Patent Application
20160075069
The invention relates to a method and device for producing a plastics band with projections transversely to its surface, as well as to the plastics band which is thus obtained. More specifically, the invention relates to a continuous process for the extrusion of such a band, wherein the desired projections are provided directly after the extrusion step, and to an apparatus for performing such a method.
A continuous extrusion process of this type is known from EP0267193 for the production of a fastener band with hook-like projections (such as for instance Velcro® band). Following the extrusion, the band is led between a pair of interacting cooled rollers. In the surface of one of the rollers, the forming roller, suitable hook-shaped depressions or recesses are made. The plastic (a soft plastic such as nylon or polypropylene) is pressed therein between the rollers for the formation of the hook-shaped projections. The band which has thus been treated travels onward over the surface of the forming roller until the roller has sufficiently cooled the band. Next, the band equipped on one side with projections is pulled off from the forming roller. The projections are thus hereupon released from the recesses. Owing to the hook shape of the projections, this process is only possible, however, for relatively soft and bendable thermoplastic plastics. U.S. Pat. No. 3,089,191 relates to a similar process for, for example, bands made of PVC or polyethylene with an added softener.
It is also known to equip plastics plates or sheets with projections along one side in a discontinuous process by, for example, injection moulding or by hot compression moulding. However, this is generally a slow process which, moreover, often absorbs more energy.
US2009/2253353 discloses a device for forming optical lenses by roll pressing. This process, however, does not allow to obtain a plastic band which has a projection at one side, but does nevertheless not have a deformation at the other side.
It is an object of embodiments of the present invention to provide a good method and device for manufacturing in a continuous manner a plastics band having a plurality of projections transversely to its surface.
It is an advantage of particular embodiments of the present invention that, in a continuous process, plastics bands can be produced with projections from plastics material harder than polyethylene (PE), further also referred to as “harder plastics”. Harder plastics in the context of the present invention have a Young's modulus (modulus of elasticity) higher than 2.109 N/m2. Examples of harder plastics are polycarbonate, polystyrene and acetal. The harder plastics used in embodiments of the present invention may for example consist of, or comprise mainly (e.g. for more than 80% of its volume, for instance more than 90% or its volume) polycarbonate, and/or polystyrene.
It is an advantage of particular embodiments of the present invention that such plastics bands can be produced on which, moreover, the fitted projections shall later be able to be precisely joined with their top faces, to another plastics substrate by, for example, ultrasonic welding. A complementary strip or sheet may then sometimes be able to be intercalated between this substrate and the plastics band, for example a plastics strip which has difficulty attaching to the harder base material of the said plastics band. In this strip, appropriate openings may therefore then be provided opposite the said projections, in which openings the projections can accurately engage and penetrate to that surface of the substrate which is to be joined thereto. Such a layered structure of band with strip and substrate is described in EP 1008459 for use in a multi-page passport booklet. More precisely, EP 1008459 describes the connection process on the basis of a plastics band having a preformed strip with openings and substrate. The major problem remains, however, to provide in a continuous and easy manner, for use in, for example, the said passport booklets, a plastics band made of the harder plastic and having the very precise projections with a tolerance below 0.01 mm, for instance between 5 and 10 μm, as a suitable intermediate product for the purpose of an easy and accurate subsequent connection to the strip and the substrate.
It is an advantage of embodiments of the plastics band according to the invention that, simultaneously with the formation of the projections on one flat side of the band, the top side of this band remains perfectly even and flat.
It is additionally advantageous that the plastics band according to embodiments of the present invention can be expediently marked for the realization of an easy positioning for the purpose of a subsequent correct mechanical joining to other material layers, sheets, substrates, preferably in a continuous process.
It is also an advantage of embodiments of the present invention to enable to provide a plastics band made of harder plastic, which bears projections on both flat sides.
Methods according to embodiments of the present invention for the continuous production, more specifically for the extrusion of a plastics band and for the following continuous application of a precise relief of plastics projections to one or both flat sides of the band, surprisingly provide at least some of the above advantages by the use of the following steps.
After the extrusion of the molten plastic through a suitable extrusion gap, the freshly extruded band is fed through between a pair of interacting and cooled revolving elements. A first revolving element here possesses suitable recesses in its surface, at the location of the projections to be fitted on the flat side of the plastics band. The still soft plastic of the freshly extruded band between the revolving elements can thus penetrate into these recesses and fill them as required. Downstream of the thus filled recesses, the cooled revolving elements compress the extruded band transversely to their side faces. They hereupon fill the recesses in a further appropriate manner for the realization of the final form of the projections with the desired precise relief. According to a general aspect of the invention, and in particular e.g. if the invention is used to apply the relief to just one flat side, the procedure is as follows. During the rotation of the freshly extruded band between the revolving elements, the depth of the recesses in the first revolving element will gradually increase from the starting point of the compression zone between the revolving elements to just past the press nip of the through-running, freshly extruded plastics band with the (second) counterpressure revolving element. This has the very positive result that the still soft plastics face, after the extrusion, can penetrate into the successive recesses in a very gradual and controlled manner. This guarantees still better that the top side of the extruded band with projections (thus the side opposite to the one with the projections) remains then completely flat and even.
The method thus enables to produce a really unique plastics band with precise projections on one side and at the same time a perfectly controlled flat back side. This unique feature is an additional advantage for security applications such as e.g. in passports where extra anti-counterfeiting features (such as a controlled flat back side) are always welcome.
After this, the plastics band which is thus formed, in contact with at least the first rotating cooled revolving element, is led onward and cooled sufficiently to form a rigid band. According to an additional facultative characteristic of the invention, care can hereinafter be taken to ensure that the depth of the said recesses decreases appropriately, so that the formed and cooled projections from the surface, in particular the projection islands, of the at least first revolving element can be ejected correctly and intact for the removal of the cooled band having the precisely desired final form. Finally, if need be, the plastics band which is thus obtained, is cut off, e.g. close to its longitudinal margins, in the direction of extrusion.
In a first aspect, the present invention provides a method for extruding a plastics band through an extrusion gap and for next continuously applying a relief, preferably a precise relief with a tolerance below 0.01 mm, for instance between 5 and 10 μm, of plastics projections in at least one flat side of the band. The method comprises:
feeding-through of a still soft plastic material in the form of a freshly extruded band between a pair of interacting and cooled revolving elements comprising a first and a second revolving element, whereof at least the first revolving element, at a location of the projections to be provided on the at least one said flat side, possesses suitable recesses in its surface, wherein the still soft plastic material of the through-running freshly extruded band can penetrate into these recesses and can fill them;
wherein, downstream of the thus filled recesses, the revolving elements further transversely compress the extruded band in order to obtain the plastics band having a desired final form with a relief, preferably a precise relief, of the projections;
wherein the formed plastics band is subsequently led onward and cooled, and wherein a depth of the recesses in the revolving element(s) gradually increases from zero, with the onward rotation thereof from a starting point of a compression zone between the revolving elements to an end point just past the press nip of the through-running extruded band, so that the still soft plastic can there penetrate in a controlled manner into the recesses.
It is an advantage of supplying a continuous stream of heated, still soft plastics material, e.g. by means of a heat extrusion head, in the form of an elongated strip, because it allows the formation of an elongated plastics band, in a continuous process. It is to be noted that in fact several processes occur simultaneously: receiving the still soft plastics material, forming the projections, and cooling the band; but they occur at different places of the band, and hence can be described as occurring one after another, as seen from a particular location on the plastics band.
In a method according to embodiments of the present invention, downstream of the filled recesses, the depth of the said recesses may gradually decrease upon the further rotation of the revolving elements for a correct ejection of the formed projections from the surface of the revolving element(s) for the removal of the band having the desired final form.
It was surprisingly found that by gradually increasing the space of the recess, rather than providing the maximum space of the recess at once, offers a better qualitative result in terms of improved tolerances, less defects and improved flatness at the side of the band opposite to the side where the projection is provided.
In a second aspect, the present invention provides a method for extruding a plastics band through an extrusion gap and for next continuously applying a relief, for instance a precise relief with a tolerance below 0.01 mm, for instance between 5 and 10 μm, of plastics projections in at least one flat side of the band. A method according to embodiments of the second aspect comprises:
feeding-through of a still soft plastic material in the form of a freshly extruded band between a pair of interacting and cooled revolving elements comprising a first and a second revolving element, whereof at least the first revolving element, at a location of the projections to be provided on the at least one said flat side, possesses suitable recesses in its surface, wherein the still soft plastic material of the through-running freshly extruded band can penetrate into these recesses and can fill them;
wherein, downstream of the thus filled recesses, the revolving elements further transversely compress the extruded band in order to obtain the plastics band having a desired final form with a relief, preferably a precise relief, of the projections;
wherein the formed plastics band is subsequently led onward and cooled,
and wherein, downstream of the filled recesses, the depth of the said recesses gradually decreases upon the further rotation of the revolving elements for a correct ejection of the formed projections from the surface of the revolving element(s) for the removal of the band having the desired final form.
In a method according to embodiments of the first or second aspect of the present invention, during extrusion, identification means for the band may be added to the still soft plastics material.
The identification means can e.g. be provided by means of co-extrusion of a second strip, preferably arranged in such a manner that it will be completely surrounded by the deformable plastics materials mentioned above. The co-extrusion may be continuous or not, and one or more (traceable) means of identification for the plastics band can be added (in a metered manner) to the plastics melt.
In a method according to embodiments of the first or second aspect of the present invention, the recesses may be appropriately vented during the formation of the said projections.
Appropriate venting can e.g. be achieved by choosing appropriate tolerances between the recess and the pressing punch, but is also facilitated by the gradual movement of the pressing punch, which allows gradual filling and thus gradual venting of the recess space. The gradual movement of the pressing punch may be a to-and-fro movement. Such to-and-fro movement may comprise a gradually inward and outward movement of the pressing punch.
In a method according to embodiments of the first or second aspect of the present invention, a marking may be provided in the plastics band between the interacting revolving elements, in the form of a notch or through-bore of the freshly extruded band, simultaneously between two successive projections, at regular spacing.
The notches may be spaced apart by a constant distance.
In a method according to embodiments of the first or second aspect of the present invention, the still soft plastic of the through-running band may fill the recesses for the formation of projections having at least one inner cavity.
Hereto, a pin may be provided on the periphery of one or both of the revolving elements, thus being pushed into the still soft plastic material. The pin would automatically be withdrawn from the formed plastics band due to the rotation of the revolving elements, thus forming a cavity, after cooling of the deformable plastics band.
In a third aspect, the present invention provides a device for implementing the method according to any of the embodiments of the first or second aspects. The device comprises an extrusion head having an extrusion gap and, downstream of the gap, a pair of interacting and cooled revolving revolving elements comprising a first and a second revolving element. At least the first revolving element comprises in its surface a series of suitable recesses for the formation of the said projections, and in each recess is located a pressing punch which is movable to and fro in a direction transversely to the surface. The device comprises control means for controlling the to-and-fro movement of the pressing punch.
Preferably the extrusion head is a heated extrusion head.
Preferably the revolving elements have a substantially cylindrical outer surface, apart from one or more projections and/or one or more recesses, such that the band is substantially flat, except at predefined locations where a projection, or a blind hole, or a through hole is to be made in the plastics band.
It is an advantage that at least the first revolving element is actively or passively cooled, so that the plastics material leaving the extrusion gap and entering the space between the two revolving elements is still warm and weak, but gradually cools down and stiffens, such that it is not damaged when being pushed out of the recess.
It is an advantage of the control means that it provides a gradual increase of the recess space, rather than a large opening. This allows time for the plastics material to move into said recess under the pressure exerted by the revolving elements. This guarantees projections of very precise dimensions and shape, and suitable venting.
The use of recesses of variable depth below the surface of the second revolving element yields also the advantage that these recesses can be appropriately vented, as will be explained further. This increases the guarantee that the projections will always perfectly achieve their intended final form.
It is an advantage of the moving pressing punch in that it can be used to push the hardened plastics material out of the recess, so that pulling the material out of the recess can be avoided. This considerably reduces the risk of deformation and/or tearing and/or braking of the plastics band.
In a device according to embodiments of the present invention, the pressing punch may be connected to a control pin for performing the to-and-fro movement of the pressing punch in its recess.
Preferably the control pin is oriented in a direction perpendicular to the movement of the pressing punch, parallel to the axis of the revolving elements, and extending on both sides of the revolving element, such that movement of the pressing punch can be controlled by driving or moving one or both ends of said control pin from the side of the revolving element. This allows cheap and elegant solutions, e.g. purely mechanical solutions to be used for driving the pressing punch.
A device according to embodiments of the present invention may further comprise:
a suitable stationary cam-forming guideway arranged close to a side flank of at least the first revolving element, at least one bearing arranged for moving in said cam-forming guideway upon rotation of the first revolving element and for holding one end of the control pin, the at least one cam-forming guideway having a shape such that, upon rotation of the first revolving element, the at least one bearing makes said to-and-fro movement with respect to the first revolving element.
It is an advantage that the movement of the pressing punch(es) can be controlled by a stationary passive mechanical entity, namely the cam-forming guideway. The shape of the guideway defines a passageway, in which the bearing can roll as the revolving elements rotate. In this way, the angular position of the control pin is determined by the angular position of the revolving elements, but the radial position of the control pin and thus also the radial position of the pressing punch is determined by the shape of the guideway.
The outer surface of the revolving elements determines the position and size of the projections on the plastics band, while the shape of the guideway controls the timing and speed of movement of the punches. For a given surface of a revolving element, the skilled person can easily design a suitable guideway, taking into account the cooling of the band, for example by trial and error.
Rather than moving the control pin in the guideway directly, it is an advantage of using one, preferably two bearings, in that such that the bearing(s) can hold the control pin while allowing rotation thereof, while the bearing itself can “roll” in the guideway path. In this way, wear is considerably reduced.
In a device according to embodiments of the present invention, the guideway may be mounted in such a way that said stationary position has an adjustable radial position and/or an adjustable angular position.
It is an advantage of mounting the guideway in such a way that its position and/or orientation can be adapted or fine-tuned. By doing so, the timing of pulling the pressing punch inwardly in the recess (for allowing the recess to be filled with plastics), and the timing of pushing the pressing punch outwardly (for ejecting the projections and thus the band when sufficiently cooled) can easily be fine-tuned, without having to modify the shape of the guideway itself.
In a device according to embodiments of the present invention, the interacting revolving revolving elements may be rollers.
In a device according to embodiments of the present invention, at least one upright tooth may be located on the surface of at least one of the revolving elements for applying a relief to a flat side of the band.
As the cooperating revolving elements rotate, the tooth will define a space not to be filled with plastics material, but it will be surrounded with plastics material, hence a notch or blind hole is formed, because the tooth has a length which does not reach towards the surface of the other one of the cooperating revolving elements.
It is advantageous if the tooth is slightly tapering or conical towards its top, as such a tooth can be more easily removed from the cooled plastics band.
The formed relief may comprise e.g. a notch or a blind hole in the plastics band.
In a device according to embodiments of the present invention, at least one upright pin on the surface of a first revolving element extends directly opposite the particular recess for the formation of projections having cavities. The upright pin on one revolving element is “arranged to meet” the particular recess on the other revolving element, when passing through the compression zone.
It is an advantage that a pin arranged in such a way will generate a projection with a “cavity on the opposite side”, meaning that if the projection is visible from one side of the plastics band, the cavity is visible from the other side of the plastics band.
The pressing punch may bear in the particular recess an upright member, so that the cavities there comprise through-bores in projections transversely to the side faces of the band.
In contrast to the cavity produced by the “pin” as described in the previous embodiment, the “member” of this embodiment will create a projection with a “cavity on the same side as the projection”, meaning that if the projection is visible from one side of the plastics band, the cavity is visible from the same side of the plastics band.
The skilled person can choose a suitable length of the “member” for forming either a blind hole or said through hole.
Optionally the second revolving element may comprise a corresponding pin or other kind of projection arranged so as to meet the member on the punch. In this way, the length of the member on the pressing punch can be decreased, and the risk of bending or breaking can be decreased, and the tolerances can be improved.
In a device according to embodiments of the present invention, the extrusion gap may have an increased transverse opening over at least part of its width for providing a plastics band with a locally increased thickness for the formation of a protruding continuous rib as a projection.
It is an advantage that the extrusion gap has an opening with a non-uniform height for making plastics bands such as those having an elongated rib, as this requires more plastics material at the location of the rib. By increasing the height of the extrusion gap only locally, it is avoided that the height is increased over its entire width, which would cause more waste.
In a device according to embodiments of the present invention, each of the revolving elements may possess recesses in its surface with pressing punches for the formation of projections on both sides of the plastics band.
This allows the production of a plastics band with projections on both sides.
Preferably in this case, the pressing punches of the second revolving element are mounted and controlled in the same manner as the punches of the first revolving element, e.g. by using a second stationary guideway mounted adjacent the second revolving element for guiding the control pins of said pressing punches.
In order to be able to realize projections with different shapes and/or volumes and with an appropriate distribution over the surface of the plastics band, the invention additionally in certain cases provides for the adoption of extrusion gaps having locally a larger transverse opening. This constitutes an additional interesting aspect of the versatility of the invention. In particular, the said transverse opening, at least at or close to the sites (for example of certain longitudinal strips in the band), distributed over the width of the extrusion gap, where the projections must be located, will be able to be larger for the formation there of protruding ribs, for example.
The device for implementing the above-described method comprises, in the first place, a heated extrusion head having a suitable extrusion gap. Downstream of the extrusion gap, the device is equipped with a pair of interacting and cooled revolving revolving elements. At least the first revolving element comprises in its surface a series of successive local recesses for the formation of the aforementioned projection islands. In each such recess there is a pressing punch which can be moved to and fro. This pressing punch is connected to means, for example to a control pin for the to-and-fro movement of the pressing punch in its recess. The control pin can extend via one or both of its free ends into a suitable cam-forming guideway. This guideway is mounted, for example, close to a side flank of the revolving element, but does not rotate along with the revolving elements. This characteristic provides a surprisingly versatile device, inter alia because, as a result of this mounting, an appropriate static, either variable or adjustable, cam-forming guideway can be used for any situation, as is explained below.
In a further aspect, the present invention provides a plastics band obtained with any of the methods according to embodiments of the present invention, the plastics band comprising a thermoplastic plastic harder than polyethylene, for instance a thermoplastic plastic material having a Young's modulus (modulus of elasticity) higher than 2.109 N/m2, such as e.g. polycarbonate.
It is advantageous to use a harder plastic, e.g. a plastic having a Young's modulus higher than 2.109 N/m2, such as for instance polycarbonate, because such material is a relatively hard thermoplastic material. It is more resistant (than e.g. polyethylene) to undesired deformation or damage or scratches after its formation, e.g. during further use when making a passport or booklet, or the like.
A plastics band according embodiments of the present invention may comprise a series of successive projection islands, each of which has a shape approximating to a truncated pyramid.
With “truncated pyramid-like shape” is meant a beam-shape with a rectangular cross-section in a plane parallel to the plastics band, and having inclined upright walls. It is an advantage of such shapes that they can be more easily removed from the recess, without being damaged during the removal.
A plastics band according to embodiments of the present invention may comprise, close to one of its longitudinal margins, at least one protruding rib.
It is an advantage of the rib that it improves the straightness of the plastics band. The rib may be formed on only one side of the plastics band, e.g. only on the top side, allowing the other side of the plastics band to be completely flat. Alternatively, the rib may be provided on both sides of the plastics band (i.e. both the top and bottom side).
While in embodiments of the present invention, the rib may be only provided on one edge, it is of course also possible to provide another rib on the other edge. This would further increase the stiffness and straightness of the plastics band still more.
A plastics band according to embodiments of the present invention may further comprise, at regular intervals over its length, markings obtained with a method according to embodiments of the present invention.
A plastics band according to embodiments of the present invention may further comprise a trail, applied by co-extrusion, of identification means.
A plastics band according to embodiments may be obtained with a method according to embodiments of the present invention, wherein the cavity is a notch or a through-bore in the particular projection.
The plastics band obtained with the method or device preferably comprises a relatively hard thermoplastic plastic, such as, for example, a plastics material with a Young's modulus higher than 2.109 N/m2, e.g. polycarbonate. With a view to certain applications in which the plastics band must be able to be connected, for example by ultrasonic welding, to other objects, the projections have a form, for example, which approximates to a truncated pyramid.
All this will now be explained in greater detail with reference to an embodiment of the invention and in the light of the appended figures. Numerous important additional details and their advantages will here be explained. The protection is not, of course, limited to the embodiments described. Numerous variants thereof which are evident to the person skilled in the art are deemed to form a constituent part of the protection formulated and claimed in the claims.
Where in the present document reference is made to a “relatively hard” or “harder plastic”, reference is made to a plastic material “harder than polyethylene”, e.g. a plastics material having a Young's modulus (modulus of elasticity) higher than 2.109 N/m2.
Where in the present invention reference is made to a “revolving element”, reference is made to rolling means, such as rollers. These may include, but are not limited to, revolving means of transportation belts.
Where in the present invention reference is made to “an upright element or member” (in relation to a e.g. cylindrical surface), reference is made to such an element or member extending from said surface, e.g. perpendicular to that surface.
The second roller 3, acting as a counterpressure roller, compresses the freshly extruded band 38 transversally against the first roller 4 acting as forming roller. A part of the plastic is thus hereupon spread out somewhat over the width of the band 1 (in the depth direction of
The suitable pressing punches 5 are placed in a radially displaceable manner in these recesses 12 (see
Towards the end of segment C, the guideway 10 forces the punches 5 back slightly outwards. It hereupon gradually forces the projections 11 out of their recesses 12 as a transitional step towards the segment D. In this segment D, the meanwhile definitively formed and sufficiently cooled and stiffened band 1 with its projections 11 is completely pushed away by the punches 5 of the roller 4 and removed from the surface 29 of the roller 4. Finally, the pin 8 of punch 5 in segment E leaves the guideway 10 and rotates freely through segment F until repeat of its cycle in segment A. The guideway 10 of
It is an additional advantage of certain embodiments of the invention that the guideway 10 can be statically fixedly mounted in various adjustable and variable angular displacement positions as suggested with arrow 23 in
In
As shown in the left half of
Further to the left of the left part of
Finally,
Self-evidently, the invention permits innumerable variant embodiments of the plastics band in accordance with the specific requirements of shape and characteristics for the plastics band. Apart from polycarbonate (PC) as the base material for the band 1, as an example of a harder (engineering) plastic, for example, polysulphone (PS), polyetherimide (PEI) or polyethersulphone (PES), or even plastic filled with glass fibre, can also be used. The dimensions of the plastics band 1 and its projections 11, 13, 16 are, for example, of the order of magnitude described in relation to FIGS. 1 to 4 in EP 1008459. For example, the thickness of the band 1 may be between 0.10 mm and 0.90 mm, for example lie in the range of 0.76 mm+/−0.08 mm, or lie in the range of 0.10 mm to 0.40 mm. Instead of a cam-forming guideway 10, as shown in
If it is wished, for example, to temporarily join a polycarbonate (PC) band 1 to a polypropylene (PP) strip to form a combined band, as can be used for application in passports or other ID's in the shape of a book, such as booklets for recording medical data and the like, then, apart from projections 11, 16, 13, at regular intervals, a second group of somewhat higher projections 42 (see
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013/0292 | Apr 2013 | BE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2014/058556 | 4/28/2014 | WO | 00 |
