EP0730914A2 - Method and device for coating surfaces with hot-melt adhesives in a grid pattern using an intaglio printing technique - Google Patents

Abstract

A roller printing process is claimed for coating a grid pattern of adhesive onto flexible sheet materials such as interlining materials for clothing. The process comprises (a) partly filling the cup-shaped depressions in a cup roller (1) with a hot-melt adhesive powder (2) with the aid of a first spreader (3 or 3a), (b) covering the powder filling with a dispersion paste (5) based on a non- or only slightly-heat-activatable plastic material with a lower melt flow index than (2), using another spreader (4 or 4a), and (c) transferring the double-layer fillings from the roller cups onto the sheet material (7) which is preheated on at least one press roller (6). Also claimed is an appts. for this process, with spreaders (3/3a) and 4/4a) arranged in sequence around a cup roller (1), and with a heated roller (6) pressing onto (1) and rotating at the same speed. External heating is applied (a) to the surface of the cup roller between the second spreader (4) and the heated press roller (6) and/or (b) to the sheet material on the cup roller, between the points of contact of press roller (6) and a further press roller (11).

Description

This invention describes a method and an apparatus for the grid-like coating of web-like flexible sheets with hot melt adhesives. The coating consists of two grid layers that sit on top of one another: a base layer that is not or only weakly thermally activated and a cover layer of a thermally activated hot-melt adhesive that is formed from powder and has a higher flowability in the melt state than the basic layer. Both layers are applied using the gravure printing process and represent a grid-like double coating.

Double coating processes which have already become known have been described in the "Handbook of Textile Fixing Inserts" by Sroka, 3rd extended edition 1993, pages 131 to 136. Of the 4 specified processes, the dot-Riesel process, which is still used almost alone today, in which the paste print is sprinkled with hot-melt adhesive powder on a insert screen with a screen printing stencil and then the excess powder not adhering to the print is removed again by shaking, blowing and sucking . The disadvantage of this method is that the scattering powder also adheres to the edges of the pressure points beyond their contact surface on the carrier and, in addition, fine-grain powder, particularly in the case of very fine-fiber synthetic articles, is difficult to remove between the pressure points. In this method, too, there are often clear differences in size and shape of the scattered pressure points, in particular when textile fabrics which are not woven or knitted sufficiently densely and have a translucent or lattice structure are used as coating substrates. At the pressure points at which the perforations of the screen template are largely or fully covered with the weft, warp or knitting threads, the point learning is comparatively small and at the pressure points where the perforations are The point formation is greater, largely due to the empty spaces between the weft, warp or knitting threads. This often leads to wavy increasing or decreasing adhesion and can sometimes cause wavy blistering after cleaning or washing. The risk of puncture and kickback is also increased and wavy grip hardening is possible.

The double powder dot process, which is also mentioned, works in gravure printing with two funnel doctor blades, one behind the other, on an engraving roller. In order to be able to carry out this method, two coordinated different types of hot-melt adhesive powder are required, which separate from the engraving recesses under the same temperature conditions of the engraving and heating rollers, which greatly limits the applicability of the method. In addition, it cannot be avoided that the powders mix in an uncontrolled manner in the engraving recesses and in the powder bed in front of the second doctor blade. Finally, there are also differences in size and shape of the transferred colons. The phenomena are reversed here as in the point-trickle method above. Weft, warp or knitting threads, which largely or completely cover the engraving recesses, ensure full powder emptying of the engraving recesses and depressions, which largely lie on empty gaps between weft, warp or knitting threads, can only cause partial emptying. Here, too, differences in adhesion, blistering and increased tendency to breakdown and kickback can occur. This process was therefore no longer used.

A double paste dot process has also already been described, in which two different pastes are printed and positioned one above the other with a screen printing stencil with two inner doctor blades. A satisfactorily working embodiment has not yet been found with this method and therefore the method has not found its way into practice.

Finally, in the manual mentioned above, there is a rollcoater coating process that has been practiced for a while. In the first step, the base layer is screen-printed paste coated, and in the second step, the dried and sintered paste points of the base layer with the tips are dipped into a very uniformly thin film of a hot-melt adhesive dispersion or solution on a roll shell of a roll coater. The main disadvantage of the method was that fine screens are unsuitable for this, a high level of precision is required for the uniformity of the film formation on the roll coater, and the mechanical and production engineering outlay is high.

More recently, it has been proposed to produce the double-layer structure by arranging two exactly the same screen printing round stencils extremely closely one behind the other and applying the points of the base layer with the first and the points of the cover layer exactly congruently with those of the base layer . The extraordinarily high requirements for realizing the offset-free positioning of all pressure points of the two stencils one above the other make it practically unlikely that this method can be carried out, at least with fine screens.

The object of the present invention was therefore to find a simple and safe to use, rationally working method for double coating, which only requires a modest amount of additional mechanical work, is accurate, feasible even with very fine screen dots, avoids hardness and largely uniform shape and size the coating points are also produced with translucent and less densely woven and knitted textile carriers.

Figur I,

die eine erfindungsgemäße Tiefdruckvorrichtung,

Figur II,

einen Ausschnitt aus einer anderen geeigneten Vorrichtung,

Figur III,

einen weiteren Ausschnitt einer teilweise anderen Vorrichtung

Figur IV,

eine Rütteleinrichtung,

Figur V,

einen Rührstab,

Figur VI,

eine modifizierte Näpfchenwalze und

Figur VII,

eine Näpfchenvertiefung mit dem Umriß einer kleinen zylinderförmigen Scheibe

darstellen, ist das erfindungsgemäße Verfahren zum rasterförmigen Beschichten von bahnförmigen flexiblen Flächengebilden, wie Einlagestoffen für Kleidungsstücke mit Schmelzklebern durch Auftragen von zwei übereinandersitzenden rasterförmigen Klebstoffschichten aus Basis- und Deckschicht mit geringerem Schmelzfluß der Basisschicht als der darauf sitzenden aus Pulver gebildeten Deckschicht eines thermoaktivierbaren Schmelzklebers, im Tiefdruckverfahren, dadurch gekennzeichnet, daß in die Näpfchen einer mit Vertiefungen versehenen Näpfchenwalze (1) das die Deckschicht auf dem Fertigprodukt bildende Schmelzkleberpulver (2) mit Rakel (3) eingerakelt und auf diese Pulverfüllungen mit einer weiteren Rakel (4) oder (4a) eine Dispersionspaste (5) aufgesetzt wird, die am Fertigprodukt die Basisschicht aus einer nicht oder nur abgeschwächt thermoaktivierbaren Kunststoffmasse ausbildet, und anschließend die nun doppelschichtigen Näpfchenfüllungen aus Pulver und Paste mit dem mindestens von einer Preßwalze (6) aufgeheizten Flächengebilde (7) in Kontakt gebracht und dann unter Herauslösen der Füllungen aus den Näpfchen auf dieses Flächengebilde übergeben wird.Surprisingly, it is possible to achieve these tasks with a suitably modified double-point powder coating process that works in gravure printing. With reference to

Figure I,

a gravure printing device according to the invention,

Figure II,

a section of another suitable device,

Figure III,

another section of a partially different device

Figure IV,

a vibrating device,

Figure V,

a stir bar,

Figure VI,

a modified well roller and

Figure VII,

a well with the outline of a small cylindrical disc

represent, the inventive method for grid-shaped coating of sheet-like flexible sheets, such as interlinings for garments with hot melt adhesives by applying two superimposed grid-shaped adhesive layers from the base and top layer with a lower melt flow of the base layer than the top layer of a thermoactivatable hot melt adhesive formed from powder, im Gravure printing process, characterized in that the hot-melt adhesive powder (2) forming the cover layer on the finished product is knife-coated with a doctor blade (3) into the wells of a well roller (1) and one is applied to these powder fillings with a further doctor blade (4) or (4a) Dispersion paste (5) is placed, which forms the base layer on the finished product from a plastic mass that cannot be thermally activated or is only weakened, and then the double-layered cup fillings made of powder and paste with the min at least brought into contact with a sheet (7) heated by a press roll (6) and then transferred to this sheet while removing the fillings from the cups.

The process can often be carried out with the conventional powder point systems, which work with cups and heating rollers, with relatively modest cultivation and surprisingly in almost the same How to perform a conventional powder spot coating. The attachment consists primarily of a second doctor blade (4) or (4a). The coating edge of the squeegee (4) forms an acute angle with the rounding of the engraving roll on the contact line, for example by appropriate positioning and / or by chamfering the coating edge (4 '), as a result of which a slight compression effect is exerted on the dispersion paste (5) provided. Such a squeegee positioning with a beveled edge of the doctor blade is shown in FIG. Figures I and III show another doctor blade variant (4a) with a stronger compression effect on the paste. Here, the squeegee edge (4a ') should be sharply ground and form an acute angle with the well roller wall on the ground tip to the side of the paste template. The paste can be fed through a tube with a large number of bores, the diameter of which changes successively and is coordinated in such a way that the paste discharge is as uniform as possible over the entire printing width of the cup roller. To further homogenize the paste distribution, the paste can exit the bores of the tube into a prechamber, from which the paste then runs onto the paste template in front of the doctor blade via a slot die. It can also be advantageous to feed the paste from both sides of the well roller via two tubes in equal amounts and to allow the paste to emerge from its bores into a common antechamber.

Surprisingly, when pastes are applied, which can be foamed even with a relatively small increase in volume and thereby lose viscosity, the mechanical influence on the powder fillings in the wells is almost completely eliminated, so that a perfect two-layer structure can be formed and practically no powder is mixed with the paste template. In addition, the avoidance of a partial mixing of the paste template with the powder of the cup fillings can be ensured by using rollers instead of conventional cup rolls with a half-moon-like cup shape, the cup outline of which reproduces the shape of very small cylindrical disks (19) and (19a), such as emerges from Figures VI and VIII.

After the powder fillings of the cells have been covered with the dispersion paste under the second doctor blade (4) or (4a), the surface of the cell roller comes with the fabric (7) which is heated by a hot press roller (6) and is pressed against the cell roller and pressed against it. in contact and takes over the fabric either over a distance of half the cup roller circumference or releases it immediately after passing through the line contact with the press roller. Due to the press contact of the hot fabric with the comparatively cool cup roller filling, a shock-like heat transfer takes place, which may already be sufficient to cause the filling of powder and paste to detach from the cup and to transfer it to the sheet. On the way about half the cup roller circumference from the landing of the fabric with the press roller (6) to the removal from the cup roller, exposure to heat rays or a heated air stream can also take place, which is carried out by a mild suction device (10) between the cup roller and under the well roller attached hood is guided. The air flow heating can be effected or supported by the current sliding past the press roll (6). Another press roller (11), which detaches the fabric after about half the distance on the cup roller circumference, can, if it is heated, support the heating of the air flow and finally additional heating can be carried out by the heat radiators. The application of heat on the path from the press roll (6) to the press roll (11) can be expedient in the first place when pastes containing crosslinkable components are applied with a doctor (4) or (4a). In many cases, however, it can also be omitted when these pastes are used, and in particular when the pastes are set to be heat-sensitive and they coagulate like a shock under the action of heat from the pressed hot sheet.

When the sheet (7) is removed from the cup roller, the sheet generally peels out the entire filling without any residues remaining in the cups. The entire cup filling is also peeled off when the less densely woven and knitted somewhat lattice and translucent textile carriers can be used as flat structures for coating. The coating points taken over from the textile carriers all have almost the same shape and size.

In order to promote the peeling out of the cup fillings, the internally heated press roll (6) and / or the press roll (11) can be covered with a thin elastic layer up to approximately 1 mm thick, which layer consists of silicone rubber or several layers of a fine, temperature-resistant aramid fabric. which is treated with silicone rubber in the outermost layer. It is also possible to coat the fabric to be coated in the area of contact with the cup roller with a circumferential band of thermally resistant fiber material, e.g. B. with a fabric made of aramid fibers, which tape is guided from the heated press roll (6) to the press roll (11) under tension on the cup roll (1) and then returns to the press roll (6).

The now coated surface structure (8) can be dried and sintered on the circumference of the press roller (11) if it is heated. The drying and sintering can also take place in a downstream sintering and drying channel, not shown. In Figure I, a preheating roller (13) is also sketched, which causes a further heating of the supplied fabric. It may also be advantageous to gently smooth the surface of the coating after drying and sintering by applying a low pressure, e.g. by applying a soft or foam rubber roller to a cooled smooth steel roller, through the line of contact of which the coated hot sheet is passed.

In the case of pastes which are free of crosslinkable components, the powder fillings in the wells under doctor blade (4) or (4a) can be covered with pasty pastes of finely powdered polymers with reduced thermal activation on the basis of copolyamides, copolyesters or polyethlenes , which produce the blocking base layer on the finished product with a reduced melt flow compared to the cover layer. The dry substances of the pastes should be in the melting range over approx. 120 ° C and their melt index according to DIN 53 735 should be less than 10 g / 10 min at 21.6 N nozzle load and 160 ° C measuring temperature. Water-containing pasty dispersions which contain very finely divided crosslinkable fractions, such as crosslinkable polyurethane, polyacrylates, polybutadiene-acrylonitriles, polybutadiene-styrene-acrylonitriles or vinyl acetate copolymers, are advantageously suitable. These crosslinkable water-containing dispersion pastes can additionally contain fine plastic powders with reduced thermal activity, such as hot-melt adhesive powder based on copolyamides, copolyesters and polyethylenes, as well as PVC powder and mineral fillers, and finally fatty acids, paraffins, waxes, heat sensitizers, thickeners and lubricants. The powder additives promote the detachment from the wells. It is also advantageous if the pastes have a dry residue of at least 40%. Also suitable dispersions with a particularly high residue of almost 100% are spreadable plastisols made from PVC copolymers and liquid plasticizers, which are also used to cover the powder fillings in the wells and can form a suitable barrier layer. The crosslinkable dispersion pastes can also be slightly foamed to about 1.2 times the volume.

In order to avoid gelation, coagulation or drying of the applied pastes, especially when regulating the well roller surface to a raised temperature, it can be expedient to cool the funnel walls between which the paste is poured, as shown in FIGS. I, II and III with the Illustration of funnel walls through which water flows can be seen.

The squeegee (3) or (3a), with which the cells are filled with powder, should have a sharply ground brushing edge and sit with this coating edge at an obtuse angle to the side of the powder template on the cell roller. For the production of fixable interlinings for outer clothing, the doctor blade (3) or (3a) fine powder hot melt adhesive with a grain size below 100 mµ and preferably below 80 mµ should be presented as an intensely moving powder bed, the copolyamides or copolyesters are with a melting range of about 95 to 115 ° C and a melt index according to DIN 52 735 from 15 to 100 g / 10 min at 160 ° C measuring temperature and 21.6 N nozzle load.

In the powder bed, which is located in the hopper made of doctor blade (3) or (3a) and opposite wall (15), such a strong movement should take place that any bridging of the fine powder cannot occur and occur relatively quickly, for example and in 0.5 to 1 sec. Instead of a shaking device (16), a stirring rod can also be used, which rotates above the roller surface parallel to the well roller axis and is provided with pins sitting close together, the tips of which come close to the roller surface. Such a stir bar (17) is sketched in FIGS. II and V. A foam rubber roller (18), which is provided with a textile covering and which brushes the powder into the wells, can also be used according to FIG. III.

Preheat roller (13) and press roller (6) are heated to an outer jacket temperature of 150 to 200 ° C, as with conventional powder single coating. Press roll (11) can also be heated to this temperature. The surface temperature of the cup roller should be between 25 and 50 ° C in the area of the doctor blade (4) and (4a). The application weight can be varied between approx. 7 and approx. 30 g / m ² and the grid can be used between 11 and 33 mesh. The weight ratio of the base layer to the top layer can be varied between approximately 20:80 to 50:50.

The cups can be crescent-shaped. Preferably, however, the inner walls of the cells should reflect the outline of small cylindrical platelets or round disks, so that platelets or round disks also form during coating. Surprisingly, such round disks have a pronounced adhesive power that is hardly weakened when the disks are weakly smoothed. On the other hand, a weak smoothing significantly reduces the tendency to break through through thin outer fabrics. Particularly noteworthy are the high softness of the coated and thus fixed fabrics and the material savings, which can be realized with the coating according to the invention. The cups can be stamped into the surface of metal rollers using appropriate tools. However, it is advantageously possible to use a well roller which consists of an internally heatable metal roller core which is covered with a vulcanized soft rubber layer, which can also be foamed and has a thickness of approx. 1-3 mm. A screen printing stencil with a close contact is smoothly drawn on the outside. The cup fillings can be removed particularly easily with a cup roller formed in this way. Apparently, with such a screen printing stencil underlaid with a metal roller core and rubber coating, the paste covering of the powder fillings is caused to protrude somewhat raised from the now cup-shaped holes in the stencil, whereby a coherent anchoring of each individual filling is brought about completely on the fabric with the formation of a transfer-like coating.

In addition to a foamed or non-foamed rubber pad sitting directly on the metal roller, a rubber tube pulled over the roller core can be used, between which and the metal roller surface as a cushion a liquid, such as water or ethylene glycol, is pressed after covering the round screen printing stencil and which the tube presses against the template. The distance between the inner wall of the template and the metal roller surface can be approximately 1.5 to 2 mm with a rubber thickness of the hose of 1 mm.

Claims (23)

Process for the grid-like coating of sheet-like flexible sheet-like structures, such as interlinings for garments with hot-melt adhesives, by applying two grid-like adhesive layers, one on top of the other, from the base and cover layers with a lower melt flow of the base layer than the cover layer of a thermo-activatable hot-melt adhesive formed from powder, by gravure printing, characterized in that that with a cup roller provided with cup-shaped recesses (1) the hot melt adhesive powder (2) forming the cover layer on the finished product is scraped with a first doctor blade (3) or (3a) and onto this powder filling with another doctor blade (4) or (4a) a dispersion paste (5) is placed, which forms the base layer of the finished product from a plastic mass which cannot or only to a limited extent be thermally activated, and then the now double-layered cup fillings made of powder and paste with that of at least one he press roll (6) heated sheet material (7) is brought into contact and then transferred to the latter while removing the fillings from the wells. A method according to claim 1, characterized in that the dispersion paste (5) is filled with a doctor blade (4) with its coating edge (4 ') which forms an acute angle with the rounding of the engraving roll at the contact line. Method according to claim 1, characterized in that the dispersion paste (5) is filled into the wells with a sharply ground doctor blade (4a) which forms an acute angle with the rounding of the engraving roller to the side of the paste template on the doctor blade tip (4a '). Method according to one of claims 1 to 3, characterized in that the to the well roller (1) applied fabric (7) on the path from the application with the press roller (6) to the removal of the cup roller with a heated, generated by the suction device (10) and guided between the cup roller (1) and cover (9) air flow. Method according to one of claims 1 to 4, characterized in that the press roll (6) and / or press roll (11) is covered with a thin elastic layer up to about 1 mm thick, which layer consists of silicone rubber or of several layers of a fine aramid fabric, which is impregnated with silicone rubber in the outermost layer. Method according to one of claims 1 to 5, characterized in that the surface structure to be coated is enclosed in the area of contact with the well roller by a rotating belt made of thermally resistant fiber material, for example by a fabric made of aramid fibers, which belt from the press roll (6) to the press roll ( 11) is guided with tension on the cup roller (1) and then returns to the press roller (6). Method according to claim (4), characterized in that the paste applied with the aid of the doctor blade (4) or (4a) contains dispersions with finely divided crosslinkable polyacrylates, polyurethanes, polybutadiene-acrylonitriles, polybutadiene-styrene-acrylonitriles or acetate polymers. Process according to Claim 5, characterized in that the cells are filled with paste inclinations which form hot-melt adhesives which can be activated to a reduced extent and produce the base layer on the finished product with a lower melt flow than the cover layer. A method according to claim (6), characterized in that with the help of the doctor (4) or (4a) applied paste with cross-linkable portions additionally fine-particle hot-melt adhesive powder with reduced thermal activation based on copolyamides, copolyesters or polyethylenes, as well as PVC powder, mineral fillers, fatty acids. Contains waxes and thickeners. Method according to one of claims 1 to 9, characterized in that the paste applied with the aid of the doctor blade (4) or (4a) contains heat sensitizing agents. Method according to one of claims 1-9, characterized in that the paste applied with the aid of the doctor blade (4) or (4a) consists of plastisols, ie of spreadable pastes of PVC copolymers and liquid plasticizers. Method according to one of claims 1 to 11, characterized in that the paste applied with the aid of the doctor blade (4) or (4a) is poured into a funnel with cooled walls which is seated on the cup roller. Method according to one of claims 1 to 12, characterized in that the doctor blade (3) or (3a) has a coating edge with which hot-melt adhesive powder with a grain size of less than 100 mµ and preferably less than 80 mµ of copolyamides, copolyesters or polyethylene is scraped into the wells. Method according to one of claims 1 to 14, characterized in that the powder bed in front of the doctor blade (3) or (3a) is moved intensively with a vibrating device (16) comprising a vibrating bar which is equipped with a larger number of stirring arms. Method according to one of claims 1 to 12, characterized in that the powder bed in front of the doctor blade (3) or (3a) is moved intensively with a stirring rod (17) which is arranged parallel to the well roller axis and which is provided with pins sitting closely next to one another. Method according to one of claims 1 to 12, characterized in that a foam rubber roller (18) which is moved in the powder bed and is covered with a fine textile covering or a film, brushes the powder into the wells. Method according to one of claims 1 to 14, characterized in that the coating is carried out with a well roller, the wells (19) or (19a) of which represent the outline of very small round disks. Method according to one of claims 1 to 15, characterized in that the coating is carried out with a well roller, which consists of a metal roller covered with foamed or non-foamed soft rubber layer, onto which an externally ground screen printing stencil is tightened. Device for carrying out the method according to one of claims 1 to 16, which device has a cup roller (1) which can be rotated in a circular manner and has recesses arranged in a grid, which are provided with two doctor blades (3) or (3a) and (4) or () 4a) are filled with plastic masses in two superimposed layers and furthermore has a heating roller (6) which can be rotated at the same circumferential speed as the well roller and can be pressed onto the well roller, which heats the fabric to be coated and leads it to the well roller and presses it, thereby a transfer of the cup fillings to the fabric is effected, characterized in that preheating of the cup roll surface from the outside is provided between the second doctor blade (4) or (4a) and the heated press roll (6). Device for performing the method according to a of claims 1 to 16, which device has a cup roller (1) which can be rotated in a concentric manner and which has recesses arranged in a grid-like manner, which has two doctor blades (3) or (3a) and (4) or (4a) arranged one behind the other with plastic masses in two lying layers are filled and furthermore has a heating roller (6) which can be rotated at the same circumferential speed as the well roller and can be pressed onto the well roller, which heats up the sheet to be coated and brings it up to and presses against the well roller, thereby transferring the well fillings to the sheet is effected, characterized in that between the contact point of the press roll (6) and the contact point of a subsequent further press roll (11) an external heating of the surface structure resting on the cup roll surface is provided. Device for carrying out the method according to one of claims 1 to 17, characterized in that a well roller is used, the wells of which represent the outline of very small round disks (19) or (19a). Device according to one of claims 1 to 18, characterized in that the cup roller consists of an internally heatable metal roller (21) covered with a soft rubber layer (20), onto which an externally ground screen printing round template (22) is tightened. Device according to one of claims 1-19, characterized in that the cup roller consists of an internally heatable metal roller (21) on which a soft rubber tube (20) is seated, which with liquid introduced between the metal roller and the rubber tube, such as water or glycol, is applied to the ground surface that is pulled over it Screen printing round template (22) is pressed.

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