JP7265333B2 - Method for producing molded body of cellulose fiber - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a molded product of cellulose fibers.

Cellulose nanofibers (CNF), which are obtained by defibrating cellulose fibers to the nano level, are expected to be used in various applications because they are excellent in strength, elasticity, thermal stability, and the like. One of them is a molded body of cellulose nanofibers obtained by drying and molding a slurry of cellulose nanofibers. For example, Patent Literature 1 proposes a high-strength material (molded body) containing cellulose nanofibers as a main component. The document makes various proposals specifying the physical properties of cellulose nanofibers.

However, although the cellulose fiber molded article is sometimes used at high temperatures, the heat resistance of the molded article is not sufficiently studied in this document.

JP 2013-11026 A

The main problem to be solved by the present invention is to provide a method for producing a cellulose fiber molded article having excellent heat resistance.

While conducting various tests to solve the above problems, the present inventors first found that cellulose nanofibers are cellulose fibers used for increasing strength, but all cellulose fibers are disentangled fibers. The inventors have found that the heat resistance of a part of pulp is superior to that of a certain cellulose nanofiber. In addition, the inventors have found that microfibrillated cellulose (MFC, microfiber cellulose) is partially or wholly more excellent in heat resistance in terms of tensile strength than cellulose nanofibers. . Furthermore, it was found that the defibrated fiber, which is partially composed of cellulose nanofiber as a complementary material of microfibrillated cellulose, is superior in heat resistance in terms of tensile elastic modulus, rather than wholly (entirely) composed of microfibrillated cellulose. I found out. The following means have been conceived based on such knowledge.

(Means according to claim 1)
A method for producing a molded body containing cellulose fibers as a main component,
including pulp and defibrated fiber as the cellulose fiber,
Including microfibrillated cellulose having an average fiber diameter of 0.1 to 10 μm as the defibrated fiber and cellulose nanofiber having an average fiber diameter of 10 to 90 nm as a complementary material of the microfibrillated cellulose ,
A tensile modulus at 23°C of 5 GPa or more and a tensile strength at 23°C of 10 MPa or more,
A method for producing a molded body of cellulose fibers, characterized by:

(Means according to claim 2)
A slurry is prepared from the cellulose fibers, a wet paper web is formed from the slurry of the cellulose fibers, and the wet paper web is dehydrated, pressurized and heated to form a compact.
The method for producing a cellulose fiber molded article according to claim 1 .

(Means according to claim 3)
The content of the cellulose nanofibers in the cellulose fibers exceeds 0% by mass and is 70% by mass or less,
The method for producing a cellulose fiber molded article according to claim 1 or 2.

(Means according to claim 4)
The pulp has an average fiber diameter of 10 to 100 μm ,
The content of the pulp in the cellulose fibers is 5 to 20% by mass,
The method for producing a cellulose fiber molded article according to claim 1 or 2 .

According to the present invention, there is provided a method for producing a cellulose fiber molded article having excellent heat resistance.

It is explanatory drawing of the manufacturing method of a molded object.

Next, the form for implementing this invention is demonstrated. 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 molded article of the present embodiment contains cellulose fibers as a main component. The cellulose fibers also include pulp and defibrated fibers. Further, the fibrillated fibers contain microfibrillated cellulose, and preferably further contain cellulose nanofibers as a complementary material for the microfibrillated cellulose.

The cellulose fiber molded body of the present embodiment is produced, for example, by preparing a slurry of cellulose fibers using pulp and fibrillated fibers, forming a wet paper web from the slurry of the cellulose fibers, dehydrating and pressurizing the wet paper web. Obtained by heating or the like. They will be described in order below.

(cellulose nanofiber)
In this embodiment, cellulose nanofibers are used as a complementary material for microfibrillated cellulose. In other words, cellulose nanofibers have a role to complement the role of microfibrillated cellulose. In this regard, when microfibrillated cellulose is used as defibrated fibers, heat resistance is improved in terms of tensile strength, but heat resistance in terms of tensile elastic modulus may not be sufficiently improved. However, if cellulose nanofibers are included as defibrated fibers, heat resistance is sufficiently improved in terms of tensile modulus as well. Therefore, the defibrated fiber of this form is premised on containing microfibrillated cellulose, and does not include a form containing only cellulose nanofibers without containing microfibrillated cellulose.

Cellulose nanofibers increase the number of hydrogen bonding points in cellulose fibers, thereby playing a role in compensating for strength development of molded articles and the like. Cellulose nanofibers can be obtained by defibrating (miniaturizing) raw material pulp.

Raw material pulp for cellulose nanofibers includes, for example, wood pulp made from broad-leaved trees and coniferous trees, non-wood pulp made from straw, bagasse, cotton, hemp, pistil fibers, etc., recovered waste paper, waste paper, etc. It is possible to select and use one or more of waste paper pulp (DIP) and the like. The various raw materials described above may be in the form of pulverized materials such as cellulose powder.

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

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

Examples of mechanical pulp include stone ground pulp (SGP), pressure stone ground pulp (PGW), refiner ground pulp (RGP), chemi ground pulp (CGP), thermo ground pulp (TGP), ground pulp (GP), One or more of thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), refiner mechanical pulp (RMP), bleached thermomechanical pulp (BTMP) and the like can be selected and used.

Prior to defibration of cellulose nanofibers, pretreatment can also be performed by a chemical method. Examples of chemical pretreatments include hydrolysis of polysaccharides with acid (acid treatment), hydrolysis of polysaccharides with enzymes (enzyme treatment), swelling of polysaccharides with alkali (alkali treatment), and oxidation of polysaccharides with an oxidizing agent ( oxidation treatment), reduction of polysaccharides with a reducing agent (reduction treatment), and the like.

Alkali treatment prior to fibrillation dissociates some of the hydroxyl groups of hemicellulose and cellulose in the pulp, anionizing the molecules, weakening intramolecular and intermolecular hydrogen bonds, and promoting the dispersion of cellulose fibers during fibrillation. be.

Alkali used for alkali treatment include, for example, sodium hydroxide, lithium hydroxide, potassium hydroxide, aqueous ammonia solution, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, and the like. An organic alkali or the like can be used. However, from the viewpoint of production cost, it is preferable to use sodium hydroxide.

If enzymatic treatment, acid treatment, or oxidation treatment is performed prior to fibrillation, the water retention of cellulose nanofibers can be lowered, the degree of crystallinity can be increased, and homogeneity can be increased. In this respect, if the water retention of the cellulose nanofibers is low, dehydration is facilitated, and the dewaterability of the cellulose fiber slurry is improved.

Enzyme treatment, acid treatment, and oxidation treatment of the raw material pulp decomposes the hemicellulose and amorphous regions of cellulose in the pulp. can be improved. The dispersibility of the cellulose fibers contributes to the homogeneity of the molded article, for example, when the molded article is produced from the 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, beaters, high-pressure homogenizers, homogenizers such as high-pressure homogenizers, grinders, stone mills such as grinders, single-screw kneaders, multi-screw kneaders, kneader refiners, jet mills, etc. It can be carried out by beating the raw material pulp using However, it is preferable to use a refiner or a jet mill.

The fibrillation of the raw material pulp has the average fiber diameter, average fiber length, water retention, crystallinity, peak value of pseudo particle size distribution, pulp viscosity, and B-type viscosity of the dispersion liquid of the obtained cellulose nanofiber, as shown below. It is preferable to carry out 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, and particularly preferably 20 to 80 nm. If the average fiber diameter of the cellulose nanofibers is less than 10 nm, the dewaterability may deteriorate. In addition, there is a risk that the molded article or the like will become too dense, resulting in poor drying properties.

On the other hand, if the average fiber diameter of the cellulose nanofiber exceeds 100 nm, the effect of increasing 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.

A 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 3 times with 20 ml of t-butanol. Replace. It is then freeze-dried and coated with osmium to form a sample. This sample is observed with 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 observation image, and three straight lines passing through the intersections of the diagonal lines are arbitrarily drawn. Furthermore, the width of a total of 100 fibers intersecting with these three straight lines is visually measured. Then, the median diameter of the measured value is taken as the average fiber diameter.

The average fiber length (single fiber length) 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 the cellulose nanofibers is less than 0.3 μm, the proportion of fibers that flow out during the dehydration process increases and the strength of the molded article cannot be secured when the molded article or the like is produced. may disappear.

On the other hand, if the average fiber length of the cellulose nanofibers exceeds 2000 μm, the fibers are likely to be entangled with each other, and the surface properties of the molded article may deteriorate.

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

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. Let the median length of the measured value be the average fiber length.

The water retention of cellulose nanofibers is, for example, 90-600%, preferably 200-500%, more preferably 240-460%. If the water retention of the cellulose nanofibers is less than 90%, the dispersibility of the cellulose nanofibers deteriorates, and there is a risk that it will not be possible to mix them uniformly with pulp or the like.

On the other hand, if the water retention rate of the cellulose nanofibers exceeds 600%, the water retention capacity of the cellulose nanofibers themselves increases, possibly deteriorating the dewaterability of the cellulose fiber slurry.

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

The water retention rate of cellulose nanofiber is determined by JAPAN TAPPI No. 26 (2000).

The cellulose nanofiber crystallinity is preferably 45-90%, more preferably 55-88%, and particularly preferably 60-86%. If the crystallinity of the cellulose nanofibers is within the above range, the strength of the molded article or the like can be ensured.

The degree of crystallinity can be arbitrarily adjusted, for example, by selection of raw material pulp, pretreatment, fibrillation, and the like.

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 are excellent in dewatering properties of the cellulose fiber slurry.

The peak value of cellulose nanofibers is, for example, 1-100 μm, preferably 3-800 μm, more preferably 5-60 μm.

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

The peak value of cellulose nanofiber is the value measured according to 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 analyzer (laser diffraction/scattering particle size distribution analyzer manufactured by Seishin Enterprise Co., Ltd.). Next, the median diameter of cellulose nanofibers is measured from this distribution. Let this median diameter be a peak value.

The pulp viscosity of the cellulose nanofibers is preferably 1-10 cps, more preferably 1-9 cps, and particularly preferably 1-8 cps. The pulp viscosity is the viscosity of the solution after dissolving cellulose in the 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 dewatering properties to the slurry and maintain the mechanical properties when formed into a compact.

Cellulose nanofibers obtained by fibrillation can be dispersed in an aqueous medium to prepare a dispersion, if necessary, prior to mixing with microfibrillated cellulose or pulp. It is particularly preferred that the aqueous medium is entirely water (aqueous solution). However, the aqueous medium may be another liquid partially compatible with water. As other liquids, for example, lower alcohols having 3 or less carbon atoms can be used.

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

The B-type viscosity (solid concentration: 1%) of the cellulose nanofiber dispersion is a value measured according to JIS-Z8803 (2011) "Method for measuring viscosity of liquids". The B-type viscosity is the resistance torque when the dispersion is stirred, and means that the higher the viscosity, the greater the energy required for stirring.

(microfibrillated cellulose)
In the present embodiment, the microfibrillated cellulose has a role of increasing the hydrogen bonding points and improving the heat resistance of the molded article in terms of tensile strength while ensuring dehydration.

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

When the average fiber diameter of microfibrillated cellulose is less than 0.1 μm, it is no different from cellulose nanofibers, and the effect of increasing strength (especially bending elastic modulus) cannot be sufficiently obtained. In addition, defibration takes a long time, and a large amount of energy is required. Furthermore, the dewaterability of the cellulose fiber slurry deteriorates. If the dehydration property is deteriorated, a large amount of energy is required for drying the molded article, etc., in the case of producing a molded article, etc. from the cellulose fiber slurry. may decrease.

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

Microfibrillated cellulose can be obtained by defibrating (refining) raw material pulp. As raw material pulp, the same material as cellulose nanofiber can be used, and it is preferable to use the same material as cellulose nanofiber.

In addition, raw material pulp for microfibrillated cellulose can be pretreated and defibrated in the same manner as in the case of cellulose nanofibers. However, the degree of defibration differs, and it is necessary to defibrate within a range in which, for example, the average fiber diameter remains at 0.1 μm or more. The following description will focus on 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, the fibers may not form a three-dimensional network, and the reinforcing effect may be reduced.

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

Regarding the fiber length of the microfibrillated cellulose, the ratio of 0.2 mm or less is preferably 60% or more, more preferably 70% or more, and particularly preferably 75% or more. If the ratio is less than 60%, a sufficient reinforcing effect may not be obtained.

On the other hand, the fiber length of the microfibrillated cellulose does not have an upper limit of 0.2 mm or less, and may be 0.2 mm or less.

The aspect ratio of the microfibrillated cellulose is 1 to 10000 when it is necessary to improve the strength while maintaining the ductility of the molded article to some extent in the production of the molded article from the cellulose fiber slurry. is preferred, and 5 to 5,000 is more preferred.

The aspect ratio is a value obtained by dividing the average fiber length by the average fiber width. It is thought that the larger the aspect ratio, the more places in the pulp where catching occurs, so that the reinforcing effect increases, but on the other hand, the ductility of the molded product, etc., is reduced by the amount of catching.

The fibrillation rate of the microfibrillated cellulose is preferably 0.5% or more, more preferably 1.0% or more, and particularly preferably 1.5% or more. Also, 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 dehydration may become difficult even if defibration is possible within the range where the average fiber width remains at 0.1 μm or more. .

On the other hand, if the fibrillation rate is less than 0.5%, hydrogen bonding between fibrils is so small that it may not be possible to form a strong three-dimensional network.

The 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 45%, although the miscibility with pulp and cellulose nanofibers is improved, the strength of the fiber itself is reduced, so there is a risk that the strength cannot be guaranteed.

On the other hand, the crystallinity of the microfibrillated cellulose is preferably 90% or less, more preferably 88% or less, particularly preferably 86% or less. If the degree of crystallinity exceeds 90%, the ratio of strong hydrogen bonds in the molecule increases and the fiber itself becomes rigid, so the hydrogen bonding points with the pulp do not increase sufficiently, and it is possible to form a molded product from the cellulose fiber slurry. In the case of manufacturing, there is a possibility that the strength of the molded article or the like may 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 refining 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, it may not be possible to sufficiently suppress the aggregation of microfibrillated cellulose.

The freeness of the microfibrillated cellulose is preferably 200 cc or less, more preferably 150 cc or less, and particularly preferably 100 cc or less. If the freeness of the microfibrillated cellulose exceeds 200 cc, the average fiber diameter of the microfibrillated cellulose exceeds 10 μm, and there is a possibility that the effect on strength cannot be sufficiently obtained.

The water retention of the microfibrillated cellulose is preferably 500% or less, more preferably 450% or less, particularly preferably 400% or less. If the water retention of the microfibrillated cellulose exceeds 500%, the dehydration property tends to be poor, and aggregation may occur.

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

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

On the other hand, when the content of microfibrillated cellulose exceeds 50% by mass, the content of pulp and cellulose nanofibers is relatively decreased, and the effect of containing pulp and cellulose nanofibers may not be obtained. There is

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

(pulp)
In the present embodiment, the pulp has a role of greatly improving the dewaterability of the cellulose fiber slurry. Pulp also plays a role in improving the strength of molded articles when used together with microfibrillated cellulose.

However, the pulp content is preferably within a predetermined range (described later), and the water retention ratio (value obtained by dividing the water retention of the cellulose fiber slurry by the water retention of the cellulose nanofibers) and the dehydration of the cellulose fiber slurry by its own weight. It is more preferable to include it so that the property is within a predetermined range (described later). By adding such a limitation, when a molded article or the like is produced from the cellulose fiber slurry, the strength of the molded article or the like is ensured. Details of the water retention ratio and self-weight dehydration will be described later.

When the average fiber diameters of microfibrillated cellulose, pulp, and cellulose nanofiber are set within a specific range, the content of pulp in cellulose fibers is preferably 1 to 50% by mass, more preferably 3 to 40% by mass. , particularly preferably 5 to 20 mass %. If the pulp content is less than 1% by mass, the dewaterability of the cellulose fiber slurry may not be sufficiently improved. Further, if the pulp content is less than 1% by mass, the strength of the molded article or the like may not be ensured when the molded article or the like is produced from the cellulose fiber slurry.

On the other hand, if the content of pulp exceeds 50% by mass, the content of microfibrillated cellulose and the like is reduced as a result. it may not be done.

As pulp, the same pulp as raw material pulp for microfibrillated cellulose or cellulose nanofiber can be used. However, as the pulp, it is preferable to use the same pulp as the raw material pulp for microfibrillated cellulose or cellulose nanofiber. If the same pulp as the raw material pulp for microfibrillated cellulose or cellulose nanofibers is used, the affinity with cellulose fibers is improved, and as a result, the homogeneity of cellulose fiber slurries, moldings, and the like is improved.

As the pulp, lignin-containing pulp is preferably used, mechanical pulp is more preferably used, and BTMP is particularly preferably used. The use of these pulps further improves the dewaterability of the cellulose fiber slurry.

The average fiber diameter (average fiber width, average diameter of single fibers) of pulp is preferably 10 to 100 μm, more preferably 10 to 80 μm, particularly preferably 10 to 60 μm. When the average fiber diameter of the pulp is within the above range, the dewaterability of the cellulose fiber slurry is further improved by setting the pulp content within the range described above.

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

The method for measuring the average fiber diameter of pulp is as follows.
First, 100 ml of an aqueous dispersion of pulp having 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 3 times with 20 ml of t-butanol. . It is then freeze-dried and coated with osmium to form a sample. This sample is observed with an electron microscope SEM image at a magnification of 100 times to 1000 times depending on the width of the constituent fibers. Specifically, two diagonal lines are drawn on the observation image, and three straight lines passing through the intersections of the diagonal lines are arbitrarily drawn. Furthermore, the width of a total of 100 fibers intersecting with these three straight lines is visually measured. Then, the median diameter of the measured value is taken as the average fiber diameter.

The freeness of the pulp is preferably 10-800 ml, more preferably 350-780 ml, particularly preferably 400-750 ml. If the freeness of the pulp exceeds 800 ml, although the dewatering property of the cellulose fiber slurry can be improved, the surface of the molded product tends to be uneven, and the fibers become rigid and microfibrillated cellulose or cellulose nano. It may not be integrated with the fiber and the density may not be improved.

On the other hand, if the freeness of the pulp is less than 10 ml, the dewatering property of the cellulose fiber slurry may not be sufficiently improved, and the rigidity of the pulp fibers themselves may be reduced, so that they may not function as fibers that support the molded article or the like. There is

The freeness of pulp is a value measured according to JIS P8121-2 (2012).

(Slurry preparation)
As shown in FIG. 1, fine fibers (microfibrillated cellulose or microfibrillated cellulose and cellulose nanofibers) C and pulp P are mixed at a predetermined ratio, preferably the content of pulp P is within the range described above. to prepare a slurry S of cellulose fibers (slurry preparation step 10). The fine fibers C and the pulp P can also be mixed in the form of a dispersion.

When the fine fibers C and the pulp P are mixed, it is preferable to adjust the solid content concentration of the cellulose fibers in the cellulose fiber slurry S by adding a medium W such as water. The solid content concentration of the cellulose fibers is preferably 1-15% by mass, more preferably 1-12% by mass, and particularly preferably 1-10% by mass. When the solid content concentration of the cellulose fibers is less than 1% by mass, the fluidity is high, and the risk of the cellulose fibers flowing out in the dehydration step 30 increases.

On the other hand, when the solid content concentration of the cellulose fibers exceeds 15% by mass, the fluidity is significantly reduced and the processability is deteriorated. Getting a body can be difficult.

The medium (aqueous medium) W such as water is preferably water in its entirety. However, the aqueous medium W may be another liquid partially compatible with water. Other liquids that can be used include, for example, lower alcohols having 3 or less carbon atoms and ketones having 5 or less carbon atoms.

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

In addition to the above, the cellulose fiber slurry preferably has a self-weight dewatering property of 1.1 to 3.0, preferably 1.4 to 2.0, by appropriately adjusting the type and content of pulp. 8 is more preferred, and 1.5 to 2.5 is particularly preferred.

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 finally obtained molded body (final product) X can be secured.

The water retention of the cellulose fiber slurry S is a value measured by the following method.
First, a slurry of cellulose fibers (concentration: 2% by mass) is dehydrated using a centrifuge (conditions: 3000 G, 15 minutes), and the mass of the resulting dehydrated product is measured. Next, the dehydrated product is completely dried, and the mass of the dried product obtained is measured. Water retention (%)=(mass of dehydrated matter−mass of dried matter)/mass of cellulose fiber slurry×100.

The 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 dewaterability. In addition, a lower water retention ratio indicates that the water retention has decreased from the original cellulose nanofiber slurry, indicating that the dewaterability has increased.

On the other hand, the self-weight dewaterability 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 wide x 10 cm long x 2 mm thick) on the water-absorbing substrate and left for 2 minutes. Dehydration property under its own weight = concentration of solid content after standing for 2 minutes/concentration of solid content before coating.

(Molded body)
The slurry thus obtained can be appropriately subjected to wet paper formation 20, dehydration 30, pressurization and heating 40, etc. to obtain a compact X. There are various methods for producing the molded article X from the slurry S, but for example, the method described in JP-A-2018-62727 (cellulose nanofiber molded article) is suitable. The method for forming the wet paper web has been described above as a preferred example, and the manufacturing method of the present embodiment is not intended to be limited to this.

The molded article X obtained as described above preferably has a tensile modulus at 23° C. of 5 to 25 GPa or more, more preferably 7 to 24 GPa, and particularly preferably 9 to 23 GPa. Also, the tensile strength at 23° C. is preferably 10 MPa or more, more preferably 20 to 200 MPa, and particularly preferably 30 to 150 MPa. When the tensile modulus of elasticity at 23° C. of the molded article X is 5 GPa or more and the tensile strength at 23° C. is 10 MPa or more, the heat resistance is improved as is clear from the examples described later.

The tensile modulus at 23°C was measured according to JIS K7127:1999. The test piece (sheet) was in the form of a No. 2 tensile dumbbell defined by JIS-K6251. The test speed was 10 mm/min. In addition, the measurement was performed in an environment with a temperature of 23° C. and a humidity of 50%.

The tensile strength at 23°C was measured according to JIS K7127:1999. The test piece (sheet) was in the form of a No. 2 tensile dumbbell defined by JIS-K6251. The test speed was 10 mm/min. In addition, the measurement was performed in an environment with a temperature of 23° C. and a humidity of 50%.

The compact X obtained as described above preferably has a density of 0.8 to 1.5 g/m ³ , more preferably 0.9 to 1.4 g/m ³ , particularly preferably 1.0 to 1.4 g/m 3 . 1.3 g/ ^m3 . If the density of the compact X is less than 0.8 g/m ³ , the strength may be considered insufficient due to the decrease in hydrogen bonding points.

The density of the compact X is a value measured according to JIS-P-8118:1998.

The tensile breaking strain of the compact X is preferably 10% or less, more preferably 5% or less, particularly preferably 4% or less, and most preferably 3% or less. If the quoted breaking strain exceeds the above upper limit, the strain may be large and the application may be limited. On the other hand, the tensile breaking strain of the compact X is best at 0%, but for example, 1 to 3% is acceptable.

The tensile fracture strain of molded body X is a value measured in accordance with JIS K7127: 1999, in an environment at a temperature of 23 ° C., with a test piece in the shape of a No. 2 tensile dumbbell specified by JIS-K6251, and at a test speed of 10 mm / min. is.

(others)
Additives such as antioxidants, corrosion inhibitors, light stabilizers, ultraviolet absorbers, heat stabilizers, dispersants, antifoaming agents, slime control agents, preservatives, etc. may be added to the slurry S of cellulose fibers, if necessary. can be added.

The molded article X of this embodiment is suitable for use in fields requiring heat resistance. Specifically, for example, parts of transportation equipment such as automobiles, ships, and trains, parts of electric appliances such as microwave ovens, refrigerators, and personal computers, mobile communication devices such as mobile phones, and power storage devices such as batteries and capacitors. Parts, video playback equipment, printing equipment, copier equipment, sporting goods, office equipment, buildings, furniture, office equipment such as stationery, etc. Other uses in the field of packaging, containers such as trays, protective members, etc. Suitable for

Next, examples of the present invention will be described.
First, a slurry of cellulose fibers was prepared using microfibrillated cellulose, pulp, and cellulose nanofibers as cellulose fibers. LBKP was used as raw pulp and pulp for microfibrillated cellulose and cellulose nanofiber. The microfibrillated cellulose was obtained by preliminarily beating raw material pulp (moisture content: 98% by mass) with a refiner. This microfibrillated cellulose was an aqueous dispersion with a concentration of 2.5 mass %. The resulting microfibrillated cellulose had an average fiber diameter of 1 μm, a water retention rate of 296% and a crystallinity of 75%. On the other hand, cellulose nanofibers were obtained by fibrillating the above microfibrillated cellulose with 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 rate of 348%, and a crystallinity rate of 75%. Microfibrillated cellulose, pulp, and cellulose nanofiber were mixed at the ratios shown in Table 1 to give a solid content concentration of 2.0% by mass.

Next, a 100 μm-thick sheet (molded body) is prepared from the slurry of the obtained cellulose fibers, and the tensile modulus and tensile strength of the molded body at 23° C. and the tensile modulus and tensile strength at 90° C. are examined. did the test. Specifically, first, a wet paper was produced from a slurry of cellulose fibers, and the wet paper was dehydrated under pressure and heated under pressure to produce a compact. Pressure dehydration was performed at 25° C. and 2 MPa for 5 minutes. Moreover, pressure heating was performed at 120° C. and 2 MPa for 5 minutes. The density of the obtained compact was 1.0 g/m ³ .

Table 1 shows the results. The methods for measuring water retention, self-weight dehydration, and tensile elastic modulus and tensile strength at 23°C are as described above. Also, the method of measuring the tensile modulus and tensile strength at 90°C is different from the case at 23°C, and the environment for measurement is changed to a temperature of 90°C. In addition, for the tensile modulus and tensile strength at 90°C, the ratio of the tensile modulus and tensile strength at 23°C (tensile modulus and tensile strength at 90°C/tensile modulus and tensile strength at 23°C) is shown. there is

(Discussion)
Table 1 shows that the combination of pulp and microfibrillated cellulose improves heat resistance in terms of tensile strength. Moreover, in this case, it can be seen that when the cellulose fibers further contain cellulose nanofibers at a content rate of 70% by mass or less, the heat resistance is improved also in terms of the tensile modulus.

In addition, the tensile modulus of elasticity at 90° C./tensile modulus of elasticity at 23° C. is considered to be preferably 0.8 to 1.0. Further, it is considered that the tensile strength at 90° C./tensile strength at 23° C. is preferably between 0.8 and 1.0.

INDUSTRIAL APPLICABILITY The present invention can be used as a method for producing a molded body of cellulose fibers.

10 Slurry preparation step 20 Wet paper forming step 30 Dehydration step 40 Pressure heating step C Fine fiber P Pulp W Medium such as water X Molded body

Claims (4)

A method for producing a molded body containing cellulose fibers as a main component,
including pulp and defibrated fiber as the cellulose fiber,
Including microfibrillated cellulose having an average fiber diameter of 0.1 to 10 μm as the defibrated fiber and cellulose nanofiber having an average fiber diameter of 10 to 90 nm as a complementary material of the microfibrillated cellulose ,
A tensile modulus at 23°C of 5 GPa or more and a tensile strength at 23°C of 10 MPa or more,
A method for producing a molded body of cellulose fibers, characterized by: A slurry is prepared from the cellulose fibers, a wet paper web is formed from the slurry of the cellulose fibers, and the wet paper web is dehydrated, pressurized and heated to form a compact.
The method for producing a cellulose fiber molded article according to claim 1 . The content of the cellulose nanofibers in the cellulose fibers exceeds 0% by mass and is 70% by mass or less,
The method for producing a cellulose fiber molded article according to claim 1 or 2. The pulp has an average fiber diameter of 10 to 100 μm ,
The content of the pulp in the cellulose fibers is 5 to 20% by mass,
The method for producing a cellulose fiber molded article according to claim 1 or 2 .

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