WO1998031535A1

WO1998031535A1 - Method and apparatus for treating strands with pulverulent material

Info

Publication number: WO1998031535A1
Application number: PCT/NL1997/000691
Authority: WO
Inventors: Johannes Albertus Petrus Merkelbach
Original assignee: Beleggingsmaatschappij 'ab-Ovo' B.V.
Priority date: 1996-12-16
Filing date: 1997-12-12
Publication date: 1998-07-23
Also published as: NL1004796C1; AU5347098A

Abstract

Method for treating strands comprising filaments with a pulverulent processing medium, wherein the strands are spread and the spread strands thus obtained are then passed into a processing chamber, wherein the pulverulent processing medium, as a powder/fluid, preferably powder/gas mixture, at the start of the processing chamber, is passed over the entire width of the spread strands, at a velocity which is at least as high as the velocity of the spread strands, in a direction which runs parallel to the direction of movement of the spread strands or at an angle of at most 60° with that parallel direction towards the spread strands. An apparatus suitable for implementing the above method comprises one or more members for spreading the strands and a chamber in which the processing takes place.

Description

METHOD AND APPARATUS Ft⁾R TREATING STRANDS WITH PULVERULENT MATERIAL

The invention relates to a method and an apparatus for treating strands, which are composed of filaments, with a pulverulent material. Such a method and apparatus are disclosed by WO-87/OO563-A. According to the method describe^ in this international patent, strands composed of filaments are treated with a pulverulent medium, a separation between the filaments, or spreading of the strands, being effected and the processing medium being suspended in a liquid or in a gas, whereupon the suspension thus obtained is directed, under controllable pressure, against the material to be treated. This needs to rake place under a certain angle, spreading of the strands being achieved Simultaneously with impregnation of the spread strands.

It has been found, however, that simultaneous spreading and impregnation of the strands does not lead to optimum results. In particular, impregnation of the strands with the processing medium j.s inadequate inasmuch as the uptake of the medium in the strands is not readily controllable. A possible cause of this is that the spread of the strand is not equally good all over, and as a result too little processing medium is taken up at those points where the spread i inadequate. As a result, the reproducibility of the end products leaves much to be desired. One of the objects of the invention is to improve this uptake of processing medium as well as the controllability thereof.

US-5.057,338 discloses a method for impregnating strands consisting of filaments, wherein the strands are first spread before being impregnated with a powdered plastic. The impregnation step comprises the use of a fluidized bed through which the spread strands are passed. The plastic particles are blown from the top of the impregnating chamber onto the spread fibre bundles moving in the longitudinal direction. Underneath the fibre bundle, the powder which has not impregnated is then collected by suction and, via a tube, carried back to the top of the impregnating chamber. The plastic particles are kept in suspension within the fluidized bed by means of the wall of the impregnating chamber being caused to vibrate continuously.

US-A-5,102,690 discloses a similar method for impregnating fibres with powdered plastic. Again, use is made in the impregnating step of a fluidized bed. In this case, however, the powder particles are kept in motion by vibration means which are fixed to the wall of the impregnating chamber and which are activated by a frequency chosen from audible and ultrasonic frequencies.

It was found that the use of a fluidized bed does not lead to optimum impregnation of the strands. Moreover, maintaining a homogeneous fluidized bed is a very complex operation in practice, which is undesirable from a process control point of view. In addition, using a fluidized bed has the drawback that proportioning of the powder taken up by the strands is not easily kept at a constant level, βs a result of which unacceptably large differences in concentration of powder taken up by impregnation can occur within a Single strand. It ±ε obvious that this is undesirable in terms of the properties of the final strand.

It is an object of the invention to overcome the above- described drawbacks of the known methods by providing a method which leads to optimal impregnation under readily controllable conditions, the end product being of high-grade and reproducible quality. The invention therefore relates to a method far treating strands comprising filaments with 'a pulverulent processing medium, wherein the strands are spread and the spread H rends thus obtained are then passed into a processing chamber, wherein the pulverulent processing medium, as a powder/fluid mixture, at the start of the processing chamber, is passed over the entire width of the spread strands, at a velocity which is at least as high as the velocity of the spread strands, in a direction h ch runs parallel to the direction of movement of the spread strands or at an angle of at most 60" with that parallel direction towards the spread strands. Very suitably, the fluid can be a gas, preference being given to air, because of the price. If the processing medium is reactive with respect to compounds present in the air, an inert gas should preferably be used. If it is preferable for the processing medium to be introduced into a liquid, this can be a solvent or a suεpension medium. The method according to the invention allows composites to be produced which can serve as semifinished products which cah undergo further processing. If the processing medium used is. for example, a thermoplastic or thermoBetting powdered plastic, composites are obtained which are made of the plastic employed and in which the filaments of the strands act as reinforcing material , The compositeB themselves can alβo very suitably be employed as reinforcing material, for example wound around steel or plastic pipelines or (high) pressure vessels, The composites themselves can also be used for the fabrication of pipelines. Equally, they can very εuitably bθ processed into other products or to make other products, a high mechanical strength and/or stiffness in conjunction with low dead weight being of great importance irt this context. Examples of possible applications include car bodies or sailcloth. The strands or filament bundles which are treated by means of the method according to the invention will, as a rule, come from a plurality o bobbins and are combined into a row or band of strands situated next to one another, which are preferably all kept at roughly the same tension, before they are subjected to the method according to the invention. In addition, the strands can, if appropriate, be preheated before being subjected to the method according to the invention. All this is known, however, and a manner in which this can be implemented is described, for example, in the abovementioned international patent

Spreading of the strands, or separation of the filaments of which the βtrands consist, can be effected in ways known per βe. for example as described in the above-described patents US-5, 057,338 or US-A-5ιl02,690. Very suitably, spreading of the strands is achieved by means of an r stream, i.e. an air stream separates the filaments in the individual reinforcing fibres from one another, so that a homogeneous web of more or less parallel filaments with fairly regular spacings is produced. This web is then treated with a processing medium. Preferably, a so-called air knife is used which is positioned above the strands and perpendicular to their direction of movement. In the course of the treatment Of the spread strands, the pulverulent processing medium, in the form of a suspension in a gas, is brought into contact with the spread strands in a specific manner. Very expediently, this is done in chamber which is open both at the side where the spread strands are fed in and at the side where the treated strands are withdrawn. At the open side where the spread strands enter the processing chamber, the powder/ as mixture, or the powder suspended in gas, is injected, over the entire width of the spread strands, into the chamber in a direction which is roughly parallel to the direction of movement of the spread Strands or in a direction which differs by at most 60°, preferably at most 4 ". towards the 'Spread strands, from that parallel direction. Excellent results are achieved if this latter angle is at most 30^* ,

This can be implemented by a row of nozzles being located above and transverse to the direction of movement of the spread strands and at the side where these strands enter the processing chamber. The injection direction of the powder/gas mixture is then adjusted via _the angle at which the nozzles are positioned. This angle is primarily determined by weight and size of the powder particles. An important point in this context is that a cloud of particles must be created in the processing chamber, so that optimum uptake of the powder particles by the spread strands can take place, in particular owing to settling. Powders consisting of relatively small powder particles and/or particles having a relatively low weight are therefore preferably injected into the processing chamber at a direction approximately parallel to the direction of movement of the spread strantjs. whereas the slightly larger particles and/or the particles having a relatively high weight can be blown into the processing chamber at an angle. The particles which then pass through the spread strands bounce against the bottom of the processing chamber and thus re-enter t a processing chamber. Thus a powder cloud is formed whpge turbulence and residence time in the processing chamber is such that the spread strands are optimally penetrated by the powder particles, resulting in a product having excellent properties.

In general, the velocity at which the powder particles are blown into the processing chamber is chosen so as to allow optimum utilization of the internal volume of the processing chamber in allowing the powder particles to settle on the spread strands while the latter move through the chamber. The powder particles are blown into the chamber at a velocity which is higher than the velocity at which the spread Strands move through the chamber. A velocity which is from 2 to 20 times the velocity of the spread strands is very suitable, a velocity of from 5 to 1 times greater being preferable. However, this velocity again depends on the size and weight of the powder particles. The velocity is preferably chosen so as to ensure that at the end of the processing chamber, where the treated spread strands leave the chamber, the velocity of the powder particles has been reduced to virtually zero.

The velocity at which the spread strands move is generally between 10 and 100 metres per minute, preferably between 30 and 80 metres per minute. Homogeneous impregnation is thus obtained, a high proportion of ppwder being taken up. The gas used for the powder/gaB mixture ig preferably air, but other gases in which the processing medium^' is stable can also be used.

Since_, the processing chamber is also open at the side where the treated strands leave the chamber, there is a pressure differential between the point where the powder/gas mixture enters the chamber and where the treated strands leave the chamber. As a result, the powder/gas mixture moves cocurrently in the direction of movement of the spread strands, whereas the powder particles from that powder/gas mixture settle onto the spread strands and come to rest between the filaments. Excess powder and powder which has not been taken up properly can be collected by suction when the treated strands emerge from the processing chamber, or can be removed in some other way.

The strands which can be treated by the method according to the invention comprise, in particular fibres which are known for their high mechanical strength and/or stiffness. Suitable strands are, in particular, those strands which comprise aramid fibres, carbon fibres, glass fibres, ceramic fibres, polyethylene fibres, polypropylene fibres, and strands comprising mixtures of two or more of these materials. Strands comprising aramid fibres, carbon fibres or glass fibres are to be pre erre . however .

Many materials are potentially suitable as the pulverulent processing medium, O-87 OO563-A lists a large number of suitable materials. The contents of that patent application are incorporated herein by reference. Apart from thoβe materials it is also possible. to use rubber powder and mixtures of various materials such as. for example, a mixture of ceramic and thermoplastic powder. An important aspect in this context is that it must be possible for the processing material used to be fixed by elevated temperature. Processing or impregnating media suitable in particular comprise one or more of the following plastics: rubber, polyamide- 2, polyamide-6, polybutylene terephthalate , polyetherester, polyetheretherketone, polyethersulphone , polyetherimide , polypropylene, polyphenylene sulphide, polyurethane and poly (vinylidene fluoride) . As to the particle Size of the pulverulent processing medium to be used, there are no strict rules. Powders of various particle size distributions can be used in the method according to the invention. Obviously, at least a fraction of the powder particles should be sufficiently small to be able to be accommodated between the filaments of the spread strands. Good results with the abovementioned plastics can be achieved if the particle size distribution of the pulverulent processing ^' medium is such that at least 90 v %_ of the particles have a diameter in the range of from 20 to 250 μm. preferably from 25 to 200 urn.

After the strands have been impregnated with the pulverulent processing medium, the treated βtrands are combined into a single strand having a preset width and thickness and are subjected to a series of further steps so as to obtain the ultimate composite. These further steps, their sequence end the way in which they can be carried ou_t are known per se. for example from WO-87/OO563-A, US-A-5,102,690 and US-A-5,057,338. and successively comprise heating, cooling and winding. Heating in an oven is necessary tα fix the powder particles between the filaments of the strands. Heating by exposure to infrared radiation s a very suitable method, but other methods such as exposure to hot air can also be used. Heating generally takes place to temperatures above the melting temperature of the impregnated plastic, but below the degradation temperature of this plastic. Cooling is preferably effected by means of air cooling, but water cooling is also a very suitable option. After winding onto a bobbin, the composite is ready for further use.

The invention further relates to an apparatus for implementing the above- escribed method, said apparatus comprising one or more members for spreading the strands and a chamber in hich the treatment takes place, wherein said chamber; (i) is open at the side where the spread strands are fed in and at the Side where the treated strands are withdrawn, and (ii) at the side where the spread strands are fed in is provided, over its entire width, with one or more conduits for supplying the gas stream containing, suspended therein, the pulverulent processing medium, (iii) at the aide where the treated strands are withdrawn from the chamber is provided, below the level of the emerging strands, with means for collecting and removing any excess processing material .

The members used for spreading the strands can be members ■ already known. Preferably, however, use is made of an air knife, air being directed, under high pressure, perpendicular to the direction of movement of the strands. This is preferably done just before a roller, so that the spread strands can be supported immediately and conveyed further.

The chamber in which the treatment takes place is preferably rectangular in shape and has a width which is slightly larger than the width of the spread strands. The difference is preferably no more than 1 cm. The height of the processing chamber iβ small and iB preferably no more than 10 cm. whereas a height of at most 5 cm is most preferable. If required, the bottom of the chamber nay be provided with vibration means. BO that it can be set to vibrate continuously or periodically to remove excess powder which has remained behind. This can be done fairly simply, since the chamber is open at both ends. The bottom may also be provided with a moving belt to remove residual powder, either continuously or periodically.

The conduits for supplying the powder are disposed at the infeed side of the processing chamber over the entire width of the chamber. The conduits can be connected to a manifold which is connected to a proportioning unit for either gravimetric DΓ volumetric proportioning of the powder. Gravimetric proportioning is preferable, because of the greater accuracy. Powder proportioning units are known and commercially available.

Disposed at the discharge side of the processing chamber and below the level of the emerging strandβ are means for collecting and removing any excess powder. Such means may comprise a discharge reservoir provided with suction-removal means such as a suction orifice. The powder removed by suction can be recycled to the proportioning unit for reuse,

The invention is further illustrated with reference to Figures 1. 2 and 3, Figure 1 is a side view of an apparatus according to the invention.

Figure 2 is a plan view frotϋ above of an apparatus according to the invention.

Figure 3 is a side view of an installation with the aid of which the method according to the invention can be implemented.

In Figure 1 (from the side) and Figure 2 (plan view from above) the strands (1) running parallel are spread at point (3) by means of air knife (2), whereupon the spread strands (5) are passed, via roller (4) into the processing chaober (7). Via supply lines (6), a mixture of pulverulent processing medium and gas is paεβed to the processing chamber (7), into which it is blown by means of nozzles (not shown). Each supply line (6) is connected to. such a nozzle, whereas the supply lines (6) may expediently merge into a single conduit which coaπunicates directly with the proportioning unit. The treated spread βtrands leave the impregnation box (7), and the powder not taken up within the strands is collected an ^' weighed by means of collection and discharge reservoir (8) and conduit . (9). The treated strands are then, via roller (10), brought together again by being guided between guide elements (11). whereupon the combined, treated strands (12) are guided away via roller (13) for further treatment.

In Figure 3. the strandB to be treated are unreeled from reeling unit (14), and the strands running parallel are then kept at roughly the same tension by tension control unit (15). The strands kept at approximately identical tension are then preheated in hot-air heaters (16). This preheating step can also be dispensed with if desired. Then spreading of the strands takes place via air knife (2) , and the spread strands are then, via roller (4). passed into the processing chamber (7). The processing medium is passed to the processing chamber from proportioning unit (26) by means of conduits (6). After treatment, any excess powder and/or powder which has not been taken up can be weighed via collection and discharge reservoir (8). The treated, spread strands are combined via roller (10) and guide elements (11). and the treated, combined strands (i.e. the "precursor composite") (12) are then guided towards the oven section. Passing the precursor composite (12) through a number of ovens (17), for example infrared ovens, ensures that the powder particles taken up will melt, as a result of which a single entity is formed comprising a plastic matrix with reinforcing strands. The hot precursor composite is then given the correct shape by means of calender rolls (20) and ovens (19) ■ and the composite thus obtained is then cooled in cooling unit (21). The rolls (22) are driven rolls which draw the Strands through the entire processing apparatus. The composite thuθ obtained can either be granulated, giving composite granules, by means of cutting unit (24) or be wound onto one of the bobbins (25)- Both options are schematically indicated in Figure _ .

Claims

1. Method for treating strands comprising filaments with a pulverulent processing medium, wherein the strands are spread and the spread strands thus obtained are then passed into a processing chamber, wherein the pulverulent processing medium, as a powder/fluid mixture, at the start of the processing chamber, is passed over the entire width of the spread strands, at a velocity which is at least as high as the velocity of the spre d str╬▓nds, in a direction which runs parallel to the direction of movement of the spread strands or at an angle of at most 60* with that parallel direction towards the sp ead strands.

2. Method according to Claim 1, wherein the fluid in the powder/fluid mixture is gas.

3. Method according to Claim 2, wherein the gas is an inert gas.

4. Method according to any one of ClaimB 1 to 3 inclusive, wherein the strands to be treated comprise aramid fibres, carbon fibres or glass ibres .

5. Method according to one or more of the preceding claims, wherein the pulverulent processing medium comprises one or more of the following plastics: rubber, polyamide-12, ╧üolyamide-6, polybutylene terephthalate, polyetherester, polye heretherketone, polyethersulphone. polyetherimide , polypropylene, polyphenylene sulphide, polyurethane and pol tvinylidene fluoride).

6. Method according to Claim 5_t wherein the particle size distribution of the pulverulent processing medium is such that at least 90 wt% of the particles have a diameter in the range of from 20 to 250 ╬╝m, preferably from 25 to 200 ╬╝a.

7. Method according to one or more of the preceding claims, wherein the powder/gas mixture is blown into the processing chamber at a velocity which is from 2 to 20 times, preferably from 5 to 1 times the velocity of the spread strands.

8. Apparatus for implementing the method according to one or more of Claims 1 to 7 inclusive, said apparatus comprising one or more members for spreading the strands and a chamber in which the treatment takes place, wherein said chamber; (i) i╬╡ open at the side where the Hpread strands are fed in and at the side where the treated strands are withdrawn, and (ii), at the side where the spread Btrands are fed in is provided, over its entire width, with one or more conduits for supplying the gas stream containing, suspended therein, the pulverulent processing medium, (iii) at the side where the treated strands are withdrawn from the chamber is provided, below the level of the emerging strands, with means for collecting and removing any excess processing material .