JPS643809B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a method for producing calcium aluminate hydrate, particularly 3CaO・Al ₂ O ₃・6H ₂ O (hereinafter referred to as
_The present invention relates to a method for producing calcium aluminate hydrate having a large content of _C3AH6 ). _{C3AH6 _}
is a cubic crystal containing 28.5% water of crystallization per mole, and when heated under atmospheric pressure,
The water of crystallization is separated. The dehydration temperature varies depending on purity, shape, particle size, etc., but is between 240 and 275
Dehydration begins rapidly between 400°C and at least 21% (75% of the total water) of water has been dehydrated. Therefore, this hydrate is used as an inorganic filler useful for making synthetic resins flame retardant. purer than before
Synthesis of C ₃ AH ₆ was possible in the laboratory.
However, a technology for industrially producing pure C ₃ AH ₆ at low cost has not yet been established. today,
Industrially produced calcium aluminate hydrate has _C3AH6 as its main component, and its content is limited to 87-88%, and the rest is calcium aluminate hydrate, which is a metastable mineral _. rate, for example C ₄ AHx (x: 7, 11, 13, 19).
In order to use calcium aluminate hydrate containing C ₃ AH ₆ as a flame retardant filler for synthetic resins, it is necessary that the dehydration start temperature be close to the decomposition temperature of the resin and that the temperature rise of the resin can be suppressed. It is. For this reason, it is desired that the dehydration start temperature of the filler used here be about 240° C. or higher. However, the conventional calcium aluminate hydrate filler containing C ₃ AH ₆ has a dehydration start temperature of 240°C or lower, 200 to 230°C, and especially when used in thermoplastic synthetic resins, it does not start to dehydrate during the heating and molding stage. Crystal water partially dissociates, creating bubbles and deteriorating the quality of the molded product. Therefore, conventional fillers are only used in thermosetting synthetic resins that are molded at low temperatures, but cannot be used in thermoplastic synthetic resins that are molded at high temperatures, and their range of use is limited. In addition, conventional production methods require a long time for reaction and have a poor production rate of C ₃ AH ₆ , and products containing calcium aluminate hydrate, which is a metastable mineral that dehydrates at low temperatures other than C ₃ AH ₆ It was becoming. Therefore, the content of crystallization water was low, and the dehydration starting temperature was also low. Furthermore, regarding the particle size, it is known that the finer the particle size, the more pronounced the flame retardant effect is expected to be. However, it has been generally pointed out that conventional methods have the disadvantage that hydrates with large particle sizes are produced. Note that if the particle size is made too small, secondary aggregation will occur and the dispersibility in the synthetic resin will deteriorate, so it is preferable to have an appropriate particle size of 1 to 3 μm. The present invention was developed in order to solve the conventional problems in the manufacturing method of calcium aluminate hydrate fine powder.As the first step, aluminum hydroxide and lime are used at a solid content/water ratio of 1 to 1. /20 slurry, heated at 120 to 245°C while stirring in an autoclave for hydrothermal synthesis, and here
Calcium aluminate hydrate containing 3CaO・Al ₂ O ₃・6H ₂ O as the main component is produced, and as the second step, this is extracted from the autoclave and heated to 150 to 200 ml.
After air heating treatment at ℃, 3CaO・
A calcium aluminate hydrate characterized by dehydrating and decomposing calcium aluminate hydrate existing as a metastable mineral other than Al ₂ O ₃ .6H ₂ O to transform it into 3CaO .Al ₂ O ₃ .6H ₂ O This is a method for producing fine powder. This invention will be explained below. Aluminum hydroxide, which is one of the raw materials used in the present invention, can be arbitrarily selected from Gizasite [Al(OH) ₃ ], boehmite [AlOOH], amorphous aluminum, etc., but it is preferable to use one with the highest possible purity in terms of reaction yield. is preferred. In addition, calcium hydroxide and quicklime can be used as other lime raw materials, but lime with high activity is desirable in terms of reactivity with aluminum hydroxide. That is, quicklime should contain less undecomposed CaCO ₃ during firing, and calcium hydroxide should have a high digestibility and a low content of impurities such as CaCO ₃ . The raw material mixing ratio of aluminum hydroxide and lime is Al(OH) ₃ :Ca(OH) ₂ = molar ratio.
The standard is 2:3. Although this mixing ratio may be used from the beginning, it is also possible to make the mixture rich in aluminum or calcium at the beginning of the reaction, and then add the insufficient amount of aluminum or calcium during the reaction to adjust the standard molar ratio or standard molar ratio. It is also possible to control the production rate of C ₃ AH ₆ close to the ratio. The raw materials having the above blending ratio are mixed with water to form a slurry, placed in an autoclave, and reacted at a temperature of 120 to 245°C with stirring.
The slurry concentration (solid content/moisture content) is in the range of 1 to 1/20. When the slurry concentration is greater than 1, the solid content increases, the viscosity of the slurry increases, and uniform stirring becomes impossible, reducing the production of C ₃ AH ₆ . Also,
If the slurry concentration is less than 1/20, the generation of nuclei at the initial stage of the reaction will be small, and most of the subsequent reaction energy will be spent on the growth of the nuclei, resulting in a crystal grain size of 5 μm or more, which is not preferable. The slurry concentration affects the production rate and crystal grain size, and it is necessary to set it to 1 to 1/20. The raw materials must be thoroughly stirred during the reaction in the autoclave. If stirring is not sufficient, the kinetic energy of the solid content decreases, causing a partial sedimentation phenomenon and reducing the production rate of C ₃ AH ₆ . The heating temperature is within the range of 120 to 245°C.
If the temperature is lower than 120°C, the reaction rate is slow and the production rate of C ₃ AH ₆ is not sufficient. Furthermore, if the temperature exceeds 245℃, C ₃ AH ₆ will be rapidly generated at the beginning of the reaction, but
This is a metastable mineral that thermally decomposes quickly ₄ C ₃ A ₃ H ₃
etc., so this is not preferable. Heating synthesis temperature 120
By setting the temperature in the range of ~245°C, the production rate of C ₃ AH ₆ is good and the reaction rate is also fast. During the reaction in the autoclave, samples were taken from inside the autoclave at appropriate times during the reaction, and the dried samples were analyzed by powder X-ray diffraction method to determine the amount of product produced.
The process is stopped when the X-ray diffraction intensity ratio of C ₃ AH ₆ and unreacted slaked lime (IC ₃ AH ₆ /I′Ca(OH _{) 2 )} becomes constant. Calcium aluminate hydrate as a component is
Next, this is heat treated. The heat treatment here is
The slurry may be carried out as it is using a spray dryer, or it may be filtrated or made into a cake using a centrifugal separator, and this may be heated using a device such as a band dryer or a rotary dryer. As a result, the metastable phase of calcium aluminate hydrate contained in the slurry or cake is dehydrated and decomposed into C ₃ AH ₆ .
That is, C ₄ AHx, which is a metastable mineral, becomes C ₃ AH ₆ in an equiaxed crystal system through the reaction shown in the following formula. For example, C ₄ AH ₁₃ is transferred to C ₃ AH ₆ using the following formula. C ₄ AH ₁₃ →C ₃ AH ₆ +CH+6H The heating temperature here is 120 to 200°C. 120℃
If it is less than C ₃ AH ₆ , metastable phase calcium aluminate hydrate other than C 3 AH 6 will not dissociate reliably, resulting in a product with a dehydration start temperature of 240° C. or lower. Furthermore, if the temperature exceeds 200°C, a phenomenon in which part of the crystal water is released as the temperature rises, especially when the treatment time is long, is undesirable. The C ₃ AH _hexahydrate obtained by such treatment is pulverized by a conventional method. That is, when the calcium aluminate hydrate containing C ₃ AH ₆ as a main component obtained in the first stage of hydrothermal synthesis is once made into a cake shape and then heat-treated, it is in the form of lumps, so it is crushed. In addition, when heat-treating using a spray dryer, a powder of 0.3 to 5 μm can be obtained as is. According to the present invention, as the first step,
Calcium aluminate hydrate containing C ₃ AH ₆ as the main component and the rest being metastable minerals other than C ₃ AH ₆ is produced in an autoclave, and in the second step, the metastable minerals mentioned above are produced. Since it is transferred to C ₃ AH ₆ , the production of C ₃ AH ₆ is rapid and efficient. The calcium aluminate hydrate obtained here can have a C ₃ AH ₆ content of up to 95-96% or more. Previously, the limit was 87-88%. Therefore,
The dehydration start temperature was previously as low as 200-230℃, but
According to the present invention, the dehydration start temperature can now be set to 240°C or higher. Moreover, according to the present invention, the crystal particle size can be adjusted by adjusting the slurry concentration, etc.
It can be controlled in the range of 0.3 to 5μ,
It is possible to produce white fine powder of calcium aluminate hydrate, which has an appropriate particle size and is mainly composed of C ₃ AH ₆ . Since the fine powder of calcium aluminate hydrate obtained by the present invention has a high dehydration start temperature, it does not dehydrate during molding even when used as a filler for thermoplastic synthetic resins that are heat molded at high temperatures. It has become possible to prevent air bubbles from being included in the molded product and deteriorating the quality of the molded product. Example 1 270 g of aluminum hydroxide and 360 g of slaked lime having the quality characteristics shown in Table 1 were placed in a stainless steel autoclave with a capacity of 5.5 and equipped with a stirrer, and 3.5 g of water was added.
and while stirring, adjust the temperature to 50℃, 90℃, 120℃,
The reaction was carried out at 150°C, 200°C, 245°C, and 250°C for 7 hours.

[Table] Samples were taken out from the autoclave at appropriate times during the reaction and immediately overwashed. A porcelain Buchna funnel was used. The paper used was 5A and the suction pressure was 150.
mmAg. The cake was first washed with tap water, and then washed with acetone in an amount of 1/3 of the amount of slurry to stop hydration. Next, this cake was heat-treated at a treatment temperature of 150°C±5°C (air heating using an air oven) to obtain various synthetic samples for each reaction temperature. The extent of these reactions was determined by powder X-ray diffraction. The degree of reaction was determined by the X-ray intensity ratio (IC ₃ AH ₆ /I′Ca(OH) ₂ ) between the generated C ₃ AH ₆ and unreacted slaked lime. The results are shown in FIG. In Figure 1, 1...50℃, 2...90
℃, 3...120℃, 4...150℃, 5...200℃, 6...245
℃、7...Hydrothermal synthesis at 250℃ (in an autoclave)
This is what I did. Incidentally, FIG. 2b shows the relationship between the reaction temperature (° C.) in the autoclave and the X-ray intensity ratio (IC ₃ AH ₆ /I′Ca(OH) ₂ ) (7 hours reaction). Figure a shows a similar situation when the reaction time was 3 hours. Further, Table 2 shows the relationship between the X-ray intensity ratio and the C ₃ AH ₆ content in the synthesized sample.

[Table] Example 2 Synthesis was carried out in the same manner as in Example 1 using the same raw materials as in Example 1. However, the synthesis temperature in the autoclave was changed to 50℃, 90℃, 120℃, 150℃, and 200℃.
There were seven types: ℃, 245℃, and 250℃. Differential thermogravimetric analysis (TG, DTA) of the synthesized product obtained here
The dehydration start temperature and dehydration loss were determined.
The results are shown in FIGS. 3 and 4. As is clear from Figure 3, the influence of the reaction temperature on the dehydration initiation temperature is remarkable, and this is because the reaction temperature is 50℃,
At 90℃, 120℃, 150℃, 200℃, 245℃, 250℃,
Approximately 225-230℃, 235-240℃, 240-245℃, 245
~255℃255~260℃, 260~265℃, 250~255℃. In addition, the hydrothermal reaction temperature is 245
It is recognized that the dehydration start temperature moves to a higher temperature as the temperature increases up to ℃. However, when the hydrothermal reaction temperature is, for example, 250°C, as shown in the micrographs in Figures 5 and 6, at the initial stage of the reaction,
When C ₃ AH ₆ is formed, it immediately thermally decomposes to form C ₄ A ₃ H ₃ (see Figure 5), which is a rectangular plate-shaped metastable mineral, which is converted into the initial product ( C ₃ AH ₆ ) (see Figure 6), the dehydration start temperature is actually lower than when the hydrothermal reaction temperature is 245°C. As a representative example of the present invention, a scanning electron micrograph and an X-ray diffraction diagram of a sample synthesized at a hydrothermal reaction temperature of 200° C. are shown in FIGS. 7 and 8. As seen in Figure 7, the C ₃ AH ₆ produced here is a polyhedral crystal close to spherical.
Its particle size is 1 to 3μ. Example 3 Using the same raw materials as in Example 1, hydrothermal synthesis was carried out in the same manner as in Example 1 while stirring in an autoclave. However, the reaction temperature in this case was 150°C and the reaction time was 7 hours. The obtained reaction product is
After cooling, it was filtered in the same manner as in Example 1 and washed with acetone to obtain a cake-like sample. This cake-like sample was divided into 50℃, 85℃, 105℃, 125℃, 150℃, and 180℃.
℃, 200℃, and 230℃ for 8 hours until a constant weight was achieved to obtain TG and DTA samples. In addition,
Heating was performed at 50°C and 85°C by vacuum heat treatment, and at other times air heat treatment was performed in an air oven. Eight different heat treatment temperatures were used here. For these, the dehydration start temperature and the rapid first dehydration loss immediately after the start of dehydration were determined using TG and DTA. 3rd result
The table and Figures 9 and 10 are shown.

【table】

[Table] Example 4 Using the same raw materials as in Example 1, hydrothermal synthesis was carried out in the same manner as in Example 1 while stirring in an autoclave. However, in this case, the reaction temperature is 200℃,
The reaction time was 7 hours. The resulting slurry of the reaction product was treated using a spray dryer at a heating temperature of 190° C. and a heating time of 2 to 3 seconds. As a result, a spherical fine white powder of C ₃ AH ₆ with a purity of approximately 100% and an average particle diameter of 10 μm or less was obtained. An X-ray diffraction chart of this product is shown in FIG. In addition, differential thermogravimetric analysis (TG, DTA) was performed to determine the dehydration initiation temperature (265°C), and the TG and DTA chart is shown in Figure 12.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between reaction time and X-ray intensity ratio for samples whose hydrothermal synthesis reaction temperature was changed. FIG. 2 is a diagram showing the relationship between reaction temperature and X-ray intensity ratio of the sample used to show FIG. 1. In the figure, a shows a reaction time of 3 hours, and b shows a reaction time of 7 hours. Figure 3 shows the relationship between reaction temperature and dehydration start temperature for samples with different hydrothermal synthesis reaction temperatures. Figure 4 shows heating temperature and dehydration loss for the samples used to show Figure 3. Diagram showing the relationship between. Figure 5 is an optical micrograph (1000
Figure 6 is an optical micrograph (1000x) used as a drawing of the product cooling process shown in Figure 5. Figure 7 shows
FIG. 8 is a scanning electron micrograph (6000x) of the calcium aluminate hydrate fine powder obtained by the present invention, which is an X-ray diffraction diagram of the hydrate fine powder shown in FIG. The figure shows the temperature of the hydrothermal synthesis reaction.
A diagram showing the dehydration start temperature when the heat treatment temperature was changed to 150°C, and FIG. 10 is a diagram showing the dehydration loss (%) at that time. Figure 11 is an X-ray diffraction chart of a product heat-treated with a spray dryer at a hydrothermal synthesis temperature of 200°C and a reaction time of 7 hours, and Figure 12 shows the relationship between dehydration start temperature and dehydration loss. Line diagram.

Claims (1)

[Claims] 1 Solids/water ratio of aluminum hydroxide and lime: 1
Make a slurry of ~1/20 and heat it at 120-245℃ while stirring in an autoclave for hydrothermal synthesis.
Calcium aluminate hydrate containing 3CaO・Al ₂ O ₃・6H ₂ O as the main component is produced, and then this is extracted from the autoclave and air heat treated at 150 to 200°C to contain metastable minerals in the product. A method for producing calcium aluminate hydrate fine powder, which comprises dehydrating and decomposing existing calcium aluminate hydrate to transform it into stable mineral 3CaO.Al ₂ O ₃ .6H ₂ O.