Method of producing cellulose nanofiber

Abstract

To provide a production method capable of producing a cellulose nanofiber of excellent quality, even when low production-cost mechanical fibrillation is employed.SOLUTION: Damaged paper generated in a paper making process, usable as a paper making raw material, is blended with water and a cellulase-based enzyme to prepare an aqueous dispersion, which is subjected to a mechanical fibrillation step. The mechanical fibrillation step preferably is divided into a rough fibrillation step and a micronizing step subsequently, and the mechanical fibrillation step is carried out using a stone-mill type grinder constituted by a pair of whetstone plates. The raw material concentration, the clearance between the whetstone plates and the rotation speed of the whetstone plates are used as adjustment parameters in the micronizing step. HERCOBOND (registered trademark) 8922, 8988 are preferably used as cellulase-based enzymes. High-quality cellulose nanofibers distributed with peak particle sizes ranging from nanoscale to microscale, whose fibrillation is readily promoted, can be obtained.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing cellulose nanofibers, and in particular to a method for producing high-quality cellulose nanofibers using broken paper generated during the papermaking process as a raw material. [Background technology]

[0002] Cellulose nanofiber is a material made by breaking down and finely grinding plant fibers, the main component of which is cellulose, to nanometer sizes (1 nanometer is one billionth of a meter). In addition to being strong and lightweight, it has multiple properties, including high elasticity, low thermal expansion, high transparency, high water absorption, high viscosity retention, and transparency, and is expected to be used not only as a structural material, but also in hygiene and daily necessities such as shampoo, cosmetics, and toilet paper, taking advantage of the diverse properties of this material, and even in the food industry, taking advantage of the fact that it is a natural material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-131725 A Summary of the Invention [Problem to be solved by the invention]

[0004] As described in Patent Document 1, a method for producing cellulose nanofibers from pulp has already been established. However, the currently mainstream production method uses chemical treatments such as TEMPO oxidation, and although it is true that this method can produce high-quality cellulose nanofibers with uniform fiber length, i.e., particle size, the high production costs drive up the selling price, preventing wider use. On the other hand, if the current mechanical fiber-opening method is used, the cost can be reduced, but the particle size will vary, resulting in quality problems, which is particularly frustrating when long fibers are desired.

[0005] The present invention is intended to solve the above-mentioned problems, and has an object to provide a production method that can produce high-quality cellulose nanofibers even when mechanical defibration is performed. [Means for solving the problem]

[0006] While a uniform particle size has been used as an indicator of the quality of cellulose nanofibers, the inventors believed that, at least in terms of strength, a distribution of particle sizes with a peak from nano to micro sizes and promoted fibrillation would be an indicator of good quality. In addition, in paper companies, broke paper is inevitably generated during the papermaking process, and paper that has not yet been printed or otherwise processed is generally circulated or recirculated within the same process. However, the present inventors noticed that this broken paper has already been beaten. Based on these findings, the inventors have discovered a manufacturing method that uses the above-mentioned broken paper as a raw material and, with further ingenuity, can produce high-quality cellulose nanofibers even when mainly using mechanical defibration, thereby completing the present invention.

[0007] The present invention is a method for producing cellulose nanofibers, which comprises using broken paper generated during the papermaking process and usable as a papermaking raw material as the cellulose nanofiber raw material, combining it with water and a cellulase-based enzyme agent to form an aqueous dispersion, and then subjecting it to a mechanical defibration treatment process.

[0008] The mechanical fiberization process is preferably divided into a rough fiberization process and a subsequent fine fiberization process. Preferably, the mechanical fiberization process is carried out using a millstone grinder consisting of two grindstones. In the micronization process, the particle size of the cellulose nanofibers is adjusted using the raw material concentration, the clearance between the grindstones, and the rotation speed of the grindstones as adjustment parameters.

[0009] Preferably, the cellulase-based enzyme agent used is Hercobond 8922 or 8988 "HERCOBOND (registered trademark)". Effect of the Invention

[0010] According to the manufacturing method of the present invention, by making good use of broken paper that is easily available to paper companies, high-quality cellulose nanofibers can be produced even when mainly using mechanical defibration. It is also easy to adjust the concentration and peak particle size of the cellulose nanofiber that is ultimately obtained in paste form, allowing it to be customized according to the application. [Brief description of the drawings]

[0011] [Figure 1] 1A to 1C are process diagrams of a manufacturing method according to an embodiment of the present invention. [Diagram 2] 1 shows particle size data for cellulose nanofibers produced in the examples. [Diagram 3] An image of the cellulose nanofibers in Figure 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The method for producing cellulose nanofibers of the present invention will be described below, divided into materials and steps. <Material> [Cellulose nanofiber raw material] After wood chips and waste paper are pulped, the pulp is sent to the wire part, press part, and dryer part in the papermaking process to make base paper, which is then wound around a reel to make a jumbo roll, and then sent to the winder / cutter for finishing.

[0013] In the papermaking process, there are two types of paper: the recycled paper, which is returned to the papermaking process as it is and used as a raw material for papermaking, and the in-feed paper, which is stored in the papermaking factory or company and used as a raw material for papermaking later. These types of paper breakage are unavoidable and occur on a daily basis, even if papermaking factories try to minimize them. Both types of paper breakage are fully beaten and have not yet been printed. In the present invention, this broke paper is used as the raw material for cellulose nanofibers. Not only is it suitable in terms of characteristics, but it is also advantageous in that it is easily available.

[0014] A well-known example of pulp derived from hardwoods is LBKP (hardwood kraft pulp). A well-known example of pulp derived from softwoods is NBKP (softwood kraft pulp). Hardwood pulp has short cellulose fibers and is highly valued because it is easy to improve the texture of the paper surface, but it is said that softwoods, which have long cellulose fibers, can produce better cellulose nanofibers than hardwoods. In addition, LBKP and NBKP have low levels of impurities such as lignin and hemicellulose, making them advantageous for defibration. The base paper for toilet paper rolls (jumbo rolls) usually contains 20% or more of coniferous wood pipes as NBKP, making it particularly advantageous as a raw material for the cellulose nanofibers of the present invention. At the current laboratory stage, scraps of base paper (jumbo rolls), in particular, from the waste paper generated during the toilet paper roll manufacturing process, are being used.

[0015] [Cellulase enzymes] Cellulase-based enzyme preparations are functional additives that have traditionally been used as paper strength agents in paper mills to promote fibrillation of pipes and thereby increase paper strength. In the present invention, this cellulase-based enzyme agent is used to promote defibration when mechanical defibration is performed. This use shortens the time required for mechanical fiberization, which is expected to reduce energy and labor costs, but it also has an impact on the quality of the cellulose nanofibers, as will be described in detail later.

[0016] As cellulase-based enzyme agents, the use of product names: Hercobond 8922, 8988 "HERCOBOND (registered trademark)" (manufacturer: Riken Green Co., Ltd.) is recommended. It is recommended that cellulase enzyme agents be added at a ratio of 0.05 to 0.3% by mass per 100% by mass of raw material (dried broke). Less than this amount will not produce a significant effect, but experimental results to date have confirmed that 0.3% by mass is sufficient.

[0017] <Process> [Preparation] The raw material is waste paper from the base paper (jumbo roll) produced during the toilet paper roll manufacturing process. Add the ingredients and water, and leave the ingredients submerged in the water for half a day to a day. Taking into consideration ease of processing in subsequent steps, the standard ratio is approximately 8L of water for every 160g of raw material. In the following, the type of equipment used and its operating conditions are described based on the absolute amount of raw material being 160 g.

[0018] First, put the raw materials into a container (bucket), then spray water from a straight nozzle using water pressure. The raw material is dry paper, but it swells due to the water injection and subsequent leaving to stand.

[0019] [Mixing] The swollen material as described above is placed in a stirrer and stirred to form an aqueous dispersion. The stirrer is a so-called homogenizer, and as an example, a high-power mixer manufactured by ASONE is used. When the above-mentioned example of the stirrer is used, it is operated at a rotation speed of 2000 to 2300 rpm for about 30 minutes.

[0020] The cellulase enzyme agent is placed in the mixer and mixed with the raw materials, etc. Through this mixing, an aqueous dispersion is formed.

[0021] [Mechanical fiber defibration processing] The mixture thus stirred is subjected to a rough mechanical fiber defibration treatment. The processing equipment includes a grinder type, a homogenizer type, a kneader type, an underwater collision type, etc., but in the present invention, it is recommended to use a stone mill type grinder, which is a type of grinder type. In a stone mill type grinder, the raw material is fed between two grinding plates, at least one of which rotates in opposition to each other, and fiberized. As an example, a product named Masscolloider (manufacturer: Masuko Sangyo Co., Ltd.) is used. The mechanical fiberization process is divided into coarse fiberization and fine fiberization, with first the coarse fiberization and then the fine fiberization.

[0022] (roughly defibrated) Since the raw material has already been beaten, it is easier to defibrate in the mechanical defibration process after being stirred. One grinding plate is fixed and the other is rotated. In one example, the rotation speed is set to about 1800 rpm and the clearance of the grinding plates is set to about 500 μm, and the millstone grinder is operated. The entire amount of the mixed raw materials is added at once, and then 1L of water is added. Since the number of passes is two, the total amount of water is 10L. Due to the large clearance, the raw materials are discharged smoothly.

[0023] After that, the device is washed and the following is carried out.

[0024] (miniaturization) Next, one grinding plate is fixed and the other is rotated. In one example, the rotation speed is set to about 1500 rpm and the clearance of the grinding plates is set to about 150 μm, and the millstone grinder is operated. In one example, the number of passes is set to two. The speed at which the material falls is slower than in the case of rough defibration, so instead of waiting for the material added the first time to completely pass and fall before adding the second, the material is added in small amounts at a time. The time required for this pulverization is, in one example, about 1 hour and 15 minutes. If a cellulase-based enzyme agent is not added, the time is about 2 hours, but adding a cellulase-based enzyme agent shortens the time.

[0025] In addition, in the present invention, the raw material has already been beaten, and by adding a cellulase enzyme agent, the clearance is kept large at about 150 μm, and the material can be loosened to nanometer size and then refined to the final stage, so that the obtained cellulose nanofibers have a peak particle size distribution from nano to micro sizes, and fibrillation is promoted. In other words, the cellulose nanofibers have many whiskers. In addition, the peak particle size can be shifted by adjusting the raw material concentration, the clearance between the grinding wheels, and the rotation speed of the grinding wheels as adjustment parameters.

[0026] [Post-processing] If necessary, add water to adjust the concentration. As a result, manufacturing efficiency is greatly improved, resulting in lower costs.

[0027] In one practical application, it is applied to the core of a coreless toilet paper roll to reinforce its strength and improve the core strength. EXAMPLES

[0028] The raw material was waste paper from the base paper (jumbo roll) produced during the toilet paper manufacturing process. This waste paper had a NBKP / LBKP ratio of 25 / 75 by mass, and the peak fiber particle size was about 1200 μm. The mixture was subjected to stirring and mechanical fiberization treatment using the device shown in the embodiment and the operating conditions of the device. The obtained cellulose nanofiber contained water and was in a paste-like state, and the amount of water was finally adjusted so that the water content was 98 mass%.

[0029] When the particle size distribution of the cellulose nanofibers was measured, the results shown in Figure 2 were obtained. The particle size peak was 46 μm, and the fiber length peak was longer. In addition, the particles were mixed from nano to micro sizes. Furthermore, the image of the cellulose nanofiber was as shown in Figure 3. As indicated by the arrows, there were many hairs sticking out.

[0030] Although the embodiment and examples of the present invention have been described in detail above, the scope of the present invention is not limited to these, and even if the design is changed within the scope of the present invention, it is included in the present invention.

Claims

1. This method for producing cellulose nanofibers is characterized in that broken paper generated during the papermaking process and usable as a papermaking raw material is used as the cellulose nanofiber raw material, which is mixed with water and a cellulase-based enzyme agent to form an aqueous dispersion, and then subjected to a mechanical fiberization treatment process.

2. The method for producing cellulose nanofibers according to claim 1, A manufacturing method characterized in that the mechanical fiberization process is divided into a rough fiberization process and a subsequent fine fiberization process.

3. In the method for producing cellulose nanofibers according to claim 2, This manufacturing method is characterized in that the mechanical fiber-defibrating process is carried out using a stone mill type grinder composed of two grinding plates.

4. The method for producing cellulose nanofibers according to claim 3, This is a manufacturing method characterized in that in the micronization process, the particle size of the cellulose nanofibers is adjusted using the raw material concentration, the clearance between the grinding wheels, and the rotation speed of the grinding wheels as adjustment parameters.

5. The method for producing cellulose nanofibers according to claim 1, The method is characterized in that Hercobond 8922 and 8988 (HERCOBOND (registered trademark)) are used as the cellulase enzyme agent.

6. The method for producing cellulose nanofibers according to any one of claims 1 to 5, A manufacturing method characterized by using waste paper from the toilet paper roll paper manufacturing process.

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