JP2009101536A - Inkjet recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording medium which has excellent glossy outlook and can inhibit print unevenness even during inkjet recording with pigmented ink. <P>SOLUTION: This inkjet recording medium has an ink receptive layer including a pigment and a binder applied, by the cast coating process, to at least, one surface of the base paper. The base paper contains a rosetta-type light calcium carbonate whose ash content stipulated by JIS-P8251 is 5 to 25 mass%, with not less than 10% glossiness, at 20° of the surface of the ink receptive layer, stipulated by JIS-Z8741. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an inkjet recording medium having gloss suitable for an inkjet recording system.

  An ink jet recording medium has a structure in which an ink receiving layer containing a porous pigment such as silica or alumina and a binder is provided on the surface of a base paper such as paper, and an ink liquid is provided on the ink receiving layer. Drops are fixed. With the remarkable progress of ink jet printers in recent years and the remarkable spread of digital cameras, the quality required for ink jet recording media is increasing year by year. In particular, in an inkjet recording medium having a gloss comparable to that of a conventional silver salt photograph, quality requirements are strict and technological development is actively being carried out.

  The inkjet recording medium having gloss described above is generally produced by a cast coating method using a cast coater from the viewpoint of production cost. The cast coating method is a method of applying a coating liquid mainly composed of a pigment and a binder onto a base paper to provide a coating layer, and finishing the coating layer with a cast drum, This gloss coating layer becomes the ink receiving layer. The cast coating method includes (1) a wet casting method (direct method) in which a coating layer is pressed onto a mirror-finished heating drum while the coating layer is wet, and (2) a wet coating layer is once dried. Alternatively, a semi-dried, rewetting method that is swollen and plasticized with a re-wetting solution, and is pressed onto a mirror-finished heating drum and dried. (3) A heated coating drum that is mirror-finished after the wet coating layer is gelled by coagulation There are generally known three types of gelation cast methods (coagulation methods) in which pressure is bonded to the substrate and dried. The principle of each method is the same in that the wet coating layer is pressed against the mirror-finished surface to give gloss to the coating layer surface.

The quality characteristics required for such a glossy inkjet recording medium include high gloss on the surface of the recording medium, high print density, no ink overflow or bleeding, and uneven printing (light / dark unevenness). In order to improve these characteristics, it is necessary to improve the ink receiving layer. For example, a technique has been reported in which the ink receiving layer has a layer structure of one or more layers, and at least one layer contains colloidal particles having an average particle diameter of 300 nm or less and a cationic resin (for example, see Patent Document 1). In addition, a technology containing colloidal silica having a primary particle diameter of 30 to 100 nm and a ratio of the secondary particle diameter to the primary particle diameter of 1.5 to 2.5 in the cast coating layer has been reported. (For example, refer to Patent Document 2).
In addition, a pigment and a binder are attached to at least one side of a base paper mainly composed of pulp and a rosette-type light calcium carbonate having an average particle size of 1.6 μm or more and an oil absorption of 90 to 200 ml / 100 g. An ink jet recording sheet in which one or more ink receiving layers containing an agent are provided, and the ash content of the base paper defined in JIS-P8251 is 15 to 40% is disclosed (for example, see Patent Document 3).

Japanese Patent Laid-Open No. 9-263039 JP-A-2005-35169 JP 2006-256001 A

However, the techniques described in Patent Documents 1 and 2 have room for improvement in terms of increasing the glossiness of the recording medium, and there is a problem that uneven printing occurs when ink jet recording is performed with pigment ink. It was. The printing unevenness referred to here refers to unevenness in density that occurs when a solid portion is output by the ink jet recording method, and is considered to be caused by a crack on the surface of the ink receiving layer. In the case of the technique described in Patent Document 2, since there are no relatively large cracks on the surface of the ink receiving layer, printing unevenness can be suppressed when printing with dye ink, but minute cracks remain, and printing unevenness when printing with pigment ink. (For example, color loss or solid density unevenness in a solid print portion) occurs.
In the case of the technique described in Patent Document 3, the base paper contains high ash content and rosette-type light calcium carbonate. However, since the ink receiving layer is not provided by the cast coating method, high gloss is obtained. Absent.
Accordingly, an object of the present invention is to provide an ink jet recording medium which is excellent in gloss and can suppress printing unevenness even when ink jet recording is performed using a pigment ink.

As a result of various investigations by the present inventors, the inclusion of rosetta-type calcium carbonate as a filler in a gas-permeable base paper has a very large gloss development effect when an ink receiving layer is provided by the cast coating method. And found the present invention.
In addition, the present inventors have already stated in Patent Document 2 that the cause of printing unevenness is caused by fine cracks on the surface of the coating layer provided by the cast coating method, and by using a predetermined colloidal silica. It discloses that printing unevenness with respect to dye ink can be prevented. Furthermore, as a particular problem when the pigment ink is used, the present inventors have a problem that if the ink absorbency is small, the colored pigment aggregates due to surface tension while the solvent of the pigment ink stays in the ink receiving layer. It was found that the color pigment was selectively absorbed in the cracks, causing a density difference between the cracked part and the part without the crack, resulting in uneven printing. It has been found that when the above rosette type calcium carbonate is used as a filler, it is possible to prevent such uneven printing with respect to the pigment ink.

  That is, in the ink jet recording medium of the present invention, an ink receiving layer containing a pigment and a binder is provided on at least one surface of a base paper by a cast coating method, the base paper contains rosetta type light calcium carbonate, and The 20 degree glossiness of the surface of the ink receiving layer specified in JIS-Z8741 is 10% or more.

It is preferable that the ash content of JIS-P8251 of the Rosetta-type light calcium carbonate in the base paper is 5 to 25% by mass.
The pigment of the ink receiving layer preferably contains colloidal silica.

  According to the present invention, an ink jet recording medium that is excellent in gloss, further suppresses uneven printing even when ink jet recording is performed using pigment ink, and has high print density when using dye ink and pigment ink. Is obtained.

  Embodiments of the present invention will be described below. In the ink jet recording medium of the present invention, an ink receiving layer containing a pigment and a binder is provided on at least one surface of a base paper by a cast coating method.

(Base paper)
As the base paper used in the present invention, any material can be used as long as it has a gas permeability sufficient to transmit water vapor generated in the cast drum during cast coating. Etc. is preferably used. The base paper is composed of pulp fibers and fillers. The raw pulp includes chemical pulp (conifer bleached or unbleached kraft pulp, hardwood bleached or unbleached kraft pulp, etc.), mechanical pulp (grand pulp, thermomechanical pulp, Chemi-thermomechanical pulp, etc.), deinked pulp, etc. can be used alone or mixed in any proportion. It is preferable that softwood pulp is contained as the raw material pulp. When softwood pulp is blended in the base paper, the strength of the base paper is improved and the glossiness of the ink receiving layer tends to be improved. However, since the surface property of the base paper tends to decrease when the content of softwood pulp increases, the content of softwood pulp is preferably 30% by mass or less in the total pulp. The pH of the base paper may be acidic, neutral or alkaline.

(Filler)
The base paper contains rosette type light calcium carbonate as an essential filler. Rosetta-type light calcium carbonate is obtained by agglomerating primary particles of spindle-shaped light calcium carbonate in a radial manner to form Rosetta-type secondary particles. Specifically, Specialty Minerals Inc. Products such as Albuquer HO, Albuquer 5970, Albuquer LO, etc. can be preferably mentioned. Here, the term “radial” refers, for example, to the longitudinal direction of each primary particle extending radially from the vicinity of the center of the secondary particle.

  Light calcium carbonate is excellent in terms of production cost, operability, and addition amount, and at least high opacity can be obtained.Rosetta-type light calcium carbonate has a special shape, so if it is added to the base paper at a high ratio, The opacity of the paper is greatly improved, and the back-through during ink jet recording is effectively prevented. Furthermore, since Rosetta-type light calcium carbonate has a larger specific surface area than conventional light calcium carbonate, a base paper excellent in ink absorbability can be obtained. In particular, when the amount of the ink receiving layer applied is small, a large effect can be obtained by using rosetta type light calcium carbonate.

  The average particle size of the rosetta type light calcium carbonate is preferably 1.5 to 5.0 μm. When the average particle size is less than 1.5 μm, the transparency of the base paper is lowered due to the improved light transmission. As a result, the printed image can be seen through from the back side of the recording paper, or the back-through occurs. Sometimes. On the other hand, when the average particle size exceeds 5.0 μm, the filler distribution is non-uniform, and the opacity of the base paper is lowered, and there is a tendency that the back-through occurs or the quality stability is lowered.

  The oil absorption of Rosetta-type light calcium carbonate is preferably 90 to 200 ml / 100 g, and particularly preferably 90 to 140 ml / 100 g. When the oil absorption is less than 90 ml / 100 g, the ink absorbability of the obtained ink jet recording paper tends to be lowered. On the other hand, when the oil absorption exceeds 200 ml / 100 g, the absorbability of the base paper becomes too large, and only the binder component easily penetrates into the base paper when the ink-receiving layer coating liquid is applied. The surface strength of the receiving layer may be reduced, and problems such as powder falling off during cutting may occur.

  FIG. 1 is an electron microscopic image showing an example of the form of Rosetta-type light calcium carbonate (secondary particles) in a state dispersed in a liquid. In this figure, the bases of the respective primary particles are aggregated, and each primary particle extends radially toward the tip. In addition, each primary particle has a slightly larger width (diameter) at the base and narrows toward the tip. In addition, micron in a figure shows micrometer.

When an ink receiving layer is provided by a cast coating method on a base paper containing Rosetta type light calcium carbonate as a filler, it is specified in JIS-Z8741 as compared with the case of using a base paper not containing Rosetta type light calcium carbonate as a filler. The 20 degree glossiness of the surface of the ink receiving layer is improved. The reason for this is not clear, but is thought to be as follows.
First, when Rosetta-type light calcium carbonate is blended in the base paper, the density of the base paper is lowered to make the paper bulky, and the cushioning property is improved. For this reason, when the ink receiving layer coating layer is pressed against the cast drum during cast coating, the coating layer tends to adhere to the cast drum surface, and as a result, the glossiness of the obtained ink receiving layer is improved. Conceivable. The higher the 20 ° gloss value, the better the glossiness. In the present invention, the 20 ° gloss value needs to be 10% or more. Further, the higher the value of image clarity, the better the glossiness. In the present invention, the image clarity is preferably 40% or more, and particularly preferably 60% or more.
The density of the base paper is preferably 0.8 or less.

In addition, when Rosetta-type light calcium carbonate is contained in the base paper, printing unevenness when using pigment ink can be suppressed. The reason is considered as follows.
Causes of uneven printing include fine cracks and cracks on the surface of the ink receiving layer, but when the ink receiving layer coating liquid is applied to normal base paper, the ink receiving layer binder component soaks into the base paper. Therefore, it is considered that minute cracks are generated on the surface of the ink receiving layer. In particular, when such fine cracks are present, printing unevenness occurs during printing of pigment ink.
On the other hand, when Rosetta-type light calcium carbonate is contained in the base paper, the absorbability of the base paper is improved, so that the ink receiving layer binder component penetrates into the base paper uniformly, and the above-described cracks (cracks) are less likely to occur. It is considered to be. As a result, printing unevenness during printing of pigment ink is reduced. Further, since the penetration into the base paper is uniform, the pigment is uniformly present in the ink receiving layer, and the ink absorbability of the ink receiving layer is increased. As a result, it is possible to prevent the colored pigment from aggregating due to surface tension while the solvent of the pigment ink stays in the ink receiving layer and selectively absorbing the colored pigment in the cracks to cause printing unevenness.
When the ink receiving layer contains colloidal silica having a predetermined primary particle size and particle size ratio (secondary particle size / primary particle size), which will be described later, large cracks on the surface of the ink receiving layer can be suppressed. Printing unevenness can be further reduced.

(ash)
The ash content defined in JIS-P8251 of Rosetta-type light calcium carbonate in the base paper is preferably 5 to 25% by mass, and more preferably 10 to 20% by mass. The higher the ash content of calcium carbonate in the base paper, the greater the glossiness of the ink receiving layer surface provided by the cast coating method, and the greater the effect of suppressing printing unevenness when printing with pigment ink.
When the ash content of the rosetta type light calcium carbonate is less than 5% by mass, the gloss improvement effect may be small. In addition, the higher the ash content of Rosetta-type light calcium carbonate, the higher the effect of improving gloss and suppressing printing unevenness. However, if the ash content exceeds 25% by mass, powder falling or the strength of the base paper decreases. The problem may occur. Therefore, in consideration of the balance between the manufacturing cost and the effect, it is preferable that the ash content of the rosetta-type light calcium carbonate does not exceed 25% by mass.
The ash content defined in JIS-P8251 represents the amount of ash residue after burning a sample (paper) at a temperature of 525 ± 25 ° C. as a percentage of the absolute dry weight of the sample.

As long as the effects of the present invention are not impaired, from among known fillers such as hydrated silicic acid, white carbon, talc, kaolin, clay, calcium carbonate (other than rosetta-type light calcium carbonate), titanium oxide, and synthetic resin fine particles. It can be appropriately selected and used in combination with the above-mentioned rosetta type calcium carbonate. The filler other than the rosetta-type calcium carbonate is preferably 30% by mass or less of the entire filler in the base paper, and more preferably no filler other than the rosetta-type calcium carbonate is contained.
From the viewpoint of production efficiency of the ink jet recording medium, the air permeability of the base paper is preferably 1000 seconds or less, and from the viewpoint of coating properties, the Steecht sizing degree of the base paper is preferably 5 seconds or more. .

(Pigment of ink receiving layer)
As pigments in the ink receiving layer, synthetic silica, colloidal silica, aluminum hydroxide, alumina sol, colloidal alumina, pseudoboehmite and other aluminas (α-type crystal alumina, θ-type crystal alumina, γ-type crystal alumina, etc.) and alumina Known inorganic fine particles such as hydrate, kaolin, talc, calcium carbonate, titanium dioxide, clay, and zinc oxide can be used. Among these pigments, it is preferable to contain a pigment (particularly colloidal silica) having a primary particle size of 100 nm or less in terms of high gloss. When colloidal silica is contained, it is possible to reduce printing unevenness during printing of pigment ink while improving the glossiness of the ink receiving layer surface.

When colloidal silica (peanut-shaped colloidal silica) having a primary particle diameter of 30 to 70 nm and a ratio of the secondary particle diameter to the primary particle diameter of 1.5 to 3.0 is used as the colloidal silica, the glossiness is increased. It is further preferable in terms of improving and suppressing printing unevenness during printing of pigment ink. If the colloidal silica has a primary particle size of less than 30 nm, the transparency of the ink-receiving layer is increased, but fine cracks are generated on the surface thereof, printing unevenness occurs during printing of pigment ink, and the printing density also decreases. There is. In particular, when printing with an ink jet printer using a pigment ink containing colored particles having a particle size of about 30 to 150 nm in the ink, it is effective that the primary particle size of the colloidal silica is 30 nm or more.
On the other hand, as the primary particle diameter is larger, cracks on the surface of the ink receiving layer are reduced, and printing unevenness when using pigment ink tends to be reduced. However, if the primary particle diameter exceeds 70 nm, the transparency of the ink receiving layer is lowered, the printing density during printing of the dye ink is lowered, and the suitability of the dye ink may be deteriorated.

When the ratio of the secondary particle diameter to the primary particle diameter of the colloidal silica is less than 1.5, the ink absorption of the ink receiving layer is lowered, and when it exceeds 3.0, the gloss of the ink receiving layer tends to be lowered. The primary particle diameter of colloidal silica can be measured by the BET method, and the secondary particle diameter can be measured by a dynamic light scattering method or the like.
In addition, when the said colloidal silica normally observes the dispersion state with a microscope, many things which two or three spherical single colloidal silica (primary particle) continued are observed. For convenience, this is expressed as a peanut shape. A value obtained by averaging the number of connected primary particles substantially corresponds to the above ratio. Peanut-like colloidal silica is composed of chain-like (or pearl necklace-like) colloidal silica and tuft-like colloidal silica (when microscopically observed, at least 5 spherical single colloidal silicas are aggregated, usually 10 or more. And the above ratio is also 5 or more). The term “excluded” as used herein does not mean that no tufted colloidal silica is observed at the time of microscopic observation, but some tufted colloidal silica may be observed. It means that the value of the ratio of the secondary particle diameter to the primary particle diameter is less than 3.

  Peanut-like colloidal silica is synthesized by sol-gel method using alkoxysilane as a raw material, and the primary particle size (BET method particle size) and secondary particle size (dynamic light scattering method particle size) are controlled by the synthesis conditions. It is not preferable to use pulverized silica obtained by adjusting the secondary particle diameter by mechanically pulverizing synthetic silica that has become secondary particles. As a peanut-shaped colloidal silica that can be preferably used, a trade name Quartron series manufactured by Fuso Chemical Industry Co., Ltd. can be raised.

  The blending amount of the peanut-shaped colloidal silica is preferably 5 to 80 parts by mass, more preferably 30 to 70 parts by mass with respect to 100 parts by mass of the total pigment in the ink receiving layer. When the blending amount of the peanut-like colloidal silica is less than 5 parts by mass of the total pigment, not only the glossiness is lowered, but also the effect of improving ink absorbability and color developability at the time of inkjet printing is insufficient, Printing unevenness may not be improved. Moreover, when a compounding quantity exceeds 80 mass parts, the operativity at the time of coating may fall.

Synthetic amorphous silica can be used as a pigment other than the peanut-like colloidal silica in the ink receiving layer. Synthetic amorphous silica can be roughly classified into wet process silica and gas phase process silica depending on the production method. Synthetic amorphous silica produced by a wet process is inferior to gas phase process silica in pigment transparency, but is excellent in paint stability when used in combination with polyvinyl alcohol. Furthermore, wet process silica has better dispersibility than gas phase process silica without internal voids, and can increase the coating concentration. Therefore, the ratio of the pigment (to the binder) in the ink receiving layer can be increased, and the absorbability of the ink receiving layer can be increased, so that the ink absorbability can be improved and the color developability of the dye ink can be improved. The secondary particle diameter of the synthetic amorphous silica (synthetic silica other than peanut-like colloidal silica) is preferably 1 to 5 μm, and the BET specific surface area is 150 to 500 m ² / g from the viewpoint of obtaining high gloss. It is preferable that

Increasing the blending ratio of synthetic amorphous silica with respect to all pigments in the ink receiving layer improves ink absorbency, but coloring pigments are more likely to enter the ink receiving layer, improving color development during pigment ink printing. Tend to be insufficient. Further, when the blending ratio of the synthetic amorphous silica is small, the ink absorptivity decreases, and as a result, the printing unevenness tends to increase.
As the pigment in the ink receiving layer, it is best to use a mixture of the peanut-like colloidal silica and the synthetic amorphous silica. When the ink receiving layer contains synthetic amorphous silica other than peanut-shaped colloidal silica, the blending ratio of synthetic amorphous silica (other than peanut-shaped colloidal silica) is 100 parts by mass of the total pigment in the ink receiving layer. It is preferable that it is 20-80 mass parts with respect to it, More preferably, it is 30-70 mass parts.

(Binder for ink receiving layer)
As the binder in the ink receiving layer, a polymer compound capable of forming a film can be used. For example, as a binder, starches such as starch, oxidized starch, and esterified starch; cellulose derivatives such as carboxymethylcellulose and hydroxyethylcellulose; polyvinyl alcohol; polyvinylpyrrolidone; casein; gelatin; soy protein; styrene-acrylic resin and derivatives thereof Styrene-butadiene resin, acrylic resin, vinyl acetate resin, vinyl chloride resin, urethane resin, urea resin, alkyd resin, and derivatives thereof can be used alone or in combination. The amount of the binder is preferably 5 to 30 parts by mass with respect to 100 parts by mass of the total pigment in the ink receiving layer, but is particularly limited as long as the required coating layer strength is obtained. It is not something.

The polymer compound used as the binder is preferably aqueous. “Aqueous” means that the resin is dissolved or dispersed and stabilized (water-soluble or / and water-dispersible resin emulsion) in water or a medium composed of water and a small amount of an organic solvent. These binders are dissolved or dispersed as particles in the coating liquid to be applied to the base paper, but after coating and drying, they become pigment binders and form an ink receiving layer.
In particular, it is preferable to use partially saponified polyvinyl alcohol as the water-based polymer compound. The addition amount of polyvinyl alcohol is preferably 3 to 30 parts by mass with respect to 100 parts by mass of the total pigment in the ink receiving layer.

  The ink receiving layer contains the above-described pigment and binder, but other components such as a thickener, an antifoaming agent, an antifoaming agent, a pigment dispersant, a release agent, a foaming agent, a pH adjusting agent, and a surface. Sizing agent, coloring dye, coloring pigment, fluorescent dye, ultraviolet absorber, antioxidant, light stabilizer, preservative, water resistance agent, dye fixing agent, surfactant, wet paper strength enhancer, water retention agent, cation A functional polymer electrolyte or the like can be appropriately added within a range not impairing the effects of the present invention.

  The coating method for the ink receiving layer on the base paper includes blade coater, air knife coater, roll coater, brush coater, kiss coater, squeeze coater, curtain coater, die coater, bar coater, gravure coater, and gate roll coater. A known coating machine such as a short dwell coater can be appropriately selected from the coating methods used on-machine or off-machine.

The coating amount of the ink receiving layer can be arbitrarily adjusted within the range where the surface of the base paper is covered and sufficient ink absorbability is obtained, but from the viewpoint of achieving both recording density and ink absorbency, is preferably 5 to 30 g / ^{m 2} in terms of solid content, in particular, when considering also the productivity is preferably 10 to 25 g / ^{m 2.} If it exceeds 30 g / m ² , the peelability from the mirror-finished surface of the cast drum is lowered, and problems such as adhesion of the coating layer to the mirror-finished surface may occur.

  In the present invention, when a large coating amount of the ink receiving layer is required, the ink receiving layer can be multi-layered. Further, an undercoat layer having various functions such as ink absorptivity, adhesiveness and the like may be provided between the base paper and the ink receiving layer. Further, a back coat layer having various functions such as ink absorbability, writing property, printer printability and the like may be further provided on the side opposite to the surface on which the ink receiving layer is provided.

(Formation of ink receiving layer)
In the present invention, gloss is imparted by forming the outermost ink receiving layer by a cast coating method. Here, the cast coating method is a method in which a coated surface in a wet state after coating is pressure-bonded to a heated finished surface and dried. Preferably, the ink receiving layer is preferably formed using a gelled cast coating method (coagulation method) in terms of providing a surface feeling and gloss comparable to silver salt photography.

  The cast coating method is performed as follows, for example. First, a coating liquid to be an ink receiving layer is applied to the base paper. Next, a treatment liquid having an action of coagulating a binder (particularly an aqueous binder) in the coating liquid is applied to the coating layer, and the coating layer is wetted. Then, the ink-receiving layer is formed by press-bonding the wet coating layer to the heated mirror-finished surface and drying to give gloss to the surface. The coating layer at the time of applying the treatment liquid may be in a wet state or a dry state, but in particular when it is in a wet state, it is easy to copy the mirror-finished surface, and the coating layer surface has a minute amount. Since the unevenness can be reduced, it is easy to give the obtained ink-receiving layer glossiness equivalent to that of a silver salt photograph. Examples of the method for applying the treatment liquid include, but are not limited to, a roll, a spray, and a curtain method.

  Next, the case where the gelation cast method is used will be described. In this method, in the cast coating method, after applying the coating layer, the undried coating layer is gelled with a coagulating liquid, and then pressed and dried on a heated mirror-finished surface. If the coating layer is in a dry state when applying the coagulation liquid, it is difficult to copy the mirror drum surface, and the resulting ink-receiving layer surface has many minute irregularities, making it difficult to obtain a glossiness similar to that of a silver salt photograph. . The coagulation liquid has the action of coagulating the aqueous binder in the wet coating layer, for example, formic acid, acetic acid, citric acid, tartaric acid, lactic acid, hydrochloric acid, sulfuric acid and other calcium, zinc, magnesium, etc. Salt is used. In particular, when polyvinyl alcohol is used as the aqueous binder, it is preferable to use a liquid containing boric acid and borate as the coagulating liquid. By mixing and using boric acid and borate, it becomes easy to make the hardness at the time of solidification moderate, and it is possible to impart a good gloss to the ink receiving layer. The method for applying the coagulating liquid is not particularly limited as long as it can be applied to the coating layer, and can be appropriately selected from known methods (for example, roll method, spray method, curtain method, etc.).

  Moreover, a release agent can be added to the coating layer and / or the coagulating liquid as necessary. The melting point of the release agent is preferably 90 to 150 ° C, and particularly preferably 95 to 120 ° C. In the above temperature range, since the melting point of the release agent is substantially equal to the temperature of the mirror finish surface, the ability as a release agent is maximized. The release agent is not particularly limited as long as it has the above characteristics, but it is preferable to use a polyethylene wax emulsion.

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these examples. “Part” and “%” represent “part by mass” and “% by mass”, respectively, unless otherwise specified.
Further, the primary particle size of the colloidal silica and the ratio of the secondary particle size to the primary particle size (particle size ratio) are manufacturer's measured values (catalog values are almost the same).

Rosetta-type light calcium carbonate (Albuquer 5970: manufactured by SMI) as a filler for a pulp slurry having a beating degree of 350 ml comprising 90 parts of hardwood bleached kraft pulp (L-BKP) and 10 parts of softwood bleached kraft pulp (N-BKP) Was added to an ash content of 20%, and 1.0 part of aluminum sulfate, 0.15 part of AKD, and 0.05 part of a yield improver were added. Using this slurry, a paper machine was used to make paper, and at that time, 5% starch and 0.2% surface sizing agent (AKD) were applied to a solid content of 1.5 g / m ^2, and 180 g / m ² was applied. An m ² base paper was obtained.
This base paper was coated with 15 g / m ^{2 of} coating liquid A with a roll coater, and solidified with coagulating liquid B while the coating layer was in a wet state, and then heated through a press roll. The mirror surface was copied by pressure bonding to the finished surface, and an ink jet recording medium of 195 g / m ² was obtained.

Coating liquid A: 60 parts of colloidal silica as a pigment (Quarton PL-2: trade name, manufactured by Fuso Chemical Industries, Ltd., primary particle diameter is 20 nm and the ratio of the secondary particle diameter to the primary particle diameter is 2.5) Method synthetic amorphous silica (Aerosil 200V: manufactured by Nippon Aerosil Co., Ltd.) 20 parts, wet method synthetic amorphous silica (Fine Seal X-37B: manufactured by Tokuyama Co., Ltd.) 20 parts, polyvinyl alcohol (PVA224: Kuraray Co., Ltd. product name) 12 parts, fluorescent dye (BLANKOPHOR P liquid01: product name made by LANXESS) 1.5 parts, mold release agent (Mecatex HP68: product name made by Meisei Chemical Industry Co., Ltd.) 0.5 Part, 0.1 part of antifoaming agent (S N deformer 4 8 0: trade name of San Nopco) was mixed to prepare a coating solution having a concentration of 25%.
Coagulating liquid B: Borax 2%, boric acid 4% (mass ratio of borax / boric acid = 1/2, calculated in terms of Na ₂ B ₄ O ₇ and H ₃ BO ₃ ), malic acid 0.2%, mold release The coagulation liquid was adjusted by adding 0.5 parts of an agent (Mecatex HP68: trade name manufactured by Meisei Chemical Co., Ltd.) and 0.01% of an antifoaming agent (S N deformer 4 80: product name manufactured by San Nopco). did.

  An ink jet recording medium was obtained in the same manner as in Example 1 except that the blending amount was changed so that the ash content of Rosetta type light calcium carbonate (Albuquer 5970: manufactured by SMI) was 10%.

  An ink jet recording medium was obtained in the same manner as in Example 1 except that the blending amount was changed so that the ash content of Rosetta type light calcium carbonate (Albuquer 5970: manufactured by SMI) was 5%.

  An ink jet recording medium was obtained in the same manner as in Example 1 except that the blending amount was changed so that the ash content of Rosetta type light calcium carbonate (Albuquer 5970: manufactured by SMI) was 25%.

  Colloidal silica (Quortron PL-2: trade name manufactured by Fuso Chemical Industry Co., Ltd.) in the coating liquid A was changed to colloidal silica (Quartron PL-5: trade name manufactured by Fuso Chemical Industry Co., Ltd., primary particle diameter of 50 nm with respect to the primary particle diameter. An ink jet recording medium was obtained in the same manner as in Example 1 except that the ratio of the secondary particle diameter was changed to 2.2).

  40 parts of colloidal silica (Quatron PL-5: product name manufactured by Fuso Chemical Industries) was used instead of blending colloidal silica (Quortron PL-2: product name manufactured by Fuso Chemical Industry Co., Ltd.) in the coating liquid A. Furthermore, the blending amount of wet method synthetic amorphous silica (Fine Seal X-37B: manufactured by Tokuyama Co., Ltd.) was changed to 50 parts, and vapor phase synthetic amorphous silica (Aerosil 200V: manufactured by Nippon Aerosil Co., Ltd.) ) Was changed to 10 parts in the same manner as in Example 1 to obtain an ink jet recording medium.

  The colloidal silica (Quarton PL-2: trade name manufactured by Fuso Chemical Industry Co., Ltd.) in the coating liquid A was changed to colloidal silica (Snowtex HS-M-20: trade name manufactured by Nissan Chemical Industries, Ltd., spherical silica). Except for this, an ink jet recording medium was obtained in the same manner as in Example 1.

  Colloidal silica (Quatron PL-2: trade name manufactured by Fuso Chemical Industry Co., Ltd.), a wet method synthetic amorphous silica (Fine Seal X-37B: manufactured by Tokuyama Corporation), which is a pigment in the coating liquid A, and a gas phase Method synthetic amorphous silica (Aerosil 200V: manufactured by Nippon Aerosil Co., Ltd.) is not blended. Instead, 62 parts of alumina (AKP-G015: trade name of Sumitomo Chemical Co., Ltd.), finely pulverized silica (Silojet 703C: Inkjet recording medium in the same manner as in Example 1 except that 38 parts of Grace's trade name) were mixed as pigments, and 3 parts of magnesium nitrate was added to coating liquid B to prepare the coating liquid. Got.

<Comparative Example 1>
Example 1 except that light calcium carbonate (TP-121: trade name manufactured by Okutama Kogyo Co., Ltd.) was used as a base paper filler instead of rosetta type light calcium carbonate (Albuquer 5970: manufactured by SMI). Thus, an ink jet recording medium was obtained.

<Comparative Example 2>
Rosetta-type light calcium carbonate (Albuquer 5970: manufactured by SMI) is not blended as a filler for the base paper. Instead, light calcium carbonate (TP-121: trade name manufactured by Okutama Kogyo Co., Ltd.) has an ash content of 5%. An ink jet recording medium was obtained in the same manner as in Example 1 except that it was blended as described above.

<Comparative Example 3>
Rosetta-type light calcium carbonate (Albuquer 5970: made by SMI) is not blended as a filler for the base paper, but instead talc (IRK-085: trade name made by Iraqi Kaolin) has an ash content of 5%. An ink jet recording medium was obtained in the same manner as in Example 1 except that it was blended in the above.

<Comparative Example 4>
As a filler for the base paper, light calcium carbonate (TP-121: trade name manufactured by Okutama Kogyo Co., Ltd.) is blended in place of Rosetta-type light calcium carbonate (Albuquer 5970: manufactured by SMI), and further in coating liquid A Example 1 except that the colloidal silica (Quarton PL-2: trade name, manufactured by Fuso Chemical Industry Co., Ltd.) was changed to colloidal silica (Snowtech HS-M-20: product name, spherical form, manufactured by Nissan Chemical Industries, Ltd.). In the same manner, an ink jet recording medium was obtained.

<Comparative Example 5>
As a filler for the base paper, light calcium carbonate (TP-121: trade name manufactured by Okutama Kogyo Co., Ltd.) is blended in place of Rosetta-type light calcium carbonate (Albuquer 5970: manufactured by SMI), and further in coating liquid A The amount of wet synthetic synthetic amorphous silica (Fine Seal X-37B: manufactured by Tokuyama Corporation) was changed to 80 parts. Except that, an ink jet recording medium was obtained in the same manner as in Example 1.

(Evaluation)
1. Pigment ink printability
A predetermined pattern was recorded on the obtained inkjet recording medium using a pigment inkjet printer (PX-G900: trade name, manufactured by Epson Corporation), and evaluated according to the following criteria.
1-1. Vividness when printing pigment ink (print density)
The vividness of the recorded image portion of the predetermined pattern was visually evaluated. If the overall evaluation is Δ or more, there is no practical problem.
◎: Very vivid ○: Vivid △: Slightly inferior in vividness X: Not vivid 1-2. Unevenness of pigment ink printing portion The degree of unevenness of the solid printing portion was visually evaluated by a four-step evaluation. The visual evaluation A was the best (no unevenness), and the visual evaluation x was the worst (conspicuous unevenness). If the evaluation is Δ or more, there is no practical problem.
◎: No unevenness ○: Some unevenness △: There is unevenness ×: There is significant unevenness

2. Dye ink printing suitability
Using a dye ink jet printer (PM-970C: a product name manufactured by Epson Corporation) on the obtained ink jet recording medium, bleeding (boundary bleeding) of each color boundary portion of the solid printing portion and unevenness (solid printing portion) The degree was visually evaluated by a five-step evaluation. The visual evaluation 5 was the best (no bleeding and unevenness), and the visual evaluation 1 was the worst (significant bleeding and unevenness). If the overall evaluation is Δ or more, there is no practical problem.
A: Visual evaluation of boundary bleeding and solid printing unevenness is 5 (no bleeding and unevenness) or more ○: Visual evaluation of boundary bleeding and solid printing unevenness is 4.5 (both or unevenness is slightly There is no problem but level)
Δ: Either the boundary bleeding or the visual evaluation of solid printing unevenness is 4 (there is bleeding or unevenness)
X: Any of the visual evaluation of boundary bleeding and solid printing unevenness is 3.5 or less (there is significant bleeding and unevenness)

3. Image clarity (image clarity)
It measured using the image clarity measuring device (model number: ICM-1DP, Suga Test Instruments Co., Ltd.) with respect to the obtained inkjet recording medium according to JISK7105. The MD direction of the paper was measured under the conditions of a measurement angle of 60 degrees and a comb width of 2 mm. If the image clarity is 50% or more, the reflected image is clearly visible and the glossiness is excellent. When the image clarity is less than 50%, the reflected image appears unclear and the glossiness is inferior.
4. 20 ° glossiness
The 20 ° glossiness of the unprinted portion on the surface of the ink receiving layer of the obtained inkjet recording medium was measured according to JIS-Z8741. It measured using the glossiness meter (Murakami Color Research Laboratory make, True GLOSS GM-26PRO). If the 20 degree glossiness is 10% or more, there is no practical problem.

  The obtained results are shown in Tables 1 and 2.

As is apparent from Table 1, in each of the examples, the printability (print density and print unevenness) when using pigment ink was excellent, and the print density when using dye ink was also excellent. In each example, the gloss was high and the image clarity was excellent.
In Examples 1 to 4, only the ash content was changed with the other conditions being the same. However, as the ash content increased, the printing unevenness and the printing density during pigment ink printing tended to be improved.
Of Examples 1, 5 to 8 having the same ash content, Examples 1, 5, and 6 using peanut-like silica are evaluated as ◯ for both printing unevenness and printing density at the time of pigment ink printing. This was superior to the above example (either printing unevenness or printing density during pigment ink printing was Δ).

On the other hand, in the case of Comparative Examples 1, 4, and 5 in which normal light calcium carbonate was used in place of Rosetta type light calcium carbonate as the filler in the base paper at an ash content of 20%, compared with Example 1 having the same ash content The printing density and printing unevenness at the time of pigment ink deteriorated, and the image clarity also deteriorated.
In the case of Comparative Examples 2 and 3 in which normal light calcium carbonate or talc was used as a filler in the base paper in place of Rosetta-type light calcium carbonate at an ash content of 5%, the glossiness was higher than that of Example 3 having the same ash content. And the image clarity deteriorated, and the printing density and printing unevenness with pigment ink deteriorated.

  From each example, the glossiness is preferably 25% or more, and the image clarity is preferably 60% or more.

Claims (3)

  An ink jet recording medium in which an ink receiving layer containing a pigment and a binder is provided on at least one surface of a base paper by a cast coating method, wherein the base paper contains rosetta type light calcium carbonate, and JIS-Z8741 An ink jet recording medium having a 20 degree glossiness of 10% or more on the surface of the ink receiving layer as defined in 1.   2. The ink jet recording medium according to claim 1, wherein an ash content of JIS-P8251 of the rosetta-type light calcium carbonate in the base paper is 5 to 25 mass%.   The inkjet recording medium according to claim 1, wherein the pigment of the ink receiving layer contains colloidal silica.