EP0390733B1 - Method for binding paper sheets - Google Patents

Description

The invention relates to a method for connecting layers of paper.

Methods of connecting layers of paper have been known for decades. They are an essential part of bookbinding. Innovations in the technology of joining paper layers became apparent with the advent of high-performance printing systems that can produce up to 100,000 printed products per hour.

Adhesive binding, thread stitching and wire stitching have proven particularly effective for the mass binding of paper layers, such as occur in printing houses.

The perfect binding is preferably used for binding books, catalogs and specialist magazines.

Different gluing processes are often combined. For example, a low-viscosity layer of high wetting is applied first, followed by layers that improve adhesion. On in this way the bandage quality can be significantly increased compared to the simpler processes.

For glued booklets, the width of the glue application is usually 4 mm. Approx. 15,000 copies / hour can be bound by gluing, whereby the glue drying on the assembly line must be allowed a considerable distance.

A major disadvantage of the process is the drying time that must be granted to the adhesive.

In summary, perfect binding can be viewed as a successfully used method for binding books, catalogs and specialist journals. Because of the long drying time required for the gluing process, the processes described are, with a few exceptions, less suitable for binding booklets in the shingled stream of the separated paper layers of a printing material processing machine.

Another proven method for stapling layers of paper is thread stitching. However, this process has been pushed into the background by adhesive binding. This process only regained importance when the stapling performance increased significantly.

Thread stitching has a number of advantages and disadvantages compared to perfect binding. While the quality of the perfect binding largely depends on the type of paper, the thread binding is largely independent of the paper quality.

In summary, thread stitching can be seen as a relatively slow method and well suited for high-quality binding of books.

Wire stitching is of the greatest importance for stapling printed material in the form of booklets and brochures. Rotary wire stitchers have a high performance but are relatively expensive. A copy of a booklet can be up to 100 pages long. In rotary wire stitching, the wire clamp is pressed against an abutment without a locking mechanism by the spreading paper.

Single wire stitchers perform less than rotary wire stitchers in units of time; but they are also expensive. However, the product can contain up to 300 pages. Single wire stitchers have a stitch abutment with a locking mechanism.

One advantage of wire stitching is the ability to fully open the booklet. There is no closed fold edge that covers part of the print information.

A disadvantage of wire stitching is the fact that the material is applied through the clip in the back, which limits the stackability of the products. Furthermore, the selection, storage and processing of the suitable wire material requires additional effort. There are also limits to the reliability of wire stitching - especially when it comes to thick, more than 200 pages of paper.

A method is also known from European patent application EP-A1-0014946 in which the setting of glue is shortened by means of ultrasound treatment, as a result of which the above-mentioned disadvantages of the gluing method can be partially avoided. It is also described, for example, in the patents US-4149288 or FR-1382415 that paper layers can be bonded with ultrasound without the application of a glue. However, it turns out that such connections are very weak.

There is therefore an interest in a method which can be integrated into the processing process of the printed matter of a high-performance printing press and which therefore has a performance comparable to that of the wire binding method, but does not have the disadvantages mentioned, such as the use of metal, for example. When looking for such a method, the main focus should be on the fact that the individual sheets of paper are not separately subjected to extensive preparation, such as the application of glue strips, and that no buffer or. Interim storage times due to long drying times have to be accepted.

It is therefore an object of the invention to provide a method for connecting layers of paper while avoiding the disadvantages of the known paper stitching methods.

The object is achieved by moistening the paper layers to be connected and connecting them under the action of ultrasound, in accordance with the definition of the invention in patent claim 1.

As already mentioned, it is known to weld layers of paper under the influence of ultrasound. Like the ultrasonic welding of metal or plastic, the method is based on the fact that the weld metal is heated under the influence of ultrasound due to its internal friction in the contact region in such a way that the material to be joined is melted and thus welded. It is in this connection to the writing "Ultrasound for plastic joining" by R. Altena, W.-R.Behnke, L.Horvath, H.-J.Rheinhardt and W.Ruhland, published by Branson Schallkraft GmbH, Industriestrasse 48, D-6056 Heusenstamm.

It is difficult to combine organic fibers such as paper, cardboard, wood, fabrics and non-woven materials with ultrasound, since such materials usually decompose under the influence of heat caused by ultrasound and may even catch fire in the presence of oxygen. Above all, they cannot be converted into a liquid phase, which is necessary for welding.

However, based on our own investigations, it was found that a very thin coating is sufficient to ensure sufficient adhesion between the paper layers. This coating can be, for example, a printing ink that is applied during printing or a thin, quick-drying plastic film. If necessary, a suitable binder can already be incorporated during paper production. The simultaneous action of heat, pressure and a vibration movement ensures sufficient adhesion of the paper layers even when a very small amount of binding material is present.

The connection of paper layers by gluing is known, but this method requires that glue must be applied to the adhesive immediately prior to gluing. On the one hand, this requires an additional work step in which the paper sheets are individually provided with adhesive and, on the other hand, it must be ensured that the paper sheets prepared for connection do not touch prematurely. The proposed ultrasound process, on the other hand, allows the paper to be pretreated simultaneously with the printing for the subsequent connection can - the pre-treatment process can be integrated into the printing process - and above all that the further processing of the printed matter, such as cutting, arranging the individual sheets and folding the paper layers, is not impaired by the connection pre-treatment. It is particularly advantageous that the paper layers can be connected in analogy to wire or thread stitching.

Fig. 1

zeigt eine Prinzip-Darstellung einer Ultraschall-Schweissvorrichtung wie sie beispielsweise zum Verbinden von Kunststoffen verwendet wird,

Fig. 2

veranschaulicht das Prinzip einer Ultraschallwandler-Booster-Sonotroden-Vorrichtung,

Fig. 3

zeigt eine erste mögliche konische Formgebung der Spitze der Sonotrode,

Fig. 4

ist eine Darstellung einer zweiten, als Schneide ausgebildete Formgebung der Sonotrode und

Fig. 5

zeigt eine dritte mögliche Formgebung der Sonotrode in Form einer Schneide mit Einkerbungen.

Fig. 6

ist eine Darstellung eines Papierblattes mit streifenförmiger Vorbehandlung,

Fig. 7

zeigt eine Darstellung einer Vorrichtung zum Ultraschallverschweissen von Papierlagen mittels eines plattenförmigen Widerlagers und

Fig. 8

zeigt die entsprechende Verschweissung von Papierlagen auf einem Rücken mittels eines leistförmigen Widerlagers.

Fig. 9

ist eine Darstellung eines Beispiels für eine Druckanlage, in die eine Ultraschallschweiss-Vorrichtung integriert ist.

For example, information and devices for making such connections are described using the following figures:

Fig. 1

shows a schematic diagram of an ultrasonic welding device as used, for example, for connecting plastics,

Fig. 2

illustrates the principle of an ultrasonic transducer booster sonotrode device,

Fig. 3

shows a first possible conical shape of the tip of the sonotrode,

Fig. 4

is a representation of a second, designed as a cutting edge shape of the sonotrode and

Fig. 5

shows a third possible shape of the sonotrode in the form of a cutting edge with notches.

Fig. 6

is an illustration of a paper sheet with strip-shaped pretreatment,

Fig. 7

shows a representation of a device for ultrasonic welding of paper layers by means of a plate-shaped abutment and

Fig. 8

shows the corresponding welding of layers of paper on a back by means of a power abutment.

Fig. 9

is an illustration of an example of a printing system in which an ultrasonic welding device is integrated.

1 shows an example of the basic structure of an ultrasound device as it is used for welding plastics:

The control unit 10 consists of a power supply unit 11, the amplifier 12, the high-frequency transformer 13 and a tunable positive coupler 14. The latter is connected to the input of the amplifier 12 and the high-frequency transformer 13 via the positive feedback circuit 15. The ultrasonic oscillator 20 is connected to the high-frequency transformer as a frequency-determining element. This circuit ensures that the ultrasonic vibrator 20 can be operated in acoustic resonance, which is necessary for a good transmission of the vibration power from the source to the working point. The phase position of the high-frequency oscillator can be optimized by tuning the co-coupler 14.

The basic structure of the ultrasonic vibrator 20 is shown in FIG. 2. This device is generally composed of an ultrasonic transducer 21 and the vibrating tool, the so-called sonotrode 24. The ultrasound transducer 21 consists of a stack of piezo-ceramic plates 22 connected in parallel. If necessary, a sound amplitude transformer, a so-called booster 23, is interposed between the ultrasound transducer and the sonotrode. This passive element 23 causes an increase or decrease in the vibration amplitude. The sonotrode, the real one Connection tool ensures at its tip 25 the transmission of the ultrasonic power to the weld metal 26 to be connected. An abutment 27 serves to absorb the contact pressure which the sonotrode end exerts on the weld metal 26. The abutment 27 must be designed in such a way that it absorbs as little as possible of the ultrasonic power used, ie it must have the highest possible mechanical inertia with respect to the weld metal 26 and be as undeformable as possible.

As mentioned, the system of ultrasonic transducer 21 - booster 23 - sonotrode 24 is operated in acoustic resonance. A longitudinal vibration is excited in most applications. Ultrasonic welding machines generally work at a frequency of 20 kHz to 40 kHz. Typically, the longitudinal oscillation amplitude at the tip 25 of the sonotrode 24 is approximately 100 μm at 20 kHz operation and approximately 50 μm at 40 kHz.

The device, consisting of the control device 10 and the ultrasonic oscillator 20, is usually operated by means of a control system in such a way that the mechanical amplitude at the sonotrode end 25 has a constant, predetermined value, regardless of the damping by the weld metal 26. In the case of more convenient ultrasonic welding systems, in addition to the ultrasonic power, the contact pressure which the sonotrode end 25 exerts on the weld metal 26 and the time of the ultrasonic action can be specified.

The choice of the booster 23 and the shape of the sonotrode 24 depend on the type of the weld metal 26 and the welding to be carried out. Examples of the most common sonotrode shapes are in the previously mentioned work "Ultrasound for plastic joining" by R. Altena, W.-R.Behnke, L.Horvath, H.-J.Rheinhardt and W.Ruhland.

3 to 5 show some examples of sonotrodes which are particularly favorable for applications which will be mentioned later. 3 shows a conical, 31, in a tip 32 tapering sonotrode 24, which is suitable for creating spot welds.

4 illustrates a sonotrode with a flat sonotrode end 41 and a cutting-shaped welding edge 42. This embodiment of the sonotrode 24 is particularly suitable for producing a long, narrow weld seam.

FIG. 5 shows a combination of the two embodiments from FIGS. 3 and 4. The flat sonotrode end 41 is designed in a similar cutting shape to that, 42, from FIG. 4. However, in order to increase the local contact pressure between the sonotrode 24 and the abutment 27, the knife-shaped welding edge 42 provided with notches 53. Welding points lying in a long and narrow weld seam can thus be generated simultaneously.

Layers of dry, unprinted paper, as already mentioned, cannot be connected with devices as shown in FIGS. 1 to 5. Corresponding tests showed only a blackening, which was due to the ultrasound-induced thermal action. Another step would be to allow the individual paper fibers to become matted during the ultrasonic movement - especially if one is transverse to the paper surface Ultrasonic movement is carried out. Such matting could be weakly demonstrated with a longitudinal movement.

Significantly better results can be achieved if the paper layers are slightly moistened. In this case, the paper structure is easily destroyed - a paper pulp is formed locally, as is present in the paper production. During the subsequent ultrasound-related heating and pressing, the paper fibers are felted and glued in analogy to the actual paper production process. In this way, limited liability of the paper layers is already possible.

However, better results can be achieved if the paper is provided with a meltable coating, although a very thin film is quite sufficient. Already when separating two layers of paper, one of which is printed using ordinary printing ink and the other is unprinted, a partial transfer of the printing ink to the unprinted sheet can be determined after the action of ultrasound. This means that the adhesion of the printing ink to the unprinted sheet is just as good as the adhesion of the original application. A strong print, for example dark brown tones on glossy paper, as is available locally in illustrated magazines, results in very good adhesion under the influence of ultrasound.

To ensure a reliable connection, pretreatment of the paper, as mentioned, is recommended. There are various ways of doing this.

6 shows an illustration of a paper sheet which has been pretreated for the ultrasonic welding. A laterally delimited strip 63 is defined in the fold region 62 of the booklet of the paper sheet 61 and is provided with a printing dye or a plastic which melts at a higher temperature. Such strips 63 can, for example, additionally or alternatively be applied in regions 64 of sheet 61, where insert sheets, registration and receipt forms, or art prints are later inserted. The stripe regions 63, 64 can either be applied as part of the printing process - for example by multiple coating using printing inks, a special printing dye containing a large amount of binder - or in an additional processing step on the paper 61.

Another possibility of the pretreatment for the subsequent ultrasonic welding of the paper 61 consists in the application of a colorless binder, for example a very thin plastic film, which is not sharply delimited. Such pretreatment does not require a change in the printing process, for example by using a special printing dye. The pretreatment could be accomplished, for example, by spraying the printed sheet in the binding region. The material application, which usually falls in the fold region anyway, would hardly be disruptive due to the minimal material application.

A further paper treatment consists in that the paper sheet is pretreated on all sides either during the production process during or after the printing process for the ultrasonic welding. With a pretreatment during or immediately after papermaking, respectively. Before or during the printing process, for example, a desired gloss effect, moisture protection or the like could also be added can be achieved.

As a further type of pretreatment, binder or water can be injected, for example, into the fold region 63 of the paper layers already stacked. The paper layers can be pre-perforated and, at the same time or subsequently, provided with binder or water by means of hollow needles or cannulated needles. There is also the possibility of shooting drops of liquid into the paper layers. (See further details in the patent application EP-A-0390734 filed in parallel with the title "Process for the Perfect Binding of Paper Layers".)

As already mentioned, an abutment 27 is necessary to absorb the contact pressure that the sonotrode 24 exerts on the weld metal 26. this abutment can be a plate, as is shown in Fig. 7.

Another possibility is that the abutment is an instep-shaped device 27 ', on which the paper layers in the scale flow of the printing press, as shown in Fig. 8, are stored. In this case, the abutment can be rod-shaped or instep-shaped.

9 shows an example of a basic illustration of a printing system with an integrated ultrasonic welding device for paper layers. The paper passes from the paper loading device 90 to the printing device 91, which can consist of several printing stages. The printed material is then cut lengthwise and, if necessary, fed to a cutting device 92. The printed matter then reaches, for example, the welding pretreatment device 94, where binder is printed or sprayed on. The print material will then appear bundled and transported further. If necessary, a welding pretreatment can be carried out by binding the binder on the bundled layers of paper. The printed matter then arrives in the ultrasonic welding device 95, where the paper layers are connected. The bound products are then accepted, for example as a shingled stream 93, by the removal device 96.

Claims (4)

1. Method for joining paper layers in the form of booklets, brochures or books or for fixing enclosed leaves in booklets, brochures or books, wherein the paper layers to be joined are joined with an ultrasonic action, characerized in that for improving the joint, the paper layers, at least in the areas to be joined are wetted.
2. Method according to claim 1, characterized in that the pretreatment consists of spraying the paper layers with water.
3. Method according to claim 1, characterized in that the pretreatment consists of injecting water into the paper layers.
4. Method according to one of claims 1 to 3, characterized in that the pretreatment and the ultrasonic action are effected in areas which have the form of points or stripes.

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