Title: Production method of cellulose film, cellulose film, protective film for polarizing plate, optical functional film, polarizing plate, and liquid crystal display
Abstract: A production method of cellulose film wherein cellulose film is produced by preparing a polymer solution through dissolving cellulose ester in a solvent containing a prescribed organic solvent as the main component, forming a filmy object from the prepared polymer solution, and evaporating the solvent in the filmy object; the residual amount of the organic solvent is reduced while the film quality is not degraded, and the production efficiency is degraded to a least possible extent; a poor solvent, highest in boiling point among the materials contained in the solvent, is added in the content ranging from 0.1 wt % to 1.0 wt %, taking the total amount of the solvent in the prepared polymer solution to be 100 wt %; and the solubility of cellulose ester in the poor solvent is inferior to the solubility of the cellulose ester in the organic solvent which is the main component of the solvent.
Patent Number: 6,887,415 Issued on 05/03/2005 to Yamazaki, et al.
| Inventors:
|
Yamazaki; Hidekazu (Minami-Ashigara, JP);
Nakamura; Toshikazu (Minami-Ashigara, JP);
Miyachi; Hiroshi (Minami-Ashigara, JP)
|
| Assignee:
|
Fuji Photo Film Co., Ltd. (Kanagawa, JP)
|
| Appl. No.:
|
385857 |
| Filed:
|
March 12, 2003 |
Foreign Application Priority Data
| Mar 12, 2002[JP] | 2002-067086 |
| Current U.S. Class: |
264/217 |
| Intern'l Class: |
B29D 007//00 |
| Field of Search: |
264/207,217,200
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Eashoo; Mark
Attorney, Agent or Firm: Young & Thompson
Claims
1. A production method of cellulose film which produces cellulose film by preparing
a polymer solution through dissolving cellulose ester in a solvent containing a
prescribed organic solvent as the main component, forming a filmy object from the
prepared polymer solution, and evaporating the solvent remaining in the filmy object;
and wherein:
the polymer solution is prepared by adding a poor solvent, which is highest in
boiling point among the materials contained in the solvent, in the content of 0.1
to 1.0 wt %, where the total solvent amount contained in the prepared polymer solution
is taken to be 100 wt %; and
the solubility of cellulose ester in the poor solvent is inferior to the solubility
of cellulose ester in the organic solvent which is the main component of the solvent.
2. The production method of cellulose film according to claim 1 wherein the organic
solvent as the main component is dichloromethane, and the polymer solution is prepared
by adding an alcohol having 1 to 2 carbon atoms in addition to the poor solvent.
3. The production method of cellulose film according to claim 2 wherein the polymer
solution is prepared by adding dichloromethane in a content of 70 to 99 wt %, and
simultaneously an alcohol having 1 to 2 carbon atoms in a content of 0.9 to 29.0
wt % where the total amount of the solvent in the prepared polymer solution is
taken as 100 wt %.
4. The production method of cellulose film according to claim 1 wherein the poor
solvent is an alcohol having the boiling point falling in the range from 80 to
170° C.
5. The production method of cellulose film according to claim 1 wherein, in the
case where the poor solvent is mixed in an in-line mode, a static mixer arranged
in the piping is used for adding and mixing the poor solvent.
6. The production method of cellulose film according to claim 1 wherein the solid
content of the polymer solution falls in the range from 15 to 30 wt %.
7. The production method of cellulose film according to claim 1 wherein a material
containing as the main component thereof the cellulose acetate synthesized from
wood pulp is used as the cellulose ester.
8. The production method of cellulose film according to claim 1 wherein at least
two or more kinds of polymer solutions of cellulose ester are simultaneously or
successively subjected to flow casting.
9. The production method of cellulose film according to claim 8 wherein in the
process of forming film by flow casting of the polymer solutions of cellulose ester,
swelling the film, on the way of the drying process thereof or after drying, and dried.
10. The production method of cellulose film according to claim 8 wherein in the
process of forming film by flow casting of the polymer solutions of cellulose ester,
swelling the film by watersoaking the film, on the way of the drying process thereof
or after drying, and dried.
11. The production method of cellulose film according to claim 8 wherein in the
process of forming film by flow casting of the polymer solutions of cellulose ester,
swelling the film by applying water vapor thereto, on the way of the drying process
thereof or after drying, and dried.
12. The production method of cellulose film according to claim 8 wherein in the
process of forming film by flow casting of the polymer solutions of cellulose ester,
swelling the film by applying a solvent onto the film, on the way of the drying
process thereof or after drying, and dried.
13. The production method of cellulose film according to claim 8 wherein in the
process of forming film by flow casting of the polymer solutions of cellulose ester,
swelling the film by applying a solvent gas thereto, on the way of the drying process
thereof or after drying, and dried.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a production method of cellulose film in which
cellulose film is produced by preparing a polymer solution through dissolving cellulose
ester in a solvent containing a prescribed organic solvent as the main component,
forming a filmy object from the prepared polymer solution, and evaporating the
solvent in the filmy object, and a cellulose film thus produced; and protective
film for polarizing plate, optical functional film, polarizing plate, and liquid
crystal displays produced by the above described production method of cellulose film.
2. Description of the Related Art
Conventionally, cellulose film is used as optical materials for optical
functional films for use in widening the viewing angle and preventing glare; protective
films for the polarizing plates in liquid crystal displays; and the like. The cellulose
films used for such optical materials are produced by means of the solution method
for forming film. In the solution method for forming film, a filmy object is formed
from a polymer solution in which cellulose ester or the like is dissolved in an
organic solvent, the filmy object formed is heated to evaporate the organic solvent
in the filmy object, and a polymer film is thereby obtained. In this connection,
when the organic solvent remains in the produced cellulose film, there occur adverse
effects on the dimensional stability of the film, or the coloring of the film is
degraded. Accordingly, the control of the residual amount of the organic solvent
in the produced cellulose film has heretofore been performed from the viewpoint
of the quality. The produced cellulose film is subjected to saponification and
the like in post-processes, and subsequently is commercialized as optical functional
film, or protective film for polarizing plate.
Now, when the cellulose film produced by the solution method for forming film
is considered from the standpoint of the environment conservation, nowadays considered
to be important, there is concern that, with the level of the residual amount of
the organic solvent as controlled from the viewpoint of the quality, a slight amount
of the organic solvent is evaporated from the produced film in the post-processes
subsequent to the film production.
However, as for the residual amount of the organic solvent, investigation
has hitherto been performed from the viewpoint of the quality, but no investigation
has been performed from the viewpoint of the environment conservation, and hence
it is not clear how far the level of the residual amount of the organic solvent
should be lowered so that the effects on the environment substantially vanish.
Additionally, in order to reduce the residual amount of the organic
solvent, the following treatments are suggested: the heating period of time is
extended in the evaporation process, the heating temperature is raised, and the
amount of the organic solvent is reduced in relation to the amount of cellulose
ester. However, in the current solution method for forming film, the production
efficiency is improved while the quality of the film being maintained at a high
level, and hence a variety of measures are adopted for shortening the time required
for the evaporation process as much as possible; these measures include the following
measures in which the amount of the organic solvent is decreased to a level as
low as possible in relation to the amount of cellulose ester, and the heating temperature
is raised to a level below which cellulose ester is not thermally decomposed. Consequently,
it is anticipated that not only the quality of the film is degraded, but also the
production efficiency is remarkably degraded, owing to extending of the heating
time in the evaporation process, raising the heating temperature, and reducing
the amount of the organic solvent in relation to the amount of cellulose ester,
for the purpose of reducing the residual amount of the organic solvent.
SUMMARY OF THE INVENTION
The present invention, in view of the above circumstances, takes as its object
the provision of a production method of cellulose film which can reduce the residual
amount of the organic solvent, without degrading the film quality, and with degrading
the production efficiency to the least possible extent; a cellulose film which
substantially has little effects on the environment due to the residual organic
solvent; and protective film for polarizing plate, optical functional film, polarizing
plate, and a liquid crystal display produced by the above described production
method of cellulose film.
The production method of cellulose film of the present invention, which achieves
the above described object, is a production method of cellulose film which method
produces cellulose film by preparing a polymer solution through dissolving cellulose
ester in a solvent having a prescribed organic solvent as the main component, forming
a filmy object from the prepared polymer solution, and evaporating the solvent
in the filmy object; and wherein:
the polymer solution is prepared by adding a poor solvent, having the highest
boiling point among the materials contained in the solvent, so as to have the content
of 0.1 to 1.0 wt % where the total amount of the solvent in the prepared polymer
solution is taken as 100 wt %; and
the solubility of cellulose ester in the poor solvent is inferior to the solubility
of cellulose ester in the organic solvent which is the main component of the solvent.
The addition amount of the poor solvent is very small, so that the addition of
the poor solvent scarcely degrades the production efficiency of the cellulose film.
Additionally, since the poor solvent is highest in boiling point among the materials
contained in the solvent, it is most difficult to be evaporated and tends to remain.
Furthermore, since the solubility of cellulose ester in the poor solvent is inferior
to the solubility of cellulose ester in the organic solvent which is the main component
of the solvent, the intermolecular bond between the poor solvent and the cellulose
ester is difficult to be formed as compared to the intermolecular bond between
the main-component organic solvent and the cellulose ester. In the solvent during
the evaporation process, the action of the remaining poor solvent prevents the
formation of the intermolecular bond between the main-component organic solvent
and cellulose ester, and the evaporation of the main-component organic solvent
is thereby promoted. Additionally, the remaining poor solvent hardly forms the
intermolecular bond with cellulose ester so that cellulose ester is scarcely restrained
by cellulose ester, and the addition amount of the poor solvent is very small;
hence the poor solvent is evaporated at the end of the evaporation process, and
the added poor solvent does not affect the film characteristics.
Additionally, in the production method of cellulose film of the present
invention, the main-component organic solvent is dichloromethane, and it is preferable
that the polymer solution is prepared by adding an alcohol having one to two carbon
atoms in addition to the poor solvent.
The compatibility of dichloromethane with cellulose ester is satisfactory, and
hence adoption of dichloromethane as the main component of the solvent leads to
reduction of the total amount of the solvent in relation to the amount of cellulose
ester. Additionally, addition of alcohols having 1 to 2 carbon atoms improves the
dimensional stability (self-supporting property) of the filmy object, making the
transportation of the film-like material be convenient.
Furthermore, in the production method of cellulose film of the present
invention, taking the total amount of the solvent in the prepared polymer solution
to be 100 wt %, it is preferable to prepare the polymer solution in such a way
that dichloromethane is added in a content of 70 to 99 wt %, and simultaneously
an alcohol having 1 to 2 carbon atoms is added in a content of 0.9 to 29.0 wt %.
Additionally, in the production method of cellulose film of the present
invention, it is preferable that the poor solvent is an alcohol having the boiling
point in the range from 80 to 170° C.
The boiling point of dichloromethane, the main solvent component of the solvent,
is about 40° C.; accordingly, when the boiling point of the added alcohol
is 80° C. or above, the alcohol remains in the solvent during the evaporation
process, preventing without fail the intermolecular bonding formation of dichloromethane
with cellulose ester. On the other hand, when the boiling point of the added alcohol
is chosen to be 170° C. or below, the alcohol can be evaporated in the final
stage of the evaporation process without causing the thermal decomposition of cellulose ester.
In this connection, in the production method of cellulose film of the present
invention, when the mixing of the poor solvent is performed in an in-line mode,
a static mixer may be used in the piping for addition and mixing; or
at least two or more kinds of polymer solutions may be subjected to simultaneous
flow casting or successive flow casting.
Additionally, in the production method of cellulose film of the present
invention, it is also preferable that the polymer solution of cellulose ester film
has the solid content ranging from 15 to 30 wt %.
Additionally, in the production method of cellulose film of the present
invention, it is also preferable that the material containing the cellulose acetate
synthesized from wood pulp as the main component is used as cellulose ester.
As cellulose ester, the cellulose acetate synthesized from cotton linter is known,
in addition to the cellulose acetate synthesized from wood pulp; however, adoption
of the cellulose acetate synthesized from wood pulp as the main component makes
it possible to reduce the costs for cellulose film.
Additionally, in the production method of cellulose film of the present
invention, it is preferable that the film is made to be swollen and then dried
on the way of the drying process thereof, or after drying, during the film formation
process by flow casting of the polymer solution of cellulose ester.
As above, through swelling once the filmy object, while the solvent being evaporated
from the filmy object, or after the solvent has been evaporated, even when the
molecules composing the solvent form the intermolecular bond with cellulose ester,
the intermolecular bond can be broken; namely, the evaporation of the solvent can
be further promoted by swelling once the filmy object and then evaporating the
solvent therein again.
In this connection, it is preferable that for the purpose of swelling once the
film (filmy object), the film may be swollen with water, a solvent may be applied
onto the film, or exposure to a solvent gas may be performed. Incidentally, it
is preferable that an alcohol-based substance (for example, an alcohol having 1
to 2 carbon atoms, etc.) is used as the solvent to be applied and the solvent gas.
The cellulose film of the present invention, which achieves the object of the
present invention, is characterized in that, in the form of the finished film product,
the residual amount of dichloromethane is 0.1 wt % or less, and additionally the
total residual amount of the solvent is 0.5 wt % or less.
By controlling the residual amount of dichloromethane, and the total residual
amount of the solvent to the values as specified above, the effects on the environment
of the residual solvent in the cellulose film having been produced can be substantially prevented.
The protective film for polarizing plate, optical functional film, polarizing
plate, and liquid crystal displays, which achieve the object of the present invention,
are characterized in that each thereof is produced by use of the production method
of cellulose film of the present invention, or by use of the cellulose film of
the present invention.
As above, the present invention can provide the production method of cellulose
film in which the residual amount of the organic solvent in the film can be reduced,
without degrading the film quality and with degrading the production efficiency
to a least possible extent; the cellulose film which gives the substantially vanishing
effects of the residual solvent on the environment; and the protective film for
polarizing plate, optical functional film, polarizing plate, and a liquid crystal
display, all produced by the aforementioned production method of cellulose film.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified schematic view of the production line while the cellulose
film is being produced by flow casting of the polymer solution onto a round cylindrical
drum; and
FIG. 2 is a simplified schematic view of the production line while the cellulose
film is being produced by flow casting of the polymer solution onto an endless belt.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Description will be made below on the embodiments of the present invention.
In the embodiments of the production method of cellulose film of the present
invention,
the cellulose film is produced by flow casting of a polymer solution onto a supporting
body. The supporting bodies onto which the flow casting of the polymer solution
is performed include the following two bodies, a round cylindrical drum and an
endless belt. Now, with reference to FIG. 1, description is made on the production
line wherein a cellulose film is produced by the flow casting of the polymer solution
onto the round cylindrical drum.
FIG. 1 is a simplified schematic view of the production line while the cellulose
film is being produced by flow casting of the polymer solution onto a round cylindrical drum.
The production line
1 shown in FIG. 1 is one embodiment of the production
method of cellulose film of the present invention, namely, a production line of
TAC (triacetyl cellulose) film; from the upstream side of the production line
1
in order, there are arranged a polymer solution preparation apparatus
100,
a flow casting die
200, a flow casting drum
300, and a peeling roll
400.
In the production line
1, there are arranged three polymer solution preparation
apparatuses
100, each preparing a different type of polymer solution. Here,
as an example, description will be made on the polymer solution preparation apparatus
100 shown on the right in FIG.
1. The polymer solution preparation
apparatus
100 prepares the polymer solution of triacetyl cellulose. In preparation
of the polymer solution, triacetyl cellulose is dissolved in a solvent containing
dichloromethane as the main component, and a small amount of n-butanol is added
to the solution in which triacetyl cellulose is dissolved. n-Butanol is higher
in boiling point than dichloromethane. Additionally, the solubility of triacetyl
cellulose in n-butanol is inferior to the solubility of triacetyl cellulose in
dichloromethane. The polymer solution preparation apparatus
100 comprises
a storage tank
110, a liquid delivery pump
120, a poor solvent supply
device
130, a static mixer
140, and a filter
150. In the storage
tank
110, a mixed solution CM of dichloromethane and methanol wherein triacetyl
cellulose is dissolved is stored while being stirred by stirring blades
111.
The solution CM stored in the storage tank
110 is delivered to a flow casting
die
200 by the liquid delivery pump
120; the static mixer
140
and the filter
150 are arranged in some midway points along the liquid delivery
path. Additionally, the poor solvent supply device
130 supplies n-butanol
B to the static mixer
140 under favor of a liquid delivery pump
131.
In the static mixer
140, n-butanol B is added to and mixed with the mixed
solution CM. The addition amount of n-butanol is so small that the adding and mixing
of n-butanol little degrades the production efficiency of the TAC film. Incidentally,
instead of using the poor solvent supply device
130, n-butanol may be added
to and mixed in the storage tank
110. The filter
150 removes, from
the solution delivered from the static mixer
140, foreign objects, undissolved
raw materials, etc., and then the solution is delivered to a flow casting die
200.
In the flow casting die
200, the polymer solutions prepared respectively
in the three polymer solution preparation apparatuses
100 are supplied.
More specifically, from the polymer solution preparation apparatus
100 depicted
at the right of FIG. 1, of the three polymer solution preparation apparatuses,
the polymer solution constituting the film surface layer is delivered; from the
polymer solution preparation apparatus
100 depicted at the center, the polymer
solution constituting the film central part is delivered; and from the polymer
solution preparation apparatus
100 depicted on the left, the polymer solution
constituting the film back surface layer is delivered. The respective delivered
polymer solutions are discharged from the outlet of the flow casting die
200.
Incidentally, the number of the polymer solution preparation apparatuses
100
is not necessarily limited to 3, but it may be one, two, or more than three depending
on the specification of the produced cellulose film.
The flow casting drum
300 is revolved along the direction of the arrow
A. The flow casting die
200 is arranged above the flow casting drum
300
in such a way that the outlet faces onto the circumferential surface of the flow
casting drum
300.
The respective polymer solutions discharged from the outlet of the flow casting
die
200 are subjected to simultaneous flow casting onto the circumferential
surface of the flow casting drum
300 rotating along the direction of the
arrow A. The polymer solutions discharged onto the circumferential surface of the
flow casting drum
300, during about three-quarter revolution along the direction
of the arrow A, is water-cooled from the inside of the flow casting drum
300
and simultaneously air-cooled from the outside by blasting cooling air, and accordingly
the gelation is promoted to form a filmy object having self-supporting property.
Subsequently, the filmy object reaches the position, where a peeling roll
400
is installed, to be peeled off.
A winding device
500 is arranged at the downstream end of the production
line
1 shown in FIG. 1. A soft film drying zone
11 and a late stage
drying zone
12 are arranged between the peeling roll
400 and the
winding roll
500, both zones being the zones where the solvent in the filmy
object is evaporated. Furthermore, a swelling device
600 is arranged between
the soft film drying zone
11 and the late stage drying zone
12. The
filmy object peeled off by the peeling roll
400 is delivered by two driving
rolls along the direction of the arrow B, via the soft film drying zone
11→the
swelling device
600→the late stage drying zone
12, and wound
by the winding roll
500.
A tenter
700 is arranged in the soft film drying zone
11. The filmy
object peeled off by the peeling roll
400 is delivered to the soft film
drying zone
11, and passes through the interior of the tenter
700.
Inside the tenter
700, the filmy object is heated, the solvent contained
in the filmy object is further evaporated. The filmy object discharged from the
tenter
700 is delivered to the swelling device
600. A swelling device
is a device in which the filmy object delivered thereto is once made to be swollen;
the swelling device
600 in FIG. 1 is a device where the solvent gas composed
of ethanol is sprayed onto the filmy object being delivered. Incidentally, instead
of ethanol, alcohols such as methanol and water vapor may be sprayed. The filmy
object discharged from the swelling device
600 is delivered to the late
stage drying zone
12. Plural rolls
800 are arranged in the late stage
drying zone
12, and the filmy object is delivered while being wrapped around
the plural rolls
800. The filmy object is heated in the upstream section
12a of the late stage drying device
12, and the solvent remaining
in the filmy object is evaporated.
As for the n-butanol added to and mixed in the polymer solution preparation apparatus
100, it is most resistant to evaporation and tends to remain in the solvent,
since n-butanol is highest in boiling point among the materials contained in the
solvent. Additionally, since the solubility of triacetyl cellulose in n-butanol
is inferior to the solubility of triacetyl cellulose in dichloromethane, it is
more difficult to form the intermolecular bond of n-butanol with triacetyl cellulose
than the intermolecular bond of dichloromethane with triacetyl cellulose. In the
solvent having been added and mixed with n-butanol, the action of n-butanol breaks
the intermolecular bond between dichloromethane and triacetyl cellulose, promoting
the evaporation of dichloromethane. Additionally, since the remaining n-butanol
does not tend to form intermolecular bond with triacetyl cellulose, it does not
tend to be engaged to triacetyl cellulose, and its addition amount is small, it
is evaporated by the time when the filmy object has passed the upstream section
12a of the late stage drying zone
12, so that the added n-butanol
does not affect adversely the characteristics of the film. Furthermore, since in
the production line
1, the solvent in the filmy object is once evaporated
in the soft film drying zone
11 and is subsequently swollen by the swelling
device
600, even the intermolecular bond between dichloromethane and triacetyl
cellulose which remains unbroken by n-butanol can be broken. Then, in the upstream
section
12a of the late stage drying zone
12, the solvents
remaining in the filmy object, such as the dichloromethane broken out of triacetyl
cellulose by the swelling action, is evaporated. Consequently, in the production
line
1, the evaporation of the solvent in the filmy object is promoted,
and the remaining amount of dichloromethane in the filmy object having passed the
delivery zone
12 can be reduced to be 0.1 wt % or less, and simultaneously
the total residual amount of the solvent is also reduced to be 0.5 wt % or less.
In the downstream section
12b of the late stage drying zone
12,
the filmy object is cooled down to room temperature, and the filmy object (TAC
film) takes the form of the finished TAC film product. The filmy object (TAC film)
discharged from the late stage drying zone
12 is wound by the winding device
500. The TAC film thus produced is subsequently delivered to the subsequent
processes, unshown in the figure, and is commercialized as the optical functional
films such as protective film for polarizing plate and anti-glare film. Additionally,
polarizing plate is formed by attaching the protective film for polarizing plate
onto both sides of a polarization element made of polyvinyl alcohol etc.; and a
part of a liquid crystal display is made by using the polarizing plate.
Now, with reference to FIG. 2, description will be made below on the production
line wherein cellulose film is produced by flow casting of the polymer solution
onto an endless belt.
FIG. 2 is a simplified schematic view of the production line while the cellulose
film is being produced by flow casting of the polymer solution onto an endless belt.
The production line
2 shown in FIG. 2 is the TAC (triacetyl cellulose)
film production line which is an embodiment of the production method of cellulose
film of the present invention, as the production line
1 shown in FIG. 1,
wherein a flow casting band
900 is arranged instead of the flow casting
drum
300 arranged in the production line
1 shown in FIG.
1.
With the same reference numerals for the same constituent elements as those of
the production line
1 in FIG. 1, description is made below with a focus
on the points different from those in the production line
1 shown in FIG.
1.
In the production line
2 shown in FIG. 2, the three same polymer solution
preparation apparatuses
100 as the three polymer solution preparation apparatuses
shown in FIG. 1, and three flow casting dies
200 are arranged. The three
polymer solution preparation apparatuses
100 are respectively connected
to the three flow casting dies
200 in a one-to-one relation. Additionally,
the three flow casting dies
200, flow casting band
900, and peeling
roll
400 are arranged in a drying chamber
10.
The flow casting band
900 is formed by wrapping an endless belt
930
around a driving drum
910 and a driven drum
920. The belt
930
displaces circularly along the direction of the arrow C in the drying chamber
10.
The three flow casting dies
200 are arranged along the running direction
of the belt
930 and above the belt
930, with the die outlets facing
onto the surface of the belt
930.
The polymer solutions delivered to the respective flow casting dies
200
are successively subjected to flow casting onto the surface of the belt
930
circularly running along the direction of the arrow C, the solvent is gradually
evaporated while the belt
930 is circularly running in the drying chamber
10, and becomes a film to yield the self-supporting property. Namely, the
evaporation of the solvent leads to a filmy object having shape stability. After
the belt
930 has finished about one round, the filmy object is peeled off
by the peeling roll
400, and delivered to the soft film drying zone
11.
In the soft film delivery zone
11 of the production line
2 shown
in FIG. 2, plural rolls are arranged; the filmy object going into the soft film
drying zone
11 is delivered along the direction of the arrow D, by being
guided by the plural rolls. The swelling device
600 is arranged in a midway
position in the soft film delivery zone
11. Incidentally, the swelling device
600 may be arranged in a midway position in the upstream section
12a
of the late stage drying zone
12. The swelling device
600 shown
in FIG. 2 is different from the swelling device shown in FIG. 1 in that the filmy
object being delivered is watersoaked and rinsed with water. Incidentally, the
application of an alcohol such as ethanol may replace the watersoaking. Both in
the upstream section and in the downstream section of the swelling device
600
of the soft film drying zone
11, dry air is blasted onto the filmy object
being delivered, resulting in evaporation of the solvent in the filmy object. In
the upstream section
12a of the late stage drying zone
12,
next to the soft film delivery zone
11, the filmy object is heated, and
the solvent remaining in the filmy object is evaporated. Additionally, in the downstream
section
12b of the late stage drying zone
12, the filmy object
is cooled down nearly to room temperature, to take a form of the finished TAC film
product. The filmy object (TAC film) discharged from the late stage drying zone
12 is wound by the winding device
500.
Now, detailed description is made below on the preparation of the polymer solution.
In the polymer solution preparation performed in the polymer solution preparation
apparatuses
100 as shown in FIGS. 1 and 2, at the beginning, triacetyl cellulose
grains are dissolved in an organic solvent having dichloromethane as the main component,
in the storage tank
110. The triacetyl cellulose is a mixture of those synthesized
from wood pulp and cotton linter, wherein the content of that synthesized from
wood pulp is 60 wt % and the rest of 40 wt % is allotted to that synthesized from
cotton linter. As above, making that synthesized from wood pulp be the main component
can reduce the cost for the TAC film. Incidentally, that synthesized from cotton
linter may be completely excluded to make the whole comprise only that synthesized
from wood pulp. The compatibility between the dichloromethane and triacetyl cellulose
is satisfactory, and hence adopting dichloromethane as the main component of the
organic solvent leads to the reduction of the total amount of the solvent in relation
to the amount of triacetyl cellulose. Additionally, the organic solvent in the
storage tank
110 contains methanol as a component of the mixed solvent.
The addition of methanol leads to the improvement of the shape stability (self-supporting
property) of the filmy object peeled off by the peeling roll
400, and the
easiness in transporting the filmy object. The composition ratio between the dichloromethane
and methanol is so adjusted in the storage tank
110 that dichloromethane
is contained in the content of from 70 wt % to 99 wt %, and methanol is contained
in the content of from 0.9 wt % to 29.0 wt %, taking the total amount of the solvent
in the polymer solution prepared in the polymer solution preparation apparatus
100 to be 100 wt %. Incidentally, ethanol may replace methanol, or water
may be added with modified composition ratio of methanol. Furthermore, in the organic
solvent in the storage tank
110, a plasticizer, an ultra violet light absorber,
an anti-deterioration agent, etc. are dissolved as additives. In the storage tank
110, the solid content such as triacetyl cellulose and the additives is
adjusted so as to be from 15 to 30 wt %, taking the amount of the polymer solution
prepared in the polymer solution preparation apparatus
100 to be 100 wt %.
n-Butanol, a poor solvent, is so added that the content thereof falls
in the range from 0.1 wt % to 1.0 wt %, taking the amount of the polymer solution
prepared in the polymer solution preparation apparatus
100 to be 100 wt
%. Incidentally, as a poor solvent, any alcohol having the boiling point in the
range from 80 to 170°, other than n-butanol, may be used. The boiling point
of dichloromethane is about 40° C.; accordingly, when the boiling point of
the poor solvent is 80° C. or higher, the poor solvent remains in the solvent
during evaporation of the solvent, and the intermolecular bonding of dichloromethane
to triacetyly cellulose is prevented without fail. On the other hand, when the
boiling point of the poor solvent is 170° C. or lower, the poor solvent can
be evaporated without thermally decomposing triacetyl cellulose.
As a result of the preparation described above, the solvent of the polymer solution
delivered to the flow casting die
200 is composed of dichloromethane and
n-butanol. Additionally, the composition ratios thereof are such that the content
of dichloromethane ranges from 70 wt % to 99 wt %, the content of methanol ranges
from 0.9 wt % to 29.0 wt %, and the content of n-butanol ranges from 0.1 wt % to
1.0 wt %, talking the total amount of the solvent to be 100 wt %.
Incidentally, until this point, description has been made on the production
method of TAC film using the polymer solution in which triacetyl cellulose is dissolved
in the solvent containing dichloromethane as the main component; however, in the
production method of cellulose film of the present invention, the main solvent
component may be an organic solvent such as lower fatty alcohols, and a chloride
of a lower fatty hydrocarbon other than dichloromethane. Additionally, the solute
may be a cellulose ester other than triacetyl cellulose. Furthermore, the added
poor solvent is not limited to n-butanol, but it may be any solvent which is highest
in boiling point among the materials contained in the solvent of the prepared polymer
solution, and is inferior in the solubility of cellulose ester to the organic solvent
which is the main component of the solvent.
EXAMPLES
Description will be made below on the TAC film production by applying
the production method of cellulose film of the present invention, and the performed
measurement of the residual amounts of the organic solvents, together with the
comparative examples.
At the beginning, example 1 produced the TAC film by using the production line
1 shown in FIG. 1. In the preparation of the polymer solution, the
triacetyl cellulose synthesized from cotton linter was not mixed; the triacetyl
cellulose synthesized from wood pulp (20 parts by weight), a plasticizer (2.2 parts
by weight), and an ultraviolet light absorber (0.02 parts by weight) were used;
and the solvent was prepared so as to give the composition ratios specified below,
for which the polymer solution prepared by the polymer solution preparation apparatus
100 was taken to be 100 wt %. Additionally, in the swelling device 600,
a solvent gas composed of nitrogen gas and added methanol (methanol:nitrogen=2:8)
was sprayed onto the filmy object discharged from the soft film drying zone 11,
thereby swelling once the filmy object.
Example 1
Dichloromethane: 79.6 wt %
Methanol: 19.9 wt %
n-Butanol: 0.5 wt %
Additionally, in examples 2 to 4, the TAC films were produced under
the same conditions as those in example 1, except that the conditions under which
the filmy object discharged from the soft film drying zone 1 was once swollen,
was changed to each condition specified below. In other words, the composition
ratios of the polymer solutions were the same as those in example 1.
Example 2
Application of a solvent (methanol:water=1:1) in 0.5 cc/m
2.
Example 3
Spray of Water vapor at 120° C.
Example 4
Rinsing with water by watersoaking.
Furthermore, in example 5, the TAC film was produced under the same
conditions (the composition ratios of the polymer solution, etc.) as those in example
1, except that the filmy object discharged from the soft film drying zone 11
was not once swollen.
Example 5
Between the soft film drying zone 11 and the late stage drying zone
12 shown in FIG. 1, the filmy object was not once swollen, and the filmy
object discharged from the soft film drying zone 11 was delivered to the
late stage drying zone 12, thereby performing the continuous drying.
Additionally, furthermore, in respective examples 6 and 7 and comparative
examples 1 and 2, the TAC films were produced under the same conditions as those
in example 5, except that the solvent composition ratios of the polymer solution
were changed as the respective conditions specified below. In other words, in the
same manner as that in Example 5, the filmy object discharged from the soft film
drying zone 11 was not once swollen.
Example 6
Dichloromethane: 99.0 wt %
Methanol: 0.9 wt %
n-Butanol: 0.1 wt %
Example 7
Dichloromethane: 70.0 wt %
Methanol: 29.0 wt %
n-Butanol: 1.0 wt %
Comparative Example 1
Dichloromethane: 79.6 wt %
Methanol: 20.31 wt %
n-Butanol: 0.09 wt %
Comparative Example 2
Dichloromethane: 79.6 wt %
Methanol: 19.29 wt %
n-Butanol: 1.01 wt %
On the TAC films produced in respective examples 1 to 7 and comparative examples
1 and 2, described above, the total residual amount of the organic solvent, the
residual amount of dichloromethane, and the residual amount of n-butanol were respectively
measured by gas chromatography, and the results as shown in Table 1 were obtained.
| |
Table 11 |
| |
| |
Total |
Residual |
Residual |
| |
residual |
amount of |
amount |
| |
amount |
dichloromethane |
of n-butanol |
| |
(wt %) |
(wt %) |
(wt %) |
| |
| |
| Example 1 |
0.34 |
0.03 |
0.31 |
| [0.5 Wt %, Solvent gas] |
| Example 2 |
0.34 |
0.03 |
0.31 |
| [0.5 Wt %, Solvent |
| application] |
| Example 3 |
0.35 |
0.04 |
0.31 |
| [0.5 Wt %, Water vapor] |
| Example 4 |
0.35 |
0.04 |
0.31 |
| [0.5 Wt %, Water soaking] |
| Example 5 |
0.37 |
0.05 |
0.32 |
| [0.5 Wt %, No swelling] |
| Example 6 |
0.18 |
0.09 |
0.09 |
| [0.1 Wt %, No swelling] |
| Example 7 |
0.48 |
0.04 |
0.44 |
| [1.0 Wt %, No swelling] |
| Comparative Example 1 |
0.45 |
0.11 |
0.34 |
| [0.09 Wt %, No swelling] |
| Comparative Example 2 |
0.51 |
0.03 |
0.48 |
| [1.01 Wt %, No swelling] |
Table 1 shows the total residual amount (wt %) of the organic solvent, the
residual amount of dichloromethane (wt %), and the residual amount of n-butanol
(wt %), in a single horizontal row, for each example or each comparative example.
These three residual amounts are the residual amounts in the TAC film immediately
after having been discharged from the late stage drying zone 12.
The present inventors discovered, as a result of diligent research, that in order
to substantially reduce the effects on the environment ascribable to the solvent
remaining in the TAC film after production, in the form of the finished TAC film
product, the residual amount of dichloromethane is required to be 0.1 wt % or less,
and additionally the total residual amount of the organic solvent is required to
be 0.5 wt % or less. From the results shown in Table 1, for the TAC film produced
in any of examples 1 to 7, the residual amount of dichloromethane is 0.1 wt % or
less, and additionally the total residual amount of the organic solvent is 0.5
wt % or less. Accordingly, in the TAC film produced in any of examples, the effects
of the residual solvent on the environment can substantially be suppressed. However,
in the TAC film produced in comparative example 1, wherein the content of n-butanol
is 0.09 wt %, the total residual amount of the organic solvent is 0.5 wt % or less,
but the residual amount of dichloromethane takes a slightly higher value of 0.11
wt %. On the contrary to comparative example 1, in the TAC film produced in comparative
example 2, wherein the content of n-butanol is 1.01 wt %, the residual amount of
dichloromethane is 0.1 wt % or less, but the total residual amount of the organic
solvent takes a slightly higher value of 0.51 wt %. As can be seen from these results,
in order to produce the cellulose film which substantially vanishes the effects
of the residual solvent on the environment, n-butanol has only to be added in the
content range from 0.10 wt % to 1.00 wt % in the preparation process of the polymer
solution, taking the total amount of the solvent in the prepared polymer solution
to be 100 wt %. Turning to a comparison of example 1 with example 5, both examples
being the same in the addition amount of n-butanol, the residual amount of dichloromethane
remaining in the TAC film is larger in example 5 than in example 1. Such a matter
is also the case in comparison of any example of examples 2 to 4 with example 5.
As can be seen from these results, by swelling once the filmy object between the
soft film drying zone 11 and the late stage drying zone 12, the evaporation
of dichloromethane in the late stage drying zone 12 is promoted. A comparison
of examples 1 and 2 with examples 3 and 4 indicates that the evaporation of dichloromethane
is more promoted by swelling the filmy object with a solvent than with water. Incidentally,
the peeling off operation with the peeling roll was able to be more rapidly performed
in the production of the TAC film in any example than in the production of the
TAC film in any comparative example.
*
