MXPA97008479A - Device for hardening a layer on a sustr - Google Patents

Abstract

According to the invention, a radiation-hardening layer is located on the surface of a substrate of paper, glass, plastic, wood or metal, the layer on the substrate, which is guided through a step of hardening, it is subjected to radiation with ultraviolet light at the same time that the lamp chamber is directly flooded with a gas. The layer can be tempered and turned inert at the same time be treated in an active chemical way.

Description

DEVICE FOR HARDENING DMA CAPA ON A SUBSTRATE The invention relates to a device for hardening a layer applied on a substrate according to the main concept of claim 1. The invention is concerned with the treatment of substances, especially dyes containing as a monomer a double bond which must be polymerized with ultraviolet light. It is known to polymerize double bonds with electrons or cationically. In order for the ultraviolet irradiation to be able to start the photoreaction, in the mixture subject to treatment, for example, of a dye, a so-called photoinitiator is needed. This photoinitiator is used in an excess so that the polymerization reaction initiated by ultraviolet light is not interrupted to the extent that the dye radical reacts with the oxygen di-radical. Therefore, to date, a relatively high concentration of the photoinitiator has been working so that the probability for a dye radical to impinge on an oxygen radical to be penetrated by it, and against the probability of touching it, becomes relatively lower. another monomer with double bond radicalizing it.

Central roll machines are known with which different dyes are applied on a paper web or on a plastic film, each layer being dried before applying the next dye layer. To dry these different layers of dyes ultraviolet light irradiators are used and cooling is done with air. In this case, an ultraviolet lamp with an outside temperature of the order of 800 ° C is cooled by suction of the air passing through the lamp. A drawback in this construction is the continuous generation of ozone, the movement of large amounts of contaminant particles and the heating of the coated substrate, which especially in the case of heat sensitive plastic films can lead to serious defects. Deviations or variations in the known cooling system by cooling by water around or in front of the ultraviolet lamp lead to yield losses. In the meantime, buildings with a water-cooled housing and reflector and reflector are being used, and possibly also with a counter-pressure cylinder, cooled with water, with successful results. It is true that this way of building can be used from the technical point of view of heat, but do not move particular pollutants if ozone is not generated, however in the case of cooling with water surrounding the ultraviolet lamp one should have with considerable losses in terms of performance. European Patent EP-AO 161 540 discloses a method for hardening a hardenable silicone layer that is applied to a substrate surface consisting of paper, the layer present in a driven substrate being subjected to a hardening step. to an irradiation with ultraviolet light under rinsing of the area where the ultraviolet lamp with gas is. In this case, the space of the ultraviolet lamp is separated from the hardening zone through which the substrate is conducted by means of a quartz glass sheet, in a gas-proof manner. The cooling gas, preferably air, is blown into the interior through the side walls of the chamber constituting the space of the ultraviolet lamp and from this latter chamber is removed by a discharge conduit. Nitrogen, as an inert gas, is introduced separately into the hardening space, in which, by means of the particular lock assembly, it is ensured that the entry of oxygen from the air into the hardening space is not possible. In this known equipment, which is technically expensive, considerable quantities of cooling gas are required, in the order of 200 to 300 m 3 / min.

In the North American Memory US-A-4 143 278 has been described a reactor with irradiation system that serves for the hardening of layers, paints and the like, in which the ambient air is conducted and circulated inside the housing, above the lamps and on the surface of the substrate. An application of an inert gas is not envisaged here. The heat of the circulating air is removed by a particular cooling device. From EP-A-0 589 260 a flexo-pressure machine structured in a modular system is known, in which printing mechanism a metal film is printed with a paint or dye that hardens under ultraviolet rays. The printed or printed band is fed to a cooling and ultraviolet irradiation unit comprising a cooling cylinder whose inner cooling jacket is traversed by cooling water. In the system of hardening by ultraviolet rays according to French Memory FR-A-2 370 071 a cooling system with water is provided in the reflector area. The inert gas stream occurs here against the conveyor direction of the band subjected to treatment and generates an overpressure in the direction of the band. In addition, cooling through the inert gas must occur here. In this system a high level of infrared irradiation with an unequal cooling profile is produced through the conduction of the gas from one side of the electrode to the other, ie along the pipe. This produces an irradiation shift in the different ultraviolet bands. In view of the fact that photoinitiators precisely demonstrate the disadvantage of having on the one hand a relatively strong odor of their own and on the other hand they are quite expensive, there exists, starting from the European Report EP-AO 161 504, the technical problem according to the invention of offering a device in which the quantity of photoinitiators can be considerably reduced. The solution to this problem is achieved according to the present invention with a device according to claim i. Other effective advances of the device according to the invention are mentioned in claims 2 to 6. According to the present invention, in the case of a printing dye, the dye containing a maximum of only 20% of photoinitiators is applied to a film of aluminum or plastic or in its case a paper band and with the help of ultraviolet light hardens and dries, following here two basic stages. The first stage is that the film, which as a rule is very sensitive to heat and has a thickness of 10 to 50 microns, must be cooled during ultraviolet irradiation. On the other hand, the present invention consists precisely of executing the second stage, that is to say, carrying out the operation of printing and drying / hardening within an atmosphere of flushing gas. If inert gas is used, preference is given to nitrogen or carbon dioxide. The rinse gas will not necessarily be an inert gas, but depending on the layer subjected to hardening it can also be dry air, humid air or another reactive gas. Thus, for example, there are chemical systems that are not sensitive to oxygen, but to moisture. When on the other hand, for example, adhesives are applied on a paper strip or an aluminum plastic film, they require water to be able to react and harden better. A polyamide film, on the other hand, has the inclination to bind or fix a considerable amount of moisture on its surface. Due to this, in such a case the gas must be chosen in such a way that this film before the printing operation, that is, before applying the dye, is subjected to moisture extraction, so that fundamentally more favorable conditions will be present than in the case of applying the dye on a monomolecular wet film. The proposal according to the present invention is particularly applicable with great advantage in a flexopressure cylinder machine that works at high speed, in which, for example, films are prepared for the packaging of provisions, or where glued coatings must be made. Not only can a remarkable adhesion of the dye be achieved on the paper / plastic or aluminum films, but the serious problem of unpleasant odor is also solved, thanks to a considerable reduction of the photoinitiator, since the hardening and drying of the different Dye layers are now produced in an atmosphere of protection and quickly. The laminar stream including oxygen, in particular, can also be replaced in front of the entrance of the substrate in the hardening stage in the form of the ultraviolet dryer by nitrogen, the dye being released here on the surface also of the rapidly absorbed oxygen. According to the present invention, therefore, 80% of the amount required to date of photoinitiators can be dispensed with., so that there are also considerable savings in terms of costs for printing dyes that harden with ultraviolet light. The invention is illustrated in greater detail in the following with examples of embodiment, and with reference to the attached drawing: In the drawing: Figure 1 schematically represents in the axial direction of a cylinder carrying coated substrate, a device for hardening a layer on the substrate.

Figure 2 is a front and partial view on the outer side wall with the bodies of the nozzles mounted therein. As shown in Figure 1, a housing 1 carries the side walls 4, 5. This housing is open at its lower end pointing towards a counter-pressure cylinder 14, which is a hollow cylinder, and whose wall carries steps for cooling agent 17, through which water, for example, can flow. While the side wall 5 with the cylinder surface defines a groove 8, it is provided in! Figure 1 a slot 9 on the right side between the side wall 4 of the housing 1, and the surface of the back pressure cylinder 14; the two grooves 8, 9 have a width of approximately 2 mm in the illustrated embodiment. The rotating cylinder carries a substrate that has been coated before it enters the housing 1 as a hardening step, with a layer. On the outer faces of the side walls 4, 5 nozzle bodies are provided, while between these nozzle bodies 6a, 7a and the surface of the counter-pressure cylinder carrying the substrate are also provided columns whose width correspond to the grooves 8, 9. Inside the housing 1 there is a reflector 2, which is corrugated in its upper area, and which aims the rays of an ultraviolet lamp 3 directly on the substrate that is passing, in order to dry, or in its case harden the layer applied on the substrate. Both the housing 1 and also the reflector 2, are crossed with channels for cooling agent 15, 16, so that these parts can be tempered or cooled when through these channels 15, 16 circulates a cooling medium, preferably Water. A source of rinse gas Q is mounted, which removes a cleaning gas from the hardening stage or, if necessary, removes it from it. To this end, a line of flushing gas 11 is extended from the flushing gas source Q through a gas and quantity regulator 10 through a hole 12a present in the upper wall of the housing, and ends in a nozzle provided in the reflector 2. Thus, the rinsing gas can be rinsed out of the space which is located below the reflector 2 to exit the slot 8, 9. It also extends from the regulator of the gas stream and 10 another line for rinsing gas 12 to the nozzle body 6a, so that through the nozzle column 6 is also noted rinse gas on the input substrate, whose conveyor direction is indicated by an arrow in the Figure 1. Another line for rinsing gas 13 leads from the regulator of the current and quantity of gas to the nozzle body 7a, and is in communication with a nozzle slot 7. Therefore, the rinse also on the exit side of the substrate on the last layer, especially that layer applied therein. The rinsing gas from the nozzle slot 7 has an additional action, since within the space surrounded by the reflector 2 it generates a subatmospheric pressure and thus removes the rinsing gas therein from the outlet slot 9. The size of this sub-atmospheric pressure can be adjusted by the regulator 10 and a valve V, which is mounted on the line for flushing gas 11. Such suctioning action can also be exerted by the nozzle slot 6, from which the gas Rinsing is not only pointed towards the input substrate layer. It is preferred to configure the nozzle slots 6, 7 in an adjustable manner with respect to their current inlet angle, as described below. Although, in the illustrated embodiment, the nozzle bodies 6a and 7a are in each case on the outer face of the side walls 4, 5, it is also possible to integrate these bodies in the side walls. As shown in Figure 2, a nozzle body 7a is mounted in the area of the lower section of the side wall 4, which at the same time operates as a light protector, and is glued and screwed to the side wall. The nozzle slot 7 is produced because another nozzle body 18 is held against the nozzle body 7a, with the help of an adjusting screw, this adjusting screw having an enlarged head, the inner edge of which rests against a staggering of the nozzle body. . According to the screwing depth of this screw 19, the nozzle groove 7 can be adjusted in its width. To this nozzle slot 7 the flushing gas is fed through a channel 20 which is in current communication with the line for flushing gas 13. In Figure 2 the direction of movement of the substrate not specifically drawn is indicated. by means of an arrow 8, while the substrate is guided through the slot 9 located between the nozzle body and the counter-pressure cylinder. When it is convenient to point the rinsing gas above the substrate and as a final operation suction the gas from the space below the reflector, by changing the regulator 10, the rinsing gas line 11 is set in suction operation, while the two rinsing gas lines 12, 13 conduct the rinsing gas towards the nozzle bodies 6a, 7a. In other words, depending on the choice and depending on the substrate subject to treatment, it is possible to let the rinsing gas lines 11, 12 and 13 work as a pressure or suction line. EXAMPLE The reduction of the usual photoinitiator portions by about 20% is in the normal case translated into a crosslinking reaction and sufficient of the printing dye. However, when the oxygen in the air (approximately 24%) has been largely expelled by nitrogen (about 75%), then the polymerizing reaction of the photoinitiator and binder combination no longer has highly reactive molecules available. In view of the fact that with regard to the reception of ultraviolet-type dyes, it is necessary to work with oxygen scavengers, this system comes to a very high extent in the case of a reduction in oxygen. a) V = 80 m / min (belt speed), 20% of the usual concentration of the initiator, a low yield of the ultraviolet lamp of approximately 50 / cm >; deposit of the dye on the diverting cylinders. b) The same conditions, but now with a nitrogen rinse between the application of the printing dyes and the ultraviolet irradiation > , complete hardening is achieved, and no deposit has been determined on the deflection rollers. (Speed of the band). The two comparative tests show a great saving potential for the most expensive element of the recipe (initiator), with good reduction of odor influences and better cross-linking with less inclination towards migration. A relatively high direct light input angle means correspondingly high working efficiencies of the ultraviolet light, with the drawback of a possible heating of the substrate, which, on the other hand, is compensated for by corresponding cylinder cooling. The reflecting rays, bounce in a reflector system cooled with water. At the same time, the housing is cooled and the interior can be filled with gas, such as nitrogen. The usual light shutters for protecting the personnel are arranged in this embodiment example drawn in such a way that they at the same time work as gas nozzles. To achieve a "peeling effect", according to the surface of the substrate, the adjustment angle of the gas nozzle is adjustable. A zone coating is also possible, in order to have to use a smaller amount of gas, for example, in the case of smaller widths of the substrate. The gas supply is programmed according to the regulating technique through the operation system of the equipment. The so-called light strip and rinsing gas can be operated independently of the ultraviolet irradiator unit, that is, before a printing station to release a rough surface of oxygen, before applying the dye. The combination of a gas with rinsing, for example, in front of the ultraviolet irradiator and a suction after the ultraviolet irradiator, allows the possibility of a regulated circulation of the gas, in which higher dosages are made according to the needs. This example can be used according to the present invention, for example, in the case of air conditioning (wet content). This case is interesting in a reaction catalyzed with water. As other examples for the controlled application of gasification reactions, we mention the following systems: 1. PVA / water / ammonium chromate In the preparation of coatings with polyvinyl alcohol dissolved in water, or alternatively as dissolved polyvinylpyrrolidone, a photoinitiator is used on the diazonium salt base, or also ammonium chromate9 (NJ4) 2 Cr207. The coating mass is applied, dried and exposed to ultraviolet light or exposure with some residual moisture within the film layer. This reaction is strongly influenced by the residual moisture and the pH value in the film, and is carried out in accordance with the present invention by conditioning with defined moisture of the gas and a defined content of CO2, for example, in a rinse with nitrogen . One field of application of this reaction is, for example, the development of image protectors for cathode ray tubes in televisions (literature: 1. G. Bolte in Farbe and Lack, year 88 7/1982, pages 528,533; 2. JC Colbert, Modern Coating Technologie, Noyes Data Corp., 1982, page 128, etc.). 2. Other possibilities with rinsing gas can be, for example, reaction reinforcements or systems to ensure reactions, through, for example, a controlled adjustment of the pH: Isocyanate reaction Isocyanates (solid phase) + alcohols (phase steam) > polyurethanes pH adjustment: Ammonia, H2COOH, for example, enriched in inert gas (N2). For these variants, it is useful to feed or discharge the gas in an ultraviolet irradiator, with a combined regulation of the composition of the gases. The amount of rinse gas, whose pressure is regulated in the zone of the hardening stage, which is first fed and then discharged, can be controlled depending on the speed of the substrate and / or one or more measurement parameters. As such magnitudes or measurement parameters, the following are mentioned, for example: a) Measurement of oxygen at the surface of the substrate to regulate the amount of nitrogen. b) Determination of the differential pressure to achieve a defined overpressure of the internal gas in the hardening region. c) Measurement of the temperature of the gas to determine the chilling action and within this concept the regulation of the quantities of the rinse gas. d) Measurements of concentrations of chemical components of the rinse gas, water vapor, C02 and others. An example of embodiment is the achievement of a defined brightness degree of the dyes by changing the lamp performances of at least two ultraviolet lamps placed one behind the other in the running direction of the substrate and the controlled change of the residual amount of oxygen during each pass below the lamp.

Claims (6)

CLAIMS;

1. A device for hardening a layer of printing dye, lacquer, adhesive or silicone, with which a substrate of paper, plastic, glass, wood or metal is coated, with a housing (1), which is open in the direction towards a body conveyor (14) that transports the substrate and covers the substrate while retaining slots in and out of the substrate (8, 9), and with an ultraviolet lamp (3) arranged inside the housing, with a reflector (2), which aims the ultraviolet light on the passing substrate, in which case at least one line for rinsing gas (11) on one side is connected to a source of flushing gas (Q), and on the other hand to the internal enclosure of the housing ( 1), through a nozzle (12), characterized in that rinse gas nozzles (6, 7) are preferably mounted next to the substrate inlet slot (8) and the substrate outlet slot (9). water-cooled, whose angles of current direction s on adjustable in relation to the passing substrate and that are in current communication with a steering regulator and quantities of gas (10), having provided a tempering device (17) to cool the substrate that is passing, and because the nozzles of rinse gas (6, 7) are provided in the side walls of the housing (4, 5), and because cooling channels (15, 16, 17) are mounted in the housing (1), the reflector (2) and the transporting body (14).

2. The device according to claim 1, car »r < - "curly because the rinse gas nozzles (6, 7) are connected through the lines (12, 13) to the regulator (10), and are outside the housing (1), so that a gas rinse of the substrate also occurs before and after the passage of the substrate

3. The device according to claim 1, characterized in that the flushing gas nozzles (6, 7) are mounted as shutters for the protection of light, which are assembled in the form adjustable on the outer sides of the side walls of the housing (4, 5)

4. The device according to claims 1 and 2, characterized in that the gas lines (11, 12, 13) can be operated by the regulator (10). ) optionally as lines for gas extraction or as lines for gas supply

5. The device according to claim 1, characterized in that it is mounted as a component of a central cylinder machine on the circumference of a central cylinder, and carries in front or behind in each case, an applicator mechanism. The device according to claim 1, characterized in that a valve is provided inside the housing (1), that is, a shutter valve, cooled with water, which can be moved between the ultraviolet lamp and the substrate.