JP5239961B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus and an image forming method, and more particularly to an image forming apparatus and an image forming method using an ultraviolet curable ink.

  As an image forming apparatus such as a printer, a facsimile, a copying apparatus, a plotter, and a complex machine of these, for example, an ink jet recording apparatus or the like is used as an image forming apparatus of a liquid discharge recording method using a recording head that discharges ink droplets as an image forming means. Are known. This liquid discharge recording type image forming apparatus means that ink droplets are transported from a recording head (not limited to paper, including OHP, and can be attached to ink droplets and other liquids). Yes, it is also ejected to a recording medium or recording medium, medium, recording paper, recording paper, etc.) to form an image (recording, printing, printing, and printing are also used synonymously). A serial type image forming apparatus that forms an image by ejecting liquid droplets while the recording head moves in the main scanning direction, and a line that forms an image by ejecting liquid droplets without moving the recording head There is a line type image forming apparatus using a type head.

  In the present application, the “image forming apparatus” of the liquid discharge recording method is an apparatus that forms an image by discharging liquid onto a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, or the like. In addition, “image formation” means not only giving an image having a meaning such as a character or a figure to a medium but also giving an image having no meaning such as a pattern to the medium (simply It also means that a droplet is deposited on a medium). The “ink” is not limited to what is called ink, and is not particularly limited as long as it becomes a liquid when ejected. For example, a DNA sample, a resist, a pattern material, etc. Is also included.

  In such an image forming apparatus, an apparatus using ultraviolet curable ink as an ink is known. For example, a recording head that discharges ink that is cured by being irradiated with ultraviolet rays from a nozzle toward a recording medium, an ultraviolet irradiation unit that irradiates ink discharged onto the recording medium with ultraviolet rays, a recording head, and an ultraviolet irradiation unit And an optical trap that opens toward the recording medium side that captures the ultraviolet rays irradiated from the ultraviolet irradiation section, and reduces the amount of ultraviolet rays incident on the nozzle surface, thereby ensuring stable ink ejection over a long period of time. There is something that can be performed (Patent Document 1).

  In addition, the nozzle top plate and protective plate have UV absorption and UV ink resilience so that UV rays reflected and absorbed toward the recording head can be absorbed. Since the ink meniscus of the resting nozzle is slightly vibrated and the ink thickened in the nozzle is stirred to improve the intermittent discharge property (Patent Document 2). .

  Furthermore, a plate material for preventing primary reflection of ultraviolet rays to the recording head is disposed in the respective areas of the home position and the head moving direction conversion position so as to be close to the lower side of the emission port of the ultraviolet irradiation device in the area. When the head part moves to the home position and the head moving direction conversion position, the primary reflected light of the ultraviolet ray emitted from the ultraviolet ray irradiation device hits the nozzle of the recording head, the ink is cured, and the ink passage of the head part is clogged. There is also known one that prevents the above (Patent Document 3).

Japanese Patent Application Laid-Open No. 2004-167871 JP-A-2005-47261 JP 2004-338264 A

  As described above, when image formation is performed using ultraviolet curable ink, after ultraviolet curable ink is ejected from the nozzle of the recording head onto the recording medium, ultraviolet light is irradiated from an ultraviolet light source provided in the vicinity of the recording head. The ink attached to the recording medium is cured. At this time, in order to improve the recording accuracy and improve the quality of the recorded image, it is preferable to cure the ink by irradiating with ultraviolet light at the moment when the ink adheres to the recording medium or immediately after that. As long as the exit of the ultraviolet light source exits, it must be as close to the nozzle as possible.

  However, when the emitted ultraviolet light is reflected on the recording medium surface and the reflected light is incident on the recording head surface, the ink adhering to the surface of the recording head is solidified and fixed, and special maintenance is performed to remove it. A process is required. In addition, when the ink is cured by the incidence of ultraviolet rays on the nozzle portion of the recording head, it becomes impossible to discharge, or the ink discharge amount and the discharge direction at the nozzle opening changes, and the ink discharge characteristics deteriorate. This causes the image quality to deteriorate.

  For this purpose, various conventional configurations described above are employed. In these configurations, when the ultraviolet irradiation unit is sufficiently away from the nozzle unit, the ultraviolet rays reaching the nozzle are reduced by multiple reflection. Particularly effective, when the ultraviolet irradiation part is close to the nozzle part, there is a problem that the reflected light from the surface of the recording medium directly reaches the nozzle part and the ink is cured at the nozzle part.

  The present invention has been made in view of the above-described problems, and can be cured by irradiating with ultraviolet light at the moment when ink is deposited on the recording medium or immediately after that, and is reflected on the surface of the recording medium. An object of the present invention is to reduce the amount of ultraviolet rays reaching the nozzle surface of the image forming means, to stably discharge ink, and to stably form a high quality image.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
Image forming means having a nozzle for discharging ink that is cured by absorbing ultraviolet rays onto a recording medium;
Curing means for irradiating and curing the ink deposited on the recording medium with ultraviolet light; and
The curing means has a polarizing element that transmits a linearly polarized component of ultraviolet light emitted from an ultraviolet light source, and is configured to irradiate the ink with polarized ultraviolet light.

  Here, the polarizing element can be configured to transmit ultraviolet light composed of a polarization vibration component (P-polarized light) perpendicular to the surface of the recording medium.

  Further, the optical axis incident angle of the polarized ultraviolet light irradiated on the recording medium with respect to the surface of the recording medium is an angle at which the reflected light of the ultraviolet light on the surface of the recording medium is minimized. And can.

  In this case, the exit of the polarized ultraviolet light from the curing unit can be provided adjacent to the image forming unit.

  The image forming unit and the curing unit are provided integrally, and the nozzle of the image forming unit opens at a position where the polarized ultraviolet light from the curing unit is regularly reflected on the surface of the recording medium. It can be configured.

An image forming method according to the present invention includes:
A printing step in which ink that is cured by absorbing ultraviolet rays from the nozzles of the image forming means is ejected and adhered onto a recording medium;
A curing step of irradiating and curing the ink deposited on the recording medium with ultraviolet light, and
In the curing step, ultraviolet light emitted from an ultraviolet light source is polarized and irradiated through a polarizing element that transmits a linearly polarized light component to cure the ink.

  According to the image forming apparatus and the image forming method according to the present invention, the ink deposited on the recording medium is cured by irradiating the polarized ultraviolet light through the polarizing element that transmits the linearly polarized light component. The amount of ultraviolet light reflected on the surface of the recording medium is reduced, ink can be stably ejected, and high-quality images can be stably formed.

1 is a schematic explanatory diagram of an image forming apparatus according to a first embodiment of the present invention. It is explanatory drawing with which it uses for description of the relationship between the incident angle of polarized light, and a reflectance. It is explanatory drawing with which it uses for description of the angle from which a reflectance becomes the minimum. FIG. 6 is a schematic explanatory diagram of an image forming apparatus according to a second embodiment of the present invention. It is typical explanatory drawing with which it uses for description of an effect | action of the apparatus.

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, an image forming apparatus according to a first embodiment of the present invention will be described with reference to a schematic explanatory diagram of FIG.
The image forming apparatus includes a recording head 4 that is an image forming unit (ink ejection unit) having a nozzle 3 that ejects ultraviolet curable ink 2 that is cured by absorbing ultraviolet rays on a recording medium 1, and a target. A curing unit 5 for irradiating and curing the droplet-shaped ink 2 deposited on the recording medium 1 with ultraviolet light, and a conveying unit 8 for conveying the recording medium 1 are provided.

  Here, as the recording medium 1, various papers such as plain paper, recycled paper, glossy paper, various fabrics, various non-woven fabrics, resin, glass, or a composite sheet of these materials can be used. It is. In particular, the ultraviolet curable ink is particularly effective for glass, resin, coated paper whose surface is coated with resin, glossy paper, and the like. In addition, the form of the recording medium 1 may be any form such as a roll, a cut sheet, and a plate.

  The ultraviolet curable ink 2 contains at least a polymerizable compound, a photoinitiator, and a color material as main components. In addition, additives such as a leveling agent, a reaction accelerator, a reaction inhibitor, and a sensitizer may be included. UV curable inks are broadly classified into radically polymerizable inks containing radically polymerizable compounds and cationically polymerizable inks containing cationically polymerizable compounds as polymerizable compounds. Both types of inks can be applied. There may be used a mixed system. In addition to black, cyan, magenta, yellow, white, and the like as the color material, it is also possible to use a clear ink or a light color ink that enriches gradation expression. In the present embodiment, any one color ink is ejected from one recording head 4, and the recording head 4 is provided for each color (not shown).

  The recording head 4 includes a plurality of nozzles 3 arranged in a row on the lower surface thereof and ink chambers corresponding to the respective nozzle positions, and actuator means (piezoelectric actuators, thermal actuators, static actuators) provided corresponding to the respective ink chambers. By changing the volume of each ink chamber by means of an electric actuator or the like, a liquid ejection head that can eject droplets of ink 2 from a required nozzle 3 at a required timing is constituted. The plurality of nozzles 3 are arranged in one or a plurality of rows. The recording head 4 is supplied with ink of each color from the ink supply means 10.

  The curing means 5 includes an ultraviolet light source 11 that emits ultraviolet light 9 and a polarizing element 13 that emits ultraviolet light 12 that is polarized by polarizing the ultraviolet light 9 from the ultraviolet light source 11.

  As the ultraviolet light source 11, a low-pressure mercury lamp, a high-pressure mercury lamp, a metal halide lamp, a hot cathode tube, a cold cathode tube, an LED, or the like is applicable. In particular, a light source having a narrow wavelength distribution of irradiation light such as an LED is suitable for the present invention. Although not shown, the irradiation optical system is preferably one that irradiates parallel light after condensing.

  The polarizing element 13 is an element that allows only linearly polarized light to pass through, and in particular, the deflecting element 13 is adjusted to an angle that transmits only the vertical vibration component (P-polarized light) with respect to the surface of the recording medium 1. Further, the substrate of the polarizing element 13 is preferably quartz or the like that absorbs less ultraviolet light, and the surface on the side of the ultraviolet light source 11 is preferably subjected to antireflection treatment. Here, referring to FIG. 2A, assuming an incident surface 101 perpendicular to the glass surface 100, the vibration component perpendicular to the glass surface 100 is P-polarized light and perpendicular to the incident surface 101. Such a vibration component is called S-polarized light, and the reflectance with respect to the incident angle of each deflection (P-polarized light, S-polarized light) is as shown in FIG. 2B when the refractive index of the glass surface 100 is 1.5.

  The exit 13a of the polarized ultraviolet light 12 emitted from the polarizing means 13 is disposed adjacent to the recording head 4, and the moment when the ink 2 ejected from the recording head 4 has landed on the recording medium 1 or its Immediately after that, the polarized ultraviolet light 12 is applied to the ink 2 that has landed.

  As the conveying means 8, a conveying belt 16 wound around a driving roller 14 and a driven roller 15 is used, but is not limited to this. A thing using a conveyance roller, a thing using an XY stage, the combination, etc. can be utilized. In this case, when the recording medium 1 is not a continuous paper or a roll-shaped medium, the surface is made of a material excellent in transparency at the ultraviolet wavelength in order to prevent irregular reflection of ultraviolet light on the conveying surface of the conveying means. A smooth material is preferable, and a material having a high ultraviolet absorption rate is also preferable.

Next, an image forming method according to the present invention in the image forming apparatus configured as described above will be described.
Here, a roll-shaped transparent resin film is used as the recording medium 1, and an image is formed by ejecting the ultraviolet curable ink 2 from the plurality of nozzles 3 of the recording head 4 while the transparent resin film is being conveyed by the conveying means 8. To do.

  At this time, the ink 2 ejected from the nozzle 3 is deposited on the recording medium 1 approximately 1 mm below, and is moved by the conveying means 8 in the horizontal direction, and irradiated with the polarized ultraviolet light 12 immediately after the deposition. . Since the polarized ultraviolet light 12 has a lower reflectivity at the surface (recording medium surface) 1a of the recording medium 1, the ultraviolet light reaching the nozzle 3 of the recording head 4 and its periphery by reflection from the recording medium surface 1a. The amount of light is reduced, and it is possible to prevent the ink 2 from being cured by the ultraviolet light reflected from the nozzle 3 and its surroundings, or the viscosity from increasing, thereby causing an ejection failure.

  In particular, as described above, when the polarized ultraviolet light 12 is composed of a polarization vibration component (P-polarized light) perpendicular to the recording medium surface 1a, the reflectance on the recording medium surface 1a can be effectively reduced. it can.

  In this case, as shown in FIG. 3, the angle θ at which the polarized ultraviolet light 12 is incident on the recording medium surface 1a is Brewster's angle (when the refractive index of the recording medium surface 1a is n, θ = arctan (n ), The amount of reflected light 17 can be minimized (theoretically, the amount of reflected light becomes zero) In the case of glass or resin film, as shown in FIG. Since it is 1.5, reflection from the recording medium 1 can be minimized when the incident angle θ is about 56 degrees.

  By setting the conditions for polarized light irradiation, it is possible to effectively reduce the reflection of ultraviolet rays. Therefore, it is possible to irradiate ultraviolet light from the very vicinity of the nozzle 3 which has been difficult due to the problem of nozzle curing. . On the other hand, although it was possible to reduce the multiple reflected light in the past, it is not possible to prevent the direct reflected light from the recording medium surface 1a from reaching the nozzle 3, so that the ultraviolet light from the vicinity of the nozzle 3 can be prevented. Irradiation with light was not possible.

  As a result, it is possible to cure the ink 2 immediately or immediately after the ink 2 has landed on the recording medium 1, and to suppress bleeding of the ink 2 and mixing of the ink 2 on the recording medium 1. As a result, a higher quality image can be stably obtained.

  In this way, the ink that has landed on the recording medium is cured by being irradiated with ultraviolet light that has been polarized through a polarizing element that transmits a linearly polarized component, so that it is reflected on the surface of the recording medium. The amount of ultraviolet light to be reduced is reduced, ink can be stably ejected, and high-quality images can be stably formed.

Next, a second embodiment of the image forming apparatus according to the present invention will be described with reference to FIG.
Here, the recording head 4 and the curing means 11 are provided integrally, and the exit 19 of the polarized ultraviolet light 12 is disposed adjacent to the recording head 4. The nozzle 3 is open at a position where it is regularly reflected (optical path indicated by a broken line) on the recording medium surface 1a with respect to the optical axis of the polarized ultraviolet light 12 (P-polarized light). This position is determined by the Brewster angle (incident angle at which the reflectance of P-polarized light is theoretically zero) calculated from the refractive index of the recording medium surface 1 a and the distance between the recording medium surface 1 a and the nozzle 3. Is done. Note that since the orthogonal light on the surface 1a of the P-polarized recording medium is almost zero, there is no problem even if the nozzle 3 exists at the position of the regular reflection.

  With this configuration, the reflected light 17 is small even when the incident angle is shifted up and down in the vicinity of the Brewster angle due to the waviness of the surface 1a of the recording medium, based on the relationship between the reflectance and the angle (FIG. 2). The influence on the nozzle 3 is small. When the incident angle is greatly changed by the ink 2 or the like that has become droplets on the surface 1a of the recording medium, the reflected light 17 is directed away from the nozzle 3 as shown in FIG. There is no direct impact.

  Similarly, the amount of light that reaches the nozzle 3 is considered to be small because the amount of scattered light caused by the surface roughness of the recording medium 1 is close to zero in the optical path toward the nozzle 3.

  As a result, the ink 3 can be cured at the moment when the ink 2 is deposited on the recording medium 1 or immediately after that, and the bleeding of the ink 2 and the mixing of the ink 2 on the recording medium 1 are suppressed. High-quality images can be stably formed.

  In addition, it is difficult to be affected by the undulation of the surface of the recording medium 1 or ink droplets, and it is possible to prevent ejection problems due to ink curing in the nozzles 3 and improve ejection reliability. Furthermore, by integrating the recording head as the ejection unit and the curing unit, the number of parts is reduced and positioning becomes easy, which is effective in reducing process costs.

  The recording medium used in this embodiment is particularly effective when the surface is smooth, transparent, and has a UV-absorbing glass or resin film.

DESCRIPTION OF SYMBOLS 1 Recording medium 2 Ink 3 Nozzle 4 Recording head (image formation means)
5 Curing means 11 Ultraviolet light source 12 Polarized ultraviolet light 13 Polarizing element

Claims (6)

Image forming means having a nozzle for discharging ink that is cured by absorbing ultraviolet rays onto a recording medium;
Curing means for irradiating and curing the ink that has landed on the recording medium with ultraviolet light;
The image forming apparatus, wherein the curing unit includes a polarizing element that transmits a linearly polarized component of ultraviolet light emitted from an ultraviolet light source, and irradiates the ink with polarized ultraviolet light.   The image forming apparatus according to claim 1, wherein the polarizing element transmits ultraviolet light composed of a polarization vibration component (P-polarized light) in a direction perpendicular to a surface of the recording medium.   An optical axis incident angle of the polarized ultraviolet light applied to the recording medium with respect to the surface of the recording medium is an angle at which reflected light of the ultraviolet light on the surface of the recording medium is minimized. The image forming apparatus according to claim 2.   The image forming apparatus according to claim 3, wherein an exit of the polarized ultraviolet light from the curing unit is provided adjacent to the image forming unit.   The image forming unit and the curing unit are provided integrally, and the nozzle of the image forming unit opens at a position where the polarized ultraviolet light from the curing unit is regularly reflected on the surface of the recording medium. The image forming apparatus according to claim 3. A printing step in which ink that is cured by absorbing ultraviolet rays from the nozzles of the image forming means is ejected and adhered onto a recording medium;
A curing step of irradiating and curing the ink landed on the recording medium with ultraviolet light, and
In the curing step, the ink is cured by irradiating the ultraviolet light emitted from the ultraviolet light source through a polarizing element that transmits a linearly polarized light component.

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