NZ622911B2 - A method for binding leaves and a binding element and binding device applied thereto - Google Patents

Abstract

binding element, a method for binding a bundle of leaves in a binding element, and a binding device for use in a method for binding a bundle of leaves is disclosed. The binding element is comprises a U-shaped back (2) of a pliable and thermally conductive material, with a base (3) and two upright arms (4) and two cover sheets (5) that are each connected by an edge (6) to a free edge (7) of the arms (4). A hot-melt 30 adhesive (8) is provided on the inside of the back (2) at least on a part of the base (3) of the back (2). The arms (4) of the binding element (1) are of such a height (F) that the free ends (7) of the arms (4) are foldable against one another, when they are folded towards one another symmetrically over an angle (D) with respect to the base (3). The binding device (see 16, figure 8) is provided with a seat (see 15, figure 8) for supporting the base (3) of the binding element (1) in a closely-fitting manner, two parallel pressure bars (see 17, figure 8) that extend on either side of the seat (15) and above the level of the seat (15) and means (see 20, figure 8) for moving the pressure bars (17) towards one another. The means for moving the pressure bars (17) are provide a certain force against the upright arms (4) of the back (2) when the binding element (1) is placed with the base (3) on the seat (15) and with the bundle of leaves (11) introduced with the edge to be bound (12) against the hot-melt adhesive (8) in the back (2), in order to fold the arms (4) of the back (2) of the binding element (1) towards one another to clamp the bundle of leaves (11) therein. Additionally provided are means (see 26, figure 9) for determining the force exerted by the pressure bars (17) and means (20) to again move the pressure bars (17) away from one another when the determined force has reached a certain desired value, after this force has been maintained for a short period. arms (4) and two cover sheets (5) that are each connected by an edge (6) to a free edge (7) of the arms (4). A hot-melt 30 adhesive (8) is provided on the inside of the back (2) at least on a part of the base (3) of the back (2). The arms (4) of the binding element (1) are of such a height (F) that the free ends (7) of the arms (4) are foldable against one another, when they are folded towards one another symmetrically over an angle (D) with respect to the base (3). The binding device (see 16, figure 8) is provided with a seat (see 15, figure 8) for supporting the base (3) of the binding element (1) in a closely-fitting manner, two parallel pressure bars (see 17, figure 8) that extend on either side of the seat (15) and above the level of the seat (15) and means (see 20, figure 8) for moving the pressure bars (17) towards one another. The means for moving the pressure bars (17) are provide a certain force against the upright arms (4) of the back (2) when the binding element (1) is placed with the base (3) on the seat (15) and with the bundle of leaves (11) introduced with the edge to be bound (12) against the hot-melt adhesive (8) in the back (2), in order to fold the arms (4) of the back (2) of the binding element (1) towards one another to clamp the bundle of leaves (11) therein. Additionally provided are means (see 26, figure 9) for determining the force exerted by the pressure bars (17) and means (20) to again move the pressure bars (17) away from one another when the determined force has reached a certain desired value, after this force has been maintained for a short period.

Description

PCT/IBZOlZ/001727 A_ method for binding leaves and a binding element and binding device applied o.

The present invention relates to a method for binding leaves and a binding element and g device applied thereto.

For- binding it is known to make use of a conventional binding element in the form of a folder with a U-shaped back with a base and two upright arms and two cover sheets that are each connected by an edge to an edge of one of the arms of the back, whereby the inside of the back, more specifically at least a part of the base of the back, is provided with a hotwmelt adhesive.

Hot-melt adhesive here meanS' an adhesive that is hard at room temperature and which becomes liquid upon g, and after cooling to room temperature becomes hard again.

.In order to bind a bundle of loose leaves, a free edge to be bound of the bundle is pushed into the back up against the 'hot—melt adhesive, and. the folder is placed, with its back downwards, on a heating element of‘ a binding device provided to this end, in order to raise the hot—melt adhesive to a iently high temperature to melt the The leaves of the bundle thus sink as it were, with the -30 aforementioned edge to be bound, into the leten hot~melt adhesive .

WO 50843 PCT/IBZOlZ/001727 -Then the back of the binding element with the bundle of leaves in it is allowed to cool, such that the hot—melt adhesive solidifies again and the leaves are- as it were bonded to the base of the back.

A. problem- that arises is that during binding not all the leaves of the bundle sink into the molten adhesive, or do not sink in sufficiently , in order to obtain a good bond. This problem primarily occurs with the outermost leaves of the bundle, possibly because when ng the folder in the device they are somewhat held back by the cover sheets that are held together by the user in order to _secure the folder to the bundle therein.

Another problem is that preferably a. vely large number of different sizes of "back widths of the binding elements must be kept in stock.

Indeed, a good binding result is only ed if the thickness of the bundle of leaves to be bound fits relatively closely between the arms of the back.

For a given thickness of a bundle, a binding element is thus chosen with a" suitable back width.

With the known binding systems <3f the aforementioned type 12 sizes of back widths are available are example, from 1mm to 36 mm, each with a few millimetres difference between successive sizes .

In the absence of the right ‘size of back width, it is mes attempted to resort to a back with an oversized back lflidth. whose opening between the arms of the back is then artificially narrowed by ing the ends of the arms partly closed.

However, this rarely or never leads to a satisfactory result as it is difficult to squeeze the arms closed uniformly, and er the base of the back becomes bulbous as a result, such that the contact with the heating t of the binding device is not optimum, resulting in a poor bond.‘ The purpose of the present invention is to provide a solution to at least one of the aforementioned and. other disadvantages.

To this end the ion. concerns a method for binding a bundle of leaves in a binding element in the form of a folder ”with a U—shaped back of a pliable and thermally conductive material, preferably steel, with a base o upright arms and two cover sheets that are each ted by an edge to a free edge of the arms, whereby a hot—melt adhesive is provided on the inside of the back, at least on a part of the base of the' back, and. whereby the method consists of introducing the bundle of leaves, with the edge to be bound against the hot-melt adhesive in the back, and then heating up the back to melt the- hot—melt adhesive, characterised in that an oversized binding element is chosen in which the bundle with the thickness of the edge to be bound is received with a certain sideways play between the arms of the back, and that the folder with the bundle therein and the hot—melt adhesive in the molten state, is placed with the base of the back on a seat that fits closely to the base with the arms between two parallel pressure bars that are moved towards one another with a force in order to press the base of the back against the seat and at the same time to fold the arms symmetrically towards one another at an angle with respect to the base until the bundle, with a desired force from the re bars, is d in between the arms of the back, after which the re bars, possibly after a short period during which the force has been ined, are again moved away from one another in order to be able to remove the bound folder, whereby the desired force is chosen such that by clamping in the bundle a force is exerted on the bundle that ‘is ed towards the base of the back.

An age is that when folding the arms of the. back, the free ends of the arms and the cover sheets .of the binding element attached thereto are moved closer to the back, whereby these ends and/or cover sheets pull‘the bundle, and in particular the outermost leaves of the bundle, towards the back and the edge to be bound of the bundle is thereby firmly pushed into the molten adhesive, whereby it is guaranteed, that after the adhesive has cooled, all leaves are firmly secured in the adhesive.

Another advantage is that when clamping in the back it is perfectly secured in its place on the seat, which fosters the symmetrical squeezing close of the arms of the back.

WO 50843 PCT/lBZOlZ/001727 'An advantage of this symmetry is of an tic nature. r advantage of the method is that the back fits perfectly with the clamped bundle, and there is thus no gap between the free ends of the arms h which the adhesive could be seen in the back, which also contributes to the professional appearance of the bound folder.

Another important advantage is that bundles of different thicknesses ~ can be bound in the same binding element, so that the entire range of the usual bundle thicknesses can be bound with a limited number of sizes of binding elements .

By using "the force as a control parameter of the method, the method isindependent of the thickness of the back of the chosen binding element, such that an extra adjustment is not ed whenever different sizes of folders are used.

The invention also relates to a binding device for use in the method as described above, whereby the device is provided with a seat for the close—fitting t of the base' of the back of a folder to be bound that is placed with this base on the seat, two parallel pressure bars that extend on either side of the seat and above the level of the seat, and means for moving the pressure bars towards one another with a certain force in order to fold the arms of the back of the folder on the seat towards one another symmetrically at an angle with respect to the base. Means for determining the force exerted by the pressure bars and means to again move the pressure bars away from one r when the thus determined force has reached a n desired value, possibly after this force has been maintained for a short period.

This device has the advantage that, the arms are folded perfectly symmetrically and that the device does not require any adjustment, not even when different sizes of binding ts are used after one another.

The invention also relates to a binding element. in the form of a folder that is suitable for use in a method and with a binding device as described above, and this binding element is ucted in the form of a folder with a U—shaped back of a pliable and thermally tive material, preferably steel, with a.base and two upright arms. and two cover sheets that are each'connected by an edge to a free edge of the arms, whereby a hot—melt adhesive is provided on the inside of the back, at least on a part of the base of the back, characterised in that the arms of the binding element are of such a height that the free ends of the arms can be folded against one another, when they are folded towards one another symmetrically over an angle with respect to the seat .

Such a binding element offers the-advantage that very thin bundles can also be bound, irrespective of the width of the back of the chosen binding element.

Thus for example with a g element with a back width of approximately 15 mm and a height of the arms of the back W0 2013/050843 i of approximately 10 to 1-1 mm, 90% of the cemmonest thicknesses of the bundles_ of leaves to be bound can be 'bound with a single size of binding element.

With the intention of better showing the characteristics of the ion, a preferred embodiment of a g element and binding device according to the invention, and this for the application of a method according 'to the invention, is described hereinafter by way of an example, without any limiting nature, with reference to the accompanying gs, wherein: Figure 1 schematically shows a cross-section of ha binding element according to the invention; figure 2 shows the part indicated in figure 1 by F2 on a larger scale; figures 3 to 6 show successive steps during the binding of a bundle of leaves according to the method of the invention, in a binding t ing to figure 1, whereby figure 4 is an enlargement of the part indicated in figure 3 by F4; figure '7 is an illustration of the last step caf the aforementioned method as shown in figure 6, but this for g a thinner bundle; figure 8 schematically shows a perspective cutaway view :of a. binding ~device~ according to the invention for application of a method according to the invention; figure .9 shows a side ‘view according to arrow F9 in figure 8; figure 10 shows the part indicated in figure 9 by box F10 on a larger scale; figures 11 to 14 show successive steps of the use of the binding device according to figures 8 to 10 for application of the method according to the invention.

The binding element 1 of figure 1 primarily consists of a folder with a ed back 2 that is manufactured from a pliable, more specifically a plastically pliable, and thermally conductive material, ‘preferably steel, with a base 3 and two upright arms 4 and two cover sheets 5 that are each connected by an edge 6 to a free edge 7 of the arms 4 .

The binding element 1 is provided with a lt adhesive 8 on the inside of the back 2, in ular at least on' a part of the base of the back 3 .- The hot—melt adhesive 8 in the back 2 preferably s over almost the entire length of the back, and in the example shown extends to the inside of the arms 4, although this is not strictly ary.

In this case the cover sheets 5 are connected to the arms 4 'of the back 2 by a film hinge 9, which is formed for example by a covering 10 that is affixed around the cover sheets 5 and which runs up to the back 2 on which the covering is secured, for example because it goes around the back 2 and is bonded to it, for example by means of a cold- set adhesive.

Generally the back 2 of the binding ' element 1 is manufactured from metal, preferably steel, or another material that is lly conductive to efficiently and evenly distribute the heat of the binding device over the material of the back 2 as well as over the hot—melt adhesive 8 .

In the example shown, the base 3 of the back 2 is constructed flat.

The use of the g element 1 described above for the ation of the method according to the invention is illustrated on the basis of figures 3 to 6.

According to the invention an oversized binding element 1 is hereby assumed with a width of the back 2 that is such that the distance A between the arms of the back is greater, for e at least 4 mm r, than the ess. B of a bundle of loose leaves 11 to be bound.

Figure 3 starts with a situation in which the bundle of loose leaves 12 to be bound is introduced between the cover sheets 5 of the binding element 1 . rThe edge 12 to be bound of the bundle 11 is thereby introduced in, themback» 2 with a certain sideways play C, due to the oversized choice of the binding. element 1, and is thereby in contact with the hot—melt adhesive 8.

The binding element 1 with the bundle 11 in it is placed upright with the base 3 of the back 2 on a heating element 13 that is suitable for g the back 2 and the aforementioned edge 12 of the bundle 11 to -a sufficiently - high temperature in order to melt the hot—melt adhesive 8.

When the hot—melt adhesive 8 is molten, the edge 12 of the bundle of leaves 11 to be bound sinks‘ into the molten adhesive 8, whereby it often occurs, . as shown in figure 4, that the outermost leaves 14 of the bundle 11 do not sink, or do not sink sufficiently deeply, into the hot—melt adhesive 8, possibly because they are somewhat held back by the contact with the cover sheets 5.

In a next step of the method according to the ion, as illustrated in figure 5, the binding element 1 with the bundle 11 n and the adhesive 8 in the molten state, with the base 3 placed [on a close fitting unheated flat seat 15 and a‘force is exerted on either side of the back 2 lin‘ order to fold the arms 4 of the back 2 towards one another in a symmetrical way with respect to the plane of symmetry X-X' of the back, which runs parallel to the arms 4, whereby the arms 4 with the base 3 of the back 2 enclose the same rical angle D as illustrated on the basis of figure 5 .

In a next step, as shown -in figure 6, the arms 4 are moved further towards one" another until the aforementioned force has d a desired value.

It is clear‘ that due to the downward movement of the free ends 7 of the arms 4 in the direction of the base 3 of the back 2, a force is exerted in this direction that pushes the bundle 11, in particular the outermost leaves 14 of the bundle 11, deeper into the molten adhesive 8, helped by the fact that due to this movement of the free ends 7 of the arms 4 of the back 2, the cover sheets 5 of the binding element 1 are pulled in the direction of the molten adhesive 8 on the base 3 of the-back 2.

The forces exerted on the arms 4 are preferably equal over the entire length of the back 2 and such that the arms 4, when folding, do not or practically do not deform, and in other words remain flat.

According to a practical application, the entioned forces, as shown, are exerted in a direction that is parallel to the flat seat 15 and this at a perpendicular distance from the seat E that corresponds to two thirds of the height F of the arms 4 of the back 2 .

If necessary the aforementioned .forces are maintained for a short period in order to give the molten adhesive 8' time to at least partially fy, after which the forces are d and the bundle 11 is thus firmly bound in the binding element 1 in a professional way, whereby all leaves of the bundle 11, in particular the outermost leaves 14, are secured sufficiently deeply in the solidified ve 8, as illustrated i.n...figure 6.- Figure 7 shows the last step of the method, analogous to the step shown in figure 6, but this for a r bundle ll of only a few loose leaves.

W0 2013/050843 J PCT/IBZOIZ/001727 Hereby the arms 4 of the back 2 are analogously bent as in the case of a r bundle 11, with the application of the same forces, so that no other ment of these forces is required than in the case of the thicker bundle Preferably the height F of the arms 4 of the back 2 are such that the free ends 7 of .the arms 4 can be folded against one another when they are pressed er symmetrically in the aforementioned way.

In this way it is possible, with the oversized binding element 1, even to bind only a single loose leaf 'in the binding element 1 and nonetheless to be certain that this ,leaf is bonded deeply enough in the adhesive.

The height F of the arms 4 is thereby preferably such that, when the free ends 7 of the arms 4 are folded up to "against one another, the aforementioned angle D that is ed with the seat 15 is not less than 45°, such that this prevents the arms 4, upon application of a horizontal force, from deforming and thus the end result of the bound binding element 1 leaving something to be desired.

This aspect of the binding element 1 can be translated mathematically by stating that the height F of the arms_4 may not be less than half the width G of the back 2, multiplied by the square root of two.

Figure 8 shows a practical embodiment of a binding device 16 ing to the invention that enables the method 2012/001727 described above to be applied to a binding element 1 according to the ion.

The binding device 16 is equipped in a usual way with a heating element 13 tormelt the hot—melt adhesive 8 in the back 2.

Furthermore, the binding device 16 according to the invention is provided with a seat 15 for supporting the base 2 of the back of a binding element 1 to be bound that has this base 2 placed on the seat 15, as shown in figure The form of a seat 15 is preferably such that the base 3 of the back 2 is well supported over its entire length and width G. .g The binding device 16 also contains two parallel pressure bars 17 that extend on either side of the seat 15 and above the level of the seat 15, the ends of which are provided with flat sions 18 that are held, while be able to slide but not rotate, in a guide 19 of a housing of the binding device 16 not shown, and this guide is shown in dotted lines in figure 9, and which in the example concerned extends parallel to the seat 15.

The binding device 16 is equipped with means 20 to move the pressure bars 17 towards one another with a certain force, and these means 20 in this case are formed by a gear rack 21 at each end of the pressure bars 17 and eels 22 meshed with it, which for each pressure bar 17, are mounted PCTIJB2012/001727 on a common shaft 23 that extends along the longitudinal direction of the pressure bars 17- The' aforementioned gearwheels 22 are identical to one another whereby the two eels 22 at the same end of the pressure bars 17 mesh with one r, such that an angular displacement of one gearwheel 22 in a certain direction of rotation causes an equal but contrary angular displacement of the other gearwheel, all such that h this movement the 'pressure bars 17 move simultaneously and symmetrically with respect to the central perpendicular plane of the aforementioned seat 15.

One of the aforementioned gearwheels 22 is driven by a drive gearwheel 24, which itself, via a system of other gearwheels, ' is driven by a motor 25 that can be driven in two ions .

The motor 25 is equipped with means 26 that enable the force to be ined that is exerted by the pressure bars 17 on the arms 4 of the back 2, and these means 26 can be formed for example by an ammeter for ing the current received by the motor 25 and which is a measure of the force exerted.

The aforementioned means 20 also enable the pressure bars 17 to move away from one another again, as a function of a control signal generated by a controller 27 when the said force has reached a desired set value, possibly after this force has been maintained for a short period.

W0 2013/050843 PCT/132012/001727 The sides of the pressure bars oriented towards one another are provided with a cylindrical profile 28 oriented towards the inside whose geometric axis 29 is a perpendicular distance E from the aforementioned seat 15, which preferably corresponds to around two thirds of the height F of the arms 4 of the back 2 of the binding element 1.

The operation of the binding device l is very simple and as follows.

The binding element 1 with the bundle of loose leaves 11 to be bound is placed with the base 3 of the back 2 on the heating element 13 to melt the hot—melt adhesive 8.

When the adhesive 8 has melted, the binding Ielement l is placed with the base 3 of the back 2 on the seat 15 and the motor 25 is driven in a, suitable direction to move the pressure bars _17 towards one another, as shown in figure , until the arms 4 of the back 2 are clasped, as shown in figure 11, and r ’to fold. the arms 4 towards one another, as shown in figure 12, until the time that the measured current has reached the set value, as shown in figure 13, after which, ly after a short period of a few s, the motor 25 is driven in the contrary direction to move the pressure bars 17 away from one r, in so doing to remove the finished binding element 1 from the binding device 16.

The profiled 'form of the sides of the pressure bars 17 ed towards one another is such that the local contact point H of the pressure bars 17 on the arms 4 of the back 2 -is practically invariable, such that the covering 10 of the back 2 cannot be damaged by the frictional forces that could otherwise arise between the arms 4 and the pressure bars 17.

Alternatively with respect to the example shown, these profiles can be construCted as rollers that are fastened at the aforementioned 2/3 height of the arms 4 to the pressure bars 17 and are freely rotatable around an axis parallel to the udinal direction of the pressure bars 17, such that all friction is ruled out.

It is clear that the forces exerted by the pressure bars 17 on the arms 4 of the back 2 do not necessarily have to be el to the seat 15, but that these forces can also have a component that is ed towards the seat 15 in order to secure the g element 1 firmly on the seat For the rest it is not necessary for the pressure bars 17 to make a sliding movement, but it is also possible for the pressure bars 17 to be mounted in a pivotable way around an axis that extends parallel to the pressure bar-17.

The present invention is by no means limited to the embodiment described as an example and shown in the drawings, but . a binding element and binding device according to the invention can be realised in all kinds of variants and ions, without ing from the scope o f the invention. ________

Claims (1)

1.— Method for binding a bundle of leaves (11) in a 5 binding element (1) in the form of a folder with a U-shaped back (2) of a pliable and thermally conductive material, with a base (3) and two upright arms (4) and two cover sheets (5) that are each connected by an edge (6) to a free edge (7) of the arms, whereby a hot-melt adhesive (8) is 10 provided on the inside of the back (2), at least on a part of the base (3), and whereby the method consists of introducing the bundle of leaves (11) with the edge to be bound (12) t the hot-melt adhesive (8) in the back (2), and then heating up the back (2) to melt the hot-melt 15 adhesive (8), characterised in that an oversized binding element (1) is chosen in which the bundle (11) with the thickness (B) of the edge (12) to be bound is received with a certain sideways play (C) between the arms (4) of the back (2), and that the binding element (1) with the bundle 20 (11) n and the hot-melt adhesive (8) in the molten state, is placed with the base (3) of the back (2) on a seat (15) that fits closely to the base (2) with the arms (4) n two el pressure bars (17) that are moved towards one another with a force against the upright arms 25 (4) of the back (2) in order to press the base (3) of the back (2) against the seat (15) and at the same time to fold the arms (4) symmetrically towards one another at an angle (D) with respect to the base (3) until the bundle (11) with a desired force from the pressure bars (17), is clamped in 30 between the arms (4) of the back (2), after which the pressure bars (17), after a short period during which the force has been maintained, are again moved away from one another in order to be able to remove the finished binding element (1) with the bound bundle (11), whereby the desired force is chosen such that by clamping in the bundle (11) a force is exerted on the bundle (11) that 5 is directed towards the base (3) of the back (2) . 2.— Method ing to claim 1, characterised in that the base (3) of the ) and the seat (15) that fits closely to the base (3) of the back (2) are flat and 10 that the pressure bars (17) are moved towards one another along a direction parallel to the aforementioned seat (15). 3.— Method ing to claim 1 or 2, characterised in 15 that the aforementioned desired value of the forces d by the pressure bars (17) on the arms (4) is chosen such that the arms (4) of the back (2) remain primarily flat. 20 4.— Method according to any one of the previous claims, characterised in that the forces exerted by the pressure bars (17) on the arms (4) of the back (2) locally grip at around two thirds of the height (F) of the upright arms (4) of the back (2) . 5.— Binding element in the form of a folder with a U- shaped back (2) of a pliable and thermally conductive material, with a base (3) and two upright arms (4) and two cover sheets (5) that are each connected by an edge 30 (6) to a free edge (7) of the arms (4), whereby a hotmelt adhesive (8) is provided on the inside of the back (2), at least on a part of the base (3) of the back (2), characterised in that the arms (4) of the binding element (1) are of such a height (F) that the free ends (7) of the arms (4) are foldable against one another, when they are folded towards one r symmetrically 5 over an angle (D) with respect to the base (3). 6.— Binding element according to claim 15, characterised in that, when the free ends (7) of the arms (4) are folded to against one another, the aforementioned angle 10 (D) enclosed with the seat (D) is not less than 45°. 7.- Binding element ing to claim 15, characterised in that the height (F) of the arms (4) is not less than half the width (G) of the back (2) multiplied by the 15 square root of two. 8.— A binding device for use in a method for binding a bundle of loose leaves (11) in a binding element (1) according to claim 5, characterised in that the device 20 (1) is provided with a seat (15) for supporting the base (3) of the said g element (1) in a closely-fitting manner when the binding element (1) is placed with this base (3) on the seat (15); two parallel re bars (17) that extend on either side of the seat (15) and 25 above the level of the seat (15), and means (20) for moving the pressure bars (17) towards one another with a certain force against the upright arms (4) of the back (2) when the binding element (1) is placed with said base (3) on the seat (15) and with the bundle of leaves 30 (11) introduced with the edge to be bound (12) against the hot-melt adhesive (8) in the back (2), in order to fold the arms (4) of the back (2) of the binding element (2) on the seat (1) towards one another symmetrically at an angle (D) with respect to the base (3) until the bundle (11), with a desired force from the pressure bars (17), is clamped in between the arms (4) of the back 5 (2); means (26) for determining the force exerted by the pressure bars (17) and means (20) to again move the pressure bars (17) away from one another when the thus determined force has d a certain d value, after this force has been maintained for a short period, 10 whereby the desired force is chosen such that by clamping in the bundle (11) a force is exerted on the bundle (11) that is directed towards the base (3) of the back (2). 15 9.— Binding device ing to claim 8, characterised in that the seat (15) is a flat seat and that the pressure bars (17) are affixed, while being able to slide, in guides (19) that extend parallel to the seat. 20 10.— Binding device according to claim 9, characterised in that each pressure bar (17) is equipped with a gear rack (21) and that each of the pressure bars (17) are moveable in an aforementioned guide (19) by means of a gearwheel (22) that meshes with the aforementioned gear 25 rack (21) of the pressure bar (17) concerned, y the gearwheels (22) of both re bars (17) are constructed identically and these gearwheels (22) mesh together. 30 11.— Binding device according to claim 10, characterised in that each pressure bar (17) is equipped at both ends with a gear rack (21) and a gearwheel (22) that meshes with it, whereby the gearwheels (22) are ted together at the ends of one pressure bar (17) by the same shaft (23) that is parallel to the pressure bars (17). 12.— Binding device according to claim 10 or 11, terised in that one of the two gearwheels (22) is driven by a drive eel (24), itself driven by a drive motor (25) that can be driven in the one or the 10 other direction in order to move the pressure bars (17) to or from one another. 13.— Binding device according to claim 10, characterised in that the means (26) for determining the force exerted 15 by the pressure bars (17) are formed by an ammeter for ing the current that is taken by the motor (25), and which is a measure of the force exerted. 14.— Binding device according to any one of the claims 20 10 to 13, characterised in that the sides of the pressure bars (17) oriented towards one another are provided with a cylindrical profile (28) oriented to the inside whose geometric axis (29) is at a perpendicular ce (E) from the aforementioned seat (15). 15.— Binding device according to claim 14, characterised in that the aforementioned distance (E) of the geometric shaft (29) from the seat (15) corresponds to approximately two thirds of the height (F) of the arms 30 (4) of the back (2) of the binding element (1) . 16.— Binding device according to any one of the claims 8 to 15, characterised in that the device (16) is ed with a heating element (13) for heating the back (2) in order to melt the hot-melt adhesive (8) in the back (2).