Spindle-shaped calcium carbonate dispersible ultrafine particles as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of calcium carbonate materials, and relates to fusiform calcium carbonate dispersible ultrafine particles as well as a preparation method and application thereof. The fusiform calcium carbonate dispersible ultrafine particle has a specific surface area of 5.5-9.5 m < 2 > / g, D50 of 2.20-2.80 [mu] m, D97 of 5.20-6.50 [mu] m, an oil absorption value of 32-45g DOP / 100g and a sedimentation volume of 4.5-7.8 mL / g, has the characteristics of narrow particle size distribution, large sedimentation volume and good covering power, is free of additives, is particularly suitable for manufacturing high-grade cigarette paper, and has a wide market application prospect. Meanwhile, the invention also provides a preparation method of the calcium carbonate, the method can be used for preparing narrow-distribution superfine calcium carbonate at a relatively high concentration, the product index is stable and controllable, and the method has certain economic advantages and is suitable for industrial large-scale production and application.

Description

Technical Field

[0001] The invention discloses spindle-shaped dispersible ultrafine calcium carbonate particles, a preparation method and application thereof. The calcium carbonate product can be used for manufacturing cigarette paper, and belongs to the technical field of calcium carbonate inorganic salt special materials. Background Art

[0002] Cigarette paper is a special paper with controlled air permeability and combustibility. By adding special calcium carbonate into the fiber to match its burning speed and facilitate the shaping of the ash, it is a widely used technical means in high-end cigarette paper. Special calcium carbonate becomes the key material, with a specific surface area greater than 5m 2 / g (primary particles less than 1.0μm) and moderately agglomerated spindle or plum blossom-shaped crystal structures are two essential technical characteristics of this specialty calcium carbonate. The so-called high specific surface area requires that the spindle-shaped primary particles be smaller than 1.0μm, ensuring the development of breathable micropores in the cigarette paper while providing opacity (the hiding power of calcium carbonate). Moderate agglomeration can reduce calcium carbonate loss during the papermaking process and provide ash formation strength. Generally, the largest calcium carbonate agglomerates in high-end cigarette paper are preferably less than 7μm.

[0003] According to the research of Cai Xiaoming et al. (Cai Xiaoming, Morphological characteristics and optimization control of calcium carbonate for high-end cigarette paper, Paper Chemicals, Issue 5, 2010), the use of spindle-shaped narrow-distribution calcium carbonate (narrow particle size distribution calcium carbonate PCC is considered to be one of the important characteristics of PCC for cigarette paper; and PCC for high-end cigarette paper has a relatively complete spindle-shaped crystal form, uniform and neat particle size, and the particle size is mainly distributed in the range of 1 to 2 μm, without large particles) can achieve the purpose of high-end cigarette paper calcium application. At the same time, they also studied this spindle-shaped agglomerate narrow-distribution calcium carbonate The preparation method uses citric acid as an auxiliary agent, stirs and carbonizes in a 5% low-concentration calcium hydroxide emulsion, and the starting temperature is 45-65°C to obtain spindle-shaped narrow-distribution calcium carbonate. Mizhuang Lime's Japanese patent application JPA198590818 discloses a method using cubic nano-calcium carbonate as a seed crystal and aging it for one week, then adding calcium hydroxide for secondary carbonization. Under a certain seed crystal ratio, spindle-shaped calcium carbonate of 0.1-1.0 μm can be prepared. Shiraishi Industry first conducted a calcium hydroxide emulsion test in its JPS5373498A application. Mechanical grinding pretreatment is performed, and then the initial concentration of calcium hydroxide is adjusted to 3-10%wt and carbonized at 5-30℃ to obtain spindle-shaped calcium carbonate of 0.1-1.0μm. Obviously, the particles obtained by these two patented methods are too small and not suitable for cigarette paper. Public information similar to the method applied by Shiraishi Industry JPS5373498A is also available in the Chinese patent application CN113104878A of East China University of Science and Technology, a method for preparing light calcium carbonate for cigarette paper. From the analysis of existing technical solutions, the concentration of calcium hydroxide in the existing technology is generally maintained at 4-8 %wt, using secondary carbonization of nano-calcium seeds or auxiliary technical means such as additives, which leads to low calcium carbonate production capacity and high economic cost pressure. In order to increase production capacity, it is relatively difficult to prepare spindle-shaped narrow-distribution calcium carbonate that meets both the conditions of primary crystals less than 1.0μm and aggregates less than 7μm under high calcium hydroxide concentration conditions. In other words, there is still a lack of advanced and applicable technical solutions to control small particle agglomeration and obtain spindle-shaped calcium carbonate with good dispersion. In order to overcome the above technical defects, the technical solution of the present invention is proposed. Summary of the Invention

[0004] The purpose of the present invention is to solve the above technical problems and to provide a technical solution for a spindle-shaped dispersible ultrafine calcium carbonate particle and a preparation method thereof, wherein the spindle-shaped dispersible ultrafine calcium carbonate particle is prepared at a relatively high calcium hydroxide concentration.

[0005] The technical solutions adopted by the present invention to achieve the above-mentioned purpose are as follows:

[0006] The present invention provides a spindle-shaped dispersible ultrafine calcium carbonate particle, wherein the spindle-shaped dispersible ultrafine calcium carbonate particle has a specific surface area of ​​5.5 to 9.5 m 2 / g,D 50 2.20~2.80μm, D 97 5.20-6.50 μm, oil absorption value 32-45 gDOP / 100 g, sedimentation volume 4.5-7.8 mL / g. By adopting the technical solution, the hiding power of calcium carbonate is further improved.

[0007] Preferably, the primary particle size of the spindle-shaped dispersible ultrafine calcium carbonate particles is not greater than 1.0 μm.

[0008] The present invention also provides a method for preparing the above-mentioned spindle-shaped dispersible ultrafine particles of calcium carbonate, wherein the method comprises continuously introducing a gas containing carbon dioxide into a calcium hydroxide emulsion having a concentration of 10 to 14% by weight and a temperature of 31 to 33° C., and carbonizing the solution under additional shearing and stirring conditions until the pH drops to a target value. The reaction is terminated to obtain the spindle-shaped dispersible ultrafine particles of calcium carbonate.

[0009] By adopting the technical solution, under shear conditions, while satisfying the concentration and temperature conditions, the size of the spindle-shaped agglomerates can be effectively controlled and good repeatability can be obtained. However, at a relatively low calcium hydroxide emulsion concentration, for example, about 7% wt, the same shear conditions cannot achieve the purpose of the invention. Below the temperature range, the BET value of the product exceeds the required range of the present invention, and more oval and spherical particles appear in the product. At an initial temperature above the range of the invention, more slender needles or rods appear, and the BET value is also low, which does not meet the purpose of the invention and the calcium carbonate of the present invention cannot be obtained.

[0010] Preferably, the preparation method of the calcium hydroxide emulsion is not particularly limited, and an existing method of lime digestion can be adopted, and there is no particular limitation on the lime; after digestion, the concentration of the lime milk is adjusted with water and adjusted to within a specified temperature range, and then the carbonization process can be carried out.

[0011] Preferably, the carbon dioxide content and gas flow rate of the carbon dioxide-containing gas have negligible effects on the reaction structure. The gas may be pure CO2 gas, or a gas containing 1% to 99% carbon dioxide by volume; more preferably, the carbon dioxide content is 24% to 40% by volume; the gas may be purified lime kiln gas; and more preferably, the gas flow rate of the carbon dioxide-containing gas is 1.0 to 1.62 L / min / L of emulsion. This solution has certain economic advantages and is more easily applicable to current production lines.

[0012] Preferably, the shear stirring can be carried out in different ways: 1) by setting a shear device inside the reaction device, that is, setting a shear device inside the reactor or bubble tower, to carry out shear stirring, and / or, 2) by setting a shear circulation pump outside the reaction device to carry out shear stirring.

[0013] More preferably, the annular gap of the shearing device or shear circulation pump does not exceed 2.0 mm, and / or the relative linear velocity of the moving and stationary disks forming the annular gap is 18 to 25 m / s. By adopting the technical solution of the present invention, the product particle size can be better controlled with lower energy consumption. However, at lower shear speeds, the agglomerate size of the product can easily exceed the aforementioned inventive range, affecting the hiding power of the calcium carbonate. At higher shear speeds, energy consumption is excessively high, and the tips of the spindle-shaped particles may be broken, which may affect the bulk and hiding power of the cigarette paper when used, hindering its application in papermaking.

[0014] Preferably, the reaction is terminated after carbonization until the pH drops to no more than 6.5. More preferably, after carbonization to a pH value no more than 6.5, carbonization is continued for 5-10 minutes to further ensure complete carbonization. More preferably, after the carbonization reaction is completed, conventional post-processing steps are performed to obtain calcium carbonate dry powder. More preferably, the post-processing steps may include at least one of filtration, drying, crushing, and screening.

[0015] The present invention also provides an application of the spindle-shaped dispersible ultrafine calcium carbonate particles in the field of papermaking.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention's spindle-shaped dispersed ultrafine calcium carbonate particles have primary particles smaller than 1.0 μm, and the aggregated particles exhibit a narrow particle size distribution, large sedimentation volume, and excellent hiding power. The absence of additives makes them particularly suitable for the production of high-end cigarette paper and possesses broad market application prospects. The present invention's method for preparing spindle-shaped ultrafine calcium carbonate particles enables the production of narrowly distributed ultrafine calcium carbonate at relatively high concentrations. The product's performance indicators are stable and controllable, offering significant economic advantages and suitability for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Attachment Figure 1 This is a scanning electron microscope photograph of the calcium carbonate sample of Example 1.

[0019] Attachment Figure 2 This is a scanning electron microscope photo of the calcium carbonate sample of Example 2.

[0020] Attachment Figure 3 This is a scanning electron microscope photo of the calcium carbonate sample of Example 3.

[0021] Attachment Figure 4 The scanning electron microscope photograph of the calcium carbonate sample of Example 4 is shown.

[0022] Attachment Figure 5 This is a scanning electron microscope photo of the calcium carbonate sample of Example 5.

[0023] Attachment Figure 6 This is a scanning electron microscope photograph of the calcium carbonate sample of Comparative Example 1.

[0024] Attachment Figure 7 This is a scanning electron microscope photo of the calcium carbonate sample of Comparative Example 2.

[0025] Attachment Figure 8 This is a scanning electron microscope photo of the calcium carbonate sample of Comparative Example 3.

[0026] Attachment Figure 9 This is a scanning electron microscope photo of the calcium carbonate sample of Comparative Example 4. DETAILED DESCRIPTION

[0027] In order to better clarify and understand the purpose, process scheme and advantages of the present invention, the technical scheme and implementation method of the present invention are further clearly, completely and in detail described below through specific examples and in combination with the accompanying drawings. It should be noted that the embodiments described in the present invention are implemented on the premise of the technical scheme of the present invention, and detailed implementation methods and specific operating processes are given, but they are only part of the embodiments of the present invention, not all of the embodiments. The specific implementation methods described are limited to illustrating and explaining the present invention and do not limit the present invention. Based on the embodiments in the present invention, all other implementation methods obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] The experimental methods and conditions used in the embodiments of the present invention are conventional methods and conventional conditions unless otherwise specified. The materials, reagents, instruments, devices, etc. used in the embodiments are conventional substances or equipment known to those skilled in the art and can be obtained from commercial channels or prepared by conventional methods unless otherwise specified. The reaction conditions embodied in the summary of the invention of the present invention are all capable of achieving the described reactions and obtaining products with the desired effects. Due to space limitations, some examples are listed below to further illustrate the advantages of the technical solutions of the present invention.

[0029] In the present invention, the specific surface area of ​​calcium carbonate is tested by weighing 0.2-0.5 g of calcium carbonate powder into a quartz sample tube, measuring the nitrogen adsorption amount using a JW-BK400 specific surface area and pore size analyzer (Beijing Jingwei Gaobo Science and Technology Co., Ltd.), and calculating the specific surface area (BET) of the calcium carbonate product. 2 / g).

[0030] Calcium carbonate particle morphology scanning electron microscopy test method: take a dry powder sample, spray the powder on a single crystal silicon substrate, and use low-temperature plasma gold spraying for 50 seconds to prepare a scanning electron microscope sample. Use PHENOMPRO (PHENOM-World, the Netherlands) to observe and photograph at different magnifications to obtain SEM photos.

[0031] Determination of calcium carbonate content, pH value, sedimentation volume, oil absorption value, and particle size distribution: in accordance with the "Analysis Method of Calcium Carbonate" standard GB / T 19281-2014, 3.3 Determination of Calcium Content, 3.18 Determination of pH, 3.22 Determination of Sedimentation Volume, 3.20 Determination of Oil Absorption, 3.26.2.2 Laser Particle Size Analyzer Method.

[0032] Determination of hiding power of calcium carbonate:

[0033] Binder, polyvinyl alcohol (PVA) brand 1788, chemically pure.

[0034] Coating sample preparation: Weigh 17.4 g of PVA into 180 g of distilled water in a waterbath at 60°C and stir until the PVA is completely dissolved. Weigh 20 g of dry calcium carbonate (calcium carbonate powder passed through a 320-mesh sieve) and add it to the stirred PVA solution. Simultaneously, add 2 ml of anhydrous ethanol (to eliminate foaming). Continue stirring for 30 minutes after adding the calcium carbonate to prepare the coating sample.

[0035] Apply the test paint sample to black and white test cardboard with a scraper to a thickness of 200 μm. After scraping, let it sit at room temperature for 1 hour, then place it in an 80°C oven to dry for 1 hour. Then, let it sit at room temperature for 30 minutes before testing it in a whiteness meter. Test the whiteness Wwi and blackness Wbi at three points (three times) to obtain the average whiteness Ww and blackness Wb. Calculate the contrast ratio:

[0036] Contrast ratio = Ww ÷ Wb × 100%

[0037] Peel off the coating film from the cardboard and use a thickness gauge to measure the average thickness h of the coating film in μm. Calculate the relative contrast ratio:

[0038] Relative contrast ratio = contrast ratio / (h / 30)

[0039] Where 30 is the probable thickness or design thickness of the coating film. The relative contrast ratio is used to characterize the hiding power of calcium carbonate.

[0040] Example 1

[0041] 4L of calcium hydroxide emulsion is packed into the 6L stainless steel flat-bottomed cylindrical reactor with an internal diameter of 180mm, with a calcium hydroxide concentration of 13.96%wt and a temperature of 31.5°C. The center of the cylinder is inserted and a homogenizing emulsifier (Shanghai Moxuan Industrial Co., Ltd. manufactures MS-B25 type, with a rotating speed of 7000-28000rpm adjustable, a shear annular gap of 1.5mm, and a maximum linear velocity of 25m / s) is fixed. The homogenizing emulsifier is opened and adjusted to a shear linear velocity of 22m / s. Simultaneously, gas having a carbon dioxide volume concentration of 26.8% is introduced from the reactor near the bottom, with a gas flow of 5.6L / min and a gas flow rate of 1.4L / min / L emulsion. The system is stirred until pH reaches 6.5. Ventilation is continued for 5min, ventilation is stopped, and shear stirring is stopped.

[0042] The carbonized calcium carbonate suspension was taken out from the reactor and filtered. The filter cake was placed in a 100°C forced air drying oven and dried for 4 hours. It was crushed with a powder grinder and sieved through a 200-mesh sieve to obtain calcium carbonate dry powder. The calcium carbonate content was tested to be 98.54%. Other performance indicators are shown in Table 1. An electron microscope photo of calcium carbonate is attached. Figure 1 From the electron microscope photos, it can be seen that the crystal shape is spindle-shaped, and no agglomerates larger than 6μm are seen in the field of view.

[0043] Example 2

[0044] The same as Example 1, except that the concentration of the calcium hydroxide emulsion is 10.02%wt, the temperature is 31.8°C, the shear linear velocity is 19m / s, the concentration of carbon dioxide is 37.5%V, the gas flow rate is 4.0L / min, and the corresponding gas flow rate is 1.0L / min / L emulsion.

[0045] The calcium carbonate content is 98.72%. The other properties are shown in Table 1. The electron microscope photo of calcium carbonate is attached. Figure 2 From the attached Figure 2 As can be seen from the photos, the vast majority of primary crystal particles are spindles, and the maximum particle size of the particle clusters is less than 5μm.

[0046] Example 3

[0047] A stainless steel flat-bottomed carbonizing cylinder with an inner diameter of 150 mm and a height of 1500 mm was loaded with 18 L of calcium hydroxide emulsion (12.3% wt calcium hydroxide content) at a temperature of 31.7° C. A flange was connected to a side hole 300 mm from the bottom of the cylinder. The side hole flange was mounted with a shearing emulsifier (DE300-1.5 manufactured by Nantong Claire Mixing Equipment Co., Ltd., with a shear annular gap of 1.7 mm, a rotating disk outer diameter of 110 mm, and a maximum linear speed of 30 m / s). The shear head of the emulsifier was positioned exactly at the center of the carbonizing cylinder. The emulsifier was turned on and the speed was set to a shear linear speed of 24.0 m / s. Simultaneously, gas with a carbon dioxide concentration of 36.8% was introduced from near the bottom of the carbonizing cylinder at a gas flow rate of 19.0 L / min, corresponding to a gas velocity of 1.06 L / min / L of emulsion, until the system pH reached 6.5. Aeration was continued for 5 minutes, then aeration was stopped, and the emulsifier was stopped.

[0048] The calcium carbonate suspension was discharged from the carbonization cylinder and filtered. The filter cake was placed in a 100°C forced air oven and dried for 4 hours. It was crushed by a powder beater and sieved through a 200-mesh sieve to obtain calcium carbonate dry powder. The calcium carbonate content was 98.63%. The other properties are shown in Table 1. The electron microscope photo of the calcium carbonate sample is attached. Figure 3 .From the attached Figure 3 As can be seen from the photos, most of the primary particle crystals are spindle-shaped, and the maximum size of the agglomerate particles is less than 7μm.

[0049] Example 4

[0050] The same as Example 3, except that the concentration of the calcium hydroxide emulsion is 11.13%wt, the temperature is 32.9°C, the carbon dioxide concentration in the gas is 31.8%V, the gas flow rate is 22.0L / min, and the corresponding gas velocity is 1.22L / min / Lemulsion.

[0051] The calcium carbonate content was 98.66%, and the other properties are shown in Table 1. Electron microscope photos of the calcium carbonate sample are attached. Figure 4 .From the attached Figure 4 As can be seen from the photos, most of the primary particle crystals are spindle-shaped, and the maximum size of the agglomerate particles is less than 7μm.

[0052] Example 5

[0053] The same as Example 3, except that the calcium hydroxide concentration was 14.00% wt, the temperature was 31.2° C., the shear linear velocity was set to 18.0 m / s, the carbon dioxide concentration was 24.1% V, the gas flow rate was 29.0 L / min, and the corresponding gas velocity was 1.61 L / min / L emulsion.

[0054] The calcium carbonate content was 98.54%. The other properties are shown in Table 1. The electron microscope photo of the calcium carbonate sample is attached. Figure 5 From the attached Figure 3 As can be seen from the photos, most of the primary particle crystals are spindle-shaped, and the maximum size of the agglomerate particles is less than 7μm.

[0055] Comparative Example 1

[0056] Same as Example 1, except that the starting temperature of the lime milk is 34.5°C. Figure 6 , from the attached Figure 6 As can be seen in the photograph, the primary crystals are mostly needle-shaped, and the maximum size of the aggregated particles is approximately 9 μm. The calcium carbonate content is 98.56%. Other properties are shown in Table 1.

[0057] Comparative Example 2

[0058] The same as Example 2, except that the shearing speed is 15.0 m / s. The calcium carbonate content of the calcium carbonate sample is 98.73%, and the other properties are shown in Table 1. The electron microscope photo of the calcium carbonate sample is shown in the attached Figure 7 , it can be seen that there is an obvious parallel structure of spindle-shaped crystals, and its original particle morphology deviates from the spindle. It can be seen that at a low shear rate, it has deviated from the basic requirements of the invention product.

[0059] Comparative Example 3

[0060] The same as Example 3, except that the concentration of the calcium hydroxide emulsion is 7.15%wt and the temperature is 32.8°C. The calcium carbonate content of the obtained calcium carbonate sample is 98.64%, and the other properties are shown in Table 1. The electron microscope photo of calcium carbonate is shown in the attached Figure 8 From the attached Figure 8 As can be seen from the photos, most of the primary particle crystals are spindle-shaped, but the maximum size of the agglomerate particles is close to 9μm, and the large particles in the agglomerates account for a large proportion. This may be due to the low concentration and low viscosity of the system, resulting in insufficient shear.

[0061] Comparative Example 4

[0062] The same as Example 3, except that the starting temperature of the calcium hydroxide emulsion is 30.2°C. The calcium carbonate content of the obtained calcium carbonate sample is 98.58%, and the other properties are shown in Table 1. The electron microscope photo of the calcium carbonate sample is shown in the attached Figure 9 , a large number of obvious oval and spherical primary particles can be seen.

[0063] Table 1 Performance indicators of calcium carbonate dry powder obtained in each embodiment and comparative example

[0064]

[0065] It can be seen from the comparison of the relative contrast ratios of the examples and the comparative examples in Table 1 that the relative contrast ratios of the examples are significantly higher than those of the comparative examples, which indicates that the covering power of the calcium carbonate of the examples is significantly better than that of the calcium carbonate products of the comparative examples; from the comparative analysis of the key indicators of the dispersibility of the particle agglomerates D50 and D90 data, the D97 of the examples is generally smaller than that of the comparative examples. In other words, the dispersibility of the examples is significantly better than that of the comparative examples.

[0066] From the comparative analysis of the narrow distribution test data of each agglomerate particle listed in Table 1, whether using a 4L stirred tank or an 18L carbonization cylinder, within the process conditions listed in the technical solution of the present invention, the desired narrow particle agglomerate structure size of the present invention is obtained.

[0067] The above-described embodiments are only preferred solutions of the present invention and are not intended to limit the present invention in any form. Other variations and modifications are possible without exceeding the technical solutions described in the claims.

Claims

1. A spindle-shaped dispersible ultrafine particle of calcium carbonate, characterized in that: The spindle-shaped calcium carbonate dispersed ultrafine particles have a specific surface area of ​​5.5 to 9.5 m 2 / g,D 50 2.20~2.80μm, D 97 5.20~6.50μm, oil absorption value 32~45gDOP / 100g, sedimentation volume 4.5~7.8mL / g.

2. A spindle-shaped dispersible ultrafine particle of calcium carbonate according to claim 1, characterized in that, The primary particle size of the spindle-shaped dispersible ultrafine calcium carbonate particles is no more than 1.0 μm.

3. A method for preparing spindle-shaped dispersible ultrafine particles of calcium carbonate according to claim 1 or 2, characterized in that: The method comprises the following steps: continuously introducing a gas containing carbon dioxide into a calcium hydroxide emulsion having a concentration of 10 to 14% by weight and a temperature of 31 to 33° C., and carbonizing the emulsion under additional shearing and stirring conditions until the pH drops to a target value. The reaction is terminated to obtain spindle-shaped dispersed ultrafine calcium carbonate particles.

4. The method for preparing spindle-shaped dispersible ultrafine calcium carbonate particles according to claim 3, wherein: The carbon dioxide-containing gas is pure CO2 gas, or a gas in which the volume percentage of carbon dioxide is 1%-99%.

5. The method for preparing spindle-shaped dispersible ultrafine particles of calcium carbonate according to claim 4, wherein: The carbon dioxide volume ratio of the carbon dioxide-containing gas is 24% to 40%, and / or the flow rate of the carbon dioxide-containing gas is 1.0 to 1.62 L / min / L emulsion.

6. The method for preparing spindle-shaped dispersible ultrafine particles of calcium carbonate according to claim 3, wherein: 1) by providing a shearing device inside the reaction apparatus to perform shear stirring, and / or, 2) by providing a shearing circulation pump outside the reaction apparatus to perform shear stirring.

7. A method for preparing spindle-shaped dispersible ultrafine particles of calcium carbonate according to claim 6, characterized in that: The maximum annular gap of the shearing device or shear circulation pump does not exceed 2.0 mm, and / or the relative linear speed of the moving disk and the stationary disk constituting the annular gap is 18 m / s to 25 m / s.

8. A method for preparing spindle-shaped dispersible ultrafine calcium carbonate particles according to claim 3, characterized in that: The reaction is terminated by carbonization until the pH drops to no more than 6.

5.

9. The method for preparing spindle-shaped dispersible ultrafine particles of calcium carbonate according to claim 8, wherein: After carbonization to a pH value no higher than 6.5, continue carbonization for 5-10 minutes.

10. Use of the spindle-shaped dispersible ultrafine particles of calcium carbonate according to claim 1 or 2 or the spindle-shaped dispersible ultrafine particles of calcium carbonate prepared according to the preparation method according to any one of claims 3 to 9 in the field of papermaking.

Images