JP3699096B2 - Inkjet recording medium - Google Patents

Description

  The present invention relates to an inkjet recording medium 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 support such as paper, and ink droplets are formed on the ink receiving layer. Has become established. 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 in which a coating liquid mainly composed of a pigment and a binder is applied onto a base paper to provide a coating layer, and the coating layer is gloss-finished using a cast drum. The 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 a high ink drying speed, a high print density, and no ink overflow or bleeding, which improve these characteristics. For this purpose, 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). Further, in the cast coating layer, (1) fine silica particles having an average primary particle size of 3 to 40 nm and secondary particles having an average particle size of 10 to 400 nm, and (2) an average particle size of 200 nm A technique containing the following colloidal silica has been reported (for example, see Patent Document 2).

Japanese Patent Laid-Open No. 9-263039 JP 2000-85242 A

  However, in each of the above-described techniques, although a high glossy recording medium can be obtained, there is a problem that printing unevenness, particularly cyan printing unevenness, is bad. The printing unevenness here refers to unevenness in density that occurs when a solid portion is output by an inkjet recording method. Accordingly, an object of the present invention is to provide an ink jet recording medium which is excellent in gloss and has no printing unevenness, particularly cyan printing unevenness.

As a result of the investigation, the inventors have found that cracks occur on the surface of the coating layer provided by the cast coating method, and that ink is selectively absorbed in the cracks, and there are cracked portions and uncracked portions. As a result, it was found that a density difference occurred and printing unevenness occurred as a result.
As a result of various studies, it was found that the above-mentioned problems can be solved by using the following colloidal silica as the pigment in the ink receiving layer, and the present invention has been achieved.
That is, the inkjet recording medium of the present invention is an inkjet recording medium in which an ink-receiving layer containing a pigment and a binder is provided on at least one surface of a gas-permeable support by a cast coating method. The pigment contains colloidal silica and synthetic amorphous silica produced by a wet method, and the colloidal silica has a primary particle size of 30 to 100 nm and a ratio of the secondary particle size to the primary particle size of 1.5. It is -2.5. The ink receiving layer preferably contains 5 to 50% by weight of the colloidal silica based on the total pigment. Moreover, it is preferable that the ink receiving layer is provided by a gelled cast method.

  According to the present invention, it is possible to obtain an inkjet recording medium that is excellent in gloss and has no printing unevenness (particularly cyan).

  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 gas-permeable support by a cast coating method.

(Support)
Although the support body used for this invention should just have air permeability, paper, such as coated paper and uncoated paper, is used, for example. The raw material pulp of the paper includes chemical pulp (conifer bleached or unbleached kraft pulp, hardwood bleached or unbleached kraft pulp, etc.), mechanical pulp (ground pulp, thermomechanical pulp, chemisermomechanical pulp, etc.), deinking Pulp or the like can be used alone or mixed at an arbitrary ratio. The pH of the paper may be acidic, neutral or alkaline. Further, in order to improve the opacity, it is preferable to contain a filler in the paper, but this filler is hydrated silicic acid, white carbon, talc, kaolin, clay, calcium carbonate, titanium oxide, synthetic resin fine particles, etc. It can be appropriately selected from known fillers. From the viewpoint of operability, the air permeability of the paper is preferably 1000 seconds or less, and from the viewpoint of coating properties, the Steecht size of the base paper is preferably 5 seconds or more.

(Pigment of ink receiving layer)
As the pigment in the present invention, a pigment containing synthetic amorphous silica and colloidal silica produced by a wet method is used. The reason for using synthetic amorphous silica produced by a wet method is to improve the color developability. On the other hand, although it is not clear why the printing unevenness (particularly cyan unevenness) can be improved by using the colloidal silica specified above as a pigment, if the colloidal silica is present in the ink receiving layer, the cast The size of cracks generated on the surface of the ink receiving layer formed by the coating method is reduced, while the number of cracks in the unit area is increased. As a result, it is considered that the density difference between the cracked portion and the portion without the crack becomes inconspicuous and unevenness is suppressed. The colloidal silica is usually spherical.

  The primary particle diameter of the colloidal silica is 30 to 100 nm, preferably 50 to 75 nm. When the primary particle diameter is less than 30 nm, the ink-receiving layer is highly transparent, but the voids between the particles are impaired and the ink absorbability is lowered. When the primary particle diameter exceeds 100 nm, the voids between the particles increase and the ink absorbability of the ink receiving layer becomes good, but the opacity increases, so the color developability at the time of ink jet recording decreases. In particular, when printing is performed with an ink jet printer using a pigment ink containing colored particles having a particle diameter of 50 to 150 nm in the ink, the ink coloring property is greatly reduced.

  Further, the ratio of the secondary particle diameter to the primary particle diameter of the colloidal silica is set to 1.5 to 2.5. This is because when the ratio is less than 1.5, the ink absorption of the ink receiving layer decreases, and when it exceeds 2.5, the gloss of the ink receiving layer decreases. The primary particle size and secondary particle size of colloidal silica can be measured by the BET method, dynamic light scattering method, or the like. In addition, when the colloidal silica in this invention is normally observed 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. The colloidal silica in the present invention is mainly tufted colloidal silica (when microscopically observed, at least 5 spherical single colloidal silicas, usually 10 or more continuous, the ratio is also 5 or more). Does not include what to do. 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. The value of the ratio of the secondary particle diameter to the primary particle diameter is more than 2.5 (usually 5 or more).

  The 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 according to the synthesis conditions. preferable. As such colloidal silica, a trade name Quatron manufactured by Fuso Chemical Industry Co., Ltd. can be raised.

  The compounding amount of colloidal silica is preferably 5 to 50 parts by weight, more preferably 10 to 30 parts by weight, and most preferably 15 to 30 parts by weight with respect to 100 parts by weight of the total pigment in the ink receiving layer. . When the blending amount of colloidal silica is less than 5 parts by weight of the total pigment, the effect of improving ink absorbability and color developability at the time of ink jet printing becomes insufficient, and printing unevenness may not be improved. Further, when the blending amount exceeds 50 parts by weight, the ink absorbability at the time of ink jet printing is good, but the effect of improving the color developability is reduced, and the operability at the time of coating may be lowered. .

  The blending ratio of the synthetic amorphous silica and the colloidal silica is preferably such that the value of (synthetic amorphous silica) / (colloidal silica) is within the range of 95/5 to 50/50. Is in the range of 90/10 to 60/40.

  As the pigment, other pigments such as aluminum hydroxide, alumina sol, colloidal alumina, pseudoboehmite and the like (alpha-type crystal alumina, as long as the ink absorbability, color developability and glossiness at the time of ink jet recording are not impaired. θ-type crystal alumina, γ-type crystal alumina, etc.), alumina hydrate, synthetic silica, kaolin, talc, calcium carbonate, titanium dioxide, clay, zinc oxide, and the like may be used in combination.

(Binder for ink receiving layer)
In the present invention, a polymer compound capable of forming a film can be used as a binder. 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, soybean 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 blending amount of the binder is preferably 5 to 30 parts by weight with respect to 100 parts by weight of the pigment, but is not particularly limited as long as the necessary coating layer strength is obtained.

  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. It is particularly preferable to use partially and / or completely saponified polyvinyl alcohol. The addition amount of polyvinyl alcohol is preferably 3 to 30 parts by weight with respect to 100 parts by weight of the pigment. In the case of using an organic solvent, it is necessary that the mixing ratio is less than 50% by weight, preferably less than 10% by weight, with no flash point of the resin liquid. These binders are dissolved or dispersed in the coating liquid to be applied to the support, but after coating and drying, they become pigment binders to form an ink receiving layer.

  In particular, when forming an ink receiving layer using a gelation cast method (coagulation method) described later, casein is preferably added to the binder. When casein is blended, the coating property of the coating liquid that becomes the ink receiving layer is improved. The amount of casein is preferably about 5 to 20% by weight in the ink receiving layer (coating liquid). If the amount of casein is less than 5% by weight, the coagulation property is lowered and the productivity tends to be lowered, and if it exceeds 20% by weight, the ink absorbability of the ink receiving layer is lowered.

  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.

  As a method of applying a coating liquid to be an ink receiving layer on a support, blade coater, air knife coater, roll coater, brush coater, kiss coater, squeeze coater, curtain coater, die coater, bar coater, gravure coater, gate roll A known coating machine such as a coater or a short dwell coater can be appropriately selected from on-machine or off-machine coating methods.

The coating amount of the ink receiving layer can be arbitrarily adjusted within the range where the surface of the support is covered and sufficient ink absorbency 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 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 and adhesiveness may be provided between the support 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 formed using a gelled cast coating method (coagulation method) in that it can provide 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 a support. 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 wet coating layer is pressure-bonded to a heated mirror-finished surface and dried to form an ink receiving layer, and gloss is imparted 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 and magnesium 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 weight” and “% by weight”, respectively, unless otherwise specified.

Production of support body 4 parts of calcium carbonate, 1 part of cationized starch, 0.3 part of polyacrylamide with respect to 100 parts of pulp made from hardwood kraft pulp (L-BKP) and having a freeness of 350 mlc.s.f. Add 0.5 part of alkyl ketene dimer emulsion, make paper using conventional paper machine, pre-dry, then size 5% phosphate esterified starch and 0.5% polyvinyl alcohol After apply | coating so that it might become dry weight 3.2g / m < ² > with a press, post-drying and the machine calendar process were given, and the support body of 100 g / m < ² > basis weight was obtained.

As a pigment, 80 parts of synthetic amorphous silica (trade name: Fine Seal X-37B, manufactured by Tokuyama Corporation, BET specific surface area of 260 to 320 m ² / g), and the primary particle sizes and secondary particle sizes shown in Table 1 are secondary. 20 parts of colloidal silica having a particle size ratio (trade name: Quatron PL-3, manufactured by Fuso Chemical Industry Co., Ltd.) and a binder (trade name: SN-) made of styrene-butadiene latex in addition to the above pigments. 335R, manufactured by Japan A & L Co., Ltd. 30 parts, casein (ALACID lactic casein, New Zealand) 10 parts, release agent (trade name: Nopcoat C-104-H, Sannopco) 5 parts solid content concentration 25 % Cast layer coating solution was prepared. The synthetic amorphous silica is produced by a wet method.
Next, using a comma coater, this pigment was applied to the support at a target coating amount of 18 g / m ² , and then coagulated with the following coagulating liquid. While the coating layer was in a wet state, The film was pressed onto a mirror-finished metal surface heated and dried to produce a cast-coated paper for inkjet recording. As the coagulation liquid, a liquid containing 5% calcium formate (manufactured by Asahi Chemical Industry Co., Ltd.) and 1% of a dye fixing agent (trade name: DAIFIX YK-50, manufactured by Daiwa Chemical Co., Ltd.) was used.

  Instead of the colloidal silica of Example 1, colloidal silica having a primary particle diameter and a ratio of the secondary particle diameter to the primary particle diameter shown in Table 1 (trade name: Quatron PL-5, manufactured by Fuso Chemical Industry Co., Ltd.) is used. Except for the above, cast coated paper for ink jet recording was produced in the same manner as in Example 1.

  The amount of the synthetic amorphous silica is 95 parts, and instead of the colloidal silica of Example 1, colloidal silica having a primary particle diameter and a ratio of the secondary particle diameter to the primary particle diameter shown in Table 1 (trade name: Quatron) A cast-coated paper for inkjet recording was produced in the same manner as in Example 1 except that 5 parts of PL-7 (manufactured by Fuso Chemical Industry Co., Ltd.) was blended.

  A cast coated paper for inkjet recording was produced in exactly the same manner as in Example 3, except that the blending amount of the synthetic amorphous silica was 90 parts and the blending amount of the colloidal silica was 10 parts.

  A cast coated paper for inkjet recording was produced in exactly the same manner as in Example 3 except that the blending amount of the synthetic amorphous silica was 80 parts and the blending amount of the colloidal silica was 20 parts.

  A cast coated paper for ink jet recording was produced in the same manner as in Example 3 except that the amount of synthetic amorphous silica was 70 parts and the amount of colloidal silica was 30 parts.

  A cast coated paper for ink jet recording was produced in exactly the same manner as in Example 3 except that the blending amount of the synthetic amorphous silica was 60 parts and the blending amount of the colloidal silica was 40 parts.

Comparative Example 1
In place of the colloidal silica of Example 1, colloidal silica having the shape and primary particle size shown in Table 1 (trade name: Snowtex N30G, manufactured by Nissan Chemical Industries, Ltd., substantially secondary particle size with spherical single particles) The cast coated paper for ink jet recording was produced in the same manner as in Example 1 except that the above was used.

Comparative Example 2
Instead of the colloidal silica of Example 1, colloidal silica (trade name: Quarton PL-1, manufactured by Fuso Chemical Industries) having the primary particle diameter and the ratio of the secondary particle diameter to the primary particle diameter shown in Table 1 was used. Except that, a cast coated paper for inkjet recording was produced in exactly the same manner as in Example 1.

Comparative Example 3
Instead of the colloidal silica of Example 1, colloidal silica (trade name: Quartron PL-2, manufactured by Fuso Chemical Industries) having the primary particle diameter and the ratio of the secondary particle diameter to the primary particle diameter shown in Table 1 was used. Except that, a cast coated paper for inkjet recording was produced in exactly the same manner as in Example 1.

Comparative Example 4
A cast-coated paper for inkjet recording was produced in exactly the same manner as in Example 1 except that synthetic amorphous silica was not used as a pigment for the cast layer coating solution and only 100 parts of colloidal silica was blended.

Comparative Example 5
Instead of the colloidal silica of Example 1, colloidal silica having a shape, a primary particle diameter, and a ratio of the secondary particle diameter to the primary particle diameter shown in Table 1 (trade name: Quatron PL-30, manufactured by Fuso Chemical Industries, Ltd.) ) Was used in the same manner as in Example 1 except that a coated paper for inkjet recording was produced.

Comparative Example 6
Instead of the colloidal silica of Example 6, colloidal silica (trade name: Snowtex OUP, manufactured by Nissan Chemical Industries, Ltd.) having the shape shown in Table 1, the primary particle diameter, and the ratio of the secondary particle diameter to the primary particle diameter is used. A cast coated paper for ink jet recording was produced in exactly the same manner as in Example 6 except that it was used.

Comparative Example 7
In place of the colloidal silica of Example 1 except that silica having a primary particle size and a ratio of secondary particle size to primary particle size shown in Table 1 (trade name: Aerosil 50, manufactured by Nippon Aerosil Co., Ltd.) was used. A cast coated paper for inkjet recording was produced in exactly the same manner as in Example 1.

Evaluation Each example was evaluated by the following method.

1. Characteristics of colloidal silica a) Measurement of primary particle diameter The specific surface area (nitrogen adsorption method) of the sample was measured, and the primary particle diameter was determined by calculation according to the following formula (1).
d = 6000 / (ρ × S) (1)
In the formula (1), d: primary particle diameter (nm), ρ: silica density (= 2.2 g / m ³ ), and S: specific surface area S (m ² / g).
b) Measurement of secondary particle size
Measurement was performed using ZETASIZER 3000HSA manufactured by MALVERN INSTRUMENTS.
However, for the silica of Comparative Example 7 (trade name: Aerosil 50), MALVERN
Measurement was performed using MASTERSIZER S manufactured by INSTRUMENTS.

2. Printing unevenness evaluation Using an inkjet printer PM-970C (manufactured by Seiko Epson Corporation), printing was performed for each example, and the following evaluation was performed on the obtained printed matter.
a) Cyan unevenness Print unevenness (darkness unevenness) of the cyan solid print portion was visually evaluated according to the following criteria.
A: Good level with no printing unevenness B: Slight printing unevenness but satisfactory level for practical use B: Slight printing unevenness, slightly unsatisfactory level for practical use ) White character omission White characters were created in a solid image of green (mixed color of cyan and yellow), and the degree of collapse of the white characters was visually evaluated according to the following criteria.
○: Almost no white characters are crushed.
Δ: Some white characters are crushed.
×: White characters are significantly crushed.

3. Glossiness Evaluation Specular glossiness at 75 ° and 20 ° was measured using a gloss meter (True GLOSS GM-26PRO, manufactured by Murakami Color Research Laboratory).

  The obtained results are shown in Table 1. The “particle size ratio” in the table indicates the ratio of the secondary particle size to the primary particle size. In addition, the Macbeth density is a value when using an EPSSON glossy paper recommended by the company using an inkjet printer PM-970C (manufactured by Seiko Epson). In addition, the shape of colloidal silica is classified by representing the state of aggregation of the colloidal silica observed with a microscope for convenience. “Peanuts” are those in which about two primary particles are combined to look like peanuts. Although shown, it is not strictly specified.

  As is clear from Table 1, in Examples 1 to 6, the gloss was excellent, the cyan unevenness evaluation and the white character missing evaluation were both good, and there was no unevenness in printing. In particular, in Examples 5 and 6 in which the primary particle diameter of colloidal silica is 50 nm or more and the blending amount is 20 to 30 parts by weight, cyan unevenness evaluation was particularly excellent.

On the other hand, in Comparative Examples 1, 2, 3, and 6 in which the primary particle diameter of colloidal silica was less than 30 nm, the cyan unevenness evaluation was inferior and was not suitable for practical use. Moreover, in the case of the comparative example 4 which did not mix | blend amorphous synthetic silica, the solidification property of the coating layer was insufficient and the coated paper could not be obtained. Moreover, in the case of the comparative example 5 whose particle size ratio is less than 1.8, white character omission evaluation was inferior. In the case of Comparative Example 7 in which the particle size ratio exceeded 2.5, the cyan unevenness evaluation was inferior and was not suitable for practical use.

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 gas-permeable support by a cast coating method, wherein the pigment is produced by a colloidal silica and a wet method Synthetic colloidal silica, wherein the colloidal silica has 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. Inkjet recording medium.   The inkjet recording medium according to claim 1, wherein the ink receiving layer contains 5 to 50 wt% of the colloidal silica with respect to all pigments.   The inkjet recording medium according to claim 1, wherein the ink receiving layer is provided by a gelled cast method.