EP0044855B1 - Method and device for coloring or printing elongated articles - Google Patents

Abstract

Method and device for decorating (printing) elongated articles particularly the ski sliding surfaces of thermoplastic materials such as olefins and the like where the coating (2, 22, 42) is brought, while being exposed to heat, on a printed carrier (3, 23, 43) on which a printed image has been previously formed by means of a sublimated and diffused colouring matter. The printed carrier is pressed by means of an endless belt against the coating (2, 22, 42). Finally follows an annealing at a controlled temperature in order to release all internal stresses of the coating (2, 22, 42). By this method and the device for its application, a printing without the distortions especially on polyethylene coatings may be achieved.

Description

The invention relates to a method for dyeing or printing sheet-like objects, in particular ski coverings, from thermoplastics, such as olefins, in particular high and low pressure polyethylene.

• - Der Mittelbau besteht im allgemeinen aus einem Holz- oder Hartschaum-Kern, der seitlich mit duroplastischem Kunstharz-Schichtstoff kaschiert ist;
• - der Oberbau besteht meistens aus einem mit dem Kern verklebten Aluminiumblech und/oder Laminat aus glasfaserverstärktem Kunststoff (GFK), worauf als Deckbelag eine Kunststoff-Folie aufkaschiert ist, die in weiteren Arbeitsvorgängen dekorativ ausgestaltet wird;
• - der Unterbau besteht seinerseits aus einem Aluminiumblech oder einer Schicht aus glasfaserverstärktem Kunststoff (GFK), das bzw. die an einer Seite mit dem Kern verklebt ist und an der anderen Seite (gegebenenfalls über verschiedene weitere Schichten) schliesslich mit dem eigentlichen Lauf-Belag verklebt ist, der im allgemeinen ein transparenter 1 bis 2 mm dicker Kunststoff-Belag ist, und zwar vorzugsweise aus Polyäthylen, nämlich Hoch- oder Niederdruck-Polyäthylen, oder Polytetrafluoräthylen [Teflon (Wz)].

It has been known for a long time that so-called multi-layer skis have been produced by gluing several layers (see, for example, DE-OS 2 804 943), which in turn form a lower, middle and upper structure.

• - The middle section generally consists of a wood or hard foam core, which is laminated on the side with thermosetting resin laminate;
• - The superstructure mostly consists of an aluminum sheet and / or laminate made of glass fiber reinforced plastic (GRP) glued to the core, whereupon a plastic film is laminated on as a cover, which is decoratively designed in further work processes;
• - The substructure in turn consists of an aluminum sheet or a layer of glass fiber reinforced plastic (GRP) that is glued to the core on one side and finally glued to the actual tread on the other side (possibly via various other layers) is, which is generally a transparent 1 to 2 mm thick plastic covering, and preferably made of polyethylene, namely high or low pressure polyethylene, or polytetrafluoroethylene [Teflon (Wz)].

Normally, the inside of the tread (or the decking) is printed to reflect the ski manufacturer, type designations, etc. in particular; this pressure is then visible through the transparent covering.

So far, only high and low pressure polyethylene ski bases have been used.

• - Es wird stückweise, also nicht kontinuierlich bzw. endlos, vorgegangen, nämlich durch Siebdruck (von Mustern, Schriftzügen oder dgl.) mit Epoxid-Druckfarben, wobei zusätzlich der Belag vor dem Bedrucken vorbehandelt werden muss, z.B. thermisch (Beflammen), elektrisch (Korona-Entladung) oder chemisch (Ätzen), da sonst die (Epoxid-) Druckfarbe nicht haften würde.
• - nach dem Bedrucken muss etwa 10 bis 20 Stunden lang getrocknet werden, worauf dann der bedruckte und getrocknete Belag zum weiteren Dekorieren mit einer opaken (gefärbten) epoxidhaltigen Vergussmasse (einem opaken Decklack) einschliesslich Härter abgegossen wird, um eine Hintergrundfarben-Schicht für den transparenten Belag zu schaffen;
• - diese Vergussmassen-Schicht wird dann mittels eines Klebers normalerweise mit einer Schicht aus glasfaserverstärktem Kunststoff (GFK) verklebt, allerdings erst nach einigen Stunden, nachdem aus der Vergussmasse vollständig das Lösungsmittel, entwichen, also die Masse ausgehärtet ist.

Decorating, in particular printing, such coverings and further processing has so far been very complex and yet often with poor print quality.

• - The process is carried out piece by piece, i.e. not continuously or endlessly, namely by screen printing (of patterns, lettering or the like) with epoxy printing inks, whereby the covering must also be pretreated before printing, e.g. thermally (flaming), electrically ( Corona discharge) or chemical (etching), otherwise the (epoxy) printing ink would not adhere.
• - After printing, it has to be dried for about 10 to 20 hours, after which the printed and dried covering is poured off for further decoration with an opaque (colored) epoxy-containing potting compound (an opaque top coat) including hardener to form a background color layer for the transparent Creating topping;
• - This potting compound layer is then normally glued to a layer of glass fiber reinforced plastic (GRP) by means of an adhesive, but only after a few hours after the solvent has completely escaped from the potting compound, that is to say the mass has hardened.

Despite this particularly complex manufacturing process, it has so far not been possible to ensure consistent print quality in the finished ski.

• - unzureichende Haftungs-Vorbehandlung des Belags vor dem Bedrucken;
• - Angreifen des Druckbilds durch den Kleber, so dass sich Farbtöne ändern, die Konturen des Druckbilds verschwimmen oder Risse innerhalb des Druckbilds auftreten;
• - mangelnde Elastizität der Vergussmasse gegenüber dem Belag bzw. unzureichende Haftung der opaken Vergussmasse am z.B. Polyäthylen des Belags, so dass das Ablösen der Vergussmasse sich in hellen Flecken auf der Laufflächen-Seite äussert;
• - unzureichendes Abdunsten des Lösungsmittels aus der opaken Vergussmasse, so dass dieses . durch Blasenbildung zusätzlich Haftungsschwierigkeiten zwischen der Vergussmasse und dem z.B. Polyäthylen des Belags und damit unschöne helle Flecken verursacht.

The following are particularly numerous errors that often occur quite late, namely 3 to 10 months after the ski was manufactured:

• - insufficient pre-treatment of adhesion of the covering before printing;
• - attack of the print image by the adhesive, so that color tones change, the contours of the print image blur or cracks occur within the print image;
• - lack of elasticity of the casting compound with respect to the covering or insufficient adhesion of the opaque casting compound to, for example, polyethylene of the covering, so that the detachment of the casting compound manifests itself in bright spots on the tread side;
• - insufficient evaporation of the solvent from the opaque potting compound, so that this. due to the formation of bubbles, additional difficulties in adhesion between the casting compound and, for example, the polyethylene of the covering, and thus unsightly bright spots.

Difficulties similar to those for the running covering occur when an appropriate covering to be decorated is used as the covering covering.

These difficulties are still a serious problem (despite at least about 10 years of experience) because the sources of error have not been researched in detail, so that ski buyers often complain to the ski manufacturers.

Finally, despite all the effort, even the print quality that can be achieved at best is very limited to only relatively coarse-structured print images, i.e. printing halftone photographs is practically impossible.

From DE-OS 2 804 943 it is still known to apply an adhesive varnish produced on the basis of a certain copolymer and an epoxy resin and provided with fillers and dyes, which simultaneously functions as an opaque potting compound (opaque topcoat) and adhesive (cf. above); As a particular advantage of this adhesive varnish, it is claimed that it has a practically unlimited drip time at room temperature, which is why it is possible to store a large number of running surfaces with an adhesive varnish layer after printing and then add any according to the respective requirements Time to process the finished ski.

With this process, which has only recently become known, a single process step is saved at most, without, however, changing anything in principle in the time-consuming, piece-wise and risky production of ski coverings (running and cover coverings) or similar sheet-like objects.

The transfer printing process has also proven to be relatively complex and difficult to control DE-OS 2 642 350, in which, in order to avoid migration promotion, the surface to be printed on high-pressure and low-pressure polyethylene is previously provided with a dye-affine thermoplastic layer, such as a polyurethane or polyester layer, which can be printed without difficulty is.

DE-OS 2 731 121 now teaches, among other things, to print on polyethylene in that the side to be printed on a molded body made of polyethylene is subjected to a heat effect, which causes the side to be printed to melt, in contact with a printing medium, e.g. Paper print carrier is brought onto which a print image of dyes that have first been sublimed and then diffused in has been applied beforehand. 160 to 220 ° C. is stated as an advantageous temperature. The pressure carrier should be brought into contact with the molded body under light and long-term pressure (cf. page 6, paragraph 2 of DE-OS2 731 121). It has been shown that exactly the same migration problems occur under the conditions specified in DE-OS 2 731 121, which DE-OS 2 642 350 seeks to avoid by coating the side to be printed beforehand separately. It has also been shown that the depth of penetration of the dyes is barely perceptible, so that a permanent printed image is not obtained. The reason for this apparently lies in the use of only a «light» contact pressure between the print carrier and the side of the molded body to be printed. When using higher contact pressures, obviously major migration problems are expected.

When reworking the method described in DE-OS 2 731 121, it is also found that the melting of the surface to be printed on in the shaped body creates such large thermal stresses (stress peaks) that printing on relatively thin-walled, e.g. sheet-like objects, in particular ski coverings, is not possible without additional treatment to achieve an internal tension compensation. In the area of the boundary line between the melted pressure side and the bottom, which is still in a solid state, there is an extreme voltage drop, which leads to warping of the printed surface during normal cooling.

Finally, DE-OS 2 731 121 likewise gives no suggestion for continuous printing of sheet-like objects of the type in question here.

Furthermore, a method according to the preamble of claim 1 is known from US-A-4 138 945. With this method, a flat ink transfer is carried out with low contact pressure and without an annealing process, which leads to blurred printed images on rejected objects.

The present invention has for its object to provide a method of the type mentioned, which ensures sharp, distortion-free brilliant prints and in which no warping problems occur after the color transfer.

According to the invention, the object is achieved by the teaching according to the characterizing part of claim 1.

The present invention represents a method which ensures an intensive, migration-free penetration of the dyes into the printed object. Surprisingly, migration is avoided by using a high line pressure of approximately 20 to 30 N / cm.

The temperature-controlled tempering avoids the warpage problems that are otherwise unavoidable with thin-walled objects.

It is particularly advantageous that, according to the invention, the side of the covering opposite the printing side can be embossed simultaneously with the printing.

By laminating the printed covering with a transparent or bright adhesive onto a reinforcing material layer, the color strength of the printing (color strength) can be increased further or a better color contrast can be achieved. In addition, this lamination or gluing enables a slight transfer of printing ink from the covering (film) into the adhesive and / or the reinforcing material layer, which "fixes" the printed image even more deeply in the finished composite component.

The invention is explained in more detail below with reference to the drawing.

A film-like covering that has been unwound from a supply roll 1 and is to be printed runs simultaneously with a print carrier 3, which in turn has been unwound from a supply roll 4, into a largely known (see e.g. NL-A-7 509 513) double-belt press. The covering can later be used as a ski-topping or ski-covering, floor covering, wall covering or the like.

The double belt press has two endless belts 5 and 6 arranged one above the other, which must be high-strength and therefore preferably consist of steel. The belts 5 and 6 run around deflection or drive rollers 7 and 8 or 9 and 10 in synchronism. For a constant belt tension e.g. hydraulically controlled belt tensioning devices (not shown) are provided.

The double belt press also has a combined contact heat treatment device 12 which is divided into a plurality of sections 12a-12d in order to apply the contact pressure or temperature to the film-like covering 2 and the pressure carrier 3 separately in each section. The contact pressures are generated by hydraulic or pneumatic cylinders 14, which act on the covering 2 and the pressure carrier 3 via contact rollers 13, which in turn are supported by a contact table 11. The first pressure roller 13 causes a relatively high line pressure of approximately 20 to 30 N / cm. The separate temperature setting is carried out by heat treatment plates 15 in the vicinity of the covering 2 and the pressure carrier 3, the temperature being the highest in the first section 12a. The heat treatment plates 15 in the (in the conveying direction) first three sections 12a to 12c serve to supply heat to the covering 2 and to the pressure carrier 3 (ie as heating sections). In the last section 12d, the heat treatment plate 15 is used for heat discharge (cooling section). The heat treatment plates 15 (ie in sections 12a to 12c) can be heated, for example, by τhermo-oil.

It goes without saying that the number of sections 12a to 12d (here four) and the contact pressure and temperature distribution are selected depending on the material to be processed.

Annealing takes place in the remaining sections 12b to 12d following the first section 12a in order to fix the diffused dyes and to achieve an internal tension compensation of the printed covering.

Claims (9)

1. A process for dyeing or printing weblike articles (2) by transferring, from a continuously moving print carrier (3) to which a printed image made up of first sublimable and then diffusing dyestuffs has been applied, the colour under the action of heat and pressure to the article (2) continuously moving in the same way, by melting the weblike article (2) on the side to be printed and pressing the print carrier (3) under the action of an endless belt (5, 6) against this side of the article (2) in such a way that the print carrier (3) rests against that side of the article (2) to be printed without an intermediate layer inbetween, characterised inthat weblike articles (2), in particular ski coatings, made of olefines, in particular highpressure and low-pressure polyethylene, are dyed or printed by transferring the colour to the weblike article (2) under the action of a line pressure of about 20 to 30 N/cm at a right-angle to the common transport direction of the article and the print carrier and in that the printed article (2') is then heat-treated to equalise internal stresses.

2. The process according to claim 1, characterised in that the print carrier used is made of metal, plastics material or pretreated paper.

3. The process according to claim 1 or 2, characterised in that the dyestuffs used are light-fast dyestuffs known per se.

4. The process according to any one of claims 1 to 3, characterised in that the print carrier is brought to rest against the coating under controlled pulling tension.

5. The process according to any one of claims 1 to 4, characterised in that the coating and the print carrier are passed inbetween two revolving endless belts of a twin-belt press.

6. The process according to any one of claims 1 to 5, characterised in that, before the printing, the coating is passed over a preheating roll and the print carrier is passed over a heating roll, and, after the printing, the printed coating is passed over a cooling roll close to where the print carrier is moved away from the position where it was resting against the coating.

7. The process according to any one of claims 1 to 6, characterised in that the printed coating is aftertreated by means of:

- high-frequency corona discharge,

- surface-oxidising flame treatment or chemically, by means of a primer.

8. The process according to any one of claims 1 to 7, characterised in that the printed coating is laminated onto a layer of reinforcing material which is made of, for example, light-coloured glassfibre-reinforced plastic, by means of a transparent or pale adhesive, in particular a polyurethane adhesive.

9. The process according to any one of claims 1 to 8, characterised in that the coating (2) is simultaneously embossed by means of that rotating endless belt (5) with which it is in contact.

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