JP2010167671A - Inkjet image forming method and inkjet recording device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording method which can form a high quality image on regular paper. <P>SOLUTION: In an ink-jet image forming method, when the amount of ink applied on regular paper is a constant amount of 0.5-6.0 pl, a self-dispersing pigment, an organic carboxylic acid salt, water, and a water soluble compound having a relative degree of intimacy hydrature coefficient of formula (A): the relative degree of intimacy hydrature=ä(water activity value of 20% aqueous solution)-(molar fraction of water of 20% aqueous solution)}/ä1-(molar fraction of water of 20% aqueous solution)} of 0.26 or above are contained, surface tension is 34 mN/m or below, the total amount of ink applied on a fundamental matrix is 5.0 μl/cm<SP>2</SP>or below, and ink of one color is 80% duty or above, an application process (B) (the application of the ink of one color on the fundamental matrix is 1-200 msec and carried out at least twice in timing, the amount of the ink of one color applied in each timing is 0.7 μl/cm<SP>2</SP>or below) is carried out at least twice in a range of the application of the ink of one color of 4,000 msec or below with a time difference of 200 msec or above. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an inkjet image forming method and an inkjet recording apparatus.

  With the widespread use of inkjet recording systems, there is a demand for higher recording speed and improved quality of recorded images such as characters and photographs when recording on plain paper by inkjet recording.

  For example, it is required to record various information posted on office documents, digital camera photographic images, homepages, etc. on plain paper at high speed on both sides. Further, a clear image quality such as a recorded image obtained by recording with a laser beam printer is required. Furthermore, when a character image is printed, a high image density can be obtained, and it is required that the character image is sharp even for small lowercase characters and suppresses the collapse of the character.

  Further, in a recorded image such as a color photograph or table, it is also required to suppress bleeding (bleeding) at a color boundary portion caused by contact of a plurality of recording inks of different colors.

That is, the requirements for the inkjet recording system are as follows.
1) Fast ink fixing.
2) Bleeding between inks in the recorded image is suppressed.
3) The recorded images have good water resistance and fixability.
4) The recorded image is clear with high density.
5) Even when a small character is printed, the character is sharp and the collapse of the character is suppressed.
6) Back-through of recorded images is suppressed.

  In response to such demands, it is known that super penetrating ink having high permeability to plain paper is effective for the demands 1) to 3). Super-penetrating ink penetrates quickly after landing on plain paper, and the color material is fixed, so that high-speed fixing is possible. In addition, bleeding is suppressed because it does not mix with other ink on the plain paper surface. Further, since the fixed color material is fixed in the deep part of plain paper, the water resistance and the fixing property are good.

  However, since the coloring material is fixed in the deep part of plain paper, the recording density decreases, the image becomes unclear, and when small characters are printed, the characters are crushed, and the recorded image shows through. It was. That is, the above requirements 4) to 6) could not be satisfied.

  Japanese Patent Application Laid-Open No. H10-228561 discloses a technique for promoting the volatilization of ink by heating plain paper and fixing the color material on the surface layer before the super-penetrable ink penetrates into the deep part of the plain paper.

Patent Document 2 discloses 2) a technique for suppressing bleeding by a so-called multi-pass method in which printing is performed in a plurality of times. Further, since the recording density is lowered at that time, 4) a technique for suppressing the reduction of the recording density by ejecting more ink than in the normal single pass is disclosed.
JP-A-11-129460 JP 05-031919 A

  However, since the method described in Patent Document 1 requires an auxiliary machine such as a heater, there is a case where the inkjet recording apparatus is increased in size and power consumption is increased.

  Further, the method described in Patent Document 2 causes a new problem that the strikethrough of 6) becomes more noticeable and the ink consumption increases due to an increase in the amount of ink applied.

  As described above, it is difficult for the conventional inkjet image forming method to achieve both high-speed printing and high-quality image recording, and there is no inkjet image forming method that can satisfy all of the problems 1) to 6) at the same time. Absent.

  An object of the present invention is to provide an ink jet image forming method and an ink jet recording apparatus that sufficiently satisfy the above problems 1) to 6) at the same time without using an auxiliary machine or the like and without increasing the amount of ink applied. .

The above object is achieved by the present invention described below. That is, the present invention is an ink jet image forming method for forming an image by applying an ink of one color to plain paper by an ink jet recording method, and the ink of the one color to be applied is 0.5 pl or more and 6.0 pl. The following quantification contains a self-dispersing pigment, an organic carboxylate, water, a water-soluble compound having a hydrophilicity / hydrophobicity coefficient of 0.26 or more as defined by the following formula (A), and a surface tension of 34 mN. / M or less, the total amount of ink applied to the basic matrix for forming the image is 5.0 μl / cm ² or less, and the duty of the one color ink applied to the basic matrix is 80 When the duty ratio is equal to or greater than% duty, the application of one color ink to the basic matrix is within the range of 4000 msec or less, and the following application step (B) is performed within each range within each application step ( ) Is an inkjet image forming method, which comprises carrying out by a plurality of times the time difference as above 200msec between.
Formula (A)

Application process (B)
The application of the one color ink to the basic matrix is performed at a plurality of times within a range of 1 msec or more and 200 msec or less, and the application amount of the one color ink applied at each timing is 0.7 μl / cm ^2. Steps to be described below.

According to a second aspect of the present invention, there is provided an ink jet image forming method for forming an image by applying inks of a plurality of colors to plain paper by an ink jet recording method, wherein the ink is applied to a basic matrix for forming the image. 1 color ink to the basic matrix when the total applied amount is 5.0 μl / cm ² or less and the duty of at least one color of the ink applied to the basic matrix is 80% duty or more. Is applied within a range of 4000 msec or less, and the following application step (B) is performed a plurality of times within the above range with a time difference between each application step (B) being 200 msec or more. Is a quantification of 0.5 pl or more and 6.0 pl or less, and is defined by self-dispersing pigment, organic carboxylate, water, and the above formula (A) Hydrophilicity-hydrophobicity coefficients contain 0.26 or more water-soluble compound, an inkjet image forming method, wherein the surface tension is less than 34 mN / m.

According to a third aspect of the present invention, there is provided an ink jet recording apparatus having a recording head for forming an image by applying one color ink to plain paper by an ink jet recording method, wherein the one color ink applied is 0 0.5 pl or more and 6.0 pl or less, a self-dispersing pigment, an organic carboxylate, water, and a water-soluble compound having a hydrophilicity / hydrophobicity coefficient defined by the above formula (A) of 0.26 or more And the surface tension is 34 mN / m or less, the total amount of ink applied to the basic matrix for forming the image is 5.0 μl / cm ² or less, and the first applied to the basic matrix When the duty of the color ink is 80% duty or more, the application of one color ink to the basic matrix is within the range of 4000 msec or less and within the range, the following application step (B Which is the ink jet recording apparatus characterized by comprising a control mechanism carried out by a plurality of times the time difference between each application step (B) as above 200 msec.

According to a fourth aspect of the present invention, there is provided an ink jet recording apparatus comprising a recording head for forming an image by applying inks of a plurality of colors to plain paper by an ink jet recording method, and a basic matrix for forming the image When the total amount of ink applied to the ink is 5.0 μl / cm ² or less and the duty of at least one of the inks applied to the basic matrix is 80% duty or more, There is a control mechanism for applying one color of ink within a range of 4000 msec or less, and performing the following application step (B) within the above range multiple times with a time difference between each application step (B) being 200 msec or more. The one color ink to be applied has a fixed amount of 0.5 pl or more and 6.0 pl or less, and is a self-dispersing pigment and an organic carboxylate , Water, hydrophilicity-hydrophobicity coefficient defined by the above formula (A) is contained 0.26 or more water soluble compounds is an ink jet recording apparatus characterized by the surface tension is less than 34 mN / m.

  According to the ink jet image forming method and the ink jet recording apparatus of the present invention, when ink is applied to plain paper, the ink can be fixed at high speed. In addition, even when a small letter is printed with sufficient water resistance and image density, the characters are sharp and it is possible to suppress the collapse of the characters. These are remarkable effects that cannot be predicted from the prior art, and are manifested only when all of the above-described constituent requirements of the present invention are obtained, as well as ink and the recording method.

  Hereinafter, the present invention will be described in more detail with reference to preferred embodiments.

  The present inventors have provided an inkjet image forming method suitable for high-speed printing and double-sided printing, which provides a clear and high-quality image that is fixed on plain paper at high speed, has sufficient water resistance and image density, and An ink jet recording apparatus was examined. As a result, it is possible to precisely control the ink composition, ink physical properties, ink amount controlled on the recording device side, and ink split application conditions after solid-liquid separation of the pigment and aqueous medium after landing on plain paper. The inventors have found that these act synergistically to achieve the object.

  Hereinafter, the present invention will be described in more detail with reference to preferred embodiments.

  In the present invention, the amount of ink applied at one time is a fixed amount of 0.5 pl or more and 6.0 pl or less. Preferably it is 1.0 pl or more, More preferably, it is 1.5 pl or more. Moreover, Preferably it is 5.0 pl or less, More preferably, it is 4.5 pl or less. If it is less than 0.5 pl, the image fixability and water resistance may be inferior. If it exceeds 6.0 pl, when a small character of about 2 points (1 point≈0.35 mm) to about 5 points is printed, the character may be crushed due to the character thickening.

  Since the ink ejection volume greatly affects the see-through of the ink, it is also important in terms of application to double-sided printing. In ordinary paper, pores having a size of 0.1 μm to 100 μm are generally distributed centering on 0.5 μm to 5.0 μm. In the present invention, plain paper refers to commercially available copy paper such as medium-quality paper and PPC paper, bond paper, and the like that are used in large quantities in printers and copiers. Penetration phenomenon of water-based ink into plain paper includes fiber absorption in which the ink is directly absorbed into the cellulose fiber itself of plain paper and pores that are absorbed into the pores (pores) formed between the cellulose fibers. Broadly divided into absorption. As will be described later, the ink used in the present invention is an ink mainly composed of pore absorption. For this reason, when the ink used in the present invention is applied to plain paper and a part of the ink comes into contact with large pores of about 10 μm or more existing on the plain paper surface, the ink is larger in accordance with the Lucas-Washburn formula. It is absorbed and penetrates into concentrated pores. As a result, the ink penetrates particularly deeply in this portion, which is extremely disadvantageous in developing high color on plain paper. On the other hand, the smaller the ink is, the lower the probability of contact with the larger pore per drop of ink, so it is less likely to be concentrated and absorbed into the larger pore. Furthermore, even if it contacts a large pore, if the ink is small, only a small amount of ink penetrates deeply. As a result, an image obtained on plain paper is highly colored.

  The critical value of the upper limit of 6.0 pl for the ink was experimentally obtained according to the present invention. Assuming that 6.0 pl of ink is a sphere, when it lands on plain paper, the diameter is about 23 μm. Considering the distribution state of large pores of about 10 μm or more on plain paper, if the ink is less than this diameter, the contact probability at the time of landing of the large pores and the ink is lowered, and a preferable state in which deep penetration does not occur It is thought that it becomes.

  In the present invention, the fixed amount of ink means ink ejected in a state where the nozzle structure constituting the recording head is not changed between the nozzles and the drive energy to be applied is not changed. That is, in such a state, even if there is a slight variation in ejection due to manufacturing errors of the apparatus, the amount of ink applied is quantitative. By determining the amount of applied ink, the penetration depth of the ink is stabilized, the image density of the recorded image is high, and the uniformity of the image is improved. On the other hand, according to a system or the like based on the premise that the amount of applied ink is changed, the ink is not fixed, and inks of different volumes are mixed, so that the dispersion of the ink penetration depth becomes large. In particular, in a high-duty portion of a recorded image, due to variations in penetration depth, there are places where the image density of the recorded image is low, and the uniformity of the image is not good.

  As an application method suitable for quantifying the ink, a thermal ink jet recording method in which the ink is applied by the action of thermal energy is preferable from the viewpoint of the ejection mechanism. That is, according to the thermal ink jet recording method, variation in the penetration depth of the ink is suppressed, and the recorded image has a high density and good uniformity. Furthermore, the thermal ink jet recording method is suitable for increasing the number of nozzles and increasing the density as compared with the method of applying ink using a piezoelectric element, and is also suitable for high-speed recording.

  An object of the present invention is required when an image in which the duty of one color ink is 80% duty or more is formed in a basic matrix for forming an image. The minimum part for calculating the duty is 50 μm × 50 μm. An image having an 80% duty or more is an image formed by applying ink to 80% or more of the grids in the matrix of the portion for calculating the duty. The size of the grid is determined by the resolution of the basic matrix. For example, when the resolution of the basic matrix is 1200 dpi × 1200 dpi, the size of one lattice is 1/1200 inch × 1/1200 inch.

  An image in which the duty of one color ink is 80% duty or more in the basic matrix will be described. Note that one color in the present invention is preferably the same one color and one color tone, but one color is used even if there is a slight difference in density or the like. That is, in the case of using four colors of black, cyan, magenta, and yellow, this is an image having at least one of these colors and having a portion that is 80% duty or more in the basic matrix. On the other hand, an image in which the duty of one color ink does not exceed 80% duty in the basic matrix has relatively little overlap between the landed inks, and problems such as collapsed characters occur even if the printing process is not devised. Often not.

  The basic matrix of the present invention can be freely set by a recording device or the like. The resolution of the basic matrix is preferably 600 dpi or higher, and more preferably 1200 dpi or higher. Moreover, 4800 dpi or less is preferable. If the resolution is within this range, the vertical and horizontal directions may be the same or different.

The present invention is also required when forming an image in which the total amount of ink applied to the basic matrix is 5.0 μl / cm ² or less. That is, in the case of using four colors of black, cyan, magenta, and yellow, the image is such that the total applied amount of ink of all these colors is 5.0 μl / cm ² or less. The part for calculating the total applied amount is the same as the part for calculating the duty. When forming an image having a portion in which the total amount of ink of all colors exceeds 5.0 μl / cm ² , a clear image may not be obtained, or back-through may occur and may not be suitable for double-sided printing. is there. Further, when a more severe anti-through-through property is required for a thin paper having a basis weight of 70 g / m ² or less and a paper thickness of 100 μm or less, the total applied amount is 3.0 μl / cm ² or less. Images are preferred. More preferably, the image is 1.4 μl / cm ² or less. With such an image, the effect of the present invention can be more remarkably exhibited.

In the present invention, the total amount of ink applied to the basic matrix for forming an image is 5.0 μl / cm ² or less, and the duty of at least one of the inks applied to the basic matrix is 80% duty. In such a case, the application of one color ink to the basic matrix is within a range of 4000 msec or less, and within the above range, the following application process (B) is set to have a time difference of 200 msec or more between the application processes (B). Do this multiple times.

Application process (B)
The application of the one color ink to the basic matrix is performed at a plurality of times within a range of 1 msec or more and 200 msec or less, and the application amount of the one color ink applied at each timing is 0.7 μl / cm ^2. Steps to be described below.

The amount of the one color ink applied at each timing of the applying step B is 0.7 μl / cm ² or less. Preferably it is 0.6 microliter / cm < ² > or less, More preferably, it is 0.5 microliter / cm < ² > or less. Further, preferably 0.1 [mu] l / cm ² or more. If the amount of applied ink of one color at each timing exceeds 0.7 μl / cm ² , there may be a case where behind-the-scenes, character collapse, or bleeding occurs.

  In the present invention, when the image in the basic matrix is formed, the applying step (B) is performed two or more times. By printing in this way, the image density can be greatly improved, and an effect of remarkably preventing the show-through can be obtained.

  In general, if all of the super-penetrating ink with high penetrability is applied at one time, the amount of ink applied per time increases, and the ink penetrates deep into the plain paper before the ink solvent volatilizes. It becomes a trend. A schematic diagram of a cross section of plain paper on which an image is formed by such a method is shown in FIG. As shown in the schematic diagram of FIG. 1, since the pigment 11 penetrates to the deep part of the plain paper 12 and is fixed, the density of the pigment fixed on the surface of the plain paper becomes low, and it is difficult to obtain a clear image. Further, since the pigment is fixed in the deep part of the plain paper, that is, in the vicinity of the back surface, the back-through is likely to occur. FIG. 2 shows a schematic diagram of a cross section of plain paper when the ink application amount necessary for image formation, that is, the ink application amount per unit area is increased. In this case, the density of the pigment 11 fixed in the vicinity of the surface layer of the plain paper 12 becomes high and it becomes possible to obtain a clear image. It's easy to do.

  On the other hand, the present invention uses ink that quickly solid-liquid separates the pigment and the aqueous medium, divides the ink into a plurality of application steps, and controls the ink application amount per time. As a result, the volatilization of the ink solvent is promoted, and the ink can be fixed to the surface layer before penetrating into the deep portion of the plain paper. FIG. 3 shows a schematic view of a cross section of plain paper when an image is formed according to the present invention. As shown in FIG. 3, since the pigment 11 does not penetrate into the deep part of the plain paper 12 and is fixed only on the surface layer, the pigment density on the surface layer becomes high and a clear image can be obtained. Further, since the pigment density in the deep part of the plain paper, that is, in the vicinity of the back surface is low, it is possible to suppress the see-through. Further, the image forming method of the present invention has an advantage that the consumption of ink can be suppressed because it is not necessary to increase the total applied amount of ink in order to obtain a high image density.

  In the present invention, the ink application of one color in the application step (B) is performed with a time difference of 1 msec or more between each timing. Thereby, the color development and the character quality of lowercase letters are remarkably improved. This is because when printing is divided into a plurality of times, a certain period of time is required from the time when the first droplet, when ink is applied to the basic matrix, to the recording medium, until the last droplet lands. It is shown that it is preferable to leave a gap. When the next droplet lands before the first droplet is fixed on plain paper, the ink droplets are combined to form a large droplet (beading). Since the large droplets penetrate deeply from the large pores on the plain paper, the color developability deteriorates. Moreover, since the large ink droplet spreads in the horizontal direction along the direction of the fiber in the plain paper, the sharpness of the character is lost. Moreover, even if the time difference between the timings in the applying step (B) is set to a time longer than 200 msec, there is not much change from the effect when the time difference is set to 200 msec. Therefore, in the present invention, the upper limit is set to 200 msec in order to achieve high-speed printing.

  Furthermore, in this invention, the time difference between each provision process (B) shall be 200 msec or less. Thus, by providing the time between the application steps (B), a very high image density and a clear image can be obtained. In order to achieve high-speed printing, the time from the start to the end of ink application to the basic matrix until the final image is completed is set to 4000 msec or less.

  In the present invention, the image is formed by performing the applying step (B) a plurality of times at least twice. Preferably it is 4 times or less, and particularly preferably 2 times. If the application step (B) is performed more than 4 times, it is effective for suppressing bleeding and printing with good small letters, but the concealment ratio of the ink on the plain paper surface is lowered and the color developability is deteriorated. It becomes a trend.

  In order to achieve such application timing, it is preferable to apply the ink of one color to the basic matrix by the same recording head at all timings.

  Next, the ink of the present invention and the ink jet recording apparatus will be described.

<Ink>
(Coloring material)
The color material used in the ink used in the present invention is a self-dispersing pigment. Black, cyan, magenta, and yellow are the basic ink sets when forming an image using multiple colors of ink, but red, blue, green, gray, light cyan, light magenta, etc. are added. May be. The pigments contained in these inks are also preferably self-dispersing pigments. When a self-dispersing pigment is used in the image forming process according to the present invention, good water resistance is exhibited. Further, the self-dispersing pigment exhibits a synergistic effect with the water-soluble compound used in the present invention, and the solid-liquid separation proceeds smoothly after the ink has landed on the paper. Thereby, color developability is excellent. In the present invention, by using a self-dispersing pigment, it acts synergistically with the ink application conditions, so that, for example, solid-liquid separation can be performed more smoothly than when a resin dispersion type pigment is used, and the pigment itself Becomes difficult to penetrate deeply into plain paper, and the color developability is very good.

  The self-dispersing pigment is basically a pigment which does not require a dispersant and is water-solubilized by introducing a water-soluble functional group directly or via another atomic group on the pigment surface. Various types of pigments can be used before the water-solubilization.

Carbon black is preferably used as the pigment used in the black ink. For example, carbon black pigments such as furnace black, lamp black, acetylene black and channel black. As the characteristics of the carbon black pigment, the following characteristics are preferable. Primary particle size is 15 nm to 40 nm, specific surface area by BET method is 50 m ² / g or more, 400 m ² / g or less, DBP oil absorption is 40 ml / 100 g or more, 200 ml / 100 g or less, volatile content is 0.5 wt% or more and 10 wt. % Or less.

  As the pigment used in the color ink, an organic pigment is preferably used. Specifically, the following pigments can be mentioned. Insoluble azo pigments such as toluidine red, toluidine maroon, Hansa yellow, benzidine yellow and pyrazolone red. Water-soluble azo pigments such as Ritolol Red, Helio Bordeaux, Pigment Scarlet, and Permanent Red 2B. Derivatives from vat dyes such as alizarin, indanthrone and thioindigo maroon. Phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green. Quinacridone pigments such as quinacridone red and quinacridone magenta. Perylene pigments such as perylene red and perylene scarlet. Isoindolinone pigments such as isoindolinone yellow and isoindolinone orange. Imidazolone pigments such as benzimidazolone yellow, benzimidazolone orange, and benzimidazolone red. Pilanthrone pigments such as pyranthrone red and pyranthrone orange. Thioindigo pigment. Condensed azo pigment. Thioindigo pigment. Diketopyrrolopyrrole pigment. Pigments such as flavanthrone yellow, acylamide yellow, quinophthalone yellow, nickel azo yellow, copper azomethine yellow, perinone orange, anthrone orange, dianthraquinonyl red, dioxazine violet.

  The organic pigment is indicated by a color index (CI) number. C. I. Pigment Yellow 12, 13, 14, 17, 20, 24, 55, 74, 83, 86, 93, 97, 98. C. I. Pigment Yellow 109, 110, 117, 120, 125, 128, 137, 138, 139, 147, 148, 150, 151, 153, 154, 155, 166, 168, 180, 185. C. I. Pigment Orange 16, 36, 43, 51, 55, 59, 61, 71. C. I. Pigment Red 9, 48, 49, 52, 53, 57, 97, 122, 123, 149, 168, 175, 176, 177, 180, 192. C. I. Pigment Red 202, 209, 215, 216, 217, 220, 223, 224, 226, 227, 228, 238, 240.254, 255, 272. C. I. Pigment violet 19, 23, 29, 30.37, 40, 50. C. I. Pigment Blue 15, 15: 1, 15: 3, 15: 4, 15: 6, 22, 60, 64. C. I. Pigment Green 7, 36. C. I. Pigment Brown 23, 25, 26. The above can be illustrated. Among these pigments, the following pigments are more preferable. Examples of yellow pigments include C.I. I. Pigment Yellow 13, 17, 55, 74, 93, 97, 98, 110, 128, 139, 147, 150, 151, 154, 155, 180, 185. Examples of magenta pigments include C.I. I. Pigment red 122, 202, 209, C.I. I. Pigment violet 19. Examples of cyan pigments include C.I. I. Pigment Blue 15: 3, 15: 4. Of course, pigments other than those described above can also be used.

The hydrophilic group introduced into the self-dispersing pigment using the above pigment as a raw material can be directly bonded to the surface of the pigment. Alternatively, another atomic group may be interposed between the pigment surface and the hydrophilic group as described above, and the hydrophilic group may be indirectly bonded to the pigment surface. Examples of the anionic functional group to be introduced include the following. A hydrophilic group such as —COO (M), —SO ₃ (M), —PO ₃ (M) ₂ (wherein M represents a hydrogen atom, an alkali metal, ammonium or organic ammonium) is bonded. It has been made. Among those expressed as “M” in the hydrophilic group, specific examples of the alkali metal include Li, Na, K, Rb and Cs. Specific examples of organic ammonium include the following. Examples thereof include methylammonium, dimethylammonium, trimethylammonium, ethylammonium, diethylammonium, triethylammonium, monohydroxymethyl (ethyl) ammonium, dihydroxymethyl (ethyl) ammonium, trihydroxymethyl (ethyl) ammonium, triethanolammonium and the like. Among these, ammonium is particularly preferable for improving color developability and lowercase quality.

Specific examples of the intervening atomic group include, for example, a linear or branched substituted or unsubstituted alkylene group having 1 to 12 carbon atoms, a substituted or unsubstituted phenylene group, a substituted or unsubstituted group, and the like. A naphthylene group is mentioned. As a substituent of an alkylene group, a phenylene group, and a naphthylene group, a hydroxyl group or a C1-C6 linear or branched alkyl group is mentioned, for example. Specific examples of the combination of another atomic group and the hydrophilic group, for _{example, -C 2 H 4 -COO (M} ), - Ph-SO 3 (M), - Ph-COO (M), - Ph -PO _{3 (M) 2,} etc. (where, Ph is a phenyl group), and the like.

  Specific examples of the production method for directly introducing a water-soluble group onto the surface of the pigment include a method of oxidizing carbon black with sodium hypochlorite. According to this method, a —COO (M) group or a lactone group, which is a hydrophilic group, can be introduced on the surface of carbon black, and can be used particularly well in the present invention.

  When a cationic group is introduced as the water-soluble group, for example, at least one aromatic group such as a phenyl group, benzyl group, phenacyl group, or naphthyl group, or a heterocyclic group such as a pyridyl group, and at least one cation It preferably consists of a sex group. More preferably, the cationic group bonded to the surface of carbon black is a quaternary ammonium group.

  The average particle size of the self-dispersing pigment used in the present invention is determined by a dynamic light scattering method in a liquid, preferably 60 nm or more, more preferably 70 nm or more, and further preferably 75 nm or more. . Moreover, it is preferably 145 nm or less, more preferably 140 nm or less, and further preferably 130 nm or less. As a specific method for measuring the average particle size, FPAR-1000 (manufactured by Otsuka Electronics Co., Ltd., cumulant method analysis), Nanotrack UPA 150EX (manufactured by Nikkiso Co., Ltd., 50% integrated value) using laser light scattering is used. ) Etc. In the present invention, the average particle size is defined by the scattering average particle size.

  Two or more kinds of pigments can be combined in the same ink as necessary.

  The amount of the above self-dispersing pigment added to the ink is preferably 0.5% by mass or more, more preferably 1% by mass or more, and further preferably 2% by mass or more with respect to the total amount of the ink. Further, it is preferably 15% by mass or less, more preferably 10% by mass or less, and further preferably 8% by mass or less.

(Organic carboxylate)
The ink used in the present invention contains an organic carboxylate. By containing the organic carboxylate, the image density and the character quality at the time of lowercase printing are greatly improved. The reason for this is as follows. When the organic carboxylate is used in combination, the organic carboxylate promotes the precipitation of the pigment after the ink droplet is driven into the recording medium, so that the solid-liquid separation that occurs between the pigment and the aqueous medium is promoted. As a result, the pigment is fixed on the surface layer and can contribute to high color development. Since the time from the arrival of the ink droplets to the recording medium to the fixing is shortened, bleeding can be suppressed, and the character quality at the time of lowercase printing is improved. Further, the power to conceal the sizing agent scattered on the surface of the plain paper is increased, and the effect of preventing the so-called white spot phenomenon in the solid recording portion is recognized.

  The organic carboxylate is not particularly limited as long as 1 to 3 carboxyl groups are bonded to a skeleton having a carbon atom. Specific examples include salts of citric acid, succinic acid, benzoic acid, acetic acid, propionic acid, phthalic acid, oxalic acid, tartaric acid, gluconic acid, tartronic acid, maleic acid, malonic acid, adipic acid and derivatives thereof. It is. Of these, salts with dicarboxylic acids such as phthalic acid, succinic acid, adipic acid, tartaric acid and maleic acid are preferred, and phthalate is particularly preferred. Other preferred organic carboxylates include salts with aromatic carboxylic acids such as benzoic acid and phthalic acid. Further, the pKa value of the organic carboxylic acid is more preferably 2.5 or more and 5.5 or less. When the organic carboxylic acid has two or more carboxylic acid groups, an organic carboxylic acid in which the pKa value of at least one of the carboxylic acid groups is 2.5 or more and 5.5 or less is more preferable. By using these organic carboxylates in combination, the effect of the recording method of the present invention is increased.

  As the counter ion to be a salt, alkali metal, ammonium, organic ammonium, or the like can be used as in the case of the counter ion of the self-dispersing pigment. The same counter ion of the self-dispersing pigment added in the same ink is preferably used as the counter ion of the organic carboxylic acid.

  Specific examples of the alkali metal as the counter ion include Li, Na, K, Rb, and Cs. Moreover, the following are mentioned as a specific example of organic ammonium. For example, methylammonium, dimethylammonium, trimethylammonium, ethylammonium, diethylammonium, triethylammonium, monohydroxymethyl (ethyl) ammonium, dihydroxymethyl (ethyl) ammonium, trihydroxymethyl (ethyl) ammonium, triethanolammonium and the like. Among them, an organic carboxylic acid ammonium salt is particularly preferable for improving the color developability and the lower case quality.

  The amount of these organic carboxylates added to the ink is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and further preferably 0.2% by mass or more. Moreover, Preferably it is 3 mass% or less, More preferably, it is 2 mass% or less, More preferably, it is 1 mass% or less.

(Aqueous medium)
The ink according to the present invention contains water as an essential component, but the content of water in the ink is preferably 30% by mass or more based on the total mass of the ink. Moreover, it is preferable that it is 95 mass% or less. Furthermore, in addition to water, a water-soluble compound is contained to obtain an aqueous medium. This water-soluble compound is a highly hydrophilic compound that is mixed with water at a concentration of 20% by mass without being phase separated from water. Further, those that easily evaporate from the standpoint of solid-liquid separation and clogging prevention are not preferred, and materials having a vapor pressure at 20 ° C. of 0.04 mmHg or less are preferred.

The ink according to the present invention includes a water-soluble compound having a hydrophilicity / hydrophobicity coefficient defined by the following formula (A) of 0.26 or more as an essential component. Further, depending on the recording medium, the ink containing a water-soluble compound having a hydrophilicity / hydrophobicity coefficient defined by the formula (A) of 0.26 or more and 0.37 or less and a water-soluble compound of 0.37 or more is lowercase. This is preferable in order to improve printing characteristics. In addition, depending on the recording medium, it contains a water-soluble compound having a hydrophilicity / hydrophobicity coefficient of 0.26 or more and 0.37 or less, and two or more water-soluble compounds having a hydrophilicity / hydrophobicity coefficient of 0.37 or more, thereby printing lowercase letters. In order to improve the characteristics, it may be a more preferable mode. These water-soluble compounds having a hydrophilicity / hydrophobicity coefficient of 0.37 or more have a relatively low affinity with water, self-dispersing pigments and cellulose fibers after the ink has landed on the paper, so that solid-liquid separation from the self-dispersing pigments is possible. Since it has a role to promote strongly, it is considered that the above-mentioned effects can be obtained depending on the recording medium.
Formula (A)

What is the water activity value in the formula?
Water activity value = (water vapor pressure of aqueous solution) / (water vapor pressure of pure water)
It is shown by. There are various methods for measuring the water activity value, and none of the methods is specified, but the chilled mirror dew point measurement method is particularly suitable for the material measurement used in the present invention. The values in this specification are obtained by measuring a 20% aqueous solution of each water-soluble compound at 25 ° C. using Aqua Arab CX-3TE (manufactured by DECAGON) according to this measurement method.

  According to Raoul's law, the vapor pressure drop rate of dilute solutions is equal to the solute mole fraction and is independent of the solvent and solute type, so the water mole fraction and water activity value in the aqueous solution are equal. . However, when the water activity value of aqueous solutions of various water-soluble compounds is measured, the water activity value often does not coincide with the molar fraction of water.

  When the water activity value of the aqueous solution is lower than the molar fraction of water, the water vapor pressure of the aqueous solution is smaller than the theoretical calculation value, and the evaporation of water is suppressed by the presence of the solute. From this, it is understood that the solute is a substance having a high hydration power. Conversely, when the water activity value of the aqueous solution is higher than the molar fraction of water, the solute is considered to be a substance having a low hydration power.

  The inventors of the present invention have the effect that the hydrophilicity or hydrophobicity of the water-soluble compound contained in the ink has a large influence on the promotion of solid-liquid separation between the self-dispersing pigment and the aqueous medium, and on various ink performances. I focused on. From this, a coefficient called hydrophilicity / hydrophobicity coefficient shown in the formula (A) was defined. The water activity value is measured at a uniform concentration of 20% by weight for various water-soluble compounds, but by converting to the formula (A), the molecular weight of the solute is different and the molar fraction of water is different. However, a relative comparison of the degree of hydrophilicity or hydrophobicity of various solutes is possible. Further, since the water activity value of the aqueous solution does not exceed 1, the maximum value of the hydrophilicity / hydrophobicity coefficient is 1.

  Table 1 shows the hydrophilicity / hydrophobicity coefficient of the water-soluble compound obtained by the formula (A). However, the water-soluble compound of the present invention is not limited to these.

  As the water-soluble compound, a water-soluble compound having a desired hydrophilicity / hydrophobicity coefficient can be selected from various water-soluble compounds having suitability as inks for inkjet recording.

  In the inkjet image forming method of the present invention, the present inventors examined the relationship between the water-soluble compound contained in the ink and the lower-case printing characteristics such as bleeding and character thickening. As a result, with respect to the ink containing the self-dispersing pigment of the present invention and an ammonium salt of an organic carboxylic acid, when a water-soluble compound having a hydrophilicity / hydrophobicity coefficient of 0.26 or more and having a small hydrophilic tendency is used, the above characteristics are extremely good. I found out that Among them, a class of glycol structures having a carbon number not substituted with a hydrophilic group beyond the number of carbon atoms substituted with a hydrophilic group in the glycol structure was particularly preferable. These water-soluble compounds have a relatively low affinity with water, self-dispersing pigments, and cellulose fibers after the ink has landed on the paper, and are thought to play a role in strongly promoting solid-liquid separation from the self-dispersing pigments. It is done.

  Trimethylolpropane is particularly preferred when the solvent in the ink is a single system. When the water-soluble compound having a hydrophilicity / hydrophobicity coefficient of 0.37 or more is used, the water-soluble compound is preferably a diol having 4 to 7 carbon atoms such as hexanediol, pentanediol, and butanediol. More preferred are diols having 6 carbon atoms, and particularly preferred are 1,2-hexanediol and 1,6-hexanediol. The mixing ratio when containing two or more water-soluble compounds having a hydrophilicity / hydrophobicity coefficient of 0.37 or more is not particularly limited, but 1,2-hexanediol and 1,6-hexanediol are 1/10 to 10 / It is preferable to use the ratio of 1. More preferably, 1,2-hexanediol and 1,6-hexanediol are used in a ratio of 1/5 to 5/1. Moreover, when using 2 or more types of water-soluble compounds with a hydrophilicity-hydrophobicity coefficient of 0.37 or more, it is preferable that each hydrophilicity coefficient has a difference of 0.1 or more.

  The total content of the water-soluble compounds in the ink is preferably 5% by mass or more, more preferably 6% by mass or more, and further preferably 7% by mass or more. Further, it is preferably 40% by mass or less, more preferably 35% by mass or less, and further preferably 30% by mass or less. When the water-soluble compound having a hydrophilicity / hydrophobicity coefficient of 0.37 or more is included, the total content of the water-soluble compounds is preferably 3% or more, and more preferably 5% or more.

(Surfactant)
The ink used in the present invention preferably contains a surfactant in the ink in order to obtain a more balanced ejection stability. Among these, it is preferable to contain a nonionic surfactant. Among the nonionic surfactants, polyoxyethylene alkyl ethers and ethylene oxide adducts of acetylene glycol are particularly preferable. These nonionic surfactants have an HLB value (Hydrophile-Lipophile Balance) of 10 or more. The content of the surfactant used in this manner is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and further preferably 0.5% by mass or more in the ink. Moreover, Preferably it is 5 mass% or less, More preferably, it is 4 mass% or less, More preferably, it is 3 mass% or less.

(Other additives)
In addition to the above-described components, the ink according to the present invention includes, as necessary, a viscosity modifier, an antifoaming agent, an antiseptic, and an antifungal agent in order to obtain an ink having a desired physical property value. Antioxidants, penetrants and the like can be added.

(surface tension)
The surface tension of the ink used in the present invention is 34 mN / m or less. The surface tension of the ink is more preferably 33 mN / m or less, and further preferably 32 mN / m or less. Further, it is preferably 27 mN / m or more, more preferably 28 mN / m or more, and further preferably 29 mN / m or more. By controlling the surface tension of the ink within this range, the effect of the ink of the present invention is maximized.

  Unlike plain paper, glossy paper and matte paper, which are dedicated to inkjet, have a porous ink-receiving layer formed on the paper surface, so that ink can penetrate quickly without being affected by the surface tension of the ink. Progresses.

  However, since plain paper is internally and / or externally added with a water-repellent sizing agent, ink penetration is often inhibited. That is, plain paper has a lower critical surface tension, which is an index of whether or not the surface can be quickly wetted by ink, than that of inkjet-only paper.

  If the surface tension of the ink is higher than 34 mN / m, it will be higher than the critical surface tension of plain paper. Therefore, even if the ink lands on the paper, it does not get wet immediately and does not start to penetrate quickly. When the surface tension is high, even if the wettability with the paper is slightly improved and the contact angle between the ink and the paper is reduced, it is difficult to fix at high speed. Furthermore, the fixability tends to deteriorate. When the surface tension of the ink is 34 mN / m or less, pore absorption is mainly used, and when it is higher than 34 mN / m, fiber absorption is mainly used. With respect to the absorption rate of ink into paper by these two types of absorption, pore absorption is overwhelmingly faster. Therefore, in the present invention, high-speed fixing is realized by using ink mainly composed of pore absorption.

(viscosity)
The viscosity of the ink used in the present invention is preferably 6.0 mPa · s or less. When using an apparatus for ink jet recording by using thermal energy, if the viscosity is higher than this, ink supply to the nozzles may not be in time, and an unclear image may be recorded. The viscosity of the ink is more preferably 5.0 mPa · s or less, and still more preferably 4.0 mPa · s or less.

<Inkjet recording apparatus>
Next, the ink jet recording apparatus according to the present invention will be described. The ink jet recording apparatus of the present invention is equipped with a recording head for applying a fixed amount of ink of 0.5 pl to 6 pl. The recording head of the ink jet recording apparatus of the present invention is preferably a recording head that applies thermal energy to ink. Such a recording head is more suitable for increasing the density of nozzles than a recording head that ejects ink using a piezoelectric element. Further, since it is excellent in determining the amount of ink, it is excellent in that the dispersion of the ink penetration depth is suppressed and the uniformity of the recorded image is improved.

  As a typical configuration and principle of a recording head that applies thermal energy to ink, for example, the basic principle disclosed in US Pat. No. 4,723,129 and US Pat. No. 4,740,796 is used. Are preferably performed. This method can be applied to both a so-called on-demand type and a continuous type. Of these, the on-demand type is advantageous. In other words, in the case of the on-demand type, a rapid temperature rise exceeding the nucleate boiling corresponding to the recorded information is applied to the electrothermal transducer disposed corresponding to the sheet or liquid path holding the ink. At least one driving signal is applied. By this application, heat energy is generated in the electrothermal transducer, and film boiling occurs on the heat acting surface of the recording head. As a result, bubbles in the ink corresponding to this drive signal are formed. Can do. By the growth and contraction of the bubbles, ink is ejected through the ejection opening to form at least one droplet. It is more preferable that the drive signal has a pulse shape because the growth and contraction of bubbles is performed immediately and appropriately, so that the amount of ink is fixed and ink ejection excellent in responsiveness can be achieved.

  FIG. 4 is a front view showing an outline of one embodiment of the ink jet recording apparatus according to the present invention. The carriage 20 is mounted with a recording head that performs ink jet recording, and has ink discharge ports 211 to 215 as a plurality of nozzle rows. As an aspect of the configuration in which black ink is applied in two passes in one pass, 211, 212, 213, 214, and 215 are black (K), cyan (C), magenta (M), and yellow (Y), respectively. And a mode of ejecting black (K) ink.

  Each of the ink cartridges 221 to 225 includes a recording head, ink discharge ports 211 to 215, and an ink tank for supplying ink thereto.

  Reference numeral 40 denotes a density sensor. The density sensor 40 is a reflection type density sensor, and is configured to detect the density of the test pattern recorded on the recording medium while being installed on the side surface of the carriage 20.

  A control signal or the like to the recording head is transferred via the flexible cable 23.

  The recording medium 24 exposed from cellulose fibers, such as plain paper, is sandwiched by a paper discharge roller 25 via a conveyance roller (not shown), and is conveyed in the direction of the arrow (sub-scanning direction) as the conveyance motor 26 is driven.

  The carriage 20 is guided and supported by the guide shaft 27 and the linear encoder 28. The carriage 20 is reciprocated in the main scanning direction along the guide shaft 27 via the drive belt 29 by driving the carriage motor 30.

  Inside the recording head (liquid path), a heating element (electric / thermal energy converter) that generates thermal energy for ink ejection is provided. In accordance with the reading timing of the linear encoder 28, the heat generating element is driven based on the recording signal, and ink droplets are ejected and adhered onto the recording medium to form an image.

  A recovery unit having cap portions 311 to 315 is installed at the home position of the carriage 20 disposed outside the recording area. When recording is not performed, the carriage 20 is moved to the home position, and the ink discharge ports 211 to 215 are sealed with caps 311 to 315 corresponding thereto, respectively. This can prevent clogging due to ink sticking or adhesion of foreign matter such as dust due to evaporation of the ink solvent. Further, the capping function of the cap part is used to eliminate ejection defects and clogging of ink ejection ports with low recording frequency. Specifically, the cap part is used for idle ejection for preventing ejection failure that causes ink to be ejected to the cap part in a state separated from the ink ejection port. Further, the cap portion is used for recovering the discharge of the discharge port that has caused a discharge failure by sucking ink from the ink discharge port by a pump (not shown) in the capped state.

  The ink receiving portion 33 plays a role of receiving a preliminarily ejected ink droplet when the recording head passes through the upper portion immediately before the recording operation. Further, by arranging a blade and a wiping member (not shown) at a position adjacent to the cap portion, it is possible to clean the formation surface of the ink discharge ports 211 to 215.

  As described above, it is preferable to add recovery means for the recording head, preliminary means, and the like to the configuration of the recording apparatus because the recording operation can be further stabilized. Specific examples thereof include a capping unit for the recording head, a cleaning unit, a pressurizing or suction unit, an electrothermal converter, a heating element different from this, or a preheating unit using a combination thereof. In addition, it is effective to provide a preliminary ejection mode for performing ejection different from recording in order to perform stable recording.

  In addition, a cartridge type recording head in which an ink tank is provided integrally with the recording head itself described in the above embodiment may be used. Furthermore, a replaceable chip-type recording head that can be electrically connected to the apparatus main body and supplied with ink from the apparatus main body by being attached to the apparatus main body may be used.

  FIG. 5 is a configuration diagram of a recording head having ink discharge ports 211 to 215. In the figure, the recording scanning direction of the recording head is the direction indicated by the arrow in the figure. The recording head is provided with ejection openings 211 to 215 of a plurality of nozzles arranged in a direction substantially perpendicular to the recording scanning direction. The recording head ejects ink droplets from each ejection port at a predetermined timing while moving and scanning in the recording scanning direction in the figure. Thus, an image is formed on the recording medium with a recording resolution corresponding to the nozzle arrangement density. At this time, the recording head may perform the recording operation in any direction of the recording scanning direction. Further, the recording operation may be performed either in a reciprocal manner.

  Further, the above embodiment is a serial type recording apparatus that performs recording by scanning the recording head, but is a full line type recording apparatus that uses a recording head having a length corresponding to the width of the recording medium. Also good. As a full-line type recording head, there is a configuration in which serial type recording heads as disclosed in FIG. 5 are arranged in a staggered manner or in parallel so as to be elongated to have a desired length. Alternatively, a configuration may be adopted in which one recording head is integrally formed so as to have a nozzle row that is elongated from the beginning.

  The serial type or line type recording apparatus described above is a five-discharge port array (or a four-color ink (Y: yellow, M: magenta, C: cyan, K: black) formed independently or integrally. It is an example of a head having a (nozzle array) configuration. K is arranged in 211 and 215, and Y, M, and C are arranged in 212 to 214, respectively. As a specific example of the ink application of the present invention, there is an example in which an application process of applying one color ink from each nozzle array is performed twice or more using two or more nozzle arrays in the same head. In order to perform this application process, it is necessary to dispose at least two inks of at least one of the four color inks in the same head. In the application step, a time difference of 1 msec or more is preferably provided between ink application, and the same ink is preferably arranged as far as possible in the same head. Therefore, for example, it is preferable to adopt a configuration in which one color ink is arranged at both ends as shown in FIG. When the head of FIG. 5 scans the basic matrix twice or more, the application step can be applied two or more times, that is, ink can be applied to the basic matrix four times. Alternatively, the ink application of the present invention can also be performed by mounting two or more heads of FIG. 5 on the same line.

In the application step (B), the ink application amount of one color at each timing is 0.7 μl / cm ² or less. Moreover, 0.1 microliter / cm < ² > or more is preferable. The ink jet recording apparatus of the present invention has a control mechanism for performing the applying step. By this control mechanism, the operation of the ink jet recording head and the timing of the plain paper feeding operation are controlled, and this application step is performed.

  The number of divisions when applying ink can be set according to desired recording conditions. FIG. 6 shows an example in which two identical inks are arranged in the same head and the application process of dividing and printing twice is performed twice, and printing is performed by dividing into four times in total. In this example, the resolution of the basic matrix is 1200 dpi (horizontal) × 1200 dpi (vertical), and a 100% duty portion of the image is formed. In FIG. 6, the landing position of the first ink is the first ink, the landing position of the second ink is the second ink, the landing position of the third ink is the third ink, and the landing position of the fourth ink. Is shown as a fourth ink. In this example, the first and second inks land in the first application step, and the third and fourth inks land in the second application step. Each of the first to fourth inks is quantitative.

  Next, the present invention will be described more specifically with reference to examples and comparative examples. In the following description, “part” and “%” are based on mass unless otherwise specified.

  First, the manufacturing method of the pigment dispersion contained in the ink of an Example and a comparative example is demonstrated.

(Manufacture of pigment dispersion)
<Production of self-dispersed pigment dispersion A>
500 g of carbon black having a specific surface area of 320 m ² / g and a DBP oil absorption of 110 ml / 100 g was added to 3750 g of ion-exchanged water, and the temperature was raised to 50 ° C. with stirring. Thereafter, an aqueous solution of 4500 g of sodium hypochlorite (effective chlorine concentration 12%) was added dropwise at 50 ° C. over 3 hours while pulverizing with a bead mill using 0.5 mm zirconia beads. Thereafter, the mixture was pulverized for 30 minutes to obtain a reaction liquid containing self-dispersing carbon black. The reaction solution was fractionated, neutralized with aqueous ammonia, and desalted with an ultrafiltration device until the conductivity reached 1.5 mS / cm. After adjusting the concentration of the self-dispersing carbon black to be 10%, the mixture was filtered through a combined system of a prefilter and a 1 μm filter to obtain a self-dispersing pigment dispersion A. 500 g of carbon black having a specific surface area of 220 m ² / g and a DBP oil absorption of 160 ml / 100 g was added to 3750 g of ion-exchanged water, and the temperature was raised to 50 ° C. while stirring. Thereafter, an aqueous solution of 4500 g of sodium hypochlorite (effective chlorine concentration 12%) was added dropwise at 50 ° C. over 3 hours while pulverizing with a bead mill using 0.5 mm zirconia beads. Thereafter, the mixture was pulverized for 30 minutes to obtain a reaction liquid containing self-dispersing carbon black. The reaction solution was fractionated, neutralized with aqueous ammonia, and desalted with an ultrafiltration device until the conductivity reached 1.5 mS / cm. After adjusting the concentration of the self-dispersing carbon black to be 10%, the mixture was filtered through a combined system of a prefilter and a 1 μm filter to obtain a self-dispersing pigment dispersion A.

<Production of self-dispersing pigment B>
100 g of carbon black having a specific surface area of 220 m ² / g and a DBP oil absorption of 105 ml / 100 g and 34.1 g of p-aminobenzoic acid were mixed well with 720 g of water, and then 16.2 g of nitric acid was added dropwise thereto. Stir at ° C. Ten minutes later, a solution of 10.7 g of sodium nitrite dissolved in 50 g of water was added, and the mixture was further stirred for 1 hour. The obtained slurry was filtered with a filter paper (trade name: Toyo Filter Paper No. 2; manufactured by Advantis), and the pigment particles collected by filtration were sufficiently washed with water and dried in an oven at 90 ° C. The self-dispersing black pigment which introduce | transduced p-benzoic acid group into the surface of carbon black by the above method was obtained. The pigment was adjusted with ion-exchanged water so that the concentration became 10%, and then adjusted to pH 7.5 with an aqueous ammonia solution. Furthermore, it filtered using the pre filter and the 1 micrometer filter together, and obtained the self-dispersion pigment dispersion B. 500 g of carbon black having a specific surface area of 320 m ² / g and a DBP oil absorption of 110 ml / 100 g was added to 3750 g of ion-exchanged water, and the temperature was raised to 50 ° C. with stirring. Thereafter, an aqueous solution of 4500 g of sodium hypochlorite (effective chlorine concentration 12%) was added dropwise at 50 ° C. over 3 hours while pulverizing with a bead mill using 0.5 mm zirconia beads. Thereafter, the mixture was pulverized for 30 minutes to obtain a reaction liquid containing self-dispersing carbon black. The reaction solution was fractionated, neutralized with aqueous ammonia, and desalted with an ultrafiltration device until the conductivity reached 1.5 mS / cm. After adjusting the concentration of the self-dispersing carbon black to be 10%, the mixture was filtered through a combined system of a prefilter and a 1 μm filter to obtain a self-dispersing pigment dispersion B.

<Production of self-dispersing pigment C in which an anionic functional group represented by the following chemical formula (1) is bonded to the surface>
Chemical formula (1)

After 10 g of carbon black having a specific surface area of 320 m ² / g and a DBP oil absorption of 110 ml / 100 g and 3.2 g of 4-aminobenzenephosphonic acid were mixed well with 70 g of water, 1.62 g of nitric acid was added dropwise thereto. Stir at 70 ° C. A few minutes later, a solution of 1 g of sodium nitrite dissolved in 5 g of water was added, and the mixture was further stirred for 1 hour. The obtained slurry was filtered with a filter paper (trade name: Toyo Filter Paper No. 2; manufactured by Advantis), and the pigment particles collected by filtration were sufficiently washed with water and dried in an oven at 90 ° C. The black pigment which introduce | transduced group shown by chemical formula (I) on the surface of carbon black by the above method was produced.

  When the surface functional group density of the black pigment prepared above was neutralized with sodium hydroxide and the surface functional group density was converted from the value, it was 600 μmol / g. The 50% cumulative particle diameter of the black pigment produced above was measured with Nanotrac UPA 150EX (manufactured by Nikkiso) and found to be 120 nm. The pigment was adjusted with ion-exchanged water so that the concentration became 10%, and then adjusted to pH 7.5 with an aqueous sodium hydroxide solution. Furthermore, it filtered with the combined system of a pre filter and a 1 micrometer filter, and obtained the self-dispersion pigment dispersion C.

<Production of self-dispersed pigment dispersion D>
C. instead of carbon black I. A self-dispersed pigment dispersion C was obtained in the same manner as in the production of the self-dispersed pigment dispersion B except that CI Pigment Yellow 74 was used.

<Production of self-dispersed pigment dispersion E>
C. instead of carbon black I. A self-dispersed pigment dispersion D was obtained in the same manner as in the production of the self-dispersed pigment dispersion B except that CI Pigment Red 122 was used.

<Production of self-dispersed pigment dispersion F>
C. instead of carbon black I. A self-dispersed pigment dispersion E was obtained in the same manner as in the production of the self-dispersed pigment dispersion B except that CI Pigment Blue 15: 3 was used.

(Ink adjustment)
Next, adjustment examples of the inks of Examples and Comparative Examples of the present invention will be described. Water used was ion exchange water. The inks used in the examples and comparative examples are described below.

<Adjustment of ink 1>
All the following constituents were made 100 parts in total, mixed for 2 hours, and then filtered using a 2.5 μm filter to obtain an ink 1 of an example of the present invention. The surface tension was 32.0 mN / m, the particle size of the self-dispersing pigment was 130 nm, and the viscosity was 4.4 mPa · s.
-Self-dispersion pigment dispersion A: 50 parts-Trimethylolpropane (hydrophobicity coefficient 0.31): 20 parts-Diammonium phthalate: 0.5 parts-Isopropyl alcohol: 1 part-Ethylene oxide adduct of acetylene glycol (Product name: Olfin E1010, manufactured by Nissin Chemical Industry, HLB value of 10 or more): 1 part.

<Adjustment of ink 2>
All the following constituents were made 100 parts in total, mixed for 2 hours, and then filtered using a 2.5 μm filter to obtain an ink 1 of an example of the present invention. The surface tension was 30.0 mN / m, the particle size of the self-dispersing pigment was 130 nm, and the viscosity was 3.5 mPa · s.
-Self-dispersing pigment dispersion A: 50 parts-Trimethylolpropane (hydrophobicity coefficient 0.31): 15 parts-1,2-hexanediol (hydrophobicity coefficient 0.97): 5 parts-Diammonium phthalate : 0.5 part · Isopropyl alcohol: 1 part · Ethylene oxide adduct of acetylene glycol (trade name: Orphine E1010, manufactured by Nissin Chemical Industry Co., Ltd., HLB value of 10 or more): 1 part · Water: remainder.

<Adjustment of ink 3>
All the following constituents were made 100 parts in total, mixed for 2 hours, and then filtered using a 2.5 μm filter to obtain an ink 1 of an example of the present invention. The surface tension was 31.0 mN / m, the particle size of the self-dispersing pigment was 130 nm, and the viscosity was 3.5 mPa · s.
Self-dispersing pigment dispersion A: 50 parts Trimethylolpropane (hydrophobic coefficient 0.31): 10 parts 1,2-hexanediol (hydrophobic coefficient 0.97): 5 parts 1,6- Hexanediol (hydrophobicity coefficient 0.76): 5 parts ・ Diammonium phthalate: 0.5 part ・ Isopropyl alcohol: 1 part ・ Acetylene glycol ethylene oxide adduct (trade name: Olphine E1010, manufactured by Nissin Chemical Industry) , HLB value of 10 or more): 1 part, water: remainder.

<Adjustment of ink 4>
All the following constituents were made 100 parts in total, mixed for 2 hours, and then filtered using a 2.5 μm filter to obtain an ink 1 of an example of the present invention. The surface tension was 29.0 mN / m, the particle size of the self-dispersing pigment was 110 nm, and the viscosity was 3.1 mPa · s.
Self-dispersing pigment dispersion B: 50 parts Trimethylolpropane (hydrophobicity coefficient 0.31): 10 parts 1,2-hexanediol (hydrophobicity coefficient 0.97): 10 parts Diammonium phthalate : 0.5 part · Isopropyl alcohol: 1 part · Ethylene oxide adduct of acetylene glycol (trade name: Orphine E1010, manufactured by Nissin Chemical Industry Co., Ltd., HLB value of 10 or more): 1 part · Water: remainder.

<Adjustment of ink 5>
All the following constituents were made 100 parts in total, mixed for 2 hours, and then filtered using a 2.5 μm filter to obtain an ink 1 of an example of the present invention. The surface tension was 31.0 mN / m, the particle size of the self-dispersing pigment was 120 nm, and the viscosity was 3.0 mPa · s.
-Self-dispersing pigment dispersion C: 50 parts-Trimethylolpropane (hydrophobicity coefficient 0.31): 15 parts-1,2-hexanediol (hydrophobicity coefficient 0.97): 5 parts-Diammonium phthalate : 0.5 part · Isopropyl alcohol: 1 part · Ethylene oxide adduct of acetylene glycol (trade name: Orphine E1010, manufactured by Nissin Chemical Industry Co., Ltd., HLB value of 10 or more): 1 part Water: remainder.

<Adjustment of ink 6>
The following all components were made into a total of 100 parts, and after mixing for 2 hours, it filtered using a 2.5 micrometer filter, and obtained the ink 16 of the Example of this invention. The surface tension was 31.0 mN / m, and the particle size of the self-dispersing pigment was 120 nm.
-Self-dispersing pigment dispersion C: 50 parts-Trimethylolpropane (hydrophobicity coefficient 0.31): 15 parts-1,2-hexanediol (hydrophobicity coefficient 0.97): 5 parts-Isopropyl alcohol: 1 Parts / ethylene oxide adduct of acetylene glycol (trade name: Olphine E1010, manufactured by Nissin Chemical Industry, HLB value of 10 or more): 1 part / water: remainder.

<Adjustment of ink 7>
All the following constituents were made 100 parts in total, mixed for 2 hours, and then filtered using a 2.5 μm filter to obtain an ink 1 of an example of the present invention. The surface tension was 43.040 mN / m, and the particle size of the self-dispersing pigment was 130 nm.
-Self-dispersing pigment dispersion A: 50 parts-Trimethylolpropane (hydrophilicity coefficient 0.31): 20 parts Diammonium phthalate: 0.5 parts Isopropyl alcohol: 1 part-Ethylene oxide adduct of acetylene glycol (product) Name: Olphine E1010, manufactured by Nissin Chemical Industry, HLB value of 10 or more): 0.1 part, water: remaining part.

<Preparation of ink 8>
Ink 8 was obtained by the same treatment as that of ink 2 except that self-dispersed pigment dispersion A (50 parts) was replaced with self-dispersed pigment dispersion D (40 parts). The surface tension was 29 mN / m, and the particle size of the self-dispersing pigment was 125 nm.

<Preparation of ink 9>
Ink 9 was obtained by the same treatment as that of ink 2 except that self-dispersed pigment dispersion A (50 parts) was replaced with self-dispersed pigment dispersion E (40 parts). The surface tension was 29 mN / m, and the particle size of the self-dispersing pigment was 85 nm.

<Preparation of ink 10>
Ink 10 was obtained by the same treatment as that of ink 2 except that self-dispersed pigment dispersion A (50 parts) was replaced with self-dispersed pigment dispersion F (40 parts). The surface tension was 29 mN / m, and the particle size of the self-dispersing pigment was 105 nm.

(Image forming method)
An image forming method used in this embodiment and the comparative example will be described.

<2 split 2 passes>
The ink was ejected from two ink ejection ports in the head to form a solid image (100% duty). In forming a solid image, the ink application to the basic matrix was performed by scanning the recording head twice and performing the application process of applying ink at two timings through two ink ejection openings. (2 divisions, 2 passes). That is, the ink application was divided into four times to form an image. The difference in ink application time to the basic matrix in the application process was 12 msec, the time difference between the application process and the application process was 580 msec, and image formation was completed in a total of 604 msec.

<Normal 2 passes>
The ink was ejected from two ink ejection ports in the head to form a solid image. In forming a solid image, the ink was applied to the basic matrix by scanning the head twice. This is a printing method which is usually called two-pass printing. The difference in ink application time was 600 msec.

<Normal 1 pass>
The ink was ejected from two ink ejection ports in the head to form a solid image. In forming a solid image, ink was applied to the basic matrix only by scanning the head once. This is a printing method generally referred to as one-pass printing.

(recoding media)
The plain paper, which is a recording medium used in this example and the comparative example, will be described.
・ PPC / BJ co-paper office planner paper (plain paper, manufactured by Canon Marketing Japan, product code 5553A012 [AB].)
EW-100 (plain paper, manufactured by Canon Marketing Japan, product code 5565A012 [AA].)
(Evaluation conditions)
Printer: F930 (manufactured by Canon. Recording head: 6 ejection port arrays, 512 nozzles each. Ink amount 4.0 pl (quantitative). Basic matrix resolution: 1200 dpi (horizontal) × 1200 dpi (vertical))
(Record evaluation methods and standards)
(Image density)
O. of solid image. D. Was measured with a densitometer (Macbeth RD915: manufactured by Macbeth).
AA: 1.60 or more A: 1.50 or more and less than 1.60.
B: 1.40 or more and less than 1.50.
C: It was less than 1.40.
(Fixability)
10 seconds after printing the solid image, the Sylbon paper was pressed, and the degree of transfer was visually evaluated according to the following evaluation criteria.
A: Transcription is not recognized.
B: Slight transfer is observed.
C: Transcription is clearly recognized.
(Lowercase printing)
The sharpness of kanji lowercase letters was visually evaluated according to the following evaluation criteria.
A: Even complex characters can be expressed.
B: For complicated characters, the outline is slightly disturbed, but is within an allowable range.
C: Complex characters cannot be expressed sufficiently.
D: Even simple characters may be confused.
(Uniformity)
The degree of occurrence of white spots in the solid image was visually evaluated according to the following evaluation criteria.
A: White spots are not recognized.
B: Slight white spots are observed.
C: White spots are clearly recognized.
(Betrayal)
The degree of back-through of the solid image was visually evaluated from the back according to the following evaluation criteria.
A: No see-through is observed, suitable for double-sided printing B: Slightly see-through is recognized, double-sided printing is possible C: Back-through is clearly recognized, double-sided printing is difficult The above ink, image forming method, paper type Tables 1 to 9 and Comparative Examples 1 to 11 configured by the combination are shown in Table 2. The image evaluation formed by each example and comparative example is also shown. In addition, the total applied amount of ink applied when performing image formation and the applied amount per time when divided are also shown. Unless otherwise specified, the unit of ink application amount is μl / cm ² .

  According to Table 2, regardless of the ink type and paper type, by performing image formation by two-pass two-pass, it is possible to achieve both high image density of OD1.5 or more, fixing property, lowercase printing, uniformity and back-through characteristics. It turns out that it is possible. In particular, in Example 8, an extremely high image density of OD 1.6 or higher, which was difficult to achieve with the conventional superpermeable ink + plain paper, was realized.

  Tables 3 to 6 show combinations in which the ink types and paper types in Table 2 are unified and only the image forming method is changed.

  According to Tables 3 to 6, it can be seen that high OD and good small letter printing and uniformity that could not be obtained by the conventional image forming method can be obtained by performing image formation by two-divided two passes of the present invention. . Next, Table 7 shows the difference in printing characteristics depending on the ink type while fixing the image forming method and the paper type.

  The ink 6 used in Comparative Example 9 is the same ink except that diammonium phthalate was not added to the ink 5 used in Example 9. As shown in Table 7, even if the image forming method and the paper type are the same, the printing characteristics differ greatly depending on the presence of the ink type and diammonium phthalate. From this result, the high OD, good lower-case printing, uniformity and strike-through characteristics of the present invention can be expressed only by using the ink added with the organic carboxylate of the present invention. I understand that.

  Next, Table 8 compares an example in which the ink type and paper type are fixed and the total applied amount of ink is increased.

As shown in Table 8, it is possible to obtain a high image density equivalent to the two-divided two-pass method of the present invention by increasing the total ink application amount twice even in the normal two-pass method. However, as seen in Comparative Example 11, when the amount of ink applied once was increased, the show-through was significant. In other words, when the amount of ink applied per basic matrix is large, the effect of preventing show-through was observed by limiting the amount applied once. Further, when the amount of ink applied per unit matrix is 1.4 μl / cm ² or less, the effect of preventing the back-through is further improved, which is more preferable.

FIG. 6 is a schematic diagram of a cross section of plain paper on which an image is formed by applying all inks necessary for image formation at once without being divided into a plurality of times. FIG. 6 is a schematic diagram of a cross section of plain paper on which an image is formed by increasing the total ink application amount per unit area. It is a schematic diagram of a cross section of plain paper on which an image is formed by the image forming method of the present invention. FIG. 2 is a front view showing the outline of the serial type ink jet recording apparatus according to an embodiment applicable to the present invention. 1 is a configuration diagram of a recording head applicable to an embodiment of the present invention. It is explanatory drawing which shows an example of the formation method of a recording dot.

DESCRIPTION OF SYMBOLS 11 Pigment 12 Plain paper 20 Carriage 23 Flexible cable 24 Recording medium 25 Paper discharge roller 26 Conveyance motor 27 Guide shaft 28 Linear encoder 29 Drive belt 30 Carriage motor 33 Ink receiving part 40 Density sensor 211-215 Ink discharge port 221-225 Ink cartridge 311 to 315 cap

Claims (13)

An inkjet image forming method for forming an image by applying one color ink to plain paper by an inkjet recording method,
The one color ink to be applied is a fixed amount of 0.5 pl or more and 6.0 pl or less, and is a self-dispersing pigment, an organic carboxylate, water, and a hydrophilicity / hydrophobicity coefficient defined by the following formula (A) Contains a water-soluble compound of 0.26 or more, the surface tension is 34 mN / m or less,
When the total amount of ink applied to the basic matrix for forming the image is 5.0 μl / cm ² or less, and the duty of the one color ink applied to the basic matrix is 80% duty or more. Application of one color ink to the basic matrix is performed a plurality of times within a range of 4000 msec or less, and within the range, the following application step (B) is performed at a time difference of 200 msec or more between each application step (B). An ink jet image forming method comprising:
Formula (A)

Application process (B)
The application of the one color ink to the basic matrix is performed at a plurality of times within a range of 1 msec or more and 200 msec or less, and the application amount of the one color ink applied at each timing is 0.7 μl / cm ^2. Steps to be described below. An inkjet image forming method for forming an image by applying inks of a plurality of colors to plain paper by an inkjet recording method,
The total amount of ink applied to the basic matrix for forming the image is 5.0 μl / cm ² or less, and the duty of at least one of the inks applied to the basic matrix is 80% duty or more. In this case, the application of the one color ink to the basic matrix is within a range of 4000 msec or less, and the following application step (B) within the range is set to a time difference of 200 msec or more between the application steps (B). Done by doing multiple times,
The ink of one color to be applied is a quantitative amount of 0.5 pl or more and 6.0 pl or less, and is a self-dispersing pigment, an organic carboxylate, water, and a hydrophilicity / hydrophobicity coefficient defined by the following formula (A) Containing a water-soluble compound of 0.26 or more and a surface tension of 34 mN / m or less.
Formula (A)

Process (B)
The application of the one color ink to the basic matrix is performed at a plurality of times within a range of 1 msec or more and 200 msec or less, and the application amount of the one color ink applied at each timing is 0.7 μl / cm ^2. Steps to be described below.   3. The ink jet image forming method according to claim 1, wherein the ink of one color is applied to the basic matrix at a plurality of times by the same recording head at all timings.   The inkjet image forming method according to claim 1, wherein a resolution of the basic matrix is 600 dpi or more and 4800 dpi or less.   The ink contains a water-soluble compound having a hydrophilicity / hydrophobicity coefficient defined by the formula (A) of 0.26 or more and 0.37 or less and a water-soluble compound of 0.37 or more. The inkjet image formation method of any one of 1-4.   6. The inkjet image forming method according to claim 5, wherein the ink contains two or more water-soluble compounds having a hydrophilicity / hydrophobicity coefficient defined by the formula (A) of 0.37 or more.   The inkjet image forming method according to claim 1, wherein the organic carboxylate is an organic carboxylate ammonium salt.   The inkjet image forming method according to claim 1, wherein the self-dispersing pigment has an average particle size of 60 nm or more and 145 nm or less.   The ink-jet image forming method according to claim 1, wherein the ink is applied by the action of thermal energy. An ink jet recording apparatus including a recording head that forms an image by applying one color ink to plain paper by an ink jet recording method,
The one color ink to be applied is a fixed amount of 0.5 pl or more and 6.0 pl or less, and is a self-dispersing pigment, an organic carboxylate, water, and a hydrophilicity / hydrophobicity coefficient defined by the following formula (A) Contains a water-soluble compound of 0.26 or more, the surface tension is 34 mN / m or less,
The total amount of ink applied to the basic matrix for forming the image is 5.0 μl / cm ² or less, and the duty of at least one of the inks applied to the basic matrix is 80% duty or more When the application of the one color ink to the basic matrix is within a range of 4000 msec or less, and within the range, the following application step (B) is performed with a time difference of 200 msec or more between the application steps (B). An ink jet recording apparatus comprising: a control mechanism that performs a plurality of times.
Formula (A)

Application process (B)
The application of the one color ink to the basic matrix is performed at a plurality of times within a range of 1 msec or more and 200 msec or less, and the application amount of the one color ink applied at each timing is 0.7 μl / cm ^2. Steps to be described below. An inkjet recording apparatus including a recording head that forms an image by applying inks of a plurality of colors to plain paper by an inkjet recording method,
The total amount of ink applied to the basic matrix for forming the image is 5.0 μl / cm ² or less, and the duty of at least one of the inks applied to the basic matrix is 80% duty or more. In this case, the application of the one color ink to the basic matrix is within a range of 4000 msec or less, and the following application step (B) within the range is set to a time difference of 200 msec or more between the application steps (B). It has a control mechanism that performs by performing multiple times,
The ink of one color to be applied is a quantitative amount of 0.5 pl or more and 6.0 pl or less, and is a self-dispersing pigment, an organic carboxylate, water, and a hydrophilicity / hydrophobicity coefficient defined by the following formula (A) Containing a water-soluble compound having a surface tension of 34 mN / m or less.
Formula (A)

Process (B)
The application of the one color ink to the basic matrix is performed at a plurality of times within a range of 1 msec or more and 200 msec or less, and the application amount of the one color ink applied at each timing is 0.7 μl / cm ^2. Steps to be described below.   The inkjet recording apparatus according to claim 10 or 11, wherein the recording head is a recording head that applies ink by the action of thermal energy.   The inkjet recording according to any one of claims 10 to 12, wherein the recording head has a plurality of nozzle rows and applies at least one color ink divided by two or more nozzle rows. apparatus.