EP2072255A1 - Reflector assembly for uv radiation - Google Patents
Reflector assembly for uv radiation Download PDFInfo
- Publication number
- EP2072255A1 EP2072255A1 EP07150209A EP07150209A EP2072255A1 EP 2072255 A1 EP2072255 A1 EP 2072255A1 EP 07150209 A EP07150209 A EP 07150209A EP 07150209 A EP07150209 A EP 07150209A EP 2072255 A1 EP2072255 A1 EP 2072255A1
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- EP
- European Patent Office
- Prior art keywords
- radiation
- area
- reflector
- radiation source
- source
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- 230000005855 radiation Effects 0.000 title claims abstract description 107
- 239000000758 substrate Substances 0.000 claims abstract description 26
- 238000000576 coating method Methods 0.000 claims abstract description 10
- 239000011248 coating agent Substances 0.000 claims abstract description 7
- 238000007639 printing Methods 0.000 claims description 35
- 238000011144 upstream manufacturing Methods 0.000 claims description 17
- 238000001723 curing Methods 0.000 description 36
- 239000000976 ink Substances 0.000 description 35
- 238000003848 UV Light-Curing Methods 0.000 description 10
- 238000005286 illumination Methods 0.000 description 4
- 238000007641 inkjet printing Methods 0.000 description 4
- 238000005266 casting Methods 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 230000002457 bidirectional effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000006116 polymerization reaction Methods 0.000 description 1
- 238000009423 ventilation Methods 0.000 description 1
- 238000013022 venting Methods 0.000 description 1
Images
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41F—PRINTING MACHINES OR PRESSES
- B41F23/00—Devices for treating the surfaces of sheets, webs, or other articles in connection with printing
- B41F23/04—Devices for treating the surfaces of sheets, webs, or other articles in connection with printing by heat drying, by cooling, by applying powders
- B41F23/0403—Drying webs
- B41F23/0406—Drying webs by radiation
- B41F23/0409—Ultraviolet dryers
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
- B41J11/00—Devices or arrangements of selective printing mechanisms, e.g. ink-jet printers or thermal printers, for supporting or handling copy material in sheet or web form
- B41J11/0015—Devices or arrangements of selective printing mechanisms, e.g. ink-jet printers or thermal printers, for supporting or handling copy material in sheet or web form for treating before, during or after printing or for uniform coating or laminating the copy material before or after printing
- B41J11/002—Curing or drying the ink on the copy materials, e.g. by heating or irradiating
- B41J11/0021—Curing or drying the ink on the copy materials, e.g. by heating or irradiating using irradiation
- B41J11/00214—Curing or drying the ink on the copy materials, e.g. by heating or irradiating using irradiation using UV radiation
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B3/00—Drying solid materials or objects by processes involving the application of heat
- F26B3/28—Drying solid materials or objects by processes involving the application of heat by radiation, e.g. from the sun
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
- B41J3/00—Typewriters or selective printing or marking mechanisms characterised by the purpose for which they are constructed
- B41J3/54—Typewriters or selective printing or marking mechanisms characterised by the purpose for which they are constructed with two or more sets of type or printing elements
- B41J3/543—Typewriters or selective printing or marking mechanisms characterised by the purpose for which they are constructed with two or more sets of type or printing elements with multiple inkjet print heads
Definitions
- the present invention is directed to curing of ink or coatings with UV radiation.
- a reflector assembly for reflecting UV radiation from a UV-radiation source onto a substrate movable relative to the source and having a surface at least partially covered with a UV-curable ink or coating.
- UV radiation ultraviolet
- UV radiation source generally in the form of a high intensity UV lamp
- a UV radiation source is moved past the substrate in order to irradiate the substrate with direct and indirect radiation from the source, the indirect radiation being reflected by a reflector or reflector assembly before it reaches the ink.
- the UV radiation will catalyze polymerization reactions in the ink thereby curing or drying the ink.
- the ink should be completely cured or dried before the printed matter leaves the printer.
- the curing speed on the surface of the ink layer can be quite different from the curing speed in the bulk of the ink layer depending on the intensity of the UV radiation used for curing. If the intensity of the UV radiation is too high, only the ink on the surface of the layer is cured, while the ink in the bulk of the layer still remains uncured. If the intensity is too low, only the ink in the bulk of the layer is cured, while the ink on the surface of the layer still remains uncured. This will complicate the printing and will delay the delivery of user ready printed matter, especially printed multicolor images.
- US Patent No. 3,983,039 proposes a lamp unit for curing photosensitive inks and coatings, comprising a UV lamp mounted in a reflector.
- the reflector has a first curved reflecting surface partially surrounding the UV lamp for providing a region of peaked relatively high intensity illumination and a second plane reflecting surface for providing a region of relatively lower intensity illumination. It is said that the region of relatively low intensity illumination was effective for pre-curing the ink while the region of peaked relatively high intensity illumination beneath the UV lamp was well suited for performing the main curing operation.
- a reflector assembly for reflecting UV radiation from a UV-radiation source onto a substrate movable relative to the source and having a surface at least partially covered with a UV-curable ink or coating.
- the reflector assembly comprises at least one first curved reflector and at least one second reflector.
- the first curved reflector focuses UV radiation from the source onto the surface in a first area for providing a peak intensity in that area.
- the second reflector reflects UV radiation from the source onto the surface in at least one second area for providing a relatively lower intensity in that area.
- the second reflector has a curved reflecting surface; the cross sectional profile of the curved reflecting surface in the relative-motion direction is described by a polynomial of second or higher order.
- a reflector assembly for reflecting UV radiation from a UV-radiation source onto a substrate movable relative to the source and having a surface at least partially covered with a UV-curable ink or coating.
- the reflector assembly comprises means for casting UV radiation from the source onto the surface in a first area for providing a peak intensity in that area; and means for casting UV radiation from the source onto the surface in at least one second area for providing a relatively lower intensity in that area.
- a printing apparatus comprising a reflector assembly for reflecting UV radiation from a UV-radiation source onto a substrate movable relative to the UV-radiation source and having a surface at least partially covered with an UV curable ink or coating.
- the reflector assembly comprises at least one first curved reflector and at least one second reflector.
- the first reflector focused UV radiation from the UV radiation source onto the surface in a first area for providing a peak intensity distribution in said first area.
- the second reflector reflects UV radiation from the UV radiation source onto the surface in at least one second area for providing a relatively lower intensity distribution in said at least one second area.
- the second reflector has a curved reflecting surface. The cross sectional profile of said curved reflecting surface in a direction of the relative motion is described by a polynomial of second or higher order.
- Some of the embodiments show a reflector assembly for reflecting UV radiation from a UV radiation source onto a surface of a substrate.
- the substrate is movable relative to the UV radiation source.
- the surface is at least partially covered with an UV curable ink or coating.
- a first curved reflector is provided that, in some embodiments, focuses UV radiation from the UV radiation source onto the surface in a first area opposite from the UV radiation source for providing a peak intensity distribution in said first area.
- At least one second reflector in some embodiments, reflects UV radiation from the UV radiation source onto the surface in at least one second area adjacent to said first area for providing a relatively lower intensity distribution in said at least one second area.
- the at least one second reflector has a curved reflecting surface.
- the cross sectional profile of the curved reflecting surface in a direction of the relative motion can be described by a polynomial of second or higher order.
- a printing apparatus e.g. an inkjet printer
- the reflector assembly permits a more efficient transfer of UV radiation to the printed ink and therefore a significantly reduced curing time and an increased motion speed of the substrate with respect to the UV radiation source. Furthermore the lesser the time the printed matter is exposed to the UV radiation, the lesser is the heat absorption and heat rise in the printed matter.
- UV radiation from a single UV radiation source can be configured such that the curing speed of bulk curing is equal to the curing speed of surface curing in order to achieve a complete curing of the surface and of the bulk of the ink layer while the substrate is treated with the UV radiation.
- the UV radiation from a single UV radiation source is portioned into a dose for bulk curing and a dose for surface curing at which doses for a given UV intensity of the UV radiation source the curing speed of bulk curing is equal to the curing speed of surface curing.
- UV curing apparatus and reflector assembly are efficient, particularly for inkjet printing, where it is possible to increase the speed of the relative motion of the substrate with respect to the UV radiation source in order to achieve a complete curing of the printing ink concurrently with the printing of the substrate.
- the curing dose i.e. the UV radiation to be emitted by the UV radiation source in order to provide a complete curing of the ink.
- the first area is opposite from the UV-radiation source, and the second area is adjacent to said first area.
- the at least one second reflector is arranged on a side of the UV radiation source facing away from the substrate in order to reflect stray radiation from the radiation source, i.e. the radiation that is emitted by the source on a side facing away from the substrate, onto the surface in the second area.
- the intensity distribution of the UV radiation across said second area is essentially constant.
- Some of the embodiments provide for at least one third reflector for reflecting UV radiation from the UV radiation source onto the surface in the second area in an overlapping or overlying relationship with the UV radiation reflected by the at least one second reflector. This will make it easier to provide a desired UV radiation intensity distribution in the second area.
- the UV radiation from the UV radiation source reflected by the at least one second reflector and the UV radiation from the UV radiation source reflected by the at least one third reflector cover the same areas.
- the calculation of the curvature of the cross sectional profile of the reflecting surfaces of the at least one second reflector and/or the at least one third reflector is done based on desired intensity and distribution of the UV radiation in the at least one second area, a distance between the UV radiation source and the substrate, a minimum distance between the UV radiation source and the at least one second and/or third reflector and a collection angle defined by rays reflected from two opposite ends or edges of the at least one second and/or third reflector.
- the desired intensity distribution in the at least one second area may be such that the intensity distribution is essentially constant or homogenous throughout the second area.
- the reflecting surface of the at least one first reflector may have an elliptical cross section in the direction of relative motion.
- the at least one first reflector is located between the UV radiation source and the substrate in order to shield a part of the second area from direct UV radiation from the UV radiation source and to reflect and focus this UV radiation onto the first area of the substrate.
- the reflector assembly has two first reflectors for reflecting UV radiation from the UV-radiation source onto said surface in said first area in an overlapping or overlying relationship, wherein in the direction of relative motion one of the first reflectors is located upstream of said UV-radiation source and the other one of said first reflectors is located downstream of said UV-radiation source.
- the reflecting surfaces of all of the reflectors may be symmetrical with respect to a plane extending through the UV radiation source and being transverse to the direction of relative motion.
- the reflector assembly has two second reflectors, wherein in the direction of relative motion one of the second reflectors is located upstream of said UV-radiation source and reflects UV radiation from said UV-radiation source to said second area upstream of said first area, and the other one of the second reflectors is located downstream of the UV-radiation source and reflects UV radiation emitted from said UV-radiation source to said second area downstream of said first area.
- the reflector assembly further has two third reflectors, wherein in the direction of relative motion one of the third reflectors is located upstream of said UV-radiation source and reflects UV radiation from said UV-radiation source to said second area upstream of said first area, and wherein the other one of the third reflectors is located downstream of the UV-radiation source and reflects UV radiation emitted from said UV radiation source to said second area downstream of said first area.
- the first area is irradiated with direct UV radiation from the UV-radiation source.
- At least a part of the at least one second area is irradiated with direct UV radiation from the UV-radiation source.
- the UV-radiation source is an elongated UV lamp extending transverse to the direction of relative motion.
- FIG. 1 there is shown a perspective side view of an ink jet printing unit 10 for printing a UV curable printing ink on a flat substrate in the form of a large rectangular sheet of paper 12 placed on a flat upper surface of a support table 14.
- the printing unit 10 is movable in a plane parallel to the upper surface of the support table 14 along an X-axis and a Y-axis, which are orthogonal to each other.
- the printing unit 10 comprises in its central part two ink jet printing heads 16 and 18, the left one 16 for printing onto the sheet of paper 12 when the printing unit 10 is moved across the support table 14 in the direction of the arrow A in Fig.
- the printing can be done alternately with both printing heads 16 and 18 during the forward and the backward motion of the printing unit, or alternatively with only one printing head 16 or 18 respectively during the forward or during the backward motion of the printing unit 10.
- the printing unit 10 will be moved one step in the direction of the arrow C, i.e. in parallel to the Y-axis, and will then be moved again in parallel to the X-axis to print an adjacent line.
- the printing unit 10 Adjacent to each printing head 16 and 18 respectively the printing unit 10 further comprises first and a second UV curing apparatus 20 and 22 for curing the UV-curable ink which has just been printed onto the sheet of paper 12 by the adjacent printing head 16 and 18 respectively.
- first UV curing apparatus 20 will be used to cure the ink just having been printed by the printing head 16
- second UV curing apparatus 22 will be used to cure the ink just having been printed by the other printing head 18.
- the UV curing apparatus 20 and 22 each comprise a rectangular housing 24 with a shallow roof shaped top 26 and a flat open bottom 28 the latter facing towards the sheet of paper 12 and being located in a small distance above the upper surface of the support table 14.
- the housing 24 accommodates a UV radiation source in the form of a elongated UV lamp 30 mounted approximately in the middle of the housing 24 and extending transverse to the direction of motion of the printing unit 10 with respect to the support table 14, i.e. transverse to the direction of the arrows A and B.
- the UV lamp 30 comprises a cylindrical high-intensity UV light source 32 mounted in a transparent quartz glass tube 34 so that it will emit UV radiation in all directions radial to a center axis of the light source 32.
- the input power of the UV lamp 30 can be controlled by means not depicted in the drawing.
- the housing 24 further accommodates a reflector assembly 36, comprising two first reflectors 38a and 38b located on both sides of the UV lamp 30 between the latter and the open bottom 28 of the housing 24, two second reflectors 40a and 40b located on both sides and above of the UV lamp 30 between the latter and the top 26 of the housing 24, and two third reflectors 42a and 42b located on opposite sides of the UV lamp 30, i.e. in the direction of motion of the printing unit 10 upstream and downstream from the UV lamp 30.
- a reflector assembly 36 comprising two first reflectors 38a and 38b located on both sides of the UV lamp 30 between the latter and the open bottom 28 of the housing 24, two second reflectors 40a and 40b located on both sides and above of the UV lamp 30 between the latter and the top 26 of the housing 24, and two third reflectors 42a and 42b located on opposite sides of the UV lamp 30, i.e. in the direction of motion of the printing unit 10 upstream and downstream from the UV lamp 30.
- the UV lamp 30 and the reflectors 38a, 38b, 40a, 40b and 42a, 42b of the reflector assembly 36 are supported by a support structure 44 comprising a number of beams 46 made of extruded metal which are located inside the housing 24 and also serve to support the housing walls 48 and the housing top 26.
- a vertical ventilation tube 50 in the middle of the housing top 26 above the UV lamp 30 is for venting the housing interior and for discharging heated air from the vicinity of the UV lamp 30 when being in operation.
- the two first reflectors 38a and 38b are symmetrical to each other with respect to a plane 52 through the center axis of the light source 32 and each have an elliptical reflecting surface 54 in order to focus part of the UV light emitted from the UV lamp 30 onto a narrow strip 56 on the upper surface of the paper sheet 12 on both sides of the plane 52 directly below the UV lamp 30 so that together with direct light emitted from the UV lamp on this strip 56 an area of peak intensity distribution is generated.
- This peak intensity distribution can be seen in Fig. 6 depicting the intensity distribution as measured on the upper surface of the paper sheet 12 below the open bottom 26 of the housing 24 when the UV lamp 30 is in operation.
- the numbers on the horizontal axis are the distance from the plane 52 in mm and the numbers on the vertical axis are the light intensity in W/cm 2 , which has a maximum of about 10 W/cm 2 in the middle of the strip 56.
- Each of the pair of second reflectors 40a and 40b and the pair of third reflectors 42a and 42b also have reflecting surfaces 58 and 60 respectively which are symmetrical to the plane 52 through the center axis of the light source 32.
- Both pairs of reflectors 40a and 40b serve to reflect stray UV light from the UV lamp 30, which is not directed downwardly towards the sheet of paper 12 or towards the reflecting surfaces 54 of the pair of first reflectors 38a and 38b.
- the stray UV light is reflected by the reflectors 40a and 40b onto two broad strips 62a and 62b of the upper surface of the paper sheet 12 on both sides of the narrow strip 56, i.e.
- the desired light intensity distribution is a relatively constant or homogenous light intensity distribution throughout the whole length of the strips 62a and 62b in the direction of motion of the printing unit 10 being about 1-2 W/cm 2 .
- the reflector geometry i.e. the cross section of the two second and third reflectors 40a, 40b and 42a, 42b in the direction of motion of the printing unit 10 or the arrows A and B is calculated according to these settings, as have been listed above.
- f(x) describing the curvature of each reflecting surface 58, 60
- f(x) is a polynomial of second or higher order
- x is the distance from the plane 52 through the center axis of the light source 34 in the direction of motion of the printing unit 10 and the settings mentioned above are parameters in the polynomial.
- each of the second reflectors 40a and 40b is described by a polynomial of the second order.
- the second reflectors 40a and 40b are provided with a parabolic reflecting surface 58.
- the configuration of the reflecting surfaces 58 and 60 of the second reflector 40a and the adjacent third reflector 42a is such that the rays from the UV light source 32 reflected by the upstream edge 66 of the second reflector 40a and the downstream edge 68 of the third reflector 42a will both be directed to the downstream limit of the strip 62a whereas the rays from the UV light source 32 reflected by the downstream edge 68 of the second reflector 40a and the upstream edge 66 of the third reflector 42a will both be directed to the upstream limit of the strip 62a.
- a similar condition applies for the rays reflected by the other pair of reflectors 40b and 42b. This leaves more possibilities of reflector design in order to create a homogeneous light intensity distribution in the areas 62a and 62b.
- the reflector assembly 36 described above it is possible to portion the UV radiation from the UV lamp 30 including the direct light from the UV lamp 30 and the light reflected by the reflecting surfaces 54, 58 and 60 of the first, second and third reflectors 38a, 38b, 40a, 40b and 42a, 42b into a dose for surface curing and a dose for bulk curing such that a balanced curing will occur, where the curing speed of the bulk curing is about equal to the curing speed of surface curing.
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Abstract
A reflector assembly (36) for reflecting UV radiation from a UV-radiation source (30) onto a substrate (12) movable relative to the source (30) and having a surface at least partially covered with a UV-curable ink or coating. A first curved reflector (38a, 38b) focuses UV radiation from the source (30) onto the surface in a first area (56) for providing a peak intensity in that area (56). At least one second reflector (40a, 40b) reflects UV radiation from the source (30) onto the surface in at least one second area (62a, 62b) for providing a relatively lower intensity in that area (62a, 62b). The second reflector (40a, 40b) has a curved reflecting surface (58). The cross sectional profile of the curved reflecting surface (58) in the relative-motion direction is described by a polynomial of second or higher order.
Description
- The present invention is directed to curing of ink or coatings with UV radiation. For example, it is directed to a reflector assembly for reflecting UV radiation from a UV-radiation source onto a substrate movable relative to the source and having a surface at least partially covered with a UV-curable ink or coating.
- The curing of photosensitive coatings and inks with ultraviolet (UV) radiation is being used increasingly in a number of technical fields, for example in inkjet printing.
- In general, for treating an UV curable ink on a printed matter substrate in the form of a continuous web or an individual sheet with UV radiation in an inkjet printer, either the substrate is moved past a UV radiation source, generally in the form of a high intensity UV lamp, or a UV radiation source is moved past the substrate in order to irradiate the substrate with direct and indirect radiation from the source, the indirect radiation being reflected by a reflector or reflector assembly before it reaches the ink. When reaching the ink the UV radiation will catalyze polymerization reactions in the ink thereby curing or drying the ink. In order to allow immediate use of the printed matter the ink should be completely cured or dried before the printed matter leaves the printer.
- However this is difficult to achieve because for a specific thickness of the ink layer the curing speed on the surface of the ink layer can be quite different from the curing speed in the bulk of the ink layer depending on the intensity of the UV radiation used for curing. If the intensity of the UV radiation is too high, only the ink on the surface of the layer is cured, while the ink in the bulk of the layer still remains uncured. If the intensity is too low, only the ink in the bulk of the layer is cured, while the ink on the surface of the layer still remains uncured. This will complicate the printing and will delay the delivery of user ready printed matter, especially printed multicolor images.
- In order to solve this problem in some prior approaches a number of UV radiation sources were used in order to achieve a simultaneous curing of the ink on the surface and in the bulk of the layer. However when used in connection with inkjet printers this solution would raise the cost of the printers and complicate printer service.
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US Patent No. 3,983,039 , proposes a lamp unit for curing photosensitive inks and coatings, comprising a UV lamp mounted in a reflector. The reflector has a first curved reflecting surface partially surrounding the UV lamp for providing a region of peaked relatively high intensity illumination and a second plane reflecting surface for providing a region of relatively lower intensity illumination. It is said that the region of relatively low intensity illumination was effective for pre-curing the ink while the region of peaked relatively high intensity illumination beneath the UV lamp was well suited for performing the main curing operation. - According to a first aspect, a reflector assembly is provided for reflecting UV radiation from a UV-radiation source onto a substrate movable relative to the source and having a surface at least partially covered with a UV-curable ink or coating. The reflector assembly comprises at least one first curved reflector and at least one second reflector. The first curved reflector focuses UV radiation from the source onto the surface in a first area for providing a peak intensity in that area. The second reflector reflects UV radiation from the source onto the surface in at least one second area for providing a relatively lower intensity in that area. The second reflector has a curved reflecting surface; the cross sectional profile of the curved reflecting surface in the relative-motion direction is described by a polynomial of second or higher order.
- According to a second aspect, a reflector assembly is provided for reflecting UV radiation from a UV-radiation source onto a substrate movable relative to the source and having a surface at least partially covered with a UV-curable ink or coating. The reflector assembly comprises means for casting UV radiation from the source onto the surface in a first area for providing a peak intensity in that area; and means for casting UV radiation from the source onto the surface in at least one second area for providing a relatively lower intensity in that area.
- According to a third aspect, a printing apparatus is provided that comprises a reflector assembly for reflecting UV radiation from a UV-radiation source onto a substrate movable relative to the UV-radiation source and having a surface at least partially covered with an UV curable ink or coating. The reflector assembly comprises at least one first curved reflector and at least one second reflector. The first reflector focused UV radiation from the UV radiation source onto the surface in a first area for providing a peak intensity distribution in said first area. The second reflector reflects UV radiation from the UV radiation source onto the surface in at least one second area for providing a relatively lower intensity distribution in said at least one second area. The second reflector has a curved reflecting surface. The cross sectional profile of said curved reflecting surface in a direction of the relative motion is described by a polynomial of second or higher order.
- Other features are inherent in the devices disclosed or will be apparent to those skilled in the art from the following description of the embodiments and its accompanying drawings.
- Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:
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FIG. 1 is an elevational side view of an ink jet printer having an UV curing apparatus for curing UV curable ink on a printed substrate; -
FIG. 2 is a perspective top view of the UV curing apparatus; -
FIG. 3 is a perspective bottom view of the UV curing apparatus; -
FIG. 4 is a cross-sectional side view of the UV curing apparatus showing a UV radiation source and a reflector assembly; -
FIG. 5 is a cross-sectional side view of the reflector assembly of the UV curing apparatus; -
FIG. 6 is a graphical representation of the intensity of UV radiation on the surface of the printed substrate located below the reflector assembly ofFig. 6 ; -
FIG. 7 is a schematic side view of a UV radiation source and a reflector for explaining a collection angle of the reflector. - The drawings and the description of the drawings are of embodiments of the invention and not the invention itself.
- Some of the embodiments show a reflector assembly for reflecting UV radiation from a UV radiation source onto a surface of a substrate. The substrate is movable relative to the UV radiation source. The surface is at least partially covered with an UV curable ink or coating. A first curved reflector is provided that, in some embodiments, focuses UV radiation from the UV radiation source onto the surface in a first area opposite from the UV radiation source for providing a peak intensity distribution in said first area. At least one second reflector, in some embodiments, reflects UV radiation from the UV radiation source onto the surface in at least one second area adjacent to said first area for providing a relatively lower intensity distribution in said at least one second area. In some embodiments, the at least one second reflector has a curved reflecting surface. In some of the embodiments, the cross sectional profile of the curved reflecting surface in a direction of the relative motion can be described by a polynomial of second or higher order.
- In some embodiments, a printing apparatus, e.g. an inkjet printer, is equipped with the reflector assembly. This permits a more efficient transfer of UV radiation to the printed ink and therefore a significantly reduced curing time and an increased motion speed of the substrate with respect to the UV radiation source. Furthermore the lesser the time the printed matter is exposed to the UV radiation, the lesser is the heat absorption and heat rise in the printed matter.
- With the reflector assembly and apparatus of the aforementioned type, UV radiation from a single UV radiation source can be configured such that the curing speed of bulk curing is equal to the curing speed of surface curing in order to achieve a complete curing of the surface and of the bulk of the ink layer while the substrate is treated with the UV radiation. The UV radiation from a single UV radiation source is portioned into a dose for bulk curing and a dose for surface curing at which doses for a given UV intensity of the UV radiation source the curing speed of bulk curing is equal to the curing speed of surface curing.
- The above-mentioned UV curing apparatus and reflector assembly are efficient, particularly for inkjet printing, where it is possible to increase the speed of the relative motion of the substrate with respect to the UV radiation source in order to achieve a complete curing of the printing ink concurrently with the printing of the substrate.
- Furthermore, it is possible to minimize the curing dose, i.e. the UV radiation to be emitted by the UV radiation source in order to provide a complete curing of the ink.
- In some embodiments, the first area is opposite from the UV-radiation source, and the second area is adjacent to said first area.
- In one of the embodiments the at least one second reflector is arranged on a side of the UV radiation source facing away from the substrate in order to reflect stray radiation from the radiation source, i.e. the radiation that is emitted by the source on a side facing away from the substrate, onto the surface in the second area. This allows achieving bulk curing of the ink with the relatively lower intensity distribution of the stray radiation in the second area before the ink reaches the first area where the peak intensity distribution resulting from the focusing of the UV radiation and direct UV radiation from the UV radiation source will result in surface curing.
- In some of the embodiments, the intensity distribution of the UV radiation across said second area is essentially constant.
- Some of the embodiments provide for at least one third reflector for reflecting UV radiation from the UV radiation source onto the surface in the second area in an overlapping or overlying relationship with the UV radiation reflected by the at least one second reflector. This will make it easier to provide a desired UV radiation intensity distribution in the second area.
- In some of the embodiments the UV radiation from the UV radiation source reflected by the at least one second reflector and the UV radiation from the UV radiation source reflected by the at least one third reflector cover the same areas.
- In some of the embodiments the calculation of the curvature of the cross sectional profile of the reflecting surfaces of the at least one second reflector and/or the at least one third reflector is done based on desired intensity and distribution of the UV radiation in the at least one second area, a distance between the UV radiation source and the substrate, a minimum distance between the UV radiation source and the at least one second and/or third reflector and a collection angle defined by rays reflected from two opposite ends or edges of the at least one second and/or third reflector. The desired intensity distribution in the at least one second area may be such that the intensity distribution is essentially constant or homogenous throughout the second area.
- In order to focus the UV radiation from the UV radiation source onto the first area having a relatively high UV intensity distribution the reflecting surface of the at least one first reflector may have an elliptical cross section in the direction of relative motion.
- In some embodiments, the at least one first reflector is located between the UV radiation source and the substrate in order to shield a part of the second area from direct UV radiation from the UV radiation source and to reflect and focus this UV radiation onto the first area of the substrate.
- In some embodiments the reflector assembly has two first reflectors for reflecting UV radiation from the UV-radiation source onto said surface in said first area in an overlapping or overlying relationship, wherein in the direction of relative motion one of the first reflectors is located upstream of said UV-radiation source and the other one of said first reflectors is located downstream of said UV-radiation source.
- In certain embodiments, for example, in case of the relative motion of the substrate and the UV radiation source being bidirectional, there are two of the first reflectors and two of the second and/or the third reflectors, and the reflecting surfaces of all of the reflectors may be symmetrical with respect to a plane extending through the UV radiation source and being transverse to the direction of relative motion.
- In some embodiments, the reflector assembly has two second reflectors, wherein in the direction of relative motion one of the second reflectors is located upstream of said UV-radiation source and reflects UV radiation from said UV-radiation source to said second area upstream of said first area, and the other one of the second reflectors is located downstream of the UV-radiation source and reflects UV radiation emitted from said UV-radiation source to said second area downstream of said first area.
- In some embodiments, the reflector assembly further has two third reflectors, wherein in the direction of relative motion one of the third reflectors is located upstream of said UV-radiation source and reflects UV radiation from said UV-radiation source to said second area upstream of said first area, and wherein the other one of the third reflectors is located downstream of the UV-radiation source and reflects UV radiation emitted from said UV radiation source to said second area downstream of said first area.
- In some of the embodiments the first area is irradiated with direct UV radiation from the UV-radiation source.
- In some embodiments at least a part of the at least one second area is irradiated with direct UV radiation from the UV-radiation source.
- In some embodiments the UV-radiation source is an elongated UV lamp extending transverse to the direction of relative motion.
- Turning now to
Fig. 1 , there is shown a perspective side view of an inkjet printing unit 10 for printing a UV curable printing ink on a flat substrate in the form of a large rectangular sheet ofpaper 12 placed on a flat upper surface of a support table 14. Theprinting unit 10 is movable in a plane parallel to the upper surface of the support table 14 along an X-axis and a Y-axis, which are orthogonal to each other. Theprinting unit 10 comprises in its central part two ink jet printing heads 16 and 18, theleft one 16 for printing onto the sheet ofpaper 12 when theprinting unit 10 is moved across the support table 14 in the direction of the arrow A inFig. 1 along a straight line parallel to the X-axis, and theright one 18 for printing onto the sheet ofpaper 12 when theprinting unit 10 is moved in the opposite direction of the arrow B inFig. 1 . The printing can be done alternately with both printing heads 16 and 18 during the forward and the backward motion of the printing unit, or alternatively with only oneprinting head printing unit 10. After finishing the printing of one line having approximately the width of theprinting unit 10 theprinting unit 10 will be moved one step in the direction of the arrow C, i.e. in parallel to the Y-axis, and will then be moved again in parallel to the X-axis to print an adjacent line. - Adjacent to each
printing head printing unit 10 further comprises first and a secondUV curing apparatus paper 12 by theadjacent printing head printing unit 10 is moved in the direction of the arrow A the firstUV curing apparatus 20 will be used to cure the ink just having been printed by theprinting head 16, whereas when theprinting unit 10 is moved in the direction of the arrow B the secondUV curing apparatus 22 will be used to cure the ink just having been printed by theother printing head 18. - As can be best seen from
Figs. 2 to 5 theUV curing apparatus rectangular housing 24 with a shallow roof shapedtop 26 and a flat open bottom 28 the latter facing towards the sheet ofpaper 12 and being located in a small distance above the upper surface of the support table 14. - As depicted in
Figs. 3 to 5 thehousing 24 accommodates a UV radiation source in the form of aelongated UV lamp 30 mounted approximately in the middle of thehousing 24 and extending transverse to the direction of motion of theprinting unit 10 with respect to the support table 14, i.e. transverse to the direction of the arrows A and B. TheUV lamp 30 comprises a cylindrical high-intensityUV light source 32 mounted in a transparentquartz glass tube 34 so that it will emit UV radiation in all directions radial to a center axis of thelight source 32. The input power of theUV lamp 30 can be controlled by means not depicted in the drawing. - The
housing 24 further accommodates areflector assembly 36, comprising twofirst reflectors UV lamp 30 between the latter and theopen bottom 28 of thehousing 24, twosecond reflectors UV lamp 30 between the latter and the top 26 of thehousing 24, and twothird reflectors UV lamp 30, i.e. in the direction of motion of theprinting unit 10 upstream and downstream from theUV lamp 30. - The
UV lamp 30 and thereflectors reflector assembly 36 are supported by asupport structure 44 comprising a number ofbeams 46 made of extruded metal which are located inside thehousing 24 and also serve to support thehousing walls 48 and thehousing top 26. Avertical ventilation tube 50 in the middle of thehousing top 26 above theUV lamp 30 is for venting the housing interior and for discharging heated air from the vicinity of theUV lamp 30 when being in operation. - The two
first reflectors plane 52 through the center axis of thelight source 32 and each have an elliptical reflectingsurface 54 in order to focus part of the UV light emitted from theUV lamp 30 onto anarrow strip 56 on the upper surface of thepaper sheet 12 on both sides of theplane 52 directly below theUV lamp 30 so that together with direct light emitted from the UV lamp on thisstrip 56 an area of peak intensity distribution is generated. This peak intensity distribution can be seen inFig. 6 depicting the intensity distribution as measured on the upper surface of thepaper sheet 12 below theopen bottom 26 of thehousing 24 when theUV lamp 30 is in operation. InFig. 6 the numbers on the horizontal axis are the distance from theplane 52 in mm and the numbers on the vertical axis are the light intensity in W/cm2, which has a maximum of about 10 W/cm2 in the middle of thestrip 56. - Each of the pair of
second reflectors third reflectors surfaces plane 52 through the center axis of thelight source 32. Both pairs ofreflectors UV lamp 30, which is not directed downwardly towards the sheet ofpaper 12 or towards the reflectingsurfaces 54 of the pair offirst reflectors reflectors broad strips paper sheet 12 on both sides of thenarrow strip 56, i.e. upstream and downstream of thisstrip 56 in the direction of motion of theprinting unit 10 parallel to the X-axis, in order to generate in both of theses strips 62a and 62b an area of considerably lower light intensity with a desired intensity distribution. This can be seen inFig. 6 , where the desired light intensity distribution is a relatively constant or homogenous light intensity distribution throughout the whole length of thestrips printing unit 10 being about 1-2 W/cm2. - In order to create this desired light intensity distribution, after setting the desired intensity and distribution of the UV light, setting the height of the center axis of the
UV lamp 30 above the upper surface of the support table 14, setting the minimum distance from the reflectingsurfaces third reflectors UV light source 34 and after setting a collection angle α of the two second andthird reflectors third reflectors printing unit 10 or the arrows A and B is calculated according to these settings, as have been listed above. The calculation is done by means of an algorithm f(x) describing the curvature of each reflectingsurface plane 52 through the center axis of thelight source 34 in the direction of motion of theprinting unit 10 and the settings mentioned above are parameters in the polynomial. - In the
reflector assembly 36 depicted inFigs. 4 and5 the curvature of the reflectingsurface 58 of each of thesecond reflectors second reflectors surface 58. - Next the collection angle α of the second and the
third reflectors Fig. 7 showing a single reflector with a curved reflecting surface, where the collection angle α is delimited by two rays from the center axis of theUV light source 32 to the upstream anddownstream edge - The reflecting surfaces 58 and 60 of each pair consisting of one
second reflector third reflector plane 52 through the center axis of the light source 42, have such a configuration, i.e. such a curvature and length, that the limits on both sides of thesurface area surfaces surfaces second reflector 40a and the adjacentthird reflector 42a is such that the rays from the UVlight source 32 reflected by theupstream edge 66 of thesecond reflector 40a and thedownstream edge 68 of thethird reflector 42a will both be directed to the downstream limit of thestrip 62a whereas the rays from the UVlight source 32 reflected by thedownstream edge 68 of thesecond reflector 40a and theupstream edge 66 of thethird reflector 42a will both be directed to the upstream limit of thestrip 62a. A similar condition applies for the rays reflected by the other pair ofreflectors areas - With the
reflector assembly 36 described above it is possible to portion the UV radiation from theUV lamp 30 including the direct light from theUV lamp 30 and the light reflected by the reflectingsurfaces third reflectors
Claims (10)
- Reflector assembly (36) for reflecting UV radiation from a UV-radiation source (30) onto a substrate (12) movable relative to the source (30) and having a surface at least partially covered with a UV-curable ink or coating, comprising
at least one first curved reflector (38a, 38b) for focusing UV radiation from the source (30) onto the surface in a first area (56) for providing a peak intensity in that area (56); and
at least one second reflector (40a, 40b) for reflecting UV radiation from the source (30) onto the surface in at least one second area (62a, 62b) for providing a relatively lower intensity in that area (62a, 62b), wherein said second reflector (40a, 40b) has a curved reflecting surface (58), wherein the cross sectional profile of said curved reflecting surface (58) in the relative-motion direction is described by a polynomial of second or higher order. - Reflector assembly (36) according to claim 1, wherein the polynomial of second or higher order is a function of at least one of a desired intensity and distribution of said UV radiation onto said at least one second area (62a, 62b), a distance between said UV-radiation source (30) and said substrate (12), a minimum distance between said UV-radiation source (30) and said at least one second reflector (40a, 40b) and a collection angle (α) defined by rays reflected from two opposite ends or edges (66, 68) of said at least one second reflector (40a, 40b).
- Reflector assembly (36) according to claim 1 or 2, comprising at least one third reflector (42a, 42b) for reflecting UV radiation from the UV-radiation source (30) onto said surface in said second area (62a, 62b) in an overlapping or overlying relationship with said UV radiation reflected by said second reflector (40a, 40b).
- Reflector assembly (36) according to claim 3, wherein the UV radiation from the UV-radiation source (30) reflected by the at least one second reflector (40a, 40b) and the UV radiation from the UV-radiation source (30) reflected by the at least one third reflector (42a, 42b) cover essentially the same areas (62a, 62b).
- Reflector assembly (36) according to any one of claims 1 to 4, wherein the intensity distribution of the UV radiation across said second area (62a, 62b) is essentially constant.
- Reflector assembly (36) according to any one of claims 1 to 5, comprising two of said second reflectors (40a, 40b), wherein in the direction of relative motion one of said second reflectors (40a) is located upstream of said UV-radiation source (30) and reflects UV radiation from said UV-radiation source to said second area (62a, 62b) upstream of said first area (56), and wherein the other one of said second reflectors (40b) is located downstream of the UV-radiation source (30) and reflects UV radiation emitted from said UV-radiation source (30) to said second area (62a, 62b) downstream of said first area (56).
- Reflector assembly (36) according to any one of claims 3 to 6, comprising two of said third reflectors (42a, 42b), wherein in the direction of relative motion one of said third reflectors (42a) is located upstream of said UV-radiation source (30) and reflects UV radiation from said UV-radiation source (30) to said second area (62a, 62b) upstream of said first area (56), and wherein the other one of said third reflectors (42b) is located downstream of the UV-radiation source (30) and reflects UV radiation emitted from said UV radiation source (30) to said second area (62a, 62b) downstream of said first area (56).
- Reflector assembly (36) according to any one of claims 1 to 7, comprising two of said first reflectors (38a, 38b) for reflecting UV radiation from the UV-radiation source (30) onto said surface in said first area (56) in an overlapping or overlying relationship, wherein in the direction of relative motion one of said first reflectors (38a) is located upstream of said UV-radiation source (30) and the other one of said first reflectors (38b) is located downstream of said UV-radiation source (30).
- Reflector assembly (36) according to any one of claims 1 to 8, wherein said first area (56) is irradiated with direct UV radiation from the UV-radiation source (30) and/or at least a part of said at least one second area (62a, 62b) is irradiated with direct UV radiation from the UV-radiation source (30).
- Printing apparatus (10), comprising a reflector assembly (36) according to any one of claims 1 to 9.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP07150209A EP2072255A1 (en) | 2007-12-20 | 2007-12-20 | Reflector assembly for uv radiation |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP07150209A EP2072255A1 (en) | 2007-12-20 | 2007-12-20 | Reflector assembly for uv radiation |
Publications (1)
Publication Number | Publication Date |
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EP2072255A1 true EP2072255A1 (en) | 2009-06-24 |
Family
ID=39338373
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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EP07150209A Withdrawn EP2072255A1 (en) | 2007-12-20 | 2007-12-20 | Reflector assembly for uv radiation |
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Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
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WO2020213247A1 (en) * | 2019-04-17 | 2020-10-22 | 株式会社ミマキエンジニアリング | Inkjet printer |
CN113164289A (en) * | 2018-12-17 | 2021-07-23 | 宝洁公司 | Method and apparatus for reweaving nonwoven substrates |
CN113334925A (en) * | 2021-06-10 | 2021-09-03 | 海盐西美印刷股份有限公司 | UV ink printing, curing and drying device for packaging paper card |
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US3983039A (en) | 1975-03-03 | 1976-09-28 | Fusion Systems Corporation | Non-symmetrical reflector for ultraviolet curing |
US4924599A (en) * | 1985-11-04 | 1990-05-15 | American Screen Printing Equipment Company | UV curing apparatus |
FR2653868A1 (en) * | 1989-10-31 | 1991-05-03 | France Rayonnement | Method for designing a UV reflector, and reflector thus obtained |
US5825041A (en) * | 1997-03-14 | 1998-10-20 | Loctite Corporation | System for optical curing |
US6305796B1 (en) * | 1999-01-26 | 2001-10-23 | Xerox Corporation | Thermal ink jet printer having dual function dryer |
EP1849615A1 (en) * | 2006-04-25 | 2007-10-31 | Ushiodenki Kabushiki Kaisha | Light irradiation apparatus and inkjet printer |
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US3983039A (en) | 1975-03-03 | 1976-09-28 | Fusion Systems Corporation | Non-symmetrical reflector for ultraviolet curing |
US4924599A (en) * | 1985-11-04 | 1990-05-15 | American Screen Printing Equipment Company | UV curing apparatus |
FR2653868A1 (en) * | 1989-10-31 | 1991-05-03 | France Rayonnement | Method for designing a UV reflector, and reflector thus obtained |
US5825041A (en) * | 1997-03-14 | 1998-10-20 | Loctite Corporation | System for optical curing |
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Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
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CN113164289A (en) * | 2018-12-17 | 2021-07-23 | 宝洁公司 | Method and apparatus for reweaving nonwoven substrates |
CN113164289B (en) * | 2018-12-17 | 2022-11-04 | 宝洁公司 | Method and apparatus for reweaving nonwoven substrates |
WO2020213247A1 (en) * | 2019-04-17 | 2020-10-22 | 株式会社ミマキエンジニアリング | Inkjet printer |
JP2020175563A (en) * | 2019-04-17 | 2020-10-29 | 株式会社ミマキエンジニアリング | Ink jet printer |
CN113334925A (en) * | 2021-06-10 | 2021-09-03 | 海盐西美印刷股份有限公司 | UV ink printing, curing and drying device for packaging paper card |
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