A polylactic acid / calcium carbonate paper coating composite pigment, a preparation method and application thereof

Abstract

The application discloses a polylactic acid / calcium carbonate papermaking coating composite pigment and a preparation method and application thereof, and belongs to the technical field of papermaking. In the application, under high-speed stirring at pH 7.6-7.8, a carbonate aqueous solution is added dropwise into a calcium salt solution, and porous amorphous calcium carbonate particles are prepared through reaction; the porous amorphous calcium carbonate particles are added into polylactic acid, the polylactic acid fills the internal pores of the porous amorphous calcium carbonate particles and coats the particles, and the polylactic acid / calcium carbonate papermaking coating composite pigment is obtained. The polylactic acid / calcium carbonate papermaking coating composite pigment prepared in the application has uniform particle size distribution, improved light scattering capacity, low coating viscosity, good coating performance, high surface strength, smoothness, whiteness and opacity of coated paper; the polylactic acid is biodegradable and environment-friendly, and the mechanical strength, wear resistance and thermal stability of the coating are improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of papermaking, and particularly relates to a polylactic acid / calcium carbonate papermaking coating composite pigment as well as a preparation method and application thereof. BACKGROUND

[0002] The information disclosed in this Background section is for the purpose of increasing the understanding of the background of the present application and therefore it not to be taken as an acknowledgement or any form of suggestion that it forms prior art of any form to the present application.

[0003] The coating of the pigment-coated paper is a porous covering layer formed by applying a mixture of pigments, adhesives and a small amount of additives to the surface of the paper sheet through a certain coating method, and the purpose is to improve the optical and printing properties of the paper sheet.

[0004] Pigment is the main solid component of the coating of the pigment-coated paper, which is insoluble in water or oil, can fill and cover the uneven surface of the base paper, improve the whiteness of the paper, increase the opacity, and make the paper have a uniform absorbency and a suitable printing surface. Calcium carbonate is the main type of coating pigment, which is a multifunctional inorganic compound with a chemical formula of CaCO3. The whiteness is higher than that of kaolin, usually more than 90%, the refractive index is 1.49-1.66, and the specific gravity (relative volume mass) is 2.6-2.7. The crystal structure mainly includes calcite type, aragonite type and october stone type. According to the production method, calcium carbonate can be divided into two types of heavy calcium carbonate (GCC) and light calcium carbonate (PCC). After being used in the coating, the whiteness, opacity, ink absorbency and drying speed of the coating can be improved.

[0005] However, due to structural limitations, the roles of GCC and PCC in improving the performance of coated paper are limited. With the increasing demand for high-performance coated paper, improving the performance of coated paper by improving the properties of pigments is an important development direction. The preparation technology of pigments still needs to be continuously developed, and the demand for new high-performance coating pigments is urgent. SUMMARY

[0006] In order to solve the problems of the prior art, the present application aims to provide a polylactic acid / calcium carbonate papermaking coating composite pigment as well as a preparation method and application thereof. The polylactic acid / calcium carbonate papermaking coating composite pigment provided by the present application has uniform particle size distribution, improved light scattering ability, low coating viscosity, good coating performance, high surface strength, smoothness, whiteness and opacity of the coated paper; the polylactic acid is biodegradable and environmentally friendly, and the mechanical strength, wear resistance and thermal stability of the coating are improved.

[0007] In order to achieve the above-mentioned purposes, the technical scheme of the present application is as follows:

[0008] The first aspect of the present application provides a preparation method of a polylactic acid / calcium carbonate paper coating composite pigment, comprising the following steps:

[0009] Under high-speed stirring at pH 7.6-7.8, the carbonate aqueous solution is added dropwise into the calcium salt solution to prepare the porous amorphous calcium carbonate particles by reaction.

[0010] The porous amorphous calcium carbonate particles are added into the polylactic acid to fill the internal pores of the porous amorphous calcium carbonate particles and coat the particles, thereby obtaining the polylactic acid / calcium carbonate paper coating composite pigment.

[0011] In some embodiments of the present application, the molar concentration of calcium ions in the calcium salt solution is 0.8-1.2 mol / L.

[0012] Preferably, the calcium salt is calcium chloride and calcium sulfate, and the molar content of calcium sulfate in the calcium salt solution is 5%-10%.

[0013] In some embodiments of the present application, the stirring speed of the high-speed stirring is 1000-1500 rpm, and the reaction temperature is 20-35℃.

[0014] In some embodiments of the present application, the concentration of the carbonate aqueous solution is 0.8-1.2 mol / L, and the molar ratio of carbonate ions to calcium ions added into the reaction system is 1:1.

[0015] Preferably, the carbonate is sodium carbonate.

[0016] In some embodiments of the present application, the pH value is controlled to be 7.6-7.8 by adding the alkali solution into the calcium salt solution.

[0017] Preferably, the concentration of the alkali solution is 0.08-0.12 mol / L; further preferably, the alkali includes potassium hydroxide and sodium hydroxide, preferably sodium hydroxide.

[0018] In some embodiments of the present application, after the reaction of calcium ions and carbonate ions is completed, the precipitate is centrifuged, washed, and dried to obtain the porous amorphous calcium carbonate particles.

[0019] In some embodiments of the present application, the step of adding the porous amorphous calcium carbonate particles into the polylactic acid specifically comprises the following steps:

[0020] The porous amorphous calcium carbonate particles are added into the polylactic acid organic solution, ultrasonically dispersed, then an emulsifier is added and ultrasonically dispersed again.

[0021] Preferably, after ultrasonic dispersion after adding the emulsifier, the product is filtered, washed, and dried after removing the solvent to obtain the polylactic acid / calcium carbonate paper coating composite pigment.

[0022] In some embodiments of the present application, the concentration of the polylactic acid organic solution is 55-80 g / L; preferably, the organic solvent in the polylactic acid organic solution is dichloromethane.

[0023] The mass ratio of the porous amorphous calcium carbonate particles to the polylactic acid is 0.5-1.0:1.

[0024] The emulsifier is polyoxyethylene (10) cetyl ether, and the mass of the polyoxyethylene (10) cetyl ether is 0.3%-0.8% of the mass of the polylactic acid.

[0025] After the addition of the porous amorphous calcium carbonate particles, the frequency of ultrasonic dispersion is 100-300 kHz, and the time is 2-4 min; after the addition of the emulsifier, the frequency of ultrasonic dispersion is 100-300 kHz, and the time is 3-5 min.

[0026] In a second aspect of the present application, a polylactic acid / calcium carbonate papermaking coating composite pigment is provided, which is prepared by the preparation method of the first aspect.

[0027] In a third aspect of the present application, the polylactic acid / calcium carbonate papermaking coating composite pigment of the second aspect is used as a coating pigment to improve the performance of coated paper.

[0028] The application is that the polylactic acid / calcium carbonate papermaking coating composite pigment is prepared into a coating, and then coated on paper to obtain a pigment coated paper.

[0029] In some embodiments of the present application, the coating is prepared by mixing and stirring the components, and the stirring process controls the pH to be 8-9; in terms of mass fraction, the components of the coating include: 100 parts of the polylactic acid / calcium carbonate composite pigment, 10 parts of butadiene-styrene latex, 0.25 parts of polyvinyl alcohol, 0.7 parts of lubricant, and 0.2 parts of water-resistant agent.

[0030] Preferably, the lubricant is polyethylene wax, and the water-resistant agent is zirconium carbonate.

[0031] Preferably, the pH is controlled to be 8-9 by adding sodium hydroxide.

[0032] Preferably, the coating amount of the coating is 14-16 g / m 2 .

[0033] The present application has the following beneficial effects:

[0034] The polylactic acid / calcium carbonate paper coating composite pigment prepared by this invention has a uniform particle size distribution and a porous structure that facilitates the uniform distribution of PLA, improving light scattering ability and resulting in high whiteness and opacity of the coated paper. The prepared coating has high solids content, low viscosity, good coating performance, and is easy to dry. The coating is easy to level, improving the coverage, adhesion, and uniformity of the coating pigment, resulting in high smoothness, good surface strength, and high paper bulk. Compared with GCC and PCC used as coating pigments, this invention further improves the performance of coated paper.

[0035] Furthermore, this invention uses polylactic acid (PLA) to fill the gaps in porous amorphous calcium carbonate. PLA is biodegradable and environmentally friendly. By combining it with calcium carbonate, its physical properties can be improved, enhancing its performance in coating pigments while maintaining its biodegradability. PLA also improves mechanical strength, abrasion resistance, and thermal stability. This composite improves the durability and service life of coating pigments. Detailed Implementation

[0036] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0037] Example 1

[0038] A method for preparing a polylactic acid / calcium carbonate paper coating composite pigment includes the following steps:

[0039] To prepare a mixed solution of CaCl2 and CaSO4, Ca 2+ The molar concentration of CaSO4 was 0.9 mol / L, the molar proportion of CaSO4 in the total Ca was 9%, and 1.1 mol / L Na2CO3 was slowly added dropwise to the calcium salt mixed solution over 120 min. The reaction temperature was 25℃, the stirring speed was 1400 rpm, and the final Ca added to the reaction system was... 2+ With CO3 2- The molar ratio was 1:1. During the reaction, 0.1 mol / L NaOH solution was added dropwise to control the pH of the system to 7.6-7.8. After the reaction, the mixture was centrifuged, the precipitate was washed, and dried to obtain calcium carbonate particles. The specific surface area of ​​the obtained calcium carbonate particles was 598 m². 2 / cm 3 The porosity was 49.2%, and based on this data, the obtained calcium carbonate particles were determined to be porous amorphous calcium carbonate particles.

[0040] PLA was dissolved in DCM with a concentration of 70 g / L, the prepared calcium carbonate particles were added, the mass ratio of calcium carbonate to PLA was 0.8:1, and the frequency was 100 kHz for ultrasonic dispersion for 4 min. An emulsifier polyoxyethylene (10) hexadecyl ether aqueous solution with a concentration of 0.8% was added, and the mass of the emulsifier was 0.7% of the mass of PLA. The emulsion was ultrasonically dispersed at a frequency of 100 kHz for 3.5 min. The product was filtered, and after the residual solvent was volatilized, the calcium carbonate was washed with distilled water, and dried to obtain a polylactic acid / calcium carbonate composite pigment.

[0041] The obtained pigment was made into a coating. The formula: pigment 100 parts, styrene-butadiene latex 10 parts; PVA 0.25 parts, lubricant polyethylene wax 0.7 parts, water resistance agent zirconium carbonate 0.2 parts. The pigment and chemical additives were added in sequence to prepare the coating by stirring, NaOH was added to adjust the pH value to 8-9, the prepared coating had a viscosity of 5985 cP, and the viscosity of the coating was significantly reduced. Bleached softwood pulp 30% and bleached hardwood pulp 70% were mixed to make the coating base paper, which was coated by a blade coater, the coating amount was 15 g / m 2 , the drying speed was 30.2 kg / (m 2 ·h), the drying speed was improved, and the steam consumption was reduced by 6.5%.

[0042] The bulk of the prepared paper sheet was 2.21 g / cm 3 , the whiteness was 85.9% ISO, the opacity was 88.7%, the light reflection ability was improved, the whiteness and opacity were improved, the gloss was 59.1%, the smoothness was 465 s, the paper sheet surface was smoother, and the printing pick strength was 1.42 m / s, the surface strength of the coating was improved.

[0043] Comparative Example 1

[0044] The coating formula of the conventional calcium carbonate pigment: heavy calcium carbonate 40 parts, light calcium carbonate 60 parts, styrene-butadiene latex 10 parts; PVA 0.25 parts, lubricant polyethylene wax 0.7 parts, water resistance agent zirconium carbonate 0.2 parts. The pigment and chemical additives were added in sequence to prepare the coating by stirring, NaOH was added to adjust the pH value to 8-9, the prepared coating had a viscosity of 6328 cP. Bleached softwood pulp 30% and bleached hardwood pulp 70% were mixed to make the coating base paper, which was coated by a blade coater, the coating amount was 15 g / m 2 , the drying speed was 28.6 kg / (m 2 ·h).

[0045] The bulk of the prepared paper sheet was 2.17 g / cm 3 , the whiteness was 84.6% ISO, the opacity was 86.4%, the gloss was 57.2%, the smoothness was 421 s, and the printing pick strength was 1.21 m / s.

[0046] Examples 1-5 were all compared with this result.

[0047] Comparative Example 2

[0048] A method for preparing a polylactic acid / calcium carbonate composite pigment, comprising the following steps:

[0049] Comparing with Example 1, all calcium salts in the preparation system are CaCl2, and the rest conditions are the same as those in Example 1.

[0050] The coating viscosity is 6240 cP. The coating base paper is made by mixing 30% of bleached coniferous pulp and 70% of bleached broadleaf pulp, and is coated by a blade coater with a coating amount of 15 g / m 2 , a drying speed of 28.7 kg / (m 2 ·h), a bulk of the paper sheet of 2.18 g / cm 3 , a whiteness of 85.1% ISO, an opacity of 86.2%, a gloss of 57.1%, a smoothness of 420 s, and a print pick strength of 1.22 m / s.

[0051] Comparative Example 3

[0052] A method for preparing a polylactic acid / calcium carbonate composite pigment, comprising the following steps:

[0053] Comparing with Example 1, no PLA is added in the preparation system, and the rest conditions are the same as those in Example 1.

[0054] The coating viscosity is 6212 cP. The coating base paper is made by mixing 30% of bleached coniferous pulp and 70% of bleached broadleaf pulp, and is coated by a blade coater with a coating amount of 15 g / m 2 , a drying speed of 28.9 kg / (m 2 ·h), a bulk of the paper sheet of 2.17 g / cm 3 , a whiteness of 85.0% ISO, an opacity of 85.2%, a gloss of 57.3%, a smoothness of 424 s, and a print pick strength of 1.26 m / s.

[0055] Comparative Example 4

[0056] A method for preparing a polylactic acid / calcium carbonate composite pigment, comprising the following steps:

[0057] Comparing with Example 1, no emulsifier is added in the preparation system, and the rest conditions are the same as those in Example 1.

[0058] The coating viscosity is 6250 cP. The coating base paper is made by mixing 30% of bleached coniferous pulp and 70% of bleached broadleaf pulp, and is coated by a blade coater with a coating amount of 15 g / m 2 , a drying speed of 28.3 kg / (m 2 ·h), a bulk of the paper sheet of 2.16 g / cm 3, brightness 85.3% ISO, opacity 86.7%, gloss 57.6%, smoothness 430 s, print pick strength 1.25 m / s.

[0059] Example 2

[0060] A method for preparing a polylactic acid / calcium carbonate composite pigment comprises the following steps:

[0061] A mixed solution of CaCl2 and CaSO4 is prepared, the molar concentration of CaCl2 is 0.8 mol / L, and the molar ratio of CaSO4 in the total Ca is 10%. 2+ A 1.0 mol / L Na2CO3 solution is slowly added dropwise into the mixed solution of calcium salts within 100 min, the reaction temperature of the system is 32°C, the stirring speed is 1300 rpm, and the final Ca 2+ The molar ratio of Ca2+ to CO3 2- is 1:1, and a 0.1 mol / L NaOH solution is added dropwise during the reaction to control the pH value of the system to be 7.6-7.8. After the reaction is completed, the precipitate is treated by centrifugation, washed, and dried to obtain calcium carbonate particles.

[0062] PLA is dissolved in DCM at a concentration of 74 g / L, the prepared calcium carbonate particles are added, the mass ratio of calcium carbonate to PLA is 1.0:1, and the particles are dispersed by ultrasonic waves at a frequency of 200 kHz for 2 min. An emulsifier polyoxyethylene (10) hexadecyl ether aqueous solution with a concentration of 0.8% is added, and the mass of the emulsifier is 0.8% of the mass of PLA. The emulsion is dispersed by ultrasonic waves at a frequency of 200 kHz for 4.5 min. The product is filtered, and after the residual solvent is volatilized, the calcium carbonate is washed with distilled water and dried to obtain a polylactic acid / calcium carbonate composite pigment.

[0063] The obtained pigment is made into a coating. The formula is: 100 parts of pigment, 10 parts of butadiene-styrene latex, 0.25 parts of PVA, 0.7 parts of lubricant polyethylene wax, and 0.2 parts of water-resistant agent zirconium carbonate. The pigment and chemical additives are added in sequence and stirred to prepare the coating. NaOH is added to adjust the pH value to 8-9. The viscosity of the prepared coating is 5790 cP, and the viscosity of the coating is reduced. A mixture of 30% bleached softwood pulp and 70% bleached hardwood pulp is used to make the base paper, which is coated by a blade coater at a coating amount of 15 g / m 2 , and the drying speed is 30.4 kg / (m 2 ·h). The drying speed is improved, and the steam consumption is reduced by 6.6%.

[0064] The bulkiness of the prepared paper sheet is 2.22 g / cm 3Whiteness 86.1% ISO, opacity 88.9%, improved light reflection ability, increased whiteness and opacity, gloss 59.4%, smoothness 473s, smoother paper surface, printing fuzzing strength 1.45m / s, improved coating surface strength.

[0065] Example 3

[0066] A method for preparing a polylactic acid / calcium carbonate composite pigment includes the following steps:

[0067] To prepare a mixed solution of CaCl2 and CaSO4, Ca 2+ The molar concentration of CaSO4 was 1.0 mol / L, the molar proportion of CaSO4 in the total Ca was 5%, and 1.2 mol / L Na2CO3 was slowly added dropwise to the calcium salt mixture over 105 min. The reaction temperature was 30℃, the stirring speed was 1500 rpm, and the final Ca added to the reaction system was... 2+ With CO3 2- The molar ratio of the reactants was 1:1. During the reaction, 0.1 mol / L NaOH solution was added dropwise to control the pH of the system at 7.6-7.8. After the reaction was completed, the mixture was centrifuged, the precipitate was washed, and dried to obtain calcium carbonate particles.

[0068] PLA was dissolved in DCM at a concentration of 60 g / L. Prepared calcium carbonate particles were added, with a calcium carbonate to PLA mass ratio of 0.5:1. The mixture was ultrasonically dispersed at 150 kHz for 3 min. A 0.8% aqueous solution of polyoxyethylene (10) hexadecyl ether emulsifier was added, with the emulsifier mass being 0.4% of the PLA mass. The emulsion was ultrasonically dispersed at 300 kHz for 3.0 min. The product was filtered, and after the residual solvent evaporated, the calcium carbonate was washed with distilled water and dried to obtain a polylactic acid / calcium carbonate composite pigment.

[0069] The obtained pigments were made into a coating. The formula was: 100 parts pigment, 10 parts styrene-butadiene latex, 0.25 parts PVA, 0.7 parts polyethylene wax (lubricant), and 0.2 parts zirconium carbonate (water-resistant agent). The pigments and chemical additives were added in sequence and stirred to form the coating. NaOH was added to adjust the pH to 8-9. The prepared coating had a viscosity of 5860 cP, indicating a decrease in viscosity. A base paper was made by mixing 30% bleached softwood pulp and 70% bleached hardwood pulp, and coated using a doctor rod coater with a coating weight of 15 g / m². 2 The drying rate is 30.1 kg / (m²). 2 The drying speed was increased by 6.4%, and steam consumption was reduced by 6.4%.

[0070] The bulk of the prepared paper sheet is 2.24 g / cm. 3, brightness 86.0% ISO, opacity 88.9%, improved light reflection, increased brightness and opacity, gloss 59.2%, smoothness 457s, the paper surface is smoother, print pick strength 1.43 m / s, the surface strength of the coating is improved.

[0071] Example 4

[0072] A method for preparing a polylactic acid / calcium carbonate composite pigment, comprising the following steps:

[0073] A mixed solution of CaCl2 and CaSO4 is prepared, the molar concentration of CaCl2 is 1.2 mol / L, the molar ratio of CaSO4 in the total Ca is 8%, 0.9 mol / L of Na2CO3 is slowly added to the mixed solution of calcium salt within 90 min, the reaction temperature of the system is 28°C, the stirring speed is 1000 rpm, the final Ca 2+ in the reaction system is 0.1 mol / L, the molar ratio of Ca 2+ to CO3 2- is 1:1, and 0.1 mol / L of NaOH solution is added dropwise during the reaction to control the pH value of the system to be 7.6-7.8. After the reaction is completed, centrifugal treatment is performed, the precipitate is washed, and after drying, calcium carbonate particles are obtained.

[0074] PLA is dissolved in DCM with a concentration of 80 g / L, the prepared calcium carbonate particles are added, the mass ratio of calcium carbonate to PLA is 0.9:1, ultrasonic dispersion is performed at a frequency of 250 kHz for 3.5 min, 0.8% of an emulsifier polyoxyethylene (10) hexadecyl ether aqueous solution is added, the mass of the emulsifier is 0.3% of the mass of PLA. The emulsion is ultrasonically dispersed at a frequency of 250 kHz for 4 min. The product is filtered, after the residual solvent is volatilized, the calcium carbonate is washed with distilled water, and after drying, a polylactic acid / calcium carbonate composite pigment is obtained.

[0075] The obtained pigment is made into a coating. The formula is: 100 parts of pigment, 10 parts of butadiene-styrene latex; 0.25 parts of PVA, 0.7 parts of lubricant polyethylene wax, and 0.2 parts of water-resistant agent zirconium carbonate. The pigment and chemical additives are sequentially added and stirred to prepare the coating, NaOH is added to adjust the pH value to 8-9, the viscosity of the prepared coating is 5920 cP, and the viscosity of the coating is reduced. A mixture of 30% bleached coniferous pulp and 70% bleached broadleaf pulp is used to make a coating base paper, a blade coater is used for coating, the coating amount is 15 g / m 2 , the drying speed is 30.5 kg / (m 2 ·h), the drying speed is improved, and the steam consumption is reduced by 6.8%.

[0076] The bulkiness of the prepared paper sheet is 2.24 g / cm 3, brightness 86.3% ISO, opacity 89.0%, improved light reflection, increased brightness and opacity, gloss 59.5%, smoothness 472s, the paper surface is smoother, print pick strength 1.45 m / s, the surface strength of the coating is improved.

[0077] Example 5

[0078] A method for preparing a polylactic acid / calcium carbonate composite pigment, comprising the following steps:

[0079] A mixed solution of CaCl2 and CaSO4 is prepared, the molar concentration of CaCl2 is 1.1 mol / L, the molar ratio of CaSO4 in the total Ca is 6%, 0.8 mol / L of Na2CO3 is added dropwise into the mixed solution of calcium salt within 110 min, the reaction temperature of the system is 35°C, the stirring speed is 1200 rpm, the molar ratio of CaCl2 to CO3 2+ in the final addition to the reaction system is 1:1, and 0.1 mol / L of NaOH solution is added dropwise during the reaction to control the pH value of the system to be 7.6-7.8. After the reaction is completed, centrifugal treatment is performed, the precipitate is washed, and after drying, calcium carbonate particles are obtained. 2+ 2-

[0080] PLA is dissolved in DCM at a concentration of 55 g / L, the prepared calcium carbonate particles are added, the mass ratio of calcium carbonate to PLA is 0.6:1, ultrasonic dispersion is performed at a frequency of 300 kHz for 2.5 min, 0.8% of an emulsifier polyoxyethylene (10) hexadecyl ether aqueous solution is added, the mass of the emulsifier is 0.6% of the mass of PLA. The emulsion is ultrasonically dispersed at a frequency of 150 kHz for 5 min. The product is filtered, after the residual solvent is volatilized, the calcium carbonate is washed with distilled water, and after drying, a polylactic acid / calcium carbonate composite pigment is obtained.

[0081] The obtained pigment is made into a coating. The formula is: 100 parts of pigment, 10 parts of butadiene-styrene latex; 0.25 parts of PVA, 0.7 parts of lubricant polyethylene wax, and 0.2 parts of water-resistant agent zirconium carbonate. The pigment and chemical additives are sequentially added and stirred to prepare the coating, NaOH is added to adjust the pH value to 8-9, the viscosity of the prepared coating is 5880 cP, and the viscosity of the coating is reduced. Bleached coniferous pulp 30% and bleached broadleaf pulp 70% are mixed to make the base paper, a blade coater is used for coating, the coating amount is 15 g / m 2 , the drying speed is 30.1 kg / (m 2 ·h), the drying speed is improved, and the steam consumption is reduced by 6.4%.

[0082] The bulkiness of the prepared paper sheet is 2.22 g / cm 3 ​​Brightness 85.7% ISO, opacity 88.6%, improved light reflection, increased brightness and opacity, gloss 59.2%, smoothness 472s, paper surface is smoother, print pick strength 1.45 m / s, increased strength of coating surface.

[0083] The preferred embodiments of the present application have been described above with the preferred embodiments, but the present application is not limited to the above examples, and various modifications and changes can be made by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for producing a polylactic acid / calcium carbonate paper coating composite pigment, characterized by, It comprises the following steps: Under high-speed stirring at pH 7.6-7.8, the carbonate aqueous solution is added dropwise into the calcium salt solution to prepare porous amorphous calcium carbonate particles by reaction; The porous amorphous calcium carbonate particles are added into polylactic acid to fill the internal pores of the porous amorphous calcium carbonate particles and coat the particles, thereby obtaining polylactic acid / calcium carbonate paper coating composite pigment; The calcium salt is calcium chloride and calcium sulfate, and the molar content of calcium sulfate in the calcium salt solution is 5%-10%, and the molar concentration of calcium ions in the calcium salt solution is 0.8-1.2 mol / L; The concentration of the carbonate aqueous solution is 0.8-1.2 mol / L, and the molar ratio of carbonate ions to calcium ions added into the reaction system is 1:1; The polylactic acid is added into an organic solution of polylactic acid, and after ultrasonic dispersion, an emulsifier is added and ultrasonic dispersion is performed again. The stirring speed of the high-speed stirring is 1000-1500 rpm, and the reaction temperature is 20-35℃.

2. The preparation method of the polylactic acid / calcium carbonate paper coating composite pigment according to claim 1, characterized in that, The carbonate is sodium carbonate.

3. The preparation method of the polylactic acid / calcium carbonate paper coating composite pigment according to claim 1, characterized in that, The pH value is controlled to be 7.6-7.8 by adding alkali solution into the calcium salt solution.

4. The preparation method of the polylactic acid / calcium carbonate paper coating composite pigment according to claim 1, characterized in that, The concentration of the alkali solution is 0.08-0.12 mol / L.

5. The method of claim 4, wherein the polylactic acid / calcium carbonate paper coating composite pigment is prepared by the steps of: (a) mixing a polylactic acid and a calcium carbonate to obtain a mixture; (b) adding a dispersant to the mixture; (c) adding a surface modifier to the mixture; and (d) drying the mixture. The alkali includes potassium hydroxide or sodium hydroxide.

6. The preparation method of the polylactic acid / calcium carbonate paper coating composite pigment as described in claim 5, characterized in that, The alkali is sodium hydroxide.

7. The preparation method of the polylactic acid / calcium carbonate paper coating composite pigment as described in claim 6, characterized in that, After the reaction of calcium ions and carbonate ions is completed, the precipitate is centrifuged, washed, and dried to obtain the porous amorphous calcium carbonate particles.

8. The preparation method of the polylactic acid / calcium carbonate paper coating composite pigment according to claim 1, characterized in that, After ultrasonic dispersion after adding the emulsifier, the product is filtered, washed, and dried to obtain the polylactic acid / calcium carbonate composite pigment.

9. The preparation method of the polylactic acid / calcium carbonate paper coating composite pigment according to claim 1, characterized in that, The concentration of the organic solution of polylactic acid is 55-80 g / L.

10. The preparation method of the polylactic acid / calcium carbonate paper coating composite pigment as described in claim 1, characterized in that, The organic solvent in the organic solution of polylactic acid is dichloromethane.

11. The method of producing a poly lactic acid / calcium carbonate paper coating composite pigment according to claim 1, characterized by, The mass ratio of the porous amorphous calcium carbonate particles to polylactic acid is 0.5-1.0:

1. The emulsifier is polyoxyethylene (10) hexadecyl ether, and the mass of the polyoxyethylene (10) hexadecyl ether is 0.3%-0.8% of the mass of polylactic acid. After adding the porous amorphous calcium carbonate particles, the ultrasonic dispersion frequency is 100-300 kHz, and the time is 2-4 min; after adding the emulsifier, the ultrasonic dispersion frequency is 100-300 kHz, and the time is 3-5 min. The polylactic acid / calcium carbonate paper coating composite pigment is prepared by the preparation method of any one of claims 1-11.

12. A polylactic acid / calcium carbonate paper coating composite pigment, characterized by, 13. A polylactic acid / calcium carbonate paper coating composite pigment according to claim 12 for use as a coating pigment to improve the performance of coated paper. The use is to prepare a coating by using the polylactic acid / calcium carbonate paper coating composite pigment, and then coat the coating on paper to obtain pigment-coated paper. The coating is prepared by mixing and stirring the components, and the stirring process controls the pH to be 8-9.

14. The use of the polylactic acid / calcium carbonate paper coating composite pigment according to claim 13 as a coating pigment for improving the properties of coated paper, characterized in that, In mass parts, the components of the coating include: polylactic acid / calcium carbonate paper coating composite pigment 100 parts, butyl rubber latex 10 parts, polyvinyl alcohol 0.25 parts, lubricant 0.7 parts, and water repellent 0.2 parts. The lubricant is polyethylene wax, and the water repellent is zirconium carbonate.

15. The use of the polylactic acid / calcium carbonate paper coating composite pigment according to claim 14 as a coating pigment for improving the properties of coated paper, characterized in that, ​ 16. The use of the polylactic acid / calcium carbonate paper coating composite pigment according to claim 13 as a coating pigment for improving the properties of coated paper, characterized in that, The coated coated amount is 14-16 g / m 2 .