JP5178027B2 - Layered double hydroxides that peel in water and process for producing the same - Google Patents

Description

  The present invention relates to a layered double hydroxide imparted with a property of peeling in water by intercalating magnesium lactate into an intermediate layer of the layered double hydroxide and a method for producing the same.

Layered double hydroxides (LDH) of the general formula ^{_{[M 2+ 1-x M 3+ x}} (OH) 2 ] ^{x +} layered with anion exchange ability represented by ^{_{[A n- x / n · yH 2}} O ] A compound. The crystal structure is composed of a regular octahedral hydroxide layer (basic layer) in which a part of divalent metal ions is replaced by trivalent metal ions, and an intermediate layer composed of anions and interlayer water. The feature of LDH is that there are various combinations of types and ratios of metal ions in the basic layer and types of intermediate anions. Many types of LDH have been synthesized so far, and much research has been conducted on uptake by inorganic and organic anion intercalation.

In general, in LDH, the charge density of the base layer is large, and the electrostatic attraction between the base layer and the intermediate layer is strong. Therefore, the delamination phenomenon as seen in many clay minerals is unlikely to occur. Therefore, although there are few reports on LDH that easily peels in water, there is JP-A-2004-189671. Here, an aromatic aminocarboxylic acid, particularly p-aminobenzoic acid, is intercalated as an anion in the intermediate layer, whereby a dispersion liquid dispersed in a lower alcohol such as water or ethanol is obtained. It is reported that. This is explained as a result of expanding the distance of the base layer by intercalating aromatic aminocarboxylic acid ions as compared with LDH intercalating CO ₃ ^2- ions. However, this LDH peeling phenomenon is complete in ethanol, which is a good solvent for aromatic aminocarboxylic acids such as p-aminobenzoic acid, but is incomplete in water with low solubility. For this reason, there is a need for a new type of LDH that peels substantially completely in water.

  The present inventors previously disclosed an underwater peelable LDH in which an MgH, Zn or Ce salt of acetic acid was intercalated in an intermediate layer of LDH in WO2006 / 068118. The LDH is dispersed as nano-sized fine particles in water to form a transparent dispersion sol. When this dispersed sol is applied to, for example, a metal substrate and dried, a dense transparent film is formed, and this is baked at a high temperature to obtain a hard scratch-resistant film. For this reason, this LDH is useful as a vehicle or rust preventive pigment for water-based metal protective coating compositions. The LDH can also be used as a humectant or stabilizer in cosmetics such as lotions, creams or foundations.

  However, LDH intercalated with a divalent metal acetate such as Mg has a unique acetic acid odor in its aqueous dispersion and dried powder. Therefore, it is desired to provide an odorless underwater peelable LDH.

The present invention relates to a compound of formula (I):
Mg _1-x Al _x (OH) ₂ (I)
(Wherein x is 0.2 to 0.33) and a layered structure comprising a metal double hydroxide base layer and a cumulative product in which magnesium lactate and interlayer water are interleaved between the base layers. Provide double hydroxide.

Furthermore, the present invention provides a compound of formula (II):
[(Mg _1-x Al _x (OH) ₂ ] [(CO ₃ ) _{x / 2} · yH ₂ O]
(Wherein x is 0.2 to 0.33, y is a real number greater than 0), and pyrolyzing the carbonated layered double hydroxide;
Adding the resulting pyrolyzate to an aqueous solution of magnesium lactate and reacting;
Separating the resulting solid reaction product from the reaction solution;
The method for producing the layered double hydroxide of the present invention comprising the steps of drying and grinding the separated solid. Carbonated LDH of formula (II) is known as hydrotalcite.

  The LDH of the present invention is dispersed as nano-sized fine particles separated from water. This dispersion or dispersion sol is translucent, and if it is also dehydrated and dried, it is restored to the original LDH. Thus, for example, a dispersion or sol can be applied onto a metal substrate, dried, and optionally fired to form a scratch-resistant transparent hard coating. Furthermore, the dispersed dispersion of LDH can be added to water-based paints containing known anti-rust pigments to enhance the anti-rust effect, and can also be added to emulsions or suspensions of ethylene-vinyl acetate copolymer (EVA). Thus, a composite sheet can be formed, and the reinforcement or pyrolysis temperature can be increased.

  The LDH of the present invention can be prepared according to a method similar to the reconstruction method for the production of LDH intercalated with carbonated LDH and magnesium lactate to be intercalated.

  In the reconstruction method, carbonated LDH is calcined in advance at a temperature of 400 ° C. to 800 ° C., and a pyrolyzate from which most of carbonate ions have been removed is reacted with other anions in water to generate reconstructed LDH. Is the method. In the present invention, a thermal decomposition product of carbonate-type LDH is added to an aqueous solution of magnesium lactate and reacted at room temperature.

Carbonated LDH of formula (II) exists naturally as hydrotalcite or can be synthesized by known methods. This product is marketed by Kyowa Chemical Industry Co., Ltd. as DHT-6, for example. The ratio of magnesium lactate to pyrolysis product of carbonate type LDH is preferably at least equimolar to the Al content in the pyrolysis product in terms of Al ₂ O ₃ . The reaction is preferably carried out at room temperature (25 ° C.) with stirring or shaking for 10 to 30 hours. After the reaction, the solid reaction product is separated by filtration, centrifugation, etc., dried at 100 ° C. or lower, and pulverized to obtain the LDH of the present invention.

  In the solid product, a diffraction pattern peculiar to LDH, which is a layered structure, is seen in the X-ray diffraction image, and the peak is shifted to the lower angle side compared with the carbonic acid type LDH. This suggests that the result of the incorporation of magnesium lactate has expanded.

  From the FT-IR spectrum, an absorption spectrum derived from a carboxylic acid corresponding to the incorporated magnesium salt was confirmed.

  LDH incorporating magnesium lactate rapidly changed to a translucent gel when dispersed in water and aqueous lactic acid solutions, indicating delamination in water.

  Utilizing these properties, the LDH of the present invention is useful as a protective coating material for metal substrates. The aqueous dispersion (colloid solution and sol) of the LDH of the present invention is applied to a substrate and dried to form a transparent film by itself. By baking the dried film at a high temperature of 350 ° C. or higher, a very hard scratch-resistant transparent protective film can be obtained.

  The LDH of the present invention can be added as a filler to a known aqueous metal protective coating composition. It is known that a flake filler such as mica, talc or kaolin is blended in a metal protective coating composition, and a barrier layer against the invasion of corrosion factors is formed by orienting the flakes in the major axis direction. By replacing these flaky fillers with the LDH of the present invention, a barrier layer against a corrosion factor can be formed on the same principle. The LDH of the present invention in a peeled state has a significantly larger aspect ratio than known flaky fillers and a thickness of about 6 to 10 nm, which is significantly smaller than the thickness of carbonated LDH of about 40 to 50 nm. Therefore, since the orientation in the major axis direction is easier than that of carbonated LDH having a comparable major axis, a more effective barrier layer is formed.

  Delaminated LDH can be composited into a polymeric material that can be reinforced and flame retardant. For example, in the case of an ethylene-vinyl acetate copolymer, a composite sheet obtained by adding a dispersion of LDH to an emulsion or suspension, coating on a Teflon sheet, and drying is proportional to the blending amount of LDH. When the content was 5 wt%, the maximum value was 3.8 MPa, and the elongation was also maximum. It has been shown that the pyrolysis temperature is improved when blended up to 25 wt%. This increase in the thermal decomposition temperature is presumed that the dispersed LDH layer prevented air in the atmosphere from entering the EVA and hindered polymer chain scission due to combustion.

Part I Production of LDH exfoliating in polar solvent Example 1
Mg-Al-based carbonate double hydroxide (DHT-6 manufactured by Kyowa Chemical Industry Co., Ltd.), which was previously heat-treated at a temperature of 700 ° C. for 20 hours in an aqueous 0.28 mol / L (56.7 g / L) magnesium lactate solution; Add a 0.28 mol / L (96.3 g / L) aqueous solution of LDH). After stirring at room temperature for 15 hours, the obtained solid product (gel) was separated by filtration, dried in a 90 ° C. dryer for 10 hours, and pulverized. This is called Mg-Lact / LDH.

Comparative Example 1
Except for changing magnesium lactate to magnesium acetate, the same operation as in Example 1 was performed to obtain Mg-Ac / LDH.

Part II Characterization of LDH (visible light transmittance of aqueous dispersion)
A 0.5% aqueous dispersion of Mg-Lact / LDH, Mg-Ac / LDH and carbonic acid LDH was prepared, respectively, and the transmittance in the visible light region (400 nm to 780 nm) was measured with a spectrophotometer (double beam direct ratio photometric method) Measurement was performed using a 1 cm quartz cell with a spectrophotometer: UV3100 manufactured by Shimadzu Corporation. In the case of LDH carbonate, the transmittance was almost 0% in the visible light region of 400 nm to 780 nm. However, in Mg-Lact / LDH and Mg-Ac / LDH, the transmittance in the above wavelength range was in any region. It showed 50% or more.
This means that Mg-Lact / LDH and Mg-Ac / LDH are almost completely exfoliated in water to form a colloidal solution, whereas carbonic acid LDH is dispersed as particles that retain the crystal structure of LDH. It shows that. From the series of measurement results in the transmittance measurement, the reason for this large difference that occurs simply by encapsulating the Mg salt of the carboxylic acid is that the above-mentioned “peeling phenomenon” occurs when the layered double hydroxide is added with water. It is thought that “double hydroxide” was formed and these were finely dispersed in water to achieve high transmittance. In addition, when the polyvalent metal salt of the carboxylic acid of the present invention was dispersed in a solvent and its dispersion state was confirmed, it was excellent in dispersibility with respect to a polar solvent, particularly water.

(Atomic force microscope observation)
When Mg-Lact / LDH, Mg-Ac / LDH and carbonic acid LDH are dispersed in water and the thickness is observed with an atomic force microscope (Nanoprobe microscope nanoscope III manufactured by Nihon Beco), 8.7 nm and 6.8 nm, respectively. 49.6 nm.
This also proves that when Mg-Lact / LDH and Mg-Ac / LDH are dispersed in water, delamination occurs in water, unlike carbonated LDH.

Part III Use as Metal Protective Coating Film-forming Mg-Lact / LDH A 3.0% aqueous dispersion of Mg-Lact / LDH powder was prepared and various no. And a film was formed by drying at 90 ° C. for 48 hours. In any case, a smooth transparent thin film was formed even though no binder or the like was used.
For each thin film obtained, the thickness of the film was measured using an electromagnetic film thickness meter (Electromagnetic induction film thickness meter: LE-200J manufactured by Kett Science Laboratory). The used bar coater No. Table 1 shows the thickness (μm) of the obtained thin film.

As in the case of the aqueous dispersion, the visible light transmittance in the 400 nm to 750 nm region was measured with a spectrophotometer for each of the thin films prepared above, and the transmittance was 70% or more in any thin film. Was showing.
Next, the prepared glass plate holding the film was placed in a baking furnace and baked in a temperature environment of 500 ° C. for 1 hour, and then the coating film hardness was confirmed by JIS K5600-5-4 scratch hardness (pencil method). .
The results are shown in Table 2.

By baking, it became a scratch-resistant hard film.

Part IV Cosmetic additive The LDH (Mg-Lact / LDH) of the present invention peels off in water to form a colloidal solution or sol, thus increasing skin cosmetics such as creams, emulsions, lotions and foundations. It can be added as a sticky or humectant. An example is shown below.

Lotion
Ingredient Weight
L-Arginine 1.5
Sodium citrate 0.05
Preservative 0.2
1,3-butylene glycol 3.0
Glycyrrhizin dipotassium 0.1
Sodium pyrrolidonecarboxylate 2.0
Citric acid appropriate amount Fragrance 0.05
Mg-Lact / LDH 2.0
Purified water
Total 100

Latex
Ingredient Weight
Stearic acid 0.2
Cetyl alcohol 1.5
Vaseline 6.0
Squalane 6.0
Glycerol 2.0
2-Ethylhexanoic acid ester 0.5
Sorbitan monooleate 2.0
Dipropylene glycol 2.0
Triethanolamine 1.0
Fragrance 0.1
Mg-Lact / LDH 0.1
Purified water 78.6
Total 100

Vanishing cream
Ingredient Weight
Stearic acid 7.5
Stearyl alcohol 4.0
Butyl stearate 5.5
Ethyl parahydroxybenzoate 0.5
Fragrance 0.1
Mg-Lact / LDH 0.2
Purified water 73.8
Total 100

Foundation
Ingredient Weight
Talc 20.5
Mica 34.5
Kaolin 5.5
Titanium dioxide 10.0
Bright pigment (titanium mica) 3.0
Zinc stearate 1.0
Yellow iron oxide 2.8
Black iron oxide 0.2
Nylon powder 10.0
Squalane 6.0
Octyldodecyl myristylate 2.0
Vaseline 2.5
Ethyl parahydroxybenzoate 0.5
Fragrance 0.1
Mg-Lact / LDH 0.5
Total 100

Part V Odor Evaluation 10 g each of Mg-Lact / LDH and Mg-Ac / LDH was collected in a petri dish, and 10 petalers sniffed the petri dish in order, and evaluated according to the following evaluation criteria.
(Evaluation)
A: No odor is felt at all.
○: No smell is felt.
Δ: A slight odor is felt.
X: A pungent odor is felt.
The evaluation results are shown in Table 3.

The peelable double hydroxide made of Mg-Ac / LDH (magnesium acetate / LDH) has been confirmed to have an irritating odor, but the product of the present invention produces a peelable double hydroxide having no irritating odor. It became possible to do.

Claims (6)

Formula (I):
Mg _1-x Al _x (OH) ₂ (I)
(Wherein x is 0.2 to 0.33) and a cumulative product in which magnesium lactate and interlayer water are intercalated in the middle of the basic layer. Layered double hydroxide. The double hydroxide according to claim 1, wherein at least an equimolar amount of magnesium lactate is intercalated with respect to the basic layer converted to Al ₂ O ₃ .   The double hydroxide according to claim 1 or 2, wherein the double hydroxide is separated into nano-sized particles in water. Formula (II):
[(Mg _1-x Al _x (OH) ₂ ] [(CO ₃ ) _{x / 2} · yH ₂ O]
(Wherein x is 0.2 to 0.33, y is a real number greater than 0), and pyrolyzing the carbonated layered double hydroxide;
Adding the resulting pyrolysate to an aqueous solution of magnesium lactate;
Separating the reacted solid product from the reaction solution; and drying and grinding the separated solid;
A process for producing a layered double hydroxide according to claim 1 comprising:   The method according to claim 4, wherein the thermal decomposition of the carbonate-type layered double hydroxide is carried out at a temperature of 400 ° C to 800 ° C. The method according to claim 4, wherein at least an equimolar amount of magnesium lactate is reacted with the thermally decomposed carbonate-type layered double hydroxide converted to Al ₂ O ₃ .