JPH0269315A - Fine-grain aluminum hydroxide - Google Patents

Abstract

PURPOSE:To obtain the title fine-grain aluminum hydroxide which hardly causes dilatancy at high shear rate and high concn. when used as aq. slurry and is useful as a coating slurry for paper by specifying the aggregation degree and standard viscosity. CONSTITUTION:The secondary grains are cracked by dry or wet crushing to control the aggregation degree to <=3.0 shown by the ratio of the secondary- grain average particle diameter to the primary-grain average particle diameter and the standard viscosity to <=5 poise shown by the apparent viscosity of the slurry contg. 65% solid.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to fine particles of aluminum hydroxide that exhibit properties suitable for use as coating slurry for paper manufacturing, filler for plastics, and the like.

[Prior Art] It is known that fine aluminum hydroxide particles are fine and have a high degree of whiteness, and therefore, when surface coated on paper, an excellent smooth surface and gloss can be obtained.

These are used as a slurry by adding water, a dispersant, etc. Recently, high-speed coating methods have been trending toward improving productivity, but for this purpose, it is necessary to minimize the amount of water evaporation in the coated slurry. There is a growing tendency to do so. At the same time, good rheological properties at high shear rates are also required.

This fine-grained aluminum hydroxide crystallizes in a short time using a batch method, whereas the general-purpose Bayer process aluminum hydroxide crystallizes over a long period of time using a continuous crystallization method to grow primary particles. It is produced by filtering and drying the fine particles. Examples of commercially available products include H-42 and H-43 manufactured by Showa Denko ■.
Examples include C-301 and C-3005 manufactured by Sumitomo Chemical ■, and OL-107 manufactured by Martinsberg ■.

These have a BET specific surface area of 3 ni'/g or more, and an average primary particle diameter of 2
The secondary particle average diameter (visible average diameter) is 3 or less as measured by a laser diffraction particle size analyzer.

In terms of crystal form, they are all gibbsite.

[Problems to be Solved by the Invention] However, when such fine particles of aluminum hydroxide are made into an aqueous slurry and the shear rate is increased, they tend to exhibit a dilatancy phenomenon in which stress is rapidly applied. During slurry handling such as stirring, a sudden load is applied and there is a risk of causing trouble, so in the paper industry where slurry is actually used, it is particularly dangerous, and operations are often stopped if the slurry is below the desired concentration. The current situation is that

These dilatancy phenomena can be easily quantified by examining the flow characteristics of the slurry. for example,
When the flow curve of fine aluminum hydroxide slurry is measured with a rheometer, shear stress suddenly rises at a certain shear rate, indicating a dilatancy phenomenon. The shear rate at this time can be used as an index of the dilatancy phenomenon,
This is called DI (DIlatancy Inclex)
). The higher the DI, the less likely the glatancy phenomenon will occur, and it can be said that the fine particle aluminum hydroxide or slurry is better.

The commercially available fine aluminum hydroxide mentioned above has a solid concentration of 6
When dpj is determined using a rheometer (Rheomat 115 from Cordix ■) using a 5% slurry, the DI is mostly in the range of 0 to 80001/s.

Regarding the factors involved in the occurrence of this dilatancy phenomenon, the surface activity of the primary particles, the particle size distribution of the secondary particles, the agglomeration ratio of the primary particles (hereinafter referred to as the degree of aggregation), the amount of impurities, etc. are considered, but it is still insufficient. has not been elucidated.

[Means for Solving the Problems] In view of the above-mentioned current situation, the present inventors have conducted extensive research and found that the degree of aggregation of fine aluminum hydroxide is the main factor causing the dilatancy phenomenon of aqueous slurry, and that the degree of aggregation is 3.
．． The inventors have discovered that the dilatancy phenomenon is significantly improved when it is 0 or less, and have arrived at the present invention.

In other words, the degree of agglomeration (hereinafter referred to as A) is expressed as (secondary particle average diameter)/
(Primary particle average diameter) When A is 3.0 or less, the DI significantly increases and the dilatancy phenomenon is significantly improved. The average secondary particle diameter as used herein refers to the average particle diameter of visible particles (hereinafter referred to as D2) determined by 1 fPI using a laser diffraction particle size analyzer. In addition, the primary particle average diameter (hereinafter referred to as D1) is calculated from the BET specific surface area (hereinafter referred to as BET), or -6/ + (BET)
(true specific gravity)) is used.

Generally, the dilatancy phenomenon is said to be caused by volumetric expansion due to shearing.

General fine-grained aluminum hydroxide has many fine pores between aggregated primary particles, and when this is made into a slurry and sheared, free water is trapped in the pores, and at the same time, The secondary particles swell and become entangled with each other, generating sudden stress. This dilatancy phenomenon is
It is thought that the larger the number of vacancies, the more pronounced this becomes. In other words, depending on the degree of cohesion A, the shear rate D at which shear stress suddenly appears
I can say that it will be determined. When A is high, DI is low;
When A is low, Dl becomes high. In particular, when A becomes 3.0 or less, DI becomes significantly high.

As a method for loosening agglomerates, dry or wet grinding may be used, but a particularly preferred method is dry grinding. These have the power to crush only up to the primary grains, and the primary grains will not disintegrate even if processed for a long time (afterwards, the primary grains will not be disintegrated, i.e., the pulverization up to the primary grains will be disintegrated. ). However, in crushing methods that use strong crushing force, such as vibration mills, ball mills, sand mills, and mills, the primary particles may also be disintegrated. In other words, it is crushed in the initial stage, but as the crushing time elapses, it collapses down to the primary particles (hereinafter, crushing in which even the primary particles collapse is referred to as over-pulverization).

This collapse of primary grains can be detected by BET.

In other words, the BET does not change during the crushing stage, but the BET clearly increases during the over-pulverizing stage. In such a state of over-pulverization, as seen in Japanese Patent Publication No. 62-28823,
The viscosity of the lapel pin increases. The standard viscosity referred to here is
The apparent viscosity of a slurry with a solid concentration of 65% is approximately 1 to 10 voids for H-42 and H-43 manufactured by Showa Denko Corporation. When the standard viscosity is high, similar to the dilatancy phenomenon,
Not suitable as paper coating slurry. Further, this standard viscosity tends to decrease by crushing and can be reduced to 5 poise or less, but if it is over-pulverized, it rapidly increases to 10 poise or more. However, among commercially available products, there are some products whose agglomerations cannot be loosened no matter how hard one tries to disintegrate them. This is thought to be due to the strong bond between the primary particles, and this may be due to the crystallization conditions of the fine particles of aluminum hydroxide, the drying conditions, etc.

No matter how many operations are carried out for crushing such fine aluminum hydroxide, there is no change in A, and DI7> (low), making it impossible to obtain a good slurry.

The content of the present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples.

[Example] (Example 1) As an example, 6 pieces of crushed products (No. 1 to No. 8 to No.
3), 7 conventional products as comparative examples (No. 1 to NQ, 7.
) cohesion degree A, standard viscosity η (hereinafter referred to as η) and DI
The jjpj determination results are shown in Table 1.

Table 1 N (Ll to N (L7's conventional product is H-4 manufactured by Showa Denko ■)
It is 2.

Nos. 8 to 13 were subjected to crushing treatment, and the treatment method was as follows.

For N8, Nα5 was dry-crushed using Seishin Corporation's jet mill and single track mill.

For Nα9, Nα4 was dry crushed using a current jet mill CJ-25 manufactured by Nisshin Engineering ■.

For Nα10, No. 3 was dry-pulverized using a current jet mill CJ-25 manufactured by Nisshin Engineering ■ at a grinding degree lower than that of N11L9.

For No. 11, No. 1 was dry crushed using Nissin Engineering ■'s Turbo Crunchifier T C-15N.
After classification, each classified product was mixed again.

For No. L2, No. 1 was made into a slurry with ion-exchanged water, and Aron A from Toagosei Chemical ■ was added to this as a dispersant.
200 was added at 1% based on the solid content to adjust the slurry to a solid concentration of 65%. This was installed at Nippon Seiki's Ultrasonic Generator (US-300).
Disintegrated for 0 minutes.

For Nα13, No. 11 was treated with N (for 10 minutes using the same wet crushing method as L12).

Next, the measurement method will be explained.

D2 is a laser diffraction particle size analyzer Leeds & No.
rLhrup lnsLrumenLsii! It was determined to be a+ using the Microtrac SPA model. As a method, in order to better represent the visible particle size, first, 20 ml of 50 g/M sodium hexametaphosphate was added as a dispersant to a recirculator (L
VR), and the dispersant concentration in the circulating fluid is 0.3g/I.
Add dry powder or slurry to D.
-5000, and after circulating and dispersing for 3 minutes, the Mj was determined. D2 was defined as the 50% particle size of this cumulative particle size distribution.

BET is QUANTACHRO's specific surface area measurement device QUANTASORB (Model No. Q S-14
).

The slurry was dried at 110° C. for 12 hours and then measured. For the true specific gravity of fine aluminum hydroxide when calculating D1, Gibbsite's theoretical value of 2.42 was used. This is k1, No, 5, No, 8,
This is because the crystal peak pattern of the diffraction X-ray of No. I3 is only gibbsite, and even when measured by the pyranometer method, results similar to the theoretical values were obtained. Based on the above results, Dl is 6/ + (BET)X CQ specific gravity))
It was calculated as the equivalent sphere diameter using the well-known calculation formula. Further, A is an index representing aggregation, and in the present invention, it is expressed as the ratio of Dl to D. That is, A-D2/D1.

Next, η and DI will be explained. In the case of dry powder, first add 132 ml of ion-exchanged water, 30 ml of Toagosei Chemical's Aron A-200U diluted to 10%, and Sample 3.
00g were mixed to form a slurry with a solids concentration of 65%.

In the case of slurry, 276 ml was dispersed. The entire amount of the mixture was put into Matsushita Electric's National Mixer MX 120, the voltage was lowered to 40 V using a slidex, and the mixture was stirred for 5 minutes.

The rotation speed at this time was 4500 rpm. 200 ml of this stirred slurry was taken out and its viscosity was measured using a B-type viscometer (BM) manufactured by Tokyo Keiki Seisakusho ■.

The rotor used is No. 3, and the rotation speed was 80 rpm.
+ and the reading 1 minute after the start of rotation was converted into viscosity. The viscosity at this time was defined as the standard viscosity η. During these series of operations, care was taken to maintain the slurry temperature at 25±0.5°C.

Also, DI is at Cordix ■ Leomat 115,
It was determined by measuring the flow curve of the slurry.

That is, 30 ml of the remaining stirred slurry was taken out and transferred to a Rheomat measurement container equipped with a measurement system MS-H3115, and the temperature in the container was kept at 20° C. and measured. The measurement conditions at this time are MAX 5PEED 7gOrpm
, RAMP UP TIME 120sec.

MESUREMENT POINT 20ports.

Figure 2 shows a flow curve obtained by measuring k4.

As the shear rate was increased, the shear stress increased rapidly from 85001/s, indicating a dilatancy phenomenon. In the present invention, the shear rate immediately before the shear stress suddenly increases is used as an index of the likelihood of dilatancy occurring. In other words, the shear rate at this time is DI, and in Magic 4, DI is [1
It was 50017s. Furthermore, since the maximum shear rate of Rheomat 115 is 200,001/s, anything higher than this is indicated as 20,000 or more.

Samples No. 8 to No. 13 were obtained by crushing any of the samples No. 1 to No. 7, but when comparing the physical properties after crushing, D2 became finer after treatment. , BET and Dl remained almost unchanged. For this reason, the degree of aggregation A showed a clear decrease, indicating that the degree of aggregation had decreased considerably. Along with this, η decreased and DI showed a remarkable increase, clearly indicating that the slurry had improved. For example, Nα9 is obtained by crushing NO.4, and compared to No. 4, A is 4.0 to 2.
．． 2, η decreased, and DI increased more than three times from 65,001/s to more than 200,001/s. The flow curves of Nα4 and Nα9 at this time are shown in FIGS. 2 and 3. The slope connecting each point on the flow curve and (0,0) is
These correspond to the viscosity at each point, but compared to the shear rate at constant ηΔIII of about 201/s, it can be said that these are viscosities in a considerably higher speed range. As can be seen from Figures 2 and 3, No. 9 has a lower slope and lower viscosity. In addition, the DI was 2QQO01/s or more, and the flow curve showed that it was a good slurry.

Scanning electron micrographs of Na4 and patient 9 are shown in Figure 1(a).
, (b). This was taken with a JEOL scanning electron microscope JSM-T300, and the magnification is 50.
00 times. (a) is a photograph showing the crystal structure of NQ4 (conventional product) with a high degree of aggregation, and (b) is a photograph showing the crystal structure of N11L9 (product of the present invention) with a low degree of aggregation. It can also be seen from this photograph that the fine particles of aluminum hydroxide No. 9 were well crushed without breaking the primary particles.

Next, when A and DI from Nα1 to Nα13 are plotted, the result is as shown in FIG. It can be seen that as A becomes lower, DI becomes higher, and when A approaches 3.0, it rises rapidly. In other words, when A was 3.0 or less, the dilatancy phenomenon became almost undetectable, and the slurry showed a significant improvement.

(Example 2) N[L3. No, 6. kg, NO, I
D when the solid concentration of O is increased to 68% and 70%
Table 2 shows the changes in I.

The measurement method in Table Dl is the same as in Example 1, but the method for adjusting the solid concentration is as follows: 300 g of sample and Aron A20U 30
m1 was fixed and the amount of ion-exchanged water was changed, that is, 68
%, 111m1.70%, 99m1
And so.

As shown in Table 2, by increasing the solid concentration,
Although the DI shows a decreasing tendency, the rate of decrease is almost the same regardless of the DI at 65%.If the degree of agglomeration A is 3.0 or less, the DI will decrease even if the solid concentration is 70%. I was able to maintain Bo-1=H+1/S or higher.

(Example 3) Two samples No. 1 and Nα10 of Example 1 were made into slurry, the crushing time was changed, and the crushing effect was confirmed.

The slurry had a solids concentration of 65%, and the formulation was the same as the D I 1 Tll I fixed time of Example 1. As for the crushing method, Matsushita Electric's National Mixer MX 120 with the rotation speed adjusted to 4,500 rpm was used, and the stirring time was 0. 5. 10/15/20 level was set. The results are shown in Table 3.

(Left below) #j Standard method, same as in the case of the slurry in Example 1.

Based on the results in Table 3, D2. D.

Figure 5(a) shows the changes in A and DI.

(b), (C), and (d), and FIG. 6 shows the relationship between A and DI.

As can be seen from Figure 5, as the stirring time elapses, the agglomerated grains are broken down and D2 becomes finer, but Dl, which is represented by BET, hardly changes, and the primary grains are broken down. I found out that it wasn't. At this time, the degree of agglomeration A, which is an index of the crushing effect, also became low (as D2 decreased), indicating that the particles were being crushed.

On the other hand, the DI increased with the passage of time and reached 20,000 or more, and as the crushing progressed, an improvement in the dilatan sealing layer was observed. Furthermore, the relationship between A and DI in FIG. 6 almost coincided with the curve shown in FIG. 4.

(Example 4) The sample of NO.1 of Example 1 was over-pulverized, and changes in its characteristics were investigated. As for the pulverization method, first, 200 g of sample No. 1, 88 ml of ion-exchanged water, and 1 ml of dispersant were added.
Aron A-20U diluted to 0% was mixed, and the solid concentration was 6.
A 5% slurry was prepared. Add this to 1 10φ alumina ball.
400 g of alumina magnetic 0.8. The mixture was placed in a Q-pot and wet-pulverized using a Kawasaki Heavy Industries ■S Mo, 6-vibration mill. The grinding time is 0. There were five levels: 5, 10, 15, and 20 hours. The results of this grinding are shown in Table 4.

The measurement method in Table 4 is the same as in Example 1, but for η,
For items that could not be measured using rotor No. 3, other rotors were used.

Based on Table 4, D2. Figure 7 shows the changes over time in Dl, A, η, and DI. As can be seen from FIG. 7, D2 became finer as the grinding time increased, but BET and Dl did not remain constant unlike the grinding in Example 3; BET increased and Dl became finer as the grinding time increased. Ta. this is,
It can be seen that it is in a state of over-pulverization and the primary grains are broken.

The standard viscosity η at this time decreased once after 5 hours, but showed a rapid thickening phenomenon after 10 hours. The decrease in η after 5 hours is probably due to crushing being the main cause and the influence of over-grinding being still small. This thickening phenomenon due to over-grinding was also confirmed in the flow curves for different grinding times shown in Figure 8. Looking at the viscosity at each point as explained in Example 1, the viscosity is 5.10.15.
It was found that the viscosity increased in the order of 20 hours. However, although the viscosity increased, the dilatancy phenomenon did not occur in the crushed product. In addition, the one with a grinding time of 10 hours has been modified to have an A of 2.9 and a DI of 200001/s or more, but due to excessive grinding, the standard viscosity η is 0.5.
It showed a considerable increase in viscosity. This kind of slurry is
This does not meet the purpose of the present invention.

[Effect] When fine-grained aluminum hydroxide with a degree of agglomeration of 3.0 or less and a standard viscosity of 5 voids or less is made into an aqueous slurry, dilatancy phenomenon extremely occurs even at high shear rates and high concentrations. low viscosity even in high shear rate ranges. In addition, since there are almost no agglomerated particles, the smoothness and gloss are further improved when coated on the surface of paper, making it particularly useful as a coating slurry for paper.

Furthermore, when kneaded into plastic, a low-viscosity kneaded product is obtained, and a well-dispersed product is obtained, resulting in a high-strength composite material. For this reason, it is also useful as a filler for plastics.

[Brief explanation of the drawing]

FIG. 1 is an electron micrograph showing the crystal structure of fine-grained aluminum hydroxide of a conventional product (a) and a product of the present invention (b). Figure 2 shows the results of Rheomat 11 using N (L4) fine particle aluminum hydroxide with a high degree of agglomeration as a slurry with a solid concentration of 65%.
This is the flow curve measured in No. 5. Figure 3 shows Rheomat 115, a slurry of Nα9 fine particles of aluminum hydroxide with a low degree of agglomeration, at a solid concentration of 65%.
This is the flow curve measured at . FIG. 4 shows the relationship between the degree of cohesion and DI. FIG. 5 shows changes in characteristics over time during wet crushing treatment using a mixer. FIG. 6 shows the relationship between the degree of agglomeration and DI after wet crushing in a mixer. FIG. 7 shows the change in characteristics over time during wet pulverization using a vibrating mill. FIG. 8 shows a flow curve over time during wet pulverization using a vibrating mill.

Claims (1)

[Claims] 1. Fine particle aluminum hydroxide, characterized in that the degree of aggregation expressed by the ratio of the average secondary particle diameter to the average primary particle diameter is 3.0 or less, and the standard viscosity is 5 poise or less.