Method for producing cellulose fiber water dispersion

Abstract

When a high-viscosity aqueous dispersion liquid of cellulose fibers is mixed with a liquid having a significantly different viscosity, such as water, mixing for a long time may be required until a uniform dispersion liquid is obtained SOLUTION: A method for producing a cellulose fiber water dispersion liquid, the method comprising a step of mixing a high-viscosity cellulose fiber dispersion liquid and water using a specific mixing apparatus, specifically one or a combination of two or more selected from the group consisting of a tornado stirrer, a stirrer with a mixing blade, a disper, a cornell disper, a concentric twin-screw mixer, and a planetary mixer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing an aqueous dispersion of fibrous cellulose. [Background technology]

[0002] In recent years, plant-derived cellulose fibers have attracted attention as a versatile material with low environmental impact. In particular, finely divided fibrous cellulose (also known as cellulose nanofibers) exhibits unique viscosity behavior in the form of aqueous dispersions, such as thixotropy, and is therefore sometimes provided as aqueous dispersions that can easily exhibit these properties.

[0003] For example, Patent Document 1 discloses an aqueous dispersion of cellulose nanofibers to which a sugar-type biosurfactant and a specific sugar-type surfactant have been added in order to enhance the thixotropy of the cellulose nanofibers. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-028203 Summary of the Invention [Problem to be solved by the invention]

[0005] Aqueous dispersions of fibrous cellulose may have high viscosity when left standing, depending on the content of fibrous cellulose, fiber width, etc. On the other hand, depending on the intended use, they may be further diluted with water before use for ease of handling. However, when an aqueous dispersion of fibrous cellulose is mixed with a liquid with a significantly different viscosity, such as water, it may take a long time to mix until a uniform dispersion is obtained. This problem is particularly pronounced when preparing fibrous cellulose dispersions in volumes of 1 L or more by dilution. [Means for solving the problem]

[0006] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by mixing a fibrous cellulose dispersion with water using a specific mixing device. [Effects of the Invention]

[0007] According to the production method of the present invention, a highly viscous aqueous dispersion of fibrous cellulose and a low-viscosity liquid such as water can be homogenized in a short period of time. DETAILED DESCRIPTION OF THE INVENTION

[0008] That is, the present invention provides the following <1> and <2> The present invention includes, but is not limited to, one embodiment of the present invention. <1> A method for producing an aqueous dispersion of fibrous cellulose, comprising the following steps (I) and (II) in this order: (I) A transfer step of transferring a fibrous cellulose aqueous dispersion having a viscosity of 1,000 Pa·s or more in a static state and water into the same container. (II) A mixing step of obtaining an aqueous dispersion of fibrous cellulose having a viscosity of 500 Pa·s or less at rest using a mixing device. <2> The method for producing an aqueous dispersion of fibrous cellulose, wherein the mixing device is one or a combination of two or more selected from the group consisting of a tornado mixer, a mixer with a mixing blade, a disper, a Cornell disper, a concentric twin-shaft mixer, and a planetary mixer.

[0009] <Transfer process> In the transfer step, the container into which the fibrous cellulose aqueous dispersion having a viscosity of 1,000 Pa·s or more in a stationary state and the water are transferred is not particularly limited, but is preferably a container having a capacity of 1 L or more, more preferably a container having a capacity of 30 L or more, and even more preferably a container having a capacity of 100 L or more.

[0010] The ratio of the weight of water to the weight of the fibrous cellulose aqueous dispersion having a viscosity of 1,000 Pa·s or more in a stationary state in the transfer step is not particularly limited, but the lower limit is, for example, 0.5, preferably 0.7, and the upper limit is, for example, 10, preferably 5.

[0011] The viscosity of the aqueous fibrous cellulose dispersion in a stationary state in the transfer step is not particularly limited as long as it is 1,000 Pa·s or more, but is preferably 2,000 Pa·s or more, and more preferably 4,000 Pa·s or more. The "viscosity of the aqueous fibrous cellulose dispersion in a stationary state" refers to the value measured when the fibrous cellulose dispersion is allowed to stand at 23°C for 24 hours and then rotated at 23°C at 3 rpm for 3 minutes using a Brookfield viscometer (LV-2T viscometer).

[0012] The content of fibrous cellulose in the aqueous dispersion of fibrous cellulose in the transfer step is, for example, 1% by weight or more and 10% by weight or less.

[0013] The aqueous dispersion of fibrous cellulose in the transfer step contains fibrous cellulose and water. The aqueous dispersion of fibrous cellulose in the transfer step may contain additives such as a water-dispersible organic solvent, a preservative, and a pH adjuster, as long as the aqueous dispersion has a viscosity of 1,000 Pa s or more when left standing.

[0014] The fiber width of the fibrous cellulose in the transporting step is, for example, 100 μm or less.

[0015] The number average fiber width of the fibrous cellulose in the transporting step is, for example, 100 μm or less.

[0016] The number average fiber width of the fibrous cellulose in the transport step can be measured in accordance with ISO 16065-2 or using an electron microscope.

[0017] The fiber length of the fine fibrous cellulose in the transport step is not particularly limited, but is, for example, 0.1 μm to 1000 μm, preferably 0.1 μm to 800 μm, and more preferably 0.1 μm to 600 μm. By keeping the fiber length within the above range, destruction of the crystalline regions of the fine fibrous cellulose can be suppressed.

[0018] The fiber length of the fibrous cellulose in the transport step can be determined by image analysis using, for example, TEM, SEM, or atomic force microscope (AFM).

[0019] The axial ratio (fiber length / fiber width) of the fibrous cellulose in the transfer step is not particularly limited, but is preferably 50 or more and 10,000 or less, more preferably 100 or more and 5,000 or less, for example.

[0020] The fibrous cellulose in the transfer step preferably has an ionic substituent. The ionic substituent may include, for example, either or both of an anionic group and a cationic group. In this embodiment, it is particularly preferable that the ionic substituent has an anionic group. Furthermore, the ionic substituent is preferably a group that is introduced into the fibrous cellulose via an ester bond or an ether bond, and more preferably a group that is introduced into the fibrous cellulose via an ester bond. In this case, the ester bond is preferably formed by dehydration condensation between the fibrous cellulose and a compound that becomes the ionic substituent.

[0021] Examples of the anionic group as the ionic group include a phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group (sometimes simply referred to as a phosphorus oxo acid group), a carboxy group or a substituent derived from a carboxy group (sometimes simply referred to as a carboxy group), a sulfur oxo acid group or a substituent derived from a sulfur oxo acid group (sometimes simply referred to as a sulfur oxo acid group), a xanthate group or a substituent derived from a xanthate group (sometimes simply referred to as a xanthate group), a phosphonic group or a substituent derived from a phosphonic group, a phosphine group or a substituent derived from a phosphine group, a sulfonic group or a substituent derived from a sulfonic group, and a carboxyalkyl group. Among these, the anionic group is preferably at least one selected from the group consisting of a phosphorus oxoacid group, a substituent derived from a phosphorus oxoacid group, a carboxy group, a sulfur oxoacid group, a substituent derived from a sulfur oxoacid group, a carboxymethyl group, a carboxyethyl group, and a sulfone group, more preferably at least one selected from the group consisting of a phosphorus oxoacid group, a substituent derived from a phosphorus oxoacid group, a carboxy group, a sulfur oxoacid group, and a substituent derived from a sulfur oxoacid group, and even more preferably a phosphorus oxoacid group. By introducing a phosphorus oxoacid group as the anionic group, the dispersibility of the fibrous cellulose can be further improved, for example, even under alkaline or acidic conditions.

[0022] More specifically, the phosphorus oxo acid group or the substituent derived from the phosphorus oxo acid group may be a phosphate group (-POH), a salt of the phosphate group, a phosphorous acid (phosphonic acid) group (-POH), or a salt of the phosphorous acid (phosphonic acid). The phosphorus oxo acid group or the substituent derived from the phosphorus oxo acid group may also be a group condensed with a phosphate group (e.g., a pyrophosphate group), a group condensed with a phosphonic acid (e.g., a polyphosphonic acid group), a phosphate ester group (e.g., a monomethyl phosphate group, a polyoxyethylene alkyl phosphate group), or an alkyl phosphonic acid group (e.g., a methyl phosphonic acid group).

[0023] The fibrous cellulose in the transporting step can be obtained by a production method including a defibration step of defibrating a fibrous raw material containing cellulose.

[0024] The cellulose-containing fiber raw material is not particularly limited, but pulp is preferably used because it is readily available and inexpensive. Examples of pulp include wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include, but are not limited to, chemical pulps such as hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), and oxygen-bleached kraft pulp (OKP), semi-chemical pulps such as semi-chemical pulp (SCP) and chemi-groundwood pulp (CGP), and mechanical pulps such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP).

[0025] In the defibration step, for example, a defibration treatment device can be used. The defibration treatment device is not particularly limited, but examples that can be used include a high-speed defibrator, a grinder (stone mill type grinder), a high-pressure homogenizer, an ultra-high-pressure homogenizer, a high-pressure collision type grinder, a ball mill, a bead mill, a disk type refiner, a conical refiner, a twin-screw kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, and a beater.

[0026] The fibrous cellulose in the transport step is preferably obtained by a production method further including an ionic substituent introduction step of introducing an ionic substituent into the cellulose-containing fiber raw material. Examples of the ionic substituent introduction step include a phosphorus oxo acid group introduction step, a carboxyl group introduction step, a sulfur oxo acid group introduction step, a xanthate group introduction step, a phosphonic or phosphine group introduction step, a sulfonic group introduction step, and a cationic group introduction step. <Mixing process>

[0027] As the mixing device in the mixing step, for example, a tornado agitator, an agitator with a mixing blade, a disper, a Cornell disper, a concentric twin-shaft mixer, or a planetary mixer can be used.

[0028] The tornado agitator is an agitator having at least one rotating shaft with a propeller-type agitating blade at the tip thereof, and an example thereof is PM-202 (manufactured by AS ONE Corporation).

[0029] The agitator with a mixing blade is an agitator having at least one rotating shaft and a disc portion at the tip thereof, and an agitator blade having shearing teeth arranged intermittently along the outer periphery of the disc portion and extending perpendicular to the surface of the disc portion, and an example of such an agitator is UT1305 (manufactured by Makita Corporation).

[0030] The disperser is a mixer having at least one rotating shaft and a disc portion at the tip thereof and a mixing blade (hereinafter referred to as a disperser blade) having shearing teeth arranged intermittently along the outer periphery of the disc portion and extending in the surface direction of the disc portion, and an example of such a mixer is the MH-200 (manufactured by Asada Iron Works Co., Ltd.).

[0031] The Cornell Disper is a mixer having at least two rotating shafts that rotate at different speeds, the first rotating shaft being a high-speed shaft with a disper blade at the tip, and the second rotating shaft being a low-speed shaft with a scraping blade that comes into contact with the side and / or bottom of the container, and an example of such a mixer is the MHK-7.5 (manufactured by Asada Iron Works Co., Ltd.).

[0032] A concentric twin-shaft mixer is a mixer that has at least one rotating shaft, a stirring shaft with a turbine blade-type stirring impeller at the tip, and a frame-type blade that rotates along the side and bottom of the container, and an example of such a mixer is CDM-200 (manufactured by Inoue Seisakusho Co., Ltd.).

[0033] A planetary mixer is a mixer having at least one rotating and revolving frame blade and / or twisted blade and at least one rotating shaft with a stirring blade at the tip, and examples include PD-50 (manufactured by Inoue Seisakusho Co., Ltd.) and PVM-50-2D (manufactured by Asada Iron Works Co., Ltd.).

[0034] When stirring is performed by a mixer in the mixing step, the rotation speed is, for example, 100 rpm or more and 5,000 rpm or less.

[0035] When stirring is performed using a mixer in the mixing step, the stirring time is, for example, 15 minutes or less.

[0036] The viscosity of the fibrous cellulose aqueous dispersion obtained in the mixing step in a static state is not particularly limited as long as it is 500 Pa·s or less, but is preferably 300 Pa·s or less, and more preferably 200 Pa·s or less.

[0037] The fibrous cellulose content of the fibrous cellulose aqueous dispersion obtained in the mixing step is, for example, 0.2% by weight or more and 4% by weight or less. [Example]

[0038] The features of the present invention will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0039] <Manufacturing example A> Softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m 2To 100 parts by mass (bone dry weight) of 700 mL of disintegrated sheet-form pulp (manufactured by Oji Paper Co., Ltd., Canada Standard Freeness (CSF) measured according to JIS P 8121-2:2012), a mixed aqueous solution of ammonium dihydrogen phosphate and urea was added to obtain a chemical-impregnated pulp containing 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water. The resulting chemical-impregnated pulp was then heated in a hot air dryer at 165°C for 250 seconds to introduce phosphate groups into the cellulose in the pulp, yielding a phosphorylated pulp. 10 L of ion-exchanged water was added to 100 g (bone dry weight) of phosphorylated pulp, and the mixture was stirred to uniformly disperse the pulp. The mixture was then filtered and dewatered until the electrical conductivity of the filtrate reached 100 μS / cm or less. The washed phosphorylated pulp was diluted with 10 L of ion-exchanged water, and then a 1 N aqueous solution of sodium hydroxide was added little by little while stirring to obtain a phosphorylated pulp slurry with a pH of 12 to 13. The phosphorylated pulp slurry was then dehydrated and washed to obtain a neutralized phosphorylated pulp.

[0040] Ion-exchanged water was added to the resulting phosphorylated pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was treated twice at a pressure of 150 MPa using a wet atomizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain fine fibrous cellulose dispersion A. The fiber width of the fine fibrous cellulose contained in fine fibrous cellulose dispersion A was measured using a transmission electron microscope and found to be 3 to 5 nm. Furthermore, the viscosity in a static state, measured by the method described in the "Viscosity Measurement" section below, was 4,000 Pa·s or more.

[0041] <Manufacturing example B> Ion-exchanged water was added to phosphorylated pulp obtained in the same manner as in Production Example A to prepare a slurry with a solids concentration of 3% by mass. This slurry was processed five times through a single-disc refiner with a clearance set to 75 μm to obtain fibrous cellulose dispersion B. The number-average fiber width of the fibrous cellulose contained in fibrous cellulose dispersion B was measured using a Valmet FS5 and found to be 20 μm. Furthermore, the viscosity in a stationary state, measured by the measurement method described in [Viscosity Measurement] below, was 4,000 Pa s or more.

[0042] Example 1 400 g of the fine fibrous cellulose aqueous dispersion A was placed in a 1 L plastic cup, and 440 g of ion-exchanged water was added. A tornado agitator (PM-202, AS ONE Corporation) was used as the mixing device, and a stirring blade with a diameter of 6 inches was attached. The mixture was stirred at 1000 rpm for 5 minutes to obtain diluted fibrous cellulose dispersion 1. The viscosity of the obtained fibrous cellulose dispersion 1, measured by the measurement method described in the "Viscosity Measurement" section below, was 160 Pa s.

[0043] <Example 2> 1.7 kg of the fibrous cellulose aqueous dispersion B was placed in a 30 L stainless steel tank, and 8.3 kg of ion-exchanged water was added. A mixing blade-equipped agitator (UT1305, manufactured by Makita Corporation) was used as the mixing device, and the mixture was stirred at 1,300 rpm for 5 minutes to obtain fibrous cellulose dispersion 2. The viscosity of the obtained fibrous cellulose dispersion 2, measured by the measurement method described in the "Viscosity Measurement" section below, was 2,500 mPa s.

[0044] Example 3 14 kg of the fine fibrous cellulose aqueous dispersion A was placed in a 40 L stainless steel tank, and 14 kg of ion-exchanged water was added. A mixing blade-equipped agitator (UT1305, manufactured by Makita Corporation) was used as the mixing device, and the mixture was stirred at 1,300 rpm for 5 minutes to obtain fibrous cellulose dispersion 3. The viscosity of the obtained fibrous cellulose dispersion 3, measured by the measurement method described in the "Viscosity Measurement" section below, was 160 Pa s.

[0045] Example 4 75 kg of the fine fibrous cellulose aqueous dispersion A was placed in a 200 L stainless steel tank, and 75 kg of ion-exchanged water was added. A Disper (MH-200, manufactured by Asada Iron Works Co., Ltd.) was used as a mixer, and the mixture was stirred at 900 rpm for 5 minutes to obtain fibrous cellulose dispersion 4. The viscosity of the obtained fibrous cellulose dispersion 4, measured by the measurement method described in the "Viscosity Measurement" section below, was 160 Pa s.

[0046] <Example 5> 75 kg of the fine fibrous cellulose aqueous dispersion A was placed in a 200 L stainless steel tank, and 75 kg of ion-exchanged water was added. A Cornell Disper (MHK-7.5, manufactured by Asada Iron Works Co., Ltd.) was used as a mixer, and the mixture was stirred for 10 minutes with the stirring shaft at 1,000 rpm and the scraping shaft at 10 rpm, to obtain Fibrous Cellulose Dispersion 5. The viscosity of the obtained Fibrous Cellulose Dispersion 5, measured by the method described in the "Viscosity Measurement" section below, was 160 mPa s.

[0047] Example 6 60 kg of the fine fibrous cellulose aqueous dispersion A was placed in a 200 L stainless steel tank, and 60 kg of ion-exchanged water was added. A concentric twin-shaft mixer (CDM-200, manufactured by Inoue Seisakusho Co., Ltd.) was used as the mixing device, and the mixture was stirred for 5 minutes at a high-speed shaft of 900 rpm and a low-speed shaft of 10 rpm, yielding fibrous cellulose dispersion 6. The viscosity of the obtained fibrous cellulose dispersion 6, measured by the method described in the "Viscosity Measurement" section below, was 160 mPa s.

[0048] Example 7 20 kg of the fine fibrous cellulose aqueous dispersion A was placed in a 57 L stainless steel tank, and 20 kg of ion-exchanged water was added. A planetary mixer (PLM-50, manufactured by Inoue Seisakusho Co., Ltd.) equipped with two twisted blades and one rotating shaft with a turbine blade-type stirring impeller at the tip was used as the mixing device. The mixture was stirred for 5 minutes at a twisted blade rotation speed of 20 rpm, a revolution speed of 30 rpm, and a stirring impeller rotation speed of 1,000 rpm, to obtain Fibrous Cellulose Dispersion 7. The viscosity of the obtained Fibrous Cellulose Dispersion 7, measured by the method described in the "Viscosity Measurement" section below, was 160 Pa s.

[0049] [Viscosity measurement] The fibrous cellulose dispersions 1 to 7 obtained in Examples 1 to 7 were allowed to stand at 23°C for 24 hours, and then their viscosities were measured using a B-type viscometer (LV-2T viscometer, manufactured by BLOOKFIELD Corp.) The measurement conditions were 23°C, and the viscosity was measured at a rotation speed of 0.3 rpm for the cellulose dispersions of Production Examples A and B, and at a rotation speed of 3 rpm for the fibrous cellulose dispersions of Examples 1 to 7, after rotating for 3 minutes.

Claims

1. A method for producing an aqueous dispersion of fibrous cellulose, comprising the following steps (I) and (II) in this order: (I) A transfer step of transferring a fibrous cellulose aqueous dispersion having a viscosity of 1,000 Pa·s or more in a static state and water into the same container. (II) A mixing step of obtaining an aqueous dispersion of fibrous cellulose having a viscosity of 500 Pa·s or less in a stationary state using a mixing device.

2. The method for producing an aqueous dispersion of fibrous cellulose, wherein the mixing device is one or a combination of two or more selected from the group consisting of a tornado mixer, a mixer with a mixing blade, a disper, a Cornell disper, a concentric twin-shaft mixer, and a planetary mixer.