Lightweight paper with high caliper and high opacity and method of making the same

Abstract

The application discloses light paper with high bulk and high opacity and a preparation method thereof. The light paper comprises wood pulp, fillers, auxiliaries and surface sizing agent; wherein the fillers are composite fillers prepared by compounding calcium carbonate and porous calcium silicate, and the porous calcium silicate has the following characteristics: bulk density < 0.1 g / cm 3 , sedimentation volume > 8.0 ml / g, and D90 mainly in the range of 35-40 microns. The application further provides a preparation method of the light paper with high bulk and high opacity. In the preparation method of the light paper, the calcium carbonate and the porous calcium silicate are used for composite filling. Compared with the light paper filled with only calcium carbonate, the bulk and the opacity of the light paper are significantly improved, and the light paper has the advantages of simple papermaking process and low cost.

Description

Technical Field

[0001] This invention relates to paper and its preparation method, and more particularly to a lightweight paper with high bulk and high opacity and its preparation method, belonging to the field of lightweight paper preparation. Background Technology

[0002] Lightweight paper is an uncoated, low-density printing paper primarily made from chemimechanical pulp. It is characterized by its loose, thick texture, high opacity, and matte surface. Primarily used for printing textbooks, teaching materials, books, and magazines, lightweight paper offers advantages not found in other types of paper: high bulk, resulting in a higher sheet yield for the same thickness compared to ordinary offset paper, thus reducing costs; soft hues with no reflective properties, protecting eyesight; lightweight printed materials, saving on postage and shipping costs, especially beneficial for reducing the burden on school bags for primary and secondary school students; the use of high-yield pulp, increasing the utilization rate of wood fibers and contributing to environmental sustainability; and the absence of chlorine bleaching agents and whitening agents during production, making it a typical environmentally friendly product.

[0003] Bulk density is a very important technical indicator for lightweight paper; it refers to the volume of a given weight of paper, measured in cm³. 3 / g. High bulk means that lightweight paper can have a lower basis weight while maintaining the same thickness. Many factors influence bulk, such as pulp type and properties, pulp beating degree, papermaking conditions, sizing agents, and fillers. Improving the bulk performance of lightweight paper generally involves optimizing the following aspects: chemimechanical pulping process, refining process, calendering process, and filler addition amount. Fillers are particularly important, as their presence alters the paper's bulk. Traditionally, high filler content results in low bulk. To ensure sufficient bulk in lightweight paper, only a small amount of filler is added, and some varieties even omit it entirely. Adding fillers not only increases paper opacity and improves the paper's appearance, solving the problem of bleed-through, but also improves smoothness and uniformity, and enhances softness and hand feel. Fillers are inexpensive, replacing some fibers and saving on papermaking raw materials; they also improve paper drying, facilitating higher paper machine speeds, reducing steam consumption, and lowering production costs. To improve the bulk of lightweight paper, adding no filler or only a small amount of filler will affect the paper's optical properties, physical properties, printability, and production costs, especially its opacity, feel, and printability. Therefore, in the process of preparing lightweight paper, adding a certain amount of filler may lead to low bulk, while not adding or adding too little filler may lead to a decrease in the opacity of the lightweight paper. These issues need to be addressed. Summary of the Invention

[0004] One of the objectives of this invention is to provide a lightweight paper with high bulk and high opacity;

[0005] A second objective of this invention is to provide a method for preparing lightweight paper with high bulk and high opacity.

[0006] To achieve this objective, in a basic implementation, one aspect of the present invention is to provide a lightweight paper with high bulk and high opacity, comprising the following components: wood pulp, filler, additives and surface sizing agent; wherein the filler is a compound filler obtained by compounding calcium carbonate and porous calcium silicate; preferably, the ratio of calcium carbonate to porous calcium silicate by mass is (60-75):(25-40).

[0007] Preferably, the weight parts of each component are: 750-780 parts wood pulp, 250-220 parts filler, 25-45 parts additives, and 50-90 parts surface sizing agent.

[0008] The wood pulp described in this invention includes sulfate-bleached softwood pulp and hardwood bleached chemimechanical pulp, with the weight proportions of the two pulps being 5-8 parts of sulfate-bleached softwood pulp and 95-92 parts of hardwood bleached chemimechanical pulp.

[0009] The calcium carbonate described in this invention can be ground calcium carbonate (GCC), precipitated calcium carbonate (PCC), or a mixture of ground calcium carbonate and precipitated calcium carbonate in any proportion.

[0010] The porous calcium silicate described in this invention has the following properties or characteristics: bulk density < 0.1 g / cm³. 3 The sedimentation volume is >8.0 ml / g, and the D90 is mainly in the range of 35-40 micrometers (D90: 90% of the particles are below 40 micrometers, usually in the range of 35-40 micrometers); more preferably, the whiteness of the porous calcium silicate is above 91% ISO, and the abrasion degree is <5.0 mg / 2000 times.

[0011] The present invention provides a method for preparing the porous calcium silicate, the method comprising: (1) processing quicklime to prepare lime milk; (2) mixing lime milk, quartz sand, caustic soda and water together and performing a hydrothermal synthesis reaction by heating from room temperature to reaction temperature; (3) washing and purifying the product of the synthesis reaction to obtain porous calcium silicate.

[0012] In a preferred embodiment of the present invention, in step (1), quicklime is crushed and then digested, aged, and sieved to prepare lime milk; more preferably, the effective calcium content of the quicklime is >85% and the activity is >300; when the quicklime is crushed and digested, the ratio of quicklime to water is preferably 1:4 to 8; the aging time is preferably 8 to 24 hours; more preferably, quicklime and water are digested at a volume ratio of 1:5, aged for 12 hours, and then sieved to obtain lime milk.

[0013] In a preferred embodiment of the present invention, the quartz sand in step (2) has a SiO2 content > 95%, a loss on ignition < 0.5%, and an average particle size < 20 μm.

[0014] In a preferred embodiment of the present invention, the amount of quartz sand in step (3) is calculated based on SiO2, the amount of caustic soda is calculated based on NaOH, and the amount of lime slurry is calculated based on Ca(OH)2. The molar mass ratio of quartz sand, caustic soda and lime slurry is preferably 1:2 to 4:0.8 to 1.2, and more preferably 1:2.5:1.1.

[0015] In a preferred embodiment of the present invention, the mass ratio of the mixture of quartz sand, caustic soda and lime milk in the synthesis reaction in step (3) to water is 1:4 to 20; preferably 1:9.

[0016] In a preferred embodiment of the present invention, in step (3), the heating rate is controlled at 3℃-5℃ / min when heating from room temperature to reaction temperature, preferably at 3℃ / min; the reaction temperature is preferably 150~190℃, most preferably 150~170℃; the reaction time is preferably 1~5h, most preferably 3h.

[0017] In a preferred embodiment of the present invention, the synthesis reaction in step (3) is preferably carried out under stirring, and the stirring speed is preferably 100-500 rpm, and most preferably 300 rpm.

[0018] The method for preparing porous calcium silicate provided by this invention eliminates the sodium silicate preparation step. In addition, when carrying out the hydrothermal synthesis reaction, the heating rate is controlled at 3℃-5℃ / min when slowly heating from room temperature to the reaction temperature, and the reaction temperature is 150-190℃. This not only significantly shortens the process flow, but also results in the prepared porous calcium silicate product exhibiting improved quality stability, reduced bulk density, and increased sedimentation volume, with significant improvements or enhancements in various properties.

[0019] The additives described in this invention include an internal sizing agent, cationic starch, a retention and filtration aid, and a bactericide. The weight percentages of each additive are as follows: internal sizing agent 15-25 parts, cationic starch 8-10 parts, retention and filtration aid 2-3 parts, and bactericide 0.2-0.5 parts. The internal sizing agent is preferably an alkyl ketene dimer (AKD). The cationic starch is preferably a quaternary ammonium cationic starch, which can be corn starch, wheat starch, or cassava starch, etc. The retention and filtration aid is preferably composed of polyacrylamide, bentonite, and organic microparticles.

[0020] The organic microparticles are highly cross-linked anionic polymers with a three-dimensional structure. They are emulsion products and can be purchased through various commercial channels.

[0021] The bactericide is preferably an organic bromide.

[0022] All the additives used in this invention are conventional raw materials in the papermaking industry, which can be purchased through various commercial channels and are applicable to this invention.

[0023] The surface sizing agent described in this invention can be a product obtained by modifying surface sizing starch through oxidation or enzymatic conversion. The surface sizing starch can be various starches such as cassava starch or corn starch. Obtaining surface sizing starch by oxidizing or enzymatic conversion of these starches are conventional techniques in the field and are well known to those skilled in the art. In addition, surface sizing agents can also be purchased from the market and are applicable to this invention.

[0024] Another aspect of the present invention is to provide a method for preparing the aforementioned lightweight paper with high bulk and high opacity, comprising: (1) beating bleached sulfate softwood pulp and bleached hardwood chemimechanical pulp separately to obtain bleached sulfate softwood pulp and bleached hardwood chemimechanical pulp respectively, and mixing the two pulps together to obtain a mixed pulp; (2) preparing filler: mixing the dispersion products obtained by dispersing calcium carbonate and porous calcium silicate separately in a mass ratio of (60-75):(25-40) to obtain filler; (3) adding filler and additives to the mixed pulp and mixing evenly to obtain paper stock, which is then diluted, purified, screened and fed to the wire; (4) dewatering, pressing, drying, surface sizing with a surface sizing agent, drying, calendering and curling are performed on the wire section of a long-wire paper machine to obtain the final product.

[0025] In a preferred embodiment of the present invention, the conditions for beating bleached sulfate softwood pulp in step (1) are controlled as follows: beating concentration of 3-4% and beating degree of 40-44°SR; the conditions for beating bleached hardwood chemimechanical pulp are controlled as follows: beating concentration of 3.5-4.5% and beating degree of 33-38°SR.

[0026] In a preferred embodiment of the present invention, in step (1), bleached sulfate softwood pulp and bleached hardwood chemimechanical pulp are mixed together in a mass ratio of (5-8):(95-92) to obtain a mixed pulp.

[0027] In a preferred embodiment of the present invention, in step (2), calcium carbonate is dispersed to obtain a dispersion product with a dispersion concentration of 30-40%, and porous calcium silicate is dispersed to obtain a dispersion product with a dispersion concentration of 8-15%.

[0028] In a preferred embodiment of the present invention, the concentration of the surface sizing agent in step (4) is 6-12%, the temperature is 50-60°C, and the application rate is 4-5 g / m². 2 .

[0029] The method for preparing lightweight paper in this invention employs a composite filler of calcium carbonate and porous calcium silicate. Compared to lightweight paper with only calcium carbonate filler, both the bulk and opacity are significantly improved, achieving a bulk of 60 g / m². 2 Taking lightweight paper as an example, when the porous calcium silicate content is approximately 92 kg / t of paper, the bulk of the finished paper increases from 1.84 cm. 3 / g increased to 2.04cm 3 / g, the opacity increased by 2.0% to 89.6%, which not only significantly improved the bulk and opacity of lightweight paper products, but also has the advantages of simple papermaking process and low cost. Attached Figure Description

[0030] Figure 1 The particle size distribution diagram is shown for the porous calcium silicate prepared in Comparative Example 2.

[0031] Figure 2 Scanning electron microscope image (×5000) of the porous calcium silicate prepared in Preliminary Example 1.

[0032] Figure 3 Scanning electron microscope image (×1000) of the porous calcium silicate prepared in Preliminary Example 1.

[0033] Figure 4 Scanning electron microscope image (×5000) of the porous calcium silicate prepared in Preliminary Example 2.

[0034] Figure 5 Scanning electron microscope image (×1000) of the porous calcium silicate prepared in Preliminary Example 2. Detailed Implementation

[0035] The specific embodiments of the present invention will be further described below with reference to examples.

[0036] Preliminary Example 1: Preparation of Porous Calcium Silicate

[0037] Quartz sand, caustic soda, and lime slurry were added to a reaction vessel in a molar ratio of SiO2:NaOH:Ca(OH)2 = 1:2.5:1.1 and mixed with water. The synthesis reaction was carried out using a hydrothermal method, with the temperature slowly increased from room temperature to the reaction temperature at a rate controlled at 3℃ / min. The reaction temperature was 150℃. The mass ratio of the quartz sand, caustic soda, and lime slurry mixture to water was 1:9. The reaction time was 3 hours, and the stirring speed was 300 rpm. After the reaction was completed, the mixture was filtered, and the filter cake was washed and dried to obtain porous calcium silicate. Preliminary Example 2: Preparation of Porous Calcium Silicate

[0038] Quartz sand, caustic soda, and lime slurry were added to a reactor in a molar ratio of SiO2:NaOH:Ca(OH)2 = 1:2.5:1.1 and mixed with water. The synthesis reaction was carried out by hydrothermal synthesis. The temperature was slowly increased from room temperature to the reaction temperature at a rate of 3℃ / min. The reaction temperature was 170℃. The mass ratio of the mixture of quartz sand, caustic soda, and lime slurry to water was 1:9. The reaction time was 3 hours and the stirring speed was 300 rpm. After the reaction was completed, the mixture was filtered, and the filter cake was washed and dried to obtain porous calcium silicate.

[0039] Preliminary Example 3: Preparation of Porous Calcium Silicate

[0040] Quartz sand, caustic soda, and lime slurry were added to a reactor in a molar ratio of SiO2:NaOH:Ca(OH)2 = 1:2.5:1.1 and mixed with water. The synthesis reaction was carried out by hydrothermal synthesis. The temperature was slowly increased from room temperature to the reaction temperature at a rate of 3℃ / min. The reaction temperature was 180℃. The mass ratio of the mixture of quartz sand, caustic soda, and lime slurry to water was 1:9. The reaction time was 3 hours and the stirring speed was 300 rpm. After the reaction was completed, the mixture was filtered, and the filter cake was washed and dried to obtain porous calcium silicate.

[0041] Preliminary Example 4: Preparation of Porous Calcium Silicate

[0042] Quartz sand, caustic soda, and lime slurry were added to a reactor in a molar ratio of SiO2:NaOH:Ca(OH)2 = 1:2.5:1.1 and mixed with water. The synthesis reaction was carried out by hydrothermal synthesis. The temperature was slowly increased from room temperature to the reaction temperature at a rate of 3℃ / min. The reaction temperature was 190℃. The mass ratio of the mixture of quartz sand, caustic soda, and lime slurry to water was 1:9. The reaction time was 3 hours and the stirring speed was 300 rpm. After the reaction was completed, the mixture was filtered, and the filter cake was washed and dried to obtain porous calcium silicate.

[0043] Preliminary Example 5: Preparation of Porous Calcium Silicate

[0044] Quartz sand, caustic soda, and lime slurry were added to a reactor in a molar ratio of SiO2:NaOH:Ca(OH)2 = 1:2.5:1.1 and mixed with water. The synthesis reaction was carried out by hydrothermal synthesis. The temperature was slowly increased from room temperature to the reaction temperature at a rate of 3℃ / min. The reaction temperature was 170℃. The mass ratio of the mixture of quartz sand, caustic soda, and lime slurry to water was 1:9. The reaction time was 2 hours, and the stirring speed was 300 rpm. After the reaction was completed, the mixture was filtered, and the filter cake was washed and dried to obtain porous calcium silicate.

[0045] Preliminary Example 6: Preparation of Porous Calcium Silicate

[0046] Quartz sand, caustic soda, and lime slurry were added to a reactor in a molar ratio of SiO2:NaOH:Ca(OH)2 = 1:2.5:1.1 and mixed with water. The synthesis reaction was carried out by hydrothermal synthesis. The temperature was slowly increased from room temperature to the reaction temperature at a rate of 3℃ / min. The reaction temperature was 170℃. The mass ratio of the mixture of quartz sand, caustic soda, and lime slurry to water was 1:9. The reaction time was 5 hours and the stirring speed was 300 rpm. After the reaction was completed, the mixture was filtered, and the filter cake was washed and dried to obtain porous calcium silicate.

[0047] Preliminary Example 7: Preparation of Porous Calcium Silicate

[0048] Quartz sand, caustic soda, and lime slurry were added to a reactor in a molar ratio of SiO2:NaOH:Ca(OH)2 = 1:2.5:1.1 and mixed with water. The synthesis reaction was carried out by hydrothermal synthesis. The temperature was slowly increased from room temperature to the reaction temperature at a rate of 3℃ / min. The reaction temperature was 170℃. The mass ratio of the mixture of quartz sand, caustic soda, and lime slurry to water was 1:9. The reaction time was 3 hours and the stirring speed was 100 rpm. After the reaction was completed, the mixture was filtered, and the filter cake was washed and dried to obtain porous calcium silicate.

[0049] Preliminary Example 8: Preparation of Porous Calcium Silicate

[0050] Quartz sand, caustic soda, and lime slurry were added to a reactor in a molar ratio of SiO2:NaOH:Ca(OH)2 = 1:2.5:1.1 and mixed with water. The synthesis reaction was carried out by hydrothermal synthesis. The temperature was slowly increased from room temperature to the reaction temperature at a rate of 3℃ / min. The reaction temperature was 170℃. The mass ratio of the mixture of quartz sand, caustic soda, and lime slurry to water was 1:9. The reaction time was 3 hours and the stirring speed was 500 rpm. After the reaction was completed, the mixture was filtered, and the filter cake was washed and dried to obtain porous calcium silicate.

[0051] Preliminary Example 9: Preparation of Porous Calcium Silicate

[0052] Quartz sand, caustic soda, and lime slurry were added to a reactor in a molar ratio of SiO2:NaOH:Ca(OH)2 = 1:2.5:1.1 and mixed with water. The synthesis reaction was carried out by hydrothermal synthesis. The temperature was slowly increased from room temperature to the reaction temperature at a rate of 5℃ / min. The reaction temperature was 170℃. The mass ratio of the mixture of quartz sand, caustic soda, and lime slurry to water was 1:9. The reaction time was 3 hours and the stirring speed was 300 rpm. After the reaction was completed, the mixture was filtered, and the filter cake was washed and dried to obtain porous calcium silicate.

[0053] Comparative Example 1: Preparation of Porous Calcium Silicate

[0054] Quartz sand, caustic soda, and lime slurry were added to a reactor in a molar ratio of SiO2:NaOH:Ca(OH)2 = 1:2.5:1.1 and mixed with water. The synthesis reaction was carried out by hydrothermal synthesis. The temperature was slowly increased from room temperature to the reaction temperature at a rate of 10℃ / min. The reaction temperature was 170℃. The mass ratio of the mixture of quartz sand, caustic soda, and lime slurry to water was 1:9. The reaction time was 3 hours and the stirring speed was 300 rpm. After the reaction was completed, the mixture was filtered, and the filter cake was washed and dried to obtain porous calcium silicate.

[0055] Table 1. Reaction parameters of Preliminary Examples 1-9 and Comparative Example 1

[0056] 1 3℃ / min 150 3 300 2 3℃ / min 170 3 300 3 3℃ / min 180 3 300 4 3℃ / min 190 3 300 5 3℃ / min 170 2 300 6 3℃ / min 170 5 300 7 3℃ / min 170 3 100 8 3℃ / min 170 3 500 9 5℃ / min 170 3 300 Comparative Example 1 10℃ / min 170 3 300

[0057] Comparative Example 2: Preparation and Performance Testing of Porous Calcium Silicate

[0058] Porous calcium silicate was prepared according to the method described in Example 1 of CN104975535A.

[0059] The prepared porous calcium silicate has a wide particle size range and uneven particle size distribution. Although it is mainly distributed in the range of 7-50 micrometers, there are a large number of fine particles smaller than 7 micrometers. Figure 1 ).

[0060] The properties of the porous calcium silicate prepared in this comparative example were tested using the same testing methods as in Preliminary Examples 1-9. The specific test results are as follows: the bulk density of the calcium silicate is 0.25 g / cm³. 3 The sedimentation volume was 3.7 ml / g, the whiteness was 90.2%, the D90 was 30.62 micrometers, and the abrasion resistance was 6.8 mg / 2000 cycles.

[0061] Example 1: Preparation of lightweight paper

[0062] Bleached sulfate softwood pulp and bleached hardwood chemimechanical pulp were beaten separately to a beating concentration of 3.5% and 4.5%, respectively, with freeness of 42°SR and 35°SR, respectively, and a ratio of 5:95.

[0063] Preparation of filler: precipitated calcium carbonate and porous calcium silicate were dispersed at concentrations of 35% and 12% respectively, and then mixed at a mass ratio of 65:35 to obtain the filler;

[0064] The fillers and additives were added to the slurry delivery system according to conventional processes. The dosages of each additive were as follows: alkyl ketene dimer (AKD) 16 kg / t paper, quaternary ammonium cationic starch (Jingzhou Xusheng Chemical Additives Co., Ltd., trade name: STS-1 cationic starch) 8 kg / t paper, polyacrylamide 0.25 kg / t paper, bentonite 2 kg / t paper, organic microparticles (purchased from Zhengzhou Foster Chemical Co., Ltd., trade name: organic microparticles) 0.3 kg / t paper, and organic bromide (purchased from Qingzhou Xindi Chemical Co., Ltd., trade name: organic bromide bactericide) 0.3 kg / t paper.

[0065] After the pulping and conditioning process described above, the paper stock is diluted, purified, and screened before being fed to the wire section of a fourdrinier paper machine. The paper undergoes dewatering, pressing, drying, surface sizing, drying, calendering, and winding to obtain lightweight paper with high bulk and opacity. The surface sizing agent is corn enzyme-converted starch at a concentration of 8%, a temperature of 55℃, and a sizing amount of 4.0 g / m². 2 .

[0066] Preparation of corn starch by corn starch enzyme conversion: Corn starch (purchased from Jinan Zhongcheng Chemical Co., Ltd.) was mixed with water to form a starch paste, α-amylase (purchased from Taian Wanrun Chemical Co., Ltd.) was added, and the mixture was heated to convert the starch. The reaction was terminated after the desired viscosity was reached, and the starch was diluted to obtain the final product.

[0067] Example 2: Preparation of lightweight paper

[0068] Bleached sulfate softwood pulp and bleached hardwood chemimechanical pulp were pulped to a pulping concentration of 3.5% and 4.5%, respectively, with freeness of 41°SR and 37°SR, respectively, and a ratio of 5:95.

[0069] Preparation of filler: Grinded calcium carbonate and precipitated calcium carbonate are dispersed at a concentration of 40%, and porous calcium silicate is dispersed at a concentration of 10%. The ground calcium carbonate, precipitated calcium carbonate and porous calcium silicate are mixed in a mass ratio of 32:32:36 to obtain the filler.

[0070] The fillers and additives were added to the slurry delivery system according to conventional processes. The dosages of each additive were as follows: alkyl ketene dimer (AKD) 15 kg / t paper, quaternary ammonium cationic starch (Jingzhou Xusheng Chemical Additives Co., Ltd., trade name: STS-1 cationic starch) 8 kg / t paper, polyacrylamide 0.25 kg / t paper, bentonite 1.5 kg / t paper, organic microparticles (purchased from Zhengzhou Foster Chemical Co., Ltd., trade name: organic microparticles) 0.3 kg / t paper, and organic bromide (purchased from Qingzhou Xindi Chemical Co., Ltd., trade name: organic bromide bactericide) 0.3 kg / t paper.

[0071] After pulping and conditioning, the paper stock is diluted, purified, and screened before being fed to the wire section of a fourdrinier paper machine. It then undergoes dewatering, pressing, drying, surface sizing, drying, calendering, and winding to obtain lightweight paper with high bulk and opacity. The surface sizing agent is corn enzyme-converted starch at a concentration of 10%, applied at 55°C, with a sizing rate of 4.3 g / m². 2 The preparation of starch by corn enzyme conversion is the same as in Example 1.

[0072] Example 3: Preparation of lightweight paper

[0073] Bleached sulfate softwood pulp and bleached hardwood chemimechanical pulp were pulped to a pulping concentration of 3.5% and 4.5%, respectively, with freeness of 43°SR and 36°SR, respectively, and a ratio of 7:93.

[0074] Preparation of filler: precipitated calcium carbonate was dispersed at a concentration of 35%, and porous calcium silicate was dispersed at a concentration of 10%. The dispersed precipitated calcium carbonate and porous calcium silicate were mixed at a mass ratio of 64:36 to obtain the filler.

[0075] The fillers and additives were added to the slurry delivery system according to conventional processes. The dosages of each additive were as follows: alkyl ketene dimer (AKD) 17 kg / t paper, quaternary ammonium cationic starch (Jingzhou Xusheng Chemical Additives Co., Ltd., trade name: STS-1 cationic starch) 8 kg / t paper, polyacrylamide 0.25 kg / t paper, bentonite 1.5 kg / t paper, organic microparticles (purchased from Zhengzhou Foster Chemical Co., Ltd., trade name: organic microparticles) 0.25 kg / t paper, and organic bromide (purchased from Qingzhou Xindi Chemical Co., Ltd., trade name: organic bromide bactericide) 0.3 kg / t paper.

[0076] After pulping and conditioning, the paper stock is diluted, purified, and screened before being fed to the wire section of a fourdrinier paper machine. It then undergoes dewatering, pressing, drying, surface sizing, drying, calendering, and winding to obtain lightweight paper with high bulk and opacity. The surface sizing agent is corn enzyme-converted starch at a concentration of 11%, applied at 55°C, with a sizing rate of 4.6 g / m². 2The preparation of starch by corn enzyme conversion is the same as in Example 1.

[0077] Comparative Example 1: Preparation of Lightweight Paper

[0078] Except for the fact that the filler is precipitated calcium carbonate, which is different from Example 1, all other contents (including raw materials and preparation process) are the same as in Example 1.

[0079] Comparative Example 2: Preparation of Lightweight Paper

[0080] Except for the fact that the filler is a mixture of ground calcium carbonate and precipitated calcium carbonate in a 1:1 mass ratio, everything else (including raw materials and preparation process) is the same as in Example 2.

[0081] Comparative Example 3: Preparation of Lightweight Paper

[0082] Except for the fact that the filler is only precipitated calcium carbonate, everything else (including raw materials and preparation process) is the same as in Example 3.

[0083] Test Example 1: Performance Testing of Porous Calcium Silicate

[0084] The properties of the porous calcium silicate prepared in Preliminary Examples 1-9 and Comparative Example 1 were tested, and the test results are shown in Table 2.

[0085] Table 2 shows the test results of various properties of calcium silicate prepared in Preliminary Examples 1-9 and Comparative Example 1.

[0086] Preliminary Example 1 35.04 0.097 9.5 91.5 4.6 Preliminary Example 2 36.72 0.080 10.7 91.5 3.8 Preliminary Example 3 37.43 0.090 9.5 91.7 4.2 Preliminary Example 4 39.27 0.095 9.2 91.2 4.4 Preliminary Example 5 34.80 0.096 9.0 91.1 4.8 Preliminary Example 6 37.02 0.097 8.8 91.0 5.0 Preliminary Example 7 38.93 0.081 10.6 91.5 3.8 Preliminary Example 8 35.62 0.081 10.7 91.5 3.8 Preliminary Example 9 39.70 0.080 10.7 91.5 3.8 Comparative Example 1 52.86 0.150 7.7 91.0 6.0

[0087] Scanning electron microscope (SEM) images of the porous calcium silicate prepared in Preliminary Example 1 are shown below. Figure 2 (×5000) and Figure 3 As shown in (×10000), from Figure 2 and Figure 3 It can be seen that the porous calcium silicate has a good porous structure and a very uniform particle size, with a D90 of 35.04 micrometers. No excessively small or large particle size was found.

[0088] Scanning electron microscope images of porous calcium silicate obtained in Preliminary Example 2 are shown below. Figure 4 (×5000) and Figure 5 As shown in (×10000), from Figure 4 and Figure 5 It can be seen that the porous calcium silicate has a good porous structure, uniform particle size, and a D90 of 36.72 micrometers. No excessively small or large particle size was found.

[0089] The porous calcium silicate prepared in Examples 1-9 of this application has a very uniform particle size, with D90 in the range of 35-40 micrometers, good pore structure, low packing density, and large settling volume.

[0090] In contrast, the porous calcium silicate prepared in Comparative Example 1 has a larger particle size, with a D90 of 52.86 micrometers, a relatively poor pore structure, a higher packing density, and a smaller settling volume.

[0091] Test Example 2: Performance Testing of Lightweight Paper

[0092] The properties of the lightweight paper prepared in Example 1 and the lightweight paper prepared in Comparative Example 1 were tested, and the specific test results are shown in Table 3.

[0093] Table 3. Performance test results of the lightweight paper prepared in Example 1 and Comparative Example 1

[0094]

[0095] As shown in Table 3, with other process conditions remaining unchanged, when the porous calcium silicate content of the lightweight paper product prepared by compounding porous calcium silicate and precipitated calcium carbonate filler is approximately 80 kg / t of paper, the bulk after calendering reaches 2.02 cm. 3 / g; Compared with Comparative Example 1, which only added precipitated calcium carbonate, the opacity increased by 1.3% to 87.7%, and all other indicators also met the requirements of GB / T26705-2023 for lightweight printing paper.

[0096] The properties of the lightweight paper prepared in Example 2 and the lightweight paper prepared in Comparative Example 2 were tested, and the specific test results are shown in Table 4.

[0097] Table 4. Performance test results of the lightweight paper prepared in Example 2 and Comparative Example 2

[0098]

[0099] As shown in Table 4, compared with Comparative Example 2 (the filler is composed of a mixture of ground calcium carbonate and precipitated calcium carbonate in a 1:1 ratio), under the same process conditions, the lightweight paper product prepared by Example 2 (the filler is a mixture of 32% ground calcium carbonate + 32% precipitated calcium carbonate + 36% porous calcium silicate) has a porous calcium silicate content of approximately 83 kg / t of paper. The bulk after calendering is increased by 10.7%, the opacity is increased by 1.7% to 88.6%, and the other indicators also meet the requirements of GB / T26705-2023 for lightweight printing paper.

[0100] The properties of the lightweight paper prepared in Example 3 and the lightweight paper prepared in Comparative Example 3 were tested, and the specific test results are shown in Table 5.

[0101] Table 5. Performance test results of the lightweight paper prepared in Example 3 and Comparative Example 3

[0102]

[0103]

[0104] As shown in Table 5, compared with Comparative Example 3 (where the filler's entire composition was precipitated calcium carbonate), the lightweight paper product prepared by Example 3 using a composite filler composed of porous calcium silicate and precipitated calcium carbonate in a mass ratio of 64:36, with a porous calcium silicate content of approximately 92 kg / t paper, exhibited a 3% increase in ash content and a paper bulk of 2.04 cm. 3 / g, the opacity increased by 2.0% to 89.6%, and all other indicators also met the requirements of GB / T 26705-2023 for lightweight printing paper.

[0105] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims and their equivalents, this invention is also intended to include these modifications and variations. The above embodiments or implementations are merely illustrative examples of this invention, and it can also be implemented in other specific ways or forms without departing from its gist or essential characteristics. Therefore, the described embodiments should be considered illustrative rather than limiting in any respect. The scope of this invention should be defined by the appended claims, and any changes equivalent to the intent and scope of the claims should also be included within the scope of this invention.

Claims

1. A lightweight paper with high bulk and high opacity, characterized in that, It comprises the following components: wood pulp, filler, additives, and surface sizing agent; wherein the filler is a composite filler obtained by blending calcium carbonate and porous calcium silicate; the porous calcium silicate has the following characteristics: bulk density < 0.1 g / cm³. 3 The sedimentation volume is >8.0 ml / g, and the D90 is mainly in the range of 35~40 micrometers; the mass ratio of calcium carbonate to porous calcium silicate is (60~75):(25~40). The wood pulp is composed of sulfate-bleached softwood pulp and hardwood bleached chemimechanical pulp, with a mass ratio of (5~8):(95~92). The method for preparing porous calcium silicate includes: (1) preparing lime milk by processing quicklime; (2) mixing lime milk, quartz sand, caustic soda and water together and carrying out a synthesis reaction by heating from room temperature to reaction temperature using a hydrothermal synthesis method; (3) washing and purifying the product of the synthesis reaction to obtain porous calcium silicate. In step (2), the heating rate is controlled at 3℃-5℃ / min when heating from room temperature to reaction temperature; the reaction temperature is 150~190℃; and the reaction time is 1~5h.

2. The lightweight paper according to claim 1, characterized in that, The porous calcium silicate has a whiteness of 91% ISO or higher and an abrasion rate of <5.0 mg / 2000 cycles.

3. The lightweight paper according to claim 1, characterized in that, The weight parts of each component are: 750-780 parts wood pulp, 250-220 parts filler, 25-45 parts additives, and 50-90 parts surface sizing agent.

4. The lightweight paper according to claim 1, characterized in that, The calcium carbonate mentioned is ground calcium carbonate, precipitated calcium carbonate, or a mixture of ground calcium carbonate and precipitated calcium carbonate in any proportion; The additives include an internal sizing agent, cationic starch, retention and filtration aids, and a bactericide; wherein the internal sizing agent is an alkyl ketene dimer; the cationic starch is a quaternary ammonium cationic starch; the retention and filtration aids are polyacrylamide, bentonite, and organic microparticles; and the bactericide is an organic bromide. The surface sizing agent is a product obtained by modifying surface sizing starch through oxidation or enzymatic conversion.

5. The method for preparing lightweight paper according to any one of claims 1-4, characterized in that, include: (1) Bleached sulfate softwood pulp and bleached hardwood chemimechanical pulp are beaten separately to obtain bleached sulfate softwood pulp and hardwood bleached chemimechanical pulp respectively. The two pulps are mixed together to obtain a mixed pulp. (2) Filler preparation: Calcium carbonate and porous calcium silicate are dispersed separately and the resulting dispersion products are mixed in a mass ratio of (60~75):(25~40) to obtain filler. (3) Filler and additives are added to the mixed pulp and mixed evenly to obtain paper stock. After pulp dilution, purification and screening, the paper stock is sent to the wire section of the wire paper machine. (4) After dewatering, pressing and drying of the wire section of the wire paper machine, surface sizing with surface sizing agent, drying, calendering and curling are performed to obtain the final product.

6. The method according to claim 5, characterized in that, In step (1), the conditions for beating the bleached sulfate softwood pulp are controlled as follows: beating concentration of 3-4% and freeness of 40-44%. o SR; The conditions for beating bleached chemimechanical pulp of hardwood are controlled as follows: beating concentration 3.5~4.5%, beating degree 33~38. o SR; In step (1), bleached sulfate softwood pulp and bleached hardwood chemimechanical pulp are mixed together in a mass ratio of (5-8):(95-92) to obtain a mixed pulp.

7. The method according to claim 5, characterized in that, In step (2), calcium carbonate is dispersed to obtain a dispersion product with a dispersion concentration of 30-40%, and porous calcium silicate is dispersed to obtain a dispersion product with a dispersion concentration of 8-15%.

8. The method according to claim 5, characterized in that, The surface sizing agent concentration in step (4) is 6-12%, the temperature is 50-60℃, and the application rate is 4-5 g / m². 2 .

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