Patent Application
20120038703
1. Field of the Invention
The present invention relates to an inkjet printing apparatus and an inkjet printing method, and particularly relates to a construction for improving a gloss of a printed matter printed in ink.
2. Description of the Related Art
There is provided an inkjet printing apparatus which realizes high image fastness by using an ink using an aqueous dispersion pigment (hereinafter, called “a pigment ink”). However, a printed matter printed in a pigment ink generally has the characteristic of being excellent in water resistance and light resistance of an image, that is, fastness of the image, but being relatively low in the glossiness of the image. This is because the pigment ink hardly penetrates to the inside of a print medium, is fixed on the surface to form asperities on the surface of the print medium easily to impair smoothness of the image surface.
As an inkjet printing technology of improving the glossiness of an image by a pigment ink, Japanese Patent Laid-Open No. 2008-149514 describes the technology of improving non-uniformity of the glossiness on a printed matter caused by use of the pigment ink by applying a clear ink onto the printed matter. More specifically, by regulating an application amount of the clear ink in accordance with an application amount of the pigment ink, the difference in the gloss level due to the density of the pigment ink is decreased, and the glossiness on the printed matter using the pigment ink is made uniform.
Further, Japanese Patent Laid-Open No. 2001-039006 describes the technology of injecting a top coat solution formed from resin emulsion and water onto a surface of a printed matter to form a top coat layer thereon, thereby improving the glossiness of the printed matter using a pigment ink.
As the index for expressing the gloss level of a printed matter, “image clarity” showing the sharpness of a reflected image on the printed matter, and “specular gloss level” showing the brightness of the reflected image on the printed matter are often used. In order to realize the high gloss level equivalent to a silver halide photo and offset printing, both the image clarity and specular gloss level are desirably high.
The specular gloss level depends dominantly on a reflectance which is determined by a refractive index of a material of the printed matter surface and a surface roughness, and if a material with a high refractive index such as a resin is applied onto the printed matter surface, the specular gloss level can be improved. Meanwhile, the image clarity depends dominantly on smoothness on the printed matter surface, and in the printed matter using the pigment ink, the image clarity can be improved by smoothing the unevenness formed on the printed mater surface.
Japanese Patent Laid-Open No. 2008-149514 discloses the method for applying a clear ink onto a printed matter for the purpose of originally making the glossiness thereon uniform, and has the high effect of improving the sense of discomfort of an image due to uneven glossiness. However, Japanese Patent Laid-Open No. 2008-149514 is designed not to improve the gloss level itself to be higher but to make the glossiness uniform, and therefore, has the difficulty in realizing a high gloss level similar to that of the silver halide photo and the offset printing.
The technology described in Japanese Patent Laid-Open No. 2001-039006 can enhance a specular gloss level by using a resin as a coating layer of a printed matter. However, there are some cases where in the structure of simply applying a top coat solution or a clear ink onto a printed matter as described in Japanese Patent Laid-Open No. 2001-039006, the unevenness on the printed matter surface can not be smoothed. In such a case, the image clarity can not be enhanced, and therefore, realization of the high gloss level becomes difficult.
More specifically, on the printed matter by the pigment ink, the permeation speed of the clear ink differs depending on the kind and density of the applied pigment ink. When the permeation speed of the clear ink varies in this manner, since the resin of the clear ink flows into and deposits on a portion of the printed matter where the permeation speed is higher, a deposition amount of the clear ink resin also differs depending on the portion. Thus, simply by applying the clear ink onto the printed matter, the deposition amount thereof differs thereon, and as a result, in some cases the printed matter surface becomes uneven even though the clear ink is applied thereon.
An object of the present invention is to provide an inkjet printing apparatus and an inkjet printing method which can improve glossiness, in particular, image clarity of a printed matter by a pigment ink.
In a first aspect of the present invention, there is provided an inkjet printing apparatus that uses a printing head for ejecting pigment ink containing a pigment as a coloring agent and clear ink containing no coloring agent and having film-forming property on a print medium and ejects ink from the printing head to the print medium for performing printing, the apparatus comprising: a printing unit configured to cause the printing head to eject a plurality of pigment inks, which contain different coloring agents from each other, from the printing head to the print medium for printing an image; a first applying unit configured to apply the clear ink to at least a part of a region of the image on the print medium, the region being printed by that the printing unit ejects the plurality of pigment inks that contain different coloring agents from each other, by causing the printing head to eject the clear ink to at least the part of the region; and a second applying unit configured to apply the clear ink to a region, to which the clear ink is applied by the first applying unit, by causing the printing head to eject the clear ink to the region, after the first applying unit applies the clear ink, wherein at least one time of application of the clear ink is performed by each of the first and second applying units.
In a second aspect of the present invention, there is provided an ink jet printing method that uses a printing head for ejecting pigment ink containing a pigment as a coloring agent and clear ink containing no coloring agent and having film-forming property on a print medium and ejects ink from the printing head to the print medium for performing printing, the method comprising: a printing step of causing the printing head to eject a plurality of pigment inks, which contain different coloring agents from each other, from the printing head to the print medium for printing an image; a first applying step of applying the clear ink to at least a part of a region of the image on the print medium, the region being printed by that the printing unit ejects the plurality of pigment inks that contain different coloring agents from each other, by causing the printing head to eject the clear ink to at least the part of the region; and a second applying step of applying the clear ink to a region, to which the clear ink is applied by the first applying step, by causing the printing head to eject the clear ink to the region, after the first applying step applies the clear ink, wherein at least one time of application of the clear ink is performed by each of the first and second applying steps.
According to the above configuration, after the clear ink which is applied at the first time becomes the film, the second application of the clear ink is performed. Thereby, the second clear ink permeates at a uniform permeation speed to be fixed. As a result, the clear ink which is applied at the second time does not generate unevenness on the surface since it has no difference in the permeation speed, and therefore, a smooth printed matter surface can be formed. Thereby, the glossiness, in particular, the image clarity of the printed matter can be improved.
Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
The embodiments of the present invention use a pigment ink for printing images and a clear ink which does not contain a coloring agent. The pigment ink is a color ink which contains a color pigment. The pigment ink may be of mono-color, but a plurality of kinds of inks such as cyan, magenta, yellow and black may be prepared. The clear ink is a colorless ink which is prepared by dissolving a vinyl resin (styrene acrylic resin, acid value 170) in water, and containing an organic solvent, and a surfactant therein.
As described above, the present invention is to solve the problem that there are some cases where, when a clear ink is simply applied on a printed matter, smoothness of the printed matter can not be obtained by it. The problem can be described in more detail as follows.
For example, in a case where between two adjacent regions A and B in a surface of a printed matter, a thickness of a pigment ink layer of the region A is larger as compared with a thickness of a pigment ink layer of the region B, and a permeation speed of a clear ink into the pigment ink layer of the region A is higher as compared with that of the region B, much clear ink resins deposit on the region A. As a result, the region A which originally has a thicker pigment ink layer further increases in thickness, and the unevenness on the printed matter surface results in increasing. On the other hand, in a case where the thickness of the pigment ink layer of the region A is small as compared with the thickness of the pigment ink layer of the region B, and the permeation speed of the clear ink into the pigment ink layer of the region A is higher as compared with that of the region B, much clear ink resins deposit on the region A also in this case. However, the region A which originally has a smaller pigment ink layer increases in thickness to reduce the unevenness to the region B.
In general, the film thickness of a pigment ink layer is mainly determined by the solid contents contained in the ink, and the permeation speed of a clear ink is determined by the size of pores formed in the pigment ink layer and the surface energy. Both of them depend greatly on the material property, pigment inks made of different materials according to colors differ in deposition film thickness and permeation speed of the clear ink according to colors. As a result, the applied clear ink increases or decreases unevenness depending on the film thickness of the pigment ink layer and the permeation speed of the clear ink. That is, a smooth surface can not be always obtained by an application of the clear ink. Thus, when a clear ink is applied to a printed matter such as a photograph which is constructed by pigment inks of various kinds or colors, the unevenness is resultantly generated on the printed matter in such a manner that the unevenness is partially reduced and the unevenness is partially increased, and a smooth surface sometimes cannot be obtained.
On the other hand,
The present invention has the feature in which the application process of a clear ink has the application process of two stages. The application of the first stage has the function of forming a film of the clear ink on the region of the printed matter surface where it is desired to obtain gloss, and making the permeation speed of the clear ink into the printed matter uniform. The application of the second stage is the process of applying the clear ink again onto the region to which the clear ink is applied in the application process of the first stage, and has the function of smoothing the printed matter surface.
In the application process of the first stage, the clear ink is applied without a blank space onto the region of the printed matter surface in which it is desired to obtain the gloss. After the clear ink is applied, the clear ink permeates into the region and dries to be fixed, whereby the film of the clear ink is formed on the region of the printed matter surface in which it is desired to obtain the gloss. At this time, the clear ink resin may generate unevenness in accordance with the variation in permeation of the clear ink on the printed matter surface. Therefore, frequently the gloss level is not enhanced in the application process of the first stage. Meanwhile, the region on the printed matter in which it is desired to obtain gloss is covered with the clear ink film, whereby permeation of the solution (clear ink) which will be applied next in this region becomes uniformly slow, and a variation in the permeation speed of the solution is substantially eliminated. As described above, the application process of the first stage performs the function of eliminating the variation in the permeation speed of the solution in the region on the printed matter in which it is desired to obtain the gloss surface.
In the application process of the first stage (first application process), the clear ink is preferably applied without a blank space as described above. If the blank space is formed, the permeation speed of the blank space portion differs from that of the other portions, and the object of making the permeation speed uniform is not attained. It should be noted that the state “without a blank space” described here may have some microscopic blank spaces. More specifically, there is no problem if the clear ink resin substantially uniformly covers 80% of the area in the region of the printed matter surface in which it is desired to obtain the gloss. “Substantially uniform” means the state without a remarkable deviation in the distribution of the blank spaces, and shows that the deviation is such that the standard deviation σ of the coverage factor measurement at 10 spots is 10% or less according to an experiment.
As is obvious from
For measurement of the coverage factor of the clear ink resin, an optical microscope is used. First, the printed matter after the application of the clear ink of the first stage is photographed by the optical microscope. In this measurement, the photography is performed by using the optical microscope with a ten-power objective lens and a digital camera of 1.2 million pixels. Since the thin film of the clear ink resin deposits on the portion covered with the clear ink, the portion looks so as to change in coloring due to thin film interference. The color which is changed by the thin film interference and the color which is not changed are divided into two regions by image processing software or the like, the area of each of the regions is calculated, by which the coverage factor of the clear ink resin is obtained.
In the application process of the second stage (second application process), the clear ink is applied to the region where the variation in the permeation speed is eliminated by formation of the clear ink layer in the application process of the first stage. The application is such that for the region to which the clear ink is applied in the first stage, the area of 80% or more is substantially uniformly covered with the clear ink resin.
In the application process of the second stage, the clear ink by the application step of the first stage has been preferably formed as a film. Formation of the film advances by the solvent of the clear ink permeating the printed matter or drying for removal. The easiest method of formation of the film is the method which dries the clear ink by leaving it for a fixed time after the application process of the first stage. The time required for formation of the film differs depending on the material of the clear ink and the kind of the printed matter by the pigment ink. The time required for the film formation can be obtained by variously changing the time between the application processes of the first stage and the second stage and measuring the resultant change of image clarity.
Each of the application processes may be carried out by a plurality of times in order to perform the function thereof. For example, there may be estimated some cases where by performing the application of the first stage only once, the film of the clear ink is thin, and the effect of reducing the permeation variation is small, depending on the material for use in the clear ink. In such a case, it is desirable to perform the application process of the first stage twice or more. Similarly, there may be estimated some cases where by performing the application of the second stage only once, the unevenness on the printed matter surface still remains though the unevenness is reduced depending on the clear ink material. In such a case, it is desirable to perform the application process of the second stage twice or more.
The printing heads 304, 305 and 306 are so-called full line type printing heads in which the ejection openings are arranged over the range equivalent to or larger than the width of the print medium P, and can perform printing on a whole surface of the print medium P by conveying the print medium P once. The four printing heads 304 are printing heads which respectively eject the pigment inks of cyan (C), magenta (M), yellow (Y) and black (K). Further, at a downstream side in the conveying direction of the print medium P, the similar two full line type printing heads 305 and 306 which eject the clear ink are provided. /
By the arrangement of the printing heads, the inks of C, M, Y and K are ejected to the print medium P which is conveyed, from the printing heads 304 according to the printing data, thereby printing an image thereon. The image on the print medium is sequentially opposed to the printing heads 305 and 306, and the clear ink is ejected to the image. That is, the application process of the clear ink in the first stage is performed by the printing head 305. Thereafter, the application process of the clear ink in the second stage is performed by the printing head 306. Here, a space provided in the conveying direction between the printing head 305 and the printing head 306 is a distance corresponding to the aforementioned time during which the clear ink applied in the application process of the first stage becomes the film. Thereby, in the middle where the print medium P is conveyed at a constant speed, the printing process by C, M, Y and K inks, the application process of the first stage by the clear ink, the process of the film formation of the clear ink, and the application process of the second stage by the clear ink are sequentially executed. A heater as a mechanism for promoting the film formation may be disposed between a nozzle array (first nozzle array) of the printing head 305 and a nozzle array (second nozzle array) of the printing head 306, and thereby, the distance between the two printing heads may be reduced.
As another mode for realizing the printing method according to the present invention, a serial type inkjet printing apparatus also may be used.
The printing head 404 is detachably mounted on a carriage 408. The carriage 408 can reciprocate in a main scan direction along two guide rails 409 and 410 by the drive force of a carriage motor, and ejects an ink or a clear ink from the printing head 404 in accordance with printing data in the process of the movement, thus performing printing. Such printing scan by the printing head 404 and the conveyance operation of the print medium are alternately repeated, and thereby, an image is formed on the print medium P stepwise.
The printing apparatus of the present embodiment has a mode of carrying out multi-pass printing. The multi-pass printing performs conveyance of the print medium P by a width shorter than the above described d in a period between scans of the printing head 404, and thereby, performs a plurality of scans of the printing head for a printing area of the short width. Thereby, printing can be performed by assigning different nozzles in each scan for the area. Thus, a density variation and a streak due to variations in the individual nozzles can be reduced. In general, in the case of M-pass printing which completes an image by printing scans of M times, conveyance of the print medium is performed by a width of d/M in a period between the respective printing scans. Hereinafter, an image area having a width d/M, image of which is completed by M times of scans in such multi-pass printing will be called the same image area. In the printing process mainly using a pigment ink, the multi-pass printing is used. On the other hand, applications of the clear inks of the first stage and the second stage do not aim at formation of an image, and therefore, the multi-pass printing does not necessarily have to be used.
The present embodiment has the mode of applying a clear ink, and the mode of not applying the clear ink, and uses printing methods differing between them. The mode of not applying the clear ink will be described with reference to
In the mode of applying the clear ink, any one of three printing methods shown as follows can be used.
In the first method, a clear ink application of the first stage is performed after completion of the printing process by color inks, and after completion of the clear ink application of the first stage, a clear ink application of the second stage is performed in sequence.
The second method is executed such that the printing process and the clear ink application of the first stage are completed while conveyance is carried out in the sub-scan direction of one time, and the clear ink application of the second stage is carried out after the completion thereof.
After the film formation, in an application process 1202 of the second stage, the conveying roller 401 and the sheet discharge roller 405 are rotated inversely, and clear ink application of the second stage is performed by using the nozzle array 503 while the print medium P is conveyed in the reverse direction from the sub-scan direction. The conveyance amount of the print medium at this time also can be set to the width d of the nozzle arrangement range of the nozzle array 503. Though the clear ink of the second stage is applied while the print medium P is conveyed in the reverse direction from the sub-scan direction, the clear ink may be applied by the regular printing method which feeds the print medium P again after completion of the printing process, and conveys the print medium P in the sub-scan direction.
The third method is constructed such that the printing process, the clear ink application of the first stage, and the clear ink application of the second stage are carried out while performing conveyance at one time in the sub-scanning direction.
For the storage medium 34, a ROM, an FD, a CD-ROM, an HD, a memory card, a magneto-optical disk and the like can be applied. The storage contents stored in the storage medium 34 include information 34a relating to the kind of the print medium and information 34b related to inks. Further, the contents also include information 34c relating to presence or absence and the position of a defect nozzle, information 34d relating to the environment such as a temperature and humidity at the time of printing, various control programs 34e and the like. Reference numeral 35 denotes a RAM, which is used as a work area at the time of execution of the various programs stored in the storage medium 34, and as a temporary save area of needed data at the time of error processing. The gloss level data of giving/not giving the high gloss to the entire image surface described above is also stored herein. Further, various data stored in the storage medium 34 also can be temporarily copied in the RAM 35. The CPU 33 can change the copied data content in the storage medium 34, and can further proceeds with image processing while referring to the changed data.
Reference numeral 36 denotes an image data processing section. The image data processing section 36 executes quantization processing of converting multi-value image data inputted from the image data input section 31 into ejection data of a lower-level value which the printing head can print. For example, when the data inputted from the image data input section 31 is multi-value image data which is expressed by 8 bits (256 gradation levels) x three colors (RGB), the image data processing section 36 executes the process of separating the data into four (C, N, Y, K) of gray scale data, first. Next, based on the gray scale data of each separated color, the data is converted into dot data which the corresponding printing head can print. Here, when the printing head is capable of printing with only two pieces of information composed of ejection and non-ejection, data is converted into binary data in accordance with a dot arrangement pattern which is defined as any one of printing and non-printing. Further, in a case where the printing head can control an ejection amount by dividing it in a plurality of stages, the data value is reduced to the number of stages with which printing is enabled. At this time, as the method for reducing a data value, a generally known multi-value error diffusion method can be used. Further, other arbitrary halftone processing methods such as an average density conservation method and a dither matrix method can be used. In regard to gloss level data, the data is converted into dot data which the corresponding printing head can print in accordance with the position on the image and the binary data of giving/not giving the high gloss. The conversion method is similar to the aforementioned image data, but in the portion which is given the high gloss, dot data is created so that the application amount of the clear ink is an amount to the extent that 80% or larger of the area of the region in which it is desired to obtain a gloss is covered with the clear ink resin. That is, the image data with the printing duty being 80% is set, and, based on the image data, the above-described dot data is created. With regard to the portion which is not given the high gloss, data that shows no dot arrangement is created.
In the case of performing the multi-pass printing by using the serial type inkjet printing apparatus or in the case of the printing head having a plurality of nozzle arrays of the same color, among the above-described constructions, the process of dividing an image for the scans or nozzle arrays is executed in the image data processing section 36. More specifically, in the case of the multi-pass printing, ejection is dispersed to a plurality of printing scans, and in the case of having a plurality of nozzles, ejection is dispersed to the nozzle arrays. The method may include the case of dividing the aforesaid gray scale data into more (low-density) data at the time of creation of the aforesaid gray scale data, and the method of integration of masks, which are set for each path and each nozzle array, for the dot data.
Reference numeral 37 denotes an image printing part which performs image output, which generates pulses for driving the printing head in accordance with the ejection pattern created by the image data processing section 36, and ejects an ink from ejection openings of the printing head. Reference numeral 38 denotes a bus which transfers various data, which transmits address signals, data, control signals and the like in the storage device.
Hereinafter, with respect to the printed matter outputted by the first clear ink application method using the serial type inkjet printing apparatus among the aforementioned constructions, the examination content for verification of glossiness and the result will be described.
First, the clear ink was used, which was obtained by being prepared with the following composition and thereafter, being adjusted with a potassium hydroxide solution so that pH was 9.
Further, as the pigment inks, PFI-101C (hereinafter, cyan), PFI-101M (hereinafter, magenta), PFI-101Y (hereinafter, yellow), and PFI-103BK (hereinafter, black) made by Canon Inc. were used. As the printing apparatus, Inkjet Printer iPF-5100 made by Canon Inc. was used, and the resolution at the time of printing was set at 1200 dpi (dot/inch) in the sub-scan direction, and at 2400 dpi in the main scan direction. Further, as the print medium, LFM-GP101R made by Canon Inc. was used. The volume per droplet of the ink is 4.8 pico-liter.
For evaluation of the gloss level, the following two kinds of methods were used. As the specular gloss level, 20-degree gloss value was adopted as the specular gloss level by using GMX-203 made by MURAKAMI COLOR RESEARCH LABORATORY CO., Ltd. A higher value of the 20-degree gloss means a higher specular gloss level.
With regard to image clarity, the value of the sharpness which was measured was adopted as the value of the image clarity by using DIAS DOI Image Analysis System made by QEA Inc. The sharpness value is defined as follows. With a white LED as a light source, a knife edge is located between the light source and a measurement sample, and the reflection image of the knife edge on the sample is photographed by a CCD camera (three hundred thousand pixels: 5 per pixel). The pixel visual field is 2.4 mm square. The luminance distribution of the knife edge portion of the reflection image is subjected to the first derivation, and the inverse of the half-value width thereof is defined as the Sharpness value. Accordingly, as a Sharpness value is the larger, the sharper reflection image is obtained, which means that the image clarity is high.
Comparative example B shown in
As is understood from
As described above, according to the printing method of the present embodiment, the permeation speed variation on the printed matter surface is reduced by the clear ink application of the first stage, the unevenness on the printed mater can be reduced by the clear ink application of the second stage, and both the specular gloss level and the image clarity can be enhanced.
The embodiment described above has an object of obtaining the gloss of the printed matter, and the present invention is also effective for value-added printing which partially gives a high gloss to an arbitrary spot on the printed matter. When a picture and a letter are printed on a pigment ink printed matter with a low gloss by using the present invention, only the portion has a high gloss and can be emphasized. For example, the present invention can be used in such a manner as to give a high gloss to only the picture portion of the document including a picture, give a high gloss to only a commodity product portion of the poster of the commodity product, and print a letter such as no copying” on a printed matter as a latent image. Such value-added printing is already in practical use in the electro-photography and the like, but in the inkjet printing apparatus for printing in pigment inks, such value-added printing is not in practical use since no means for realizing the high gloss is available irrespective of the state of the printed matter (pigment inks which are applied). Use of the present method enables the value-added printing at a lower cost as compared with the electro-photography.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2010-174765, filed Aug. 3, 2010, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-174765 | Aug 2010 | JP | national |
