JPH03197317A - Production of heat-resistant aluminum hydroxide - Google Patents

Abstract

PURPOSE:To efficiently adsorb a Si compound and a Ca compound on the surface of aluminum hydroxide particles by adsorbing the Si compound and the Ca compound on the surface of Al(OH)3 particles while controlling hydrogen ion concentration of aqueous solution of the compound. CONSTITUTION:In a method of producing heat-resistant aluminum hydroxide by adsorbing a silicon compound and a calcium compound on the surface of aluminum hydroxide particles, when aluminum hydroxide is brought into contact with an aqueous solution containing both or one of the silicon compound and the calcium compound, the hydrogen ion concentration of the aqueous solution is controlled. In the case of using the aqueous solution containing both the silicon compound and the calcium compound and adsorbing, the pH is preferably adjusted to >=7. In the case of using 2 solutions containing each single compound by two-stage treatment, the pH is preferably regulated also to >=7.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to improving the thermal stability of crystallized water of aluminum hydroxide, which is used as a filler in rubber, plastic, and paper, and particularly relates to the improvement of the heat resistance stability of crystalline water of aluminum hydroxide, which is used as a filler in rubber, plastic, and paper. As electrical and electronic insulating materials such as composite copper-clad laminates made of fuel wire compound, epoxy, glass cloth non-woven fabric base material, etc.
The present invention relates to a method for producing aluminum hydroxide with excellent heat resistance, which can be molded at temperatures of 0° C. or higher.

[Conventional technology]

In recent years, flame-retardant cables containing halogen-based polymers and flame retardants generate large amounts of corrosive gas and smoke in the event of a fire.
Accidents that cause great damage to human life and peripheral equipment are occurring. As a result, the trend toward non-halogen flame retardants, which do not contain halogen elements, has increased, and development technology has progressed rapidly. Non-halogen flame retardants are made by blending about 150 parts of an inorganic filler with water of crystallization, such as aluminum hydroxide, into a polyolefin polymer, and are characterized by producing less harmful gas smoke.

A material in which such a large amount of aluminum hydroxide is blended with a polyolefin polymer has the disadvantage that the melt viscosity increases significantly during extrusion processing, resulting in a decrease in processing performance. Therefore, a method to improve processing performance is generally to raise the temperature of the extruder, but when the temperature of the extruder approaches 200°C, some of the crystallized water of aluminum hydroxide decomposes. The problem is that the generated water vapor causes the material to foam, making it impossible to extrude.

Against this background, there is a demand for heat-resistant aluminum hydroxide, which has a higher decomposition initiation temperature than existing aluminum hydroxide, as a filler for halogen-free flame-retardant wire materials.

In addition, glass cloth non-woven fabric composite copper clad laminate (OEM-
In 3), a filler such as aluminum hydroxide is added to the epoxy resin to ensure dimensional stability in the thickness direction of the substrate. Recent trends include raising the temperature of the solder bath to speed up the board production line, and the introduction of reflow soldering technology, which means that laminates are exposed to higher temperatures than before.

As a result, a portion of the aluminum hydroxide in the substrate is thermally decomposed, causing a problem in which the copper foil peels off.

Therefore, aluminum hydroxide with stable crystal water and excellent heat resistance is desired even at high temperatures.

Several methods have been proposed to date to improve the heat resistance of aluminum hydroxide used as a filler. for example,
JP-A-82-24696 or JP-A-59-204
In No. 632, it was discovered that Na 20, an impurity, has the effect of promoting dehydration during the heating dehydration process of aluminum hydroxide, and a method was proposed to improve heat resistance by reducing Na 20 to 0.10 vt% or less. has been done. In addition, the present inventors have proposed that silicon compounds and calcium compounds be adsorbed onto the surface of aluminum hydroxide to reduce the increase in the starting temperature of the dehydration reaction and the weight loss of 250°C (Patent Application No. 63 -225779). However, although the former method has been put into practical use as a non-halogen flame retardant and a filler for composite substrates, the properties are insufficient to meet the required level. In the present invention, the latter manufacturing method has been further improved to make it industrially extremely effective.

[Problem to be solved by the invention]

Aluminum hydroxide used as a filler generally begins to decompose and dehydrate at around 200°C. However, when kneaded into a polymer and processed, it is known that even at a temperature lower than 200° C., some of the crystals and water decompose and generate water, resulting in foaming and silver marks.

The inventors investigated this phenomenon using thermal instrumentation! The thermal decomposition behavior of aluminum hydroxide was precisely analyzed using (differential thermal analysis and thermobalance Wl).

As shown in FIG. 3, in addition to the main dehydration reaction that starts at 200° C. or higher (positions ■ and ■), a weight loss accompanied by a small endotherm occurs from around 170° C. to the position ■. Analysis of this reaction product revealed that it was water. The amount of water dissociated is
Although the amount is less than lvt%, since it becomes water vapor and increases in volume, it is considered to be enough to cause air bubbles inside the molded product, surface roughness, and silver marks. Furthermore, among the main dehydration reactions, an endothermic reaction at around 250°C is known as a reaction in which a portion of aluminum hydroxide is transferred to boehmite.

As mentioned above, in order to suppress the minute dehydration reaction and the transfer reaction of boehmite at temperatures below 200°C, the patent application No. 63-2
The invention of No. 25779 is that in conventional aluminum hydroxide,
A method for producing a new type of heat-resistant aluminum hydroxide, which suppresses the unobtainable low-temperature dehydration reaction and further reduces the boehmite transfer reaction, is provided by adsorption of silicon compounds and calcium compounds.

The present invention aims to further improve the above invention and provide a method for efficiently adsorbing silicon compounds and calcium compounds onto the surfaces of aluminum hydroxide particles.

[Means to solve the problem]

The present invention provides a method for efficiently adsorbing silicon compounds and calcium compounds onto the surface of aluminum hydroxide as an adsorption treatment method for significantly reducing low-temperature dehydration behavior and boehmite transfer reaction.

That is, the present invention has discovered a phenomenon in which silicon compounds, particularly colloidal silica and calcium ions dissolved in water, are selectively adsorbed onto aluminum hydroxide within a certain hydrogen ion concentration range, and the present invention has discovered a phenomenon in which silicon compounds, particularly colloidal silica and calcium ions dissolved in water, are selectively adsorbed onto aluminum hydroxide within a certain hydrogen ion concentration range. This method was completed based on the fact that aluminum hydroxide can be obtained with adsorption above a certain concentration.

That is, the gist of the present invention is as follows: In a method for producing heat-resistant aluminum hydroxide by adsorbing a silicon compound and a calcium compound onto the surface of aluminum hydroxide particles, an aqueous solution containing both or one of a silicon compound and a calcium compound and hydroxide This is a method for producing heat-resistant aluminum hydroxide, characterized by controlling the hydrogen ion concentration of the aqueous solution when bringing it into contact with aluminum particles.

For heat-resistant aluminum hydroxide, it is necessary that both a silicon compound and a calcium compound be adsorbed on the aluminum hydroxide particles.

In the case of adsorption using an aqueous solution in which a silicon compound and a calcium compound coexist, pi is preferably controlled to 7 or more, and in the case of two-stage treatment using a single aqueous solution containing each single compound. In a solution containing a calcium compound, the pH is preferably controlled to 7 or higher.

The adsorption phenomenon of aluminum hydroxide can be confirmed by the following experiment. 1.5 μm of aluminum hydroxide crystallized from a supersaturated sodium aluminate solution was filtered,
Washed with ion-exchanged water to remove adhering alkaline components. Next, colloidal silica (100, 1,000, 5
The wet cake of aluminum hydroxide was reslurried in an aqueous solution containing 1,000, 10,000 .mu./fl), allowed to adsorb for 30 minutes, and then filtered with suction. The resulting cake was dried and the concentration of silicon compounds in aluminum hydroxide (
The SiO2 concentration (hereinafter referred to as SiO2 concentration for convenience) was analyzed. Similarly, calcium hydroxide (100,500
, 1,000■/g), calcium chloride (100,1,
000, 5,000 .mu./N), the concentration of the calcium compound (in terms of CaO, hereinafter referred to as CaO concentration for convenience) was determined. Figure 1 shows that SiOCa (OH) Ca Cj! in aqueous solution for aluminum hydroxide. 2
This is experimental data showing the concentration and amount of adsorption on 2'2' aluminum hydroxide. The adsorption amount of a silicon compound increases with the addition concentration, and when 1% is added to an aqueous solution, the adsorption amount is 3%, and is dominated by the concentration. On the other hand, calcium compounds include Ca CR
With the 2 reagent, there is hardly any adsorption, and with the Ca(OH) 2 reagent, the amount of adsorption is about aoopp-.

In order to investigate this remarkable difference in adsorption properties of calcium compounds in more detail, the present inventor conducted an experiment in which the hydrogen ion concentration in the aqueous solution was varied, with a silicon compound and a calcium compound coexisting, and a single solution.

As a result, the relationship shown in FIG. 2 was changed. Calcium compounds are hardly adsorbed in the acidic region, and in the alkali, region (p
It was confirmed that adsorption occurs at temperatures higher than H7).

To evaluate the heat resistance of aluminum hydroxide adsorbed with silicon compounds or calcium compounds, a certain amount of dry powder (1
50 ■) Precisely weigh and measure the starting temperature of low-temperature dehydration (Td) and the amount of dehydration up to 250℃ (W# -2
50) was measured. Furthermore, a fluorescent X-ray analyzer was used to measure the amount of silicon compounds and calcium compounds adsorbed onto aluminum hydroxide.

As a result, no change was observed in those to which a silicon compound or calcium compound was adsorbed alone, and no improvement in heat resistance was observed compared to those in which no silicon compound or calcium compound was adsorbed. Therefore, the second
As illustrated in the figure, it was confirmed that pH is strongly involved in the production of heat-resistant aluminum hydroxide using an aqueous solution containing a silicon compound and a calcium compound, and that adsorption in an alkaline region is desirable. .

The effect of improving heat resistance due to the adsorption of silicon compounds and calcium compounds increases in proportion to the amount of adsorption, but in practical terms silicon compounds have an S l 02 equivalent of 500 to 5,000.
0 ppm, calcium compound is 100-2.
000 pp Maro is preferred. Below this level, the low-temperature dehydration phenomenon cannot be eliminated, and even if it exceeds this level, the effect of improving heat resistance reaches saturation, which is not economical.

When a silicon compound and a calcium compound are adsorbed using an aqueous solution in which both compounds coexist, if a highly concentrated aqueous solution is used, the adsorption properties will worsen.

The reason for this is not fully understood, but calcium ions mix with silicon ions in the aqueous solution.
Water-soluble silica aggregates to form flocs. It is inferred that this silica floc is interfering with adsorption.

In order to avoid this floc formation as much as possible, it is desirable to adsorb from a low concentration solution, and as a method, the aqueous solution of the silicon compound and calcium compound at a predetermined concentration is not added all at once, but is added intermittently in multiple times, or, It is effective to add the adsorbent gradually and continuously to reduce the silicon ions and calcium ions in the adsorbent to a low level (less flocs).

In addition, as a method to avoid the coexistence of silicon compounds and calcium compounds, a two-step process in which silicon compounds are first adsorbed and then calcium compounds are adsorbed (or the order is reversed) is also used to combine silicon ions and calcium ions in an aqueous solution. This is effective because there is no direct contact between the two.

In addition, the concentration of the aqueous solution to obtain the above adsorption amount is 50 to 5.000 ppm for silicon compounds, 50 to 2 ppm for calcium compounds,
DDOppm is preferred, and the compounds are preferably sodium orthosilicate, sodium metasilicate, colloidal silica, calcium hydroxide, and calcium chloride.

〔Example〕

The content of the present invention will be explained in more detail below with reference to Examples, but the technical scope of the present invention is not limited thereto.

Example 1 A hydrated alumina gel was prepared by mixing an aqueous solution of an alkali aluminate salt and an aqueous solution of an acid compound and carrying out a neutralization reaction. Alumina concentration 120t/II, caustic soda concentration t5
0 g/N supersaturated sodium aluminate solution was maintained at 80 °C, hydrated alumina fist gel was added as seed crystals,
The precipitation reaction was carried out for 16 hours while stirring. The precipitated aluminum hydroxide was placed on a Buchner type filter funnel, and the aluminate liquid was separated by vacuum suction. A wet cake (solid content: 50 m) of aluminum hydroxide (average diameter 1.5 m) with alkali adhering on the funnel thus obtained.
%) 100. was washed with distilled water to remove adhering alkaline components. 100g of this alkali-removed aluminum hydroxide wet cake was mixed with colloidal silica (
Oxide equivalent: 2001g/j! ), calcium hydroxide (200 mg/l in terms of oxide) was added, and NaO
Aqueous solution adjusted to pH 31 with H and HCl (Example 1-1
piIa, s, Example 1-2 potx, e, Comparative Example 1-1 pH 4,6, Comparative Example 1-2 pH 8,8
) Re-slurry in IJ - After stirring for 630 minutes, suction filtration was performed.

Rinse each wet cake with 300ml of distilled water,
The mixture was dried in an oven at 00° C. overnight to obtain a dry powder of aluminum hydroxide. Table 1 shows the results of differential thermal analysis (heating rate: 4°C/min, held at 100°C for 2 hours) and the analysis values of SiO2 and CaO for each powder.

In the acidic region of Comparative Example 1-1.1-2, adsorption of silicon compounds is observed, but hardly any calcium compounds are adsorbed. As a result, the heat resistance data showed almost no effect on low-temperature dehydration and boehmite transition, and the heat resistance was comparable to that of Comparative Example 1-3.

On the other hand, in the alkaline region of Example 1-1.1-2, adsorption of both silicon compounds and calcium compounds was observed, and the heat resistance was also improved.

As conditions for producing aluminum hydroxide with excellent heat resistance by adsorbing silicon compounds and calcium compounds from an aqueous solution containing silicon compounds and calcium compounds, the pH of the aqueous solution containing silicon compounds and calcium compounds is
Must be in the alkaline range.

In Comparative Example 1-3, the alkali content was removed using distilled water.

Example 2 100 g of the alkali-adhered aluminum hydroxide wet cake (solid content 50%) prepared in Example 1 was prepared using colloidal silica, sodium orthosilicate, sodium metasilicate, and calcium hydroxide as the calcium compound component. The slurry was added to aqueous solution II having the following composition and calcium chloride was stirred for 630 minutes, and then filtered under suction. After that, wash with 300ml of distilled water and
Dry at °C.

Each dried powder was analyzed for impurities and differential thermal balance analysis. The results are shown in Table 2.

■ Colloidal silica 200 g/1. in distilled water. Dissolved calcium hydroxide 2DOag/l (Example 2-
1) ■ Colloidal silica 200 g/I and calcium chloride 200 g/g dissolved in distilled water (Example 2-
2) ■ Sodium orthosilicate 200μ/II and calcium hydroxide 200μ/g dissolved in distilled water (Example 2-
3) ■ Sodium orthosilicate 200μ/fl and calcium chloride 200μ/1 dissolved in distilled water (Example 2-4)
) ■ 200 mg/R of sodium metasilicate and 200 μ/1 of calcium hydroxide dissolved in distilled water (Example 2-5)
) ■ Sodium metasilicate 200mg/j in distilled water! , in which 200 g/l of calcium chloride was dissolved (Example 2
-6) ■ Washed with 300ml of distilled water (Comparative Example 2-1)
Example 3 Alkali-adhered aluminum hydroxide wet cake (solid content 50%) obtained in the same manner as Example 1 1
00 [11] was slurried in an aqueous solution having the following composition, stirred for 30 minutes, and filtered under suction. Distilled water 3o.

ml of each wet cake was dried at 100'C to obtain a dry powder of aluminum hydroxide. Table 3 shows the differential thermal balance analysis and impurity analysis values for each powder.

■ Colloidal silica (Nissan Chemical Co., Ltd./-5) in distilled water.
-”/’) 2096 minutes) 50mg/j!
(S i O2 conversion), calcium chloride 50■/I
(CaO equivalent) added and dissolved (Example 3-1
) ■ Add and dissolve colloidal silica at 200 ■/I and calcium chloride at 200 ■/II in distilled water (
Example 3-2) 1. 7B of colloidal silica in distilled water.

Calcium chloride was added and dissolved at 200 μg/g (Example 3-3) ■ Colloidal silica was added to distilled water at 5,000 μg/1,
Calcium chloride added and dissolved at 200 μ/I (Example 3-4) ■ Colloidal silica (only 200 μ/J added to distilled water (Comparative Example 3-1)) ■ Distilled water with chloride added Added only calcium (200 g/l) (Comparative Example 3-2) ■ Only distilled water (Comparative Example 3-3) Example 3-1~
3-4, which adsorbed silicon compounds and calcium compounds, suppressed low-temperature dehydration below 200°C and lowered the boehmite transition rate, resulting in a heating temperature of 250°C.
The amount of dehydration has decreased considerably. On the other hand, adsorption of silicon compounds or calcium compounds alone (Comparative Example 3-
1 to 3-2) As with the reslurry using distilled water (Comparative Example 3-3), the dehydration peak in the low temperature region clearly appears and the amount of dehydration is large.

Example 4 Aluminum hydroxide wet cake 1 obtained in Example 1
Re-slurry 00g (solid content 50%) into distilled water of II.
did. Next, a highly concentrated sodium orthosilicate solution (Si
While stirring, 200 ml of calcium chloride aqueous solution (000q/I calculated as CanIl) was added to aluminum hydroxide slurry.
Continuous additions were made for minutes.

After 30 minutes, the slurry was filtered and the wet cake was dried with distilled water. As a result of differential thermal analysis of this powder, the powder had a Td of 205° C. and a Wl of 0.88.

Example 5 A wet cake of aluminum hydroxide obtained in the same manner as in Example 1 was mixed with 200 μ/I of sodium silicate (in terms of oxide).
The mixture was reslurried in 1 g of solution, stirred for 30 minutes, and then filtered with suction. Next, mix this cake with calcium chloride 200■/1
1 (calculated as CaO), and after stirring again for 30 minutes, suction filtration was performed. As a result of drying the wet cake and performing differential thermal analysis, Td was 203°C and WI was 0.86.
%Met.

〔Effect of the invention〕

As detailed above, the heat-resistant aluminum hydroxide produced by the method of the present invention has superior heat resistance than conventional aluminum hydroxide, and can be used in polyolefin-based halogen-free flame-retardant compounds and copper-clad composites. Used as a filler in laminates.

It is an extremely effective material commercially.

[Brief explanation of drawings]

Figure 1 shows SiO2, Ca(OH)2C in aqueous solution.
aCj! 2 concentration and silicon compounds (S l 02 conversion) and calcium compounds (calculated as S l 02) adsorbed on aluminum hydroxide.
The relationship between adsorption amount (in terms of CaO) is shown. FIG. 2 shows the relationship between the pH of the aqueous solution and the adsorption amount of silicon compounds (in terms of S102) and calcium compounds (in terms of CaO). FIG. 3 shows the thermal decomposition behavior of ordinary aluminum hydroxide using differential thermal analysis and a thermobalance.

Claims (5)

[Claims] (1) In a method for producing heat-resistant aluminum hydroxide by adsorbing a silicon compound and a calcium compound onto the surface of aluminum hydroxide particles, aluminum hydroxide particles are brought into contact with an aqueous solution containing both or one of a silicon compound and a calcium compound. A method for producing heat-resistant aluminum hydroxide, which comprises controlling the hydrogen ion concentration of the aqueous solution. (2) The method for producing heat-resistant aluminum hydroxide according to claim (1), wherein the aqueous solution containing both a silicon compound and a calcium compound, or only a calcium compound, has a pH of 7 or more. (3) The heat-resistant water according to claim (1), wherein the silicon compound contained in the aqueous solution is one or more of sodium orthosilicate, sodium metasilicate, and colloidal silica. Method for producing aluminum oxide. (4) The method for producing heat-resistant aluminum hydroxide according to claim (1), wherein the calcium compound contained in the aqueous solution is calcium hydroxide and/or calcium chloride. (5) In a method for producing heat-resistant aluminum hydroxide by adsorbing silicon compounds and calcium compounds onto the surface of aluminum hydroxide particles, an aqueous solution containing silicon compounds and calcium compounds is added to the aluminum hydroxide slurry intermittently or continuously. A method for producing heat-resistant aluminum hydroxide, characterized by adding the heat-resistant aluminum hydroxide to.