JP2024078170A - Cellulose fiber composite resin and method for producing cellulose fiber composite resin - Google Patents

Abstract

To provide: a cellulose fiber composite resin which can be suitably subjected to strand fabrication even when the fiber blending ratio is increased; and a method for producing the same.SOLUTION: A cellulose fiber composite resin comprises: carbamate-modified fine fibers having an average fiber diameter of 5-19 μm; and a resin, wherein the melt viscosity of the composite resin at a shear rate of 2432 s-1 is 230 Pa s or less. Further, a method for producing a cellulose fiber composite resin comprises: kneading carbamate-modified fine fibers having an average fiber diameter of 5-19 μm with a resin at a kneading energy of 0.10 kw/kg or more; and adjusting the melt viscosity at a shear rate of 2432 s-1 to 230 Pa s or less.SELECTED DRAWING: None

Description

The present invention relates to a cellulose fiber composite resin and a method for producing the cellulose fiber composite resin.

In recent years, fine fibers such as cellulose nanofibers and microfiber cellulose (microfibrillated cellulose) have been attracting attention for their use as reinforcing materials for resins. However, because fine fibers are hydrophilic while resins are hydrophobic, there is a problem with the dispersibility of the fine fibers when using them as reinforcing materials for resins. Therefore, the present inventors have proposed replacing the hydroxyl groups of the fine fibers with carbamate groups (carbamate modification, carbamate formation) (see Patent Document 1). This proposal improves the dispersibility of the fine fibers, thereby improving the reinforcing effect of the resin.

However, cellulose fiber composite resins that have been compounded by adding fine fibers may also be commercialized as so-called masterbatches, composite resins at a stage prior to adjustment to the desired physical properties of the composite resin. In this case, to allow flexibility in the fiber content of the final composite resin, it is desirable for the masterbatch (composite resin) to have a high fiber content; for example, a composite resin with a fiber content of 50% by mass or more is desirable. However, if the fiber content is increased, for example, the composite resin may break under its own weight during strand processing, making subsequent pellet processing, etc. difficult.

JP 2019-1876 A

The problem that the invention aims to solve is to provide a cellulose fiber composite resin and a method for producing the same that can perform strand processing appropriately even when the fiber content is increased.

The means for solving the above problem is
The present invention comprises carbamate-modified fine fibers having an average fiber diameter of 5 to 19 μm and a resin,
The melt viscosity at a shear rate of 2432 s ^-1 is 230 Pa s or less;
The cellulose fiber composite resin is characterized by the above.

Also,
A carbamate-modified fine fiber having an average fiber diameter of 5 to 19 μm and a resin,
The mixture is kneaded with a kneading energy of 0.1 kW/kg or more, and the melt viscosity at a shear rate of 2432 s ^-1 is 230 Pa s or less.
The present invention relates to a method for producing a cellulose fiber composite resin.

The invention provides a cellulose fiber composite resin and a method for producing the same that allows for proper strand processing even when the fiber content is increased.

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

The cellulose fiber composite resin of this embodiment includes carbamate-modified fine fibers having an average fiber diameter of 5 to 19 μm and a resin, and has a melt viscosity of 230 Pa·s or less at a shear rate of 2432 s ^-1 . Here, carbamate modification means that some or all of the hydroxyl groups (-OH groups) of the cellulose fibers (also called "fibrous cellulose") are substituted with carbamate groups. In addition, in the manufacturing method of the cellulose fiber composite resin of this embodiment, the carbamate-modified fine fibers having an average fiber diameter of 5 to 19 μm and the resin are kneaded with a kneading energy of 0.1 kW/kg or more, and the melt viscosity at a shear rate of 2432 s ^-1 is set to 230 Pa·s or less. The details will be described below.

(Cellulose fiber)
In this embodiment, the cellulose fibers that are fine fibers are microfiber cellulose (microfibrillated cellulose, MFC) with an average fiber diameter of 5 to 19 μm. When the cellulose fibers are microfiber cellulose, the reinforcing effect of the resin is significantly improved. In addition, microfiber cellulose is easier to modify with carbamate groups (carbamation) than cellulose nanofiber, which is also a fine fiber. However, it is more preferable to carbamate the cellulose fibers before they are pulverized, and in this case, microfiber cellulose and cellulose nanofiber are equivalent.

In this embodiment, microfiber cellulose means a fiber having a larger average fiber diameter (width) than cellulose nanofiber. Specifically, the average fiber diameter is, for example, 5 to 19 μm, preferably 8 to 17 μm, and more preferably 10 to 15 μm. When the average fiber diameter of microfiber cellulose falls below 5 μm (below), self-aggregation due to hydrogen bonds occurs significantly during drying, and a strong aggregate is formed that does not break even when shear is applied while melting during resin composite formation, so that the strand may break from the aggregate during strand processing, making stable production difficult. In addition, since the aggregate cannot fully exert the reinforcing properties of the resin unlike the fiber form, there is a risk that the effect of improving the strength of the resin (especially the bending modulus) may not be fully obtained. In addition, the fiberization time is long, and a large amount of energy is required. Furthermore, the dehydration of the cellulose fiber slurry is deteriorated. When the dehydration is deteriorated, a large amount of energy is required for drying, and if a large amount of energy is applied for drying, the microfiber cellulose may thermally deteriorate and the strength may decrease. On the other hand, if the average fiber diameter of the microfiber cellulose exceeds 19 μm (exceeding this), it becomes no different from pulp, and there is a risk that the reinforcing effect will be insufficient.

The method for measuring the average fiber diameter of the microfibrous cellulose is as follows.
First, 100 ml of an aqueous dispersion of fine fibers (microfiber cellulose) 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, the sample is freeze-dried and osmium-coated to obtain a sample. This sample is observed using an electron microscope SEM image at a magnification of 3,000 to 30,000 times depending on the width of the fibers that constitute it. Specifically, two diagonal lines are drawn on the observed image, and three straight lines passing through the intersection of the diagonal lines are arbitrarily drawn. Furthermore, the width of a total of 100 fibers that intersect with these three straight lines is visually measured. The median diameter of the measured value is then taken as the average fiber diameter.

Microfiber cellulose can be obtained by defibrating (refining) cellulose raw material (hereinafter also referred to as "raw material pulp"). As the raw material pulp, one or more of the following can be selected and used: wood pulp made from broadleaf trees, coniferous trees, etc.; non-wood pulp made from straw, bagasse, cotton, hemp, bast fiber, etc.; waste paper pulp (DIP) made from recycled waste paper, broke paper, etc.; plant-derived fibers; animal-derived fibers; and microbial-derived fibers. The above various raw materials may be in the form of, for example, a pulverized material (powdered material) called cellulose-based powder.

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

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

As mechanical pulp, one or more types can be selected and used from, for example, stone ground pulp (SGP), pressed stone ground pulp (PGW), refiner ground pulp (RGP), chemi-ground pulp (CGP), thermo-ground pulp (TGP), ground pulp (GP), thermo-mechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), refiner mechanical pulp (RMP), bleached thermo-mechanical pulp (BTMP), etc.

The raw pulp can be pretreated by a chemical method prior to defibration. Examples of pretreatment by a chemical method include hydrolysis of polysaccharides by acid (acid treatment), hydrolysis of polysaccharides by enzymes (enzyme treatment), swelling of polysaccharides by alkali (alkali treatment), oxidation of polysaccharides by an oxidizing agent (oxidation treatment), and reduction of polysaccharides by a reducing agent (reduction treatment). However, as a pretreatment by a chemical method, it is preferable to carry out an enzyme treatment, and it is more preferable to additionally carry out one or more treatments selected from acid treatment, alkali treatment, and oxidation treatment. The enzyme treatment will be described in detail below.

As the enzymes used in the enzymatic treatment, it is preferable to use at least one of cellulase enzymes and hemicellulase enzymes, and it is more preferable to use both in combination. The use of these enzymes makes it easier to defibrate the cellulose raw material. Note that cellulase enzymes cause the decomposition of cellulose in the presence of water. Also, hemicellulase enzymes cause the decomposition of hemicellulose in the presence of water.

Examples of cellulase enzymes that can be used include enzymes produced by the genera Trichoderma (filamentous fungi), Acremonium (filamentous fungi), Aspergillus (filamentous fungi), Phanerochaete (basidiomycetes), Trametes (basidiomycetes), Humicola (filamentous fungi), Bacillus (bacteria), Schizophyllum (basidiomycetes), Streptomyces (bacteria), and Pseudomonas (bacteria). These cellulase enzymes can be purchased as reagents or commercial products. Examples of commercially available products include Celluleucin T2 (manufactured by HPI), Meicelase (manufactured by Meiji Seika Kaisha), Novozyme 188 (manufactured by Novozyme), Multifect CX10L (manufactured by Genencor), and cellulase enzyme GC220 (manufactured by Genencor).

As the cellulase enzyme, either EG (endoglucanase) or CBH (cellobiohydrolase) can be used. EG and CBH can be used alone or in combination. They can also be used in combination with a hemicellulase enzyme.

As hemicellulase enzymes, for example, xylanase, which is an enzyme that breaks down xylan, mannase, which is an enzyme that breaks down mannan, and arabanase, which is an enzyme that breaks down araban, can be used. In addition, pectinase, which is an enzyme that breaks down pectin, can also be used.

Hemicellulose is a polysaccharide excluding pectins found between cellulose microfibrils in plant cell walls. Hemicellulose is diverse and differs depending on the type of wood and between the layers of the cell wall. The main component of the secondary wall of softwood is glucomannan, while the main component of the secondary wall of hardwood is 4-O-methylglucuronoxylan. Therefore, when obtaining fine fibers from softwood bleached kraft pulp (NBKP), it is preferable to use mannase. Also, when obtaining fine fibers from hardwood bleached kraft pulp (LBKP), it is preferable to use xylanase.

The amount of enzyme added to the cellulose raw material is determined by, for example, the type of enzyme, the type of wood used as the raw material (coniferous or broadleaf), the type of mechanical pulp, etc. However, the amount of enzyme added to the cellulose raw material is preferably 0.1 to 3 mass%, more preferably 0.3 to 2.5 mass%, and particularly preferably 0.5 to 2 mass%. If the amount of enzyme added is less than 0.1 mass%, the effect of adding the enzyme may not be sufficient. On the other hand, if the amount of enzyme added is more than 3 mass%, the cellulose may be saccharified, and the fiber yield may decrease. There is also the problem that the effect may not be improved commensurate with the increase in the amount added.

When using a cellulase enzyme as the enzyme, the pH during the enzyme treatment is preferably in the weak acidic range (pH = 3.0 to 6.9) from the viewpoint of the reactivity of the enzyme reaction. On the other hand, when using a hemicellulase enzyme as the enzyme, the pH during the enzyme treatment is preferably in the weak alkaline range (pH = 7.1 to 10.0).

The temperature during the enzyme treatment is preferably 30 to 70°C, more preferably 35 to 65°C, and particularly preferably 40 to 60°C, regardless of whether a cellulase enzyme or a hemicellulase enzyme is used as the enzyme. If the temperature during the enzyme treatment is 30°C or higher, the enzyme activity is less likely to decrease, and the treatment time can be prevented from being prolonged. On the other hand, if the temperature during the enzyme treatment is 70°C or lower, the enzyme can be prevented from being inactivated.

The time for enzyme treatment depends on, for example, the type of enzyme, the temperature of the enzyme treatment, the pH during the enzyme treatment, etc. However, the general time for enzyme treatment is 0.5 to 24 hours.

After the enzyme treatment, it is preferable to inactivate the enzyme. Methods for inactivating the enzyme include, for example, adding an alkaline aqueous solution (preferably pH 10 or higher, more preferably pH 11 or higher) and adding hot water at 80 to 100°C.

Next, the method of alkali treatment will be described.
When the pulp is treated with alkali prior to defibration, some of the hydroxyl groups in the hemicellulose and cellulose contained in the pulp are dissociated and the molecules are anionized, weakening intra- and intermolecular hydrogen bonds and promoting the dispersion of the cellulose raw material during defibration.

Examples of alkalis that can be used in the alkaline treatment include sodium hydroxide, lithium hydroxide, potassium hydroxide, aqueous ammonia, and organic alkalis such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, and benzyltrimethylammonium hydroxide. However, from the viewpoint of production costs, it is preferable to use sodium hydroxide.

By carrying out enzyme treatment, acid treatment, or oxidation treatment prior to defibration, it is possible to reduce the water retention of the microfiber cellulose, increase the degree of crystallinity, and increase the homogeneity. In this regard, if the water retention of the microfiber cellulose is low, it becomes easier to dehydrate, and the dehydration of the cellulose fiber slurry is improved.

When raw pulp is treated with enzymes, acids, or oxidation, the hemicellulose and amorphous regions of cellulose contained in the pulp are broken down. As a result, the energy required for defibration can be reduced, and the uniformity and dispersibility of the cellulose fibers can be improved. However, since pretreatment reduces the aspect ratio of microfiber cellulose, it is preferable to avoid excessive pretreatment when using it as a reinforcing material for resins.

The raw pulp can be defibrated (refined) by beating the raw pulp using, for example, a homogenizer such as a beater, high-pressure homogenizer, or high-pressure homogenizer, a grinder, a mill-type friction machine such as a grinder, a single-shaft kneader, a multi-shaft kneader, a kneader refiner, or a jet mill. However, it is preferable to use a refiner or a jet mill.

The average fiber length of the microfiber cellulose (average length of single fibers) is preferably 0.20 to 0.50 mm, more preferably 0.25 to 0.47 mm, and particularly preferably 0.30 to 0.45 mm. If the average fiber length is less than 0.25 mm, a three-dimensional network cannot be formed between the fibers, and the reinforcing effect of the composite resin (particularly the bending modulus) may decrease. In particular, if the average fiber length is less than 0.20 mm, although the melt viscosity is sufficiently reduced on the strand processing surface, the cellulose fibers tend to aggregate, and the aggregated areas become extremely rigid locally, so that the composite resin added to the resin and composited may have poor suitability for strand processing. On the other hand, if the average fiber length exceeds 0.5 mm, the fluidity of the composite resin decreases, the melt viscosity increases, etc., and the resin may become too rigid during strand processing, breaking under its own weight, resulting in poor suitability for processing.

The average fiber length of the cellulose raw material used to make microfiber cellulose is preferably 0.50 to 5.00 mm, more preferably 1.00 to 3.00 mm, and particularly preferably 1.50 to 2.50 mm. If the average fiber length of the cellulose raw material is less than 0.50 mm, the reinforcing effect of the resin may not be sufficient when the material is defibrated. On the other hand, if the average fiber length exceeds 5.00 mm, a large amount of energy is required to prepare microfiber cellulose of a specified fiber size, which is not industrially preferable.

The average fiber length of microfiber cellulose can be adjusted as desired, for example, by selecting the raw pulp, pre-treating, defibrating, etc.

The average fiber length and the percentage of fiber lengths over 0.02 mm below are measured using a fiber analyzer "FS5" manufactured by Valmet.

The proportion of microfiber cellulose fibers with a length of more than 0.02 mm is preferably 20% or more, more preferably 40% or more, and particularly preferably 60% or more. If this proportion falls below 20%, the reinforcing effect of the resin may not be sufficiently obtained. On the other hand, there is no upper limit to the proportion of microfiber cellulose fibers with a length of more than 0.02 mm, and all fibers may be more than 0.02 mm.

The aspect ratio of the microfiber cellulose is preferably 2 to 15,000, and more preferably 10 to 10,000. If the aspect ratio is less than 2, a three-dimensional network cannot be constructed, and even if the average fiber length exceeds 0.20 mm, the reinforcing effect may be insufficient. On the other hand, if the aspect ratio exceeds 15,000, the microfiber cellulose may become highly entangled, resulting in insufficient dispersion in the resin.

The aspect ratio is the average fiber length divided by the average fiber width. The larger the aspect ratio, the more points there are for snagging, and therefore the greater the reinforcing effect. On the other hand, the more snagging there is, the more points of contact with the resin there are, which results in an increase in the melt viscosity of the composite resin, and the strands become too rigid when processed into strands, which can cause them to break under their own weight and reduce processability.

The fibrillation rate of microfiber cellulose is preferably 0.1 to 3.0%, more preferably 0.3 to 2.8%, and particularly preferably 0.5 to 2.5%. If the fibrillation rate exceeds 3.0%, the contact area with water becomes too large, so dehydration may be difficult even if the fibers are defibrated to an average fiber width of 5 μm or more. In particular, if the fibrillation rate exceeds 3.0%, the fibers may become entangled with each other, the fluidity of the composite resin obtained by adding the fibers may decrease, and the melt viscosity may increase, resulting in poor suitability for strand processing. On the other hand, if the fibrillation rate is below 0.1%, there may be few hydrogen bonds between the fibrils, making it impossible to form a strong three-dimensional network.

The fibrillation rate is the ratio of the projected area of small fibers to the projected area of the entire fiber, i.e., the fuzzed area/the entire fiber including fuzz. This value can be measured, for example, using a fiber analyzer "FS5" manufactured by Valmet.

The crystallinity of the microfiber cellulose is preferably 60% or more, more preferably 62% or more, and particularly preferably 65% or more. If the crystallinity is less than 60%, the mixability with pulp and cellulose nanofibers will improve, but the strength of the fiber itself will decrease, and there is a risk that the strength of the resin will not be improved. On the other hand, the crystallinity of the microfiber cellulose is preferably 85% or less, more preferably 83% or less, and particularly preferably 80% or less. If the crystallinity exceeds 85%, the proportion of strong hydrogen bonds in the molecule will increase, the fiber itself will become rigid, and dispersibility will be poor. In addition, the rigidity of the fiber itself will increase the melt viscosity of the composite resin, and the strands will become too rigid during strand processing, making them more likely to break under their own weight, which may reduce processability.

The crystallinity of microfiber cellulose can be adjusted as desired, for example, by selecting the raw pulp, pre-treating it, and refining it.

The degree of crystallinity is a value measured by X-ray diffraction in accordance with JIS-K0131 (1996) "General Rules for X-ray Diffraction Analysis." Note that fine fibers have amorphous and crystalline parts, and the degree of crystallinity refers to the proportion of crystalline parts in the entire fine fiber.

The pulp viscosity of the microfiber cellulose is preferably 2 cps or more, more preferably 4 cps or more. If the pulp viscosity of the microfiber cellulose is below 2 cps, it may be difficult to suppress the aggregation of the microfiber cellulose.

Pulp viscosity is measured in accordance with TAPPI T 230.

The freeness of the microfiber cellulose is preferably 100 to 300 ml, more preferably 120 to 280 ml or less, and particularly preferably 150 to 250 ml or less. If the freeness of the microfiber cellulose exceeds 300 ml, the fiber size becomes too large, for example, the average fiber diameter of the microfiber cellulose exceeds 19 μm, and the melt viscosity increases due to an increase in flow resistance derived from the fibers in the composite resin, and the strands become too rigid during strand processing, causing breakage under their own weight, which may cause problems with strand processing. If the freeness is below 100 ml, the fibers are too fine, and the fine fibers strongly aggregate with each other in the process of removing the dispersion medium from the dispersion liquid, and the resulting aggregates do not break even when shear is applied in the composite resin, becoming local defects during strand processing, and may cause problems with strand processing, such as being prone to breaking during processing.

Freeness is a value measured in accordance with JIS P8121-2 (2012).

The water retention of the microfiber cellulose is preferably 80 to 400%, more preferably 90 to 350%, and particularly preferably 100 to 300%. If the water retention is below 80%, the reinforcing effect may be insufficient because it is no different from the raw pulp. In addition, when the water retention is below 80%, the fibers are not in sufficient contact with the surroundings, so that when compounded with the resin, the contact area between the resin and the fibers is small, and even if the melt viscosity can be adjusted to an appropriate range, it may result in local defects during strand processing, which may cause problems in strand processing. On the other hand, if the water retention exceeds 400%, the dewatering property tends to be poor and the fibers are easily aggregated. In this regard, the water retention of the microfiber cellulose can be lowered by replacing the hydroxyl groups of the cellulose fibers with carbamate groups, and the dewatering and drying properties can be improved. Furthermore, when the water retention exceeds 400%, the fibers are in a state where they can fully come into contact with their surroundings, but because their affinity with water is too high, they will clump together in a resin that has poor affinity with water, and as a result, the clumped areas in the composite resin will become extremely rigid locally. Therefore, even if the melt viscosity can be adjusted to the appropriate range, these locally rigid areas will be prone to breaking during strand processing, which may cause problems with strand processing.

The water retention of microfiber cellulose can be adjusted as desired, for example, by selecting the raw pulp, pre-treating it, defibrating it, etc.

The water retention value was measured in accordance with JAPAN TAPPI No. 26 (2000).

The microfiber cellulose of this embodiment has a carbamate group. There is no particular limitation on how the carbamate group is provided. For example, the cellulose raw material may be carbamed to have the carbamate group, or the microfiber cellulose (finely divided cellulose raw material) may be carbamed to have the carbamate group.

Incidentally, "having a carbamate group" means that a carbamate has been introduced into the fibrous cellulose. The carbamate group is a group represented by -O-CO-NH-, for example, a group represented by -O-CO-NH ₂ , -O-CONHR, -O-CO-NR ₂ , etc. In other words, the carbamate group can be represented by the following structural formula (1).

Here, n is an integer of 1 or more. Each R is independently at least one of hydrogen, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an aromatic group, and a derivative group thereof.

Examples of saturated linear hydrocarbon groups include linear alkyl groups having 1 to 10 carbon atoms, such as methyl, ethyl, and propyl groups.

Examples of saturated branched hydrocarbon groups include branched alkyl groups having 3 to 10 carbon atoms, such as isopropyl, sec-butyl, isobutyl, and tert-butyl groups.

Examples of saturated cyclic hydrocarbon groups include cycloalkyl groups such as cyclopentyl, cyclohexyl, and norbornyl.

Examples of unsaturated linear hydrocarbon groups include linear alkenyl groups having 2 to 10 carbon atoms, such as ethenyl, propen-1-yl, and propen-3-yl, and linear alkynyl groups having 2 to 10 carbon atoms, such as ethynyl, propyn-1-yl, and propyn-3-yl.

Examples of unsaturated branched hydrocarbon groups include branched alkenyl groups having 3 to 10 carbon atoms, such as propen-2-yl, buten-2-yl, and buten-3-yl groups, and branched alkynyl groups having 4 to 10 carbon atoms, such as butyn-3-yl groups.

Examples of aromatic groups include phenyl, tolyl, xylyl, and naphthyl groups.

Examples of derivative groups include groups in which one or more hydrogen atoms in the above-mentioned saturated linear hydrocarbon groups, saturated branched hydrocarbon groups, saturated cyclic hydrocarbon groups, unsaturated linear hydrocarbon groups, unsaturated branched hydrocarbon groups, and aromatic groups are substituted with a substituent (e.g., a hydroxy group, a carboxy group, a halogen atom, etc.).

In microfiber cellulose having carbamate groups (introduced with carbamate groups), some or all of the highly polar hydroxyl groups are replaced with carbamate groups, which have relatively low polarity. Therefore, microfiber cellulose having carbamate groups has low hydrophilicity and high affinity with resins, etc., which have low polarity. As a result, microfiber cellulose having carbamate groups has excellent uniform dispersion with resins. In addition, a slurry of microfiber cellulose having carbamate groups has good handleability.

The substitution rate (introduction rate) of the carbamate group to the hydroxyl group of the microfiber cellulose is preferably 0.5 to 2.0 mmol/g, more preferably 0.6 to 1.5 mmol/g, and particularly preferably 0.1 to 1.0 mmol/g. When the substitution rate is 0.5 mmol/g or more, the effect of introducing the carbamate, particularly the effect of improving the bending elongation of the resin, is reliably achieved. Furthermore, since the affinity with the organic acid-modified resin is increased, the dispersibility in the composite resin is improved, and localized aggregation that causes breakage during strand processing can be reduced. On the other hand, if the substitution rate exceeds 2.0 mmol/g, although the affinity with the organic acid-modified resin is increased, the costs of the chemicals, energy, etc. required for modification become enormous, which is not industrially preferable.

The carbamate group substitution rate (mmol/g) refers to the amount of carbamate groups contained in 1 g of cellulose raw material having carbamate groups. Cellulose is a polymer whose structural unit is anhydroglucose, and has three hydroxyl groups per structural unit.

<Carbamate formation>
Regarding the introduction of carbamate (carbamation) into microfiber cellulose (when carbamate is performed before defibration, it is a cellulose raw material. Hereinafter, the same is also referred to as "microfiber cellulose, etc."), there are a method of carbamate-ifying the cellulose raw material and then pulverizing it, as described above, and a method of pulverizing the cellulose raw material and then carbamate-ifying it. In this regard, in this specification, defibration of the cellulose raw material is explained first, and then carbamate-ification (modification) is explained. However, either defibration or carbamate-ification can be performed first. However, it is preferable to perform carbamate-ification first and then defibration. This is because the cellulose raw material before defibration has a high dehydration efficiency, and the cellulose raw material is in a state where it is easily defibrated by the heating accompanying carbamate-ification.

The process of carbamate-forming microfiber cellulose and the like can be mainly divided into, for example, a mixing process, a removal process, and a heat treatment. The mixing process and the removal process can be collectively called a preparation process for preparing a mixture to be subjected to a heat treatment. In addition, the carbamate-forming process does not require the use of an organic solvent.

In the mixing process, microfiber cellulose, etc. (as mentioned above, it may be a cellulose raw material; the same applies below) and urea and/or a urea derivative (hereinafter simply referred to as "urea, etc.") are mixed in a dispersion medium.

Examples of urea and urea derivatives that can be used include urea, thiourea, biuret, phenylurea, benzylurea, dimethylurea, diethylurea, tetramethylurea, and compounds in which the hydrogen atoms of urea are substituted with alkyl groups. These urea and urea derivatives can be used alone or in combination. However, it is preferable to use urea.

The lower limit of the mixture mass ratio of urea etc. to microfiber cellulose etc. (urea etc./microfiber cellulose etc.) is preferably 8/100, more preferably 5/100. On the other hand, the upper limit is preferably 20/100, more preferably 15/100. By making the mixture mass ratio 5/100 or more, the efficiency of carbamate formation is improved. On the other hand, even if the mixture mass ratio exceeds 20/100, the amount of urea that does not react with microfiber cellulose increases, and the amount of ammonia gas generated by thermal decomposition of urea increases, and large-scale equipment such as scrubbers required for gas treatment is required, which increases costs and is not industrially preferable.

The dispersion medium is usually water. However, other dispersion media such as alcohol, ether, and mixtures of water with other dispersion media may also be used.

In the mixing process, for example, microfiber cellulose, etc. and urea, etc. may be added to water, microfiber cellulose, etc. may be added to an aqueous solution of urea, etc., or urea, etc. may be added to a slurry containing microfiber cellulose, etc. Furthermore, stirring may be performed after addition to ensure uniform mixing. Furthermore, the dispersion containing microfiber cellulose, etc. and urea, etc. may contain other components.

In the removal process, the dispersion medium is removed from the dispersion liquid containing the microfiber cellulose, etc. and urea, etc. obtained in the mixing process. By removing the dispersion medium, the urea, etc. can be reacted efficiently in the subsequent heating process.

The dispersion medium is preferably removed by volatilizing it through heating. This method allows the dispersion medium to be efficiently removed while leaving behind components such as urea.

When the dispersion medium is water, the lower limit of the heating temperature in the removal process is preferably 50°C, more preferably 70°C, and particularly preferably 90°C. By setting the heating temperature at 50°C or higher, the dispersion medium can be efficiently volatilized (removed). On the other hand, the upper limit of the heating temperature is preferably 120°C, more preferably 100°C. If the heating temperature exceeds 120°C, the dispersion medium and urea may react, resulting in the urea decomposing independently.

The heating time in the removal process can be adjusted appropriately depending on the solids concentration of the dispersion liquid. Specifically, it is, for example, 6 to 24 hours.

In the heat treatment following the removal process, a mixture of the microfiber cellulose and urea is heat-treated. In this heat treatment, some or all of the hydroxyl groups of the microfiber cellulose react with urea and are replaced with carbamate groups. More specifically, when urea is heated, it is decomposed into isocyanic acid and ammonia as shown in the following reaction formula (1). Isocyanic acid is highly reactive and forms carbamate groups on the hydroxyl groups of cellulose, for example, as shown in the following reaction formula (2).

NH ₂ -CO-NH ₂ → H-N=C=O + NH ₃ ... (1)

Cell-OH + H-N=C=O → Cell-O-CO-NH ₂ ... (2)

The lower limit of the heating temperature in the heat treatment is preferably 120°C, more preferably 130°C, particularly preferably above the melting point of urea (about 134°C), even more preferably 140°C, and most preferably 150°C. By setting the heating temperature at 120°C or higher, carbamate formation is carried out efficiently. The upper limit of the heating temperature is preferably 200°C, more preferably 180°C, and particularly preferably 170°C. If the heating temperature exceeds 200°C, the microfiber cellulose etc. may decompose, resulting in insufficient reinforcing effect.

The lower limit of the heating time in the heat treatment is preferably 1 minute, more preferably 5 minutes, particularly preferably 30 minutes, even more preferably 1 hour, and most preferably 2 hours. By setting the heating time to 1 minute or more, the carbamate reaction can be carried out reliably. On the other hand, the upper limit of the heating time is preferably 15 hours, more preferably 10 hours. A heating time of more than 15 hours is not economical, and carbamate reaction can be carried out sufficiently in 15 hours.

However, prolonged heating time leads to deterioration of the cellulose fibers. Therefore, the pH conditions in the heat treatment are important. The pH is preferably 9 or more, more preferably 9 to 13, and particularly preferably 10 to 12, which is an alkaline condition. As a second best option, the pH is 7 or less, preferably 3 to 7, and particularly preferably 4 to 7, which is an acidic or neutral condition. Under neutral conditions of pH 7 to 8, the average fiber length of the cellulose fibers is shortened, and the reinforcing effect of the resin may be inferior. On the other hand, under alkaline conditions of pH 9 or more, the reactivity of the cellulose fibers is increased, the reaction with urea, etc. is promoted, and the carbamate reaction occurs efficiently, so that the average fiber length of the cellulose fibers can be sufficiently secured. On the other hand, under acidic conditions of pH 7 or less, the reaction of decomposing urea, etc. into isocyanic acid and ammonia proceeds, the reaction with cellulose fibers is promoted, and the carbamate reaction occurs efficiently, so that the average fiber length of the cellulose fibers can be sufficiently secured. However, if possible, it is preferable to perform the heat treatment under alkaline conditions. This is because acidic conditions can lead to acid hydrolysis of cellulose.

The pH can be adjusted by adding an acidic compound (e.g., acetic acid, citric acid, etc.) or an alkaline compound (e.g., sodium hydroxide, calcium hydroxide, etc.) to the mixture.

For example, a hot air dryer, a papermaking machine, a dry pulp machine, etc. can be used as the heating device in the heat treatment.

The mixture after the heat treatment may be washed. This washing can be done with water or the like. This washing can remove any unreacted urea or other substances that remain.

If necessary, the microfiber cellulose is dispersed in an aqueous medium to form a dispersion (slurry). It is particularly preferable that the aqueous medium is entirely water, but an aqueous medium in which a part of the medium is other liquids that are compatible with water can also be used. As the other liquid, lower alcohols having 3 or less carbon atoms, etc. can be used.

The solids concentration of the dispersion is preferably 0.1 to 10.0% by mass, and more preferably 0.5 to 5.0% by mass. If the solids concentration is below 0.1% by mass, excessive energy may be required for dehydration and drying. On the other hand, if the solids concentration is above 10.0% by mass, the fluidity of the dispersion itself may decrease, making it difficult to mix uniformly when a dispersant is used.

(Non-interacting powder)
The cellulose fiber of this embodiment is preferably mixed with a powder that does not interact with the cellulose fiber to form a cellulose fiber-containing material. By including a powder that does not interact with the cellulose fiber in the cellulose fiber-containing material, the cellulose fiber can be made to have a form that can exhibit the reinforcing properties of the resin. In other words, when the cellulose fiber-containing material is a slurry, it is preferable to remove the aqueous medium contained in the slurry before compounding with the resin. However, when the aqueous medium is removed, the cellulose may irreversibly aggregate due to hydrogen bonding, and the reinforcing effect of the fiber may not be fully exhibited. Therefore, by including a powder that does not interact with the cellulose fiber-containing material (slurry), the hydrogen bonding between the cellulose may be physically inhibited.

Here, "not interacting" means that there is no strong bond with the cellulose fibers through covalent bonds, ionic bonds, or metallic bonds (i.e., hydrogen bonds and bonds through van der Waals forces are included in the concept of not interacting). Preferably, the strong bond is a bond with a bond energy of more than 100 kJ/mol.

The non-interacting powder is preferably at least one of inorganic powder and resin powder, which have little effect of dissociating the hydroxyl groups of the cellulose fibers into hydroxide ions when they coexist in a slurry. According to this embodiment, when the cellulose fiber-containing material is compounded with a resin or the like, the cellulose fibers and the powder that does not interact with the cellulose fibers can be easily dispersed in the resin or the like. In particular, inorganic powders are advantageous in terms of operation. Specifically, the drying method of the composite resin includes, for example, a method of drying by directly applying the aqueous dispersion to a metal drum, which is a heat source (e.g., drying with a Yankee dryer or cylinder dryer, etc.), and a method of heating the aqueous dispersion without directly contacting the heat source, that is, drying in the air (e.g., drying with a thermostatic dryer, etc.). However, when resin powder is used, when it is dried by contacting it with a heated metal plate (e.g., Yankee dryer, cylinder dryer, etc.), a film is formed on the surface of the metal plate, which deteriorates heat conduction and significantly reduces the drying efficiency. Inorganic powders are advantageous in that such problems are unlikely to occur.

The average particle size of the non-interacting powder is preferably 1 mm or less, more preferably 0.9 to 0.0001 mm, and particularly preferably 0.8 to 0.001 mm. When the average particle size is within the above range, the effect of entering the gaps between cellulose fibers and inhibiting aggregation is effectively exerted. Moreover, it has excellent kneading properties with resin, and does not require large amounts of energy, making it economical. On the other hand, when the average particle size exceeds 1 mm, there is a risk that the effect of entering the gaps between cellulose fibers and inhibiting aggregation is not exerted when removing the aqueous medium from the slurry containing cellulose fibers. However, when the average particle size is less than 0.0001 mm, the particles are too fine and may not be able to inhibit the hydrogen bonds between microfiber cellulose. In addition, there is a risk that the particles may aggregate together in the aqueous dispersion.

In addition, resin powders melt during kneading and do not affect the appearance as particles, so particles with large particle sizes can be used relatively effectively. On the other hand, even in the case of inorganic powders, if the average particle size of the inorganic powder is within the above range, it will enter the gaps between the cellulose fibers and inhibit aggregation, but since the size of the inorganic powder does not change significantly even when kneaded, if the particle size is too large, it may affect the appearance as particles.

In this specification, the average particle size of a non-interacting powder is the median size calculated from the volume-based particle size distribution measured using a particle size distribution measuring device (e.g., a laser diffraction/scattering particle size distribution measuring device manufactured by Horiba, Ltd.) with the powder as is or in the form of a water dispersion.

Examples of inorganic powders include, for example, Fe, Na, K, Cu, Mg, Ca, Zn, Ba, Al, Ti, silicon, and other metal elements in Groups I to VIII of the periodic table, as well as oxides, hydroxides, carbonates, sulfates, silicates, sulfites, and various clay minerals made of these compounds. Specific examples include barium sulfate, calcium sulfate, magnesium sulfate, sodium sulfate, calcium sulfite, zinc oxide, heavy calcium carbonate, light calcium carbonate, aluminum borate, alumina, iron oxide, calcium titanate, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, sodium hydroxide, magnesium carbonate, calcium silicate, clay, wollastonite, glass beads, glass powder, silica gel, dry silica, colloidal silica, silica sand, silica stone, quartz powder, diatomaceous earth, white carbon, and glass fiber. A plurality of these inorganic powders may be contained. In addition, they may be those contained in waste paper pulp, or so-called recycled fillers obtained by regenerating inorganic matter in papermaking sludge.

However, it is preferable to use at least one inorganic powder selected from calcium carbonate, talc, white carbon, clay, calcined clay, titanium dioxide, aluminum hydroxide, and recycled fillers, which are suitable for use as fillers and pigments for papermaking. It is more preferable to use at least one inorganic powder selected from calcium carbonate, talc, and clay, and it is particularly preferable to use at least one of light calcium carbonate and heavy calcium carbonate. When calcium carbonate, talc, and clay are used, it is easy to form a composite with a matrix such as a resin. In addition, since they are general-purpose inorganic materials, there is an advantage that there are few restrictions on their use. Furthermore, calcium carbonate is particularly preferable for the following reasons. When light calcium carbonate is used, it is easy to control the size and shape of the powder to a constant value. For this reason, there is an advantage that the size and shape can be adjusted to match the size and shape of the cellulose fibers so that they can easily penetrate into the gaps and suppress the aggregation of the cellulose fibers, making it easier to exert the effect in a pinpoint manner. In addition, the use of heavy calcium carbonate has the advantage that, because the heavy calcium carbonate is amorphous, it can penetrate into the gaps during the process of the fibers agglomerating when the aqueous medium is removed, thereby suppressing the aggregation of the cellulose fibers, even if there are fibers of various sizes in the slurry.

On the other hand, the resin powder can be the same as the resin used to obtain the composite resin. Of course, different types of resins may be used, but it is preferable that the resins are the same.

The amount of non-interacting powder to be blended is preferably 9900 to 1% by mass, more preferably 1900 to 5% by mass, and particularly preferably 900 to 10% by mass, relative to the cellulose fibers. If the blending amount is less than 1% by mass, the powder may not penetrate into the gaps between the cellulose fibers and suppress aggregation insufficiently. On the other hand, if the blending amount exceeds 9900% by mass, the cellulose fibers may not function as intended. If the non-interacting powder is an inorganic powder, it is preferable to blend it in a ratio that does not interfere with thermal recycling.

As powders that do not interact with each other, inorganic powders and resin powders can also be used in combination. When inorganic powders and resin powders are used in combination, they have the effect of preventing each other from agglomerating, even when mixed under conditions in which inorganic powders or resin powders agglomerate with each other. In addition, powders with small particle sizes have a large surface area and are more susceptible to intermolecular forces than to gravity, and as a result are more likely to agglomerate. Therefore, when the powder is mixed with microfiber cellulose, the powder may not be properly loosened in the slurry, or the powders may agglomerate when the aqueous medium is removed, which may result in the effect of preventing the agglomeration of microfiber cellulose being insufficient. However, it is believed that the agglomeration of the powders themselves can be mitigated by using inorganic powders and resin powders in combination.

When inorganic powder and resin powder are used in combination, the ratio of the average particle size of the inorganic powder to the average particle size of the resin powder is preferably 1:0.1 to 1:10,000, and more preferably 1:1 to 1:1000. When it is in this range, problems caused by the strength of its own cohesive force (for example, problems such as the powder not being able to be properly loosened in the slurry when mixing the powder with microfiber cellulose, or the powder particles coagulating when the aqueous medium is removed) do not occur, and it is believed that the effect of preventing the coagulation of microfiber cellulose is fully exerted.

When inorganic powder and resin powder are used in combination, the ratio of inorganic powder mass % to resin powder mass % is preferably 1:0.01 to 1:100, and more preferably 1:0.1 to 1:10. When it is in this range, it is believed that different powders can inhibit their own aggregation. When it is in this range, problems caused by the strength of their own cohesive force (for example, problems such as the powder not being able to be properly loosened in the slurry when mixing the powder with microfiber cellulose, or the powders agglomerating when the aqueous medium is removed) do not occur, and it is believed that the effect of preventing the aggregation of microfiber cellulose is fully exerted.

(Acid-modified resin)
In this embodiment, it is preferable to use an acid-modified resin as the resin to be contained together with the cellulose fibers. This resin can also function as a resin powder that does not interact with other powders. In the acid-modified resin, the acid group can form an ionic bond with some or all of the carbamate groups. This ionic bond improves the reinforcing effect of the resin.

As the acid-modified resin, for example, an acid-modified polyolefin resin, an acid-modified epoxy resin, an acid-modified styrene-based elastomer resin, etc. can be used. However, it is preferable to use an acid-modified polyolefin resin. An acid-modified polyolefin resin is a copolymer of an unsaturated carboxylic acid component and a polyolefin component.

As the polyolefin component, for example, one or more alkene polymers such as ethylene, propylene, butadiene, and isoprene can be selected and used. However, it is preferable to use polypropylene resin, which is a polymer of propylene.

As the unsaturated carboxylic acid component, for example, one or more selected from maleic anhydrides, phthalic anhydrides, itaconic anhydrides, citraconic anhydrides, citric anhydrides, etc. can be used. However, it is preferable to use maleic anhydrides. In other words, it is preferable to use maleic anhydride-modified polypropylene resin (MAPP).

The amount of the acid-modified resin mixed is preferably 30 to 100 parts by mass, more preferably 35 to 90 parts by mass, and particularly preferably 40 to 80 parts by mass, per 100 parts by mass of microfiber cellulose. In particular, when the acid-modified resin is a maleic anhydride-modified polypropylene resin, the amount is preferably 35 to 65 parts by mass, more preferably 40 to 60 parts by mass. If the amount of the acid-modified resin mixed is less than 30 parts by mass, it becomes difficult to suppress the aggregation of the fine cellulose fibers, and the aggregated fine cellulose fibers become a defect equivalent to a foreign matter present locally in the composite resin, and when an external force is applied, they easily break, which may cause problems in strand processing. On the other hand, if the amount mixed exceeds 100 parts by mass, although the above-mentioned aggregation is suppressed, the acid-modified resin, which does not have excellent mechanical properties in itself, enters the material in too much amount, and the mechanical properties of the material as a whole may be reduced.

The weight average molecular weight of the maleic anhydride modified polypropylene is, for example, 1,000 to 200,000, preferably 3,000 to 100,000.

The acid value of the maleic anhydride-modified polypropylene is preferably 1 mgKOH/g or more and 200 mgKOH/g or less, and more preferably 10 mgKOH/g or more and 100 mgKOH/g or less.

The density of the resin, particularly the acid-modified resin, is preferably 0.80 to 1.00 g/cm ³ , more preferably 0.85 to 0.95 g/cm ³ , and particularly preferably 0.88 to 0.93 g/cm ^3. If the density of the resin is less than 0.80 g/cm ³ , the difference in density with the fine cellulose fibers becomes too large, and there is a risk that the resin will separate from the fine cellulose fibers without interacting with them in the dispersion medium and float in the supernatant of the dispersion medium. On the other hand, if the density of the resin exceeds 1.00 g/cm ³ , when the dispersion medium is water, there is a risk that the resin will separate from the fine cellulose fibers without interacting with them in the dispersion medium and settle to the bottom of the dispersion medium.

The resin density is measured in accordance with JIS K7112.

(Dispersant)
The powder that does not interact with microfiber cellulose or cellulose fibers is more preferably mixed with a dispersant, which is preferably an aromatic compound having an amine group and/or a hydroxyl group, or an aliphatic compound having an amine group and/or a hydroxyl group.

Examples of compounds having an amine group and/or a hydroxyl group in the aromatic group include anilines, toluidines, trimethylanilines, anisidines, tyramines, histamines, tryptamines, phenols, dibutylhydroxytoluenes, bisphenol A, cresols, eugenols, gallic acids, guaiacols, picric acids, phenolphthalein, serotonins, dopamines, adrenalines, noradrenalines, thymols, tyrosines, salicylic acids, methyl salicylates, anilines, These include alcohols, salicyl alcohols, sinapyl alcohols, diphenidol, diphenylmethanol, cinnamyl alcohols, scopolamine, tryptophol, vanillyl alcohols, 3-phenyl-1-propanol, phenethyl alcohols, phenoxyethanol, veratryl alcohols, benzyl alcohols, benzoins, mandelic acids, mandelonitriles, benzoic acids, phthalic acids, isophthalic acids, terephthalic acids, mellitic acids, and cinnamic acids.

In addition, examples of compounds having an amine group and/or a hydroxyl group in the aliphatic group include capryl alcohols, 2-ethylhexanols, pelargonic alcohols, capric alcohols, undecyl alcohols, lauryl alcohols, tridecyl alcohols, myristyl alcohols, pentadecyl alcohols, cetanols, stearyl alcohols, elaidyl alcohols, oleyl alcohols, linoleyl alcohols, methylamines, dimethylamines, trimethylamines, ethylamines, diethylamines, ethylenediamines, These include triethanolamines, N,N-diisopropylethylamines, tetramethylethylenediamines, hexamethylenediamines, spermidines, spermines, amantadines, formic acids, acetic acids, propionic acids, butyric acids, valeric acids, caproic acids, enanthic acids, caprylic acids, pelargonic acids, capric acids, lauric acids, myristic acids, palmitic acids, margaric acids, stearic acids, oleic acids, linoleic acids, linolenic acids, arachidonic acids, eicosapentaenoic acids, docosahexaenoic acids, and sorbic acids.

The above dispersants inhibit hydrogen bonding between cellulose fibers. Therefore, when the cellulose fibers and resin are mixed, the microfiber cellulose is reliably dispersed in the resin. The above dispersants also improve the compatibility of the microfiber cellulose and the resin. In this respect, the dispersibility of the microfiber cellulose in the resin is improved.

It is possible to add a compatibilizer (chemical) separately when kneading the cellulose fibers and resin, but mixing the microfiber cellulose with the dispersing agent (chemical) beforehand rather than adding the chemical at this stage will ensure that the chemical sticks to the microfiber cellulose evenly, and will be more effective at improving compatibility with the resin.

For example, polypropylene has a melting point of 160°C, so cellulose fibers and resin are mixed at around 180°C. However, if a dispersant (liquid) is added in this state, it dries out in an instant. Therefore, it is preferable to create a master batch (a composite resin with a high concentration of microfiber cellulose) using a resin with a low melting point, and then reduce the concentration with a normal resin.

The amount of dispersant mixed is preferably 0.1 to 1000 parts by mass, more preferably 1 to 500 parts by mass, and particularly preferably 10 to 200 parts by mass, per 100 parts by mass of microfiber cellulose. If the amount of dispersant mixed is less than 0.1 parts by mass, the improvement in resin strength may not be sufficient. On the other hand, if the amount mixed is more than 1000 parts by mass, it becomes excessive and the resin strength tends to decrease.

In this regard, the acid-modified resin described above is intended to improve compatibility by forming ionic bonds between the acid groups and the carbamate groups of the microfiber cellulose, thereby enhancing the reinforcing effect, and is thought to be compatible with the resin due to its large molecular weight, thereby contributing to improved strength. On the other hand, the dispersant described above is intended to intervene between the hydroxyl groups of the microfiber cellulose to prevent aggregation, thereby improving dispersibility in the resin, and since its molecular weight is smaller than that of the acid-modified resin, it can enter the narrow spaces between the microfiber cellulose that the acid-modified resin cannot enter, thereby improving dispersibility and improving strength. From the above perspective, the molecular weight of the acid-modified resin described above is preferably 2 to 2000 times, preferably 5 to 1000 times, the molecular weight of the dispersant.

To explain the above in more detail, the non-interacting powder physically intervenes between the microfiber cellulose, inhibiting hydrogen bonding, thereby improving the dispersibility of the microfiber cellulose. However, when the non-interacting powder is an acid-modified resin, the acid group and the carbamate group of the microfiber cellulose are ionically bonded to improve compatibility, thereby increasing the reinforcing effect. In this respect, the dispersant inhibits hydrogen bonding between the microfiber cellulose, but the non-interacting powder is on the micro-order, so it physically intervenes and suppresses hydrogen bonding. Therefore, although the dispersibility is lower than that of the dispersant, especially in the case of resin powder, it does not contribute to a decrease in physical properties because it melts itself and becomes a matrix. On the other hand, in the case of inorganic powder, the inorganic powder itself is rigid, so when it is composited with resin, etc., it contributes to improving the physical properties of the resin. On the other hand, the dispersant is at the molecular level and is extremely small, so it covers the microfiber cellulose, inhibiting hydrogen bonding, and is highly effective in improving the dispersibility of the microfiber cellulose. However, it may remain in the resin and work to reduce physical properties.

(Production method)
A mixture of microfiber cellulose and non-interacting powders (cellulose fiber-containing material) is slurried, dried, and pulverized into a powder prior to kneading with resin. This form eliminates the need to dry the cellulose fibers when kneading with resin, and provides good thermal efficiency. In particular, when non-interacting powders, dispersants, etc. are mixed into the mixture, there is little risk that the fibrous cellulose (microfiber cellulose) will not redisperse even if the mixture is dried.

The mixture (slurry) preferably has a carbamate-modified microfiber cellulose concentration of 1.5% by mass or more, more preferably 1.8 to 5.0% by mass, and particularly preferably 2.0 to 4.0% by mass. In this regard, if the concentration is below 1.5% by mass, after mixing with a powder that does not interact with the microfiber cellulose and stirring, the MFC and the powder gradually separate in the slurry due to the density difference between the microfiber cellulose and the powder (for example, MFC is about 1.5 g/cm ³ , and 0.9 g/cm ³ when the powder is PP) and the difference in SP value described below, and the MFC and the powder are already in a separated state when entering the next process. As a result, the microfiber cellulose aggregates with each other. However, if the concentration is 1.5% by mass or more, the viscosity of the slurry increases, so the fluidity of the slurry decreases, and separation due to the density difference and SP value difference between the MFC and the powder is suppressed. In other words, although a method of reducing the density difference and the SP value difference also contributes to suppressing aggregation, these methods have limitations, so in this embodiment, the aggregation suppression is attempted to be complete by adjusting the concentration. The SP value of the powder is the same as that of the resin described later, and will be described in detail later.

From the above viewpoints, the viscosity of the slurry is preferably adjusted to 1000 to 10000 cps, more preferably 1500 to 9000 cps, and particularly preferably 2000 to 8000 cps. This adjustment can be made by adjusting the concentration of the MFC, or by using a thickener, for example.

The viscosity of the slurry was measured in accordance with JIS-Z8803 (2011) "Method for measuring viscosity of liquids."

From the above viewpoints, the density ratio of the non-interacting powder to the density of the carbamate-modified microfibrous cellulose is preferably 0.4 to 2.2, more preferably 0.5 to 2.1, and particularly preferably 0.6 to 2.0.

Furthermore, it is preferable to adjust the concentration of MFC with water. Adjusting with water has the advantage that the cost of the solvent itself is low and there is no need for the treatment and recovery equipment required for organic solvents, minimizing the environmental impact.

On the other hand, as mentioned above, when an acid-modified resin is used as a non-interacting powder, the concentration of the acid-modified resin in the slurry is preferably 0.5% by mass or more, more preferably 0.8 to 5.0% by mass, and particularly preferably 1.0 to 4.0% by mass. If the concentration of the acid-modified resin is 0.5% by mass or more, it is believed that the effect of preventing aggregation of the carbamate-modified microfibrous cellulose that occurs when the slurry is dried is sufficiently exhibited.

When the concentration (mass%) of microfiber cellulose is taken as 1, the concentration ratio of the non-interacting powder is, for example, 50 to 0.1, preferably 20 to 0.5, and more preferably 10 to 1.0. If the concentration ratio is below 0.1, the effect of suppressing the aggregation of microfiber cellulose during drying may not be fully exerted. On the other hand, if the concentration ratio exceeds 50, it becomes impossible to increase the blending ratio of microfiber cellulose in the composite resin, and the effect of blending microfiber cellulose may not be fully exerted.

After forming the mixture into a slurry, it is dehydrated prior to drying to form a dehydrated product. This dehydration can be carried out using one or more dehydration devices selected from the following: belt press, screw press, filter press, twin roll, twin wire former, valveless filter, center disc filter, membrane treatment, centrifuge, etc.

The mixture can be dried using one or more of the following: rotary kiln drying, disk drying, air flow drying, media flow drying, spray drying, drum drying, screw conveyor drying, paddle drying, single-axis kneading drying, multi-axis kneading drying, vacuum drying, and stirring drying.

The dried mixture (dried material) is pulverized to produce a powder. The dried material can be pulverized using one or more of a bead mill, kneader, disperser, twist mill, cut mill, hammer mill, etc.

The average particle size of the powder is preferably 1 to 10,000 μm, more preferably 10 to 5,000 μm, and particularly preferably 100 to 1,000 μm. If the average particle size of the powder exceeds 10,000 μm, it may be difficult to knead with resin. On the other hand, a large amount of energy is required to reduce the average particle size of the powder to less than 1 μm, which is not economical.

The average particle size of powdered materials can be controlled by controlling the degree of grinding, as well as by classification using classification devices such as filters and cyclones.

The bulk density of the mixture (powder) is preferably 0.03 to 1.0, more preferably 0.04 to 0.9, and particularly preferably 0.05 to 0.8. A bulk density of more than 1.0 means that the hydrogen bonds between the cellulose fibers are stronger, making it difficult to disperse them in the resin. On the other hand, a bulk density of less than 0.03 is disadvantageous in terms of transportation costs.

The bulk density is a value measured in accordance with JIS K7365.

The moisture content of the mixture (powdered material) is preferably 50% or less, more preferably 30% or less, and particularly preferably 10% or less. If the moisture content exceeds 50%, the energy required to knead with the resin becomes enormous, which is not economical.

The moisture content was calculated by the following formula using a sample kept at 105° C. for 6 hours or more in a constant temperature dryer, and the mass after drying was determined as the mass at which no change in mass was observed.
Moisture content (%) = [(mass before drying - mass after drying) ÷ mass before drying] x 100

The powdered material (material containing cellulose fibers) obtained in the above manner is kneaded with resin to obtain a cellulose composite resin. This kneading can be performed, for example, by mixing the resin in pellet form with the powdered material, or by first melting the resin and then adding the powdered material to the melt. A dispersant can also be added at this stage.

For the kneading process, one or more of a single-shaft or multi-shaft kneader having two or more shafts, a mixing roll, a kneader, a roll mill, a Banbury mixer, a screw press, a disperser, etc. can be selected and used. Of these, it is preferable to use a multi-shaft kneader having two or more shafts. Two or more multi-shaft kneaders having two or more shafts may be used in parallel or in series.

The kneading process is preferably carried out so that the kneading energy is 0.10 kW/kg or more, more preferably 0.12 to 1.00 kW/kg, and particularly preferably 0.15 to 0.95 kW/kg. If the kneading energy is less than 0.10 kW/kg, the resin and the fine cellulose fibers will not blend sufficiently, and there will be localized areas with high concentrations of the fine cellulose fibers, which may make them more likely to break during strand processing. On the other hand, if the kneading energy exceeds 1.00 kW/kg, although the resin and the fine cellulose fibers will blend sufficiently, there is a risk that the composite resin will become discolored due to the application of too much mechanical energy.

In this embodiment, the kneading energy (kW/kg) is calculated by the amount of electricity required for kneading (kW) divided by the amount of raw material input (kg).

The temperature for the kneading process is equal to or higher than the glass transition point of the resin, and varies depending on the type of resin, but is preferably 80 to 280°C, more preferably 90 to 260°C, and particularly preferably 100 to 240°C.

As the resin, in addition to the acid-modified resin described above, at least one of a thermoplastic resin and a thermosetting resin can be used.

As the thermoplastic resin, one or more of the following may be selected and used: polyolefins such as polypropylene (PP) and polyethylene (PE); polyester resins such as aliphatic polyester resins and aromatic polyester resins; polyacrylic resins such as polystyrene, methacrylate, and acrylate; polyamide resins; polycarbonate resins; and polyacetal resins.

However, it is preferable to use at least one of polyolefin and polyester resin. As the polyolefin, it is preferable to use polypropylene. Furthermore, as the polyester resin, examples of aliphatic polyester resins include polylactic acid and polycaprolactone, and examples of aromatic polyester resins include polyethylene terephthalate, but it is preferable to use a biodegradable polyester resin (also simply called "biodegradable resin").

As the biodegradable resin, for example, one or more types can be selected from hydroxycarboxylic acid-based aliphatic polyesters, caprolactone-based aliphatic polyesters, dibasic acid polyesters, etc.

As the hydroxycarboxylic acid-based aliphatic polyester, one or more of homopolymers of hydroxycarboxylic acids such as lactic acid, malic acid, glucose acid, 3-hydroxybutyric acid, etc., and copolymers using at least one of these hydroxycarboxylic acids can be selected and used. However, it is preferable to use polylactic acid, copolymers of lactic acid and the above hydroxycarboxylic acids other than lactic acid, polycaprolactone, and copolymers of at least one of the above hydroxycarboxylic acids and caprolactone, and it is particularly preferable to use polylactic acid.

For example, L-lactic acid or D-lactic acid can be used as the lactic acid, and these lactic acids can be used alone or in combination of two or more types.

As the caprolactone-based aliphatic polyester, one or more types can be selected and used from, for example, a homopolymer of polycaprolactone, a copolymer of polycaprolactone or the like with the above-mentioned hydroxycarboxylic acid, etc.

As the dibasic acid polyester, for example, one or more of polybutylene succinate, polyethylene succinate, polybutylene adipate, etc. can be selected and used.

Biodegradable resins may be used alone or in combination of two or more types.

Examples of thermosetting resins that can be used include phenolic resins, urea resins, melamine resins, furan resins, unsaturated polyesters, diallyl phthalate resins, vinyl ester resins, epoxy resins, urethane resins, silicone resins, and thermosetting polyimide resins. These resins can be used alone or in combination of two or more.

When blending microfiber cellulose and resin, first, in producing a master batch, the blending ratio of microfiber cellulose is preferably 50 to 70 mass%, more preferably 52 to 69 mass%, and particularly preferably 55 to 67 mass%. If the blending ratio is less than 50 mass%, strand processing will not be a problem, but the options for dilution to an arbitrary fine cellulose fiber concentration will be narrowed. On the other hand, if the blending ratio exceeds 70 mass%, the range of options for fine cellulose fiber concentration will be wider, but the high fiber blending ratio will make the strands too rigid and prone to breaking under their own weight, which may cause problems in strand processing.

In addition, when resin is added to the master batch to reduce the concentration of cellulose fibers, the blending ratio of microfiber cellulose is preferably 1 to 40 mass%, more preferably 5 to 30 mass%, and particularly preferably 10 to 20 mass%. If the blending ratio is less than 1 mass%, the amount of fine cellulose fibers present in the composite resin may be too small, and properties such as fiber reinforcement may not be exhibited. On the other hand, if the blending ratio exceeds 40 mass%, the fluidity required for moldability may be insufficient, and molding into the desired shape may not be possible. In addition, if the temperature is raised too high in an attempt to force molding, the material may become discolored or may become denatured, such as scorched.

The microfiber cellulose content of the final cellulose fiber composite resin is usually the same as the above-mentioned microfiber cellulose content.

In this embodiment, when the kneaded material containing microfiber cellulose and resin is used as a master batch, the melt viscosity at a shear rate of 2432 s ^-1 is preferably 230 Pa.s or less, more preferably 10 to 229 Pa.s, and particularly preferably 50 to 228 Pa.s. If the melt viscosity exceeds 230 Pa.s, the strands become too rigid during strand processing, so that the strands tend to break under their own weight, making it difficult to perform continuous strand processing, and there is a risk of interfering with processing into a pellet shape. On the other hand, if the melt viscosity is less than 10 Pa.s, the strands tend to adhere to each other during strand processing, and if they adhere, it is difficult to perform continuous strand processing, and there is a risk of interfering with processing into a pellet shape.

When cellulose fibers and resin are mixed, hydrophobic resin components are present around the cellulose fibers. On the other hand, in a dispersion of cellulose fibers, a hydrophilic medium such as water is present around the cellulose fibers. In a hydrophilic medium, the interaction between the cellulose fibers and the medium is very large, and the viscosity of the slurry increases significantly even for fine fibers with a high degree of defibration. On the other hand, the melt viscosity of the composite resin decreases as the fiber size becomes smaller, but if the fiber size is too small, the cohesive force of the fibers generated when removing water from the aqueous dispersion is too large, making it difficult to disintegrate by shear during mixing, and there is a risk of the master batch remaining with agglomerates that cause a decrease in physical properties.

In this embodiment, the shear rate is a value measured in the range of 24 to 12,160 s ^-1 . The melt viscosity is a value measured at a shear rate of 2,432 ^s-1 using a Capilograph 1D (manufactured by Toyo Seiki Co., Ltd.) according to a method in accordance with JIS K 7199.

In this embodiment, the density of the kneaded product containing microfiber cellulose and resin is preferably 1.10 to 1.40 g/cm ³ , more preferably 1.12 to 1.30 g/cm ³ , and particularly preferably 1.14 to 1.25 g/cm ³ when used as a master batch. By setting the density within the range of 1.10 g/cm ³ or more, when compounding (diluting) with other resin, the density becomes close to other resin (generally about 0.9 to 2.0 g/cm ³ ), and it is possible to prevent extreme bias between the master batch and the dilution resin caused by vibration during compounding. More specifically, if the density of the kneaded product (master batch) is less than 1.10 g/cm ³ , the fine cellulose fibers exist as agglomerates containing air, and even if the cellulose concentration is adjusted to a predetermined concentration and used, the agglomerates may not exhibit the desired effect such as resin reinforcement. On the other hand, if the density of the kneaded product (master batch) exceeds 1.40 g/ ^cm3 , when compounding (diluting) with other resins, depending on the resin used, there is a risk that unevenness will occur and it will not be possible to compound uniformly.

The above densities are values measured in accordance with JIS K 7112.

In this embodiment, the Charpy impact strength (notched) of the kneaded product containing microfiber cellulose and resin, when used as a master batch, is preferably 2.0 kJ/m ² or more, more preferably 2.1 to 10.0 kJ/m ² , and particularly preferably 2.2 to 5.0 kJ/m ^2. If the Charpy impact strength (notched) is less than 2.0 kJ/m ² , the interfacial adhesion between the cellulose fiber and the resin is insufficient, and when used after diluting with another resin, the cellulose fiber is isolated in the resin and does not act as a reinforcing fiber, and conversely, the cellulose fiber becomes a defect and is likely to break when subjected to an external force.

The above Charpy impact strength (notched) values were measured in accordance with JIS K 7111.

In this embodiment, the deflection temperature under load of the kneaded material containing microfiber cellulose and resin is preferably 145°C or higher, more preferably 147 to 160°C, and particularly preferably 149 to 155°C, when used as a master batch. If the deflection temperature under load is less than 145°C, the cellulose fibers will not disperse in the resin and will be unevenly distributed. When diluted with other resin for use, the cellulose fibers will not disperse well in the resin, compromising homogeneity and raising the risk of deformation, etc.

The above deflection temperatures under load were measured in accordance with JIS K 7191.

In this embodiment, the melt flow rate (190°C) of the kneaded product containing microfiber cellulose and resin is preferably 0.001 or more, more preferably 0.005 to 3.0, and particularly preferably 0.01 to 1.0. If the melt flow rate is less than 0.001, a large amount of energy is required during dilution and kneading, and there is a risk of discoloration during dilution and kneading, or a decrease in physical properties.

The melt flow rates above are values measured in accordance with JIS K 7210.

The difference in the solubility parameters (cal/cm ³ ) ^1/2 (SP value) of the microfiber cellulose and the resin can be expressed as "difference in SP value = SP _MFC value - SP _POL value" when the SP MFC value of the microfiber cellulose and the SP _POL value of the resin are taken as the SP _MFC value of the microfiber cellulose and the SP POL value of the resin. The difference in SP value is preferably 10 to 0.1, more preferably 8 to 0.5, and particularly preferably 5 to 1. If the difference in SP value exceeds 10, the microfiber cellulose may not disperse in the resin and the reinforcing effect may not be obtained. On the other hand, if the difference in SP value is less than 0.1, the microfiber cellulose may dissolve in the resin and not function as a filler, and the reinforcing effect may not be obtained. In this regard, the smaller the difference between the SP _POL value of the resin (solvent) and the SP _MFC value of the microfiber cellulose (solute), the greater the reinforcing effect.

The solubility parameter (cal/cm ³ ) ^1/2 (SP value) is a measure of the intermolecular force acting between a solvent and a solute, and the closer the SP values of a solvent and a solute are, the higher the solubility.

(Molding process)
The kneaded mixture of the cellulose fiber-containing material and the resin can be molded into a desired shape after being kneaded again if necessary. The size, thickness, shape, etc. of the molded product are not particularly limited, and can be, for example, a sheet, pellet, powder, fiber, etc.

The temperature during the molding process is equal to or higher than the glass transition point of the resin, and varies depending on the type of resin, but is, for example, 90 to 260°C, preferably 100 to 240°C.

The kneaded material can be molded by, for example, mold molding, injection molding, extrusion molding, hollow molding, foam molding, etc. The kneaded material can also be spun into fibers and mixed with the above-mentioned plant materials to form a mat or board shape. The fibers can be mixed by, for example, simultaneous deposition using air laying.

As a machine for molding the kneaded material, for example, one or more of an injection molding machine, a blow molding machine, a hollow molding machine, a blow molding machine, a compression molding machine, an extrusion molding machine, a vacuum molding machine, a pressure molding machine, etc. can be selected and used.

The above molding can be carried out following kneading, or the kneaded material can be cooled and chipped using a crusher or the like, and the chips can then be fed into a molding machine such as an extrusion molding machine or an injection molding machine. Of course, molding is not an essential requirement of the present invention.

(others)
The cellulose fiber-containing material may contain cellulose nanofibers together with microfiber cellulose. Cellulose nanofibers are fine fibers like microfiber cellulose, and play a role in complementing microfiber cellulose in improving the strength of resins. However, if possible, it is preferable to use only microfiber cellulose as fine fibers without including cellulose nanofibers. The average fiber diameter of the cellulose nanofibers (average fiber width; average diameter of a single fiber) is preferably 4 to 100 nm, more preferably 10 to 80 nm.

The cellulose fiber-containing material may also contain pulp. Pulp plays a role in significantly improving the dewaterability of the cellulose fiber slurry. However, as with cellulose nanofibers, it is most preferable not to include pulp, i.e., to have a content of 0% by mass.

The resin composition (cellulose fiber composite resin) can contain, or may contain, in addition to fine fibers and pulp, fibers derived from plant materials obtained from various plants such as kenaf, jute, Manila hemp, sisal, gampi, mitsumata, paper mulberry, banana, pineapple, coconut, corn, sugarcane, bagasse, palm, papyrus, reed, esparto, sabai grass, wheat, rice, bamboo, various coniferous trees (such as cedar and cypress), broadleaf trees, and cotton.

For example, one or more of antistatic agents, flame retardants, antibacterial agents, colorants, radical scavengers, foaming agents, etc. may be selected and added to the resin composition within a range that does not impair the effects of the present invention. These raw materials may be added to the dispersion liquid of microfiber cellulose, to the cellulose fiber-containing material (slurry), when the cellulose fiber-containing material and resin are kneaded, to these kneaded materials, or by other methods. However, from the viewpoint of production efficiency, it is preferable to add them when the cellulose fiber-containing material and resin are kneaded.

The resin composition may contain an ethylene-α-olefin copolymer elastomer or a styrene-butadiene block copolymer as a rubber component. Examples of α-olefins include butene, isobutene, pentene, hexene, methyl-pentene, octene, decene, and dodecene.

Next, an embodiment of the present invention will be described.
A urea aqueous solution with a solid content of 40% was added to softwood bleached kraft pulp or hardwood bleached kraft pulp or a mixture thereof having a moisture content of 50% or less, so that the mass ratio of pulp to urea was 100:10 in terms of solid content, and the mixture was then dried at 105° C. Then, the mixture was allowed to stand at 170° C. for 1 hour to cause a reaction, and a carbamate-modified pulp was obtained.

The resulting carbamate-modified pulp was diluted with distilled water, stirred, and dehydrated and washed twice to adjust the solids concentration to 3.0% by mass, yielding a washed carbamate-modified pulp.

After washing, the carbamate-modified pulp was beaten using a beater until the fine ratio (the proportion of fibers with a length distribution of 0.2 mm or less as measured by FS5) reached 40% or more, yielding carbamate-modified microfiber cellulose (average fiber diameter 14-19 μm).

15 g of maleic anhydride modified polypropylene (by bone dry weight) and 0 to 8 g of polypropylene powder (by bone dry weight) were added to 1000 g of carbamate modified microfiber cellulose with a solid content concentration of 3.0% by mass, stirred, and then heated and dried using a contact dryer heated to 140°C to obtain a material containing carbamate modified cellulose fibers. The moisture content of this material containing carbamate modified cellulose fibers was 5 to 20%.

The carbamate-modified cellulose fiber-containing material obtained in the above manner was kneaded in a twin-screw extruder with a diameter of 15 mm at 165°C to 180°C, 75 to 200 rpm, and a specific energy during kneading of 0.1 to 1.0. The material was then cut into cylindrical shapes with a diameter of 2 mm and a length of 2 mm, yielding a carbamate-modified cellulose fiber composite resin with a fiber loading ratio of 55.0 to 66.7%.

A carbamate-modified cellulose fiber composite resin with a fiber loading ratio of 55.0 to 66.7% and PP pellets were dry-blended so that the fiber loading ratio after mixing was 10.0%, and the mixture was kneaded in a twin-screw kneader at 180°C and 200 rpm, and cut into cylindrical shapes with a diameter of 2 mm and a length of 2 mm using a pelleter, to obtain a carbamate-modified cellulose fiber composite resin with a fiber loading ratio of 10%.

Carbamate-modified cellulose fiber composite resins with a fiber loading rate of 10% were injection molded at 180°C into rectangular specimens (length 59 mm, width 9.6 mm, thickness 3.8 mm). Each specimen was examined for strand formation, melt viscosity, flexural modulus, and flexural strength. The test methods were as follows:

Strandability (processability): If the length that can be pulled from the extruder outlet is 150 cm or more, it is rated as ◎, if it is 10-150 cm, it is rated as △, and if it is 10 cm or less, it is rated as ×.

Flexural modulus: In a bending test conforming to JIS K7171, 2.0 GPa or more was rated as ◯, and less than 2.0 GPa was rated as ×.

Bending strength: In bending tests conforming to JIS K7171, 65.0 MPa or more was rated as ◯, and less than 65.0 MPa was rated as ×.

The present invention can be used as a cellulose fiber composite resin and a method for producing the same.

Claims (8)

The present invention comprises carbamate-modified fine fibers having an average fiber diameter of 5 to 19 μm and a resin,
The melt viscosity at a shear rate of 2432 s ^-1 is 230 Pa s or less;
A cellulose fiber composite resin characterized by: The blending ratio of the fine fibers is 50 to 90%.
The cellulose fiber composite resin according to claim 1. The density of the resin is 0.80 to 1.00 g/cm ³ ;
The cellulose fiber composite resin according to claim 1 or 2. The resin is maleic anhydride modified polypropylene.
The cellulose fiber composite resin according to claim 1 or 2. The average fiber length of the fine fibers is less than 0.5 mm.
The cellulose fiber composite resin according to claim 1. The fibrillation rate of the fine fibers is 3% or less.
The cellulose fiber composite resin according to claim 1. The carbamate ratio of the fine fibers is 2.0 mmol/g or less.
The cellulose fiber composite resin according to claim 1. A carbamate-modified fine fiber having an average fiber diameter of 5 to 19 μm and a resin,
Kneading is performed with a kneading energy of 0.10 kW/kg or more, and the melt viscosity at a shear rate of 2432 s ^-1 is set to 230 Pa s or less.
A method for producing a cellulose fiber composite resin comprising the steps of: