JP2006044136A - Image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image forming method enabling a color tone of printed matters to be reproduced enough while capable of obtaining a proof with the same halftone as of a regular printing by an ink-jet method. <P>SOLUTION: Using the inks of seven colors consisting of yellow, magenta, cyanogen, black, red, blue and green, the proof of the printed matter formed by halftone images is prepared by the image forming method. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming method for creating a proof of a printed material composed of a halftone image by an inkjet method.

  In prepress printing work to obtain a very large amount of printed matter, before actual printing (hereinafter referred to as “main printing”), it is necessary to confirm that the desired finish is specified for characters, colors, layout, imposition, etc. Proofreading printing is performed. A printed matter obtained by this proof printing is a so-called proof. Conventionally, for such proof printing, a method of printing from a final positive film onto a PS plate and printing with a flat table proofing machine has been widely used. However, recently, a CTP method for directly outputting an image edited on a computer to a printing plate has become widespread, and in such a case, a DCP (Direct Color Image) that directly obtains a color image without using a film from data on a computer. Digital color proof) is being used. As DCP, various methods such as a sublimation type / melting heat transfer method, a silver salt photography method, an electrophotographic method, and an ink jet method have been tried.

  When these various types of DCP are roughly classified by performance, printing halftone dots can be reproduced and both color proofing and plate inspection can be confirmed, and printing halftone dots cannot be reproduced and used only for color proofing. It is divided roughly into. Color proofing is the most important point in proof printing, but it is important to be able to check whether there is a problem with not only the color but also the output data in order to prevent accidents during printing. In addition, as a proof in the CTP era in which film removal is not performed, it is highly desired as a DCP that halftone dots can be confirmed and output data can be confirmed. In addition, it is said that images formed with the same halftone dots are excellent for subtle reproduction of the texture of printing.

  As described above, as DCP, a method capable of halftone dot reproduction is desired, but in order to enable halftone dot reproduction, a method capable of obtaining a high-quality image is necessary. Generally, apparatus cost and running cost are required. There is a disadvantage that productivity is inferior due to costs such as the above. Among them, a system using a silver salt photographic system as disclosed in Japanese Patent Laid-Open No. 2001-235816 is capable of forming a high-quality image such as an accurate halftone image, and productivity per hour. And the running cost is relatively low, it is widely used.

  Inkjet image forming methods have been vigorously developed for applications such as home color printers, and improvements in image reproducibility have rapidly progressed in recent years, making it possible to reproduce photographic image quality. As proof applications, improvements in printing media and color management software, such as those disclosed in JP-A Nos. 2002-231348 and 2002-120451, have reached a level that can be used for color calibration for printing applications. Yes. In addition, the ink jet system is low in both the apparatus cost and the running cost, and has come to be used for the production of printed materials with reduced costs. For this reason, a proof capable of halftone dot reproduction by an ink jet method is desired as a proof having both low cost, high color reproducibility and plate inspection.

  In fact, with the high resolution of the device, the level of halftone dot reproduction has become possible. However, when trying to form an image with the same halftone dot as in actual printing by the inkjet method, the color tone of the printed matter is sufficiently There was a problem that could not be reproduced.

  An inkjet image forming method using seven colors of ink is known as a method for improving gradation reproducibility and improving image quality without causing blur in the inkjet method (Patent Document 1). However, Patent Document 1 does not mention a complete area gradation image forming method such as a halftone dot method for printed matter.

  In addition, the effect of the invention is that, in the ink jet method in which one pixel is formed with multi-valued dots, Y, M, C, and K inks are usually applied to one pixel in the case of a secondary color and a tertiary color. Since several drops are struck in layers, the ink absorption amount of the image receiving paper that receives the ink exceeds the total amount of ink, so the problem of bleeding is significant. In order to reduce the amount of overlapping inks, it is described that seven colors of ink are used.

  However, the area gradation image forming method used in printed materials behaves differently, and even when an image is formed with four types of inks of Y, M, C, and K, only one drop of the same type of ink is used for the same pixel. In order not to be ejected, and to be able to reproduce printing halftone dots, a resolution of 2400 dpi or higher is required. To achieve this, one ink droplet is a fine droplet of 1 pl or less, Since there are at most four ink droplets ejected to the same place, it is considered that there is little wrinkle that causes bleeding, and no major problem in principle is caused in terms of image degradation.

  On the other hand, when an image is formed with Y, M, C, and K inks by a method in which normal multi-valued dots are given a gradation by the error calculation diffusion method, there are problems such as graininess, but the same as for printed matter. The color tone is more approximate to the printed matter than when the image is formed with halftone dots, and the effect of the present invention that achieves color reproduction that approximates the printed matter using the area gradation image forming method is disclosed in Japanese Patent Application Laid-Open No. 10-44473. This effect is considered to be different from the mechanism of color reproduction.

  Rather, when creating a proof that requires color reproduction similar to a printed matter using an area gradation image forming method using an inkjet method, the primary colors Y, M, C, and K are generated. When an image is formed with four types of ink, there is a problem that the color tone does not match.

  When creating a proof by the ink jet method, it is important to approximate the actual printing, hue, glossiness, and the like. For example, in Patent Document 2, ink is applied to paper having whiteness and glossiness equivalent to printing paper. A method of using a recording medium on which a receiving layer is formed is described.

  In printed matter, when printing inks with different color tones on the ink, it is known that there is a so-called trapping rate problem such that 100% ink does not deposit on the portion where the ink is placed (colored portion). Yes. Also in the ink jet method, particularly when pigment ink or the like is used, this trapping phenomenon is observed, and color problems are likely to occur.

  In addition, when overprinting each primary color, there is a phenomenon that the appearance of the color differs depending on the printing order. This is due to the phenomenon that the background color is erased by the shielding effect of the overstrike ink. This is because mixing of the primary colors does not occur sufficiently, and similarly causes a color shift from the printed document.

As a result of intensive studies, the inventors have found that the color tone of the printed matter can be faithfully reproduced by forming an image with the same halftone dot as that of the main printing by the inkjet method using the method of the present invention. That is, it is particularly important to obtain color reproduction that is faithful to the original when using a halftone dot based on the area gradation image forming method and creating a proof of the printed original by the inkjet method. It has been found that the method using the seven-color ink of the present invention, which directly uses the secondary color and the tertiary color, is a particularly suitable and superior method rather than forming an image with only the primary color.
JP 10-44473 A JP 2002-120451 A

  Accordingly, an object of the present invention is to obtain an image forming method capable of sufficiently reproducing the color tone of a printed material when forming an image for obtaining a proofed material (proof) by an ink jet method with the same dot as that of actual printing. It is in.

  The above object of the present invention can be achieved by the following method.

(Claim 1)
An image forming method comprising producing a proof of a printed matter composed of a halftone image with seven color inks of yellow, magenta, cyan, black, red, blue and green.

(Claim 2)
In an image forming method for creating a proof of a printed matter consisting of halftone dots by an ink jet method using seven colors of yellow, magenta, cyan, black, red, blue, and green on an image receiving paper,
The water absorption of the image receiving paper is 50 ml / m ² or less,
The ink droplet is 1 pl or less,
The image forming method according to claim 1, wherein the resolution of the obtained image is 2400 dpi or more.

(Claim 3)
3. The image forming method according to claim 2, wherein a pigment ink is used for at least one of the seven colors of ink.

  According to the present invention, it is possible to create a proof (proof) having a color reproduction similar to a printed matter by using the area gradation image forming method by the ink jet method.

  Next, the best mode for carrying out the present invention will be described, but the present invention is not limited thereto.

  In order to solve the above problems, the ink jet recording apparatus of the present invention is characterized by including inks of seven colors of yellow, magenta, cyan, black, red, blue, and green. For print data that has been color-separated into four colors, yellow, magenta, cyan, and black, when yellow and magenta overlap the same pixel, it is replaced with red, and when magenta and cyan overlap, it is replaced with blue. When yellow and yellow overlap, it is replaced with green.

  Usually, the pigment component of red ink is a combination of the same amount of pigment component of yellow ink and the pigment component of magenta ink, and the same amount of pigment component of blue ink, the pigment component of magenta ink and the pigment component of cyan ink. In addition, the pigment component of the green ink is a combination of the same amount of the pigment component of the cyan ink and the pigment component of the yellow ink. In printing, Y (yellow), M (magenta) , C (cyan) and K (black) inks are overprinted, it is known that the transfer of the ink in the post-printing is not complete, and only transfers at a certain rate (trapping rate). Also, because of the shielding effect, the proof that faithfully reproduces the printed matter is that the secondary color is not a simple mixture of the primary colors, but a tone optimized for the secondary colors. Rukoto is preferable.

  As shown in FIG. 1, the print document data is sent from the host computer 10 to the inkjet recording apparatus, and the ink ejection of the recording head is controlled according to the print document data by the control means of the inkjet recording apparatus, and the printed material data is printed on the recording paper. Record the proof (proof).

  In the present invention, when the color data sent from the host computer 10 to the inkjet recording apparatus is Y, M, C data, for example, according to the conversion table of FIG. ) To determine the ink (after conversion) to be used for the pixel. In practice, the superposition of Y and M is replaced with R, the superposition of M and C is replaced with B, the superposition of C and Y is replaced with G, and the superposition of Y, M and C is replaced with K. I do. By this conversion, it is possible to make only one color of ink constituting each pixel, and it is possible to compensate for the color shift due to the transfer rate and the shielding effect. This conversion can be performed by software calculation using a CPU that is the control means 13 in the ink jet apparatus, or can be converted by hardware by detecting each color data of Y, M, C, and K. It is. FIG. 3 is a conversion table when the color data sent from the host computer is Y, M, C, K data. In the conversion table of FIG. 2, when the color data before K conversion is “1” (recording), conversion is made only to K ink regardless of the Y, M, and C color data.

  In the above embodiment, the color data of three or four colors sent from the host computer is converted into data corresponding to the seven colors of ink in the control means 13 of the ink jet recording apparatus. In addition, it is obvious that the same effect can be obtained in a method of sending data for seven colors converted in advance from the host computer.

  Next, the ink used in the present invention will be described. The ink used in the present invention uses R (red), G (green), and B (blue) inks in addition to the conventional Y, M, C, and K inks. The purpose of this is not to reproduce the color of the original data, for example, the colors generated by the superposition of Y, M, and C change depending on the printing order, etc. , R, G, and B inks are used to reproduce pixels. In other words, instead of reproducing the R component of the pixel by using the Y ink pigment component and the M ink pigment component, the color reproduction of the R pixel, which is the secondary color, is reproduced by the R ink pigment component. To improve. Similarly, the dye component of B ink is the same amount of the dye component of M ink and the dye component of C ink, and the dye component of G ink is the same amount of the dye component of C ink and the dye component of Y ink. It should be combined.

  Also, unlike conventional Y, M, and C inks that are adjusted to reproduce hues by mixing R, G, and B, the Y, M, C, R, G, B, and K dedicated according to the present invention Since it is not necessary to consider using the mixed ink as a mixed color, the ink can be adjusted so that each color has an ideal hue. In FIG. 3, Gy is gray.

  Accordingly, as described above, the ink jet recording apparatus used in the image forming method of the present invention is characterized by including seven colors of ink of yellow, magenta, cyan, black, red, blue, and green.

  As the ink used for image recording, a water-based ink composition, an oil-based ink composition, a solid (phase change) ink composition, or the like can be used, but a water-based ink composition (for example, 10% by mass or more per total ink mass) Water-based ink jet recording liquid containing the above water can be used particularly preferably.

  As the color material used in the water-based inkjet ink used in the image forming method of the present invention, various color materials such as water-soluble dyes and pigments are used, but the color material is likely to be localized on the support (difficult to diffuse). Pigment ink is preferable because of the closeness of the optical dot gain to the printed matter.

  As the pigment used in the pigment ink, an organic pigment, carbon black, and the like can be preferably used.

Examples of preferred pigments used in the ink of the present invention are not particularly limited,
C. I Pigment Yellow-1, 3, 12, 13, 14, 17, 81, 83, 87, 95, 109, 42, 180,
C. I Pigment Orange-16, 36, 38,
C. I Pigment Red-5, 22, 38, 48: 1, 48: 2, 48: 4, 49: 1, 53: 1, 57: 1, 63: 1, 144, 146, 184, 185, 101,
C. I Pigment Violet-19, 23,
C. I Pigment Blue-15: 1, 15: 3, 15: 4, 18, 60, 27, 29,
C. I Pigment Green-7, 36,
C. I Pigment White-6, 18, 21,
C. I Pigment Black-7,
And the like.

  Each ink is prepared using these pigments as coloring materials. Among the seven inks, the red, blue, and green inks, which are secondary colors, can be used by using the pigment itself having the color tone. The red ink pigment component is the yellow ink pigment component and the magenta ink pigment component, the blue ink pigment component is the magenta ink pigment component and the cyan ink pigment component, and the green ink pigment component is the cyan ink pigment. The pigment component of the yellow ink and the pigment component of the yellow ink may be combined.

  For these pigments, a pigment dispersant may be used as necessary. Examples of pigment dispersants that can be used include higher fatty acid salts, alkyl sulfates, alkyl ester sulfates, alkyl sulfonates, sulfosuccinates. Acid salt, naphthalene sulfonate, alkyl phosphate, polyoxyalkylene alkyl ether phosphate, polyoxyalkylene alkyl phenyl ether, polyoxyethylene polyoxypropylene glycol, glycerin ester, sorbitan ester, polyoxyethylene fatty acid amide, amine Activators such as oxides, or styrene, styrene derivatives, vinyl naphthalene derivatives, acrylic acid, acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, fumaric acid derivatives Block copolymer comprising a monomer of the above, a random copolymer and can be exemplified salts thereof.

  As a method for dispersing the pigment, for example, various dispersing machines such as a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, and a paint shaker can be used. It is also preferable to use a centrifugal separator or a filter for the purpose of removing the coarse particles of the pigment dispersion.

  The average particle diameter of the pigment particles in the pigment ink is selected in consideration of stability in the ink, image density, glossiness, light resistance, etc. In addition, the image forming method of the present invention improves glossiness, textures. It is preferable to select the particle size as appropriate from the viewpoint of improvement. In the present invention, the reason why the glossiness or texture is improved is not clear at this stage, but in the formed image, the pigment is preferably dispersed in the film in which the thermoplastic resin is melted. I guess it is related. For the purpose of high-speed processing, the thermoplastic resin must be melted and formed into a film in a short time, and the pigment must be sufficiently dispersed in the film. At this time, it is considered that the surface area of the pigment has a great influence, and therefore there is an optimum region for the average particle diameter.

  The water-based ink composition which is a preferable form as the pigment ink preferably uses a water-soluble organic solvent in combination. Examples of the water-soluble organic solvent that can be used in the present invention include alcohols (for example, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, pentanol, hexanol, cyclohexanol, benzyl). Alcohol), polyhydric alcohols (for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol Etc.), polyhydric alcohol ethers (for example, ethylene glycol monomethyl ether, ethylene glycol) Ether monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether , Triethylene glycol monobutyl ether, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, etc.), amines (for example, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, mole) Phosphorus, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.), amides (eg, formamide, N, N-dimethylformamide, N , N-dimethylacetamide, etc.), heterocyclic rings (for example, 2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, etc.), sulfoxides ( For example, dimethyl sulfoxide etc.), sulfones (for example, sulfolane etc.), urea, acetonitrile, acetone etc. are mentioned. Preferable water-soluble organic solvents include polyhydric alcohols. Furthermore, it is particularly preferable to use a polyhydric alcohol and a polyhydric alcohol ether in combination.

  The water-soluble organic solvent may be used alone or in combination. The total amount of the water-soluble organic solvent added to the ink is 5 to 60% by mass, preferably 10 to 35% by mass.

  The ink composition may be prepared by adding various known additives such as viscosity according to the purpose of improving ejection stability, print head and ink cartridge compatibility, storage stability, image storage stability, and other various performances as necessary. Adjusting agents, surface tension adjusting agents, specific resistance adjusting agents, film forming agents, dispersants, surfactants, ultraviolet absorbers, antioxidants, anti-fading agents, anti-fouling agents, rust inhibitors, etc. are appropriately selected and used. For example, polystyrene, polyacrylic acid esters, polymethacrylic acid esters, polyacrylamides, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, or a copolymer thereof, urea resin, melamine resin, etc. Organic latex fine particles, liquid paraffin, dioctyl phthalate, tricresyl phosphate, silicone oil and other oil droplet fine particles, Thion or nonionic surfactants, ultraviolet absorbers described in JP-A-57-74193, JP-A-57-87988, and JP-A-62-261476, JP-A-57-74192, JP-A-57-87989, 60-72785, 61-146591, anti-fading agents described in JP-A-1-95091 and 3-13376, JP-A-59-42993, 59-52689, 62- 280069, 61-242871, and JP-A-4-219266, etc., optical brighteners, pH adjusters such as sulfuric acid, phosphoric acid, citric acid, sodium hydroxide, potassium hydroxide, potassium carbonate, etc. Can be mentioned.

  The ink composition has a viscosity at the time of flight of preferably 40 mPa · s or less, and more preferably 30 mPa · s or less. The ink composition has a surface tension during flight of preferably 20 mN / m or more, and more preferably 30 to 45 mN / m.

  In the present invention, various types of paper such as printing paper and ink jet dedicated paper are used as image receiving paper. In addition, as the ink jet dedicated paper, either a water-absorbing support or a non-water-absorbing support can be used, but from the viewpoint that the non-water-absorbing support is free from wrinkles, a higher quality proof can be obtained. preferable.

  The water-absorbing support is typically a paper support mainly composed of natural pulp, but may be a mixture of synthetic pulp and natural pulp.

  Examples of the non-water-absorbing support include a plastic resin film support or a support in which both surfaces of paper are covered with a plastic resin film.

  As a plastic resin film support body, a polyester film, a polyvinyl chloride film, a polypropylene film, a cellulose triacetate film, a polystyrene film etc. are mentioned, for example.

  A particularly preferred support in the present invention is a reflective support in which both sides of paper are coated with a plastic resin. Paper with both sides of the paper coated with plastic resin is relatively close to the touch of paper, and since the paper surface is covered with plastic resin, the discoloration of the paper itself over time is small. This is preferable because the effect is remarkably exhibited. Most preferred is a support having both sides of paper coated with a polyolefin resin.

  Hereinafter, a support in which both sides of paper, which is a particularly preferable support in the present invention, is coated with a polyolefin resin will be described.

  The paper used for the support according to the present invention is made from wood pulp as a main raw material and, if necessary, paper making using synthetic pulp such as polypropylene or synthetic fibers such as nylon or polyester in addition to wood pulp. As wood pulp, for example, any of LBKP, LBSP, NBKP, NBSP, LDP, NDP, LUKP, NUKP can be used, but more LBKP, NBSP, LBSP, NDP, LDP with more short fibers are used. Is preferred. However, the ratio of LBSP or LDP is preferably 10 to 70% by mass.

  The pulp is preferably a chemical pulp (sulfate pulp or sulfite pulp) with few impurities, and a pulp having a whiteness improved by bleaching is also useful.

  In paper, sizing agents such as higher fatty acids and alkyl ketene dimers, white pigments such as calcium carbonate, talc and titanium oxide, paper strength enhancers such as starch, polyacrylamide and polyvinyl alcohol, fluorescent whitening agents, polyethylene glycols A water retaining agent such as a dispersant, a softening agent such as a quaternary ammonium, and the like can be appropriately added.

  The freeness of the pulp used for papermaking is preferably 200 to 500 ml as defined by CSF, and the fiber length after beating is the remaining 24% by mass as defined in JIS-P-8207 and 42 mesh fraction. 30 to 70% of the sum with the mass% of is preferable. In addition, it is preferable that the mass% of 4 mesh remainder is 20 mass% or less.

  The basis weight of the paper is preferably 50 to 180 g, and most preferably 60 to 140 g. The thickness of the paper is preferably 50 to 180 μm.

The paper can be given a high smoothness by calendering at the paper making stage or after paper making. The paper density is generally 0.7 to 1.2 g / m ² (JIS-P-8118). Furthermore, the base paper stiffness is preferably 20 to 300 g under the conditions specified in JIS-P-8143.

  A surface sizing agent may be applied to the paper surface. As the surface sizing agent, the same sizing agents that can be added to the base paper can be used.

  The pH of the paper is preferably 5 to 9 when measured by the hot water extraction method specified in JIS-P-8113. Next, the polyolefin resin that covers both sides of the paper will be described.

  The polyolefin resin used for this purpose is preferably a polyolefin such as a copolymer mainly composed of polyethylene, polypropylene, polyisobutylene, ethylene or propylene, but polyethylene is particularly preferable.

  Hereinafter, particularly preferred polyethylene will be described. The polyethylene covering the paper surface and the back surface is mainly low density polyethylene (LDPE) and / or high density polyethylene (HDPE), but other LLDPE, polypropylene, etc. can also be used in part.

  In particular, as the polyolefin layer on the ink absorbing layer side, a layer in which rutile or anatase type titanium oxide is added to a polyolefin resin to improve opacity and whiteness can be used. Content of the titanium oxide used here is 0.1-20 mass% normally with respect to polyolefin resin, Preferably it is 1-13 mass%.

  In order to adjust the white background in the polyolefin layer, it is preferable to add a pigment having high heat resistance or a fluorescent brightening agent in order to obtain an image receiving paper (recording paper) for ink jet recording.

  Examples of the color pigment include ultramarine blue, bitumen blue, cobalt blue, phthalocyanine blue, manganese blue, cerulean, tungsten blue, molybdenum blue, and anthraquinone blue.

  Examples of the optical brightener include dialkylaminocoumarin, bisdimethylaminostilbene, bismethylaminostilbene, 4-alkoxy-1,8-naphthalenedicarboxylic acid-N-alkylimide, bisbenzoxazolylethylene, dialkylstilbene, etc. Is mentioned.

  The amount of polyethylene used on the front and back of the paper is selected to optimize the curl at low and high humidity after the ink absorption layer thickness and back layer are provided, but generally the ink absorption layer is applied. The polyethylene layer on the side to be processed is in the range of 5 to 40 μm, and the back layer side is in the range of 10 to 30 μm.

  In particular, when the basis weight of the paper is 120 g or less, it is preferable to make the polyethylene on the ink receiving layer side thinner than the polyethylene on the opposite side from the viewpoint of preventing curling fluctuation due to humidity after the porous ink receiving layer is provided. Df <Db + 5 μm is preferable. Here, Df and Db are the film thicknesses of polyethylene on the ink receiving layer side and on the opposite side, respectively.

Furthermore, the polyethylene-coated paper support preferably has the following characteristics.
1. Tensile strength: The strength defined by JIS-P-8113 is preferably 2-30 kg in the vertical direction and 1-20 kg in the horizontal direction.
2. Tear strength: 10 to 200 g in the vertical direction and 20 to 200 g in the horizontal direction are preferable according to a method defined by JIS-P-8116.
3. Opacity: 80% or more, particularly 85% or more is preferable when measured by the method defined in JIS-P-8138.
4). Clark stiffness: support Clark stiffness in the carrying direction is 50~300cm ^2/100 of the recording paper is preferred,
5. Moisture in the base paper: 4 to 10% by mass is preferable with respect to the middle paper,
The ink-jet image receiving paper used in the present invention may be a so-called glossy surface with respect to the glossiness of the surface, or a surface having irregular or regular fine-grained irregularities on the surface on the ink absorbing layer side. It may be of quality, matte surface or semi-matte surface. The unevenness referred to here is a centerline average roughness (Ra) of 0 when measured with a reference length of 2.5 mm and a cut-off value of 0.8 mm defined in JIS-B-0601 on the surface of the ink absorbing layer side. An image receiving paper having a surface roughness of 0.5 to 3.0 μm.

  For the various surface properties as described above, a matting agent is added to the surface of the ink receiving layer, the surface is cleaned after the ink receiving layer is formed, or the surface of the support is previously cleaned. It can be obtained by providing an ink absorbing layer on a support.

  When the ink absorbing layer is cleaned, the surface cleaning tends to decrease after ink jet recording. Therefore, it is preferable to use a support that has been cleaned in advance and a matting agent for the ink absorbing layer. In particular, when an ink-jet image receiving paper having a matte surface or a semi-matte surface is obtained, it is preferable to combine an ink absorbing layer containing a matting agent with a support that has been previously cleaned.

  In the case of a support that is a particularly preferable support, in which both sides of the paper are coated with a polyolefin resin, it is preferable that the polyolefin resin surface is subjected to a molding treatment after the paper is coated with the polyolefin resin.

  A typical method for forming the unevenness on the surface of the polyolefin resin in advance is performed by extruding a molten polyolefin resin on a base paper and then applying pressure to a forming roller to form a fine unevenness. For this patterning, resin-coated paper obtained by melt extrusion is embossed with a calendar near room temperature, and a cooling roll engraved with a pattern on the roll surface during polyolefin resin extrusion coating is used for cooling. However, the latter method is preferable because the latter can be molded with a relatively weak pressure, and more accurate and uniform molding can be performed.

  A preferable method for changing the shape of the unevenness on the surface of the support is performed by using a cooling roll having a different size, shape or height.

  The relationship between the unevenness of the surface of the support and the surface of the ink absorption layer depends on the characteristics of the ink absorption layer, but the ink absorption layer has a high ink absorption rate and is a porous film having voids that can provide a higher quality print. In some cases, since the dry film thickness is increased, the level difference of the support surface tends to decrease.

  In the case of inkjet image-receiving paper obtained by applying an ink absorbing layer to a support having an uneven surface provided in advance, the surface roughness of the support should be higher than the desired height difference of the surface of the ink absorbing layer. It is preferable to use a support having a surface roughness Ra of 0.6 to 5 μm.

Next, the whiteness of the ink jet image receiving paper of the present invention will be described. In general, the preferred whiteness of inkjet image-receiving paper is determined by its application and preference, similar to the general whiteness of paper, but in the case of printing paper, it is measured by the method defined in JIS-Z-8722. In general, whiteness such that a ^* and b ^* are −2 to 2 and −4 to 4 when displayed in accordance with JIS-Z-8730 is generally required. If this is a photographic application, a smaller value for b ^* , ie, -10 to 0, appears to be accepted as the preferred whiteness.

  In order to achieve the above whiteness, as described above, it can be obtained by providing an ink absorbing layer containing a small amount of a coloring dye or coloring pigment on a reflective support, but in the inkjet image receiving paper used in the present invention, Needs to be provided with a slightly colored ink absorbing layer so that the difference ΔabL between the whiteness of the support surface on the application surface side of the ink absorbing layer and the whiteness of the surface of the ink absorbing layer is 7 or less. It is.

  When ΔabL exceeds 7, discoloration increases due to storage of inkjet image-receiving paper, and therefore Δab is preferably 5 or less.

As described above, when used for printing paper or the like, the whiteness of the surface of the ink absorbing layer is generally such that a ^* and b ^* are −2 to 2 and −4 to 4, respectively. In order to obtain such whiteness, it is necessary to use a support in which a ^* and b ^* are −4 to 4 and −8 to 8, respectively, as the whiteness of the reflective support. preferable.

Further, the lightness index L ^* of the image receiving paper surface is preferably 88 or more, and particularly preferably 89 or more. In order to obtain such a brightness index, L ^{* of the} reflective support is 85 or more, preferably 88 or more.

  The ink absorbing layer can be slightly colored by adding various known dyes and pigments to the ink absorbing layer. The dye may be either a water-soluble or oil-soluble dye. In the case of a water-soluble dye, either an anionic dye or a cationic dye can be used.

  The water-soluble or oil-soluble dye may be added directly to the coating solution for forming the ink absorbing layer, or the dye solution may be overcoated after the ink absorbing layer is formed. In addition, a method of emulsifying and dispersing the oily dye together with other oils and adding it to the coating solution is also preferably used. In the case of a pigment, it is finely dispersed by a known disperser such as a ball mill or a sand mill and added to a coating solution. In this case, it is preferable that the particle size is dispersed to an average particle size of about 0.1 to 0.05 μm. In the case of a pigment, it is preferable to use a pigment having a uniform particle size distribution as much as possible because the covering ratio changes depending on the particle size of the pigment particles and the color tone tends to fluctuate. Preferred colorants are water-soluble or oil-soluble dyes.

  In addition, when using for printing, it is preferable not to use what is called a fluorescent whitening agent in an ink absorption layer. When a fluorescent whitening agent is used, white color tends to fluctuate greatly visually due to differences in viewing conditions (especially, differences in the proportion of ultraviolet rays).

The amount of the dye or pigment added varies widely depending on the type of the dye or pigment, but is preferably in the range of 0.01 to 200 mg per m ² of the image receiving paper.

  Two or more of these dyes and pigments can be used in combination. In the present invention, the whiteness of the reflective support opposite to the side where the ink absorbing layer is provided is not particularly limited from the viewpoint of the present invention. From the viewpoint of more reliably providing front and back discrimination, the difference in whiteness between the white surface of the ink absorbing layer and the back surface of the support may be large (for example, ΔabL> 20). There is no need to satisfy such conditions.

  These ink jet image receiving papers are particularly suitable for printing and proofing thereof, but preferably have a relatively low gloss. A preferable glossiness is 10 to 25% in 60 ° glossiness specified in JIS-Z-8741.

  As such glossiness, the support having an uneven surface as described above, and the ink receiving layer containing a matting agent has a small decrease in color density at the time of ink jet recording, and is suitable. It is preferable because it causes a reduction in gloss.

  The matting agent used individually is one having an average particle size of usually 1 to 30 μm, preferably about 2 to 20 μm. The matting agent is more preferably monodispersed. When the particle size distribution of the matting agent is measured, the dispersion obtained by dividing the standard deviation by the average particle size is 2 or less, preferably 0.5 or less.

  Next, the ink absorbing layer provided on the support will be described. The ink absorbing layer may be provided on only one side of the support, or may be provided on both sides. At this time, the ink absorption layers provided on both sides may be the same or different.

  The ink absorbing layer of the ink jet image receiving paper of the present invention is a porous ink absorbing layer having voids with a high ink absorbing speed.

  The void-type ink absorbing layer is preferably a porous film having a void layer containing inorganic fine particles and a small amount of a hydrophilic polymer.

  Examples of such inorganic fine particles include light calcium carbonate, heavy calcium carbonate, magnesium carbonate, kaolin, clay, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc hydroxide, zinc sulfide, zinc carbonate, White inorganic pigments such as hydrotalcite, aluminum silicate, diatomaceous earth, calcium silicate, magnesium silicate, synthetic amorphous silica, colloidal silica, alumina, colloidal alumina, pseudoboehmite, aluminum hydroxide, lithopone, zeolite, magnesium hydroxide, etc. Can be mentioned.

  Such inorganic fine particles can be used as primary particles or in a state where secondary agglomerated particles are formed.

  In the present invention, silica or pseudoboehmite is particularly preferable from the viewpoint of forming fine voids, and silica, colloidal silica, and pseudoboehmite synthesized by a gas phase method having an average particle size of 100 nm or less are particularly preferable. Furthermore, silica synthesized by a gas phase method with an average particle size of 100 nm or less forms a high colorability and a high porosity, and a cationic polymer for enhancing the fixability of a dye when ink jet recording is performed. It is most preferable from the viewpoint of easy coexistence.

  The average particle size of the inorganic fine particles can be obtained as a simple average value (number average) by observing the particle itself or the cross section or surface of the void layer with an electron microscope and determining the particle size of 100 arbitrary particles. Here, each particle size is represented by a diameter assuming a circle equal to the projected area.

  Examples of the hydrophilic polymer used in the void layer include gelatin (for example, alkali-treated gelatin, acid-treated gelatin, derivative gelatin obtained by blocking an amino machine with phenyl isocyanate, phthalic anhydride, etc.), polyvinyl alcohol (average polymerization degree). 300-4000, saponification degree is preferably 80-99.5%), polyvinylpyrrolidone, polyethylene oxide, hydroxylethylcellulose, polyacrylamide, agar, pullulan, dextran, acrylic acid, carboxymethylcellulose, casein, alginic acid, etc. Two or more types can be used in combination. Particularly preferred in the present invention is polyvinyl alcohol.

  The polyvinyl alcohol preferably used in the present invention includes, in addition to ordinary polyvinyl alcohol obtained by hydrolyzing polyvinyl acetate, modified polyvinyl alcohol such as polyvinyl alcohol having a cation-modified terminal and anion-modified polyvinyl alcohol having an anionic group. Alcohol is also included.

  As the polyvinyl alcohol obtained by hydrolyzing vinyl acetate, those having an average polymerization degree of 300 or more are preferably used, and those having an average polymerization degree of 1000 to 5000 are particularly preferably used. The saponification degree is preferably 70 to 100%, particularly preferably 80 to 99.5%.

  When the void layer contains polyvinyl alcohol as a hydrophilic polymer, boric acid or a salt thereof can be contained as a curing agent in order to improve the film forming property of the film and increase the strength of the film. .

  As boric acid or its salt, oxygen acid having boron atom as a central atom and its salt are shown. Specifically, orthoboric acid, metaboric acid, hypoboric acid, tetraboric acid, pentaboric acid and their salts are included. .

  The amount of boric acid or a salt thereof used can vary widely depending on the amount of inorganic fine particles and hydrophilic polymer in the coating solution, but is usually 1 to 60% by mass, preferably 5 to 40% by mass with respect to the hydrophilic polymer.

  In addition to the above boric acid-based curing agents, or in combination with borates, epoxy curing agents, aldehyde curing agents, isocyanate curing agents, ethyleneimino curing agents, and organic curing agents such as melamine curing agents are used. It is also possible to do.

  In the present invention, since the ink absorption speed is high, image unevenness is small, and the amount of the hydrophilic polymer used is relatively small, curling is relatively small. Is preferred.

  Various additives other than those described above can be added to the ink absorbing layer of the inkjet image receiving paper. Among these, a cationic mordant is preferable for improving water resistance and moisture resistance after printing.

  As the cationic mordant, a polymer mordant having a primary to tertiary amino group and a quaternary ammonium base is used, but there is little discoloration or deterioration of light resistance over time, and the dye mordant has a sufficiently high mordant ability. Therefore, a polymer mordant having a quaternary ammonium base is preferable.

  A preferred polymer mordant is obtained as a homopolymer of a monomer having the quaternary ammonium base, a copolymer with another monomer, or a condensation polymer.

  Other than the above, for example, ultraviolet absorbers described in JP-A-57-74193, JP-A-57-87988, and JP-A-62-261476, JP-A-57-74192, and JP-A-57-87989, JP-A-60-72785, JP-A-61-146591, JP-A-1-95091, JP-A-3-13376, and the like, various anionic, cationic or nonionic surfactants, Fluorescent whitening agents and antifoams described in JP-A-59-42993, JP-A-59-52689, JP-A-62-280069, JP-A-61-228771 and JP-A-4-219266 Various known additives such as a lubricant, a lubricant such as diethylene glycol, an antiseptic, a thickener, an antistatic agent, and a matting agent may be contained.

  Prior to application of the ink absorbing layer on the support, it is preferable to subject the support to corona discharge treatment, subbing treatment, or the like for the purpose of increasing the adhesive strength between the support surface and the coating layer. As the undercoat layer, the hydrophilic polymer used in the ink absorbing layer described above, various latexes, or a combination thereof is used. The thickness of the undercoat layer is generally 0.01 to 0.5 μm.

  Various back layers are provided on the side opposite to the side having the ink absorbing layer of the ink jet image receiving paper of the present invention in order to prevent curling and to further improve the sticking resistance and the ink transfer resistance when superimposed immediately after printing. Can be provided.

  The configuration of the back layer varies depending on the type and thickness of the support and the configuration and thickness on the front side, but generally a hydrophilic binder or a hydrophobic binder is used. The thickness of the back layer is usually in the range of 0.1 to 10 μm.

  Further, the back layer is preferably roughened in order to prevent sticking with other image receiving paper, improve writing performance, and further improve transportability in the ink jet recording apparatus. Organic or inorganic fine particles having a particle diameter of 2 to 20 μm are preferably used for this purpose. These back layers may be provided in advance, or may be provided after applying the coating composition according to the present invention.

  The smoothness of the back layer is preferably Ra = 0.4-5 μm, Rz = 1-30 μm, Rmax = 2-40 μm, and the glossiness is preferably 5-30%.

  As an ink absorption layer coating method, a roll coating method, a rod bar coating method, an air knife coating method, a spray coating method, a curtain coating method, or an extrusion coating method using a hopper described in US Pat. No. 2,681,294 Is preferably used.

  When polyolefin resin-coated paper is used as the support, it is preferable that drying be performed in the range of approximately 0 to 80 ° C. If the temperature exceeds 80 ° C., the polyolefin resin softens, making it difficult to convey, and unevenness in the gloss of the recording layer surface. A preferable drying temperature is 0 to 70 ° C.

Furthermore, the surface of the ink absorbing layer according to the present invention preferably has the following characteristics.
1. Beck smoothness: 200 to 2000 seconds (ink absorption layer side), 50 to 1000 seconds (back layer side)
2. Friction coefficient: front and back dynamic friction coefficient is 0.2 to 1.0
3. Opacity: 88-98%
As the water absorption amount of the image receiving paper increases, the ink absorption layer (image receiving layer) must be thickened, and thus the approximation to printed matter tends to be impaired. In the method of the present invention, the water absorption of the image receiving paper is preferably 50 ml / m ² or less, more preferably 20 ml / m ² or less, and particularly preferably 10 ml / m ² or less.

  In order to reproduce a halftone dot of a printed matter, a resolution of 2400 dpi or more (dpi represents the number of dots per 2.54 cm) which is a printing resolution is usually preferable. In order to achieve such high resolution in the ink jet system, the ink droplet is preferably 1 pl or less. More preferably, it is 0.5 pl or less. A piezo method or a bubble jet method is used as an emission method for flying such fine droplets, but a method as disclosed in JP-A-2004-114377 is preferably used.

  In the present invention, an ink jet capable of discharging a fine ink droplet of 1 pl or less, preferably several hundred fl (femtoliter), and recording a high-quality halftone image with ultra fine dots having a resolution of 2400 dpi. It is necessary to use a recording device.

In the inkjet image recording method used in the present invention, in order to reproduce a halftone dot image with high precision, the ink droplet ejected from the nozzle has a small amount of droplets per droplet and at the same time has closeness to printed matter. The water absorption amount of the image receiving paper is preferably 50 ml / m ² or less, more preferably 20 ml / m ² or less, and particularly preferably 10 ml / m ² or less, so that the thickness of the ink absorbing layer is adjusted so as not to be damaged. There is a need to.

  Accordingly, the nozzle diameter (internal diameter) of the ink jet recording apparatus used in the present invention is preferably 30 [μm] or less, more preferably 20 [μm], in order to eject the fine ink droplets. Less than, more preferably 8 [μm] or less, and further preferably 4 [μm] or less. The nozzle diameter is preferably larger than 0.2 [μm].

(Overall configuration of inkjet recording apparatus)
Hereinafter, an ink jet recording apparatus that can be suitably used in the present invention described in JP-A-2004-114377 will be described with reference to FIG.

  FIG. 4 is a schematic configuration diagram of the ink jet recording apparatus. The ink jet recording apparatus 100 includes a platen 102 for supporting a predetermined substrate K, a recording head 20 disposed above the platen 102, and a platen 102. The conveying rollers 103a and 103b arranged on the upstream side and the downstream side of the substrate S in the conveying direction, and the pressure contact that is pressed against the conveying rollers 103a and 103b and sandwiches the substrate K between the conveying rollers 103a and 103b. Rollers 104a and 104b.

(Configuration of recording head and members related to recording head)
As shown in FIG. 5, the recording head 20 is provided with an ultra-fine nozzle 21 that ejects ink droplets of chargeable ink from its tip. The nozzle 21 is directed to the platen 102. A counter electrode 23 is provided below the nozzle 21 of the recording head 20 so as to face the nozzle 21. The counter electrode 23 is formed integrally with the platen 102, has a counter surface facing the tip of the nozzle 21, and supports the substrate K that receives ink droplet landing on the counter surface. The recording head 20 is connected to an ink supply unit that supplies ink to the flow path 22 in the nozzle 21 and an ejection voltage application unit 25 that applies an ejection voltage to the ink in the nozzle 21.

  6A and 6B are explanatory diagrams showing the relationship between the ink ejection operation and the voltage applied to the ink. FIG. 6A shows a state in which ejection is not performed, and FIG. 6B shows the ejection state.

  A part of the nozzle 21 and the ink supply unit and a part of the discharge voltage applying unit 25 are integrally formed by a nozzle plate 26.

  The recording head 20 is a scanning recording head that can be scanned in a direction orthogonal to the conveyance direction (left direction in FIG. 4) of the substrate K by a driving mechanism (not shown). It has. In this embodiment, the recording head 20 includes seven colors such as yellow (Y), magenta (M), cyan (C), black (K), red (R), blue (B), and green (G). Each process color ink containing a color material is supplied from an ink tank, which will be described later, of the ink supply means, and the recording head 20 ejects each process color ink as a droplet from each nozzle 21.

(nozzle)
The nozzle 21 is integrally formed with a lower surface layer 26c of the nozzle plate 26 described later, and is erected vertically from the flat plate surface of the nozzle plate 26. Further, the nozzle 21 is formed with an in-nozzle flow path 22 penetrating from the tip portion along the center line.

  The nozzle 21 will be further described in detail. The nozzle 21 is formed with an ultrafine diameter. As described above, the inner diameter at the tip of the nozzle 21 is 30 μm or less, but may be less than 20 μm, 8 μm or less, or 4 μm or less. As an example of specific dimensions of each part, the internal diameter of the nozzle internal flow path 22 is 1 [μm], the external diameter at the tip of the nozzle 21 is 2 [μm], and the root diameter of the nozzle 21 is 5 [μm]. [mu] m] and the height of the nozzle 21 is set to 100 [[mu] m], and the shape thereof is formed in a truncated cone shape that is close to a conical shape. The entire nozzle 21 is formed of an insulating resin material together with the lower surface layer 26 c of the nozzle plate 26.

  In addition, each dimension of a nozzle is not limited to the said example. In particular, the nozzle inner diameter is a range in which the discharge voltage that enables ink droplet discharge due to the effect of electric field concentration described later is less than 1000 [V], for example, the nozzle diameter is 70 [μm] or less, and more Desirably, the diameter is 20 [μm] or less, and the diameter within a range where it is feasible to form a through-hole through which ink is passed by the current nozzle forming technique is set as the lower limit.

(Ink supply means)
The ink supply means is provided at a position inside the nozzle plate 26 and at the base of the nozzle 21 and also supplies ink to the ink chamber 24 from an external ink tank (not shown). An ink supply path 27 is provided, and a supply pump (not shown) that applies ink supply pressure to the ink chamber 24 is provided.

  Each process color ink is stored in the ink tank, and the supply pump supplies each process color ink to the tip of the nozzle 21 and maintains a supply pressure in a range that does not spill from the tip. Then, each process color ink is supplied to the recording head 20 (see FIG. 6A).

(Discharge voltage application means)
The discharge voltage application means 25 includes a discharge electrode 28 for applying a discharge voltage provided in a boundary position between the ink chamber 24 and the nozzle flow path 22 inside the nozzle plate 26, and a constant direct current is supplied to the discharge electrode 28. A bias power source 30 that applies a bias voltage and an ejection voltage power source 29 that applies a pulse voltage that is superimposed on the bias voltage and that is a potential required for ejection to the ejection electrode 28 are provided.

The discharge electrode 28 is in direct contact with the ink inside the ink chamber 24 to charge the ink and apply a discharge voltage.
The bias voltage from the bias power source 30 is applied in a constant range within a range where ink is not ejected, thereby reducing in advance the width of the voltage to be applied during ejection, thereby improving the reactivity during ejection. Yes.

  The ejection voltage power supply 29 applies the pulse voltage superimposed on the bias voltage only when ejecting ink. At this time, the value of the pulse voltage is set so that the superimposed voltage V satisfies the following equation.

V> (2γkr / ε ₀ ) ^1/2
Where γ: ink surface tension, ε ₀ : vacuum dielectric constant, r: nozzle radius, k: proportional constant depending on nozzle shape (1.5 <k <8.5).
As an example, the bias voltage is applied at DC 300 [V] and the pulse voltage is marked at 100 [V]. Therefore, the superimposed voltage at the time of ejection is 400 [V].

(Nozzle plate)
The nozzle plate 26 includes a base layer 26a positioned at the uppermost layer in FIG. 5, a flow path layer 26b that forms an ink supply path positioned below the base layer 26a, and a lower layer formed below the flow path layer 26b. 26c, and the discharge electrode 28 described above is interposed between the flow path layer 26b and the upper surface layer 26c.

  The base layer 26a is formed of a silicon substrate or a highly insulating resin or ceramic, forms a soluble resin layer on the base layer 26a, and removes only a portion that follows the pattern of the supply path 27 and the ink chamber 24, An insulating resin layer is formed as a flow path layer 26b in the removed portion. Then, a discharge electrode 28 is formed on the lower surface of the insulating resin layer by plating with a conductive material (for example, NiP), and an insulating resist resin layer is formed as a lower surface layer 26c from below to provide a thickness in consideration of the height of the nozzle 21. Formed with. Then, this insulating resist resin layer is exposed by an electron beam method or a femtosecond laser to form a nozzle shape. The nozzle internal flow path 22 is also formed by laser processing. Then, the dissolvable resin layer according to the pattern of the supply path 27 and the ink chamber 24 is removed, and the supply path 27 and the ink chamber 24 are opened to complete the nozzle plate.

(Counter electrode)
The counter electrode 23 has a counter surface perpendicular to the nozzle 21 and supports the substrate K along the counter surface. As an example, the distance from the tip of the nozzle 21 to the opposing surface of the opposing electrode 23 is set to 100 [μm].
Since the counter electrode 23 is grounded, the ground potential is always maintained. Therefore, when a pulse voltage is applied, the ink droplet ejected by the electrostatic force generated by the electric field generated between the tip of the nozzle 21 and the opposing surface is guided to the opposing electrode 23 side.

  The ink jet recording apparatus 20 ejects ink droplets by increasing the electric field strength by concentrating the electric field at the tip of the nozzle 21 by making the nozzle 21 ultrafine, so that the ink can be discharged without induction by the counter electrode 23. Although it is possible to discharge droplets, it is desirable that induction by electrostatic force is performed between the nozzle 21 and the counter electrode 23. In addition, the charge of the charged ink droplet can be released by grounding the counter electrode 23.

  More specifically, the ink has a viscosity of 0.1 to 1000 mPa · s (preferably 1 to 100 mPa · s) and a surface tension of 20 to 70 mN / m (preferably 25 to 50 mN / m). Some inks are applicable. When the viscosity of the ink is less than 0.1 mPa · s or greater than 1000 mPa · s, the ink ejection from the nozzle 21 becomes unstable. Further, when the surface tension of the ink is less than 20 mN / m, the ink droplets ejected from the nozzle 21 are likely to bleed into the substrate S. When the surface tension of the ink is greater than 70 mN / m, each pixel of the substrate S cannot be completely filled with the ink droplets ejected from the nozzle 21, and the amount of ink attached to the substrate S per color is increased. I have to do more. Eventually, in this case, conventional problems such as ink bleeding on the base material, poor drying of the ink itself, and cockling of the base material due to ink adhering to the base material cannot be suppressed.

(Image recording operation by inkjet recording device)
Next, the operation of the inkjet recording apparatus 100 will be described with reference to FIG.

First, by rotating the transport roller 103a, the predetermined substrate S is transported to the platen 102 while being sandwiched between the transport roller 103a and the pressure roller 104a.
The substrate S is intermittently conveyed by the conveying roller 103a and the pressure roller 104a while the substrate S is supported by the platen 102, and the scanning type recording head 20 is perpendicular to the conveying direction of the substrate S. Each process color ink is ejected from the recording head 20 while scanning a desired image on the substrate S. The substrate S after image recording is nipped by the transport roller 103b and the pressure roller 104b and removed from the platen 102.

(Discharge operation of minute ink droplets by recording head)
The operation of the recording head 20 will be described with reference to FIGS.

  Ink is supplied to the nozzle flow path 22 by the supply pump of the ink supply means, and in this state, a bias voltage is applied to the ink via the discharge electrode 28 by the bias power supply 30. In such a state, the ink is charged, and a meniscus that is recessed by the ink is formed at the tip of the nozzle 21 (FIG. 6A). When a pulse voltage is applied by the discharge voltage power supply 29, the ink is guided to the tip end side of the nozzle 21 by the electrostatic force due to the electric field strength of the concentrated electric field at the tip portion of the nozzle 21, and protrudes outside to the convex meniscus. Is formed, and the electric field is concentrated by the apex of the convex meniscus. Finally, a minute ink droplet is ejected toward the counter electrode 23 against the surface tension of the ink (FIG. 6B).

  In this way, ink droplets having a droplet amount of 1 pl or less per droplet are ejected from the nozzle 21.

  In addition, since these nozzles have a small diameter, it is possible to easily perform control to reduce the discharge flow rate per unit time due to the low nozzle conductance, and to sufficiently reduce the ink without narrowing the pulse width. Realizes droplet ejection. From these facts, a high-quality halftone image having an area gradation can be recorded with ultra-fine dots with a high resolution of 2400 dpi.

  The ejection voltage application means 25 constantly applies a bias voltage and ejects ink droplets using a pulse voltage as a trigger, but always applies an alternating current or continuous rectangular wave with the amplitude required for ejection and increases or decreases its frequency. It is good also as a structure which discharges by switching.

  Furthermore, in the above-described embodiment, as shown in FIG. 7A, a recording method in which recording is performed while the recording head 20 is scanned in a direction orthogonal to the conveyance direction of the substrate S, or the recording head 20 is moved in a predetermined direction. 7B, a recording system in which the substrate S is reciprocally moved in a direction orthogonal to the moving direction of the recording head 20, and many in a direction orthogonal to the conveying direction of the substrate S. The recording method shown in FIG. 7C using a line head in which the nozzles 21 are arranged may be used.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these.

Example 1
(1) Preparation of target printed matter The digital test chart for NDK process management is printed under the printing conditions in accordance with the production conditions of the test chart for printing process management of JEOL (NDK). It was printed.

Next, as an inkjet apparatus, an on-demand inkjet printer equipped with a 7-color piezo inkjet head having 128 nozzles for each color is used, and a print document is sent from the host 21 as shown in FIG. Y, M sent to a certain pixel based on Y, M, C, K separated digital data in the digital test chart for printing process management of the Japan Electronics Manufacturing Industry Association (NDK) , C, K color data (before conversion), the ink used for the pixel (after conversion) is obtained according to the conversion table of FIG. Was used for printing. The ink droplets were output at a volume of 1 pl and a resolution of 2400 dpi.
This conversion was performed by calculation by software in the CPU of the control means 20 of the ink jet recording apparatus.

  As the ink, a water-soluble ink having the following formulation was used.

Color material Y: Water Yellow 6 (Orient Chemical Industries, Ltd.)
Coloring material M: Chuganol-First Red 3B (manufactured by Chugai Kasei Co., Ltd.)
Color material C: Kayara Star Coyze-Blue GL (Nippon Kayaku Co., Ltd.)
Color material K; Special Black 7984 (manufactured by Bayer)
When proof printing was performed using seven colors of ink according to the conversion table of FIG. 3 based on the digital data, a proof printed material having a color tone very close to the target printed material was obtained.

Example 2
<Preparation of printing ink for ink jet>
Each additive was mixed at the following composition ratio (mass%), and dispersed using a horizontal bead mill (System Zetamini manufactured by Ashizawa) filled with 0.3 mm zirconia beads at a volume ratio of 60%. Y, N, C A dispersion of K ink was obtained.

John creel 61; acrylic-styrene resin (manufactured by Johnson)
Next, the dispersion was mixed and stirred at the following composition ratio (mass%), and filtered through a 1 μm filter to prepare a pigment ink.
The composition of the R, G, and B inks was set so that the 100% solid color tone was the closest to the printed matter.

EG; ethylene glycol DEG; diethylene glycol surfactant; olefin E1010 (manufactured by Shin-Etsu Chemical Co., Ltd.)
<Creation of image-receiving paper>
According to the method of Example 2 of Japanese Patent Laid-Open No. 2003-231348, an image receiving paper that approximates to a printing paper and has a gap amount of the gap type image receiving paper 5B and each coating layer set to 40%, and only the white color tone is adjusted to 5B. 6B was produced. The water absorption of the image receiving paper, 5B, at 6B, were respectively ^{55ml / m 2, 18ml / m} 2.

  The water absorption amount of the image receiving paper was measured as follows.

(Water absorption)
The ink-jet image receiving paper is cut into a size of 10 cm × 10 cm, and the appearance when dried (this is referred to as (a)) is measured. Then, it is immersed in pure water for 30 seconds, and the surface after immersion is measured by wiping the surface water (this is referred to as (b)). The scale (c) of only the base material without the ink absorbing layer is measured. From these, the amount of water absorption is calculated as follows. Incidentally, since the base material is RC paper (paper support coated with polyethylene on both sides), it was assumed that the water absorption amount of the base material itself was zero.

Water absorption = ((b)-(a)) / ((a)-(c))
<Inkjet device>
As the ink jet recording apparatus, the ink jet recording apparatus described in JP-A-2004-114377, Example 1 was used. The number of ink nozzles: 128 nozzles for each color, distance between nozzles and image receiving paper: 0.5 mm, applied voltage: 300 V, the amount of ink droplets was 0.5 pl, and output was performed at a resolution of 2400 dpi.

<Creating output>
(1) Preparation of target printed matter The digital test chart for NDK process management is printed under the printing conditions in accordance with the production conditions of the test chart for printing process management of JEOL (NDK). It was printed.

(2) Proof creation Using Y, M, C, K ink and Y, M, C, K, B, G, R ink, 2400 dpi, a digital test chart for NDK process management using the ink jet recording apparatus, Output was performed on a 175 line square screen. At this time, in one pixel of the image data, the image data was output according to the rules shown in FIGS.

<Evaluation methods>
(Pattern color)
About the color tone of the pattern of the test chart for NDK process control, the created proof samples were visually evaluated as follows.
A: The color of the pattern is very close to the printed matter, and the difference cannot be recognized.
○: A slight difference is observed when observed in detail.
Δ: A slight difference in color tone between the printed matter and the pattern is recognized, but it is within a range where there is no practical problem as a proof.
X: The difference in color tone is large, and it cannot be used as a proof.

(Texture texture)
About the pattern of the test chart for NDK process management, the sharpness and texture were visually evaluated as follows for each of the produced proof samples.
A: The texture of the pattern is very close to the printed matter, and the difference cannot be recognized.
○: A slight difference is observed when observed in detail.
Δ: A slight difference in texture between the printed material and the pattern is recognized, but it is in a range where there is no practical problem as a proof.
X: The difference in texture is large, and it cannot be used as a proof.

  As shown by the results in Table 4, it can be seen that the proof produced using the method of the present invention is excellent in color tone and texture and useful as a proof.

The figure which shows the structure of the inkjet recording device concerning this invention used for preparation of the proofreading material of printed matter. It is a figure which shows an example of the conversion table of this invention. It is a figure which shows another example of the conversion table of this invention. It is a schematic block diagram of an inkjet recording device. It is sectional drawing of the member concerning a recording head and a recording head. It is a figure which shows the relationship between the discharge operation of an ink, and the voltage applied to an ink. It is the schematic which shows an inkjet recording system. 10 is a color conversion table when using the four color inks used in the second embodiment. 10 is a color conversion table in the case where the seven colors of ink used in Example 2 are used.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Host 11 Main scanning motor 12 Sub scanning motor 13 Control means 19-1 to 19-7 Recording head 100 Inkjet recording apparatus 20 Recording head 20a Line head 21 Nozzle 22 Channel 23 Counter electrode 24 Ink chamber 25 Discharge voltage application means 26 Nozzle Plate 27 Ink supply path 28 Ejection electrode 29 Ejection voltage power supply 30 Bias power supply 40 Drum 41 Intermediate transfer member 102 Platen 103a, 103b Conveyance roller 104a, 104b Pressure roller S Substrate

Claims (3)

An image forming method comprising producing a proof of a printed matter composed of a halftone dot image using seven color inks of yellow, magenta, cyan, black, red, blue and green. In an image forming method for creating a proof of a printed matter consisting of halftone dots by an ink jet method using seven colors of yellow, magenta, cyan, black, red, blue, and green on an image receiving paper,
The water absorption of the image receiving paper is 50 ml / m ² or less,
The ink droplet is 1 pl or less,
The image forming method according to claim 1, wherein the resolution of the obtained image is 2400 dpi or more. The image forming method according to claim 2, wherein pigment ink is used for at least one of the seven colors of ink.

Images