JPH02199020A - Aluminum hydroxide for resin filler and production thereof - Google Patents

Abstract

PURPOSE:To obtain the title aluminum hydroxide with both low specific surface area and oil absorption by centrifugation of a secondary flocculated particle slurry of specific Al(OH)3 produced by the Bayer process. CONSTITUTION:A secondary flocculated particle slurry of Al(OH)3 consisting of primary particles 1-4mum in average size is first prepared by introducing (1) a mixture prepared by converting into crystalline Al(OH)3 part of an alumina gel produced by introducing an Al salt into a sodium aluminate solution obtained by the Bayer process into (2) sodium aluminate to be decomposed. Thence, this slurry is fed into a continuous-type centrifugal separator and put to solid- liquid separation by application of a centrifugal force of >=1000G, thus obtaining the objective Al(OH)3 for resin filler having the following characteristics: (a) average particle size - 2-8mum; (b) surface roughness factor Sn/Sc - <3 (Sn is specific surface area determined by the nitrogen absorption technique; Sc is specific surface area calculated from the average particle size using the sphere approximation technique); and (c) linseed oil absorption (in compliance with JIS K-5101) - <=30cc/100g.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to aluminum hydroxide suitable for use as a resin filler and a method for producing the same.

BACKGROUND OF THE INVENTION The use of aluminum hydroxide in resin filler applications is known.

Aluminum hydroxide can be written as the chemical formula A (OH)i or AM, 03 ・: 1H20, 2
It releases water vapor from within the crystal at a temperature of 00°C or higher, and exhibits a large amount of heat absorption at that time, so when used as a resin filler, excellent flame retardancy can be obtained.

In addition, aluminum hydroxide has excellent low smoke emission properties, arc resistance and tracking resistance, and is low in cost, so it can be said to be an extremely useful flame retardant.

Conventionally, for this purpose, the average diameter obtained from the Bayer method was 50 ~
Approximately 60 gm of coarse aluminum hydroxide as it is,
Alternatively, it has been used by pulverizing it with a ball mill or other pulverizer. However, when coarse-grained aluminum hydroxide is used as a filler, it has poor compatibility with resins.

Furthermore, when filled with a resin having a low viscosity, aluminum hydroxide will precipitate. Furthermore, there were other problems such as not being able to obtain a smooth surface of the molded product and poor flame retardant effect.

To prevent this, it is necessary to use aluminum hydroxide, which is widely used in resin filler applications, which has been pulverized to a finer particle size, or to grind it to a particle size that is less likely to cause sedimentation (generally less than 101L on average). Requires energy. In addition, the crystals of pulverized aluminum hydroxide are destroyed and contain a large amount of fine particles due to chipping, so the specific surface area of the powder is large, and as a result,
There was a problem that the amount of adsorbed water was too large. Using aluminum hydroxide as a filler, which has a large amount of adsorbed water,
Depending on the application, filler dispersion may be poor, resin curing may be poor,
This may be undesirable since it may cause a decrease in the hardness of the molded product, poor insulation, and foaming during kneading. Furthermore, as is generally the case with pulverized materials, the finer the particles, the greater the oil absorption of the filler, making it more difficult to fill the resin with high levels.

(Invention or problem to be solved) In order to solve the above problems, it is effective to some extent to surface the crushed aluminum hydroxide with a surface treatment agent such as stearic acid, its metal salt, or a silane coupling agent. Or, the disadvantage is that it costs more.

Furthermore, methods for precipitating fine particles of aluminum hydroxide using alumina gel as a precipitation-inducing material have been known for a long time, such as in US Pat. No. 2,549,541 and French Patent No. 2,041,750. The fine-grained aluminum hydroxide obtained by this method has a smaller specific surface area than the same level of ground aluminum hydroxide, and either has a small adsorbed water content or is in the form of fine primary particles or agglomerated secondary agglomerates. It has a very large oil absorption capacity, and it is extremely difficult to fill it with aluminum hydroxide in a sufficient amount to impart sufficient flame retardancy to the resin for use as a filler. Published Patent Publication No. 59-501711 discloses a method of precipitating fine particles of aluminum hydroxide using crushed aluminum hydroxide as a precipitation-inducing material, and the aluminum hydroxide obtained by this method also has a very large oil absorption capacity. I know that.

In Japanese Patent Application No. 129527/1983, the average diameter of primary particles is 4.
Disclosed is a method for producing aluminum hydroxide for artificial marble with a low specific surface area and low resin-filled viscosity, which is characterized by pulverizing secondary agglomerated particles limited to ~8 particles until they become approximately equal to the average diameter of the primary particles. ing.

According to this method, it is true that aluminum hydroxide with low oil absorption can be obtained, or because the secondary agglomerated particles are disintegrated by a ball mill, destruction of the primary particles occurs, although only slightly, which is not the objective of the present invention. It was extremely difficult to obtain finely divided aluminum hydroxide with a low specific surface area.

[Means to solve the problem]

In view of these circumstances, the inventors of the present invention conducted extensive studies with the aim of providing at low cost fine particulate aluminum hydroxide with low oil absorption and low specific surface area suitable for filler applications, and as a result, they developed a method using a continuous centrifugal separator. Perhaps due to the large centrifugal effect that occurs, secondary agglomerated particles of aluminum hydroxide are produced without destroying the primary crystal particles.

It was discovered that crushing is extremely effective, and the present invention was completed.

That is, the present invention has the following characteristics: 1. i) Average particle diameter is 2 to 8 l; ii) Surface roughness coefficient S*/SC<3 (;: Iron SR is the specific surface area measured by the nitrogen adsorption method; , S
C is the specific surface area calculated by spherical approximation from the average particle diameter, that is, iii) The linseed oil film amount (according to JIS K51 old standard) is 30 cc/100 g or less. A solvent is added to secondary agglomerated particles of aluminum hydroxide consisting of fine particles of specific surface area aluminum hydroxide and primary particles with an average diameter of 1 to 4 μm obtained by the Bayer method, and a slurry is prepared using a continuous centrifugal separator. 100O
The above-mentioned low specific surface 8 for resin filler is characterized in that secondary agglomerated particles of aluminum hydroxide are crushed by applying a centrifugal force of G or more to the slurry to concentrate and separate the solid content.
! It is an object of the present invention to provide a method for producing fine grained water-brew aluminum.

First, the reason for the numerical limitation of the invention set forth in claim 1 will be explained.

The average particle diameter of aluminum hydroxide is measured by a sedimentation method, and needs to be within the range of 2 to 8 to 1. If the average particle diameter is smaller than 2 gm, the amount of oil absorbed will be large and it will not be possible to highly fill the resin. In addition, the specific surface area becomes large, resulting in disadvantages such as an increase in the amount of adsorbed water.

If the average particle size is larger than 8 gm, a problem of sedimentation may occur. In addition, in terms of sedimentation, the average particle diameter is more preferably 4.
less than IL-.

The surface roughness coefficient is the specific surface area S measured by nitrogen adsorption method.
R and the specific surface area SC calculated by spherical approximation from the average particle diameter
The ratio, expressed as SR/SC, must be less than 3.

The surface roughness coefficient represents the roughness of the aluminum hydroxide particle surface and the amount of chipping particles.
The larger this value is, the larger the amount of water adsorbed will be, and this will lead to disadvantages such as poor dispersibility in the resin.

The amount of linseed oil film oil is a value measured in accordance with JIS K5010, and must be 30 cc/100 g or less. If this value is exceeded, it becomes difficult to fill the resin with enough aluminum hydroxide to impart sufficient flame retardancy, making it unsuitable for use as a filler.

Next, the reason for the numerical limitation of the invention of claim 2 will be explained.

] The primary particle size of the aluminum hydroxide secondary agglomerated particles obtained from R Bayer and ε must be within the range of 1 to 4 μm. If the primary particle size is smaller than T4, the oil absorption amount of the crushed powder will exceed 30cc/100g, and if it is larger than 4μ, the crushing effect of centrifugal force will not effectively crush the secondary agglomerated particles. The oil absorption amount is 30.
cc/l00g, and the average particle size is larger than 8mm. The primary particle diameter of aluminum hydroxide may be measured by observation using an electron microscope, but the following method is more convenient.

Mold 1 shown in Fig. 1 (cylindrical crucible shape, diameter round I, depth 5
15 g of aluminum hydroxide 2, which had been left in an atmosphere of 23° C. and 65% relative humidity for 1 hour, was charged into a container (0.0) and pressurized with a hydraulic press at a pressure of 0.75 t/crn' for 30 seconds. Next, the aluminum hydroxide was taken out from the mold, placed in a plastic film bag, and the compacted powder was loosened using finger pressure.The average particle size (
Measure the brane diameter).

Secondary agglomerated aluminum hydroxide having a primary particle size with an average diameter of 1 to 4 ILw is disclosed in, for example, US Pat. No. 25495
No. 49, an aluminum salt was introduced into a sodium aluminate solution obtained by the Bayer method to obtain an alumina gel. The primary particle size of the obtained aluminum hydroxide can be obtained by introducing the mixture into the sodium aluminate to be decomposed and stirring continuously to induce the precipitation of extremely fine aluminum hydroxide. If it is finer than the particle size, secondary agglomerated aluminum hydroxide having the desired primary particle size can be produced by using the aluminum hydroxide as a seed crystal and further decomposing a supersaturated sodium aluminate solution. . The secondary particle size of the secondary agglomerated aluminum hydroxide is not particularly limited in the present invention.
It is preferably less than or equal to μ.

The centrifugal force applied to the slurry containing aluminum hydroxide by the continuous centrifugal separator is 1000 times the force of gravity (I
I)OOG) or higher is required.

If the centrifugal force is less than 1000 times the gravity, the secondary agglomerated particles of aluminum hydroxide are not effectively broken down, and as a result, the oil absorption remains large. A continuous centrifugal separator refers to a device that continuously separates slurry using centrifugal force, and refers to a device that has the function of separating the solid content of the slurry while applying centrifugal force. A typical example of this device is, for example, a horizontal decanter with a continuous discharge type described in the revised intaglio edition of "Chemical Engineering Handbook" (edited by Chemical Engineering Handbook) with a pH of 19. That is, it is a type that combines a rotating cylinder or cone with a helical conveyor that rotates with a slight difference, and continuously discharges the settled solids. The device according to the invention may also be of the same type and of vertical type.

[Effect]

The mechanism by which secondary agglomerated particles of aluminum hydroxide are effectively crushed by the continuous centrifugal separator is considered to be as follows.

When slurry containing secondary agglomerated particles of aluminum hydroxide is led to a continuous centrifugal separator, the solid content is strongly pressed against the rotating cylinder or cone of the centrifugal separator due to the large centrifugal effect, resulting in secondary agglomeration. The grains come into strong contact with each other. Under these conditions, when solids are forcibly discharged by a rotating cylinder or a helical conveyor that rotates with a slight difference from the cone, the aluminum hydroxide
The secondary agglomerated grains move while in strong contact with each other, and as a result,
It is thought that a crushing effect of the secondary agglomerated grains occurs due to mutual rubbing.

This continuous centrifugal separator can be used to crush conventionally used crushing methods that utilize the impact force caused by collisions between media, as well as crushing methods that utilize the grinding effect between cylinders and rollers such as Raymond roller mills, and jet This is similar to the pulverization law that uses collisions between particles such as a mill.

(Examples) Here, the content of the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples.

The sodium aluminate solution (Na2O concentration = 120 g/l AfL2036 degrees = 120 g/fL) obtained by Bayer's solution will be simply referred to as aluminate solution in the following Examples and Comparative Examples.

In addition, evaluation as a resin filler was conducted on the following items using a composite copper-clad laminate.

(]) Epoxy resin containing face viscosity hardening agent 100 parts Aluminum hydroxide 70 parts Solvent
The viscosity at 25° C. of 100 parts of the above formulation was measured.

If it exceeds 10,000 cp, the impregnating property into the glass nonwoven fabric will deteriorate.

(2) Sedimentation The resin face was impregnated into a glass nonwoven fabric of 75 g/rn' and dried to obtain a prepreg of 780 g/rn' (hereinafter referred to as prepreg A). Also, 200g/r
A prepreg of 400 g/rn' (hereinafter referred to as prepreg B) was obtained by impregnating and drying an epoxy resin face containing a curing agent into a glass cloth of n'.

Next, stack three sheets of prepreg A, and prepreg B on both sides.
A laminate was obtained by placing a copper foil with a thickness of 0.0185 m through each layer. Sandwich this between metal plates and press 50
kg/c rn" and molded at 170°C for 100 minutes to obtain an electrical laminate with a thickness of 1.6 mm.

Sedimentability was evaluated based on the following criteria.

◎Very good. There is no warping of the two boards.

○Good: The warpage of the substrate is not enough to cause a problem.

x Defective: The problem may be board warping.

If particles settle during molding, it causes the substrate to warp.

Example 1 A neutralization equivalent amount of an aqueous solution of sulfuric acid was added to the aluminate solution to form a gel-like hydrated alumina solution (AfL2oz equivalent concentration:
170 g/yet) was obtained. This was used as a seed liquid, and added to the aluminate liquid at a seed rate of 1% (An zO in the seed liquid: + acid / amount of A203 in the aluminate liquid x 100), and while keeping it at 60°C. , - Stirring was continued day and night. After separating a small amount of the precipitate, the aluminum hydroxide obtained by washing with water and drying had an average particle diameter of 2.71 L, and an average primary particle diameter of 1.5 microns.

The obtained slurry was separated into
While applying a centrifugal force of 500 G, the cake separated once after solidification and clarification was passed through the steps of washing with water, filtration, and drying.

Table 1 shows the characteristic values of the obtained dry powder.

Example 2 An aluminate solution was further added to the slurry obtained in Example 1 so that the seed rate was 10%, and stirring was continued day and night while keeping the slurry at 60°C. The average particle size of aluminum hydroxide obtained by separating a small amount of precipitate in a furnace, washing with water, and drying is 5.4 mm, and the average primary particle size is 1.5 ILm.
Met.

The obtained slurry was centrifuged at 300°C using a continuous centrifugal separator.
After solid-liquid separation while applying a centrifugal force of 0 G, the separated cake was passed through the steps of washing with water, filtration, and drying.

Table 1 shows the characteristic values of the obtained dry powder.

Example 3 Aluminum hydroxide was produced in the same manner as in Example 2, and the centrifugal force applied to the slurry was 150 OG.

Table 1 shows the characteristic values of the obtained dry powder.

Example 4 An aluminate solution was further added to the slurry obtained in Example 1 so that the seed rate was 5%, and stirring was continued day and night while keeping the slurry at 60°C.

The average particle diameter of aluminum hydroxide obtained by separating a small amount of the precipitate in a furnace, washing with water, and drying was 7.9 gm, and the average diameter of primary particles was 1.3 gm.

The obtained slurry was centrifuged at 300°C using a continuous centrifugal separator.
After solid-liquid separation while applying a centrifugal force of 0 G, the separated cake was passed through the steps of washing with water, filtering, and drying.

Table 1 shows the characteristic values of the obtained dry powder.

Example 5 An aluminate solution was further added to the slurry obtained in Example 1 so that the seed rate was 2%, and stirring was continued day and night while keeping the slurry at 60°C. After removing a small amount of precipitate from the furnace,
The average particle size of aluminum hydroxide obtained by washing with water and drying was 11. The average diameter of the primary particles was 3.7 mm.

The obtained slurry was centrifuged at 300°C using a continuous centrifugal separator.
After solid-liquid separation while applying a centrifugal force of 0 G, the separated cake was passed through the steps of washing with water, filtration, and drying.

Table 1 shows the characteristic values of the obtained dry powder.

(Left below) Comparative Example 1 A neutralization equivalent amount of an aqueous solution of sulfuric acid was added to the aluminate solution to form a gel-like hydrated alumina solution (AfL20i equivalent concentration:
170g/view) was obtained. This was used as a seed liquid and added to the aluminate liquid so that the seed rate was 2%, and stirring was continued day and night while keeping the mixture at 60°C. The average particle diameter of aluminum hydroxide obtained by separating a small amount of the precipitate in a furnace, washing with water, and drying was 1.7 μI, and the average primary particle diameter was 0.8μI.

The obtained slurry was separated by a continuous centrifugal separator at 280
After solid-liquid separation while applying a centrifugal force of 0 G, the separated cake was passed through the steps of washing with water, filtration, and drying.

Table 2 shows the characteristic values of the obtained dry powder.

Comparative Example 2 An aluminate solution was further added to the slurry obtained in Example 2 so that the seed rate was 30%, and stirring was continued day and night while keeping the slurry at 60°C. Less precipitate? The average particle size of aluminum hydroxide obtained by furnace separation, washing with water, and drying was 20.2 JL, and the average primary particle size was 5.2 gm.
Met.

The obtained slurry was centrifuged at 300°C using a continuous centrifugal separator.
After solid-liquid separation while applying a centrifugal force of 0 G, the separated cake was passed through the steps of washing with water, filtration, and drying.

Table 2 shows the characteristic values of the obtained dry powder.

Comparative Example 3 Aluminum hydroxide was produced in the same manner as in Example 2, but the centrifugal force applied to the slurry was 500G.

Table 2 shows the characteristic values of the obtained dry powder.

Comparative Example 4 The slurry obtained in Example 2 was separated into solid and liquid using a laboratory centrifugal separator, the liquid was discarded, and the solid was washed and dried.

Table 2 shows the characteristic values of the obtained dry powder.

Comparative Example 5 The slurry obtained in Example 4 was filtered with a normal filter, then washed and dried.

Table 2 shows the characteristic values of the pulverized powder obtained by pulverizing the obtained dry powder for 20 minutes using an attritor (Mitsui Miike Kako AT).

Comparative Example 6 Table 2 shows the characteristic values of commercially available pulverized fine aluminum hydroxide (8W-703 manufactured by Nippon Light Metal Co., Ltd.).

(Left below) (Effects of the invention) The aluminum hydroxide obtained by the present invention has the advantage of achieving both low specific surface area and low oil absorption, which were impossible with conventional fine-grained aluminum hydroxide. The value of the debt is recognized. In addition, the method of crushing secondary agglomerates using a continuous centrifugal separator, which is the key point of the method for producing aluminum hydroxide according to the present invention, does not cause chipping.
It is completely revolutionary in that it can crush primary particles.
Moreover, it is an extremely excellent process and has great industrial value.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a mold used in a pressure crushing method for measuring the average diameter of primary particles of aluminum hydroxide.

Claims (1)

[Claims] 1. i) Average particle diameter is 2 to 8 μm ii) Surface roughness coefficient S_R/S_C<3 (S_R is the specific surface area measured by the nitrogen adsorption method, and S_C is the spherical surface roughness from the average particle diameter. (represents the specific surface area calculated by approximation) iii) Linseed oil film oil amount (according to JISK5101) is 3
Aluminum hydroxide for resin filler, characterized in that it is 0cc/100g or less. 2. Using a continuous centrifugal separator, a centrifugal force of 1000 G or more is applied to a slurry of secondary agglomerated particles of aluminum hydroxide consisting of primary particles with an average diameter of 1 to 4 μm obtained by the Bayer method to determine the solid content of the slurry. 2. The method for producing aluminum hydroxide for resin filler according to claim 1, wherein the aluminum hydroxide is concentrated and separated.