EP1991031A1 - Printing paste and its use for manufacturing an electro-luminescent film - Google Patents

Abstract

Printing paste (I) for the production of electroluminescent layers (3) on deep-drawable plastic film (1), contains (a) a UV-curable, acrylate-based printing varnish, (b) inorganic electroluminophores and (c) a plasticiser. Independent claims are also included for (1) a method for the production of electroluminescent film by making deep-drawable plastic film with a first electrically-conductive layer (2), forming an electroluminescent layer (3) by applying the paste (I) and exposing it to UV light and then forming a second conductive layer (5) (2) electroluminescent film obtained by this method .

Description

The present invention relates to a printing paste, in particular a printing paste for the production of an electroluminescent layer on a thermoformable plastic film. Furthermore, the present invention relates to a method for producing an electroluminescent film in which an electroluminescent layer is produced on a thermoformable plastic film.

Electroluminescent films with inorganic luminescent pigments (also referred to as electroluminophores) are widely used as flat illuminants, for example for the backlighting of displays, the backlighting of control elements and the like. The structure of an electroluminescent film always comprises a film substrate, two electrode layers and an electroluminescent layer arranged between the electrode layers, which contains the electroluminophores. The latter are often microencapsulated, incorporated into a binder matrix and can be composed, for example, of zinc sulfides which, depending on doping or co-doping and preparation process, produce different, relatively narrow-band emission spectra.

The luminescence is caused by an alternating electric field, which is created by applying the electrode layers to an AC voltage source.

Most electroluminescent films are constructed by printing technology, i. a suitable, possibly already conductive coated (such as ITO vapor-deposited or sputtered) plastic film substrate is printed with the necessary to create an electroluminescent structure layers.

In practical application, for example in the lighting of controls in the automotive industry, there is often the desire not only a flat or slightly curved surface backlight; but use more curved, possibly even complex three-dimensionally shaped lighting surfaces.

Here, the technology used so far often reaches its limits, especially if the molded surfaces are also to be back-injected to improve the mechanical stability and to better seal against environmental influences.

The conventionally preferably used printing pastes require high drying temperatures, which often prevents or at least severely restricts the use of heat-sensitive plastic film substrates. In the rear injection with hot masses, the problem is compounded.

So far, the use of heat-stabilized PET or PC films, which are printed with solvent-based systems, and exposed to about six to ten minutes drying at 120 ° C manages.

However, the possibilities for deformation, for injection molding and press laminating are still very limited in such conventional electroluminescent films. So the process temperatures must still be kept as low as possible. Furthermore, the possible depth of both concave and convex formations is severely limited to avoid loss of quality or even failure of the finished illuminant.

The present invention is therefore based on the object to provide opportunities for printing in particular good deformable and hinterspritzbarer electroluminescent, and thereby allow the user as possible free choice of material when using the Kunststoffoliensubstrats.

According to one aspect of the present invention, this object is achieved by means of a printing paste according to claim 1. Advantageous embodiments may be designed according to one of claims 2-7.

According to a further aspect of the present invention, the underlying object is achieved by a method according to claim 8. Advantageous embodiments of the method according to the invention can be configured according to one of claims 9-24.

According to another aspect of the present invention, the underlying object by an electroluminescent film according to claim 25.

In principle, any variant of the invention described or indicated in the context of the present application may be particularly advantageous, depending on the economic and technical conditions in the individual case. Unless otherwise stated, or as far as technically feasible, individual features of the described embodiments are interchangeable or can be combined with one another and also with measures known per se from the prior art.

In the following, it will be explained in more detail, with the aid of the attached drawing, by way of example, how particularly preferred embodiments of the present invention can be carried out. The drawing is a purely schematic and, for the sake of clarity, not to scale representation. In particular, ratios of dimensions to each other may differ from actual embodiments. For example, the thickness of individual film layers or layers is greatly exaggerated.

It shows Fig. 1 a deep-drawable electroluminescent film which can be produced by a process according to the invention.

example

The illustrated example makes it possible to provide a deep drawable, re-sprayable electroluminescent film, i. in particular, to design an electroluminescent layer structure such that it can also be printed on heat-sensitive materials such as, for example, PMMA, PVC and (in particular not heat-stabilized) PC. Also for the creation of a backlighting of lenticular sheets, the invention is particularly suitable.

The application of the individual layers can be carried out batchwise or continuously in strip mode. A mixture of both modes is possible.

First, an at least partially transparent or even clear plastic substrate 1 is provided, which is provided with a conductive layer 2. This can be generated beforehand by printing with a water-based organic conductive ink (or otherwise applying the same). The substrate thickness may preferably be 175 to 800 micrometers.

On the conductive layer 2, the electroluminescent layer 3 is applied. Under certain circumstances, however, it may be advantageous to apply a non-conductive intermediate layer (not shown) before the electroluminescent layer 3 is produced.

To produce the electroluminescent layer 3, a printing paste is used, which is preferably applied to the conductive layer 2 (or the above-mentioned intermediate layer) by means of screen printing, but possibly also with another suitable technique.

The basis of the printing paste is a known, transparent, acrylate-based UV printing varnish, as it is commercially available in many types, for example under the name DMU TYPE (2240563_02) (manufacturer COATES SCREEN INKS GmbH) . An advantageous composition may comprise 25-50% of monoalkyl or monoaryl or monoalkylaryl esters of acrylic acid, 25-50% of other acrylates and 10-25% of 1-vinyl-2-pyrrolidine (EC No. 201-800-4; CAS-No 88-12-0) (in percentage by mass). The UV printing varnish is mixed with the latter at least in the ratio of two parts by weight to three parts by weight of electroluminophores (also referred to as EL phosphors or luminescent pigments). The highest Anpastverhältnis is two parts by weight of electroluminophores to a part of printing ink, otherwise there is no sufficient adhesion to the substrate.

The selection of the (known per se) electroluminophores as in conventional inorganic electroluminescent depending on the desired luminous properties, in particular luminescent color.

Due to the high pigment enrichment and resulting layer thickness of about 35-45 micrometers, the deformability would be significantly impaired. To compensate for this, a phthalic acid plasticizer (commercially available, for example, Benzyloctyl phthalate type Santicizer 261A from the supplier Ferro) is added in a proportion of at least 0.2% by weight to at most 1.5% by weight.

If the paste is printed directly onto the conductive layer 2 of water-based organic conductive ink, it is preferred to use a silane coupling agent in order to achieve good adhesion and temperature resistance (also against about 265 ° C hot injection molding compound with subsequent back molding). This has two different activatable molecule branches. One side reacts with the atoms on the printed Leitlackschicht 2 to a solid compound. The other side reacts with the resin molecules of the printing paste. The minimum amount of adhesion promoter to the printing paste is 0.1 Weight percent; the maximum amount added is 0.7 weight percent to ensure ductility.

By applying, preferably printing a dielectric paste, the dielectric layer 4 is formed. For the dielectric paste is preferably selected a similar composition as for the printing paste. Instead of the luminescent pigments, however, a filler, preferably a mixture of barium titanate and titanium dioxide, is used here. In order to achieve the highest possible relative dielectric constant (εr value), the barium titanate content should be at least 80 percent by weight. The remaining 20 percent of titanium dioxide serve for white pigmentation, as a result of which the dielectric layer 4 also has the function of a reflector layer. Minimum paste ratio is two parts by weight of filler to one part by weight (acrylate-based, UV-curable) pressure varnish. The maximum pasting ratio is 13 to 5 parts by weight. Preferably, a plasticizer, in particular a plasticizer of the type mentioned above is also added here. A particularly good homogenization is possible with this mixture with a three-roll mill with the smallest possible gap width adjustment and multiple passes.

By using UV radiation, a stack-dry state is achieved, the optimal adhesion, chemical resistance, temperature resistance is achieved by a thermal post-drying, either each single layer or even after pressure of all layers, under certain circumstances by subsequent injection back with correspondingly hot spray mass.

The back electrode 5 can advantageously be produced by applying (preferably by pressure) a highly filled silver conductive paste already used for conventional electroluminescent elements.

A highly filled silver conductive paste reflects UV radiation so strongly that drying through at belt speeds of about three meters per minute, which is advantageous in order to avoid excessive substrate heating, is no longer guaranteed. As a remedy, the pressure of the back electrode 5 in two thin layers (screen-printed fabric such as polyester 130 S) with the addition of a photoinitiator in an amount of 0.1 weight percent to a maximum of 2 weight percent can be done here. The initiator is in particular a mixture of 2-hydroxy-2-methyl-1-phenyl-1-propanone and 2,4,6-Trimethylbenzoyldiphenylphosphinoxid in question, if the emission width of commercial emitters to be covered. The selected photoinitiator excess accelerates the reactivity and at the same time improves the ink adhesion by better pronounced depth hardening. The photoinitiator is yellowing free and thus does not affect the color location of the electroluminescent film used as a light source.

It is preferable to pre-dry the electroluminescent sheet printed above as before the deforming of the electroluminescent sheet and, if appropriate, subsequent injection of the deformed electroluminescent sheet at 50 ° C. for at least 48 hours, in order to avoid bubble formation.

Claims (25)

Printing paste for the production of an electroluminescent layer (3) on a thermoformable plastic film (1), wherein the printing paste a UV-curable, acrylate-based printing lacquer, - inorganic electroluminophores and - a plasticizer as constituents. A printing paste according to claim 1, wherein the ratio of the mass fraction of the electroluminophores to the mass fraction of the printing ink is at least 3 to 2 and at most 2 to 1. Printing paste according to one of the preceding claims, wherein the plasticizer comprises a phthalic acid derivative. Printing paste according to one of the preceding claims, wherein the mass fraction of the plasticizer to the printing paste is at least 0.2 percent and at most 1.5 percent. Printing paste according to one of the preceding claims, to which a bonding agent is added. Printing paste according to claim 6, wherein the mass fraction of the adhesion promoter to the printing paste is at least 0.1 percent and at most 0.7 percent. Printing paste according to one of the preceding claims, wherein the adhesion promoter is a silane coupling agent. Process for producing an electroluminescent film, comprising the following steps: Providing a thermoformable plastic film provided with a first electrically conductive layer (2), Producing an electroluminescent layer (3) by applying a printing paste according to one of claims 1-7 and subsequent exposure to UV radiation, Producing a second electrically conductive layer (5) A method according to claim 8, wherein the plastic film comprises a film substrate (1) consisting predominantly of polyvinyl chloride, polymethyl methacrylate, polycarbonate or polypropylene. The method of any of claims 8-9, wherein providing the plastic film comprises applying a water-based organic conductive ink to a film substrate (1). A method according to any one of claims 8-10, wherein prior to the application of the second electrically conductive layer (5), a dielectric layer (4) is produced by applying a paste. The method of claim 11, wherein a paste is applied, which a UV-curable, acrylate-based printing lacquer, inorganic filler and - a plasticizer as constituents. A method according to claim 12, wherein the filler used contains a white pigment. Process according to claim 13, wherein the filler used is a mixture of barium titanate and titanium dioxide. The method of claim 14, wherein the ratio of the mass fraction of the barium titanate to the mass fraction of the titanium dioxide is at least 80 to 20. A method according to any one of claims 12-15, wherein the ratio of the mass fraction of the filler to the mass fraction of the pressure varnish is at least 2 to 1 and at most 13 to 5. A method according to any one of claims 8-16, wherein the second electrically conductive layer (5) is produced by applying a silver conductive paste. A method according to claim 17, wherein the silver-conductive paste is applied in two layers, A method according to claim 18, wherein the silver conductive paste is added with a photoinitiator. A process according to claim 19, wherein the photoinitiator contains 2-hydroxy-2-methyl-1-phenyl-1-propanone and / or 2,4,6-trimethylbenzoyldiphenylphosphine oxide. A method according to any one of claims 19 or 20, wherein the silver conductive paste is added at least 0.1% by mass and at most 2% by mass of photoinitiator. A method according to any one of claims 8-21, wherein a drying of at least 24 hours at least 40 ° C and at most 60 ° C takes place. A method according to any one of claims 8-22, wherein the electroluminescent film is plastically deformed after forming the second electrically conductive layer (5). A method according to claim 23, wherein the electroluminescent film is back-injected after molding. An electroluminescent film produced by a method according to any one of claims 8-24.

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