JP2019184348A - Evaluation method of mixture liquid of dispersion liquid including rubber constituent and cellulose nanofiber dispersion liquid - Google Patents

Abstract

To provide an evaluation method capable of easily determining presence or absence of an aggregated cellulose nanofibers, which cannot be visually determined, in a mixture liquid comprising dispersion liquid of a rubber constituent and a cellulose nanofiber dispersion liquid.SOLUTION: Provided is an evaluation method, including steps (1) to (4), of a mixture liquid of a dispersion liquid including a rubber constituent and a cellulose nanofiber dispersion liquid. A step (1) prepares the mixture liquid of the dispersion liquid including the rubber constituent and the cellulose nanofiber dispersion liquid. A step (2) adds a colored pigment into the mixture liquid. A step (3) observes the mixture liquid, described in the step (1), added with the colored pigment using an optical microscope. A step (4) calculates area ratio of a cellulose nanofiber aggregate in the mixture liquid added with the colored pigment, described in the step (3), of the dispersion liquid including the rubber constituent and the cellulose nanofiber dispersion liquid.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for evaluating a mixed solution of a rubber component and a cellulose nanofiber dispersion.

A rubber composition containing a rubber component and cellulose nanofiber has low compatibility. Therefore, when mixing and stirring a dispersion of rubber components such as latex and cellulose nanofibers, cellulose nanofibers are difficult to uniformly disperse in the mixture, and when cellulose nanofibers aggregate together, physical properties of the rubber composition There has been a problem that the improvement effect cannot be obtained.
Therefore, when manufacturing the rubber composition, it is confirmed in advance that the cellulose nanofibers are uniformly dispersed in the mixed liquid of the rubber component and the cellulose nanofiber dispersion (no aggregate is formed). In order to improve the physical properties of the rubber, it is effective to remove the aggregates produced as necessary. However, since cellulose nanofibers are very thin fibers and have very high transparency, even if aggregates of cellulose nanofibers are present, they cannot be visually confirmed.

WO2016 / 133076

An object of the present invention is to provide an evaluation method that can easily determine the presence / absence of aggregates of cellulose nanofibers in a mixture of a rubber component dispersion and a cellulose nanofiber dispersion, which cannot be visually determined. .

The present invention provides the following [1] to [5].
[1] A method for evaluating a mixed liquid of a dispersion containing a rubber component and a cellulose nanofiber dispersion, comprising the following steps (1) to (3).
(1) The process of preparing the liquid mixture of the dispersion liquid containing a rubber component, and a cellulose nanofiber dispersion liquid.
(2) A step of adding a colored pigment to the mixed liquid of (1).
(3) The process of observing the cellulose nanofiber aggregate in the liquid mixture which added the colored pigment of (2) using an optical microscope.
[2] The method for evaluating a mixed liquid of the dispersion containing the rubber component according to [1] and the cellulose nanofiber dispersion, wherein the colored pigment has an average particle size of 10 μm or less.
[3] The rubber component according to [1] or [2], wherein the colored pigment dispersion is added to a mixture of a dispersion containing a rubber component and a cellulose nanofiber dispersion. The evaluation method of the liquid mixture of a dispersion liquid and a cellulose nanofiber dispersion liquid.
[4] A method for evaluating a mixed solution of a dispersion containing a rubber component and a cellulose nanofiber dispersion, which comprises the following steps 1) to 4):
1) The process of preparing the liquid mixture of the dispersion liquid containing a rubber component, and a cellulose nanofiber dispersion liquid.
2) The process of diluting the liquid mixture of 1) so that the solid content density | concentration of the said cellulose nanofiber may be 0.5%.
3) A step of adding a colored pigment to the mixed liquid of 2).
4) The mixed liquid added with the colored pigment of 3) is sandwiched between two glass plates to form a film thickness of 0.15 mm, observed with an optical microscope at a magnification of 100 times, and the area ratio is calculated by the following formula. Process.

Formula) Area of luminance distribution within luminance range ÷ Area of measurement range × 100

[5] A mixed liquid of a dispersion containing a rubber component and a cellulose nanofiber dispersion, wherein the area ratio of the cellulose nanofiber aggregate is 10% or less, evaluated by the method according to [4].

  According to the present invention, it is possible to visualize the degree of dispersion of cellulose nanofibers in latex before preparing a dry rubber product, and by calculating the area of cellulose nanofiber aggregates in the mixed solution, cellulose nanofibers are calculated. The degree of dispersion can be quantified.

The observation result by the optical microscope of the liquid mixture of the dispersion liquid containing the rubber component in Example 1 and a cellulose nanofiber dispersion liquid is shown. The observation result by the optical microscope of the liquid mixture of the dispersion liquid containing the rubber component in Example 2, and a cellulose nanofiber dispersion liquid is shown. The observation result by the optical microscope of the liquid mixture of the dispersion liquid containing the rubber component in Example 3 and a cellulose nanofiber dispersion liquid is shown. The observation result by the optical microscope of the liquid mixture of the dispersion liquid containing the rubber component in the comparative example 1 and a cellulose nanofiber dispersion liquid is shown.

The method for evaluating a cellulose nanofiber dispersion of the present invention includes (1) a step of preparing a mixture of a rubber component dispersion and a cellulose nanofiber dispersion, and (2) a step of adding a colored pigment to the mixture. (3) It has the process of observing the said liquid mixture which added the colored pigment with an optical microscope.
In the invention, the aggregate of cellulose nanofibers means a cellulose nanofiber network structure produced in a mixed solution with a rubber component. In any of these, the aggregate is filled with the solvent of the mixed solution, and is highly transparent in the visible light region and cannot be visually discriminated.
(Cellulose nanofiber)
In the present invention, the cellulose nanofiber is a fine fiber having a fiber width of about 4 to 500 nm and an aspect ratio of 100 or more, and chemical treatment (cationization, anionization: carboxylation (oxidation), carboxymethylation, etc.) It can be obtained by defibrating cellulose having a functional functional group introduced therein.

(Cellulose raw material)
Examples of cellulose raw materials for producing chemically modified cellulose include plant materials (for example, wood, bamboo, hemp, jute, kenaf, farmland waste, cloth, pulp (conifer unbleached kraft pulp (NUKP), conifer bleach). Kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP), softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP) thermomechanical pulp (TMP), regenerated pulp , Waste paper, etc.), animal materials (for example, ascidians), algae, microorganisms (for example, acetic acid bacteria (Acetobacter)), microbial products, etc., any of which can be used. Is a cellulose fiber derived from plants or microorganisms, more preferably derived from plants It is a cellulose fiber.
(Carboxymethylation)
In the present invention, when carboxymethylated cellulose is used as the chemically modified cellulose, the carboxymethylated cellulose may be obtained by carboxymethylating the above cellulose raw material by a known method, or a commercially available product is used. May be. In any case, it is preferable that the degree of carboxymethyl group substitution per anhydroglucose unit of cellulose is 0.01 to 0.50. The following method can be mentioned as an example of the method of manufacturing such carboxymethylated cellulose. Cellulose is used as a starting material, and water and / or lower alcohol 3 to 20 times as a solvent, specifically water, methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary A single solvent such as butanol or a mixed medium of two or more is used. In addition, the mixing ratio of the lower alcohol when mixing the lower alcohol is 60 to 95% by mass. As the mercerizing agent, 0.5 to 20 times moles of alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide is used per anhydroglucose residue of the bottoming material. A bottoming raw material, a solvent, and a mercerizing agent are mixed, and a mercerization treatment is performed at a reaction temperature of 0 to 70 ° C., preferably 10 to 60 ° C., and a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Thereafter, a carboxymethylating agent is added in an amount of 0.05 to 10.0 times mol per glucose residue, a reaction temperature of 30 to 90 ° C., preferably 40 to 80 ° C., and a reaction time of 30 minutes to 10 hours, preferably 1 hour. Perform etherification reaction for ~ 4 hours.
(Carboxylation)
In the present invention, when carboxylated (oxidized) cellulose is used as chemically modified cellulose, carboxylated cellulose (also referred to as oxidized cellulose) can be obtained by carboxylating (oxidizing) the above cellulose raw material by a known method. it can. Although not particularly limited, at the time of carboxylation, the amount of carboxyl groups should be adjusted to 0.6 to 2.0 mmol / g with respect to the absolute dry mass of anion-modified cellulose nanofibers. Is preferable, and it is more preferable to adjust so that it may become 1.0 mmol / g-2.0 mmol / g.
As an example of a carboxylation (oxidation) method, a cellulose raw material is oxidized in water using an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromide, iodide, or a mixture thereof. A method can be mentioned. By this oxidation reaction, the primary hydroxyl group at the C6 position of the glucopyranose ring on the cellulose surface is selectively oxidized, and the cellulose fiber having an aldehyde group and a carboxyl group (—COOH) or a carboxylate group (—COO—) on the surface. Can be obtained. The concentration of cellulose during the reaction is not particularly limited, but is preferably 5% by mass or less.
The N-oxyl compound refers to a compound that can generate a nitroxy radical. As the N-oxyl compound, any compound can be used as long as it promotes the target oxidation reaction. For example, 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) and its derivative (for example, 4-hydroxy TEMPO) are mentioned. The amount of the N-oxyl compound used is not particularly limited as long as it is a catalytic amount capable of oxidizing cellulose as a raw material. For example, 0.01 to 10 mmol is preferable, 0.01 to 1 mmol is more preferable, and 0.05 to 0.5 mmol is more preferable with respect to 1 g of absolutely dry cellulose. Moreover, about 0.1-4 mmol / L with respect to a reaction system is good.
Bromide is a compound containing bromine, examples of which include alkali metal bromides that can dissociate and ionize in water. Further, an iodide is a compound containing iodine, and examples thereof include alkali metal iodide. The amount of bromide or iodide used can be selected as long as the oxidation reaction can be promoted. The total amount of bromide and iodide is, for example, preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, and still more preferably 0.5 to 5 mmol with respect to 1 g of absolutely dry cellulose.
As the oxidizing agent, known ones can be used, and for example, halogen, hypohalous acid, halous acid, perhalogen acid or salts thereof, halogen oxide, peroxide and the like can be used. Of these, sodium hypochlorite is preferable because it is inexpensive and has a low environmental impact. The appropriate amount of the oxidizing agent used is, for example, preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, further preferably 1 to 25 mmol, and most preferably 3 to 10 mmol with respect to 1 g of absolutely dry cellulose. . For example, 1-40 mol is preferable with respect to 1 mol of N-oxyl compounds.
The cellulose oxidation process allows the reaction to proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature is preferably 4 to 40 ° C, and may be room temperature of about 15 to 30 ° C. As the reaction proceeds, a carboxyl group is generated in the cellulose, so that the pH of the reaction solution is reduced. In order to advance the oxidation reaction efficiently, an alkaline solution such as an aqueous sodium hydroxide solution is added to maintain the pH of the reaction solution at about 8 to 12, preferably about 10 to 11. The reaction medium is preferably water because it is easy to handle and hardly causes side reactions.
The reaction time in the oxidation reaction can be appropriately set according to the degree of progress of oxidation, and is usually 0.5 to 6 hours, for example, about 0.5 to 4 hours.
The oxidation reaction may be performed in two stages. For example, by oxidizing the oxidized cellulose obtained by filtration after the completion of the first-stage reaction again under the same or different reaction conditions, the efficiency is not affected by the reaction inhibition by the salt generated as a by-product in the first-stage reaction. Can be oxidized well.
Another example of the carboxylation (oxidation) method is a method of oxidizing by contacting a gas containing ozone and a cellulose raw material. By this oxidation reaction, at least the hydroxyl groups at the 2nd and 6th positions of the glucopyranose ring are oxidized and the cellulose chain is decomposed. The ozone concentration in the gas containing ozone is preferably 50 to 250 g / m 3, and more preferably 50 to 220 g / m 3. The amount of ozone added to the cellulose raw material is preferably 0.1 to 30 parts by mass, and more preferably 5 to 30 parts by mass when the solid content of the cellulose raw material is 100 parts by mass. The ozone treatment temperature is preferably 0 to 50 ° C, and more preferably 20 to 50 ° C. The ozone treatment time is not particularly limited, but is about 1 to 360 minutes, and preferably about 30 to 360 minutes. When the conditions for the ozone treatment are within these ranges, the cellulose can be prevented from being excessively oxidized and decomposed, and the yield of oxidized cellulose is improved. After the ozone treatment, an additional oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used for the additional oxidation treatment is not particularly limited, and examples thereof include chlorine compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. For example, these oxidizing agents can be dissolved in a polar organic solvent such as water or alcohol to prepare an oxidizing agent solution, and a cellulose raw material can be immersed in the solution for additional oxidation treatment.
The amount of carboxyl groups in the oxidized cellulose can be adjusted by controlling the reaction conditions such as the added amount of the oxidizing agent and the reaction time.
(Cationization)
In the present invention, when carboxylated (oxidized) cellulose is used as the chemically modified cellulose, cationization such as glycidyltrimethylammonium chloride, 3-chloro-2hydroxypropyltrialkylammonium hydride or its halohydrin type is used as the cellulose raw material. A cation-modified cellulose can be obtained by reacting an agent and an alkali metal hydroxide (such as sodium hydroxide or potassium hydroxide) in the presence of water and / or an alcohol having 1 to 4 carbon atoms. . In this method, the cation substitution degree per glucose unit of the cation-modified cellulose obtained is controlled by the amount of the cationizing agent to be reacted, the composition ratio of water and / or alcohol having 1 to 4 carbon atoms. Can be adjusted.
The degree of cation substitution per glucose unit in the cation-modified cellulose is preferably 0.02 to 0.50. By introducing a cationic substituent into cellulose, the celluloses repel each other electrically. For this reason, the cellulose which introduce | transduced the cation substituent can be nano-defibrated easily. In addition, when the cation substitution degree per glucose unit is smaller than 0.02, nano-fibrosis cannot be sufficiently performed. On the other hand, if the degree of cation substitution per glucose unit is more than 0.50, it may swell or dissolve, and may not be obtained as a nanofiber. In order to efficiently perform defibration, it is preferable that the oxidized cellulose-based material obtained above is washed.
(Esterification)
In this invention, when using the cellulose which introduce | transduced the phosphoric acid group as a chemically modified cellulose, as a compound which has a phosphoric acid group in a cellulose raw material, phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, phosphoric acid Trisodium, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid Examples include triammonium, ammonium pyrophosphate, and ammonium metaphosphate. These may be used alone or in combination of two or more to introduce a phosphate group. The ratio of the compound having a phosphate group to the cellulose raw material is preferably 0.1 to 500 parts by mass, and 1 to 400 parts by mass in terms of the amount of phosphorus converted to 100 parts by mass of the solid content of the cellulose raw material. More preferably, it is 2 to 200 parts by mass.
(Defibration)
There are no particular limitations on the apparatus used to fibrillate the anion-modified cellulose, but apparatuses such as a high-speed rotation type, a colloid mill type, a high-pressure type, a roll mill type, and an ultrasonic type can be used. In defibration, it is preferable to apply a strong shearing force to the aqueous dispersion of anion-modified cellulose. In particular, for efficient defibration, it is preferable to use a wet high-pressure or ultrahigh-pressure homogenizer that can apply a pressure of 50 MPa or more to the aqueous dispersion and can apply a strong shearing force. The pressure is more preferably 100 MPa or more, and further preferably 140 MPa or more. In addition, prior to defibration and dispersion treatment with a high-pressure homogenizer, if necessary, the aqueous dispersion may be pretreated using a known mixing, stirring, emulsifying, and dispersing device such as a high-speed shear mixer. Good.
(Rubber component)
The rubber component in the present invention is a component having an organic polymer as a main component and having a high elastic limit and a low elastic modulus. The rubber component is roughly classified into natural rubber and synthetic rubber, and any of them may be used in the present invention, or both may be combined. Natural rubber may be natural rubber in a narrow sense without chemical modification, and natural rubber such as chlorinated natural rubber, chlorosulfonated natural rubber, epoxidized natural rubber, hydrogenated natural rubber, and deproteinized natural rubber. Are chemically modified. Examples of the synthetic rubber include butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), isoprene rubber (IR), butyl rubber (IIR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), styrene- Diene rubber such as isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, isoprene-butadiene copolymer rubber, ethylene-propylene rubber (EPM, EPDM), acrylic rubber (ACM), epichlorohydrin rubber ( CO, ECO), fluorine rubber (FKM), silicone rubber (Q), urethane rubber (U), and chlorosulfonated polyethylene (CSM).
(Mixture of rubber component dispersion and cellulose nanofiber dispersion)
The mixture of the rubber component dispersion and the cellulose nanofiber dispersion in the present invention is obtained by mixing and stirring the cellulose nanofibers in the rubber component dispersion. The liquid mixture is mainly used as a raw material for a masterbatch for producing a rubber composition. In order to improve the strength of the rubber composition, it is important that the cellulose nanofibers are uniformly dispersed in the mixed solution.
(Colored pigment)
In the present invention, the colored pigment is a pigment having a color such as white, black, blue, red, yellow, green, etc., and the shape is not particularly limited and can be used without any particular limitation such as a plate shape, a spherical shape, or a scale shape. For example, carbon black, iron black, composite metal oxide black, zinc chromate, lead chromate, red lead, zinc phosphate, vanadium phosphate, calcium phosphate, aluminum phosphomolybdate, calcium molybdate, aluminum tripolyphosphate, bismuth oxide , Bismuth hydroxide, basic bismuth carbonate, bismuth nitrate, bismuth silicate, hydrotalcite, zinc dust, mica-like iron oxide, calcium carbonate, barium sulfate, alumina white, silica, diatomaceous earth, kaolin, talc, clay, mica , Barita, organic bentonite, white carbon, titanium oxide, zinc oxide, antimony oxide, lithopone, lead white, perylene black, molybdenum red, cadmium red, bengara, cerium sulfide, yellow lead, cadmium yellow, yellow iron oxide, ocher, bismuth Rho, Shena, Amber, Green clay, Mars violet, Ultramarine, Bitumen, Basic lead sulfate, Basic lead silicate, Zinc sulfide, Antimony trioxide, Calcium composite, Phthalocyanine blue, Phthalocyanine green, Ocher, Aluminum powder, Copper Powder, brass powder, stainless steel powder, titanium oxide coated mica, iron oxide coated mica, zinc copper oxide, silver particles, anatase type titanium oxide, iron oxide-based fired pigment, conductive metal powder, electromagnetic wave absorbing ferrite and other inorganic pigments; quinacridone Red, polyazo yellow, anthraquinone red, anthraquinone yellow, polyazo red, azo lake yellow, berylene, phthalocyanine blue, phthalocyanine green, isoindolinone yellow, watching red, permanent red, para red, toluidine maroon, benzy Emissions yellow, fast sky blue, singly or two or more mixtures of the organic pigments, such as Brilliant Carmine 6B and the like.
The average particle diameter of the colored pigment is 10 μm or less, preferably 0.01 to 10 μm, more preferably 0.01 to 1 μm. By using a pigment of 10 μm or less, preferably 1 μm or less, the dispersibility of the colored pigment is stabilized in the cellulose nanofiber dispersion, so that the evaluation becomes easy. On the other hand, although there is no restriction on the lower limit value, if the average particle size is smaller than 0.01 μm, it is considered that the aggregate cannot be observed with an optical microscope because a colored pigment may enter the aggregate.
In the present invention, it is preferable to add a colored pigment dispersion obtained by stably dispersing a colored pigment in an aqueous solvent using a dispersant or the like to a mixture of a rubber component dispersion and a cellulose nanofiber dispersion. By using a colored pigment dispersion, observation with an optical microscope becomes easy.
Examples of the aqueous solvent include water, methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary butanol, linear or branched pentanediol, aliphatic ketones (for example, acetone, methyl ethyl ketone, diacetone). Alcohols), polyols (eg, ethylene glycol, diethylene glycol, triethylene glycol, etc.), polyglycols having a molar mass of 200-2000 g / mol, propylene glycol, dipropylene glycol, tripropylene glycol, trimethylolpropane, glycerol, thio Diglycol, 2-pyrrolidone, N-methylpyrrolidone, N-ethylpyrrolidone, 1,3-dimethylimidazolidinone, dimethylacetamide, and dimethyl Alone such as formamide, or a mixture of two or more medium.
Examples of the dispersant include higher fatty acid, higher fatty acid amide, metal soap, glycerin ester, hydrotalcite, polyethylene wax, polypropylene wax, glue, gelatin and the like, or a mixture of two or more kinds.
Moreover, although content of the colored pigment in a colored pigment dispersion liquid is not limited, It is preferable that it is about 5 to 20 weight%. When the content of the colored pigment is small, the observation photograph of the optical microscope becomes light. On the other hand, when the content of the colored pigment is large, aggregates of the colored pigment may be generated. In the present invention, the colored pigment has clear brightness and darkness when observed with an optical microscope, has a good color that hardly transmits light (is easy to absorb light), and is preferably black. Moreover, what does not produce aggregation by secondary aggregation or interaction with a cellulose nanofiber during observation is preferable. For example, black ink, pigment ink for an ink jet printer, or the like can be used as the colored pigment dispersion.
Black ink is a surface-treated carbon black whose surface is coated with a water-based resin, exhibits excellent dispersibility when mixed with a binder resin, and is difficult to secondary agglomerate. Even a dispersion can exhibit sufficiently high blackness. Ink drops are an aqueous dispersion containing surface-treated carbon black. For example, the surface of an irregular furnace black produced by the furnace method in which petroleum or coal-based oil is incompletely burned in a high-temperature gas is used as an aqueous dispersion. It is manufactured by coating with resin, adding a glycol-based antifreezing agent and preservative as necessary, and mixing and slurrying. As the ink drops, for example, commercially available ink (for example, “ink drops” manufactured by Kuretake Co., Ltd.) can be used. The surface-treated carbon black or an aqueous dispersion thereof can be prepared based on a known method (for example, JP-A-7-188597 and JP-A-6-234946). Ink juice, pigment inks for ink jet printers and the like may be used alone or in combination of two or more.
(Observation with an optical microscope)
In the present invention, the concentration of the cellulose nanofiber dispersion is not particularly limited, but is about 0.01 to 10% by mass, preferably about 0.1 to 2% by mass. When the concentration is low, the amount of agglomerates is reduced. On the other hand, when the concentration is high, the viscosity is high and it is difficult to disperse the colored pigment, so that the observation accuracy decreases.
In the present invention, an optical microscope that uses a mixed liquid of a dispersion of a rubber component to which a colored pigment is added and a cellulose nanofiber dispersion is not particularly limited, and a general optical microscope (including a microscope) is used. ) Can be used. Moreover, the magnification at the time of observing a cellulose nanofiber dispersion liquid with an optical microscope is not specifically limited, However, It is preferable that it is 50 to 1000 times.
(Measurement of area ratio)
In the observation with the optical microscope of the present invention, a method for quantitatively evaluating the dispersibility of the cellulose nanofiber aggregate includes a method of calculating the area ratio of the aggregate.
Dilute with pure water so that the solids concentration of cellulose nanofibers in the mixture of the dispersion containing the rubber component and the cellulose nanofiber dispersion is 0.5%. 2 drops of 10%), vortex mixer (manufactured by IUCHI, instrument name: Automatic Lab-mixer HM-10H) is set to the maximum rotation speed scale, and stirred for 30 seconds. Next, a mixture of natural rubber latex containing black ink droplets and cellulose nanofiber dispersion is sandwiched between two glass plates so that the film thickness becomes 0.15 mm, and an optical microscope (including a microscope) is used. Observe at a magnification of 100 times.
The area ratio of the cellulose nanofiber aggregate is measured by using the area measurement mode of the luminance extraction region of the digital microscope VHX-2000 manufactured by KEYENCE. Specifically, this is a method of setting the luminance range of the cellulose nanofiber aggregate, extracting a region within the luminance range, and calculating the area of the luminance distribution. Details are described on pages 9-26 of the user's manual of the digital microscope VHX-2000 manufactured by KEYENCE. The luminance range of the cellulose nanofiber aggregate is preferably 180 to 260.
The area ratio is expressed by the following formula.

Formula) Area of luminance distribution within luminance range ÷ Area of measurement range × 100

The area ratio of the cellulose nanofiber aggregate is preferably 10.0% or less. 5.0% or less is more preferable, and 1.0% or less is more preferable.

<Manufacture of cellulose nanofiber dispersion>
Add 500 g of bleached unbeaten kraft pulp derived from conifers (whiteness 85%) (absolutely dry) to 500 ml of an aqueous solution in which 780 mg of TEMPO (Sigma Aldrich) and 75.5 g of sodium bromide are dissolved, until the pulp is uniformly dispersed Stir. An aqueous sodium hypochlorite solution was added to the reaction system to 6.0 mmol / g to initiate the oxidation reaction. During the reaction, the pH in the system was lowered, but 3M aqueous sodium hydroxide solution was successively added to adjust the pH to 10. The reaction was terminated when sodium hypochlorite was consumed and the pH in the system no longer changed. The reaction mixture was filtered through a glass filter to separate the pulp, and the pulp was sufficiently washed with water to obtain oxidized pulp (carboxylated cellulose). The pulp yield at this time was 90%, the time required for the oxidation reaction was 90 minutes, and the amount of carboxyl groups was 1.6 mmol / g.

  The oxidized pulp obtained in the above process was adjusted to 1.0% (w / v) with water, treated with an ultra-high pressure homogenizer (20 ° C., 150 Mpa) three times, and carboxylated cellulose nanofiber (TEMPO oxidized cellulose). Nanofiber) dispersion was obtained. The obtained fiber had an average fiber diameter of 4 nm and an aspect ratio of 150.

(Method for measuring the amount of carboxyl groups)
Prepare 60 ml of 0.5% by weight slurry (aqueous dispersion) of carboxylated cellulose, add 0.1 M hydrochloric acid aqueous solution to pH 2.5, then add 0.05 N aqueous sodium hydroxide solution dropwise to adjust the pH to 11 The electrical conductivity was measured until the amount of sodium hydroxide consumed in the neutralization stage of the weak acid with a slow change in electrical conductivity (a) was calculated using the following formula: g carboxylated cellulose] = a [ml] × 0.05 / carboxylated cellulose mass [g].

(Measuring method of average fiber diameter and aspect ratio)
The average fiber diameter and average fiber length of the carboxylated cellulose nanofibers were analyzed for 200 fibers selected at random using an atomic force electron microscope (AFM). The aspect ratio was calculated by the following formula:
Aspect ratio = average fiber length / average fiber diameter
[Example 1]
As the cellulose nanofiber, TEMPO oxidized cellulose nanofiber (carboxyl group amount: 1.6 mmol / g, average fiber diameter: 4 nm, aspect ratio: 150) was used.
As a rubber component, 154 g of natural rubber latex (trade name: HA Latex, Restex, solid concentration 65%) and 500 g of TEMPO oxidized cellulose nanofiber solid concentration 1% aqueous dispersion are added to the Hi-Flex Homogenizer (manufactured by SMT). The mixture was stirred for 1 minute at a rotational speed of 6000 rpm to obtain a mixed solution of the rubber component dispersion and the cellulose nanofiber dispersion (solid concentration of cellulose nanofibers 0.8%).
10 g of the obtained mixed solution was diluted with pure water so that the solid content concentration of TEMPO-oxidized cellulose nanofibers was 0.5%, and 2 drops of ink drops (made by Kuretake Co., Ltd., 10% solid content) were dripped, and vortexed. The rotation speed scale of the mixer (IUCHI, device name: Automatic Lab-mixer HM-10H) was set to the maximum and stirred for 30 seconds. Next, a mixture of a natural rubber latex containing black ink droplets and a cellulose nanofiber dispersion was sandwiched between two glass plates, and observed at 100 times magnification using an optical microscope so that the film thickness was 0.15 mm. .
For observation with an optical microscope, a digital microscope VHX-2000 manufactured by KEYENCE was used. By observation, an image of 2500 μm in length × 3400 μm in width was obtained. Using the area measurement mode of the luminance extraction area, set the luminance range to 180-260, extract the area within the luminance range, calculate the area of the cellulose nanofiber luminance distribution per image, The area ratio of the cellulose nanofiber aggregate per sheet was measured. The results are shown in FIG. The area ratio of the cellulose nanofiber aggregates in the observation range was 4.6%.
[Example 2]
When stirring the liquid mixture of the natural rubber latex and the cellulose nanofiber dispersion, the stirring time was changed to 10 minutes.
The obtained mixture was observed using the same method as in Example 1. The results are shown in FIG. The gel particle area ratio in the observation range was 0.6%.
[Example 3]
When stirring the liquid mixture of the natural rubber latex and the cellulose nanofiber dispersion, the number of rotations was changed to 1000 rpm, and the mixture was stirred for 1 minute.
The obtained mixture was observed using the same method as in Example 1. The results are shown in FIG. The gel particle area ratio in the observation range was 21.5%.
[Comparative Example 1]
The ink mixture was observed with an optical microscope without dropping ink drops on the mixed solution used in Example 1. The results are shown in FIG.
<Result>
In the observation results of the mixed liquid containing aggregates (FIGS. 1 and 4), a difference depending on the presence or absence of ink drops was observed. From this result, it was clarified that the presence or absence of aggregates in the mixed liquid, which was difficult in the past, can be easily determined by observing the mixed liquid to which the ink drop is added with an optical microscope.

Claims (5)

The evaluation method of the liquid mixture of the dispersion liquid containing a rubber component, and a cellulose nanofiber dispersion liquid which has the process of following (1)-(3).
(1) The process of preparing the liquid mixture of the dispersion liquid containing a rubber component, and a cellulose nanofiber dispersion liquid.
(2) A step of adding a colored pigment to the mixed liquid of (1).
(3) The process of observing the cellulose nanofiber aggregate in the liquid mixture which added the colored pigment of (2) using an optical microscope.   2. The method for evaluating a mixed liquid of a dispersion containing a rubber component and a cellulose nanofiber dispersion according to claim 1, wherein an average particle diameter of the colored pigment is 10 [mu] m or less.   The dispersion containing a rubber component according to claim 1 or 2, wherein the colored pigment dispersion is added to a mixture of a dispersion containing a rubber component and a cellulose nanofiber dispersion. Evaluation method of mixed liquid with fiber dispersion. The evaluation method of the liquid mixture of the dispersion liquid containing a rubber component, and a cellulose nanofiber dispersion liquid which has the process of following 1) -4).
1) The process of preparing the liquid mixture of the dispersion liquid containing a rubber component, and a cellulose nanofiber dispersion liquid.
2) The process of diluting the liquid mixture of 1) so that the solid content density | concentration of the said cellulose nanofiber may be 0.5%.
3) A step of adding a colored pigment to the mixed liquid of 2).
4) The mixed liquid added with the colored pigment of 3) is sandwiched between two glass plates to form a film thickness of 0.15 mm, observed with an optical microscope at a magnification of 100 times, and the area ratio is calculated by the following formula. Process.

Formula) Area of luminance distribution within luminance range ÷ Area of measurement range × 100
  A mixed liquid of a dispersion containing a rubber component and a cellulose nanofiber dispersion, wherein the area ratio of the cellulose nanofiber aggregate is 10% or less, evaluated by the method according to claim 4.

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