JP2007245368A - Method for forming image by inkjet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming an image by inkjet capable of forming the image with a high resolution even when an inkjet image is formed with a UV ink on a UV ink undercoat layer. <P>SOLUTION: The method comprises an undercoating process wherein a UV-curable ink is provided on a face to be printed as the undercoat layer 3, a first light exposing process wherein the undercoat layer 3 is irradiated with half-curing ultraviolet rays to perform half-curing, an image forming process wherein the inkjet image 4 is formed with the ultraviolet rays-curable ink on the undercoat layer under a half-curing condition, and a second light exposing process wherein the inkjet image 4 and the undercoat layer 3 are irradiated with full curing ultraviolet rays to perform full curing. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming method by ink jet using an ultraviolet curable ink (hereinafter referred to as UV ink) having good adhesion to printed materials such as resin, glass, and metal other than paper, and particularly high resolution. The present invention relates to an image forming method using an ink jet capable of forming an image (that is, having good image quality).

  In recent years, many image forming methods using an ink jet printer have been used as image forming methods capable of forming images easily and inexpensively.

Patent Document 1 shown below is shown as an example of a conventional inkjet recording apparatus for a printed material such as paper.
JP-A-7-164644

  Now, in order to form a clear image without blur using an inkjet printer, an undercoat layer (acceptance) for accurately receiving fine ink ejected from the nozzles of the inkjet head (printer head) on the printing surface. Layer, image receiving layer) must be provided. Further, when clear printing is performed on a printed material whose printing surface is not white (especially when color printing is performed), it is necessary to provide a white or light single color undercoat layer.

  Water-based dye inks, water-based pigment inks, solvent inks, oil-based inks, and UV inks are known as ink types used in ink-jet printers. When water-based dye inks, water-based pigment inks, and oil-based inks are used, ink jet printers are used. An undercoat layer is essential for accurately receiving fine ink ejected from the ink.

  On the other hand, UV ink adheres well to printed materials such as resin other than paper, metal, glass, etc., and has the feature of good durability of printed images. Various industrial products other than paper (resin products such as optical disks) It is also effective for printing on glass products and metal products). An undercoat layer is not essential to ensure adhesion, but it is necessary to perform clear color printing on printed materials whose printed surface is not white. It is necessary to provide a white or light single color undercoat layer.

  The quality of image quality in an ink jet printer is determined by how accurately the fine ink ejected from the ink jet head is fixed (accepted) to the printing surface. Ink jet printers generally used at present are capable of clear printing because they are printed on a dedicated paper having a layer for accurately receiving the ejected fine ink. When a color image is formed by UV ink inkjet on a printed material other than paper, it is desirable to provide a UV ink primer layer. However, UV ink exposed and cured with ultraviolet rays is ejected from an inkjet printer. There is a problem that it does not have a function of accurately accepting the finely divided UV ink. That is, after UV ink as an undercoat layer is provided on a printing surface of a printing material by a method such as printing or painting, the surface is cured by UV curing. When UV ink is printed on the cured UV ink by an ink jet printer, the discharged fine UV ink has fluidity, so the area becomes large as shown in FIG. As shown in (C), the fine ink moves and overlaps the adjacent fine ink, so that a fine image cannot be formed.

  In view of the above points, the present invention provides an ink jet image forming method capable of forming a high resolution image even when an ink jet image is formed with a UV ink on an undercoat layer of the UV ink. Objective.

  Other objects and novel features of the present invention will be clarified in embodiments described later.

  In order to achieve the above object, an inkjet image forming method according to the present invention includes an undercoating step of providing an ultraviolet curable ink as an undercoat layer on a printing surface, and irradiating the undercoat layer with semi-curing ultraviolet rays. A first exposure step of semi-curing, an image forming step of forming an inkjet image with an ultraviolet curable ink on the semi-cured undercoat layer, and ultraviolet rays for complete curing on the inkjet image and the undercoat layer And a second exposure step of complete curing by irradiation.

  In the image forming method using ink jet, the image forming step repeats a rough image forming step of forming a rough image having a low resolution by discharging ultraviolet curable ink from the ink jet head onto the printing surface a plurality of times. When the inkjet image is formed, each rough image forming step may include a third exposure step in which the rough image is irradiated with a semi-curing ultraviolet ray to be semi-cured.

  In the rough image forming step, the relative movement direction of the inkjet head with respect to the printing surface and the resolution in one or both directions perpendicular to the relative movement direction are set to a plurality of desired resolutions. An image should be formed.

  In the third exposure step, semi-curing ultraviolet irradiation may be performed immediately after the ultraviolet curable ink particles are discharged onto the printing surface in the coarse image forming step.

  The third exposure step may be omitted for the coarse image in the final coarse image forming step.

  The exposure light source for generating the semi-curing ultraviolet light preferably does not include the ultraviolet wavelength range that completely cures the ultraviolet curable ink.

  The exposure light source that generates the semi-curing ultraviolet light may be one that does not completely cure the undercoat layer even after multiple irradiations.

  The exposure light source that generates the semi-curing ultraviolet light preferably does not include a wavelength region shorter than about 380 nm.

  The exposure light source that generates the semi-curing ultraviolet light may be a light source that generates a complete curing ultraviolet light by adding an ultraviolet filter to remove a wavelength region shorter than about 380 nm.

  The ink jet image forming method according to the present invention uses a semi-cured UV ink primer layer provided on a printing surface, and the primer layer loses its fluidity as a liquid. However, the surface and the inside have moderate flexibility. Therefore, since the fine ink composing the ink jet image ejected by the ink jet does not spread to the periphery, the ejected shape can be maintained. The UV ink of the semi-cured undercoat layer and the UV ink for image formation printed by inkjet can be simultaneously completely cured (cured both on the surface and inside) by irradiating with UV light for complete curing.

  Further, in the image forming step for forming the inkjet image, when the rough image forming step for forming a rough image with low resolution by discharging UV ink from the inkjet head onto the printing surface is repeated a plurality of times, The coating layer is not cured and is maintained in a semi-cured state, and the fine particles constituting the coarse image are formed by semi-curing by irradiating semi-curing ultraviolet rays after discharging the fine particle ink in each coarse image forming step. Since the ink loses its fluidity as a liquid, the interference between the fine inks in the coarse image forming process before and after the rough image forming process (the phenomenon that they overlap each other or move and overlap) is maintained. Disappear. As a result, a high-resolution inkjet image using UV ink can be formed.

  By using the inkjet image forming method of the present invention, a clear and durable print can be made on the surface of a printed material other than paper such as resin products such as optical disks, glass products, and metal products.

  Hereinafter, as the best mode for carrying out the present invention, an embodiment of an image forming method using ink jet will be described with reference to the drawings.

  1 and 2 show an embodiment of an image forming method by ink jet according to the present invention, and an image forming on an optical disk will be described as an example.

  Optical discs (CD, DVD, CD-R, DVD-R, etc.) have a high appearance on the label surface (printed surface) due to the influence of the metal film processing (evaporation or sputtering) layer necessary for the function of the optical disc. Yes. Conventionally, offset printing or screen printing has been used for label printing of optical discs. However, even if an image such as a photograph is printed in color with the label surface left unprocessed, the image can be printed clearly on white media. Must not. For this reason, normally, white ink is printed by screen printing before color printing. The same applies to color printing on the label surface by an inkjet printer, and it is necessary to print white ink as an undercoat layer.

  For this reason, first, in the undercoating step of FIG. 1A, white UV ink is screen-printed, offset-printed, and printed by an inkjet printer as the undercoat layer 3 in the image forming area of the label surface 2 that is the printing surface of the optical disc 1. Etc. (such as printing and coating). Usually, screen printing is relatively simple and preferable for providing the primer layer 3.

  Next, in the semi-curing exposure step of FIG. 1B, the semi-curing ultraviolet ray a is irradiated onto the undercoat layer 3 to be semi-cured. That is, the fluidity of the undercoat layer 3 as the liquid of the UV ink is lost, but the surface and the internal flexibility remain. The exposure light source 10 that generates the semi-curing ultraviolet light includes a wavelength region of 380 nm or more, but does not include a wavelength region shorter than 380 nm. Specifically, the exposure light source 10 has a wavelength of 365 nm that can completely cure the UV ink. An ultraviolet filter 12 is added to the ultraviolet light source 11 capable of generating ultraviolet light including a spectrum, and the ultraviolet light from the ultraviolet light source (ultraviolet lamp) 11 is passed through the ultraviolet filter 12 to remove the ultraviolet wavelength region shorter than 380 nm and undercoat. What can irradiate the layer 3 can be used.

  The image forming process of FIG. 1C is executed after the semi-curing exposure process of FIG. 1B. Here, the relative movement direction of the inkjet head with respect to the printing surface is orthogonal to the relative movement direction. The operation of forming a rough image (hereinafter referred to as a rough image) on the printing surface is repeated four times by setting the resolution in both directions to a half of the desired resolution (for example, 300 dpi) (for example, 150 dpi). A case where an inkjet image having the desired resolution is formed will be described.

  First, in the first pass rough image forming step (1-1) in the image forming step of FIG. 1C, the ink jet head H of the ink jet printer of FIG. 2 is formed on the surface of the primer layer 3 of the semi-cured white UV ink. From this, fine UV ink for coarse image formation is ejected. In the case of FIG. 2, the resolution in the relative movement direction (X direction) of the inkjet head H with respect to the printing surface 20 provided with the undercoat layer 3 is set to ½ of the desired resolution and is orthogonal to the X direction. The resolution in the direction (Y direction) is also set to ½ of the desired resolution, and the first pass rough image 4-1 by the ink dots 21 is applied to the undercoat layer 3 by the inkjet head H as shown in FIG. To form. For example, assuming that the desired resolution is 300 dpi, the arrangement interval of the ink dots 21 in the X direction is 170 μm (equivalent to 150 dpi), and the arrangement interval in the Y direction is 170 μm (equivalent to 150 dpi).

  The surface of the undercoat layer 3 of the semi-cured UV ink is a surface having moderate flexibility, and the fine UV ink constituting the coarse image by the ink jet ejected by the ink jet is around the periphery as shown in FIG. Since it does not spread, the discharged shape can be maintained.

  Thereafter, in the semi-curing exposure step (1-2) in the first pass rough image forming step, the first pass rough image 4-1 formed with the ink dots 21 from the exposure light source that generates semi-curing ultraviolet rays is applied. Semi-curing ultraviolet ray b is irradiated. This exposure light source can also be used as the exposure light source 10 and includes a wavelength range of 380 nm or more, but does not include an ultraviolet wavelength range shorter than 380 nm. By the irradiation of the semi-curing ultraviolet rays, the ink dots 21 of the first pass rough image are in a semi-cured state, and the fluidity as a liquid is lost.

  Next, in the second pass rough image forming step (2) of FIG. 1, a rough image is formed on the surface of the undercoat layer 3 of the semi-cured white UV ink from the ink jet head H of the ink jet printer as shown in FIG. The fine UV ink for forming is ejected, and the second pass rough image 4-2 having the same resolution as the first pass rough image forming step (1-1) is formed by the ink dots 22. At this time, since the undercoat layer 3 is kept in a semi-cured state, its surface is a surface having moderate flexibility, and the fine UV ink constituting the coarse image ejected by the ink jet does not spread to the periphery. It can be made to keep the shape. Further, since the ink dots 21 of the first pass rough image 4-1 are already in a semi-cured state, the ink amount of the ink dots 22 of the second pass rough image 4-2 is temporarily large (when the color is dark) (There is a large amount of ink) Even if the ink dot 21 partially overlaps, bleeding and movement of the ink dot do not occur.

  Thereafter, in the semi-curing exposure process in the second pass rough image forming process, ink dots 22 are formed from the exposure light source 10 (using the semi-curing exposure process (1-2)) that generates semi-curing ultraviolet rays. The second pass rough image 4-2 is irradiated with the semi-curing ultraviolet ray c.

  Similarly, in the third pass coarse image forming step (3) of FIG. 1, a rough image is formed on the surface of the primer layer 3 of the semi-cured white UV ink from the inkjet head H of the inkjet printer as shown in FIG. The fine UV ink for forming is ejected, and a third pass rough image 4-3 having the same resolution as the first pass rough image forming step (1-1) is formed by the ink dots 23. At this time, since the undercoat layer 3 is kept in a semi-cured state, its surface is a surface having moderate flexibility, and the fine UV ink constituting the coarse image ejected by the ink jet does not spread to the periphery. It can be made to keep the shape. Further, since the ink dots 21 and 22 of the first and second pass rough images 4-1 and 4-2 are already in a semi-cured state, the ink amount of the ink dot 23 of the third pass rough image 4-3 is Even if the ink dots 21 and 22 partially overlap with each other, bleeding or movement of the ink dots does not occur.

  Thereafter, in the semi-curing exposure process in the third pass rough image forming process, the semi-curing ultraviolet light is applied to the third pass rough image 4-3 formed by the ink dots 23 from the exposure light source 10 that generates the semi-curing ultraviolet light. Irradiate d.

  In the fourth pass rough image forming step (4) of FIG. 1, fine particles for forming a rough image are formed on the surface of the undercoat layer 3 of the semi-cured white UV ink from the ink jet head H of the ink jet printer of FIG. UV ink is ejected to form a fourth pass rough image 4-4 having the same resolution as the first pass rough image forming step (1-1) with ink dots 24. At this time, since the undercoat layer 3 is kept in a semi-cured state, its surface is a surface having moderate flexibility, and the fine UV ink constituting the coarse image ejected by the ink jet does not spread to the periphery. It can be made to keep the shape. Further, since the ink dots 21, 22, and 23 of the first, second, and third pass coarse images 4-1, 4-2, and 4-3 are already in a semi-cured state, the fourth pass coarse image 4- Even if the ink amount of the fourth ink dot 24 is so large that it partially overlaps the ink dots 21, 22 and 23, no bleeding or movement of the ink dots occurs.

  Thereafter, in the semi-curing exposure process in the fourth pass rough image forming process, the semi-curing ultraviolet light is applied to the fourth pass rough image 4-4 formed by the ink dots 24 from the exposure light source 10 that generates the semi-curing ultraviolet light. Irradiate e.

  When the fourth pass rough image forming step (4) is the last rough image forming step, the semi-curing exposure step in the rough image forming step may be omitted. The reason for this is that a complete curing exposure step of simultaneously irradiating the inkjet image and the undercoat layer 3 with the ultraviolet for complete curing is immediately reserved.

  After completion of the image forming process in FIG. 1C, the UV ink is completely removed from the ultraviolet light source 11 (the configuration in which the ultraviolet filter 12 is removed from the semi-curing exposure light source 10) in the complete curing exposure process in FIG. The inkjet image 4 consisting of the rough images 4-1 to 4-4 and the undercoat layer 3 are irradiated with ultraviolet rays f having a wavelength of 365 nm that can be cured to completely cure them.

  The UV ink that can be used in the present embodiment is, for example, prepared and manufactured with the following composition. The main materials (corresponding to ordinary solvent-based ink vehicles) are as follows.

a. Acrylic monomer
Acrylic compound that is not polymerized. The viscosity is low.
b. Acrylic oligomer An oligomer having an acryloyl group in the molecule and a molecular weight of up to about 10,000. Viscosity is high.
(A and b are mixed and adjusted to a viscosity suitable for the purpose. All are transparent. Occupies almost 50% by weight or more of UV ink.)
c. In the case of pigment ink, in the case of paint, an appropriate pigment (inorganic pigment such as black or white) or an organic pigment such as red, blue or green is used, and several kinds of pigments are usually mixed in order to obtain a desired color tone. It accounts for about 3 to 30% by weight. In the case of white ink, it may occupy around 50% by weight.
d. Photopolymerization initiator Upon receiving the energy of UV light or thermal energy, the molecule breaks and bonds with the surrounding substance (in the case of ink or paint, the above acrylic monomer or oligomer) to cause cross-linking. This cures (hardens).
e. Photopolymerization initiator auxiliaries and sensitizers The above initiators are generally expensive chemicals, and are substances whose purpose is to assist the action and increase the effect. d and e are mixed amounts of several percent or less by weight.
f. Stabilizers Since UV inks and UV paints are generally more expensive than solvent-based inks and paints, stabilizers are added to prevent gelation during transportation and storage.
g. Additives Various substances that improve the physical properties of ink or paint (adhesiveness, cohesiveness, viscosity, etc. on printed materials and coated materials).

  The present inventor has shown that, in the existing UV ink as described above, the UV ink is completely cured by the ultraviolet ray including the spectrum of 365 nm, but the UV ink is irradiated by the ultraviolet ray from which the wavelength region shorter than 380 nm is removed. It has been found that the semi-cured state is maintained even if the time is relatively long.

  According to this embodiment, the following effects can be obtained.

(1) When UV ink is used as the undercoat layer 3, if it is in a semi-cured state, fluidity as a liquid is lost, but moderate flexibility remains, so fine particles for forming an inkjet image ejected by inkjet It is possible to maintain the discharge shape without spreading the UV ink around.

(2) A rough image forming process in which an image forming process for forming an ink jet image forms a rough image having a low resolution by ejecting UV ink from the ink jet head H onto the printing surface (undercoat layer 3). When the above is repeated a plurality of times, the undercoat layer 3 is kept in a semi-cured state without being cured, and is irradiated with a semi-curing ultraviolet ray after the fine particle ink is discharged in each coarse image forming step to be semi-cured. Since the fine ink constituting the coarse image loses its fluidity as a liquid, it maintains the shape ejected on the undercoat layer and interferes with the fine ink in the coarse image forming process before and after (both overlap and overlap each other). Or the phenomenon of moving and overlapping) disappears. As a result, a high-resolution inkjet image using UV ink can be formed.

(3) An exposure light source 10 that generates semi-curing ultraviolet light is obtained by adding an ultraviolet filter 12 to the light source 11 that generates full curing ultraviolet light and removing an ultraviolet wavelength region shorter than 380 nm. Since the short ultraviolet wavelength region is removed, the UV ink maintains a semi-cured state even if the irradiation time is relatively long. For this reason, even if the irradiation of the semi-curing ultraviolet ray is repeated a plurality of times in the process of repeating the rough image forming process a plurality of times, the undercoat layer 3 is in a semi-cured state, and the fine UV ink is placed around the periphery as shown in FIG. Keeps the discharged shape without spreading.

(4) Both the undercoat layer 3 and the inkjet image are formed using UV ink and have high durability against water, light, and the like.

(5) Since the ink-jet image formation is performed on the semi-cured undercoat layer 3, the surface of the print image is flat (the swell of ink-jet image formation is small), and the surface of the resulting print image has good gloss. Yes, you can eliminate the rough feeling. That is, the finish is close to offset printing.

  In the above embodiment, the inkjet image is formed by four passes of the first to fourth coarse image forming steps. However, the inkjet image may be formed by one pass (one time), and the required resolution is obtained. Accordingly, it may be 5 or more passes.

  Further, the semi-curing exposure process in each coarse image forming process is performed by adhering the head adjacent to the ink jet head H of the ink jet printer when the rough image is formed on the image forming area of the label surface 2 in FIG. It is preferable to provide a semi-curing exposure light source 10 so as to move together with H, and to irradiate ultraviolet rays immediately after ejection of the fine UV ink by the inkjet head H.

  The exposure light source for generating semi-curing ultraviolet light may be a light source for generating full curing ultraviolet light to which an ultraviolet filter is added to remove an ultraviolet wavelength region shorter than 380 nm. It is of course possible to use an ultraviolet exposure light source that does not include a shorter ultraviolet wavelength range.

  When forming a color image, it is possible to form a color image by inkjet by ejecting three primary color inks of yellow (yellow), magenta (red), and cyan (blue) and black ink respectively from a plurality of inkjet heads. is there. In order to improve the image quality, in addition to the three primary color inks and the black ink, a light indigo ink and a light red ink may be used.

  The undercoat layer is usually white, but if it has a special effect, it is also possible to use a light single color other than white (light yellow, etc.).

  In the present embodiment, the optical disk has been described as an example. However, the method of the present invention can be applied to the printing surface of various printed materials such as resin products, glass products, and metal products. In addition, it is possible to form a durable inkjet image with good adhesion.

  In the above embodiment, white or a light single color other than white (that is, an opaque undercoat layer) can be used as the undercoat layer, but it is also possible to use a transparent undercoat layer of UV ink. . For example, backside printing of transparent resin or transparent film is often used for automobile meters, home appliances, audio products, mobile phone keypads, and the like. In these cases, if a transparent UV ink is used as the undercoat layer, the effect can be exerted also on the above-mentioned products having high quality requirements. In the case of the above product, an inkjet image (for example, a single color image of the special color ink) can be formed by using special color inks other than the three primary color inks and the black ink.

  Although the embodiments of the present invention have been described above, it will be obvious to those skilled in the art that the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the claims.

It is explanatory drawing which shows embodiment of the image forming method by the inkjet which concerns on this invention. It is explanatory drawing which shows the example of the image formation process which repeats the rough image formation process which forms a rough image with a low resolution in multiple times, and forms an inkjet image. It is explanatory drawing which shows typically the adhesion state of the fine particle UV ink for inkjet image formation about the case of the undercoat layer of the UV ink after a hardening process, and the case of the undercoat layer of the UV ink of a semi-hardened state.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk 2 Label surface 3 Undercoat layer 4 Inkjet image 10 Exposure light source 11 Ultraviolet light source 12 Ultraviolet filter 20 Printed surface 21, 22, 23, 24 Ink dot H Inkjet head

Claims (9)

  An undercoating step of providing an ultraviolet curable ink as an undercoat layer on the surface to be printed; a first exposure step of semi-curing the undercoat layer by irradiating semi-curing ultraviolet rays; and on the undercoating layer in a semi-cured state And an image forming step of forming an inkjet image with an ultraviolet curable ink, and a second exposure step of completely curing the inkjet image and the undercoat layer by irradiating with ultraviolet rays for complete curing. Image forming method by ink jet.   When the image forming step forms the inkjet image by repeating a rough image forming step of forming a rough image with low resolution by discharging ultraviolet curable ink from the inkjet head onto the printing surface, a plurality of times. 2. The ink jet image forming method according to claim 1, wherein each of the rough image forming steps includes a third exposure step in which the rough image is semi-cured by irradiating semi-curing ultraviolet rays.   In the rough image forming step, the relative movement direction of the inkjet head with respect to the printing surface and the resolution in one or both directions perpendicular to the relative movement direction are set to a plurality of desired resolutions. The image forming method by ink jet according to claim 2, wherein an image is formed.   4. The image formation by inkjet according to claim 2, wherein in the third exposure step, irradiation with semi-curing ultraviolet rays is performed immediately after the ultraviolet curable ink particles are ejected onto the printing surface in the rough image forming step. Method.   5. The ink jet image forming method according to claim 2, 3 or 4, wherein the third exposure step is omitted for the rough image in the last rough image forming step.   6. The ink jet image forming method according to claim 1, wherein the exposure light source for generating the semi-curing ultraviolet rays does not include an ultraviolet wavelength region for completely curing the ultraviolet curable ink.   7. The image forming method by ink jet according to claim 1, wherein the exposure light source for generating the semi-curing ultraviolet ray does not completely cure the undercoat layer even by a plurality of irradiations.   8. The ink jet image forming method according to claim 1, wherein the exposure light source for generating the semi-curing ultraviolet ray does not include a wavelength region shorter than about 380 nm.   9. The ink jet according to claim 8, wherein the exposure light source for generating the semi-curing ultraviolet light is obtained by adding an ultraviolet filter to the light source for generating the complete curing ultraviolet light to remove a wavelength region shorter than about 380 nm. Image forming method.

Images