Coating liquid for printing medium, ink for inkjet, imaging method, set of coating liquid for printing medium and ink for inkjet and inkjet recording device

The present invention relates to a coating liquid for a print medium for applying a coating liquid for a print medium to a part or the entire surface of a print medium before or after an image is formed on at least a part of the print medium by an inkjet recording method or the like. Is. The present invention also relates to an inkjet ink used in an inkjet recording method for ejecting ink to record an image. The present invention also relates to an image forming method for forming an image using the coating liquid for a print medium and the ink for an inkjet. Furthermore, the present invention relates to a set of the coating liquid for a print medium and the ink for an inkjet. Furthermore, the present invention relates to an inkjet recording apparatus equipped with a set of the coating liquid for a print medium and an ink for inkjet.

The inkjet recording method is a method of recording images, characters, etc. by flying minute droplets of ink and adhering them to a print medium (paper, etc.) based on various operating principles. It has features such as ease, high flexibility of recording patterns, and no need for development and fixing, and is rapidly becoming widespread in various applications. However, when plain paper is used as the print medium, curl phenomena such as warping and curling of the paper may occur. This curl phenomenon is largely due to the addition of water. That is, it is known that the curl phenomenon occurs remarkably when the area to which water is applied is large and when the amount of water applied is large.

Conventionally, several methods have been proposed as methods for alleviating and suppressing curl. For example, an inkjet ink containing a solid substance having four or more hydroxyl groups in its molecular structure and being soluble in water or an aqueous organic solvent has been proposed (see, for example, Patent Document 1). Further, inks containing sugars, sugar alcohols, and specific amide compounds have been proposed as curl inhibitors (see, for example, Patent Documents 2 to 5). Further, an ink containing a combination of a specific polyhydric alcohol and glycerin has been proposed (see, for example, Patent Document 6). Further, inks containing a solvent, a polymer binder, a medium dye, a water-soluble curl-preventing compound, a water-soluble degluing compound, a light-resistant compound, an antifoaming agent and the like have been proposed (see, for example, Patent Document 7).

Further, as a means for forming an image by using the inkjet recording method, a liquid (coating liquid) for making an image good is prepared in addition to the usual inkjet ink as described above, and the liquid is used as an ink. Various methods have been proposed for forming an image by adhering the ink on a print medium prior to the injection of the ink. For example, by applying a liquid composition containing polyvalent metal ions to a printing medium in advance and then printing an ink reactive with the liquid composition, image characteristics such as image uniformity and image density can be improved. A recording method (hereinafter referred to as a two-component system) has been proposed (see, for example, Patent Documents 8 to 10).<patcit num="1"><text>Japanese Unexamined Patent Publication No. 4-332775</text></patcit><patcit num="2"><text>Japanese Patent Application Laid-Open No. 6-157955</text></patcit><patcit num="3"><text>Japanese Unexamined Patent Publication No. 6-240189</text></patcit><patcit num="4"><text>Japanese Unexamined Patent Publication No. 9-16539</text></patcit><patcit num="5"><text>Japanese Unexamined Patent Publication No. 9-176538</text></patcit><patcit num="6"><text>Japanese Unexamined Patent Publication No. 10-130550</text></patcit><patcit num="7"><text>Japanese Unexamined Patent Publication No. 2000-19826</text></patcit><patcit num="8"><text>Japanese Unexamined Patent Publication No. 9-234943</text></patcit><patcit num="9"><text>Japanese Unexamined Patent Publication No. 11-115303</text></patcit><patcit num="10"><text>Japanese Unexamined Patent Publication No. 2000-94825</text></patcit>

<p> Curling can be suppressed to some extent by incorporating a conventional curl-preventing compound in the ink. However, in recent years when high-speed printing and high image quality are required, there is a demand for a coating liquid or ink which can improve ejection stability and reliability and more effectively alleviate and suppress the curl phenomenon. In particular, in a system in which a print medium is conveyed in a recording device after the print medium coating liquid is applied to the entire surface of the print medium and then ink is applied, the ink is applied to the print medium to which the print medium coating liquid is applied. The print medium may be curled during the transfer until the process is completed, which may cause a transfer defect, and it has been a big problem to suppress the curl more than before.</p><p> Therefore, an object of the present invention is to provide a coating liquid for a print medium capable of alleviating and suppressing curl generated when a water-soluble component is applied to a print medium.</p><p> Another object of the present invention is to sufficiently suppress curl generated by leaving the product printed on plain paper using inkjet ink, and further, in an environment of normal temperature and humidity, the printing / writing portion is disturbed at the start of printing. It is an object of the present invention to provide an ink jet ink having excellent ejection stability, which is said to prevent fading and the like.</p><p> Further, another object of the present invention is to provide a coating liquid that achieves both a curl suppressing effect when the coating liquid for a print medium contains polyvalent metal ions and storage stability as a coating liquid for a print medium. is there.</p><p> Further, another object of the present invention is to suppress curl of a recorded material obtained by a two-component system that forms an image using a set of a coating liquid for a print medium and an ink for an inkjet.</p>

<p> The above object is achieved by the following invention. That is, the coating liquid for a printing medium of the present invention is a coating liquid for a printing medium containing water and a water-soluble organic compound having water retention, and the water-soluble organic compound has a temperature of 23 ° C. and a humidity of 45%. It is composed only of water-soluble organic compounds having a difference of 36% or less between the water-retaining power in the environment and the water-retaining power in an environment with a temperature of 30 ° C and a humidity of 80%, and the content of the water-soluble organic compound is It is characterized in that it is 15% by mass or more with respect to the total amount of the coating liquid for a print medium.</p><p> The inkjet ink of the present invention is an inkjet ink containing a coloring material, water, and a water-retaining water-soluble organic compound, and the water-soluble organic compound is in an environment where the temperature is 23 ° C and the humidity is 45%. Consists of only water-soluble organic compounds with a difference of 36% or less between the water-retaining power in the environment and the water-retaining power in an environment of temperature 30 ° C and humidity 80%, and the content of the water-soluble organic compound is inkjet. It is characterized in that it is 15% by mass or more with respect to the total amount of ink for use.</p><p> Further, the coating liquid for a print medium of the present invention is a coating liquid for a print medium used in combination with an ink. Further, the print medium coating liquid and the inkjet ink of the present invention are a step of applying an ink containing a coloring material in a dissolved state or a dispersed state to the print medium, and applying the print medium coating liquid to the print medium. It is characterized by being a coating liquid for a print medium and an ink for an inkjet used in an image forming method having a step.</p><p> Further, the image forming method of the present invention is an image forming method including a step of applying ink to a print medium and a step of applying a coating liquid for a print medium to the print medium, and the ink is used for inkjet as described above. It is an ink, and the coating liquid for a print medium is the coating liquid for a print medium described above.</p><p> Further, as another embodiment of the present invention, a set of the coating liquid for a print medium of the present invention and the ink for inkjet of the present invention can be mentioned.</p><p> Furthermore, as another embodiment of the present invention, there is an inkjet recording apparatus using the coating liquid for a print medium of the present invention and the inkjet ink of the present invention.</p><p> In order to more effectively suppress curl after applying ink, it is preferable that the coating liquid for print media contains multivalent metal ions. Further, it is more preferable that the ink for inkjet and the coating liquid for print media satisfy the following conditions.</p><p> (Conditions) The maximum absorption wavelength in the visible region after mixing 50 g of the 800-fold diluted aqueous solution of the coating solution for print media and 0.3 g of the 5-fold diluted aqueous solution of the ink and filtering with a 0.2 μm filter after 15 minutes ( When carbon black is used as the coloring material, the absorbance at (wavelength 550 nm) is (A), and the absorbance at the maximum absorption wavelength in the visible region of a mixture of 0.3 g of a 5-fold diluted aqueous solution of the inkjet ink and 50 g of pure water. When (B), (A) and (B) satisfy the following relationship. (A) / (B) &lt;0.85 However, when the coating liquid for print media contains polyvalent metal ions, the coating liquid for print media changes due to storage, and high optical density cannot be obtained, or the initial stage. The image quality obtained after a lapse of time may differ. Therefore, when the coating liquid for a print medium contains a polyvalent metal ion, it is more preferable to contain a conjugate base of a strong acid and a conjugate base of a weak acid that acts as a buffer against a change in hydrogen ion concentration.</p>

<p> According to the present invention, a coating liquid for a print medium capable of suppressing the generation of curl by applying to a print medium can be obtained. Further, with respect to inkjet recording, curl can be sufficiently controlled, and printed matter on plain paper can be made easy to handle. In addition, an inkjet ink can be obtained in which recording stability can be obtained at the same time in the inkjet recording method. Further, even in a two-component system in which a print medium to which a coating liquid for a print medium is applied is conveyed in a recording device and then ink is applied, it is possible to prevent a transfer failure of the print medium to which the coating solution for a print medium is applied. Further, it becomes possible to sufficiently suppress curl after applying ink. Further, even when the coating liquid for a print medium contains multivalent metal ions, the coating liquid for a print medium is provided which has excellent storage stability and has no problem in contact with equipment members. Will be done. That is, even when the coating liquid for print media is stored for a long period of time, high-quality image quality with high density and high color development can be stably obtained with print media such as plain paper without strike-through of the coloring material on the back side of the print. Be done.</p>

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments.

[Water-retaining water-soluble organic compound]

Since the curl after applying a liquid medium containing water to plain paper is considered to have some correlation with the evaporation of water applied to the plain paper, the present inventors usually apply it to inkjet inks and coating liquids. The following detailed studies were conducted on the water retention capacity of commonly used water-soluble organic compounds.

First, 20% by mass aqueous solutions of various water-soluble organic compounds were prepared, 10 g each of them was precisely weighed in a glass petri dish, and left in an environment with a temperature of 23 ° C and a humidity of 45%. At the same time, pure water containing no water-soluble organic compound was also left in the same manner. As the water evaporates, the amount of solution in the petri dish decreases, and the mass eventually becomes constant. Since all of the pure water has evaporated at this point in the pure water-only chalet left at the same time, what remains in the chalet containing the water-soluble organic compound is the water-soluble organic compound and its substance. The water retention capacity of each compound was calculated by the following formula.

<maths num="1"><img file="JP2005297548A_D0001.tif" /></maths>

Next, move the above petri dish to an environment with a temperature of 30 ° C and a humidity of 80%, wait for equilibrium to be reached in the same manner, measure the residual weight in this environment, and determine the water retention capacity according to the above formula. It was. Furthermore, the same petri dish was moved to an environment with a temperature of 23 ° C and a humidity of 45% again, the residual weight was measured, and the water retention capacity was determined in the same manner. The results obtained are shown in Fig. 7. Furthermore, Fig. 8 shows the difference in water retention capacity under both environments.

The present inventors considered that there is some correlation between the difference in water retention capacity under the above-mentioned environment and the curl generation of plain paper. Therefore, when the aqueous solution containing the water-soluble organic compound examined above was applied to plain paper and the occurrence of curl was investigated, the water retention capacity in an environment with a temperature of 23 ° C and a humidity of 45% and a temperature of 30 ° C were determined. It was discovered that water-soluble organic compounds with a difference in water retention capacity of 36% or less in an environment with a humidity of 80% significantly suppress curl. Therefore, an ink containing only a coloring material, an additive, and these water-soluble organic compounds was further prepared, and the occurrence of curl was observed. As a result, it was confirmed that curl did not occur even after being left at room temperature for several days after printing, and the present invention was reached.

After printing on plain paper, the curl is caused by the moisture given by printing once entering between the fibers and the hydrogen bonds between the fibers, and the tension applied at the beginning is loosened as the moisture moves due to evaporation or the like. It is considered to occur when only the printed part shrinks. It is presumed that the water-soluble organic compound whose water retention capacity does not change easily suppresses the generation of curl because it is considered that a certain amount of water is stably retained and hardly moves with the evaporation of water. To do.

Further, as a result of further detailed examination, it was observed that a water-soluble organic compound having a difference in water retention capacity of 17.5% or more suppresses curling of printed matter for a longer period of time. It is speculated that water-soluble organic compounds with a difference in water retention capacity of 17.5% or more have weak hydrogen bonding power, so although they once enter the hydrogen bonding between paper cellulose, they may gradually migrate and move. I wonder if there is.

The water-retaining water-soluble organic compound in the present invention is a water-soluble organic compound having a water retention capacity of 5% or more in an environment of a temperature of 23 ° C. and a humidity of 45%, and further has a water retention capacity of 6. A water-soluble organic compound having a content of% or more and 23% or less is more preferable in terms of curl suppressing effect.

According to the present invention, the water-soluble organic compound contained in the coating liquid for a print medium has a water retention capacity in an environment of a temperature of 23 ° C and a humidity of 45% and an environment of a temperature of 30 ° C and a humidity of 80%. The curl-preventing effect of the present invention can be obtained if it is composed only of a water-soluble organic compound having a difference in water retention capacity of 36% or less. Specific examples of these water-soluble organic compounds are polyhydric alcohols having an amide bond, polyethylene glycols having a molecular weight of 200 to 300; N, N'-bis- (2-hydroxylethyl) -urea; bishydroxyethyl sulfone; 1, 2,6-Hexantriol; 1,5-pentanediol, trimethylolpropane and the like. Among these, polyethylene glycol having a molecular weight of 200, trimethylolpropane and N, N'-bis- (2-hydroxylethyl) -urea are more preferable.

The feature of the present invention is that the solvent or moisturizer constituting the coating liquid for print media and the ink for inkjet is composed of only the water-soluble organic compound having water retention as described above, and thus the conventional coating liquid or The point is that curling can be suppressed more efficiently than ink. Further, even when an image is formed as a set by combining a coating liquid for a print medium and an ink, the use of the coating liquid for a print medium of the present invention and the ink for inkjet is more efficient than a conventional ink set. It is possible to suppress curl.

[Coating liquid for print media]

The components, physical characteristics, coating method, coating amount, etc. of the coating liquid for print media according to the present invention will be described in detail.

(Component) The coating liquid for print media of the present invention has a difference of 36% between the water retention capacity in an environment of temperature 23 ° C and humidity 45% and the water retention capacity in an environment of temperature 30 ° C and humidity 80%. In addition to the following water-soluble organic compounds having water retention, inorganic compounds such as polyvalent metal salts may be contained. By including polyvalent metal ions in the coating liquid for print media, ink containing a coloring material in a dissolved or dispersed state is applied to the print medium, and then the coating liquid for print media is brought into contact with the ink to make ink. By destabilizing the dissolved state or dispersed state of the color material inside, good fixability of the color material can be obtained, and curl of the recorded material thus obtained can be suppressed more effectively. ..

(Water-retaining water-soluble organic compound) The water-retaining water-soluble organic compound in the coating liquid for print media has the ability to retain water in an environment with a temperature of 23 ° C and a humidity of 45%, and a temperature of 30 ° C and humidity. The curl-preventing effect of the present invention can be obtained if it is composed only of a water-soluble organic compound having a difference in water retention capacity of 36% or less in an environment of 80%. Specific examples of these water-soluble organic compounds are polyhydric alcohols having an amide bond, polyethylene glycols having a molecular weight of 200 to 300; N, N'-bis- (2-hydroxylethyl) -urea; bishydroxyethyl sulfone; 1, 2,6-Hexantriol; 1,5-pentanediol, trimethylolpropane and the like. Among these, polyethylene glycol having a molecular weight of 200, trimethylolpropane and N, N'-bis- (2-hydroxylethyl) -urea are more preferable.

It is sufficiently possible to suppress curl by containing a specified amount of the water-soluble organic compound mentioned above. However, when the means for applying the coating liquid for print media of the present invention to the recording medium is a means using an inkjet method or a means for transferring using a plurality of rollers, the coating liquid for print media evaporates. Considering the accompanying sticking between the inkjet head and the rollers, it is preferable that at least one of the water-soluble organic compounds is liquid at room temperature (25 ° C). Further, more preferably, a combination of trimethylolpropane having high water retention and low molecular weight polyethylene glycol having a relatively low viscosity is more preferable.

(Multivalent metal ion and salt thereof) Specifically, a preferable polyvalent metal ion that can be used in the coating liquid for a printing medium according to the present invention is, for example, Ca.²⁺, Cu²⁺, Ni²⁺, Mg²⁺, Zn²⁺, Sr²⁺And Ba²⁺Divalent metal ions such as, Al³⁺, Fe³⁺, Cr³⁺And Y³⁺Trivalent metal ions such as, but are not limited to this. In order to contain these multivalent metal ions in the coating liquid for print media, a salt of the multivalent metal is used. The salt is a metal salt composed of polyvalent metal ions as described above and anions bonded to these ions, but it is required to be soluble in water. Preferred anions for forming salts include conjugate bases of strong acids in terms of solubility, for example NO, which are conjugate bases of strong acids nitric acid, sulfuric acid and hydrochloric acid.₃^-, SO₄^2-, Cl^-Is preferable, especially NO₃^-Is suitable because it has excellent solubility in water.

In addition, it was found that among these, strong acids containing metal ions, which have a high ability to destabilize the components in the ink, tend to have a lower pH. The present inventors used a 4% by mass carbon black dispersion aqueous solution (dispersant: styrene-acrylic acid, acid value 200, mass% of dispersant / mass% of pigment = 0.2) of each polyvalent metal ion. When examined with nitrates, Fe³⁺, Y³⁺, Al³⁺&gt; Cu²⁺, Ca²⁺&gt; Mg²⁺, Sr²⁺The ability to destabilize was high in the order of, and the pH was likely to decrease in this order. When a salt composed of these polyvalent metal ions and a strong acid is used, Fe is used as the metal ion concentration present in the coating liquid for print media.³⁺, Al³⁺And Y³⁺0.2% by mass or more, Ca²⁺And Cu²⁺0.5% by mass or more, Mg²⁺And Sr²⁺It is preferable to add 1% by mass or more in terms of reactivity with the ink.

Also, Mg, which has a relatively low ability to destabilize ink²⁺, Sr²⁺Fe with higher ability even in salt with³⁺, Al³⁺And Y³⁺It has been confirmed that the pH of the coating liquid for print media tends to decrease with time when trying to obtain the same ability as that of salt.

In the present invention, the multivalent metal ion is Ca in terms of reactivity, colorability, ease of handling, and the like.²⁺, Mg²⁺, Sr²⁺, Al³⁺And Y³⁺Is particularly preferable, and moreover, Ca²⁺Is preferable.

The content of the multivalent metal ion in the coating liquid for print media is preferably 0.01% or more and 10% by mass or less with respect to the total amount of the coating liquid for print media. More preferably, it is 1% by mass or more and 5% by mass or less, and in order to sufficiently exert the function of destabilizing the ink and obtain a high level of image uniformity and optical density, it is 2 with respect to the coating liquid for print media. It is preferable to contain polyvalent metal ions of mass% or more and 4 mass% or less. It is also possible to contain more than 10% by mass of multivalent metal ions in the coating liquid for print media. However, even if more than 10% by mass is added, it is usually not necessary to add an excessive amount because there is a reason that a significant increase in the function of destabilizing the ink cannot be expected.

(Factors of change due to storage) However, when the coating liquid for print media contains polyvalent metal ions, the coating liquid for print media changes due to storage, and high optical density cannot be obtained. It turned out that the image quality obtained later may be different. The factors that cause the above phenomenon are presumed as follows.

An acid group such as a carboxyl group generated by oxidation of an organic compound in a coating liquid for a print medium reacts with a polyvalent metal ion, and a counter ion (polyvalent metal anion) of the polyvalent metal ion and the acid group The protons generate an acid, which lowers the pH of the coating solution for print media. If the pH fluctuates, the reactivity of the coating liquid for the print medium changes, so that the obtained image quality also changes. For example, if the reactivity of the coating liquid for a print medium is lowered, the color material permeates the print medium, so that a high optical density cannot be obtained or the color material reaches the vicinity of the back side of the print medium. (So-called strike-through phenomenon of colored materials).

Therefore, when the coating liquid for a print medium contains a polyvalent metal ion, the present inventors include both a conjugate base of a strong acid and a conjugate base of a weak acid that has a buffering effect on a change in hydrogen ion concentration. Therefore, the coating liquid for the print medium has a buffering action, and it is possible to minimize the above-mentioned decrease in pH. In addition, since the metal ions caused by the buffer used to obtain the buffering action also contribute to the destabilization of the coloring material, a high optical density that cannot be obtained simply by using the multivalent metal ions is obtained. You can get it. The pH in the present invention is a value measured by a conventional method at 25 ° C.

(Combinated base of weak acid) The "buffering action against change in hydrogen ion concentration" in the present invention means that 1.0 ml of a nitric acid aqueous solution specified in 0.1 is added to 50 ml of a coating solution for a printing medium before and after the addition of the nitric acid aqueous solution. Later change in hydrogen ion concentration is 1 × 10^-4It is to be as follows (hereinafter referred to as "buffering action"). The change in hydrogen ion concentration can be calculated from the change in pH. The change in hydrogen ion concentration when the initial pH is a and the pH after addition of the aqueous nitric acid solution is b can be calculated from the following formula (hereinafter referred to as "change in hydrogen ion concentration"). Change in hydrogen ion concentration (mol / L) = (10^-b)-(10^-a) In the present invention, a weak acid conjugate base is contained in the coating liquid for a print medium in order to obtain a buffering action. Preferred specific examples of the conjugate base of a weak acid include acetate ion, phosphate ion, carbonate ion, phthalate ion and the like. It is also possible to add a weak acid salt instead of adding a conjugate base of a weak acid. Specific examples of weak acid salts include acetates such as sodium acetate, potassium acetate and lithium acetate, hydrogen phosphates and bicarbonates, and hydrogen polyvalent carboxylic acids such as sodium hydrogen phthalate and potassium hydrogen phthalate. Salt can be used. Further, specific examples of polyvalent carboxylic acids include malonic acid, maleic acid, succinic acid, fumaric acid, itaconic acid, phthalic acid, isophthalic acid, terephthalic acid, adipic acid, sebacic acid, dimer acid, in addition to phthalic acid. Examples thereof include pyromellitic acid and trimellitic acid.

(Physical characteristics) The physical characteristics and coating conditions of the coating liquid for print media are not specified. However, the coating liquid for print media contains polyvalent metal ions, and the coating liquid for print media is brought into contact with the ink to destabilize the dissolved state or dispersed state of the coloring material in the ink2. When used as the coating liquid for a print medium for a liquid system, it is preferable to define the physical characteristics of the coating liquid for a print medium as follows in order to further suppress the curl of the obtained recorded material.

The present inventors have applied a coating liquid for a print medium to an ink containing a coloring material in a dissolved state or a dispersed state in the print medium, and by contacting the ink, the dissolved state or the dispersed state of the coloring material in the ink is determined. As a result of examining it as a coating liquid for a printing medium for a two-component system used in combination with a liquid composition containing a polyvalent metal ion that destabilizes, the degree of curl of the recorded material obtained by the two-component system is printed. It was found that the more the color material agglomerates in the medium are present on the surface layer, the more relaxed they are.

A condition for allowing the agglomerates to be present at a portion where the agglomerates have penetrated slightly from the surface layer portion of the print medium is to control the reactivity of the coating liquid for the print medium and the ink. Furthermore, it is important that a sufficient amount of multivalent metal ions to agglomerate the colorant be present within approximately 30 μm from the surface of the print medium. In order for a large amount of multivalent metal ions contained in the coating liquid for print media to be present within approximately 30 μm from the surface layer surface of the print medium, the amount of multivalent metal ions contained in the coating liquid for print media must be large. Of course, it is considered that the permeability of the coating liquid for the print medium to the print medium and the coating amount are greatly involved.

The coating liquid for a print medium comes into contact with the print medium and at the same time permeates along the fibers of the print medium under the influence of a solvent or a surfactant. Furthermore, it is presumed that the permeated liquid begins to evaporate at the same time as this permeation, and a part of the polyvalent metal that has lost its dissolving power begins to precipitate. That is, by increasing the reactivity of the print medium coating liquid with a small coating amount, the permeation and evaporation of the liquid into the print medium are promoted. As a result, it is possible to leave a large number of multivalent metal ions in a place where they have penetrated slightly from the surface layer of the print medium in the depth direction.

From the above, in order to ensure the more effective permeability of the coating liquid for printing media of the present invention containing polyvalent metal ions into plain paper, the Ka value obtained by the Bristow method is 1.3 mL · m.^-2 Msec^-1/2As mentioned above, the coating amount is 0.5g / m²More than 5g / m²The following is preferable, and more preferably, the Ka value is 3.0 mL · m.^-2 Msec^-1/2As mentioned above, the coating amount is 2.0 g / m²More than 3.0g / m²We came to the conclusion that:

Further, the pH of the coating liquid for print media is preferably 2 or more. If the pH is less than 2, the components in the coating liquid for print media may erode the surface of members such as tanks and rollers, and the constituent components of the members may elute into the coating liquid for print media, adversely affecting the image. Therefore, it is not preferable. It is preferable to keep the pH of the coating liquid for print media in the range of 2 or more and 7 or less, more preferably 3 or more and 6 or less. Within this range, the multivalent metal ion can be more stably present in the coating liquid for the print medium, so that the reactivity of the coating liquid for the print medium can be sufficiently ensured and a sufficient buffering action can be obtained. Therefore, the long-term storage stability of the coating liquid for print media can be maintained.

Furthermore, when the pH of the coating liquid for print media is lower than the pH of the ink, the reaction between the ink and the coating liquid for print media is more likely to occur, and the solid uniformity and strike-through property of the printed matter, etc. It is more preferable from the viewpoint of.

(Method of coating on print medium and amount of coating) Next, a method of applying the coating liquid for print media of the present invention to a print medium will be described in detail. Examples of the method of applying the coating liquid for a printing medium of the present invention to a printing medium include a coating method by a roller coating method, a bar coating method, a spray coating method and the like. Further, it is also possible to use an inkjet recording method as in the case of ink, and to selectively adhere the coating liquid for a print medium only to the image forming region to which the ink adheres and the vicinity of the image forming region.

As a result of examining several methods for applying the coating liquid for print media to the print medium as described above, the present inventors have made a two-component system in which the coating liquid for print media contains a reactant such as a polyvalent metal ion. Especially when used as a coating liquid for print media, the distribution of multivalent metal ions, which are reaction components in the vicinity of the surface layer of the print medium, becomes more uniform than other means even with a small amount of application, resulting in unevenness after ink application. We have come to the view that the roller coating method, which enables us to obtain excellent images, is the best.

However, when the conventional coating liquid is applied to the print medium by the roller coating method, the liquid is applied to a wide range of the print medium, so that the curl phenomenon is very likely to occur. Further, in the case of a two-component system in which the print medium is conveyed in the recording device after the conventional coating liquid is applied to the entire surface of the print medium and then ink is applied, the print medium is clogged in the middle of being conveyed in the recording device. There was a phenomenon that the image was lost.

Therefore, the present inventors aimed to sufficiently suppress the curl phenomenon even with a small amount of the coating liquid for print media, and as a result of further studies, the composition of the coating liquid for print media of the present invention was water. The difference between the water retention capacity in an environment with a temperature of 23 ° C and a humidity of 45% and the water retention capacity in an environment with a temperature of 30 ° C and a humidity of 80% is 36% or less. It was concluded that the content is preferably 15% by mass or more based on the total amount of the coating liquid for print media.

Even when the water-soluble organic compound is 15% by mass or less based on the total amount of the coating liquid for the print medium, curling can be suppressed to some extent when the amount applied to the print medium is extremely large. However, when it is used as a coating liquid for a print medium to be applied to a print medium before or after the ink is applied, the coating amount should be small in consideration of the fixability of the printed portion after the ink is applied. Need to be done. Even when the amount of coating applied to the print medium is small in this way, the specific amount is 3.0 g / m.²Even in the following cases, in order to obtain a sufficient curl suppressing effect, the content of the water-soluble organic compound needs to be 15% by mass or more with respect to the total amount of the coating liquid for the printing medium.

Furthermore, it was also found that the curl suppressing effect was more efficiently exhibited by setting the water content to 77% by mass or less with respect to the total amount of the coating liquid for print media.

(Other components) The components used in the coating solution for print media are components other than water and polyvalent metal ions, water and water-retaining water-soluble compounds, and are used as coating solutions for print media having desired physical properties. Therefore, surfactants, antifoaming agents, preservatives, fungicides and the like can be appropriately added as long as the effects of adding them can be obtained and the objective effects of the present invention are not impaired.

[Inkjet ink]

The components and the like constituting the inkjet ink according to the present invention will be described in detail.

(Component) In addition to the above-mentioned water-retaining water-soluble organic compound, the ink of the present invention can be used as a colorant, water, and, if necessary, a coating liquid for a printing medium having desired physical property values. , Surfactant, antifoaming agent, preservative, fungicide, etc. As the coloring material, use one selected from water-soluble dyes, water-dispersible pigments (microencapsulating pigments, coloring resins, etc. are also included in the category of pigments in the present specification) and combinations of two or more of them. Can be done. The amount of these coloring materials is not particularly limited, but is 0.1% by mass or more and 10% by mass or less in the ink, and in the case of a water-dispersible pigment, 0.1% by mass in the ink including the resin used for dispersion. It is preferable that the content is 20% by mass or less in order to make various performances such as viscosity suitable. Hereinafter, these coloring materials will be described in detail.

(Water-Retaining Water-Soluble Organic Compound) The inkjet ink of the present invention has a water retention capacity in an environment of a temperature of 23 ° C and a humidity of 45% in order to suppress curl more effectively than a conventional inkjet ink. It is composed of a water-soluble organic compound having a difference in water retention capacity of 36% or less in an environment with a temperature of 30 ° C and a humidity of 80%. In particular, when the water-soluble organic compound is contained in the ink, the molecular weight Mw is multivalent having an amide bond in the range of 100 Mw 1000 in order to satisfy many other performances as an ink for inkjet. Alcohol, Polyethylene Glycol with a Molecular Weight of 200-300, N, N'-Bis- (2-Hydroxyethyl) -Urea, Bishydroxyethyl Sulphon, 1,2,6-Hexanetriol, 1,5-Pentanediol, Trimethylol Propane Etc. are preferable. Of these, N, N'-bis- (2-hydroxylethyl) -urea is particularly preferred.

The molecular weight of the water-soluble organic compound having a molecular weight distribution, such as the polyhydric alcohol having an amide bond and polyethylene glycol, was an average molecular weight determined by any of the following. (1) JIS Handbook Chemical Analysis According to K0118 and K0123, mass spectrometric measurement, gas chromatography mass spectrometry (GC-MS) method, and liquid chromatography mass spectrometry (LC-MS method) were performed to measure the molecular weight. (2) For polyethylene glycol having a molecular weight distribution, the average molecular weight was calculated from the size exclusion chromatography method (GPC method) according to JIS Handbook Chemical Analysis K0124 and used as the molecular weight. (3) The structure of the compound was specified and the molecular weight was determined.

These water-soluble compounds can be used alone or in combination of two or more. In the present invention, in order to select and use a water-retaining water-soluble organic compound in order to suppress curl, urea, glycerin, etc., which are usually used to impart suitability as an inkjet ink to the ink. No organic solvent is used. Therefore, when the inkjet ink according to the present invention is used in an inkjet recording apparatus, it is preferable to use an inkjet ink having a configuration capable of suppressing ejection stability, nozzle clogging, and the like.

As a result of further investigation on this point, among water-soluble compounds having a change in water retention capacity of 36% or less, polyhydric alcohols having an amide bond having a molecular weight Mw in the range of 100 Mw 1000, N, N By using at least one of'-bis- (2-hydroxylethyl) -urea and bishydroxyethyl sulfone, preferably two or more, more preferably three or more, even a small droplet and high-speed inkjet head can be used. The result was that it was fully usable. Among polyhydric alcohols having an amide bond having a molecular weight Mw in the range of 100 Mw 1000, one of the two or three types to be combined may be N, N'-bis (2-hydroxylethyl) -urea. Most preferred. The reason for this is that N, N'-bis (2-hydroxylethyl) -urea has the ability to prevent association from a structure similar to urea, so when used in combination, it prevents association of other water-soluble compounds, respectively. It is thought that this is to make it easier to bring out the performance such as clogging prevention and dye solubility.

(Coloring Material) Examples of the coloring material used in the ink of the present invention include pigments such as carbon black and organic pigments. The pigment may be used alone or in combination of two or more. Further, as the form of the pigment, a pigment dispersed with a dispersant, a self-dispersing pigment, colored fine particles / microcapsules and the like can be used. These will be described in detail below.

-Carbon black Specific examples of carbon black are carbon black pigments such as furnace black, lamp black, acetylene black, and channel black. For example, Raven 7000, Raven 5750, Ravan 5250, Ravan 5000, Ravan 3500, and Ravan 2000. , Rayvan 1500, Rayvan 1250, Rayvan 1200, Rayvan 1190 ULTRA-II, Rayvan 1170, Rayvan 1255 (manufactured by Colombia), Black Pearls L, Regal 400R, Legal 330R, Legal 660R, Mogul ) L, Monarch 700, Monarch 800, Monac 880, Monac 900, Monac 1000, Monac 1100, Monac 1300, Monarch 1400, Valcan XC-72R (manufactured by Cabot), Color Black (Color) Black) FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U , Printex 140V, Special Black 6, Special Black 5, Special Black 4A, Special Black 4 (manufactured by Degussa), No.25, No.33, No.40, No.47, No.52 , No.900, No.2300, MCF-88, MA600, MA7, MA8, MA100 (manufactured by Mitsubishi Chemical Corporation), etc. can be used. Of course, the present invention is not limited to these, and 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 pigment Specific examples of organic pigments include insoluble azo pigments such as toluidine red, toluidine maroon, hanza ero, benzine ero, and pyrazolone red, soluble azo pigments such as litol red, heliobordeaux, pigment scarlet, and permanent red 2B, alizarin, and indantron. Derivatives from building dyes such as thioindigo maroon, phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green, quinacridone pigments such as quinacridone red and quinacridone magenta, perylene pigments such as perylene red and perylene curlet, isoindolinone yellow, Isoindolinone pigments such as isoindolinone orange, imidazolone pigments such as benzimidazolone yellow, benzimidazolone orange, benzimidazolone red, pyranthron pigments such as pyranthron red and pyranthron orange, thioindigo pigments, condensation Examples of other pigments such as azo pigments, thioindigo pigments, flavanthron eros, acylamide eros, quinophthalone eros, nickel azo eros, copper azomethine eros, perinone oranges, anthron oranges, dianthraquinonyl reds, dioxazine violet, etc. it can.

Further, when the organic pigment is indicated by the color index (CI) number, the following can be exemplified. Of course, other than the above, conventionally known organic pigments can be used. CI Pigment Yellow: 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 109, 110, 117, 120, 125, 128, 137, 138, 147, 148, 151, 153, 154, 166, 168 C.I. Pigment Orange: 16, 36, 43, 51, 55, 59, 61 C.I. Pigment Red: 9, 48, 49, 52, 53, 57, 97, 122, 123, 149, 168, 175, 176, 177, 180, 192, 215, 216, 217, 220, 223, 224, 226, 227, 228, 238, 240C.I. Pigment Violet: 19, 23, 29, 30, 37, 40, 50C .I. Pigment Blue: 15, 15: 1, 15: 3, 15: 4, 15: 6, 22, 60, 64 C.I. Pigment Green: 7, 36 C.I. Pigment Brown: 23, 25, 26 Dispersant When the above-mentioned carbon black or organic pigment is used, it is preferable to use a dispersant in combination. As the dispersant, those capable of stably dispersing the above pigment in an aqueous medium by the action of an anionic group are preferably used. Specific examples of the dispersant include, for example, a styrene-acrylic acid copolymer, a styrene-acrylic acid-alkyl ester copolymer, a styrene-maleic acid copolymer, and a styrene-maleic acid-alkyl ester copolymer. , Styrene-methacrylic acid copolymer, styrene-methacrylic acid-alkyl ester copolymer, styrene-maleic acid half ester copolymer, vinylnaphthalene-acrylic acid copolymer, vinylnaphthalene-maleic acid copolymer, Styrene-maleic anhydride-maleic acid half ester copolymers, salts thereof and the like are included. Further, these dispersants preferably have a weight average molecular weight in the range of 1,000 to 30,000, and particularly preferably in the range of 3,000 to 15,000.

-As a self-dispersing pigment, a pigment that can be dispersed in an aqueous medium without a dispersant by binding an ionic group (anionic group) to the pigment surface, a so-called self-dispersing pigment, can also be used. Examples of such pigments include self-dispersing carbon black. Examples of the self-dispersing carbon black include anionic carbon black in which an anionic group is bonded to the surface of the carbon black.

-Anionic carbon black Anionic carbon black is applied to the surface of carbon black, for example, -COOM, -SO.₃M, -PO₃HM, -PO₃M₂The one in which at least one anionic group selected from the above is bonded is mentioned. In the above formula, M represents a hydrogen atom, an alkali metal, ammonium or organic ammonium. Of these, especially -COOM and -SO₃Carbon black, in which M is bonded to the surface of carbon black and charged anionicly, has good dispersibility in ink and can be particularly preferably used in the present invention.

By the way, among those represented by "M" in the above hydrophilic groups, specific examples of alkali metals include, for example, Li, Na, K, Rb and Cs, and specific examples of organic ammonium include, for example. Examples thereof include methylammonium, dimethylammonium, trimethylammonium, ethylammonium, diethylammonium, triethylammonium, methanolammonium, dimethanolammonium, and trimethanolammonium.

The ink of the present invention containing self-dispersing carbon black in which M is ammonium or organic ammonium can further improve the water resistance of the recorded image, and can be particularly preferably used in this respect. It is considered that this is due to the effect that when the ink is applied onto the print medium, ammonium is decomposed and ammonia is evaporated. Here, the self-dispersing carbon black in which M is ammonium is, for example, a method of substituting self-dispersing carbon black in which M is an alkali metal with ammonium by an ion exchange method, or an H-type by adding an acid. Then, a method of adding ammonium hydroxide to convert M to ammonium can be mentioned.

Examples of the method for producing anionic carbon black include a method in which carbon black is oxidized with sodium hypochlorite, and the -COONa group can be chemically bonded to the surface of the carbon black by this method.

By the way, various hydrophilic groups as described above may be directly bonded to the surface of carbon black. Alternatively, another atomic group may be interposed between the carbon black surface and the hydrophilic group, and the hydrophilic group may be indirectly bonded to the carbon black surface. Specific examples of other atomic groups here include, for example, a linear or branched alkylene group having 1 to 12 carbon atoms, a substituted or unsubstituted phenylene group, and a substituted or unsubstituted naphthylene group. Here, examples of the substituent of the phenylene group and the naphthylene group include a linear or branched alkyl group having 1 to 6 carbon atoms. Specific examples of combinations of hydrophilic groups with other atomic groups include, for example, -C.₂H₄COOM, -Ph-SO₃Examples include M, -Ph-COOM, etc. (where Ph represents a phenylene group).

By the way, in the present invention, two or more of the above-mentioned self-dispersing carbon blacks may be appropriately selected as the color material of the ink. The amount of self-dispersing carbon black added to the ink is preferably in the range of 0.1% by mass or more and 15% by mass or less, particularly 1% by mass or more and 10% by mass or less with respect to the total amount of ink. Within this range, the self-dispersing carbon black can maintain a sufficient dispersed state in the ink. Further, for the purpose of adjusting the color tone of the ink, a dye may be added as a coloring material in addition to the self-dispersing carbon black.

-Colored fine particles / microencapsulated pigments In addition to the above-mentioned colored materials, pigments microencapsulated with a polymer or the like, colored fine particles in which the periphery of resin particles is coated with a colored material, or the like can also be used. Originally, the microcapsules have dispersibility in an aqueous medium, but in order to improve the dispersion stability, a dispersant as described above may be further coexisted in the ink. When the colored fine particles are used as a coloring material, it is preferable to use the above-mentioned anionic dispersant or the like.

(Aqueous medium) As the ink used in the two-component system, the ink for inkjet of the present invention, that is, the coloring material, water, and the water retention capacity in an environment of temperature 23 ° C and humidity 45% and temperature 30 ° C, humidity By using an ink for inkjet containing a water-soluble organic compound having a difference in water retention capacity of 36% or less in an environment of 80%, it is possible to further suppress curl of recorded matter.

However, even if a conventional ink (an ink that does not contain the water-retaining water-soluble organic compound of the present invention or contains an organic solvent other than the water-retaining water-soluble organic compound) is used, it can be used as a coating liquid for a printing medium. By using the coating liquid for print media of the present invention, it is possible to suppress curl at least as much as in the conventional two-component system. Therefore, the inkjet ink of the present invention is not always indispensable as the ink used in the two-component system of the present invention.

Examples of the aqueous medium used in the ink composition when an ink other than the present invention is used include water or a mixed solvent of water and a water-soluble organic solvent. As the water-soluble organic solvent, those having an effect of preventing the ink from drying are particularly preferable. Specifically, alkyl alcohols having 1 to 4 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, and tert-butyl alcohol; dimethylformamide and dimethylacetamide. Amids such as; ketones such as acetone and diacetone alcohols or keto alcohols; ethers such as tetrahydrofuran and dioxane; polyalkylene glycols such as polyethylene glycol and polypropylene glycol; ethylene glycol, propylene glycol, butylene glycol and triethylene glycol. , 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol and other alkylene glycols containing 2 to 6 carbon atoms; lower alkyl ether acetate such as polyethylene glycol monomethyl ether acetate; glycerin Lower alkyl ethers of polyhydric alcohols such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether; polyhydric alcohols such as trimethylolpropane and trimethylolethane. ; N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like can be mentioned. The above water-soluble organic solvent can be used alone or as a mixture. Further, it is preferable to use deionized water (ion-exchanged water) as the water.

The content of the water-soluble organic solvent contained in the ink composition other than the present invention is not particularly limited, but is preferably in the range of 3% by mass or more and 50% by mass or less with respect to the total mass of the ink composition. The water content is preferably in the range of 50% by mass or more and 95% by mass or less with respect to the total mass of the ink composition.

(Other ingredients) In addition to the above ingredients, a moisturizer can be added as needed, as well as a surfactant, antifoaming agent, and antiseptic to obtain a coating solution for print media with desired physical properties. Agents, antifungal agents and the like may be added as long as the effects obtained by adding them are obtained and the objective effects of the present invention are not impaired.

[Set of coating liquid for print media and ink for inkjet]

The present inventors have conducted further studies with the aim of further improving the curl of a recorded material obtained by a two-component system that forms an image using a coating liquid for a print medium and an ink for an inkjet, and as a result, the print medium. It was found that the curl of the obtained recorded matter can be more effectively suppressed by satisfying the following conditions for the ink jet ink and the coating liquid for the print medium applied to the product.

(Conditions) The maximum visible region after mixing 50 g of the 800-fold diluted aqueous solution of the coating solution for print media and 0.3 g of the 5-fold diluted aqueous solution of the injet ink and filtering with a 0.2 μm filter after 15 minutes. The absorbance at the absorption wavelength (when carbon black is used as the coloring material, the wavelength is 550 nm) is (A), and the maximum absorption in the visible region of the mixture of 0.3 g of the 5-fold diluted aqueous solution of the injet ink and 50 g of pure water. When the absorbance at the wavelength is (B), (A) and (B) satisfy the following relationship. (A) / (B) &lt;0.85 The present inventors speculate the mechanism by which the recorded material obtained by using the coating liquid for print media and the ink for inkjet defined as described above can suppress curl more effectively as follows. The above-mentioned relational expression defines the reaction force between the coating liquid for print media and the ink for inkjet. By defining the reactivity as described above, most of the agglomerates generated by the contact between the polyvalent metal ion contained in the coating liquid for the print medium and the coloring material contained in the ink for inkjet are the print medium. Since it is present on the surface layer, it is presumed that the shrinkage of cellulose that occurs after water is applied can be suppressed.

The print medium coating liquid and the inkjet ink used in the two-component system are most effective in suppressing curl of the obtained recorded matter by using the print medium coating liquid and the inkjet ink of the present invention in combination. is there. However, even if a conventional ink is used, curling can be suppressed at least much more effectively than a conventional two-component system when used in combination with the coating liquid for a print medium of the present invention.

[Inkjet recording device]

Next, an example of a recording device for forming an image using the coating liquid for print media and / and the ink for inkjet is shown.

FIG. 1 shows an example of an inkjet recording device as a partial cross-sectional view. This image forming apparatus employs a serial type inkjet recording method, and includes a recording head 1, a paper feed tray 17 for feeding a print medium (hereinafter, also referred to as recording paper) 19, and a print of the present invention. The paper feed cassette 16 in which the means for applying the coating liquid for a medium is integrally formed, the driving means for reciprocating the recording head in the direction orthogonal to the transport direction of the recording paper, and the driving of these components. It has a control means for controlling the above.

The recording head 1 is mounted on the carriage 2 so that the surface on which the ink ejection port is formed is oriented toward the platen 11. Although not shown, the recording head 1 has the ink ejection port, a plurality of electric heat converters (for example, heat generation resistance elements) for heating the ink liquid, and a substrate supporting the ink ejection port. The recording head 1 has an ink cartridge mounted in a carriage above the recording head 1.

The carriage 2 is equipped with the recording head 1 and can reciprocate along two guide shafts 9 extending in parallel along the width direction of the recording paper 19. Further, the recording head 1 is driven in synchronization with the reciprocating movement of the carriage, and ejects ink droplets onto the recording paper 19 to form an image. The paper cassette 16 can be attached to and detached from the image forming apparatus main body. The recording paper 19 is loaded and stored on the paper feed tray 17 in the paper feed cassette 16. At the time of paper feeding, the uppermost sheet is pressed against the paper feed roller 10 by the spring 18 that presses the paper feed tray 17 upward. The paper feed roller 10 is a roller having a substantially half-moon shape in cross section, is driven and rotated by a motor (not shown), and feeds only the top sheet (recording paper 19) by a separation claw (not shown).

The separately fed recording paper 19 is conveyed along the transfer surface of the paper feed cassette 16 and the transfer surface of the paper guide 27 by the large-diameter intermediate roller 12 and the small-diameter coating roller 6 that is in pressure contact with the intermediate roller 12. Will be done. These transport surfaces consist of curved surfaces that draw an arc concentric with the intermediate roller 12. Therefore, the recording paper 19 reverses its transport direction by passing through these transport surfaces. That is, the surface on which the recording paper 19 is printed faces downward until it is conveyed from the paper feed tray 17 and reaches the intermediate roller 12, but when it faces the recording head 1, it faces upward (recording). Face to the head side). Therefore, the printing surface of the recording paper always faces the outside of the image forming apparatus.

The means for applying the coating liquid for print media are provided in the paper feed cassette 16 and in a state where a replenishment tank 22 for supplying the coating liquid for print media 15 and a part of the peripheral surface are immersed in the tank 22. It has an intermediate roller 12 that is rotatably supported, and a coating roller 6 that is arranged so as to be parallel to the intermediate roller and that comes into contact with the intermediate roller 12 and rotates in the same direction. Further, the coating roller 6 is arranged so that the peripheral surface of the intermediate roller 12 for transporting the recording paper 19 is in contact with and parallel to the intermediate roller 12. Therefore, when the recording paper 19 is conveyed, the intermediate roller 12 and the coating roller 6 rotate as the intermediate roller 12 rotates. As a result, the coating liquid 15 for the printing medium is supplied to the peripheral surface of the coating roller 6 by the supply roller 13, and the printing medium 19 is evenly sandwiched between the coating roller 6 and the intermediate roller 12. The coating liquid is applied by the supply roller 6.

Further, in this inkjet recording device, a float 14 is provided in the replenishment tank 22. The float 14 is a substance having a lighter specific gravity than the coating liquid 15 for a print medium, and is a printing medium containing a reaction component from the outside through a remaining amount display window 21 which is a transparent member by floating on the liquid surface of the coating liquid for a print medium. The remaining amount of the coating liquid for use can be visually confirmed.

FIG. 2 is a front view of the remaining amount display unit. The remaining amount display unit is provided with a display indicating the degree of remaining amount along the longitudinal direction of the remaining amount display window 21. In the figure, the full state is when the liquid level of the coating liquid for print media or the float 14 reaches the position displayed as Full. On the other hand, when the liquid level of the coating liquid for print media or the float 14 is at the position indicated by "Add", it indicates that the coating liquid for print media is low. Therefore, it is obvious that the coating liquid for the print medium should be replenished when the coating liquid 15 for the print medium gradually decreases and the float 14 drops to the Add line.

As shown in FIG. 3, the method of replenishing the coating liquid for print media is composed of a rubber member having a notch at the tip of the injection device 23 with the paper feed cassette 16 pulled out from the image forming apparatus main body. The coating liquid for print media is injected into the replenishment tank 22 by inserting it into the injection port 20.

In this way, the recording paper coated with the coating liquid for the print medium is then fed by the main transport roller 7 and the pinch roller 8 in pressure contact with the main transport roller 7 in a predetermined amount and transported to the recording unit, and the ink is conveyed from the recording head 1. Is given. In the above configuration, the paper-feeding and printed recording sheet 19 is ejected and conveyed by the paper ejection roller 3 and the spur 4 that is in pressure contact with the paper ejection roller 3, and is stacked on the paper ejection tray 5.

Further, when the coating liquid for print media is applied by a roller or the like, the ink is effectively destabilized with a small amount of application when the viscosity of the coating liquid for print media is higher than the viscosity of the ink. It is preferable because it can be formed and has good fixability of the recorded material.

FIG. 4 shows another example of the inkjet recording device. In FIG. 4, reference numeral 61 denotes a blade as a wiping member, one end of which is held and fixed by a blade holding member, and forms a cantilever. The blade 61 is arranged at a position adjacent to the recording area of the recording head 65, and in this example, is held in a protruding form in the movement path of the recording head 65.

Reference numeral 62 denotes a cap on the protruding port surface of the recording head 65, which is placed in the home position adjacent to the blade 61 and moves in the direction perpendicular to the moving direction of the recording head 65 to come into contact with the ink ejection port surface for capping. It has a configuration to be performed. Further, reference numeral 63 denotes an ink absorber provided adjacent to the blade 61, which, like the blade 61, is held in a protruding form in the movement path of the recording head 65. The blade 61, the cap 62, and the ink absorber 63 constitute the ejection recovery unit 64, and the blade 61 and the ink absorber 63 remove moisture, dust, and the like from the ejection port surface. In addition, the ink of the recording head, the ink at the ejection port of the coating liquid for the print medium, and the like are sucked through the cap by a pump (not shown) to obtain the original ink of the recording head or the ink. It also constitutes a recovery system unit that restores the original ejection performance of the coating liquid for print media.

Reference numeral 65 denotes a recording head having an ejection energy generating means and ejecting ink to a print medium facing the ejection port surface on which the ejection port is arranged for recording. 66 is a recording head equipped with the recording head 65 and moving 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 driven by a motor 68 (not shown). As a result, the carriage 66 can be moved along the guide shaft 67, and the recording head 65 can move the recording area and the adjacent area thereof. 51 is a paper feeder for inserting a print medium, and 52 is a paper feed roller driven by a motor (not shown).

With these configurations, the print medium is fed to a position facing the 65 ejection port surface of the recording head, and as the recording progresses, the paper is ejected to the paper ejection section where the paper ejection roller 53 is arranged. In the above configuration, when the recording head 65 finishes recording and returns to the home position, the cap 62 of the discharge recovery unit 64 is retracted from the moving path of the recording head 65, but the blade 61 protrudes into the moving path. As a result, the discharge port of the recording head 65 is wiped. When the cap 62 comes into contact with the discharge surface of the recording head 65 for capping, the cap 62 moves so as to protrude in 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 positions as those at the time of wiping described above. As a result, the discharge port surface of the recording head 65 is wiped even in this movement.

The above-mentioned movement of the recording head to the home position is performed not only at the end of recording or recovery of discharge, but also at a predetermined interval while the recording head moves the recording area for recording to the home position adjacent to the recording area. Then, the wiping is performed along with this movement.

FIG. 5 shows an example of a cartridge 45 containing a member for supplying a coating liquid for a print medium that does not contain ink or a coloring material to the recording head, for example, an ink or a coating liquid for a print medium supplied via a tube. It is a figure which shows. Here, reference numeral 40 denotes a storage portion, for example, a bag containing ink for supply or a coating liquid for a print medium, and a rubber stopper 42 is provided at the tip thereof. By inserting a needle (not shown) into the stopper 42, the ink in the bag 40 or the coating liquid for a print medium can be supplied to the head. Reference numeral 44 denotes an absorber that receives a waste ink or a coating liquid for a waste print medium. The accommodating portion 40 preferably has a liquid contact surface with an ink or a coating liquid for a print medium formed of polyolefin, particularly polyethylene. As shown in FIG. 6, such a cartridge is configured to be detachably attached to a recording head 901 that discharges ink or a coating liquid for a print medium, and is in a state where the cartridge 45 is attached to the recording head. The ink or the coating liquid for a print medium is configured to be supplied to the recording head 901.

[Ink characteristics; Inkjet ejection characteristics, permeability to print media]

The set of the coating liquid for a print medium and the ink for inkjet according to the present invention is particularly preferably used for inkjet recording. Inkjet recording methods include a recording method in which mechanical energy is applied to ink to eject droplets, and a recording method in which thermal energy is applied to ink to eject droplets by foaming the ink. The inkjet ink of the present invention and the coating liquid for a print medium can also be used. In that case, it is preferable that the coating liquid and ink for a print medium having the above-described configuration according to the present invention have characteristics that can be ejected from the inkjet head. From the viewpoint of ejection property from the inkjet head, the characteristics of these liquids are, for example, the viscosity of 1 to 15 mPa · s, the surface tension of 25 mN / m (dyne / cm) or more, and particularly the viscosity of 1 to 5 mPa. It is preferable that s and surface tension are 25 to 50 mN / m (dyne / cm). Further, since the coating liquid for print media of the present invention needs to react only with a specific ink on a print medium such as a paper surface, the coating liquid for print media is placed in a place different from the recording portion using the specific ink. It is preferable that the surface tension of the coating liquid for the print medium is set within a range that can be ejected from the inkjet head and is larger than that of the ink to be destabilized by the coating liquid for the print medium so as not to bleed. ..

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded. In the following description, parts and% are based on mass unless otherwise specified.

[Evaluation of coating liquid for print media]

(Preparation of coating liquid for print media) Mix each component according to Table 1 below, stir well to dissolve, press-filter with a microfilter (manufactured by Fujifilm) with a pore size of 1 μm, and apply coating liquid for print media 1 ~ 16 was prepared. The unit is mass%.

<tables num="1"><img file="JP2005297548A_D0002.tif" /></tables>

(Presence / absence of buffering action) The pH of the obtained coating liquids 4, 6 to 10, 14, and 15 for print media was measured. Furthermore, the pH when 1.0 ml of a 0.1 specified nitric acid aqueous solution was added to 50 ml of the coating liquid for print media was measured, and the amount of change in hydrogen ion concentration was measured to determine whether or not the coating liquid for print media had a buffering effect. I examined. The results are shown in Table 2 below.

<tables num="2"><img file="JP2005297548A_D0003.tif" /></tables>

(Evaluation of curl) After applying the obtained coating liquids 1 to 16 for print media to the print medium with a coating roller, the curled state was observed by the evaluation method shown below. The amount of the coating liquid for the print medium applied to the print medium is 2.4 g / m.²The speed of the roller and the contact pressure of the roller with the print medium were adjusted so as to be. In addition, Canon PB paper was used as the print medium. The curl evaluation method is as follows.

The printed matter was left at a temperature of 24 ° C. and a humidity of 50% immediately after printing (within 1 minute), 1 hour later, 1 day, 2 days, 3 days, and 7 days, and then the curl amount was measured over time. The distance from the tip of the curled paper to the ground plane of the paper was measured with a ruler, with + (plus curl) when the printed paper was curled in the concave direction and- (minus curl) when it was curled in the convex direction. .. The curl judgment criteria are as follows. The evaluation results are shown in Table 3 below.

AA: Within ± 10 mm A: Greater than ± 10 mm, within ± 25 mm B: Greater than ± 25 mm, within ± 40 mm C: The tip of the paper is curled or curled up inside the paper surface

<tables num="3"><img file="JP2005297548A_D0004.tif" /></tables>

[Ink evaluation]

(Preparation of ink) Each component was mixed according to Table 4 below, and after sufficiently stirring and dissolving, pressure filtration was performed with a membrane filter (manufactured by Fujifilm) having a pore size of 0.2 μm to prepare inks 1 to 10. The unit is mass%.

<tables num="4"><img file="JP2005297548A_D0005.tif" /></tables>

(Preparation of Pigment Ink) Next, the pigment dispersions 1 and 2 shown below were prepared. Pigment inks were prepared using the obtained pigment dispersions 1 and 2. In preparing the pigment ink, each component was mixed according to Table 5 below, and after sufficient stirring, pressure filtration was performed with a membrane filter (manufactured by Fujifilm) having a pore size of 0.3 μm to prepare inks 11 to 13.

Pigment dispersion 1 As a pigment, 10 parts of Monac 880 (manufactured by Cabot), anionic polymer P-1 (styrene / M230G (methoxypolyethylene glycol methacrylate: manufactured by Shin-Nakamura Chemical Co., Ltd.) / acrylic acid copolymer (copolymerization ratio (copolymerization ratio)) Mass ratio) = 65/12/25), acid value 160, weight average molecular weight 8,000, solid content 10% aqueous solution (neutralizer: potassium hydroxide)) 40 parts, pure water 50 parts, batch type vertical It was charged in a mold sand mill (manufactured by Imex), filled with 250 parts of 0.3 mm diameter zirconia beads, and dispersed for 10 hours while being cooled with water. Further, this dispersion was centrifuged to remove coarse particles. Then, as a final preparation, a pigment dispersion 1 having a solid content of about 14.0% and a weight average particle size of 110 nm was obtained.

Pigment dispersion 2 As a pigment, 10 parts of Monac 880 (manufactured by Cabot), anionic polymer P-2 (styrene / acrylic acid copolymer (copolymerization ratio (mass ratio) = 70/30), acid value 180, weight An aqueous solution with an average molecular weight of 10,000 and a solid content of 10%, a neutralizer: potassium hydroxide) 40 parts, and pure water 50 parts are mixed and charged into a batch vertical sand mill (manufactured by Imex), and 150 mm diameter zirconia beads are added. The dispersion treatment was carried out for 10 hours while partially filling and cooling with water. Further, this dispersion was centrifuged to remove coarse particles. Then, as a final preparation, a pigment dispersion 2 having a solid content of about 14% and a weight average particle size of 110 nm was obtained. An aqueous solution of anionic polymer P-3 (ethyl acrylate / acrylate copolymer (copolymerization ratio (mass ratio) = 87/13), acid value 100, weight average molecular weight 11000, solid content 10%) in the dispersion. (Neutralizer: Potassium hydroxide)) 30 parts was added to obtain a pigment dispersion 2.

<tables num="5"><img file="JP2005297548A_D0006.tif" /></tables>

(Evaluation of curl and ejection stability) Printing of the above inks 1 to 13 using an inkjet recording device having an on-demand multi-recording head that ejects the ink by applying thermal energy corresponding to the recording signal to the ink. It was given to the medium. The inkjet recording device used has a discharge rate of 2.8 pL per dot and a recording density of 2400 x 1200 dpi, and the drive conditions are A4 full solid (20 x 25 cm) using a device with a drive frequency of 10 kHz. A color image was formed. The print medium used for the evaluation was A4 size PPC paper (manufactured by Canon). In addition, printing is performed by 2-pass printing in which the print area is scanned twice, and the amount of inkjet ink applied to the print medium is 12.5 g / m.²Is.

-Curl evaluation method The curl evaluation method of the ink is the same as when the coating liquid 15 for the print medium is used. The evaluation results are shown in Table 6 below.

-Ejection stability (start-up characteristics) evaluation method As an evaluation of ink ejection stability, it was confirmed in an environment of normal temperature and humidity that the printed part was not disturbed or blurred at the start of printing. The criteria for discharge stability (startup characteristics) are as follows. The evaluation results are shown in Table 6 below.

A: No blur B: The exported part is slightly blurred C: The exported part is greatly blurred

<tables num="6"><img file="JP2005297548A_D0007.tif" /></tables>

[Curl evaluation of recorded materials obtained by two-component system]

Next, after applying the coating liquid for the print medium, the curl of the recorded material obtained in the system for applying the ink (two-component system) was confirmed. Further, the coating liquid for the print medium is stored for a long period of time, and the coating liquid for the print medium before and after the storage is used as the coating liquid for the print medium for the system to form an image, and the degree of change in the image quality of the obtained recorded matter. It was confirmed.

(Preparation of Recorded Material in Two-Liquid System) As the coating liquid for the print medium, the coating liquids 1 and 10 for the print medium were applied to the print medium by the roller coating method using the coating rollers having the configuration shown in FIG. The amount of the coating liquid for the print medium applied to the print medium is 2.4 g / m.²The speed of the roller and the contact pressure of the roller with the print medium were adjusted so as to be. The print medium used was Canon PB paper (A4 size).

Ink 1, 3, 4 using an inkjet recording device having an on-demand multi-recording head that ejects ink by applying thermal energy corresponding to a recording signal to the ink immediately after applying the coating liquid for print media. , 6-9 and 11-13 were given, and the following evaluations were made. The inkjet recording device used has a discharge rate of 2.8 pL per dot and a recording density of 2400 x 1200 dpi, and the drive conditions are A4 full solid (20 x 25 cm) using a device with a drive frequency of 10 kHz. A color image was formed. The print medium used for the evaluation was A4 size PPC paper (manufactured by Canon). In addition, printing is performed by 2-pass printing in which the print area is scanned twice, and the area where the inkjet ink adheres to the print medium is 12.5 g / m.²Is.

(Reactivity between ink and coating liquid for print media) Using the following coating liquid for print media and a set of ink, they were mixed under the following conditions, the absorbance was measured, and the reactivity was evaluated. The results are shown in Table 7 below.

50 g of an 800-fold diluted aqueous solution of the coating liquid for print media and 0.3 g of a 5-fold diluted aqueous solution of ink were mixed, and after 15 minutes, the absorbance at 550 nm after filtering with a 0.2 μm filter was determined (A). The absorbance of a mixture of 0.3 g of a 5-fold diluted aqueous solution and 50 g of pure water at 550 nm was defined as (B), and the values of (A) / (B) as an index of reactivity were determined. In the inks 1, 3, 4, and 6 in which the ink does not contain a pigment as a coloring material, the inks were mixed with the coating liquid for a print medium by the same method as described above, but the values of (A) / (B) were obtained. Was 1, showing no reactivity.

<tables num="7"><img file="JP2005297548A_D0008.tif" /></tables>

(Evaluation of curl) The curl evaluation method is the same as when the coating liquid for print media is used. The evaluation results are shown in Table 8 below.

<tables num="8"><img file="JP2005297548A_D0009.tif" /></tables>

(Evaluation of image change due to storage) After applying the coating liquids 4, 6 to 10, 14 and 15 for the print medium to the print medium, apply ink 11 to the center of the print medium to make a solid print with a width of 2 cm and a length of 2 cm. Then, the strike-through of the coloring material was visually observed from the back side of the printed surface, and the print density on the front side of the printed surface was measured. In addition, using a coating solution for print media that had been hermetically stored in a 60 ° C oven for one month, the strike-through of the coloring material was observed and the concentration was measured in the same procedure.

The change in image quality before and after storage of the coating liquid for print media was evaluated according to the following criteria. The inkjet recording device used had a discharge rate of 2.8 pL per dot and a recording density of 2400 × 1200 dpi, and the drive conditions used were a device with a drive frequency of 10 kHz. The amount of the coating liquid for the print medium applied to the print medium is 2.4 g / m.²The speed of the roller and the contact pressure of the roller with the coating liquid for the print medium were adjusted so as to be. Evaluation Criteria for changing image quality are as follows. The evaluation results are shown in Table 9 below.

A: Compared to the comparative example, there is almost no change in the degree of strike-through and the change in concentration.

B: Either the change in the degree of strike-through or the change in the concentration is equal to or higher than that of the comparative example.

C: The degree of strike-through and the change in concentration are equal to or higher than those in the comparative example.

<tables num="9"><img file="JP2005297548A_D0010.tif" /></tables>

Furthermore, the same evaluation as the evaluation of the image change due to the above storage was performed using each reaction solution after storing in a 60 ° C oven for 1 month. As a result, the reactivity of Examples 25 to 27 was obtained before and after storage. There was no difference in strike-through property, but in Comparative Examples 10 and 11, the degree of strike-through changed before and after storage.

<figref num="1">It is a schematic side sectional view which shows an example of an inkjet recording apparatus.</figref><figref num="2">It is a front sectional view of the liquid composition remaining amount display part provided in the inkjet recording apparatus of FIG.</figref><figref num="3">It is the schematic side sectional view which shows the replenishment state of the liquid composition to the inkjet recording apparatus of FIG.</figref><figref num="4">It is a schematic perspective view which shows an example of an inkjet recording apparatus.</figref><figref num="5">It is a vertical sectional view which shows an example of an ink cartridge.</figref><figref num="6">It is a schematic plan view which shows the state which the ink cartridge is attached to the recording head.</figref><figref num="7">It is a figure which shows the measurement result (difference by environment) of the water retention capacity of a water-soluble organic compound.</figref><figref num="8">It is a figure which shows the difference of the water-retaining power of a water-soluble organic compound.</figref>

Code description

1: Recording head 2: Carriage 3: Paper ejection roller 4: Acceleration 5: Paper ejection tray 6: Coating roller 7: Main transport roller 8: Pinch roller 9: Guide shaft 10: Paper feed roller 11: Platen 12: Intermediate roller 13 : Supply roller 14: Float 15: Liquid composition 16: Paper cassette 17: Paper tray 18: Spring 19: Recording medium (recording paper) 20: Injection port 21: Remaining amount display window 22: Refill tank 23: Injection equipment 27: Paper Guide 40: Bag 42: Stopper 44: Absorber 45: Ink Cartridge 51: Paper Feed 52: Paper Feed Roller 53: Paper Discharge Roller 61: Blade 62: Cap 63: Ink Absorber 64: Discharge Recovery Unit 65 : Recording head 66: Carriage 67: Guide shaft 68: Motor 69: Belt 901: Recording head