A kind of low-fluorescence calcium carbonate for papermaking and its preparation method and application

Abstract

The present invention provides a low-fluorescence calcium carbonate for papermaking and a preparation method and application thereof, belonging to the field of preparation of inorganic non-metallic mineral powders. The preparation method is as follows: mixing calcium carbonate ore with grinding aid No. 1 and ball milling to obtain calcium carbonate powder; removing grinding aid No. 1 from the calcium carbonate powder and mixing with water to obtain pre-grinding slurry, mixing the pre-grinding slurry with grinding aid No. 2 and grinding to obtain calcium carbonate slurry. The above calcium carbonate powder and calcium carbonate slurry are used for papermaking, and the obtained paper has no fluorescent effect, which effectively solves the problem that there are many sources of fluorescent substances in existing calcium carbonate products and the paper production standards cannot be met.

Description

Technical Field

[0001] The invention relates to the field of preparation of inorganic non-metallic mineral powders, and in particular to low-fluorescence calcium carbonate for papermaking and a preparation method and application thereof. Background Art

[0002] Paper is closely related to daily life and can be seen everywhere in production and life. After years of development, my country's papermaking industry has a wide variety of paper. Now in the food field, paper tableware has replaced some plastic tableware, such as paper straws, paper packaging boxes, etc. The connection between paper and food is getting closer and closer, and higher requirements are also placed on the safety of paper. In the early days, it was revealed that paper towels contained a large amount of fluorescent brighteners. It is now stipulated that napkins cannot contain fluorescent brighteners, because the fluorescent brighteners in napkins contain groups such as benzene and naphthalene, which are easily absorbed by the mucous tissue of the human digestive system and are not easy to be decomposed, posing a risk of cancer. With the improvement of people's living standards, people have a stronger awareness of health and higher requirements for paper products. Some paper companies also have higher corporate standards, requiring strict control of papermaking raw materials.

[0003] Calcium carbonate is the largest filler used in papermaking. Many paper companies include the detection of fluorescent substances in the technical indicators of products from upstream calcium carbonate suppliers. Not all raw materials used in papermaking will produce fluorescence. The generation of fluorescence must meet certain conditions, which is related to the molecular structure of the substance itself. Generally, substances with characteristics such as conjugated π bonds and rigid planar structures in the molecule are prone to fluorescence. Most of the calcium carbonate used in papermaking on the market is heavy calcium carbonate produced by physical grinding. It is a common phenomenon to detect fluorescent substances in calcium carbonate products. This is a major technical problem faced by calcium carbonate additive manufacturers. There are many sources of fluorescent substances in calcium carbonate products. The introduction of fluorescent substances in raw ore and processing is the main reason. Among them, raw ore can avoid the appearance of fluorescent substances by beneficiation, and the processing usually involves the addition of grinding aids. Some commonly used grinding aids contain conjugated double bonds and rigid structures. The introduction of such aids can cause calcium carbonate products to have fluorescent reactions. How to provide a low-fluorescence calcium carbonate for papermaking and its preparation method and application is an urgent problem to be solved by those skilled in the art. Summary of the invention

[0004] The purpose of the present invention is to provide a low-fluorescence calcium carbonate for papermaking and a preparation method and application thereof, so as to solve the problem that fluorescent substances are generally present in existing calcium carbonate products for papermaking and it is difficult to meet the production requirements of paper towels.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing low-fluorescence calcium carbonate for papermaking, comprising the following steps:

[0007] 1) mixing calcium carbonate ore with grinding aid No. 1 and ball milling to obtain calcium carbonate powder;

[0008] 2) removing the grinding aid No. 1 from the calcium carbonate powder and mixing it with water to obtain a pre-grinding slurry, and mixing the pre-grinding slurry with the grinding aid No. 2 and grinding to obtain a calcium carbonate slurry;

[0009] The low-fluorescence calcium carbonate for papermaking comprises calcium carbonate powder and calcium carbonate slurry.

[0010] Preferably, in step 1), the grinding aid No. 1 comprises one or two of coconut oil, ethylene glycol, and propylene glycol; the calcium carbonate content of the calcium carbonate ore is ≥ 97%; and the mass ratio of the grinding aid No. 1 to the calcium carbonate ore is 0.8-1.2:100.

[0011] Preferably, the mass fraction of coconut oil in the No. 1 grinding aid is 50-60%.

[0012] Preferably, the particle size of the calcium carbonate powder in step 1) is 550-650 mesh.

[0013] Preferably, the solid content of the pre-grinding slurry in step 2) is 70-80%;

[0014] The grinding aid No. 2 comprises an inorganic small molecule dispersant and an organic dispersant, and the mass ratio of the inorganic small molecule dispersant to the organic dispersant is 0.5 to 1:1.

[0015] Preferably, the inorganic small molecule dispersant comprises one or more of sodium phosphate, sodium tripolyphosphate, and sodium hexametaphosphate; the organic dispersant comprises one or more of starch, isopropyl alcohol, and hydroxypropyl methylcellulose.

[0016] Preferably, in step 2), the mass ratio of grinding aid No. 2 to calcium carbonate powder is 0.8-1.2:100.

[0017] Preferably, the solid content of the calcium carbonate slurry in step 2) is 70-75%, and the fineness of the calcium carbonate slurry is ≥95% of particles below 2 μm.

[0018] The invention provides low-fluorescence calcium carbonate for papermaking.

[0019] The invention also provides an application of low-fluorescence calcium carbonate for papermaking in papermaking, wherein the calcium carbonate powder is used for filling paper, and the calcium carbonate slurry is used for coating the surface of paper.

[0020] The present invention has at least the following beneficial effects:

[0021] 1. The grinding aids selected in the present invention have no fluorescence phenomenon. The mixed use of multiple grinding aids can improve the grinding efficiency. The coconut oil component of the auxiliary agent used for dry grinding has a natural comprehensive antibacterial ability. The calcium carbonate ground by such grinding aids can be added to paper to improve the anti-mildew and anti-bacterial effect of the paper.

[0022] 2. The present invention separates the grinding aid from the dry powder during the preparation process and then wet grinds it, which can reduce the impact of the No. 1 grinding aid on the subsequent grinding to prepare calcium carbonate slurry.

[0023] 3. This calcium carbonate product has a low content of fluorescent substances. When added to pulp fibers, the paper made from it shows no fluorescence when tested by fluorescent equipment. DETAILED DESCRIPTION

[0024] The present invention provides a method for preparing low-fluorescence calcium carbonate for papermaking, comprising the following steps:

[0025] 1) mixing calcium carbonate ore with grinding aid No. 1 and ball milling to obtain calcium carbonate powder;

[0026] 2) removing the grinding aid No. 1 from the calcium carbonate powder and mixing it with water to obtain a pre-grinding slurry, and mixing the pre-grinding slurry with the grinding aid No. 2 and grinding to obtain a calcium carbonate slurry;

[0027] The low-fluorescence calcium carbonate for papermaking comprises calcium carbonate powder and calcium carbonate slurry.

[0028] In the present invention, the grinding aid No. 1 in step 1) comprises one or two of coconut oil, ethylene glycol, and propylene glycol; the calcium carbonate content of the calcium carbonate ore is ≥97%, preferably 97.5-99.5%, more preferably 98-99%, and more preferably 98.5%; the mass ratio of the grinding aid No. 1 to the calcium carbonate ore is 0.8-1.2:100, preferably 0.9-1.1:100, more preferably 0.95-1.5:100, and more preferably 1:100.

[0029] In the present invention, the particle size of the calcium carbonate ore in step 1) is 4 to 7 cm, preferably 5 to 6 cm.

[0030] In the present invention, the mass fraction of coconut oil in the grinding aid No. 1 is 50-60%, preferably 52-58%, more preferably 54-56%, and more preferably 55%.

[0031] In the present invention, the particle size of the calcium carbonate powder in step 1) is 550-650 mesh, preferably 570-630 mesh, more preferably 590-610 mesh, and more preferably 595-605 mesh.

[0032] In the present invention, the solid content of the pre-grinding slurry in step 2) is 70-80%, preferably 72-78%, and more preferably 74-76%.

[0033] In the present invention, grinding aid No. 2 comprises an inorganic small molecule dispersant and an organic dispersant, and the mass ratio of the inorganic small molecule dispersant to the organic dispersant is 0.5 to 1:1, preferably 0.6 to 0.9:1, and more preferably 0.7 to 0.8:1.

[0034] In the present invention, the method for removing grinding aid No. 1 in step 2) is heating removal, the heating temperature is 150-200°C, preferably 160-190°C, and more preferably 170-180°C, and the heating time is 5-10 minutes, preferably 6-9 minutes, and more preferably 7-8 minutes.

[0035] In the present invention, the inorganic small molecule dispersant includes one or more of sodium phosphate, sodium tripolyphosphate, and sodium hexametaphosphate; the organic dispersant includes one or more of starch, isopropyl alcohol, and hydroxypropyl methylcellulose.

[0036] In the present invention, the mass ratio of the No. 2 grinding aid to the calcium carbonate powder in step 2) is 0.8-1.2:100, preferably 0.9-1.1:100, more preferably 0.95-1.05:100, and more preferably 1:100.

[0037] In the present invention, the solid content of the calcium carbonate slurry in step 2) is 70-75%, preferably 71-74%, and more preferably 72-73%; the fineness of the particles in the calcium carbonate slurry is ≥95% below 2 μm, preferably 95-99%, more preferably 96-98%, and more preferably 97-98%.

[0038] In the present invention, the grinding equipment in step 1) and step 2) are all ceramic-lined equipment, and the grinding media are all ceramic balls.

[0039] The invention provides low-fluorescence calcium carbonate for papermaking, comprising calcium carbonate powder and calcium carbonate slurry.

[0040] The invention also provides an application of low-fluorescence calcium carbonate for papermaking in papermaking, wherein the calcium carbonate powder is used for filling paper, and the calcium carbonate slurry is used for coating the surface of paper.

[0041] In the present invention, the adding is to add 25-30% of the mass of the pulp calcium carbonate powder during the papermaking process, preferably 27-29% of the mass of the pulp calcium carbonate powder.

[0042] In the present invention, the calcium carbonate slurry is mixed with the coating liquid for paper surface coating, and the calcium carbonate slurry accounts for 80-90% of the total mass of the system, preferably 83-88%, and more preferably 85%.

[0043] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0044] Example 1

[0045] Marble ore with a calcium carbonate content of 98% was selected and crushed into fragments with a particle size of 4 to 7 cm by a jaw crusher. Coconut oil and glycerol were mixed at a mass ratio of 1:1 to obtain grinding aid No. 1. Grinding aid No. 1 with a mass ratio of 1.2:100 was mixed with calcium carbonate ore with a particle size of 4 to 7 cm, and dry ball milling was performed in a ceramic-lined grinder using ceramic balls as grinding media to obtain calcium carbonate powder with a particle size of 600 mesh.

[0046] A portion of the calcium carbonate powder was dried at 180°C for 10 minutes and then mixed with water to obtain a pre-grinding slurry with a solid content of 73%. Sodium phosphate and hydroxypropyl methylcellulose were mixed in a mass ratio of 1:1 to obtain a grinding aid No. 2, and 1.1% of the mass of the calcium carbonate powder was mixed with the pre-grinding slurry, and wet-grinded in a ceramic-lined grinder using ceramic balls as grinding media to obtain a calcium carbonate slurry in which particles with a particle size of less than 2 μm accounted for 95% of the total number of particles.

[0047] Take pulp fibers with a beating degree of 45°SR and good dissociation, add 30% of the total weight of the calcium carbonate powder prepared in the above process during the stirring process, and make sheets on a sheet making machine to obtain paper. Coat the surface of the obtained paper with a coating liquid consisting of 90wt% of calcium carbonate slurry, 0.25wt% of sodium carboxymethyl cellulose and 9.75wt% of Dow styrene butadiene latex, and dry to obtain a finished paper. The fluorescence effect and antibacterial properties of the paper are tested.

[0048] Example 2

[0049] Marble ore with a calcium carbonate content of 97% was selected and crushed into pieces with a particle size of 4 to 7 cm by a jaw crusher. Coconut oil and ethylene glycol were mixed at a mass ratio of 6:4 to obtain grinding aid No. 1. Grinding aid No. 1 with a mass ratio of 1:100 was mixed with calcium carbonate ore with a particle size of 4 to 7 cm, and dry ball milling was performed in a ceramic-lined grinder using ceramic balls as grinding media to obtain calcium carbonate powder with a particle size of 600 mesh.

[0050] A portion of the calcium carbonate powder was dried at 200°C for 6 minutes and then mixed with water to obtain a pre-grinding slurry with a solid content of 72%. Sodium hexametaphosphate and isopropanol were mixed in a mass ratio of 0.5:1 to obtain a grinding aid No. 2, and 1.2% of the mass of the calcium carbonate powder No. 2 grinding aid was mixed with the pre-grinding slurry, and wet-grinded in a ceramic-lined grinder using ceramic balls as grinding media to obtain a calcium carbonate slurry in which particles with a particle size of less than 2 μm accounted for 95% of the total number of particles.

[0051] Take pulp fibers with a beating degree of 45°SR and good dissociation, add 27% of the total weight of the calcium carbonate powder prepared in the above process during the stirring process, and make sheets on a sheet making machine to obtain paper. Coat the surface of the obtained paper with a coating liquid consisting of 85wt% of calcium carbonate slurry, 0.25wt% of sodium carboxymethyl cellulose and 14.75wt% of Dow styrene butadiene latex, and dry to obtain a finished paper. The fluorescence effect and antibacterial properties of the paper are tested.

[0052] Example 3

[0053] Marble ore with a calcium carbonate content of 98.5% was selected and crushed into fragments with a particle size of 4 to 7 cm by a jaw crusher. Coconut oil and ethylene glycol were mixed at a mass ratio of 5.8:4.2 to obtain grinding aid No. 1. Grinding aid No. 1 with a mass ratio of 0.9:100 was mixed with calcium carbonate ore with a particle size of 4 to 7 cm, and dry ball milling was performed in a ceramic-lined grinder using ceramic balls as grinding media to obtain calcium carbonate powder with a particle size of 630 meshes.

[0054] A portion of the calcium carbonate powder was dried at 200°C for 6 minutes and then mixed with water to obtain a pre-grinding slurry with a solid content of 76%. Sodium hexametaphosphate and isopropanol were mixed in a mass ratio of 0.7:1 to obtain a grinding aid No. 2, and 1.0% of the mass of the calcium carbonate powder was mixed with the pre-grinding slurry, and wet-grinded in a ceramic-lined grinder using ceramic balls as grinding media to obtain a calcium carbonate slurry in which particles with a particle size of less than 2 μm accounted for 96.3% of the total number of particles.

[0055] The pulp fiber with a beating degree of 45°SR and good dissociation is added with 25% of the total weight of the calcium carbonate powder prepared in the above process during the stirring process, and the paper is made on a sheet making machine. The surface of the obtained paper is coated with a coating liquid consisting of 88wt% of calcium carbonate slurry, 0.25wt% of sodium carboxymethyl cellulose and 11.75wt% of Dow styrene butadiene latex, and dried to obtain a finished paper.

[0056] Example 4

[0057] Marble ore with a calcium carbonate content of 97% was selected and crushed into pieces with a particle size of 4 to 7 cm by a jaw crusher. Coconut oil and glycerol were mixed at a mass ratio of 6:4 to obtain grinding aid No. 1. Grinding aid No. 1 with a mass ratio of 1.1:100 was mixed with calcium carbonate ore with a particle size of 4 to 7 cm, and dry ball milling was performed in a ceramic-lined grinder using ceramic balls as grinding media to obtain calcium carbonate powder with a particle size of 600 mesh.

[0058] A portion of the calcium carbonate powder was dried at 180°C for 8 minutes and then mixed with water to obtain a pre-grinding slurry with a solid content of 72%. Sodium hexametaphosphate and starch were mixed in a mass ratio of 0.5:1 to obtain a grinding aid No. 2, and 1.2% of the mass of the calcium carbonate powder No. 2 grinding aid was mixed with the pre-grinding slurry, and wet-grinded in a ceramic-lined grinder using ceramic balls as grinding media to obtain a calcium carbonate slurry in which particles with a particle size of less than 2 μm accounted for 96.8% of the total number of particles.

[0059] The pulp fiber with a beating degree of 45°SR and good dissociation is added with 28% of the total weight of the calcium carbonate powder prepared in the above process during the stirring process, and the paper is made on a sheet making machine. The surface of the obtained paper is coated with a coating liquid consisting of 83wt% of calcium carbonate slurry, 0.25wt% of sodium carboxymethyl cellulose and 16.75wt% of Dow styrene butadiene latex, and dried to obtain a finished paper.

[0060] Comparative Example 1

[0061] The difference between this comparative example and Example 1 is that commercially available Guangxi Kelong 600 mesh heavy calcium carbonate powder and Dongsheng New Materials 95 grade calcium carbonate slurry are used for papermaking, and their fluorescence effect and antibacterial properties are tested.

[0062] In the above embodiments, the antibacterial detection standard refers to QB / T 2591-2003, and the fluorescence detection standard refers to GB / T5009.78-2003.

[0063] Table 1 Test results of properties of finished paper prepared in the examples and comparative examples

[0064]

[0065] It can be seen from Table 1 that the paper prepared by using the low-fluorescence calcium carbonate material for papermaking prepared by the present invention not only has no obvious fluorescence effect but also has excellent antibacterial properties compared with the paper prepared by using the commercially available calcium carbonate material.

[0066] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing low-fluorescence calcium carbonate for papermaking, characterized in that: The following steps are involved: 1) mixing calcium carbonate ore with grinding aid No. 1 and ball milling to obtain calcium carbonate powder; 2) removing the grinding aid No. 1 from the calcium carbonate powder and mixing it with water to obtain a pre-grinding slurry, and mixing the pre-grinding slurry with the grinding aid No. 2 and grinding to obtain a calcium carbonate slurry; The low-fluorescence calcium carbonate for papermaking comprises calcium carbonate powder and calcium carbonate slurry; In step 1), the grinding aid No. 1 is coconut oil; the calcium carbonate content of the calcium carbonate ore is ≥ 97%; the mass ratio of the grinding aid No. 1 to the calcium carbonate ore is 0.8-1.2:100; The particle size of the calcium carbonate powder in step 1) is 550-650 mesh; The solid content of the pre-ground slurry in step 2) is 70-80%; The grinding aid No. 2 comprises an inorganic small molecule dispersant and an organic dispersant, and the mass ratio of the inorganic small molecule dispersant to the organic dispersant is 0.5 to 1:1; The inorganic small molecule dispersant includes one or more of sodium phosphate, sodium tripolyphosphate, and sodium hexametaphosphate; the organic dispersant includes one or more of starch, isopropyl alcohol, and hydroxypropyl methylcellulose; In the step 2), the solid content of the calcium carbonate slurry is 70-75%, and the fineness of the calcium carbonate slurry is ≥95% of particles below 2 μm.

2. The method for preparing low-fluorescence calcium carbonate for papermaking according to claim 1, characterized in that: The mass fraction of coconut oil in the No. 1 grinding aid is 50-60%.

3. The method for preparing low-fluorescence calcium carbonate for papermaking according to claim 1, characterized in that: In the step 2), the mass ratio of the No. 2 grinding aid to the calcium carbonate powder is 0.8-1.2:

100.

4. Low-fluorescence calcium carbonate for papermaking prepared by the method for preparing low-fluorescence calcium carbonate for papermaking according to any one of claims 1 to 3.

5. The use of the low-fluorescence calcium carbonate for papermaking according to claim 4 in papermaking, characterized in that: Calcium carbonate powder is used for filling paper, and calcium carbonate slurry is used for coating the surface of paper.

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