JPH0432004B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing spherical corundum particles having no cutting edge, and is used as a filler for sealing materials for electronic components, raw materials for finishing wrapping materials, refractories, glass, ceramics, and the like. The present invention relates to a method for producing spherical corundum particles that have low abrasiveness and excellent flow characteristics and are useful as spherical aggregates in composite materials containing the present invention. (Prior art) In recent years, as electronic components have become smaller and have higher capacities, the demand for rubber/plastic-based insulating materials with excellent heat dissipation has increased, and alumina, which has high heat conductivity, has attracted attention as a filler. It is beginning to be used in place of fused silica and crystalline silica. Especially IC
For semiconductor encapsulation material applications such as
Coarse particles of 5 μm or more, preferably 10 μm or more, and a wide particle size distribution from fine particles of 1 μm to coarse particles of 44 μm or more are required. Corundum (alpha alumina) has a high Mohs hardness and is known to cause severe wear in mechanical equipment. Therefore, it is desirable that the particles have a rounded spherical shape without cutting edges. In addition, by making the irregularly shaped aggregate particles and fine particles that have traditionally been used in castable refractories into spherical or spheroidal shapes, it is possible to improve the low moisture fluidity of castable materials, reduce firing shrinkage, and heat crack resistance. Spherical corundum particles with an average particle diameter of 5 μm or more, preferably 10 μm or more are required as one of the materials. Pulverized products of fused alumina and sintered alumina are known as such corundum particles, but both are irregularly shaped particles with sharp cutting edges, and are therefore useful as grinding and abrasive materials.
Furthermore, as a method for producing spherical alumina particles, a so-called thermal spraying method is known in which Bayer process alumina is injected into high-temperature plasma or oxyhydrogen flame, melted, and rapidly cooled to become spherical. However, this method has a large heat unit and is not economical, and the alumina obtained is α-Al ₂ O ₃ (corundum).
Although it is the main component, it usually has δ-Al ₂ O ₃ etc. as a subcomponent. The presence of these subcomponents is undesirable because it causes a decrease in the thermal conductivity of alumina. In order to solve the problems of the conventional method, the particle size
α-Al ₂ O ₃ (corundum) with a regular shape of 5 μm or more
A few new methods have been proposed for making particles. For example, according to Special Publication No. 60-33763,
A method is disclosed in which aluminum hydroxide containing high sodium content is pre-dehydrated, a specific mineralizing agent is added thereto, and the aluminum hydroxide is calcined in a rotary kiln to obtain coarse-grained alumina. Furthermore, JP-A-58-181725 shows that similar alumina coarse particles can be obtained by adding a mineralizing agent containing fluorine and/or boron to dry absorbed alumina and firing it in a rotary kiln. There is. However, the shape of the coarse alumina produced by these methods is a rounded spherical shape with regular cutting edges, as illustrated in the drawing (micrograph) of the specification of JP-A-58-181725. It doesn't belong to. (Problem to be solved by the invention) Alumina has a high Mohs hardness, and when mixed and filled into plastics, rubber, and other materials, or when molding and processing composite materials filled with alumina particles, it is difficult to knead and mold the material. Known to seriously damage equipment. Especially IC, LSI,
If you try to use existing alumina (especially crushed products of fused alumina and sintered alumina used in abrasives and refractories) as a filler for resin sealing materials for electronic components such as VLSI, the sharp edges A major drawback is that the bonding edge causes severe grinding and wear, and that it can damage bonding wires and semiconductor elements. Such drawbacks are IC,
Alumina is filled not only in resin encapsulants for LSI, VLSI, etc., but also in a wide range of electrical insulation resins for electronic components and engineering plastics for structural materials, and is used to improve thermal conductivity and abrasion resistance. This has become a major obstacle. (Means for Solving the Problems) In view of the above-mentioned current situation, the present inventors have developed a method for grinding and polishing particles with less force without impairing the characteristics inherent to corundum particles such as thermal conductivity, electrical insulation, and hardness. The present invention was achieved as a result of various research aimed at developing corundum for fillers or aggregates. That is, the gist of the present invention is to add one or more of a halogen compound, a boron compound, and an alumina hydrate to a pulverized product of fused alumina and/or sintered alumina having a specific particle size, and to This is a method for producing spherical corundum particles, characterized by heat treatment at 1000°C to 1550°C and then crushing. The present inventors have developed a pulverized product of fused alumina or sintered alumina, which has been conventionally used as fine aggregate for abrasives and refractories, and has an average particle size in the range of 5 μm to 35 μm, preferably 10 to 25 μm. Particle size (for example, Showa Denko K.K. products RW220F, SRW325F, etc.)
However, it was noted that the particle size distribution was almost the same as that of pulverized fused silica or crystalline silica (α-SiO ₂ ) currently used as a filler for sealing materials for electronic components. These aluminas are melted or heat-treated at high temperatures of 1500°C to 1850°C, so the alumina crystals are fully developed and the pulverized product has a particle size distribution desirable as a filler. It is not used in practical use as a filler because it produces staining edges. Therefore, the present inventors conducted intensive research on improving the particle shape while maintaining the particle size distribution of these coarse particles, and found that halogen compounds,
A method in which a small amount of a well-known agent, such as a boron compound, conventionally known as an alumina mineralizing agent or crystal growth agent, is added to a pulverized product of fused alumina or sintered alumina, and the mixture is heat-treated at a temperature of 1000° to 1550°C. As a result, the present invention was completed by discovering that the sharp corners, ie, cutting edges, of these coarse alumina particles are reduced, and at the same time, the shape becomes spherical. The alumina coarse particles used as a starting material in the present invention may be either electrified alumina or sintered alumina produced by a known method, and the particle size distribution of the pulverized product of electrified or sintered alumina is an average particle obtained by a sedimentation method. The diameter is in the range of 5 μm to 35 μm, preferably 10 μm to 25 μm, and the maximum particle size does not exceed 150 μm, preferably 74 μm or less. When the average diameter is 5 μm or less, it is not necessary to apply the present invention because particles with a rounded shape can be obtained by a known method of adding a crystal growth agent to aluminum hydroxide. In addition, the average diameter of the raw material is 35μm
If the number of particles larger than 150 μm increases, the cutting edge of coarse particles will not be sufficiently reduced, which is not preferable. In addition, in order to promote the spheroidization of coarse particles, it is possible to mix alumina hydrate, particularly aluminum hydroxide, alumina gel, or fine-grained alumina with good thermal reactivity with fused alumina or sintered alumina, and then heat-treat the mixture. It was found to be effective. From an economical point of view, Bayer process aluminum hydroxide (gibbsite crystal) is preferred, and those with an average particle diameter of 10 μm or less are optimal.
According to the observations of the present inventors, such a spheroidization accelerator acts synergistically with the below-mentioned agent on coarse-grained alumina, and is selectively absorbed into the irregular sharp cutting edges, resulting in spheroidization, a surprising phenomenon. was recognized. Furthermore, as a secondary effect, the addition of aluminum hydroxide or alumina hydrate such as alumina gel weakens the cohesive force of the heat-treated agglomerates, making it easier to disintegrate them into primary particles. Characteristics were recognized. The optimum amount of the spheroidization accelerator varies depending on the particle size of the pulverized fused alumina or sintered alumina, but when aluminum hydroxide is added, it is 5wt% to 100wt%.
(in terms of alumina, ratio to fused alumina or sintered alumina) is preferable. If it is less than 5 wt%, the cohesive force of the agglomerates will be strong, and if it exceeds 100 wt%, excessive aluminum hydroxide will be mixed into the product as free fine particles of alumina, which is not preferable. Chemicals added during heat treatment include halogen compounds known as alumina crystal growth promoters alone or in combination, particularly NaF, CaF ₂ , AlF ₃ ,
Fluorine compounds such as MgF ₂ , Na ₃ AlF ₆ and/or
Boron compounds such as B ₂ O ₃ , H ₃ BO ₃ , mNa ₂ O·nB ₂ O ₃ and borofluorine compounds are preferable, and a combination of a fluoride and a boron compound or a borofluorine compound is particularly preferable. Although the amount of the chemical added varies depending on the heating temperature, residence time in the furnace, and type of heating furnace, it was found that the effective concentration is 0.1 to 4.0% by weight based on the total alumina content. The type of heating furnace may be any known means such as a single kiln, tunnel kiln, or rotary kiln, and the heating temperature is a temperature at which alumina hydrate such as aluminum hydroxide is substantially converted to α-alumina when coexisting with it. That is, the temperature must be about 1150°C or higher, and if they do not coexist, the object of the present invention can be achieved at a temperature of 1000°C or higher. In either case, a particularly preferable heat treatment temperature range is 1350°C or higher and 1550°C or lower. At temperatures above 1550°C, the cohesive force of the agglomerates becomes strong even in the presence of aluminum hydroxide, making it difficult to disintegrate into primary particles. Although the residence time in the heating furnace varies depending on the heating temperature, a residence time of 30 minutes or more, preferably about 1 to 3 hours, is required in order for the particles to become spherical. Since the spherical alumina particles produced by this method take the form of secondary agglomerated particles, they are crushed into the desired particle size distribution by a known crushing means such as a ball mill, vibration mill, jet mill, etc. for a short time. spherical corundum particles are obtained. In addition, in the above manufacturing method, spherical corundum particles with a low α-ray emission amount can be produced by using fused alumina or sintered alumina with a low content of radioactive elements such as uranium and thoria, and aluminum hydroxide as a spheroidization promoter. can be manufactured. Spherical alumina, which has a low amount of α-ray radiation (0.01c/cm ² .hr), can be used as a resin encapsulant filler for highly integrated ICs, LSIs, and VLSIs to prevent memory device malfunctions (so-called soft errors) caused by α-rays. Particularly useful for preventive purposes. As mentioned above, the gist of the present invention is as follows. Hereinafter, the present invention will be explained by giving examples. Example 1 Commercially available sintered alumina pulverized product (manufactured by Showa Denko Co., Ltd.)
SRW-325F, average particle size 12μm, maximum particle size 48μm)
Add 20g each of reagent-grade anhydrous aluminum fluoride and boric acid to 1000g, mix, charge into an alumina ceramic heat-resistant container, heat in a Kanthal electric furnace at 1450℃ for 3 hours, and then remove from the furnace. The hardness of the fired product was evaluated, and the fired product was further processed in a vibrating ball mill (manufactured by Kawasaki Heavy Industries, Ltd.).
SM0: 6, 100 g of fired product and 1000 g of 10 mmφ HD alumina balls were crushed for 30 minutes, the total Na ₂ O content of this crushed material was determined, and the particle size distribution was determined by laser diffraction method (Cirrus). At the same time, scanning electron micrographs were taken (magnification: 2500). The results are shown in Table 1, the column of Example 1, and FIG. 1a. Example 2 Commercially available pulverized electrofused alumina (RW- manufactured by Showa Denko Co., Ltd.)
92 (325F), average particle size 13μm, maximum particle size 48μm)
A baked product and a crushed product thereof were obtained using the same additives, blending amounts, and method as in Example 1.
The hardness of the fired product, the total Na ₂ O content, particle size distribution, α-alumina particles and shape of the crushed product were determined in the same manner as in Example 1. It is shown in Figure 1b. Comparative Example 1 The same pulverized sintered alumina product as in Example 1 was heat-treated alone under the same conditions as in Example 1 without adding any chemicals to obtain a fired product and its crushed product.
These samples were evaluated in the same manner as in Example 1, and the results are shown in Table 1, the column for Comparative Example 1, and FIG. 2a. Comparative Example 2 Table 1 compares the evaluation results of the fired and crushed products obtained by heat-treating the same pulverized electrofused alumina as in Example 2 under the same conditions as in Example 2 without adding any chemicals. It is shown in the column of Example 2 and in Figure 2b.

[Table] From the above results, corundum particles produced by the method of the present invention (Examples 1 and 2) have an average particle size of
16.0 μm, the maximum particle size is 50 μm (Table 1), and the size is 5 μm to 50 μm as shown in Figure 1 a and b.
It is obtained as rounded spherical α-alumina (corundum) particles of m. On the other hand, the samples of Comparative Examples 1 and 2 showed no change in shape before and after the heat treatment, and were found to be irregularly shaped particles with sharp cutting edges. According to the above Examples and Comparative Examples, the particles produced by the method of the present invention are completely different from the irregular shapes with sharp cutting edges, which are conventional products, and have uniform particle shapes and cutting edges. It is clear that the particles are spherical corundum particles without any. Example 3 Average diameter for sintered alumina similar to Example 1
A sample was prepared by adding and mixing 10% (external weight % in terms of alumina) of 1 μm fine particles of aluminum hydroxide, adding the same type and amount of chemicals as in Example 1, and calcining and crushing in the same manner. Obtained. As a result of conducting the same evaluation as in Example 1, the results shown in Table 2, Example 3 column were obtained. Example 4 The results of a sample obtained in the same manner as in Example 3 except that the amount of aluminum hydroxide added was 17% are shown in the column of Example 4 in Table 2. Example 5 The results of a sample obtained in the same manner as in Example 3 except that the amount of aluminum hydroxide added was 30% are shown in the column of Example 5 in Table 2. Comparative Example 3 The results of a sample obtained in the same manner as in Example 5 without adding any drug are shown in the column of Comparative Example 3 in Table 2. According to the results of Examples 3 to 5 and Comparative Example 3 above, the sample of Comparative Example 3 in which no chemicals were added was a mixture of two components: fine alumina particles generated from fine aluminum hydroxide and coarse sintered alumina particles. The particles were mixed together, and no change in the shape of the latter particles was observed. On the other hand, in all of the samples of Examples 3 to 5 in which chemicals were mixed, aluminum hydroxide was absorbed into sintered alumina, and the particles were coarse, round, spherical corundum particles. Example 6 Sintered alumina SRW325F at a temperature of about 1350
Ammonium borofluoride was sprayed into the furnace at a concentration of 0.2% by weight (ratio to alumina) using compressed air from one firing port while continuously supplying the rotary kiln from the bottom of the rotary kiln adjusted to ℃. The amount of sintered alumina supplied was adjusted so that the residence time in the sintering zone at 1000° C. or higher was about 3 hours. The fired product obtained from the fire pit was crushed in a vibrating ball mill for 15 minutes, and the same evaluation as in Examples 1 to 5 was performed. Particles observed under a microscope are approximately 3μm to 40μm in size.
They were coarse spherical particles of m. Example 7 Commercially available coarse grain refractory aggregate grade sintered alumina (SRW48F manufactured by Showa Denko K.K.) was ground in a vibrating ball mill for 1 hour, and passed through a 150 mesh sieve (Tyler sieve, opening 104 μm). , coarse grain residue

【table】

[Table] 30% by weight of aluminum hydroxide with an average particle size of about 5 μm was mixed with the product from which the components were removed, and 2.0% by weight each of anhydrous aluminum fluoride and boric acid were added as chemicals. The evaluation results for the samples obtained by firing and crushing according to the method are shown in Table 3, in the column of Example 7. Example 8 Commercially available fused alumina (RW-92 manufactured by Showa Denko Co., Ltd.)
(220F), average particle size 28.5μm, maximum particle size 196μm)
Table 3 shows the evaluation results for samples obtained using the same method as in Example 7 for 150 mesh particles.
It is shown in the column of Example 8. For comparison, a similar test was also conducted on a sample that did not contain aluminum hydroxide. (Not shown) In the operations of Examples 7 and 8 in which aluminum hydroxide was not mixed, the particles of the fired product were bonded together in a semi-molten state, making it difficult to crush with a mill. The one in which aluminum hydroxide coexisted could be easily crushed down to primary particles.

【table】

[Table] The samples of Examples 7 and 8 were also measured for particle size distribution and observed using an electron microscope, and as shown in Table 3, the particle size of both Examples 7 and 8 was
It was confirmed that it was composed of coarse spherical α-alumina particles of 5 μm to 80 μm. Example 9 Commercially available low α-ray type alumina (α-ray radiation amount
Electro-fused alumina with an average diameter of 20 μm and a maximum particle size of 74 μm obtained by crushing, crushing, and classifying ingots obtained by electro-melting (0.01c/cm ²・hr or less) under conditions that do not contain radioactive element contamination. Coarse particles (α-ray radiation amount
0.005c/cm ² hr) and 30wt% of aluminum hydroxide (average diameter 5μm) of low α-ray type (α ray radiation amount 0.005c/cm ² hr) obtained by a known method, and boric acid as a chemical. and 0.5wt each of anhydrous aluminum fluoride
% and charged into a heat-resistant container made of alumina/ceramic, and heated in a Kanthal electric furnace at a temperature of 1500°C for 3 hours. When the fired product was ground in a vibrating ball mill for about 30 minutes and the particle size distribution and particle size and shape were evaluated using an electron microscope, it was found that it had changed to spherical coarse alumina particles with a size of 3 microns to 50 μm. I made sure of that. Further, the α-ray radiation amount of this sample was 0.004c/cm ² ·hr. (Effects of the Invention) As is clear from the above, the alumina particles produced by the method of the present invention all have a wide particle size distribution, each particle has a shape that is similar to that of the semiconductor encapsulating resin. It is useful as a filler that causes less wear on mechanical equipment and has good flow during molding. Furthermore, it is expected to improve flow characteristics, strength, and heat crack resistance as a raw material for finished wrapping materials that do not cause cutting scratches on the ground surface, and as a coarse aggregate component in applications such as castable refractories, glass, and ceramics. Ru.

[Brief explanation of drawings]

FIG. 1 shows an electron micrograph of spherical corundum particles produced by the method of the present invention, and FIG. 2 shows a scanning electron micrograph (magnification: 2500) of conventional corundum particles. Figure 1a Corundum particles of Example 1, Figure 1b
Corundum particles of Example 2, Figure 2a Comparative Example 1
Corundum particles of Comparative Example 2.

Claims (1)

[Scope of Claims] 1. A pulverized product of fused alumina and/or sintered alumina whose single particles have a maximum diameter of 150 μm or less and an average particle diameter of 5 to 35 μm, containing a halogen compound, a boron compound, and an alumina hydrate. 1. A method for producing spherical corundum particles, which comprises adding one or more of the following, heat-treating at a temperature of 1000°C to 1550°C, and then crushing. 2 The halogen compound is AlF ₃ , NaF, CaF ₂ ,
The method for producing spherical corundum particles according to claim 1, characterized in that one or more of MgF ₂ and Na ₃ AlF ₆ is used. 3 Boron compounds are B ₂ O ₃ , H ₃ BO ₃ , mNa ₂ .
Claim 1 characterized in that it is one or more types of nB ₂ O ₃ and borofluorine compounds.
A method for producing spherical corundum particles as described in . 4. The method for producing spherical corundum particles according to claim 1, wherein the alumina hydrate is Bayer process aluminum hydroxide and/or alumina gel. 5. The method for producing spherical corundum particles according to claim 1, wherein the alpha ray radiation amount of fused alumina, sintered alumina, and alumina hydrate is 0.01 c/cm ² ·hr or less.