JP4110184B2 - Aqueous ink, ink jet recording method, ink cartridge, recording unit, and ink jet recording apparatus - Google Patents

Description

  The present invention relates to an aqueous ink containing a resin and a pigment.

It is known that a pigment is used as an ink coloring material in order to improve the fastness such as light resistance, gas resistance and water resistance of an image obtained by the ink jet recording method. Further, in order to improve the scratch resistance and marker resistance of an image, a resin-dispersed pigment in which a pigment is dispersed using a resin as a dispersant, and a self-dispersed pigment in which a hydrophilic group is bonded to the surface of the pigment; It is known to use an ink with a water-soluble resin (see Patent Document 1).
JP-A-5-179183

  The present inventors have developed a resin-dispersed pigment for the purpose of improving light fastness, gas resistance, water fastness and other fastness of images obtained by an ink jet recording method, as well as scratch resistance and marker resistance. Detailed investigations were made on the inks contained. As a result, it has been found that depending on the type and characteristics of the resin functioning as the dispersant, the ink ejection characteristics are greatly affected.

  Accordingly, the present inventors have studied in more detail about the resin used as the dispersant in order to improve the image fastness, scratch resistance, marker resistance, and ink ejection characteristics. . As a result, it was found that an ink in which a pigment is dispersed using a hydroxyl group-containing resin can solve the above-described problems together.

  However, if an ink cartridge filled with ink in which a pigment is dispersed using a hydroxyl group-containing resin is mounted on an ink jet recording apparatus and then left for a long time without discharging ink, the following new technical problems will occur. I understood. That is, it has been found that the ejection characteristics deteriorate when the resin in the ink oozes out from the ejection port of the recording head, adheres to the vicinity of the ejection port, and further adheres.

  Therefore, the object of the present invention is to use the following aqueous ink containing a resin-dispersed pigment in which a pigment is dispersed using a hydroxyl group-containing resin as a dispersant: An object of the present invention is to provide a water-based ink capable of solving the problems. That is, it is an object to provide a water-based ink that has excellent scratch resistance and marker resistance of an image, and further suppresses a resin bleeding phenomenon even when stored for a long period of time, and can suppress deterioration of ejection characteristics. .

  Another object of the present invention is to provide an ink cartridge, a recording unit, and an ink jet recording method 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 resin having a hydroxyl group, a pigment, and an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent, wherein the water-soluble organic solvent has a molecular weight. A polyhydric alcohol having a value of the number of hydroxyl groups / number of carbon atoms of 0.40 or less, wherein the resin having a hydroxyl group is a copolymer of a segment having a hydroxyl group and a segment having no hydroxyl group Ri resin der, the pigment is characterized that you have been dispersed in the aqueous medium by the polyvinyl alcohol resin.
An aqueous ink according to another embodiment of the present invention is an aqueous ink containing a resin having a hydroxyl group, a pigment, and an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent, the water-soluble organic The solvent is at least one selected from the group consisting of 1,2-hexanediol, 1,6-hexanediol, and 1,5-pentanediol, and the hydroxyl group-containing resin has hydroxyl groups and hydroxyl groups. A segment having no segment is a copolymerized polyvinyl alcohol resin, and the pigment is dispersed in the aqueous medium by the polyvinyl alcohol resin.

  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, wherein the ink is a water-based ink having the above-described configuration. To do.

  An ink cartridge according to another embodiment of the present invention is an ink cartridge provided with an ink storage portion for storing ink, wherein the ink is a water-based ink having the above-described configuration.

  According to another embodiment of the present invention, there is provided a recording unit comprising an ink storage portion for storing ink and a recording head for discharging ink, wherein the ink is a water-based ink having the above-described configuration. It is characterized by being.

  An ink jet recording apparatus according to another embodiment of the present invention is an ink jet recording apparatus comprising an ink containing portion for containing ink and a recording head for ejecting ink, wherein the ink is water-based as described above. It is characterized by being ink.

  According to the present invention, when an aqueous ink containing a resin-dispersed pigment in which a pigment is dispersed using a hydroxyl group-containing resin as a dispersant, an aqueous ink that can solve the following problems can be provided. it can. That is, it is possible to provide a water-based ink that is excellent in image scratch resistance and marker resistance, and further suppresses a resin oozing phenomenon even when stored for a long period of time, and can suppress deterioration in ejection characteristics. .

  According to another embodiment of the present invention, an ink cartridge, a recording unit, and an ink jet recording method using the water-based ink can be provided.

  Hereinafter, the present invention will be described in more detail with reference to the best mode for carrying out the invention.

  The inventors of the present invention have conducted detailed studies on inks containing resin-dispersed pigments for the purpose of improving the scratch resistance and marker resistance of images obtained by the ink jet recording method. Furthermore, considering that the discharge characteristics can be improved by increasing the hydrophilicity of the pigment, investigations have been made on the use of a resin having a hydroxyl group as a dispersant for the resin-dispersed pigment. However, if an ink cartridge filled with an ink containing a resin-dispersed pigment in which a pigment having a hydroxyl group resin as a dispersant is dispersed is mounted on an ink jet recording apparatus and left for a long period of time without discharging ink, the following problems occur. It was found to occur. That is, it was confirmed that a phenomenon in which the resin in the ink exudes from the ejection port of the recording head occurred. Therefore, the present inventors examined the cause of the phenomenon described above. As a result, it has been concluded that one of the causes is that the phenomenon described below occurs in the nozzles of the recording head. Hereinafter, the mechanism of the resin oozing out will be described in detail with reference to FIG.

  FIG. 1 is a schematic diagram showing how the state of an ink containing a resin-dispersed pigment in which a pigment is dispersed with a hydroxyl group-containing resin changes with time in a nozzle.

  FIG. 1A shows a state after ink is ejected from the ejection port 1 by the thermal energy applied by the heater 2. As shown in FIG. 1A, in the nozzle, water molecules 4, a pigment 5 on which a resin is adsorbed, a water-soluble organic solvent 6, and a resin having a hydroxyl group not adsorbed on the pigment (free resin 7 having a hydroxyl group). ) Exist in a uniformly distributed state. In the present invention, the resin not adsorbed on the pigment is referred to as “free resin”, and the resin having a hydroxyl group not adsorbed on the pigment is referred to as “free resin having a hydroxyl group”. .

  FIG. 1B shows a state after being left for a certain period in the state of FIG. 1A. As shown in FIG. 1B, in the nozzle, first, water evaporates (evaporated water molecules 8) from the discharge port 1 as time elapses. Further, as time elapses, the water molecules 4 inside the nozzle move in the direction of the discharge port 1. At this time, the free resin 7 having a hydroxyl group that forms a hydrogen bond with the water molecule 4 also moves in the direction of the discharge port 1 together with the water molecule 4.

  FIG. 1C shows a state after further elapse of time. As shown in FIG. 1C, the free resin 7 having a hydroxyl group that forms a hydrogen bond with the water molecule 4 oozes out from the discharge port 1 and adheres to the orifice surface 3 around the discharge port 1. The free resin 7 having a hydroxyl group immediately after adhering to the orifice surface 3 is kept dissolved by the bonded water molecules 4. However, since the water molecules 4 bonded with time evaporate, the free resin 7 having a hydroxyl group loses solubility and adheres to the periphery of the discharge port 1 as a fixed substance.

  Due to the mechanism described above, a phenomenon in which the resin in the ink oozes out from the ejection port of the recording head occurs, and as a result, the presence of a fixed substance is considered to deteriorate the ejection characteristics.

  It is unknown whether all free resins having a hydroxyl group present in the ink according to the present invention form hydrogen bonds with water molecules. However, since the resin having a hydroxyl group exists more stably in the ink, it is assumed that many of them exist in a state where hydrogen bonds are formed with water molecules.

  As described above, the resin that exudes is a resin having a hydroxyl group that is not adsorbed to the pigment, that is, a free resin having a hydroxyl group. That is, it is considered that the deterioration of the ejection characteristics can be suppressed by reducing the content of the free resin having a hydroxyl group in the ink.

  Therefore, it is considered that the above phenomenon can be suppressed by performing the following measures within a range where the ejection characteristics do not deteriorate and the scratch resistance and marker resistance are sufficiently obtained. . That is, the free resin having a hydroxyl group in the ink is reduced as much as possible, or the hydrophobicity of the monomer constituting the dispersant is increased, thereby increasing the adsorption power between the pigment and the dispersant, and the free resin having a hydroxyl group. It is conceivable to avoid generating as much as possible. However, it is very difficult to actually perform the method as described above. Therefore, the present inventors have studied a means for solving the above-described phenomenon by devising an ink formulation.

  As a result, it was found that the phenomenon that the free resin having a hydroxyl group oozes out from the discharge port can be suppressed by adding polyhydric alcohol as the water-soluble organic solvent to the ink. Although it is not clear why the phenomenon that the free resin having a hydroxyl group oozes from the discharge port can be suppressed, the present inventors presume as follows.

  FIG. 2 is a schematic diagram showing the relationship between a free resin having a hydroxyl group, a water molecule, and a polyhydric alcohol in an ink containing a resin-dispersed pigment in which a pigment is dispersed by a resin having a hydroxyl group.

  FIG. 2A shows a state where the free resin 7 having a hydroxyl group forms a hydrogen bond with the water molecule 4 when the ink does not contain a polyhydric alcohol. The free resin 7 having a hydroxyl group includes a segment 9 having a hydroxyl group and a segment 10 having no hydroxyl group. In the present invention, the segment is a repeating unit constituting the resin. FIG. 2B shows the state of the free resin 7 having a hydroxyl group and the polyhydric alcohol 11 when the ink contains a polyhydric alcohol.

  As can be seen from FIG. 2B, the free resin 7 having a hydroxyl group that is relatively hydrophobic compared to the water molecule 4 is located in the vicinity of the polyhydric alcohol 11 that is relatively hydrophobic compared to the water molecule 4. Tend to exist. As a result, the free resin 7 having a hydroxyl group selectively forms hydrogen bonds with the polyhydric alcohol 11 instead of the water molecules 4. The free resin 7 having a hydroxyl group that does not form a hydrogen bond with the water molecule 4 does not move to the discharge port as the water molecule evaporates as shown by B and C in FIG. As a result, it is considered that the phenomenon that the free resin having a hydroxyl group exudes from the discharge port can be suppressed.

  Furthermore, the present inventors examined various polyhydric alcohols based on the above-described mechanism. As a result, it is necessary to reduce the hydrophilicity of the polyhydric alcohol to some extent in order to develop an interaction by efficiently forming a hydrogen bond between the polyhydric alcohol and the free resin having a hydroxyl group. all right. When the polyhydric alcohol has high hydrophilicity, the polyhydric alcohol can be completely dissolved in the aqueous medium, so that the ratio of forming a hydrogen bond with the free resin having a hydroxyl group tends to decrease. On the other hand, when the hydrophilicity of the polyhydric alcohol is low, the proportion existing in the vicinity of the free resin having a hydroxyl group that is relatively hydrophobic tends to increase more than the proportion in which the polyhydric alcohol is dissolved in the aqueous medium. is there. As a result, it is considered that hydrogen bonds are easily formed between the polyhydric alcohol and the free resin having a hydroxyl group.

  Therefore, in the present invention, the value of the number of hydroxyl groups in the molecule / number of carbon atoms (hereinafter referred to as OH / C value) is used as an index representing the degree of hydrophilicity of the polyhydric alcohol. A high OH / C value indicates that the number of hydroxyl groups in the molecule is large or the number of carbon atoms is small, and that the polyhydric alcohol is highly hydrophilic. On the other hand, a low OH / C value indicates that the number of hydroxyl groups in the molecule is small or the number of carbon atoms is large, and that the polyhydric alcohol has low hydrophilicity.

  The present inventors determined OH / C values for various polyhydric alcohols. Furthermore, using a free resin having a hydroxyl group and an ink containing only the polyhydric alcohol as a water-soluble organic solvent, how much difference is in the effect of suppressing the phenomenon that the free resin having a hydroxyl group exudes from a discharge port. I checked if there was any. As a result, it was confirmed that when the polyhydric alcohol had an OH / C value of 0.50 or less, an effect of suppressing the bleeding phenomenon was obtained. From the above, it was concluded that the polyhydric alcohol contained in the ink needs to have a value of the number of hydroxyl groups in the molecule / the number of carbon atoms, that is, an OH / C value of 0.50 or less. It was. In order to more effectively suppress the bleeding phenomenon, the OH / C value of the polyhydric alcohol is more preferably 0.40 or less, and further preferably 0.35 or less. Moreover, it is preferable that OH / C value is 0.10 or more.

<Ink>
Below, each component which comprises the ink concerning this invention is demonstrated.

(Polyhydric alcohol whose number of hydroxyl groups in the molecule / number of carbon atoms is 0.50 or less)
The ink according to the present invention must contain a polyhydric alcohol having a number of hydroxyl groups in the molecule / number of carbon atoms (OH / C value) of 0.50 or less. In the present invention, the polyhydric alcohol refers to a compound in which a saturated carbon atom has a plurality of hydroxyl groups.

Examples of the polyhydric alcohol having an OH / C value of 0.50 or less include the following.
1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol and the like. 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,3-pentanediol, 2,4-pentanediol and the like. 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, 1,5-hexanediol, 1,6-hexanediol, 2,3-hexanediol, 2,4-hexanediol, 2 , 5-hexanediol, 3,4-hexanediol and the like. 1,2,3-hexanetriol, 1,2,4-hexanetriol, 1,2,5-hexanetriol, 1,2,6-hexanetriol and the like. 1,3,4-hexanetriol, 1,3,5-hexanetriol, 1,3,6-hexanetriol and the like. 2,3,4-hexanetriol, 2,3,5-hexanetriol, 3,4,5-hexanetriol and the like. 1,2-heptanediol, 1,3-heptanediol, 1,4-heptanediol, 1,5-heptanediol, 1,6-heptanediol, 1,7-heptanediol and the like. 1,2-octanediol, 1,3-octanediol, 1,4-octanediol, 1,5-octanediol, 1,6-octanediol, 1,7-octanediol, 1,8-octanediol and the like.

  Among them, it is particularly preferable to use a polyhydric alcohol having an OH / C value of 0.50 or less and having a boiling point of 80 ° C. or higher at normal pressure. This is to prevent the polyhydric alcohol from evaporating even in an environment where water molecules evaporate from the discharge port.

  Moreover, in this invention, it is preferable to use what is a poor solvent with respect to the free resin which has a hydroxyl group among the polyhydric alcohol whose boiling point in a normal pressure is 80 degreeC or more. This is because the ink containing a poor solvent causes the free resin having a hydroxyl group to move from the discharge port to the inside of the nozzle (in the direction of the heater 2 in FIG. 1), that is, to cause a backward phenomenon. For this reason, even when the content of the polyhydric alcohol contained in the ink is small, it is possible to effectively suppress the resin bleeding phenomenon. The effect of the above-described receding phenomenon can be obtained only when the free resin having a hydroxyl group hydrates with the polyhydric alcohol when the ink contains the polyhydric alcohol. In other words, when the ink does not contain a polyhydric alcohol, or when the free resin having a hydroxyl group and the polyhydric alcohol cannot be sufficiently hydrated because the polyhydric alcohol content is small, the ink contains a poor solvent. Even so, the effect of the backward phenomenon may not be obtained. In addition, when using a water-soluble organic solvent that is a good solvent for a free resin having a hydroxyl group, or a water-soluble organic solvent that is a poor solvent for a free resin having a hydroxyl group, In order to obtain the effect more effectively, the following configuration is preferable. That is, the content of the water-soluble organic solvent that is a poor solvent for the free resin having a hydroxyl group is made larger than the content of the water-soluble organic solvent that is a good solvent for the free resin having a hydroxyl group in the ink. Is preferred.

  In the present invention, a water-soluble organic solvent having low solubility in a resin is defined as a poor solvent, and a water-soluble organic solvent having high solubility in a resin is defined as a good solvent. Specifically, a poor solvent and a good solvent can be determined by the following method.

  0.5 g of a 10% by mass aqueous solution of the resin to be determined is dropped into an aqueous solution diluted with water so that the water-soluble organic solvent becomes 50% by mass, and left for 4 days in a sealed state at room temperature. Then, compared to the initial state, when the liquid becomes cloudy or when the presence of oily substances or precipitates is confirmed, the water-soluble organic solvent is a poor solvent, and the water-soluble organic solvent that does not particularly change the liquid Is a good solvent.

  Although the poor solvent and the good solvent that can be used in the present invention vary depending on the type of resin, the following water-soluble organic solvents are exemplified. Examples of the poor solvent include alkanediols such as 1,3-propanediol, 1,5-pentanediol, 1,2-hexanediol, and 1,6-hexanediol, polyethylene glycol having an average molecular weight of 600 or more, 2-pyrrolidone, N -Methyl-2-pyrrolidone and the like. Examples of the good solvent include glycerin, diethylene glycol, 1,2,6-hexanetriol, and the like.

  The polyhydric alcohol having a boiling point of 80 ° C. or higher at normal pressure as described above may be used alone or in combination of two or more. Moreover, you may use together with another water-soluble organic solvent in the range by which the effect by adding these is acquired and the objective effect of this invention is not impaired.

  In addition, the content of the polyhydric alcohol having a boiling point of 80 ° C. or higher at normal pressure is not particularly limited as long as the phenomenon that the free resin having a hydroxyl group oozes out from the discharge port can be suppressed. Since the hydroxyl group-containing resin used in the present invention is highly hydrophilic, it is easy to desorb from the hydrophobic pigment surface. For this reason, the lower limit of the total number of hydroxyl groups of the polyhydric alcohol having an OH / C value of 0.50 or less in the ink is 100 times or more, further 300 times the total number of hydroxyl groups of the free resin having a hydroxyl group. It is preferable to adjust the content so that it is as described above. Further, the upper limit is preferably 440 times or less, and more preferably 330 times or less, since the effect does not change when the upper limit is made larger. Furthermore, the content of the polyhydric alcohol is preferably 8 to 22 times the content of the resin having a hydroxyl group.

(Total number of hydroxyl groups in the free resin having hydroxyl groups in the ink)
In the present invention, the total number of hydroxyl groups of the free resin having hydroxyl groups in the ink can be measured by the following method. Of course, the present invention is not limited to the following method, and values measured using other methods may be used.

The ink is centrifuged under conditions of 400,000 G for 16 hours, and 95% by mass of the supernatant liquid is collected. Thereafter, the obtained liquid is acidified to separate the free resin. Furthermore, the component analysis of the monomer which comprises resin is performed about the obtained free resin using ¹³ C-NMR, gas chromatography, etc., and the total number of the hydroxyl groups of the free resin which has a hydroxyl group in an ink is calculated.

(Resin having a hydroxyl group)
The ink according to the present invention must contain a hydroxyl group-containing resin. Examples of the resin having a hydroxyl group include a resin obtained by copolymerizing a monomer having a hydroxyl group in a part of the acrylic ester monomer among acrylic ester polymers obtained by copolymerizing an acrylic ester monomer.

  Examples of the monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, and polypropylene glycol mono (meth) acrylate.

  As the monomer copolymerized with the monomer having a hydroxyl group, a general-purpose monomer can be used. For example, examples of the acrylic ester monomers include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, and the like. In addition to the acrylic ester monomer, a monomer having a double bond copolymerizable with a monomer having a hydroxyl group can also be used. For example, styrene monomer, vinyl acetate monomer, 1,3-butadiene and the like can be mentioned.

  As a resin having a hydroxyl group, a resin obtained by saponifying a vinyl acetate-acrylic ester polymer obtained by copolymerizing an acrylic ester monomer and a vinyl acetate monomer with a strong base such as sodium hydroxide, that is, a polyvinyl alcohol resin is used. Is particularly preferred.

  If the resin has hydroxyl groups, the original purpose of adding the resin to the ink, the scratch resistance and marker resistance of the image, as well as the ejection characteristics can be improved. Chain, random copolymerization, block copolymerization, etc. are not particularly specified. However, in order to suppress the phenomenon of resin desorption from the pigment surface as much as possible, the molecular weight of the segment portion having a hydroxyl group is preferably 20,000 or less.

  Further, when the resin having a hydroxyl group is a copolymer of a segment having a hydroxyl group and a segment having no hydroxyl group, it is preferably a block copolymer, and further, a monomer having a hydroxyl group is present at the end of the resin. It is preferable that it is a block copolymer. This is because when the hydrophobic portion of the resin having a hydroxyl group adsorbed on the pigment surface is concentrated at the terminal, the adsorption force of the resin having a hydroxyl group on the pigment surface is increased. When the ink according to the present invention is applied to an ink jet recording method in which an ink is ejected by applying thermal energy to the ink and an image is formed on a recording medium, the higher the hydrophilicity of the resin, the more stable the ejection characteristics. Tend to be. Therefore, it is particularly preferable to use a polyvinyl alcohol resin.

  In the ink according to the present invention, the content (mass%) of the resin having a hydroxyl group in the ink is supposed to be excellent in the scratch resistance and marker resistance of the image, which is the original purpose, and also in the ejection characteristics. If possible, there is no particular limitation. However, in the present invention, it is preferable to reduce the content of the hydroxyl group-containing resin as much as possible in order to reduce the content of the free resin having a hydroxyl group that causes the bleeding phenomenon. Accordingly, when the content (mass%) of the pigment in the ink based on the total ink mass is 100, the content (mass%) of the resin having a hydroxyl group based on the total ink mass is 5.0. % To 100.0%, more preferably 7.0% to less than 20.0%. The content (% by mass) of the resin having a hydroxyl group is preferably less than 1.0% by mass, and more preferably less than 0.8% by mass, based on the total mass of the ink.

  The effect of the poor solvent described above is not a phenomenon peculiar to an ink containing a resin-dispersed pigment, but an ink containing a self-dispersing pigment and a resin having a hydroxyl group, an ink containing a dye and a resin having a hydroxyl group. It has been confirmed that it is also effective against However, as described above, the resin having a hydroxyl group is very hydrophilic. Therefore, in order to make the scratch resistance and marker resistance, which are the original purposes of the present invention, excellent, the resin adsorbs to the pigment, not just an ink in which a resin having a hydroxyl group is simply added to the ink. It is preferable that the ink use a resin dispersed pigment as a coloring material.

  In the present invention, the content of the free resin having a hydroxyl group in the ink varies somewhat depending on the structure of the resin and the pigment used together with the resin, but in this case, it can be appropriately adjusted by ultrafiltration or the like. it can.

(Content of free resin having hydroxyl group in ink)
In the present invention, the content of the free resin having a hydroxyl group in the ink can be measured by the following method. Of course, the present invention is not limited to the following method, and values measured using other methods may be used.

  The ink is centrifuged under conditions of 400,000 G for 16 hours, and 95% by mass of the supernatant liquid is collected. Thereafter, the obtained liquid is acidified to separate the free resin. Further, the obtained free resin is dried to determine the solid content. Then, the content of the free resin based on the total mass of the ink is obtained from the ratio to the charged amount. Here, a fine pigment may be contained in the supernatant liquid collected after centrifugation under the above-described conditions. However, since the amount of the pigment is very small, in the present invention, the solid content obtained by acid precipitation according to the above-described procedure is regarded as the substantial solid content of the free resin. Here, when the resin in the ink is only a resin having a hydroxyl group, the solid content of the free resin is the solid content of the free resin having a hydroxyl group, and from this value, the hydroxyl group based on the total mass of the ink is determined. The content (% by mass) of the free resin is determined.

In addition, the ink may contain two or more types of free resins, for example, a free resin having a hydroxyl group and a free resin having no hydroxyl group. In such a case, in order to quantify the content of the free resin having a hydroxyl group, it is necessary to devise the following. That is, by using MALDI-TOF / MS (combination of matrix-assisted laser desorption / ionization method and time-of-flight mass spectrometer), devising acid deposition conditions, and collecting resins having hydroxyl groups by GPC or the like. To do. Furthermore, the component analysis of the monomer which comprises resin is performed using ¹³ C-NMR, gas chromatography, etc. Based on this analysis result, a 1% by mass aqueous solution (standard sample) of a resin having a hydroxyl group having the same structure as that of the resin contained in the ink is prepared. Thereafter, the infrared absorption spectrum is measured under the same conditions for the aqueous solution containing 1% by mass of the free resin obtained above and the standard sample. Mass conversion is performed from the measurement result of the infrared absorption spectrum in the aqueous solution containing the standard sample and the free resin, and the content (% by mass) of the free resin having a hydroxyl group based on the total mass of the ink is obtained.

(Pigment)
Examples of the pigment that can be used in the ink according to the present invention include carbon black and organic pigments. The pigment content (% by mass) is preferably 0.1% by mass or more and 10.0% by mass or less based on the total mass of the ink.

〔Carbon black〕
For example, carbon black such as furnace black, lamp black, acetylene black, and channel black can be used as the carbon black. Of course, the present invention is not limited to the following.
Ray Van: 1170, 1190 ULTRA-II, 1200, 1255, 1250, 1500, 2000, 3500, 5000, 5250, 5750, 7000, etc. (made in Colombia). Black Pearls L, Legal: 330R, 400R, 660R, Mogul L, Monak: 700, 800, 880, 900, 1000, 1100, 1300, 1400, Vulcan XC-72R, etc. (manufactured by Cabot). Color Black: FW1, FW2, FW2V, FW18, FW200, S150, S160, S170, Printex: 35, U, V, 140U, 140V, Special Black: 4, 4A, 5, 6 etc. (manufactured by Degussa).
No. 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. 2300, MCF-88, MA7, MA8, MA100, MA600, etc. (manufactured by Mitsubishi Chemical).

  Other than the above, conventionally known carbon black can be used. Further, magnetic fine particles such as magnetite and ferrite, titanium black and the like may be used as the black pigment.

[Organic pigments]
Specific examples of the organic pigment include the following.
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 pigment. Condensed azo pigment. Thioindigo pigment. Flavanthrone yellow, acylamide yellow, quinophthalone yellow, nickel azo yellow, copper azomethine yellow, perinone orange, anthrone orange, dianthraquinonyl red, dioxazine violet, etc.

Moreover, the following are mentioned when an organic pigment is shown by a color index (CI) number. Of course, conventionally known organic pigments can be used other than the following.
C. I. Pigment Yellow: 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 109, 110, 117, 120, 125, 128, 137, 138, 147, 148, 151, 153, 154, 166 168 mag. C. I. Pigment Orange: 16, 36, 43, 51, 55, 59, 61 etc. C. I. Pigment Red: 9, 48, 49, 52, 53, 57, 97, 122, 123, 149, 168, 175, 176, 177, 180, 192, 215, 216, 217, 220, 223, 224, 226, 227 228, 238, 240 etc. C. I. Pigment violet: 19, 23, 29, 30, 37, 40, 50, and the like. C. I. Pigment Blue: 15, 15: 3, 15: 1, 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.

(Dispersant)
In the ink according to the present invention, it is essential to use a resin having a hydroxyl group as a dispersant in consideration of scratch resistance, marker resistance, and ejection characteristics. Furthermore, the ink according to the present invention may be used in combination with other resins as a dispersant as long as the effects obtained by adding these are obtained and the object effects of the present invention are not impaired.

  As other dispersants, those capable of stably dispersing a pigment in an aqueous medium by the action of an anionic group are suitably used. For example, the following can be used.

  Styrene-acrylic acid copolymer, styrene-acrylic acid-alkyl acrylate copolymer or salts thereof. Styrene-maleic acid copolymer, styrene-maleic acid-acrylic acid alkyl ester copolymer, or salts thereof. Styrene-methacrylic acid copolymer, styrene-methacrylic acid-alkyl acrylate copolymer or salts thereof. Styrene-maleic acid half ester copolymer, vinyl naphthalene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer, styrene-maleic anhydride-maleic acid half ester copolymer or salts thereof.

  The weight average molecular weight of the dispersant used in the present invention is 1,000 to 30,000, more preferably 3,000 to 15,000, particularly 5,000 to 14,000, and particularly 8,000 to 12 in particular. 1,000 or less.

(Aqueous medium)
The ink according to the present invention can use water or an aqueous medium that is a mixed solvent of water and various water-soluble organic solvents.

  In the present invention, it is essential that the water-soluble organic solvent is at least a polyhydric alcohol having a value of the number of hydroxyl groups / number of carbon atoms in the molecule of 0.50 or less. However, other water-soluble organic solvents may be used in combination as long as the effects of adding these are obtained and the object effects of the present invention are not impaired. When the polyhydric alcohol having an OH / C value of 0.50 or less and other water-soluble organic solvent are used in combination, when the other water-soluble organic solvent is a good solvent for the resin having a hydroxyl group, It is preferable to adopt the configuration. That is, the content of the water-soluble organic solvent that is a good solvent for the resin having a hydroxyl group is preferably smaller than the content of the polyhydric alcohol.

The water-soluble organic solvent is not particularly limited as long as it is water-soluble, and the following can be used.
C1-C4 monohydric alkyl alcohols such as ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol and the like.
Amides such as dimethylformamide and dimethylacetamide. Ketones or ketoalcohols such as acetone and diacetone alcohol. Ethers such as tetrahydrofuran and dioxane. Polyalkylene glycols such as polyethylene glycol and polypropylene glycol. Alkylene glycols in which the alkylene group contains 2 to 6 carbon atoms, such as diethylene glycol, propylene glycol, triethylene glycol, and thiodiglycol; Lower alkyl ether acetates such as polyethylene glycol monomethyl ether acetate. Bishydroxyethyl sulfone. Lower alkyl glycol ethers such as ethylene glycol monomethyl (or ethyl, butyl) ether, diethylene glycol monomethyl (or ethyl, butyl) ether, and triethylene glycol monomethyl (or ethyl, butyl) ether. Lower dialkyl glycol ethers such as triethylene glycol dimethyl (or ethyl) ether and tetraethylene glycol dimethyl (or ethyl) ether. Alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine. Sulfolane, N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like. 1,2-ethanediol (ethylene glycol), 1,2-propanediol, 1,3-propanediol, 1,2,3-propanetriol (glycerin) and the like. Also, 1,2,3-butanetriol, 1,2,4-butanetriol and the like. In addition, 1,2,3-pentanetriol, 1,2,4-pentanetriol, 1,2,5-pentanetriol, 1,3,4-pentanetriol, 1,3,5-pentanetriol and the like. In addition, OH / C values of 1,2,3,4-pentanetetraol, 1,2,3,5-pentanetetraol, 1,2,3,4,5-pentanepentaol, etc. are from 0.50 Large polyhydric alcohols.

  In the present invention, when the ink contains polyethylene glycol having an average molecular weight of 600 or more and 1,500 or less, the discharge characteristics, particularly the discharge characteristics when continuously discharging ink can be improved. Particularly preferred. In particular, the content of polyethylene glycol having an average molecular weight of 600 or more and 1,500 or less is preferably 0.5 times or more with respect to the content of the pigment (solid content) in the ink.

  The content (mass%) of the water-soluble organic solvent including the polyhydric alcohol in which the number of hydroxyl groups in the molecule / number of carbon atoms is 0.50 or less is 3.0 mass based on the total mass of the ink. % To 50.0% by mass, more preferably 7.0% to 50.0% by mass.

  Moreover, it is preferable to use deionized water (ion exchange water) as the water. The water content (% by mass) is preferably 40.0% by mass or more and 95.0% by mass or less based on the total mass of the ink.

(Other additives)
In the ink used in the present invention, in addition to the above-mentioned components, a moisturizing agent may be added as necessary. In addition, in order to obtain an ink having desired physical properties, surfactants and antifoaming agents are used. Further, an antiseptic, an antifungal agent and the like may be added.

  However, when a resin-dispersed pigment is used as a coloring material as in the present invention, the surfactant tends to adsorb on the hydrophobic surface of the pigment surface. For this reason, when a resin having a high hydrophilicity and easily desorbing from the pigment surface, such as a resin having a hydroxyl group, is used as the dispersant, the content of the surfactant in the ink is preferably as small as possible. Specifically, when the content (mass%) of the pigment (solid content) in the ink is 100, the content (mass%) of the surfactant is 25% or less, further 12.5% or less. It is preferable to do.

<Inkjet recording method, ink cartridge, recording unit, and inkjet recording apparatus>
An example of the ink jet recording apparatus will be described below. First, an example of the configuration of a recording head, which is a main part of an ink jet recording apparatus using thermal energy, is shown in FIGS. 3 is a cross-sectional view of the recording head 13 along the ink flow path, and FIG. 4 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. 5 is an external view of an example of a multi-head in which a large number of recording heads shown in FIG. 3 are arranged. The multi-head includes a glass plate 27 having multi-nozzles 26 and a recording head 28 similar to that shown in FIG.

  FIG. 6 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, contacts the ink ejection port surface, and performs capping. The structure to perform is provided. 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 where 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. 7 is a diagram illustrating an example of an ink cartridge that stores 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. 8, a unit in which they are integrated can be suitably used. In FIG. 8, 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 may be used in which the ink container is an ink bag with a spring or the like inside without using an ink absorber. 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. 6 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. 9 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 composed of a substrate 84 that supports and fixes 82 and the like. 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.

EXAMPLES Next, although an Example , a reference example, and a comparative example are given and this invention is demonstrated more concretely, unless the summary is exceeded, this invention is not limited by the following Example. In the text, “parts” and “%” are based on mass unless otherwise specified.

<Preparation of pigment dispersion>
In the preparation of the following pigment dispersion, the following carbon black and resin were used. Of course, the present invention is not limited to this.
Carbon black: a specific surface area of 210m ² / g DBP oil absorption amount is 74ml / 100g.
Resin A: Polyvinyl acetate-b-poly (styrene-co-acrylic acid) having a weight average molecular weight of 8,000 (composition (molar ratio) 20:60:20) is saponified with a 10% by mass aqueous potassium hydroxide solution. And a resin obtained by neutralization.
Resin B: a resin obtained by neutralizing poly (benzyl methacrylate-co-acrylic acid) having a weight average molecular weight of 12,000 (composition (molar ratio) 70:30) with a 10% by mass aqueous potassium hydroxide solution .
Resin C: 10% by mass of poly (2-hydroxyethyl methacrylate) -b-poly (styrene-co-acrylic acid) (composition (molar ratio) 20:60:20) having a weight average molecular weight of 8,000 Resin obtained by neutralization with aqueous potassium oxide solution.
Resin D: Poly (vinyl acetate-co-styrene-co-acrylic acid) having a weight average molecular weight of 8,000 (composition (molar ratio) 20:60:20) was saponified with a 10% by mass aqueous potassium hydroxide solution. Resin obtained by neutralization.

(Preparation of black pigment dispersion 1)
10 parts of carbon black, A2 parts resin, by mixing 88 parts of ion-exchanged water, was dispersed for 3 hours using a batch type vertical sand mill. After the coarse particles were removed by centrifuging the obtained dispersion, the resin dispersion type black pigment 1 was prepared by pressure filtration with a micro filter (manufactured by Fuji Film) having a pore size of 3.0 μm. Furthermore, water was added to the resin-dispersed black pigment 1 obtained above to disperse it so that the pigment concentration became 10% by mass to prepare a dispersion. A black pigment dispersion 1 was obtained by the above method. The obtained black pigment dispersion 1 was ultrafiltered to adjust the content of the free resin having a hydroxyl group. The mass ratio (pigment: resin A) of the pigment content and the resin A content in the black pigment dispersion 1 was 100: 18.

(Preparation of black pigment dispersion 2)
10 parts of carbon black, 2 parts of resin A, 2 parts of resin B, and 86 parts of ion-exchanged water were mixed and dispersed for 3 hours using a batch type vertical sand mill. Coarse particles were removed by centrifuging the resulting dispersion, and then pressure filtration was performed with a microfilter (manufactured by Fuji Film) having a pore size of 3.0 μm to prepare resin-dispersed black pigment 2. Further, water was added to the resin-dispersed black pigment 2 obtained above to disperse the pigment so that the pigment concentration became 10% by mass to prepare a dispersion. Black pigment dispersion 2 was obtained by the above method. The obtained black pigment dispersion 2 was ultrafiltered to adjust the content of the free resin having a hydroxyl group. In order to determine the mass ratio of the pigment content and the resin A content in the black pigment dispersion 2, the following operation was performed. After the black pigment dispersion 2 obtained above was dried, this solid was dissolved in tetrahydrofuran to obtain a solution. Thereafter, the obtained liquid was subjected to pressure filtration with a micro filter (manufactured by Fuji Film) having a pore size of 3.0 μm to separate a solution containing a pigment and a resin. Furthermore, GPC (gel permeation chromatography) was performed on the solution containing the resin, and the resin A and the resin B were fractionated. The mass ratio of the pigment content and the resin A content in the black pigment dispersion 2 (pigment: resin A) was 100: 16.

(Preparation of black pigment dispersion 3)
10 parts of carbon black, 2 parts of resin A, and 88 parts of ion exchange water were mixed and dispersed for 3 hours using a batch type vertical sand mill. Coarse particles were removed by centrifuging the resulting dispersion, and then pressure filtration was performed with a microfilter (manufactured by Fuji Film) having a pore size of 3.0 μm to prepare resin-dispersed black pigment 3. Further, water was added to the resin-dispersed black pigment 3 obtained above to disperse it so that the pigment concentration became 10% by mass to prepare a dispersion. Black pigment dispersion 3 was obtained by the above method. The obtained black pigment dispersion 3 was ultrafiltered to adjust the content of the free resin having a hydroxyl group. The mass ratio (pigment: resin A) of the pigment content and the resin A content in the black pigment dispersion 3 was 100: 16.

(Preparation of black pigment dispersion 4)
10 parts of carbon black, 3 parts of resin A, and 87 parts of ion exchange water were mixed and dispersed for 3 hours using a batch type vertical sand mill. Coarse particles were removed by centrifuging the obtained dispersion, followed by pressure filtration with a microfilter (manufactured by Fuji Film) having a pore size of 3.0 μm to prepare resin-dispersed black pigment 4. Further, water was added to the resin-dispersed black pigment 4 obtained above to disperse it so that the pigment concentration became 10% by mass to prepare a dispersion. A black pigment dispersion 4 was obtained by the above method. The obtained black pigment dispersion 4 was subjected to ultrafiltration under the same conditions as in the black pigment dispersion 1 to adjust the content of the free resin having a hydroxyl group. The mass ratio (pigment: resin A) of the pigment content and the resin A content in the black pigment dispersion 4 was 100: 20.

(Preparation of black pigment dispersion 5)
10 parts of carbon black, 2 parts of resin C, and 88 parts of ion exchange water were mixed and dispersed for 3 hours using a batch type vertical sand mill. Coarse particles were removed by centrifuging the obtained dispersion, followed by pressure filtration with a microfilter (manufactured by Fuji Film) having a pore size of 3.0 μm to prepare resin-dispersed black pigment 5. Further, water was added to the resin-dispersed black pigment 5 obtained above to disperse it so that the pigment concentration became 10% by mass to prepare a dispersion. A black pigment dispersion 5 was obtained by the above method. The obtained black pigment dispersion 5 was ultrafiltered to adjust the content of the free resin having a hydroxyl group. The mass ratio (pigment: resin C) of the pigment content and the resin C content in the black pigment dispersion 5 was 100: 19.

(Preparation of black pigment dispersion 6)
10 parts of carbon black, 2 parts of resin D, and 88 parts of ion exchange water were mixed and dispersed for 3 hours using a batch type vertical sand mill. Coarse particles were removed by centrifuging the resulting dispersion, and then pressure filtration was performed with a microfilter (manufactured by Fuji Film) having a pore size of 3.0 μm to prepare resin-dispersed black pigment 6. Further, water was added to the resin-dispersed black pigment 6 obtained above to disperse the pigment concentration to 10% by mass, thereby preparing a dispersion. A black pigment dispersion 6 was obtained by the above method. The obtained black pigment dispersion 6 was subjected to ultrafiltration under the same conditions as the black pigment dispersion 1 to adjust the content of the free resin having a hydroxyl group. The pigment content and the mass ratio of the resin D (pigment: resin D) in the black pigment dispersion 6 were 100: 18.

<Preparation of ink>
Ingredients shown in Table 1 below were mixed and sufficiently stirred, and then pressure filtration was performed with a micro filter (manufactured by Fuji Film) having a pore size of 1.0 μm to prepare inks 1 to 18.

<Quantification of free resin and free resin having hydroxyl group>
The content (mass%) of the free resin in the ink and the content (mass%) of the free resin having a hydroxyl group were quantified by the following method. The results are shown in Tables 1 and 2.

  The ink was centrifuged under conditions of 400,000 G and 16 hours, and 95% by mass of the supernatant liquid was collected. Thereafter, the obtained liquid was subjected to acid precipitation to separate a free resin. The obtained free resin was dried to determine the solid content. Then, the content of the free resin based on the total mass of the ink was determined from the ratio to the charged amount.

  In addition, in the ink 2 containing two kinds of resins in the ink, the content of the free resin having a hydroxyl group in the ink was determined by performing the following operation in addition to the above procedure. That is, the structure of the resin A was determined by a conventional method, and a 1% by mass aqueous solution (standard sample) of the resin A was prepared. Then, the infrared absorption spectrum was measured under the same conditions for the aqueous solution containing 1% by mass of the free resin obtained above and the standard sample. Mass conversion was performed from the measurement result of the infrared absorption spectrum in the aqueous solution containing the standard sample and the free resin, and the content (% by mass) of the free resin having a hydroxyl group based on the total mass of the ink was obtained.

<Determination of poor and good solvents>
About each water-soluble organic solvent used for ink preparation, the poor solvent and the good solvent were determined. To an aqueous solution diluted with ion-exchanged water so that the water-soluble organic solvent is 50% by mass, 0.5 g of a 10% by mass aqueous solution of Resin A, Resin C, or Resin D is dropped and sealed at room temperature for 4 days. I left it alone. After that, compared to the initial state, when the liquid became cloudy or when the presence of oily matter or precipitate was confirmed, the water-soluble organic solvent was determined to be a poor solvent, and the liquid was not particularly changed. In this case, the water-soluble organic solvent was determined as a good solvent. The results are shown in Table 3. In Table 3, the case of being a poor solvent is indicated by ◯, and the case of being a good solvent is indicated by ×.

<Calculation of OH / C value of water-soluble organic solvent>
For each water-soluble organic solvent used for preparing the ink, the number of hydroxyl groups in the molecule / number of carbon atoms (OH / C value) was calculated. The results are shown in Table 3. In addition, since polyethylene glycol (average molecular weight 1,000) has molecular weight distribution, OH / C value cannot be calculated.

<Evaluation>
(Bleeding phenomenon)
The ink obtained above was filled in an ink cartridge, and the ink jet recording apparatus PIXUS 860i (manufactured by Canon Inc.) was remodeled, but mounted on the cyan ink position. Thereafter, the head cleaning operation was performed twice, and after confirming that the ink reached the ejection port, the main power supply of the ink jet recording apparatus was turned off. In this state, the ink jet recording apparatus was left at room temperature for 2 weeks. Then, without turning on the main power of the ink jet recording apparatus, the recording head was removed from the main body while the ink cartridge was still mounted, and the state near the discharge port (nozzle) was observed using a microscope. Thereafter, the recording head was again mounted on the ink jet recording apparatus, the main power supply was turned on, and the head cleaning operation was performed once. Thereafter, a nozzle check pattern was recorded. The bleeding phenomenon was evaluated based on the state of the nozzle and the nozzle check pattern. The standard of the bleeding phenomenon is as follows. The evaluation results are shown in Table 4.

[Evaluation criteria for bleeding phenomenon]
A: For all the nozzles, the bleeding phenomenon is not confirmed, and no recording failure is confirmed in the nozzle check pattern.
B: The bleeding phenomenon was confirmed in less than 1% of all nozzles, but no recording failure was confirmed in the nozzle check pattern.
C: The bleeding phenomenon is confirmed in 1% or more and less than 5% of all nozzles, and a recording defect is confirmed in the nozzle check pattern with some nozzles.
D: The bleeding phenomenon is confirmed in 5% or more of all the nozzles, and further, a recording defect is confirmed in the nozzle check pattern.

Among Examples and Reference Examples , Reference Examples 1 to 3, Example 4 to 6, Reference Example 8, Example 9, Reference Example 11 , Example 12 and Reference Example 13 in which the evaluation result of the bleeding phenomenon was A. , and the ink for the 14 was repeated 5 times to evaluate the bleeding phenomenon in the same manner as above. As a result, the inks of Reference Example 11 and Example 12 were twice evaluated as B. That is, the inks of Reference Example 11 and Example 12 exhibited a bleeding phenomenon as compared with the inks of Reference Examples 1 to 3, Examples 4 to 6, Reference Example 8, Example 9, Reference Examples 13 and 14. Suppressing effect is slightly reduced.

(Abrasion resistance)
Each of the inks 1 to 3, 8 and 13 obtained above was filled in an ink cartridge, and the ink jet recording apparatus PIXUS 860i (manufactured by Canon Inc.) was remodeled and mounted on the black ink position. Thereafter, a solid portion of 2 cm × 2 cm and characters were recorded on a recording medium (PB Paper; manufactured by Canon) to produce a recorded matter. The discharge amount per dot of ink is within 30 ng ± 10%.

The printer driver selected the default mode.
-Paper type: Plain paper-Print quality: Standard-Color adjustment: Automatic After leaving the recorded matter obtained above at room temperature for 1 minute, rubbing the recording part with a finger, The extent was visually confirmed to evaluate scratch resistance. The standard of abrasion resistance is as follows. The evaluation results are shown in Table 5.

[Evaluation criteria for scratch resistance]
A: Both the solid part and the characters are hardly noticeable in the recording part, and the finger is not dirty.
B: The solid part or the character part is shaved and the finger is dirty.

(Marker resistance)
Each of the inks 1 to 3, 8 and 13 obtained above was filled in an ink cartridge, and the ink jet recording apparatus PIXUS 860i (manufactured by Canon Inc.) was remodeled and mounted on the black ink position. Thereafter, a solid portion of 2 cm × 2 cm and characters were recorded on a recording medium (PB Paper; manufactured by Canon) to produce a recorded matter. The discharge amount per dot of ink is within 30 ng ± 10%.

The printer driver selected the default mode.
-Paper type: Plain paper-Print quality: Standard-Color adjustment: Automatic After the recorded material obtained above is left at room temperature for 1 hour, use a yellow highlighter (spot lighter; manufactured by Pilot) to print characters. The part was marked once with normal writing pressure, and the degree of stain on the recorded material and the pen tip was visually confirmed to evaluate the marker resistance. The standard of marker resistance is as follows. The evaluation results are shown in Table 5.

[Evaluation criteria for marker resistance]
A: Bleeding of recorded matter and white background are not recognized, and the pen tip is not dirty.
B: The recorded material is not stained on the white background, but the pen tip is slightly dirty.
C: Dirt on the white background is recognized in the recorded material.

(Discharge characteristics)
Each of the inks 1 to 3, 8 and 13 obtained above was filled in an ink cartridge, and the ink jet recording apparatus PIXUS 860i (manufactured by Canon Inc.) was remodeled and mounted on the black ink position. Thereafter, the recording frequency was changed to 100 Hz, 1 kHz, 5 kHz, 10 kHz, and 15 kHz on a recording medium (PB Paper; manufactured by Canon), and a solid part having a recording density of 100% was recorded at 2 cm × 8 cm, thereby producing a recorded matter. did. The discharge amount per dot of ink is within 30 ng ± 10%.

The printer driver selected the default mode.
-Paper type: Plain paper-Print quality: Standard-Color adjustment: Automatic Observe visually the image density and unevenness of the solid image of the recorded matter obtained above, and the state of non-ejection when recording, The ejection characteristics were evaluated. The criteria for the ejection characteristics are as follows. The evaluation results are shown in Table 5.

[Evaluation criteria for ejection characteristics]
A: There is no non-ejection up to 15 kHz, and when comparing solid images obtained by recording at 15 kHz and 100 Hz, the image density and unevenness are comparable.
B: There is no non-ejection up to 15 kHz, but when solid images obtained by recording at 15 kHz and 100 Hz are compared, the image density and unevenness in the 15 kHz solid image are inferior.
C: There was no non-ejection up to 10 kHz, but there was unevenness in the solid image due to the presence of non-ejection nozzles and misalignment at 15 kHz.

It is a schematic diagram showing a mode that the state of an ink changes with time in a nozzle. It is a schematic diagram showing the relationship between the free resin which has a hydroxyl group, a water molecule, and a polyhydric alcohol. FIG. 2 is a longitudinal sectional view of a recording head. It is a vertical and horizontal view of a 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 1 Discharge port 2 Heater 3 Orifice surface 4 Water molecule 5 Pigment which resin adsorbed 6 Water-soluble organic solvent 7 Free resin having a hydroxyl group 8 Evaporated water molecule 9 Segment having a hydroxyl group 10 Segment having no hydroxyl group 11 Polyhydric alcohol 13 Recording head 14 Nozzle 15 Heating element substrate 16 Protective layer 17-1, 17-2 Electrode 18 Heating resistor layer 19 Heat storage layer 20 Substrate 21 Ink 22 Discharge 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 70 Recording unit 71 Recording head 72 Atmospheric communication port 80 Ink flow path 81 Orifice plate 82 Vibration plate 83 Piezoelectric element 84 Substrate 85 Discharge port

Claims (12)

A water- based ink containing a resin having a hydroxyl group, a pigment, and an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent,
The water-soluble organic solvent contains a polyhydric alcohol having a value of the number of hydroxyl groups in the molecule / number of carbon atoms of 0.40 or less,
Resin having a hydroxyl group, Ri polyvinyl alcohol resin der the segment without the segment and hydroxyl group is copolymerized with a hydroxyl group,
Wherein the pigment is an aqueous ink characterized that you have been dispersed in the aqueous medium by the polyvinyl alcohol resin. The total number of hydroxyl groups of the polyhydric alcohol having a value of the number of hydroxyl groups in the molecule / number of carbon atoms in the ink of 0.40 or less is adsorbed to the pigment in the polyvinyl alcohol resin in the ink. The water-based ink according to claim 1, wherein the water-based ink is at least 100 times the total number of hydroxyl groups contained in the resin. 3. The water-based ink according to claim 1, wherein the value of the number of hydroxyl groups in the molecule of the polyhydric alcohol / number of carbon atoms is 0.10 or more. The water-based ink according to any one of claims 1 to 3, wherein the polyvinyl alcohol-based resin is a block copolymer. The water-based ink according to any one of claims 1 to 4, wherein the polyvinyl alcohol-based resin has a weight average molecular weight of 8,000 to 12,000. The content of the polyvinyl alcohol resin based on the total mass of the ink in the aqueous ink when the content (% by mass) of the pigment based on the total mass of the ink in the aqueous ink is 100. The water-based ink according to claim 1, wherein (% by mass) is 5.0% or more and 100.0% or less. The content of the polyvinyl alcohol resin based on the total mass of the ink in the aqueous ink when the content (% by mass) of the pigment based on the total mass of the ink in the aqueous ink is 100. The water-based ink according to claim 1, wherein (% by mass) is 7.0% or more and less than 20.0%. An ink jet recording method in which ink is ejected by an ink jet method to perform recording on a recording medium, wherein the ink is the water-based ink according to any one of claims 1 to 7 . An ink cartridge comprising an ink containing portion for containing ink, wherein the ink is the water-based ink according to any one of claims 1 to 7 . A recording unit comprising an ink containing portion for containing ink and a recording head for ejecting ink, wherein the ink is the water-based ink according to any one of claims 1 to 7. To record unit. An ink jet recording apparatus comprising an ink containing portion for containing ink and a recording head for ejecting ink, wherein the ink is the water-based ink according to any one of claims 1 to 7. An inkjet recording apparatus. A water- based ink containing a resin having a hydroxyl group, a pigment, and an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent,
The water-soluble organic solvent is at least one selected from the group consisting of 1,2-hexanediol, 1,6-hexanediol, and 1,5-pentanediol;
Resin having a hydroxyl group, Ri polyvinyl alcohol resin der the segment without the segment and hydroxyl group is copolymerized with a hydroxyl group,
Wherein the pigment is an aqueous ink characterized that you have been dispersed in the aqueous medium by the polyvinyl alcohol resin.

Images