JP6228634B2 - Ink jet recording ink and ink jet recording method - Google Patents

Description

  The present invention relates to an ink for ink jet recording, an ink jet recording method, an ink jet recording head and an ink jet recording apparatus using the ink, and is particularly suitable for thermal ink jet recording, particularly when applied to a line type recording head. It is related to useful technology.

  Inkjet recording devices have advantages such as low noise, low running cost, easy miniaturization of the device, and easy printing of small amounts of full-color. It is widely applied to machines and the like, and its use is wide-ranging for home use, office use, and industrial use.

  There are two types of recording methods for inkjet recording devices: the thermal method and the piezo method. Among them, the thermal method that generates bubbles in the ink in the nozzles by heating and ejects the ink has a relatively simple head structure and has a high printing speed. There is an advantage that it is excellent in high speed and high density of printing pixels. The structure of inkjet recording heads (also referred to as recording heads or simply heads) has evolved and is compatible with paper widths in addition to the conventional serial method in which paper is sent while reciprocating the head left and right. A line system that uses a long head and performs printing by feeding only paper without moving the head has been adopted. The line method is suitable for high-speed printing because paper can be sent under a fixed long head, making it suitable for high-speed printing and industrial applications that require high-quality printing and high-speed printing. It is being adopted in the field of printers.

  In the thermal ink jet recording method, moisture is evaporated from the ink in the nozzles when heated, and the viscosity of the ink increases. This causes clogging of the nozzles and the ink sticks to the head. There is a problem that image defects such as ink ejection failure and twisting are likely to occur. On the other hand, in the serial method, the inside of the nozzle is always kept fresh by performing an operation (preliminary ejection) for discharging the ink evaporated in the nozzle to the cap every time one scan is completed. However, in the case of the line method, since the head is fixed, the recovery operation such as preliminary discharge performed by the serial method cannot be performed. When nozzle clogging or sticking occurs in the line-type head, it is necessary to stop printing and restore the head state so that ink is normally ejected from the nozzle row. For this reason, if the head recovery operation is frequently performed in the case of a line-type head, printing must be stopped each time, so that productivity is lowered. In addition, if the ink is firmly fixed, even a serial-type head cannot be easily recovered by a cleaning operation such as preliminary ejection, so even if the ink adheres to the head, the head can be properly operated by a simple cleaning operation. There is a need to be able to recover to a new state.

  Due to the above circumstances, in particular, ink jet recording using a line-type head (hereinafter also referred to as a line-type head) is stable without image defects such as discharge failure and twisting without reducing its productivity. In order to print a simple image, it is required for the ink for ink jet recording to be used that an image defect due to nozzle clogging does not occur even when exposed to air.

  On the other hand, as a method for suppressing clogging of the nozzles of the ink for ink jet recording, it is possible to use ink that does not contain moisture such as oil-based ink or solid ink. However, safety, environmental impact, energy saving From the viewpoint, there is a strong demand for water-based ink. For this reason, in the water-based ink for ink jet recording, various proposals have been made so far to suppress the occurrence of nozzle clogging.

  For example, an ink comprising a self-dispersing pigment having a phosphonic acid group whose surface is modified as a functional group, and ethylene urea as a water-based inkjet recording ink in which nozzle discharge ports are not easily clogged Has been proposed (Patent Document 1). In Patent Document 1, the ink for ink jet recording having the above-described configuration suppresses the retention of ink in the cap for covering the recording head, and the reliability that the fixing and recovering property of the ink in the recording head is excellent. It is described that both the image characteristics of being able to record an image excellent in density and bleeding resistance are compatible.

  In addition, a recording liquid (ink) having a water activity (Aw) of 0.70 to 0.90 has been proposed as a water-based inkjet recording ink that is less likely to clog the discharge port (patent) Reference 2). Patent Document 2 describes that, by using the above-described configuration, the ink hardly causes precipitation of solid content or changes in physical properties during storage, and nozzle clogging hardly occurs.

  In addition, a water-based inkjet ink containing a water-soluble compound having a hydrophilicity / hydrophobicity coefficient of 0.26 or more determined from a water activity value and defining the total amount of anionic functional groups of the self-dispersing pigment and the amount of cesium ions contained in the ink A recording ink has been proposed (Patent Document 3). Patent Document 3 describes that, by adopting the above-described configuration, the optical density of an image obtained while ink penetrates quickly into plain paper is high, and further, clogging at a nozzle is suppressed. Has been.

JP 2012-31350 A JP-A 61-157666 JP 2011-195826 A

  However, according to detailed studies by the present inventors, in the techniques described in the above-mentioned Patent Documents 1 to 3, the ink in the vicinity of the nozzles is particularly used when performing high-speed printing with a line-type head in thermal ink jet recording. However, evaporation may progress too much, and ink clogging may occur in the nozzles. As described above, in the case of an image failure such as ink ejection failure or twist due to ink clogging, the line head stops printing and ink is normally ejected from the nozzle array. Thus, it is necessary to recover the state of the head. In particular, suppression of ink clogging is an important problem. In addition, due to the recent demand for higher image quality for inkjet recording, ejected ink droplets are becoming smaller and the nozzle opening area tends to be smaller. From this point as well, suppression of nozzle clogging is a solution. It is an important issue to be done. Furthermore, it is possible to suppress the occurrence of ink sticking to the head regardless of the structure of the head, and at the same time, even if ink sticking occurs on the head, the head quickly returns to a normal state by a simple recovery operation. Development of an ink excellent in solubility and fixing recovery is desired.

  The problem of ink clogging described above is more marked when pigment inks using pigments are used as coloring materials than inks using dyes as coloring materials. Ink clogging tends to occur when a resin-dispersed pigment is used as a color material. Here, in particular, in a thermal ink jet recording ink, a block copolymer having a hydrophobic block and a hydrophilic block has been conventionally used as a polymer dispersant used for dispersing a pigment. By using the coalescence for pigment dispersion, stable ink ejection and storage stability have been achieved. On the other hand, with the progress toward industrial use, mainly from the economical point of view, studies have been made on polymer dispersants used for pigment dispersion, replacing block copolymers that are difficult to design and synthesize. Thus, random copolymers can be used. However, since it has not been used so far, the ink eye generated when an ink using a resin dispersed pigment using a random copolymer as a polymer dispersant as a coloring material is used for thermal ink jet recording. Suppression of clogging, in particular, suppression of ink clogging that occurs when recording with a line-type head has not been sufficiently studied, and the present inventors have also considered clogging of ink, particularly in such a case. As a result, it has been recognized that there is an urgent need to develop an ink for ink jet recording that can effectively and stably suppress ink.

  Therefore, the present invention, which is likely to occur particularly when performing thermal ink jet recording, can effectively prevent clogging even when ink evaporation proceeds, and has good remeltability and fixing recovery. The object is to provide ink. More specifically, the object of the present invention is to effectively suppress the occurrence of clogging and sticking of the nozzles of the recording head due to its high re-dissolvability, and at the same time, even if the ink sticks to the head, the high sticking Provided is a water-based ink for ink jet recording suitable for recording with a line-type head compatible with high-speed printing, in which the head can be quickly recovered to a normal state by a simple cleaning operation due to the recoverability. There is.

  The above object is achieved by the ink jet recording ink, ink jet recording method, ink jet recording head, and ink jet recording apparatus of the present invention having the following configurations.

[1] Ink jet recording ink:
The present invention relates to an ink jet recording ink containing a pigment, water, and a water-soluble compound, wherein the pigment has an acid value of 100 mgKOH / g or more and 160 mgKOH / g or less. A resin-dispersed pigment dispersed by a random copolymer of the above, wherein the water-soluble compound comprises at least ethylene urea and a water-soluble compound having a hydrophilicity / hydrophobicity coefficient defined by the following formula (A) of 0.37 or less. And the total content of the water-soluble compounds is 22% by mass or more and 50% by mass or less with respect to the total amount of the ink, and the content of the ethylene urea is 11.0% by mass or more with respect to the total amount of the ink. And an ink for inkjet recording, characterized in that the proportion of ethylene urea in the total amount of the water-soluble compound is 50% or less on a mass basis That.

[2] Inkjet recording method:
The present invention is an ink jet recording method for performing recording by ejecting ink from a nozzle row by a thermal method, wherein each nozzle has an opening area of 100 to 350 μm ² , and the ink is the above ink. I will provide a.

  The present invention is an ink jet recording method for performing recording by ejecting ink from a nozzle array by a thermal method, wherein the total number of nozzles per nozzle array is 1200 or more, and the length of the nozzle array is 2 inches or more. Provides an ink jet recording method which is the above ink.

[3] Inkjet head:
The present invention is an ink jet recording head that contains ink and ejects the ink from a nozzle array by a thermal method. The opening area of each nozzle is 100 to 350 μm ² , and the total number of nozzles per nozzle array is 1200. As described above, there is provided an ink jet recording head in which a nozzle row has a length of 2 inches or more and the stored ink is the above ink.

  The present invention relates to an inkjet recording head that contains ink and ejects the ink from a nozzle row by a thermal method, and includes a common liquid chamber in which a plurality of nozzle passages communicate with each other as the nozzle row, and the common liquid chamber An opening in communication with the main liquid supply chamber in communication with the opening, a liquid supply path in communication with the main liquid supply chamber, a liquid supply chamber in communication with the liquid supply path, and the liquid supply chamber. Provided in a part of the main liquid supply chamber, a supply filter disposed so as to be separated into a first liquid supply chamber and a second liquid supply chamber from the upstream side along the flow at the time of liquid supply A gas-liquid separator, and an air chamber communicating with the gas-liquid separator, the nozzle channel, the common liquid chamber, the opening, the main liquid supply chamber, and the liquid supply path The liquid supply chamber and the supply filter The gas-liquid separation part and the air chamber are arranged on a plane parallel to a plane including the arrangement direction of the nozzle flow paths and the liquid discharge direction, and the main liquid supply chamber and the liquid The supply path, the supply filter, the gas-liquid separator, and the air chamber are arranged without being stacked, and the ink stored therein is the above-described ink. provide.

[4] Inkjet recording apparatus:
The present invention relates to an ink jet recording apparatus including an ink storage portion and a recording head for ejecting ink, wherein the ink mounted on the ink storage portion is the ink described above, and the recording head is An ink jet recording apparatus characterized by being one of the above-described ink jet recording heads is provided.

  According to the present invention, the occurrence of clogging can be effectively suppressed even after evaporation of the ink, which is likely to occur particularly when performing thermal ink jet recording, and the re-dissolution property and the fixing recovery property are good. Ink is provided. More specifically, according to the present invention, the high remeltability can effectively suppress the clogging and fixing of the nozzles of the recording head, and at the same time, even if the ink is fixed to the head, the high fixing Inkjet that can recover the head to a normal state promptly with a simple cleaning operation due to its resilience, especially when applied to high-resolution line-type heads that support high-speed printing A water-based ink for recording is provided.

FIG. 3 is a top view schematically showing an internal structure of a nozzle of a recording head. It is a side view which shows typically the internal structure of the nozzle shown to FIG. 1A. It is a front view which shows typically the ink discharge port of the nozzle shown to FIG. 1A. FIG. 3 is a front view schematically showing the recording head of the present invention. It is AA sectional drawing of the recording head shown to FIG. 2A. It is a BB sectional view of the recording head shown in FIG. 2A. It is an expanded sectional view of an ink tank. FIG. 3 is an enlarged cross-sectional view of a recording head. FIG. 5 is an enlarged perspective view of the ink holding member shown in FIG. 4. It is Vb-Vb sectional drawing of the ink holding member shown to FIG. 5A. 1 is a schematic configuration diagram schematically illustrating an overall configuration of an ink jet recording apparatus. It is a block block diagram of the control system of the recording apparatus shown in FIG. 6 is a flowchart showing a recording head recovery sequence process.

  Hereinafter, the present invention will be described in detail. However, the present invention is not limited to the following embodiment, and includes all objects having the invention-specific matters. In this specification, “recording” refers not only to forming significant information such as characters, figures and symbols on a recording medium, but also to forming images, patterns, patterns, etc. that have no special meaning. Something to do is included.

  As a result of intensive studies to solve the above-described problems of the prior art, the present inventors have designed ink compositions useful for inks using resin-dispersed pigments as coloring materials, particularly inks for thermal ink jet recording, among others. By improving the composition of the water-soluble compound to be used, it is particularly effective for inkjet recording when recording is performed using a line-type head that cannot perform recovery operations frequently because printing needs to be stopped. The inventors have found that an ink can be provided and have arrived at the present invention. In other words, in the present invention, by improving the composition of the water-soluble compound contained in the ink, it is possible to remarkably improve the suppression of ink clogging, and at the same time, even if the ink sticks to the recording head. Provided is an ink for ink jet recording (hereinafter, also simply referred to as ink) having good re-dissolvability and fixing recovery, which can quickly restore the head to a normal state by a simple cleaning operation.

  The background to the present invention will be described below. As described above, for example, the technique described in the cited document 1 is a technique using a self-dispersing pigment whose dispersibility is improved by modifying the pigment itself as a coloring material, This cannot be applied as it is to an ink using a random copolymer, which is difficult to obtain more stable dispersibility than a block copolymer as a resin-dispersed pigment, particularly a dispersant. Further, the ink having a water activity (Aw) described in the cited document 2 of 0.70 to 0.90 is considered not to cause nozzle clogging, but according to the study by the present inventors. Even with such an ink, the problem of nozzle clogging may not be improved, and it is difficult to stably suppress nozzle clogging particularly in thermal ink jet recording using a line-type head. Further, in the above case as well, no detailed study has been made on means for suppressing the occurrence of ink clogging when the dispersant for the resin-dispersed pigment used as the colorant is a random copolymer. For such a situation, as described above, particularly in inkjet recording using a line-type head, it is necessary to interrupt printing for the nozzle recovery operation. Even in the above-described cases, ink clogging can be reliably and stably suppressed, and image formation such as image distortion caused by ink clogging does not occur. In view of the urgent need to develop a water-based pigment ink capable of achieving this, the present invention has been achieved through detailed studies.

  In particular, in the aqueous pigment ink using a resin-dispersed pigment having a random copolymer as a dispersant, which is inferior in dispersion stability to a block copolymer, the occurrence of ink clogging or In order to suppress the sticking to the head, it is important to further improve the dispersion stability of the pigment in the ink, and a detailed study was conducted on a water-soluble compound having a large influence on the dispersion stability. In the process of studying the present invention, particularly in thermal ink jet recording, when ink is ejected, water in the ink is evaporated by the head, and the ink is in a concentrated state. This causes clogging and sticking of the ink in the nozzle, so if the concentrated ink in such a state can be quickly re-dissolved by the newly transported ink to the nozzle, We thought that the above-mentioned problems could be solved all at once. As a result, the present inventors use a water-soluble compound having a hydrophilicity / hydrophobicity coefficient of 0.37 or less as a water-soluble compound to be used with water. In that case, the amount of these water-soluble compounds is reduced. While there is a problem that a solvent shock occurs when the number is increased, the configuration specified in the present invention can realize good and stable ink ejection, effectively preventing the occurrence of ink clogging. The present invention has been found by finding that the ink has a good balance with excellent solubility and fixing recovery.

  In the ink of the present invention, the content of the water-soluble compound in the aqueous pigment ink is 22% by mass or more and 50% by mass or less with respect to the total amount of the ink, and the water-soluble compound used has a hydrophilicity / hydrophobicity coefficient of 0. The water-soluble compound of 37 or less and solid ethylene urea are used in combination, and ethylene urea is used in an amount of 11.0% by mass or more based on the total amount of the ink. The proportion of ethylene urea in the amount was 50% or less on a mass basis. Specifically, examples of the water-soluble compound having a hydrophilicity / hydrophobicity coefficient of 0.37 or less as defined in the present invention include glycerin and the like. When the content of glycerin increases, the viscosity of the ink increases. As a result, there is a problem that the ink discharge performance is impaired. On the other hand, it was confirmed that the content of the water-soluble compound in the ink can be increased by using ethylene urea together. That is, when a water-soluble compound having a hydrophilicity / hydrophobicity coefficient of 0.37 or less and ethylene urea are used in combination, the water-soluble compound is 22% by mass or more and 50% by mass with respect to the total amount of the ink without causing a solvent shock. It can be contained in the following range.

  Furthermore, as described above, when the amount of ethylene urea is included in the range that satisfies the requirements defined in the present invention, the ink is difficult to evaporate, and the dried ink after the moisture of the ink has evaporated When the dried ink is mixed with new ink, it quickly redissolves in a good state without deposits. Even if the ink adheres to the head, it can be quickly cleaned with a simple cleaning operation. The present invention was found by finding that the ejection state of the head can be recovered to a good one. Specifically, the ink of the present invention is used in combination with a water-soluble compound having a hydrophilicity / hydrophobicity coefficient of 0.37 or less, and the amount of solid ethylene urea is 11.0% by mass or more based on the total amount of the ink. However, the ratio of ethylene urea in the total amount of the water-soluble compound is designed to be 50% or less on a mass basis. If the proportion of ethylene urea in the total amount of the water-soluble compound exceeds 50%, when the dry ink is mixed with new ink, the dry ink dissolves, but ethylene urea is deposited, The discharge stability is impaired. Hereinafter, the structure of the ink characterizing the present invention will be described.

[1] Ink jet recording ink:
The ink for ink jet recording of the present invention (hereinafter simply referred to as ink) contains, as essential components, a pigment, water, and a water-soluble compound, and the pigment has an acid value of 100 mgKOH / g or more and 160 mgKOH / g or less. It is a resin-dispersed pigment dispersed by a certain (meth) acrylic acid ester-based random copolymer, and the production method is a conventional method, and can be obtained by, for example, the method disclosed in Japanese Patent No. 49596917. The water-soluble compound includes at least ethylene urea and a water-soluble compound having a hydrophilicity / hydrophobicity coefficient defined by the following formula (A) of 0.37 or less. The ink of the present invention may contain a water-soluble compound having a hydrophilicity / hydrophobicity coefficient of 0.37 or more, a surfactant, and other solvents and additives as necessary. Hereinafter, it demonstrates for every component.

[1-1] Water-soluble compound:
The ink of the present invention contains ethylene urea and a water-soluble compound having a hydrophilicity / hydrophobicity coefficient defined by the following formula (A) of 0.37 or less as essential components.

  The water activity value in the formula (A) is expressed by water activity value = (water vapor pressure of aqueous solution) / (water vapor pressure of pure water). 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 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 hydrophilicity or hydrophobicity of various solutes is possible. Moreover, 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 coefficients of various water-soluble compounds obtained by the formula (A). As the water-soluble compound used in the present invention, 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. For example, any water-soluble compound having a hydrophilicity / hydrophobicity coefficient of 0.37 or less among those listed in Table 1 can be used for the ink of the present invention. It is not limited. Examples of particularly preferred water-soluble compounds for the ink of the present invention include glycerin, triethylene glycol, and bishydroxyethyl sulfone.

  As described above, the present inventors use a water-soluble compound having a hydrophilicity / hydrophobicity coefficient of 0.37 or less as mentioned above in combination with ethylene urea, and the content thereof is defined in the present invention. When the ink content is within the range, the ink is difficult to evaporate, the moisture retention is good even after drying, and the ink is found to have good re-dissolvability and fixing recovery property of the dried ink, thereby achieving the present invention. .

[1-2] Color material:
The color material of the ink of the present invention is obtained by dispersing a pigment in a water-soluble medium. Also, it is a type called pigment-resin dispersion (resin dispersion pigment), and among them, a (meth) acrylic ester random copolymer having an acid value of 100 mgKOH / g or more and 160 mgKOH / g or less is adsorbed to form an aqueous solution. It is dispersed in a medium. The production method is based on a conventional method, and can be obtained by, for example, the method disclosed in Japanese Patent No. 4956917.

[1-2A] Pigment:
Examples of the pigment relating to the present invention include carbon black and organic pigments. These pigments can be used alone or in combination of two or more.

Specific examples of carbon black are carbon black pigments such as furnace black, lamp black, acetylene black, and channel black. For example, as a trade name, Ray Van (manufactured by Lombia), Black Pearls L, Legal, Mogul L, Monarch, Vulcan (Cabot), Color Black, Printex, Special Black (Degussa), Mitsubishi Carbon Those having a title such as black (manufactured by Mitsubishi Chemical Corporation) can be used. Of course, it is not limited to these, and conventionally known carbon black can also be used. Physically, the carbon black used in the present invention has a primary particle size of 10 nm to 40 nm, a specific surface area by the BET method of 50 to 400 m ² / g or less, an oil supply amount of 40 to 200 ml / 100 g or less, and a volatile content. The carbon black is preferably 0.5 to 10% and the pH is 2 to 9. Particularly, when it has such characteristics, it effectively acts on the effects of the present invention. The DBP absorption is measured by the JIS K6221 A method.

  Specific examples of organic pigments include insoluble azo pigments such as toluidine red, toluidine maroon, Hansa Yellow, Benzidine Yellow, and pyrazolone red, soluble azo pigments such as Ritolol Red, Helio Bordeaux, Pigment Scarlet, and Permanent Red 2B, Alizarin, Indantron , Derivatives from vat dyes such as 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 yellow Isoindolinone pigments such as isoindolinone orange, imidazolone face such as benzimidazolone yellow, benzimidazolone orange, and benzimidazolone red , Pyranthrone pigments such as pyranthrone red, pyranthrone orange, thioindigo pigment, condensed azo pigment, thioindigo pigment, flavanthrone yellow, acylamide yellow, quinophthalone yellow, nickel azo yellow, copper azomethine yellow, perinone orange, Other pigments such as anthrone orange, dianthraquinonyl red, dioxazine violet can be exemplified.

Moreover, when an organic pigment is shown by a color index (CI) number, the following can be illustrated. Of course, conventionally known organic pigments can be used other than the following.
C. 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
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: 1, 15: 3, 15: 4, 15: 6, 22, 60, 64
C. I. Pigment Green: 7, 36
C. I. Pigment Brown: 23, 25, 26

[1-2B] Resin that functions as a dispersant:
In the ink of the present invention, a resin-dispersed pigment dispersed with a (meth) acrylic acid ester-based random copolymer is used as a color material. In the present invention, a (meth) acrylic ester copolymer more preferable from the viewpoint of dischargeability is used as a dispersant. The (meth) acrylic acid ester copolymer used in the present invention is obtained by copolymerizing (meth) acrylic acid, (meth) acrylic acid ester and a monoethylenically unsaturated monomer copolymerizable therewith. Can be obtained. Examples of (meth) acrylic acid include acrylic acid or methacrylic acid, and (meth) acrylic acid is preferably used considering that the coexistence range of the electrical neutral state and the anion state can be controlled widely. The (meth) acrylic acid ester-based copolymers include those having a random structure, a block structure, and a graft structure. Among them, the random copolymer is used in the present invention. This is because, other than random copolymers, for example, block copolymers and the like have many other problems in which the hydrophilicity of the pigment is high and the printed image formed is often inferior in water resistance.

[1-2B-1] Monomer component for producing resin:
Examples of (meth) acrylic acid include acrylic acid or methacrylic acid. Among them, considering that the coexistence range of the electrical neutral state and the anion state can be widely controlled, availability, price, etc. Acrylic acid is preferred. Examples of the (meth) acrylic acid ester include methyl (meth) acrylate, n-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, and (meth) acrylic acid. Alkyl (meth) acrylates such as dodecyl, octadecyl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, Hydroxyalkyl (meth) acrylates such as 3-hydroxypropyl (meth) acrylate, diethylene glycol mono (meth) acrylate, triethylene glycol mono (meth) acrylate, polyethylene glycol mono (meth) acrylate, propylene glycol mono (meta) Acrylate, dipropylene glycol mono (meth) acrylate, tripropylene glycol mono (meth) acrylate, tetramethylene ether glycol mono (meth) acrylate, random polymer glycol of polyethylene oxide-polypropylene oxide or mono (meth) of the block polymer glycol Examples include acrylate, alkylene oxide mono (meth) acrylate such as polyethylene oxide-polytetramethylene ether random polymer glycol or mono (meth) acrylate of the same block polymer glycol, glycidyl (meth) acrylate, benzyl (meth) acrylate, and the like. It is done.

  The (meth) acrylic acid ester-based copolymer used in the ink of the present invention is a styrene-based monomer in addition to the above-mentioned (meth) acrylic acid, (meth) acrylic acid ester, monoethylenically unsaturated monomer. The body can also be included. Here, examples of the styrene monomer include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, pt-butylstyrene, 4-methoxystyrene, and 4-chlorostyrene. Etc. That is, the above (meth) acrylic acid ester copolymer is preferably a styrene- (meth) acrylic acid copolymer having a styrene monomer.

[1-2B-2] Characteristics of resin:
In the ink of the present invention, a (meth) acrylic acid ester copolymer synthesized from the above-described monomer is used, and an acid having an acid value of 100 mgKOH / g or more and 160 mgKOH / g or less is used. More preferably, it is 110 mgKOH / g or more and 150 mgKOH / g or less. When the acid value exceeds 160 mgKOH / g, the hydrophilicity of the pigment is increased, so that the pigment is dissolved due to adhesion of water or the like, and bleeding of the printed matter is likely to occur. On the other hand, when the acid value is less than 100 mgKOH / g, the discharge stability of the aqueous pigment ink in the thermal method of the ink jet printer tends to be lowered. Here, the acid value is the amount (mg) of KOH required to neutralize 1 g of resin and can serve as an index indicating the hydrophilicity. The acid value in this case can also be obtained by calculation from the composition ratio of each monomer constituting the resin dispersant. As a specific method for measuring the acid value of the resin dispersed pigment, the acid value is determined by potentiometric titration. It can be measured using Titrino (manufactured by Metrohm) or the like.

  The weight average molecular weight of the (meth) acrylic acid ester copolymer used in the ink of the present invention is preferably in the range of 6,000 to 12,000 in terms of weight average molecular weight (Mw) in terms of styrene. More preferably, it is in the range of 000 to 9,000. By setting it in the above range, the dispersion stability of the resin-dispersed pigment can be increased, the viscosity can be set low, the kogation in the heater portion can be suppressed, and stable printing can be performed for a long time. If the weight average molecular weight is less than 6,000, the dispersion stability of the aqueous resin-dispersed pigment itself is lowered, which is not preferable. On the other hand, if it exceeds 12,000, not only is the viscosity of the aqueous resin-dispersed pigment increased, but also a tendency for the dispersibility to decrease is observed, which is not preferable. Furthermore, since the kogation for the heater portion becomes severe and causes a non-ejection of ink droplets from the nozzle tip of the thermal ink jet printer, it is not preferable.

[1-2B-3] Amount of resin relative to pigment:
In the ink of the present invention, the resin-dispersed pigment described above is applied to the coloring material. In this case, the ratio of the pigment and the (meth) acrylic acid ester-based copolymer maintains the dispersibility of the dispersion. From the viewpoint of keeping the viscosity of the ink low, it is adjusted so that the (meth) acrylic acid ester copolymer is in the range of 0.2 to 1.0 part by mass with respect to 1 part by mass of the pigment in terms of this mass. It is preferable.

[1-2C-1] Resin-dispersed pigment The resin-dispersed pigment used in the ink of the present invention is prepared, for example, by coating the above-mentioned pigment with a (meth) acrylic ester polymer as described above. it can. The average particle diameter of the resin-dispersed pigment used in the present invention is preferably 70 nm or more and 150 nm or less, more preferably 80 nm or more and 120 nm or less, as determined by a dynamic light scattering method in liquid. . When the particle diameter exceeds 150 nm, the ink sedimentation is promoted, and dispersion stability over a long period of time is impaired, which is not preferable. On the other hand, when the particle diameter is smaller than 70 nm, it is not preferable because sufficient color forming property for forming an image and sufficient weather resistance for the obtained image cannot be obtained. As a specific method for measuring the average particle size, for example, FPAR-1000 (manufactured by Otsuka Electronics Co., Ltd., cumulant method analysis), Nanotrac UPA 150EX (manufactured by Nikkiso, 50% integrated value) using laser light scattering And the like.

  The amount of the above-described resin dispersed pigment added to the ink is 0.5% by mass or more and 10% by mass or less, more preferably 1.0% by mass or more and 8.0% by mass or less, and still more preferably based on the total amount of the ink. Is preferably 1.5% by mass or more and 6.0% by mass or less. When the pigment concentration is less than 0.5% by mass, it is not possible to obtain sufficient color developability to form an image, and when it exceeds 10.0% by mass, the viscosity of the aqueous pigment ink increases. Since discharge becomes difficult, it is not preferable.

[1-2C-2] Manufacturing Method In the ink of the present invention, the resin-dispersed pigment as described above is used for the color material, and the resin-dispersed pigment can be obtained by the following manufacturing method. For example, as a method of coating a pigment with a (meth) acrylic acid ester-based polymer, it is preferable to incorporate an acid precipitation step in the production process. In this case, the acid precipitation step is performed by adding an acidic substance to a liquid medium containing a pigment and a (meth) acrylic acid ester copolymer dissolved in an aqueous solution of a basic substance to acidify it. The anionic group in the (meth) acrylic acid ester copolymer is returned to the functional group before being neutralized to precipitate the polymer.

  As a specific acid precipitation step performed at this time, an acid such as hydrochloric acid, sulfuric acid or acetic acid is added to an aqueous dispersion obtained through a dispersion step and a distillation step carried out as necessary, and then acidified, And a step of depositing a (meth) acrylic ester copolymer in a dissolved state by forming a salt with the pigment particle surface. By carrying out such a step, the interaction between the pigment and the (meth) acrylic ester copolymer can be further enhanced. As a result, the pigment particles can be dispersed in the aqueous medium, and as an aqueous resin dispersed pigment, the physical properties such as the dispersion arrival level, the time required for dispersion and the dispersion stability, the solvent resistance, etc. In terms of suitability for use, a more excellent effect can be fully exhibited. A filtration step is carried out to separate the precipitate obtained by enhancing the interaction in this way, and more preferably, the precipitate is washed after the filtration step and washed to be adsorbed in the resin-dispersed pigment. An aqueous resin-dispersed pigment that is more excellent in dispersion stability can be obtained by removing the existing free polymer and performing a redispersion step in which the free polymer is dispersed again in the aqueous medium together with the basic substance.

[1-3] Surfactant:
In the present invention, the surface tension of the ink, which will be described later, is controlled to arbitrarily control the degree of ink bleed and penetrability in the recording medium, to improve the wettability of the ink in the head, and to control the ink on the heater surface. For the purpose of preventing gating and improving ejection, if necessary, the ink comprising the above-described components may further contain a surfactant. Such a surfactant is not particularly limited, and examples thereof include the following. These surfactants may be used alone or in combination.

[Nonionic surfactant]
Polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, polyoxyethylene alkylphenyl ether, polyoxyethylene / polyoxypropylene block copolymer, and the like. Fatty acid diethanolamide, acetylene glycol ethylene oxide adduct, acetylene glycol surfactant, and the like.

[Anionic surfactant]
Polyoxyethylene alkyl ether sulfate, polyoxyethylene alkyl ether sulfonate, polyoxyethylene alkyl phenyl ether sulfate, polyoxyethylene alkyl phenyl ether sulfonate, and the like. Alpha sulfo fatty acid ester salts, alkylbenzene sulfonates, alkylphenol sulfonates, alkylnaphthalene sulfonates, alkyltetralin sulfonates, dialkylsulfosuccinates and the like.

[Cationic surfactant]
Alkyltrimethylammonium salt, dialkyldimethylammonium chloride and the like.

[Amphoteric surfactant]
Alkyl carboxybetaines and the like.
Among these, acetylene glycol surfactants, polyoxyethylene alkyl ethers, and the like are particularly preferably used because they can improve ink ejection stability.

  As the acetylene glycol surfactant, the compound (1) represented by the following general formula (1) (2,4,7,9-tetramethyl-5-decyne-4,7-diol, or an ethylene oxide adduct thereof) ) Is used.

(In General Formula (1), U + V is an integer of 0 to 20)

[1-4] Other solvents:
The ink of the present invention may further contain another water-soluble organic solvent as necessary. The type of the water-soluble organic solvent is not particularly limited, but various water-soluble substances such as alcohols, polyhydric alcohols, glycol ethers, carboxylic acid amides, heterocyclic rings, ketones, alkanolamines, ureas, etc. Organic solvents can be used.

[1-5] Other additives:
The ink of the present invention may contain other additives as required. Examples of the additive include a pH adjuster, a rust preventive, a preservative, a fungicide, an antioxidant, a reduction inhibitor, and a salt.

[1-6] Water:
As water, it is preferable to use deionized water (ion exchange water). The water content is not particularly limited. However, it is preferably 30% by mass or more and 90% by mass or less with respect to the total mass of the ink, more preferably 40% by mass or more and 85% by mass or less, and further preferably 50% by mass or more and 80% by mass or less. is there. By setting it as 30 mass% or more, a pigment and a water-soluble compound can be hydrated, and aggregation of a pigment or a water-soluble compound can be prevented. On the other hand, by setting the amount to 90% by mass or less, even when the amount of the water-soluble organic compound is relatively increased and the volatile component (water or the like) in the aqueous medium is volatilized, the pigment dispersion state is maintained. And the precipitation and solidification of the pigment can be prevented.

[1-7] Surface tension:
The surface tension γ of the ink of the present invention is preferably 25 mN / m or more and 45 mN / m or less. By setting the surface tension to 25 mN / m or more, the meniscus of the ink discharge port can be maintained, and a problem that ink flows out from the ink discharge port can be prevented. In addition, by setting the surface tension to 45 mN / m or less, it is possible to optimize the absorption speed of the ink onto the recording medium, and it is possible to prevent the problem of fixing failure due to insufficient ink absorption.

  The surface tension of the ink of the present invention is a plate method using a platinum plate using an automatic surface tension meter (for example, “CBVP-Z type” manufactured by Kyowa Interface Science Co., Ltd.) under the conditions of a temperature of 25 ° C. and a humidity of 50%. Means the value measured by. The surface tension of the packing liquid for logistics can be adjusted by the addition amount of the surfactant, the kind and content of the water-soluble organic solvent, and the like.

[1-8] Viscosity:
The ink viscosity η of the present invention is preferably from 1.5 mPa · s to 5.0 mPa · s, more preferably from 1.6 mPa · s to 3.5 mPa · s, and even more preferably 1.7 mPa · s. It is good to set it as s or more and 3.0 mPa * s or less. By setting the viscosity to 1.5 mPa · s or more, good ink droplets can be formed. On the other hand, by setting the pressure to 5.0 mPa · s or less, the fluidity of the ink is improved, and the ink supply property to the nozzle, and thus the ejection stability of the ink is improved.

  The viscosity of the ink means a value measured using an E-type viscometer (for example, “RE-80L viscometer” manufactured by Toki Sangyo Co., Ltd.) under a temperature of 25 ° C. in accordance with JIS Z 8803. And The viscosity of the ink can be adjusted by the type and amount of the water-soluble organic solvent in addition to the type and amount of the surfactant.

[1-9] pH:
The pH of the ink of the present invention is preferably 7.5 or more and 10.0 or less, more preferably 8.5 or more and 9.5 or less. When the pH is less than 7.5, the dispersion stability of the pigment particles is deteriorated, and the aggregation of the pigment particles tends to occur. On the other hand, if the pH exceeds 10.0, the pH of the ink is too high, and depending on the member of the device used, a chemical attack is caused by contact with the ink, thereby causing organic and inorganic substances to elute into the ink. As a result, defective discharge is caused, which is not preferable. The pH of the ink means a value measured using a pH meter (for example, HRIBA (manufactured) D-51) under the condition of a temperature of 25 ° C.

[2] Recording head:
Hereinafter, an embodiment of a recording head of the present invention will be described with reference to the drawings. However, the recording head of the present invention is not limited to the configuration described below.

[2-1] Nozzle part structure:
First, the structure of the nozzle portion will be described with reference to FIGS. 1A to 1C. FIG. 1A is a top view schematically showing the internal structure of the nozzles of the recording head. FIG. 1B is a side view schematically showing the internal structure of the nozzle shown in FIG. 1A. FIG. 1C is a front view schematically showing an ink discharge port of the nozzle shown in FIG. 1A.

  As shown in the figure, the thermal recording head has a nozzle row composed of a plurality of nozzle flow paths 159 partitioned by a nozzle wall 153, and a plurality of ink discharge ports 151 communicating with the nozzle flow paths 159. An ink discharge heater 152 is disposed inside the nozzle flow path 159. The head having such a structure can cause ink droplets to fly from the ink discharge ports 151 by heating the ink filled in the nozzle flow path 159 with the heater 152 and causing the ink to foam.

  In the illustrated form, a nozzle filter 155 is provided between the nozzle channel 159 and the common liquid chamber 112 for trapping foreign matter floating in the ink channel in the head. The top plate member 113 to which the nozzle top plate 162 is attached has an ink supply opening (not shown) formed by anisotropic etching or the like, and introduces ink from the outside from the common liquid chamber 112 to the nozzle channel 159. It is configured to be possible.

  In addition to the right and left side surfaces of the nozzle channel 159 being partitioned by the nozzle wall 153, the upper surface side is partitioned by the nozzle top plate 162 and the bottom surface side is partitioned by the nozzle bottom plate 164. That is, the nozzle flow path 159 is a substantially rectangular columnar internal space that is partitioned from the surrounding space with the nozzle wall 153, the nozzle top plate 162, and the nozzle bottom plate 164 as partition walls. The nozzle top plate 162 is attached to a top plate member 113 made of Si or the like, and the nozzle bottom plate 164 is attached to the heater substrate 111.

The ink discharge port 151 is an opening that discharges ink formed at one end of the nozzle flow path 159 and communicates with the common liquid chamber 112 via the nozzle flow path 159. The ink discharge port 151 is formed on the face surface. In the illustrated example, the face surface is formed integrally with the nozzle wall 153, but a face plate may be separately provided to form the face surface. The opening area of the ink ejection port 151 is configured to be 100 μm ² or more and 350 μm ² or less. By setting the opening area to 100 μm ² or more, it is possible to prevent the occurrence of an undischarge nozzle. On the other hand, by setting it to 350 μm ² or less, it is possible to form minute droplets in which the amount of one ink droplet is 10 pL or less, and the resolution can be 600 dpi or more. The opening area is represented by the product of the discharge port width 171 and the discharge port height 172.

  The recording head is a line type head in which nozzle rows are formed by a plurality of nozzle flow paths. The number of nozzle flow paths forming the nozzle row is not particularly limited. However, in order to achieve the effect of the present invention, the total number of nozzles in the nozzle row needs to be 1200 or more, preferably 1200 or more and 9600 or less, and more preferably 1200 or more and 4800 or less. . The length of the nozzle row needs to be 2 inches or more, and preferably 2 inches or more and 4 inches or less.

  The heater 152 is a heating unit for heating and foaming the ink filled in the nozzle channel 159. The heater 152 is installed on the heater substrate 111. As the heater 152, a resistor (for example, a resistor made of tantalum nitride) can be used. An electrode (not shown) made of aluminum or the like for energization is connected to the heater 152, and a switching transistor (not shown) for controlling energization to the heater 152 is connected to one of the heaters 152. . The drive of the switch transistor is controlled by an IC including a circuit such as a control gate element, and the switch transistor is driven in a predetermined pattern by a signal from the outside of the head.

  The recording head can be driven at a driving frequency of 1 kHz to 10 kHz. By driving at a driving frequency of 1 kHz or more, even when the amount of ink per droplet is very small, the amount of ink applied per unit time can be increased, and the amount of image data and the number of recording dots can be increased. That is, a high-quality image can be printed at high speed. By driving at a driving frequency of 10 kHz or less, such a problem that the ink supply amount to the nozzle is insufficient with respect to the ink discharge amount at the time of high-speed printing as described above and the ejection stability is reduced is suppressed. In order to obtain the effect more reliably, it is preferable that the driving can be performed at a driving frequency of 3 kHz or more and 8 kHz or less. The recording head of the present invention can be driven at a driving frequency of 6 kHz or more and 10 kHz or less because the ejection stability is unlikely to deteriorate even under a high driving frequency and nozzle non-discharge is difficult to occur. preferable.

  The overall length of the nozzle is preferably 200 μm or more and 300 μm or less. In this case, the “total length of the nozzle” means the length of the nozzle flow path 159, specifically, the common liquid chamber 112 from the end of the nozzle wall 153 constituting the nozzle flow path 159 on the ink discharge port 151 side. It means the length to the end of the side.

  The nozzle flow path 159 includes a nozzle front portion 181 that is a portion from the heater center 157 to the end portion on the ink discharge port 151 side, and a nozzle rear portion 182 that is a portion from the heater center 157 to the end portion on the common liquid chamber 112 side. It is divided into. From the viewpoint of the discharge speed, the flow resistance (front resistance) of the nozzle front part 181 and the flow resistance (rear resistance) of the nozzle rear part 182 have a front resistance / rear resistance value of 0.3 to 0.8. It is preferable. The flow resistance can be calculated by the Hagen-Poiseuille law from values such as the cross-sectional area of the flow path, the flow path length, and the viscosity of the ejected ink. That is, if the ink to be used (and its viscosity) is determined, the value of the front resistance / rear resistance can be adjusted by the flow path cross-sectional area of the nozzle, the flow path length, and the like.

[2-2] Nozzle material:
The nozzle wall 153, the nozzle top plate 162, and the nozzle bottom plate 164 that partition the nozzle flow path 159 can be formed of, for example, a photosensitive resin. As the photosensitive resin, a negative photoresist or the like can be used. Specific commercial products include, for example, “SU-8 series”, “KMPR-1000” (above, manufactured by Kayaku Microchem Corp.), “TMMR”, “TMMR S2000”, “TMMF S2000” (above, Tokyo Ohka). (Manufactured by Kogyo Co., Ltd.). Among these, it is preferable to use an epoxy photosensitive resin excellent in solvent resistance and strength as a nozzle wall. As a specific commercial product, “TMMR S2000” manufactured by Tokyo Ohka Kogyo Co., Ltd. is particularly preferable.

[2-3] Hydrophilic region and water-repellent region:
The recording head of the present invention preferably has a hydrophilic region or a water-repellent region formed at the periphery of the ink discharge port. Which of the hydrophilic region and the water repellent region is formed may be determined in consideration of the type of the color material of the ink to be used and the surface tension.

  For example, when the color material is a pigment or when ink having a surface tension of 34 mN / m or less is used, a recording head (hydrophilic head) in which a hydrophilic region is formed at the periphery of the ink discharge port is preferable. Further, it is preferable that a hydrophilic region having a contact angle of 60 ° or less with the ink to be used is formed at the periphery of the ink discharge port. The hydrophilic region having the contact angle of 0 ° (that is, forming no contact angle). It is more preferable that a sex region is formed. Note that the contact angle of the hydrophilic region or the water repellent region is measured by the ATAN1 / 2θ method using a contact angle meter (for example, trade name “SIMage-mini”, manufactured by Excimer Co., Ltd.) in accordance with JIS R 3257. be able to. Also in the examples described later, the contact angle is measured by the above method.

  The hydrophilic region includes a method in which a member (face material) in which ink discharge ports are formed is made of a hydrophilic material, a method in which a surface of the face material (face surface) is subjected to a hydrophilic treatment, and a hydrophilic film on the face surface. It can form by the method of providing.

  As the face material, for example, a resin such as an epoxy resin, particularly an epoxy-based photosensitive resin can be used.

Examples of the method for hydrophilic treatment of the face surface include a method of roughening the face surface. Examples of the roughening method include laser irradiation treatment, UV / O ₃ treatment, plasma treatment, heat treatment, oxidation treatment, and embossing treatment. Lasers such as excimer laser, YAG laser, and CO ₂ laser can be used for the laser irradiation treatment. Alternatively, the peripheral portion of the ink discharge port may be treated by a method of immersing in a highly hydrophilic liquid for a long time. Examples of the “hydrophilic liquid” include pigment inks. For example, what is necessary is just to immerse in the pigment ink which uses a face material for 10 minutes or more.

  Examples of a method for providing a hydrophilic film on the face surface include a method of forming a metal film or a hydrophilic resin film on the face surface. The hydrophilic film is preferably formed of a material having good adhesion to the face material as well as hydrophilicity. Examples of such a material include a composition containing a water-soluble resin and a water-insoluble low molecular weight compound. For example, a water-soluble resin (such as hydroxypropylcellulose) and a water-insoluble low molecular weight compound (such as bisphenol A) are dissolved in a suitable solvent (such as dimethylformamide), and the solution is applied to the face and dried. Accordingly, a hydrophilic film can be formed by treatment with alcohol or the like.

The formation of the hydrophilic region may be appropriately selected from the above methods according to the material constituting the face material. In addition, the hydrophilic region may be formed by combining two or more of the above methods. Among the above methods, a method in which the peripheral portion of the nozzle is made of an epoxy-based photosensitive resin, and the peripheral portion of the nozzle is subjected to a UV / O ₃ treatment and further immersed in pigment ink to perform a hydrophilic treatment.

  For example, when the color material is a dye and an ink having a surface tension of more than 34 mN / m is used, a recording head (water-repellent head) in which a water-repellent region is formed at the periphery of the ink discharge port is preferable. . Further, it is more preferable that a water-repellent region having a contact angle of 90 ° or more with the ink to be used is formed at the periphery of the ink discharge port, and a water-repellent region having a contact angle with the ink to be used of 100 ° or more. It is particularly preferred that it is formed.

  The water repellent region can be formed by a method of providing a water repellent film on the surface (face surface) of the member (face material) on which the ink discharge ports are formed.

  Examples of the method for providing the water repellent film on the face surface include a method of forming a super water repellent resin film on the face surface. The super water-repellent resin film can be formed by a conventionally known method. For example, a method of forming a resin film by applying a fluororesin, a silicone resin or the like on the face surface, a method of forming a fluororesin film by plasma polymerizing a fluorine-based monomer on the face surface, and the like can be given. Further, a method of forming a water- and oil-repellent resin film on the face surface may be employed. Examples thereof include a method of forming a film made of a fluororesin obtained by polymerizing a fluorocarbon compound. Among them, fluorine-containing silicones are used in fluorine-based solvents (“CXT-809A” manufactured by Asahi Glass, “<Novec> HFE-7100”, “<Novec> HFE-7200”, “<Novec> HFE-71IPA”, etc., manufactured by Sumitomo 3M Ltd.). A method of forming a water-repellent film by preparing a solution in which a coupling agent (for example, “KP-801M” manufactured by Shin-Etsu Chemical Co., Ltd.) is dissolved and vapor-depositing this solution on the face surface is preferable.

[2-4] Overall structure of recording head:
Next, the overall structure of the recording head will be described with reference to FIGS. 2A to 2C. A recording head having a structure as shown in FIGS. 2A to 2C is disclosed in Japanese Patent Laid-Open No. 2013-014111. Therefore, in the present specification, the contents of the above publication are cited, and only an outline thereof is described. 2A is a front view schematically showing the recording head of the present invention, FIG. 2B is a cross-sectional view taken along line AA in FIG. 2A, and FIG. 2C is a cross-sectional view taken along line BB in FIG. 2A. . For convenience of explanation, the liquid supply case cover is omitted from the front view.

  As shown in the drawing, the recording head of the present invention includes a common liquid chamber 112 that communicates with a plurality of nozzle channels forming a nozzle row, a liquid supply port 127 that communicates with the common liquid chamber 112, and a liquid type head. A main liquid supply chamber 126 that communicates with the supply port 127, a liquid supply path 137 that communicates with the main liquid supply chamber 126, and a liquid supply chamber that communicates with the liquid supply path 137 (the first liquid supply chamber 134 and the second liquid supply chamber). 135), a supply filter 118 disposed so as to separate the liquid supply chamber into the first liquid supply chamber 134 and the second liquid supply chamber 135 from the upstream side along the flow in supplying the liquid, and the main liquid It is preferable that a gas-liquid separator 120 provided in a part of the supply chamber 126 and an air chamber 141 communicating with the gas-liquid separator 120 are provided.

  The nozzle channel, the common liquid chamber 112, the liquid supply port 127, the main liquid supply chamber 126, the liquid supply path 137, and the liquid supply chamber (the first liquid supply chamber 134 and the second liquid supply chamber 135) The supply filter 118, the gas-liquid separator 120, and the air chamber 141 are arranged on a plane parallel to the plane including the nozzle channel arrangement direction and the liquid discharge direction, and the main liquid supply chamber 126. The liquid supply path 137, the supply filter 118, the gas-liquid separation unit 120, and the air chamber 141 are preferably arranged without being stacked.

  The recording head having the structure shown in FIGS. 2A to 2C is referred to as a gas-liquid separation type recording head. Since the gas-liquid separation type recording head fills the nozzles with ink by utilizing its own weight, it is extremely difficult to ensure the ejection stability as compared with the recording head having a conventional structure. Therefore, it can be said that the gas-liquid separation type recording head is one of the forms in which the effects of the present invention can be most enjoyed.

  A ceramic base plate 110 supports a heater substrate 111 formed of silicon. The heater substrate 111 has a plurality of electrothermal transducers (heaters or energy generators) as liquid discharge energy generating elements and a plurality of flow path walls for constituting nozzles corresponding to these electrothermal transducers. Is formed. The heater substrate 111 is also formed with a liquid chamber frame surrounding the common liquid chamber 112 communicating with each nozzle. A top plate member 113 that forms the common liquid chamber 112 is joined to the side wall of the nozzle and the liquid chamber frame formed in this manner. Accordingly, the heater substrate 111 and the top plate member 113 are laminated and bonded to the base plate 110 in an integrated state. Such lamination adhesion is performed with an adhesive having good thermal conductivity such as silver paste. A mounted electrical wiring board (PCB 114) is supported by a double-sided tape (not shown) behind the heater board 111 in the base plate 110. Each ejection energy generating element on the heater substrate 111 and the PCB 114 are electrically connected by wire bonding corresponding to each wiring.

  A liquid supply member 115 is joined to the top surface of the top plate member 113. The liquid supply member 115 includes a liquid supply case 116 and a liquid supply case cover 117. When the liquid supply case cover 117 closes the upper surface of the liquid supply case 116, a liquid chamber and a liquid supply path to be described later are formed. . The liquid supply case 116 and the liquid supply case cover 117 are joined by, for example, a thermosetting adhesive. The liquid supply case 116 is provided with a supply filter 118 and a discharge filter 119. The supply filter 118 is intended to remove foreign matters in the liquid supplied to the liquid supply member 115, and the discharge filter 119 is intended to prevent foreign matters from entering from the outside of the recording head. Each filter is fixed to the liquid supply case 116 by heat welding. Furthermore, a gas-liquid separation unit 120 is formed in a part of the liquid supply case 116, and a liquid level detection sensor 121 is mounted from the outside so as to protrude from the gas-liquid separation unit 120. Control the amount.

  Here, the configuration of the liquid chamber, the liquid supply path, and the like formed by fitting the two parts of the liquid supply case and the 116 liquid supply case cover 117 will be described. A liquid supply port 127 that is a rectangular opening is formed on the joint surface of the liquid supply case 116 with the top plate member 113 and is substantially parallel to the nozzle arrangement direction and across the width of the nozzle row. A storage liquid main liquid supply chamber 126 is formed on the extension of the mouth 127. That is, the main liquid supply chamber 126 is formed substantially parallel to the nozzle row and across the width of the nozzle row. Further, the top surface on the side opposite to the liquid supply port 127 constitutes an inclination (main liquid supply chamber inclination 129) with the gas-liquid separation part 120 as the uppermost portion over almost the entire area. Two openings are formed in the main liquid supply chamber inclination 129, one being the liquid communication part 131 and the other being the gas-liquid separation part 120.

  The gas-liquid separator 120 is formed as a part of the main liquid supply chamber 126 and has a depth larger than that of the other parts of the main liquid supply chamber 126. This is to enhance the effect of breaking bubbles that are mixed in the liquid in the liquid chamber, as will be described later. In the illustrated form, three stainless steel electrodes are mounted inside the gas-liquid separator 120, and are an upper limit detection electrode 123, a ground electrode 124, and a lower limit detection electrode 125 from the left side in the figure. The liquid level in the main liquid supply chamber 126 is maintained between the upper limit and the lower limit by energization between the ground electrode 124 and the upper limit detection electrode 123 and energization between the ground electrode 124 and the lower limit detection electrode 125. In the inkjet head of the illustrated form, the detection reliability can be improved by detecting the liquid level of the liquid that has undergone gas-liquid separation.

  On the extension of the gas-liquid separation unit 120, there is an air communication unit 130, and the tip is an air chamber 141 that functions as an air flow path. Further, the above-described discharge filter 119 is disposed and communicates with the discharge joint 133. The discharge filter 119 is made of a material having water repellency. If a liquid flows into the air flow path (air chamber 141) and the ink adheres to the discharge filter 119, an ink meniscus is formed inside the filter. However, the capillary force of the filter portion can be reduced by the water repellency, and the ink can be easily removed.

  On the other hand, a liquid supply path 137 is provided via a liquid communication portion 131 provided in the main liquid supply chamber inclination 129. The liquid supply path 137 has a tubular shape from the liquid communication portion 131 to the vicinity of the supply filter 118 and is formed on substantially the same plane as the main liquid supply chamber 126. The supply filter 118 is also disposed on substantially the same plane as the main liquid supply chamber 126. The supply filter 118 is disposed so as to separate the liquid supply chamber into two chambers, and the chamber on the side communicating with the supply joint 132, that is, the upstream chamber along the flow of liquid supply in the recording head is the first liquid supply. The chamber 134 and the downstream chamber are the second liquid supply chamber 135. Since the supply filter 118 is disposed on substantially the same plane as the main liquid supply chamber 126, the first liquid supply chamber 134 and the second liquid supply chamber 135 adjacent to both surfaces of the supply filter 118 are also the main liquid supply chamber. 126 and the ink discharge port array surface 139 are arranged on a plane substantially parallel to the surface.

  The second liquid supply chamber 135 has an opening above the supply filter 118 (hereinafter referred to as a second liquid supply chamber opening 136), and communicates with the liquid supply path 137 through the opening. In addition, the top surface of the second liquid supply chamber 135 is formed with an inclination (hereinafter referred to as a second liquid supply chamber inclination 138) with this opening as the uppermost portion.

  As described above, the main liquid supply chamber 126, the gas-liquid separator 120, the liquid supply path 137, the supply filter 118, the first liquid supply chamber 134, and the second liquid supply chamber 135 are each substantially the same as the ink discharge port arrangement surface 139. Set on a parallel plane. On the other hand, as shown in the AA cross section, it is important to arrange the main liquid supply chamber 126, the liquid supply path 137, the supply filter 118, and the gas-liquid separator 120 so as not to overlap each other in the vertical direction of the plane.

The supply filter 118 is preferably a stainless steel mesh having a filter pore diameter of 1 μm to 10 μm and a filter area of 10 mm ^{2 to} 500 mm ² . By setting the filter hole diameter to 1 μm or more and the filter area to 10 mm ² or more, the flow path resistance (pressure loss) can be reduced, and the bubbles in the recording head can be easily moved. In order to obtain the above effect more reliably, the filter area is more preferably 200 mm ² or more. On the other hand, when the filter hole diameter is 10 μm or less, dust can be reliably prevented from flowing into the nozzle, and when the filter area is 500 mm ² or less, the recording head can be downsized. In order to obtain the effect more reliably, it is more preferable that the filter pore diameter is 3 μm or more and 8 μm or less.

[2-5] Filling ink:
In the recording head of the present invention, the ink for ink jet recording is filled in the internal space communicating with the ink discharge port of the line type head. The ink is preferably filled in at least a portion of the internal space from the ink discharge port to the common liquid chamber (that is, the nozzle flow path and the common liquid chamber).

[3] Inkjet recording apparatus:
The ink jet recording apparatus of the present invention is an ink jet recording apparatus provided with a recording head for ink jet recording and an ink containing portion for containing ink to be supplied to the recording head. The recording head is a recording head according to the present invention. The form of the ink container is not particularly limited. For example, an ink tank as shown in FIG.

[3-1] Ink tank:
FIG. 3 is an enlarged sectional view of the ink tank. The ink tank 230 is a liquid storage container, and a liquid chamber (ink chamber 231) for storing ink is formed therein. The ink chamber 231 is a closed space in which only the joint portion 232 can communicate with the outside. The ink tank 230 is configured to be detachable from the recording head. The ink tank 230 is provided in the upper part of the recording head. The ink chamber 231 is formed of a flexible member, and a negative pressure generating spring 233-1 and a pressure plate 233-2 connected to the spring 233-1 are incorporated therein. The spring 233-1 urges the ink chamber 231 from the inside to the outside via the pressure plate 233-2, and expands the internal space of the ink chamber 231. That is, the spring 233-1 generates a predetermined negative pressure inside the ink chamber 231, and the spring 233-1, the pressure plate 233-2, and the ink chamber 231 together constitute a negative pressure generating unit 233. ing. The joint portion 232 is provided with a non-woven filter 234.

  FIG. 4 is an enlarged cross-sectional view of the recording head. The recording head 220 includes an energy generation element (not shown) such as an electrothermal conversion element (ink ejection heater). By this energy generating element, the ink I in the ink chamber 221 (liquid in the liquid chamber) is discharged from the discharge port 220A. In the ink chamber 221, air (gas) is present together with the ink I. Accordingly, in the ink chamber 221, an ink storage part (liquid storage part) in which ink I is stored and an air storage part (gas storage part) in which air (gas) is stored are formed. .

  An ink supply unit 222 for connecting the ink chamber 221 and the ink chamber of the ink tank is provided above the ink chamber 221. The average width of the ink supply unit 222 is about 10 mm. A filter member 223 is provided at the opening of the ink supply unit 222. The illustrated filter member 223 is formed of a SUS mesh. The mesh has a structure in which metal fibers are woven. Since the filter member 223 has fine eyes, it is difficult for dust to enter the recording head from the outside.

  The lower surface of the filter member 223 is pressed against an ink holding member 224 that can hold ink. 5A is an enlarged perspective view of the ink holding member shown in FIG. 4, and FIG. 5B is a Vb-Vb sectional view of the ink holding member shown in FIG. 5A. As shown in FIGS. 5A and 5B, the ink holding member 224 has a plurality of channels 224A having a circular cross section. The diameter of each flow path 224A is about 1.0 mm.

  As shown in FIG. 4, an opening 225 is provided in the upper part of the ink chamber 221. The opening 225 is provided with a filter 226. The opening 225 is configured to be connectable to a transfer unit (not shown) that is an external flow path. This transfer part is a flow path capable of transferring liquid and / or gas. The opening 225 allows the ink I and / or gas in the ink chamber 221 to flow out, or allows liquid (such as ink) and / or gas outside the recording head 220 to flow into the ink chamber 221. It is configured. That is, the opening 225 is formed so that not only the liquid can flow out and flow in alone, but also the gas can flow out and flow in with the liquid.

  The ink tank 230 shown in FIG. 3 and the recording head 220 shown in FIG. 4 are directly connected by connecting the joint part 232 of the ink tank 230 shown in FIG. 3 and the ink supply part 222 of the recording head 220 shown in FIG. Connected. At this time, the filter 234 of the ink tank 230 shown in FIG. 3 and the filter member 223 of the recording head 220 shown in FIG. 4 are in pressure contact with each other from above and below. The connecting portion between the ink tank and the recording head formed in this manner is surrounded by a rubber elastic cap member to maintain hermeticity. The structure in which the recording head and the ink tank are directly connected as described above is preferable in that the ink supply path (liquid supply path) between them can be extremely shortened.

[3-2] Overall configuration of recording apparatus:
Other structures of the ink jet recording apparatus are not particularly limited. For example, a recording apparatus 300 as shown in FIG. 6 can be suitably used.

  FIG. 6 is a schematic configuration diagram schematically showing the overall configuration of the ink jet recording apparatus. An external host device (computer device 308) is connected to the recording device 300. The recording apparatus 300 is configured to record an image by ejecting ink from the recording head 305 based on the recording data input from the computer apparatus 308.

  In the recording apparatus 300, a label sheet temporarily attached with a plurality of labels is used as the recording medium 301. The recording medium 301 is set in a state wound in a roll shape. However, in the ink jet recording apparatus of the present invention, any material can be used as long as it can accept not only paper, but also ink such as cloth, plastic film, metal plate, glass, ceramics, wood, and leather. Can be used.

  The recording apparatus 300 includes a conveyance motor 303, a conveyance roller 302, a rotary encoder 310, and a roll motor 311 as conveyance means for conveying the recording medium 301. By driving the conveyance roller 302 by the conveyance motor 303, the recording medium 301 can be conveyed at a constant speed in the direction of arrow A. The rotary encoder 310 can detect the conveyance speed and conveyance amount of the recording medium 301. The roll motor 311 can rewind the recording medium 301 in the direction opposite to the arrow A direction. The paper detection sensor 304 is a sensor that detects a specific portion of the recording medium 301. In the illustrated example, the tip of each label temporarily attached to the label sheet is detected. The recording timing of the image can be determined based on the detection.

  The recording apparatus 300 includes four recording heads 305 and ink tanks 306 corresponding to the four recording heads 305 at the top thereof. The four recording heads are recording heads for ejecting black, cyan, magenta, and yellow ink, respectively.

  The recording head 305 is a so-called line-type head configured to be wider than the maximum width recording width of the recording medium 301 and includes a plurality of nozzles that can eject ink. The ink discharge port of the nozzle is opened on the lower surface side of the recording head 305. The recording head 305 is disposed so that its longitudinal direction intersects with the conveyance direction of the recording medium 301 (direction orthogonal to the arrow A in the figure), and a plurality of nozzles are arranged along the longitudinal direction. As a result, a nozzle row is formed.

  In the recording apparatus 300, the conveyance roller 302 is driven by the conveyance motor 303, and the recording medium 301 is conveyed at a constant speed in the direction of arrow A by the conveyance roller 302. When a specific portion of the recording medium 301 is detected by the paper detection sensor 304, ink is sequentially discharged from the ink discharge ports of the four recording heads 305 based on the detection position. At this time, ink is supplied from the ink tank 306 to the recording head 305. Thus, when the recording medium 301 passes under the recording head 305, ink is ejected from the plurality of nozzles of the recording head 305, and an image is recorded on the recording medium 301. Note that since the recording head 305 is a line-type head, ink is ejected while being fixed at a fixed position. That is, ink is not ejected while reciprocating left and right like a serial head.

  The recording apparatus 300 includes a capping mechanism 307, a blade 309, and the like as a recovery mechanism for performing a recovery operation of the recording head 305.

  The recovery operation is an operation for recovering the recording head 305 so as to exhibit an appropriate ejection performance similar to the initial state. For example, operations such as suction recovery, pressure recovery, preliminary discharge, and wipe recovery can be given. The suction recovery is an operation of sucking and removing the thickened ink in the nozzles of the recording head 305 to the capping mechanism 307, and the pressure recovery is pressurizing the thickened ink in the nozzles of the recording head 305 to the capping mechanism 307. Preliminary ejection is an operation that discharges the thickened ink in the nozzles to the capping mechanism 307 by ejection, and stabilizes the ink meniscus. Wipe recovery means that the face surface of the recording head is wiped by the blade 309. In this operation, dust and ink attached to the face surface are removed. These recovery operations can also be implemented in combination.

  The capping mechanism 307 is a mechanism for capping the ink discharge port of each recording head 305 and is disposed below the recording head 305. The recording head 305 and the capping mechanism 307 are configured to be relatively movable in the left-right direction in FIG. On the other hand, the blade 309 is a member that wipes the face surface of each recording head 305, and is disposed below the recording head 305.

  When performing suction recovery, the inside of the buffer tank (not shown) of the capping mechanism 307 is decompressed by a tube pump (not shown) while the recording head 305 is capped by the capping mechanism 307. As a result, the thickened ink in the nozzles of the recording head 305 is removed by suction to the capping mechanism 307, and the nozzles are refreshed.

  When pressure recovery is performed, the inside of the nozzles of the recording head 305 is pressurized while the recording head 305 is capped by the capping mechanism 307. As a result, the thickened ink in the nozzle is pressurized and discharged into the cap of the capping mechanism 307, and the inside of the nozzle is refreshed.

  When performing wipe recovery, the blade 309 is driven by a blade motor (not shown), the face of the nozzle of the recording head 305 is wiped, and pressure recovery (preliminary ejection) is performed. Thereby, the face surface of the nozzle is cleaned, and the meniscus at the ink discharge port is adjusted.

  The ink accumulated in the capping mechanism 307 by these recovery operations is sucked by a tube pump (not shown) and discarded in a waste ink tank (not shown) when it is accumulated to a predetermined amount.

[3-3] Control system:
Next, control of the ink jet recording apparatus will be described. FIG. 7 is a block diagram of the control system of the recording apparatus shown in FIG. In addition to a recording mechanism including a recording head, the recording apparatus includes a control system component such as a CPU (Central Processing Unit), a USB interface unit, and a ROM. The CPU 401 executes a program stored in the program ROM 402 and controls each unit of the recording apparatus. A program ROM 402 stores programs and data for controlling the recording apparatus. The processing of the recording apparatus is realized by the CPU 401 reading and executing a program in the program ROM 402.

  The recording data output from the computer device 308 is input to the interface controller 403 of the recording device. Commands that specify the number, type, size, and the like of the recording medium (label) are also input to the interface controller 403 and analyzed. In addition to analyzing these commands, the CPU 401 executes arithmetic processing for controlling the entire recording apparatus, such as recording data input, recording operation, and recording medium handling. The arithmetic processing is executed based on a processing program stored in the program ROM 402. The program includes a program corresponding to the procedure of the flowchart shown in FIG. A work RAM 404 is used as a working memory for the CPU 401. The EEPROM 405 is a rewritable nonvolatile memory. The EEPROM 405 is specific to the recording apparatus, such as the time when the previous recovery operation was performed, the mutual distance of a plurality of recording heads, and correction values for finely adjusting the recording position in the transport direction (vertical registration). Parameters are stored.

  More specifically, after analyzing the input command, the CPU 401 develops the image data of each color component of the recording data in the image memory 406 as a bitmap. Drawing is performed based on this data. Further, the CPU 401 controls the transport motor 303, the roll motor 311, the capping motor 409, the head motor 410, and the pump motor 418 via the input / output circuit 407 and the motor driving unit 408. The capping motor 409 is a motor for driving the capping mechanism 307, the head motor 410 is a motor for moving the recording heads 305K, 305Y, 305M, and 305C, and the pump motor 418 is a motor for driving the tube pump. It is. The recording heads 305K, 305Y, 305M, and 305C are moved between the capping position, the recording position, and the recovery position. The capping position is a position capped by the capping mechanism 307, the recording position is a position for recording an image, and the recovery position is a position for performing a recovery operation.

  When an image is recorded by the recording apparatus, the conveyance roller 302 is driven by the conveyance motor 303 as shown in FIG. 6 to convey the recording medium 301 (label paper in the illustrated example) at a constant speed. The rotary encoder 310 detects the conveyance speed and conveyance amount of the recording medium 301. In the control system shown in FIG. 7, the leading edge of the label is detected by the paper detection sensor 304 in order to determine the recording timing of the image on the recording medium conveyed at this constant speed. A detection signal from the paper detection sensor 304 is input to the CPU 401 via the input / output circuit 411. When the recording medium is conveyed by the conveyance motor, the CPU 401 sequentially reads out image data for each color from the image memory 406 in synchronization with a signal from a rotary encoder (not shown). The image data is transferred to one of the corresponding recording heads 305K, 305Y, 305M, and 305C via the recording head control circuit 412. Accordingly, the recording heads 305K, 305Y, 305M, and 305C eject ink based on the image data.

  The driving of the pump motor 413 for driving the pump is controlled via the input / output circuit 407 and the motor driving unit 408. The operation panel 414 is connected to the CPU 401 via the input / output circuit 415. Further, the environmental temperature and environmental humidity of the recording apparatus are detected by a temperature / humidity sensor 416 and input to the CPU 401 via the A / D converter 417.

[3-4] Recovery sequence:
When the environmental temperature is 40 ° C. or higher and the water evaporates, the ink sticks easily to the recording head. Accordingly, it is preferable to insert a recovery sequence for recovering the face surface of the recording head when the head cap is removed from the recording head and the moisture evaporates.

  FIG. 8 is a flowchart showing the steps of the printhead recovery sequence. The recovery sequence shown in FIG. 8 is activated when a cap opening condition (condition 501) in which the recording head is released from the cap is satisfied. When the recovery sequence is activated, the ambient temperature and ambient humidity of the recording apparatus are acquired (detected) by the temperature and humidity sensor (step 502). As a result of the detection, when the environmental temperature is 40 ° C. or more, the environmental humidity is 70% or less (condition 503), and the cumulative time from the previous suction recovery is one hour or more (condition 504), the inside of the nozzle Pressure recovery (preliminary ejection) for refreshing the ink and wipe recovery for wiping and cleaning the face surface are performed (step 505). The condition 504 is reset when suction recovery is performed.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. However, the present invention is not limited to the configurations of the following examples. In the following description, “part” and “%” are based on mass unless otherwise specified.

[Synthesis Example: Synthesis of (meth) acrylic ester random copolymer]
1000 parts of methyl ethyl ketone was charged into a reaction vessel equipped with a stirring device, a dropping device, a temperature sensor, and a reflux device having a nitrogen introducing device at the top, and the inside of the reaction vessel was purged with nitrogen while stirring. After raising the temperature in the reaction vessel to 80 ° C. while maintaining a nitrogen atmosphere, 63 parts of 2-hydroxyethyl methacrylate, 141 parts of methacrylic acid, 417 parts of styrene, 188 parts of benzyl methacrylate, glycidyl methacrylate, were added from a dropping device. 25 parts, 33 parts of a polymerization degree modifier (manufactured by NOF Corporation, trade name: “Blenmer TGL”) and 67 parts of t-butyl peroxy-2-ethylhexanoate were mixed, and the resulting mixture was taken over 4 hours. And dripped. After completion of the dropping, the reaction was further continued at the same temperature for 10 hours, and a (meth) acrylic acid ester random copolymer having an acid value of 110 mgKOH / g, a glass transition point (Tg) of 89 ° C., and a weight average molecular weight of 8,000. A solution (A-1) (resin content: 45.4%) was obtained.

[Preparation of Black Pigment Dispersion Used for Ink Color Material]
In a mixing tank equipped with a cooling jacket, a solution (resin content: 45.4%) of (meth) acrylate random copolymer (A-1) obtained by preparing a polymer solution, 25% potassium hydroxide An aqueous solution, water and a carbon black pigment were charged, stirred and mixed to obtain a mixed solution. Here, each charge amount is 1000 parts of carbon black pigment, (meth) acrylic acid ester type random copolymer is in an amount of 40% in terms of non-volatile content with respect to carbon black, and 25% potassium hydroxide aqueous solution is The amount by which the acid value of the (meth) acrylic acid ester random copolymer is neutralized by 100% and the amount of water are the amount necessary to make the nonvolatile content of the mixed solution 27%. The obtained mixed solution was passed through a dispersing device filled with zirconia beads having a diameter of 0.3 mm and dispersed by a circulation method for 4 hours. The temperature of the dispersion was kept at 40 ° C. or lower.

  After the dispersion liquid was extracted from the mixing tank, the mixing tank and the flow path of the dispersion apparatus were washed with 10,000 parts of water, and the cleaning liquid and the dispersion liquid were mixed to obtain a diluted dispersion liquid. The obtained diluted dispersion was put into a distillation apparatus, and the whole amount of methyl ethyl ketone and a part of water were distilled off to obtain a concentrated dispersion. The concentrated dispersion which had been allowed to cool to room temperature was added dropwise with 2% hydrochloric acid while stirring to adjust the pH to 4.5, and then the solid content was filtered with a Nutsche filter and washed with water. The obtained solid (cake) was put in a container, water was added, and then redispersed using a dispersion stirrer, and the pH was adjusted to 9.5 with a 25% aqueous potassium hydroxide solution. Thereafter, using a centrifuge, coarse particles were removed at 6000 G for 30 minutes, and then the nonvolatile content was adjusted to obtain a carbon black pigment dispersion (nonvolatile content: 20%). Furthermore, pure water was added and adjusted so that the pigment concentration of the obtained aqueous black pigment dispersion was about 14%, and this was used as a black pigment dispersion used for ink preparation described later.

[Preparation of Cyan Pigment Dispersion Used for Ink Color Material]
The cyan pigment dispersion was prepared in the same manner as the black pigment dispersion except that Pigment Blue 15: 3 was used as the colorant.

[Preparation of Magenta Pigment Dispersion Used for Ink Color Material]
The magenta pigment dispersion was prepared in the same manner as the black pigment dispersion except that Pigment Red 122 was used as a colorant and the resin to pigment ratio was changed from 40% to 30%.

[Preparation of Yellow Pigment Dispersion Used for Ink Color Material]
The yellow pigment dispersion was prepared in the same manner as the black pigment dispersion except that Pigment Yellow 74 was used as a colorant and the ratio of the resin to the pigment was changed from 40% to 35%.

[Preparation of ink]
Example 1
Ink 1 of Example 1 was prepared by the following method. Add 21.4 parts of a black pigment dispersion (pigment concentration of about 14%) as a coloring material to the container, and 27.5 parts of a 40% aqueous solution of solid ethylene urea as a water-soluble compound (solid content of ethylene urea: 11 parts) 7 parts of glycerin, 2 parts of triethylene glycol, and 3.1 parts of a 65% aqueous solution of solid bishydroxyethyl sulfone (bishydroxylethyl sulfone solid content: 2 parts) were added. Furthermore, 0.5 parts of nonionic surfactant acetylenol E100 (manufactured by Kawaken Fine Chemicals) and 1.0 part of BC-20 (manufactured by Nikko Chemicals) were added, and the remaining pure water (ion exchange water) was added. The total was 100 parts. These were stirred for 30 minutes or more with a propeller stirrer, and then filtered with a filter having a pore size of 3.0 μm to obtain black ink jet recording ink 1 of Example 1.

(Examples 2-6, Comparative Examples 1-3)
Inks 2 to 6 of Examples 2 to 6 and Inks 7 to 9 of Comparative Examples 1 to 3 were prepared using the previously prepared black pigment dispersion and changing the composition of the water-soluble compound and the like. Specifically, inks of Examples and Comparative Examples were obtained in the same manner as in Example 1 except that the components shown in Table 2 were used in the amounts shown in Table 2.

[Evaluation]
Using the inks of Examples and Comparative Examples obtained above, images were formed by an inkjet recording apparatus, and each ink was evaluated by the method described later. The evaluation results are shown in Table 2. Specifically, a thermal ink jet recording apparatus (“LXD5500” manufactured by Canon Finetech Co., Ltd.) was used as the ink jet recording apparatus. And the said apparatus provided with the inkjet head of the structure shown to FIG. 1A-FIG. 1C and FIG. 2A-FIG. 2C was used as an inkjet recording head. Specific specifications are shown in Table 3.

<Re-solubility and adhesion test>
As an ink jet recording apparatus, LXP5500 (manufactured by Canon Finetech) was used, and printing was performed as follows under an environment of a temperature of 15 ° C. and a humidity of 10%. Each ink shown in Table 2 is stored in the ink tank of the ink jet recording apparatus, and ink is dropped one by one from 4800 ejection ports arranged in a row at a density of 1200 dpi on the recording head of the above specifications. The nozzle check pattern was printed with each ink. At that time, a mat label manufactured by Canon Finetech Co., Ltd. was used as the medium (recording medium).
After the above test, the cap was sealed, left in a 60 ° C. environment for 2 weeks, and the status of nozzle check pattern printing when a recovery operation was performed was evaluated according to the following criteria.
○: Normal printing can be performed with one cleaning operation.
X: Normal printing can be performed by two or more cleaning operations.

<Precipitation of solid matter>
Each ink was filled in the recording head having the above specifications, then left at room temperature for 2 weeks without a sealing cap, the tip of the nozzle was observed, and evaluated according to the following criteria.
(Evaluation criteria)
○: No solid matter is deposited at the nozzle tip.
X: Precipitation of solid matter is observed at the nozzle tip.

  As shown in Table 2, it was confirmed that the inks of Examples 1 to 6 were able to print with the properties by recovering the nozzles with a single cleaning operation. The reason for this is that, as will be described later, from the comparison with the case of using the ink of the comparative example, the content of ethylene urea and the water-soluble compound in the ink is within the range specified in the present invention. It is considered that re-solubility and adhesion were obtained.

  As shown in Table 2, the ink of Comparative Example 1 is less than 11% by mass of ethylene urea in the ink of the above-described example, and the dried ink after the ink moisture is evaporated When mixed with new ink by the cleaning operation, the re-solubility becomes inferior, and the cleaning operation is required twice or more. In the ink of Comparative Example 2, the ratio of ethylene urea in the total amount of the water-soluble compound exceeded 50%. As a result, the moisture retention was not sufficient and the fixing property was poor. Further, in the ink of Comparative Example 3, although the dry ink was dissolved, the solid matter was deposited, and the fixing property was inferior.

  The pigment of the black pigment dispersion in Table 2 was changed to the pigment of each color obtained by adjusting the cyan, magenta, and yellow dispersions, and inks were prepared in the same manner, and the same evaluation as in the case of the black ink was performed. As a result, all the inks prepared using the pigments of the pigment dispersion liquids of each color showed preferable results as in the case of the black ink of the example. The comparative example was inferior to the black ink in terms of re-dissolvability and solid precipitation. From this, even if any pigment dispersion of cyan, magenta, and yellow is used, the ink composition specified in the present invention, particularly by designing to satisfy the water-soluble compound, there is no precipitation of solid matter. It was confirmed that an ink having good re-solubility and fixing property can be obtained.

110: base plate, 111: heater substrate, 112: common liquid chamber, 113: top plate member, 115: liquid supply member, 116: liquid supply case, 117: liquid supply case cover, 118: supply filter, 119: discharge filter, 120: Gas-liquid separator, 121: Liquid level detection sensor, 123: Upper limit detection electrode, 124: Ground electrode, 125: Lower limit detection electrode, 126: Main liquid supply chamber, 127: Liquid supply port, 129: Main liquid supply chamber Inclination, 130: air communication portion, 131: liquid communication portion, 132: supply joint, 133: discharge joint, 134: first liquid supply chamber, 135: second liquid supply chamber, 136: second liquid supply chamber opening, 1
37: liquid supply path, 138: second liquid supply chamber inclination, 139: ink discharge port arrangement surface, 141: air chamber, 151: ink discharge port, 152: heater, 153: nozzle wall, 155: nozzle filter, 157: Heater center, 159: nozzle flow path, 162: nozzle top plate, 164: nozzle bottom plate, 171: discharge port width, 172: discharge port height, 181: nozzle front part, 182: nozzle rear part, 220: recording head, 220A: discharge port, 221: ink chamber, 222: ink supply unit, 223: filter member, 224A: flow path, 225: opening, 226: filter, 230: ink tank, 231: ink chamber 232: joint part, 233: negative pressure generating part, 2333-1: spring, 233-2: pressure plate, 234: filter, 300: notation Device 301: Recording medium 302: Conveying roller 303: Conveying motor 304: Paper detection sensor 305, 305K, 305Y, 305M, 305C: Recording head 306: Ink tank 307: Capping mechanism 308: Computer device 309: blade, 310: rotary encoder, 311: roll motor, 401: CPU, 402: program ROM, 403: interface controller, 404: work RAM, 405: EEPROM, 406: image memory, 407: input / output circuit, 408: motor drive unit, 409: capping motor, 410: head motor, 411: input / output circuit, 412: recording head control circuit, 413: pump motor, 414: operation panel, 415: input / output circuit, 416: temperature / humidity sensor 417: A / D converter, 418: pump motor, 501: Conditions, 502: Step 503: Condition 504: Condition 505: step I: Ink.

Claims (6)

Ink jet recording ink discharged by a thermal type line type recording head,
The ink contains a pigment, water, and a water-soluble compound;
The pigment is a resin-dispersed pigment dispersed by a (meth) acrylic acid ester-based random copolymer having an acid value of 100 mgKOH / g or more and 160 mgKOH / g or less,
The water-soluble compound includes at least ethylene urea and a water-soluble compound having a hydrophilicity / hydrophobicity coefficient defined by the following formula (A) of 0.37 or less, and the hydrophilicity / hydrophobicity coefficient is 0.37 or less. Is a glycerin, triethylene glycol, bishydroxyethylsulfone, trimethylolpropane, 1,2,6-hexanetriol, 1,2,3-butanetriol, sorbitol, urea, diethylene glycol, 1,2, At least one compound selected from the group consisting of 4-butanetriol and diglycerin,
The total content of the water-soluble compounds is 22% by mass or more and 50% by mass or less based on the total amount of the ink,
The ethylene urea content is 11.0% by mass or more based on the total amount of ink, and
The proportion of ethylene urea in the total amount of the water-soluble compound having the ethylene urea and the hydrophilicity / hydrophobicity coefficient of 0.37 or less is 50% or less on a mass basis,
An ink for ink jet recording characterized by the above.   The ink for inkjet recording according to claim 1, wherein the total content of the water-soluble compound is 22% by mass or more and 24% by mass or less based on the total amount of the ink.   The water-soluble compound having a hydrophilicity / hydrophobicity coefficient of 0.37 or less is at least one compound selected from the group consisting of glycerin, triethylene glycol, bishydroxyethylsulfone and trimethylolpropane. The ink for inkjet recording as described. The recording head has a nozzle row for ejecting ink, the opening area of each nozzle is 100 to 350 μm ² , the total number of nozzles per nozzle row is 1200 or more, and the length of the nozzle row is 2 inches or more. Item 4. The ink for inkjet recording according to any one of Items 1 to 3. The recording head has a common liquid chamber in which a plurality of nozzle flow paths communicate with each other as a nozzle row, an opening in communication with the common liquid chamber, a main liquid supply chamber in communication with the opening, and the main liquid supply chamber. A liquid supply path communicating with the liquid supply chamber; a liquid supply chamber communicating with the liquid supply path; and a first liquid supply chamber and a second liquid supply chamber from the upstream side along the flow in the liquid supply A supply filter disposed so as to be separated, a gas-liquid separation unit provided in a part of the main liquid supply chamber, and an air chamber communicating with the gas-liquid separation unit,
The nozzle flow path, the common liquid chamber, the opening, the main liquid supply chamber, the liquid supply path, the liquid supply chamber, the supply filter, the gas-liquid separator, and the air Chambers are arranged on a parallel plane with respect to a plane including the arrangement direction of the nozzle channels and the discharge direction of the liquid,
The main liquid supply chamber, the liquid supply path, the supply filter, the gas-liquid separation unit, and the air chamber are arranged without being stacked,
The ink for ink-jet recording according to any one of claims 1 to 3.   An ink jet recording method for performing recording by discharging the ink according to claim 1 with a thermal type line type recording head.