JP6008679B2 - Ink, ink cartridge, and ink jet recording method - Google Patents

Description

  The present invention relates to an ink, an ink cartridge, and an ink jet recording method.

  The ink jet recording method is a recording method capable of recording an image on various recording media. For this reason, as inks used in the ink jet recording method, there have been proposed many inks mainly for recording photographic images and inks mainly for recording business documents on plain paper.

  In recent years, the need for an ink jet recording method in the business field has improved, and an ink capable of recording an image excellent in marker resistance has been demanded. In addition to the conventional black ink, many color inks using organic pigments as coloring materials have been proposed. In addition, an ink jet recording apparatus used in the business field is also required to increase the recording speed from the viewpoint of improving productivity.

  In response to the market demand as described above, an ink using a self-dispersing organic pigment has been proposed as an ink capable of obtaining a high color developability particularly on plain paper (Patent Document 1). In addition, pigment inks to which various polyurethane resins are added have been studied for the purpose of improving the marker resistance required for plain paper documents for business use (Patent Documents 2 and 3).

JP 2000-513396 JP 2005-515289 A JP 2008-179657 A

  The inventors of the present invention have made a detailed study on increasing the recording speed required in recent years. Specifically, an ink jet recording apparatus (trade name “PIXUS iP3100” (product name “PIXUS iP3100”), which is prepared by preparing each ink disclosed in Patent Documents 1 to 3 and doubling the carriage moving speed for high speed recording. The following studies were conducted using Canon)). A self-dispersing organic pigment was used as the coloring material.

  First, using the inkjet recording apparatus, a solid image of 19 cm × 26 cm and 10 images each having a grid of 0.5 mm width ruled lines at intervals of about 1 cm were recorded on plain paper. When the obtained image was visually observed, when high-speed recording was performed using the inks described in Patent Documents 1 to 3, it was confirmed that a streak was observed in the recorded matter or the image of the ruled line was distorted. The discharge stability decreased. Furthermore, with respect to the ink described in Patent Document 3, it was also confirmed that the marker resin of the resulting image was not sufficient because the polyurethane resin used was excessively stiff on the paper surface.

  Accordingly, an object of the present invention is to provide an ink having high ink ejection stability and high marker resistance of an obtained image. Another object of the present invention is to provide an ink cartridge and an ink jet recording method using the ink.

The above object is achieved by the present invention described below. That is, according to the present invention, there is provided a water-based ink for use in an ink jet recording method for recording an image on a recording medium by ejecting ink from a recording head by the action of heat energy . I. Pigment red 122 and C.I. I · Pigment Blue 15: self-dispersible organic pigment is a hydrophilic group via at least one of organic pigments phenylene group on the particle surfaces of the three attached, and contains a polyurethane resin, wherein the hydrophilic group is, -COOM and —SO ₃ M (“M” represents hydrogen atom, alkali metal, ammonium, or organic ammonium), and the self-dispersing organic pigment has a surface charge of 0.5 μmol / m ² or more. 5 μmol / m ² or less, and the polyurethane resin has a unit derived from a polyisocyanate, a unit derived from a polyether polyol having no acid group, and a unit derived from a diol having an acid group, and the polyurethane resin The acid value of is 40 mgKOH / g or more and 140 mgKOH / g or less Link is provided.

  According to the present invention, it is possible to provide an ink having high ink ejection stability and high marker resistance of an obtained image. In addition, according to the present invention, it is possible to provide an ink cartridge and an ink jet recording method using this ink.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments. First, a detailed study was made of the mechanism by which the ejection stability of ink decreases when high-speed recording is performed using conventional ink. The present inventors presume this mechanism as follows.

(Mechanism that ink ejection stability decreases during high-speed recording)
(1) In the case of an ink containing a self-dispersing organic pigment but not containing a polyurethane resin First, an ink containing a self-dispersing organic pigment as a coloring material but not containing a polyurethane resin was examined. When high-speed recording is performed using this ink, it is assumed that the following phenomenon occurs. When recording at a higher speed than before, the temperature of the heater board of the recording head is likely to increase as the ink ejection frequency increases. As a result, the self-dispersing organic pigment contained in the ink existing in the vicinity of the heater board is given a large amount of heat as compared with the case of recording at low speed.

  Generally, an organic pigment has a lower decomposition temperature than an inorganic pigment (for example, carbon black). Although the decomposition temperature of the organic pigment varies depending on the color material type, it is presumed to be close to the maximum temperature instantaneously reached on the heater board surface. That is, when high-speed recording is performed, heat at a temperature close to the decomposition temperature of the organic pigment is applied. Therefore, it is presumed that the self-dispersing organic pigment is decomposed in the ink using the self-dispersing organic pigment as a coloring material.

Furthermore, it is considered that a hydrophilic group is also present on the particle surface of the self-dispersing organic pigment after decomposition. However, since the specific surface area of the pigment particles increases dramatically with pyrolysis, the surface of the self-dispersing organic pigment particles after pyrolysis has an amount of hydrophilic groups necessary to maintain dispersion stability. Not done. For this reason, the part where the hydrophilic group does not exist on the particle surface, that is, the hydrophobic part of the pigment increases, and it becomes difficult to maintain the dispersion stability. In such a state, it is considered that the decomposed pigment cannot be stably present in the ink, but accumulates on the heater board and prevents normal ink ejection. Note that the self-dispersing organic pigment surface charge amount 0.3 [mu] mol / m ^2, even in the case of using any of the surface charge amount 2.5 .mu.mol / m ² of the self-dispersing organic pigment, the deposits on the heater board It was confirmed that the discharge stability was lowered.

(2) In the case of an ink containing a self-dispersing organic pigment and a polyurethane resin having an acid value of less than 40 mgKOH / g Next, the ink contains a self-dispersing organic pigment as a coloring material, and further includes an acid described in Patent Documents 2 and 3. An ink containing a polyurethane resin having a value of less than 40 mgKOH / g (for example, a polyurethane resin having an acid value of 30 mgKOH / g) was examined. As in the case of (1), the thermal dispersion of the self-dispersing organic pigment occurs when high-speed recording is performed, but in the case of (2), it is presumed that the polyurethane resin is adsorbed on the hydrophobic portion of the decomposed pigment. However, polyurethane resin having an acid value of less than 40 mgKOH / g adsorbs to the hydrophobic part of the decomposed pigment, but the acid value is too low to improve dispersion stability. Will occur. Furthermore, due to the acid value of the polyurethane resin being too low, the pigment degradation products adhere more firmly to each other via the polyurethane resin adsorbed on the pigment degradation product surface, resulting in more deposition on the heater board. Presumed to give rise to things. Note that the self-dispersing organic pigment surface charge amount 0.3 [mu] mol / m ^2, even in the case of using any of the surface charge amount 2.5 .mu.mol / m ² of the self-dispersing organic pigment, the deposits on the heater board It was confirmed that the discharge stability was lowered.

  As a result of further detailed studies, the present inventors have found a requirement for obtaining ink having high ejection stability even when high-speed recording is performed. That is, it has been recognized that it is essential to combine the surface charge amount of the self-dispersing organic pigment, the polyurethane resin having a specific structure, and the polyurethane resin having a specific acid value. Hereinafter, the reason why ink ejection stability can be obtained even when high-speed recording is performed by combining specific requirements will be described.

(Mechanism that discharge stability does not decrease)
As a result of detailed studies, the inventors have confirmed that ink ejection stability can be obtained even when high-speed recording is performed when the following requirements (i) to (iii) are satisfied. did. The inventors presume this reason as follows.
(I) the surface charge amount of the self-dispersing organic pigment is 0.5 [mu] mol / m ² or more 1.5μmol / m ² or less.
(Ii) A polyurethane resin having an acid value of 40 mgKOH / g or more and 140 mgKOH / g or less is contained.
(Iii) The polyurethane resin includes a unit derived from a polyisocyanate, a unit derived from a polyether polyol having no acid group, and a unit derived from a diol having an acid group (hereinafter also referred to as an acid group-containing diol).

  First, a self-dispersing organic pigment having a surface charge amount in the above numerical range has a hydrophobic part to some extent on the particle surface, in which no hydrophilic group is present. The hydrophobic part and the polyurethane resin interact hydrophobicly, and the polyurethane resin is adsorbed on the surface of the pigment particles. Further, since the acid value of the polyurethane resin is 40 mgKOH / g or more and 140 mgKOH / g or less, in addition to the above-mentioned hydrophobic interaction, the unit is derived from an acid group-containing diol that is a hydrophilic part of the polyurethane resin. It is thought that hydrophilic interaction acts. In addition, when the acid value of the polyurethane resin is less than 40 mgKOH / g, the ejection stability is lowered as described above. On the other hand, it was found that when the acid value of the polyurethane resin is more than 140 mgKOH / g, the marker resistance of the obtained image is insufficient. The reason will be described later.

  As described above, when the acid value of the polyurethane resin is 40 mgKOH / g or more and 140 mgKOH / g or less, the polyurethane resin is adsorbed on the particle surface of the pigment in the ink, and the dispersion stability of the self-dispersing organic pigment is improved. Next, a case where high-speed recording is performed using ink in such a state will be described.

  As described above, in the case of high-speed recording, the temperature of the heater board that gives thermal energy to the ink rises as the ink discharge frequency increases from the head, and the temperature instantaneously reaches the decomposition temperature of the organic pigment on the heater board surface. To rise. As a result, the organic pigment is considered to be decomposed. However, it is considered that a hydrophilic group is present on the surface of the decomposed organic pigment particles and a polyurethane resin having a predetermined acid value is adsorbed. Since the dispersion of the organic pigment decomposed by the adsorbed polyurethane resin is stabilized, deposits are less likely to be present on the heater board, and ink ejection stability can be obtained even when high-speed recording is performed. it is conceivable that.

(Surface charge of self-dispersing organic pigment)
Next, the surface charge amount of the self-dispersing organic pigment will be described. The ink of the present invention, the surface charge amount using a self-dispersing organic pigment of 0.5 [mu] mol / m ² or more 1.5μmol / m ² or less. When the surface charge amount of the self-dispersing organic pigment is less than 0.5 μmol / m ² , since the hydrophilic group is small, the dispersion stability of the pigment is lowered. The pigment degradation product generated during high-speed recording has a very small amount of hydrophilic group bonds, so even if the polyurethane resin is adsorbed, the dispersion of the decomposed organic pigment cannot be stabilized, and the ink ejection Stability is reduced.

On the other hand, a self-dispersing organic pigment having a surface charge amount exceeding 1.5 μmol / m ² is presumed to have many hydrophilic groups on the pigment particle surface and few hydrophobic portions as described above. Even when a polyurethane resin is added to such an ink containing a self-dispersing organic pigment, it is presumed that the polyurethane resin hardly interacts with the particle surface of the pigment and is hardly adsorbed on the surface. When high-speed recording is performed using such an ink, it is presumed that the dispersion of the thermally decomposed organic pigment cannot be stabilized and the ejection stability of the ink is lowered.

In addition, the present inventors made similar investigations by adding a plurality of polyurethane resins having different acid values to the ink using the self-dispersing organic pigment having a surface charge amount exceeding 1.5 μmol / m ² . However, even when any ink is used, streaks and blurring occur in the obtained image, and the ink ejection stability is low.

(Polyurethane resin structure)
Next, the relationship between the structure of the polyurethane resin contained in the ink of the present invention and the ejection stability will be described in detail. The polyurethane resin used in the ink of the present invention is essentially composed of a unit derived from a polyisocyanate, a unit derived from a polyether polyol having no acid group, and a unit derived from a diol having an acid group. The present inventors presume the reason why the ejection stability is maintained even when high-speed recording is performed by using the polyurethane resin having such a structure as follows.

  Among the units constituting the polyurethane resin, the unit derived from the polyether polyol having no acid group has both flexibility derived from the structure and hydrophilicity derived from the polyol portion. In the present invention, the polyether polyol having no acid group is at least one selected from polyethylene glycol, polypropylene glycol, poly (1,2-butylene glycol), and poly (1,3-butylene glycol). Is preferred. When these polyether polyols are used, the strength and flexibility of the polyurethane resin are increased and the hydrophilicity is further increased. Moreover, the unit derived from the diol which has an acid group also has hydrophilicity derived from the hydroxyl group. It is presumed that the two hydrophilic portions present in the polyurethane resin have the following interactions with the hydrophilic groups present on the surface of the self-dispersing organic pigment.

  In the polyurethane resin used in the ink of the present invention, it is considered that the polyol portion having flexibility efficiently exhibits a hydrophilic interaction with the hydrophilic group on the surface of the pigment particle. In addition, in the polyurethane resin, there are also units derived from a site capable of hydrophilic interaction, that is, a diol having an acid group. For this reason, it is estimated that said hydrophilic interaction is strengthening. Further, as a result of studies by the present inventors, it has been confirmed that when polypropylene glycol is used as the polyether polyol having no acid group, the water solubility of the polyurethane resin is improved and the ink ejection stability is further improved. That is, by controlling the flexibility and hydrophilicity derived from the structure of the polyurethane resin, it is considered possible to cause an effective interaction with the pigment. On the other hand, the unit derived from the polyisocyanate in the polyurethane resin has hydrophobicity. For this reason, it is considered that the unit derived from polyisocyanate can be efficiently adsorbed on the surface of the hydrophobic particles of the pigment by the flexibility of the entire polyurethane resin.

  Thus, by controlling the hydrophilicity and hydrophobicity of the polyurethane resin, it becomes possible to efficiently adsorb the polyurethane resin on the surface of the pigment particles. As a result, even when a large amount of heat is applied during high-speed recording and the self-dispersing organic pigment is decomposed, both the polyurethane resin and the hydrophilic group derived from the pigment are present on the surface of the pigment decomposition product. . For this reason, it is thought that the dispersion stability of a pigment decomposition product can be improved. By the mechanism as described above, the present inventors presume that by using a specific polyurethane resin, deposition of a pigment decomposition product on the heater board is suppressed and ink ejection stability is maintained. The content of the polyurethane resin in the ink of the present invention is preferably 0.05 times or more and 2.0 times or less by mass ratio with respect to the content of the self-dispersing organic pigment. When the ratio is 0.05 times or more, it is particularly effective for improving the marker resistance of the image. Further, it was confirmed that when the ratio is 2.0 times or less, the dispersion stability of the pigment decomposition product is improved, and the ink ejection stability is more effectively improved.

  Furthermore, the present inventors also examined water-soluble resins other than polyurethane resins. Specifically, the case where a water-soluble acrylic resin was added instead of the polyurethane resin was examined. As the water-soluble acrylic resin, one obtained by random polymerization of monomers such as styrene, acrylic acid, and methacrylic acid was used. The acid value of the water-soluble acrylic resin used was about 160 mgKOH / g. As a result, unlike the case of using polyurethane resin, blurring and ruled lines were confirmed in the image when high-speed recording was performed. The inventors presume this reason as follows.

  It is considered that the hydrophobic portion of the water-soluble acrylic resin is adsorbed on the hydrophobic particle surface of the pigment by interaction. However, it is considered that there is a difference in the ease of interaction with the hydrophilic group on the pigment surface between the water-soluble acrylic resin and the polyurethane resin used in the ink of the present invention. That is, the interaction between the hydrophilic part of the water-soluble acrylic resin and the hydrophilic group on the pigment surface is smaller than the interaction between the hydrophilic part of the polyurethane resin and the hydrophilic group on the pigment surface. It is thought that the adsorption power of is weaker. As a result, the amount of the water-soluble acrylic resin with respect to the pigment decomposition product is reduced, it becomes impossible to maintain the dispersion stability of the pigment decomposition product, and it is estimated that the pigment decomposition product is deposited on the heater board. The

(When the pigment used is carbon black)
The present inventors have conducted a more detailed study on the difference in pigment type. Specifically, high-speed recording was performed by replacing the self-dispersing organic pigment made of an organic pigment with self-dispersing carbon black. As the self-dispersing carbon black, a trade name “Cab-O-Jet300” (manufactured by Cabot) was used. The self-dispersing carbon black had a surface charge of 0.5 μmol / m ² .

  As a result of the above examination, it was confirmed that when the self-dispersing carbon black and the polyurethane resin were combined, the ejection stability was lowered, and the image was blurred or wrinkled. The present inventors presume this phenomenon as follows. In general, carbon black is known to be stable even at high temperatures, and its decomposition temperature is very high compared to organic pigments. For this reason, when a large amount of heat is applied from the heater to the self-dispersing carbon black, it can be estimated that the following phenomenon occurs. Due to its high heat resistance, self-dispersing carbon black is predicted not to decompose even when a large amount of heat is applied from a heater. However, the heat resistance of the hydrophilic group treated on the surface is lower than that of carbon black itself. For this reason, it is considered that the hydrophilic group is decomposed by the heat from the heater and the dispersion stability of the self-dispersing carbon black is lowered.

  The polyurethane resin used in the ink of the present invention is considered to exert a hydrophobic interaction and a hydrophilic interaction as described above also to the self-dispersing carbon black. However, it is considered that the level of maintaining the dispersion stability does not reach the level of maintaining the dispersion stability of carbon black that occurs when high-speed recording is performed. Further, it is presumed that the carbon blacks that have lost dispersion stability form aggregates via the polyurethane resin adsorbed on the pigment surface, thereby accelerating the deposition on the heater board. As described above, it is presumed that the carbon black itself is deposited on the heater board due to the decrease in dispersion stability of the carbon black that occurs during high-speed recording and the formation of aggregates by the polyurethane resin.

(Polyurethane resin structure)
As a result of intensive studies, the present inventors have found that the types of compounds constituting the polyurethane resin have a great influence on improving the marker resistance of images. Details are shown below.

  A general polyurethane resin has two segments: (1) a hard segment composed of a polyisocyanate, a short-chain diol, and a chain extender, and (2) a soft segment composed of a polyol. The hard segment mainly contributes to strength, and the soft segment mainly contributes to flexibility. Since both segments have a microphase separation structure, the polyurethane resin film can exhibit high elasticity having both strength and flexibility. Such film characteristics are closely related to the development of marker resistance of the image.

  In order to obtain a highly hydrophilic polyurethane resin, it is common to increase the acid value of the polyurethane resin. The acid value of the polyurethane resin roughly depends on the amount of units derived from the compound having an acid group in the polyurethane resin. Therefore, in order to raise the acid value of a polyurethane resin, it is necessary to increase the usage-amount of the compound which has an acid group used when synthesize | combining a polyurethane resin. Examples of the compound having an acid group that can be used when synthesizing a polyurethane resin generally include (a) a polyol having an acid group and (b) a diol having an acid group.

  Examples of the polyol (a) having an acid group include acid-modified polyols such as carboxylic acid-modified polycaprolactone diols. However, it has been found that when a polyurethane resin synthesized using only a polyol having an acid group is used as the compound having an acid group, the marker resistance of the image is significantly lowered. This phenomenon occurred not only when the acid value was high, but also when the acid value was low (when the amount of polyol having an acid group was small). This is presumably because the balance between strength and flexibility is lost due to the presence of acid groups in the soft segment of the polyurethane resin synthesized using polyols having acid groups. From the above, it was found that even when a polyurethane resin synthesized using only a polyol having an acid group as the compound having an acid group is used for the ink, the marker resistance of the image is not improved.

  On the other hand, examples of the (b) diol having an acid group include diols having an acid group such as a carboxyl group, a sulfonic acid group, and a phosphoric acid group in the molecule. The diol having an acid group is preferably a short chain diol having less than 10 carbon atoms. Examples of the short-chain diol having an acid group include dimethylolacetic acid, dimethylolpropionic acid, and dimethylolbutanoic acid. Among them, it is preferable to use at least one of dimethylolpropionic acid (hereinafter also referred to as “DMPA”) and dimethylolbutanoic acid (hereinafter also referred to as “DMBA”). As the amount of DMPA or DMBA used is increased to increase the acid value of the polyurethane resin, the number of hydroxyl groups in the system also increases. For this reason, the amount of the polyol component that has a hydroxyl group and reacts with the isocyanate in the same manner as DMPA or DMBA needs to be relatively reduced as the amount of DMPA or DMBA increases. As a result, since the soft segment is reduced and the flexibility is lowered, the polyurethane resin film becomes very rigid, and the marker resistance of the obtained image tends to be low. That is, it was found that when a polyurethane resin having an acid value increased using DMPA or DMBA is used for the ink, the marker resistance of the image is lowered.

  From the above examination results, the present inventors have found that the decrease in the marker resistance of an image that occurs when a polyurethane resin having a high acid value (high hydrophilicity) is used is largely related to the structure of the polyurethane resin. I found. And it discovered that it was necessary not to change the hydrophilicity / hydrophobicity of the polyurethane resin by paying attention only to the high and low acid values, but to design the polyurethane resin by paying attention to the two segment structures of the hard segment and the soft segment.

When the present inventors examined various polyurethane resins, using a polyurethane resin that satisfies the following requirements (1) and (2) can improve not only ejection stability but also marker resistance of an image. It came to the conclusion that it is important to improve. The reason for this will be described below.
(1) It has a unit derived from an acid group-containing diol.
(2) The acid value is 40 mgKOH / g or more and 140 mgKOH / g or less.

  In general, when a polyurethane resin is synthesized, polyester polyol, polyether polyol, polycarbonate diol, polycaprolactone polyol, or the like is used as the polyol. Especially, when a polyether polyol is used, a highly flexible polyurethane resin can be obtained. For this reason, the polyurethane resin which has the soft segment comprised by the polyether polyol which does not have an acid group does not produce the softness | flexibility fall by the reduction | decrease of the above-mentioned soft segment easily. Therefore, even if the acid value is increased to some extent, a polyurethane resin with sufficiently maintained flexibility can be obtained. As a result of studies by the present inventors, if the acid value of the polyurethane resin is 140 mgKOH / g or less, the flexibility of the polyurethane resin is sufficiently maintained, and an image in which high marker resistance is maintained can be recorded. I understood.

  As described above, the effects of the present invention can be achieved by the synergistic effects of each component of the polyurethane resin. A suitable content of the polyurethane resin contained in the ink will be described later.

  The present inventors have found that by defining the surface charge amount of a self-dispersing organic pigment composed of an organic pigment, the acid value of a polyurethane resin, and the structure of the polyurethane resin, an effect that cannot be assumed in the past can be obtained. The invention has been completed. Both the unit derived from the polyether polyol having no acid group that exhibits flexibility in the polyurethane resin and the unit derived from the acid group-containing diol interact with the hydrophilic group present on the surface of the organic pigment. Thereby, the hydrophilic group and the polyurethane resin coexist on the pigment surface, and the effect of greatly increasing the dispersion stability of the pigment is exhibited. In addition, by setting the acid value of the polyurethane resin in a specific range, the hydrophobicity of the unit derived from polyisocyanate, the hydrophilicity of the unit derived from the polyether polyol having no acid group and the unit derived from the acid group-containing diol The balance with sex is in a good state. As a result, it is considered that the ejection stability of ink during high-speed recording is improved without causing deposits on the heater board.

[ink]
The ink of the present invention is an ink used in an ink jet recording method for recording an image on a recording medium by ejecting ink from a recording head by the action of thermal energy. Hereinafter, each component constituting the ink of the present invention will be described.

<Self-dispersing organic pigment>
As the self-dispersing organic pigment, a self-dispersing organic pigment in which at least one hydrophilic group is bonded to the particle surface of the organic pigment directly or through another atomic group is used. The hydrophilic group in the ink may be partially dissociated or all dissociated. When the molecular weight of the atomic group is 1,000 or less, the problem of the present invention is likely to occur, and thus the effect of the present invention is more exhibited, which is preferable.

Examples of the hydrophilic group introduced into the particle surface of the pigment include —COOM, —SO ₃ M, —PO ₃ HM, and —PO ₃ M ₂ . In the formula, “M” represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium. In the formula, it is preferable that “M” is an alkali metal such as lithium, sodium, or potassium because the ink ejection stability is improved as compared with the case of ammonium or organic ammonium. The hydrophilic group may be bonded to the particle surface of the pigment directly or via another atomic group (—R—). Other atomic groups (—R—) include linear or branched alkylene groups having 1 to 12 carbon atoms, arylene groups such as phenylene groups and naphthylene groups, amide groups, sulfone groups, amino groups, carbonyl groups, and esters. Groups and ether groups. Moreover, the group etc. which combined these groups can be mentioned. As the organic pigment, any of those conventionally used for inks can be used. Specific examples include azo pigments, phthalocyanine pigments, quinacridone pigments, and isoindolinone pigments.

The surface charge amount of the self-dispersing organic pigment used in the ink of the present invention is 0.5 [mu] mol / m ² or more 1.5μmol / m ² or less. In the present invention, the surface charge amount of the pigment is determined by colloid titration. In Examples described later, a pigment in a pigment dispersion is obtained by colloidal titration using a potential difference using an automatic potentiometric titrator (AT-510; manufactured by Kyoto Electronics Industry Co., Ltd.) equipped with a streaming potential titration unit (PCD-500). The surface charge amount of was measured. At this time, methyl glycol chitosan was used as a titration reagent. Of course, it is also possible to measure the surface charge amount using a pigment extracted from the ink by an appropriate method. If necessary, the content of the pigment in the ink may be adjusted with water.

  In the present invention, a method for verifying whether or not the pigment contained in the ink is a self-dispersing pigment is as follows. Specifically, after adding an excessive amount of acid to the ink, the precipitate is collected by centrifugation. In the case of a pigment dispersion, after adding an excessive amount of acid to the pigment dispersion, a precipitate is collected. The collected sediment is poured into a petri dish, stirred and redispersed. After 1 day, if no precipitate is formed in the petri dish and the pigment is dispersed, it is judged as a self-dispersion type pigment.

<Polyurethane resin>
The polyurethane resin contained in the ink of the present invention has a unit derived from a polyisocyanate, a unit derived from a polyether polyol having no acid group, and a unit derived from an acid group-containing diol. Hereinafter, details of the polyurethane resin will be described.

(Polyisocyanate)
The “polyisocyanate” in the present invention means a compound having two or more isocyanate groups. Examples of the polyisocyanate include aliphatic polyisocyanate, alicyclic polyisocyanate, aromatic polyisocyanate, and araliphatic polyisocyanate. The proportion (% by mass) of units derived from polyisocyanate in the polyurethane resin is preferably 10% by mass or more and 80% by mass or less.

  Examples of the aliphatic polyisocyanate include tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, and 2-methylpentane. -1,5-diisocyanate, 3-methylpentane-1,5-diisocyanate and the like. Examples of the alicyclic polyisocyanate include isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4-dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, 1,3-bis (isocyanatomethyl) cyclohexane, and the like. be able to. As aromatic polyisocyanates, tolylene diisocyanate, 2,2-diphenylmethane diisocyanate, 2,4-diphenylmethane diisocyanate, 4,4-diphenylmethane diisocyanate, 4,4-dibenzyl diisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate Examples thereof include isocyanate, 1,3-phenylene diisocyanate, and 1,4-phenylene diisocyanate. Examples of the araliphatic polyisocyanate include dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, and α, α, α, α-tetramethylxylylene diisocyanate. These polyisocyanates can be used alone or in combination of two or more as required. In the present invention, among the polyisocyanates, hexamethylene diisocyanate is preferably used. Further, it is more preferable to use hexamethylene diisocyanate in combination with other polyisocyanates. The reason is as follows.

  Hexamethylene diisocyanate (hereinafter also referred to as “HDI”) has a linear structure, a small steric hindrance, and a high molecular symmetry. For this reason, when synthesizing a polyurethane resin using HDI, HDI molecules are likely to gather due to hydrogen bonds derived from urethane bonds. For this reason, in the polyurethane resin synthesized using HDI, hard segments including units derived from polyisocyanate are more localized. As a result, microphase separation of a sea-island structure in which hard segments exist in continuous soft segments tends to occur, and the flexibility of the polyurethane resin becomes very high. On the other hand, polyisocyanates other than HDI having a branched structure or a ring structure in the molecule have a large steric hindrance, and the molecules are difficult to hydrogen bond with each other. However, since many hard segments are present due to the interaction between the ring structures and the hydrophobic interaction, the strength of the polyurethane resin becomes very high. Therefore, by using HDI and other polyisocyanates in combination, a polyurethane resin having flexibility derived from HDI and strength derived from other polyisocyanates can be obtained. For this reason, it is possible to obtain an ink capable of recording an image having a higher level of marker resistance.

(Polyether polyol having no acid group)
The polyether polyol having no acid group preferably has a polystyrene-equivalent number average molecular weight (Mn) of 450 or more and 4,000 or less obtained by GPC. When the number average molecular weight (Mn) of the polyether polyol having no acid group is less than 450, the flexibility of the polyurethane resin may be weak with respect to the strength. On the other hand, when the number average molecular weight (Mn) of the polyether polyol having no acid group exceeds 4,000, the strength of the polyurethane resin may be weak against flexibility. In any case, the balance between strength and flexibility of the polyurethane resin is lost, and the marker resistance of the image is lowered. Moreover, it is preferable that the ratio (mass%) of the unit derived from the polyether polyol which does not have an acid group in a polyurethane resin is 0.1 to 80.0 mass%. In addition, you may synthesize | combine a polyurethane resin using the polyol which does not have acid groups other than polyether polyol with the polyether polyol which does not have an acid group. In this case, the ratio (mol%) of the unit derived from the polyether polyol having no acid group in the unit derived from the polyol having no acid group in the polyurethane resin is 80 mol% or more and 100 mol% or less. Preferably there is. It is preferable not to use castor oil-modified polyol from the viewpoint of ink ejection stability.

  Examples of polyether polyols include polyalkylene glycols and addition polymers of alkylene oxides with dihydric alcohols or trihydric or higher polyhydric alcohols. Examples of the polyalkylene glycol include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, poly (1,2-butylene glycol), poly (1,3-butylene glycol), and ethylene glycol-propylene glycol copolymer. be able to. Examples of the dihydric alcohol include hexamethylene glycol, tetramethylene glycol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 4,4-dihydroxyphenylpropane, 4,4-dihydroxyphenylmethane and the like can be mentioned. Examples of the trihydric or higher polyhydric alcohol include glycerin, trimethylolpropane, 1,2,5-hexanetriol, 1,2,6-hexanetriol, and pentaerythritol. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, α-olefin oxide, and the like. 1 type (s) or 2 or more types can be used for said polyether polyol as needed.

  In the present invention, the polyether polyol having no acid group is (i) polyethylene glycol, (ii) polypropylene glycol, (iii) poly (1,2-butylene glycol), and (iv) poly (1,3- It is preferably at least one selected from the group consisting of butylene glycol). The total proportion (mol%) of units derived from each of the above (i) to (iv) in the total amount of units derived from the polyether polyol in the polyurethane resin is preferably 80 mol% or more and 100 mol% or less. . Further, the polyether polyol having no acid group is more preferably polypropylene glycol. Moreover, it is preferable that the ratio (mass%) of the unit derived from the polyol which occupies for a polyurethane resin is 5.0 to 60.0 mass%.

(Diol having an acid group)
In the present invention, the “diol having an acid group” means a diol having an acid group such as a carboxyl group, a sulfonic acid group, or a phosphoric acid group. In the present invention, the diol having an acid group preferably has less than 10 carbon atoms. The diol having an acid group may be present in the form of an alkali metal salt such as Li, Na, or K, or an organic amine salt such as an ammonium salt or dimethylamine. In the present invention, it is preferable to use dimethylolpropionic acid and dimethylolbutanoic acid as the diol having an acid group. These diols having an acid group can be used alone or in combination of two or more as required. The proportion (% by mass) of units derived from the acid group-containing diol in the polyurethane resin is preferably 5.0% by mass or more and 40.0% by mass or less.

(Chain extender)
In the present invention, a chain extender may be used when a polyurethane resin is synthesized. The chain extender is a compound that reacts with residual isocyanate groups that have not formed urethane bonds among the polyisocyanate units of the urethane prepolymer. In this invention, it is preferable that the molar ratio of the urethane bond and urea bond in a polyurethane resin will be 85.0 / 15.0 or more and 100.0 / 0 or less. It is preferable to use a chain extender as appropriate so that the molar ratio of the urethane bond to the urea bond in the polyurethane resin satisfies the above range. Examples of the chain extender include, for example, trimethylolmelamine and derivatives thereof, dimethylolurea and derivatives thereof, dimethylolethylamine, diethanolmethylamine, dipropanolethylamine, dibutanolmethylamine, ethylenediamine, propylenediamine, diethylenetriamine, hexylenediamine, Examples thereof include polyamine compounds such as triethylenetetramine, tetraethylenepentamine, isophoronediamine, xylylenediamine, diphenylmethanediamine, hydrogenated diphenylmethanediamine, and hydrazine, polyamide polyamine, and polyethylene polyimine. Further, ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, Ethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol, 3-methyl-1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-cyclohexanediol 1,4-cyclohexanedimethanol, hydrogenated bisphenol A, glycerin, trimethylolpropane, pentaerythritol and the like. These chain extenders can use 1 type (s) or 2 or more types as needed.

(Crosslinking agent)
The polyurethane resin used in the ink of the present invention may be crosslinked with a crosslinking agent. Examples of the method for crosslinking the polyurethane resin include a method using a trifunctional or higher functional compound as the crosslinking agent as the polyisocyanate, polyol, or chain extender described above.

  The crosslinked polyurethane resin has more hard segments in the above-described microphase separation structure of the polyurethane resin. This is because, for example, when a trifunctional crosslinking agent is used, three urethane bonds are formed for one crosslinking agent. As a result, the strength becomes very strong. Furthermore, since the number of urethane bonds present in the vicinity increases, the number of hydrogen bonds between urethane bonds increases. As a result, since the hard segments are present in a more densely assembled form, microphase separation with a sea-island structure is likely to occur, and the flexibility of the polyurethane resin can be maintained high. Therefore, the cross-linked polyurethane resin has a very high strength and also has flexibility, so that the marker resistance of the image is further improved.

  Examples of the trifunctional or higher functional compound that can be used as the crosslinking agent include trifunctional or higher functional polyisocyanates, trifunctional or higher functional polyols, and trifunctional or higher functional chain extenders. A crosslinked polyurethane resin is obtained by synthesizing a polyurethane resin using at least one of these compounds. Examples of the trifunctional or higher functional polyisocyanate include polyisocyanurate type polyisocyanate, adduct type polyisocyanate, burette type polyisocyanate, and the like. Examples of the tri- or higher functional polyol include glycerin, trimethylolpropane, 1,2,5-hexanetriol, 1,2,6-hexanetriol, pentaerythritol, polyoxypropylenetriol, and glycol in the above polyether polyol. Examples include added compounds. Examples of the tri- or higher functional chain extender include trimethylolmelamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine and the like. Among these crosslinking agents, it is preferable to use at least one selected from the group consisting of glycerin, trimethylolpropane, pentaerythritol, and polyoxypropylenetriol.

(Characteristics of polyurethane resin)
The content (% by mass) of the polyurethane resin in the ink of the present invention is preferably 0.1% by mass or more and 10.0% by mass or less based on the total mass of the ink. If it is less than 0.1% by mass, the effect of improving the marker resistance of the image may not be sufficiently obtained. On the other hand, if it exceeds 10.0% by mass, polyurethane resin may adhere to the nozzle internal path of the recording head due to the influence of flexibility inherent to the polyurethane resin, and ink droplet ejection may become unstable. . The ink may further contain a resin other than the polyurethane resin as long as the effects of the present invention are not impaired.

  The weight average molecular weight (Mw) in terms of polystyrene obtained by GPC of the polyurethane resin used in the ink of the present invention is preferably 30,000 or more and 150,000 or less. When the weight average molecular weight (Mw) of the polyurethane resin is less than 30,000, the strength of the polyurethane resin is lowered, and the effect of improving the marker resistance of the image may not be sufficiently obtained. On the other hand, when the weight average molecular weight (Mw) of the polyurethane resin exceeds 150,000, the viscosity of the ink tends to increase, and the effect of improving the ejection stability of the ink may not be sufficiently obtained.

The acid value of the polyurethane resin used in the ink of the present invention, should Ru or less 40 mg KOH / g or more 140 mg KOH / g. The acid value of the polyurethane resin used in the ink of the present invention can be adjusted by the amount of units derived from a diol having an acid group.

(Polyurethane resin synthesis method)
The polyurethane resin used in the ink of the present invention can be synthesized by a generally used method. For example, a polyurethane resin can be synthesized by the following method. First, a polyisocyanate, a polyether polyol having no acid group, and an acid group-containing diol are reacted in an equivalent ratio such that an isocyanate group becomes excessive, in the presence or absence of an organic solvent having a boiling point of 100 ° C. or less. Let Thereby, a urethane prepolymer having an isocyanate group at the molecular end is obtained. Next, the acid group of the urethane prepolymer is neutralized using a neutralizing agent. And the urethane prepolymer which neutralized the acid group is thrown into water containing a crosslinking agent, and is made to react. Thereafter, when an organic solvent is contained in the system, the polyurethane resin can be obtained by removing the organic solvent.

(Method of analyzing polyurethane resin)
The composition, molecular weight, and acid value of the polyurethane resin contained in the ink can be analyzed by examining the sediment and supernatant of the centrifuged ink. Further, since the pigment is insoluble in the organic solvent, the polyurethane resin can be separated by solvent extraction. Furthermore, each analysis can be performed even in an ink state, but the analysis accuracy is further improved by using the extracted polyurethane resin. Specifically, the polyurethane resin can be separated by acid precipitation of the supernatant obtained by centrifuging the ink at 80,000 rpm and then drying.

(1) Composition of polyurethane resin The dried acid precipitate (polyurethane resin) is dissolved in deuterated dimethyl sulfoxide (deuterated DMSO) and analyzed by proton nuclear magnetic resonance ( ¹ H-NMR). Alternatively, the dried acid deposit (polyurethane resin) is analyzed by pyrolysis gas chromatography. Each type of polyisocyanate, polyether polyol having no acid group, and acid group-containing diol can be confirmed from the chemical shift of the obtained NMR chart and the analysis result of pyrolysis gas chromatography. Moreover, each composition ratio is computable from ratio of the peak integrated value of the chemical shift of a NMR chart.

(2) Measuring method of molar ratio of urethane bond and urea bond in polyurethane resin The molar ratio of urethane bond and urea bond in the polyurethane resin can be measured by the following method. First, an acid deposit of a polyurethane resin dissolved in heavy DMSO is analyzed by a carbon nuclear magnetic resonance method ( ¹³ C-NMR). Next, the molar ratio of the urethane bond and the urea bond can be determined from the ratio of the integrated values of the respective peaks of the urethane bond and the urea bond in the obtained NMR chart. However, the positions of the peaks of the urethane bond and the urea bond vary depending on the type of the compound (polyisocyanate, polyether polyol having no acid group, acid group-containing diol) which is a raw material of the polyurethane resin to be used. Therefore, it is necessary to examine the positions of the peaks of the urethane bond and the urea bond in the case where a compound that is a raw material of the polyurethane resin is used. The method is shown below.

First, compounds (polyisocyanate, polyether polyol having no acid group, and acid group-containing diol) as raw materials for the polyurethane resin are prepared. Next, (i) a reaction product of a polyisocyanate and a polyether polyol having no acid group, (ii) a reaction product of a polyisocyanate and an acid group-containing diol, and (iii) a reaction product of polyisocyanate and water, respectively. To do. And what dried these reaction materials is each melt | dissolved in heavy DMSO, and < ¹³ > C-NMR is measured. From the results of (i) and (ii), the position of the peak derived from the urethane bond of each reaction product can be confirmed. Further, from the result of (iii), the position of the peak derived from the urea bond can be confirmed. For example, when isophorone diisocyanate is used as the polyisocyanate, the peak of the urethane bond appears around 155 ppm and the peak of the urea bond appears around 158 ppm.

(3) Measuring method of acid value of polyurethane resin The whole acid value of the polyurethane resin can be measured by a titration method. In the examples described below, the polyurethane resin is dissolved in THF, and an acid difference is titrated with a potassium hydroxide ethanol titrant using an automatic potentiometric titrator (trade name “AT-510”, manufactured by Kyoto Electronics Industry Co., Ltd.). The value was measured.

(4) Method for measuring weight average molecular weight of polyurethane resin The weight average molecular weight of the polyurethane resin is measured by GPC. The measurement conditions of GPC in the present invention are as follows.
・ Device: Trade name “Alliance GPC 2695” (manufactured by Waters)
・ Column: Quadruple column of trade name “Shodex KF-806M” (manufactured by Showa Denko)
・ Mobile phase: THF (special grade)
・ Flow rate: 1.0 mL / min
・ Oven temperature: 40.0 ℃
-Sample solution injection volume: 0.1 mL
・ Detector: RI (refractive index)
Polystyrene standard samples: trade names “PS-1” and “PS-2” (both manufactured by Polymer Laboratories, molecular weights: 7,500,000, 2,560,000, 841,700, 377,400, 320,000) , 210,500, 148,000, 96,000, 59,500, 50,400, 28,500, 20,650, 10,850, 5,460, 2,930, 1,300, 580)

(5) Method for measuring number average molecular weight of polyether polyol having no acid group A polyurethane resin dissolved in heavy DMSO is measured by ¹³ C-NMR, and the number of repetitions of the polyether polyol having no acid group is calculated. From the calculated number of repetitions, the number average molecular weight of the polyether polyol having no acid group can be calculated.

<Polyoxyethylene alkyl ether having an HLB value of 14.5 or more>

  In order to more effectively suppress the deposition of the organic pigment decomposition product on the heater board, it is preferable to further include polyoxyethylene alkyl ether having an HLB value of 14.5 or more by the Griffin method in the ink. The present inventors presume the mechanism for obtaining such an effect as follows.

  The polyurethane resin used in the ink of the present invention has a hydrophilic portion including a unit derived from a polyether polyol having no acid group and a unit derived from an acid group-containing diol. The hydrophilic part of this polyurethane resin and the ethylene oxide group which is the hydrophilic group of the polyoxyethylene alkyl ether having an HLB value of 14.5 or more interact to adsorb the polyoxyethylene alkyl ether to the polyurethane resin. This is presumed to be a hydrogen bonding interaction. Moreover, since the ethylene oxide group of polyoxyethylene alkyl ether has a softness | flexibility, it is estimated that it can interact with a polyurethane resin more efficiently. Therefore, it is considered that the ink containing both the polyurethane resin and the polyoxyethylene alkyl ether has higher dispersion stability of the pigment decomposition product due to their interaction than the ink containing only the polyurethane resin. As a result, it is presumed that deposition of the pigment decomposition product on the heater board can be more efficiently suppressed.

  The upper limit of the HLB value is 20.0 as will be described later, and the upper limit of the HLB value of polyoxyethylene alkyl ether that can be used in the ink of the present invention is also 20.0. The HLB value by the Griffin method will be described later. Moreover, in order to obtain the deposit suppressing action more effectively, it is preferable to use polyurethane resin and polyoxyethylene alkyl ether in the following ratio. That is, the content (% by mass) of the polyoxyethylene alkyl ether in the ink is preferably 0.5 to 2.0 times the content (% by mass) of the polyurethane resin contained in the ink. . By setting the content of the polyoxyethylene alkyl ether within the above ratio, the polyurethane resin and the polyoxyethylene alkyl ether interact effectively, and the dispersion stability of the pigment decomposition product is increased. For this reason, it is estimated that the deposit suppression effect improves more. It was also confirmed that no change occurred in the marker resistance of the recorded image even when the polyurethane resin and the polyoxyethylene alkyl ether interacted.

  Next, the Griffin method will be described. The HLB value by the Griffin method is calculated by the following formula (1) from the formula weight of the hydrophilic group of the surfactant and the molecular weight of the surfactant. The HLB value indicates the degree of hydrophilicity or lipophilicity of the surfactant (compound) in the range of 0.0 to 20.0. The lower the HLB value, the higher the lipophilicity (hydrophobicity) of the compound. On the other hand, the higher the HLB value, the higher the hydrophilicity of the compound.

Polyoxyethylene alkyl ether has a structure represented by R—O— (CH ₂ CH ₂ O) _n H. In the formula, R represents a hydrocarbon group, and n represents an integer. Examples of the hydrocarbon group represented by R which is a hydrophobic group include a cetyl group, a lauryl group, a palmitoleyl group, an oleyl group, a linoleyl group, and a myristolyl group. In the present invention, polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, or polyoxyethylene cetyl ether is preferably used as the polyoxyethylene alkyl ether having an HLB value of 14.5 or more. Moreover, what is necessary is just to determine the number of ethylene oxide groups which are hydrophilic groups represented by n in the said formula from the relationship between the kind of R, and an HLB value. In the present invention, n is preferably 10 or more, more preferably 15 or more, and particularly preferably 40 or more. Further, n is preferably 100 or less, more preferably 80 or less, and particularly preferably 60 or less.

<Aqueous medium>
In the ink of the present invention, water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent can be used. The content (% by mass) of the water-soluble organic solvent in the ink is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the ink. As the water-soluble organic solvent, any conventionally used water-soluble organic solvent can be used. Examples of the water-soluble organic solvent include alkyl alcohols having 1 to 4 carbon atoms, amides, ketones, keto alcohols, ethers, polyalkylene glycols, glycols, and alkylene groups having 2 to 6 carbon atoms. Alkylene glycols, polyhydric alcohols, alkyl ether acetates, alkyl ethers of polyhydric alcohols, nitrogen-containing compounds, sulfur-containing compounds, and the like. These water-soluble organic solvents can be used alone or in combination of two or more as required. It is preferable to use deionized water (ion exchange water) as the 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. The ink viscosity at 25 ° C. is preferably 6 mPa · s or less. The viscosity of the ink can be adjusted, for example, by changing the configuration and content of the aqueous medium. If the viscosity of the ink at 25 ° C. is larger than 6 mPa · s, the ink ejection stability may not be sufficiently improved.

<Acrylic resin>
The ink of the present invention may contain an acrylic resin as a resin other than the polyurethane resin. In the present invention, the “acrylic resin” is a polymer using (meth) acrylic acid or (meth) acrylic acid alkyl ester as a monomer. In this specification, “(meth) acrylic acid” and “(meth) acrylate” refer to “acrylic acid, methacrylic acid” and “acrylate, methacrylate”, respectively. In the present invention, it may be a copolymer of (meth) acrylic acid or (meth) acrylic acid alkyl ester and other monomers. As the other monomer copolymerized with (meth) acrylic acid or (meth) acrylic acid alkyl ester, any known monomers can be used. Among them, α, β-ethylenically unsaturated compounds having an aryl group such as styrene, α-methylstyrene, phenyl vinyl acetate, benzyl (meth) acrylate, and 2-phenoxyethyl (meth) acrylate are preferable. When the acrylic resin is a copolymer, it may be a random copolymer or a block copolymer. In the present invention, it is more preferable to use a copolymer of (meth) acrylic acid, (meth) acrylic acid alkyl ester, and styrene.

  In this invention, it is preferable that the polystyrene equivalent weight average molecular weights (Mw) obtained by GPC of an acrylic resin are 3,000 or more and 10,000 or less. The weight average molecular weight of the acrylic resin was measured by the same method as the acid value of the polyurethane resin. The content (% by mass) of the acrylic resin is preferably 0.5% by mass or more and 3.0% by mass or less based on the total mass of the ink. Furthermore, it is more preferable that it is 1.0 mass% or more and 2.4 mass% or less. The total content (% by mass) of all the resins in the ink is preferably 0.01% by mass or more and 10.00% by mass or less based on the total mass of the ink. Further, the content (mass%) of the acrylic resin in the ink is 0.5 times or more and 2.0 times or less in mass ratio with respect to the content (mass%) based on the total mass of the polyurethane resin ink. Preferably there is.

<Other additives>
In addition to the above-described components, the ink of the present invention includes water-soluble organic compounds that are solid at room temperature, such as polyhydric alcohols such as trimethylolpropane and trimethylolethane, and urea derivatives such as urea and ethyleneurea. A compound may be contained. Furthermore, in the ink of the present invention, a resin other than the polyurethane resin, a surfactant, a pH adjuster, a rust inhibitor, an antiseptic, an antifungal agent, an antioxidant, an anti-reduction agent, and an evaporation accelerator are added as necessary. Various additives such as an agent and a chelating agent may be contained.

[ink cartridge]
The ink cartridge of the present invention includes an ink and an ink storage unit that stores the ink, and the ink stored in the ink storage unit is the ink of the present invention described above. As for the structure of the ink cartridge, the ink storage portion includes an ink storage chamber that stores liquid ink and a negative pressure generation member storage chamber that stores a negative pressure generation member that holds the ink therein by a negative pressure. Things can be mentioned. Alternatively, the ink cartridge may be an ink container that does not have an ink storage chamber for storing liquid ink and is configured to hold the entire storage capacity by a negative pressure generating member. Further, the ink cartridge may be configured to have an ink storage portion and a recording head.

[Inkjet recording method]
In the inkjet recording method of the present invention, the ink used in the inkjet recording method of ejecting ink from a recording head by the action of thermal energy and recording an image on a recording medium is the ink of the present invention described above. Features. In the “recording” in the present invention, in addition to a mode of recording on a recording medium such as glossy paper or plain paper, a mode of recording on a non-liquid-absorbing substrate such as glass, plastic, or film. Is also included. Among these, when recording is performed on plain paper using the ink of the present invention, the effect of the present invention is particularly exerted, which is preferable.

Hereinafter, the present invention will be described in more detail using Examples and Comparative Examples. The present invention is not limited in any way by the following examples as long as the gist thereof is not exceeded. In the description of the following examples, “part” and “%” are based on mass unless otherwise specified. Abbreviations in the specification and tables are as follows.
IPDI: isophorone diisocyanate HDI: hexamethylene diisocyanate MDI: dicyclohexylmethane diisocyanate PPG: polypropylene glycol PEG: polyethylene glycol PC: polycarbonate diol PES: polyester polyol DMPA: dimethylolpropionic acid DMBA: dimethylolbutanoic acid EDA: ethylenediamine PR122: pigment red 122
PB15: 3: Pigment Blue 15: 3
C. B. :Carbon black

<Preparation of polyurethane (PU) resin dispersion>
A four-necked flask equipped with a thermometer, a stirrer, a nitrogen introduction tube, and a reflux tube, polyisocyanate (part A and part B), polyol (part C), diol having an acid group (part D), and methyl ethyl ketone (300 parts) was charged and reacted at 80 ° C. for 6 hours in a nitrogen gas atmosphere. Thereafter, a crosslinking agent (E part) was added and reacted at 80 ° C. After the reaction, the reaction mixture was cooled to 40 ° C., ion-exchanged water was added, and an aqueous potassium hydroxide solution was added while stirring at high speed with a homomixer. The obtained solution is heated and reduced in pressure to distill off methyl ethyl ketone, and the polyurethane resin dispersion PU-1 to the resin content is 20% and the weight average molecular weight of the resin is 30,000 to 150,000. 12 was obtained. Table 1 shows the preparation conditions and material properties of the polyurethane (PU) resin dispersion.

<Preparation of pigment dispersion>
(Pigment dispersion 1)
A pigment dispersion was prepared as described below with reference to the method described in Patent Document 1.
To dilute hydrochloric acid prepared by dissolving 5 g of concentrated hydrochloric acid in 5.5 g of water, 1.1 g of p-aminobenzoic acid was added at 5 ° C. This was stirred while being cooled in an ice bath, and an aqueous sodium nitrite solution obtained by dissolving 1.2 g of sodium nitrite in 9 g of water at 5 ° C. was further added in a state where the temperature was constantly kept at 10 ° C. or lower. After stirring for 15 minutes, 6 g of Pigment Red 122 having a specific surface area of 130 m ² / g was further added in a mixed state. Thereafter, the mixture was further stirred for 15 minutes to obtain a slurry. The obtained slurry was ultrafiltered, and then filtered with a trade name “Toyo Filter Paper No. 2” (manufactured by Advantis). The pigment particles were sufficiently washed with water and dried in an oven at 110 ° C. to obtain a self-dispersing organic pigment A having a —C ₆ H ₄ —COONa group introduced on the surface of Pigment Red 122. Water was added to the obtained self-dispersing organic pigment A to prepare a pigment dispersion 1 having a pigment content of 10%. The surface charge amount of the self-dispersing organic pigment A contained in the prepared pigment dispersion 1 was measured and found to be 1.0 μmol / m ² . The method for measuring the surface charge is shown below.

  Using a potentiometric titration apparatus (trade name “AT-510”) and a flow potential titration unit (trade name “PCD-500”) manufactured by Kyoto Denshi Kogyo Co., Ltd. by self-potential titration using methylene glycol chitosan as a titration reagent. The surface charge of the dispersed organic pigment was measured.

(Pigment dispersions 2, 3, 6 and 7)
Except that the amounts of p-aminobenzoic acid and sodium nitrite were appropriately changed, the same procedures as in the case of preparing the pigment dispersion 1, followed by pigment dispersions 2, 3, 6, And 7 were prepared. The surface charge amount of the self-dispersing organic pigment contained in the pigment dispersion 2 was 0.5 μmol / m ² . The surface charge amount of the self-dispersing organic pigment contained in the pigment dispersion 3 was 1.5 μmol / m ² . The surface charge amount of the self-dispersing organic pigment contained in the pigment dispersion 6 was 0.4 μmol / m ² . Further, the surface charge amount of the self-dispersing organic pigment contained in the pigment dispersion liquid 7 was 1.6 μmol / m ² .

(Pigment dispersion 4)
A self-dispersing organic pigment having a surface charge of 1.0 μmol / m ^{2 according to} the same procedure as that for preparing the pigment dispersion 1 except that Pigment Blue 15: 3 having a specific surface area of 90 m ² / g was used. A pigment dispersion 4 containing 10% of the pigment was obtained.

(Pigment dispersion 5)
Except that the amount of p-aminobenzoic acid and p-aminobenzenesulfonic acid was 1.2 g, and the amount of sodium nitrite was 2.0 g, the same procedure as in the case of preparing the pigment dispersion 1, A pigment dispersion 5 having a pigment content of 10% was prepared. The surface charge amount of the self-dispersing organic pigment contained in the pigment dispersion 5 was 0.5 μmol / m ² .

(Pigment dispersion 8)
A trade name “Cab-O-Jet300” (manufactured by Cabot) (surface charge amount is 0.5 μmol / m ² ), which is commercially available as a self-dispersing carbon black having a hydrophilic group bonded to the surface of carbon black, was prepared. . This was diluted with water and sufficiently stirred to obtain a pigment dispersion 8 having a pigment content of 10%.

(Pigment dispersion 9)
300 g of Pigment Red 122 having a specific surface area of 130 m ² / g, 45 g of aminophenyl (2-sulfoethyl) sulfone, and 900 g of distilled water were placed in a reactor, and the mixture was stirred at a temperature of 55 ° C. and a rotation speed of 300 rpm for 20 minutes. Thereafter, 40 g of 25% aqueous sodium nitrite solution was added dropwise over 15 minutes, 50 g of distilled water was further added, and the mixture was reacted at 60 ° C. for 2 hours to obtain a reaction product. The obtained reaction product was taken out while being diluted with distilled water, and adjusted so that the solid content was 15.0%. Centrifugation treatment and purification treatment were performed to remove impurities to obtain a dispersion (1). Pigment Red 122 in the dispersion (1) was in a state in which the functional group of aminophenyl (2-sulfoethyl) sulfone was bonded to the surface thereof. The number of moles of the functional group bonded to Pigment Red 122 in the obtained dispersion (1) is determined by measuring the concentration of sodium ions, which are counter ions of the functional group bonded to Pigment Red 122, using a probe-type sodium electrode. Was determined by

  The dispersion (1) was dropped into a pentaethylenehexamine solution kept at room temperature with vigorous stirring over 1 hour to obtain a mixture. The amount (mol) of pentaethylenehexamine was 1 to 10 times the mol number of sodium ions measured previously. The amount of the pentaethylenehexamine solution was the same as that of the dispersion (1). The resulting mixture was stirred for 18 to 48 hours and then purified to obtain a dispersion (2) having a solid content of 10.0%. Pigment Red 122 in the obtained dispersion (2) was in a state in which pentaethylenehexamine was bonded to the surface thereof.

  190 g of a styrene-acrylic acid copolymer having a weight average molecular weight of 8,000, an acid value of 140 mgKOH / g, and a polydispersity Mw / Mn (weight average molecular weight Mw, number average molecular weight Mn) of 1.5 was weighed. . To this styrene-acrylic acid copolymer, 1,800 g of distilled water and potassium hydroxide necessary to neutralize the resin were added and stirred to prepare an aqueous styrene-acrylic acid copolymer solution. Next, while stirring the prepared styrene-acrylic acid copolymer aqueous solution, 500 g of the dispersion (2) was added dropwise to obtain a mixture. The obtained mixture was transferred to an evaporating dish and heated at 150 ° C. for 15 hours to dry, and then the obtained dried product was cooled to room temperature. The obtained dried product was added to an aqueous potassium hydroxide solution having a pH of 9.0 and dispersed using a disperser. Under stirring, a 1.0 mol / L potassium hydroxide aqueous solution was added to adjust the pH to 10 to 11. Thereafter, desalting treatment and purification treatment were performed to remove impurities and coarse particles, and a pigment dispersion 9 in which the resin-bound organic pigment (Pigment Red 122) was dispersed in water was obtained. In the obtained pigment dispersion 9, the content of the resin-bound organic pigment (the total content of the pigment and the resin) was 10%, and the pH was 10.1.

(Pigment dispersion 10)
A styrene-acrylic acid copolymer having an acid value of 200 mg KOH / g and a weight average molecular weight of 10,000 was neutralized using a 10% aqueous potassium hydroxide solution. And 10 parts of pigment red 122 whose specific surface area is 130 m < ² > / g, 20 parts of neutralized styrene-acrylic acid copolymer (solid content), and 70 parts of water were mixed. After the mixture obtained using a sand grinder was dispersed for 1 hour, centrifugal separation was performed to remove coarse particles, and pressure filtration was performed with a micro filter (manufactured by Fuji Film) having a pore size of 3.0 μm. By the above method, the pigment dispersion liquid 10 in a state where the organic pigment (Pigment Red 122) was dispersed in water with a resin was obtained. The pigment dispersion 10 thus obtained had a pigment content of 10%, a resin content of 20%, and a pH of 10.0.

<Preparation of ink>
(Example 1 8,10～ 20, Comparative Examples 1 to 6, and Reference Examples 1 to 5)
The pigment dispersion and PU resin dispersion obtained above were mixed with the following components in the combinations shown in Table 2, and sufficiently stirred and dispersed. Then, pressure filtration was performed with a micro filter (manufactured by Fuji Film) having a pore size of 3.0 μm to prepare inks of Examples 1 to 8 , 10 to 20, Comparative Examples 1 to 6, and Reference Examples 1 to 5. .
・ Pigment dispersion (pigment content 10%) 30.0%
・ PU resin dispersion (resin content: 20%) See Table 2. ・ Polyoxyethylene alkyl ether (detailed later) See Table 2. ・ Glycerin 7.0%
・ 2-pyrrolidone 5.0%
・ Tetraethylene glycol 5.0%
・ Surfactant (trade name “acetylenol E100”, manufactured by Kawaken Fine Chemicals)
0.5%
-Ion-exchanged water balance The balance of ion-exchanged water is such that the total of all components constituting the ink is 100.0%. Moreover, only the Example 14 and the reference example 1 added the following component as an addition resin.
・ Acrylic resin (Brand name "Joncry 683", manufactured by BASF, solid content 20%)
6.0%

The acrylic resin was used in the state of an aqueous solution neutralized with potassium hydroxide. Moreover, the following product (HLB value by Griffin method) made by Nikko Chemicals was used as the polyoxyethylene alkyl ether. Further, Table 2 shows the mass ratio of pigment solids and polyurethane resin solids contained in the ink.
-NIKKOL BC15 which is polyoxyethylene cetyl ether (HLB value 14.6)
-NIKKOL BC20 which is polyoxyethylene cetyl ether (HLB value 15.7)
-NIKKOL BO15 which is polyoxyethylene oleyl ether (HLB value 14.2)
-NIKKOL BO50 which is polyoxyethylene oleyl ether (HLB value 17.8)

(Comparative Example 7)
The ink of Comparative Example 7 was prepared according to the method described below with reference to the description of Example 1 of Patent Document 2 (Japanese Patent Publication No. 2005-515289). Self-dispersing carbon black 6.5 parts, polyurethane resin 1.6 parts, glycerin 9.5 parts, ethylene glycol 6 parts, trade name "Surfinol 465" (manufactured by Air Products and Chemicals) 0.8 part, and 75.6 parts of water were mixed. Thus, an ink of Comparative Example 7 was prepared. The self-dispersing carbon black used was surface-treated by ozone oxidation produced according to the description of WO 01/94476. The polyurethane resin used was 0.1 part of a polyurethane resin dispersion (trade name “Hybridur 580”) and 1.5 parts of a polyurethane resin dispersion (trade name “Mace 85-302-1”). “Hybridur 580” is a trade name of a polyurethane resin dispersion manufactured by Air Products and Chemicals. “Mace 85-302-1” is a trade name of a polyurethane resin dispersion manufactured by Mace Adhesive & Coatings.

(Comparative Example 8)
With reference to the description in Example 1 of Patent Document 3 (Japanese Patent Application Laid-Open No. 2008-179657), an ink of Comparative Example 8 was prepared according to the following method. In a four-necked flask, 95 g of a trade name “Placcel 205BA” (manufactured by Daicel Chemical Industries), 11 g of trimethylolpropane, 120 g of methyl ethyl ketone, and 0.54 g of 1,4-diazabicyclo [2.2.2] octane were charged. The four-necked flask is provided with a thermometer, a stirrer, a nitrogen introduction tube, and a cooling tube. “Placcel 205BA” is a trade name of a carboxylic acid-modified polycaprolactone diol obtained by lactone-modifying dimethylolbutanoic acid. After stirring for 30 minutes, 74 g of isophorone diisocyanate was further added and stirred at room temperature for 1 hour in a nitrogen atmosphere. Then, it heated up at 70 degreeC and reacted for 4 hours. After the reaction, the mixture was cooled to room temperature to obtain a urethane prepolymer solution having a concentration of 60%. Furthermore, 17.1 g of 50% potassium hydroxide aqueous solution and 350 g of ion-exchanged water were added, and the mixture was stirred at room temperature for 30 minutes together with 250 g of the urethane prepolymer solution. After raising the temperature to 80 ° C. in a nitrogen atmosphere, a chain extension reaction was performed for 2 hours. After the reaction, methyl ethyl ketone and a part of water are removed using a rotary evaporator and an aspirator, and then ion-exchanged water is added so that the recovered amount is 429 g to obtain a polyurethane resin dispersion (A) having a polyurethane concentration of 35%. It was. The acid value of the polyurethane resin contained in the obtained polyurethane resin dispersion (A) was 70 mgKOH / g, and the weight average molecular weight was 47,000.

  3 kg of carbon black (trade name “MA-100”, manufactured by Mitsubishi Chemical) was mixed with 10 kg of water, and then added to 4.5 kg of a sodium hypochlorite solution (effective chlorine concentration 12%). After stirring for 10 hours at 100-105 ° C., the resulting product was filtered. The wet crystals obtained by drying were washed with water and then dried at 80 ° C. to obtain 2.5 kg of oxidized carbon black. The obtained oxidized carbon black and ion-exchanged water were mixed to prepare a slurry. The prepared slurry was dialyzed using a polymethyl methacrylate dialysis module (trade name “FILTRIZER B3-20A”, manufactured by Toray Industries, Inc.). Then, it dried and the sodium ion and chlorine ion in oxidation treatment carbon black were removed, and the oxidation treatment carbon black dialyzed material was obtained. 120 g of the resulting oxidized carbon black dialyzate, 180 g of triethylene glycol monobutyl ether, and 700 g of ion-exchanged water were mixed and stirred using a homodisper to prepare a slurry. A beaker containing the prepared slurry was connected to a circulating bead mill disperser (trade name “Dynomill KDL-A”, manufactured by Willy et Bacofen) with a tube. A zirconia bead having a diameter of 0.3 mm was used as a medium, and the dispersion treatment was continued at 1,600 rpm for 3 hours to obtain an aqueous black pigment dispersion. To 41.7 g of the obtained aqueous black pigment dispersion, 0.7 g of 50% potassium hydroxide aqueous solution, 0.5 g of ion-exchanged water, and 7.1 g of polyurethane resin dispersion (A) were added, and the aqueous black pigment dispersion was added. Obtained. The resulting aqueous black pigment dispersion had a pigment content of 10% and a polyurethane resin content of 5%. Next, 25.8 g of ion-exchanged water, 3.5 g of glycerol, 1.7 g of 2-pyrrolidone, and 1.5 g of ethylene glycol were added to 17.5 g of the obtained aqueous black pigment dispersion to prepare an ink of Comparative Example 8. did.

<Evaluation>
Each of the following evaluations was performed using a modified machine in which an inkjet recording apparatus (trade name “PIXUS iP3100”, manufactured by Canon Inc.) was modified so that the moving speed of the carriage was 40 inches / second. The recording conditions were: temperature: 23 ° C., relative humidity: 55%, discharge amount per drop: 28 ng (within ± 10%). In the above-described ink jet recording apparatus, an image recorded under a condition in which one droplet of about 28 ng of ink is applied to a unit area of 1/600 inch × 1/600 inch with a resolution of 600 dpi × 600 dpi has a recording duty of 100%. Is defined as

(Discharge stability)
Each ink obtained above was filled in an ink cartridge and mounted on the ink jet recording apparatus. Then, an image of vertical ruled lines formed of 4 dots was recorded on PPC paper GF-500 (manufactured by Canon) (image before the ejection test). Then, 10 solid images of 19 cm × 26 cm (images with a recording duty of 100%) were recorded, and then images of vertical ruled lines formed of 4 dots were recorded (images after the first ejection test). Further, after performing the same ejection test, an image of vertical ruled lines formed by 4 dots was recorded (image after the second ejection test). For the images before and after the first ejection test, the irradiance values of the vertical ruled lines were measured using a personal image quality evaluation system PersonalIAS (manufactured by Quality Engineering Associates). Furthermore, the ejection stability of the ink was evaluated by visually confirming the image of the vertical ruled lines. In addition, it is evaluated that the smaller the difference between the ruggedness values of the vertical ruled lines before and after the ejection test, the higher the ink ejection stability. The evaluation criteria for ink ejection stability are as follows. In the evaluation of ink ejection stability, 1 and 2 were acceptable levels and 3 to 5 were unacceptable levels in the following evaluation criteria. The evaluation results are shown in Table 3.
1: The difference in the ruggedness value before and after the ejection test was less than 2, and there was no change in the image of the vertical ruled lines.
2: The difference in the radiance value before and after the ejection test was 2 or more and less than 4, and the change in the image of the vertical ruled line was not so large as to be confirmed.
3: The difference in the ruggedness value before and after the ejection test was 4 or more and less than 6, and a slight change was observed in the image of the vertical ruled line.
4: The difference in the ruggedness value before and after the ejection test was 6 or more, and a clear change was observed in the image of the vertical ruled line.
5: White streaks and blurring were observed in the solid image during the ejection test.

(Marker resistance of the image)
Each ink obtained above was filled in an ink cartridge and mounted on the ink jet recording apparatus. A vertical ruled line having a thickness of 1/10 inch was recorded on PPC paper (trade name “GF-500”, manufactured by Canon Inc.). After marking with a yellow line marker (trade name “OPTEX2”, made by Zebra) on the vertical ruled line portion on the obtained recorded matter, immediately marking on the white background portion on the recorded matter, contamination of the marker nib and white background The marking on the part was confirmed to be dirty. This operation was performed 5 minutes and 1 day after recording. The evaluation criteria for marker resistance are shown below. In the evaluation of marker resistance of an image, in the following evaluation criteria, 1 to 3 are acceptable levels, and 4 and 5 are unacceptable levels. The evaluation results are shown in Table 3.
1: After 5 minutes and after 1 day, the pen tip of the marker was not contaminated, and no stain was generated even when marking on a white background.
2: After 5 minutes, the marker nib was contaminated, but even when marking on the white background, there was little contamination. Furthermore, the pen tip of the marker was not contaminated after one day, and no stain was generated even when marking on the white background.
3: The marker nib was contaminated both after 5 minutes and after 1 day. However, even when marking was performed on the white background portion, the stain was hardly generated.
The marker nib was contaminated after 4: 5 minutes, but the level of dirt was not noticeable even when marking on the white background. Furthermore, although the marker nib was contaminated after one day, there was almost no stain even when marking on the white background.
5: After 5 minutes and 1 day, the marker nib was contaminated, and stains occurred when marking on the white background.

Claims (9)

A water-based ink used in an ink jet recording method for ejecting ink from a recording head by the action of thermal energy and recording an image on a recording medium,
C. I. Pigment red 122 and C.I. I · Pigment Blue 15: contains 3 self-dispersing organic pigment and polyurethane resin hydrophilic group is bonded through at least one of organic pigments phenylene group on the particle surfaces of,
The hydrophilic group is, -COOM and -SO ₃ M ( "M" is a hydrogen atom, an alkali metal, ammonium or organic ammonium) is at least one of,
The surface charge amount of the self-dispersing organic pigment is at 0.5 [mu] mol / m ² or more 1.5μmol / m ² or less,
The polyurethane resin has a unit derived from a polyisocyanate, a unit derived from a polyether polyol having no acid group, and a unit derived from a diol having an acid group, and the acid value of the polyurethane resin is 40 mgKOH / g or more. An ink having 140 mgKOH / g or less.   The ink according to claim 1, wherein the content (% by mass) of the polyurethane resin is 0.1% by mass or more and 10.0% by mass or less based on the total mass of the ink.   3. The ink according to claim 1, wherein the content of the polyurethane resin is 0.05 to 2.0 times in terms of mass ratio with respect to the content of the self-dispersing organic pigment.   The ink according to any one of claims 1 to 3, wherein the polyether polyol having no acid group contains polypropylene glycol.   The ink according to any one of claims 1 to 4, further comprising a polyoxyethylene alkyl ether having an HLB value of 14.5 or more according to the Griffin method.   The ink according to claim 5, wherein a content (% by mass) of the polyoxyethylene alkyl ether is 0.5 times or more and 2.0 times or less with respect to a content (% by mass) of the polyurethane resin.   The ink according to any one of claims 1 to 6, wherein the polyisocyanate contains hexamethylene diisocyanate. An ink cartridge comprising ink and an ink containing portion for containing the ink,
The ink cartridge according to claim 1, wherein the ink is the ink according to claim 1. An ink jet recording method for recording an image on a recording medium by discharging ink from a recording head by the action of thermal energy,
An ink jet recording method, wherein the ink is the ink according to claim 1.