ES2650472T3 - Device for inertization with UV irradiation in open flow continuous installations - Google Patents

Abstract

Device for inerting the irradiation zone in UV crosslinking and photochemical surface structuring of acrylate and methacrylate based coatings on substrates in the form of tape or plate, especially with high requirements at a reduced remaining oxygen level and uniform lateral distribution , depending on the case of application <100 ppm, <50 ppm and <10 ppm, in an irradiation channel with inert gas supply, preferably pure nitrogen, formed by an irradiation channel for UV hardening or for a matte combination of VUV excimer and UV hardening with a feed zone (1), a transport device (2) or genre of tape (13), an input screen (3), an inerting nozzle (4), a volumetric filling nozzle (6), an excimer lamp with nitrogen input (7) through the ceiling of the lamp, a medium-pressure mercury lamp (8) with quartz disk or LED unit UV (9), a sensor for measuring the remaining oxygen with a sensor (10) and, in the case of covering of substrates in the form of a plate, with a gas barrier on the exit side, made as a sealing skirt or brush or similar ( 11) or, in the case of irradiation of coated tape genre, made as a maze (15), characterized in that for the realization of a high relative speed between the surface of the product (13) and the inert gas flow oriented, without influencing negatively in the liquid coating in order to avoid turbulence and to guarantee the elimination of oxygen also from the coating (figure 1), the flat construction of the irradiation channel (1) in continuous flow installations above the coated surface of the product (13 ) is configured so that the height of the channel can be adapted, thanks to its regulability, the height of the product and the consistency of the coating, and why the inlet screen (3) and the gas barrier The output side (11 or 15) consists of segments of adjustable height (12 or 16).

Description

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DESCRIPTION

Device for inertization with UV irradiation in open flow continuous installations

The invention relates to a device for the inertization of the irradiation zone in oxygen sensitive processes of UV hardening and surface structuring that occur during continuous operation.

Chemical and physical oxygen-sensitive surface processes, such as photochemical polymerization of acrylate-based paints and their surface structuring by short-wave UV radiation, must be carried out in an atmosphere as poor as possible in oxygen to avoid effects such as the formation of peroxiradicales and ozone, as well as energy losses.

For this purpose, the so-called inertization technologies are used, as is known.

A reaction space is swept with an inert gas such as nitrogen, argon or CO2, preferably pure nitrogen, to displace atmospheric oxygen.

Almost a quarter of a century ago, the inertization was introduced in the UV technique in the extraordinarily oxygen sensitive polymerization of silicone acrylates, the so-called siliconization of separation coatings (DE 34 16502 A1 and EP 0161540 A1).

Meanwhile the inertization technology in the field of UV hardening is part of the state of the art to achieve high quality coatings.

Other advantages of inertization are the possibility of reducing the photoinitiator content by more than 80% and, thanks to the lower electrical power of UV lamps, a 50% energy saving or alternatively a possible increase in the flow rate of products.

All devices invented and developed so far have in common the contribution of inert gas through inlet holes, for example, nozzles, to the reaction chamber or to the channel and, since in the case of continuous flow installations of Products are open systems, equipment with gas barriers on the sides of the products in and out, in order to reduce the consumption of inert gas to a minimum.

In most cases of application of UV hardening and excimer-VUV matting, the content of oxygen remaining in the inert gas of the channel is now also measured, thus regulating the inert gas supply.

Since in the case of the inert gas scanning of the irradiation channel it is a meta-stable aerodynamic system and that not only a remnant oxygen content is required as low as possible, but a largely homogeneous inert gas atmosphere, in addition to the measures for the retention of the introduction of atmospheric oxygen into the channel, constructive measures for a uniform distribution of inert gas and to avoid disturbances in the flow profile in the channel must be adopted.

There are already a series of inventions and development that, according to the advancement of knowledge, have been perfected successively, however some of the supposed solutions to the problem have not yielded good results.

With the introduction of UV siliconization (see documents DE 34 16502 A1 and EP 0161540 A1) for the isolation of the inert atmosphere in the irradiation channel against the cooling air of the medium mercury pressure lamp open below, and a transparent quartz disk of UV rays was used, which is still used today as an effective solution.

The attempt of an internal nitrogen circuit of the UV lamp, in which the quartz disk was dispensed with to avoid a loss in the UV transmission has not been feasible either because it is too complicated and because it does not provide any inert gas savings (DE 000019916474 A1 and WO 002000061999 A1).

On the other hand, what has evidently yielded good results is the uniform supply of inert gas across the width of the channel through the use of porous gas distribution elements, preferably sintered metal, with a defined pressure loss, which prevents jet effect supported by a predistribution unit (DE 20 2005 021 576 U1).

This gas distribution is installed in 172 nm excimer projectors, which are used for the microstructuring of acrylic paint surfaces (physical matting by photochemical micro-folding), on the ceiling of the lamp. With the cold pure nitrogen the projector thus cools evenly throughout the entire length of the projector and, since the Excimer lamp does not require any quartz disc, the nitrogen flows for inerting from the lower hole of the lamp to the channel irradiation An automatic adjustment of the differential pressure is even proposed by varying the effective surface of the porous gas distribution element.

In the case of a classic UV hardening with a quartz disk below the UV medium pressure mercury lamp, the inert gas is supplied over the entire width of the channel by means of a so-called volumetric filling nozzle, which can also work at base of a porous gas distribution element. On the input side of the product it is used, for the best retention of atmospheric oxygen and for the "exfoliation" of oxygen

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from the surface of the paint, a so-called "scraper or exfoliation nozzle". However, the amount of inert gas introduced through it must be adapted to the flow rate of the product, in the case of a better regular variable speed, to avoid an entry of air from the outlet side of the product.

As a gas barrier on the input side of the product, a simple height-adjustable screen is generally used throughout the width of the channel or also a labyrinth (WO 2005 075111 A1), and a sealing skirt is used on the output side of the product of rubber, a brush element or also a labyrinth for a non-contact variant, being able to perform inert labyrinths an introduction of inert gas and a measurement of the remaining oxygen (wO 2005 075111 A1).

Of great importance is the measurement of oxygen remaining in the inert gas of the irradiation zone. For this purpose, the use of a zirconium oxide solid electrolyte sensor has been established, which, thanks to its wide measurement range (1 ppm at> 21% O2) and its short reaction time, is even suitable for quantity regulation of inert gas. For the measurement during the bypass operation the gas is continuously aspirated by means of a small gas pump, by a tubular probe arranged in the roof of the channel, almost always in the center of the channel, through the measuring cell.

The type and shape of the product and the consequent transport technique, as well as the best possible adaptation of the entry and exit gas barriers also exert a great influence on the concentration of the remaining oxygen.

The best solution is achieved in the coating of tapes from roll to roll with a conduction of the tape through a cooling roller and with an inertized UV technical system arranged above. More problematic is the UV hardening of a plate coating in inert conditions, since each piece carries atmospheric oxygen in the form of a “bow wave” into the irradiation channel, also contributing to the transport system to a considerable extent considerable. In this case, the important thing is especially the inert gas introduction nozzles and their arrangement.

Although commercial UV inertization systems in principle work, they are considered, in relation to the stability of the inert regime, that is, lateral concentration of uniform remaining oxygen and reduced temporal fluctuations in the flow, as well as in relation to consumption of inert gas, sensitive and insufficient.

In addition, for a good quality of a UV paint coating it is not only important to remove oxygen from the surface, but also from the liquid or pasty paint layer. In relation to the viscosity-dependent oxygen diffusion coefficients (see figure 1) and with the material transfer coefficients dependent on the relative velocity between the paint surface and the inert gas, the residence time of the paint layer o Liquid / pasty UV varnish in the atmosphere of oxygen-poor inert gas before reaching the irradiation zone plays an essential role.

The contribution of quantities of inert gas adapted to the product and the flow rate alone does not solve the problem of stability, since here it is not worth the “much help a lot”, since as a result of turbulence in the channel because of different Local gas velocities can produce an aspiration of air from the inlet and outlet side.

The knowledge of the state of the art should be attributed to the knowledge that only with a configuration of the channel, of the gas barriers and of the number and of the arrangement of nozzles adapted to the respective product and the consequent transport system and with its handling can a stable inertization regime and optimum product quality. This refers especially to processes with high demands on the level of remaining oxygen and the homogeneity of the lateral distribution of the remaining oxygen, such as excimer vUv (O2 <100 ppm), siliconization with silicone acrylates (O2 < 50 ppm) and UV hardening without photoinitiators (UV hardening with VUV / UVC photons (O2 <10 ppm) (DE 10 2008 061 244 A1).

The objective of the present invention is therefore to propose a device for the inertization of the irradiation zone with which, with a minimum consumption of inert gas, a stable and homogeneous inertization of the irradiation zone can be achieved, so that UV hardening and photochemical surface structuring can be carried out under advantageous technical conditions.

Essential characteristics according to the invention lie in the fact that the irradiation channel is used in a version as flat as possible, resulting in a high relative velocity between the coated surface of the product and the flow of inert gas which, without However, it does not negatively influence the uniformity of the coating, in order to achieve a positive effect on the transfer coefficients of O2 material and a rapid evacuation of the substituted oxygen and at the same time ensure an oriented flow of the inert gas, thereby excluding largely the vertical and horizontal turbulence that could lead to the entry of air.

The device according to the invention also has an inertized inlet section in front of the UV lamp with a length that allows for the elimination of oxygen from the coating the necessary residence time is available, having an advance zone like this also a positive effect on the flow profile and, therefore, on the uniformity of the distribution of the remaining oxygen.

According to an idea of the invention, the adjustment of the slit of the product side and the outlet side is adapted in terms of resistance, so that the greater gas barrier is formed on the output side, whereby the inert gas

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It has to exit from the side of the product in the opposite direction to the transport direction of the product. This means that a maze like the one proposed in WO 2005 075111 A1 should not be provided on the output side of the product. As regards the adjustment of the level of remaining oxygen and the inert gas demand, a slit height is also dependent on the speed of the inlet screen, which makes it advisable to adjust the height of the slit depending on the velocity analogous to the amount of inert gas through the measurement of the remaining oxygen.

The device according to the invention has a diffused chamfered entry screen by means of which the turbulence of detachment and dead zones is reduced. The device also has a segmentation of the entrance screen and the exit barrier (shutter skirt or labyrinth) to exclude, through adaptation to the width of the product, lateral areas of resistance less than above the surface of the product and thus to counteract a negative influence of the gas flow in the channel and air aspiration phenomena.

The slit side of the input screen segments of a tape system is provided with a soft sealing material such as felt or a rubber skirt with closed pores, to achieve a better sealing effect on a roller cooling and to avoid, in case of a lateral deviation of the belt, a break of the same by the segment.

Another feature to solve the task is the choice of a suitable transport system for the bale flow installations, and a number and arrangement of effective inert gas supply nozzles adapted thereto. If, for example, a closed conveyor belt is chosen for flat sheets, it is convenient that the belt has a surface roughness as small as possible. For thicker plates, which can drag a relatively large amount of air inward, it is recommended at speeds normally below 20 m / min, a roller line or a rod or net line and an underground nozzle in the area input

Next, the device according to the invention is described in greater detail in view of the figures. These show in the

Figure 2 schematically a side section of an inertized flat irradiation channel for the combination of plates coated with a VUV excimer matte and UV hardening with a long feed zone (1), a perforated conveyor belt (2), an input screen chamfering (3), an inerting nozzle (4), an underground nozzle (5), a volumetric filling nozzle (6), a nitrogen-powered excimer lamp (7) through the lamp ceiling, a lamp of medium mercury UV pressure (8) with quartz disk or UV LED unit (9), a remaining oxygen measuring probe with sensor (10) and a shutter skirt on the outlet side (11),

Figure 3 schematically the front view of the product input side with the segmented input screen (12) of the plate installation,

Figure 4 schematically a side section of an inertization for the UV hardening of genre in coated tape (13) arranged around a cooling roller (14) with an adjustable chamfered inlet screen (3), an inertization nozzle (4), a volumetric filling nozzle (6), a medium pressure mercury UV lamp (8) with a quartz disk or alternatively a UV LED unit, a remaining oxygen measuring probe with sensor (10) and a maze on the outlet side (fifteen),

Figure 5 schematically the front view of the product input side with the segmented input screen of the tape installation (16).

The effect and advantages of the elements of the device according to the invention are illustrated by means of technical process examples.

Example 1:

An inertization device according to Figure 2 is used for the simple hardening of UV paint on a continuous sheet with a single medium-pressure mercury lamp of a specific electrical power of 200 W / cm. The internal height of the channel is 10 mm and the internal width of the channel is 600 mm. The 500 mm wide blade passes through the device at 100 m / min. With an inlet slit height of 1 mm and a slit height of a labyrinth used by the outlet side of 1 mm, 300 ppm of remaining oxygen content is recorded with a nitrogen flow of 9 Nm3 / h. The coating with a UV paint based on medium viscosity urethane acrylate, whose hardening kinetics at 200 ppm can be seen in Figure 6, is approximately 10 µm thick. According to Figure 1, for a removal of oxygen from the layer at a pressure of oxygen particles against 5 ppm in the inert gas, a minimum residence time of 250 ms would be required.

First, an inert channel length of 300 mm was made between the input screen and the UV lamp. As expected according to the kinetics of Figure 6, with a residence time of 180 ms below 300 ppm O2 and a UV dose of 125 mJ / cm2, only a double bond yield C = C of 41 is recorded. % by infrared spectroscopy (ATR). From the technical point of view of application this is expressed in a poor microhardness of only 165 N / mm2 and in a degree of brightness (60 ° geometry) of 67 GP (brightness points).

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An extension of the inlet channel to 1500 mm led, with the same nitrogen flow and with a reduction of the remaining oxygen content to 200 ppm with a residence time of 900 ms, to an evident improvement of the characteristics. As expected according to the hardening kinetics of Figure 6, with 200 ppm of O2 and a residence time of 900 ms, after a hardening with 125 mJ / cm2 it has been possible to demonstrate a performance of infrared spectroscopy (ATR). double bond C = C of 86%. Consequently, a microhardness of 212 N / mm2 and a brightness degree of 84 GP (brightness points) have been measured.

Example 2:

The influence of the height of the inlet groove is demonstrated by means of a UV UV hardening on belts coated through a cooling roller according to Figure 4.

In figure 7 it can be seen that, surprisingly, with the increase in the speed of the belt, the nitrogen consumption decreases first until reaching 50 ppm of oxygen remaining in the irradiation zone with the increase in the inlet groove, existing however, an optimal value in the adjustment of the inlet groove and the nitrogen flow for each belt speed.

Example 3:

An installation according to Figure 2 is used for the physical matting of MDF plates coated with UV paint by means of 172 nm excimer photons and subsequent long-wave UV light hardening of a mercury medium pressure lamp of 160 W / cm. The internal height of the inert channel is 30 mm and the internal width of the channel is 1400 mm. The plates with dimensions of 2000 x 1200 x 22 (LxAxA) are moved by the VUV / UV installation on a metal grid belt at a speed of 10 m / min.

The microstructure of the paint surface by photochemical micro-folding reacts very sensitively to a non-homogeneous content of oxygen remaining in the irradiation zone, since the 172 nm photons are absorbed by the oxygen under ozone formation, occurring in the zones problematic a decrease in the VUV dose, which causes visible local brightness differences.

The transport of bales is always accompanied by a so-called “bow wave” of oxygen in front of the product that every time causes a brief increase in the oxygen concentration and, in case of too high peak values, structural alterations.

The inertization nitrogen is provided through the excimer lamp (7), an inertization nozzle (4) and, optionally, an underground nozzle (5). In this respect, the effect of an entrance area of different length and of an adjustment of the inlet groove according to Figure 3 is demonstrated. On the output side a sealing skirt forms the nitrogen barrier. The oxygen measurement point is located just in front of the excimer lamp.

The variation of parameters can be seen in Table 1 and the effect on the increase of the remaining oxygen and the wavy development is represented in Figure 8.

It is seen that a prolonged entry zone, as well as a decrease of the chamfered lateral segments as a diffuser of the entrance screen according to Figure 3, give rise to a lower remaining oxygen value and a more uniform distribution across of the cross section of the channel. The threshold value caused by the “bow wave” is clearly reduced with the use of the underground nozzle.

Claims (14)

5 10 fifteen twenty 25 30 35 40 Four. Five fifty 55 60 1. Device for the inertization of the irradiation zone in UV crosslinking and photochemical surface structuring of acrylate and methacrylate based coatings on substrates in the form of a tape or plate, especially with high requirements at a reduced remaining level of oxygen and distribution uniform lateral, depending on the case of application <100 ppm, <50 ppm and <10 ppm, in an irradiation channel with inert gas, preferably pure nitrogen, formed by an irradiation channel for UV hardening or for a combination of VUV excimer matting and UV hardening with a feed zone (1), a transport device (2) or genre of tape (13), an inlet screen (3), an inerting nozzle (4), a nozzle volumetric filling (6), an excimer lamp with nitrogen input (7) through the ceiling of the lamp, an average mercury pressure lamp (8) with quartz disk or L unit ED UV (9), a sensor for measuring the remaining oxygen with sensor (10) and, in the case of covering of substrates in the form of a plate, with a gas barrier on the exit side, made as a sealing skirt or brush or similar (11) or, in the case of irradiation of coated tape, made as a maze (15), characterized in that for the realization of a high relative speed between the surface of the product (13) and the inert gas flow oriented, without negatively influence the liquid coating in order to avoid turbulence and to guarantee the elimination of oxygen from the coating as well (figure 1), the flat construction of the irradiation channel (1) in continuous flow installations above the coated surface of the product ( 13) it is configured so that the height of the channel can be adapted, thanks to its regulability, the height of the product and the consistency of the coating, and because the entrance screen (3) and the barrier of g The output side (11 or 15) consists of segments of adjustable height (12 or 16). 2. Device according to claim 1, characterized in that in case of using a bale flow installation the transport device (2) is a conveyor belt or a roller line. 3. Device according to claim 2, characterized in that the conveyor belt is perforated. Device according to claim 2 or 3, characterized in that in the case of using a continuous flow system of bales an underground nozzle (5) is arranged in the feed zone (1). 5. Device according to claim 1, characterized in that the feed zone (1) important for inertization is configured so as to guarantee a minimum residence time that in the continuous flow installation of bales is 1 s and in installations of 0.3 s tape. Device according to claim 1, characterized in that all the nozzles (4, 5, 6 and 7) for the uniform distribution of the gas are provided with porous or perforated distribution elements of defined differential pressure and a predistribution chamber. 7. Device according to claim 1 and 6, characterized in that the inerting nozzle (4) is arranged so that it acts at an angle of 25 ° to 60 ° with respect to the vertical one against the direction of travel of the belt. Device according to claim 1, characterized in that the segments that form the inlet screen (3) are chamfered as a diffuser in the direction of the gas flow and against the direction of the product. Device according to claim 1 and 8, characterized in that the input screen (3) formed by the height-adjustable segments (12) can be adapted by means of a separate regulation of the height of the segments (12) to the product width Device according to claim 1, characterized in that the height of the inlet groove is adapted by means of the inlet screen (3) formed by the height-adjustable segments (12) depending on the speed and the passage of gas inert and is regulated according to the remaining oxygen content. Device according to claim 1, characterized in that the exit barrier (11 or 15) formed by segments of adjustable height (12) can be adapted to the width of the product by means of a height adjustment separated from the segments (12 ). 12. Device according to one of the preceding claims, characterized in that in the tape installations the irradiation channel is arranged, both for a simple UV hardening with a medium pressure lamp of mercury or an LED unit, as well as for a matte of VUV excimer, in a combination of excimer lamp and mercury medium pressure lamp or of an LED unit around a cylindrical roller (14), preferably around a cooling roller, the surface of the cylinder forming the bottom of the channel and , therefore, under the UV lamps, the counter-screen and the channel being dynamically obtained in front of the cylinder (14). 13. Device according to claim 12, characterized in that the lower faces of the input screen segments are covered with a soft sealing material. 14. Device according to claim 13, characterized in that the sealing material is made of felt or of a special rubber skirt with closed pores.