The present invention relates to a nozzle for simultaneous application of a string of glue on two facing, adjacent disc surfaces, especially for gluing together two optical 5 disc elements of a digital video disc.

Our previously filed Swedish patent application SE-A-9601263-8 describes a pro¬ cess and a device for gluing together two optical disc elements, especially substrates for digital audio, video or computer discs, such as DVD:s (Digital Video Discs).

10 The gluing together of the two disc elements is done by placing them coaxial to each other on individual holders in such a manner that a preferably radially out¬ wardly widening gap is formed between the disc elements, whereafter a tubular glue injection nozzle is inserted into the gap to dispense a liquid adhesive so that it will essentially come into simultaneous contact with facing sides of the two disc ele-

15 ments, which are rotated at the same time one rotation to form a circular string of glue in contact with the two disc elements. When inserting the nozzle tube into the gap, they come very close to the disc elements. There will be only a few tenth of a millimeter play between the nozzle tube and the disc elements.

20 By increasing the rotational speed of the disc elements when applying glue and in¬ creasing at the same time the dispensing pressure of me adhesive, it is possible to increase the distance between the nozzle opening and the location on the disc ele¬ ments where the glue string is to be applied and thus achieve a greater margin of safety against contact or Mtting between the nozzle and the disc elements. o 5

In order to assure that a major portion of the glue flow from the nozzle is directed towards and strikes the opposing disc element surfaces at the same time and that a smaller portion of the glue flow will flow straight ahead into the gap between the disc elements, it is suggested in accordance with the present invention that the 30 nozzle have a channel outlet opening with upper and lower outlet areas and there¬ between a constricted outlet area.

According to a preferred embodiment of the invention the nozzle has the shape of a tubular element with an axially forwardly directed, constricted end opening and two diametrically opposite, radially outwardly directed openings near the end of the tubular element.

The invention will be described in more detail below with reference to the accom¬ panying drawings of which:

Figure 1 shows schematically a cross-section of a device for gluing together two disc elements in a stage when a glue application nozzle is inserted into a widened gap between the disc elements;

Figure 2 shows on a larger scale a first example of the configuration of the outlet opening of the glue application nozzle;

Figure 3 shows a second embodiment on a larger scale where the outlet cross- section of the glue application nozzle is made in an hour-glass shape by means of a micromechanical production process;

Figure 4 is a plan view of a blank for a preferred embodiment of the nozzle according to the invention;

Figure 5 is an end view of the blank in Figure 4;

Figure 6 shows a finished nozzle in plan view based on the blank in Figure 4; Figure 7 is an end view of the nozzle in Figure 6; and

Figure 8 is a side view of the nozzle in Figure 6.

Figure 1 shows a device, generally designated 10, for gluing together two disc ele¬ ments 12,14 to form a so-called DVD. The device 10 comprises a lower disc holder 16 and an upper disc holder 18, preferably of identical construction. The disc hol¬ ders 16, 18 are rotatable about a center shaft 20. The holders 16,18 have outer and inner sealing rings 22 and 24, respectively, and are otherwise of the construction described in more detail in our co-pending patent application SE-A-9601815-5 to make possible, with the aid of vacuum, bending or curving of the radially outer por- tion of the disc elements 12, 14 to thereby form a radially outwardly widening gap 26 therebetween, so that the glue application nozzle 28 can be inserted into the gap

26 and at the same time apply a string of glue 30 on the facing surfaces of the disc elements 12, 14.

A previously used glue application nozzle has in this context had a circular cross- section wim an outlet opening, which has provided a somewhat disadvantageous distribution of the dispensed adhesive in the gap between the disc elements. Accord¬ ing to the present invention, there is now suggested a nozzle which has relatively large upper and lower outlet areas and, located therebetween, a middle outlet area of relativelv small or non-existent outlet cross-sectional area.

Figure 2 shows a first example of a nozzle 28a according to the invention, where the outlet opening has essentially the cross-sectional shape of an eight with upper and lower outlet areas 32 and 34, respectively, and an intermediate constricted sec¬ tion 36. It should be kept in mind that the cross-sectional dimensions of the nozzle opening are in practice very small. For example, the height of the nozzle opening in Figure 2 can be less than one millimeter.

Figure 3 shows another embodiment 28b of the nozzle according to the present in¬ vention, where the opening configuration has an hour-glass shape with upper and lower outlet areas 38 and 40, respectively, and an intermediate constricted area 42. The manufacture of the nozzle configuration according to Figure 3 can be achieved by micromechanical technology, which is known per se, applied to the shaping of separate portions 44 and 46 which define the nozzle walls 48, 50.

Figure 4 shows a preferred embodiment of a blank 52 of a nozzle 28c (Figs 6-8) according to the present invention. The blank 52 consists of a tubular element, the end of which has a cavity 54 which expands axially inwards in diametrically oppos¬ ed portions in the end portion of the tubular element. Opposing wall legs 56 are thus formed in the tubular element. These wall legs 56 are bent in a working step to- wards each other to converging shape, as shown in Figure 6. This forms a constrict¬ ed axial outlet operiing 58 of oval shape and two diametrically opposite radial outlet

openings 60, which narrow towards the axial opening 58. Via a small gap 62, the radial openings 60 can be joined to the axial opening 58 (Figs 6 and 7). In its posi¬ tion for use, the major axis of the oval axial outlet opening 58 is oriented vertically.

Figure 8 shows the nozzle 28c in a side view, i.e. in a position corresponding to the position of the nozzle 28 in Figure 1.

By virtue of the suggested cross-sectional configuration of the nozzle opening, the height dimension of the nozzle tube can be made smaller and thus the outlet area of the opening correspondingly smaller with a larger pressure drop and a higher flow speed as a result. The flow distribution of the injected glue can, however, be steered towards the disc elements in the desired manner by the suggested opening configu¬ ration. It is in this case also conceivable to angle the upper and lower opening areas somewhat away from each other so that diverging jets of glue are produced.