Light trap for UV radiation during the curing of ink on a printing substrate and printing press with a light trap

Description

invention

[0001] The invention relates to a light trap for UV radiation during the curing of ink on a printing material having the features of the preamble of claim 1 and to a printing machine with a light trap according to the invention according to claim 7. field of technology

[0002] The invention lies in the technical field of the graphic industry and there in particular in the field of printing and UV curing of printing fluids such as paint, varnish, primer and / or liquid ink on sheet, web, film or label-shaped printing materials, preferably made of paper, cardboard, paperboard, plastic, metal or composite material. State of the art

[0003] When printing UV inks on substrates, preferably in the so-called inkjet printing process, it is already known to cure the ink on the substrate with UV radiation. Care must be taken to prevent reflected or scattered UV radiation from reaching the inkjet print head and curing the ink on the sensitive nozzle surface. Various precautions are already known, using apertures or light traps.

[0004] DE102018210836A1 discloses a device for printing and drying printing materials. The device comprises a light trap for protecting the sensitive inkjet print heads from radiation from a dryer. A surface of the light trap facing the printing material has a comb-like structure of spaced-apart, rectangular shaped elements.

[0005] DE102019209327A1 discloses a similar device with a comb-like structure made up of spaced-apart form elements tapering towards the printing material.

[0006] EP1974936B1 discloses an inkjet printer for printing with UV ink. The printer comprises a UV radiation source and associated apertures that act as light traps. The apertures are designed as simple surfaces and can be arranged perpendicularly or at an angle other than 90° to the plane of the substrate to be irradiated.

[0007] JP2005125792A discloses a similar device. It also provides a shielding surface at an angle other than 90° to the plane of the substrate to be irradiated as a shield against radiation.

[0008] EP1579995B1 also discloses a similar device with vertical, shielding surfaces.

[0009] EP3718777 discloses a device for curing UV ink on a printing substrate. The device comprises a plurality of emitters and a plurality of optical elements, with each emitter being assigned an optical element. The optical elements are arranged in a plane between the plane of the emitters and a plane of the printing substrate. The optical elements can be pinholes. According to one embodiment, the pinholes can be provided with a so-called blaze grating on their inner walls. The blaze grating does not face the printing substrate.

[0010] JP2012116097A discloses a generic light trap having the features of the preamble of claim 1. However, such a light trap can be difficult to clean; the same applies to the light traps disclosed in documents WO2020 / 045775A1, JP2020001296A, DE60305366T2, and JP2014184666A.

[0011] The familiar light traps and baffles can still have the problem that disruptive UV radiation is not adequately shielded from the print heads, resulting in printhead failures or the need for additional cleaning steps. Both lead to production downtime and corresponding costs.

[0012] Furthermore, the well-known light traps and apertures can have the problem that they are difficult to clean due to their shape, which increases cleaning times and shortens production times, resulting in corresponding costs.

[0013] It is already known to provide light traps with an additional absorbing coating. However, even then, the problem of inadequate shielding can persist. Better coatings can be expensive, and their service life may be inadequate. Technical task

[0014] It is therefore an object of the present invention to provide an improvement over the prior art, which in particular makes it possible to further improve the UV shielding by means of the light trap and at the same time to simplify the cleaning of the light trap. Inventive solution to the problem

[0015] This object is achieved according to the invention by a device according to claim 1 and a printing machine according to claim 7.

[0016] Advantageous and therefore preferred developments of the invention emerge from the subclaims as well as from the description and the drawings.

[0017] A light trap according to the invention for UV radiation during the curing of ink on a printing material, which is moved in a transport direction (6) along the light trap, wherein the light trap comprises a shaped body with more than two successive shaped elements, wherein a side of the shaped body facing the printing material is designed in a step-like manner with step elements as shaped elements, wherein each step element comprises a pair of a step surface and a step shoulder, wherein the step surfaces and the step shoulders are different to

[0018] are inclined in the transport direction of the printing material and wherein the step surface has a step length L and the step heel has a step height H, is characterized in that the step elements are designed as flat steps with rounded transitions between the step elements, wherein the transition radius between the step surface and step heel is between 0.1 mm and 0.4 mm and where: L > 3H.

[0019] A printing machine for printing a printing substrate with a UV-curable fluid, with a print head for transferring drops of fluid onto the printing substrate and a UV emitter for curing the fluid on the printing substrate with UV light, wherein at least one light trap for UV light is arranged between the print head and the emitter on one side of the printing substrate and / or wherein at least one light trap for UV light is arranged on the other side of the printing substrate, is characterized in that the light trap is designed according to the invention. Advantageous embodiments and effects of the invention

[0020] The invention advantageously makes it possible to further improve the UV shielding by means of the light trap and at the same time to simplify the cleaning of the light trap.

[0021] The inventive shape of the body differs significantly from existing comb-like shapes. It was discovered through testing and computer simulations and has been further optimized. The flat shape surprisingly results in better shielding from UV radiation, while simultaneously allowing for easier cleaning of the molded surface of the body. Sharp edges, which are usually present in comb-like shapes, can be avoided, significantly reducing the risk of injury during manual cleaning. Existing configurations with, for example, the comb-like shapes can be easily retrofitted.

[0022] The stair-step arrangement of the step elements improves the effect as a light trap: less scattered and / or reflected UV radiation reaches the print heads and curing of ink on the sensitive nozzle surface or in the nozzle openings can be avoided.

[0023] The step elements are preferably substantially identical in shape, particularly preferably identical. The step elements are flat, i.e., at least twice and in particular at least three times as long as they are high. This flat shape is particularly advantageous in terms of the shielding effect and, at the same time, ease of cleaning. The step elements are preferably inclined in or against a transport direction of the printing substrate and / or with respect to an opposite plane of the printing substrate, particularly preferably only slightly inclined, i.e., less than 10° (or 180°-10°). The transitions between the step elements are preferably rounded.

[0024] A step element with L > 3H can be described as a flat step. Extensive computer simulations conducted during the further development of the light trap have surprisingly shown that a design according to the invention with L > 3H significantly improves the effectiveness of the light trap: "Flat" steps are therefore more effective and therefore preferred. Further developments of the invention

[0025] Preferred further developments of the light trap according to the invention (short: further developments) are described below.

[0026] A further development can be characterized in that the molded body is arranged opposite a printing substrate transported in a transport direction along the light trap, preferably at a distance. The distance can be chosen to be larger than in the prior art when using comb-like structures.

[0027] A further development can be characterized by the fact that the shaped body is arranged in a stationary manner.

[0028] A further development can be characterized in that an angle between the step surface and the (upstream or downstream) step landing is preferably chosen in the range of approximately 90°.

[0029] A further development can be characterized by the step elements following one another in or against the direction of transport. A further development can be characterized by the step elements following one another directly. A further development can be characterized by the step surfaces and step landings following one another in or against the direction of transport. A further development can be characterized by the step surfaces and step landings following one another directly. A further development can be characterized by the step surfaces and step landings following one another alternately; for example, long step surfaces and short step landings can alternate.

[0030] A further development can be characterized in that a) the step surfaces are inclined in the transport direction and the step heels are inclined against the transport direction, or b) the step surfaces are inclined against the transport direction and the step heels are inclined in the transport direction. The inclined step surface is preferably closer to the horizontal, and the inclined step heel is preferably closer to the vertical. For example, it can be provided that the step surfaces face the spotlight and the step heels face away from the spotlight.

[0031] A further development can be characterized in that the step surfaces are a) inclined by less than 90° or b) by more than 90° to the direction of transport. A further development can be characterized in that the inclination of the step surfaces a) is in the range between 4° and 10° or between 5° and 9° or between 6° and 8° or b) is in the range between 176° and 170° or between 175° and 171° or between 174° and 172°. A further development can be characterized in that the inclination of the step surfaces is a) 7° or b) 173°.

[0032] A further development can be characterized by the fact that the step edges are a) inclined by more than 90° or b) less than 90° to the direction of transport. A further development can be characterized by the fact that the inclination of the step edges a) lies between 99° and 95° or between 98° and 96° or b) lies between 78° and 88° or between 81° and 85°. A further development can be characterized by the fact that the inclination of the step edges a) lies at 97° or b) lies at 83°.

[0033] The aforementioned case distinctions a) and b) can be understood as follows: case a) describes a light trap which is arranged directly upstream of a radiator in the transport direction of the printing material (printing material first passes the light trap and then the radiator) and case b) describes a light trap which is arranged directly downstream of a radiator in the transport direction of the printing material (printing material first passes the radiator and then the light trap).

[0034] A further development can be characterized by the following: L > 4H, L > 5H, or L > 10H. A further development can be characterized by the step length being between 6.00 mm and 6.30 mm, or between 6.05 mm and 6.25 mm, or between 6.10 mm and 6.20 mm, or 6.15 mm.

[0035] A further development can be characterized by the fact that the transition radius between the step surface and the step heel is between 0.2 mm and 0.3 mm or 0.25 mm.

[0036] A further development can be characterized by the step elements being provided with an absorbent coating.

[0037] A further development can be characterized in that the molded body is designed in such a way that it reduces UV light emitted by a UV ink dryer and reflected and / or scattered by a printing material printed with ink.

[0038] A further development of the printing machine can be characterized by the fact that the light trap is arranged at a distance of 0.4 mm to 0.9 mm from the printing material.

[0039] A further development of the printing machine can be characterized by the fact that a web of paper, cardboard, paperboard, plastic film or metal foil or a web equipped with labels is provided as the printing material.

[0040] A further development of the printing machine can be characterized by the fact that two light traps are present, with one light trap being arranged in front of the spotlight and one light trap being arranged after the spotlight in the transport direction of the printing material. List of reference symbols

[0041] 1Printing machine 2Ink print head(s) 3Lamps / UV ink dryers 4Transport rollers 5Printing material 6Transport direction 7Ink / Fluid 10Light trap(s) 10aFirst light trap 10bSecond light trap 10cFurther light traps 11Shaped body 12Side of the shaped body 13UV radiation / UV light 14Reflected and / or scattered radiation 20Step elements (as form elements) 21Stair-shaped arrangement 22Zigzag line 23Pair 24Step surface 25Step landing 26Coating WAngle, e.g. W1 and W2 LStep length HStep height RTransition radius ADistance to the substrate

Claims

1. Light trap for UV radiation for curing ink on a printing substrate which is moved along the light trap in a transport direction (6), wherein the light trap (10) comprises a molded body (11) with more than two successive mold elements (20), wherein a side (12) of the molded body (11) facing the printing substrate (5) is constructed in the form of steps (21) with step elements (20) as mold elements, wherein each step element (20) comprises a pair (23) of a step surface (24) and a step shoulder (25), wherein the step surfaces (24) and the step shoulders (25) are inclined differently to the transport direction (6) of the printing substrate (5) and wherein the step surface (25) has a step length L (L) and the step shoulder has a step height H (H), characterized in that the step elements (20) are constructed as flat steps with rounded transitions between the step elements, wherein the transition radius between the step surface and the step shoulder is between 0.1 mm and 0.4 mm, and wherein the following applies: L > 3H.

2. Light trap according to one of the preceding claims, characterized in that the step elements (20) follow one another in or against the transport direction (6).

3. Light trap according to claim 2, characterized in that the step surfaces (24) and step shoulders (25) follow one another in or against the transport direction (6).

4. Light trap according to any one of claims 2 or 3, characterized in that a) the step surfaces (24) are inclined in the transport direction (6) and the step shoulders (25) are inclined against the transport direction (6) or b) the step surfaces (24) are inclined against the transport direction (6) and the step shoulders (25) are inclined in the transport direction (6).

5. Light trap according to claim 4, characterized in that the step surfaces (24) are inclined a) less than 90° or b) more than 90° to the transport direction (6).

6. Light trap according to claim 4, characterized in that the step shoulders (25) are inclined a) more than 90° or b) less than 90° to the transport direction (6).

7. Printing press for printing a printing substrate with a UV-curable fluid, with a print head (2) for transferring drops of fluid (7) onto the printing substrate (5) and a UV radiator (3) for curing the fluid (7) on the printing substrate (5) with UV light (13), wherein at least one light trap (10, 10a, 10b) for UV light (13) is arranged between the print head (2) and the UV radiator (3) on one side of the printing substrate (5) and / or wherein at least one light trap (10, 10c) for UV light is arranged on the other side of the printing substrate (5), characterized in that the light trap (10) is constructed according one of the preceding claims.

8. Printing press according to claim 7, characterized in that the light trap (10) is arranged at a distance (A) of 0.4 mm to 0.9 mm from the printing substrate (5).