JP2009108192A - Aqueous ink, inkjet recording method, ink cartridge, and inkjet recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink that gives an image having satisfactory scratch resistance and water resistance and does not suffer from lowering of alkali resistance in the case that the ink is reserved for long periods when it contains a resin comprising at least an alkyl acrylate copolymerized thereinto as a monomer. <P>SOLUTION: The inkjet ink comprises a pigment, a resin comprising at least an alkyl acrylate copolymerized thereinto as a monomer, and a water-soluble organic solvent comprising the first and second water-soluble organic solvents. The content of the first water-soluble organic solvent having a specific dielectric constant and a specific dipole moment is at least 10.0 mass% and the content of the second water-soluble organic solvent which is a water-soluble organic solvent other than the first one is at least 3.0 mass% and less than 10.0 mass%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an aqueous ink containing a resin in which at least an alkyl acrylate is copolymerized as a monomer, and an ink jet recording method, an ink cartridge, an ink cartridge, and an ink jet recording apparatus using the aqueous ink.

  A water-based ink using a pigment as a coloring material may use a water-soluble resin as a dispersant in order to stably disperse the pigment in an aqueous medium (see Patent Document 1). In addition, in order to improve glossiness, abrasion resistance, water resistance, and the like of an image formed using a water-based ink, an ink containing a water-soluble resin or emulsion may be used (patent document). 2).

When such a resin has an ester bond, the ester bond may cause a hydrolysis reaction. For example, unsaturated polyester resins are often used for paints and industrial equipment. However, when such an unsaturated polyester resin is used for a long period of time under severe temperature and humidity conditions, the resin may deteriorate due to a hydrolysis reaction of the ester bond and an increase in acid value. is there. In response to the above-described problem, a method for suppressing deterioration of the resin has been proposed (see Patent Document 3).
Japanese Patent Laid-Open No. 9-122846 Japanese Patent Laid-Open No. 10-338829 JP-A-9-124582

  In order to improve the scratch resistance and water resistance of an image formed using a water-based ink containing a pigment, the present inventors have studied an ink added with a resin. In the process, it was found that a new problem arises that the recorded part is peeled off when an image formed with a finger with sweat attached is touched. For this reason, the present inventors not only have the scratch resistance and water resistance of the formed image, but even if an alkaline component as a sweat component adheres, the image does not deteriorate, that is, the alkali resistance of the image is improved. A study was conducted on excellent ink.

  As a result, it was found that an ink capable of forming an image excellent in alkali resistance, which is the main object of the present invention, can be obtained by incorporating a resin copolymerized with at least an alkyl acrylate as a monomer. Therefore, the present inventors have further studied using the above ink containing a resin in which at least an alkyl acrylate is copolymerized as a monomer. However, it was confirmed that the following problems occur in the process of the examination. Specifically, in order to confirm the storage stability of the ink, the ink is put in a sealed container and stored at a temperature of 60 ° C. for one month, and then the ink is taken out from the container and the ink-jet recording method is used. An image was formed using ink. As a result, it has been found that the alkali resistance of the image, which had no problem before storage at a temperature of 60 ° C. for one month, is reduced with the ink after storage under the above conditions.

  Accordingly, an object of the present invention is to satisfy the image scratch resistance and water resistance, and to maintain the alkali resistance of an image even when a long-term storage of an aqueous ink containing a resin copolymerized with at least an alkyl acrylate as a monomer. An object of the present invention is to provide a water-based ink that does not decrease. Another object of the present invention is to provide an ink jet recording method, an ink cartridge, an ink cartridge, and an ink jet recording apparatus using the water-based ink.

  The above object is achieved by the present invention described below. That is, the water-based ink according to the present invention is a water-based ink containing a pigment, a resin copolymerized with at least an alkyl acrylate as a monomer, and a water-soluble organic solvent, wherein the water-soluble organic solvent is a first water-soluble solvent. An organic solvent and a second water-soluble organic solvent, wherein the first water-soluble organic solvent has a dielectric constant of 35 F / m or less at a temperature of 20 ° C. and a dipole moment of 2.5 D or more. The content (% by mass) of the first water-soluble organic solvent in the ink is 10.0% by mass or more based on the total mass of the ink, and the second water-soluble organic solvent is the first water-soluble organic solvent. A water-soluble organic solvent other than the water-soluble organic solvent, and the content (% by mass) of the second water-soluble organic solvent in the ink is 3.0% by mass or more and 10.0% by mass based on the total mass of the ink. Less than And wherein the Rukoto.

  An ink jet recording method according to another embodiment of the present invention is an ink jet recording method in which ink is ejected by an ink jet method to perform recording on a recording medium, and the above-described aqueous ink is used as the ink. And

  In addition, an ink cartridge according to another embodiment of the present invention is an ink cartridge including an ink storage unit that stores ink, and the ink stored in the ink storage unit is the water-based ink described above. Features.

  A recording unit according to another embodiment of the present invention is a recording unit including an ink storage portion that stores ink and a recording head that discharges ink, and the ink stored in the ink storage portion is stored in the recording unit. The water-based ink described above.

  An ink jet recording apparatus according to another embodiment of the present invention is an ink jet recording apparatus that includes an ink storage portion that stores ink and a recording head that discharges ink, and is stored in the ink storage portion. The ink is the water-based ink described above.

  According to the present invention, the alkali resistance of an image is deteriorated even when an aqueous ink containing a resin copolymerized with at least an alkyl acrylate as a monomer is satisfied for a long period of time, satisfying the scratch resistance and water resistance of the image. A water-based ink can be provided. Moreover, according to another embodiment of the present invention, an ink jet recording method, an ink cartridge, an ink cartridge, and an ink jet recording apparatus using the water-based ink can be provided.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments. In the following description, the water-based ink may be simply referred to as “ink”.

  First, the present inventors formed an image using an ink containing a resin containing at least alkyl acrylate copolymerized as a monomer for a long period of time, compared with an image formed using the ink before storage. The cause of the decrease in alkali resistance was examined.

  Since the present inventors originally aimed mainly to improve the scratch resistance and water resistance of images, a resin having a low acid value was particularly selected as a resin having excellent image characteristics. It was. However, in order to dissolve a resin having a low acid value, it is necessary to increase the content of the neutralizing agent (alkaline component) in the ink. Therefore, the pH of the ink is much higher than that of a general ink. It was as high as 9.0. Here, the pH of a general ink containing an alkali-soluble resin is about 7.0 to 8.5.

  If an alkyl acrylate derived from a resin in which at least an alkyl acrylate is copolymerized as a monomer is present in a liquid having a pH higher than 7.0, the alkyl acrylate generates an alkyl alcohol by a hydrolysis reaction, and simultaneously generates acrylic acid. To do. For this reason, the resin in which at least an alkyl acrylate is copolymerized as the monomer has a higher acid value with an increase in the acrylic acid, while the alkali resistance tends to be lowered. Therefore, for example, when an alkyl acrylate derived from a resin in which at least an alkyl acrylate is copolymerized as a monomer is present in an ink having a pH of about 9.0, specifically about 8.8 to 9.3, the alkyl acrylate The hydrolysis reaction of is accelerated rapidly. For this reason, it is considered that the phenomenon that the alkali resistance of the image decreases with time has occurred remarkably. In the present invention, the phenomenon that the alkali resistance of the image as described above decreases with time begins to occur when the pH of the ink exceeds 8.0, and becomes more prominent when the ink pH exceeds 9.0. Confirmed that it happened.

  Therefore, the present inventors have studied to suppress the hydrolysis reaction of alkyl acrylate. As a result, it was found that the characteristics of the water-soluble organic solvent contained in the ink, specifically, the dielectric constant and the dipole moment of the water-soluble organic solvent greatly affect the hydrolysis reaction of the alkyl acrylate. The reason for this is not clear, but the present inventors presume the reason as follows. The water-soluble organic solvent is classified into a polar solvent and an apolar solvent based on its polarity, and the polar solvent is classified into a protic polar solvent and an aprotic polar solvent. Here, the hydrolysis reaction of the polyester resin is more likely to proceed in an environment in which a hydrophilic solvent is present than in an environment in which a hydrophobic solvent is present. For this reason, compared with the environment where a nonpolar solvent or an aprotic polar solvent is present, the hydrolysis reaction is promoted more when the alkyl acrylate is present in the environment where the protic polar solvent is present. Like the polyester resin, since the alkyl acrylate also has an ester bond, the hydrolysis reaction is promoted more when the alkyl acrylate is present in the environment where the protic polar solvent is present, as in the mechanism described above. Conceivable.

  Whether the water-soluble organic solvent is a polar solvent, a protic polar solvent, or an aprotic polar solvent as described above depends on the dielectric constant of the water-soluble organic solvent (unit: F / m) And the dipole moment (unit: D: Debye). From this, the present inventors selected the water-soluble organic solvent as the water-soluble organic solvent used in the ink in consideration of the values of the dielectric constant and the dipole moment. It was concluded that can be suppressed.

  Therefore, the present inventors have further studied in detail the relationship between the alkyl acrylate and the dielectric constant and dipole moment of the water-soluble organic solvent based on the above idea. As a result, the water-soluble organic solvent that can most effectively suppress the hydrolysis reaction is a water-soluble organic solvent having a dielectric constant of 35 F / m or less at a temperature of 20 ° C. and a dipole moment of 2.5 D or more. It turns out that there is. Hereinafter, in the present invention, a water-soluble organic solvent having a dielectric constant of 35 F / m or less at a temperature of 20 ° C. and a dipole moment of 2.5 D or more is referred to as “first water-soluble organic solvent”. I will call it.

  Furthermore, as a result of the study by the present inventors, since the polarity is high, water-soluble organic solvents other than the first water-soluble organic solvent are more alkylated than water that is considered to most accelerate the hydrolysis reaction of alkyl acrylate. It has been found that there is a tendency to accelerate the hydrolysis reaction of acrylates. Hereinafter, in the present invention, a water-soluble organic solvent other than the first water-soluble organic solvent is referred to as a “second water-soluble organic solvent”. That is, the second water-soluble organic solvent is a water-soluble organic solvent having a dielectric constant of greater than 35 F / m at a temperature of 20 ° C. and a dipole moment of less than 2.5D.

  From what has been described so far, the present inventors need to use the first water-soluble organic solvent as a water-soluble organic solvent used in an ink containing a resin copolymerized with at least an alkyl acrylate as a monomer. I came to the conclusion.

  However, as a result of the study by the present inventors, in order to obtain an ink for ink jet, the above-mentioned second water-soluble solution is used in order to satisfy the reliability required for the ink jet recording method, such as the light emission property and the fixing recovery property. It was found that it was necessary to use an organic solvent. The uniformity is an ejection property when ink is ejected from the ejection port for a certain period of time and then ejected again. During recording with an inkjet recording apparatus, a specific ejection port is used for a short period of time. Even when it is not used, a decrease in uniformity may occur. Further, the fixing recovery property is a performance for recovering clogging caused by thickening or drying and solidifying ink adhering to the vicinity of the ejection port.

  Therefore, the present inventors set the content of the second water-soluble organic solvent in the ink to 3.0% by mass or more, which is considered to be the minimum necessary for satisfying the above-described uniformity and fixability. In addition, the constitution of the ink capable of suppressing the hydrolysis reaction of the alkyl acrylate was examined. As a result, the content of the first water-soluble organic solvent is 10.0% by mass or more, and the content of the second water-soluble organic solvent is less than 10.0% by mass, so that It was found that the decomposition reaction can be sufficiently suppressed.

  From the above, the water-soluble organic solvent used in the ink of the present invention has a content of the first water-soluble organic solvent of 10.0% by mass or more, and a content of the second water-soluble organic solvent. It is necessary to satisfy that the content is 3.0% by mass or more and less than 10.0% by mass. In addition, said content is content based on the total mass of ink.

  In the present invention, in order to keep the dispersion state of the pigment stable even after storing the ink for a long period of time, that is, to improve the storage stability, the alkyl acrylate in the resin in which at least the alkyl acrylate is copolymerized as the monomer is butyl acrylate. It is preferable that Among the alkyl acrylates, the reason why the effect of improving the storage stability as described above can be obtained by using butyl acrylate is not clear, but the present inventors presume the reason as follows. ing. Among the alkyl acrylates, ethyl acrylate and the like are easily dissociated in the ink. Therefore, when the ink is stored for a long period of time, the dispersion concentration of the pigment may decrease due to an increase in the salt concentration in the ink. As a result of the study by the present inventors, when an ink containing a resin copolymerized with ethyl acrylate is stored for a long period of time, the ink is stored for a long period of time as compared with an ink containing a resin copolymerized with butyl acrylate. The increase rate of the average particle diameter of the pigment before and after was obviously large.

  When the present inventors further examined the hydrolysis reaction of butyl acrylate, the amount of butanol generated by the hydrolysis reaction and the content of butyl acrylate in the ink were such that the butyl acrylate content was 2.0% by mass. In the range up to less than, it became a proportional relationship. However, when the content of butyl acrylate in the ink is 2.0% by mass or more, the amount of carboxyl groups produced increases, and the progress rate of the hydrolysis reaction of the resin also increases rapidly, so the amount of butanol generated increases rapidly. It turned out to increase. For these reasons, the content (% by mass) of butyl acrylate constituting the resin is preferably less than 2.0% by mass based on the total mass of the ink. The content (mass%) of butyl acrylate constituting the resin based on the total mass of the ink is the resin content (mass%) obtained by copolymerizing butyl acrylate in the ink. It is a value obtained by multiplying the composition (mass) ratio of butyl acrylate and dividing by 100. The composition (mass) ratio of butyl acrylate is a numerical value when the sum of the composition (mass) ratios of all the monomers constituting the resin is 100%.

  The present inventors further examined the relationship between the monomer and the hydrolysis reaction by paying attention to monomers other than butyl acrylate in the resin copolymerized with butyl acrylate. As a result, it was found that the hydrolysis reaction can be more effectively suppressed by using a monomer having an SP value smaller than that of butyl acrylate as the monomer other than butyl acrylate in the resin copolymerized with butyl acrylate. The reason for this is not clear, but the present inventors presume the reason as follows. The resin copolymerized with a highly hydrophobic monomer is in a state where micelles are formed in the ink and the resin chains are entangled. And most of the butyl acrylate portions in the resin are in a state of being oriented in the interior of the micelles, so that it is considered that the hydrolysis reaction of butyl acrylate hardly occurs. According to the study by the present inventors, in order to orient most of the butyl acrylate portion inside the micelle, it is preferable that the resin is copolymerized with a monomer that is hydrophobic, that is, has a smaller SP value than butyl acrylate.

  At this time, it is preferable that the copolymerization ratio (mass ratio) of the monomer having an SP value smaller than that of butyl acrylate is not less than the copolymerization ratio (mass ratio) of butyl acrylate. Furthermore, it is particularly preferable that the copolymerization ratio (mass ratio) of the monomer having an SP value smaller than that of butyl acrylate is three times or more of the copolymerization ratio (mass ratio) of butyl acrylate. In addition, since the ink of the present invention is an ink jet ink, if a resin in which only a monomer having a small SP value is copolymerized is used, the above-described ejection property, in particular, the light emission property may be easily lowered. . For this reason, it is preferable that the copolymerization ratio (mass ratio) of the monomer having an SP value smaller than that of butyl acrylate is less than 5 times the copolymerization ratio (mass ratio) of butyl acrylate.

  In addition, said SP value is a parameter | index which shows the hydrophobicity of resin (monomer which comprises), and can be calculated | required from a following formula.

δ: SP value (solubility parameter)
ΔH: heat of molar evaporation V: molar volume R: gas constant T: temperature

<Water-based ink>
Hereinafter, each component constituting the water-based ink of the present invention will be described.

(resin)
The resin used in the ink of the present invention needs to be a resin in which at least an alkyl acrylate is copolymerized as a monomer. This is because the present invention solves a problem that occurs when an ink containing a resin in which at least an alkyl acrylate is copolymerized is used as a monomer. A monomer other than the alkyl acrylate constituting the resin is not particularly defined, and any monomer may be copolymerized.

Specific examples of the monomer constituting the resin include the following monomers.
Styrene, α-methylstyrene, n-butyl acrylate, n-hexyl acrylate, benzyl methacrylate and the like. Monomers having a carboxyl group such as acrylic acid, methacrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid and fumaric acid. Monomers having a sulfonic acid group such as styrenesulfonic acid, sulfonic acid-2-propylacrylamide, acrylic acid-2-ethyl sulfonate, methacrylic acid-2-ethyl sulfonate, and butylacrylamide sulfonic acid. Monomers having a phosphonic acid group such as ethyl methacrylate-2-phosphonate and acrylic acid-2-ethyl phosphonate.

  In the present invention, as described above, it is particularly preferable to use a resin copolymerized with a monomer having a small SP value such as styrene as the monomer other than the alkyl acrylate.

  An object of the present invention is to improve the scratch resistance and water resistance in addition to the alkali resistance of an image. For this reason, it is preferable that the resin has a property of fixing on a recording medium and forming a film. As a result of the study by the present inventors, it has been found that a resin having an acid value of 90 mgKOH / g or more and 150 mgKOH / g or less may be used as such a resin. When the acid value exceeds 150 mgKOH / g, the number of anionic groups in the resin increases, and the buffering action against salts and protons contained in the recording medium increases. As a result, the aggregation of the resin on the recording medium is suppressed, and the ratio of the resin remaining on the recording medium tends to decrease, which is not preferable for improving the scratch resistance. Furthermore, as described above, a high acid value is not preferable because the hydrolysis reaction of the resin tends to be accelerated. On the other hand, if the acid value is less than 90, the resin cannot be dissolved with an alkali, or the resin may precipitate when the ink is stored for a long period of time.

  The weight average molecular weight of the resin is preferably 5,000 to 15,000, more preferably 6,000 to 9,000. If the weight average molecular weight is less than 5,000, the scratch resistance of the image may not be sufficiently obtained. On the other hand, if the weight average molecular weight exceeds 15,000, it is considered to be an influence of steric hindrance, but it is confirmed as a result of measurement by ELS6500 (manufactured by Otsuka Electronics) that the resin is difficult to form micelles.

  Considering improvement in image scratch resistance, the resin content (% by mass) in the ink is 0.5% by mass or more and 5.0% by mass or less, and further 1.2% by mass based on the total mass of the ink. % Or more and 4.0% by mass or less is preferable. Further, the resin content (mass%) and the pigment content (mass content of resin / pigment content = 1.2 times or more based on the total mass of the ink are preferable.

(Aqueous medium)
The ink of the present invention preferably contains an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. In the present invention, as described above, the water-soluble organic solvent is classified into the first water-soluble organic solvent and the second water-soluble organic solvent from the characteristics of the dielectric constant and the dipole moment, and each of the specific water It is necessary to make it contain in ink as content.

  As the first water-soluble organic solvent (dielectric constant at a temperature of 20 ° C. is 35 F / m or less and dipole moment is 2.5 D or more), triethylene glycol, 2-pyrrolidone, N-methylpyrrolidone, triethanolamine Etc.

  As the second water-soluble organic solvent (water-soluble organic solvent other than the first water-soluble organic solvent; the dielectric constant at a temperature of 20 ° C. exceeds 35 F / m and the dipole moment is less than 2.5 D), For example, the following are mentioned. Alcohols such as ethanol, isopropyl alcohol and n-butanol; Carboxylic acid amides such as N, N-dimethylformamide and N, N-dimethylacetamide. Ketones or ketoalcohols such as acetone, methyl ethyl ketone, 2-methyl-2-hydroxypentan-4-one; Cyclic ethers such as tetrahydrofuran and dioxane. Glycerin. Glycols such as ethylene glycol, diethylene glycol, 1,2- or 1,3-propylene glycol, 1,2- or 1,4-butylene glycol, polyethylene glycol, and thiodiglycol; Alkanediols such as 1,2,6-hexanetriol, 1,3-butanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol and the like. Acetylene glycol derivatives and the like. Glycol ethers such as diethylene glycol monomethyl (or ethyl) ether and triethylene glycol monoethyl (or butyl) ether.

  As described above, the content (% by mass) of the first water-soluble organic solvent in the ink needs to be 10.0% by mass or more based on the total mass of the ink. The content (% by mass) of the second water-soluble organic solvent in the ink needs to be 3.0% by mass or more and less than 10.0% by mass based on the total mass of the ink. Furthermore, the total (mass%) of the content of the first water-soluble organic solvent and the content of the second water-soluble organic solvent in the ink is 13.0 mass% or more based on the total mass of the ink. It is necessary and it is preferable that it is 50.0 mass% or less.

  The water is preferably deionized water (ion exchange water). The content (% by mass) of water in the ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink.

(Pigment)
The ink of the present invention includes a resin dispersion type pigment (resin dispersion type pigment) in which a pigment is dispersed using a dispersant, and a self dispersion type pigment (self-dispersion type pigment) in which a hydrophilic group is introduced on the surface of pigment particles. ) Can be used. In addition, pigments (resin-bonded self-dispersing pigments) in which organic groups containing polymers are chemically bonded to the surface of the pigment particles, microcapsule type that increases the dispersibility of the pigment and enables dispersion without using a dispersant Pigments can also be used. Of course, these pigments having different dispersion methods may be used in combination. The content (% by mass) of the pigment in the ink is 0.1% by mass to 15.0% by mass and more preferably 1.0% by mass to 10.0% by mass based on the total mass of the ink. preferable.

  For black ink, it is preferable to use carbon black such as furnace black, lamp black, acetylene black and channel black as a pigment. Specifically, for example, the following commercially available products can be used.

  Ray Van: 1170, 1190 ULTRA-II, 1200, 1250, 1255, 1500, 2000, 3500, 5000 ULTRA, 5250, 5750, 7000 (above Colombia). Black Pearls L, Legal: 330R, 400R, 660R, Mogul L, Monak: 700, 800, 880, 900, 1000, 1100, 1300, 1400, 2000, Vulcan XC-72R (above, manufactured by Cabot). Color Black: FW1, FW2, FW2V, FW18, FW200, S150, S160, S170, Printex: 35, U, V, 140U, 140V, Special Black: 6, 5, 4A, 4 (above, manufactured by Degussa). No. 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. 2300, MCF-88, MA600, MA7, MA8, MA100 (above, manufactured by Mitsubishi Chemical).

  Also, newly prepared carbon black can be used. Of course, the present invention is not limited to these, and any conventional carbon black can be used. Further, the material is not limited to carbon black, and magnetic fine particles such as magnetite and ferrite, titanium black, and the like may be used as a pigment.

  In the color ink, it is preferable to use an organic pigment as the pigment. Specifically, for example, the following can be used.

  Water-insoluble azo pigments such as Toluidine Red, Toluidine Maroon, Hansa Yellow, Benzidine Yellow, and Pyrazolone Red. Water-soluble azo pigments such as Ritolol Red, Helio Bordeaux, Pigment Scarlet, and Permanent Red 2B. Derivatives from vat dyes such as alizarin, indanthrone and thioindigo maroon. Phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green. Quinacridone pigments such as quinacridone red and quinacridone magenta. Perylene pigments such as perylene red and perylene scarlet. Isoindolinone pigments such as isoindolinone yellow and isoindolinone orange. Imidazolone pigments such as benzimidazolone yellow, benzimidazolone orange, and benzimidazolone red. Pilanthrone pigments such as pyranthrone red and pyranthrone orange. Indigo pigments, condensed azo pigments, thioindigo pigments, diketopyrrolopyrrole pigments. Flavanthrone yellow, acylamide yellow, quinophthalone yellow, nickel azo yellow, copper azomethine yellow, perinone orange, anthrone orange, dianthraquinonyl red, dioxazine violet, etc. Of course, the present invention is not limited to these.

  Moreover, when an organic pigment is shown by a color index (CI) number, the following can be used, for example. C. I. Pigment Yellow: 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 97, 109, 110, 117, 120, 125, 128, and the like. 137, 138, 147, 148, 150, 151, 153, 154, 166, 168, 180, 185, etc. C. I. Pigment Orange: 16, 36, 43, 51, 55, 59, 61, 71, etc. C. I. Pigment Red: 9, 48, 49, 52, 53, 57, 97, 122, 123, 149, 168, 175 and the like. 176, 177, 180, 192, 215, 216, 217, 220, 223, 224, 226, 227, 228, 238, 240, 254, 255, 272, etc. C. I. Pigment violet: 19, 23, 29, 30, 37, 40, 50, and the like. C. I. Pigment Blue: 15, 15: 1, 15: 3, 15: 4, 15: 6, 22, 60, 64, and the like. C. I. Pigment Green 7, 36, etc. C. I. Pigment Brown: 23, 25, 26, etc. Of course, the present invention is not limited to these.

(Dispersant)
As the dispersant for dispersing the pigment, it is preferable to use a water-soluble resin dispersant. As the water-soluble resin, a resin in which at least an alkyl acrylate is copolymerized as the monomer described above, which is essential for use in the ink of the present invention, may be used. Of course, a water-soluble resin generally used for ink for inkjet recording may be used.

(Other ingredients)
The ink of the present invention may contain a moisturizing solid content such as urea, urea derivatives, trimethylolpropane, trimethylolethane, etc. in addition to the above-described components. The content (% by mass) of the moisturizing solid content in the ink is 0.1% by mass or more and 20.0% by mass or less, and further 3.0% by mass or more and 10.0% by mass or less based on the total mass of the ink. It is preferable that

  Furthermore, it contains various additives such as pH adjusters, rust preventives, antiseptics, antifungal agents, antioxidants, anti-reduction agents, etc., in order to obtain inks having desired physical properties as required. Also good.

<Inkjet recording method, ink cartridge, recording unit, and inkjet recording apparatus>
An example of the ink jet recording apparatus will be described below. First, FIG. 1 and FIG. 2 show an example of the configuration of a recording head that is a main part of an ink jet recording apparatus using thermal energy. FIG. 1 is a cross-sectional view of the recording head 13 along the ink flow path, and FIG. 2 is a cross-sectional view taken along the line AB of FIG. The recording head 13 includes a member having an ink flow path (nozzle) 14 and a heating element substrate 15. The heating element substrate 15 includes a protective layer 16, electrodes 17-1 and 17-2, a heating resistor layer 18, a heat storage layer 19, and a substrate 20.

  When pulsed electric signals are applied to the electrodes 17-1 and 17-2 of the recording head 13, the region indicated by n of the heating element substrate 15 rapidly generates heat, and bubbles are generated in the ink 21 in contact with the surface. Occurs. Then, the meniscus 23 protrudes due to the pressure of the bubbles, and the ink 21 is ejected as an ink droplet 24 from the ejection port 22 of the nozzle 14 toward the recording medium 25.

  FIG. 3 is an external view of an example of a multi-head in which a large number of recording heads shown in FIG. 1 are arranged. The multihead includes a glass plate 27 having multinozzles 26 and a recording head 28 similar to that shown in FIG.

  FIG. 4 is a perspective view showing an example of an ink jet recording apparatus incorporating a recording head. The blade 61 is a wiping member, one end of which is held by a blade holding member, and forms a cantilever. The blade 61 is disposed at a position adjacent to the recording area by the recording head 65 and is held in a form protruding in the moving path of the recording head 65.

  Reference numeral 62 denotes a cap on the ejection port surface of the recording head 65, which is disposed at a home position adjacent to the blade 61, moves in a direction perpendicular to the moving direction of the recording head 65, abuts on the ink ejection port surface, and performs capping. It has a configuration to perform An ink absorber 63 provided adjacent to the blade 61 is held in a form protruding in the moving path of the recording head 65, similarly to the blade 61. The ejection recovery unit 64 includes a blade 61, a cap 62, and an ink absorber 63. The blade 61 and the ink absorber 63 remove moisture, dust, and the like from the discharge port surface.

  Reference numeral 65 denotes a recording head which has discharge energy generating means and performs recording by discharging ink onto a recording medium facing the discharge port surface on which the discharge port is arranged. Reference numeral 66 denotes a movement of the recording head 65 by mounting the recording head 65. It is a carriage for performing. The carriage 66 is slidably engaged with the guide shaft 67, and a part of the carriage 66 is connected to a belt 69 (not shown) driven by a motor 68. As a result, the carriage 66 can move along the guide shaft 67, and the recording area by the recording head 65 and the area adjacent thereto can be moved.

  Reference numeral 51 denotes a paper feeding unit for inserting a recording medium, and 52 denotes a paper feed roller driven by a motor (not shown). With these configurations, the recording medium is fed to a position facing the ejection port surface of the recording head 65 and discharged to a paper discharge unit having a paper discharge roller 53 as recording progresses. When recording by the recording head 65 is completed and the recording head returns to the home position, the cap 62 of the ejection recovery unit 64 is retracted from the moving path of the recording head 65, but the blade 61 protrudes into the moving path. Yes. In this way, the ejection port of the recording head 65 is wiped.

  When the cap 62 is in contact with the ejection port surface of the recording head 65 to perform capping, the cap 62 moves so as to protrude into the moving path of the recording head. When the recording head 65 moves from the home position to the recording start position, the cap 62 and the blade 61 are in the same position as in the wiping described above. As a result, the ejection port surface of the recording head 65 is wiped even during this movement. The recording head moves to the home position adjacent to the recording area at a predetermined interval not only when the recording is completed or when the ejection is recovered, but also while the recording head moves the recording area for recording. However, wiping is also performed with this movement.

  FIG. 5 is a diagram illustrating an example of an ink cartridge that contains ink supplied to the recording head via an ink supply member, for example, a tube. Here, reference numeral 40 denotes an ink container, for example, an ink bag, in which supply ink is stored, and a rubber plug 42 is provided at the tip thereof. By inserting a needle (not shown) into the stopper 42, the ink in the ink bag 40 can be supplied to the recording head. An ink absorber 44 receives waste ink.

  The recording head and the ink cartridge are not limited to separate units, and as shown in FIG. 6, a unit in which the recording head and the ink cartridge are integrated can be suitably used. In FIG. 6, reference numeral 70 denotes a recording unit, in which an ink storage unit that stores ink, for example, an ink absorber is stored, and a recording head unit in which the ink in the ink absorber has a plurality of ejection openings. 71 is ejected as ink droplets. Alternatively, a structure in which the ink container is an ink bag with a spring or the like inside without using an ink absorber may be used. Reference numeral 72 denotes an atmosphere communication port for communicating the inside of the cartridge with the atmosphere. The recording unit 70 is used in place of the recording head 65 shown in FIG. 4 and is detachable from the carriage 66.

  Next, an ink jet recording apparatus using mechanical energy will be described. A nozzle forming substrate having a plurality of nozzles, a pressure generating element composed of a piezoelectric material and a conductive material, and ink that fills the surroundings of the pressure generating element are provided. The pressure generating element is displaced by an applied voltage, and ink droplets are ejected from ejection ports. It has a feature of having a recording head. FIG. 7 is a schematic diagram showing an example of the configuration of the recording head. The recording head includes an ink flow path 80 communicating with an ink chamber, an orifice plate 81, a vibration plate 82 that applies pressure to ink, a piezoelectric element 83 that is bonded to the vibration plate 82 and is displaced by an electric signal, the orifice plate 81, and the vibration plate. It is comprised with the board | substrate 84 which supports and fixes 82 etc. The distortion stress generated by applying a pulsed voltage to the piezoelectric element 83 deforms the vibration plate bonded to the piezoelectric element 83 and pressurizes the ink in the ink flow path 80, thereby causing the discharge port of the orifice plate 81 to discharge. Ink droplets are ejected from 85. Such a recording head can be used by being incorporated in an ink jet recording apparatus similar to that shown in FIG.

  Hereinafter, the present invention will be described in more detail with reference to Examples, Comparative Examples, and Reference Examples. The present invention is not limited in any way by the following examples as long as the gist thereof is not exceeded. “Part” or “%” is based on mass unless otherwise specified.

<Preparation of pigment dispersion>
1,500 rpm using a sand mill (manufactured by Kanada Rika Kogyo Co., Ltd.) filled with 10 parts of carbon black, 10 parts of each resin shown in Table 1 below, and 80 parts of water with a filling rate of 0.6 mm zirconia beads at 70%. For 5 hours. Thereafter, the mixture is centrifuged at 5,000 rpm for 10 minutes to remove the aggregated components, and pigment dispersions 1 to 12 having a pigment content of 10.0% by mass and a resin content of 10.0% by mass. Respectively. Carbon black having a specific surface area of 220 m ² / g and DBP oil absorption of 130 mL / 100 g was used. Each resin was previously added with water and potassium hydroxide equivalent to the acid value and stirred at 80 ° C. to obtain an aqueous solution. In each of the pigment dispersions 1 to 12 thus obtained, the pigment was stably dispersed, and the average dispersed particle size was 98 nm.

<Preparation of ink>
After mixing each component shown in the upper part of the following Table 2 and Table 3 and stirring sufficiently, ink 1-22 was prepared by performing pressure filtration with a polypropylene filter (made by Pole) having a pore size of 1.2 μm. . Tables 2 and 3 show the values of the pigment and resin contents in each ink. Table 4 summarizes the characteristics of each ink.

<Evaluation>
(Alkali resistance)
Each of the inks obtained above was mounted on an ink jet recording apparatus (PIXUS iP3100; manufactured by Canon) using thermal energy. Then, an image having a recording duty of 100% was formed on a recording medium (PR-101; manufactured by Canon) (referred to as an “before storage” image). Each ink obtained above is stored in an oven at a temperature of 60 ° C. for one month, and after returning to room temperature, an image similar to the above is formed using the same ink jet recording apparatus and recording medium as described above. (The image is “after saving”). About each image before and after storage obtained in this way, the alkali resistance of the image was evaluated using an artificial sweat solution defined in JIS L0848. Specifically, 1 mL of artificial sweat was dripped onto the image, and the artificial sweat dripped 10 seconds later was wiped off with Sylbon paper. Subsequent images were visually confirmed to evaluate alkali resistance. The evaluation criteria for alkali resistance are as follows. The results are shown in Table 5.
AA: Ink did not flow out of the image.
A: Ink slightly flowed out of the image, but was hardly noticeable.
B: Ink flowed out of the image, and the recording medium was partially exposed.
C: Ink started to flow from the image and the image could not be confirmed.

(Storage stability)
For each of the inks obtained above, the particle size of the pigment particles in the ink was measured (the particle size was “before storage”). The ink obtained above is put in a container made of polytetrafluoroethylene and sealed, stored in an oven at a temperature of 60 ° C. for one month, returned to room temperature, and then pigment particles in the ink. The particle size was measured (the particle size “after storage”). From the respective particle sizes before and after storage thus obtained, the rate of change in particle size is calculated based on the following formula: rate of change in particle size (times) = particle size after storage / particle size before storage. The storage stability of the ink was evaluated from the obtained results. The evaluation results of storage stability are as follows. The results are shown in Table 5. The particle size of the pigment was measured with a particle size measuring device (ELS8000; manufactured by Otsuka Electronics Co., Ltd.).
A: The change rate of the particle size is 1.0 times or more and less than 1.3 times.
B: The change rate of the particle diameter is 1.3 times or more and less than 1.5 times.
C: The change rate of the particle size is 1.5 times or more.

(Abrasion resistance)
Each of the inks obtained above was mounted on an ink jet recording apparatus (PIXUS iP3100; manufactured by Canon) using thermal energy. Then, an image having a recording duty of 100% was formed on a recording medium (PR-101; manufactured by Canon). After this image was left at room temperature for 1 day, the image was scratched by applying pressure to the nail so as not to damage the non-recorded portion of the recording medium, and the image was visually confirmed to evaluate the scratch resistance. . The evaluation criteria for scratch resistance are as follows. The results are shown in Table 5.
AA: The scratched recording medium cannot be seen.
A: The scratched recording medium is slightly visible.
B: About half of the scratched recording medium is exposed.
C: The scratched recording medium is exposed.

(Adhesive recovery)
Each ink obtained above was filled in an ink cartridge of an ink jet recording apparatus (PIXUS iP3100; manufactured by Canon) using thermal energy, and this ink cartridge was mounted on a recording head. Thereafter, the recording head was exposed to the atmosphere for 2 weeks in an environment of a temperature of 35 ° C. and a humidity of 10% by mass. Thereafter, the recording head was mounted on the ink jet recording apparatus, and the sticking recoverability was evaluated by the number of suction recovery operations performed until ink ejection became possible. The results are shown in Table 5.
A: The suction recovery operation is 3 times or less, and all the discharge ports can be discharged.
B: The suction recovery operation is performed 4 or 5 times, and all the discharge ports can be discharged.
C: There are discharge ports that cannot be discharged even if the suction recovery operation is performed six times or more.

(Uniformity)
Each of the inks obtained above was mounted on an ink jet recording apparatus (PIXUS iP3100; manufactured by Canon) using thermal energy. Thereafter, the ink jet recording apparatus was left in a constant temperature and humidity chamber having a temperature of 15 ° C. and a humidity of 10% for 1 hour. Further, after ejecting ink droplets from a certain ejection port, the ejection port was not used for 1 minute, and then the ink droplets were ejected again from the same ejection port as described above to evaluate the uniformity. The evaluation criteria for the uniformity are as follows. The results are shown in Table 5.
A: Recording is possible normally.
B: Although there is a slight disturbance in recording, there is no problem in actual use.
C: There is ejection failure or recording disorder.

FIG. 2 is a longitudinal sectional view of a recording head. It is a cross-sectional view of the recording head. FIG. 2 is a perspective view of a recording head in which the recording head shown in FIG. It is a perspective view which shows an example of an inkjet recording device. It is a longitudinal cross-sectional view of an ink cartridge. It is a perspective view which shows an example of a recording unit. FIG. 3 is a schematic diagram illustrating an example of a configuration of a recording head.

Explanation of symbols

DESCRIPTION OF SYMBOLS 13 Recording head 14 Nozzle 15 Heat generating element board | substrate 16 Protective layer 17-1, 17-2 Electrode 18 Heating resistor layer 19 Heat storage layer 20 Substrate 21 Ink 22 Ejection port 23 Meniscus 24 Ink droplet 25 Recording medium 26 Multi nozzle 27 Glass plate 28 Recording head 40 Ink bag 42 Plug 44 Ink absorber 45 Ink cartridge 51 Paper feed unit 52 Paper feed roller 53 Paper discharge roller 61 Blade 62 Cap 63 Ink absorber 64 Discharge recovery unit 65 Recording head 66 Carriage 67 Guide shaft 68 Motor 69 Belt 70 Recording Unit 71 Recording Head 72 Air Communication Port 80 Ink Flow Channel 81 Orifice Plate 82 Vibrating Plate 83 Piezoelectric Element 84 Substrate 85 Discharge Port

Claims (9)

A water-based ink for ink-jet recording comprising a pigment, a resin copolymerized with at least an alkyl acrylate as a monomer, and a water-soluble organic solvent,
The water-soluble organic solvent includes a first water-soluble organic solvent and a second water-soluble organic solvent,
The first water-soluble organic solvent has a dielectric constant of 35 F / m or less at a temperature of 20 ° C. and a dipole moment of 2.5 D or more, and contains the first water-soluble organic solvent in the ink. The amount (% by mass) is 10.0% by mass or more based on the total mass of the ink,
The second water-soluble organic solvent is a water-soluble organic solvent other than the first water-soluble organic solvent, and the content (% by mass) of the second water-soluble organic solvent in the ink is the total mass of the ink. The water-based ink is characterized by being 3.0% by mass or more and less than 10.0% by mass based on the above.   The water-based ink according to claim 1, wherein the alkyl acrylate is butyl acrylate.   The water-based ink according to claim 2, wherein the content (% by mass) of butyl acrylate constituting the resin is less than 2.0% by mass based on the total mass of the ink.   The resin is obtained by further copolymerization of a monomer having an SP value smaller than that of butyl acrylate, and the copolymerization ratio (mass ratio) of the monomer having an SP value smaller than that of the butyl acrylate is that of the butyl acrylate. The water-based ink according to claim 2 or 3, which has a copolymerization ratio (mass ratio) or more.   5. The water-based ink according to claim 1, wherein the acid value of the resin is 90 mgKOH / g or more and 150 mgKOH / g or less. An ink jet recording method for recording on a recording medium by discharging ink by an ink jet method,
An ink jet recording method using the water-based ink according to claim 1 as the ink.   An ink cartridge comprising an ink containing part for containing ink, wherein the ink contained in the ink containing part is the water-based ink according to any one of claims 1 to 5. cartridge.   6. A water-based recording medium according to any one of claims 1 to 5, wherein the recording unit includes an ink storage unit that stores ink and a recording head that discharges ink, and the ink stored in the ink storage unit. A recording unit which is ink.   6. An ink jet recording apparatus comprising an ink containing portion that contains ink and a recording head that discharges ink, wherein the ink contained in the ink containing portion is according to claim 1. An ink jet recording apparatus, which is a water-based ink.

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