1. Field of the Invention
The present invention relates to a transfer inkjet recording method.
2. Description of the Related Art
A transfer inkjet recording method has been known in which an intermediate image is formed by applying an ink to the image-forming face of an intermediate transfer member to which aggregating agent has been applied, and then the intermediate image is transferred to a recording medium, thereby forming a final image. In order to transfer the intermediate image satisfactorily, it is desirable that the image-forming face of the intermediate transfer member have high releasability (or repel inks). It is however difficult to uniformly apply an aggregating agent to a highly releasable image-forming face. Accordingly, Japanese Patent Laid-Open No. 2008-18719 discloses a method of uniformly forming on the image-forming face a pattern (lyophilic portions) that can be easily wetted with an aggregating agent. According to this method, the aggregating agent can be deposited only on the lyophilic portions, consequently being uniformly applied there.
However, the present inventors have found that this method has some disadvantages when the amount of aggregating agent is increased to enhance the aggregation power. Specifically, the disadvantages are as below.
In order to increase the amount of aggregating agent, the area of each lyophilic portion compatible with the aggregating agent can be increased. By increasing the area of each lyophilic portion, not only the base area of the aggregating agent deposited on the lyophilic portions, but also the height of the aggregating agent, is increased. Consequently, the amount of aggregating agent can be increased relative to the case where only the number of the lyophilic portions is increased to increase the base area.
However, the pitch of the lyophilic portions (center-to-center distance between the lyophilic portions) cannot be reduced to less than the diameter (maximum diameter) of the lyophilic portion. If the pitch of the lyophilic portions is smaller than the diameter of the lyophilic portions, the lyophilic portions overlap with one another. Therefore, as the area of each lyophilic portion is increased, the pitch of the lyophilic portions increases accordingly. This may affect the shape of ink dots. The (α) side of
In contrast, if the area of each lyophilic portion is reduced, the variations in ink dot shape and reproduction resolution can be reduced, but the amount of aggregating agent on the lyophilic portions is reduced. Consequently, it becomes difficult to collect the ink sufficiently. Consequently, bleeding (color mixing) occurs in the intermediate image and the final image formed on a recording medium some cases.
The present invention provides a transfer inkjet recording method that can prevent the deformation of ink dots, the variation in reproduction resolution, and bleeding in the image.
According to an aspect of the invention, in the transfer inkjet recording method, an aggregating agent capable of aggregating a coloring material contained in an ink is applied onto an image-forming face of an intermediate transfer member. The image-forming face has a pattern including lyophilic portions and a lyophobic portion. The lyophilic portions include at least two types of portions having different areas. Then, an intermediate image is formed by applying the ink onto the image-forming face on which the aggregating agent has been applied. The intermediate image is transferred to a recording medium by pressing the recording medium on the image-forming face on which the intermediate image has been formed.
The transfer inkjet recording method can prevent the deformation of ink dots, the variation in reproduction resolution, and bleeding in the image.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
The invention will be further described in detail.
When an intermediate image is formed on the image-forming face of an intermediate transfer member, in theory, as the uniformity of the pattern formed by the aggregating agent, which is applied before the ink, is increased, the intermediate image is more difficult to deform irregularly. According to this idea, it has been believed that it is desirable that the pattern of lyophilic portions be uniform in such a manner that the regions having the same area and the same shape are regularly arranged at constant intervals, and such a design has been applied to the pattern of the lyophilic portions.
The present inventors however have found that such a uniform pattern has a disadvantage. More specifically, as mentioned above, relationships among the area of each lyophilic portion, the amount of aggregating agent on the lyophilic portions, and the shape and reproduction resolution of ink dots are subject to some constraints.
In general, for reproducing a high-definition photographic image by inkjet recording, a high-resolution output of 1200 dpi or more is used.
In a practical color image, however, three color inks may overlap with each other, and the amount of ink can exceed 20 mg per square inch in dense color regions. The amount of ink coming into contact with the aggregating agent on the intermediate transfer member increases to 100 times the amount of the aggregating agent on a mass basis. Accordingly, the ink is unlikely to be aggregated sufficiently, and thus bleeding may occur in the intermediate image and the final image.
However, when an ink image is formed over the surfaces of such lyophilic portions, the dots of the ink may be deformed so as to be drawn by the lyophilic portions and the aggregating agent, as shown in
The present invention has been accomplished on the basis of these disadvantages. In the present embodiment, the lyophilic portions include regions having at least two different areas, as shown in
In the pattern shown in
In a pattern including the same lyophilic portions having the same area as in the known pattern, even if the area of the lyophilic portions is optimized, it is difficult to reduce the deformation of the ink dots and the variation in reproduction resolution at a high level while the amount of aggregating agent is maintained. In the present embodiment, the different types of lyophilic portions having different areas function to produce contradictory effects according to their respective areas so that the lyophilic portions having a small area reduce the deformation of ink dots and the variation in reproduction resolution while the lyophilic portions having a large area maintain the amount of aggregating agent.
The patterns of lyophilic portions according to the present embodiment include the following four types:
1. Irregular arrangement at a constant pitch,
2. Regular arrangement at a constant pitch,
3. Irregular arrangement at different pitches,
4. Regular arrangement at different pitches,
An appropriate pattern can be selected from these four patterns according to the desired image and quality, and the ink and aggregating agent to be used. For any pattern, the lyophilic portions can be provided so that a droplet of ink can come into contact with both the large lyophilic portion and the small lyophilic portion. The amount of ink that can be aggregated by a unit mass of aggregating agent depends on the composition of the aggregating agent. When a unit mass of aggregating agent can aggregate a large amount of ink, the number of large lyophilic portions with which an ink droplet comes into contact can be minimized, from the viewpoint of reducing the deformation of ink dots and the variation in reproduction resolution.
At least one period of the repetitions of the lyophilic portions in the pattern used can be higher than or equal to the designed resolution used for outputting an inkjet image. The largest lyophilic portions of at least two types of lyophilic portions, having the largest area, can have a diameter (maximum diameter) smaller than the maximum diameter of the spread of ink dots ejected from an inkjet head. The diameter (maximum diameter) of the lyophilic portions is the length of the longest straight line between edges of the region of the largest lyophilic portion. The maximum diameter of the spread of ink dots is about 80 μm. Accordingly, the diameter of the largest lyophilic portion can be 80 μm or less. Also, the area of the largest lyophilic portions can be smaller than the area of the ink dots, and is, for example, 5000 μm2 or less. In this instance, naturally, the diameter of the smallest lyophilic portions is smaller than the maximum diameter of the spread of the ink dots, and their area is smaller than that of the ink dots. However, if the area of the smallest lyophilic portions is excessively small, the aggregating agent cannot be held on the lyophilic portions. Accordingly, the diameter of the smallest lyophilic portions can be 2 μm or more, and their area can be 4 μm2 or more. All the lyophilic portions can be circular, as shown in
The pattern of lyophilic portions can be formed by a known method. For example, a resist method, a mask method, a printing method, or a direct method using a laser can be applied. Among those, the resist method can advantageously perform very fine patterning. Thus, the lyophilic portions are formed so as to have at least two types of portions having different areas by patterning or the like.
The transfer inkjet recording method according to an embodiment will now be described with reference to
In
The intermediate transfer member 1 rotates in the direction indicated by the arrow shown in
The apparatus shown in
Elements and steps in the transfer inkjet recording method of the present embodiment will now be described.
The intermediate transfer member has a pattern including lyophilic portions and a lyophobic portion, and can be in any form as long as its surface can come into at least line contact with the recording medium. For example, it may be a roller, a belt or a sheet, depending on the form of the recording apparatus or the recording medium to be used. The image-forming face of the intermediate transfer member can be made of an elastic material, such as rubber or plastic. For example, the image-forming face has an elasticity corresponding to a hardness in the range of 10° to 100° when it is measured with a type A durometer (in accordance with JIS K 6253). If the hardness is in the range of 40° to 80°, more types of recording media can be used. Although
The image-forming face of the intermediate transfer member may not absorb liquid. A surface that cannot absorb liquid is easily kept clean by cleaning with the cleaning unit, and, in addition, can be advantageously used in an inkjet recording method such as variable data printing. The image-forming face can have such releasability as can stably transfer intermediate images to the recording medium.
The intermediate transfer member may be a blanket used for ordinary printing, which may be surface-treated, or a rubber sheet, such as that of NBR, urethane rubber, silicone rubber, fluorocarbon rubber, nitrile rubber, chloroprene rubber, or natural rubber. Such an intermediate transfer member can be disposed in a replaceable manner. These materials may be directly formed into a shape of a belt or a roller. For example, a silicone rubber intermediate transfer member may be used.
The aggregating agent used in the present embodiment aggregates the coloring material in the ink used for forming images. In the step of applying the aggregating agent, the aggregating agent is applied onto the image-forming face of the intermediate transfer member. The aggregating agent can be appropriately selected according to the type of the ink used for forming images. For example, if a dye ink is used, a polymeric aggregating agent can be used. If a pigment ink is used, an aggregating agent containing a metal ion can be used. If a metal ion and a polymeric aggregating agent are used in combination for a dye ink, a pigment having the same hue as the dye can be added to the ink, or white or transparent particles that are unlikely to affect the color of the ink may be added.
Examples of the polymeric aggregating agent include cationic polymer aggregating agents, anionic polymer aggregating agents, nonionic polymer aggregating agents, and amphoteric polymer aggregating agents. Examples of the metal ion include divalent metal ions, such as Ca2+, Cu2+, Ni2+, Mg2+, and Zn2+, and trivalent metal ions, such as Fe3+ and Al3+. For applying an aggregating agent containing these metal ions, it can be applied as an aqueous solution of a metal salt. The anion of the metal salt may be Cl−, NO3−, SO42−, I−, Br−, ClO3−, or RCOO− (R represents an alkyl group). Materials having opposite properties to the ink can be used as the aggregating agent. For example, when the ink is anionic or alkaline, a cationic or acid aggregating agent can be used.
The aggregating agent can be prepared so as to be easy to deposit to the lyophilic portions of the intermediate transfer member, and easy to repel from the lyophobic portion. For preparing such an aggregating agent, a surfactant can be used. The surfactant may be an anionic surfactant, a cationic surfactant, a nonionic surfactant, an amphoteric surfactant, a silicone surfactant, or a fluorinated surfactant. Although any surfactant can be appropriately used, it should be avoided that an anionic surfactant is used in a cationic aggregating agent. Many of the surfactants are dispersed in water so that their molecules are aligned along the interface with a gas to function as intended. Since even a trace amount of surfactant can produce an effect, it can adjust the characteristics of the aggregating agent without changing the composition of the aggregating agent. For example, an aqueous aggregating agent can be used because its characteristics are easy to adjust.
Since the image-forming face of the intermediate transfer member used in the present embodiment has a pattern including lyophilic portions and a lyophobic portion, the aggregating agent can be uniformly and stably applied with a very simple application device. The application device 3 for applying the aggregating agent, shown in
For the application of the aggregating agent, devices other than application rollers can be used. For example, a contact process may be applied, such as doctor coating, die coating, wire-bar coating, or gravure roller application. Liquid ejection or other noncontact processes may be applied by using a spray coater or an inkjet head. Spin coating or dip coating may be applied, or an air knife may be used. These application methods may be combined as needed.
In the step of forming an intermediate image, an ink containing a coloring material is applied onto the image-forming face of the intermediate transfer member on which the aggregating agent has been applied, thereby forming an intermediate image. The ink contains, for example, a dye or a pigment as the coloring material. If the aggregating agent contains a metal salt, a pigment ink can react at an extremely high rate, and is therefore advantageous in terms of high-speed image recording.
Widely and generally used dyes may be used in the ink. Examples of such a dye include C. I. Direct Blues 6, 8, 22, 34, 70, 71, 76, 78, 86, 142 and 199; C. I. Acid Blues 9, 22, 40, 59, 93, 102, 104, 117, 120, 167 and 229; C. I. Direct Reds 1, 4, 17, 28, 83 and 227; C. I. Acid Reds 1, 4, 8, 13, 14, 15, 18, 21, 26, 35, 37, 249, 257 and 289; C. I. Direct Yellows 12, 24, 26, 86, 98, 132 and 142; C. I. Acid Yellows 1, 3, 4, 7, 11, 12, 13, 14, 19, 23, 25, 34, 44 and 71; C. I. Food Blacks 1 and 2; and C. I. Acid Blacks 2, 7, 24, 26, 31, 52, 112 and 118.
Widely and generally used pigments may also be used. Examples of such a pigment include C. I. Pigment Blues 1, 2, 3, 15:3, 16 and 22; C. I. Pigment Reds 5, 7, 12, 48(Ca), 48(Mn), 57(Ca), 112 and 122; C. I. Pigment Yellows 1, 2, 3, 13, 16 and 83; carbon black Nos. 2300, 900, 33, 40 and 52; MA7, MA8 and MCF88 (each produced by Mitsubishi Chemicals); RAVEN 1255 (produced by Columbian Chemicals); REGAL 330R, 660 μl and MOGUL (produced by Cabot); and Color Blacks FW1, FW18, 5170, 5150 and Printex 35 (produced by Degussa).
These pigments may be self-dispersible, resin-dispersible, or microencapsulated. A water-soluble resin having a weight average molecular weight in the range of 1000 to 15000 can be sued as a dispersant of the pigment. Examples of such a dispersant resin include block or random copolymers or their salts containing some of styrene and its derivatives, vinyl naphthalene and its derivatives, aliphatic alcohol esters of α,β-ethylenic unsaturated carboxylic acids, acrylic acid and its derivatives, maleic acid and its derivatives, itaconic acid and its derivatives, and fumaric acid and its derivatives, and salts of these polymers.
In order to enhance the fastness of the final image on the recording medium, a water-soluble resin or a water-soluble crosslinking agent may be added to the ink. Any of the above-cited dispersant resins can be further added as the water-soluble resin. The water-soluble crosslinking agent can be oxazoline or carbodiimide, which are less reactive, in view of the stability of the ink.
If the ink contains an organic solvent, the organic solvent content is one of the factors of the ejection property and drying property of the ink. Since the ink immediately before being transferred to the recording medium 9 contains substantially only a coloring material and a high-boiling point organic solvent, the organic solvent content is controlled to an optimal value in this state. The organic solvent can be soluble in water and have a high boiling point and a low vapor pressure. Examples of such an organic solvent include polyethylene glycol, polypropylene glycol, ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, thiodiglycol, hexylene glycol, diethylene glycol, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, and glycerin. In addition, an alcohol, such as ethyl alcohol or isopropyl alcohol, may be added to adjust the viscosity, the surface tension or the like.
The proportions of the constituents in the ink can be appropriately adjusted according to the ejection power of the inkjet recording method or the inkjet recording head, and the diameter of the nozzles. For example, the ink can have the composition containing 0.1% to 10.0% by mass of coloring material, 0.1% to 10.0% by mass of water-soluble resin, 5.0% to 40.0% by mass of organic solvent, 0.1% to 5.0% by mass of surfactant, and the balance of water.
When the ink is ejected from an inkjet recording head and comes into contact with the aggregating agent on the image-forming face of the intermediate transfer member, the fluidity of the ink is reduced. Consequently, the occurrence of bleeding and beading can be reduced. Since the aggregating agent on the intermediate transfer member is controlled so as to be thin and uniform, the image disruption is unlikely to occur. In addition, because of the effect of the lyophobic portion disposed with constant spaces on the intermediate transfer member, the intermediate image on the intermediate transfer member is not displaced throughout the process up to the transfer, and thus the quality of the image can be kept high.
In the inkjet recording method, the ink may be ejected by a thermal jet method using a thermal energy, or a piezoelectric method using a mechanical energy. Also, the inkjet recording method may be performed in an on-demand manner or a continuous manner. A method using a dispenser or the like may be applied. The inkjet recording head used in, for example, the configuration shown in
Any type of intermediate image can be formed without limitation, including characters, illustrations, natural images, simple patterns, and industrial patterns such as electronic circuit diagrams. For forming an image, allowing for transfer that reverses the image, the ink can be ejected so as to form a mirror-reverse image.
In the step of transferring, a recording medium is pressed on the image-forming face on which the intermediate image has been formed. Thus, the intermediate image on the image-forming face is transferred to the recording medium, thereby forming an image. In
In order to reduce the volume of the ink, the rotation speed may be reduced so that more time can be taken to evaporate the water in the ink. Allowing for cases where high-speed recording is required, a water removal accelerator 7 and/or a heating roller 8 may be used to remove the water, as shown in
In the configuration shown in
The transfer inkjet recording method will be further described in detail with reference to Examples. In the following examples, the apparatus shown in
A pattern including lyophilic portions and a lyophobic portion was formed on the image-forming face of an intermediate transfer member. First, the surface of a 0.4 mm thick PET film was coated with a silicone rubber having a hardness of 40° (KE-1310, produced by Shin-Etsu Chemical) at a thickness of 0.2 mm. The resulting film was used as the intermediate transfer member. A resist layer was formed over the entire surface (image-forming face) of the intermediate transfer member to a thickness of 0.5 μm by applying a positive resist (OFPR-700, produced by Tokyo Ohka Kogyo) using a spin coater, and then drying the resist. The dried resist layer was exposed to light through a photomask having the pattern shown in
Then, the surface of the intermediate transfer member on which the resist pattern had been formed was subjected to surface modification with a parallel plate plasma apparatus under the following conditions:
A plasma gas reached the silicone rubber surface through the openings in the resist layer and thus turns lyophilic the portions of the silicone rubber corresponding to the openings. On the other hand, the portion of the silicone rubber masked with the resist layer was not turned lyophilic and resulted in a lyophobic portion. Thus, the pattern including lyophilic portions and a lyophobic portion was formed on the image-forming face of the intermediate transfer member.
Subsequently, the entire surface of the resist pattern was exposed to light. After a predetermined development was performed, the resist layer was removed from the intermediate transfer member. Thus, a pattern having no steps between the lyophilic portions and the lyophobic portion was formed on the image-forming face of the intermediate transfer member.
The resulting intermediate transfer member was wound around an aluminum drum and secured to the transfer inkjet recording apparatus shown in
The aggregating agent was selectively deposited on the lyophilic portions. The contact angle of the aggregating agent with the lyophilic portions was 38°, and the contact angle of the aggregating agent with the lyophobic portion was 68°. The amount of aggregating agent applied to the intermediate transfer member was 0.37 mg per square inch.
Using an inkjet apparatus (nozzle density: 1200 dpi; ejection amount: 4.8 μL; driving frequency: 12 kHz), a mirror-reverse intermediate image was formed (resolution: 1200 dpi) by applying an ink onto the intermediate transfer member on which the aggregating agent had been applied. The compositions of inks were as follows (four color inks containing respective pigments were prepared).
At the time when the intermediate image was formed on the intermediate transfer member, whether or not image disruption (bleeding) occurred was determined by visual observation. Image disruption was not observed even in dense color regions (where 20 mg per square inch of ink had been applied). The reproduction resolution was constant, and image disruption was not observed even in single-color fine line drawings or characters.
After the water in the intermediate image was removed to reduce the fluidity, a recording medium (Aurora Coat, manufacture by Nippon Paper Industries, basis weight: 63 g) was brought into contact with the intermediate image by a pressure roller to transfer the image to the recording medium. It was visually confirmed that a high-quality final image was recorded on the recording medium. After the transfer, the ink was hardly left on the intermediate transfer member, and subsequent recording was able to be performed satisfactorily without treatment of the intermediate transfer member.
The following pattern including lyophilic portions and a lyophobic portion was formed on the image-forming face of an intermediate transfer member through a photomask having the pattern shown in
Then, the same aggregating agent was applied onto the surface of the intermediate transfer member by the same procedure as in Example 1. The aggregating agent was selectively deposited on the lyophilic portions, as in Example 1. The contact angle of the aggregating agent with the lyophilic portions was 35°, and the contact angle of the aggregating agent with the lyophobic portion was 70°. The contact angles were substantially the same as in Example 1. The amount of aggregating agent applied to the intermediate transfer member was 0.34 mg per square inch.
An intermediate image was formed on the intermediate transfer member to which the aggregating agent had been applied, by the same procedure as in Example 1.
At the time when the intermediate image was formed on the intermediate transfer member, whether or not image disruption (bleeding) occurred was determined by visual observation. Image disruption was not observed even in dense color regions (where 20 mg per square inch of ink had been applied). The reproduction resolution was constant, and image disruption was not observed even in single-color fine line drawings or characters.
After the water in the intermediate image was removed to reduce the fluidity, a recording medium (Aurora Coat, manufacture by Nippon Paper Industries, basis weight: 63 g) was brought into contact with the intermediate image by a pressure roller to transfer the image to the recording medium. It was visually confirmed that a high-quality final image was recorded on the recording medium. After the transfer, the ink was hardly left on the intermediate transfer member, and subsequent recording was able to be performed satisfactorily without treatment of the intermediate transfer member.
The following pattern including lyophilic portions and a lyophobic portion was formed on the image-forming face of an intermediate transfer member through a photomask having the pattern shown in
Then, the same aggregating agent was applied onto the surface of the intermediate transfer member by the same procedure as in Example 1. The aggregating agent was selectively deposited on the lyophilic portions, as in Example 1. The contact angle of the aggregating agent with the lyophilic portions was 38°, and the contact angle of the aggregating agent with the lyophobic portion was 68°. The contact angles were substantially the same as in Example 1. The amount of aggregating agent applied to the intermediate transfer member was 0.16 mg per square inch.
An intermediate image was formed to the intermediate transfer member to which the aggregating agent had been applied, by the same procedure as in Example 1.
At the time when the intermediate image was formed on the intermediate transfer member, whether or not image disruption (bleeding) occurred was determined by visual observation. As a result, color mixing was observed in dense color regions (where 20 mg per square inch of ink had been applied), clearly showing that aggregation of the inks had been insufficient.
The following pattern including lyophilic portions and a lyophobic portion was formed on the image-forming face of an intermediate transfer member through a photomask having the pattern shown in
Then, the aggregating agent having the following composition was applied onto the surface of the intermediate transfer member by the same procedure as in Example 1.
The aggregating agent was selectively deposited on the lyophilic portions, as in Example 1. The contact angle of the aggregating agent with the lyophilic portions was 38°, and the contact angle of the aggregating agent with the lyophobic portion was 68°. The contact angles were substantially the same as in Example 1. The amount of aggregating agent applied to the intermediate transfer member was 0.38 mg per square inch.
An intermediate image was formed on the intermediate transfer member to which the aggregating agent had been applied, by the same procedure as in Example 1.
At the time when the intermediate image was formed on the intermediate transfer member, whether or not image disruption (bleeding) occurred was determined by visual observation. Image disruption was not observed even in dense color regions (where 20 mg per square inch of ink had been applied). However, the reproduction resolution was varied. The single-color fine drawings were disrupted, and many of the characters were distorted and thickened.
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. 2010-242466 filed Oct. 28, 2010, which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | Kind |
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2010-242466 | Oct 2010 | JP | national |