Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
1999-07-09
2002-07-09
Wilson, James O. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C536S037000, C536S038000
Reexamination Certificate
active
06417344
ABSTRACT:
TECHNICAL ART
The present invention relates to a method for producing acetylated pyroxylin (or, in another parlance, cellulose acetate nitrate) used as starting materials for explosives, paints, etc. More particularly, the present invention provides a fine fiber form of acetylated pyroxylin having improved heat resistance and stability.
BACKGROUND ART
Acetylated pyroxylin, in which heat resistance is imparted to pyroxylin (or, in another parlance, nitrocellulose), is obtained by dissolving pyroxylin in a suitable organic solvent for an actylation reaction with anhydrous acetic acid, etc. in the presence of a suitable catalyst, and precipitating the reaction product in water or an alcohol (see JP-A's 56-82849 and 8-277301).
One problem with this reaction for forming an acetic acid ester with respect to a residual hydroxyl group in pyroxylin is that the efficiency of using the starting anhydrous acetic acid is low. This is because any fast progress of the reaction is unachievable unless the anhydrous acetic acid is used in an amount that is 2 to 20 times as large as the theoretically required amount. An unreacted extra portion of the anhydrous acetic acid then reacts with a water or alcohol precipitation agent at the next precipitation step, and so changes to acetic acid or an acetic acid ester such as ethyl acetate, rendering it impossible to recover the anhydrous acetic acid as such. Another problem is the need of using a costly high-speed agitator at the precipitation step. Yet another problem is that the powder particle size of acetylated pyroxylin varies due to precipitation, causing the reaction solution component to be included in particles having a large diameter. This then appears in the form of impurities which result in unstable quality.
DISCLOSURE OF THE INVENTION
In view of the aforesaid problems, an object of the invention is to provide a method capable of recovering an extra portion of anhydrous acetic acid taking no part in a reaction with pyroxylin. Another object of the invention is to provide an acetylated pyroxylin product having improved heat resistance and stability by dispensing with any precipitation step and thereby simplifying production installations and eliminating an unstable quality factor due to product particle size variations.
As a result of study after study, the inventors have now found that pyroxylin is first subjected to an acetylation reaction while the pyroxylin is dispersed in a sort of dispersion medium and kept in a solid phase state, and acetylated pyroxylin is then separated from a reaction solution by means of filtration, so that an extra portion of the anhydrous acetic acid taking no part in the reaction can be immediately recovered and, hence, any precipitation step can be dispensed with to eliminate an unstable product quality factor due to product particle size variations.
Thus, the present invention provides a method for producing acetylated pyroxylin by action of an acetylating agent and a catalyst on pyroxylin, characterized by dispersing said pyroxylin in a dispersion medium to subject said pyroxylin to an acetylation reaction while said pyroxylin is kept in a solid phase state, and separating acetylated pyroxylin from a reaction solution by means of filtration.
The present invention also provides a fine fiber form of acetylated pyroxylin having improved heat resistance and stability.
According to one aspect, the present invention is embodied as follows.
(1) A method for producing acetylated pyroxylin by action of an acetylating agent and a catalyst on pyroxylin, characterized by dispersing said pyroxylin in a dispersion medium to subject said pyroxylin to an acetylation reaction while said pyroxylin is kept in a solid phase state, thereby obtaining crude acetylated pyroxylin, separating said crude actylated pyroxylin from a reaction solution by means of filtration, and washing said crude acetylated pyroxylin upon separation.
(2) The actylated pyroxylin production method according to (1), characterized in that said acetylating agent is anhydrous acetic acid, and said dispersion medium is an organic solvent which has a boiling point between 40° C. and 200° C. at normal pressure, in which said pyroxylin and said acetylated pyroxylin are insoluble and which is unreactive with said anhydrous acetic acid.
(3) The acetylated pyroxylin production method according to (2), characterized in that said dispersion medium comprises an aromatic hydrocarbon selected from the group consisting of aromatic hydrocarbons having 6 to 10 carbon atoms or a mixture of two or more such aromatic hydrocarbons.
(4) The acetylated pyroxylin production method according to any one of (1) to (3), characterized in that said catalyst is selected from the group consisting of p-toluenesulfonic acid and perchloric acid.
(5) The acetylated pyroxylin production method according to any one of (1) to (4), characterized in that a washing agent used for washing said crude acetylated pyroxylin is water and/or an organic solvent in which said acetylated pyroxylin is insoluble and which has a boiling point between 40° C. and 200° C. at normal pressure.
(6) The acetylated pyroxylin production method according to (5), characterized in that said organic solvent used as said washing agent is an alcohol having 1 to 4 carbon atoms.
(7) The acetylated pyroxylin production method according to (5), characterized in that a compound or compounds of an alkali metal and/or an alkaline earth metal are added into said water used as said washing agent.
(8) The acetylated pyroxylin production method according to any one of (1) to (7), characterized in that a process of washing said crude acetylated pyroxylin includes a step of holding said crude acetylated pyroxylin in said washing agent at a temperature of 60° C. to 105° C.
(9) An acetylated pyroxylin characterized in that fine fibers having a fiber diameter of 0.01 mm to 0.05 mm and a fiber length of at least 0.2 mm account for at least 90% by weight of all fibers, and characterized by showing a heat generation peak of at least 207° C. upon differential thermal analysis as performed in an argon stream at a heating rate of 10° C./min and a sample amount of 1 mg.
(10) The acetylated pyroxylin according to (9), characterized in that fine fibers having a fiber diameter of 0.015 mm to 0.04 mm and a fiber length of at least 0.4 mm account for 90% by weight of all fibers.
According to another aspect, the present invention is embodied as follows.
(11) The acetylated pyroxylin production method according to any one of (1) to (3), characterized in that said catalyst is at least one acid from the group consisting of p-toluenesulfonic acid and perchloric acid.
(12) The acetylated pyroxylin production method according to any one of (1) to (4), characterized in that a washing agent used for washing said crude acetylated pyroxylin is water and/or an organic solvent in which said acetylated pyroxylin is insoluble and which has a boiling point of 40° C. to 200° C. at normal pressure.
(13) The acetylated pyroxylin production method according to any one of (1) to (4), characterized in that a washing agent used for washing said crude acetylated pyroxylin is water and/or an organic solvent in which said acetylated pyroxylin is insoluble and which has a boiling point of 40° C. to 200° C. at normal pressure.
(14) The acetylated pyroxylin production method according to (5), characterized in that a compound or compounds of an alkali metal and/or an alkaline earth metal are added to said water used as said washing agent.
(15) The acetylated pyroxylin production method according to (5), characterized in that a compound or compounds of an alkali metal and/or an alkaline earth metal are added to said water used as said washing agent.
(16) An acetylated pyroxylin obtained by the production method according to any one of (1) to (8) and (11) to (15).
(17) The acetylated pyroxylin according to (16), characterized by being an acetylated pyroxylin as recited in (9) or (10).
(18) The production method according to any one of (1) to (8) and (11) to (15), characterized
Nishioka Kazuhiro
Tanaka Tokuji
Armstrong Westerman & Hattori, LLP
Daicel Chemical Industries Ltd.
Maier Leigh C.
Wilson James O.
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