JP2008200882A - Image forming method and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming method and an image forming apparatus for realizing high-speed fixing on a recording medium in an image forming method using an aqueous ultraviolet curable ink, particularly an image forming method using an ink jet method.
SOLUTION: An aqueous ultraviolet curable ink containing water, a photopolymerization initiator, and a polymerizable polymer is ejected by an inkjet method using a recording head to irradiate an image formed on a recording medium with ultraviolet rays by ultraviolet irradiation means. In the image forming method, in the aqueous ultraviolet curable ink, hot air obtained by cooling the ultraviolet irradiation means is blown onto the image to evaporate water in the aqueous ultraviolet curable ink forming the image. An image having a step of increasing an apparent content of the photopolymerization initiator and the polymerizable polymer, and a step of curing the image by irradiating the image with ultraviolet rays by the ultraviolet irradiation means. Forming method.
[Selection] Figure 1

Description

  The present invention relates to an image forming method and an image forming apparatus. More specifically, an image forming method for forming an image on a recording medium by irradiating ultraviolet rays and curing the ink after recording on a recording medium using an ultraviolet (UV) curable ink, and an ink jet recording apparatus; and The present invention relates to an image forming apparatus.

There are the following types of ultraviolet curable inks that are cured by irradiating with ultraviolet rays after recording on a recording medium. Patent Document 1 discloses a so-called non-aqueous ultraviolet curable ink using alcohol as a main solvent. Patent Documents 2 to 4 disclose water-based ultraviolet curable inks mainly composed of water. A typical example of the ultraviolet curable ink has the following configuration. That is, after recording on a recording medium with a recording apparatus, the photopolymerization initiator in the ink is excited by irradiating with ultraviolet rays, and the polymerizable oligomer in the ink also causes radical polymerization reaction by this excitation energy. Converts to polymer in a short time. As a result, the ink is cured at a high speed. As a result, the ink can be fixed on the recording medium at a high speed, and a high-quality image free from bleeding or dullness can be obtained at a high speed.
Japanese Patent Publication No. 5-64667 Japanese Patent Laid-Open No. 5-186725 JP-A-7-224241 JP 2000-186242 A

  By the way, in recent years, in consideration of environmental problems, it has been required to reduce the content of an organic solvent for dissolving and dispersing the photopolymerization initiator and the polymerizable oligomer used in the ultraviolet curable ink. . In the case of inkjet recording, it is preferable to use a low-viscosity aqueous ultraviolet curable ink mainly composed of water in consideration of ejection characteristics, ink behavior on the recording medium, and the like. Considering these facts, it is considered that water-based ultraviolet curable ink will become the mainstream in future inkjet recording.

  Photopolymerization initiators and polymerizable oligomers must be added to the ink to prevent clogging of the nozzles of the recording head and to suppress ejection instability. It is particularly preferable that it is easily dissolved in water.

  However, in order to obtain high-speed fixability, if the content of the water-soluble polymerizable oligomer that is converted into a polymer by radical polymerization reaction is increased, the viscosity of the ink increases and the low viscosity, which is a characteristic of water-based ink used for inkjet recording, is reduced. Some things may be spoiled. This adversely affects the ejection characteristics of ink jet recording and the behavior of ink on the recording medium. However, if the amount of the water-soluble polymerizable oligomer added is reduced, the amount of polymer produced by the radical polymerization reaction is reduced, so that high-speed fixing cannot be realized.

  There is also a technique for suppressing an increase in ink viscosity by using a low molecular weight water-soluble polymerizable oligomer. However, in this method, the lower the molecular weight of the water-soluble polymerizable oligomer, the stronger the binding force between the oligomer molecule and water, so that the polymer is converted into a polymer having a molecular weight of a size necessary for ink curing by radical polymerization. Requires more excitation energy.

  Therefore, it is necessary to increase the excitation energy necessary for radical polymerization by increasing the content of the photopolymerization initiator and the irradiation amount of ultraviolet rays. However, when the content of the photopolymerization initiator in the ink is increased, the content combined with the content of the low molecular weight polymerizable oligomer is increased, and when combined with the amount of the low molecular weight water-soluble polymerizable oligomer, The amount occupied in the ultraviolet curable ink increases, and as a result, the content of the organic solvent increases and the viscosity of the ink increases. Also, increasing the amount of ultraviolet irradiation increases the amount of heat generated from the lamp, adversely affects the recording medium, and reduces the image quality.

  Accordingly, an object of the present invention is to solve the above-described problems and to achieve high-speed fixing on a recording medium in an image forming method using an aqueous ultraviolet curable ink, particularly an image forming method using an ink jet recording apparatus. An object is to provide an image forming method and an image forming apparatus.

  The above object is achieved by the present invention described below. That is, the image forming method according to the present invention is an aqueous ultraviolet curable ink containing water, a photopolymerization initiator, and a polymerizable polymer (hereinafter sometimes simply referred to as “ink”) by an inkjet method using a recording head. In the image forming method of irradiating ultraviolet rays by ultraviolet irradiation means to an image formed on a recording medium by discharging, the aqueous ultraviolet curing for forming the image by blowing hot air obtained by cooling the ultraviolet irradiation means to the image Increasing the apparent content of the photopolymerization initiator and the polymerizable polymer in the aqueous ultraviolet curable ink by evaporating water in the mold ink, and then irradiating the image with ultraviolet rays by the ultraviolet irradiation means And the step of curing the image.

  An image forming apparatus according to another embodiment of the present invention includes a water-based ultraviolet curable ink containing water, a photopolymerization initiator, and a polymerizable polymer, which is ejected to a recording medium by an inkjet method using a recording head. In an image forming apparatus using an image forming method in which the formed image is irradiated with ultraviolet rays by an ultraviolet irradiation means to cure the image, hot air obtained by cooling the ultraviolet irradiation means is blown onto the image, and the image is Means for increasing the apparent content of the photopolymerization initiator and the polymerizable polymer in the aqueous ultraviolet curable ink by evaporating water in the aqueous ultraviolet curable ink to be formed; and hot air on the image It has a means for hardening the image by irradiating ultraviolet rays after spraying.

  As described above, according to the present invention, in an image forming method in which an image formed on a recording medium using an aqueous ultraviolet curable ink is irradiated with ultraviolet rays according to ultraviolet irradiation means, the image is cured. Prior to curing, hot air obtained by cooling the ultraviolet lamp bulb is blown to evaporate water and volatile components in the aqueous ultraviolet curable ink forming the image. As a result, the apparent content of the photopolymerization initiator and the polymerizable polymer in the aqueous ultraviolet curable ink for forming an image increases. Thereafter, the image is cured by irradiating with ultraviolet rays.

  For this purpose, a cooling fan provided in the ultraviolet irradiation means for sending cooling air for cooling the ultraviolet lamp bulb is placed at a position in the ultraviolet irradiation means opposite to the image on which the hot air is blown with respect to the ultraviolet lamp bulb. By installing, the cooling air taken in from the cooling fan strikes the ultraviolet lamp bulb to become hot air, and a linear wind flow is provided inside the ultraviolet irradiation means such that the hot air is blown onto the image.

  According to the present invention, it is possible to fix an aqueous ultraviolet curable ink at high speed by using an image forming method using these methods and an image forming apparatus using the image forming method.

  The best mode for carrying out the invention will be described below with reference to the drawings. Note that the embodiments are not limited to the examples of the present specification and other specific shapes as long as the idea of the present invention is satisfied.

  For example, the shape and configuration of the recording head, the shape and configuration of the ultraviolet irradiation means, and the positional relationship between the recording head and the ultraviolet irradiation means may be different. In addition, if a polymer is generated by causing a radical polymerization reaction, not only a combination of a photopolymerization initiator and a polymerizable oligomer, but also a polymerizable oligomer obtained by adding a function as a photopolymerization initiator to the polymerizable oligomer is used. You can also.

  FIG. 1 is a cross-sectional view illustrating the configuration of an image forming apparatus used in an image forming method according to the present invention. In FIG. 1, 1 is an ultraviolet irradiation means. In this embodiment, an electrodeless lamp system is employed. This electrodeless lamp system uses the same microwave (2.45 GHz) energy as that in a microwave oven to excite a light emitting substance such as mercury in the lamp bulb 4 to generate plasma and convert it into light energy to convert ultraviolet light into ultraviolet light. Is generated.

  When the ultraviolet light is emitted, the surface of the lamp bulb 4 is heated, so that there is a cooling fan 2 for cooling the glass tube so that the glass tube of the lamp bulb 4 does not melt too much. Ultraviolet rays 6 emitted from the lamp bulb 4 are collected by the reflector 3. In FIG. 1, the ultraviolet irradiation means 1 is arranged so that the ultraviolet rays 6 condensed by the reflector 3 are in focus at the position of the image 7 by the aqueous ultraviolet curable ink 12 discharged from the recording head 11. The recording head 11 and the ultraviolet irradiation means 1 are installed at a certain distance. This distance is determined by the relationship between the aqueous ultraviolet curable ink 12 used and the ability of the image forming method used in this embodiment to cure.

  In this embodiment, the recording head 11 and the ultraviolet irradiation means 1 move from the left to the right (in the direction of the arrow in the figure) and record on the recording medium while maintaining a certain distance. By focusing the ultraviolet ray 6 on the image 7 formed on the recording medium 8 as described above, the ultraviolet energy can be efficiently transmitted to the photopolymerization initiator in the ink.

  The screen 5 in FIG. 1 is for preventing microwaves from leaking out. Although not shown, it is necessary to arrange the screen 5 at a place where microwaves are likely to leak from the ultraviolet irradiation means 1.

  Further, the cooling air 21 sent from the cooling fan 2 passes through the opening 9 provided in the reflection plate 3, takes away the heat of the surface of the lamp bulb 4, becomes hot air 22, and becomes the ultraviolet irradiation means 1. Discharged outside. The discharged hot air 22 is blown onto the image 7 on the recording medium 8 by the aqueous ultraviolet curable ink 12 discharged from the recording head 11. At this time, it is important that the hot air 22 is blown onto the image 7 between the recording head 11 and the ultraviolet ray 6. For this purpose, it is effective to mount the cooling fan 2 at an angle as shown in FIG.

  FIG. 3 shows an example of the mounting position of the cooling fan 2 in the conventional ultraviolet irradiation means 31. The conventional cooling fan is installed in the upper direction of the lamp bulb, passes through the upper opening 39 of the reflector 33, and blows the cooling air 21 from the upper portion of the lamp bulb, thereby reflecting the effect of the reflector 33, that is, ultraviolet rays. Thus, it is possible to cool the lamp bulb 4 by drawing out the condensing force to the maximum. However, since the cooling air 21 that has taken away the heat from the surface of the lamp bulb 4 becomes hot air 22 and is blown onto the recording medium 8 from the upper surface of the recording medium 8 together with ultraviolet irradiation, the present invention is carried out. Is difficult.

  In the present embodiment, the cooling fan 2 is tilted and installed at a position in the ultraviolet irradiation means 1 on the opposite side to the image on which the hot air 22 is blown with the lamp bulb 4 as a reference, so that the cooling air 21 taken in from the cooling fan 2 is obtained. Hits the lamp bulb 4 to become hot air 22, and a linear wind flow is provided in the ultraviolet irradiation means 1 such that the hot air 22 is blown onto the image 7.

  Thereby, the water component, the volatile solvent, etc. in the water-based ultraviolet curable ink forming the image 7 recorded by the recording head 11 are evaporated by the hot air 22, so that the content of the photopolymerization initiator and the content of the polymerizable oligomer are contained. The amount is substantially increased to create a state in which the photopolymerization initiator and the polymerizable oligomer dissolved and dispersed in the aqueous ultraviolet curable ink increase the probability of encountering each other.

  At this time, an opening 9 as shown in FIGS. 2A, 2B, and 2C is provided on the oblique upper portion of the reflecting plate 9, thereby reflecting the ultraviolet rays 6 generated by the lamp bulb and cooling air. 21 is allowed to pass through. Here, (a), (b), and (c) three types of opening pattern are shown, but it is not necessary to be caught by this pattern as long as the performance of the present embodiment is satisfied.

  After that, by irradiating the image 7 with the ultraviolet rays 6 collected by the reflecting plate 9, the photopolymerization initiator in the aqueous ultraviolet curable ink forming the image 7 is excited, and the excitation energy also causes the same in the ink. These polymerizable oligomers cause a radical polymerization reaction and are converted into a polymer in a short time. Further, the water in the aqueous ultraviolet curable ink that forms the image 7 is evaporated by the hot air 22, so that the drying speed of the ink is also increased.

  By combining these, it is possible to realize high-speed fixing of an aqueous ultraviolet curable inkjet ink having a high water content.

  As a next embodiment, FIG. 4 is a cross-sectional view for explaining the configuration of the image forming apparatus as in the first embodiment.

  The configuration of the ultraviolet irradiation means 1 and the recording head 11 is the same as that of the first embodiment. In this embodiment, a partition wall 41 is provided on the recording head side of the ultraviolet irradiation means 1. By providing the partition wall 41, the hot air 21 obtained by cooling the lamp bulb 4 does not hit the recording head 11. This has the following advantages. First, the discharge port surface of the recording head 11 is dried by hot air 22 to solidify the ink, so that the discharge port is not blocked and the ink discharge direction is not bent. Accordingly, the quality of the image 7 formed by the recording head 11 is improved.

  Next, the direction of the hot air 22 hitting the partition wall 41 changes and hits the surface of the image 7 on the recording medium 8, thereby evaporating moisture and the like in the aqueous ultraviolet curable ink that forms the image 7 by the hot air 22. It will increase further. By changing the shape of the partition wall 41, it becomes possible to change the direction of hot air or to gather hot air more effectively. Further, when a reflecting plate is provided on the wall surface of the partition wall 41, it is possible to reflect the ultraviolet rays 6 that are not collected by the reflecting plate 9 on the image 7 after the hot air 22 is applied.

  As described above, by providing the partition wall 41 on the recording head 11 side of the ultraviolet irradiation means 1, the hot air 22 obtained by cooling the lamp bulb 4 can be reused more effectively.

  This makes it possible to achieve high-speed fixing of aqueous ultraviolet curable ink having a high water content.

  As a next embodiment, FIG. 5 shows a cross-sectional view for explaining the configuration of the image forming apparatus as in the first embodiment.

  The configuration of the ultraviolet irradiation means 1 and the recording head 11 is the same as that of the first embodiment. In this embodiment, a cooling air introduction wall 51 is provided around the cooling fan 2 inside the ultraviolet irradiation means 1. By providing the introduction wall 51, the cooling air 21 sucked from the cooling fan 2 can be applied to the lamp bulb 4 through the opening 9 of the reflector 3 more effectively than in the first embodiment. As a result, more hot air 22 obtained by cooling the lamp bulb 4 can be applied to the surface of the image 7 on the recording medium 8, so that the moisture in the aqueous ultraviolet curable ink that forms the image 7 by the hot air 22. The effect of evaporating etc. is further increased. If this method is used, it is possible to install the cooling fan 2 on the upper part of the ultraviolet irradiation means 1 as shown in FIG.

  However, if all the cooling air 21 sucked by the cooling fan 2 is applied to the lamp bulb 4 through the opening 9 of the reflecting plate 3, the cooling air 21 for cooling the back surface of the reflecting plate 3 is eliminated. When the back surface of the reflecting plate 3 is not cooled, although depending on the material, the reflecting plate 3 may thermally expand and the condensing position of the ultraviolet rays 6 may change. Therefore, it is important to determine the shape of the cooling air introduction wall 51 so that the cooling air 21 for cooling the back surface of the reflecting plate 3 is generated.

  Thereby, the hot air 22 obtained by cooling many lamp bulbs 4 can be utilized. Therefore, it is possible to realize high-speed fixing of the aqueous ultraviolet curable ink having a high water content.

  As a next embodiment, FIG. 7 shows a cross-sectional view illustrating the configuration of the image forming apparatus as in the third embodiment.

  The configuration of the ultraviolet irradiation means 1 and the recording head 11 is the same as that of the third embodiment. In this embodiment, a cooling air suction wall 71 is provided in the vicinity of the cooling fan outside the ultraviolet irradiation means.

  By providing this suction wall, when both the ultraviolet irradiation means and the recording head move relative to the recording medium, for example, when moving from left to right in FIG. 7, more air can be sent to the cooling fan. . Thereby, more cooling air can be used for reflector back surface cooling and lamp bulb cooling. Therefore, it is possible to realize high-speed fixing of the aqueous ultraviolet curable ink having a high water content.

  As a next embodiment, FIG. 8 is a cross-sectional view for explaining the configuration of the image forming apparatus as in the first embodiment.

  Although the configuration of the ultraviolet irradiation means 1 and the recording head 11 is the same as that of the first embodiment, a heating platen 81 is provided on the back side of the recording medium 8 in this embodiment. By installing the heating platen 81, the recording medium 8 can be warmed. Thereby, the heat transmitted from the hot air 22 obtained by cooling the lamp bulb 4 to the recording medium 8 is reduced, and more heat from the hot air 22 can be transmitted to the image 7 on the recording medium 8. The effect of evaporating moisture or the like in the aqueous ultraviolet curable ink that forms the image 7 can be further increased.

  Obviously, the combination of the above embodiments does not impair the characteristics of the present embodiment. In the above embodiment, the recording head is used as the recording means. However, the use of screen printing or transfer printing does not impair the characteristics of this embodiment.

1 is a cross-sectional view illustrating a configuration of an image forming apparatus used in an embodiment of the present invention. It is a figure explaining the Example in this invention. It is sectional drawing explaining the structure of the image forming apparatus used for a prior art example. 1 is a cross-sectional view illustrating a configuration of an image forming apparatus used in an embodiment of the present invention. 1 is a cross-sectional view illustrating a configuration of an image forming apparatus used in an embodiment of the present invention. 1 is a cross-sectional view illustrating a configuration of an image forming apparatus used in an embodiment of the present invention. 1 is a cross-sectional view illustrating a configuration of an image forming apparatus used in an embodiment of the present invention. 1 is a cross-sectional view illustrating a configuration of an image forming apparatus used in an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ultraviolet irradiation means 2 Cooling fan 3 Reflector 4 Lamp bulb 5 Screen 6 Ultraviolet 7 Image 8 Recording medium 9 Opening part 11 Recording head 12 Water-based ultraviolet curing ink 21 Cooling air 22 Hot air 31 Ultraviolet irradiation means (conventional example)
33 Reflector (conventional example)
39 Opening (conventional example)
41 Partition 51 Cooling air introduction wall 71 Cooling air suction wall 81 Heating platen

Claims (20)

An image forming method of irradiating an image formed on a recording medium by ejecting an aqueous ultraviolet curable ink containing water, a photopolymerization initiator, and a polymerizable polymer by an inkjet method using a recording head, by ultraviolet irradiation means In
A photopolymerization initiator in the aqueous ultraviolet curable ink is obtained by spraying hot air obtained by cooling the ultraviolet irradiation means on the image and evaporating water in the aqueous ultraviolet curable ink forming the image; An image forming method comprising a step of increasing an apparent content of a polymerizable polymer, and a step of curing the image by irradiating the image with ultraviolet rays by the ultraviolet irradiation means.   A cooling fan provided in the ultraviolet irradiating means for sending cooling air for cooling the ultraviolet irradiating means is provided in the ultraviolet irradiating means opposite to the image on which the hot air is blown with respect to the ultraviolet irradiating means. By installing at the position, the cooling air taken in from the cooling fan hits the ultraviolet irradiation means to become the hot air, and a linear wind flow is created in the ultraviolet irradiation means such that the hot air is blown to the image. The image forming method according to claim 1.   The image forming method according to claim 2, wherein the cooling fan is provided obliquely inside the ultraviolet irradiation unit.   The image forming method according to claim 1, wherein the cooling air sent from the cooling fan is blown to the ultraviolet irradiation unit through an open portion provided on a reflection plate in the ultraviolet irradiation unit.   The opening provided in the reflection plate has a mesh structure, the opening reflects the ultraviolet rays irradiated by the ultraviolet irradiation means, and allows the cooling air sent from the cooling fan to pass through. The image forming method according to claim 1, wherein both are performed.   A partition is provided between the ultraviolet irradiation means and the recording head so that the hot air obtained by cooling the ultraviolet irradiation means does not hit the ink jet recording apparatus, and the hot air hitting the partition emits the ultraviolet light. The image forming method according to claim 1, wherein the image is sprayed on the image before being cured by irradiation.   The image forming method according to claim 5, wherein a reflection plate is provided on the partition wall, and the image is irradiated after the ultraviolet light is reflected by the reflection plate.   2. The cooling air introduction wall is provided around the cooling fan provided in the ultraviolet irradiation unit, and the cooling air sucked from the cooling fan is guided to an opening provided in the reflection plate. Image forming method.   A cooling air suction wall is provided in the vicinity of the cooling fan outside the ultraviolet irradiation means, and the ultraviolet irradiation means and the recording head are collected by the cooling air suction wall when moving with respect to the recording medium. The image forming method according to claim 1, wherein the heated air is sent to the cooling fan.   The image forming method according to claim 1, wherein means for heating the recording medium is provided on a side opposite to a surface on which the image of the recording medium is formed to warm the recording medium. An image formed on a recording medium by ejecting an aqueous ultraviolet curable ink containing water, a photopolymerization initiator, and a polymerizable polymer by an inkjet method using a recording head, and irradiating the image with ultraviolet rays by an ultraviolet irradiation means. In an image forming apparatus using an image forming method for curing
A photopolymerization initiator in the aqueous ultraviolet curable ink is obtained by spraying hot air obtained by cooling the ultraviolet irradiation means on the image and evaporating water in the aqueous ultraviolet curable ink forming the image; An image forming apparatus comprising: means for increasing an apparent content of a polymerizable polymer; and means for curing the image by irradiating ultraviolet rays after spraying hot air on the image.   A cooling fan provided in the ultraviolet irradiation means for sending cooling air for cooling the ultraviolet irradiation means is disposed inside the ultraviolet irradiation means opposite to the image to which the hot air is blown around the ultraviolet irradiation means. By installing at the position, the cooling air taken in from the cooling fan hits the ultraviolet irradiation means to become the hot air, and a linear wind flow is created in the ultraviolet irradiation means such that the hot air is blown to the image. The image forming apparatus according to claim 11, further comprising a unit.   The image forming apparatus according to claim 12, wherein the cooling fan is provided obliquely inside the ultraviolet irradiation unit.   The image forming apparatus according to claim 11, wherein the cooling air sent from the cooling fan is blown to the ultraviolet irradiating unit through an opening provided on a reflection plate in the ultraviolet irradiating unit.   The opening provided in the reflection plate has a mesh structure, the opening reflects the ultraviolet rays irradiated by the ultraviolet irradiation means, and allows the cooling air sent from the cooling fan to pass through. The image forming apparatus according to claim 11, wherein both are performed.   A partition is provided between the ultraviolet irradiation means and the recording head so that the hot air obtained by cooling the ultraviolet irradiation means does not hit the ink jet recording apparatus, and the hot air hitting the partition emits the ultraviolet light. The image forming apparatus according to claim 11, wherein the image forming apparatus is sprayed on the image before being cured by irradiation.   The image forming apparatus according to claim 16, wherein a reflection plate is provided on the partition wall, and the image is irradiated after the ultraviolet light is reflected by the reflection plate.   12. The cooling air introduction wall is provided around the cooling fan provided in the ultraviolet irradiation means, and the cooling air sucked from the cooling fan is guided to an opening provided in the reflector. Image forming apparatus.   A cooling air suction wall is provided in the vicinity of the cooling fan outside the ultraviolet irradiation means, and the ultraviolet irradiation means and the recording head are collected by the cooling air suction wall when moving with respect to the recording medium. The image forming apparatus according to claim 11, wherein the heated air is sent to the cooling fan.   The image forming apparatus according to claim 11, wherein means for heating the recording medium is provided on a side opposite to a surface on which the image of the recording medium is formed to warm the recording medium.

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