JP2011079157A - Lighting system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lighting system in a simple cooling structure which radiates ultraviolet rays suitable for curing a photo-curable ink, can be instantaneously turned ON/OFF, can prevent the temperature rise of a work with less radiation of light of a wavelength region unnecessary for curing, has a long service life of a light source, has a good maintainability, and can secure surface-hardening. <P>SOLUTION: The lighting system which cures the photo-curable ink by irradiating the ink applied on the work with ultraviolet rays includes a first light source equipped with a discharge lamp which forms dielectric barrier discharge, and a second light source equipped with an LED. An irradiation region by the first light source and an irradiation region by the second light source overlap with each other on the work surface. The first light source is arranged on the side proximate to the work, and the second light source is arranged behind the first light source. It is preferable for the system to be constituted so that the light from the second light source penetrates the first light source and reaches the work. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a light source device that emits ultraviolet light suitable for curing a photocurable ink.

  Generally, ink used for printing includes photocurable ink and oil-based ink. Among these, the photocurable ink is composed of an ink, a monomer, a prepolymer, a polymerization initiator, a sensitizer, and the like, and irradiates ultraviolet rays having a wavelength range of 200 nm to 450 nm to excite the polymerization initiator to cure the ink. Is. This photo-curable ink is quick-drying compared to oil-based inks and does not contain organic solvents, so it has a relatively low odor and can be recorded on recording media that are not fast-drying and ink-absorbing as well as special paper. It attracts attention because it can be done.

  In such an ink jet printer using photo-curable ink, the ink is discharged as a fine droplet onto a recording medium and then cured by irradiating with ultraviolet rays. A light source device for irradiating ultraviolet rays is disposed in the vicinity of a recording head that discharges ink as droplets onto a recording medium, and an ultraviolet light source is provided on an image recording area (an area where an image is recorded by the recording head). Lights up and cures by irradiating ultraviolet rays onto the ink immediately after landing on the recording medium.

As an ultraviolet light source for this purpose, a long arc type discharge lamp such as a high pressure mercury lamp, a low pressure mercury lamp, or a metal halide lamp is usually applied. Currently, these lamp light sources have no major problems in curing performance, but potentially have the following problems.
(1) Since it cannot be instantaneously turned on / off, it is necessary to always light up, which is inefficient. Moreover, since it always lights, a shutter function is usually required.
(2) Since the light emitted from the lamp includes light in a wavelength region that is not necessary for curing, the temperature of the workpiece is increased.
(3) The apparatus becomes larger due to lamp cooling.
(4) The lamp life is short, and maintenance costs such as replacement are increased.
For these reasons, development of a new light source for solving the problem is expected.

  Recently, in order to meet expectations for ultraviolet light sources suitable for new cures, LEDs (Light-Emitting Diodes) that emit ultraviolet light have been developed, and in various directions, as light sources for photo-curable inks, Studies are underway on the replacement of lamps with LEDs.

However, the practical use of LED light sources still has major problems. Hereinafter, this reason will be described.
It is known that currently used radical polymerization photocurable inks cause reaction inhibition when they come into contact with oxygen during curing. This is because the radical derived from the initiator in the ink or the radical at the polymerization active end easily reacts with oxygen in the air, and the activity of the UV curable ink is reduced, and the ink is sufficiently cured. Because it will not promote.
Of the solutions to the polymerization inhibition caused by oxygen, the following method can be considered as a countermeasure on the irradiation side irrespective of the ink composition or the like.
A method of performing UV irradiation in a gas atmosphere that does not contain oxygen such as nitrogen.
A method of increasing the irradiation UV intensity and processing in a short time.
A method of irradiating short-wave UV light having high photon energy and large absorption on the ink surface.

For example, Japanese translations of PCT publication No. 2008-512711 list hardening effects for each wavelength region of ultraviolet rays. According to this, (1) UV-A radiation (wavelength: 320-400 nm) has a relatively large penetration depth and causes a relatively strong volume effect, ie polymerization of the entire layer volume of the final image, (2) UV -B radiation (wavelength: 280 to 320 nm) has a relatively shallow penetration depth, so the surface of the material is harder than inside the final image carrier. (3) UV-C radiation (wavelength: 200 to 280 nm) used.
That is, to summarize the above contents, in order to realize reliable curing of the ink, UV irradiation of 200 to 320 nm contributing to surface curing is required in addition to the 320 to 400 nm region causing the entire polymerization.

  However, as an ultraviolet LED capable of obtaining a practical output, an LED of 365 nm or less has a problem that a substantial effect cannot be obtained. Specifically, when compared with LEDs of 365 nm or more due to problems such as material absorption, the output is about 1/10 to 1/1000, so the practical short wavelength LED has a lower limit of 365 nm. Because it ends up. For this reason, even if it is going to harden photocurable ink using LED as a light source, the situation where the surface does not dry finally arises as a result of inhibition of radical polymerization by oxygen.

  Of course, in order to eliminate such problems on the LED side, the ink manufacturer can increase the sensitivity wavelength range of the photoinitiator as UV-LED ink, and polymerization can be started even at the LED wavelength (≧ 365 nm). Ink is being developed. However, there are still many problems such as an increase in the cost of ink containing a photoinitiator, surface wrinkles, and other problems such as problems in the surface cured state and poor light resistance.

Special table 2008-512711 gazette

  Accordingly, the problem to be solved by the present invention is a light source device that emits ultraviolet light suitable for curing a photocurable ink, can be instantaneously turned on and off, and emits light in a wavelength region unnecessary for curing. An object of the present invention is to provide a light source device that can prevent a temperature rise of a workpiece, has a simple cooling structure, has a long light source life, has good maintainability, and can ensure surface hardening.

In order to solve the above problems, a light source device according to the present invention is a light source device that cures the ink by irradiating the photocurable ink deposited on the workpiece with ultraviolet rays,
A first light source unit including a discharge lamp for forming a dielectric barrier discharge and a second light source unit including an LED;
The irradiation area by the first light source unit and the irradiation area by the second light source unit overlap on the work surface.
In addition, the first light source unit is disposed on the side close to the workpiece, the second light source unit is disposed behind the first light source unit, and light from the second light source unit is transmitted to the first light source unit. It is good to provide the structure which permeate | transmits a light source part and arrives at the said workpiece | work.
Moreover, it is preferable that the light emitting part in the first light source part and the light emitting part in the second light source part are arranged so as to be parallel to each other.
The emission wavelength region of the discharge lamp may be 200 to 350 nm, and the emission wavelength region of the LED may be 350 to 400 nm.

  According to the present invention, the discharge lamp and the LED that form the dielectric barrier discharge are both light sources that can be instantaneously turned on and off, have a fast rise, and need only be lit during a period that requires ink curing. It is possible to provide a light source device that requires less replacement of the light source and has good maintainability. And a discharge lamp can radiate | emit light with a wavelength less than 365 nm which is not in a practical wavelength with an LED light source, and it can implement | achieve ultraviolet radiation of 200-400 nm region by combining with a LED light source. In addition, since neither light source emits light in the wavelength region of visible light or infrared light that is unnecessary for curing, it is possible to prevent the temperature of the workpiece from being increased, and to provide a photocurable ink that can ensure curing. A light source device that emits ultraviolet rays suitable for curing can be provided.

It is a schematic perspective view explaining the mechanism of the printer carrying the light source device which concerns on 1st Embodiment of this invention. It is a section for explanation showing the state where the light source device concerning the present invention was cut along the sub-scanning direction (SS). It is a perspective view of the light source device shown in FIG. It is explanatory drawing which shows an example of the irradiation area | region in the workpiece | work surface formed from the light source device which concerns on this invention. It is a section for explanation showing the composition of the light source device concerning other embodiments of the present invention. It is a figure which shows an example of the illumination intensity distribution of the light source device which concerns on this invention.

A first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a schematic perspective view for explaining a mechanism of a printer equipped with a light source device according to the first embodiment of the present invention. 2 is a cross-sectional view illustrating the light source device of FIG. 1 cut along the sub-scanning direction (SS), FIG. 3 is a perspective view of the light source device shown in FIG. 2, and FIG. It is explanatory drawing which shows an example of the irradiation area | region in the workpiece | work surface formed from a light source device.
The printer shown in FIG. 1 is of an ink jet type, and includes, for example, a printing head 3 as a recording head that makes photocurable ink have a fine particle diameter and adheres to a printing paper P that is a work. The head 3 is pulled by a pulling belt 32 driven by a motor (not shown) and moves along the guide rail 31. Although not shown here, an ink cartridge for supplying ink to the print head 3 is mounted on the print head 3. The ink used is a photocurable ink that is cured by light in the ultraviolet region.

  When printing is completed in the scanning direction, the printing paper P is sequentially sent in the direction of the arrow along the sub-scanning direction SS and moves to the irradiation region of the light source device 1 that emits ultraviolet rays.

As illustrated in FIGS. 2 to 3, the light source device 1 according to the present embodiment includes a first light source unit 10 and a second light source unit 20 inside a housing 1 </ b> A. These two light source units 10 and 20 are arranged in a state in which the first light source unit 10 is positioned on the side close to the printing paper P and the second light source unit 20 is positioned behind the first light source unit 10.
Further, the first light source unit 10 and the second light source unit 20 are configured so that the light emitting units (light emitting surfaces) 10A and 20A are parallel to each other, and the irradiation areas of the light source units 10 and 20 are workpieces. By arranging such a configuration, light having different wavelength ranges is superimposed from the two light source units 10 and 20 to simultaneously and uniformly emit light on the surface of the printing paper P. It becomes possible to irradiate.

The first light source unit 10 includes a discharge lamp 11 made of an excimer lamp as a light source.
The configuration of the discharge lamp 11 will be described in detail. The arc tube 12 is made of glass having a material transmissive to light having a wavelength of 200 to 400 nm, for example, quartz glass, and is formed in a flat rectangular box shape. External electrodes 13 and 14 are disposed on the upper and lower surfaces of the arc tube 12. The external electrodes 13 and 14 are formed in a mesh shape so as to have optical transparency, or are configured by a transparent electrode (ITO) so as to have optical transparency, and the lamp itself has optical transparency. It is configured as follows. A power feeding portion is provided at the longitudinal end of the arc tube 12 of the discharge lamp 11, and a high frequency high voltage is applied to a pair of external electrodes from a lamp power source (not shown), and the arc tube is made of a dielectric wall. 12, that is, a dielectric barrier discharge is formed.
The discharge lamp 11 has an effective light emitting area having a predetermined width dimension W2 (see FIG. 2) along the sub-scanning direction SS of the printing paper P in the inkjet printer. 20 is larger than the maximum width (L) of the maximum paper handled.

  The discharge gas sealed in the arc tube 11 is filled with a gas that emits excimer light by this discharge. The discharge gas emits ultraviolet rays in a wavelength range of 200 to 400 nm, particularly in a necessary wavelength range of 200 to 350 nm, and is specifically as shown in Table 1. Such a discharge gas may have a single composition or may be used in an appropriate combination.

  In addition to taking out such excimer light, various types can be used regardless of this example as long as dielectric barrier discharge is used. For example, a discharge gas that emits excimer light having an emission wavelength of 200 nm or less is enclosed in the arc tube, and is excited by ultraviolet rays obtained by light emission, so that ultraviolet rays in a necessary wavelength band (200 to 350 nm) are obtained. A lamp that emits light in a desired ultraviolet region by irradiating a fluorescent material that emits light may be used.

  In any case, a discharge lamp using a dielectric barrier discharge has excellent startability, has a fast start-up after voltage application, can be turned on instantaneously, and discharges ink after starting printing from the printer control circuit. It can be used by lighting only during the curing period. Therefore, it is not necessary to always turn on the lamp, the use of electric power can be suppressed, and it is not necessary to use a light shielding shutter, so that the configuration of the entire light source device can be simplified.

Next, the second light source unit will be described.
The second light source unit includes a plurality of LEDs 22 that emit ultraviolet rays, a circuit board 21 that supports these LEDs 22, a light source device drive circuit (not shown) that controls light emission and extinction of each LED 22, and a plurality of LEDs 22. And a lens 25 for mixing and uniformizing the radiated light within a predetermined region.
The circuit board 21 has a plate-like structure having a predetermined width dimension W2 (see FIG. 2) along the sub-scanning direction SS of the printing paper P in the ink jet printer, and the length dimension is the maximum that the printer 20 can handle. It is set larger than the width dimension (L) of the paper.

  The LED 22 has a configuration molded on the lens body 23 and is connected to and supported by the circuit board 21. On the back surface of the circuit board 21, in order to dissipate heat generated from the LEDs 22, a heat dissipating part 24 in which a member having good heat conductivity is formed in a fin shape is provided.

  The lens 25 arranged in front of the LED light source 22 is made of, for example, a condenser lens, and light emitted from each LED 22 light source so that the irradiation region overlaps the irradiation region where the first light source unit irradiates the printing paper P. Is collected and emitted. Such a lens can be replaced by another optical system, and is not essential for carrying out the present invention.

  As shown in FIG. 2, the circuit board 21 is arranged in parallel to the arc tube 12 of the discharge lamp 11, and the mounting surface 21 a to which the LED light source 22 is attached is opposed to the discharge lamp 11 and is not shown. It is supported by the support member.

  In the case of the present embodiment, the LED used is one that emits ultraviolet rays of a predetermined wavelength band, and a preferable wavelength band is 320 to 400 nm necessary for initiating polymerization of the entire photocurable ink. Ultraviolet rays in the region. However, an LED that emits ultraviolet light having a wavelength of less than 365 nm has low efficiency, and when it is not practical, an LED that emits light having a wavelength of about 350 nm to 400 nm is preferable. Of course, an LED that emits ultraviolet light having a wavelength shorter than 350 nm may be used as long as it can achieve the required efficiency. It is only necessary that the type of discharge gas of the discharge lamp is selected in accordance with the wavelength range of light emitted from the LED, and as a result, the wavelength range of 200 to 400 nm can be complemented.

  In this way, the emitted light from the first light source unit 10 directly irradiates the printing paper P, and the emitted light from the second light source unit passes through the first light source unit 10 to be the first. The print paper P is irradiated with the light emitted from the light source unit. As a result, the printing paper P is irradiated with ultraviolet rays having a wavelength of 200 to 400 nm, and both the surface curing and the entire polymerization treatment can be completed, so that the ink can be reliably cured.

FIG. 4 is an explanatory diagram illustrating an example of an irradiation area on the work surface (that is, the printing paper P) formed by the light source device 1.
In the figure, the irradiation area Q1 from the first light source section is formed to have a larger dimension than the irradiation area Q2 from the second light source section, and the irradiation areas Q1 and Q2 are portions that overlap on the work surface. Have Here, the irradiation regions Q1 and Q2 by each light source unit do not have to be completely coincident as shown in the figure, and at least in the portion where light is superimposed (the portion coincident with Q2 in the figure), the length direction and width Any device having a predetermined size in the direction may be used. By disposing the first and second light source units so that the irradiation regions overlap in this way, it becomes possible to simultaneously irradiate the workpiece with light having different emission wavelength ranges.

As described above, by using the LED and the discharge lamp in combination, it is possible to irradiate ultraviolet rays in a wavelength range of 200 to 400 nm while realizing high efficiency, and any light source that is unnecessary for curing is visible light or infrared light. Therefore, it is possible to provide a light source device that can prevent the temperature of the workpiece from being increased and ensure the curing. In addition, since both the discharge lamp and the LED light source can be turned on and off instantaneously, the start-up is fast, and it is only necessary to turn on only during a period where curing is necessary. Thus, a light source device with good maintainability can be obtained. It is also eco-friendly because it does not consume unnecessary power.
In particular, an LED that emits light having a wavelength of 350 to 400 nm in the wavelength band and a discharge lamp that emits light having a wavelength of 200 to 350 nm or less are used. Can be provided.

In the above-mentioned present invention, it can change suitably. For example, regarding the discharge lamp, a light emitting tube having a substantially box shape with a rectangular cross section is used. However, the present invention is not limited to such an example, and a cylindrical tube may be used.
FIG. 5 shows a configuration of a light source device according to such another embodiment. In the description of FIG. 5, the same components as those previously described in FIGS. 1 to 4 are denoted by the same reference numerals and detailed description thereof is omitted.
The discharge lamp 15 includes cylindrical arc tubes sealed at both ends, and is arranged side by side so that the tube axes are parallel to each other and parallel to the workpiece (printing paper P) surface. Has been. The discharge lamp 15 also forms a dielectric barrier discharge. Although not shown in the figure, a pair of electrodes are arranged with a dielectric composed of an arc tube interposed therebetween, so Connected to voltage power source.
With these discharge lamps 15, the first light source unit 10 forms a planar light source. A second light source unit is disposed behind the first light source unit. The irradiation region by the first light source unit, the irradiation region by the second light source unit, and the work (printing paper P) surface. It is configured to overlap.

  Even in such a light source device according to another embodiment, a region having a constant illuminance distribution in the width direction of the light source device can be obtained, and it becomes possible to simultaneously irradiate light having different emission wavelength ranges. Curing can be performed reliably.

FIG. 6 shows an example of the illuminance distribution in the cross-sectional direction along the sub-scanning direction SS in the light source device according to the present invention.
FIG. 6 shows a light source device based on the configuration shown in FIG. 2 to FIG. 3, using a first illuminometer having sensitivity at a wavelength of 254 nm and a second illuminometer having sensitivity at a wavelength of 365 nm. It is a figure which shows illuminance distribution when illuminance is measured along a subscanning direction. In the figure, a curve (A) is a measured value by a first illuminometer, and a curve (A) is a measured value by a second illuminometer.
As is clear from this result, the first light source unit and the second light source unit are arranged so that the respective light emission surfaces are parallel to each other and the irradiation regions are overlapped, so that the width direction of the light source device is obtained. In (W1, W2), a region with a constant illuminance distribution is obtained, and light having different emission wavelength ranges can be irradiated uniformly at the same time.

If the light emission part (surface) of the first light source part and the light emission part (surface) of the second light source part are not positioned in a parallel state, a difference in illuminance occurs on the work surface, There are cases where the curing of the ink cannot be sufficiently promoted.
On the other hand, according to the present invention, the first light source unit and the second light source unit are arranged so that the respective light emission surfaces are parallel to each other and the irradiation regions are overlapped. The illuminance distribution can be made constant, and the ink can be reliably cured.

DESCRIPTION OF SYMBOLS 1 Light source device 1A Case 10 1st light source part 10A Light emission part (surface)
DESCRIPTION OF SYMBOLS 11 Discharge lamp 12 Light-emitting tube 13, 14 External electrode 15 Discharge lamp Q1 Irradiation area 20 by 1st light source part 2nd light source part 20A Light-emitting part (surface)
21 Circuit board 22 LED
23 Lens body 24 Heat radiation part 25 Lens Q2 Irradiation area P by the second light source part Printing paper

Claims (4)

A light source device that cures the ink by irradiating the photocurable ink applied to the workpiece with ultraviolet rays,
A first light source unit including a discharge lamp for forming a dielectric barrier discharge and a second light source unit including an LED;
The light source device characterized in that an irradiation region by the first light source unit and an irradiation region by the second light source unit overlap on the work surface. The first light source unit is disposed on the side close to the workpiece, and the second light source unit is disposed behind the first light source unit,
The light source device according to claim 1, wherein the light from the second light source unit passes through the first light source unit and reaches the workpiece. 2. The light source device according to claim 1, wherein the light emitting unit in the first light source unit and the light emitting unit in the second light source unit are arranged in parallel to each other. The emission wavelength region of the discharge lamp is 200 to 350 nm,
4. The light source device according to claim 1, wherein an emission wavelength region of the LED is in a range of 350 to 400 nm.

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