Patent Publication Number: US-2005128274-A1

Title: Ink jet printer

Description:
TECHNICAL FIELD  
      The present invention relates to an ink jet printer.  
     BACKGROUND ART  
      There has been known a UV ink jet printer that carries out printing with use of UV ink curable with irradiation of ultraviolet (UV) rays.  
      In printing images by the UV ink jet printer, first, recording heads or the like eject and deposit UV ink on a recording medium such as a film, for example, then a UV irradiating means irradiates ultraviolet rays onto the recording medium to cure and fix the UV ink on the recording medium.  
      Such a UV ink jet printer described above usually uses as the UV irradiating means a high pressure ultraviolet lamp which has high illumination of ultraviolet rays and high curability of the UV ink. This UV ink jet printer can print images even on a recording medium which does not absorb ink at all.  
      There has been also known an ink jet printer having an excimer laser device which irradiates laser beams as the light to cure the ink (see, for example, patent document 1).  
      (Patent Document 1)  
      Japanese Patent Publication (Laid-Open) No. Tokukai-2001-310454 (page 4, FIG. 1)  
      However, the high pressure UV lamp generates lots of heat because most of supplied electric power is converted into heat. Therefore, a large capacity of power source is needed to secure sufficient illumination for curing the ink, which leads to a problem of increasing a device cost. Additionally, it is needed to provide a duct for exhausting the heat, which produces a problem of increasing a manufacturing cost as well as a large printer size. Meanwhile, if an excimer laser is used as the irradiating means as disclosed in the patent document 1, this also leads to a problem of making a printer size larger.  
      Further, the temperature rise of a recording medium due to the heat generated by the high pressure UV lamp causes another problem when a recording medium is, for example, plastic base material or the like that is easily deformed by heat, in that curling or melting of the recording medium disables high precision printing. Particularly, when using a shrinkable film that gets close contact with containers or the like by shrinkage with given heat, it has been difficult to print on the medium by the UV ink jet printer because of the medium shrinkage during printing.  
      It is therefore an object of the invention to provide a small-sized ink jet printer capable of printing on various types of recording mediums at a lower cost.  
     DISCLOSURE OF THE INVENTION  
      The present invention is an ink jet printer that carries out printing by depositing UV ink which is curable by irradiation of an ultraviolet ray, on a recording medium, and irradiating ultraviolet rays on the recording medium, wherein the printer comprises an UV irradiating unit to enable irradiation of an ultraviolet ray on the ink deposited on the recording medium, and the UV irradiating unit comprises either a semiconductor laser or an LED, which enables emitting light the peak wavelength of which includes any one of wavelengths in an ultraviolet range which allow to cure the UV ink.  
      According to the invention, since the UV irradiating means includes either a semiconductor laser or LEDs, irradiation of ultraviolet rays generates little heat, thereby to improve energy efficiency of the UV irradiating means. Accordingly, the ink jet printer can have a smaller capacity of power source and does not need to have a duct or the like for exhausting the heat. As a result, it is possible to lead to a lower cost and small-sized ink jet printer.  
      Little heat generated with the irradiation of ultraviolet rays from the UV irradiating means does not cause deformation of the recording medium even if the medium is apt to be deformed by the heat. According to the invention, it is possible to print on various types of recording mediums.  
      Further, when a semiconductor laser is employed as the light source, an attenuation of light intensity is smaller relative to a longer irradiating distance. Therefore, the semiconductor laser can be arranged apart from the recording medium, so that it is possible to prevent the recording medium from being affected by the heat generation of the light source securely.  
      In the ink jet printer, the recording medium may be a resin base material or a shrinkable film which shrinks by heating.  
      The following components are preferably usable as the resin base material: polyester, polyolefin, polyamide, polyester amide, polyether, polyimide, polyamideimide, polystyrene, polycarbonate, poly-p-phenylene sulfide, polyether ester, polyvinyl chloride, poly-(meth)acrylate, polyethylene, polypropylene, nylon and the like. Further, copolymer or mixture, of these resins, and cross-linked resins can be also applied. Particularly, oriented polyethylene terephthalate, polystyrene, polypropylene and nylon are preferable from the viewpoints of their transparency, dimension stability, rigidity, environmental load and cost.  
      As component material of a shrinkable film (thermo-shrinkable synthetic resin film), the following thermo-shrinkable films as generally used for shrinkable labels are applicable: polyethylene terephthalate film, polystyrene film, vinyl chloride film, polypropylene film and the like.  
      According to the invention, even if the recording medium is of resin base material or a shrinkable film that shrinks by heating, the little heat generation at the time of irradiation of ultraviolet rays does not raise the temperature of the recording medium so much as it is deformed.  
      In the ink jet printer, the recording medium may be a long-length film which is in rolled states before and after a printing area.  
      According to the invention, since the recording medium is a long-length film which is in rolled states before and after a printing area, the volume occupied by the recording medium can be limited, whereby the recording medium can be installed without making the ink jet printer large-sized.  
      In the ink jet printer, the UV ink may be of a cationic polymerization type.  
      According to the invention, in addition to the same effects as that of the invention described above, the light intensity necessary to cure the UV ink deposited on the recording medium can be reduced because the UV ink has particularly cationic polymerizable property, while the cationic polymerization type UV ink is more sensitive to ultraviolet rays than radical polymerization type UV ink and oxygen hardly inhibits polymerization. With this reason, it is not needed to increase the number of provided semiconductor laser or LED devices, which act as a lower illumination light source compared with the high pressure UV lamp, whereby irradiation energy necessary to cure the UV ink can be sufficiently given without making the printer large-sized. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a side view showing main portion of the UV ink jet printer according to one embodiment of the invention; and  
       FIG. 2  is a plan view showing the main portion of the UV ink jet printer of  FIG. 1 . 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      A description will be given of a UV ink jet printer  1  according to an embodiment of the invention with reference to the drawings. The printer  1  performs printing an image by ejecting and depositing UV ink which is curable by irradiation of ultraviolet (UV) rays, on a recording medium M, and irradiating it after the deposition.  
      The outer portion of the UV ink jet printer  1  is covered, for example, by a case  2 . The ink jet printer includes a recording medium feeding section  3  for feeding the recording medium M during printing, a carriage  4  having recording heads (not shown) mounted thereon for ejecting and depositing the UV ink on the recording medium M, and a UV-LED light source (UV irradiating means)  5  for irradiating ultraviolet rays onto the recording medium M on which the ink is deposited.  
      The recording medium M is, for example, a long-length thermo-shrinkable polyethylene terephthalate film (shrinkable film) that shrinks by heating. The thickness of the recording medium M is preferably 2 to 100 μm, more preferably 6 to 50 μm, and further preferably 10 to 30 μm.  
      The recording medium feeding section  3  is, for example, disposed at the lower portion of the case  2 , and has a supplying portion  31  for rolling the recording medium M before image printing, a receiving portion  32  for rolling up the medium M after image printing, and a platen  33  arranged substantially horizontally between the supplying portion  31  and the receiving portion  32  for supporting the backside surface of the recording medium M on its upper surface.  
      The recording medium feeding section  3 , at the time of printing, moves the recording medium M in a direction of the arrow X in  FIG. 2  by rolling up the medium M to the receiving portion  32  every time the ejection of UV ink (to be described later) is completed for a predetermined area on the medium M. Meanwhile, the recording medium M is to be printed on the upper surface.  
      Above the platen  33 , the carriage  4  and the UV-LED light source  5  are also provided.  
      The carriage  4  accommodates a plurality of recording heads corresponding to the number of colors to be used for printing images on the recording medium M, each head having nozzle orifices (not shown) facing downward.  
      The carriage  4  is reciprocally movable by a moving mechanism (not shown) in a direction of the arrow Y in  FIG. 2  with respect to the main body of the UV ink jet printer  1 , and repetition of this reciprocal movement constitutes recording head scanning.  
      Each recording head ejects UV ink supplied from an ink supply means (not shown) through a plurality of nozzle orifices toward the recording medium M with a plurality of jetting means (not shown) provided in the head energized.  
      The UV ink is composed of, for example, a pigment, a polymerizable compound, and a photo reaction initiator. The UV ink has the property of being cured by cross-linking or polymerization with the initiator acting as a catalyst by irradiation of ultraviolet rays.  
      The UV ink used in the embodiment will be described below in more detail.  
      As the UV ink used in the embodiment, a UV ink adapted in “Curing System Utilizing Photo-Acid and Base Generating Agent (Section 1)” or “Photo-induced Alternating Copolymerization (Section 2)” of “Photo-Curing System (Chapter 4)” in “Photo-Curing Technique—Selection and Compounding Condition of Resin and Initiator, and Measurement and Assessment of Curing Degree (Technical Association Information)” can be applied. A UV ink curable by normal radical polymerization can be also applied.  
      Concretely, the UV ink used in the embodiment is curable by irradiation of ultraviolet rays, and contains as a main component at least polymerizable compound (including well-known polymerizable compound), initiator, color material and the like. However, when the ink which is adapted to the above described “Photo-Induced Alternating Copolymerization (Section 2)” is used as the UV ink in the embodiment, photo reaction initiator may be excluded.  
      The UV ink is broadly categorized into radical polymerization type UV ink including a radical polymerizable compound, and cationic polymerization type UV ink including a cationic polymerizable compound, as a polymerizable compound. Both types of UV ink are applicable as the UV ink in the embodiment. Hybrid type UV ink which is mixed with the radical polymerization type UV ink and the cationic polymerization type UV ink may also be applied as the ink to be used in the embodiment.  
      However, the cationic polymerization type UV ink, which is more sensitive to ultraviolet rays and in which oxygen hardly inhibits polymerization, is particularly used in the embodiment because of the superiority in its functionality and generality.  
      The cationic polymerization type UV ink used in the embodiment is specifically a mixture containing at least a cationic polymerizable compound, e.g., oxetane compound, epoxide compound, vinyl ether compound or the like, a photo cationic initiator and a coloring agent, and has a property curable by irradiation of ultraviolet rays as described above.  
      The recording heads eject and deposit UV ink droplets to a predetermined area on the recording medium M according to image information sent from a control means (not shown) during the scanning that the heads move from one end to the other end of the recording medium M in the Y direction in  FIG. 2 .  
      After carrying out ejection of UV ink to the predetermined area on the recording medium M with proper times of the scanning, the recording medium feeding section  3  properly advances the medium M in the X direction in  FIG. 2 . Thereafter, the recording heads scan again and eject UV ink to a next predetermined area adjacent to the former predetermined area in the X direction in  FIG. 2 .  
      Repetition of the operations described above allows forming an image with UV ink droplets aggregated on the recording medium M.  
      The UV-LED light source  5  is disposed in a side of the receiving portion  32  with respect to the carriage  4 , and has a plurality of LEDs (light emitting diodes) arranged in an LED array (not shown). Each LED can emit light with stable irradiation energy, the peak wavelength of which is within a wavelength range of ultraviolet rays that can cure the UV ink. Each LED is provided so that the emitting portion thereof faces downward. The peak wavelength of the LED is preferably in the range of 200 nm to 420 nm.  
      The UV-LED light source  5  has a shape substantially equal to the maximum size which can be set by the UV ink jet printer  1  in the predetermined area on the recording medium M to which UV ink is ejected during one time scanning of the recording heads, or a larger shape than the predetermined area so as to cover the whole predetermined area on the medium M.  
      The wavelength of ultraviolet rays irradiated by the UV-LED light source  5  can be changed, if necessary, by exchanging the LED array. The irradiation energy of ultraviolet rays irradiated by the UV-LED light source  5  can be also changed properly, for example, by control of a control means.  
      The control means includes a CPU (central processing unit), a ROM (read only memory), a RAM (random access memory) and an interface so as to control each component constructing the UV ink jet printer  1 .  
      A description will now be given of the operations of printing images on the recording medium M by the UV ink jet printer  1 .  
      First, the recording heads eject UV ink toward the recording medium M to start printing images. As described above, the recording heads eject the ink on the medium M by a control of the control means on the basis of the image data to be printed, while moving in the predetermined area on the medium M with the carriage  4  driven. On the other hand, the receiving section  32  rolls up the recording medium M so as to move it in the X direction in  FIG. 2 , every time the ejection of UV ink is completed for the predetermined area.  
      As the recording medium M moves in the X direction in  FIG. 2 , the predetermined area on the medium M is irradiated by ultraviolet rays under the UV-LED light source  5 . The ink on the medium M is rapidly cured upon irradiation of ultraviolet rays and fixed on the medium M. The wavelength and the irradiation energy of ultraviolet rays emitted from the light source  5  are properly set depending on the material of the recording medium M and the kind of UV ink used for printing images.  
      By repeating the operations explained above, images are printed on the recording medium M.  
      As described above, according to the UV ink jet printer  1  in the embodiment, because the UV-LED light source  5  has an LED array as a light source, it generates little heat when irradiating ultraviolet rays, whereby energy efficiency of the UV-LED light source  5  is improved. Therefore, the UV ink jet printer  1  can have a smaller capacity of power source and does not need to have a duct or the like for exhausting the heat. As a result, it is possible to provide a lower cost and small sized printer  1 .  
      Additionally, the little heat generated with the irradiation of ultraviolet rays by the UV-LED light source  5  does not cause deformation of the recording medium M even if the medium M tends to be deformed by the heat. As a result, the printer permits printing on various kinds of recording mediums M.  
      Further, even if the recording medium M is a polyethylene terephthalate shrinkable film that shrinks with heating, little heat generation during irradiation of ultraviolet rays does not raise surrounding temperature so much as the recording medium M is deformed.  
      In addition, since the recording medium M is a long-length film and is rolled at positions before and after printing an image, the volume occupied by the recording medium M can be limited. Therefore, the recording medium M can be installed on the UV ink jet printer  1  without making the printer large-sized.  
      Further, because the cationic polymerization type UV ink is applied as the UV ink, the light intensity necessary to cure the UV ink deposited on the recording medium M can be reduced. Therefore, irradiation energy necessary to cure the UV ink can be sufficiently given without making the UV ink jet printer  1  large-sized which may be required by increasing the number of LEDs each of which is a lower illumination light source in comparison with the high pressure UV lamp.  
      As a UV irradiating means, although the UV-LED light source  5  is used in the embodiment, it is not limited thereto. A semiconductor laser which is capable of emitting a light beam including any one of wavelengths within a range of ultraviolet rays that can cure the UV ink, as the peak wavelength, may also be employed. That is, the semiconductor laser beam (the beam, for example, including a peak wavelength within 200-420 nm) may be scanned by using a galvano mirror or a polygon mirror so as to irradiate the ink on the recording medium M. According to such a structure, because the semiconductor which forms a light source can be disposed apart from the recording medium M, it is possible to prevent the medium M from being affected by the heat generated from the UV irradiating means.  
      As the recording medium M, although a shrinkable polyethylene terephthalate film is used in the embodiment, it is not limited thereto. Any component recording medium on which images can be printed, for example, a resin base medium may be applicable.  
     Industrial Applicability  
      As described above, the invention is particularly appropriate to an ink jet printer that can print on various kinds of recording mediums and is required to be small-sized.