JP2000281330A - Production of dispersion of silica fine particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing silica fine particles which are capable of rapidly absorbing a large amount of ink when they are used in an ink absorbing layer of ink-jet recording sheet, thereby the surface of the absorbing layer becomes glossy and a clear full color image thick in color density can be obtained. SOLUTION: In this method for producing a dispersion of silica fine particles by hydrolyzing an alkoxy silane, the hydrolysis is carried out by using water in an amount of 40-800 mol per mole of silicon without using catalysts, thereby the silica fine particles having specific surface area of 150-500 m2/g, aggregated particle sizes of 100-250 nm when the sizes are measured using a laser particle size analyzer and a volume of 0.5-1.5 ml/g are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording material used in an ink jet recording method, and to a method for producing a silica fine particle dispersion suitably used as an ink absorbing layer.

[0002]

2. Description of the Related Art Conventionally, various systems such as a wire dot recording system, a thermosensitive color recording system, a fusion heat transfer recording system, a sublimation recording system, an electrophotographic recording system, and an ink jet recording system have been developed. I have. Among these, the ink jet recording method using an aqueous ink has been recognized as a recording method suitable for personal use because of its low running cost and compact and inexpensive hardware. Further, in recent years, the achievement of full color and high resolution has attracted attention as a means for easily outputting a color image, and is becoming widespread. In general, an ink jet recording sheet is provided with an ink receiving layer having an ink absorption property to which a porous pigment is applied to control color and sharpness that determine image quality, thereby improving color reproducibility and image reproducibility. ing.
An ink-absorbing ink-receiving layer must have many voids in the ink-receiving layer to absorb and retain the ink. As a pigment used in such an application, there is silica manufactured from water glass, an industrial product, which is available at a low cost. For example, Japanese Patent Application Laid-Open No. 9-95042 discloses an aqueous solution of alkali silicate containing 45 to 45% of sulfuric acid necessary for neutralizing the alkali silicate while maintaining the solution temperature at 30 ° C to 40 ° C.
The solution is brought to 85 ° C. to 95 ° C.
There has been disclosed a method of obtaining a hydrous silicate amorphous silica by raising the temperature to 0 ° C., continuously adding sulfuric acid until the pH becomes 3 to 4, obtaining a powder, and then pulverizing and classifying the powder. However, since the pigment obtained by such a method is large compared to the wavelength of light, the light incident on the ink receiving layer is scattered or the transmission is hindered, so that the ink becomes opaque and the ink penetrated into the voids As light hardly reaches the image, the image becomes whitish, and the color reproducibility and color density decrease. In addition, since the ink receiving layer having many voids has a porous surface, it is difficult to obtain high gloss.

[0003] Japanese Patent Application Laid-Open No. 2-278870 discloses that
An ink receiving layer comprising pseudo-boehmite is disclosed.
Water and a solvent (occupying 90% or more of the ink components) having a relatively small molecular weight in the ink are absorbed between the small primary particles, and the dye in the ink is absorbed and fixed between the large secondary particles. . In this case, the pseudo-boehmite itself has a certain degree of transparency, is excellent in fixing an anionic dye because it has cationic properties, and has a higher water resistance than an ink receiving layer composed of a water-soluble polymer. Although excellent, the following challenges remain. In other words, pseudo-boehmite is a type of alumina crystal, and the particles have a hexagonal plate shape.Secondary particles composed of primary particles having such a shape are slits in which thin plate crystals are folded over each other. It has a void structure called a pore type (Colloid Science, I Fundamentals and Dispersion / Adsorption, Chemical Society of Japan, p. 27)
4) Such pores have a relatively small void volume as compared to pores formed by secondary particles composed of spherical silica primary particles. Therefore, when used as a pigment for ink jet recording, there is a disadvantage that the ink absorbency is inferior to that of a silica pigment. In addition, ink having poor coloring properties with alumina (for example, Acid Red 52 (edible red 106)
Not suitable for red). Furthermore, pseudo-boehmite has a high cost and is not suitable for general use.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to improve the disadvantages of the conventional silica for ink jet recording sheets,
An object of the present invention is to provide a method for producing fine silica which is suitably used for an ink absorbing layer of an ink jet recording sheet. In other words, an object of the present invention is to provide a method for producing fine silica capable of quickly absorbing a large amount of ink, having a high gloss on the surface of the absorption layer, and obtaining a bright full-color image with a high color density by using the ink absorption layer. .

[0005]

Means for Solving the Problems In order to solve the above problems, the present inventors have made various studies on silica pigments.
As a method for obtaining silica, a method in which alkali silicate is treated with a mineral acid and then pulverized as described above is generally used,
The silica obtained by this method has a structure in which primary particles are aggregated. However, the silica obtained by this method has a large ink absorption capacity, but has the disadvantage that the secondary particle diameter is too large, so that the color density is low and the gloss of the ink jet recording sheet is low.

Further, it was found that the colloidal silica in which the primary particles were dispersed without agglomeration provided the transparency and gloss of the ink jet recording sheet, but had a small ink absorption capacity.

However, it has been found that fine particles obtained by hydrolyzing alkoxysilane under specific conditions become secondary particles in which primary particles are aggregated, have a large ink absorption amount, and have high transparency. Reached.

It is known that silica is formed when an alkoxysilane is hydrolyzed. The alkoxysilane is hydrolyzed using an acidic or basic catalyst to synthesize a gel composed of silica fine particles, and then the gel is dried. Thereafter, a method for producing quartz glass by firing is well known (for example, “Sol-gel method science” by Sakubana S., p28,
Agune Shofusha Publishing). It is also known that monodisperse silica can be produced by hydrolyzing alkoxysilane (W.
Stover et al., JOURNAL OF COLLOID
AND INTERFACE SCIENCE, 26th
Vol. 62-69, 1968). However, the inventors of the problem is neither in monodisperse silica gel, particle size specific surface area is caused by the silica primary particles aggregate is ^{150m 2 / g~500m 2 / g 10nm~250nm} ,
The present invention also relates to a method for producing a dispersion in which secondary particles having a pore volume of 0.5 ml / g to 1.5 ml / g are stably dispersed in a solvent.

According to the present invention, a much larger amount of water is used in hydrolyzing an alkoxysilane than that used in the conventional sol-gel method, and a hydrolysis catalyst such as an acid or a base is used in performing the hydrolysis. By doing so, a dispersion of the desired silica fine particles is obtained.When the silica fine particles are used in the ink receiving layer of the inkjet recording sheet, a large amount of ink can be absorbed, and high gloss and print density can be obtained. Was found. The present invention is based on such findings.

The first aspect of the present invention is a method for producing a silica fine particle dispersion by hydrolyzing an alkoxysilane, wherein the hydrolysis is carried out using 40 to 800 mol of water per mol of silicon, and using a catalyst. by performing without using the specific surface area of 150m ² / g~500m ² / g,
Secondary particle size by laser granulometer is 10nm ~ 250n
m and the pore volume is 0.5 ml / g to 1.5 ml / g
A method for producing a silica fine particle dispersion, characterized by obtaining silica fine particles.

[0011] The second invention of the present invention relates to the method described in the first invention, wherein the temperature of water and the alkoxysilane is previously adjusted to 25 ° C. or less, mixed, and then the mixture is heated with stirring to carry out hydrolysis. And the method for producing a silica fine particle dispersion according to the first aspect of the present invention. Here, the hydrolysis is preferably performed at a temperature between 40 ° C and 100 ° C.

[0012]

The specific surface area of silica fine particles produced by DETAILED DESCRIPTION OF THE INVENTION The present invention is 150m ² / g~500m ² / g,
Secondary particle size by laser granulometer is 10nm ~ 350n
m and the pore volume is 0.5 ml / g to 1.5 ml /
g. A small specific surface area means that the primary particle diameter is large, and a large specific surface area means that the primary particle diameter is small. When the spherical silica particles are monodisperse colloidal silica, the diameter of the particles is D (nm) = 2.727 × 1
0 ³ / specific surface area (m ² / g), but it is difficult to accurately determine the diameter of the primary particles of the silica fine particles of the present invention because the primary particles are chemically bonded to form secondary particles. It is. When the silica fine particles produced by the present invention were observed with a transmission electron microscope (trade name: H-300 type Hitachi Electron Microscope, manufactured by Hitachi, Ltd.), a structure in which spherical primary particles having a diameter of 5 nm to 20 nm were loosely aggregated was observed. Was. For this reason, in the present invention, the particle diameter of the primary particles is represented by the specific surface area. When the silica specific surface area of the present invention is smaller than the above range, when applied as an inkjet receiving layer, light scattering is increased, the transparency of the ink receiving layer is reduced, and the print density is undesirably reduced. Conversely, if it is larger than the above range, various problems occur. For example, since the primary particles are too small, it is difficult to concentrate the silica fine particle dispersion, and when the silica fine particles are forcibly concentrated, the silica particles excessively aggregate and gelation of the dispersion is caused. Further, when a dilute solution of silica fine particles is applied without sufficiently concentrating, it is difficult to obtain a sufficient coating amount. In addition, if the specific surface area of the silica fine particles is larger than the above range, the capillary shrinkage of the ink receiving layer becomes remarkably large, so that cracks are caused at the time of drying, surface smoothness is reduced, and various problems such as a decrease in gloss occur. By controlling the specific surface area within the above range, a silica fine particle dispersion having high transparency and excellent workability can be obtained.

The silica fine particles produced by the present invention have a secondary particle size of 10 nm to 250 nm as measured by a laser granulometer. The secondary particle diameter of the present invention was measured using a laser granulometer utilizing the principle of the dynamic light scattering method. The suspended solution and the fine particles dispersed in the solution have Brownian motion.
The movement is slow for large particles and fast for small particles. When this solution is irradiated with laser light (He-Ne laser), the light is scattered by Rayleigh scattering, causing a Doppler shift. By observing and analyzing the shift of the frequency using the photon detection method, the particle size and the particle size distribution can be obtained. In the present invention, the particle diameter was measured in a state where the fine particles obtained by synthesis were sufficiently diluted in water. Since the primary particle diameter of the present invention has a size of at least about 5 nm, the secondary particle diameter does not take a value smaller than the above range. When the secondary particle diameter is larger than the above range, when fine particles are applied to the ink receiving layer, micro unevenness occurs on the surface, and the gloss is reduced.

The fine silica particles produced in the present invention have a pore volume of 0.5 ml / g to 1.5 ml / g. When the pore volume is smaller than the above range, when the ink is mixed with the binder and applied, the voids in the ink receiving layer are reduced, and the ink cannot be sufficiently absorbed. It is not preferable to obtain a void volume larger than the above range because it is necessary to further reduce the primary particles. The pore volume as referred to in the present invention is determined by applying a silica fine particle dispersion to a PET film, drying at 105 ° C., peeling the coating film from the dispersion, and then subjecting the sample to nitrogen adsorption using Coulter SA3100. Means the integrated volume of pores having a diameter of 100 nm or less as the corresponding pore diameter.

Hereinafter, the manufacturing method will be described in detail. As the alkoxysilane used in the present invention, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetra-n-butoxysilane, tetra-sec-
Butoxysilane, tetra-tert-butoxysilane and the like can be used as a raw material, and an oligomer obtained by condensation of these alkoxysilanes may be used. Among them, tetraethoxysilane is particularly preferable.

According to the present invention, 40 to 800 moles, preferably 50 moles, per mole of silicon contained in the alkoxysilane is used.
To form secondary particles after forming primary particles by subjecting to hydrolysis and polycondensation by adding water of ８００800 mol, more preferably 100-400 mol.

If the hydrolysis is carried out with less than 50 moles of water per mole of silicon contained in the alkoxysilane, the aggregation of particles is excessively promoted and coarse secondary particles are formed, which is not suitable. Conversely, water per mole of silicon is 8
If it exceeds 00 mol, secondary particles are not formed, probably because the frequency of collision between the primary particles of the hydrated silica in the aqueous solution is relatively low.

In the present invention, it is important to carry out the hydrolysis without using a catalyst. It is known that the reaction mechanism of the hydrolysis of alkoxysilane is different under acidic conditions and basic conditions (for example, “Sol-gel method science” by Sakuhana Sakubana, p160, Agne Shofusha Publishing, Ceramics 31, 1996, No. 6). When hydrolysis is carried out under acidic conditions, a large number of clusters of hydrated silicic acid are generated, probably due to the formation of chain polysiloxanes, and the resulting primary particles tend to be too small. Because the surface energy of the generated silica fine particles is large,
When concentrated, the primary particles tend to agglomerate and the secondary particles tend to be too large. Conversely, when hydrolysis is performed under basic conditions, silica particles having a large primary particle diameter are obtained, probably because the hydrolysis and condensation reactions are performed three-dimensionally. However, it has been found that the fine particles obtained in this way do not produce secondary particles that can sufficiently absorb the ink, probably because the primary particles are too large.

In the production method of the present invention, the temperatures of the water and the alkoxysilane are previously adjusted to 25 ° C. or less, and then mixed,
It is then desirable to carry out the hydrolysis by heating the mixture with stirring. 25 ° C when mixing
Above, the primary particle size tends to be small and the secondary particle size tends to be too large. The reason for this phenomenon is unknown, but when the temperature is high, hydrolysis starts from the moment water and alkoxysilane are mixed, and a large number of silica hydrate particles are generated due to the formation of a large number of hydrated silica clusters. To form small primary particles. In the present invention, the hydrolysis temperature when producing the silica fine particles is preferably from 40 ° C to 100 ° C, and more preferably from 70 ° C to 100 ° C.
C is more preferred. If the temperature is lower than 40 ° C., the dispersion stability of the resulting silica fine particles is deteriorated due to the small size of the primary particles of the hydrated silicic acid produced, and the dispersion may gel or the secondary particle diameter may be excessive. is there. If the temperature exceeds 100 ° C., bumping of ethanol produced by hydrolysis may occur. The hydrolysis time is preferably between 3 and 40 hours, more preferably between 6 and 24 hours. If the time is less than 3 hours, the hydrolyzed hydrated silica is not sufficiently condensed, and the desired effect cannot be obtained. If the hydrolysis time exceeds 40 hours, the aggregation of the particles will proceed too much, and the dispersion may be gelled, which is not preferable from the viewpoint of productivity.

After the hydrolysis is completed, it is preferable to remove excess water and alcohol generated as a result of the hydrolysis to concentrate the silica fine particles, and an evaporator or an ultrafiltration membrane can be used as a concentration device.

The surface of the obtained fine particles may be modified with a silane coupling agent,
It is also possible to modify the silica surface with various compounds such as a cationizing agent to impart various functions such as light resistance.

[0022]

EXAMPLES The present invention will be described in more detail with reference to the following examples. The method of measuring test items described in the examples and comparative examples is as follows.

<Measurement of Surface Area, Pore Diameter, and Pore Volume> A silica fine particle dispersion was applied to a PET film, dried at 105 ° C.
The measurement was performed by a nitrogen adsorption method using a model SA3100 manufactured by ER Co., Ltd.

<Method for Measuring Secondary Particle Size of Fine Particles> Laser particle size distribution meter (trade name LPA3000, manufactured by Otsuka Electronics Co., Ltd.)
/ 3100). The measurement principle is based on the laser method. This measurement is based on a light scattering method based on the principle that particles in a liquid undergoing Brownian motion are irradiated with He-Ne laser light, light is scattered by Rayleigh scattering, and Doppler shift is caused by the motion of the particles. is there.

Example 1 5 liter glass reaction vessel (separable flask, stirring blade, thermometer)
And 1440 g of distilled water is charged and kept at 18 ° C. Next, 92.3 g of tetraethoxysilane (0.421 mol, manufactured by Wako Pure Chemical Industries, held at 20 ° C. while stirring)
(Purity: 95%) (H ₂ O (mol) / Si (mol) = 190), and then reacted at 95 ° C. for 24 hours. The obtained reaction solution was concentrated to obtain silica having a solid content of 12%. A fine particle dispersion was obtained.

The specific surface area of the obtained silica fine particles is 311
m ² / g, and the secondary particle diameter was 56 nm. The pore diameter was 16 nm, and the pore volume was 0.978 ml / g.

<Example 2> In Example 1, the temperature of distilled water was 25 ° C, and the temperature of tetraethoxysilane was 10 ° C.
C., the amount of addition was 331 g (1.51 mol) (H ₂ O (mol) / Si (mol) = 53), and the dispersion of silica fine particles was carried out in the same manner as in Example 1 except that the temperature after the addition was 75 ° C. A liquid was obtained. The specific surface area of the obtained silica fine particles is 455 m ² /
g, the secondary particle diameter was 220 nm. Average pore size is 2
2 nm and the pore volume was 1.40 ml / g.

<Example 3> In Example 1, the temperature of distilled water was set at 5 ° C and the temperature of tetraethoxysilane was set at 20 ° C.
° C, the addition amount was 22.3 g (0.102 mol) (H ₂
O (mol) / Si (mol) = 785), 65 ° C. after addition
A silica fine particle dispersion was obtained in the same manner as in Example 1 except that the reaction was carried out for 8 hours. The specific surface area of the fine particles in the obtained silica fine particle dispersion was 430 m ² / g, and the secondary particle size was 52 nm. The pore size was 10.1 nm and the pore volume was 1.03 ml / g.

Example 4 Same as Example 1 except that the temperature of distilled water was 5 ° C., the temperature of tetraethoxysilane was 5 ° C., and the reaction was carried out at 95 ° C. for 48 hours after the addition. Thus, a silica fine particle dispersion was obtained. The specific surface area of the fine particles in the obtained silica fine particle dispersion is 208 m ² /
g and the secondary particle size was 82.2 nm. The pore size was 25 nm and the pore volume was 0.901 ml / g.

Example 5 In Example 1, the temperature of distilled water was 30 ° C., and the temperature of tetraethoxysilane was 28
A silica fine particle dispersion was obtained in the same manner as in Example 1 except that the temperature was changed to ° C. The specific surface area of the fine particles in the obtained silica fine particle dispersion is 383 m ² / g, and the secondary particle size is 250 n.
m. The pore size is 10 nm and the pore volume is 1.
03 ml / g.

Comparative Example 1 In Example 1, the temperature of distilled water was set at 18 ° C., and the temperature of tetraethoxysilane was set at 20.
° C, the amount of tetraethoxysilane added was 501 g (0.1
02 mol) (H ₂ O (mol) / Si (mol) = 3
5) A silica fine particle dispersion was obtained in the same manner as in Example 1 except that the reaction was carried out at 95 ° C. for 24 hours after the addition. The specific surface area of the fine particles in the obtained silica fine particle dispersion was 583 m ² / g, and the secondary particle size was 365 nm. The pore diameter is 24 nm and the pore volume is 1.63 m
1 / g.

<Comparative Example 2> A silica fine particle dispersion was obtained in the same manner as in Example 1 except that hydrochloric acid was added to distilled water so as to have a concentration of 0.0001 N. The specific surface area of the fine particles in the obtained silica fine particle dispersion is 865.
m ² / g, and the secondary particle size was 3.90 μm. The pore size was 4 nm and the pore volume was 0.877 ml / g.

Comparative Example 3 A silica fine particle dispersion was obtained in the same manner as in Example 1 except that ammonia water was added to distilled water so as to have a concentration of 0.0001 N.
The specific surface area of the fine particles in the obtained silica fine particle dispersion is 1
It was 86 m ² / g, and the secondary particle size was 29.2 nm.
The pore size is 16 nm and the pore volume is 0.475 ml /
g.

[Evaluation] With respect to the silica fine particle dispersions obtained in the above Examples and Comparative Examples, ink jet recording sheets were prepared and evaluated by the following methods, and the results are shown in Tables 1 and 2.

<Preparation of Ink-Jet Recording Sheet> A coating liquid for an ink receiving layer was prepared by adding 30% by weight of silicon-containing polyvinyl alcohol (trade name: R2105, manufactured by Kuraray Co., Ltd.) to the silica solid content of the silica fine particle dispersion. A film (manufactured by Toray, trade name: Lumirror) was coated with a Meyer bar so that the coating amount after drying was 25 g / m ^2, and dried to prepare an ink jet recording sheet.

<Evaluation of Inkjet Recording Sheet> The inkjet recording sheet obtained by the above-mentioned production method was evaluated by the following method.

<Ink Absorption> An ink jet printer (manufactured by Canon Inc.,
(Trademark: BJC700J), solid printing (super photo mode) in each color of cyan, magenta, yellow, and black was evaluated. The ink absorbency was evaluated by observing the degree of ink bleeding. What completely absorbs ink,
A slightly bleeding was marked with △, and an overflowing was marked with ×.

<Transparency> The ink jet recording sheets prepared in the respective Examples and Comparative Examples were laid flat, and the transparency was visually evaluated by irradiating light from an oblique upper surface. What has good transparency,
Those that were slightly cloudy were marked with x.

<Print Density> A commercially available coated paper was spread under each ink jet recording sheet, and the print density of the solid black portion was measured by a Macbeth reflection densitometer (Macbeth, RD-920).

<Glossiness of Printed Area> The glossiness of the printed area was visually evaluated by observing the printed area from an angle of 20 degrees. ◎
Has a gloss as high as that of a color photographic paper. Thereafter, the gloss was evaluated in the order of △, and a non-glossy one was evaluated as x.

[0041]

[Table 1]

[0042]

[Table 2]

As is clear from Tables 1 and 2, Examples 1 to
Since the silica fine particles obtained in Step 5 have a small particle size and a large pore volume, the ink jet recording sheet obtained by coating them has good ink absorption, high print density, high gloss, and high transparency. Was excellent.

[0044]

As described above, the silica fine particle dispersion produced by the present invention can form a porous layer which is excellent in ink absorbency, transparent and glossy when applied to a substrate.

Claims (3)

[Claims] 1. A method for producing a silica fine particle dispersion by hydrolyzing an alkoxysilane, wherein the hydrolysis uses 40 to 800 mol of water per mol of silicon, and
By performing without using a catalyst, a specific surface area of 150
a m ² / g~500m ² / g, a secondary particle size 10nm~250nm by laser granulometer, that pore volume to obtain a silica fine particle is 0.5ml / g~1.5ml / g A method for producing a silica fine particle dispersion. 2. The temperature of the water and the alkoxysilane is previously set at 2
2. The method for producing a silica fine particle dispersion according to claim 1, wherein the hydrolysis is performed by adjusting the temperature to 5 ° C. or lower, mixing, and then heating the mixture while stirring. 3. The method for producing a silica fine particle dispersion according to claim 2, wherein the hydrolysis is performed at 40 ° C. to 100 ° C.