Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
2001-05-08
2004-01-27
Barts, Samuel (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C536S056000, C536S058000, C536S070000, C536S071000, C536S076000
Reexamination Certificate
active
06683174
ABSTRACT:
This the National Phase Application of PCT/JP99/06337, filed Nov. 12, 1999.
TECHNICAL FIELD
The present invention relates to a cellulose triacetate employed preferably as a protective film for a plate of polarization, a color filter, a photosensitive material film or a fibrous material, and to a method for producing the cellulose triacetate.
PRIOR ART
A film obtained from a cellulose triacetate is employed as a support of an optical film such as a photosensitive material film, a protecting film for a plate of polarization in a liquid crystal display and a color filter, since it is tough, has excellent dimensional stability and thermal stability and also exhibits an optically isotropic behavior. In addition, a fiber made from a cellulose triacetate is employed widely as a fiber for various clothing due to its excellent texture and gloss.
Cellulose triacetate is usually produced by various processes such as activation, acetylation and saponification ripening treatments followed by purification and drying treatments. Among these manufacturing processes, a saponification ripening process is performed for reducing the acetylation degree to an intended level, and effected at a temperature of 60 to 70° C. by means of an external heating or an introduction of steam into the reaction system for the purpose of reducing the treatment period.
However, cellulose triacetate produced via the saponification ripening process described above contains fine inclusions which could not be removed by filtration. Accordingly, such fine inclusions, when contained in a large amount, causes plugging of a spinning nozzle in a spinning step, resulting in a reduced productivity.
DISCLOSURE OF THE INVENTION
An objective of the present invention is to provide a cellulose triacetate which is capable of suppressing the formation of fine inclusions which are difficult to filter out and which allows the inclusions to be removed easily by means of a filtration, and a method for producing the cellulose triacetate.
The inventors focused on the causes for the generation of fine inclusions in a saponification ripening process being an unevenly proceeding saponification reaction which leads to an inconsistent acetylation degree of the resultant cellulose triacetate and a large amount of a highly substituted component (completely acetylated glucose unit). Then they discovered that such an uneven reaction is attributable to the uneven temperature in the reaction system, particularly to a partial exposure to a high temperature. Since a reaction system upon completion of an acetylation process is in the state of a highly viscous solution, an external heating mode, even when combined with a stirring means, allows the highly viscous solution in contact with the inner wall of a vessel to be mixed only insufficiently and exposed to the high temperature for a prolonged period, resulting in an increased tendency of the more-deacetylated component formation On the other hand, an internal heating method using a superheated steam allows a cellulose triacetate in contact with water condensed from the superheated steam to precipitate to form a solid phase, resulting in a retarded saponification and an increased residual level of highly acetylated components. Accordingly, they discovered that a cellulose triacetate containing a smaller amount of fine inclusions and exhibiting a satisfactory filtration performance can be obtained by utilizing reaction heat generated uniformly throughout the entire reaction system to prevent the uneven temperature of the reaction system described above, thereby establishing the present invention.
Thus, the present invention provides a cellulose triacetate having an occlusion constant (K) of 70 or less, determined by the following method: Method:
The cellulose triacetate is dissolved in a solvent mixture of methylene chloride/methanol (=9/1 w/w) to form a 16% by weight (as a solid concentration) solution, which is then filtered under a constant pressure at the filtration pressure of 3 kg/cm
2
and the temperature of 25° C. using a muslin filter to determine a filtered volume with the lapse of time, from which the slope of a linear curve represented by t/V−t (wherein t is a filtration time (sec) and V is a filtered volume (ml)) is calculated to obtain an occlusion constant (K) where K=slope×2×10
4
.
The present invention also provides a method for producing a cellulose triacetate described above comprising an acetylation process and a saponification ripening process, wherein a saponification ripening treatment is performed only by means of the elevation of the temperature due to the reaction heat between the water added for quenching the acetylating reaction and remaining unreacted acetic anhydride without any external heating. In other words, the method provided is a method for producing a cellulose triacetate comprising acetylating cellulose followed by a saponification ripening treatment only by means of the elevation of the temperature due to the reaction heat between the water added for quenching the acetylating reaction and remaining unreacted acetic anhydride without any external heating Preferably, cellulose is subjected to a pretreatment activation, an acetylation and then a saponification ripening treatment at a temperature of 40° C. or higher but below 60° C. only by means of the elevation of the temperature due to the reaction heat between the water added for quenching the acetylating reaction and remaining unreacted acetic anhydride without any external heating.
Since cellulose triacetate of the present invention contains an extremely small amount of fine inclusions which are difficult to filter out, it does not plug a filter, even when the pore size is small, and allows any inclusions to be filtered out easily. As a result, it prevents the occlusion of a spinning nozzle and allows a fiber having a stable cross-sectional configuration to be produced, even when the spinning is continued for a prolonged period with the cellulose triacetate of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The cellulose triacetate of the present invention is one whose occlusion constant (K) determined by the following method is 70 or less, preferably 60 or less. An occlusion constant not higher than 70 serves to improve the filtration performance and allows any inclusions, which are undesirable in a spinning process, to be filtered out easily.
Method:
The cellulose triacetate is dissolved in a solvent mixture of methylene chloride/methanol (=9/1 w/w) to form a 16% by weight (as a solid concentration) solution, which is then filtered under a constant pressure at the filtration pressure of 3 kg/cm
2
and the temperature of 25° C. using a muslin filter to determine a filtered volume with the lapse of time, from which the slope of a linear curve represented by t/V−t (wherein t is a filtration time (sec) and V is a filtered volume (ml)) is calculated to obtain an occlusion constant (K) where K=slope×2×10
4
. The curve of t/V−t is discussed for example in “*POLYMER ENGINEERING (KOBUNSHIKOGAKUKOZA)* 4, Chemical fiber spinning and film formation (11)”, Ed. by *The society of Polymer Science, Japan, page 116 to 125, 1965.
The cellulose triacetate of the present invention has an average acetylation degree preferably of 59 to 62.5%, more preferably 59.5 to 62.0%, and most preferably 60 to 61.5%. An average acetylation degree of 59% or higher allows the cellulose acetate to have a low moisture absorption, which leads to an improvement in the mechanical strength of a molded article such as the modulus of the elasticity and the tensile strength. An average acetylation degree of 62.5% or less enables the production by a reaction of acetic anhydride employing a sulfuric acid catalyst.
An acetylation degree can be determined in accordance with ASTM D-817-91 (testing method for cellulose acetates and the like) for determining an acetylation degree. First, 1.9 g of a dried cellulose triacetate is weighed accurately, dissolved in 150 ml of a mixtu
Ogawa Hiroshi
Ozaki Toru
Sasai Hirofumi
Barts Samuel
Daicel Chemical Industries Ltd.
Flynn ,Thiel, Boutell & Tanis, P.C.
Henry Michael C.
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