Process and device for the application of an adhesive

The invention pertains to a process for the operation of a mouthpiece for the intermittent supply of an adhesive through at least one discharge opening to a surface moving with respect to this mouthpiece, where at least in the pauses between discharges, the edges of the discharge openings are sprayed with a rinsing medium. The invention also pertains to a mouthpiece for the application of an adhesive with one or more rinsing medium discharge openings situated upstream from the glue discharge openings. As a result of these measures, glue residues are effectively prevented from accumulating at the edges of the discharge openings.

BACKGROUND OF THE INVENTION 
The application of an adhesive in the form of a specific pattern or line to 
a surface, such as the surface of parts to be glued to each other, by 
means of a mouthpiece which moves relative to the surface is known in 
practice. In this connection the problem occurs that, whenever the 
application is stopped, such as at the beginning of a pause in the 
discharge of the adhesive, residues of adhesive often remain hanging from 
the edge of the discharge opening. This leads to the phenomenon that is 
referred to in practice as the formation of "beards". The formation of 
these "beards" interferes with the good application of the adhesive, i.e., 
exclusively within the intended boundaries and in the previously specified 
quantity. 
It is conceivable that the discharge openings could be cleaned periodically 
by switching the flow through the discharge opening from the adhesive to a 
flushing medium, but it is evident that such a solution is associated with 
many complications and is therefore unacceptable. 
The invention provides a process by means of which the difficulty described 
above is eliminated. This process consists in that the edges of the 
discharge opening(s) are sprayed with a rinsing medium at least during the 
pauses between the applications of the glue. 
The surprising discovery was made in practice that the formation of beards 
can be effectively prevented by means of this extremely simple measure. 
It is preferable to supply the rinsing medium through at least one 
distributor, which, with respect to the discharge openings, is located 
upstream from the mouthpiece in the direction of motion and which produces 
a flat stream of the rinsing medium. 
Especially good results are obtained when the adhesive is a cold glue and 
when water is used as the rinsing medium. 
The invention also pertains to a mouthpiece with one or more rinsing medium 
discharge openings situated upstream from the glue discharge openings. 
This mouthpiece is preferably designed such that a rinsing medium 
discharge opening is protected by a cover plate situated a short distance 
away from the surface of the mouthpiece, the cover plate extending from 
the discharge opening to one or more adhesive discharge openings situated 
downstream therefrom, thus forming a flat distributor for the rinsing 
medium. The mouthpiece surface carries a thin plate with one or more 
cutouts opening toward the adhesive discharge openings, these cutouts 
being covered by a cover plate. Thus, a rinsing medium distributor of very 
simple design is obtained, the configuration and height of which is 
determined by the shape of the cutouts and by thickness of the plate, 
respectively, and can thus be easily and quickly adjusted to different 
conditions. The invention is explained on the basis of the drawings in 
which:

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
An example of a mouthpiece which embodies the invention is designated as a 
whole in the ures by reference number 2. The design shown consists of a 
solid block 4, surface 6 of which passes by way of a sloping edge 8 and a 
receding edge 10 into surface 12. Next to rear edge 14 of surface 12, 
there is a series of adhesive discharge openings 16. In the embodiment 
shown, they are arranged in three groups 18a, 18b, 18c of four each. 
Naturally, the arrangement and the number of discharge openings are 
functions of the intended application, i.e., of the glue pattern to be 
applied to the substrate. 
Each discharge opening 16 is the orifice of a channel 20 (see FIG. 5), and 
these channels 20 are thus also arranged in groups of four, i.e., groups 
22a, 22b, 22c. The adhesive is supplied intermittently in a controlled 
manner in accordance with a previously defined pattern to the individual 
discharge openings 16 via feed openings 28a, 28b, 28c, connecting channels 
26a, 26b, 26c, and distribution channels 24a, 24b, 24c, to which the 
connecting channels lead. From there, the glue is applied in the form of 
an adhesive "bead" 24, as shown in FIG. 3, to a substrate 22 traveling by 
under mouthpiece 4 in the direction of arrow 20. The thickness of bead 24 
is determined by the height of edge 10, indicated as "h" in FIG. 4, by the 
size of the discharge opening, and by the pressure under which the 
adhesive is being supplied. 
So that discharge openings 16 can be cleaned or, in accordance with the 
invention, "rinsed off" periodically, such as during pauses or 
intermittent shut-off periods, certain measures are provided in accordance 
with the invention. As seen upstream from openings 16 in the direction of 
arrow 20, surface 12 has three openings 30a, 30b, 30c, which are the 
orifices of feed channels 32a, 32b, 32c, through which a suitable rinsing 
medium such as water can be discharged intermittently in a controlled 
manner. So that this rinsing medium forms a flat sheet of mist to rinse 
openings 16, openings 30a, 30b, 30c are situated in rectangular cutouts 
34a, 34b, 34c made in a thin plate 36 (for example, 0.1 mm thick), and 
this plate 36 is covered by a thin cover 38 with a thickness of, for 
example, 0.2 mm. The thickness of plate 36 plus the thickness of cover 38 
is the same as height "h" of edge 10, that is, the distance between 
surface 12 and substrate 22. Cover 38 carries four internally threaded 
bushes 40, into which countersunk fastening screws 42, inserted through 
suitable bores 44 in block 4, are screwed. In this way, cover 38 is 
fastened to block 4 in an easily replaceable manner. 
The rinse water supplied through openings 30a-30c forms flat streams 
proceeding in a single direction to rinse openings 16 as indicated in FIG. 
1 by reference number 46. 
FIGS. 7A and 7B illustrate the effect of the measures according to the 
invention. FIG. 7A shows how mouthpiece 2 applies beads of adhesive 24 to 
substrate 22, moving continuously in the direction of arrow 20 under 
mouthpiece 2. Whenever the application of the adhesive is interrupted, a 
film 46 of water is sprayed via openings 30a-30c across openings 16, with 
the result that adhesive cannot accumulate at these orifices. 
FIG. 8 shows a highly schematic diagram of a complete installation in which 
the process according to the invention is implemented. The Figure shows 
mouthpiece 2 with common feed connection 28d, which leads to adhesive feed 
channels 28a-28c. Line 50 and valve 52 connect the feed connection to a 
schematically indicated source 54, from which adhesive is supplied; valve 
52 is controlled by a schematically indicated central controller 56. 
Controller 56 also controls valve 58, which regulates the supply of rinse 
water from a schematically indicated source 60 to connection 32d, to which 
water channels 32a-32c are connected.