Method for producing carbamate cellulose fiber

Abstract

To provide a method for producing carbamate cellulose fibers capable of mass-production.SOLUTION: In producing carbamate cellulose fibers, a pulp sheet containing urea is heated by passing it between a pair of rolls at a speed of 300 to 3000 m / min, and this heating causes denaturation, and multiple sets of the pair of rolls are continuous. A preceding set or sets are a drying part, the following set or sets are a reaction part, and the temperature of the rolls belonging to the drying part is 80 to 130°C, and the temperature of the rolls belonging to the reaction part is 220°C or higher. A method for producing carbamate cellulose fibers, which is characterized in that the number of pairs of rolls is such that the passing time of the drying part is 8 seconds or more and the passing time of the reaction part is 8 seconds or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing carbamate cellulose fibers. [Background technology]

[0002] Fine fibers such as cellulose nanofibers and microfiber cellulose (microfibrillated cellulose) have been attracting attention for some time, and in recent years, there have been proposals to introduce anionic groups into cellulose fibers (modify them with anionic groups) (see Patent Document 1).

[0003] Furthermore, while fine fibers are attracting attention for their use as a reinforcing material for resins, a proposal has been made to substitute the hydroxyl groups of the fine fibers with carbamate groups because the fine fibers are hydrophilic while the resin is hydrophobic (see Patent Document 2). This proposal improves the dispersibility of the fine fibers, thereby improving the reinforcing effect of the resin.

[0004] However, in the above proposals, the cellulose fibers must be in the form of an aqueous dispersion when they are modified, which is unsuitable for mass production. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-75665 [Patent Document 2] Japanese Patent Application Publication No. 2019-1876 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a method for producing carbamate cellulose fibers that can be mass-produced. [Means for solving the problem]

[0007] First, the present inventors came up with the idea that the technology for producing pulp sheets in the papermaking technical field could be used to mass-produce carbamate cellulose fibers. However, while the pulp sheet itself is the target product in the papermaking technical field, in the present invention, the pulp sheet is only used temporarily in its form or shape. Therefore, in terms of rapidly carrying out carbamate conversion, papermaking technology cannot be directly adopted. Therefore, after conducting numerous tests, the inventors focused particularly on carbamate conversion and came up with the following means.

[0008] That is, in producing carbamate cellulose fibers in which some or all of the hydroxy groups of cellulose fibers have been modified with carbamate groups, A pulp sheet containing at least one of urea and a urea derivative, which is formed into a strip shape by papermaking raw pulp. Add and heating the mixture to effect said denaturation. The moisture content of the pulp sheet is 0.1 to 10% before the urea and / or the urea derivative are added. The present invention relates to a method for producing carbamate cellulose fibers, characterized in that: [Effects of the Invention]

[0009] The present invention provides a method for producing carbamate cellulose fibers that can be mass-produced. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is an explanatory diagram of the process for obtaining carbamate fine fibers from raw pulp. DETAILED DESCRIPTION OF THE INVENTION

[0011] Next, an embodiment of the present invention will be described. Note that this embodiment is an example of the present invention, and the scope of the present invention is not limited to the scope of this embodiment.

[0012] As shown in FIG. 1, the manufacturing method of this embodiment can be mainly divided into a step X1 in which a cellulose fiber-containing material P2 that can be used as a "pulp sheet containing at least one of urea and a urea derivative (also simply referred to as "urea, etc.")" is obtained from raw pulp P1, a step X2 in which urea, etc. is reacted with cellulose fibers after this step X1 to obtain carbamate cellulose fibers P3, and a step X3 in which the carbamate cellulose fibers P3 are defibrated after this step X2 to obtain carbamate fine fibers P4.

[0013] The process X1 for obtaining the cellulose fiber-containing material P2 can be divided into a papermaking process 100 in which the raw pulp P1 is made into a strip-shaped pulp sheet, and a coating process 200 in which urea or the like is coated on the pulp sheet. These processes will be explained in order below.

[0014] (raw pulp) As the raw material pulp P1, one or more types can be selected from, for example, wood pulp made from hardwood, softwood, etc.; non-wood pulp made from straw, bagasse, cotton, hemp, bast fiber, etc.; and decomposed paper pulp (DIP) made from recycled waste paper, broke paper, etc.

[0015] However, in order to minimize the inclusion of impurities, it is preferable to use wood pulp as the raw material pulp P1. 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.

[0016] 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 bleached softwood kraft pulp, unbleached softwood kraft pulp, or semi-bleached softwood kraft pulp.

[0017] However, it is preferable to use NKP (preferably NBKP) and LKP (preferably LBKP) in combination. In this regard, NKP has thick and long cellulose fibers, which improves the strength of the cellulose fiber-containing material but deteriorates the formation. On the other hand, LKP has thin and short cellulose fibers, which reduces the strength of the pulp sheet when paper is made but improves the formation. In view of these properties, when NKP and LKP are used in combination, the NKP blending ratio is preferably 1 to 99% by mass, more preferably 5 to 95% by mass, and particularly preferably 10 to 90% by mass. If the NKP blending ratio is less than 10% by mass, paper breaks may occur during the papermaking process or coating process, which are thought to be due to insufficient tensile strength or tear strength. On the other hand, if the NKP blending ratio exceeds 90% by mass, that is, if the LKP blending ratio is less than 10% by mass, properties such as the reinforcing effect of the resin may not be sufficiently obtained.

[0018] On the other hand, as the mechanical pulp, one or more types can be selected and used from, for example, stone ground pulp (SGP), pressurized 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.

[0019] The freeness of the raw pulp P1, measured in accordance with JIS P 8121-2, is preferably 200 to 700 cc, more preferably 250 to 650 cc, and particularly preferably 300 to 600 cc. If the freeness is less than 200 cc, the dewatering in the wire part, which will be described later, may be poor, making it difficult to increase the papermaking speed. On the other hand, if the freeness exceeds 700 cc, the formation may be poor, and the paper may break in the subsequent coating step.

[0020] It is preferable to internally and / or externally add a sizing agent to the raw pulp P1 as necessary to adjust the Stoeckigt sizing degree (JIS P 8122) or Cobb sizing degree (JIS P 8140). The Stoeckigt sizing degree is a test that measures the time required for a chemical solution to penetrate a pulp sheet and change color; the lower the value, the higher the permeability. On the other hand, the Cobb sizing degree is a test that measures the amount of water absorbed (mass) when one side of a pulp sheet is in contact with water for a certain period of time; the higher the value, the higher the water absorbency. Therefore, the Stoeckigt sizing degree, which is an index of permeability, and the Cobb sizing degree, which is an index of water absorbency, differ significantly between a pulp containing a sizing agent and a pulp without a sizing agent. However, if the amount of sizing agent is too large, the amount of urea or the like added (penetration amount) in the coating process described below may be insufficient, resulting in insufficient reaction. On the other hand, if the amount of sizing agent is too small, the wet paper strength may decrease, leading to paper breakage. Therefore, it is necessary to adjust the amount of sizing agent added, and this amount should be determined based on the Stockigt sizing degree or Cobb sizing degree of the pulp sheet before coating with urea or the like.

[0021] Specifically, the Stockigt sizing degree measured in accordance with JIS P 8122 is preferably 0.1 to 100 seconds, more preferably 0.2 to 80 seconds, and particularly preferably 0.5 to 50 seconds. Also, the Cobb sizing degree (10 seconds) measured in accordance with JIS P 8140 is preferably 10 to 600 g / m 2 , more preferably 20 to 580 g / m 2 , particularly preferably 30 to 550 g / m 2 is.

[0022] The ash content of the raw material pulp P1 measured in accordance with JIS P 8251 is preferably 0 to 20% by mass, more preferably 0 to 15% by mass, and particularly preferably 0 to 10% by mass. If the ash content exceeds 20% by mass, the strength of the pulp sheet in a wet state decreases, and there is a possibility that the sheet may break, particularly during the coating process.

[0023] It should be noted that the manufacturing method of this embodiment is not a paper manufacturing method, but merely utilizes the state or form of a pulp sheet to efficiently react with urea, etc. Therefore, knowledge regarding the addition of ash in paper manufacturing technology cannot be directly utilized, and for example, when defibration is performed in a later process, the amount of ash can affect the progress of defibration.

[0024] (Paper making process) In the manufacturing method of this embodiment, raw pulp P1 is made into a belt-shaped pulp sheet in a papermaking step 100. Here, "belt-shaped" means a continuous, elongated sheet having a predetermined width (e.g., 300 to 10,000 mm), and has a shape similar to or equivalent to a wet paper web or paper web in the paper manufacturing process.

[0025] Examples of papermaking equipment used in the papermaking process 100 include a Fourdrinier former having a wire part 110 and a press part 120, a former combining a Fourdrinier former with an on-top former, and a gap former.

[0026] However, using a gap former, which immediately clamps the stock jet ejected from the headbox between two wires, has the advantage of reducing the difference between the front and back sides and allowing urea and other substances to penetrate the pulp sheet evenly in the thickness direction (Z-axis direction) of the pulp sheet.

[0027] Although this gap former has the advantage of having little difference between the front and back sides, it has the characteristic of being inferior in flatness because both sides are wire surfaces, and also has the characteristic of having inferior formation because the formation is determined the moment the stock is blown onto the wire. Since the purpose of this form is not paper production itself, flatness and formation may not be an issue in some cases, but in relation to the subsequent coating method and the penetration of chemical solutions, an on-top linear former is preferable as it has better flatness and formation. In particular, attaching a shaking device (a device that shakes the wire sideways) to the wire is preferable as it further improves formation.

[0028] The pulp sheet (paper layer) of the wire part 110 flows (is transferred) to the press part 120, where it is dewatered.

[0029] The press used in the press part 120 may be, for example, a straight-through type, an Invar type, a reverse type, or a combination of these. However, a straight-through type without an open draw is preferred because it is easier to hold the pulp sheet and there are fewer operational problems such as paper breaks.

[0030] The pulp sheet (wet paper) that has passed through the press part 120 can be transferred to, for example, a single-deck or double-deck pre-dryer part 130 for drying. However, a no-open draw single-deck dryer is preferred for the pre-dryer part 130, as it reduces paper breakage and allows for highly efficient drying without reducing the bulk.

[0031] The drying temperature in the pre-dryer part 130 is preferably 80 to 140°C, more preferably 85 to 135°C, and particularly preferably 90 to 130°C. If the drying temperature exceeds 140°C, partial over-drying may occur, which may impair the penetration of urea and the like in the coating step 200. On the other hand, if the drying temperature is less than 80°C, partial insufficient drying may occur, which may cause paper breaks in the insufficiently dried parts.

[0032] The moisture content of the pulp sheet that has passed through the pre-dryer part 130 is preferably 0.1 to 10%, more preferably 1 to 9%, and particularly preferably 2 to 8%. If the moisture content is less than 0.1%, the sheet will be over-dried, which may result in poor penetration of urea and the like in the coating step 200. On the other hand, if the moisture content exceeds 10%, the sheet will be insufficiently dried, which may result in sheet breakage in the coating step 200.

[0033] In this embodiment, the moisture content is a value measured by infrared radiation using a BM (Basis weight / Moisture) meter.

[0034] The belt-shaped pulp sheet obtained in the papermaking process 100 preferably has a basis weight measured in accordance with JIS P 8124 of 60 to 800 g / m 2 , more preferably 80 to 750 g / m 2 , particularly preferably 100 to 700 g / m 2 The basis weight is 50 g / m 2 If the basis weight is less than 800 g / m, the sheet may break due to insufficient strength, especially in the coating step 200. 2 If the weight exceeds this, there is a possibility that urea and the like will not penetrate sufficiently in the coating process 200. Note that the above basis weight is for a single-layer paper. For multi-layer paper with two or more layers, there is a possibility that the chemicals will remain at the interface between the layers.

[0035] The urea or other chemicals applied in the coating process 200 may contain any papermaking chemicals. There are no limitations on the type of papermaking chemicals, and the concentration of the papermaking chemicals can be adjusted as needed. However, it goes without saying that the purpose of applying the urea or other chemicals must not be compromised, and adjustments may be necessary. For example, in this embodiment, in which urea or other chemicals are used in the coating process 200, papermaking is carried out in the papermaking process 100 so that the concentration of each of the following papermaking chemicals is preferably 0 to 10%, more preferably 0.1 to 9%, and particularly preferably 0.2 to 8%: various starches; papermaking chemicals with hydroxyl groups such as CMC (carboxymethyl cellulose); papermaking chemicals with silanol groups or other elements bonded to an -OH group such as colloidal silica and aluminum sulfate; rosin sizing agents; ASA (alkenyl succinic anhydride); AKD (alkyl ketene dimer); various starches; and CMC. The above papermaking chemicals are subject to denaturing reactions with urea, etc., so if the papermaking chemicals contain a large amount of these chemicals, the utilization of urea, etc. in reaction step X2 is hindered accordingly. These chemicals are not dependent on whether they are internally or externally added.

[0036] On the other hand, the amount of dye depends on the subsequent use. For example, if the use is to use as a reinforcing material for resin and coloring by fine fibers is not desirable, the amount of dye is preferably 0 to 10%, more preferably 0.1 to 5%, and particularly preferably 0.2 to 3% when making paper.

[0037] From the same viewpoint, the brightness of the pulp sheet measured in accordance with JIS P 8148 is preferably 80% or more, more preferably 82% or more, and particularly preferably 85% or more. When LBKP and NBKP are used as the raw material pulp P1, as in the above-mentioned example, the brightness is usually 80% or more, and there is no need to adjust the brightness.

[0038] The tensile strength of the pulp sheet measured in accordance with JIS P 8113 is preferably 10 MPa or more, more preferably 15 MPa or more, and particularly preferably 20 MPa or more. If the tensile strength is less than 10 MPa (1 kN / m, thickness 100 μm), the sheet may break during the coating process 200. Although increasing the basis weight increases the tensile strength, as mentioned above, increasing the basis weight makes it more difficult for urea and the like to penetrate during the coating process 200. Therefore, the balance between tensile strength and basis weight is also important, and it is suitable to set the specific tensile strength (tensile strength / basis weight) to preferably 1 to 10,000 Nm / g, more preferably 5 to 5,000 Nm / g, and particularly preferably 10 to 1,000 Nm / g.

[0039] Meanwhile, the wet strength of the pulp sheet measured in accordance with JIS P 8135 is preferably 0.1 kN / m or more, more preferably 0.2 kN / m or more, and particularly preferably 0.5 kN / m or more. If the wet strength is less than 0.1 kN / m, the sheet may break during the coating process 200. Although increasing the basis weight increases the wet strength, as mentioned above, increasing the basis weight makes it more difficult for urea and the like to penetrate during the coating process 200. Therefore, the balance between wet strength and basis weight is also important, and it is suitable to set the specific wet strength (wet strength / basis weight) to preferably 0.1 to 5000 Nm / g, more preferably 0.5 to 1000 Nm / g, and particularly preferably 1 to 500 Nm / g.

[0040] (Coating process) The pulp sheet dried in the pre-dryer part 130 is coated with urea or the like in the coater part 210 between the pre-dryer part 130 and the after-dryer part 220. Here, in this specification, "coating" simply means the act of "applying" and is not intended to limit the state of the urea or the like after it has been applied. Therefore, it includes, for example, a form in which the urea or the like remains on the surface of the pulp sheet and a coating layer is formed, as well as a form in which all the urea or the like has soaked into the pulp sheet and no coating layer is formed on the surface of the pulp sheet, i.e., a form in which the pulp sheet is simply impregnated.

[0041] In the coater part 210, urea and the like can be applied by a coating method such as bevel blade coating, size press coating, bent blade coating, rod coating, dip coating, spray coating, and comma coating. However, bent blade coating is preferably used for coating in the coater part 210. In this regard, bent blade coating is a type of blade coating, but whereas bevel blade coating, which is also a type of blade coating, scrapes off urea and the like sprayed with a fountain, bent blade coating applies urea and the like by forcing it into the pulp sheet. Therefore, it is suitable for this embodiment, which greatly requires that urea and the like penetrate into the pulp sheet.

[0042] On the other hand, impregnation coating and comma coating each have the following characteristics. That is, first, in this embodiment, the impregnation method means a method in which coating is performed by running a pulp sheet through a container containing urea, etc. Also, the comma coating method means a method in which a liquid pool is created between two rolls and a blade, and the pulp sheet runs through a clearance that adjusts the amount of coating.

[0043] The concentration of urea or the like can be adjusted as needed, but in the present embodiment where carbamate formation is performed, it is preferably 20 to 50% by mass, more preferably 25 to 45% by mass, and particularly preferably 30 to 40% by mass. If the concentration of urea or the like is less than 20% by mass, the carbamate formation rate will be insufficient and drying may become difficult. On the other hand, if the concentration of urea or the like exceeds 50% by mass, the endothermic reaction caused by the melting of urea or the like during preparation of urea water may lower the temperature of the solution, causing precipitation of urea or the like.

[0044] The viscosity of the urea water (concentration 40%) measured in accordance with JIS-Z8803 (2011) is preferably 2000 cps or less, more preferably 1700 cps or less, and particularly preferably 1500 cps or less. If the viscosity exceeds 2000 cps, the urea water will have difficulty penetrating the pulp sheet.

[0045] In the manufacturing method of this embodiment, the coating process 200 can be performed either offline or online. However, when the manufacturing speed is 300 m / min or higher, it is preferable that the papermaking process 100 and the coating process 200 are incorporated in order as continuous processes on the machine (online). If the process is performed online, not only is manufacturing efficiency improved, but the coating quality can be made uniform without being affected by the storage state of the pulp sheet, etc.

[0046] In the production method of this embodiment, urea or the like can be applied to only one side or both sides of the pulp sheet, although from the viewpoint of uniformity of the reaction carried out in the subsequent step, it is preferable to apply it to both sides.

[0047] When the coating of urea or the like is performed offline on both sides of the pulp sheet, there is an advantage in that the amount of coating can be made different on the front and back sides depending on the characteristics of the pulp sheet.

[0048] The coating mass ratio of urea etc. to cellulose fiber (urea etc. / cellulose fiber) is preferably 10 to 400 kg / pt (pulp ton), more preferably 20 to 300 kg / pt, and particularly preferably 45 to 200 kg / pt. If the coating mass ratio is less than 45 kg / pt, carbamate formation may not proceed sufficiently. On the other hand, if the coating mass ratio exceeds 200 kg / pt, excessive coating may occur, and excess urea etc. may adhere to the equipment. Note that the coating amount is usually 1 m 2 However, in this embodiment, since urea or the like is an agent (reactant) for reacting with cellulose fibers, it is preferable to specify the amount of urea per unit mass of cellulose fibers.

[0049] After passing through the coater part 210, the pulp sheet proceeds to the after-dryer part 220 where it is dried.

[0050] For drying in the after-dryer part 220, drying devices such as a hot air dryer, a gas heater dryer, or an infrared dryer can be used. However, using an infrared dryer can cause urea and the like to solidify on the surface of the pulp sheet, potentially hindering the penetration of the urea and the like. Therefore, it is preferable to use a hot air dryer. In particular, since the temperature of a hot air dryer is easy to control, providing multiple hot air dryers in stages and designing them so that the temperature gradually increases allows drying to proceed without hindering the penetration of the urea and the like.

[0051] In the after-dryer part 220, the drying temperature is preferably 80 to 140°C, more preferably 85 to 135°C, and particularly preferably 90 to 130°C. If the drying temperature is below 80°C, drying may be insufficient if the drying time is short, and therefore it is not suitable for high-speed production. On the other hand, if the drying temperature exceeds 140°C, by-products such as urea may be generated.

[0052] The moisture content of the pulp sheet that has passed through the after-dryer part 220 is preferably 0 to 10%, more preferably 0 to 8%, and particularly preferably 0 to 7%. If the moisture content exceeds 10%, the reaction efficiency may decrease in the reaction part of the heating step described below.

[0053] In the after-dryer part 220, the moisture content is a value measured by infrared radiation using a BM (Basis weight / Moisture) meter.

[0054] The surface temperature of the pulp sheet after passing through the after-dryer part 220 is preferably 30 to 95°C, more preferably 35 to 90°C, and particularly preferably 40 to 85°C. If the surface temperature is below 40°C, drying may be insufficient. On the other hand, if the surface temperature exceeds 95°C, by-products may be generated from the reactants.

[0055] In this embodiment, the purpose is not to manufacture paper itself, but to merely temporarily utilize the form of paper (pulp sheet), so the process may proceed to a calendaring step after this, or the calendaring step may be omitted and the process may proceed to a reaction step.

[0056] (Heating process (carbamate process)) The pulp sheet (pulp fiber-containing material) that has passed through the after-dryer part 220 can be temporarily wound in a winder part (not shown) and stored as a wound web. Thereafter, the wound web can be subjected to treatments such as heating and cooling while still wound, thereby allowing the cellulose fibers to react with urea or the like. In this embodiment, however, the pulp sheet is pulled out from the wound web and treated to promote carbamate formation.

[0057] When the pulp sheet is wound into a roll, the pulled-out pulp sheet is dried to a moisture content of preferably 10% by mass or less, more preferably 9% by mass or less, and particularly preferably 8% by mass or less, in order to increase the reaction efficiency.

[0058] However, as described above, the production efficiency decreases when the pulp sheet is wound into a roll. Therefore, it is preferable to continuously advance (transfer) the pulp sheet that has passed through the after-dryer part 220 to the carbamate formation step X2. In this case, the drying of the pulp sheet prior to the carbamate formation can be omitted.

[0059] In the carbamate formation step X2, urea and the like contained in the pulp sheet, i.e., the cellulose fiber-containing material, are reacted with the cellulose fibers. This reaction will now be described in detail.

[0060] First, carbamate modification means modifying cellulose fibers to have carbamate groups, i.e., bringing cellulose fibers into a state in which carbamate (an ester of carbamic acid) is introduced.

[0061] A carbamate group is a group represented by -O-CO-NH-, for example, a group represented by -O-CO-NH2, -O-CONHR, -O-CO-NR2, etc. That is, a carbamate group can be represented by the following structural formula (1).

[0062] [ka]

[0063] Here, n represents an integer of 1 or greater. 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 derivatives thereof. Additionally, examples include crosslinked carbamate cellulose in which a crosslinked structure is formed between cellulose molecules or fibers via carbamate groups.

[0064] Examples of saturated linear hydrocarbon groups include linear alkyl groups having 1 to 10 carbon atoms, such as methyl, ethyl, and propyl groups.

[0065] Examples of the saturated branched hydrocarbon group include branched alkyl groups having 3 to 10 carbon atoms, such as an isopropyl group, a sec-butyl group, an isobutyl group, and a tert-butyl group.

[0066] Examples of the saturated cyclic hydrocarbon group include cycloalkyl groups such as a cyclopentyl group, a cyclohexyl group, and a norbornyl group.

[0067] Examples of the unsaturated linear hydrocarbon group 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.

[0068] Examples of the unsaturated branched hydrocarbon group include branched alkenyl groups having 3 to 10 carbon atoms, such as a propen-2-yl group, a buten-2-yl group, and a buten-3-yl group, and branched alkynyl groups having 4 to 10 carbon atoms, such as a butyn-3-yl group.

[0069] Examples of the aromatic group include a phenyl group, a tolyl group, a xylyl group, and a naphthyl group.

[0070] Examples of the derivative group include groups in which one or more hydrogen atoms of the above-mentioned saturated linear hydrocarbon group, saturated branched hydrocarbon group, saturated cyclic hydrocarbon group, unsaturated linear hydrocarbon group, unsaturated branched hydrocarbon group, and aromatic group have been substituted with a substituent (for example, a hydroxy group, a carboxy group, a halogen atom, etc.).

[0071] In cellulose fibers having carbamate groups (carbamate-introduced fibers), some or all of the highly polar hydroxyl groups are substituted with relatively less polar carbamate groups. Therefore, these cellulose fibers have low hydrophilicity and high affinity with low-polarity resins. As a result, the fine fibers obtained by defibrating these cellulose fibers have properties such as excellent uniform dispersion in resins. Furthermore, the slurry of these fine fibers has low viscosity and good handleability.

[0072] The lower limit of the degree of substitution of carbamate groups for hydroxy groups of cellulose fibers is preferably 0.05, more preferably 0.1, and particularly preferably 0.2. When the degree of substitution is 0.05 or more, the effect of introducing carbamate can be reliably achieved. On the other hand, the upper limit of the degree of substitution is preferably 1, more preferably 0.5, and particularly preferably 0.4. In this respect, cellulose fibers with a high degree of substitution have the problem of being expensive.

[0073] Cellulose is a polymer with anhydroglucose as a structural unit, and has three hydroxyl groups per structural unit. Therefore, if all the hydroxyl groups are substituted with carbamate groups, the degree of substitution is 3.

[0074] The amount of carbamate groups introduced into cellulose fibers is preferably 0.5 to 4.5 mmol / g, more preferably 0.6 to 4.0 mmol / g, and particularly preferably 0.7 to 3.5 mmol / g. If the substitution rate is less than 0.5 mmol / g, sufficient reinforcing effect may not be obtained when composited with a resin. On the other hand, if the substitution rate exceeds 4.5 mmol / g, excessive urea may be required.

[0075] Regarding the introduction of carbamate into cellulose fibers (carbamation), there are two methods: one is to carbamate the cellulose fibers and then finely pulverize them, and the other is to finely pulverize the cellulose fibers to form fine fibers and then carbamate them. However, as in the present embodiment, it is preferable to first perform carbamate conversion and then defibrate the fibers. This is because cellulose fibers before defibration have high dehydration efficiency and the heating involved in carbamate conversion makes the cellulose fibers more easily defibrated.

[0076] Conventionally, processes for carbamate-converting cellulose fibers have included, for example, a mixing process, a removing process, and a heating process. In the mixing process, cellulose fibers and urea or the like are mixed in a dispersion medium. However, the addition of this process significantly reduces production efficiency. Therefore, in this embodiment, urea or the like is reacted with cellulose fibers in the form of a strip-shaped pulp sheet. In this case, the pulp sheet may be in the form of a rolled web or in the form of a sheet unwound from the rolled web. From the viewpoint of excellent reaction efficiency and uniformity, the pulp sheet is in the unwound state.

[0077] 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 ureas and urea derivatives can be used alone or in combination. However, it is preferable to use urea.

[0078] In the carbamate formation step X2 of this embodiment, a pulp sheet, i.e., a cellulose fiber-containing material P2 containing urea or the like, is heat-treated. In this carbamate formation step X2, some or all of the hydroxy groups of the cellulose fibers react with urea or the like to be substituted with carbamate groups. More specifically, when urea or the like is heated, it is decomposed into isocyanic acid and ammonia as shown in the following reaction formula (1). Isocyanic acid is highly reactive and, for example, forms carbamate with the hydroxyl groups of cellulose as shown in the following reaction formula (2).

[0079] NH2-CO-NH2→ HN=C=O + NH3…(1)

[0080] Cell-OH + HN=C=O → Cell-O-CO-NH2…(2)

[0081] As mentioned above, the pulp sheet may be heated in a wound state or after being unwound from the wound web. When the pulp sheet is heated in a wound state, a heating device such as a hot air heating system, a high-frequency heating system, or a rotary kiln system may be used. On the other hand, when the pulp sheet is unwound from the wound web and then heated, a heating device such as an induction heating roll, an oil heating roll, a hot air heating system, a far-infrared heating system, or a microwave heating system may be used.

[0082] Here, the features of the use of the above heating device will be described. First, heating methods can be broadly divided into two types: batch and continuous (roll-to-roll). Batch methods include high-frequency heating devices and rotary kilns, which are equipment capable of reacting large amounts of sample at once. In high-frequency heating devices, when an object to be heated is placed inside the electrodes, polarization occurs inside the object, generating an electric charge, and the molecules are heated by intense internal friction due to changes in frequency speed. On the other hand, rotary kilns are rotating, high-temperature firing devices that are used in the paper industry in the chemical recovery process of kraft pulping.

[0083] On the other hand, roll-to-roll heating, in which pulp sheets are heated by passing them between a pair of rolls, includes induction heating rolls, oil heating rolls, and continuous heating methods such as hot air heating, far-infrared heating, and microwave heating. Induction heating rolls generate heat through an electrically generated magnetic field and are also used in calendering equipment in the papermaking process. Oil heating rolls circulate heated oil inside the rolls to heat the roll surface. Hot air heating involves spraying hot air onto the top and bottom surfaces of the pulp sheet from nozzles located above and below the conveyor, heating the pulp sheet as it passes through. Far-infrared heating utilizes infrared radiation with wavelengths between 3 μm and 1 mm, which causes interatomic contraction and bending. Microwave heating utilizes frictional heat generated between the molecules that make up the pulp sheet depending on the frequency (300 MHz to 30 GHz), and is commonly used in microwave ovens.

[0084] Reaction equipment using induction heating rolls is preferred because it has better reaction efficiency and energy efficiency than oil heating rolls. On the other hand, batch heating using the state of the wound raw material, especially heating using high frequency, heats a large amount of sample at once, which causes uneven reaction and makes it difficult to achieve a uniform carbamate reaction.

[0085] On the other hand, in the case of continuous heating other than roll-to-roll heating such as induction heating rolls or oil heating rolls, for example, non-contact heating methods such as hot air heating or far-infrared heating, the carbamate reaction can be promoted by increasing the reaction temperature.

[0086] In conclusion, it is particularly preferable to pass a pulp sheet containing urea and the like, which is made into a strip by papermaking the raw material pulp P1, between a pair of rolls and heat it, and carry out the reaction by this heating. However, when the sheet width of the pulp sheet is 300 to 1000 mm, it is more preferable that at least one of the pair of rolls is a heating roll.

[0087] However, first, the pulp sheet is preferably passed between a pair of rolls at a speed (line speed) of 300 to 3,000 m / min, more preferably 400 to 2,500 m / min, and particularly preferably 500 to 2,000 m / min. If the line speed is less than 300 m / min, the production speed is slow and not suitable for mass production. On the other hand, if the line speed exceeds 3,000 m / min, the pulp sheet may tear (break).

[0088] Preferably, the pair of rolls is a series of multiple sets, with the leading set or sets being a drying part and the trailing set or sets being a reaction part. By allocating part of the heating process to the drying part rather than the reaction part in this way, the reaction (modification), i.e., carbamate conversion, is sufficiently carried out, and the physical properties of the pulp sheet flowing into the reaction part are made uniform, resulting in a uniform carbamate conversion rate, etc.

[0089] It is also possible to dry the pulp sheet prior to the heating step. However, unlike the case where a portion of the pulp sheet is allocated to a drying part rather than a reaction part during the heating step, drying prior to the heating step will be affected when moving between steps (apparatuses). Furthermore, when a portion of the pulp sheet is allocated to a drying part rather than a reaction part during the heating step, the inlet moisture content of the reaction part is 5% by mass or less. In other words, the part where the moisture content exceeds 5% by mass is the drying part.

[0090] In the carbamation step X2 of this embodiment, the temperature (drying temperature) of the rolls belonging to the drying part is preferably 80 to 130°C, more preferably 90 to 130°C, and particularly preferably 100 to 130°C. If the drying temperature is below 80°C, the carbamation in the reaction part following the drying part may not be carried out sufficiently. On the other hand, if the drying temperature exceeds 130°C, moisture and urea may react and decompose, and the carbamation may not be carried out sufficiently. It is more preferable that the drying temperature of all rolls belonging to the drying part is within the above range.

[0091] In the carbamate formation step X2 of this embodiment, the temperature (reaction temperature) of the rolls belonging to the reaction part is preferably 220 to 280°C, more preferably 230 to 270°C, and particularly preferably 240 to 260°C. If the reaction temperature is below 220°C, the reaction (carbamation) may not be sufficient. On the other hand, if the reaction temperature exceeds 280°C, urea and the like may thermally decompose, and coloration may become significant. It is more preferable that the reaction temperature of all rolls belonging to the reaction part is within the above range.

[0092] The number of pairs of rolls belonging to the drying section and the number of pairs of rolls belonging to the reaction section may be one or two or more. However, the number of pairs is preferably set so that the passage time through the drying section is 8 seconds or more and the passage time through the reaction section is 8 seconds or more, more preferably set so that the passage time through the drying section is 8 to 30 seconds and the passage time through the reaction section is 8 to 30 seconds, and particularly preferably set so that the passage time through the drying section is 10 to 20 seconds and the passage time through the reaction section is 10 to 20 seconds. If the passage time is shorter (the number of pairs of rolls is smaller), carbamate conversion may be insufficient. On the other hand, if the passage time is longer (the number of pairs of rolls is larger), carbamate conversion may plateau in the drying section, and carbamate conversion may plateau in the reaction section, resulting in cellulose degradation.

[0093] When the heating process is divided into a drying part and a reaction part as described above, the moisture content of the pulp sheet entering the drying part is preferably 15% or less, more preferably 10% or less, and particularly preferably 8% or less. If the moisture content exceeds 15%, the drying energy required in the drying part may become enormous.

[0094] In this embodiment, the moisture content is a value measured by infrared radiation using a BM (Basis weight / Moisture) meter.

[0095] Furthermore, when the heating step is divided into a drying part and a reaction part, the surface temperature of the pulp sheet entering the drying part is preferably set to 15 to 130°C, more preferably 20 to 100°C, and particularly preferably 25 to 70°C. If the surface temperature is below 15°C, extra heating energy may be required in the drying part. On the other hand, if the surface temperature exceeds 130°C, urea may decompose before the reaction.

[0096] Furthermore, when the heating process is divided into a drying part and a reaction part, the basis weight of the pulp sheet entering the drying part is 50 to 800 g / m 2 It is preferable to keep it at 80 to 400 g / m 2 It is more preferable to set the basis weight at 50 g / m 2 On the other hand, if the basis weight is less than 800 g / m, productivity is poor and it is not economical. 2 If the temperature exceeds this range, the sheet will become thick and the drying efficiency and reaction efficiency may decrease.

[0097] The basis weight of the pulp sheet is a value measured in accordance with JIS P 8124.

[0098] (defibration process) In this embodiment, the carbamate cellulose fibers P3 obtained as described above are pulverized as necessary and then defibrated (refined) in the defibration step X3, to obtain carbamate fine fibers P4.

[0099] In this embodiment, the term "fine fibers" refers to cellulose fibers having an average fiber width of 0.01 to 19 μm. Examples of fine fibers include microfiber cellulose (microfibrillated cellulose) and cellulose nanofibers.

[0100] Furthermore, although the reacted cellulose fiber P3 can be immediately defibrated by crushing or the like, it is preferable to disintegrate the sheet-like or crushed reacted cellulose fiber P3 in water prior to defibration, and then dehydrate and wash the reacted cellulose fiber P3 using a dehydration device such as a valveless filter. Furthermore, when a valveless filter is used for dehydration, washing can be made more thorough by showering the mat-like reacted cellulose fiber P3 after dehydration. Washing can remove unreacted reaction liquid, by-products of the reaction liquid, and water-soluble impurities.

[0101] In this embodiment, microfibrous cellulose refers to fibers with a larger average fiber diameter than cellulose nanofibers. Specifically, it is, for example, 0.1 to 19 μm, preferably 0.2 to 10 μm. When the average fiber diameter of microfibrous cellulose is less than 0.1 μm, it becomes no different from cellulose nanofibers. For example, when kneaded with a resin, the effect of improving the strength of the resin (particularly the flexural modulus) may not be sufficient. Furthermore, the defibration time becomes longer, requiring a large amount of energy. Furthermore, the dewaterability of the cellulose fiber slurry deteriorates. When dewaterability deteriorates, a large amount of energy is required for drying, and applying a large amount of energy for drying may cause thermal degradation of the cellulose fibers, resulting in a decrease in strength. On the other hand, when the average fiber diameter of microfibrous cellulose exceeds 19 μm, it becomes no different from pulp, and the reinforcing effect of the resin may not be sufficient.

[0102] The average fiber diameter of fine fibers (microfiber cellulose and cellulose nanofiber) is measured as follows. First, 100 ml of an aqueous dispersion of fine fibers with a solid content of 0.01 to 0.1% by mass is filtered through a Teflon® membrane filter and solvent-substituted once with 100 ml of ethanol and three times with 20 ml of t-butanol. The sample is then freeze-dried and osmium-coated to obtain a sample. This sample is then observed using an SEM image at a magnification of 3,000x to 30,000x, depending on the width of the fibers that make up the sample. Specifically, two diagonal lines are drawn on the observed image, and three straight lines are arbitrarily drawn passing through the intersections of the diagonal lines. The widths of a total of 100 fibers intersecting with these three straight lines are then visually measured. The median diameter of the measured values ​​is then taken as the average fiber diameter.

[0103] The carbamate cellulose fiber P3 or its pulverized product can be subjected to a pretreatment or bleaching treatment by a chemical method before being defibrated.

[0104] 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), oxidation of polysaccharides with an oxidizing agent (oxidation treatment), and reduction of polysaccharides with a reducing agent (reduction treatment). However, as a chemical pretreatment, enzyme treatment is preferred, and it is more preferred to additionally perform one or more treatments selected from acid treatment, alkali treatment, and oxidation treatment. Enzyme treatment will be described in detail below.

[0105] The enzymes used in the enzymatic treatment are preferably at least one of cellulase enzymes and hemicellulase enzymes, and more preferably both. The use of these enzymes makes it easier to defibrate cellulose fibers. Cellulose enzymes decompose cellulose in the presence of water. Hemicellulase enzymes decompose hemicellulose in the presence of water.

[0106] Examples of cellulase enzymes that can be used include enzymes produced by species of 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 are available as reagents or commercially available products. Examples of commercially available products include Celluleucin T2 (manufactured by HPI), Meicerase (manufactured by Meiji Seika Kaisha), Novozym 188 (manufactured by Novozym), Multifect CX10L (manufactured by Genencor), and cellulase enzyme GC220 (manufactured by Genencor).

[0107] In addition, 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.

[0108] Examples of hemicellulase enzymes that can be used include 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. Also usable is pectinase, which is an enzyme that breaks down pectin.

[0109] Hemicellulose is a polysaccharide, excluding pectins, found between the cellulose microfibrils of plant cell walls. Hemicellulose is diverse and varies depending on the type of wood and the wall layers of the cell wall. Glucomannan is the main component in the secondary walls of softwoods, while 4-O-methylglucuronoxylan is the main component in the secondary walls of hardwoods. Therefore, when obtaining fine fibers from softwood bleached kraft pulp (NBKP), it is preferable to use mannase. Furthermore, when obtaining fine fibers from hardwood bleached kraft pulp (LBKP), it is preferable to use xylanase.

[0110] The amount of enzyme added to cellulose fibers is determined by, for example, the type of enzyme, the type of wood used as raw material (coniferous or broadleaf), the type of mechanical pulp, etc. However, the amount of enzyme added to cellulose fibers 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 fully obtained. On the other hand, if the amount of enzyme added is more than 3 mass%, the cellulose may be saccharified, resulting in a decrease in the yield of fine fibers. Another problem is that the improvement in effect may not be commensurate with the increase in the amount added.

[0111] When a cellulase enzyme is used as the enzyme, the pH during the enzymatic treatment is preferably in the weak acidic range (pH = 3.0 to 6.9) from the viewpoint of the reactivity of the enzymatic reaction. On the other hand, when a hemicellulase enzyme is used as the enzyme, the pH during the enzymatic treatment is preferably in the weak alkaline range (pH = 7.1 to 10.0).

[0112] 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 prolonged treatment time can be prevented. On the other hand, if the temperature during the enzyme treatment is 70°C or lower, deactivation of the enzyme can be prevented.

[0113] The time for the enzyme treatment is determined depending on, for example, the type of enzyme, the temperature of the enzyme treatment, the pH during the enzyme treatment, etc. However, the time for the enzyme treatment is generally 0.5 to 24 hours.

[0114] After the enzymatic treatment, it is preferable to inactivate the enzyme. Examples of methods for inactivating the enzyme include 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.

[0115] Next, the alkali treatment method will be described. When cellulose fibers are treated with alkali prior to defibration, some of the hydroxyl groups in the hemicellulose and cellulose contained in the fibers are dissociated, and the molecules become anionic, weakening the intramolecular and intermolecular hydrogen bonds, which promotes the dispersion of the cellulose fibers during defibration.

[0116] Examples of the alkali used in the alkali treatment include organic alkalis such as sodium hydroxide, lithium hydroxide, potassium hydroxide, aqueous ammonia, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, and benzyltrimethylammonium hydroxide. However, from the viewpoint of production costs, it is preferable to use sodium hydroxide.

[0117] If the microfibers are subjected to an enzyme treatment, acid treatment, or oxidation treatment prior to defibration, the water retention of the fine fibers can be reduced, the crystallinity can be increased, and the homogeneity can be improved. In this regard, if the water retention of the microfiber cellulose is low, it becomes easier to dehydrate, and the dewatering property of the cellulose fiber slurry is improved.

[0118] When cellulose fibers are treated with enzymes, acids, or oxidation, the hemicellulose and amorphous regions of cellulose in the pulp are decomposed. As a result, the energy required for defibration can be reduced, and the uniformity and dispersibility of the cellulose fibers can be improved. However, because pretreatment reduces the aspect ratio of microfiber cellulose, excessive pretreatment is preferably avoided when using it as a reinforcing material for resins.

[0119] On the other hand, the bleaching treatment may be peroxide bleaching, hypochlorite bleaching, chlorine dioxide bleaching, persulfate bleaching, oxone bleaching, a multi-stage bleaching treatment combining these, or reduction bleaching using hydrosulfite, sodium borohydride, or the like.

[0120] The cellulose fibers can be defibrated by beating the raw material pulp using, for example, a homogenizer such as a beater, a high-pressure homogenizer, a counter-impingement homogenizer, or a high-pressure homogenizer, a grinder, a millstone-type friction machine such as a grinder, a single-shaft kneader, a multi-shaft kneader, a kneader refiner, a jet mill, etc. However, it is preferable to use a refiner or a jet mill.

[0121] The average fiber length (average length of single fibers) of the microfiber cellulose is preferably 0.02 to 2.0 mm, more preferably 0.05 to 1.5 mm, and particularly preferably 0.1 to 1.0 mm. If the average fiber length is less than 0.02 mm, a three-dimensional network cannot be formed between the fibers, which may reduce the reinforcing effect of the resin. On the other hand, if the average fiber length exceeds 2.0 mm, the reinforcing effect may be insufficient because the length is the same as that of the raw material pulp.

[0122] The average fiber length of the microfibrous cellulose can be adjusted as desired by, for example, selecting the raw material pulp P1, pre-treating it, defibrating it, and the like.

[0123] The proportion of microfiber cellulose fibers with a length of 0.2 mm or less (fine ratio) is preferably 20% or more, more preferably 40% or more, and particularly preferably 60% or more. If this proportion is less than 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 0.2 mm or less, and all fibers may be 0.2 mm or less.

[0124] The aspect ratio of the microfibrous cellulose is preferably 2 to 15,000, more preferably 10 to 10,000. If the aspect ratio is less than 2, a three-dimensional network cannot be constructed, which may result in insufficient reinforcing effect. On the other hand, if the aspect ratio is more than 15,000, the microfibrous cellulose may become highly entangled with itself, resulting in insufficient dispersion in the resin.

[0125] The aspect ratio is the average fiber length divided by the average fiber width. The larger the aspect ratio, the more points of snagging occur, which increases the reinforcing effect, but on the other hand, it is thought that the increased snagging reduces the ductility of the resin.

[0126] The fibrillation rate of the microfibrous cellulose is preferably 1.0 to 30.0%, more preferably 1.5 to 20.0%, and particularly preferably 2.0 to 15.0%. If the fibrillation rate exceeds 30.0%, the contact area with water becomes too large, which may make dehydration difficult even if the cellulose is defibrated to an average fiber width of 0.1 μm or more. On the other hand, if the fibrillation rate is less than 1.0%, there may be few hydrogen bonds between fibrils, making it impossible to form a strong three-dimensional network.

[0127] The fiber length and fibrillation rate of the fiber are measured using a Valmet fiber analyzer "FS5." In particular, the fibrillation rate is the ratio of the small fiber projection area to the entire fiber projection area, and is the entire fiber including the fuzzed area / fuzzed area.

[0128] The crystallinity of the microfibrous cellulose is preferably 50% or more, more preferably 55% or more, and particularly preferably 60% or more. If the crystallinity is below 50%, although the mixability with pulp and cellulose nanofibers is improved, the strength of the fiber itself is reduced, which may make it impossible to improve the strength of the resin. On the other hand, the crystallinity of the microfibrous cellulose is preferably 95% or less, more preferably 90% or less, and particularly preferably 85% or less. If the crystallinity is above 95%, the proportion of strong hydrogen bonds within the molecule increases, the fiber itself becomes rigid, and dispersibility deteriorates.

[0129] The crystallinity of the microfiber cellulose can be adjusted as desired by, for example, selecting the raw material pulp P1, pre-treating it, and refining it.

[0130] The crystallinity is a value measured in accordance with JIS K 0131 (1996).

[0131] The viscosity of the microfibrous cellulose is preferably 2 cps or more, more preferably 4 cps or more. If the pulp viscosity of the microfibrous cellulose is less than 2 cps, it may be difficult to suppress the aggregation of the microfibrous cellulose.

[0132] The viscosity of the microfiber cellulose is a value measured in accordance with TAPPI T 230.

[0133] The freeness of the microfibrous cellulose is preferably 500 ml or less, more preferably 300 ml or less, and particularly preferably 100 ml or less. If the freeness of the microfibrous cellulose exceeds 500 ml, the average fiber diameter of the microfibrous cellulose will exceed 10 μm, and the strength improving effect of the resin may not be sufficiently obtained.

[0134] The freeness is a value measured in accordance with JIS P8121-2 (2012).

[0135] The zeta potential of the microfibrous cellulose is preferably -150 to 20 mV, more preferably -100 to 0 mV, and particularly preferably -80 to -10 mV. If the zeta potential is below -150 mV, compatibility with the resin may be significantly reduced, resulting in insufficient reinforcing effect. On the other hand, if the zeta potential is above 20 mV, dispersion stability may be reduced.

[0136] The water retention of the microfibrous 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 material pulp. On the other hand, if the water retention is above 400%, the dewatering ability tends to be poor and the microfibrous cellulose is prone to aggregation. In this regard, the water retention of the microfibrous cellulose can be further reduced by substituting the hydroxyl groups of the fibers with carbamate groups, thereby improving the dewatering ability and drying ability.

[0137] The water retention of the microfiber cellulose can be adjusted as desired by, for example, selecting the raw material pulp P1, pre-treating it, defibrating it, and the like.

[0138] The water retention of the microfiber cellulose is a value measured in accordance with JAPAN TAPPI No. 26 (2000).

[0139] Next, cellulose nanofibers will be described. In this embodiment, the cellulose nanofibers are fine fibers similar to microfiber cellulose, and play a unique role in improving the strength of resins.

[0140] First, cellulose nanofibers can be obtained by defibrating (refining) carbamate cellulose fibers P3. The raw material pulp P1 can be the same as the microfiber cellulose, and it is preferable to use the same as the microfiber cellulose.

[0141] The raw fibers of cellulose nanofibers can be pretreated and defibrated in the same way as microfiber cellulose. However, the degree of defibration differs; for example, it must be performed so that the average fiber diameter is less than 0.1 μm. Below, we will mainly explain the differences from microfiber cellulose.

[0142] The average fiber diameter (average fiber width; average diameter of a single fiber) of cellulose nanofibers is preferably 4 to 100 nm, more preferably 10 to 80 nm. If the average fiber diameter of cellulose nanofibers is less than 4 nm, dehydration may deteriorate. Furthermore, when cellulose nanofibers are mixed with a dispersant, the dispersant may not sufficiently cover (stick to) the cellulose nanofibers, and dispersibility may not be sufficiently improved. On the other hand, if the average fiber diameter of cellulose nanofibers exceeds 100 nm, they can no longer be called cellulose nanofibers.

[0143] The average fiber diameter of the cellulose nanofibers can be adjusted, for example, by selecting the raw material pulp P1, pre-treating it, defibrating it, etc.

[0144] The methods for measuring the physical properties of cellulose nanofibers are the same as those for microfiber cellulose, unless otherwise specified.

[0145] The average fiber length (single fiber length) of the cellulose nanofibers is preferably 0.1 to 1,000 μm, more preferably 0.5 to 500 μm. If the average fiber length of the cellulose nanofibers is less than 0.1 μm, a three-dimensional network cannot be formed between the cellulose nanofibers, and the reinforcing effect may be insufficient. On the other hand, if the average fiber length of the cellulose nanofibers is more than 1,000 μm, the fibers may easily become entangled, and dispersibility may not be sufficiently improved.

[0146] The average fiber length of the cellulose nanofibers can be adjusted, for example, by selecting the raw material pulp P1, pre-treating it, defibrating it, etc.

[0147] The crystallinity of the cellulose nanofiber is preferably 95 to 50%, more preferably 90 to 60%. If the crystallinity of the cellulose nanofiber is within the above range, the strength of the resin can be reliably improved.

[0148] The crystallinity can be adjusted as desired by, for example, selecting the raw pulp P1, pre-treating it, defibrating it, and the like.

[0149] The pulp viscosity of the cellulose nanofiber is preferably 1.0 cps or more, more preferably 2.0 cps or more. Pulp viscosity is the viscosity of the solution obtained after dissolving cellulose in a copper ethylenediamine solution, and a higher pulp viscosity indicates a higher degree of polymerization of cellulose. A pulp viscosity of 1.0 cps or more can impart dewaterability to the slurry while suppressing decomposition of the cellulose nanofiber when kneaded with a resin, thereby achieving a sufficient reinforcing effect.

[0150] If necessary, the cellulose nanofibers obtained by defibration can be dispersed in an aqueous medium to form a dispersion before mixing with other cellulose fibers. It is particularly preferable that the aqueous medium is entirely water (aqueous dispersion). However, the aqueous medium may also contain other liquids, some of which are compatible with water. Examples of other liquids that can be used include lower alcohols with 3 or fewer carbon atoms.

[0151] The Brookfield viscosity of the cellulose nanofiber dispersion (1% concentration) is preferably 10 to 2,000 cp, and more preferably 30 to 1,500 cp. If the Brookfield viscosity of the dispersion is within this range, it becomes easier to mix with other cellulose fibers and the dewatering properties of the cellulose fiber slurry are improved.

[0152] The B-type viscosity of the dispersion (solid content 1%) is a value measured in accordance with JIS-Z8803 (2011) "Method for measuring viscosity of liquids." B-type viscosity is the resistance torque when stirring the dispersion, and the higher the viscosity, the more energy is required for stirring.

[0153] If necessary, the carbamate-modified fine fibers are dispersed in an aqueous medium to form a dispersion (slurry). The aqueous medium is preferably entirely water, but an aqueous medium containing a part of another liquid compatible with water can also be used. Examples of the other liquid include lower alcohols having 3 or less carbon atoms.

[0154] The solid content of the slurry is preferably 0.1 to 10.0% by mass, more preferably 0.5 to 5.0% by mass. If the solid content is less than 0.1% by mass, excessive energy may be required for dehydration and drying. On the other hand, if the solid content is more than 10.0% by mass, the fluidity of the slurry itself may decrease, making it difficult to uniformly mix the dispersant. [Example]

[0155] Next, an embodiment of the present invention will be described. First, a predetermined sizing agent was added to the pulp slurry, and the resulting paper was made in the wire section to a predetermined Cobb sizing degree. The paper was then passed through the press section and pre-dryer section to produce a pulp sheet with a predetermined basis weight. Next, in the coater section, the pulp sheet was impregnated with a urea solution of a predetermined concentration, and then dried in the post-dryer section to obtain a urea-coated sheet.

[0156] The resulting urea-coated sheet was reacted in a roll-to-roll reactor at a predetermined drying temperature, reaction time, and residence time to obtain a carbamate sheet. The carbamate sheet was then diluted with water to a solids concentration of 5% using a disintegrator and disintegrated. The disintegrated carbamate pulp aqueous dispersion was dehydrated and washed twice. The washed carbamate pulp was defibrated in a refiner to a predetermined fineness value to obtain carbamate microfiber cellulose (fiber width 15 μm).

[0157] The carbamate group introduction rate (mmol / g) of each of the obtained carbamate-modified microfibrous celluloses was examined. The results are shown in Table 1. The moisture content of the sheet at the inlet of the drying section was 8% by mass, and the surface temperature was 20°C.

[0158] [Table 1] [Industrial Applicability]

[0159] The present invention can be used as a method for producing carbamate cellulose fibers. [Explanation of symbols]

[0160] 100 Paper making process 110 Wire Part 120 Press Part 130 Pre-dryer part 200 Coating process 210 Coater Part 220 After-drying part P1 Raw pulp P2 Cellulose fiber content P3 Carbamate cellulose fiber P4 Carbamate Microfiber X1 Papermaking and coating process X2 Carbamate formation process X3 Defibration process

Claims

1. In producing carbamate cellulose fibers in which some or all of the hydroxy groups of cellulose fibers have been modified with carbamate groups, a pulp sheet containing at least one of urea and a urea derivative formed into a strip shape by papermaking a raw material pulp, and the denaturation is carried out by this heating; The moisture content of the pulp sheet is 0.1 to 10% before the urea and / or the urea derivative is added. A method for producing carbamate cellulose fibers, comprising:

2. The pulp sheet containing at least one of the urea and the urea derivative is dried at 80 to 140°C to have the moisture content. A method for producing the carbamate cellulose fiber according to claim 1.

3. The pulp sheet containing at least one of urea and a urea derivative has a basis weight measured in accordance with JIS P 8124 of 60 to 800 g / m 2 . A method for producing the carbamate cellulose fiber according to claim 1 or 2.

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