JPH054336B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] 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 Al(OH) ₃ or Al ₂ O ₃ 3H ₂ O with the chemical formula, 200
It releases water vapor from within the crystal at temperatures above 0.degree. C. and exhibits a large amount of heat absorption, 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, coarse particles of aluminum hydroxide with an average diameter of about 50 to 60 .mu.m obtained by the Bayer process have been used as they are or after being pulverized 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 problems such as not being able to obtain a smooth surface of the molded product and poor flame retardant effect.
To prevent this, aluminum hydroxide, which has been pulverized to a finer particle size, is widely used for resin filler applications. Requires a lot of energy. Also,
Since the crystals of the pulverized aluminum hydroxide are destroyed and it contains a large amount of fine particles due to chipping, the specific surface area of the powder is large, resulting in a problem of a large amount of adsorbed water. Depending on the application, using aluminum hydroxide as a filler, which has a large amount of adsorbed water, may lead to poor dispersion of the filler, poor curing of the resin, decreased hardness of the molded product, poor insulation,
This may cause foaming during kneading, which may be undesirable. Furthermore, as is generally true of pulverized materials, the finer the particles, the greater the oil absorption of the filler, making it more difficult to highly fill the resin. [Problems to be Solved by the Invention] In order to solve the above-mentioned 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. However, it has the disadvantage of high cost. 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 and less adsorbed water than the same level of ground aluminum hydroxide, but it has the form of secondary agglomerated particles in which fine primary particles aggregate. has,
Since the oil absorption is very large, it is very difficult to fill aluminum hydroxide in a sufficient amount to impart sufficient flame retardancy to the resin for use as a filler. Publication of Patent Publication No. 59-501711 discloses a method of precipitating fine particles of aluminum hydroxide using crushed aluminum hydroxide as a precipitation-inducing material, but the aluminum hydroxide obtained by this method also has a very high oil absorption. I know it's big. In Japanese Patent Application No. 129527/1986, the average diameter of primary particles is 4.
A method for producing aluminum hydroxide for artificial marble with a low specific surface area and low resin-filled viscosity is disclosed, which is characterized by pulverizing secondary agglomerated particles limited to ~8 μm to a size approximately equal to the average diameter of primary particles.
According to this method, it is true that aluminum hydroxide with low oil absorption can be obtained, but it can be obtained by using a ball mill.
Since the secondary agglomerated particles are crushed, the primary particles are slightly destroyed, making it extremely difficult to obtain fine particles of aluminum hydroxide with a low specific surface area, which is the object of the present invention. [Means for Solving the Problems] In view of the above circumstances, the present inventors have conducted intensive 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. As a result, the large centrifugal effect generated by the continuous centrifugal separator
The secondary agglomerated grains are processed without destroying the primary crystal grains.
It was discovered that crushing is extremely effective, and the present invention was completed. That is, the present invention has the following characteristics: 1 Average particle diameter is 2 to 8 μm Surface roughness coefficient S _R /S _C <3 (here, S _R is the specific surface area measured by the nitrogen adsorption method, and S _C
is the specific surface area calculated by spherical approximation from the average particle diameter, that is, S = 6/ρ・d ρ: specific gravity of aluminum hydroxide d: average particle diameter) Linseed oil absorption (according to JIS K5101) is 30
cc/100g or less Low specific surface area fine particle aluminum hydroxide for resin filler represented by above) ~) 2. 1 with an average diameter of 1 to 4 μm obtained by the Bayer method
A solvent is added to the secondary agglomerated particles of aluminum hydroxide consisting of secondary particles to form a slurry, and a centrifugal force of 1000 G or more is applied to the slurry using a continuous centrifugal separator to concentrate and separate the solid content. Another object of the present invention is to provide a method for producing the above-mentioned low specific surface area fine particle aluminum hydroxide for resin fillers, which comprises crushing secondary agglomerated particles. 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 μm. If the average particle diameter is smaller than 2 μm, the amount of oil absorbed will be large, making it impossible to highly fill the resin. In addition, the specific surface area becomes large and the amount of adsorbed water increases. If the average particle size is larger than 8 μm, sedimentation problems will occur. In addition, from the viewpoint of sedimentation, the average particle diameter is more preferably less than 4 μm. The surface roughness coefficient is the ratio of the specific surface area S _R measured by the nitrogen adsorption method to the specific surface area S _C calculated by spherical approximation from the average particle diameter, expressed as S _R /S _C , and is less than 3. It is necessary that The surface roughness coefficient represents the roughness of the aluminum hydroxide particle surface and the amount of chipping particles, and the larger this value is, the greater the amount of moisture absorbed and the worse the dispersibility into the resin. Such disadvantages arise. The linseed oil absorption is a value measured in accordance with JIS K5010, and must be 30c.c./100g or less. If this value is exceeded, it becomes difficult to fill the resin with an amount of aluminum hydroxide that can 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 diameter of the aluminum hydroxide secondary agglomerated particles obtained by the Bayer method needs to be within the range of 1 to 4 μm. When the primary particle size is smaller than 1 μm, the oil absorption amount of the crushed powder exceeds 30 c.c./100 g, and when it is larger than 4 μm, the crushing effect of centrifugal force effectively crushes secondary agglomerated particles. As a result, the oil absorption amount exceeds 30 c.c./100 g and the average particle size becomes larger than 8 μm. The primary particle size of aluminum hydroxide may be measured by observation using an electron microscope, but the following method is more convenient. Mold 1 (cylindrical crucible shape, diameter 30 mm) shown in Figure 1
aluminum hydroxide 2 left in an atmosphere of 23°C and 65% relative humidity for 1 hour.
g and pressurized with a pressure of 0.75t/ ^cm2 using a hydraulic press.
Apply pressure for 30 seconds. Next, the aluminum hydroxide is taken out from the mold, placed in a bag made of resin film, and the compacted powder is loosened by finger pressure.The average particle diameter (Blane diameter) of the resulting crushed powder is measured by an air permeation method. Secondary agglomerated aluminum hydroxide having a primary particle size of 1 to 4 μm in average size is disclosed in, for example, US Pat.
An alumina gel is obtained by introducing an aluminum salt into a sodium aluminate solution obtained by the Bayer process as described in No. The resulting mixture is introduced into sodium aluminate to be decomposed, and stirring is continued to induce the precipitation of extremely fine aluminum hydroxide. If the primary particle size is smaller than the desired primary particle size, use the aluminum hydroxide as a seed crystal and further decompose the supersaturated sodium aluminate solution to obtain secondary agglomerated aluminum hydroxide with the desired primary particle size. Can be manufactured. Although the secondary particle size of the secondary agglomerated aluminum hydroxide is not particularly limited in the present invention, it is preferably 20 μm or less. The centrifugal force exerted on the slurry containing aluminum hydroxide by the continuous centrifugal separator is equal to the force of gravity.
It needs to be 1000 times (1000G) or more.
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 concentrates and 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 representative example of this device is, for example, the revised 4th edition “Chemical Engineering Handbook” (edited by the Chemical Engineering Society).
An example is the horizontal decanter continuous discharge type described on page 1119. 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 be of the same type and of vertical type. [Operation] The mechanism by which secondary agglomerated particles of aluminum hydroxide are effectively crushed by the continuous centrifugal separator is thought 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
It is thought that the secondary agglomerated particles move while strongly contacting each other, and as a result, a crushing effect of the secondary agglomerated particles occurs due to mutual rubbing. This continuous centrifugal separator can be used for crushing using the conventional crushing method that utilizes the impact force caused by collision between media, or using the crushing effect between cylinders and rollers such as Raymond roller mills.
Unlike any other pulverization method that utilizes collisions between particles, such as jet mills, this method is revolutionary in that it hardly destroys the secondary crystals of aluminum hydroxide during pulverization. [Example] 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. Sodium aluminate solution obtained by Bayer's solution (Na ₂ O concentration = 120 g/, Al ₂ O ₃ concentration =
120g/) will be simply referred to as aluminate liquid in the following Examples and Comparative Examples. The resin filler was evaluated using a composite copper-clad laminate with regard to the following items. (1) Varnish viscosity Hardener-containing epoxy resin 100 parts Aluminum hydroxide 70 parts Solvent 100 parts The viscosity at 25°C of the above formulation was measured. If it exceeds 10,000 cp, the impregnating property into the glass nonwoven fabric will deteriorate. (2) Sedimentation property The above resin varnish was impregnated into 75 g/m ² of glass nonwoven fabric and dried, and 780 g/m ² of prepreg (hereinafter referred to as
Prepreg A) was obtained. Also, 200g/m ²
400g/ ^m2 prepreg (hereinafter referred to as
Prepreg B) was obtained. Next, three sheets of prepreg A were stacked, and copper foil with a thickness of 0.018 mm was placed on both sides of each sheet with one sheet of prepreg B interposed therebetween to obtain a laminate. This was sandwiched between metal plates and molded for 100 minutes at a pressure of 50 kg/cm ² and 170°C.
An electrical laminate with a thickness of 1.6 mm was obtained. Sedimentability was evaluated based on the following criteria. ◎Very good: There is no warping of the board at all. ○ Good: The warpage of the board is not enough to cause a problem. ×Defect: Warpage of the board becomes a problem. When particles settle during molding, it causes warping of the substrate. Example 1 A neutralization equivalent amount of an aqueous solution of sulfuric acid was added to the aluminate solution to obtain a gel-like hydrated alumina solution (concentration in terms of Al ₂ O ₃ : 170 g/). This is used as seed liquid,
Seed ratio in aluminate solution ( _Al2O3 amount in seed solution _/
The amount of Al ₂ O ₃ in the aluminate solution x 100) was added to the solution to be 1%, and stirring was continued all day and night while keeping the temperature at 60°C. The average particle size of aluminum hydroxide obtained by separating a small amount of precipitates, washing with water, and drying was 2.7μ.
m, the average primary particle diameter was 1.5 μm. The obtained slurry was passed through a continuous centrifugal separator (Shear Press Super Decanter P-660; hereinafter the same).
After solid-liquid separation while applying a centrifugal force of 2500 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 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 all day and night while keeping the slurry at 60°C. After separating a small amount of the precipitate, the aluminum hydroxide obtained by washing with water and drying had an average particle diameter of 5.4 μm and an average primary particle diameter of 1.5 μm. The obtained slurry was subjected to solid-liquid separation using a continuous centrifugal separator while applying a centrifugal force of 3000 G, and the separated cake was passed through the steps of washing with water, filtering, and drying. Table 1 shows the characteristic values of the dried powder obtained. Example 3 Aluminum hydroxide was produced in the same manner as in Example 2, but the centrifugal force applied to the slurry was 1500G. 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 all day and night while keeping the slurry at 60°C.
After separating a small amount of the precipitate, the aluminum hydroxide obtained by washing with water and drying had an average particle diameter of 7.9 μm and an average primary particle diameter of 3.3 μm. The obtained slurry was subjected to solid-liquid separation using a continuous centrifugal separator while applying a centrifugal force of 3000 G, and 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 all day and night while keeping the slurry at 60°C. After separating a small amount of the precipitate, the aluminum hydroxide obtained by washing with water and drying had an average particle diameter of 11.7 μm and an average primary particle diameter of 3.7 μm. The obtained slurry was subjected to solid-liquid separation using a continuous centrifugal separator while applying a centrifugal force of 3000 G, and 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.

[Table] Comparative Example 1 An aqueous solution of sulfuric acid chloride in an amount equivalent to neutralization was added to the aluminate solution to obtain a gel-like hydrated alumina solution (concentration in terms of Al ₂ O ₃ : 170 g/). This is used as seed liquid,
The mixture was added to the aluminate solution so that the seed rate was 2%, and stirring was continued all day and night while keeping the mixture at 60°C. After separating a small amount of the precipitate, the aluminum hydroxide obtained by washing with water and drying had an average particle diameter of 1.7 μm and an average primary particle diameter of 0.8 μm. The obtained slurry was subjected to solid-liquid separation using a continuous centrifugal separator while applying a centrifugal force of 2800 G, and the separated cake was passed through the steps of washing with water, filtering, 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 all day and night while keeping the slurry at 60°C. After separating a small amount of the precipitate, the aluminum hydroxide obtained by washing with water and drying had an average particle diameter of 20.2 μm and an average primary particle diameter of 5.2 μm. The obtained slurry was subjected to solid-liquid separation using a continuous centrifugal separator while applying a centrifugal force of 3000 G, and the separated cake was passed through the steps of washing with water, filtering, 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 through a normal filter, 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 Kakoki). Comparative Example 6 Table 2 shows the characteristic values of commercially available pulverized fine aluminum hydroxide (BW-703 manufactured by Nippon Light Metal Co., Ltd.).

〔Effect of the invention〕

The aluminum hydroxide obtained by the present invention is
Its excellent value is recognized in that it achieves both low specific surface area and low oil absorption, which were impossible with conventional fine-grained aluminum hydroxide. In addition, the method of crushing secondary agglomerates using a continuous centrifugal separator, which is the key point of the aluminum hydroxide manufacturing method of the present invention, is completely revolutionary in that it can crush down to the primary particles without causing chipping. target,
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 Average particle diameter is 2 to 8 μm 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 approximation from the average particle diameter. (represents the specific surface area calculated by) Linseed oil absorption amount (according to JIS K5101) is 30 c.c.
Aluminum hydroxide for resin filler, characterized in that it weighs 100g or less. 2 1 with an average diameter of 1 to 4 μm obtained by the Bayer method
Using a continuous centrifugal separator, the slurry of secondary agglomerated particles of aluminum hydroxide consisting of
2. The method for producing aluminum hydroxide for resin fillers according to claim 1, wherein the solid content of the slurry is concentrated and separated by applying the above centrifugal force.