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Patented Dec. 24, 1946
par cas'rma common or onnwnosr:
Gilbert w. Brant, Buffalo, N. Y., assignor to n. I.
du Pont de Nemours A‘: Company, Wilmington,
Del., a corporation of Delaware
No Drawing. Application January 19, 1944,
Serial No. 518,887
(Cl- 106—181)
This invention relates to improvements in the
manufacture of cellulose acetate ?lm. More par
ticularly, this invention relates to ‘an improved
cellulose acetate composition suitable for dry
casting by conventional methods, and which after
evaporation of the major portion of the ‘solvent,
glycollic acid, mixed others, etc., are suitable for
the purposes 01' my invention.
The amount of cellulose ether incorporated in
the film-forming composition Ifnay be varied quite
widely. Useful results may be obtained with as
little as 0.1% based on the total weight of the
can be easily stripped from the casting surface.
Heretoi'ore, in the manufacture or cellulose
solid comprising the ?lm-forming composition,
ing surface.- Materials used for this purpose are
weight unless otherwise indicated.
although in some cases as much as 5% may be
used advantageously without changing the essen
acetate ?lms by the evaporative casting method,
it has been customary to add to the casting dope, 10, tial character of the cellulose acetate ?lm.
To further illustrate this invention, the fol
a small amount of material to render the par
lowing speci?c example is given. Parts are by
tially dried ?lm readily strippable from the cast
usually electrically conductive in character.
Example 7
When this type ?lm is used for electrical pur 16
casting solution was pre
poses as, for example, covering on wires. the in
pared by dissolving 74.8 parts of acetone-soluble
sulation resistance is very markedly impaired due
cellulose acetate (about 54.5% combined acetic
to the presence of the electrically conductive
acid), 0.2 part of ethyl cellulose (about 49%
stripping agent. On the other hand,’ when an
attempt is made to dry-cast cellulose acetate ?lm 20 ethoxy content) and 25 parts of dibutyl phth‘al
ate in 300 parts of acetone. Alter thoroughly
from solutions containing no stripping agent, the
mixing, ?ltering and deaerating. the dope was
removal of the partially dried ?lm from the cast
spread out on a heated, smooth, nickel-surfaced
ing surface requires so much tension that the
casting plate by means or a doctor kniie to a uni
?lms are badly distorted and not infrequently are
torn, and may even cause an interruption in the 25 form and constant thickness. When the solvent
continuity of the process.
It is, therefore, an object of this invention to
provide a new cellulose acetate ?lm-forming com
position which ls free of electrically conductive
had substantially completely evaporated, the ?lm
was stripped vfrom the plate and the stripping
tension noted. It was iound that the tension
required to strip the ?lm from the plate was
only about 120 grams whereas a ?lm similarly
materials and therefore capable of producing a 30 ' formed from a like composition but containing
?lm having desirable electrical properties and
no ethyl cellulose or other stripping agent re
without casting dimculties. A further object is
quired a. stripping tension of about 250 grams.
to provide a method for decreasing the adhesion
Similarly it was found that by taking cellulose
between freshly dry-cast cellulose acetate ?lm
acetate butyrate or cellulose acetate propionate
and the casting surface. Still another object is 35 the stripping tension could be markedly improved
to prepare electricallynon-conducting cellulose
by incorporating a small amount of ethyl cellu
acetate dry-cast ?lm which is easily removable
lose in the casting solution. For example, ?lm
from the casting surface. Other objects will be
apparent from the description thatfollows.
compositions comprised of about 71% cellulose
I have found that if a small amount of a wa
ter-lnsoluble cellulose ether which is not com
with 4% ethyl cellulose and 25% dibutyl phthal
acetate butyrate or cellulose acetate propionate '
ate as a plasticizer were found to strip easily and
patible with cellulose acetate is incorporated in
with only about 11% of the tension required if
the cellulose acetate casting solution, .the parti
the composition contained no ethyl cellulose or
ally dried ?lm i'ormed therefrom is easily stripped 45 other stripping agent. Likewise a cellulose ace
from the casting surface with greatly reduced
tate composition containing 4% benzyl cellulose
was found to strip with only about V3 of the ten
By the term “cellulose acetate” as used
sion required to strip a similar ?lm containing
throughout this speci?cation, I not only include
no benzyl cellulose or other stripping agent.
the simple ester but cellulose acetate mixed esters
Not only does a small amount of the water?
so long as the substituent groups are predomi
insoluble cellulose ether greatly improve the
nantly acetate.
strippability ‘of cellulose acetate ?lm from metal
Any of the cellulose ethers which are insoluble
casting surfaces, such as nickel, chromium, stain
in water and incompatible with cellulose acetate,
less steel, etc., but the ?lm produced has good
e. g., ethyl cellulose, benzyl cellulose, cellulose 55 slip on its casting surface side. This is another
important advantage of this invention because
cut sheets of ?lm piled up or a roll of ?lm can
be separated from the adjacent surfaces with
much less di?iculty than was heretofore possible
a cellulose acetate con?linlnl. as a strip agent,
from 0.1% to 5% of a water-insoluble cellulose
ether not compatible with cellulose acetate.
2. An organic solvent, dry casting solution of
a cellulose acetate containing, as a strip agent,
from 0.1% to 5% or ethyl cellulose.
lose acetate, particularly if plasticized, are usu
3. A dry casting solution of cellulose acetate
ally sized with a size containing electrically con
dissolved in acetone and containing, as a strip
ductive materials in order to obtain enough slip
agent, from 0.1% to 5% of a water-insoluble
to cause' adjacent surfaces to slide and wind up
without wrinkling and to‘ prevent sticking or 10 cellulose ether not compatible with cellulose
blocking. Furthermore, the absence of an elec
4. A dry casting solution of cellulose acetate
trolyte in the cellulose acetate ?lm, makes it
and a plasticizer dissolved in acetone and con
generally suitable for electrical purposes where
taining, as a strip agent, from 0.1% to 5% of
high insulation resistance and high dielectric
in the case of many ?lms. Thin ?lms ‘of cellu
strength are needed.
As many apparently widely different embodi
ments of this invention may be made without de
parting from the spirit and scope thereof, it is
to be understood that this invention is not lim
ited to the speci?c embodiments thereof except :0
as de?ned in the appended claims.
I claim:
1. An organic solvent, dry casting solution of
ethyl cellulose.
5. A dry casting solution consisting of 74.8 parts
by weight of acetone-soluble cellulose acetate, 25
parts of dibutyl phthalate, 0.2 part of ethyl cellu
lose, and 300 parts of acetone.
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