JP2002079741A - Ink jet recording medium dispersion and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly dense and highly productive ink jet recording medium dispersion and its manufacturing method and the ink jet recording medium having high voids. SOLUTION: In this ink jet recording medium, in which at least one ink accepting layer including inorganic particles and a binder is provided on a base material, its ink accepting layer coating liquid includes the dispersion of a vapor phase method silica, which is kneaded and dispersed at pH of 5 to 8 in the presence of a boric acid compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dispersion liquid used for an ink jet recording medium having an ink receiving layer containing at least one layer of inorganic fine particles and a binder on a base material, and a method for producing the same. And a method for producing a dispersion having a high content.

[0002]

2. Description of the Related Art Ink-jet recording is a method in which fine droplets of ink are caused to fly according to various operating principles and adhere to a recording sheet such as paper to record images and characters. It has advantages such as easy noise and multicoloring.

With respect to nozzle clogging and maintenance, which has been a problem in the conventional method, improvements have been made in both ink and apparatus.
It is rapidly spreading in various fields such as facsimile and computer terminals.

The recording paper used in this ink jet recording method has a high density of print dots, a bright and vivid color tone, and the ink absorbs quickly so that even if the print dots overlap, the ink may flow out. It is required that bleeding does not occur, that the diffusion of print dots in the horizontal direction is not unnecessarily large, and that the periphery is smooth and not blurred. In particular, when the ink absorption speed is low, when ink droplets of two or more colors are printed in an overlapping manner, the droplets cause a repelling phenomenon on the recording paper to become uneven, or a boundary region of a different color. Therefore, it is necessary to provide a recording sheet with high ink absorbency, since the colors tend to blur and the image quality is likely to be greatly reduced.

[0005] To solve these problems, a great many techniques have been proposed. For example, JP
JP-A-5-53012 describes a recording paper in which a coating for surface processing is wetted on a low-size base paper.
No. 5830, a recording paper provided with an ink-absorbing coating layer on the surface of a support, and a non-colloidal silica powder as a pigment in a coated layer described in JP-A-56-157. Recording paper, a recording paper using a combination of an inorganic pigment and an organic pigment described in JP-A-57-107878,
JP-A-58-11287 discloses a recording paper having two pore distribution peaks.
No. 1782, recording paper comprising two upper and lower porous layers, JP-A-59-68292 and JP-A-59-12.
Recording papers having irregular cracks described in JP-A Nos. 3696 and 60-18383.
No. 135786, No. 61-148092 and No. 62
And recording paper having a fine powder layer described in JP-A-149475, JP-A-63-252779,
-108083, 2-136279, 3-65
Nos. 376 and 3-27976, recording papers containing pigments having specific physical properties and fine-particle silica, JP-A-57-14091 and JP-A-60-2190.
No. 83, No. 60-210984, No. 61-20797
No. 61-188183, JP-A-5-278324
Nos. 6-92091, 6-183134, 7
Recording paper containing fine-particle silica such as colloidal silica described in JP-A-137431 and JP-A-7-276789, and JP-A-2-276671, JP-A-3-27671.
Nos. 67684, 3-215082 and 3-25
No. 1488, No. 4-67986, No. 4-263983
And a large number of recording papers containing alumina hydrate fine particles described in JP-A-5-16517 and JP-A-5-16517 are known.

[0006] Among them, a gap type recording paper using minute inorganic fine particles and a hydrophilic binder and having minute gaps formed in the ink receiving layer is preferable as a high quality glossy paper because relatively high gloss can be obtained. It is. It is preferable to use, as such inorganic fine particles, fine particle silica having an anionic surface, since excellent gloss can be obtained.

As the silica, a wet method, a gas phase method (dry method)
Silica is well known. As a method for producing a high-concentration wet silica (water-dispersible silica or colloidal silica) colloidal dispersion, a wet silica powder is heat-treated as disclosed in JP-A-10-329412, and then dispersed at a high pH (up to 11). Techniques for reducing viscosity have been disclosed. However, as described above, wet silica is often dispersed in an alkali having a pH of 8 to 12, but has a large number of surface silanol groups, and when formed into a coating film, the particles are oriented with high density, and it is difficult to obtain a high porosity. At a high pH, there is a problem that it is difficult to uniformly adsorb the cationic polymer as a mordant.

On the other hand, fumed silica generally has a pH of 4 when dispersed.
Although it shows an acidity of ~ 5, there was a problem that the thixotropic property was high and the silica solid content concentration could not be increased in production. The inventor has conducted intensive studies to disperse the fumed silica in the presence of a boric acid compound to form a dispersion having a lower viscosity than the acidic region in the neutral region at pH 5 to 8, which is a region where the gelation rate is high. I found that it can be manufactured. JP-A-6-220
No. 354 discloses a gas phase method comprising the addition of dry silica or dry aluminum silicate, and at least one colloidal auxiliary selected from the group consisting of phosphoric acid compounds, molybdate compounds, borate compounds and silicate compounds. A technique for suppressing the formation of a network structure of silica in water and reducing the viscosity has been disclosed.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a dispersion of an ink jet recording medium having high concentration and high productivity, a method for producing the same, and an ink jet recording medium having a high porosity.

[0010]

[Means for Solving the Problems] An ink receiving layer coating solution of an ink jet recording medium having an ink receiving layer containing at least one inorganic fine particle and a binder on a substrate is kneaded at pH 5 to 8 in the presence of a boric acid compound.
An ink jet recording medium dispersion containing a dispersion of fumed silica dispersed therein.

2. After kneading and dispersing the fumed silica at a pH of 5 to 8 in the presence of a boric acid compound, the cationic resin is p-pulverized.
2. The inkjet recording medium dispersion according to the above 1, wherein the dispersion is added and dispersed in H2 to H7.

3. An ink receiving layer coating solution of an ink jet recording medium having at least one ink receiving layer containing at least one inorganic fine particle and a binder on a base material has a hydrophilic particle having a primary particle diameter of 5.0 to 30 nm with respect to a hydrophilic solvent. An ink jet recording medium dispersion comprising a dispersion in which a hydrophobic silica particle and a hydrophobically treated silica particle are mixed and dispersed at a solid content ratio of 90:10 to 70:30.

4. 4. The method for producing a dispersion of an ink jet recording medium, wherein the step of kneading and dispersing the dispersion of the ink jet recording medium according to any one of the above 1 to 3 is a continuous method.

5. 4. An ink jet recording medium, wherein at least one layer of the ink jet recording medium dispersion liquid according to any one of the above items 1 to 3 is applied on a substrate.

Hereinafter, the present invention will be described in detail. Aerosil series manufactured by Nippon Aerosil Co., Ltd., for example, is commercially available as fine-particle silica synthesized by a gas phase method. The primary particle diameter of the silica particles is preferably from 5.0 to 30 nm, more preferably from 7.0 to 15 nm. If it is 30 nm or more, light scattering is large, and sufficient transparency cannot be obtained. On the other hand, when the particle size is 5.0 nm or less, the dispersion step becomes extremely difficult. Here, the average particle size of the inorganic fine particles is obtained as a simple average value (number average) by observing the particle size of 100 arbitrary particles by observing with an electron microscope. Here, each particle size is represented by a diameter assuming a circle equal to the projected area.

The boric acid compound is a boric acid or a salt thereof, which is an oxyacid having a boron atom as a central atom and a salt thereof, specifically, orthoboric acid, diboric acid, metaboric acid, tetraboric acid, and pentaboric acid. And octaboric acid and their salts. Most preferably, orthoboric acid, tetraborate or a mixture thereof is preferred.

The pH of the mixed dispersion of fumed silica and boric acid compound is preferably 5.5 to 7.0. 5.5-
6.5 is preferred. In general, when the pH is 6 to 8, the gel acceleration of silica is high, so that it has not been conventionally performed in this pH range.

The inventor of the present invention has studied diligently that a boric acid compound is mixed with fumed silica particles and the pH is adjusted to a specific value so that an increase in viscosity and gelation of fumed silica at a high concentration can be suppressed. Was found. When the pH is 8 to 9, silanol groups on the silica surface are largely dissociated and the viscosity of the dispersion can be reduced, but it is difficult to uniformly adsorb the cationic polymer to the silica particles. At a pH higher than this, the silica particles are dissolved, and the surface properties change.
On the other hand, the pH value of an aqueous dispersion of a fumed silica is usually 3.5 to 3.5.
In the region of 4.5, the viscosity increases due to the hydrogen bond between the silanol groups, and the effect of mixing the boric acid compound is lost.

The concentration of the silica dispersion according to the present invention is preferably 25% or more, more preferably 30% or more when the primary particle diameter is 7.0 nm.

In the present invention, the fumed silica particles are preferably used by forming cationic composite particles together with a cationic polymer represented by the following general formula (1).

[0021]

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In the general formula (1), R and R 'are a hydrogen atom or an alkyl group having 1 to 4 carbon atoms,
Preferably it is a hydrogen atom or a methyl group. R ₁ , R ₂ ,
R ₃ , R ₁ ′, R ₂ ′ and R ₃ ′ each represent an alkyl group, preferably a methyl group or an ethyl group. Each of the alkyl groups may have a substituent. A and J represent a divalent linking group, where A is a mere bond, -C
It is preferably ONH- or -COO-. J is preferably a simple bond or a -CON (R ")-group (R" represents a hydrogen atom or an alkyl group which may have a substituent). X ₁ ^- and X ₂ ^- represent anion groups (halogen ion, methyl sulfate ion, p-toluenesulfonic acid ion, etc.). Q represents a repeating unit derived from a monomer having an ethylenically unsaturated group. Specific examples of the monomer of Q include, for example, styrene, butadiene, methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, hydroxyethyl methacrylate, vinyl acetate, vinyl ether, acrylamide, N-methylacrylamide , N-vinylimidazole, 4-vinylpyridine, N-vinylpyrrolidone, vinyl chloride and the like. Q includes the case where two or more monomers are copolymerized. x is 10 to 95 mol%, preferably 20 to 80 mol%, y is 5 to 90 mol%,
Preferably it is 10 to 60 mol%, and z is 0 to 60 mol%, preferably 0 to 40 mol%. The cationic polymer represented by the general formula (1) needs to have a number average molecular weight of 100,000 or less. Preferably it is 50,000 or less. The lower limit of the number average molecular weight is about 2 from the viewpoint of the water resistance of the dye.
000 or more, and particularly preferably 5000 or more. The ratio of the silica particles to the cationic polymer can vary depending on the particle size of the silica particles, or the type and average molecular weight of the cationic polymer, but is generally from 1: 0.01 to 1: 1.

Next, specific examples of the cationic polymer composition represented by the general formula (1) will be shown.

[0024]

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[0025]

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[0026]

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[0027]

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[0028]

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The pH at the time of preparing the cationic dispersion is 2
To 7, more preferably 4 to 6. Since the surface of the silica particles is anionic, once the cationic polymer is added, aggregation occurs once. For this reason, it is preferable to further perform dispersion in order to return to the original aggregation diameter.

Generally, silica particles have a hydrophilic surface,
The feature of the fumed silica is that the surface silanol group is small. In the void-type ink receiving layer, the silica particles form secondary aggregates, and the gaps between the aggregates become voids. At this time, it is considered that the number of surface silanol groups affects the formation of voids, and therefore, control of the number of surface silanol groups is important. Silanol groups on the fumed silica surface can be chemically modified with halosilanes, alkoxysilanes, siloxane, and the like. The hydrophobically treated silica particles have features such as low moisture adsorption and low silanol group density. Hydrophobic silica can reduce the thickening effect in a liquid, so that it can be dispersed in a state of relatively low viscosity even at a high concentration by being mixed with hydrophilic silica. As the hydrophobizing treatment, 60% to 90% of the hydrophilic silanol group is preferable, and 70% to 80% is more preferable. If it is less than 60%, the effect of the viscosity reduction is reduced. On the other hand, if it exceeds 90%, it becomes difficult to disperse it in a hydrophilic solvent even when mixed with hydrophilic silica. The degree of the hydrophobization treatment can be known from a change in the number of silanol groups such as an infrared spectrum.

The mixing ratio of the hydrophilic silica to the hydrophobic silica is 90:10 to 70:30 by mass, but is 85:15 to 8
0:20 is more preferred. As the proportion of hydrophobic silica decreases, the effect of viscosity reduction also decreases. Further, it becomes difficult to disperse the hydrophobic silica in the hydrophilic solvent.

The hydrophilic silica and the hydrophobic silica may be mixed in a powder state and then kneaded and dispersed, or they may be separately dispersed and then mixed, but the former is more preferable. Further, alcohols may be added.

The viscosity of the silica dispersion obtained according to the present invention is preferably 2 Pa · s or less, more preferably 1 Pa · s or less.

The production of fumed silica used in the present invention comprises a step of mixing and kneading silica powder and a hydrophilic solvent, and a dispersion step of atomizing silica aggregates to a desired particle size. An ordinary kneader can be used for kneading the fumed silica used in the present invention. For example, horizontal cylindrical type, V type and other container rotary mixers, screws, lots, pins,
A mechanical stirring-type mixer using a double-shaft paddle, a gas-flow stirring-type mixer, or the like can be used. In the present invention, a mechanical stirring type mixer particularly subject to high shear is most preferable.

For dispersing the fumed silica used in the present invention, an ordinary disperser can be used. As the dispersion treatment method, various types of conventionally known dispersers such as a high-speed rotation disperser, a medium stirring type disperser (such as a ball mill and a sand mill), an ultrasonic disperser, a colloid mill disperser, a roll mill disperser, and a high-pressure disperser can be used. Although it can be used, a sand mill disperser is most preferred. Ultrasonic dispersers are usually 20-25
Irradiating ultrasonic waves of kHz disperses energy by concentrating energy on the solid-liquid interface, and is dispersed very efficiently. However, when a large amount of dispersion liquid needs to be prepared, it is not suitable. Absent.

The kneading / dispersing step may be carried out in any of a batch mode and a continuous mode. However, in the present invention, it is preferable to use a continuous type kneading / dispersing apparatus having no stagnation of the dispersion liquid. High-concentration fumed silica dispersion has a large increase in viscosity over time,
If there is a stagnation due to a waiting time in the manufacturing process or a failure, the workability and operability of the liquid will be significantly deteriorated due to the increase in viscosity,
As the productivity decreases, physical properties such as film strength after coating change. The time from the production of the silica dispersion to the coating and drying is preferably within 5 hours, more preferably within 3 hours.

FIG. 1 is a schematic diagram of a completely continuous dispersion system in which a plurality of dispersion machines are connected in series according to the present invention.

After producing the silica dispersion of the present invention, the dispersion is mixed with a hydrophilic binder to produce a recording medium. As the hydrophilic binder used in the present invention, conventionally known various hydrophilic binders are used, and a hydrophilic binder which does not show aggregation or a remarkable thickening action when mixed with the cationic composite fine particles of the present invention is preferable. . Examples of such a hydrophilic binder include gelatin (preferably acid-treated gelatin), polyvinylpyrrolidone (preferably having an average molecular weight of about 200,000 or more), pullulan,
Polyvinyl alcohol or a derivative thereof, polyethylene glycol (preferably having an average molecular weight of 100,000 or more), hydroxyethyl cellulose, dextran, dextrin, and water-soluble polyvinyl butyral can be used. These hydrophilic binders may be used alone. Two or more kinds may be used in combination. Particularly preferred hydrophilic binders are polyvinyl alcohol or cation-modified polyvinyl alcohol.

The polyvinyl alcohol preferably used in the present invention preferably has an average degree of polymerization of 300 to 4,000, and is particularly preferable because the film having an average molecular weight of 1,000 or more has good brittleness.
The saponification degree of polyvinyl alcohol is 70 to 100.
%, Particularly preferably 80 to 100%.

The hydrophilic binder is used in a relatively small amount with respect to the inorganic fine particles so that the ink absorbing layer becomes a void layer, so that the film is formed stably and the adhesion to the support can be sufficiently maintained. It is preferred to use as little as possible in the range. In general, the weight ratio is about 1/3 to 1/10, particularly 1/4 to 1/8, relative to the inorganic fine particles.

In the production process of the present invention, various additives other than those described above can be added. For example, organic latex fine particles such as polystyrene, polyacrylates, polymethacrylates, polyacrylamides, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, or a copolymer thereof, a urea resin, or a melamine resin. , Liquid paraffin, dioctyl phthalate, tricresyl phosphate, fine oil droplets such as silicone oil, various cationic or nonionic surfactants, JP-A-57-74193, and JP-A-57-8.
Ultraviolet absorbers described in JP-A Nos. 7988 and 62-261476, JP-A-57-74192 and JP-A-57-74192.
87989, 60-72785, 61
Discoloration inhibitors described in JP-A-146591, JP-A-1-95091 and JP-A-3-13376, JP-A-59-42993, JP-A-59-5268.
No. 9, No. 62-280069, No. 61-24
No. 2871 and JP-A-4-219266, a fluorescent whitening agent, a pH adjuster such as sulfuric acid, phosphoric acid, citric acid, sodium hydroxide, potassium hydroxide, potassium carbonate, an antifoaming agent, Various known additives such as a preservative, a thickener, an antistatic agent and a matting agent can be added. The addition may be carried out during the production process, but preferably after silica dispersion, and more preferably after addition of a hydrophilic binder.

[0042]

The present invention will be described below with reference to examples of the present invention.
The present invention is not limited to these examples.

Example 1 [Preparation of Silica Dispersion A] Gas-phase method silica fine particles (average primary particle diameter: 7 nm, Aerosil A300 (manufactured by Nippon Aerosil Co., Ltd.)) 250 g Ion-exchanged water 881 ml Ion-exchanged water at 25 ° C. Was added to the mixture and pre-dispersed for 20 minutes using a dissolver. Thereafter, the mixture was further dispersed for 20 minutes using a sand mill disperser to obtain a 25% by mass silica fine particle dispersion. P of the resulting dispersion
H was 3.70. An aqueous solution containing 20% by mass of the cationic polymer P-1 (average molecular weight = about 25,000), 3% by mass of n-propanol, and 1% by mass of ethanol (pH = 2.5, Sannobco Co., Ltd.) in 534 ml of this dispersion liquid 80 ml of an antifoaming agent SN381 (containing 0.2 g) was added at room temperature with stirring. Next, boric acid and borax 1:
1 mixed aqueous solution (boric acid and borax are each 7% by mass
74 ml) was added slowly with stirring. Subsequently, the dispersion was further performed for 20 minutes using a post-sand mill disperser to obtain a silica dispersion A having a solid content of 21% and a pH of 4.55.

The viscosity after dispersion was about 0.85 Pa · s as measured by a B-type viscometer. The turbidity value is 15pp
m.

[Preparation of Silica Dispersion B] Vapor-phase method silica fine particles (average primary particle diameter: 7 nm, Aerosil A300 (manufactured by Nippon Aerosil Co., Ltd.)) 300 g ion-exchanged water 858 ml Silica fine particles in ion-exchanged water at 25 ° C. Was added and pre-dispersed for 30 minutes using a dissolver. Thereafter, the mixture was further dispersed for 25 minutes using a sand mill disperser to obtain a 30% by mass silica fine particle dispersion. P of the resulting dispersion
H was 3.60. An aqueous solution containing 20% by mass of cationic polymer P-1 (average molecular weight = about 25,000), 3% by mass of n-propanol, and 1% by mass of ethanol (pH = 2.5, Sannobco Co., Ltd.) in 904 ml of this dispersion liquid 93 ml of an antifoaming agent SN381 (containing 0.2 g) was added at room temperature with stirring. Next, boric acid and borax 1:
1 mixed aqueous solution (boric acid and borax are each 7% by mass
86 ml) was added slowly with stirring. Subsequently, dispersion was further performed for 20 minutes using a post-sand mill disperser to obtain a silica dispersion B having a solid concentration of 24.5% and a pH of 4.50. The dispersion had a viscosity of 1.93 Pa · s and a turbidity value of 43 ppm.

[Preparation of Silica Dispersion C] Vapor-phase method silica fine particles (average primary particle diameter: 7 nm, Aerosil A300 (manufactured by Nippon Aerosil Co., Ltd.)) 300 g Deionized water 772 ml 1: 1 of boric acid and borax 86 ml of the mixed aqueous solution (containing 7% by mass each of boric acid and borax) At 25 ° C., silica fine particles were added to ion-exchanged water, and pre-dispersed using a dissolver for 30 minutes. Thereafter, the mixture was further dispersed for 25 minutes using a sand mill disperser to obtain a 30% by mass silica fine particle dispersion. P of the resulting dispersion
H was 5.8. To 904 ml of this dispersion, 20% by mass of cationic polymer P-1 (average molecular weight = about 25,000), 3% by mass of n-propanol, and 1% of ethanol were added.
93 ml of an aqueous solution (pH = 2.5, containing 0.2 g of an antifoaming agent SN381 manufactured by Sannobuco) containing 8% by mass and pure water 8
6 ml were added with stirring at room temperature. Subsequently, the mixture was further dispersed for 20 minutes using a post-sand mill disperser to obtain a silica dispersion C having a solid concentration of 24.5% and a pH of 4.55. The viscosity of the dispersion was 1.20 Pa · s, and the turbidity value was 17 ppm.

[Preparation of Silica Dispersion D] Vapor-phase-processed silica fine particles (average primary particle diameter: 7 nm, Aerosil A300 (manufactured by Nippon Aerosil Co., Ltd.)) 300 g Deionized water 772 ml 1: 1 of boric acid and borax 86 ml of mixed aqueous solution (both of 7% by weight each of boric acid and borax) 5 mol / L nitric acid aqueous solution pH 4.5 necessary adjustment amount Dispersion solution before addition of cationic polymer Dispersion except for adding nitric acid aqueous solution so that pH becomes 4.5 A silica dispersion D was obtained in the same manner as for the liquid C. The viscosity and turbidity values of the dispersion are shown in Table 1.

[Preparation of Silica Dispersion E] Vapor-phase-processed silica fine particles (average primary particle diameter: 7 nm, Aerosil A300 (manufactured by Nippon Aerosil Co., Ltd.)) 300 g Deionized water 772 ml 1: 1 of boric acid and borax 86 ml of a mixed aqueous solution (both of 5% by weight each of boric acid and borax) 10% aqueous solution of sodium hydroxide pH 7.0 Adjustment required Aqueous sodium hydroxide solution is added so that the pH of the dispersion before adding the cationic polymer becomes 7.0. Except for the above, a silica dispersion E was obtained in the same manner as the dispersion C. The viscosity and turbidity values of the dispersion are shown in Table 1.

[Preparation of Silica Dispersion F] Vapor-phase method silica fine particles (average primary particle diameter: 7 nm, Aerosil A300 (manufactured by Nippon Aerosil Co., Ltd.)) 300 g ion-exchanged water 772 ml 1: 1 of boric acid and borax 86 ml of the mixed aqueous solution (both of 7% by weight each of boric acid and borax) 10% aqueous solution of sodium hydroxide pH 8.5 Necessary amount for adjustment Add the aqueous solution of sodium hydroxide so that the pH of the dispersion before adding the cationic polymer becomes 8.5. Except for the above, a silica dispersion F was obtained in the same manner as in the dispersion C. The viscosity and turbidity values of the dispersion are shown in Table 1.

Using the dispersions A to F obtained, the following additives were sequentially added at 45 ° C. to prepare coating solutions.

<Preparation of Coating Solution A> Dispersion A 100 ml Polyvinyl alcohol (PVA203 manufactured by Kuraray Co., Ltd.) 10% aqueous solution 1 ml Polyvinyl alcohol (PVA235 manufactured by Kuraray Co., Ltd.) 5% aqueous solution 63 ml Pure water 26 ml <Coating solutions B to F Preparation> Dispersions B to F 100 ml Polyvinyl alcohol (PVA203 manufactured by Kuraray Co., Ltd.) 10% aqueous solution 1.2 ml Polyvinyl alcohol (PVA235 manufactured by Kuraray Co., Ltd.) 5% aqueous solution 75.6 ml Pure water 26 ml Coating obtained as described above The solution was coated on a paper support (thickness: 24 g) coated with polyethylene on both sides of 170 g / m ² base paper
0 μm, on the recording surface side, a 35 μm thick polyethylene layer containing 9% by mass of anatase type titanium dioxide, the back surface having a thickness of about 30 μm polyethylene layer) on the recording surface side (75 ° glossiness of the support: 32%, gelatin about 0.1 g / m ²
Was applied so as to have a film thickness of 35 μm after drying.

Using a Bristow tester type II (pressurized type) manufactured by Kumagaya Riki Kogyo Co., Ltd., the transfer amount (ml / m ² ) in a contact time of 2 seconds was determined as the void volume for the obtained sample. It is shown in Table 1.

[0053]

[Table 1]

As can be seen from Table 1, since the concentration of the fumed silica fine particles in the dispersion A is low, the viscosity and turbidity values are low, and the void amount does not decrease. However, in the dispersion B in which the concentration of the fumed silica fine particles was 1.2 times under substantially the same conditions, the viscosity and the turbidity value increased, and the void amount also decreased. On the other hand, the dispersion C of the present invention has a low viscosity and a low turbidity value, and the void amount does not decrease even though the concentration of the fumed silica fine particles is the same as that of the dispersion B. Similarly, in dispersions DF in which the pH of the dispersion is changed,
It can be seen that only the dispersion E of the present invention has a low viscosity of the dispersion and the void amount does not decrease despite the high concentration.

Example 2 [Preparation of Silica Dispersion G] Ion-exchanged water 586.4 ml Ethanol 13.46 ml 1: 1 mixed aqueous solution of boric acid and borax 147.3 ml (both acid and borax each contained 7% by mass Aqueous solution containing 20% by mass of cationic polymer P-1 (average molecular weight = about 25,000), 3% by mass of n-propanol, and 1% by mass of ethanol (pH = 2.5, defoamer manufactured by Sannobuco) 132 g of SN381).
After mixing and dissolving 3 ml, 250 g of fumed silica fine particles (average primary particle diameter: 7 nm, Aerosil A300 (manufactured by Nippon Aerosil Co., Ltd.)) was added, and pre-dispersion was performed for 30 minutes using a dissolver. Thereafter, the mixture was further dispersed for 25 minutes using a sand mill disperser to obtain a 25% by mass silica fine particle dispersion. The pH of the resulting dispersion was 4.50. The viscosity of the dispersion was 1.95 Pa · s and the turbidity value was 40 ppm.

[Preparation of Silica Dispersion H] The silica fine particles of the silica dispersion G were prepared by the following gas phase method (hydrophilic) silica fine particles (average primary particle diameter: 7 nm, Aerosil A300 (manufactured by Nippon Aerosil Co., Ltd.)) 225 g hydrophobic Silica dispersion H having a pH of 4.50 was obtained in the same manner as the dispersion G except that the particle size of the silica was 25 g (average primary particle diameter: 12 nm, Aerosil R974 (manufactured by Nippon Aerosil Co., Ltd.)). The viscosity of the dispersion is 1.76 Pa
s and the turbidity value was 19 ppm.

[Preparation of Silica Dispersion I] A silica dispersion I was prepared in the same manner as the dispersion G except that the mixing ratio of the fumed silica and the hydrophobic silica was changed to 8: 2. The viscosity and turbidity values of the dispersion are shown in Table 2.

[Preparation of silica dispersion J] A silica dispersion J was prepared in the same manner as the dispersion G except that the mixing ratio of the fumed silica and the hydrophobic silica was changed to 6: 4. The viscosity and turbidity values of the dispersion are shown in Table 2.

Using the dispersions G to J obtained, coatings G to J were prepared in the same manner as in the preparation of coatings B to F in Example 1.

The coating solution obtained as described above was
0 g / m ² base paper coated on both sides with polyethylene coated paper support (240 μm thick, 9 μ% of anatase type titanium dioxide in a 35 μm thick polyethylene layer on the recording side, about 30 μm thick on the back side Coated on the recording surface side (75 ° glossiness of the support is 32%, gelatin is about 0.1 g / m ^{2, which is} already coated as a subbing layer) so that the film thickness after drying is 35 μm. did.

Using a Bristow tester type II (pressurized type) manufactured by Kumagai Riki Kogyo Co., Ltd., the transition amount (ml / m ² ) in a contact time of 2 seconds was determined as the void volume for the obtained sample. It is shown in Table 2.

[0062]

[Table 2]

As can be seen from Table 2, since the dispersion liquid G was only the fumed silica fine particles, the viscosity and turbidity values increased, and the void amount also decreased. On the other hand, the dispersions H and I of the present invention are obtained by mixing fumed silica fine particles and hydrophobic silica fine particles, and the mixing ratio is within the range of the present invention. The viscosity and turbidity values are low and the void volume does not decrease. However, even when the fumed silica fine particles and the hydrophobic silica fine particles were mixed, the dispersion J in which the mixing ratio was outside the present invention had an increased turbidity value, and the viscosity and void amount could not be measured.

Example 3 [Preparation of silica dispersion K] A silica dispersion was obtained by the following dispersion in the scheme of FIG.

Preparation of Aqueous Solution K Ion-exchanged water 58.6 L Ethanol 1.35 L 1: 1 mixed aqueous solution of boric acid and borax 14.7 L (both acid and borax each contained 7% by mass) Cationic polymer P-1 ( An aqueous solution containing 20% by mass (average molecular weight = about 25,000), 3% by mass of n-propanol, and 1% by mass of ethanol (pH = 2.5, containing 0.2 g of an antifoaming agent SN381 manufactured by Sannobuco). 13.2
L was mixed and dissolved.

Dispersion Vapor-phase method silica fine particles (average primary particle diameter: 7 nm Aerosil A300 (manufactured by Nippon Aerosil Co., Ltd.)) 22.5 kg Hydrophobic silica fine particles (average primary particle diameter: 12 nm Aerosil R974 (Nippon Aerosil Co., Ltd.) In FIG. 1, a 2.5 kg mixture was added at a rate of 0.4 kg / min and an aqueous solution K at a rate of 1.4 L / min in a spiral pin mixer SPM25W (manufactured by Taiheiyo Koki, hereinafter referred to as SPM). Supplied. Thereafter, the dispersion was also supplied to the SPM as a dispersing machine 2. Thereafter, LMK-4 (a continuous wet media type pulverizer, manufactured by Ashizawa; hereinafter, referred to as LMK) was used as the disperser 3, and the dispersion discharged from the disperser 2 was supplied to the LMK using a mono pump. The peripheral speed of SPM is 36m /
sec, residence time 30 seconds, LMK is 0.5 mm in bead diameter
The test was performed with a zirconia peripheral speed of 8 m / sec and a residence time of 2 minutes.

The viscosity of the obtained dispersion is 1.68 Pa ·
s, turbidity value was 17 ppm. A dispersion having low viscosity and low turbidity despite high concentration could be produced with high productivity.

[0068]

According to the present invention, a dispersion of an ink jet recording medium having a high concentration and high productivity, a method for producing the same, and an ink jet recording medium having a high porosity can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a completely continuous dispersion system in which a plurality of dispersion machines are connected in series according to the present invention.

Claims (5)

[Claims] An ink receiving layer coating solution of an ink jet recording medium having an ink receiving layer containing at least one inorganic fine particle and a binder on a substrate is kneaded and dispersed at a pH of 5 to 8 in the presence of a boric acid compound. An ink jet recording medium dispersion comprising a fumed silica dispersion. 2. Kneading and dispersing fumed silica at a pH of 5 to 8 in the presence of a boric acid compound, and then setting the cationic resin to a pH
The ink-jet recording medium dispersion according to claim 1, wherein the dispersion is added and dispersed in 2 to 7. 3. The coating liquid for an ink receiving layer of an ink jet recording medium having an ink receiving layer containing at least one layer of inorganic fine particles and a binder on a substrate has a primary particle diameter of 5.0 relative to a hydrophilic solvent. An ink-jet recording medium dispersion comprising a dispersion liquid in which hydrophilic silica particles having a diameter of 30 nm and silica particles subjected to hydrophobic treatment are mixed and dispersed at a solid content ratio of 90:10 to 70:30. liquid. 4. A method for producing a dispersion of an ink-jet recording medium, wherein the step of kneading and dispersing the dispersion of an ink-jet recording medium according to claim 1 is a continuous method. 5. An ink jet recording medium, wherein at least one layer of the ink jet recording medium dispersion liquid according to claim 1 is applied onto a substrate.