JPH02129019A - Decomposition retarder for lamellar calcium carbonate composite - Google Patents

Abstract

PURPOSE:To improve stability of a lamellar CaCO3 composite by using a specific polyacrylic acid(salt) as decomposition retarder. CONSTITUTION:An acrylic acid(salt) is first polymerized in the presence of a polymerization catalyst (e.g., sodium persulfate) to prepare a decomposition retarder consisting of a polyacrylic acid(salt) 1000-50000 in number-average molecular weight and 1-3 in dispersion degree D (weight-average molecular weight/number-average molecular weight). Thence, 100 pts.wt. of a lamellar CaCO3 composite of the formula (x is 0.5-1.0; y is 0.7-1.5) 0.2-2mum in mean granular size and 3-20 in aspect ratio is incorporated with 0.3-9 pts.wt. of the above decomposition retarder.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a decomposition inhibitor for platy calcium carbonate complexes and its use. To explain in detail, 2C
A decomposition inhibitor for a complex that has a plate-like form represented by the composition formula of aC03.xCa(OH)2.yH2O, a plate-like composite composition, and a method for suppressing the decomposition of a plate-like complex using the inhibitor. It is related to.

(Prior Art) General precipitated calcium carbonate is commercially available in various shapes such as cubic, spindle-like, columnar, needle-like, and chain-like. It is widely used as a white pigment in the rubber, plastic, and paint industries.

However, when calcium carbonate of the above shape was used as a paper coating pigment, properties such as gloss and smoothness were insufficient compared to plate-shaped kaolin clay, which is used in the largest amount as a pigment.

For this reason, there has been a strong desire to develop plate-like calcium carbonate having quality characteristics such as excellent gloss and smoothness in addition to the excellent whiteness and ink absorption properties of precipitated calcium carbonate. Therefore, in order to satisfy these requirements, 2CaCO3
A plate-shaped calcium carbonate complex has been proposed, which is represented by the composition formula: xCa (OH)2yH2O.

However, such plate-like composites have the disadvantage that they are susceptible to chemical changes and decomposition during secondary treatment steps such as drying, storage in an aqueous medium, pigment manufacturing steps, and the like. However, when a chemical change occurs, it decomposes into calcium carbonate and slaked lime, and the plate-like form is destroyed, resulting in the loss of the excellent quality characteristics of the plate-like calcium carbonate composite.

(Problems to be Solved by the Invention) Therefore, an object of the present invention is to provide a novel decomposition inhibitor for platy calcium carbonate complexes and a method for using the same. Another object of the present invention is 2CaC03.xCa(
Provided is a decomposition inhibitor for a platy calcium carbonate complex represented by the composition formula of OH)2 yH2O, a platy calcium carbonate composite composition, and a method for inhibiting the decomposition of a platy calcium carbonate complex using the inhibitor. There is a particular thing. Still another object of the present invention is to provide excellent whiteness and ink absorption of conventional precipitated calcium carbonate and excellent gloss and smoothness of kaolin clay when used as a coating pigment for papermaking, for example. A decomposition inhibitor that improves the chemical and morphological instability of platy calcium carbonate complexes that have excellent quality characteristics, a platy calcium carbonate composite composition, and a platy calcium carbonate composite using the inhibitor. The object of the present invention is to provide a method for inhibiting decomposition.

(Means for solving the problem) These items have a number average molecular weight of 1. 000-50
．． 000 and a polyacrylic acid or a salt thereof having a dispersity D (weight average molecular weight/number average molecular weight) of 1 to 3.
2 yH2O (wherein, X is 0.5 to 1.0
This is achieved by a plate-shaped calcium carbonate complex decomposition inhibitor represented by the composition formula (where y is 0°7 to 1.5).

These items are 2CaC03・xCa(OH)2
- Per 100 parts by weight of a plate-like calcium carbonate complex represented by the composition formula yH2O (wherein, X is 0.5 to 1.0 and y is 0.7 to 1.5), The decomposition inhibitor has a number average molecular weight of 1,000 to 50,000 and a dispersity D (weight average molecular weight/number average molecular weight) of 1 to 50.000.
This can also be achieved by a plate-shaped calcium carbonate composite composition containing polyacrylic acid or a salt thereof in the range of 0.3 to 9 parts by weight.

These items are 2CaCO3 x Ca (OH)2
・For 100 parts by weight of a plate-like calcium carbonate complex represented by the composition formula of yH2O (wherein, X is 0.5 to 1.0, and y is 0.7 to 1.5) As a decomposition inhibitor, the number N1'i and the average molecular weight are 1,000 to 50.
,000 and a dispersity D (weight average molecular weight/number average molecular weight) of 1 to 3 is 0.3 to 9! T1
This can also be achieved by a method for suppressing the decomposition of a plate-like calcium carbonate complex, which is characterized in that the composition is blended at a ratio of 1.5 parts.

(Function) The plate-like calcium carbonate complex in the present invention has the following compositional formula I 2CaCO3.xCa (OH)2 -YH2O (1)
(However, in the formula, X is 0.5 to 1.0, and y
is 0.7 to 1.5), and the average particle size is 0.2
~2 μm 1 preferably 0.3 to 1 μm 1 aspect ratio 3
-2O, preferably 4-8.

The complex can be prepared, for example, by mixing slaked lime milk with a carbon dioxide-containing gas in a reaction vessel under certain conditions, e.g.
~15g/100ml, preferably 6-10g/100
It is produced by carbonation reaction at a concentration of m1.

When this plate-shaped calcium carbonate composite is stored in a closed container with a solid content of 13% by weight, for example, decomposition occurs in an aqueous medium as shown in FIG. Such decomposition becomes faster as the storage temperature increases. Note that the decomposition rate α is expressed by the following formula (■).

α=Z/Zo (II) (where, Z is the strongest line intensity of calcium carbonate (calcite) in X-ray diffraction, and Zo is calcium carbonate (calcite) in X-ray diffraction when completely decomposed. Calcite) has the highest line strength). In addition, in Figure 1, curve A is 6
Curve B shows the change over time at 0°C, curve C shows the change over time at 70°C, and curve C shows the change over time at 80°C.

Polyacrylic acid or a salt thereof used as a decomposition inhibitor in the present invention can be used in either an acid form or a salt form, but the salt form is particularly preferred since it has better decomposition inhibiting ability. As a salt form of polyacrylate,
Partially neutralized products or completely neutralized products of polyacrylic acid with monovalent metals, divalent metals, ammonia, organic amines, etc. can be mentioned.

-Valent metals include sodium, potassium, lithium, etc.; divalent metals include calcium, magnesium, zinc, etc.; and organic amines include monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine. Alkylamines such as , monoisopropylamine, diisopropylamine, and butylamine; alkanolamines such as monoethanolamine, jetanolamine, triethanolamine, monoisopropanolamine, and dimethylethanolamine; and pyridine. However, sodium, which is available at low cost, is particularly preferred.

The polyacrylic acid or its salt used in the present invention has a number average molecular weight of 1°000 to 50,000 and a dispersity D
It is necessary that (weight average molecular weight/number average molecular weight) be within the range of 1 to 3. If either the number average molecular weight or the degree of dispersion is outside the above range, the ability to inhibit decomposition is insufficient. Preferably, the number average molecular weight is 2.00
It ranges from 0 to 10.000, and the degree per minute ranges from 1 to 2.5. Here, the number average molecular weight and weight average molecular weight are calculated using aqueous GPC (2 columns: G-3000pw + G-4) using polyethylene glycol as a standard substance.
000pW%)'--manufactured by Thor Co., Ltd.).

In the present invention, polyacrylic acid or a salt thereof has the above formula I
0.0% per 100 parts by weight of the plate-like calcium carbonate composite represented by It is used in an amount of 3 to 9 parts by weight, preferably 0.7 to 7 parts by weight. That is, if the amount used is less than 0.3 parts by weight, it is difficult to suppress decomposition, and even if the amount used exceeds 9 parts by weight, an improvement in the decomposition suppressing effect commensurate with the increased amount cannot be expected.

Among polyacrylic acids or salts thereof used in the present invention, polyacrylic acid may be obtained by polymerizing acrylic acid, and polyacrylates may be obtained by neutralizing polyacrylic acid or polymerizing acrylates.

In this case, the polymerization method is not particularly limited and any known method may be adopted, but the polymerization conditions must be appropriately selected so that the number average molecular weight and degree of dispersion of the obtained polyacrylic acid or its salt are within the above ranges. Must be. For example, in the case of aqueous polymerization, persulfates such as sodium persulfate and potassium persulfate,
(Bi)sulfite, hydrogen peroxide, 2,2'-azobis(2
-amidinopropane) hydrochloride, 4.4' -azobis-
It can be produced by a conventional method using a water-soluble azo compound such as 4-cyanovaleric acid as a polymerization catalyst, and alcohols such as methanol and isopropanol, ethers such as tetrahydrofuran and dioxane, benzene,
In the case of polymerization in organic solvents such as aromatic hydrocarbons such as xylene and toluene or ketones such as methyl ethyl ketone and methyl isobutyl ketone, organic peroxides such as benzoyl peroxide, lauroyl peroxide, and peracetic acid, azobis It can be produced by a conventional method using an oil-soluble azo compound such as isobutyronitrile or 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) as a polymerization catalyst. It is also possible to use sulfur-containing molecular ffi modifiers such as 2-mercaptoethanol, thioglycerol, thiomalic acid, and dodecylmercaptan, and copper-containing molecular weight modifiers such as formic acid steel and copper acetate. Further, the polyacrylic acid or its salt used in the present invention is preferably a homopolymer of acrylic acid or its salt, but if necessary, it may be copolymerized with acrylic acid or its salt within a range that does not impair the effects of the present invention. It is of course possible to copolymerize other possible monomers. Examples of other copolymerizable monomers include methacrylic acid, crotonic acid, or their monovalent metals,
Unsaturated products such as partially or completely neutralized products with divalent metals, ammonia, organic amines, etc. (nocarboxylic acid monomers, maleic acid, fumaric acid, itaconic acid, silaconic acid or their monovalent metals, divalent Unsaturated dicarboxylic acid monomers partially or completely neutralized with valent metals, ammonia, organic amines, etc.; ) Hydrophobic monomers such as acrylic esters, styrene, 2-methylstyrene, vinyl acetate, vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acid, 2-
Acrylamido-2-methylpropanesulfonic acid, sulfoethyl (meth)acrylate, sulfopropyl (meth)acrylate, 2-hydroxysulfopropyl (meth)acrylate, sulfoethylmaleimide, 3-allyloxy-2-hydroxypropanesulfonic acid or one thereof Unsaturated sulfonic acid monomers partially or completely neutralized with valent metals, divalent metals, ammonia, organic amines, etc., amide monomers such as (meth)acrylamide, t-butyl (meth)acrylamide, etc. Hydrophobic monomers such as (meth)acrylic acid ester, styrene, 2-methylstyrene, vinyl acetate, 2-hydroxylethyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate Acrylate, allyl alcohol, polyethylene glycol monoallyl ether, polypropylene glycol monoallyl ether, 3-methyl-3-buten-1-ol (
isoprenol), polyethylene glycol monoisobrenol ether, polypropylene glycol monoisobrenol ether, 3-methyl-2-buten-1-ol (prenol), polyethylene glycol monobrenol ether, polypropylene glycol monoprenol ether, 2- Methyl-3-buten-2-ol (
isoprene alcohol), polyethylene glycol monoisoprene alcohol ether, polypropylene glycol monoisoprene alcohol ether, N-methylol(meth)acrylamide, glycerol mono(meth)
Hydroxyl group-containing unsaturated monomers such as acrylate, glycerol monoacrylic ether, and vinyl alcohol; cationic monomers such as dimethylaminoethyl (meth)acrylate and dimethylaminopropyl (meth)acrylamide;
Nitrile monomers such as (meth)acrylonitrile, phosphorus-containing monomers such as (meth)acrylamide methanephosphonic acid, (meth)acrylamide methanephosphonic acid methyl ester, and 2-(meth)acrylamide-2-methylpropanephosphonic acid. , ethylene, propylene, 1-butene, isobutylene, α-amylene, 2-methyl-1-butene,
Examples include α-olefin monomers such as 3-methyl-1-butene (α-isoamylene), 1-hexene, and 1-heptene. However, when using these other monomers, it is preferable to use less than 30 mol% of the total monomer components in order to fully exhibit the characteristics of the present invention.

In order to suppress the decomposition of the platy calcium carbonate complex represented by formula I using the decomposition inhibitor made of polyacrylic acid or a salt thereof, it is usually necessary to add This is carried out by blending the decomposition inhibitor described above. The solid content concentration of the composite at this time is not particularly limited and can be within a wide range, but depending on the purpose, it is preferably 10 to 75% by weight, particularly 30 to 65% by weight. In particular, when blending at a high concentration (for example, 25% by weight or more), dehydration is performed using a press filter or the like to form a cake, and the decomposition inhibitor is added in an amount of 0.3 to 9 parts by weight per 100 parts of solid content. The decomposition inhibitor is coated on the surface of the plate-shaped composite by stirring and mixing using a high-speed stirrer or the like. Alternatively, the decomposition inhibitor may be added to the aqueous suspension of the plate-shaped calcium carbonate complex, and after decomposition inhibition treatment is performed using a high-speed stirrer or the like, dehydration treatment may be performed using a press filter or the like. Furthermore, this decomposition inhibiting treatment may be carried out by adding a decomposition inhibitor to the plate-shaped calcium carbonate composite obtained or when used as a pigment, but in the manufacturing process of the composite, an aqueous suspension It is most preferable to add it to the body or to the cake obtained by concentrating it.

Note that the effect of the decomposition inhibitor is not impaired even if it is used in combination with a surfactant or a known inorganic pigment dispersant such as sodium pyrophosphate or sodium hexametaphosphate.

(Example) Next, the present invention will be specifically explained with reference to Examples.
The present invention is not limited to these examples. In addition, in the following Reference Examples, Examples, and Comparative Examples, unless otherwise specified, all "parts" mean 1 part of mff, and all "%" mean % by weight.

Reference Example 1 2.4 parts of industrial quicklime was put into 17.6 parts of water at 40°C, and slaked for 15 minutes with stirring. Thereafter, it was sieved using a classifier to take out the slaked lime milk that passed 74 μm, and water was added thereto to obtain 20 parts of slaked lime milk with a slaked lime concentration of 10%. This is a reaction vessel (inner diameter 345 mta, height 360 mta)
+nra, internal volume 40 g) and stirred (paddle-shaped blade, diameter 100 mm).

After cooling to 10° C. (500 rpm), 100% carbon dioxide gas was introduced at a rate of 25 g/ml. The relative carbon dioxide gas blowing speed at this time was 12. 5ml/m1n 1z Ca
It was (OH)2. After continuing cooling for at least 15 minutes from the start of the reaction and maintaining the liquid temperature below 15°C, the electrical conductivity was 4. The blowing of carbon dioxide gas was stopped at 5ms/cm. When the reaction product was observed with a scanning electron microscope, it had a polygonal plate shape with an average width of 063 μm and thickness of 0.08 μm. In addition, as a result of diffraction X-ray measurement of this product,
Almost no peaks for calcium carbonate and slaked lime were observed, and thermogravimetric analysis showed that the composition formula was 2CaCO:+ ・0
．． 630a (OH)2 .0.86H2O.

Reference Example 2 327.4 parts of deionized water was charged into a 1 g glass round bottom flask equipped with a thermometer, a reflux condenser, and a gas inlet tube with a sintered filter at the tip. While bubbling a small amount of air into the liquid through the gas introduction tube, 571.4 parts of a 35% aqueous sodium acrylate solution and 101.2 parts of a 35% aqueous sodium bisulfite solution were each dropped from separate dropping nozzles over a period of 2 hours. In addition, the polymerization temperature was 25°C from beginning to end.
The temperature was controlled to be ℃. After the dropwise addition was completed, the same temperature was maintained for 30 minutes to complete the polymerization. The obtained polyacrylate (1), which is sodium polyacrylate, had a weight average molecular weight ff of 11,800 and a number average molecular weight of 1,500 (D value 1.2). The results were as shown in the column of Example 1 in Table 1.

Reference Examples 3 to 8 Polyacrylic acid (salt) (2) to
(7) was obtained. These polyacrylic acids (salts) (2) ~
The number average molecular weight and D value of (7) are Table 1 Example 2~
It was as shown in column 7.

Comparative Reference Examples 1 to 5 Comparative polymers (1) to (5) were obtained according to the method of Reference Example 2. The number average molecular weights and D values of these comparative polymers (1) to (5) were as shown in the Comparative Examples 1 to 5 columns of Table 2.

Example 1 2CaCO3・0.63Ca(OH)2 obtained in Reference Example 1
- A 13% aqueous suspension of a plate-like calcium carbonate composite represented by 0.86H2O was dehydrated using a press filter to obtain an aqueous plate-like composite with a solid content of 60%. 100 parts of this plate-like composite were placed in a processing container (inner diameter φ60 mm, height 15 mm).
0 mm), 2.0 parts of a decomposition inhibitor consisting of the polyacrylate (1) obtained in Reference Example 2 was added as a solid content to the plate-shaped composite, and a Daysilver stirrer (stirring blade diameter Decomposition suppression treatment was carried out at 200 rpm for 15 minutes with a diameter of 40 mm. The aqueous plate-like composite subjected to the decomposition-inhibiting treatment was placed in a sealed container and kept at 60° C. for 48 hours in a constant temperature bath.

After 48 hours, the sealed container was removed from the thermostatic chamber, the aqueous plate-like calcium carbonate complex was vacuum dried, and diffraction X-ray measurement was performed.
The decomposition inhibition rate [β] was calculated from the measurement results. The decomposition suppression rate α is expressed by the following formula.

β-[1-(Z/Zo) ko ×100Z zX
Strongest line intensity (cps) of calcium carbonate (calcite) determined from a ray diffraction diagram Zo: Strongest line intensity (cps) of calcium carbonate (calcite) determined from an X-ray diffraction diagram when completely decomposed. is the number of counts per second.

Next, using this decomposition suppression rate β, the decomposition suppression ability was determined using the four-level evaluation shown below.

Decomposition suppression ability ◎: 90≦β≦100 Same as above O near 0≦β<90 Same as above △: 50≦β<70 Same as above X: Less than 50 Decomposition suppression ability is shown in Table 1. The plate-like composite that underwent this decomposition inhibition treatment had a high decomposition inhibition rate, and when its morphology was observed with a scanning electron microscope (20,000x magnification),
The plate-like form (Fig. 7) was the same as the form immediately after manufacture (Fig. 6). Furthermore, as is clear from the X-ray diffraction diagram shown in Figure 2, the composite immediately after manufacture has the strongest line intensity of 178 cps when 2θ is 29.4 degrees. IIC (manufactured by Rigaku Denki Co., Ltd.)], whereas the treated one had a
The strongest line intensity when θ was 29.4 degrees was 182 cpS, and the decomposition suppression rate was 95.4%.

Examples 2 to 8 Using the aqueous plate-like composite with a solid content of 60% used in Example 1, polyacrylic acid (salt) (2
) to (7) in the predetermined amounts shown in Table 1, and
Decomposition suppression treatment was carried out in the same manner as in 1, and the decomposition suppression ability was determined.

The results are shown in Table 1.

Examples 9 to 13 Polyacrylates (1) to (1) obtained in Reference Example 2 were added to a 13% aqueous suspension of the plate-like composite obtained in Reference Examples 2 to 6.
The decomposition inhibitor consisting of 5) was added in a predetermined amount shown in Table 1 as a solid content to 100 parts by weight of the plate-shaped composite, and the mixture was stirred at 2O. 0
0rpn+, decomposition suppression treatment was performed for 15 minutes. Thereafter, it was dehydrated using a press filter to obtain an aqueous plate-like composite having a solid content of 60%, and the aqueous plate-like composite was placed in a closed container and kept at 45° C. for 48 hours in a constant temperature bath. After 48 hours, diffraction X-ray measurement was performed in the same manner as in Example 1 to determine the decomposition suppressing ability. The results are shown in Table 1.

Comparative Example 1 2CaCO3・0.63Ca(OH)2 obtained in Reference Example 1
O. A 13% concentrated aqueous suspension of a platy calcium carbonate complex represented by 86H2O was dehydrated with a press filter,
It was made into an aqueous plate-like composite with a solid content of 60%. 100 parts of this plate-like composite were placed in a processing container (inner diameter φ60 mm, height 150 mm).
), and the comparative polymer (1) was placed in Comparative Reference Example 1.
Adding a predetermined amount of a decomposition inhibitor shown in Table 2,
2000 with Daysilver stirrer (stirring blade diameter φ40mm)
Decomposition suppression treatment was carried out at rpm s l for 5 minutes.

The aqueous plate-like composite subjected to the decomposition-inhibiting treatment was placed in a sealed container and maintained at 60°C in a constant temperature bath. After 48 hours, it was taken out, and the decomposition inhibition rate β was calculated in the same manner as in Example 1 to determine the decomposition inhibition ability. The results are shown in Table 2.

The decomposition inhibition rate of the plate-like composites subjected to this decomposition inhibition treatment was low, and when the morphology was observed with a scanning electron microscope (magnification: 20.000x), a spindle-like morphology was confirmed in addition to the plate-like morphology ( Figure 8). Also, as is clear from Figure 4, 2θ
When the temperature was 29.4 degrees, the strongest line strength was 142Ocps, and the gas decomposition suppression rate was 63.7%.

Comparative Examples 2 to 5 Comparative polymers (2) to (2) obtained in Comparative Reference Examples 2 to 5 using the 60% solids aqueous plate composite used in Example 1.
5) A predetermined amount shown in Table 2 was added, and the decomposition suppression treatment was performed in the same manner as in Example 1 to determine the decomposition suppression ability. The results are shown in Table 2.

Comparative Examples 6 to 10 Polyacrylates (1) to 1 obtained in Reference Examples 2 to 6 were added to an aqueous suspension of the plate-like composite obtained in Reference Example 1 at a concentration of 13% by weight.
(5) was added in the predetermined amount shown in Table 2, and Examples 9 to 1
Decomposition suppression treatment was performed in the same manner as in 3, and after dehydration using a press filter, an aqueous plate-like composite with a solid content of 60% was obtained. This plate-like composite was placed in a sealed container and kept at 45° C. for 48 hours in a constant temperature bath. After 48 hours, diffraction X-ray measurement was performed in the same manner as in Example 1 to determine the decomposition suppressing ability. The results are shown in Table 2.

Comparative Example 11 The 60% solids content aqueous plate-like composite used in Example 1 was placed in a sealed container as it was without using a decomposition inhibitor, and was kept in a constant temperature bath for 6 days.
It was held at 0°C for 48 hours. After 48 hours, it was taken out and subjected to diffraction X-ray measurement in the same manner as in Example 1 to determine the decomposition suppressing ability. The results are shown in Table 2. The morphology of the plate-like composite without this decomposition-inhibiting treatment was observed using a scanning electron microscope (magnification: 2O).
．． When observed at a magnification of 1,000 times, the plate-like morphology changed to a mixture of plate-like and spindle-like forms (Figure 9). Also, the fifth
As is clear from the figure, the strongest line intensity when 2θ is 29.4 degrees is 2543 cps, and the decomposition suppression rate is 35.0%.
Met.

/ Table 1 Table 2 (Effects of the Invention) As described above, the present invention has a number average molecular weight of i, oo
0 to 50.000 and a dispersity D (weight average molecular weight/number average molecular weight) of 1 to 3.
・Since it is used as a decomposition inhibitor for the plate-like calcium carbonate complex represented by the composition formula of yH2O,
The plate-shaped composite containing this decomposition inhibitor is extremely stable, and the problem of decomposition due to chemical changes is solved even when the temperature rises, and the excellent quality characteristics of the plate-shaped calcium carbonate composite are fully maintained. By demonstrating this, it becomes possible to use it for applications in various fields. For example, when used as a coating pigment for paper manufacturing, improvements in whiteness, gloss, smoothness, ink absorption, etc. can be achieved, and excellent quality can be obtained. It is also promising as a filler for rubber and plastics, a paint pigment, etc.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the aging time and decomposition rate of a plate-shaped calcium carbonate composite, Figure 2 is an X-ray diffraction diagram of the plate-shaped composite immediately after production, and Figure 3 is a decomposition inhibitor according to the present invention. Figure 4 is an X-ray diffraction diagram of a plate-like composite when a polymer outside the scope of the present invention is used, and Figure 5 is an X-ray diffraction diagram of a plate-like composite when a polymer outside the scope of the present invention is used. FIG. 6 is a scanning electron micrograph showing the morphology of the plate-like composite immediately after production, and FIG. 7 is when the decomposition inhibitor according to the present invention is used. Figure 8 is a scanning electron micrograph showing the morphology of a plate-like composite when a polymer outside the scope of the present invention is used; FIG. 9 is a scanning electron micrograph showing the morphology of a plate-like composite when no decomposition inhibitor is used.

Claims (3)

[Claims] (1) 2CaCO_3, which is characterized by being made of polyacrylic acid or a salt thereof having a number average molecular weight of 1,000 to 50,000 and a dispersity D (weight average molecular weight/number average molecular weight) of 1 to 3. xCa(OH)_2・yH_2
O (wherein, x is 0.5 to 1.0, and y
is 0.7 to 1.5). (2) 2CaCO_3・xCa(OH)_2・yH_2
O (wherein, x is 0.5 to 1.0, and y
is 0.7 to 1.5) per 100 parts by weight of a plate-like calcium carbonate composite having a composition formula of A plate-shaped calcium carbonate composite composition comprising polyacrylic acid or a salt thereof having an average molecular weight/number average molecular weight of 1 to 3 in a proportion of 0.3 to 9 parts by weight. (3) 2CaCO_3・xCa(OH)_2・yH_2
O (wherein, x is 0.5 to 1.0, and y
is 0.7 to 1.5) and has a number average molecular weight of 1,000 to 50,000 and a dispersity D ( 1. A method for inhibiting decomposition of a plate-like calcium carbonate composite, comprising blending polyacrylic acid or a salt thereof having a weight average molecular weight/number average molecular weight of 1 to 3 in a proportion of 0.3 to 9 parts by weight.