JP2008246965A - Inkjet recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an inkjet recording medium which requires only a small amount of coating and has both of a high gloss and a high ink absorbency. <P>SOLUTION: The inkjet recording medium is manufactured by a method wherein a water-based coating composition containing a cationic submicron pigment and polyvinyl alcohol is applied on a substrate and then subjected to casting by a direct method. The coating composition contains a univalent cationic sulfate or sulfuric acid of 1-20 mmol per 100 g of the submicron pigment. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an inkjet recording medium, and more particularly to an inkjet recording medium having a glossiness with at least a high coating amount.

  In recent years, the technology of inkjet printers has advanced rapidly, and it has become possible to obtain recorded matter having an image quality equivalent to or higher than that obtained by a general silver salt photography method. Along with this, there is a demand for ink jet recording media having high gloss on the surface equivalent to recording media used in silver salt photography.

Examples of such a recording medium include those based on a plastic film such as a polyester film proposed in Patent Document 1 or the like, or a so-called resin-coated paper obtained by laminating a plastic such as polyethylene on a base paper. However, in order to produce a recording medium having sufficient ink absorbency by these techniques, a large amount of ink absorbing layer is necessarily applied, specifically 20 g / m ² or more, more preferably 25 g / m. ^Two or more ink absorbing layers must be applied, and in order to prevent cracks on the surface, a drying time of at least about 60 seconds is required. In terms of cost, it was not necessarily preferable.

In Patent Document 2, etc., as a means for producing a glossy recording medium for inkjet at a relatively low cost, a glossy surface is provided by providing an ink-absorbing coating layer directly on a base paper and pressing the surface onto a heated metal surface. It is proposed to use a so-called casting method to obtain According to this technique, a part of the required ink absorption can be borne on the base paper, and it is possible to obtain an ink jet recording medium having good ink absorbency with a relatively small coating amount. In order to achieve a glossiness comparable to that of the above technique and a good ink absorbency, a coating amount of about 15 g / m ² or more was still necessary.

When such a large amount of coating is provided, not only the amount of necessary raw materials increases, but also the drying process takes time, so the casting process speed has to be slowed, which is disadvantageous in terms of cost. It was. Furthermore, there is a problem that curling occurs due to a change in humidity, the transportability on the printer is remarkably deteriorated, and the coating layer falls off from the base paper when the recording medium is bent. On the other hand, in Patent Document 3, as a technique for obtaining a high gloss with a relatively small coating amount, a coating made of a polymer resin and a specific polyvalent metal salt is formed on an original fabric coated with an undercoat layer. Although it has been proposed to produce a recording medium by applying a liquid and casting, according to the present technology, a recording medium having an excellent ink absorption capacity can be obtained, but ink absorption In terms of speed, it is extremely insufficient, and when recording is performed using a recent high-speed inkjet printer, it is inevitable that unevenness and blurring occur in the printed image.
JP 2001-150795 A JP-A-63-264391 Japanese Patent Laid-Open No. 10-6539

  An object of the present invention is to provide an ink jet recording medium having good gloss, ink absorption capacity and ink absorption speed even when the coating amount is small, which has been difficult to realize in the past.

  An ink jet recording medium produced by applying an aqueous coating composition containing a cationic submicron pigment and polyvinyl alcohol on a substrate and then performing a cast treatment by a direct method, The working composition is an ink jet recording medium comprising 1 to 20 mmol of monovalent cation sulfate or sulfuric acid per 100 g of submicron pigment.

  According to the present invention, an ink jet recording medium having a gloss, ink absorption capacity, and ink absorption speed, which has not been obtained in the past, is obtained.

  As the base material used in the present invention, paper is usually used, but materials other than paper such as various nonwoven fabrics may be used as necessary. There is no particular restriction on the type and basis weight of the paper used as the base material in the present invention. However, in order to complete drying in the casting process in a short time, the air resistance measured by JIS P 8117 (1998 edition) is required. It is preferable to use one that is 50 (s) or less.

  As the pulp constituting the paper used in the present invention, it is possible to use chemical pulp such as kraft pulp and sulfite pulp, semi-chemical pulp, mechanical pulp manufactured from various conifers and hardwood, bagasse pulp, kenaf pulp It is also possible to use non-wood pulp such as cotton pulp such as linter pulp, straw pulp and bamboo pulp. If the pulp used in the present invention is low in whiteness as the pulp constituting the paper, coloring substances such as lignin derived from it diffuse into the coating layer and cause significant coloration over time. When disliked, it is preferable to use one having a whiteness degree of 75 or more as defined in JIS P 8212 (1998 edition).

  In the present invention, the cationic submicron pigment is a submicron pigment exhibiting a positive zeta potential at pH 6, preferably a zeta potential of +10 mV or higher. Examples thereof include boehmite sol, pseudo boehmite sol, and γ-alumina sol. Alumina compound or diallyldimethylammonium on the surface of silica such as alumina sol, silica sol, gel method silica, precipitation method silica and other wet synthetic silica pulverized to the required particle size using a pulverizer such as colloid mill and high pressure homogenizer And those modified with a cationic organic polymer compound such as These cationic submicron pigments may be used alone or in combination of two or more.

Among such cationic submicron pigments, a silica sol whose surface is modified with an aluminum compound is preferably used because it can achieve both high gloss and good ink absorbability. In particular, it is preferable to use a material having a specific surface area measured by the BET method of 100 m ² or more per gram because a high color density can be obtained.

  In the present invention, the coating composition contains polyvinyl alcohol. In order to achieve both good ink absorbability and coating layer strength, the mass ratio of submicron pigment: polyvinyl alcohol in the present invention is preferably 100: 2 to 100: 8.

  The coating composition of the present invention contains 1 mmol or more and 20 mmol or less of sulfate ions per 100 g of the mass of the submicron pigment. In general, the addition of a polyvalent anion such as sulfate ion to a coating composition containing a cationic submicron pigment causes aggregation of the submicron pigment, resulting in a significant decrease in gloss or viscosity of the coating composition. However, the present invention is considered to be unfavorable because the coating operation becomes extremely difficult, but by adding an appropriate amount of sulfate ions to the coating composition, the present invention can achieve good gloss and low gloss even when the coating amount is small. A method for producing an ink jet recording medium having ink absorptivity is presented. Although the mechanism by which such an effect is obtained has not been verified, the weak higher-order structure formed by the action of an appropriate amount of sulfate ions on the surface of the submicron pigment has a favorable effect on gloss development and ink absorbency. It is presumed to be exerting.

  In the present invention, monovalent cation sulfates such as sodium sulfate, potassium sulfate, potassium hydrogen sulfate, and ammonium sulfate and sulfuric acid can be used as the sulfuric acid source for containing sulfate ions in the coating composition. In the latter case, it should be noted that the pH of the coating composition is naturally lowered. When submicron pigment and monovalent cation sulfate or sulfuric acid are mixed in the absence of polyvinyl alcohol, excessive agglomeration may occur and high gloss may not be obtained. It is preferable to mix polyvinyl alcohol with monovalent cation sulfate or sulfuric acid.

  As a supply source of sulfate ions to the coating composition in the present invention, sulfates of polyvalent metal ions such as zinc sulfate, magnesium sulfate, and aluminum sulfate can be used when the required amount of sulfate ions is added. Is undesirably increased. Of course, poorly water-soluble sulfates such as calcium sulfate and barium sulfate do not produce the required amount of sulfate ions, and are therefore used as a sulfate ion source for incorporating sulfate ions into the coating composition of the present invention. It is not possible. However, it is possible to add these poorly water-soluble sulfates to the coating composition of the present invention for the purpose other than the sulfate ion source.

  In the present invention, the content of the monovalent cation sulfate or sulfuric acid in the coating composition needs to be 1 mmol or more per 100 g of the mass of the submicron pigment. Ink absorption is not obtained. On the other hand, in the present invention, when the content of monovalent cation sulfate or sulfuric acid in the coating composition exceeds 20 mmol per 100 g of the mass of the submicron pigment, the gloss of the resulting recording medium decreases, This is not preferable because the viscosity of the coating composition is remarkably increased and the coating operation becomes extremely difficult.

  In order for the present invention to exert its effect, it is essential that the coating composition before coating contains a monovalent cation sulfate or sulfuric acid. When a monovalent cation sulfate or sulfuric acid is added to the medium, or when the coagulation method described later is used as a casting method, a coating composition substantially free of a monovalent cation sulfate or sulfuric acid is used. The effect of the present invention can be achieved by applying a monovalent cation sulfate or sulfuric acid-containing coagulation chemical solution after coating on the base paper, or by adding a monovalent cation sulfate or sulfuric acid to the substrate in advance. Can't get.

  In the present invention, the cast treatment refers to pressing a coated layer in a wet state onto a heated mirror surface, transferring the mirror surface shape to the surface of the coating layer, and removing moisture from the coated layer to dry the recording medium. Say the process to give. The apparatus used for the casting process (casting apparatus) is usually an apparatus having a structure in which the coated paper is continuously crimped to the surface of the cylinder whose surface is chrome-plated using an elastic roll. A device having another structure having the same action may be used.

  As a method of casting used for producing the ink jet recording medium of the present invention, a method called a direct method is used, in which a coating composition is applied to a mirror surface of a casting apparatus as it is without losing plasticity after coating. The direct method is sometimes called a wet method. In the present invention, if the coating composition after coating does not lose plasticity, the moisture of the coating composition may be removed, but the moisture is lost to such an extent that the plasticity is lost before being pressed. If this happens, it will no longer be possible to obtain a good gloss even if moisture is applied again. In addition, insufficient moisture may be added to increase plasticity, but if there is too much moisture, it will be squeezed at the crimping part and the desired coating amount will not be obtained, or the amount of moisture that will evaporate through the paper will increase. As a result, irregularities may occur on the paper surface and the texture may be impaired. Specifically, the moisture content of the coating layer immediately before the web after coating contacts the cylinder of the casting apparatus is preferably not less than 40%, and preferably not more than 85%.

  In addition, as a method of casting treatment included in the category of the direct method, a chemical solution (coagulation solution) is applied to the coated composition, gelled on a base material, and then pressure-bonded to a mirror surface of a casting apparatus. Gelation methods are known. Also in the coagulation method, by adding a monovalent cation sulfate or sulfuric acid to the coating composition, good gloss and ink absorbency, which are the effects of the present invention, can be obtained. However, as mentioned above, monovalent cation sulfate or sulfuric acid must be included in the coating composition before coating, and even if monovalent cation sulfate or sulfuric acid is added to the coagulation liquid, it is glossy. The improvement effect cannot be obtained.

  As a method of casting for producing glossy paper, there is another method called indirect method or rewet method, which is a method of applying a coating composition, drying it once and then re-wetting it, and then crimping it to the mirror surface of the casting device There is. However, even if the coating composition of the present invention, that is, an aqueous coating solution containing a cationic submicron pigment, polyvinyl alcohol and a specific amount of a monovalent cation sulfate or sulfuric acid is cast by an indirect method, The gloss does not improve compared to the case where a known coating composition is used, or rather decreases in most cases. This is presumably because the above-described weak aggregate structure acts in the direction of decreasing the gloss rather in the indirect method.

  In the present invention, a release agent such as an oily substance or an aqueous dispersion of an oily substance is added to the coating composition of the present invention for the purpose of improving the peelability from the mirror surface in the casting apparatus, or in the casting process. It is preferable to perform the coating in advance, because a high-speed casting process is possible. Substances that can be used as a release agent in the present invention include higher alkylamines such as dimethyloctylamine and dimethyloctadecylamine, higher alkyl quaternary ammonium salts such as trimethyloctylammonium chloride and trimethyloctadecylammonium chloride, oleic acid, stearin Acids, higher carboxylic acids such as caprylic acid or salts thereof, higher alcohols such as octyl alcohol and octadecyl alcohol, vegetable oils, fatty acid triglycerides such as glycerol tristearate, glycerol trilaurate, vegetable oil partial hydrolysates, Glycerol distearate, glycerol dioleate, glycerol dilaurate, glycerol monostearate, glycerol monooleate, glycerol mono Ureto, sorbitan dioleate, polyhydric alcohol fatty acid partial esters such as sorbitan monooleate, liquid paraffin, polyethylene wax, and the like can be exemplified silicone oil.

  In the coating composition of the present invention, for the purpose of promoting gloss expression and improving coating layer strength, zirconium salts such as boric acid, borate, ammonium zirconium acetate, isocyanate compounds, epoxy compounds, aldehydes, etc. It is also possible to add a crosslinking agent.

  A thermoplastic resin dispersion such as acrylic, styrene-acrylic or polyurethane can also be added to the coating composition of the present invention for the purpose of promoting gloss development and improving coating layer strength. . In addition, when these resins are anionic, an agglomerated structure is formed with the submicron pigment, and high gloss may not be obtained. Therefore, it is preferable to use a nonionic or cationic one.

  The coating composition of the present invention also has a high water solubility such as methylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, guar gum, starch, dextrin and the like for the purpose of promoting gloss development and improving coating layer strength. It is also possible to add sugars.

  In the ink jet recording medium of the present invention, a pigment such as silica, latex, polyvinyl alcohol and the like are used between the substrate and the coating layer formed by the cast treatment for the purpose of improving the color and further improving the ink absorbability. It is also possible to provide an undercoat layer made of a binder such as. Also, for the purpose of improving the color and curling, a backing layer comprising a pigment such as kaolin, talc or calcium carbonate and a binder such as polyvinyl alcohol, starch or SBR is provided on the side opposite to the ink absorbing layer. It can also be provided. Various agents such as a fluorescent brightener and a colorant can be added to these layers in accordance with the purpose of improving the appearance.

  Examples of the present invention will be described below. In the examples, unless otherwise specified, parts are parts by mass, and% is mass%.

  [Example 1]

[Preparation of undercoat layer coating composition]
296 parts of water and 4 parts of 50% aqueous sodium hydroxide solution (2 parts of non-volatile content) are mixed, 100 parts of amorphous silica (Fine Seal X37B manufactured by Tokuyama Corporation) is added, and dispersed using a disperser having a saw blade. did. Here, 2 parts of a fluorescent whitening agent as a nonvolatile content, a saponification degree of 98.5 mol%, and a 4% aqueous solution having a viscosity of 26 mPa · second, 400 parts of a 10% aqueous solution of polyvinyl alcohol (Kuraray Kuraray Poval PVA117) (nonvolatile) 40 parts) and 30 parts of a 50% aqueous solution of methylamine-epichlorohydrin condensate (non-volatile part 15 parts) were added and mixed until uniform to prepare an undercoat layer coating composition.

[Coating of undercoat layer]
On the non-coated paper commercially available basis weight 157 g / m ² (manufactured by Mitsubishi Paper Mills diamond form), an undercoat layer coating composition above, as the coating amount after drying of 5 g / m ² air knife Coating was performed using a coater and dried with an air dryer to prepare an original fabric coated with an undercoat layer.

[Preparation of coating composition]
250 parts of water and 40 parts of cationic colloidal silica (Ludox Cl-P manufactured by Grace Devison Co., Ltd.) 250 parts (nonvolatile part 100 parts) have a saponification degree of 88 mol% and a 4% aqueous solution having a viscosity of 40 mPa · sec. 50 parts of a 10% aqueous solution of polyvinyl alcohol (Kuraray Poval PVA224 manufactured by Kuraray Co., Ltd.) (nonvolatile content: 5 parts) was added and mixed with stirring. 10 parts of monooleic acid glycerin ester mixed with 3.4 parts (non-volatile part 0.136 parts) of an aqueous solution of ammonium sulfate having a non-volatile content of 4% and 90 parts of water while stirring this, and processed until uniform with a homogenizer 10 Part (1 part of non-volatile content) was added to prepare a coating composition. In calculation, this coating composition contains 1.0 mmol of ammonium sulfate per 100 g of cationic colloidal silica.

[Cast process]
The above coating composition is coated on the undercoat layer coating raw material prepared above so that the coating amount after drying is 5 g / m ^2, and is crimped to a cylinder of a casting apparatus heated to 95 ° C. The ink jet recording medium was prepared by peeling off after drying.

[Example 2]
An inkjet recording medium was produced in the same manner as in Example 1 except that the amount of the ammonium sulfate aqueous solution added to the coating composition was 16.5 parts (non-volatile content 0.66 parts). In calculation, this coating composition contains 5.0 mmol of ammonium sulfate per 100 g of cationic colloidal silica.

[Example 3]
An ink jet recording medium was prepared in the same manner as in Example 1 except that the amount of the ammonium sulfate aqueous solution added to the coating composition was changed to 66.0 parts (non-volatile content: 2.64 parts). In calculation, this coating composition contains 20.0 mmol of ammonium sulfate per 100 g of cationic colloidal silica.

[Example 4]
[Preparation of coating composition]
Mix 298 parts of water with 2 parts of acetic acid, add 100 parts of alumina hydrate (Pseudoboehmite Dispersal HP-14 manufactured by Sasol Germany, Inc.) while stirring, and continue stirring for 2 hours. Was prepared. To this, 100 parts of a 10% aqueous solution of polyvinyl alcohol (Kuraray Kuraray Poval PVA224 manufactured by Kuraray Co., Ltd.) whose viscosity of the 4% aqueous solution was 40 mPa · sec was added and mixed with stirring. 10 parts of monooleic acid glycerin ester mixed with 3.4 parts (non-volatile part 0.136 parts) of an aqueous solution of ammonium sulfate having a non-volatile content of 4% and 90 parts of water while stirring this, and processed until uniform with a homogenizer 10 Part (1 part of non-volatile content) was added to prepare a coating composition. In calculation, this coating composition contains 1.0 mmol of ammonium sulfate per 100 g of alumina hydrate.

[Cast process]
An inkjet recording medium was produced by the same operation as in Example 1 except that the coating composition prepared above was used.

[Example 5]
An inkjet recording medium was produced in the same manner as in Example 4 except that the amount of the ammonium sulfate aqueous solution added to the coating composition was changed to 16.5 parts (non-volatile content 0.66 parts). In calculation, this coating composition contains 5.0 mmol of ammonium sulfate per 100 g of alumina hydrate.

[Example 6]
An ink jet recording medium was produced in the same manner as in Example 4 except that the amount of the ammonium sulfate aqueous solution added to the coating composition was changed to 66.0 parts (non-volatile content: 2.64 parts). In calculation, this coating composition contains 20.0 mmol of ammonium sulfate per 100 g of alumina hydrate.

[Comparative Example 1]
An inkjet recording medium was prepared in the same manner as in Example 1 except that the aqueous ammonium sulfate solution was not added to the coating composition.

[Comparative Example 2]
An ink jet recording medium was prepared in the same manner as in Example 1 except that the amount of the aqueous ammonium sulfate solution added to the coating composition was 2.7 parts (non-volatile content: 0.11 part). In calculation, this coating composition contains 0.82 mmol of ammonium sulfate per 100 g of cationic colloidal silica.

[Comparative Example 3]
A coating composition was prepared in the same manner as in Example 1 except that the amount of the aqueous ammonium sulfate solution added to the coating composition was 80 parts (non-volatile content: 3.2 parts), but this coating composition can be applied. Did not have a good fluidity. In calculation, this coating composition contains 24 mmol of ammonium sulfate per 100 g of cationic colloidal silica.

[Comparative Example 4]
An ink jet recording medium was produced in the same manner as in Example 4 except that the aqueous ammonium sulfate solution was not added to the coating composition.

[Comparative Example 5]
An ink jet recording medium was produced in the same manner as in Example 4 except that the amount of the aqueous ammonium sulfate solution added to the coating composition was 2.7 parts (non-volatile content: 0.11 part). In calculation, this coating composition contains 0.82 mmol of ammonium sulfate per 100 g of alumina hydrate.

[Comparative Example 6]
A coating composition was prepared in the same manner as in Example 4 except that the amount of the aqueous ammonium sulfate solution added to the coating composition was 80 parts (non-volatile content: 3.2 parts). Did not have possible fluidity. In calculation, this coating composition contains 24 mmol of ammonium sulfate per 100 g of alumina hydrate.

[Comparative Example 7]
After coating the coating composition of Comparative Example 1 on the undercoat layer coating raw material of the example so that the coating amount after drying was 5 g / m ² , 1.56 g /% of 2% aqueous ammonium sulfate solution was applied. The ink-jet recording medium was prepared by applying m ² , then pressure-bonding to a cylinder of a casting apparatus heated to 95 ° C., and peeling off after drying. In addition, the amount of ammonium sulfate applied in this step in calculation is 5 mmol per 100 g of colloidal silica.

[Comparative Example 8]
After coating the coating composition of Comparative Example 4 on the undercoat layer coating raw material of the example so that the coating amount after drying was 5 g / m ² , 1.49 g /% of 2% ammonium sulfate aqueous solution was applied. The ink-jet recording medium was prepared by applying m ² , then pressure-bonding to a cylinder of a casting apparatus heated to 95 ° C., and peeling off after drying. The amount of ammonium sulfate applied in this step is 5 mmol per 100 g of alumina hydrate.

[Comparative Example 9]
A casting apparatus in which the coating composition of Example 1 was coated on the undercoat layer coating raw material, dried once, then dipped in water for 0.6 seconds to wet the coating layer, and then heated to 95 ° C. The ink jet recording medium was prepared by pressure-bonding to the cylinder and peeling off after drying.

[Comparative Example 10]
A casting apparatus in which the coating composition of Example 4 was coated on the undercoat layer coating raw material, then once dried and then immersed in water for 0.6 seconds to wet the coating layer and then heated to 95 ° C. The ink jet recording medium was prepared by pressure-bonding to the cylinder and peeling off after drying.

[Comparative Example 11]
As a coating composition, 350 parts of water, anionic colloidal silica having a nonvolatile content of 40% (Ludox HS-40 manufactured by Grace Debison) 250 parts (nonvolatile content of 100 parts), a nonvolatile content of 45%, and a softening temperature of the dried product An aqueous polyurethane dispersion at 85 to 90 ° C. (Bondic HW-311 manufactured by Dainippon Ink & Chemicals, Inc.) 100 parts (nonvolatile content 45 parts) was added and mixed with stirring. While stirring this, 25 parts of zinc sulfate aqueous solution containing 4% as heptahydrate (1 part as heptahydrate), 90 parts of water and 10 parts of ammonium oleate were mixed and processed with a homogenizer until uniform. Although the thing which added 10 parts (1 part of non volatile matters) was prepared, this coating composition did not have the fluidity | liquidity which can be applied. In terms of calculation, this coating composition contains 3.5 mmol of zinc sulfate per 100 g of colloidal silica, and 2.4 mmol of zinc sulfate per 100 g of the total nonvolatile content of colloidal silica and polyurethane aqueous dispersion.

[Comparative Example 12]
As a coating composition, 193 parts of water, 45% of non-volatile content, 222 parts of a polyurethane aqueous dispersion (bonded HW-311 manufactured by Dainippon Ink & Chemicals, Inc.) having a softening temperature of 85 to 90 ° C. (non-volatile content of 100) Part) was added and mixed with stirring. While stirring this, 100 parts of zinc sulfate aqueous solution containing 4% as heptahydrate (4 parts as heptahydrate), 90 parts of water and 10 parts of ammonium oleate were mixed and treated with a homogenizer until uniform. An ink jet recording medium was prepared in the same manner as in Example 1 except that 10 parts (1 part of non-volatile content) added were used. In calculation, this coating composition contains 13.9 mmol of zinc sulfate per 100 g of the nonvolatile content of the aqueous polyurethane dispersion.

[Gloss evaluation]
Glossiness was classified into 5 levels (best) and 5-1 (worst) by visual observation.

[Evaluation of ink absorbency]
The quality of the ink absorptivity was evaluated by printing an evaluation image with an ink jet printer and observing whether various image defects due to insufficient ink absorption capacity or ink absorption speed occurred. Specifically, a predetermined evaluation image was printed using a Canon Pixus iP3100 inkjet printer. The ink absorbability was classified into five levels, (best) 5-1 (worst), based on the quality of the obtained image, in particular, the blur of the boundary between different colors and the uniformity of the solid image.

  By comparing each example and each comparative example, especially Example 1 and Comparative Example 1, Example 4 and Comparative Example 4, according to the present invention, an inkjet having at least good glossiness and ink absorbency with a coating amount. It can be seen that a recording medium is obtained. As can be seen by comparing Example 1 and Comparative Example 2, and Example 4 and Comparative Example 5, the present invention contains 1 mmol or more of monovalent cation sulfate or sulfuric acid per 100 g of the cationic submicron pigment. If the amount of monovalent cation sulfate or sulfuric acid is less than this, it is not possible to obtain the good gloss that is the effect of the present invention, and as can be seen from Comparative Examples 3 and 6. It is not preferable to add monovalent cation sulfate or sulfuric acid in an amount exceeding 20 mmol per 100 g of the cationic submicron pigment because the fluidity of the coating composition is remarkably deteriorated.

  As can be seen by comparing Example 2 and Comparative Examples 7 and 9, and Example 4 and Comparative Examples 8 and 10, the effect of the present invention is the coating composition before coating with monovalent cation sulfate or sulfuric acid. It can be used only when cast by the direct method, and after applying the coating composition to the base material, it can contain monovalent cation sulfate or sulfuric acid, or after coating. In the case of performing the casting process by the indirect method, the effect of adding a monovalent cation sulfate or sulfuric acid cannot be obtained.

  As can be seen from Comparative Example 11, when a sulfate of a polyvalent cation is used as a sulfate ion supply source, the coating composition is remarkably thickened so that the coating operation is impossible. As can be seen from Comparative Example 12, even if the sulfate of polyvalent cation is used in a small amount so as not to increase the viscosity, the object of the present invention cannot be achieved.

Claims (1)

  An ink jet recording medium produced by applying an aqueous coating composition containing a cationic submicron pigment and polyvinyl alcohol on a substrate and then performing a cast treatment by a direct method, An inkjet recording medium, wherein the working composition contains 1 to 20 mmol of monovalent cation sulfate or sulfuric acid per 100 g of the submicron pigment.