JP7686460B2 - Recording medium - Google Patents

Description

The present invention relates to a recording medium.

As a recording medium used in inkjet recording methods, there is a matte-tone recording medium with a restrained gloss and a calm and deep look. A method using inorganic particles with a large secondary particle diameter is known as a method for obtaining such a matte-tone recording medium with a restrained gloss. In recent years, there has been a demand for matte-tone recording media, such as art paper, which has an uneven surface. For such recording media, it is required that the uneven shape of the substrate is reflected on the surface on which the image is recorded (printing section, printing section), that the image does not have unevenness due to the unevenness, and that images with high optical density and excellent color development can be recorded.

As a matte recording medium suitable for recording painting-like or calligraphy-like images, for example, an inkjet recording medium having an ink-receiving layer in which the surface roughness, center line average roughness, and Oken smoothness are controlled within specific numerical ranges has been proposed (Patent Document 1).

JP 2001-287440 A

When an image was recorded on the recording medium proposed in Patent Document 1 using aqueous pigment ink, it was found that it was possible to record an image with a certain level of optical density. However, when using aqueous dye ink, it was found to be difficult to record an image with the high level of optical density that is currently required.

The object of the present invention is therefore to provide a recording medium capable of recording images with high optical density, in which the texture of the substrate is maintained in the solid printed areas and unevenness is suppressed, even when aqueous dye ink is used.

The above object can be achieved by the present invention described below. That is, according to the present invention, there is provided a recording medium having an absorbent substrate and an ink receiving layer provided on the absorbent substrate, the ink receiving layer containing inorganic particles and a binder, the dry coating weight of the ink receiving layer being 6.0 g/ ^m2 or more and 11.0 g/ ^m2 or less, the arithmetic mean roughness Ra1 (μm) of the surface of the absorbent substrate as defined in ISO 4287:1997 satisfies the relationship of the following formula (1), the arithmetic mean roughness Ra1 and the arithmetic mean roughness Ra2 (μm) of the surface of the ink receiving layer as defined in ISO 4287:1997 satisfies the relationship of the following formula (2), and the average length RSm1 (mm) of the roughness curve element as defined in ISO 4287:1997 of the surface of the absorbent substrate and the average length RSm2 (mm) of the roughness curve element as defined in ISO 4287:1997 of the surface of the ink receiving layer satisfy the relationship of the following formula (3).
Ra1≧5.0μm...(1)
Ra2/Ra1≧0.87...(2)
RSm2/RSm1≦1.40 (3)

The present invention provides a recording medium capable of recording images with high optical density, in which the texture of the substrate is maintained in the solid printed areas and unevenness is suppressed, even when aqueous dye ink is used.

<Recording media>
The present invention will be described in more detail below with reference to preferred embodiments. Hereinafter, the inkjet recording medium will also be referred to simply as the "recording medium". The present inventors have conducted extensive research to provide a recording medium capable of recording an image with high optical density, in which the unevenness of the substrate in the solid printed portion is maintained and unevenness is suppressed, even when an aqueous dye ink is used. As a result, the present inventors have found that the above object can be achieved by the following configuration, and have completed the present invention. That is, the recording medium of the present invention is a recording medium suitable for inkjet recording, which has an absorbent substrate and an ink receiving layer containing inorganic particles and a binder provided on the absorbent substrate. The arithmetic mean roughness Ra1 (μm) of the surface of the absorbent substrate measured in accordance with ISO 4287:1997 satisfies the relationship of the following formula (1).
Ra1≧5.0μm...(1)

By making the arithmetic mean roughness Ra1 of the surface of the absorbent substrate 5.0 μm or more, even if an ink receiving layer is provided on this absorbent substrate, it is possible to obtain a recording medium with a rough surface texture having clear irregularities. If the arithmetic mean roughness Ra1 of the surface of the absorbent substrate is less than 5.0 μm, no clear irregularities will appear on the surface of the ink receiving layer provided on the absorbent substrate, and it is not possible to obtain a recording medium with a rough surface texture. In addition, there is no particular upper limit to the arithmetic mean roughness Ra1 of the surface of the absorbent substrate, but it is preferable that it be, for example, 10.0 μm or less.

The above arithmetic mean roughness Ra1 and the arithmetic mean roughness Ra2 (μm) of the surface of the ink receiving layer defined in ISO 4287:1997 satisfy the relationship of the following formula (2).
Ra2/Ra1≧0.87...(2)

The ink receiving layer can be disposed on the absorbent substrate by applying a coating liquid for the ink receiving layer to the absorbent substrate and drying the coating layer. Although it is affected by the sizing degree of the absorbent substrate, the concentration, viscosity, and coating amount of the coating liquid, and the drying conditions of the coating layer, the arithmetic mean roughness Ra2 of the surface of the ink receiving layer is controlled within a range that is somewhat similar to the arithmetic mean roughness Ra1 of the surface of the absorbent substrate. When the value of "Ra2/Ra1" is 0.87 or more, the surface irregularities of the absorbent substrate generally follow the surface irregularities of the ink receiving layer, and there is almost no difference in thickness within the ink receiving layer. Therefore, even if ink is applied to the ink receiving layer of the recording medium, there is almost no difference in density within the ink receiving layer, and a uniform image without unevenness can be recorded.

If the value of "Ra2/Ra1" is less than 0.87, the surface irregularities of the ink receiving layer do not sufficiently follow the surface irregularities of the absorbent substrate. Therefore, the ink receiving layer is thin at the locations corresponding to the convex portions of the absorbent substrate, and is thick at the locations corresponding to the concave portions of the absorbent substrate. Therefore, when ink is applied to the ink receiving layer of such a recording medium, density unevenness occurs in the ink receiving layer, and it is not possible to record a uniform image without unevenness. It is preferable that the arithmetic mean roughness Ra1 of the surface of the absorbent substrate and the arithmetic mean roughness Ra2 of the surface of the ink receiving layer satisfy the relationship of the following formula (6). This makes it possible to record a more uniform image with further reduced unevenness.
0.91≦Ra2/Ra1≦1.05 ... (6)

The arithmetic mean roughness Ra2 of the surface of the ink receiving layer is not particularly limited as long as it satisfies the relationship of the above formula (2), but is preferably, for example, 4.4 μm or more and 10.5 μm or less. When the ink receiving layer has two or more layers, the arithmetic mean roughness Ra2 of the surface of the ink receiving layer in the present invention means the arithmetic mean roughness of the surface of the arithmetic mean roughness of the ink receiving layer that is the outermost layer located at the position furthest from the substrate.

The average length RSm1 (mm) of the roughness curve element of the surface of the absorbent substrate as defined in ISO 4287:1997, and the average length RSm2 (mm) of the roughness curve element of the surface of the ink-receiving layer as defined in ISO 4287:1997 satisfy the relationship of the following formula (3).
RSm2/RSm1≦1.40 (3)

Although it is influenced by the sizing degree of the absorbent substrate; the concentration, viscosity, and coating amount of the coating liquid; and the drying conditions of the coating layer, the average length RSm2 of the roughness curve element of the ink receiving layer is controlled within a range that is somewhat similar to the average length RSm1 of the roughness curve element of the surface of the absorbent substrate. When the value of "RSm2/RSm1" is 1.40 or less, the surface irregularities of the absorbent substrate generally follow the surface irregularities of the ink receiving layer, and there is almost no difference in thickness within the ink receiving layer. Therefore, even when ink is applied to the ink receiving layer of the recording medium, there is almost no difference in concentration within the ink receiving layer, and a uniform image without unevenness can be recorded.

If the value of "RSm2/RSm1" exceeds 1.40, a mismatch occurs between the period of the surface irregularities of the ink receiving layer and the period of the surface irregularities of the absorbent substrate, resulting in an excessively large difference in thickness within the ink receiving layer. Therefore, when ink is applied to the ink receiving layer of such a recording medium, density unevenness occurs within the ink receiving layer, making it impossible to record a uniform image without unevenness. It is preferable that the average length RSm1 of the surface roughness curve element of the absorbent substrate and the average length RSm2 of the surface roughness curve element of the ink receiving layer satisfy the relationship of the following formula (7). This allows for a more uniform image with further reduced unevenness to be recorded.
0.95≦RSm2/RSm1≦1.30 ... (7)

The average length RSm1 of the roughness curve element of the surface of the absorbent substrate is not particularly limited as long as it satisfies the relationship of the above formula (3), but it is preferably, for example, 0.20 mm or more and 0.60 mm or less. Also, the average length RSm2 of the roughness curve element of the surface of the ink receiving layer is not particularly limited as long as it satisfies the relationship of the above formula (3), but it is preferably, for example, 0.28 mm or more and 0.78 mm or less.

The dry coating amount of the ink receiving layer is 6.0 g/m ² or more and 11.0 g/m ² or less, preferably 7.0 g/m ² or more and 10.0 g/m ² or less. By setting the dry coating amount of the ink receiving layer within the above range, it is possible to obtain a recording medium capable of recording an image with high optical density in which the unevenness of the substrate in the solid printed portion is maintained and unevenness is suppressed. If the dry coating amount is less than 6.0 g/m ² , it becomes difficult to sufficiently cover the surface of the absorbent substrate having large unevenness. Therefore, the coated portion and the uncoated portion of the absorbent substrate coexist, and unevenness occurs in the recorded image. On the other hand, if the dry coating amount exceeds 11.0 g/m ² , the absorbent substrate will be excessively coated. Therefore, the unevenness of the surface of the absorbent substrate will not be clearly visible, and it will be difficult to obtain the unevenness of the substrate. In addition, since the ink receiving layer becomes too thick, the optical density of the image recorded with the aqueous dye ink cannot be increased.

(Absorbent Substrate)
In this specification, the term "absorbent substrate" refers to a substrate having a Cobb water absorbency of 5.0 g/ ^m2 or more after 30 seconds measured according to ISO 535:1991. Any substrate can be used as long as it satisfies the above Cobb water absorbency. Examples of absorbent substrates include cast-coated paper, baryta paper, unsized paper with appropriate sizing, coated paper, cotton paper, etc. Among them, cotton paper is preferably used as the absorbent substrate from the viewpoint of texture, etc. By using an absorbent substrate, a recording medium that exhibits sufficient absorbency even when the amount (coating amount) of the coating liquid used to form the ink receiving layer is small can be obtained, and the ink receiving layer can be provided without impairing the surface unevenness of the absorbent substrate.

(Ink Receiving Layer)
The ink receiving layer provided on the absorbent substrate contains inorganic particles and a binder. The ink receiving layer can be disposed on the absorbent substrate by applying a coating liquid containing the materials contained in the ink receiving layer onto the absorbent substrate and drying the coating layer formed. That is, the materials contained in the ink receiving layer are generally the same as the materials contained in the coating liquid for the ink receiving layer.

In the ink receiving layer, the ratio of the inorganic particle content P to the binder content B (P/B ratio) is preferably 100/30 or more and 100/70 or less. By setting the P/B ratio value within the above range, it is possible to impart sufficient strength to the ink receiving layer and improve the color development of the image and the ink absorption.

The ink receiving layer may be a single layer or may be two or more layers. However, when providing two or more ink receiving layers, it is preferable to apply two or more coating liquids simultaneously. When providing ink receiving layers sequentially, the coating liquid for the second ink receiving layer is applied onto the first ink receiving layer. In this case, the absorption and drying conditions of the coating liquid will vary greatly, so it may be somewhat difficult to form an ink receiving layer with the desired uneven texture.

[Inorganic particles]
The average secondary particle diameter of the inorganic particles is preferably 3.0 μm or more. By using inorganic particles having an average secondary particle diameter of 3.0 μm or more, an ink receiving layer having a more matte surface quality can be formed. There is no particular upper limit to the average secondary particle diameter of the inorganic particles, but it is preferably 15.0 μm or less, for example. In this specification, the "average secondary particle diameter" of inorganic particles means the cumulative 50% particle diameter (D50) on a volume basis measured by a laser diffraction method.

As the inorganic particles, white pigments such as silica, alumina, and precipitated calcium carbonate can be used. Among them, it is preferable to use amorphous silica. Amorphous silica may be produced by any production method. Examples of the production method of amorphous silica include a dry method and a wet method. Dry methods are broadly divided into a combustion method and a heating method. On the other hand, wet methods are broadly divided into a precipitation method and a gelation method.

The combustion method, which is one of the dry methods, is also known as the gas phase method, and is a method in which a mixture of vaporized silicon tetrachloride and hydrogen is burned in air at 1,500 to 2,000°C to produce amorphous silica.

The precipitation method, which is one of the wet methods, is a method in which sodium silicate and sulfuric acid, etc. are reacted in an aqueous solution to obtain amorphous silica as a precipitate. In this precipitation method, the primary particle size of the obtained amorphous silica can be adjusted by controlling conditions such as the reaction temperature and the rate at which the acid is added. Furthermore, in the precipitation method, the secondary particle size of the obtained amorphous silica can also be adjusted by controlling the drying conditions and grinding conditions.

Among the wet methods, the gelation method is a method for obtaining amorphous silica by simultaneously adding sodium silicate and sulfuric acid. This gelation method can obtain amorphous silica with a three-dimensional hydrogel structure in which polymerization between silica particles has progressed due to dehydration condensation of silanol groups. In addition, amorphous silica produced by the gelation method has a relatively small hydrogel structure, so it has a larger specific surface area than amorphous silica produced by the precipitation method. In particular, it is preferable to use amorphous silica produced by the gelation method.

The inorganic particles preferably include a first amorphous silica and a second amorphous silica. The first amorphous silica and the second amorphous silica have different average secondary particle diameters. The arithmetic mean roughness Ra1 (μm) of the surface of the absorbent substrate and the average secondary particle diameter D1 (μm) of the first amorphous silica preferably satisfy the relationship of the following formula (4). Furthermore, the arithmetic mean roughness Ra1 (μm) of the surface of the absorbent substrate and the average secondary particle diameter D2 (μm) of the second amorphous silica preferably satisfy the relationship of the following formula (5). By satisfying the relationship of the following formulas (4) and (5), the color development of the image recorded with the aqueous dye ink can be further improved. The mixing ratio (mass ratio) of the first amorphous silica and the second amorphous silica is preferably the content of the first amorphous silica: the content of the second amorphous silica = 30:70 to 70:30.
D1≦Ra1 (4)
D2 ≧ Ra1 ... (5)

The oil absorption of the amorphous silica measured in accordance with JIS K6217-4:2017 is preferably 150 mL/100 g or more and 350 mL/100 g or less, more preferably 180 mL/100 g or more and 330 mL/100 g or less. The pore volume of the amorphous silica measured by the BET method is preferably 1.0 mL/g or more, more preferably 1.3 mL/g or more. The specific surface area of the amorphous silica measured by the BET method is preferably 200 m ² /g or more and 500 m ² /g or less.

[Binder]
Examples of the binder include polyvinyl alcohol (PVA), oxidized starch, etherified starch, phosphated starch, carboxymethyl cellulose, hydroxyethyl cellulose, casein, gelatin, soy protein, polyvinylpyrrolidone, maleic anhydride resin, conjugated polymer latexes such as styrene-butadiene copolymers, methyl methacrylate-butadiene copolymers, and the like, acrylic polymer latexes such as polymers of acrylic acid esters and methacrylic acid esters, vinyl polymer latexes such as ethylene-vinyl acetate copolymers, melamine resins, urea resins, (co)polymer resins of acrylic acid esters and methacrylic acid esters such as polymethyl methacrylate, polyurethane resins, unsaturated polyester resins, vinyl chloride-vinyl acetate copolymers, polyvinyl butyral, alkyd resins, and the like.

The above binders can be used alone or in combination of two or more. Among them, it is preferable to use polyvinyl alcohol (PVA) as the binder. The average polymerization degree of PVA is preferably 1,500 or more and 5,000 or less. The saponification degree of PVA is preferably 70% or more and 100% or less. Modified PVA such as silanol-modified PVA having silanol groups at its terminals can also be used as the binder.

[Additives]
The ink receiving layer and the coating liquid for the ink receiving layer may contain additives such as a pigment dispersant, a fastness improver, and a surfactant. Among them, it is preferable to contain a cationic polymer in the coating liquid for the ink receiving layer, since it is possible to increase the dispersibility of the coating liquid and to improve the fastness and water resistance of the recorded image. Examples of the cationic polymer include polymers having primary to tertiary amino groups in the molecule and polymers having quaternary ammonium salt groups. Examples of the cationic polymer include polyalkylene polyamines, derivatives of polyalkylene polyamines, dicyan-based cationic resins, polyamine-based cationic resins, epichlorohydrin-dimethylamine addition polymers, dimethyldiallylammonium chloride polymers, and diallylamine salt polymers.

The content of additives in the ink receiving layer and the coating liquid for the ink receiving layer is preferably 0.1 parts by mass or more and 30.0 parts by mass or less per 100 parts by mass of inorganic particles such as amorphous silica.

(Method of manufacturing recording medium)
The method for producing the recording medium is not particularly limited. For example, it is preferable to produce the recording medium by a production method including a step of preparing a coating liquid for the ink receiving layer (a coating liquid preparation step) and a step of applying the prepared coating liquid to an absorbent substrate (a coating step).

In the coating liquid preparation process, a coating liquid for the ink receiving layer is prepared. The coating liquid can be prepared by mixing the aforementioned components according to standard methods.

In the coating process, the prepared coating liquid is applied to the absorbent substrate to form a coating layer. To apply the coating liquid to the absorbent substrate, a gate roll coater, size press, bar coater, blade coater, air knife coater, roll coater, brush coater, curtain coater, gravure coater, spray device, etc. can be used. The coating liquid may be appropriately heated before application.

It is preferable to dry the coating layer formed by applying the coating liquid to the absorbent substrate. To dry the coating layer, a hot air dryer such as a linear tunnel dryer, an arch dryer, an air loop dryer, or a sine curve air float dryer can be used. Dryers that utilize infrared rays, heated dryers, microwaves, etc. can also be used. The heating temperature during drying can be, for example, 80 to 130°C.

Before applying the coating liquid to the absorbent substrate, a surface treatment liquid containing a surface treatment agent may be applied to the surface of the absorbent substrate (the surface to which the coating liquid is applied). By applying the surface treatment liquid to the surface of the absorbent substrate in advance, the wettability of the coating liquid to the absorbent substrate is increased, and the adhesion between the ink receiving layer formed and the absorbent substrate can be improved. Examples of surface treatment agents include thermoplastic resins such as acrylic resins, polyurethane resins, polyester resins, polyethylene resins, polyvinyl chloride resins, polypropylene resins, polyamide resins, and styrene-butadiene copolymers; silane coupling agents; and the like. The surface treatment liquid may contain inorganic particles such as titanium oxide, calcium carbide, silica, and alumina, as necessary.

<Image recording method>
An image can be recorded on the recording medium by ejecting ink from an inkjet recording head and applying it to the above-mentioned recording medium. Methods for ejecting ink include a method for ejecting ink by applying mechanical energy to the ink, and a method for ejecting ink by applying thermal energy to the ink. As the ink, a water-based ink containing a dye as a coloring material (aqueous dye ink) or a water-based ink containing a pigment as a coloring material (aqueous pigment ink) can be used. Among them, it is preferable to use a water-based dye ink.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way to the following examples as long as it does not deviate from the gist of the invention. "Parts" and "%" used to describe the amounts of components are by weight unless otherwise specified.

<Production of absorbent substrate>
(Absorbent Substrates A, B, and C)
Water was added to the stock having the composition shown below to adjust the solid content to 3.0%. "CSF" is an abbreviation for Canadian Standard Freeness.
[Paper material]
Cotton linter pulp with a freeness of 330 mL CSF: 100 parts Cationic starch: 0.6 parts Heavy calcium carbonate: 10 parts Light calcium carbonate: 15 parts Alkyl ketene dimer: 0.2 parts Cationic polyacrylamide: 0.05 parts

Then, the paper was made using a fourdrinier paper machine, and after three-stage wet pressing, it was dried using a multi-cylinder dryer. Using a size press, the paper was impregnated with an aqueous solution of oxidized starch so that the solid content was 1.0 g/ ^m2 , and dried. Then, machine calendar finishing was performed to obtain an absorbent substrate A having a basis weight of 150 g/ ^m2 , an arithmetic mean roughness Ra1=6.6 (μm) as defined in ISO 4287:1997, and an average length of roughness curve element RSm1=0.31 (mm). The Cobb water absorbency after 30 seconds of the obtained absorbent substrate A measured in accordance with ISO 535:1991 was 25 g/ ^m2 .

Furthermore, by appropriately changing the pressing conditions and calendaring conditions, an absorbent substrate B having Ra1 = 5.1 (μm) and RSm1 = 0.29 (mm) and an absorbent substrate C having Ra1 = 4.4 (μm) and RSm1 = 0.25 (mm) were obtained. The Cobb water absorbency of the obtained absorbent substrate B and absorbent substrate C was 23 g / m ² and 22 g / m ² , respectively.

(Absorbent substrate D)
Water was added to a stock having the composition shown below, and the solids concentration was adjusted to 3.0%.
[Paper material]
Hardwood bleached kraft pulp (LBKP) with a freeness of 450 mLCSF: 80 parts Softwood bleached kraft pulp (NBKP) with a freeness of 480 mLCSF: 20 parts Cationic starch: 0.6 parts Heavy calcium carbonate: 10 parts Light calcium carbonate: 15 parts Alkyl ketene dimer: 0.1 parts Cationic polyacrylamide: 0.03 parts

Next, the paper was made using a fourdrinier paper machine, and after three-stage wet pressing, it was dried using a multi-cylinder dryer. Using a size press device, the paper was impregnated with an aqueous solution of oxidized starch so that the solid content was 1.0 g/ ^m2 , and then dried. Then, by machine calendaring, an absorbent substrate D was obtained with a basis weight of 150 g/ ^m2 , an arithmetic mean roughness Ra1=6.6 (μm) measured according to ISO 4287:1997, and an average length of roughness curve elements RSm1=0.31 (mm). The Cobb water absorbency of the obtained absorbent substrate D was 23 g/ ^m2 .

<Manufacture of recording media>
(Preparation of Dispersions A and B)
A dispersant (trade name "Sharol DC-902", manufactured by Daiichi Kogyo Seiyaku) was added to pure water in an amount of 10 parts per 100 parts of silica to obtain a dispersant solution. Amorphous silica A (trade name "Nipgel AY-603", manufactured by Tosoh Silica, D50: 10 μm) was added to the obtained dispersant solution in an amount of 19% solid content concentration, and the mixture was thoroughly stirred with a stirrer to obtain a dispersion. The obtained dispersion was appropriately diluted with pure water to obtain a dispersion A in which the solid content concentration of the amorphous silica powder was 18%.

Dispersion B with a solids concentration of 18% was obtained in the same manner as dispersion A described above, except that amorphous silica B (product name "Gasil 23F", manufactured by PQ Corporation, D50: 6 μm) was used instead of amorphous silica A.

(Preparation of Coating Solutions A and B for Ink Receiving Layer)
Polyvinyl alcohol (trade name "PVA235", manufactured by Kuraray) was dissolved in ion-exchanged water to obtain a PVA aqueous solution with a solid content of 8%. Dispersion A, dispersion B, and the PVA aqueous solution were mixed so that the mass ratio of amorphous silica A: amorphous silica B: binder (PVA) was 50:50:40. Pure water was added and stirred so that the total solid content was 13%, to obtain coating solution A for the ink receiving layer.

Coating liquid B for the ink receiving layer was obtained in the same manner as for coating liquid A described above, except that dispersion liquid A and the PVA aqueous solution were mixed so that the mass ratio of amorphous silica A:binder (PVA) was 100:40 (dispersion liquid B was not used).

(Recording medium 1)
Coating solution A was applied onto absorbent substrate A so that the dry coating amount was 10.0 g/ ^m2 to form a coating layer. The formed coating layer was dried with hot air at 100°C to form an ink receiving layer, and recording medium 1 was obtained.

(Recording medium 2)
Recording medium 2 was obtained in the same manner as in the case of recording medium 1 described above, except that coating solution A was applied so that the dry coating amount was 11.0 g/ ^m2 .

(Recording medium 3)
Recording medium 3 was obtained in the same manner as in the case of recording medium 1 described above, except that coating liquid A was applied so that the dry coating amount was 10.5 g/ ^m2 .

(Recording medium 4)
Recording medium 4 was obtained in the same manner as in the case of recording medium 1 described above, except that coating liquid A was applied so that the dry coating amount was 7.0 g/ ^m2 .

(Recording medium 5)
Recording medium 5 was obtained in the same manner as in the case of recording medium 1 described above, except that coating solution A was applied so that the dry coating amount was 8.0 g/ ^m2 .

(Recording medium 6)
Recording medium 6 was obtained in the same manner as in the case of recording medium 1 described above, except that Coating Solution A was applied so that the dry coating amount was 9.0 g/ ^m2 , and the coating layer was dried with hot air at 110°C to form an ink-receiving layer.

(Recording medium 7)
Recording medium 7 was obtained in the same manner as in the case of recording medium 6 described above, except that Coating Solution A was applied so that the dry coating amount was 12.0 g/ ^m2 .

(Recording medium 8)
Recording medium 8 was obtained in the same manner as in the case of recording medium 6 described above, except that coating solution A was applied so that the dry coating amount was 10.0 g/ ^m2 .

(Recording medium 9)
Recording medium 9 was obtained in the same manner as in the case of recording medium 6 described above, except that Coating Solution A was applied so that the dry coating amount was 11.0 g/ ^m2 .

(Recording medium 10)
Recording medium 10 was obtained in the same manner as in the case of recording medium 6, except that the coating layer was dried with hot air at 90° C. to form an ink-receiving layer.

(Recording medium 11)
Recording medium 11 was obtained in the same manner as in the case of recording medium 6, except that the coating layer was dried with hot air at 80° C. to form an ink-receiving layer.

(Recording medium 12)
Recording medium 12 was obtained in the same manner as in the case of recording medium 6, except that the coating layer was dried with hot air at 70° C. to form an ink-receiving layer.

(Recording medium 13)
Recording medium 13 was obtained in the same manner as in the case of recording medium 1 described above, except that Coating Solution A was applied so that the dry coating amount was 9.5 g/ ^m2 .

(Recording medium 14)
Recording medium 14 was obtained in the same manner as in the case of recording medium 1 described above, except that coating liquid B was used instead of coating liquid A.

(Recording medium 15)
Recording medium 15 was obtained in the same manner as in the case of recording medium 1 described above, except that absorbent substrate D was used in place of absorbent substrate A.

(Recording medium 16)
Recording medium 16 was obtained in the same manner as in the case of recording medium 1 described above, except that Coating Liquid A was applied so that the dry coating amount was 6.0 g/ ^m2 .

(Recording medium 17)
Recording medium 17 was obtained in the same manner as in the case of recording medium 1 described above, except that Coating Liquid A was applied so that the dry coating amount was 5.0 g/ ^m2 .

(Recording medium 18)
Recording medium 18 was obtained in the same manner as in the case of recording medium 1 described above, except that absorbent substrate C was used in place of absorbent substrate A.

(Recording medium 19)
Recording medium 19 was obtained in the same manner as in the case of recording medium 1 described above, except that absorbent substrate B was used in place of absorbent substrate A.

Details of the obtained recording medium are shown in Table 1.

<Evaluation>
(Image recording)
An inkjet recording device (product name "PIXUS TS6030", manufactured by Canon) was used in the "swelling paper" mode to record an image (solid print area) of (R, G, B) = (0, 0, 0) on each of recording media 1 to 19. The ink used was a water-based dye ink (product name "BCI-351", manufactured by Canon, black (Bk) ink) that is a genuine ink for the inkjet recording device.

(Evaluation of unevenness in solid printed areas)
The recorded image (solid printed area) was visually observed, and unevenness in the solid printed area was evaluated according to the following evaluation criteria. Unevenness in the solid printed area means unevenness (non-uniformity) in print density. The results are shown in Table 2. In the evaluation criteria shown below, "A", "B", and "C" were considered to be preferable levels, and "D" was considered to be an unacceptable level.
A: There was almost no unevenness.
B: Slight unevenness was observed.
C: Some unevenness was observed, but was at a level that did not cause any practical problems.
D: A level at which clear unevenness was observed.

(Evaluation of unevenness in solid printed areas)
The recorded image (solid printed area) and blank area were visually observed, and the unevenness of the solid printed area was evaluated according to the following evaluation criteria. The results are shown in Table 2. In the evaluation criteria shown below, "A" and "B" were considered to be preferable levels, and "C" was considered to be an unacceptable level. A: There was almost no difference in the unevenness between the solid printed area and the blank area.
B: The unevenness of the solid printed area was somewhat inferior to that of the blank area, but was not at a problematic level.
C: The unevenness of the solid printed area was significantly impaired as compared with the blank area.

(Evaluation of dye color development)
After the image was recorded, the image was stored for 2 days in an environment of 25° C. and 50% RH (relative humidity).
Thereafter, the O.D. value (optical density) of the image was measured using a spectrophotometer (trade name "Spectrolino", manufactured by Gretag Macbeth), and the dye color development was performed according to the following evaluation criteria. The results are shown in Table 2. In the following evaluation criteria, "A" and "B" were considered to be favorable levels, and "C" was considered to be an unacceptable level.
A: The O.D. value was 1.60 or more.
B: The O.D. value was 1.50 or more and less than 1.60.
C: The O.D. value was less than 1.50.

Claims (9)

A recording medium having an absorbent substrate and an ink receiving layer provided on the absorbent substrate, the ink receiving layer containing inorganic particles and a binder,
The dry coating weight of the ink receiving layer is 6.0 g/m2 or ^more and 11.0 g/ ^m2 or less,
The arithmetic mean roughness Ra1 (μm) of the surface of the absorbent substrate as defined in ISO 4287:1997 satisfies the relationship of the following formula (1),
the arithmetic mean roughness Ra1 and the arithmetic mean roughness Ra2 (μm) of the surface of the ink receiving layer defined in ISO 4287:1997 satisfy the relationship of the following formula (2),
A recording medium, characterized in that an average length RSm1 (mm) of a roughness curve element defined in ISO 4287:1997 of the surface of the absorbent substrate and an average length RSm2 (mm) of a roughness curve element defined in ISO 4287:1997 of the surface of the ink receiving layer satisfy the relationship of the following formula (3):
Ra1≧5.0μm...(1)
Ra2/Ra1≧0.87...(2)
RSm2/RSm1≦1.40 (3) the inorganic particles include a first amorphous silica and a second amorphous silica;
The arithmetic average roughness Ra1 and the average secondary particle diameter D1 (μm) of the first amorphous silica satisfy the relationship of the following formula (4),
2. The recording medium according to claim 1, wherein the arithmetic mean roughness Ra1 and the average secondary particle diameter D2 (μm) of the second amorphous silica satisfy the relationship of the following formula (5).
D1≦Ra1 (4)
D2 ≧ Ra1 ... (5) 3. The recording medium according to claim 1, wherein the arithmetic mean roughness Ra1 and the arithmetic mean roughness Ra2 satisfy the relationship of the following formula (6).
0.91≦Ra2/Ra1≦1.05 ... (6) 4. The recording medium according to claim 1, wherein the average length RSm1 of the roughness curve elements and the average length RSm2 of the roughness curve elements satisfy the relationship of the following formula (7).
0.95≦RSm2/RSm1≦1.30 ... (7) 5. The recording medium according to claim 1, wherein the arithmetic mean roughness Ra1 satisfies the following formula (8):
Ra1≧6.6μm...(8) 6. The recording medium according to claim 1, wherein the arithmetic mean roughness Ra2 satisfies the following formula (9):
4.4μm≦Ra2≦10.5μm (9) 7. The recording medium according to claim 1, wherein the absorbent substrate has a Cobb water absorbency after 30 seconds, measured according to ISO 535:1991, of 5.0 g/ ^m2 or more. 8. The recording medium according to claim 1, wherein the absorbent substrate is cotton paper. 9. The recording medium according to claim 1, which is for ink-jet use.