JPH046648B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to aluminum hydroxide for producing artificial marble such as onyx-like or marble-like marble obtained by filling unsaturated polyester resin, acrylic resin, etc. with aluminum hydroxide, and a method for producing the same. [Prior Art] It is well known to fill an unsaturated polyester resin or acrylic resin with aluminum hydroxide to obtain an onyx-like or marble-like molded product. Recently, fine-grained aluminum hydroxide has been used as a filler for the purpose of improving the strength, surface smoothness, boiling resistance, and settling of the filler in a paste state. In addition, when obtaining a molded product by press molding BMC (bulk molding compound) and SMC (sheet molding compound), the particle size of the filler is adjusted to prevent separation of the resin and filler during pressing. It is advantageous to use fine aluminum hydroxide. [Problems to be Solved by the Invention] However, when aluminum hydroxide with a small particle size, that is, a large specific surface area, is used as a resin filler, there are problems such as poor dispersion of the filler into the resin and high resin filling viscosity. Therefore, it is inevitable that high filler filling becomes difficult. In addition, unsaturated polyester resin compositions using aluminum hydroxide, which has a large specific surface area, as a filler have gels because an oil-soluble curing accelerator such as cobalt naphthenate, which is used as a curing accelerator, is trapped on the surface of the aluminum hydroxide. There are problems such as a delay in curing time, a decrease in productivity, and a yellowish tinge to the molded product. [Means for Solving the Problems] As a result of intensive studies to solve the above problems, the inventor succeeded in developing aluminum hydroxide suitable for use in artificial marble. When manufacturing aluminum by pulverizing it, the primary particle size of precipitated aluminum hydroxide, which is the raw material for pulverization, and the content of Na ₂ O, which is an impurity, have a very large effect on the specific surface area of the pulverized product and the resin filling viscosity. Based on this discovery, we have completed the present invention. In other words, the present invention uses aluminum hydroxide with a low specific surface area and resin-filled viscosity, and secondary agglomerated particles with a primary particle diameter approximately equal to the average particle diameter of the target pulverized aluminum hydroxide, and with a low content of Na ₂ O impurities. To provide a method for producing aluminum hydroxide for use in artificial marble, which is characterized in that precipitated aluminum hydroxide with a small amount of aluminum hydroxide is used as a pulverizing raw material, and is produced by pulverizing the same. That is, the gist of the present invention is to provide an unsaturated material having an average particle diameter of 4 to 8 μm as measured by a sedimentation method, a specific surface area of 2 m ² /g or less as measured by a nitrogen adsorption method, and a viscosity of 10 poise at 20°C. A blend of 100 parts by weight of polyester resin filled with 200 parts by weight of aluminum hydroxide has a resin filling viscosity of 1000 poise or less, measured at 35°C with a Burckfield viscometer, and a proportion of particles with a particle size of 45 μm or more. Aluminum hydroxide for artificial marble, characterized by having a whiteness of 96 or more and a whiteness of 96 or more, and an average particle size of 20 μm consisting of primary particles with an average diameter in the range of 4 to 8 μm as measured by a pressure crushing method. Fixed Na ₂ O content of 0.20 at ~50 μm
It is an object of the present invention to provide a method for producing aluminum hydroxide for artificial marble, which comprises pulverizing secondary agglomerated particles of aluminum hydroxide in an amount of not more than 0.15% by weight, preferably not more than 0.15% by weight. Here, the whiteness refers to a value measured with a photoelectric whiteness meter. The average diameter of primary particles is . This is the value obtained by crushing under pressure at a pressure of 0.75 t/cm ² and measuring the average diameter using an air permeation method. _Na2O content is the so-called fixed _Na2O
It does not contain so-called adhering soda content, which is removed by washing with water. The method for pulverizing the secondary agglomerated particles of aluminum hydroxide is not particularly limited, but a general method for pulverizing powder particles, such as a ball mill, may be employed. First, the reasons for limiting the numerical values for aluminum hydroxide of the present invention will be explained. The average particle diameter measured by the sedimentation method must be within the range of 4 to 8 μm; if it is less than 4 μm, it will be impossible to achieve both low specific surface area and low viscosity, and if it is more than 8 μm, the strength of the molded product will decrease. , surface smoothness deteriorates, and in addition, it becomes difficult to prevent separation of the resin and filler during press molding of BMC and SMC. The specific surface area measured by the BET method must be 2 m ² /g or less, and if it exceeds this, it may cause poor dispersion of the filler into the resin or when curing unsaturated polyester resin with a peroxide curing catalyst. This results in a significant delay in gelation time. Resin filling viscosity is 35℃
It is essential that the value is 1000 poise or less. If this value is exceeded, it becomes difficult to knead the resin and filler or mold by casting, and the amount of filler filled cannot be increased, so the target color feeling cannot be achieved. In addition, in BMC, etc., it is not possible to increase the amount of glass fiber mixed in, so the target strength cannot be obtained, and it is not possible to achieve high filler filling, which causes problems such as poor flow characteristics during pressing. happen. It is essential that the proportion of particles with a particle size of 45 μm or more is 1% or less; if this exceeds this, the surface smoothness of the molded product will deteriorate, and BMC,
Additionally, it becomes difficult to prevent separation of the resin and filler during press molding of SMC. The whiteness measured with a photoelectric whiteness meter must be 96 or higher; if it is less than this, the resulting molded product will be colored pale yellow or light brown, and the color tone will be good and suitable for artificial marble. will not be obtained. Next, the reason for limiting the numerical value of the secondary agglomerated particles of aluminum hydroxide, which is the raw material to be crushed in the method for producing aluminum hydroxide of the present invention, will be explained. The average particle diameter measured by the sedimentation method must be within the range of 20 to 50 μm; if it is less than 20 μm, the particle size distribution of the crushed product will be too narrow, resulting in an increase in resin filling viscosity, and if it exceeds 50 μm. This increases the amount of coarse particles remaining in the pulverized material, resulting in poor surface smoothness and making it difficult to prevent separation of the resin and filler during press molding of BMC and SMC. It is essential that the average diameter of the primary particles obtained by crushing under a pressure of 0.75t/cm ² and measuring the average diameter using an air permeation method is within the range of 4 to 8 μm. Outside this range, the specific surface area when crushed to an average diameter of 4 to 8 μm and the resin filling viscosity become high. Specifically, the average primary particle diameter of aluminum hydroxide is measured by the following method. In other words, a mold like the one shown in Figure 1 (cylindrical crucible shape, diameter 30 mm)
15 g of aluminum hydroxide, which had been left in an atmosphere of 23° C. and RH 65% for 1 hour, was charged into a chamber (23° C. and 50 mm deep) and pressurized with a hydraulic press at a pressure of 0.75 t/cm ² for 30 seconds. Next, the aluminum hydroxide is taken out from the mold, placed in a resin film bag, 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. Fixation contained in agglomerated particles of aluminum hydroxide
It is essential that the Na ₂ O content be below 0.20 wt%, with a more preferred level being below 0.15 wt%. The reason for this will be explained later. The diameter of the ball serving as the grinding medium is preferably within the range of 3 to 20 mmφ. If it is less than 3 mmφ, the particle size distribution of the crushed aluminum hydroxide becomes too narrow and the resin filling viscosity becomes high, and if it exceeds 20 mmφ, the cleavage and chipping of the primary particles increases or progresses, so the specific surface area of the crushed aluminum hydroxide increases, so it is preferable. do not have. [Function] The reason why the primary particle size of precipitated aluminum hydroxide has a large effect on the specific surface area and resin filling viscosity of the pulverized product is considered as follows. Figure 2 shows an average particle diameter of 70 μm and an average primary particle diameter of
Figure 3 shows the precipitated aluminum hydroxide with a thickness of 25 μm.
This is an electron micrograph of aluminum hydroxide that was ground to an average particle size of 9 μm using a forced stirring mill using 5 mm diameter alumina balls. Figure 4 shows precipitated aluminum hydroxide with an average particle size of 30μm and a primary particle average diameter of 7μm, and Figure 5 shows precipitated aluminum hydroxide with an average primary particle diameter of 7μm.
This is an electron micrograph of aluminum hydroxide pulverized to an average particle size of 6 μm using a forced stirring mill using φ alumina balls. As is clear from the photo, when aluminum hydroxide with an average primary particle diameter of 25 μm is crushed to an average particle diameter of 9 μm, the primary particles naturally break, and due to the cleavage properties of aluminum hydroxide, plate-like and amorphous particles are formed. As a result, the viscosity increases when the resin is highly filled. Furthermore, since the primary particles must be destroyed, the grinding time becomes longer, the particle surface becomes rougher, a large amount of chipped particles are generated, and the specific surface area becomes larger. On the other hand, pulverizing aluminum hydroxide with an average primary particle diameter of 7 μm to an average particle diameter of 6 μm is, so to speak, the disintegration of secondary agglomerated particles, with almost no destruction of the primary particles, and the crushed The particle shape of
Since the rounded particle shape of the primary particles of precipitated aluminum hydroxide is well maintained, the viscosity is low when the resin is highly filled. Furthermore, since the grinding time is short, the specific surface area is also small. Furthermore, even if the primary particle size of precipitated aluminum hydroxide is in the range of 4 to 8 μm, the ease of crushing into primary particles varies greatly depending on the fixed Na ₂ O content. In other words, the lower the Na ₂ O content, the more
It becomes easier to crush into secondary particles, and a crushed product with uniform particle shape and small specific surface area can be obtained. Conversely, Na ₂ O
As the content increases, it becomes more difficult to crush into primary particles, and the proportion of chipped particles and irregularly shaped particles increases. The reason why the Na ₂ O content affects the ease of crushing is considered to be as follows. It is estimated that a part of the Na ₂ O impurity incorporated into the aluminum hydroxide particles during the precipitation reaction is unevenly distributed at the grain boundaries of the crystals, that is, at the interfaces between primary particles. Na ₂ O, which is unevenly distributed at the interface, is thought to have a binder-like effect that strengthens the bonds between the primary particles of aluminum hydroxide. As a result, it becomes difficult to disintegrate the primary particles;
It was confirmed that cleavage and chipping of secondary particles progressed. In other words, even with aluminum hydroxide in the form shown in Figure 4, this phenomenon becomes noticeable when the Na ₂ O content exceeds 0.20%, and when the crushed material was examined in detail with an electron microscope, it was found that the primary particles were Many connected amorphous particles and chipping particles were observed. If the fixed Na ₂ O content is below 0.20%,
Although the product of the present invention can be obtained, in order to shorten the crushing time and obtain particles with a more uniform shape, it is necessary to
More preferably, the Na ₂ O content is 0.15% or less. [Examples] The present invention will be specifically described below with reference to Examples shown in Table 1 and Comparative Examples shown in Table 2. The resin/aluminum hydroxide composite compositions shown in the table were evaluated as follows. It goes without saying that the present invention is not limited to these Examples. 1 Resin filling viscosity and 2 Dispersion time (compounding) Unsaturated polyester resin ^*1 100 parts Aluminum hydroxide 200 parts The above composition is stirred and kneaded, and the time until it becomes completely paste-like is defined as the dispersion time, and the viscosity at that time ( Using a BS type viscometer, 35℃) is the resin filling viscosity. The resin filling viscosity is preferably 1000 poise or less, and the dispersion time is preferably 10 minutes or less. *1 Rigoratsuku 2004WM-2 manufactured by Showa Kobunshi Co., Ltd.
Viscosity 9P (20℃) 3. Color tone of molded object, 4. Gelation time and 5. Surface smoothness of molded object (compound) Unsaturated polyester resin ^*2 100 parts MEKPO (Methyl Ethyl Ketone Peroxide Product Name: Permek N NOF) Co., Ltd.) 1 part 6% Cobalt naphthenate 0.2 parts Aluminum hydroxide 150 parts *2 Refractive index 1.52, viscosity 18p (25℃) The above formulation was stirred and kneaded, and the composition was heated in a constant temperature bath at 25℃. The viscosity is measured continuously, and the time until the viscosity starts to increase due to curing of the resin is defined as the gelation time. The gelation time is preferably 60 minutes or less. In addition, defoaming kneading was performed with the above formulation, and 3 mφ×
The color tone of the cured product was poured into a 15 mm thick mold, cured overnight at room temperature (25°C), and then heated at 50°C for 3 hours using Color Tester SM-4- manufactured by Suga Test Instruments Co., Ltd.
Measured in CH and expressed in Hunter chromaticity coordinates Lab.
This is the color tone of the molded product. Hunter chromaticity coordinates are expressed as (L, a, b), where axis L represents lightness;
a and b are perceptual chromaticity indexes, which have sides and represent red and green, yellow and blue, respectively. For artificial marble, b, which represents yellowness, is important, and is preferably 10 or less. The surface smoothness of the molded product is the result of observing the surface properties of the cured product with the naked eye. In the table, × indicates no surface gloss, △ indicates poor surface gloss, and ○ indicates good surface gloss. . Examples 1 to 5 Sodium hydroxide with a purity of 95% or more was dissolved in purified water to create a solution with a NaOH concentration of 150 g/.
Reagent-grade aluminum hydroxide with a purity of 60 to 70 wt% in terms of Al ₂ O ₃ is dissolved in this solution by heating, and the A/C is
A 0.65 supersaturated sodium aluminate solution was prepared. In addition, A is Al ₂ O ₃ concentration (g/), and C is
NaOH concentration (g/). Aluminum hydroxide having an average diameter of 1 μm was added as seed crystals in a predetermined concentration range to the above sodium aluminate solution, and precipitation was performed while maintaining the temperature of the solution at 70° C. or higher. Furthermore, 1 from the slurry after the completion of precipitation.
A portion was extracted and used as a seed crystal for a second precipitation. Repeat the precipitation operation in this way,
By changing the seed concentration and solution temperature level at that time, the average particle size shown in the first example, 1
Precipitated aluminum hydroxide according to claim 2 having an average diameter of secondary particles and a Na ₂ O content was obtained. The precipitated aluminum hydroxide was separated from the solution by vacuum filtration, washed with purified water, and then dried at 100°C. A bead mill (manufactured by Mitsui Miike Kakoki) with a crushing capacity of 1 is used as a crushing media of 5 m/mφ or 10 m/mφ.
7.7 kg of alumina ceramic beads and 1 kg of the above aluminum hydroxide were placed in a container and crushed for 8 minutes at an agitator rotation speed of 300 rpm. As shown in Figure 5, the pulverized aluminum hydroxide all maintained the shape of the primary particles of the precipitated aluminum hydroxide, and the proportion of chipped particles and cleaved amorphous particles was small. . Table 1 shows the properties of the pulverized product and its properties when filled in resin. Despite the fine particle size with an average diameter ranging from 4.5 μm to 7.5 μm, the specific surface area is 2.
m ² /g or less, the resin paste viscosity is low, the dispersibility in the resin is good, and the curing characteristics (gelling time) are low.
is also excellent. Even less yellow (b
A molded article with a color tone (low value) was obtained. Comparative Examples 1 to 3 A/C of aluminate liquid is 0.55 (Comparative Examples 1 and 2)
Or, except that it is 0.82 (comparative example 3),
Precipitated aluminum hydroxide (Comparative Examples 1 to 3) having an average particle diameter or an average primary particle diameter outside of Claim 2 was obtained under substantially the same condition range as in Example 1. This was crushed in the same manner as in the example to obtain a crushed product. The crushed precipitate with an average diameter of 15 μm (Comparative Example 1) had a sharper particle size distribution and a higher resin filling viscosity than the crushed material of the example. In addition, the average diameter of the primary particles is
When the 17μ precipitate (Comparative Example 2) was crushed to an average particle size of 6μ, chipping and cleavage particles increased and only particles with a large specific surface area were obtained. Also, 1
In the precipitate having an average primary particle diameter of 3.5 μm (Comparative Example 3), the proportion of agglomerated primary particles in the crushed material was higher than that in the crushed material of the example, and the resin filling viscosity was increased. Comparative Example 4 Except for the temperature of the aluminate solution at the time of precipitation being 55°C, the operation was performed under substantially the same range of conditions as in the example, and the average particle diameter and average primary particle diameter were within the range of claim 2. Fixed Na ₂ O, which is an impurity although contained in
Precipitated aluminum hydroxide with a content of 0.20% or more was obtained. When the material was crushed under the same conditions as in the example, the average particle size of the crushed particles was large, so the crushing time was extended for an additional 10 minutes to obtain a crushed product with an average particle size of 6 μm. When the crushed material was observed under an electron microscope, cleaved particles in which primary particles remained bonded and many chipping particles were observed. Comparative Examples 5 to 6 In the operation of crushing the precipitated aluminum hydroxide in Example 1, the diameter of the crushing media in Example 2 was
m/m (Comparative Example 5) and 30 m/m (Comparative Example 6), crushed materials were obtained. In the case of crushing with beads of 2 m/m, the proportion of agglomerated particles increased, probably due to insufficient crushing force, and only those with high resin filling viscosity could be obtained. On the other hand, if a 30m/mφ media is used, the crushing force is too strong and the primary particles themselves are destroyed.
The specific surface area became larger and the gelation time became longer. Comparative Examples 7 to 8 Among the conditions for crushing precipitated aluminum hydroxide in Example 1, the crushing time was changed to 3 minutes and 20 minutes, and the average particle size was 15 μm (Comparative Example 7) and 3 μm (Comparative Example 8) of ground aluminum hydroxide was obtained. When the average particle size was 15μ, many aggregated coarse particles remained, the resin filling viscosity increased, and the surface smoothness of the molded product decreased. On the other hand, in the case of 3μ, the primary particles themselves are destroyed,
BET specific surface area increased significantly. Comparative Example 9 Pulverized aluminum hydroxide with an average diameter of 6 μm was obtained in the same manner as in Example, except that ordinary Bayer's solution prepared at an A/C of 0.65 was used as the precipitation solution, but the whiteness of the powder was was small, and the molded body filled with resin was colored yellow. From these results, the fine-grained aluminum hydroxide according to the present invention has a smaller specific surface area than conventional ones, so it has good dispersibility in resin, and also has a shorter gelation time when filled into unsaturated polyester resin. It can be seen that there is an effect of suppressing the delay, the color tone of the molded product is less likely to be yellowish, and in addition, the viscosity when filled into the resin is low, so high filling is possible. Moreover, it can be seen that the aluminum hydroxide for artificial marble of the present invention can be produced by the method of the present invention.

【table】

【table】

[Table] [Effects] The quality of the aluminum hydroxide thus obtained has been specially designed to be used as a filler for artificial marble, and exhibits its excellent properties when used for this purpose. For example, when the aluminum hydroxide of the present invention is used as a filler when filling unsaturated polyester resin and manufacturing washstands and kitchen countertops by casting, the aluminum hydroxide of the present invention can be used as a filler because it has good dispersibility in the resin. Stirring and kneading can be done in a short time. In addition, even if a high filler is used to reduce the resin content for the purpose of cost reduction, the viscosity is low, making it easy to perform casting operations. Furthermore, the curing time of the unsaturated polyester resin is much shorter than that of the conventional case filled with fine-grained aluminum hydroxide, resulting in excellent productivity. In addition, since the cured product has little yellow tinge, products with beautiful colors can be obtained both when pigments are not added and when pigments are added. Furthermore, when the aluminum hydroxide of the present invention is used as a filler when manufacturing washstands, bathtubs, etc. using the BMC or SMC press molding method,
High filling is possible and has excellent flow characteristics during pressing. Furthermore, since the obtained molded product has excellent surface smoothness, it has a luxurious feel and also has excellent stain resistance.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a mold used in the pressure crushing method for measuring the average diameter of primary particles, and FIGS. 2 to 5 are electron micrographs showing the particle structure of aluminum hydroxide.

Claims (1)

[Claims] 1. The average particle diameter measured by a sedimentation method is 4 to 8 μm,
A blend of 100 parts by weight of an unsaturated polyester resin with a specific surface area of 2 m ² /g or less as measured by the nitrogen adsorption method (BET method) and a viscosity of 10 poise at 20°C and 200 parts by weight of aluminum hydroxide is used. Water for artificial marble, characterized by having a resin filling viscosity of 1000 poise or less, a proportion of particles with a particle size of 45 μm or more being 1% or less, and a whiteness of 96 or more, as measured at 35°C with a Burckfield viscometer. Aluminum oxide. 2. The average particle diameter is 20-50 μm, which is composed of primary particles with an average diameter of 4-8 μm measured by pressure pulverization method.
2. The method for producing aluminum hydroxide for artificial marble according to claim 1, wherein secondary agglomerated particles of aluminum hydroxide having a fixed Na ₂ O content of 0.20% by weight or less are pulverized. 3 Pulverization of secondary agglomerated particles of aluminum hydroxide,
3. The method for producing aluminum hydroxide for artificial marble according to claim 2, characterized in that the process is carried out using a ball mill or the like having a ball diameter of 3 to 20 mm as a grinding medium.