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Патент USA US2404422

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Patented July 23, 1946'
2,404,422
UNITED STATES a PATE NT‘
2,403,422
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OFFICE
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TRANSPARENT PLASTIC MATERiAL
Bjorn Andersen, Maplewood, N. .L, assignor_to_
Celanese Corporation of America, a corporation
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‘of Delaware
No Drawing. ‘Original application January 28,
1939, Serial No. 253,251. Divided and this ap
plication February 12, 194,2, Serial No. 430,618‘ ‘
6 Claims. (Cl. 2.29--3~.5)
‘
1
This invention relates to the production of
tate, or other certain synthetic resins, such- as.
transparent plastic materials of improved prop
erties, and relates more particularly to the'pro
polymerized vinyl resins, polymerized. acrylic acid
and methacrylic acid esters, urea formaldehyde,
duction of a non-foggingv type of transparent ma
terial.
etc. were used as or in the container, it was.
5 found that these plastic materials also failed to
resist fogging or sweating._ Thisv lack of resist
ance of a transparent plastic material to fogging
or sweating was due to thefact-that such plastic
,This invention is a division of the invention
described in my co-pending application S. No.
253,251, ?led January 28, 1939.
An object of‘ this invention is to provide a
transparent plastic- material which is not sus
ceptible to fogging or sweating when exposed to
moisture-laden atmosphere, or at low: tempera
tures conducive to moisture condensation.
Another object of this invention is the provi
sion of 1a transparent plastic material suitable 16
vent clear’ visibility therethrough but would also
for use as or in packages for moisture-containing
permit air to pass therethrough which, in. the
substances.
case of some foods, would cause deterioration.
>
Other objects of this invention will appear from
the following detailed description.
materials were all made more or less Water-in
soluble to minimized‘ moisture absorption. These‘
plastic materials could; of course, be made more
porous, and sponge-like and. thus absorb‘ mois
ture, but there is‘ always the danger that the.
plastic material ‘being porous would not only pre
In‘ac'cordanc'e with my invention, I produce a
,
transparent plastic material having non-fogging
In recent years certain plastic. materials have 20 and non-sweating characteristics, which trans
been utilized in the manufacture of cartons for
foods or other moisture-containing materials.
parent plastic material retains its non-porous
character, bytreating one or both surfaces of a
However, the plastic materials suffered from the
disadvantage of fogging or sweating when mois
derivative of cellulose sheet leaving'the inner por
tion or- core thereof in a'substantially unaffected
ture-containing foods or other substances were 25 condition. Such a sheet is substantially impervi
sealed up or enclosed in containers made of the
plastic material or having windows thereof. To
ous to both moisture and gas and has a. layer,
on one‘ or both surfaces thereof, which. is water'
overcome in some measure the fogging orsweat
absorptive. The treatment comprises super?cial.
ly saponifying, hydrolyzing ‘or de-est'eri-fying
made to utilize a thin sheet of gelatin orother 30 sheet material comprising esters-of cellulose, such‘
moisture absorptive transparent medium on the
as cellulose nitrate, cellulose propionate, cellu
inside of the plastic material, 1. e. between the
lose acetopropionate, cellulose butyrate, cellulose
plastic material and the moisture-containing sub
aceto-butyrate; and-'particuarly cellulose acetate.
stances. These gelatin inserts or linings suffered
As stated above, either one orboth surfaces may
from a number of disadvantages. For example, 35 :be saponi?ed. In order to obtain sheets which
under certain conditions, the gelatin swells, be
are perfectly ?at and free from distortion, “knife
comingsticky, wrinkled and pu-trescent. Fur
lines” etc. it is preferable to heat press and polish
thermore, the gelatin coatings when exposed. to an
thesheets before and after treatment with the
extremely dry warm atmosphere tend to shrink
and crack and, therefore, do not afford a clear 40
Super?cial saponi?cation of the‘cellulose ester
vision through the transparent container.
sheet material may be effected in any convenient
ing that takes place, attempts have hitherto been
saponifying
The inherent disadvantages of gelatin as a
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manner such as by treatment in an alkaline ‘bath
or by padding or otherwise mechanically impreg
coating have led investigators to try other ex
pedients to prevent the fogging or sweating. For
nating the sheet‘ material with the requisite quan
instance, attempts have been made to use on the
plastic material chemical compositions found on
tity of saponifying agent.
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The alkaline bath used for super?cially sapon;
ifying the cellulose ester sheet material may be
the market for spraying onto glass Windshields
to prevent frosting, water condensation or sweat,
etc.
agent.
either of low concentration or high concentration
These chemical compositions were often not
depending on the temperature and duration'of
satisfactory for use, particularly where food came 50 treatment. “If an alkaline solution of low con;
in contact therewith. Another objection is that
centration is used higher temperatures-may be
their water-solubility resulted in the eventual
removal thereof from the plastic material.
employed in theprocess, whereasv if alkaline ‘so
lutions of high concentrations are employed low
7 Where transparent plastic materials made
from cellulose derivatives,’ such as cellulose ace
65
temperatures of treatment are used. If' a solu
tion of intermediate concentration is employed,
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32,404,422
3
bing. The surfaces of the sheets are then dried
intermediate temperatures of treatment should
thoroughly by Wiping with Chamois and by stor
be used. The saponifying bath may contain any
suitable alkali or alkaline salt for producing hy
droxyl ions in aqueous .solution. The alkalies
ing the sheets at room temperature between tis
sue-lined “falulah” boards for a period of 3 to
4 hours to 3 days depending on the thickness of
‘ which may be used are sodium hydroxide, po
the sheet employed. For example, sheets of a'
tassium hydroxide ‘or ammonia. Examples of
thickness of}. 0.005 to 0.010 of an inch are dried
at’ room‘temerature for 3 to'4 hours, whereas
alkaline salts are sodium or potassium carbon-v
ates, sodium potassium or ammonium sulphide.
sheets having a thickness of 0.060 of an inch are
or hydrosulphide, sodium or potassium silicate‘and I
tri-sodium phosphate. In order to promote in 10 preferably dried for 24 hours at room temper
' ature vbetween the boards, then are transferred
tense surface’saponi?cation of the cellulose -es
to dry pads and further dried for 24 hours at‘
ter sheet material, salts or modifying agents such
120° F. and then 24 hours at 140° F. When the
sheets are thoroughly dried they are flattened ‘
anates, boraX, alcohol, glycol and polyglycol or
their derivatives such as methyl glycol, etc. may 15 between polishing plates in a pre-heated press for 7
about 20 minutes at 50 to 150, preferably 125,
be addedto the saponifying bath. The sheet materials usedin accordance with‘ pounds of steam under from 500 to 1500, prefer
this invention may contain, besides the cellulose viably 1250, pounds of hydraulic pressure per
as soap, sodium acetate, sodium “oleate', thiocy-f '
square inch. vThis removes any surface irreg
ester, effect materials for modifying the prop- _,
erties of said sheet materials, such as plasticizers, 20 ularities, distortions, knife lines, etac. The pol
ished sheets are then ready for use.
?llers, dyes ,or lakes, ?re retardants, etc. For
Aswill appear from theyfollowing tables, the
‘ instance, the sheet material may contain about
cellulose ester sheets treated in accordance with
5to~30or more parts of plasticizer which may
this invention have physical characteristics which
be any suitable one for the particular cellulose
ester employed. vThe plasticizers maybe any of 25 are quite different from those of the untreated
the high boiling solvents or softening agents as,
The chemical formula of the sheets‘ tested is
for example, the aryl sulphonamides such as
sheet.
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cellulose aceate 1007 parts by weight and dim'eth
para ethyl toluol sulphonamide, the alkyl phthal
oxy ethyl phthalate (plasticizer) 30 parts by
ates such as dimethyl phthalate, the 'dialkyl tar
trates such asdibutyl tartrate, the alkoxy es 30 Weight.’ This composition is, however, only illus
ters of polybasic organic acids such as dimeth
‘
trative.
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(A) Untreated sheet,
oxy ethyl phthalate, the polybasic acid esters of
the mono alkyl ethers of polyhydricalcohols such
(thousandth;
of
Thickness
V"
as diethylene glycol ethyl ether ester of phthalic
inch) ______ __1_-__‘__" _____ _~_ *5
acid, the alkyl esters of ‘phosphoric acid such as 35 Fog resistance (in seconds)___ ' 2
triethyl glycol phosphate, tricresyl phosphate, the
Tensile strength, in pounds
mixed alkyl and aryl phosphatesgand camphor.
A mixture of, any of the foregoing plasticizers
may beemployed if desired. The ?re retardants
vwhich- may be, employed in the cellulose ester
sheet material may be tricresyl phosphate, tri
persq.in.:
A. Yield
10
2
20
V
2
"
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p0int____'___'____
_
_
_ 6160 "4825 _ ‘5260"
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VB. Break point __I__-____-__ 7730;- 6150 15860
Elongation (percentage) _v_;__ 38.7‘ 35.5‘ 32.1
phenyl phosphate, chlorinated naphthalenes,‘
chlorinated. diphenyls, compounds containing
Hardness __________ __' _____ __
6.66
6.34‘
Moistureabsorption;1 _____ __
3.94
4.05v 4.50
‘6.74
bromine and other like ?re retardants known to
be compatible, with the cellulose ester employed.
The ?re retardants may be added to the sheet
y *(B) . Treated; sheet v(Inon-f0.997mg)
material in a quantity of about 15 or more'parts
by weight. If desired, water-soluble plasticizers
Thickness
inch) ___v_'
‘_ (thousandths.
____ __~__>__~__'____
"of
"5 "710
- - Y‘ ‘20
and/or ?re retardants may be used to some ex
tent as, for example, to secure a greater depth 50 Fog resistance (in seconds) _-_“ 4' 90
140 >120‘
of porosity.
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yWhile any of the vforegoing saponifrying agents’
Tensile
..persq_in_-:
A. Yield
strength,
‘point>..
____
in pounds
__,__'___' 9850',I 8850
7.; l7300
may be used in making the sheet material of my
invention, I prefer to use ‘an aqueous solution
B. Break point '___-i ____ ___ 9850 2‘8850 - 7560
of ammonia. In the preferred process of treat
ing the cellulose acetate sheet material the sheets
which may vary in thickness from about 0.001
to 0.100 of van inchpor more are ?rst cleaned and
Elongation (percentage) ‘___"__~'_l10.2’
20.6 ' '30
Hardness l___;_-___~ _____ _"__;_1_' 10.6
Moisture absorption__-_,__-_;__ 8.83
10.6 "9.13
"7.73 " 5.96
then polished in the usual manner between heat- '
Water
age)‘ ______
shrinkage
_. ___________
(percent_-__- - 074'
- 1; .125 ' ~~ i209
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' ed ; polishing , plates.
These sheets are then im
mersed for a period of from 2 to 6 hours, de
pending on the thickness, in a saponifying bath
containing ammonia in a concentration of about
15 to 20%, at a temperature between 60 to 75°
F., preferably 65° F. If the temperature exceeds
'75"v F.- an undesirable distortion of the sheet ma
terial- may‘ take place. After the sheets are‘
taken from the bath they are washed in running
Water at a temperature of 60 to ‘75° F., prefer
ably 65° F., for from 20 to 300_hours depending
upon the thickness of the sheet being treated.
In order to. prevent discoloration of thesheet.
material it is preferable, to exclude air from the
sheets until all of‘ the ammoniayand degraded
Heat 1055 ____ __4..'__'____~_._"__’_I_'. .329v .258
.211’
In the tables the ?gures _for_ “fog resistance" were
obtained by ?rst preconditioning the sampleof
the sheet to be tested for one hour at 80° F. and
5.0% relative humidity.
The sheet was then
placed ?at over the mouth of a one quart; Mason
jar containing onepintof water at 140?,F.,-_ the
jar being in turn placed'over- a newspaper..~'i‘he~
time in seconds was noted-when fogging ?rst be:
gan to. appear and the newsprint became illegible;
730 By
this test, treated’ ornon-fvogging plastic sheet:
‘ing is fog resistant for. not less‘ than goseconqsl.
usually from 90' to >150seconds, whereasuntreated,
plastic Sheeting and glass Wil1...fQg in-~.twb.eeqéeiis'
PKQQQCWPW? been removed by ‘57.351.11.119. 91' .5339: 7.5 0r.- .less-1Tha?guréstori/hardness ae-eaesa
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ciably'minimi‘zed. This quality is alsoiofmate
as Brinell hardness in kilograms per’ square‘mil;
rial aid when it is“ desired to ‘make antifog'ging, ,
limeter with a 3.5 ‘millimeter ball; liliikilogram
shatterproof glass lenses, Windshields,‘ et'c'.,;wliere
load, 1 minute; Thei'moistur'e absorption figures
one or both ‘sides of-theglassh'a's'a- treated sheet
were obtained by‘ conditioning the sheet material
of cellulose'es'ter laminated thereto. "The'toughl
for 24 hours at'zeropercentage relative-humide
ity, and noting the gain in weightafter 48’hours
at 90% relative ‘humidity. To obtain the ?gures
for water shrinkage, the sheet material was ?rst
ness and resiliency of the treated plastic sheet
ing, compared with an untreated sheet‘, make for
added safety.
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If desired, a roll of cellulose acetate ?lmrmay
ity. “The sheet material was then immersed'in 10 have one or both‘ sides saponi?ed or de-esterified
su?icieritly so that a thin coating or substratum
water‘ for?» hours'and then conditioned: again
of gelatin may be effectively applied; After the
for 24 hours at 50% relative humidity. [ The ?g
?lm is thus “subbed” say in continuous lengths,
ures' given in the tables represent the percentage
a thicker adhesive layer of glue, gelatin,' gum
shrinkage in length. The ?gures for‘ heat ‘loss
conditionedfor 24 hours at 50% relativehumid;
arable, casein, sodium silicate‘, egg albumin, ‘dex
trin, glyceryl or glycolbo'ri-borate resins, etc,
may be subsequently appliedso"v that the ?nal,
represent the percentage of loss‘in weight after
heating thesheet material'for 3 days at ‘70° C. >
From the above tables itwill beseen that the
treated sheet material of plasticized cellulose ace
tate is remarkably stronger than the untreated
plasticized cellulose acetate although the percent
dried coated ?lmt orlsheeti’n‘g may ‘be‘stuck to a
. variety of surfaces-‘suchv as glass, wood, metal,
paper, etc, by the-mere application'of water as .
in the'sticking of ‘a postage stamp. In thepast
it has been quite difficult to apply gelatin coat
ings, even though extremely thin, directly to plas
ticized cellulose acetate materials, for example,
in motion picture and X-ray ?lm, where a heavier
vcoating of light sensitive ‘gelatin emulsions is
usually applied over the thingelatin substratum.
This‘ di?iculty in securing proper anchorage of
age of elongation is less. ’ The latter, however, in
creases with the thickness of the sheet material
whereas in the untreated plasticized- cellulose ace
tate sheet material it decreases as the‘ thickness
increases. The treated material is moreover-‘de
cidedly harder and more scratch-resisting than
the untreated sheet material. This is probably
due to the case hardening e?ect oflthe sapohify
ing treatment and the absence on the surface ‘of
any substance such as a plasticizer. Indeed, celé
lulose acetate sheets treated in this manner ap
the gelatin to the surface’ of the ?lm is generally
attributed to the incompatibility of the oily,
Water-insoluble or hydrophobic plasticizer in or
pear to approximate the good mechanical prop
erties of the well known product, Celluloid, such
as resiliency and stiffness Without brittleness,
gelatin. The saponi?cation of the cellulose ester
and plasticizer results in a porous, water absorp
on the ?lm with a hydrophilic colloid such as
try. The light transmission of the treated'sheet
tive layer making possible more e?ective gelatin
substrating. Ordinary glued paper labels‘ may
material is over 90% of white light which is prac
tically unalfected by long exposure to sun or ultra
violet light. For example, one hundred hours ex—
fogging sheet by mere application of‘ moisture.
This feature is also quite desirable for packaging
which are so‘much ‘desired in the plastics indus
posure in a standard “Fadeometer” testing ma
chine caused only a slight bleaching of color with
no apparent e?ect on light transmission.
i4.
also be readily stuck to the surface of the non
40 material.
While this invention thus ?nds exceedingly
useful applications in many ?elds, the physical
properties of the sheet material treated in ac
The tables also show that the moisture absorp
cordance with this invention makes the same emi
.tion is very high in the treated plasticized cellu
lose acetate sheet material as_ compared with the ;- nently suitable for use where non-fogging, trans
parent sheet material is desired. For example,
untreated plasticized cellulose acetate sheet ma
when sheet material of this invention is used as
terial, while the water shrinkage is less. A
containers or as windows in food cartons, the
marked difference will also be noted in the Weight
said material will not fog or sweat due to the
loss at elevated temperatures, the untreated plas
ticized cellulose acetate sheet material losing ap 50 condensation moisture thereon, such as may be
induced by exposure to low outside temperatures
preciably after 3 days at 70° C. The case-harden
or by conditions obtaining within the food car
ing saponi?ed layer in the treated sheet mate
ton. This feature, as indicated above, is due to
rial acts as a seal and prevents further volatility
the porous and moisture absorptive character of
of the plasticizer from the core of the sheet ma
terial. This is a very signi?cant ?nding. Its 55 the surface of the sheet material. No droplets
of the moisture (fog) Will appear on the surface
bene?ts are appreciated in the case of printing
of the sheet to mar the transparency thereof.
cellulose acetate sheets and subsequently polish
Moreover, the treated material will not Wrinkle
ing same. The dii‘?culties of ink transfer as
or become sticky and distorted in use due to
brought out in U. S. Patent No. 1,931,485 are con
siderably diminished. Due to the porous surface 60 shrinkage or swelling, but will remain strong,
?exible, non-tacky, non-moldy, clear and durable.
the ink is more readily absorbed. In polishing
Treated material will also exhibit less “static”
the sheet any tendency of the plasticizer to exude
than untreated material which is highly desir
is offset by this super?cial absorption. Indeed,
able in the case of packaging material. The
the treated sheets may be readily marked with
ordinary ink and pen, and for this reason are very 65 treated surface is also more resistant to spotting
by solvents such as acetone, alcohol, etc.
suitable for tracing cloth purposes. This ease of
printing is utilized to advantage in marking or
If desired, the treated sheets or ?lms may be
printing the non-fogging material, particularly
suitably composited or laminated to one or both
sides of other plastic materials, such as those
when it is used for packaging purposes.
The saponi?ed, porous surface also renders pos 70 made of cellulose derivatives, synthetic resins such
as Vinyloid, Lucite, Styrol, condensation prod
sible an easier lamination of the material to glass
uts of urea-formaldehyde, phenol-formaldehyde,
with cements such as gelatin, etc. The exuda
glycerol-phthalic anhydride, etc.
tion of plasticizer on the surface of the sheet
forming an oily skin interfering with proper ad
_While this invention has been described pri
hesion to the glass or gelatin coating is appre 75 marily with reference to the treatment of sheets,
BEST AVAILABLE copr
‘an.
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containing an ester of cellulose, said sheet ma?
terial being saponi?ed so that at least’ its inner
or unexposed surfaceis; capable of absorbing
itis obvious vthat the cellulose es‘ er;w material
being treated may be in any otherioi‘m such- as
a'molded article of irregular shape and thick
ness. For example, threaded lens tops for?/ash
lights are generally made by the so-called injec
moisture and the sheet material'as a'whole being
resistant to‘the penetration of water and gases.
4. A container for holding food and other
tion Jmolding of cellulose acetate. 'Such a ?n
ished molded article may be subjected‘ ‘to a
.saponi?cation treatment to render the lens non
products yielding moi'sturetending to condense
Within the container, said' container having a
window comprising transparent sheet material
It is to be understood, therefore, that the fore 10 containing cellulose acetate, said sheet 'mate
rial being saponi?ed so that at least ‘its inner 'or
going detailed description is givenrmerely by way
unexposed surface is capable of absorbing mois
of illustration and that many variations may be
fogsing.
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made therein without departing ,from the spirit
ture and the sheet material as a whole being
of my invention.
resistant to the penetration of water and gases.
5. A container for holding food and other
i
Having described my invention, what I desire 15
to secure by Letters Patent is:, I
Y‘
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products yielding moisture tending to condense
p
within the container, said container having a
l. A container for holding food and other prod_
window comprising transparent sheet material
ucts yielding moisture tending to’ condense with
in the container, comprising substantially im§
pervious transparent sheet material containing an ester of cellulose; 'said sheet material being
saponi?ed so that at least its inner or unexposed
containing cellulose ester sheet material sap'onie
?ed at least on one surface thereof, which sheet
material is characterized by being hard, resistant’
to the penetration of water and gases, of low
water shrinkage and heat loss, of high tensile
surface is capable of absorbing moisture and said
sheet material is free from the tendency to fog
strength and having a fog resistance of 50 to15‘0
orsweat.v
seconds.
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=76. A container for holding food and other
2.'A ‘container for holding food and other
products'yielding moisture tending to condense
products yielding moisture tending to condense
Within the container», comprising. substantially
impervious transparent sheetlmaterial contain
ing cellulose acetate, said sheet material being
within the container, said container having a
window comprising transparent sheet material
30 containing
cellulose ‘ acetate
sheet
material
said sheet material is free from the tendency to
saponi?ed at least on one surface thereof, which
sheet material is characterized by being hard, re
sistant to the penetration of water and gases; of
fog or sweat. '
low water shrinkage and heat loss, of high ten
saponi?ed so that ‘at least its inner or unexposed
surface is capable of absorbing moisture and
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3. A container for holding food and other ,
products yielding moisture tending to condense
Within the container, said container having a
window comprising transparent sheet material
sile strength and having a fog' resistance of‘ 50 ‘
to 150 seconds.
7
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BJORN ANDERSEN.
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