JP2015052054A - Inkjet recording ink, recording head, and inkjet recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet recording ink exhibiting a favorable dispersion stability of pigment particles even at the time of ink discharge, unlikely to entail ink discharge failures or print ink character kinks, capable of maintaining a favorable printing performance over an extended period, and yielding an image having an excellent water resistance.SOLUTION: The provided inkjet recording ink includes water, carbon black, a resin dispersant, and a nonionic surfactant. The carbon black has primary particle diameters of 15 nm or above and 40 nm or below; the resin dispersant is a (meth)acrylic acid ester copolymer having an acid value of 100 mgKOH/g or above and 160 mgKOH/g or below; the nonionic surfactant is a POE alkyl ether having an HLB of 15 or below and 20 or below; the ratio of the mass of the nonionic surfactant with respect to the mass of the carbon black is 0.1 or above and 0.5 or below; the ratio of the mass of the (meth)acrylic acid ester copolymer with respect to the mass of the carbon black is 0.2 or above and 0.5 or below.

Description

  The present invention relates to an ink for ink jet recording, a recording head, and an ink jet recording apparatus.

  Inkjet recording apparatuses are widely used in printers, copiers, and the like because they are low in noise, low in running cost, easy to downsize, and easy to color.

  In industrial printers, specifications such as high image quality and high-speed printing are strongly demanded than home printers. In particular, in industrial printed matter, the fastness of the printed matter is one of the particularly important image quality. For example, in printed materials often used outdoors, weather resistance and water resistance are important. As an ink coloring material used for such a purpose, a water-insoluble pigment is used. Therefore, in an industrial printer, a resin dispersion type pigment ink in which water-insoluble pigment particles are dispersed in water by a resin dispersant is preferably used.

  For example, an A block that is a hydrophilic polymer block, a B block that is a polymer block that can be bonded to a granular solid, and a C block that is a hydrophobic or hydrophilic polymer block different from the A block and the B block In addition, an ink having improved dispersion stability of pigment particles has been proposed by using an ABC triblock polymer having an A block and a B block as a terminal block as a resin dispersant. (Patent Document 1). The ink has high dispersion stability of pigment particles, and can be expected to improve the image quality and fastness of printed matter. However, under severe conditions in which industrial printed materials are used, and when a recording medium (media) with a thin ink receiving layer is used to reduce costs, the water resistance of the printed materials is satisfactory. It was not a thing.

  In order to improve the water resistance of printed matter, a pigment dispersion using a random copolymer having a lower acid value as a resin dispersant has been proposed. However, a random copolymer having a low acid value has low water solubility, and lowers the dispersibility of pigment particles. In the case of a thermal ink jet recording method, the process of foaming by heating the ink from room temperature to 300 ° C. or higher in the foaming part (phase change from liquid to gas) is continuously performed. Accordingly, the resin may cause kogation in the heater portion (foaming portion), and in a severe case, there is a possibility that a droplet may not be ejected from the recording head (non-ejection).

  In order to improve such problems, an aqueous pigment dispersion for an ink jet printer containing a nonionic surfactant having a specific HLB and a (meth) acrylic acid ester copolymer having a specific acid value A body has been proposed (Patent Document 2).

Japanese Patent No. 2675956 Japanese Patent No. 4956517

  Patent Document 2 discloses that even when a recording liquid (ink) prepared using this aqueous pigment dispersion uses a random copolymer having a relatively low acid value as the copolymer, ejection stability and printing It describes that the product is excellent in scratch resistance and bleeding resistance. However, since the nonionic surfactant used in the recording liquid (ink) described in Patent Document 2 has a relatively high molecular weight and is difficult to dissolve in water, it has the following problems. . That is, when the ink containing the nonionic surfactant is thickened and fixed in the vicinity of the ink discharge port of the recording head where water easily evaporates, problems such as non-ejection of ink and printing misalignment occur. There is a problem that the ejection stability is insufficient. In addition, there is a problem that the ink is fixed inside the capping mechanism of the recording head and the tube connected thereto, and the tube is clogged. These problems may occur particularly remarkably in a thermal recording head.

  By the way, in recent years, instead of the serial method in which printing is performed by feeding paper while reciprocating the recording head left and right, a recording head (line type head) wider than the paper width is used, and only the paper is moved without moving the line type head. A line method has been adopted in which printing is performed in one pass. The line method is suitable for high-speed printing because paper can be sent at a stroke under a fixed line-type head, and is used in the industrial printer field where high image quality and high-speed printing are required. It is going

  Such a line-type head cannot frequently perform a recovery operation of the recording head because of its structure. In addition, the line-type head passes only once through one portion of the paper, and only one nozzle passes through one portion of the paper. Therefore, in a line-type head, even if one nozzle is used, ink ejection becomes unstable, or if ink is not ejected from the nozzle (nozzle non-ejection), a line-like image defect occurs, which immediately reduces image quality. Cause it. Therefore, the line type head is required to have a higher level of ejection stability than the serial head. For these reasons, it is difficult to use, as a resin dispersant, a low-acid-value random copolymer that is inferior in the ability to disperse pigment particles (that is, difficult to disperse) in the ink for a line-type head. Met.

  The present invention has been made to solve the above-described problems of the prior art. That is, the present invention has good dispersion stability of pigment particles even when ink is ejected even when a low acid value random copolymer is used as a resin dispersant, and non-ejection caused by ink sticking. It is an object of the present invention to provide an ink for ink-jet recording that is less likely to cause printing distortion and can maintain good printing performance over a long period of time. Ink for ink-jet recording that can be suitably used for a thermal recording head in which the resin is likely to cause kogation in the heater portion (foaming portion), particularly a line-type head that cannot frequently perform recovery operation of the recording head. Is to provide.

  The present inventors diligently studied the above problem. As a result, a low acid value (meth) acrylic acid ester copolymer having an acid value of 160 mgKOH / g or less is used as a resin dispersant, and a high HLB value is 15 or more as a nonionic surfactant. The inventors have conceived that the above problems can be solved by using a POE alkyl ether having a value, and have completed the present invention. That is, according to the present invention, the following ink for ink jet recording, a recording head, an ink jet recording apparatus, and an ink jet recording method are provided.

[1] Ink:
According to the present invention, an ink for inkjet recording containing water, carbon black, a resin dispersant for dispersing the carbon black, and a nonionic surfactant, the carbon black having a primary particle size of 15 nm or more. The resin dispersant is a (meth) acrylic acid ester copolymer having an acid value of 100 mgKOH / g or more and 160 mgKOH / g or less, and the nonionic surfactant has an HLB of 15 or less. The POE alkyl ether is 20 or less, the mass ratio of the nonionic surfactant to the mass of the carbon black is 0.1 or more and 0.5 or less, and the (meth) acrylic acid with respect to the mass of the carbon black. Ink jet recording, wherein the mass ratio of the ester copolymer is 0.2 or more and 0.5 or less Ink use; is provided.

In the ink of the present invention, the copolymer is a random copolymer, and the copolymer is neutralized after being adsorbed to the pigment by an acid precipitation method; the carbon black is a ratio by the BET method. It is preferably carbon black having a surface area of 100 m ² / g or more and 400 m ² / g or less and a DBP oil supply amount of 40 ml / 100 g or more and 200 ml / 100 g or less.

  In the ink of the present invention, the POE alkyl ether has an alkyl group having 10 to 20 carbon atoms; the ink further contains a water-soluble compound, and the water-soluble compound is water-soluble. It is preferably at least one selected from the group of organic solvents and water-soluble compounds that are solid at 25 ° C.

[2] Recording head;
According to the present invention, a nozzle row composed of a plurality of nozzle flow paths partitioned by a nozzle wall is formed, a plurality of ink discharge ports communicating with the nozzle flow paths are formed, and ink is formed inside each nozzle flow path. A heater for discharge is disposed, the opening area of the ink discharge port is 100 μm ² or more and 350 μm ² or less, and the internal space communicating with the ink discharge port is filled with ink for ink jet recording; There is provided a recording head for ink jet recording, wherein the ink is the ink described in [1].

  The recording head of the present invention is preferably a line-type head in which the total number of nozzles in the nozzle row is 1200 or more and the length of the nozzle row is 2 inches or more.

  In the recording head of the present invention, the line-type head has a common liquid chamber that communicates with the plurality of nozzle flow paths that form the nozzle row, a liquid supply port that communicates with the common liquid chamber, and the liquid supply A main liquid supply chamber that communicates with the opening; a liquid supply passage that communicates with the main liquid supply chamber; a liquid supply chamber that communicates with the liquid supply passage; and the liquid supply chamber upstream along the flow during liquid supply. A supply filter disposed so as to be separated into a first liquid supply chamber and a second liquid supply chamber from the side, a gas-liquid separation unit provided in a part of the main liquid supply chamber, and the gas-liquid separation unit An air chamber in communication with the nozzle channel, the common liquid chamber, the liquid supply port, the main liquid supply chamber, the liquid supply path, the liquid supply chamber, and the supply filter. And the gas-liquid separator and the air chamber The main liquid supply chamber, the liquid supply path, the supply filter, and the gas-liquid separator are arranged on a parallel plane with respect to a plane including the arrangement direction of the nozzle flow paths and the liquid discharge direction. And the air chambers are preferably arranged without being laminated.

[3] Inkjet recording apparatus:
According to the present invention, there is provided an ink jet recording apparatus including a recording head for ink jet recording and an ink storage unit that stores ink to be supplied to the recording head, wherein the recording head is described in [2]. An ink jet recording apparatus, which is a recording head, is provided.

  The ink of the present invention has good dispersion stability of pigment particles even during ink ejection, hardly causes non-ejection and printing deviation due to ink fixation, and can maintain good printing performance over a long period of time. it can.

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.

  In solving the problems of the prior art, the present inventors have a reason why the discharge stability of a low acid number copolymer that is a resin dispersant and an ink containing a nonionic surfactant is insufficient. investigated. As a result, the following was found.

  When ink is ejected continuously, the ink is heated to 40 ° C. or more in the vicinity of the ink ejection port by the driving heat of the recording head. This heating evaporates water molecules hydrated to the hydrophilic groups of the nonionic surfactant molecules and the hydrophilic groups of the low acid number polymer, and the hydrophilic groups of the nonionic surfactant molecules and The hydrophilic group of the low acid number polymer is exposed. The exposed hydrophilic groups of the nonionic surfactant molecules adhere to the exposed hydrophilic groups of the low acid number polymer. The hydrophilic group of the low acid value polymer is covered with the hydrophobic group of the nonionic surfactant molecule, and the low acid value polymer (resin dispersant) loses the dispersibility. For this reason, once the ink is once dried and fixed in the vicinity of the ink discharge port, the pigment particles are not easily redispersed even when coming into contact with ink (water that is the medium) discharged later. For the reasons described above, it is considered that the ejection stability of the ink containing the low acid value polymer as the resin dispersant and the nonionic surfactant is insufficient.

  The inventors have also found that the above phenomenon is influenced by the surface condition of the pigment particles, and is particularly remarkable when the ink contains carbon black having a relatively high hydrophilicity on the particle surface. It was.

  As a result of further investigations based on the above facts, the present inventors have found that even when a (meth) acrylic acid ester copolymer having a low acid value of 160 mgKOH / g or less is used as the resin dispersant, It has been found that the discharge stability problem can be solved by using a POE alkyl ether having a high HLB value of 15 or more as the ionic surfactant.

  The ink of the present invention having the composition as described above has high dispersion stability and is excellent in recoverability even when the ink is once dried and fixed. In addition, the ink of the present invention solves the problems of the prior art without changing the techniques relating to resin dispersants that have been established so far and the techniques relating to surface modification that are appropriate for each pigment. It is useful in that it becomes possible.

  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.

[1] Ink:
The ink of the present invention is an ink for inkjet recording containing water, carbon black, a resin dispersant for dispersing the carbon black, and a nonionic surfactant. That is, the ink of the present invention relates to a black ink.

[1-1] Carbon black:
The ink contains carbon black as a pigment. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black.

  The carbon black has a primary particle size of 15 nm to 40 nm. By setting the primary particle size to 15 nm or more, a high image density can be obtained. By setting it to 40 nm or less, the dispersion stability in the ink is increased, and the storage stability is improved. The primary particle diameter means an arithmetic average diameter obtained by observing carbon black particles with an electron microscope.

The carbon black preferably has a specific surface area of 100 m ² / g or more and 400 m ² / g or less by the BET method. By setting the specific surface area to 100 m ² / g or more, a high image density can be obtained. By setting it to 400 m ² / g or less, the dispersion stability in the ink becomes high and the storage stability becomes good. In order to obtain the effect more reliably, the BET specific surface area is more preferably 200 m ² / g or more and 400 m ² / g or less.

  Further, the carbon black preferably has a DBP oil supply amount of 40 ml / 100 g or more and 200 ml / 100 g or less. By setting the DBP oil supply amount to 40 ml / 100 g or more, a high image density can be obtained. By setting it to 200 ml / 100 g or less, the dispersion stability in the ink becomes high and the storage stability becomes good. The DBP oil supply amount means a value measured according to JIS K6221 A method.

Carbon black is, for example, the “RAVEN” series made by Columbian Carbon;
Cabot “REGAL” series, “MOGUL” series, “BLACK PEARLS” series, “MONARCH” series;
Degussa's “COLOR BLACK” series, “PRINTEX” series, “SPECIAL BLACK” series, “NIPEX” series;
“No.” series, “MCF” series, “MA” series made by Mitsubishi Chemical;
And the like satisfying the above-mentioned characteristics may be appropriately selected and used.

More specifically, “MONARCH880” manufactured by Cabot is a carbon black having a primary particle diameter of 16 nm, a DBP oil supply amount of 112 ml / 100 g, and a BET specific surface area of 220 m ² / g, and can be suitably used in the present invention. it can. However, carbon black is not limited to these products.

  The content (% by mass) of carbon black is preferably 0.5% by mass or more and 10.0% by mass or less, more preferably 1.0% by mass or more and 8.0% by mass or less, based on the total mass of the ink. It is particularly preferably 1.5% by mass or more and 6.0% by mass. By setting the content to 0.5% by mass or more, an image density necessary as an ink for an ink jet printer can be obtained. By setting the content to 10.0% by mass or less, characteristics such as viscosity necessary for ejection as an ink for an ink jet printer are satisfied.

[1-2] (Meth) acrylic ester copolymer:
In the present invention, a (meth) acrylic acid ester copolymer is used as a resin dispersant for dispersing the pigment. The (meth) acrylic acid ester-based copolymer can be obtained, for example, by copolymerizing (meth) acrylic acid, (meth) acrylic acid ester, and an ethylenically unsaturated monomer copolymerizable therewith. it can. In view of the fact that the coexistence range of the electrical neutral state and the anion state can be widely controlled, availability, and price, it is preferable to use (meth) acrylic acid. Specific examples of (meth) acrylic acid include acrylic acid and methacrylic acid.

  The (meth) acrylic acid ester copolymer may be a copolymer having any structure such as a random copolymer, a block copolymer, and a graft copolymer. Among these, a random copolymer is preferable. Conventional thermal ink jet recording methods have demanded inks with high hydrophilicity in order to improve ink ejection properties, and block copolymers that have a high effect of improving hydrophilicity are used as resin dispersants. It was often done. However, depending on the block copolymer to be used, the hydrophilicity of the ink becomes too high and the water resistance of the image may be lowered, and a random copolymer is often used as a resin dispersant. The ink of the present invention is extremely effective not only when it contains a block copolymer as a resin dispersant, but also when it contains a random copolymer.

  Specific examples of (meth) acrylic acid esters include methyl (meth) acrylate, n-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, and (meth) acrylic. Alkyl (meth) acrylates such as dodecyl acid, octadecyl (meth) acrylate, cyclohexyl (meth) acrylate, and 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 (meth) Acrylate, dipropylene glycol mono (meth) acrylate, tripropylene glycol mono (meth) acrylate, tetramethylene ether glycol mono (meth) acrylate, polyethylene oxide-polypropylene oxide random polymer glycol mono (meth) acrylate, polyethylene oxide- Polypropylene oxide block polymer glycol mono (meth) acrylate, polyethylene oxide-polytetramethylene ether random polymer glycol mono (meth) acrylate, polyethylene oxide-polytetramethylene ether block polymer glycol mono (meth) acrylate, etc. Alkylene glycol mono (meth) acrylate; glycidyl (meth) acrylate; (meth) And benzyl acrylic acid.

  As a monomer for obtaining a (meth) acrylic acid ester copolymer, a styrene monomer can be used. Specific examples of the styrene monomer include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, pt-butylstyrene, 4-methoxystyrene, 4-chlorostyrene, and the like. Can be mentioned. The (meth) acrylic acid ester copolymer preferably contains a structural unit derived from a styrene monomer.

  The acid value of the (meth) acrylic acid ester copolymer is 100 mgKOH / g or more and 160 mgKOH / g or less, preferably 110 mgKOH / g or more and 150 mgKOH / g or less. When the acid value of the (meth) acrylic acid ester copolymer exceeds 160 mgKOH / g, the bleeding resistance of the recorded image (printed matter) tends to be lowered. On the other hand, when the acid value of the (meth) acrylic acid ester copolymer is less than 100 mgKOH / g, the ejection stability tends to be lowered when used in an ink jet recording apparatus that ejects ink by a thermal method.

  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 is a value determined by potentiometric titration. Potentiometric titration can be measured using an automatic titrator (such as “Titrino” manufactured by Metrohm).

  The weight average molecular weight (Mw) in terms of styrene of the (meth) acrylic acid ester copolymer is preferably 6,000 or more and 12,000 or less, and more preferably 7,000 or more and 9,000 or less. . When the weight average molecular weight of the (meth) acrylic acid ester copolymer is within the above range, ink ejection stability is improved, kogation in the heater is suppressed, and the viscosity of the ink is reduced. Since dispersion stability is improved, printing can be stably performed for a long period of time. When the weight average molecular weight of the (meth) acrylic acid ester copolymer is less than 6,000, the dispersion stability of the pigment tends to be lowered. On the other hand, when the weight average molecular weight of the (meth) acrylic acid ester copolymer exceeds 12,000, the viscosity of the ink becomes too high and the dispersion stability of the pigment tends to decrease. Further, kogation is likely to occur with a heater, and ink non-ejection tends to occur when used in an inkjet recording apparatus that ejects ink by a thermal method.

  The mass ratio of the (meth) acrylic acid ester copolymer to the mass of carbon black is 0.2 or more and 0.5 or less (0.2 mass part or more and 0.5 mass part per 1 mass part of carbon black). Part or less). By making the mass ratio 0.2 or more, the dispersion stability of the pigment can be maintained. On the other hand, when the mass ratio is 0.5 or less, the viscosity of the ink can be kept low, and the ejection stability can be improved.

  In the ink of the present invention, it is preferable that the pigment and the (meth) acrylic acid ester copolymer interact strongly, and the pigment particles are dispersed in the aqueous medium. More specifically, it is preferable that a resin-dispersed pigment formed by coating pigment particles with a (meth) acrylic acid ester copolymer is dispersed in an aqueous medium. In order to coat the pigment particles with a (meth) acrylic ester copolymer and form a resin-dispersed pigment, it is preferable to incorporate an acid precipitation step in the process of preparing the ink. In the acid precipitation step, for example, an acid such as hydrochloric acid, sulfuric acid, or acetic acid is added to an aqueous dispersion containing a pigment and a (meth) acrylic acid ester copolymer dissolved in an aqueous solution of a basic substance. Then, by making the aqueous dispersion acidic, the (meth) acrylic acid ester copolymer in a dissolved state is precipitated on the particle surface of the pigment.

  By carrying out this step, it is possible to form a resin-dispersed pigment in which the interaction between the pigment and the (meth) acrylic ester copolymer is further enhanced. In addition, after depositing the (meth) acrylic acid ester copolymer on the particle surface of the pigment, a filtration step for separating the precipitate may be performed. After completion of the filtration process, a washing process for washing the precipitate, and a redispersion process for neutralizing with a basic substance and dispersing the pigment in an aqueous medium, thereby obtaining an ink with superior dispersion stability. Can do.

  The average particle diameter of the resin-dispersed pigment is preferably 70 nm or more, and more preferably 80 nm or more in consideration of the dispersion stability of the pigment in the ink and the image density. Moreover, it is preferable that it is 150 nm or less, and it is still more preferable that it is 120 nm or less. The average particle diameter means a value measured by a dynamic light scattering method. For example, the measurement can be performed using a concentrated particle size analyzer (Otsuka Electronics "FPAR-1000", cumulant method analysis), which is a measuring device that uses laser light scattering.

[1-3] Nonionic surfactant:
In the present invention, a POE (polyoxyethylene) alkyl ether having an HLB of 15 to 20 is used as the nonionic surfactant. HLB (Hydrophile-Lipophile Balance) is a value indicating the degree of affinity of a surfactant for water or oil (hydrophobic organic compound). By setting the HLB within the above range, it is possible to improve the dispersion stability of the ink even when a (meth) acrylic acid ester copolymer having a low acid value is used. Further, it is possible to balance the hydrophilicity of the entire ink, to prevent the ink from sticking in the vicinity of the ink discharge port, and to suppress the non-discharge of the ink, the printing deviation, and the like. In order to obtain the above effect more reliably, it is preferable to use a POE alkyl ether having an HLB of 15 or more and 18 or less.

  The POE alkyl ether preferably has an alkyl group having 10 to 20 carbon atoms. In the case of having an alkyl group having 10 or more carbon atoms, the ejection properties can be further improved. On the other hand, when it has an alkyl group having 20 or less carbon atoms, it has an appropriate water solubility and improves the storage stability of the ink. Further, it is possible to suppress the problem of increasing the viscosity of the ink.

  As the POE alkyl ether, for example, those satisfying the above-mentioned conditions may be appropriately selected from “NIKKOL” series manufactured by Nikko Chemical.

  More specifically, POE (15) cetyl ether ("NIKKOL BC-15", HLB 15.5) as HLB 15 or more and 16 or less compound, POE (20) cetyl ether ("NIKKOL" as HLB 17 or more and 18 or less compound. BC-20 ", HLB17.0) and the like. These have a cetyl group which is an alkyl group having 16 carbon atoms.

  The mass ratio of the nonionic surfactant to the mass of carbon black is 0.1 or more and 0.5 or less (0.1 to 0.5 parts by mass with respect to 1 part by mass of carbon black). . By setting the mass ratio to 0.1 or more, it is possible to improve ink ejection stability. On the other hand, by setting the mass ratio to 0.5 or less, it is possible to prevent sticking of ink in the vicinity of the ink discharge port, and to suppress non-discharge of ink, printing deviation, and the like.

[1-3] 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, more preferably 40% by mass or more and 85% by mass or less, and still more preferably 50% by mass or more and 80% by mass with respect to the total mass of the ink. It is particularly preferred that By setting the content to 30% by mass or more, the pigment and the water-soluble compound can be hydrated, and aggregation of the pigment and the 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.

[1-4] Water-soluble compounds:
The ink of the present invention further contains a water-soluble compound, and the water-soluble compound is preferably at least one selected from the group of a water-soluble organic solvent and a water-soluble compound that is solid at 25 ° C.

  The “water-soluble compound” as used herein means a compound that is freely miscible with water or has a solubility in water (25 ° C.) of 20 g / 100 g or more. It is at least one selected from the group of water-soluble organic solvents and water-soluble compounds that are solid at 25 ° C. By containing the water-soluble compound, water can be prevented from evaporating and ink sticking due to drying can be prevented.

  Examples of water-soluble compounds include various water-soluble organic solvents such as alcohols, polyhydric alcohols, glycol ethers, carboxylic acid amides, heterocycles, ketones, and alkanolamines as listed below. Can do. A water-soluble compound that is solid at 25 ° C., such as urea, ethylene urea, trimethylol propane, or the like can also be used.

(1) Alcohols:
Chain alcohols having 1 to 5 carbon atoms such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, n-pentyl alcohol;
(2) Polyhydric alcohols:
Ethylene glycol (ethanediol), propanediol (1,2-, 1,3-), butanediol (1,2-, 1,3-, 1,4-), 1,5-pentanediol, 1,2 -Alkanediols such as hexanediol;
Condensates of alkanediols such as diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol, polypropylene glycol;
Polyhydric alcohols other than alkanediols such as glycerin, trimethylolpropane, 1,2,6-hexanetriol, thiodiglycol;
(3) Glycol ethers:
Monomethyl ether of ethylene glycol;
Monomethyl ether, monoethyl ether of diethylene glycol;
Monomethyl ether, monoethyl ether, monobutyl ether, dimethyl ether, diethyl ether of triethylene glycol;
Tetraethylene glycol dimethyl ether, diethyl ether;
(4) Carboxylic acid amides:
N, N-dimethylformamide, N, N-dimethylacetamide;
(5) Heterocycles:
Cyclic ethers such as tetrahydrofuran and dioxane;
Nitrogen-containing heterocycles such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-methylmorpholine;
Sulfur-containing heterocycles such as sulfolane;
(6) Ureas:
Ureas such as urea, ethylene urea, 1,3-dimethyl-2-imidazolidinone (N, N≡-dimethylethylene urea);
(7) Ketones:
Ketones such as acetone and methyl ethyl ketone;
Keto alcohols such as 4-hydroxy-4-methyl-2-pentanone (diacetone alcohol);
(8) Alkanolamines:
Monoethanolamine, diethanolamine, triethanolamine;
(9) Other:
Sulfur-containing compounds such as dimethyl sulfoxide and bishydroxyethyl sulfone;

  Among the water-soluble organic solvents, polyhydric alcohols are preferable, and glycerin is more preferable. Glycerin is preferable in that it hardly evaporates and is excellent in the effect of preventing ink sticking. Moreover, the said water-soluble organic solvent may be used individually by 1 type, and 2 or more types may be mixed and used for it. For example, it is also preferable to use glycerin and a polyhydric alcohol other than glycerin in combination. At this time, triethylene glycol or the like can be used as the polyhydric alcohol other than glycerin. Such a mixed solvent is preferable in that the effect of preventing the viscosity increase of the ink is high.

  The content rate of the water-soluble organic compound is not particularly limited. However, in order to prevent the aqueous medium from evaporating and to obtain the effect of preventing ink sticking due to drying, the content is preferably 5% by mass or more, more preferably 10% by mass or more, and still more preferably based on the total mass of the ink. Is preferably 15% by mass or more. On the other hand, from the viewpoint of being able to cope with a high drive frequency and preventing the occurrence of mold, it is preferably 50% by mass or less, more preferably 40% by mass or less, and further preferably 30% by mass with respect to the total mass of the ink. % Or less is particularly preferable.

  As the water-soluble compound that is solid at 25 ° C., urea, ethylene urea, or the like is preferably used, and ethylene urea is particularly preferably used. The content of the water-soluble compound that is solid at 25 ° C. is not particularly limited. However, in order to prevent the aqueous medium from evaporating and to obtain the effect of preventing ink sticking due to drying, the content is preferably 3% by mass or more, more preferably 5% by mass or more with respect to the total mass of the ink. . On the other hand, in order to prevent problems due to excessive addition, the content is preferably 30% by mass or less, more preferably 15% by mass or less, based on the total mass of the ink.

[1-6] Other additives:
The ink of the present invention may contain an additive other than the surfactant depending on the purpose. Examples of such additives include pH adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, reduction inhibitors, salts, and the like.

［式中、ＵおよびＶは、エチレンオキサイドの付加モル数を示す。］ The ink of the present invention may contain a nonionic surfactant other than POE alkyl ether. For example, it may contain an acetylene glycol surfactant. As an acetylene glycol surfactant, compound (1) (2,4,7,9-tetramethyl-5-decyne-4,7-diol or an ethylene oxide adduct thereof) represented by the following general formula (1) is used. It is preferable to use it. By using the compound, ink wettability can be improved, and ink ejection stability can be improved.

[Wherein U and V represent the number of moles of ethylene oxide added. ]

  “The number of moles of ethylene oxide added” is the average number of moles of ethylene oxide added per molecule of acetylene glycol. In the example of the compound (1), it means an average value of U + V. U + V is not particularly limited. However, U + V is preferably 0 or more and 10 or less, and U + V is more preferably 4 or more and 10 or less. When the number of moles of ethylene oxide added to the compound (1) is 0 or more, the compound has a certain degree of hydrophilicity, so that the surface tension of the ink can be increased and the ejection stability of the ink can be improved. . When the number of moles of ethylene oxide added to the compound (1) is 10 or less, the compound maintains a certain degree of hydrophobicity, so that the wettability of the ink to the nozzle wall made of, for example, an epoxy photosensitive resin is improved. Can be made. Accordingly, the performance of supplying ink to the nozzles is improved, and the ink ejection stability is improved.

  The acetylene glycol surfactant is preferably contained at a ratio of 1% by mass or less with respect to the total mass of the ink. By setting the content to 1% by mass or less, an increase in viscosity due to excessive addition is suppressed, the ink has an appropriate surface tension, and ink ejection stability is improved. The lower limit of the content of the acetylene glycol surfactant is not particularly limited. However, in order to obtain the addition effect of the acetylene glycol surfactant, it is preferable that the acetylene glycol-based surfactant is contained at a ratio of 0.1% by mass or more with respect to the total mass of the ink.

[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 preferable to set it to 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] 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 means a value measured by a plate method using a platinum plate at a temperature of 25 ° C. and using an automatic surface tension meter (for example, “CBVP-Z type” manufactured by Kyowa Interface Science). The surface tension of the ink can be adjusted by the amount of the surfactant added, the type and content of the water-soluble organic solvent, and the like.

[1-10] 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, HORIBA (manufactured) D-51, etc.) 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 partitioned from the surrounding space by using the nozzle wall 153, the nozzle top plate 162, and the nozzle bottom plate 164 as partitions. 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 an 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 on the side wall of the nozzle and the liquid chamber frame formed in this manner. Therefore, 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. 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 from the ink discharge port to the common liquid chamber (that is, the nozzle flow path and the common liquid chamber) in the internal space.

[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. Therefore, in the ink chamber 221, an ink storage part (liquid storage part) in which the 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. This 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 the correction value 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 environmental temperature and the environmental humidity of the recording apparatus are acquired (detected) by the temperature / 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, “parts” and “%” are based on mass unless otherwise specified.

<Synthesis of (meth) acrylic ester random copolymer>
(Synthesis Example 1)
(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. The temperature inside the reaction vessel was raised to 80 ° C. while maintaining a nitrogen atmosphere, and then from a dropping device, 63 parts of 2-hydroxyethyl methacrylate, 141 parts of methacrylic acid, 417 parts of styrene, 188 parts of benzyl methacrylate, and 25 parts of glycidyl methacrylate. , 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 added dropwise over 4 hours. . After completion of the dropwise addition, 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 mg KOH / g glass transition point (Tg) 89 ° C. and a weight average molecular weight of 8,000 ( A solution of A-1) (resin content: 45.4%) was obtained.

<Preparation of aqueous pigment dispersion>
(PK1)
In a mixing vessel equipped with a cooling jacket, a solution of (meth) acrylic ester random copolymer A-1 (acid value 110 mgKOH / g), 25% potassium hydroxide aqueous solution, water, and carbon black described in Table 2 B1 was charged and stirred and mixed to obtain a mixed solution. In addition, the (meth) acrylic acid ester random copolymer A-1 was used in such an amount that the nonvolatile content was 40% with respect to 1,000 parts of carbon black. Moreover, the 25% potassium hydroxide aqueous solution used the quantity by which (meth) acrylic acid ester system random copolymer A-1 is neutralized 100%. Furthermore, the water used the quantity which makes the non volatile matter of the obtained liquid mixture 27%. The obtained mixed solution was passed through a dispersing device (trade name “SC Mill SC100 / 32”, manufactured by Mitsui Mining Co., Ltd.) filled with zirconia beads having a diameter of 0.3 mm, and dispersed for 4 hours by a circulation method. The number of revolutions of the dispersing device was 2,700 rpm, and the temperature of the dispersion was kept at 40 ° C. or lower by passing cold water through the cooling jacket.

  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 glass distillation apparatus, and all 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 using 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 black aqueous pigment dispersion PK1 (pigment content: 14%). It was 82 nm when the average particle diameter of the resin dispersion pigment of the produced pigment dispersion was measured by “FPAR-1000” manufactured by Otsuka Electronics.

(PK2)
In place of carbon black B1, carbon black B2 shown in Table 2 (primary particle size: 24 nm, DBP oil supply amount: 115 ml / 100 g, specific surface area 110 m ² / g) was used, and “PK1” described above was used. Similarly, a black aqueous pigment dispersion PK2 (pigment content: 14%) was obtained. It was 91 nm when the average particle diameter of the resin dispersion pigment was measured similarly to PK1.

(PK3)
The same as “PK1” described above, except that the amount of the (meth) acrylic acid ester random copolymer A-1 is 10% in terms of nonvolatile content with respect to 1,000 parts of carbon black. Thus, a black aqueous pigment dispersion PK3 (nonvolatile content: 20%) was obtained. It was 102 nm when the average particle diameter of the resin dispersion pigment was measured similarly to PK1.

(PK4)
The same as “PK1” described above, except that the amount of the (meth) acrylic acid ester random copolymer A-1 is an amount that gives a ratio of 60% in non-volatile content to 1,000 parts of carbon black. Thus, a black aqueous pigment dispersion PK4 (nonvolatile content: 20%) was obtained. It was 77 nm when the average particle diameter of the resin dispersion pigment was measured similarly to PK1.

<Preparation of ink (Examples 1 to 6, Comparative Examples 1 to 5)>
The aqueous pigment dispersion, the POE alkyl ether described in Table 3 and other components are put into a container so as to have the composition shown in Table 4 (total: 100 parts), and stirred for 30 minutes or more using a propeller stirrer. did. When the pH was measured and was lower than 8.5, the pH was adjusted to 9.0 with a 10% aqueous solution of potassium hydroxide. Thereafter, the ink was prepared by filtration through a filter having a pore diameter of 3 μm. In addition, 15 parts of the aqueous pigment dispersion was added, and the carbon black was adjusted to 3.0 parts.

  As the ink jet recording apparatus, a thermal type ink jet recording apparatus (“LX-P5500” manufactured by Canon Finetech Co., Ltd.) was used. As the recording head, the recording head for the ink jet recording apparatus was used. In this recording head, a hydrophilic region is formed at the periphery of the ink discharge port. Specifically, the recording head has the structure shown in FIGS. 1A to 1C and FIGS. 2A to 2C. Specific specifications of the recording head are shown in Table 5.

  Inks of Examples 1 to 6 and Comparative Examples 1 to 5 are respectively injected into ink tanks, and the ink tanks are connected to the recording apparatus 300 shown in FIG. Filled with ink.

[Evaluation]
The inks of Examples and Comparative Examples were evaluated. The evaluation method and evaluation criteria are shown below. Each evaluation item has a five-level evaluation. If the evaluation is ◯ or higher, it is a pass level with no problem in actual use. The results are shown in Table 6.

(Clogging adhesion)
The recording head was released from the cap and exposed for 1 day in an environment of a temperature of 40 ° C. and a humidity of 10%, and then printing was performed by the recording apparatus. A glossy label 4 × 5 inches (manufactured by Canon) was used as a recording medium. The resolution was 1200 dpi × 1200 dpi. Nozzle check pattern corresponding to each nozzle is printed on the recording medium ("LX-P5500" built-in test pattern: a pattern corresponding to each nozzle and confirming whether the nozzle is undischarged or twisted) did. The number of suction recovery operations required until each ink is normally ejected from the recording head, and after the suction recovery, twist printing and line-like image defects (due to the presence of undischarge nozzles) in the printed image. Evaluation was performed depending on whether or not there was.
A: Normal printing (no twist printing, no line defects) can be achieved with one suction recovery.
○: No twist printing in printing after one suction recovery, 5 or less line defects.
(Triangle | delta): There is twist printing by printing after suction recovery once, and it is 10 or less line-like defects.
X: No twist printing in printing after 2 times of suction recovery, 5 or less line defects.
XX: Two or more suction recovery operations are required for normal printing.

(Dischargeability)
Using an ejection characteristic measuring device, the ejection performance of each ink was evaluated for the recording head in an environment of 25 ° C. and humidity of 50%. The evaluation was performed based on the discharge speed and frequency response. The design values of the recording head are a discharge speed of 10 m / s or more and a frequency response of 6 kHz or more.
A: Discharge speed of 10 m / s or more. Frequency response 6kHz or more.
○: Discharge speed of 10 m / s or more. Frequency response 5kHz or more and less than 6kHz.
(Triangle | delta): The discharge speed is 8 m / s or more and less than 10 m / s. Frequency response 4 kHz or more and less than 5 kHz.
X: The discharge speed is 5 m / s or more and less than 8 m / s. Frequency response less than 4kHz.
Xx: The discharge speed is less than 5 m / s. Frequency response less than 4kHz.

(Intermittent discharge)
In an environment of a temperature of 15 ° C. and a humidity of 10%, ink is ejected drop by drop from 4800 ink ejection ports of the recording head mounted on the recording apparatus, and one line image (reference line width of about 50) is obtained. ± 5 μm) was printed. A mat label (manufactured by Canon Finetech) was used as the recording medium. Printing was performed by changing the head exposure time from preliminary ejection to printing between 3 and 10 seconds. The printed line image was visually confirmed, and it was confirmed that there was no printing twist, line-like defect (nozzle discharge failure), and line variation, and normal printing was performed. When normal printing could be performed even if the exposure time was long, it was judged that the intermittent ejection property (uniformity) was good, and the evaluation was performed according to the following criteria.
(Double-circle): The exposure time which can perform normal printing is 10 seconds or more.
○: Exposure time for normal printing is 8 seconds or more and less than 10 seconds.
(Triangle | delta): The exposure time which can perform normal printing is 5 second or more and less than 8 second.
X: The exposure time in which normal printing can be performed is 3 seconds or more and less than 5 seconds.
XX: The exposure time for normal printing is less than 3 seconds.

  As shown in Table 6, the inks of Examples 1 to 6 showed good results in clogging adhesion, ejection performance, and intermittent ejection performance. In particular, the inks of Examples 1 and 4 showed particularly good results in all items of initial discharge property, discharge property, and intermittent discharge property.

  Inks of Comparative Examples 1 and 2 are mass ratios of (meth) acrylate random copolymer to carbon black, Comparative Examples 3 and 4 are mass ratios of POE alkyl ether to carbon black, and Ink of Comparative Example 5 is POE alkyl. The ether HLB does not meet the requirements of the present invention. For this reason, all of the inks of Comparative Examples 1 to 5 were clogged and poor in fixing property, and at least one of the discharging property and the intermittent discharging property was defective.

  The ink of the present invention can be used as an ink for inkjet recording. In particular, the ink can be suitably used as an ink ejected from a thermal recording head in which the resin is likely to cause kogation in the heater portion (foaming portion), in particular, from a line-type head in which the recovery operation of the recording head cannot be frequently performed.

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 part, 131: liquid communication part, 132: supply joint, 133: discharge joint, 134: first liquid supply chamber, 135: second liquid supply chamber, 136: second liquid supply chamber opening, 137 : Liquid supply path, 138: second liquid supply chamber inclination, 139: ink discharge port arrangement surface, 141: air chamber, 151: ink discharge 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: ejection port, 221: ink chamber, 222: ink supply part, 223: filter member, 224: ink holding 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: Recording Device 301: recording medium 302: transport roller 303: transport motor 304: paper detection sensor 305 305K 05Y, 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: Print 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: Condition, 502: Process, 503: Condition, 504: Condition 5 05: Process, I: Ink.

Claims (9)

An ink for ink jet recording containing water, carbon black, a resin dispersant for dispersing the carbon black, and a nonionic surfactant,
The carbon black has a primary particle size of 15 nm to 40 nm,
The resin dispersant is a (meth) acrylic acid ester copolymer having an acid value of 100 mgKOH / g or more and 160 mgKOH / g or less,
The nonionic surfactant is a POE alkyl ether having an HLB of 15 to 20,
The mass ratio of the nonionic surfactant to the mass of the carbon black is 0.1 or more and 0.5 or less,
An ink for inkjet recording, wherein a mass ratio of the (meth) acrylic ester copolymer to a mass of the carbon black is 0.2 or more and 0.5 or less. The copolymer is a random copolymer;
The ink according to claim 1, wherein the copolymer is neutralized after adsorbing to the pigment by an acid precipitation method. 3. The ink according to claim 1, wherein the carbon black is carbon black having a specific surface area of 100 m ² / g to 400 m ² / g and a DBP oil supply amount of 40 ml / 100 g to 200 ml / 100 g by the BET method.   The ink according to any one of claims 1 to 3, wherein the POE alkyl ether has an alkyl group having 10 to 20 carbon atoms. The ink further contains a water-soluble compound;
The ink according to any one of claims 1 to 4, wherein the water-soluble compound is at least one selected from the group of a water-soluble organic solvent and a water-soluble compound that is solid at 25 ° C. A nozzle row composed of a plurality of nozzle flow paths partitioned by a nozzle wall is formed, a plurality of ink discharge ports communicating with the nozzle flow paths are formed, and a heater for ink discharge is arranged inside each nozzle flow path The opening area of the ink discharge port is 100 μm ² or more and 350 μm ² or less,
The internal space communicating with the ink discharge port is filled with ink for ink jet recording,
A recording head for ink jet recording, wherein the ink is the ink according to any one of claims 1 to 5.   The recording head according to claim 6, wherein the recording head is a line type head having a total number of nozzles of the nozzle row of 1200 or more and a length of the nozzle row of 2 inches or more. The line-type head includes a common liquid chamber that communicates with the plurality of nozzle channels forming the nozzle row, a liquid supply port that communicates with the common liquid chamber, and a main liquid supply chamber that communicates with the liquid supply port. A liquid supply path communicating with the main liquid supply chamber, a liquid supply chamber communicating with the liquid supply path, and a first liquid supply chamber and a first liquid supply chamber from the upstream side along the flow when the liquid is supplied to the liquid supply chamber. A supply filter disposed so as to be separated into a two-liquid supply chamber, a gas-liquid separator provided in a part of the main liquid supply chamber, and an air chamber communicating with the gas-liquid separator. ,
The nozzle flow path, the common liquid chamber, the liquid supply port, the main liquid supply chamber, the liquid supply path, the liquid supply chamber, the supply filter, the gas-liquid separator, An air chamber is disposed on a plane parallel to a plane including the arrangement direction of the nozzle flow paths and the liquid discharge direction;
The recording according to claim 6 or 7, wherein the main liquid supply chamber, the liquid supply path, the supply filter, the gas-liquid separator, and the air chamber are arranged without being stacked. head. An inkjet recording apparatus comprising: a recording head for inkjet recording; and an ink storage unit that stores ink to be supplied to the recording head,
An ink jet recording apparatus, wherein the recording head is the recording head according to claim 6.

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