JP2001226657A - Adhesive containing scaly silica particle and method of producing adhesion structural body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an adhesive capable of forming a bonded body strong even at normal temperature. SOLUTION: This adhesive comprises a foliate silica secondary particle which is formed by orientating the planes of scaly silica flake primary particles mutually is parallel and piling the plural primary particles and has a particle shape of independently existing layered structure and a volatile liquid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adhesive capable of forming a strong adhesive at room temperature, and more particularly, to a hardened adhesive layer having both acid resistance, alkali resistance and heat resistance. It relates to an adhesive which can be formed.

[0002] This adhesive is used for metal, glass, ceramics, slate, cement hardened material, plastic, wood,
It is useful as an adhesive that can be applied to bonding between similar or different materials such as paper.

[0003]

2. Description of the Related Art Conventionally, various organic and inorganic adhesives have been used. Organic adhesives have the advantage that they can be cured at room temperature, but have the disadvantage of poor organic solvent resistance and heat resistance.

On the other hand, inorganic adhesives generally have high resistance to organic solvents and generally high heat resistance, but they all require a heat treatment at 100 to 150 ° C. when cured. There is.

Accordingly, development of an adhesive which can be cured at room temperature and which has heat resistance, acid resistance, alkali resistance and organic solvent resistance has been pursued.

Colloidal silica and an aqueous solution of alkali silicate are known as those containing a silica component and having an adhesive function. However, in the case of colloidal silica, the alkali resistance is poor, and the curing time is 400 to 600 C.
° heat treatment is required. Further, it is difficult for the aqueous adhesive containing colloidal silica to form a thick adhesive layer, and stable adhesive strength cannot be exhibited. On the other hand, in the case of alkali silicate, there is a problem that heat treatment at 100 to 600 ° C. is required for curing, and it is similarly difficult to form a thick adhesive layer.

[0007] An aqueous solution of a water-soluble polymer such as polyvinyl alcohol, polyvinylpyrrolidone, methylcellulose, carboxymethylcellulose and gelatin can form an adhesive layer. There is a problem in the durability of the.

Further, other silicas such as silica gel,
Hydrous silicic acid (so-called white carbon), quartz,
Silica other than colloidal silica, such as cristobalite and tridymite, does not have an adhesive function in the first place.

In any case, as described above, none of the conventional adhesives has room temperature curing, organic solvent resistance, acid resistance, alkali resistance, and heat resistance.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a conventional adhesive, especially a silica-based adhesive which basically solves these disadvantages of the conventional silicon-based material. is there.

[0011]

Means for Solving the Problems The present inventors have conducted intensive studies in view of the importance of the above-mentioned problems, and as a result, in synthesizing micro-scale low-crystalline silica, controlled the fine structure of the particle form thereof, The particle form of the micro-scale silica is a micro-scale-like particle form of a laminar structure substantially composed of secondary particles of flaky silica formed by stacking a plurality of primary flake particles in parallel with each other with their planes oriented parallel to each other. Surprisingly, it has been found that the above-mentioned problem can be basically solved by an adhesive containing silica, and the present invention has been completed.

That is, according to the present invention, the primary particles of flaky silica flakes are substantially composed of secondary particles of foliar silica formed by overlapping a plurality of layers with their planes oriented parallel to each other. An adhesive is provided, which contains secondary particles of foliar silica having a particle structure of an existing laminated structure and a volatile liquid.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

(Scaly Silica Particles Having Particle Structure of Laminated Structure) The present invention is an adhesive containing flaky silica particles having a specific structure. First, the flaky silica particles and a method for producing the same will be described.

The flaky silica particles in the present invention are first created by the present inventors, and the flaky silica secondary particles are formed by overlapping a plurality of flake primary particles with their planes oriented in parallel with each other. It is a flaky silica (hereinafter also referred to as “leaf-like silica secondary particles” in the present invention) having a very characteristic form having a particle form of a layered structure substantially consisting of particles.

Here, the flake primary particles have a thickness of 0.0
It is from 0.1 to 0.1 μm. Such flake primary particles are oriented parallel to each other to form one or a plurality of overlapping leaf-like silica secondary particles, and the thickness of the secondary particles is 0.001 to 3 μm. , Preferably 0.00
5 to 2 μm, and the minimum length ratio (aspect ratio) of the leaf-like secondary particles (plates) to the thickness is at least 10, preferably 30 or more, and more preferably 50 or more. The ratio of the minimum length of the secondary particles (plates) is flaky silica having at least 2, preferably 5 or more, more preferably 10 or more. The secondary particles exist independently of each other without binding.

When the thickness of the leaf-like secondary particles is less than 0.001 μm, the mechanical strength of the leaf-like secondary particles is insufficient, which is not preferable. On the other hand, when the thickness of the leaf-like secondary particles is larger than 3 μm, the characteristics as an adhesive cannot be sufficiently exhibited when used for an adhesive.

The upper limit of the ratio of the longest length to the thickness of the leaf-like secondary particles and the upper limit of the minimum length are not particularly specified, but the former is practically 300 or less, preferably 200 or less. The latter is practically 150 or less, preferably 100 or less.

As described above, the thickness and length of the leaf-like secondary particles in the present invention mean the average value of the secondary particles unless otherwise specified.

In the present invention, the term "scale" means that the particles have a substantially thin plate-like shape, and this may be partially or wholly bent or twisted. .

Such silica aggregate particles (tertiary particles) having gaps formed by three-dimensionally overlapping leaf-like secondary particles further irregularly overlap with each other, so-called silica-X
(Hereinafter also referred to as SiO ₂ -X), silica-Y (also referred to as SiO ₂ -Y), etc., have been known as objects of academic research. It was what was.

The secondary particles of foliar silica in the present invention are obtained by temporarily synthesizing such tertiary aggregate particles (tertiary particles) of silica (for example, SiO ₂ —X or SiO ₂ —Y), which will be described later. In this method, leaf-like secondary particles are crushed by a specific means, but a method of synthesizing the tertiary aggregate particles themselves in a short time has not been known.

Silica-X and the like, which are tertiary aggregated particles of silica, are intermediate or quasi-particles generated in the process of forming cristobalite or quartz (quartz) by hydrothermally treating amorphous silica. A stable phase,
It is a weak crystalline phase that can be called quasicrystalline silica.

Although the X-ray diffraction patterns of silica-X and silica-Y are different, the appearance of the particles observed by an electron microscope is very similar, and both give the foliar silica secondary particles of the present invention. It can be preferably used for the purpose.

Thus, the silica X and the silica Y themselves are:
Although it is known, a conventional typical method for producing silica-X or the like uses silica gel (silica xerogel), aerosil, or precipitated silica as a starting material, and hydrothermally treats the starting material. There was a problem that it was long. For example, Heydemann, who first discovered silica-X
Uses precipitated silica and aerosil (ultrafine amorphous silica obtained by pyrolyzing SiCl ₄ at a high temperature) as starting materials, and converts it to silica-X in an autoclave at 180 ° C. for 1 hour. It takes an extremely long time of 5 to 24 days (Heydemann, A., Beitr. Mineral.
etrogr., 10, 242-259 (1964)).

On the other hand, with respect to silica-Y, Mitsyuk et al. Used silica gel having a specific surface area of 600 to 700 m ² / g as a starting material and prepared a solution of 145 to 155 in a solution such as NaOH.
C. for a long time (200 to 220 hours) to obtain silica-Y (Mitsyuk, BA et al. Geoc).
13, 101-111 (1976)) and Kitahara et al. use silica gel having a specific surface area of 600 m ² / g (silica gel (G) manufactured by Wako Pure Chemical Industries, Ltd.) as a starting material in a KOH solution containing NaCl. , 150-160 ° C for a long time (7
0-170 hours) By hydrothermal treatment, silica-Y
(Kitahara S, etal. Proc. Inst. Symp.
Hydrotherm. React. 1st (1983)).

Thus, the method of converting silica gel to silica-X or the like by hydrothermal treatment using silica gel as a starting material requires an extremely long reaction time (hydrothermal treatment time) for industrial application. was there. Of course, it is possible to shorten the time by increasing the temperature of the hydrothermal treatment, but in that case, the stability of the operation range is lost, and there is a major problem that quartz (quartz) and cristobalite are easily generated. Provoke. Thus, silica-X or the like, which is a tertiary silica aggregate particle (tertiary particle) serving as a precursor for obtaining the foliar silica secondary particles in the present invention, can be used at a lower temperature and industrially. A technique for producing quartz and the like in a sufficiently short time without generating quartz or the like is desired.

(1) Formation of Tertiary Agglomerate Particles of Silica The secondary particles of leaf-like silica in the present invention are tertiary aggregate particles of silica (tertiary particles) (hereinafter also referred to as tertiary silica particles of the present invention). ) Is obtained by pulverizing, and the present inventors first studied a method for producing tertiary aggregated silica particles as precursor particles thereof.

From the above viewpoint, the present inventors have developed two more preferable methods for producing the tertiary aggregated silica particles in the present invention, instead of the conventional method using silica gel (silica xerogel) as a starting material. Proposed.

The first method is to carry out hydrothermal treatment using a silica sol containing specific amounts of a silica source and an alkali source, that is, an aqueous dispersion of colloidal silica as a starting material.
This is a method for industrially producing tertiary aggregated silica particles such as silica-X in a shorter time and with good stability.
29317). According to this method, aggregates that are tertiary particles having gaps formed by three-dimensionally foliated silica secondary particles of the present invention overlapping irregularly (that is, tertiary silica aggregate particles of the present invention) are formed. It has the advantage that it can be obtained as it is.

This means that the silica source and the alkali source are
A hydrothermal treatment of the silica sol containing
As the sol, a silica / alkali molar ratio (SiO 2)_Two /
Me _Two O, where Me is Al, such as Li, Na or K
Indicates potash metal. same as below. ) Is 1.0-3.4m
ol / mol alkali silicate aqueous solution
Dealkalized by the exchange resin method or the electrodialysis method, etc.
Silica sol is preferably used. In addition, the alkali silicate
As the aqueous solution, for example, water glass is appropriately diluted with water.
Are preferred.

The silica / alkali molar ratio of silica sol (S
iO ₂ / Me ₂ O) is preferably in the range of 3.5~20mol / mol, more preferably in the range of 4.5~18mol / mol. The silica concentration in the silica sol is
It is preferably from 2 to 20% by mass, particularly preferably from 3 to 15% by mass.

The silica particle diameter in the silica sol means an average particle diameter and is not particularly limited, but is preferably 100 nm or less, and particularly preferably what is called active silicic acid of 20 nm or less. . The lower limit of the particle size is not particularly limited, but is preferably 1.0 nm or more. If the particle diameter is too large, exceeding 100 nm, the stability of the silica sol is undesirably reduced.

The method for measuring the silica particle diameter is not particularly limited as long as the particle diameter can be measured. Examples of the method include a laser light scattering particle size measuring apparatus and a scale measurement of a particle image size taken by a transmission electron microscope. Can be measured.

Using the silica sol as a starting material as described above,
This is heated in a heating pressure vessel such as an autoclave and subjected to hydrothermal treatment to produce tertiary silica aggregate particles in the present invention.

Although the type of the autoclave is not particularly limited, any autoclave having at least a heating means, a stirring means, and preferably a temperature measuring means may be used.

In order to hydrothermally treat the silica sol, the silica concentration can be adjusted to a desired range by adding purified water such as distilled water or ion-exchanged water before charging the silica sol in an autoclave.

The hydrothermal treatment is carried out at 150 to 2 to increase the reaction rate as much as possible and to reduce the progress of crystallization.
It is performed in a temperature range of 50 ° C, more preferably 170 to 2
20 ° C.

The required time for the hydrothermal treatment can vary depending on the temperature of the hydrothermal treatment, the presence or absence of seed crystals, and the like, but is usually 3 to 50 hours, preferably 3 to 40 hours, and more preferably 5 to 40 hours. It is about 25 hours.

In order to efficiently advance the hydrothermal treatment and to shorten the treatment time, it is not essential to add the same.
More preferably, about 001 to 1% by mass of a seed crystal is added. As a seed crystal, silica-X, silica-Y, or the like can be used as it is or after being appropriately pulverized.

After the completion of the hydrothermal treatment, the hydrothermally treated product is taken out of the autoclave, filtered and washed with water. The particles after the water washing treatment have a pH of 5 when prepared as a 10% by mass water slurry.
It is preferably from 9 to 9, and more preferably the pH is from 6 to
8

On the other hand, the second method is a method in which a silica hydrogel is used as a starting material and a hydrothermal treatment is performed in the presence of an alkali metal, and the silica tertiary aggregate particles silica-X and silica-Y in the present invention are used. This is a more preferable method because it can be produced in a high yield at a low temperature and in a short time without producing crystals such as quartz (Japanese Patent Application No. 10-291336).

The silica hydrogel suitable for use as a starting material here is a particulate silica hydrogel.
The particle shape of the silica hydrogel may be true spherical (spherical) or irregular granular, and the granulation method can be appropriately selected.

Taking the case of a spherical silica hydrogel as an example, as has been known for a long time, a silica hydrosol may be formed by solidifying into a spherical shape in a petroleum or other medium. Preferably, Japanese Patent Publication No. 48-138
As described in No. 34, an aqueous solution of an alkali silicate and an aqueous solution of a mineral acid are mixed to produce a silica sol in a short time, and at the same time, the silica sol is released into a gaseous medium and is produced by a method of gelling in a gas. Things.

[0045] That is, an aqueous alkali silicate solution and an aqueous mineral acid solution, is introduced from a separate inlet into a container equipped with a discharge outlet instantaneously mixed uniformly, in terms of SiO ₂ concentration 130
g / l or more, and a silica sol having a pH of 7 to 9 is immediately released from the discharge port into a gaseous medium such as air, and gelled in the air while drawing in a parabola. . An aging tank filled with water is placed at the drop point, and the ripening tank is dropped here and ripened for several minutes to several tens of minutes.

A spherical silica hydrogel obtained by adding an acid to lower the pH and washing with water is a preferable spherical silica hydrogel for use in the present invention.

The silica hydrogel is a transparent and elastic spherical particle having a uniform particle diameter of about ₂ to 10 mm. In an example, the silica hydrogel contains about four times as much water as SiO ₂ by weight. (That is, about 20% by weight of SiO _{2 and} about 80% by weight of water).

The silica hydrogel particles are actually an aggregate of a large number of primary silica particles having a particle size of about several nm, and it is presumed that the water exists on the surfaces and gaps of the primary particles. Have been.

In the silica hydrogel usable in the present invention,
SiO_Two The concentration is set at 15 from the viewpoint of availability and reactivity.
~ 75% by mass (i.e., a water content of 85 to 25% by mass)
It is preferable to dry it and adjust the water content within this range
May be. The amount of water in the silica hydrogel
Is measured as follows. That is,
After drying the silica hydrogel sample at 180 ° C for 2 hours,
Sample weight of dried sample _Two And the mass loss
It is the amount of water in the lycahydrogel.

Incidentally, the silica hydrogel particles were
A dried silica gel (manufactured and sold industrially) which is sufficiently dried with a drier or the like at a temperature of about 150 to 180 ° C. to remove pores and hydrogel water on the surface.
Silica xerogel), the conventional silica-
In the method for producing X and silica-Y, the dried silica gel is used as a starting material silica for hydrothermal treatment.

Using such a silica hydrogel as a starting material and using it as a first method using silica sol,
Hydrothermal treatment is carried out by heating in a heating pressure vessel such as an autoclave to produce tertiary silica particles of the present invention. In that case, the spherical silica hydrogel may be used as it is, but preferably, the one obtained by pulverizing or coarsely pulverizing to a particle size of about 0.1 to 6 mm can more effectively perform stirring in an autoclave. Desirable for.

When the silica hydrogel is charged in an autoclave for hydrothermal treatment, it is preferable to adjust the concentration of the silica hydrogel to a desired range by adding purified water such as distilled water or ion-exchanged water. The total silica concentration in the processing solution in the autoclave depends on the stirring efficiency,
It is selected in consideration of crystal growth rate, yield, etc.
1-30 wt% as SiO ₂ in total feedstock reference, preferably 10 to 20 wt%. Here, the total silica concentration in the treatment liquid means the total silica concentration in the system, which is only silica in the silica hydrogel, and when sodium silicate or the like is used as an alkali metal salt, the total This is the value to which silica brought into the system by sodium or the like is also added. Note that the total silica concentration can be higher than the method using the first silica sol.

In the hydrothermal treatment, an alkali metal salt is allowed to coexist in the silica hydrogel, the pH of the treatment liquid is adjusted to the alkali side, the silica solubility is increased appropriately, and the so-called Ostwal is used.
The crystallization rate based on the aging of d is increased, and the conversion of silica hydrogel to silica-X or the like is promoted.

Here, the alkali metal salt means alkali hydroxide, alkali silicate or alkali carbonate.
As the alkali metal, Li, Na, or K is preferable. The pH of the system is preferably pH 7 or higher, more preferably pH 8 to 13, and even more preferably pH 9 to 1.
2.5.

If the preferred amount of alkali is represented by a silica / alkali molar ratio (SiO ₂ / Me ₂ O), it is 4 to 1
In the range of 5 mol / mol, 7 to 13 mol / mo
The range of 1 is more preferred. As described above, silica indicates the total amount of silica in the treatment liquid in the system, and is a value obtained by adding silica brought into the system by sodium silicate or the like to silica of the silica hydrogel.

The hydrothermal treatment is performed in a temperature range of 150 to 220 ° C., preferably 160 to 200 ° C., more preferably 170 to 195 ° C.

If the temperature is too low, it takes an extremely long time to obtain the intended silica tertiary aggregate particles of the present invention. It is not preferable because the tertiary aggregate particles are hardly obtained as a single phase such as silica-X or silica-Y. This is because, as described above, silica-X or the like is considered to be an intermediate phase or a metastable phase, and tends to undergo a phase transition to cristobalite or quartz sequentially with the progress of hydrothermal treatment. In the case of exceeding, the crystallization speed becomes high and a mixture with cristobalite or quartz is formed, or the crystallization reaction is too fast to control and all are changed to cristobalite or quartz.

The required time for the hydrothermal treatment may vary depending on the temperature of the hydrothermal treatment, the presence or absence of seed crystals, etc., but is usually 3 to 50 hours, preferably 5 to 40 hours, more preferably 5 to 40 hours. About 25 hours, more preferably 5 to 12
About an hour.

In order to promote the hydrothermal treatment efficiently and to shorten the treatment time, it is not essential to add the hydrothermal treatment.
It is more preferable to add a seed crystal of about mass%. As the seed crystal, as in the first method, silica-X or silica-
It is preferable to use Y or the like as it is or by appropriately pulverizing it.

According to the study of the present inventors, when silica-X is used as a seed crystal, aggregate particles composed of silica-X are easily formed, and when silica-Y is used as a seed crystal, silica-X is used. Aggregate particles composed of -Y are easily formed. After the completion of the hydrothermal treatment, the hydrothermally treated product is taken out of the autoclave, filtered and washed with water as in the first method.
Adjust H.

As described above, the particles obtained by filtering and washing the cake of the hydrothermally treated product obtained by the first method of hydrothermally treating the silica sol or the second method of hydrothermally treating the silica hydrogel, Observation using a scanning electron microscope (SEM) shows that silica-agglomerated particles, which are tertiary particles having gaps formed by three-dimensionally overlapping individual leaf-like secondary particles, are formed. Can be identified.
This is the silica tertiary aggregate particle in the present invention.

However, as described later, the scanning electron microscope (SEM) cannot identify the primary particles, which are ultra-thin particles, and the primary particles, which are ultra-thin particles, are oriented in parallel between planes. Thus, it is possible to identify only a plurality of overlapping leaf-like secondary particles. On the other hand, when observed using a transmission electron microscope (TEM), primary particles that are ultra-thin flake particles that partially transmit an electron beam can be identified. This leaf-like secondary particle is the leaf-like silica secondary particle in the present invention, and it can be identified that the primary particle is formed of a plurality of layers whose surfaces are parallel to each other. Note that it is substantially difficult to separate and isolate the flaky primary particles, which are constituent units thereof, one by one from the leaf-like secondary particles in which the primary particles are layered. That is, in the layered overlap of the primary particles, the bond between the layers is extremely strong and is completely fused and integrated. Therefore, the leaf-like secondary particles in the present invention are no longer crushed into primary particles. It is difficult.

Of the above methods, a method using silica hydrogel as a starting material is better and more preferable than a method using silica sol (active silicic acid or the like) as a starting material. In addition to the method using silica sol and silica hydrogel as other starting materials, hydrated silica (such as so-called white carbon) can be used to synthesize the silica tertiary aggregate particles of the present invention in the same manner as described above.

(2) Crushing and Dispersing Silica Tertiary Aggregate Particles into Leaf-Like Silica Secondary Particles The present inventors first converted such silica tertiary aggregate particles into leaf-like silica secondary particles. Various methods for crushing and dispersing have been proposed (Japanese Patent Application No. 11-351182).

As the secondary silica particles in the present invention, the secondary silica particles can be obtained as a slurry (hereinafter, referred to as secondary particle slurry in the present invention). For this purpose, for example, any of the following methods can be adopted.

A method of crushing tertiary silica aggregate particles in a water slurry to form a secondary particle slurry in the present invention

In the above method, the tertiary silica aggregate particles obtained in the form of a water slurry are first washed with water using a solid-liquid separation / washing device such as a belt filter, a filter cloth centrifuge, or a decanter. Solid-liquid separation Further, if necessary, further re-pulp with water to obtain an SiO ₂ concentration comprising silica tertiary aggregate particles of the present invention having an average particle diameter of 1 to 10 μm substantially not containing an alkali metal salt. A water slurry of 1 to 30% by mass is used.

The above-mentioned slurry is crushed by a wet bead mill of a type in which the slurry is mechanically stirred at high speed using medium beads.
It is carried out by supplying to a wet pulverizing apparatus (crushing apparatus) such as a wet ball mill to pulverize the flaky silica tertiary aggregate particles. At this time, it is desirable to disintegrate and disperse the foliar silica secondary particles as much as possible without pulverizing or breaking them.
Among the above methods, a wet bead mill using medium beads such as alumina or zirconia having a diameter of 0.2 to 1.0 mm is particularly preferable. Thus, the crushing step crushes the tertiary particles to the secondary particles. That is, the obtained slurry is a slurry substantially composed of the flaky silica secondary particles of the present invention in which a plurality of flake primary particles substantially free of tertiary particles are oriented parallel to each other and overlapped with each other. It is.

If the concentration of SiO ₂ in the silica slurry supplied to the wet grinding apparatus is less than 1% by mass, the solid concentration is too low, and consequently there is a problem in economy such as the necessity of concentration in a later step. Is generated. On the other hand, when the SiO ₂ concentration is 3
If it exceeds 0% by mass, the viscosity of the crushed slurry becomes extremely large, and a problem occurs in handling.

FIG. 1 shows a scanning electron microscope (SEM) of the thus-obtained secondary particles of foliar silica according to the present invention.
It is a photograph. The scanning electron microscope can identify the leaf-like secondary particles, but cannot identify the ultrathin primary particles. From this, it can be seen that the foliar silica secondary particles exist independently of each other without binding or agglomeration.

FIG. 2 is a transmission electron microscope (TEM) photograph of the secondary particles of foliar silica in the present invention.
According to the TEM, it can be confirmed that the ultra-thin flake primary particles and the primary particles are leaf-like secondary particles in which a plurality of sheets are overlapped with their planes oriented in parallel.

A method for producing a dry powder comprising tertiary aggregated silica particles, and then wet-grinding (crushing) the resulting powder into a slurry of the secondary particles of foliar silica in the present invention.

In the above production process, the tertiary silica aggregate particles obtained in the form of a water slurry are first washed with water using a solid-liquid separation / washing apparatus such as a belt filter, a filter cloth centrifuge, a decanter or the like. -An SiO ₂ concentration of 1 to 30 consisting of silica tertiary aggregate particles having an average particle diameter of 1 to 10 µm substantially free of alkali metal salts by solid-liquid separation and, if necessary, repulping with water. A mass% of water slurry.

In this case, prior to obtaining leaf-like secondary particles dispersed by dry pulverization, first, the average particle diameter is 1 to 1
It is necessary to obtain a fine powder of 0 μm dispersed tertiary silica aggregate particles of the present invention by drying. However, the silica tertiary aggregate particles have a unique property that the aggregate particles are extremely easy to aggregate and bind during the drying operation. According to the study of the present inventors, when using a medium fluidized bed dryer as a drying device, for the first time,
A sufficiently dispersed dry powder of silica tertiary aggregate particles having an average particle diameter of 1 to 10 μm is obtained.

On the other hand, other drying devices, for example, a flash dryer, a spray dryer, a fluidized-bed dryer, a stirring dryer, a cylindrical dryer, a box dryer, a band dryer, a hot air dryer, and a vacuum dryer When a dryer, a vibration dryer, or the like is used, the tertiary particles are further aggregated during drying, and a large number of gaps (voids or pockets) formed by irregular overlapping of the leaf-like secondary particles are formed. Since the particle morphology is almost unrecognizable, the original sufficiently dispersed average particle diameter of 1 to 10
It is difficult to obtain silica tertiary aggregate particles of μm.

FIG. 3 is a scanning electron microscope (SEM) photograph showing the silica tertiary aggregate particles of the present invention obtained by drying in a medium fluidized bed drier. Foliate 2
It can clearly be seen that the secondary particles overlap irregularly, forming silica aggregate particles (tertiary particles) in which a number of gaps (voids or pockets) created by the overlap exist. The agglomerated particles can take on various forms, such as a cabbage, an onion, a petal, a bud, and a conch, in appearance.

Next, the above well-dispersed average particle diameter of 1
Water and / or a liquid organic medium is added to a dry fine powder of silica tertiary aggregate particles having a SiO ₂ concentration of 1 to 30 μm.
% By mass of the slurry.

The slurry is supplied to a wet bead mill (disintegration device) such as a wet bead mill or a wet ball mill in which mechanical high-speed stirring is performed using grinding medium beads in the same manner as described above, and silica tertiary aggregate particles are formed. By performing the crushing treatment, the secondary particle slurry of the present invention is obtained.

In the above, the secondary particles in the present invention are obtained as a slurry, but they can also be obtained as dry particles.

As a method for obtaining a dry fine powder of secondary particles of foliar silica (hereinafter also referred to as a dry powder of secondary particles in the present invention) in the present invention, for example, any of the following methods can be adopted.

Method for Obtaining Dry Powder of Secondary Particles in the Present Invention from Water Slurry of Secondary Particles of Leaf-like Silica

The monodispersed dry powder of leaf-like secondary particles is necessary when the secondary particles of leaf-like silica having an average particle diameter of 1 to 10 μm are to be used as a non-aqueous solvent-based adhesive.

As described above, the water slurry of the foliar silica secondary particles in the present invention described above has a unique property that the particles are extremely easily aggregated and bound during the drying operation. .

Accordingly, as a drying device, a flash dryer, a fluidized bed dryer, a medium fluidized bed dryer, a stirring dryer, a cylindrical dryer, a box dryer, a band dryer, a hot air dryer, a vacuum dryer, a vibration dryer, When a dryer or the like is used, the leaf-like secondary particles aggregate, and it is extremely difficult to obtain monodisperse leaf-like silica secondary particles.

In this case, using a spray dryer as a drying device, the water slurry comprising the foliar silica secondary particles of the present invention obtained in the above was dried, and the SiO ₂ concentration in the supply slurry was adjusted to 1 to 4. It has been found that, by adjusting to 5% by mass, preferably 1 to 3% by mass and spray-drying, for the first time, sufficiently dispersed leaf-like secondary particles having an average particle size of 1 to 10 μm can be obtained. If the SiO ₂ concentration in the slurry supplied to the spray dryer is less than 1% by mass, the amount of water to be evaporated is too large relative to silica, and this is problematic in terms of economy. On the other hand, S in the slurry
When the iO ₂ concentration exceeds 5% by mass, coagulation during drying is promoted, so that the leaf-like secondary particles aggregate and bind, and it is difficult to obtain monodisperse leaf-like silica secondary particles. .

A method for obtaining dried foliar silica secondary particles of the present invention from the above aqueous slurry of foliar secondary particles.

The dry powder of the monodispersed foliar silica secondary particles can be obtained by supplying a water slurry to a spray dryer in the same manner as described above and drying. However, in this case, for the same reason, the SiO ₂ concentration in the supply slurry is 1 to
It is preferable to adjust the amount to 7% by mass, preferably 1 to 5% by mass, and spray-dry.

A method of producing a dry powder composed of tertiary aggregated silica particles, followed by dry pulverization (crushing) to obtain the fine powder of the secondary foliar silica particles of the present invention.

The average particle size obtained above is 1 to 10 μm.
The dry powder of the silica tertiary aggregate particles of the present invention,
Dry pulverizer / classifier consisting of a combination of a dry pulverizer function and a dry classifier function, for example, using both a jet mill and a high-speed rotary classifier or an air classifier in combination, foliated with an average particle diameter of 1 to 10 μm It can be continuously crushed into silica secondary particles. That is, the raw material is continuously supplied to the jet mill, the pulverized product from the jet mill is classified by a dry classifier, and coarse particles larger than a desired particle size are continuously recycled to the jet mill and pulverized to a predetermined size or less. This is to form a system for continuously taking out what has been removed from the system.

As a method for obtaining a water slurry of secondary particles of foliar silica in the present invention described above, the method described in above is more preferable since a water slurry of secondary particles of foliar silica more suitable for an adhesive is obtained.

On the other hand, as a method for obtaining a dry fine powder of the secondary silica particles described above, the method described in 1 above is more preferable since a dry fine powder of the secondary secondary leaf particles which is most suitable for an adhesive is obtained. preferable.

The secondary particles of foliar silica obtained in the present invention obtained as described above are composed of secondary particles of flaky silica formed by laminating primary particles of flaky silica in parallel with each other with their planes oriented parallel to each other. It has a particle form of a laminated structure characterized by being substantially composed of particles and existing independently of each other.

[0093] Due to such a form, a hardened product made of strong silica can be easily formed even at room temperature, and this hardened product is an adhesive hardened product having a very specific adhesive function. I found it. That is, the present invention is an adhesive basically containing the above-mentioned foliar silica secondary particles as a main component based on such knowledge (hereinafter, also referred to as the adhesive of the present invention).

The above-mentioned foliar secondary particle slurry of the present invention comprises the foliar silica secondary particles defined in claim 1 and a volatile liquid, that is, water and / or a volatile liquid other than water (benzene, toluene, xylene, (A volatile organic solvent such as kerosene, light oil, etc.), which is made of metal, glass, ceramics, slates,
Same type of hardened cement, plastic, wood, paper, etc.
Alternatively, after applying to the surfaces of different kinds of substrates to be adhered and bringing the two substrates into close contact with each other and then drying the volatile liquid, a very tough adhesive cured body layer (adhesive layer) is easily formed on the adhered surface. Is done. Drying at room temperature or a method of drying at a temperature of 80 ° C. or less can be applied to shorten the required drying time.

This is actually a surprising phenomenon. For example, a water slurry of silica gel, which is the same as the present invention and is composed of amorphous porous particles composed of SiO ₂ particles, is coated and dried on the surface of the substrate to be bonded in the same manner. Even so, this is in sharp contrast to the fact that no adhesion function between the substrates was observed.

The function of forming the cured body having strong adhesiveness and the solidity of the formed film (adhesive layer) are considered to be due to the following reasons.

FIG. 4 is a SEM photograph of a layer cross section of an adhesive cured product comprising leaf-like silica secondary particles formed by applying and drying the secondary particle slurry in the present invention on a substrate to be adhered. Looking at this, the foliar silica secondary particles are basically configured by laminating the particles in parallel, but more specifically, the particle morphology has a moderate bend, respectively. It is clearly seen that they are oriented in a bent state and closely overlap. Since they bend and overlap with each other in a wavy manner in this manner, it is considered that they are unlikely to slide in the longitudinal direction (plane direction). Also, since a large number of minute irregularities are formed on the surface of the particles, they are entangled with each other like hooks, and exhibit a locking action like an anchor or a magic fastener. (A direction perpendicular to the direction), and it is considered that a strong adhesive cured body layer is formed as a whole.

The secondary particles are formed by laminating flake-like primary particles, and the flake primary particles are separated into individual flakes of the constituent unit by ordinary means. The foliar silica secondary particles of the present invention are strongly bonded and integrated with each other to such an extent that it is difficult to carry out. This is considered to be the reason why the adhesive cured layer formed of the foliated silica secondary particles in the present invention, in which the secondary particles are formed as constituent units (ie, so-called building blocks), is extremely strong.

It is to be noted that the secondary particles are layered in parallel on the surface of the substrate to be adhered and have a large contact area, and that the secondary particles of foliar silica have a large number of silanol groups on the surface as described below. Therefore, it is considered that having some kind of chemical adhesive action (for example, condensation of silanol groups) with the substrate to be adhered also contributes to the development of this strong adhesiveness.

Further, the adhesive layer was peeled off from the substrate to be bonded by using a razor, and an X-ray diffraction diagram of the surface of the cured body in contact with the substrate to be bonded, and the fine powder used to form the adhesive layer It was compared with the X-ray diffraction pattern.

Taking silica-X as an example, the two main peaks corresponding to ASTM card 16-0380, ie,
2θ is 26.0 for a peak height of 2θ of 4.9 °.
The ratio of the peak height in ° was 1 to 5 in the powder, while it was a small value of 0.0 to 0.5 in the adhesive layer. This seems to indicate a remarkable orientation of the crystal grains in the adhesive layer. Here, the peak height refers to the height of the zero count from the baseline.

On the other hand, the foliar silica 2 of the present invention was used.
Particles formed by three-dimensionally overlapping secondary particles (silica tertiary aggregate particles) have poor adhesion,
A strong film cannot be formed. That is, FIG. 5 is a SEM photograph of a cross section of a cured body layer composed of the tertiary aggregated silica particles. In this case, since the particle morphology is not basically leaf like secondary particles in the present invention,
It is clearly observed that it is difficult to form a tightly adhered and cured body layer because the layers cannot be laminated and closely overlap with each other.

Here, the specific basic physical properties of the foliar silica secondary particles in the present invention will be described. The SiO ₂ purity of the silica in the silica secondary particles is 99.0% by mass or more. The pH is 6.0 to 8.0, and the spectrum of X-ray diffraction is ASTM (American
Society for Testing and Materials) card (hereinafter simply referred to as an ASTM card) number 1
2θ = 4.9 °, 26.0 ° corresponding to 6-0380,
And the main peaks at 2θ = 5.6 °, 25.8 °, and 28.3 ° corresponding to Silica-X and / or ASTM card number 31-1233, characterized by a main peak at 28.3 ° and 28.3 °. This is silica composed of silica-Y. Coulter counter (manufactured by Coulter Electronics)
Mean particle size is 1 to 10 μm. Oil absorption (J
IS K 5101) is 100 to 150 ml / 100
g.

When the pore distribution of the silica secondary particles was measured by the BET method (trade name: Bellsorp-28, manufactured by Nippon Bell Co., Ltd.), the pore volume was 0.05 to 0.15 ml / g.
The specific surface area is 30~80m ² / g.

It should be particularly noted that the pore distribution curve shows a sharp large peak at a pore diameter of 2 to 6 nm, especially around 3.5 to 4.0 nm.

This indicates that pores in the mesopore region (a region having a pore diameter of 2 to 50 nm between micro and macro) are remarkably present. That is, the foliar silica secondary particles in the present invention have a laminar structure or a lamellar structure particle form in which a plurality of flake primary particles of flaky silica are oriented parallel to each other and overlap each other. It is presumed that voids formed between the overlapping flakes are measured as pores having the size of the meso region.

The infrared absorption spectrum (FT-IR) of the silica (SiO _{2 at} room temperature without heat treatment)
Is 3600-3700 cm ^-1 , 3400-3500c
Silica having silanol groups each having one absorption band at m ^-1 . Further, the amount of silanol groups per specific surface area by the BET method has a large value of 50 to 70 μmol / m ² (several times that of silica gel).

By having such a silanol group, the adhesive layer formed from the silica secondary particles in the present invention is subjected to a heat treatment at about 100 to 600 ° C., preferably about 200 to 600 ° C., and more preferably about 400 to 600 ° C. Thereby, the silanol group can be subjected to a condensation reaction to further improve the adhesive strength.

The heat resistance of the secondary particles of foliar silica in the present invention is 500 to 1000 in an air atmosphere.
After heating at ℃ for 1 hour, use a scanning electron microscope to
A change in the dimensions was observed, but no particular change was observed.

The saturated solubility of the foliar silica secondary particles in an aqueous acid solution and an aqueous alkali solution at 20 ° C. is low. That is, the dissolved SiO ₂ concentration is 0.008% by mass for a 10% by mass aqueous HCl solution, 0.006% by mass for ion-exchanged water, and 0% for a 5% by mass NaOH aqueous solution. It is 0.79% by mass with respect to an aqueous solution of 0.55% by mass and 10% by mass of NaOH, indicating that it has small solubility in both acids and alkalis and has acid resistance and alkali resistance. In particular, it has a very small solubility in an aqueous alkali solution as compared to silica gel or colloidal silica, and indicates that it has alkali resistance.

(3) Method of Using the Adhesive of the Present Invention The adhesive of the present invention comprises the secondary particles of foliar silica according to the present invention in a volatile liquid, that is, water and / or a volatile liquid other than water (benzene). , A volatile organic solvent such as toluene, xylene, kerosene, or light oil), that is, a water slurry and / or a volatile organic solvent slurry. This adhesive can be used for metals, glass, ceramics, slates, hardened cement, plastics,
It is useful as an adhesive applicable to adhesion between materials of the same kind or different kinds (substrates to be adhered) such as wood and paper.

Further, according to the present invention, in general, in an adhesive structure formed by bonding two substrates to be bonded via an adhesive layer, the adhesive layer is composed of flake primary particles of flaky silica. An adhesive structure is provided, which is an adhesive cured body layer composed of leaf-like silica secondary particles formed by overlapping a plurality of sheets with their planes oriented in parallel. This is the form defined in claim 4.

When the distance between the two substrates to be bonded is relatively narrow, the foliar silica secondary particles are more likely to be arranged in a direction parallel to the surface of the substrate to be bonded.
In the obtained adhesive structure, the adhesive layer is an adhesive cured layer formed by further laminating the above-mentioned secondary silica particles in parallel. This is the form defined in claim 5.

The means for applying the adhesive containing the silica secondary particles of the present invention to a substrate to be adhered to form an adhesive structure (hereinafter, also referred to as an adhesive) is not a specific one, but may be hand-painted. Means generally used for coating such as coating with a brush, coating with a bar coater, and spray coating can be used. There is no particular limitation on the drying after the application, and any means applicable to general drying can be used.

The adhesive of the present invention basically comprises the following:
As defined in the above, an adhesive containing flaky silica particles substantially consisting of the foliate silica secondary particles of the present invention and having a layered particle form independent of each other and a volatile liquid, When the volatile liquid in the adhesive is water, the mixture may be used in combination with at least one of an aqueous alkali silicate solution, colloidal silica, and a water-soluble polymer.

In this case, the aqueous alkali silicate solution has a solid content concentration of 1 to 60% by mass and a silica / alkali molar ratio (SiO ₂ / Me ₂ O, where Me is L
Indicates an alkali metal such as i, Na or K. ) Is 0.
1 to 3.8 mol / mol, preferably 0.5 to 3.8
mol / mol, more preferably 1.0 to 3.8 mo
1 / mol is desirable.

When the volatile liquid in the adhesive is an organic solvent, it can be used by mixing it with ethyl polysilicate, organoalkoxysilane, or the like. Above all, it is preferable to use a mixture with an aqueous silicate aqueous solution and an aqueous adhesive such as silica sol because of easy handling. In particular, an alkali silicate aqueous solution is preferable because the strength of the adhesive layer can be further improved.

As described above, the aqueous adhesive containing colloidal silica or the like has a problem that it is difficult to form a thick adhesive layer by itself, and there is a problem that the adhesive strength varies when the adhesive is made thicker. By mixing the adhesive of the present invention consisting essentially of the secondary particles and the aqueous adhesive containing colloidal silica or the like, a thick adhesive layer can be formed, and the adhesive strength can be stably exhibited. Become. The advantage of forming a thick adhesive layer is that even if the surface of the non-adhesive substrate is not a surface with high surface accuracy but a rough surface, reliable adhesion can be achieved.

As the water-soluble polymer, polyvinyl alcohol, polyvinylpyrrolidone, methylcellulose, carboxymethylcellulose, gelatin and the like can be used.

The proportion of solid content in the slurry adhesive of the present invention is as follows:
1 to 30% by mass, 1 to 50% by mass when colloidal silica is mixed with foliar silica secondary particles, 1 to 30% by mass when alkali silicate is mixed, and 1 to 30% by mass when water-soluble polymer is mixed , 1 to 30 mass. Note that water is most preferable as the volatile liquid.

The adhesive of the present invention may further contain other binders, fillers, additives and the like.

In the present invention, colloidal silica refers to silica particles having a particle size of 100 nm or less, preferably 50 nm or less, more preferably 10 nm or less, and 1 nm or more, and includes sol particles contained in colloidal silica and silica sol. The particle size of the silica particles is a value measured by a dynamic light scattering method (laser light scattering method), and the particle shape may be any one of an isotropic shape such as a substantially spherical shape, a chain shape, and an anisotropic shape. No problem. Thus, when the adhesive of the present invention contains at least one selected from the group consisting of colloidal silica, an aqueous solution of an alkali silicate and a water-soluble polymer (aspect of claim 2), Foliar silica secondary particles and / or colloidal silica and / or alkali silicate aqueous solution and / or alkali silicate aqueous solution and / or alkali silicate aqueous solution and / or alkali silicate other than foliar silica secondary particles, based on the total solid content in aqueous colloidal silica and / or water-soluble polymer It is desirable that the proportion of the total solid content in the conductive polymer is 2 to 90% by mass, preferably 5 to 85% by mass.

The thickness of the adhesive layer between the substrates to be adhered is basically several μm to several hundred μm. However, if desired, it can be used as a so-called putty or sealant with a thickness of several tens mm for joints or the like.

The adhesive of the present invention exhibits extreme anisotropy in the adhesive strength of the adhesive layer, especially when the adhesive is substantially composed of foliar silica secondary particles and when the substrate to be adhered is paper. A surprising peculiar phenomenon is observed.

That is, after the adhesive of the present invention has been applied to the ends of two sheets of paper, the adhesive structure dried and adhered to the surface of the paper against the horizontal (deviation) pull. ,
Although the adhesive strength is high enough to break the paper, the adhesive layer can be peeled off very easily against the force of peeling in the direction perpendicular to the surface of the paper.

This phenomenon is considered to be due to the following reasons. When the two sheets of paper to which the ends are bonded are peeled in the direction perpendicular to the paper surface, since the paper is a flexible substrate material to be bonded, a large bending deformation is directly applied to the bonding layer.
It is considered that the adhesive layer is easily broken by the force perpendicular to the paper surface due to the destruction of the adhesive layer.

On the other hand, it is considered that almost no bending deformation is applied to the adhesive layer when the paper is pulled in the horizontal direction with respect to the paper surface.

Since the adhesive of the present invention has a release property based on such a unique anisotropy, it is also used for an easy-release adhesive for a flexible substrate material such as paper and a temporary fixing. Available.

The foliar silica secondary particles in the present invention are useful as an adhesive applicable to adhesion between the fine particles even when the substrate to be bonded is fine particles.
The fine particles may be fine particles of the same or different materials.

For example, the foliar silica secondary particles can be suitably used for a coating agent for a recording medium for an ink jet printer (eg, paper, plastic sheet, etc.). That is, this is because the particle shape is spherical or amorphous, the oil absorption is large (200 ml / 100 g or more),
Suitable for use as an adhesive between the same or different material fine particles by using in combination with colloidal particles such as silica gel fine particles or alumina sol (boehmite) having an average particle diameter of 1 to 30 μm or organic polymer fine particles having a large oil absorption. it can. A recording medium for an ink jet printer using the secondary particles of foliar silica has a characteristic feature that the ink absorption speed is high and the color density is high.

[0131]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments.

[Example 1] (Production of tertiary silica aggregate particles using hydrogel as starting material) A silica hydrogel as a starting material was prepared using sodium silicate as an alkali source as follows. SiO ₂ / N
a ₂ O = 3.0 (molar ratio), 2,000 ml / min of sodium silicate aqueous solution with SiO ₂ concentration of 21.0 mass%
And a sulfuric acid aqueous solution having a sulfuric acid concentration of 20.0% by mass are introduced into a container provided with a discharge port through separate inlets, and are mixed instantaneously and uniformly. Was adjusted to 7.5 to 8.0, and the silica sol solution uniformly mixed was continuously discharged into the air from the discharge port. The released liquid became spherical droplets in the air, and gelled in the air while flying in a parabola for about 1 second. At the drop point, leave an aging tank filled with water,
Dropped here and aged.

After aging, the pH was adjusted to 6, and the mixture was sufficiently washed with water to obtain a silica hydrogel. The obtained silica hydrogel particles have a spherical particle shape and an average particle diameter of 6
mm. SiO ₂ in the silica hydrogel particles
The mass ratio of water to mass was 4.55 times, and the residual sodium in the silica hydrogel particles was 110 ppm.
Met.

The silica hydrogel particles were coarsely pulverized to an average particle diameter of 2.5 mm using a double roll crusher and used in the next hydrothermal treatment step.

In a 50,000 ml autoclave (electrically heated, with anchor-type stirring blades), the total Si in the system was
The silica hydrogel having a particle diameter of 2.5 mm (SiO ₂ 18% by mass) so that the O ₂ / Na ₂ O molar ratio is 12.0.
23.7 kg and sodium silicate aqueous solution (SiO ₂ 2
8.75% by mass, 9.3% by mass of Na ₂ O, SiO ₂ / N
5.5 kg of a ₂ O = 3.17 (molar ratio) was added, and 10.7 kg of ion-exchanged water was added thereto, and a hydrothermal treatment was performed at 185 ° C. for 8 hours while stirring at 50 rpm. The total silica concentration in the system was 15% by mass as SiO ₂ .

The slurry after the hydrothermal treatment was subjected to filtration and water washing using a filter cloth type vertical centrifugal separator (manufactured by Toko Kikai Co., Ltd., TU-18 type) to give a solid water content of 69.7% by mass (solid content concentration). 3
0.3% by mass) of a silica wet cake.

Water was added to the wet cake and repulped.
After a slurry of silica having a SiO ₂ concentration of 7.0% by mass was formed, a medium fluidized bed drier (manufactured by Okawara Seisakusho, SFD-MI)
NI type) and dried at a hot air temperature of 300 ° C.
kg of dry fine powder was obtained.

The product phase of the resulting fine powder was identified by the powder X-ray diffraction spectrum. As a result, the X-ray diffraction spectrum of 2θ = 4.9 ° and 26.0 ° corresponding to ASTM card No. 16-0380 was obtained. In addition to the main peak of silica-X characterized by the main peak, peaks corresponding to ASTM card numbers 31-1235 and 37-0386 were observed. Also. The ratio of the peak height at 2θ of 26.0 ° to the peak height at 2θ of 4.9 ° was 2.5.

The oil absorption of this fine powder (JIS K
5101) was 110 ml / 100 g.

The morphology of the formed particles was determined by a transmission electron microscope (TE).
When observed in M), it was observed that the scale-like flake primary particles were oriented parallel to each other between the planes, and a plurality of sheets were overlapped to form leaf-like silica secondary particles.

On the other hand, when the morphology of the formed particles was observed with a scanning electron microscope (SEM), the primary particles could not be identified, and were observed as if the secondary particles of foliar silica were primary particles. Was. The shape of the leaf-like particles was scaly, and it was observed that the tertiary silica aggregate particles having a large number of gaps (voids or pockets) were irregularly overlapped and formed. This is the silica tertiary aggregate particle in the present invention.

With respect to the average thickness of the portion of the leaf-like particles (corresponding to the secondary particles in the TEM) of 0.06 μm observed by the scanning electron microscope (SEM), the average maximum length of the plate with respect to the thickness is as follows. , The aspect ratio is 90 at 5.4 μm,
The average minimum length of the plate is 1.6 μm and the aspect ratio is 27
Met.

The average particle diameter of the fine powder (silica tertiary aggregate particles) was measured using a Coulter Counter (MAII, manufactured by Coulter Electronics Co., Ltd., aperture tube diameter: 50).
μm (same in the following examples), it was 6.1 μm.

Further, when the amount of crystalline free silicic acid of the fine powder was measured by X-ray diffraction analysis, it was found that the amount was below the detection limit (2% or less).

[Example 2] (Production of tertiary aggregated silica particles using hydrogel as starting material) A silica hydrogel as a starting material was prepared as follows using NaOH as an alkali source. SiO ₂ / Na ₂ O =
A sodium silicate aqueous solution having a concentration of 3.0 (molar ratio) and an SiO ₂ concentration of 21.0 mass% and a sulfuric acid aqueous solution having a sulfuric acid concentration of 20.0 mass% were separately placed in a container provided with a discharge port. The liquid introduced from the inlet is instantaneously mixed uniformly, and the pH of the liquid discharged into the air from the outlet is 7.5 to 7.5.
The flow rate ratio of the two liquids was adjusted so as to be 8.0, and the uniformly mixed silica sol liquid was continuously discharged into the air from the discharge port. The released liquid became spherical droplets in the air, and gelled in the air while flying in a parabola for about 1 second. An aging tank filled with water was placed at the dropping point, and the ripening tank was dropped and ripened.

After aging, the pH was adjusted to 6, and the mixture was sufficiently washed with water to obtain a silica hydrogel. The obtained silica hydrogel particles have a spherical particle shape and an average particle diameter of 6
mm. SiO ₂ in the silica hydrogel particles
The mass ratio of water to mass is 4.38 times, and the residual sodium in the silica hydrogel particles is 112 ppm.
Met.

The above silica hydrogel particles were coarsely pulverized to an average particle diameter of 2.5 mm using a double roll crusher and used in the next hydrothermal treatment step.

In a 5000 ml autoclave (electrically heated, with anchor-type stirring blades), the total SiO 2 in the system was
2688 g of the above silica hydrogel having a particle diameter of 2.5 mm (18.6% by mass of SiO ₂ ) and an aqueous solution of sodium hydroxide (NaOH) so that the molar ratio of ₂ / Na ₂ O is 11.0.
126 g of 48.5 mass%), 1186 g of ion-exchanged water was added thereto, and 0.5 g of a seed crystal was added thereto.
Hydrothermal treatment was performed at 180 ° C. for 12 hours while stirring at rpm. The total silica concentration in the system was 12.5 as SiO _2.
% By mass.

The slurry after the hydrothermal treatment was subjected to filtration and water washing using a filter cloth type vertical centrifugal separator (manufactured by Toko Kikai Co., Ltd., TU-18 type) to give a solid water content of 66.7% by mass (solid content concentration). 3
(3.3% by mass) of silica was obtained.

Water was added to the wet cake and repulped.
After a slurry of silica having a SiO ₂ concentration of 7.0% by mass was formed, a medium fluidized bed drier (manufactured by Okawara Seisakusho, SFD-MI)
NI type) and dried at a hot air temperature of 300 ° C.
g of dry fine powder was obtained.

The generated fine powder was identified by a powder X-ray diffraction spectrum to identify the generated phase.
ASTM card number 31-
In addition to the main peak of silica-Y characterized by main peaks of 2θ = 5.6 ° and 25.8 ° corresponding to 1233, AST
Peaks corresponding to M card numbers 35-63 and 25-1332 were observed.

The oil absorption of this fine powder (JIS K
5101) was 100 ml / 100 g.

The morphology of the produced particles was determined by a transmission electron microscope (TE).
When observed in M), it was observed that the scale-like flake primary particles were oriented parallel to each other between the planes, and a plurality of sheets were overlapped to form leaf-like silica secondary particles.

On the other hand, when the morphology of the formed particles was observed with a scanning electron microscope (SEM), the primary particles could not be identified, and were observed as if the secondary particles of foliar silica were primary particles. Was. The shape of the leaf-like particles was scaly, and it was observed that the tertiary silica aggregate particles having a large number of gaps (voids or pockets) were irregularly overlapped and formed.

The average longest length of the plate with respect to the average thickness of 0.07 μm of the leaf-like particles (corresponding to the secondary particles in the TEM) observed with the scanning electron microscope (SEM) Is 6.0 μm and its aspect ratio is 8
6. The average minimum length of the plate was 1.8 μm and the aspect ratio was 26.

The average particle size of the fine powder was measured using a Coulter Counter (manufactured by Coulter Electronics, MA
It was 6.5 μm when measured using Type II).

Further, the amount of crystalline free silicic acid of the fine powder was X
When measured by X-ray diffraction analysis, it was below the detection limit (2
% Or less).

[Example 3] (Production of slurry-like secondary particles of foliar silica from the wet cake of Example 1) 1000 g of a wet cake after filtration and washing with a centrifuge shown in Example 1 (solid content: 30.3) Mass%) in water 102
0 g was added and repulped to prepare a silica slurry having a solid content of 15% by mass. In this slurry state, the average particle size measured by a Coulter counter was 7.2 μm, and the viscosity measured by a B-type viscometer was 0.010 Pa · s.

Next, this slurry was mixed with a medium stirring bead mill (Dynomill KD, manufactured by Shinmaru Enterprises Co., Ltd.).
L-PILOT A type (vessel capacity 1.4L, diameter 0.5mm, filled with zirconia beads 80%)), shaft rotation speed 3400rpm, flow rate 30L / h, 1 pass
Then, the silica tertiary aggregate particles were crushed and dispersed.

The average particle diameter of the fine particles in the crushed and dispersed slurry measured by a Coulter counter was 1.6 μm. The viscosity of the slurry was measured with a B-type viscometer and found to be 0.13 Pa · s.

Next, a dried powder was obtained by the following method in order to examine the physical properties of the dried foliated silica secondary particles close to the state of the fine particles in the slurry.

Since the slurry has a peculiar property that it is extremely easily aggregated by drying, in order to obtain a monodispersed dry powder, a water slurry having an extremely low concentration is dried while preventing aggregation. There is a need.

That is, the slurry (solids concentration 15
Water), and the slurry concentration was adjusted to a solid concentration of 0.3% by mass.

The slurry was supplied using a small spray dryer (GA32, manufactured by Yamato Scientific Co., Ltd.) at a slurry supply rate of 1.7 ml / min and a spray pressure of 0.3 MPa.
(G), spray drying was performed at a hot air temperature of 130 ° C. to obtain a dry fine powder. The average particle size of the obtained dry fine powder measured by a Coulter counter was 1.9 μm.

The fine powder is subjected to a scanning electron microscope (SEM)
As a result, substantially no silica tertiary aggregate particles were observed, and it was found that the particles were substantially composed of the secondary particles of foliar silica of the present invention.

When the product phase of this fine powder was identified by a powder X-ray diffraction spectrum, the powder was identified as an X-ray diffraction spectrum, corresponding to ASTM card number 16-0380.
ASTM card number 31-1 in addition to the main peak of silica-X characterized by main peaks at θ = 4.9 ° and 26.0 °
235, 37-0386.

The ratio of the peak height at 2θ of 26.0 ° to the peak height at 2θ of 4.9 ° was 1.4.

The morphology of the formed particles was determined by a transmission electron microscope (TE).
When observed in M), it was observed that the scale-like flake primary particles were oriented parallel to each other between the planes, and a plurality of the flake-like primary particles of the present invention were formed to overlap with each other.

Further, this fine powder was embedded in an epoxy resin, ultra-thin sections were prepared with an ultramicrotome, and observed with a transmission electron microscope (TEM). The thickness of the primary particles was found to be 1 to 10 nm. It turned out to be very thin.

The fine powder had a pore volume of 0.12 ml / g and a specific surface area of 65 m ² / g by a BET method pore distribution measuring apparatus (manufactured by Nippon Bell Co., Ltd., type Bellsorpe 28).
In the pore distribution curve, a sharp large peak in the mesopore region was observed around 3.6 nm. Further, an infrared absorption spectrum of the fine powder (FT-IR51, manufactured by Nicole Japan)
0) 3600-3700 cm ^-1 , 3400
Silanol groups having one absorption band at ~ 3500 cm ^-1 were observed.

Also, the amount of the silanol group (SiOH) is
From the difference between the loss on drying at 120 ° C. for 2 hours and the loss on heating at 1200 ° C. for 3 hours (W mass%), silanol groups per unit mass of silica (SiOH) = W × 111.
According to a calculation formula of 1.1 (μmol / g), 36
It was 50 μmol / g, which was a large value of 56.2 μmol / m ² per specific surface area according to the BET method.

Regarding heat resistance, 500
At ~ 1000 ° C, no particular change was observed by observation with a scanning electron microscope.

20 for acid aqueous solution and alkaline aqueous solution
For saturated solubility at 0 ° C., the dissolved SiO ₂ concentration is 1
0% by mass, 0.008% by mass for HCl aqueous solution, 0.006% by mass for ion exchanged water, 0.55% by mass for 5% by mass NaOH aqueous solution, 10% by mass
It was 0.79% by mass with respect to the mass% NaOH aqueous solution. Particularly with respect to alkali, the solubility was very small as compared with, for example, silica gel.
6.5% by mass).

[Example 4] (Production of slurry-like secondary particles of foliar silica from the wet cake of Example 2) [0174] Using the wet cake after filtration and washing with a centrifuge shown in Example 2, Medium stirring bead mill (Shinmaru Enterprises, Dino Mill KDL-PIL
OT A type (vessel capacity 1.4 L, diameter 0.5 mm, filled with 80% zirconia beads)) and shaft rotation number 340
The mixture was subjected to 1 pass at 0 rpm and a flow rate of 30 L / h to crush and disperse the tertiary aggregated silica particles to obtain a water slurry of foliar silica secondary particles having a solid content of 15% by mass.

The average particle diameter of the fine particles in the slurry after crushing and dispersing was 1.7 μm as measured by a Coulter counter. The viscosity of this slurry was measured with a B-type viscometer, and was 0.11 Pa · s.

Example 1 A slurry composed of secondary particles of foliar silica having a solid content of 15% by mass in the medium stirring bead mill described in Example 3 (average particle diameter: 1.6 μm)
Was put into a 50 ml beaker, and sufficiently stirred and mixed with a stirrer to obtain a slurry adhesive.

Next, test pieces (steel plate, stainless steel plate, glass plate, 25 mm × 1) according to JIS K 6848
(Thickness: 00 mm x 2 mm) were prepared, and an adhesion test of a plate of the same material was performed. The test method is as follows:
A 2.5 mm portion was used as an adhesive portion, and one drop of the slurry was applied using a dropper, superposed, and allowed to stand horizontally. A load of 1 kg was applied from above and dried at room temperature for 48 hours to obtain a test piece.

The adhesive per unit area of the adhesive layer was a very small amount of about 3 g / m ^{2 in} terms of solid content, and the thickness of the adhesive layer was about 5 μm. Further, the appearance of the glass-bonded surface was translucent, and no cracks or the like were observed, and it was uniform.

As a method of evaluating the adhesive strength, the tensile shear adhesive strength was measured according to JIS K 6850, and the compressive shear adhesive strength was measured according to JIS K 6852. Table 1 shows the results.

[0180]

[Table 1]

[Example 2] A slurry composed of foliate silica secondary particles (average particle size: 1.7 µm) using a medium-dispersed bead mill described in Example 4 and subjected to monodispersion treatment at a solid content of 15% by mass.
Was put into a 50 ml beaker, and sufficiently stirred and mixed with a stirrer to obtain a slurry adhesive.

Next, a test piece (stainless steel plate, 25 mm × 100 mm × 2 mm) according to JIS K 6848
Thickness) were prepared, and an adhesion test of a steel plate was performed. As a test method, a 12.5 mm end of the material plate was used as an adhesive portion, and the slurry was applied with a drop using a dropper, and the layers were superposed and allowed to stand horizontally. A load of 1 kg was applied from above, and 48 hours at room temperature. It dried and was set as the test piece.

The adhesive per unit area of the adhesive layer is about 3 g / m ² in terms of solid content, and the thickness of the adhesive layer is about 5 μm.
Met.

The appearance of the steel sheet bonding surface is translucent,
Cracks and the like were not observed and were uniform.

As a method of evaluating the adhesive strength, the tensile shear adhesive strength was measured according to JIS K 6850, and the compressive shear adhesive strength was measured according to JIS K 6852. Table 2 shows the results.

[0186]

[Table 2]

[Example 3] A slurry composed of foliar silica secondary particles having a solid content of 15% by mass using a medium stirring bead mill described in Example 3 (average particle diameter: 1.6 µm)
Is placed in a 50 ml glass bottle, and then colloidal silica (catalyst SI-30, manufactured by Catalyst Chemical Industry Co., Ltd., trade name: Cataroid SI-30, 30% by mass of SiO ₂ , particle size: 10 to 14 n)
m) was added, and the bottle was shaken well to mix uniformly to obtain a slurry adhesive. The mass ratio of the secondary particles of the foliated silica to the colloidal silica based on the solid content is 50:50.

Next, two test pieces (glass plate, 25 mm × 100 mm × 2 mm thickness) in accordance with JIS K 6848 were prepared, and an adhesion test of the glass plates was performed. As a test method, a 12.5 mm end of the material plate was used as an adhesive portion, and the slurry was applied with a drop using a dropper, and the layers were superposed and allowed to stand horizontally. A load of 1 kg was applied from above, and 48 hours at room temperature. After drying, heat treatment was performed at 450 ° C. for 1 hour to obtain a test piece.

The adhesive per unit area of the adhesive layer is about 4 g / m ² in terms of solid content, and the thickness of the adhesive layer is about 5 μm.
Met.

The appearance of the glass plate bonded surface was substantially translucent, with no cracks and the like, and was uniform.

As a method of evaluating the adhesive strength, the tensile shear adhesive strength was measured according to JIS K 6850, and the compressive shear adhesive strength was measured according to JIS K 6852. Table 2 shows the results.

[Example 4] A slurry composed of foliar silica secondary particles having a solid content of 15% by mass in the medium stirring bead mill described in Example 3 (average particle diameter: 1.6 µm)
Was placed in a 50 ml glass bottle, and then an aqueous solution of sodium silicate (Na ₂ O: 18.0% by mass, Si
O ₂ : 36.5 mass%, SiO ₂ / Na ₂ O molar ratio:
5.5 g of 2.1) was added, and the bottle was shaken to mix uniformly to obtain a slurry adhesive. The solid content-based mass ratio of the foliar silica secondary particles to sodium silicate is 50:50.

Next, two test pieces (glass plate, 25 mm × 100 mm × 2 mm thickness) according to JIS K 6848 were prepared, and an adhesion test of the glass plates was performed. As a test method, a 12.5 mm end of the material plate was used as an adhesive portion, one drop of the slurry was applied using a dropper, superposed, and allowed to stand horizontally.
It dried at 2 degreeC for 2 hours, and was set as the test piece.

The adhesive per unit area of the adhesive layer was extremely small at about 5 g / m ^{2 in} terms of solid content, and the thickness of the adhesive layer was about 5 μm.

Further, the appearance of the glass-bonded surface was translucent, and no cracks were observed, and it was uniform.

As a method of evaluating the adhesive strength, the tensile shear adhesive strength was measured according to JIS K 6850, and the compressive shear adhesive strength was measured according to JIS K 6852. Table 2 shows the results.

[Example 5] A slurry composed of foliar silica secondary particles having a solid content of 15% by mass in the medium stirring bead mill described in Example 3 (average particle diameter: 1.6 µm)
Was placed in a 50 ml glass bottle, and then an aqueous solution of sodium silicate (Na ₂ O: 18.0% by mass, Si
O ₂ : 36.5 mass%, SiO ₂ / Na ₂ O molar ratio:
2.3) g of 2.1) was added, and the bottle was shaken to mix uniformly to obtain a slurry adhesive. The solid content-based mass ratio of the foliar silica secondary particles to sodium silicate is 70:30.

Next, two test pieces (glass plate, 25 mm × 100 mm × 2 mm thickness) according to JIS K 6848 were prepared, and an adhesion test of the glass plates was performed. As a test method, a 12.5 mm tip of the material plate was used as an adhesive portion, and the slurry was coated with one drop using a dropper, superposed, and allowed to stand horizontally. A load of 1 kg was applied from above, and the load was applied at room temperature for 24 hours. After drying, it was heated at 450 ° C. to obtain a test piece.

The adhesive per unit area of the adhesive layer was a very small amount of about 7 g / m ^{2 in} terms of solid content, and the thickness of the adhesive layer was about 8 μm.

Further, the appearance of the glass-bonded surface was translucent, no cracks were observed, and the surface was uniform.

As for the evaluation method of the adhesive strength, the tensile shear adhesive strength was measured according to JIS K 6850, and the compressive shear adhesive strength was measured according to JIS K 6852. Table 2 shows the results.

Example 6 Slurry consisting of secondary particles of foliar silica having a solid content of 15% by mass in the medium stirring bead mill described in Example 3 (average particle diameter: 1.6 μm)
In a 50 ml glass bottle of 10.0 g, and then an aqueous solution of polyvinyl alcohol (MA2, manufactured by Shin-Etsu Chemical Co., Ltd.)
6, solid content: 9.46% by mass) and uniformly mixed with a spatula to obtain a slurry adhesive. The solid content-based mass ratio of the foliar silica secondary particles to polyvinyl alcohol is 50:50.

Next, two test pieces (glass plates, 25 mm × 100 mm × 2 mm thickness) in accordance with JIS K 6848 were prepared, and an adhesion test of the glass plates was performed. As a test method, a 12.5 mm front end of the material plate was used as an adhesive portion, one drop of the slurry was applied using a spatula, superposed, and allowed to stand horizontally.
It dried at 2 degreeC for 2 hours, and was set as the test piece.

The adhesive per unit area of the adhesive layer was a very small amount of about 6 g / m ^{2 in} terms of solid content, and the thickness of the adhesive layer was about 5 μm.

Further, the appearance of the glass-bonded surface was translucent, and no cracks or the like were observed, and it was uniform.

As a method for evaluating the adhesive strength, the tensile shear adhesive strength was measured according to JIS K 6850, and the compressive shear adhesive strength was measured according to JIS K 6852. Table 2 shows the results.

[Example 7] A slurry composed of secondary particles of foliar silica having a solid content of 15% by mass in the medium stirring bead mill described in Example 3 (average particle diameter: 1.6 µm)
Was put into a 50 ml beaker and sufficiently stirred and mixed with a stirrer to obtain a slurry adhesive.

Next, A4 size copy paper (neutral P
(PC paper) were prepared, and a paper adhesion test was performed. As a test method, a portion at the leading end 20 mm on the short width side of the paper was used as an adhesive portion, the above-mentioned adhesive was applied, only the adhesive portion of the paper was overlaid and left horizontally, allowed to dry at room temperature for 48 hours, and dried. And The amount of adhesive per unit area is about 1 in solid content.
It was 0 g / m ² .

[0209] The paper of the bonded test piece was placed horizontally, and both ends thereof were strongly pulled by hand in opposite horizontal directions. As a result, the bonded portion did not peel off, and the non-bonded portion of the paper was broken.

Next, two sheets of A4 size copy paper similar to those described above were prepared, and similarly, the portion of the short width side of the leading end of 20 mm was used as an adhesive portion, and the above-mentioned adhesive was applied. Alone, and left horizontally, and dried at room temperature for 48 hours to obtain a test piece. The amount of the adhesive per unit area was about 10 g / m ² in terms of solid content.

[0211] The paper of the bonded test piece was held vertically with the bonded portion facing down, and the upper unbonded ends were slowly pulled by hand in opposite horizontal directions.
The whole bonded part was peeled off very easily. When the sheet was held horizontally and both ends were strongly pulled by hand in opposite horizontal directions, the bonded portion did not peel off, and the non-bonded portion of the paper was broken.

[0212]

As described above, the adhesive of the present invention can form a strong adhesive at room temperature, and can be used for metal, ceramics, slate, hardened cement, plastic, wood, paper and glass. It is suitably used for bonding materials.

Since the foliar silica secondary particles used in the adhesive of the present invention have the above-mentioned unique form,
By subjecting the outer surface of the particles to a surface treatment such as an electroless plating method or a sputtering method, the particles can be coated with an electrically conductive metal thin film. The plated leaf-like particles, for imparting a radio wave absorbing function or an electromagnetic wave shielding function to a housing or a component such as an electronic device,
It can be suitably used as a filler for a resin compound or a filler for a conductive paint.

[0214] Similarly, particles in which the outer surfaces of the leaf-like silica secondary particles are coated with a metal coating of gold, silver, a nickel-phosphorus alloy or the like by an electroless plating method or a sputtering method or the like can be suitably used as a brilliant pigment or the like. .

Further, the present inventors have found that the secondary particles of foliar silica have an effect of improving the dispersibility of the fine particles when mixed with other functional fine particles. Therefore, it can be suitably used as a non-curable composition in which the intrinsic function of the functional fine particles is maximized by blending the functional fine particles with a low-volatile liquid or the like. For example, the foliar silica secondary particles are mixed with a functional fine particle having an ultraviolet shielding function such as titanium oxide, zinc oxide, cerium oxide, and zirconium oxide, and a low-volatile liquid such as silicone oil to have an ultraviolet shielding function. It can be suitably used for cosmetics and sunscreen creams. In addition, it is also possible to mix | blend a volatile liquid with this as needed.

The reason that the foliar silica secondary particles in the present invention promotes the dispersibility of the functional fine particles is that along the surface of the silica secondary particles, the particle size is much smaller than 0.01 to 0.5 μm. This is presumably because the functional fine particles having a particle size of the order are supported with good dispersibility.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph showing the structure of secondary particles of foliar silica in the present invention.

FIG. 2 is a transmission electron micrograph showing the secondary particle structure of foliar silica in the present invention.

FIG. 3 is a scanning electron micrograph showing a silica tertiary aggregate particle structure according to the present invention.

FIG. 4 is a scanning electron micrograph of a cross-sectional structure of an adhesive cured body layer composed of leaf-like silica secondary particles according to the present invention.

FIG. 5 is a scanning electron micrograph of a cross-sectional structure of a cured body layer composed of tertiary silica aggregate particles.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Atsushi Fujii, Inventor 13-1, Kitaminato-machi, Wakamatsu-ku, Kitakyushu-shi, Fukuoka Prefecture (72) Inventor Takayoshi Sasaki Kitaminato-cho, Wakamatsu-ku, Kitakyushu-shi, Fukuoka No. 13-1 Dokai Chemical Industry Co., Ltd. (72) Inventor Shiyuki Minohara No. 13-1 Dokai Chemical Industry Co., Ltd. 13-2 Kitaminato-cho, Wakamatsu-ku, Kitakyushu-shi, Fukuoka Prefecture (72) Inventor Yoshimi Oba Wakamatsu, Kitakyushu-shi, Fukuoka 13-1 Kitaminatocho, Ward Dokai Chemical Industry Co., Ltd. F-term (reference) 4G072 AA28 AA38 BB20 CC13 EE07 GG02 HH21 JJ13 JJ15 JJ22 JJ47 MM01 MM02 MM21 MM31 PP17 RR06 RR12 RR20 TT30 UU30 4J002 DJ031 DJ011 FB016 FD016 FD017 FD208 GJ01 HA06 4J040 AA011 AA012 HA126 HA301 HA302 HA311 HA312 JA02 JA03 KA01 KA03 KA23 LA07 LA08 MA02 MA04 MA05 MA06 MA08 MA09 MA10

Claims (7)

[Claims] 1. A flake-like silica primary particle is substantially composed of a plurality of leaf-like silica secondary particles formed by laminating a plurality of flake-like silica primary particles which are oriented parallel to each other, and have a laminated structure independent of each other. An adhesive comprising secondary silica particles having a form and volatile liquid. 2. The adhesive according to claim 1, further comprising at least one selected from the group consisting of colloidal silica, an aqueous solution of an alkali silicate, and a water-soluble polymer. 3. The adhesive according to claim 1, wherein the foliar silica secondary particles are silica whose main peak in the X-ray diffraction analysis of the silica particles corresponds to silica-X and / or silica-Y. . 4. An adhesive structure formed by bonding two substrates to be bonded via an adhesive layer, wherein the adhesive layer is composed of a plurality of flake-like silica flake primary particles whose primary surfaces are oriented in parallel with each other. An adhesive structure, characterized in that it is an adhesive cured layer composed of leaf-like silica secondary particles formed in an overlapping manner. 5. The adhesive structure according to claim 4, wherein the adhesive layer is an adhesive cured layer formed by further laminating the leaf-like silica secondary particles in parallel. 6. The adhesive structure according to claim 4, wherein a main peak of the adhesive layer in X-ray diffraction analysis is silica corresponding to silica-X and / or silica-Y. 7. An X-ray diffraction pattern measured on the surface of the cured layer in contact with the substrate to be bonded, wherein the main peak is composed of silica-X, and 2θ is 26. 0 ° peak height ratio of 0.0 to 0.5
The adhesive structure according to claim 6, which is: