U.S. patent application number 12/259286 was filed with the patent office on 2009-03-05 for method of adjusting the degree of substitution with acetyl group of cellulose acetate.
This patent application is currently assigned to Daicel Chemical Industries, Ltd.. Invention is credited to Tanemi Asai, Masaaki Ito, Tohru SHIBATA, Yuichiro Shuto.
Application Number | 20090062525 12/259286 |
Document ID | / |
Family ID | 27346245 |
Filed Date | 2009-03-05 |
United States Patent
Application |
20090062525 |
Kind Code |
A1 |
SHIBATA; Tohru ; et
al. |
March 5, 2009 |
METHOD OF ADJUSTING THE DEGREE OF SUBSTITUTION WITH ACETYL GROUP OF
CELLULOSE ACETATE
Abstract
A process for adjusting an intermolecular or intramolecular
degree of acetyl substitution of cellulose acetate is disclosed.
The process comprises ripening cellulose acetate in the presence of
a catalyst, an acetyl donor, and water or an alcohol. The amount of
water and the alcohol is in the range of 0.1 to 10 mol % based on
the amount of the acetyl donor.
Inventors: |
SHIBATA; Tohru; (Hyogo,
JP) ; Shuto; Yuichiro; (Hyogo, JP) ; Ito;
Masaaki; (Hiroshima, JP) ; Asai; Tanemi;
(Hyogo, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
Daicel Chemical Industries,
Ltd.
Osaka
JP
|
Family ID: |
27346245 |
Appl. No.: |
12/259286 |
Filed: |
October 27, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10257645 |
Oct 15, 2002 |
|
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PCT/JP02/02410 |
Mar 14, 2002 |
|
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12259286 |
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Current U.S.
Class: |
536/69 |
Current CPC
Class: |
C08B 3/24 20130101; C08B
3/06 20130101 |
Class at
Publication: |
536/69 |
International
Class: |
C08B 3/06 20060101
C08B003/06 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 14, 2001 |
JP |
2001-73076 |
Jun 28, 2001 |
JP |
2001-195843 |
Nov 5, 2001 |
JP |
2001-339692 |
Claims
1. Cellulose acetate having a degree of acetyl substitution in the
range of 2.636 to 2.958, wherein the cellulose acetate shows a
distribution curve of an intermolecular substitution degree in
which the maximum peak has a half width of less than 0.080, and
wherein the degrees of acetyl substitution at 2-, 3- and
6-positions satisfy the following formula (I):
2DS+3DS<6DS.times.4-1.70 (I) in which 2DS is the degree of
acetyl substitution at 2-position; 3DS is the degree of acetyl
substitution at 3-position; and 6 DS is the degree of acetyl
substitution at 6-position.
2. The cellulose acetate as defined in claim 1, wherein the maximum
peak has a half width of less than Y defined in the following
formula: Y=-0.17788X+0.5788 in which X is the degree of acetyl
substitution.
3. Cellulose acetate having a degree of acetyl substitution in the
range of 2.636 to 2.958, wherein the cellulose acetate shows a
distribution curve of an intermolecular substitution degree in
which the maximum peak has a half width of less than Y defined in
the following formula: Y=-0.17788X+0.5788 in which X is the degree
of acetyl substitution, and wherein the degrees of acetyl
substitution at 2-, 3- and 6-positions satisfy the following
formula (I): 2DS+3DS<6DS.times.4-1.70 (I) in which 2DS is the
degree of acetyl substitution at 2-position; 3DS is the degree of
acetyl substitution at 3-position; and 6DS is the degree of acetyl
substitution at 6-position.
4. Cellulose acetate showing an infrared absorption spectrum,
wherein the absorption spectrum has the absorption maximum in the
wave number range of 3450 to 3550 cm.sup.-1 in which the absorption
maximum has a half width of 135 cm.sup.-1 or less, wherein the
degrees of acetyl substitution at 2-, 3- and 6-positions satisfy
the following formula (I): 2DS+3DS<6DS.times.4-1.70 (I) in which
2DS is the degree of acetyl substitution at 2-position; 3DS is the
degree of acetyl substitution at 3-position; and 6DS is the degree
of acetyl substitution at 6-position.
5. Cellulose acetate in which the degrees of acetyl substitution at
2-, 3- and 6-positions satisfy the following formulas (I) to (III):
2DS+3DS<6DS.times.4-1.70 (I) 2DS+3DS<-6DS.times.4+5.70 (II)
2DS+3DS>1.80 (III) in which 2DS is the degree of acetyl
substitution at 2-position; 3DS is the degree of acetyl
substitution at 3-position; and 6DS is the degree of acetyl
substitution at 6-position.
6. The cellulose acetate defined in claim 5, wherein the degrees of
acetyl substitution at 2-, 3- and 6-positions further satisfy the
following formula (VI): 2DS+3DS-6DS<1 (VI) in which 2DS is the
degree of acetyl substitution at 2-position; 3DS is the degree of
acetyl substitution at 3-position; and 6DS is the degree of acetyl
substitution at 6-position.
7. The cellulose acetate defined in claim 5, wherein the degrees of
acetyl substitution at 2- and 3-positions further satisfy the
following formula (VII): 2DS+3DS>1.82 (VII) in which 2DS is the
degree of acetyl substitution at 2-position; and 3DS is the degree
of acetyl substitution at 3-position.
8. The cellulose acetate defined in claim 7, wherein the degrees of
acetyl substitution at 2- and 3-positions further satisfy the
following formula (VIII): 2DS+3DS>1.84 (VIII) in which 2DS is
the degree of acetyl substitution at 2-position; and 3DS is the
degree of acetyl substitution at 3-position.
9. Cellulose acetate in which the degrees of acetyl substitution at
2-, 3- and 6-positions satisfy the following formulas (I), (III)
and (IV): 2DS+3DS<6DS.times.4-1.70 (I) 2DS+3DS>1.80 (III)
3DS<2DS (IV) in which 2DS is the degree of acetyl substitution
at 2-position, 3DS is the degree of acetyl substitution at
3-position, and 6DS is the degree of acetyl substitution at
6-position.
10. The cellulose acetate defined in claim 9, wherein the degree of
acetyl substitution at 6-position further satisfies the following
formula (IX): 6DS<0.98 (IX) in which 6DS is the degree of acetyl
substitution at 6-position.
11. The cellulose acetate defined in claim 9, wherein the degrees
of acetyl substitution at 2- and 3-positions further satisfy the
following formula (VII): 2DS+3DS>1.82 (VII) in which 2DS is the
degree of acetyl substitution at 2-position; and 3DS is the degree
of acetyl substitution at 3-position.
12. The cellulose acetate defined in claim 11, wherein the degrees
of acetyl substitution at 2- and 3-positions further satisfy the
following formula (VIII): 2DS+3DS>1.84 (VIII) in which 2DS is
the degree of acetyl substitution at 2-position; and 3DS is the
degree of acetyl substitution at 3-position.
13. The cellulose acetate defined in claim 9, wherein the cellulose
acetate has a degree of acetyl substitution in the range of 2.636
to 2.958, and wherein the cellulose acetate shows a distribution
curve of an intermolecular substitution degree in which the maximum
peak has a half width of less than 0.080.
14. The cellulose acetate defined in claim 9, wherein the cellulose
acetate has a degree of acetyl substitution in the range of 2.636
to 2.958, and wherein the cellulose acetate shows a distribution
curve of an intermolecular substitution degree in which the maximum
peak has a half width of less than Y defined in the following
formula: Y=-0.17788X+0.5788 in which X is the degree of acetyl
substitution.
15. The cellulose acetate defined in claim 9, wherein the cellulose
acetate shows an infrared absorption spectrum, and wherein the
absorption spectrum has the absorption maximum in the wave number
range of to 355 cm.sup.-1 in which the absorption maximum has a
half width of 135 cm.sup.-1 or less.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 10/257,645, filed Oct. 15, 2002, which is the national phase
under 35 U.S.C. .sctn. 371 of PCT International Application No.
PCT/JP02/02410 filed Mar. 14, 2002 which claims priority of
Japanese Patent Application Nos. 2001-73076 filed Mar. 14, 2001;
2001-195843 filed Jun. 28, 2001 and 2001-339692 filed May 11, 2001,
the complete disclosures of which are hereby incorporated by
reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a process for adjusting
intermolecular or intramolecular degree of acetyl substitution by
ripening cellulose acetate.
BACKGROUND OF THE INVENTION
[0003] Cellulose acetate, particularly cellulose acetate having a
degree of acetyl substitution of 2.6 or more (generally classified
into cellulose triacetate), is tough and excellent in
heat-resistance. Therefore, cellulose acetate has been used in
various technical fields. For example, a cellulose acetate film is
a representative photographic support. Further, a cellulose acetate
film shows an excellent optical isotropy. Accordingly, a cellulose
acetate film is used in a liquid crystal display, which has
recently extended its market. In the liquid crystal display, the
cellulose acetate film is used as a protective film of a polarizing
plate, a phase retardation film or a color filter.
[0004] A cellulose acetate film is generally formed according to a
solvent cast method, in which a cellulose acetate solution (dope)
is cast onto a support, and dried to evaporate the solvent to form
a film.
[0005] In preparation of a cellulose acetate product such as the
film according to the solvent cast method, a degree of acetyl
substitution of the cellulose acetate is closely related to a
solubility of the cellulose acetate in a solvent and physical
characteristics (including optical characteristics) of the
products. It has been well known that cellulose acetate having a
high degree of acetyl substitution shows a low solubility in a
solvent, but forms a product of excellent physical characteristics.
On the other hand, cellulose acetate having a low degree of acetyl
substitution shows a high solubility in a solvent, but forms a
product having problems in physical characteristics.
[0006] Dichloromethene is the most conventional solvent of
cellulose acetate. Cellulose acetate is well dissolved in
dichloromethane. Therefore, cellulose acetate having a high degree
of acetyl substitution has been dissolved in dichloromethane to
prepare a cellulose acetate product having excellent physical
characteristics according to a conventional solvent cast method.
The low solubility of the cellulose acetate having a high degree of
acetyl substitution cannot be a problem where dichloromethane is
used as the solvent.
[0007] However, use of hydrocarbon halides such as dichloromethane
has recently been restricted severely to protect the global
environment. Further, dichloromethane is apt to vaporize in the
process for the preparation of a product, because it has a low
boiling point (41.degree. C.). Accordingly, dichloromethane may
cause problems in the working environment. Therefore, the process
is conducted under closed conditions.
[0008] Japanese Patent Provisional Publication Nos. 9(1997)-95544,
9(1997)-95557, 9(1997)-95538 propose a process for preparing the
cellulose acetate solution, which comprises the steps of cooling a
mixture of cellulose acetate and an organic solvent, and then
heating the mixture to prepare the solution. The process comprising
the cooling and heating steps (which is sometimes referred to as a
cooling dissolution method) makes it possible to prepare a solution
from cellulose acetate and an organic solvent in which cellulose
acetate cannot be dissolved according to a conventional process.
Therefore, the cooling dissolution method is very advantageous
particularly where a film is prepared from cellulose triacetate
(having a degree of acetyl substitution of 2.6 or more), which has
poor solubility.
SUMMARY OF THE INVENTION
[0009] The cooling dissolution method now makes it possible to
prepare a cellulose acetate product from poorly soluble cellulose
triacetate (having a degree of acetyl substitution of 2.6 or more)
according to a solvent cast method without use of hydrocarbon
halides such as dichloromethane.
[0010] However, cellulose acetate having a high degree of acetyl
substitution still shows a low solubility in an organic solvent
even if a cooling dissolution method is used. Further, a solution
of cellulose acetate having a high degree of acetyl substitution in
an organic solvent has a problem in stability.
[0011] An object of the present invention is to improve solubility
of cellulose acetate having a relatively high degree of acetyl
substitution.
[0012] Another object of the invention is to provide a cellulose
acetate in which the relation among the degrees of acetyl
substitution at 2-, 3- and 6-positions is properly controlled.
[0013] A further object of the invention is to prepare a cellulose
acetate solution whose solubility and viscosity are easily
controlled.
[0014] A furthermore object of the invention is to prepare a
cellulose acetate film having preferable properties and optical
characters.
[0015] A still further object of the invention is to prepare a
cellulose acetate film having excellent physical characteristics by
using a solution of cellulose acetate having a relatively high
degree of acetyl substitution.
[0016] The present invention provides a process for adjusting an
intermolecular or intramolecular degree of acetyl substitution of
cellulose acetate, which comprises ripening cellulose acetate in
the presence of a catalyst, an acetyl donor, and water or an
alcohol, and under a condition that the amount of water and the
alcohol is in the range of 0.1 to 10 mol % based on the amount of
the acetyl donor.
[0017] The invention also provides a process for preparation of
cellulose acetate which comprises the steps of: reacting cellulose
in a solvent with acetic acid or acetic anhydride in the presence
of an acid catalyst to synthesize cellulose acetate; and ripening
the synthesized cellulose acetate in the presence of the remaining
acid catalyst, an acetyl donor, and water or an alcohol, and under
a condition that the amount of water and the alcohol is in the
range of 0.1 to 10 mol % based on the amount of the acetyl
donor.
[0018] The invention further provides a process for preparation of
cellulose acetate which comprises the steps of: reacting cellulose
in a solvent with acetic acid or acetic anhydride in the presence
of an acid catalyst to synthesize cellulose acetate; neutralizing
the acid catalyst to stop to stop the synthesizing reaction; and
ripening the synthesized cellulose acetate in the presence of a
catalyst, and under a condition that the amount of water and an
alcohol is less than 10 mol % based on the amount of the acetyl
donor.
[0019] The above-mentioned processes can form cellulose acetate
having new characteristics.
[0020] The invention provides cellulose acetate having a degree of
acetyl substitution in the range of 2.636 to 2.958, wherein the
cellulose acetate shows a distribution curve of an intermolecular
substitution degree in which the maximum peak has a half width
(unit: difference of intermolecular substitution degrees) of less
than 0.080.
[0021] The invention also provides cellulose acetate having a
degree of acetyl substitution in the range of 2.636 to 2.958,
wherein the cellulose acetate shows a distribution curve of an
intermolecular substitution degree in which the maximum peak has a
half width of less than Y defined in the following formula:
Y=-0.17788X+0.5788
in which X is the degree of acetyl substitution.
[0022] The invention further provides cellulose acetate showing an
infrared absorption spectrum, wherein the absorption spectrum has
the absorption maximum in the wave number range of 3450 to 3550
cm.sup.-1 in which the absorption maximum has a half width of 135
cm.sup.-1 or less.
[0023] The invention furthermore provides cellulose acetate in
which the degrees of acetyl substitution at 2-, 3- and 6-positions
satisfy the following formulas (I) to (III):
2DS+3DS<6DS.times.4-1.70 (I)
2DS+3DS<-6DS.times.4+5.70 (II)
2DS+3DS>1.80 (III)
in which 2DS is the degree of acetyl substitution at 2-position;
3DS is the degree of acetyl substitution at 3-position; and 6DS is
the degree of acetyl substitution at 6-position.
[0024] The invention still furthermore provides a cellulose acetate
in which the degrees of acetyl substitution at 2-, 3- and
6-positions satisfy the following formulas (III) to (V):
2DS+3DS>1.80 (III)
3DS<2DS (IV)
6DS>0.80 (V)
in which 2DS is the degree of acetyl substitution at 2-position,
3DS is the degree of acetyl substitution at 3-position, and 6DS is
the degree of acetyl substitution at 6-position.
[0025] According to study of the present inventors, the
intermolecular degree of acetyl substitution can be adjusted to be
uniform by ripening cellulose acetate in the presence of a
catalyst, an acetyl donor, and water or an alcohol, and under a
condition that the amount of water and the alcohol is in the range
of 0.1 to 10 mol % based on the amount of the acetyl donor.
[0026] Each of T. R. Floyd (J. Chromatogr., 629, 243 (1993) and
Kawai (Articles of polymer (written in Japanese), Vol. 54, No. 9,
526 (1997) reports an intermolecular degree of acetyl substitution
about cellulose diacetate having a low degree of acetyl
substitution, which was evaluated by using a reverse phase HPLC.
However, there is no report about cellulose triacetate having a
high degree of acetyl substitution.
[0027] The inventors have further studied cellulose acetate having
a uniform intermolecular degree of acetyl substitution, and found
that cellulose acetate having the uniform degree shows an excellent
solubility even though the substitution degree is relatively high
(2.636 to 2.958). Now, a cellulose acetate product having excellent
physical characteristics can be prepared by using a solution of
cellu- of cellulose acetate having excellent solubility according
to the present invention.
[0028] According to further study of the inventors, the degrees of
acetyl substitution at 2-, 3- and 6-positions can be easily and
properly controlled by ripening cellulose acetate under a condition
that the amount of water and an alcohol is in the range of 0.1 to
10 mol % based on the amount of the acetyl donor.
[0029] The degrees of acetyl substitution at 2-, 3- and 6-positions
can be effectively controlled as is mentioned above to prepare
cellulose acetate satisfying the formulas (I) to (III) or (III) to
(V).
[0030] The cellulose acetate having the properly controlled degrees
of acetyl substitution makes it possible to prepare easily a
cellulose acetate solution whose solubility and viscosity can be
easily controlled. Further, the invention also makes it possible to
prepare easily a cellulose acetate film having excellent physical
and optical characteristics.
[0031] The study of the inventors furthermore revealed that
cellulose acetate having good solubility shows a specific infrared
absorption spectrum in which an absorption maximum having a half
width of 135 cm.sup.-1 or less is in the range of 3450 to 3550
cm.sup.-1. The absorption maximum is attributed to cellulose
acetate from which a cellulose acetate solution dissolving
cellulose acetate well can be prepared. Further, from the
thus-prepared solution a cellulose acetate film having preferable
properties and optical characters can be formed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a graph showing a distribution curve of an
intermolecular substitution degree of cellulose acetate prepared in
Example 4.
[0033] FIG. 2 is a graph showing a distribution curve of an
intermolecular substitution degree of cellulose acetate prepared in
Comparison Example 4.
[0034] FIG. 3 is a graph showing degrees of acetyl substitution
regulated by the formulas (I) to (III) and (VI) to (VIII), and also
shows the degrees of acetyl substitution of cellulose acetates in
Examples 1 to 9, 12 to 14 and Comparison Example 1.
[0035] FIG. 4 is a graph showing degrees of acetyl substitution
regulated by the formulas (III), (IV), (VII), (VIII) and (X), and
also shows the degrees of acetyl substitution of cellulose acetates
in Examples 1 to 9, 12 to 14 and Comparison Examples 1 and 2.
[0036] FIG. 5 is a spectrum showing a half-width of the absorption
maximum in an infrared absorption spectrum.
[0037] FIG. 6 shows infrared absorption spectra of Examples 10 and
11 and Comparison Examples 5 and 6.
DETAILED DESCRIPTION OF THE INVENTION
Preparation of Cellulose Acetate
[0038] Cellulose as the starting material for preparation of
cellulose acetate can be obtained from cotton linters or wood pulp.
A mixture of raw pulp can be also used.
[0039] Cellulose (the starting material) is reacted in a solvent
with acetic acid or acetic anhydride in the presence of a catalyst
to synthesize cellulose acetate. In the synthesis, acetic acid as
the solvent, sulfuric acid as the catalyst and acetic anhydride as
the acetyl donor are usually used.
[0040] Migita et al. (Mokuzai Kagaku (Wood Chemistry, written in
Japanese), 1968, Kyoritsu Shuppan, pp. 180 to 190) describe the
principle of cellulose acetate synthesis. A typical synthesis
method is a homogeneous acetylation process with a system of acetic
anhydride (acetyl donor)-acetic acid (solvent)-sulfuric acid
(catalyst). The process comess comprises the steps of: pretreating
cellulose (starting material) such as wood pulp with an adequate
amount of acetic acid, and then pouring the material into a cooled
acetylation mixture to prepare cellulose acetate. The acetylation
mixture generally comprises acetic acid as the solvent, acetic
anhydride as the acetyl donor (esterifying agent) and sulfuric acid
as the catalyst. The amount of acetic anhydride is usually in
stoichiometrical excess of the total amount of water and cellulose
to react in the system. Accordingly, after the acetylation reaction
is completed, an aqueous solution of neutralizing agent (e.g.,
carbonates, acetates and oxides of sodium, potassium, calcium,
magnesium, iron, aluminum, zinc and ammonium) is added so as to
neutralize the remaining excess acetic anhydride and esterifying
catalyst.
[0041] In a conventional process, the prepared cellulose acetate is
kept at 50 to 90.degree. C. in the presence of a little amount of
acetylation catalyst (generally, sulfuric acid) to conduct
saponification (ripening). The degrees of acetyl substitution and
polymerization of cellulose acetate is appropriately adjusted at
the ripening process. After the cellulose acetate is ripened, the
above-described neutralizing agent can be added to neutralize
completely the remaining catalyst. The cellulose acetate can also
be used at the next step without neutralizing process. The obtained
cellulose acetate solution is poured into water or diluted acetic
acid (or water or diluted acetic acid is poured into the solution)
to separate cellulose acetate from the solution. The separated
cellulose acetate is then washed, and is subjected to a stabilizing
treatment.
[0042] In Japanese Patent Provisional Publication No.
11(1999)-5851, the acetylation reaction is performed with a small
amount of sulfuric acid to obtain cellulose acetate whose degree of
acetyl substitution at 6-position is relatively high. However,
cellulose acetate prepared with such a small amount of sulfuric
acid often has poor solubility. Further, white insoluble materials
are often formed in a solution of the cellulose acetate. The
acetylation reaction slowly proceeds as solid cellulose (starting
material) is gradually acetylated and dissolved. Therefore,
cellulose dissolved earlier is different in a reaction speed from
cellulose dissolved later in the reaction under a condition of a
small amount of sulfuric acid. Consequently, the reaction gives
cellulose acetate inhomogeneous with respect to the intermolecular
degree of acetyl substitution.
[0043] The inventors have found that cellulose acetate having a
uniform intermolecular degree of acetyl substitution can be
prepared by ripening cellulose acetate in the presence of a
catalyst, an acetyl donor, and water or an alcohol, and under a
condition that the amount of water and an alcohol is in the range
of 0.1 to 10 mol % (0.1 mol % or more and less than 10 mol %) based
on the amount of the acetyl donor.
[0044] The inventors have also found that the degrees of acetyl
substitution at 2-, 3- and 6-positions can be easily and properly
controlled by ripening cellulose acetate in the presence of a
catalyst, an acetyl donor, and water or an alcohol, and under a
condition that the amount of water and an alcohol is 0.1 to 10 mol
% (0.1 mol % or more and less than 10 mol %) based on the amount of
the acetyl donor.
[0045] In the case where synthesis and ripening (controlling degree
of acetyl substitution) of cellulose acetate are successively
conducted, neutralizing treatment (neutralization of an acid
catalyst used in the synthesis reaction) need not be conducted, or
can partially be conducted to use all or a part of the remaining
catalyst in an ripening reaction at the next stage.
[0046] The acetyl donor is a compound having acetyl group
(--COCH.sub.3) that can be given to remaining hydroxyl (--OH) of
cellulose acetate through the ester-exchanging reaction or
esterifying reaction in the presence of a catalyst. The acetyl
donor preferably is acetic acid or an acetic ester, and more
preferably is acetic acid or an acetic ester of an alcohol.
[0047] According to the study of the inventors, if the amount of
water and an alcohol is 10 mol % or more based on the amount of the
acetyl donor, the acetyl groups are liable to be eliminated from
highly substituted cellulose acetate (degrees of acetyl
substitution at 2-, 3- and 6-positions in total is 2.6367 or more,
particularly 2.70 or more).
[0048] In contrast, when the amount of water and an alcohol is less
than 10 mol % (preferably, less than 7 mol %), the acetylation of
dissociated hydroxyl proceeds at a speed comparable to the reaction
speed of elimination of acetyl groups. As a result, the reactions
converge on an equilibrium point. Therefore, the amount of water
and an alcohol is set to be less than 10 mol % based on the amount
of the acetyl donor, and thereby the reaction between the acetyl
donor and cellulose acetate is made to be reversible. An
equilibrium between a glucose unit having remaining hydroxyl (at
2-, 3- or 6-position) with an acetyl donor (R--O--COCH.sub.3 in
which R is hydrogen or an alkyl group) and a glucose unit having no
hydroxyl (acetyl groups are combined to 2-, 3- and 6-positions)
with water or an alcohol (R--OH, in which R is hydrogen or an alkyl
group) is controlled to obtain a uniform intermolecular degree of
acetyl substitution.
[0049] Water or an alcohol (0.1 mol % or more based on the acetyl
donor) is essential for the above-mentioned equilibrium.
[0050] Further, the intramolecular degrees of substitution at 2-,
3- or 6-positions can also be easily adjusted where the reaction
between the acetyl donor and cellulose acetate is reversible. The
equilibrium shown below between the acetyl donor (R--O--COCH.sub.3
in which R is hydrogen or an alkyl group) and a glucose unit having
hydroxyl at 2-, 3- or 6-position is so controlled that the degrees
of acetyl substitution at 2-, 3- and 6-positions can effectively be
adjusted.
##STR00001##
[0051] The catalyst used in the ripening step is preferably an acid
or a metal (e.g., titanium, tin) ion. The acid may be a Lewis acid
as well as a normal proton acid. If the the ripening step is
carried out in ethyl acetate (acetyl donor)-alcohol (solvent)
system, metal alkoxides and organic bases (e.g.,
dialkylaminopyridine, N-methylimidazole) may be used as the
catalyst. The most preferred catalyst is an acid.
[0052] The acid catalyst preferably is a strong acid (e.g.,
sulfonic acid, perchloric acid, sulfuric acid, boron trifluoride,
tetrafluoroboric acid). In consideration of availability,
stability, toxicity and corrosiveness, sulfuric acid is most
preferred. If the reaction temperature is 100.degree. C. or more,
acetic acid used as the acetyl donor can function as the acid
catalyst. The present invention includes the embodiment using
acetic acid as the acid catalyst as well as the acetyl donor.
[0053] The amount of catalyst is determined according to the
reaction temperature and the catalytic ability (acidity in the case
of acidic catalyst).
[0054] The ripening step has usually been carried out in acetic
acid (acetyl donor)-water (solvent) system. In a conventional
ripening step, however, the amount of water is 10 mol % or more
based on the amount of acetic acid. Under that condition, the
decomposition of ester linkage in cellulose acetate predominantly
proceeds, and consequently the degrees of substitution are lowered.
Therefore, it is impossible to control properly the degrees of
acetyl substitution at 2-, 3- and 6-positions under that
conventional condition.
[0055] In the present invention, the amount of water and an alcohol
is set to be less than 10 mol % (preferably, less than 7 mol %)
based on the amount of acetyl donor, and thereby the degrees of
acetyl substitution at 2-, 3- and 6-positions can be properly
controlled.
[0056] Generally, an excess amount of acetic anhydride is used in
the step for preparing cellulose acetate. The remaining acetic
anhydride is preferably hydrolyzed into acetic acid before the
ripening step, so that the ripening can be carried out without
acetic anhydride.
[0057] The acetyl donor can function as a solvent at the ripening
step. Therefore, it is not necessary to use another solvent.
However, a liquid inactive to the reaction can be used as the
solvent. The amount of the solvent other than the acetyl donor is
preferably not more than five times the amount of the acetyl donor.
The solvent other than the acetyl donor is selected from liquid
dissolving cellulose acetate at the ripening step. Examples of the
solvents include hydrocarbon halides (e.g., dichloromethane,
chloroform, 1,1,2,2-tetrachloroethane), nitro compounds (e.g.,
nitromethane, nitrobenzene), sulfones (e.g., sulfolane) and ethers
(e.g., dioxane).
[0058] In the case that an acid catalyst (e.g., sulfonic acid,
perchloric acid, sulfuric acid) is used, the amount of the acid
catalyst at the ripening step is preferably in the range of 0.1 to
10 mol %, and more preferably in the range of 0.2 to 2 mol % based
on the amount of the acetyl donor. At the ripening step, the amount
of the catalyst is essentially not changed within the
above-mentioned preferred range.
[0059] The ripening temperature is preferably in the range of 20 to
125.degree. C., and more preferably in the range of 30 to
70.degree. C.
[0060] The ripening time is preferably in the range of 10 minutes
to 10 hours, and more preferably in the range of 30 minutes to 3
hours.
[0061] The amount of water and alcohol (X) based on the acetyl
donor, the amount of the catalyst (Y) based on the acetyl donor,
the ripening temperature (T) and the ripening time (t) are
preferably adjusted as important reaction conditions. The relation
among the conditions is also preferably adjusted to obtain an
appropriate equilibrium between the acetyl donor and cellulose
acetate. For the pur- For the purpose of that, the ripening
condition are preferably so controlled that the reaction parameter
(R) defined by the following formula is more than 20. The reaction
parameter (R) is more preferably more than 30, and most preferably
more than 40.
R(Reaction parameter)=.cndot.YZ/Xdt
[0062] In the formula, X is the molar ratio (%) of water and an
alcohol based on the amount of the acetyl donor, Y is the molar
ratio (%) of the catalyst based on the amount of the acetyl donor,
Z is the temperature reduction coefficient (3.sup.(T-30)/20 in
which T is the reaction temperature (.degree. C.)), and t is the
reaction time (unit: minute). In the case where X is less than 0.1
mol %, X is regarded as 0.1 to calculate the R.
(Intermolecular Substitution Degree of Cellulose Acetate)
[0063] The process according to the present invention can form
cellulose acetate in which an intermolecular acetyl substitution is
uniform.
[0064] Cellulose acetate having a uniform degree of acetyl
substitution can be purified (for example by a chromatography) from
cellulose acetate having different degrees of acetyl substitution.
However, cellulose acetate having a uniform degree of acetyl
substitution is preferably obtained in a more economical way, in
which cellulose acetate can be directly synthesized by improving
the process as is mentioned above.
[0065] The average degree of acetyl substitution is preferably in
the range of 2.636 to 2.958.
[0066] The degree of acetyl substitution can be measured by NMR
according to a method of Tezuka (Carbohydr. Res., 273, 83 (1995)).
Free hydroxyl groups in a cellulose acetate sample are reacted with
propionic anhydride to form propionate ester in pyridine. The
obtained sample is dissolved solved in chloroform-d.sub.1, and the
spectrum of carbon-13 is measured. The acetyl carbon signals are
shown in the range of 169 ppm to 171 ppm in the order of 2-, 3- and
6-positions from a higher magnetic field. The propionyl carbon
signals are shown in the range of 172 ppm to 174 ppm in the same
order. The ratio of acetyl to propionyl at the corresponding
position can give the degree of acetylation in the original
cellulose acetate.
[0067] The average degree of acetyl substitution of cellulose
acetate has conventionally determined from a value of acetic acid
content, which can be measured according to ASTM-D-817-91 (testing
method for cellulose acetate or the like). The acetic acid content
obtained according to ASTM can be converted into the degree of
substitution according to the following formula.
DS=162.times.AV.times.0.01/(60-40.times.AV.times.0.001)
[0068] In the formula, DS is the degree of acetyl substitution, and
AV is the acetic acid content (%).
[0069] The calculated degree of substitution may usually be
somewhat different from the value measured by NMR described above.
If the values are different from each other, the value measured by
NMR is prior to the ASTM value. If the values measured by various
NMR methods are different from each other, the value measured
according to the method of Tezuka is prior to the other values.
[0070] In the present specification, the uniform intermolecular
degree of acetyl substitution means that cellulose acetate shows a
distribution curve of an intermolecular substitution degree in
which the maximum peak has a half width of less than 0.080, or has
a half width of less than Y defined in the following formula:
Y=-0.17788X+0.5788
in which X is the degree of acetyl substitution.
[0071] The cellulose acetate most preferably shows a distribution
curve of an intermolecular substitution degree in which the maximum
peak has a half width of less than 0.080 and less than Y defined in
the formula.
[0072] The distribution curve of an intermolecular substitution
degree of cellulose acetate can be obtained by converting the
abscissa (the horizontal axis) of an elution curve (elution time)
to the degree of acetyl substitution (0 to 3). The elution curve is
measured by a reverse phase HPLC.
[0073] The conditions of the reverse phase HPLC are shown
below.
TABLE-US-00001 Eluent: Linear gradient by 28 minutes from
chloroform/methanol (9/1, v/v)):methanol/water (8/1, v/v) = 20:80
to chloroform/methanol (9/1, v/v) = 100 Column: Nova Packphenyl of
3.9 .times. 150 mm (Waters) Column temperature: 30.degree. C. Flow
rate: 0.7 ml per minute Conc. of sample: 2 mg per ml Injected
amount: 20 .mu.l Detector: Evaporative light scattering detector
(ELSD-MK-III, Varex) Drift tube temp.: 80.degree. C. Gas flow: 2.1
SLPM
[0074] Before the elution curve is converted into the distribution
curve of an intermolecular substitution degree, at least four
samples having different substitution degrees are measured under
the same conditions to determine elution time. A formula of
converting the elution time (T) to the degree of substitution (DS)
can be obtained from the determined elution time. The relation
between the elution time (T) and the degree of substitution (DS)
can give a calibration curve according to the least squares method.
The function is usually given in a secondary formula shown be- dary
formula shown below.
DS=aT.sup.2+bT+c
[0075] In the formula, DS is the degree of acetyl substitution, T
is the elution time, and a, b and c are coefficients of the
conversion formula.
[0076] FIG. 1 is a graph showing a distribution curve of an
intermolecular substitution degree of cellulose acetate prepared in
Example 4.
[0077] FIG. 2 is a graph showing a distribution curve of an
intermolecular substitution degree of cellulose acetate prepared in
Comparison Example 4.
[0078] The DS of the abscissa (the horizontal axis) in FIGS. 1
& 2 means the degree of acetyl substitution. The intensity of
the ordinate (the vertical axis) in FIGS. 1 & 2 means the
amount of cellulose acetate having the degree of acetyl
substitution corresponding to the abscissa.
[0079] The distribution curve of an intermolecular substitution in
FIG. 1 shows the maximum peak (E) at the degree of substitution of
2.795. The distribution curve of an intermolecular substitution in
FIG. 2 shows the maximum peak (E) at the degree of substitution of
2.851.
[0080] A base line (A-B) tangent is drawn from the base point (A)
on the low substitution degree side to the base point (B) on the
high substitution degree side. Independently, a line perpendicular
to the horizontal axis is drawn from the maximum peak (E) of the
curve to determine the intersection (C) of the perpendicular line
and the base line (A-B). The midpoint (D) between the peak (E) and
the intersection (C) is then determined. A line including the
midpoint (D) is drawn parallel to the base line (A-B) to determine
two intersections (A', B') of the line and the distribution curve
of the intermolecular substitution. From each of the intersections
(A', B'), a line perpendicular to the horizontal axis is drawn. The
interval between the feet of the interval between the feet of the
thus-drawn perpendiculars is defined as the half-width of the
maximum peak.
(Intramolecular Substitution Degree of Cellulose Acetate)
[0081] The process according to the present invention can also form
cellulose acetate in which degrees of acetyl substitution at 2-, 3-
and 6-positions are properly controlled.
[0082] A cellulose acetate film having preferable properties and
optical characters can be made of cellulose acetate in which the
degrees of acetyl substitution at 2-, 3- and 6-positions satisfy
the following formulas (I) to (III).
2DS+3DS<6DS.times.4-1.70 (I)
2DS+3DS<-6DS.times.4+5.7 (II)
2DS+3DS>1.80 (III)
[0083] In the formulas (I) to (III), 2DS is the degree of acetyl
substitution at 2-position, 3DS is the degree of acetyl
substitution at 3-position, and 6DS is the degree of acetyl
substitution at 6-position.
[0084] The degrees of acetyl substitution at 2-, 3- and 6-positions
also preferably satisfy the following formula (VT).
2DS+3DS-6DS<1 (VI)
[0085] In the formula (VI), 2DS is the degree of acetyl
substitution at 2-position, 3DS is the degree of acetyl
substitution at 3-position, and 6DS is the degree of acetyl
substitution at 6-position.
[0086] The degrees of acetyl substitution at 2- and 3-positions
further preferably satisfy the following formula (VII), and
furthermore preferably satisfy the following formula (VIII).
2DS+3DS>1.82 (VII)
2DS+3DS>1.84 (VIII)
[0087] FIG. 3 is a graph showing the conditions of degrees of
acetyl substitution regulated by the formulas (I) to (III), (VI) to
(VIII), and the graph also shows the degrees of acetyl substitution
of cellulose acetates in Examples 1 to 9, 12 to 14 and Comparison
Example 1. In the graph, the sum of the degrees of acetyl
substitution at 2- and 3-positions (2DS and 3DS) are plotted on the
abscissa (the horizontal axis), and the degree of acetyl
substitution at 6-position (6DS) is plotted on the ordinate (the
vertical axis).
[0088] Cellulose acetate satisfying the formula (I) is shown in the
area below the line of (I) in FIG. 3 in which
2DS+3DS=6DS.times.4-1.70.
[0089] Cellulose acetate satisfying the formula (II) is shown in
the area above the line of (II) in FIG. 3 in which
2DS+3DS=-6DS.times.4+5.70.
[0090] Cellulose acetate satisfying the formula (III) is shown in
the area at the right side of the line of (III) in FIG. 3 in which
2DS+3DS=1.80.
[0091] Cellulose acetate satisfying the formula (VI) is shown in
the area at the left side of the line of (VI) in FIG. 3 in which
2DS+3DS-6DS=1.
[0092] Cellulose acetate satisfying the formula (VII) is shown in
the area at the right side of the line of (VII) in FIG. 3 in which
2DS+3DS=1.82.
[0093] Cellulose acetate satisfying the formula (VIII) is shown in
the area at the right side of the line of (VIII) in FIG. 3 in which
2DS+3DS=1.84.
[0094] The solid circles 1 to 9 and 12 to 14 correspond to Examples
1 to 9 and 12 to 14, respectively. The open circle C1 corresponds
to Comparison Example 1. Cellulose acetate of Comparison Example 2
is out of the range shown in the graph.
[0095] A cellulose acetate solution whose solubility and viscosity
are easily controlled can be prepared from the cellulose acetate in
which the degrees of acetyl substitution at 2-, 3- and 6-positions
satisfy the following formulas (III) to (V):
2DS+3DS>1.80 (III)
3DS<2DS (IV)
6DS>0.80 (V)
[0096] In the formulas (III) to (V), 2DS is the degree of acetyl
substitution at 2-position, 3DS is the degree of acetyl
substitution at 3-position, and 6DS is the degree of acetyl
substitution at 6-position.
[0097] The degrees of acetyl substitution at 2- and 3-positions
further preferably satisfy the following formula (VII), and
furthermore preferably satisfy the following formula (VIII).
2DS+3DS>1.82 (VII)
2DS+3DS>1.84 (VIII)
[0098] The degrees of acetyl substitution at 2- and 3-positions
also preferably satisfy the following formula (X).
3DS>2DS.times.2-1 (X)
[0099] FIG. 4 is a graph showing the conditions of degrees of
acetyl substitution regulated by the formulas (III), (IV), (VII),
(VIII) and (X), and also shows the degrees of acetyl substitution
of cellulose acetates in Examples 1 to 9, 12 to 14 and Comparison
Examples 1 and 2. In the graph, the degree of acetyl substitution
at 2-positions (2DS) is plotted on the abscissa (the horizontal
axis), and the degree of acetyl substitution at 3-position (3DS) is
plotted on the ordinate (the vertical axis).
[0100] Cellulose acetate satisfying the formula (III) is shown in
the area above the line of (III) in FIG. 4 in which
2DS+3DS=1.80.
[0101] Cellulose acetate satisfying the formula (IV) is shown shown
in the area below the line of (IV) in FIG. 4 in which 3DS=2DS.
[0102] Cellulose acetate satisfying the formula (VII) is shown in
the area above the line of (VII) in FIG. 4 in which
2DS+3DS=1.82.
[0103] Cellulose acetate satisfying the formula (VIII) is shown in
the area above the line of (VIII) in FIG. 4 in which
2DS+3DS=1.84.
[0104] Cellulose acetate satisfying the formula (X) is shown in the
area at the left side of the line of (X) in FIG. 4 in which
3DS=2DS.times.2-1.
[0105] The solid circles 1 to 5 and 7 to 10 correspond to Examples
1 to 5 and 7 to 10, respectively. The open circles C1 and C2
correspond to Comparison Examples 1 and 2, respectively.
[0106] Cellulose acetate preferably satisfies at least four
formulas, more preferably satisfies at least five formulas, further
preferably satisfies at least six formulas, furthermore preferably
satisfies at least seven formulas, and most preferably satisfies at
least eight formulas of (I) to (X). Cellulose acetate particularly
preferably satisfies all the formulas (I) to (X).
[0107] The degrees of acetyl substitution at 2-, 3- and 6-positions
can be determined by means of .sup.13C-NMR after the cellulose
acetate is subjected to a process of forming propionate ester. The
measurement of degrees of acetyl substitution is described in
detail in Tezuka et al. (Carbohydr. Res., 273, 83-91 (1995)).
(Infrared Absorption Spectrum]
[0108] The process according to the present invention can also form
cellulose acetate, which shows an infrared absorption spectrum in
which an absorption maximum having a half width of 135 cm.sup.-1 or
less is in the wave number range of 3450 to 3550 cm.sup.-1. The
absorption maximum is more preferably in the range of 3455 to 3540
cm.sup.-1, and further preferably in the range of 3460 to 3530
cm.sup.-1. The half width of the absorption maximum is more
preferably 130 cm.sup.-1 or less, and further preferably 125
cm.sup.-1 or less.
[0109] The infrared absorption spectrum of cellulose acetate is
measured in the form of a film, which is formed by the solvent cast
method. Concrete procedures of the measurement are described in
Example 6.
[0110] From the measured spectrum (ordinate: absorbance), the
position and the half-width of the absorption maximum are obtained.
The analysis of the infrared absorption spectrum is described in
"Kobunshi no Kozo (Structure of polymer), written in Japanese", H.
Tadokoro, (1976), 219-221, Kagaku-Dojin.
[0111] FIG. 5 is a spectrum showing a half-width of the absorption
maximum in an infrared absorption spectrum.
[0112] In the spectrum in FIG. 5, there is an absorption band
attributed to hydroxyl at about 3500 cm.sup.-1. The half-width is
obtained in the following manner. First, a base line (A-B) tangent
to both of the base point (A) on the higher energy side (at about
3700 cm.sup.-1) and the base point (B) on the lower energy side (at
about 3250 cm.sup.-1) is drawn. Independently, a line perpendicular
to the horizontal axis is drawn from the peak (E) of the band so as
to determine the intersection (C) of the perpendicular and the base
line (A-B). The midpoint (D) between the peak (E) and the
intersection (C) is then determined, and a line including the
midpoint (D) is drawn parallel to the base line (A-B) to determine
intersections (A', B') of the line and the spectrum. From each of
the intersections (A', B'), a line perpendicular to the horizontal
axis is drawn. The interval between the feet of the thus-drawn
perpendiculars is defined as the half-width
(.DELTA..nu..sub.1/2).
[0113] If the absorption band has two or more peaks in the range of
3459 to 3550 cm.sup.-1, the maximum peak is regarded as the peak of
the band (E in FIG. 5).
[0114] The infrared absorption spectrum of methylcellulose is
described in "Cellulose", 4, 281 (1997), Kondo et al.
[0115] It is also preferred for an already produced cellulose
acetate film (such as a film product)) to show an infrared
absorption spectrum in which an absorption maximum having a half
width of 135 cm.sup.-1 or less is in the range of 3450 to 3550
cm.sup.-1. In that case, since additives (for example, ultraviolet
absorbers) often affect the spectrum, the absorption spectrum
attributed to cellulose acetate itself is selectively measured.
(Organic Solvent)
[0116] Cellulose acetate is usually dissolved in an organic solvent
to prepare a cellulose acetate solution, from which various
products (e.g., film) are produced. Examples of the organic solvent
include ketones, esters, ethers, hydrocarbons and alcohols.
[0117] Although halogenated hydrocarbons such as methylene chloride
are also usable from the technical viewpoint, they are not
preferred in consideration of the environment. The organic solvent,
therefore, preferably contains halogenated hydrocarbons in an
amount of less than 5 wt. % (more preferably less than 2 wt. %). It
is also preferred that no halogenated hydrocarbon be found in the
produced cellulose acetate film.
[0118] The organic solvent preferably contains a solvent selected
from the group consisting of an ether having 2 to 12 carbon atoms,
a ketone having 3 to 12 carbon atoms and an ester having 2 to 12
carbon atoms.
[0119] The ether, the ketone or the ester may have a cyclic
structure. A compound having two or more functional groups of
ether, ketone or ester (--O--, --CO-- or --COO--) is also usable as
the solvent. The organic solvent may have other functional groups
such as alcoholic hydroxyl. If the solvent is the compound having
two or more functional groups, the number of carbon atoms is in any
of the above ranges.
[0120] Examples of the ether having 2 to 12 carbon atoms include
dimethyl ether, methyl ethyl ether, diisopropyl ether,
dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolan,
tetrahydrofuran, anisole and phenetole.
[0121] Examples of the ketone having 3 to 12 carbon atoms include
acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone,
cyclohexanone, methylcyclohexane and acetylacetone.
[0122] Examples of the ester having 2 to 12 carbon atoms include
methyl formate, ethyl formate, propyl formate, pentyl formate,
methyl acetate, ethyl acetate and pentyl acetate. An organic
solvent containing methyl acetate in an amount of 50 wt. % or more
is particularly preferably used.
[0123] Examples of the compound having two or more functional
groups include 2-ethoxyethyl acetate, 2-methoxy ethanol and
2-butoxy ethanol.
[0124] A particularly preferred solvent is a mixture of three
different kinds of solvents. In the mixture, the first solvent is a
ketone having 3 to 12 carbon atoms or an ester having 2 to 12
carbon atoms, the second solvent is a monovalent straight-chained
alcohol having 1 to 5 carbon atoms, and the third solvent is an
alcohol having a boiling point of 30 to 170.degree. C. or a
hydrocarbon having a boiling point of 30 to 170.degree. C.
[0125] The ketone or ester used as the first solvent is the same as
that described above. The first solvent may be a mixture thereof.
For example, a mixture of ketone (e.g., acetone) and ester (e.g.,
methyl acetate) can be used as the first solvent.
[0126] The second solvent is a monovalent straight-chained alcohol
having 1 to 5 carbon atoms. In the alcohol, hydroxyl may be
connected to either the terminal of the straight hydrocarbon chain
(i.e., primary alcohol) or the middle of the chain (i.e., secondary
alcohol). Examples of the alcohol for the second solvent include
methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol,
1-pentanol, 2-pentanol and 3-pentanol. The number of carbon atoms
in the alcohol is preferably 1 to 4, more preferably 1 to 3, and
most preferably 1 or 2. Ethanol is particularly preferred.
[0127] The third solvent is an alcohol having a boiling point of 30
to 170.degree. C. or a hydrocarbon having a boiling point of 30 to
170.degree. C. The alcohol is preferably monovalent. The
hydrocarbon moiety of the alcohol may have a straight chain
structure, a branched chain structure or a cyclic structure. The
hydrocarbon moiety is preferably a saturated aliphatic hydrocarbon.
The alcohol for the third solvent may be a primary alcohol, a
secondary alcohol or a tertiary alcohol.
[0128] Examples of the alcohol for the third solvent include
methanol (boiling point: 64.65.degree. C.), ethanol (boiling point:
78.325.degree. C.), 1-propanol (boiling point: 97.15.degree. C.),
2-propanol (boiling point: 82.4.degree. C.), 1-butanol (boiling
point: 117.9.degree. C.), 2-butanol (boiling point: 99.5.degree.
C.), t-butyl alcohol (boiling point: 82.45.degree. C.), 1-pentanol
(boiling point: 137.5.degree. C.), 2-methyl-2-butanol (boiling
point: 101.9.degree. C.), cyclohexanol (boiling point: 161.degree.
C.), 2-fluoroethanol (boiling point: 103.degree. C.),
2,2,2-trifluoroethanol (boiling point: 80.degree. C.),
2,2,3,3-tetrafluoro-1-propanol (boiling point: 109.degree. C.),
1,3-difluoro-2-propanol (boiling point: 55.degree. C.),
1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol (boiling point:
hexafluoro-2-methyl-2-propanol (boiling point: 62.degree. C.),
1,1,1,3,3,3-hexafluoro-2-propanol (boiling point: 59.degree. C.),
2,2,3,3,3-pentafluoro-1-propanol (boiling point: 80.degree. C.),
2,2,3,4,4,4-hexafluoro-1-butanol (boiling point: 114.degree. C.),
2,2,3,3,4,4,4-heptafluoro-1-butanol (boiling point: 97.degree. C.),
perfluoro-tert-butyl alcohol (boiling point: 45.degree. C.),
2,2,3,3,4,4,5,5-octafluoro-1-pentanol (boiling point: 142.degree.
C.), 2,2,3,3,4,4-hexafluoro-1,5-pentanediol (boiling point:
111.5.degree. C.),
3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-1-octanol (boiling point:
95.degree. C.),
2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluoro-1-octanol (boiling
point: 165.degree. C.), 1-(pentafluorophenyl)ethanol (boiling
point: 82.degree. C.) and 2,3,4,5,6-pentafluorobenzyl alcohol
(boiling point: 115.degree. C.).
[0129] The alcohol for the third solvent is defined as the same as
that for the second solvent described above. However, the alcohol
for the third solvent is selected so that it may be different from
the alcohol for the second solvent. For example, if ethanol is used
as the second solvent, other alcohols defined in the description
for the second solvent (e.g., methanol, 1-propanol, 2-propanol,
1-butanol, 2-butanol, 1-pentanol, 2-pentanol and 3-pentanol) can be
used as the third solvent.
[0130] The hydrocarbon for the third solvent may have a straight
chained, branched chained or cyclic structure. The hydrocarbon may
be either aliphatic or aromatic. If it is aliphatic, the
hydrocarbon may be either saturated or unsaturated.
[0131] Examples of the hydrocarbon include cyclohexane (boiling
point: 80.7.degree. C.), hexane (boiling point: 69.degree. C.),
benzene (boiling point: 80.1.degree. C.), toluene (boiling point:
110.6.degree. C.) and xylene (boiling point: 138.4 to 144.4.degree.
C.).
[0132] In the mixed solvent of three different kinds of solvents,
the content of the first solvent is preferably in the range of 50
to 95 wt. %, more preferably in the range of range of 60 to 92 wt.
%, further preferably in the range of 65 to 90 wt. %, and most
preferably in the range of 70 to 88 wt. %. The content of the
second solvent is preferably in the range of 1 to 30 wt. %, more
preferably in the range of 2 to 27 wt. %, further preferably in the
range of 3 to 24 wt. %, and most preferably in the range of 4 to 22
wt. %. The content of the third solvent is preferably in the range
of 1 to 30 wt. %, more preferably in the range of 2 to 27 wt. %,
further preferably in the range of 3 to 24 wt. %, and most
preferably in the range of 4 to 22 wt. %.
[0133] To the mixed solvent, another organic solvent is added so as
to prepare a mixed solvent of four solvents. In that case, the
fourth solvent is preferably selected from the three kinds of
solvents described above. Further, ethers having 3 to 12 carbon
atoms (e.g., diisopropyl ether, dimethoxyethane, diethoxyethane,
1,4-dioxane, 1,3-dioxofuran, tetrahydrofuran, anisole, phenetole)
and nitromethane can be used besides the above three kinds of
solvents.
[0134] The organic solvent has a boiling point preferably in the
range of 20 to 300.degree. C., more preferably in the range of 30
to 200.degree. C., further preferably in the range of 40 to
100.degree. C., and most preferably in the range of 50 to
80.degree. C.
[0135] Into the above organic solvent, cellulose acetate is
dissolved preferably by the cooling dissolution method. The cooling
dissolution method comprises a swelling step, a cooling step and a
warming step. Even if cellulose acetate can be dissolved in a
solvent at room temperature, the cooling dissolution method makes
it possible to prepare a homogeneous solution rapidly.
(Swelling Step)
[0136] At the first step, cellulose acetate is mixed with a solvent
to swell the polymer in the solvent. The swelling step is
preferably conducted at a temperature of -10 to 55.degree. C. The
swelling step is usually conducted at room temperature.
[0137] The ratio of cellulose acetate to the mixture is determined
depending on a concentration of a solution to be obtained. The
amount of cellulose acetate in the mixture is preferably in the
range of 5 to 30 wt. %, more preferably in the range of 8 to 20 wt.
%, and most preferably in the range of 10 to 15 wt. %.
[0138] The mixture of cellulose acetate and the solvent is
preferably stirred until the cellulose acetate is enough swelled.
The stirring time is preferably in the range of 10 to 150 minutes,
and more preferably in the range of 20 to 120 minutes.
[0139] At the swelling step, additives such as a plasticizer, a
deterioration inhibitor, a dye and an ultraviolet absorbent can be
added to the mixture.
(Cooling Step)
[0140] At the next step, the swelled mixture is cooled to a
temperature of -100 to -10.degree. C. The swelled mixture
preferably solidifies at the cooling step.
[0141] The cooling rate is preferably 4.degree. C. per minute or
more, more preferably 8.degree. C. per minute or more, and most
preferably 12.degree. C. per minute or more. The cooling rate is
preferably as fast as possible. However, a theoretical upper limit
of the cooling rate is 10,000.degree. C. per second, a technical
upper limit is 1,000.degree. C. per second, and a practical upper
limit is 100.degree. C. per second.
[0142] The cooling rate means the change of temperature at the
cooling step per the time taken to complete the cooling step. The
change of temperature means the difference between the temperatures
at which the cooling step is started and at which the cooling step
is completed. The cooling rate in the examples of Japanese patent
Provisional publi- sional publication Nos. 9(1997)-95544,
9(1997)-95557 and 9(1997)-95538 is about 3.degree. C. per
minute.
[0143] The mixture is preferably cooled in a sealed vessel to
prevent contamination of water, which may be caused by dew
condensation at the cooling step. Further, the mixture may be
cooled under a reduced pressure, and thereby the time taken to
complete the cooling step can be shortened. A vessel resisting
pressure is preferably used to conduct the procedures under a
reduced pressure.
[0144] Various methods and apparatus can be used to perform the
cooling step.
[0145] For example, the swelled mixture is conveyed while stirred
into a cylinder, which is then cooled from the outside, and thereby
the mixture is rapidly and homogeneously cooled. For this
procedure, an apparatus comprising a cylindrical vessel, a screw
conveyer which transports the mixture while stirring into the
vessel and a cooling means provided around the vessel is preferably
used.
[0146] A supplemental solvent beforehand cooled at a temperature of
-105 to -15.degree. C. may be added to the swelled mixture, so as
to cool more quickly.
[0147] Further, the swelled mixture can be cooled further quickly
by extruding the mixture into a liquid beforehand cooled at a
temperature of -100 to -10.degree. C. The extruded mixture is in
the form of fiber having a diameter in the range of 0.1 to 20.0 mm.
There is no specific limitation with respect to the liquid for
cooling the mixture.
[0148] If the swelled mixture is extruded into the cooled liquid,
the extruded mixture in the form of fiber is preferably separated
from the cooled liquid after the cooling step and before the
warming step.
[0149] The extruded mixture usually solidifies to gel at the
cooling step, and hence it is easy to separate the solid fiber from
a liquid. For example, the solid fiber in the liquid can be taken
out in a net. A board having small small holes or slits can be used
in place of the net. The net or the board is made of a plastic or
metal that is not dissolved in the cooled liquid. The mesh of the
net, the diameter of the hole or the width of the slit should be
adjusted to the diameter of the fiber to prevent the fiber from
passing through the net or the board. Further, the conveyer may be
made of a net so as to separate the fiber from the liquid while
transporting the fiber from a cooling device to a warming
device.
(Warming Step)
[0150] The cooled mixture is warmed to a temperature of 0 to
200.degree. C. The temperature of the obtained solution after the
warming step is usually room temperature.
[0151] The warming rate is 4.degree. C. per minute or more, more
preferably 8.degree. C. per minute or more, and most preferably
12.degree. C. per minute or more. The warming rate is preferably as
fast as possible. However, a theoretical upper limit of the cooling
rate is 10,000.degree. C. per second, a technical upper limit is
1,000.degree. C. per second, and a practical upper limit is
100.degree. C. per second.
[0152] The warming rate means the change of temperature at the
warming step per the time taken to complete the warming step. The
change of temperature means the difference between the temperature
at which the warming step is started and the temperature at which
the warming step is completed. The warming rate in the examples of
Japanese patent Provisional publication Nos. 9(1997)-95544,
9(1997)-95557 and 9(1997)-95538 is about 3.degree. C. per
minute.
[0153] The mixture may be warmed under an increased pressure, and
thereby the time taken to complete the warming step can be
shortened. A vessel resisting pressure is preferably used to
conduct the procedures under an increased pressure.
[0154] Various methods and apparatus can be used to perform the
warming step.
[0155] For example, the swelled mixture is conveyed while stirred
into a cylinder, which is then warmed from the outside, and thereby
the mixture is rapidly and homogeneously warmed. For this
procedure, an apparatus comprising a cylindrical vessel, a screw
conveyer which transports the mixture while stirring into the
vessel and a warming means provided around the vessel is preferably
used.
[0156] The swelled mixture can be warmed further quickly by
extruding the mixture into a liquid beforehand warmed. The extruded
mixture is in the form of fiber having a diameter in the range of
0.1 to 20.0 mm. There is no specific limitation with respect to the
liquid for warming the mixture.
[0157] If the mixture is extruded in the form of a fiber at the
cooling step, the cooled fiber is immersed in the beforehand warmed
liquid at the warming step. If the cooling step is conducted by
other procedures, the cooled mixture is extruded in the form of a
fiber into the warmed liquid. If the extrusion into a fiber is
successively performed, the produced cellulose acetate solution can
be used as the liquid for warming the next swelled mixture. In that
case, the swelled mixture in the form of a fiber is immersed into a
warm cellulose acetate solution produced before, so as to warm the
mixture rapidly to prepare a new cellulose acetate solution, which
is then used as the liquid for warming the next mixture.
[0158] Further, the cooled swelled mixture may be introduced into a
cylindrical vessel, in which the flow of the mixture is repeatedly
divided and rotated. While repeatedly divided and rotated, the
mixture is warmed from the outside of the vessel. The vessel having
a partition by which the flow of the mixture is divided and rotated
is generally known as a static mixer. For example, in a typical
static typical static mixer (TM, Kenix), two elements are provided.
One of them divides the mixture into two flows, and rotates the
flows counterclockwise (counterclockwise element) by 180.degree..
The other divides the mixture into two flows, and rotates the flows
clockwise (clockwise element) by 180.degree.. Those elements are
placed perpendicularly to each other.
[0159] The swelled mixture may be heated to a temperature above the
boiling point of the solvent under a pressure controlled so that
the solvent may not boil. The temperature is determined according
to the solvent, but is generally in the range of 60 to 200.degree.
C. The pressure is determined in consideration of the temperature
and the boiling point, but is generally in the range of 1.2 to 20
kgw/cm.sup.2.
(Post Treatment after Preparation of Solution)
[0160] The prepared solution can be subjected to post treatment
such as adjustment of concentration (or dilution), filtration, and
adjustment of temperature or addition of components.
[0161] The additional components are determined according to use of
cellulose acetate solution. Examples of the representative
additives include a plasticizer, a deterioration inhibitor (e.g., a
peroxide decomposer, a radical inhibitor, a metal inactivator, an
acid scavenger), a dye and an ultraviolet absorbent. In this step,
fine particles (preferably, fine particles dispersed in a diluted
cellulose acetate solution) are preferably added.
(Fine Particles)
[0162] The cellulose acetate film of the invention can contain fine
particles having a mean particle size of 1.0 .mu.m or less. The
fine particles function as a slipping agent, and improve the
kinetic friction coefficient of the film.
[0163] The fine particles are preferably inorganic compounds.
Examples of the inorganic compound include silicon dioxide,
titanium dioxide, aluminum oxide, zirconium oxide, calcium
carbonate, talc, clay, burned kaolin, burned calcium silicate,
hydrated calcium silicate, aluminum silicate, magnesium silicate
and calcium phosphate. Preferred are silicon dioxide, titanium
dioxide and zirconium oxide, and particularly preferred is silicon
dioxide.
[0164] Onto the surface of the inorganic fine particles, methyl can
be introduced through a surface treatment. For example, fine
particles of silicon oxide are treated with dichlorodimethylsilane
or bis(trimethylsilyl)amine.
[0165] Fine particles of silicon oxide are commercially available
(e.g., Aerozil R972.TM., R972D.TM., R974.TM. and R812.TM., from
Japan Aerozil Co., Ltd.). Fine particles of zirconium oxide are
also commercially available (e.g., Aerozil R976.TM. and R811.TM.,
from Japan Aerozil Co., Ltd.).
[0166] The mean particle size of the fine particles is preferably
1.0 .mu.m or less, more preferably in the range of 0.1 to 1.0
.mu.m, and most preferably in the range of 0.1 to 0.5 .mu.m.
[0167] The amount of the fine particles is preferably in the range
of 0.005 to 0.3 wt. %, more preferably in the range of 0.01 to 0.1
wt. % based on the amount of cellulose acetate.
[0168] The fine particles may be added in any step of the film
forming process described below. Preferably, a diluted solution
analogous to the organic solution of cellulose acetate is prepared,
and in the diluted solution the fine particles are dispersed. The
thus-prepared dispersion and the organic solution of cellulose
acetate are mixed, and from the mixture a film is prepared. Thus, a
film containing the fine particles evenly dispersed can be
obtained.
(Plasticizer)
[0169] The cellulose acetate film generally contains a
plasticizer.
[0170] As the plasticizer, phosphoric esters and carboxylic esters
are used. Examples of the phosphoric esters include triphenyl
phosphate, tricresyl phosphate, octyldiphenyl phosphate, triethyl
phosphate and tributyl phosphate. Typical carboxylic esters are
phthalic esters, citric esters, oleic esters and linoleic esters.
Examples of the phthalic esters include dimethyl phthalate, diethyl
phthalate, dibutyl phthalate, dimethoxy phthalate, dioctyl
phthalate and diethylhexyl phthalate. Examples of the citric esters
include triethyl acetylcitrate and tributyl acetylcitrate. Examples
of the oleic esters include butyl oleate. Examples of other
carboxylic esters include ethylphthalylethyl glycolate,
butylphthalylbutyl glycolate, triacetin, methylacetyl ricinolate,
dibutyl sebacate and various trimellitic esters.
[0171] The amount of plasticizer is generally in the range of 0.1
to 40 wt. %, more preferably in the range of 1.0 to 20 wt. % based
on the amount of cellulose acetate.
(Deterioration Inhibitor)
[0172] The cellulose acetate film preferably contains a
deterioration inhibitor. Examples of the deterioration inhibitor
include a peroxide decomposer, a radical inhibitor, a metal
inactivator and an acid scavenger. The deterioration inhibitor is
described in Japanese Patent Provisional Publication Nos.
3(1991)-199201, 5(1993)-1907073, 5(1993)-194789, 5(1993)-271471 and
6(1994)-107854. A particularly preferred example of the
deterioration inhibitor is butylated hydroxytoluene (BHT).
[0173] The amount of deterioration inhibitor is preferably in the
range of 0.01 to 0.5 wt. %, more preferably in the range of 0.05 to
0.2 wt. % based on the amount of cellulose acetate.
(Ultraviolet Absorbent)
[0174] The cellulose acetate film may contain an ultraviolet
absorbent, which improves aging stability of the film. The
ultraviolet absorbent preferably has no absorption band in the
visible wavelength region.
[0175] Examples of the ultraviolet absorbent include benzophenone
compounds (e.g., 2,4-dihydroxybenzophenone,
2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-noctoxybenzophenone,
4-dodecyloxy-2-hydroxy benzophenone,
2,2',4,4'-tetrahydroxybenzophenone,
2,2'-dihydroxy-4,4'-dimethoxybenzophenone), pentotriazole compounds
(e.g., 2-(2'-hydroxy-5-methylphenyl)benzotriazole,
2-(2'-hydroxy-3',5'-di-t-butylphenyl)benzotriazole,
2-(2'-hydroxy-3'-di-t-butyl-5'-methylphenyl)benzotriazole) and
salicylic compounds (e.g., phenyl salicylate, methyl
salicylate).
[0176] The amount of ultraviolet absorbent preferably in the range
of 0.5 to 20 wt. %, more preferably in the range of 1 to 10 wt. %
based on the amount of cellulose acetate film.
(Dye)
[0177] A dye may be incorporated into the cellulose acetate film,
so as to prevent the light piping phenomenon.
[0178] The hue of the dye is preferably gray. A compound showing
good heat resistance in the temperature range for preparing the
cellulose acetate film and having good compatibility with cellulose
acetate is preferably used as the dye.
[0179] Two or more dyes may be used in combination.
(Film Formation)
[0180] The process for preparing the organic solution of cellulose
acetate (dope) according to the cooling dissolution method is very
different from a usual process (in which a material mixture is only
stirred at room temperature or elevated temperature) for preparing
a solution for the solvent cast method. However, the step for
forming a film from the prepared solution can be carried out in the
same manner.
[0181] The cellulose acetate solution is cast on a support, and the
solvent is evaporated to form a film. Before casting the solution,
the concentration of the solution is preferably so adjusted that
the solid content of the solution is in the range of 18 to 35 wt.
%. The surface of the support is preferably polished to give a
mirror plane. A drum or a band is used as the support. The casting
and drying steps of the solvent cast method are described in U.S.
Pat. Nos. 2,336,310, 2,367,603, 2,492,078, 2,492,977, 2,492,978,
2,607,704, 2,739,069, 2,739,070, British Patent Nos. 640,731,
736,892, Japanese Patent Publication Nos. 45(1970)-4554,
49(1974)-5614, Japanese Patent Provisional Publication Nos.
60(1985)-176834, 60(1985)-203430 and 62(1987)-115035.
[0182] Preferably, the cellulose acetate film formed on the support
is peeled off before completely dried (while the organic solvent
still remains in an amount of 30 wt. % or more based on the weight
of the film), and then is further dried. For this procedure, the
solution cast on the support must gel quickly. In promoting the
gelation, a poor solvent such as alcohols (the above-described
third solvent) is effective. The casting method can be modified to
promote the gelation.
[0183] The solution is cast on the support beforehand cooled at
10.degree. C. or below, and thereby the gelation is promoted (ref.
Japanese Patent Publication No. 5(1993)-17844). The 17844). The
support can be cooled with cooling media or cold air. In this
cooling step, dry air may be blown over the support for 2 or more
seconds to dry the film on the support. The formed film is peeled
off the support, and can be further dried with air to remove the
solvent remaining in the film. The temperature of the air can be
gradually elevated from 100 to 160.degree. C.
[0184] Otherwise, the solution is cast on the support beforehand
warmed at 30.degree. C. or more, and then the support is cooled to
20.degree. C. or below. Through this procedure, the gelation can be
also promoted (ref. Japanese Patent Provisional Publication Nos.
61(1986)-148013 and 61(1986)-158413). The support can be warmed
with a heater provided on the surface of the support, or hot air
may be blown over the support. Further, hot water may be circulated
in the drum support to warm the film. It is preferred that the
temperature be elevated immediately after the solution is cast on
the support. At the beginning of warming, much latent heat is
required because of evaporation of the solvent. Accordingly,
besides the above heating means, auxiliary heating means such as
heaters (steam heater, IR heater) are preferably used to heat the
support, or hot air is preferably blown over the bottom surface of
the support at the beginning of warming. For cooling the support,
the warmed support may be left to cool down. Otherwise, the support
may be forced to cool down by blowing cold air or by circulating
cold water.
[0185] Having excellent optical character and properties, the
thus-formed cellulose acetate film can be widely used. The film of
the invention is particularly effective in liquid crystal
displays.
[0186] The cellulose acetate film may be subjected to AG
(anti-glare) treatment or AR (anti-reflection) treatment. The AG
treatment improves the transmittance of the film by about 3%. In
the AR treatment, an anti-reflection film (consisting of one layer,
two layers or three or more layers) is provided to lower loss by
reflection. Materials for the anti-reflection film are described in
`Thin Film Handbook (written in Japanese)`, Ohom-sha, Dec. 10
(1983), 818-821.
(Protective Film for Polarizing Plate and Liquid Crystal
Display)
[0187] The cellulose acetate film is particularly preferably used
in a liquid crystal display as a protective film for polarizing
plate or a phase retarder.
[0188] A liquid crystal display generally has a liquid crystal
display device and a polarizing plate.
[0189] The liquid crystal display device comprises a liquid crystal
layer, a substrate supporting the layer and an electrode layer
which has a function of applying a voltage to the liquid crystal.
The substrate and the electrode layer are made of transparent
materials for displaying. As the transparent substrate, a glass
thin plate or a resin film is used. If the device must have slight
flexibility, a resin film must be used. In addition to high
transparency, the transparent substrate must have a low
birefringent index and a high heat-resistance. The device may have
a phase retarder, which is a birefringent film for removing
undesirable colors of displayed images. A resin film is also used
as the phase retarder, but the phase retarder must have a high
birefringent index
[0190] The polarizing plate comprises a protective film and a
polarizing membrane. The polarizing membrane is a resin film
containing iodine and dichromatic dye for polarizing. The
protective film is provided on one or each surface of the
polarizing membrane for protection. In the case where the
protective film is provided on only one surface of the membrane,
the aforementioned substrate generally serves as a protective film
for the other surface. Since the protec- face. Since the protective
film must have a high transmittance and a low refringent index (a
low retardation value), the cellulose acetate film of the invention
is particularly advantageously used as the protective film.
[0191] As the polarizing membrane, an iodine polarizing membrane, a
polyene polarizing membrane and a dichromatic dye polarizing
membrane are known. Those are generally prepared from polyvinyl
alcohol films.
[0192] The protective film for the polarizing plate has a thickness
preferably in the range of 25 to 350 .mu.m, more preferably in the
range of 50 to 200 .mu.m. The protective film may contain an
ultraviolet absorbent, a slipping agent, a deterioration inhibitor
or a plasticizer.
[0193] The surface of the protective film may be further covered
with a surface treatment film, which works for hard coating,
anti-fogging and anti-glare.
[0194] The polarizing plate and the protective film thereof are
described in Japanese Patent Provisional publication Nos.
4(1992)-219703, 5(1993)-212828 and 6(1994)-51117.
EXAMPLE 1
Synthesis of Cellulose Acetate
[0195] Wood pulp (water content: 7.31 wt. %) containing
.alpha.-cellulose in the amount of about 97 wt. % was broken into
pieces. To 302.1 g of the pulp, 140 g of glacial acetic acid was
evenly sprinkled. The resulting mixture was then stirred. After
left at room temperature for 90 minutes, the mixture was poured
into another mixture of 769.7 g of cooled acetic anhydride, 1170.3
g of acetic acid and 23.08 g of 98% sulfuric acid. The temperature
of the obtained mixture was linearly elevated for 60 minutes from
0.degree. C. (when the reaction was started) to 37.degree. C. The
temperature was then kept at 37.degree. C. for 90 minutes, to
synthesize cellulose acetate.
(Ripening of Cellulose Acetate)
[0196] To a solution of the above-prepared cellulose acetate, 62.05
g of 26 wt. % aqueous solution of acetic acid was added. The
mixture was heated to 47.degree. C., and kept at the temperature
for 90 minutes to ripen the cellulose acetate. The amounts of
acetic acid (acetyl donor), water and sulfuric acid (catalyst) in
the mixture were 1,658 weight parts, 23.3 weight parts and 22.6
weight parts, respectively, based on 499 weight parts of cellulose
acetate. Accordingly, the ratio of water to acetic acid (acetyl
donor) was 4.68 mol. %.
[0197] The reaction parameter (R=.cndot.YZ/Xdt) in this ripening
step was calculated and found 41.
(Post Treatment)
[0198] After the ripening step was completed, 188 g of 24 wt. %
aqueous solution of magnesium acetate was added. The resulting
mixture was stirred, and then the solution was poured while stirred
vigorously into about 6 L of 10 wt. % aqueous solution of acetic
acid. The formed precipitates were collected by filtration, and
then washed successively with flowing water, with hot water and
again with flowing water. After the solvent was removed with
centrifugation, the precipitates were dried at 50.degree. C.
(Analysis of Cellulose Acetate)
[0199] With respect to the prepared cellulose acetate, the degree
of acetyl substitution (average in total) and the degree of
polymerization were measured.
[0200] Further, the elution curve of a reverse phase HPLC was
measured, and converted into a distribution curve of intermolecular
substitution degree to determine the half width of the maximum
peak.
[0201] The results are set forth in Table 1.
[0202] Next, the degrees of substitution at 2-, 3- and 6-positions
(2DS, 3DS and 6DS) were measured. The results are set forth in
Table 2. The degrees of substitution at 2-, 3- and 6-positions
(2DS, 3DS and 6DS) are plotted as the solid circle 1 in FIGS. 3 and
4.
[0203] The degrees of substitution were measured according to
Tezuka, Carbohydr. Res., 273, 83 (1995). First, dissociated
hydroxyls in the sample (cellulose acetate) were changed into
propionate esters with propionic acid anhydride in pyridine. The
obtained sample was then dissolved in heavy chloroform, and a
.sup.13C-spectrum was measured. The carbonyl carbons in the acetyls
at 2-, 3- and 6-positions give signals in the order from higher
magnetic field in the range of 169 to 171 ppm. The carbonyl carbons
in the propionate esters at 2-, 3- and 6-positions give signals in
the order from higher magnetic field in the range of 172 to 174
ppm. According to the obtained signals, the ratio between the
acetyl and the propionyl at 2-, 3- or 6-position was determined to
obtain the distribution of acetyls in the sample cellulose
acetate.
(Preparation of Cellulose Acetate Solution)
[0204] At room temperature, 17 weight parts of prepared cellulose
acetate, 80.28 weight parts of a mixed solvent of methyl
acetate/methanol/n-butanol (ratio: 80/15/5 wt. %) and 2.72 weight
parts of triphenyl phosphate (plasticizer) were mixed. In the
mixture, the cellulose acetate was not dissolved but swelled. The
obtained swelled mixture was in the form of slurry.
[0205] The swelled mixture was placed in a container having an
outer jacket. While the mixture was slowly stirred, water and
ethylene glycol as refrigerant were poured into the outer jacket.
The refrigerant cooled the mixture in the inner container to
-30.degree. C. at the cooling rate of 8.degree. C. per minute, and
kept cooling for 30 minutes until the mixture mixture was
homogeneously solidified.
[0206] The refrigerant was then removed from the jacket, and
instead hot water was poured into the jacket. Becoming in the form
of a sol to a degree, the mixture was stirred to warm to room
temperature at the warming rate of 8.degree. C. per minute.
[0207] The above cooling and warming procedures were repeated.
[0208] The solution prepared by the cooling dissolution method was
stored at room temperature (23.degree. C.), and then observed. As a
result, even after 20 days, the solution kept good transparency and
homogeneity, and accordingly exhibited good solubility and
stability.
(Formation of Cellulose Acetate Film)
[0209] The prepared solution was cast on a band of 6 m (effective
length) to form a film having the thickness of 100 .mu.m. The
temperature of the band was 0.degree. C. After air was blown for 2
seconds to dry, the film was peeled off the band. The film was then
further dried step by step at 100.degree. C. for 3 minutes, at
130.degree. C. for 5 minutes and at 160.degree. C. for 5 minutes
with the ends of the film fixed, and thereby the solvent remaining
in the film was removed. The prepared film was further dried at
120.degree. C. for 3 hours. Thus, a cellulose acetate film was
formed.
[0210] The formed film exhibited preferable optical characters
(high optical isotropy and transparency).
EXAMPLE 2
Ripening of Cellulose Acetate
[0211] Commercially available cellulose acetate (polymerization
degree: 360, degree of substitution determined by NMR: 2.84), which
was obtained by acetylating cotton linter under normal conditions,
was used. The cellulose acetate in the amount of 200 g was
dissolved in a mixture of 1,167 ml of 1,167 ml of dichloromethane
and 834 ml of acetic acid. From the obtained solution,
dichloromethane was distilled off by means of a rotary evaporator.
To the resulting liquid, 2,050 g of acetic acid, 2.65 g of water
and 24.4 g of 70 wt. % aqueous solution of perchloric acid were
added to dissolve the cellulose acetate. The ratio of water (total
amount of added water and water contained in the aqueous solution
of perchloric acid) to acetic acid (acetyl donor) was 1.63 mol.
%.
[0212] The obtained solution was kept at 30.degree. C. for 3 hours
to ripen the cellulose acetate.
[0213] The reaction parameter (R=.cndot.YZ/Xdt) in this ripening
step was calculated and found 55.
(Post Treatment)
[0214] After the ripening step was completed, sodium acetate in 2
equivalent weights based on the amount of perchloric acid (1.75
weight parts based on 1 weight part of 70 wt. % perchloric acid
aqueous solution) was added. The resulting mixture was stirred
well, and then about 7.5 L of water was gradually added to the
solution with the solution stirred vigorously. The formed
precipitates were washed with flowing water until acetic acid did
not smell. After water was removed with centrifugation, the
precipitates were further washed with flowing water. Water was
again removed with centrifugation, and then the precipitates were
dried at 50.degree. C.
(Analysis of Cellulose Acetate)
[0215] The obtained cellulose acetate was analyzed in the same
manner as in Example 1. The results are set forth in Tables 1 &
2. The degrees of substitution at 2-, 3- and 6-positions (2DS, 3DS
and 6DS) are plotted as the solid circle 2 in FIGS. 3 & 4.
(Preparation of Cellulose Acetate Solution)
[0216] A cellulose acetate solution was prepared in the same manner
as in Example 1, except that the obtained cellulose acetate was
used.
[0217] The prepared solution was stored at room temperature
(23.degree. C.), and then observed. As a result, even after 20
days, the solution kept good transparency and homogeneity, and
accordingly exhibited good solubility and stability.
(Formation of Cellulose Acetate Film)
[0218] A cellulose acetate film was formed in the same manner as in
Example 1, except that the prepared solution was used.
[0219] The formed film exhibited preferable optical characters
(high optical isotropy and transparency).
EXAMPLE 3
Ripening of Cellulose Acetate
[0220] The commercially available cellulose acetate used in Example
2 in the amount of 200 g was dissolved in a mixture of 1,167 ml of
dichloromethane and 834 ml of acetic acid. From the obtained
solution, dichloromethane was distilled off by means of a rotary
evaporator. To the resulting liquid, 2,050 g of acetic acid, 2.65 g
of water and 24.4 g of 70 wt. % aqueous solution of perchloric acid
were added to dissolve the cellulose acetate. The ratio of water
(total amount of added water and water contained in the aqueous
solution of perchloric acid) to acetic acid (acetyl donor) was 1.63
mol. %.
[0221] The obtained solution was kept at 30.degree. C. for 5 hours
to ripen the cellulose acetate.
[0222] The reaction parameter (R=.cndot.YZ/Xdt) in this ripening
step was calculated and found 92.
(Analysis of Cellulose Acetate)
[0223] The ripened cellulose acetate was treated and analyzed in
the same manner as in Example 2. The results are set forth in
Tables 1 & 2. The degrees of substitution at 2-, 3- and
6-positions (2DS, 3DS and 6DS) are plotted as the solid circle 3 in
FIGS. 3 & 4.
(Preparation of Cellulose Acetate Solution)
[0224] A cellulose acetate solution was prepared in the same manner
as in Example 1, except that the obtained cellulose acetate was
used.
[0225] The prepared solution was stored at room temperature
(23.degree. C.), and then observed. As a result, even after 20
days, the solution kept good transparency and homogeneity, and
accordingly exhibited good solubility and stability.
(Formation of Cellulose Acetate Film)
[0226] A cellulose acetate film was formed in the same manner as in
Example 1, except that the prepared solution was used.
[0227] The formed film exhibited preferable optical characters
(high optical isotropy and transparency).
EXAMPLE 4
Ripening of Cellulose Acetate
[0228] The commercially available cellulose acetate used in Example
2 in the amount of 200 g was dissolved in a mixture of 1,167 ml of
dichloromethane and 834 ml of acetic acid. From the obtained
solution, dichloromethane was distilled off by means of a rotary
evaporator. To the resulting liquid, 2,050 g of acetic acid, 18.35
g of water and 24.4 g of 70 wt. % aqueous solution of perchloric
acid were added to dissolve the cellulose acetate. The ratio of
water (total amount of added water and water contained in the
aqueous in the aqueous solution of perchloric acid) to acetic acid
(acetyl donor) was 4.18 mol. %.
[0229] The obtained solution was kept at 30.degree. C. for 10 hours
to ripen the cellulose acetate.
[0230] The reaction parameter (R=.cndot.YZ/Xdt) in this ripening
step was calculated and found 72.
(Analysis of Cellulose Acetate)
[0231] The ripened cellulose acetate was treated and analyzed in
the same manner as in Example 2. The results are set forth in
Tables 1 & 2. The degrees of substitution at 2-, 3- and
6-positions (2DS, 3DS and 6DS) are plotted as the solid circle 4 in
FIGS. 3 & 4.
(Preparation of Cellulose Acetate Solution)
[0232] A cellulose acetate solution was prepared in the same manner
as in Example 1, except that the obtained cellulose acetate was
used.
[0233] The prepared solution was stored at room temperature
(23.degree. C.), and then observed. As a result, even after 20
days, the solution kept good transparency and homogeneity, and
accordingly exhibited good solubility and stability.
(Formation of Cellulose Acetate Film)
[0234] A cellulose acetate film was formed in the same manner as in
Example 1, except that the prepared solution was used.
[0235] The formed film exhibited preferable optical characters
(high optical isotropy and transparency).
EXAMPLE 5
Ripening of Cellulose Acetate
[0236] The commercially available cellulose acetate used in Example
2 in the amount of 200 g was dissolved in a mixture of 1,167 ml of
dichloromethane and 834 ml of acetic acid. From the obtained
solution, dichloromethane was distilled off by means of a rotary
evaporator. To the resulting liquid, 2,050 g of acetic acid, 18.35
g of water and 24.4 g of 70 wt. % aqueous solution of perchloric
acid were added to dissolve the cellulose acetate. The ratio of
water (total amount of added water and water contained in the
aqueous solution of perchloric acid) to acetic acid (acetyl donor)
was 4.18 mol. %.
[0237] The obtained solution was kept at 30.degree. C. for 15 hours
to ripen the cellulose acetate.
[0238] The reaction parameter (R=.cndot.YZ/Xdt) in this ripening
step was calculated and found 107.
(Analysis of Cellulose Acetate)
[0239] The ripened cellulose acetate was treated and analyzed in
the same manner as in Example 2. The results are set forth in
Tables 1 & 2. The degrees of substitution at 2-, 3- and
6-positions (2DS, 3DS and 6DS) are plotted as the solid circle 5 in
FIGS. 3 & 4.
(Preparation of Cellulose Acetate Solution)
[0240] A cellulose acetate solution was prepared in the same manner
as in Example 1, except that the obtained cellulose acetate was
used.
[0241] The prepared solution was stored at room temperature
(23.degree. C.), and then observed. As a result, even after 20
days, the solution kept good transparency and homogeneity, and
accordingly exhibited good solubility and stability.
(Formation of Cellulose Acetate Film)
[0242] A cellulose acetate film was formed in the same manner as in
Example 1, except that the prepared solution was used.
[0243] The formed film exhibited preferable optical characters
(high optical isotropy and transparency).
COMPARISON EXAMPLE 1
Ripening of Cellulose Acetate
[0244] The cellulose acetate prepared in Example 1 in the amount of
200 g was dissolved in a mixture of 1,167 ml of dichloromethane and
834 ml of acetic acid. From the obtained solution, dichloromethane
was distilled off by means of a rotary evaporator. To the resulting
liquid, 2,050 g of acetic acid, 54.13 g of water and 24.4 g of 70
wt. % aqueous solution of perchloric acid were added to dissolve
the cellulose acetate. The ratio of water (total amount of added
water and water contained in the aqueous solution of perchloric
acid) to acetic acid (acetyl donor) was 10.00 mol. %.
[0245] The obtained solution was kept at 30.degree. C. for 20 hours
to ripen the cellulose acetate.
[0246] The reaction parameter (R=.cndot.YZ/Xdt) in this ripening
step was calculated and found 60.
(Analysis of Cellulose Acetate)
[0247] The ripened cellulose acetate was treated and analyzed in
the same manner as in Example 2. The results are set forth in
Tables 1 & 2. The degrees of substitution at 2-, 3- and
6-positions (2DS, 3DS and 6DS) are plotted as the open circle C1 in
FIGS. 3 & 4.
(Preparation of Cellulose Acetate Solution)
[0248] A cellulose acetate solution was prepared in the same manner
as in Example 1, except that the obtained cellulose acetate was
used.
[0249] The prepared solution was stored at room temperature
(23.degree. C.), and then observed. As a result, the solution
showed white turbidity, and opaque lump was observed.
COMPARISON EXAMPLE 2
Ripening of Cellulose Acetate
[0250] The cellulose acetate prepared in Example 1 in the amount of
200 g was dissolved in a mixture of 1,167 ml of dichloromethane and
834 ml of acetic acid. From the obtained solution, dichloromethane
was distilled off by means of a rotary evaporator. To the resulting
liquid, 2,050 g of acetic acid, 54.13 g of water and 24.4 g of 70
wt. % aqueous solution of perchloric acid were added to dissolve
the cellulose acetate. The ratio of water (total amount of added
water and water contained in the aqueous solution of perchloric
acid) to acetic acid (acetyl donor) was 10.00 mol. %.
[0251] The obtained solution was kept at 30.degree. C. for 30 hours
to ripen the cellulose acetate.
[0252] The reaction parameter (R=.cndot.YZ/Xdt) in this ripening
step was calculated and found 90.
(Analysis of Cellulose Acetate)
[0253] The ripened cellulose acetate was treated in the same manner
as in Example 1.
[0254] Next, the degrees of substitution at 2-, 3- and 6-positions
(2DS, 3DS and 6DS) were measured. The results are set forth in
Table 2. The degrees of substitution at 2-, 3- and 6-positions
(2DS, 3DS and 6DS) are plotted as the solid circle 1 in FIG. 4
(while the open circle C2 is out of the range shown in FIG. 3).
(Preparation of Cellulose Acetate Solution)
[0255] A cellulose acetate solution was prepared in the same manner
as in Example 1, except that the obtained cellulose acetate was
used.
[0256] The prepared solution was stored at room temperature
(23.degree. C.), and then observed. As a result, the solution was
transparent, but partially not uniform.
COMPARISON EXAMPLE 3
Synthesis of Cellulose Acetate
[0257] To 100 weight parts of cellulose (made from wood pulp), 14.2
weight parts of sulfuric acid, 260 weight parts of acetic anhydride
and 360 weight parts of acetic acid were added. The mixture was
subjected to an acetylation reaction at 40.degree. C. for 95
minutes. Two third of sulfuric acid was neutralized with magnesium
acetate to form magnesium sulfate.
[0258] The amount of water to acetic acid (acetyl donor) after
neutralizing reaction was 20 mol %.
(Ripening of Cellulose Acetate)
[0259] The obtained solution was kept at 65.degree. C. for 100
minutes to ripen cellulose acetate. The solution was treated in the
same manner as in Example 1, and cellulose acetate was separated
from the solution.
[0260] The reaction parameter (R=.cndot.YZ/Xdt) in this ripening
step was calculated and found 15.
(Analysis of Cellulose Acetate)
[0261] The ripened cellulose acetate was analyzed in the same
manner as in Example 1. The results are set forth in Tables 1 &
2.
(Preparation of Cellulose Acetate Solution)
[0262] A cellulose acetate solution was prepared in the same manner
as in Example 1, except that the obtained cellulose acetate was
used.
[0263] The prepared solution was stored at room temperature
(23.degree. C.), and then observed. As a result, the solution was
transparent, but partially not uniform.
COMPARISON EXAMPLE 4
Synthesis of Cellulose Acetate
[0264] To 550 g of cotton linter, 2747 g of acetic acid, 1630 g of
acetic anhydride and 64.4 g of sulfuric acid were added in a
kneader. The mixture was heated from 0.degree. C. to 40.degree. C.
for 120 minutes to conduct acetylation reaction.
(Ripening of Cellulose Acetate)
[0265] To the obtained solution, 328 g of 24 wt. % aqueous solution
of magnesium acetate was added. The resulting solution (in
consideration of water contents of stating materials) comprised 979
g of cellulose acetate, 4053 g of acetic acid, 10.1 g sulfuric acid
and 177 g of water. The ratio of water/acetyl donor was 14.5 mol
%.
[0266] The obtained solution was kept at 52.degree. C. for 100
minutes to ripen cellulose acetate.
[0267] The reaction parameter (R=.cndot.YZ/Xdt) in this ripening
step was calculated and found 3.7.
(Post Treatment)
[0268] After ripening cellulose acetate, 376 g of 24 wt. % aqueous
solution of magnesium acetate was added to the cellulose acetate,
and the mixture was stirred. The obtained solution was poured into
about 12 liter of 10 wt. % aqueous solution of acetic acid while
stirring vigorously. The formed precipitates were filtered off,
washed with water flow, washed with hot water, washed with water
flow again, flow again, centrifuged from liquid, and dried at
50.degree. C.
(Analysis of Cellulose Acetate)
[0269] With respect to the prepared cellulose acetate, the degree
of acetyl substitution (average in total) and the degree of
polymerization were measured.
[0270] Further, the elution curve of a reverse phase HPLC was
measured, and converted into a distribution curve of intermolecular
substitution degree to determine the half width of the maximum
peak.
[0271] The results are set forth in Table 1.
TABLE-US-00002 TABLE 1 Total Maximum peak Cellulose degree of
Degree of Half Value Degree of acetate substitution
substitution.sup.1) width of Y.sup.2) polymerization
Solubility.sup.3) Ex. 1 2.854 2.847 0.066 0.069 284 A Ex. 2 2.854
2.854 0.067 0.069 302 A Ex. 3 2.856 2.853 0.059 0.068 284 A Ex. 4
2.786 2.795 0.067 0.081 305 A Ex. 5 2.765 2.811 0.071 0.084 291 A
Comp. 1 2.684 2.692 0.100 0.097 350 C Comp. 3 2.733 2.737 0.096
0.089 292 B Comp. 4 2.844 2.851 0.086 0.070 298 B (Remarks)
.sup.1)Degree of substitution at the maximum peak .sup.2)Y =
-0.1788X + 0.5788 (wherein X is the total degree of substitution)
.sup.3)A: Transparent uniform solution B: Transparent but not
uniform C: White, turbid and not transparent
TABLE-US-00003 TABLE 2 Degree of Amount Reaction substitution of
Cellulose of water parameter cellulose acetate Degree of acetate
(mol %) (R) 2DS 3DS 6DS polymerization Ex. 1 4.68 41 0.959 0.955
0.940 284 Ex. 2 1.63 55 0.962 0.960 0.932 302 Ex. 3 1.63 92 0.960
0.953 0.943 284 Ex. 4 4.18 72 0.937 0.917 0.932 305 Ex. 5 4.18 107
0.929 0.896 0.940 291 Comp. 1 10.00 60 0.917 0.869 0.898 350 Comp.
2 10.00 90 0.882 0.826 0.907 339 Comp. 3 19.67 15 0.947 0.947 0.839
292
EXAMPLE 6
Synthesis of Cellulose Acetate
[0272] To 100 weight parts of cellulose prepared from cotton
linter, 9.2 weight parts of sulfuric acid, 276 weight parts of
acetic anhydride and 551 weight parts of acetic acid were added.
The cellulose was then subjected to an ester forming reaction in a
conventional manner. After neutralized with magnesium acetate, the
reaction mixture was kept at 62.degree. C. for 40 minutes to
prepare cellulose acetate.
(Ripening of Cellulose Acetate)
[0273] The obtained cellulose acetate was ripened in the manner
described in Example 1 except that the ratios of water and
perchloric acid (catalyst) to acetic acid (acetyl donor) and the
reaction parameter (R=.cndot.YZ/Xdt) were changed into 1.63 mol. %,
0.498 mol. % and 55, respectively.
(Analysis of Cellulose Acetate)
[0274] The ripened cellulose acetate was analyzed in the same
manner as in Example 1. The results are set forth in Table 3. The
degrees of substitution at 2-, 3- and 6-positions (2DS, 3DS and
6DS) are plotted as the solid circle 6 in FIGS. 3 & 4.
(Measurement of Infrared Absorption Spectrum)
[0275] In 5 g of a mixed solvent of methylene chloride/methanol
(9/1, by weight), 200 mg of the cellulose acetate dried well was
dissolved. The solution was cast on a glass plate by means of a bar
coater so that the thickness might be even. The solution layer on
the plate was dried by air to form a film. The thickness of the
film was adjusted so that the transmittance (at the peak attributed
to non-substituted hydroxyl of the cellulose acetate) might be
about 40%.
[0276] The formed film was dried in vacuum at 105.degree. C. for 30
minutes or more, and then cut into pieces having enough sizes (24
mm.times.27 mm) for a flame of IR generator so that IR rays might
not be interrupted by a sample holder.
[0277] The film sample was kept under nitrogen atmosphere until the
absorption peak at about 3650 cm.sup.-1 attributed to adsorbed
water disappeared. The infrared absorption spectrum was measured by
means of FT-IR1650 (Parkin-Elmer). The measured spectrum was
analyzed in the manner described above to obtain a half-width
(.DELTA..nu..sub.1/2). The results are set forth in Table 3.
EXAMPLE 7
Ripening of Cellulose Acetate
[0278] Commercially available cellulose acetate (polymerization
degree: 360, degree of substitution determined by NMR: 2.84), which
was obtained by acetylating cotton linter under normal conditions,
was used. The cellulose acetate in the amount of 1,150 weight parts
was dissolved in a mixture of 8,220 weight parts of dichloromethane
and 4,800 weight parts of acetic acid. From the obtained solution,
dichloromethane was distilled off by means of a rotary evaporator.
The obtained liquid was transferred into a reaction tank, and
11,788 weight parts of acetic acid, 78 weight parts of water and 98
weight parts of perchloric acid were added. The ratio of water to
acetic acid (acetyl donor) was 2.2 mol. %.
[0279] The obtained solution was kept at 30.degree. C. for 5 hours
to ripen the cellulose acetate.
[0280] The reaction parameter (R=.cndot.YZ/Xdt) in this ripening
step was calculated and found 67.5.
(Post Treatment)
[0281] After the ripening step was completed, 1.75 equivalent
weights (based on the amount of perchloric acid) of sodium acetate
in 10 wt. % acetic acid solution was added. The resulting mixture
was stirred for 10 minutes to stop the reaction. Thus, cellulose
acetate (viscosity average molecular weight: 288, degree of
substitution: 2.84) was prepared.
(Analysis of Cellulose Acetate)
[0282] The obtained cellulose acetate was analyzed in the same
manner as in Example 1. The results are set forth in Table 3. The
degrees of substitution at 2-, 3- and 6-positions (2DS, 3DS and
6DS) are plotted as the solid circle 7 in FIGS. 3 & 4.
(Measurement of Infrared Absorption Spectrum)
[0283] The infrared absorption spectrum of the cellulose acetate
was measured in the same manner as in Example 6 to obtain a
half-width (.DELTA..nu..sub.1/2). The results are set forth in
Table 3.
(Preparation of Cellulose Acetate Solution)
[0284] The prepared cellulose acetate in the amount of 15 weight
parts was mixed in room temperature (25.degree. C.) with 68 weight
parts of methyl acetate and 17 weight parts of acetone, to prepare
a slurry of 15 wt. %. The slurry was almost in the form of a
transparent gel, but some opaque jellied parts were observed.
[0285] The slurry was cooled for 2 hours in cold methanol bath
beforehand cooled at -40.degree. C. with dry ice. In the
thus-cooled slurry, many bubbles were formed by penetration of the
solvent. After left at room temperature for 10 minutes, the slurry
was kept for 10 minutes in water bath at 40.degree. C. The thus
obtained cellulose acetate solution had good transparency and
fluidity.
EXAMPLE 8
Ripening of Cellulose Acetate
[0286] Commercially available cellulose acetate (polymerization
degree: 360, degree of substitution determined by NMR: 2.84), which
was obtained by acetylating cotton linter under normal conditions,
was used. The cellulose acetate in the amount of 200 weight parts
was dissolved in a mixture of 1,600 weight parts of dichloromethane
and 867 weight parts of acetic acid. From the obtained solution,
dichloromethane was distilled off by means of a rotary evaporator.
The obtained liquid was transferred into a reaction tank, and 2,050
weight parts of acetic acid, 18.7 weight parts of water and 24.3
weight parts of 70 wt. % aqueous solution of perchloric acid were
added. The ratio of water to acetic acid (acetyl donor) was 4.2
mol. %.
[0287] The obtained solution was kept at 30.degree. C. for 10 hours
to ripen the cellulose acetate.
[0288] The reaction parameter (R=.cndot.YZ/Xdt) in this ripening
step was calculated and found 71.
(Post Treatment)
[0289] After the ripening step was completed, 1.75 equivalent
weights (based on the amount of perchloric acid) of sodium acetate
in 10 wt. % acetic acid solution was added. The resulting mixture
was stirred for 10 minutes to stop the reaction. Thus, cellulose
acetate (viscosity average molecular weight: 318, degree of
substitution: 2.81) was prepared.
(Analysis of Cellulose Acetate)
[0290] The obtained cellulose acetate was analyzed in the same
manner as in Example 1. The results are set forth in Table 3. The
degrees of substitution at 2-, 3- and 6-positions (2DS, 3DS and
6DS) are plotted as the solid circle 8 in FIGS. 3 & 4.
(Measurement of Infrared Absorption Spectrum)
[0291] The infrared absorption spectrum of the cellulose acetate
was measured in the same manner as in Example 6 to obtain a
half-width (.DELTA..nu..sub.1/2). The results are set forth in
Table 3.
(Preparation of Cellulose Acetate Solution)
[0292] The prepared cellulose acetate in the amount of 15 weight
parts was mixed in room temperature (25.degree. C.) with 68 weight
parts of methyl acetate and 17 weight parts of acetone, to prepare
a slurry of 15 wt. %. The slurry was almost in the form of a
transparent gel, but some opaque jellied parts were observed.
[0293] The slurry was cooled for 2 hours in cold methanol bath
beforehand cooled at -40.degree. C. with dry ice. In the
thus-cooled slurry, many bubbles were formed by penetration of the
solvent. After left at room temperature for 10 minutes, the slurry
was kept for 10 minutes in water bath at 40.degree. C. The thus
obtained cellulose acetate solution had good transparency and
fluidity.
EXAMPLE 9
Ripening of Cellulose Acetate
[0294] Commercially available cellulose acetate (polymerization
degree: 360, degree of substitution determined by NMR: 2.84), which
was obtained by acetylating cotton linter under normal conditions,
was used. The cellulose acetate was ripened in the manner described
in Example 1 except that the time for ripening, the ratios of water
and perchloric acid (catalyst) to acetic acid (acetyl donor) nor)
and the reaction parameter (R=.cndot.YZ/Xdt) were changed into 15
hours, 4.18 mol. %, 0.498 mol. % and 107, respectively.
(Analysis of Cellulose Acetate)
[0295] The obtained cellulose acetate was analyzed in the same
manner as in Example 1. The results are set forth in Table 3. The
degrees of substitution at 2-, 3- and 6-positions (2DS, 3DS and
6DS) are plotted as the solid circle 9 in FIGS. 3 & 4.
(Measurement of Infrared Absorption Spectrum)
[0296] The infrared absorption spectrum of the cellulose acetate
was measured in the same manner as in Example 6 to obtain a
half-width (.DELTA..nu..sub.1/2). The results are set forth in
Table 3.
TABLE-US-00004 TABLE 3 Degree of Amount Reaction substitution of
Degree of water parameter Reaction cellulose acetate of Ex. (mol %)
(R) time.sup.1) Half width.sup.2) 2DS 3DS 6DS polymerization 6 1.63
55 3 128 0.965 0.963 0.933 300 7 2.20 67.5 5 123 0.959 0.943 0.937
288 8 4.18 71 10 121 0.945 0.926 0.935 318 9 4.18 107 15 119 0.925
0.896 0.941 301 (Remarks) .sup.1)Time for ripening cellulose
acetate (hours), .sup.2)Half-width (cm.sup.-1) of the absorption
peak in the region of 3450 to 3550 cm.sup.-1
EXAMPLE 10
Measurement of Infrared Absorption Spectrum
[0297] With respect to cellulose acetate (total degree of
substitution 2DS+3DS+6DS: 2.896, 2DS+3DS-6DS: 0.896), the infrared
absorption spectrum was measured in the same manner as in Example
6. The obtained spectrum is shown in FIG. 6, and the half-width
(.DELTA..nu..sub.1/2) was found 90.
EXAMPLE 11
Measurement of Infrared Absorption Spectrum
[0298] With respect to cellulose acetate (total degree of
substitution 2DS+3DS+6DS: 2.877, 2DS+3DS-6DS: 0.967), the infrared
absorption spectrum was measured in the same manner as in Example
6. The obtained spectrum is shown in FIG. 6, and the half-width
(.DELTA..nu..sub.1/2) was found 118.
COMPARISON EXAMPLE 5
Measurement of Infrared Absorption Spectrum
[0299] With respect to cellulose acetate (total degree of
substitution 2DS+3DS+6DS: 2.845, 2DS+3DS-6DS: 1.069), the infrared
absorption spectrum was measured in the same manner as in Example
6. The obtained spectrum is shown in FIG. 6, and the half-width
(.DELTA..nu..sub.1/2) was found 137.
COMPARISON EXAMPLE 6
Measurement of Infrared Absorption Spectrum
[0300] With respect to cellulose acetate (total degree of
substitution 2DS+3DS+6DS: 2.925, 2DS+3DS-6DS: 1.075), the infrared
absorption spectrum was measured in the same manner as in Example
6. The obtained spectrum is shown in FIG. 6, and the half-width
(.DELTA..nu..sub.1/2) was found 137.
EXAMPLE 12
Ripening of Cellulose Acetate
[0301] A dried commercially available cellulose acetate
(polymerization degree: 311, degree of substitution determined by
NMR: 2.85), which was obtained by acetylating wood pulp under
normal conditions, was obtained. The cellulose acetate in the
amount of 500 g was dissolved in a mixture of 1,333 g of
dichloromethane and 1,033 g of acetic acid. With the solution
stirred, 150 g of acetic acid containing 13.3 g of water was added.
After homogenized, the solution was kept at 40.degree. C. While the
solution was stirred, 150 g of acetic acid containing 36.92 g of
toluenesulfonic acid monohydrate was added to start ripening. The
ratio of water to acetic acid (acetyl donor) was 4.2 mol. %. After
7 hours, 260 g of acetic acid containing 29 g of sodium acetic
anhydride was dropped to stop ripening.
[0302] The reaction parameter (R=.cndot.YZ/Xdt) in this ripening
step was calculated and found 151.
(Post Treatment)
[0303] From the reacted solution, dichloromethane was distilled off
by means of a rotary evaporator. To the resulting solution, about
4.5 L of water was gradually added with the solution stirred
vigorously in the same manner as in Example 2. The formed
precipitates were collected, washed, and the solvent was removed by
centrifugation. The precipitates were further washed with flowing
water, and the solvent was removed again by centrifugation. The
precipitates were then dried at 50.degree. C.
(Analysis of Cellulose Acetate)
[0304] The obtained cellulose acetate was analyzed in the same
manner as in Example 1. The results are set forth in Table 4. The
degrees of substitution at 2-, 3- and 6-positions (2DS, 3DS and
6DS) are plotted as the solid circle 12 in FIGS. 3 & 4.
EXAMPLE 13
Ripening of Cellulose Acetate
[0305] The cellulose acetate was ripened and subjected to post
treatment in the manner described in Example 12 except that the
amount of water (the ratio of water to acetic acid (acetyl donor))
and the reaction time were changed into 2.91 g (1.6 mol. %) and 140
minutes, respectively.
[0306] The reaction parameter (R=.cndot.YZ/Xdt) in this ripening
step was calculated and found 132.
(Analysis of Cellulose Acetate)
[0307] The ripened cellulose acetate was analyzed in the same
manner as in Example 1. The results are set forth in Table 4. The
degrees of substitution at 2-, 3- and 6-positions (2DS, 3DS and
6DS) are plotted as the solid circle 13 in FIGS. 3 & 4.
EXAMPLE 14
Synthesis of Cellulose Acetate
[0308] Wood pulp (water content: 8.2 wt. %) was broken into pieces.
To 1,520 g of the pulp, 698 g of acetic acid was evenly sprinkled.
The resulting mixture was then stirred. After left at room
temperature for 90 minutes, the mixture was poured into another
mixture of 3930.6 g of acetic anhydride beforehand cooled at about
-10.degree. C., 5755 g of acetic acid and 115.4 g of 98% sulfuric
acid. The temperature of the obtained mixture was linearly elevated
for 70 minutes for 70 minutes from 0.degree. C. (when the reaction
was started) to 37.degree. C. The temperature was then kept at
37.degree. C. for 80 minutes, to synthesize cellulose acetate.
(Ripening of Cellulose Acetate)
[0309] To a solution of the above-prepared cellulose acetate, 383.7
g of 30% aqueous solution of acetic acid was added. The mixture was
heated to 47.degree. C., and kept at the temperature for 130
minute. The ratio of water to acetic acid (acetyl donor) was 6.0
mol. %. After that, 297 g of aqueous solution of magnesium acetate
tetrahydrate was added to stop ripening.
[0310] The reaction parameter (R=.cndot.YZ/Xdt) in this ripening
step was calculated and found 43.
(Post Treatment)
[0311] The resulting solution was poured into about 30 L of 10%
acetic acid aqueous solution with the solution stirred vigorously.
The formed precipitates were collected, washed successively with
flowing water, with hot water and again with flowing water, and
then the solvent was removed by centrifugation. The precipitates
were then dried at 50.degree. C.
(Analysis of Cellulose Acetate)
[0312] The obtained cellulose acetate was analyzed in the same
manner as in Example 1. The results are set forth in Table 4. The
degrees of substitution at 2-, 3- and 6-positions (2DS, 3DS and
6DS) are plotted as the solid circle 14 in FIGS. 3 & 4.
TABLE-US-00005 TABLE 4 Amount Reaction Degree of substitution
Cellulose of water parameter of cellulose acetate Degree of acetate
(mol %) (R) 2DS 3DS 6DS polymerization Ex. 12 4.20 151 0.953 0.936
0.925 288 Ex. 13 1.60 132 0.972 0.967 0.916 298 Ex. 14 6.00 43
0.973 0.967 0.923 303
* * * * *