JPH05170424A - Production of silica sol - Google Patents

Abstract

PURPOSE:To provide a silica sol for which the average particle diameter and the sharp particle diameter distribution suitable for the thickness of a polyester film are arbitrarily controlled in a polar solvent such as ethylene glycol and no particles of large size of >=3.0mum is included and particles are uniformly and stably dispersed and such a form that they easily stick to the film and are hard to separate or fall from the film surface is provided. CONSTITUTION:Silica hydrogel for which an alkali silicate solution is decomposed and precipitated by neutralization reaction to obtain or the dried one is wetcrushed in a polar solvent.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a thermoplastic resin, a thermosetting resin, and more particularly to silica fine particles used as an anti-blocking material for polyester films. More specifically, in order to improve the slipperiness and abrasion resistance of the polyester film, the polyester film is uniformly and stably dispersed in a polar solvent such as ethylene glycol which is a starting material, and the average particle size and the particle size distribution are arbitrarily set. The present invention relates to a method for producing a silica sol that can be controlled. The silica sol according to the present invention is used, for example, in rubber, cosmetics, paints, dentifrices, papermaking, abrasives and the like.

[0002]

2. Description of the Related Art As a method for producing a silica sol, fine silica powder obtained by oxidative decomposition of silicon halide at high temperature is dispersed in a solvent, and a metal (silicon) alkoxide is used as an alkali catalyst in a water-alcohol solvent. Method of hydrolysis in the presence, method of exchanging alkali ions with hydrogen ions by using hydrogen type ion exchange resin in alkali silicate solution, decomposition precipitation by neutralization reaction of alkali silicate solution with mineral acid etc. The method of making it practical is industrially used. There is also known a silica sol obtained by treating an alkaline silicate solution with a hydrogen ion exchange resin or by deflocculating precipitated silica obtained by a neutralization reaction with an acid or an alkali.

Polyester film, which is a promising application of such silica sol, has excellent physical and chemical properties and is used as a main base material for magnetic recording materials, photographic films, capacitors, etc. It has a wide range of uses such as packaging, textiles, and containers.

Among the above-mentioned uses, magnetic recording materials have been rapidly developing in recent years, and are used for audios, video tapes, floppy disks, etc. by coating a magnetic layer on a polyester film as a base. In particular, magnetic recording tapes such as audio and video tapes are becoming higher in density and performance in response to the development trend of AV equipment.
Improving the surface properties of films has become an important issue recently. Further, along with the miniaturization of magnetic recording tapes and the recording for a long time (recording), it has been required to reduce the thickness of a polyester film as a base thereof.

Basically, a smooth surface is required in order to improve the electromagnetic conversion characteristics relating to sound quality and image quality, but if the surface of the film is smoothed to a certain level or more, the films adhere to each other and become difficult to peel off, resulting in winding. Performance and tape runnability become poor. Therefore, in order to maintain electromagnetic conversion characteristics and improve running stability, a protrusion is formed on the side opposite to the magnetic surface, the so-called back surface, to reduce the contact area between the films and to achieve an appropriate roughening. Has been done.

In general, glycols such as ethylene glycol, which is a starting material for polyester, have an average particle size of 0.
A polyester film is produced by dispersing inert inorganic particles such as silica, calcium carbonate, titanium dioxide, talc, and kaolin having a particle size of about 05 to 3.0 μm to form projections on the film surface, and the film has a slip property and a friction coefficient. A method for improving the above is adopted (see, for example, Japanese Patent Laid-Open Nos. 3-160033 and 3-185033).

However, when coarse particles of 3.0 μm or more are present in the inert inorganic particles, coarse projections are formed during film formation, and projections are formed on the surface of the magnetic layer even after coating the magnetic layer, which causes a decrease in S / N ratio. Drops of signals (dropout), poor compatibility with the polyester film, and spherical particle shape caused by repeated running of the tape causes particles on the film surface that form protrusions to peel off. It is also known to have a bad influence on the product, such as easy falling off.

In order to solve these problems, the following properties are required for the inert inorganic particles used as the anti-blocking material for the polyester film. That is,
(1) An average particle diameter adapted to the film thickness in glycol such as ethylene glycol, having a sharp particle size distribution, and containing no coarse particles of 3.0 μm or more, (2)
Uniformly and stably dispersed in glycol such as ethylene glycol, (3) Good compatibility with film, (4)
It has a shape that does not easily peel off or fall off the film surface. The average particle size here, the particle size distribution is a value measured by a particle size measuring device, not the primary particle size observed by an electron microscope, and refers to secondary particles in which the primary particles are appropriately aggregated into any particle size. , Is the most important physical property for forming protrusions on the film.

In the silica sol described above, a silica sol obtained by a method of hydrolyzing a metal (silicon) alkoxide in a water-alcohol solvent in the presence of an alkali catalyst is easy to control the particle size, and a monodispersed sol is obtained. However, since the particles are spherical, they have the drawback that they are easily peeled off from the film surface when the tape is repeatedly used and the raw material is expensive.

A silica sol obtained by dispersing fine silica powder obtained by oxidative decomposition of silicon halide at a high temperature in a solvent has a primary particle close to a spherical shape and has the same drawbacks as the above method. With a silica sol obtained by exchanging alkali ions with hydrogen ions by using a hydrogen type ion exchange resin in an alkali silicate solution, projections are formed on the film surface because the maximum particle size of secondary particles is 0.1 μm or less. The effect is insufficient.

The silica sol obtained by decomposing and precipitating an alkali silicate solution by a neutralization reaction is cheaper than the above two methods and is porous, so that it is well compatible with the film, but particles are easily aggregated. There is a drawback that it is difficult to control the dispersion and the secondary particle size.

The silica sol produced by the above-mentioned method generally has a sol.
Primary particles of about 01 to 0.2 μm are grape-like 5 to 50
It exhibits agglomerates of about μm, and few of the dry powders and liquids have a single primary particle. Therefore, it is difficult to uniformly disperse the silica particles produced by this method uniformly in the reaction system, and even if the obtained silica hydrogel is tried to be dispersed using a homogenizer, ultrasonic waves, etc., the particle size distribution is broad. Therefore, coarse particles of 3.0 μm or more are present.

Then, the silica hydrogel is dried,
It is considered that silica fine particles finely pulverized with a fine pulverizer such as a jet mill are dispersed in ethylene glycol using a homogenizer or ultrasonic waves, but even if dispersed by this method, the particle size distribution is broad. Therefore, similarly to the above, coarse particles of 3.0 μm or more are likely to be contained. To solve this problem, by performing wet or dry classification, 3.0 μm
There is a method of removing coarse particles as described above, but about 1.0 μm in wet centrifugal classification and 3.0 in dry wind classification.
It is a drawback that removal of about μm or more is difficult, classification accuracy is poor, and the yield is reduced and the cost is increased.

[0014]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and has an average particle size and a sharpness suitable for the thickness of a polyester film in a polar solvent such as ethylene glycol. The particle size distribution can be controlled arbitrarily, and it does not contain coarse particles of 3.0 μm or more and is dispersed uniformly and stably. It has a good fit with the film and is difficult to peel off from the film surface. It is an object to provide a silica sol having the same.

[0015]

Means for Solving the Problems The present invention is achieved by subjecting the above problems to wet pulverization of silica hydrogel or a dried product thereof obtained by decomposing and precipitating an alkali silicate solution by a neutralization reaction in a polar solvent. ,Solve.

In order to stabilize the silica sol to be obtained, the pH may be adjusted to 9 to 11 by which the silanol groups on the surface of the silica are dissociated due to the stability of the silica particles. Is desirable. As the alkali, ammonia, alkali metal hydroxide such as sodium hydroxide, amines may be used alone or in combination of two or more kinds. The time for adding the alkali is preferably during wet grinding and / or after wet grinding. In addition, as a known method of stabilizing silica in a wide pH range, there is a method of adding aluminum chloride, sodium aluminate or the like and modifying the surface of the silica sol with aluminum ions.

[0017]

The silica hydrogel or its dried product is wet-ground in a polar solvent to give an average particle size of 0.03 to
A silica sol that can be arbitrarily controlled within a range of 2.0 μm and a particle size distribution of 0.01 to 3.0 μm and is uniformly and stably dispersed can be obtained. The specific surface area of the dried product is 20-80.
Since it is porous at 0 m ² / g, it fits well with the film.

This silica sol is added to glycol such as ethylene glycol, and in a polyester film using this as a starting material, silica particles are uniformly present in the film without agglomeration.

Therefore, in the polyester film using the silica sol according to the present invention, the slipperiness for improving the running stability of audio and video tapes is improved, and the particles from the surface of the tape during the repeated running of the tape. The silica sol of the present invention is most suitable as an anti-blocking material for polyester films, because it has the advantages that it does not easily peel off or fall off, it has excellent abrasion resistance, and that it can be used for thinning tapes.

The above constitution of the present invention and the saliency of its operation will be more clearly understood from the following description.

In the method of the present invention, the synthesized silica has a primary particle diameter of about 0.01 to 0.2 μm, and this forms a large unit of secondary particles that are aggregated in a grape shape. The grinding energy works to break up these secondary particles. Therefore, by appropriately performing wet pulverization, the secondary particles finally approach the primary particles infinitely, and the primary particles are not pulverized, and a sharp particle size distribution containing no fine particles or coarse particles is obtained. .. Therefore, it is not necessary to classify the coarse particles, and the total amount of the treated particles can be obtained. Therefore, there is an advantage that the yield is improved and the manufacturing cost is low. Furthermore, since the secondary particles of large units become secondary particles having a small particle size by the wet pulverization, the shape of the obtained silica sol particles is not spherical but primary particles of about 0.01 to 0.2 μm. The particles have an indefinite shape in which the particles have an arbitrary particle size and a specific surface area of 20 to 80.
Since it is porous at 0 m ² / g, it has good compatibility with the film and has an advantage that it is unlikely to peel off from the film surface.

The wet pulverizer applicable in the present invention includes:
Examples thereof include ball mills such as a ball mill, a tube mill, a conical mill, a vibrating ball mill and a planetary mill, a tower mill, an attritor, a dyno mill, a sand grinder and an aniler mill. In the present invention, it is desirable that the silica hydrogel or the dried product thereof and the polar solvent are wet pulverized with a pot mill filled with a medium having a diameter of about 0.1 to 6.0 mm. The inventors of the present invention arbitrarily change the wet pulverization time to obtain an average particle size of 0.03 to 2.0 μm and a particle size distribution of 0.01 to
It has been found that it can be controlled arbitrarily within the range of 3.0 μm.

As described above, silica hydrogel having a primary particle size of 0.01 to 0.2 μm obtained by decomposing and precipitating an alkali silicate solution by a neutralization reaction or a dry powder thereof is used as a raw material in a sol in a polar solvent. The average particle diameter of the secondary particles is 0.03 to
It is possible to obtain a silica sol in which the particle size is 2.0 μm and the particle size distribution can be arbitrarily controlled in the range of 0.01 to 3.0 μm, and is uniformly and stably dispersed, and the particle shape is indefinite.

[0024]

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

In these Examples and Comparative Examples, the methods for measuring the primary particle diameter, average particle diameter, particle size distribution, and methods for indicating the slipperiness and abrasion resistance of the film will be shown below.

[Primary particle size] The particle size confirmed by a scanning electron microscope or a transmission electron microscope is measured arbitrarily at 50 particles,
The average value was used.

[Average Particle Size, Particle Size Distribution] The average particle size of silica particles dispersed in a polar solvent by a light transmission type centrifugal sedimentation type particle size measuring apparatus (manufactured by Shimadzu Corporation; SA-CP3L),
The particle size distribution was measured. The average particle size was 50% in total, and the particle size distribution was data of differential type particle size distribution.

[Sliding and Scratch Resistance of Film] Polyethylene terephthalate obtained by adding the silica sol obtained in the following Examples and Comparative Examples in a solid content concentration of 1.0% to the polymer was used. The film was melt extruded at 90 ° C., stretched 3.5 times in the longitudinal direction at 90 ° C. and 3.5 times in the transverse direction at 130 ° C., and then heat-treated at 220 ° C. to produce a film having a thickness of 15 μm.

The film prepared by adding the silica sol obtained in each of the Examples and Comparative Examples and slitting it in the widthwise direction was put on a winder, and rubbed on a metal guide roll installed in the middle for a long time at a high speed. I ran for hours. At this time, the magnitude of the tape tension and the amount of white powder generated were measured, and the slipperiness and abrasion resistance are shown in Table 1 as follows.

Sliding Low tension ・ ・ ・ ○ Medium tension ・ ・ ・ △ High tension ・ ・ ・ × Scraping resistance Small amount of white powder ・ ・ ・ ○ Medium amount of white powder ・ ・ ・ △ Large amount of white powder ・ ・ ・ × Example 1 3070 g of No. 3 sodium silicate solution in 12800 pure water
After diluting with ml and heating to 90 ° C with stirring, the sodium silicate aqueous solution is adjusted to pH 10.5 until 22.
A 7 g / l sulfuric acid solution was added dropwise over 10 minutes. After dropping the sulfuric acid solution, aging was performed for 60 minutes while maintaining 90 ° C. Immediately after aging, it was rapidly cooled, then suctioned, filtered, washed with water and dehydrated to obtain a silica hydrogel having a solid content concentration of 23.8%.

840 g of this silica hydrogel and 1160 g of ethylene glycol were wet milled in a pot mill for 44 hours to form a sol.

As shown in Table 1, the obtained silica sol had an average particle diameter of 0.08 μm and a particle size distribution of 0.04 to 0.04.
It was 0.15 μm. The particle size distribution is shown in FIG. Also,
When observed with a scanning electron microscope, primary particles of about 0.05 μm were aggregated and secondary particles having an irregular shape were confirmed. This photograph is shown in FIG.

Further, Table 1 shows the characteristics of the film produced by using the obtained silica sol.

Example 2 A silica sol was obtained in the same manner as in Example 1 except that wet pulverization was carried out for 31 hours.

As shown in Table 1, the obtained silica sol had an average particle size of 0.10 μm and a particle size distribution of 0.04 to 0.04.
It was 0.3 μm. The particle size distribution is shown in FIG.

Further, Table 1 shows the characteristics of the film produced by using the obtained silica sol.

Example 3 2000 g of the silica hydrogel obtained in Example 1 was wet pulverized with a pot mill for 15 hours to form a sol.

As shown in Table 1, the obtained silica sol had an average particle size of 0.21 μm and a particle size distribution of 0.08-
It was 0.6 μm. The particle size distribution is shown in FIG.

Further, Table 1 shows the characteristics of the film produced by using the obtained silica sol.

Example 4 The silica hydrogel obtained in Example 1 had a solid content of 15%.
Silica sol pre-treated by wet pulverization after diluting with water so that it becomes a spray dryer (manufactured by Tokyo Rika Kikai;
Spray drying was performed using SD-1) to obtain a dried silica product.

400 g of this dried product and 1600 g of ethylene glycol were wet pulverized in a pot mill for 7 hours to obtain a silica sol.

As shown in Table 1, the obtained silica sol had an average particle size of 0.29 μm and a particle size distribution of 0.08-.
It was 1.0 μm. The particle size distribution is shown in FIG.

Further, Table 1 shows the characteristics of the film produced by using the obtained silica sol.

Example 5 A silica sol was obtained in the same manner as in Example 4 except that wet pulverization was carried out for 4 hours.

The obtained silica sol has an average particle size of 0.43 μm and a particle size distribution of 0.1 to 1, as shown in Table 1.
It was 5 μm. The particle size distribution is shown in FIG.

Further, Table 1 shows the characteristics of the film produced by using the obtained silica sol.

Example 6 A silica sol was obtained in the same manner as in Example 4 except that wet pulverization was carried out for 1 hour.

As shown in Table 1, the obtained silica sol had an average particle size of 0.87 μm and a particle size distribution of 0.2 to 3.
It was 0 μm. The particle size distribution is shown in FIG.

Further, Table 1 shows the characteristics of the film produced by using the obtained silica sol.

Example 7 2500 ml of No. 3 sodium silicate solution was diluted with 1280 pure water.
Dilute with 0 ml, warm to 90 ° C with stirring and then 2
A 27 g / l sulfuric acid solution was added dropwise over 60 minutes until the pH reached 3.0. After dropping the sulfuric acid solution, keep the temperature at 90 ° C.
Aged for minutes. Immediately after aging, it is rapidly cooled, then suctioned, filtered, washed with water and dehydrated to obtain a solid content of 21.2.
% Silica hydrogel was obtained.

2000 g of this silica hydrogel was wet-milled in a pot mill for 24 hours to form a sol. The obtained silica sol was liable to settle, and it was necessary to loosen the precipitate at the time of use, and it was difficult to handle. Therefore, in order to stabilize the silica particles, a 10% sodium hydroxide solution was added with stirring until the pH reached 10.0,
A stable dispersed silica sol was obtained.

As shown in Table 1, the obtained silica sol had an average particle diameter of 0.16 μm and a particle size distribution of 0.05 to
It was 0.4 μm. The particle size distribution is shown in FIG. Further, when observed with a scanning electron microscope, primary particles of about 0.02 μm were aggregated, and secondary particles having an irregular shape were confirmed.

Further, Table 1 shows the characteristics of the film produced by using the obtained silica sol.

Comparative Example 1 Silica hydrogel was obtained in the same manner as in Example 1, dried, coarsely crushed, and then jet mill (manufactured by Seishin Enterprise Co., Ltd.).
Was finely pulverized. 200 g of this finely divided silica and 1800 g of ethylene glycol were dispersed by vigorous stirring without wet grinding.

As shown in Table 1, the obtained silica sol had an average particle size of 0.91 μm and a particle size distribution of 0.2 to 5.
It was 0 μm. The particle size distribution is shown in FIG.

Further, Table 1 shows the characteristics of the film produced by using the obtained silica sol.

Comparative Example 2 Silica hydrogel was obtained in the same manner as in Example 1, and 840 g of this silica hydrogel and 1160 of ethylene glycol were used.
and g were dispersed using a homogenizer.

The silica sol thus obtained has an average particle size of 2.19 μm and a particle size distribution of 0.1 to 1, as shown in Table 1.
It was 0.0 μm. The particle size distribution is shown in FIG.

Further, Table 1 shows the characteristics of the film produced by using the obtained silica sol.

[0060]

As is apparent from the above description, the present invention has the following effects.

The silica sol according to the present invention has an average secondary particle size of 0.03 to 2.0 depending on the degree of wet pulverization.
It can be controlled arbitrarily in the range of μm and particle size distribution of 0.01 to 3.0 μm. For example, when it is used as an anti-blocking material for polyester film, (1) it is adapted to the film thickness in glycol such as ethylene glycol. Having an average particle size, a sharp particle size distribution, and not containing coarse particles of 3.0 μm or more, (2) uniformly and stably dispersed in glycol such as ethylene glycol, (3) with film It has excellent properties as an anti-blocking material for polyester films, such as good compatibility and (4) having a shape that does not easily peel off from the film surface. Therefore, the sliding property for improving the running stability of the audio or video tape having the polyester film using the silica sol according to the present invention as the base film, the friction coefficient is improved, and the particles are not easily peeled off from the film surface and are resistant to abrasion. It has excellent properties and can cope with thinning of the tape.

The silica sol according to the present invention can be effectively applied to plastic films, rubbers, cosmetics, paint dentifrices, papermaking, abrasives and the like.

[0063]

[Table 1]

[Brief description of drawings]

FIG. 1 is a diagram showing a differential particle size distribution of a silica sol obtained in Example 1.

FIG. 2 is a diagram showing a differential particle size distribution of silica sol obtained in Example 2.

FIG. 3 is a diagram showing a differential particle size distribution of the silica sol obtained in Example 3.

FIG. 4 is a diagram showing a differential particle size distribution of the silica sol obtained in Example 4.

5 is a diagram showing a differential particle size distribution of the silica sol obtained in Example 5. FIG.

FIG. 6 is a diagram showing a differential particle size distribution of the silica sol obtained in Example 6.

FIG. 7 is a diagram showing a differential particle size distribution of the silica sol obtained in Example 7.

8 is a diagram showing a differential particle size distribution of the silica sol obtained in Comparative Example 1. FIG.

9 is a diagram showing a differential particle size distribution of the silica sol obtained in Comparative Example 2. FIG.

10 is a scanning electron micrograph showing the particle shape of the silica sol obtained in Example 1 at a magnification of 10,000. FIG.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiro Maeno 1-8-8 Sakasedai, Takarazuka-shi, Hyogo A305

Claims (2)

[Claims] 1. A method for producing a silica sol, which comprises wet pulverizing a silica hydrogel obtained by decomposing and precipitating an alkali silicate solution by a neutralization reaction or a dried product thereof in a polar solvent. 2. The method for producing a silica sol according to claim 1, wherein the silica sol to be obtained is adjusted to have a pH of 9 to 11.