Paper, papermaking pulp, papermaking filler, and method for producing the same

Abstract

The application provides a paper product, a papermaking pulp, a papermaking filler and a preparation method thereof; the preparation method of the papermaking filler comprises the following steps: preparing a water solution of ground calcium carbonate; adding a first cationic coating reagent into the solution; adding microfibrillated cellulose into the solution; and adding a second cationic coating reagent into the solution. The preparation method of the papermaking filler provided in the embodiments of the application can greatly improve the retention rate of the filler and the strength of the paper sheet by adopting a ternary coating technology to pre-flocculate the filler (the first cationic coating reagent is added first, then the microfibrillated cellulose is added, and finally the second cationic coating reagent is added), and can also reduce the influence of the polyhydroxy property of the microfibrillated cellulose on the paper sheet filtration, so that the hydroxyl crosslinking between fibers can be fully utilized.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of papermaking pulp preparation, and in particular to paper products, papermaking pulp, papermaking fillers and preparation methods thereof. BACKGROUND

[0002] How to improve the retention rate of fillers is a problem that the papermaking industry has been seeking to solve. In order to solve this problem, in some schemes, a binary retention and drainage aid system composed of cationic nanocellulose and guar gum is used. According to the micro-flocculation mechanism, first, cationic guar gum is added to the tobacco sheet pulp to form larger flocculates with fibers and fillers. When the flocculates are damaged by high shear force, they will be dispersed into small flocculates. Then, cationic nanocellulose is added. The large specific surface area and fiber affinity of cationic nanocellulose enable it to form small and dense flocculates with the dispersed small flocculates in the pulp through charge neutralization and bridging, thereby improving the retention and drainage performance of the pulp. The appropriate addition of guar gum and nanocellulose not only improves the retention, but also improves the uniformity of the sheet base.

[0003] In other schemes, two kinds of high molecular compounds are used to pre-flocculate the fillers to control the median particle size of the filler flocculates to 10-150 um, which can improve the amount and retention rate of the fillers. In addition, there is a preparation method of microfibrillated fiber-filler composite. The microfibrillated fiber material is anionic, the filler has a negative Zeta potential, and the cationic polymer is used as a bridge between the microfibrillated fiber and the filler. The microfibrillated fiber-filler composite reduces the agglomeration of the fillers and enables the fillers to be uniformly attached to the surface of the microfibrillated fiber without agglomeration. The absolute dry mass of the microfibrillated cellulose material is 0.1-10% of the mass of the filler, which is equivalent to using the microfibrillated cellulose material as a seed to uniformly adsorb the filler particles on the surface of the cellulose. The average size of the filler particles is within 5 um, and the large size of the microfibrillated cellulose is used to improve the retention rate of the fillers.

[0004] With the same amount of GCC (Ground Calcium Carbonate, hereinafter referred to as GCC, ground calcium carbonate) added, the specific surface area of the coated filler flocculates is smaller, and the number of binding points between fibers is reduced, which can reduce the damage of GCC to the paper strength at high filler loading. The flocculated fillers can only reduce the damage of the filler to the paper strength to a certain extent, but when the filler loading is increased, the strength of the paper will still decrease significantly due to the lack of binding strength between the flocculates and the fibers.

[0005] Microfibrillated cellulose can improve the retention of microfibrillated cellulose by using charge effect through cationization, but when used in large quantities, the large number of hydrophilic hydroxyl groups on the surface of microfibrillated cellulose will greatly affect the dewatering efficiency of the high-speed board paper machine. Microfibrillated cellulose-filler composite technology allows fillers to adhere to the surface of cellulose, which can improve the retention rate of fillers. This also requires cellulose to have a larger size. Similar to the filler flocculation body produced by coating fillers with polymers, a larger overall particle size can still be retained under the action of high vacuum suction, but the fillers on the surface of the composite have no binding force with the fibers of the paper sheet, and only the retention rate of the fillers is simply improved, without playing the strength advantage brought by the high hydroxyl content of microfibrillated cellulose. SUMMARY

[0006] The first aspect of the embodiments of the present application provides a preparation method of papermaking filler, the preparation method comprising:

[0007] preparing a water solution of ground calcium carbonate;

[0008] adding a first cationic coating reagent to the solution;

[0009] adding microfibrillated cellulose to the solution;

[0010] adding a second cationic coating reagent to the solution.

[0011] In some embodiments, the amount of microfibrillated cellulose added is 1.0-3.0 kg / ton of filler; and the aspect ratio of the microfibrillated cellulose is greater than 1000.

[0012] In some embodiments, the first cationic coating reagent comprises a cationic polyacrylamide macromolecule or a cationic polyacryl imine macromolecule.

[0013] In some embodiments, the solution PCD of the first cationic coating reagent is 3 million-5 million ueq / l, the molecular weight is 5 million-10 million, the solid content is 35%-45%, and the viscosity is 200-600 cps.

[0014] In some embodiments, the second cationic coating reagent comprises a cationic polyacrylamide macromolecule.

[0015] In some embodiments, the solution PCD of the second cationic coating reagent is +800000 to +1500000 ueq / l, the molecular weight is 40 million-80 million, the solid content is 35%-45%, and the viscosity is 500-1000 cps.

[0016] In some embodiments, the step of adding the first cationic coating agent to the solution forms first filler flocculates, the median particle size of the first filler flocculates being 1.5-3.0 um; the step of adding the microfibrillated cellulose to the solution forms second filler flocculates, the median particle size of the second filler flocculates being 5.0-10.0 um; the step of adding the second cationic coating agent to the solution forms third filler flocculates, the particle size of the third filler flocculates being: D10 being 15-30 um, D50 being 35-70 um, and D90 being 100-200 um.

[0017] In a second aspect, the embodiments of the present application provide a papermaking filler, which is prepared by the preparation method described in the above embodiments.

[0018] In a third aspect, the embodiments of the present application provide a papermaking slurry, which comprises paper pulp and the papermaking filler described in the above embodiments.

[0019] In a fourth aspect, the embodiments of the present application provide a paper product, which is prepared by the papermaking slurry described in the above embodiments.

[0020] The preparation method of the papermaking filler provided by the embodiments of the present application uses a ternary coating technology to pre-flocculate the filler (firstly adding a first cationic coating agent, then adding microfibrillated cellulose, and finally adding a second cationic coating agent), which can greatly improve the retention rate of the filler and the strength of the paper sheet, and also can reduce the influence of the multi-hydroxyl property of the microfibrillated cellulose on the paper sheet drainage, and fully play the hydroxyl bonding effect between fibers. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0022] Figure 1 is a flowchart of an embodiment of the preparation method of the papermaking filler of the present application;

[0023] Figure 2 is a schematic diagram of the micro-particle structure of the filler in the preparation method of the papermaking filler of the present application. DETAILED DESCRIPTION

[0024] The application will be described in further detail below in connection with the drawings and embodiments. It is particularly pointed out that the following embodiments are only for illustration of the application and do not limit the scope of the application. Similarly, the following embodiments are only part of the embodiments of the application, and all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the application.

[0025] The terms "first", "second", "third" in the embodiments of the application are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second", "third" can explicitly or implicitly include at least one of the features. In the description of the application, the meaning of "a plurality of" is at least two, such as two, three, etc., unless otherwise specifically limited. All directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the application are only used to explain the relative positional relationship, movement condition, etc. between the components in a certain posture (as shown in the drawings), and if the certain posture changes, the directional indications also change accordingly. The terms "include" and "have" and any variations thereof in the embodiments of the application are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but can optionally include steps or units not listed, or can optionally include other steps or components inherent to the process, method, product or device.

[0026] In this document, reference to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearance of the phrase in various places in the specification does not necessarily all refer to the same embodiment, nor does it necessarily refer to a particular embodiment that is independent of or alternative to other embodiments. It is explicitly and implicitly understood that the embodiments described herein can be combined with other embodiments.

[0027] In view of the problems mentioned in the background art, the inventors studied how to play the high specific surface area and the hydrogen bonding effect of a large number of hydroxyl groups of microfibrillated cellulose to realize the reinforcing effect of microfibrillated cellulose. Therefore, a preparation method of a papermaking filler is proposed, please refer to Figure 1 , Figure 1 is a flowchart of an embodiment of the preparation method of the papermaking filler of the application, which includes but is not limited to the following steps.

[0028] Step S100, preparing a water solution of ground calcium carbonate.

[0029] In this step, specifically, an industrial ground calcium carbonate (GCC) slurry with a solid content of about 58% can be used, wherein the particle size of the GCC is: the proportion of 2 um is ≥ 55%, and the dispersant used during the grinding and dispersion of the GCC can be a polyacrylate salt. The addition amount of the dispersant needs to be controlled within 0.2%.

[0030] Under the condition of stirring and dispersion, the 58% GCC slurry is diluted to a solid content of 18-22% using white water as dilution water. The PCD (particle charge detector) of the GCC after dilution with white water is -3000 to -1000 ueq / l. The white water can be a clear filtrate obtained by disc mill filtration of the core layer, and the PCD of the white water is controlled to be -600 to -200 ueq / l.

[0031] Please continue to refer to Figure 1 The preparation method in this embodiment further includes a step S200 of adding a first cationic coating agent to the solution.

[0032] The addition amount of the first cationic coating agent is 0.2-1.0 kg / ton of filler, and can be 0.2 kg / ton of filler, 0.23 kg / ton of filler, 0.35 kg / ton of filler, 0.44 kg / ton of filler, 0.5 kg / ton of filler, 0.7 kg / ton of filler, 0.81 kg / ton of filler, 0.9 kg / ton of filler, 1.0 kg / ton of filler, etc., which is not limited specifically here.

[0033] Alternatively, the first cationic coating agent can include a cationic polyacrylamide macromolecule or a cationic polyacryl imine macromolecule, etc. The solution PCD of the first cationic coating agent is 3 million-5 million ueq / l, the molecular weight is 50-100 million, the solid content is 35%-45%, and the viscosity is 200-600 cps.

[0034] In this step, the first filler flocculation can be obtained by stirring at 1500 rpm for 30 s, wherein the median particle size of the first filler flocculation is 1.5-3.0 um, and the median particle size can be 1.6 um, 1.65 um, 1.77 um, 1.81 um, 1.9 um, 2.2 um, 2.5 um, 2.8 um, and 3.0 um, etc.

[0035] Please continue to refer to Figure 1 The preparation method in this embodiment further includes a step S300 of adding microfibrillated cellulose to the solution.

[0036] According to the morphology and preparation method of nanocellulose, it is mainly divided into three categories, namely: cellulose nanocrystal (CNC), nanocellulose fibril (NFC) and microfibrillated cellulose (MFC). Microfibrillated cellulose (MFC) is a one-dimensional nanometer cellulose material obtained by mechanical defibration of plant fibers. MFC is a random network composed of numerous cellulose microfibrils with high aspect ratio. After microfibrillation treatment, the specific surface area of cellulose increases and a large number of hydroxyl groups are exposed on the surface, so that it has high water retention value, good dispersibility and stability.

[0037] Optionally, in this embodiment, the addition amount of microfibrillated cellulose is 1.0-3.0 kg / ton of filler, which can be 1.0 kg / ton of filler, 1.2 kg / ton of filler, 1.35 kg / ton of filler, 2.14 kg / ton of filler, 2.5 kg / ton of filler, 2.6 kg / ton of filler, 2.61 kg / ton of filler, 2.8 kg / ton of filler and 3.0 kg / ton of filler, etc. The aspect ratio of the microfibrillated cellulose is greater than 1000.

[0038] In this step, it can be specifically stirred at a speed of 500-800 rpm for 1-2 min to obtain the second filler flocculation body, and the PCD is controlled to be 10-300 thousand ueq / l, and the median particle size of the second filler flocculation body is 5.0-10.0 um. The median particle size of the second filler flocculation body can be 5 um, 5.2 um, 5.5 um, 5.8 um, 6.1 um, 7 um, 8.5 um, 9.0 um and 1.0 um, etc. Here, it is not enumerated and described in detail.

[0039] Please continue to refer to Figure 1 The preparation method in this embodiment further includes the step S400 of adding a second cationic coating reagent to the solution.

[0040] Optionally, the second cationic coating reagent can be a cationic polyacrylamide polymer. The PCD of the solution of the second cationic coating reagent is +800,000 to +1,500,000 ueq / l, the molecular weight is 4-8 million, the solid content is 35%-45%, and the viscosity is 500-1,000 cps. The addition amount of the second cationic coating reagent is controlled to be 1.0-3.0 kg / ton of filler, which can be 1.0 kg / ton of filler, 1.2 kg / ton of filler, 1.35 kg / ton of filler, 2.14 kg / ton of filler, 2.5 kg / ton of filler, 2.6 kg / ton of filler, 2.61 kg / ton of filler, 2.8 kg / ton of filler and 3.0 kg / ton of filler, etc. Here, it is not specifically limited.

[0041] The coated GCC slurry is stirred with a grinding dispersant at 1500 rpm for 2 min, wherein the particle size of the third filler flocculate formed in this step is: D10 of 15-30 um, D50 of 35-70 um, and D90 of 100-200 um.

[0042] The preparation method of the papermaking filler in this embodiment adopts a ternary coating technology to pre-flocculate the filler, thereby improving the retention rate of the filler and the strength of the paper sheet. The first cationic coating agent has strong positive charges and pre-flocculates the filler dispersion with negative charges, so that the average particle size of the filler is processed to 2-4 um. The weakly cationic microfibrillated cellulose is added to re-flocculate the pre-flocculated filler particles, so that the particle size of the flocculated filler is 8-12 um. The high-molecular cationic polymer is further added to flocculate the micro-flocculate, thereby forming the microfibrillated cellulose-filler-high-molecular material flocculate with a median particle size of 40-150 um.

[0043] Please refer to Figure 2 , Figure 2 is a schematic diagram of the microstructure of the filler in the papermaking filler preparation method embodiment of the present application, wherein, in the diagram, 101 represents the GCC filler particles, 102 represents the first filler flocculate, 103 represents the second filler flocculate, and 104 represents the third filler flocculate. In the preparation method, the filler is coated and flocculated layer by layer, and the micro-nano cellulose can be used as the skeleton of the large flocculate to improve the firmness and internal bonding strength of the flocculate. The cationic microfibrillated cellulose has a large specific surface area and a large aspect ratio. Part of the fibers forms a flocculate with the filler, and part of the fibers is exposed outside the flocculate. During the paper sheet forming, the cationic property and the hydrogen bond interaction between the fibers and the flocculate can be synergized through the size effect, thereby improving the retention rate of the filler and the MFC (micro-nano cellulose). The hydrogen bond interaction between the hydroxyl groups of the microfibrillated cellulose on the surface of the flocculate and the hydroxyl groups of the pulp fibers can also improve the bonding strength between the filler flocculate and the fibers, thereby solving the problem that the filler flocculate and the fibers do not form a bond, and the high filler loading damages the hydrogen bond interaction between the fibers and reduces the strength of the paper sheet. This technology can also reduce the influence of the multi-hydroxyl property of the microfibrillated cellulose on the drainage of the paper sheet, fully play the role of the hydrogen bond interaction between the fibers, and enable the microfibrillated cellulose to be applied on a high-speed board paper machine.

[0044] The application of a papermaking filler will be introduced below. A pulp with a solid content of approximately 1.0% consisting of 5% hardwood bleached chemical pulp (LBKP), 30% poplar pulp, 45% chemi-mechanical pulp (APMP), and 20% broke paper is weighed, and the pulp is stirred at 1000 rpm. Cationic starch, dry strength agent, coated filler, retention and drainage aid, etc. are added to the pulp to make hand sheets. The amount of filler added is 200-300 kg.

[0045] The papermaking filler can be dispersed by a polyacrylic anionic high polymer, and the dispersant on the surface of the filler makes the filler as a whole negatively charged. The first agent (first cationic coating agent) is a high-molecular-weight polymer with strong positive charge and low molecular weight. The cationic polymer compound can flocculate the filler through electrostatic adsorption. The strong positive charge and low molecular weight can make the filler have strong binding force with other fillers and control the size to only 2-3 um, and preferentially react with GCC in the papermaking filler with a particle size of less than 0.5 um to make it flocculate. The addition of cationized microfibrillated cellulose adsorbs the anionic dispersant through charge interaction, and the high aspect ratio (length up to 50 um or more) of the microfibrillated cellulose can wrap the GCC. The microfibrillated cellulose bridges the fillers to form micro-flocs. Then a high-molecular-weight polymer with strong positive charge is added, and the long carbon chain structure makes the filler and MFC form larger flocs. The microfibrillated cellulose in the embodiment has a high aspect ratio and a low degree of cationic modification, and most of the hydroxyl groups are retained. The microfibrillated cellulose wraps the GCC and participates in bridging. The microfibrillated cellulose inside the filler coating can play the role of "reinforcing" skeleton, improving the internal bonding strength of the floc; the microfibrillated cellulose on the edge of the filler coating has abundant hydroxyl groups, which can form hydrogen bonds with fibers, improving the bonding strength between the filler coating and the fibers. Due to the improvement of the internal bonding strength of the filler coating and the strength between the filler and the fiber, the fiber strength can still be maintained when the filler content is more than 20%.

[0046] The filler coating agent and micro-nano cellulose are both cationic, and the stability of the coating body under high shear is derived from the charge and physical wrapping of MFC. When the total amount of coating agent A and micro-nano cellulose (MFC) exceeds 3 kg / ton of filler, the charge interaction between the second prepolymer and the second cationic coating agent weakens, and the coating body will disperse under high shear. The small particle size of the filler flocs increases, which is not conducive to the retention of the filler.

[0047] The following table shows the parameters of several different embodiments.

[0048]

[0049]

[0050]

[0051] It should be noted that the filler treatment agent A and the first branch agent in the above table are represented as the first cationic coating agent, the filler treatment agent C and the first branch agent are represented as the second cationic coating agent, and the second branch agent is represented as MFC (i.e. microfibrillated cellulose). From the above comparison, it can be known that the ternary filler coating technology containing MFC has better shear resistance and internal bonding strength than the binary filler coating, and can improve the dewatering of the pulp and the ash content and strength of the paper sheet.

[0052] The application mode of MFC-ternary filler coating in the embodiment of the present application makes full use of the high aspect ratio, high specific surface area and rich hydroxyl characteristics of microfibrillated cellulose, solves the difficulties of low retention rate and influence on paper sheet dewatering when microfibrillated cellulose is applied in papermaking, and improves the retention rate of MFC and filler. The hydroxyl structure of MFC allows the filler flocculation to form a binding force between the fibers, the paper sheet strength can be maintained under the condition that the ash content of the hand sheet is increased by 2%, and the technical problems of increasing the filling amount and reducing the paper sheet cohesion are solved, which provides an important application technology for subsequent paperboard ash content improvement and fiber raw material saving.

[0053] In addition, the paper product can be prepared by the paper pulp in the above embodiment, and other preparation process characteristics and parameters of the paper product are within the understanding range of those skilled in the art, which will not be described here.

[0054] The above only describes some embodiments of the present application, and does not limit the protection scope of the present application, and any equivalent device or equivalent process transformation using the content of the specification and drawings, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for the preparation of a papermaking filler, characterized in that, The preparation method comprises: preparing a water solution of ground calcium carbonate; adding a first cationic coating agent to the solution, the solution PCD of the first cationic coating agent being 3-5 million ueq / l, the molecular weight being 5-10 million, the solid content being 35-45%, and the viscosity being 200-600 cps; adding microfibrillated cellulose to the solution, the addition amount of the microfibrillated cellulose being 1.0-3.0 kg per ton of filler; the aspect ratio of the microfibrillated cellulose being greater than 1000; adding a second cationic coating agent to the solution, the solution PCD of the second cationic coating agent being +800000 to +1500000 ueq / l, the molecular weight being 4-8 million, the solid content being 35-45%, and the viscosity being 500-1000 cps.

2. The production method according to claim 1, characterized by, The first cationic coating agent comprises a cationic polyacrylamide macromolecule or a cationic polyacryl imine macromolecule.

3. The preparation method according to claim 1, characterized in that, The second cationic coating agent comprises a cationic polyacrylamide macromolecule.

4. The method of claim 1, wherein, The step of adding the first cationic coating agent to the solution forms first filler flocculates, the median particle size of the first filler flocculates being 1.5-3.0 um; the step of adding the microfibrillated cellulose to the solution forms second filler flocculates, the median particle size of the second filler flocculates being 5.0-10.0 um; and the particle size of third filler flocculates formed by the step of adding the second cationic coating agent to the solution is as follows: D10 being 15-30 um, D50 being 35-70 um, and D90 being 100-200 um.

5. A papermaking filler, characterized by The papermaking filler is prepared by the preparation method of any one of claims 1-4.

6. A papermaking pulp, characterized in that, The papermaking pulp comprises paper pulp and the papermaking filler of claim 5.

7. A paper product, characterized by The paper product is prepared by the papermaking pulp of claim 6.

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