Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
2001-02-20
2003-07-29
Barts, Samuel (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C536S058000, C536S063000, C536S076000, C536S085000, C536S124000
Reexamination Certificate
active
06600034
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods of making cellulose polymers, and specifically to method of making cellulose polymer powders and solutions in which cellulose polymers are dissolved at a high concentration.
BACKGROUND OF THE INVENTION
Cellulose polymers, particularly cellulose esters, have advantageous features of a high dimensional stability, an excellent heat resistance and a good adhesive nature compared to ordinary synthetic polymer materials. Owing to these features, cellulose esters are widely used as a component for plastic or lacquer, and also formed to various molding articles such as film or fiber. Cellulose ester films represent the base (support) material for photographic light-sensitive materials, and, due to their optical isotropic nature, are further used as parts of liquid crystal display devices. Such parts include the protecting film for polarizers, the substrate for optical compensation sheets and color filters. Moreover, cellulose polymers are recently attracting social attention from the environmental viewpoint, since the need for biodegradable polymers are increasing.
Though the significance of cellulose polymers represented by cellulose esters must increase in a near future, the manufacture of cellulose ester films has been based on the use of chlorine-containing organic solvents such as methylene chloride to dissolve these esters. The reason why such solvents have been used is the high solubility and the ease of their removal due to their low boiling points. As chlorine-containing solvents are harmful exhibiting carcinogenesis and destroying the ozone layer, their use is more and more rigorously being restricted. In the case of methylene chloride, the discharge into the air is seriously restricted so as not to destroy the ozone layer.
Recently, there are various research activities to solve these problems, part of which is already disclosed. For example, the use of cyclic diether such as 1,3-dioxane and 1,3-dioxolane (JP-A-8-143708 and JP-A-8-323785, the term “JP-A” as used herein means an “unexamined published Japanese patent application”) the use of fluoroalcohol such as trifluoroethanol (JP-A-8-143709 and JP-A-11-60807) are proposed. However, cyclic diethers have a problem of insufficient safety including a high inflammability. On the other hand, fluoroalcohols are very expensive and thus are not practically suited for massive use as the solvent for polymer forming.
Though many investigations for inexpensive and safe solvents are being made, there is still another industrial problem; it is very difficult to dissolve cellulose polymers such as cellulose esters in an inexpensive solvent to a concentration required for the manufacturing operation only by simple mixing. Various methods of raising the solubility are also under study. Some examples of such methods include; (1) one based on cooled dissolving described in
Makromol. Chem.,
143, 105 (1971) (JP-A-9-95538 and JP-A-9-95544), (2) one based on the application of ultra high pressure and the use of organic solvents mainly comprising acetone (JP-A-11-21379), (3) one using ultrasonic wave (JP-A-11-71463), and (4) one using a two-component fluid mixture of acetone, triacetyne, methanol or ethanol with carbon dioxide under a high pressure (JP-A-8-232115,
Journal of Supercritical Fluids,
13, 135(1988)).
Among these methods, those of (1) to (4) are effective for solubility improvement, but are still accompanied by some problems from the viewpoint of industrial manufacture. In method (1), an extraordinary temperature as low as −70° C. is necessary to achieve a sufficiently high solubility, requiring a very costly equipment. Method (2) also needs an ultra high pressure of about 100 MPa (about 1,000 atmospheric pressure) to achieve a sufficiently high solubility in a short period, and its industrial implementation is quite difficult. Method (3) needs an ultrasonic wave generator of an industrial scale, and at present the development of such a generator is fairly difficult. Method (4) can achieve a concentration level too low to apply to film formation, as the reported concentration in the patent specification and the literature lies between 2 and 4% by weight. In addition, this method based on the use of carbon dioxide has a drawback that the solution once prepared tends to gel partially during a prolonged storage at room temperature.
As is evident from the above description, there is no film forming method by dissolving cellulose polymers without using environmentally harmful chlorine-containing organic solvents and requiring manufacturing equipment of a reasonable cost. Accordingly, new methods are still eagerly expected.
SUMMARY OF THE INVENTION
The invention aims to provide a manufacturing method for readily soluble cellulose polymer powders, which method is safe having a low environmental load and needs a reasonable investment in the manufacturing equipment.
The invention also aims to provide a manufacturing method for cellulose polymer solutions in a very stable solving state, which method is safe and can satisfy the condition for environmental load.
As a result of an extensive investigation carried out to achieve those aims, the inventors of the invention found that by subjecting a dispersion of a cellulose polymer in a chlorine-free organic solvent to a temperature/pressure condition that belongs to the critical, supercritical or nearcritical region of the solvent, the cellulose polymer readily dissolves in the solvent, that the solution does not separate out the polymer even after the solution is kept under ordinary conditions, and further that the polymer, which once has been dissolved by the present method and pulverized after solvent removal, exhibits a higher solubility than the one not having been subjected to such heat treatment. The invention is based on those newly found facts. Accordingly, the above problems have been solved by the following embodiments.
(1) A method of making cellulose polymer powders, comprising dissolving a cellulose polymer raw material in a chlorine-free organic solvent system under a high temperature and a high pressure condition belonging to the nearcritical or the supercritical region of said system, and then removing said solvent.
(2) A method of making cellulose polymer solution, comprising dissolving a cellulose polymer raw material in a chlorine-free organic solvent system under a high temperature and a high pressure condition belonging to the nearcritical or the supercritical region of said system.
(3) The method described in item (1) or (2) above, wherein the temperature and the pressure under which a cellulose polymer raw material is dissolved in a chlorine-free organic solvent system belong to the nearcritical region of said system.
(4) The method described in item (3) above, wherein the dissolving temperature is not lower than the boiling point and not higher than the critical temperature of said chlorine-free organic solvent system and the dissolving pressure is not lower than 1.013 Mpa (10 kgf/cm
2
).
(5) The method described in item (3) above, wherein the dissolving temperature is not lower than the boiling point+50K and not higher than the critical temperature of said chlorine-free organic solvent system and the dissolving pressure is not lower than 1.013 Mpa (10 kgf/cm
2
) and not exceeding the critical pressure of said system.
(6) The method described in item (1) or (2) above, wherein the dissolving temperature is not lower than 423K and not higher than the critical temperature of said chlorine-free organic solvent system and the dissolving pressure is not lower than 1.013 Mpa (10 kgf/cm
2
) and not exceeding the critical pressure of said system.
(7) The method described in item (1) or (2) above, wherein the dissolving temperature is not lower than 423K and not higher than the critical temperature of said chlorine-free organic solvent system and the dissolving pressure is not lower than 2.026 Mpa (20 kgf/cm
2
) and not exceeding the critical pressure of said system.
(8) The method described in item (1) or
Onishi Hiroshi
Sato Tadahisa
Tsujimoto Tadahiro
Yamakawa Katsuyoshi
Barts Samuel
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Henry Michael C.
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