NO149060B - APPLIANCES FOR RADIATION TREATMENT OF ELEVATED GOODS - Google Patents

Description

The present invention relates to an apparatus for continuous irradiation treatment of the surface of a coated product in motion, and more particularly an apparatus for irradiation of the surface of a coated product in motion in an essentially inert atmosphere.

Subjecting a curable polymer coating to irradiation energy to improve the properties, particularly the surface properties of the coating, has been an area of intense study for many years.

It has long been recognized that the effectiveness of such irradiation as well as the curing rate can be increased by maintaining an inert atmosphere over the surface of the coated product during the irradiation period. This applies in particular when electromagnetic energy or high-energy electrons are used as the irradiation medium. Under controlled laboratory conditions, there has been no difficulty in maintaining an inert atmosphere over the surface of the coated product. In the case of industrial electricity operation, one of the main considerations is the operating costs, which are primarily due to the high consumption of inert gas. It is thus clear that any savings in gas consumption over a period of time, e.g. in a year with round-the-clock operation leads to significantly reduced operating costs, which can be decisive for the commercial applicability of such processes.

To be commercially acceptable, the irradiation must take place in the production line and must therefore be compatible with the other equipment's working speed, which can vary from minimum speeds of around 18.3 m/min. to today's maximum speed of around 183 m/min. A coated product moving at the operating speed carries with it on its surface a thin film of air which must be substantially displaced by inert gas to permit effective surface curing when the surface is subjected to radiant energy. The displacement of such air must take place before the "exposure time", which is hereinafter defined as the time interval during which the surface of a given coated product is exposed to irradiation energy. At working speeds of

183 m/min. is for a treatment chamber with a total length of

e.g. 91.5 cm and an irradiation length of 30.5 cm, the chamber residence time 0.3 sec. and the exposure time 0.1 sec., which gives a maximum time of only equal to or less than 0.2 sec. to displace the air film on the surface of the coated product.

Generally applies to a fixed geometry for such a chamber

that the faster the coated product moves through the chamber, the higher the flow of inert gas to the chamber must be to maintain an inert atmosphere. In addition, higher working speeds give reduced time to achieve a stabilization of the flow patterns in the chamber, and any concentration difference for inert gas along the surface of the coated product, especially a wide product, can result in non-uniform curing. One can greatly increase the flow rate to blow off atmospheric air that would otherwise be drawn in with the product or, alternatively, reduce the work rate. However, the practice is that the working speed is fixed in the production line and the inert gas system must be compatible with this speed. Furthermore will. the commercial user of the process wishes to determine the gas flow rate only once and for economic reasons set this as low as possible. Furthermore, not only will the production line speed be periodically varied for adaptation to particular product applications, but also product size, especially product widths which are periodically varied below a maximum value.

In order to therefore satisfy commercial requirements, the irradiation system must be able to provide an acceptable uniform cure regardless of variations in the normal production line with a view to product width and production line speed, preferably using only a single fixed total flow rate. Furthermore, the system should be linearly adjustable for dimensions and flow requirements to allow uniform processing of a product of any width at any required operating speed. Thus, when the system dimensions have been created for a maximum product width and working speed, the system must give equal treatment to products with significantly reduced width and/or working speed without changing the system parameters.

French Patent Nos. 2,058,090 and 2,058,091 deal directly with this idea. Both patents describe various alternative constructions for creating a relatively pure inert nitrogen atmosphere in a partially closed chamber through which the product is passed for treatment. In the examples given, the working speed is set at around 54.8 m/min. and.the products processed are limited to a width of no more than 381 mm. In practice, the product width will depend on the commercial application and will be varied accordingly in the production line to suit such an application. A product width of up to 203.2 mm is not unusual. Although a relatively low gas flow rate is mentioned, there is no indication that the system design is linearly variable to process substantially wider products and/or narrower products at varying operating speeds.

The main purpose of the present invention is thus to produce an apparatus for continuous "in-line" irradiation treatment of the coated surface of a moving product in which an inert gas atmosphere is maintained over the coated product during the treatment, which apparatus is linearly adjustable, expressed by the inert gas flow rate required to process any product width at any desired rate.

The apparatus further requires only a relatively small, essentially constant, inert gas flow rate to maintain the inert atmosphere regardless of normal product variations with regard to product width or production speed below a predetermined maximum.

The present invention aims to improve the known technique and thus relates to an apparatus for irradiation treatment of elongated objects comprising a first and a second tunnel with a constant cross-section, and a treatment chamber with at least one irradiation source, which chamber is arranged between the outlet end from the first tunnel and the inlet end to the other, so that the treatment chamber and the two tunnels, possibly together with the elongated object, form a closed unit, through which the objects are to be passed, as well as a pressure; chamber for inert gas and an opening through which the gas is to flow into the apparatus for providing an inert atmosphere, and this apparatus is characterized in that the pressure chamber is connected to a gas injector channel which ends in a slot in the wall of the first tunnel and at a distance from this tunnel's inlet) end which is at least ten times the smallest cross-sectional dimension of this tunnel, the outlet gap extending across the longitudinal axis of the first tunnel and having a length substantially equal to the length of the irradiation zone measured across the longitudinal axis of the first tunnel along the sides of the elongated object which is to be irradiated, and is arranged in such a way that the inert gas is directed vertically towards the surface of the object to be irradiated, or in a direction opposite to the forward direction of the object at an acute angle to the surface to be irradiated, the angle being at least 45°.

Other objects and advantages of the invention will become clear from the following description of the invention in connection with the accompanying drawings, where: fig. 1 in longitudinal section schematically shows the apparatus according to the invention;

fig. 2 is an enlarged perspective view of the main chamber

and the inert gas injector channel in fig. 1;

fig. 3 is a top view of the apparatus according to fig. 1,

shown partially in perspective;

fig. 4 a-c^ show three typical tunnel configurations in perspective;

fig. 5 a-b show in perspective typical apparatus geometries

for round or triangular substrates;

fig. 6 is a diagram illustrating the flow paths of discrete elementary volumes of inert gas leaving the injector channel and flowing out through the inlet and outlet tunnels, respectively;

fig. 7 shows in perspective a typical apparatus according to the invention;

fig. 8 is a longitudinal section along the line 8-8 in fig. 7;

fig. 9 is a side view along the line 9-9 in fig. 8.

Static systems for maintaining an inert gaseous environment around a work area are well known. The underlying construction concept which is the basis for all such systems is to create an inert gas flow pattern which will cause the air in the working space to be replaced by the inert gas, without allowing the inert gas to mix with air. The difficulties lie in adapting this to a dynamic system where the coated product is in motion in relation to the work area. The coated product in motion tends to draw air into the work area, which disturbs the flow conditions and creates turbulence. The problem is further accentuated in chemical irradiation processes where only a slight presence of oxygen on the surface of the coated product can inhibit surface hardening.

Fig. 1 schematically shows an apparatus according to the invention. The product P which can represent a chemical coating or a coated substrate of continuous length, such as a web, or of defined length such as e.g. a foam board, is passed through the treatment chamber 10, where it is exposed to electromagnetic radiation from an unshown source of radiant energy. The radiation energy source is placed in the irradiation chamber 12 with suitable optics (not shown) to direct the electromagnetic radiation energy towards the product P when it passes by. Any source of electromagnetic radiation energy may be used although an internally cooled or uncooled source is preferred. If the source requires external cooling, an optically transparent medium must be provided to physically separate the radiation zone 14 from the radiation chamber 12.

Internally cooled sources and non-cooled sources require no physical separation from the irradiation zone 14 and thus form an integral part of treatment chambers .10. A typical preferred internally cooled electromagnetic radiation source is a plasma arc as described in US Patent Nos. 3,364,387 and 3,597,650. Typical preferred uncooled electromagnetic radiation sources are low pressure short wave ultraviolet mercury tubes or germicidal lamps.

The treatment chamber 10 further comprises an entrance or intake part 16, an injector channel 18 through which inert gas is led from a chamber 20 and an outlet tunnel 24. Inert gas is delivered to the chamber 20 from a source for inert gas supply not shown. Although any inert gas may be used, nitrogen is preferred.

The term "tunnel" in the present description is defined as a hollow passage of uniform cross-section which may either have a self-closing periphery or a partially closed periphery which becomes substantially completely closed when the coated product in motion is present. The length of the entrance tunnel 16 as well as the length of the exit tunnel 24 should be as long as practicable.

The placement, geometry and orientation of the injector channel 18

is essential to achieve a non-turbulent and non-mixing inert gas flow in the treatment chamber 10, so that a gas flow below about 46,545 liters/hour and m tunnel width and preferably below about 37,236 liters/hour and m tunnel width is all that is necessary to achieve a uniform inert blanket over the coated surface of the product in motion, regardless of product speeds up to about 183 m/min. Once a gas flow rate as specified for a given maximum tunnel width has been established, the processing unit will adapt and uniformly cover the coated surface of a moving product of any width up to said given tunnel width at any speed up to about 183 m/min.

The injector channel 18 must be located upstream of the intake end 27 of the entrance tunnel 16 at a distance of at least 10 times the smallest cross-sectional dimension of the tunnel 16. The height H in the channel 18 should ideally be at least about 4 times greater than the width W, i.e. the distance between the side surfaces of the channel as shown earlier in fig. 2. The length L of the channel must at least substantially correspond to the width of the product P and preferably correspond to the width of the entrance tunnel 16 and must be oriented substantially parallel to the tunnel width. Furthermore, the channel 18 must also be oriented so that the inert gas is directed through the channel opening 26 to the enclosure 10 at an angle with the enclosure 10's longitudinal axis of between 45 and 90°, preferably 90°. The distance between the opening 26 and the moving product P should be as small as normal product surface irregularities allow. The ratio between the height H and the width W is not so important if a porous medium is used to fill the channel space, but this makes the installation somewhat more difficult and somewhat more expensive. Although the channel 18 is shown in FIG. 1 as a pair of flat plates extending from a slot in the upper wall of the tunnel 16, the slot itself may represent the channel, provided that the upper wall of the tunnel 16 has a sufficient thickness to satisfy the desired ratio between height H and width W .

The gas supplied to the injector channel 18 flows from the chamber 20, which chamber is a gas reservoir with a substantially larger cross-section than the longitudinal cross-section of the channel 18. The chamber 20 should preferably have a cross-sectional area which, when considered perpendicular to the length L of the injector channel, is at least about 10 times the longitudinal cross-sectional area of the channel 18.

Both the entrance tunnel 16 and the exit tunnel 24 are extensions

of the irradiation chamber 12 and serves to limit the loss of inert gas from the enclosure 10 as well as to direct the outflowing inert; gas over the coated surface of the product P so that most of the air is pushed away from the surface of the product P before the product enters the area of irradiation 14. A small but sufficient pressure gradient exists between the injector channel opening 26 and the intake end 27 of the entrance tunnel 16, which creates a backflow of inert gas out of the entrance tunnel 16

to prevent unacceptable amounts of air from being drawn in with the coated surface of the product P. The exit tunnel 24 also serves as a bypass for the smaller amounts of air that flow into the enclosure 10 on the coated surface of the product P and are carried away by the product . The inert gas holds such air on the coated surface of the product P and sweeps such air out through the exit tunnel 24 with the product as opposed to

allow such air to mix with the inert atmosphere in chamber 12 and accumulate to an unacceptable level.

The cross-sectional dimensions of the entrance and exit tunnels 16 and 24 are preferably chosen to match the cross-sectional dimensions of the coated product P to be processed. Figures 4 a-c show the geometry of three typical tunnels for three typical product shapes, respectively rectangular, triangular and cylindrical.

As shown in fig. 5a and b, the injector channel 18 and the chamber 20

in the same way in geometry fit the cross-sectional geometry of the coated product P. This also applies to the irradiation chamber 12, where uniform irradiation is desired around the entire periphery of the product, but this need not mean that the radiation energy source

has to have such a geometry because with the help of suitable optics in the chamber 12 the same result can be achieved.

As mentioned earlier, the tunnel length must be TT Li for the injector channel

for any tunnel configuration be about 10 times the smallest cross-sectional dimension of the tunnel. For a rectangular tunnel geometry, T^<=> is thus 10 Tfl and TH < Tw, where T„ = the tunnel height and TTT = the tunnel width; for a triangular tun-W > >

nail geometry (Fig. 5a) is TT = 10 T„ = Tr7; and for a cylindrical

j_l y Cl W

tunnel geometry (Fig. 5b) is T = 10 D, where D is the diameter of the cylinder.

When the coated product P is present in the enclosure 10 and extends through it, the coated product itself can form the bottom of each tunnel. In such cases where the coated product P is continuously present, such as at a web, the coated product P effectively forms the bottom of the chamber and no additional bottom is required. In general, there should be no part of the irradiation area 14 that is physically lower than the bottom of the exposed surface for the entrance and exit tunnels 16 and 24, respectively. If it is necessary that any part of the irradiation area 14 is lower than any of the lower surfaces in the tunnel, in such cases there should be regulated emissions to the atmosphere along such a physically lower surface. In such a case, the inert nitrogen atmosphere will displace any air carried in with the product P and force this air out through the venting devices. The geometry of the enclosure 10 is described above in connection with the use of inert gases which are lighter than oxygen. It should be clear that, with suitable selection of controlled vents, a gas that is heavier than oxygen can be used. Furthermore, if desired, the chamber can also be turned around.

The injector channel 18 ensures a uniform current distribution of inert gas to the enclosure 10 with said current directed essentially towards the surface of the coated product P in motion and uniformly distributed over the width of the product P. The geometry of the injector channel 18 as described above is intended to cause each elementary volume of inert gas essentially follows parallel flow paths of corresponding length to the intake opening of the entrance tunnel 16 and parallel flow paths of equal length to the outlet opening of the exit tunnel 24. This is in the form of a diagram shown in fig. 6 where v^-vn represent essentially equal discrete elementary volumes of inert gas flowing towards the opening 27 and V^l-V 1 represent essentially equal discrete elementary volumes of inert gas flowing towards the opening 29. The discrete elementary volumes V2~vn need not be equal to discrete elementary volumes V,1-V 1. Furthermore need

ln

not the flow path length from the opening 26 to the intake end 27

i in the tunnel 16 be equal to the flow path length from the opening 26 to the outlet end 29 of the outlet tunnel 24. However, it is important to note that the flow of inert gas coming out of the injector channel 18 cancels out vectorially in all directions except in the longitudinal direction. This phenomenon is the primary factor for

> to achieve a uniform inert gas blanket over the width of the coated product and to create the linearly adjustable relationship between inert gas flow and tunnel width completely independent of the width of the coated product. Thus, as long as the tunnel openings are wide enough to fit the coated product P, any narrower coated product, no matter how narrow, can be treated in the same way without changing the physical dimensions or the flow rate. Furthermore, the product speeds can be varied as desired up to around 183 m/min. without affecting the treatment under the conditions stated above, even if the exposure time at the higher speeds is significantly shortened.

Fig. 7 shows in perspective a typical apparatus according to the invention, as it might look installed in a product line. A conveyor 30 carries the coated product P to the processing chamber 10, which is supported by a frame 34. Pressure-operated cylinders 32 regulate the height of the tunnels for the processing chamber 10 above the conveyor 30. The cylinders 32 are manually adjustable to adjust the tunnel height as well as to automatically responds to

a passing product with an irregular or domed surface that should not be processed. When such a product passes, the processing chamber 10 is automatically raised to a predetermined level, while a shutter is activated which is placed under the irradiation chamber 12. The shutter prevents the emission of radiation energy, as will be explained in more detail in connection with fig.8.

The radiation chamber 12 houses the electromagnetic radiation source and suitable optics to direct the radiation energies towards the irradiation zone 14. It should be noted that in a typical system according to fig. 7, the conveyor surface is partly used as a bottom surface in the processing chamber 10. The conveyor surface and the coated product P thus form, when it extends through the processing chamber 10, an integral part of the chamber and act as a bottom in it. This is shown more clearly in fig. 8 and 9.

The injector channel 18 is preferably designed as an elongated slot in the wall of the chamber 20. However, it must have the geometrical relationship described above, i.e. it must be positioned so that it directs the inert gas towards the product which moves at an angle to the longitudinal axis of the enclosure of between 45° and 90°.

The channel 18 should also have a ratio between height and width of at least 4:1. In the manufactured prototype, the height H is made up of a 12.7 mm thick plate with a channel width of 1.59 mm (W). Between the conveyor parts 38 and 40, resting on the frame 34, is a platform device, 4 2 which in connection with the conveyor surfaces forms the bottom surface of the treatment chamber 10. The platform 4 2 consists of a first sheet of "teflon" with a number of mirror sections 44 which is directly exposed before the radiation chamber 12 and a second carrier sheet which lies below the first sheet. The mirror sections 44 for the platform 42 reflect some of the electromagnetic energy to the edges and underside of the product being passed.

As previously mentioned in connection with fig. 7, when a product arrives at the apparatus which is not to be processed due to an irregular surface or for some other reason, the pressure-operated cylinders 32 will automatically be put into operation by means of devices not shown, thereby raising the processing chamber 10 to a predetermined height above the conveyors 38 and 40 and the platform 42. In such cases, a further pressure-operated cylinder 36 works in connection with the pressure-operated cylinders 32. The cylinder 36 has a piston rod 46, the free end of which is connected to a bracket 48 which is fixed by means of ball bearings to a fixed shaft 52. The bracket 48 is also connected to a shutter 50 which is also mounted for axial movement on the fixed shaft 52. The bottom surface of the shutter 50 represents the upper surface of the exit tunnel 24. When the cylinder 36 is activated, the piston rod moves 46 back and causes the shutter 50 to extend below and close the radiation chamber 12. A cooling medium is passed through the connecting line n 54 to cool the shutter 50.

Fig. 9 is a section along the line 9-9 in fig. 8. The tunnel passage leading to the irradiation zone 14 is shown with the upper surface represented by the chamber surface 56 and the bottom surface represented by the platform 42. When the treatment chamber 10 is lowered to the operating position, the spacer plates 58 which are placed on opposite sides of this will rest against the platform 42 and forms a pair of side walls for the entire treatment chamber 10. A pair of side flaps not shown can also be used if it is desired with controlled operating variation in the tunnel height above the first fixed level determined by the distance plates 58.

In the apparatus shown in fig. 7-9, the internal width of the chamber is approximately 127 cm, i.e. that a product of any width up to a maximum of around 122 cm can be processed. The height of the tunnels 16 and 24 in the operating position is 9.5 mm. The length of the enclosure 10 from end to end is 152.4 cm. The distance from the intake end of the intake tunnel 16 to the injector channel is approximately 457 mm while the distance from the injector channel 18 to the irradiation chamber 12 is approximately 152 mm. The irradiation chamber 12 has a length of approximately 457 mm. The physical dimensions given here are illustrative only and may be enlarged or reduced to suit a particular production programme. It should be noted that because the requirements regarding gas flow can be fixed in advance, the physical dimensions can be chosen according to the available space at the production site.

When the above-described apparatus is in operation, the flow of inert gas, preferably nitrogen, can be determined according to the ratio between flow and tunnel width as stated earlier, namely about 37,236 liters/hour and m tunnel width. Alternatively, a total flow corresponding to a normal product width and thus the maximum tunnel width for a particular commercial user can be determined without the need for further adjustment for product width variations.

Below are some examples where the total flow rate was set to around 42,480 l/hour for products with widely varying widths up to a maximum of around 122 cm, and greatly varying speeds from 54.9 m/min. to 152.4 m/min. The thickness of the product varied up to 6.35 mm.

A coating mixture was prepared from 50 g of acrylated epoxidized soybean oil, 30 g of hydroxyethyl acrylate and 20 g of neopentyl glycol diacrylate. To units of 10 g of this mixture, 0.01 mol of various sensitizers was added. The coatings were applied at a wet film thickness of 0.05 mm on "Bonderite No. 37" steel plates and irradiated for the indicated exposure times under a nitrogen blanket using a plasma arc radiation source. The analysis results for the cured films are given below:

Claims (1)

Apparatus for irradiation treatment of elongated objects, comprising a first and a second tunnel (16, 24) of constant cross-section, and a treatment chamber (12) with at least one irradiation source, which chamber is arranged between the outlet end of the first tunnel and the inlet end of the second, so that the processing chamber (12) and the two tunnels (16, 24) possibly together with the elongated object, form a closed unit through which the objects must be passed, as well as a pressure chamber (20) for inert gas and an opening through which the gas must flow into the apparatus for providing an inert atmosphere, characterized in that the pressure chamber (20) is connected to a gas injector channel (18) which ends in a slot (26) in the wall of the first tunnel (16) and at a distance from this tunnel's (16) inlet end which is at least ten times the smallest cross-sectional dimension of this tunnel (16), with the outlet gap (26) extending across the longitudinal axis of the first tunnel (16) and having a length substantially equal to gden of the irradiation zone (14) measured across the longitudinal axis of the first tunnel along the sides of the elongated object to be irradiated, and is arranged so that the inert gas is directed perpendicular to the surface of the object to be irradiated, or in a direction opposite to the direction of advance for the object at an acute angle to the surface to be irradiated, the angle being at least 45°.