JP2798755B2 - Method for producing heat-resistant aluminum hydroxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an improvement in the heat stability of water of crystallization of aluminum hydroxide used as a filler for rubber, plastics and paper, and particularly to halogen-free materials. As an electric and electronic insulating material, such as composite copper clad laminate made of fuel wire compound, epoxy, glass cloth non-woven fabric base, etc.
The present invention relates to a method for producing aluminum hydroxide which can be molded at a temperature of 0 ° C. or more and has excellent heat resistance.

[Conventional technology]

2. Description of the Related Art In recent years, fire-retardant cables containing halogen-based polymers and flame retardants generate a large amount of corrosive gas and smoke when fired, causing accidents that cause serious damage to human life and peripheral equipment. As a result, the trend toward non-halogen flame retardants that do not contain halogen elements has increased, and the development technology has rapidly advanced. Non-halogen flame retardant is obtained by adding inorganic filler with water of crystallization such as aluminum hydroxide to polyolefin polymer.
It is characterized by low emission of harmful gas smoke.

A material in which such a large amount of aluminum hydroxide is blended with a polyolefin-based polymer has a drawback that the melt viscosity is significantly increased at the time of extrusion and the processing performance is reduced.
Therefore, as a method of improving the processing performance, a method of raising the temperature of the extruder is generally used, but when the temperature of the extruder approaches 200 ° C., a part of the water of crystallization of aluminum hydroxide is decomposed, There is a problem that the material is foamed by the generated water vapor and cannot be extruded.

Against this background, heat-resistant aluminum hydroxide having a higher decomposition initiation temperature than existing aluminum hydroxide is required as a filler for halogen-free flame-retardant electric wire materials.

In addition, glass cloth non-woven composite copper clad laminate (CEM-
In 3), a filler such as aluminum hydroxide is mixed with the epoxy resin to measure dimensional stability in the thickness direction of the substrate. Recent trends include increasing the temperature of the solder bath in order to speed up the substrate line and the introduction of reflow soldering technology, whereby the laminates have been exposed to higher temperatures than before.

For this reason, there is a problem that a part of the aluminum hydroxide in the substrate is thermally decomposed and the copper foil is peeled off. Therefore, there is a demand for an aluminum hydroxide having stable crystallization water even at high temperatures and excellent heat resistance.

Several methods have been proposed to improve the heat resistance of aluminum hydroxide used for fillers. For example, Japanese Unexamined Patent Publication No. Sho 62-24696 or Japanese Unexamined Patent Publication No. Sho 59-204632 discloses that Na ₂ O which is an impurity
0.10 Na ₂ O but found that an effect of promoting the dehydration
A method for improving heat resistance by reducing the content to wt% or less has been proposed. In addition, the present inventors have proposed that a silicon compound and a calcium compound be adsorbed on the surface of aluminum hydroxide to reduce the increase in the dehydration reaction start temperature and the weight loss at 250 ° C. -225779). However, the former method has been put to practical use as a halogen-free flame retardant or a filler for a composite substrate, but is insufficient in characteristics to a required level. In the present invention, the latter manufacturing method has been further improved to be industrially extremely effective.

[Problems to be solved by the invention]

It is generally said that aluminum hydroxide used as a filler starts to decompose and dehydrate at around 200 ° C. However, when kneading and processing into a polymer, it is known that even at a temperature lower than 200 ° C., some of the crystals and water decompose and generate water to cause foaming and silver marks.

To this phenomenon, the present inventors analyzed the thermal decomposition behavior of aluminum hydroxide precisely using a thermal analyzer (differential thermal analysis and thermobalance device).

As shown in FIG. 3, in addition to the main dehydration reaction (and position) starting at 200 ° C. or more, a weight loss accompanied by a small endothermic occurs at a position from around 170 ° C. The reaction product was analyzed to be water. The amount of water dissociated is 1w
Although the amount is less than t%, it is considered to be sufficient to cause bubbles inside the molded product, surface cracks, and silver marks because the volume increases due to water vapor. Further, among the main dehydration reactions, an endothermic reaction at around 250 ° C. is known as a reaction in which the entrance of aluminum hydroxide is transferred to boehmite.

As described above, in order to suppress a minute dehydration reaction at 200 ° C. or less and a boehmite transfer reaction, Japanese Patent Application No. 63-2257
The invention of 79 relates to a method for producing a new type of heat-resistant aluminum hydroxide in which a low-temperature dehydration reaction, which cannot be obtained with conventional aluminum hydroxide, is obtained, and a boehmite transfer reaction is further reduced. Provided by adsorption.

The present invention is intended to further improve the above-mentioned invention and to provide a method for efficiently adsorbing a silicon compound and a calcium compound on the surface of aluminum hydroxide particles.

[Means for solving the problem]

The present invention provides a method for efficiently adsorbing a silicon compound and a calcium compound on an aluminum hydroxide surface as an adsorption treatment method for remarkably reducing low-temperature dehydration behavior and boehmite transfer reaction.

That is, the present invention finds a phenomenon in which silicon compounds, particularly colloidal silica and calcium ions dissolved in water, are selectively adsorbed on aluminum hydroxide in a certain hydrogen ion concentration range, and both are found in a certain hydrogen ion concentration range. It has been completed based on the fact that aluminum hydroxide adsorbed at a certain concentration or more can be obtained.

That is, the gist of the present invention is to provide a method for producing a heat-resistant aluminum hydroxide by adsorbing a silicon compound and a calcium compound on the surface of aluminum hydroxide particles, wherein an aqueous solution containing both or one of the silicon compound and the calcium compound is hydroxylated. A method for producing a heat-resistant aluminum hydroxide, wherein the pH of the aqueous solution is 7 or more when the aqueous solution is brought into contact with aluminum particles.

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

In the case of performing adsorption using an aqueous solution in which a silicon compound and a calcium compound coexist, the pH is controlled to 7 or more, and in the case of performing a two-stage treatment using a single aqueous solution containing each single compound, calcium is added. In solutions containing compounds, the pH is kept above 7;

The adsorption phenomenon of aluminum hydroxide can be confirmed by the following experiment. 1.5 μm of aluminum hydroxide crystallized from the supersaturated sodium aluminate solution was separated by filtration and washed with ion-exchanged water to remove attached alkali components. Next, colloidal silica (100, 1,000, 5,000, 10,000 mg
The wet cake of aluminum hydroxide was reslurried in an aqueous solution containing (/), adsorbed for 30 minutes, and suction-filtered. The obtained cake was dried, and the concentration of silicon compound in aluminum hydroxide (in terms of SiO ₂ , hereinafter referred to as SiO ₂ concentration for convenience) was analyzed. Similarly, calcium hydroxide (100,
500,1,000mg /), calcium chloride (100,1,000,5,000m
g /), the concentration of a calcium compound (in terms of CaO, hereinafter referred to as convenience CaO concentration) was determined. FIG. 1 shows that SiO ₂ , Ca (OH) ₂ , CaC
l is an experimental data showing the adsorption amount adsorbed to ₂ concentration of aluminum hydroxide. The amount of silicon compound adsorbed increases with the concentration of addition, and shows 1% of 3% adsorbed by adding 1% to the aqueous solution.
Concentration dominated. In contrast, the calcium compound is Ca
The Cl ₂ reagent hardly adsorbs, and the Ca (OH) ₂ reagent adsorbs about 800 ppm.

In order to investigate in more detail the remarkable difference in the adsorption characteristics of the calcium compound, the present inventor conducted an experiment in which the hydrogen ion concentration in the aqueous solution was changed when the silicon compound and the calcium compound coexisted and were used alone. As a result, the relationship shown in FIG. 2 was obtained. It was confirmed that the calcium compound was hardly adsorbed in the acidic region, and was adsorbed in the alkaline region (pH 7 or more).

Evaluation of the thermal properties of aluminum hydroxide adsorbing a silicon compound or a calcium compound was performed by precisely weighing a certain amount (150 mg) of a dry powder and subjecting it to low-temperature dehydration with a differential thermal balance (Rigaku Denki Co., Ltd. Thermoflex TG8110). Starting temperature (T
d) and the amount of dehydration up to 250 ° C (Wl-250) were measured. An X-ray fluorescence analyzer was used to measure the amounts of silicon compounds and calcium compounds adsorbed on aluminum hydroxide.

As a result, in the case of adsorbing the silicon compound or the calcium compound alone, no change was observed and no improvement in heat resistance was observed as compared with the case of not adsorbing the silicon compound or the calcium compound. Therefore, the second
As shown in the figure, in the production of heat-resistant aluminum hydroxide using an aqueous solution in which a silicon compound and a calcium compound coexist, it has been confirmed that pH is strongly involved and adsorption in an alkaline region is desirable. Was.

Such a silicon compound, the heat resistance improving effect by calcium compound adsorption increases in proportion to the amount of adsorption,
Practically silicon compound in terms of SiO ₂ 500～5,000Ppm, calcium compounds terms of CaO 100~2,000ppm are preferred. Below this level, the low-temperature dehydration phenomenon cannot be lost, and even if this level is exceeded, the effect of improving heat resistance is almost saturated, so it is not economical.

When a silicon compound and a calcium compound are adsorbed using a coexisting aqueous solution of both compounds, the use of a high-concentration aqueous solution rather deteriorates the adsorbability.

Although the reason has not been fully elucidated, water-soluble silica is aggregated to form flocs by mixing calcium ions with silicon ions in the aqueous solution. It is presumed that this silica floc hinders the adsorptivity.

In order to avoid this floc formation as much as possible, adsorption from a low-concentration solution is desirable.As a method, a predetermined concentration aqueous solution of a silicon compound and a calcium compound is not added all at once, or is added intermittently in a plurality of times, or It is effective to continuously and gradually add silicon ions and calcium ions in the adsorbing liquid to a low level (there is little floc) to adsorb.

As a method for avoiding the coexistence of a silicon compound and a calcium compound, a two-step treatment in which a silicon compound is first adsorbed and then a calcium compound is adsorbed (or the order is reversed) is also carried out in an aqueous solution using silicon ion and calcium ion. Is effective because they do not directly contact.

The aqueous solution concentration for obtaining the above adsorption amount is preferably a silicon compound 50 to 5,000 ppm, a calcium compound 50 to 2,000 ppm, and the compound includes sodium orthosilicate, sodium metasilicate, colloidal silica, calcium hydroxide, and calcium chloride. desirable.

〔Example〕

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

Example 1 An aqueous solution of alkali aluminate and an aqueous solution of an acid compound were mixed, and a hydrated alumina gel was prepared by a neutralization reaction. A supersaturated sodium aluminate solution having an alumina concentration of 120 g / caustic soda concentration of 150 g / was kept at 80 ° C., and a hydrated alumina gel was added as seed crystals, and stirred for 16 hours.
The precipitation reaction was performed for a time. The precipitated aluminum hydroxide was put on a Buchner-type filtration funnel, and suctioned under vacuum to separate an aluminate solution. The aluminum hydroxide (with an average diameter of 1.5) adhered to the alkali on the funnel thus obtained.
100 μm) of a wet cake (50% solid content) was washed with distilled water to remove attached alkali components.
100 g of this alkali-removed aluminum hydroxide particle wet cake is colloidal silica (200 mg / oxide equivalent),
Add calcium hydroxide (200 mg / oxide equivalent) and add Na
Aqueous solution adjusted to pH with OH and HCl (Example 1-1, pH8.8,
Example 1-2 pH 11.6, Comparative Example 1-1 pH 4.6, Comparative Example 1-2 pH 6.8) 1 was reslurried, stirred for 30 minutes, and filtered by suction.

Wash each wet cake with 300 ml of distilled water, 100 ℃
In an oven overnight to obtain a dry powder of aluminum hydroxide. For each powder, the result of differential thermal balance analysis (heating rate 4 ° C./min, holding at 100 ° C. for 2 hours) and SiO ₂ ,
The analytical values of CaO are shown in Table 1.

In the acidic region of Comparative Examples 1-1 and 1-2, adsorption of a silicon compound is recognized, but almost no calcium compound is adsorbed. As a result, the heat resistance data showed almost no effect on the low-temperature dehydration and the boehmite transition, and showed the same heat resistance as Comparative Example 1-3.

On the other hand, in the alkaline region of Examples 1-1 and 1-2, adsorption of both the silicon compound and the calcium compound was recognized, and the heat resistance was also improved.

As a condition for producing an aluminum hydroxide excellent in heat resistance by adsorbing a silicon compound and a calcium compound from an aqueous solution in which a silicon compound and a calcium compound coexist, the pH of an aqueous solution in which a silicon compound and a calcium compound coexist is
Must be alkaline.

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

Example 2 Colloidal silica, sodium orthosilicate, and 100 g of a wet cake (solid content: 50%) of aluminum hydroxide adhered to an alkali prepared in Example 1 were used as a silicon compound component.
The slurry was reslurried in an aqueous solution 1 having the following composition to which sodium metasilicate and calcium hydroxide, calcium hydroxide and calcium chloride were added, and stirred for 30 minutes, followed by suction filtration. Then, it was further washed with 300 ml of distilled water and dried at 100 ° C.

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

200 mg / colloidal silica / 200 mg / calcium hydroxide dissolved in distilled water (Example 2-1) 200 mg / colloidal silica / 200 mg / calcium chloride dissolved in distilled water (Example 2-2) Sodium orthosilicate 200 mg / calcium hydroxide 200 mg / dissolved (Example 2-3) Sodium orthosilicate 200 mg / calcium chloride 200 mg / dissolved in distilled water (Example 2-4) 200 mg / sodium acid / 200 mg / calcium hydroxide dissolved (Example 2-5) 200 mg / sodium metasilicate / 200 mg / calcium chloride dissolved in distilled water (Example 2-6) Washing with 300 ml of distilled water (Comparative Example 2-1) Example 3 100 g of a wet cake (50% solids content) of alkali-adhered aluminum hydroxide obtained in the same manner as in Example 1
Is reslurried in an aqueous solution having the following composition, and stirred for 30 minutes.
Suction filtration was performed. Each wet cake washed with 300 ml of distilled water was dried at 100 ° C. to obtain a dry powder of aluminum hydroxide. Table 3 shows the differential thermal balance analysis and the analysis value of impurities for each powder.

Distilled water colloidal silica (manufactured by Nissan Chemical Snowtex 20% purity) 50 mg / (SiO ₂ equivalent), which calcium chloride was dissolved was added 50 mg / (CaO equivalent) (Example 3-1) distilled water 200 mg / of colloidal silica and 200 mg / of calcium chloride were added and dissolved (Example 3-
2) 1,000 mg / colloidal silica and 200 mg / calcium chloride were added to and dissolved in distilled water (Example 3).
3) Colloidal silica 5,000 mg / and calcium chloride 200 mg / were added and dissolved in distilled water (Example 3).
4) Distilled water containing only colloidal silica (200 mg /) (Comparative Example 3-1) Distilled water containing only calcium chloride (200 mg /) (Comparative Example 3-2) Distilled water only ( Comparative Example 3-3) What adsorbed the silicon compound and the calcium compound of Examples 3-1 to 3-4, the low-temperature dehydration of 200 ° C. or less was suppressed, and the boehmite transition rate was reduced. As a result, the amount of dehydration up to the heating temperature of 250 ° C. Has dropped considerably. On the other hand, in the case where the silicon compound or the calcium compound was solely adsorbed (Comparative Examples 3-1 to 3-2), the dehydration peak in the low-temperature portion was sharp as in the case of reslurrying with distilled water (Comparative Example 3-3). The amount of dehydration is large.

Example 4 Wet cake of aluminum hydroxide obtained in Example 1
100 g (50% solids) was reslurried in one distilled water.
Next, a high-concentration sodium orthosilicate solution (1,00 equivalent in terms of SiO ₂ )
0mg /) and calcium chloride aqueous solution (1,000mg /
) Was continuously added to the aluminum hydroxide slurry with stirring for 30 minutes.

After 30 minutes, the slurry was filtered and the wet cake was dried with distilled water. The powder was subjected to differential thermal balance analysis to find that the Td of the powder was 205 ° C and the Wl was 0.88.

Example 5 A wet cake of aluminum hydroxide obtained in the same manner as in Example 1 was reslurried in a solution 1 containing 200 mg of sodium silicate / (in terms of oxide), stirred for 30 minutes, and then subjected to suction filtration. Next, this cake was reslurried in an aqueous solution of 200 mg / calcium chloride (calculated as CaO), stirred again for 30 minutes, and then subjected to suction filtration. The wet cake was dried and subjected to differential thermal analysis. As a result, Td was 203 ° C. and Wl was 0.86%.

〔The invention's effect〕

As described in detail above, the heat-resistant aluminum hydroxide produced by the method of the present invention has characteristics that are more heat-resistant than conventional aluminum hydroxide, and is a polyolefin-based halogen-free flame-retardant compound or composite copper-clad. It is a very industrially effective material as a filler for laminates.

[Brief description of the drawings]

FIG. 1 shows the relationship between the concentration of SiO ₂ and Ca (OH) ₂ CaCl ₂ in an aqueous solution and the amount of silicon compound (SiO ₂ equivalent) and calcium compound (CaO equivalent) adsorbed on aluminum hydroxide. Use Figure 2 is a pH of the aqueous solution, the silicon compound (SiO ₂ terms. 3 shows the relationship between adsorption amount of calcium compound (CaO equivalent), typically in the differential thermal analysis and thermogravimetry of aluminum hydroxide Thermal decomposition behavior.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C01F 7/02

Claims (5)

(57) [Claims] 1. A method for producing heat-resistant aluminum hydroxide by adsorbing a silicon compound and a calcium compound on the surface of aluminum hydroxide particles, wherein an aqueous solution containing both the silicon compound and the calcium compound is brought into contact with the aluminum hydroxide particles. Wherein the pH of the aqueous solution is 7 or more. 2. A method for producing a heat-resistant aluminum hydroxide by adsorbing a silicon compound and a calcium compound on the surface of aluminum hydroxide particles, wherein the aqueous solution containing a silicon compound and the aqueous solution containing a calcium compound and the aluminum hydroxide particles are individually used. A method of producing a heat-resistant aluminum hydroxide, wherein the pH of the aqueous solution containing a calcium compound is two or more at the time of two-stage contact. 3. The method according to claim 1, wherein the silicon compound contained in the aqueous solution is at least one of sodium orthosilicate, sodium metasilicate and colloidal silica.
A method for producing heat-resistant aluminum hydroxide, wherein the method is any one of the above types. 4. A method for producing a 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. A method for producing a heat-resistant aluminum hydroxide by adsorbing a silicon compound and a calcium compound on the surface of aluminum hydroxide particles, wherein an aqueous solution containing the silicon compound and the calcium compound in the aluminum hydroxide slurry is intermittently or The method for producing heat-resistant aluminum hydroxide according to claim 1, wherein the aluminum hydroxide is continuously added.