JP2007313840A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus favorably reproducing the gradient in a low-density region while suppressing a temperature rise which may involve fluctuations and decrease in luminous efficiency from a light source and performing curing of low-density regions having a comparatively low droplet-stroke density, at high sensitivity, in cases where an image recording is carried out in the environment with a comparatively high relative-humidity. <P>SOLUTION: The image forming apparatus forms an image by affording it through an inkjet method in which ink is cured by an active energy ray, wherein in the presence of an image region with an ink amount of 10 g/m<SP>2</SP>or less for composing an image, the temperature of the region selectively irradiated by the ultraviolet ray is increased by a heating element 17. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that forms an image by ejecting an active energy ray-curable ink onto a recording medium by an ink jet method.

  Conventionally, UV-curable inks that are cured by ultraviolet (UV) irradiation are widely known as inks having fading resistance and the like. When such ink is used, an image can be obtained by irradiating and curing an active energy ray after the ink is deposited (recorded) on the recording medium in a desired image form. In this case, a system using radical polymerization or cationic polymerization of monomer components is generally used for curing.

  It is desirable that curing after recording can be performed satisfactorily regardless of various conditions such as the energy intensity and environmental conditions of the active energy ray. For this purpose, it is preferable that the sensitivity of the ink to the active energy ray is stably high. . Therefore, various studies have been made on techniques for obtaining high sensitivity from the viewpoint of ink composition. If the sensitivity is low and the curing is insufficient, the recorded image often suffers from scratching or peeling off due to rubbing or the like, and also becomes a hindrance when performing high-speed recording.

On the other hand, in relation to the above, from a viewpoint other than the composition, a technique is disclosed in which curing is performed in a short time by exposure using a light emitting diode having a wavelength of 305 to 375 nm when the amount of droplet ejection is small (for example, , See Patent Document 1). In addition, an image forming method is disclosed in which actinic light curable ink is used, and the landed ink is irradiated with actinic light and heated. Here, it is said that stable recording can be performed under various printing environments. (For example, refer to Patent Document 2).
JP 2004-181951 A JP 2004-25479 A

  However, with regard to photocuring, good curing performance cannot always be obtained depending on the amount of ink to be ejected, that is, the droplet ejection density that varies depending on the type and density of the recorded image.

That is, for example, in order to obtain an image with high reproducibility in a low density region, it is important to reproduce the image so that it becomes a continuous tone. To that end, it is necessary to reduce the amount of droplet ejection in the low density region. Is required. When an image is formed with one type of ink for each color, it is necessary to reduce the droplet ejection amount, particularly when a low density region is expressed. In other words, when the maximum value of the droplet ejection amount in the high density region, that is, the region with a high droplet ejection density is 20 g / m ² , the minimum droplet ejection amount required to improve the image reproduction in the low density region is 1/1000, that is, 20 mg / m ² or less, and preferably 1/4000, that is, 5 mg / m ² or less. Also, when an image is to be formed with two or more inks for each color, for example, when an ink having a high color material content and an ink having a low color material content are used, the color material content of the low ink is 1 The minimum droplet ejection amount necessary for improving the image reproduction in the low density region is 10 to 25 mg / m ² . Thus, in the low density region, the droplet ejection amount is greatly reduced.

Then, when the droplet ejection amount is large, that is, the image portion having a high droplet ejection density, and when the droplet ejection amount is small, that is, the image portion having a low droplet ejection density, the polymerization sensitivity when irradiated with light tends to be greatly different. .
This is because when the droplet ejection amount is small, the droplets that have landed on the substrate are exposed in a state where the droplets are separated from each other. It is presumed that the area in contact with the hit air becomes large and is easily affected by the surrounding environment. In addition, it is considered that the cationic polymerization type ink is subjected to polymerization inhibition due to moisture in the air. For example, in an atmosphere where the relative humidity in the air is 40% or more, the sensitivity is reduced to a practical level, and particularly when the humidity is 60% or more, the reduction is significant. This causes a decrease, and a high-power light source is used, or long exposure is required, leading to an increase in cost or an increase in printing time. Further, the sensitivity reduction is not controlled only by the relative humidity of the environment, but also changes depending on the temperature.

  In addition, as in the above-mentioned Patent Document 2, in the case of using a method of heating ink after light irradiation, the temperature inside the apparatus tends to rise remarkably in order to heat the ink to a constant temperature. When is used, the luminous efficiency fluctuates or decreases, and as a result, photocuring cannot be performed with high sensitivity when the amount of ink is small.

  The present invention has been made in view of the above, and when image recording is performed in an environment where the relative humidity is relatively high (for example, 40% RH or more (especially 60% RH or more)), the light emission efficiency of the light source varies. Provides an image forming apparatus that can perform high-sensitivity curing of low density areas with relatively low droplet ejection density and achieve good gradation reproduction in low density areas, while suppressing temperature rise that is accompanied by a decrease. It is an object to achieve this purpose.

Specific means for achieving the above object are as follows.
<1> An image forming apparatus that forms an image by applying ink that is cured by an active energy ray by an inkjet method, and is selected when the amount of the ink that forms the image is 10 g / m ² or less. An image forming apparatus that raises the temperature of a region to which an active energy ray is applied.

According to the image forming apparatus according to <1>, droplet density when, i.e. ink amount of ink image formed using the ink that is curable by active energy rays there is a region to be 10 g / m ² or less When forming a low density region having a low density, an ink droplet polymerization is selectively performed by increasing the temperature of a region that encloses at least a part of an image and is provided with an active energy ray (for example, a low density region). The reaction can be promoted, and polymerization inhibition when the contact with air (especially moisture) is large is suppressed. Therefore, the temperature rise more than necessary is suppressed. As a result, when a semiconductor light emitting device (including a light emitting diode) is used. While suppressing the decrease in light emission efficiency of the device, it is possible to polymerize and cure with high sensitivity even in a low density region where the droplet ejection density is low and ink droplets do not coalesce, and images with good gradation reproducibility can be obtained. Gain Can.

  The “active energy rays” are actinic rays that generate radicals or cations from the photopolymerization initiator, and include ultraviolet rays (UV light), visible rays, γ rays, α rays, X rays, and other electron rays.

  This is particularly effective when using cationic polymerization inks that are easily affected by moisture in the air. For example, by increasing the temperature of the ink droplets that have landed, the sensitivity reduction due to the effects of polymerization inhibition is effectively reduced. can do.

<2> a recording head that discharges ink cured by an active energy ray to a recording medium according to image information, and an energy applying unit that gives an active energy ray to a region including at least the ink ejected by the recording head; When there is a heating unit that heats the region to which the active energy ray is applied and an image region in which the amount of the ejected ink is 10 g / m ² or less, the active energy ray is applied by the energy applying unit. The image forming apparatus according to <1>, further including a temperature control unit that performs temperature increase control for increasing the temperature of the region.

According to the image forming apparatus described in <2>, when there is a region where the amount of ink ejected from the head by the temperature control unit is 10 g / m ² or less, the active energy ray is generated by the energy applying unit. Since the temperature of the given area is raised by automatically controlled heating means, it is effective to suppress polymerization inhibition due to contact with air (especially moisture) and to prevent the temperature from rising more than necessary. .

  <3> Detection means for detecting the temperature and / or humidity of the region to which the active energy ray is applied, and determination means for determining whether the temperature and / or humidity detected by the detection means is within a predetermined range. The image forming apparatus according to <1> or <2>, further comprising: the temperature control unit raising the temperature according to a temperature and / or humidity range determined by the determination unit. It is.

  According to the image forming apparatus described in <3>, since the degree of polymerization inhibition varies depending on the temperature and / or humidity, the temperature and / or humidity near the atmosphere in which the polymerization reaction occurs is detected, and the detected temperature and Based on the humidity and / or the humidity, depending on the temperature and / or humidity range, that is, whether or not polymerization curing is not performed well, the temperature of the region where the active energy ray is selectively given is increased. Therefore, it is possible to reduce the influence of polymerization inhibition while suppressing an increase in temperature more than necessary, and thus suppressing a decrease in luminous efficiency of the element when a semiconductor light emitting element (including a light emitting diode) is used. it can. As a result, regardless of the temperature and / or humidity environment, polymerization and curing can be performed with high sensitivity even in a low density region, and an image with good gradation reproducibility can be obtained.

  <4> The image forming apparatus according to <2> or <3>, wherein the energy applying unit is a light emitting diode having a wavelength of 390 nm or less.

According to the image forming apparatus described in <4>, the configuration using the light-emitting diode is configured because the polymerization is likely to be hindered because the temperature rise in the apparatus is small when the semiconductor light-emitting element with less self-heating is configured. In this case, the effect of increasing the temperature of the region to which the active energy ray is applied is large. Particularly, a light emitting diode having a wavelength of 390 nm or less has a high curing ability with respect to an ultraviolet curable ink. An image with good gradation reproducibility can be obtained with sensitivity.
Further, the apparatus uses the heat generated by itself, such as a configuration in which a light source accompanied by heat generation such as a lamp that generates ultraviolet rays by discharge, such as a metal halide lamp, which has been conventionally used, is used to constantly heat to a desired temperature. The temperature inside the ink rises significantly, and the ink discharge amount changes due to fluctuations in ink physical properties, especially viscosity and surface tension, resulting in fluctuations in density and color. It is also possible to avoid a problem such as a tendency to occur or a decrease in luminous efficiency when a light emitting diode is used.

  According to the present invention, it is possible to perform curing in a low concentration region with a relatively low droplet ejection density with high sensitivity while suppressing a temperature increase that accompanies a change in light emission efficiency and a decrease in light emission accompanying a temperature increase, It is possible to provide an image forming apparatus that can reproduce gradations in a low density region.

  Hereinafter, an embodiment of an image forming apparatus of the present invention will be described in detail with reference to the drawings.

(First embodiment)
A first embodiment of an image forming apparatus of the present invention will be described with reference to FIGS. The image forming apparatus according to the present embodiment performs temperature increase control for increasing the temperature of an image (ink) using a heating element according to whether or not a predetermined ink amount calculated from captured image information has reached a threshold value. The configuration is to be performed.

  In this embodiment, the case where an image is formed by loading five colors of white (W), black (BK), yellow (Y), magenta (M), and cyan (C) on the recording head as the colored ink is mainly used. Explained. However, the present invention is not limited to the following embodiment.

As shown in FIGS. 1 and 2, an inkjet recording apparatus that is an image forming apparatus according to the present embodiment includes a conveyance roll 16 that conveys a sheet 20 that is a recording medium in a certain direction, and a direction perpendicular to the conveyance direction of the sheet 20. A guide member 18 provided along a specific direction, and supported by the guide member 18 and movably disposed along the guide member 18, and five head units that discharge colored ink for each color are incorporated. The recording head carriage 13 that houses the recording head 11 and the LED exposure device 12 that is an energy applying means for irradiating ultraviolet light having a wavelength of 390 nm or less, and a low density region in which the amount of the colored ink that is ejected is 10 g / m ² or less Through a sheet of paper 20 and a control device 14 that performs temperature increase control for increasing the temperature of the region irradiated with ultraviolet light including the low-concentration region. And a heating element 17 (heater) for raising the temperature of the image (ink droplet) on the paper 20.

  The recording head carriage 13, the control device 14, the transport roll 16, the heating element 17, and the guide member 18 that house the recording head 11 and the LED exposure device 12 are held by a main body housing (not shown). Further, image information is sent to the recording head carriage 13 through a signal line formed on a flexible substrate.

  The moving direction (main scanning direction) of the recording head carriage 13 is indicated by an arrow M (see FIG. 3), and the moving direction (sub-scanning direction) of the paper 20 is indicated by an arrow S (see FIG. 1).

In addition, as shown in FIGS. 1 to 3, a plurality of nozzles (not shown) are provided as head units 11 </ b> A below the recording heads 11 of the respective colors. In addition, an ink tank 11B for supplying ink to each head unit 11A is disposed above the head unit 11A, and the recording head 11 for each color includes an ink tank 11B and a head unit 11A. .
The number of ink tanks 11B is provided so as to correspond to the number of recording heads 11 of each color, and is five in this embodiment. Thereby, a full color image can be recorded by discharging five colored inks.

  As shown in FIG. 4, the recording head 11 includes an ink discharge head unit for each color, and includes a white (W) ink discharge head unit, a black (BK) ink discharge head unit, and a yellow (Y). Five head units, an ink discharge head unit, a magenta (M) ink discharge head unit, and a cyan (C) ink discharge head unit, have W / BK / Y / M / C from the side close to the LED exposure device 12. They are arranged in order.

  Each of the five head units is composed of Spectra's SE-128, and the nozzle density is 50 nozzles (= 50 drop / inch; dpi) per 25.4 mm (1 inch). In total, 128 nozzles are arranged at equal intervals. Each head unit is arranged so that nozzle rows in which nozzles are arranged at equal intervals in the sub-scanning direction are parallel to the main scanning direction, and using five heads, cyan, magenta, yellow, black, white Are ejected at 4 KHz, and main scanning is performed at 340 mm / s, and droplets are ejected at a density of 300 dpi in the main scanning direction in one scan on the recording medium. Yes. When the main scanning is completed, the recording medium is configured to move a predetermined amount in the nozzle row direction (parallel to the sub-scanning direction) with respect to the five heads, and image formation is performed in 24 scans. An image of 600 dpi can be formed in both the main scanning direction and the sub-scanning direction.

By providing five head units in which a plurality of nozzles arranged with a plurality of nozzles are arranged in a plurality of rows, it is possible to form a color image at high speed. Further, as described in Japanese Patent Laid-Open No. 63-160849, nozzles are arranged by a width equal to or greater than the width of the image to form a so-called line head, and in the sub-operation direction simultaneously with droplet ejection from these nozzles. By moving to, it is possible to form an image at higher speed.
When the speed is increased in this way, the image forming apparatus of the present invention is more effective in that the image forming apparatus can be cured with high sensitivity and gradation can be reproduced well in a low density region.

As each head unit of the recording head 11, a known inkjet head can be appropriately selected and used in addition to the above-mentioned SE-128 manufactured by Spectra.
For example, charge control method that ejects ink using electrostatic attraction force, drop-on-demand method (pressure pulse method) that uses oscillating pressure of piezo element, radiation pressure by irradiating ink by changing electrical signal to acoustic beam Any type of head may be used, such as an acoustic ink jet system that ejects ink by using a thermal ink jet system that heats ink to form bubbles and uses generated pressure. The ink jet method includes a method of ejecting a large number of low-density inks called photo inks in a small volume and a method of improving image quality using a plurality of inks having substantially the same hue and different densities.
Among these, a drop-on-demand type (pressure pulse type) ink jet head using a piezoelectric element is suitable.

In addition, the recording head 11 can include an ink holding unit that holds ink, such as an ink tank 11B shown in FIG. A known ink cartridge can be suitably applied to the ink holding means, and it is preferable that the colored ink and the transparent ink of each color are separately filled in the ink cartridge, as described in JP-A-5-16377. It is also possible to store in a deformable container to form a tank. Further, when a sub tank is provided as described in JP-A-5-16382, the supply of ink to the head is further stabilized. Further, as described in JP-A-8-174860, it is possible to use a cartridge that supplies ink by moving a valve when the pressure in the ink supply chamber decreases.
In these ink holding means, a method for applying a negative pressure to appropriately maintain the meniscus in the head includes a method using the height of the ink holding means, that is, a water head pressure, and a method using a capillary force of a filter provided in the ink flow path. A method of controlling the pressure with a pump or the like, a method of holding an ink in an ink absorber described in JP-A-50-74341, and applying a negative pressure by its capillary force are suitable.

  The image forming apparatus of the present invention preferably includes a stabilizing means for stabilizing the temperature of the colored ink. The part that keeps the temperature constant covers all of the piping system and members from the ink holding means (ink cartridge, tank, etc. (intermediate tank if there is an intermediate tank)) that holds the ink to the nozzle ejection surface.

  Ink ejection is preferably performed after each ink is heated to 40 to 80 ° C. and the viscosity of the ink is lowered to 30 mPa · s or less, preferably 20 mPa · s or less, from the viewpoint of improving ejection stability. . In general, an active energy ray-curable ink generally has a higher viscosity than a water-based ink, and therefore has a large viscosity fluctuation range due to temperature fluctuations. It is important to keep the temperature of the ink as constant as possible, since the ink viscosity fluctuation has a great influence on the droplet size and the droplet ejection speed and easily causes image quality deterioration. Accordingly, it is preferable to include a detection unit that detects the temperature of the ink, an ink heating unit that heats the ink, and a control unit that controls heating by the ink heating unit in accordance with the detected temperature of the ink.

  The method for controlling the temperature of the ink is not particularly limited. For example, it is desirable to provide a plurality of temperature sensors in each piping portion so that heating control according to the ink flow rate and the environmental temperature can be performed. Moreover, it is preferable that the head unit is thermally blocked or insulated so as not to be affected by the temperature from the outside air. In order to shorten the printer start-up time required for heating or to reduce the loss of thermal energy, it is preferable to insulate from other parts and reduce the heat capacity of the object to be heated. Alternatively, it is also preferable to control the energy applied to the recording head according to the ink temperature.

  The temperature of the ink is preferably set temperature ± 5 ° C., more preferably set temperature ± 2 ° C., and still more preferably set temperature ± 1 ° C.

  The LED exposure device 12 applies ink droplets on the recording medium ejected from the recording head 11 and landed on the upstream side in the main scanning direction of the head in the apparatus, that is, on the right hand side in the sub-scanning direction of the head in FIG. It is provided so that it can be irradiated. A light emitting diode (LED) that emits light having a wavelength of 365 nm is attached to the LED exposure device 12 so that light having a wavelength of 365 nm can be irradiated simultaneously with or after ejection from the recording head 11.

The light emitting diode (LED) is configured by arranging a plurality of chips at equal intervals in the sub-scanning direction. For example, in the apparatus shown in this embodiment, specifically, eight NCCU 033 ( Wavelength 365 nm (manufactured by Nichia Chemical Industry Co., Ltd.) is arranged at a distance of about 10 mm from the recording medium on which the ink has landed at intervals of 7 mm parallel to the nozzle rows of the head unit. This LED consumes 2.25 W of power per chip and emits light with a light output of about 100 mW. In this way, the exposure power of about 170 mW / cm ² can be obtained on the recording medium by arranging in rows and disposing at a position about 10 mm apart.

  Further, the LED exposure device 12 is connected and integrated with the recording head 11, so that each head unit can move while ejecting ink as necessary, and at the same time, the LED exposure device 12 can also move. It is configured. When ink is ejected from the recording head 11 onto the recording medium, or simultaneously after the ink is ejected, the LED is irradiated with light, and both the recording head and the exposure device move in the main scanning direction orthogonal to the nozzle row. Thus, the ink curing reaction is started before the landing or immediately after the landing.

The energy applying means constituting the image forming apparatus of the present invention is not limited to the LED exposure apparatus (light emitting diode) described above. For example, a mercury lamp, a metal halide lamp, or the like may be used, or a semiconductor laser or a fluorescent lamp. Etc. may be used. In addition, a light source, an electromagnetic wave, or the like in which a polymerization reaction of ink proceeds, such as a hot cathode tube, a cold cathode tube, an electron beam, or an X-ray, can be used.
A method using an optical fiber described in WO99 / 54415 or a method of irradiating UV light by applying a collimated light source to a mirror surface provided on the side surface of the head unit may be used.
When a metal halide lamp is used, the lamp is preferably 10 to 1000 W / cm.
The illuminance on the surface of the recording material is preferably in the range of 1 mW / cm ^{2 to} 100 W / cm ² .

  Moreover, when using a high pressure mercury lamp, a metal halide lamp, etc. for an energy provision means, since these generate | occur | produce ozone with discharge, it is preferable to have an exhaust means. The exhaust means is preferably arranged so as to also collect ink mist generated during ink ejection.

Next, preferable irradiation conditions for active energy rays will be described.
The basic irradiation method is described in Japanese Patent Application Laid-Open No. 60-132767. Specifically, an energy applying means is provided in the vicinity of the head unit or on both sides, and scanning is performed integrally with the recording head. Yes. Curing may be completed using another light source that is not driven.
Irradiation can be performed simultaneously with the ejection of the ink or after a certain period of time after the ink has landed. When irradiating at a certain time after landing, the time from landing to irradiation is preferably 0.01 to 0.5 seconds, more preferably 0.01 to 0.3 seconds, and still more preferably 0.01. ~ 0.15 seconds. By making the time from landing to irradiation extremely short, it is possible to prevent the ink from bleeding before curing.

  When active energy rays for curing are applied to the ink discharge nozzles, ink mist attached to the surface of the nozzle surface may solidify and hinder ink discharge. In order to stop, it is preferable to take measures such as shading. Specifically, it is preferable to provide a partition wall that prevents the nozzle plate from being irradiated, or to provide means for limiting the incident angle to the recording material so as to reduce stray light.

  In the ink jet recording apparatus according to the present embodiment, as shown in FIG. 1, the transport roll 16 transports the paper 20 on the support base 34 that is a support means, and reciprocates the recording head carriage 13, according to the image information. Ink droplets are ejected onto the surface of the paper 20 to form an image on the paper 20.

  The support base 34 is disposed to face the recording head 11 and includes an aluminum base 33 and a heating element (heater) 17 that directly supports the paper 20 disposed on the top surface of the base 33. Is configured to support the paper 20 when the ink 52 is ejected and to heat the ink droplets that have landed on the paper 20 via the paper 20.

  The heating element 17 is an aluminum foil heater in which two aluminum foils are bonded together so that a heating wire is embedded therein. In addition to the aluminum foil heater, a heating element having a smaller heat capacity than that of the recording medium can be selected and used.

The LED exposure device 12 is disposed adjacent to the recording head 11 as shown in FIGS. 2 to 3, and the ink 52 (see FIG. 1) that has landed on the paper 20 is transferred from the LED exposure device 12. It is comprised so that it may harden | cure with the emitted ultraviolet light. When there is an image area with an ink amount of 10 g / m ² or less in the area irradiated with ultraviolet light, which is an active energy ray, the heating element 17 is turned on, and the image (ink) on the paper 20 is passed through the paper 20. ) Can be cured at a high temperature.

At this time, when the temperature of the region to which the ultraviolet light (active energy ray) is applied by the heating element as the heating means is increased, the image region is formed when an image region having an ink amount of 10 g / m ² or less is formed. The heating is performed so as to increase the temperature, but at least the image (ink) or the portion of the heating element 17 that supports the paper 20 on which the image is formed may be selectively driven and heated.

  Further, the heating element 17 and the pedestal 33 are provided with a plurality of suction holes 56 as suction means for sucking paper, and the paper 20 that is conveyed by sucking air from the suction holes 56 by the pump 58. The image (ink) on the paper can be efficiently heated.

The recording head 11, the LED exposure device 12, the transport roll 16, the heating element 17, and the like are electrically connected to the control device 14, and the operation timing is controlled by the control device 14. The control device 14 ejects ink droplets according to the image information as described above, and controls whether or not the temperature of the region including the image region (ink droplet) to be photocured with the ink 10 g / m ² as a threshold can be increased. It is responsible for temperature control.

  Hereinafter, image formation performed using the image forming apparatus of the present embodiment will be described with reference to FIGS. 5 to 6 focusing on an image forming process performed by controlling the temperature by the control device 14.

  FIG. 5 shows a basic signal flow (control process) when an image is formed in this embodiment. Here, conventionally, a signal flow as shown in FIGS. 10A to 10B is generally used. However, in the present embodiment, a configuration (operation unit, Heating unit), specifically, calculation of ink droplet ejection amount necessary for image formation (step 120 in FIG. 6), and signal transmission to the head drive circuit at the time of print control, heating element (heating) A path (steps 140, 160, and 200 in FIG. 6) that waits for the presence or absence of heating by the vessel is provided.

When the print control is started, the image information stored in the memory in the device is sent to the droplet ejection signal processing section, and the heating element (heater) is selectively driven according to the appropriate amount corresponding to the droplet ejection signal. Without being driven or driven, ink is ejected by the corresponding head unit through the head drive circuit and LED drive circuit in synchronization with the main scan of the recording head, the LED is turned on, and further, the sub-scan operation is performed to perform image scanning. Finish formation.
Hereinafter, the temperature increase control routine shown in FIG. 6 will be specifically described.

When a request for image formation is made from an information processing apparatus (not shown) (for example, a computer) electrically connected to the image forming apparatus of this embodiment, a temperature increase control routine shown in FIG. 6 is executed.
When this routine is executed, first, in step 100, image information stored in the image memory in the apparatus is taken into the droplet ejection signal processing unit, and in step 120, a visible image is formed based on the image information. The required droplet ejection amount corresponding to the droplet ejection signal, specifically, the image is divided into 1 mm square regions, and the droplet ejection amounts (W ink, BK ink, Y ink, M ink, The required ink ejection amount for each of the C inks is calculated, and the ink amount for each color is determined.

In step 140, the droplet ejection amount value (total amount of W ink, BK ink, Y ink, M ink, and C ink) calculated by dividing the image into 1 mm square areas is 10 g / m ² or less. Whether or not it is necessary to raise the temperature for good photocuring is determined.

If it is determined in step 140 that the ink droplet ejection amount is 10 g / m ² or less, the LED exposure apparatus 12 may be insufficiently cured by ultraviolet irradiation. The heating element 17 corresponding to the sheet position where the ultraviolet irradiation region, that is, the low density region constituted by the ink amount of 10 g / m ² or less is formed is turned on (ON) and driven.

  After turning on the heating element 17 where the image (ink) to be photocured is positioned as described above, in step 180, the head units of the respective colors are driven in synchronization with the main scanning of the recording head 11. The LED of the LED exposure device 12 is turned on. At this time, when trying to form a low-density image with a small amount of colored ink and a low droplet ejection density, there are generally many ink droplets that exist independently without the ink droplets being united, The photo-curing reaction is likely to be hindered by the influence of moisture, etc., but by increasing the temperature of the ink to cause the photo-curing reaction to be carried out, the curing reaction is accelerated and curing can be performed with high sensitivity. Good gradation reproducibility can be obtained in the density region.

After the main scanning is completed, in step 220, the recording head is moved by performing a sub scanning by a predetermined amount.
If it is determined in step 140 that the ink droplet ejection amount exceeds 10 g / m ² , there is no possibility that the LED exposure apparatus will be insufficiently cured by ultraviolet irradiation. The process proceeds to step 220 while keeping OFF.

  In step 240, it is determined whether or not formation of a desired image has been completed. If it is determined that an image has not yet been formed, the process returns to step 120 and the same operation as described above is repeated. If it is determined in step 240 that the image formation has been completed, this routine is terminated.

As described above, in this embodiment, for each 1 mm square area, the droplet ejection amount of the colored ink is calculated from the captured image information, and the required ink amount as a result of the calculation is a small amount of 10 g / m ² or less. Sometimes, at least the temperature of the image area is controlled to be selectively increased.

  In the present embodiment, the heating element 17 is provided on the support base to increase the temperature of the ink image formed on the paper through the paper so that the photocuring can be performed satisfactorily. The method of raising the temperature of the region including the image region that is photocured by irradiation with ultraviolet rays is not limited to the method of raising the temperature via the paper (recording medium) by the heating element. For example, (1) infrared rays Can be selected as appropriate according to the device configuration, purpose, etc., such as a method of selectively irradiating, (2) a method of scanning infrared laser light, and (3) a method of selectively lighting an infrared LED array. .

  In forming an image, the landing diameter of the colored ink on the recording material is preferably in the range of 10 to 500 μm. Therefore, the diameter of the ink droplets at the time of ejection is preferably in the range of 5 to 250 μm. The nozzle diameter at this time is preferably 15 to 100 μm.

  When an image is formed, 50 to 2400 dpi is preferable. For this purpose, the nozzle density of the head is preferably 10 to 2400 dpi. Here, even if the nozzle density of the head is low, high-density landing can be achieved with a head having a large nozzle interval by tilting with respect to the recording material conveyance direction or by disposing multiple head units relative to each other. Is possible. In addition, by reciprocating the head or the recording material as described above, each time the head moves at a low nozzle pitch, the recording material is conveyed by a predetermined amount, and the ink droplets are landed at different positions, so that a high-density image is obtained. Recording can be realized.

In order to achieve this, the amount of colored ink applied to the recording material can be arbitrarily controlled within the range of 0.05 to 25 g / m ² from the viewpoint of reproducing good gradation. It is preferable to control the size and quantity of ink droplets ejected from the head.

  The interval between the recording head and the recording material is preferably about 0.5 to 2 mm. When the distance is within the above range, the flying of the ink droplets is not disturbed by the air flow accompanying the movement of the head or the recording material, and the landing position accuracy is not deteriorated. It is possible to avoid the danger of both coming into contact with each other due to vibrations and the like caused by.

  Hereinafter, the recording material and the ink (including the colored ink) will be described in detail. The details of the recording material and ink described here are the same in the second embodiment described later.

[Recording material]
As the recording medium, both an ink-permeable recording medium and an ink-impermeable recording medium can be used.
Examples of the ink-permeable recording medium include plain paper, inkjet exclusive paper, coated paper, electrophotographic co-paper, cloth, non-woven fabric, porous film, and polymer absorber. These are described as “recording materials” in Japanese Patent Application Laid-Open No. 2001-181549.

  Examples of the ink-impermeable recording medium include art paper, synthetic resin, rubber, resin-coated paper, glass, metal, earthenware, and wood. In addition, in order to add each function, a base material in which a plurality of these materials are combined and combined can also be exemplified.

  Although any synthetic resin can be used as the synthetic resin, for example, polyesters such as polyethylene terephthalate and polybutadiene terephthalate; polyolefins such as polyvinyl chloride, polystyrene, polyethylene, polyurethane, and polypropylene; and acrylic resins , Polycarbonate, acrylonitrile-butadiene-styrene copolymer, diacetate, triacetate, polyimide, cellophane, celluloid, and the like.

The shape (thickness) of the base material using the synthetic resin may be a film shape, a card shape or a block shape, and is not particularly limited and can be appropriately selected according to a desired purpose.
The synthetic resin may be transparent or opaque. As a usage form of the synthetic resin, it is one of the preferred embodiments to be used in the form of a film used for so-called soft packaging, and various non-absorbable plastics and films thereof can be used. Examples of various plastic films include PET film, OPS film, OPP film, ONy film, PVC film, PE film, and TAC film.

  Examples of the resin-coated paper include a transparent polyester film, an opaque polyester film, an opaque polyolefin resin film, and a resin-coated paper in which both sides of the paper are laminated with a polyolefin resin. The resin-coated paper is particularly preferable.

[ink]
The ink includes at least a polymerizable compound and a photopolymerization initiator and / or a sensitizer, and is configured to be capable of curing a recorded image by irradiation with active energy rays after image recording, and is configured as a colored ink. In some cases, it further comprises a color material. Further, the ink can be constituted using other components such as an organic solvent and various additives as required.

  The polymerizable compound is a compound that causes a polymerization reaction by an active species generated from a photopolymerization initiator and cures, and examples thereof include a radical polymerizable compound and a cationic polymerizable compound. It can be selected appropriately.

The radical polymerizable compound is a compound having at least one ethylenically unsaturated bond capable of radical polymerization in the molecule, and includes those having a chemical form such as a monomer, an oligomer, and a polymer. Either a monofunctional compound or a polyfunctional compound having two or more functional groups can be used, and a polyfunctional compound is preferred. For example, (meth) acrylate is suitable, and monofunctional and bifunctional or higher (meth) acrylate can be appropriately selected.
As the cationic polymerizable compound, various known cationic polymerizable monomers known as photo cationic polymerizable monomers can be used. For example, in JP-A-6-9714, JP-A-2001-31892, JP-A-2001-40068, JP-A-2001-55507, JP-A-2001-310938, JP-A-2001-310937, and JP-A-2001-220526. Examples thereof include vinyl ether compounds, oxetane compounds, and oxirane compounds.

  The photopolymerization initiator is a compound that generates a chemical change through the action of an active energy ray or the interaction with an electronically excited state of a sensitizing dye to generate at least one of a radical, an acid, or a base. Specifically, an active radical species is generated by application of active energy rays to initiate and accelerate polymerization curing of the polymerizable compound (ie, ink), and a cationic species is generated by application of active energy rays. Includes an initiator that initiates and accelerates the polymerization and curing of the polymerizable compound (that is, the ink composition), and can be appropriately selected from the following polymerization initiators.

As photopolymerization initiators, for example, Bruce M. Monroe et al., Chemical Revue, 93, 435 (1993), RSD Davidson, Journal of Photochemistry and biology A: Chemistry, 73.81 (1993), JP Faussier “Photoinitiated Polymerization- Theory and Applications ": Rapra Review vol. 9, Report, Rapra Technology (1998)., M. Tsunooka et al., Prog. Polym. Sci., 21, 1 (1996). In addition, it is described as a chemical amplification type photoresist or a compound used for photocationic polymerization in “Organic Materials for Imaging” (see Organic Electronics Materials Research Group, Bunshin Publishing (1993), p. 187 to 192). Compounds. Furthermore, FDSaeva, Topics in Current Chemistry, 156, 59 (1990) .GG Maslak, Topics in Current Chemistry, 168, 1 (1993) .HB Shuster et al, JACS, 112, 6329 (1990) .IDFEaton A group of compounds that undergo oxidative or reductive bond cleavage through interaction with the electronically excited state of a sensitizing dye, as described in et al, JACS, 102, 3298 (1980).
Preferred photopolymerization initiators include aromatic ketones, aromatic onium salt compounds, organic peroxides, hexaarylbiimidazole compounds, ketoxime ester compounds, borate compounds, azinium salt compounds, metallocene compounds, active ester compounds, carbon halogens. Examples thereof include a compound having a bond.

Examples of the sensitizer include those belonging to the compounds listed below and having an absorption wavelength in a wavelength region of 350 nm to 450 nm.
For example, polynuclear aromatics (eg, pyrene, perylene, triphenylene, 2-ethyl-9,10-dimethoxyanthracene, etc.), xanthenes (eg, fluorescein, eosin, erythrosine, rhodamine B, rose bengal, etc.), cyanine (Eg, thiacarbocyanine, oxacarbocyanine, etc.), merocyanines (eg, merocyanine, carbomerocyanine, etc.), thiazines (eg, thionine, methylene blue, toluidine blue, etc.), acridines (eg, acridine orange, chloroflavin, etc.) , Acriflavine, etc.), anthraquinones (eg, anthraquinone, etc.), squaliums (eg, squalium), and coumarins (eg, 7-diethylamino-4-methylcoumarin).

  The ink according to the present invention (including a colored ink) preferably contains at least one of the photopolymerization initiator and the sensitizer.

  There is no restriction | limiting in particular in the said color material, According to a use, well-known various color materials (pigment, dye) can be selected suitably, and can be used. For example, a pigment is preferable from the viewpoint of forming an image having excellent weather resistance. The dye is preferably an oil-soluble dye.

The pigment is not particularly limited, and all commercially available organic pigments and inorganic pigments or pigments dispersed in an insoluble resin or the like as a dispersion medium, or a resin is grafted on the pigment surface. Can be used. Moreover, what dye | stained the resin particle with dye can be used.
Examples of these pigments include, for example, “Pigment Dictionary” (2000), edited by Seijiro Ito. Herbst, K.M. Hunger “Industrial Organic Pigments”, JP 2002-12607 A, JP 2002-188025 A, JP 2003-26978 A, and JP 2003-342503 A3.

  The volume average particle diameter of the pigment particles is preferably 0.02 to 0.60 μm, the maximum particle diameter is preferably 3 μm or less, more preferably 1 μm or less, selection of pigment, dispersant, dispersion medium, and dispersion conditions The filtration conditions can be set.

The pigment can be used in a dispersed manner. For example, a ball mill, sand mill, attritor, roll mill, jet mill, homogenizer, paint shaker, kneader, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, pearl mill, wet jet A dispersing device such as a mill can be used.
It is also possible to add a dispersant to the dispersion of the pigment. As the dispersant, a hydroxyl group-containing carboxylic acid ester, a salt of a long-chain polyaminoamide and a high molecular weight acid ester, a salt of a high molecular weight polycarboxylic acid, a high molecular weight unsaturated Examples include acid esters, polymer copolymers, modified polyacrylates, aliphatic polycarboxylic acids, naphthalene sulfonic acid formalin condensates, polyoxyethylene alkyl phosphate esters, and pigment derivatives. It is also preferable to use a commercially available polymer dispersant such as Solsperse series manufactured by Lubrizol.

  As said dye, it can select from a conventionally well-known compound (dye) suitably, and can use it. Specific examples include the dyes described in paragraphs [0023] to [0089] of JP-A No. 2002-114930.

  Examples of yellow dyes include, for example, phenols, naphthols, anilines, pyrazolones, pyridones, aryl or heteryl azo dyes having open-chain active methylene compounds as coupling components, for example, open-chain active methylene compounds as coupling components Azomethine dyes having, for example, methine dyes such as benzylidene dyes and monomethine oxonol dyes, for example, quinone dyes such as naphthoquinone dyes and anthraquinone dyes, and other dyes include quinophthalone dyes and nitro dyes Nitroso dyes, acridine dyes, acridinone dyes and the like. Examples of magenta dyes include phenols, naphthols, anilines, pyrazolones, pyridones, pyrazolotriazoles, and ring-closing active methylene compounds (for example, dimedone, barbituric acid, 4- Aryl or heteroaryl azo dyes having hydroxycoumarin derivatives), electron-rich heterocycles (eg pyrrole, imidazole, thiophene, thiazole derivatives), eg azomethine dyes having pyrazolones, pyrazolotriazoles as coupling components, eg arylidene dyes , Styryl dyes, merocyanine dyes, methine dyes such as oxonol dyes, carbonium dyes such as diphenylmethane dyes, triphenylmethane dyes, xanthene dyes, such as naphthoquinone, anthraquinone Quinone dyes such anthrapyridone, can be mentioned condensed polycyclic dyes such as, for example, dioxazine dye. Examples of cyan dyes include azomethine dyes such as indoaniline dyes and indophenol dyes, cyanine dyes, oxonol dyes, polymethine dyes such as merocyanine dyes, carbonium such as diphenylmethane dyes, triphenylmethane dyes, and xanthene dyes. Dyes; phthalocyanine dyes, anthraquinone dyes such as phenols, naphthols, anilines, pyrrolopyrimidin-one, aryl or heterylazo dyes having a pyrrolotriazin-one derivative, and indigo / thioindigo dyes.

  Among the dyes, oil-soluble ones are preferable. “Oil-soluble” means that the solubility in water at 25 ° C. (mass of pigment dissolved in 100 g of water) is 1 g or less, preferably 0.5 g or less, more preferably 0.1 g or less. . Therefore, so-called water-insoluble oil-soluble dyes are preferred.

  As a dispersion medium for various components such as pigments, a solvent may be added, or the polymerizable compound which is a low molecular weight component without a solvent may be used as a dispersion medium. When the ink is composed of an active energy ray curable ink, it is preferably solventless in order to cure the ink after it is deposited on the recording medium. This is because if the solvent remains in the cured ink image, the solvent resistance is deteriorated or a problem of VOC (Volatile Organic Compound) of the remaining solvent occurs. From this point of view, it is preferable to use a polymerizable compound as the dispersion medium, and in particular, to select a cationic polymerizable monomer having the lowest viscosity in terms of dispersion suitability and ink handling properties.

  At least one of the inks in the present invention is preferably a cationic polymerizable ink, and a system using the above cationic polymerizable compound is suitable.

  In addition to the above components, the ink contains surfactants, sensitizing dyes, co-sensitizers that have functions such as further improving sensitivity or suppressing polymerization inhibition by oxygen, polymerization inhibitors, and anti-fading depending on the purpose. UV absorbers and organic and metal complex anti-fading agents, anti-oxidants to improve stability, conductive salts for controlling injection properties, organic solvents, and film properties Various additives such as molecular compounds can be used in combination.

Next, preferred physical properties of the ink (including the colored ink) will be described in detail.
The ink preferably has a viscosity of 5 to 30 mPa · s, more preferably 7 to 20 mPa · s at the temperature at the time of ejection. For this reason, it is preferable to adjust and determine a composition ratio suitably so that it may become the said range. Further, the viscosity of the ink at room temperature (25 to 30 ° C.) is preferably 7 to 120 mPa · s, and more preferably 10 to 80 mPa · s.
The viscosity is measured using an RE80 viscometer (manufactured by Toki Sangyo Co., Ltd.).

  The surface tension (25 ° C.) of the colored ink and the colorless ink is preferably 10 mN / m or more, and more preferably 20 to 50 mN / m. When recording on various recording media such as polyolefin, PET, coated paper, and non-coated paper, the surface tension is preferably 30 mN / m or more from the viewpoint of bleeding or penetration, and 40 mN / m or less in terms of wettability. It is preferable. The surface tension is measured using a surface tension meter CAVP-A3 (manufactured by Kyowa Interface Science Co., Ltd.).

(Second Embodiment)
A second embodiment of the image forming apparatus of the present invention will be described with reference to FIGS. The present embodiment detects the temperature and humidity of an image area irradiated with light having a wavelength of 390 nm or less as an active energy ray, and at least the temperature of the image area from the detected temperature and humidity and the amount of colored ink to be ejected. The temperature rise control is performed to raise the temperature.

  The basic configuration of the image forming apparatus is the same as that of the first embodiment, and the same reference numerals are given to the same components as those of the first embodiment, and detailed description thereof is omitted. Further, the description will focus on the case where five colors of white (W), black (BK), yellow (Y), magenta (M), and cyan (C) are loaded into the recording head as the colored ink to form an image. .

  As shown in FIG. 7, the temperature sensor 15 is disposed in the vicinity of the heating element 17 so that the temperature of the recording medium can be detected, and is electrically connected to the control device 14. When the heating element 17 is turned on by the controller 14, the temperature reaches instantaneously 35 ° C., and the temperature of the paper 20 can be raised in a short time.

  In addition to providing the temperature sensor 15 in the vicinity of the heating element, the temperature sensor 15 may be disposed on a pedestal 33 that conveys the paper 20 to detect the temperature of the paper, or the temperature of the exposure unit near the recording head 11 may be detected. You may arrange | position so that a detection can be performed.

The humidity sensor 16 is attached in the vicinity of the ejection head 11 at a position where the humidity of the atmosphere in the vicinity of the irradiated surface of the paper 20 in the ink jet recording apparatus can be detected, and is electrically connected to the control device 14. Yes.
And the detected temperature and humidity are sent according to the discharge timing according to the request | requirement from the control apparatus 14. FIG.

  Note that the vicinity of the irradiated surface of the paper means a range within 300 mm from the surface of the irradiated portion of the paper, and disposing the humidity sensor within this range is effective for ensuring a good curing reaction.

The temperature sensor 15 and the humidity sensor 16 are electrically connected to the control device 14 together with the recording head 11 and the LED exposure device 12, and the operation timing is controlled by the control device 14. Here, the control device 14 calculates the droplet ejection amount of the colored ink from the captured image information, and the detected temperature when the condition that the required ink amount as the calculation result is 10 g / m ² or less is satisfied. It is responsible for temperature control for controlling the necessity of temperature increase in at least the region including the low concentration region according to the humidity condition.

  Hereinafter, image formation performed using the image forming apparatus of the present embodiment will be described with reference to FIGS. 8 to 9 focusing on an image forming process performed by controlling the temperature by the control device 14.

  FIG. 8 shows a basic signal flow (control process) when an image is formed in this embodiment. In the present embodiment, a configuration (temperature / humidity sensor, calculation unit) where “*” in FIG. 8 is shown with respect to a general signal flow as shown in FIGS. 10- (a) to (b). , Heater), specifically, the temperature and humidity from the temperature / humidity sensor during print control (step 340 in FIG. 9) and signal transmission to the head drive circuit during print control. A path (steps 400, 420, and 460 in FIG. 9) that waits for the presence or absence of heating by the (heater) is provided.

Hereinafter, the temperature increase control routine shown in FIG. 9 will be specifically described.
When an image formation request is made from an information processing apparatus (not shown) (for example, a computer) electrically connected to the image forming apparatus of the present embodiment, a temperature increase control routine shown in FIG. 9 is executed.

  When this routine is executed, first, in step 300, the image information stored in the image memory in the apparatus is taken into the droplet ejection signal processing unit, and in step 320, a visible image is formed based on the image information. The required droplet ejection amount corresponding to the droplet ejection signal, specifically, the image is divided into 1 mm square regions, and the droplet ejection amounts (W ink, BK ink, Y ink, M ink, The required ink ejection amount for each of the C inks is calculated, and the ink amount for each color is determined.

  When the temperature t and the humidity s are captured in step 340, it is determined in step 360 whether or not the captured temperature t exceeds 35 ° C.

When it is determined in step 360 that the temperature t does not exceed 35 ° C. (below 35 ° C.), it is determined in step 380 whether the incorporated humidity s is less than 40% RH. When it is determined in 380 that the humidity s is 40% RH or higher, in step 400, the droplet ejection amount values (W ink, BK ink, Y ink, M, and the like) calculated by dividing the image into 1 mm square areas are obtained. It is determined whether or not the total amount of ink and C ink is 10 g / m ² or less, that is, whether or not a temperature rise is necessary for good photocuring.

  On the other hand, when it is determined in step 360 that the temperature t exceeds 35 ° C., and in step 380, when it is determined that the humidity is less than 40% RH, both are cured by UV irradiation of the LED exposure apparatus. Therefore, the heating element is turned off in step 460, and the process proceeds to step 480.

If it is determined in step 400 that the ink droplet ejection amount is 10 g / m ² or less, the LED exposure apparatus may be insufficiently cured by ultraviolet irradiation. 12, the heating element 17 corresponding to the paper position where the low-density region composed of the ink amount of 10 g / m ² or less is formed is turned on (ON) and driven.

Note that if it is determined in step 400 that the ink droplet ejection amount exceeds 10 g / m ² , there is no possibility that curing due to ultraviolet irradiation will be insufficient, and therefore in step 460 the heating element 17 is turned off (OFF). Then, the process proceeds to step 480.
In step 420, after the heating element 17 where the image (ink) to be photocured is positioned is turned on, the processing in steps 440 to 500 is the same as in steps 180 to 240 in the first embodiment. Done.

  Also in the present embodiment, when forming a low density image with a small amount of colored ink and a low droplet ejection density, the photocuring reaction is performed with the temperature of the ink raised as described above, thereby curing. The reaction can be accelerated to cure with high sensitivity, and good gradation reproducibility can be obtained in a low density region.

  In this embodiment, both temperature and humidity are detected, and control is performed based on both temperature and humidity. However, it is not necessarily required to be based on both temperature and humidity, either temperature or humidity. You may make it control based on one side.

  Also in the present embodiment, a method for increasing the temperature of a region including an image region to be photocured by irradiation of ultraviolet rays (a region to which an active energy ray is applied) is the same as in the first embodiment. For example, (1) a method of selectively irradiating infrared rays, (2) a method of scanning infrared laser light, and (3) a selective infrared LED array. The method of lighting can be appropriately selected according to the apparatus configuration, purpose, and the like.

In the above-described embodiment, the determination as to whether or not the ink has been cured with high sensitivity is performed by repeatedly discharging and curing the colored ink, applying paper to the surface of the ink image immediately after the ultraviolet irradiation, and a pressure of 100 kg / m ² . The ink can be transferred depending on whether the ink has been transferred to the paper side. At this time, it is assumed that curing is insufficient (insufficient sensitivity) when transferred to the paper side, and curing is good (high sensitivity) when not transferred.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof.

Example 1
As described in detail in the first embodiment described above, as shown in FIGS. 1 to 5, supported by the guide member 18 and movably disposed along the guide member 18, the colored ink is ejected. There is a recording head 11 having a head unit therein, a recording head carriage 13 that houses an LED exposure device 12 that emits light having a wavelength of 365 nm, and a low-concentration region in which the amount of discharged colored ink is 10 g / m ² or less. Control device 14 for performing temperature increase control for increasing the temperature of the region irradiated with ultraviolet light including the low concentration region, and a heating element for increasing the temperature of the ink droplets on the paper 20 via the paper 20 17 was prepared. Nozzles and LEDs are as described above. In this embodiment, the discharge head is loaded with cyan ink in the C ink discharge head unit so that only the cyan image is recorded.

  In addition, a PET (polyethylene terephthalate) film is used as the recording medium, and the PET film on which the ink lands is 10 mm in length and width together with the aluminum foil of the aluminum foil heater provided on the airtight aluminum upper surface. It is placed on a 5 mm thick aluminum plate with holes with a diameter of 0.5 mm at intervals, so that it is sucked by the pump through the suction tube connected to the box. It has become.

  Using the above-described ink jet recording apparatus, an image was formed as follows according to the temperature increase control routine shown in FIG. 9 described above.

<Preparation of pigment dispersion>
First, the pigment shown in Table 1 below, a polymerizable compound, and a dispersant were placed in a ball mill and dispersed for 16 hours using zircon beads having a diameter of 0.6 mm to obtain Pigment Dispersion-1. The average particle size of the pigment dispersion was measured with a transmission electron microscope (TEM).

<Preparation of cyan ink>
Each component in the following composition was mixed by stirring and filtered through a 5.0 μm membrane filter to prepare a cyan ink.
<Composition>
・ Monomer: (3 ′, 4′-epoxycyclohexane) methyl-3,4-epoxycyclohexanecarboxylate 30 g
(Celoxide 2021A, manufactured by Daicel-Cytec)
Monomer: bis [1-ethyl (3-oxetanyl)] methyl ether 70 g
(Aron Oxetane OXT-221, manufactured by Toa Gosei Co., Ltd.)
Pigment dispersion: Pigment dispersion-1 in Table 1 ... 10 g
-Photopolymerization initiator: (4-isobutylphenyl) 4-methylphenyliodonium hexafluorophosphate and propylene carbonate (Irgacure 250: manufactured by Ciba Specialty Chemicals)… 6.0 g
・ Sensitizer: Isopropylthioxanthone (Darocur ITX, manufactured by Ciba Specialty Chemicals)… 3.0 g
・ Surfactant: MegaFuck F475 (manufactured by DIC) ... 0.2 g

<Image formation>
First, the image information to be recorded is captured, the image is divided into 1 mm square areas, and the amount of cyan ink deposited in each image area is calculated, and then the temperature sensor and humidity sensor attached to the inkjet recording apparatus are used. The temperature and humidity were taken in (the temperature and humidity environment at this time was a temperature of 25 ° C. and a humidity of 60% RH). Then, the heating element is turned on based on the droplet ejection amount calculated every 1 mm square, and selectively heated to 35 ° C. at the time of low density recording of 10 g / m ² or less to support the PET film. While transporting on the 34 heating elements 17, 30 p1 (picoliter) of cyan ink is applied in an amount of 1.05 g / m ² for 150 dpi (about 0.17 mm interval) in the main scanning direction and every 150 dpi in the sub-scanning direction. Ink droplets were superposed on each other and ejected.
At this time, the actually measured humidity after heating to 35 ° C. was 34% RH.

  Subsequently, cyan ink was ejected onto the PET film from the ejection head, and at the same time, the LED was irradiated with ultraviolet light having a wavelength of 365 nm. Irradiation was performed by moving the ejection head and the LED irradiation device together in the sub-scanning direction perpendicular to the nozzle row. Curing of the ink is started by light irradiation immediately after landing. A cyan image was formed as described above.

The degree of curing after exposure was determined by observing whether or not the ink was transferred to the paper side by applying a pressure of 100 kg / m ² by applying paper to the surface of the cyan image immediately after light irradiation, and transferring it to the paper side. The degree of cure (%) was determined from the area ratio that was not obtained. The paper used here is C2 manufactured by Fuji Xerox Co., Ltd., and the transfer environment is an environment with a temperature of 23 ° C. and a relative humidity of 60%.
As a result, the degree of cure immediately after exposure was 50%, and the degree of cure after 10 minutes was 100%. It is considered that the curing proceeds with time because the polymerization reaction proceeds even after light irradiation (so-called dark reaction proceeds). The results of ink droplet ejection amount and degree of cure are shown in Table 2 below.

(Examples 2-3, Comparative Examples 1-3)
In Example 1, the ink ejection amount (g / m ² ) of cyan ink and the presence or absence of heating at 35 ° C. selectively performed at the time of low density recording (10 g / m ² or less) are shown in Table 2 below. A cyan image was formed and the degree of cure (%) was determined in the same manner as in Example 1 except for changing to. The results are shown in Table 2 below.

(Examples 4-6, Comparative Examples 4-6)
A cyan image was obtained in the same manner as in Examples 1 to 3 and Comparative Examples 1 to 3, except that the temperature and humidity environment was changed to 30 ° C. and humidity 60% RH in Examples 1 to 3 and Comparative Examples 1 to 3. And the degree of cure (%) was determined. The results are shown in Table 3 below.

As shown in Tables 2 to 3, in the examples, curing after exposure could be performed satisfactorily. In contrast, in the comparative example, the degree of cure immediately after exposure was low, and a good degree of cure was not obtained even after 10 minutes.
In Examples 4 to 6, where the temperature is higher than in Examples 1 to 3, although curing proceeds more, it is understood that the sensitivity is low in the case of a small amount of droplet ejection due to high humidity. It was possible to keep the sensitivity high.

  In the above, the ink droplet ejection amount is calculated by calculating the cumulative droplet ejection amount within a predetermined area and performing the heating control. However, the total droplet ejection amount that is superimposed and deposited is calculated in advance, Control may be performed for each main scan based on the calculated value.

1 is a cross-sectional view illustrating a schematic configuration of an ink jet recording apparatus according to a first embodiment of the present invention when a recording head and a support base are viewed from a main scanning direction. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a conceptual diagram for explaining a schematic overall configuration of an ink jet recording apparatus according to a first embodiment of the present invention. 1 is a cross-sectional view illustrating a conceptual configuration of an ink jet recording apparatus according to a first embodiment of the present invention when a recording head and a support base are viewed from a sub-scanning direction. FIG. 2 is an enlarged conceptual diagram illustrating a head configuration and an irradiation unit configuration of the ink jet recording apparatus according to the first embodiment of the present invention. 3 is a flowchart for explaining a flow of a signal for print control executed in the ink jet recording apparatus according to the first embodiment of the present invention. 3 is a flowchart showing a droplet ejection control routine for performing print control of the ink jet recording apparatus according to the first embodiment of the present invention. It is a conceptual diagram for demonstrating the schematic whole structure of the inkjet recording device which concerns on 2nd Embodiment of this invention. It is a flowchart for demonstrating the flow of the signal of the print control performed in the inkjet recording device which concerns on 2nd Embodiment of this invention. It is a flowchart which shows the droplet ejection control routine which performs print control of the inkjet recording device which concerns on 2nd Embodiment of this invention. (A) is a flowchart for explaining the flow of a signal for print control executed in a conventional apparatus, and (b) is a flowchart showing a routine for print control in a conventional apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Discharge head 12 ... LED exposure apparatus 14 ... Control apparatus 15 ... Temperature sensor 16 ... Humidity sensor 17 ... Heating body (heater)
20: Recording medium

Claims (4)

An image forming apparatus that forms an image by applying an ink that is cured by active energy rays by an inkjet method,
An image forming apparatus that selectively raises the temperature of a region to which an active energy ray is given when there is a region where the amount of ink forming the image is 10 g / m ² or less. A recording head that discharges ink that is cured by active energy rays to a recording medium according to image information;
Energy applying means for providing an active energy ray to a region including at least the ink ejected by the recording head;
Heating means for heating the region to which the active energy rays are applied;
Temperature control means for performing temperature increase control for increasing the temperature of the area to which the active energy ray is applied by the energy applying means when there is an image area in which the amount of the ejected ink is 10 g / m ² or less;
The image forming apparatus according to claim 1, further comprising: Detection means for detecting the temperature and / or humidity of the region to which the active energy ray is applied;
Determination means for determining whether the temperature and / or humidity detected by the detection means is within a predetermined range;
The image forming apparatus according to claim 1, further comprising: the temperature control unit configured to increase the temperature in accordance with a temperature and / or humidity range determined by the determination unit.   The image forming apparatus according to claim 2, wherein the energy applying unit is a light emitting diode having a wavelength of 390 nm or less.

Images