JP4177829B2 - Inkjet recording medium - Google Patents

Description

  The present invention relates to an ink jet recording medium, and more particularly to an ink jet recording medium suitable for printing with dyes and pigment inks and capable of obtaining glossiness similar to a silver salt photograph.

  In general, the ink jet recording method uses a variety of mechanisms to eject ink droplets and deposit them on the recording paper to form dots and perform recording. However, compared with the dot impact type recording method, noise is generated. In addition, there is an advantage that full color is easy and high-speed printing is possible. 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.

  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 of the recording medium have been diversified, and in particular, there has been a growing demand for a recording medium having glossiness similar to that of a silver salt photograph.

  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 Documents 1 and 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 the coating layer in a plastic state after being wetted is cast drum. This is a method of pressing against the mirror-finished surface and gloss finishing. This method includes (1) a wet casting method (direct method) in which a coating layer is pressed against a heated drum that has been mirror-finished while the coating layer is wet (direct method), and (2) a wet coating layer is temporarily (half) Re-wet cast method (re-wetting method), which is swelled and plasticized with a re-wetting liquid after drying and then pressed against a mirror-finished heating drum and dried (3). Generally, it can be divided into three types, that is, a gelling cast method (coagulation method) in which a heated drum is pressed and dried.

  On the other hand, colloidal silica is also added to the cast layer in order to impart high gloss. A typical colloidal silica is one in which spherical silica particles of 5 to 50 nm are dispersed in water in a stable colloidal state without secondary aggregation. Since these spherical silica particles are extremely fine particles, a very transparent and highly glossy coating film can be obtained when dried (see Patent Documents 3 and 4).

  However, most of colloidal silica is a spherical particle, and each primary particle is monodispersed without agglomeration. Therefore, in a dry state, the particles are closely packed and have a structure with very few voids between the particles. . Accordingly, the pore volume of colloidal silica is generally less than 0.4 ml / g, and when blended in a cast layer, the ink absorption rate becomes slow, causing ink overflow called bleeding and uneven density. There were drawbacks.

  In addition, synthetic silica fine particles (gas phase method silica) produced by a gas phase method are blended in the ink absorption layer (see Patent Documents 5 and 6). Vapor phase silica is an ultrafine particle having an average primary particle size of several nanometers to several tens of nanometers, and is characterized by high gloss. Vapor phase method silica is produced by a method in which a volatile silicon compound is decomposed at a high temperature in a flame, and is silica agglomerated particles having excellent dispersibility and transparency (see, for example, Patent Document 7). Vapor phase method silica is a bulky powder, and it is easy to mechanically form an aqueous dispersion as compared with wet method silica. When this aqueous dispersion is applied, a coating film having relatively high gloss and good ink absorbability can be formed. However, when using vapor-phase process silica, the bond between the aggregated primary particles is relatively weak, so when creating a coating film, the aggregated state is caused by the strong capillary force that occurs between the voids caused by the drying of water. There is a major drawback that cracks of several millimeters that are easily visible to the naked eye easily enter the cast layer.

JP-A-62-95285 JP-A-5-59694 JP-A-5-338348 Japanese Patent Laid-Open No. 10-217599 Japanese Patent Laid-Open No. 10-81064 Japanese Patent Laid-Open No. 11-34481 Japanese Examined Patent Publication No. 59-169922

  The production methods of Patent Documents 1 and 2 both form an ink-receiving layer composed of a pigment mainly composed of synthetic silica and a binder using the above-mentioned cast coating method, and produce a high gloss cast coated paper. However, since the printing density was low and the glossiness of the outermost layer was low, the glossiness equivalent to that of a silver salt photograph could not be obtained. The reason for this is that, in the case of the above-described technique, since the pigment particle size is large, paper with high glossiness cannot be obtained, and because the transparency of the pigment is low, high print density cannot be obtained.

  Moreover, when the colloidal silica and gas phase method silica with a small particle diameter of a pigment are used to improve glossiness as in the techniques described in Patent Documents 3 to 5, only the above-described problems occur. However, when printing is performed using pigment ink containing colorant particles having a particle diameter of 50 nm to 150 nm in the ink, sinking of the ink particles into the coating layer (ink receiving layer) increases, and the print density is reduced. A high ink jet recording medium cannot be obtained.

  On the other hand, there is a technique for containing polyvinyl alcohol in the ink receiving layer. Such an ink jet recording paper is preferable because it is excellent in terms of color developability and gloss. However, when it is cut into a small size with a guillotine or a cutter, the cut surface is easily roughened and fluffed, and a lot of paper dust is generated. It was easy to do, and there was a fault that cutting processing aptitude was inferior.

  Therefore, the present invention has a glossiness as high as that of a silver salt photograph, has high print density and ink absorbency even when ink-jet recording is performed using not only dye ink but also pigment ink, and generation of paper dust during cutting. An object of the present invention is to provide a small number of inkjet recording media.

As a result of studies to solve the above problems, the inventors have found that the above problems can be solved by defining the pigment and binder in the under layer.
Therefore, the object of the present invention is an ink jet recording medium in which an under layer and an ink receiving layer each containing a pigment and a binder are provided in this order on a support , and the ink receiving layer is the outermost surface . The under layer mainly contains synthetic silica as a pigment, 20% by mass or more of the synthetic silica is synthetic silica having a secondary particle diameter of 5 to 15 μm, and the under layer is a water-soluble polymer as a binder. And an ethylene / vinyl acetate copolymer, and the 75 ° specular glossiness of the ink receiving layer surface is 50% or more, (the coating amount of the under layer) / (the coating amount of the ink receiving layer) The ink receiving layer contains colloidal silica and gas phase method silica as pigments in a ratio of (colloidal silica) / (gas phase method silica) = 60/40 to 80/20, Above Ink receiving layer, characterized in that while the surface of the coating layer formed by applying an ink receiving layer coating liquid in a wet state, provided in pressure contact and drying the metal mirror surface heated to coating coating layer And achieved by the inkjet recording medium.
Since the ink receiving layer is provided by pressing and drying the heated metal mirror surface while the surface of the coating layer formed by applying the ink receiving layer coating liquid is in a wet state, Greatly reduces paper dust.

It is preferable that the water-soluble polymer is polyvinyl alcohol because color developability is excellent.
When the glass transition point of the ethylene / vinyl acetate copolymer is 0 ° C. or less, and the ethylene / vinyl acetate copolymer is a dried product of an ethylene / vinyl acetate copolymer resin emulsion having a particle diameter of 1 μm or less, cutting is performed. This is preferable because paper dust at the time is reduced and color developability is improved.
The coating amount of the under layer is 10 to 20 g / m ² , the coating amount of the ink receiving layer is 3 to 15 g / m ² , and (the coating amount of the under layer) / (the coating of the ink receiving layer). It is preferable that the ratio represented by (work rate) is more than 1 and 4 or less because paper dust is further reduced.

The primary particle diameter of the colloidal silica is 10 to 50 nm, the ratio of the secondary particle diameter to the primary particle diameter of the colloidal silica is 1.5 to 3.0, and the specific surface area of the vapor phase silica is 130 to 300 m ² / g is preferred because of excellent color developability when printed with dye ink and pigment ink.

It is preferable that the image clarity on the surface of the ink receiving layer is 20% or more because the effect of reducing paper dust is particularly large .

  According to the present invention, an ink jet recording medium having glossiness as high as that of a silver salt photograph and excellent in print density and ink absorbency even when ink jet recording is performed not only with dye ink but also with pigment ink. Can do. Furthermore, according to the present invention, the generation of paper dust at the time of cutting is suppressed, and the processing suitability is improved.

Hereinafter, embodiments 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 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 admixture at any ratio. 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)
The under layer includes a pigment and a binder containing a water-soluble polymer and an ethylene / vinyl acetate copolymer.

1. Binder Water-soluble polymer is used to ensure the coating liquid properties of the underlayer coating liquid. If the water-soluble polymer is not included in the binder, the coating liquid physical properties Will not be reasonable. Although there is no restriction | limiting in particular as water-soluble polymer used for a binder, When the polyvinyl alcohol (henceforth "PVA" suitably) which is a highly transparent binder is used, the color density of a printing part will improve. Therefore, it is preferable. In particular, fully saponified polyvinyl alcohol is more preferable. The polymerization degree of polyvinyl alcohol is preferably 500 to 2400, more preferably 1000 to 2000.
When an ethylene / vinyl acetate copolymer (hereinafter appropriately referred to as “EVA”) is used as a binder, the coating layer strength is increased and paper dust at the time of cutting is reduced. Further, since the contact angle of the ethylene / vinyl acetate copolymer itself with water is smaller than that of other synthetic resins (for example, styrene butadiene copolymer (SBR)), the ink absorbency of the under layer is improved. In particular, when the following polyvinyl alcohol / ethylene / vinyl acetate graft copolymer is used, these effects increase.

  The ethylene / vinyl acetate copolymer is, for example, a dry emulsion obtained by copolymerizing ethylene and vinyl acetate in an aqueous system in which polyvinyl alcohol is present as an emulsifier. The polymerization initiator mainly acts on ethylene and vinyl acetate, but depending on the reaction conditions and the amount of polyvinyl alcohol as an emulsifier, the ethylene / vinyl acetate copolymer is branched from the polyvinyl alcohol chain, and grows polyvinyl alcohol / ethylene. -An emulsion of vinyl acetate graft copolymer may be formed. As the ethylene / vinyl acetate copolymer used in the present invention, it is preferable to use an emulsion in which a number of molecules obtained by grafting an ethylene / vinyl acetate copolymer onto polyvinyl alcohol is increased. In addition, an under layer is formed by apply | coating the coating liquid containing an above-described emulsion, the pigment mentioned later, etc., and drying.

The glass transition point (Tg) of the ethylene / vinyl acetate copolymer is preferably 0 ° C. or less, and the particle diameter of the emulsion is preferably 1 μm or less. When Tg is 0 ° C. or lower, the cutting edge at the time of cutting the cutter is improved, the falling off of the coating layer (under layer and ink receiving layer) is reduced, and the generation of paper dust tends to be further reduced. This is presumably because the flexibility of the coating layer (under layer and ink receiving layer) is increased. On the other hand, when the particle size is 1 μm or less, the transparency of the under layer increases, and the printing color density tends to improve (particularly in the case of dye ink). The effect of improving the cut at the time of cutting described above is particularly great when an ink receiving layer is provided by a casting method described later.
On the other hand, when Tg exceeds 0 ° C., the flexibility of the coating layer is lowered, so that the amount of paper dust generated during cutting tends to increase. On the other hand, when the particle diameter exceeds 1 μm, the transparency is lowered and the transparency of the obtained coating layer is also lowered, so that the printing color density tends to be lowered.

The blending amount of the ethylene / vinyl acetate copolymer in the binder for the under layer is not particularly limited, but is preferably 10 to 50 parts by mass, more preferably 20 to 40 parts by mass with respect to 100 parts by mass of the pigment. When the blending amount of the ethylene / vinyl acetate copolymer exceeds 50 parts by mass, the hydrophobicity of the binder becomes remarkable and the ink absorbability tends to decrease.
Further, the blending amount of the water-soluble polymer (for example, PVA) in the binder for the under layer is not particularly limited, but 100 parts by mass of the pigment from the viewpoint of having coating layer strength, ink absorbability, coating suitability, and the like. The amount is preferably 2 to 50 parts by mass, and more preferably 3 to 25 parts by mass.

2. Pigment The pigment used for the under layer mainly contains synthetic silica, and 20% by mass or more of the synthetic silica is synthetic silica having a secondary particle diameter of 5 to 15 μm. Thereby, the coating layer intensity | strength of an under layer improves and it can reduce paper dust generation | occurrence | production at the time of cutting. In particular, it is preferable to use a synthetic silica produced by a gel method since the coating layer strength is improved, and a synthetic silica produced by a precipitation method is used because the color developability is improved.
When the secondary particle diameter is less than 5 μm, the coating layer strength decreases, and a large amount of paper dust is generated during cutting. In order to improve the coating layer strength, the secondary particle diameter of the synthetic silica is preferably larger, and more preferably 7 μm or more. However, if it exceeds 15 μm, the voids of the layer will increase, and on the under layer The ink receiving layer to be provided is not uniformly formed. On the other hand, if it exceeds 15 μm, the coating property of the underlayer coating solution is lowered, and the productivity is lowered, which is not preferable. The secondary particle diameter of synthetic silica can be measured by a laser diffraction / scattering method.

Further, when the ratio of the synthetic silica having a secondary particle diameter of 5 to 15 μm is less than 20 mass% in the whole synthetic silica, the ink absorption of the under layer is good, but the coating layer strength is lowered. The blending amount of the synthetic silica having the secondary particle size is preferably large, preferably 30% by mass or more, more preferably 60% by mass or more of the total synthetic silica in the pigment for the under layer. All of the synthetic silica may be synthetic silica having the secondary particle size.
The proportion of synthetic silica in the entire pigment is preferably 90% by mass or more.

3. Other Components In addition to the above-described components, a known pigment that can be contained in the ink receiving layer described later and a known binder can be used in combination with the under layer, as long as the effects of the present invention are not impaired. Other additives include dye fixing agents, pigment dispersants, thickeners, fluidity improvers, antifoaming agents, antifoaming agents, mold release agents, foaming agents, penetrating agents, colored dyes, colored pigments, fluorescent enhancers. Whitening agents, ultraviolet absorbers, antioxidants, preservatives, antibacterial agents, water resistance agents, wet paper strength enhancers, dry paper strength enhancers, and the like can be appropriately blended in the under layer.

(Ink receiving layer)
The ink receiving layer in the present invention contains a pigment and a binder as main components. The pigment preferably contains colloidal silica and gas phase method silica shown below.
(Colloidal silica)
As the colloidal silica, those having a primary particle diameter of 10 to 50 nm and a ratio of the secondary particle diameter to the primary particle diameter of 1.5 to 3.0 are preferably used. This colloidal silica has a shape in which two to three spherical primary particles are bonded when the dispersion state is observed with a microscope, and this is appropriately referred to as “peanut shape”. When so-called spherical colloidal silica, in which spherical primary particles are monodispersed, is used in the ink receiving layer, the ink absorption may be inferior, but colloidal silica aggregated in a peanut shape is glossy, ink color development, ink absorption Both sex can be satisfied.

  When the average primary particle diameter of the colloidal silica is smaller than 10 nm, the transparency of the ink receiving layer is increased, but voids between particles present in the ink receiving layer are impaired, and the ink absorbability tends to be lowered. On the other hand, when the average primary particle diameter of colloidal silica is larger than 50 nm, the voids between the particles are good, but the opacity increases, so that the color developability during ink jet recording tends to be lowered.

Further, when the ratio expressed by (secondary particle diameter) / (primary particle diameter) is smaller than 1.5, the transparency is good, but the ink absorbability is inferior due to insufficient gaps between the particles. There is a tendency. On the other hand, when the ratio exceeds 3.0, the ink absorbability is good, but the opacity increases, so that the color developability during ink jet recording tends to decrease. The ratio is more preferably 1.8 to 2.8. Further, the average value of the number of primary particles bonded (aggregated) in the secondary particles is a value substantially corresponding to the above ratio.
The primary particle size (measured by the BET method) and the secondary particle size (measured by the dynamic light scattering method) can be controlled by the production conditions of the colloidal silica. As such colloidal silica, a trade name Quatron manufactured by Fuso Chemical Industry Co., Ltd. can be raised.

  In this embodiment, when the dispersion state of the colloidal silica is observed with a microscope, it is not necessary that no colloidal silica other than the peanut-like colloidal silica is observed, and the ratio of the secondary particle diameter to the primary particle diameter is measured. If the value (macro physical properties) does not exceed 3.0, other colloidal silica or a single primary particle may be included.

(Gas phase method silica)
As the vapor phase silica, those having a specific surface area of 130 to 300 m ² / g are preferably used. Vapor phase silica is also called dry silica or fumed silica, and can generally be produced by flame hydrolysis. Specifically, it is manufactured by gas-phase hydrolysis of volatile silane compounds such as silicon tetrachloride in an oxyhydrogen flame. Conditions such as the temperature of the flame, the supply ratio of oxygen and hydrogen, the supply amount of silicon tetrachloride as a raw material, etc. By changing, vapor phase silica can be obtained. Instead of silicon tetrachloride, silanes such as methyltrichlorosilane and trichlorosilane can be used alone, or silicon tetrachloride and these silanes can be used in a mixed state. Vapor phase silica is commercially available from Aerosil Co., Ltd. as Aerosil, and from Tokuyama Co., Ltd. as the Leolosil QS type. The average primary particle size of the vapor phase method silica is preferably 5 to 50 nm.

If the specific surface area of the fumed silica (BET method) is 130m ² / g~300m ² / g, the higher the transparency of the ink receiving layer, and has good stability when formulated into coating liquid This is preferable. When the specific surface area is smaller than 130 m ² / g, the opacity of the ink receiving layer increases, and there is a tendency to cause problems such as a decrease in printing density when printing with an inkjet printer. On the other hand, if the specific surface area exceeds 300 m ² / g, the transparency of the ink receiving layer is good and the printing density is high, but the stability of the coating liquid tends to be poor, which causes a problem in coating properties. There is a tendency.

  The compounding ratio of the colloidal silica and the gas phase method silica in the ink receiving layer is preferably 45/55 to 95/5, expressed as (colloidal silica) / (gas phase method silica). The ratio is more preferably 60/40 to 80/20. When the proportion of colloidal silica increases and the blending ratio increases, the transparency of the coating layer is high and the printing density is high, but the ink absorbability tends to decrease. On the other hand, when the proportion of colloidal silica is small and the blending ratio is small, the ink absorptivity is good but the glossiness tends to decrease.

  In addition, one or more known pigments can be mixed in the ink receiving layer as long as the effects of the present invention are not impaired. For example, synthetic amorphous silica, colloidal silica, alumina, colloidal alumina, pseudoboehmite, aluminum hydroxide, light calcium carbonate, heavy calcium carbonate, magnesium carbonate, kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide White inorganic pigments such as zinc sulfide, zinc carbonate, satin white, aluminum silicate, diatomaceous earth, calcium silicate, magnesium silicate, lithopone, zeolite, hydrous halloysite, and magnesium hydroxide; styrene plastic pigment, acrylic plastic pigment, polyethylene Organic pigments such as microcapsules, urea resins, and melamine resins can be used alone or in combination.

(Binder)
The ink receiving layer of the present invention contains at least one binder. The binder is particularly preferably an aqueous binder. The aqueous binder referred to in the present invention means a water-soluble resin and a water-dispersible resin. Specific examples of the binder include polyvinyl alcohol and derivatives thereof; polyvinyl pyrrolidone; urethane resin derived from urethane resin emulsion; starches such as oxidized starch and esterified starch; cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose; casein; Gelatin; soy protein; styrene-acrylic resin and derivatives thereof; styrene-butadiene resin latex, acrylic resin emulsion, vinyl acetate resin emulsion, vinyl chloride resin emulsion, urea resin emulsion, alkyd resin emulsion, and derivatives thereof; These binders can be used alone or in combination.

  In the present invention, partially saponified and / or completely saponified polyvinyl alcohol (including derivatives thereof) is contained in the ink receiving layer as a binder from the viewpoint of good balance between ink absorbability, color developability and glossiness. It is preferable. In this case, it is possible to further blend other binders described above within a range not impairing ink absorbability, color developability and glossiness upon ink jet recording.

  The binder is preferably contained in the ink receiving layer at a rate of 3 to 28% by mass, and more preferably 9 to 25% by mass. When the content of the binder in the ink receiving layer is large, the ink absorbability tends to decrease, and when the content is small, the strength of the ink receiving layer tends to decrease.

  For the ink receiving layer, other additives include dye fixing agents, pigment dispersants, thickeners, fluidity improvers, antifoaming agents, foam inhibitors, mold release agents, foaming agents, penetrants, colored dyes, coloring Pigments, fluorescent brighteners, ultraviolet absorbers, antioxidants, preservatives, antibacterial agents, water resistance agents, wet paper strength enhancers, dry paper strength enhancers, and the like can be appropriately blended. Moreover, when providing an ink receiving layer by the cast coat method mentioned later, a release agent can be contained in an ink receiving layer for the purpose of improving the peelability from a cast drum. The melting point of the release agent to be added is preferably 90 to 150 ° C, and particularly preferably 95 to 120 ° C. In the above temperature range, the melting point of the release agent is almost the same as the metal surface temperature of the mirror finish, so that the ability as a release agent is maximized. The release agent is not particularly limited as long as it has the above characteristics.

(Glossy)
In the ink jet recording medium of the present invention, it is preferable that the 75 ° specular gloss measured from the surface of the ink receiving layer is 50% or more because it becomes a glossy ink jet recording medium like a silver salt photograph. Further, it is preferable that the image clarity of the ink receiving layer surface is 20% or more because glossiness is improved. The 75 ° specular gloss is measured according to JIS-P8142, and the image sharpness is measured according to JIS-K7105.

  In the present invention, the reason why the printing density is improved not only in dye ink but also in ink jet recording using pigment ink is not clear, but particularly in ink jet recording using pigment ink, the secondary layer is used as a secondary layer pigment. Cracks that appear to occur on the surface of the ink receiving layer by using synthetic silica with a particle size of 5 to 15 μm and containing a water-soluble polymer and an ethylene / vinyl acetate copolymer as an under layer binder Can be reduced, and as a result, the print density is considered to be improved.

(Cast coat method)
In the present invention, an ink receiving layer is preferably provided by a so-called cast coating method from the viewpoint that an ink jet recording medium having high gloss can be obtained. The cast coating method is a method in which the surface of the coating layer formed by applying the coating solution for the ink receiving layer to the surface on which the ink receiving layer is applied is wet and the metal is heated while the coating layer is in a plastic state. This is a method of pressing against a mirror surface (cast drum, etc.) to give a glossy finish.

As the cast coating method, any of the direct method, the coagulation method, and the rewet method can be used. However, the coagulation method is reproducible from the viewpoint of improving the productivity because high gloss can be obtained. A wet method is preferred.

  When the ink-receiving layer is provided by the coagulation method cast coating method, the ink-receiving layer coating solution is applied onto the under layer, and the binder in the coating layer is removed while the coating layer is in a wet state. A treatment liquid having a solidifying (or cross-linking) action is applied on the coating layer, and then the coating layer is pressure-bonded to a 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. In particular, a treatment liquid containing boric acid and borate is preferable. By mixing and using boric acid and borate, it is easy to obtain a solidified state with an appropriate hardness, and a cast coated paper for ink jet recording having a good gloss feeling can be obtained.

  When the ink receiving layer is provided by the rewet method cast coating method, the ink receiving layer coating solution is applied and dried on the under layer, and the binder in the coating layer is plasticized on the dried coating layer. Then, a treatment liquid having a function to be converted is applied, and then a coating layer is pressure-bonded to a heated mirror surface to give gloss. In the case of the rewet cast coating 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 there are many minute irregularities on the surface, resulting in slight glossiness. Although it tends to fall, the coating speed can be increased as compared with other methods, so that productivity is improved.

(Formation of under layer and ink receiving layer)
As a method for applying the under layer coating liquid and the ink receiving layer coating liquid on the support, blade coater, air knife coater, roll coater, brush coater, kiss coater, squeeze coater, curtain coater, die coater, bar coater And those appropriately selected from coating methods using a known coating machine such as a gravure coater. Moreover, examples of the method for applying the treatment liquid include a roll, a spray, and a curtain method, but are not particularly limited.

The coating amount of the under layer can be arbitrarily adjusted as long as it covers the surface of the base paper and sufficient ink absorbability is obtained, and is usually about 5 to 30 g / m ^{2 in} terms of solid content per side. be able to. From the viewpoint of achieving both recording density and ink absorbability, a more preferable range of the coating amount of the under layer is 10 to ²⁰ g / m ² .
The coating amount of the ink receiving layer can be arbitrarily adjusted as long as it covers the surface of the under layer and sufficient ink absorbability is obtained, and is usually about 5 to 30 g / m ^{2 in} terms of solid content per side. It can be. From the viewpoint of achieving both recording density and ink absorbability, a more preferable range of the coating amount of the ink receiving layer is 3 to 15 g / m ² . When the coating amount of the ink receiving layer exceeds 30 g / m ² , the peelability of the ink receiving layer from the mirror drum is lowered, and problems such as adhesion of the ink receiving layer to the mirror drum may occur.

(Ratio of coating amount of under layer and ink receiving layer)
Increasing the coating amount of the under layer and the ink receiving layer, which is excellent in ink absorbability, makes it possible to reduce the total coating amount of the under layer and the ink receiving layer (for example, cast layer). When the total coating amount is reduced, it is preferable because paper dust (dropping of the coating layer) is reduced when the inkjet recording medium is cut using a rotary cutter or a guillotine cutter.
For this reason, the coating amount of the under layer is set to 10 to 20 g / m ² , the coating amount of the ink receiving layer is set to 3 to 15 g / m ² , and (the coating amount of the under layer) / (ink receiving layer) When the ratio expressed by (Coating amount) is more than 1 and 4 or less , it is preferable from the viewpoint of reducing paper dust. When the ratio is small, the processability is inferior, and when the ratio is large, the print quality tends to be inferior. In the present invention, by setting the above ratio to more than 1 and 4 or less , it is possible to achieve both printing quality (printing density and ink absorbency) and processing suitability (suppression of paper dust generation during cutting).
Further, as the amount of ink-receiving layer applied is reduced within the above range, the missing (chip) of the coating layer at the end when full-surface printing is performed is reduced. The reason for this is not clear, but it is thought that the strength of the ink receiving layer is improved.

  In the present invention, if necessary, a back coat layer for imparting writing property, antistatic property, antifouling property, slipperiness, etc. is provided on the surface of the support opposite to the surface on which the ink receiving layer is provided. Is also possible.

  In addition, the coating liquid for forming the ink receiving layer, and the treatment liquid for forming the ink receiving layer in the cast coat may include a pigment dispersant, a water retention agent, a thickener, an antifoaming agent, an antiseptic, as necessary. A colorant, a water-resistant agent, a wetting agent, a fluorescent dye, an ultraviolet absorber, a cationic polymer electrolyte, and the like can be appropriately added.

(Example)
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples. Unless otherwise specified, “part” and “%” described below represent “part by mass” and “% by mass”, respectively.

(Manufacture of support)
A pulp slurry consisting of 100 parts of hardwood bleached kraft pulp (L-BKP) with a beating degree of 285 ml, 10 parts of talc, 1.0 part of aluminum sulfate, 0.1 part of a synthetic sizing agent, and 0.02 part of a yield improver. It was added and paper was made with a paper machine. At the time of papermaking, starch was applied on both sides so that the solid content per side was 2.5 g / m ² to obtain a support having a basis weight of 170 g / m ² .
(Under layer)
On one side of this support, coating solution A was applied with a blade coater so that the coating amount was 15 g / m ^2, and air-dried at 140 ° C. to form an under layer.
Coating solution A: As a pigment, 50 parts of precipitated silica (Fine Seal X-12: manufactured by Tokuyama Co., Ltd., secondary particle size: 9-12 μm) and gel silica (Mizukasil P-50: manufactured by Mizusawa Chemical Co., Ltd.) 50 parts of secondary particle size: 10 μm), 5 parts of completely saponified polyvinyl alcohol (PVA-117, manufactured by Kuraray Co., Ltd.) and ethylene / vinyl acetate copolymer emulsion (AM-3150, Tg) as a binder : -4 ° C., emulsion particle size: 750 nm, Showa High Polymer Co., Ltd., 30 parts, blended with 30 parts of cationic ink fixing agent (Polyfix 700, Showa High Polymer Co., Ltd.) 5 parts, And 5 parts of a cationic sizing agent (Polymaron 360, manufactured by Arakawa Chemical Industries, Ltd.) were mixed to prepare a coating solution having a solid content of 25%.
Incidentally, both precipitated silica and gel silica are synthetic silica.

(Ink receiving layer)
On the surface coated with coating liquid A, 10 g / m ^{2 of} coating liquid B is applied with a roll coater, and solidified using coagulating liquid C while the coating layer is in a wet state, and then press roll The coating layer was pressure-bonded to the mirror-finished surface heated through the film, and the mirror surface was copied to form an ink receiving layer, whereby an ink jet recording medium having a basis weight of 185 g / m ² was obtained.
Coating liquid B: Colloidal silica as a pigment (Quarton PL-2: manufactured by Fuso Chemical Industry Co., Ltd., average primary particle size: 23 nm, ratio expressed by (secondary particle size / primary particle size) is 2.2) 70 parts And 30 parts of vapor phase silica (Aerosil 200V: Nippon Aerosil Co., Ltd., specific surface area 200 m ² / g) are blended, and completely saponified polyvinyl alcohol (PVA105: Kuraray Co., Ltd., polymerization degree 500) is used as a binder. Part and partially saponified polyvinyl alcohol (PVA617: manufactured by Kuraray Co., Ltd., polymerization degree 1700) were blended, and 0.2 part of antifoaming agent was further blended to prepare a coating solution having a concentration of 20%.
Coagulating liquid C: Borax 2%, boric acid 2% ((borax / boric acid) mass ratio = 1/1, borax is calculated as Na ₂ B ₄ O ₇ , boric acid is calculated as H ₃ BO ₃₎ ) And 0.2% release agent (FL-48C: manufactured by Toho Chemical Industry Co., Ltd.) to prepare a coagulation liquid.

  As a binder for the coating liquid B for the ink receiving layer, the amount of completely saponified polyvinyl alcohol (PVA105: manufactured by Kuraray Co., Ltd., polymerization degree 500) was changed to 3.3 parts, and partially saponified polyvinyl alcohol ( An ink jet recording medium was obtained in exactly the same manner as in Example 1 except that the blending amount of PVA617 (manufactured by Kuraray Co., Ltd., polymerization degree 1700) was changed to 6.7 parts.

  Example except that the gel method silica (Mizukasil P-50) was not blended as the pigment of the coating liquid A for the under layer, and only 100 parts of the precipitation method silica (Fine Seal X-12) was blended. In the same manner as in Example 1, an ink jet recording medium was obtained.

  As the pigment of the coating liquid A for the under layer, the amount of the gel method silica (Mizukasil P-50) is changed to 25 parts, and the amount of the precipitation method silica (Fine Seal X-12) is changed to 75 parts. An ink jet recording medium was obtained in exactly the same manner as in Example 1 except for the change.

  As the pigment of the coating liquid A for the under layer, the blending amount of the gel method silica (Mizukasil P-50) is changed to 25 parts, and the precipitation method silica (fine seal X-12) is used instead of the precipitation method silica (Fine Seal X-12). An ink jet recording medium was obtained in exactly the same manner as in Example 1 except that 75 parts of Fine Seal X-37B: manufactured by Tokuyama Corporation, secondary particle size: 3.5 to 3.9 μm) were blended.

<Comparative Example 1>
As a pigment for the coating liquid A for the under layer, the gel silica (Mizukasil P-50) and the precipitation silica (Fine Seal X-12) are not blended, but the precipitation silica (Fine Seal X-37B). An ink jet recording medium was obtained in the same manner as in Example 1 except that only 100 parts of the ink was blended.

<Comparative Example 2>
As the binder for the coating liquid A for the under layer, the amount of the completely saponified polyvinyl alcohol (PVA-117) was 35 parts and the EVA (AM-3150) was not blended. An ink jet recording medium was obtained in exactly the same manner as in Example 1.

<Comparative Example 3>
As a binder for the coating liquid A for the under layer, the blending amount of the completely saponified polyvinyl alcohol (PVA-117) is 5 parts, and the EVA (AM-3150) is not blended. An ink jet recording medium was obtained in exactly the same manner as in Example 1 except that 30 parts of (LX438C manufactured by Sumitomo Science Co., Ltd., abbreviated as “SBR”) were blended.

  The ink jet recording media of each Example and Comparative Example were evaluated by the following method.

(1) Glossiness The glossiness of the ink receiving layer surface was evaluated according to the following criteria.
○: 75 degree specular gloss is 50% or more and image definition is 40% or more Δ: 75 degree specular gloss is 50% or more and image definition is 20 to 40% ×: 75 degree specular Glossiness of 50% or less and image sharpness of 20% or less 75 degree specular glossiness is measured according to ISO 8254-1, gloss meter (Murakami Color Research Laboratory, True GLOSS GM-26PRO). ).
The image definition was measured according to JIS K7105 using a image clarity measuring device (model number: ICM-1DP, manufactured by Suga Test Instruments Co., Ltd.). The MD direction of the paper was measured under the conditions of a measurement angle of 60 degrees and a comb width of 2 mm.

(2) Applicability of dye ink and pigment ink Inkjet printer using dye ink (PM-950C: trade name of Epson Corporation) and inkjet printer using pigment ink (PM-4000px: trade name of Epson Corporation) Was used to print and record a predetermined pattern on an inkjet recording medium and evaluated according to the following criteria.
2-1) Ink absorbability (bleeding)
The blur at the boundary of the solid print portion mixed with red and green was visually evaluated. If the evaluation is ○, there is no practical problem.
○: The color boundary part is clearly separated. Δ: The color boundary part has a slight blur, but the degree of the blur is relatively small. X: The color boundary part has a very large blur. 2) Vividness (print density)
The vividness of the recorded image portion printed was visually evaluated. If the evaluation is Δ or ○, there is no practical problem.
◎: Very vivid ○: Vivid △: Slightly inferior x: Invisible

(3) Processing suitability (suppressing paper dust)
100 sheets of the obtained inkjet recording media were stacked, cut from the ink receiving layer side with a guillotine cutter, and the amount of paper dust was visually observed and evaluated. If the evaluation is ○, there is no practical problem.
○: No paper dust △: Some paper dust ×: Many paper dust

(4) Coating layer strength Borderless printing (full surface printing) was performed on the ink receiving layer surface of the obtained ink jet recording paper using an ink jet printer (PM-950C: trade name of Epson Corporation). After 2 hours, the surface opposite to the surface on which the ink receiving layer is provided (this back surface) is printed with the same printer (PM-950C). The presence or absence of missing layers (ink receiving layer and under layer) was evaluated. If the following evaluation is Δ or more, there is no practical problem.
◎: No omission ○: There are a few very small omissions △: There are some small omissions X: There are very many omissions

(5) Particle size measurement of colloidal silica 5-1) Primary particle diameter The specific surface area (nitrogen adsorption method) of the colloidal silica sample was measured, and the primary particle diameter was determined by calculation according to the following formula (1).
d = 6000 / (ρ × S) (1)
In the formula (1), d: primary particle diameter (nm), ρ: silica density (= 2.2 g / m ³ ), and S: specific surface area S (m ² / g).
5-2) Secondary particle size
The secondary particle diameter of colloidal silica was measured using ZETASIZER 3000HSA manufactured by MALVERN INSTRUMENTS.

  The obtained results are shown in Tables 1 and 2.

As is clear from Table 2, in the case of the ink jet recording medium of each Example, high evaluation was obtained in all of glossiness, suitability for dye ink and pigment ink, suitability for processing (paper dust suppression), and coating layer strength .

On the other hand, in the case of Comparative Example 1 which did not contain synthetic silica having a secondary particle size of 5 to 15 μm as the pigment of the under layer, the glossiness and ink suitability were good, but the processing suitability (paper dust suppression) was inferior. Ink jet recording medium with a good balance of the above could not be obtained.
In the case of Comparative Example 2 which did not contain an ethylene / vinyl acetate copolymer as the binder for the under layer, it was inferior in suitability for dye ink and pigment ink, and further inferior in workability (paper dust suppression). . This is presumably because the binder of the under layer is made only of PVA, so that the under layer is hard and brittle.
In the case of Comparative Example 3 in which the binder for the under layer did not contain ethylene / vinyl acetate copolymer (EVA) and SBR was used, the suitability of the dye ink and the pigment ink was inferior. This is because SBR is also a synthetic resin similar to EVA, so it is softer than water-soluble resins such as PVA, and the under layer is soft (excellent in processability), but the ink absorbability due to the low wettability of SBR. This is thought to be due to a decrease in printability.

Claims (6)

An underlayer containing a pigment and a binder and an ink receiving layer are provided on a support in this order , and the ink receiving layer is the outermost surface of the ink jet recording medium, and the under layer is mainly used as a pigment. Synthetic silica is contained, and 20% by mass or more of the synthetic silica is synthetic silica having a secondary particle diameter of 5 to 15 μm, and the under layer includes a water-soluble polymer and an ethylene / vinyl acetate copolymer as a binder. The 75 degree specular gloss of the ink receiving layer surface is 50% or more, and the ratio represented by (the coating amount of the under layer) / (the coating amount of the ink receiving layer) is 1. beyond, the ink-receiving layer comprises a ratio of the colloidal silica and fumed silica as pigment (colloidal silica) / (vapor phase silica) = 60 / 40-80 / 20, the ink-receiving layer, the ink receiving layer While the surface of the coating layer formed by coating a coating liquid in a wet state, the ink jet recording medium, characterized in that provided in pressure contact and drying the metal mirror surface heated to coating coating layer.   The inkjet recording medium according to claim 1, wherein the water-soluble polymer is polyvinyl alcohol.   The glass transition point of the ethylene / vinyl acetate copolymer is 0 ° C. or less, and the ethylene / vinyl acetate copolymer is a dried product of an ethylene / vinyl acetate copolymer resin emulsion having a particle diameter of 1 μm or less. The ink jet recording medium according to claim 1, wherein the ink jet recording medium is a recording medium. The coating amount of the under layer is 10 to 20 g / m ² , the coating amount of the ink receiving layer is 3 to 15 g / m ² , and (the coating amount of the under layer) / (the coating of the ink receiving layer). The inkjet recording medium according to any one of claims 1 to 3, wherein a ratio expressed by (work amount) is more than 1 and 4 or less. The primary particle diameter of the colloidal silica is 10 to 50 nm, the ratio of the secondary particle diameter to the primary particle diameter of the colloidal silica is 1.5 to 3.0, and the specific surface area of the vapor phase silica is 130 to The inkjet recording medium according to claim 1, wherein the inkjet recording medium is 300 m ² / g.   6. The ink jet recording medium according to claim 1, wherein the image clarity of the ink receiving layer surface is 20% or more.