DESCRIPTION Title of Invention: CELLULOSE DERIVATIVE, THERMO-MOLDING MATERIAL, MOLDED BODY AND METHOD FOR PREPARATION THEREOF, AND CASE FOR ELECTRIC AND ELECTRONIC DEVICES Technical Field [0001] The present invention relates to a cellulose derivative, a thermo-molding material, a molded body and a method for preparation thereof, and a case for electric and electronic devices. Background Art [0002] In members constituting electric and electronic devices such as a copy machine and a printer, various materials are used in consideration of characteristics and functions required for the members. For example, for a member (case) that plays a role of receiving a driving apparatus of an electric and electronic device or the like, and protecting the driving apparatus, a large amount of PC (polycarbonate), an ABS (acrylonitrile-butadiene-styrene) resin, PC/ABS or the like are generally used (Patent Document 1). These resins are prepared by reacting compounds obtained by using petroleum as a raw material. [0003] By the way, fossil resources, such as petroleum, coal and natural gas, include carbon fixed under the earth over a long period of time as a main component. In the case where carbon dioxide is discharged into the atmosphere by combusting such fossil resources or products using the fossil resources as a raw material, carbon that does not exist in the atmosphere but is fixed deeply under the earth, is rapidly discharged as carbon dioxide, and thus, carbon dioxide in the atmosphere is largely increased, thereby causing a global warming. Accordingly, a polymer such as ABS and PC having petroleum, which is a fossil resource, as a raw material has excellent properties as a material of the member for electric and electronic devices, but since petroleum, which is a fossil resource, is used as the raw material, it is preferable that the amount used is decreased from the standpoint of preventing the global warming. [0004] Meanwhile, a plant-derived resin is basically generated by a photosynthesis reaction using water and carbon dioxide in the atmosphere as raw materials by plants. Therefore, there is an opinion that, although carbon dioxide is generated by combusting a plant-derived resin, the carbon dioxide corresponds to carbon dioxide previously existing in the atmosphere, and thus, the balance of carbon dioxide in the atmosphere becomes zero-sum, such that the total amount of CO2 in the atmosphere is not increased. Based on this opinion, the plant-derived resin is called a "carbon neutral" material. The use of the carbon neutral material instead of the petroleum-derived resin has gained importance in preventing the current global warming. [0005] Therefore, in the PC polymer, there is proposed a method for decreasing petroleum-derived resources by using plant-derived resources such as starch as a portion of the petroleum-derived raw materials (Patent Document 2). However, there is a need for further improvement from the standpoint of targeting a more perfect carbon neutral material. [0006] As a known cellulose derivative, hydroxypropylmethylacetyl cellulose is described in Patent Documents 3 and 4. Patent Documents 3 and 4 describe that the hydroxypropylmethylacetyl cellulose is useful as an additive for reducing the vapor pressure of organic solvents which are easily volatilized. Further, for the degree of substitution of each substituent in the hydroxypropylmethylacetyl cellulose described in Patent Documents 3 and 4, for example, it is described that a molar degree of substitution (MS) of a hydroxypropyl group is in a range of about 2 to about 8, a degree of substitution of a methyl group is in a range of about 0.1 to about 1, and a degree of substitution of an acetyl group is in a range of about 0.8 to about 2.5. [0007] Moreover, as a use of coating of medicaments, hydroxypropylmethylpropyl cellulose, hydroxypropylmethylbutyl cellulose, and the like (Patent Document 5), and hydroxypropyl methylcellulose phthalate, and the like, (Patent Document 6) are disclosed. Related Art Patent Document [0008] Patent Document 1: Japanese Patent Application Laid-Open No. Sho 56-55425 Patent Document 2: Japanese Patent Application Laid-Open No. 2008-24919 Patent Document 3: US Patent No. 3,979,179 Patent Document 4: US Patent No. 3,940,384 Patent Document 5: International Publication No. WO 09/010837 Patent Document 6: Japanese Patent No. 3017412 Disclosure of Invention Problems to Be Solved by the Invention [0009] The present inventors paid an attention on using cellulose as a carbon neutral resin. However, cellulose, generally having no thermoplasticity, is not appropriate for molding processing due to difficulty in molding by heating and the like. In addition, even if thermoplasticity could be imparted to cellulose, there still is the problem that strength such as impact resistance is largely deteriorated. Furthermore, there is also room for improvement on heat resistance. For example, the cellulose derivatives described in Patent Documents 3, 4 and 6 are water-soluble or swellable, and thus, are not preferable as a molding material. Further, although the cellulose derivative described in Patent Document 5 is described as water-soluble, there is only a description in the text, and there are no specific disclosures on a synthesis method, a use form thereof, and the like, in the form of Example, and the like. An object of the present invention is to provide a cellulose derivative and a thermo-molding material that have good thermoplasticity, strength and heat resistance, and are suitable for molding processing. Means for Solving the Problems [0010] The present inventors found out, in consideration of a molecular structure of cellulose, that good thermoplasticity, impact resistance and heat resistance are exhibited when using a cellulose derivative having a specific structure as the cellulose, thereby accomplishing the present invention. That is, the above object may be accomplished by the following means. [1] A thermo-molding material comprising a water-insoluble cellulose derivative, wherein the water-insoluble cellulose derivative comprises: A) a hydrocarbon group; B) a group containing an acyl group: -CO-RB1 and an alkyleneoxy group: -RB2-0- (RB1 represents a hydrocarbon group, and RB2 represents an alkylene group having 3 carbon atoms); and C) an acyl group: -CO-Rc (Re represents a hydrocarbon group). [2] The thermo-molding material of [1] above, wherein A) the hydrocarbon group is an alkyl group having 1 to 4 carbon atoms. [3] The thermo-molding material of [1] above, wherein A) the hydrocarbon group is a methyl group or an ethyl group. [4] The thermo-molding material of any one of [1] to [3] above, wherein each of Rb1 and Re independently represents an alkyl group or an aryl group. [5] The thermo-molding material of any one of [1] to [4] above, wherein each of Rb1 and Re independently represents a methyl group, an ethyl group, or a propyl group. [6] The thermo-molding material of any one of [1] to [5] above, wherein the alkyleneoxy group is a group represented by the following formula (1) or formula (2). [0011] [Chem. 1] [7] The thermo-molding material of any one of [1] to [6] above, wherein B) the group containing an acyl group: -CO-RB1 and an alkyleneoxy group: -RB2-0- is a group containing a structure represented by the following Formula (3): [0012] [Chem. 2] Formula (3) [0013] (wherein, Rb1 represents a hydrocarbon group, and RB2 represents an alkylene group having 3 carbon atoms.) [8] The thermo-molding material of any one of [1] to [7] above, wherein the cellulose derivative has substantially no carboxyl group. [9] A water-insoluble cellulose derivative, comprising al) an ethyl group; bl) a group containing an acyl group: -CO-Rbl and an alkyleneoxy group: -Rb2-0-(Rbl represents a hydrocarbon group, and Rb2 represents an alkylene group having 3 carbon atoms); and cl) an acyl group: -CO-Rc (Re represents a hydrocarbon group). [10] A water-insoluble cellulose derivative, comprising a2) a methyl group; b2) a group containing an acyl group: -CO-Rbl and an alkyleneoxy group: -Rb2-0-(Rbl represents a hydrocarbon group, and Rb2 represents an alkylene group having 3 carbon atoms); and c2) an acyl group: -CO-Rc (Re represents a hydrocarbon group), wherein a degree of substitution of a2) the methyl group is 1.1 or more and a molar degree of substitution (MS) of the alkyleneoxy group is 1.5 or less. [11] The cellulose derivative of [9] or [10] above, wherein each of Rbl and Re independently represents a methyl group, an ethyl group, or a propyl group. [12] The cellulose derivative according of any one of [9] to [11] above, wherein the cellulose derivative has substantially no carboxyl group. [13] A case for electric and electronic devices, composed of a molding body obtained by molding the thermo-molding material of any one of [1] to [8] above or the cellulose derivative of any one of [9] to [12] above. [14] A method for manufacturing a molded body, comprising: a step of heating and molding the thermo-molding material of any one of [1] to [8] above or the cellulose derivative of any one of [9] to [12] above. Effects of the Invention [0014] The cellulose derivative or thermo-molding material of the present invention has excellent thermoplasticity, and thus, may be manufactured into a molded body. Further, a molded body formed by the cellulose derivative or thermo-molding material of the present invention has good impact resistance, heat resistance, and the like, and thus, may be used appropriately as component parts such as automobiles, home electric appliances, electric and electronic devices, mechanical parts, materials for housing and construction, and the like. In addition, the cellulose derivative or thermo-molding material of the present invention is a plant-derived resin and is a material which may contribute to the prevention of global warming, and thus, the cellulose derivative or thermo-molding material of the present invention may replace petroleum-derived resins of the related art. Furthermore, the cellulose derivative and thermo-molding material of the present invention exhibit biodegradability, and thus, are expected to be used as a material with less environmental load. Embodiments for Carrying Out the Invention [0015] A thermo-molding material of the present invention contains a water-insoluble cellulose derivative containing A) a hydrocarbon group, B) a group containing an acyl group: -CO-RB1 and an alkyleneoxy group: -RB2-0- (RB1 represents a hydrocarbon group and RB2 represents an alkylene group having 3 carbon atoms), and C) an acyl group: -CO-Rc (Re represents a hydrocarbon group). Hereinafter, the present invention will be described in detail. [0016] 1. Cellulose Drivative A cellulose derivative contained in the thermo-molding material of the present invention has: A) a hydrocarbon group, B) a group containing an acyl group: -CO-RB1 and an alkyleneoxy group: -RB2-0- (RB1 represents a hydrocarbon group and RB2 represents an alkylene group having 3 carbon atoms), and C) an acyl group: -CO-Rc (Re represents a hydrocarbon group). That is, the cellulose derivative in the present invention is obtained by substituting at least a portion of hydrogen atoms of a hydroxyl group contained in the cellulose {(C6HioOs)n} with A) a hydrocarbon group, B) a group containing an acyl group (-CO-Rb1) and an alkyleneoxy group (-RB2-0-), and C) an acyl group (-CO-Rc). More specifically, the cellulose derivative in the present invention has a repeating unit represented by the following Formula (A). [0017] [Chem. 3] Formula (A) [0018] In the formula, each of R2, R3 and R6 independently represents a hydrogen atom, A) a hydrocarbon group, B) a group containing an acyl group (-CO-RB1) and an alkyleneoxy group (-RB2-0-), or C) an acyl group (-CO-Rc). Each of RB1 and Re independently represents a hydrocarbon group. RB2 represents an alkylene group having 3 carbon atoms. However, at least a portion of R2, R3 and R6 represents a hydrocarbon group and at least a portion of R2, R3 and R6 represents a group containing an acyl group (-CO-RB1) and an alkyleneoxy group (-RB2-0-), and at least a portion of R2, R3 and R6 represents an acyl group (-CO-Rc). [0019] As described above, the cellulose derivative of the present invention may exhibit thermoplasticity because at least a portion of the hydroxyl groups of the P-glucose ring is etherified and esterified by A) the hydrocarbon group, B) the group containing an acyl group (-CO-RB1) and an alkyleneoxy group (-RB2-0-), and C) the acyl group (-CO-Rc), thereby being appropriate for molding processing. Further, the cellulose derivative is water-insoluble and may also exhibit excellent strength and heat resistance as a molded body. Furthermore, since cellulose is a completely plant-derived component, cellulose is carbon neutral, and may greatly reduce the environmental load. As used herein, "water-insoluble" means that the solubility thereof in 100 parts by mass of water (pH 3 to 11) at 25°C is 5 parts by mass or less. [0020] As used herein, "cellulose" means a polymer compound in which a plurality of glucoses are linked by p-l,4-glycoside bonds with the hydroxyl groups bonded to the carbon atoms at the 2-, 3- and 6-position of each glucose ring of the cellulose being unsubstituted. Further, "hydroxyl groups contained in cellulose" represents hydroxyl groups which are bonded to the carbon atoms at the 2-, 3- and 6-position of each glucose ring of the cellulose. [0021] The cellulose derivative in the present invention contains: at least one group in which a hydrogen atom of a hydroxyl group contained in the cellulose is substituted by A) a hydrocarbon group, at least one group in which a hydrogen atom of a hydroxyl group contained in the cellulose is substituted by B) a group containing an acyl group (-CO-RB1) and an alkyleneoxy group (-RB2-0-), and at least one group in which a hydrogen atom of a hydroxyl group contained in the cellulose is substituted by C) an acyl group (-CO-Rc). The cellulose derivative of the present invention may have two or more different kinds of groups as the A) to C). The cellulose derivative may contain A) the hydrocarbon group, B) the group containing an acyl group (-CO-RB1) and an alkyleneoxy group (-RB2-0-), and C) the acyl group (-CO-Rc) at any one part of the whole thereof, and may be composed of the same repeating units and of plural kinds of repeating units. In addition, it is not necessary for the cellulose derivative to contain all the substituents of the A) to C) in a single repeating unit. As more specific aspects, there may be the following aspects. (1) A cellulose derivative composed of a repeating unit in which a portion of R2, R3 and R6 is substituted with A) a hydrocarbon group, a repeating unit in which a portion of R2, R3 and R6 is substituted with B) a group containing an acyl group (-CO-RB1) and an alkylene group (-RB2-0-), and a repeating unit in which a portion of R2, R3 and R6 is substituted with C) an acyl group (-CO-Rc). (2) A cellulose derivative composed of the same repeating units in which any one ofR2, R3 and R6 in one repeating unit is substituted with A) a hydrocarbon group, B) a group containing an acyl group (-CO-RB1) and an ethyleneoxy group (-RB2-0-), and C) an acyl group (-CO-Rc) (that is, having all the substituents of the A) to C) in one repeating unit). (3) A cellulose derivative in which repeating units of different substitution positions or different kinds of the substituents in the A) to C) are randomly bonded. In addition, a part of the cellulose derivative may contain an unsubstituted repeating unit (that is, a repeating unit in which all of R2, R3 and R6 are a hydrogen atom in Formula (1)). [0022] A) the hydrocarbon group may be any one of an aliphatic group and an aromatic group. When the hydrocarbon group is an aliphatic group, it may be straight, branched or cyclic and may have an unsaturated bond. Examples of the aliphatic group include an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group and the like. Examples of the aromatic group include a phenyl group, a naphthyl group, a phenanthryl group, an anthryl group, and the like. A) the hydrocarbon group is preferably an aliphatic group, more preferably an alkyl group, and even more preferably an alkyl group having 1 to 4 carbon atoms (a lower alkyl group). Specific examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a pentyl group, a hexyl group, a heptyl group, a 2-ethylhexyl group, a tert-butyl group, an isoheptyl group and the like, with a methyl group or an ethyl group being preferred. [0023] In the acyl group (-CO-RB1), RB1 represents a hydrocarbon group. RB1 may be any one of an aliphatic group and an aromatic group. When the hydrocarbon group is an aliphatic group, it may be straight, branched or cyclic and may have an unsaturated bond. Examples of the aliphatic group include an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group and the like. Examples of the aromatic group may include a phenyl group, a naphthyl group, a phenanthryl group, an anthryl group, and the like. RB1 is preferably an alkyl group or an aryl group. Rb1 is more preferably an alkyl group having 1 to 12 carbon atoms or an aryl group, even more preferably an alkyl group having 1 to 12 carbon atoms, further more preferably an alkyl group having 1 to 4 carbon atoms, and most preferably an alkyl group having 1 or 2 carbon atoms (that is, a methyl group or an ethyl group). Specific examples of the Rb1 include a methyl group, an ethyl group, a propyl group, ah isopropyl group, a butyl group, an isobutyl group, a pentyl group, a hexyl group, a heptyl group, a 2-ethylhexyl group, a tert-butyl group, an isoheptyl group, a phenyl group, a naphthyl group and the like. Preferably, RB1 is a methyl group, an ethyl group, a propyl group and a phenyl group, and more preferably, RB1 is a methyl group, an ethyl group or a propyl group. [0024] In addition, in the alkyleneoxy group (-RB2-0-), an alkylene group moiety (RB2) having 3 carbon atoms may be straight, branched or cyclic, but is preferably straight or branched, and more preferably branched. Specifically, as the alkyleneoxy group (-RB2-0-), the following structure can be exemplified. [0025] [Chem. 4] [0026] Among the above-mentioned groups, a group represented by the following formula (1) or (2), wherein the alkylene group moiety, is branched is preferred. [0027] [Chem. 5] [0028] A plurality of the alkyleneoxy groups may be contained in the group of B), but a single alkyleneoxy group is preferably contained. When a plurality of the alkyleneoxy groups are contained, a structure of the alkylene group moiety having 3 carbon atoms may be the same or different. Further, the bonding direction of the alkyleneoxy group to the cellulose derivative is not particularly limited. However, it is preferred that an alkylene group moiety of the alkyleneoxy group is bonded to a side of a cellulose derivative molecule (a side of a glucose ring). [0029] B) the group containing an acyl group (-CO-RB1) and an alkyleneoxy group (-RB2-0-) is preferably a group containing a structure represented by the following formula (3). [0030] [Chem. 6] Formula (3) [0031] In the formula, RB1 represents a hydrocarbon group, and RB2 represents an alkylene group having 3 carbon atoms. The definition and preferable range of RB1 and RB2 in formula (3) are the same as those previously described. The group of B) may include a plurality of alkyleneoxy groups, or only one group. More specifically, the group of B) may be represented by the following Formula (T). [0032] [Chem. 7] Formula (V) [0033] In the formula, RB1 represents a hydrocarbon group, and RB2 represents an alkylene group having 3 carbon atoms, n represents a repeating number, and is a number of 1 or more. The definition and preferable range of RB1 and RB2 in formula (1') are the same as those previously described. The upper limit of n is not particularly limited and changes depending on the amount of alkyleneoxy groups introduced, and the like. However, the upper limit is, for example, about 10. Further, in the cellulose derivative, the group containing only one alkyleneoxy group (a group in which n is 1 in formula (1')) in B) and the group containing two or more alkyleneoxy groups (a group in which n is 1 in Formula (1')) in B) may be contained by mixture. [0034] In C) the acyl group (-CO-Rc), Re represents a hydrocarbon group. As a hydrocarbon group represented by Re, one exemplified in the RB may be applied. The preferable range of Re is also the same as that of the RB1. [0035] In the cellulose derivative, A) the hydrocarbon group, the hydrocarbon group represented by the RB1 and Re, and the alkylene group having 3 carbon atoms, represented by RB2 may have further substituents, or may be unsubstituted, but is preferably unsubstituted. In particular, when RB1 and Re have further substituents, it is preferred that a substituent which imparts water solubility, for example, a sulfonic acid group, a carboxyl group and the like, is not contained. A cellulose derivative which is water-insoluble and a molding material composed of the cellulose derivative may be obtained by excluding such a group. Further, when the cellulose derivative has a sulfonic acid group, a carboxyl group or the like, it is known that those groups deteriorate the stability of a compound, and it is preferred that the cellulose derivative does not contain these groups because these groups accelerate a thermal decomposition. [0036] When A) the hydrocarbon group, RB1, RC and RB2 have further substituents in the cellulose derivative, examples of the substituent include a halogen atom (for example, a fluorine atom, a chlorine atom, a bromine atom and an iodine atom), a hydroxyl group, an alkoxy group (the carbon number of an alkyl group moiety is preferably 1 to 5), an alkenyl group and the like. Meanwhile, when A) the hydrocarbon group, RB1, RC and RB2 are other than an alkyl group, it is possible to have an alkyl group (preferably 1 to 5 carbon atoms) as a substituent. [0037] Further, it is preferred that the cellulose derivative in the present invention has substantially no water-soluble substituent such as a carboxyl group, a sulfonic acid group and salts thereof. The cellulose derivative may have substantially no carboxyl group so as to allow a thermo-molding material to be water-insoluble, thereby improving moldability. Meanwhile, as used herein, "having substantially no carboxyl group" means to include the case where the cellulose derivative in the present invention has absolutely no carboxyl group, as well as the case where the cellulose derivative in the present invention has a very small amount of a carboxyl group in a range that the cellulose derivative is water-insoluble. For example, when a carboxyl group is contained in cellulose as a raw material cellulose, a cellulose derivative in which the substituent of A) to C) is introduced by using the cellulose may contain a carboxyl group. However, the cellulose derivative is meant to be included in "a cellulose derivative having substantially no carboxyl group". The carboxyl group contained in the cellulose derivative of the present invention is included in an amount of preferably 1 mass% or less, and more preferably 0.5 mass% or less, based on the cellulose derivative. [0038] In addition, the cellulose derivative in the present invention is preferably water-insoluble. Here, "water-insoluble" means that the solubility in 100 parts by mass of water (pH 3 to 11) at 25°C is 5 parts by mass or less. [0039] Specific examples of the cellulose derivative of the present invention include Acetoxypropylmethylacetyl cellulose, acetoxypropylethylacetyl cellulose, Acetoxypropylpropylacetyl cellulose, acetoxypropylbutylacetyl cellulose, Acetoxypropylpentylacetyl cellulose, acetoxypropylhexylacetyl cellulose, acetoxypropylcyclohexylacetyl cellulose, acetoxypropylphenylacetyl cellulose, acetoxypropylnaphthylacetyl cellulose, [0040] propionyloxypropylmethylacetyl cellulose, propionyloxypropylethylacetyl cellulose, propionyloxypropylpropylacetyl cellulose, propionyloxypropylbutylacetyl cellulose, propionyloxypropylpentylacetyl cellulose, propionyloxypropylhexylacetyl cellulose, propionyloxypropylcyclohexylacetyl cellulose, propionyloxypropylphenylacetyl cellulose, propionyloxypropylnaphthylacetyl cellulose, [0041] Valerooxypropylmethylvaleroyl cellulose, acetoxypropylpropionyloxypropylmethylacetylpropionyl cellulose, butyryloxypropylmethylacetyl cellulose, acetoxypropylbutyryloxypropylmethylacetylbutyryl cellulose, benzoyloxypropylmethyl cellulosebenzoate and the like. [0042] The positions of substitution of A) the hydrocarbon group, B) the group containing an acyl group (-CO-RB1) and an alkyleneoxy group (-RB2-0-), and C) the acyl group (-CO-Rc) in the cellulose derivative and the numbers of each substituent per p-glucose ring unit (the degrees of substitution) are not particularly limited. [0043] For example, the degree of substitution DSa of A) the hydrocarbon group (the number of A) the hydrocarbon groups with respect to the hydroxyl groups at the 2-, 3- and 6-positions of a P-glucose ring in a repeating unit) is preferably 1.0 30 g of hydroxypropylmethyl cellulose (trade name: Marpolose 60MP-4000; manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.; H-l) and 2,250 mL of N,N-dimethyl acetamide were measured and put into a 5-liter three-necked flask equipped with a mechanical stirrer, a thermometer, a cooling tube and a dropping funnel, followed by stirring at room temperature. After it was confirmed that the reaction system became transparent and was completely dissolved, 84 mL of acetyl chloride was slowly added dropwise, followed by increasing the temperature of the system to 80°C to 90°C. Stirring was continued for 3 hr, and then the reaction system was cooled to room temperature. The reaction solution was introduced into 10 L of water while vigorously stirring, whereupon a white solid was precipitated. The white solid was separated by suction filtration, and washed three times with large quantities of water. The obtained white solid was dried under vacuum at 100°C for 6 hr to obtain a desired cellulose derivative (C-l) (acetoxypropylmethylacetyl cellulose; the degrees of substitution thereof are described in Table 1) as a white powder (33.7 g). [0108] 60 g of hydroxypropylmethyl cellulose (trade name: Marpolose 65MP-4000; manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.; H-2) and 2,100 mL of N,N-dimethyl acetamide were measured and put into a 5-liter three-necked flask equipped with a mechanical stirrer, a thermometer, a cooling tube and a dropping funnel, followed by stirring at room temperature. After it was confirmed that the reaction system became transparent and was completely dissolved, 124 mL of acetyl chloride was slowly added dropwise, followed by increasing the temperature of the system to 80°C to 90°C. Stirring was continued for 3 hr, and then the reaction system was cooled to room temperature. The reaction solution was introduced into 10 L of water while vigorously stirring, whereupon a white solid was precipitated. The white solid was separated by suction filtration, and washed three times with large quantities of water. The obtained white solid was dried under vacuum at 100°C for 6 hr to obtain a desired cellulose derivative (C-2) (acetoxypropylmethylacetyl cellulose; the degrees of substitution thereof are described in Table 1) as a white powder (73.2 g). [0109] 60 g of hydroxypropylmethyl cellulose (trade name: Marpolose 90MP-4000; manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.; H-3) and 2,100 mL of N,N-dimethyl acetamide were measured and put into a 5-liter three-necked flask equipped with a mechanical stirrer, a thermometer, a cooling tube and a dropping funnel, followed by stirring at room temperature. After it was confirmed that the reaction system became transparent and was completely dissolved, 168 mL of acetyl chloride was slowly added dropwise, followed by increasing the temperature of the system to 80°C to 90°C. Stirring was continued for 3 hr, and then the reaction system was cooled to room temperature. The reaction solution was introduced into 10 L of water while vigorously stirring, whereupon a white solid was precipitated. The white solid was separated by suction filtration, and washed three times with large quantities of water. The obtained white solid was dried under vacuum at 100°C for 6 hr to obtain a desired cellulose derivative (C-3) (acetoxypropylmethylacetyl cellulose; the degrees of substitution thereof are described in Table 1) as a white powder (78.7 g). [0110] 30 g of hydroxypropylmethyl cellulose (trade name: Marpolose 90MP-4000; manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.; H-3) and 1,500 mL of N,N-dimethyl acetamide were measured and put into a 5-liter three-necked flask equipped with a mechanical stirrer, a thermometer, a cooling tube and a dropping funnel, followed by stirring at room temperature. After it was confirmed that the reaction system became transparent and was completely dissolved, 20.6 mL of acetyl chloride was slowly added dropwise, followed by increasing the temperature of the system to 80°C to 90°C. Stirring was continued for 3 hr, and then the reaction system was cooled to room temperature. The reaction solution was introduced into 10 L of water while vigorously stirring, whereupon a white solid was precipitated. The white solid was separated by suction filtration, and washed three times with large quantities of water. The obtained white solid was dried under vacuum at 100°C for 6 hr to obtain a desired cellulose derivative (C-4) (acetoxypropylmethylacetyl cellulose; the degrees of substitution thereof are described in Table 1) as a white powder (34.0 g). [0111] 60 g of hydroxypropylmethyl cellulose (trade name: Marpolose 90MP-4000; manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.; H-3) and 2,100 mL of N,N-dimethyl acetamide were measured and put into a 5-liter three-necked flask equipped with a mechanical stirrer, a thermometer, a cooling tube and a dropping funnel, followed by stirring at room temperature. After it was confirmed that the reaction system became transparent and was completely dissolved, 192 mL of propionyl chloride was slowly added dropwise, followed by increasing the temperature of the system to 80°C to 90°C. Stirring was continued for 3 hr, and then the reaction system was cooled to room temperature. The reaction solution was introduced into 10 L of water while vigorously stirring, whereupon a white solid was precipitated. The white solid was separated by suction filtration, and washed three times with large quantities of water. The obtained white solid was dried under vacuum at 100°C for 6 hr to obtain a desired cellulose derivative (C-5) (propionyloxypropylmethylpropionyl cellulose; the degrees of substitution thereof are described in Table 1) as a white powder (84.5 g). [0112] 60 g of hydroxypropylmethyl cellulose (trade name: Metolose 90SH-100; manufactured by Shin-Etsu Chemical Co., Ltd.; H-4) and 2,100 mL of N,N-dimethyl acetamide were measured and put into a 5-liter three-necked flask equipped with a mechanical stirrer, a thermometer, a cooling tube and a dropping funnel, followed by stirring at room temperature. After it was confirmed that the reaction system became transparent and was completely dissolved, 101 mL of acetyl chloride was slowly added dropwise, followed by increasing the temperature of the system to 80°C to 90°C. Stirring was continued for 3 hr, and then the reaction system was cooled to room temperature. The reaction solution was introduced into 10 L of water while vigorously stirring, whereupon a white solid was precipitated. The white solid was separated by suction filtration, and washed three times with large quantities of water. The obtained white solid was dried under vacuum at 100°C for 6 hr to obtain a desired cellulose derivative (C-6) (acetoxypropylmethylacetyl cellulose; the degrees of substitution thereof are described in Table 1) as a white powder (79.4 g). [0113] 60 g of hydroxypropylmethyl cellulose (trade name: Marpolose 90MP-4000; manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.; H-3) and 2,100 mL of N,N-dimethyl acetamide were measured and put into a 5-liter three-necked flask equipped with a mechanical stirrer, a thermometer, a cooling tube and a dropping funnel, followed by stirring at room temperature. After it was confirmed that the reaction system became transparent and was completely dissolved, 147 mL of butyryl chloride was slowly added dropwise, followed by increasing the temperature of the system to 80°C to 90°C. Stirring was continued for 3 hr, and then the reaction system was cooled to room temperature. 100 mL of methanol and 800 ml of water were added dropwise, followed by introduction of a reaction solution into 10 L of water while vigorously stirring. The white solid was separated by suction filtration, and washed three times with large quantities of water. The obtained white solid was dried under vacuum at 100°C for 6 hr to obtain a desired cellulose derivative (C-7) (butyryloxypropylmethylbutyryl cellulose; the degrees of substitution thereof are described in Table 1) as a white powder (75.1 g). [0114] 60 g of hydroxypropylmethyl cellulose (trade name: Marpolose 90MP-4000; manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.; H-3) and 2,100 mL of N,N-dimethyl acetamide were measured and put into a 5-liter three-necked flask equipped with a mechanical stirrer, a thermometer, a cooling tube and a dropping funnel, followed by stirring at room temperature. After it was confirmed that the reaction system became transparent and was completely dissolved, a mixture solution of 66.4 mL of acetyl chloride and 81.2 mL of propionyl chloride was slowly added dropwise, followed by increasing the temperature of the system to 80°C to 90°C. Stirring was continued for 3 hr, and then, the reaction system was cooled to room temperature and left to stand overnight. 100 mL of methanol and 800 mL of water were added dropwise, followed by introduction of a reaction solution into 10 L of water while vigorously stirring. The white solid was separated by suction filtration, and washed three times with large quantities of water. The white solid was dissolved in methanol, and a white solid obtained by dropping the resulting solution into water was dried under vacuum at 100°C for 6 hr to obtain a desired cellulose derivative (C-8) (acetoxypropylpropionyloxypropylmethylacetylpropionyl cellulose; the degrees of substitution thereof are described in Table 1) as a white powder (77.1 g). [0115] 60 g of hydroxypropylmethyl cellulose (trade name: Marpolose 90MP-4000; manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.; H-3) and 2,100 mL of N,N-dimethyl acetamide were measured and put into a 5-liter three-necked flask equipped with a mechanical stirrer, a thermometer, a cooling tube and a dropping funnel, followed by stirring at room temperature. After it was confirmed that the reaction system became transparent and was completely dissolved, a mixture solution of 66.4 mL of acetyl chloride and 40.6 mL of propionyl chloride was slowly added dropwise, followed by increasing the temperature of the system to 80°C to 90°C. Stirring was continued for 3 hr, and then the reaction system was cooled to room temperature and left to stand overnight. 100 mL of methanol and 800 mL of water were added dropwise, followed by introduction of a reaction solution into 10 L of water while vigorously stirring. The white solid was separated by suction filtration, and washed three times with large quantities of water. The white solid was dissolved in methanol, and a white solid obtained by dropping the resulting solution into water was dried under vacuum at 100°C for 6 hr to obtain a desired cellulose derivative (C-9) (acetoxypropylpropionyloxypropylmethylacetylpropionyl cellulose; the degrees of substitution thereof are described in Table 1) as a white powder (70.1 g). [0116] 60 g of hydroxypropylmethyl cellulose (trade name: Marpolose 90MP-4000; manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.; H-3) and 2,100 ml of N,N-dimethyl acetamide were measured and put into a 5-liter three-necked flask equipped with a mechanical stirrer, a thermometer, a cooling tube and a dropping funnel, followed by stirring at room temperature. After it was confirmed that the reaction system became transparent and was completely dissolved, a mixture solution of 50.4 mL of acetyl chloride and 73.5 mL of butyryl chloride was slowly added dropwise, followed by increasing the temperature of the system to 80°C to 90°C. Stirring was continued for 3 hr, and then the reaction system was cooled to room temperature and left to stand overnight. 100 mL of methanol and 800 mL of water were added dropwise, followed by introduction of a reaction solution into 10 L of water while vigorously stirring. The white solid was separated by suction filtration, and washed three times with large quantities of water. The white solid was dissolved in methanol, and a white solid obtained by dropping the resulting solution into water was dried under vacuum at 100°C for 6 hr to obtain a desired cellulose derivative (C-10) (acetoxypropylbutyryloxypropylmethylacetylbutyryl cellulose; the degrees of substitution thereof are described in Table 1) as a white powder (74.3 g). [0117] 60 g of hydroxypropylmethyl cellulose (trade name: Marpolose 90MP-4000; manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.; H-3) and 2,100 mL of N,N-dimethyl acetamide were measured and put into a 5-liter three-necked flask equipped with a mechanical stirrer, a thermometer, a cooling tube and a dropping funnel, followed by stirring at room temperature. After it was confirmed that the reaction system became transparent and was completely dissolved, a mixture solution of 60.9 mL of propionyl chloride and 73.5 mL of butyryl chloride was slowly added dropwise, followed by increasing the temperature of the system to 80°C to 90°C. Stirring was continued for 3 hr, and then the reaction system was cooled to room temperature and left to stand overnight. 100 mL of methanol and 800 mL of water were added dropwise, followed byintroduction of a reaction solution into 10 L of water while vigorously stirring. The white solid was separated by suction filtration, and washed three times with large quantities of water. The obtained white solid was dried under vacuum at 100°C for 6 hr to obtain a desired cellulose derivative (C-l 1) (butyryloxypropylpropionyloxypropylmethylbutyrylpropionyl cellulose; the degrees of substitution thereof are described in Table 1) as a white powder (69.6 g). [0118] 30 g of hydroxypropylmethyl cellulose (trade name: Marpolose 90MP-4000; manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.), 0.74 g of methane sulfonic acid and 57.4 ml of anhydrous acetic acid were measured and put into a 1-liter kneader (a biaxial Werner type kneader equipped with a sigma blade as a stirrer) and stirred at room temperature for 10 min, and then the reaction system was heated to 35°C, and 120 ml of acetic acid was added dropwise over 30 min and maintained for another 2 hr to perform acetylation. 180 ml of water was slowly added dropwise while stirring. This doping solution was introduced into 420 ml of 10% diluted acetic acid while stirring, whereupon a white solid was precipitated. The white solid was separated by suction filtration, and washed with large quantities of water. The obtained white solid was dried under vacuum at 100°C for 6 hr to obtain a desired cellulose derivative (C-12) (acetoxypropylmethylacetyl cellulose; the degrees of substitution thereof are described in Table 1) as a white powder (35.5 g). [0119] 30 g of hydroxypropylmethyl cellulose (trade name: Marpolose 90MP-4000; manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.), 0.37 g of sulfuric acid and 57.4 ml of anhydrous acetic acid were measured and put into a 1-liter kneader (a biaxial Werner type kneader equipped with a sigma blade as a stirrer) and stirred at room temperature for 10 min, and then the reaction system was heated to 35°C, and 120 ml of acetic acid was added dropwise over 30 min and maintained for another 2 hr to perform acetylation. 180 ml of water was slowly added dropwise while stirring. This doping solution was introduced into 420 ml of 10% diluted acetic acid while stirring, whereupon a white solid was precipitated. The white solid was separated by suction filtration, and washed with large quantities of water. The obtained white solid was dried under vacuum at 100°C for 6 hr to obtain a desired cellulose derivative (C-13) (acetoxypropylmethylacetyl cellulose; the degrees of substitution thereof are described in Table 1) as a white powder (34.2 g). [0120] 30 g of hydroxypropylmethyl cellulose (trade name: Marpolose 90MP-4000; manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.), 0.74 g of methane sulfonic acid and 77.2 ml of anhydrous propionic acid were measured and put into a 1-liter kneader (a biaxial Werner type kneader equipped with a sigma blade as a stirrer) and stirred at room temperature for 10 min, and then the reaction system was heated to 35°C, and 120 ml of propionic acid was added dropwise over 30 min and maintained for another 3 hr to perform esterification. 180 ml of water was slowly added dropwise while stirring. This doping solution was introduced into 420 ml of 10% diluted propionic acid while stirring, whereupon a white solid was precipitated. The white solid was separated by suction filtration, and washed with large quantities of water. The obtained white solid was dried under vacuum at 100°C for 6 hr to obtain a desired cellulose derivative (C-14) (propionyloxypropylmethylpropionyl cellulose; the degrees of substitution thereof are described in Table 1) as a white powder (34.5 g). [0121] 30 g of hydroxypropylmethyl cellulose (trade name: Metolose 90SH-100; manufactured by Shin-Etsu Chemical Co., Ltd.), 0.74 g of methane sulfonic acid and 57.4 ml of anhydrous acetic acid were measured and put into a 1-liter kneader (a biaxial Werner type kneader equipped with a sigma blade as a stirrer) and stirred at room temperature for 10 min, and then the reaction system was heated to 35°C, and 120 ml of acetic acid was added dropwise over 30 min and maintained for another 2 hr to perform acetylation. 180 ml of water was slowly added dropwise while stirring. This doping solution was introduced into 420 ml of 10% diluted acetic acid while stirring, whereupon a white solid was precipitated. The white solid was separated by suction filtration, and washed with large quantities of water. The obtained white solid was dried under vacuum at 100°C for 6 hr to obtain a desired cellulose derivative (C-15) (acetoxypropylmethylacetyl cellulose; the degrees of substitution thereof are shown in Table 1) as a white powder (33.5 g). [0122] 30 g of hydroxypropylmethyl cellulose (trade name: Marpolose 65MP-4000; manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.), 0.74 g of methane sulfonic acid and 57.4 ml of anhydrous acetic acid were measured and put into a 1-liter kneader (a biaxial Werner type kneader equipped with a sigma blade as a stirrer) and stirred at room temperature for 10 min, and then the reaction system was heated to 35°C, and 120 ml of acetic acid was added thereto dropwise over 30 min and maintained for another 2 hr to perform acetylation. 180 ml of water was slowly added dropwise while stirring. This doping solution was introduced into 420 ml of 10% diluted acetic acid while stirring, whereupon a white solid was precipitated. The white solid was separated by suction filtration, and washed with large quantities of water. The obtained white solid was dried under vacuum at 100°C for 6 hr to obtain a desired cellulose derivative (C-16) (acetoxypropylmethylacetyl cellulose; the degrees of substitution thereof are described in Table 1) as a white powder (35.4 g). [0123] 30 g of hydroxypropylmethyl cellulose (trade name: Marpolose 90MP-4000; manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.) and 60 ml of acetic acid were commercially obtained, and sufficiently impregnated over 6 hr. The hydroxypropylmethyl cellulose impregnated in the acetic acid was put into a 1-liter kneader (a biaxial Werner type kneader equipped with a sigma blade as a stirrer) while stirring, and the temperature was set at 50°C. 57.4 ml of anhydrous acetic acid was added to the acetification reactor, and then the pressure in the acetification reactor was reduced by a vacuum pump to control the degree of vacuum to 60 Torr. A mixture solution of 0.74 g of methane sulfonic acid and 60 ml of acetic acid was put into the acetification reactor over 30 min to initiate a reaction (the reaction was initiated at a time point when the mixture solution of methane sulfonic acid and acetic acid began to be put). The reaction system was in a boiling state, and the mixed vapor of acetic acid and anhydrous acetic acid was removed. After 60 min of the reaction initiation, the pressure reduction was released. The amount of the solution which had been distilled away until this point was 75 ml. 180 ml of water was slowly added dropwise while stirring. This doping solution was introduced into 420 ml of 10% diluted acetic acid while stirring, whereupon a white solid was precipitated. The white solid was separated by suction filtration, and washed with large quantities of water. The obtained white solid was dried under vacuum at 100°C for 6 hr to obtain a desired cellulose derivative (C-17) (acetoxypropylmethylacetyl cellulose; the degrees of substitution thereof are described in Table 1) as a white powder (35.8 g). [0124] 30 g of hydroxypropylmethyl cellulose (trade name: Marpolose 90MP-4000; manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.), 0.74 g of methane sulfonic acid and 57.4 ml of anhydrous acetic acid were measured and put into a 1-liter kneader (a biaxial Werner type kneader equipped with a sigma blade as a stirrer) and stirred at room temperature for 10 min, and then the reaction system was heated to 35°C, and 120 ml of acetic acid was added dropwise over 30 min and maintained for another 2 hr to perform acetylation. 15 g of 10% calcium acetate was put into the reaction solution to stop the reaction. 180 ml of water was slowly added dropwise while stirring. This doping solution was introduced into 420 ml of 10% diluted acetic acid while stirring, whereupon a white solid was precipitated. The white solid was separated by suction filtration, and washed with large quantities of water, followed by washing with a 0.1% calcium hydroxide aqueous solution. The obtained white solid was dried under vacuum at 100°C for 6 hr to obtain a desired cellulose derivative (C-18) (acetoxypropylmethylacetyl cellulose; the degrees of substitution thereof are described in Table 1) as a white powder (36.0 g). [0125] 50 g of hydroxypropylmethyl cellulose (trade name: Marpolose 90MP-4000; manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.; H-3), 300 ml of ethyl acetate, and 700 ml of acetic acid were measured and put into a 3-liter three-necked flask equipped with a mechanical stirrer, a thermometer, a cooling tube and a dropping funnel. The internal temperature was increased to 65°C while stirring, 161.7 ml of anhydrous acetic acid was added, and 0.49 g of methane sulfonic acid was also added. Stirring was continued for 5 hr, and then the reaction system was cooled to 30°C. 100 ml of water was added to the reaction solution, 150 ml of methanol was subsequently added, and 1.2 L of water was added dropwise, followed by stirring for 10 min. The stirring was stopped and the reaction system was left to stand for 10 min to allow a slurry to settle. 1.5 L of supernatant was taken out, 150 ml of methanol was added thereto while stirring, and 1 L of water was added dropwise, followed by stirring for 30 min. The precipitated white solid was separated by suction filtration, and washed with 1 L of water. The obtained white crystal was dried under vacuum at 100°C for 6 hr to obtain a desired cellulose derivative (C-19) (acetoxypropylmethylacetyl cellulose; the degrees of substitution thereof are described in Table 1) as a white powder (56.2 g). [0126] 50 g of hydroxypropylmethyl cellulose (trade name: Marpolose 90MP-4000; manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.; H-3), 300 ml of ethyl acetate, and 700 ml of acetic acid were measured and put into a 3-liter three-necked flask equipped with a mechanical stirrer, a thermometer, a cooling tube and a dropping funnel. The internal temperature was increased to 65°C while stirring, 161.7 ml of anhydrous acetic acid was added, and 0.25 g of sulfuric acid was also added. Stirring was continued for 4 hr, and then the reaction system was cooled to 30°C. 100 ml of water was added to the reaction solution, 150 ml of methanol was subsequently added, and 1.2 L of water was added dropwise, followed by stirring for 10 min. The stirring was stopped and the reaction system was left to stand for 10 min to allow a slurry to settle. 1.5 L of supernatant was taken out, 150 ml of methanol was added while stirring, and 1 L of water was added dropwise, followed by stirring for 30 min. The precipitated white solid was separated by suction filtration, and washed with 1 L of water. The obtained white crystal was dried under vacuum at 100 hr for 6 hr to obtain a desired cellulose derivative (C-20) (acetoxypropylmethylacetyl cellulose; the degrees of substitution thereof are described in Table 1) as a white powder (55.0 g). [0127] 50 g of hydroxypropylmethyl cellulose (trade name: Marpolose 90MP-4000; manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.; H-3), 300 ml of ethyl acetate, and 700 ml of propionic acid were measured and put into a 3-liter three-necked flask equipped with a mechanical stirrer, a thermometer, a cooling tube and a dropping funnel. The internal temperature was increased to 65°C while stirring, 217 ml of anhydrous propionic acid was added, and 1.23 g of methane sulfonic acid was also added. Stirring was continued for 5 hr, and then the reaction system was cooled to 30°C. 100 ml of water was added to the reaction solution, 150 ml of methanol was subsequently added, and 1.2 L of water was added dropwise, followed by stirring for 10 min. The stirring was stopped and the reaction system was left to stand for 10 min to allow a slurry to settle. 1.5 L of supernatant was taken out, 150 ml of methanol was added thereto while stirring, and 1 L of water was added dropwise, followed by stirring for 30 min. The precipitated white solid was separated by suction filtration, and washed with 1 L of water. The obtained white crystal was dried under vacuum at 100 hr for 6 hr to obtain a desired cellulose derivative (C-21) (propionyloxypropylmethylpropionyl cellulose; the degrees of substitution thereof are described in Table 1) as a white powder (61.5 g). [0128] 50 g of hydroxypropylmethyl cellulose (trade name: Marpolose 90MP-4000; manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.; H-3), 500 ml of acetonitrile, and 500 ml of acetic acid were measured and put into a 3-liter three-necked flask equipped with a mechanical stirrer, a thermometer, a cooling tube and a dropping funnel. The internal temperature was increased to 45°C while stirring, 161.9 ml of anhydrous acetic acid was added, and 0.37 g of methane sulfonic acid was also added. Stirring was continued for 4 hr, and then the reaction system was cooled to 30°C. 200 ml of methanol was added to the reaction solution, and 1.5 L of water was added dropwise, followed by stirring for 10 min. The stirring was stopped and the reaction system was left to stand for 10 min to allow a slurry to settle. 2.4 L of supernatant was taken out, 500 ml of methanol was added while stirring, and 1 L of water was added dropwise, followed by stirring for 30 min. The precipitated white solid was separated by suction filtration, and washed with 500 mL of water. The obtained white crystal was dried under vacuum at 100 hr for 6 hr to obtain a desired cellulose derivative (C-22) (acetoxypropylmethylacetyl cellulose; the degrees of substitution thereof are described in Table 1) as a white powder (56.2). [0129] 75 g of hydroxypropylmethyl cellulose (90MP-4000: manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.), and 2,500 mL of pyridine were measured and put into a 5-liter three-necked flask equipped with a mechanical stirrer, a thermometer, a cooling tube and a dropping funnel, followed by stirring at room temperature. 250 mL of benzoyl chloride was slowly added thereto dropwise under water cooling, followed by stirring at 60°C for 3 hr. Next, the reaction system was returned to room temperature, and 250 mL of benzoyl chloride was slowly added dropwise, followed by stirring at 60°C for 3 hr. After the reaction, the reaction system was returned to room temperature, and 1,500 mL of methanol was slowly added dropwise under ice cooling to precipitate a white solid. Supernatant was removed by decantation, 3,000 mL of methanol was added, and the white solid was separated by suction filtration, followed by washing three times with large quantities of the methanol solvent. The obtained white solid was dried under vacuum at 80°C for 6 hr to obtain benzoyloxypropylmethyl cellulose benzoate (C-23). [0130] Meanwhile, with respect to the compounds obtained in the above, the kinds of functional groups substituted with the hydroxyl groups (R2, R and R ) contained in cellulose, and DSa, MS, and DSb+DSc were observed and determined by 'H-NMR by using the method as described in Cellulose Communication 6, 73-79(1999). [0131] The number average molecular weight (Mn) and weight average molecular weight (Mw) of the obtained cellulose derivatives were measured. The measurement method thereof will be described below. [Molecular weight and molecular weight distribution] The number average molecular weight (Mn) and the weight average molecular weight (Mw) were determined by using a gel permeation chromatography (GPC). Specifically, N-methylpyrrolidone as a solvent and a polystyrene gel were used, and the molecular weight was obtained by using a reduced molecular weight calibration curve previously obtained from a standard monodispersion polystyrene constitution curve. As the GPC device, HLC-8220 GPC (manufactured by Tosoh Corp.) was used. [0132] The number average molecular weight (Mn), weight average molecular weight (Mw), and degree of substitution were incorporated and shown in Table 1. [0133] MS represents a molar degree of substitution of alkyleneoxy groups [0134] In Table 1, any one of "B) a group containing an acyl group and an alkyleneoxy group" in the cellulose derivatives C-1 to C-4, C-6, C-12, C-13, C-15 to C-20 and C-22 is a group containing a structure of the following Formula (3-1-1), and any one of "B) a group containing an acyl group and an alkyleneoxy group" in the cellulose derivatives C-5, C-14, and C-21 is a group containing a structure of the following Formula (3-1-2). Further, "B) a group containing an acyl group and an alkyleneoxy group" in the C-7 is a group containing a structure of the following Formula (3-1-3), any one of "B) a group containing an acyl group and an alkyleneoxy group" in the C-8 and C-9 is a group containing a structure of the following formula (3-1-1) and a structure of the following Formula (3-1-2), "B) a group containing an acyl group and an alkyleneoxy group" in the C-10 is a group containing a structure of the following Formula (3-1-1) and a structure of the following Formula (3-1-3), "B) a group containing an acyl group and an alkyleneoxy group" in the C-11 is a group containing a structure of the following Formula (3-1-2) and a structure of the following Formula (3-1-3), and "B) a group containing an acyl group and an alkyleneoxy group" in the C-23 is a group containing a structure of the following Formula (3-1-4). [0135] [Chem. 8] [0136] The melting initiation temperatures of the obtained cellulose derivatives, and Marpolose and Metolose as raw materials were measured. The measurement method thereof will be described below. [Melting Initiation Temperature (Tm)] A melting initiation temperature was obtained by measuring the flow initiation temperature of a resin while increasing the temperature at a temperature increasing rate of 5°C/min with a load of 100 kg in a flow tester (manufactured by Shimadzu Corporation). The melting initiation temperature is shown in Table 2. [0137] The thermal decomposition initiation temperatures of the obtained cellulose derivatives, and Marpolose and Metolose as raw materials were measured. The measurement method thereof will be described below. [Thermal Decomposition Initiation Temperature (Td)] A thermal decomposition initiation temperature was obtained by measuring a 2% weight reduction temperature of a sample while increasing the temperature at a rate of 10°C/min under nitrogen atmosphere by using a thermogravimetric/differential thermal analysis apparatus (manufactured by Seiko Instruments Inc.). The thermal decomposition initiation temperature is shown in Table 2. [0138] [0140] As can be seen from Table 2, it can be seen that the melting initiation temperature of the obtained cellulose derivative has been greatly reduced for Marpolose and Metolose as raw materials. Further, Td-Tm has been greatly increased, which indicates that molding is easily carried out by using the thermoplasticity. [0141] In addition, Td of the hydroxypropylmethyl cellulose phthalate 55 and the hydroxypropylmethyl cellulose phthalate 50 (all manufactured by ACROS Co., Ltd.) having a carboxyl group was measured and all the values were 200°C or less. From this point, it can be also known that it is preferred that a carboxyl group is not contained. [0142] The solubilities of the obtained cellulose derivative and Marpolose and Metolose as raw materials in water were measured. The measurement method of the solubility will be described below. [Measurement of solubility in water] Each sample was added to 100 g of water at 25°C and stirred to confirm whether the sample was dissolved. The results are shown in the following Table 3. Meanwhile, in the following Table 3, an amount of dissolution of 5 g or less is referred to as "insoluble" and an amount of dissolution of more than 5 g is referred to as "soluble". [0143] Table 3 [0144] Table 3 (Continued) [0145] From Table 3, it can be known that hydroxypropylmethyl cellulose is soluble in water, while the cellulose derivative in the present invention is insoluble in water. [0146] [Preparation of Test Piece] The cellulose derivative (C-l) obtained as described above was fed to an injection molding apparatus (manufactured by Imoto machinery Co., Ltd., semi-automatic injection molding apparatus), and molded into a test piece for multipurposes (impact test piece and thermal deformation test piece) having a size of 4x10x80 mm at a cylinder temperature of 200°C, a mold temperature of 30°C and an injection pressure of 1.5 kgf/cm2. The mold temperature was set to 30°C. [0147] In the same manner as in Example 1, test pieces were prepared by molding the cellulose derivatives (C-2) to (C-23), and the raw materials hydroxypropylmethyl cellulose (H-1) to (H-4) and (H-5) (manufactured by The Dow Chemical Company: ethylcellulose, the degree of ethoxy substitution 2.6), and (H-6) (manufactured by Eastman Chemical Company: celluloseacetatepropionate, the degree of acetyl substitution 0.1 and the degree of propionyl substitution 2.5) as comparative compounds under the molding conditions of Table 4. [0148] With respect to the obtained test pieces, the Charpy impact strength and heat deformation temperature (HDT) were measured by the following method. The results are shown in Table 4. [Charpy Impact Strength] In accordance with ISO 179, the test pieces molded by injection molding were provided with a notch having the front end of 0.25±0.05 mm and an incident angle of 45±0.5°, and stood still under the conditions of 23°C±2°C and 50%±5% RH for 48 hours or more, and then the impact strength was measured by a Charpy impact tester (manufactured by Toyo Seiki Seisaku-Sho, Ltd.) with the edge wise. [Heat Deformation Temperature (HDT)] In accordance with IS075, the temperature was measured when a predetermined bending load (1.8 MPa) was applied to the center of a test piece (in a flatwise direction), the temperature was increased at a constant rate, and thus, a deformation of the center portion reaches 0.34 mm. [0149] [0151] From the results in Table 4, it is understood that hydroxypropylmethyl celluloses (H-l) to (H-4) do not show thermolplasticity, while cellulose derivatives (C-1) to (C-23) in Examples 1 to 23, which are modified with acyl groups in the celluloses, are given an appropriate thermolplasticity and thus, are moldable, as well as exhibit high impact resistance and heat resistance. In addition, although (H-5) and (H-6) in Comparative Examples 5 and 6 were thermo-moldable, it can be understood that cellulose derivatives (C-1) to (C-23) in Examples 1 to 23 are moldable at low temperatures and equivalent or better results are imparted to the cellulose derivatives (C-1) to (C-23) in terms of Charpy impact strength and HDT, when compared to the (H-5) and (H-6). Industrial Applicability [0152] The cellulose derivative or thermo-molding material of the present invention has excellent thermoplasticity, and thus, may be manufactured into a molded body. Further, a molded body formed by the cellulose derivative or thermo-molding material of the present invention has good impact resistance, heat resistance and the like, and thus, may be used appropriately as component parts such as automobiles, home electric appliances and electric and electronic devices, mechanical parts, materials for housing and construction, and the like. In addition, the cellulose derivative is a plant-derived resin, and a material which may contribute to the prevention of global warming, and thus, the cellulose derivative may replace petroleum-derived resins of the related art. Furthermore, the cellulose derivative and thermo-molding material of the present invention exhibit biodegradability, and thus, are expected to be used as a material with less environmental load. Although the present invention has been described with reference to detailed and specific embodiments thereof, it is obvious to those skilled in the art that various changes or modifications may be made without departing from the spirit and scope of the present invention. The present application claims priority from Japanese Patent Application No. 2009-187415 filed on August 12, 2009 and Japanese Patent Application No. 2009-295107 filed on December 25, 2009, the disclosure of which is incorporated herein by reference in its entirety. Claims [1] A thermo-molding material comprising a water-insoluble cellulose derivative, wherein the water-insoluble cellulose derivative comprises: A) a hydrocarbon group; B) a group containing an acyl group: -CO-RB1 and an alkyleneoxy group: -RB2-0- (RB1 represents a hydrocarbon group, and RB2 represents an alkylene group having 3 carbon atoms); and C) an acyl group: -CO-Rc (Re represents a hydrocarbon group). [2] The thermo-molding material of claim 1, wherein A) the hydrocarbon group is an alkyl group having 1 to 4 carbon atoms. [3] The thermo-molding material of claim 1, wherein A) the hydrocarbon group is a methyl group or an ethyl group. [4] The thermo-molding material of any one of claims 1 to 3, wherein each of RB1 and Re independently represents an alkyl group or an aryl group. [5] The thermo-molding material of any one of claims 1 to 4, wherein each of RB1 and Re independently represents a methyl group, an ethyl group, or a propyl group. [6] The thermo-molding material of any one of claims 1 to 5, wherein the alkyleneoxy group is a group represented by the following formula (1) or formula (2). [7] The thermo-molding material of any one of claims 1 to 6, wherein B) the group containing an acyl group: -CO-RB1 and an alkyleneoxy group: -RB2-0- is a group containing a structure represented by the following Formula (3): Formula (3) (wherein, RB1 represents a hydrocarbon group, and RB2 represents an alkylene group having 3 carbon atoms.) [8] The thermo-molding material of any one of claims 1 to 7, wherein the cellulose derivative has substantially no carboxyl group. [9] A water-insoluble cellulose derivative, comprising al) an ethyl group; bl) a group containing an acyl group: -CO-Rbl and an alkyleneoxy group: -Rb2-0-(Rbl represents a hydrocarbon group, and Rb2 represents an alkylene group having 3 carbon atoms); and cl) an acyl group: -CO-Rc (Re represents a hydrocarbon group). [10] A water-insoluble cellulose derivative, comprising a2) a methyl group; b2) a group containing an acyl group: -CO-Rbl and an alkyleneoxy group: -Pvb2-0-(Rbl represents a hydrocarbon group, and Rb2 represents an alkylene group having 3 carbon atoms); and c2) an acyl group: -CO-Rc (Re represents a hydrocarbon group), wherein a degree of substitution of a2) the methyl group is 1.1 or more and a molar degree of substitution (MS) of the alkyleneoxy group is 1.5 or less. [11] The cellulose derivative of claim 9 or 10, wherein each of Rbl and Re independently represents a methyl group, an ethyl group, or a propyl group. [12] The cellulose derivative according of any one of claims 9 to 11, wherein the cellulose derivative has substantially no carboxyl group. [13] A case for electric and electronic devices, composed of a molding body obtained by molding the thermo-molding material of any one of claims 1 to 8 or the cellulose derivative of any one of claims 9 to 12. [14] A method for manufacturing a molded body, comprising: a step of heating and molding the thermo-molding material of any one of claims 1 to 8 or the cellulose derivative of any one of claims 9 to 12.