JPH06191837A - Production of high heat resistant aluminum hydroxide - Google Patents

Abstract

PURPOSE:To obtain an inexpensive aluminum hydroxide free from boehmite dislocation at the initial thermal decomposing stage and excellent in heat resistance. CONSTITUTION:By this method for producing aluminum hydroxide by adding a seed aluminum hydroxide into a supersaturated alkali aluminate solution, the high heat-resistant aluminum hydroxide is produced using an aluminum hydroxide having 0.1-mum-3mum average secondary particle diameter as the seed aluminum hydroxide prepared by; (1) after obtaining a gel having <=0.05mum average particle diameter by adding an acid into the supersaturated alkali aluminate solution under stirring, (2) adding 0.1wt.% expressed in terms of Al2O3 this neutralized gel per aluminum quantity in the alkali aluminate solution to the alkali aluminate solution having 1.3-2.5mol/l alkali conc. under stirring.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing heat resistant aluminum hydroxide filled in rubber or plastic. More specifically, the present invention relates to a method for producing high heat-resistant aluminum hydroxide used for electric wire coating rubber, insulating materials, electric uses such as printed wiring boards, flame retardants to be filled in wall covering materials, interior materials, and artificial marble filling. .

[0002]

2. Description of the Related Art In recent years, from the viewpoint of safety and disaster prevention, resin materials used for home electric appliances, office automation equipment, electric wires, wall covering materials, interior materials for automobiles, etc. are required to have flame retardancy far superior to conventional ones. It has been. More recently, not only is the spread of fire prevented,
It is required to reduce the generation of smoke, toxic gas, corrosive gas, etc., and to make it flame-retardant, including prevention of secondary disasters.

At present, various addition type flame retardants such as phosphoric acid ester type, halogen type, antimony oxide and metal hydroxide have been developed and put to practical use. Among them, metal hydroxides such as aluminum hydroxide and magnesium hydroxide exhibit the flame retardant effect by endothermic and dehydration reactions accompanying heating, and are the most widely used non-halogen flame retardant materials that do not generate toxic gas. It is used. Further, as an application utilizing the optical characteristics of aluminum hydroxide, it is often used as an artificial marble filled with unsaturated polyester resin or MMA resin.

As described above, aluminum hydroxide widely used as a filler is a gibbsite type crystal (Al ₂ O ₃ .3H ₂ O) obtained at a relatively low cost by the Bayer method.
Aluminum hydroxide consisting of is common. Gibbsite type aluminum hydroxide is heated to 200 ° C to 30 ° C.
It has the property of releasing water of crystallization at 0 ° C and rearranging to intermediate alumina. While being used as a flame retardant by taking advantage of this characteristic, various problems occur when aluminum hydroxide is actually filled in a resin or rubber and used for various purposes. For example, when applied to an electronic substrate, the electronic substrate is usually exposed to a solder melting temperature of about 260 ° C. in the soldering process, but aluminum hydroxide is thermally decomposed at this point to release a part of crystal water. , The substrate is swollen or cracked.

When it is filled with a thermoplastic resin such as polyolefin or polystyrene, the processing temperature of the resin is 200
Since the temperature is relatively high, such as around ℃, the thermal decomposition of aluminum hydroxide has already started in the resin molding process, and problems such as foaming appear in the molded product. Artificial marble is also used in bathtubs, kitchen counters, etc., and is required to have heat resistance and hot water resistance as a molded body. Therefore, high heat resistance of aluminum hydroxide itself as a filler is strongly required.

[0006] One of the methods for obtaining highly heat-resistant aluminum hydroxide that satisfies these requirements is to raise the thermal decomposition initiation temperature of aluminum hydroxide. For example, in JP-A-59-204632, the total Na ₂ O concentration is 0.1.
%, Resin compositions using gibbsite type aluminum hydroxide have been proposed.

Also, gibbsite type aluminum hydroxide heats up.
Rearrangement from intermediate alumina to α-alumina by decomposition
At this time, a part of boehmite type aluminum hydroxide (Al₂O
₃・ H ₂O). Boehmite type aluminum hydroxide
The dislocation to um progresses at 230-250 ° C and is accompanied by the formation of crystals.
Reduces the rate of boehmite rearrangement by releasing part of crystal water
Less, ie at about 230 to about 250 ° C
From the point that suppressing the endothermic reaction is also effective for high heat resistance,
Heat treatment of gibbsite type aluminum hydroxide in advance
Minute boehmite treatment (boehmite conversion during reheating)
Aluminum hydroxide used as a filler
(Japanese Patent Application Laid-Open No. 61-143444, Japanese Patent Application Laid-Open No. 62-5)
9021) and the like have also been proposed.

Further, in place of gibbsite type aluminum hydroxide, boehmite type aluminum hydroxide (Japanese Patent Laid-Open No. 6-58242)
2-71643) and a method using magnesium hydroxide (Japanese Patent Laid-Open Nos. 63-128038 to 63-128044) are known to suppress initial thermal decomposition and improve solder heat resistance.

However, the above conventional technique has the following problems. First, when a gibbsite type aluminum hydroxide having a Na ₂ O concentration of 0.1% or less is used as a filler, the effect of improving solder heat resistance is observed, but it is not sufficiently satisfactory. Further, gibbsite type aluminum hydroxide or boehmite type aluminum hydroxide partially boehmite is produced by heating gibbsite type aluminum hydroxide by heat treatment or hydrothermal treatment in air, resulting in high cost. Furthermore, boehmite-type aluminum hydroxide and magnesium hydroxide have one-third or two-thirds of the water of crystallization per Al atom, respectively, as compared with gibbsite-type aluminum hydroxide. It has a drawback that the amount of water released is small and the effect as a flame retardant is poor.

[0010]

In view of such circumstances, the present inventor does not perform a special operation such as a heat treatment or a hydrothermal treatment, but is a gibbsite type aluminum hydroxide which is inexpensive and has a large endothermic amount, but has a high heat resistance. As a result of diligent research aimed at finding a method for obtaining high heat-resistant aluminum hydroxide with few dislocations to boehmite in the initial stage of decomposition,
Using seed aluminum hydroxide obtained under specific conditions, aluminum hydroxide is precipitated from an alkaline aluminate solution,
When it was obtained, it was found that high heat resistant aluminum hydroxide satisfying all of the above objects was obtained, and the present invention was completed.

[0011]

[Means for Solving the Problems] That is, the present invention provides a method for producing seed aluminum hydroxide by adding seed aluminum hydroxide to a supersaturated alkaline aluminate solution, wherein (1) supersaturated aluminate is used as seed aluminum hydroxide. While stirring the alkaline solution, an acid was added and the average particle size was adjusted to 0.
After obtaining the following neutralization gel 05μ, (2) the neutralization gel, Al ₂ against the amount of aluminum in the solution in the alkali aluminate solution of an alkali concentration 1.3~2.5mol / l of stirred To provide a method for producing high heat-resistant aluminum hydroxide, characterized by using aluminum hydroxide having an average secondary particle diameter of 0.1 µ to 3 µ obtained by adding 0.1% by weight or more in terms of O _3. is there.

The method of the present invention will be described in more detail below.
A feature of the present invention is, in a method for producing aluminum hydroxide by adding seed aluminum hydroxide to a supersaturated alkaline aluminate solution, as seed aluminum hydroxide,
(1) An acid was added under stirring of a supersaturated alkaline aluminate solution to obtain a neutralized gel having an average particle size of 0.05 μ or less, and (2) the neutralized gel was stirred under an alkaline concentration of 1 μm. ．
An average secondary particle diameter of 0.1 obtained by adding 0.1% by weight or more in terms of Al ₂ O ₃ to an aluminum aluminate solution of 3 to 2.5 mol / l, based on the amount of aluminum in the solution.
The point is that aluminum hydroxide having a size of μ to 3 μ is used.

In the present invention, the average particle size is 0.05 μm.
The following neutralized gel is a supersaturated alkali aluminate, for example, an aluminate alkali solution obtained by extracting the alumina content from an alumina-containing ore such as bauxite with an alkaline solution such as caustic soda, or metallic aluminum or aluminum hydroxide. It is possible to add an aluminum salt such as aluminum sulfate, aluminum chloride or aluminum nitrate, or a mineral acid such as hydrochloric acid or sulfuric acid to an alkaline aluminate solution obtained by dissolving the above with an alkaline solution such as caustic soda. However, the addition of acid to the alkaline aluminate solution is carried out while stirring the alkaline aluminate solution,
In addition, it is essential that the gel is prevented from agglomerating and growing due to the addition of acid and that the average particle size is about 0.05 μm or less. The average particle size of the neutralized gel is about 0.05
When it exceeds μ, the heat resistance of the obtained aluminum hydroxide is lowered even if the condition (2) of the method of the present invention is satisfied.

The concentration of the alkaline aluminate solution used for producing the gel is not particularly limited, and is not particularly limited as long as it produces an alumina gel by adding an acid, but usually the alkaline concentration is about 1 mol / l to About 10
mol / l, precipitation temperature 10 ° C. to 60 ° C., the amount of acid added to the alkali aluminate solution is 0.6 to the neutralization equivalent.
It may be carried out in the range of 1.0.

The obtained gel is used as it is, or after being filtered, or washed with water, filtered, and optionally dried, the alkali concentration is 1.3-
0.1 mol% in terms of Al ₂ O _{3 in} 2.5 mol / l alkali aluminate solution with respect to the amount of aluminum in the solution.
The above is added. Under conditions where the alkali concentration is less than 1.3 mol / l, aggregates of several μm to several tens of μm are deposited and cannot be used as seeds. Also, the concentration of alkali metal contained in the precipitated aluminum hydroxide increases at a concentration higher than 2.5 mol / l, probably because the heat resistance improving effect of aluminum hydroxide obtained by using this as seed aluminum hydroxide decreases. It is not preferable.

The temperature at which the neutralized gel is added to the alkaline aluminate solution to precipitate the seed aluminum hydroxide is a condition that governs the supersaturation degree of the solution and the crystallization reaction rate, but is usually about 30 ° C to about 80 ° C. It may be carried out within the range.

The amount of the neutralized gel added to the alkaline aluminate solution is about 0.1% by weight or more, usually about 0.1% by weight, calculated as Al ₂ O _{3 with} respect to the amount of aluminum in the solution. About 10
It is 0% by weight, preferably about 0.5 to about 10% by weight.
When the amount of the neutralized gel added is less than 0.1% by weight, the precipitated aluminum hydroxide is remarkably aggregated, and the effect of improving the heat resistance of the aluminum hydroxide obtained by using this as seed is not observed. On the other hand, the upper limit is naturally determined from the desired average secondary particle size of seed aluminum hydroxide.

The average secondary particle size of the desired seed depends on the particle shape of the desired product aluminum hydroxide, the degree of heat resistance required, the alkali concentration of the alkali aluminate solution for obtaining the product aluminum hydroxide, and the like. However, when the average secondary particle diameter of the desired product aluminum hydroxide is about 0.5 μ to about 10 μ,
The average secondary particle size of seed aluminum hydroxide is usually about 0.
It is 1 μ to about 3 μ, preferably about 0.3 μ to about 1.0 μ.

In carrying out the method of the present invention, the product aluminum hydroxide may be obtained by adding the aluminum hydroxide obtained by the above method as seeds to a supersaturated alkaline aluminate solution. The precipitation conditions are not particularly limited as long as the desired secondary particle size of the product can be obtained, but usually the alkali concentration is about 1 mol / l to about 10 mol.
/ L, preferably about 1.5 mol / l to about 6.5 mol
/ L, N when using soda as alkali
The molar ratio of a ₂ O / Al ₂ O ₃ is 1.2 to 4.0, preferably using alkali aluminate solution of 1.5 to 2.5,
A relative to the amount of aluminum in the alkaline aluminate solution
About 1 wt% to about 50 wt% of seed aluminum hydroxide is added in terms of l ₂ O ₃ , and the solution temperature is about 30 ° C. to about 80 ° C. In the present invention, the precipitation of the product aluminum hydroxide by the addition of seeds can be carried out in one step to obtain the product aluminum hydroxide having a desired particle size, but a method of repeatedly carrying out several steps using an alkali aluminate solution having a thin alkali concentration, In batchwise precipitation, it is also possible to employ a method of continuously supplying an alkali aluminate solution, or a continuous crystallization method in a continuous tank. In this method, an aluminum hydroxide having a small alkali concentration is used, and the aluminum hydroxide obtained by repeating several steps is capable of obtaining excellent aluminum hydroxide having high heat resistance even if it has a large particle size. .

[0020]

INDUSTRIAL APPLICABILITY The present invention relates to a method for precipitating aluminum hydroxide from an alkaline aluminate solution using aluminum hydroxide obtained under specific conditions as seeds. The aluminum hydroxide obtained by the method is ,
Despite being a gibbsite type aluminum hydroxide with a large endothermic amount, it is inexpensive and does not require special operations such as hydrothermal treatment by an autoclave as in the past, and is highly heat resistant hydroxide with few rearrangements to boehmite in the initial stage of thermal decomposition. Since it is aluminum, it is required to have high heat resistance as a filler such as rubber or plastic. It is used for electric wire coating rubber, insulating materials, printed wiring boards, electrical applications, wall covering materials, interior materials, and artificial marble. It can be used for and its industrial value is enormous.

[0021]

EXAMPLES The method of the present invention will now be described in more detail with reference to examples, but the present invention is not limited thereto. In the examples of the present invention, the heat resistance of aluminum hydroxide is determined by the presence or absence of an endothermic shoulder seen at 230 ° C. to 250 ° C. in a DSC curve measured using a differential scanning calorimeter DSC41 manufactured by Shimadzu Corporation, and It was determined from the shoulder endotherm (measured at a temperature rising rate of 10 ° C./min). The average particle diameter of the gel is measured from a transmission electron micrograph, the average secondary particle diameter of the seed aluminum hydroxide is measured from a scanning electron microscope photograph, and the average secondary particle diameter of the product aluminum hydroxide is measured by a sedimentation balance method. did.

Example 1 Highly heat-resistant aluminum hydroxide was obtained as follows. 1) Manufacture of gel In a 2 liter reaction vessel with a baffle immersed in a constant temperature bath at 10 ° C., a Na ₂ O concentration of 125 g / l and a molar ratio (Na ₂ O
/ Al ₂ O ₃ ) 1.55 sodium aluminate solution was added, and aluminum sulfate having an Al ₂ O ₃ concentration of 5.3 wt% was gradually added to the neutralization equivalent ratio of 0.6 while stirring at 1700 rpm. Then, the mixture was stirred for 1 hour. The average primary particle diameter of the gel thus obtained was 0.02μ. 2) Production of seed aluminum hydroxide using gel 1) The gel obtained in 1) was added to a sodium aluminate solution having a Na ₂ O concentration of 50 g / l and a molar ratio of 1.55, and Al ₂ O ₃ was added to aluminum in the solution. Add 3% by weight, 60 ℃
While maintaining at 1, the mixture was continuously stirred at 200 rpm for 1 hour to crystallize aluminum hydroxide. The average secondary particle diameter of the obtained aluminum hydroxide was 0.6 μm. 3) Production of product aluminum hydroxide The seed aluminum hydroxide obtained in 2) was added to a sodium aluminate solution having a Na ₂ O concentration of 50 g / l and a molar ratio of 1.55 to convert the aluminum in the solution to Al ₂ O _3. In 1
Add 0 wt%, hold at 60 ℃, 72 at 200 rpm
The stirring was continued for a while to crystallize aluminum hydroxide, followed by solid-liquid separation, drying and crushing to obtain aluminum hydroxide. The average secondary particle diameter of the obtained aluminum hydroxide was 1.2 μ, and no boehmite shoulder was observed in the differential scanning calorimetry of the aluminum hydroxide.

Example 2 Aluminum hydroxide was obtained in the same manner as in Example 1 except that the concentration of the sodium aluminate solution in 3) in Example 1 was changed to 125 g / l. The average secondary particle diameter of the obtained aluminum hydroxide was 1.0 μ, and no boehmite shoulder was observed in the differential scanning calorimetry of the aluminum hydroxide.

Example 3 Aluminum hydroxide having an average secondary particle size of 1.2 μm obtained in Example 1 was added to a sodium aluminate solution having a Na ₂ O concentration of 50 g / l and a molar ratio of 1.55 with respect to aluminum in the solution. Add 10% by weight calculated as Al ₂ O ₃ and hold at 60 ° C.
Aluminum hydroxide was crystallized by continuing stirring at 200 rpm for 72 hours, followed by solid-liquid separation, drying and crushing to obtain aluminum hydroxide. The average secondary particle diameter of the obtained aluminum hydroxide was 2.6 μ, and no boehmite shoulder was observed in the differential scanning calorimetry of the aluminum hydroxide.

Comparative Example 1 In the method of Example 1, stirring was carried out 10 times in the production of the gel of 1).
Seed aluminum hydroxide was obtained in the same manner as in Example 1 except that the gel having an average particle size of 0.2 µ obtained by carrying out at 0 rpm for 0.2 hours was used, and further a product aluminum hydroxide was obtained. The average secondary particle diameter of the obtained aluminum hydroxide was 3 μ, and the shoulder endothermic amount was 10 mj / mg as measured by a DSC thermal analysis chart.

Comparative Example 2 The gel obtained by the method 1) in the method of Example 1 was treated with Na ₂
In a sodium aluminate solution having an O concentration of 125 g / l and a molar ratio of 1.55, Al ₂ O ₃ was added to aluminum in the solution.
Add 0.5 wt% in conversion, hold at 60 ℃, 200r
It was taken out after crystallization for 72 hours under stirring at pm, separated by solid-liquid separation, washed and dried. The average secondary particle diameter of the obtained aluminum hydroxide was 0.8 μ, and the shoulder endothermic amount was 3.2 mj / mg as measured by a DSC thermal analysis chart.

Comparative Example 3 In the production of seed aluminum hydroxide using the gel obtained by the method of 1) in the method of Example 1, the gel was changed to Na ₂
0.5% by weight of Al ₂ O _{3 in} terms of Al ₂ O ₃ was added to sodium aluminate having an O concentration of 125 g / l and a molar ratio of 1.55, and the mixture was kept at 60 ° C. and stirred at 200 rpm for 1 hour. Aluminum hydroxide was crystallized. The average secondary particle diameter of the obtained seed aluminum hydroxide is 0.5.
It was μ. This seed aluminum hydroxide was added under the same conditions as in Example 2 to obtain a product aluminum hydroxide. The average secondary particle diameter of the obtained aluminum hydroxide was 1.2 μ, and the shoulder endothermic amount was 17.2 mj / mg as measured by a DSC thermal analysis chart.

Claims (1)

[Claims] 1. A method of producing seed aluminum hydroxide by adding seed aluminum hydroxide to a supersaturated alkaline aluminate solution, wherein the seed aluminum hydroxide is (1)
After adding an acid with stirring of a supersaturated alkaline aluminate solution to obtain a neutralized gel having an average particle size of 0.05 μ or less,
(2) The neutralized gel is stirred to obtain an alkali concentration of 1.3-
0.1 mol% in terms of Al ₂ O _{3 in} 2.5 mol / l alkali aluminate solution with respect to the amount of aluminum in the solution.
The average secondary particle diameter obtained by the above addition is 0.1 μ
A method for producing highly heat-resistant aluminum hydroxide, which comprises using 3 µm of aluminum hydroxide.