JP2007307747A - Liquid for head, inkjet recording apparatus and cleaning method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid for a head capable of improving wiping properties for ink residue comprising a pigment dispersed with an anionic substance or a pigment with an anionic group on its surface stick on a delivering opening face, and/or suppressing clogging of a nozzle. <P>SOLUTION: The liquid for the head fed to the face with the delivering opening for delivering an inkjet ink (called as an anionic pigment ink) comprising the pigment dispersed with the anionic substance or the pigment with the anionic group on its surface, and whose pH is higher than pH of the inkjet ink, an inkjet recording apparatus, and a method for cleaning the face with the delivering opening face for the ink, are provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a head liquid, an ink jet recording apparatus using the head liquid, and a cleaning method. More specifically, the head used for efficiently removing ink residue and the like adhering to the surface having the ejection port for ejecting ink from the recording head, and for suppressing nozzle clogging (hereinafter also referred to as adhesion within the nozzle). Liquid for

  The ink jet recording method is a system that converts input image data into an output image using ink, which is liquid, as a medium. For this reason, if the surface (hereinafter also referred to as the ejection port surface) having the ejection port of the recording head that ejects ink is contaminated, the input image data is not accurately reflected in the output image. Accordingly, the discharge port surface cleaning technique is an important factor.

  A recording head ejects ink onto a recording medium from a fine nozzle (hereinafter, a collective term for an ejection port, a liquid path communicating with the element, and an element for generating energy used for ink ejection unless otherwise specified). It is. Accordingly, when the ejected ink hits the recording medium and rebounds, or when the ink is ejected, fine ink droplets may be ejected in addition to the main ink involved in the recording and drift in the atmosphere. These may become mist and adhere around the ink discharge port of the recording head. Further, dust or the like drifting in the air may adhere to the periphery of the ink discharge port. Then, the attached ink pulls the ejected main ink droplets to change the ink ejection direction, that is, the straightness of the main ink droplets may be hindered. In the conventional ink jet recording apparatus, as a technique for cleaning the discharge port surface with respect to the deposit, the discharge port surface of the recording head is swept with a wiping member (wiper) made of an elastic material such as rubber at a predetermined timing. What is called wiping to remove is performed.

  On the other hand, recently, an ink containing a pigment (pigment ink) instead of a conventional dye is often used as a coloring material for the purpose of improving the optical density, water resistance, light resistance, and the like of recorded matter. It is coming. The pigment ink is obtained by dispersing a water-insoluble colorant in an aqueous medium by introducing a functional group on the surface of the pigment or a dispersant represented by a dispersion resin (polymer dispersant) or a surfactant. . For this reason, the pigment ink adhering to the discharge port surface changes into a dry fixed substance as the moisture evaporates. The dry fixed matter of the pigment ink causes more damage to the discharge port surface and the like than the dry fixed matter of the dye ink in which the color material itself is dissolved as a molecule in the aqueous medium. In the case of a so-called resin dispersion pigment dispersed by the action of the dispersion resin, there is also a tendency that the dispersion resin is easily adsorbed to the discharge port surface.

  In response to these problems, a head liquid is applied to the ejection port surface when the recording head is wiped. By applying the liquid for the head, the wear of the wiper is reduced, and the ink residue accumulated in the recording head is removed well. Further, a thin film of the head liquid is formed on the recording head by application of the head liquid, thereby preventing foreign matter from adhering to the recording head, thereby improving the wiping property. And the liquid for heads used at the time of wiping that can obtain the above-described effects is configured to be stored inside the ink jet recording apparatus main body (see, for example, Patent Documents 1 and 2).

Japanese Patent Laid-Open No. 10-138503 JP 2000-203037 A

  The inventors of the present invention performed cleaning of the discharge port surface by the method disclosed in the above-mentioned patent document, and confirmed the effect. As a result, it was found that the wiping property of an ink residue containing a pigment dispersed by an anionic substance or a pigment having an anionic group on the surface was insufficient. Furthermore, the present inventors have found a problem that a pigment ink residue remains on the discharge port surface even after wiping, and a problem that a wiping trace remains on the discharge port surface. As a result of investigations by the present inventors, it has been found that the above-described phenomenon is particularly noticeable in the following configuration. That is, an ink containing 2% by mass or more of an anionic substance, or a pigment having an average particle diameter of 20% or more after evaporation of the ink is increased by 10% or more compared to that of the ink before evaporation. When the dispersibility is relatively unstable, the above-mentioned phenomenon is noticeable. Furthermore, it has been found that the above-described phenomenon is noticeable when a pigment ink containing a volatile alkali component such as ammonia is wiped off. Therefore, the present inventors have analyzed these phenomena in detail. As a result, it was found that the pigment ink residue remained for the following reason even though the ejection port surface was cleaned with the head liquid. That is, it has been found that there is a main cause of insufficient redissolution of the pigment ink residue when the head liquid is supplied to the pigment ink residue. Accordingly, the first technical problem of the present invention is to promote the re-dissolution of the pigment ink residue by fundamentally reviewing the composition of the head liquid supplied to the ejection port surface.

  Furthermore, the present inventors have considered that it is important to solve the following problems in order to use the ink as an ink for ink jet. That is, when pigment ink is used for inkjet recording, ink droplets are ejected from the ejection port due to the dispersion and destruction of the pigment generated as the ink near the nozzles evaporates and the precipitation of the resin used as the dispersant. There is a case where the ink is not ejected or a deviation occurs in the ink ejection direction. As a method for solving these problems, it is a common practice to add a high-boiling polyhydric alcohol into the ink. However, when a high-boiling polyhydric alcohol is added to the ink, the viscosity of the ink is increased and the ejection performance may be deteriorated.

  A method of reducing the concentration of solids such as pigments and dispersants in the ink is also conceivable, but this method sacrifices optical density, color reproduction range, and image fastness. As described above, at present, no means has yet been found for solving the sticking in the nozzle without impairing the optical density, color reproduction range, and image fastness. Therefore, the second technical problem of the present invention is to find a means for solving this problem.

  Accordingly, an object of the present invention is to provide a technique capable of solving the first and / or second problems described above. That is, it is possible to improve the wiping property of an ink residue containing a pigment dispersed by an anionic substance adhering to the discharge port surface or a pigment having an anionic group on the surface, and to further prevent nozzle clogging. Is the purpose.

  In order to solve the above-mentioned problems, the inventors of the present invention have made studies with the main purpose of how to promote re-dissolution of ink residues generated as a result of evaporation of ink adhering to the ejection port surface. In addition, the main purpose of the study was to suppress the dispersion and destruction of the pigment in the ink in the nozzle accompanying the evaporation of the ink in the vicinity of the nozzle. As a result, the present invention has been achieved.

  That is, the first embodiment according to the present invention ejects an ink jet ink (hereinafter referred to as an anionic pigment ink) containing a pigment dispersed by an anionic substance or a pigment having an anionic group on the surface. The head liquid is supplied to a surface having a discharge port for the head, and has a pH higher than that of the inkjet ink.

  The invention according to the second aspect is a head liquid supplied to a surface having an ejection port for ejecting each anionic pigment ink of black ink, cyan ink, magenta ink, and yellow ink, and the pH thereof is The head liquid is characterized by having a pH higher than that of any anionic pigment ink.

  Another embodiment of the present invention uses a head liquid having the above structure in an ink jet recording apparatus having a discharge port for discharging an anionic pigment ink and a cleaning mechanism for cleaning a surface having the discharge port. An inkjet recording apparatus characterized by the above.

  Furthermore, another embodiment of the present invention is a method for cleaning a surface having an ejection port for ejecting an anionic pigment ink with a liquid for a head, wherein the surface having the ejection port is formed on the inkjet ink. A method for cleaning a surface having an ejection port for inkjet ink, characterized by cleaning with a head liquid having a pH higher than pH.

  According to the head liquid of the present invention, redissolving of the pigment ink residue remaining on the discharge port surface is promoted, and the wiping property of the pigment ink residue on the discharge port surface is improved. In addition, when the head liquid enters the nozzle during wiping, the dispersibility of the pigment in the ink in the nozzle and the solubility of the polymer are improved, and the dispersion and destruction of the pigment accompanying the evaporation of the ink in the nozzle Polymer precipitation is alleviated. As a result, sticking in the nozzles is suppressed, and ink ejection stability in ink jet recording can be improved.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. In the present invention, the pH was measured at 25 ° C. using a pH meter F-21 (manufactured by Horiba) and the surface tension was measured using an automatic surface tension meter CBVP-Z (manufactured by Kyowa Interface Chemical).
As described above, the present invention aims to solve a problem that is particularly noticeable when an anionic pigment ink is used for ink jet recording, and the problem is solved by using the head liquid of the present invention. First, a pigment dispersed by an anionic substance constituting an anionic pigment ink or a pigment having an anionic group on the surface will be described.

  Pigments typified by carbon black and organic pigments that are generally used as colorants for ink jets have a very poor affinity for water because of their strong surface hydrophobicity. As means for dispersing a pigment having such properties in water, the following is performed. That is, modification of pigment surface represented by modification of pigment surface by ionic hydrophilic group or nonionic hydrophilic group, ionic hydrophilic group or nonionic hydrophilic property represented by resin or surfactant, etc. Often, amphiphiles containing groups in their structure are used as dispersants.

  In general, an ionic hydrophilic group is ionized by the action of an acid or an alkali, thereby exhibiting an affinity for water. The pigment dispersed by the anionic substance used in the present invention or the pigment having an anionic group on the surface dissociates the anionic group by the action of the alkali component and is stably dispersed in water.

  Next, the problem and solution of the present invention will be described in detail. First, a solution for promoting the re-dissolution of the pigment ink residue, which is the first technical problem described above, will be described. In the anionic pigment ink attached to the ejection port surface, volatile components such as moisture in the ink evaporate over time. At that time, the number of dissociated anionic groups present in the pigment surface or the dispersed resin skeleton is reduced, and it is assumed that the dispersion destruction product of the pigment or the precipitation of the dispersed resin is caused. The pigment dispersion destruction product or the dispersion resin precipitate produced on the discharge port surface in this way has a high viscosity and, in some cases, exists as a wax-like solid. The pigment ink residue remaining on the discharge port surface not only hinders the straightness of the main ink droplets, but also may deteriorate the discharge port surface.

  The present inventors have made various studies in order to solve the above problems. As a result, the head liquid is designed in consideration of the characteristic relationship between the head liquid and the anionic pigment ink when the ink residue adhering to the discharge port surface is wiped off using the head liquid. It came to the technical idea that this is effective. The present inventors can promote the re-dissolution of the residue of the anionic pigment ink and can impart fluidity to the ink residue. As a result, the head can improve the wiping property of the ink residue. Found the composition of the liquid.

  In order to realize the above technical idea, it is necessary to promote dissociation of undissociated anionic groups present on the pigment surface or the dispersed resin skeleton. Therefore, the present inventors tried various methods for promoting dissociation of undissociated anionic groups. As a result, it has been concluded that the above technical idea can be realized by setting the pH of the head liquid used in combination with the anionic pigment ink to be higher than the pH of the anionic pigment ink.

  The pH of the head liquid, which is a solution to the first technical problem described above, is set higher than that of the anionic pigment ink because of redispersion of the pigment dispersed and destroyed by evaporation or re-dissolution of the precipitated dispersed resin. The aim is to promote and impart fluidity to these. Therefore, the head liquid needs to have a pH at which the following phenomenon can be confirmed. That is, an anionic pigment ink in which the average particle diameter of the pigment is increased by 20% or more by evaporation of volatile components such as moisture in the ink and the liquid for the head are mixed at 1: 1 (mass ratio). To prepare a mixture. At this time, the pH must be set such that the phenomenon that the average particle diameter of the pigment in the mixed liquid becomes smaller than the average particle diameter of the evaporated ink before mixing can be confirmed.

  More specifically, the ink in which the average particle diameter of the pigment is increased by about 20% by evaporation of volatile components such as moisture in the ink and the head liquid are mixed at 1: 1 (mass ratio), and the mixed liquid is mixed. Prepare. At this time, the pH of the head liquid is set so that the increase rate of the average particle diameter in the mixed liquid is 20% or less with respect to the average particle diameter of the pigment of the ink before the volatile component is evaporated. Is preferred. In addition, when the pH of the anionic pigment ink rapidly increases or when the anionic pigment ink comes into contact with a liquid having a large pH difference, the electrolyte concentration in the ink rapidly increases. Destruction or dispersion resin precipitation may occur. This phenomenon means that an anionic pigment ink and a head liquid need to have an appropriate pH difference. However, since the degree of occurrence of the above phenomenon varies greatly depending on the characteristics of the dispersion resin in the ink, it is not possible to define a specific difference between the pH of the head liquid and the pH of the anionic pigment ink. However, as a result of the study by the present inventors, the difference in pH between the head liquid and the anionic pigment ink is 0.5 or more and 3.0 or less, and further 0.5 or more and 1.5 or less. It is also preferable that the pH of the mixed solution is higher than 7.0.

  In consideration of the dispersion stability of the pigment and the solubility of the dispersion resin, the present inventors can use the first anionic pigment ink having a pH set to 7.0 or higher. Confirmed that technical problems could be solved. According to the study by the present inventors, it is preferable that the pH of the anionic pigment ink is 7.0 or more in consideration of the dispersion stability and the solubility of the dispersion resin. Further, from the relationship with the pH of the ink, the pH of the head liquid is preferably higher than 7.0, and more preferably 8.0 or higher. Also, in order to prevent the head liquid adhering to the discharge port surface from corroding the material constituting the discharge port surface and the nozzle, the pH of the head liquid and the ink should both be 10.0 or less. Is preferred. However, the pH of the head liquid may exceed 10.0, depending on the stability of the ink to be used with respect to fluctuations in pH and the resistance to the pH of the discharge port surface of the head to be used and the material constituting the nozzle. In the present invention, a laser zeta electrometer ELS-8000 (manufactured by Otsuka Electronics Co., Ltd.) was used for measurement of the average particle diameter of the pigment in the ink or the mixed liquid.

  Next, a solution to the above-described second technical problem of the present invention, which is to suppress the sticking in the nozzle without impairing the optical density, color reproduction range and image fastness, will be described. In the examination process for solving the first problem, the present inventors actively utilize the phenomenon that the head liquid enters the inside of the nozzle when wiping the discharge port surface with the head liquid. We considered that it would be possible to solve the second problem. The clogging (adherence) in the nozzle, which is the second technical problem, is considered to occur due to the following mechanism. That is, with the evaporation of the volatile solvent from the nozzle when the recording head is not used, the pigment in the anionic pigment ink in the nozzle breaks down or the dispersion resin deposits. This is thought to cause sticking in the nozzles because the ink is thickened and solid in some cases. As described above, this phenomenon is also considered to be caused by a decrease in the number of anionic groups dissociated by the alkali component present on the pigment surface or the dispersed resin skeleton caused by the change in the ink composition accompanying evaporation. It is done.

  As described above, the second technical problem is caused by the decrease in the number of anionic groups dissociated by the alkali component present in the pigment surface or the dispersed resin skeleton as the volatile solvent evaporates from the nozzle. This is thought to occur. That is, when the number of anionic groups dissociated by the alkali component is decreased, the pigment or the dispersed resin in the anionic pigment ink in the nozzle is precipitated, and as a result, the ink is thickened and solidified in some cases. it is conceivable that.

  As a result of intensive studies based on the above findings, the present inventors have found that a head liquid having a pH set higher than that of an anionic pigment ink has the following functions. That is, when the head liquid is supplied to the inside of the nozzle during wiping, the pH of the ink in the nozzle rises, and the dissociated anionic groups are reduced due to evaporation of volatile components such as moisture. It was found to be suppressed. That is, the alkali component in the head liquid is supplied to the inside of the nozzle, thereby suppressing a decrease in dissociated anionic groups that are responsible for the dispersion stability of the pigment and the dispersion resin. As a result, the dispersion stability of the pigment and the solubility of the dispersion resin are improved, and clogging in the nozzle is suppressed.

  As a result of the study by the present inventors, a phenomenon in which the ink pH in the nozzle rises more efficiently by intentionally supplying the head liquid having a pH higher than that of the anionic pigment ink into the nozzle can be more efficiently performed. In order to wake up, it has been found that the following is preferable. That is, it has been found that it is preferable that the pH of the head liquid is higher than the pH of the anionic pigment ink and that the surface tension of the head liquid is lower than the surface tension of the anionic pigment ink. The present inventors presume that the relationship between the surface tension of the head liquid and the surface tension of the ink affects the supply of the head liquid into the nozzle as follows.

  The present inventors have confirmed a phenomenon in which when two types of liquids having different surface tensions come into contact with each other, a liquid having a low surface tension moves toward a liquid having a high surface tension. According to further studies by the present inventors, it has been found that the liquid flow phenomenon using the surface tension as described above appears if the difference in the surface tension of the liquid is 1 mN / m. Therefore, in order to solve the second technical problem of the present invention, it is preferable that the difference in surface tension between the head liquid and the anionic pigment ink is 1 mN / m or more. The surface tension of the anionic pigment ink is preferably 25.0 mN / m to 50.0 mN / m, and more preferably 30.0 mN / m to 45.0 mN / m. The surface tension of the head liquid is preferably 25.0 mN / m to 66.0 mN / m, and more preferably 30.0 mN / m to 40.0 mN / m.

  When wiping is performed, many droplets of anionic pigment ink are present on the ejection port surface. For this reason, when the surface tension of the head liquid is made lower than the surface tension of the ink as described above, the phenomenon that ink droplets are attracted toward the head liquid during wiping can be suppressed. As a result, it is possible to suppress the head liquid from being contaminated by ink. In addition, since the transfer efficiency of the head liquid to the discharge port surface is also increased, the pigment ink residue, which is the first technical problem of the present invention, is that the pH of the head liquid satisfies the condition higher than the pH of the ink. It becomes possible to further promote the re-dissolution of.

  A recording head mounted on an ink jet recording apparatus is capped with a rubber member or the like during a non-recording operation or the like for the purpose of preventing drying in the nozzles or preventing dust or the like from adhering to the discharge port surface. In order to maximize the effect of suppressing the sticking in the nozzle, which is the effect of the head liquid of the present invention, before the capping operation described above, the head liquid into the nozzle accompanying the wiping of the discharge port surface is performed. It is preferred that the feed be made and then capped.

  Heretofore, the means for solving the first and second technical problems in the present invention have been individually described. In the present invention, by setting the pH of the head liquid higher than the pH of the anionic pigment ink, it is possible to solve the above two technical problems at the same time.

  Furthermore, the present inventors have also found that the head liquid of the present invention exhibits a higher effect when used with an anionic pigment ink in which an anionic group is dissociated by a volatile alkali such as ammonia. It was. In order to obtain a recorded material having both excellent image performance and image fastness, an anionic pigment ink having the above-described configuration may be used. In such an anionic pigment ink, the alkaline component that promotes dissociation of undissociated ionic groups present on the pigment surface or in the dispersed resin skeleton is volatile, so that the pH decreases as the ink evaporates. As a result, the state change speed of the pigment ink is faster than that of the anionic pigment ink dissociated by the non-volatile alkali. For this reason, the pigment ink residue remains on the discharge port surface in a relatively short time. For the same reason, sticking in the nozzle is also promoted.

  It can be easily imagined to take measures such as changing the timing of wiping and increasing the number of wiping in order to use the ink as described above. However, these means cause adverse effects such as deterioration of the discharge port surface and a decrease in throughput. On the other hand, when the head liquid of the present invention is used, as described above, not only the redispersion of the dispersed and destroyed pigment and the re-dissolution of the precipitated dispersed resin is promoted, but also the pH in the nozzle is increased. It also has a function to Therefore, if the head liquid of the present invention is used, it becomes possible to stably use the anionic pigment ink having the above-described configuration without changing the ink configuration (with the conventional ink configuration). A very high effect is obtained.

  As described above, an unprecedented problem solving means can be realized by using the head liquid of the present invention for wiping. That is, not only can the wiping property of the pigment ink residue on the discharge port surface be further improved, but also when the discharge port surface is wiped, the head liquid of the present invention inevitably enters the nozzle. At the same time, the sticking can be suppressed. Hereinafter, a preferred configuration of the head liquid of the present invention and a configuration of an anionic pigment ink used together with the head liquid of the present invention will be described.

(Liquid for head)
As described above, in order to solve the first and second technical problems of the present invention, the pH of the head liquid of the present invention is configured to satisfy the relationship of being higher than the pH of the anionic pigment ink. There is a need. The means for adjusting the pH of the head liquid of the present invention is not particularly defined, but is preferably as follows. That is, it is preferable that the head liquid of the present invention contains a hydroxide such as an alkali metal or an organic amine, and is adjusted to be higher than the pH of the anionic pigment ink. Examples of the alkali metal hydroxide used at that time include LiOH, NaOH, KOH, RbOH, and CsOH. Examples of the organic amine include monoethanolamine, diethanolamine, triethanolamine, and aminemethylpropanol. Note that when the pH is adjusted using a volatile alkali component such as ammonia, the pH is lowered as the alkali component volatilizes. Therefore, it is not preferable to adjust the pH of the head liquid using the volatile alkali component.

  Further, as described above, it is preferable to adjust the pH of the head liquid to 10.0 or less so as not to cause corrosion of the material constituting the discharge port surface and the nozzle. The amount of alkali metal hydroxide or the like to be added to the head liquid when adjusting the pH is not particularly limited as long as the problem of the present invention can be solved. However, in the present invention, the content of alkali metal hydroxide, organic amine or the like added to the head liquid is 1 ppm or more and 100,000 ppm or less, more preferably 10 ppm or more and 100,000 ppm based on the total mass of the head liquid. The following is preferable. These alkali metal hydroxides and organic amines may exist as ions in the head liquid. In the present invention, these alkali metal hydroxides and organic amines are included including such states. Call it.

The head liquid of the present invention preferably contains a non-volatile water-soluble organic solvent in order to suppress evaporation during distribution or under various use environments. Specific examples of the non-volatile water-soluble organic solvent to be used include the following. For example, polyalkylene glycols such as polyethylene glycol and polypropylene glycol;
Alkylene glycols in which an alkylene group contains 2 to 6 carbon atoms, such as ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol;
Lower alkyl ether acetates such as polyethylene glycol monomethyl ether acetate;
Although glycerin etc. can be used, it is not limited to the said compound. Furthermore, it is necessary to consider that the head liquid of the present invention is stably supplied to the discharge port surface and prevents liquid leakage due to posture change or vibration during distribution. As a preferable configuration of the head liquid that satisfies these requirements, it is preferable that the content of the nonvolatile water-soluble organic solvent is larger than the content of water.

  The head liquid of the present invention is for the purpose of more stably supplying the head liquid into the nozzle when wiping the discharge port surface, and making the head liquid having a desired surface tension. Further, it may be one containing a surfactant or the like. At that time, in order to make the second effect of the present invention more excellent, the surfactant contained in the head liquid is an interface contained in the anionic pigment ink used together with the head liquid of the present invention. It is preferable to use the same activator. Furthermore, in addition to the above components, the head liquid of the present invention may contain an antifoaming agent, a preservative, an antifungal agent, and the like as necessary.

(Anionic pigment ink)
The head liquid of the present invention has been developed to solve the problems in the case of using an anionic pigment ink. Next, the anionic pigment ink will be described. The anionic pigment ink contains a pigment dispersed by an anionic substance or a pigment having an anionic group on the surface. First, a usable pigment will be described in detail.

<Pigment>
Examples of the pigment that can be used include carbon black and organic pigments. One of various pigments listed below can be used, or two or more pigments can be used in combination. The content (% by mass) of the pigment in the anionic pigment ink is 0.1% by mass or more and 15.0% by mass or less, and further 1.0% by mass or more and 10.0% by mass based on the total mass of the ink. The following is preferable.

[Carbon black]
For example, carbon black pigments such as furnace black, lamp black, acetylene black, and channel black can be used as the carbon black. Specifically, for example, the following can be used.
For example, Raven: 7000, 5750, 5250, 5000, 3500, 2000, 1500, 1250, 1200, 1190 ULTRA-II, 1170, 1255 (above Colombia);
Black Pearls L;
Legal: 400R, 330R, 660R;
Mogul L;
Monarch: 700, 800, 880, 900, 1000, 1100, 1300, 1400;
Vulcan XC-72R (above Cabot);
Color Black: FW1, FW2, FW2V, FW18, FW200, S150, S160, S170;
Printex: 35, U, V, 140U, 140V;
Special Black: 6, 5, 4A, 4 (made by Degussa);
No. 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. 2300, MCF-88, MA600, MA7, MA8, MA100 (manufactured by Mitsubishi Chemical).
Of course, in the present invention, it is not limited to these, and conventionally known carbon black can be used. Further, magnetic fine particles such as magnetite and ferrite, titanium black and the like may be used as the pigment.

[Organic pigments]
Specifically, for example, the following can be used as the organic pigment. For example, insoluble azo pigments such as toluidine red, toluidine maroon, Hansa yellow, benzidine yellow, pyrazolone red;
Water-soluble azo pigments such as ritole red, helio bordeaux, pigment scarlet, permanent red 2B;
Derivatives from vat dyes such as alizarin, indanthrone, 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;
Pyranthrone pigments such as pyranthrone red and pyranthrone orange;
Indigo pigments;
Condensed azo pigments;
Thioindigo pigments;
Flavanthrone yellow, acylamide yellow, quinophthalone yellow, nickel azo yellow, copper azomethine yellow, perinone orange, anthrone orange, dianslaquinonyl red, dioxazine violet, and the like.

Moreover, when an organic pigment is shown by a color index (CI) number, the following can be used, for example. Of course, conventionally known organic pigments can be used other than the following.
For example, C.I. I. Pigment Yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 109, 110, 117, 120, 125, 128, 137, 138, 147, 148, 151, 153, 154, 166, 168;
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, 215, 216, 217, 220, 223, 224, 226, 227, 228, 238, 240;
C. I. Pigment violet 19, 23, 29, 30, 37, 40, 50;
C. I. Pigment blue 15, 15: 3, 15: 1, 15: 4, 15: 6, 22, 60, 64;
C. I. Pigment green 7, 36;
C. I. Pigment brown 23, 25, 26, and the like.

[Dispersion resin (polymer dispersant)]
In the case of an anionic pigment ink using the above-described carbon black or organic pigment as a coloring material, it is preferable to disperse the pigment with an anionic substance, that is, to use the pigment in combination with a dispersion resin (polymer dispersing agent). As the dispersion resin, a resin that can stably disperse the pigment in an aqueous medium by the action of an anionic group is suitably used. Specific examples of the dispersion resin include, for example, a styrene-acrylic acid copolymer, a styrene-acrylic acid-acrylic acid alkyl ester copolymer;
Styrene-maleic acid copolymer, styrene-maleic acid-acrylic acid alkyl ester copolymer;
Styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic acid alkyl ester copolymer;
A styrene-maleic acid half ester copolymer, a vinyl naphthalene-acrylic acid copolymer, a vinyl naphthalene-maleic acid copolymer, a styrene-maleic anhydride-maleic acid half ester copolymer, or a salt thereof is included. In addition, these dispersion resins preferably have a weight average molecular weight in the range of 1,000 to 30,000, and particularly preferably in the range of 3,000 to 15,000. The content (mass%) of the pigment in the anionic pigment ink is (content of pigment / content of dispersion resin) 10.0 to 300.0 with respect to the content (mass%) of the dispersion resin. Furthermore, it is preferable that they are 30.0% or more and 90.0% or less.

  In addition to the effect of dispersing the pigment, the dispersion resin as described above has a scratch resistance and water resistance of an image recorded on a recording medium such as plain paper, and also an image recorded on a recording medium having gloss. It has the effect of improving glossiness. For this reason, it can be added as an anionic substance in an ink containing a self-dispersing pigment, colored fine particles, microencapsulated pigment, and the like described below.

[Self-dispersing pigment]
The anionic pigment ink used in the present invention is a pigment that can be dispersed in an aqueous medium without a dispersant by bonding an ionic group (anionic group) to the pigment surface as a coloring material, a so-called self-dispersing pigment. Can also be used. An example of such a pigment is self-dispersing carbon black. Examples of the self-dispersing carbon black include an anionic carbon black in which an anionic group is bonded to the surface of the carbon black.

Examples of the anionic carbon black include those obtained by bonding at least one anionic group selected from —COOM, —SO ₃ M, —PO ₃ HM, and —PO ₃ M ₂ to the surface of the carbon black. In the above formula, M represents a hydrogen atom, an alkali metal, ammonium or organic ammonium. Since these carbon black was allowed anionically charged in particular combine -COOM or -SO ₃ M surface of the carbon black in the dispersibility in the ink good, those that can be used particularly suitably to the present invention .

  By the way, among those represented as “M” in the hydrophilic group, specific examples of the alkali metal include, for example, Li, Na, K, Rb and Cs, and specific examples of the organic ammonium include the following. Things. For example, methyl ammonium, dimethyl ammonium, trimethyl ammonium, ethyl ammonium, diethyl ammonium, triethyl ammonium, methanol ammonium, dimethanol ammonium, trimethanol ammonium and the like.

  An anionic pigment ink containing a self-dispersing carbon black in which M in the above formula is ammonium or organic ammonium can further improve the water resistance of a recorded image, and in this respect, it is particularly preferably used in the present invention. be able to. This is considered to be due to the fact that when the ink is applied to the recording medium, ammonium is decomposed and ammonia is evaporated. Here, the self-dispersing carbon black in which M is ammonium can be prepared by the following method. For example, a self-dispersing carbon black in which M is an alkali metal is replaced with ammonium using an ion exchange method, or an ammonium hydroxide is added after adding acid to form H to add M to ammonium. And the like. An example of a method for producing an anionically charged self-dispersing carbon black is a method in which carbon black is oxidized with sodium hypochlorite. By this method, a —COONa group is chemically bonded to the carbon black surface. be able to.

By the way, various hydrophilic groups as described above may be directly bonded to the surface of carbon black, but other atomic groups are interposed between the surface of carbon black and the hydrophilic group, and the hydrophilic group May be indirectly bonded to the carbon black surface. Specific examples of the other atomic groups include a linear or branched alkylene group having 1 to 12 carbon atoms, a substituted or unsubstituted phenylene group, and a substituted or unsubstituted naphthylene group. Here, examples of the substituent of the phenylene group and the naphthylene group include a linear or branched alkyl group having 1 to 6 carbon atoms. Also, specific examples of the combination of another atomic group and the hydrophilic group is, for _{example, -C 2 H 4 COOM, -Ph} -SO 3 M, -Ph-COOM , etc. (where, Ph represents a phenylene group) include It is done.

  The anionic pigment ink used in the present invention may be one in which two or more types are appropriately selected from the above-described self-dispersing carbon blacks, and these are used as ink coloring materials. The content (mass%) of the self-dispersing carbon black in the ink is 0.1 mass% or more and 15.0 mass% or less, particularly 1.0 mass% or more and 10. It is preferable to make it the range of 0 mass% or less. By setting this range, the self-dispersing carbon black can maintain a sufficiently dispersed state in the ink. Further, for the purpose of adjusting the color tone of the ink, a dye may be added as a coloring material in addition to the self-dispersing carbon black. When carbon black is used as a color material, the above-described dispersion resin or the like can be further used in order to improve the scratch resistance, water resistance, and glossiness of the image.

[Colored fine particles / microencapsulated pigment]
The anionic pigment ink used in the present invention may include pigments microencapsulated with a resin or the like, colored fine particles in which the periphery of resin particles is covered with a color material, and the like, in addition to the above-described color materials. The microcapsules inherently have dispersibility in an aqueous medium, but a dispersion resin as described above may further coexist in the ink in order to improve dispersion stability. In addition, when the colored fine particles are used as a color material, it is preferable to further use a dispersion resin as described above.

<Volatile alkali component>
Examples of the volatile alkali component in the present invention include those that exhibit the property of volatilizing at room temperature. Specifically, it is preferable to use ammonia or the like. As described above, in the anionic pigment ink containing a volatile alkali component, the pigment ink residue tends to remain on the discharge port surface. For this reason, it is preferable that the content of the volatile alkali component is sufficient to keep the pigment in a stable state in the ink. In the anionic pigment ink, for example, ammonia exists in the form of NH ₄ ⁺ , but in the present invention, it is referred to as containing a volatile alkali component including such a state.

<Aqueous medium>
The aqueous medium in which the color material is dispersed is not particularly limited as long as it can be used for ink. When adhering to a recording medium by an ink jet method (for example, bubble jet (registered trademark) method, etc.), it is preferable to prepare the ink to have a desired viscosity and surface tension so as to have ink jet discharge characteristics.

Examples of the aqueous medium used in the anionic pigment ink used in the present invention include water or a mixed solvent of water and a water-soluble organic solvent. Specific examples of the water-soluble organic solvent include alkyl having 1 to 4 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, and the like. Alcohols;
Amides such as dimethylformamide and dimethylacetamide;
Ketones or ketoalcohols such as acetone and diacetone alcohol;
Ethers such as tetrahydrofuran and dioxane;
Polyalkylene glycols such as polyethylene glycol and polypropylene glycol;
Alkylene glycols in which an alkylene group contains 2 to 6 carbon atoms, such as ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol;
Lower alkyl ether acetates such as polyethylene glycol monomethyl ether acetate;
Glycerin;
Lower alkyl ethers of polyhydric alcohols such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether;
Polyhydric alcohols such as trimethylolpropane and trimethylolethane;
N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like can be mentioned.

  The water-soluble organic solvents as described above can be used alone or as a mixture. Moreover, it is preferable to use deionized water (ion exchange water) as the water. The content (% by mass) of the water-soluble organic solvent in the anionic pigment ink is 3.0% by mass or more and 50.0% by mass or less, and further 5.0% by mass or more and 20% by mass based on the total mass of the ink. It is preferable that it is 0 mass% or less. The content (% by mass) of water in the anionic pigment ink is 50.0% by mass or more and 95.0% by mass or less, and further 70.0% by mass or more and 85.0% by mass based on the total mass of the ink. The following is preferable.

  Furthermore, in addition to the above-mentioned components, the anionic pigment ink used in the present invention may be added with a moisturizing agent if necessary, and in order to have a desired physical property value, Preservatives and antifungal agents may be added. Further, for the purpose of obtaining an anionic pigment ink having a desired surface tension, an ink containing a surfactant may be used.

(Embodiment of inkjet recording apparatus)
FIG. 1 is a schematic perspective view of a main part of an ink jet recording apparatus according to an embodiment of the present invention. In the illustrated ink jet recording apparatus, the carriage 100 is fixed to the endless belt 5 and is movable along the guide shaft 3. The endless belt 5 is wound around a pair of pulleys 503, and one pulley 503 is connected to a drive shaft of a carriage drive motor (not shown). Accordingly, the carriage 100 is reciprocally main-scanned in the left-right direction in the drawing along the guide shaft 3 as the motor rotates. On the carriage 100 is mounted a recording head 1 that detachably holds the ink tank 2. Here, in the recording head 1, the ink ejection port array faces the recording medium 6, and the arrangement direction coincides with a direction different from the main scanning direction (for example, the sub-scanning direction that is the conveyance direction of the recording medium 6). Mounted on the carriage 100. Note that the number of ink ejection port arrays and ink tanks 2 can be provided in a number corresponding to the ink color to be used, and in the example shown in the figure, four sets corresponding to four colors (for example, black, yellow, magenta, and cyan). Is provided.

  The recording medium 6 is intermittently conveyed in a direction orthogonal to the scanning direction of the carriage 100. The recording medium 6 is supported by a pair of roller units (not shown) provided on the upstream side and the downstream side in the transport direction, and is transported in a state where a certain tension is applied and the flatness with respect to the ink discharge ports is ensured. Then, recording on the entire recording medium 6 is performed while alternately repeating the recording of the width corresponding to the array width of the ejection ports of the recording head 1 accompanying the movement of the carriage 100 and the conveyance of the recording medium 6. The illustrated apparatus is provided with a linear encoder 4 for the purpose of detecting the movement position of the carriage in the main scanning direction.

  The carriage 100 stops at the home position as necessary at the start of recording or during recording. Near the home position, a recovery mechanism 7 including a cap and a cleaning device described later with reference to FIG. 2 is installed. The cap is supported so as to be movable up and down, and in the raised position, the ejection port surface of the recording head 1 can be capped to protect it during a non-recording operation, or to perform suction recovery. During the recording operation, it is set at a lowered position that avoids interference with the recording head 1 and can receive preliminary ejection by facing the ejection port surface.

  FIG. 2 is a schematic side view showing an example of the cleaning mechanism constituting the ink jet recording apparatus of the present invention, as seen from the direction of the arrow in FIG. Wiper blades 9A and 9B made of an elastic member such as rubber are fixed to the wiper holder 10, and the wiper holder 10 has an ink discharge port arranged in the left-right direction (the direction orthogonal to the main scanning direction of the recording head 1). In the other direction). The wiper blades 9A and 9B have different thicknesses. When the wiper blades 9A and 9B are in sliding contact with the ejection port surface 11 of the recording head 1, the former is bent with a relatively large side and the latter is bent with a relatively small edge. , Each comes into contact.

  2 in FIG. 2 is a supply device for transferring the head liquid to the wiper blade when the wiper blade comes into contact. In the present invention, the head liquid of the present invention is stored in a tank (container). It may be in the form. In addition, an absorber that holds a predetermined amount of the head liquid and exudes the head liquid in response to the contact with the wiper blade can be provided at least in the contact portion. Furthermore, a stirring device or the like for obtaining a uniform mixed state of the liquid component for the head may be added. Reference numeral 14 denotes a water replenishing device, which is preferably arranged so that the head liquid of the present invention can be maintained in a suitable component ratio range even when moisture evaporation occurs due to an extreme environmental change. .

  This water replenishing device is, for example, a non-volatile water-soluble organic solvent and water that are the preferred head liquid of the present invention described above, and the non-volatile water-soluble organic solvent content is water-containing. There is no need to operate as long as it maintains more than the quantity. Furthermore, if this water replenishing device is used, the mixing ratio of the components constituting the head liquid can be appropriately changed or maintained within the range disclosed by the present invention depending on the desired conditions. Naturally, when the ink jet recording apparatus is installed in an abnormal environment, or when it is left in an unsuitable state, a situation that cannot be normally predicted occurs, the water constituting the head liquid of the present invention is lost. There is. In this case, it is preferable that the ratio of glycerin and water of the head liquid in the present invention is kept within a suitable range by replenishing water by means 14.

  From this point, as a preferred embodiment of the ink jet recording apparatus of the present invention, it is possible to use the head liquid and have the following means. That is, means for supplying the head liquid for cleaning the discharge port surface on which the discharge port for discharging the anionic pigment ink is formed by arbitrary control and driving, and replenishing the head liquid with water And a means for performing the above.

  In the cleaning operation of the ejection port surface, first, the recording head 1 is in a standby state at a position away from the home position, or before the head is moved to the home position, the head liquid is transferred by contacting the wiper blade with the supply device 12. To do. Then, the wiper holder 10 is returned to the illustrated position, the recording head is set to the home position, and then the wiper holder 10 is moved again in the direction of the arrow. In the course of this movement, the relatively long wiper blade 9A first comes into sliding contact with the discharge port surface 11, followed by the relatively short wiper blade 9B.

  FIG. 3 is an explanatory diagram of this process. The wiper blade 9 </ b> A is bent relatively large, and its side portion is in sliding contact with the discharge port surface 1, and the head liquid 16 is efficiently transferred to the discharge port surface 1. Even if there is an ink residue on the ejection port surface 1, it is dissolved by the application of the head liquid 16. In this state, the tip (edge) of the wiper blade 9B comes into contact with the discharge port surface 1, whereby the dissolved ink residue is efficiently scraped, and the discharge port surface is cleaned.

  As a result of the wiping, dissolved ink residue is adhered on the wiper blade. When this is caused to flow down along the wiper blade according to the action of gravity, a member for receiving this can be provided below the position of the illustrated wiper holder 10. However, a means (sponge, scraper, etc.) or a process for positively receiving the melt from the wiper blade by contacting the wiper blades 9A and 9B in the vicinity of the supply device 12 to clean the wiper blade is provided. Is preferred. If the liquid for the head is transferred after the wiper blade is in a clean state, it can be immediately prepared for the next wiping.

  Also in performing such cleaning, it is preferable to employ the configuration of the head liquid of the present invention. The wiper blade is made of a material to obtain a desired transfer amount (a transfer amount from the supply device to the wiper blade and a transfer amount from the wiper blade to the discharge port surface) in accordance with the sliding contact with the supply device 12 and the discharge port surface 11. The relative position with respect to the shape, dimensions and sliding contact should be determined. On the other hand, if the weight variation or physical property change of the liquid for the head due to the environmental change is large, a desired transfer amount cannot be obtained and the cleaning property may be deteriorated.

  Next, an Example and a comparative example are given and this invention is demonstrated concretely. The present invention is not limited by the following examples unless it exceeds the gist. In the text, “part” or “%” is based on mass unless otherwise specified.

[Preparation of pigment dispersion]
Each pigment dispersion was prepared by the method described below.
(Preparation of pigment dispersion Bk1)
To a solution of 5 g of concentrated hydrochloric acid dissolved in 5.3 g of water, 1.58 g of anthranilic acid was added while being cooled to 5 ° C. Next, the solution containing the solution is placed in an ice bath and the solution is stirred to keep the solution at 10 ° C. or lower. To this, 8.7 g of water at 5 ° C. and 1.78 g of sodium nitrite are added. The dissolved solution was added. After stirring this solution for another 15 minutes, 7 g of carbon black having a specific surface area of 220 m ² / g and a DBP oil absorption of 105 mL / 100 g was added with stirring. Thereafter, the mixture was further stirred for 15 minutes. After the obtained slurry was filtered with a filter paper (trade name: Standard filter paper No. 2; manufactured by Advantech), the pigment particles were sufficiently washed with water and dried in an oven at 110 ° C. to prepare self-dispersing carbon black 1. . Furthermore, water was added to the self-dispersing carbon black 1 obtained above to disperse the pigment so that the pigment concentration became 10% by mass to prepare a dispersion. By the above method, pigment dispersion Bk1 was obtained in which self-dispersing carbon black 1 having —Ph—COONH ₄ groups introduced therein was dispersed in water on the surface of carbon black particles.

(Preparation of pigment dispersion Bk2)
10 parts of carbon black, 20 parts of an aqueous solution obtained by neutralizing a styrene-acrylic acid copolymer having an acid value of 100 and a weight average molecular weight of 10,000 with 10% ammonia water, and 70 parts of ion-exchanged water were mixed. The carbon black has a specific surface area of 210 m ² / g and a DBP oil absorption of 74 ml / 100 g. Then, it was dispersed for 3 hours using a batch type vertical sand mill. Thereafter, coarse particles were removed by a centrifugal separation treatment, and pressure filtration was performed with a microfilter (manufactured by Fuji Film) having a pore size of 3.0 μm to obtain a pigment dispersion Bk2.

(Preparation of pigment dispersion Bk3)
10 parts of carbon black, 20 parts of an aqueous solution obtained by neutralizing a styrene-acrylic acid copolymer having an acid value of 100 and a weight average molecular weight of 10,000 with a 10% aqueous sodium hydroxide solution, and 70 parts of ion-exchanged water were mixed. . The carbon black has a specific surface area of 210 m ² / g and a DBP oil absorption of 74 ml / 100 g. Then, it was dispersed for 3 hours using a batch type vertical sand mill. Thereafter, coarse particles were removed by centrifugal separation treatment, and pressure filtration was further performed with a microfilter (manufactured by Fuji Film) having a pore size of 3.0 μm to obtain a pigment dispersion Bk3.

(Preparation of pigment dispersion C)
10 parts of pigment (CI Pigment Blue 15: 3), 20 parts of a 10% sodium hydroxide neutralized aqueous solution of a styrene-acrylic acid copolymer having an acid value of 100 and a weight average molecular weight of 10,000, and ions 70 parts of exchange water was mixed. Then, it was dispersed for 3 hours using a batch type vertical sand mill. Thereafter, coarse particles were removed by centrifugal separation treatment, and pressure filtration was further performed with a microfilter (manufactured by Fuji Film) having a pore size of 3.0 μm to obtain pigment dispersion C.

(Preparation of pigment dispersion M)
10 parts of a pigment (CI Pigment Red 122), 20 parts of a 10% sodium hydroxide neutralized aqueous solution of a styrene-acrylic acid copolymer having an acid value of 100 and a weight average molecular weight of 10,000, and ion exchange 70 The parts were mixed. Then, it was dispersed for 3 hours using a batch type vertical sand mill. Thereafter, coarse particles were removed by centrifugal separation, and pressure filtration was further performed with a microfilter (manufactured by Fuji Film) having a pore size of 3.0 μm to obtain a pigment dispersion M.

(Preparation of pigment dispersion Y)
10 parts of pigment (CI Pigment Yellow 74), 20 parts of a 10% sodium hydroxide neutralized aqueous solution of a styrene-acrylic acid copolymer having an acid value of 100 and a weight average molecular weight of 10,000, and ion-exchanged water 70 parts were mixed. Then, it was dispersed for 3 hours using a batch type vertical sand mill. Thereafter, coarse particles were removed by a centrifugal separation treatment, and pressure filtration was further performed with a micro filter (manufactured by Fuji Film) having a pore size of 3.0 μm to obtain a pigment dispersion Y.

[Preparation of aqueous resin solution]
A resin aqueous solution was prepared by the method described below. A resin aqueous solution was obtained by using a 10% by mass aqueous solution of a styrene-acrylic acid copolymer neutralized with sodium hydroxide and having an acid value of 100 and a weight average molecular weight of 10,000.

[Preparation of head liquid and ink]
By mixing each component according to the following Tables 1 and 2 and stirring sufficiently, the liquids for heads 1 to 3, black (Bk) inks 1 to 4, cyan (C) ink, magenta (M) ink, yellow ( Y) Each anionic pigment ink was prepared. Further, the ink set 1 was obtained by combining the Bk ink 4, the C ink, the M ink, and the Y ink.
Tables 1 and 2 show the pH and surface tension values of each head liquid and each anionic pigment ink. The pH was measured at 25 ° C. using a pH meter F-21 (manufactured by Horiba) and the surface tension was measured using an automatic surface tension meter CBVP-Z (manufactured by Kyowa Interface Chemical).

[Evaluation]
(Evaluation 1) Wiping Durability Test A wiping durability test was conducted using the head liquid, ink, and ink set obtained above in the combinations shown in Table 3 below. Assuming an environment in which an ink jet recording apparatus is actually used, the recording apparatus was used and the discharge port surface cleaning operation was continuously performed 5,000 times to confirm changes in the recording state before and after the test. Specifically, the nozzle check pattern built in the ink jet recording apparatus was printed on high-quality exclusive paper (HR-101; manufactured by Canon Inc.), and the displacement (displacing) of the dot formation position was observed.

  As the ink jet recording apparatus, a PIXUS 860i (manufactured by Canon) recovery system modified to have the configuration shown in FIG. 1 was used. Further, an ink tank BCI-3e color (manufactured by Canon) was used as a head liquid and a container for containing the head liquid. The ink tank includes a first liquid chamber portion that stores ink as it is, and a second liquid chamber portion that stores an absorber for impregnating and holding ink to generate a negative pressure that is preferable for the nozzles of the recording head. Is. However, modification was made so that the sliding contact of the wiper blade and the transfer of the liquid for the head were good. The temperature was evaluated at 15 ° C. assuming an environment where an actual ink jet recording apparatus is used.

The obtained nozzle check pattern was visually confirmed and evaluated. The evaluation criteria for the wiping durability test are as follows. The evaluation results are shown in Table 3.
[Evaluation criteria]
A: There is no twist in the nozzle check pattern.
B: Twist occurs in part of the nozzle check pattern.
C: A twist occurs in the entire nozzle check pattern.
D: A part of the nozzle check pattern cannot be recorded.

(Evaluation 2) Evaluation of Adhesion in the Nozzle Adhesion in the nozzle was evaluated using the head liquid, ink, and ink set obtained above in the combinations shown in Table 3 below. The ink jet recording apparatus similar to that used in the wiping durability test was capped with a capping rubber using a capping rubber in a state where the recording head subjected to the suction recovery operation and the ink containing portion were combined, and the temperature was 35 ° C. and the humidity was 10 % Environment for 2 weeks. Then, it was left for 2 hours in an environment of temperature 25 ° C. and humidity 50%. Thereafter, the suction recovery system of the ink jet recording apparatus was used to measure how many times the suction recovery operation returned the recording to the normal state. The evaluation criteria for sticking in the nozzle are as follows. The evaluation results are shown in Table 3.

[Evaluation criteria]
A: Recovery is performed in 3 or less suction recovery operations.
B: Recovered by suction recovery operation 4 times or more and 7 times or less.
C: Recovered by suction recovery operation 8 times or more and 10 times or less.
D: No matter how many times the suction recovery operation is performed, there is non-ejection and the recording does not return to normal.

［判定基準］
Ａ：平均粒径増大率が２０％以下
Ｂ：平均粒径増大率が２０％を上回る (Evaluation 3) Evaluation of Average Particle Size Increasing Rate Volatile components such as moisture in the ink are increased to an extent that the average particle size of the pigment in each ink and each ink constituting the ink set 1 shown in Table 3 is increased by 20%. After evaporation (this ink is referred to as “evaporated ink”), each evaporated ink and each head liquid are mixed at a 1: 1 (mass ratio) to prepare a mixed solution, and the pigment in each mixed solution The average particle size of was measured. In addition, the laser zeta electrometer ELS-8000 (made by Otsuka Electronics) was used for the measurement of the average particle diameter of a pigment. Thereafter, the average particle diameter of the pigment in the ink before evaporation and the average particle diameter of the pigment in the mixed liquid were determined, and the average particle diameter increase rate was calculated according to the following formula. The evaluation criteria for the average particle size increase rate are as follows. The evaluation results are shown in Table 4.

[Criteria]
A: Average particle size increase rate is 20% or less B: Average particle size increase rate exceeds 20%

  In the wiping durability test (Evaluation 1), the same results as in Table 3 were obtained even when the evaluation was performed at 30 ° C. From Table 3 above, it was confirmed that when the pH of the head liquid was set higher than the pH of the ink, the wiping property of the discharge port surface was improved and sticking in the nozzle was suppressed. Furthermore, the accuracy of the dot formation positions of Examples 1, 4, and 6 was higher than the accuracy of the dot formation positions of Examples 2, 3, and 5. Therefore, by setting the surface tension of the liquid for the head to be lower than the surface tension of the ink, not only the sticking in the nozzle is further suppressed, but also the wiping property of the pigment ink residue adhering to the discharge port surface is also achieved. It was also confirmed that it improved further.

1 is a schematic perspective view of a main part of an ink jet recording apparatus according to an embodiment of the present invention. It is a typical side view which shows an example of the cleaning apparatus applied to the inkjet recording device of FIG. It is a schematic diagram for demonstrating operation | movement of the cleaning apparatus of FIG.

Explanation of symbols

1: Recording head 2: Ink tank 3: Guide shaft 4: Linear encoder 5: Endless belt 6: Recording medium 7: Recovery mechanism 9A, 9B: Wiper blade 10: Wiper holder 11: Discharge port surface 12: Head liquid supply device 14 : Water replenishing device 16: Liquid for head 100: Carriage 503: Pulley

Claims (11)

  A liquid for a head supplied to a surface having an ejection port for ejecting an ink jet ink containing a pigment dispersed by an anionic substance or a pigment having an anionic group on the surface, the head liquid A liquid for a head, wherein the pH of the liquid is higher than the pH of the ink-jet ink.   The head liquid according to claim 1, wherein a surface tension of the head liquid is lower than a surface tension of the inkjet ink.   On the surface having an ejection port for ejecting each of the inkjet inks of black ink, cyan ink, magenta ink, and yellow ink containing a pigment dispersed by an anionic substance or a pigment having an anionic group on the surface. A head liquid to be supplied, wherein the pH of the head liquid is higher than the pH of all the inkjet inks.   The head liquid according to claim 3, wherein a surface tension of the head liquid is lower than a surface tension of all the inkjet inks.   The head liquid according to claim 1, wherein the inkjet ink further contains a volatile alkali component.   The head liquid according to claim 1, wherein the head liquid is stored in a container.   Inkjet having a discharge port for discharging an inkjet ink comprising a pigment dispersed by an anionic substance or a pigment having an anionic group on the surface, and a cleaning mechanism for cleaning the surface having the discharge port An ink jet recording apparatus using the head liquid according to claim 1 in the recording apparatus.   Inkjet recording, wherein the cleaning mechanism includes means for supplying the head liquid according to any one of claims 1 to 6 to a surface having an ejection port, and means for replenishing the head liquid with water. apparatus.   9. The ink jet recording apparatus according to claim 7, wherein in the cleaning mechanism, the head liquid is supplied via an application member that moves relative to a surface having an ejection port.   A method of cleaning a surface having a discharge port for discharging an inkjet ink comprising a pigment dispersed by an anionic substance or a pigment having an anionic group on the surface with a liquid for a head. A method for cleaning a surface having an ejection port for inkjet ink, wherein the surface having an outlet is cleaned with a head liquid having a pH higher than that of the inkjet ink. The method for cleaning a surface having an ejection port for inkjet ink according to claim 10, wherein a surface tension of the head liquid is lower than a surface tension of the inkjet ink.

Images