JPS636493B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a highly concentrated and low viscosity precipitated aqueous calcium carbonate dispersion with good suspension stability. Precipitated calcium carbonate has traditionally been widely used as a filler for rubber and plastics and as an extender pigment in paints, depending on its particle size and shape, and in the paper manufacturing industry as a coating pigment or filler for paper making. There is. In Japan, this precipitated calcium carbonate is produced by passing carbon dioxide gas through an aqueous suspension of calcium hydroxide to precipitate calcium carbonate, and then using a filter press or other dehydrator to produce a calcium carbonate solid content of at least 50% by weight. We can dehydrate the water to a maximum of
Alternatively, it is further dried and supplied to the market as a powder product. The water-containing product obtained by subjecting the precipitated calcium carbonate to a dehydrator takes the form of a hard cake (hereinafter referred to as "cake") when the solid content concentration exceeds 50% by weight, and has no fluidity and is transported through a pipe. It is a very difficult muddy substance such as. This is thought to be due to the formation of a thick hydrated layer strongly adsorbed on the fine particles of calcium carbonate, which immobilizes a fairly large amount of water, which inevitably reduces the amount of free water that contributes to the fluidity of the system. Cake-like hydrated calcium carbonate has far fewer secondary agglomerates than one that has been dried and pulverized into powder, so it can be used in fields where precipitated calcium carbonate can be used in aqueous systems, such as coated paper. When used in easily dispersible extender pigments such as industrial pigments, water-based paints, and inks, cakes with less secondary aggregates are used to improve the physical properties of these products such as opacity, gloss, and printability. It is preferable to use hydrated calcium carbonate. However, when used in such applications, the non-flowable, hard cake-like hydrated calcium carbonate requires a great deal of manual or mechanical effort during the loading and unloading of containers during shipping or use, as well as during the pigment preparation and pigment dispersion processes. Although it requires energy, if it could be converted into a high- and low-concentration calcium carbonate aqueous dispersion with fluidity and good suspension stability, it would be possible to use it with simple operations, and it would also be possible to use it as a paper coating. There are great advantages in terms of the use of hydrated calcium carbonate, such as the ability to increase the concentration of calcium carbonate pigments in paints and inks.
Particularly in the paper manufacturing industry, there is an urgent need to develop coating colors with higher concentrations as a means of reducing the drying cost of coated paper and obtaining coated paper with good gloss on the coated paper surface. ,
Low viscosity aqueous calcium carbonate dispersions are desired. Conventionally, such high concentration and low viscosity calcium carbonate aqueous dispersions with good suspension stability have most commonly used dispersants such as phosphoric acids such as sodium hexametaphosphate and sodium pyrophosphate, lignosulfonates, Anionic surfactants such as naphthylsulfonate, polycarboxylic acids such as citric acid, malic acid, or their salts, polymeric polycarboxylic acids such as acrylic acid polymers, and copolymers of acrylic acid and maleic acid. Alternatively, it is known that sodium salts, ammonium salts, and the like are added to an aqueous calcium carbonate dispersion system. However, these methods are effective to some extent for relatively large particle size calcium carbonate with little hydration layer formation on the particle surface of precipitated calcium carbonate particles, but they are effective for colloidal precipitated calcium carbonate with an average particle size of 1 μm or less. However, it cannot be said to be effective enough to obtain an aqueous calcium carbonate dispersion that exhibits free-flowing properties at a solid content of 60% by weight or more, and also has the disadvantage of requiring a large amount of dispersant. Furthermore, the amount of precipitated calcium carbonate aqueous dispersions exhibiting the free-flowing properties required in recent fields such as paints and paper manufacturing has reached 70% by weight or more, and this requirement can be met using the above-mentioned known dispersants. It is nearly impossible to produce an aqueous calcium carbonate dispersion.
In addition, a large amount of the above-mentioned known dispersant was added, and 70
Even if it were possible to produce a precipitated calcium carbonate aqueous dispersion that exhibits free-flowing properties of more than 1% by weight, it would thicken in a short period of time and change into a pudding-like or even sponge-like dispersion, and the dispersion would not be suitable for actual use. It becomes something you don't do. Furthermore, even if a free-flowing aqueous calcium carbonate dispersion could be used for a short period of time by adding a large amount of dispersant as described above for paper coating, the excess dispersant would have an adverse effect on the coating. Scratching and beading are likely to occur during processing, and the resulting coated paper may have uneven coating or a decrease in gloss. The present invention eliminates these drawbacks and provides a highly concentrated aqueous dispersion of precipitated calcium carbonate that is sufficiently peptized with a very small amount of dispersant and is stable with low viscosity over a long period of time. In a precipitated calcium carbonate aqueous dispersion consisting of precipitated calcium carbonate, water, and a high molecular weight polycarboxylic acid or its alkali salt, Sr salt or
Ba salt or both are added,
It is characterized by being prepared by stirring and mixing. In the present invention, colloidal precipitated calcium carbonate, polymeric polycarboxylic acid dispersant and Sr salt or
The reason why a dispersion consisting of a Ba salt or a combination of both has a remarkable effect is not yet clear, but the main reason is thought to be as follows. That is, regarding the dispersibility improvement and viscosity reduction effect of high molecular weight polycarboxylic acids or their alkali salts in calcium carbonate aqueous dispersions, generally speaking, high molecular weight polycarboxylic acids or their alkali salts form on the surface of calcium carbonate particles with a hydration layer. It is thought that it adsorbs and assists in the dispersion of calcium carbonate particles through charge and steric hindrance, preventing aggregation and reducing viscosity. In that case, if Sr salt or Ba salt or both are used in combination with a high molecular weight polycarboxylic acid or its alkali salts, the adsorption of the high molecular weight polycarboxylic acid or its alkali salts on the surface of calcium carbonate particles with a hydration layer can be prevented. Compared to the case of using high-molecular polycarboxylic acid or its alkali salt alone without Sr salt or Ba salt, adsorption by replacing the hydration layer is carried out sufficiently, and even if a small amount is added, it is effectively adsorbed in a dense state. Therefore, it is thought that free water increases and the viscosity lowering effect becomes more pronounced. The colloidal precipitated calcium carbonate according to the present invention (usually with an average particle size of 1 μm or less) is carbon dioxide produced by the so-called carbonation method obtained by the reaction of a calcium hydroxide aqueous suspension with carbon dioxide gas. Calcium, calcium carbonate produced by the so-called calcium chloride method obtained by adding an aqueous solution of sodium carbonate or ammonium carbonate to an aqueous calcium chloride solution, and precipitated calcium carbonate produced by any other method can be used. The polymeric polycarboxylic acids or alkali salts thereof used in the present invention include acrylic acid polymers, acrylic acid and acrylate copolymers, acrylic acid and maleic acid copolymers, maleic acid and styrene, vinyl acetate, ethylene, butylene. , copolymers with monomers such as isobutylene and butadiene, etc., with a molecular weight of 500 to 100,000, preferably 1,000 to
50,000 and the carboxylic acid group in this polymer is at least
Examples include polymers containing 15% or more, preferably 20% or more, and water-soluble alkali salts thereof such as alkali metal salts, ammonium salts, and amine salts. The amount of these polymeric polycarboxylic acids or their alkali salts to be used varies depending on the calcium carbonate used or the viscosity of the aqueous dispersion to be finally obtained, but the average particle size of calcium carbonate in the present invention A content of 0.1 to 5% by weight is sufficient to obtain an aqueous dispersion with a low viscosity of 1 μm or less. Furthermore, examples of the Sr salt or Ba salt in the present invention include carbonates, sulfates, chlorides, hydroxides, oxides, and the like. The amount of Sr salt, Ba salt, or both added must be 0.005% or more, preferably 0.01% or more, based on the calcium carbonate constituting the aqueous dispersion. If the amount of both of them is less than 0.005%, it is difficult to confirm the effect of their addition, and the results are not very different from those obtained by adding a high molecular weight polycarboxylic acid or an alkali salt thereof alone. In addition, these Sr salts or Ba
The salt or both can be added at the time of producing a calcium carbonate cake, a high-molecular polycarboxylic acid, or an alkali salt thereof to produce a calcium carbonate aqueous dispersion, but it is more preferable to add the calcium carbonate aqueous dispersion. The precipitated calcium carbonate used in the above method may be added before or during the carbonation process, or added to the calcium carbonate suspension obtained after the carbonation process is completed. is preferred. Generally used stirring devices for producing the aqueous calcium carbonate dispersion of the present invention are sufficient, and include, for example, ribbon mixers, kneaders, ball mills, high-speed dispersers, and homogenizers. The calcium carbonate aqueous dispersion obtained in this way has a low viscosity despite the high calcium carbonate solid content concentration of 50 to 75% by weight, and is a stable suspension that does not become pudding-like or spongy even if left for a long period of time. The present invention makes it possible for the first time to provide a new industrially useful composition that has good properties and is not available in the past. The calcium carbonate aqueous dispersion of the present invention imparts excellent mechanical and optical properties to paper, rubber, latex, water-based synthetic resins, paints, inks, adhesives, etc., and also has very good operability. It can be used as an easily dispersible filler or pigment, but
Depending on the purpose and use, the calcium carbonate aqueous dispersion of the present invention may be used as a base, and other fillers, pigments,
It can also be used as an easily dispersible mixed dispersion by appropriately mixing other necessary additives in the form of powder or water dispersion, which is useful industrially as one of the methods of using the present invention. be. Examples will be specifically described below. Examples 1 to 5, Comparative Example 1 30 containing calcium hydroxide at a concentration of 145 g/
The carbon dioxide concentration in milk of lime 180℃ prepared at
20% by volume of carbon dioxide gas was introduced at a rate of 1500/hr, and the carbonation reaction was carried out while stirring the reaction solution at a stirring rate of 360 rpm. 16 hours after the start of the reaction, the pH was 7.0 and the temperature was
The carbonation reaction was stopped at 70°C. The calcium carbonate obtained in this way has a particle size of 0.2 to 0.4 μm (the size of a primary particle according to an electron microscope field),
It was calcium carbonate with a field of view (hereinafter referred to as an electron micrograph field). After the carbonation reaction had stopped, the calcium carbonate aqueous suspension was divided into 6 equal parts and transferred to 6 containers.
Sr salt and Ba salt were added to all but one of them as shown in Table 1, stirring was continued for 1 hour, and then each calcium carbonate aqueous suspension was dehydrated using a filter press. Approximately 71% press cake was obtained. After adding a dispersant [a sodium salt of a copolymer of acrylic acid and maleic acid (molar ratio: 100/30) with a molecular weight of 14,000] to the press cake of calcium carbonate obtained in this way, a high-speed laboratory disper (special machine) was added. A calcium carbonate aqueous dispersion was prepared using a dissolver-type stirring blade manufactured by Kakogyo Co., Ltd., blade diameter 50 mm, rotation speed 4000 rpm (the same applies hereinafter). Table 1 shows the names of the additives, the addition rates of Sr and Ba, the addition rate of the dispersant, the solid content concentration and viscosity changes of the calcium carbonate aqueous dispersion. From the results in Table 1, the products of the present invention (Examples 1 to 5) show better results than Comparative Example 1, which does not use Sr salt or Ba salt.
It is clear that the addition of Sr or Ba salts is essential for the preparation of low viscosity calcium carbonate aqueous dispersions. Comparative Example 2 30 containing calcium hydroxide at a concentration of 145g/
The carbon dioxide concentration in milk of lime prepared at 30°C is 20°C.
% carbon dioxide gas is conducted at a rate of 500/hr,
The carbonation reaction was carried out while stirring the reaction solution at a stirring speed of 360 rpm, and 12 hours after the start of the reaction, the pH was 7.2 and the temperature was 65℃.
The carbonation reaction was stopped. The calcium carbonate thus obtained had a particle size (electron micrograph field) of 0.2 to 0.4 μm. After the carbonation reaction was terminated, the calcium carbonate aqueous suspension was dehydrated using a filter press to obtain a press cake of about 71%. After adding a dispersant [a sodium salt of a copolymer of acrylic acid and maleic acid (molar ratio: 100/80) with a molecular weight of 13,000] to the press cake of calcium carbonate obtained in this way, a high-speed laboratory disper (special A calcium carbonate aqueous dispersant was prepared using a calcium carbonate aqueous dispersant (manufactured by Kika Kogyo Co., Ltd.). Addition rate of dispersant,
Table 2 shows the solid content concentration and viscosity changes of the calcium carbonate aqueous dispersion. Examples 6, 7, 8 Milk of lime used in Comparative Example 2 was added as shown in Table 2.
An aqueous calcium carbonate dispersion was prepared in the same manner as in Comparative Example 2, except that the carbonation reaction was performed after adding Sr salt or Ba salt at the addition rate shown in Table 2. Table 2 shows the names of the additives, the addition rates of Sr and Ba, and the solid content concentration and viscosity changes of the calcium carbonate aqueous dispersion. In addition, all the calcium carbonates obtained in Examples 6 to 8 have a diameter of 0.2 to 0.4 μm (electron micrograph field of view).
It was calcium carbonate with a particle size of . Table -
From the results of 2, the products of the present invention (Examples 6 to 8) show better results than Comparative Example 2, and the addition of Sr salt or Ba salt makes it possible to prepare a calcium carbonate aqueous dispersion with high concentration and low viscosity. It is clear that this is essential. Comparative Example 3 The amount of additive SrCO ₃ used in Example 6 was reduced to 1/30.
Carbonation was performed in the same manner as in Example 6, except for changing to , and an aqueous calcium carbonate dispersion was prepared in the same manner. The calcium carbonate thus obtained had a particle size of 0.2 to 0.4 μm (electron micrograph field of view). In Comparative Example 3, Table 3 shows the solid content concentration and viscosity changes of Sr, dispersant, and calcium carbonate aqueous dispersion with respect to calcium carbonate in the calcium carbonate aqueous dispersion.
Although 0.0033% SrCO ₃ is added as Sr to the calcium carbonate in the calcium carbonate aqueous dispersion, the results in Table 3 show that there is not much difference from the results of Comparative Example 2.
The effect of adding SrCO ₃ has not been confirmed.

【table】

【table】

[Table] Examples 9 to 11, Comparative Example 4 12 containing calcium hydroxide at a concentration of 120 g/
Carbon dioxide concentration in milk of lime adjusted to 180 °C is 25
% by volume of carbon dioxide gas was introduced at a rate of 20,000/hr for 15 minutes, then the same carbon dioxide gas was introduced at a rate of 2,000/hr, and the carbonation reaction was carried out while stirring the reaction solution at a stirring rate of 360 rpm. PH 10 hours after starting the reaction
7.2, the carbonation reaction was stopped at a temperature of 60°C. The calcium carbonate obtained in this way is 0.07 to 0.1 μm.
The particles had a particle size (electron micrograph field of view) of . Divide the calcium carbonate aqueous suspension into four equal parts,
Sr salt and Br salt were added to all but one of them as shown in Table 4, stirred for 1 hour, and then each calcium carbonate suspension was dehydrated using a filter press to approx. Obtained 61% press cake. This press cake is coated with a dispersant [acrylic acid,
After adding an ammonium salt of a copolymer of itaconic acid and styrene sulfonic acid (molar ratio: 100/22/3) with a molecular weight of 10,000, an aqueous calcium carbonate dispersion was prepared in the same manner as in Example 1. Table 4 shows the names of the additives, the addition rates of Sr and Br, and the solid content concentration and viscosity changes of the calcium carbonate aqueous dispersion. From the results in Table 4, it can be seen that the present invention (Examples 9 to 11) can be applied even when it is difficult to use slurry in the past (Comparative Example 4).
It can be understood that this makes it possible to prepare a stable aqueous dispersion of calcium carbonate with high concentration and low viscosity.

[Table] Examples 12 to 17 Calcium carbonate aqueous dispersions were prepared in the same manner as in Example 1, except that the dispersant used in Example 1 was changed to the dispersant shown in Table 5. Table 5 shows the additive name, Sr addition rate, composition of the dispersant used, dispersant addition rate, solid content concentration and viscosity change of the calcium carbonate aqueous dispersion.

[Table] Comparative Examples 5 to 10 In Examples 12 to 17, calcium carbonate aqueous dispersions were prepared in the same manner as in Examples 12 to 17, except that SrCO ₃ was not used. Table 6 shows the composition of the dispersant used, the addition rate of the dispersant, the solid content concentration and viscosity change of the calcium carbonate aqueous dispersion.

[Table] Application Example 1 A paper coating test was conducted using each of the aqueous calcium carbonate dispersions produced in Example 6 and Comparative Example 2. First, calcium carbonate 51.15% by weight, starch (MS4600) 3.5% latex (JSR0616) 5.0% by weight
A coating liquid consisting of 0.35% by weight of dispersant and 40% by weight of water was prepared, and this was coated on one side of course paper with a 64g/m ² basis weight at a rate of 11g/m ² using a coating rod. A coated paper was obtained by supercalendering at 70° C. and passing the paper three times at a nip pressure of 50 kg/cm. The results are shown in Table-7.

[Table] The evaluation of each test was performed by the following method. 1 60rpm Low-Vis: Measured with a B-type viscometer at 25℃ 2 4400rpmHi-Vis: Hercules viscometer at 25℃
Measured with 3 White paper gloss: Gloss meter 75-75° measurement 4 Print gloss: Same as above 5 Opacity: Hunter whiteness meter measurement 6 Surface strength: IGT printability tester measurement From the above coated paper test results As is clear, the calcium carbonate aqueous dispersion obtained by the method of the present invention is confirmed to have good properties for paper coating.

Claims (1)

[Scope of Claims] 1. In a precipitated calcium carbonate aqueous dispersion consisting of precipitated calcium carbonate, water, and a high molecular weight polycarboxylic acid or its alkali salt, Sr salt or Ba
1. A precipitated calcium carbonate aqueous dispersion, which is prepared by adding a salt or both and stirring and mixing. 2. The aqueous dispersion according to claim 1, characterized in that the amount of Sr or Ba or both added is 0.005% or more based on calcium carbonate.