Method for producing hydroxyalkyl alkyl cellulose

Abstract

To provide a method for producing a hydroxyalkyl alkyl cellulose having a high storage modulus (thermal gel strength) and a small number of undissolved fibers.SOLUTION: There is provided a method for producing a hydroxyalkyl alkyl cellulose including at least steps of: bringing sheet-shaped pulp having a pore volume of 0.55 mL / g or more and less than 1.00 mL / g or chip-shaped pulp obtained by cutting the sheet-shaped pulp into contact with a first alkali metal hydroxide solution to obtain an alkali cellulose mixture; removing a liquid from the alkali cellulose mixture to obtain alkali cellulose; reacting the alkali cellulose with an alkylating agent and a hydroxyalkylating agent to obtain a first reaction mixture; mixing the first reaction mixture with a second alkali metal hydroxide solution to obtain a second reaction mixture, and purifying the second reaction mixture to obtain a hydroxyalkyl alkyl cellulose.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Honeycomb-shaped ceramic extrusions are used as supports for exhaust gas purification catalysts, filters, and heat exchangers in the automotive and various industrial fields. These ceramic extrusions are produced, for example, by mixing, calcining, and pulverizing a ceramic base material to form a non-plastic ceramic powder, adding a binder, water, and, if necessary, a plasticizer, a lubricant, etc. to impart plasticity to the powder, kneading the mixture using a roll mill or a continuous kneader to form a clay, molding the clay using the clay, and then firing it to form a base body.

[0003] Known binders include cellulose derivatives, particularly methylcellulose and hydroxypropylmethylcellulose, which form strong gels at high temperatures, improving the shape retention of the clay and facilitating the extrusion of thin-walled honeycomb structures. Among these, hydroxypropyl methylcellulose is useful because it has a higher thermal gelation temperature than methyl cellulose and can be applied to high extrusion temperatures.

[0004] As a method for obtaining hydroxypropyl methylcellulose having high thermal gel strength, a method has been proposed in which the alkalinization step of cellulose pulp with an alkali metal hydroxide solution and / or the etherification reaction step are each divided into multiple stages. For example, there is a method in which cellulose pulp is alkalized with an alkali metal hydroxide solution in a first step, an alkylating agent and a hydroxypropoxylating agent are added to cause an etherification reaction, and then an alkali metal hydroxide solution in a second step is slowly added to continue the etherification reaction, thereby obtaining hydroxypropyl methylcellulose (Patent Document 1). On the other hand, as the starting material for the etherification reaction, sheet-like pulp having a pore volume of less than 1.00 ml / g has been avoided from use because it is difficult to produce cellulose ether with a low undissolved fiber content (Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2014-503004 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-155534 Summary of the Invention [Problem to be solved by the invention]

[0006] The hydroxypropyl methylcellulose obtained by the method disclosed in Patent Document 1 has high thermal gel strength, but contains a large amount of undissolved fibers. When hydroxypropyl methylcellulose containing a large amount of undissolved fibers is used, pores of about several μm in size are formed in the sintered ceramic compact, reducing the strength of the sintered ceramic. Furthermore, these pores also reduce the withstand voltage characteristics of sintered ceramic compacts for electrostatic devices such as capacitors. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a hydroxyalkyl alkyl cellulose having a high storage modulus (thermal gel strength) and a small number of undissolved fibers, and a method for producing the same. [Means for solving the problem]

[0007] As a result of extensive research to achieve the above object, the present inventors have found that it is possible to produce a hydroxyalkyl alkyl cellulose having a high storage modulus G' (80°C) and a small number of undissolved fibers by dividing an alkali metal hydroxide multiple times and using, as a raw material, sheet-like or chip-like pulp having a specific pore volume that has been avoided in the past, and have thus completed the present invention. According to one embodiment of the present invention, there is provided a method for producing an alkali cellulose mixture by contacting a pulp sheet having a pore volume of 0.55 ml / g or more and less than 1.00 ml / g or pulp chips obtained by cutting the pulp sheet with a first alkali metal hydroxide solution; obtaining alkali cellulose by deliquoring the alkali cellulose mixture; reacting the alkali cellulose with an alkylating agent and a hydroxyalkylating agent to obtain a first reaction mixture; combining the first reaction mixture with a second alkali metal hydroxide solution to obtain a second reaction mixture; and purifying the second reaction mixture to obtain hydroxyalkyl alkyl cellulose. According to one embodiment of the present invention, the sheet density of the pulp sheet can be 0.55 to 0.80 g / ml. According to one embodiment of the present invention, the intrinsic viscosity of the pulp sheet may be 3.0 to 15.0 dl / g. According to one embodiment of the present invention, the step of mixing the first reaction mixture with the second alkali metal hydroxide solution includes adding the second alkali metal hydroxide solution to the first reaction mixture, and the temperature of the first reaction mixture can be increased from the start to the end of the addition of the second alkali metal hydroxide solution. According to one embodiment of the present invention, the rate of temperature increase can be 10.0 to 30.0° C. / hr. According to one embodiment of the present invention, the addition rate of the second alkali metal hydroxide in the second alkali metal hydroxide solution, expressed as the number of moles of the second alkali metal hydroxide added per unit time relative to the number of moles of the pulp sheet or pulp chips when 1 mole of anhydroglucose units is used, can be 2.76 to 7.50 mol / mol hr. [Effects of the Invention]

[0008] According to the present invention, it is possible to produce a hydroxyalkyl alkyl cellulose having a high storage modulus G' (80°C) and a small number of undissolved fibers. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will be described in more detail below. Examples of raw materials for the sheet-like pulp include wood pulp and cotton linter pulp, but wood pulp is particularly preferred from the viewpoint of reducing the number of undissolved fibers. Wood species that can be used include conifers such as pine, spruce, and hemlock; and broad-leaved trees such as eucalyptus and maple. Pine is preferred from the viewpoint of producing hydroxyalkyl alkyl cellulose with a small number of undissolved fibers.

[0010] The sheet pulp can be classified into kraft pulp obtained by cooking wood with a chemical solution mainly containing sodium hydroxide and sodium sulfide, and sulfite pulp obtained by cooking wood with an acidic sulfite solution, and either can be used. From the viewpoint of producing hydroxyalkyl alkyl cellulose with a small number of undissolved fibers, it is preferable to use kraft pulp.

[0011] The pore volume of the sheet-form pulp is 0.55 ml / g or more but less than 1.00 ml / g, preferably 0.65 to 1.00 ml / g, and more preferably 0.65 to 0.95 ml / g. If the pore volume is less than 0.55 ml / g, it becomes difficult to produce a hydroxyalkyl alkyl cellulose having a low number of undissolved fibers. If the pore volume is 1.0 ml / g or more, it becomes difficult to produce a hydroxyalkyl alkyl cellulose having a high storage modulus G' (80°C). It is surprising that a hydroxyalkyl alkyl cellulose with a low undissolved fiber content can be produced using a sheet-form pulp with a pore volume of less than 1.00 ml / g, which has traditionally been avoided due to the difficulty in producing cellulose ether with a low undissolved fiber content. The pore volume of a pulp sheet is the total volume of minute voids per unit mass of a dried pulp sheet, as measured by mercury intrusion porosimetry. The method for measuring the pore volume of a pulp sheet includes the following steps: drying a sample at 105°C for two hours under atmospheric pressure; cutting the dried sample into strips of approximately 1.2 x 2.4 cm (the thickness of the strips can be the same as that of the pulp sheet, since any thickness can be converted to a unit mass); arranging three of the strips in a triangular shape in a cell (e.g., a cell attached to a Shimadzu Autopore 9520) so that they do not overlap during mercury intrusion; and measuring the pore volume using a porosimeter (e.g., a Shimadzu Autopore 9520) under mercury pressures of 5.5 kPa (equivalent to a pore diameter of approximately 220 μm) to 411 MPa (equivalent to a pore diameter of approximately 0.003 μm).

[0012] The thickness of the pulp sheet is preferably 0.1 to 5.0 mm, more preferably 0.5 to 2.0 mm, from the viewpoint of ease of handling during the deliquor process. The density of the pulp sheet is preferably 0.80 g / ml or less, more preferably 0.55 to 0.80 g / ml, from the viewpoints of productivity, suppressing variations in the alkali cellulose composition, and reducing the number of undissolved fibers. The density was measured using the method described in JIS P8215. The alpha cellulose content of the pulp sheet is preferably 90% by mass or more in order to prevent a decrease in yield during the refining process. The alpha cellulose content can be measured by the method described in TEST METHOD T429 of TAPPI (Technical Association of the Pulp and Paper Industry).

[0013] The intrinsic viscosity, which is an index of the degree of polymerization of the pulp, is preferably less than 15.0 dL / g, more preferably less than 14.0 dL / g, from the viewpoint of producing a hydroxyalkyl alkyl cellulose having a small number of undissolved fibers. The lower limit of the intrinsic viscosity is preferably 3.0 dL / g. The intrinsic viscosity can be measured by the viscosity measurement method described in JIS P8215.

[0014] Furthermore, the sheet-like pulp can be used as it is, or the sheet-like pulp can be cut into chips and used. The chip-like pulp is preferably pulp in the form of chips obtained by cutting a sheet-like pulp having a thickness of 0.1 to 5.0 mm. There are no limitations on the method for producing the chip-like pulp, and in addition to a slitter cutter, existing cutting devices can be used. The cutting device used is advantageous in terms of investment costs if it is capable of continuous processing. The chips preferably have a side length of 2 to 100 mm, more preferably 3 to 50 mm, from the viewpoint of ease of handling during the immersion operation and reducing the number of undissolved fibers.

[0015] Next, the step of contacting a pulp sheet or pulp chips with a first alkali metal hydroxide solution to obtain an alkali cellulose mixture and the step of deliquoring the obtained alkali cellulose mixture to obtain alkali cellulose will be described.

[0016] In order to achieve a high storage modulus G' and a small number of undissolved fibers, the alkali metal hydroxide solution is mixed in multiple batches, preferably in two or three stages, and more preferably in two stages from the viewpoint of reducing the complexity of the operation.

[0017] The first alkali metal hydroxide solution used is not particularly limited as long as it can produce alkali cellulose, but for economic reasons, it is preferably an aqueous solution of sodium hydroxide or potassium hydroxide. The concentration of the first alkali metal hydroxide solution is preferably 23 to 60 mass %, more preferably 35 to 55 mass %. The first alkali metal hydroxide solution is preferably an aqueous solution, but may also be an alcohol solution such as ethanol, or a mixed solution of a water-soluble alcohol and water.

[0018] The method for contacting the pulp sheet with the first alkali metal hydroxide solution includes immersing the pulp sheet in the alkali metal hydroxide solution, and for pulp chips, adding a required amount of the alkali hydroxide solution to the pulp chips.

[0019] The temperature at which the sheet- or chip-form pulp is brought into contact with the first alkali metal hydroxide solution is preferably 10 to 70°C, more preferably 15 to 60°C, from the viewpoint of suppressing solidification of the first alkali metal hydroxide solution and suppressing variation in the composition of the alkali cellulose. The time for contacting the sheet- or chip-form pulp with an excess of the first alkali metal hydroxide solution is preferably 10 to 600 seconds, more preferably 15 to 120 seconds, from the viewpoint of obtaining alkali cellulose of the desired composition, suppressing variation in the alkali cellulose composition, and operability during contact.

[0020] The mass ratio of the first alkali metal hydroxide in the first alkali metal hydroxide solution to the solid components in the starting pulp material (first alkali metal hydroxide / solid components in pulp) when the sheet-like pulp or chip-like pulp is contacted with the first alkali metal hydroxide solution is preferably 1.5 to 2,500, more preferably 5 to 100, and even more preferably 10 to 30, from the viewpoint of reducing the scale of the equipment and the number of undissolved fibers. The solid matter content in pulp refers to the components in pulp other than moisture. The mass of the solid matter in pulp can be calculated from the dry matter content determined by the JIS P8203:1998 Pulp - Dry Matter Content Test Method. The dry matter content is the ratio of the mass of a sample at constant weight after drying at 105±2°C to the mass before drying, expressed as a percentage by mass. The solid matter in pulp includes, in addition to the main component cellulose, very small amounts of organic matter such as low-molecular-weight cellulose, hemicellulose, lignin, and resin, as well as inorganic matter such as silicon and iron. Furthermore, since the content of low-molecular-weight cellulose in commercially available pulp obtained by cooking and bleaching wood is very small, the cellulose content and alpha cellulose content of the solid matter in pulp can be considered to be approximately the same.

[0021] From the viewpoint of achieving both a high storage modulus G' (80°C) and a reduced number of undissolved fibers, the molar amount of the first alkali metal hydroxide in the first alkali metal hydroxide solution is preferably 2.43 to 3.65 mol / mol, more preferably 2.83 to 3.44 mol / mol, and even more preferably 2.91 to 3.24 mol / mol, as a ratio of the number of moles of the first alkali metal hydroxide to the number of moles of the solid components in the starting pulp when the molecular weight of an anhydroglucose unit (AGU) is 1 mole. The amount of the first alkali metal hydroxide solution used in the contacting step is selected so that the ratio is within this range. The mass of the first alkali metal hydroxide component can be calculated by neutralization titration.

[0022] The ratio of the mass of the first alkali metal hydroxide to the total mass of the first alkali metal hydroxide in the first alkali metal hydroxide solution and the second alkali metal hydroxide in the second alkali metal hydroxide solution (first alkali metal hydroxide / total alkali metal hydroxide) is preferably 0.6 to 0.8, more preferably 0.62 to 0.78. If the ratio of the mass of the first alkali metal hydroxide to the total mass of the first and second alkali metal hydroxides is less than 0.6, it may be impossible to produce a hydroxyalkyl alkyl cellulose having a low number of undissolved fibers. On the other hand, if the ratio of the mass of the first alkali metal hydroxide to the total mass of the first and second alkali metal hydroxides is more than 0.8, it may be impossible to produce a hydroxyalkyl alkyl cellulose having a high storage modulus G' (80°C) that provides high thermal gel strength.

[0023] The alkali cellulose can be obtained by contacting a sheet or chip-like pulp with an excess of a first alkali metal hydroxide solution to obtain an alkali cellulose mixture, and then deliquoring the obtained alkali cellulose mixture to remove the excess first alkali metal hydroxide solution. Examples of the deliquoring method include a method in which a pulp sheet is immersed in a bath containing the first alkali metal hydroxide solution and then compressed with a roller or other device, and a method in which a pulp chip is immersed in a bath containing the first alkali metal hydroxide solution and then compressed by centrifugation or other mechanical means.

[0024] Next, the step of reacting the obtained alkali cellulose with an alkylating agent and a hydroxyalkylating agent to obtain a first reaction mixture will be described. The obtained alkali cellulose can be fed to the reactor as is or, if necessary, after cutting. From the viewpoint of reducing the number of undissolved fibers, the reactor is preferably one that reacts with the alkylating agent and the hydroxyalkylating agent while loosening the pulp-derived fibers of the alkali cellulose by mechanical force. Therefore, a reactor having an internal stirring mechanism is preferred, such as a plow-type shovel blade mixer. It is also possible to pre-crush the alkali cellulose using a separate device with an internal stirring mechanism before feeding it into the reactor. After feeding the alkali cellulose into the reactor, it is preferable to remove oxygen from the reactor using a vacuum pump or the like and replace it with an inert gas, preferably nitrogen. It is also preferable that the reactor be equipped with a measuring instrument that can measure the internal temperature.

[0025] For the purpose of suppressing localized heat generation in the reactor, an organic solvent that will not be used in the etherification reaction, such as dimethyl ether, may be added to the system after the addition of the alkali cellulose.

[0026] Examples of the alkylating agent include methyl chloride, dimethyl sulfate, and methyl iodide. Methyl chloride is preferred from the viewpoint of obtaining a hydroxyalkyl alkyl cellulose having a high storage modulus G' (80°C) and from the viewpoint of economy. Examples of the hydroxyalkylating agent include ethylene oxide, propylene oxide, and butylene oxide. From the viewpoint of obtaining a hydroxyalkyl alkyl cellulose having a high storage modulus G' (80°C) and from the viewpoint of economy, propylene oxide is preferred.

[0027] The temperature inside the reactor when reacting the alkylating agent and the hydroxyalkylating agent is preferably 40 to 90°C, more preferably 50 to 80°C, from the viewpoint of reaction control.

[0028] From the viewpoint of achieving both high thermal gel strength and a reduced number of undissolved fibers, as well as from an economic viewpoint, the molar amount of alkylating agent is preferably 2.43 to 9.30 mol / mol, more preferably 3.04 to 7.89 mol / mol, in terms of the number of moles of alkylating agent relative to the number of moles of solid components in the starting pulp when the molecular weight of an anhydroglucose unit (AGU) is 1 mole (number of moles of alkylating agent / number of moles of solid components in pulp). From the viewpoint of achieving both high thermal gel strength and a small number of undissolved fibers, the amount of hydroxyalkyl alkylating agent blended is preferably 0.53 to 2.51 mol / mol, more preferably 0.55 to 2.09 mol / mol, in terms of the ratio of the number of moles of hydroxyalkyl alkylating agent to the number of moles of solid components in the starting pulp when the molecular weight of anhydroglucose unit (AGU) is 1 mol.

[0029] The alkylating agent and the hydroxyalkylating agent are preferably added to the alkali cellulose. The order of addition of the alkylating agent and the hydroxyalkylating agent is not limited, and the addition of the alkylating agent can be started before, during, or after the addition of the hydroxyalkylating agent. However, from the viewpoint of productivity, it is preferable to start the addition of the alkylating agent before or during the addition of the hydroxyalkylating agent. The addition time of the alkylating agent is preferably 30 to 120 minutes, more preferably 40 to 90 minutes, from the viewpoints of reaction control and productivity. The addition time of the hydroxyalkylating agent is preferably 5 to 30 minutes, more preferably 10 to 30 minutes, from the viewpoint of reaction control and productivity.

[0030] The degree of substitution (DS) of the alkoxy group of the hydroxyalkyl alkyl cellulose in the first reaction mixture is preferably 0.75 to 1.68, more preferably 0.81 to 1.68, and even more preferably 0.99 to 1.37, from the viewpoint of obtaining a desired thermal gel strength. The degree of substitution (MS) of the hydroxyalkoxy group is preferably 0.03 to 0.28, and more preferably 0.05 to 0.25, from the viewpoint of obtaining a desired thermal gel strength and thermal gelation temperature. The degree of substitution (DS) is the average number of alkoxy groups per unit of anhydroglucose, and the molar substitution (MS) is the average number of moles of hydroxyalkoxy groups per mole of anhydroglucose. For hydroxyalkyl alkyl cellulose, the DS and MS can be determined by converting values ​​measured in accordance with the analytical method for hypromellose in the 17th edition of the Japanese Pharmacopoeia.

[0031] Next, a description will be given of the step of mixing a second alkali metal hydroxide solution with the obtained first reaction mixture to continue the reaction and obtain a second reaction mixture. The second alkali metal hydroxide solution is not particularly limited, and examples thereof include solutions of sodium hydroxide and potassium hydroxide, but from an economical viewpoint, an aqueous sodium hydroxide solution is preferred. The first alkali metal hydroxide in the first alkali metal hydroxide solution and the second alkali metal hydroxide in the second alkali metal hydroxide solution may be the same type or different types, but from the viewpoint of operability, it is preferable that they are the same type.

[0032] The method of blending the second alkali metal hydroxide solution is preferably one in which the second alkali metal hydroxide solution is added to the first reaction mixture. For example, there are methods in which the second alkali metal hydroxide solution is added dropwise directly and methods in which the second alkali metal hydroxide solution is sprayed. However, the method of spraying the second alkali metal hydroxide solution is preferred because it provides good uniformity of the second alkali metal hydroxide in the resulting first reaction mixture.

[0033] From the viewpoints of etherification reaction efficiency and ease of handling, the concentration of the second alkali metal hydroxide solution is preferably 10 to 60 mass %, more preferably 30 to 50 mass %. The first alkali metal hydroxide solution and the second alkali metal hydroxide solution preferably have the same concentration, but may have different concentrations.

[0034] When the second alkali metal hydroxide solution is added to the first reaction mixture, i.e., the timing of starting the addition of the second alkali metal hydroxide solution is preferably after the addition of 80 mass% or more of the total amount of alkylating agent to be added has been completed and the addition of the hydroxyalkylating agent to be added has been completed, more preferably after the addition of the alkylating agent and the hydroxyalkylating agent has been completed. If the timing of starting the addition of the second alkali metal hydroxide solution is before the addition of 80 mass% or more of the total amount of alkylating agent to be added has been completed, a hydroxyalkyl alkyl cellulose having a high storage modulus G' (80°C) may not be produced.

[0035] From the viewpoint of achieving both a high storage modulus G' (80°C) and a small number of undissolved fibers, the amount of the second alkali metal hydroxide in the second alkali metal hydroxide solution is preferably 0.70 to 2.50, more preferably 0.80 to 1.9, in terms of the number of moles of the second alkali metal hydroxide relative to the number of moles of solid components in the starting pulp when the molecular weight of anhydroglucose units is 1 mole (molar ratio of second alkali metal hydroxide / solid components in pulp).

[0036] The temperature inside the reactor at the start of adding the second alkali metal hydroxide solution to the first reaction mixture, i.e., the temperature of the first reaction mixture at the start of adding the second alkali metal hydroxide solution to the first reaction mixture, is preferably 65 to 90°C, more preferably 70 to 85°C, and even more preferably 75 to 85°C, from the viewpoint of producing a hydroxyalkyl alkyl cellulose having a high storage modulus G' (80°C) and from the viewpoint of reaction control. Furthermore, from the viewpoint of obtaining a hydroxyalkyl alkyl cellulose having high thermal gel strength, the temperature inside the reactor (the temperature of the mixture of the first reaction mixture and the second alkali metal hydroxide solution) when the addition of the second alkali metal hydroxide solution is completed is preferably 80° C. to 100° C., more preferably 85° C. to 95° C. In order to increase the temperature inside the reactor, preferably at a constant rate, the temperature at the start of the addition is preferably lower than the temperature at the completion of the addition, and the temperature difference is preferably 3° C. to 20° C., more preferably 4° C. to 15° C.

[0037] The addition rate of the second alkali metal hydroxide in the second alkali metal hydroxide solution is preferably 2.76 to 7.50 mol / mol·hr, more preferably 2.76 to 5.00 mol / mol·hr, and even more preferably 2.76 to 4.50 mol / mol·hr, as expressed as the molar amount (molar ratio) of the second alkali metal hydroxide added per unit time relative to the number of moles of solid components in the starting pulp when the molecular weight of anhydroglucose units (AGU) is 1 mole. If the addition rate of the second alkali metal hydroxide is less than 2.76 mol / mol·hr, it may be impossible to produce a hydroxyalkyl alkyl cellulose that achieves both high thermal gel strength and a reduced number of undissolved fibers. On the other hand, if the addition rate of the second alkali metal hydroxide exceeds 7.50 mol / mol·hr, it may be impossible to produce a hydroxyalkyl alkyl cellulose with high thermal gel strength.

[0038] After the second alkali metal hydroxide solution is added to the first reaction mixture, it is preferable to carry out stirring and mixing.

[0039] In the step of adding the second alkali metal hydroxide solution to the first reaction mixture, in order to obtain a hydroxyalkyl alkyl cellulose having high gel strength, it is preferable to carry out the compounding while increasing the temperature inside the reactor at a constant rate from the start to the completion of the addition of the second alkali metal hydroxide solution. The rate of temperature increase is preferably 10.0 to 30.0°C / hr, more preferably 15.0 to 30.0°C / hr.

[0040] In general, alkali cellulose obtained by mixing cellulose pulp with an alkali metal hydroxide solution is converted into hydroxyalkyl alkyl cellulose by an etherification reaction with an alkylating agent and a hydroxyalkyl alkylating agent. In this case, the alkylating agent and hydroxyalkylating agent in the reaction system are gradually consumed as the etherification reaction proceeds. When the temperature inside the reactor is constant, the reaction rate of the etherification reaction gradually decreases as the alkylating agent and hydroxyalkyl alkylating agent in the reaction system are consumed. Therefore, by adding the second alkali metal hydroxide solution while increasing the temperature inside the reactor at a constant rate, the decrease in the reaction rate of the etherification reaction associated with the consumption of the alkylating agent and hydroxyalkylating agent is suppressed, and the etherification reaction rate associated with the addition of the second alkali metal hydroxide solution is relatively increased. This allows for the production of hydroxyalkyl alkyl cellulose with high thermal gel strength.

[0041] In the above-described method, the second alkali metal hydroxide solution is added to the first reaction mixture without further adding an alkylating agent or a hydroxyalkylating agent to obtain a second reaction mixture. From the viewpoint of efficiently reducing the number of undissolved fibers, it is particularly preferable not to separate the alkylating agent and the hydroxyalkylating agent, and the alkylating agent and the hydroxyalkylating agent are added in the first step of adding the first alkali metal hydroxide solution.

[0042] In addition to the above-mentioned methods, it is also possible to separate the alkylating agent into a first alkylating agent and a second alkylating agent, or the hydroxyalkylating agent into a first hydroxyalkylating agent and a second hydroxyalkylating agent, and then mix the first alkylating agent and the first hydroxyalkylating agent to obtain a first reaction mixture, and then further mix the second alkylating agent and / or the second hydroxyalkylating agent to obtain a second reaction mixture.

[0043] When the alkylating agent is added in two separate portions, the amount of the second alkylating agent added to the first reaction mixture is, from the viewpoint of achieving both high thermal gel strength and a reduced number of undissolved fibers, and from an economic viewpoint, preferably 0.05 to 3.72, more preferably 0.05 to 2.50, in terms of the ratio of the number of moles of the second alkylating agent to the number of moles of the solid components in the starting pulp when the molecular weight of an anhydroglucose unit (AGU) is 1 mole (molar ratio: second alkylating agent / solid components in pulp). Furthermore, the molar ratio of the second alkylating agent to the total molar amount of the first alkylating agent and the second alkylating agent is preferably 0.01 to 0.40, more preferably 0.01 to 0.35, from the viewpoint of achieving both high thermal gel strength and a reduced number of undissolved fibers, and from the viewpoint of economy. When the alkylating agent is mixed in two separate portions, the amount of the first alkylating agent mixed is preferably selected so that the molar ratio of the second alkylating agent to the total molar amount of the first alkylating agent and the second alkylating agent falls within the above range.

[0044] When the hydroxyalkylating agent is added in two separate portions, the amount of the second hydroxyalkylating agent added to the first reaction mixture is, from the viewpoint of achieving both high thermal gel strength and a reduced number of undissolved fibers, and from an economic viewpoint, preferably 0.05 to 1.00, more preferably 0.05 to 0.80, in terms of the ratio of the number of moles of the second hydroxyalkylating agent to the number of moles of the solid components in the starting pulp when the molecular weight of an anhydroglucose unit (AGU) is 1 mole (second hydroxyalkylating agent / solid components in pulp). Furthermore, the molar ratio of the second hydroxyalkylating agent to the total molar amount of the first hydroxyalkylating agent and the second hydroxyalkylating agent (second hydroxyalkylating agent / total hydroxyalkylating agents) is preferably 0.01 to 0.40, more preferably 0.01 to 0.35, from the viewpoint of achieving both high thermal gel strength and a reduced number of undissolved fibers, as well as from an economic viewpoint. When the hydroxyalkylating agent is added in two separate installments, the amount of the first hydroxyalkylating agent added is preferably selected so that the molar ratio of the second hydroxyalkylating agent to the total molar amount of the first hydroxyalkylating agent and the second hydroxyalkylating agent falls within the above-mentioned range.

[0045] The internal temperature of the reactor at the start of blending when a second alkylating agent and / or a second hydroxyalkylating agent is further blended with the first reaction mixture, preferably the internal temperature of the reactor at the start of addition when the second alkylating agent and / or the second hydroxyalkylating agent is added to the first reaction mixture, is preferably 65 to 90°C, more preferably 70 to 85°C, and even more preferably 75 to 85°C. The blending time when a second alkylating agent and / or a second hydroxyalkylating agent is further blended into the first reaction mixture, preferably the addition time when a second alkylating agent and / or a second hydroxyalkylating agent is further added to the first reaction mixture, is preferably 3 to 60 minutes, more preferably 5 to 40 minutes, from the viewpoint of productivity.

[0046] When a second etherification agent is not used, a second alkali metal hydroxide solution is blended with the first reaction mixture. When a second etherification agent (a second alkylating agent and / or a second hydroxyalkylating agent) is used, the second alkali metal hydroxide solution and the etherification agent are blended with the first reaction mixture, and stirring and mixing are continued to complete the etherification reaction, thereby obtaining a second reaction mixture. To complete the reaction, heating is preferably performed after each blending. In each case, the internal temperature of the reactor during stirring and mixing after blending is preferably 80 to 120°C, more preferably 85 to 100°C, from the viewpoint of reaction controllability. In each case, the stirring and mixing time after blending is preferably 10 to 60 minutes, more preferably 20 to 40 minutes, from the viewpoint of productivity.

[0047] The first reaction mixture may be mixed with the second alkali metal hydroxide solution, the second alkylating agent, and the second hydroxyalkylating agent in the following manner: (1) A second alkali metal hydroxide solution is combined with a first reaction mixture to obtain a second reaction mixture; (2) An embodiment in which either one or both of a second alkylating agent and a second hydroxyalkylating agent are added to a first reaction mixture, and then a second alkali metal hydroxide solution is added to obtain a second reaction mixture; (3) A second alkylating agent is added to the first reaction mixture, followed by a second hydroxyalkylating agent and then a second alkali metal hydroxide solution to obtain a second reaction mixture; (4) A second hydroxyalkylating agent is added to the first reaction mixture, followed by adding a second alkylating agent and then adding a second alkali metal hydroxide solution to obtain a second reaction mixture; (5) An embodiment in which a second alkali metal hydroxide solution is added to the first reaction mixture, and then either or both of a second alkylating agent and a second hydroxyalkylating agent are added to obtain a second reaction mixture; (6) A second alkali metal hydroxide solution is added to the first reaction mixture, followed by addition of a second alkylating agent and then a second hydroxyalkylating agent to obtain a second reaction mixture; (7) A second alkali metal hydroxide solution is added to the first reaction mixture, followed by adding a second hydroxyalkylating agent and then adding a second alkylating agent to obtain a second reaction mixture; (8) An embodiment in which a second alkylating agent is added to the first reaction mixture, followed by adding a second alkali metal hydroxide solution, and then adding a second hydroxyalkylating agent to obtain a second reaction mixture; (9) An embodiment in which a second hydroxyalkylating agent is added to a first reaction mixture, followed by adding a second alkali metal hydroxide solution, and then adding a second alkylating agent to obtain a second reaction mixture; (10) An embodiment in which a second alkali metal hydroxide solution and a second alkylating agent or a second hydroxyalkylating agent are combined with the first reaction mixture to obtain a second reaction mixture; (11) An embodiment in which a second alkali metal hydroxide solution and a second alkylating agent are added to a first reaction mixture, and then a second hydroxyalkylating agent is added to obtain a second reaction mixture; (12) An embodiment in which a second alkali metal hydroxide solution and a second hydroxyalkylating agent are added to the first reaction mixture, and then a second alkylating agent is added to obtain a second reaction mixture; (13) An embodiment includes a method in which both the second alkali metal hydroxide solution and the second hydroxyalkylating agent, as well as the second alkylating agent, are mixed with the first reaction mixture to obtain a second reaction mixture. From the viewpoint of obtaining a hydroxyalkyl alkyl cellulose with a high storage modulus G' (80°C) and reducing the complexity of the operation, (1) an embodiment in which a second alkali metal hydroxide solution is blended with the first reaction mixture, followed by obtaining a second reaction mixture, and (13) an embodiment in which both the second alkali metal hydroxide solution and the second hydroxyalkylating agent, and the second alkylating agent are blended with the first reaction mixture, followed by obtaining a second reaction mixture, are preferred, and (1) an embodiment in which a second alkali metal hydroxide solution is blended with the first reaction mixture, followed by obtaining a second reaction mixture, is particularly preferred.

[0048] Next, the step of purifying the resulting second reaction mixture to obtain hydroxyalkyl alkyl cellulose will be described. The resulting second reaction mixture can be purified in the same manner as in the conventional purification method for crude hydroxyalkyl alkyl cellulose to obtain hydroxyalkyl alkyl cellulose. For example, the purification method involves mixing the second reaction mixture with water at 60 to 100°C in a stirring vessel to form a slurry, dissolving salts generated as by-products during the reaction in the stirring vessel, and then subjecting the slurry to a separation operation to remove the salts in order to obtain the desired purified cellulose ether. For example, a pressure rotary filter can be used for the separation operation. After the separation operation, the mixture is dried using a dryer, such as a conductive heat transfer groove-type agitator dryer.

[0049] If necessary, the obtained hydroxyalkyl alkyl cellulose can be pulverized to a desired particle size using a conventional pulverizer such as a ball mill, a roller mill, or an impact pulverizer, and the particle size can then be adjusted by classification using a sieve.

[0050] The degree of substitution (DS) of the alkyloxy group of the obtained hydroxyalkyl alkyl cellulose is preferably 1.60 to 2.00, more preferably 1.65 to 1.95, even more preferably 1.70 to 1.95, and particularly preferably 1.80 to 1.95, from the viewpoint of achieving both high thermal gel strength and a reduced number of undissolved fibers. The molar substitution (MS) of the hydroxyalkoxy group of the hydroxyalkyl alkyl cellulose is preferably 0.03 to 0.35, more preferably 0.05 to 0.30, even more preferably 0.15 to 0.30, and particularly preferably 0.15 to 0.27, from the viewpoint of achieving the desired thermal gel strength and thermal gelation temperature. Although the degree of substitution (DS) of the alkoxy groups of the hydroxyalkyl alkyl cellulose increases by mixing the first reaction mixture with the second alkali metal hydroxide solution, the increase in the hydroxyalkoxy groups (MS) of the hydroxyalkyl alkyl cellulose is smaller than the increase in the degree of substitution (DS) of the alkoxy groups after mixing the first reaction mixture with the second alkali metal hydroxide solution.

[0051] Examples of hydroxyalkyl alkyl cellulose include hydroxypropyl methyl cellulose and hydroxyethyl methyl cellulose. Hydroxypropyl methylcellulose has a degree of substitution (DS) of methoxy groups of preferably 1.60 to 2.00, more preferably 1.65 to 1.95, even more preferably 1.70 to 1.95, and particularly preferably 1.80 to 1.95, and a molar degree of substitution (MS) of hydroxypropoxy groups of preferably 0.03 to 0.35, more preferably 0.05 to 0.30, even more preferably 0.15 to 0.30, and particularly preferably 0.15 to 0.27. The hydroxyethyl methylcellulose has a degree of substitution (DS) of methoxy groups of preferably 1.60 to 2.00, more preferably 1.65 to 1.95, even more preferably 1.70 to 1.95, and particularly preferably 1.80 to 1.95, and a molar degree of substitution (MS) of hydroxyethoxy groups of preferably 0.03 to 0.35, more preferably 0.05 to 0.30, even more preferably 0.15 to 0.30, and particularly preferably 0.15 to 0.27.

[0052] The viscosity of a 2% by mass aqueous solution of hydroxyalkyl alkyl cellulose at 20°C is preferably 1000 to 200,000 mPa·s, more preferably 1000 to 100,000 mPa·s, even more preferably 1000 to 20,000 mPa·s, and particularly preferably 1000 to 10,000 mPa·s, from the viewpoint of achieving both viscosity suitable for the intended use or high thermal gel strength and a low number of undissolved fibers. The viscosity of a 2% by mass aqueous solution of hydroxyalkyl alkyl cellulose at 20°C can be measured using a single-cylinder rotational viscometer in accordance with the rotational viscometer method of the viscosity measurement method in the general testing methods described in the 17th edition of the Japanese Pharmacopoeia.

[0053] From the viewpoint of improving the shape retention of the clay when used as a binder, the storage modulus G'(80°C) of a 2.0% by mass aqueous solution of hydroxyalkyl alkyl cellulose at 80°C is preferably 5 to 200 Pa, more preferably 8 to 150 Pa, even more preferably 10 to 100 Pa, and particularly preferably 10 to 30 Pa. In general, the storage modulus represents the elastic component of the solution, that is, the component with the property of returning to its original shape when deformation caused by the application of force to an object is removed, and is an index of thermal gel strength.

[0054] A 2.0% by mass aqueous solution of hydroxyalkyl alkyl cellulose is prepared as follows: An amount equivalent to 6.00 g of hydroxyalkyl alkyl cellulose (calculated as dry matter) is accurately weighed into a wide-mouth bottle (a 350 ml container with a diameter of 65 mm and a height of 120 mm), and hot water (98°C) is added to make 300.0 g. The container is then capped and stirred at 350-450 revolutions per minute for 20 minutes using a stirrer until a uniform dispersion is obtained. The solution is then dissolved in a water bath at or below 5°C for 40 minutes while stirring, to prepare the sample solution. The storage modulus G'(80°C) of a 2.0 mass % aqueous solution of hydroxyalkyl alkyl cellulose at 80°C can be measured using, for example, rheometers MCR500, MCR501, and MCR502 manufactured by Anton Paar. The sample measurement section of the rheometer is pre-heated to 30°C, and a 2.0% by mass aqueous solution of hydroxyalkyl alkyl cellulose is poured into a CC27 measuring cup (a cylindrical container with a diameter of 30 mm and a height of 80 mm) up to the marked line (25 ml). Measurement is then initiated at a frequency of 1 Hz and a strain amplitude of 0.5%. The sample measurement section is heated to 80°C at a rate of 2°C per minute. Data is collected at two points per minute. The storage modulus G' obtained in this measurement changes as the temperature of the measurement system increases, and the storage modulus when the temperature of the measurement system reaches 80°C is defined as the storage modulus G' (80°C) in this invention.

[0055] The number of undissolved fibers having a size of 8 to 200 μm when measured by the Coulter counter method in 2 ml of a 0.1% by mass aqueous solution of hydroxyalkyl alkyl cellulose at 25°C is preferably 2,500 or less, more preferably 500 to 1,800, and even more preferably 500 to 1,600, from the viewpoint of product quality. Specifically, the number of undissolved fibers measured by the Coulter Counter method is determined by first dissolving hydroxyalkyl alkyl cellulose in a thermostatic bath of an ISOTON II electrolyte solution for Coulter Counter (manufactured by Beckman Coulter) at 25°C to give a 0.1% by mass aqueous solution. Next, the number of undissolved fibers with a size of 8 to 200 μm present in 2 ml of this aqueous solution is measured using a Coulter Counter TA II model (manufactured by Beckman Coulter) with a 400 μm diameter aperture tube. [Example]

[0056] EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. Example 1 Pine pulp had a pore volume of 0.84 ml / g, a pulp density of 0.58 g / ml, and an intrinsic viscosity of 5.9 dl / g. The pulp sheet was immersed in a 49% by mass aqueous solution of sodium hydroxide at 20°C as a first alkali metal hydroxide solution, and then squeezed to remove excess 49% by mass aqueous solution of sodium hydroxide, thereby obtaining alkali cellulose (hereinafter also referred to as "starting alkali cellulose"). The contact time between the pulp sheet and the 49% by mass aqueous solution of sodium hydroxide was 30 seconds, and the mass ratio of the 49% by mass aqueous solution of sodium hydroxide to the solid components in the pulp during the immersion step (sodium hydroxide solution / solid components in the pulp) was 20 kg / kg. The molar amount (molar ratio) of the first sodium hydroxide per mole of anhydroglucose units in the obtained alkali cellulose was 2.95 mol / mol. The mass ratio of the first sodium hydroxide to the total mass of the first sodium hydroxide in the first aqueous sodium hydroxide solution and the second sodium hydroxide in a second aqueous sodium hydroxide solution described below was 0.66. 11.6 kg of the obtained alkali cellulose was charged into a jacketed internally stirred pressure reactor, and vacuum nitrogen substitution was performed several times to thoroughly remove oxygen from the reactor. Next, the reactor was stirred while controlling the temperature to 60 ° C., followed by adding 2.2 kg of dimethyl ether, and the temperature was controlled to maintain the reactor temperature at 60 ° C. After the addition of dimethyl ether, the reactor temperature was raised from 60 ° C. to 80 ° C., and the first alkylating agent, methyl chloride, was added over 60 minutes so that the molar amount of the first methyl chloride per mole of anhydroglucose units of cellulose in the starting alkali cellulose was 5.81 [mol / mol]. Simultaneously with the start of the addition of methyl chloride, the first hydroxyalkylating agent, propylene oxide, was added over 10 minutes so that the molar amount of the first propylene oxide per mole of anhydroglucose units of cellulose in the starting alkali cellulose was 1.34 [mol / mol], to obtain a first reaction mixture. Following completion of the first methyl chloride addition, a second alkali metal hydroxide solution (49% by mass sodium hydroxide aqueous solution) was added at an addition rate of 3.04 mol / mol hr per mole of anhydroglucose units in the starting alkali cellulose, so that the molar amount (molar ratio) of second sodium hydroxide per mole of anhydroglucose units in the starting alkali cellulose was 1.52 mol / mol, forming a second reaction mixture. The reactor temperature at the start of the second sodium hydroxide aqueous solution addition was 80 °C, and the reactor temperature was increased at a rate of 18.0 °C / hr from the start to the completion of the second sodium hydroxide aqueous solution addition. The reactor temperature at the completion of the second sodium hydroxide aqueous solution addition was 89 °C. After completion of the second sodium hydroxide aqueous solution addition, stirring was continued for 30 minutes to complete the etherification reaction. The resulting second reaction mixture was slurried by adding hot water at 95°C, washed using a rotary pressure filter, dried in a blower dryer, and then crushed in a Victory Mill, an impact crusher, and classified using a sieve to obtain hydroxypropyl methylcellulose. The experimental conditions are shown in Table 1. Table 2 shows the methoxy groups (DS), hydroxypropoxy groups (MS) of the obtained hydroxypropyl methylcellulose, the viscosity of a 2% by mass aqueous solution at 20°C, the storage modulus G' (80°C) of a 2% by mass aqueous solution of hydroxypropyl methylcellulose at 80°C, and the number of undissolved fibers having a size of 8 to 200 μm when measured in 2 ml of a 0.1% by mass aqueous solution at 25°C.

[0057] Example 2 Alkali cellulose was obtained in the same manner as in Example 1, except that chip-form pulp made from hemlock wood and having a pore volume of 0.70 ml / g, a pulp density of 0.72 g / ml, and an intrinsic viscosity of 13.0 dl / g was used. The contact time between the pulp and the 49% by mass aqueous sodium hydroxide solution was 48 seconds, and the mass ratio of the 49% by mass aqueous sodium hydroxide solution to the solid components in the pulp (sodium hydroxide solution / solid components in the pulp) during the immersion step was 180 kg / kg. The molar amount (molar ratio) of the first sodium hydroxide per mole of anhydroglucose unit in the obtained alkali cellulose was 3.04 mol / mol. The mass ratio of the first sodium hydroxide to the total mass of the first sodium hydroxide in the first aqueous sodium hydroxide solution and the second sodium hydroxide in the second aqueous sodium hydroxide solution described below was 0.66. 11.6 kg of the obtained alkali cellulose was charged into a jacketed internally stirred pressure reactor, and vacuum nitrogen substitution was performed once to remove oxygen from the reactor. Thereafter, a first reaction mixture was prepared in the same manner as in Example 1, except that methyl chloride was used as the first methylating agent and the molar amount (molar ratio) of the first alkylating agent per mole of anhydroglucose unit in the starting alkali cellulose was 6.00 [mol / mol]. Next, a 49% by mass aqueous solution of sodium hydroxide was used as the second alkali metal hydroxide solution, and the aqueous solution of sodium hydroxide was added at an addition rate of 3.14 [mol / mol·hr] per mole of anhydroglucose unit in the starting alkali cellulose so that the molar amount (molar ratio) of the second sodium hydroxide per mole of anhydroglucose unit in the starting alkali cellulose was 1.57 [mol / mol].The temperature inside the reactor was raised at 16.1°C / hr from the start to the completion of the addition of the second aqueous sodium hydroxide solution, and the temperature inside the reactor at the completion of the addition of the second aqueous sodium hydroxide solution was 90.7°C.The procedure was the same as in Example 1, except that The resulting second reaction mixture was purified and pulverized to obtain hydroxypropyl methylcellulose in the same manner as in Example 1. The experimental conditions are shown in Table 1. Table 2 shows the methoxy group (DS), hydroxypropoxy group (MS) of the obtained hydroxypropyl methylcellulose, the viscosity of a 2% by mass aqueous solution at 20°C, the storage modulus G' (80°C) of a 2% by mass aqueous solution of hydroxypropyl methylcellulose at 80°C, and the number of undissolved fibers having a size of 8 to 200 μm when measured in 2 ml of a 0.1% by mass aqueous solution at 25°C using an aperture tube with a diameter of 400 μm.

[0058] Example 3 Alkali cellulose was obtained in the same manner as in Example 1, except that sheet-form pulp made from hemlock wood, having a pore volume of 0.70 ml / g, a pulp density of 0.72 g / ml, and an intrinsic viscosity of 13.0 dl / g, was used. The contact time between the pulp and the 49% by mass aqueous sodium hydroxide solution was 55 seconds, and the mass ratio of the 49% by mass aqueous sodium hydroxide solution to the solid components in the pulp (sodium hydroxide solution / solid components in the pulp) during the immersion step was 20 kg / kg. The molar amount (molar ratio) of the first sodium hydroxide per mole of anhydroglucose unit in the obtained alkali cellulose was 3.35 mol / mol. The mass ratio of the first sodium hydroxide to the total mass of the first sodium hydroxide in the first aqueous sodium hydroxide solution and the second sodium hydroxide in the second aqueous sodium hydroxide solution described below was 0.740. The obtained alkali cellulose was converted into a first reaction mixture using the same method as in Example 1, except that methyl chloride was used as the first methylating agent and the molar ratio of the first methylating agent per mole of anhydroglucose unit in the starting alkali cellulose was 6.00 [mol / mol]. Following completion of the addition of the first methyl chloride, a 49% by mass aqueous solution of sodium hydroxide was used as the second alkali metal hydroxide solution, and the aqueous solution of sodium hydroxide was added at an addition rate of 2.83 [mol / mol hr] per mole of anhydroglucose unit in the starting alkali cellulose so that the molar amount (molar ratio) of the second sodium hydroxide per mole of anhydroglucose unit in the starting alkali cellulose was 1.18 [mol / mol]. From the start to the completion of the addition of the second aqueous solution of sodium hydroxide, the temperature inside the reactor was raised at 18.0°C / hr, and the temperature inside the reactor at the start of the addition of the second aqueous solution of sodium hydroxide was 79°C, and the temperature inside the reactor at the completion of the addition of the second aqueous solution of sodium hydroxide was 91°C. The same procedure as in Example 1 was repeated, except that The resulting second reaction mixture was purified and pulverized to obtain hydroxypropyl methylcellulose in the same manner as in Example 1. The experimental conditions are shown in Table 1. Table 2 shows the methoxy group (DS), hydroxypropoxy group (MS) of the obtained hydroxypropyl methylcellulose, the viscosity of a 2% by mass aqueous solution at 20°C, the storage modulus G' (80°C) of a 2% by mass aqueous solution of hydroxypropyl methylcellulose at 80°C, and the number of undissolved fibers having a size of 8 to 200 μm when measured in 2 ml of a 0.1% by mass aqueous solution at 25°C using an aperture tube with a diameter of 400 μm.

[0059] Example 4 Alkali cellulose was obtained in the same manner as in Example 1, except that spruce pulp chips with a pore volume of 0.56 ml / g, a pulp density of 0.76 g / ml, and an intrinsic viscosity of 13.5 dL / g were used. The contact time between the pulp and the 49% by mass aqueous sodium hydroxide solution was 68 seconds, and the mass ratio of the 49% by mass aqueous sodium hydroxide solution to the solid components in the pulp (sodium hydroxide solution / solid components in the pulp) during the immersion step was 180 kg / kg. The molar amount (molar ratio) of the first sodium hydroxide per mole of anhydroglucose unit in the obtained alkali cellulose was 2.95 mol / mol. The mass ratio of the first sodium hydroxide to the total mass of the first sodium hydroxide in the first aqueous sodium hydroxide solution and the second sodium hydroxide in the second aqueous sodium hydroxide solution described below was 0.66. 11.6 kg of the obtained alkali cellulose was charged into a jacketed, internally stirred pressure-resistant reactor, and the reactor was evacuated and purged with nitrogen once to remove oxygen from the reactor. Thereafter, a first reaction mixture was prepared in the same manner as in Example 1. Next, a 49% by mass aqueous solution of sodium hydroxide was used as the second alkali metal hydroxide solution, and the aqueous solution of sodium hydroxide was added at an addition rate of 3.08 [mol / mol·hr] per mole of anhydroglucose unit in the starting alkali cellulose so that the molar amount (molar ratio) of the second sodium hydroxide per mole of anhydroglucose unit in the starting alkali cellulose was 1.54 [mol / mol].The temperature inside the reactor was raised at 18.0°C / hr from the start to the completion of the addition of the second aqueous sodium hydroxide solution, and the temperature inside the reactor at the completion of the addition of the second aqueous sodium hydroxide solution was 90.5°C.The procedure was the same as in Example 1, except that The resulting second reaction mixture was purified and pulverized to obtain hydroxypropyl methylcellulose in the same manner as in Example 1. The experimental conditions are shown in Table 1. Table 2 shows the methoxy group (DS), hydroxypropoxy group (MS) of the obtained hydroxypropyl methylcellulose, the viscosity of a 2% by mass aqueous solution at 20°C, the storage modulus G' (80°C) of a 2% by mass aqueous solution of hydroxypropyl methylcellulose at 80°C, and the number of undissolved fibers having a size of 8 to 200 μm when measured in 2 ml of a 0.1% by mass aqueous solution at 25°C using an aperture tube with a diameter of 400 μm.

[0060] Example 5 Alkali cellulose was obtained in the same manner as in Example 1, except that a spruce pulp sheet having a pore volume of 0.56 ml / g, a pulp density of 0.76 g / ml, and an intrinsic viscosity of 13.5 dL / g was used. The contact time between the pulp and the 49% by mass aqueous sodium hydroxide solution was 73 seconds, and the mass ratio of the 49% by mass aqueous sodium hydroxide solution to the solid components in the pulp (sodium hydroxide solution / solid components in the pulp) during the immersion step was 20 kg / kg. The molar amount (molar ratio) of the first sodium hydroxide per mole of anhydroglucose unit in the obtained alkali cellulose was 2.95 mol / mol. The mass ratio of the first sodium hydroxide to the total mass of the first sodium hydroxide in the first aqueous sodium hydroxide solution and the second sodium hydroxide in the second aqueous sodium hydroxide solution described below was 0.66. 11.6 kg of the obtained alkali cellulose was charged into a jacketed, internally stirred pressure-resistant reactor, and the reactor was evacuated and purged with nitrogen once to remove oxygen from the reactor. Thereafter, a first reaction mixture was prepared in the same manner as in Example 1. Next, a 49% by mass aqueous solution of sodium hydroxide was used as the second alkali metal hydroxide solution, and the aqueous solution of sodium hydroxide was added at an addition rate of 3.08 [mol / mol·hr] per mole of anhydroglucose unit in the starting alkali cellulose so that the molar amount (molar ratio) of the second sodium hydroxide per mole of anhydroglucose unit in the starting alkali cellulose was 1.54 [mol / mol].The temperature inside the reactor was raised at 19.0°C / hr from the start to the completion of the addition of the second aqueous solution of sodium hydroxide, and the temperature inside the reactor at the completion of the addition of the second aqueous solution of sodium hydroxide was 91.0°C.The procedure was the same as in Example 1, except that The resulting second reaction mixture was purified and pulverized to obtain hydroxypropyl methylcellulose in the same manner as in Example 1. The experimental conditions are shown in Table 1. Table 2 shows the methoxy group (DS), hydroxypropoxy group (MS) of the obtained hydroxypropyl methylcellulose, the viscosity of a 2% by mass aqueous solution at 20°C, the storage modulus G' (80°C) of a 2% by mass aqueous solution of hydroxypropyl methylcellulose at 80°C, and the number of undissolved fibers having a size of 8 to 200 μm when measured in 2 ml of a 0.1% by mass aqueous solution at 25°C using an aperture tube with a diameter of 400 μm.

[0061] Example 6 Alkali cellulose was obtained in the same manner as in Example 1, except that chip-form pulp made from pine wood, having a pore volume of 0.84 ml / g, a pulp density of 0.58 g / ml, and an intrinsic viscosity of 5.9 dl / g, was used. The contact time of the chip-form pulp with the 49% by mass aqueous sodium hydroxide solution was 35 seconds, and the mass ratio of the 49% by mass aqueous sodium hydroxide solution to the solid components in the pulp (sodium hydroxide solution / solid components in pulp) during the immersion step was 180 kg / kg. The molar amount (molar ratio) of the first sodium hydroxide per mole of anhydroglucose unit in the obtained alkali cellulose was 3.20 mol / mol. The mass ratio of the first sodium hydroxide to the total mass of the first sodium hydroxide in the first aqueous sodium hydroxide solution and the second sodium hydroxide in the second aqueous sodium hydroxide solution described below was 0.75. The obtained alkali cellulose (11.6 kg) was charged into a jacketed internally stirred pressure reactor, and vacuum nitrogen substitution was performed several times to thoroughly remove oxygen from the reactor. Then, methyl chloride was used as the first methylating agent, and the molar amount (molar ratio) of the first alkylating agent per mole of anhydroglucose units in the starting alkali cellulose was 5.55 [mol / mol], and propylene oxide was used as the first hydroxyalkylating agent, and the molar amount (molar ratio) of the first propylene oxide per mole of anhydroglucose units in the starting alkali cellulose was 0.67 [mol / mol]. The first reaction mixture was prepared in the same manner as in Example 1. Next, a 49% by mass aqueous solution of sodium hydroxide was used as the second alkali metal hydroxide solution, and the aqueous solution of sodium hydroxide was added at an addition rate of 2.92 [mol / mol·hr] per mole of anhydroglucose unit in the starting alkali cellulose so that the molar amount (molar ratio) of the second sodium hydroxide per mole of anhydroglucose unit in the starting alkali cellulose was 1.07 [mol / mol].The temperature inside the reactor was raised at 15.9°C / hr from the start to the completion of the addition of the second aqueous sodium hydroxide solution, and the temperature inside the reactor at the completion of the addition of the second aqueous sodium hydroxide solution was 89.3°C.The procedure was the same as in Example 1, except that The resulting second reaction mixture was purified and pulverized to obtain hydroxypropyl methylcellulose in the same manner as in Example 1. The experimental conditions are shown in Table 1. Table 2 shows the methoxy group (DS), hydroxypropoxy group (MS) of the obtained hydroxypropyl methylcellulose, the viscosity of a 2% by mass aqueous solution at 20°C, the storage modulus G' (80°C) of a 2% by mass aqueous solution of hydroxypropyl methylcellulose at 80°C, and the number of undissolved fibers having a size of 8 to 200 μm when measured in 2 ml of a 0.1% by mass aqueous solution at 25°C using an aperture tube with a diameter of 400 μm.

[0062] Example 7 Alkali cellulose was obtained in the same manner as in Example 1, except that a sheet-form pulp made from pine wood, having a pore volume of 0.93 ml / g, a pulp density of 0.61 g / ml, and an intrinsic viscosity of 8.2 dL / g, was used. The contact time between the pulp and the 49% by mass aqueous sodium hydroxide solution was 25 seconds, and the mass ratio of the 49% by mass aqueous sodium hydroxide solution to the solid components in the pulp (sodium hydroxide solution / solid components in pulp) during the immersion step was 20 kg / kg. The molar amount (molar ratio) of the first sodium hydroxide per mole of anhydroglucose unit in the obtained alkali cellulose was 2.95 mol / mol. The mass ratio of the first sodium hydroxide to the total mass of the first sodium hydroxide in the first aqueous sodium hydroxide solution and the second sodium hydroxide in the second aqueous sodium hydroxide solution described below was 0.66. 11.6 kg of the obtained alkali cellulose was charged into a jacketed, internally stirred pressure-resistant reactor, and the reactor was evacuated and purged with nitrogen several times to thoroughly remove oxygen from the reactor. Thereafter, a first reaction mixture was prepared in the same manner as in Example 1. Next, the second aqueous sodium hydroxide solution was added at an addition rate of 3.04 [mol / mol·hr] per mole of anhydroglucose unit in the starting alkali cellulose so that the molar amount (molar ratio) of the second sodium hydroxide per mole of anhydroglucose unit in the starting alkali cellulose was 1.52 [mol / mol], and the temperature inside the reactor was raised at 21.4°C / hr from the start to completion of the addition of the second aqueous sodium hydroxide solution, and the temperature inside the reactor at the completion of the addition of the second aqueous sodium hydroxide solution was 90.7°C. The procedure was the same as in Example 1, except for this. The resulting second reaction mixture was purified, pulverized, and treated in the same manner as in Example 1 to obtain hydroxypropyl methylcellulose. The experimental conditions are shown in Table 1. Table 2 shows the methoxy group (DS), hydroxypropoxy group (MS) of the obtained hydroxypropyl methylcellulose, the viscosity of a 2% by mass aqueous solution at 20°C, the storage modulus G' (80°C) of a 2% by mass aqueous solution of hydroxypropyl methylcellulose at 80°C, and the number of undissolved fibers having a size of 8 to 200 μm when measured in 2 ml of a 0.1% by mass aqueous solution at 25°C using an aperture tube with a diameter of 400 μm.

[0063] Comparative Example 1 Wood pulp with a pulp density of 0.58 g / ml and an intrinsic viscosity of 5.9 dl / g was ground in a grinder to obtain powdered cellulose pulp. A portion of this powdered cellulose pulp, equivalent to 6.0 kg of cellulose content, was placed in a jacketed, internally stirred, pressure-resistant reactor and subjected to one vacuum nitrogen purge to remove oxygen from the reactor. Next, the reactor was stirred while maintaining an internal temperature of 60°C. A 49% by mass aqueous sodium hydroxide solution was added as a first alkali metal hydroxide solution at a rate of 10.72 mol / mol hr per mole of anhydroglucose units in the starting cellulose pulp, so that the molar amount (molar ratio) of the first sodium hydroxide per mole of anhydroglucose units in the alkali cellulose was 2.68 mol / mol. This produced a first alkali cellulose (hereinafter also referred to as "starting alkali cellulose"). The mass ratio of the first sodium hydroxide to the total mass of the first sodium hydroxide in the first aqueous sodium hydroxide solution and the second sodium hydroxide in a second aqueous sodium hydroxide solution described below was 0.60. 11.6 kg of the obtained alkali cellulose was charged into a jacketed, internally stirred pressure-resistant reactor, and the reactor was evacuated and purged with nitrogen several times to thoroughly remove oxygen from the reactor. Thereafter, a first reaction mixture was prepared in the same manner as in Example 1. Following completion of the first methyl chloride addition, a second reaction mixture was prepared by adding a 49% by mass aqueous sodium hydroxide solution as the second alkali metal hydroxide solution at a rate of 3.58 mol / mol h per mole of anhydroglucose unit in the starting alkali cellulose, so that the molar ratio of the second sodium hydroxide per mole of anhydroglucose unit in the starting alkali cellulose was 1.79 mol / mol. The reactor temperature was 80.5°C at the start of the second aqueous sodium hydroxide addition, and the reactor temperature was increased at a rate of 19.0°C / h from the start to the completion of the second aqueous sodium hydroxide addition. The reactor temperature was 90°C at the completion of the second aqueous sodium hydroxide addition. After the second aqueous sodium hydroxide addition was completed, stirring was continued for 30 minutes to complete the etherification reaction. The ratio of the mass of the first sodium hydroxide to the total mass of the first and second sodium hydroxides in the first and second aqueous sodium hydroxide solutions was 0.6. The resulting second reaction mixture was purified and pulverized to obtain hydroxypropyl methylcellulose in the same manner as in Example 1. The experimental conditions are shown in Table 1. The methoxy group (DS), hydroxypropoxy group (MS) of the obtained hydroxypropyl methylcellulose, the viscosity of a 2% by mass aqueous solution at 20°C, the storage modulus G' (80°C) of a 2% by mass aqueous solution of hydroxypropyl methylcellulose at 80°C, and the number of undissolved fibers having a size of 8 to 200 μm when measured in 2 ml of a 0.1% by mass aqueous solution at 25°C using an aperture tube with a diameter of 400 μm are shown in Table 2. Compared to Example 1, the storage modulus G' (80°C) was higher, but the number of undissolved fibers was also higher.

[0064] Comparative Example 2 A first alkali cellulose was prepared in the same manner as in Comparative Example 1, except that the first aqueous sodium hydroxide solution was added at an addition rate of 14.64 [mol / mol hr] per mole of anhydroglucose unit in the starting cellulose pulp so that the molar amount (molar ratio) of first sodium hydroxide per mole of anhydroglucose unit in the alkali cellulose was 3.66 [mol / mol]. The mass ratio of the first sodium hydroxide to the total mass of the first sodium hydroxide in the first aqueous sodium hydroxide solution and the second sodium hydroxide in the second aqueous sodium hydroxide solution described below was 0.80. The obtained alkali cellulose was prepared as a first reaction mixture in the same manner as in Example 1, except that methyl chloride was used as the first alkylating agent, the molar amount (molar ratio) of the first methyl chloride per mole of anhydroglucose units in the starting alkali cellulose was 5.93 [mol / mol], and propylene oxide was used as the first hydroxyalkylating agent, the molar amount (molar ratio) of the first propylene oxide per mole of anhydroglucose units in the starting alkali cellulose was 1.35 [mol / mol]. Following completion of the first methyl chloride addition, a 49% by mass aqueous sodium hydroxide solution was used as the second alkali metal hydroxide solution. The second aqueous sodium hydroxide solution was added at an addition rate of 1.82 mol / mol hr per mole of anhydroglucose unit in the starting alkali cellulose, so that the molar amount (molar ratio) of the second sodium hydroxide per mole of anhydroglucose unit in the starting alkali cellulose was 0.92 mol / mol, forming a second reaction mixture. The reactor temperature at the start of the second aqueous sodium hydroxide addition was 79.5 °C, and the reactor temperature was increased at a rate of 25.0 °C / hr from the start to the completion of the second aqueous sodium hydroxide addition. The reactor temperature at the completion of the second aqueous sodium hydroxide addition was 92.0 °C. After completion of the second aqueous sodium hydroxide addition, stirring was continued for 30 minutes to complete the etherification reaction. The resulting second reaction mixture was purified and pulverized to obtain hydroxypropyl methylcellulose in the same manner as in Example 1. The experimental conditions are shown in Table 1. The methoxy group (DS), hydroxypropoxy group (MS) of the obtained hydroxypropyl methylcellulose, the viscosity of a 2% by mass aqueous solution at 20°C, the storage modulus G' (80°C) of a 2% by mass aqueous solution of hydroxypropyl methylcellulose at 80°C, and the number of undissolved fibers having a size of 8 to 200 μm when measured in 2 ml of a 0.1% by mass aqueous solution at 25°C using an aperture tube with a diameter of 400 μm are shown in Table 2. Compared to Example 1, the storage modulus G' (80°C) was similar, but the number of undissolved fibers was higher.

[0065] Comparative Example 3 A spruce pulp sheet having a pore volume of 1.25 ml / g, a pulp density of 0.47 g / ml, and an intrinsic viscosity of 13.5 dl / g was immersed in a 49% by mass aqueous solution of sodium hydroxide at 20°C as a first alkali metal hydroxide solution, followed by squeezing to remove excess 49% by mass aqueous solution of sodium hydroxide, yielding alkali cellulose. The contact time between the pulp and the 49% by mass aqueous solution of sodium hydroxide was 10 seconds, and it was difficult to shorten the time from contact with the sodium hydroxide aqueous solution to deliquification by squeezing. The mass ratio of the 49% by mass aqueous solution of sodium hydroxide to the solid component in the pulp during the immersion step was 20 kg / kg. The molar amount (molar ratio) of the first sodium hydroxide per mole of anhydroglucose units in the obtained alkali cellulose was 3.70 mol / mol. The mass ratio of the first sodium hydroxide to the total mass of the first sodium hydroxide in the first aqueous sodium hydroxide solution and the second sodium hydroxide in a second aqueous sodium hydroxide solution described below was 0.85. The obtained alkali cellulose (11.6 kg) was charged into a jacketed internally stirred pressure reactor, and vacuum nitrogen substitution was performed once to remove oxygen from the reactor. Thereafter, the molar amount (molar ratio) of the first methyl chloride per mole of anhydroglucose unit in the starting alkali cellulose was set to 5.65 [mol / mol], and propylene oxide was used as the first hydroxyalkylating agent. The molar amount (molar ratio) of the first propylene oxide per mole of anhydroglucose unit in the starting alkali cellulose was set to 1.38 [mol / mol]. A first reaction mixture was obtained using the same method as in Example 1. Following completion of the first methyl chloride addition, a 49% by mass aqueous sodium hydroxide solution was used as the second alkali metal hydroxide solution. The second aqueous sodium hydroxide solution was added at an addition rate of 1.30 mol / mol hr per mole of anhydroglucose units in the starting alkali cellulose, so that the molar amount (molar ratio) of the second sodium hydroxide per mole of anhydroglucose units in the starting alkali cellulose was 0.65 mol / mol, forming a second reaction mixture. The reactor temperature at the start of the second aqueous sodium hydroxide addition was 80.5 °C, and the reactor temperature was increased at a rate of 18.0 °C / hr from the start to the completion of the second aqueous sodium hydroxide addition. The reactor temperature at the completion of the second aqueous sodium hydroxide addition was 89.5 °C. After completion of the second aqueous sodium hydroxide addition, stirring was continued for 30 minutes to complete the etherification reaction. The resulting second reaction mixture was purified and pulverized to obtain hydroxypropyl methylcellulose in the same manner as in Example 1. The experimental conditions are shown in Table 1. The methoxy group (DS), hydroxypropoxy group (MS) of the obtained hydroxypropyl methylcellulose, the viscosity of a 2% by mass aqueous solution at 20°C, the storage modulus G' (80°C) of a 2% by mass aqueous solution of hydroxypropyl methylcellulose at 80°C, and the number of undissolved fibers having a size of 8 to 200 μm when measured in 2 ml of a 0.1% by mass aqueous solution at 25°C using an aperture tube with a diameter of 400 μm are shown in Table 2. Compared to Example 3, the number of undissolved fibers was lower, but the storage modulus G' (80°C) was also lower.

[0066] Comparative Example 4 Alkali cellulose was obtained in the same manner as in Comparative Example 3, except that spruce pulp chips with a pore volume of 1.12 ml / g, a pulp density of 0.55 g / ml, and an intrinsic viscosity of 7.0 dl / g were used. The mass ratio of the 49% by mass aqueous sodium hydroxide solution to the solid components in the pulp during the soaking step was 180 kg / kg. The molar amount (molar ratio) of the first sodium hydroxide per mole of anhydroglucose unit in the obtained alkali cellulose was 3.66 mol / mol. The mass ratio of the first sodium hydroxide to the total mass of the first sodium hydroxide in the first aqueous sodium hydroxide solution and the second sodium hydroxide in the second aqueous sodium hydroxide solution described below was 0.849. 11.6 kg of the obtained alkali cellulose was charged into a jacketed internally stirred pressure reactor, and vacuum nitrogen substitution was performed once to remove oxygen from the reactor. A first reaction mixture was prepared in the same manner as in Example 1, except that the molar amount (molar ratio) of the first methyl chloride per mole of anhydrous glucose units in the starting alkali cellulose was 4.44 [mol / mol], and the molar amount (molar ratio) of the first propylene oxide per mole of anhydrous glucose units in the starting alkali cellulose was 0.67 [mol / mol]. Following completion of the addition of the first methyl chloride, a second alkali metal hydroxide solution (49% by mass sodium hydroxide aqueous solution) was added at a rate of 1.30 mol / mol·hr per mole of anhydroglucose unit in the starting alkali cellulose, so that the molar amount of second sodium hydroxide per mole of anhydroglucose unit in the starting alkali cellulose was 0.65 mol / mol. Simultaneously with the addition of the second alkali metal hydroxide solution, methyl chloride was added over 15 minutes as a second alkylating agent so that the molar amount of second methyl chloride per mole of anhydroglucose unit in the starting alkali cellulose was 1.16 mol / mol, forming a second reaction mixture. The molar amount of the second alkylating agent relative to the total molar amount of the first and second alkylating agents was 0.2. The temperature inside the reactor at the start of the addition of the second aqueous sodium hydroxide solution was 80.5°C, and the temperature inside the reactor was increased at a rate of 18.0°C / hr from the start to the completion of the addition of the second aqueous sodium hydroxide solution. The temperature inside the reactor at the completion of the addition of the second aqueous sodium hydroxide solution was 89.5°C. After the addition of the second aqueous sodium hydroxide solution was completed, the etherification reaction was completed in the same manner as in Example 1. The ratio of the mass of the first sodium hydroxide to the total mass of the first and second sodium hydroxides in the first and second aqueous sodium hydroxide solutions was 0.85. The resulting second reaction mixture was purified and pulverized to obtain hydroxypropyl methylcellulose in the same manner as in Example 1. The experimental conditions are shown in Table 1. The methoxy groups (DS), hydroxypropoxy groups (MS) of the obtained hydroxypropyl methylcellulose, the viscosity of a 2% by mass aqueous solution at 20°C, the storage modulus G' (80°C) of a 2% by mass aqueous solution of hydroxypropyl methylcellulose at 80°C, and the number of undissolved fibers having a size of 8 to 200 μm when measured in 2 ml of a 0.1% by mass aqueous solution at 25°C using an aperture tube with a diameter of 400 μm are shown in Table 2. Compared to Example 2, the number of undissolved fibers was lower, but the storage modulus G' (80°C) was also lower.

[0067] Comparative Example 5 Alkali cellulose was obtained in the same manner as in Comparative Example 3, except that spruce pulp chips having a pore volume of 1.15 ml / g, a pulp density of 0.50 g / ml, and an intrinsic viscosity of 10.0 dl / g were used. The molar amount (molar ratio) of first sodium hydroxide per mole of anhydroglucose unit in the obtained alkali cellulose was 3.68 [mol / mol]. The mass ratio of the 49% by mass aqueous sodium hydroxide solution to the solid component in the pulp in the soaking step was 180 [kg / kg]. The mass ratio of the first sodium hydroxide to the total mass of the first sodium hydroxide in the first aqueous sodium hydroxide solution and the second sodium hydroxide in the second aqueous sodium hydroxide solution described below was 0.850. 11.6 kg of the obtained alkali cellulose was charged into a jacketed, internally stirred pressure reactor, and vacuum and nitrogen substitution were performed several times to thoroughly remove oxygen from the reactor. Thereafter, a first reaction mixture was prepared in the same manner as in Comparative Example 3. Following completion of the addition of the first methyl chloride, a 49% by mass aqueous sodium hydroxide solution was used as the second alkali metal hydroxide solution. The second aqueous sodium hydroxide solution was added at an addition rate of 1.30 [mol / mol hr] per mole of anhydroglucose unit in the starting alkali cellulose, so that the molar amount (molar ratio) of the second sodium hydroxide per mole of anhydroglucose unit in the starting alkali cellulose was 0.65 [mol / mol], to obtain a second reaction mixture. The reactor temperature at the start of the addition of the second aqueous sodium hydroxide solution was 80.5°C, and the reactor temperature was increased at a rate of 18.0°C / hr from the start to the completion of the addition of the second aqueous sodium hydroxide solution. The reactor temperature at the completion of the addition of the second aqueous sodium hydroxide solution was 89.5°C. After completion of the addition of the second aqueous sodium hydroxide solution, the etherification reaction was completed in the same manner as in Example 1. The ratio of the mass of the first sodium hydroxide to the total mass of the first and second sodium hydroxides in the first and second aqueous sodium hydroxide solutions was 0.85. The resulting second reaction mixture was purified and pulverized to obtain hydroxypropyl methylcellulose in the same manner as in Example 1. The experimental conditions are shown in Table 1. The methoxy groups (DS), hydroxypropoxy groups (MS) of the obtained hydroxypropyl methylcellulose, the viscosity of a 2% by mass aqueous solution at 20°C, the storage modulus G' (80°C) of a 2% by mass aqueous solution of hydroxypropyl methylcellulose at 80°C, and the number of undissolved fibers having a size of 8 to 200 μm when measured in 2 ml of a 0.1% by mass aqueous solution at 25°C using an aperture tube with a diameter of 400 μm are shown in Table 2. Compared to Example 2, the number of undissolved fibers was lower, but the storage modulus G' (80°C) was also lower.

[0068] Comparative Example 6 Alkali cellulose was obtained in the same manner as in Comparative Example 3, except that a spruce pulp sheet having a pore volume of 1.15 ml / g, a pulp density of 0.50 g / ml, and an intrinsic viscosity of 10.0 dl / g was used. The molar amount (molar ratio) of first sodium hydroxide per mole of anhydroglucose unit in the obtained alkali cellulose was 3.68 [mol / mol]. The mass ratio of the 49% by mass aqueous sodium hydroxide solution to the solid component in the pulp in the soaking step was 180 [kg / kg]. The mass ratio of the first sodium hydroxide to the total mass of the first sodium hydroxide in the first aqueous sodium hydroxide solution and the second sodium hydroxide in the second aqueous sodium hydroxide solution described below was 0.850. 11.6 kg of the obtained alkali cellulose was charged into a jacketed, internally stirred pressure reactor, and vacuum and nitrogen substitution were performed several times to thoroughly remove oxygen from the reactor. Thereafter, a first reaction mixture was prepared in the same manner as in Comparative Example 3. Following completion of the addition of the first methyl chloride, a 49% by mass aqueous sodium hydroxide solution was used as the second alkali metal hydroxide solution. The second aqueous sodium hydroxide solution was added at an addition rate of 1.30 [mol / mol hr] per mole of anhydroglucose unit in the starting alkali cellulose, so that the molar amount (molar ratio) of the second sodium hydroxide per mole of anhydroglucose unit in the starting alkali cellulose was 0.65 [mol / mol], to obtain a second reaction mixture. The reactor temperature at the start of the addition of the second aqueous sodium hydroxide solution was 80.5°C, and the reactor temperature was increased at a rate of 19.0°C / hr from the start to the completion of the addition of the second aqueous sodium hydroxide solution. The reactor temperature at the completion of the addition of the second aqueous sodium hydroxide solution was 90.5°C. After completion of the addition of the second aqueous sodium hydroxide solution, the etherification reaction was completed in the same manner as in Example 1. The ratio of the mass of the first sodium hydroxide to the total mass of the first and second sodium hydroxides in the first and second aqueous sodium hydroxide solutions was 0.85. The resulting second reaction mixture was purified and pulverized to obtain hydroxypropyl methylcellulose in the same manner as in Example 1. The experimental conditions are shown in Table 1. The methoxy group (DS), hydroxypropoxy group (MS) of the obtained hydroxypropyl methylcellulose, the viscosity of a 2% by mass aqueous solution at 20°C, the storage modulus G' (80°C) of a 2% by mass aqueous solution of hydroxypropyl methylcellulose at 80°C, and the number of undissolved fibers having a size of 8 to 200 μm when measured in 2 ml of a 0.1% by mass aqueous solution at 25°C using an aperture tube with a diameter of 400 μm are shown in Table 2. Compared to Example 3, the number of undissolved fibers was lower, but the storage modulus G' (80°C) was also lower.

[0069] Comparative Example 7 Alkali cellulose was obtained in the same manner as in Example 1, except that spruce pulp chips with a pore volume of 0.49 ml / g, a pulp density of 0.76 g / ml, and an intrinsic viscosity of 15.0 dl / g were used. The contact time between the pulp and the 49% by mass aqueous sodium hydroxide solution was 80 seconds, and the mass ratio of the 49% by mass aqueous sodium hydroxide solution to the solid components in the pulp (sodium hydroxide solution / solid components in the pulp) during the immersion step was 20 kg / kg. The molar amount (molar ratio) of the first sodium hydroxide per mole of anhydroglucose unit in the obtained alkali cellulose was 2.95 mol / mol. The mass ratio of the first sodium hydroxide to the total mass of the first sodium hydroxide in the first aqueous sodium hydroxide solution and the second sodium hydroxide in the second aqueous sodium hydroxide solution described below was 0.66. 11.6 kg of the obtained alkali cellulose was charged into a jacketed, internally stirred pressure-resistant reactor, and the reactor was evacuated and purged with nitrogen once to remove oxygen from the reactor. Thereafter, a first reaction mixture was prepared in the same manner as in Example 1. Next, a 49% by mass aqueous solution of sodium hydroxide was used as the second alkali metal hydroxide solution, and the aqueous solution of sodium hydroxide was added at an addition rate of 3.04 [mol / mol·hr] per mole of anhydroglucose unit in the starting alkali cellulose so that the molar amount (molar ratio) of the second sodium hydroxide per mole of anhydroglucose unit in the starting alkali cellulose was 1.54 [mol / mol].The temperature inside the reactor was raised at 19.0°C / hr from the start to the completion of the addition of the second aqueous solution of sodium hydroxide, and the temperature inside the reactor at the completion of the addition of the second aqueous solution of sodium hydroxide was 90.0°C.The procedure was the same as in Example 1, except for this. The resulting second reaction mixture was purified and pulverized to obtain hydroxypropyl methylcellulose in the same manner as in Example 1. The experimental conditions are shown in Table 1. The methoxy group (DS), hydroxypropoxy group (MS) of the obtained hydroxypropyl methylcellulose, the viscosity of a 2% by mass aqueous solution at 20°C, the storage modulus G' (80°C) of a 2% by mass aqueous solution of hydroxypropyl methylcellulose at 80°C, and the number of undissolved fibers having a size of 8 to 200 μm when measured in 2 ml of a 0.1% by mass aqueous solution at 25°C using an aperture tube with a diameter of 400 μm are shown in Table 2. The number of undissolved fibers was higher than in Example 4.

[0070] Comparative Example 8 Alkali cellulose was obtained in the same manner as in Example 1, except that spruce pulp chips with a pore volume of 0.49 ml / g, a pulp density of 0.76 g / ml, and an intrinsic viscosity of 15.0 dl / g were used. The contact time between the pulp and the 49% by mass aqueous sodium hydroxide solution was 85 seconds, and the mass ratio of the 49% by mass aqueous sodium hydroxide solution to the solid components in the pulp (sodium hydroxide solution / solid components in the pulp) during the immersion step was 180 kg / kg. The molar amount (molar ratio) of the first sodium hydroxide per mole of anhydroglucose unit in the obtained alkali cellulose was 2.95 mol / mol. The mass ratio of the first sodium hydroxide to the total mass of the first sodium hydroxide in the first aqueous sodium hydroxide solution and the second sodium hydroxide in the second aqueous sodium hydroxide solution described below was 0.66. 11.6 kg of the obtained alkali cellulose was charged into a jacketed, internally stirred pressure-resistant reactor, and the reactor was evacuated and purged with nitrogen once to remove oxygen from the reactor. Thereafter, a first reaction mixture was prepared in the same manner as in Example 1. Next, a 49% by mass aqueous solution of sodium hydroxide was used as the second alkali metal hydroxide solution, and the aqueous solution of sodium hydroxide was added at an addition rate of 3.04 [mol / mol·hr] per mole of anhydroglucose unit in the starting alkali cellulose so that the molar amount (molar ratio) of the second sodium hydroxide per mole of anhydroglucose unit in the starting alkali cellulose was 1.54 [mol / mol].The temperature inside the reactor was raised at 18.0°C / hr from the start to the completion of the addition of the second aqueous solution of sodium hydroxide, and the temperature inside the reactor at the completion of the addition of the second aqueous solution of sodium hydroxide was 90.5°C.The procedure was the same as in Example 1, except that The resulting second reaction mixture was purified and pulverized to obtain hydroxypropyl methylcellulose in the same manner as in Example 1. The experimental conditions are shown in Table 1. The methoxy group (DS), hydroxypropoxy group (MS) of the obtained hydroxypropyl methylcellulose, the viscosity of a 2% by mass aqueous solution at 20°C, the storage modulus G' (80°C) of a 2% by mass aqueous solution of hydroxypropyl methylcellulose at 80°C, and the number of undissolved fibers having a size of 8 to 200 μm when measured in 2 ml of a 0.1% by mass aqueous solution at 25°C using an aperture tube with a diameter of 400 μm are shown in Table 2. The number of undissolved fibers was higher than in Example 5.

[0071] [Table 1]

[0072] [Table 2]

Claims

1. A method for producing a hydroxyalkyl alkyl cellulose, the method comprising: a step of contacting wood pulp having a pore volume of 0.55 ml / g or more and less than 1.00 ml / g or pulp chips obtained by cutting the wood pulp with a first alkali metal hydroxide solution to obtain an alkali cellulose mixture; deliquoring the alkali cellulose mixture to obtain alkali cellulose; reacting the alkali cellulose with an alkylating agent and a hydroxyalkylating agent to obtain a first reaction mixture; combining the first reaction mixture with a second alkali metal hydroxide solution to obtain a second reaction mixture; purifying the second reaction mixture to obtain a hydroxyalkyl alkyl cellulose; At least the step of mixing the first reaction mixture with the second alkali metal hydroxide solution includes adding the second alkali metal hydroxide solution to the first reaction mixture, and the addition rate of the second alkali metal hydroxide in the second alkali metal hydroxide solution is 2.76 to 7.50 mol / mol hr, expressed as the number of moles of the second alkali metal hydroxide added per unit time relative to the number of moles of the wood pulp or pulp chips, where 1 mole of anhydroglucose unit is taken as 1; a ratio of the mass of the first alkali metal hydroxide to the total mass of the first alkali metal hydroxide in the first alkali metal hydroxide solution and the second alkali metal hydroxide in the second alkali metal hydroxide solution is 0.6 to 0.8; the storage modulus G' of the obtained hydroxyalkyl alkyl cellulose in a 2.0% by mass aqueous solution at 80°C is 10 to 30 Pa, and the number of undissolved fibers having a size of 8 to 200 μm when measured by a Coulter counter method in 2 ml of a 0.1% by mass aqueous solution of the obtained hydroxyalkyl alkyl cellulose at 25°C is 500 to 2,500. A method for producing the hydroxyalkyl alkyl cellulose.

2. 2. The method for producing hydroxyalkyl alkyl cellulose according to claim 1, wherein the sheet density of the wood pulp is 0.55 to 0.80 g / ml.

3. The method for producing hydroxyalkyl alkyl cellulose according to claim 1 or 2, wherein the intrinsic viscosity of the wood pulp is 3.0 to 15.0 dl / g.

4. A method for producing a hydroxyalkyl alkyl cellulose as described in claim 1 or 2, wherein the first reaction mixture is heated from the start to the end of the addition of the second alkali metal hydroxide solution.

5. The method for producing hydroxyalkyl alkyl cellulose according to claim 4, wherein the temperature increase rate is 10.0 to 30.0 ° C. / hr.

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