JP7346018B2 - Method for producing cellulose fiber slurry - Google Patents

Description

The present invention relates to a method for producing cellulose fiber slurry.

Cellulose nanofibers (CNF), which are obtained by defibrating cellulose fibers to the nano-level, have excellent strength, elasticity, thermal stability, etc., and are therefore expected to be used in a variety of applications. One of the uses of cellulose nanofibers is molded bodies of cellulose nanofibers (hereinafter also simply referred to as "molded bodies, etc.") obtained by drying, molding, etc., a slurry of cellulose nanofibers. For example, Patent Document 1 proposes "a CNF molding method characterized by filling a CNF-containing slurry into a mold using a vapor permeation means, applying a load to the CNF-containing slurry, and concentrating it." . The document describes ``a CNF molding method that allows easy adjustment of drying conditions, no shrinkage or cracking, and can stably obtain CNF molded products with a sophisticated three-dimensional structure with high productivity, and CNF obtained by the molding method. ``The purpose is to provide molded objects.''

However, this document is an invention that focuses on the mold used in the production of a CNF molded product and the production method itself to improve drying properties, and does not focus on the dehydration properties of the cellulose fiber slurry used. However, if the dehydration properties of the cellulose fiber slurry can be improved, there are advantages such as the ability to improve the drying properties of molded articles and the like.

JP2016-94683A

The main problem to be solved by the present invention is to provide a method for producing a cellulose fiber slurry with excellent dehydration properties.

While conducting various tests to solve the above problems, the present inventors first found that cellulose nanofibers are cellulose fibers used for high strength, but microfibrillated cellulose (MFC). It has been found that by using cellulose (sometimes referred to as cellulose), it is possible to improve the dehydration properties of cellulose fiber slurry while ensuring a certain degree of strength. Furthermore, it has been found that the strength of molded articles and the like can be improved by using a combination of microfibrillated cellulose and pulp. Furthermore, when microfibrillated cellulose and pulp are used in combination, using cellulose nanofibers as a complementary material to microfibrillated cellulose helps to simultaneously achieve the dehydration properties of cellulose fiber slurry and the strength of molded objects. I found out. Based on this knowledge, we came up with the following method.

(Means according to claim 1 )
A method for producing cellulose fiber slurry containing cellulose fibers as the main component,
As the cellulose fibers, microfibrillated cellulose having an average fiber diameter of 0.1 to 10 μm and pulp having an average fiber diameter of 10 to 100 μm are used, and as a complementary material to the microfibrillated cellulose, cellulose nano having an average fiber diameter of 10 to 90 nm. Include fiber,
The water retention degree of the microfibrillated cellulose is 500% or less,
A method for producing cellulose fiber slurry , characterized by :

(Means according to claim 2 )
The solid content concentration of the cellulose fiber is 1.0 to 15% by mass,
A method for producing a cellulose fiber slurry according to claim 1 .

(Means according to claim 3 )
When heated under pressure (120° C., 1 MPa, 5 minutes) to form a sheet with a moisture content of 10% by mass or less and a density of 1.0 g/cm ³ , the tensile strength is 10 to 250 MPa.
A method for producing a cellulose fiber slurry according to claim 1 or 2 .

(Means according to claim 4 )
When heated under pressure (120° C., 1 MPa, 5 minutes) to form a sheet with a water content of 10% by mass or less and a density of 1.0 g/cm ³ , the tensile modulus is 5 to 25 GPa.
A method for producing a cellulose fiber slurry according to any one of claims 1 to 3 .

According to the present invention, a method for producing cellulose fiber slurry having excellent dehydration properties is provided.

Next, a mode for carrying out the present invention will be described. Note that this embodiment is an example of the present invention. The scope of the present invention is not limited to the scope of this embodiment.

The cellulose fiber slurry of this embodiment (hereinafter also simply referred to as "slurry") contains cellulose fibers as a main component (preferably 1% by mass or more). Furthermore, the cellulose fibers include microfibrillated cellulose, or microfibrillated cellulose and pulp, and preferably contain cellulose nanofibers as a complementary material to the microfibrillated cellulose.

The cellulose fiber slurry of this embodiment can be made into a molded article by, for example, dehydration, molding, etc. However, the use of the cellulose fiber slurry of this embodiment is not limited to molded bodies, etc., and can also be used, for example, as an ink raw material for 3D printers. Below, cellulose nanofibers, microfibrillated cellulose, pulp, and cellulose fiber slurry will be explained in this order.

(cellulose nanofiber)
In this embodiment, cellulose nanofibers are used as a complementary material to microfibrillated cellulose, and supplement the role of microfibrillated cellulose. Therefore, the cellulose fiber of this form is based on the inclusion of microfibrillated cellulose, and the effects of the present invention cannot be obtained depending on the form containing only cellulose nanofibers without containing microfibrillated cellulose. .

Cellulose nanofibers have the role of increasing the number of hydrogen bonding points in cellulose fibers and thereby supplementing the strength development of molded objects. Cellulose nanofibers can be obtained by defibrating (refining) raw material pulp.

Raw material pulp for cellulose nanofibers includes, for example, wood pulp made from hardwoods, softwoods, etc., non-wood pulp made from straw, bagasse, cotton, hemp, dust fibers, etc., recovered waste paper, waste paper, etc. One type or two or more types can be selected and used from waste paper pulp (DIP) and the like. The various raw materials mentioned above may be in the form of a pulverized product called cellulose powder, for example.

However, in order to avoid contamination with impurities as much as possible, it is preferable to use wood pulp. As the wood pulp, one or more types can be selected and used from, for example, chemical pulps such as hardwood kraft pulp (LKP) and softwood kraft pulp (NKP), mechanical pulp (TMP), and the like.

The hardwood kraft pulp may be a bleached hardwood kraft pulp, an unbleached hardwood kraft pulp, or a semi-bleached hardwood kraft pulp. Similarly, the softwood kraft pulp may be a bleached softwood kraft pulp, an unbleached softwood kraft pulp, or a semi-bleached softwood kraft pulp.

Mechanical pulps include, for example, stone ground pulp (SGP), pressurized stone ground pulp (PGW), refiner ground pulp (RGP), chemical ground pulp (CGP), thermoground pulp (TGP), ground pulp (GP), One or more types can be selected and used from thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), refiner mechanical pulp (RMP), bleached thermomechanical pulp (BTMP), and the like.

From the viewpoint of dewaterability of the cellulose fiber slurry, it is preferable to use pulp containing lignin as the raw material pulp, more preferably to use mechanical pulp, and particularly preferably to use BTMP.

Prior to fibrillation of cellulose nanofibers, they can also be pretreated by chemical methods. Examples of pretreatments using chemical methods include hydrolysis of polysaccharides with acids (acid treatment), hydrolysis of polysaccharides with enzymes (enzyme treatment), swelling of polysaccharides with alkalis (alkali treatment), and oxidation of polysaccharides with oxidizing agents ( Examples include oxidation treatment), reduction of polysaccharide with a reducing agent (reduction treatment), and the like.

When treated with alkali prior to defibration, some of the hydroxyl groups of hemicellulose and cellulose in the pulp dissociate, and the molecules become anions, weakening intramolecular and intermolecular hydrogen bonds, promoting the dispersion of cellulose fibers during defibration. Ru.

Examples of the alkali used in the alkali treatment include sodium hydroxide, lithium hydroxide, potassium hydroxide, ammonia aqueous solution, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, etc. Organic alkalis and the like can be used. However, from the viewpoint of manufacturing cost, it is preferable to use sodium hydroxide.

If enzyme treatment, acid treatment, or oxidation treatment is performed prior to fibrillation, the degree of water retention of cellulose nanofibers can be lowered, the degree of crystallinity can be increased, and the homogeneity can be increased. In this regard, when cellulose nanofibers have a low water retention degree, they are easily dehydrated, and the dehydration properties of the cellulose fiber slurry are improved.

When raw pulp is treated with enzymes, acid, or oxidation, the hemicellulose and amorphous regions of cellulose in the pulp are decomposed, and as a result, the energy required for micronization processing can be reduced, and the uniformity and dispersibility of cellulose fibers can be improved. can be improved. The dispersibility of cellulose fibers contributes to the homogeneity of a molded product, for example, when a molded product is produced from a cellulose fiber slurry. However, since pretreatment reduces the aspect ratio of cellulose nanofibers, it is preferable to avoid excessive pretreatment.

For defibration of raw material pulp, for example, a beater, a high-pressure homogenizer, a homogenizer such as a high-pressure homogenizer, a grinder, a stone mill friction machine such as a mill, a single-shaft kneader, a multi-shaft kneader, a kneader refiner, a jet mill, etc. This can be done by beating the raw material pulp. However, it is preferable to use a refiner or jet mill.

Defibration of the raw material pulp is performed until the average fiber diameter, average fiber length, water retention, crystallinity, peak value of pseudo particle size distribution, pulp viscosity, and type B viscosity of the dispersion of the obtained cellulose nanofibers are as shown below. It is preferable to perform the evaluation so as to obtain a desired value or evaluation.

The average fiber diameter (average fiber width; average diameter of single fibers) of cellulose nanofibers is preferably 10 to 100 nm, more preferably 15 to 90 nm, particularly preferably 20 to 80 nm. When the average fiber diameter of cellulose nanofibers is less than 10 nm, there is a possibility that dehydration properties may be deteriorated. In addition, the molded body etc. may become too dense and the drying properties may deteriorate.

On the other hand, if the average fiber diameter of the cellulose nanofibers exceeds 100 nm, the effect of increasing the number of hydrogen bonding points may not be obtained.

The average fiber diameter of cellulose nanofibers can be adjusted by, for example, selection of raw material pulp, pretreatment, fibrillation, and the like.

The method for measuring the average fiber diameter of cellulose nanofibers is as follows.
First, 100 ml of an aqueous dispersion of cellulose nanofibers with a solid content concentration of 0.01 to 0.1% by mass was filtered through a Teflon (registered trademark) membrane filter, and the solvent was filtered once with 100 ml of ethanol and three times with 20 ml of t-butanol. Replace. Next, it is freeze-dried, coated with osmium, and used as a sample. This sample is observed using an electron microscope SEM image at a magnification of 3,000 times to 30,000 times depending on the width of the constituent fibers. Specifically, two diagonal lines are drawn on the observed image, and three straight lines passing through the intersections of the diagonals are arbitrarily drawn. Furthermore, the widths of a total of 100 fibers that intersect with these three straight lines are visually measured. Then, the median diameter of the measured value is taken as the average fiber diameter.

The average fiber length (length of a single fiber) of cellulose nanofibers is preferably 0.3 to 2000 μm, more preferably 0.4 to 200 μm, particularly preferably 0.5 to 20 μm. If the average fiber length of cellulose nanofibers is less than 0.3 μm, when producing molded objects, a large proportion of fibers will flow out during the dehydration process, and the strength of the molded objects cannot be guaranteed. There is a risk that it will disappear.

On the other hand, if the average fiber length of the cellulose nanofibers exceeds 2000 μm, the fibers tend to become entangled with each other, and the surface properties of the molded product etc. may deteriorate.

The average fiber length of cellulose nanofibers can be adjusted by, for example, selection of raw material pulp, pretreatment, fibrillation, etc.

The average fiber length of cellulose nanofibers is measured by visually measuring the length of each fiber in the same manner as the average fiber diameter. The median length of the measured value is taken as the average fiber length.

The water retention degree of cellulose nanofibers is, for example, 90 to 600%, preferably 220 to 500%, more preferably 240 to 460%. When the water retention degree of cellulose nanofibers is less than 200%, the dispersibility of cellulose nanofibers deteriorates, and there is a possibility that it may not be possible to mix uniformly with pulp.

On the other hand, when the water retention degree of cellulose nanofibers exceeds 600%, the water retention capacity of the cellulose nanofibers themselves becomes high, and there is a possibility that the dehydration properties of the cellulose fiber slurry may deteriorate.

The water retention degree of cellulose nanofibers can be adjusted by, for example, selection of raw material pulp, pretreatment, fibrillation, and the like.

The water retention level of cellulose nanofiber is JAPAN TAPPI No. 26 (2000).

The cellulose nanofiber crystallinity is preferably 45 to 90%, more preferably 55 to 88%, particularly preferably 60 to 86%. If the crystallinity of the cellulose nanofibers is within the above range, the strength of the molded object etc. can be ensured.

The degree of crystallinity can be arbitrarily adjusted, for example, by selecting the raw material pulp, pretreatment, fibrillation, etc.

The peak value in the pseudo particle size distribution curve of cellulose nanofibers is preferably one peak. When there is one peak, the cellulose nanofibers have high uniformity in fiber length and fiber diameter, and the cellulose fiber slurry has excellent dehydration properties.

The peak value in the pseudo particle size distribution curve of cellulose nanofibers is, for example, 1 to 100 μm, preferably 3 to 80 μm, and more preferably 5 to 60 μm.

The peak value in the pseudo particle size distribution curve of cellulose nanofibers can be adjusted by, for example, selection of raw material pulp, pretreatment, fibrillation, etc.

The peak value in the pseudo particle size distribution curve of cellulose nanofibers is a value measured in accordance with ISO-13320 (2009). More specifically, first, the volume-based particle size distribution of the aqueous dispersion of cellulose nanofibers is examined using a particle size distribution measuring device (laser diffraction/scattering type particle size distribution measuring device manufactured by Seishin Enterprise Co., Ltd.). Next, the median diameter of cellulose nanofibers is measured from this distribution. This median diameter is taken as the peak value.

The pulp viscosity of cellulose nanofibers is preferably 1 to 10 cps, more preferably 1 to 9 cps, particularly preferably 1 to 8 cps. Pulp viscosity is the viscosity of a solution obtained by dissolving cellulose in a copper ethylenediamine solution, and the higher the pulp viscosity, the higher the degree of polymerization of cellulose. If the pulp viscosity is within the above range, it is possible to impart dehydration properties to the slurry while maintaining mechanical properties when formed into a molded product.

If necessary, the cellulose nanofibers obtained by fibrillation can be dispersed in an aqueous medium to form a dispersion before being mixed with microfibrillated cellulose or pulp. It is particularly preferable that the aqueous medium consists entirely of water (aqueous solution). However, the aqueous medium may be another liquid that is partially compatible with water. As other liquids, for example, lower alcohols having 3 or less carbon atoms can be used.

The type B viscosity of the cellulose nanofiber dispersion (1% concentration) is preferably 10 to 4000 cps, more preferably 80 to 3000 cps, particularly preferably 100 to 2000 cps. When the B-type viscosity of the dispersion liquid is within the above range, mixing with microfibrillated cellulose and pulp becomes easy, and the dehydration properties of the cellulose fiber slurry are improved.

The B-type viscosity (solid content concentration 1%) of the cellulose nanofiber dispersion is a value measured in accordance with JIS-Z8803 (2011) "Liquid viscosity measurement method". Type B viscosity is the resistance torque when stirring a dispersion liquid, and means that the higher the viscosity, the more energy is required for stirring.

(Microfibrillated cellulose)
In this embodiment, microfibrillated cellulose has the role of increasing hydrogen bonding points while ensuring dehydration properties.

Microfibrillated cellulose means fibers with a larger average fiber diameter than cellulose nanofibers. Specifically, it is, for example, 0.1 to 10 μm, preferably 0.3 to 5 μm, and more preferably 0.5 to 2 μm.

If the average fiber diameter of microfibrillated cellulose is less than 0.1 μm, it will not be different from cellulose nanofibers, and the effect of increasing strength (especially flexural modulus) will not be sufficiently obtained. Furthermore, the defibration time becomes longer and a large amount of energy is required. Furthermore, the dehydration properties of the cellulose fiber slurry deteriorate. If dehydration properties deteriorate, when producing molded objects from cellulose fiber slurry, a large amount of energy will be required to dry the molded objects, etc., and if large amounts of energy are applied to drying, cellulose fibers such as microfibrillated cellulose will deteriorate due to heat. As a result, the strength may decrease.

On the other hand, when the average fiber diameter of microfibrillated cellulose exceeds 10 μm, the dispersibility tends to be poor, and mixing with pulp and cellulose nanofibers may become difficult.

Microfibrillated cellulose can be obtained by defibrating (refining) raw material pulp. As the raw material pulp, the same material as cellulose nanofibers can be used. In addition, pretreatment and fibrillation can be performed in the same manner as in the case of cellulose nanofibers. However, the degree of defibration is different, and, for example, it is necessary to perform defibration within a range where the average fiber diameter remains at least 0.1 μm. The following will mainly explain the differences from the case of cellulose nanofibers.

The average fiber length (average length of single fibers) of microfibrillated cellulose is, for example, 0.01 to 1 mm, preferably 0.03 to 0.7 mm, and more preferably 0.05 to 0.5 mm. If the average fiber length is less than 0.01 mm, a three-dimensional network of fibers cannot be formed, and the reinforcing effect may be reduced.

The average fiber length can be arbitrarily adjusted, for example, by selecting the raw material pulp, pretreatment, fibrillation, etc.

The fiber length of the microfibrillated cellulose is preferably 60% or more, more preferably 70% or more, particularly preferably 75% or more with a fiber length of 0.2 mm or less. If the ratio is less than 60%, there is a possibility that a sufficient reinforcing effect cannot be obtained. On the other hand, the fiber length of microfibrillated cellulose has no upper limit of 0.2 mm or less, and may be entirely 0.2 mm or less.

The aspect ratio of microfibrillated cellulose is 1 to 10,000 when it is necessary to improve the strength of the molded product while maintaining a certain degree of ductility when producing a molded product from a cellulose fiber slurry. is preferable, and more preferably from 5 to 5,000.

Note that the aspect ratio is a value obtained by dividing the average fiber length by the average fiber width. The larger the aspect ratio, the more places in the pulp where snags occur, increasing the reinforcing effect, but on the other hand, it is thought that the greater the number of snags, the lower the ductility of the molded article.

The fibrillation rate of microfibrillated cellulose is preferably 0.5% or more, more preferably 1.0% or more, and particularly preferably 1.5% or more. Further, the fibrillation rate is preferably 10% or less, more preferably 9% or less, and particularly preferably 8% or less. If the fibrillation rate exceeds 10%, the contact area with water becomes too large, so even if defibration is possible within a range where the average fiber width remains at least 0.1 μm, dehydration may become difficult. . On the other hand, if the fibrillation rate is less than 0.5%, there are few hydrogen bonds between fibrils, and a strong three-dimensional network may not be formed.

The degree of crystallinity of the microfibrillated cellulose is preferably 45% or more, more preferably 55% or more, and particularly preferably 60% or more. If the degree of crystallinity is less than 50%, although the mixability with pulp and cellulose nanofibers is improved, the strength of the fiber itself decreases, so there is a risk that the strength cannot be guaranteed.

On the other hand, the crystallinity of microfibrillated cellulose is preferably 90% or less, more preferably 88% or less, and particularly preferably 86% or less. When the degree of crystallinity exceeds 90%, the proportion of strong hydrogen bonds within the molecules increases and the fiber itself becomes rigid, so the number of hydrogen bonding points with the pulp does not increase sufficiently, making it difficult to form molded objects from cellulose fiber slurry. In the case of manufacturing, there is a possibility that the strength of the molded article etc. will not be sufficiently improved.

The degree of crystallinity of microfibrillated cellulose can be arbitrarily adjusted by, for example, selection of raw material pulp, pretreatment, and micronization treatment.

The pulp viscosity of the microfibrillated cellulose is preferably 1 cps or more, more preferably 2 cps or more. If the pulp viscosity is less than 1 cps, there is a possibility that aggregation of microfibrillated cellulose may not be sufficiently suppressed.

The freeness of the microfibrillated cellulose is preferably 200 cc or less, more preferably 150 cc or less, particularly preferably 100 cc or less. If the freeness of the microfibrillated cellulose exceeds 200 cc, the average fiber diameter of the microfibrillated cellulose will exceed 10 μm, and there is a possibility that sufficient strength-related effects may not be obtained.

The water retention degree of microfibrillated cellulose is preferably 500% or less, more preferably 450% or less, particularly preferably 400% or less. When the water retention degree of microfibrillated cellulose exceeds 500%, dehydration properties tend to be poor and there is a possibility of agglomeration.

The water retention degree of microfibrillated cellulose can be arbitrarily adjusted by, for example, selection of raw material pulp, pretreatment, fibrillation, etc.

The content of microfibrillated cellulose in the cellulose fibers is preferably 1 to 90% by weight, more preferably 5 to 80% by weight, particularly preferably 10 to 50% by weight. If the content of microfibrillated cellulose is less than 1% by mass, a sufficient reinforcing effect may not be obtained.

On the other hand, if the content of microfibrillated cellulose exceeds 90% by mass, the content of pulp and cellulose nanofibers will be relatively reduced, and the effects of containing pulp and cellulose nanofibers may not be obtained. There is.

The methods for measuring various physical properties of microfibrillated cellulose are the same as those for cellulose nanofibers and pulp, unless otherwise specified.

(pulp)
In this embodiment, the pulp has the role of significantly improving the dehydration properties of the cellulose fiber slurry. However, it is preferable that the pulp content be within a predetermined range (described later), and the water retention ratio (the value obtained by dividing the water retention of cellulose fiber slurry by the water retention of cellulose nanofibers) and the dead weight dewatering of cellulose fiber slurry It is more preferable to include the compound so that its properties fall within a predetermined range (described later). By adding such a limitation, when a molded body or the like is manufactured from the cellulose fiber slurry, the strength of the molded body or the like is ensured. Note that details of the water retention ratio and self-weight dehydration properties will be described later.

When the average fiber diameter of microfibrillated cellulose, pulp, and cellulose nanofibers is within a specific range, the pulp content in the cellulose fibers is preferably 1 to 50% by mass, more preferably 3 to 40% by mass. , particularly preferably 5 to 20% by weight. If the pulp content is less than 1% by mass, the dehydration properties of the cellulose fiber slurry may not be sufficiently improved. Furthermore, when producing a molded article or the like from the cellulose fiber slurry, the strength of the molded article or the like may not be ensured.

On the other hand, if the content of pulp exceeds 50% by mass, the content of microfibrillated cellulose will decrease as a result, so even if a complementary effect of cellulose nanofibers is expected, the strength of the above-mentioned molded articles etc. cannot be guaranteed. There is a risk.

As the pulp, the same pulp as the raw material pulp for microfibrillated cellulose and cellulose nanofibers can be used. However, it is preferable to use the same pulp as the raw material pulp for microfibrillated cellulose and cellulose nanofibers. When the same pulp as the raw material pulp for microfibrillated cellulose and cellulose nanofibers is used, the affinity of cellulose fibers is improved, and as a result, the homogeneity of cellulose fiber slurry, molded articles, etc. is improved.

The average fiber diameter (average fiber width; average diameter of single fibers) of the pulp is preferably 10 to 100 μm, more preferably 10 to 80 μm, particularly preferably 10 to 60 μm. If the average fiber diameter of the pulp is within the above range, the dehydration properties of the cellulose fiber slurry will be further improved by controlling the pulp content within the above range.

The average fiber diameter of the pulp can be adjusted, for example, by selecting the raw material pulp, light defibration, etc.

The method for measuring the average fiber diameter of pulp is as follows.
First, 100 ml of an aqueous dispersion of pulp with a solid content concentration of 0.01 to 0.1% by mass is filtered through a Teflon (registered trademark) membrane filter, and the solvent is replaced once with 100 ml of ethanol and three times with 20 ml of t-butanol. . Next, it is freeze-dried, coated with osmium, and used as a sample. This sample is observed using an electron microscope SEM image at a magnification of 100x to 1000x depending on the width of the constituent fibers. Specifically, two diagonal lines are drawn on the observed image, and three straight lines passing through the intersections of the diagonals are arbitrarily drawn. Furthermore, the widths of a total of 100 fibers that intersect with these three straight lines are visually measured. Then, the median diameter of the measured value is taken as the average fiber diameter.

The freeness of the pulp is preferably 10 to 800 ml, more preferably 200 to 780 ml, particularly preferably 400 to 750 ml. If the freeness of the pulp exceeds 800 ml, the dehydration properties of the cellulose fiber slurry can be improved, but when it is formed into a molded product, the surface is likely to be uneven, and the fibers become rigid, resulting in microfibrillated cellulose and cellulose nano. There is a risk that it will not integrate with the fiber and the density will not improve.

On the other hand, if the freeness of the pulp is less than 10 ml, the dehydration properties of the cellulose fiber slurry may not be sufficiently improved, and the rigidity of the pulp fibers themselves may decrease, and there is a risk that they may no longer function as fibers that support molded objects, etc. There is.

The freeness of pulp is a value measured in accordance with JIS P8121-2 (2012).

(Slurry of cellulose fibers)
Microfibrillated cellulose, pulp, and cellulose nanofibers are mixed at a predetermined ratio, preferably so that each cellulose fiber has the above-mentioned content, thereby forming a slurry of cellulose fibers. Note that the microfibrillated cellulose, pulp, and cellulose nanofibers can also be mixed in the form of a dispersion.

When mixing microfibrillated cellulose, pulp, and cellulose nanofibers, it is preferable to adjust the solid concentration of cellulose fibers in the cellulose fiber slurry by adding a medium such as water. The solid content concentration of the cellulose fibers is preferably 1.0 to 15% by weight, more preferably 1.2 to 7.0% by weight, particularly preferably 1.4 to 5.0% by weight. When the solid content concentration of cellulose fibers is less than 1.0% by mass, the fluidity is high, and when manufacturing molded objects etc. from cellulose fiber slurry, there is a high risk that cellulose fibers will flow out during the dehydration process etc. .

On the other hand, if the solid content concentration of cellulose fibers exceeds 10% by mass, the fluidity decreases significantly and the processability deteriorates, so that, for example, in the process of manufacturing a molded article, uneven thickness tends to occur, making it difficult to form a homogeneous molded product. It may be difficult to obtain the body.

The medium such as water (aqueous medium) is preferably entirely water. However, the aqueous medium may be another liquid that is partially compatible with water. As other liquids, for example, lower alcohols having 3 or less carbon atoms can be used.

The slurry of cellulose fibers preferably has a water retention ratio of 0.50 to 0.99 by appropriately adjusting the content of each cellulose fiber, and preferably 0.55 to 0.98. It is more preferable that the ratio be 0.60 to 0.97.

In addition to the above, the slurry of cellulose fibers preferably has a self-weight dehydration property of 1.1 to 3.0, preferably 1.1 to 2.0, by appropriately adjusting the content of each cellulose fiber. More preferably, the value is 0, and particularly preferably 1.2 to 1.8.

By setting the water retention ratio of the cellulose fiber slurry S to 0.50 or more and the self-weight dehydration property to 3.0 or less, the strength of the molded article or the like can be ensured.

The water retention of cellulose nanofiber slurry and cellulose fiber slurry is a value measured by the following method.
First, a slurry of cellulose nanofibers (concentration: 2% by mass) or a slurry of cellulose fibers (concentration: 2% by mass) is dehydrated using a centrifuge (conditions: 3000G, 15 minutes), and the mass of the resulting dehydrated product is measured. do. Next, the dehydrated product is completely dried, and the mass of the obtained dried product is measured. Then, water retention (%) = (mass of dehydrated product - mass of dry product)/mass of dry product x 100.

Further, the water retention ratio is calculated based on the above water retention according to the following formula.
(Water retention ratio = Water retention of cellulose fiber slurry ÷ Water retention of cellulose nanofiber slurry)
Water retention is the amount of water remaining in the slurry after applying a certain centrifugal force, and the lower the water retention, the better the dewatering performance. In addition, the lower the water retention ratio, the lower the water retention from the original cellulose nanofiber slurry, and the higher the dehydration property.

On the other hand, the self-gravity dehydration property of the cellulose fiber slurry is a value measured by the following method.
A slurry of cellulose fibers is applied to a wire mesh (300 mesh, 10 cm width x 10 cm length x 2 mm thickness) on a water-absorbing substrate and left for 2 minutes. Then, dead weight dehydration property=solid content concentration after being left for 2 minutes/solid content concentration before coating.

The slurry of cellulose fibers is heated under pressure (120° C., 1 MPa, 5 minutes) by adjusting the types and content ratios of microfibrillated cellulose, pulp, and cellulose nanofibers to a water content of 10% by mass or less, And when the sheet has a density of 1.0 g/cm ³ , the tensile modulus is preferably 5 to 25 GPa, more preferably 7 to 24 GPa, and 9 to 23 GPa. It is particularly preferable to If the tensile modulus is less than 5 GPa, there is a possibility that the strength of the molded product, etc., cannot be ensured when the molded product, etc. is manufactured from the cellulose fiber slurry.

In addition, the cellulose fiber slurry was heated under pressure (120°C, 1 MPa, 5 minutes) to a water content of 10% by mass by adjusting the types and content ratios of microfibrillated cellulose, pulp, and cellulose nanofibers. The tensile strength of the sheet below and having a density of 1.0 g/cm ³ is preferably 10 to 250 MPa, more preferably 20 to 200 MPa, and 30 to 150 MPa. It is particularly preferable to do so. If the tensile strength is less than 10 MPa, there is a possibility that the strength of the molded product, etc., cannot be ensured when the molded product, etc. is manufactured from the cellulose fiber slurry.

The above tensile modulus and tensile strength are values measured in accordance with JIS K7127:1999. The test piece (sheet) has a tensile type 2 dumbbell shape as defined in JIS-K6251. The test speed is 10 mm/min. Further, the measurement is performed under an environment of a temperature of 23° C. and a humidity of 50%.

When producing a sheet as described above, the slurry of cellulose fibers is prepared such that the density of the sheet is 0.95 to 1.50 g/m ³ , more preferably 1.00 to 1.45 g/m ³ . do. If the density of the sheet is less than 0.95 g/m ³ , there is a risk that the strength of the molded product, etc., produced from the cellulose fiber slurry will not be sufficiently ensured due to a decrease in hydrogen bonding points.

The density of the sheet is a value measured in accordance with JIS-P-8118:1998.

The tensile failure strain of the sheet is preferably 10% or less, more preferably 5% or less, particularly preferably 4% or less, and most preferably 3% or less. If the quoted fracture strain exceeds the above upper limit, the strain may be large and the applications may be limited. On the other hand, the tensile failure strain of the sheet is best set to 0%, but a tensile strain of 1 to 3% is also acceptable, for example.

The tensile fracture strain of the sheet is a value measured in accordance with JIS K7127:1999 in an environment at a temperature of 23°C, using a test piece in the shape of a tensile type 2 dumbbell specified by JIS-K6251, and at a test speed of 10 mm/min. .

(others)
If necessary, additives such as antioxidants, corrosion inhibitors, light stabilizers, ultraviolet absorbers, heat stabilizers, dispersants, antifoaming agents, slime control agents, and preservatives may be added to the cellulose fiber slurry. Can be added.

Next, examples of the present invention will be described.
A slurry of cellulose fibers was prepared using microfibrillated cellulose, pulp, and cellulose nanofibers as cellulose fibers, and tests were conducted to examine water retention and self-weight dewatering properties. LBKP, which is paper pulp, was used as the raw material pulp and pulp for microfibrillated cellulose and cellulose nanofibers. Microfibrillated cellulose was obtained by preliminary beating raw material pulp (moisture content: 98% by mass) using a refiner. This microfibrillated cellulose was an aqueous dispersion with a concentration of 2.5% by mass. The obtained microfibrillated cellulose had an average fiber diameter of 1 μm, a water retention degree of 296%, and a crystallinity degree of 75%. On the other hand, cellulose nanofibers were obtained by fibrillating the above microfibrillated cellulose using a high-pressure homogenizer. This cellulose nanofiber was an aqueous dispersion with a concentration of 2.0% by mass. The obtained cellulose nanofibers had an average fiber diameter of 30 nm, a water retention degree of 348%, and a crystallinity degree of 75%. Microfibrillated cellulose, pulp, and cellulose nanofibers were mixed at a predetermined ratio, and the solid content concentration was 2.0% by mass.

Next, a sheet (molded body) having a thickness of 100 μm was produced from the obtained slurry of cellulose fibers, and a test was conducted to examine the tensile modulus and tensile strength of the formed body. Specifically, first, a wet paper was made from a slurry of cellulose fibers, and this wet paper was dehydrated and heated under pressure to produce a molded article. Pressurized dehydration was performed at 25° C. and 2 MPa for 5 minutes. Further, pressure heating was performed at 120° C. and 2 MPa for 5 minutes. The density of the obtained molded body was 1.0 g/m ³ .

The results are shown in Table 1. The methods for measuring water retention, self-weight dehydration, tensile modulus, and tensile strength are as described above.

(Consideration)
Table 1 shows that the combination of microfibrillated cellulose and pulp has the effect of improving dewaterability and strength. Furthermore, although it is sufficient to use microfibrillated cellulose in terms of dehydration properties, it is found that it is preferable to also include pulp when considering strength. Furthermore, it can be seen that cellulose nanofibers have a complementary effect on strength.

The present invention is directed to cellulose fibers that can be used, for example, as raw materials for cellulose fiber molded bodies, raw inks for 3D printers, raw materials and additives for various structures (including, for example, outer walls and inner walls of buildings). It can be used as a method for producing slurry.

Claims (4)

A method for producing cellulose fiber slurry containing cellulose fibers as the main component,
As the cellulose fibers, microfibrillated cellulose having an average fiber diameter of 0.1 to 10 μm and pulp having an average fiber diameter of 10 to 100 μm are used, and as a complementary material to the microfibrillated cellulose, cellulose nano having an average fiber diameter of 10 to 90 nm. Include fiber,
The water retention degree of the microfibrillated cellulose is 500% or less,
A method for producing cellulose fiber slurry , characterized by : The solid content concentration of the cellulose fiber is 1.0 to 15% by mass,
A method for producing a cellulose fiber slurry according to claim 1 . When heated under pressure (120° C., 1 MPa, 5 minutes) to form a sheet with a moisture content of 10% by mass or less and a density of 1.0 g/cm ³ , the tensile strength is 10 to 250 MPa.
A method for producing a cellulose fiber slurry according to claim 1 or 2 . When heated under pressure (120° C., 1 MPa, 5 minutes) to form a sheet with a water content of 10% by mass or less and a density of 1.0 g/cm ³ , the tensile modulus is 5 to 25 GPa.
A method for producing a cellulose fiber slurry according to any one of claims 1 to 3 .