JP2006305855A - Inkjet recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording medium excellent in ink absorption, enables attainment of a feel of gloss equivalent to that of a silver salt photo and also excels in cutting workability. <P>SOLUTION: The inkjet recording medium has a constitution wherein one or more under layers containing a pigment and a binder are provided at least on one side of a substrate and one or more ink accepting layers are provided on the surface of the under layers. The pigment of the under layer contains calcium carbonate wherein the rate of particles having a particle diameter of 2 μm or less is 95% or above and synthetic amorphous silica of which the oil absorption is 200 ml/100 g or above, and the ratio expressed by (mass of the synthetic amorphous silica)/(mass of the calcium carbonate) is 50/50-80/20. The binder of the under layer contains starch or a derivative thereof and polyvinyl alcohol and the rate of content of the starch or the derivative thereof in the binder is 20 mass% or above. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink jet recording medium, and preferably relates to an ink jet recording medium excellent in ink absorbability, providing glossiness similar to that of a silver salt photograph and excellent in cutting processability.

  In general, the ink jet recording system performs recording by forming dots by ejecting ink droplets by various mechanisms and attaching them to recording paper. The ink jet recording method has advantages such as noise reduction, easy full color, and high-speed printing compared to the dot impact type recording method. On the other hand, inks used for ink jet recording are usually water-based inks using direct dyes, acid dyes, etc., and thus have a drawback of poor drying properties.

  On the other hand, recently, with the widespread use of high-resolution digital video, digital cameras, scanners and personal computers, there are many opportunities to handle high-definition images, and these hard copies are often output by inkjet printers. Along with this, the required characteristics for recording media have been diversified, and in particular, there has been a growing demand for recording media having glossiness comparable to silver salt photographs.

  The characteristics required for the ink jet recording paper used in such an ink jet recording method are that the ink drying speed is high, the print density is high, there is no overflow or bleeding of the ink, and the paper is absorbed by absorbing the ink. Is not wavy. A method of manufacturing a high-quality inkjet recording paper satisfying these characteristics by a cast coating method has already been proposed (see Patent Document 1 and Patent Document 2).

  In the cast coating method, a coating liquid mainly composed of a pigment and a binder is coated on a base paper to provide a coating layer that serves as an ink receiving layer, and a wet and plastic coating layer is formed on a cast drum ( This is a method of applying a gloss finish to the mirror finished surface). The cast coating method generally includes (1) a wet cast method (direct method) in which a coating layer is pressed onto a mirror-finished heating drum while the coating layer is in a wet state, and (2) a wet coating layer once. (Semi-) Rewetting cast method (rewetting method) in which it is swelled and plasticized with a rewetting liquid after drying, and pressed onto a mirror-finished heated drum (drying method). (3) The wet coating layer is made into a gel state by solidification treatment Then, it can be divided into three types, that is, a gelling cast method (coagulation method) in which pressure is applied to a heated mirror drum and dried.

  By the way, as a method for improving the ink absorbability of the ink jet recording paper, it is common to increase the coating amount of the ink receiving layer. However, in the case of the cast coating method described above, since the drying efficiency of the coating layer is poor, it is difficult to increase the coating amount when the ink receiving layer is cast coated. For this reason, it has been studied that the coating amount of the ink receiving layer is reduced, and further, an under layer having a high ink absorbency is formed in the lower layer and cast coating is performed.

In the case of such cast-coated paper with a multi-layer structure, if the strength of the under layer is weak, the recording layer strength of the final product after cast processing will also be weak, and the amount of paper dust will increase at the time of cutting guillotine, and printer transport trouble will occur There is a handling problem such as. For this reason, the under layer is required to have an absorption capacity that compensates for insufficient ink absorbability by the cast layer (ink receiving layer) alone and a strength that does not cause problems when handling the final product.
Heavy calcium carbonate containing 95% by weight or more of synthetic amorphous silica (A) having an oil absorption of 200 ml / 100 g or more and particles having a particle diameter of 2 μm or less as a technique for increasing the strength of the under layer in cast coated paper having a multilayer structure A technique containing (B) as an underlayer pigment is disclosed (see Patent Document 3).

  In general, as a method for improving the ink absorbability of the coating layer, it is conceivable to use silica having a large oil absorption amount for the pigment contained in the coating layer. In general, there are a lot of paper dusts at the time of cutting, and the handling properties are usually poor.

JP-A-62-95285 JP-A-5-59694 JP 2003-285543 A

In the case of the technology described in Patent Document 3 described above, the strength of the under layer is maintained, but the ink absorbability is reduced, and the coating amount of the cast layer (ink receiving layer) must be increased accordingly. is there. Therefore, the cost is increased, and handling may be deteriorated such as generation of paper dust.
Further, if the proportion of the pigment in the coating layer is increased in order to improve the ink absorbability, the color developability of the printed image is lowered and the coating layer strength is likely to be lowered. On the other hand, when the blending amount of the binder is increased in order to ensure the coating layer strength, the ink absorptivity tends to decrease or paper powder tends to be generated.
Thus, since the factors that improve the ink absorbability and the coating layer strength are contradictory, it is difficult to improve both the ink absorbability and the strength of the ink receiving layer.
The present invention has been made to solve the above-described problems, and an object thereof is to provide an ink jet recording medium excellent in both ink absorbency and coating layer strength.

As a result of various studies, the inventors of the present invention, in an inkjet recording medium having a multilayer structure having an under layer and an ink receiving layer, contain a predetermined amount of synthetic amorphous silica and calcium carbonate in a predetermined ratio in the under layer. Furthermore, it has been found that the above problem can be solved by adding 20% by mass or more of starch or a derivative thereof to the binder.
In order to achieve the above object, the ink jet recording medium of the present invention is provided with at least one under layer containing a pigment and a binder on at least one side of a support, and an ink receiving layer on the surface of the under layer. In which the pigment of the under layer comprises calcium carbonate in which the ratio of particles having a particle diameter of 2 μm or less is 95% or more and synthetic amorphous silica having an oil absorption of 200 ml / 100 g or more. And the ratio represented by (mass of the synthetic amorphous silica) / (mass of the calcium carbonate) is 50/50 to 80/20, and the content ratio of starch or a derivative thereof in the binder Is an ink jet recording medium having a content of 20% by mass or more.

  The under layer is a coating liquid obtained by mixing the pigment dispersion obtained by dispersing the synthetic amorphous silica and the calcium carbonate in the presence of a cationic dispersant, the binder, and the cationic ink fixing agent. It is preferable that it is formed by coating. The outermost layer of the ink receiving layer is preferably provided by a cast coating method.

  According to the present invention, an ink jet recording medium excellent in both ink absorbability and coating layer strength can be obtained.

  Hereinafter, an inkjet recording medium according to an embodiment of the present invention will be described.

<Support>
As the support used in the present invention, a sheet-like material such as paper, cloth, resin film, and resin-coated paper can be preferably used, but particularly preferably paper (coated paper, uncoated paper, etc.). Is used. As the raw material pulp of the paper, chemical pulp (coniferous bleached or unbleached kraft pulp, hardwood bleached or unbleached kraft pulp, etc.), mechanical pulp (ground pulp, thermomechanical pulp, chemithermomechanical pulp, etc.), deinked pulp Etc. can be used alone or in combination at any ratio. Further, the pH of the paper may be acidic, neutral or alkaline. In addition, when a filler is included in the paper, the opacity of the paper tends to be improved. Therefore, it is preferable to include a filler. Examples of the filler include hydrated silicic acid, white carbon, talc, kaolin, clay, calcium carbonate. Well-known fillers such as titanium oxide and synthetic resin fillers can be used.

<Under layer>
One or more under layers are provided on at least one side of the support and contain the following pigment and binder.
(Pigment)
The pigment of the under layer contains synthetic amorphous silica having an oil absorption of 200 ml / 100 g or more and calcium carbonate in which the proportion of particles having a particle size of 2 μm or less is 95% or more. Synthetic amorphous silica mainly improves ink absorbency, but if the proportion of synthetic amorphous silica increases too much, the binder is adsorbed on the silica, and the effective amount of the binder decreases, resulting in a coating layer strength. Decreases. Therefore, adsorption of the binder to silica is suppressed by using calcium carbonate as a pigment.

  When the amount of oil absorption of the synthetic amorphous silica is less than 200 ml / 100 g, the ink absorbability becomes insufficient, and particularly an image color mixture portion having a large amount of ink adhesion is markedly defective. Therefore, the oil absorption amount is specified in the above range. Preferably, the oil absorption is 300 ml / 100 g or more. The particle size of the synthetic amorphous silica is not particularly limited, but the preferable particle size is 5 μm or less.

When calcium carbonate having a particle size of less than 95% is used, the number of particles having a large particle size in the under layer increases and the concealability of the layer increases, so the printed image becomes whitish. The following disadvantage arises.
Moreover, it is preferable that the average particle diameter of a calcium carbonate is 0.5-0.7 micrometer. When the average particle diameter of calcium carbonate is larger than 0.7 μm, the surface area of calcium carbonate becomes small, and the ink absorbability of calcium carbonate itself tends to be lowered. If the blending ratio of the synthetic amorphous silica in the pigment is increased in order to ensure ink absorbability, the coating layer strength is reduced, so that it is necessary to increase the blending amount of the binder. It tends to be difficult to reduce dividends (reduction of blending amount). On the other hand, when the average particle size of calcium carbonate is larger than 0.7 μm, the concealing property of the layer is increased, so that the defect that the image becomes whitish is likely to occur.
On the other hand, when the average particle size of calcium carbonate is smaller than 0.5 μm, the transparency is improved and the printing density is improved, but the coating layer strength is lowered, and it is necessary to increase the amount of the binder accordingly. It becomes difficult to reduce the amount of binder.
This is because the smaller the particle size of calcium carbonate, the greater the required surface area of the pigment and the greater the required amount of binder.

  In the present invention, the average particle size and particle size distribution (ratio of particles having a particle size of 2 μm or less) of the pigment can be measured with a laser particle size measuring device.

  The ratio represented by (mass of the synthetic amorphous silica) / (mass of the calcium carbonate) needs to be 50/50 to 80/20. When the ratio is less than 50/50, the blending ratio of the synthetic amorphous silica is reduced, and the ink absorbability is extremely inferior. On the other hand, when the ratio exceeds 80/20, the blending ratio of calcium carbonate decreases, and the effect of reducing the blending amount of the binder by calcium carbonate is lost. Preferably, the ratio is 50/50 to 70 /.

(Binder)
The binder used for the under layer is starch or a derivative thereof (hereinafter, these are collectively referred to as “starches”) in order to ensure ink absorbability and coating layer strength. On the other hand, it is contained in an amount of 20% by mass or more, and polyvinyl alcohol is an essential component. When the content ratio of starches in the binder is less than 20% by mass, the ink absorptivity is lowered, the under layer strength is lowered, and the generation of paper dust becomes conspicuous. In addition, the content rate of the starches in a binder shall be 80 mass% or less.
Examples of starch or derivatives thereof include natural starch or its derivatives, hydroxyalkylated starch, oxidized starch and the like. In particular, from the viewpoint of improving ink absorbability, it is preferable to use oxidized starch or hydroxyalkylated starch, and hydroxyethylated starch is most preferable.
Here, oxidized starch is obtained by treating natural starch such as corn starch with an oxidizing agent, and sodium hypochlorite or the like is used as the oxidizing agent. Hydroxyalkylated starch is a product obtained by introducing hydroxyethyl group, hydroxypropyl group, etc. into natural starch, and hydroxyethylated starch (hereinafter referred to as “HES” as appropriate) in terms of excellent ink absorbability. It is preferable to use it.

Hydroxyethylated starch is considered to be highly effective in reducing paper dust because it is firmly fixed to pulp fibers and pigments due to the interaction of hydroxylethyl groups through hydrogen bonding. Although the reason is not clear, the ink absorbability is improved when hydroxyethylated starch is used.
If the weight average molecular weight of the hydroxyethylated starch is large, the viscosity of the coating liquid may increase and coating unevenness may occur. Therefore, HES having a weight average molecular weight of about 300,000 to 700,000 is preferable.

  The under layer is required to have ink absorbability, transparency, and layer strength. In order to satisfy these requirements, a polyvinyl alcohol that is a hydrophilic binder and excellent in transparency and binding power is used in combination. For the under layer, vinyl acetate, casein, gelatin, soy protein, carboxymethyl cellulose, SB latex, NB latex, acrylic latex, ethylene, as long as the ink absorbability and transparency of the coating layer are not impaired as required. One or more kinds of vinyl acetate latex, polyurethane, unsaturated polyester resin and the like can be mixed and used.

  The total blending amount of the binder is preferably 2 to 50 parts by mass, more preferably 5 to 30 parts by mass with respect to 100 parts by mass of the pigment. When the amount of the binder exceeds 50 parts by mass, the ink absorbability tends to be insufficient. On the other hand, if the blending amount of the binder is less than 2 parts by mass, the layer strength tends to decrease. Therefore, the blending amount of the binding agent is an optimal amount within a range that can ensure the surface strength necessary for the under layer. It is preferable to adjust.

(Other ingredients)
In the present invention, a known pigment that can be contained in the ink receiving layer described later and a known binder can be used in combination in the under layer as long as the effects of the present invention are not impaired. Other additives include sizing agents, ink fixing agents, pigment dispersants, viscosity modifiers, fluidity improvers, antifoaming agents, antifoaming agents, mold release agents, penetrating agents, colored dyes, colored pigments, fluorescent enhancers. A whitening agent, an ultraviolet absorber, an antioxidant, an antiseptic, an antibacterial agent, a water-proofing agent, and the like can be appropriately blended.

  In particular, in order to improve water resistance, it is preferable to add a (cationic) ink fixing agent to the under layer. As the ink fixing agent, a cationic polymer compound is preferably used. However, when the ink fixing agent is added to the coating liquid, the viscosity increases, and the coating suitability may decrease. For this reason, it is preferable to use a polyamide epichlorohydrin polymer because the coating suitability is improved. Further, when the molecular weight of the ink fixing agent increases, the coating suitability tends to decrease. For this reason, it is preferable to use an ink fixing agent having a weight average molecular weight of 20000 or less.

(Under layer coating)
The under layer can be formed, for example, by applying a coating liquid (such as an aqueous coating liquid) containing each of the above components on a support. In this case, it is preferable to use a pigment dispersion obtained by mixing the synthetic amorphous silica and calcium carbonate in the presence of a cationic dispersant, and a coating liquid obtained by mixing the binder. For dispersion of the synthetic amorphous silica or calcium carbonate in the coating solution, it is not necessary to use a dispersant. However, if a cationic dispersant is present in the coating solution, the cationic ink fixing agent is used as the coating solution. Since the fall of the compatibility which arises at the time of adding can be avoided, it is preferable.
As the under layer coating method, known coating apparatuses such as various blade coaters, air knife coaters, roll coaters, curtain coaters, kiss coaters, bar coaters, gate roll coaters, and gravure coaters can be used.

(Under layer coating amount)
The coating amount of the under layer can be changed according to the purpose, but if the coating amount is large, the drying time becomes longer, and the binding agent in the coating solution penetrates into the support, and effective binding is achieved. Since the amount of the adhesive is reduced, the under layer strength tends to be lowered. Further, the productivity decreases as the coating amount of the under layer increases. For this reason, it is preferable that the coating amount of the under layer is 20 g / m ² or less as long as the amount of paper dust at the time of cutting does not increase and the productivity is impaired. However, since the ink absorption capacity becomes insufficient if the coating amount of the under layer is too small, the coating amount of the under layer is preferably 4 g / m ² or more.

<Ink receiving layer>
The ink receiving layer contains a pigment and a binder, and one or more layers are provided on the surface of the under layer.
Examples of the pigment for the ink receiving layer include synthetic amorphous silica, colloidal silica, alumina, calcium carbonate, magnesium carbonate, aluminum hydroxide, kaolin, calcined kaolin, talc, titanium dioxide, zinc oxide, and various plastic pigments. Various pigments can be mentioned, and one or a plurality of these can be selected and used. Among these, porous pigments such as synthetic amorphous silica and alumina form a porous layer with excellent ink absorbency compared to other pigments, become relatively transparent in the coating layer, and are suitable for ink jet recording. Since the ink coloring property of the ink is improved, it is preferably used.

  As the binder constituting the ink receiving layer, starches such as oxidized starch and esterified starch, cellulose derivatives such as carboxymethylcellulose and hydroxyethylcellulose, proteins such as gelatin, casein and soybean protein, polyvinyl alcohol, polyvinylpyrrolidone, Examples of known binders include acrylic resin, styrene-acrylic resin, vinyl acetate resin, vinyl chloride resin, urea resin, urethane resin, alkyd resin, polyester resin, polycarbonate resin, styrene-butadiene latex, and derivatives thereof. It is done. One or more of these binders can be selected and used, but from the viewpoint of improving the coating layer strength and transparency, the binder preferably contains at least polyvinyl alcohol.

  The mixing ratio of the pigment and the binder in the ink receiving layer can be changed according to the properties, formulation and support, and can be set as appropriate within the range where the required quality such as ink absorbability is not impaired.

  In the ink receiving layer, as other additives, ink fixing agents, pigment dispersants, thickeners, fluidity improvers, antifoaming agents, antifoaming agents, lubricants, penetrating agents, colored dyes, colored pigments, fluorescent whitening An agent, an ultraviolet absorber, an antioxidant, an antiseptic, an antibacterial agent, a water-proofing agent and the like can be appropriately blended. Further, when the ink receiving layer is provided by a cast coating method described later, a release agent can be contained in the ink receiving layer for the purpose of improving the peelability from the cast drum. The melting point of the release agent is preferably 90 to 150 ° C, and particularly preferably 95 to 120 ° C. In the above range, since the melting point of the release agent is substantially equal to the metal surface temperature of the mirror finish, the ability as a release agent is maximized. The release agent is not particularly limited as long as it has the above characteristics.

<Cast coat>
In the present invention, it is preferable that the outermost ink-receiving layer is provided by a cast coating method from the viewpoint that an inkjet recording medium having high gloss can be obtained.
In the cast coating method, a coating liquid mainly composed of a pigment and a binder is coated on a base paper to provide a coating layer that serves as an ink receiving layer, and a wet and plastic coating layer is formed on a cast drum ( This is a method of applying a gloss finish to the mirror finished surface). As the cast coating method, (1) a wet casting method (direct method) in which a coating layer is pressed onto a mirror-finished heating drum and dried while the coating layer is in a wet state (direct method), and (2) a wet coating layer is temporarily ( Semi) Rewetting cast method (rewetting method) in which it is swelled and plasticized with a rewetting liquid after drying, and pressed onto a mirror-finished heating drum (drying method). (3) The wet coating layer is made into a gel state by coagulation treatment. And a gelled cast method (coagulation method) in which the product is pressed against a mirror-finished heating drum and dried.

  In the present invention, any of the direct method, the coagulation method, and the rewet method may be used, but the coagulation method is preferable from the viewpoint of obtaining a high gloss, and the rewet method from the viewpoint of improving productivity. Is preferred.

(Coagulation method)
When using the coagulation method, apply the coating liquid for the ink receiving layer on the under layer, and apply a treatment liquid that solidifies (or crosslinks) the binder while the coating layer is wet. Then, the coated layer is pressure-bonded to the heated mirror surface to give gloss. For example, when polyvinyl alcohol is used as the binder, any aqueous solution containing a compound capable of coagulating polyvinyl alcohol can be used for the treatment liquid. A treatment liquid containing borate is preferable. By mixing and using boric acid and borate, it becomes easy to obtain solidification with an appropriate hardness, and a cast-coated paper having a good gloss feeling can be obtained.

(Rewetting method)
When using the rewetting method, the ink receiving layer coating liquid is applied onto the under layer and dried, and then a treatment liquid having an action of plasticizing the binder is applied to the dried coating layer. Thereafter, the coating layer is pressure-bonded to the heated mirror surface to give gloss. In the case of the rewet method, the ink-receiving layer is in a dry state when the treatment liquid is applied, so it is difficult to copy the mirror drum surface, and the surface has a lot of minute irregularities and the glossiness tends to be slightly reduced. Since the coating speed can be increased as compared with other methods, productivity is improved.

  As a method of applying the ink receiving layer coating liquid, a known coating machine such as a blade coater, an air knife coater, a roll coater, a brush coater, a kiss coater, a squeeze coater, a curtain coater, a die coater, a bar coater, or a gravure coater is used. It can be appropriately selected from the methods used. Examples of the method for applying the treatment liquid include, but are not limited to, a roll, a spray, and a curtain method.

(Amount of ink receiving layer)
The coating amount of the ink receiving layer can be arbitrarily adjusted within the range that covers the surface of the under layer and sufficient ink absorbency is obtained, but from the viewpoint of achieving both recording density and ink absorbency, The solid content is preferably 5 to 30 g / m ² . Further preferred coating weight range is ^{5g / m 2 ~20g / m 2} . When the coating amount exceeds 30 g / m ² , the drying load of the coating layer during the cast coating treatment is large and inefficient, and the coating layer tends to be insufficiently dried and the peelability from the mirror drum is reduced. The layer tends to cause problems such as adhesion to the mirror drum.

<Other layers>
In the present invention, if necessary, a back layer for imparting writing property, antistatic property, antifouling property, slipperiness, etc. can be provided on the support opposite to the surface on which the ink receiving layer is provided. is there.

<Example>
EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Further, “parts” and “%” shown in the examples represent parts by mass and% by mass unless otherwise specified.

10 parts of talc, 1.0 part of aluminum sulfate, 0.1 part of synthetic sizing agent and 0.02 part of yield improver are added to a pulp slurry consisting of 100 parts of hardwood bleached kraft pulp (L-BKP) with a beating degree of 285 ml. The support was added and paper was made with a paper machine. Starch was applied to both sides of the paper so that the solid content per side was 1.5 g / m ² to obtain a base paper having a basis weight of 170 g / m ² .
On one side of this base paper, the undercoat coating solution 1 was applied with a blade coater so that the dry coating amount was 8 g / m ^2, and dried by blowing at 140 ° C.
Furthermore, the cast layer (ink receiving layer) coating solution is applied on the surface coated with the under layer coating solution 1 with a roll coater so that the dry coating amount is 15 g / m ^2. Is solidified using the following coagulating liquid while it is in a wet state, and then the coated layer is pressure-bonded to the mirror-finished surface heated through a press roll, and the mirror surface is copied to obtain an inkjet having a basis weight of 193 g / m ² A recording medium was obtained.

(Under layer coating solution 1)
As a pigment, calcium carbonate-silica mixture (FMT-IJ 511: manufactured by Phimatech Co., Ltd., average particle diameter of the mixture is about 6 μm, oil absorption of silica: 300 ml / 100 g, average particle diameter of calcium carbonate is 0.66 μm, and 100 parts of a particle having a particle size of 2 μm or less (95.0%) was blended, 10 parts of completely saponified polyvinyl alcohol (PVA-117, trade name, manufactured by Kuraray Co., Ltd.) as a binder, and oxidized starch (MS #) 3600: Nippon Food Processing Co., Ltd. (15 parts), cationic ink fixing agent (DK-6860: Seiko PMC Co., polyamide epichlorohydrin polymer, weight average molecular weight 7500) 20 parts, cationic sizing agent (SE-) 2250: manufactured by Seiko PMC Co.) was mixed to prepare a coating liquid (color) having a solid concentration of 25%.

(Cast layer coating solution)
As a pigment, 50 parts of high-purity alumina (UA5605: manufactured by Showa Denko KK) and 50 parts of high-purity alumina (AKP-G015: manufactured by Sumitomo Chemical Co., Ltd.) are blended, and a completely saponified polyvinyl alcohol is used as a binder. (PVA105: trade name made by Kuraray Co., Ltd.) 15 parts, and partially saponified PVA (PVA217: trade name made by Kuraray Co., Ltd.) 5 parts, 0.2 parts of antifoaming agent, and solid content concentration A 28% coating solution was prepared.
(Coagulation liquid)
2% borax, 2% boric acid (mass ratio of borax / boric acid = 1/1, calculated in terms of Na ₂ B ₄ O ₇ and H ₃ BO ₃ ), release agent (FL-48C: manufactured by Toho Chemical Industry Co., Ltd.) ) 0.2% was added to adjust the coagulation liquid.

An ink jet recording medium was obtained in the same manner as in Example 1 except that the under layer coating solution 2 was used instead of the under layer coating solution 1.
(Under layer coating solution 2)
A coating solution was prepared in exactly the same manner as in Example 1 except that 15 parts of hydroxyethyl etherified starch (Penford Gum 295: manufactured by Penford) was blended in place of 15 parts of oxidized starch as a binder. did.

An ink jet recording medium was obtained in the same manner as in Example 1 except that the under layer coating solution 3 was used instead of the under layer coating solution 1.
(Under layer coating solution 3)
A coating solution was prepared in exactly the same manner as in Example 1 except that 15 parts of starch (phosphate esterified starch MS # 4400: manufactured by Nippon Shokuhin Kako Co., Ltd.) was blended in place of 15 parts of oxidized starch as a binder. Prepared.

An ink jet recording medium was obtained in exactly the same manner as in Example 1, except that the under layer coating solution 4 was used instead of the under layer coating solution 1.
(Under layer coating solution 4)
As pigments, 80 parts of synthetic amorphous silica (Psyroid ED3: Grace Devison, oil absorption 300 ml / 100 g) and calcium carbonate (Supercoat 95: Pfematec, average particle size 0.67 μm, particle size 2 μm or less) The proportion of the particles is 95.2%) 20 parts, 10 parts of completely saponified polyvinyl alcohol (PVA-117: manufactured by Kuraray Co., Ltd.) and oxidized starch (MS # 3600: manufactured by Nippon Food Processing Co., Ltd.) 5 parts of cationic ink fixing agent (Polyfix 700: manufactured by Showa Polymer Co., Ltd., amine compound, weight average molecular weight 800,000), cationic sizing agent (Polymalon 360: manufactured by Arakawa Chemical Industries) 5 Parts were mixed to prepare a coating solution having a solid content concentration of 25%.

An ink jet recording medium was obtained in the same manner as in Example 1 except that the under layer coating solution 5 was used instead of the under layer coating solution 1.
(Under layer coating solution 5)
As pigments, synthetic amorphous silica (Thyroid ED3: manufactured by Grace Devison, oil absorption 300 ml / 100 g) and calcium carbonate (Super Coat 95: manufactured by PMMA Tech, average particle size 0.67 μm, particle size of 2 μm or less) The mixture was dispersed at a mass ratio of 80:20 in the presence of a cationic dispersant (SN Dispersant 7347C, manufactured by San Nopco) to form a slurry. For 100 parts of this pigment dispersion (in terms of solid content), 10 parts of completely saponified polyvinyl alcohol (PVA-117: manufactured by Kuraray Co., Ltd.) and oxidized starch (MS # 3600: manufactured by Nippon Food Processing Co., Ltd.) 15 5 parts of a cationic ink fixing agent (Polyfix 700: manufactured by Showa Polymer Co., Ltd.) and 5 parts of a cationic sizing agent (Polymalon 360: manufactured by Arakawa Chemical Industries, Ltd.) are mixed, and the solid content concentration is 25%. The coating liquid was adjusted.

An ink jet recording medium was obtained in the same manner as in Example 1 except that the under layer coating solution 6 was used instead of the under layer coating solution 1.
(Under layer coating solution 6)
When dispersing the synthetic amorphous silica and the calcium carbonate in the presence of a cationic dispersant, the coating was carried out in the same manner as in Example 5 except that the dispersion ratio was 50:50 instead of 80:20. A working solution was prepared.

<Comparative Example 1>
An ink jet recording medium was obtained in the same manner as in Example 1 except that the under layer coating solution 7 was used instead of the under layer coating solution 1.
(Under layer coating solution 7)
As a pigment, 100 parts of the above calcium carbonate-silica mixture (FMT-IJ 511: manufactured by Pfematech Co., Ltd., average particle diameter of about 6 μm) is blended, and as a binder, completely saponified polyvinyl alcohol (PVA-117, Kuraray). 5 parts ethylene vinyl acetate copolymer (Polysol AM-3150: Showa Polymer Co., Ltd., abbreviated as “EVA”) 29 parts, and oxidized starch (MS # 3600: manufactured by Nippon Food Processing Co., Ltd.) ) 5 parts, 5 parts of a cationic ink fixing agent (Polyfix 700: manufactured by Showa Polymer Co., Ltd.) and 5 parts of a cationic sizing agent (Polymalon 360: manufactured by Arakawa Chemical Industries, Ltd.) are mixed to obtain a solid concentration of 25 % Coating solution was prepared.

<Comparative Example 2>
An ink jet recording medium was obtained in the same manner as in Example 1 except that the under layer coating solution 8 was used instead of the under layer coating solution 1.
(Under layer coating solution 8)
As a pigment, 100 parts of the above calcium carbonate-silica mixture (FMT-IJ 511: manufactured by Pfematech Co., Ltd., average particle diameter of about 6 μm) is blended, and as a binder, completely saponified polyvinyl alcohol (PVA-117, Kuraray). 5 parts of cationic ink fixing agent (Polyfix 700: manufactured by Showa Polymer Co., Ltd.) and 5 parts of cationic sizing agent (Polymalon 360: manufactured by Arakawa Chemical Industries, Ltd.) By mixing, a coating solution having a solid content concentration of 25% was prepared.

<Comparative Example 3>
An ink jet recording medium was obtained in the same manner as in Example 1 except that the under layer coating solution 9 was used instead of the under layer coating solution 1.
(Under layer coating solution 9)
As a binder, instead of 25 parts of the above fully saponified polyvinyl alcohol, 10 parts of completely saponified polyvinyl alcohol (PVA-117, trade name of Kuraray Co., Ltd.) and 5 parts of carboxymethyl cellulose (Sunrose Nippon Paper Chemicals Co., Ltd.) Manufactured, and abbreviated as “CMC”), and a coating solution was prepared in exactly the same manner as Comparative Example 2.

<Comparative Example 4>
An ink jet recording medium was obtained in the same manner as in Example 1 except that the under layer coating solution 10 was used instead of the under layer coating solution 1.
(Under layer coating solution 10)
As a pigment, 100 parts of precipitated silica (Fine Seal X-37B: Tokuyama Co., Ltd., secondary particle size: 3.5 to 3.9 μm) is blended, and as a binder, completely saponified polyvinyl alcohol (PVA). -117, 10 parts of Kuraray Co., Ltd. trade name) and 15 parts of oxidized starch (MS # 3600: manufactured by Nippon Food Processing Co., Ltd.), and a cationic ink fixing agent (Polyfix 700: manufactured by Showa Polymer Co., Ltd.) 5 parts and 5 parts of a cationic sizing agent (Polymaron 360: manufactured by Arakawa Chemical Industries) were mixed to prepare a coating solution having a solid concentration of 25%.

The physical properties of the under layer coating solution used in each Example and Comparative Example, the ink absorbability of ink jet recording paper, and the evaluation of paper dust (guillotine cutting processability) were performed by the following methods.
(1) Coating liquid physical properties The B-type viscosity of each underlayer coating liquid was measured. Moreover, the fluidity | liquidity of the coating liquid was confirmed visually, and it ranked as follows. If evaluation is (circle) and (triangle | delta), there is no problem practically.
○: Viscosity is less than 2000 mP · s, fluidity is good Δ: Viscosity is 2000 to 4000 mP · s, fluidity is poor ×: Viscosity is 4000 mP · s or more, almost no fluidity

(2) Ink absorbability Ink-jet recording of a predetermined pattern using an ink-jet printer using dye ink (PM-950C: product name manufactured by Epson Corporation), and bleeding is visually observed at the boundary between the red and green mixed color solid parts. Ink absorption (bleeding) was evaluated according to the following criteria. If the evaluation is ○, there is no practical problem.
○: The color boundary part is clearly separated △: The color boundary part has a slight blur ×: The color boundary part has a very large blur

(3) Paper dust 250 sheets of the obtained inkjet recording paper (A4 size) are stacked so that the glossy surfaces (cast layer surface) do not overlap each other, and the surface is opposite to the surface provided with the cast layer with a guillotine cutter. The paper was cut and evaluated by visually observing the amount of paper dust. If the evaluation is ○, there is no practical problem.
○: No paper dust △: Some paper dust ×: Many paper dust

As is clear from Table 1, in the case of each example, high evaluation was obtained in all of the coating liquid physical properties, ink absorbability, and paper dust (workability).
In particular, in Examples 1 to 3 using an ink fixing agent having a weight average molecular weight of 20000 or less, the water resistance was excellent, the physical properties of the coating liquid were very good, and the productivity was improved.

On the other hand, in the case of Comparative Example 1 in which the starch content in the binder for the under layer was less than 20% by mass, the ink absorbability deteriorated.
In the case of Comparative Example 2 using only polyvinyl alcohol and containing no starch as a binder in the under layer, the ink absorption and processing suitability were inferior although the coating liquid properties were good.
In the case of Comparative Example 3 which did not contain starch as a binder in the under layer and used both PVA and CMC, the physical properties of the paint and the ink absorbability were inferior.
In the case of Comparative Example 4 where calcium carbonate was not used as the pigment in the under layer, the coating liquid properties and ink absorbability were good, but the processability was poor.

Claims (3)

An ink jet recording medium comprising at least one under layer containing a pigment and a binder on at least one side of a support, and one or more ink-receiving layers on the surface of the under layer, The pigment contains calcium carbonate in which the ratio of particles having a particle size of 2 μm or less is 95% or more and synthetic amorphous silica having an oil absorption of 200 ml / 100 g or more, (mass of the synthetic amorphous silica) / (carbonic acid) The ratio expressed by the mass of calcium) is 50/50 to 80/20, and the binder of the under layer contains starch or a derivative thereof and polyvinyl alcohol, and the starch in the binder or its An ink jet recording medium having a derivative content of 20% by mass or more.   The under layer is a coating liquid obtained by mixing the pigment dispersion obtained by dispersing the synthetic amorphous silica and the calcium carbonate in the presence of a cationic dispersant, the binder, and the cationic ink fixing agent. The ink jet recording medium according to claim 1, wherein the ink jet recording medium is formed by coating.   The inkjet recording medium according to claim 1, wherein an outermost layer of the ink receiving layer is provided by a cast coating method.