JP2006205428A - Inkjet recording sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording sheet with advantages such as low cost, excellent pigment handling properties at the time of preparing a coating material, excellent white paper gloss/color developing properties, and best suitability for on-demand printing. <P>SOLUTION: This inkjet recording sheet comprises an ink receptive layer containing a wet silica and a binder, formed on a support. The wet silica can be obtained in the following way: (1) a mineral acid of 35 to 45% neutralization equivalent, is added to an aqueous solution of silicate of soda to which a sodium sulfate is previously added, in a first stage to partially neutralize the aqueous solution, (2) this neutralized mixture is adjusted so that the concentration of a silicon dioxide in the aqueous solution is 6.0 to 8.0 g/100 ml and the concentration of the sodium sulfate is 3.5 to 4.1 g/100 ml, and (3) the aqueous solution is heated up to 85-95°C under a stirring action, and the mineral acid is added to the aqueous solution in a second stage to complete the neutralization process. However, the drying process is dispensed with. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ink jet recording sheet, and in particular, provides an ink jet recording sheet that is inexpensive, excellent in handling of pigments at the time of preparing a paint, and excellent in blank paper gloss and color development and suitable for on-demand printing. To do.

In recent years, as a means for displaying image information and the like created on a personal computer on a recording paper, an ink jet recording method has been used in which an image is formed by ejecting liquid ink from a nozzle onto the recording paper using heat or pressure as a driving source. ing. In particular, in recent years, with the progress of ink droplet control technology and the improvement of ink and recording sheet performance, progress has been made to obtain images comparable to silver halide photographs.

Also in the field of commercial printing, on-demand printing is an ink-jet recording method that is optimal for printing a small number of copies and variable information printing (variable printing) because digital information can be printed directly on media such as paper without making a plate. In particular, inkjet printers equipped with line heads are attracting particular attention because they are much faster in printing.
As a recording sheet used in the ink jet recording system equipped with this line head, improvements have been made in terms of apparatus and ink composition in order to use high-quality paper and coated paper used in normal printing and writing. However, with the improvement of the performance of the ink jet recording apparatus such as higher speed, higher definition or full color of the apparatus and the expansion of applications, more advanced characteristics are required for the recording sheet. In other words, the recording sheet has a high density of printed dots and a bright and vivid color tone, ink absorption is fast, and even when the printed dots overlap, the ink does not flow out or bleed, Therefore, high image reproducibility is required such that the horizontal diffusion of the image is not unnecessarily large and the periphery is smooth and unblurred. Above all, since on-demand printing is for commercial printing rather than personal use, in addition to the above characteristics, the paper used is strongly required to have an appearance close to that of general coated paper for offset printing and low cost.

In response to such a demand for an on-demand printing ink jet recording sheet, none of the conventional ink jet recording sheets is satisfactory. For example, amorphous silica obtained by a vapor phase method or a wet method is excellent in performance. Among them, a wet method silica obtained by adding sulfuric acid to a sodium silicate aqueous solution (for example, see Patent Documents 1 and 2). ) Is relatively inexpensive and has potential for on-demand printing. However, this method is a method of drying once after the neutralization reaction, dry pulverizing this, and then further classifying to adjust the particle size and particle size distribution, and the manufacturing process up to the product is long and complicated. There were many losses along the way and the yield was low, so that it was not very inexpensive. Further, in this method, since amorphous silica as a product is obtained as a powder, when the coating material for inkjet paper is prepared with a stirrer such as Cowles, the powder is scattered and there is a problem in handling.
As a method for improving the handling of silica powder, sodium silicate is divided into three stages and neutralized with mineral acid in stages, and after completion of the first stage of neutralization, wet pulverization is performed during the ripening period. To obtain a silica dispersion (for example, see Patent Document 3), until a mineral acid is continuously added to a sodium silicate aqueous solution heated to 60 ° C. or higher until a neutralization equivalent of 70 to 100% is reached. A method of obtaining a silica dispersion by adjusting the pH of the system to a range of 8 to 3 after performing wet pulverization within the reaction time is known (for example, see Patent Document 4). However, it has been found that when the silica dispersion obtained by this method is used as a pigment for an ink receiving layer, a product having good white paper gloss and color developability cannot be obtained even if it is subjected to a calendar treatment.

Japanese Patent Laid-Open No. 10-329412 JP-A-9-95042 JP-A-8-91820 JP 2004-299936 A

  An object of the present invention is to obtain an ink jet recording sheet which is excellent in handling of a pigment at the time of preparing a coating material and excellent in blank paper gloss and color development and suitable for on-demand printing.

As a result of intensive studies, the inventors of the present invention added sodium sulfate to a sodium silicate aqueous solution in advance before starting neutralization with a mineral acid, and added the mineral acid in two stages. The inventors have found that very good silica can be obtained as a raw material for the ink receiving layer coating liquid, and have completed the present invention.
(1) In an ink jet recording sheet in which an ink receiving layer containing a wet process silica and a binder is provided on a support, the wet process silica is added to a sodium silicate aqueous solution to which sodium sulfate has been added in advance. 35-45% mineral acid was added to the first stage to partially neutralize, so that the silicon dioxide concentration in the aqueous solution was 6.0-8.0 g / 100 ml, and the sodium sulfate concentration was 3.5- After adjusting to 4.1 g / 100 ml, the aqueous solution was heated to 85-95 ° C. with stirring, and then neutralization was completed by adding the second stage mineral acid, and An ink jet recording sheet obtained without going through a drying step.

(2) The wet-process silica is a product obtained by further wet-grinding and / or wet-classifying the obtained slurry after adding the second stage mineral acid to complete neutralization, and performing a drying step. The inkjet recording sheet according to (1), which is obtained without passing through.
(3) The above-mentioned wet process silica is obtained by adding the second-stage mineral acid to complete neutralization, then separating the aqueous solution by filtration and removing the silica, and then redispersing it in water. And the inkjet recording sheet as described in (1) obtained without passing through a drying process.
(4) After the wet method silica has completed the neutralization by adding the second stage mineral acid, the aqueous solution is separated by filtration, and the silica cake is taken out and washed with water. The inkjet recording sheet according to (3), which is dispersed and obtained without going through a drying step.
(5) After the wet process silica is added with the second stage mineral acid to complete neutralization, the aqueous solution is separated by filtration to take out the silica cake, and the silica cake is washed as it is or after being washed with water. The ink jet recording sheet according to any one of (3) to (4), which is redispersed in water, further wet pulverized and / or wet classified, and obtained without going through a drying step.
(6) The wet-process silica has an average particle diameter in the range of 0.2 to 10 μm, and particles having a particle diameter of 30 μm or less occupy at least 70% or more of the whole (1) to (5) Inkjet recording sheet.

  The ink jet recording sheet of the present invention is an ink jet recording sheet that is excellent for handling on-demand printing, excellent in handleability of pigments at the time of preparing a paint, and excellent in gloss and color development of white paper, and is extremely useful in practice. .

  The wet method silica used in the present invention causes the neutralization reaction by adding the mineral acid in two stages to the sodium silicate aqueous solution to which sodium sulfate has been added before the neutralization with the mineral acid is started. In the first stage addition, primary particles are mainly formed, and in the second stage addition, secondary particles that are mainly aggregates of primary particles are formed. In the present invention, in order to obtain silica preferable as a raw material for the ink receiving layer, it is extremely important to adjust the reaction conditions in the particle formation process.

In the present invention, the mineral acid of 35 to 45% of the neutralization equivalent is used in the first stage of the addition of the mineral acid twice, and added to the sodium silicate aqueous solution to which sodium sulfate has been added in advance with stirring. The The mineral acid concentration is not particularly limited, but usually 10 to 30% by mass. The precipitation rate of hydrated silicic acid (silica) is affected by the temperature of the system, the concentration of the mineral acid and the addition rate, and the higher the temperature and the higher the concentration and addition rate of sulfuric acid, the faster. In the present invention, the time for adding the mineral acid is not particularly limited, but in order to prevent local precipitation of hydrated silicic acid (silica) or gelation and perform a uniform reaction, normal stirring is performed. It is preferable to add over 8 to 15 minutes under conditions. In this case, the aqueous solution temperature is preferably 60 ° C. or lower. The aqueous solution after the first stage mineral acid addition is then heated to a temperature of 85-95 ° C. with stirring. At this time, the concentrations of silicon dioxide (SiO ₂ ) and sodium sulfate (Na ₂ SO ₄ ) in the aqueous solution greatly affect the viscosity of the hydrated silica (silica) slurry and the performance of the hydrated silica (silica). Therefore, in the present invention, the silicon dioxide (SiO ₂ ) concentration is 6.0 to 8.0 g / 100 ml, and the sodium sulfate (Na ₂ SO ₄ ) concentration is 3.5 to 4.1 g / 100 ml. The sodium silicate concentration and the amount of sodium sulfate aqueous solution added are adjusted. If the silicon dioxide (SiO ₂ ) concentration in the aqueous solution is less than 6.0 g / 100 ml, the primary particles of hydrated silicic acid (silica) are insufficiently aggregated, and the desired inkjet suitability (ink absorbability) is obtained. A sheet cannot be obtained. On the other hand, if the silicon dioxide concentration exceeds 8.0 g / 100 ml, the primary particles agglomerate rapidly, resulting in insufficient and non-uniform chemical reaction inside the particles, and the desired effect cannot be obtained.

  The addition of sodium sulfate to the reaction system has the effect of suppressing the viscosity increase of the system in the above temperature raising step and further reducing the viscosity of the resulting hydrated silicic acid (silica) slurry. Increases the processing capacity in subsequent processes such as classification. In addition, when the sodium sulfate concentration in the aqueous solution is less than 3.5 g / 100 ml, the slurry viscosity becomes high, and the processing ability is lowered in the subsequent steps such as wet pulverization and wet classification. On the other hand, when the concentration of sodium sulfate exceeds 4.1 g / 100 ml, the primary particle size becomes large, and the inkjet recording sheet using this hydrated silicic acid (silica) has a rough coating surface, and powder fallen or industrial use. The guide roll stain of the line head ink jet printer occurs, which is not preferable.

  In general, wet silica is formed by agglomerating primary particles of hydrated silicic acid (silica) having a particle diameter of 10 to 50 nm to form secondary particles. Depending on the size of the particle diameter of the primary particles, The size and number of configured pore diameters change, and the pore volume changes. In the wet process silica according to the present invention, the diameter of the primary particles is preferably 30 to 40 nm. Therefore, it is essential that the sulfuric acid in the first stage is in the range of 35 to 45% of the neutralization equivalent. It is. Incidentally, if the sulfuric acid in the first stage is less than 35% of the neutralization equivalent, the primary particle does not grow sufficiently, so that the pore volume does not reach a sufficient amount, and the desired inkjet suitability (ink absorbability) is obtained. I can't. On the other hand, when the use ratio of the first-stage sulfuric acid is 45% or more, the pore volume becomes a sufficient amount, and the desired inkjet suitability (ink absorbability) can be obtained. ) Is not suitable because the viscosity of the slurry becomes extremely high and subsequent handling such as wet pulverization and reduction in classification becomes extremely difficult.

  The temperature rise after the first neutralization is performed to promote precipitation of hydrated silicic acid (silica) particles. The rate of temperature increase is not particularly limited, but in the case of a rapid temperature increase such that the temperature increase gradient is 3 ° C./min, neutralization of the second stage after temperature increase (stop of primary particle growth and secondary It is desirable that the primary particles are aged by providing a holding time of 5 to 10 minutes before moving to (particle formation). On the other hand, in the case of a moderate temperature increase of 1 ° C./min, it is not necessary to provide the above holding time. In the most preferred embodiment of the present invention, the neutralization of the first stage is completed at 40 to 50 ° C., and then over a period of 20 to 30 minutes, at a rate of 1.5 to 2.5 ° C./min. The temperature is raised to ˜95 ° C., and then the second stage neutralization is performed without providing a holding time.

  In the present invention, the reaction is completed by neutralization in the second stage, but the addition of the second stage mineral acid is usually performed over 20 to 40 minutes. However, this addition rate is not particularly limited.

  Examples of the mineral acid used for neutralization include inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid. Among them, the use of sulfuric acid is preferable.

  The hydrated silicic acid (silica) slurry that has been neutralized in the second stage can be directly mixed with a binder or the like to prepare an ink-receiving layer coating solution. In addition, this hydrated silicic acid (silica) slurry is filtered and separated by a filtration device such as a belt filter, filter press, screw press and the like to remove sodium sulfate, and water is added to the obtained cake and mixed and stirred. After preparing a slurry having a solid content concentration of 8 to 12% by weight, it can be mixed with a binder or the like to prepare an ink receiving layer coating solution. Further, after filtration and separation, the obtained cake may be washed with water and used. The slurry temperature during filtration is usually in the range of 40 to 60 ° C. in consideration of the filtration rate and changes in the properties of the hydrated silicic acid. When the slurry temperature is less than 40 ° C, the filtration rate is slow, and when the slurry temperature exceeds 60 ° C, the property of the hydrated silicic acid (silica) is changed and the performance is deteriorated.

  Among the above, those prepared by mixing with a binder or the like as it is without filtering and washing with water and adjusting the ink receiving layer coating liquid tend to have a lower viscosity of the coating liquid than those filtered and washed with water. Since a coating solution having a higher concentration than the result can be used, the coating speed is preferably increased. In addition, after filtration, without washing with water, mixing with a binder or the like to prepare a coating liquid for the ink-receiving layer, the viscosity of the coating liquid is higher than that without filtration and washing with water. It tends to be lower than that washed with water, which is preferable.

  Hydrated silicic acid (silica) slurry before or after removal of sodium sulfate is treated with a wet homogenizer such as a continuous homomixer, colloid mill, disc refiner, sand grinder, ball mill, rod mill, etc. Is done. Moreover, it processes with classifiers, such as a vibrating screen, and a big particle is removed.

  Among the silicas used in the present invention, those having an average particle diameter in the range of 0.2 to 10 μm and particles having a particle diameter of 30 μm or less occupy at least 70% or more of the total are particularly preferable. When the average particle size is less than 0.2 μm, the specific surface area increases, the fluidity of the slurry deteriorates, and the viscosity of the ink receiving layer coating liquid increases, which is not preferable. When the thickness exceeds 10 μm, the obtained inkjet recording sheet has a weak surface strength of the coating layer, which causes problems such as powder falling. The reason for this is not clear, but it is conceivable that the binder is difficult to enter into the voids of the secondary particles of the grown silica, or the secondary particles are likely to collapse and the surface strength is likely to be lowered.

In wet pulverization and classification of hydrated silicic acid (silica), the lower the slurry viscosity, the higher the processing efficiency is preferable, and an operation for appropriately reducing the viscosity is performed as necessary. For example, aluminum sulfate (Al ₂ (SO ₄ ) ₃ ) is added to the slurry obtained by re-dispersing the cake obtained by filtration to adjust the pH to a range of 4 to 5.

  As described above, in the present invention, since the coating liquid for the ink receiving layer is prepared using the silica produced without passing through the drying step, the step of redispersing the powder can be omitted, as in the case of handling the silica powder. There are no problems such as scattering and dirt, and the coating preparation can be completed in a short time, and there are advantages such that water and energy required for stirring can be reduced.

  Said silica is normally mix | blended in the coating liquid for ink receiving layers in 45-98 mass% (solid content). Especially, it is 60-90 mass% (solid content) preferably. If it is less than 45% by mass, it is difficult to obtain the merit of low cost and high performance of the present invention. Moreover, when it exceeds 98 mass%, although it is excellent in terms of price and inkjet suitability, it tends to be inferior in surface strength.

In the present invention, as the pigment of the ink receiving layer coating liquid, in addition to the wet method silica, other pigments may be blended as necessary. Examples of the other pigment include the above-mentioned gas phase method silica and the like. Silica, kaolin, clay, calcined clay, zinc oxide, aluminum oxide, aluminum hydroxide, calcium carbonate, satin white, aluminum silicate, alumina, zeolite, synthetic zeolite, sepiolite, smectite, synthetic smectite, diatomaceous earth, magnesium silicate, carbonic acid Inorganic pigments such as magnesium, magnesium oxide, silica composite calcium carbonate with silica supported on calcium carbonate, silica composite kaolin with silica supported on kaolin, styrene, ethylene, vinyl chloride, polyurethane, acrylic, vinyl acetate, polycarbonate, Polymer such as nylon And various pigments known in the general coated paper manufacturing field such as solid pigments or hollow plastic pigments such as plastic pigments made of these copolymers, urea resin plastic pigments, benzoguanamine plastic pigments, etc. These can be used alone or in combination of two or more.
Among such pigments, the hollow plastic pigment has a great effect of improving the glossiness of blank paper, and the plastic pigment having a hollow ratio of 51% or more is particularly effective. In addition, when the average particle size is 5 μm or less, the effect of improving the white paper gloss is large, and when the glass transition point of the resin of the hollow plastic pigment is in the range of 30 to 120 ° C., the effect of improving the white paper gloss is large.
The other pigment is usually blended in the ink receiving layer coating liquid in the range of 0 to 50% by mass (solid content). When it exceeds 50% by mass, it is difficult to obtain the high performance merit of the present invention.

  Examples of the binder for the ink receiving layer coating solution include cationic starch, amphoteric starch, oxidized starch, enzyme-modified starch, thermochemically modified starch, esterified starch, etherified starch, and the like, carboxymethylcellulose, hydroxyethylcellulose, and the like. Cellulose derivatives, natural or semi-synthetic polymer compounds such as gelatin, casein, soybean protein, natural rubber, polydienes such as polyvinyl alcohol, polyisoprene, polyneoprene, polybutadiene, polyalkenes such as polybutene, polyisobutylene, polypropylene, and polyethylene , Vinyl halides, vinyl acetate, styrene, (meth) acrylic acid, (meth) acrylic acid esters, (meth) acrylamide, methyl vinyl ether and other vinyl polymers and copolymers, styrene-butadiene, methyl meta Relate - synthetic rubber latices of butadiene such as polyurethane resins, polyester resins, polyamide resins, olefin - maleic anhydride resins, synthetic resins such as melamine resins and the like. Among these, one or more kinds are appropriately selected and used according to the purpose.

  A binder is normally mix | blended with the coating liquid for ink receiving layers in 5-50 mass% (solid content). Especially, it is preferably 10 to 30% by mass (solid content). When the blending amount is less than 5% by mass, it is difficult to obtain surface strength. When it exceeds 50% by mass, only those having poor ink water absorption can be obtained.

Further, the ink receiving layer coating liquid may contain a cationic or anionic substance having an action of enhancing the fixing property between the ink receiving layer and the ink according to the ionicity of the ink. Examples of the cationic substance include polyalkylene polyamine resins or derivatives thereof, acrylic resins having tertiary amino groups and quaternary ammonium groups, polyethyleneimine resins, polyamide resins, polyamide epichlorohydrin resins, polyamine epichlorohydrins. Cationic resins such as polyethylene resins, polyamide polyamine epichlorohydrin resins, polydiallylamine resins, polyamine resins, dicyandiamide condensates, and the like. Specific examples include polyethyleneamine, polypropylene polyamine, dicyandiamide-polyethyleneamine, dicyandiamide formaldehyde, Acrylic amine, cationic polyvinyl pyrrolidone, poly-trimethyl ammonium methacrylate, vinyl imidazolium methacrylate-vinyl Lidon copolymer, diallyldimethyl quaternary ammonium hydrochloride, dicyandiamide-polyethylene polyamine, dimethylaminopropylacrylamide-methyl chloride quaternary salt polymer, acrylamide-diallylamine copolymer, polyoxypropyl quaternary ammonium salt, diallyldimethylammonium hydrochloride Salt-acrylamide copolymer, polydimethylamine-ammonia-epichlorohydrin, dimethylaminopropylacrylamide polymer, polyalkoxydialkyl quaternary ammonium salt, monoallylamine-diallylamine hydrochloride copolymer, polyallylamine hydrochloride, dicyandiamide-formalin heavy Condensate, dicyandiamide-diethylenetriamine polycondensate, epichlorohydrin-dimethylamine addition polymer, dimethyldialysate Ammonium chloride · SO ₂ copolymer, diallylamine salt · SO ₂ copolymer, dimethyl diallyl ammonium chloride polymer, polymer of allylamine salt, dialkylaminoethyl (meth) acrylate quaternary salt polymer, acrylamide - diallylamine salt copolymerization A cationic polymer such as a coalescence is preferably used.
Examples of anionic substances include water-insoluble metal salts such as phosphotungstic acid and phosphomolybdic acid, ammonium salts of styrene-maleic anhydride copolymers, ammonium salts of α-olefin-maleic anhydride copolymers, anion modification Anionic polymers such as PVA and carboxymethylcellulose are listed.

  For the ink receiving layer coating solution, various auxiliary agents such as surfactants, pH regulators, viscosity modifiers, softeners, gloss imparting agents, waxes, dispersants, flow modifiers, stabilizers, antistatic agents An agent, a cross-linking agent, a sizing agent, a fluorescent brightening agent, a colorant, an ultraviolet absorber, an antifoaming agent, a water-proofing agent, a plasticizer, a lubricant, an antiseptic, and a fragrance are appropriately blended as necessary.

  The ink receiving layer coating solution is not particularly limited, but is usually prepared at a concentration of 20 to 60%.

The coating amount of the ink receiving layer coating liquid onto the support is preferably per side ^1g / ^{m 2 ~15g} / m 2 in solids. If it is less than 1 g / m < ² >, even if it performs a calendar process, only the thing with inferior white paper gloss will be obtained. On the other hand, if it is more than 15 g / m ² , the desired performance can be obtained, but the effect of the present invention is saturated and the cost is increased, which is not preferable.

As a method for applying the ink receiving layer coating liquid to the support, generally, a conventional coating apparatus such as a blade coater, an air knife coater, a spray coater, a roll coater, a reverse roll coater, a bar coater, a curtain coater, or a die slot coater is used. A gravure coater, a champlex coater, a brush coater and a two roll, and a metering blade type size press coater, a bill blade coater, a short dwell coater, a lip coater, and a gate roll coater can be used. Coating is performed either on-machine or off-machine.

The support used in the present invention is not particularly limited, and examples thereof include a sheet-like paper substrate, a film, and a joined product of the film and the sheet-like paper substrate. The support sheet is preferably the surface has a water absorption, among others, the Cobb method water absorbency contact time of 30 seconds with water as defined in JIS P8140 ^is, the support of 15g / ^{m 2} ~400g / m 2 by weight, more ^preferably from ^{17g / m 2 ~300g / m 2} . When using a support having a Cobb method water absorption of less than 15 g / m ² , there is practicality, but it is slightly inferior in terms of ink absorbability, and when it is greater than 400 g / m ² , Since the penetration of the coating liquid into the base paper is large, the glossiness may be lowered.

There are no particular limitations on the method and type of pulp constituting the sheet-like paper substrate, for example, chemical pulp such as KP, mechanical pulp such as SGP, RGP, BCTMP, and CTMP, waste paper pulp such as deinked pulp, kenaf, Non-wood pulp such as bamboo, straw, hemp, etc. is used. In addition, organic synthetic fibers such as polyamide fibers and polyester fibers, recycled fibers such as polynosic fibers, and inorganic fibers such as glass fibers, ceramic fibers, and carbon fibers can be mixed. Among these, use of chlorine-free pulp such as ECF pulp and TCF pulp is preferable.

In addition, a filler may be blended in the sheet-like paper substrate as necessary. As the filler, various pigments generally used for fine paper can be used, such as kaolin, calcined kaolin, calcium carbonate, calcium sulfate, barium sulfate, titanium dioxide, talc, zinc oxide, alumina, magnesium carbonate, magnesium oxide, Silica, white carbon, bentonite, zeolite, inorganic pigments such as sericite and smectite, as well as fine hollow particles, solid particles and penetrating polystyrene resins, urea resins, melamine resins, acrylic resins and vinylidene chloride resins Examples thereof include organic pigments such as pore-type particles.
In addition to the pulp fibers and fillers, various anionic, nonionic, and cationic materials that have been used in the past are included in the paper material when the sheet-like paper substrate is made, as long as the desired effects of the present invention are not impaired. Various auxiliary agents for papermaking such as a neutrality or amphoteric yield improver, freeness improver, paper strength enhancer, and internal sizing agent can be appropriately selected and used as necessary. Furthermore, internal additives for papermaking such as dyes, fluorescent brighteners, pH adjusters, antifoaming agents, pitch control agents, slime control agents and the like can be added as necessary.

The paper-making method of the sheet-like paper substrate is not particularly limited. For example, an acid paper-making method performed at a paper-making pH of about 4.5, an alkaline filler such as calcium carbonate as a main component, and a paper-making pH of about 6 from weak acidity. All papermaking methods such as neutral papermaking with a weak alkaline pH of about 9 can be applied. As for the paper machine, a long net paper machine, a twin wire paper machine, a round net paper machine, and a Yankee paper machine are used as appropriate. Can be used.
Weight of the sheet paper substrate used in the present invention (basis weight) is not particularly limited, it is used in the range of usually ^{30g / m 2 ~200g / m 2} .

  Examples of the film used as the support of the present invention include acetate film, cellulose triacetate film, nylon film, polyester film, polycarbonate film, polystyrene film, polyphenylene sulfide film, polypropylene film, polyimide film, and cellophane. I can do it. As the film, those containing additives such as inorganic pigments, organic pigments, ultraviolet absorbers, light stabilizers, antioxidants, fluorescent dyes, crosslinking agents, lubricants, mold release agents and the like are used as necessary. The method for producing the film is not particularly limited, and a known method can be used. The film used in the present invention includes what is generally called synthetic paper. Although the thickness of the film used as a support body is not specifically limited, The thing of the range of 50 micrometers-300 micrometers is used normally.

  The joined product of the film and the sheet-like paper substrate used as the support of the present invention can be obtained by a known method. The thickness of the joined product of the film and the sheet-like paper substrate used as the support is not particularly limited, but usually a thickness in the range of 50 μm to 300 μm is used.

The ink jet recording sheet of the present invention is provided with an ink receiving layer on one side or both sides of the support, but the coating on one side can be performed twice or more. In the case of double-sided coating or multilayer coating on the same surface, the composition and the coating amount of each coating liquid need not be the same. Further, the support may be provided with a coating layer other than the ink receiving layer, if necessary. For example, when it is desired to further improve the fixability of the ink receiving layer and the ink, or when the Cobb method water absorption of the support is low, or when the adhesion between the ink receiving layer and the support is insufficient, and peeling easily occurs. Before forming the ink receiving layer, an undercoat layer mainly composed of a cationic polymer or an anionic polymer, or an undercoat layer mainly composed of a pigment and an adhesive can be provided. Examples of the cationic polymer or anionic polymer used in the undercoat layer include the above-described cationic polymers or anionic polymers mentioned as the materials for the ink receiving layer coating liquid. Such a polymer is used alone or in combination with a nonionic polymer such as starch or polyvinyl alcohol. Examples of the pigment and adhesive used for the undercoat layer include the pigments and adhesives mentioned above as the materials for the ink receiving layer coating solution. In addition, when the ink receiving layer is provided on one side, various known coating layers are provided on the back side for preventing charging, preventing curling, improving adhesion, imparting printing suitability, improving feeding / discharging suitability with a printer, and the like. Can be provided. In addition, when the ink receiving layer is a single side, it is of course possible to add application suitability by performing various processing on the back side, for example, post-processing such as adhesion, magnetism, flame retardancy, heat resistance, water resistance, oil resistance, and slip resistance. Is possible.

  The coated paper is subjected to a calender treatment as necessary. For the calendar processing, a smoothing processing device such as a normal super calendar, gloss calendar, soft calendar, shoe nip calendar is used, and the processing is appropriately performed on-machine or off-machine. The processing conditions such as the configuration of the pressure device, the number of pressure nips, and heating are appropriately adjusted according to the desired paper quality. Although not particularly limited, in the present invention, the surface of the ink receiving layer is usually subjected to a calendar treatment so that the glossiness at 75 degrees measured in accordance with JIS Z 8741 is 30% or more. . The silica used in the present invention is characterized in that the balance between the glossiness and color developability of the surface of the ink receiving layer after the calendering treatment is superior to silica obtained by other production methods. The calendering process is performed at least once after the ink receiving layer is formed, but the calendering process may be performed on the support before the ink receiving layer is formed.

  The present invention will be specifically described by the following examples, but of course, they are not intended to limit the scope of the present invention. In the examples, “parts” and “%” represent “parts by mass (solid component)” and “mass%” unless otherwise specified.

Example 1
[Preparation of silica slurry]
In a reaction vessel (300 liters), a sodium silicate aqueous solution (SiO ₂ / Na ₂ O molar ratio = 3.05, SiO ₂ concentration = 20% by mass) was added and diluted with water to obtain 8% by mass as SiO _2. A diluted sodium silicate aqueous solution was prepared, and sodium sulfate was further added and dissolved. Next, after heating this aqueous solution to 45 ° C., under a sufficiently strong stirring that does not generate a giant gel, dilute sulfuric acid having a concentration of 20% by mass at a dropping rate of 1.3 kg / min is 37% by mass of the neutralization equivalent. Until neutralization of the first stage was completed. The silicon dioxide (SiO ₂ ) concentration after the addition was 7.2 g / 100 ml, and the sodium sulfate (Na ₂ SO ₄ ) concentration was 3.9 g / 100 ml.

  Next, this aqueous solution was heated to 95 ° C. over 20 minutes with stirring, and subsequently dilute sulfuric acid having a concentration of 10% by mass was added at a dropping rate of 0.5 kg / min with vigorous stirring. Completed eye neutralization. The resulting silica slurry had a pH of 5.0.

[Production of sheet-like support]
LBKP (freeness (CSF) = 450 ml) 100 parts of pulp slurry, 0.05 part of alkenyl succinic anhydride (trade name: Fibran 81K, manufactured by Arakawa Chemical Industries) as an internal sizing agent, cationized as a fixing agent 0.7 parts of starch (trade name: Oji Ace K, manufactured by Oji Constarch) and 0.5 part of sulfuric acid band are added, and 10 parts of calcium carbonate is added as a filler, and the mixture is diluted with white water. A paper stock having a pH of 7 and a solid content concentration of 0.8% was prepared. The paper stock is subjected to a papermaking machine to make paper, and the resulting wet paper is subjected to size press using a size press solution containing oxidized starch (trade name: Oji Ace A, manufactured by Oji Constarch Co., Ltd.) at a concentration of 6%. The coating weight is applied with an apparatus so that the dry weight is 2 g / m ² , dried, and further smoothed using a machine calendar so that the Beck smoothness becomes 50 seconds, and the basis weight is 127 g / m ^2. A sheet-like support of m ² was produced.
[Preparation of ink receiving layer coating solution]
The silica slurry is subjected to a sand grinder treatment and pulverized to an average particle size of 5 to 6 μm, and then 100 parts of the pigment is collected, and an acrylic ester emulsion (trade name: Mobile 718, Clariant Polymer Co., Ltd.) is used as a binder. 50 parts), 12 parts of polyamine epichloric cation resin (trade name: DK-6854, manufactured by Seiko PMC Co.) are added and stirred, and water is further added to form a coating solution for an ink receiving layer having a solid content concentration of 15%. Was prepared.

[Formation of ink receiving layer on sheet-like support]
The obtained ink receiving layer coating solution was applied to both sides of the sheet-like support using an air knife coater and dried so that the dry coating weight per side was 7 g / m ^2. Formed.
[Calendar processing]
The ink receiving layer forming sheet obtained as described above was passed through a pressure nip composed of a metal roll and an elastic roll to obtain an ink jet recording sheet having a basis weight of 141 g / m ² . The evaluation results of the obtained ink jet recording sheet are shown in Table 1.

Example 2
The silica slurry before pulverization obtained in the same manner as in Example 1 was filtered with a centrifugal dehydrator to obtain a silica cake. Next, the cake was taken out, water was added thereto, and the mixture was vigorously stirred to obtain a slurry having a concentration of 8% by mass. Subsequently, this slurry was subjected to a sand grinder treatment and pulverized to an average particle size of 5 to 6 μm, and then 100 parts of the pigment was separated, and an acrylic ester emulsion (trade name: Mobile 718, Clariant Polymer) was used as a binder. 50 parts, 12 parts of polyamine epichloric cation resin (trade name: DK-6854, manufactured by Seiko PMC Co., Ltd.) and stirred, and further water is added to form an ink-receiving layer having a solid content of 15%. A liquid was prepared. The viscosity of this coating liquid was higher than that of Example 1. Subsequently, an ink jet recording sheet was obtained in the same manner as in Example 1 except that the obtained coating liquid was used. The evaluation results of the obtained ink jet recording sheet are shown in Table 1.

Example 3
The silica slurry before pulverization obtained in the same manner as in Example 1 was filtered with a centrifugal dehydrator and further washed to obtain a silica cake. Next, water was added to the cake and vigorously stirred to obtain a slurry having a concentration of 8%. Subsequently, this slurry was subjected to a sand grinder treatment and pulverized to an average particle size of 5 to 6 μm, and then 100 parts of the pigment was separated, and an acrylic ester emulsion (trade name: Mobile 718, Clariant Polymer) was used as a binder. 50 parts, 12 parts of polyamine epichloric cation resin (trade name: DK-6854, manufactured by Seiko PMC Co., Ltd.) and stirred, and further water is added to form an ink-receiving layer having a solid content of 15%. A liquid was prepared. The viscosity of this coating solution was higher than that of Example 2. Subsequently, an ink jet recording sheet was obtained in the same manner as in Example 1 except that the obtained coating liquid was used. The evaluation results of the obtained ink jet recording sheet are shown in Table 1.

Comparative Example 1
A sodium silicate aqueous solution (SiO ₂ / Na ₂ O molar ratio = 2.18, SiO ₂ concentration = 20% by mass) is diluted with water in a reaction vessel (300 liters), and 5% by mass diluted silicic acid as SiO ₂ A soda aqueous solution was prepared. After heating this sodium silicate aqueous solution to 85 ° C., dilute sulfuric acid having a concentration of 10% by mass was added at a dropping rate of 270 g / min under sufficiently strong stirring that does not generate a coarse gel. From the point of time when this dilute sulfuric acid was added to 40% by weight of the neutralization equivalent, the cyclic pulverization process was started with a horizontal sand grinder, and the pulverization process was performed for 90 minutes to a neutralization equivalent of 80% by weight with a target particle size of 5-6 μm It was. Even after the pulverization treatment, sulfuric acid having the same concentration was continuously added to the reaction solution at an addition rate of 270 g / min, and the pH of the reaction solution was adjusted to 6 to obtain a silica slurry.
Next, this silica slurry was filtered and further washed with water to obtain a silica cake. Then, water was added to the cake and vigorously stirred to obtain a slurry having a concentration of 8% by mass. Subsequently, an amount corresponding to 100 parts of the pigment was separated, and 50 parts of an acrylic ester emulsion (trade name: Movinyl 718, manufactured by Clariant Polymer Co.) as a binder and a polyamine epichloro cationic resin (trade name: DK-6854). (Manufactured by Starlight PMC) was added and stirred, and water was further added to prepare a coating solution for an ink receiving layer having a solid content concentration of 15%. Subsequently, an ink jet recording sheet was obtained in the same manner as in Example 1 except that the obtained coating liquid was used. The evaluation results of the obtained ink jet recording sheet are shown in Table 1.

Comparative Example 2
(1) First stage neutralization step (neutralization rate 40%); sodium silicate aqueous solution (SiO ₂ / Na ₂ O molar ratio = 2.18, SiO ₂ concentration = 20 mass% in reaction vessel (300 liters)) ) Was diluted with water to prepare a 6.7% by weight diluted sodium silicate aqueous solution as SiO ₂ . Subsequently, this aqueous solution was heated to 85 ° C. with stirring, and then an amount of sulfuric acid (concentration 98% by mass) corresponding to 40% of the neutralization equivalent was sufficiently dropped at a dropping rate of 240 g / min so that a coarse gel was not generated. Under vigorous stirring. After completion of the addition, the partially neutralized liquid thus obtained was subjected to aging treatment with stirring, and at the same time subjected to cyclic pulverization treatment with a horizontal sand grinder targeting a particle size of 5 to 6 μm. The aging and pulverization processes took 2 hours. (2) Second stage neutralization step (neutralization rate 40%, cumulative neutralization rate 80%); Next, while maintaining the temperature of the reaction solution at 85 ° C., sulfuric acid having the same concentration as the first step is added to the first step. Under the same conditions as in the neutralization step, 80% by mass of the neutralization equivalent was added. After completion of the addition, the resulting partially neutralized solution was aged for 30 minutes with stirring. (3) Third stage neutralization step (neutralization rate 20%, cumulative neutralization rate 100%); Subsequently, sulfuric acid having the same concentration was added to the reaction solution after aging at the same rate at 1640 g / min, followed by reaction. The pH of the liquid was adjusted to 6 to obtain a silica slurry.

Next, the silica slurry after completion of the third step was filtered, and further washed with water to obtain a silica cake. Then, water was added thereto and stirred vigorously to obtain a slurry having a concentration of 8% by mass. Subsequently, an amount corresponding to 100 parts of the pigment was separated, and 50 parts of an acrylic ester emulsion (trade name: Movinyl 718, manufactured by Clariant Polymer Co.) as a binder and a polyamine epichloro cationic resin (trade name: DK-6854). (Manufactured by Starlight PMC) was added and stirred, and water was further added to prepare a coating solution for an ink receiving layer having a solid content concentration of 15%. Subsequently, an ink jet recording sheet was obtained in the same manner as in Example 1 except that the obtained coating liquid was used. The evaluation results of the obtained ink jet recording sheet are shown in Table 1.
Comparative Example 3
As a commercially available silica, 100 parts of Mizukasil P705 (manufactured by Mizusawa Chemical Co., Ltd.) is blended with the same compound as in Example 1 to prepare an ink receiving layer coating solution. In the same manner, an ink jet recording sheet was obtained. The evaluation results of the obtained ink jet recording sheet are shown in Table 1.
The obtained inkjet recording sheet was evaluated by the following method.
"Blank gloss"
The 75 degree specular glossiness defined in JIS Z 8741 was measured.

"Print density"
Using an ink jet printer (PM-800G) manufactured by Epson Corporation, the standard ink was used as the ink, black solid printing was performed, and the printing density was measured with Macbeth RD914.
"Handling"
The silica scattering state at the time of preparing the paint was visually judged and evaluated as ○ when there was little scattering and there was no problem in the working environment, and × when there was much scattering and there was a problem in the working environment.

表１からわかるように、本発明のインクジェット記録シートは、白紙光沢および印字濃度が高く、良好である（実施例１、２、３）。一方、本発明とは異なる合成法で作成したシリカでは、白紙光沢の低下（比較例１）や印字濃度の低下（比較例２）がみられ、また中和反応後に一度乾燥したシリカは、塗料をカウレス等の攪拌機によって調製する際に、粉体が飛散し、ハンドリングに問題がある（比較例３）。

As can be seen from Table 1, the ink jet recording sheet of the present invention has good white paper gloss and printing density (Examples 1, 2 and 3). On the other hand, silica produced by a synthesis method different from that of the present invention shows a decrease in white paper gloss (Comparative Example 1) and a decrease in printing density (Comparative Example 2). When the powder is prepared with a stirrer such as Cowles, the powder is scattered and there is a problem in handling (Comparative Example 3).

The ink jet recording sheet according to the present invention is an ink jet recording sheet that is excellent for handling on-demand printing, excellent in handleability of pigments at the time of preparing a paint, and excellent in white paper gloss and color development, and is excellent in practical use. is there.

Claims (6)

In an inkjet recording sheet in which an ink-receiving layer containing a wet process silica and a binder is provided on a support, the wet process silica is added to a sodium silicate aqueous solution in which sodium sulfate is added in advance to a neutralization equivalent of 35 to 45. % Mineral acid was added to the first stage to partially neutralize, so that the silicon dioxide concentration in the aqueous solution was 6.0 to 8.0 g / 100 ml, and the sodium sulfate concentration was 3.5 to 4.1 g. / 100 ml, the aqueous solution is heated to 85 to 95 ° C. with stirring, and then neutralized by adding the second stage mineral acid to obtain a drying step. An ink jet recording sheet obtained without passing through. The above wet process silica is a product obtained by further wet-grinding and / or wet-classifying the obtained slurry after adding the second stage mineral acid to complete neutralization, and without undergoing a drying step. The inkjet recording sheet according to claim 1, which is obtained. The wet process silica is the one obtained by adding the second stage mineral acid to complete neutralization, and then separating the aqueous solution by filtration to take out the silica cake, which is then redispersed in water, and 2. The ink jet recording sheet according to claim 1, which is obtained without passing through a drying step. The wet process silica is the one in which the mineral acid in the second stage is added to complete neutralization, the aqueous solution is separated by filtration, the silica cake is taken out, washed with water, and then redispersed in water. 2. The ink jet recording sheet according to claim 1, wherein the ink jet recording sheet is obtained without going through a drying step. After the wet method silica has completed the neutralization by adding the second stage mineral acid, the aqueous solution is separated by filtration to take out the silica cake, and the silica cake is washed as it is or after being washed with water, and then reconstituted with water. The ink jet recording sheet according to claim 3, which is dispersed and further wet pulverized and / or wet classified, and obtained without passing through a drying step. The ink jet recording sheet according to claim 1, wherein the wet process silica has an average particle diameter in the range of 0.2 to 10 μm, and particles having a particle diameter of 30 μm or less occupy at least 70% of the whole.