Paper product, papermaking pulp, papermaking filler and preparation method thereof

Abstract

The invention provides a paper product, papermaking pulp, papermaking filler and a preparation method thereof. The preparation method of the papermaking filler comprises the following steps: preparing an aqueous solution of ground calcium carbonate; adding a first cation coating reagent to the solution; adding microfibrillated cellulose to the solution; and adding a second cation coating reagent to the solution. According to the preparation method of the papermaking filler provided by the embodiment of the invention, the filler is pre-flocculated by adopting a ternary coating technology (the first cation coating reagent is firstly added, then the microfibrillated cellulose is added, and finally the second cation coating reagent is added), so that the retention rate and the paper sheet strength of the filler can be greatly improved; in addition, the influence of the polyhydroxy characteristic of the microfibrillated cellulose on water filtration of paper sheets can be reduced, and the hydroxyl combination effect between fibers can be fully exerted.

Description

Technical Field

[0001] The present application relates to the technical field of papermaking pulp preparation, and in particular to a paper product, papermaking pulp, papermaking filler and a preparation method thereof. Background Art

[0002] How to improve the filler retention rate is a problem that the papermaking industry has been seeking to solve. In order to solve this problem, some solutions use a dual retention and drainage system composed of cationic nanocellulose and guar gum. According to the micro-flocculation mechanism, cationic guar gum is first added to the tobacco sheet slurry to form larger flocs with fibers and fillers. When the flocs are destroyed by high shear forces, they will disperse into small flocs, and then cationic nanocellulose is added. The huge specific surface area and fiber affinity of cationic nanocellulose allow it to form densely structured and smaller flocs with dispersed small aggregates in the slurry through charge neutralization, bridging and other effects, thereby improving the retention and drainage performance of the slurry. The appropriate addition of guar gum and nanocellulose can not only play a retention role, but also contribute to the uniformity of the sheet base.

[0003] In other schemes, two polymer compounds are used to pre-flocculate the filler so that the median particle size of the filler floccules is controlled at 10um-150um, which can increase the amount and retention rate of the filler. In addition, there is a method for preparing a microfibrillated fiber-filler composite, which is composited with anionic microfibrillated fiber materials, fillers with negative Zeta potential, and cationic polymer substances. By introducing positively charged cationic polymers as a bridge between microfibrillated fibers and fillers, the agglomeration of fillers in the microfibrillated fiber-filler composite is reduced, and the fillers can be evenly attached to the surface of the microfibrillated fibers without filler 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 the base seed to uniformly adsorb the filler particles on the cellulose surface. The average size of the filler particles is within 5um, and the large size of the microfibrillated cellulose is used to improve the filler retention rate.

[0004] At the same GCC (Ground Calcium Carbonate, hereinafter referred to as GCC, ground calcium carbonate) addition amount, the specific surface area of ​​the coated filler flocs becomes smaller, and fewer fiber-fiber bonding points are occupied, which can reduce the damage of GCC to the strength of the paper sheet at high addition. The flocculated filler can only reduce the damage to the strength of the paper sheet by adding fillers to a certain extent, but when the addition amount is increased, due to the bonding strength of the flocs themselves and the lack of bonding strength between the flocs and the fibers, the strength of the paper sheet will still be greatly reduced.

[0005] Microfibrillated cellulose can be cationized to improve the retention of microfibrillated cellulose by utilizing the charge effect. However, when used in large quantities, the large amount of hydrophilic hydroxyl groups on the surface of microfibrillated cellulose will greatly affect the dehydration efficiency of high-speed paperboard machines. 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 that the cellulose has a larger size, similar to the polymer-coated filler to produce filler flocs. A larger overall particle size can still be retained under the action of high vacuum suction. However, there is no binding force between the filler on the surface of the composite and the paper fiber. It simply improves the retention rate of the filler, without giving full play to the strength advantage brought by the high hydroxyl content of microfibrillated cellulose. Summary of the invention

[0006] A first aspect of the present application provides a method for preparing a papermaking filler, the method comprising:

[0007] preparing an aqueous solution of ground calcium carbonate;

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

[0009] adding microfibrillated cellulose to the solution;

[0010] A second cationic coating agent is added to the solution.

[0011] In some embodiments, the added amount of the microfibrillated cellulose 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 agent includes a cationic polyacrylamide polymer or a cationic polypropyleneimine polymer.

[0013] In some embodiments, the solution PCD of the first cationic coating agent is 3 million to 5 million ueq / l, the molecular weight is 500,000 to 1 million, the solid content is 35% to 45%, and the viscosity is 200 to 600 cps.

[0014] In some embodiments, the second cationic coating agent comprises a cationic polyacrylamide polymer.

[0015] In some embodiments, the solution PCD of the second cationic coating agent is +800,000 to +1,500,000 ueq / l, the molecular weight is 4 million to 8 million, the solid content is 35% to 45%, and the viscosity is 500-1,000 cps.

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

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

[0018] In a third aspect, an embodiment of the present application provides a papermaking pulp, wherein the papermaking pulp includes pulp and the papermaking filler described in the above embodiment.

[0019] In a fourth aspect, an embodiment of the present application provides a paper product, which is prepared using the papermaking pulp described in the above embodiment.

[0020] The preparation method of papermaking filler provided in the embodiment of the present application adopts a ternary coating technology to pre-flocculate the filler (first 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. In addition, it can also reduce the effect of the multi-hydroxy characteristics of microfibrillated cellulose on the water filtration of the paper sheet, and give full play to the hydroxyl bonding effect between fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 It is a schematic flow chart of an embodiment of a method for preparing a papermaking filler of the present application;

[0023] Figure 2 It is a schematic diagram of the microscopic particle structure of the filler in the embodiment of the method for preparing papermaking filler of the present application. DETAILED DESCRIPTION

[0024] The present application is further described in detail below in conjunction with the accompanying drawings and examples. It is particularly noted that the following examples are only used to illustrate the present application, but are not intended to limit the scope of the present application. Similarly, the following examples are only some embodiments of the present application rather than all embodiments, and all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present application.

[0025] The terms "first", "second", and "third" in the embodiments of the present application are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Thus, the features defined as "first", "second", and "third" can expressly or implicitly include at least one of the features. In the description of the present application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. In the embodiments of the present application, all directional indications (such as up, down, left, right, front, back...) are only used to explain the relative position relationship, movement, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication also changes accordingly. The terms "including" and "having" in the embodiments of the present application and any of their variations are intended to cover non-exclusive inclusions. 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 optionally also includes steps or units that are not listed, or optionally also includes other steps or components inherent to these processes, methods, products, or devices.

[0026] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0027] In view of the problems mentioned in the background technology, the inventors studied how to make use of the high specific surface area and hydrogen bonding of a large number of hydroxyl groups of microfibrillated cellulose to achieve the reinforcing effect of microfibrillated cellulose. Therefore, a method for preparing papermaking filler is proposed, please refer to Figure 1 , Figure 1 It is a flow chart of an embodiment of a method for preparing a papermaking filler of the present application, and the preparation method includes but is not limited to the following steps.

[0028] Step S100, preparing an aqueous solution of ground calcium carbonate.

[0029] In this step, industrial ground calcium carbonate (GCC) slurry may be used, with a solid content of about 58%, wherein the particle size of GCC: 2 um accounts for ≥ 55%, and the dispersant used in the grinding and dispersion of GCC may be polyacrylate, and the amount of the dispersant added needs to be controlled within 0.2%.

[0030] In the state of stirring and dispersing, use white water as dilution water to dilute 58% GCC mud to 18-22% solid content. The PCD (particle charge detector) of GCC after dilution with white water is -3000 to -1000ueq / l. White water can be the clear filtrate after the core layer is filtered through the disc grinding. The PCD of white water is controlled at -600 to -200ueq / l.

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

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

[0033] Optionally, the first cationic coating agent may include cationic polyacrylamide polymer or cationic polypropylene imine polymer, etc. The first cationic coating agent solution has a PCD of 3-5 million ueq / l, a molecular weight of 500,000-1 million, a solid content of 35%-45%, and a viscosity of 200-600cps.

[0034] In this step, the first filler flocs may be obtained by stirring at 1500 rpm for 30 seconds, wherein the median particle size of the first filler flocs is 1.5-3.0 um, and the median particle size may specifically 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, 3.0 um, and the like.

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

[0036] Nanocellulose is mainly divided into three categories according to its morphology and preparation methods, namely: cellulose nanocrystals (CNC), nanocellulose fibrils (NFC) and microfibrillated cellulose (MFC). Microfibrillated cellulose (MFC) is a one-dimensional nanoscale cellulose material obtained by mechanical fibrillation using plant fibers as raw materials. MFC is an irregular network composed of numerous cellulose microfibrils with high aspect ratios. After microfibrillation, the specific surface area of ​​cellulose increases and a large number of hydroxyl groups are exposed on the surface, making it have a higher water retention value, good dispersibility and stability.

[0037] Optionally, in this embodiment, the amount of microfibrillated cellulose added is 1.0-3.0 kg / ton of filler, specifically 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., which are not specifically limited here. The aspect ratio of the microfibrillated cellulose is greater than 1000.

[0038] In this step, the mixture is stirred at a speed of 500-800 rpm for 1-2 minutes to obtain a second filler floc, wherein the PCD is controlled at 100,000-300,000 ueq / l, and the median particle size of the second filler floc is 5.0-10.0 um. The median particle size of the second filler floc may be 5 um, 5.2 um, 5.5 um, 5.8 um, 6.1 um, 7 um, 8.5 um, 9.0 um, 1.0 um, etc. These are not listed or described in detail here.

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

[0040] Optionally, the second cationic coating agent can be a cationic polyacrylamide polymer. Wherein, the solution PCD of the second cationic coating agent is +800000 to +1500000ueq / l, the molecular weight is 4 million-8 million, the solid content is 35%-45%, and the viscosity is 500-1000cps. The addition amount of the second cationic coating agent is controlled at 1.0-3.0kg / ton of filler, specifically 1.0kg / ton of filler, 1.2kg / ton of filler, 1.35kg / ton of filler, 2.14kg / ton of filler, 2.5kg / ton of filler, 2.6kg / ton of filler, 2.61kg / ton of filler, 2.8kg / ton of filler and 3.0kg / ton of filler, etc., which are not specifically limited here.

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

[0042] The preparation method of the papermaking filler in this embodiment adopts a ternary coating technology to pre-flocculate the filler to improve the retention rate of the filler and the strength of the paper sheet. Among them, the first cationic coating agent has a strong positive charge, pre-flocculates the negatively charged filler dispersion, and processes the average particle size of the filler to 2-4um; weakly cationic microfibrillated cellulose is added to re-flocculate the pre-flocculated filler particles, and the filler particle size after flocculation is 8-12um; and then a high molecular cationic polymer is added to further flocculate the micro-flocculates to form flocculated particles of microfibrillated cellulose-filler-polymer material with a median particle size of 40-150um.

[0043] See also Figure 2 , Figure 2 This is a schematic diagram of the microscopic structure of the microscopic particles of the filler in the embodiment of the papermaking filler preparation method of the present application, wherein the label 101 in the figure represents the GCC filler particles, the label 102 represents the first filler floccules, the label 103 represents the second filler floccules, and the label 104 represents the third filler floccules. In the preparation process, the fillers with small particle sizes are coated and flocculated layer by layer, and the micro-nano cellulose can be used as the skeleton of the large floccules to improve the fastness and internal bonding strength of the floccules. Due to its large specific surface area and large aspect ratio, part of the cationic microfibrillated cellulose fiber forms floccules with the filler, and part of it will be exposed outside the floccules. When the paper sheet is formed, it can cooperate with the size effect of the floccules through its cationic properties and hydrogen bonding with the pulp fibers, and at the same time improve the retention rate of the filler and MFC (micro-nano cellulose). In addition, the hydrogen bonding between the hydroxyl groups of microfibrillated cellulose on the surface of the flocs and the hydroxyl groups of pulp fibers can also improve the bonding strength between the filler flocs and the fibers, solving the problem that there is no bonding between the simple filler flocs and the fibers, and when the filler is added in large amounts, the hydrogen bonding between the fibers is destroyed, reducing the strength of the paper sheet. This technology can also reduce the impact of the multi-hydroxyl characteristics of microfibrillated cellulose on the water filtration of the paper sheet, give full play to the bonding effect of the hydroxyl groups between the fibers, and the microfibrillated cellulose can be applied to high-speed board and paper machines.

[0044] The following is an application of a papermaking filler. Prepare a slurry with a solid content of approximately 1.0% consisting of 5% hardwood bleached chemical pulp (LBKP), 30% poplar pulp, 45% chemimechanical pulp (APMP) and 20% broke paper, weigh a certain weight of the slurry, add pharmaceutical cationic starch, dry strength agent, coated filler, retention and drainage aid, etc. under stirring at 1000rpm, and make hand sheets. The amount of filler added is 200-300kg.

[0045] Among them, the filler for papermaking can be dispersed by polyacrylic acid anionic polymer, and the dispersant on the surface of the filler makes the filler as a whole carry a negative charge. The first drug (the first cationic coating agent) is a polymer with a strong positive charge and a 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 binding force between the fillers strong and the size is only controlled at 2-3um, and preferentially react with GCC with a particle size of less than 0.5um in the papermaking filler to flocculate it. Cationic microfibrillated cellulose is added, and the cationic group and the anionic dispersant are adsorbed through the charge effect, and the high aspect ratio of microfibrillated cellulose (length reaches more than 50um) can entangle GCC, and micro-flocculates are generated between fillers through microfibrillated cellulose bridges. Then a strong cationic polymer is added, and its molecular weight reaches more than 3 million. The long carbon chain structure allows the filler and MFC to form larger floccules. The microfibrillated cellulose in the embodiment of the present application has a high aspect ratio, a low degree of cationic modification, and retains most of the hydroxyl groups. The microfibrillated cellulose is wrapped around GCC to participate in bridging. The microfibrillated cellulose inside the filler coating can play the role of a "reinforcement" skeleton, thereby improving the internal bonding strength of the flocculent as a whole. The microfibrillated cellulose at the edge of the filler coating can form hydrogen bonds with the fiber due to its abundant hydroxyl groups, thereby improving the bonding strength between the filler coating and the fiber. Since the internal bonding strength of the filler coating itself and the strength between the filler and the fiber are improved, the paper sheet can still maintain the fiber strength when the filling amount reaches more than 20%.

[0046] Both the filler coating agent and micro-nano cellulose are cationic. The stability of the coating under high shear, that is, the bonding strength between the GCC particles in the coating, comes from the physical entanglement of the charge and 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 is weakened, the coating will disperse under the action of high shear, and the small-particle filler flocs will increase, which is not conducive to the retention of the filler.

[0047] The following table is a comparison of parameters of several different embodiments.

[0048]

[0049]

[0050]

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

[0052] The coating application method of MFC-ternary filler 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 low retention rate of microfibrillated cellulose in papermaking and the difficulty of affecting paper dehydration, and improves the retention rate of MFC and filler. The hydroxyl structure of MFC is used to form a binding force between the filler floccules and the fibers. When the ash content of the hand-made sheet is increased by 2%, the strength of the paper sheet can be maintained, which solves the technical problem of increased filling amount and decreased cohesion of the paper sheet, and provides an important application technology for subsequent paperboard to increase the ash content and save fiber raw materials.

[0053] In addition, the embodiment of the present application further provides a paper product, which can be obtained by using the pulp in the above embodiment. Other preparation process characteristics and parameters of the paper product are within the scope of understanding of those skilled in the art and will not be described in detail here.

[0054] The above descriptions are only some embodiments of the present application, and do not limit the protection scope of the present application. Any equivalent device or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly used in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for preparing a papermaking filler, characterized in that: The preparation method comprises: preparing an aqueous solution of ground calcium carbonate; adding a first cationic coating agent to the solution; adding microfibrillated cellulose to the solution; A second cationic coating agent is added to the solution.

2. The preparation method according to claim 1, characterized in that: The addition amount of the microfibrillated cellulose is 1.0-3.0 kg / ton of filler; and the aspect ratio of the microfibrillated cellulose is greater than 1000.

3. The preparation method according to claim 1, characterized in that: The first cationic coating agent includes cationic polyacrylamide polymer or cationic polypropylene imine polymer.

4. The preparation method according to claim 3, characterized in that: The solution PCD of the first cationic coating reagent is 3 million to 5 million ueq / l, the molecular weight is 500,000 to 1 million, the solid content is 35% to 45%, and the viscosity is 200 to 600 cps.

5. The preparation method according to claim 1, characterized in that: The second cationic coating agent includes cationic polyacrylamide polymer.

6. The preparation method according to claim 5, characterized in that: The solution PCD of the second cationic coating agent is +800,000 to +1,500,000 ueq / l, the molecular weight is 4 million to 8 million, the solid content is 35% to 45%, and the viscosity is 500 to 1,000 cps.

7. The preparation method according to claim 1, characterized in that: The step of adding the first cationic coating agent to the solution forms a first filler floc, and the median particle size of the first filler floc is 1.5-3.0um; the step of adding microfibrillated cellulose to the solution forms a second filler floc, and the median particle size of the second filler floc is 5.0-10.0um; the step of adding the second cationic coating agent to the solution forms a third filler floc, and the particle sizes of the third filler floc are: D10 is 15-30um, D50 is 35-70um, and D90 is 100-200um.

8. A papermaking filler, characterized in that: The papermaking filler is prepared by the preparation method described in any one of claims 1 to 7.

9. A papermaking pulp, characterized in that: The papermaking slurry comprises pulp and the papermaking filler according to claim 8.

10. A paper product, characterized in that: The paper product is prepared using the papermaking pulp described in claim 9.

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