Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
2002-09-20
2004-10-12
Wilson, James O. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C536S058000, C536S071000
Reexamination Certificate
active
06803458
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to cellulose acetate which, when dissolved in a solvent, produces an inconsiderable amount of fine insoluble matters and exhibits excellent filterability and to a process of making this cellulose acetate. More specifically, it relates to cellulose acetate which can reduce the risk of occurrence of optical defects of films due to leakage in filtration in the manufacture of films to be used in optical applications in particular and to a process for producing the cellulose acetate.
Further, the present invention relates to cellulose acetate which, when dissolved in a solvent, leads to a solution having an inconsiderable elasticity and excellent processability such as spreadable film casting and fiber spinnability and to a process for producing the cellulose acetate.
Still further, the present invention relates to cellulose acetate whose filterability and elasticity are all improved and to a process for producing the cellulose acetate.
PRIOR ART
Cellulose acetate includes cellulose triacetate and cellulose diacetate. Cellulose acetate is widely used in various applications such as films for photographic use, protective films of polarizing plates, fibers for clothing, cigarette filters, hollow fibers for artificial kidneys, etc.
When cellulose acetate is used in these applications, cellulose acetate is dissolved in an organic solvent and is thereafter formed into respective articles. For example, when cellulose triacetate is made into a film, a solvent cast process, comprising casting a concentrated solution (dope), which is prepared by dissolving cellulose acetate in a solvent such as methylene chloride, onto a support (drum, band, etc.) whose surface is finished in a mirror polished state, and peeling off the film after being dried, is employed. Meanwhile, when cellulose diacetate is made into fibers, a dry spinning process, which comprises ejecting into blowing hot air a concentrated solution (dope) prepared by dissolving cellulose acetate in a solvent such as acetone from a nozzle having many fine holes so that the solvent is removed, is employed.
At the time of casting or spinning of the film, if an insoluble matter in the solvent of the dope is present, problems of quality of formed articles and problems pertaining to production occur. For example, the presence of an insoluble matter in the dope leads to problems in the optical properties (light transmittance, refractive index, etc.) of the film when cellulose acetate is to be used as a film, and when the cellulose acetate is to be used as fibers, it also leads to reduction in productivity due to the occurrence of fiber breaking at the time of spinning.
Accordingly, prior to casting or spinning, the dope is filtered so as to remove the insoluble matter. When the filtration is carried out, the use of a filter material having a smaller pore diameter leads to better removal of the insoluble matter. However, the use of a filter material having a smaller pore diameter tends to cause the choking of the pores and reduces the working efficiency owing to, for example, replacement of the filter material. From the foregoing, it will be appreciated that what is needed in the art is cellulose acetate which has a smaller amount of insoluble matters causing the choking and excellent filterability.
In the field of optical applications such as protective films of polarizing plates, since bright spotty matters cause optical defects, normally the filtration is carried out under strict conditions. However, leakage in filtration is sometimes inevitable because it is impossible to remove 100% of the target insoluble matters. For this reason, cellulose acetate having a smaller amount of bright spotty matters is desired from the viewpoint of minimizing the risk of the leakage that may occur.
Further, when a solution (dope) is prepared by dissolving cellulose acetate in a solvent and the dope is processed for forming, the forming may be adversely affected if the elasticity of the dope is large. For example, when a film is cast from a dope of cellulose acetate, an excessively large elasticity of the dope leads to such disadvantages as productivity reduction because of the long time required for obtaining sufficient smoothness of the dope surface after the extrusion of the dope onto a casting band and, in an extreme case, failure to obtain a film having sufficient surface smoothness. Similarly, when fibers are spun from a dope of cellulose acetate, an excessively large elasticity of the dope leads to productivity reduction because the spinning speed cannot be increased. It is therefore desirable to provide cellulose acetate having a small elasticity of the dope mainly from the viewpoint of the enhancement of productivity.
In order to fulfill such requirement by the improvement of the manufacturing process, in the manufacture of cellulose diacetate, JP-A 56-59801 discloses a technique of a high-temperature acetylation-high-temperature aging process in which an acetylation reaction is carried out at a high temperature in the range of 50 to 850° C. and hydrolysis is carried out at a high temperature in the range of 110 to 120° C. during an aging step. Meanwhile, JP-B 58-20961 discloses a high-temperature aging process in which hydrolysis is carried out at a high temperature in the range of 125 to 170° C. during an aging step.
However, none of the above-described techniques satisfactorily meet a high-level demand for quality at the time when the formed articles are used in a frontier technical field, a demand for high qualities by general consumers, and the pursuit of a high-level productivity by manufacturers.
An object of the present invention is to provide cellulose acetate which has a smaller content of insoluble matters and excellent filterability of dope, and to provide a process for producing the cellulose acetate.
Another object of the present invention is to provide cellulose acetate which leads to a dope having a small elasticity, and to provide a process for producing the cellulose acetate.
Further, the present invention provides cellulose acetate which leads to a dope whose filterability and elasticity are improved, and provides a process for producing the cellulose acetate.
DISCLOSURE OF THE INVENTION
As a means to solve the above-mentioned problems, the present inventors have already filed an application on an invention relating to cellulose triacetate whose clogging constant (K) is not more than 70 (see Japanese Patent Application No. 10-329165). The present invention relates to the improvement of this anticipatory invention.
The present inventors made intensive studies on the insoluble matters of a dope when cellulose acetate was dissolved in a solvent. As a result, they found that the amount of the insoluble matters, which are present as bright spotty matters when a film formed from the dope is observed under a polarizing microscope, has a high correlation with the choking of the pores of the filter material; the bright spotty matters are the fine fragments derived from the breakdown of insufficiently reacted cellulose fibers; and the amount of the insoluble matters in the dope can be markedly reduced by preventing these fine fragments from entering into the acetylation reaction system. Based on these findings, they accomplished the present invention.
The present invention is cellulose acetate satisfying at least one requirement selected from the following requirements (A), (B) and (C), provided that the case where (B) alone is satisfied is excluded.
Requirement (A): Bright spotty matters in sizes of 20 &mgr;m or more are not more than 20 units/mm
Method of Measuring Bright Spotty Matters
Cellulose acetate is dissolved in a mixed solvent consisting of methylene chloride/methanol=9/1(weight ratio) so as to obtain a solution (dope) having a concentration of 15% by weight (as solid concentration). This dope is cast onto a sheet of slide glass and dried so as to obtain a film-like sample having a thickness of about 100 &mgr;m on the slide glass. The sample is observed under a polariz
Nakai Michiyo
Ozaki Toru
Sasai Hirofumi
Suzuki Shinsuke
Taniguchi Hiroki
Daicel Chemical Industries Ltd.
Flynn ,Thiel, Boutell & Tanis, P.C.
Krishnan Ganapathy
Wilson James O.
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