JP2011073265A - Inkjet recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording medium having a taste of offset printing coated paper, excellent scuff resistance and printing quality for printing part subjected to inkjet recording with pigment ink, and having little difference in paging easiness in the vertical and lateral directions. <P>SOLUTION: The inkjet recording medium has a prime coat layer having calcium carbonate and a binder as principal components formed on one surface or both faces of base paper having wood pulp as the principal component, and has an ink receiving layer on the surface of the prime coat layer, having kaolin with particle distribution of particles of 0.4-4.2 μm being 60% or more of the whole of the integrated value on the volumetric base in the laser diffraction type particle size distribution measuring, synthetic amorphous silica with an average secondary particle size of 0.5-4 μm, and a binder as the principal components. The aspect ratio (T/Y) of bending resistance value by ISO 2493 are 1.4-1.8, and white paper glossiness of 75° light incidence angles by JIS Z8741 is 35-70%. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an inkjet recording medium having a texture of coated paper for offset printing.

The ink jet recording system has been used in many applications along with the rapid improvement in printing performance because it is easy to achieve full color and has low printing noise. These applications include, for example, document recording from document creation software, recording of digital images such as digital photographs, reproduction of beautiful printed materials such as silver halide photographs and books captured by a scanner, and a relatively small number of posters. For example, creating an image for exhibition.
In addition, ink jet recording media having configurations suitable for these applications have been proposed. For example, when simply recording characters, a plain paper type medium that is recorded directly on paper is used. To obtain a resolution and color reproducibility comparable to silver halide photography, an ink receiving layer is provided as a coating layer. Coated paper type is used. When particularly high glossiness is required, for example, a cast paper type in which a coated paper type coating layer is formed by a casting method is used. In the case of posters and display applications, a roll type having a coating layer is developed and used.

One of the developments of the ink jet recording system in various fields is the printing field. Conventionally, an offset method has been mainly used in this field. However, this printing method requires a plate and undergoes plate making and printing processes, so that it takes a certain amount of time to complete a printed matter. On the other hand, the ink jet recording method is very efficient because a printed matter can be obtained simply by forming an image directly on a recording medium, and the printed matter can be produced at low cost. However, since it is an alternative to the conventional printed matter, the printed matter is required to have a texture equivalent to that of the offset printed matter.
In addition, in the ink jet recording method, not only can the same information and symbols be continuously printed, but also it is possible to continuously print by changing the information and symbols for each sheet. Taking advantage of this feature, there are increasing opportunities to print various utility bills, receipts, credit card usage statements, direct mail, text, booklets, catalogs, books, etc. by inkjet.
On the other hand, when used for booklets, catalogs, books, etc., the ease of turning varies greatly depending on the vertical and horizontal characteristics of machine-drawn paper, so the information to be printed and the print direction of the pattern are restricted. There is a case. Therefore, there is a high demand for a recording sheet whose easiness of turning in the vertical and horizontal directions does not change much. Note that “vertical” refers to the papermaking direction of mechanical papermaking, and “horizontal” refers to a direction perpendicular to the papermaking direction.

By the way, when printing a high-quality inkjet recording image, as the color reproducibility of the image is improved, the amount of ink ejected from the printer increases, so an ink receiving layer needs to be formed. Requires sufficient ink absorption performance (speed and capacity). For this reason, there are many examples in which a porous material such as synthetic amorphous silica is used for the ink receiving layer of the ink jet recording medium. However, when a porous material is used, the ink absorbability is improved, but there are problems that the glossiness is low and the texture is different from that of the offset printed matter.
In addition, in the case of a cast paper type ink jet recording medium in which the glossiness of the ink receiving layer is increased, the glossiness is very high compared to general coated paper for offset printing, and the paper is thick, so that the offset is also required. The texture is different from the printed material.
Furthermore, since these ink jet recording media use a large amount of expensive raw materials such as silica, alumina, polyvinyl alcohol, ethylene vinyl acetate emulsion, ink fixing agents (polyamine, DADMAC, polyamidine, etc.) Manufacturing costs are higher than coated paper for offset printing.

  On the other hand, when printing with general inkjet printing paper containing kaolin or calcium carbonate as a pigment for the coating layer with an inkjet printer, the ink absorption capacity of the coating layer is low, so feathering (bleeding) Phenomena such as bleeding (color boundary bleeding), solid printing unevenness (density unevenness in the printing portion), cockling (waving the printing portion), and rusting (scratching of the printing portion) occur.

In order to solve these problems, studies have been made from both the ink and paper aspects. For example, an ink jet recording sheet containing 90 parts by mass or more of kaolin as a pigment for forming an ink receiving layer, and having an average particle diameter of 5 to 15 parts by mass of kaolin out of the kaolin is 1.5 μm or more is used. As an ink for printing, an aqueous pigment ink for ink jet in which the ratio of the pigment and the hydrophilic polymer compound is 60/40 to 95/5 has been proposed (Patent Document 1).
In addition, as an ink jet recording medium having a texture close to that of general coated paper, a lower layer ink receiving layer mainly containing kaolin and amorphous synthetic silica on the support surface, and an upper layer ink containing gas phase method alumina as a main pigment The thing which provided the receiving layer is disclosed (patent document 2).
Furthermore, as an ink jet recording sheet excellent in suitability not only for pigment ink but also for dye ink, an ink receiving layer containing 10 to 90% by mass of silica and 90 to 10% by mass of calcium carbonate and / or kaolinite. (Patent Document 3).
In the recording layer (ink receiving layer), the average particle diameter is 0.2 to 2.0 μm, and 1 ≦ L / W ≦ 50 (L is the long diameter of the particle, and W is the short diameter (thickness) of the particle. ), And an ink jet recording paper having a 75 ° glossiness of 40% or more according to JIS Z8741 is disclosed (Patent Document 4).

JP 2004-91627 A JP 2005-103827 A JP 2005-297473 A JP 2004-209965 A

However, the pigment ink disclosed in Patent Document 1 described above can obtain a certain degree of scratch resistance on the printing portion when printing on a recording paper (matte inkjet recording paper) having a low blank glossiness. However, it cannot be said that the other recording papers have sufficient scratch resistance. In particular, when recording on a recording paper (glossy inkjet recording paper) having a high white paper glossiness, the pigment ink disclosed in Patent Document 1 cannot provide sufficient scratch resistance.
In addition, in the ink jet recording medium described in Patent Document 2, it is necessary to form two ink receiving layers, resulting in an increase in cost.
The ink jet recording sheet described in Patent Document 3 contains both silica, calcium carbonate, and kaolin in the ink receiving layer, and thus achieves both improved ink absorbability and glossiness similar to coated paper for offset printing. Is difficult. Similarly, the ink jet recording paper described in Patent Document 4 has excellent glossiness but lacks ink absorbability and scratch resistance of the printed portion.

  Therefore, the present invention has a texture of coated paper for offset printing, is excellent in scratch resistance and print quality of a printed part that has been ink jet recorded with pigment ink, and is further processed into a booklet, catalog, book, etc. An object of the present invention is to provide an ink jet recording medium with little difference in ease of turning in the vertical and horizontal directions.

  As a result of various studies, the inventors have formed an undercoat layer containing calcium carbonate on the base paper, thereby reducing the difference in ease of turning in the vertical and horizontal directions with the aspect ratio of the bending resistance value of the inkjet recording medium being in a certain range. As a result, the inventors have found out that the present invention can be achieved. Also, it has been found that the inclusion of synthetic amorphous silica having a predetermined average secondary particle size in the ink-receiving layer makes the smoothness and gloss of the ink jet recording medium closer to the texture of coated paper for offset printing. It was.

  That is, in the ink jet recording medium of the present invention, at least one undercoat layer mainly composed of calcium carbonate and a binder is formed on one side or both sides of a base paper mainly composed of wood pulp, and on the surface of the undercoat layer, In the laser diffraction particle size distribution measurement, a particle having a particle size distribution in which particles of 0.4 μm or more and less than 4.2 μm are 60% or more of the total volume-based integrated value, an average secondary particle diameter measured by the Coulter Counter It has a synthetic amorphous silica of 0.5 μm or more and 4 μm or less, and an ink receiving layer mainly composed of a binder, and the aspect ratio (T / Y) of bending resistance value according to ISO 2493 is 1.4 to 1.8. The white paper glossiness at a light incident angle of 75 degrees according to JIS Z8741 is 35 to 70%.

The synthetic amorphous silica is preferably gel silica.
The ink receiving layer preferably contains an organic pigment as a pigment.

  According to the present invention, it has a texture of coated paper for offset printing, is excellent in scratch resistance and print quality of a printed portion that has been ink jet recorded with pigment ink, and is further processed into a booklet, catalog, book, etc. In addition, an ink jet recording medium with little difference in ease of turning in the vertical and horizontal directions can be obtained.

  Embodiments of the present invention will be described below. In the ink jet recording medium of the present invention, an undercoat layer is formed on at least one surface of a base paper, and an ink receiving layer is provided on the surface of the undercoat layer.

(Base paper)
The base paper is based on wood pulp. Pulp such as chemical pulp (conifer bleached or unbleached kraft pulp, hardwood bleached or unbleached kraft pulp), mechanical pulp (ground pulp, thermomechanical pulp, chemical thermomechanical pulp, etc.), deinked pulp, etc. Can be used alone or in admixture at any ratio.
The papermaking pH of the base paper may be acidic, neutral or alkaline. Further, since the opacity of the paper tends to improve as the amount of the filler in the base paper increases, it is preferable to contain the filler in the paper. As the filler, known fillers such as hydrated silicic acid, white carbon, talc, kaolin, clay, calcium carbonate, titanium oxide, synthetic resin filler and the like can be used. Furthermore, the base paper may contain auxiliary agents such as a sulfuric acid band, a sizing agent, a paper strength enhancer, a yield improver, a colorant, a dye, an antifoaming agent, and a pH adjuster as necessary. The basis weight of the base paper is not particularly limited, but a paper having a basis weight of about 25 to 400 g / m ² can be suitably used.

(Undercoat layer)
At least one undercoat layer mainly composed of calcium carbonate and a binder is provided on one side or both sides of the base paper. When the ink receiving layer is provided on both sides, the undercoat layer is also provided on both sides of the base paper. In the case where the ink receiving layer is provided on only one side, an undercoat layer may be provided on at least the surface on which the ink receiving layer is provided, but an undercoat layer may be provided on both sides of the base paper.
In the present invention, “having calcium carbonate and a binder as main components” means that the ratio of calcium carbonate and binder exceeds 50% by mass with respect to all components contained in the undercoat layer.

As the pigment used for the undercoat layer, calcium carbonate (heavy calcium carbonate or light calcium carbonate) is mainly used from the viewpoint of cost, but in addition, kaolin, talc, satin white, silica, titanium dioxide, etc. may be used in combination as appropriate. it can. The binder used for the undercoat layer is, for example, starches such as oxidized starch, etherified starch and esterified starch; latexes such as styrene / butadiene copolymer (SB) latex and acrylonitrile / butadiene copolymer (NB) latex. Polyvinyl alcohol and modified products thereof; one or more of binders such as casein, gelatin, carboxymethylcellulose, polyurethane, vinyl acetate, and unsaturated polyester resin can be appropriately selected and used. In particular, from the viewpoint of fluidity and coating suitability of the coating material prepared as the undercoat layer, it is preferable to use latexes or starches, or a mixture thereof as a binder.
Further, in the undercoat layer, a fluorescent dye, a conductive agent, a water retention agent, a water resistance agent, a pH adjuster, an antifoaming agent, a lubricant, an antiseptic, and a surfactant are added as necessary within the range not impairing the effects of the present invention. Etc. may be included in any proportion.
Note that simply forming an undercoat layer containing calcium carbonate on the base paper does not significantly improve the aspect ratio (T / Y) of the bending resistance value. It has been found that (T / Y) is remarkably improved when provided.

The method for providing the undercoat layer is not particularly limited, but a two-roll size press, a film transfer type gate roll coater or blade, a rod metering size press, or a blade coater is installed in the base paper machine. It is preferable to provide an undercoat layer with an apparatus.
The coating amount of the undercoat layer is not particularly a limit, if provided in the apparatus installed in the base paper of the paper machine is preferably less than one side per 1 g / m ² or more 10 g / m ² base paper , especially preferably per side 3 g / ^{m 2 to} less than 7 g / ^{m 2} base paper. When the coating amount of the undercoat layer is less than 1 g / m ² per side, the base paper cannot be sufficiently covered, so that the effect of improving the aspect ratio (T / Y) of the bending resistance value described later is sufficiently obtained. Absent. On the other hand, when the coating amount of the undercoat layer is 10 g / m ² or more, the drying load of the paint is increased, so that the operability may be lowered.

(Ink receiving layer)
The ink receiving layer is provided on the surface of the undercoat layer, and contains the following kaolin, synthetic amorphous silica, and binder as main components. Here, “having kaolin, synthetic amorphous silica, and binder as main components” means that the proportion of kaolin, synthetic amorphous silica, and binder is 50% by mass with respect to all components contained in the ink receiving layer. It means exceeding.

(Pigment of ink receiving layer)
The pigment of the ink receiving layer is mainly kaolin having a particle size distribution in which particles of 0.4 μm or more and less than 4.2 μm are 60% or more of the total volume-based integrated value in laser diffraction particle size distribution measurement. Here, the main component means that kaolin is 50% by mass or more with respect to all the pigments of the ink receiving layer. Kaolin is a clay containing at least one kind of kaolin minerals such as kaolinite, halloysite, dickite, and nacklite, and any known kaolin used in general coated paper for offset printing can be used. Good. The kaolin is not limited to, for example, Georgia, Brazil, China, etc. or grades such as grade 1, grade 2, and delami. Can be used. For the particle size distribution, a sample slurry is dropped and mixed in pure water to obtain a uniform dispersion, and a value measured with a laser particle size measuring device (device used: Mastersizer S type manufactured by Malvern) is used.

The kaolin having the above particle size distribution has a sharp particle size distribution, uniform particle size, low pigment particle packing density, and a porous and bulky ink receiving layer as compared with general kaolin. The porous ink receiving layer has excellent ink absorbability because the average pore diameter is larger than that of the ink receiving layer having a dense pigment filling. The sharper the particle size distribution of kaolin, the easier it is to form a porous ink receiving layer. In particular, particles with a particle size of 0.4 μm or more and less than 4.2 μm are 65% or more of the total volume-based integrated value in laser diffraction particle size distribution measurement. The particle size distribution is preferably as follows.
The kaolin is preferably unfired. When kaolin is fired, the crystal system is broken, and the particle size distribution is significantly different from that of the unfired material. Therefore, the presence or absence of firing can be distinguished from the particle size distribution.

  Instead of kaolin having the above particle size distribution, kaolin having a particle size distribution in which particles of 0.4 μm or more and less than 4.2 μm are less than 60% of the total volume-based value in laser diffraction particle size distribution measurement. When kaolin containing a large number of particles having a particle diameter of less than 0.4 μm is used, the ink-receiving layer is dense and ink absorbability is lowered. Further, in the laser diffraction particle size distribution measurement, kaolin having a particle size distribution in which particles of 0.4 μm or more and less than 4.2 μm have a particle size distribution that is less than 60% of the total in terms of volume-based integration, When kaolin containing a large amount of particles is used, in addition to the ink receiving layer becoming dense, the gap between the pigment particles existing on the surface of the ink receiving layer is reduced, so that the ink absorbability is lowered.

  The ink receiving layer contains, in addition to kaolin, synthetic amorphous silica having an average secondary particle size of 0.5 μm or more and 4 μm or less measured by a Coulter counter method. When the average secondary particle diameter of the synthetic amorphous silica exceeds 4 μm, the smoothness and glossiness of the resulting ink jet recording medium are different from those of coated paper for offset printing, and the ink penetration is excessive and the color developability is high. Deterioration or printing unevenness occurs. When the average secondary particle diameter of the synthetic amorphous silica is less than 0.5 μm, the ink absorbability is lowered, or the viscosity of the paint is increased when the pigment is dispersed, so that the dispersibility of the paint is deteriorated. In particular, the average secondary particle diameter of the synthetic amorphous silica is preferably 0.6 μm or more and 3 μm or less.

  The amount of oil absorption of the synthetic amorphous silica is not particularly limited, but is preferably 150 ml / 100 g or more and 500 ml / 100 g or less. If the oil absorption is less than 150 ml / 100 g, the ink holding capacity of the ink receiving layer may not be sufficient, and the scratch resistance and ink absorbability of the printed part may be inferior. When the oil absorption exceeds 500 ml / 100 g, when the pigment is dispersed, the viscosity of the paint may increase and the dispersibility of the paint may deteriorate. The oil absorption amount of the synthetic amorphous silica is more preferably 200 ml / 100 g or more and 400 ml / 100 g or less. Note that the oil absorption amount can be measured by a method defined in JIS K5101.

The synthetic amorphous silica is preferably gel silica. Gel silica is a wet method obtained by agglomeration while suppressing the growth of primary particles by advancing the neutralization reaction of sodium silicate and mineral acid (usually sulfuric acid) in the acidic pH range. Synthetic amorphous silica fine particles. Compared with precipitated silica (manufactured by proceeding neutralization reaction of sodium silicate and mineral acid in an alkaline pH range), gel method silica has a longer reaction time after agglomeration and strong bond between primary particles. , The pore volume tends to increase. For this reason, it is excellent in ink absorbability and scratch resistance and is preferably used.
In addition, it is preferable that the mass blending ratio (kaolin / synthetic amorphous silica) of the above-described kaolin and synthetic amorphous silica in the ink receiving layer is 95/5 to 50/50. When the blending ratio of silica is small, it is difficult to obtain the desired ink absorbability and scratch resistance. On the other hand, if the silica content is too large, cracks may occur on the surface of the ink receiving layer, ink permeation may be excessive, color development may deteriorate, and unevenness may occur. Further, as the blending ratio of silica increases, it tends to move away from the texture of offset printing paper, and it becomes difficult to obtain glossiness, so it may be difficult to obtain glossy recording paper.

  In addition to kaolin and synthetic amorphous silica, the ink receiving layer may contain other inorganic pigments. As these other inorganic pigments, any known pigments that are used in general coated paper for offset printing may be used. As other inorganic pigments described above, kaolin other than kaolin having the above particle size distribution, heavy calcium carbonate and light calcium carbonate other than synthetic amorphous silica having the above average secondary particle diameter, silica, silica composite calcium carbonate, Inorganic pigments such as talc, calcined kaolin obtained by calcining the above-mentioned calcined kaolin, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, alumina, magnesium carbonate, magnesium oxide, calcium silicate, bentonite, zeolite, sericite and smectite One type or two or more types can be appropriately selected from among them. The blending amount of these inorganic pigments is desirably 10% by mass or less based on the total amount of kaolin and synthetic amorphous silica in the ink receiving layer.

In the present invention, in order to improve the white paper glossiness on the surface of the ink receiving layer, it is preferable to appropriately contain an organic pigment such as a plastic pigment in the ink receiving layer. The blending ratio of the organic pigment is preferably 0 to 40 parts by mass, more preferably 0 to 30 parts by mass with respect to 100 parts by mass of the inorganic pigment (total amount of all inorganic pigments in the ink receiving layer containing kaolin and synthetic amorphous silica). The amount can be 1 part by mass, more preferably 1 to 25 parts by mass.
When no organic pigment is blended in the ink receiving layer, there is no problem in producing the matte inkjet recording medium in the present invention, but glossiness may not be sufficient when producing glossy inkjet paper. . In particular, the glossiness of the ink receiving layer decreases in inverse proportion to the increase in the blending ratio of the synthetic amorphous silica used in the present invention. It is necessary to increase the blending amount of the organic pigment in proportion to the blending ratio of the porous silica. When the organic pigment is blended in an amount of more than 40 parts by mass, the organic pigment melts and sticks to the metal roll when passing through a calendar heated to a high temperature, causing tears, paper breakage troubles, and the like. In addition, the compounding quantity of the organic pigment when manufacturing the mat-like inkjet paper is not particularly limited.

  As the organic pigment used in the ink receiving layer, a solid type, a hollow type, a core-shell type, or the like can be used singly or as a mixture of two or more types as necessary. As the constituent polymer component of the organic pigment, a monomer such as styrene and / or methyl methacrylate is preferably used as a main component, and other monomers copolymerizable with these as necessary. Examples of the copolymerizable monomer include olefinic aromatic monomers such as α-methylstyrene, chlorostyrene, and dimethylstyrene, methyl (meth) acrylate, ethyl (meth) acrylate, and butyl (meth) acrylate. Monoolefin monomers such as 2-ethylhexyl (meth) acrylate, glycidyl (meth) acrylate, (meth) acrylonitrile, and monomers such as vinyl acetate. If necessary, for example, olefinic unsaturated carboxylic acid monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid and crotonic acid; hydroxyethyl, hydroxyethyl methacrylate, hydroxypropyl acrylate Olefinic unsaturated hydroxy monomers such as hydroxypropyl methacrylate; olefinic unsaturated amide monomers such as acrylamide, methacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, N-methoxymethylacrylamide; divinylbenzene, etc. These dimer vinyl monomers can be used singly or in combination of two or more. These monomers are examples, and any other copolymerizable monomer can be used.

(Binder for ink receiving layer)
As the binder used in the ink receiving layer, any known binder used for general offset printing coated paper may be used. Examples of binders include starches such as oxidized starch, etherified starch, and esterified starch; latexes such as styrene / butadiene copolymer (SB) latex and acrylonitrile / butadiene copolymer (NB) latex; polyvinyl alcohol and its modification One or more kinds of binders such as casein, gelatin, carboxymethylcellulose, polyurethane, vinyl acetate and unsaturated polyester resin can be appropriately selected and used. From the viewpoint of fluidity and coating suitability, it is preferable to use latexes or starches, or a mixture thereof.

The ratio of the binder to 100 parts by mass of the total of all inorganic pigments contained in the ink receiving layer is preferably 4 parts by mass or more and 35 parts by mass or less. When the content of the binder is less than 4 parts by mass, the strength of the ink receiving layer tends to be insufficient. On the other hand, when the content of the binder exceeds 35 parts by mass, voids existing in the ink receiving layer are filled with the binder, and the ink absorption capacity is reduced. Therefore, it tends to be difficult to obtain good print quality. .
It is more preferable that the ratio of the binder with respect to 100 parts by mass of the inorganic pigment is 5 parts by mass or more and less than 30 parts by mass.

(Other ingredients)
For the ink receiving layer, pigment dispersant, thickener, water retention agent, lubricant, antifoaming agent, foam suppressor, mold release agent, foaming agent, coloring dye, coloring pigment, fluorescent dye, antiseptic, etc. Auxiliaries such as agents, water-resistant agents, surfactants, pH adjusters and the like can be added as appropriate.

(Amount of ink receiving layer)
The coating amount of the ink receiving layer is not formed in particular limited, it is less than per one side 1 g / ^{m 2} or more 40 g / ^{m 2} is preferable, and 4g / ^{m 2} or more 30 g / ^m less than ² per side preferable. The greater the coating amount, the greater the amount of voids in the ink receiving layer, and the better the ink absorbability. When the coating amount of the ink receiving layer is less than 1 g / m ² per side, the base paper as a base material cannot be sufficiently coated, and the coated paper surface remains rugged and resembles non-coated paper Take on a texture. In this case, it is difficult to obtain the desired white paper glossiness according to the present invention, and it is not possible to obtain an inkjet recording medium having the texture of the intended coated paper for offset printing. In addition, when the coating amount is less than 1 g / m ² per side, the ink receiving layer has an insufficient absorption capacity, and printing defects such as feathering and bleeding are likely to occur. On the other hand, when the coating amount of the ink receiving layer is 40 g / m ² or more per side, the drying load during coating is large, resulting in poor workability and an increase in cost.

  As a method for providing an ink receiving layer, a general coating apparatus such as a blade coater, a roll coater, an air knife coater, a bar coater, a gate roll coater, a curtain coater, a gravure coater, a flexographic gravure coater, a spray coater, a size press, etc. The various devices can be used on-machine or off-machine. The ink receiving layer may be provided on one side or both sides of the base paper, and may be provided in one layer or two or more layers. In the present invention, sufficient performance can be obtained even with a single ink-receiving layer. Therefore, it is preferable to provide only one layer from the viewpoint of cost reduction.

(Bending resistance)
The aspect ratio (T / Y) of the bending resistance value according to ISO 2493 of the ink jet recording medium obtained as described above is 1.4 to 1.8. By setting the aspect ratio of the bending resistance value in the range of 1.4 to 1.8, there are no restrictions on the printing direction. For example, even in the A4 vertical recording medium, the A4 horizontal recording medium (A3 is used in half. Etc.) can also be used for printing.
In addition, in the present invention, the aspect ratio of the bending resistance value can be reduced as much as possible by adjusting the arrangement of pulp fibers in the longitudinal direction, shrinkage during drying, machine draw, etc. By providing the base paper with the undercoat layer and the ink receiving layer as described above, the aspect ratio of the bending resistance value of the base paper can be reduced.
The bending resistance value according to ISO 2493 can be measured by, for example, an L & W bending tester CODE160 (manufactured by Lorentzen & Wettre). In the present invention, “vertical” refers to the papermaking direction of mechanical papermaking, and “horizontal” refers to a direction perpendicular to the papermaking direction.

When the aspect ratio of the bending resistance is less than 1.4, there is no difference in the ease of turning, but it is good, but it is not practical because a special paper machine is required when manufacturing the base paper. This is because a general paper machine inevitably causes a difference in bending resistance value in the vertical and horizontal directions due to the effect of the arrangement of pulp fibers in the vertical direction, shrinkage during drying, machine draw, and the like. If a special paper machine is used, it is possible to reduce the difference between vertical and horizontal directions, but the base paper obtained due to inferior productivity is expensive, lacks versatility, and greatly reduces practicality. In addition, the aspect ratio of a sheet having an extremely small bending resistance value may be less than 1.4. However, such a sheet is very stiff and difficult to turn.
On the other hand, when the aspect ratio of the bending resistance exceeds 1.8, the vertical and horizontal differences in ease of turning when processing into booklets, catalogs, books, etc. are greatly different. There are restrictions on the direction, and printing is possible only in one direction.

(Blank gloss)
The blank paper glossiness at a light incident angle of 75 degrees according to JIS Z8741 on the surface of the ink receiving layer of the inkjet recording medium is 35 to 70%. When the blank paper glossiness is less than 35%, the texture of the offset printing paper cannot be obtained, and when the blank paper glossiness exceeds 70%, the conditions of the calendar process for obtaining high glossiness become severe, so that the ink is used. The voids of the receiving layer are reduced, and good ink absorbability cannot be obtained.
The blank paper glossiness is determined by using a calendar device such as a machine calendar, mat calendar, super calendar, soft calendar, shoe calendar, etc. after providing an ink receiving layer, processing temperature, processing speed, processing linear pressure, number of processing steps and roll diameter, It can be obtained by appropriately adjusting and selecting conditions such as the material and performing surface treatment.

  The ink jet recording medium of the present invention exhibits excellent performance when printed on an ink jet printer, particularly a printer equipped with an aqueous pigment ink, but can also be used for an electrophotographic printer or a melt thermal transfer printer. is there.

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.
The particle size distribution of kaolin is a value measured with a laser method particle size measuring instrument (master sizer S type manufactured by Malvern Co., Ltd.) by dropping and mixing a sample slurry containing kaolin in pure water to make a uniform dispersion. Adopted.
The average secondary particle diameter of the synthetic amorphous silica was measured by a Coulter counter method (device used: Multisizer 3 manufactured by Beckman Coulter, Inc.).

(Preparation of base paper A)
To 100% by mass of hardwood bleached kraft pulp (freeness 380 ml), 0.5% of cationized starch is added to pulp, 0.6% of sulfuric acid band is added to pulp, and 12% of calcium carbonate is added to pulp. And made paper. A base paper A was manufactured by forming a web using an on-top twin-wire type paper machine using this paper stock and performing drying by performing a three-stage wet press.

(Preparation of base paper B)
To 100% by mass of hardwood bleached kraft pulp (freeness 380 ml), 0.5% of cationized starch is added to pulp, 0.6% of sulfuric acid band is added to pulp, and 12% of calcium carbonate is added to pulp. And made paper. Using this stock, a paper web was formed with an on-top twin-wire type paper machine, dried by performing a three-stage wet press, and a base paper B was produced.

(Preparation of base paper C)
To 100% by mass of hardwood bleached kraft pulp (freeness 380 ml), cationized starch 0.5% to pulp, alkyl ketene dimer 0.05% to pulp, and sulfate band to pulp 0.8% % And calcium carbonate 15% to pulp was added to make a paper stock. A base paper C was produced by forming a web using an on-top twin-wire type paper machine using this stock, followed by drying by performing a three-stage wet press.

(Forming undercoat paper)
On the base paper A, the following undercoat layer coating F was applied with a gate roll coater at a rate of 5 g / m ² (as solids) per side and a total of 10 g / m ² (as solids) on both sides, dried again, Undercoat paper A having a basis weight of 83.0 g / m ² was obtained. The undercoating paper A had a bending resistance value in the vertical direction of 130 mN, a bending resistance value in the horizontal direction of 62.1 mN, and an aspect ratio (T / Y) of 2.09.
Similarly, apply the following undercoat paint F to the base paper B with a gate roll coater at 5 g / m ² (as solids) per side and a total of 10 g / m ² (as solids) on both sides. Dried to obtain an undercoat paper B having a basis weight of 97.9 g / m ² . The undercoat paper B had a bending resistance value in the vertical direction of 224 mN, a bending resistance value in the horizontal direction of 107 mN, and an aspect ratio (T / Y) of 2.09.
Undercoat coating F: 100 parts of light calcium carbonate having an average particle size of 1.5 μm, 0.2 parts of sodium polyacrylate dispersant, 18 parts of phosphate esterified starch as a binder and styrene-butadiene copolymer ( SB) 5 parts of latex was mixed to obtain an undercoat paint F having a solid content of 46%.

On the other hand, a 10% strength by weight oxidized starch aqueous solution was applied to the base paper C with a gate roll coater at a rate of 2.5 g / m ² (as a solid content) per side and a total of 5 g / m ² (as a solid content) on both sides. After drying again, an undercoat paper C having a basis weight of 83.0 g / m ² was obtained. The undercoating paper C had a bending resistance value in the vertical direction of 165 mN, a bending resistance value in the horizontal direction of 74.7 mN, and an aspect ratio (T / Y) of 2.21.

<Example 1>
The following ink-receiving layer coating material K was coated on both sides of primer paper A using a blade coater so that the coating amount per side was 14 g / m ² . After coating, the paper was dried until the moisture content in the paper became 5%, and an ink jet recording medium was obtained by supercalendering so that the white paper glossiness at a light incident angle of 75 degrees based on JIS Z8741 was 55%. The inkjet recording medium had a bending resistance value in the vertical direction of 132 mN, a bending resistance value in the horizontal direction of 82.0 mN, and an aspect ratio (T / Y) of 1.61.
Ink-receptive layer coating K: Kaolin A (Product name: Capim DG, manufactured by Rio Capim, 80% by volume of particles having a particle diameter of 0.4 μm or more and less than 4.2 μm: 71%), synthetic amorphous Silica A (Product name: NIPGEL AY-200, manufactured by Tosoh Silica Corporation, average secondary particle diameter 1.8 μm) 20 parts, Organic pigment A (modified styrene copolymer, product name: L8900, manufactured by Asahi Kasei Chemicals) 20 parts, 10 parts of styrene / butadiene copolymer (SB) latex (glass transition temperature 15 ° C.) as a binder, 0.2 part of sodium hydroxide, 0.2 part of sodium polyacrylate as a dispersant, and dilution water A paint having a solid content of 40% was obtained by mixing.

<Example 2>
An ink jet recording medium was obtained in the same manner as in Example 1 except that the conditions of the super calendar process were changed and the white paper glossiness at a light incident angle of 75 degrees based on JIS Z8741 was 65%. The inkjet recording medium had a bending resistance value in the vertical direction of 114 mN, a bending resistance value in the horizontal direction of 75.1 mN, and an aspect ratio (T / Y) of 1.52.

<Example 3>
An ink jet recording medium was obtained in the same manner as in Example 1 except that the undercoat paper B was used. The inkjet recording medium had a longitudinal bending resistance value of 218 mN, a lateral bending resistance value of 127 mN, and an aspect ratio (T / Y) of 1.72.

<Example 4>
An ink jet recording medium was obtained in the same manner as in Example 1 except that the supercalender treatment conditions were changed and the white paper glossiness at a light incident angle of 75 degrees based on JIS Z8741 was 36%. The inkjet recording medium had a bending resistance value in the vertical direction of 179 mN, a bending resistance value in the horizontal direction of 100 mN, and an aspect ratio (T / Y) of 1.79.

<Comparative Example 1>
An ink jet recording medium was obtained in the same manner as in Example 1 except that the undercoat paper C was used. The inkjet recording medium had a bending resistance value in the vertical direction of 165 mN, a bending resistance value in the horizontal direction of 90.6 mN, and an aspect ratio (T / Y) of 1.82.

<Comparative Example 2>
An ink jet recording medium was obtained in the same manner as in Example 2 except that the undercoat paper C was used. The inkjet recording medium had a bending resistance value in the vertical direction of 149 mN, a bending resistance value in the horizontal direction of 80.4 mN, and an aspect ratio (T / Y) of 1.85.

<Comparative Example 3>
An ink jet recording medium was obtained in the same manner as in Example 1 except that the conditions of the super calendar process were changed and the white paper glossiness at a light incident angle of 75 degrees based on JIS Z8741 was 75%. This inkjet recording medium had a bending resistance value in the vertical direction of 191 mN, a bending resistance value in the horizontal direction of 113 mN, and an aspect ratio (T / Y) of 1.69.

<Comparative example 4>
The following ink receiving layer coating material L was coated on both sides of the undercoat paper A using a blade coater so that the coating amount per side was 13 g / m ² . After coating, the paper was dried until the moisture content in the paper reached 5%, and supercalendered so that the white paper glossiness at a light incident angle of 75 degrees based on JIS Z8741 was 30% to obtain an ink jet recording medium. This inkjet recording medium had a bending resistance value in the vertical direction of 69.5 mN, a bending resistance value in the horizontal direction of 47.7 mN, and an aspect ratio (T / Y) of 1.46.
Ink-receiving layer coating material L: Kaolin A 80 parts, synthetic amorphous silica E (product name: NIPGEL AY-601, manufactured by Tosoh Silica Co., Ltd., average secondary particle size 6.0 μm) 20 parts, organic pigment A 30 parts, binder 10 parts of SB latex (glass transition temperature 15 ° C.), 0.2 part of sodium hydroxide, 0.2 part of sodium polyacrylate as a dispersant and dilution water were mixed to obtain a paint having a solid content of 40%.

<Comparative Example 5>
The following ink receiving layer coating material M was coated on both sides of the undercoating paper C using a blade coater so that the coating amount per side was 13 g / m ² . After coating, the paper was dried until the moisture content in the paper became 5%, and was subjected to supercalender treatment so that the white paper glossiness at a light incident angle of 75 degrees based on JIS Z8741 was 60%, to obtain an ink jet recording medium. The inkjet recording medium had a bending resistance value in the vertical direction of 134 mN, a bending resistance value in the horizontal direction of 67.7 mN, and an aspect ratio (T / Y) of 1.98.
Ink-receiving layer coating material M: Kaolin B (Product name: KCS, manufactured by Imeris Co., Ltd., the ratio of the volume-based integrated value of 0.4 μm or more and less than 4.2 μm: 53%, particles having a particle diameter of less than 0.4 μm 80%, synthetic amorphous silica A 20 parts, organic pigment A 20 parts, SB latex serving as a binder (glass transition temperature 15 ° C.) 10 parts Then, 0.2 part of sodium hydroxide, 0.2 part of sodium polyacrylate as a dispersing agent and dilution water were mixed to obtain a paint having a solid content of 40%.

<Evaluation method>
1. Blank paper quality 1-1. Bending resistance In accordance with ISO 2493, the bending resistance value of each inkjet recording medium at a sample width of 38 mm, a bending length of 50 mm, and a bending angle of 15 ° was measured with an L & W bending tester CODE 160 (manufactured by Lorentzen & Wettre).
1-2. White Paper Glossiness According to JIS Z8741, the white paper glossiness at a light incident angle of 75 degrees on the surface of each inkjet recording medium was measured using a gloss meter (manufactured by Murakami Color Research Laboratory, True GLOSS GM-26PRO).

2. Inkjet printing quality Printing was performed on each inkjet recording medium with the following commercially available pigment inkjet printer, and printing evaluation was performed according to the following evaluation method.
Evaluation printer: Seiko Epson, PX-V630
2-1. Dryability (ink absorption)
A black straight line with a thickness of 1.5 points was printed with an evaluation printer (photo paper / clean mode), and rubbed with a finger 10 minutes after printing, and the drying property was evaluated according to the following criteria.
○: The printed part hardly extends even when rubbed with a finger, the ink absorption speed is fast, and the level is good.
[Delta]: When rubbed with a finger, the printed portion is slightly extended and the ink absorption speed is slightly slow, but it is at a level that causes no practical problems.
X: When rubbed with a finger, the printed part is extended, the ink absorption speed is slow, and it is at a level unbearable for practical use.

2-2. Scratch resistance of printed part Five black straight lines with a thickness of 1.5 points were printed side by side with an evaluation printer (photo mat paper / clean mode), and rubbed with a dry cotton swab 5 hours after printing. Friction was evaluated.
○: The ink does not peel off even when rubbed with a cotton swab, which is a good level.
(Triangle | delta): Although ink peels off a little when rubbed with a cotton swab, it is a level which is satisfactory practically.
X: The ink peeled off when rubbed with a cotton swab, and it was at a level unbearable for practical use.
2-3. Texture of offset printing coated paper A predetermined pattern (color test chart No. 2 based on JIS X6933) was ink jet printed on each ink jet recording medium with the evaluation printer. The same pattern as this was offset printed on coated paper for offset printing (Aurora coat: Nippon Paper Industries, Ltd., basis weight 104.7 g / m ² ). The appearance and texture of each inkjet printed material was compared with the offset printed material and evaluated according to the following criteria.
○: The texture such as appearance and touch is close to the coated paper for offset printing, and has a texture of offset printed matter.
X: Unlike the coated paper for offset printing, the texture such as appearance and touch is not the texture of the offset printed material.

3. Sense of turning when a booklet is made Use a commercially available pigment ink jet printer (manufactured by Hewlett Packard, CM8060) to continuously apply a predetermined pattern (standard test pattern J12 / Ver.1 for JEITA printer) to each ink jet recording medium. Printed and produced A4 size booklets with vertical eyes (fibers running parallel to the long side of the paper) and horizontal eyes (fibers running parallel to the short side of the paper). And the uncomfortable feeling of page turning of each booklet was evaluated according to the following criteria. Longitudinal is usually standard. The evaluation may be ○ or △.
○: Turns in the same way without any sense of incongruity between the vertical and horizontal eyes. △: The feeling of turning slightly differs between the vertical and horizontal eyes.
X: There is a large difference in turning feeling between the vertical and horizontal eyes.

  The obtained results are shown in Tables 1 and 2.

  As is clear from Tables 1 and 2, in each example, the image has good scratch resistance, excellent ink absorption, satisfies various qualities in a well-balanced manner, and feels of coated paper for offset printing. Furthermore, it was found that the difference between the vertical and horizontal directions of the turning feeling when the booklet was made was small, and the printing direction of the inkjet recording medium was not restricted.

On the other hand, in the case of Comparative Examples 1 and 2 in which the undercoat layer does not contain calcium carbonate and the aspect ratio of the bending resistance exceeds 1.8, the feeling of turning of the booklet is greatly different in the vertical and horizontal directions. It turns out that direction is restricted. In addition, when Examples 1 and 2 were compared with Comparative Examples 1 and 2, respectively, it was found that the aspect ratio of the bending resistance value was hardly affected by the glossiness (that is, supercalender processing conditions).
Further, in Comparative Example 3 in which the glossiness exceeded 70%, the ink absorbability was lowered and the scratch resistance of the printed portion was also inferior. This is presumably because the voids in the ink receiving layer were reduced.
In the case of Comparative Example 4 in which the average secondary particle diameter of the synthetic amorphous silica in the ink receiving layer exceeded 4 μm, the texture of the offset printed matter was not obtained. This is considered to be due to the fact that the surface is very rough and glossy even after the calendar treatment.
In the case of Comparative Example 5 in which the particle size distribution of kaolin in the ink receiving layer is such that particles of 0.4 μm or more and less than 4.2 μm are less than 60% of the total volume-based integrated value, the ink absorbency Decreased significantly.

Claims (3)

At least one undercoat layer mainly composed of calcium carbonate and a binder is formed on one side or both sides of a base paper mainly composed of wood pulp, and 0.4 μm is measured on the surface of the undercoat layer by laser diffraction particle size distribution measurement. A kaolin having a particle size distribution in which particles less than 4.2 μm are 60% or more of the total volume-based integrated value, and a non-synthetic material having an average secondary particle size of 0.5 μm or more and 4 μm or less measured by the Coulter Counter method An inkjet recording medium having an ink-receiving layer mainly composed of crystalline silica and a binder,
An inkjet recording medium having a bending resistance value aspect ratio (T / Y) of 1.4 to 1.8 according to ISO 2493 and a blank paper glossiness of 35 to 70% at a light incident angle of 75 degrees according to JIS Z8741.   The ink jet recording medium according to claim 1, wherein the synthetic amorphous silica is gel silica.   The inkjet recording medium according to claim 1, wherein the ink receiving layer contains an organic pigment as a pigment.