EP0860212A1 - Hot melt adhesive applicator and adhesive stick for feeding this applicator - Google Patents

Abstract

A hot melt adhesive applicator has an elongated chamber (3') with an inlet end (4') conforming to a stick (5') of the adhesive and an outlet end (6') fitted with a molten adhesive distribution nozzle (7'), the stick (5') being progressively pushed into the chamber where it is electrically heated. The novelty is that heating is effected by one or more heating elements (131) in the form of a resistive track (151) which is connected to an electricity source and which is formed on an electrically insulating surface of a substrate (141) to be in direct thermal contact with the adhesive mass within the chamber (3'). Preferably, the resistive track (151) is formed by screen printing of a metal or ruthenium and/or indium oxide resistive paste on a substrate (141) of alumina, enamelled sheet or a dielectric layer-covered stainless steel sheet, the track material preferably having a positive temperature coefficient of resistance and a resistivity of 1-1000 OMEGA /square for a 8-20 mu m thickness. Also claimed is a solid adhesive stick for feeding into the above applicator, the stick having a cylindrical shape with a polygonal cross-section conforming to that of the chamber inlet.

Description

The present invention relates to an applicator hot melt glue and a designed glue stick to power such an applicator.

There is shown in Figure 1 of the accompanying drawing a hot melt glue applicator of a type currently widely spread. It takes the form of a pistol whose the handle 1 extends beyond a body 2. The body 2 comprises an elongated chamber 3 having a first end 4 shaped as an inlet for a stick 5 of glue hot-melt, and a second end 6 equipped with a nozzle 7 for dispensing molten glue. The applicator still includes mechanical means (not shown) actuated by pressing a trigger 8 to gradually push the glue stick 5 into the bedroom 3, and mounted electric heating means around chamber 3 to melt the material hot melt stick 5 contained in this chamber. These means are arranged in a volume 9 around the bedroom 3 and are powered by an energy source electric outdoor (the sector for example), by through an electric cable 10 crossing the handle.

The drops of molten glue coming out of the nozzle 7 can be used to assemble many parts between them, or to supports, for example to fix rods or cladding pieces on walls, ceilings, etc. etc.

The heating means currently incorporated into such applicators are essentially of two types. According to the first, these means consist of a cylindrical cartridge filled with a constituent material an electrical resistance and having a coefficient of positive temperature. The cartridge is fed electrically and mounted in a metal sleeve crossed by chamber 3, so as to heat this sheath by thermal conduction. Due to the coefficient of positive temperature of the material contained in the cartridge, the resistance of this material increases with its temperature, which ensures current regulation electric heating.

The use of such a cartridge is advantageous due to its low cost, its small size and of the regulatory function it provides. On the other hand, the applicators equipped with this cartridge present long warm-up times (around 10 minutes) and limited heating power. In addition, the cartridges being supplied by manufacturers specialist, the designer of the applicator is limited in its choices by the nominal performance of the cartridge, as chosen by the manufacturer, particularly with regard to temperature maximum heating.

According to another type of heating means currently used in the applicators in question, these means take the form of an electrical resistance wire-like insulated, wound around chamber 3 on a metallic sheath crossed by this chamber. With this technology, we reach rise times shorter temperature (about 5 minutes), you can vary the power of the device by calibrating suitably the resistance used and you can adjust the maximum heating temperature using a thermostat (a bimetallic strip for example).

On the other hand, we must associate with the resistance of means of thermal and electrical insulation which increase the price of the applicator. When resistance is mounted on a glass wire, it becomes brittle at along due to the variations in heat flux that it undergoes. It's harder to get regulation accurate heating current than with cartridges mentioned above and the assembly and adjustment of the applicator require relatively long labor times which increase the price of the applicator.

In the two types of heating means described above, we heat the whole of a sheath and not only the glue to melt. A sensitive part of the electrical energy released by these means is therefore lost elsewhere than in the glue.

The present invention therefore aims to achieve a glue applicator which does not have the disadvantages mentioned above of the applicators of the prior art and which, in particular, goes up very quickly in temperature, has a yield high thermal and high melt glue flow.

The present invention also aims to achieve such an applicator which is reliable, which has a good electrical safety for the user, and which is low manufacturing cost price.

These objects of the invention are achieved, as well as others which will appear on reading the description which will follow, with a hot melt glue applicator comprising a) an elongated chamber having a first end shaped as an inlet for a stick of said hot-melt adhesive and a second end equipped with a molten glue distribution nozzle, b) means for gradually pushing said rod in said room and c) heating means the part of the stick contained in the bedroom. According to the invention, said heating means include at least one heating element consisting of a track made of an electrically resistant material and provided with means for connection to an energy source electric, said track being formed on a surface electrically insulating of a substrate arranged so as to be in close thermal contact with a mass of glue contained in said room.

Thanks to the close thermal contact thus established between the resistive track of the heating element and this mass glue, the thermal energy emitted by the track due to of the Joule effect is almost entirely absorbed by the mass of glue, which considerably improves the thermal efficiency of the heating means of the applicator according to the invention, compared to those of means of the prior art described above.

According to a preferred embodiment of the invention, the substrate of a heating element is planar. The heating element is then placed in a wall side of the room. Alternatively, it can be arranged in a central position in this room.

According to another embodiment, the applicator includes a plurality of such elements, these elements lining the wall of the room, the faces of their substrates which carry the resistive tracks being facing the axis of said chamber. Advantageously, said chamber has a taper of vertex placed from side of the glue dispensing nozzle. Substrates heating elements then each have the shape of an elongated triangle, adapted to said taper of the bedroom.

• la figure 1 est une vue en perspective d'un applicateur de colle de la technique antérieure, décrit dans le préambule de la présente invention,
• les figures 2 et 3 sont des vues en coupe axiale et en coupe transversale, respectivement, d'un corps de chauffe de colle incorporé à un applicateur suivant l'invention,
• les figures 4 à 6 sont des représentations schématiques de trois modes de réalisation d'un élément chauffant incorporé au corps de chauffe des figures 2 et 3,
• la figure 7 représente schématiquement un autre mode de réalisation du corps de chauffe de l'applicateur de colle suivant l'invention,
• la figure 8 représente schématiquement l'élément chauffant incorporé au corps de chauffe de la figure 7,
• la figure 9 est une vue en coupe du corps de chauffe de la figure 7, selon le trait de coupe IX,
• la figure 10 est une vue en coupe similaire à celle de la figure 9, d'une variante du corps de chauffe des figures 7 à 9, et
• les figures 11 et 12 représentent schématiquement deux autres variantes du corps de chauffe.

Other characteristics and advantages of the present invention will appear on reading the description which follows and on examining the appended drawing in which:

• FIG. 1 is a perspective view of an adhesive applicator of the prior art, described in the preamble of the present invention,
• FIGS. 2 and 3 are views in axial section and in cross section, respectively, of an adhesive heating body incorporated in an applicator according to the invention,
• FIGS. 4 to 6 are schematic representations of three embodiments of a heating element incorporated in the heating body of FIGS. 2 and 3,
• FIG. 7 schematically represents another embodiment of the heating body of the glue applicator according to the invention,
• FIG. 8 schematically represents the heating element incorporated in the heating body of FIG. 7,
• FIG. 9 is a sectional view of the heater body of FIG. 7, along the section line IX,
• FIG. 10 is a sectional view similar to that of FIG. 9, of a variant of the heating body of FIGS. 7 to 9, and
• Figures 11 and 12 schematically represent two other variants of the heating body.

We refer to Figures 2 and 3 of the accompanying drawing where the heater shown is designed to be installed in place of a conventional heater, in the volume 9 delimited in FIG. 1. The body comprises a socket 11 preferably made of a material electrically and thermally insulating. She presents advantageously, but not exclusively, a form taper of axis X, a ring 12 being mounted on the inlet 4 'from the sleeve to guide a 5' glue stick pushed, according to arrow F, in an elongated chamber 3 ' internal to the socket 11 and centered on the X axis. other end 6 ', the socket is fitted with a nozzle 7' stick adhesive distribution, after melting this in the heating body. It is clear that the elements or organs 3 ', 4', 6 'and 7' are identical or equivalent to elements 3,4,6 and 7 respectively of the prior art applicator shown in the figure 1.

According to the present invention, the wall of the chamber 3 'is lined with at least one, and preferably several, heating elements 13 ₁ , 13 ₂ , ... 13 ₆ distributed symmetrically around the axis X so as to cover substantially the entire surface of this wall. For this purpose, the sleeve 11 is advantageously hollowed out, at the level of the wall of the chamber, of axial notches each conforming to a heating element 13 _i (1 = 1 to 6) which it must accommodate, as appears on the sectional view of FIG. 3. Each heating element is retained in its notch by wedging and / or gluing.

According to a characteristic of the present invention, each heating element 13 _i (see FIG. 4) comprises a flat substrate 14 _i in the shape of a very elongated triangle, adapted to the conicity of the chamber 3 '. It is understood that the frustoconical shape given to this chamber, with the apex placed on the side of the nozzle 7 ', allows the mass of molten glue that the chamber 3' contains in operation, to gradually taper towards the nozzle 7 'for s 'adapt to the small diameter of a channel passing through this nozzle.

The substrate 14 _i in the form of an elongated triangle which constitutes the base of a heating element 13 _i has an insulating surface which carries a track 15 _i made of an electrically resistant material, track itself covered with a layer of electrical insulation ( not shown). The electrical resistance of this material is chosen so that the passage of an adequate electric current through all of the tracks 15 _i of the heating body quickly ensures the softening and then the melting of the adhesive of a stick 5 'introduced into the chamber. 3 '. To do this, the tracks 15 are turned towards the axis X of the chamber 3 '(see FIG. 3). They are thus advantageously in close contact with the mass of adhesive which is in the chamber 3 ', through the thin layer of electrical insulation which separates each track from this adhesive.

A heating element such as that shown in the Figure 4 can be achieved using the means used for manufacturing hybrid layer circuits thick. We know that such a circuit is made up conventionally of a substrate, of alumina, of enamelled sheet or in stainless steel sheet covered with a dielectric by example, receiving by screen printing a network of tracks conductive and resistance and supplemented by active and / or passive components reported on the substrate.

We also realize multilayer circuits either in stacking screen-printed and baked alumina substrates one on the other or, alternatively, by covering a basic substrate with an insulating paste, then itself screen printed.

This is how the heating element of FIG. 4 can be produced by depositing on a first substrate a conductive track 16 _i , and by covering the track with an insulating paste on which the resistive track 15 _i is screen printed. It is finally covered with a layer of electrical insulation, as we saw above.

Tracks 15 _i and 16 _i are connected through a via disposed at the end 17 _i of the element. Contacts 18 _i , 19 _i are welded to the ends of the tracks 15 _i , 16 _i respectively, for the connection of these tracks to a source of electrical energy.

Such a bilayer circuit could also be implemented by the technique of "co-cooked" multilayer circuits, so as to avoid multiple cooking stages necessary for the manufacturing procedure described above.

The resistive track 15 _i of the heating element of FIG. 4 takes the form of a coil to increase its surface, and therefore the value of its electrical resistance. In the heating element 13 ′ _i shown in FIG. 5, the resistive track 15 ′ _i is straight, just like the conductive return track 16 ′ _i , adjacent and formed in the same layer as the track 15 ′ _i .

In FIG. 6, the circuit of the heating element 13 " _i shown is also monolayer, the resistive track 15" _i running on two opposite longitudinal edges of one face of the substrate 14 _i .

Of course, geometries of tracks other than those shown in FIGS. 4 to 6 are possible, these are given only by way of example.

As mentioned above, these tracks are performed by screen printing following a well-defined procedure known in the manufacture of hybrid layer circuits thick with electrical resistances. The track is then constituted by a resistive "ink" deposited at the pasty state on the substrate through a mask and then dried to remove the solvents incorporated into the paste filed. These steps are followed by high cooking temperature (about 850 ° C) to give a good stability to the heating element. Many compositions well known to those skilled in the art are usable in the present invention. For exemple illustrative and not limiting, we can use pastes based on metals and ruthenium oxide or indium, for example, with resistance included between 1 Ω / □ and 1000 Ω / □, for a track thickness of 8 to 20 µm.

Advantageously, an ink with a positive temperature coefficient will be chosen to regulate the supply current of the heating elements. Those skilled in the art have at their disposal a wide range of inks having temperature coefficients up to 3,500.10 ^-6 / degrees C.

The inks referenced 5091, 5092, 5093 in the DuPont de Nemours catalogs have been successfully used to make the elements heaters of the applicator according to the invention.

The nature and the positions of the heating elements of the heating body of the adhesive applicator according to the invention are favorable for obtaining a rapid rise in temperature of the adhesive and a high thermal efficiency of the applicator, for the following reasons. On the one hand, the position of each heating element, in close contact with the surface of the adhesive volume, ensures direct heat transfer between the heating element and the adhesive. This is not the case in the glue applicators mentioned in the preamble to this description where the heating elements serve to heat a metal sheath which, in turn, transfers calories to the glue. The efficiency of this double thermal transfer is lower than that of the direct thermal transfer operated in an applicator according to the invention. On the other hand, the efficiency of the latter is further increased by the fact that the heat radiated by the heating elements is focused in the mass of adhesive. An appropriate choice of materials constituting the substrates 14 _i of the tracks and the sleeve 11 makes it possible to minimize the losses by thermal conduction in these materials.

Thanks to the improved thermal efficiency thus obtained, we can consider feeding an applicator according to the invention from a battery rather than from the sector alone, as is generally the case currently. This improvement in the autonomy of the user of the applicator according to the invention is a significant advantage brought by it.

The use of proven technologies in the manufacturing thick film hybrid circuits for make the applicator's heating elements according to the invention, ensures reliability and job security of it while lowering its manufacturing cost price thanks to the high degree automation of mass manufacturing carried out in these technologies. In this regard, we understand that we can manufacture, in the same rectangular plate of substrate, a large number of heating elements in placing these side by side, and head to tail, on the plate so as to maximize the useful surface of the substrate. All resistive tracks are deposited then dried simultaneously. The heating elements are finally individualized by sawing the substrate, or by any other cutting means.

Taking into account the polygonal cross section given to the chamber 3 ′ (see FIGS. 2 and 3) by the presence of the heating elements 13 _i , the cross section of the adhesive stick 5 ′ is advantageously conformed according to the invention ( see figure 2) so as to facilitate its introduction into the chamber and to bring the outer surface of the stick closer to that of the heating elements.

Of course, the invention is not limited to embodiments described and shown which have not been given as an example. This is how the wall of chamber 3 'could take a cylindrical shape rather than conical and that its cross section could have a polygonal shape other than hexagonal, or even a circular shape. One or more resistive tracks helical in shape can then be formed on the wall of the chamber 3 ', to constitute the elements heated.

It is thus also that, according to another mode of realization of the heating body of an adhesive applicator according to the present invention, shown in the figures 7 to 9, this comprises a socket 20 pierced with a cylindrical chamber 21 suitable for accommodating a stick of glue of the same shape, in the solid state. Room 21 accommodates a heating element 22 extending along the longitudinal axis of the chamber 21 in a plane substantially diametral thereof (see Figure 9).

The heating element 22 consists of a planar substrate 23 of structure similar to the substrates 14 _i of the heating elements 13 _i described above. This substrate is covered, on at least one face, by a track 24 made of an electrically resistant material, covered with a layer of electrical insulation (not shown). Terminals 25, 26 ensure the connection of this track to an external electrical energy source.

The glue stick is introduced into the body of heats by the end 21a of the chamber 21. The end of the substrate 23 of the heating element 22 therein is cut at point 27 to facilitate entry of the rod in chamber 21, this rod then impaling itself on the heating element. This action is facilitated by the fact that the calories released by the heating element soften the glue stick as its penetration into chamber 21.

The central position of the heating element 22 in chamber 21 ensures complete absorption of calories by the mass of the glue stick, which is favorable from the point of view of the thermal efficiency of the body of heated. To ensure uniform heating of the mass glue, preferably choose a substrate 23 having good thermal conductivity, such as suitably electrically insulated metal substrate, so that the heat given off by track 24 diffuses on both sides of the substrate.

Alternatively, to perfectly homogenize the heating glue stick, we can have on the other side from the substrate 22 another conductive track 24 '.

In another variant, the heating element 22 can be arranged as shown in Figure 10 so that constitute part of the wall of a chamber 29 formed in a heater 28, the single track 24 being facing the interior of this room, which accommodates the glue stick.

The invention is also not limited to planar heating elements. Thus, these could be formed on conical or cylindrical substrates of revolution, for example, so as to adapt perfectly to the shape of the chamber of the heating body which receives the stick of glue. FIG. 11 shows a heating body constituted by a cylindrical envelope 30 partially cut away in the figure, made of a thermal insulation material, for example, a cylindrical heating element 32 being slid against the wall of an elongated chamber 31 passing through the envelope 30. The element 32 comprises a cylindrical substrate 33 on the inner wall of which one or more tracks 34 ₁ , .... are formed of an electrically resistant material.

FIG. 12 represents a variant of the embodiment of FIG. 11 which differs from it only in that the conductive track or tracks 34 _i are formed on the external wall of the substrate 33, so as to facilitate the realization of these tracks. In this case, it is necessary that the substrate 33 used be thin (a few tenths of a mm for example) and made of a material which is good conductor of heat so as to allow the radiation of the heat emitted towards the interior of the chamber 31.

Claims (17)

Hot melt adhesive applicator comprising a) an elongated chamber (3 ';21;29; 31) having a first end (4') shaped as an inlet for a stick (5 ') of said hot melt adhesive and a second end (6') equipped with a nozzle (7 ') for dispensing molten glue, b) means for progressively pushing said stick into said chamber and c) means for electric heating of the part of the stick contained in the chamber, characterized in that said heating means comprise at least one heating element (13 _i ; 13 '_i; 13 "_i;22; 32) constituted by a track (15 _i ; 15'_i;15"_i;24; 24 '; 34 _i ) in an electrically resistant material and provided with means for connection to a source of electrical energy, said track being formed on an electrically insulating surface of a substrate (14 _i ; 23; 33) arranged so as to be in close thermal contact with a mass of glue contained in said chamber (3 ';21;29; 31). Applicator according to claim 1, characterized in that said substrate (14 _i ; 22) is planar. Applicator according to claim 2, characterized in that said heating element (22) to planar substrate (23) is disposed in a central position of said chamber (21), along the axis thereof (Figure 9). Applicator according to claim 3, characterized in that said substrate (23) of said element heater (22) is cut into a point (27) on the side of the entrance (21a) of a stick of glue into the chamber (21). Applicator according to any of claims 3 and 4, characterized in that each of two faces of the substrate (23) carries a track in one electrically resistant material (24; 24 '). Applicator according to claim 2, characterized in that said heating element (22) to planar substrate is arranged in a side wall of the chamber (29) (Figure 10). Applicator according to claim 1, characterized in that the heating element (32) comprises a non-planar substrate (33). Applicator according to claim 7, characterized in that said substrate (32) is cylindrical and applied against the wall of the chamber (31). Applicator according to claim 2, characterized in that it comprises a plurality of heating elements (13 _i ; 13 '_i; 13 " _i ) lining the wall of the chamber (3'), the faces of their substrates which carry the resistive tracks (15 _i ; 15 '_i; 15 " _i ) being turned towards the axis (X) of said chamber. Applicator according to claim 9, characterized in that said chamber (3 ') has a taper of vertex placed on the side of the nozzle (7 ') of glue distribution. Applicator according to claim 10, characterized in that the substrates of the elements each have the shape of a triangle elongated adapted to said conicity of the chamber (3 '). Applicator according to any one of Claims 1 to 11, characterized in that the resistive track (15 _i ; 15 '_i; 15 "_i;24.24'; 34 _i ) carried by each heating element is produced by screen printing a resistive paste on the substrate (14 _i ; 23; 33), according to the technology for producing thick-film hybrid circuits. Applicator according to claim 12, characterized in that the material constituting said track (15 _i ; 15 '_i; 15 "_i;24.24'; 34 _i ) has a positive temperature coefficient. Applicator according to any of claims 12 and 13, characterized in that said pulp includes metals, ruthenium oxides and / or indium. Applicator according to any of claims 12 to 14, characterized in that said substrate is chosen from: an alumina substrate, a enamelled sheet substrate, a stainless sheet substrate covered with a dielectric layer. Applicator according to any of claims 12 to 15, characterized in that said track has a resistance between 1 Ω / □ and 1000 Ω / □, for a thickness of approximately 8 to 20 µm. Stick (5 ') of glue in solid state, for the supply to the applicator chamber (3 ') according to any one of claims 9 to 16, characterized in that said stick has a shape cylindrical with a polygonal cross section conforming to that from the entrance to said room (3 ').

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