JPH0725132A - Ink jet recording sheet - Google Patents

Abstract

PURPOSE:To provide a thin coating type ink jet recording sheet excellent in ink absorbability, imparting an image enhanced in density and sharpness and obtaining a recording dot having an almost circular shape. CONSTITUTION:In an ink jet recording sheet, raw paper is neutral paper containing calcium carbonate as a filler and an anionic neutral rosin size as an internal size and a recording surface wherein the surfaces of the pulp fibers of the surface of the raw paper are coated with a compsn. based on ultrafine inorg. pigment particles is provided on the raw paper. The shapes of the pulp fibers applied to the recording surface can be visually confirmed by a scanning electromicroscope and a surface coating ratio is set to 70% or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording sheet, and more specifically, it has excellent ink absorbency without uneven bleeding of ink, high density and sharpness of recorded image, and a perfect circle. The present invention relates to a slightly coated ink jet recording sheet that can obtain recording dots close to the above.

The ink jet recording system is a system in which minute droplets of ink are ejected and adhered to a recording sheet such as paper by various operating principles to record images, characters, etc. It has features such as easy colorization, great flexibility in recording patterns, and no need for development-fixing, and is rapidly spreading in various applications as a recording device for various figures including Kanji and color images. Further, an image formed by a multicolor ink jet system can obtain a recording comparable to that of multicolor printing by a plate making system or printing by a color photographic system. Further, in applications requiring a small number of copies, it is being widely applied to the field of full-color image recording because it is cheaper than the photographic technique.

As a recording sheet used in this ink jet recording system, efforts have been made from the aspect of the apparatus and ink composition so as to use high-quality paper or coated paper used for ordinary printing and writing. However, as the performance of the inkjet recording apparatus has been improved and the applications have been expanded, such as speeding up, high definition, or full-color of the apparatus, more advanced characteristics have been required for the recording sheet. That is, as the recording sheet, the density of print dots is high, the color tone is bright and vivid, the ink does not run or bleed even when the print dots overlap and the print dots overlap. It is required that the diffusion in the direction is not unnecessarily large and that the periphery is smooth and not blurred.

As the form of the ink jet recording sheet, an ink receiving layer is provided on a support surface such as plain paper type represented by so-called high-quality paper / bonded paper, paper such as high-quality paper, synthetic paper, synthetic resin film and the like. It is roughly divided into coating type.

The coating type includes a low coating type of about 1 to 10 / m ^{2, a} medium coating type of about 10 to 20 g / m ² ,
There are high coating type inkjet recording sheets of 20 g / m ² or more. In particular, in recent years, even a low coating type, a lower coating amount of 0.5 to 5 g / m ² of a fine coating type is close to that of plain paper, which is preferable in terms of appearance and handling. The coating type has been desired. However, in the case of color recording, not only single color recording of yellow, magenta, cyan, and black but also superposition of these colors is performed for multi-color recording, and the amount of ink adhered is extremely large.
In the case of the light coating type, the ink cannot be completely absorbed in the coating layer, so use a base paper of a relatively low size,
It has become necessary to absorb a part of the attached ink by the base paper itself of the support.

To solve these problems, Japanese Patent Publication No.
JP-A-26665 discloses an example of an ink jet recording paper in which a coating layer containing fine silica particles and a water-soluble polymer binder is provided on a base paper having a basis weight of 60 g / m ² and a Steckigt sizing degree of 4 seconds or less. Japanese Patent Laid-Open No. 59-3808.
JP-A-59-9516 discloses an example of an ink jet recording material in which an ink absorbing layer is provided on a substrate having a sizing degree of 0 to 10 seconds. JP-A-59-9516 discloses a Steckigt sizing degree of 0. An example of an inkjet recording paper in which polyvinyl pyrrolidone or the like is impregnated into a base paper for 5 seconds is disclosed.

Further, as an ink jet recording sheet having high ink absorbency and capable of obtaining a good recording dot shape,
There is JP-A-60-63191. The publication is characterized in that the recording material (inkjet recording sheet) has a surface layer in which a filler and a fibrous material are mixed. Here, it is described that it has a base material made of a fibrous material and filler particles attached to the surface of the base material so as to be dispersed very thinly. However, in this publication, there is no mention of the state in which the surface layer filler and the fibrous material are mixed, and the fibrous material forming the base material is exposed in the surface layer.

[0008]

As described above, when the ink receiving layer has a low coating amount, the base material itself having a relatively low size is used to absorb a part of the attached ink. The uniformity of the sizing property in a minute area varies depending on the size. In addition, the ink receiving layer coated on the support is not uniformly coated on the surface of the entangled irregularities of the pulp fiber, so that the exposure of the pulp fiber is significant. Therefore, the deposited ink penetrates into the support, that is, the base paper along the exposed pulp fibers without forming recording dots having a desired shape on the surface of the ink receiving layer, and the recording dots spread and spread. It will take on a shape. In other words, the recorded image lacks sharpness.

An object of the present invention is to provide an ink jet recording sheet of a slightly coated type even with an ink jet recording sheet, which has excellent ink absorbency without uneven bleeding of ink, high density and sharpness of a recorded image, and The purpose of the present invention is to obtain an inkjet recording sheet from which recording dots close to a circle can be obtained.

[0010]

Means for Solving the Problems As a result of intensive studies in view of the above, the present inventors have found that there is no ink bleeding, the ink absorbency is excellent, the density of a recorded image is high, and a recording dot near a perfect circle is formed. The inventors have invented the resulting inkjet recording sheet. That is, the inkjet recording sheet of the present invention is an inkjet recording sheet having a recording surface on a base paper, and the base paper contains calcium carbonate as a filler and an anionic neutral rosin sizing agent as an internal sizing agent. The recording surface of the recording sheet is the recording surface surface-coated with a composition mainly comprising ultrafine inorganic pigments along the pulp fiber surface in an entangled state of the base paper surface,
The shape of the pulp fiber coated on the recording surface can be visually confirmed by a scanning electron microscope, and the surface coverage of the pulp fiber on the recording surface is 70% or more.

The ink jet recording sheet of the present invention will be described in detail below. In the ink jet recording sheet of the present invention, the base paper is a neutral paper containing calcium carbonate as a filler and an anionic neutral rosin sizing agent as an internal sizing agent.
The reason is that the anionic neutral rosin sizing agent in the neutral paper has a size developing property in a minute region, which shows uniformity at a relatively low size degree, and therefore deforms the dot shape of the ink absorbed in the base paper portion. Rarely. On the other hand, the alkyl ketene dimer (AKD) and alkenyl succinic anhydride (ASA) sizing agents that are commonly used in neutral papermaking have uneven sizing properties in the micro area, and it is necessary to absorb ink in the base paper part. In the case of such a slightly coated inkjet recording sheet, the dot shape factor becomes large.

The neutral rosin sizing agent as used in the present invention means p
It is an emulsion type rosin sizing agent obtained by emulsifying various surfactants or water-soluble polymers used in the neutral region of H6-9. Here, as the rosin substance,
Roms such as gum rosin, wood rosin, tall oil rosin, hydrogenated rosin, disproportionated rosin, polymerized rosin, aldehyde-modified rosin and rosin ester, and further rosins and acrylic acid, maleic anhydride, fumaric acid, itaconic acid, etc. Examples of the heated reaction product with α, β-unsaturated carboxylic acid include, but insolubilization treatment such as polymerization and water resistance can be performed for the purpose of suppressing elution of the rosin substance in the neutral region.

The ionicity of the neutral rosin sizing agent can be selected from anionic and cationic depending on various surfactants or water-soluble polymers used during emulsification. In the present invention, various conventionally used anionic, nonionic, cationic or amphoteric retention aids, polyethylene oxide, polyamide resins, hydrophilic crosslinked polymer particle dispersions, etc. or their derivatives or modified products, etc. As a result of studying a retention system in which a compound such as colloidal silica and bentonite is appropriately combined and used, anionic neutral rosin sizing agent and cationic or amphoteric hydrophilic crosslinked polymer particle dispersion or the like or a derivative thereof Alternatively, it is desirable to combine a yield-improving agent or a retention system whose constituent is a modified product.

Further, for the purpose of expressing the sizing property of the neutral rosin sizing agent, a polyvalent metal compound of aluminum (for example, a sulfuric acid band, polyaluminum chloride, polyaluminum silicate sulfate, sodium aluminate, etc.)
Needless to say,

Further, the ink jet recording sheet of the present invention is surface-coated so that the shape of the pulp fiber on the support, that is, the recording surface on the raw paper surface can be sufficiently discerned. The surface coating of the recording surface is uniformly covered with the ultrafine inorganic pigment along the surface of the pulp fiber, and is thinly covered according to the shape of the surface of the pulp fiber. The surface coverage of the recording surface is
The recording medium covers 70% or more of the pulp fiber surface of the recording surface, whereby the characteristics aimed at by the present invention can be sufficiently exhibited. It is preferably 80% or more, more preferably 90% or more. The reason for this is that if the recording surface is uniformly coated, when the ink is applied to the recording surface using an inkjet printer, the recording surface is uniformly coated, so This is because recording dots close to a perfect circle can be expressed without spreading and excess ink permeates from the surface coated surface in the thickness direction of the base paper. On the other hand, if the surface coverage of the recording surface covering the pulp fibers is less than 70%, the rate at which the ink spreads in the recording surface direction increases, and as a result, the recording dots have a shape deviated from a perfect circle. Further, the penetration into the base paper becomes irregular, and ink bleeding appears.

In the ink jet recording sheet of the present invention, the surface coated surface is the surface uniformly covered along the pulp fiber of the raw paper surface, and is coated using a composition mainly containing ultrafine inorganic pigments. . The primary particle diameter of the ultrafine inorganic pigment is 100 nm or less, preferably 5 with respect to the fiber diameter of the pulp fiber forming the base paper of the order of several tens of μm.
It is 0 nm or less. The finer the particle size, the more uniform the surface coating on the pulp fiber, which is preferable. As these ultrafine particle inorganic pigments, those which are dispersed in water in a colloidal state while maintaining the primary particle size are used.

In the ink jet recording sheet of the present invention, a scanning electron microscope can be used as a means for measuring the surface coverage of the recording fiber pulp surface, and the area ratio is analyzed by image analysis. To calculate.

The following can be exemplified as the ultrafine particle inorganic pigment. For example, silica (colloidal silica), alumina or alumina hydrate (alumina sol,
Colloidal alumina, cationic aluminum oxides or hydrates thereof, pseudo-boehmite, etc.), surface-treated cationic colloidal silica, aluminum silicate, magnesium silicate, magnesium carbonate and the like, more preferably primary particles are porous. However, it is preferable that even if it is non-porous, it aggregates at the time of preparing the coating liquid or further aggregates at the time of drying the coating to form a porous surface-coated surface on the pulp fiber surface. In particular, in the present invention, it is preferable to coat the pulp fiber itself with an ultrafine particle inorganic pigment having an average particle diameter of several hundredths or less of the width of the fiber for each pulp fiber on the surface of the raw paper.

Further, as the inorganic pigment which can be used in combination with the ultrafine particle inorganic pigment, any conventionally known inorganic pigment can be used. For example, light calcium carbonate, heavy calcium carbonate, kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, aluminum silicate, diatomaceous earth,
Examples thereof include calcium silicate, synthetic amorphous silica, aluminum hydroxide, lithopone, zeolite, hydrohaloysite, magnesium hydroxide and the like. Among these inorganic pigments, porous inorganic pigments are preferable, and porous synthetic amorphous silica, porous magnesium carbonate, porous alumina and the like can be mentioned, and particularly porous synthetic amorphous silica having a large pore volume is preferable. . Further, organic pigments such as styrene-based plastic pigments, acrylic-based plastic pigments, polyethylene, microcapsules, urea resins and melamine resins can be used together with the above ultrafine inorganic pigments.

As the binder used together with the ultrafine inorganic pigment for surface coating, for example, polyvinyl alcohol, vinyl acetate, oxidized starch, etherified starch, cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, casein, gelatin, soybean. Protein, silyl-modified polyvinyl alcohol, etc .; Conjugated diene copolymer latex such as maleic anhydride resin, styrene-butadiene copolymer, methyl methacrylate-butadiene copolymer; Polymer or copolymer of acrylic acid ester and methacrylic acid ester Acrylic polymer latex such as polymer, copolymer or copolymer of acrylic acid and methacrylic acid; vinyl polymer latex such as ethylene vinyl acetate copolymer; or functional group such as carboxyl group of these various polymers Polymer latex modified by functional group; water-based binder such as thermosetting synthetic resin such as melamine resin, urea resin; polymethylmethacrylate, polyurethane resin, unsaturated polyester resin, vinyl chloride-vinyl acetate copolymer, polyvinyl butyral, alkyd There may be mentioned synthetic resin binders such as resins,
At least one kind can be used. Also, a cationic resin added for the purpose of fixing a conventionally known dye can be used together.

The total amount of the binder can be appropriately adjusted according to the characteristics of the intended ink jet recording sheet, but in general, it is 5 per 100% by weight of the pigment.
-60% by weight. Furthermore, as other additives, a pigment dispersant, a thickener, a fluidity improver, a defoaming agent, a foam suppressor, a release agent, a foaming agent, a penetrant, a coloring dye, a coloring pigment, a fluorescent whitening agent, An ultraviolet absorber, an antioxidant, an antiseptic agent, an antifungal agent, a water resistance agent, a wet paper strength enhancer, a dry paper strength enhancer and the like can be appropriately blended.

In the present invention, the surface coating method may be coating or impregnation, but the coating amount on the surface coated surface is not particularly limited. Usually, in the case of directing to a plain paper like, 0.5 to 5 g / m ² is preferable, but more may be coated.

The pulp for base paper according to the present invention is LBK.
Chemical pulp such as P, NBKP, GP, PGW, RMP,
Mechanical pulp such as TMP, CTMP, CMP, CGP, D
Used paper pulp such as IP and wood pulp such as can be used. Further, the filler must contain calcium carbonate, but it can be used in combination with a conventionally known pigment. Further, in the paper material, together with the internally added sizing agent and the polyvalent metal compound of Al as described above, in a range that does not impair the desired effect of the present invention,
If necessary, various additives such as a binder and a fixing agent, a yield improving agent, a cationizing agent, and a paper strength enhancer can be used. These raw materials are mixed, and fourdrinier paper machine,
It is manufactured by various devices such as a cylinder paper machine and a twin wire paper machine, but in the present invention, both the base paper which has not been size-pressed, and the base paper which has been size-pressed with starch, polyvinyl alcohol, etc. Is included. The surface coating may be used as it is on such a base paper, or a calender device such as a machine calender, a TG calender or a soft calender may be used for the purpose of controlling flattening.

When the surface is coated, various coating methods such as blade coater, roll coater, air knife coater, bar coater, rod coater, gate roll coater, curtain coater, short dwell coater,
Various machines such as a gravure coater, a flexo gravure coater, and a size press can be used on-machine or off-machine. However, in the present invention, an air knife coater or a gate roll coater is preferable. Further, after coating or impregnation, finishing may be performed using a machine calendar, a TG calendar, a super calendar, a soft calendar or the like.

The aqueous ink referred to in the present invention is a recording liquid containing the following colorant, liquid medium, and other additives.
Examples of the colorant include water-soluble dyes such as direct dyes, acid dyes, basic dyes, reactive dyes and food dyes.

As the solvent of the aqueous ink, water and various water-soluble organic solvents such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, C1-C4 alkyl alcohols such as isobutyl alcohol; amides such as dimethylformamide and dimethylacetamide; ketones or ketone alcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran and dioxane; polyethylene glycol, polypropylene glycol Polyalkylene glycols such as ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hex Alkylene glycols having 2 to 6 alkylene groups such as len glycol and diethylene glycol; lower alkyl ethers of polyhydric alcohols such as glycerin, ethylene glycol methyl ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol and monomethyl ether Is mentioned. Among these many water-soluble organic solvents, polyhydric alcohols such as diethylene glycol and lower alkyl ethers of polyhydric alcohols such as triethylene glycol monomethyl ether and triethylene glycol monoethyl ether are preferable. Other additives include, for example, a pH adjusting agent, a sequestering agent, an antifungal agent, a viscosity adjusting agent,
Surface tension adjusting agents, wetting agents, surfactants, rust preventives and the like can be mentioned.

The ink jet recording sheet according to the present invention is not limited to use as an ink jet recording sheet, but may be used as any recording sheet using a liquid ink during recording. For example, an ink sheet in which a heat-fusible ink containing a heat-fusible substance, a pigment or the like as a main component is coated on a thin support such as a resin film, high-density paper, or synthetic paper is heated from the back surface to An image-receiving sheet for thermal transfer recording that melts and transfers ink, an inkjet recording sheet that heat-melts a heat-melting ink to form fine droplets, and flight recording, an inkjet recording sheet that uses an ink in which an oil-soluble dye is dissolved, An image receiving sheet corresponding to a light and pressure sensitive donor sheet using microcapsules containing a polymerizable monomer and a colorless or colored dye / pigment may be mentioned.

The common point of these recording sheets is that the ink is in a liquid state at the time of recording. The liquid ink penetrates or spreads in the depth direction or the horizontal direction of the ink receiving layer of the recording sheet before being cured, solidified, or fixed. The various recording sheets described above require absorptivity according to their respective methods, and the inkjet recording sheet of the present invention may be used as the various recording sheets described above without any limitation. Further, the ink jet recording sheet of the present invention can be used as a recording sheet for heating and fixing toner of an electrophotographic recording system which is widely used in copying machines, printers and the like.

[0029]

The ink jet recording sheet of the present invention is a slightly coated type ink jet recording sheet, and the recording surface of the recording sheet is a neutral paper containing an anionic neutral rosin sizing agent as an internal sizing agent. The surface coating of the pulp fiber surface along the pulp fibers in the entangled state, the shape of the pulp fiber coated on the recording surface can be visually observed by a scanning electron microscope, the surface coverage of the pulp fiber surface of the recording surface is It is characterized by being 70% or more, and the ink absorbability is excellent without uneven bleeding of the ink. This is because when the ink is applied to the recording surface of the recording sheet, the ink does not spread in the recording surface direction and penetrates into the surface coating surface, and the excess ink flows in the thickness direction of the neutral paper containing the neutral rosin sizing agent. This is due to the permeation, and it is possible to obtain the shape of the recording dot that is close to a perfect circle. Further, it is possible to obtain an ink jet recording sheet having a recorded image with high density and sharpness.

[0030]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples.
Further, “parts” and “%” shown in the examples represent parts by weight and% by weight, unless otherwise specified. The ultrafine-particle inorganic pigment was used as an aqueous dispersion, but all are shown by solid content.

Example 1 [Preparation of base paper] LBKP90 having a freeness of 450 mlcsf
Parts, pulp pulp consisting of 10 parts of NBKP having a freeness of 480 mlcsf, and light calcium carbonate (T
P-121, Okutama Industrial Co., Ltd., 10 parts, cationic starch (C
ato3210, manufactured by Oji National) 0.8 part, sulfuric acid band 1.0 part, anionic neutral rosin sizing agent 0.6 part (NT-80, manufactured by Arakawa Chemical Co., Ltd.), and papermaking drying with a Fourdrinier paper machine. Then, machine calender finish, basis weight 85
A base paper of g / m ² was prepared. The prepared paper had a Steckigt sizing degree of 27 seconds.

[Preparation of Inkjet Recording Sheet] Colloidal silica (Snowtex-YL, manufactured by Nissan Kagaku,
100 parts of primary particle diameter 50 to 80 nm, polyvinyl alcohol (PVA117, manufactured by Kuraray Co., Ltd.) 30 as an adhesive agent
Parts, a cationic resin (Polyfix 601, cation charge amount 6.9 meq./g, manufactured by Showa High Polymer Co., Ltd.) 30 parts as a dye fixing agent, and an aqueous dispersion having a solid content concentration of 10% as a main component is air knife coater. Dry solid content of 2 g /
An inkjet recording sheet was prepared by coating so as to be m ² , drying, and calendering.

Example 2 100 parts of cationic colloidal silica (Snowtex-AK (3), manufactured by Nissan Kagaku Co., Ltd., primary particle size 10 to 20 nm) was added to the base paper prepared in Example 1 and polyvinyl alcohol (PVA117 was used as an adhesive. , Kuraray Co., Ltd.) 30 parts,
Cationic resin as dye fixing agent (Sumiraz resin 1
001, cation charge amount 3.5 meq. / G, manufactured by Sumitomo Chemical Co., Ltd.) An aqueous dispersion containing 30 parts as a main component and having a solid content of 10% is dried using an air knife coater to give a dry solid content of 1 g / m.
^An inkjet recording sheet was prepared by coating so as to be ² , dried and calendered.

Example 3 100 parts of cationic colloidal silica (Snowtex-AK (3), Nissan Chemical Co., Ltd., primary particle size 10 to 20 nm) was added to the base paper prepared in Example 1 and polyvinyl alcohol (PVA117 was used as an adhesive. , Kuraray Co., Ltd.) 30 parts,
Cationic resin as dye fixing agent (Sumiraz resin 1
001, cation charge amount 3.5 meq. / G, manufactured by Sumitomo Chemical Co., Ltd.) and an aqueous dispersion having a solid content of 10% as a main component of 30 parts is coated with a rod coater to a dry solid content of 2 g / m ² , dried, and calendered. To prepare an inkjet recording sheet.

Example 4 On the base paper prepared in Example 1, alumina hydrate (Cataloid AS-3, manufactured by Catalyst Kasei Kogyo Co., Ltd., primary particle size about 10 n) was used.
m) 100 parts, polyvinyl alcohol (P
VA117, manufactured by Kuraray Co., Ltd.), 30 parts, 30 parts of a cationic resin (Polyfix 601, cation charge amount of 6.9 meq./g, Showa Polymer Co., Ltd.) as a dye fixing agent, and a solid content concentration of 15% Coating the aqueous dispersion with an air knife coater to a dry solid content of 5 g / m ² ,
An ink jet recording sheet was prepared by drying and calendering.

Example 5 The solid content concentration of the aqueous dispersion used in Example 4 was set to 10%, the dry solid content was adjusted to 0.5 g / m ² using a size press using the base paper of Example 1. An ink jet recording sheet was prepared by applying the above coating, drying, and calendering.

Example 6 The solid content concentration of the aqueous dispersion used in Example 4 was set to 10%, and the base paper of Example 1 was used to obtain a dry solid content of 2 g / m ² using a gate roll coater. Thus, the ink jet recording sheet was prepared by coating, drying and calendering.

Comparative Example 1 [Preparation of base paper] LBKP90 having a freeness of 450 mlcsf
Parts, pulp pulp consisting of 10 parts of NBKP having a freeness of 480 mlcsf, and light calcium carbonate (T
P-121, Okutama Kogyo Co., Ltd.) 10 parts, cationic starch 0.
8 parts (Cato 3210, made by Oji National), 0.4 parts of sulfuric acid band, alkyl ketene dimer (SPK-90)
(3, manufactured by Arakawa Chemical Co., Ltd.) 0.1 part is added, papermaking is dried by a Fourdrinier paper machine, machine calendering is performed, and basis weight is 85 g.
A base paper of / m ² was prepared. The prepared paper had a Steckigt sizing degree of 25 seconds.

[Preparation of Inkjet Recording Sheet] Colloidal silica (Snowtex-YL, manufactured by Nissan Kagaku Co., Ltd .;
100 parts of primary particle diameter 50 to 80 nm, polyvinyl alcohol (PVA117, manufactured by Kuraray Co., Ltd.) 30 as an adhesive agent
Part, an aqueous dispersion having a solid content concentration of 10% and containing 30 parts of a cationic resin (Polyfix 601, cation charge amount of 6.9 meq./g, Showa Polymer Co., Ltd.) as a dye fixing agent as a main component was applied to a rod coater. An ink jet recording sheet was prepared by applying the coating composition to a dry solid content of 1 g / m ² , drying, and calendering.

Comparative Example 2 Instead of the alkyl ketene dimer in the base paper of Comparative Example 1,
The same except that 0.5 part of alkenyl succinic anhydride was used, and the dry solid content was 2.0 g / m ² using a rod coater.
An inkjet recording sheet was prepared by coating, drying and calendering.

Comparative Example 3 Colloidal silica (Snowtex PST-3, manufactured by Nissan Kagaku Co., Ltd., primary particle size 300) was applied to the base paper prepared in Example 1.
± 30 nm) 100 parts, polyvinyl alcohol (PVA117, Kuraray Co., Ltd.) 30 parts as an adhesive, cationic resin (Polyfix 601, cation charge amount 6.9 meq./g, Showa Polymer Co., Ltd.) 30 as a dye fixing agent 30 An aqueous dispersion having a solid content of 10% as a main component was coated using a rod coater so as to have a dry solid content of 1 g / m ² , dried, and calendered to prepare an inkjet recording sheet.

Comparative Example 4 The base paper prepared in Example 1 was coated with silica (Nipsil E22
0A, manufactured by Nippon Silica Industry Co., Ltd., average particle size 1.0 μm) 10
0 parts, polyvinyl alcohol (PVA11 as an adhesive
7, Kuraray Co., Ltd. 30 parts, cationic resin as a dye fixing agent (Polyfix 601, cationic charge amount 6.9 m)
eq. / G, manufactured by Showa High Polymer Co., Ltd.), and an aqueous dispersion having a solid content of 10% as a main component is applied using a gate roll coater to a dry solid content of 2 g / m ^2, and dried.
An ink jet recording sheet was prepared by calendering.

Comparative Example 5 The aqueous dispersion used in Comparative Example 4 was applied to a solid content concentration of 15%, the base paper of Example 1 was used, and the dry solid content was applied to 5 g / m ² using an air knife coater. Work, dry,
An ink jet recording sheet was prepared by calendering.

Comparative Example 6 The base paper prepared in Example 1 was used as it is as an ink jet recording sheet of Comparative Example 6.

The ink jet recording sheets prepared in Examples 1 to 6 and Comparative Examples 1 to 6 were evaluated according to the following method, and the results are shown in Table 1.

[Ink Absorbency] Ink absorbency and image sharpness are determined by the boundary between solid color solid print portions, for example, red print (magenta + yellow) and green print (cyan + yellow).
The degree of ink bleeding at the boundary portion of was visually determined. When the red printed portion and the green printed portion did not overlap and were separated, the characteristics were good, and when the overlapping was large and a black line was formed, the characteristics were bad. If the ink absorption is poor,
Since the image quality (image sharpness) is remarkably impaired, it does not make any sense even if other characteristics such as image density are good. In addition, as an evaluation criterion, A indicates a good characteristic, B indicates a good practically acceptable range, C indicates a practical problem, and D indicates a poor characteristic.

[Image Density] The image density is a reflection densitometer (Macbeth RD91) for a solid printed portion of black ink.
8: manufactured by Macbeth). The higher the value, the higher the image density and the better, but normally, 1.20 or more is good.

[Surface Coverage of Recording Surface] The surface coverage (%) of the recording surface was determined by taking an X-ray image of the metal element of the material used on the pulp fiber surface of the ink jet recording sheet with a scanning electron microscope. The surface coverage of the pulp fiber surface was measured as an area ratio using an image analyzer.

[Dot shape factor] An ink jet printer (IO-720: manufactured by Sharp Co., Ltd.) is used to print a single color dot of black ink, and an image analyzer analyzes the dot perimeter L and the dot area A. Was measured, and the dot shape factor C defined by the following equation 1 was calculated. When the dot shape factor C is 1.0, the larger the distance from 1.0 as a perfect circle, the more irregular the dot shape due to dot bleeding.

[0050]

## EQU1 ## C = L ² / (4π × A) where C is the dot shape factor, L is the perimeter of the dot, and A
Represents the area of a dot.

[0051]

[Table 1]

From the results shown in Table 1, in the ink jet recording sheets of Examples 1 to 6 and Comparative Examples 1 to 6, the recording sheets in Examples had a small particle diameter of the ultrafine inorganic pigment used and a surface coverage. It was within the range of the present invention, and all were good in ink absorbency, sharpness, and image density. Also, the dot shape factor was small, and the recording dot shape was close to a perfect circle. On the other hand, in Comparative Examples 1 and 2, since the used internal sizing agent was different, the surface coverage was within the range of the present invention, but in each case, the dot shape factor was large. Further, in Comparative Examples 3 to 5, since the used particle size was large, the surface coverage was low, the image density was low, the dot shape coefficient was large, and they were defective. In Comparative Example 5, the coating amount is 5 g / m
^Although it was as high as 2, the surface coverage was low because the particle size of the inorganic pigment used was large. In particular, comparing Example 1, Example 6, Comparative Example 3, and Comparative Example 4, the surface coating had the same coating amount of ² g / m ² , but depending on the particle size of the inorganic pigment used, It was shown that the coverage on the pulp fiber was poor.

[0053]

The ink jet recording sheet of the present invention is
A recording surface obtained by coating the pulp fiber surface of the raw paper surface with a composition mainly composed of ultrafine inorganic pigments on a neutral paper containing calcium carbonate as a filler and an anionic neutral rosin sizing agent as an internal sizing agent. The shape of the pulp fiber coated on the recording surface can be visually confirmed by an electron microscope, and the surface coverage is 70% or more, so that there is no unevenness of ink bleeding, excellent ink absorption, and image density and sharpness. And a recording dot shape close to a perfect circle is obtained.

Front Page Continuation (72) Inventor Takehiko Yasujima 34-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Paper Mills, Ltd.

Claims (1)

[Claims] 1. An inkjet recording sheet having a recording surface on a base paper, wherein the base paper is a neutral paper containing calcium carbonate as a filler and an anionic neutral rosin sizing agent as an internal sizing agent. The recording surface of the sheet is a recording surface coated with a composition mainly composed of ultrafine inorganic pigments along the pulp fiber surface in the entangled state of the raw paper surface, and the shape of pulp fiber coated on the recording surface. Is visible with a scanning electron microscope, and the surface coverage of the pulp fibers coated on the recording surface is 70% or more.