FR2850606A1 - Accurately dosing high proportion of natural fibers into plastics, to give homogeneous distribution and high strength, by introduction into extruder at two or more points, useful e.g. in PVC window frames - Google Patents

Abstract

A method for accurately dosing a very high proportion of natural fibers (A) into plastics materials (I) involves: (a) introducing (A) into an extruder at at least two separate points, i.e. a first upstream point (UP) and at least one downstream point (DP); and (b) introducing (I) at UP and optionally at least one DP. Independent claims are included for: (a) apparatus for the process, comprising dosing apparatus (1, 2, 3) for (A); a device (4,5) for separating the supply of (A) into at least two secondary flows; an extruder with an UP and at least one DP for introduction of (A), each introduction point being able to receive a secondary flow of (A) and/or a flow of granules of (I); (b) (A)/(I) blends obtained by the process; (c) (A)/(I) compounds or composites obtained by the process, specifically in the form of cuttable masses, plates, canes, granules or sticks; and (d) articles (specifically moldings) consisting of or including elements obtained from the compounds or composites.

Description

i

  Method and apparatus for incorporating a high proportion of natural cut fibers into a plastics material, products obtained and applications

  TECHNICAL FIELD OF THE INVENTION The present invention relates to the technical field of incorporating cut natural fibers into a plastic material, in high proportion, and the articles thus obtained as PVC window frames and the like.

  PRIOR ART: Window profiles made of polyvinyl chloride or PVC are known. However, the PVC is not very rigid in bending, these profiles are commonly reinforced by metal inserts. The French market of this sector alone consumes about 8500 km per year of such inserts.

  These inserts can be recycled but have many disadvantages such as their weight, their creation of thermal bridges, and their insertion cost in the PVC profile.

  This problem arises for many other similar structure and destination products employing PVC or other plastics known to those skilled in the art, such as skirting boards, profiles, inserts or reinforcements for shutters, windows, partitions. , barriers ... in the building, structural parts, parts under an engine hood, interior decor or bonnet or bodywork for all types of vehicles, pleasure craft, aircraft, 25 packaging and packaging elements: crates, pallet crates; toys, technical parts ...

  In the prior art, the use of glass fibers has been attempted, but they have proved unsuitable, if only because of their short length. Their implementation is all the more complex as they are and they cause regardless of their length a very high abrasion tools.

  It has also been attempted to use natural fibers, but such fibers have great difficulties of "compounding" that is to say of intimate mixing with the plastic material, and can be more brittle.

  Problems are also encountered in finished products because of the difficulty of dosing and compounding: a very important problem which was considered unavoidable and insoluble, or at least its consequences, lies in the fact that The apparent density of the normal natural fibers is of the order of 0.1 (in volume of fibers weighed) (the actual density of the cellulose being approximately 1) while that of the granules or balls of plastic material introduced into the extruder of Compounding 15 is of the order of 0.7.

  Anyone skilled in the art will understand that this large difference in apparent density creates insurmountable problems so far when one seeks to mix for example about 30% of fibers with about 70% of plastics. In fact, despite the 30/70 ratio, the volumes to be mixed are in a reverse ratio, that is to say that 30% of fibers represent a volume approximately 10 times greater than the 70% of plastic. Flow problems in the feed hopper of the extruder are encountered, as well as problems of compounding, for example with granules or balls of plastic material which melt immediately while the fibers, by their nature, do not melt. not. Furthermore, the actual density of the cellulose being about 1 while the apparent density of the fibers is about 0.1, it is confronted during compounding to very large volumes of air that must be evacuated. The temperature must be limited in practice to 180 220 ° C max., Otherwise the fibers burn.

  The technique described in patent WO 0194094 (WO FR 010 1720) which incorporates from 10 to 50% by weight of vegetable matter of cereal or oleaginous origin is also known. However, one skilled in the art understands from reading this document that the fibrous product is granulated and then compacted, then mixed with the plastic material, and extruded "in rush" and then cut into granules. We obtain poor quality products. This patent emphasizes the difficulty of properly mixing the plastic and the fibers, and proposes a remote introduction of the extruder inlet to deagglomerate, in the extruder, the plastic pellets (additional problem) and operate a " brewing "granules melted with the fibers.

  Also known is WO 021 19 76 (WO DE 01 0 28 98) which describes a mixture of fibers and plastics. The patent indicates that the fibers and the "filiform" plastics are mixed "homogeneously", but without specifying this point, then the mixture is extracted into sheets or plates which are heated until softening, after which the pellets are cut into granules. , then finally we proceed to extrusion. This patent shows the complexity of the processes that the skilled person was obliged to implement in an attempt to solve the problems mentioned.

  Technical problem posed: The technical problem is, therefore, in front of the objective which is to seek a very high rate of natural fibers cut in a plastic material, by compounding, in order to obtain products such as profiles for windows and similar products overcoming the above obstacles, that is, including difficulty in properly dosing and then compounding the fibers with the plastic because of their texture and nature, and their density.

  These products, to meet the requirements of professionals, must be very homogeneous and have excellent mechanical properties, that is to say at least as good as those of products "metal insert", and despite their high proportion of fibers, and their method of manufacture should not be expensive, a high cost can not compete with the current products of the metal insert type.

  By "very high level of natural fibers cut" is meant according to the invention a percentage of 10% to 80%, preferably greater than 20% and more preferably 50% by weight. Beyond 50%, the transformer will have to dilute the <compound "obtained because it would be too viscous for direct use, however this does not represent a serious drawback, especially in view of the very important advantages of high rates in certain applications.

  It will be noted that in the prior art, some documents mention contents up to 50% by weight. However, we have seen that these products do not meet the quality and / or low cost requirements of the products covered by the invention. Such contents are therefore not representative of the prior art of the invention.

  There is therefore an important and recognized need for a method and an apparatus for correctly dosing a very high proportion of natural fiber (s) in at least one plastic material, to obtain by compounding an article having very good properties. mechanical, homogeneous structure, and low cost.

  Summary of the Invention: The invention relates to a method and apparatus according to which the natural fiber (s) dosed into the extruder (throughout the present application, including the claims, "natural fiber" or "natural fibers") is introduced. designates either a single type of natural fibers, or a mixture of fibers compatible with each other), at least two separate "upstream" and "downstream" introduction points and the one or more plastics is introduced (throughout the present application , including the claims, "plastics" or "plastics" means a single plastic material such as PVC or a mixture of plastics compatible with one another), at least said first "upstream" introduction point of the natural fibers and possibly (possible balance of plastic material) at the second point of introduction "downstream" of the fibers, or in one or more of the "downstream" points of introduction of the fibers, if ex is more than two points of introduction of fibers.

  The invention also relates to an apparatus for covering this process, and in particular a method and apparatus for the determination of natural fibers.

  Detailed description of the invention

  The invention therefore relates in its first aspect to a method for correctly dosing a very high proportion of natural fiber (s) in at least one plastic material, to obtain by compounding an article having very good mechanical properties, homogeneous structure, and low cost, characterized in that: - the introduced natural fiber or fibers in the extruder in at least two separate introduction points called "upstream" for the first and "downstream" 1 5 for the other (s), and - the plastics are introduced into at least said first point of "upstream" introduction of the natural fibers and possibly (possible balance of plastic) at the second point of introduction "downstream" of the fibers, or in one or more of the "downstream" fiber introduction points, if there are more than two points of introduction of the fibers.

  According to a particular embodiment, the fibers are introduced at two separate points of introduction, upstream and downstream.

  According to another particular embodiment, the fibers are introduced at three points of introduction, an "upstream" point and two "downstream" points.

  According to a particular embodiment, all of the plastic material is introduced into said upstream introduction point.

  According to another particular embodiment, the natural fibers are introduced in the uncompacted state into the extruder.

  According to a preferred embodiment, a "very high rate of natural cut fibers" is introduced into the plastics material (s), that is to say from 10% to 80%, preferably greater than 20-30% and better still 50%. % in weight.

  Beyond 50% by weight, the transformer will have to dilute the "compound" obtained.

  According to another particular embodiment, a fraction of the plastic material is introduced into the upstream point and a fraction of the plastic material is introduced into the downstream introduction point or at least one of these downstream points.

  According to the best embodiment of the invention, the dosage of natural fibers is carried out in two steps, a first coarse volumetric dosing step and a second fine gravimetric dosing step.

  The dosing apparatus will be described in more detail below.

  According to another preferred embodiment, the introduction points 15 of the natural fibers comprise, at the end of the dosing apparatus, intermediate hoppers (one for each point of introduction, or a single hopper with as many outlets as there are points). introduction), to each of the extruder feed hoppers optionally, but preferably, provided with means for "feeding" the natural fibers (a feed hopper at the point of introduction of the fibers) into the extruder. extruder.

  According to another option, the only disadvantage would be a cot and a larger footprint, each fiber feed hopper in the extruder is provided with its own metering equipment.

  The distribution of the fibers between the different points of introduction is a function of the type of fiber or mixture of fibers.

  It is possible to envisage a distribution of 50% by weight of the fibers in the upstream point, and 50% in the downstream point, or 25% and 25% in the two downstream points if there are three points of introduction. It is also possible to envisage a 30-60% distribution at the upstream point, and 70-40% at the downstream point or points, for example 40% then 30% then 30% or 50% then 30% then 20%.

  The skilled person will naturally adapt these non-limiting examples depending on the compound he wants to obtain and the equipment available to him.

  The fibers are preferably cut to a length of the order of 0.2 to 20 mm, preferably 2 to 4 mm.

  With regard to the granules of plastic material, it is possible to envisage 100% of granules at the upstream point, which is the best current embodiment, and the simplest, or a distribution of 50% by weight of the fibers in the point. upstream, and 50% in the downstream point, or 25% and 25% in the two downstream points if there are three points of introduction. We can also consider a 30 - 60% distribution at the upstream point, and 70 - 40% in the downstream point or points, for example 50% then 30% and 20%.

  Those skilled in the art will again be able to adapt these non-limiting examples according to the compound that they wish to obtain and the equipment available.

  According to another particular embodiment, the plastic granules are introduced by a separate means into the upstream fiber introduction hopper and possibly into the downstream point or at least one of said downstream points.

  According to the invention, it has also been determined that the water content or residual moisture of the fibers at the time of their introduction into the extruder must be set between 0.2 and 3% by weight of water, preferably between 0.8. and 1.5% by weight of water relative to the weight of the fibers.

  This controlled drying solves or contributes greatly to solving the compounding problems mentioned above.

  This controlled drying is carried out by any means known as a microwave apparatus, a "flash" evaporator (the fibers fall into a current of air brought to 180 ° C., a less preferred system since it may present a risk of explosion) or other means known to those skilled in the art.

  It is preferable to use a parallel twin-screw apparatus placed in a trough, slightly nested one inside the other, and the% residual water is adjusted by adjusting the heating of the screws and / or the walls of the trough, preferably by regulating the temperature of the coolant, and / or the speed of rotation of the screws, the latter method with adjustment to correct very reactively and accurately the water content, and thus to control the residual water content or fiber moisture, the invention of which has shown importance.

  According to a second aspect, the invention also relates to apparatus 10 for carrying out the above method.

  Other features and advantages of the invention will be better understood on reading the description which follows, and with reference to the appended drawing in which: FIG. 1 represents a non-limiting embodiment of the dosing apparatus according to the invention, and the preferred apparatus for dividing the fiber cake 20 into two fractions, which will be introduced into the extruder 11 in two different locations, upstream 12 and downstream 13.

  As already indicated, one could for example provide three points of introduction of the fibers, and one could also provide, not the divider device 4 shown, but two (or three ..) separate hoppers, each corresponding to a point d ' introduction.

  - Figure 2 shows the device of Figure 1, in front view, mounted above the extruder 11, which it feeds the two fiber feed hoppers 12 upstream and 13 downstream.

  - Figure 3 shows a less preferred variant of fiber sharing in two streams.

  In the appended figures, the same references have the same meanings, which are the following.

  1 receiving hopper before coarse volumetric dosing 2 oversized diameter tube o is a coarse volumetric dosing means, including a conveyor-weigher 3 conveyor belt which transfers the fibers to the system or apparatus 4 distribution or division of fibers and which simultaneously carries out a precise weighing of these natural fibers 4 apparatus (here, without limitation, hopper) division or distribution of fibers, here two secondary currents Vi and V2 through a movable plate 5 (adjustable in function of the desired distribution), with id two outlets 6 and 7 6 7 8 hopper 1 1 12 20 13 14 15 part introduction 17 18 19 20 in 1, Vi, V 27 bandE 35 30 31 32 33, 3z distribution plate upstream outlet downstream output of pivot fibers or axis of the plate 5 feeding screw (if any) in the hopper 12, the other screw in the 13 not being shown.

  extruder hopper for receiving or introducing natural fibers upstream receiving hopper or introduction of natural fibers downstream extruder screw feeding duct for pellets of plastic material or one of these granules possible conduit for bringing in the balance of any pellets not jits in 15 tooth comb of the motor comb imparting a horizontal oscillating movement schematic form of the "cake" of fibers after the passage e oscillating comb 2 secondary currents, here two, formed from the fiber cake second conveyor belt second comb that the it is possible to place above the second axis separation plate of said frame plate 30 and means for adjusting in rotation of said receiving hopper plate of the fiber currents V1 and V2. 1 0

  The invention will be better understood on reading the description which follows, and non-limiting examples below.

  The apparatus according to the invention is characterized in that it comprises - a device (1, 2, 3) for dosing natural fibers - a device (4, 5) for separating the mass of natural fibers in two ( V1, V2) or more than two so-called "secondary" fiber streams, and - an extruder (11) having at least two points of introduction of the fibers, one upstream 12, the other (or several others) downstream 13, each of said introduction points being adapted to receive a secondary current of fibers and / or a stream of plastic pellets.

  According to a particular embodiment, said extruder comprises two introduction points, one upstream 12, the other downstream 13.

  According to another particular embodiment, said extruder has three points of introduction, one upstream receiving a fraction of the fibers and all or a fraction of the granules, and two downstream introduction points, one of which (or both) receives the balance of the fibers and one (or both) receives the balance of pellets.

  The plastic granules are introduced at least in part (15) into the upstream introduction point, the possible balance of the granules being introduced (16) into the downstream point, or at least one of the downstream points if it exists more than one.

  According to a particular embodiment, all the granules of plastic material is introduced (15) into the upstream point 12 of introduction.

  According to another particular embodiment, said apparatus comprises a device for accurately measuring the mass of the fibers, characterized in that i operates in two stages, ie a first coarse volumetric dosing step (1, 2 ) in a first metering device and then a second thin weighting step (3) in a second metering device. 1 1

  According to a particular embodiment, said first step is carried out in a vertical or substantially vertical hopper 1 of large section, where the fibers descend by gravity towards a system for transferring the fibers to a conveyor belt weighing; said transfer system 2 consisting in particular, in a nonlimiting manner, of a horizontal or substantially horizontal tube of clearly oversized diameter, which comprises a horizontal or substantially horizontal transfer means such as an endless screw, the screw being adjusted so as to performing a coarse volumetric dosage of the mass (or flow) of fibers that has been pre-selected - this tube 2 producing a "bunch" of uncompacted fibers, which is deposited on a conveyor belt-weigher 3 which operates a weighing (and thus dosing) end of the mass (or flow) of fibers (second precision weighting meter).

  According to a preferred embodiment, the points of introduction of the natural fibers comprise, at the end of the dosing apparatus, intermediate hoppers 6, 7 (one for each point of introduction, or a single hopper with as many outlets as for introduction points). ) to each of the feed hoppers 12, 13 in the extruder 11 optionally, but preferably, provided with means for "feeding" natural fibers (a feed hopper for each point of introduction of the fibers) in the extruder.

  According to another option, each fiber introduction hopper in the extruder is provided with its own dosing apparatus.

  An electronic control and regulation system, not shown because known in itself or readily adaptable by any skilled person, regulates and fine-tunes the speed of rotation of the screw in the tube 2 according to the fine weighing performed by the band 3 and by comparison with the theoretical value pre-entered in the electronics.

  The tube 2 is preferably of cylindrical cross-section, or is oval or even of square or rectangular section, the essential being that it is oversized so that no blocking of the fibers occurs; according to the 1 2 section of the tube, the fiber bead is of cylindrical section, oval, square, rectangular etc ....

  Those skilled in the art will also understand that by "horizontal", "vertical", "horizontal" or "substantially horizontal" (or respectively "vertical") is meant that a slight to moderate inclination can be tolerated with respect to the vertical or horizontal respectively, however the best arrangement is the vertical arrangement of the hopper 1 and horizontal of the tube 2 and the strip 3.

  According to the best nonlimiting embodiment, said apparatus 10 comprises a device for spreading the "bead" of fibers coming from the tube 2 into a "cake" of substantially rectangular flat cross-section that is very flattened on the conveyor-weigher belt 3.

  According to a nonlimiting option, said spreading device comprises a horizontal comb 17 having vertical teeth 18, with a small clearance 15 between the lower part of the teeth and the surface of the conveyor belt weighing 3, and m by a suitable motor 19 according to a horizontal movement back and forth. Said device is placed in such a way that the lower part of the teeth is just above the strip 3. Thus, when the uncompacted fiber bundle exits the tube 2, it passes through the comb whose movement is adapted. to spread the fibers over the width of the strip. Thus, a cake of substantially rectangular cross section is very flattened, as represented by the reference 20.

  As regards the hopper 1 and the transfer tube 2, that is to say the first coarse volumetric doser, the following definitions will be given: the hopper 1 is of large section that is to say adapted for that the fibers can fall by gravity, freely, with a minimum of hindrance and without compaction - its walls are vertical or substantially vertical, in the best embodiment, which prevents any blocking or jamming of the fibers. One could consider installing a feed screw, but this is totally superfluous if the dimensions of the hopper are sufficiently large compared to the volume (flow) of fibers in said hopper.

  the tube 2 is oversized, or clearly oversized, with respect to the volume (or flow) of the fibers to be transferred, that is to say that its diameter forms a volume which is clearly greater (between 3 and 5 or 10 times ) the volume necessary to process the anticipated rate of fiber. There is no particular upper limit to oversize, other than that of reason, the objective being that, as in the hopper, the fibers undergo a minimum of stresses and a minimum of compaction, to produce at the outlet of 10 tube a bunch of uncompacted fibers able to be spread by said comb or by any other device. A good oversizing factor is between 5 and 10.

  Said device for separating the dosed mass of natural fibers into two or more so-called "secondary" fiber streams comprises, according to the best nonlimiting mode of the invention, a hopper 4 arranged vertically and adapted to receive said cake of fiber dosed and having a mobile vertical plate, able to separate said cake, falling by gravity, into two secondary currents of fibers VI and V2 separated from one another, which exit at the bottom of the hopper 4 by two separate tubes 20 and 7.

  Those skilled in the art will have understood that the separation hopper 4 can be replaced by two separate hoppers, or by three separate hoppers or by a hopper 4 comprising two type 5 plates, if three secondary currents are to be obtained, and other developments that will be directly accessible to the skilled person.

  According to another embodiment, the fiber cake is separated on a second horizontal conveyor belt 25, following the weighing belt 3, by means of an elongated vertical plate 30 which is movable or adjustable around a vertical axis 31. same fixed to a frame carrying a rotational adjusting means 32, said plate being disposed along the longitudinal axis of said second strip for a 50/50 distribution, or at a certain angle with respect to this axis for others distributions as 40/60 or 60/40, and in contact with the upper face of said second strip 25, and thus capable of dividing the fiber cake into two secondary currents V1 and V2, each on one side of said plate.

  Said plate 30 may be straight, in plan view, or slightly curved in a concave or convex shape, or in "S" very flattened, to promote the flow of the currents V1 and V2 of fibers. It can also be provided with an elastic scraping seal at its contact with the strip 25.

  It is advantageous to place a second comb 27 above this second band 25, but this is not mandatory.

  The two fiber streams Vi and V2 can then flow directly into two receiving hoppers 33 and 34 having outlets 6 and 7 as in the other option.

  Similarly, in the variant of separation by a vertical plate disposed on a second strip, it will be possible to use two or more such parallel plates between them, and adjustable in rotation independently of each other, in order to divide the cake into a corresponding number of secondary currents, with naturally as many receiving hoppers as currents.

  The band 25 may optionally be put in slight vibration to promote flow.

  Naturally, in all options, conveyor belts can be inserted to transfer fibers from one point to another in the workshop.

  The natural fibers are chosen from - hemp fibers, hemp fibers, flax fibers, kenaf, jute, sisal, abacca, wood ...

  and mixtures thereof such as hemp / hemp fibers, annual plant fibers / wood fibers, natural fibers / synthetic fibers, organic fibers and / or mineral fibers. Plastics are chosen from polyolefins such as polypropylene and high polyethylene. or low density (HDPE or LDPE), - styrene plastics such as ABS (acrylonitrilebutadiene - styrene) or polystyrene, PVC (polyvinylchlorides) - polyamides (PA) - polyurethanes, polyesters, elastomers, copolyamides - and their mixtures or alloys such as PVC / PVAC (polyvinyl acetate), ABS / PC (polycarbonate), ABS / PA, PPO (polyphenylene oxide) / PS (polystyrene) ...

  These abbreviations are known to those skilled in the art and the alloys are well known.

  The invention also relates to the mixtures of fibers and plastics introduced into the upstream and downstream hoppers of the extruder.

  Preferably, there will be introduced in the upstream hopper 12 between 10 and 70% by weight of fibers for 90 to 30% of plastic material; preferably between 40% and 40% of fibers and 80 to 60% of plastic.

  The invention also covers the compounds or composites of fibers and plastics coming out of the extruder 11 (in the apparatus above) and obtained by the above process, possibly shaped into granules, plates, etc. for a future application, in particular compounds or composites of cut natural fibers and of plastics material (s) characterized in that they are obtained by the process or in the apparatus according to the invention or by implementation mixtures according to the invention of fibers and plastics in an extruder, among other compounds or composites which are in any transportable form such as masses to be cut, plates, rods, granules, balls, or rods.

  The invention covers compounds or composites of cut natural fibers and plastics material (s) characterized in that they comprise a "very high rate of cut natural fibers" in the plastics or plastics thereof. that is, from 10% to 80% by weight, preferably greater than 20-30% by weight and more preferably 50% by weight.

  The invention also covers the applications of the process, apparatus, and compounds or composites described above in the fields of window profiles, doors and the like, in all the profiles of the building and civil engineering industry, skirting boards, profiles, inserts or reinforcements for shutters, windows, partitions, barriers ... in the building, articles for the automotive industry, such as bumpers, body parts, aerodynamic fins, etc. railway industry, in the aeronautics and space industry, in the shipbuilding industry, including pleasure craft, structural parts, parts under engine hood, interior decoration part or bonnet or bodywork for all types of vehicles, boats pleasure craft, aircraft, packaging and packaging elements: crates, pallet crates; toys, technical parts ... .and any industry where weight gain and excellent mechanical properties are sought by eliminating all or part of the use of inserts or metal profiles or mineral fibers, such as for example the "packaging" o the invention makes it possible to produce, in injection molding, honeycomb handling pallets, by way of non-limiting example, both very rigid and of low weight, thermoformed pallets, technical parts reinforced, toy elements, decorative packaging for consumer products such as home appliances, reinforcing elements and decor for the building ...

  The invention also relates to articles, in particular molded articles, corresponding to said applications, in particular profiles for windows, doors, handling palettes, etc. and all the articles and inserts or parts mentioned above, as well as those which It will be clear to those skilled in the art, which consist of, or comprise at least, an element made from a compound or composite according to the invention, in particular for the applications described.

EXAMPLES

  Description of the process for manufacturing mixtures, in the form of granules, thermoplastic materials and natural plant fibers.

  This process can be divided into three parts: - thermal, chemical and mechanical treatment of natural fibers - dosage of fibers and plastic granules - blends of fibers and plastic pellets by extrusion 1. Treatment of natural fibers 15 Natural fibers arrive in the form of balls. These are opened by means of a loader.

  The natural fibers then pass through a knife mill to be cut to an optimum length of 4 mm.

  The fibers then pass through a sieve system. This sieving makes it possible to selectively recover, on the one hand, the fiber dust, on the other hand, if appropriate, the bark particles (chenevote in the case of hemp fibers) and thus to make mixtures only with the fibers cut to the length of 4 mm.

  At the exit of the sieve, the fibers pass into a dryer that controls the moisture content of the fibers. This dryer is heated by a hot oil bath. Inside this dryer, the fibers are conveyed by two parallel worms. Chemical treatment can also be considered at the dryer. (additive additives by spray for example) Finally, the natural fibers are conveyed to the doser by a system of screws and buckets.

  2. Dosing of fibers and granules The dosage of natural fibers and the dosage of granules are gravimetric dosages.

  The dosing of the natural fibers is carried out thanks to a two-stage doser: - The first stage is fed by a vertical-walled hopper of sector identical to the entrance of the doser. This one is a coherent doser of large capacity controlled by a second doser.

  - The second metering consists of a weighing belt powered by a volumetric doser, equipped with a reciprocating doctor blade system for a good distribution of the product on the band.

  At the outlet of the metering unit, the bed is divided into two parts that can be adjusted to arrive feeding hoppers of the extruder.

  The dosage of the virgin granules is carried out thanks to a particular hopper.

  This hopper consists of two hoppers superimposed one on the other and separated by a valve. When the weight of pellets is sufficient in the lower part, the valve closes automatically. 3. Fiber blends and plastic pellets by extrusion The extruder used is a single-screw BUSS blender. The pellets are cut under water. The granules thus formed are then dried by a fluidized air bed.

  Example of prototype implementation: The fiber bales arrive in the workshop and are brought on a carpet having rows of points transverse to the scroll of the carpet. The fibers thus "defeated" then pass into a knife mill having as output a grid selecting the fibers of length less than or equal to 4 mm. It can be followed by a sieve to adjust even more precisely the length of the fibers. The cut fibers are sent to a trough having two parallel screws, the walls of the trough and the screws being heated by a heat-transfer fluid whose temperature is regulated electronically and controlled at the moisture content of the output fibers, compared to the rate pre-established humidity. In this case, the amount of residual H 2 O was adjusted to 1% by weight. The "dried" fibers are then sent through a series of archimedes screws to the upper opening of a 40 x 40 cm square-section hopper with vertical walls (hopper 1) of height 1.5 m, capable of to receive 300 kg fiber / hour. The fibers fall by gravity, without compaction or blockage, "freely", to an outlet tube (tube 2) placed under the hopper, diameter 170 mm including a screw that pushes the fibers to a belt conveyor-weigher (strip 3) . A comb is moved back and forth just above the band, and spreads the fiber bundle into a cake about 2.5 cm thick. The speed of rotation of the screw is controlled by a comparison made by electronics between the weight (or flow) weighed by the band and the weight (or flow) pre-established according to the overall ratio fibers / plastic 10 that the we want to get in the extruder. The fibers fall into a vertical hopper having an adjustable separating plate (5) into two fiber streams Vi and V2. These two streams feed an upstream feed hopper (12) of the extruder, which also receives all of the plastic pellets, and a downstream hopper which receives only the fiber stream V2. The extruder has a diameter of about 70 mm and the two hoppers are separated by about 50 cm. The extruder is provided with a hole die producing well-homogeneous fiber / plastic composite rods, which are then cut lengthwise by a rotating knife system. These cut composite elements are quenched with water to freeze and cool them. These elements have a diameter of 2 to 4 mm depending on the chosen die and a length of 3 to 4 mm. They are then centrifuged to remove "quenching" water, which is recycled. The elements are finally directed upwardly from a vertical hot air downflow fluid drying tube 25 which removes traces of residual moisture resulting from the cooling or "quenching" operation. This produces dry cylindrical elements ready to be shipped for an industrial injection molding, extrusion, blow molding, thermoforming or the like.

  The invention also covers all the embodiments and all the applications which will be directly accessible to those skilled in the art upon reading the present application, of their own knowledge, and possibly of simple routine tests.

Claims (41)

  A method for correctly dosing a very high proportion of natural fiber (s) in at least one plastic material, to obtain by compounding an article having very good mechanical properties, of homogeneous structure, and low cost , characterized in that - the natural fiber or fibers dosed into the extruder are introduced into at least two separate introduction points known as "upstream" for the first and "downstream" for the other (s), and - introduced the plastics material (s) into at least said first "upstream" introduction point of the natural fibers and optionally (possible balance of plastic material) into the second "downstream" introduction point of the fibers, or in one or more of the points "downstream" of introduction of the fibers, if there are more than two points of introduction of the fibers.   Process according to Claim 1, characterized in that the fibers are introduced at two separate points of introduction, upstream and downstream.   3 Process according to claim 1 characterized in that the fibers are introduced at three points of introduction, an "upstream" point and two "downstream" points.   4 Process according to any one of claims 1 to 3 characterized in that all of the plastic material is introduced into said upstream introduction point.   Process according to any one of Claims 1 to 4, characterized in that the natural fibers are introduced in the uncompacted state into the extruder.   Process according to any one of Claims 1 to 5, characterized in that a "very high level of natural cut fibers" is introduced into the plastics material (s), that is to say from 10% to 80%, preferably greater than 20 - 30% and more preferably 50% by weight.   7 Process according to claim 6 characterized in that beyond 50%, the transformer will dilute the "compound" obtained.   Process according to any one of claims 1 to 7, characterized in that a fraction of the plastic material is introduced into the upstream point and a fraction of the plastic material is introduced into the downstream introduction point or at least one of these downstream points.   Process according to any one of Claims 1 to 8, characterized in that the dosing of the natural fibers is carried out in two stages, a first coarse volumetric dosing step and a second fine gravimetric dosing step.   Process according to any one of Claims 1 to 9, characterized in that a distribution of 50% by weight of the fibers in the upstream point and 50% in the downstream point is established, or 25% and 25% in both. downstream points if there are three points of introduction or a distribution 30 - 60% at the upstream point, and 70 - 40% in the downstream point or points, for example 40% then 30 20% then 30% or 50% then 30 % then 20%.   1 1 Process according to any one of claims 1 to 10 characterized in that the fibers are cut to a length of the order of 0.2 to 20 mm.   12 Process according to claim 11 characterized in that the fibers are cut to a length of the order of 2 to 4 mm.   Process according to any one of Claims 1 to 12, characterized in that 100% of granules are introduced at the upstream point.   Process according to any one of Claims 1 to 13, characterized in that the water content or residual moisture content of the fibers at the time of their introduction into the extruder must be adjusted by drying between 0, 2 and 3% by weight of water, preferably between 0.8 and 1.5% by weight of water relative to the weight of the fibers.   Process according to Claim 14, characterized in that this drying is carried out in a controlled manner by means of a microwave apparatus or a "flash" evaporator.   Method according to claim 15, characterized in that said controlled drying is carried out by a parallel twin-screw apparatus placed in a trough, slightly nested one inside the other, with adjustment of the residual water percentage by regulating the heating of the screws and / or walls of the trough, preferably by adjusting the temperature of the coolant, and / or the speed of rotation of the screws.   Process according to any one of Claims 1 to 16, characterized in that the natural fibers are chosen from: - hemp fibers, hemp fibers, flax fibers, kenaf, jute, sisal, abacca, wood - and their mixtures - hemp / hemp fiber mixtures, annual plant fibers / wood fibers, natural fibers / synthetic fibers, organic and / or mineral.   Process according to any one of Claims 1 to 17, characterized in that the plastics are chosen from: polyolefins, polypropylene, high or low density polyethylene (HDPE or LDPE), styrene plastics, - ABS (acrylonitrile) butadiene styrene), polystyrene, PVC (polyvinyl chlorides) - polyamides (PA) - polyurethanes, polyesters, elastomers, copolyamides - and their mixtures or alloys - PVC / PVAC (polyvinyl acetate) mixtures or alloys, ABS / PC (polycarbonate), ABS / PA, PPO (polyphenylene oxide) / PS (polystyrene).   Process according to any one of Claims 1 to 18, characterized in that it comprises between 10 and 70% by weight of fibers for 90 to 30% by weight of plastics material; preferably between 20 and 40% of fibers and 80 to 60% of plastics material.   Apparatus for compounding very high levels of natural fibers cut into one or more plastics or alloys of plastics, characterized in that it comprises - a device (1, 2, 3) for dosing natural fibers - a device (4, 5) for separating the dosed mass of natural fibers in two (Vi, V2) or more than two so-called "secondary" fiber streams, and - an extruder (11) having at least two points of introduction of the fibers , one upstream 12, the other (or several other) downstream 13, each of said introduction points being adapted to receive a secondary stream of fibers and I or a stream of plastic pellets.   21 Apparatus according to claim 20 characterized in that said extruder comprises two points of introduction, one upstream 12, the other downstream 13.   Apparatus according to claim 20, characterized in that said extruder has three points of introduction, one upstream receiving a fraction of the fibers and all or a fraction of the granules, and two downstream introduction points, of which one (or both) receives the fiber balance and one (or both) receives the balance of pellets.   23 Apparatus according to any one of claims 20 to 22 10 characterized in that it comprises a device for accurate dosing of the fiber mass which comprises a first coarse volumetric doser (1, 2) and a second finely weighted metering device (3). ).   Apparatus according to claim 23 characterized in that - said first coarse doser comprises a hopper 1 vertical or substantially vertical, large section, o the fibers descend by gravity to a transfer system 2 fibers to a conveyor belt; said transfer system 2 consisting of a horizontal or substantially horizontal tube of clearly oversized diameter, which comprises horizontal or substantially horizontal transfer means such as a worm screw, - the screw being adjusted so as to perform a coarse volumetric dosing of the mass (or flow) of fibers that have been pre-selected - this tube 2 producing a "bead" of uncompacted fibers, which is deposited on the second finely weighted doser.   Apparatus according to claim 23 or 24, characterized in that said second finely weighted feeder comprises a conveying belt 3 which weighs (and therefore assays) the end of the mass (or flow) of fibers.   Apparatus according to any one of Claims 20 to 25, characterized in that the points of introduction of the natural fibers comprise, at the end of the dosing apparatus, intermediate hoppers 6, 7 (one for each point of introduction, or a hopper unique having as many outlets as points of introduction), to each of the introduction hoppers 12, 13 in the extruder 11 optionally provided but preferably a means of "gavage" 9 natural fibers (a hopper d). introduction by introduction point of the fibers) into the extruder.   Apparatus according to any one of claims 20 to 26, characterized in that each fiber feed hopper in the extruder is provided with its own dosing apparatus.   Apparatus according to any one of Claims 24 to 27, characterized in that an electronic control and regulation system regulates and fine-tunes the speed of rotation of the screw in the tube 2 as a function of the fine weighing performed by the belt. 3 and by comparison with the theoretical value pre-entered in the electronics.   Apparatus according to claim 28 characterized in that the tube 2 is preferably of cylindrical cross section, or is oval or even of square or rectangular section, and is oversized so that no blocking of the fibers occurs.   Apparatus according to any one of claims 24 to 29 characterized in that it comprises a device for spreading the "bead" of fibers from the tube 2 in a "cake" of substantially rectangular flat cross-section very flat on the conveyor belt -peseuse 3.   31 Apparatus according to claim 30 characterized in that said spreading device comprises a horizontal comb 17 having vertical teeth 18, with a small clearance between the lower part of the teeth and the surface of the conveyor belt weighing 3, and m by a motor 19 in a horizontal reciprocating movement, and said device is placed in such a way that the lower part of the teeth is just above the band 3 so that when the uncompacted fiber bead comes out of the tube 2, it passes through the comb whose movement is adapted to spread the fibers over the width of the strip into a cake of substantially rectangular flat cross section very flat, 20.   32 Apparatus according to any one of claims 23 to 31 characterized in that the first coarse doser has the following characteristics: - the hopper 1 is of large section adapted so that the fibers can fall by gravity, freely, with a minimum of obstruction and without compaction - its walls are vertical or substantially vertical, which prevents blocking or jamming of the fibers - the tube 2 is oversized, or clearly oversized, with respect to the volume (or flow) of the fibers to be transferred, that is to say that is, its diameter forms a volume that is much larger (between 3 and 5 or 10 times) than the volume needed to process the predicted fiber throughput, a good oversizing factor is between 5 and 10.   33 Apparatus according to any one of claims 20 to 32 characterized in that said device for separating the mass of natural fibers in two or more so-called "secondary" fiber streams comprises a hopper 4 arranged vertically and adapted to 20 receiving said fiber cake dosed and having a movable vertical plate, able to separate said cake, falling by gravity, into two secondary currents of fibers VI and V2 separated from each other, which exit at the bottom of the hopper 4 by two separate tubes 6 and 7.   34 Apparatus according to claim 33 characterized in that the separating hopper 4 is replaced by two separate hoppers, or by three separate hoppers or a hopper 4 having two type 5 plates, if it is desired to obtain three secondary currents.   Apparatus according to any one of claims 25 to 34 characterized in that the fiber cake is separated on a second horizontal conveyor belt 25, following the weighing belt 3, by means of an elongated and movable vertical plate 30 or adjustable around a vertical axis 31 itself fixed to a frame carrying a rotational adjustment means 32, this plate 30 being disposed along the longitudinal axis of said second band for a 50/50 distribution, or with a certain angle by relative to this axis for other distributions such as 40/60 or 60/40, and in contact with the upper face of said second strip 25, and thus able to divide the fiber cake into two secondary streams VI and V2, each of one side of said plate.   36 Apparatus according to claim 35 characterized in that said plate 30 may be straight, in plan view, or slightly curved in a concave or convex shape, or in "S" very flattened, to promote the flow of currents VI and V2 of fibers.   37 Apparatus according to claim 35 or 36 characterized in that a second comb 27 is placed above this second band 25.   38 Apparatus according to any one of claims 35 to 37 characterized in that the two fiber streams VI and V2 are discharged directly into two receiving hoppers 33 and 32 having outlet ducts 6 and 7.   39 Apparatus according to any one of claims 35 to 38 characterized in that two or more such plates are used parallel to each other, and adjustable in rotation independently of each other, in order to divide the cake into a corresponding number of secondary currents, with as many receiving hoppers as currents.   Apparatus according to any one of claims 35 to 39 characterized in that the band 25 is lightly vibrated to promote flow.   41 Apparatus according to any one of claims 20 to 40 characterized in that it uses between 10 and 70% by weight of fibers for 90 to 30% by weight of plastic; preferably between 20 and 40% by weight of fibers and 80 to 60% by weight of plastics material.   42 Compounds or composites of cut natural fibers and plastics material (s) characterized in that they are obtained by the process   according to any one of claims 1 to 19.   43 Compounds or composites according to claim 42 characterized in that they are in masses to cut, plates, rushes, granules or rods.   44 Compounds or composites of cut natural fibers and of plastics material (s) characterized in that they comprise a "very high rate of natural fibers cut" in the plastics or plastics that is 10O say 10% 80% by weight, preferably greater than 20-30% by weight and more preferably 50% by weight.   Compounds or composites according to Claim 44, characterized in that the natural fibers are chosen from: - hemp fibers, hemp fibers, flax fibers, kenaf, jute, sisal, abacca, wood, - and mixtures thereof, - blends hemp / hemp fiber, annual plant fiber / wood fiber, natural fiber / synthetic fiber, organic and / or mineral.   46 Compounds or composites according to claim 44 characterized in that the plastics are chosen from: - polyolefins, - polypropylene, high or low density polyethylene (HDPE or LDPE), - styrene plastics, - ABS (acrylonitrile-butadiene styrene), polystyrene, PVC (polyvinyl chlorides) - polyamides (PA) - polyurethanes, polyesters, elastomers, copolyamides - and their mixtures or alloys - PVC / PVAC (polyvinyl acetate), ABS mixtures or alloys / PC (polycarbonate), ABS / PA, PPO (polyphenylene oxide) / PS (polystyrene).   47 Applications of the method according to any one of claims 1 10 to 19 in the fields of profiles for windows, doors, in the profiles of the construction industry, skirting boards; profiles, inserts or reinforcements for shutters, windows, partitions, barriers, in the building; articles for the automobile industry, bumpers, body parts, aerodynamic fins, the railway industry, in the aerospace industry, in the shipbuilding industry, pleasure craft; structural parts, parts under an engine hood, interior decor or hood or bodywork for all types of vehicles, pleasure craft, aircraft, packaging and packaging elements: crates, pallet crates; toys, technical parts, injection molding of honeycomb pallets, thermoformed pallets 20, reinforced technical parts, toy elements, decorative packaging for consumer products such as household appliances, reinforcement and decorative elements for building.   48 Applications of the apparatus according to any one of claims 20 to 41 in the fields of window profiles, doors, in the profiles of the construction industry, skirting boards; profiles, inserts or reinforcements for shutters, windows, partitions, barriers, in the building; articles for the automobile industry, bumpers, body parts, aerodynamic fins, the railway industry, in the aerospace industry, in the shipbuilding industry, recreational craft; 30 structural parts, parts under engine hood, interior decoration part or bonnet or bodywork for all types of vehicles, pleasure boats, aircraft, packaging and packaging elements: crates, pallet crates; toys, technical parts, injection molding of honeycomb pallets, thermoformed pallets, reinforced technical parts 5, toy elements, decorative packaging for consumer products such as household appliances, reinforcement and decorative elements for building.   49 Applications of compounds or composites according to any one of claims 42 to 46 in the fields of windows profiles, 10 doors, in the profiles of the construction industry, skirting boards; profiles, inserts or reinforcements for shutters, windows, partitions, barriers, in the building; articles for the automobile industry, bumpers, body parts, aerodynamic fins, the railway industry, in the aerospace industry, in the shipbuilding industry, recreational craft; 15 structural parts, parts under engine hood, interior decoration part or bonnet or bodywork for all types of vehicles, pleasure boats, aircraft, packaging and packaging elements: crates, pallet crates; toys, technical parts, injection molding of honeycomb pallets, thermoformed pallets, reinforced technical parts 20, toy elements, decorative packaging for consumer products such as household appliances, reinforcement and decorative elements for building.   Articles, in particular molded articles, characterized in that they consist of, or comprise at least, an element made from a compound or composite according to any one of claims 42 to 46.   Articles according to claim 50 for applications according to one   any of claims 47 to 49.