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Patent-ed Jan. 23, 1945
I 2,368,062.
UNITED STATES PATENT orricr.
CELLULOSE TRIACETATE COAIIIN
‘
COMPOSITIONS
Charles Begin, Terre Haute, Ind.,- assignor ,to
Commercial Solvents Corporation, Terre Haute,
Ind., a corporation of Maryland
\
'No Drawing. Application April 22, 1942,
Serial No‘. 440,099
7 Claims. ' (01. 106-176)’ ’
The present invention relates to new and im
which exhibits greater water resistance than is
proved cellulose ester coating compositions.
exhibited by the lower acetylated cellulose ace
tate ?lms. As possible substituteslthere have
More particularly, it is concerned with a method
of producing cellulose triacetate coating compo
sitions capable of forming stable, clear, tough,
and water-resistant ?lms.
Cellulose acetate is produced commercially in a
number of grades, which differ in their degree
>
of acetylation. In the ordinary processes by
which cellulose acetate is manufactured, it is
?rst produced as a highly-esterified product pos
sessing an acetic acid content of approximately
62 per cent. This material, however, is soluble
only in a very limited number of solvents, such
i been proposed coating compositions in' which the
secondary acetates have been replaced by cellu
lose acetate butyrate, o'r cellulose acetate pro
pionate.
These materials in general, however,
, give films’ which are substantially softer than
those formed from straight cellulose acetate, and
are also more expensive. It is therefore evident
that the highly esteri?ed cellulose acetate, whose
solutions are capable of producing clear, tough,
and water-resistant ?lms, would be readily ac
cepted for use in numerous ?elds provided an
as tetrachloroethane, ethylene dichloride, etc, 15 economical and substantially non-toxic solvent
and because of the relatively high toxicity of the
latter solvents, solutions of highly acetylated cel
or solvent mixture could be provided.
I am fully aware of the fact that cellulose tri
lulose acetate are obviously impractical for most
\ acetate coating compositions have previously
coimnercial applications. The commercial grades - been prepared by using as a solvent a mixture
of cellulose acetate, 1. e., those used at the pres 20 consisting of approximately 70 per cent nitro
ent time in arti?cial silks, plastics, motion pic;
methane and 30 per cent of an aliphatic alcohol
having less than ?ve carbon atoms, or mixtures in
which approximatelyhalf oi‘ the alcohol content
ondary acetates are made by subjecting the sub
is replaced by. an aromatic hydrocarbon, such as
stantially fully-esteri?ed cellulose to treatment 25 benzene, or toluene. Such solvent mixtures will
with acidulated water, which results in partial
dissolve .cellulose triacetate satisfactorily, and the,
hydrolysis of the highly-esteri?ed material, thus
resulting solutions thus produced are in most
replacing a portion of the acetyl groups with
instances perfectly clear. I have found it im
hydroxyl groups. Because of the introduction of‘
possible for all practical purposes, however, to
hydroxyl groups into the cellulose acetate, the
produce clear ?lms by the use o£ such nitro~
ture ?lms, airplane dopes, and lacquers, are com
monly known as “secondary” acetates. These sec
solubility of the latter is considerably increased -
and it may readily be dissolved in a number of.
' the oxygenated organic solvents, such as acetone,
methane-alcohol mixturesv since the range of
nitromethane-alcohol proportions permissible
from the standpoint of solubility is very narrow,
and inasmuch 'as'these' two volatile liquids do not‘
mixtures of nitroparamns and alcohols. and the 35 evaporate at the same rate, the necessary sol
vent balance is rapidly destroyed during the dry
The ?lms formed from such cellulose “acetate
ing of the ?lm, leading to a precipitation of the
solutions possess certain disadvantages, however,
cellulose triacetate.
which tend to prevent the use of considerable
I have now discovered that the nitropara?ins, _
quantities thereof in many ?elds. For example, 40 in'general, or mixtures containing the same, when
methyl acetate, ethyl lactate, diacetone alcohol,
like.
»
'
such ?lms possess rather poor water-resistant
~ properties, and if immersed in water, or even ex
mixed with a- relatively small proportion of a
true solvent for cellulose triacetate, constitute
posed to a humid atmosphere, moisture is rap
excellent solvents'for grades of cellulose 'triace
idly absorbed thereby. resulting in a material re
tate having acetic acid contents ranging from
duction in the strength and tension of said ?lms. 45 about 58 to 62 per cent. Prior to the present
This undesirable property hampers the use of
invention, the use of-nitropara?ins in cellulose
this grade of cellulose acetate in the formulation
of airplane domes, and to-some extent in the pro
triacetate solvent mixtures was limited to nitro
methane. However, it has now been made pos
duction' of-motion picture ?lms and coated tex
sible to prepare cellulose triacetate solutions, pos
tiles. Because of these. undesirable’ properties 60 ses'sing an exceedingly high tolerance for a. wide,
; possessed by ?lms formed. from the various sec
variety of solventmixtures, and ‘which may ‘con
,ondary grades of cellulose acetate, there has been
tain the higher nitroparaf?ns, as well as nitro
an existing need for a ?lm-forming material hav
methane. It is therefore obvious that such com
ing essentially the same solubility characteristics
positions, particularly from the standpoint of
as the secondary grades of cellulose acetate, but 55 commercial application, are much more desirable
2,868,082
' 2
very rapidly when the concentration of l-nitro
propane falls below 30 per cent.
than the compositionsproduced by dissolving cel
lulose triacetate in nitromethane-alcohol mix~
In the case of solutions of cellulose triacetate
I tures, since the latter, as mentioned above, are
prepared by dissolving the latter in tetrachloro
‘subject to the disadvantage that the permissible
proportions of nitromethane and alcohol, which 5 ethane or in a mixture of 90 parts of ethylene
may be utilized in cellulose triacetate solutions.
chloride and 10'parts of anhydrous ethyl alcohol,
are restricted toavery narrow range.
it will be noted that the tolerances for l-nitro
As a further result of the present invention,
propane and for mixtures of l-nitropropane and
the quantity of true solvent required in the prepethyl alcohol are high, while the tolerances for
, aration of cellulose triacetate solution has been It) ethyl alcohol, butyl alcohol, butyl acetate, and
materially decreased. Such an improvement contoluene are very low.
stitutes a distinct advance in the art of celluThe tolerances of a solution of cellulose triace
lose triacetate coating compositions in view of
tate in a mixture consisting of '70 per cent nitro
the fact that the known true solvents for cellumethane and 30 per cent anhydrous ethyl alco
lose triacetate are comparatively toxic substances. is hol, are observedto be very high for l-nitropro
Consequently, th'isproperty has greatly hindered
pane or its mixtures with alcohols. The nitro
the wide industrial application of cellulose triacemethane-alcohol mixtures can thus be modi?ed
tate solutions in many ?elds for which they were
greatly ‘by other liquids, and can also impart
otherwise admirably suited. Furthermore, solusolvent power to the l—nitropropane.
tions of cellulose triacetate dissolved in true 501- go
As previously stated, the high toxicity of the
ventsof the aforesaid type have a very low tolertrue or active solvents for cellulose triacetate
' tune for all of- the more common volatile organic
make it desirable to employ such materials in
liquids, suohlas esters, ketones, alcohols, etc., as
minimum proportions and the factor which de
showninthe table appearing below.
termines'this minimum value is the degree of
These data, likewise show the comparatively 25 solubility of the cellulose triacetate in the par
high tolerances of solutions of cellulose triacetate
ticular solvent mixture contemplated. when
, in various true solvents therefor, for certain of
the nitropara?lns, 'as well as for mixtures of the
nitropara?lns with toluene and/or alcohols.
_
employing cellulose triacetate in the prepara
_ tion of coating compositions, I have found it
desirable to dissolve it ?rst in the form of a
Table
Composition of cellulose trlacetate solution
Diluent or diluent mixture
Tolerance
l-nitro opane
30% l~nitropro
More than 10. 0
e
}
3.9
3W" anhydrous ethyl aleohoL
}
More than 10.0
3092 l-nllxopropane ........ _
} More than 15.0
gal‘? grlilliity’grpggs etléyl alcohol.
30$
dr
40 ,, toluene ............. ..
_
_
,
I
.
20% 1 nitropropane
2m solution cranium iriacetata (00.9% acetic acid) in tetrachloroathana........ -_ @877; gggzl?ffffljlffmmI
.
'
'
20% l-nitropropane-_
o.
_
}
" ‘5
}
2‘ 0
@3110]
339%; tnt'g’mp‘m"
} More than 15. 0
‘0% 1..
3°” li‘hydmmp?ttinaara; :::}
4-15
40% Z-nitropropsne ..... --
}
4A
my, bntanol ....... __
Ethyl acetate--,
5% lolutknolcelluloso mm (02% acetic acid) ,lntetrachlorosthsno. ........
.I
.
_
.
.
v
~.
'
E36
Ethyl‘1,3522:
alcohol (auhyd)-.
018
“Haxonen____
(1.5
a
.
_
'
-~
_
I
0.6
bultyl aaat?te‘at’; an” _
mmwwmm-
1.2
More than 7.0
morethan8.0
(00.9% acetic acid) in 90-10 ethylene chloride- $1‘:mm qthyl
'
’
'
'
-
Anhydrous cthylslcoh
lmtielcid) in70-30nitromcthsno-anhydrous
’
In the above table the
(1) g
uol ............... _-
'
lbrhsgllntlcdl
(1)13
Butyl acetate
'
'
’
1~ 4
k1.
solution :ti‘h
'
0.1
Ethyl alcohol (95%)--
01
_
.'
1g
Butylaoetata
.H' ggwttcplm____
'
of the ‘solu
' tion produced- i'rom tetrachloroethane and cellu
‘I
-i
""'"'.I ......... -
llh‘?tptttl ma--..--}
More than
.
0.5
More mm 7. 5
75
stock solution containing from two to three times
the . concentration required for spray applica
tion. The resulting stock solution may then be
diluted with the appropriate thinners to the
01' l-nitropropane, alcohols, and toluene, are sub 70 proper
consistency. This procedure is particu
_. stantlally higher than'the values for the simple
larly
advantageous
inasmuch as the proportions
mixtures oi" l-nitropropane and alcohols free .
of
true
solvents
for the preparation 0!
from toluene. The results obtained also indicate
lose triacetate for the three-component mixtures
that the tolerance of tetrachloroethane for mix- '
tures of l-nitropropane andalooholsdecreases
the more concentrated stock solutions are only
16 slightly higher than those required for the prep
_
2,868,062
' 3
aration of the more dilute solutions. Since the'
rapid evaporating solvent, such as ethylene
thinners‘ employed need not contain any of the
toxic true solvents, this practice allows ‘the for
chloride, is utilized as the true solvent. The
proportion oi’ such solvents will also be found to
mulation of ?nal solvent mixtures containing a
depend ‘upon the character of the nitropara?in
minimum of said true solvents. . In this connec
mixture, greater proportions being necessary in
tion the process oi’v solution is aided considerably
by elevated temperatures. For example,.'I, have
the case of solvent mixtures containing rela
tively large percentages of comparatively slow
evaporating solvents, such as butyl alcohol,
butyl acetate, etc. .The proportion of true sol-.
vents necessary will also depend somewhat on
observed that it 'a well-dispersed mixture of cel
lulose triacetate and volatile solvents is sub-'
jected to a temperature of about 70° C. for a rela
tively short period, .e.. g.,' one-half hour, the
process of solution is improved appreciably. As
a ‘result, stock solutions prepared under such
- the nature of the cellulose triacetate used, i. e.,
the substantially completely-acetylated cellu
' lose triacetate which contains approximately 62
conditions may contain from 10 to aboutl5 per
per- cent acetic acid, or the slightly hydrolyzed
grade having an acetic acid content ‘of from 59
cent less of the true solvent than is necessary
to obtain cellulose triacetate solutions of equal
concentration at ordinary temperatures. Ade
quate agitation during the process of solutions
is also another factor to be taken into consid
eration in preparing such stock solutions of cel
lulose triacetate. For example, by the com
bined use of elevated temperatures and thor—.
ough agitation, stock solutions containing three
to 60 per cent." However, in general a number
of solvent mixtures containing as, little as from
3 to 5_per cent of one or more of the above
mentioned true cellulose triacetate solvents, will
be found to be satisfactory for the production of
cellulose triacetate solutions capable of form
ing clear, tough, and water-resistant ?lms.
The nitropa-ra?ins, in addition to nitromethane,
which may be employed, are nitroethane, 1-nitro
times as much cellulose triacetate; as is neces
sary for spraying purposes can be prepared by
propane, 2-nitropropane, the nitrobutanes, the
the use of solvent mixtures containing from 20
nitropentanes, and the like. »The quantity of
to 25 per cent tetrachloroethane, 50 per cent 1
1 nitropara?lns utilized will likewise be found tov
nitropropane and 25 to 30 per cent ethyl alco- vary with the character of the true solvents em
ho]. Such solvent ‘mixtures can be readily, di
ployed, 85 well as the acetic acid content of the
luted with thinners containing no tetrachloro
30' cellulose triacetate. In general, however, the
ethane whatever. The ?nal cellulose triacetate
solutions thus obtained will therefore contain
the true solvent, in this case tetrachloroethane,
in about one-third the amount present in the
stock solution, 1. e., 7 to 8 per cent. Thus, it may.
be seen that the cellulose triacetate solutions of
nitropara?ln content of the solvent mixture may
vary from approximately 30 per cent to 70 per
cent.
3.
\
-
The alcohols used in preparing the cellulose
triacetate compositions of the present invention
may be any of the lower saturated‘ aliphatic
the present invention are considerably less ob- ,
monohydric alcohols, and particularly those con
,iectionable than those of the" prior art from the
taining 1 to .4 carbon atoms. The proportion of
such alcohols utilized is, of course, subject to
standpoint of ‘toxicity.
1 .
.
Frequently, concentrated solutions of cellulose
triacetate containing nitropara?ins, tend to in-'
crease in viscosity and gel on aging. This par
ticular type of instability has been ‘found to be
directly connected with the richness of the so‘
vent mixtures, Such solutions of cellulose tri
acetate which contain only moderate proportions
of aromatic hydrocarbon-alcohol mixtures, are,
however, found to be fully stable to storage. In
the actual preparation and handling of such
solutions, it will therefore be advisable to em‘
ploy moderate amounts of said aromatic hydro
carbon-alcohol mixtures in the concentrated
stock bases which consist essentially of cellulose
triacetate and a true solvent therefor. Addi
tional quantities of the ‘aromatic hydrocarbon
alcohol mixture may be conveniently introduced
into the diluent mixture. Any of the customary
aromatic hydrocarbons commonly employed in
coating compositions, may be utilized for this \
purpose, such as, for example, benzene, toluene
and xylene. I prefer, however, to employv tolu
ene for most purposes.
.
Examples of the true 'or active solvents which
may be utilized in the formulation of_ cellulose‘
variation, depending upon the particular grade
of cellulose triacetate, the alcohol employed, and
the character and quantity of the other com
' ponents of the solvent mixture. In general, sat- ‘
- isfactory solutions may be prepared by employing '
- solvent mixtures containing from 20 to‘40 per
cent alcohol.
\
The amount of aromatic hydrocarbon used is
subject to substantially the same conditions as the
aforesaid alcohols. Generally the quantity of
such hydrocarbons present may constitute from
'10 to 30 per cent of the solvent mixture.
'
.
My invention may be further illustrated by th
, following examples which describe typical com
positions that may be produced in accordance.
with my discovery.
"
Example I
Cellulose triacetate having an acetic acid con
tent of 61.0 per cent was added in a ratio of 15
grams per 100 c. c. of a solvent mixture consisting
of 24 parts tetrachloroethane, 50 parts 1.-nitro
propane and 26 parts ethyl alcohol.
To the re
sulting solution was added, with thorough agita
tion, a thinner consisting of 70 parts l-nitropro
‘triacetate compositions possessing the afore- ‘ said properties, are tetrachloroethane, trichloro
ethane. ethylene chlorohydrin, dioxane, and a,
mixture consisting of ethylene chloride and from
- pane, 19 parts ethyl alcohol, 30 parts butyl alcohol
and 81 parts toluene. This solution, when ap
plied in accordance with any of the common
methods of application, produced a clear, tough
about ,5 to 25 per cent of a lower aliphatic al
cohol. 'I'he'proportion of the true cellulose tri 70 .and water-resistant ?lm.
acetate solvents of the above type necessary to
I . Example vI‘I
prevent precipitationv ‘during the drying of the
freshly-applied ?lms, will ‘vary, depending upon
Tov a solvent-mixture consisting of 25 parts
whether a slow evaporating solvent, such as,
dioxane, 48 parts l-nitropropane and 27 parts
tetrachloroethane, is employed, or a relatively - ethyl alcohol, cellulose triacetate having an acetic
‘
2,868,062
4
acid content of 59 per cent, was added in a ratio
of 20 grams of cellulose triacetate per 100 c. c.
' of solvent.
The resulting solution was slightly
cloudy; however, with the aid of heat and agita
tion it became perfectly clear. A thinner con
sisting of 100 parts l-nitropropane, 32.5 parts
butyl alcohol, 62.5 parts toluene and 30 parts
ethyl alcohol was then added thereto with agita
tion. The composition thus secured, when ap-.
plied in accordance with ordinary lacquer ap
plication methods, formed a clear, tough, and
water-resistant ?lm of cellulose triacetate.
Having now described my invention, what I
claim is:
1. A composition of matter comprising cellulose
triacetate having an acetic acid content of from
58 to 62 per cent dissolved in a solvent mixture
comprising a major proportion of a non-solvent
prising a major proportion of anon-solvent mix
ture containing nitromethane and a lower ali
phatic alcohol, the predominant portion of said
non-solvent mixture consisting of said nitro
methane, and a minor proportion of a true sol
vent for said cellulose triacetate selected from
the group consisting of tetrachloroethane, tri
chloroethane, ethylene chloride, ethylene chlo
rohydrin, and dioxane, such solvent mixture be
ing substantially non-toxic and easily capable
of maintaining thecellulose triacetate in a dis
solved state throughout the drying process when
said composition 5 applied to a smooth surface.
5. A composition of matter comprising cellu
lose triacetate dissolved in a solvent mixture
comprising a major proportion of a non-solvent
mixture containing l-nitropropane and a lower
aliphatic alcohol, the predominant portion oi said
non-solvent mixture consisting of said l-nitro
lower aliphatic alcohol, the predominant portion 20 propane, and a minor proportion of a true solvent
for said cellulose triacetate selected from the
of said non-solvent mixture consisting of said
group consisting of tetrachloroethane, trichloro
lower nitropara?in, and a minor proportion of a
mixture containing a lower nitropara?ln and a
true solvent for said cellulose triacetate selected .
ethane, ethylene chloride, ethylene chlorohydrin,
from the group consisting of tetrachloroethane,
and dioxane, such solvent mixture being sub
trichloroethane, ethylene chloride, ethylene chlo 25 stantially non-toxic and easily capable of main
rohydrin, and dioxane, such solvent mixture be
taining the cellulose triacetate in a dissolved state
throughout the drying process when said compo
of maintaining the cellulose triacetate in a dis
sition is applied to a smooth surface.
solved state throughout the drying process when
6. A composition of matter comprising cellu
said composition is applied to a smooth surface. 30 lose triacetate having an acetic acid content of
2. A composition of matter comprising cellu
from about 58 per cent to about 62 per cent dis
lose triacetate having an acetic acid content of
solved in a solvent mixture comprising a major
from about 58 per cent to about 62 per cent dis
proportion of a non-‘solvent mixture containing
solved in a solvent mixture comprising a major
nitromethane, a lower aliphatic alcohol, and an
proportion of a non-solvent mixture containing 35 aromatic hydrocarbon, the predominant portion
a lower nitroparaf?n, a lower aliphatic alcohol,
of said non-solvent mixture consisting of nitro- .
and an‘ aromatic hydrocarbon, and a minor PTO-e
methane, and a minor proportion of a true sol
portion of a true solvent for said cellulose tri
vent for cellulose triacetate selected from the
acetate selected from the group consisting of
group consisting of tetrachloroethane, trichloro
ing substantially non-toxic and easily capable
tetrachloroethane, '
trichloroethane,
ethylene
chloride, ethylene chlorohydrin and dioxane,
such solvent mixture being substantially non
toxic and easily capable of maintaining the cel
ethane, ethylene chloride, ethylene chlorohydrin,
and dioxane, such solvent mixture being ‘substan
tially non-toxic and easily capable of maintain
ing the cellulose’ tria'cetate in a dissolved state
lulose triacetate in a. dissolved state throughout
throughout the drying process when said com
45
the drying process when said composition is ap
position is applied to a smooth surface..
7.‘ The composition oif claim 6 in which l-nitro
3. The composition of claim 2 in which the
propane
is substituted for nitrcmethane'. ’
aromatic hydrocarbon is toluene.
4. A composition of matter comprising cellulose
50
CHARLES BOGIN.
triacetate dissolved in a solvent mixture com-.
plied to a smooth surface. ‘
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