Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H5/00—Special paper or cardboard not otherwise provided for
  • D21H5/12—Special paper or cardboard not otherwise provided for characterised by the use of special fibrous materials
  • D21H5/14—Special paper or cardboard not otherwise provided for characterised by the use of special fibrous materials of cellulose fibres only
  • D21H5/141—Special paper or cardboard not otherwise provided for characterised by the use of special fibrous materials of cellulose fibres only of fibrous cellulose derivatives
  • D21H5/143—Special paper or cardboard not otherwise provided for characterised by the use of special fibrous materials of cellulose fibres only of fibrous cellulose derivatives grafted or encapsulated cellulose
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B11/00—Preparation of cellulose ethers
  • C08B11/193—Mixed ethers, i.e. ethers with two or more different etherifying groups
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H5/00—Special paper or cardboard not otherwise provided for
  • D21H5/12—Special paper or cardboard not otherwise provided for characterised by the use of special fibrous materials
  • D21H5/14—Special paper or cardboard not otherwise provided for characterised by the use of special fibrous materials of cellulose fibres only
  • D21H5/141—Special paper or cardboard not otherwise provided for characterised by the use of special fibrous materials of cellulose fibres only of fibrous cellulose derivatives

Definitions

• the present invention relates to hydroxyalkyl methylcelluloses having excellent thermoreversible gel strength and improved solubility.
• hydroxypropyl methylcellulose obtained by ether-substitution of methyl groups and hydroxypropyl groups to cellulose, methoxyl groups are localized in the molecule relative to the cellulose chain. Hydroxypropyl methylcellulose has therefore “thermoreversible gelation properties”. Described specifically, when an aqueous solution of hydroxypropyl methylcellulose is heated, hydrophobic hydration of the methoxyl groups localized in the molecule occurs and it turns into a hydrous gel. When the resulting gel is cooled, on the other hand, hydrophobic hydration decreases, whereby the gel returns to the original aqueous solution. Because of such thermoreversible gelation properties, the aqueous solution shows excellent shape retention even after heating.
• hydroxyalkyl methylcellulose when hydroxyalkyl methylcellulose is used as a binder for extrusion of ceramics, the hydroxyalkyl methylcellulose dissolved in water is mixed, kneaded with ceramic particles, formed into a certain shape, and dried with heating wherein the hydroxyalkyl methylcellulose turns into a gel by heating.
• the gelled portion has high strength, defects such as cracks caused by shrinkage strain during drying can be prevented. Hydroxyalkyl methylcelluloses are therefore used exclusively as a binder for extrusion of ceramics.
• Methylcellulose having no hydroxyalkoxyl groups has excellent thermoreversible gelation performance.
• the thermoreversible gel strength of the methylcellulose is determined by placing a 2.5% by weight aqueous solution of it in a constant temperature bath of 80° C. so as to cause thermoreversible gelation after 15 minutes; inserting a cylindrical rod having a diameter of 15 mm downward into the gel at a rate of 5 cm/min; and measuring a maximum load (g) applied to the cylindrical rod when it is inserted into 2 cm inside of the gel.
• the thermoreversible gel strength is obtained by dividing the maximum load (g) by the cross-sectional area of the rod.
• the thermoreversible gel strength thus determined is as high as from 500 to 700 g/cm 2 .
• thermoreversible gel strength of 100 g/cm 2 or less For example, hydroxypropyl methylcellulose having a molar substitution of hydroxypropoxyl groups of 0.15 and a substitution degree of methoxyl groups of 1.8 renders thermoreversible gel strength of 30 g/cm 2 . Hydroxyethyl methylcellulose having a molar substitution of hydroxyethoxyl groups of 0.15 and a substitution degree of methoxyl groups of 1.8 renders thermoreversible gel strength of 25 g/cm 2 .
• methylcellulose having no hydroxyalkoxyl groups introduced is preferred.
• a water temperature has to be adjusted to 10° C. or less.
• Methylcellulose insoluble in water cannot render its original thermoreversible gel strength and therefore becomes practically useless. It is therefore difficult to use methylcellulose having no hydroxyalkoxyl groups introduced.
• Japanese Patent Application Examined Publication No. 62-059074/1987 discloses that hydroxyalkyl methylcelluloses having a molar substitution of hydroxyalkoxyl groups of 0.02 to 0.13 can dissolve in water after a predetermined time even when the temperature is set at approximately 30° C., indicating that dissolution is possible without the dissolution temperature decreased. Further, Japanese Patent Application Examined Publication No. 62-059074/1987 discloses that the thermoreversible gelation temperature of methylcellulose can be raised by introduction of hydroxyalkoxyl groups therein.
• Japanese Patent Application Examined Publication No. 62-059074/1987 discloses that methylcellulose having hydroxyalkoxyl groups introduced can have a higher thermoreversible gelation temperature than that of the methylcellulose having no hydroxyalkoxyl groups, but does not disclose whether the high thermoreversible gelation strength can be maintained or not.
• the present inventors have found that the hydroxyalkyl methylcellulose described by Japanese Patent Application Examined Publication No. 62-059074/1987 does not always have necessary thermoreversible gelation strength. Accordingly, there is a demand for the development of hydroxyalkyl methylcellulose such as hydroxypropyl methylcellulose and hydroxyethyl methylcellulose which can dissolve easily even without the temperature lowered to 10° C. or less and which has higher strength of thermoreversible gel which is produced by heating the solution of hydroxyalkyl methylcellulose.
• An object of the present invention is to provide hydroxyalkyl methylcellulose which can be dissolved at a room temperature of 20 to 30° C. and have high thermoreversible gel strength when it becomes thermoreversible gel.
• water-soluble hydroxylalkyl methylcellulose having a molar substitution of hydroxyalkoxyl groups of from 0.05 to 0.1, a substitution degree of methoxyl groups of from 1.6 to 1.9, and a ratio of (A/B) of 0.4 or greater wherein (A) is a molar fraction of substituted hydroxyalkoxyl groups having hydroxyl groups of hydroxyalkoxyl groups substituted further with methoxyl groups and (B) is a molar fraction of unsubstituted hydroxylakoxyl groups having hydroxyl groups of hydroxyalkoxyl groups not substituted further with methoxyl groups, can dissolve at a room temperature of from 20 to 30° C. and have thermoreversible gel strength comparable to that of methylcellulose having no hydroxyalkoxyl groups introduced and sufficiently higher than that of commercially available hydroxypropyl methylcellulose or
• water-soluble hydroxyalkyl methylcellulose having a molar substitution of hydroxyalkoxyl groups of from 0.05 to 0.1 and a substitution degree of methoxyl groups of from 1.6 to 1.9, wherein the hydroxyalkoxyl groups are classified into substituted hydroxyalkoxyl groups having hydroxyl groups of hydroxyalkoxyl groups substituted further with methoxyl groups and unsubstituted hydroxylakoxyl groups having hydroxyl groups of hydroxyalkoxyl groups not further substituted and a ratio (A/B) of a molar fraction (A) of the substituted hydroxyalkoxyl groups to a molar fraction (B) of the unsubstituted hydroxyalkoxyl groups is 0.4 or greater.
• the step for obtaining the water-soluble hydroxyalkyl methylcellulose comprises a stage of adding the hydroxyalkyl etherification agent and a stage of adding the methyl etherification agent after the reaction between the hydroxylalkyl etherification agent and the alkali cellulose; or a stage of adding the hydroxyalkyl etherification agent and the methyl etherification agent so that 40% by weight or greater of a stoichiometric amount of the methyl etherification agent remains unreacted upon completion of the reaction of 60% by weight or greater of a stoichiometric amount of the hydroxyalkyl etherification agent.
• a water-soluble hydroxyalkyl methylcellulose which can dissolve at a room temperature of from 20 to 30° C. and have high thermoreversible gel strength when it becomes a thermoreversible gel.
• the water-soluble hydroxyalkyl methylcellulose to be used in the present invention having a molar substitution of hydroxyalkoxyl groups of 0.05 to 0.1 and a substitution degree of methoxyl groups of 1.6 to 1.9, it may be prepared by impregnating cellulose with a predetermined amount of an aqueous alkali solution as presented in Japanese Patent Application Unexamined Publication No. 2001-302701, and then reacting the resulting alkali cellulose with necessary amounts of a methyl etherification agent (preferably methyl chloride) and a hydroxyalkyl etherification agent (preferably propylene oxide or ethylene oxide).
• a methyl etherification agent preferably methyl chloride
• a hydroxyalkyl etherification agent preferably propylene oxide or ethylene oxide
• a molar substitution of hydroxyalkoxyl groups means an average mole of hydroxyalkoxyl groups (preferably hydroxypropoxyl groups or hydroxyethoxyl groups) added per glucose ring unit of cellulose.
• a substitution degree of methoxyl groups means the average number of hydroxyl groups substituted with methoxyl groups per glucose ring unit of the cellulose.
• an addition order or rate of etherification agents can be controlled to perform substitution of many hydroxyalkoxyl groups prior to substitution of methoxyl groups
• a hydroxyalkyl etherification agent for example, propylene oxide or ethylene oxide
• a methyl etherification agent for example, methyl chloride
• a hydroxyalkyl etherification agent for example, propylene oxide or ethylene oxide
• a methyl etherification agent for example, methyl chloride
• a hydroxyalkyl etherification agent for example, propylene oxide or ethylene oxide
• a methyl etherification agent for example, methyl chloride
• a ratio of addition time of the methyl etherification agent to that of the hydroxyalkyl etherification agent may fall within a range of preferably from 1.3 to 3, especially preferably from 1.5 to 3.
• the water-soluble hydroxyalkyl methylcellulose may be preferably hydroxypropyl methylcellulose or hydroxyethyl methylcellulose.
• the hydroxyalkoxyl group introduced by the hydroxyalkyl etherification agent may be preferably a hydroxypropoxyl group or a hydroxyethoxyl group.
• the molar substitution of hydroxypropoxyl groups and a substitution degree of methoxyl groups of the hydroxyalkyl methylcellulose of the present invention can be measured in accordance with the analysis method of substitution degree of hypromellose (hydroxypropyl methylcellulose) as described in the Japanese Pharmacopoeia, Fifteenth Edition or “Standard Method of Testing HYDROXYPROPYL METHYLCELLULOSE” specified in ASTM D-2363-72/USA.
• the molar substitution and the substitution degree can also be analyzed by NMR or infrared absorption analysis.
• substitution degree of methoxyl groups of hydroxyethyl methylcellulose can be measured by the analysis method of methylcellulose as specified in The Japanese Pharmacopoeia Fifteenth Edition or “Standard Test Method for Methylcellulose” as specified in ASTM D-1347-72/USA, as well as the method described in J. G. Cobler, et al., “Determination of Alkoxyl Substitution Ether by Gas Chromatography” or in Talanta, Vol. 9, 473-481 (1962).
• the molar substitution of hydroxyethoxyl can be measured in accordance with Ying-ChiLee, et al., “Determination of Molar Substitution Ratio of Hydroxyethyl Starches by Gas Chromatography”, Anal. Chem. 55, 332-338 (1983), or “Standard Test Method for Hydroxyethylcellulose” as specified in ASTM D2364-75/USA.
• substitution of methoxyl groups follows substitution of hydroxyalkoxyl groups such as hydroxypropoxyl groups or hydroxyethoxyl groups, the hydroxyl groups of these hydroxyalkoxyl groups can be substituted further with the methoxyl groups.
• the hydroxyl groups of the cellulose are substituted with methoxyl groups, on the other hand, the methoxy groups are not substituted further with hydroxyalkoxyl groups at the substitution site of the methoxyl groups because the methoxyl groups have no hydroxyl groups.
• a substitution molar fraction of the unsubstituted hydroxyalkoxyl groups can be calculated by dividing the molar substitution of the unsubstituted hydroxyalkoxyl groups by the total moles.
• a weight average polymerization degree of the hydroxyalkyl methylcellulose thus obtained can be determined by measuring a weight average molecular weight by using a combination of gel permeation chromatography and light scattering method in accordance with a molecular weight measuring method as described in Journal of Polymer Science and Technology, 39(4), 293-298 (1982) and dividing the weight average molecular weight by a molecular weight per unit hydroxypropylmethylcellulose molecule.
• the kind or conditions of the solvent, temperature, column, or wavelength of the light scattering apparatus employed in the measurement of the weight average molecular weight are not limited to those described in the Journal of Polymer Science and Technology but can be selected as needed.
• the weight average molecular weight can also be determined by ultracentrifugation or conversion from a viscosity average molecular weight.
• Hydroxyalkyl methylcellulose having a higher weight average polymerization degree tends to exhibit higher thermoreversible gel strength when it is in the form of aqueous solutions having the same concentration. Even hydroxyalkyl methylcellulose having a low weight average polymerization degree can have necessary strength by adjustment of the concentration of the aqueous solution.
• a weight average polymerization degree which can provide high thermoreversible gel strength even if it is added in a small amount may be preferably from 100 to 10000. When the weight average polymerization degree is smaller than 100, sufficient thermoreversible gel strength may not be obtained for use as an additive and an amount to be added may exceed 10% by weight.
• the weight average polymerization degree is higher than 10000, the preparation of the hydroxyalky methylcellulose may become difficult in practice because raw material cellulose having a certain polymerization degree have to be selected or prepared.
• the cellulose (pulp) to be used for the preparation of the hydroxyalkyl methylcellulose of the present invention may include wood pulp obtained by refining the wood and cotton pulp (linter pulp) obtained from cotton fibers.
• the dissolution temperature of the hydroxypropyl methylcellulose may be measured in the following manner.
• Hydroxypropyl methylcellulose powder and hot water are placed in a 300-ml beaker so as to prepare an 1 by weight aqueous solution of the hydroxypropyl methylcellulose.
• the resulting solution is cooled while stirring at 400 rpm.
• Viscosities of the aqueous solution are measured at predetermined temperatures of the aqueous solution. The temperature at which the slope of a line connecting the viscosities plotted against temperatures starts to blunt is measured as the dissolution temperature
• thermoreversible gel strength may be determined in the following manner. A 2% by weight aqueous solution of hydroxypropyl methylcellulose is prepared, added into a 50-ml beaker and heated in a bath of 80° C. for 30 minutes to form a thermoreversible gel. The maximum force applied to a cylindrical rod having a diameter of 15 mm when the cylindrical rod is inserted by 2 cm downward into the gel at a rate of 5 cm/min is measured using a rheometer manufactured by Rheotec Co., Ltd. The thermoreversible gel strength is calculated by dividing the maximum force value by a cross-sectional area of the cylindrical rod.
• a 49% by weight sodium hydroxide solution was fed at a constant rate of 21.5 g/min from an inlet provided at a pulp feed opening to add the aqueous alkali solution to the cellulose.
• a 585.0 g portion was placed in an autoclave equipped with a Ploughshare type internal agitating blade. After the pressure was reduced to ⁇ 97 kPa, nitrogen was added into the autoclave to reach an atmospheric pressure. The pressure was then reduced again to ⁇ 97 kPa.
• the 20 g of propylene oxide and 253.9 g of methyl chloride were added via a pressure pump while setting a ratio of addition times of methyl chloride to propylene oxide at 3 (60 minutes of methyl chloride addition time to 20 minutes of propylene oxide) and fishing the addition of propylene oxide prior to the addition of methyl chloride. They were reacted for 2 hours at an internal temperature of 60° C. The temperature was then raised to 90° C. over 30 minutes and kept at 90° C. for 30 minutes, whereby an etherification reaction was completed.
• the reaction product was washed with hot water of 85° C. or greater and dried in a small Willey mill. It was analyzed in accordance with the analysis method of the substitution degree of hypromellose (hydroxypropyl methylcellulose) described in the Japanese Pharmacopoeia, Fifteenth Edition. As a result of the analysis, the hydroxypropyl methylcellulose thus obtained had a molar substitution of hydroxypropoxyl groups of 0.07 and a substitution degree of methoxyl groups of 1.8.
• the molecular weight of the hydroxypropyl methylcellulose thus obtained was determined in accordance with the molecular weight measuring method as described in Japanese Journal of Polymer Science and Technology, 39(4), 293-298 (1982) and a weight average polymerization degree was calculated to be 1200.
• a ratio (A/B) of a molar fraction (A) of substituted hydroxypropoxyl groups having hydroxyl groups of hydroxypropoxyl groups substituted further with methoxyl groups to a molar fraction (B) of unsubstituted hydroxypropoxyl groups having hydroxyl groups of hydroxypropoxyl groups not substituted further with methoxyl groups was determined based on the ratio of areas of the peaks at which the structures of decomposed components had been identified in advance by a mass analyzer.
• the ratio (A/B) was 0.8.
• the obtained hydroxypropyl methylcellulose powder and hot water were placed in a 300-ml beaker in order to prepare a 1% by weight aqueous solution of the hydroxypropylmethylcellulose.
• the resulting solution was cooled at a rate of 2° C. per 10 minutes while stirring at 400 rpm.
• the viscosity of the aqueous solution was measured relative to the temperature of the aqueous solution, and the dissolution temperature at which the slope of a line connecting the viscosities plotted against the temperature started to blunt was measured.
• the dissolution temperature was 25° C.
• thermoreversible gelation strength was 150 g/cm 2 .
• Hydroxypropyl methylcellulose was prepared in each of Examples 2 to 4 and Comparative Examples 1 to 3 in the same manner as in Example 1 except for the change of the kind of pulp, added amounts of methyl chloride and propylene oxide, and an addition time ratio of methyl chloride addition time to propylene oxide addition time as shown in Table 1.
• a substitution degree of methoxyl groups, a molar substitution of hydroxypropoxyl groups, a ratio (A/B) of a molar fraction (A) of substituted hydroxypropoxyl groups having hydroxyl groups of hydroxypropoxyl groups substituted further with methoxyl groups to a molar fraction (B) of unsubstituted hydroxypropoxyl groups having hydroxyl groups of hydroxypropoxyl groups not substituted further with methoxyl groups, a weight average polymerization degree, a dissolution temperature and a thermoreversible gel strength were determined in the same manner as in Example 1 as shown in Table 1.
• Example 2 Of the alkali cellulose obtained in Example 1, a 585.0 g portion was placed in an autoclave equipped with a Ploughshare type internal agitating blade. After the pressure was reduced to ⁇ 97 kPa, nitrogen was added into the autoclave to reach an atmospheric pressure. The pressure was then reduced again to ⁇ 97 kPa. The 20 g of propylene oxide was added to the autoclave via a pressure pump and reacted for two hours at the internal temperature controlled to 60° C. Subsequently, 253.9 g of methyl chloride were added to the autoclave which had been cooled to 20° C. The temperature of the autoclave was then raised to 90° C. over 30 minutes and kept at 90° C. for 30 minutes, whereby an etherification reaction was completed. Hydroxypropyl methylcellulose having a weight average polymerization degree of 1000, a substitution degree of methoxyl groups of 1.8 and a molar substitution of hydroxypropoxyl groups of 0.09 was obtained.
• a ratio (A/B) of a molar fraction (A) of substituted hydroxypropoxyl groups having hydroxyl groups of hydroxypropoxyl groups substituted further with methoxyl groups to a molar fraction (B) of unsubstituted hydroxyproxyl groups having hydroxyl groups of hydroxyproxyl groups not substituted further with methoxyl groups was found to be 0.9.
• the dissolution temperature and the thermoreversible gel strength of the resulting hydroxypropyl methylcellulose measured in the same manner as in Example 1 were 25° C. and 160 g/cm 2 , respectively.
• Example 2 In the same manner as in Example 1 except that the reaction took place for 2 hours at an internal temperature controlled to 55° C. while adding ethylene oxide in amounts shown in Table 2 instead of adding propylene oxide used in Examples 1 to 4 and Comparative Examples 1 to 3, hydroxyethyl methylcellulose shown in Table 2 was prepared in place of hydroxypropyl methylcellulose prepared in Examples 1 to 4 and Comparative Examples 1 to 3.
• a ratio (A/B) of a molar fraction (A) of substituted hydroxyethoxyl groups having hydroxyl groups of hydroxyethoxyl groups substituted further with methoxyl groups to a molar fraction (B) of unsubstituted hydroxyethoxyl groups having hydroxyl groups of hydroxyethoxyl groups not substituted further with methoxyl groups, a weight average polymerization degree, a dissolution temperature and a thermoreversible gel strength were measured in the same manner as in Examples 1 to 4 and Comparative Examples 1 to 3.
• the results are shown in Table 2.
• the substitution degree of methoxyl groups and the molar substitution of hydroxyethoxyl groups were measured and calculated in accordance with ASTM D1347-72/USA and ASTM D2364-75/USA, respectively. The results are shown in Table 2.
• Example 5 In the same manner as in Example 5 except that in the reaction of Example 5, ethylene oxide was added instead of propylene oxide in an autoclave and reacted for 2 hours at the internal temperature controlled to 55° C., hydroxyethyl methylcellulose having a weight average polymerization degree of 1000, a substitution degree of methoxyl groups of 1.8 and a molar substitution of hydroxyethoxyl groups of 0.08 was obtained.
• a ratio (A/B) of a molar fraction (A) of substituted hydroxyethoxyl groups having hydroxyl groups of hydroxyethoxyl groups substituted further with methoxyl groups to a molar fraction (B) of unsubstituted hydroxyethoxyl groups having hydroxyl groups of hydroxyethoxyl groups not substituted further with methoxyl groups was found to be 0.9.
• the dissolution temperature and the thermoreversible gel strength of the resulting hydroxyethyl methylcellulose measured in the same manner as in Example 1 were 30° C. and 150 g/cm 2 , respectively.

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