Antifreeze

Abstract

To provide a viscosity modifier for antifreezes that is added to a liquid antifreeze, exhibiting superior drip inhibition and applicability.SOLUTION: A viscosity modifier for antifreezes contains cellulose fine fibers.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a viscosity modifier for an antifreeze containing cellulose microfibers and an antifreeze containing the same.

Background Art

[0002] Conventional liquid antifreezes are aqueous solutions selected from acetate, formate, urea, chloride, and low molecular weight alcohols, which have a low viscosity similar to water or low molecular weight alcohols, and are generally used to prevent the freezing of road surfaces in winter.

[0003] Also, in order to prevent icing on outdoor structures and outdoor moving objects or to prevent outdoor structures and outdoor moving objects from freezing, a liquid antifreeze is applied or sprayed onto outdoor structures and outdoor moving objects.

[0004] Conventional liquid antifreezes have a low viscosity, so even when applied or sprayed onto outdoor structures and outdoor moving objects, they flow off and cannot sufficiently exhibit an antifreeze effect.

[0005] In order to solve such problems, in Patent Document 1, a water-soluble polymer is contained in a liquid antifreeze to impart viscosity.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in addition to the liquid antifreeze containing a water-soluble polymer described in Patent Document 1, there was a need for a liquid antifreeze that was even less prone to dripping. In particular, there was a need for one that was easy to spread with a brush and that did not drip after application.

[0008] Therefore, the present invention aims to provide a viscosity modifier for liquid antifreeze agents that, when added to the antifreeze agent, exhibits superior drip suppression and application properties, as well as an antifreeze agent containing this viscosity modifier. [Means for solving the problem]

[0009] The present invention provides the following: (1) A viscosity modifier for antifreeze containing cellulose microfibers. (2) The viscosity modifier for antifreeze according to (1), wherein the cellulose microfibers are anionically modified. (3) An antifreeze containing the viscosity modifier for antifreeze described in (1) or (2). (4) The antifreeze according to (3), wherein the viscosity modifier for the antifreeze is contained in an amount of 0.5 to 1.5% of the solid content of the cellulose microfibers relative to the total mass of the antifreeze. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a viscosity modifier for antifreeze agents that exhibits excellent drip suppression and application properties when added to liquid antifreeze agents, and an antifreeze agent containing this viscosity modifier. [Modes for carrying out the invention]

[0011] The viscosity modifier for antifreeze agents of the present invention will be described below. In the present invention, "~" includes the endpoints. That is, "X~Y" includes the values ​​X and Y at both ends.

[0012] The viscosity modifier for antifreeze agents of the present invention contains cellulose microfibers.

[0013] (Cellulose microfibers) The cellulose microfibers used in this invention are microfibers made from cellulose, and their average fiber diameter is not particularly limited, but is generally around 3 nm to 500 nm, and they are generally distinguished by their fiber diameter. The average fiber diameter and average fiber length of the cellulose microfibers can be obtained by averaging the fiber diameter and fiber length obtained from observing each fiber using an ABB fiber tester, a Valmet fractionator, a scanning electron microscope (SEM), an atomic force microscope (AFM), or a transmission electron microscope (TEM), which are appropriately selected according to the size of the fiber diameter. Cellulose microfibers can be produced by defibrillating cellulose.

[0014] The average aspect ratio of the cellulose microfibers used in this invention is preferably 10 or more, more preferably 15 or more, and even more preferably 20 or more. There is no particular upper limit to the aspect ratio, but it is preferably 1000 or less, more preferably 100 or less, and even more preferably 80 or less. The average aspect ratio can be calculated using the following formula: Aspect ratio = average fiber length / average fiber diameter

[0015] The cellulose raw material is not particularly limited as long as it contains cellulose, but examples include plants (e.g., wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (unbleached coniferous kraft pulp (NUKP), bleached coniferous kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), bleached hardwood kraft pulp (LBKP), bleached kraft pulp (BKP), unbleached coniferous sulfite pulp (NUSP), bleached coniferous sulfite pulp (NBSP), thermomechanical pulp (TMP), recycled pulp, waste paper, etc.), animals (e.g., sea squirts), algae, microorganisms (e.g., acetic acid bacteria (Acetobacter)), microbial products, etc. The cellulose raw material may be any one of these or a combination of two or more, but it is preferably a cellulose raw material derived from plants or microorganisms (e.g., cellulose fibers), and more preferably a cellulose raw material derived from plants (e.g., cellulose fibers).

[0016] Cellulose has three hydroxyl groups per glucose unit, and can be subjected to various chemical modifications. In the present invention, from the viewpoint of promoting the progression of defibration, it is preferable to use chemically modified cellulose fine fibers produced by defibrating a cellulose raw material (chemically modified cellulose) obtained by chemical modification.

[0017] As for chemical modification, anionic modification, which introduces anionic groups into cellulose, is preferred. Specifically, anionic modification involves introducing anionic groups into the pyranose ring by oxidation or substitution reactions. In this invention, the oxidation reaction refers to a reaction in which the hydroxyl group of the pyranose ring is directly oxidized to a carboxyl group. In this invention, a substitution reaction refers to a reaction in which anionic groups are introduced into the pyranose ring by a substitution reaction other than the oxidation described above. Examples of anionic modification include oxidation (carboxylation), carboxymethylation, and esterification. Among these, oxidation (carboxylation) and carboxymethylation are more preferred.

[0018] (chemical modification) (oxidation) As anionically modified cellulose, oxidized (carboxylated) cellulose can be used. Oxidized cellulose (also called "carboxylated cellulose") can be obtained by oxidizing (carboxylating) the above-mentioned cellulose raw material by a known method. Although not particularly limited, the amount of carboxyl groups is preferably 0.6 to 3.0 mmol / g, and more preferably 1.0 to 2.0 mmol / g, relative to the oven-dry mass of the anionically modified cellulose. As an example of an oxidation (carboxylation) method, the cellulose raw material can be 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, and mixtures thereof. This oxidation reaction selectively oxidizes the primary hydroxyl group at the C6 position of the glucopyranose ring on the surface of the cellulose, resulting in the formation of an aldehyde group and a carboxyl group (-COOH) or carboxylate group (-COOH) on the surface. ―Cellulose fibers having [specific content] can be obtained. The concentration of cellulose during the reaction is not particularly limited, but preferably 5% by mass or less.

[0019] The N - oxyl compound refers to a compound that can generate a nitroxyl radical. As the N - oxyl compound, any compound can be used as long as it can promote the target oxidation reaction. For example, 2,2,6,6 - tetramethylpiperidine - 1 - oxyl radical (TEMPO) and its derivatives (e.g., 4 - hydroxy TEMPO) can be mentioned. The usage amount of the N - oxyl compound only needs to be a catalytic amount capable of oxidizing the cellulose raw material and is not particularly limited. For example, for 1 g of absolutely dry cellulose raw material, 0.01 - 10 mmol is preferable, 0.01 - 1 mmol is more preferable, and 0.01 - 0.5 mmol is even more preferable. Also, about 0.1 - 4 mmol / L is good for the reaction system.

[0020] The bromide is a compound containing bromine, and its examples include alkali metal bromides that can dissociate and ionize in water. Also, the iodide is a compound containing iodine, and its examples include alkali metal iodides. The usage amount of the bromide or iodide can be selected within the range capable of promoting the oxidation reaction. The total amount of the bromide and iodide is, for example, preferably 0.1 - 100 mmol, more preferably 0.1 - 10 mmol, and even more preferably 0.5 - 5 mmol with respect to 1 g of absolutely dry cellulose raw material. The modification is a modification by an oxidation reaction.

[0021] As the oxidizing agent, known ones can be used. For example, halogen, hypohalogenous acid, halogenous acid, perhalogenous acid or their salts, halogen oxides, peroxides, etc. can be used. Among them, sodium hypochlorite, which is inexpensive and has a low environmental load, is preferable. The appropriate usage amount of the oxidizing agent is, for example, preferably 0.5 - 500 mmol, more preferably 0.5 - 50 mmol, and even more preferably 2.5 - 25 mmol with respect to 1 g of absolutely dry cellulose raw material. Also, for example, 1 - 40 mol is preferable with respect to 1 mol of the N - oxyl compound.

[0022] The oxidation process of the cellulose raw material can proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature is preferably 4 to 40 °C, and it may also be at room temperature of about 15 to 30 °C. As carboxyl groups are generated in the cellulose during the reaction, the pH of the reaction solution decreases. In order to efficiently proceed the oxidation reaction, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to the reaction system as needed to maintain the pH of the reaction solution at 9 to 12, preferably about 10 to 11. The reaction medium is preferably water in terms of ease of handling and difficulty of side reactions occurring. 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.

[0023] Also, the oxidation reaction may be carried out in two steps. For example, by oxidizing the oxidized cellulose obtained by filtration after the completion of the first-step reaction again under the same or different reaction conditions, carboxyl groups can be efficiently introduced into the cellulose raw material without being inhibited by the salts by-produced in the first-step reaction.

[0024] As another example of the oxidation (carboxylation) method, a method of oxidizing by ozone treatment can be mentioned. In the present invention, it is preferable to use TEMPO-oxidized cellulose microfibrils obtained by defibrating the oxidized cellulose obtained by the method of oxidizing with TEMPO (TEMPO oxidation).

[0025] The amount of carboxyl groups relative to the absolute dry mass of the cellulose microfibrils contained in the oxidized cellulose microfibrils obtained by modifying the cellulose raw material by oxidation is preferably 0.6 mmol / g or more, more preferably 0.8 mmol / g or more, and still more preferably 1.0 mmol / g or more. The upper limit is preferably 2.2 mmol / g or less, more preferably 2.0 mmol / g or less, and still more preferably 1.8 mmol / g or less. Therefore, 0.6 mmol / g to 2.2 mmol / g is preferable, 0.8 mmol / g to 2.0 mmol / g is more preferable, and 1.0 mmol / g to 1.8 mmol / g is still more preferable.

[0026] The amount of carboxyl groups in oxidized cellulose can be adjusted by controlling the reaction conditions, such as the amount of oxidizing agent added and the reaction time. The amount of carboxyl groups in oxidized cellulose is usually the same as the amount of carboxyl groups in the fine fibers.

[0027] In the present invention, the carboxyl groups introduced into the cellulose raw material in the oxidized cellulose obtained in the above process are usually of the salt type, and are alkali metal salts such as sodium salts. Before the defibration process, the alkali metal salt of the oxidized cellulose may be replaced with other cationic salts such as phosphonium salts, imidazolinium salts, ammonium salts, and sulfonium salts. The replacement can be carried out by known methods.

[0028] (carboxymethylation) Preferred anionic groups include carboxyalkyl groups such as carboxymethyl groups. Carboxyalkylated cellulose may be obtained by known methods or commercially available products may be used. The degree of carboxyalkyl substitution per anhydrous glucose unit of cellulose is preferably less than 0.60. Furthermore, if the anionic group is a carboxymethyl group, the degree of carboxymethyl substitution is preferably less than 0.60. If the degree of substitution is 0.60 or higher, the crystallinity decreases and the proportion of dissolved components increases, resulting in a loss of function as a fine fiber. The lower limit of the degree of carboxyalkyl substitution is preferably 0.01 or higher. Considering operability, the degree of substitution is particularly preferably 0.02 to 0.50, and even more preferably 0.10 to 0.30. An example of a method for producing such carboxyalkylated cellulose is a method including the following steps. This modification is a modification by a substitution reaction. Carboxymethylated cellulose will be explained as an example. i) A step of mixing the spawning raw material, solvent, and mercerizing agent, and mercerizing the mixture at a reaction temperature of 0 to 70°C, preferably 10 to 60°C, and for a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. ii) Next, a carboxymethylating agent is added in an amount of 0.05 to 10.0 moles per glucose residue, and the etherification reaction is carried out at a reaction temperature of 30 to 90°C, preferably 40 to 80°C, and for a reaction time of 30 minutes to 10 hours, preferably 1 hour to 4 hours.

[0029] The aforementioned cellulose raw material can be used as the base material. As a solvent, 3 to 20 times the mass of water or lower alcohol can be used, specifically water, methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary butanol, etc., either individually or in mixtures of two or more. When lower alcohols are mixed, the mixing ratio is 60 to 95% by mass. As a mercing agent, 0.5 to 20 times the molar amount of alkali metal hydroxide per anhydrous glucose residue of the base material can be used, specifically sodium hydroxide or potassium hydroxide.

[0030] As mentioned above, the degree of carboxymethyl substitution per glucose unit of cellulose is less than 0.06, and preferably between 0.01 and 0.60. By introducing carboxymethyl substituents to cellulose, the cellulose molecules repel each other electrically. For this reason, cellulose to which carboxymethyl substituents have been introduced can be easily defibrated. However, if the degree of carboxymethyl substituent per glucose unit is less than 0.02, defibration may not be sufficient. The degree of substitution in carboxymethylated cellulose and the degree of substitution when it is formed into fine fibers are usually the same.

[0031] In the present invention, the carboxyalkyl group introduced into the cellulose raw material in the carboxyalkylated cellulose obtained in the above process is usually in salt form, and is an alkali metal salt such as a sodium salt. Before the defibration process, the alkali metal salt of the carboxyalkylated cellulose may be replaced with other cationic salts such as phosphonium salts, imidazolinium salts, ammonium salts, or sulfonium salts. The substitution can be carried out by known methods.

[0032] (Esterification) Esterified cellulose can also be used as anionically modified cellulose. Methods include mixing a powder or aqueous solution of phosphate compound A with the cellulose raw material, or adding an aqueous solution of phosphate compound A to a slurry of the cellulose raw material. Examples of phosphate compound A include phosphoric acid, polyphosphate, phosphorous acid, hypophosphorous acid, phosphonic acid, polyphosphonic acid, or esters thereof. These may also be in the form of salts. Among the above, compounds having a phosphate group are preferred because they are low-cost, easy to handle, and can improve defibration efficiency by introducing a phosphate group into the cellulose of the pulp fiber. Examples of compounds having a phosphate group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium phosphite, potassium phosphite, sodium hypophosphite, potassium hypophosphite, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, and ammonium metaphosphate. One or more of these can be used in combination to introduce a phosphate group. Of these, phosphoric acid, sodium phosphoric acid, potassium phosphoric acid, and ammonium phosphoric acid are preferred from the viewpoint of high efficiency in introducing phosphate groups, ease of defibration in the defibration process described below, and ease of industrial application. Sodium dihydrogen phosphate and disodium hydrogen phosphate are particularly preferred. Furthermore, it is desirable to use the phosphate compound A as an aqueous solution so that the reaction can proceed uniformly and the efficiency of introducing phosphate groups is high. The pH of the aqueous solution of phosphate compound A is preferably 7 or less in order to increase the efficiency of introducing phosphate groups, but from the viewpoint of suppressing hydrolysis of pulp fibers, the pH is preferably 3 to 7.

[0033] An example of a method for producing phosphate-esterified cellulose is as follows: A phosphate compound A is added to a suspension of cellulose raw material with a solid content concentration of 0.1 to 10% by mass while stirring to introduce phosphate groups into the cellulose. When the cellulose raw material is 100 parts by mass, the amount of phosphate compound A added is preferably 0.2 to 500 parts by mass, and more preferably 1 to 400 parts by mass, in terms of phosphorus element content. If the proportion of phosphate compound A is above the lower limit, the yield of cellulose fine fibers can be further improved. However, if it exceeds the upper limit, the effect of improving the yield plateaus, which is undesirable from a cost perspective.

[0034] In addition to phosphate compound A, powder or aqueous solution of compound B may be mixed. Compound B is not particularly limited, but a nitrogen-containing compound exhibiting basicity is preferred. Here, "basicity" is defined as the aqueous solution exhibiting a pink to red color in the presence of phenolphthalein indicator, or the pH of the aqueous solution being greater than 7. The nitrogen-containing compound exhibiting basicity used in the present invention is not particularly limited as long as it achieves the effects of the present invention, but a compound having an amino group is preferred. Examples include urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, urea is preferred because it is low-cost and easy to handle. The amount of compound B added is preferably 2 to 1000 parts by mass, and more preferably 100 to 700 parts by mass, per 100 parts by mass of solid content of the cellulose raw material. The reaction temperature is preferably 0 to 95°C, and more preferably 30 to 90°C. The reaction time is not particularly limited, but is about 1 to 600 minutes, and more preferably 30 to 480 minutes. When the esterification reaction conditions are within these ranges, it is possible to prevent excessive esterification of cellulose, which can make it easily soluble, and a good yield of phosphate-esterified cellulose can be obtained. After dehydrating the obtained phosphate-esterified cellulose suspension, it is preferable to heat-treat it at 100 to 170°C from the viewpoint of suppressing hydrolysis of cellulose. Furthermore, it is preferable to heat it at 130°C or lower, preferably 110°C or lower, while water is present during the heat treatment, and then heat-treat it at 100 to 170°C after removing the water.

[0035] The degree of phosphate group substitution per glucose unit in phosphate-esterified cellulose is preferably 0.001 or more and less than 0.40. By introducing phosphate group substituents to cellulose, the cellulose molecules repel each other electrically. Therefore, cellulose with introduced phosphate groups can be easily defibrillated. If the degree of phosphate group substitution per glucose unit is less than 0.001, sufficient defibrillation is not possible. On the other hand, if the degree of phosphate group substitution per glucose unit is greater than 0.40, swelling or dissolution may occur, making it impossible to obtain fine fibers. In order to efficiently defibrillate, it is preferable that the phosphate-esterified cellulose raw material obtained above be boiled and then washed with cold water. These modifications by esterification are modifications by substitution reactions. The degree of substitution in phosphate-esterified cellulose and the degree of substitution when it is made into fine fibers are usually the same.

[0036] In the present invention, the phosphate groups introduced into the cellulose raw material in the phosphate-esterified cellulose obtained in the above process are usually of the salt type, and are alkali metal salts such as sodium salts. Before the defibration process, the alkali metal salt of the phosphate-esterified cellulose may be replaced with other cationic salts such as phosphonium salts, imidazolinium salts, ammonium salts, and sulfonium salts. The substitution can be carried out by known methods.

[0037] (Fibreation) In the present invention, the apparatus for defibrating the anion-modified cellulose raw material is not particularly limited, but it is preferable to apply a shear force to the anion-modified cellulose raw material (usually an aqueous dispersion) using an apparatus such as a high-speed rotary type, colloidal mill type, high-pressure type, roll mill type, ultrasonic type, or cavitation jet device. In particular, it is preferable to use a cavitation jet device that can efficiently defibrate at a pressure of about 7 MPa, or a wet high-pressure or ultra-high-pressure homogenizer that can apply a pressure of 50 MPa or more to the anion-modified cellulose raw material (usually an aqueous dispersion) and apply a strong shear force. Furthermore, if necessary, preliminary treatment can be performed prior to the defibration and dispersion treatment. Preliminary treatment can be performed using known mixing, stirring, emulsifying, and dispersion devices such as high-speed shear mixers. The number of treatments (passes) in the defibration device may be one or two or more, and two or more is preferable.

[0038] In dispersion processing, anionically modified cellulose is typically dispersed in a solvent. The solvent is not particularly limited as long as it can disperse the anionically modified cellulose, but examples include water, organic solvents (e.g., hydrophilic organic solvents such as methanol), and mixtures thereof.

[0039] The solid content concentration of anionically modified cellulose in the dispersion is usually 0.1% by mass or more, preferably 0.2% by mass or more, and more preferably 0.3% by mass or more. This ensures an appropriate amount of liquid relative to the amount of cellulose raw material, making it efficient. The upper limit is usually 10% by mass or less, preferably 6% by mass or less. This allows for maintaining fluidity.

[0040] Prior to defibration or dispersion, preliminary treatment may be performed as needed. Preliminary treatment can be carried out using mixing, stirring, emulsifying, and dispersion equipment such as a high-speed shear mixer.

[0041] The viscosity modifier for antifreeze agents of the present invention may be used in any form as long as it contains cellulose fine fibers, and may be in the form of a dispersion, or it may be used in the form of a powder after drying (removal of dispersion medium), grinding, and classification.

[0042] The viscosity modifier of the present invention contains cellulose microfibers. Due to the thixotropy of the cellulose microfibers, even after applying the liquid antifreeze containing this viscosity modifier to a vertical surface, it does not flow off the applied surface but remains in place, allowing the antifreeze effect to be fully exerted. During application, shear force is applied, reducing viscosity, making it easy to spread. Furthermore, the viscosity quickly recovers after application, preventing it from flowing off. Therefore, by applying, spraying, or atomizing the antifreeze containing the viscosity modifier of the present invention to, for example, the walls or doors of a cold storage warehouse, the occurrence of frost or freezing can be suppressed.

[0043] One method for adding the viscosity modifier of the present invention to an antifreeze is to first prepare an aqueous solution of the antifreeze by conventional means, and then add and mix the viscosity modifier of the present invention to this aqueous solution, either in the form of an aqueous dispersion or in powder form.

[0044] Examples of antifreeze agents to which the viscosity modifier of the present invention can be added include liquid antifreeze agents consisting of one aqueous solution selected from acetate, formate, urea, chloride, and low molecular weight alcohol.

[0045] Examples of acetates include sodium acetate, magnesium acetate, potassium acetate, and calcium acetate. It is preferable to include the acetate in the antifreeze agent at a concentration of 50% to 20% by mass.

[0046] Examples of formate salts include sodium formate, potassium formate, and magnesium formate. It is preferable to include formate salts in the antifreeze agent at a concentration of 25% to 15% by mass.

[0047] Urea is preferably included in the antifreeze agent at a concentration of 40% to 20% by mass.

[0048] Examples of chlorides include sodium chloride, calcium chloride, and magnesium chloride. It is preferable to include chlorides in the antifreeze agent at a concentration of 35% to 20% by mass.

[0049] Examples of low molecular weight alcohols include at least one selected from glycerin, propylene glycol, ethylene glycol, methyl alcohol, and ethyl alcohol. From the viewpoint of antifreeze effect, it is preferable to include polyhydric alcohols such as glycerin, propylene glycol, and ethylene glycol, and more preferably glycerin. It is preferable to include the low molecular weight alcohol in the antifreeze agent at an amount of 80% to 20% by mass.

[0050] When adding the viscosity modifier of the present invention to an antifreeze, the amount to be added is preferably such that the solid content concentration of cellulose microfibers is 0.5 to 1.5% by mass relative to the total amount of the antifreeze. A concentration that is too low may result in poor drip suppression. A concentration that is too high may result in excessive viscosity, making spraying, atomizing, or coating difficult.

[0051] When the viscosity modifier of the present invention is added to an antifreeze, the viscosity of the antifreeze after addition is preferably 100,000 mPa·s or more, and more preferably 150,000 mPa·s or more, at a shear rate of 0.001 / second, from the viewpoint of excellent drip suppression effect. Furthermore, from the viewpoint of coating suitability, it is preferably 10,000 mPa·s or less, and more preferably 1,000 mPa·s or less, at a shear rate of 1000 / second. The viscosity modifier of the present invention has coating suitability and excellent drip suppression effect. The viscosity modifier of the present invention has high thixotropy. Thixotropy refers to the property that viscosity gradually decreases when subjected to shear stress and gradually increases when at rest. A high value obtained by dividing viscosity A measured at a shear rate of 0.001 / second by viscosity B measured at a shear rate of 1000 / second indicates high thixotropy. For example, a viscosity A / viscosity B ratio of preferably 100 or more, and more preferably 1,000 or more, indicates high thixotropy. The viscosity in this specification can be measured at a predetermined shear rate using a viscoelastic rheometer (e.g., "MCR301" manufactured by Anton Paar). [Examples]

[0052] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0053] (Method for measuring the amount of carboxyl groups) The amount of carboxyl groups was measured as follows: 60 mL of a 0.5% by mass slurry (aqueous dispersion) of carboxylated cellulose was prepared, and a 0.1 M hydrochloric acid aqueous solution was added to adjust the pH to 2.5. Then, a 0.05 N sodium hydroxide aqueous solution was added dropwise until the pH became 11, and the electrical conductivity was measured. The amount of carboxyl groups was calculated from the amount of sodium hydroxide consumed during the neutralization step of the weak acid, where the change in electrical conductivity was gradual (a), using the following formula: Carboxyl group content [mmol / g carboxylated cellulose] = a [mL] × 0.05 / Mass of carboxylated cellulose [g]

[0054] (Method for measuring the degree of carboxymethyl substitution) 1) Approximately 2.0 g of carboxymethylated cellulose fiber (dry) was accurately weighed and placed in a 300 mL Erlenmeyer flask with a stopper. 2) Add 100 mL of a solution made by adding 100 mL of special grade concentrated nitric acid to 1000 mL of methanol nitric acid, and shake for 3 hours to convert carboxymethylcellulose salt (CM-modified cellulose) into hydrogen-type CM-modified cellulose. 3) 1.5 to 2.0 g of hydrogenated CM-modified cellulose (absolutely dry) was accurately weighed and placed in a 300 mL Erlenmeyer flask with a stopper. 4) Hydrogenated CM-modified cellulose was moistened with 15 mL of 80% methanol, 100 mL of 0.1 N NaOH was added, and the mixture was shaken at room temperature for 3 hours. 5) Using phenolphthalein as an indicator, excess NaOH was back-titrated with 0.1N H2SO4. 6) The degree of carboxymethyl substitution (DS) was calculated using the following formula: A = [(100 × F' - (0.1N H2SO4) (mL) × F) × 0.1] / (Oven-dry mass of hydrogenated CM cellulose (g)) DS = 0.162 × A / (1 - 0.058 × A) A: Amount of 1N NaOH required to neutralize 1g of hydrogenated CM-modified cellulose (mL) F': Factor of H2SO4 at 0.1N F: Factor of 0.1N NaOH

[0055] (Method for measuring average fiber diameter and aspect ratio) The average fiber diameter and average fiber length of cellulose microfibers were determined by AFM. The aspect ratio was calculated using the following formula. Aspect ratio = average fiber length / average fiber diameter

[0056] (Evaluation of dripping properties) 0.2 g of the liquid antifreeze obtained in the examples and comparative examples was applied to an aluminum tray using a spatula, and the tray was then stood upright to evaluate its dripping properties. Dripping properties were evaluated by visually observing the droplets of the liquid antifreeze according to the following criteria (sensory evaluation). The results are shown in Table 1. A: Liquid antifreeze does not move. B: Liquid de-icing agents hardly move. C: The liquid antifreeze gradually drips and moves, but stops midway. D: Liquid antifreeze will drip.

[0057] (Evaluation of applicability) The liquid antifreeze agents obtained in the examples and comparative examples were placed in containers, taken from the containers with a brush, and applied to the walls of acrylic glass to evaluate their applicability (sensory evaluation). The results are shown in Table 1. A: It can be applied neatly and evenly. B: It can be applied, but it is difficult to spread evenly. C: It can be applied, but it cannot be spread evenly.

[0058] (Viscosity measurement) The viscosity of the liquid antifreeze obtained in the examples and comparative examples was measured using a viscoelastic rheometer MCR301 (manufactured by Anton Paar) at shear rates of 0.001 / sec and 1000 / sec. A parallel plate (PP25) was used for measurement, with a gap of 1 mm in the measurement area. The results are shown in Table 1.

[0059] (Manufacturing Example 1) (Manufacturing of oxidized cellulose microfibers 1) 5.00 g (dry) of bleached, unbeaten kraft pulp (whiteness 85%) derived from coniferous trees was added to 500 mL of an aqueous solution containing 39 mg of TEMPO (Sigma Aldrich) and 514 g of sodium bromide, and the mixture was stirred until the pulp was uniformly dispersed. Sodium hypochlorite aqueous solution was added to the reaction system to a level of 6.0 mmol / g to initiate the oxidation reaction. During the reaction, the pH of the system decreased, but 3 M sodium hydroxide aqueous solution was added sequentially to adjust the pH to 10. The reaction was terminated when the sodium hypochlorite was consumed and the pH of the system no longer changed. The mixture after the reaction was acidified with hydrochloric acid, filtered through a glass filter to separate the pulp, and thoroughly washed with water to obtain oxidized pulp (carboxylated cellulose). The pulp yield at this time was 90%, the oxidation reaction time was 90 minutes, and the carboxyl group content was 1.6 mmol / g.

[0060] The oxidized pulp obtained in the above process was adjusted to 2.5% (w / v) with water and treated 10 times with a 7 MPa cavitation jet to obtain an aqueous dispersion of oxidized cellulose microfibers 1. The obtained oxidized cellulose microfibers 1 had an average fiber diameter of 15 nm and an aspect ratio of 262. That was the case.

[0061] (Manufacturing example 2) (Manufacturing of carboxymethylated cellulose microfibers 2) In a 5L twin-screw kneader adjusted to a rotation speed of 100 rpm, 1089 parts of isopropanol (IPA) and a solution of 31 parts sodium hydroxide dissolved in 121 parts of water were added. 200 parts of hardwood pulp (manufactured by Nippon Paper Industries Co., Ltd., LBKP), based on its dry mass after drying at 100°C for 60 minutes, were charged. The mixture was stirred and mixed at 30°C for 60 minutes to prepare mercerized cellulose. Further stirring was performed, and 117 parts of sodium monochloroacetate were added. After stirring at 30°C for 30 minutes, the temperature was raised to 70°C over 30 minutes, and the carboxymethylation reaction was carried out at 70°C for 60 minutes. The proportion of water in the reaction medium during both the mercerization and carboxymethylation reactions was 10% by mass. After the reaction was complete, the mixture was neutralized, washed with 65% aqueous methanol, dehydrated, dried, and pulverized to obtain the sodium salt of carboxymethylated cellulose with a carboxymethyl substitution degree of 0.27. The method for measuring the carboxymethyl substitution degree is as described above.

[0062] The obtained sodium salt of carboxymethylated cellulose was dispersed in water to obtain a 2.5% (w / v) aqueous dispersion. This was treated 30 times with a cavitation jet device at 7 MPa to obtain a dispersion of carboxymethylated cellulose microfibers 2. The obtained carboxymethylated cellulose microfibers 2 had an average fiber diameter of 24 nm and an aspect ratio of 87.

[0063] (Manufacturing Example 3) (Manufacturing of oxidized cellulose microfibers 3) The oxidized pulp obtained in Production Example 1 was adjusted to 3% (w / v) with water and treated three times in a high-pressure homogenizer at 150 MPa to obtain an aqueous dispersion of oxidized cellulose microfibers 3. The obtained oxidized cellulose microfibers 3 had an average fiber diameter of 4 nm and an aspect ratio of 220.

[0064] (Manufacturing example 4) (Manufacturing of carboxymethylated cellulose microfibers 4) The sodium salt of carboxymethylated cellulose obtained in Production Example 2 was dispersed in water to obtain a 3% (w / v) aqueous dispersion. This was treated three times in a 150 MPa high-pressure homogenizer to obtain a dispersion of carboxymethylated cellulose microfibers 2. The obtained carboxymethylated cellulose microfibers 4 had an average fiber diameter of 11 nm and an aspect ratio of 92.

[0065] (Example 1) A glycerin aqueous solution was prepared by dissolving 50 parts of glycerin in 18 parts of water and 32 parts of the aqueous dispersion of oxidized cellulose microfibers 1 obtained in Production Example 1. The solid content of the cellulose microfibers was adjusted to 0.8% by mass relative to the mass of the glycerin aqueous solution, and the mixture was obtained by mixing with a general-purpose stirrer to obtain the liquid antifreeze of Example 1.

[0066] (Example 2) A liquid antifreeze agent for Example 2 was obtained in the same manner as in Example 1, except that the amount of oxidized cellulose microfibers 1 added was such that the solid content of the cellulose microfibers was 1.0% by mass relative to the mass of the glycerin aqueous solution.

[0067] (Example 3) The liquid antifreeze agent of Example 3 was obtained in the same manner as in Example 1, except that the amount of oxidized cellulose microfibers 1 added was such that the solid content of the cellulose microfibers was 1.2% by mass relative to the mass of the glycerin aqueous solution.

[0068] (Example 4) The liquid antifreeze agent of Example 4 was obtained in the same manner as in Example 1, except that carboxymethylated cellulose microfibers 2 obtained in Production Example 2 were used instead of oxidized cellulose microfibers 1.

[0069] (Example 5) The liquid antifreeze of Example 5 was obtained in the same manner as in Example 4, except that the amount of carboxymethylated cellulose microfibers 2 added was such that the solid content of the cellulose microfibers was 1.0% by mass relative to the mass of the glycerin aqueous solution.

[0070] (Example 6) A liquid antifreeze agent for Example 6 was obtained in the same manner as in Example 4, except that the amount of carboxymethylated cellulose microfibers 2 added was such that the solid content of the cellulose microfibers was 1.2% by mass relative to the mass of the glycerin aqueous solution.

[0071] (Example 7) The liquid antifreeze agent of Example 7 was obtained in the same manner as in Example 1, except that oxidized cellulose microfibers 3 obtained in Production Example 3 were used instead of oxidized cellulose microfibers 1, and the amount of oxidized cellulose microfibers 3 added was such that the solid content of the cellulose microfibers was 1.0% by mass relative to the mass of the glycerin aqueous solution.

[0072] (Example 8) The liquid antifreeze agent of Example 8 was obtained in the same manner as in Example 1, except that carboxymethylated cellulose microfibers 4 obtained in Production Example 4 were used instead of oxidized cellulose microfibers 1, and the amount of carboxymethylated cellulose microfibers 4 added was such that the solid content of the cellulose microfibers was 1.0% by mass relative to the mass of the glycerin aqueous solution.

[0073] (Example 9) The liquid antifreeze agent of Example 9 was obtained in the same manner as in Example 1, except that the amount of oxidized cellulose microfibers 1 added was such that the solid content of the cellulose microfibers was 0.5% by mass relative to the mass of the glycerin aqueous solution.

[0074] (Example 10) The liquid antifreeze agent of Example 10 was obtained in the same manner as in Example 1, except that oxidized cellulose microfibers 3 obtained in Production Example 3 were used instead of oxidized cellulose microfibers 1, and the amount of oxidized cellulose microfibers 3 added was such that the solid content of the cellulose microfibers was 0.5% by mass relative to the mass of the glycerin aqueous solution.

[0075] (Comparative Example 1) Comparative Example 1's liquid antifreeze was obtained in the same manner as in Example 1, except that the same amount of water was added to the liquid antifreeze of Example 1 instead of the aqueous dispersion of oxidized cellulose microfibers 1.

[0076] [Table 1]

[0077] As is clear from the results in Table 1, when a viscosity modifier for antifreeze containing cellulose microfibers is used, the liquid antifreeze agents obtained in Examples 1 to 8 with the addition of this modifier exhibit superior drip suppression and application properties compared to the liquid antifreeze agent of Comparative Example 1 without the viscosity modifier. Furthermore, the liquid antifreeze agents of Examples 9 to 10 exhibit superior drip suppression compared to the liquid antifreeze agent of Comparative Example 1.

Claims

[Claim 1] It contains 20-80% by mass of glycerin, 0.8-1.5% by mass of oxidized cellulose fine fibers (solid content), and water. The oxidized cellulose microfibers are an antifreeze agent having a carboxyl group content of 1.0 to 1.8 mmol / g.

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