into the elongation means 10 by means of pinching rotary input rolls 12 and then pass through the comb 14, which performs an alternating translation movement between the two pairs of front pinching rotary rolls before exiting elongated after the pair of pinching rotary output rolls 16. The linen fibers are stretched with an elongation ratio between approximately 1 and 25, preferably between 3 and 10, for example, 7.

[0067] The elongation of the fibers 100 is produced simultaneously by the comb and by the speed difference (differential) of rotation of the pairs of pinching rotary rolls, the pinching rotary output rolls 16 turn more rapidly than the pinching rotary input rolls 12.

[0068] Thus, after the first segment of the elongation device, the ribbon or strand measures 1 g/m, or an elongation ratio of 7.

[0069] The fibers thus stretched then penetrate into the impregnation means 20. At this stage, the ribbon is very fragile, it then passes through an aqueous dispersion mist which is delivered by a spray system. The impregnation speed is between several m/min to several tens of m/min, preferably between approximately 5 m/min and 50 m/min, for example, 30 m/min.

[0070] To carry out the impregnation treatment with an aqueous copolyamide solution, 10 L of several solutions (aqueous copolyamide dispersions) were fabricated in a laboratory reactor.

[0071] The copolyamides used are commercial products from Arkema called Platamid® 2592 and Platamid® 1657, respectively.

[0072] Their essential characteristics are presented in Table I below.

TABLE-US-00001 TABLE I COOH functionality Type de Platamid ® Melting temperature (μeq/g) 2592 102° C. 220 1657 107° C. 180

[0073] These products were introduced in the form of a dry powder into a solution of water with soda (1% with respect to the Platamid). The final dry extract content (DE) is 30%.

[0074] The reagents are loaded into a reactor, then the atmosphere is rendered inert with nitrogen. The reagents are heated for the purpose of reaching the material temperature of 150° C. This heating phase is carried out under stirring at 1000 rpm. Between 100 and 120° C., the mixture becomes homogeneous, white and opaque. The mixture is maintained for 30 min under stirring at 1000 rpm at 150° C., then cooled under stirring at 300 rpm. The dispersions obtained are fluid, white and opaque.

[0075] The particle size (size of the particles) was measured by observations carried out by scanning electron microscopy and also by the method of laser diffraction particle size analysis. The two measurement types are in agreement. The data indicated in the table below were obtained by the method of laser diffraction particle size analysis.

[0076] The particle size, the viscosity, and the dry extract content of the dispersions used are presented in Table II below.

TABLE-US-00002 TABLE II Number Brookfield Dry extract Platamid average viscosity* content Test of the particle at 23° C. dispersion reference dispersion diameter (nm) (MPa .Math. s) (%) EP-063 Platamid ®2592 80 30 30 EP-064 Platamid ®1657 140 20 30 *The measurement was carried out with a spindle No. 1 at 60 rpm.

[0077] These aqueous dispersions thus prepared are then used in the device for treating linen fibers, in undiluted or diluted form.

[0078] The polymer impregnation content obtained by means of the impregnation means 20 is between approximately 0.1% by weight and more than 50% by weight of polymer, preferably between approximately 2% and 5% for a consolidation effect, and between approximately 35% and 50% for a pre-impregnated product. In this case, the content obtained is approximately 2.5%.

[0079] After spraying, the impregnated fibers pass through the shaping means 30 which comprise, for example, wringing rolls 32 made of rubber, between which the fibers are pressed in order to remove the excess of aqueous polymer dispersion. These two rolls 32 have a first calibration system which forms the intermediate width of the ribbon. The roll means 32 exert a wringing pressure ranging from several kg to several hundreds of kg, preferably of approximately 100 kg, equivalent to 10 MPa of stress on a ribbon 6 mm wide and 1 g/m.

[0080] Then, the fibers thus impregnated pass through a calibration or shaping die 34, in order to adjust the ribbon obtained to the very specific size in terms of thickness and of width, preferably ¼ inch or 6.35 mm wide, preferably flat, but also possibly cylindrical.

[0081] Between each step, there is a device with a pair of rolls made of treated aluminum which moves the ribbon along so that it is never under tension over too long a distance, more than 1 meter. These drive rolls for the ribbon, motor driven using an electric motor, are controlled by an electromagnetic clutch which adjusts a constant tensile stress of the ribbon.

[0082] After the calibration step, the ribbon of impregnated fibers 100 is passed through the drying means 40 which evaporate the water contained in the ribbon and melt the dispersed polymer at the core in order to consolidate the ribbon. These drying means 40 include, for example, seven series-connected 1200 Watt short-wave infrared emitters each 405 mm long. The power of each emitter can be variable, so as to obtain a specific temperature profile for the drying and the melting of the polymer. For example, the first three emitters are adjusted at 250° C., and then the next four at 180° C. The total drying length is approximately three meters, which corresponds to a drying duration of 6 seconds for a movement speed of the ribbon of 30 m/min. The drying temperature of the ribbon is between approximately 100° C. and 250° C., preferably between 100° C. and 200° C., for example, 150° C.

[0083] The degradation temperature of the linen fibers is approximately 230° C., but the fiber, after impregnation and as a function of the duration of its passage through the drying means 40, can tolerate temperatures between 250° C. and 300° C. The purpose of the drying is to evaporate the water contained in the dispersion and to melt the polymer at the core of the fiber in order to obtain a satisfactory impregnation quality.

[0084] Upon exiting the drying means 40, the ribbon has to be completely dry at the end of the drying and the thermoplastic polymer has to have gone back down below its melting temperature, or, for example, below 110° C.

[0085] At the end of the device, the impregnated, shaped and dried ribbon is wound around a winder 52 which packages the product in the form of a spool, for example, with a cardboard spool core having an internal diameter of 75 mm.

[0086] The continuous device operates at a constant linear speed. Tension measuring devices (not represented) control the tension of the ribbon by way of the electromagnetic clutch, so that there is no weakening of the fiber before the final packaging on the spool.

[0087] This device thus makes it possible in a single step to elongate, and without any twisting step, to impregnate, shape, consolidate and package a very fine ribbon made of linen fibers measuring a few g/m, preferably 1 g/m, on a spool, with a potential length of several thousand meters.

[0088] The impregnation by a copolyamide dispersion thus makes it possible to increase the force at rupture of the strand ribbon of linen fibers very significantly, while reducing its thickness/reducing its linear weight.

[0089] A 1st series of tests was carried out on a linen roving (strands of fibers) with a high yarn count of 2190 tex, with different treatments.

[0090] Except for Example 7, wherein the impregnation method is specified, in all the other cases (unless especially specified for each example), said impregnation was carried out by in-line (continuous) spraying with a spray device (spray), with a residence time under the jet of said sprayer of approximately 1 s. The drying is carried out by heating with an infrared device. The cooling is carried out in the open air.

[0091] Comparison base 1: non-impregnated strand of 2190 tex.

Example 1

[0092] EP-063 ND: impregnation with an undiluted solution (Dry extract content: 30%) of Platamid®2592.

Example 2

[0093] EP-063 D50: impregnation with a dispersion diluted to 50%, of Platamid 2592 (Dry extract content: 15%)

Example 3

[0094] EP-064 ND: impregnation with an undiluted dispersion of Platamid® 1657 (Dry extract content: 30%)

Example 4

[0095] EP-064 D50: impregnation with a dispersion diluted to 50% of Platamid® 1657 (Dry extract content: 15%)

[0096] The 2nd test series was carried out on a linen roving with low yarn count (1030 tex) having undergone a treatment with the Platamid® 1657 at different impregnation contents.

[0097] Comparison base 2: non-impregnated strand of low yarn count (0% of polymer)

Example 5

[0098] impregnation with a solution 3 diluted by a factor 4 with Dry Extract content: 7.5%

Example 6

[0099] impregnation 2 times consecutively (2 passes) with the dispersion of Example 5

Example 7

[0100] impregnation by immersion (dipping) in the aqueous dispersion with a longer residence time (10 s)

[0101] For the test of tensile strength, the linen roving is stuck to a cardboard frame. The reference length was selected to be 14 mm, it being known that the average length of a linen fiber is approximately 30 mm. The upper edges and lower edges of the cardboard are clamped between the jaws of the dynamometer (Zwick machine), while the lateral edges are cut. The roving is then subjected to traction at a speed of 1 mm/min.

[0102] In order to compare the weakly resin-impregnated (up to 10% of the polymer) rovings, the force at rupture of the different samples tested is measured. The results are presented in Table III below.

TABLE-US-00003 TABLE III Comparison Exam- Exam- Exam- Exam- Reference Base 1 ple 1 ple 2 ple 3 ple 4 Impregnation type Non- EP63- EP63- EP64- EP64- impregnated ND D50 ND D50 Resin content by 0 2-10% 2-10% 2-10% 2-10% weight Number of 5 8 5 5 5 samples Mean force at 443 775 723 888 770 rupture (N) Standard 33 98 68 23 73 deviation

[0103] Table III shows that impregnation with a copolyamide dispersion makes it possible to very significantly increase the force at rupture of the strand of linen fibers.

[0104] The two dispersions give similar results, and in the direction of consolidation (Examples 2 and 3 in contrast to the comparison base 1), which demonstrates that the consolidation dispersion proposed works, including for 50% dilutions (which corresponds to a dry extract content of 15%).

[0105] Table IV below gives the result of different impregnations with Platamid® 1657 and a strand with a low yarn count (1030 tex). One notes that with a dilution by a factor 4 with final dry extract content of 7.5%, a force at rupture equivalent to the one obtained with the non-impregnated roving with high yarn count (2190 tex) is obtained (comparison of Example 5 with the comparison base 1). Thus, it was demonstrated that the use of a copolyamide dispersion as defined above made it possible to use a strand of linen fiber having a yarn count divided by 2 in comparison to the initial strand (1030 tex versus 2190 tex), while substantially keeping the same mechanical strength (approximately the same force at rupture).

[0106] In addition, it is shown that by using several impregnation passes (by spraying) with the same dispersion, one increases the copolyamide content in the final strand (comparison between Examples 5 and 6).

[0107] To finish, by means of a test of impregnation by immersion (dipping) with a much longer spray time (10 s), it is shown that it is possible to impregnate the strand with nearly 40% (by weight) of copolyamide (Example 7). This content corresponds to a resin (polymer) content found in conventional pre-impregnated reinforcements, thus making it possible to produce composite parts directly, for example, by heat compression, or by means of a fiber placement technology such as pultrusion, without using an additional impregnation operation of the fibrous reinforcement.

[0108] Thus, the possibility, with the device according to the invention, of directly producing a ready-to-use, semi-finished composite product of the pre-impregnated type is demonstrated.

TABLE-US-00004 TABLE IV Comparison Reference base 2 Example 5 Example 6 Example 7 Impregnation Non- Product Product Impregnation type impregnated diluted by a diluted by a by immer- factor of 4 factor of 4 sion for 10 s (DE: 7.5%) (DE: 7.5%) with 2 passes Polymer 0 2.7 5.3 39.8 content (% by weight/fiber + polymer) Number of 5 5 5 3 samples Mean force at 202 449 549 948 rupture (N) Standard 15 49 65 49 deviation

[0109] This invention thus makes it possible to solve the above-described technical problems with respect to the prior art with a device for the impregnation of strands or ribbons of natural fibers, this impregnation taking place at core with a specific aqueous polymer dispersion, thus enabling said polymer to bind at the core of the fiber bundle, to one another, the fibers of said strands or of said ribbons in order to consolidate them with the fine polymer particles used after melting.

[0110] This impregnation can subsequently result in a pre-impregnated fibrous reinforcement, a strand or a ribbon with low yarn count, which can be used for the fabrication of composite materials.

[0111] The flexibility of the solution of this invention makes it possible to integrate the invention in a continuous line for fabricating said fibrous reinforcement based on natural fibers, such as linen fibers, from the treatment of the natural fibers harvested in the fields to the fabrication of a strand or of a pre-impregnated and calibrated ribbon.

[0112] Thus, in a single step, a strand or ribbon is obtained, which contains the linen fiber and the resin at a content that can be between 0 and 70% by weight of resin. There is no cutting step needed to calibrate the width of the product, since the shaping device ensures this step.

[0113] Naturally, the detailed description of the subject matter of the invention, given only as an illustration, in no way constitutes a limitation, the technical equivalents being also included in the scope of this invention.

[0114] Thus, the impregnation means 20 can include a system for dipping in a bath of the immersion type, or a contact impregnation roll.

[0115] The drying means 40 can also consist of a flow of microwaves, heating by induction or by furnace with extraction of the water, a pulsed-air oven, or calendaring on heated rolls. These drying means can include systems for channeling radiation in order to concentrate the energy towards the product to be dried.