KR101218786B1 - Preparation method of transparent alumina sols - Google Patents

Abstract

The present invention relates to a method for preparing a transparent alumina sol dispersed in methanol, and more particularly, after dissolving aluminum alkoxide in excess methanol as a starting material, hydrolysis and polycondensation reaction with a small amount of water. It is a method for producing alumina sol by forming boehmite particles through. The present invention is that the boehmite particles are dispersed in methanol, it is excellent in miscibility with the organic material and transparent to compensate for the disadvantages of the alumina sol dispersed in the existing water, and excellent storage stability plastic surface coating agent, paint It can be effectively used in various applications such as the preparation of additives, gas barrier coatings, in particular heat curing and ultraviolet curing hard coating solution.

Description

Preparation method of transparent alumina sol {Preparation method of transparent alumina sols}

The present invention relates to a method for producing an alumina sol using methanol as a dispersion medium, and more particularly, by preparing an alumina sol in which particles having a boehmite structure (see FIG. 2) are dispersed in methanol, a plastic surface coating agent, a paint coating agent, The present invention relates to a method for preparing a transparent alumina sol that can be effectively utilized for various applications such as preparing gas barrier coatings, in particular, thermal curing and ultraviolet curing hard coating solutions.

Alumina sol refers to a state in which alumina hydrate, not alumina particles, is well dispersed in a solvent in colloidal form. Alumina sol is usually produced using the sol-gel method.

Alumina is simply expressed as Al ₂ O ₃ in the chemical formula, but is widely used in various industrial fields because it is chemically stable, has a high melting point, and excellent physical properties such as electrical insulation, mechanical strength, and hardness. In particular, in order to take advantage of the excellent mechanical strength of alumina, there is a tendency to use a lot as an additive in the production of various organic coating solutions.

Alumina is one of the representative neutral refractory materials, which does not have erosion to various materials and maintains its properties even at high temperatures, and thus can be regarded as a higher inorganic binder than a silica sol binder. In addition, alumina sol is capable of forming a film, and thus a good film is formed by drying. In addition, the alumina sol has flexibility because the sol particles have a fibrous structure. In addition, alumina sol has water retention, antistatic property, ion adsorption property, and gas barrier property, and thus is used in various applications such as plastic surface coating agent, adsorbent, gas barrier coating agent, especially additive of organic-inorganic hybrid hard coating solution.

For example, aluminum alkoxide reacts violently with water to form hydrate (Hydroxide), which is divided into AlH (OH) which is boehmite phase and Al (OH) _{3 which} is baitite or gibbsite phase depending on the reaction temperature.

In other words, the hydrolysis at low temperature is gradually replaced by the OH group as the concentration of the OR group in the hydrate increases to become Al (OH) ₃ in the baeryt or gibbsite phase and become structurally unstable. On the other hand, hydrolysis at a high temperature of 80 ° C. or higher does not affect the aging due to the vigorous release of the OR group, thus limiting the dissolution of the OH group and the conversion to the baehritite or gibbsite, and to the boehmite phase AlO (OH). .

According to Yoldas, the hydrolysis reaction of aluminum alkoxide is as follows.

This proceeds with a rapid reaction of polycondensation.

The reaction proceeds with a molecular formula of Al _n O _{n -1} (OH) _{n + 2-x} (OR) _x . In this form, the number x of OR groups depends on the hydrolysis temperature and the concentration of OR groups in solution.

Hydrate, produced by hydrolysis, becomes a white, opaque liquid and particles entangle and precipitate. Dispersing these particles evenly in solution to form a transparent sol is called peptization. The role of the acid in the sol peptization is described by DP Partlow, BE Yoldas [J. Non-Crystal. Solids, 46, 153 (1981)] reported that electrolyte ions such as nitric acid (HNO ₃ ), hydrochloric acid (HCl), and ammonium hydroxide (NH ₄ OH) are strongly adsorbed on the particle surface and dispersed by repulsive forces between the particles.

1 is a schematic diagram showing the dispersion and gelation of particles precipitated after hydrolysis. In FIG. 1A, particles are randomly precipitated after hydrolysis, and acid is added as shown in B of FIG. They are uniformly dispersed by mutual repulsive force and move freely in the solution. Particles dispersed in the sol are dried and the volume is reduced with evaporation of the solvent, the movement is suppressed and there is no flow as shown in C of FIG.

Various methods are known for producing such alumina sol. For example, the method of peptizing the hydrolyzed precipitate of aluminum isopropoxide described above [BE Yoldas, Am. Ceram., Soc. Bull., 54, 289 (1975), Japanese Patent No. Hei 6-64919], Method of peptizing boehmite powder with acid [Japanese Patent No. 59-78925], intermediate raw material produced by bauer process from bauxite light And a method of solvating aluminum hydroxide obtained by reacting phosphorus NaAlO ₂ with an acid, and recently, a method of hydrating a metal aluminum powder to produce a stable sol (Japanese Patent Laid-Open No. 7-89717).

However, the conventional alumina sol has a problem in that the solvent in which the particles are dispersed is made of water, causing problems such as phase separation when mixed with a material having hydrophobic characteristics, and thus, replacing water with an organic solvent. There are restrictions on use, including the use of complex procedures.

The present invention is to solve the conventional problems, the problem of the present invention is excellent dispersion of hydrophobic organic matter by using methanol as a dispersion medium instead of water, an excellent storage stability as an additive to improve the mechanical strength of various coating agents It is to provide a method for producing an alumina sol that can be used.

In order to achieve the above object, the present invention dissolves aluminum isopropoxide, which is a starting material of an alumina sol, in methanol as a solvent, and then adds water to proceed hydrolysis and polycondensation reactions, thereby producing boehmite particles. An acid (nitric acid, hydrochloric acid, acetic acid, phosphoric acid, etc.) was added as a peptizing agent to uniformly disperse the solution in order to prepare an alumina sol which was transparent and had excellent storage stability.

The methanol-dispersed alumina sol according to the present invention is considerably superior in transparency than the alumina sol dispersed in water, and when the methanol-dispersed alumina sol is mixed with an organosilane to prepare an organic-inorganic hybrid nanosol, a hybrid nanosol having excellent mechanical properties can be obtained. There is an advantage that it can. In addition, in the case of mixing with an organic substance having a hydrophobic characteristic, it is more compatible with water-dispersed alumina sol, and thus has the advantage that a process such as replacement with an organic solvent is not necessary when using the water-dispersed alumina sol. In addition, the methanol-dispersed alumina sol is excellent in storage stability, so that its performance is maintained even after long-term storage.

1 is a schematic diagram showing the dispersion and gelation of particles precipitated after hydrolysis.
Figure 2a and Figure 2b is a graph showing the crystal pattern of the methanol-dispersed alumina sol prepared in the present invention dried X-ray diffractometer (XRD, Rint-2000, Japan), Figure 2a at 100 ℃ 2b is calcined at 1100 ° C.
3 is a graph showing the transmittance of the methanol-dispersed alumina sol prepared in the present invention and the transmittance of the water-dispersed alumina sol.
Figure 4 is a photograph of the shape of the methanol-dispersed alumina sol prepared in the present invention measured under the acceleration voltage of 80kV using TEM (EM912 Ω, Carl zeiss Inc. Germany).

Hereinafter, with reference to the accompanying drawings a preferred embodiment of the method for producing an alumina sol according to the present invention.

A method for producing an alumina sol of the present invention comprises the steps of: a) dissolving aluminum alkoxide in methanol, and then adding an appropriate amount of water to proceed hydrolysis and polycondensation to form boehmite particles; b) adding and mixing acid to peptize the agglomerated boehmite particles, and then filtering the sol to obtain a clear solution; And c) hydrophobically modifying the surface of the hydrophilic boehmite particles contained in this solution.

Aluminum alkoxides are used as starting materials for preparing alumina sol. As the type of aluminum alkoxide, any one of aluminum ethoxide, aluminum isopropoxide and aluminum secbutoxide may be used.

Methanol is a representative of lower alcohols and serves to significantly improve the storage stability and transparency of the alumina sol. The amount of methanol added may be used in a molar ratio of 50-200 moles to 1 mole of aluminum alkoxide. When less than 50 moles of methanol is used per 1 mole of alkoxide, the aluminum alkoxide is not sufficiently dissolved in the solvent and thus no transparent alumina sol is formed. In addition, when methanol is used more than 200 moles with respect to 1 mole of alkoxide, the solid content in the resulting alumina sol is small, which does not contribute significantly to the improvement of mechanical strength.

Water is added to hydrolyze the aluminum alkoxide in solution and then to polycondensate to form boehmite particles. The amount of water added is in the range of 2-20 moles per mole of aluminum alkoxide. When the amount of water is 2 mol or less, the solid content in the sol is lowered, and when it exceeds 20 mol, aggregation of particles occurs in the solution to form an opaque alumina sol, and an opaque precipitate is obtained upon storage.

The peptizing agent used in the present invention adjusts the pH of the solution or serves as a peptizing reaction to the hydrate. Acids are mainly used for this purpose, for example nitric acid (HNO ₃ ), hydrochloric acid (HCl), acetic acid (CH ₃ COOH), phosphoric acid (H ₃ PO ₄ ) and the like. This acid component is an essential component in the preparation of a transparent alumina sol and can also adjust the pH of the solution. The addition amount of peptizing agent is appropriately 0.02 mol to 0.2 mol per mole of water. When less than 0.02 mole is added, insufficient peptizing reaction causes agglomeration of boehmite particles in the solution to form an opaque sol. Opaque precipitates are formed, resulting in poor storage stability. In addition, when the content exceeds 0.2 moles, the solution may cause optical problems such as yellowing, and the solution may be strongly acidified.

Meanwhile, a silane coupling agent may be used to hydrophobically modify the prepared hydrophilic boehmite particles. Such a silane coupling agent is used for the purpose of adhesion or affinity of both by chemical bonding in a composite system of a polymer and an inorganic, organic or metal material. That is, it plays an important role in improving the adhesion between different materials and improving various properties such as mechanical strength, electrical properties, water resistance, weather resistance, and heat resistance.

As the silane coupling agent used in the present invention, methacryloxypropyl trimethoxysilane (MPTMS), glycidoxypropyl trimethoxysilane (GPTMS), methyltriethoxysilane (methylTethoxysilane; MTES) , Vinyltriethoxysilane (vinyltriethoxysilane; VTES) may be used alone, or two or more may be mixed and applied.

Hereinafter, the present invention will be described in detail with reference to Examples.

Example 1

First, 0.05 mol of Sigma Aldrich's aluminum alkoxide and 6 mol of methanol (99%, Samchun Chemical, Korea) were mixed in a 1000 mL 4-neck round flask connected with a thermometer, a cooler, and a stirrer, and then dissolved at 60-65 ° C. for 1 hour. Let's do it. Thereafter, 2 mol of water per 1 mol of aluminum alkoxide was added to the sol to proceed with the hydrolysis and polycondensation of the alkoxide, followed by reaction for 3 hours. Thereafter, 0.1 mol of nitric acid is added to the mol of the molar ratio with a peptizing agent and reacted for 20 hours. At this time, the temperature is maintained at 60 ~ 65 ℃. After filtering using a filter paper to obtain the desired alumina sol.

[Example 2]

First, 0.05 mol of Sigma Aldrich's aluminum alkoxide and 6 mol of methanol (99%, Samchun Chemical, Korea) were mixed in a 1000 mL 4-neck round flask connected with a thermometer, a cooler, and a stirrer, and then dissolved at 60-65 ° C. for 1 hour. Let's do it. Thereafter, in order to proceed with hydrolysis and polycondensation of the alkoxide to the sol, 14 mol of water per mol of aluminum alkoxide was added and reacted for 3 hours. Thereafter, 0.1 mole of nitric acid was added to the molar ratio with respect to 1 mole of water as a peptizer and reacted for 20 hours. At this time, the temperature is maintained at 60 ~ 65 ℃. After filtering using a filter paper to obtain the desired alumina sol.

[Example 3]

First, 0.05 mol of Sigma Aldrich's aluminum alkoxide and 6 mol of methanol (99%, Samchun Chemical, Korea) were mixed in a 1000 mL 4-neck round flask connected with a thermometer, a cooler, and a stirrer, and then dissolved at 60-65 ° C. for 1 hour. Let's do it. Thereafter, in order to proceed with hydrolysis and polycondensation of the alkoxide, 10 mol of water per mol of the aluminum alkoxide was added to the sol and reacted for 3 hours. Thereafter, 0.1 mole of nitric acid was added to the molar ratio with respect to 1 mole of water as a peptizer and reacted for 20 hours. At this time, the temperature is maintained at 60 ~ 65 ℃. After filtering using a filter paper to obtain the desired alumina sol.

Example 4

First, 0.05 mol of Sigma Aldrich's aluminum alkoxide and 6 mol of methanol (99%, Samchun Chemical, Korea) were mixed in a 1000 mL 4-neck round flask connected with a thermometer, a cooler, and a stirrer, and then dissolved at 60-65 ° C. for 1 hour. Let's do it. Thereafter, in order to proceed with hydrolysis and polycondensation of the alkoxide to the sol, 14 mol of water per mol of aluminum alkoxide was added and reacted for 3 hours. Thereafter, 0.1 mole of nitric acid was added to the molar ratio with respect to 1 mole of water as a peptizer and reacted for 20 hours. At this time, the temperature is maintained at 60 ~ 65 ℃. After filtering using a filter paper to obtain the desired alumina sol.

[Example 5]

First, 0.05 mol of Sigma Aldrich's aluminum alkoxide and 6 mol of methanol (99%, Samchun Chemical, Korea) were mixed in a 1000 mL 4-neck round flask connected with a thermometer, a cooler, and a stirrer, and then dissolved at 60-65 ° C. for 1 hour. Let's do it. Thereafter, 20 mol of water per mol of the aluminum alkoxide was added to the sol to proceed with the hydrolysis and polycondensation of the alkoxide, followed by reaction for 3 hours. Thereafter, 0.1 mole of nitric acid was added to the molar ratio with respect to 1 mole of water as a peptizer and reacted for 20 hours. At this time, the temperature is maintained at 60 ~ 65 ℃. After filtering using a filter paper to obtain the desired alumina sol.

[Example 6]

First, 0.05 mol of Sigma Aldrich's aluminum isopropoxide and 6 mol of methanol (99%, Samchun Chemical, Korea) were mixed in a 1000 mL 4-neck round flask connected with a thermometer, a cooler, and a stirrer. To dissolve. Thereafter, in order to proceed with hydrolysis and polycondensation reaction, 6 mol of water per mol of aluminum alkoxide was added to the sol and stirred for 3 hours. Thereafter, nitric acid (65%, Duksan Chemical, Korea) was added as a peptizing agent to the molar ratio of 0.033 moles per 1 mole of water and reacted for 20 hours. At this time, the temperature was maintained at 60 ~ 65 ℃. After filtering using a filter paper to obtain the desired alumina sol.

[Example 7]

First, 0.05 mol of Sigma Aldrich's aluminum isopropoxide and 6 mol of methanol (99%, Samchun Chemical, Korea) were mixed in a 1000 mL 4-neck round flask connected with a thermometer, a cooler, and a stirrer. To dissolve. Thereafter, 6 mol of water per mol of aluminum alkoxide was added to the sol to proceed with hydrolysis and polycondensation reaction and stirred for 3 hours. Thereafter, nitric acid (65%, Duksan Chemical, Korea) was added as a peptizing agent to the molar ratio of 0.067 moles per 1 mole of water and reacted for 20 hours. At this time, the temperature was maintained at 60 ~ 65 ℃. After filtering using a filter paper to obtain the desired alumina sol.

[Example 8]

First, 0.05 mol of Sigma Aldrich's aluminum isopropoxide and 6 mol of methanol (99%, Samchun Chemical, Korea) were mixed in a 1000 mL 4-neck round flask connected with a thermometer, a cooler, and a stirrer. To dissolve. Thereafter, in order to proceed with hydrolysis and polycondensation reaction, 6 mol of water per mol of aluminum alkoxide was added to the sol and stirred for 3 hours. Thereafter, 0.167 mole of nitric acid (65%, Duksan Chemical, Korea) was added to the mole ratio with respect to 1 mole of the peptizing agent and reacted for 20 hours. At this time, the temperature was maintained at 60 ~ 65 ℃. After filtering using a filter paper to obtain the desired alumina sol.

[Example 9]

First, 0.05 mol of Sigma Aldrich's aluminum isopropoxide and 6 mol of methanol (99%, Samchun Chemical, Korea) were mixed in a 1000 mL 4-neck round flask connected with a thermometer, a cooler, and a stirrer. To dissolve. Thereafter, in order to proceed with hydrolysis and polycondensation reaction, 6 mol of water per mol of aluminum alkoxide was added to the sol and stirred for 3 hours. Thereafter, 0.233 mole of nitric acid (65%, Duksan Chemical, Korea) was added to the mole ratio with respect to 1 mole of water as a peptizing agent and reacted for 20 hours. At this time, the temperature was maintained at 60 ~ 65 ℃. After filtering using a filter paper to obtain the desired alumina sol.

[Example 10]

First, 0.05 mol of Sigma Aldrich's aluminum isopropoxide and 6 mol of methanol (99%, Samchun Chemical, Korea) were mixed in a 1000 mL 4-neck round flask connected with a thermometer, a cooler, and a stirrer. To dissolve. Thereafter, in order to proceed with hydrolysis and polycondensation reaction, 6 mol of water per mol of aluminum alkoxide was added to the sol and stirred for 3 hours. Then, nitric acid (65%, Duksan Chemical, Korea) as a peptizing agent is added to the molar ratio of 0.30 moles per 1 mole of water and reacted for 20 hours. At this time, the temperature was maintained at 60 ~ 65 ℃. After filtering using a filter paper to obtain the desired alumina sol.

Comparative Example 1

The experiment was conducted in the same manner as in Example 8. However, by increasing the amount of each component constantly, 0.1 mol of Sigma Aldrich's aluminum isopropoxide and 12 mol of methanol (99%, Samchun Chemical, Korea) were mixed and dissolved at 60-65 ° C. for 1 hour. Thereafter, 12 mol of water per mol of aluminum alkoxide was added to the sol to proceed with hydrolysis and polycondensation, and the mixture was stirred for 3 hours. Thereafter, nitric acid was reacted for 20 hours by adding 0.334 mole to 1 mol of water as a peptizing agent. At this time, the temperature was maintained at 60 ~ 65 ℃. After filtering using a filter paper to obtain the desired alumina sol.

[Experimental Example]

The properties of the alumina sol prepared in Examples of the present invention were carried out in the following manner.

(1) Storage stability test

The viscosity change and the presence or absence of precipitates after storage at 25 ° C. for 6 months were confirmed and indicated as (O) when there was no change, (X) when there was a change, and (XX) when the change was significant. .

(2) Measurement of the transmittance of the solution

The transmittance of the prepared alumina sol was measured using a UV / VISIBLE spectrometer (UV-2450, Shimadzu). The transmittance was measured numerically at 600 nm.

(3) solid content measurement

The prepared alumina sol was evaporated at 100 ^° C. using an infrared heating evaporator to measure the solids content. The figures shown are the average values measured over three times with the same solution.

(4) Coagulation status

The presence or absence of filtration due to the aggregation state of the solution was indicated by (X) when the filtration was not possible due to severe aggregation, (△) when the filtration was possible to some extent, and (O) when the filtration was easily possible.

(5) pH measurement

The prepared solution was measured by a pH meter and represented as a numerical value. The figures shown are the average values measured over three times with the same solution.

division Filtration Storage stability Solid content (%) Solution transmittance (%) 600 nm pH Example 1 O O 1.5 90.8 2.3 Example 2 O O 3.1 97.3 2.0 Example 3 △ X 2.3 10.7 1.8 Example 4 X XX 1.1 5.5 1.8 Example 5 X XX 1.0 2.1 1.7 Example 6 X XX 1.5 0.5 3.9 Example 7 X O 2.0 1.3 2.3 Example 8 O O 3.1 100.0 1.4 Example 9 O O 3.2 99.7 1.4 Example 10 O O 3.3 100.0 1.5 Comparative Example 1 X △ 3.9 83.5 2.1

Here, the alumina sol has an amorphous structure as shown in a) of FIG. 2, and α-Al ₂ O ₃ is produced when sintered at 1100 ° C. as shown in b) of FIG. ₂ .

The methanol-dispersed alumina sol showed a high transmittance of 97.3% at 600 nm, as shown in FIG. 3, and was much more transparent than the transmittance of 38.9% of the conventional water-dispersed alumina sol. The transmittance of the methanol dispersed alumina sol is shown, and the solid line represents the transmittance of the water dispersed alumina sol.)

In addition, it can be seen that the methanol dispersed alumina sol is composed of boehmite particles having a size of 50 to 200 nm when the transmission electron microscope (TEM) is observed as shown in FIG. 4.

Claims (8)

In the alumina sol production method using methanol as a dispersion medium,
a) dissolving aluminum alkoxide in methanol and then adding an appropriate amount of water to proceed hydrolysis and polycondensation to form boehmite particles;
b) adding and mixing acid to peptize the agglomerated boehmite particles, and then filtering the sol to obtain a clear solution; And
c) surface modification of the surface of the hydrophilic boehmite particles contained in the solution hydrophobicly by using a silane coupling agent; transparent alumina sol manufacturing method comprising a.
The method of claim 1,
The aluminum alkoxide is a method for producing a transparent alumina sol, characterized in that any one of aluminum ethoxide, aluminum isopropoxide, aluminum secbutoxide.
The method of claim 1,
The amount of methanol to dissolve the aluminum alkoxide is 50 to 200 mol per mol of aluminum alkoxide, the method for producing a transparent alumina sol.
The method of claim 1,
Method for producing a transparent alumina sol, characterized in that the addition amount of water (DI water) used to proceed the hydrolysis and polycondensation reaction is 2 mol to 20 mol per mol of aluminum alkoxide.
The method of claim 1,
The acid added during peptizing is any one of nitric acid (HNO ₃ ), hydrochloric acid (HCl), acetic acid (CH ₃ COOH), phosphoric acid (H ₃ PO ₄ ) method of producing a transparent alumina sol.
The method of claim 5,
The acid is a method for producing a transparent alumina sol, characterized in that the addition of 0.02 to 0.2 mol per mole of water.
delete The method of claim 1,
The silane coupling agent is methacryloxypropyl trimethoxysilane (MPTMS), glycidoxypropyl trimethoxysilane (GPTMS), methyltriethoxysilane (MTES), vinyltriethoxy A method for producing a transparent alumina sol, characterized in that any one or a mixture of two or more of the silane (vinyltriethoxysilane; VTES).

Images